CN116207249A - Positive electrode active material, positive electrode sheet and lithium ion battery - Google Patents

Abstract

The invention provides a positive electrode active material, a positive electrode sheet and a lithium ion battery. The positive electrode material of the present invention comprises a lithium composite oxide containing at least a lithium element and a nickel element, wherein the molar ratio of the nickel element to the lithium element is (0.5 to 0.96): 1, a step of; the peak voltage V1 of the h2+h3 phase transition is determined by the dQ/dV curve, the positive electrode active material has two thermal decomposition peaks on a DSC curve under the V1 voltage, and the peak temperature difference of the two thermal decomposition peaks is C1, wherein the temperature of C1 is more than or equal to 10 ℃ and less than or equal to 50 ℃. The positive electrode active material has good stability, and can ensure that the lithium ion battery has good safety performance and cycle performance.

Description

Positive electrode active material, positive electrode sheet and lithium ion battery

Technical Field

The invention belongs to the field of lithium ion batteries and relates to a positive electrode active material, a positive electrode sheet and a lithium ion battery.

Background Art

In recent years, lithium-ion batteries have been widely used in various fields due to their good electrochemical properties, such as mobile phones, computers, power tools, electric vehicles, etc. The safety performance of lithium-ion batteries determines the safety and reliability of equipment and devices including the lithium-ion batteries.

The safety problem of lithium-ion batteries is mainly caused by thermal runaway problems caused by various factors. Common transition metal oxide positive electrode active materials usually have good electrochemical properties, but most of them will decompose and release oxygen at high temperatures. The electrolyte and diaphragm in lithium-ion batteries are easy to burn when they encounter oxygen, causing thermal runaway in lithium-ion batteries.

Therefore, it is of great significance to develop a positive electrode active material that can make lithium-ion batteries have good safety performance.

Summary of the invention

The present invention provides a positive electrode active material, which can have good structural stability and good cycle performance and thermal safety performance during charge and discharge by controlling the peak temperature difference of thermal decomposition peaks of the material at different phase change voltages.

The present invention also provides a positive electrode sheet and a lithium ion battery, which also have good cycle performance and thermal safety performance due to comprising the positive electrode active material.

The first aspect of the present invention provides a positive electrode active material, the positive electrode active material comprises a lithium composite oxide containing at least lithium and nickel elements, wherein the molar ratio of the nickel element to the lithium element is (0.5-0.96):1;

The peak voltage V1 of the H2+H3 phase transition is determined by the dQ/dV curve. The positive electrode active material has two thermal decomposition peaks at the voltage V1, and the peak temperature difference between the two thermal decomposition peaks is C1, wherein 10°C≤C1≤50°C.

During the charging process, the lithium nickel composite oxide with the above composition mainly undergoes phase transition stages in sequence as the lithium ion content changes: rhombohedral phase H1, monoclinic phase M, new rhombohedral phase H2, new rhombohedral phase H3, and the final phase change process is irreversible. The material structure changes caused by the phase change during the insertion and extraction process of the nickel lithium composite oxide during the charging process will affect the long-term cycle stability of the material. The inventors have found that there are two thermal decomposition peaks on the DSC curve of the positive electrode active material under different phase change voltages. The temperatures of the two thermal decomposition peaks determine the triggering conditions. The triggering conditions include two situations. One is that during the charging process, the battery has severe heat generation and the charging current is too large, causing the material to decompose and release oxygen, and at the same time causing a chain reaction caused by the temperature of the uncontrolled release of the material. The other is that in the case of a short circuit, the material causes a chain reaction. If the temperature difference is closer, the energy required for the two triggers is more concentrated, and it is necessary to avoid fast charging (charging current needs to be controlled), or, based on the same short circuit probability, the probability of thermal runaway of the battery including the positive electrode material is greater, and the safety of the battery is poor; if the difference is too large, that is, the heat will be dispersed, and the safety performance can be guaranteed, but the second thermal decomposition peak is the peak of lithium ion diffusion, and the temperature corresponding to the second thermal decomposition peak is very high, indicating that it is difficult for lithium ions to escape. During use, the battery has poor cycle performance, which limits the use of the battery. From the perspective of use, the closer the V1 phase change voltage is to the cut-off voltage, the lower the stability of the positive electrode active material, the easier it is to be triggered, and the heat generated by the triggering under the phase change voltage will be higher, and the easier it is to thermal runaway. Controlling the peak temperature difference C1 of the two thermal decomposition peaks of the positive electrode active material under the peak voltage V1 of the H2+H3 phase change to meet 10℃≤C1≤50℃ can enable the battery to have both good thermal safety performance and cycle performance.

Preferably, 20°C≤C1≤45°C.

In addition to the peak temperature difference C1 of the two thermal decomposition peaks on the DSC curve at V1 voltage, which is a key factor affecting the thermal safety and cycle performance of the battery, the peak temperature difference of the two thermal decomposition peaks of the positive electrode active material at the peak voltage of the H2+M phase transition and the peak temperature difference of the two thermal decomposition peaks of the positive electrode active material at the peak voltage of the H1+M phase transition during the charging process are also important factors affecting the thermal safety and cycle performance of the battery.

In a specific embodiment, the peak voltage of the positive electrode active material in the H2+M phase transition is determined to be V2 through the dQ/dV curve, and the positive electrode active material has two thermal decomposition peaks on the DSC curve at the V2 voltage, and the peak temperature difference between the two thermal decomposition peaks is C2, wherein 30°C≤C2≤70°C, preferably, 40°C≤C2≤60°C. Controlling C2 within the above range is conducive to making the battery have better thermal safety performance while having good cycle performance.

Similarly, in a specific embodiment, the peak voltage of the positive electrode active material in the H1+M phase transition is determined to be V3 through the dQ/dV curve, and the positive electrode active material has two thermal decomposition peaks on the DSC curve at the V3 voltage, and the peak temperature difference between the two thermal decomposition peaks is C3, wherein 35°C≤C3≤75°C, preferably, 45≤C3≤65°C.

The positive electrode active material of the present invention may include other metal elements in addition to lithium, nickel and oxygen. In a specific embodiment, the molecular formula of the positive electrode active material of the present invention is Li _1+a [Ni _x Co _y M _z M1 _b ]O ₂ , wherein 0.5≤x＜1, 0＜y＜0.3, 0＜z＜0.3, 0＜a＜0.2, 0＜b＜0.2, and x+y+z+b＝1; M is selected from Mn and/or Al, and M1 is selected from at least one of Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce and Y. Preferably, M1 is selected from at least one of Zr, Mg, Ti, Al, Sr, Nb, W and Mo. Among them, M1 is a doping element, and doping the positive electrode active material with the above elements can further improve the thermal safety performance and cycle performance of the material.

Furthermore, the positive electrode active material also includes a coating layer, and the coating layer includes an ion conductor. The ion conductor can be selected from metal lithium compounds or non-metal lithium compounds, wherein the metal lithium compounds can be selected from one or more of lithium iron phosphate, lithium cobalt oxide, nickel cobalt manganese oxide (nickel molar content <60%), lithium manganese oxide, lithium nickel oxide, lithium titanate, lithium aluminum titanium phosphate, lithium lanthanum titanate, lithium lanthanum tantalate, lithium germanium phosphate, lithium lanthanum zirconium oxide, lanthanum zirconium aluminum lithium oxide, niobium-doped lithium lanthanum zirconium oxide, and tantalum-doped lithium lanthanum zirconium oxide; the non-metal lithium compounds are selected from one or more of boron lithium compounds, sulfur lithium compounds, and phosphorus lithium compounds. According to the different compositions of different positive electrode active materials, the surface coating modification of the positive electrode active materials using the above ion conductors is beneficial to improve the stability, dispersibility, conductivity, cycle stability and other properties of the positive electrode active materials.

The preparation method of the positive electrode active material of the present invention is not particularly limited, and a conventional preparation method in the art can be used. For example, the hydroxide precursor of the positive electrode active material can be mixed with lithium hydroxide and then sintered to obtain the positive electrode active material. When the positive electrode active material contains a doping element, the hydroxide precursor of the positive electrode active material, lithium hydroxide and the oxide or hydroxide or simple substance of the doping element are mixed in proportion and sintered to obtain the positive electrode active material. When the positive electrode active material includes a coating layer in addition to the doping element, after the hydroxide precursor of the positive electrode active material, lithium hydroxide and the oxide of the doping element are mixed in proportion, the first sintering is completed, and then the sintered product is crushed and mixed with a coating agent, and a second sintering is performed to obtain the positive electrode active material containing the coating layer.

The second aspect of the present invention provides a positive electrode sheet, comprising the positive electrode active material provided by the first aspect of the present invention. Since the positive electrode active material of the present invention has good structural stability and cycle stability, the positive electrode sheet comprising the material can also enable the battery to obtain good cycle performance and thermal safety performance when used.

The positive electrode sheet of the present invention can adopt the composition of the positive electrode sheet conventionally used in the art, including a current collector and a positive electrode active layer, wherein the current collector adopts the positive electrode current collector conventionally used in the art, such as aluminum foil, and the positive electrode active layer includes the positive electrode active material as described above, and in addition, it can also include other conventional components such as a conductive agent and a binder. Conventional components such as a conductive agent and a binder can use materials conventionally used in the art, and the present invention does not specifically limit this.

The third aspect of the present invention provides a lithium ion battery, comprising the positive electrode sheet provided by the second aspect of the present invention. Due to the inclusion of the positive electrode sheet, the battery has both good cycle performance and thermal safety performance during the charge and discharge process.

The implementation of the present invention has at least the following beneficial effects:

1. The positive electrode active material of the present invention utilizes the phase change law of lithium nickel composite oxide during the charge and discharge process. By controlling the peak temperature difference of the thermal decomposition peak of the material at different phase change voltages, the positive electrode active material can have good structural stability and good cycle performance and thermal safety performance during the charge and discharge process.

2. The positive electrode sheet of the present invention, because it includes the above-mentioned positive electrode active material, can enable the battery to have both good cycle performance and thermal safety performance during application.

3. The lithium-ion battery of the present invention has both good cycle performance and thermal safety performance because it includes the above-mentioned positive electrode sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a dQ/dV curve of a lithium-ion battery assembled from the positive electrode active material of Example 6 of the present invention;

FIG2 is a DSC curve diagram of a button cell assembled from the positive electrode active material of Example 6 of the present invention when charged to a voltage of V1;

FIG3 is a DSC curve diagram of a button cell assembled from the positive electrode active material of Example 6 of the present invention when charged to a voltage of V2;

FIG. 4 is a DSC graph of a button-type battery assembled from the positive electrode active material of Example 6 of the present invention when charged to a voltage of V3.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Hereinafter, the positive electrode active material provided by the present invention, including the positive electrode sheet and the lithium ion battery of the positive electrode active material will be further described in detail through specific embodiments.

Unless otherwise specified, the reagents used in the following examples and comparative examples can be purchased from commercial sources or synthesized according to conventional methods in the art.

Examples 1 to 9, Examples 47 to 48 and Comparative Examples 1 to 2

The positive electrode active material of Examples 1-9, Examples 47-48 and Comparative Examples 1-2 is LiNi _0.8 Co _0.1 Mn _0.08 Zr _0.02 O ₂ , and its surface is coated with Li ₃ BO ₃ , and the coating amount is 1000 ppm calculated as B. The preparation method comprises the following steps:

1) adding a positive electrode active material precursor [Ni _0.8 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH and zirconium dioxide ZrO ₂ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Zr in _ZrO2 is 1:0.02, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 810-850° C. for a sintering time of 12-18 hours to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with a coating agent, and subjected to a second sintering. The second sintering temperature is 280° C. to 320° C., and the sintering time is 8 to 12 hours to obtain the positive electrode active materials of Examples 1 to 9, Examples 47 to 48, and Comparative Examples 1 to 2.

The specific parameters of the first sintering, the second sintering and the coating in Examples 1 to 9, Examples 47 to 48 and Comparative Examples 1 to 2 are shown in Table 1:

Table 1

Embodiments 10 to 14

The positive electrode active material of Examples 10 to 14 is LiNi _0.8 Co _0.1 Al _0.08 Mo _0.02 O ₂ , and its surface is coated with Li ₂ SO ₃ , and the coating amount is 1000 ppm calculated as S. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.8 Co _0.1 Al _0.08 ](OH) ₂ , lithium hydroxide LiOH and molybdenum trioxide MoO ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Mo in _MoO3 is 1:0.02, and Me represents the total molar amount of Ni, Co, and Al in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with sulfur as a coating agent, and subjected to a second sintering to obtain the positive electrode active materials of Examples 10 to 14.

The specific parameters of the first sintering, the second sintering and the coating in Examples 10 to 14 are shown in Table 2:

Table 2

Embodiment 15

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Al _0.08 Mg _0.02 O ₂ , and its surface is coated with Li ₂ SO ₃ , and the coating amount is 1000 ppm calculated as S. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.8 Co _0.1 Al _0.08 ](OH) ₂ , lithium hydroxide LiOH and magnesium oxide MgO into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to the Mg element in MgO is 1:0.02, and Me represents the total molar amount of Ni, Co, and Al in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 835° C. for 17 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with sulfur as a coating agent, and subjected to a second sintering process. The second sintering process is performed at a temperature of 240° C. and a sintering time of 12 h to obtain the positive electrode active material of this embodiment.

Example 16

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Al _0.08 Y _0.02 O ₂ , and its surface is coated with Li ₂ SO ₃ , and the coating amount is 1000 ppm calculated as S. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.8 Co _0.1 Al _0.1 ](OH) ₂ , lithium hydroxide LiOH and yttrium oxide Y ₂ O ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to the Y element _{in Y2O3} is 1:0.02, and Me represents the total molar amount of Ni, Co, and Al in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 840° C. for a sintering time of 16 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent sulfur/lithium sulfide, and subjected to a second sintering at a temperature of 240° C. and a sintering time of 12 h to obtain the positive electrode active material of this embodiment.

Embodiment 17

The positive electrode active material of this embodiment is LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , and its surface is coated with lithium titanate, and the coating amount is 2000 ppm calculated as Ti. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.5 Co _0.3 Mn _0.2 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 980° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent titanium dioxide, and subjected to a second sintering process. The second sintering process is performed at a temperature of 500° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 18

The positive electrode active material of this embodiment is LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , and its surface is coated with lithium titanate, and the coating amount is 2000 ppm calculated as Ti. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.6 Co _0.2 Mn _0.2 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 950° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent titanium dioxide, and subjected to a second sintering process. The second sintering process is performed at a temperature of 500° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 19

The positive electrode active material of this embodiment is LiNi _0.7 Co _0.2 Mn _0.1 O ₂ , and its surface is coated with lithium titanate, and the coating amount is 2000 ppm calculated as Ti. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.7 Co _0.2 Mn _0.1 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 905° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent titanium dioxide, and subjected to a second sintering process. The second sintering process is performed at a temperature of 500° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 20

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and its surface is coated with lithium titanate, and the coating amount is 2000 ppm calculated as Ti. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.8 Co _0.1 Mn _0.1 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 840° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent titanium dioxide, and subjected to a second sintering process. The second sintering process is performed at a temperature of 500° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 21

The positive electrode active layer material of this embodiment is LiNi _0.9 Co _0.05 Mn _0.05 O ₂ , and its surface is coated with lithium titanate, and the coating amount is 2000 ppm calculated as Ti. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.9 Co _0.05 Mn _0.05 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 780° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent titanium dioxide, and subjected to a second sintering process. The second sintering process is performed at a temperature of 500° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Example 22

The positive electrode active material of this embodiment is LiNi _0.96 Co _0.02 Mn _0.02 O ₂ , and its surface is coated with lithium titanate, and the coating amount is 2000 ppm calculated as Ti. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.9 Co _0.02 Mn _0.02 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 720° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent titanium dioxide, and subjected to a second sintering process. The second sintering process is performed at a temperature of 500° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 23

The positive electrode active material of this embodiment is LiNi _0.5 Co _0.4 Al _0.1 O ₂ , and its surface is coated with lithium cobalt oxide, and the coating amount is 3000 ppm calculated as Co. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.5 Co _0.4 Al _0.1 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio Me/Li of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Al in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 980° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent cobalt hydroxide, and subjected to a second sintering process. The second sintering process is performed at a temperature of 720° C. and a sintering time of 8 h to obtain the positive electrode active material of this embodiment.

Embodiment 24

The positive electrode active material of this embodiment is LiNi _0.6 Co _0.3 Al _0.1 O ₂ , and its surface is coated with lithium cobalt oxide, and the coating amount is 3000 ppm calculated as Co. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.6 Co _0.3 Al _0.1 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio Me/Li of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Al in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 950° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent cobalt hydroxide, and subjected to a second sintering process. The second sintering process is performed at a temperature of 720° C. and a sintering time of 8 h to obtain the positive electrode active material of this embodiment.

Embodiment 25

The positive electrode active material of this embodiment is LiNi _0.7 Co _0.2 Al _0.1 O ₂ , and its surface is coated with lithium cobalt oxide, and the coating amount is 3000 ppm calculated as Co. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.7 Co _0.2 Al _0.1 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio Me/Li of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Al in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 905° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent cobalt hydroxide oxide, and subjected to a second sintering. The second sintering temperature is 650° C. and the sintering time is 6 hours to obtain the positive electrode active material of this embodiment.

Embodiment 26

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Al _0.1 O ₂ , and its surface is coated with lithium cobalt oxide, and the coating amount is 3000 ppm calculated as Co. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.8 Co _0.1 Al _0.1 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio Me/Li of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Al in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 840° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent cobalt hydroxide oxide, and subjected to a second sintering. The second sintering temperature is 650° C. and the sintering time is 6 hours to obtain the positive electrode active material of this embodiment.

Embodiment 27

The positive electrode active material of this embodiment is LiNi _0.9 Co _0.05 Al _0.05 O ₂ , and its surface is coated with lithium cobalt oxide, and the coating amount is 3000 ppm calculated as Co. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.9 Co _0.05 Al _0.05 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio Me/Li of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Al in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 780° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent Co ₂ O _3, and subjected to a second sintering process. The second sintering process is performed at a temperature of 750° C. and a sintering time of 8 h to obtain the positive electrode active material of this embodiment.

Embodiment 28

The positive electrode active material of this embodiment is LiNi _0.96 Co _0.02 Al _0.02 O ₂ , and its surface is coated with lithium cobalt oxide, and the coating amount is 3000 ppm calculated as Co. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.96 Co _0.02 Al _0.02 ](OH) ₂ and lithium hydroxide LiOH into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio Me/Li of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, and Me represents the total molar amount of Ni, Co, and Al in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 720° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent Co ₃ O ₄ , and subjected to a second sintering at a temperature of 720° C. for 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 29

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Nb _0.02 O ₂ , and its surface is coated with lithium iron phosphate, and the coating amount is 2000 ppm calculated as PO _4. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, and niobium pentoxide Nb ₂ O ₅ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Nb in _Nb2O5 is 1:0.02, and Me represents the total molar amount of Ni, Co, and _Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 830° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent lithium iron phosphate, and subjected to a second sintering process. The second sintering process is performed at a temperature of 480° C. and a sintering time of 9 hours to obtain the positive electrode active material of this embodiment.

Embodiment 30

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 V _0.02 O ₂ , and its surface is coated with lithium iron phosphate, and the coating amount is 2000 ppm calculated as PO _4. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, and vanadium pentoxide V ₂ O ₅ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

The molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to V in _V2O5 is 1:0.02, and Me represents the total molar amount of Ni, Co, and _Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 830° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent lithium iron phosphate, and subjected to a second sintering process. The second sintering process is performed at a temperature of 480° C. and a sintering time of 9 hours to obtain the positive electrode active material of this embodiment.

Embodiment 31

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Al _0.02 O ₂ , and its surface is coated with lithium iron phosphate, and the coating amount is 2000 ppm calculated as PO _4. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, and aluminum hydroxide Al(OH) ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Al in Al(OH) ₃ is 1:0.02, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 835° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent lithium iron phosphate, and subjected to a second sintering process. The second sintering process is performed at a temperature of 480° C. and a sintering time of 9 hours to obtain the positive electrode active material of this embodiment.

Embodiment 32

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Ti _0.02 O ₂ , and its surface is coated with lithium manganate, and the coating amount is 2500 ppm calculated as Mn. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, and titanium dioxide TiO ₂ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Ti in _TiO2 is 1:0.02, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 840° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent lithium manganate, and subjected to a second sintering at a temperature of 520° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 33

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Sr _0.02 O ₂ , and its surface is coated with lithium manganate, and the coating amount is 2500 ppm calculated as Mn. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, and strontium oxide SrO into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Sr in SrO is 1:0.02, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 850° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with a coating agent, manganese dioxide, and subjected to a second sintering process. The second sintering process is performed at a temperature of 520° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 34

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Sb _0.02 O ₂ , and its surface is coated with lithium aluminate, and the coating amount is 1000 ppm calculated as Al. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, and antimony trioxide Sb ₂ O ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Sb in _Sb2O3 is 1:0.02, and Me represents the total molar amount of Ni, Co, and _Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 825° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent alumina, and subjected to a second sintering at a temperature of 550° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 35

The positive electrode active material of this embodiment is LiNi _0.5 Co _0.3 Mn _0.18 Mg _0.02 O ₂ , and its surface is coated with lithium aluminate, and the coating amount is 1000 ppm calculated as Al. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.52 Co _0.3 Mn _0.18 ](OH) ₂ , lithium hydroxide LiOH, and magnesium oxide MgO into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Mg in MgO is 1:0.02, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 980° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent alumina, and subjected to a second sintering at a temperature of 550° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 36

The positive electrode active material of this embodiment is LiNi _0.6 Co _0.2 Mn _0.18 Te _0.02 O ₂ , and its surface is coated with lithium aluminate, and the coating amount is 1000 ppm calculated as Al. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.62 Co _0.2 Mn _0.18 ](OH) ₂ , lithium hydroxide LiOH, and tellurium dioxide TeO ₂ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Te in _TeO2 is 1:0.02, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 950° C. and a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent alumina, and subjected to a second sintering at a temperature of 550° C. and a sintering time of 10 h to obtain the positive electrode active material of this embodiment.

Embodiment 37

The positive electrode active material of this embodiment is LiNi _0.9 Co _0.05 Mn _0.04 W _0.01 O ₂ , and its surface is coated with lithium phosphate Li3PO4, and the coating amount is 2000ppm calculated as PO4. The preparation method includes the following steps:

1) adding positive electrode active material precursor Ni _0.91 Co _0.05 Mn _0.04 ](OH) ₂ , lithium hydroxide LiOH, and tungsten trioxide WO ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to W in _WO3 is 1:0.02, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 780° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent ammonium dihydrogen phosphate, and subjected to a second sintering at a temperature of 580° C. and a sintering time of 12 h to obtain the positive electrode active material of this embodiment.

Embodiment 38

The positive electrode active material of this embodiment is LiNi _0.96 Co _0.02 Mn _0.01 Mo _0.01 O ₂ , and its surface is coated with lithium phosphate Li3PO4, and the coating amount is 2000ppm calculated as PO4. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.97 Co _0.02 Mn _0.01 ](OH) ₂ , lithium hydroxide LiOH, and molybdenum trioxide MoO ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Mo in _MoO3 is 1:0.02, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 720° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with the coating agent ammonium dihydrogen phosphate, and subjected to a second sintering process at a temperature of 580° C. and a sintering time of 12 h to obtain the positive electrode active material of this embodiment.

Embodiment 39

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Al _0.01 Mo _0.01 O ₂ , and its surface is coated with lithium lanthanum tantalate Li ₅ La ₃ Ta ₂ O ₁₂ , and the coating amount is 2000ppm calculated as Ta and 1200ppm calculated as La. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, molybdenum trioxide MoO ₃ and aluminum hydroxide Al(OH) ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Mo in MoO ₃ and Al in Al(OH) ₃ is 1:0.01:0.01, and Me represents the total molar amount of Ni, Co and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 830° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with coating agents tantalum pentoxide _Ta2O5 and _lanthanum trioxide _{La2O3 ,} and subjected to a second sintering at a temperature of 620°C and a sintering time of 8 hours to obtain the positive electrode active material of this embodiment.

Embodiment 40

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Zr _0.01 Nb _0.01 O ₂ , and its surface is coated with lithium lanthanum tantalate Li ₅ La ₃ Ta ₂ O ₁₂ , and the coating amount is 2000ppm calculated as Ta and 1200ppm calculated as La. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, zirconium dioxide ZrO ₂ and niobium pentoxide Nb ₂ O ₅ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Zr in _ZrO2 and Nb in _Nb2O5 is 1: _0.01 :0.01, and Me represents the total molar amount of Ni, Co and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 845° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with coating agents tantalum pentoxide _Ta2O5 and _lanthanum trioxide _{La2O3 ,} and subjected to a second sintering at a temperature of 620°C and a sintering time of 8 hours to obtain the positive electrode active material of this embodiment.

Embodiment 41

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Zr _0.01 W _0.01 O ₂ , and its surface is coated with lithium lanthanum zirconium oxide Li ₇ La ₃ Zr ₂ O ₁₂ , and the coating amount is 500ppm calculated as Zr and 1200ppm calculated as La. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, zirconium dioxide ZrO ₂ and tungsten trioxide WO ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Zr in _ZrO2 and W in _WO3 is 1:0.01:0.01, and Me represents the total molar amount of Ni, Co and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 840° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with coating agents zirconium dioxide ZrO ₂ and lanthanum trioxide La ₂ O ₃ , and subjected to a second sintering at a temperature of 640° C. for 9 hours to obtain the positive electrode active material of this embodiment.

Embodiment 42

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Al _0.01 Zr _0.01 O ₂ , and its surface is coated with lithium lanthanum zirconium oxide Li ₇ La ₃ Zr ₂ O ₁₂ , and the coating amount is 500ppm calculated as Zr and 1200ppm calculated as La. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, zirconium dioxide ZrO ₂ and aluminum hydroxide Al(OH) ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Zr in _ZrO2 and Al in Al(OH) ₃ is 1:0.01:0.01, and Me represents the total molar amount of Ni, Co and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 830° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with coating agents zirconium dioxide ZrO ₂ and lanthanum trioxide La ₂ O ₃ , and subjected to a second sintering at a temperature of 640° C. for 9 hours to obtain the positive electrode active material of this embodiment.

Embodiment 43

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Mo _0.01 Sr _0.01 O ₂ , and its surface is coated with lithium lanthanum zirconium oxide Li ₇ La ₃ Zr ₂ O ₁₂ , and the coating amount is 500ppm calculated as Zr and 1200ppm calculated as La. The preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, molybdenum trioxide MoO ₃ and strontium oxide SrO into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Mo in _MoO3 and Sr in SrO is 1:0.01:0.01, and Me represents the total molar amount of Ni, Co and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for a first sintering at a sintering temperature of 840° C. for a sintering time of 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with coating agents zirconium dioxide ZrO ₂ and lanthanum trioxide La ₂ O ₃ , and subjected to a second sintering at a temperature of 640° C. for 9 hours to obtain the positive electrode active material of this embodiment.

Embodiment 44

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Y _0.01 Ti _0.01 O ₂ , and its surface is coated with niobium-doped lithium lanthanum zirconium oxide Li ₅ La ₂ Zr ₂ Nb ₁ O ₁₂ , and the coating amount is 800ppm calculated as Zr, 1200ppm calculated as La, and 400ppm calculated as Nb. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, yttrium oxide Y ₂ O ₃ and titanium dioxide TiO ₂ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Mo in _MoO3 and Sr in SrO is 1:0.01:0.01, and Me represents the total molar amount of Ni, Co and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 850° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with coating agents zirconium dioxide _{ZrO2 ,} lanthanum trioxide _La2O3 and niobium pentoxide _{Nb2O5 ,} and subjected to a second sintering at a temperature of 680°C and a sintering time of 8 hours to obtain the positive electrode active material of this embodiment.

Embodiment 45

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Mo _0.01 Y _0.01 O ₂ , and its surface is coated with niobium-doped lithium lanthanum zirconium oxide Li ₅ La ₂ Zr ₂ Nb ₁ O ₁₂ , and the coating amount is 800ppm calculated as Zr, 1200ppm calculated as La, and 400ppm calculated as Nb. The preparation method includes the following steps:

1) adding positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, molybdenum trioxide MoO ₃ and yttrium oxide Y ₂ O ₃ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Mo in MoO ₃ and Y in Y ₂ O ₃ is 1:0.01:0.01, and Me represents the total molar amount of Ni, Co and Mn in the positive electrode active material precursor.

2) placing the mixed material into an atmosphere sintering furnace for the first sintering at a sintering temperature of 845° C. for 15 h to obtain a sintered product;

3) The sintered product obtained in step 2) is crushed, sieved, mixed with coating agents zirconium dioxide _{ZrO2 ,} lanthanum trioxide _La2O3 and niobium pentoxide _{Nb2O5 ,} and subjected to a second sintering at a temperature of 680°C and a sintering time of 8 hours to obtain the positive electrode active material of this embodiment.

Embodiment 46

The positive electrode active material of this embodiment is LiNi _0.8 Co _0.1 Mn _0.08 Zr _0.02 O ₂ , and the preparation method includes the following steps:

1) adding a positive electrode active material precursor [Ni _0.82 Co _0.1 Mn _0.08 ](OH) ₂ , lithium hydroxide LiOH, and zirconium dioxide ZrO ₂ into a high-speed mixer and mixing for 1 hour to obtain a mixed material;

Among them, the molar ratio of Me in the positive electrode active material precursor to Li in lithium hydroxide is 1:1.05, the molar ratio of Me in the positive electrode active material precursor to Zr in _ZrO2 is 1:0.02, and Me represents the total molar amount of Ni, Co, and Mn in the positive electrode active material precursor.

2) The mixed material is placed in an atmosphere sintering furnace for a first sintering at a sintering temperature of 830° C. and a sintering time of 14 h to obtain the positive electrode active material of this embodiment.

Test example

The positive electrode active materials of the above embodiments and comparative examples are prepared into lithium ion batteries, and the preparation of the lithium ion batteries comprises the following steps:

1) Preparation of positive electrode

The positive electrode active material, conductive carbon black and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an N-methylpyrrolidone solvent system at a mass percentage ratio of 95:3:24, and then coated on an aluminum foil to obtain a positive electrode active layer, wherein the thickness of the positive electrode active material layer was 100 μm, and then dried and cold pressed to obtain a positive electrode sheet.

2) Preparation of negative electrode

The negative electrode active material artificial graphite, the binder styrene butadiene rubber, and the dispersant carboxymethyl cellulose are mixed in a mass percentage ratio of 96:2:2 and dispersed in deionized water to form a slurry, which is evenly stirred and coated on a copper foil to obtain a negative electrode active layer, wherein the thickness of the negative electrode active material layer is 120 μm. After drying, a negative electrode active material layer is formed, and the negative electrode sheet is obtained after cold pressing and slitting.

3) Assembly of lithium-ion batteries

The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an outer packaging aluminum plastic film, and after dehydration at 80°C, the above electrolyte is injected and packaged, and a lithium-ion battery is obtained through a process of formation, degassing, shaping, etc.

Performance testing of positive electrode active materials and lithium-ion batteries;

1. dQ/dV curve

The lithium-ion battery is charged and discharged with a current of 0.2C, and the charge and discharge data, especially the power and voltage data, are recorded. After obtaining the data, the voltage and power data of the nth data point are subtracted from the voltage and power data of the n+1th data point to obtain dV and dQ data respectively. The dQ is divided by dV to obtain dQ/dV data. With dQ/dV as the ordinate and voltage as the abscissa, the corresponding dQ/dV curve is obtained.

FIG1 is a dQ/dV curve of a lithium-ion battery assembled from the positive electrode active material of Example 6 of the present invention. From FIG1 , it can be determined that the peak voltage V3 of the H1+M phase change of the positive electrode active material of Example 6 is 3.67V, the peak voltage V2 of the H2+M phase change is 4.01V, and the peak voltage V1 of the H2+H3 phase change is 4.18V.

2.DSC test:

Test method: The positive electrode active material is mixed into a slurry, coated on the current collector, and dried to obtain a positive electrode sheet. Then, a lithium sheet is used as the negative electrode and assembled with the positive electrode sheet into a button battery, and an electrolyte is injected (the preparation process of the electrolyte is: in an environment with a water content of less than 10ppm, lithium hexafluorophosphate and a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): vinylene carbonate (VC) = 30:48:20:2, mass percentage ratio) are prepared at a mass percentage ratio of 8:92 to form an electrolyte with a lithium salt concentration of 1 mol/L, and the lithium salt uses _LiPF6 ). The battery was charged to a specific voltage (V1, V2, V3, V4), the battery was disassembled, the positive electrode was cleaned with DMC and dried, 0.3 mL of electrolyte was added, and the thermal decomposition curve was tested using a differential scanning calorimeter to obtain the corresponding thermal decomposition starting temperature and peak temperature at a specific voltage, and the heating rate was set to 10 °C/min.

FIG2 is a DSC curve of a button cell assembled from the positive electrode active material of Example 6 of the present invention when charged to a voltage of V1. As shown in FIG2 , the corresponding temperatures of the two thermal decomposition peaks on the DSC curve are 246.7° C. and 282.1° C., respectively, and the difference C1 is 35.4° C. (the temperature difference is rounded to an integer).

FIG3 is a DSC curve of a button cell assembled with the positive electrode active material of Example 6 of the present invention when charged to a voltage of V2. As shown in FIG3 , the corresponding temperatures of the two thermal decomposition peaks on the DSC curve are 249.5° C. and 304.7° C., respectively, and the difference C2 is 55.2° C.;

Figure 4 is a DSC curve diagram of the button-type battery assembled with the positive electrode active material of Example 6 of the present invention when charged to a voltage of V3. As shown in Figure 4, the corresponding temperatures of the two thermal decomposition peaks on the DSC curve are 260°C and 317°C, respectively, and the difference C2 is 57°C.

3. Capacity retention rate test

Test method: At 45°C, charge and discharge the lithium-ion battery at 1C. After 300 cycles of testing, record the battery capacity Q2. The initial capacity of the battery is Q1, and the capacity retention rate = Q2/Q1×100%.

4. Thermal runaway test

Test method: The lithium-ion battery assembled as above is fully charged at a rate of 1C to the cut-off voltage at 25°C, and is charged at a constant voltage at the cut-off voltage to a current of 0.05C, which is considered to be 100% SOC. A heating film is added to the battery surface, and the battery is tightly fitted and closed. The temperature at which the battery thermal runaway begins is tested, and the heating rate is set to 5°C/min.

The above test results are shown in Table 3.

Table 3

It can be seen from the data in Table 3 that the present invention can achieve both a lower thermal runaway start temperature and a higher capacity retention rate for the battery by controlling C1, C2, and C3, thereby achieving both better safety performance and cycle performance for the battery.

Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. The above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims (10)

1. A positive electrode active material, characterized in that, the positive electrode active material comprises a lithium composite oxide containing at least lithium element and nickel element, and the molar ratio of the nickel element to the lithium element is (0.5～0.96): 1; Determine the peak voltage V1 of the H2+H3 phase transition through the dQ/dV curve, the positive electrode active material has two thermal decomposition peaks on the DSC curve at the V1 voltage and the peak temperature difference between the two thermal decomposition peaks is C1, where , 10°C≤C1≤50°C. 2. The positive electrode active material according to claim 1, characterized in that 20°C≤C1≤45°C. 3. The positive electrode active material according to claim 1 or 2, characterized in that, the peak voltage of the positive electrode active material at the H2+M phase transition is determined to be V2 by the dQ/dV curve, and the positive electrode active material is at There are two thermal decomposition peaks on the DSC curve of the V2 voltage, and the peak temperature difference between the two thermal decomposition peaks is C2, wherein, 30°C≤C2≤70°C. 4. The cathode active material according to claim 3, characterized in that 40°C≤C2≤60°C. 5. The positive electrode active material according to any one of claims 1-4, characterized in that, the peak voltage of the positive electrode active material at the H1+M phase transition determined by the dQ/dV curve is V3, and the positive electrode The active material has two thermal decomposition peaks on the DSC curve of the V3 voltage and the peak temperature difference between the two thermal decomposition peaks is C3, wherein, 35°C≤C3≤75°C. 6 . The cathode active material according to claim 5 , wherein 45≦C3≦65° C. 7. The positive electrode active material according to any one of claims 1-6, characterized in that, the molecular formula of the positive electrode active material is Li _1+a [ _Nix Co _y M _z M1 _b ]O ₂ , wherein, 0.5 ≤x<1, 0<y<0.3, 0<z<0.3, 0<a<0.2, 0<b<0.2, and x+y+z+b=1; M is selected from Mn and/or Al, M1 At least one selected from Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, Y. 8. The positive electrode active material according to any one of claims 1-7, characterized in that, the positive electrode active material further comprises a coating layer, and the coating layer comprises an ion conductor. 9. A positive electrode sheet, characterized in that it comprises the positive electrode active material according to any one of claims 1-8. 10. A lithium ion battery, characterized in that it comprises the positive electrode sheet according to claim 9.

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