CN114865077A - Additive for battery electrolyte, battery electrolyte and lithium ion battery - Google Patents

Abstract

The present application relates to the technical field of battery materials, and in particular, to an additive for battery electrolyte, battery electrolyte and lithium ion battery. The additive for battery electrolyte includes the compound shown in the following formula I,

In formula I, A ₁ is a single bond or an organic group with 1-20 carbon atoms; X ₁ and X ₂ are each independently selected from hydrogen and an alkyl group with 1-10 carbon atoms. The additive for the battery electrolyte of the present application can form a protective film on the surface of the electrode, suppress the side reaction between the electrode and the electrolyte, reduce the increase in impedance during the cycle, and can also take into account the high and low temperature performance, and improve the overall output performance of the battery.

Description

Additives for battery electrolytes, battery electrolytes and lithium-ion batteries

technical field

The application belongs to the technical field of battery materials, and in particular relates to an additive for battery electrolyte, battery electrolyte and lithium ion battery.

Background technique

Lithium-ion battery is a new generation of secondary battery with good competitiveness, known as "green energy", is the preferred technology to solve contemporary environmental pollution and energy problems. In the field of high-energy batteries, lithium-ion batteries have achieved great success, but consumers still expect batteries with higher overall performance, which depends on the research and development of new electrode materials and electrolyte systems. At present, electronic digital products such as smart phones and tablet computers have higher and higher energy density requirements for batteries, making it more and more difficult for commercial lithium-ion batteries to meet the requirements.

The energy density of lithium-ion batteries can generally be achieved in the following two ways: one is to select positive and negative materials with high capacity and high compaction; the other is to increase the working voltage of the battery. Pure silicon anode has a high theoretical gram capacity and is an ideal high-capacity anode material. However, when pure silicon is used as the anode of a lithium-ion battery, due to the volume effect, the battery expands and the pole piece is seriously pulverized, and the cycle performance is poor. In addition, the electrical conductivity of silicon-based materials is not good, resulting in poor low temperature performance of the battery. Combining silicon material and carbon material to form a silicon-carbon composite material can greatly improve the specific capacity and conductivity of the material, and reduce the volume effect of silicon-based materials to a certain extent. The energy density of silicon-carbon composites combined with high-capacity high-nickel cathodes can reach more than 300Wh/Kg. Therefore, the matching electrolyte has become a hot spot in lithium-ion battery electrolyte research.

Fluorinated ethylene carbonate can form a uniform and stable solid electrolyte interface film (Solid Electrolyte Interface, SEI) on the surface of silicon carbon negative electrode. Due to the particularity of the silicon-carbon anode material, it will still lead to battery swelling and severe pulverization of the pole pieces. Therefore, more film-forming additives are often required in the electrolyte system than in the graphite anode system, and a large amount of fluoroethylene carbonate is usually used; However, fluoroethylene carbonate is easily decomposed in a high temperature environment or in a high-nickel positive electrode battery system, and cannot meet the high-temperature use requirements of the battery. Therefore, there are many disadvantages when using fluoroethylene carbonate alone. In order to solve the flatulence problem of lithium ion batteries containing fluoroethylene carbonate during high temperature storage, there are patents such as CN201110157665 by adding organic dinitrile substances (NC-(CH ₂ ) _n -CN, where n= The methods of 2 to 4) suppress flatulence. However, the application of nitrile compounds to the ternary high nickel cathode material system will increase the polarization of the battery and seriously deteriorate the cycle performance and low temperature characteristics.

SUMMARY OF THE INVENTION

The purpose of the present application is to provide an additive for battery electrolyte, which aims to solve the problem that the existing battery electrolyte is easily oxidized and decomposed under high temperature conditions, resulting in the inability to balance the high temperature storage performance and low temperature discharge performance of the battery.

Another object of the present application is to provide a battery electrolyte containing the above additive for battery electrolyte and a lithium ion battery.

In order to realize the above-mentioned application purpose, the technical scheme adopted in this application is as follows:

In a first aspect, the application provides an additive for a battery electrolyte, and the additive for a battery electrolyte includes a compound shown in the following formula I,

In formula I, A ₁ is a single bond or an organic group with 1-20 carbon atoms; X ₁ and X ₂ are each independently selected from hydrogen and an alkyl group with 1-10 carbon atoms.

In one embodiment, A ₁ is selected from an organic group containing methylene, heteroatom, carbonyl, ester group, benzene ring structure or heterobenzene ring structure with 2 to 20 carbon atoms; and/or,

X ₁ and X ₂ are the same, and both are hydrogen or an alkyl group having 1 to 5 carbon atoms.

中的任意一种；其中，In one embodiment, in the compound shown in formula I, A ₁ is selected from -C _a H _2a -, -C _b H _2b -OC _b H _2b -, -C _k H _2k -OC _d H _2d -OC _k H _2k -,

any of ; of which,

a is an integer from 1 to 6, b is an integer from 1 to 3, k is an integer from 1 to 2, d is an integer from 1 to 3, e is an integer from 0 to 2, f is an integer from 0 to 2, and g is An integer from 0 to 2, i is an integer from 0 to 2, R ₁ is methyl, ethyl or n-propyl, and R ₂ is methylene, 1,2-ethylene or 1,3-n-propyl .

In one embodiment, the compound shown in formula I is selected from at least one of the following:

In a second aspect, the present application provides a battery electrolyte, the battery electrolyte includes a non-aqueous organic solvent, a lithium salt and an additive, and the additive is the above-mentioned additive for the battery electrolyte of the present application.

In one embodiment, based on the total mass of the battery electrolyte as 100%, the mass percentage of the compound shown in formula I is 0.05% to 5%, the total mass percentage of the additive is ≤15%, and the non-aqueous organic The mass percentage content of the solvent is 55% to 75%, and the mass percentage content of the lithium salt is 10% to 18%.

In one embodiment, the additives include fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,4-butane sultone, 1,4-butane sultone, in addition to the compounds shown in I. At least one of 3-propene sultone, vinyl sulfate, propylene sulfate; and/or,

Non-aqueous organic solvents include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, methyl acetate, ethyl acetate, propyl acetate, Methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, gamma-butyrolactone, gamma-valerolactone, delta-valerolactone, ε-caprolactone at least one; and/or,

The lithium salt is at least selected from lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis-oxalate borate, lithium bis-fluorooxalate borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisfluorosulfonimide A sort of.

In a third aspect, the present application provides a lithium ion battery, the lithium ion battery includes a positive electrode, a negative electrode, a separator and an electrolyte, and the electrolyte is the above-mentioned battery electrolyte of the application.

In one embodiment, the active material of the positive electrode is a transition metal oxide, and the active material of the negative electrode is graphite, a silicon-containing composite material, or lithium titanate.

In one embodiment, the transition metal oxide is Li _w Ni _x Co _y Mn _z L _(1-xyz) O ₂ , wherein 0.8≤w≤1.1, 0≤x<1, 0≤y≤1, 0≤ z<1, and 0<x+y+z≤1; L is at least one of Al, Sr, Mg, Ti, Nb, Zr, Zn, and B.

The additive for battery electrolyte provided in the first aspect of the present application includes a unique compound represented by formula I, which contains at least two carbon-carbon triple bonds, and different groups are selected between the two carbon-carbon triple bonds or at the tail end, thereby It can affect the reactivity of the compound shown in formula I on the electrode surface, thereby changing its film-forming activity and film-forming components on the electrode surface. Such additives for battery electrolytes can be preferentially reduced at the negative electrode of the battery during the first charging process. Stable SEI film, thereby improving the high temperature stability of the battery; at the same time, compounds containing carbon-carbon triple bonds can be used as strong ligands, which can easily complex high-priced metal ions at the positive electrode of the battery, inhibit the oxidative decomposition of the electrolyte at the positive electrode, and improve the lithium ion High temperature storage performance of ion batteries. To sum up, the additive for battery electrolyte containing the compound represented by formula I provided by this application can form a protective film on the surface of the electrode, suppress the side reaction between the electrode and the electrolyte, reduce the increase in impedance during the cycle, and can also take into account high and low temperature performance. , to improve the overall output performance of the battery.

The battery electrolyte provided by the second aspect of the present application includes a non-aqueous organic solvent, a lithium salt and an additive for the battery electrolyte unique to the present application. Therefore, such a battery electrolyte can form a protective film on the surface of the electrode, inhibiting the interaction between the electrode and the electrolyte. Side reactions, reducing the increase in impedance during cycling, while taking into account the high and low temperature performance, improve the overall output performance of the battery.

The third aspect of the present application provides that the lithium ion battery contains the lithium ion battery electrolyte unique to the present application. Therefore, such a lithium ion battery has good low-temperature discharge performance, as well as good cycle performance and high-temperature storage performance, so as to take into account high and low temperature performance, In order to improve the overall output performance of lithium-ion batteries.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present application more clearly, the following briefly introduces the drawings that are used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative effort.

1 is a linear voltammetry (LSV) curve diagram of Example 3 and Comparative Example 1 of the embodiment of the present application;

FIG. 2 is a capacity differential curve diagram of Example 3 and Comparative Example 1 of the embodiment of the present application.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clear, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application.

In this application, the term "and/or", which describes the relationship between related objects, means that there can be three relationships, for example, A and/or B, which can mean that A exists alone, A and B exist at the same time, and B exists alone Happening. where A and B can be singular or plural. The character "/" generally indicates that the associated objects are an "or" relationship.

In this application, "at least one" refers to one or more, and "multiple" refers to two or more. "At least one item(s) below" or similar expressions thereof refer to any combination of these items, including any combination of single item(s) or plural items(s).

It should be understood that, in various embodiments of the present application, the size of the sequence numbers of the above-mentioned processes does not imply the sequence of execution, some or all of the steps may be executed in parallel or sequentially, and the execution sequence of each process should be based on its functions and It is determined by the internal logic and should not constitute any limitation on the implementation process of the embodiments of the present application.

The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. As used in the embodiments of this application and the appended claims, the singular forms "a," "the," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise.

The weight of the relevant components mentioned in the description of the examples of this application can not only refer to the specific content of each component, but also can represent the proportional relationship between the weights of the components. It is within the scope disclosed in the description of the embodiments of the present application that the content of the ingredients is scaled up or down. Specifically, the mass described in the description of the embodiment of the present application may be a mass unit known in the chemical field, such as μg, mg, g, kg, etc.

The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implying the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature.

A first aspect of the embodiments of the present application provides an additive for a battery electrolyte, and the additive for a battery electrolyte includes a compound shown in the following formula I,

In formula I, A ₁ is a single bond or an organic group with 1-20 carbon atoms; X ₁ and X ₂ are each independently selected from hydrogen and an alkyl group with 1-10 carbon atoms.

The compound shown in formula I contains at least two carbon-carbon triple bonds, and different groups are selected between the two carbon-carbon triple bonds or at the tail, so that the compound shown in formula I can be affected on the electrode surface. Reactivity, thereby By changing its film-forming activity and film-forming components on the electrode surface, such additives for battery electrolytes can preferentially reduce to form a stable SEI film at the negative electrode of the battery during the first charging process, thereby improving the high temperature stability of the battery; at the same time, Compounds containing carbon-carbon triple bonds can be used as strong ligands, which can easily complex high-valent metal ions at the positive electrode of the battery, inhibit the oxidative decomposition of the electrolyte at the positive electrode, and improve the high-temperature storage performance of lithium-ion batteries. To sum up, the additive for battery electrolyte containing the compound represented by formula I provided in the examples of this application can form a protective film on the surface of the electrode (such as the positive electrode and/or the negative electrode), suppress the side reaction between the electrode and the electrolyte, and reduce the cycle process. The increase in the medium impedance can also take into account the high and low temperature performance and improve the overall output performance of the battery.

In one embodiment, A ₁ in formula I is a single bond, so that the two carbon-carbon triple bonds in the compound represented by I are directly connected. Alternatively, A ₁ in formula I is an organic group with 1 to 20 carbon atoms, so that the choice of different organic groups between two carbon-carbon triple bonds affects the reaction of the compound represented by formula I on the electrode surface active. "Organic group" refers to an organic group containing some active functional groups in an organic compound, and the functional groups contained therein have certain chemical properties. Specifically, in formula I, A ₁ is selected from methylene containing 2-20 carbon atoms. , heteroatom, carbonyl group, ester group, organic group of benzene ring structure or heterobenzene ring structure.

For example, A ₁ is selected from a methylene-containing organic group with 2 to 20 carbon atoms, or A ₁ is selected from a heteroatom (N, O, S, etc.)-containing organic group with 2 to 20 carbon atoms group, or A ₁ is selected from a carbonyl-containing organic group with 2 to 20 carbon atoms, or A ₁ is selected from an ester group-containing organic group with 2 to 20 carbon atoms, or A ₁ is selected from carbon atoms The functional group containing 2-20 benzene ring structure, or A ₁ is selected from the organic group containing 2-20 carbon atoms containing heterobenzene ring structure.

In one embodiment, in the compound represented by formula I, the organic group of A ₁ can be selected as follows:

For example, methylene-containing organic groups:

A ₁ is -C _a H _2a -, wherein a is an integer from 1 to 6;

For example an organic group containing methylene and heteroatom O:

A ₁ is -C _b H _2b -OC _b H _2b -, wherein b is an integer from 1 to 3;

A ₁ is -C _k H _2k -OC _d H _2d -OC _k H _2k -, wherein k is an integer from 1 to 2, and d is an integer from 1 to 3;

For example, an organic group containing a benzene ring structure or a heterobenzene ring structure:

其中e为0～2的整数； _A1 is

where e is an integer from 0 to 2;

其中f为0～2的整数； _A1 is

where f is an integer from 0 to 2;

其中g为0～2的整数， _A1 is

where g is an integer from 0 to 2,

其中i为0～2的整数， _A1 is

where i is an integer from 0 to 2,

For example, an organic group containing an ester group:

其中R₁为甲基、乙基或正丙基，R₂为亚甲基、1,2-亚乙基或1,3-亚正丙基。 _A1 is

wherein R ₁ is methyl, ethyl or n-propyl, and R ₂ is methylene, 1,2-ethylene or 1,3-n-propyl.

In the examples of the present application, the types of A ₁ are selected, the spatial structure size is appropriate, and the reactivity with the positive electrode or negative electrode of the battery is relatively good, which can facilitate the formation of a dense and stable SEI film on the positive and negative electrodes, and inhibit the electrolyte in the positive electrode. It can improve the high-temperature storage performance of lithium-ion batteries, improve the low-temperature characteristics and power characteristics of lithium-ion batteries, and improve the overall output performance of batteries.

In one embodiment, X ₁ and X ₂ are the same, and both are hydrogen or an alkyl group having 1 to 5 carbon atoms.

Specifically, the compound represented by the above formula I can be the compound represented by each structural formula in Table 1.

Table 1

A second aspect of the embodiments of the present application provides a battery electrolyte, the battery electrolyte includes a non-aqueous organic solvent, a lithium salt and an additive, and the additive is the above-mentioned additive for the battery electrolyte of the embodiment of the present application.

Because the battery electrolyte provided by the embodiment of the present application includes the specific additive for the battery electrolyte of the embodiment of the present application, such a battery electrolyte can form a protective film on the surface of the electrode, suppress the side reaction between the electrode and the electrolyte, and reduce the cycle process. The medium impedance is increased, while taking into account the high and low temperature performance, the overall output performance of the battery is improved.

In the battery electrolyte provided by the embodiments of the present application, each component is introduced as follows:

Non-aqueous organic solvent: Based on water, it has a certain influence on the formation of lithium-ion battery SEI and battery performance, which is manifested in the reduction of battery capacity, shortened discharge time, increased internal resistance, cycle capacity attenuation, and battery expansion. Therefore, in the embodiments of the present application, a non-aqueous organic solvent is used as the solvent component of the battery electrolyte. Specifically, the non-aqueous organic solvent includes ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, methyl acetate, ethyl acetate, acetic acid Propionate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, gamma-butyrolactone, gamma-valerolactone, delta-valerolactone, ε-caprolactone at least one of esters. The addition of the above-mentioned non-aqueous organic solvent makes the battery electrolyte used in the lithium ion battery to improve the more excellent comprehensive performance of the lithium ion battery. Further, based on the total mass of the battery electrolyte as 100%, the mass percentage of the non-aqueous organic solvent is 55% to 75%.

Lithium salt: The lithium salt used in the examples of this application can be selected from the lithium salts commonly used in lithium ion batteries, including but not limited to lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis-oxalate borate, lithium bis-fluorooxalate borate, One or more of lithium (trifluoromethylsulfonyl)imide and lithium bisfluorosulfonylimide. Further, based on the total mass of the battery electrolyte as 100%, the amount of lithium salt used in the lithium ion secondary battery electrolyte is 10% to 18% by mass.

Additives: Additives are mainly used to improve film-forming properties during the first charge and discharge. The additive is the above-mentioned additive for the battery electrolyte according to the embodiment of the present application, and its type selection and function have been described in detail above. In order to save space, it will not be repeated here. Further, based on the total mass of the battery electrolyte as 100%, the mass percentage content of the compound described in formula I in the additive is 0.05% to 2%. If the mass percentage content of the compound represented by formula I is less than 0.05%, the improvement effect is small; if the mass percentage content of the compound represented by formula I is higher than 2%, the protective film formed on the electrode surface is too thick.

In one embodiment, on the basis of the additive containing the compound represented by formula I, other additives may be further added to optimize the performance of the lithium ion battery. Specifically, in addition to the compounds shown in I, other additives include fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,4-butane sultone, 1,3- At least one of propylene sultone, vinyl sulfate, and propylene sulfate. Further, based on the total mass of the battery electrolyte as 100%, the mass percentage of the compound described in formula I is 0.05% to 2%, and other additives (fluoroethylene carbonate) other than the compound shown in I , vinylene carbonate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, vinyl sulfate, propylene sulfate) The mass percentage content can be 0.1%～10%. On this basis, the sum of the total mass percentages of the additives in the battery electrolyte is less than or equal to 15%.

In one embodiment, based on the total mass of the battery electrolyte as 100%, the mass percentage content of the compound shown in formula I is 0.05% to 5% (for example, the content of the compound shown in formula I may be 0.05%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, etc.), the total mass percentage of additives≤15% (for example, the total mass of additives can be is 6%, 7%, 8%, 10%, 11%, 12%, 14%, etc.), and the mass percentage of the non-aqueous organic solvent is 55% to 75% (for example, the content of the non-aqueous organic solvent can be 55%, 58%, 60%, 65%, 70%, 72%, 75%, etc.), the mass percentage of lithium salt is 10% to 18% (for example, the content of lithium salt can be 10%, 12% , 14%, 16%, 18%, etc.).

A third aspect of the embodiments of the present application provides a lithium ion battery, the lithium ion battery includes a positive electrode, a negative electrode, a separator and an electrolyte, and the electrolyte is the above-mentioned battery electrolyte of the embodiments of the present application.

Because the lithium-ion battery provided in the embodiment of the present application contains the lithium-ion battery electrolyte unique to the embodiment of the present application, such a lithium-ion battery has good low-temperature discharge performance, good cycle performance and high-temperature storage performance, so that both high and low temperature are taken into account. performance to improve the overall output performance of lithium-ion batteries.

Choice of separators include, but are not limited to, single-layer polyethylene (PE), single-layer polypropylene (PP), double-layer PP/PE, triple-layer PP/PE/PP, or ceramic separators. The positive electrode active material of the positive electrode and the positive electrode active material conventionally used in lithium ion batteries can be used in the embodiments of the present application. The negative electrode active material of the negative electrode and the negative electrode active material conventionally used in lithium ion batteries can be used in the embodiments of the present application. In one embodiment, the active material of the positive electrode is a transition metal oxide, and the active material of the negative electrode is graphite, a silicon-containing composite material, or lithium titanate.

In one embodiment, the transition metal oxide is Li _w Ni _x Co _y Mn _z L _(1-xyz) O ₂ , wherein 0.8≤w≤1.1, 0≤x<1, 0≤y≤1, 0≤ z<1, and 0<x+y+z≤1; L is at least one of Al, Sr, Mg, Ti, Nb, Zr, Zn, and B.

Specifically, the active material of the positive electrode is selected from at least one of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.83 Co _0.1 Mn _0.07 O ₂ , LiNi _0.8 Co _0.2 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , and LiCoO ₂ .

The following description will be given in conjunction with specific embodiments.

In each embodiment, the Chinese interpretation of the English abbreviation is explained as follows:

EC: ethylene carbonate; EMC: ethyl methyl carbonate; DMC: dimethyl carbonate; LiPF ₆ : lithium hexafluorophosphate; FEC: fluoroethylene carbonate; DTD: ethylene sulfate; PS: 1,3-propane sultone; PST: 1,3-propene sultone; in addition, the specific types of the compounds represented by formula I used in the examples and their corresponding letter numbers are shown in Table 1.

Example 1

A lithium ion secondary battery, comprising a positive electrode, a negative electrode, a diaphragm and an electrolyte, wherein the positive electrode active material of the positive electrode is a nickel-cobalt lithium manganate (NCM811) material; the negative electrode active material of the negative electrode is a silicon carbon composite material (Si/C ), the preparation method of lithium ion secondary battery comprises the following steps:

Mix the positive electrode active material NCM811, conductive carbon black and binder polyvinylidene fluoride in a mass ratio of 96.8:2.0:1.2, and disperse them in N-methyl-2-pyrrolidone to obtain a positive electrode slurry, and uniformly distribute the positive electrode slurry Coating on both sides of aluminum foil, drying, calendering and vacuum drying, and welding aluminum lead wires with an ultrasonic welder to obtain a positive plate (positive plate), the thickness of the positive plate is between 100 ~ 115μm;

Mix silicon carbon composite material, conductive carbon black, binder styrene-butadiene rubber and carboxymethyl cellulose in a mass ratio of 96:1:1.2:1.8, and disperse them in deionized water to obtain negative electrode slurry, which is coated with negative electrode slurry. It is clothed on both sides of the copper foil, dried, calendered and vacuum dried, and then welded with nickel lead wires with an ultrasonic welder to obtain a negative electrode plate (negative electrode sheet), and the thickness of the negative electrode plate is between 115 and 135 μm;

Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 2:1:7, and after mixing, 12.5% lithium hexafluorophosphate based on the total mass of the electrolyte was added, The total mass of the electrolyte solution was 1% of C1 in Table 1, and the electrolyte solution was prepared.

The separator is a ceramic separator prepared by coating Al ₂ O ₃ on one side.

The obtained positive electrode sheet, separator and negative electrode sheet are placed on an automatic winding machine, and a bare cell is obtained by winding; the bare cell is placed in a cylindrical steel shell, the negative electrode tab and the cap tab are welded, and the above prepared The electrolyte is injected into the dried cells, sealed, left standing, pre-charged, aged and volume-distributed to complete the preparation of the lithium ion secondary battery (18650-3.0Ah).

Example 2 to Example 34

Examples 2 to 25, except that the components in the electrolyte are different, the preparations of the remaining positive electrodes, negative electrodes, separators, and lithium ion secondary batteries are the same as those in Example 1. The content is shown in Table 2.

Example 26 In Example 34, in order to further improve the comprehensive output performance of the battery, other additives were added to the electrolyte on the basis of the compound shown in formula I. The selection of each component and its content are shown in Table 3.

Comparative Example 1 to Comparative Example 5

In Comparative Examples 1 to 5, except that the types and contents of non-aqueous organic solvents and additives in the electrolyte (based on the total mass of the electrolyte) are different, the preparations of the remaining positive electrodes, negative electrodes, separators, and lithium ion secondary batteries are performed in the same manner. Example 1, the types and contents of non-aqueous organic solvents and additives in Comparative Example 1 are shown in Table 2, and the types and contents of non-aqueous organic solvents and additives in Comparative Examples 2-4 are shown in Table 3.

Performance Testing

The lithium ion secondary batteries prepared in Examples 1 to 34 and Comparative Examples 1 to 5 were tested for performance, and the test methods were as follows:

1) Linear sweep voltammetry (LSV)

Using Pt as the working electrode and Li as the counter electrode and reference electrode, a three-electrode device was assembled to perform linear scanning on an electrochemical workstation.

2) Cycle performance test: at 25±2°C/45°C±2°C, charge the divided battery with 0.5C constant current and constant voltage to 4.2V (cut-off current is 0.01C), and then discharge with 1C constant current to 2.75V. The retention rate of the N-th cycle capacity is calculated after N cycles of charge/discharge, and the calculation formula is as follows:

Nth cycle capacity retention rate (%)=(Nth cycle discharge capacity/1st cycle discharge capacity)×100%;

3) High temperature storage performance: Charge the battery after capacity division to 4.2V with 0.5C constant current and constant voltage (cut-off current is 0.01C) at normal temperature (25~27℃), measure the initial discharge capacity of the battery, and then store it at 60℃ After 7 days of storage, the battery was discharged to 2.75V at 0.5C to measure the retention and recovery capacity. Calculated as follows:

Battery capacity retention rate (%) = retained capacity / initial capacity × 100%;

Battery capacity recovery rate (%)=recovered capacity/initial capacity×100%.

4) Discharge at low temperature: charge to 4.2V with 0.5C constant current and constant voltage at room temperature, put on hold for 5min, discharge at 0.2C to 2.75V, and check the initial capacity of the battery. Set aside for 5min, and charge to 4.2V with 0.5C constant current and constant voltage (the cut-off current is 0.01C). Put the battery in a low temperature box of -20℃ for 6h, and discharge it to 2.75V at 0.2C under this condition, and test the discharge capacity at low temperature.

Low temperature discharge retention rate (%)=low temperature discharge capacity/initial capacity×100%.

The test results are shown in Table 2 and Table 3 below.

Table 2

The battery system is NCM811 with silicon carbon composite material in Examples 1-25 and Comparative Example 1 for comparative analysis. It can be seen from Table 2 that the embodiments 1 to 25 adopting the technical solution of the present invention have good cycle performance, high temperature storage performance and low temperature discharge performance; and the lithium ion battery using the electrolyte of Comparative Example 1 has poor output performance and cannot take into account the high and low levels. Gentle cycle performance. Specifically, comparing each example with Comparative Example 1, the low-temperature discharge performance, high-temperature cycle, normal temperature cycle and high-temperature storage performance of Examples 1 to 25 containing the compound of structural formula I are significantly better than those of Comparative Example 1. Explain that the existence of compounds represented by formula I, such as C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C1+C5, C5+C13, can effectively improve the The overall output performance of the battery.

LSV evaluation and capacity differential curve (d Q/dV～V) analysis were carried out using the electrolytes of Comparative Example 1 and Example 3, and the results are shown in Figures 1 and 2 . It can be seen from Figure 1 that the sample containing C1 broadens the electrochemical window. It is inferred that the carbon-carbon triple bond of the additive is similar to the nitrile carbon-nitrogen triple bond as a strong ligand, which is easy to physically adsorb the surface of the Pt electrode and inhibit the electrolyte components on the Pt electrode. oxidative decomposition, thereby broadening the electrochemical window. It can be seen from Figure 2 that when the sample containing C1 is pre-filled to form a film for the first time, the reduction and decomposition of EC of the sample containing C1 is suppressed, and the peak intensity is slightly weakened. According to d Q/d V～V and LSV structure, it can be determined that C1 can form films on both positive and negative electrodes.

In Example 26 to Example 34 in Table 3, in order to further improve the comprehensive output performance of the battery, other additives were added on the basis of the compound shown in formula I: fluorocarbonate, 1,3-propane sultone, 1 , 3-Propene sultone, vinyl sulfate.

table 3

As can be seen from Table 3, in the technical solutions of the embodiments of the present application, the compounds shown in structural formula I combined with other additives from Examples 26 to 34 also have better cycle performance, high-temperature storage performance and low-temperature discharge performance; The battery parts of the electrolytes from Examples 2 to 5 have poor output performance, and cannot take both high and low temperature performance and cycle performance into consideration.

Therefore, through the comparison of each embodiment and the comparative example, it is found that in the embodiment of the present application, the compound represented by the structural formula I is added to the electrolyte to form a protective film on the positive and negative electrodes, so that the lithium ion secondary battery containing this non-aqueous electrolyte is obtained. Good battery output performance. Moreover, the technical solution is applied to a high-nickel positive electrode and a silicon-carbon composite negative electrode system, which has an obvious improvement effect.

The above descriptions are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection of the present application. within the range.

Claims (10)

1. an additive for battery electrolyte, is characterized in that, the additive for described battery electrolyte comprises the compound shown in the following formula I,

In formula I, A ₁ is a single bond or an organic group with 1-20 carbon atoms; X ₁ and X ₂ are each independently selected from hydrogen and an alkyl group with 1-10 carbon atoms. 2 . The additive for battery electrolyte according to claim 1 , wherein the A ₁ is selected from the group consisting of methylene group, heteroatom, carbonyl group, ester group, benzene ring structure or an organic group of a heterophenyl ring structure; and/or, The X ₁ and the X ₂ are the same, and both are hydrogen or an alkyl group having 1 to 5 carbon atoms. 3. The additive for battery electrolyte according to any one of claims 1-2, wherein in the compound shown in formula I, A ₁ is selected from -C _a H _2a -, -C _b H _2b -OC _b H _2b -, -C _k H _2k -OC _d H _2d -OC _k H _2k -,

any of ; of which, a is an integer from 1 to 6, b is an integer from 1 to 3, k is an integer from 1 to 2, d is an integer from 1 to 3, e is an integer from 0 to 2, f is an integer from 0 to 2, and g is An integer from 0 to 2, i is an integer from 0 to 2, R ₁ is methyl, ethyl or n-propyl, and R ₂ is methylene, 1,2-ethylene or 1,3-n-propyl . 4. The additive for battery electrolyte according to claim 1, wherein the compound shown in formula I is selected from at least one of the following:

5. A battery electrolyte comprising a non-aqueous organic solvent, a lithium salt and an additive, wherein the additive is the additive for battery electrolyte according to any one of claims 1-4. 6. The battery electrolyte according to claim 5, wherein, based on the total mass of the battery electrolyte as 100%, the mass percentage of the compound represented by formula I is 0.05% to 5%, so The total mass percentage of the additive is ≤15%, the mass percentage of the non-aqueous organic solvent is 55% to 75%, and the mass percentage of the lithium salt is 10% to 18%. 7. The battery electrolyte according to claim 5, wherein the additive comprises fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone in addition to the compound shown in I , at least one of 1,4-butane sultone, 1,3-propene sultone, vinyl sulfate, propylene sulfate; and/or, The non-aqueous organic solvent includes ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, methyl acetate, ethyl acetate, propyl acetate Esters, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, gamma-butyrolactone, gamma-valerolactone, delta-valerolactone, ε-caprolactone at least one of; and/or, The lithium salt is selected from lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis-oxalate borate, lithium bis-fluorooxalate borate, lithium bis(trifluoromethylsulfonyl)imide and lithium bisfluorosulfonimide at least one of. 8 . A lithium ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the battery electrolyte according to any one of claims 5 to 7 . 9 . The lithium ion battery according to claim 8 , wherein the active material of the positive electrode is a transition metal oxide, and the active material of the negative electrode is graphite, a silicon-containing composite material, or lithium titanate. 10 . 10 . The lithium ion battery according to claim 9 , wherein the transition metal oxide is Li _w Ni _x Co _y M _z L _(1-xyz) O ₂ , wherein 0.8≤w≤1.1,0 10 . ≤x<1, 0≤y≤1, 0≤z<1, and 0<x+y+z≤1; L is at least one of Al, Sr, Mg, Ti, Nb, Zr, Zn and B .

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