CN101202359B - A kind of additive composition and electrolyte solution and lithium ion secondary battery containing the additive composition - Google Patents

Abstract

An additive composition for the electrolyte of a lithium ion secondary battery, wherein the composition contains three different compounds. The use of the additive composition provided by the invention greatly improves the cycle performance, high temperature storage performance, low temperature discharge performance and rate discharge performance of the battery as a whole, and greatly improves the comprehensive performance of the battery.

Description

A kind of additive composition and electrolyte solution and lithium ion secondary battery containing the additive composition

technical field

The invention relates to an additive composition for electrolyte solution of lithium ion secondary battery, electrolyte solution and lithium ion secondary battery containing the additive composition.

Background technique

At present, the basic composition of the commonly used lithium-ion secondary battery is, including the battery case, the electrode group and the electrolyte, the electrode group and the electrolyte are sealed in the battery case, and the electrode group includes the positive electrode, the separator and the Negative electrode, lithium metal composite oxide is used as the positive electrode active material in the positive electrode, graphite, silicon and other materials are used as the negative electrode active material in the negative electrode, and the separator is used to separate the positive and negative electrodes. Most of the new lithium-ion secondary batteries use carbon materials as the negative electrode of the battery, and LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and other lithium materials that can be intercalated and deintercalated are used as the positive electrode of the battery. Among them, the electrolyte is an important part of the battery and has a great influence on the performance of the battery.

The electrolyte of a lithium-ion secondary battery is generally composed of an organic solvent and an electrolyte lithium salt. The use of additives in the electrolyte can significantly improve certain macroscopic properties of lithium-ion secondary batteries, such as electrode capacity, rate charge discharge performance, positive and negative electrode matching performance, cycle performance or safety performance. The additives have the characteristics of strong pertinence and small dosage, and can significantly improve the performance of the battery without increasing or substantially increasing the production cost and without changing the production process.

The non-aqueous solvents used in lithium-ion batteries inevitably react on the phase interface between the carbon negative electrode and the electrolyte during the first charging and discharging process of the battery, forming a passivation layer (SEI film) covering the surface of the carbon electrode. The excellent SEI film is insoluble in organic solvents, allowing lithium ions to freely enter and exit the electrode while solvent molecules cannot pass through, thereby preventing the co-intercalation of solvent molecules from damaging the electrode, and improving the cycle efficiency and reversible capacity of the battery. Therefore, additives can be added to the electrolyte to improve the performance of the SEI film, such as adding cyclic C=C double bond carbonates including ethylene carbonate as additives to form a surface film on the surface of the negative electrode to improve the performance of the SEI film under high-rate discharge. Output characteristics, improve cycle life, but this additive makes the battery's high-temperature storage performance and low-temperature discharge performance are poor; another example, the film-forming additive sultone has good film-forming performance, can improve the battery's cycle performance and high-temperature storage performance , but sultone makes the low-temperature discharge performance of the battery poor; in addition, the film-forming additive γ-butyrolactone has good film-forming performance, can improve the cycle performance of the battery, and can improve the low-temperature discharge performance of the battery and the first discharge is reversible Capacity, but gamma-butyrolactone (GBL) makes the high-temperature storage performance of the battery poor.

CN1612403A discloses an electrolyte composition, which comprises: lithium salt; organic solvent containing nitrogen-containing compound, propane sultone, and 1,2-vinylidene carbonate and/or cyclohexylbenzene. The electrolyte composition improves the safety of the battery during high-temperature operation without deteriorating the performance of the battery. However, the disadvantage of the lithium-ion secondary battery containing the electrolyte is poor low-temperature discharge performance.

Contents of the invention

The object of the present invention is to overcome the shortcoming that the additive used in the prior art makes the low-temperature discharge performance of lithium-ion secondary batteries poor, and provides a kind of lithium-ion secondary battery electrolyte that makes the low-temperature discharge performance of lithium-ion batteries better. An additive composition, and an electrolyte solution and a lithium ion secondary battery containing the additive composition are provided.

The invention provides a kind of additive composition of lithium-ion secondary battery electrolyte, wherein, the composition contains compound A shown in formula (I) or 1,4-butane sultone, ethyl methanesulfonate And one of butyl methanesulfonate, compound B shown in formula (II) and compound C shown in formula (III):

Wherein, R ₁ -R ₁₄ are the same or different, each independently selected from hydrogen or an alkyl group containing 1-4 carbon atoms.

The present invention also provides an electrolyte solution for a lithium ion secondary battery, which contains a non-aqueous solvent, an electrolyte and an additive composition, wherein the additive composition is the additive composition provided by the present invention.

The present invention also provides a lithium ion secondary battery, the battery includes a battery casing, an electrode group and an electrolyte, the electrode group and the electrolyte are sealed in the battery casing, and the electrode group includes a positive electrode, a diaphragm wound or stacked in sequence And a negative electrode, wherein the electrolyte is the electrolyte provided by the present invention.

The additive composition of the lithium-ion secondary battery electrolyte provided by the invention can improve the low-temperature discharge performance of the battery, and the electrolyte added with the additive composition of the invention makes the battery have a high discharge capacity at -10°C or -20°C. The median voltage is high and the termination internal resistance is small; it can also prolong the cycle life of the battery, greatly improve the cycle performance of the battery, the cycle expansion is small, the number of cycles is large, and the capacity remaining rate is high; it can also improve the high temperature storage performance of the battery , it is especially obvious that the recovery thickness and internal resistance increase of the battery are very small when stored at high temperature; the rate discharge performance of the battery can also be improved, and the rate of discharge of the battery under a relatively large current such as 5C and 3C after adding the additive composition of the present invention The discharge performance is high.

Therefore, the use of the additive composition provided by the present invention greatly improves the cycle performance, high-temperature storage performance, low-temperature discharge performance and rate discharge performance of the battery as a whole, and greatly improves the overall performance of the battery.

Description of drawings

Fig. 1 is the rate discharge contrast of embodiment 1-8 and comparative example 1-4;

FIG. 2 is a comparison of the remaining cycle capacity ratios of Examples 1-8 and Comparative Examples 1-4.

Detailed ways

The additive composition of lithium ion secondary battery electrolyte provided by the present invention contains compound A shown in formula (I) or 1,4-butane sultone, ethyl methanesulfonate and butyl methanesulfonate One of them, compound B shown in formula (II) and compound C shown in formula (III):

Wherein, R ₁ -R ₁₄ are the same or different, each independently selected from hydrogen or an alkyl group containing 1-4 carbon atoms.

Preferably, compound A can be one or more of 1,3-propane sultone, 1,4-butane sultone, ethyl methanesulfonate and butyl methanesulfonate; compound B It can be γ-butyrolactone; compound C can be one or more of tert-butylbenzene, 4-tert-butyltoluene and tert-amylbenzene.

According to the additive composition provided by the present invention, the compound A is 1-80 parts by weight, preferably 1-25 parts by weight, the compound B is 1-80 parts by weight, preferably 1-30 parts by weight, and the compound C It is 1-60 parts by weight, preferably 1-20 parts by weight.

The additive composition provided by the invention can suppress the decomposition of the non-aqueous solvent in the electrolyte solution of the lithium-ion secondary battery and the expansion under high-temperature storage, the overall gas volume is obviously reduced, and the interface resistance is small. Before the reduction reaction occurs in the first charge and discharge, a stable SEI film has been formed on the surface of the negative electrode of the battery, which effectively prevents the co-intercalation reaction of the solvent and the exfoliation of graphite. Moreover, in the additive composition of the present invention, the compound Bγ-butyrolactone (GBL) can also form a dense and stable SEI film on the positive electrode of the battery when it is charged and discharged for the first time, which not only prevents the slow reaction between the solvent and the positive electrode of the battery, but also has a strong Good Li ⁺ conductivity; 1,3-propane sultone (PS) (boiling point: 238°C) can increase the flash point of the electrolyte and reduce the vapor pressure; GBL (melting point -44°C, boiling point: 204°C, conductivity 14.3mS·cm ^-1 ) and tert-butylbenzenes (such as tert-butylbenzene melting point -58.1 ° C, boiling point 168.5 ° C) greatly widened the temperature range of the electrolyte and improved conductivity, so the additive of the present invention The battery cycle of the composition is greatly improved, the change of internal resistance and thickness is small when stored at high temperature, and the capacity recovery rate is high; the internal resistance of discharge at low temperature does not change much, and the median voltage is high; it also increases the Li ⁺ conduction ability. Therefore, the additive composition provided by the present invention can greatly improve circulation, high temperature storage and low temperature discharge compared with the independent additive components.

The preparation method of the electrolyte is as follows: mixing the non-aqueous solvent, the electrolyte and the additive composition together. The mixing method and order are not limited, and the performance of the electrolyte will not be affected.

The electrolyte solution of the lithium ion secondary battery provided by the present invention contains a non-aqueous solvent, an electrolyte and an additive composition, wherein the additive composition is the additive composition provided by the present invention.

According to the electrolyte solution provided by the present invention, the content of the additive composition is 0.3-22% by weight of the total amount of the electrolyte solution, preferably 0.2-5% by weight.

According to the electrolyte solution provided by the present invention, the electrolyte can use any conventional electrolyte known to those skilled in the art, such as lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ) , lithium hexafluoroarsenate (LiAsF ₆ ), lithium hexafluorosilicate (LiSiF ₆ ), lithium tetraphenylborate (LiB(C ₆ H ₅ ) ₄ ), lithium chloride (LiCl), lithium bromide (LiBr), chlorine Lithium aluminate (LiAlCl ₄ ), lithium fluorocarbon sulfonate (LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N), LiCF ₃ CO ₂ , Li(CF ₃ CO ₂ ) ₂ N and Li[(C ₂ One or more of O ₄ ) ₂ B]. The concentration of the electrolyte in the electrolytic solution is known to those skilled in the art, and is generally 0.5-1.5 mol/liter, preferably 0.8-1.2 mol/liter.

According to the electrolytic solution provided by the present invention, the non-aqueous solvent can use any conventional non-aqueous solvent known to those skilled in the art, such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), methyl formate (MF), methyl acrylate (MA), methyl butyrate (MB), ethyl acetate (EP), ethylene sulfite One or more of ester (ES), propylene sulfite (PS), methyl sulfide (DMS), diethyl sulfite (DES) and tetrahydrofuran. The proportions of various solvents are not particularly limited, and can be freely adjusted and matched according to needs. For example, the weight ratio of two solvents is 1:0.2-3.0, and the weight ratio of three solvents is 1:1-3.0:0.2-2. The weight ratio of the four solvents is 1:1-3:0.1-1.5:0.2-2.0.

The lithium ion secondary battery provided by the present invention comprises a battery casing, an electrode group and an electrolyte, the electrode group and the electrolyte are sealed in the battery casing, and the electrode group includes a positive electrode, a separator and a negative electrode wound or stacked in sequence, wherein, The electrolyte is the electrolyte provided by the present invention.

The structure of the electrode group is well known to those skilled in the art. Generally speaking, the electrode group includes a positive electrode, a separator and a negative electrode wound or stacked in sequence, and the separator is located between the positive electrode and the negative electrode. The manner of winding or stacking is well known to those skilled in the art.

The composition of the positive electrode is well known to those skilled in the art. Generally speaking, the positive electrode includes a current collector and a positive electrode material coated and/or filled on the current collector. The current collector is well known to those skilled in the art, for example, it can be selected from aluminum foil, copper foil, nickel-plated steel strip or punched steel strip. The positive electrode active material is well known to those skilled in the art, and it includes a positive electrode active material and a binder, and the positive electrode active material can be selected from conventional positive electrode active materials of lithium ion batteries. Such as lithium cobalt oxide LiCoO ₂ , lithium nickel oxide LiNiO ₂ , lithium manganese oxide LiMn ₂ O ₄ , lithium iron phosphate LiFePO ₄ and one or more of lithium nickel manganese oxide systems.

The type and content of the binder for the positive electrode are known to those skilled in the art, for example, the binder for the positive electrode can be selected from fluorine-containing resins and/or polyolefin compounds, such as polyvinylidene fluoride (PVDF) , polytetrafluoroethylene (PTFE) or one or more of styrene-butadiene rubber (SBR). Generally, the content of the positive electrode binder is 0.01-8% by weight of the positive electrode active material, preferably 1-5% by weight.

The negative electrode is a negative electrode known in the art, that is, it contains a negative electrode current collector and a negative electrode material layer coated on the negative electrode current collector. The present invention has no special limitation on the negative electrode material layer. Like the prior art, the negative electrode material layer generally includes negative electrode active materials, binders and optionally conductive agents. The negative electrode active material can adopt various negative electrode active materials commonly used in the prior art, such as carbon materials. The carbon material can be non-graphitized carbon, graphite, or carbon obtained by high-temperature oxidation of polyacetylenic polymer materials, and other carbon materials such as pyrolytic carbon, coke, organic polymer sintered material, activated carbon, etc. can also be used. The organic polymer sintered product may be a product obtained by sintering and carbonizing phenolic resin, epoxy resin and the like.

The negative electrode material provided by the present invention can also optionally contain conductive agents usually contained in negative electrode materials in the prior art. Since the conductive agent is used to increase the conductivity of the electrode and reduce the internal resistance of the battery, the present invention preferably contains a conductive agent. The content and type of the conductive agent are well known to those skilled in the art. For example, based on the negative electrode material, the content of the conductive agent is generally 0.1-12% by weight. The conductive agent may be selected from one or more of conductive carbon black, nickel powder, and copper powder.

The binder may be selected from conventional binders for lithium ion batteries, such as one or more of polyvinyl alcohol, polytetrafluoroethylene, hydroxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). Generally, the content of the binder is 0.5-8% by weight of the negative active material, preferably 2-5% by weight.

The present invention is used for the solvent of cathode material and negative electrode material and can be selected from the solvent that routinely uses in this area, as can be selected from N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N, One or more of N-diethylformamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water and alcohols. The amount of the solvent is such that the slurry can be coated on the current collector. Generally, the amount of the solvent is such that the concentration of the positive electrode active material in the slurry is 40-90% by weight, preferably 50-85% by weight.

Various methods known in the art can be used for the preparation method of the positive electrode and the negative electrode.

According to the lithium ion secondary battery provided by the present invention, the diaphragm layer is arranged between the positive electrode and the negative electrode, has electrical insulation performance and liquid retention performance, and is sealed in the battery case together with the positive electrode, negative electrode and electrolyte. The separator layer can be selected from various separator layers used in lithium-ion secondary batteries known to those skilled in the art, such as polyolefin microporous membrane, modified polypropylene felt, polyethylene felt, glass fiber felt, ultra-fine glass Composite membrane made of fiber paper vinylon felt or nylon felt and wettable polyolefin microporous membrane by welding or bonding.

According to the lithium ion battery provided by the present invention, the preparation method of the battery comprises arranging a diaphragm between the positive electrode and the negative electrode to form an electrode group, accommodating the electrode group in a battery case, injecting an electrolyte, and then sealing the battery case, Wherein, the electrolyte is the electrolyte provided by the present invention. Except that the electrolyte is prepared according to the method provided by the present invention, other steps are well known to those skilled in the art.

The following examples further illustrate the present invention, but should not be interpreted as limiting the protection scope of the present invention. Through the description of these specific examples, those skilled in the art can more clearly understand the advantages of the additive composition of the present invention.

Example 1

This example illustrates the additive composition, electrolyte, battery containing the electrolyte and their preparation methods provided by the present invention.

1. Preparation of electrolyte

50 grams of vinyl carbonate (EC), 50 grams of methyl ethyl carbonate (EMC) and 50 grams of diethyl carbonate (DEC) were mixed into a mixed solvent, and 20.81 grams of LiPF ₆ electrolyte was added to the mixed solvent, Make the electrolytic solution that concentration is 1M, then add additive composition, 1,3-propane sultone (PS) is 0.34 gram, gamma-butyrolactone (GBL) 10.69 gram, tert-butylbenzene 0.34 gram in the additive composition gram, the content of the additive composition in the prepared electrolytic solution is 6.4% by weight.

2. Preparation of positive electrode

Dissolve 90 grams of polyvinylidene fluoride in 1350 grams of N-methyl-2-pyrrolidone (NMP) solvent to prepare an adhesive solution, then add ₂₈₂₀ grams of LiCoO2 and 90 grams of acetylene black to the resulting solution, and mix well The positive electrode slurry is uniformly prepared, and the positive electrode slurry is evenly coated on a 20-micron aluminum foil, dried at 125°C for 1 hour, calendered, and cut to obtain a positive electrode sheet of about 450×44×0.125 mm. The positive electrode sheet contains 8. 10 grams of LiCoO ₂ .

3. Preparation of negative electrode

30 grams of hydroxymethyl cellulose CMC and 75 grams of styrene-butadiene rubber (SBR) latex are dissolved in 1875 grams of water to prepare a binder solution, 1395 grams of graphite are added to the binder solution, and mixed uniformly to obtain graphite Negative electrode slurry, the negative electrode slurry is evenly coated on a 12-micron thick copper foil and dried at 125°C for 1 hour, calendered and cut to obtain a negative electrode sheet of about 448×44×0.125 mm, and the negative electrode sheet contains 4.55 grams of graphite.

4. Preparation of battery

The above-mentioned positive and negative electrode sheets and a 20-micron-thick polypropylene separator are wound into an electrode group of a square lithium-ion battery, and the electrodes are assembled into a square battery aluminum shell of 5 mm × 34 mm × 50 mm, and then the above-mentioned 3.2 milliliters of the prepared electrolytic solution was injected into the battery case, and sealed to make a 053450A type lithium-ion secondary battery with a design capacity of 1150 milliampere hours.

Example 2

Electrolyte and lithium ion secondary battery are prepared according to the same method as in Example 1, except that PS is replaced with 1,4-butane sultone, and 1,4-butane sultone is 0.91 in the additive composition gram, GBL is 7.25 grams, tert-butylbenzene is 2.71 grams, and the content of additive composition in the prepared electrolytic solution is 5.7 weight %.

Example 3

Electrolyte and lithium ion secondary battery were prepared according to the same method as in Example 1, except that ethyl methanesulfonate was used to replace PS, and ethyl methanesulfonate in the additive composition was 1.43 grams, GBL was 5.35 grams, The content of tert-butylbenzene is 0.89 g, and the content of the additive composition in the prepared electrolyte is 4.3% by weight.

Example 4

Electrolyte and lithium ion secondary battery were prepared according to the same method as in Example 1, except that butyl methanesulfonate was used to replace PS, and butyl methanesulfonate was 2.16 grams, GBL was 3.60 grams, The content of tert-butylbenzene was 3.60 grams, and the content of the additive composition in the prepared electrolytic solution was 5.2% by weight.

Example 5

Electrolyte and lithium-ion secondary battery were prepared according to the same method as in Example 1, except that PS in the additive composition was 2.71 grams, GBL was 2.71 grams, and tert-butylbenzene was 4.52 grams. The additive in the prepared electrolyte The content of the composition was 5.5% by weight.

Example 6

Electrolyte and lithium-ion secondary battery were prepared according to the same method as in Example 1, except that PS in the additive composition was 3.58 grams, GBL was 1.79 grams, and tert-butylbenzene was 2.68 grams. The additive in the prepared electrolyte The content of the composition was 4.5% by weight.

Example 7

Electrolyte and lithium ion secondary battery were prepared according to the same method as in Example 1, except that in the additive composition, PS was 5.48 grams, GBL was 0.91 grams, and 4-tert-butyltoluene was 5.48 grams. The prepared electrolytic solution The content of the additive composition is 6.5% by weight.

Example 8

Electrolyte and lithium ion secondary battery were prepared according to the same method as in Example 1, except that tert-butylbenzene was replaced with tert-amylbenzene, and PS in the additive composition was 9.93 grams, GBL was 9.93 grams, tert-amylbenzene Benzene was 7.94 grams, and the content of the additive composition in the prepared electrolytic solution was 14% by weight.

Comparative example 1

Electrolyte solution and lithium ion secondary battery were prepared according to the same method as in Example 1, except that no additive composition was added.

Comparative example 2

Electrolyte and lithium-ion secondary battery were prepared according to the same method as in Example 1, except that only 3.49 grams of additive PS were added, and the content of additive in the prepared electrolytic solution was 2% by weight.

Comparative example 3

Electrolyte and lithium-ion secondary battery were prepared according to the same method as in Example 1, except that only 3.49 grams of additive GBL was added, and the content of additive in the prepared electrolytic solution was 2% by weight.

Comparative example 4

Electrolyte and lithium ion secondary battery were prepared according to the same method as in Example 1, except that only 3.49 grams of tert-butylbenzene was added, and the content of additive in the prepared electrolytic solution was 2% by weight.

The proportions of the components in the electrolytes of Examples 1-8 and Comparative Examples 1-4 are listed in Table 1.

Battery performance test

1. Determination of sub-volume capacity, thickness and internal resistance:

With the lithium ion secondary battery (30 batteries of every kind of condition, get its average value) that above-mentioned embodiment 1-8 and comparative example 1-4 gain, earlier 100 milliamps are charged to 3.9 volts, after placing 24 hours, use 550 Charge to 4.2 volts with mA constant current and constant voltage, and then discharge to 3.0 volts with 550 mA. The capacity released after the battery is charged to 4.2 V is the sub-capacity (discharge current mA×discharge time h); after measuring the capacity, the battery is recharged Take it off at 3.9 volts, measure the thickness with a caliper (take the middle point of the battery); measure the internal resistance with an internal resistance meter. The measured capacity, battery thickness and internal resistance are listed in Table 2.

Table 1

PS (grams) 1,4-butane sultone (g) Ethyl methanesulfonate (g) Butyl methanesulfonate (grams) GBL (grams) tert-butylbenzene (g) 4-tert-butyltoluene (g) tert-Amylbenzene (g) Example 1 0.34 - - 0.2 10.69 0.34 - - Example 2 - 0.91 - - 7.25 2.17 - - Example 3 - - 1.43 - 5.35 0.89 - - Example 4 - - - 2.16 3.60 3.60 - - Example 5 2.71 - - - 2.71 4.52 - - Example 6 3.58 - - - 1.79 2.68 - -

PS (grams) 1,4-butane sultone (g) Ethyl methanesulfonate (g) Butyl methanesulfonate (grams) GBL (grams) tert-butylbenzene (g) 4-tert-butyltoluene (g) tert-Amylbenzene (g) Example 7 5.48 - - - 0.91 - 5.48 - Example 8 9.93 - - - 9.93 - - 7.94 Comparative Example 1 - - - - - - - - Comparative example 2 3.49 - - - - - - - Comparative example 3 - - - - 3.49 - - - Comparative example 4 - - - - - 3.49 - -

Table 2

capacity thickness internal resistance Example 1 1148.6 5.36 40.2 Example 2 1149.5 5.35 40.0 Example 3 1151.4 5.34 40.8 Example 5 1152.5 5.32 40.1 Example 4 1154.2 5.29 40.7 Example 6 1154.8 5.3 40.5 Example 7 1151.7 5.33 40.9 Example 8 1155.1 5.34 40.7 Comparative example 1 1136.3 5.52 42.6 Comparative example 2 1133.7 5.42 41.5 Comparative example 3 1135.6 5.41 41.8 Comparative example 4 1136.3 5.40 41.3

It can be seen from Table 2 that the addition of the additive composition increases the capacity of the battery and reduces the internal resistance and gas generation of the battery. This is mainly attributed to the formation of a better SEI film and reduced solvent decomposition.

2. High temperature performance test

The lithium-ion secondary battery obtained in above-mentioned Examples 1-8 and Comparative Examples 1-4 is carried out high-temperature performance test, and test method is: battery is charged to 4.2 volts with 1100 milliampere constant current constant voltages, measure open-circuit voltage, internal resistance ( That is, initial voltage, initial internal resistance, and initial thickness), and then store the battery at (85±2)°C for 48 hours. After the storage period expires, measure the thickness of the battery (thickness after 85°C storage), and then in After standing at ±7)°C for about 1 hour, measure the open circuit voltage and internal resistance, and discharge the battery at 1100 mA to 3.0 volts, and record the discharge capacity (remaining capacity) of each battery. After the battery is fully charged and left for 5 minutes, it is discharged to 3.0 volts with a current of 1100 mA, and it is cycled three times in a row, and the capacity of each cycle (recovery capacity), the internal resistance of the third cycle of full charge (recovery internal resistance) and Thickness (recovery thickness). Calculate the capacity recovery rate, thickness increase, internal resistance increase and internal resistance change of the battery according to the following formula:

Capacity recovery rate (%) = recovery capacity of the third cycle/initial capacity × 100%;

Thickness increase (mm) = recovery thickness - initial thickness

Internal resistance increase (milliohm) = recovery internal resistance - initial internal resistance

Internal resistance change = recovery internal resistance / initial internal resistance × 100%.

Table 3 lists the above test results of capacity recovery rate, thickness increase, internal resistance increase and internal resistance change.

It can be seen from Table 3 that, compared with the batteries of Comparative Examples 1-4 at a high temperature of 85°C, the batteries of Examples 1-8 of the present invention have better suppressed the increase of battery thickness and internal resistance, and improved capacity recovery rate. This shows that the 85°C high-temperature storage performance (ie, high-temperature performance) of the battery in the embodiment of the present invention is significantly improved.

table 3

Capacity remaining rate Thickness increase (mm) Increased internal resistance (mΩ) Internal resistance change Example 1 74.03 0.73 4 9.7% Example 2 75.71 0.69 3.9 9.5% Example 3 78.54 0.69 3.6 8.8% Example 4 79.38 0.68 3.5 8.6% Example 5 83.05 0.64 3.7 9.0% Example 6 81.64 0.58 3.1 7.7% Example 7 81.58 0.66 3.8 9.3% Example 8 82.12 0.63 3.3 8.1% Comparative example 1 56.32 1.23 8.5 20.0% Comparative example 2 68.23 0.85 5.5 13.3%

Capacity remaining rate Thickness increase (mm) Increased internal resistance (mΩ) Internal resistance change Comparative example 3 61.09 1.07 6.4 15.3% Comparative example 4 63.22 0.89 6.15 14.9%

3. Low temperature discharge performance test

The lithium-ion secondary batteries obtained in the above-mentioned Examples 1-8 and Comparative Examples 1-4 were subjected to a high-temperature performance test. The test method was: the battery was charged to 4.2 volts with 1100 constant current and constant voltage, and then discharged to 3.0 volts with 1 C milliampere. volts, the discharge capacity is the initial capacity, and then the battery is charged to 4.2 volts with 1100 mA constant current and constant voltage, and discharged at -10 ℃ with 1100 mA, and the capacity when discharged to 3.0 volts and 2.75 volts is recorded respectively. Then charge the battery discharged at -10°C with 1100 mA constant current and constant voltage to 4.2 volts, and discharge at -20°C with 1100 mA, and record the capacity when discharged to 3.0 volts and 2.75 volts respectively , median voltage, and termination internal resistance. The capacity, median voltage and termination internal resistance measured at -10°C and -20°C when discharged to 3.0 volts and 2.75 volts are listed in Table 4.

Table 4

It can be seen from Table 4 that since the batteries of Examples 1-8 of the present invention form excellent SEI films, the examples with the addition of the additive composition have higher electrical conductivity and lower battery performance at low temperatures than Comparative Examples. With internal resistance and high median voltage, the capacity remaining rate is significantly improved.

4. High current discharge performance

The lithium-ion secondary batteries obtained in the above-mentioned Examples 1-8 and Comparative Examples 1-4 are tested for rate performance. The test method is as follows: the battery is charged to 4.2 volts with 1100 constant current and constant voltage, and then discharged to 3.0 volts with 220 milliamperes. volts, the discharge capacity is 0.2C capacity; then charge the battery to 4.2 volts with 1100 mA constant current and constant voltage, and discharge to 3.0 volts with 1100 mA, the discharge capacity is 1C capacity; then charge to 4.2 volts with 1100 mA constant current and constant voltage Volt, use 2200 mA to discharge to 3.0 volts, the discharge capacity is 2C capacity; use 1100 mA constant current and constant voltage to charge to 4.2 volts, use 3300 mA to discharge to 3.0 volts, the discharge capacity is 3C capacity; use 1100 mA constant current constant Charge to 4.2 volts, discharge to 3.0 volts with 5500 mA, and the discharge capacity is 5C capacity.

The magnification is calculated according to the following formula: x magnification = x capacity under C/0.2C capacity.

The obtained rate results for each example are listed in Table 5 and shown in FIG. 1 .

table 5

5C 3C 2C 1C 0.2C Example 1 60.8 79.1 95.2 97.4 100 Example 2 65.4 83.2 96.6 99.2 100 Example 3 64.6 82.4 95.8 98.7 100 Example 4 63.3 80.9 95.3 98.2 100 Example 5 61.2 78.5 95.1 98.5 100 Example 6 59.8 77.0 94.5 98.4 100 Example 7 59.7 76.9 95.2 99.6 100 Example 8 62.9 80.4 95.4 98.3 100 Comparative example 1 50.6 69.7 91.2 96.0 100 Comparative example 2 53.2 72.6 92.0 96.9 100 Comparative example 3 56.8 75.6 94.1 98.0 100 Comparative example 4 54.4 73.9 92.4 97.3 100

It can be seen from FIG. 1 that compared with Comparative Examples 1-4, Examples 1-8 added with the additive composition have a higher rate, and exhibit superior Li ion conductivity when discharged at a high rate.

5. Cycle performance test

The lithium-ion secondary batteries obtained in the above-mentioned Examples 1-8 and Comparative Examples 1-4 are subjected to a cycle performance test. The test method is as follows: the battery is loaded into the performance tester BS-9300 in the correct way, and the battery is first charged at 1100 Charge to 4.2 volts with mA constant current and constant voltage, put it aside for 5 minutes, discharge to 3.0 volts with 1100, and cycle like this, until the remaining capacity reaches 70%, record the capacity of each cycle, the internal resistance of the discharge state, and the median voltage; The remaining ratio of out-of-cycle capacity is listed in Table 6 and compared with that in Figure 2.

Capacity remaining rate of X cycles = capacity of X cycles / capacity of the first cycle × 100%

Table 6

Cycles Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative example 1 Comparative example 2 Comparative example 3 Ratio compared to 4 1 100 100 100 100 100 100 100 100 100 100 100 100 5 98.5 98.7 98.7 98.8 99.2 99.3 98.6 98.5 98.6 98.6 98.6 98.4 10 96.6 96.6 97.1 97.4 97.5 97.4 97.1 96.8 96.6 96.6 96.7 96.6 30 94.6 94.7 95.1 95.0 95.6 95.7 95.2 94.9 94.1 94.3 94.5 94.5 60 93.2 93.1 94.1 93.9 94.4 94.3 94.0 93.9 92.3 92.9 93.1 93.0 90 91.8 91.7 92.9 92.9 93.3 93.2 92.8 92.6 90.4 91.7 91.8 91.6 120 90.5 90.4 91.5 91.4 92.4 92.1 91.4 91.3 88.4 89.4 90.4 90.4 150 89.6 89.5 90.6 90.6 91.4 91.2 90.5 90.4 86.9 88.3 89.4 89.4 180 88.6 88.5 89.5 89.8 90.5 90.3 89.6 89.4 85.6 87.1 88.1 88.4 210 87.4 87.3 88.4 88.9 89.6 89.2 88.4 88.0 84.2 85.6 86.5 86.9 240 86.4 86.3 87.3 88.0 88.6 88.1 87.5 87.2 82.9 84.7 85.3 85.7 270 85.6 85.3 86.3 87.2 87.7 87.2 86.7 86.3 81.3 83.7 84.3 84.4 300 84.5 84.4 85.4 86.4 87.0 86.5 85.8 85.4 80.0 82.6 83.2 83.3 330 83.6 83.4 84.5 85.5 86.3 85.8 84.8 84.6 78.4 81.2 82.0 81.8 360 82.8 82.5 83.5 84.6 85.7 85.1 83.9 83.6 76.7 80.4 80.9 80.4 390 81.9 81.6 82.5 83.8 85.0 84.4 83.0 82.7 74.4 78.8 79.5 79.4 420 80.9 80.4 81.5 83.0 84.3 83.6 82.1 81.8 72.2 77.6 78.1 78.2

Cycles Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative example 1 Comparative example 2 Comparative example 3 Ratio compared to 4 450 79.7 79.2 79.9 82.1 83.6 82.8 81.2 80.7 70.0 76.2 76.7 77.0 480 78.1 77.6 78.9 81.3 82.9 81.9 80.3 79.3 67.2 74.5 75.0 75.9

It can be seen from Table 6 or FIG. 2 that the cycle performance of Examples 1-8 added with the additive composition is significantly enhanced compared with Comparative Examples 1-4.

As can be seen from the above test results, the additive composition provided by the present invention greatly improves the cycle performance, high-temperature storage performance, low-temperature discharge performance and rate discharge performance of the lithium-ion secondary battery, so that the overall performance of the battery is improved. Great improvement.

Claims (10)

1. the compositions of additives of an electrolyte of lithium-ion secondary battery, it is characterized in that, said composition is by the compd A or 1 shown in the formula (I), a kind of in 4-butane sultone, ethylmethane sulfonate and the butyl methyl sulfonate, the Compound C shown in compd B shown in the formula (II) and the formula (III) is formed:

Wherein, R ₁-R ₁₄Identical or different, be selected from hydrogen independently of one another or contain the alkyl of 1-4 carbon atom.

2. compositions of additives according to claim 1, wherein, the content of described compd A, compd B and Compound C is that described compd A is the 1-80 weight portion, and described compd B is the 1-80 weight portion, and described Compound C is the 1-60 weight portion.

3. compositions of additives according to claim 2, wherein, described compd A is the 1-25 weight portion, and described compd B is the 1-30 weight portion, and described Compound C is the 1-20 weight portion.

4. according to claim 1,2 or 3 described compositions of additives, wherein, described compd A is 1,3-propane sultone; Described compd B is a gamma-butyrolacton; Described Compound C is one or more in tert-butyl benzene, 4-t-butyltoluene and the tert-amyl benzene.

5. the electrolyte of a lithium rechargeable battery, this electrolyte contains nonaqueous solvents, electrolyte and compositions of additives, it is characterized in that, and described compositions of additives is any described compositions of additives of claim 1-4.

6. electrolyte according to claim 5 wherein, is benchmark with electrolyte, and the content of described compositions of additives is 0.3-22 weight %.

7. electrolyte according to claim 6, wherein, the content of described compositions of additives is 0.2-5 weight %.

8. electrolyte according to claim 5, wherein, described nonaqueous solvents is selected from one or more in vinyl carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, methyl formate, methyl acrylate, methyl butyrate, ethyl acetate, ethylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite and the oxolane; Wherein, described electrolyte is selected from LiPF ₆, LiClO ₄, LiBF ₄, LiAsF ₆, LiSiF ₆, LiB (C ₆H ₅) ₄, LiCl, LiBr, LiAlCl ₄, LiCF ₃SO ₃, Li (CF ₃SO ₂) ₂N, LiCF ₃CO ₂, Li (CF ₃CO ₂) ₂N and Li[(C ₂O ₄) ₂B] in one or more.

9. according to claim 5 or 8 described electrolyte, wherein, the concentration of described electrolyte in described electrolyte is the 0.5-1.5 mol.

10. lithium rechargeable battery, this battery comprises battery container, electrode group and electrolyte, electrode group and electrolyte are sealed in the battery container, the electrode group comprises reels or stacked positive pole, barrier film and negative pole successively, it is characterized in that described electrolyte is any described electrolyte among the claim 5-9.

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