WO2022267391A1

WO2022267391A1 - Electrolyte additive, non-aqueous electrolyte, and lithium ion battery

Info

Publication number: WO2022267391A1
Application number: PCT/CN2021/139140
Authority: WO
Inventors: 白晶; 毛冲; 王霹霹; 潘东优; 欧霜辉; 黄秋洁; 戴晓兵
Original assignee: 珠海市赛纬电子材料股份有限公司
Priority date: 2021-06-25
Filing date: 2021-12-17
Publication date: 2022-12-29
Also published as: CN113363583B; CN113363583A

Abstract

An electrolyte additive, a non-aqueous electrolyte, and a lithium ion battery. The electrolyte additive comprises a compound as represented by formula A, wherein R is fluorosulfonyl or trifluoromethylsulfonyl. The electrolyte additive has high solubility and good wettability, and can greatly improve the low-temperature cycle performance of lithium ion batteries without increasing the impedance.

Description

Electrolyte additive, non-aqueous electrolyte and lithium-ion battery thereof

technical field

The application belongs to the technical field of lithium-ion batteries, and in particular relates to an electrolyte additive, a non-aqueous electrolyte and a lithium-ion battery.

Background technique

Lithium-ion batteries are widely used in 3C digital products, power tools, electric vehicles, aerospace and other fields due to their high operating voltage, high energy density, long life, wide operating temperature range, and environmental friendliness. As people's requirements for batteries are getting higher and higher, thin and light and high energy density have become the development trend of batteries, especially for 3C digital products, such as mobile phone batteries, tablet computers and photography equipment. The existing common commercial lithium-ion cathode materials include lithium iron phosphate, lithium cobaltate, and nickel-cobalt-manganese ternary materials. Low, so the energy density is not high enough.

As the market demand for high-energy-density lithium-ion batteries is increasing, increasing the charge cut-off voltage of positive electrode materials is an effective means to increase energy density, such as the commercial lithium cobalt oxide battery voltage 4.2V→4.35V→4.4V →4.45V→4.48V→4.5V, but there are also some problems in increasing the charging cut-off voltage of the positive electrode material (≥4.5V): For example, the compatibility of the conventional electrolyte used with the positive electrode material at high voltage is extremely poor, and commonly used Carbonate-based electrolytes are prone to oxidative decomposition under high voltage, and the by-products produced have a negative impact on the performance of lithium-ion batteries. Suffering from corrosion, especially at low temperatures, the low-temperature performance of lithium-ion batteries is obviously insufficient. Therefore, how to ensure the cycle performance and high-temperature storage performance of lithium-ion batteries under the premise of increasing the cut-off voltage of cathode materials has become the focus of research.

application content

The purpose of this application is to provide an electrolyte additive, which has high solubility and good wettability, and can greatly increase the low-temperature cycle performance of lithium-ion batteries without increasing impedance.

Another object of the present application is to provide a non-aqueous electrolyte that can improve the cycle performance and high-temperature storage performance of lithium-ion batteries.

Another object of the present application is to provide a lithium-ion battery, which has better cycle performance and high-temperature storage performance.

In order to achieve the above purpose, the application provides an electrolyte additive, including the compound shown in formula A,

Wherein, R is a sulfonyl fluoride group or a trifluoromethylsulfonyl group.

Compared with the prior art, the present application provides an electrolyte additive, including a compound shown in formula A, formula A has a special structure, the electrolyte additive has a large solubility in the electrolyte, and has good wettability, and can Fully infiltrate the electrode piece in a short time, therefore, the electrolyte additive has good film-forming ability, and at the same time, the formula A has a cyclic sulfonamide group that can form an organic compound containing N and S, and an organic compound of N and S Attached to the surface of the positive and negative electrodes to form a stable SEI film. When the R group is a sulfonyl fluoride group or a trifluoromethylsulfonyl group, the sulfonyl fluoride group and the trifluoromethylsulfonyl group can regulate the LiSO ₃ and ROSO in the SEI film. ₂ The ratio of sulfur-containing compounds such as Li, in addition, some compounds such as LiF and fluorine-containing sulfonyl lithium are regenerated to further increase the ionic conductivity of the SEI film, thereby reducing the impedance of the SEI film, so lithium-ion batteries have better low-temperature cycles performance. Therefore, the compound represented by formula A not only has high solubility and good wettability, but also can greatly increase the low-temperature cycle performance of lithium-ion batteries without increasing impedance.

Specifically, when the R group is a sulfonyl fluoride group, the formula A is ASE-FSI, and the structural formula is as follows; when the R group is a trifluoromethylsulfonyl group, the formula A is ASE-TFSI, and the structural formula is as follows:

Specifically, ASE-FSI and ASE-TFSI can be prepared through the following synthetic routes:

In order to achieve the above object, the application provides a non-aqueous electrolytic solution, including lithium salt, non-aqueous organic solvent and the above-mentioned electrolytic solution additive, the mass percentage of the electrolytic solution additive in the non-aqueous electrolytic solution is 0.5-5% .

Compared with the prior art, the non-aqueous electrolyte of the present application includes a high content of the compound shown in formula A, formula A has a special structure, the electrolyte additive has a large solubility in the electrolyte, and has good wettability, and can The electrode piece is fully infiltrated in a short time, so the electrolyte additive has good film-forming ability; at the same time, the formula A has a cyclic sulfonamide group and can form an organic compound containing N and S, and an organic compound of N and S Attached to the surface of the positive and negative electrodes to form a relatively stable SEI film, and when the electrolyte additive content is high, the SEI film is thicker, which can improve the normal temperature cycle performance, high temperature cycle performance and high temperature storage performance of lithium-ion batteries. At the same time, the R-based When it is a sulfonyl fluoride group or a trifluoromethylsulfonyl group, the sulfonyl fluoride group and the trifluoromethylsulfonyl group can regulate the ratio of sulfur-containing compounds such as LiSO ₃ , ROSO ₂ Li in the SEI film, and generate some such as Compounds such as LiF and fluorine-containing sulfonyl lithium further increase the ionic conductivity of the SEI film, thereby reducing the impedance of the SEI film, thereby improving the low-temperature cycle performance of the lithium-ion battery. The non-aqueous electrolyte of the present application can improve the cycle performance and high-temperature storage performance of lithium-ion batteries, so the non-aqueous electrolyte of the present application is an electrolyte with relatively comprehensive performance.

Preferably, the lithium salt of the present application is lithium hexafluorophosphate, lithium difluorophosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, bistrifluoromethane At least one of lithium sulfonyl imide, lithium bisfluorosulfonyl imide and lithium tetrafluoromalonate phosphate.

Preferably, the mass percentage of the lithium salt of the present application in the non-aqueous electrolyte is 10-20%. Specifically but not limited to 10%, 12%, 15%, 18%, 20%.

Preferably, the non-aqueous organic solvent of the present application is ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate, butyl acetate , at least one of γ-butyrolactone, propyl propionate, ethyl propionate and ethyl butyrate.

Preferably, the mass percentage of the non-aqueous organic solvent of the present application in the non-aqueous electrolyte is 60-80%. Specifically but not limited to 60%, 65%, 70%, 75%, 80%.

Preferably, the non-aqueous electrolytic solution of the present application also includes additives, and the additives are 2,2,2-ethyl trifluorocarbonate, 2,2,2-diethyl trifluorocarbonate, 2,2 ,2-trifluoroethylene propyl carbonate, vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), diethyl pyrocarbonate, 1,3-propanesulfonate Acid lactone (PS), vinyl sulfate (DTD), tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, 4,4'-bi-1,3-dioxolane -2,2'-Diketone (BDC), 3,3-Diethylene Disulfate (BDTD), Triallyl Phosphate, Trialgyl Phosphate, Succinonitrile, Adiponitrile, 1,3,6 - at least one of hexanetrinitrile and 1,2-bis(cyanoethoxy)ethane.

Preferably, the mass percentage of the auxiliary agent of the present application in the non-aqueous electrolyte is 2-10.5%. Specifically but not limited to 2%, 5%, 7%, 9%, 10.5%.

In order to achieve the above purpose, the present application provides a lithium ion battery, including positive electrode material and negative electrode material, and also includes the above-mentioned non-aqueous electrolyte, and the highest charging voltage is 4.53V.

Compared with the prior art, the non-aqueous electrolyte of the lithium ion battery of the present application includes the compound shown in formula A, and formula A has a special structure, has greater solubility in the electrolyte, and can fully Infiltrate the electrode sheet, and the formula A can form an organic compound containing N and S, and the organic compound of N and S adheres to the surface of the positive and negative electrodes to form a relatively stable SEI film, and when the content of formula A is higher, the SEI film is thicker , the normal temperature cycle performance, high temperature cycle performance and high temperature storage performance are improved, and when the R group is a sulfonyl fluoride group or a trifluoromethylsulfonyl group, the sulfonyl fluoride group and the trifluoromethylsulfonyl group can regulate the SEI membrane. The proportion of sulfur-containing compounds such as LiSO ₃ , ROSO ₂ Li, and the regeneration of some compounds such as LiF and fluorine-containing sulfonyl lithium further increase the ionic conductivity of the SEI film, thereby reducing the impedance of the SEI film, so the low-temperature cycle performance is also improved. up. Therefore, the lithium-ion battery of the present application has better cycle performance and high-temperature storage performance.

Preferably, the positive electrode material of the lithium ion battery of the present application is lithium cobalt oxide.

Preferably, the negative electrode material of the lithium ion battery of the present application is natural graphite.

Description of drawings

Fig. 1 is the initial DCIR diagram of the lithium ion battery after the capacity of Example 1, Example 3, Example 6, Example 8, Comparative Example 1, and Comparative Example 4-7.

detailed description

In order to better illustrate the purpose, technical solutions and beneficial effects of the present application, the present application will be further described below in conjunction with specific embodiments. It should be noted that the implementation of the method described below is a further explanation of the present application, and should not be regarded as a limitation of the present application.

First, the solubility experiments of ASE-FSI, ASE-TFSI, ASE, ASE-Li, and ASE-Et were carried out, and the results are shown in Table 1.

Wherein ASE-Li and ASE-Et can be prepared by the following synthetic routes:

Solubility test: In a glove box filled with nitrogen (O ₂ <1ppm, H ₂ O<1ppm), ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed according to the mass ratio of 1 : 1:2 mixed evenly to obtain 80.0g of non-aqueous organic solvent, sealed and packaged the mixed solution and placed it in the freezer (-4°C) for 2 hours, then took it out, and put it in a nitrogen-filled glove box (O ₂ <1ppm, H ₂ O <1ppm), slowly add 20g of lithium hexafluorophosphate into the mixed solution, and mix well to make an electrolyte solution. Dissolve ASE-FSI, ASE-TFSI, ASE, ASE-Li, and ASE-Et in the above-mentioned electrolyte respectively, and test the mass of the dissolved solute when it reaches saturation in 100 grams of electrolyte, denoted as S g , according to the following formula to calculate the highest solubility of each substance.

Maximum solubility (%)=S/(S+100)×100%

Table 1 Solubility Results

添加剂additive	最高溶解度highest solubility
ASEASE	0.6％0.6%
ASE-LiASE-Li	0.4％0.4%
ASE-EtASE-Et	0.6％0.6%
ASE-FSIASE-FSI	7.5％7.5%
ASE-TFSIASE-TFSI	6.5％6.5%

It can be seen from the results in Table 1 that the solubility of ASE-FSI and ASE-TFSI in the electrolyte is significantly higher than that of ASE, ASE-Li and ASE-Et.

Example 1

In a glove box filled with nitrogen (O ₂ <1ppm, H ₂ O<1ppm), ethylene carbonate, diethyl carbonate and ethyl methyl carbonate were mixed uniformly according to the mass ratio of 1:1:2, and 79g of non-aqueous organic solvent, and then 1 g of ASE-FSI was added as an additive and a mixed solution was obtained. Seal the mixed solution and place it in the freezer (-4°C) for 2 hours, then take it out, and slowly add 20g of lithium hexafluorophosphate to the mixed solution in a nitrogen-filled glove box (O ₂ <1ppm, H ₂ O<1ppm), and mix well After that, a non-aqueous electrolyte solution is made.

The non-aqueous electrolyte formulas of Examples 2-17 and Comparative Examples 1-7 are shown in Table 2, and the steps of preparing the non-aqueous electrolyte are the same as in Example 1.

Table 2 Non-aqueous electrolyte formula

Wherein TFSI is trifluoromethanesulfonamide, and its structural formula is as follows:

Lithium cobalt oxide with the highest charging voltage of 4.53V is the positive electrode material, natural graphite is the negative electrode material, and the electrolytes of Examples 1 to 17 and Comparative Examples 1 to 7 are used to make lithium ion batteries with reference to the conventional lithium battery preparation method, and respectively Carry out low-temperature cycle performance, normal temperature cycle performance, high-temperature cycle performance, and high-temperature storage performance according to the following methods, and the test results are shown in Table 3; and Example 1, Example 3, Example 6, Example 8, Comparative Example 1, The DCIR test in the initial state was performed on the lithium-ion batteries after 4-7 minutes of capacity in Comparative Example, and the test results are shown in FIG. 1 .

Low temperature cycle test:

Place the battery in an oven at a constant temperature of -10°C, charge it at a constant current of 0.5C to 4.53V, then charge it at a constant voltage until the current drops to 0.05C, and then discharge it at a constant current of 1C to 3.0V, and so on. Record the discharge capacity of the first lap and the discharge capacity of the last lap, and calculate the capacity retention rate according to the following formula:

Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle × 100%

Normal temperature cycle performance test:

Place the lithium-ion battery in an environment of 25°C, charge it with a constant current of 1C to 4.53V, then charge it with a constant voltage until the current drops to 0.05C, and then discharge it with a constant current of 1C to 3.0V, and cycle like this, then DCIR is measured every 50 laps. Record the discharge capacity of the first cycle and the discharge capacity of the last cycle, as well as the DCIR every 50 cycles. Calculate the capacity retention rate and DCIR improvement rate of the high temperature cycle according to the following formula:

DCIR improvement rate = DCIR of the last 50 laps/DCIR of the first lap x 100%.

High temperature cycle performance test:

Put the battery in an oven with a constant temperature of 45°C, charge it with a constant current of 1C to 4.53V, then charge it with a constant voltage until the current drops to 0.05C, and then discharge it with a constant current of 1C to 3.0V, and cycle like this, and then every Measure DCIR every 50 laps. Record the discharge capacity of the first cycle and the discharge capacity of the last cycle, as well as the DCIR every 50 cycles. Calculate the capacity retention rate and DCIR improvement rate of the high temperature cycle according to the following formula:

DCIR improvement rate = DCIR of the last 50 laps/DCIR of the first lap x 100%.

High temperature storage performance test:

Charge the formed battery to 4.53V at 1C constant current and constant voltage at room temperature, measure the initial discharge capacity and thickness of the battery, store it at 85°C for 8 hours, and then discharge it to 3.0V at 1C to measure the capacity retention and recovery of the battery Capacity and battery thickness after storage. Calculated as follows:

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

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

Thickness expansion (%)=(battery thickness after storage-initial battery thickness)/initial battery thickness×100%.

Initial DCIR test:

Charge the divided battery at 1C constant current and constant voltage to 4.53V at room temperature, then discharge the battery at 0.5C constant current at room temperature until the charge capacity is 50% SOC, then leave the battery for 5 minutes and then discharge at 1C for 1s. Then put the battery on hold for 5min and then discharge it at 0.1C for 10s.

DCIR=(voltage V1 after the first discharge-voltage V2 after the second discharge)/(first discharge current I1-second discharge current I2)

Table 3 Cycle and high temperature storage performance results

From the results in Table 3, it can be seen that the low-temperature cycle performance of Examples 1-17 is significantly better than that of Comparative Examples 1-7. This is because when the compound shown in Formula A is used as an electrolyte additive, the electrolyte additive has a large solubility in the electrolyte. And it has good wettability, and can fully infiltrate the pole piece in a short time. Therefore, the electrolyte additive has good film-forming ability, and at the same time, the formula A has a cyclic sulfonamide group that can form an organic compound containing N and S. The organic compound of N and S is attached to the surface of the positive and negative electrodes to form a stable SEI film, and the sulfonyl fluoride group in ASE-FSI and the trifluoromethylsulfonyl group in ASE-TFSI can regulate the LiSO ₃ in the SEI film , ROSO ₂ Li and other sulfur-containing compounds, in addition to regenerate some compounds such as LiF, fluorine-containing sulfonyl lithium and other compounds to further increase the ionic conductivity of the SEI film, thereby achieving the purpose of reducing impedance, so the compound shown in formula A as When the electrolyte additive is used, the lithium-ion battery can have better low-temperature cycle performance.

From the results in Table 3, it can be seen that the cycle performance and high-temperature storage performance of Example 1 and Examples 3-17 are significantly better than those of Comparative Examples 1-7, because when the non-aqueous electrolyte includes a high content of the compound shown in Formula A, The compound represented by formula A can fully infiltrate the electrode sheet in a short time, and formula A can form an organic compound containing N and S, and the organic compound of N and S is attached to the surface of the positive and negative electrodes to form a relatively stable SEI film, and When the content of formula A is higher, the SEI film is thicker, which can improve the normal temperature cycle performance, high temperature cycle performance and high temperature storage performance of lithium-ion batteries. group and trifluoromethylsulfonyl group can regulate the proportion of sulfur-containing compounds such as LiSO3 and ROSO2Li in the SEI film, and regenerate some compounds such as LiF and fluorine-containing sulfonyl lithium to further increase the ionic conductivity of the SEI film, thereby The resistance of the SEI film is reduced, so the low-temperature cycle performance is also improved. Therefore, the non-aqueous electrolyte of the present application can make the lithium-ion battery have better cycle performance and high-temperature storage performance.

As can be seen from the results in Table 3, the effect of Example 1 is better than that of Comparative Example 7. This is because active hydrogen is connected to the N of ASE and trifluoromethanesulfonamide, which causes the acid value of the non-aqueous electrolyte to be too high and promotes the non-aqueous electrolyte. The electrolyte decomposes to produce HF. Although ASE and trifluoromethanesulfonamide can form a film, it will consume too much lithium salt, resulting in low conductivity of the electrolyte and deterioration of various performances. The produced hydrofluoric acid It will also corrode the positive and negative electrodes and deteriorate battery performance.

It can be seen from Table 1, Table 3 and Figure 1 that Comparative Examples 4-6 also contain cyclic sulfonamide groups, but the solubility of ASE, ASE-Li, and ASE-Et is not high, which limits their film formation in the electrolyte ability, so the high temperature cycle performance, room temperature cycle performance and high temperature storage performance are not as good as Example 1, Example 3-19, and because ASE, ASE-Li, and ASE-Et do not contain groups that can reduce impedance, low temperature cycle performance Performance is poor. Therefore, the compound represented by formula A not only has high solubility and good wettability, but also can greatly increase the low-temperature cycle performance of lithium-ion batteries without increasing impedance.

As can be seen from the results in Table 3, the cycle performance and high-temperature storage performance of Example 1 and Examples 3 to 17 are better than those of Example 2. This is because the compound shown in Formula A cannot inhibit the solvent from filming when the content is low, resulting in solvent and The additives co-form the film, so the film-forming ability of the compound shown in formula A is better than that of the compound shown in formula A when the content is low when the content is high, so the SEI formed by the compound shown in formula A when the content is high The film is more stable than the SEI film formed at low levels of the compound represented by Formula A.

From the results in Table 3, it can be seen that the cycle performance of Examples 8-14 is significantly better than that of Example 1, so adding additives or special lithium salts on the basis of the compound shown in Formula A can further improve the high-low temperature cycle of lithium-ion batteries performance and high temperature storage performance.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application rather than limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that Modifications or equivalent replacements are made to the technical solutions of the present application without departing from the essence and scope of the technical solutions of the present application.

Claims

An electrolyte additive, is characterized in that, comprises the compound shown in formula A,

Wherein, R is a sulfonyl fluoride group or a trifluoromethylsulfonyl group.
A non-aqueous electrolytic solution, characterized in that, comprising lithium salt, non-aqueous organic solvent and the electrolytic solution additive as claimed in claim 1, the mass percentage of the electrolytic solution additive in the non-aqueous electrolytic solution is 0.5-5% .
The non-aqueous electrolytic solution according to claim 2, wherein the lithium salt is lithium hexafluorophosphate, lithium difluorophosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium tetrafluoroborate , lithium tetrafluorooxalate phosphate, lithium bistrifluoromethylsulfonyl imide, lithium bisfluorosulfonyl imide and lithium tetrafluoromalonate phosphate.
The non-aqueous electrolytic solution according to claim 2, wherein the mass percentage of the lithium salt in the non-aqueous electrolytic solution is 10-20%.
The non-aqueous electrolytic solution according to claim 2, wherein the non-aqueous organic solvent is ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate, At least one of γ-butyrolactone, propyl propionate, ethyl propionate and ethyl butyrate.
The non-aqueous electrolytic solution according to claim 2, wherein the mass percentage of the non-aqueous organic solvent in the non-aqueous electrolytic solution is 60-80%.
The non-aqueous electrolytic solution according to claim 2, characterized in that, it also includes an auxiliary agent, and the auxiliary agent is 2,2,2-methylethyl trifluorocarbonate, 2,2,2-trifluorocarbonic acid Diethyl ester, 2,2,2-trifluoroethylene propyl carbonate, vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, diethyl pyrocarbonate, 1,3-propanesulfonic acid ester, vinyl sulfate, tris(trimethylsilane) phosphate, tris(trimethylsilane) phosphite, 4,4'-bi-1,3-dioxolane-2,2'-dione , 3,3-vinyl disulfate, triallyl phosphate, tripropargyl phosphate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile and 1,2-bis(cyanoethyl Oxygen) at least one of ethane.
The non-aqueous electrolytic solution according to claim 7, characterized in that, the mass percentage of the auxiliary agent in the non-aqueous electrolytic solution is 2-10.5%.
A lithium ion battery, comprising a positive electrode material and a negative electrode material, characterized in that it also includes the non-aqueous electrolyte according to any one of claims 2 to 8, and the highest charging voltage is 4.53V.
The lithium ion battery according to claim 9, wherein the positive electrode material is lithium cobalt oxide.