Electrolyte, application and lithium ion battery adapted to low temperature working conditions

Abstract

The application relates to the field of electrolyte, in particular to electrolyte suitable for low-temperature working conditions, application and lithium ion battery, wherein the electrolyte suitable for low-temperature working conditions comprises a lithium salt, an organic solvent and an additive, and the additive comprises a compound with a structure of formula 1 ( ). Researches show that the compound with the structure of formula 1 is used as the additive of the electrolyte, and based on the combination and synergy of the structure, the low-temperature cycle stability of the electrolyte can be significantly strengthened, so that the electrolyte is suitable for the application requirements of low-temperature working conditions.

Description

Technical Field

[0001] This invention relates to the field of electrolytes, and more specifically to electrolytes adapted to low-temperature operating conditions, their applications, and the field of lithium-ion batteries. Background Technology

[0002] The performance degradation of lithium-ion batteries at low temperatures is a major bottleneck restricting their widespread application in cold regions. When the temperature drops to -20°C or below, the electrolyte viscosity increases sharply, the ionic conductivity decreases significantly, and the desolvation energy barrier of lithium ions at the electrode / electrolyte interface rises, leading to increased battery polarization and a sharp decline in discharge capacity. Adding functional additives is one of the most economical and effective means to improve the low-temperature performance of the electrolyte.

[0003] Existing technologies also disclose some electrolytes suitable for low-temperature operating conditions, mainly including: 1. Modified carbonate-based low-temperature electrolytes, mainly including fluorinated solvent functional components such as fluorinated carbonate modified systems (FEC), fluorinated EMC, and propylene trifluorocarbonate. 2. Ether-based low-temperature electrolytes, mainly including fluorinated ethers. 3. Sulfone / amide-based wide-temperature low-temperature electrolytes, mainly including sulfolane and dimethyl sulfoxide. 4. Ionic liquid low-temperature electrolytes, mainly including imidazole and pyrrolidine fluorosulfonamide ionic liquids. 5. Polymer / gel low-temperature solid electrolytes. For example, CN113921914A discloses an electrolyte and an electrochemical and electronic device using it, wherein the electrolyte contains dimethyl carbonate, ethyl methyl carbonate, and lithium bis(oxalato)borate, ethyl methyl carbonate and lithium bis(oxalato)borate have specific contents in the electrolyte, and the contents of dimethyl carbonate and ethyl methyl carbonate in the electrolyte conform to a specific relationship. Patent document CN118156587A discloses a method for preparing and applying a low-temperature electrolyte for lithium metal batteries. This invention obtains the low-temperature electrolyte by co-dissolving a lithium salt with a solvent and additives. Patent document CN120933483A discloses a wide-temperature, high-voltage sulfone-based electrolyte and its preparation method. The electrolyte comprises a strongly polar solvent, a weakly polar solvent, a composite functional additive, and a lithium salt. Based on the total mass of the electrolyte (100%), the content of the strongly polar solvent is 30-40%, the content of the weakly polar solvent is 20-40%, the content of the lithium salt is 12-18%, and the content of the composite functional additive is 3-12%.

[0004] Although existing technologies disclose a number of low-temperature electrolytes, the technology of existing low-temperature electrolytes still needs to be further developed. Summary of the Invention

[0005] In view of the problems existing in the prior art, the primary objective of this invention is to provide an electrolyte suitable for low-temperature operating conditions.

[0006] The second objective of this invention is to provide an application of an electrolyte suitable for low-temperature operating conditions.

[0007] A third objective of this invention is to provide a lithium-ion battery containing an electrolyte.

[0008] An electrolyte suitable for low-temperature operating conditions includes a lithium salt, an organic solvent, and an additive, wherein the additive includes a compound having the structure of Formula 1:

[0009] Formula 1

[0010] In Formula 1, R1 and R2 are individually H or C1~C4 alkyl groups;

[0011] R3 is a sulfonyl, ester, alkyl, or substituted alkyl group.

[0012] The present invention demonstrates that using compounds of Formula 1 as additives in electrolytes can significantly enhance the low-temperature cycling stability of electrolytes based on their combined synergistic effect, making them suitable for low-temperature applications. In addition, it also provides good low-temperature fast charging performance.

[0013] In this invention, R1 and R2 are either methyl or ethyl;

[0014] The sulfonyl group is an alkyl sulfonic acid group, a benzene sulfonic acid group, or a substituted benzene sulfonic acid group;

[0015] The ester group can be an alkyl ester group, an aromatic ester group, or a benzyl ester group;

[0016] The alkyl group is a C1-C6 alkyl group;

[0017] The substituted alkyl group is a substituted alkyl group having at least one substituent of alkoxy or halogen on the C1 to C3 carbon chain.

[0018] In this invention, the additive includes at least one of Formula 1A, Formula 1B, Formula 1C, and Formula 1D;

[0019]

[0020] Formula 1A Formula 1B

[0021]

[0022] Formula 1C Formula 1D.

[0023] The additives described in this invention include Formula 1A and Formula 1D in a weight ratio of 1~3:1~3, preferably 1~2:1~2. This enables synergy, thereby effectively improving the long-cycle performance of the electrolyte at low temperatures.

[0024] In this invention, the content of additives in the electrolyte is 0.05wt% to 3.0wt%, preferably 0.1wt% to 1.5wt%, and more preferably 0.3wt% to 1.0wt%.

[0025] In this invention, the electrolyte further comprises an auxiliary additive selected from at least one of dimethyl sulfate, 1,3-propanesulfonyl lactone, vinyl sulfate, and methylene disulfonate.

[0026] The research of this invention shows that the combination of additives and auxiliary additives can further synergistically enhance the low-temperature performance of the electrolyte.

[0027] In this invention, the mass ratio of auxiliary additives to additives is 1~5:1~5. More specifically, it can be 1:1~2.

[0028] In this invention, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, and fluoroethylene carbonate.

[0029] The lithium salt is selected from at least one of LiPF6, LiFSI, LiTFSI, LiBF4, LiDFOB, LiBOB, and LiPO2F2.

[0030] The lithium salt concentration in the electrolyte is 0.5~2.0 mol / L, and can be further 0.8~1.5 mol / L.

[0031] The present invention also provides an application of the electrolyte adapted to low-temperature conditions, using it as an electrolyte in the preparation of lithium-ion batteries;

[0032] Preferably, it is prepared into a lithium-ion battery that can be used in low-temperature conditions of -40°C to 0°C; more preferably, it is prepared into a lithium-ion battery that can be used in conditions of -20°C.

[0033] The present invention also provides a lithium-ion battery comprising the electrolyte described above.

[0034] Beneficial effects

[0035] The present invention demonstrates that using Formula 1, which has a special structure, as an additive for electrolytes can achieve synergistic effects, thereby constructing an SEI structure with a special physicochemical structure in situ. This can effectively improve the low-temperature performance of the electrolyte and enhance its performance under low-temperature conditions. Attached Figure Description

[0036] Figure 1 The capacity retention rate after 100 cycles at -20°C for Comparative Example 1 and Example 4. Detailed Implementation

[0037] Example 1

[0038] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed evenly in a mass ratio of 1:1:1. LiPF6 is slowly added until the concentration reaches 1.0 mol / L, and the mixture is stirred until completely dissolved. Then, an additive (Formula 1A) is added at 0.5 wt% of the total electrolyte mass, and the mixture is stirred until completely dissolved to obtain an electrolyte suitable for low-temperature operating conditions.

[0039] A positive electrode sheet was made by coating a nickel-cobalt-manganese ternary material (NCM811) as the positive electrode active material, acetylene black as the conductive agent, and PVDF as the binder, in a mass ratio of 8:1:1. A negative electrode sheet was made by coating a graphite as the negative electrode active material, in the same 8:1:1 ratio, onto a copper foil. Celgard 2400 was used as the separator. CR2032 coin cells were assembled in a glove box.

[0040] The lithium-ion batteries obtained above were subjected to performance tests, including the following performance tests:

[0041] Low-temperature cycling test: 100 charge-discharge cycles were performed at -40℃, -20℃, 0℃, and 25℃ with a current density of 1C / 2C, and the capacity retention rate was recorded.

[0042] Example 2

[0043] Compared to Example 1, the only difference is that the type of additive was changed, and the experimental groups were as follows:

[0044] Group A: Additive is Formula 1B;

[0045] Group B: The additive is Formula 1C;

[0046] Group C: Additive is Formula 1D;

[0047] The additives, dosages, and other operations for each group are the same as in Example 1.

[0048] Example 3

[0049] Compared with Example 1, the only difference is that the additives are Formula 1A and Formula 1D in a mass ratio of 1:1, and the total amount of additives and other operations are the same as in Example 1.

[0050] Example 4

[0051] Compared with Example 3, the only difference is that the additives are Formula 1A and Formula 1D in a mass ratio of 1:1, and also include the auxiliary additive dimethyl sulfate; the weight ratio of the additives and the auxiliary additives is 1:1; the amount of additives and other operations are the same as in Example 3.

[0052] Example 5

[0053] Compared with Example 4, the only difference is that the concentration of lithium hexafluorophosphate (LiPF6) is changed to 1.2 mol / L, the amount of additive in the electrolyte is 1%, and the amount of auxiliary additive is 0.3%. All other operations and parameters are the same as in Example 4.

[0054] Comparative Example 1

[0055] Compared with Example 1, the only difference is that the additive of Formula 1 is missing, while the other operations and parameters are the same as in Example 1.

[0056] Comparative Example 2

[0057] Compared to Example 1, the only difference is that compounds with the following structures were used as additives, and the experimental groups were as follows:

[0058] Group A: Additive replaced with ;

[0059] Group B: Additive replaced with ;

[0060] Group C: The additives are replaced with an equimolar mixture of additives from Groups A and B; the total amount of the mixed additives is the same as that of the additives in Example 1;

[0061] Group D: Additive replaced with ;

[0062] Group E: Additive replaced with ;

[0063] Group F: Additive replaced with dimethyl sulfate

[0064] All other operations and parameters are the same as in Example 1.

[0065] The low-temperature cycling data for each group are shown in Table 1:

[0066] Table 1 shows the performance in low-temperature cycling tests:

[0067]

[0068] Note: The cycle retention rate in Table 1 is calculated as: capacity on the 100th cycle / capacity on the 3rd cycle under each test condition × 100%.

[0069] As demonstrated in Examples 1 and 1-2, using Formula 1, which has a special structure, as an additive for the electrolyte can achieve synergistic effects, enabling the in-situ construction of an SEI structure with a special physicochemical structure. This effectively improves the low-temperature performance of the electrolyte and enhances its performance under low-temperature conditions. Furthermore, as demonstrated in Examples 1-5, additives combining Formula 1A and Formula 1D, as well as additives combined with auxiliary additives, can further enhance the low-temperature stability of the electrolyte.

Claims

1. An electrolyte suitable for low-temperature operating conditions, comprising a lithium salt, an organic solvent, and additives, characterized in that, The additive includes compounds having the structure of Formula 1: Formula 1 In Formula 1, R1 and R2 are individually H or C1~C4 alkyl groups; R3 is a sulfonyl group, ester group, alkyl group, or substituted alkyl group.

2. The electrolyte adapted for low-temperature operating conditions as described in claim 1, characterized in that, R1 and R2 are either methyl or ethyl; The sulfonyl group is an alkyl sulfonic acid group, a benzene sulfonic acid group, or a substituted benzene sulfonic acid group; The ester group can be an alkyl ester group, an aromatic ester group, or a benzyl ester group; The alkyl group is a C1-C6 alkyl group; The substituted alkyl group is a substituted alkyl group having at least one substituent of alkoxy or halogen on the C1 to C3 carbon chain.

3. The electrolyte adapted for low-temperature operating conditions as described in claim 2, characterized in that, The additive includes at least one of Formula 1A, Formula 1B, Formula 1C, and Formula 1D; ； Formula 1A Formula 1B ； Formula 1C Formula 1D.

4. The electrolyte adapted for low-temperature operating conditions as described in claim 3, characterized in that, The additives include Formula 1A and Formula 1D in a weight ratio of 1~3:1~3.

5. The electrolyte adapted for low-temperature operating conditions as described in any one of claims 1 to 4, characterized in that, The electrolyte contains 0.05wt% to 3.0wt%, preferably 0.1wt% to 1.5wt%, and more preferably 0.3wt% to 1.0wt%.

6. The electrolyte adapted for low-temperature operating conditions as described in any one of claims 1 to 5, characterized in that, The electrolyte also contains auxiliary additives, which are selected from at least one of dimethyl sulfate, 1,3-propanesulfonyl lactone, vinyl sulfate, and methylene disulfonate.

7. The electrolyte adapted for low-temperature operating conditions as described in claim 6, characterized in that, The mass ratio of auxiliary additives to additives is 1~5:1~5.

8. The electrolyte adapted for low-temperature operating conditions as described in claim 1, characterized in that, The organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, and fluoroethylene carbonate; The lithium salt is selected from at least one of LiPF6, LiFSI, LiTFSI, LiBF4, LiDFOB, LiBOB, and LiPO2F2. The lithium salt concentration in the electrolyte is 0.5~2.0 mol / L.

9. The application of the electrolyte adapted for low-temperature operating conditions as described in any one of claims 1 to 8, characterized in that, It is used as an electrolyte in the preparation of lithium-ion batteries; Preferably, it is prepared into a lithium-ion battery that can be used in low-temperature conditions of -40℃ to 0℃; more preferably, it is prepared into a lithium-ion battery that can be used in conditions of -20℃.

10. A lithium-ion battery comprising the electrolyte according to any one of claims 1 to 8.

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