Pre-infiltration method for lithium battery

Abstract

The invention provides a pre-infiltration method for a lithium battery, which comprises the following steps of: injecting a pre-infiltration compound into a battery cell of the lithium battery, and sealing and standing, so that the battery cell is fully infiltrated by the pre-infiltration compound; injecting an electrolyte into the battery cell subjected to standing, and aging; and exhausting the aged battery cell so as to discharge the pre-impregnating compound. Compared with a traditional method, the pre-infiltration method can improve the production efficiency and the yield, reduce the negative influence on the electrical performance and improve the capacity exertion, the rate capability and the like of the battery, and is particularly suitable for high-specific-energy batteries and semi-solid batteries.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium batteries, and specifically, relates to a pre-impregnation method for lithium batteries. Background Art

[0002] Poor electrolyte wetting in lithium batteries can lead to abnormal capacity, increased battery internal resistance, lithium precipitation and other problems, resulting in reduced electrical performance and safety performance. At present, the main methods to improve the electrolyte wetting effect include pole piece structure modification (increasing porosity, reducing compaction density, etc.), process optimization (negative pressure injection, pressurized formation, etc.), pole piece surface additive coating and electrolyte modification, etc.

[0003] When optimizing pole pieces and processes, such as reducing surface density and negative pressure injection, it is usually necessary to significantly adjust processing parameters and even introduce new equipment. In addition, the optimization process is also subject to factors such as battery technology design indicators (energy density, etc.) and packaging form (cylindrical, soft pack), and is often subject to greater restrictions. In contrast, the modification of the electrolyte is more effective and more flexible.

[0004] The current schemes for modifying the wettability of electrolytes mainly include increasing the content of low-viscosity solvents, adding wetting-improving additives, and adding electrolytes in steps. The former two often deteriorate electrical performance and bring safety risks (solvent flammability, etc.), while the latter is limited by the basic properties of conventional electrolyte components and the degree of improvement is limited. Summary of the invention

[0005] In order to solve the above problems, the present application provides a pre-wetting method for lithium batteries.

[0006] Specifically, this application involves the following aspects:

[0007] A pre-wetting method for a lithium battery comprises the following steps:

[0008] Injecting a pre-wetting agent into a lithium battery cell;

[0009] injecting electrolyte into the battery cell and aging it;

[0010] The aged battery cell is vented to discharge the pre-wetting agent.

[0011] Optionally, the boiling point of the pre-wetting agent is ≤ the lowest boiling point of the components in the electrolyte.

[0012] Optionally, the boiling point of the pre-wetting agent is ≤ the lowest boiling point of the components in the electrolyte -20°C.

[0013] Optionally, the boiling point of the pre-wetting agent is 35-70°C.

[0014] Preferably, the pre-impregnating agent is injected into the battery cell of the lithium battery, and then the battery cell is sealed and left to stand, so that the pre-impregnating agent fully infiltrates the battery cell;

[0015] Optionally, the boiling point of the pre-wetting agent is 40-60°C.

[0016] Optionally, the pre-wetting agent is miscible with cyclic carbonates and their substituents, chain carbonates and their substituents, common carboxylic acid esters or ethers and their substituents.

[0017] Optionally, the pre-wetting agent is selected from one or more of the following: hydrofluoroether, (fluoro)ketone, (fluoro)alkane, (fluoro)silane, (fluoro)nitrile;

[0018] Optionally, the pre-wetting agent is a terminal fluorine-containing wetting agent

[0019] Preferably, the pre-wetting agent is a hydrofluoroether containing fluorine at the end group.

[0020] Optionally, the pre-wetting agent is a wetting agent containing fluorine at all end groups;

[0021] Preferably, the pre-wetting agent is a hydrofluoroether containing fluorine at all end groups.

[0022] Optionally, the pre-wetting agent is at least one of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, sevoflurane, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, isoflurane, α-hydrogen-octafluoroisobutyl methyl ether or trifluoroethylene ether.

[0023] Optionally, the amount of the pre-wetting agent is 1%-15% of the volume of the electrolyte to be injected.

[0024] Optionally, the standing temperature is 10-30° C., and / or the standing time is 1-6 hours.

[0025] Optionally, the exhaust temperature is 30-75° C., and / or the exhaust pressure is 10-101 KPa, and / or the exhaust time is 0.5-4 hours.

[0026] Optionally, the exhausting is performed in two stages.

[0027] Optionally, in the first stage, the temperature is T1, the pressure is P1, and the time is t1, and in the second stage, the temperature is T2, the pressure is P2, and the time is t2, wherein T1≤T2, P1≥P2, and t1≥t2.

[0028] For example, T1 is 30-50℃, P1 is 50-101Kpa, t1 is 1-2.5 hours, T2 is 40-75℃, P2 is 10-50Kpa, t2 is 0.1-1 hour.

[0029] Beneficial effects of this application:

[0030] (1) Compared with the traditional method, the pre-wetting method of the present application can greatly improve the electrolyte infiltration speed and degree, which can effectively shorten the time consumption of the corresponding links in the battery cell manufacturing process and improve production efficiency and yield rate;

[0031] (2) The pre-wetting agent used in the pre-wetting method of the present application has a low boiling point and does not participate in the solvation process. It evaporates quickly and is not easy to form azeotropes. It can fully evaporate in the discharge process, avoid participating in the subsequent battery operation, and reduce the negative impact on electrical performance;

[0032] (3) The pre-wetting method of the present application can ensure that the electrolyte fully penetrates into the interior of the electrode and effectively wraps the active particles. In addition, it can enhance the uniform dispersion of solid electrolytes, additives, etc., thereby improving the capacity and rate performance of the battery, etc., and is particularly suitable for high-energy-density batteries and semi-solid batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Shows the electrolyte pre-wetting operation process. DETAILED DESCRIPTION

[0034] The present application is further described below in conjunction with examples. It should be understood that the examples are only used to further describe and illustrate the present application and are not used to limit the present application.

[0035] Unless otherwise defined, the technical and scientific terms in this specification have the same meaning as those generally understood by those skilled in the art. Although similar or identical methods and materials as described herein may be used in experiments or practical applications, materials and methods are described herein below. In the event of a conflict, the present specification including the definitions therein shall prevail. In addition, materials, methods and examples are provided for illustration only and are not restrictive. The present application is further described below in conjunction with specific embodiments, but is not intended to limit the scope of the present application.

[0036] The present application provides a pre-wetting method for lithium batteries, such as Figure 1 As shown, the pre-wetting method comprises the following steps:

[0037] Step S1: injecting a pre-wetting agent into a cell of a lithium battery;

[0038] Step S2: injecting electrolyte into the battery cell and aging it;

[0039] Step S3: exhausting the aged battery cell to discharge the pre-wetting agent.

[0040] In step S1, in order to fully wet the battery cell, the pre-wetting agent needs to meet the following conditions: (1) It has strong wettability and can quickly penetrate into the pores of the electrode; (2) It is easy to separate, with a boiling point significantly lower than that of the electrolyte components, and can be quickly discharged and minimize electrolyte loss; (3) It is chemically inert and does not react with the electrolyte and electrode active substances; (4) It has good miscibility and can be miscible with the electrolyte.

[0041] The pre-wetting agent needs to match the electrolyte used. In some embodiments, the boiling point of the pre-wetting agent is ≤ the lowest boiling point of the components in the electrolyte. In some embodiments, the boiling point of the pre-wetting agent is < the lowest boiling point of the components in the electrolyte. In some embodiments, the boiling point of the pre-wetting agent is ≤ the lowest boiling point of the components in the electrolyte -20°C. Under this condition, the pre-wetting agent can be easily discharged in the subsequent steps.

[0042] In some embodiments, the boiling point of the pre-wetting agent is 35-70°C, for example, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, and any values ​​therebetween. In some embodiments, the boiling point of the pre-wetting agent is 40-60°C.

[0043] In some embodiments, the pre-wetting agent is miscible with cyclic carbonates and their substituents, chain carbonates and their substituents, common carboxylic acid esters / ethers and their substituents.

[0044] Among them, cyclic carbonates and their substitutes include, for example, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinylene carbonate, etc. Chain carbonates and their substitutes include, for example, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate, fluoromethyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, etc. Common carboxylates or ethers and their substitutes refer to carboxylates or ethers and their substitutes commonly used in the battery industry, including, for example, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, fluoroethyl acetate, fluoroethyl propionate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dioxolane, etc.

[0045] In some embodiments, the pre-wetting agent is selected from one or more of the following: hydrofluoroether, (fluoro)ketone, (fluoro)alkane, (fluoro)silane, (fluoro)nitrile.

[0046] In some embodiments, the pre-wetting agent is a hydrofluoroether having fluorine-containing terminal groups, wherein the fluorine-containing terminal groups may be all fluorine-containing terminal groups, or some of the terminal groups may be fluorine-free.

[0047] In some embodiments, the pre-wetting agent has a boiling point of 35-70° C. and is miscible with cyclic carbonates and their substituents, chain carbonates and their substituents, common carboxylates or ethers and their substituents.

[0048] In some embodiments, the pre-wetting agent is selected from one or more of the following: hydrofluoroethers, (fluoro)ketones, (fluoro)alkanes, (fluoro)silanes, and (fluoro)nitriles having a boiling point of 35-70° C. and being miscible with carbonates.

[0049] In some embodiments, the pre-wetting agent is a wetting agent having a boiling point of 40-60° C. and at least one terminal group containing fluorine, such as preferably hydrofluoroether.

[0050] In some embodiments, the pre-wetting agent is a wetting agent with a boiling point of 40-60° C. and all end groups containing fluorine, such as preferably hydrofluoroether.

[0051] In some embodiments, the pre-wetting agent is one or more of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, sevoflurane, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, isoflurane, Α-hydrogen-octafluoroisobutyl methyl ether, or trifluoroethylene ether.

[0052] The pre-impregnating agent of the present application quickly penetrates into the electrode, and can expel the air between the particles, which is conducive to the full infiltration of the electrolyte; the pre-impregnating agent transforms the solid-liquid diffusion after liquid injection into liquid-liquid diffusion, significantly improving the infiltration speed; the local low pressure and convection disturbance generated by the volatilization of the pre-impregnating agent accelerate the penetration of the electrolyte into the interior, ensuring full infiltration of the particles; the pre-impregnating agent evaporates quickly and is not easy to bring out electrolyte components; the pre-impregnating agent is electrochemically inert, and a small amount of residue has little effect on the performance of the battery cell.

[0053] In some embodiments, the amount of the pre-wetting agent is 1%-15% of the volume of the electrolyte, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, and any value therebetween.

[0054] In some embodiments, the pre-wetting agent is injected into the battery cell of the lithium battery, and then the battery cell is sealed and left to stand, so that the pre-wetting agent fully infiltrates the battery cell;

[0055] Those skilled in the art can understand that standing refers to placing the battery cell injected with the pre-impregnating agent for a period of time to allow the pre-impregnating agent to fully infiltrate the battery cell. When necessary, the infiltration can be enhanced by combining vibration, flipping, etc.

[0056] In some embodiments, the standing temperature is 10-30°C, for example, it can be 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, and any values ​​therebetween.

[0057] In some embodiments, the standing time is 1-6 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, and any value therebetween.

[0058] In some embodiments, the standing temperature is 10-30° C., and the standing time is 1-6 hours.

[0059] In step S2, the electrolyte can be selected from various electrolytes known in the art, which is not further limited in this application. The specific operation of aging can also be performed by referring to methods known in the art.

[0060] In step S3, different from the exhaust step after formation in the conventional battery cell preparation process, the exhaust in the present application is to exhaust the pre-wetting agent in gaseous form by heating or the like after the aging step.

[0061] In some embodiments, the exhaust temperature is 30-75°C. Too low a temperature is not conducive to the volatilization of the liquid and leads to failure to fully discharge the exhaust gas. For example, the exhaust temperature may be 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, and any values ​​therebetween.

[0062] In some embodiments, the exhaust pressure is 10-101Kpa, for example, it can be 10Kpa, 15Kpa, 20Kpa, 25Kpa, 30Kpa, 35Kpa, 40Kpa, 45Kpa, 50Kpa, 55Kpa, 60Kpa, 65Kpa, 70Kpa, 75Kpa, 80Kpa, 85Kpa, 90Kpa, 95Kpa, 100Kpa, 101Kpa, and any value between these values.

[0063] In some embodiments, the exhaust time is 0.5-4 hours, for example, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, and any value therebetween.

[0064] In some embodiments, the exhaust gas has a temperature of 30-75° C., a pressure of 10-101 KPa, and a time of 0.5-4 hours.

[0065] The exhaust can be performed in a single stage or in stages, for example, in two stages or multiple stages. In a single stage, the temperature and pressure of the exhaust remain unchanged. In two stages or multiple stages, the exhaust uses different temperatures and / or pressures in different stages. Compared with single-stage exhaust, staged exhaust can fully exhaust the pre-wetting agent while reducing the volatilization of the electrolyte.

[0066] In some embodiments, the exhaust is performed in two stages.

[0067] In some embodiments, the exhaust is divided into two stages, in the first stage the temperature is T1, the pressure is P1, and the time is t1, and in the second stage the temperature is T2, the pressure is P2, and the time is t2; wherein T1≤T2, P1≥P2, and t1≥t2.

[0068] In some embodiments, the exhaust is divided into two stages, wherein the exhaust speed in the second stage is faster and the duration is shorter than that in the first stage.

[0069] In some embodiments, the exhaust is divided into two stages, in the first stage the temperature is T1, the pressure is P1, and the time is t1, and in the second stage the temperature is T2, the pressure is P2, and the time is t2; T1 is 30-50°C, for example, it can be 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, and any values ​​therebetween; P1 is 50-10 1Kpa, for example, it can be 50Kpa, 55Kpa, 60Kpa, 65Kpa, 70Kpa, 75Kpa, 80Kpa, 85Kpa, 90Kpa, 95Kpa, 100Kpa, 101Kpa, and any value therebetween; t1 is 1-2.5 hours, for example, it can be 1 hour, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, 2 hours, 2.1 hours, 2.2 hours, 2 .3 hours, 2.4 hours, 2.5 hours, and any value therebetween; T2 is 40-75°C, for example, it can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75 ℃, and any value between these values; P2 is 10-50Kpa, for example, it can be 10Kpa, 15Kpa, 20Kpa, 25Kpa, 30Kpa, 35Kpa, 40Kpa, 45Kpa, 50Kpa, and any value between these values; t2 is 0.1-1 hour, for example, it can be 0.1 hour, 0.2 hour, 0.3 hour, 0.4 hour, 0.5 hour, 0.6 hour, 0.7 hour, 0.8 hour, 0.9 hour, 1 hour, and any value between these values.

[0070] By exhausting the pre-wetting agent in the electrolyte, its impact on subsequent processing and use can be reduced. Compared with the method of injecting components contained in the electrolyte for infiltration and then exhausting, the method of the present application has less impact on the proportion of each component in the electrolyte by exhausting the pre-wetting agent. The main impact point is the small loss of electrolyte volume; it can avoid the uncontrollable consistency caused by the change of the proportion of electrolyte components and the significant impact on electrochemical performance.

[0071] In some embodiments, the pre-wetting method includes the following steps: Step S1: injecting a pre-wetting agent into the battery cell of the lithium battery, sealing and standing, so that the pre-wetting agent fully infiltrates the battery cell; wherein the boiling point of the pre-wetting agent is ≤ the lowest boiling point of the components in the electrolyte, the standing temperature is 10-30°C, and / or the standing time is 1-6 hours; Step S2: injecting electrolyte into the battery cell after standing and aging; Step S3: exhausting the aged battery cell to discharge the pre-wetting agent. The exhaust temperature is 30-75°C, and / or the exhaust pressure is 10-101Kpa, and the exhaust time is 0.5-4 hours.

[0072] In some embodiments, the pre-wetting method comprises the following steps: Step S1: injecting a pre-wetting agent into the battery cell of the lithium battery, sealing and standing, so that the pre-wetting agent fully infiltrates the battery cell; wherein the pre-wetting agent is a hydrofluoroether with a boiling point of 40-60°C and a fluorine-containing end group, and the standing temperature is 10-30°C, and the time is 1-6 hours; Step S2: injecting an electrolyte into the battery cell after standing and aging; Step S3: exhausting the aged battery cell to discharge the pre-wetting agent. The exhaust temperature is 30-75°C, the pressure is 10-101Kpa, and the time is 0.5-4 hours.

[0073] In some embodiments, the pre-wetting method includes the following steps: Step S1: injecting a pre-wetting agent into the battery cell of the lithium battery, sealing and standing, so that the pre-wetting agent fully infiltrates the battery cell; wherein the pre-wetting agent is a hydrofluoroether with a boiling point of 40-60°C and a fluorine-containing end group, and the standing temperature is 10-30°C, and the time is 1-6 hours; Step S2: injecting an electrolyte into the battery cell after standing and aging; Step S3: exhausting the aged battery cell to discharge the pre-wetting agent. The exhaust temperature is 30-75°C, the pressure is 10-101Kpa, and the time is 0.5-3 hours. The exhaust is carried out in two stages, in the first stage, the temperature is T1, the pressure is P1, and the time is t1, and in the second stage, the temperature is T2, the pressure is P2, and the time is t2; wherein T1≤T2, P1≥P2, and t1≥t2.

[0074] Those skilled in the art will appreciate that after step S3, the process may further include a step of recovering the pre-wetting agent or performing chemical reaction on the battery cell.

[0075] The pre-impregnation method of the present application selects a specific pre-impregnation agent, standing and exhaust conditions. Among them, the pre-impregnation agent used in the present application has a low boiling point, does not participate in the solvation process, evaporates quickly and is not easy to form an azeotrope; the pre-impregnation agent is electrochemically inert, and a small amount of residue has little effect on the performance of the battery cell. The pre-impregnation method of the present application uses a volatilization process to discharge the pre-impregnation agent in the electrolyte, reducing its impact on subsequent processing and use. The pre-impregnation method of the present application can shorten the electrolyte infiltration time and increase the degree of infiltration, thereby improving battery performance.

[0076] Example

[0077] Example 1

[0078] (1) Injecting a pre-wetting agent with an electrolyte injection volume of 8% into the assembled NCM811-Gr dry battery cell through the opening, the pre-wetting agent is 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (normal pressure boiling point 50° C.), and sealing the battery cell after the injection is completed;

[0079] (2) Store the cells filled with the pre-impregnant at 25°C for 3 hours to ensure that the pre-impregnant effectively wets the cells. Vibration, flipping, etc. can be used to enhance the wetting.

[0080] (3) Inject 1M LiPF6 EC / EMC / DEC 4 / 3 / 3 as the electrolyte and seal the battery cell;

[0081] (4) The battery cell after liquid injection is placed in an environment of 25°C for 8 hours for aging;

[0082] (5) Transfer the battery cell to the exhaust chamber, and keep the dew point in the exhaust chamber ≤ 40°C; open the battery cell or open the reserved volatilization hole, and perform the pre-impregnation agent discharge treatment in the exhaust chamber: the first stage is heated to 40°C, the pressure is 100Kpa, and the exhaust is carried out for 2h, followed by the second stage of heating to 55°C, the pressure is 60Kpa, and the exhaust is carried out for 0.5h;

[0083] (6) After the exhaust is completed, the battery cell is sealed and the exhaust chamber is removed. The pre-impregnation agent is recovered through the exhaust chamber exhaust gas collection device, and the battery cell is circulated normally for subsequent steps such as formation.

[0084] (7) Battery cell test performance: The internal resistance of the battery cell formation test is 1.5mΩ, the 3C discharge capacity retention rate is 95%, and the remaining capacity of 80% corresponds to 980 cycles.

[0085] The internal resistance, 3C discharge capacity retention rate, and the corresponding cycle of 80% remaining capacity are all tested using the common test methods in the industry. Among them, the internal resistance is measured using an AC internal resistance meter. Specifically, the positive and negative electrodes of the formed battery are connected to the AC internal resistance meter, and the reading is taken as the internal resistance.

[0086] The battery cycle life is tested by charging and discharging at room temperature using a battery cycler according to given rate, voltage range and other parameters. Specifically, the test method for the 3C discharge capacity retention rate is: charge and discharge the battery at 0.33C constant current at room temperature, use this discharge capacity as Q1, continue to discharge the battery at 3C constant current, use this discharge capacity as Q2, and the 3C discharge capacity retention rate is Q2 / Q1;

[0087] The test method for the number of cycles corresponding to 80% remaining capacity is as follows: perform a 0.33C constant current charge and discharge on the battery at room temperature; continue to perform cycle tests on the battery, 0.5C constant current and constant voltage charging, the end current is 0.05C, 1C cross current discharge, record the first charge and discharge capacity Q1, when the cycle capacity drops to 80% Q1, terminate the test, and record the corresponding cycle number as the cycle corresponding to 80% remaining capacity.

[0088] Example 2

[0089] The pre-wetting agent in Example 1 was replaced with 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (normal pressure boiling point 50° C.), and the remaining steps and parameters were the same as in Example 1.

[0090] Battery cell test performance: The internal resistance of the battery cell formation test is 1.6mΩ, the 3C discharge capacity retention rate is 92%, and the remaining capacity of 80% corresponds to 850 cycles.

[0091] Example 3

[0092] The pre-wetting agent in Example 1 was replaced with sevoflurane (normal pressure boiling point 58° C.), and the remaining steps and parameters were the same as in Example 1.

[0093] Battery cell test performance: The internal resistance of the battery cell formation test is 1.9mΩ, the 3C discharge capacity retention rate is 88%, and the remaining capacity of 80% corresponds to 910 cycles.

[0094] Example 4

[0095] The exhaust chamber parameters of the pre-wetting agent discharge step in Example 1 were adjusted to single-stage exhaust (heating to 40° C., pressure 100 KPa, exhaust 2.5 h), and the remaining steps and parameters were the same as in Example 1.

[0096] Battery cell test performance: The internal resistance of the battery cell formation test is 1.7mΩ, the 3C discharge capacity retention rate is 86%, and the remaining capacity of 80% corresponds to 920 cycles.

[0097] Example 5

[0098] The exhaust chamber parameters of the pre-wetting agent discharge step in Example 1 were adjusted to single-stage exhaust (heating to 60° C., pressure 100 KPa, exhaust 2.5 h), and the remaining steps and parameters were the same as in Example 1.

[0099] Battery cell test performance: The internal resistance of the battery cell formation test is 1.6mΩ, the 3C discharge capacity retention rate is 90%, and the remaining capacity of 80% corresponds to 860 cycles.

[0100] Example 6

[0101] The step of storing in a 25° C. environment for 3 h after adding the pre-wetting agent in Example 1 was omitted, and the remaining steps and parameters were the same as in Example 1.

[0102] Battery cell test performance: The internal resistance of the battery cell formation test is 2.0mΩ, the 3C discharge capacity retention rate is 83%, and the remaining capacity of 80% corresponds to 880 cycles.

[0103] Comparative Example 1

[0104] (1) Inject 1M Li PF6 EC / EMC / DEC 4 / 3 / 3 as the electrolyte into the assembled NCM811-Gr dry cell;

[0105] (2) The battery cells after liquid injection are placed in an environment of 25°C for 8 hours for aging;

[0106] (3) The aged cells can be processed normally in subsequent processes such as formation;

[0107] (4) Battery cell test performance: The internal resistance of the battery cell formation test is 3.3mΩ, the 3C discharge capacity retention rate is 69%, and the remaining capacity of 80% corresponds to 680 cycles.

[0108] Comparative Example 2

[0109] The pre-wetting agent discharge step in Example 1 is eliminated, and the remaining steps and parameters are the same as those in Example 1.

[0110] Battery cell test performance: The internal resistance of the battery cell formation test is 3.5mΩ, the 3C discharge capacity retention rate is 58%, and the remaining capacity of 80% corresponds to 510 cycles.

[0111] Comparative Example 3

[0112] The aging time in Comparative Example 1 was extended to 24 hours in a 25°C environment, and the remaining steps and parameters were the same as those in Comparative Example 1.

[0113] Cell test performance: The cell formation test internal resistance is 2.3mΩ, the 3C discharge capacity retention rate is 80%, and the remaining capacity of 80% corresponds to 770 cycles. It can be seen that even if a longer aging and impregnation time is used, the effect of the pre-impregnation method cannot be achieved.

[0114] Comparative Example 4

[0115] The pre-wetting agent in Example 1 was replaced with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (normal pressure boiling point 92° C.), and the remaining steps and parameters were the same as in Example 1.

[0116] Battery cell test performance: The internal resistance of the battery cell formation test is 3.8mΩ, the 3C discharge capacity retention rate is 52%, and the remaining capacity of 80% corresponds to 530 cycles.

[0117] By comparing the above embodiments with the comparative examples, it can be concluded that the pre-impregnation method of the present application can effectively improve the electrolyte infiltration speed and effect, reduce internal resistance, and improve rate and cycle performance.

Claims

1. A pre-wetting method for a lithium battery, comprising the following steps: Injecting pre-wetting agent into the lithium battery cell and sealing it; injecting electrolyte into the battery cell and aging it; Exhaust the aged battery cells. 2 . The pre-wetting method according to claim 1 , wherein the boiling point of the pre-wetting agent is less than or equal to the lowest boiling point of the solvent in the electrolyte. 3 . The pre-wetting method according to claim 2 , wherein the boiling point of the pre-wetting agent is ≤ the lowest boiling point of the solvent in the electrolyte solution -20° C. 4 . The pre-wetting method according to claim 2 , wherein the boiling point of the pre-wetting agent is 35-70° C., preferably, the boiling point of the pre-wetting agent is 40-60° C.

5. The pre-wetting method according to any one of claims 1 to 4, wherein the pre-wetting agent is miscible with cyclic carbonates and their substituents, chain carbonates and their substituents, common carboxylates or ethers and their substituents. 6 . The pre-wetting method according to claim 5 , wherein the pre-wetting agent is selected from one or more of hydrofluoroether, (fluoro)ketone, (fluoro)alkane, (fluoro)silane and (fluoro)nitrile.

7. The pre-wetting method according to claim 6, wherein the pre-wetting agent is a wetting agent containing fluorine at the end group; Preferably, the pre-wetting agent is a hydrofluoroether containing fluorine at the end group.

8. The pre-wetting method according to claim 6, wherein the pre-wetting agent is a wetting agent containing fluorine at all end groups; Preferably, the pre-wetting agent is a hydrofluoroether containing fluorine at all end groups.

9. The pre-wetting method according to claim 6, wherein the pre-wetting agent is selected from at least one of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, sevoflurane, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, isoflurane, α-hydrogen-octafluoroisobutyl methyl ether or trifluoroethylene ether.

10. The pre-wetting method according to any one of claims 1 to 9, wherein the amount of the pre-wetting agent is 1% to 15% of the volume of the electrolyte to be injected.

11. The pre-wetting method according to any one of claims 1 to 10, wherein the pre-wetting agent is injected into the battery cell of the lithium battery, and then the pre-wetting agent is sealed and allowed to stand to fully wet the battery cell; Preferably, the standing temperature is 10-30° C., and / or the standing time is 1-6 hours.

12. The pre-wetting method according to any one of claims 1 to 11, wherein the temperature of the exhaust gas is 30-75°C, and / or, The exhaust pressure is 10-101Kpa, And / or, the exhaust time is 0.5-4 hours.

13. The pre-wetting method according to claim 12, wherein the exhaust is performed in two stages; Preferably, in the first stage, the temperature is T1, the pressure is P1, and the time is t1, and in the second stage, the temperature is T2, the pressure is P2, and the time is t2; Among them, T1≤T2, P1≥P2, and t1≥t2.

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