Method for evaluating influence of electrolyte on lithium manganate positive electrode manganese dissolution

Abstract

The invention relates to a method for evaluating the influence of electrolyte on lithium manganate positive electrode manganese dissolution in the technical field of lithium batteries. The method comprises the following steps: S1, preparing a soft package battery cell; the soft package battery cell comprises a positive plate, and the positive plate comprises a positive active material lithium manganate; s2, performing formation and capacity grading on the soft package battery cell, and then disassembling to obtain a positive plate; and S3, soaking the positive plate disassembled in the step S2 in a to-be-tested electrolyte, testing the manganese ion concentration of the soaked electrolyte, and evaluating the influence of the to-be-tested electrolyte on the manganese dissolution of the positive plate according to a test result. The electrolyte formula can be quickly screened and optimized, so that the battery performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for evaluating the influence of an electrolyte on the dissolution of manganese from a lithium manganate positive electrode. Background Art

[0002] As a high energy density energy storage device, lithium-ion batteries have been widely used in consumer electronics, new energy vehicles and energy storage systems. Lithium manganese oxide has become an important choice of lithium battery positive electrode material due to its abundant resources, low cost and environmental friendliness. However, lithium manganese oxide is prone to Mn 3+ Xiang Mn 2+ The disproportionation reaction during the conversion causes manganese to dissolve into the electrolyte. This phenomenon not only damages the structure of the positive electrode material, but also deposits metallic manganese on the surface of the negative electrode, further affecting the cycle life and safety performance of the battery.

[0003] Research has shown that the composition of the electrolyte and the kinetics of its reaction with the lithium manganese oxide surface have a significant impact on the extent of manganese dissolution. Traditional evaluation methods rely primarily on cycle testing after battery assembly, but this process is time-consuming and cannot quickly and accurately assess the impact of the electrolyte on manganese dissolution. To address this issue, developing an efficient and rapid evaluation method is of great significance for screening and optimizing electrolyte formulations and improving battery performance.

[0004] Existing research has used methods such as online inductively coupled plasma mass spectrometry (ICP-MS) to monitor manganese dissolution in real time, but there is still room for improvement in the specific evaluation system and operational procedures. Furthermore, the development of a high-throughput, standardized method for rapid assessment of manganese dissolution, combining electrochemical testing with material chemical properties, remains a research hotspot and a challenge in this area. Summary of the Invention

[0005] In order to solve the problem that the existing technology has complicated and tedious steps in evaluating the effect of electrolyte on manganese dissolution of lithium manganate positive electrode sheets, the present invention proposes a method for quickly evaluating the effect of electrolyte on manganese dissolution of lithium manganate positive electrodes. The technical solution of the present invention is implemented as follows:

[0006] The present invention discloses a method for evaluating the effect of an electrolyte on the dissolution of manganese from a lithium manganate positive electrode, the method comprising the following steps:

[0007] S1. Prepare a soft-pack battery cell; the soft-pack battery cell includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material, lithium manganese oxide;

[0008] S2, disassembling the soft-pack battery cell into components and obtaining a positive electrode sheet;

[0009] S3. Immerse the positive electrode sheet obtained by disassembling S2 in the electrolyte to be tested, and test the manganese ion concentration of the electrolyte after immersion. Based on the test results, evaluate the effect of the electrolyte to be tested on the manganese dissolution of the positive electrode sheet.

[0010] Preferably, in step S2, before disassembling the soft-pack battery cell, a charging step is also included to charge the soft-pack battery cell to a charging cut-off voltage.

[0011] Preferably, the charging current of the soft-pack battery cell is 0.1C to 1C.

[0012] Preferably, in step S2, after the soft-pack battery cell is charged, a rest step is further included, and the rest time is 5 minutes to 60 minutes.

[0013] Preferably, step S2 further includes cleaning the disassembled positive electrode sheet.

[0014] Preferably, the solvent for cleaning the positive electrode sheet is dimethyl carbonate;

[0015] Preferably, after cleaning, the mixture is allowed to stand for 5 to 300 minutes.

[0016] Preferably, the soft-pack battery cell includes an electrolyte, and the composition of the electrolyte to be tested is the same as that of the electrolyte.

[0017] Preferably, in step S3, before the immersion step, the step further includes blowing the electrolyte to be tested with an inert gas;

[0018] Preferably, the inert gas includes at least one of nitrogen and argon;

[0019] Preferably, the blowing time is 1 min to 60 min.

[0020] Preferably, in step S3, the positive electrode sheet and the electrolyte to be tested are placed in a sealed device;

[0021] Preferably, in step S3, the soaking time is 12 hours to 84 hours; the soaking temperature is 35° C. to 80° C.;

[0022] Preferably, in step S3, the mass of the electrolyte to be tested is 10 g to 60 g.

[0023] Preferably, in step S3, the manganese ion concentration test includes taking photos of the electrolyte to be tested after immersion to record color changes and performing ICP testing to record the manganese ion content in the electrolyte to be tested.

[0024] The advantages of the present invention are as follows:

[0025] The present invention proposes a method for rapidly evaluating the dissolution behavior of manganese (Mn) in an electrolyte in a lithium manganate positive electrode. The method of the present invention can rapidly optimize the electrolyte formulation, reduce the impact of manganese dissolution on battery performance, and improve battery cycle stability and safety. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specific embodiments are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the description and claims of the present invention and any variations thereof are intended to cover non-exclusive inclusions.

[0028] In the description of the specific embodiments of the present invention, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the technical features indicated. In the description of the embodiments of the present invention, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0029] References to "embodiments" in this disclosure mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the disclosure. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0030] In the description of the embodiments of the present invention, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exists simultaneously, and B exists alone. In addition, the character " / " in this invention generally indicates that the associated objects are in an "or" relationship.

[0031] Throughout this disclosure, numerical values ​​represent approximate measures or limits of ranges to encompass minor deviations from a given value, as well as embodiments having approximately the stated value and embodiments having the exact value stated. Except for the working examples provided at the end of the detailed description, all numerical values ​​for parameters (e.g., amounts, or conditions) in this specification (including the appended claims) should be understood as being modified in all instances by the term "about," regardless of whether "about" actually appears before the numerical value. "About" indicates that the stated numerical value allows for some minor imprecision (some degree of closeness to the exact value of the stated value; approximately or reasonably close to the stated value; nearly). If the imprecision provided by "about" is not otherwise understood in this ordinary sense in the art, "about," as used herein, at least indicates the variation that can occur due to ordinary methods of measuring and using such parameters. For example, "about" can encompass variations of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.

[0032] Additionally, disclosure of ranges includes disclosure of all values ​​within the entire range and further divided ranges, including endpoints and sub-ranges stated for such ranges.

[0033] Existing research has used methods such as online inductively coupled plasma mass spectrometry (ICP-MS) to monitor manganese dissolution in real time, but there is still room for improvement in the specific evaluation system and operational procedures. Furthermore, combining electrochemical testing with material chemical properties to develop a high-throughput, standardized method for rapid assessment of manganese dissolution remains a research hotspot and a challenge in this area.

[0034] In order to solve the above-mentioned shortcomings, the present invention proposes a method for quickly evaluating the effect of electrolyte on manganese dissolution in lithium manganate positive electrode, the method comprising the following steps:

[0035] S1. Prepare a soft-pack battery cell; the soft-pack battery cell includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material, lithium manganese oxide;

[0036] S2, disassembling the soft-pack battery cell into components and obtaining a positive electrode sheet;

[0037] S3. Immerse the positive electrode sheet obtained by disassembling S2 in the electrolyte to be tested, and test the manganese ion concentration of the electrolyte after immersion. Based on the test results, evaluate the effect of the electrolyte to be tested on the manganese dissolution of the positive electrode sheet.

[0038] In the present invention, in order to ensure the consistency of chemical composition and physical structure of each group of positive electrode sheets during testing, lithium manganese oxide (LiMn2O4) positive electrode material is used in the preparation of soft-pack batteries, thereby preparing standardized positive electrode sheets.

[0039] The positive electrode sheet was used as a test sample, and multiple groups of soft-pack battery cells were produced through the normal production process of lithium-ion batteries.

[0040] The method of the present invention can prepare multiple groups of test samples (positive electrode sheets) at one time, prepare test electrolytes with different formula components, place standard positive electrode sheets in different test electrolytes and conduct evaluation tests simultaneously, and observe the conditions of the test electrolytes after the positive electrode sheets are soaked. This can quickly evaluate the effects of different test electrolytes on the manganese dissolution of lithium manganate positive electrode sheets, and quickly optimize the electrolyte formula based on the evaluation results.

[0041] In some embodiments, in step S2, before disassembling the soft-pack battery cell, a charging step is further included to charge the soft-pack battery cell to a charging cut-off voltage.

[0042] Fully charging the soft-pack battery cell can form a CEI film on the surface of the positive electrode sheet. In this way, the fully charged positive electrode sheet disassembled is consistent with the state of the positive electrode sheet in the battery, thereby reducing test errors.

[0043] In some embodiments, the charging current of the soft-pack battery cell is 0.1C to 1C.

[0044] In specific applications, the charging current of the soft-pack battery cell can be selected as: 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, 0.6C, 0.7C, 0.8C, 0.9C, 1C, etc. The above values ​​are only examples and are not limiting. Those skilled in the art can freely implement any value within the range of 0.1C to 1C without exceeding their own understanding.

[0045] In some embodiments, in step S2, after the soft-pack battery cell is charged, a rest step is further included, and the rest time is 5 minutes to 60 minutes.

[0046] In specific applications, the rest time of the soft-pack battery cell after charging is completed can be selected as: 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 15min, 18min, 20min, 21min, 22min, 25min, 28min, 30min, 31min, 32min, 35min, 38min, 40min, 41min, 42min, 45min, 48min, 50min, 55min, 60min, etc. The above times are examples and are not limiting. Those skilled in the art can freely select any time within the range of 5min to 60min without exceeding their own understanding.

[0047] In some embodiments, step S2 further includes cleaning the disassembled positive electrode sheet.

[0048] Soft-pack batteries generally contain electrolytes, which may contain dissolved manganese ions. In order to eliminate the test errors caused by these manganese ions, after disassembling the positive electrode sheet, the electrolyte attached to the surface of the positive electrode sheet is cleaned off to make the test results more accurate.

[0049] In some embodiments, the solvent for cleaning the positive electrode sheet is dimethyl carbonate.

[0050] In specific applications, the cleaning solvent can be selected as dimethyl carbonate, but in the embodiment of the present invention, the cleaning solvent is not unique. All cleaning solvents known in the art can be used for the cleaning of the present invention as long as they do not react with the lithium manganese oxide positive plate.

[0051] In some embodiments, after washing, the mixture is allowed to stand for 5 to 300 minutes.

[0052] In order to prevent the residual cleaning solvent on the positive electrode sheet from entering the electrolyte to be tested, it is necessary to let the positive electrode sheet stand for a period of time after cleaning to allow the cleaning solvent to completely evaporate.

[0053] In specific applications, the standing time required for volatilization of the cleaning solvent can be selected from 5 min, 10 min, 15 min, 18 min, 20 min, 25 min, 28 min, 30 min, 35 min, 38 min, 40 min, 45 min, 450 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 150 min, 180 min, 200 min, 220 min, 250 min, 280 min, 300 min, etc. The above times are examples and are not limiting. Those skilled in the art can freely select any time within the range of 5 min to 300 min without exceeding their own understanding.

[0054] In some embodiments, the soft-pack battery cell includes an electrolyte, and the composition of the electrolyte to be tested is the same as that of the electrolyte.

[0055] In order to better evaluate the effect of the electrolyte to be tested on the manganese dissolution of the lithium manganese oxide positive electrode sheet, the electrolyte of the soft-pack battery cell is set to have the same composition as the electrolyte to be tested. In this way, the electrolyte environment of the positive electrode sheet before and after disassembly is completely consistent, and the test results are more accurate.

[0056] In some embodiments, in step S3, before the immersion step, the step further includes blowing the electrolyte to be tested with an inert gas.

[0057] The electrolyte to be tested may react with oxygen in the air and deteriorate when placed in the air. Therefore, blowing inert gas before testing can effectively prevent the electrolyte to be tested from deteriorating.

[0058] In some embodiments, the inert gas includes at least one of nitrogen and argon.

[0059] In specific applications, the inert gas used to blow the electrolyte to be tested can be nitrogen, argon, or a mixture of nitrogen and argon. Since these inert gases have similar properties and do not chemically react with each other, their effects will not be affected whether they are used alone or in mixture.

[0060] In addition, the implementation of the present invention is not limited to nitrogen and argon. Other inert gases with similar properties can also be used to blow the electrolyte to be tested. Those skilled in the art can make their own choices according to needs.

[0061] In some embodiments, the blowing time is 1 min to 60 min.

[0062] In specific applications, the time of using inert gas to blow the electrolyte to be measured can be selected as 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 15min, 18min, 20min, 21min, 22min, 25min, 28min, 30min, 31min, 32min, 35min, 38min, 40min, 41min, 42min, 45min, 48min, 50min, 55min, 60min etc. The above listed times are all examples and are not limiting. Those skilled in the art can freely select any time within the range of 1min~60min without exceeding their own understanding.

[0063] In some embodiments, in step S3, the positive electrode sheet and the electrolyte to be tested are placed in a sealed device.

[0064] During the test, the positive electrode and the electrolyte to be tested are placed in a sealed device, which can effectively isolate the impact of the external environment on the electrolyte to be tested, thereby ensuring more accurate evaluation results.

[0065] In some embodiments, in step S3, the soaking time is 12 hours to 84 hours; and the soaking temperature is 35° C. to 80° C.

[0066] In specific applications, the soaking time in step S3 can be selected from: 12 hours, 13 hours, 14 hours, 15 hours, 18 hours, 20 hours, 22 hours, 23 hours, 24 hours, 25 hours, 28 hours, 30 hours, 32 hours, 35 hours, 35°C to 80°C, etc. The above times are examples and are not limiting. Those skilled in the art can freely select any time within the range of 12 hours to 84 hours without exceeding their own understanding.

[0067] In a specific application, the soaking temperature in step S3 can be selected from: 35°C, 38°C, 40°C, 42°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, etc. The above values ​​are examples and are not limiting. Those skilled in the art can freely select any value within the range of 35°C to 80°C without exceeding their own understanding.

[0068] In some embodiments, in step S3, the mass of the electrolyte to be tested is 10 g to 60 g.

[0069] In a specific application, in step S3, the mass of the electrolyte to be measured can be selected as: 10g, 11g, 12g, 13g, 15g, 18g, 20g, 21g, 22g, 25g, 28g, 30g, 31g, 32g, 35g, 38g, 40g, 41g, 42g, 45g, 48g, 50g, 55g, 60g, etc. The above values ​​are examples and are not limiting. Those skilled in the art can freely select any value within the range of 10g to 60g without exceeding their own understanding.

[0070] In some embodiments, in step S3, the manganese ion concentration test includes taking a photo of the electrolyte to be tested after immersion to record color changes and performing an ICP test to record the manganese ion content in the electrolyte to be tested.

[0071] The purpose of this is to compare the manganese dissolution inhibition effects of different electrolyte formulations, so as to screen out the best electrolyte system.

[0072] Furthermore, a relationship between the color of the electrolyte to be tested and the concentration of manganese ions in the electrolyte to be tested can be established, where the darker the color, the higher the concentration of manganese ions in the electrolyte to be tested. This can further simplify the method flow.

[0073] In some embodiments, in step S3, the electrolyte to be tested is first photographed after immersion to record the color change. If the color does not change or the change is not obvious, the ICP test is continued. This can effectively simplify the process and improve production efficiency.

[0074] The following examples and comparative examples will specifically describe the embodiments of the present invention. It should be noted that the positive electrode sheets in all examples and comparative examples were standard positive electrode sheets made from commercial lithium manganese oxide. The electrolyte in the soft-pack battery cell and the electrolyte to be tested had the same composition, and the process for preparing the soft-pack battery cell was also exactly the same. The number of samples in each group was 20.

[0075] In addition, the embodiments of the present invention are not limited to these Examples.

[0076] Example 1:

[0077] Positive electrode preparation: The positive electrode active material lithium manganese oxide, the binder PVDF, and the conductive agent Super-P were mixed in a mass ratio of 97:3:2, and the solvent NMP was added to form a slurry, which was coated on aluminum foil to form a positive electrode.

[0078] Negative electrode preparation: The negative electrode active material graphite, binder SBR, CMC, and conductive agent Super-P were mixed in a mass ratio of 95:3:2:2, and the solvent NMP was added to form a slurry, which was then coated on aluminum foil to form a positive electrode.

[0079] Preparation of electrolyte: 1M LiPF6 was dissolved in a mixed electrolyte solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, and the additive was 2wt% MMDS.

[0080] Assemble the positive electrode, separator, and negative electrode into a soft-pack battery cell and inject the electrolyte.

[0081] After the cells have been fully charged, disassemble the fully charged positive electrode and clean it with DMC solution. Let the fully charged positive electrode stand for 2 hours to allow the DMC to evaporate. The charge cutoff voltage is 4.2V; the discharge cutoff voltage is 3.0V.

[0082] The test electrolyte was purged with inert gas (N2) for 0.5 h.

[0083] The cleaned positive electrode sheet was placed in an aluminum-plastic bag and soaked with 20g of the electrolyte to be verified and stored at high temperature for a specified time, which was 2 days at a storage temperature of 55°C.

[0084] After storage for a specified time, take out an appropriate amount of the sample electrolyte, pour it into a transparent glass bottle, take photos to compare the color changes; and send it for ICP testing to obtain the Mn content.

[0085] Example 2:

[0086] Positive electrode preparation: The positive electrode active material lithium manganese oxide, the binder PVDF, and the conductive agent Super-P were mixed in a mass ratio of 97:3:2, and the solvent NMP was added to form a slurry, which was coated on aluminum foil to form a positive electrode.

[0087] Negative electrode preparation: The negative electrode active material graphite, binder SBR, CMC, and conductive agent Super-P were mixed in a mass ratio of 95:3:2:2, and the solvent NMP was added to form a slurry, which was then coated on aluminum foil to form a positive electrode.

[0088] Preparation of electrolyte: 1M LiPF6 was dissolved in a mixed electrolyte solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, and the additive was 2wt% VC.

[0089] Assemble the positive electrode, separator, and negative electrode into a soft-pack battery cell and inject the electrolyte.

[0090] After the cells have been fully charged, disassemble the fully charged positive electrode and clean it with DMC solution. Let the fully charged positive electrode stand for 2 hours to allow the DMC to evaporate. The charge cutoff voltage is 4.2V; the discharge cutoff voltage is 3.0V.

[0091] The test electrolyte was purged with inert gas (N2) for 0.5 h.

[0092] The cleaned positive electrode sheet was placed in an aluminum-plastic bag and soaked with 20g of the electrolyte to be verified and stored at high temperature for a specified time, which was 2 days at a storage temperature of 55°C.

[0093] After storage for a specified time, take out an appropriate amount of the sample electrolyte, pour it into a transparent glass bottle, take photos to compare the color changes; and send it for ICP testing to obtain the Mn content.

[0094] Example 3:

[0095] Positive electrode preparation: The positive electrode active material lithium manganese oxide, the binder PVDF, and the conductive agent Super-P were mixed in a mass ratio of 97:3:2, and the solvent NMP was added to form a slurry, which was coated on aluminum foil to form a positive electrode.

[0096] Negative electrode preparation: The negative electrode active material graphite, binder SBR, CMC, and conductive agent Super-P were mixed in a mass ratio of 95:3:2:2, and the solvent NMP was added to form a slurry, which was then coated on aluminum foil to form a positive electrode.

[0097] Preparation of electrolyte: 1M LiPF6 was dissolved in a mixed electrolyte solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, and the additive was 2wt% PS.

[0098] Assemble the positive electrode, separator, and negative electrode into a soft-pack battery cell and inject the electrolyte.

[0099] After the cells have been fully charged, disassemble the fully charged positive electrode and clean it with DMC solution. Let the fully charged positive electrode stand for 2 hours to allow the DMC to evaporate. The charge cutoff voltage is 4.2V; the discharge cutoff voltage is 3.0V.

[0100] The test electrolyte was purged with inert gas (N2) for 0.5 h.

[0101] The cleaned positive electrode sheet was placed in an aluminum-plastic bag and soaked with 20g of the electrolyte to be verified and stored at high temperature for a specified time, which was 2 days at a storage temperature of 55°C.

[0102] After storage for a specified time, take out an appropriate amount of the sample electrolyte, pour it into a transparent glass bottle, take photos to compare the color changes; and send it for ICP testing to obtain the Mn content.

[0103] Example 4:

[0104] Positive electrode preparation: The positive electrode active material lithium manganese oxide, the binder PVDF, and the conductive agent Super-P were mixed in a mass ratio of 97:3:2, and the solvent NMP was added to form a slurry, which was coated on aluminum foil to form a positive electrode.

[0105] Negative electrode preparation: The negative electrode active material graphite, binder SBR, CMC, and conductive agent Super-P were mixed in a mass ratio of 95:3:2:2, and the solvent NMP was added to form a slurry, which was then coated on aluminum foil to form a positive electrode.

[0106] Preparation of electrolyte: 1M LiPF6 was dissolved in a mixed electrolyte solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, and the additive was 2wt% MMDS.

[0107] Assemble the positive electrode, separator, and negative electrode into a soft-pack battery cell and inject the electrolyte.

[0108] After the cells have been fully charged, disassemble the fully charged positive electrode and clean it with DMC solution. Let the fully charged positive electrode stand for 2 hours to allow the DMC to evaporate. The charge cutoff voltage is 4.2V; the discharge cutoff voltage is 3.0V.

[0109] The test electrolyte was purged with inert gas (N2) for 0.5 h.

[0110] The cleaned positive electrode sheet was placed in an aluminum-plastic bag and soaked with 20g of the electrolyte to be verified and stored at high temperature for a specified time, which was 5 days at a storage temperature of 55°C.

[0111] After storage for a specified time, take out an appropriate amount of the sample electrolyte, pour it into a transparent glass bottle, take photos to compare the color changes; and send it for ICP testing to obtain the Mn content.

[0112] Example 5:

[0113] Positive electrode preparation: The positive electrode active material lithium manganese oxide, the binder PVDF, and the conductive agent Super-P were mixed in a mass ratio of 97:3:2, and the solvent NMP was added to form a slurry, which was coated on aluminum foil to form a positive electrode.

[0114] Negative electrode preparation: The negative electrode active material graphite, binder SBR, CMC, and conductive agent Super-P were mixed in a mass ratio of 95:3:2:2, and the solvent NMP was added to form a slurry, which was then coated on aluminum foil to form a positive electrode.

[0115] Preparation of electrolyte: 1M LiPF6 was dissolved in a mixed electrolyte solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, and the additive was 2wt% MMDS.

[0116] Assemble the positive electrode, separator, and negative electrode into a soft-pack battery cell and inject the electrolyte.

[0117] After the battery cell is dissolved and divided into volumes, the positive electrode sheet is disassembled and cleaned with DMC solution. After cleaning, the positive electrode sheet is left to stand for 2 hours to allow the DMC to evaporate.

[0118] The test electrolyte was purged with inert gas (N2) for 0.5 h.

[0119] The cleaned positive electrode sheet was placed in an aluminum-plastic bag and soaked with 20g of the electrolyte to be verified and stored at high temperature for a specified time, which was 2 days at a storage temperature of 55°C.

[0120] After storage for a specified time, take out an appropriate amount of the sample electrolyte, pour it into a transparent glass bottle, take photos to compare the color changes; and send it for ICP testing to obtain the Mn content.

[0121] Comparative Example 1:

[0122] Positive electrode preparation: The positive electrode active material lithium manganese oxide, the binder PVDF, and the conductive agent Super-P were mixed in a mass ratio of 97:3:2, and the solvent NMP was added to form a slurry, which was coated on aluminum foil to form a positive electrode.

[0123] Negative electrode preparation: The negative electrode active material graphite, binder SBR, CMC, and conductive agent Super-P were mixed in a mass ratio of 95:3:2:2, and the solvent NMP was added to form a slurry, which was then coated on aluminum foil to form a positive electrode.

[0124] Preparation of electrolyte: 1M LiPF6 was dissolved in a mixed electrolyte solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, and the additive was 2wt% MMDS.

[0125] Assemble the positive electrode, separator, and negative electrode into a soft-pack battery cell and inject the electrolyte.

[0126] After the battery cell was fully charged after being divided into different capacities, the total amount of manganese ions in the electrolyte and on the negative electrode side was tested after circulating 100 cycles at 45° C., wherein the cycle temperature was the same as the storage temperature in Example 1.

[0127] The specific cycle process is as follows:

[0128] After the soft-pack battery cell is charged at a rate of 0.01C for the first cycle and discharged at a rate of 0.1C for the first cycle, the sample is charged and discharged at a rate of 1C, and the cycle ends after 100 cycles.

[0129] Finally, take out an appropriate amount of sample electrolyte, pour it into a transparent glass bottle, take photos to compare the color changes; and send it for ICP testing to obtain the Mn content.

[0130] Comparative Example 2:

[0131] Weigh lithium manganate powder of the same mass as the positive electrode active material in Example 1, put the lithium manganate powder into an aluminum-plastic bag and soak it with 20g of the electrolyte to be verified and store it at high temperature for a specified time, which is 7 days at a storage temperature of 55°C.

[0132] After storage for a specified time, take out an appropriate amount of the sample electrolyte, pour it into a transparent glass bottle, take photos to compare the color changes; and send it for ICP testing to obtain the Mn content.

[0133] Comparative Example 3:

[0134] Unlike Example 1, this comparative example uses lithium manganese oxide as a button cell for testing. Except for the difference in electrode size, the other technical features are the same.

[0135] The test results are shown in the following table:

[0136]

[0137]

[0138]

[0139] It can be seen from the above table:

[0140] With reference to Examples 1 to 4, the method provided by the present invention for evaluating the effect of an electrolyte on the dissolution of manganese from a lithium manganate positive electrode can quickly and accurately evaluate the compatibility of the electrolyte with the lithium manganate positive electrode. The present invention can quickly screen and optimize the electrolyte formulation, thereby improving battery performance.

[0141] With reference to Example 1 and Comparative Example 1, the test results are similar but the test time is significantly reduced.

[0142] Compared with Example 5 and Comparative Example 1, the battery was not fully charged for measurement, and the overall trend was similar, but the accuracy of the test results decreased.

[0143] Compared with Comparative Example 2 and Comparative Example 3 and Comparative Example 1, the test results are quite different.

[0144] It should be pointed out that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for evaluating the effect of electrolyte on manganese dissolution from lithium manganate cathode, characterized in that: The steps include: S1. Prepare a soft-pack battery cell; the soft-pack battery cell includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode active material, lithium manganese oxide; S2, disassembling the soft-pack battery cell into components and obtaining a positive electrode sheet; S3. Immerse the positive electrode sheet obtained by disassembling S2 in the electrolyte to be tested, and test the manganese ion concentration of the electrolyte after immersion. Based on the test results, evaluate the effect of the electrolyte to be tested on the manganese dissolution of the positive electrode sheet.

2. The method according to claim 1, characterized in that In step S2, before disassembling the soft-pack battery cell, a charging step is also included to charge the soft-pack battery cell to a charging cut-off voltage.

3. The method according to claim 2, characterized in that The charging current of the soft-pack battery cell is 0.1C to 1C.

4. The method according to claim 2, characterized in that In step S2, after the soft-pack battery cell is charged, a rest step is also included, and the rest time is 5 minutes to 60 minutes.

5. The method according to claim 2, characterized in that Step S2 also includes cleaning the disassembled positive electrode sheet.

6. The method according to claim 5, characterized in that The solvent for cleaning the positive electrode is dimethyl carbonate; Preferably, after cleaning, the mixture is allowed to stand for 5 to 300 minutes.

7. The method according to claim 1, characterized in that The soft-pack battery cell includes an electrolyte, and the composition of the electrolyte to be tested is the same as that of the electrolyte.

8. The method according to claim 1, characterized in that In step S3, before the immersion step, the electrolyte to be tested is blown with an inert gas; Preferably, the inert gas includes at least one of nitrogen and argon; Preferably, the blowing time is 1 min to 60 min.

9. The method according to claim 1, characterized in that In step S3, the positive electrode sheet and the electrolyte to be tested are placed in a sealed device; Preferably, in step S3, the soaking time is 12 hours to 84 hours; the soaking temperature is 35° C. to 80° C.; Preferably, in step S3, the mass of the electrolyte to be tested is 10 g to 60 g.

10. The method according to claim 1, characterized in that In step S3, the manganese ion concentration test includes taking photos of the electrolyte to be tested after immersion to record color changes and performing ICP testing to record the manganese ion content in the electrolyte to be tested.

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