Method for evaluating lithium-ion battery materials and use thereof

Abstract

The present disclosure provides a method for evaluating lithium ion battery materials and its application. The method first prepares the positive electrode material to be tested into a delithiated positive electrode material, then places it in an electrolyte for heating and stirring, uses the filtrate obtained after solid-liquid separation for ICP testing to obtain the main element dissolution data, at the same time, uses the powder obtained for EIS testing to obtain the interface charge transfer resistance R CT value, and finally evaluates the high-temperature storage performance of the soft package battery containing the positive electrode material to be tested according to the two data obtained. The evaluation method can simulate the actual high-temperature reaction process of the positive electrode material and the electrolyte to obtain the full charged positive electrode material and obtain the main element dissolution data and R CT value, thereby quickly evaluating the high-temperature storage performance of the positive electrode material. The evaluation method is simple to operate, low in cost, and conducive to improving the evaluation efficiency.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the field of lithium ion batteries, for example, a method for evaluating lithium ion battery materials and its application. BACKGROUND

[0002] At present, lithium ion batteries have been successful due to their high energy density, long cycle life, good rate performance and other advantages, and are widely used in portable consumer electronics, electric vehicles, energy storage and other fields. However, under high temperature conditions, the interface of the electrode material of the lithium ion battery reacts very complicatedly with the electrolyte, which not only causes performance loss at high temperature, but also may cause battery swelling and other safety problems, causing hidden dangers.

[0003] Therefore, it is necessary to test the high temperature performance of the positive electrode material of the lithium ion battery. At present, the high temperature storage performance of the positive electrode material and the lithium battery containing the same is often evaluated by preparing a soft package full battery, and the change of the electrical performance and the swelling rate of the full battery before and after storage for different times or at different temperatures under full charge state are tested. The reliability and safety are measured by comparing the degree of change of the electrical performance index and the degree of swelling of the battery.

[0004] CN108267693B discloses a rapid evaluation method for high temperature storage performance of lithium battery positive electrode material, which uses lithium ion button half battery to charge the positive electrode material at high temperature, and according to the floating capacity test data, the difference in high temperature storage performance between different positive electrode materials can be inferred. However, this rapid evaluation method can only infer the difference in high temperature storage performance between different positive electrode materials, and cannot directly represent the performance change of the positive electrode material during high temperature storage.

[0005] CN110658473B discloses a rapid evaluation method for high temperature storage performance of lithium battery positive electrode material, which simulates the environmental state of the positive electrode material in the full battery high temperature storage, and prepares the delithiated positive electrode material by chemical delithiation, and carries out equivalent high temperature storage test on the delithiated positive electrode material, and evaluates the capacity retention rate by the first discharge capacity ratio. This method obtains the delithiated positive electrode material by strengthening the oxidant, and in the process of reaction with the oxidant, the interface becomes complex, and the delithiation amount cannot be guaranteed, and the discharge capacity of the button battery prepared again is not stable, which reduces the evaluation reliability.

[0006] From the above, it can be seen that there is a need to develop a new evaluation method for rapidly judging the high temperature storage performance of the positive electrode material of the lithium ion battery, in order to improve the test efficiency and reduce the evaluation cost. SUMMARY

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] The present disclosure provides a method for evaluating lithium ion battery materials and its application. The method first prepares a positive electrode material to be tested into a delithiated positive electrode material, then places it in an electrolyte for heating and stirring, uses the filtrate obtained after solid-liquid separation for ICP testing to obtain main element dissolution data, at the same time, performs EIS testing on the powder obtained to obtain interface charge transfer resistance R CT value, and finally evaluates the high-temperature storage performance of a soft pack battery containing the positive electrode material to be tested according to the two obtained data. The evaluation method can simulate the actual high-temperature reaction process of the positive electrode material and the electrolyte to obtain the positive electrode material in a full charge state and obtain the main element dissolution data and R CT value, thereby quickly predicting and evaluating the high-temperature storage performance of the positive electrode material. The evaluation method is simple to operate, low in cost, and conducive to improving evaluation efficiency.

[0009] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0010] In a first aspect, the present disclosure provides a method for evaluating lithium ion battery materials, which comprises the following steps:

[0011] (1) preparing a positive electrode material to be tested into a delithiated positive electrode material;

[0012] (2) placing the delithiated positive electrode material in step (1) in an electrolyte for heating and stirring, performing solid-liquid separation to obtain a filtrate and a powder;

[0013] (3) performing ICP (Inductively Coupled Plasma) testing on the filtrate obtained in step (2) to obtain main element dissolution data; at the same time, preparing the powder in step (2) as a positive electrode material into a button half-cell for EIS (Electrochemical Impedance Spectroscopy) testing to obtain interface charge transfer resistance R CT value;

[0014] (4) the greater the main element dissolution data and R CT value obtained in step (3), the worse the high-temperature storage performance of the positive electrode material to be tested.

[0015] The evaluation method of the present disclosure prepares the positive electrode material into a delithiated positive electrode material, which can simulate the actual high-temperature reaction process of the positive electrode material and the electrolyte and make the positive electrode material in a full charge state (delithiated), and then performs testing to obtain the main element dissolution data and R CT value at this time, thereby quickly predicting and evaluating the high-temperature storage performance of the positive electrode material. The evaluation method is simple to operate, low in cost, and conducive to improving evaluation efficiency.

[0016] The electrolyte used in the embodiments of the present disclosure is not specifically limited, and those skilled in the art can select an electrolyte suitable for the positive electrode material to be tested according to the use.

[0017] Exemplarily, the electrolyte includes 9-15 wt% of lithium salt, 77-88 wt% of non-aqueous organic solvent and 3-8 wt% of additive, calculated based on the total mass of 100 wt%; the lithium salt includes at least one of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6) or novel lithium salt lithium bisfluorosulfonylimide (LiFSI); the non-aqueous organic solvent includes at least one of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) or methyl ethyl carbonate (EMC); the additive includes at least one of film-forming additive, high / low temperature additive, overcharge protection additive, flame retardant additive, rate type additive, for example, vinylene carbonate (VC) and / or fluoroethylene carbonate (FEC) can be selected.

[0018] The following is an optional technical solution of the embodiments of the present disclosure, but not as a limitation of the technical solutions provided by the present disclosure. Through the following technical solutions, the technical purposes and beneficial effects of the present disclosure can be better achieved and implemented.

[0019] As an optional technical solution of the embodiments of the present disclosure, the positive electrode material to be tested in step (1) includes any one or a combination of at least two of lithium cobaltate, lithium iron phosphate or ternary positive electrode material, and typical but non-limiting examples of the combination include a combination of lithium cobaltate and lithium iron phosphate, a combination of lithium cobaltate and ternary positive electrode material, or a combination of lithium iron phosphate and ternary positive electrode material.

[0020] As an optional technical solution of the embodiments of the present disclosure, the preparation method of the delithiated positive electrode material in step (1) includes:

[0021] An oxidizing agent is added to the positive electrode material to be tested to perform a delithiation reaction to obtain the delithiated positive electrode material.

[0022] As an optional technical solution of the embodiments of the present disclosure, the oxidizing agent includes any one or a combination of at least two of hypobromous acid, metaperiodic acid, hypochlorous acid, chlorous acid, permanganic acid, perbromic acid or hydrogen peroxide, and typical but non-limiting examples of the combination include a combination of hypobromous acid and metaperiodic acid, a combination of metaperiodic acid and hypochlorous acid, a combination of chlorous acid and permanganic acid, a combination of permanganic acid and perbromic acid, a combination of chlorous acid and hydrogen peroxide.

[0023] In one embodiment, the amount of the oxidizing agent used is 4-8 mL per gram of the positive electrode material to be tested, for example 4 mL, 4.5 mL, 5 mL, 5.5 mL, 6 mL, 6.5 mL, 7 mL, 7.5 mL or 8 mL, etc., and the concentration of the oxidizing agent is 1.4-8 mol / L, for example 1.4 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, 7 mol / L, 7.5 mol / L or 8 mol / L, etc., but not only limited to the listed values, other values not listed in the above numerical range are also applicable.

[0024] As an optional technical solution of the embodiments of the present disclosure, the delithiation reaction is carried out under stirring.

[0025] In one embodiment, the time of the delithiation reaction is 18-22 h, for example 18 h, 19 h, 20 h, 21 h or 22 h, etc., but not only limited to the listed values, other values not listed in the above numerical range are also applicable.

[0026] As an optional technical solution of the embodiments of the present disclosure, the solid-liquid ratio of the delithiated positive electrode material to the electrolyte in step (2) is 1 g:(1.5-2.5) g, for example 1 g:1.5 g, 1 g:1.6 g, 1 g:1.7 g, 1 g:1.8 g, 1 g:1.9 g, 1 g:2 g, 1 g:2.1 g, 1 g:2.2 g, 1 g:2.3 g, 1 g:2.4 g or 1 g:2.5 g, etc., but not only limited to the listed values, other values not listed in the above numerical range are also applicable.

[0027] In one embodiment, the amount of the electrolyte used is 20-200 mL, for example 20 mL, 50 mL, 80 mL, 110 mL, 140 mL, 170 mL or 200 mL, etc., but not only limited to the listed values, other values not listed in the above numerical range are also applicable.

[0028] As an optional technical solution of the embodiments of the present disclosure, the heating and stirring in step (3) is carried out in a vacuum or a dehumidified environment.

[0029] The heating and stirring in the embodiments of the present disclosure need to be carried out in a vacuum or a dehumidified environment to prevent the electrolyte from absorbing moisture, and the filtrate obtained should also be stored in a sealed manner to prevent water absorption.

[0030] In one embodiment, the heating and stirring in step (3) is carried out in a hydrothermal kettle with a polytetrafluoroethylene liner.

[0031] In one embodiment, the temperature of the heating and stirring in step (3) is 40-80℃, such as 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, or 80℃, but not limited to the listed values, and other values not listed in the above range are also applicable.

[0032] In one embodiment, the time of the heating and stirring in step (3) is 2-4h, such as 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, 3.2h, 3.4h, 3.6h, 3.8h, or 4h, but not limited to the listed values, and other values not listed in the above range are also applicable.

[0033] In one embodiment, the stirring rate of the heating and stirring in step (3) is 80-200r / min, such as 80r / min, 100r / min, 120r / min, 140r / min, 160r / min, 180r / min, or 200r / min, but not limited to the listed values, and other values not listed in the above range are also applicable.

[0034] As an optional technical solution of the embodiments of the present disclosure, the evaluation method step (4) further comprises:

[0035] The main element leaching data and standard R CT value are associated with the high-temperature storage performance of the soft pack battery containing the positive electrode material to be tested, a database is established, a linear relationship between the main element leaching data and the high-temperature storage performance is simulated and / or a linear relationship between the R CT value and the high-temperature storage performance is simulated; and the high-temperature storage performance of the soft pack battery containing the positive electrode material to be tested is calculated according to the linear relationship.

[0036] In one embodiment, the database includes at least 10 different main element leaching data of the positive electrode material to be tested, standard R CT value, and high-temperature storage performance data of the soft pack battery containing the positive electrode material to be tested.

[0037] As an optional technical solution of the embodiments of the present disclosure, the evaluation method comprises the following steps:

[0038] (1) adding an oxidizing agent to the positive electrode material to be tested, the amount of the oxidizing agent being 4-8 mL per gram of the positive electrode material to be tested, the concentration of the oxidizing agent being 1.4-8 mol / L, and the de-lithiation reaction being carried out for 18-22 hours under stirring to obtain the de-lithiated positive electrode material; the positive electrode material to be tested includes any one or a combination of at least two of lithium cobalt oxide, lithium iron phosphate or a ternary positive electrode material; the oxidizing agent includes any one or a combination of at least two of hypobromous acid, metaperiodic acid, hypochlorous acid, chlorous acid, permanganic acid, perbromic acid or hydrogen peroxide;

[0039] (2) in a dehumidification room, the de-lithiated positive electrode material in step (1) is mixed with an electrolyte in a polytetrafluoroethylene inner container of a hydrothermal kettle according to a solid-liquid ratio of 1 g:(1.5-2.5) g, the amount of the electrolyte being 20-200 mL, then the hydrothermal kettle is placed in an oven preheated to 40-80℃, the stirring rate being set to 80-200 r / min, and heating and stirring are carried out for 2-4 hours, after the reaction, the filtrate and powder are obtained by suction filtration, and the powder is washed and dried for standby use;

[0040] (3) the filtrate obtained in step (2) is tested by ICP to obtain the main element dissolution data; at the same time, the powder in step (2) is prepared as a positive electrode material to prepare a coin-type half battery, and EIS test is carried out to obtain the interface charge transfer resistance R CT ;

[0041] (4) the high-temperature storage performance of the soft package battery containing the positive electrode material to be tested is evaluated according to the main element dissolution data and the R CT value obtained in step (3); the greater the main element dissolution data and the R CT value, the worse the high-temperature storage performance of the positive electrode material to be tested; the main element dissolution data and the standard R CT value are associated with the high-temperature storage performance of the soft package battery containing the positive electrode material to be tested, a database including at least 10 sample data is established, the linear relationship between the main element dissolution data and the high-temperature storage performance is simulated and / or the linear relationship between the R CT value and the high-temperature storage performance is simulated; and the high-temperature storage performance of the soft package battery containing the positive electrode material to be tested is calculated according to the linear relationship.

[0042] In a second aspect, the embodiments of the present disclosure provide an application of the evaluation method according to the first aspect in the field of lithium ion battery manufacturing.

[0043] Compared with the related technical solutions, the present disclosure has at least the following beneficial effects:

[0044] The evaluation method can simulate the actual high-temperature reaction process of the positive electrode material and the electrolyte to obtain the full-charge positive electrode material and obtain the main element dissolution data and the RCT The evaluation method is simple in operation and low in cost, and is beneficial to improving the evaluation efficiency.

[0045] Other aspects can be appreciated upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0046] The technical solutions of the present disclosure are further illustrated below through specific embodiments.

[0047] Those skilled in the art should understand that the embodiments are only to help understand the present disclosure, and should not be regarded as specific limitations of the present disclosure.

[0048] The electrolyte used in the following examples and comparative examples is the lithium ion battery electrolyte disclosed in CN115117445A, which comprises a lithium salt, a non-aqueous organic solvent and an additive; specifically, in an argon glove box with a water content <10 ppm, ethylene carbonate, diethyl carbonate, methyl ethyl carbonate and fluoroethylene carbonate are mixed according to the mass percentage of 20wt%, 30wt%, 40wt% and 10wt% to obtain a mixed organic solvent, and then a fully dried lithium salt is dissolved in the mixed organic solvent; the lithium salt is a mixture of lithium hexafluorophosphate and lithium difluorobisoxalate phosphate, and the concentration of the lithium salt in the electrolyte is 1 mol / L, wherein the molar ratio of lithium hexafluorophosphate to lithium difluorobisoxalate phosphate is 95:5; the additive is a mixture of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, vinylene carbonate and vinyl sulfate, and the additive amount of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, vinylene carbonate and vinyl sulfate accounts for 1wt% of the total mass of the electrolyte; after the additive is added and stirred uniformly, the electrolyte is obtained.

[0049] Example 1

[0050] The present embodiment provides an evaluation method for lithium ion battery materials, which is used for evaluating the high-temperature storage performance of lithium cobaltate cathode materials, and comprises the following steps:

[0051] (1) Preparation of delithiated lithium cobaltate material: four different lithium cobaltate materials were selected and labeled as lithium cobaltate-1, lithium cobaltate-2, lithium cobaltate-3, and lithium cobaltate-4, respectively, and four parallel samples were prepared for each lithium cobaltate; the delithiation process was carried out in an argon-filled glove box, 5 g of the above lithium cobaltate material was taken into a beaker, 30 mL of 6.6 mol / L hydrogen peroxide H2O2 solution was added, and the beaker was placed on a magnetic stirrer with a stirring speed of 45 r / min, and stirred for 20 h to obtain delithiated lithium cobaltate; the obtained solution was quickly filtered and the residual impurities were removed using deionized water, and then the obtained delithiated lithium cobaltate material was dried in a vacuum oven for 8 h;

[0052] (2) Electrolyte powder reaction: the four different delithiated lithium cobaltate materials prepared in step (1) were mixed with electrolyte, and to prevent the electrolyte from absorbing moisture, the delithiated lithium cobaltate material was loaded into an autoclave with electrolyte in a humidity chamber, wherein 5 g of delithiated lithium cobaltate material was added to 10 g of electrolyte, and after sealing, the autoclave was placed in a preheated oven at a temperature of 70°C, and the stirring speed in the autoclave was set to 120 r / min; after the reaction was completed, the solution was quickly filtered to obtain the filtrate and powder, and the powder was repeatedly washed with ethanol to remove electrolyte impurities, and then dried in a vacuum oven for 8 h;

[0053] (3) Testing: the filtrate obtained in step (2) was subjected to ICP testing to obtain the cobalt dissolution data of the electrode sheet; the quantitative materials were weighed according to the mass ratio of positive electrode material (lithium cobaltate): conductive carbon black: PVDF = 94%:3%:3%, PVDF was dissolved in a certain amount of NMP, and the positive electrode material and conductive carbon black were added and stirred in a blender for 35 min, and the above materials were uniformly mixed to prepare a uniform positive electrode slurry. The prepared positive electrode slurry was uniformly coated on an aluminum foil to prepare an electrode sheet, which was dried in a 120°C oven to prepare a positive electrode sheet for use; the positive electrode sheet, separator, lithium sheet, electrolyte, etc. were assembled into a button-type half-cell. The button-type half-cell was subjected to EIS testing, and the frequency range of the EIS testing was 0.05-106 Hz, and the EIS testing was completed within 1.5 h;

[0054] (4) Analysis: the results obtained in step (3) are shown in Table 2, and the cobalt dissolution data and R CT value in Table 2 are the average values of four parallel samples in each group of lithium cobaltate. At the same time, in order to more directly show the high-temperature storage performance of the lithium cobaltate material, the lithium cobaltate-1, lithium cobaltate-2, lithium cobaltate-3, and lithium cobaltate-4 before delithiation were prepared into soft-pack full cells, and high-temperature storage tests were carried out at 60°C to obtain storage performance data (capacity retention rate), which are recorded in Table 1;

[0055] Table 1

[0056]

[0057] As can be seen from Table 1, the high-temperature storage performance of lithium cobaltate in different groups is positively correlated with the cobalt element dissolution amount, and the high-temperature storage performance is also positively correlated with the charge transfer impedance value obtained by EIS test. CT The greater the R value is, the worse the high-temperature storage performance of the positive electrode material to be tested is.

[0058] The above illustrates that the evaluation method provided by the embodiment can effectively and quickly evaluate the storage performance of lithium cobaltate positive electrode material.

[0059] Embodiment 2

[0060] The embodiment provides an evaluation method of lithium ion battery material, which is used for evaluating the high-temperature storage performance of a ternary positive electrode material, and comprises the following steps:

[0061] (1) Preparation of delithiated ternary positive electrode material: four different ternary positive electrode materials are selected and are marked as ternary-1, ternary-2, ternary-3 and ternary-4 respectively, and four parallel samples are prepared for each ternary positive electrode material; the delithiation process is carried out in an argon-filled glove box, 8 g of ternary material is taken into a beaker, 50 ml of 2 mol / L hypochlorous acid solution is added, the beaker is placed in a magnetic stirrer, the stirring speed is set to 55 r / min, and the stirring is performed for 24 h to obtain delithiated ternary positive electrode material; the obtained solution is quickly filtered and deionized water is used to remove residual impurities, and then the obtained delithiated ternary positive electrode material is dried in a vacuum oven for 10 h;

[0062] (2) Electrolyte powder reaction: the delithiated ternary positive electrode material prepared in step (1) is mixed with electrolyte, in order to prevent water from being absorbed in the electrolyte, the mixture is placed in a hydrothermal kettle in a dehumidification room, wherein 5 g of positive electrode material powder and 11 g of electrolyte are taken, the hydrothermal kettle is sealed, and then placed in a preheated 65 DEG C oven, the stirring speed is set to 180 r / min, after the reaction is completed, the solution is quickly filtered to obtain filtrate and powder, the powder is repeatedly cleaned with ethanol to remove electrolyte impurities, and then dried in a vacuum oven for 12 h;

[0063] (3) Test: The filtrate obtained in step (2) is subjected to ICP test to obtain the main element manganese dissolution data of the electrode sheet; according to the mass ratio of ternary positive electrode material: conductive carbon black: PVDF = 94%: 3%: 3%, the quantitative material is weighed, the PVDF is dissolved in the quantitative NMP, the positive electrode material and the conductive carbon black are added, and the stirring machine is put into stirring for 35 min, the above-mentioned materials are uniformly mixed, and the uniform positive electrode slurry is prepared. The prepared positive electrode slurry is uniformly coated on the aluminum foil to prepare the electrode sheet, which is dried in the oven at 120℃ to prepare the positive electrode sheet for use; the positive electrode sheet, the separator, the lithium sheet, the electrolyte and the like are assembled into a button type half battery. The button type half battery is subjected to EIS test, the frequency range of the EIS test is 0.05-106Hz, and the EIS test is completed within 1.5h;

[0064] (4) Analysis: the results obtained in step (3) are shown in Table 4, and the manganese element dissolution data and R CT values in Table 4 are the average values of 4 parallel samples in each group of ternary positive electrode materials. At the same time, in order to more directly show the high temperature storage performance of the ternary positive electrode material, the ternary-1, the ternary-2, the ternary-3 and the cobalt ternary-4 before delithiation are prepared into soft package full batteries, and the high temperature storage test is carried out at 60℃ to obtain the storage performance data (capacity retention rate), which is recorded in Table 2;

[0065] Table 2

[0066]

[0067] It can be seen from Table 2 that the high temperature storage performance of the ternary positive electrode material of different groups is positively correlated with the manganese element dissolution, and the high temperature storage performance is also positively correlated with the charge transfer impedance value of the EIS test. The greater the manganese element dissolution data and R CT value, the worse the high temperature storage performance of the positive electrode material to be tested.

[0068] The above description shows that the evaluation method provided by the embodiment can effectively and quickly evaluate the storage performance of the ternary positive electrode material.

[0069] Comparative Example 1

[0070] The comparative example provides an evaluation method of lithium ion battery material, wherein in step (3), only the delithiated lithium cobaltate material is mixed with the electrolyte and heated and placed, and the stirring is not started, and the other conditions are completely the same as those in Example 1.

[0071] Comparative Example 2

[0072] The comparative example provides an evaluation method of a lithium ion battery material, wherein in step (3), only the delithiated ternary positive electrode material is mixed with electrolyte and heated and left to stand without stirring, and other conditions are the same as those in example 2.

[0073] The data obtained in step (3) of comparative example 1 and comparative example 2 are shown in table 3.

[0074] Table 3

[0075]

[0076] As can be seen from table 3, the high-temperature storage performance of the lithium cobaltate positive electrode material in different groups is smaller than the cobalt element dissolution amount and the EIS test charge transfer impedance value compared with example 1, and similarly, the high-temperature storage performance of the ternary positive electrode material in different groups is smaller than the manganese element dissolution amount and the EIS test charge transfer impedance value compared with example 2; there is no difference and reliability between the values in the comparative examples, and the correlation with the storage performance is not large. This shows that stirring during the reaction with electrolyte in step (2) is crucial for simulating the storage condition and accelerating the reaction, which is beneficial to improve the accuracy of the evaluation method, that is, delithiation is a more important step.

Claims

1. A method for evaluating lithium ion battery materials, the method comprising the following steps: (1) preparing a de-lithiated positive electrode material from a positive electrode material to be tested; (2) placing the de-lithiated positive electrode material of step (1) in an electrolyte and heating and stirring, and then performing solid-liquid separation to obtain a filtrate and a powder; (3) The filtrate obtained in step (2) is subjected to ICP test to obtain the main element dissolution data; at the same time, the powder in step (2) is prepared as a button-type half cell as a positive electrode material, and subjected to EIS test to obtain the interface charge transfer impedance R CT value; (4) According to the test results obtained in step (3), the lithium ion battery material is evaluated, specifically: the main element dissolution data and R CT The greater the value, the worse the high-temperature storage performance of the positive electrode material to be tested.

2. The evaluation method according to claim 1, wherein the positive electrode material to be tested of step (1) comprises any one or a combination of at least two of lithium cobaltate, lithium iron phosphate or a ternary positive electrode material.

3. The evaluation method according to claim 1 or 2, wherein, the method for preparing the de-lithiated positive electrode material of step (1) comprises: adding an oxidizing agent to the positive electrode material to be tested to perform a de-lithiation reaction to obtain the de-lithiated positive electrode material.

4. The evaluation method according to claim 3, wherein the oxidizing agent comprises any one or a combination of at least two of hypobromous acid, metaperiodic acid, hypochlorous acid, chlorous acid, permanganate, perbromic acid or hydrogen peroxide.

5. The evaluation method according to claim 3 or 4, wherein, the amount of the oxidizing agent used is 4-8 mL per gram of the positive electrode material to be tested; and the concentration of the oxidizing agent is 1.4-8 mol / L.

6. The assessment method according to any one of claims 1 to 5, wherein, the de-lithiation reaction is performed for 18-22 hours.

7. The assessment method according to any one of claims 1 to 6, wherein, the solid-liquid ratio of the de-lithiated positive electrode material to the electrolyte of step (2) is 1 g:(1.5-2.5) g.

8. The method of assessing according to any one of claims 1 to 7, wherein, the heating and stirring of step (3) is performed in a vacuum or a dehumidified environment.

9. The assessment method according to any one of claims 1 to 8, wherein, the temperature of the heating and stirring of step (3) is 40-80℃.

10. The method of assessment according to any one of claims 1 to 9, wherein, the time of the heating and stirring of step (3) is 2-4 hours.

11. The assessment method according to any one of claims 1 to 10, wherein, the stirring rate of the heating and stirring of step (3) is 80-200 r / min.

12. The assessment method according to any one of claims 1 to 11, wherein, the method for evaluating further comprises: correlating the primary element elution data and the standard R CT values to high temperature storage performance of pouch cells containing the positive electrode material to be tested, building a database, simulating a linear relationship of the primary element elution data to the high temperature storage performance and / or simulating a linear relationship of the R CT values to the high temperature storage performance; extrapolating high temperature storage performance of pouch cells containing the positive electrode material to be tested from the linear relationship; Optionally, the database comprises at least 10 different data of main element elution of the positive electrode material to be tested, standard R CT and data of high-temperature storage performance of the soft pack battery containing the positive electrode material to be tested.

13. The assessment method according to any one of claims 1 to 12, wherein, the method for evaluating comprises the following steps: (1) adding an oxidizing agent to the positive electrode material to be tested, the amount of the oxidizing agent used is 4-8 mL per gram of the positive electrode material to be tested, the concentration of the oxidizing agent is 1.4-8 mol / L, and a de-lithiation reaction is performed for 18-22 hours under stirring to obtain the de-lithiated positive electrode material; the positive electrode material to be tested comprises any one or a combination of at least two of lithium cobaltate, lithium iron phosphate or a ternary positive electrode material; and the oxidizing agent comprises any one or a combination of at least two of hypobromous acid, metaperiodic acid, hypochlorous acid, chlorous acid, permanganate, perbromic acid or hydrogen peroxide; (2) in a dehumidified room, the de-lithiated positive electrode material of step (1) and an electrolyte are mixed in a polytetrafluoroethylene liner in a hydrothermal kettle according to a solid-liquid ratio of 1 g:(1.5-2.5) g, the amount of the electrolyte is 20-200 mL, then the hydrothermal kettle is placed in an oven preheated to 40-80℃, the stirring rate is set to 80-200 r / min, heating and stirring are performed for 2-4 hours, after the reaction is completed, the filtrate and the powder are obtained by suction filtration, the powder obtained is washed and dried for standby use; (3) The filtrate obtained in step (2) is subjected to ICP test to obtain the main element dissolution data; at the same time, the powder in step (2) is prepared as a button-type half cell as a positive electrode material, and subjected to EIS test to obtain the interface charge transfer impedance R CT value; (4) The high-temperature storage performance of the soft pack battery containing the positive electrode material to be tested is evaluated according to the major element leaching data and R CT value obtained in step (3), the major element leaching data and R CT value obtained in step (3), the greater the high-temperature storage performance of the positive electrode material to be tested is worse; and the major element leaching data and standard R CT value obtained in step (3) are associated with the high-temperature storage performance of the soft pack battery containing the positive electrode material to be tested, a database including at least 10 sample data is established, and a linear relationship between the major element leaching data and the high-temperature storage performance is simulated and / or a linear relationship between the R CT value and the high-temperature storage performance is simulated. the high-temperature storage performance of a soft-pack battery containing the positive electrode material to be tested is calculated according to the linear relationship. 14.Use of the method for evaluating according to any one of claims 1-13 in the field of lithium ion battery manufacturing.

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