A method for rapidly evaluating the cycling performance of cathode materials

Abstract

The present invention provides a method for quickly evaluating the cycle performance of a positive electrode material, the method comprising the following steps: Step S1: providing a positive electrode material A and a positive electrode material B, respectively preparing positive electrodes from the positive electrode material A and the positive electrode material B, and then respectively assembling them into batteries with the same negative electrode and separator according to the same method to obtain batteries A and B; Step S2: respectively calibrating the capacity of the two batteries and performing n charge and discharge cycles; Step S3: collecting the charge capacity Q of the two batteries after the i-th cycle charge c，i and the discharge capacity Q of the i-th cycle d，i Calculate ΔD i =Q c，i ‑Q d，i And / or, collect the capacity Q of the two batteries after the i+1th cycle charge c，n+1 Calculate ΔC i =Q c，i+1 ‑Q d，i ; A minimum of 1-2 cycles can be used to compare the cycling performance of two cathode materials.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a method for rapidly evaluating the cycle performance of positive electrode materials. Background Art

[0002] During the battery cell development process, the primary and secondary materials must be screened to ensure they meet the performance requirements of the cell design. When selecting cathode materials, in addition to confirming the properties of the cathode material itself, it's also necessary to assess its impact on the cell's cycling performance, ultimately evaluating the material's performance. This testing often includes a range of tests, including long-term cycling, high and low temperature testing, and rate testing, and the entire testing cycle can take over three months.

[0003] Given that the current conventional method for evaluating the cycle performance of positive electrode materials has a long cycle, often requiring more than 1,000 cycles, is inefficient, seriously affects the progress of project development, and is costly, time-consuming and labor-intensive, the industry urgently needs to develop a method for quickly evaluating the cycle performance of positive electrode materials. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art that the test cycle is long and the cycle performance of the positive electrode material cannot be quickly evaluated, thereby providing a method for quickly evaluating the cycle performance of the positive electrode material.

[0005] To this end, the present invention provides a method for quickly evaluating the cycle performance of a positive electrode material, the method comprising the following steps:

[0006] Step S1: providing positive electrode material A and positive electrode material B, respectively preparing positive electrodes from positive electrode material A and positive electrode material B, and then assembling them into batteries with the same negative electrode and separator according to the same method, thereby obtaining battery A and battery B;

[0007] Step S2: calibrate the capacity of the two batteries respectively and perform n charge and discharge cycles;

[0008] Step S3: Collect the charging capacity Q of the two batteries after the i-th cycle charging c，i and the discharge capacity Q of the i-th cycle d，i Calculate ΔD i =Q c，i -Q d，i ; If the ΔD of battery A i <ΔD of battery B i This means that the cycle performance of positive electrode material A is better than that of positive electrode material B; if the ΔD of battery A i >ΔD of battery B i This means that the cycle performance of positive electrode material A is worse than that of positive electrode material B; if the ΔD of battery A i Equal to ΔD of battery Bi This indicates that the cycle performance of positive electrode material A is consistent with that of positive electrode material B; n and i are positive integers, and i≤n; and / or, the discharge capacity Q of the two batteries in the i-th cycle is collected. d，i and the capacity Q after the i+1th cycle charge c，i+1 Calculate ΔC i =Q c，i+1 -Q d，i ; If the ΔC of battery A i <ΔC of battery B i This means that the cycle performance of positive electrode material A is better than that of positive electrode material B; if the ΔC of battery A i >ΔC of battery B i This means that the cycle performance of positive electrode material A is worse than that of positive electrode material B; if the ΔC of battery A i Equal to ΔC of battery B i This indicates that the cycle performance of positive electrode material A is consistent with that of positive electrode material B; n and i are positive integers, and i+1≤n.

[0009] In a preferred embodiment, the charge capacity of the two batteries after the 1st to i-th cycle and the discharge capacity of the 1st to i-th cycle are collected respectively; ΔD of each cycle is calculated. i ; and / or, respectively, collecting the discharge capacity of the two batteries from the 1st to the i-th cycle and the capacity after charging from the 2nd to the i+1th cycle, and calculating ΔC for each cycle i .

[0010] In a preferred embodiment, the ΔC of two batteries is calculated and compared simultaneously. i and ΔD i .

[0011] Furthermore, charge and discharge cycles were performed at a rate of 0.05C-0.3C.

[0012] In certain preferred embodiments, the charge-discharge cycle is performed at a rate of 0.08C-0.12C.

[0013] Furthermore, during the charge and discharge cycle, the battery is charged to an upper cut-off voltage of ±0.5V; and / or discharged to a lower cut-off voltage of ±0.5V.

[0014] In certain preferred embodiments, the upper cutoff voltage is 4.35 V and the lower cutoff voltage is 2.8 V. Preferably, the battery is charged to 4.25-4.4 V and discharged to 2.6-3.0 V. More preferably, the battery is charged to 4.3-4.4 V.

[0015] Furthermore, n is a positive integer of 1-100, and i is a positive integer of 1-100. Preferably, n is a positive integer of 1-20, and i is a positive integer of 1-5.

[0016] In certain preferred embodiments, the temperature of the cyclic charge and discharge is 25-45°C.

[0017] Furthermore, based on parts by weight, the positive electrode includes 94-98 parts of positive electrode material, 0.5-2 parts of conductive agent and 2-3 parts of binder.

[0018] Furthermore, the positive electrode material is selected from at least one of nickel manganese oxide material, lithium nickel oxide material, lithium cobalt oxide material, nickel cobalt oxide material, and nickel manganese cobalt oxide material; and / or the conductive agent is selected from at least one of acetylene black, carbon black, carbon nanotubes, and graphene; and the binder is selected from at least one of sodium carboxymethyl cellulose, polyvinylidene fluoride, acrylonitrile, and styrene-butadiene rubber.

[0019] Furthermore, the negative electrode material includes 94-98 parts of carbon material, 0.5-2 parts of conductive agent and 2-3 parts of binder.

[0020] Furthermore, the carbon material is selected from at least one of needle coke and petroleum coke; and / or the conductive agent is selected from at least one of carbon black, carbon nanotubes, and graphene; and / or the binder is selected from at least one of sodium carboxymethyl cellulose, acrylonitrile, and styrene-butadiene rubber. A lithium-containing additive is also included, selected from at least one of lithium acetate, lithium thiosulfate, lithium phenylate, lithium alkyl sulfate, and lithium cellulose.

[0021] In certain preferred embodiments, the positive electrode further comprises a current collector, to which the positive electrode material is bonded, and the bonding process can employ existing coating and cold-pressing processes. Specifically, the positive electrode material, conductive agent, and binder are uniformly mixed in conventional proportions and added to a solvent to form a positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, dried, and cold-pressed, and then die-cut and slit to form the positive electrode sheet. The solid content of the positive electrode slurry can be 70-75%, the conductive agent can be a conventional conductive agent, such as acetylene black, the binder can be a conventional binder, such as styrene-butadiene rubber or polyvinylidene fluoride (PVDF), and the solvent can be a conventional organic solvent, such as N-methylpyrrolidone (NMP).

[0022] In certain preferred embodiments, the negative electrode of the battery cell to be tested also includes a current collector, the negative electrode material is bonded to the current collector, and the negative electrode active material is selected from at least one of graphite, hard carbon, soft carbon, and mesophase carbon microbeads. The bonding process can adopt the existing coating and cold pressing process. Specifically, the negative electrode active material, the conductive agent, and the binder are mixed in a conventional proportion, added to the solvent water, mixed evenly and made into a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil, dried and cold pressed to make a negative electrode sheet. The solid content of the negative electrode slurry can be 50-55%, the conductive agent can be a conventional conductive agent, such as acetylene black, and the binder can be a conventional binder, such as styrene-butadiene rubber, acrylonitrile or sodium hydroxymethyl cellulose.

[0023] The electrode liquid of the present invention can adopt conventional commercially available lithium ion electrolyte, or can be homemade using existing conventional materials. For example, an electrolyte comprising a solvent, a lithium salt and an additive can be adopted, wherein the solvent is selected from at least one of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate. The lithium salt is selected from lithium hexafluorophosphate and / or lithium tetrafluoroborate; the additive is selected from at least one of vinylene carbonate, propylene carbonate, vinyl sulfate and lithium difluorophosphate. The molar concentration of the lithium salt is 0.8-1.2 mol / L, and a mixed solution of ethylene carbonate (EC), dimethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1-5:3:2 can be used as the solvent. The volume percentage of the additive can be 0.5-5%. The present invention can adopt existing traditional diaphragms, such as PE diaphragms, PP diaphragms, PP / PE composite films, or other commercially available diaphragms.

[0024] The technical solution of the present invention has the following advantages:

[0025] 1. The method for quickly evaluating the cycle performance of positive electrode materials provided by the present invention is to collect the charging capacity Q of two batteries after the i-th cycle charging. c，i and the discharge capacity Q of the i-th cycle d，i Calculate ΔD i =Q c，i -Q d，i And / or, collect the capacity Q of the two batteries after the i+1th cycle charge c，n+1 Calculate ΔC i =Q c，i+1 -Q d，i The performance of two cathode materials can be compared after only one to two cycles. This significantly reduces the number of cycles and the time to less than one-two-hundredth. The test results are consistent with those of traditional methods, ensuring accuracy and significantly improving material screening speed, providing a basis for material selection. This also significantly reduces costs and manpower.

[0026] 2. The method provided by the present invention for quickly evaluating the cycle performance of positive electrode materials is to control the charge to 4.25-4.4V; discharge to 2.6-3.0V, especially to control the charge to 4.3-4.4V. The difference in the offset value of the battery cell is obvious, and the probability of error in the evaluation result is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 is the ΔD value of the two groups of battery cells with different cycle numbers in Example 2 of the present invention;

[0029] Figure 2 is the ΔC value of the two groups of battery cells with different cycle numbers in Example 2 of the present invention.

[0030] Figure 3 2 are the cyclic charge and discharge curves of the two groups of battery cells in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0031] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0032] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0033] Example 1 Preparation of Battery

[0034] The positive electrode material A and the positive electrode material B to be tested in the embodiment are both nickel-cobalt-manganese materials (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2), from different manufacturers.

[0035] The battery cells were prepared using the same method as follows:

[0036] (1) Preparation of positive electrode sheet: Take the positive electrode material, the conductive agent acetylene black, and the binder polyvinylidene fluoride PVDF and mix them evenly in a mass ratio of 96:1.5:2.5 to obtain a mixture, add the solvent N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry (solid content of 70%), and mix the positive electrode slurry at a concentration of 19 mg / cm 2 The single-sided surface density is evenly coated on the positive electrode current collector aluminum foil with a thickness of 12μm. After drying at 100℃ and cold pressing, it is die-cut and slit to make the positive electrode sheet of lithium-ion battery.

[0037] (2) Preparation of negative electrode sheet: Take the negative electrode active material graphite, the conductive agent acetylene black, the binder sodium carboxymethyl cellulose (CMC), and the binder styrene butadiene rubber (SBR) and mix them in a mass ratio of 96:1:3:2 to obtain a mixture. Add the mixture into solvent water and mix well to prepare a negative electrode slurry (solid content of 50%). 2 The single-side surface density is evenly coated on the negative electrode current collector copper foil, the thickness of the copper foil is 6 μm, and it is dried at 90°C and then cold pressed to make the negative electrode sheet of the lithium-ion battery to be manufactured.

[0038] (3) Preparation of electrolyte: Lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 5:3:2 to obtain a lithium hexafluorophosphate solution with a concentration of 1.15 mol / L. 1% by volume of vinylene carbonate, 0.5% by volume of lithium difluorophosphate, and 0.5% by volume of vinyl sulfate DTD were added to obtain a lithium ion battery electrolyte.

[0039] (4) The positive electrode sheet, PE separator (purchased from Enjie Company, model: ND18), and negative electrode sheet are assembled in a stacked manner to obtain a battery electrode group, dried in a vacuum drying oven, injected with electrolyte, and sealed to obtain group A battery cells and group B battery cells.

[0040] Example 2 Evaluation

[0041] The positive electrode material cycle performance of the battery cells of group A and group B obtained in Example 1 was evaluated respectively, and the capacities of the battery cells of group A and group B obtained in Example 1 were calibrated as Ca and Cb, and the battery cells of group A and group B were cycled 21 times at a rate of 0.1C; the battery cells were kept in an empty state before the test, and the cycle voltage range was 2.8-4.35V, that is, at 45°C, they were first charged to 4.35V (charge cut-off voltage) at 0.1C, and then discharged to 2.8V (discharge cut-off voltage) at 0.1C, and cycled 21 times; the charging capacity data Q of the battery cells of group A and group B were extracted respectively c，1 to Q c，20 And discharge data Q d，1 to Q d，20 . Calculate the offsets ΔD and ΔC each time.

[0042] ΔD1=Q c，1 -Q d，1 , ΔD2=Q c，2 -Q d，2 ...ΔD 20 =Q c，20 -Q d，20

[0043] ΔC1=Q c，2 -Q d，1 ,ΔC2=Q c，3 -Q d，2 ...ΔC 20 =Q c，21 -Q d，20

[0044] See the results Figure 1 and 2 shown.

[0045] Comparing the first five groups of data, the ΔD and ΔC of group A are both smaller than those of group B. Therefore, the cycle stability of the positive electrode material of group A is better than that of group B, and the subsequent 15 groups also maintain a trend of being less than , further verifying that the cycle stability of the positive electrode material of group A is better.

[0046] Example 3 Evaluation

[0047] The cycle performance of the positive electrode materials of the battery cells of group A and group B obtained in Example 1 was evaluated respectively. The difference from Example 2 was only in the cyclic charge and discharge process. The charge cut-off voltage of this example was 4.4V.

[0048] Example 4 Evaluation

[0049] The cycle performance of the positive electrode materials of the battery cells of group A and group B obtained in Example 1 was evaluated respectively. The only difference from Example 2 was the cut-off voltage for cyclic charging and discharging. The charging cut-off voltage of this embodiment was 4.25V.

[0050] Example 5 Evaluation

[0051] The cycle performance of the positive electrode materials of the battery cells of group A and group B obtained in Example 1 was evaluated respectively. The only difference from Example 2 was the different charge cut-off voltage during the cyclic charge and discharge process. The charge cut-off voltage of this example was 4.3V.

[0052] Comparative Example 1

[0053] The cycle performance of the positive electrode materials of the battery cells of group A and group B obtained in Example 1 was tested by conventional methods. The charge and discharge cycles were carried out at 2.8-4.35V at a rate of 0.1C. The results are shown in FIG. Figure 3 As shown in the figure, the battery cells in group A showed better capacity retention than those in group B after 1000 cycles, and had better cycle performance.

[0054] The test results of each embodiment and comparative example are shown in the table below.

[0055] Table 1 Experimental results

[0056]

[0057]

[0058] It can be seen from the results in the above table that Examples 1-4 of the present application can quickly and accurately evaluate the cycle performance of the positive electrode material. The measured cycle performance of the battery cells in Group A is better than that in Group B, which is consistent with the results of conventional long-term tests (comparative examples). Especially in Examples 2, 3 and 5, the difference in offset values between the battery cells in Group A and Group B is obvious, and the probability of error in the evaluation results is lower.

[0059] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for rapidly evaluating the cycle performance of a cathode material, characterized in that: The method comprises the following steps: Step S1: providing positive electrode material A and positive electrode material B, respectively preparing positive electrodes from positive electrode material A and positive electrode material B, and then assembling them into batteries with the same negative electrode and separator according to the same method, thereby obtaining battery A and battery B; Step S2: calibrate the capacity of the two batteries respectively and perform n charge and discharge cycles; Step S3: Collect the charging capacity Q of the two batteries after the i-th cycle charging c，i and the discharge capacity Q of the i-th cycle d，i Calculate ΔD i =Q c，i -Q d，i ; If the ΔD of battery A i <ΔD of battery B i This means that the cycle performance of positive electrode material A is better than that of positive electrode material B; if the ΔD of battery A i >ΔD of battery B i This means that the cycle performance of positive electrode material A is worse than that of positive electrode material B; if the ΔD of battery A i Equal to ΔD of battery B i This indicates that the cycle performance of positive electrode material A is consistent with that of positive electrode material B; n and i are positive integers, and i≤n; and / or, collecting the discharge capacity Q of the two batteries in the i-th cycle d，i and the capacity Q after the i+1th cycle charge c，i+1 Calculate ΔC i =Q c，i+1 -Q d，i If the ΔC of battery A i <ΔC of battery B i This means that the cycle performance of positive electrode material A is better than that of positive electrode material B; if the ΔC of battery A i >ΔC of battery B i This means that the cycle performance of positive electrode material A is worse than that of positive electrode material B; if the ΔC of battery A i Equal to ΔC of battery B i This indicates that the cycle performance of positive electrode material A is consistent with that of positive electrode material B; n and i are positive integers, and i+1≤n.

2. The method for rapidly evaluating the cycle performance of a cathode material according to claim 1, wherein: The charge capacity of the two batteries from the 1st to the i-th cycle and the discharge capacity from the 1st to the i-th cycle are collected respectively; Calculate ΔD for each cycle i ; and / or, respectively, collecting the discharge capacity of the two batteries from the 1st to the i-th cycle and the capacity after charging from the 2nd to the i+1th cycle, and calculating ΔC for each cycle i .

3. The method for rapidly evaluating the cycle performance of a cathode material according to claim 1, wherein: The charge and discharge cycles were performed at a rate of 0.05C-0.3C.

4. The method for rapidly evaluating the cycle performance of a cathode material according to claim 3, wherein: The charge and discharge cycles were carried out at a rate of 0.08C-0.12C.

5. The method for rapidly evaluating the cycle performance of a cathode material according to any one of claims 1 to 4, characterized in that: During the charge and discharge cycle, the battery is charged to an upper cut-off voltage ±0.5V; and / or discharged to a lower cut-off voltage ±0.5V.

6. The method for rapidly evaluating the cycle performance of a cathode material according to claim 5, characterized in that: The upper cut-off voltage is 4.35V; the lower cut-off voltage is 2.8V.

7. The method for rapidly evaluating the cycle performance of a cathode material according to claim 6, wherein: During the charge and discharge cycle, charge to 4.25-4.4V; discharge to 2.6-3.0V.

8. The method for rapidly evaluating the cycle performance of a cathode material according to any one of claims 1 to 4, characterized in that: n is a positive integer from 1 to 100, and i is a positive integer from 1 to 100.

9. The method for rapidly evaluating the cycle performance of a cathode material according to claim 8, characterized in that: n is a positive integer from 1 to 20, and i is a positive integer from 1 to 5.

10. The method for rapidly evaluating the cycle performance of a cathode material according to any one of claims 1 to 4, characterized in that: In parts by weight, the positive electrode includes 94-98 parts of positive electrode material, 0.5-2 parts of conductive agent and 2-3 parts of binder.

11. The method for rapidly evaluating the cycle performance of a cathode material according to claim 10, characterized in that: The positive electrode material is selected from at least one of nickel cobalt manganese material, nickel manganese lithium oxide material, lithium nickel oxide material, lithium cobalt oxide material, nickel cobalt oxide material, and nickel manganese lithium cobalt oxide material; and / or the conductive agent is selected from at least one of carbon black, acetylene black, carbon nanotubes and graphene; the binder is selected from at least one of sodium carboxymethyl cellulose, polyvinylidene fluoride, acrylonitrile and styrene-butadiene rubber.

12. The method for rapidly evaluating the cycle performance of a cathode material according to any one of claims 1 to 4, characterized in that: The negative electrode material includes 94-98 parts of carbon material, 0.5-2 parts of conductive agent and 2-5 parts of binder.

13. The method for rapidly evaluating the cycle performance of a cathode material according to claim 12, wherein: The carbon material is selected from at least one of graphite, hard carbon, soft carbon, and mesophase carbon microbeads; and / or the conductive agent is selected from at least one of carbon black, carbon nanotubes, and graphene; and / or the binder is selected from at least one of sodium carboxymethyl cellulose, acrylonitrile, and styrene-butadiene rubber.

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