CN113740404A - Method for nondestructive evaluation of molar ratio of lithium to cobalt in lithium battery electrode - Google Patents
Method for nondestructive evaluation of molar ratio of lithium to cobalt in lithium battery electrode Download PDFInfo
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- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 151
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 139
- 238000000034 method Methods 0.000 title claims abstract description 111
- 229910017052 cobalt Inorganic materials 0.000 title claims abstract description 32
- 239000010941 cobalt Substances 0.000 title claims abstract description 32
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 title claims abstract description 32
- 238000011156 evaluation Methods 0.000 title claims abstract description 20
- CKFRRHLHAJZIIN-UHFFFAOYSA-N cobalt lithium Chemical compound [Li].[Co] CKFRRHLHAJZIIN-UHFFFAOYSA-N 0.000 claims abstract description 69
- 238000012360 testing method Methods 0.000 claims abstract description 53
- 230000008569 process Effects 0.000 claims abstract description 29
- 230000001066 destructive effect Effects 0.000 claims abstract description 11
- 239000011149 active material Substances 0.000 claims abstract description 4
- 208000028659 discharge Diseases 0.000 claims description 40
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 31
- 229910001416 lithium ion Inorganic materials 0.000 claims description 31
- 238000007600 charging Methods 0.000 claims description 29
- 238000007599 discharging Methods 0.000 claims description 26
- 230000008859 change Effects 0.000 claims description 17
- 238000005259 measurement Methods 0.000 claims description 14
- 239000010405 anode material Substances 0.000 claims description 11
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- 239000000126 substance Substances 0.000 claims description 7
- 238000004448 titration Methods 0.000 claims description 5
- 238000010280 constant potential charging Methods 0.000 claims description 4
- 238000010277 constant-current charging Methods 0.000 claims description 4
- 238000009616 inductively coupled plasma Methods 0.000 claims description 3
- 238000004993 emission spectroscopy Methods 0.000 claims description 2
- 239000003153 chemical reaction reagent Substances 0.000 abstract description 3
- 238000003912 environmental pollution Methods 0.000 abstract description 2
- 238000009659 non-destructive testing Methods 0.000 abstract description 2
- 239000000463 material Substances 0.000 description 53
- 239000000523 sample Substances 0.000 description 41
- 239000013074 reference sample Substances 0.000 description 19
- 238000004364 calculation method Methods 0.000 description 12
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- 239000007774 positive electrode material Substances 0.000 description 9
- KFDQGLPGKXUTMZ-UHFFFAOYSA-N [Mn].[Co].[Ni] Chemical compound [Mn].[Co].[Ni] KFDQGLPGKXUTMZ-UHFFFAOYSA-N 0.000 description 8
- 239000000843 powder Substances 0.000 description 8
- 239000002994 raw material Substances 0.000 description 7
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 6
- 238000001514 detection method Methods 0.000 description 6
- -1 nickel cobalt aluminum Chemical compound 0.000 description 6
- 239000002033 PVDF binder Substances 0.000 description 5
- 239000006258 conductive agent Substances 0.000 description 5
- 239000003792 electrolyte Substances 0.000 description 5
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 5
- 238000007789 sealing Methods 0.000 description 5
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 4
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 4
- 238000013459 approach Methods 0.000 description 4
- 239000011230 binding agent Substances 0.000 description 4
- 239000010406 cathode material Substances 0.000 description 4
- 238000005096 rolling process Methods 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical group [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 239000008151 electrolyte solution Substances 0.000 description 3
- 238000002354 inductively-coupled plasma atomic emission spectroscopy Methods 0.000 description 3
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 3
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 3
- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical compound O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 description 2
- BJWMSGRKJIOCNR-UHFFFAOYSA-N 4-ethenyl-1,3-dioxolan-2-one Chemical compound C=CC1COC(=O)O1 BJWMSGRKJIOCNR-UHFFFAOYSA-N 0.000 description 2
- SBLRHMKNNHXPHG-UHFFFAOYSA-N 4-fluoro-1,3-dioxolan-2-one Chemical compound FC1COC(=O)O1 SBLRHMKNNHXPHG-UHFFFAOYSA-N 0.000 description 2
- JGFBQFKZKSSODQ-UHFFFAOYSA-N Isothiocyanatocyclopropane Chemical compound S=C=NC1CC1 JGFBQFKZKSSODQ-UHFFFAOYSA-N 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- 239000006230 acetylene black Substances 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- PWLNAUNEAKQYLH-UHFFFAOYSA-N butyric acid octyl ester Natural products CCCCCCCCOC(=O)CCC PWLNAUNEAKQYLH-UHFFFAOYSA-N 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- ZUOUZKKEUPVFJK-UHFFFAOYSA-N diphenyl Chemical compound C1=CC=CC=C1C1=CC=CC=C1 ZUOUZKKEUPVFJK-UHFFFAOYSA-N 0.000 description 2
- 230000005611 electricity Effects 0.000 description 2
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 2
- 229910002102 lithium manganese oxide Inorganic materials 0.000 description 2
- VLXXBCXTUVRROQ-UHFFFAOYSA-N lithium;oxido-oxo-(oxomanganiooxy)manganese Chemical compound [Li+].[O-][Mn](=O)O[Mn]=O VLXXBCXTUVRROQ-UHFFFAOYSA-N 0.000 description 2
- 239000012046 mixed solvent Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- UUIQMZJEGPQKFD-UHFFFAOYSA-N n-butyric acid methyl ester Natural products CCCC(=O)OC UUIQMZJEGPQKFD-UHFFFAOYSA-N 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 description 1
- 229910007966 Li-Co Inorganic materials 0.000 description 1
- 229910032387 LiCoO2 Inorganic materials 0.000 description 1
- 229910008295 Li—Co Inorganic materials 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
- 238000012356 Product development Methods 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 235000010290 biphenyl Nutrition 0.000 description 1
- 239000004305 biphenyl Substances 0.000 description 1
- BRTALTYTFFNPAC-UHFFFAOYSA-N boroxin Chemical compound B1OBOBO1 BRTALTYTFFNPAC-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 150000005678 chain carbonates Chemical class 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 239000006184 cosolvent Substances 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 150000005676 cyclic carbonates Chemical class 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
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- 230000001939 inductive effect Effects 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- DEUISMFZZMAAOJ-UHFFFAOYSA-N lithium dihydrogen borate oxalic acid Chemical compound B([O-])(O)O.C(C(=O)O)(=O)O.C(C(=O)O)(=O)O.[Li+] DEUISMFZZMAAOJ-UHFFFAOYSA-N 0.000 description 1
- RSNHXDVSISOZOB-UHFFFAOYSA-N lithium nickel Chemical compound [Li].[Ni] RSNHXDVSISOZOB-UHFFFAOYSA-N 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 150000005677 organic carbonates Chemical class 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000004080 punching Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000012086 standard solution Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
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- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Health & Medical Sciences (AREA)
- Physics & Mathematics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Molecular Biology (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Battery Electrode And Active Subsutance (AREA)
- Secondary Cells (AREA)
Abstract
The invention relates to a method for non-destructive evaluation of the molar ratio of lithium to cobalt in a lithium battery electrode, the active material of which is defined as lithium cobaltate M1‑nThe molar ratio of lithium to cobalt in the lithium battery electrode is N1‑nSelecting the known lithium-cobalt molar ratio as N0Lithium cobaltate standard sample M0The reference electrode is made by adopting the same process as the lithium battery electrode, the reference electrode and the lithium battery electrode are assembled into a battery according to the same method and then are subjected to specific capacity test under the same condition, and the measured specific capacities of the batteries are Q0And Q1‑nThen the molar ratio of lithium to cobalt in the lithium battery electrode is N1‑n＝N0×(Q1‑n/Q0). The sample to be tested does not need to decompose a battery, has no requirement on the sample amount, can be subjected to online nondestructive testing, and is particularly suitable for evaluating the lithium-cobalt molar ratio in the cycle performance testing process. Meanwhile, the artificial interference is small, and the operation is convenient. And the reagent is obviously reduced, the environmental pollution of a laboratory is reduced, andand (5) pollution discharge.
Description
Technical Field
The invention relates to the technical field of electrochemical measurement, in particular to a method for nondestructively evaluating the molar ratio of lithium to cobalt in a lithium battery electrode.
Background
Since 1991, the lithium ion battery is applied to various fields of production and life of people, especially, the development of the lithium ion battery is rapid in recent years, the lithium ion battery not only continues to consolidate the status in the fields of 3C products such as mobile phones, notebook computers and the like, but also gradually becomes one of the main technical routes in the field of electric vehicles. The main raw materials of the lithium ion battery comprise a positive electrode material, a negative electrode material, a diaphragm, electrolyte and the like. Meanwhile, the material also comprises auxiliary materials such as a conductive agent, a binder, a shell, a current collector, an electrode leading-out terminal and the like. The electrochemical performance of the lithium ion battery depends on the performance of the raw material to the greatest extent by a specific manufacturing process, wherein the performance of the positive electrode material plays a key role. Lithium cobalt oxide, nickel cobalt manganese ternary, nickel cobalt aluminum ternary, lithium iron phosphate, lithium manganese oxide and the like are commercially available as the positive electrode material of the lithium ion battery. The lithium cobaltate positive electrode material has the advantages of high voltage, stable discharge, high compaction density, good cycle performance, suitability for large-current discharge and the like, and is widely applied to the 3C field represented by mobile phones and notebook computers. The lithium-cobalt molar ratio is an important factor influencing the electrochemical performance of the lithium cobaltate material. In the research and development and production processes, the evaluation of the molar ratio of lithium to cobalt has very important significance in controlling the quality of the anode material and analyzing the development of abnormal materials and novel materials. The lithium cobalt molar ratio is one of the important technical indexes of the commercially available lithium cobaltate material powder. In order to balance the lithium ion consumption of the cathode and the electrolyte to the anode in the formation stage of the battery, the lithium-cobalt molar ratio of the cathode material powder is usually designed to be slightly larger than the stoichiometric ratio, thereby also meaning that the lithium-cobalt molar ratio of the cathode material on the cathode sheet is usually smaller than the nominal value of the powder raw material. Thus in LiCoO2The molar ratio of lithium to cobalt is 1:1, which is not the real molar ratio of lithium to cobalt of the positive electrode material on the electrode plate, and the molar ratio of lithium to cobalt on the electrode plate must be measured to truly reflect the condition of the battery.
The conventional detection method for the lithium-cobalt molar ratio in the lithium cobaltate material powder raw material is to respectively measure the contents of cobalt and lithium elements in the lithium cobaltate material and then calculate the ratio. Usually, a chemical titration method is adopted for testing the cobalt content, and an atomic absorption method is adopted for testing the lithium content, but the two testing processes are complicated to operate and require severe results to cause unstable testing results. The invention patent CN106198495B provides a method for one-time testing of the lithium-cobalt molar ratio in a lithium cobaltate material based on inductively coupled plasma atomic emission spectroscopy, and the method carries out secondary correction on the data of a lithium cobaltate sample to be tested by drawing standard solutions of lithium cobaltate with different lithium-cobalt mass ratios and different concentrations, thereby remarkably improving the stability of a test result. Although the method can better meet the test requirement of the lithium-cobalt molar ratio in the lithium cobaltate material powder, the method has the following defects in the aspects of evaluating the lithium-cobalt molar ratio of the lithium cobaltate material on the lithium ion battery pole piece and the like: firstly, disassembling a battery and collecting a lithium cobaltate material on a pole piece, wherein the sample amount has certain requirements; secondly, the measured value of the molar ratio of lithium to cobalt depends on the discharging process step and the state of charge (SOC) of the battery before testing, and particularly, when the internal resistance polarization of the battery is large, the influence is severe; and finally, the test operation is complex, the period is long and pollution is easy to generate in the processes of battery disassembly, sample collection and test.
Disclosure of Invention
The invention aims to solve the problems of complexity and inaccuracy in the determination of the lithium-cobalt molar ratio of the existing lithium cobaltate material, and provides a method for nondestructively evaluating the lithium-cobalt molar ratio in a lithium battery electrode. By adopting the method, the molar ratio of lithium to cobalt in the anode material can be obtained under the condition of not disassembling the battery to be tested, the nondestructive evaluation technology of the molar ratio of lithium to cobalt of the lithium cobaltate material on the lithium ion battery pole piece is developed, and the method has great promotion effects on the product development of the lithium cobaltate material of the lithium ion battery, the failure analysis of the lithium cobaltate material and the online evaluation under the working condition.
The invention provides a nondestructive testing idea, which is characterized in that the lithium-cobalt molar ratio in a positive electrode material can be obtained only by disassembling a formed battery and collecting the positive electrode material. The inventor proves through a large amount of experimental studies that after the lithium cobaltate material of the lithium ion battery is manufactured into the pole piece and assembled into the battery, the lithium cobalt molar ratio of the lithium cobaltate material on the positive pole piece is slightly smaller than that of the lithium cobaltate powder used as the raw material of the positive pole through the preliminary forming process. This difference is related to the consumption of lithium ions in the lithium cobaltate material in the positive and negative electrodes and the electrolyte to different extents, and also means that the lithium-cobalt molar ratio of the lithium cobaltate powder as the positive electrode raw material cannot represent the lithium-cobalt molar ratio of the lithium cobaltate material on the positive electrode sheet. The capacity attenuation and loss of the lithium ion battery in the circulating process are obviously influenced by the lithium cobalt molar ratio of the lithium cobaltate material on the pole piece, so that the obtaining of the real numerical value of the lithium cobalt molar ratio of the lithium cobaltate material on the pole piece is very important. Namely, under the on-line working condition of the lithium ion battery, the quantitative detection of the lithium cobalt molar ratio of the lithium cobaltate material on the pole piece has very important significance.
The common evaluation method is to collect the lithium cobaltate material on the pole piece after disassembling the battery, and then to determine the lithium-cobalt molar ratio by chemical titration analysis or instrumental analysis method. The inventor indicates through careful research that when the same steady-state initial potential, namely the open-circuit potential of the lithium ion battery in a stable equilibrium state, is adopted among different lithium ion batteries, and the same potential is changed to reach another same steady-state end potential, there is a linear relationship between the specific capacity variation in the process and the lithium-cobalt molar ratio of the lithium cobaltate material on the pole piece. The present invention has been completed based on further studies.
Further research finds that not all lithium battery positive electrode materials meet the linear relationship, only a good direct proportional linear relationship exists between the charging and discharging specific capacity variation of the lithium cobaltate material and the lithium-cobalt molar ratio of the lithium cobaltate material on the pole piece, the potential interval range and the potential variation amplitude in the charging and discharging process have influence on the measurement error, and the detection accuracy can be improved and the error can be reduced by selecting proper steady-state initial voltage and potential variation amplitude.
The specific scheme is as follows:
a method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode, comprising: defining the active material of the lithium battery electrode as lithium cobaltate M1-nThe molar ratio of lithium to cobalt in the lithium battery electrode is N1-nSelecting a lithium cobaltate standard sample M0The reference electrode is made by the same process as the lithium battery electrode, and the reference electrode and the lithium battery electrode are assembled by the same methodAfter the battery is tested, the specific capacity under the same conditions is tested, and the measured specific capacity of the battery is Q0And Q1-nThen the molar ratio of lithium to cobalt in the lithium battery electrode is N1-n＝N0×(Q1-n/Q0) Wherein N is0As a standard sample M of lithium cobaltate0Lithium to cobalt molar ratio in the electrode state.
Further, the method for nondestructively evaluating the molar ratio of lithium to cobalt in the lithium battery electrode comprises the following steps:
s1, obtaining a lithium cobaltate standard sample M0And the lithium cobalt molar ratio N of the lithium cobaltate standard sample in the electrode state0；
S2, standard sample M of lithium cobaltate in S10Lithium cobaltate sample M to be measured according to the sum1-nManufacturing electrodes under the same process conditions and assembling into batteries, respectively marked as C0And C1-nCarrying out formation and specific capacity tests on the battery, and recording C under the same steady-state potential, namely the same steady-state initial potential and the same steady-state termination potential0And C1-nThe specific capacity change amounts of (A) and (B) are respectively denoted as Q0And Q1-n；
S3, calculating the molar ratio of lithium to cobalt, N, in the lithium battery electrode1-n＝N0×(Q1-n/Q0)。
Further, the standard lithium cobaltate sample is a known lithium-cobalt molar ratio N0The sample of (1);
optionally, the lithium cobaltate standard sample M0N of (A)0Unknown, obtaining N0The method comprises the following steps: the standard sample M of lithium cobaltate in S20Fabricated Battery C0And disassembling after discharging is finished, collecting the anode material, and determining the obtained lithium-cobalt molar ratio by adopting a chemical titration method or an inductively coupled plasma emission spectrometry.
Further, in S2, the specific capacity test is completed in the charging stage and/or the discharging stage of the battery, and the potential variation amplitude in the charging stage and/or the discharging stage is greater than or equal to 200 times of the potential accuracy of the selected measuring equipment.
Further, when specific capacity measurement is realized in the battery discharging stage, the steady-state initial voltage is less than or equal to the charge cut-off voltage of the tested battery system and is greater than the platform potential; specifically, the steady-state initial potential is 3.91-4.60V vs Li by taking the potential of the lithium metal electrode as a reference zero potential, and preferably, the steady-state initial potential is controlled to be 3.91-4.35V vs Li;
optionally, the steady-state end potential is selected to be 3.00-4.54V vs Li and not equal to 3.90V vs Li when the specific capacity measurement is realized in the discharge stage of the lithium ion battery, and preferably, the steady-state end potential is 3.00-4.30V vs Li and not equal to 3.90V vs Li.
Further, when the specific capacity measurement is realized in the battery charging stage, the selection range of the steady-state initial potential is larger than or equal to the discharge cut-off voltage of the tested battery system; specifically, the potential of the lithium metal electrode is taken as a reference zero potential, the steady-state initial potential is 3.00-4.54 Vvs Li and is not equal to 3.90V vs Li, preferably, the steady-state initial potential is 3.00-4.30 Vvs Li and is not equal to 3.90V vs Li;
optionally, the steady-state termination potential is 3.91-4.60V vs Li when specific capacity measurement is realized in the charging stage of the lithium battery, and preferably the steady-state termination potential is 3.91-4.35V vs Li.
Further, the control of the steady-state initial potential and/or the steady-state final potential in the charging stage and/or the discharging stage is realized by combining a constant-current charging and discharging CC process step and/or a constant-voltage charging and discharging CV process step.
Furthermore, the current magnitude of the CC process step is measured by a multiplying power value, the range is that C is more than 0 and less than or equal to 2.0, and preferably, the multiplying power of the CC process step is controlled to be more than 0 and less than or equal to 1.0; the termination condition of the CC process step is a steady-state initial potential or a steady-state termination potential of the electrochemical measurement.
Further, the charging stage and/or the discharging stage is followed by a CC process step to implement a CV process step, wherein the potential is set as a steady-state initial potential or a steady-state end potential, a duration time range of the CV process step is set to 10min < t < 180min, and preferably, the duration time of the CV process step is 60min < t < 180 min.
Has the advantages that:
1. the invention provides an electrochemical measurement method for nondestructive evaluation of lithium cobalt oxide material lithium cobalt molar ratio on a lithium battery pole piece. When the lithium-cobalt molar ratio of the reference sample is known, the lithium-cobalt molar ratio of the anode material on the electrode to be tested can be obtained without disassembling the battery, and when the lithium-cobalt molar ratio of the reference sample is unknown, the battery is only required to be disassembled for the reference sample, sufficient sample quantity is ensured, the battery is not required to be disassembled for the test sample, and the sample quantity is not required. The invention realizes the on-line nondestructive detection of the lithium-cobalt molar ratio of the cathode material, and is particularly suitable for the evaluation of the lithium-cobalt molar ratio in the cycle performance test process.
2. The invention can realize the nondestructive analysis of the lithium cobalt ratio of the lithium cobalt oxide material on the lithium electrode sheet, and compared with the conventional test method, the invention does not need to damage the battery, has small artificial interference and is convenient to operate. And the reagent consumption is obviously reduced, and the environmental pollution and the pollution emission of a laboratory are reduced.
3. According to the invention, the optimization of the steady-state initial potential and the steady-state termination potential, the potential variation amplitude control in the charging and discharging process and the condition control of the CC process step and the CV process step are adopted, so that the relative error of the test can be reduced, and the accuracy of the test result can be improved.
Detailed Description
The definitions of some of the terms used in the present invention are given below, and other non-mentioned terms have definitions and meanings known in the art:
in the invention, a two-electrode electrolytic cell system can be selected for specific capacity test, wherein the two-electrode electrolytic cell system is a button cell, and the two-electrode electrolytic cell system adopted in the invention is the button cell. The battery case can adopt any types such as CR2023, CR2025 and CR2016 which are sold on the market, the invention adopts CR2023, and the preparation method is as follows:
step 1, the positive plate adopts an aluminum foil as a current collector, the positive material of the lithium ion battery is a lithium cobaltate material, and the mass percentage of the lithium cobaltate material is controlled to be less than or equal to 96.4 percent. The common conductive agent is a carbon-based conductive agent and comprises Acetylene Black (AB), conductive carbon black, Super P and other commercially available conductive materials, wherein the Super P is adopted as the conductive agent, and the mass percentage content is controlled to be more than or equal to 1.5%. The binder system is generally a polyvinylidene fluoride (PVDF) system, and the mass percentage of the binder system is controlled to be more than or equal to 2.1 percent.
Lithium cobaltate, Super P, polyvinylidene fluoride (PVDF) and N-methyl pyrrolidone (2.4) are stirred and mixed in a defoaming machine, and the viscosity of the slurry is controlled to 7000-9000 mPas. And (3) uniformly coating the slurry on an aluminum foil by using an automatic coating machine to form a raw electrode plate, drying the raw electrode plate in a vacuum oven at 120 ℃ for 4 hours, and then placing the dried electrode plate in a blast oven at 80 ℃ for 12 hours. Setting the linear speed of a roller press to be 2.0m/min, setting the rolling pressure to be 1.3MPa as an initial value, putting the electrode plate into the roller press for rolling after the pressure is stable, detecting the thickness of the test piece in the rolling process by using a micrometer, taking the thickness of 3 different positions, wherein the difference value of any two positions is not more than 3 micrometers, and stopping rolling when the average value L of the thickness is 50 +/-3 micrometers.
And 2, respectively cutting a plurality of small electrode plates at different positions of the test piece by using a punching die with the diameter of 14 mm, selecting a balance with regular shape, flat surface and edge, weighing by using a ten-thousandth balance, putting the weighed small electrode plates into a vacuum drying oven, vacuumizing to 0.1MPa, and storing for later use.
And 3, assembling the button cell in an inert gas glove box with the mass content of water and oxygen being less than or equal to 0.0005%. The specification of the battery is CR2023, a diaphragm adopts a polypropylene film, and a negative electrode is a lithium sheet. The electrolyte solution is usually a mixed solvent of organic carbonates, for example, a mixed solvent of cyclic carbonates such as Ethylene Carbonate (EC) and Propylene Carbonate (PC) and chain carbonates such as dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC), and the electrolyte solution of the present invention is a mixed solution having an EC/DEC volume ratio of 1: 1. The conductive salt in the electrolyte adopts 1M lithium hexafluorophosphate. The electrolyte solution may be added with a cosolvent such as Ethyl Acetate (EA) or Methyl Butyrate (MB), etc., as needed, and functional additives such as Vinylene Carbonate (VC), Vinyl Ethylene Carbonate (VEC), fluoroethylene carbonate (FEC), lithium dioxalate borate (Li-BOB), Borate (BC), boroxine, biphenyl and its derivatives, 4-ethyldicyclohexylketone, etc., as needed. The sealing pressure is 800Pa and the sealing time is 5 seconds.
In the present invention, a lithium cobaltate material with a known lithium-cobalt molar ratio is selected as the standard sample M0The lithium-cobalt molar ratio is a lithium-cobalt molar ratio in a state where a lithium cobaltate material is made into an electrode, and is not a lithium-cobalt molar ratio of a lithium cobaltate material as a raw material powder. The standard sample M0And a sample M to be tested1-nThe pole pieces were made together according to the same process conditions as above and the test cells were assembled, respectively labeled C0And C1-nCarrying out formation and specific capacity test on the lithium ion battery electrical property tester after sealing; subsequently, C is recorded at two identical steady-state potentials, i.e. the same steady-state starting potential and the same steady-state ending potential0And C1-nThe specific capacity change amounts of (A) and (B) are respectively denoted as Q0And Q1-n(ii) a In the invention, the measurement process is completed in a charging stage or a discharging stage of the lithium ion battery.
When the measurement is realized in the discharge stage of the lithium ion battery, the selection range of the steady-state initial voltage is less than or equal to the charge cut-off voltage of the tested lithium ion battery system and is greater than the platform potential of the lithium ion battery system. Specifically, the steady state initial potential range is 3.91V-4.60V (vs Li) based on the potential of the lithium metal electrode as a reference zero potential, and the steady state initial potential range is further controlled to be 3.91V-4.35V (vs Li). The potential variation amplitude can be determined according to the parameters of the adopted lithium ion battery electrical property detection instrument. The amplitude of the potential change is more than or equal to 200 times of the potential precision of the selected measuring equipment. For example, when an electrical property measuring instrument with a potential accuracy of 0.3mv is used, the potential change width is 60 mv or more. The steady-state termination potential is controlled to be in the range of 3.91V to 4.54V (vs Li) or 3.0V to 3.89V (vs Li), and the steady-state termination potential is further controlled to be in the range of 3.91V to 4.30V (vs Li) or 3.0V to 3.89V (vs Li).
When the measurement is realized in the charging stage of the lithium ion battery, the selection range of the steady-state initial voltage is larger than or equal to the discharge cut-off voltage of the tested lithium ion battery system. Specifically, the steady state initial potential range is 3.91V-4.54V (vs Li) or 3.0V-3.89V (vs Li) based on the potential of the lithium metal electrode as a reference zero potential, and the steady state initial potential range is further controlled to be 3.91V-4.30V (vs Li) or 3.0V-3.89V (vs Li). The potential variation amplitude can be determined according to the parameters of the adopted lithium ion battery electrical property detection instrument. The amplitude of the potential change is more than or equal to 200 times of the potential precision of the selected measuring equipment. For example, when an electrical property measuring instrument with a potential accuracy of 0.3mv is used, the potential change width is 60 mv or more. The steady-state termination potential range is 3.91V-4.60V (vs Li), and the steady-state initiation potential range is further controlled to be 3.91V-4.35V (vs Li).
For lithium cobaltate materials, the potential plateau region, typically around 3.90v (vs li), is not suitable for selection as a steady state onset potential and a control region for the steady state onset potential, but may be included in the range of potential variation during testing.
In electrochemical measurement, the control of the steady-state initial potential and the steady-state end potential can be realized by combining constant-current charging and discharging (CC process step) and constant-voltage charging and discharging (CV process step). Wherein the current of CC process step is measured by multiplying factor value, i.e. multiplying factor of current corresponding to 1 hour discharge capacity, the range is 0< C < 2.0, and the multiplying factor of CC process step is controlled to 0< C < 1.0. The termination condition of the CC process step is a steady-state initial potential or a steady-state termination potential of the electrochemical measurement. And (3) implementing a CV step following the CC step in the electrochemical measurement, wherein the potential is set as a steady-state initial potential or a steady-state termination potential, the duration time range of the CV step is set to be 10min < t < 180min, and the further duration time of the CV step is set to be 60min < t < 180 min.
In the present invention, after the above-mentioned electrochemical measurement is completed, the standard sample M is contained0Battery C of0Continuing to discharge until the SOC approaches to 0%, then disassembling the battery and collecting the positive electrode material on the pole piece through chemical titrationMeasuring the molar ratio of lithium to cobalt by methods such as an inductive coupling plasma emission spectrometer (ICP-OES) and the like, and recording the molar ratio of lithium to cobalt as the molar ratio N of the standard sample0；
In the invention, the molar ratio N of lithium to cobalt of the sample to be tested1-nCan be represented by formula N1-n＝N0×(Q1-n/Q0) And (4) calculating.
Wherein the content of the first and second substances,
N1-nthe molar ratio of lithium to cobalt of a sample to be detected;
N0is the lithium-cobalt molar ratio of the standard sample;
Q1-nthe specific capacity variation of the sample to be detected;
Q0the specific capacity change amount of the standard sample is shown.
The method for nondestructively evaluating the molar ratio of lithium to cobalt in the lithium battery electrode provided by the invention has the main improvement that the molar ratio of lithium to cobalt of the anode material in the battery is presumed according to the test condition of the specific capacity of the battery, and other aspects, such as how to manufacture the active material into the electrode, how to assemble the electrode into the battery, the formation method, the charging and discharging method of the battery, how to measure the specific capacity in the charging and discharging process, and the like, can be the same as the prior art, and the technical personnel in the field can know that the specific capacity is not described herein again.
Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. The examples do not specify particular techniques or conditions, and are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available. In the following examples, "%" means weight percent, unless otherwise specified.
Example 1
A commercial lithium cobaltate material with a known lithium-cobalt molar ratio is selected as a reference sample and is marked as M0And simultaneously selecting the same type of commercially available lithium cobaltate material as a sample to be detected, and marking the sample as M1. Respectively mixing the reference sample and the sample to be detected with a conductive agent Super P and a binder PVDF according to the same mass ratio of 9: 0.14: and 0.2, manufacturing an electrode test piece under the same process condition and assembling the electrode test piece into the button cell. The electricity deduction specification is CR2023, the positive pole is the lithium cobaltate material of selecting for use, the negative pole is the lithium piece, the diaphragm is the polypropylene film, the electrolyte solvent is that EC/DEC volume ratio is 1:1 and the conductive salt is 1M lithium hexafluorophosphate. The sealing pressure is 800Pa and the sealing time is 5 seconds. The test cells made of the reference sample and the sample to be tested are respectively marked as C0And C1A total of 5 tests were carried out with a number of A, B, C, D, E, each test group containing 1 cell C0And 1 cell C1。
Reference sample cell C0And a sample cell C to be tested1Necessary formation and specific capacity tests were performed and then pre-charged to a state of charge (SOC) of 100%. On a lithium ion battery electrical property detector with the potential precision of 0.3mV, a discharge stage is selected to measure in a mode of combining constant current discharge (CC process step) and constant voltage discharge (CV process step). The discharge current in the constant current discharge (CC process) process is marked with a multiplying factor, and is set to 0.1C, and the duration of the constant voltage discharge (CV process) is set to 1 hour. Continuously repeating the CC-CV working steps until the potential of the test battery approaches to the discharge cut-off potential of 3.0V, and recording the reference battery C under the same steady-state potential in the process0And a battery C to be tested1The specific capacity change amount of (2).
Meanwhile, the lithium-cobalt molar ratio of the lithium cobaltate material on the battery pole piece to be detected is calculated according to the ratio of the specific capacity variation of the reference battery to the battery to be detected at the same potential and the lithium-cobalt molar ratio of the reference sample, specifically, the lithium-cobalt molar ratio of the reference sample is 0.911, and the calculation formula is as follows: n is a radical of0(Li%/6.941)/(Co%/58.933). Lithium-cobalt molar ratio N of sample to be tested1-n＝N0×(Q1-n/Q0) The calculation results are shown in Table 1.
TABLE 1 EXAMPLE 1 Battery specific Capacity test and Li-Co molar ratio calculation results
Example 2
Continuing to use reference sample cell C from example 10And a sample cell C to be tested1And data acquisition in the charging stage is carried out, and measurement is carried out by adopting a mode of combining constant current discharge (CC process step) and constant voltage discharge (CV process step). Here, the charging current for constant current charging (CC process step) is expressed by multiplying factor, and is set to 0.1C, and the duration for constant voltage charging (CV process step) is set to 1 hour. Continuously repeating the CC-CV working steps until the potential of the test battery approaches to the charge cut-off potential of 4.60V, and recording the reference battery C under the same steady-state potential in the process0And a battery C to be tested1The specific capacity change amount of (2). The lithium-cobalt molar ratio of the lithium cobaltate material on the pole piece of the battery to be tested is calculated according to the ratio of the specific capacity variation of the reference battery to the battery to be tested under the same potential and the lithium-cobalt molar ratio of the reference sample, the calculation method is the same as that of example 1, and the calculation result is shown in table 2.
Table 2 example 2 specific capacity test of battery and table of calculation results of lithium-cobalt molar ratio
Example 3
Continuing to use reference sample cell C from example 10And a sample cell C to be tested1And repeatedly acquiring data in the discharge stage, and measuring by adopting a mode of combining constant current discharge (CC process step) and constant voltage discharge (CV process step). The initial potential and the final potential of each stage are designed to be the same as those in example 1, and the constant-current discharge rate and the constant-voltage discharge holding time of each stage are changed, and specific design values are shown in the following table. Continuously repeating the CC-CV working steps until the potential of the test battery approaches to the discharge cut-off potential of 3.0V, and recording the same steady state electricity in the processReference cell C under position0And a battery C to be tested1The specific capacity change amount of (2). The lithium-cobalt molar ratio of the lithium cobaltate material on the pole piece of the battery to be tested is calculated according to the ratio of the specific capacity variation of the reference battery to the battery to be tested under the same potential and the lithium-cobalt molar ratio of the reference sample, the calculation method is the same as that of example 1, and the calculation result is shown in table 3.
Table 3 example 3 specific capacity test of battery and table of calculation results of lithium-cobalt molar ratio
Comparative example 1
The reference cell C of example 1 was continuously used0And a sample cell C1And executing a CC-CV charging step until the state of charge is 100%, wherein the charging current of the CC step is set to be 0.1C, the charging voltage of the CV step is set to be 4.60V, and the charging cut-off condition is that the multiplying current is less than 0.02C. After the charging, the cell was left to stand for 10 minutes, and then CC discharge was immediately performed, in which the discharge current was set to 0.1C, and the cell was discharged to a state of charge of 0%. Then disassembling the battery and collecting the anode material on the pole piece, determining the cobalt content by a chemical titration method, determining the lithium content by an inductively coupled plasma emission spectrometer (ICP-OES) method, then respectively calculating the lithium-cobalt molar ratio according to the ratio, and recording the lithium-cobalt molar ratio as the lithium-cobalt molar ratio of a reference sample and a sample to be detected, wherein the lithium-cobalt molar ratio of the reference sample is 0.911, and the lithium-cobalt molar ratio of the sample to be detected is 0.906.
The relative error of the test results in examples 1-3 was calculated based on the molar ratio of lithium to cobalt of the sample to be tested being 0.906 by: the relative error is 100 × (measurement-0.906)/0.906, and the calculation results are shown in table 4:
TABLE 4 example lithium cobalt molar ratio calculation error
| Examples | Measured value | Relative error | Examples | Measured value | Relative error | Examples | Measured value | Relative error |
| 1A | 0.897 | -0.99 | 2A | 0.888 | -1.99 | 3A | 0.889 | -1.88 |
| 1B | 0.910 | 0.44 | 2B | 0.928 | 2.43 | 3B | 0.906 | 0.00 |
| 1C | 0.920 | 1.55 | 2C | 0.904 | -0.22 | 3C | 0.911 | 0.55 |
| 1D | 0.886 | -2.21 | 2D | 0.910 | 0.44 | 3D | 0.873 | -3.64 |
| 1E | 0.930 | 2.65 | 2E | 0.920 | 1.55 | 3E | 0.912 | 0.66 |
As can be seen from Table 4, the electrochemical measurement method provided by the invention can better satisfy the test of on-line evaluation of the molar ratio of lithium cobaltate to lithium cobalt on the lithium ion battery pole piece, compared with the traditional method, the error range is-3.6% -2.65%, the test results with larger errors appear in a high potential interval, near a platform potential interval and near a discharge cut-off potential, therefore, the steady-state initial potential in the discharge stage is controlled to be 3.91-4.35V vs Li, the steady-state termination potential is 3.00-4.30V vs Li and is not equal to 3.90V vs Li, better and accurate test results can be obtained, the relative error is less than or equal to 2.65 percent, or the steady-state initial potential at the charging stage is 3.00-4.30V vs Li and is not equal to 3.90V vs Li, and the steady-state termination potential is 3.91-4.35V vs Li, so that a better and accurate test result can be obtained, and the relative error is less than or equal to 2.43%.
On the other hand, the error increases along with the increase of the CC process step current multiplying power, and the error decreases along with the extension of the CV process step potential holding time, so that the multiplying power of the CC process step is controlled to be 0< C < 1.0, a better and accurate test result can be obtained, and the relative error is less than or equal to 1.88%. The duration of the CV working step is more than or equal to 60min and less than or equal to 180min, better and more accurate test results can be obtained, and the relative error is less than or equal to 3.64 percent.
Comparative example 2
The testing method disclosed by the invention is more generally suitable for lithium cobaltate anode materials, and when the testing method is applied to testing other anode materials, because the capacity change of the anode materials under the same steady-state potential under the same condition is more obviously influenced by other factors such as lithium metal mixed discharge, process phase change, change of stoichiometric ratio and the like, in comparison, the accurate ratio cannot be successfully obtained. Taking a nickel-cobalt-manganese ternary material as an example for explanation, wherein a commercially available nickel-cobalt-manganese ternary material with a known lithium metal molar ratio is selected as a reference sample, and a commercially available nickel-cobalt-manganese ternary material with the same model is simultaneously selected as a sample to be detected, and a reference sample battery and a sample battery to be detected are manufactured according to a conventional process. Reference sample cell C0And a sample cell C to be tested1Necessary formation and specific capacity tests were performed and then pre-charged to a state of charge (SOC) of 100%. On a lithium ion battery electrical property detector with the potential precision of 0.3mV, a discharge stage is selected to carry out measurement in a mode of combining constant current discharge (CC process step) and constant voltage discharge (CV process step). The discharge current in the constant current discharge (CC process) process is marked with a multiplying factor, and is set to 0.1C, and the duration of the constant voltage discharge (CV process) is set to 1 hour. Wherein the steady-state start potential was set to 4.35V vs Li and the steady-state end potential was set to 3.0V VsLi, reference cell C during recording0And a battery C to be tested1The specific capacity change amount of (2). And (3) calculating the lithium metal molar ratio of the nickel-cobalt-manganese ternary material on the pole piece of the battery to be detected according to the ratio of the specific capacity variation of the reference battery to the battery to be detected at the same potential and the lithium metal molar ratio of the reference sample, wherein the lithium metal molar ratio of the reference battery refers to the method of comparative example 1. The results of the calculations are shown in Table 5.
TABLE 5 TABLE 2 TABLE OF BATTERY SPECIFIC CAPACITY TESTING AND LITHIUM METAL MOLECULAR RATIO CALCULATING RESULTS
It can be seen from table 5 that, when the electrochemical measurement method indicated by the present invention is applied to the nickel-cobalt-manganese ternary material, the relative error is larger than the test result of the lithium cobaltate material, and the possible reasons are related to the structural change of the nickel-cobalt-manganese ternary material during the charge and discharge processes, the lithium-nickel mixed-discharge degree, the slow bulk diffusion kinetics and other factors. Narrower potential variation intervals, longer constant voltage discharge (CV process step) hold times, higher precision equipment, and more stable test environments, all of which may reduce the utility, timeliness, and economics of the method of the present invention, if more accurate results are desired. Similar problems also exist in other anode materials, for example, a nickel-cobalt-aluminum ternary material is similar to a nickel-cobalt-manganese ternary material, the potential resolution is poor due to the phase change behavior of the lithium iron phosphate material in the charging and discharging processes, the stoichiometric ratio of the lithium manganese oxide material is changed in the charging and discharging processes, and the like. Therefore, the electrochemical measurement method disclosed by the invention is more generally applicable to lithium cobaltate cathode materials.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.
Claims (9)
1. A method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode, characterized by: defining the active material of the lithium battery electrode as lithium cobaltate M1-nThe molar ratio of lithium to cobalt in the lithium battery electrode is N1-nSelecting a lithium cobaltate standard sample M0The reference electrode is made by adopting the same process as the lithium battery electrode, the reference electrode and the lithium battery electrode are assembled into a battery according to the same method and then are subjected to specific capacity test under the same condition, and the measured specific capacities of the batteries are Q0And Q1-nThen the molar ratio of lithium to cobalt in the lithium battery electrode is N1-n＝N0×(Q1-n/Q0) Wherein N is0As a standard sample M of lithium cobaltate0Lithium to cobalt molar ratio in the electrode state.
2. The method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode of claim 1, wherein: the method comprises the following steps:
s1, obtaining a lithium cobaltate standard sample M0And the lithium cobalt molar ratio N of the lithium cobaltate standard sample in the electrode state0；
S2, standard sample M of lithium cobaltate in S10Lithium cobaltate sample M to be measured according to the sum1-nManufacturing electrodes under the same process conditions and assembling into batteries, respectively marked as C0And C1-nCarrying out formation and specific capacity tests on the battery, and recording C under the same steady-state potential, namely the same steady-state initial potential and the same steady-state termination potential0And C1-nSpecific capacity change amount ofAre respectively denoted as Q0And Q1-n；
S3, calculating the molar ratio of lithium to cobalt, N, in the lithium battery electrode1-n＝N0×(Q1-n/Q0)。
3. The method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode according to claim 1 or 2, characterized in that: the lithium cobaltate standard sample is a known lithium-cobalt molar ratio N0The sample of (1);
optionally, the lithium cobaltate standard sample M0N of (A)0Unknown, obtaining N0The method comprises the following steps: the standard sample M of lithium cobaltate in S20Fabricated Battery C0And disassembling after discharging is finished, collecting the anode material, and determining the obtained lithium-cobalt molar ratio by adopting a chemical titration method or an inductively coupled plasma emission spectrometry.
4. The method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode according to claim 1 or 2, characterized in that: in S2, the specific capacity test is completed in the charging stage and/or the discharging stage of the battery, and the potential variation amplitude in the charging stage and/or the discharging stage is more than or equal to 200 times of the potential accuracy of the selected measuring equipment.
5. The method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode of claim 4, wherein: selecting a steady-state initial voltage which is less than or equal to the charge cut-off voltage of the tested battery system and is greater than the platform potential when specific capacity measurement is realized in the battery discharge stage; specifically, the steady-state initial potential is 3.91-4.60V vs Li by taking the potential of the lithium metal electrode as a reference zero potential, and preferably, the steady-state initial potential is controlled to be 3.91-4.35V vs Li;
optionally, the steady-state end potential is selected to be 3.00-4.54V vs Li and not equal to 3.90V vs Li when the specific capacity measurement is realized in the discharge stage of the lithium ion battery, and preferably, the steady-state end potential is 3.00-4.30V vs Li and not equal to 3.90V vs Li.
6. The method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode of claim 4, wherein: selecting a selection range of a steady-state initial potential to be greater than or equal to a discharge cut-off voltage of a tested battery system when specific capacity measurement is realized in a battery charging stage; specifically, the potential of the lithium metal electrode is taken as a reference zero potential, the steady-state initial potential is 3.00-4.54 Vvs Li and is not equal to 3.90V vs Li, preferably, the steady-state initial potential is 3.00-4.30 Vvs Li and is not equal to 3.90V vs Li;
optionally, the steady-state termination potential is 3.91-4.60V vs Li when specific capacity measurement is realized in the charging stage of the lithium battery, and preferably the steady-state termination potential is 3.91-4.35V vs Li.
7. The method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode according to claim 5 or 6, characterized in that: and the control of the steady-state initial potential and/or the steady-state termination potential in the charging stage and/or the discharging stage is realized through a working step combining a constant-current charging and discharging CC working step and/or a constant-voltage charging and discharging CV working step.
8. The method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode of claim 7, wherein: the current magnitude of the CC process step is measured by adopting a multiplying power value, the range is that C is more than 0 and less than or equal to 2.0, and preferably, the multiplying power of the CC process step is controlled to be more than 0 and less than or equal to 1.0; the termination condition of the CC process step is a steady-state initial potential or a steady-state termination potential of the electrochemical measurement.
9. The method for non-destructive evaluation of lithium-cobalt molar ratio in a lithium battery electrode of claim 7, wherein: and the charging stage and/or the discharging stage are/is followed by a CC process step to implement a CV process step, wherein the potential is set as a steady-state initial potential or a steady-state end potential, the duration time range of the CV process step is set to be 10min < t < 180min, and preferably, the duration time of the CV process step is 60min < t < 180 min.
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