Failure analysis method for irreversible capacity fading of lithium ion battery and application

Abstract

The invention provides a failure analysis method for irreversible capacity fading of a lithium ion battery and application, and relates to the technical field of battery analysis. According to the failure analysis method, the discharge capacity of a fresh cell and the discharge capacity of a failure cell are converted into the discharge capacity of a fresh button type half cell and the discharge capacity of a failure button type half cell, and then the total loss capacity of the button type half cell is obtained; the fresh battery cell and the invalid battery cell are subjected to empty electricity disassembly and manufactured into a fresh positive electrode button type half cell, an invalid positive electrode button type half cell, a fresh negative electrode button type half cell and an invalid negative electrode button type half cell; the irreversible capacity caused by the positive electrode structure of the positive electrode end, CEI growth, the negative electrode structure of the negative electrode end, SEI and inactivated Li growth, negative electrode polarization and lithium dendrite precipitation is calculated, and the capacity loss condition of the single lithium battery cell is indirectly reflected by analyzing the proportion of various loss capacities in the total loss capacity; therefore, quantitative analysis of irreversible capacity fading is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of battery analysis, and relates to a failure analysis method and application of irreversible capacity decay of a lithium-ion battery. Background Art

[0002] For lithium-ion batteries, the capacity is determined by the capacity of the positive and negative electrodes, as well as the amount of available lithium ions. The capacity decay mechanism can be divided into two categories: thermodynamic loss and kinetic loss, which are essentially different and mutually influential. Thermodynamic loss is irreversible, such as the loss of active lithium and active materials of the positive and negative electrodes; kinetic loss is reversible, mainly manifested as an increase in impedance and polarization, such as ohmic impedance, SEI impedance, and increase in charge transfer impedance caused by electrolyte drying, SEI film thickening, and reduction of active sites for lithium intercalation and deintercalation. From a thermodynamic point of view, the irreversible decay of lithium-ion battery capacity can be attributed to the loss of available lithium ions (Loss of Lithium-ion Inventory, LLI) and the loss of active materials of the positive and negative electrodes (Loss of Active Material, LAM). In lithium-ion batteries with graphite as the negative electrode, LLI is mainly caused by the generation and growth of SEI film on the surface of negative electrode graphite, which is the main influencing factor of capacity decay, while lithium-ion batteries with LTO negative electrodes usually do not experience LLI. In addition, "dead lithium" formed by incomplete reinsertion of lithium after lithium precipitation caused by charging at low temperature or high rate conditions can also lead to LLI. LAM mainly includes the loss of positive and negative electrode materials caused by damage to the positive and negative electrode crystal structure, destruction of the conductive network, failure of the binder, and peeling of the material from the current collector. Generally speaking, LMO positive electrodes and graphite negative electrodes are prone to LAM, while for LFP, NCM positive electrodes and LTO negative electrodes, LAM is usually less.

[0003] Most of the existing patents and technologies study the effects of various impedances and polarizations on the reversible capacity decay of lithium-ion batteries from a kinetic perspective. However, from a thermodynamic perspective, there is a lack of systematic testing and evaluation methods for the irreversible capacity decay of lithium-ion batteries. The latter is not only closer to the essence of lithium-ion battery capacity decay, but also the basis and premise of the former.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] In view of the shortcomings and defects of the prior art, the present invention aims to provide a failure analysis method and application of irreversible capacity decay of lithium-ion batteries.

[0006] In order to achieve the above purpose, the following technical solutions are adopted:

[0007] The first object of the present invention is to provide a failure analysis method for irreversible capacity decay of a lithium ion battery, comprising the following steps:

[0008] S1. The discharge capacity of the fresh battery cell and the discharge capacity of the failed battery cell are converted into the discharge capacity of the fresh button half-cell and the discharge capacity of the failed button half-cell according to the area, and the total loss capacity of the button half-cell is determined; wherein the fresh battery cell and the failed battery cell are lithium battery cells;

[0009] S2. disassemble the fresh battery cell and the failed battery cell of step S1, and assemble the positive electrode sheets of the fresh battery cell and the failed battery cell obtained after disassembly into fresh positive electrode button half-cells and failed positive electrode button half-cells respectively;

[0010] Determine the positive electrode structure loss capacity of the button-type half-cell according to the discharge capacity of the fresh positive electrode button-type half-cell and the discharge capacity of the failed positive electrode button-type half-cell;

[0011] Determine the positive electrode de-intercalation loss capacity of the fresh button-type half-cell according to the discharge capacity of the fresh positive button-type half-cell and the discharge capacity of the fresh button-type half-cell; determine the positive electrode de-intercalation loss capacity of the failed button-type half-cell according to the discharge capacity of the failed positive button-type half-cell and the discharge capacity of the failed button-type half-cell;

[0012] S3. After disassembling, the negative electrode sheets of the fresh cells and the negative electrode sheets of the failed cells are tested to obtain the residual capacity of the negative electrode of the fresh cells and the residual capacity of the negative electrode of the failed cells, and the residual capacity of the negative electrode of the fresh button-type half-cell and the residual capacity of the negative electrode of the failed button-type half-cell are converted according to the area;

[0013] Determine the positive electrode CEI loss capacity of the fresh button half-cell according to the positive electrode de-intercalation loss capacity of the fresh button half-cell and the negative electrode residual capacity of the fresh button half-cell; determine the positive electrode CEI loss capacity of the failed button half-cell according to the positive electrode de-intercalation loss capacity of the failed button half-cell and the negative electrode residual capacity of the failed button half-cell; determine the loss capacity due to the growth of the positive electrode CEI of the button half-cell according to the positive electrode CEI loss capacity of the fresh button half-cell and the positive electrode CEI loss capacity of the failed button half-cell;

[0014] S4. The remaining negative electrode sheets of the fresh battery cells obtained after disassembly and the remaining negative electrode sheets of the failed battery cells are respectively assembled into fresh negative electrode button half-cells and failed negative electrode button half-cells;

[0015] According to the discharge capacity of the fresh negative electrode button half-cell and the discharge capacity of the failed negative electrode button half-cell, the loss capacity caused by the negative electrode polarization and lithium dendrites and the loss capacity of the negative electrode structure of the button half-cell are determined;

[0016] According to the negative electrode residual capacity of the fresh button half-cell and the discharge capacity of the fresh negative button half-cell, determine the negative electrode SEI and deactivated Li loss capacity of the fresh button half-cell; according to the negative electrode residual capacity of the failed button half-cell and the discharge capacity of the failed negative button half-cell, determine the negative electrode SEI and deactivated Li loss capacity of the failed button half-cell; according to the negative electrode SEI and deactivated Li loss capacity of the fresh button half-cell and the negative electrode SEI and deactivated Li loss capacity of the failed button half-cell, determine the loss capacity caused by the growth of the negative electrode SEI and deactivated Li of the button half-cell;

[0017] S5. The irreversible capacity attenuation of lithium-ion batteries containing lithium-ion battery cells is quantitatively analyzed by determining the proportion of the positive electrode structure loss capacity, the positive electrode CEI growth loss capacity, the negative electrode structure loss capacity, the negative electrode polarization and lithium dendrite loss capacity, and the negative electrode SEI and deactivated Li growth loss capacity in the total loss capacity in the button half-cell.

[0018] Further, based on the above technical solution of the present invention, in step S1, the discharge capacity C of the fresh battery cell in the nth cycle of charge and discharge is 新鲜 and the discharge capacity C of the failed cell in the nth cycle of charge and discharge 失效 , converted into the discharge capacity C of the nth week of the charge and discharge cycle of a fresh button-type half-cell according to the area 新鲜0 The discharge capacity C of the failed button half-cell in the nth cycle of charge and discharge 失效0 , and determine the total loss capacity C of the button half-cell total , that is, C total =C 新鲜0 -C 失效0 ; Wherein, the fresh battery cell and the failed battery cell are lithium battery cells, and n is 2 or 3; and / or, in step S1, the failed battery cell is a battery cell whose capacity decays to 80% SOH.

[0019] Further, on the basis of the above technical solution of the present invention, in step S2, the fresh battery cells and the failed battery cells that have undergone charge and discharge cycles in step S1 are disassembled, and the positive electrode sheets of the fresh battery cells and the positive electrode sheets of the failed battery cells obtained after disassembly are respectively assembled into fresh positive electrode button half-cells and failed positive electrode button half-cells;

[0020] According to the discharge capacity C of the nth week of charge and discharge cycle of the fresh positive electrode button half-cell 新鲜c The discharge capacity C of the failed positive electrode button half-cell in the nth cycle of charge and discharge 失效c , determine the positive electrode structure loss capacity C of the button half-cell cs , that is, C cs =C 新鲜c -C 失效c ;

[0021] According to the discharge capacity C of the nth week of charge and discharge cycle of the fresh positive electrode button half-cell 新鲜c and the discharge capacity C of the nth cycle of the fresh button half-cell 新鲜0 , determine the positive electrode de-insertion loss capacity C of a fresh button half-cell 新鲜cr , that is, C 新鲜cr =C 新鲜c -C 新鲜0 ;

[0022] According to the discharge capacity C of the failed positive electrode button half-cell charge and discharge cycle in the nth week 失效c The discharge capacity C of the failed button half-cell in the nth cycle of charge and discharge 失效0 , determine the positive electrode de-insertion loss capacity C of the failed button half-cell 失效cr , that is, C 失效cr =C 失效c -C 失效0 .

[0023] Further, on the basis of the above technical solution of the present invention, in step S2, the fresh battery cell and the failed battery cell which have been charged and discharged for n weeks in step S1 are respectively discharged to 0% SOC and then disassembled to obtain the fresh battery cell positive electrode sheet and the failed battery cell positive electrode sheet, which are soaked in a solvent for 1-2 hours, and then dried in a vacuum oven at 60-90° C. for 3-6 hours and taken out, and the active material on one side of the fresh battery cell positive electrode sheet and the failed battery cell positive electrode sheet is wiped off with dust-free paper dipped in anhydrous ethanol, and a single-sided circular positive electrode sheet is punched out with a punching machine, and the fresh positive button half-cell and the failed positive button half-cell are assembled in a glove box filled with a protective atmosphere; and / or,

[0024] In step S2, during the charge and discharge cycle of the fresh positive button half-cell and the failed positive button half-cell, the charge and discharge current used is the same, which is 0.05-0.2C; the upper limit of the charging voltage used is the same, which is 3.5-3.8V; and the lower limit of the discharge voltage used is the same, which is 1.0-2.5V.

[0025] Further, on the basis of the above technical solution of the present invention, in step S3, part of the negative electrode sheets of the fresh battery cells and part of the negative electrode sheets of the failed battery cells obtained after disassembly are respectively detected to obtain the negative electrode residual capacity C of the fresh battery cells. 新鲜ar0 and the negative electrode residual capacity C of the failed battery cell 失效ar0 , converted into the negative electrode residual capacity C of a fresh button half-cell by area 新鲜ar and the negative electrode residual capacity C of the failed button half-cell 失效ar ;

[0026] According to the positive electrode de-insertion loss capacity C of the fresh button half-cell 新鲜cr and the negative electrode residual capacity C of a fresh button half-cell 新鲜ar, determine the positive electrode CEI loss capacity C of the fresh button half-cell 新鲜CEI , that is, C 新鲜CEI =C 新鲜cr -C 新鲜ar ;

[0027] According to the positive electrode de-insertion loss capacity C of the failed button half-cell 失效cr and the negative electrode residual capacity C of the failed button half-cell 失效ar , determine the positive electrode CEI loss capacity C of the failed button half-cell 失效CEI , that is, C 失效CEI =C 失效cr -C 失效ar ;

[0028] According to the positive electrode CEI loss capacity C of the fresh button half-cell 新鲜CEI and the positive electrode CEI loss capacity C of the failed button half-cell 失效CEI , determine the loss capacity C caused by the increase of CEI of the positive electrode of the button half-cell CEI , that is, C CEI =C 失效CEI -C 新鲜CEI .

[0029] Further, on the basis of the above technical solution of the present invention, in step S4, the remaining negative electrode sheets of the fresh battery cells and the remaining negative electrode sheets of the failed battery cells obtained after disassembly are respectively assembled into fresh negative electrode button half-cells and failed negative electrode button half-cells;

[0030] According to the charge capacity C of the first cycle of the fresh negative electrode button half-cell charge and discharge cycle 新鲜a 、The charging capacity C of the nth cycle 新鲜ad And the charging capacity C of the first cycle of the failed negative electrode button half-cell charge and discharge cycle 失效a 、The charging capacity C of the nth cycle 失效ad , determine the negative electrode polarization and lithium dendrite-induced capacity loss C of the button half-cell pl , that is, C pl =C 失效a -C 新鲜a , and the negative electrode structure loss capacity C as , that is, C as =C 新鲜ad -C 失效ad .

[0031] Further, based on the above technical solution of the present invention, in step S4, according to the negative electrode residual capacity C of the fresh button half-cell 新鲜ar The charge capacity C of the first cycle of the fresh negative button half-cell 新鲜a , determine the negative electrode SEI and deactivated Li loss capacity C of the fresh button half-cell 新鲜SEI , that is, C新鲜SEI =C 新鲜ar -C 新鲜a ;

[0032] According to the negative electrode residual capacity C of the failed button half-cell 失效ar The charging capacity C of the first cycle of the failed negative electrode button half-cell 失效a , determine the negative electrode SEI and deactivated Li loss capacity C of the failed button half-cell 失效SEI , that is, C 失效SEI =C 失效ar -C 失效a , and then determine the loss capacity C caused by the growth of negative electrode SEI and deactivated Li in the button half-cell SEI , that is, C SEI =C 失效SEI -C 新鲜SEI .

[0033] Further, on the basis of the above technical solution of the present invention, in step S4, the fresh battery cell and the failed battery cell which have been charged and discharged for n weeks in step S1 are respectively discharged to 0% SOC and then disassembled to obtain the fresh battery cell negative electrode sheet and the failed battery cell negative electrode sheet, which are soaked in a solvent for 1-2 hours, and then dried in a vacuum oven at 60-90° C. for 3-6 hours and taken out, and the active material on one side of the fresh battery cell negative electrode sheet and the failed battery cell negative electrode sheet is wiped off with dust-free paper dipped in deionized water, and a single-sided circular negative electrode sheet is punched out with a punching machine, and the fresh negative electrode button half-cell and the failed negative electrode button half-cell are assembled in a glove box filled with a protective atmosphere; and / or,

[0034] In step S4, during the charge and discharge cycle of the fresh negative button half-cell and the failed negative button half-cell, the charge and discharge current used is the same, which is 0.05-0.2C; the upper limit of the charging voltage used is the same, which is 1.0-2.5V; and the lower limit of the discharge voltage used is the same, which is 0.001-0.1V.

[0035] Further, based on the above technical solution of the present invention, the lithium-ion battery is any one of a soft-pack battery, a square battery or a cylindrical battery; and / or,

[0036] The positive electrode active material of the lithium-ion battery includes one or more of a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, lithium iron phosphate or lithium manganate; and / or,

[0037] The negative electrode active material of the lithium ion battery includes one or more of graphite, mesophase carbon microspheres, lithium titanate, hard carbon, silicon oxygen or silicon carbon; and / or,

[0038] In the electrolyte of the lithium ion battery, the solvent includes one or more of propylene carbonate, ethylene carbonate, ethyl methyl carbonate or ethyl carbonate, the solute includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate or lithium bis(fluorosulfonyl)imide salt, and the additive includes one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone or vinylene sulfate.

[0039] The second object of the present invention is to provide an application of the failure analysis method of irreversible capacity decay of lithium-ion batteries according to the first object of the present invention in the field of battery analysis and selection.

[0040] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0041] (1) The present invention provides a failure analysis method for irreversible capacity decay of a lithium-ion battery. The method comprises the following steps: firstly, the discharge capacities of fresh cells and failed cells (lithium battery cells) are measured and converted into the discharge capacities of fresh button half-cells and failed button half-cells, and then the total loss capacity of the failed button half-cells is obtained. Then, the fresh cells and failed cells are disassembled and made into corresponding fresh positive button half-cells, failed positive button half-cells, and fresh negative button half-cells, and failed negative button half-cells. By using the correlation between different loss capacities, the irreversible capacities caused by the positive electrode structure, CEI growth (thickening) at the positive end of the button half-cell and the negative electrode structure, SEI and deactivated Li growth (SEI thickening and dead lithium dissolution) at the negative end, negative electrode polarization and lithium dendrite precipitation at the negative end are quantitatively calculated. Furthermore, by analyzing the proportion of various loss capacities in the button half-cell in the total loss capacity, the capacity loss of the lithium battery cell is indirectly reflected, thereby realizing quantitative analysis of the irreversible capacity decay of a lithium-ion battery containing a lithium battery cell. This method solves the testing and evaluation problems of irreversible capacity decay of lithium-ion batteries from a thermodynamic perspective and has the advantage of quantitative analysis.

[0042] (2) The present invention provides an application of a failure analysis method for irreversible capacity decay of a lithium-ion battery. In view of the advantages of the above-mentioned failure analysis method for irreversible capacity decay of a lithium-ion battery, it has certain guiding significance in the fields of battery analysis and battery development (including the selection of positive and negative electrodes, electrolytes, and auxiliary materials during battery cell development). BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Electrochemical polarization impedance diagram of fresh battery cells and failed battery cells when EIS test analysis is performed in Comparative Example 1 of the present invention;

[0044] Figure 2 This is a DC internal resistance diagram of a fresh battery cell and a failed battery cell when HPPC test analysis is performed in Comparative Example 1 of the present invention;

[0045] Figure 3 It is a dV / dQ curve diagram of a fresh battery cell and a failed battery cell in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0047] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0048] Conventional analysis methods such as hybrid pulse DC internal resistance test (HPPC), alternating current impedance test (EIS), constant current intermittent titration (GITT) are all qualitative analyses of capacity decay for ohmic polarization, electrochemical polarization, and solid phase diffusion polarization. These methods can qualitatively analyze the causes of capacity decay from a kinetic perspective (including electrolyte drying, binder failure, SEI thickening, etc.), but it is difficult to quantitatively obtain the specific proportion of active lithium ion loss and the proportion of positive and negative electrode material failure. Therefore, the present invention is proposed.

[0049] According to a first aspect of the present invention, a failure analysis method for irreversible capacity decay of a lithium-ion battery is provided, comprising the following steps:

[0050] S1. The discharge capacity of the fresh battery cell and the discharge capacity of the failed battery cell are converted into the discharge capacity of the fresh button half-cell and the discharge capacity of the failed button half-cell according to the area, and the total loss capacity of the button half-cell is determined; wherein the fresh battery cell and the failed battery cell are lithium battery cells;

[0051] S2. disassemble the fresh battery cell and the failed battery cell of step S1, and assemble the positive electrode sheets of the fresh battery cell and the failed battery cell obtained after disassembly into fresh positive electrode button half-cells and failed positive electrode button half-cells respectively;

[0052] Determine the positive electrode structure loss capacity of the button-type half-cell according to the discharge capacity of the fresh positive electrode button-type half-cell and the discharge capacity of the failed positive electrode button-type half-cell;

[0053] Determine the positive electrode de-intercalation loss capacity of the fresh button-type half-cell according to the discharge capacity of the fresh positive button-type half-cell and the discharge capacity of the fresh button-type half-cell; determine the positive electrode de-intercalation loss capacity of the failed button-type half-cell according to the discharge capacity of the failed positive button-type half-cell and the discharge capacity of the failed button-type half-cell;

[0054] S3. After disassembling, the negative electrode sheets of the fresh cells and the negative electrode sheets of the failed cells are tested to obtain the residual capacity of the negative electrode of the fresh cells and the residual capacity of the negative electrode of the failed cells, and the residual capacity of the negative electrode of the fresh button-type half-cell and the residual capacity of the negative electrode of the failed button-type half-cell are converted according to the area;

[0055] Determine the positive electrode CEI loss capacity of the fresh button half-cell according to the positive electrode de-intercalation loss capacity of the fresh button half-cell and the negative electrode residual capacity of the fresh button half-cell; determine the positive electrode CEI loss capacity of the failed button half-cell according to the positive electrode de-intercalation loss capacity of the failed button half-cell and the negative electrode residual capacity of the failed button half-cell; determine the loss capacity due to the growth of the positive electrode CEI of the button half-cell according to the positive electrode CEI loss capacity of the fresh button half-cell and the positive electrode CEI loss capacity of the failed button half-cell;

[0056] S4. The remaining negative electrode sheets of the fresh battery cells obtained after disassembly and the remaining negative electrode sheets of the failed battery cells are respectively assembled into fresh negative electrode button half-cells and failed negative electrode button half-cells;

[0057] According to the discharge capacity of the fresh negative electrode button half-cell and the discharge capacity of the failed negative electrode button half-cell, the loss capacity caused by the negative electrode polarization and lithium dendrites and the loss capacity of the negative electrode structure of the button half-cell are determined;

[0058] According to the negative electrode residual capacity of the fresh button half-cell and the discharge capacity of the fresh negative button half-cell, determine the negative electrode SEI and deactivated Li loss capacity of the fresh button half-cell; according to the negative electrode residual capacity of the failed button half-cell and the discharge capacity of the failed negative button half-cell, determine the negative electrode SEI and deactivated Li loss capacity of the failed button half-cell; according to the negative electrode SEI and deactivated Li loss capacity of the fresh button half-cell and the negative electrode SEI and deactivated Li loss capacity of the failed button half-cell, determine the loss capacity caused by the growth of the negative electrode SEI and deactivated Li of the button half-cell;

[0059] S5. The irreversible capacity decay of lithium-ion batteries containing lithium-ion cells is quantitatively analyzed by determining the proportion of the positive electrode structure loss capacity, the positive electrode CEI growth loss capacity, the negative electrode structure loss capacity, the negative electrode polarization and lithium dendrite loss capacity, and the negative electrode SEI and deactivated Li growth loss capacity in the total loss capacity in the button half-cell.

[0060] The present invention first measures the discharge capacity of fresh cells and failed cells (lithium battery cells) and converts them into the discharge capacity of fresh button half-cells and failed button half-cells, then obtains the total loss capacity of the failed button half-cells, then disassembles the fresh cells and failed cells into corresponding fresh positive button half-cells, failed positive button half-cells, and fresh negative button half-cells, failed negative button half-cells, and quantitatively calculates the positive electrode structure, CEI growth (thickness) of the positive end of the failed button half-cell by using the relationship between different loss capacities. ) and the negative electrode structure of the negative electrode, SEI and deactivated Li growth (SEI thickening and dead lithium dissolution), negative electrode polarization and irreversible capacity caused by lithium dendrite precipitation, and analyze the proportion of various loss capacities in the total loss capacity in the button half-cell, indirectly reflecting the capacity loss of lithium battery cells, thereby achieving quantitative analysis of the irreversible capacity attenuation of lithium-ion batteries containing lithium battery cells. This failure analysis method not only has the advantages of simple method, high feasibility, and quantitative calculation, but also has the advantages of good consistency of test data.

[0061] It should be noted that, since the measurement of various loss capacities requires the positive and negative electrodes to be assembled into positive half-cells and negative half-cells respectively, and the negative electrode of the half-cell is usually a metal lithium sheet, which is very active and easy to react, the assembly into half-cells needs to be carried out in a water-free and oxygen-free vacuum environment. Considering the actual assembly conditions, it is easier to assemble button-type half-cells in a glove box. Therefore, when measuring the loss capacity of lithium battery cells (such as soft-pack cells, square cells or cylindrical cells), they can be disassembled into button-type half-cells to achieve indirect analysis and measurement of the loss capacity of lithium battery cells.

[0062] As an optional implementation of the technical solution of the present invention, in step S1, the fresh battery cell is a battery cell after being converted into a capacity.

[0063] As an optional implementation of the technical solution of the present invention, in step S1, the failed battery cell is a battery cell whose capacity decays to 80% SOH.

[0064] As an optional implementation of the technical solution of the present invention, a failure analysis method for irreversible capacity decay of a lithium-ion battery comprises the following steps:

[0065] S1. The discharge capacity C of the fresh battery in the nth cycle of charge and discharge 新鲜 and the discharge capacity C of the failed cell in the nth cycle of charge and discharge 失效 , converted into the discharge capacity C of the nth week of the charge and discharge cycle of a fresh button-type half-cell according to the area 新鲜0 The discharge capacity C of the failed button half-cell in the nth cycle of charge and discharge 失效0 , and determine the total loss capacity C of the button half-celltotal , that is, C total =C 新鲜0 -C 失效0 ; Wherein, the fresh battery cell and the failed battery cell are lithium battery cells, and n is 2 or 3;

[0066] S2. disassembling the fresh battery cells and the failed battery cells after the charge and discharge cycle in step S1, and assembling the positive electrode sheets of the fresh battery cells and the positive electrode sheets of the failed battery cells obtained after disassembly into fresh positive electrode button half-cells and failed positive electrode button half-cells respectively;

[0067] According to the discharge capacity C of the nth week of charge and discharge cycle of the fresh positive electrode button half-cell 新鲜c The discharge capacity C of the failed positive electrode button half-cell in the nth cycle of charge and discharge 失效c , determine the positive electrode structure loss capacity C of the button half-cell cs , that is, C cs =C 新鲜c -C 失效c ;

[0068] According to the discharge capacity C of the nth week of charge and discharge cycle of the fresh positive electrode button half-cell 新鲜c and the discharge capacity C of the nth cycle of the fresh button half-cell 新鲜0 , determine the positive electrode de-insertion loss capacity C of a fresh button half-cell 新鲜cr , that is, C 新鲜cr =C 新鲜c -C 新鲜0 ;

[0069] According to the discharge capacity C of the failed positive electrode button half-cell charge and discharge cycle in the nth week 失效c The discharge capacity C of the failed button half-cell in the nth cycle of charge and discharge 失效0 , determine the positive electrode de-insertion loss capacity C of the failed button half-cell 失效cr , that is, C 失效cr =C 失效c -C 失效0 ;

[0070] S3. Detect part of the negative electrode sheets of the fresh battery cells and part of the negative electrode sheets of the failed battery cells respectively to obtain the residual capacity C of the negative electrode of the fresh battery cells. 新鲜ar0 and the negative electrode residual capacity C of the failed battery cell 失效ar0 , converted into the negative electrode residual capacity C of a fresh button half-cell by area 新鲜ar and the negative electrode residual capacity C of the failed button half-cell 失效ar ;

[0071] According to the positive electrode de-insertion loss capacity C of the fresh button half-cell 新鲜cr and the negative electrode residual capacity C of a fresh button half-cell 新鲜ar, determine the positive electrode CEI loss capacity C of the fresh button half-cell 新鲜CEI , that is, C 新鲜CEI =C 新鲜cr -C 新鲜ar ;

[0072] According to the positive electrode de-insertion loss capacity C of the failed button half-cell 失效cr and the negative electrode residual capacity C of the failed button half-cell 失效ar , determine the positive electrode CEI loss capacity C of the failed button half-cell 失效CEI , that is, C 失效CEI =C 失效cr -C 失效ar ;

[0073] According to the positive electrode CEI loss capacity C of the fresh button half-cell 新鲜CEI and the positive electrode CEI loss capacity C of the failed button half-cell 失效CEI , determine the loss capacity C caused by the increase of CEI of the positive electrode of the button half-cell CEI , that is, C CEI =C 失效CEI -C 新鲜CEI ;

[0074] S4. The remaining negative electrode sheets of the fresh battery cells obtained after disassembly and the remaining negative electrode sheets of the failed battery cells are respectively assembled into fresh negative electrode button half-cells and failed negative electrode button half-cells;

[0075] According to the charge capacity C of the first cycle of the fresh negative electrode button half-cell charge and discharge cycle 新鲜a 、The charging capacity C of the nth cycle 新鲜ad And the charging capacity C of the first cycle of the failed negative electrode button half-cell charge and discharge cycle 失效a 、The charging capacity C of the nth cycle 失效ad , determine the negative electrode polarization and lithium dendrite-induced capacity loss C of the button half-cell pl , that is, C pl =C 失效a -C 新鲜a , and the negative electrode structure loss capacity C as , that is, C as =C 新鲜ad -C 失效ad ;

[0076] According to the negative electrode residual capacity C of the fresh button half-cell 新鲜ar The charge capacity C of the first cycle of the fresh negative button half-cell 新鲜a , determine the negative electrode SEI and deactivated Li loss capacity C of the fresh button half-cell 新鲜SEI , that is, C 新鲜SEI =C 新鲜ar -C 新鲜a ;

[0077] According to the negative electrode residual capacity C of the failed button half-cell 失效ar The charging capacity C of the first cycle of the failed negative electrode button half-cell 失效a , determine the negative electrode SEI and deactivated Li loss capacity C of the failed button half-cell 失效SEI , that is, C 失效SEI =C 失效ar -C 失效a , and then determine the loss capacity C caused by the growth of negative electrode SEI and deactivated Li in the button half-cell SEI , that is, C SEI =C 失效SEI -C 新鲜SEI .

[0078] S5. Determine the positive electrode structure loss capacity C in the button half-cell cs , the capacity loss due to the increase of positive electrode CEI C CEI , Negative electrode structure loss capacity C as , the capacity loss caused by negative electrode polarization and lithium dendrites C pl , the capacity loss due to the growth of negative electrode SEI and deactivated Li C SEI The total loss capacity C total In order to quantitatively analyze the irreversible capacity decay of lithium-ion batteries containing lithium-ion battery cells, the proportion of

[0079] It should be noted that in step S1, n in the nth week of the charge and discharge cycle is usually 2 or 3. This is mainly because the ambient temperature in which fresh battery cells are stored after production may affect the capacity of the battery cells (the discharge capacity of the battery cells increases at high temperatures, and the discharge capacity of the battery cells decreases at low temperatures). Therefore, by subjecting the battery cells to a constant temperature (for example, 25°C) for 2 or 3 weeks of cyclic charge and discharge testing, the battery cells can be activated and the capacity can be kept stable.

[0080] Moreover, for a fresh battery cell that has just come off the production line (after being divided into capacities), it is generally believed that its capacity has almost no change after the second, third or sixth week of the cycle. This is mainly because a fresh battery cell can be cycled for more than 2,500 cycles. Even after 2,500 cycles, the capacity retention rate of the battery cell is generally still above 80%. Therefore, the capacity of a fresh battery cell after the second or third week of the charge and discharge cycle and the capacity after the sixth week can be considered unchanged. Based on this, the total loss capacity C measured in step S1 of the present invention is total , will have a certain corresponding relationship with the capacity loss after another n-cycle charge and discharge cycle in the subsequent steps S2-S5 using the fresh cells and failed cells that have undergone n-cycle charge and discharge cycles in step S1 to assemble button-type half-cells.

[0081] Compared with the traditional qualitative analysis method, the present invention can accurately analyze the whereabouts of lost active lithium by disassembling the lithium battery monomer cell when empty and charged, and making positive and negative button half-cells, including the capacity loss proportion caused by SEI growth and dead lithium, the capacity loss proportion caused by CEI growth, the capacity loss proportion caused by negative electrode polarization and lithium dendrite precipitation, the capacity loss proportion caused by positive electrode material loss, and the capacity loss proportion caused by negative electrode material loss. This has certain guiding significance for the selection of positive and negative electrode materials and electrolytes in the development process of lithium-ion battery cell platform system.

[0082] As an optional implementation of the technical solution of the present invention, in step S1, the lithium battery cell is selected from one of a soft-pack battery cell, a square battery cell or a cylindrical battery cell.

[0083] As an optional implementation scheme of the technical scheme of the present invention, in step S2, the fresh battery cells and the failed battery cells that have undergone n cycles of charge and discharge in step S1 are respectively discharged to 0% SOC and then disassembled to obtain fresh battery cell positive electrode sheets and failed battery cell positive electrode sheets, which are soaked in a solvent (such as DMC, ethanol or deionized water) for 1-2 hours, and then dried in a vacuum oven at 60-90°C for 3-6 hours and taken out, and the active material on one side of the positive electrode sheets (the fresh battery cell positive electrode sheets and the failed battery cell positive electrode sheets) is wiped off with dust-free paper dipped in anhydrous ethanol, and a single-sided circular positive electrode sheet is punched out with a punching machine, and the fresh positive button half-cell and the failed positive button half-cell are assembled in a glove box filled with a protective atmosphere.

[0084] As an optional implementation scheme of the technical solution of the present invention, in step S2, the fresh positive button half-cell and the failed positive button half-cell (positive button half-cell) use the same charge and discharge current during the charge and discharge cycle, which is 0.05-0.2C; the upper limit of the charging voltage used is the same, which is 3.5-3.8V; and the lower limit of the discharge voltage used is 1.0-2.5V.

[0085] As an optional implementation of the technical solution of the present invention, in step S3, part of the negative electrode sheets of the fresh battery cells and part of the negative electrode sheets of the failed battery cells obtained after the above-mentioned empty battery disassembly are scraped and ICP detection is performed to obtain the negative electrode residual capacity C of the fresh battery cells. 新鲜ar0 and the negative electrode residual capacity C of the failed battery cell 失效ar0 .

[0086] As an optional implementation scheme of the technical scheme of the present invention, in step S4, the fresh battery cells and the failed battery cells that have been charged and discharged for n weeks in step S1 are respectively discharged to 0% SOC and then disassembled to obtain fresh battery cell negative electrode sheets and failed battery cell negative electrode sheets, which are soaked in a solvent (such as DMC, ethanol or deionized water) for 1-2 hours, and then dried in a vacuum oven at 60-90°C for 3-6 hours and taken out, and the active material on one side of the negative electrode sheets (the fresh battery cell negative electrode sheets and the failed battery cell negative electrode sheets) is wiped off with dust-free paper dipped in deionized water, and a single-sided circular negative electrode sheet is punched out with a punching machine, and the fresh negative electrode button half-cell and the failed negative electrode button half-cell are assembled in a glove box filled with a protective atmosphere.

[0087] As an optional implementation scheme of the technical solution of the present invention, in step S4, the fresh negative button half-cell and the failed negative button half-cell (negative button half-cell) use the same charge and discharge current during the charge and discharge cycle, which is 0.05-0.2C; the upper limit of the charging voltage used is the same, which is 1.0-2.5V; and the lower limit of the discharge voltage used is the same, which is 0.001-0.1V.

[0088] The failure analysis method for irreversible capacity decay of lithium-ion batteries provided by the present invention can be used for failure analysis of various types of lithium-ion batteries. As an optional implementation of the technical solution of the present invention, the lithium-ion battery is selected from any one of a soft-pack battery, a square battery or a cylindrical battery.

[0089] As an optional implementation of the technical solution of the present invention, the positive electrode active material of the lithium-ion battery includes one or more of nickel-cobalt-manganese ternary material (NCM), nickel-cobalt-aluminum ternary material (NCA), lithium iron phosphate (LFP) or lithium manganese oxide (LMO).

[0090] As an optional embodiment of the technical solution of the present invention, the negative electrode active material of the lithium ion battery includes graphite, mesophase carbon microspheres (MCMB), lithium titanate (LTO), hard carbon, silicon oxide (Si x O) or silicon carbon (SiC) or one or more.

[0091] As an optional implementation of the technical solution of the present invention, in the electrolyte of the lithium-ion battery, the solvent includes one or more of propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC) or ethyl carbonate (DMC), the solute includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4) or lithium bis(fluorosulfonyl)imide (LiFSI), and the additive includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS) or vinylene sulfate (DTD).

[0092] As an optional implementation of the technical solution of the present invention, the active material of the positive electrode plate of the above-mentioned lithium-ion battery is lithium iron phosphate, and the active material of the negative electrode plate is artificial graphite.

[0093] As an optional implementation of the technical solution of the present invention, the above-mentioned lithium-ion battery positive electrode plate contains the following components in mass fractions: 96%-98% lithium iron phosphate, 0.5%-2% conductive carbon black, and 1.5%-2.5% polyvinylidene fluoride (PVDF).

[0094] As an optional implementation of the technical solution of the present invention, the above-mentioned lithium-ion battery negative electrode plate contains the following components in mass fractions: 95%-97% artificial graphite, 0.5%-1.5% conductive carbon black, 1.0%-2.0% sodium carboxymethyl cellulose (CMC), and 1.5%-2.5% styrene-butadiene rubber (SBR).

[0095] As an optional implementation of the technical solution of the present invention, the coating surface density of the positive electrode sheet of the lithium ion battery is 340-400g / m 2 (such as 340g / m 2 , 350g / m 2 , 360g / m 2 , 370g / m 2 , 380g / m 2 , 390g / m 2 , 400g / m 2 wait).

[0096] As an optional implementation of the technical solution of the present invention, the coating surface density of the negative electrode sheet of the lithium ion battery is 140-200g / m 2 (such as 140g / m 2 , 150g / m 2 , 160g / m 2 , 170g / m 2 , 180g / m 2 , 190g / m 2 , 200g / m 2 wait).

[0097] As an optional implementation of the technical solution of the present invention, the roller compaction density of the lithium ion battery positive electrode is 2.3-2.8 g / cm 3 (e.g. 2.3 g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 wait).

[0098] As an optional implementation of the technical solution of the present invention, the roller compaction density of the negative electrode of the lithium ion battery is 1.45-1.75g / cm 3 (e.g. 1.45 g / cm 3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 , 1.7g / cm 3 , 1.75g / cm 3 wait).

[0099] According to a second aspect of the present invention, there is also provided an application of the failure analysis method for irreversible capacity decay of a lithium-ion battery provided by the first aspect of the present invention in the field of battery analysis and selection.

[0100] In view of the advantages of the failure analysis method for irreversible capacity decay of lithium-ion batteries provided by the present invention, it is used in the material selection for the development of lithium-ion battery platform systems.

[0101] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0102] Example 1

[0103] The present embodiment provides a failure analysis method for irreversible capacity attenuation of a lithium-ion battery (lithium iron phosphate-graphite soft-pack battery cell), wherein the soft-pack battery cell uses lithium iron phosphate for the positive electrode and artificial graphite for the negative electrode, and a lamination process is adopted to manufacture a soft-pack battery cell with 13 negative electrodes and 12 positive electrodes.

[0104] Among them, the positive electrode ratio is LiFePO4:SP:PVDF=97.0%:1.0%:2.0%;

[0105] Among them, the negative electrode ratio is C:SP:CMC:SBR=96.2%:1.0%:1.2%:1.6%;

[0106] Among them, the coating surface density of the positive electrode sheet is 381g / m 2 ;

[0107] Among them, the coating surface density of the negative electrode sheet is 179g / m 2 ;

[0108] Among them, the compaction density of the positive electrode is 2.54g / cm 3 ;

[0109] Among them, the compaction density of the negative electrode sheet is 1.62g / cm 3 .

[0110] The failure analysis method of the irreversible capacity attenuation of the above-mentioned soft-pack battery cell specifically comprises the following steps:

[0111] S1. Take a fresh (soft pack) battery cell and a battery cell that has decayed to 80% SOH in the cycle (35℃ 1C / 1C cycle test for 2311 weeks, the SOH is 80.0%, hereinafter referred to as the failed (soft pack) battery cell), stand in the test cabinet (Xinwei test cabinet) for 8h, discharge to 2.5V with 0.1C constant current, leave for 10min, charge to 3.65V with 0.1C constant current and constant voltage, the cut-off current is 0.05C, leave for 10min, and then discharge to 2.5V with 0.1C constant current, cycle for 3 weeks, record the 0.1C discharge capacity of the fresh battery cell and the failed battery cell in the third week of the charge and discharge cycle, and convert the 0.1C discharge capacity C of the fresh button half-cell with a diameter of 12mm in the third week of the charge and discharge cycle according to the positive electrode plate area of ​​the soft pack battery cell and the plate area of ​​the button half-cell 新鲜0 The 0.1C discharge capacity C of the failed button half-cell in the third week of charge and discharge cycle 失效0 , and calculate the total loss capacity C of the button half-cell total , that is, C total =C 新鲜0 -C 失效0 ; Among them, the above-mentioned charge and discharge cycle constant volume temperature (charge and discharge cycle test) is 25°C.

[0112] S2. Discharge the fresh cells and the failed cells that have undergone charge and discharge cycles in step S1 to 0% SOC and then disassemble them (empty disassembly) to obtain the positive electrode sheet, soak them in DMC for 1 hour, and then dry them in a vacuum oven at 80°C for 4 hours. Use dust-free paper dipped in anhydrous ethanol to wipe off the active material on one side of the positive electrode sheet, use a punching machine to punch out a single-sided circular positive electrode sheet, and assemble the positive button half-cell in a glove box filled with a protective atmosphere. The specific assembly method is as follows:

[0113] The positive button half-cells were assembled and prepared in the order of assembling single-sided circular positive electrode plates (iron-lithium plates), separators, lithium plates, gaskets, and springs, corresponding to fresh positive button half-cells and failed positive button half-cells, respectively. Among them, the iron-lithium plates were cut with a diameter of 12 mm, the iron-lithium plates in the fresh positive button half-cells were derived from the positive plates of the fresh cells, and the iron-lithium plates in the failed positive button half-cells were derived from the positive plates of the failed cells; a single-sided ceramic polyethylene (PE)-based film was used as the separator; the electrolyte was a 1 mol / L lithium hexafluorophosphate (LiPF6) solution, and the solvent was a mixed solution of ethylene carbonate (EC): ethyl carbonate (DMC) in a volume ratio of 1:1.

[0114] The fresh positive button half-cell and the failed positive button half-cell were placed in the test cabinet for 8 hours, discharged to 2.0V at 0.1C constant current, left for 10 minutes, and charged to 3.75V at 0.1C constant current and constant voltage, with a cut-off current of 0.05C and left for 10 minutes. The cycle was repeated for 3 weeks, and the discharge capacity C of the fresh positive button half-cell in the third week was recorded. 新鲜c The third week discharge capacity C of the failed positive electrode button half-cell 失效c , the positive electrode structure loss capacity C of the button half-cell can be calculated cs , that is, C cs =C 新鲜c -C 失效c ; and based on the discharge capacity C of the fresh positive button half-cell in the third week 新鲜c and the discharge capacity C of a fresh button cell in the third week 新鲜0 , calculate the positive electrode de-insertion loss capacity C of a fresh button half-cell 新鲜cr , that is, C 新鲜cr =C 新鲜c -C 新鲜0 , based on the discharge capacity C of the failed positive button half-cell in the third week 失效c The discharge capacity C of the failed button cell in the third week 失效0 , calculate the positive electrode de-insertion loss capacity C of the failed button half-cell 失效cr , that is, C 失效cr =C 失效c -C 失效0 ;

[0115] S3. After disassembling the above empty battery from fresh cells and failed cells, the negative electrode sheets are scraped and tested by ICP to obtain the residual capacity C of the negative electrode of the fresh cells. 新鲜ar0 and the negative electrode residual capacity C of the failed battery cell 失效ar0 , converted into the negative electrode residual capacity C of a fresh button half-cell by area 新鲜ar and the negative electrode residual capacity C of the failed button half-cell 失效ar ;

[0116] According to the positive electrode de-insertion loss capacity C of the fresh button half-cell 新鲜cr and the negative electrode residual capacity C of a fresh button half-cell 新鲜ar , determine the positive electrode CEI loss capacity C of the fresh button half-cell 新鲜CEI , that is, C 新鲜CEI =C 新鲜cr -C 新鲜ar ;

[0117] According to the positive electrode de-insertion loss capacity C of the failed button half-cell 失效cr and the negative electrode residual capacity C of the failed button half-cell 失效ar , determine the positive electrode CEI loss capacity C of the failed button half-cell失效CEI , that is, C 失效CEI =C 失效cr -C 失效ar ;

[0118] According to the positive electrode CEI loss capacity C of the fresh button half-cell 新鲜CEI and the positive electrode CEI loss capacity C of the failed button half-cell 失效CEI , determine the loss capacity C caused by the increase of CEI of the positive electrode of the button half-cell CEI , that is, C CEI =C 失效CEI -C 新鲜CEI ;

[0119] S4. The remaining negative electrode sheets of the fresh battery cells obtained after disassembly and the remaining negative electrode sheets of the failed battery cells are respectively assembled into fresh negative electrode button half-cells and failed negative electrode button half-cells, and the specific assembly method is:

[0120] The negative button half-cell is assembled and prepared in the order of graphite pole piece, diaphragm, lithium sheet, gasket and spring. The cutting diameter of the graphite pole piece is 12 mm, the graphite pole piece in the fresh negative button half-cell comes from the negative pole piece of the fresh battery cell, and the graphite pole piece in the failed negative button half-cell comes from the negative pole piece of the failed battery cell; the single-sided ceramic polyethylene (PE) base film is used as the diaphragm; the electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6) solution, and the solvent is a mixed solution of ethylene carbonate (EC): ethyl carbonate (DMC) = 1:1 in volume ratio.

[0121] The fresh negative button half-cell and the failed negative button half-cell were placed in the test cabinet for 8 hours, charged to 0.005V with 0.1C constant current, left for 10 minutes, and charged to 2.0V with 0.1C constant current and constant voltage, with a cut-off current of 0.05C, left for 10 minutes, and the charge capacity C of the fresh negative button half-cell in the first week of the charge and discharge cycle was recorded respectively. 新鲜a 、Charge capacity C of the third cycle 新鲜ad 0.1C charging capacity C of the button half-cell with failed negative electrode in the first week of charge-discharge cycle 失效a 、Charge capacity C of the third cycle 失效ad ;

[0122] According to the charge capacity C of the first week of the charge-discharge cycle of the fresh negative electrode button half-cell 新鲜a The charging capacity C of the failed negative electrode button half-cell in the first week of charge and discharge cycle 失效a , calculate the negative electrode polarization and lithium dendrite loss capacity C of the button half-cell pl , that is, C pl, =C 失效a -C 新鲜a ;

[0123] According to the charge capacity C of the fresh negative electrode button half-cell charge and discharge cycle in the third week 新鲜ad The charge capacity C of the button-type half-cell with failed negative electrode in the third week of charge-discharge cycle 失效ad , calculate the negative electrode structure loss capacity C of the button half-cell as , that is, C as =C 失效ad -C 新鲜ad ;

[0124] According to the negative electrode residual capacity C of the fresh button half-cell 新鲜ar The charge capacity C of the first cycle of the fresh negative button half-cell 新鲜a , determine the negative electrode SEI and deactivated Li loss capacity C of the fresh button half-cell 新鲜SEI , that is, C 新鲜SEI =C 新鲜ar -C 新鲜a ;

[0125] According to the negative electrode residual capacity C of the failed button half-cell 失效ar The charging capacity C of the first cycle of the failed negative electrode button half-cell 失效a , determine the negative electrode SEI and deactivated Li loss capacity C of the failed button half-cell 失效SEI , that is, C 失效SEI =C 失效ar -C 失效a , and then determine the loss capacity C caused by the growth of negative electrode SEI and deactivated Li in the button half-cell SEI , that is, C SEI =C 失效SEI -C 新鲜SEI .

[0126] S5. Determine the positive electrode structure loss capacity C of the button half-cell cs , the capacity loss due to the increase of positive electrode CEI C CEI , Negative electrode structure loss capacity C as , the capacity loss caused by negative electrode polarization and lithium dendrites C pl , the capacity loss due to the growth of negative electrode SEI and deactivated Li C SEI The total loss capacity C total In order to quantitatively analyze the irreversible capacity decay of lithium-ion batteries containing lithium-ion battery cells, the proportion of

[0127] The data obtained by testing this embodiment are as follows:

[0128] The 0.1C discharge capacity of the fresh and failed cells in the third week of the charge-discharge cycle is converted into the corresponding button half-cell capacity according to the area, that is, the discharge capacity C of the fresh button half-cell in the third week of the charge-discharge cycle 新鲜0 The discharge capacity C of the failed button-type half-cell in the third week of charge and discharge cycle is 2.280 mAh.失效0 is 1.910mAh, and the total loss capacity C of the button half-cell is calculated total It is 0.370mAh.

[0129] Discharge capacity C of fresh positive electrode button half-cell in the third week 新鲜c The third week discharge capacity C of the failed positive electrode button half-cell is 2.798mAh 失效c The positive electrode structure loss capacity C of the button half-cell is calculated to be 2.775 mAh. cs The positive electrode structure loss is 0.023 mAh, and the positive electrode structure loss accounts for 6.22%. The positive electrode de-insertion loss capacity C of the fresh button half-cell is calculated. 新鲜cr The positive electrode de-insertion loss capacity C of the failed button half-cell is 0.518 mAh. 失效cr 0.865mAh;

[0130] The negative electrode residual capacity of the fresh battery cell detected is converted into the negative electrode residual capacity C of the fresh button half-cell according to the area. 新鲜ar The negative electrode residual capacity of the failed battery cell is converted into the negative electrode residual capacity C of the failed button half-cell according to the area. 失效ar 0.6644mAh; the positive electrode CEI loss capacity C of a fresh button half-cell 新鲜CEI The positive electrode CEI loss capacity C of the failed button half-cell is 0.1560mAh. 失效CEI 0.2006mAh; the loss capacity C due to the increase of positive electrode CEI CEI It is 0.0446mAh, and the loss caused by the growth of positive electrode CEI accounts for 12.05%;

[0131] The first week 0.1C charging capacity of the fresh negative electrode button half-cell is C 新鲜a 0.000mAh, 0.1C charging capacity C of failed negative electrode button half-cell in the first week 失效a 0.000mAh, calculate the loss capacity C caused by negative electrode polarization and lithium dendrites of button half-cell pl 0.000mAh; 0.1C charging capacity C of a fresh negative button half-cell in the third week 新鲜ad The 0.1C charging capacity C of the failed negative electrode button half-cell in the third week is 2.857mAh. 失效ad is 2.854mAh, calculate the negative electrode structure loss capacity C of the button half-cell as It is 0.003mAh, and the negative electrode structure loss accounts for 0.81%;

[0132] Negative electrode SEI and deactivated Li loss capacity C of button half-cell 新鲜SEIThe capacity loss of SEI and deactivated Li in the failed cell is 0.3620 mAh. 失效SEI The loss capacity C due to the growth of negative electrode SEI and deactivated Li in the button half-cell is calculated to be 0.6644 mAh. SEI It is 0.3024mAh, and the loss capacity due to the growth of negative electrode SEI and deactivated Li accounts for 81.73%.

[0133] The details are shown in Table 1.

[0134] Table 1

[0135]

[0136] It can be seen from the data in the table that the thickening of the negative electrode SEI film and the formation of dead lithium are the main reasons for the irreversible capacity decay of lithium-ion batteries. Therefore, the reasonable combination of negative electrode graphite and electrolyte and the formation process to form a thin and dense SEI film are of great significance.

[0137] The above analysis method is not only applicable to lithium iron phosphate lithium-ion battery systems, but also to other currently mainstream lithium-ion battery systems such as ternary systems, etc., which will not be repeated here.

[0138] Comparative Example 1

[0139] The difference from Example 1 is that the cause of capacity decay is qualitatively analyzed by impedance analysis (AC impedance test (EIS), hybrid pulse DC internal resistance test (HPPC) and ohmic internal resistance test (ACR)) and dV / dQ.

[0140] Specifically, the electrochemical impedance spectroscopy test was first performed on the fresh battery cells and the failed battery cells of Example 1, and the test results were also as follows: Figure 1 , Figure 2 And as shown in Table 2.

[0141] Among them, EIS was used to analyze the electrochemical polarization impedance of fresh cells and failed cells. The specific results are as follows: Figure 1 As shown in the figure, it can be seen that compared with fresh cells, the R sei and R ct There is a great degree of growth.

[0142] The DC internal resistance of fresh and failed cells was analyzed using the HPPC test (2C 10s). The specific results are as follows: Figure 2 As shown in the figure, it can be seen that after 2000 cycles, the DCR of the battery cell increases sharply.

[0143] At the same time, ACR is also used to analyze the AC internal resistance of fresh cells and failed cells. The specific results are shown in Table 2.

[0144] Table 2

[0145] Battery Cell Fresh battery cells Failed battery ACR(mΩ) 4.561 5.163

[0146] In addition, by performing dV / dQ analysis on fresh soft-pack cells and failed soft-pack cells, the test results are also as follows Figure 3 As shown in the figure, the peak shift shows that there is a certain loss of negative electrode material and serious loss of active lithium.

[0147] From the above analysis, it can be seen that as the cycle continues, the ohmic internal resistance, electrochemical polarization, and solid-phase diffusion impedance of the battery cell continue to increase, and the negative electrode material has a certain loss due to the continuous cycle, and the active lithium is lost in large quantities as the cycle proceeds. However, the above analysis cannot quantitatively analyze the specific whereabouts of the active lithium loss and the specific loss ratio of the positive electrode material and the negative electrode material.

[0148] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A failure analysis method for irreversible capacity decay of a lithium-ion battery, characterized in that: The following steps are involved: S1. The discharge capacity of the fresh battery cell and the discharge capacity of the failed battery cell are converted into the discharge capacity of the fresh button half-cell and the discharge capacity of the failed button half-cell according to the area, and the total loss capacity of the button half-cell is determined; wherein the fresh battery cell and the failed battery cell are lithium battery cells; S2. disassemble the fresh battery cell and the failed battery cell of step S1, and assemble the positive electrode sheets of the fresh battery cell and the failed battery cell obtained after disassembly into fresh positive electrode button half-cells and failed positive electrode button half-cells respectively; Determine the positive electrode structure loss capacity of the button-type half-cell according to the discharge capacity of the fresh positive electrode button-type half-cell and the discharge capacity of the failed positive electrode button-type half-cell; Determine the positive electrode de-intercalation loss capacity of the fresh button-type half-cell according to the discharge capacity of the fresh positive button-type half-cell and the discharge capacity of the fresh button-type half-cell; determine the positive electrode de-intercalation loss capacity of the failed button-type half-cell according to the discharge capacity of the failed positive button-type half-cell and the discharge capacity of the failed button-type half-cell; S3. After disassembling, the negative electrode sheets of the fresh cells and the negative electrode sheets of the failed cells are tested to obtain the residual capacity of the negative electrode of the fresh cells and the residual capacity of the negative electrode of the failed cells, and the residual capacity of the negative electrode of the fresh button-type half-cell and the residual capacity of the negative electrode of the failed button-type half-cell are converted according to the area; According to the positive electrode de-intercalation loss capacity of the fresh button half-cell and the negative electrode residual capacity of the fresh button half-cell, the positive electrode CEI loss capacity of the fresh button half-cell is determined; according to the positive electrode de-intercalation loss capacity of the failed button half-cell and the negative electrode residual capacity of the failed button half-cell, the positive electrode CEI loss capacity of the failed button half-cell is determined; according to the positive electrode CEI loss capacity of the fresh button half-cell and the positive electrode CEI loss capacity of the failed button half-cell, the loss capacity due to the growth of the positive electrode CEI of the button half-cell is determined; S4. The remaining negative electrode sheets of the fresh battery cells obtained after disassembly and the remaining negative electrode sheets of the failed battery cells are respectively assembled into fresh negative electrode button half-cells and failed negative electrode button half-cells; According to the discharge capacity of the fresh negative electrode button half-cell and the discharge capacity of the failed negative electrode button half-cell, the loss capacity caused by the negative electrode polarization and lithium dendrites and the loss capacity of the negative electrode structure of the button half-cell are determined; Determine the negative electrode SEI and deactivated Li loss capacity of the fresh button half-cell according to the negative electrode residual capacity of the fresh button half-cell and the discharge capacity of the fresh negative electrode button half-cell; According to the negative electrode residual capacity of the failed button half-cell and the discharge capacity of the failed negative electrode button half-cell, the negative electrode SEI and deactivated Li loss capacity of the failed button half-cell are determined; according to the negative electrode SEI and deactivated Li loss capacity of the fresh button half-cell and the negative electrode SEI and deactivated Li loss capacity of the failed button half-cell, the loss capacity due to the growth of the negative electrode SEI and deactivated Li of the button half-cell is determined; S5. The irreversible capacity attenuation of lithium-ion batteries containing lithium-ion battery cells is quantitatively analyzed by determining the proportion of the positive electrode structure loss capacity, the positive electrode CEI growth loss capacity, the negative electrode structure loss capacity, the negative electrode polarization and lithium dendrite loss capacity, and the negative electrode SEI and deactivated Li growth loss capacity in the total loss capacity in the button half-cell.

2. The failure analysis method for irreversible capacity decay of a lithium-ion battery according to claim 1, characterized in that: In step S1, the discharge capacity C of the fresh battery cell in the nth cycle of charge and discharge is 新鲜 and the discharge capacity C of the failed cell in the nth cycle of charge and discharge 失效 , converted into the discharge capacity C of the nth week of the charge and discharge cycle of a fresh button-type half-cell according to the area 新鲜0 The discharge capacity C of the failed button half-cell in the nth cycle of charge and discharge 失效0 , and determine the total loss capacity C of the button half-cell total , that is, C total =C 新鲜0 -C 失效0 ; Wherein, the fresh battery cell and the failed battery cell are lithium battery cells, n is 2 or 3; and / or, In step S1, the failed battery cell is a battery cell whose capacity decays to 80% SOH.

3. The failure analysis method for irreversible capacity decay of a lithium-ion battery according to claim 2, characterized in that: In step S2, the fresh battery cells and the failed battery cells that have undergone charge and discharge cycles in step S1 are disassembled, and the positive electrode sheets of the fresh battery cells and the positive electrode sheets of the failed battery cells obtained after disassembly are assembled into fresh positive electrode button half-cells and failed positive electrode button half-cells, respectively; According to the discharge capacity C of the nth week of charge and discharge cycle of the fresh positive electrode button half-cell 新鲜c The discharge capacity C of the failed positive electrode button half-cell in the nth cycle of charge and discharge 失效c , determine the positive electrode structure loss capacity C of the button half-cell cs , that is, C cs =C 新鲜c -C 失效c ; According to the discharge capacity C of the nth week of charge and discharge cycle of the fresh positive electrode button half-cell 新鲜c and the discharge capacity C of the nth cycle of the fresh button half-cell 新鲜0 , determine the positive electrode de-insertion loss capacity C of a fresh button half-cell 新鲜cr , that is, C 新鲜cr =C 新鲜c -C 新鲜0 ; According to the discharge capacity C of the failed positive electrode button half-cell charge and discharge cycle in the nth week 失效c The discharge capacity C of the failed button half-cell in the nth cycle of charge and discharge 失效0 , determine the positive electrode de-insertion loss capacity C of the failed button half-cell 失效cr , that is, C 失效cr =C 失效c -C 失效0 .

4. The failure analysis method for irreversible capacity decay of a lithium-ion battery according to claim 3, characterized in that: In step S2, the fresh battery cells and the failed battery cells which have been charged and discharged for n weeks in step S1 are respectively discharged to 0% SOC, and then disassembled to obtain the fresh battery cell positive electrode sheets and the failed battery cell positive electrode sheets, which are soaked in a solvent for 1-2 hours, and then dried in a vacuum oven at 60-90° C. for 3-6 hours and taken out, and the active materials on one side of the fresh battery cell positive electrode sheets and the failed battery cell positive electrode sheets are wiped off with dust-free paper dipped in anhydrous ethanol, and a single-sided circular positive electrode sheet is punched out with a punching machine, and the fresh positive electrode button half-cell and the failed positive electrode button half-cell are assembled in a glove box filled with a protective atmosphere; and / or, In step S2, during the charge and discharge cycle of the fresh positive button half-cell and the failed positive button half-cell, the charge and discharge current used is the same, which is 0.05-0.2C; the upper limit of the charging voltage used is the same, which is 3.5-3.8V; and the lower limit of the discharge voltage used is the same, which is 1.0-2.5V.

5. The failure analysis method for irreversible capacity decay of a lithium-ion battery according to claim 3, characterized in that: In step S3, part of the negative electrode sheets of the fresh battery cells and part of the negative electrode sheets of the failed battery cells obtained after disassembly are respectively tested to obtain the negative electrode residual capacity C of the fresh battery cells. 新鲜ar0 and the negative electrode residual capacity C of the failed battery cell 失效ar0 , converted into the negative electrode residual capacity C of a fresh button half-cell according to the area 新鲜ar and the negative electrode residual capacity C of the failed button half-cell 失效ar ; According to the positive electrode de-insertion loss capacity C of the fresh button half-cell 新鲜cr and the negative electrode residual capacity C of a fresh button half-cell 新鲜ar , determine the positive electrode CEI loss capacity C of the fresh button half-cell 新鲜CEI , that is, C 新鲜CEI =C 新鲜cr -C 新鲜ar ; According to the positive electrode de-insertion loss capacity C of the failed button half-cell 失效cr and the negative electrode residual capacity C of the failed button half-cell 失效ar , determine the positive electrode CEI loss capacity C of the failed button half-cell 失效CEI , that is, C 失效CEI =C 失效cr -C 失效ar ; According to the positive electrode CEI loss capacity C of the fresh button half-cell 新鲜CEI and the positive electrode CEI loss capacity C of the failed button half-cell 失效CEI , determine the loss capacity C caused by the increase of CEI of the positive electrode of the button half-cell CEI , that is, C CEI =C 失效CEI -C 新鲜CEI .

6. The failure analysis method for irreversible capacity decay of a lithium-ion battery according to claim 5, characterized in that: In step S4, the remaining negative electrode sheets of the fresh battery cells and the remaining negative electrode sheets of the failed battery cells obtained after disassembly are assembled into fresh negative electrode button half-cells and failed negative electrode button half-cells respectively; According to the charge capacity C of the first cycle of the fresh negative electrode button half-cell charge and discharge cycle 新鲜a 、The charging capacity C of the nth cycle 新鲜ad And the charge capacity C of the first cycle of the failed negative electrode button half-cell charge and discharge cycle 失效a 、The charging capacity C of the nth cycle 失效ad , determine the negative electrode polarization and lithium dendrite-induced capacity loss C of the button half-cell pl , that is, C pl =C 失效a -C 新鲜a , and the negative electrode structure loss capacity C as , that is, C as =C 新鲜ad -C 失效ad .

7. The failure analysis method for irreversible capacity decay of a lithium-ion battery according to claim 6, characterized in that: In step S4, according to the negative electrode residual capacity C of the fresh button half-cell 新鲜ar The charge capacity C of the first cycle of the fresh negative button half-cell 新鲜a , determine the negative electrode SEI and deactivated Li loss capacity C of the fresh button half-cell 新鲜SEI , that is, C 新鲜SEI =C 新鲜ar -C 新鲜a ; According to the negative electrode residual capacity C of the failed button half-cell 失效ar The charging capacity C of the first cycle of the failed negative electrode button half-cell 失效a , determine the negative electrode SEI and deactivated Li loss capacity C of the failed button half-cell 失效SEI , that is, C 失效SEI =C 失效ar -C 失效a , and then determine the loss capacity C caused by the growth of negative electrode SEI and deactivated Li in the button half-cell SEI , that is, C SEI =C 失效SEI -C 新鲜SEI .

8. The failure analysis method for irreversible capacity decay of a lithium-ion battery according to claim 6, characterized in that: In step S4, the fresh battery cells and the failed battery cells subjected to n cycles of charge and discharge in step S1 are respectively discharged to 0% SOC and then disassembled to obtain the fresh battery cell negative electrode sheets and the failed battery cell negative electrode sheets, which are soaked in a solvent for 1-2 hours, and then dried in a vacuum oven at 60-90° C. for 3-6 hours and taken out, and the active materials on one side of the fresh battery cell negative electrode sheets and the failed battery cell negative electrode sheets are wiped off with dust-free paper dipped in deionized water, and a single-sided circular negative electrode sheet is punched out with a punching machine, and the fresh negative electrode button half-cell and the failed negative electrode button half-cell are assembled in a glove box filled with a protective atmosphere; and / or, In step S4, during the charge and discharge cycle of the fresh negative button half-cell and the failed negative button half-cell, the charge and discharge current used is the same, which is 0.05-0.2C; the upper limit of the charging voltage used is the same, which is 1.0-2.5V; and the lower limit of the discharge voltage used is the same, which is 0.001-0.1V.

9. The failure analysis method for irreversible capacity decay of a lithium-ion battery according to any one of claims 1 to 8, characterized in that: The lithium-ion battery is any one of a soft-pack battery, a square battery or a cylindrical battery; and / or, The positive electrode active material of the lithium-ion battery includes one or more of a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, lithium iron phosphate or lithium manganate; and / or, The negative electrode active material of the lithium ion battery includes one or more of graphite, mesophase carbon microspheres, lithium titanate, hard carbon, silicon oxygen or silicon carbon; and / or, In the electrolyte of the lithium ion battery, the solvent includes one or more of propylene carbonate, ethylene carbonate, ethyl methyl carbonate or ethyl carbonate, the solute includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate or bis(fluorosulfonyl)imide lithium salt, and the additive includes one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone or vinylene sulfate.

10. Application of the failure analysis method for irreversible capacity decay of lithium-ion batteries according to any one of claims 1 to 9 in the field of battery analysis and selection.

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