CN110988086A - Method for detecting structural stability of electrode material in battery circulation process - Google Patents
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Abstract
The invention discloses a method for detecting structural stability of an electrode material in a battery circulation process, which comprises the following steps: the method comprises the following steps that firstly, a three-electrode battery is manufactured, and then a plurality of cycle stage charging and discharging tests are carried out, wherein each cycle stage test comprises a first system part and a second system part; secondly, for each cycle stage, acquiring the battery capacity Q of the three-electrode battery, the positive voltage V + and the negative voltage V-through a second standard test, and then correspondingly acquiring the dQ/dV + value of the positive electrode and the dQ/dV-value of the negative electrode; thirdly, for each cycle stage, drawing and obtaining quasi-steady-state capacity-voltage differential curves of the anode and the cathode; and fourthly, calculating the quasi-steady-state capacity differential change rate of the anode and the cathode in each cycle stage, and judging whether the structure irreversible change exists. The invention can judge whether the positive electrode material and the negative electrode material in the lithium ion battery have irreversible structural change during the battery cycle under the condition of not relating to material sampling.
Description
Technical Field
The invention relates to the technical field of battery detection, in particular to a method for detecting structural stability of an electrode material in a battery circulation process.
Background
Currently, lithium ion batteries have high energy density, high operating voltage, and good electrochemical properties, and are widely used in the consumer electronics and power fields.
In the study of high energy and high power density lithium battery systems, cycling failure is often encountered. On the premise of reasonable design of N/P (negative electrode capacity per unit area/positive electrode capacity per unit area), the cycle failures can be classified into four categories: 1. significant structural damage occurs on the surface or inside of the electrode active material; 2. the side reaction deposition product can prevent the electrochemical reaction from proceeding; 3. loss of active lithium; 4. poor contact of the conductive agent with the active material or low composition of the conductive agent.
Analysis of the cyclic failure problem must determine if there is significant irreversible structural damage to the active material. Currently, researchers typically evaluate electrode materials from the perspective of material characterization, including: x-ray diffraction analysis (XRD), high-power transmission electron microscopy analysis (HR-TEM), Raman spectroscopy (Raman), X-ray absorption near-edge structure analysis (XANES), and the like. Wherein, the ex-situ material characterization usually changes the surface state of the active material, and the testing environment is different from the actual working environment; in-situ material characterization requires a precision in-situ reaction cell, requiring varying degrees of modification to the test instrument.
However, there is no technology that can conveniently and reliably determine whether the positive electrode material and the negative electrode material in the lithium ion battery have structural irreversible changes during battery cycling, i.e., determine whether cycling failure is caused by structural changes of the active material, without involving material sampling.
Disclosure of Invention
The invention aims to provide a method for detecting structural stability of an electrode material in a battery cycling process, aiming at the technical defects in the prior art.
Therefore, the invention provides a method for detecting the structural stability of an electrode material in the battery cycling process, which comprises the following steps:
the method comprises the following steps that firstly, a three-electrode battery is manufactured, and then charging and discharging tests of a plurality of preset cycle stages are carried out, wherein each cycle stage test comprises a first system and a second system, the first system is a cycle system, and the second system is a quasi-steady-state system;
secondly, for each cycle stage, acquiring the battery capacity Q of the three-electrode battery, the positive voltage V + and the negative voltage V-through a second standard test, and then performing differential processing on the battery capacity Q of the three-electrode battery respectively relative to the positive voltage V + and the negative voltage V-to correspondingly obtain the dQ/dV + value of the positive electrode and the dQ/dV-value of the negative electrode;
step three, for each cycle stage, drawing and obtaining a quasi-steady-state capacity voltage differential curve of the anode by taking the dQ/dV + value of the anode as an ordinate and the voltage V + of the anode or the SOC of the battery as an abscissa, and drawing and obtaining a quasi-steady-state capacity voltage differential curve of the cathode by taking the dQ/dV-value of the cathode as an ordinate and the voltage V-of the cathode or the SOC of the battery as an abscissa;
and fourthly, calculating the capacity differential change rate of the anode and the capacity differential change rate of the cathode according to a preset calculation formula, correspondingly judging whether the anode material has structure irreversible change or not according to whether the capacity differential change rate of the anode is larger than a preset value or not, and correspondingly judging whether the cathode material has structure irreversible change or not according to whether the capacity differential change rate of the cathode is larger than the preset value or not.
Wherein, in the first step, the charge-discharge test of each cycle phase comprises: firstly, according to a preset first system, executing n times in a circulating way, wherein the value range of n is 50-150;
and then, executing once according to a preset second standard.
In the first step, a first standard is preset as follows:
subjecting the three-electrode battery to a first current I with a predetermined magnitude1Charging the battery at constant current to a preset upper limit cut-off voltage, and then charging the battery at constant voltage to a second current I with the current equal to the preset magnitude2After standing for a preset time, a first current I is used1Discharging at constant current to a preset lower limit cut-off voltage;
in the first step, the second standard is preset as follows:
continuously using a preset minimum current I to the three-electrode battery0Discharging the battery at constant current to a preset lower limit cut-off voltage to enable the residual capacity of the battery to approach 0; after standing still, continuing to preset minimum current I0Charging to preset upper limit cut-off voltage with constant current, standing, and charging with preset minimum current I0And discharging the constant current to a preset lower limit cut-off voltage.
Wherein, after the third step, before the fourth step, further comprising the steps of:
the fifth step: in the same figure, quasi-steady-state capacity voltage differential curves of the positive electrode in multiple cycle stages are drawn, and when the similarity of characteristic peaks in the curves reaches a preset similarity, the positive electrode material is judged to have no irreversible structural change;
and drawing quasi-steady-state capacity-voltage differential curves of the negative electrode in multiple cycle stages in the same graph, and judging that the negative electrode material has no irreversible structural change when the similarity of characteristic peaks in the curves reaches a preset similarity.
Wherein, in the fourth step, the positive or negative electrode capacity differential change rate Δ is calculated according to the following formula:
wherein, V represents the voltage of the anode or the cathode; q represents the battery capacity, x is the cycle number of the previous cycle stage, and n is the interval cycle number of the two adjacent cycle stages.
Compared with the prior art, the technical scheme provided by the invention has the advantages that the method for detecting the structural stability of the electrode material in the battery cycle process is provided, whether the structure of the anode material and the cathode material in the lithium ion battery is irreversibly changed or not in the battery cycle process can be conveniently and reliably judged under the condition of not involving material sampling, namely whether the cycle failure is caused by the structural change of the active material or not is judged, and the method has great practical significance.
Through the quasi-equilibrium state capacity differential (voltage differential) test designed by the invention, the redox states (phase change states) of the anode material and the cathode material at different stages of the cycle can be flexibly obtained, whether the anode material and the cathode material have obvious irreversible phase change or not can be determined, and the reason of cycle failure can be guided and analyzed. The detection method has the advantages of high detection sensitivity, simple operation and no need of material characterization equipment. The method of the invention is not limited to lithium ion batteries, but also includes alkali metal ion batteries such as sodium ion batteries and potassium ion batteries.
Drawings
FIG. 1 is a flow chart of a method of detecting structural stability of an electrode material during cycling of a battery according to the teachings of the present invention;
FIG. 2 is a schematic diagram of a three-electrode battery applied in a method for detecting structural stability of an electrode material in a battery cycling process according to the present invention;
fig. 3 is a schematic diagram of a cycle capacity retention rate curve of a three-electrode battery in an embodiment according to a method for detecting structural stability of an electrode material in a battery cycle process of the present invention;
FIG. 4 is a diagram illustrating a quasi-steady state capacity differential curve of a positive electrode (relative to a lithium reference electrode) in an embodiment according to a method for detecting structural stability of an electrode material during battery cycling provided by the present invention;
fig. 5 is a diagram illustrating a quasi-steady state capacity differential change rate curve of a positive electrode (relative to a lithium reference electrode) in an embodiment according to a method for detecting structural stability of an electrode material during battery cycling provided by the invention.
Detailed Description
In order that those skilled in the art will better understand the technical solution of the present invention, the following detailed description of the present invention is provided in conjunction with the accompanying drawings and embodiments.
Referring to fig. 1 to 5, the present invention provides a method for detecting structural stability of an electrode material during battery cycling, comprising the steps of:
the method comprises the following steps that firstly, a three-electrode battery is manufactured, and then charging and discharging tests of a plurality of (for example, two or three) circulation stages are preset, wherein each circulation stage test comprises a first system and a second system, the first system is a circulation system, and the second system is a quasi-steady-state system;
in a first step, the charge-discharge test of each cycle phase comprises: firstly, according to a preset first system (namely a circulating system), circularly executing charge-discharge test for preset n times (the value range of n is 50-150); and then, according to a preset second standard (namely a quasi-steady-state standard), circularly executing the charge-discharge test for a preset time, wherein the number of times is not counted into the number of times of circulation.
In the first step, the first system (i.e., the cyclic system) is preset as follows:
subjecting the three-electrode battery to a first current I with a predetermined magnitude1(e.g., 1C, C is the battery capacity) is charged with a constant current to a predetermined upper cut-off voltage (e.g., 4.35V), and then is charged with a constant voltage to a second current I having a current equal to a predetermined level at the predetermined upper cut-off voltage (e.g., 4.35V)2(e.g., 0.05C), standing for a predetermined period of time, and applying a first current I1(e.g., 1C) constant current discharge to a preset lower cutoff voltage (e.g., 3V);
in the first step, the second system (i.e., the quasi-steady-state system) is preset as follows:
continuously using a preset minimum current I to the three-electrode battery0Discharging the battery to a preset lower limit cut-off voltage (for example, 3V) at a constant current (for example, 0.05C) to enable the residual capacity of the battery to be close to 0 (for example, the residual capacity is lower than 2%); after standing still, continuing to preset minimum current I0Charging with constant current to preset upper limit cut-off voltage (such as 4.35V), standing, and charging with preset minimum current I0And discharging the constant current to a preset lower limit cut-off voltage (for example, 3V).
Certainly, in a specific implementation, the preset second system may select a preset minimum current (e.g., 0.05C, where C is a battery capacity) that enables the battery to be in a quasi-steady state according to a specific situation of the actual battery.
In a specific implementation of the present invention, a three-electrode cell includes a positive electrode, a negative electrode, and a reference electrode.
In a specific implementation, the reference electrode is a lithium sheet. The three-electrode cell may be an existing conventional three-electrode cell. The manufacturing method of the three-electrode battery is a conventional method.
Secondly, for each cycle stage, acquiring the battery capacity Q of the three-electrode battery, the positive voltage V + and the negative voltage V-through a second standard test, and then performing differential processing on the battery capacity Q of the three-electrode battery respectively relative to the positive voltage V + and the negative voltage V-to correspondingly obtain the dQ/dV + value of the positive electrode and the dQ/dV-value of the negative electrode;
step three, for each cycle stage, drawing and obtaining a quasi-steady-state capacity voltage differential curve of the anode by taking the dQ/dV + value of the anode as an ordinate and the voltage V + of the anode or the SOC of the battery as an abscissa, and drawing and obtaining a quasi-steady-state capacity voltage differential curve of the cathode by taking the dQ/dV-value of the cathode as an ordinate and the voltage V-of the cathode or the SOC of the battery as an abscissa;
and fourthly, calculating the capacity differential change rate of the anode and the capacity differential change rate of the cathode according to a preset calculation formula, correspondingly judging whether the structure of the anode material is irreversibly changed or not when the capacity differential change rate of the anode is larger than a preset value, namely judging whether the cycle failure is caused by the structure change of the anode active material, and correspondingly judging whether the structure of the cathode material is irreversibly changed or not when the capacity differential change rate of the cathode is larger than the preset value, namely judging whether the cycle failure is caused by the structure change of the cathode active material.
In the fourth step, the positive or negative electrode capacity differential change rate Δ (i.e., quasi-steady state capacity differential change rate) is calculated according to the following formula:
wherein, V represents the voltage of the anode or the cathode (specifically, the voltage of the anode V + or the voltage of the cathode V-); q represents the battery capacity, x is the cycle number of the previous cycle stage, and n is the interval cycle number of the two adjacent cycle stages. Note that the value V takes on V0，V1，V2，……，VmMust satisfy the condition that dV is equal to V1-V0＝V2-V1＝……＝Vm-Vm-1(ii) a Further, the value of Δ [ V ] is obtained by the above calculation formula1-V0]，Δ[V2-V1]，……，Δ[Vm-Vm-1]The resulting data set Δ (x + n) vs x.
In a specific implementation of the present invention, after the third step and before the fourth step, the method may further include the steps of:
the fifth step: in the same figure, capacity voltage differential curves (namely quasi-steady-state capacity differential curves) of the positive electrode at multiple cycle stages are drawn, and when the similarity of characteristic peaks in the curves reaches a preset similarity (specifically, the peak position and the peak intensity of the characteristic peaks can be judged not to be changed greatly, for example, the peak position and the peak intensity of the characteristic peaks are within a preset change range), the positive electrode material is judged not to have structural irreversible change, namely, the cycle failure is judged not to be caused by the structural change of the positive electrode active material;
and drawing capacity-voltage differential curves (namely quasi-steady-state capacity differential curves) of the negative electrode in multiple cycle stages in the same graph, and judging that the negative electrode material has no structural irreversible change when the similarity of the characteristic peaks in the curves reaches a preset similarity (specifically, the peak position and the peak intensity of the characteristic peaks can be judged not to be greatly changed, for example, the peak position and the peak intensity of the characteristic peaks are within a preset change range), namely judging that the cycle failure is not caused by the structural change of the negative electrode active material.
In the first step, before the test of the preset second standard (i.e., the quasi-steady-state standard), it is recommended to discharge the cell to a lower limit Cut-off Voltage (Low Cut-off Voltage), which may be 3V, for example.
In the first step, the stability of the positive electrode structure can be analyzed by using curves of which the dQ/dV + and the SOC are respectively the ordinate and the abscissa.
In the first step, the stability of the negative electrode structure may be analyzed using graphs in which dQ/dQ-and SOC are respectively ordinate and abscissa, and the stability of the negative electrode structure may be analyzed using graphs in which dQ-/dQ-and SOC are respectively ordinate and abscissa,
in order to more clearly understand the technical solution of the present invention, the following further description is made by using specific examples.
Examples are given.
For the method for detecting the structural stability of the electrode material in the battery cycling process, which is provided by the invention, a three-electrode battery is required to be used for implementation,
firstly, a three-electrode battery is manufactured. The specific manufacturing process of the three-electrode battery is as follows:
1. manufacturing a positive plate: mixing and stirring a nickel-cobalt-aluminum NCA ternary material, a conductive agent, polyvinylidene fluoride (PVDF glue) and N-methylpyrrolidone (NMP) according to a certain proportion (for example, the mass ratio is 66:1.5:2:30.5), and then coating, rolling and shearing to obtain the positive plate.
2. And (3) manufacturing a negative plate: mixing and stirring artificial graphite, sodium carboxymethylcellulose (CMC), a conductive agent, a binder and deionized water according to a certain proportion (for example, the mass ratio is 48:0.5:0.5:1:48), then coating, rolling and shearing to obtain the negative plate.
3. Preparing a three-electrode battery: referring to fig. 2, a three-electrode battery includes a battery case 4, a positive electrode 1, a negative electrode 2, and a reference electrode 3. The positive electrode 1, the negative electrode 2 and the reference electrode 3 are sequentially placed, assembled and packaged in a battery shell 4, a diaphragm 5 is arranged between the positive electrode 1 and the negative electrode 2 and between the negative electrode 2 and the reference electrode 3, a reference electrode tab 30 of the reference electrode 3, a positive electrode tab 10 of the positive electrode 1 and a negative electrode tab 20 of the negative electrode 2 are respectively led out of the battery shell 4, the three-electrode battery needs to be filled with electrolyte (only by adopting common and existing non-aqueous electrolyte and needing to be the same as the electrolyte of a two-electrode battery, the electrolyte can comprise lithium salt and anhydrous solvent, the lithium salt can comprise lithium hexafluorophosphate LiPF6, the molar concentration of the lithium hexafluorophosphate LiPF6 in the electrolyte is 1.0mol/L, the anhydrous solvent comprises propylene carbonate PC, ethylene carbonate EC and methyl ethyl carbonate EMC, and the volume ratio of the three is 1: 1: 3.
The following examples are merely illustrative of the steps of carrying out the present invention and are not intended to limit the scope of the invention.
The capacity retention rate of the ternary/graphite soft package battery cell (model SP475778) is 83% (fig. 3) after 1C/1C circulation for 300 times, and whether the electrode active material structure is remarkably damaged or not is analyzed.
1. And manufacturing a three-electrode cell, and performing a circulation and quasi-steady-state test.
The test involves the following two charge-discharge modes, and the multiplying power is selected according to the actual charge-discharge characteristics of the battery cell.
Presetting a first system (namely a circulating system): 1C (i.e. a first current I of a predetermined magnitude)1) Constant current charging to 4.35V (i.e. the preset upper cut-off voltage of the battery), and constant voltage charging to 4.35V until the current is equal to 0.05C (i.e. the second current I with the preset magnitude)2) And standing for 10min, and discharging the 1C constant current to 3V (namely the preset lower limit cut-off voltage of the battery).
Presetting a second system (namely a quasi-steady-state system): 0.05C (i.e. preset minimum current I)0) The battery is charged to 4.35V (namely the preset upper limit cut-off voltage of the battery) by constant current, and the battery is discharged to 3V (namely the preset lower limit cut-off voltage of the battery) by constant current at 0.05C.
After the three-electrode cell circulates to the 100 th week according to a preset first standard (namely a circulation standard), the battery is discharged to 3V (namely the preset lower limit cut-off voltage of the battery) at 0.05C. Charging and discharging according to a preset second standard (namely, a quasi-steady-state standard) to obtain 100 th-cycle quasi-steady-state Data (recorded as Data 1).
And (3) continuously performing a cycle test according to a preset first standard (namely a cycle standard), and discharging the battery to 3V at 0.05 ℃ after the cycle is performed to the 200 th week. Charging and discharging according to a preset second standard (namely, a quasi-steady-state standard) to obtain 200 th-cycle quasi-steady-state Data (recorded as Data 2).
And (3) continuously performing a cycle test according to a preset first standard (namely a cycle standard), and discharging the battery to 3V at 0.05 ℃ after the cycle is performed to the 300 th week. Charging and discharging according to a preset second standard (namely, a quasi-steady-state standard) to obtain 300-th quasi-steady-state Data (recorded as Data 3).
2. And (5) processing data of the quasi-steady-state test.
Firstly, voltage and capacity Data of a full cell, a positive electrode and a negative electrode of Data1, Data2 and Data3 are extracted at equal intervals, capacity differential curves of the full cell, the positive electrode and the negative electrode are drawn, and reversibility of an oxidation-reduction reaction is qualitatively analyzed; and calculating the capacity differential change rate, and semi-quantitatively analyzing the characteristics of the capacity differential change rate.
Then, taking the positive electrode as an example, the data analysis process is described.
a. And (3) qualitative analysis: voltage and capacity Data of the positive electrodes of Data1, Data2 and Data3 are extracted at an interval of 20mV to generate dQ/dV + and V + Data, quasi-steady state capacity differential curves (figure 4) of the positive electrodes at the 100 th week, the 200 th week and the 300 th week are drawn, and the oxidation-reduction peak position and the peak intensity are obviously not changed greatly, so that the positive electrode material is preliminarily deduced not to have obvious structural damage.
B. Semi-quantitative analysis: the quasi-steady state capacity differential rate of change Δ is calculated according to the following equation:
wherein, V represents the voltage of the anode or the cathode; q represents the battery capacity, x is the cycle count of the previous cycle stage (x equals 100, 200 in this embodiment), and n is the interval cycle count of two adjacent cycle stages (n equals 100 in this embodiment). Note that the value V takes on V0，V1，V2，……，VmMust satisfy the condition that dV is equal to V1-V0＝V2-V1＝……＝Vm-Vm-1(ii) a Further, the value of Δ [ V ] is obtained by the above calculation formula1-V0]，Δ[V2-V1]，……，Δ[Vm-Vm-1]The resulting data set Δ (x + n) vs x.
Reference judgment basis: when a plurality of sets are formed by the quasi-steady-state capacity differential change rate delta at different cycle stages, each set satisfies that the numerical value of 95 percent of elements (namely the quasi-steady-state capacity differential change rate delta) changes around 0 percent (can be evaluated by a histogram, and is omitted), and the mean value of delta is more than or equal to-2.5 percent, the electrode material is considered to have no obvious structural damage; otherwise, there is significant structural damage to the electrode material.
And (3) drawing a quasi-steady-state capacity differential change rate curve (figure 5) of the positive electrode by taking the voltage of the positive electrode as an abscissa and the quasi-steady-state capacity differential change rate delta of the positive electrode as an ordinate, wherein the quasi-steady-state capacity differential change rate fluctuates uniformly above and below 0%, the mean value of the quasi-steady-state capacity differential change rate (shown as delta 200vs 100) of the 200 th week relative to the 100 th week is-1.5%, and the mean value of the quasi-steady-state capacity differential change rate (shown as delta 300vs 200) of the 300 th week relative to the 200 th week is-1.0%, so that the positive electrode is proved to keep higher structural reversibility in the circulation process.
Similar conclusions were drawn by performing comparative analyses between quasi-steady state dQ/dV-and SOC (state of charge) for the negative electrode using similar methods. In summary, the analysis demonstrated that during the cycling test of this example, no significant irreversible structural failure occurred in both the positive and negative electrode materials, i.e., the electrode active material had good structural stability during cycling failure.
Based on the technical scheme, in the invention, through carrying out preset-system cycle test on the three-electrode battery cell, selecting different cycle times, detecting the capacity differential dQ/dV (or voltage differential dV/dQ) characteristic of the quasi-equilibrium state, and comparing the capacity differential dQ/dV (or voltage differential dV/dQ) curves of the quasi-equilibrium state at different stages, the change of characteristic peaks is qualitatively and semi-quantitatively analyzed, whether the structure stability problem exists in the anode and the cathode is determined, and important evidence is provided for cycle failure analysis.
The invention relates to a nondestructive electrochemical method for judging the structural stability of positive and negative electrode materials in a cycle test. The invention is suitable for structural failure analysis of the active materials of the lithium ion battery electrode, the sodium ion battery electrode and the potassium ion battery electrode in the circulation process.
Compared with the conventional material characterization, the nondestructive electrochemical monitoring technology provided by the invention does not relate to material sampling, does not damage the real working environment of the material, and does not need a complex characterization instrument; the method for in-situ evaluating the structural stability of the anode and the cathode in the battery cell at different cycle stages in stages has the advantages of high detection sensitivity, simplicity and easiness in operation and universality.
In summary, compared with the prior art, the method for detecting the structural stability of the electrode material in the battery cycle process provided by the invention can conveniently and reliably judge whether the positive electrode material and the negative electrode material in the lithium ion battery have structural irreversible changes in the battery cycle process under the condition of not involving material sampling, namely whether the cycle failure is caused by structural changes of the active material, and has great practical significance.
Through the quasi-equilibrium state capacity differential (voltage differential) test designed by the invention, the redox states (phase change states) of the anode material and the cathode material at different stages of the cycle can be flexibly obtained, whether the anode material and the cathode material have obvious irreversible phase change or not can be determined, and the reason of cycle failure can be guided and analyzed. The detection method has the advantages of high detection sensitivity, simple operation and no need of material characterization equipment. The method of the invention is not limited to lithium ion batteries, but also includes alkali metal ion batteries such as sodium ion batteries and potassium ion batteries.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (5)
1. A method for detecting structural stability of an electrode material in a battery cycling process is characterized by comprising the following steps:
the method comprises the following steps that firstly, a three-electrode battery is manufactured, and then charging and discharging tests of a plurality of preset cycle stages are carried out, wherein each cycle stage test comprises a first system and a second system, the first system is a cycle system, and the second system is a quasi-steady-state system;
secondly, for each cycle stage, acquiring the battery capacity Q of the three-electrode battery, the positive voltage V + and the negative voltage V-through a second standard test, and then performing differential processing on the battery capacity Q of the three-electrode battery respectively relative to the positive voltage V + and the negative voltage V-to correspondingly obtain the dQ/dV + value of the positive electrode and the dQ/dV-value of the negative electrode;
step three, for each cycle stage, drawing and obtaining a quasi-steady-state capacity voltage differential curve of the anode by taking the dQ/dV + value of the anode as an ordinate and the voltage V + of the anode or the SOC of the battery as an abscissa, and drawing and obtaining a quasi-steady-state capacity voltage differential curve of the cathode by taking the dQ/dV-value of the cathode as an ordinate and the voltage V-of the cathode or the SOC of the battery as an abscissa;
and fourthly, calculating the capacity differential change rate of the anode and the capacity differential change rate of the cathode according to a preset calculation formula, correspondingly judging whether the anode material has structure irreversible change or not according to whether the capacity differential change rate of the anode is larger than a preset value or not, and correspondingly judging whether the cathode material has structure irreversible change or not according to whether the capacity differential change rate of the cathode is larger than the preset value or not.
2. The method according to claim 1, wherein in the first step, the charge-discharge test of each cycle phase comprises: firstly, according to a preset first system, executing n times in a circulating way, wherein the value range of n is 50-150;
and then, executing once according to a preset second standard.
3. The method of claim 2, wherein in the first step, the first format is preset as follows:
subjecting the three-electrode battery to a first current I with a predetermined magnitude1Charging the battery at constant current to a preset upper limit cut-off voltage, and then charging the battery at constant voltage to a second current I with the current equal to the preset magnitude2After standing for a preset time, a first current I is used1Discharging at constant current to a preset lower limit cut-off voltage;
in the first step, the second standard is preset as follows:
continuously using a preset minimum current I to the three-electrode battery0Discharging the battery at constant current to a preset lower limit cut-off voltage to enable the residual capacity of the battery to approach 0; after standing still, continuing to preset minimum current I0Charging to preset upper limit cut-off voltage with constant current, standing, and charging with preset minimum current I0And discharging the constant current to a preset lower limit cut-off voltage.
4. A method according to any one of claims 1 to 3, characterized in that after the third step, before the fourth step, it further comprises the steps of:
the fifth step: in the same figure, quasi-steady-state capacity voltage differential curves of the positive electrode in multiple cycle stages are drawn, and when the similarity of characteristic peaks in the curves reaches a preset similarity, the positive electrode material is judged to have no irreversible structural change;
and drawing quasi-steady-state capacity-voltage differential curves of the negative electrode in multiple cycle stages in the same graph, and judging that the negative electrode material has no irreversible structural change when the similarity of characteristic peaks in the curves reaches a preset similarity.
5. The method according to any one of claims 1 to 3, wherein in the fourth step, the positive or negative electrode capacity differential change rate Δ is calculated according to the following formula:
wherein, V represents the voltage of the anode or the cathode; q represents the battery capacity, x is the cycle number of the previous cycle stage, and n is the interval cycle number of the two adjacent cycle stages.
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