CN114089202B - Method for nondestructively analyzing electrode impedance stability in battery circulation process - Google Patents
Method for nondestructively analyzing electrode impedance stability in battery circulation process Download PDFInfo
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/389—Measuring internal impedance, internal conductance or related variables
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/392—Determining battery ageing or deterioration, e.g. state of health
Abstract
The invention discloses a method for nondestructively analyzing the impedance stability of an electrode in the battery circulation process, which comprises the following steps: firstly, performing a first substep on a three-electrode cell; and then executing a second substep: performing a plurality of cycle stage charge and discharge tests, wherein each cycle stage charge and discharge test comprises a preset system one-stage test and a preset system two-stage test which are performed in sequence; secondly, recording the cathode electrode potential, the anode electrode potential and the pulse current before and after testing in the preset system two-stage test for each cycle stage charge-discharge test; thirdly, obtaining cathode impedance and anode impedance; fourthly, calculating the change rate of the cathode impedance and the change rate of the anode impedance; and fifthly, correspondingly judging whether the impedance of the cathode or the anode is stable by judging whether the impedance is smaller than a preset value. The invention can reliably judge the reason of the cycle failure of the battery without damaging the battery, judge the stability of the cathode impedance and the anode impedance and indicate the direction for improving the battery system.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to a method for nondestructively analyzing the impedance stability of an electrode in the battery circulation process.
Background
With the national emphasis on environmental pollution control and energy resource safety, lithium ion batteries are widely used in the fields of consumer batteries, power batteries, energy storage batteries and the like. However, it is not uncommon for the electrical performance of the battery to degrade due to failure and even for safety accidents to occur.
In the research process of a lithium ion battery system, the problems of battery failure such as circulating water jumping, gas storage, lithium precipitation and the like are frequently encountered. Among them, one of the most main causes of the circulating diving is: the impedance of the battery, which includes ohmic impedance, charge transfer impedance, and active material surface film impedance (i.e., SEI film impedance or CEI film impedance, SEI film being an anode solid electrolyte interface film, CEI film being a cathode electrolyte interface film), is excessively increased, and thus, factors that cause an increase in impedance are attributed, including: (1) the damage of the conductive network inside the electrode and between the electrode and the current collector caused by the change of the volume of the charge and discharge electrode, and the increase of the ohmic impedance Rohm; (2) an increase in charge transfer resistance Rct due to collapse of the electrode material structure, generation of grain boundaries, and generation of a rock-salt phase; (3) the SEI film resistance (i.e., anode solid electrolyte interfacial film resistance) or CEI film resistance (i.e., cathode electrolyte interfacial film resistance) excessively increases due to breakage of the active material and occurrence of side reactions such as decomposition of the electrolyte solution.
Therefore, the problem of battery cycle failure is analyzed, whether the battery impedance increase is caused by the cathode impedance increase or the anode impedance increase is determined, the direction can be indicated for the improvement of the next battery system, the working efficiency can be improved, the research and development period can be shortened, and the practical significance is great.
However, at present, when a cyclically failed battery is analyzed, the battery is usually disassembled in advance, and then the cathode and the anode are respectively subjected to XRD (X-ray diffraction), SEM (scanning electron microscope) and TEM (transmission electron microscope) characterization, or ac impedance EIS (electrochemical impedance spectroscopy) characterization by assembling and tapping, so that the problem of the cyclically failed battery caused by the failure of the cathode or the anode is further determined, and thus, a large amount of work is often brought, and the main reason of the cyclically failed battery is not easily and rapidly determined.
Disclosure of Invention
The invention aims to provide a method for nondestructively analyzing the impedance stability of an electrode in the battery circulation process aiming at the technical defects in the prior art.
Therefore, the invention provides a method for nondestructively analyzing the impedance stability of an electrode in the battery cycle process, which comprises the following steps:
first, a three-electrode cell is constructed using a reference electrode, and first, the first substep is performed: performing a first preset system two-stage test on the three-electrode battery to obtain cathode impedance R + and anode impedance R-which are possessed by the three-electrode battery during the first preset system two-stage test, namely obtaining cathode impedance and anode impedance which are possessed by the three-electrode battery at an initial stage without starting the test;
then, a second substep is performed: performing a plurality of cycle stage charge and discharge tests, wherein each cycle stage charge and discharge test comprises a preset system one-stage test and a preset system two-stage test which are performed in sequence, the preset system one-stage test is a cycle test, and the preset system two-stage test is a pulse test;
in the first sub-step, in the first preset mode two-stage test of the three-electrode battery, the cathode electrode potential V before the pulse test in the preset mode two-stage test is recorded1+ and anode electrode potential V1And the cathode electrode potential V after the pulse test2+ and anode electrode potential V2-, and the pulse current I0Then, according to a preset first calculation formula, calculating to obtain the cathode impedance R + and the anode impedance R-of the three-electrode battery in the first preset mode two-stage test;
secondly, recording the cathode electrode potential V before the pulse test in the preset system two-stage test for each cycle stage charge-discharge test1+ and anode electrode potential V1And the cathode electrode potential V after the pulse test2+ and anode electrode potential V2-, and the pulse current I0；
Thirdly, calculating and obtaining cathode impedance R + and anode impedance R-according to a preset first calculation formula for each cycle stage charge-discharge test;
fourthly, calculating and obtaining the change rate of the cathode impedance and the change rate of the anode impedance in the charge-discharge test at the first cycle stage; calculating and obtaining the change rate of cathode impedance and the change rate of anode impedance of each cycle phase charge-discharge test except the first cycle phase charge-discharge test;
fifthly, correspondingly judging whether the impedance of the cathode or the anode is stable or not according to whether the change rate of the impedance of the cathode or the anode is smaller than a preset value or not, and correspondingly judging the main reason of the cycle attenuation of the battery when the impedance of the cathode or the anode is unstable;
in the first substep and the third substep of the first step, the preset first calculation formula specifically includes the following formula:
cathode impedance R + (V)2+－V1+)/I0；
Anode impedance R ═ V2-－V1-)/I0；
In the fourth step, the change rate of the cathode impedance and the change rate of the anode impedance in the charge-discharge test in the first cycle stage are calculated and obtained, specifically: for the first cycle stage charge-discharge test, performing subtraction operation on corresponding cathode impedance R + and anode impedance R-obtained after the charge-discharge test in the cycle stage and cathode impedance R + and anode impedance R-obtained in the first preset system two-stage test respectively to obtain cathode impedance variation and anode impedance variation, dividing the obtained cathode impedance variation by cathode impedance R + obtained in the first preset system two-stage test, and dividing the obtained anode impedance variation by anode impedance R-obtained in the first preset system two-stage test, so as to obtain the change rate of cathode impedance and the change rate of anode impedance obtained in the first cycle stage charge-discharge test;
in the fourth step, the change rate of the cathode impedance and the change rate of the anode impedance of each cycle phase charging and discharging test except the first cycle phase charging and discharging test are calculated and obtained, specifically: for each cycle phase charge-discharge test except the first cycle phase charge-discharge test, calculating the change rate of the cathode impedance and the change rate of the anode impedance compared with the previous cycle phase charge-discharge test according to a preset second calculation formula;
presetting a second calculation formula, which specifically comprises the following formula:
the rate of change Δ of the cathode impedance or anode impedance (R)(x+N)－Rx)/Rx；
Wherein, x is the sum of the number of charging and discharging tests executed in a cycle in a preset system one-stage test carried out by the charging and discharging tests of a plurality of previous cycle stages including the charging and discharging test of the previous cycle stage, namely the total number of the charging and discharging tests of the plurality of previous cycle stages ending to the previous cycle stage;
n is the number of times of charge and discharge tests circularly executed in the test of the preset system in one stage in the charge and discharge test of the cycle stage, and is the number of times of charge and discharge tests in one cycle stage;
Rxobtaining corresponding cathode impedance R + or anode impedance R-after the charge-discharge test in the previous cycle stage;
R(x+N)the obtained corresponding cathode impedance R + or anode impedance R-after the charge-discharge test in the cycle stage.
Compared with the prior art, the method for nondestructively analyzing the electrode impedance stability in the battery circulation process has the advantages that the design is scientific, the battery can be conveniently, quickly and reliably judged without damaging the battery, the impedance change of the cathode and the anode in the battery circulation process can be conveniently, quickly and reliably judged, the reason of the battery circulation failure (namely the circulation attenuation reason of the battery) can be quickly judged, whether the impedance of the cathode is increased or the impedance of the anode is increased is accurately judged, namely the stability of the cathode impedance and the anode impedance is judged, the attenuation reason of the battery can be favorably determined, the direction is indicated for the improvement of a battery system in the next step, and the method has great guiding significance.
Drawings
FIG. 1 is a flow chart of a method of non-destructive analysis of electrode impedance stability during battery cycling in accordance with the present invention;
FIG. 2 is a simplified schematic diagram of a three-electrode cell used in a method of non-destructive analysis of the stability of the impedance of the electrodes during cycling of the cell according to the present invention;
FIG. 3 is a graph illustrating the cycle capacity retention rate of a three-electrode battery in an embodiment of a method for non-destructive analysis of the stability of electrode impedance during battery cycling according to the present invention;
FIG. 4 is a graphical representation of the rate of change of the cathode impedance and the anode impedance for an exemplary embodiment of a method of the present invention for non-destructive analysis of the stability of the electrode impedance during cycling of a battery.
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 4, the present invention provides a method for non-destructive analysis of electrode impedance stability during battery cycling, comprising the steps of:
first, a three-electrode cell is constructed using a reference electrode, and first, the first substep is performed: performing a first preset system two-stage test on the three-electrode battery to obtain cathode impedance R + and anode impedance R-which are possessed by the three-electrode battery during the first preset system two-stage test, namely obtaining cathode impedance and anode impedance which are possessed by the three-electrode battery at an initial stage without starting the test;
then, a second substep is performed: performing a plurality of cycle stage charge and discharge tests, wherein each cycle stage charge and discharge test comprises a preset system one-stage test and a preset system two-stage test which are performed in sequence, the preset system one-stage test is a cycle test, and the preset system two-stage test is a pulse test;
in the first sub-step, in the first preset mode two-stage test of the three-electrode battery, the cathode electrode potential V before the pulse test in the preset mode two-stage test is recorded1+ and anode electrode potential V1And the cathode electrode potential V after the pulse test2+ and anode electrode potential V2-, and the pulse current I0Then, according to a preset first calculation formula, calculating to obtain the cathode impedance R + and the anode impedance R-of the three-electrode battery in the first preset mode two-stage test;
secondly, recording the cathode electrode potential V before the pulse test in the preset system two-stage test for each cycle stage charge-discharge test1+ and anode electrode potential V1And the cathode electrode potential V after the pulse test2+ and anode electrode potential V2-, and the pulse current I0；
Thirdly, calculating and obtaining cathode impedance R + and anode impedance R-according to a preset first calculation formula for each cycle stage charge-discharge test;
step four, calculating and obtaining the change rate of the cathode impedance and the change rate of the anode impedance in the charge-discharge test at the first cycle stage; calculating and obtaining the change rate of cathode impedance and the change rate of anode impedance of each cycle phase charge-discharge test except the first cycle phase charge-discharge test;
fifthly, correspondingly judging whether the impedance of the cathode or the anode is stable or not according to whether the change rate of the impedance of the cathode or the anode is smaller than a preset value or not, and correspondingly judging the main reason of the cycle attenuation of the battery when the impedance of the cathode or the anode is unstable;
in the fourth step, the change rate of the cathode impedance and the change rate of the anode impedance in the charge-discharge test in the first cycle stage are calculated and obtained, specifically: for the first cycle stage charge and discharge test, performing subtraction operation on corresponding cathode impedance R + and anode impedance R-obtained after the charge and discharge test in the cycle stage and cathode impedance R + and anode impedance R-obtained in the first preset system two-stage test respectively to obtain cathode impedance variation and anode impedance variation, dividing the obtained cathode impedance variation by cathode impedance R + obtained in the first preset system two-stage test, and dividing the obtained anode impedance variation by anode impedance R-obtained in the first preset system two-stage test, thereby obtaining the cathode impedance variation rate and the anode impedance variation rate obtained in the first cycle stage charge and discharge test;
in the fourth step, the change rate of the cathode impedance and the change rate of the anode impedance of each cycle phase charging and discharging test except the first cycle phase charging and discharging test are calculated and obtained, specifically: and for each cycle phase charge and discharge test except the first cycle phase charge and discharge test, calculating the change rate of the cathode impedance and the change rate of the anode impedance compared with the previous cycle phase charge and discharge test according to a preset second calculation formula.
In the first step, the three-electrode battery may be a lithium ion, sodium ion or potassium ion battery.
In the first step, the reference electrode may be one of a lithium plate, a platinum electrode or a calomel electrode.
In a first step, a three electrode cell includes a cathode, an anode, and a reference electrode.
In the first step, in the three-electrode battery, the active material of the cathode may be commercial lithium electrode active material, sodium electrode active material, potassium electrode active material, or the like, and the active material of the anode may be carbon material such as artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, or hard carbon, silicon carbon, metal oxide material, or the like.
In the first step, each cycle phase charge-discharge test specifically comprises the following operations:
first, a preset system one-stage test (i.e., a cycle test) is performed: circularly executing preset n times of charge-discharge tests, wherein the value range of n is 10-100;
then, sleep is preset for a sleep duration t1，t1The value range is 2 h-5 h;
then, a preset system two-stage test (i.e., a pulse test) is performed: the discharge test is performed once in advance, and the number of discharge tests is not counted in the total number of cycles.
In the first step, each charge and discharge test in the preset standard one-stage test (namely, the cycle test) specifically comprises the following operations:
firstly, the three-electrode battery is applied with a first current I with a preset magnitude1(e.g., 0.5C, C being the battery capacity) constant current charging to a preset upper cut-off voltage (e.g., 4.20V);
then, the current charged to the three-electrode cell at a constant voltage with a preset upper cut-off voltage (e.g., 4.2V) is equal to a second current I of a preset magnitude2(e.g., 0.02C);
then, after standing for a preset time (e.g., 10 minutes), a first current I is applied1(e.g. 0.5C) constant current discharge to a preset lower limit cut-offVoltage (e.g., 2.5V).
In the first step, a standard two-stage test (i.e. a pulse test) is preset, and the method specifically comprises the following operations:
continuously performing pulse test on the three-electrode battery subjected to the one-stage test (namely, the cycle test) in the preset mode, namely, performing pulse current I with a preset magnitude0(e.g., 5C), constant current discharge preset pulse duration t2(e.g., 10 s).
In the first step, the pulse current I in the two-stage test is preset0The value range is I1～50I1。
In the first step, the preset pulse duration t in the two-stage test of the system is preset2The value range is 0.1 s-180 s.
In a second step, the cathode electrode potential has a value equal to the potential difference between the cathode and a reference electrode (e.g., a lithium metal reference electrode); the anode electrode potential is of a magnitude equal to the potential difference between the anode and a reference electrode, such as a lithium metal reference electrode.
In the first and third substeps of the first step, the first calculation formula is preset to obtain the cathode impedance R + and the anode impedance R-for the calculation, and specifically includes the following formula:
cathode impedance R + (V)2+－V1+)/I0；
Anode impedance R ═ V2-－V1-)/I0；
Wherein, V1+ and V2+, respectively representing the cathode electrode potentials before and after the pulse test in the preset system two-stage test; v1-and V2Respectively representing the anode electrode potentials before and after the pulse test in the preset system two-stage test, I0Representing the pulse current in the preset system two-stage test.
In the fourth step, in order to calculate the change rate of the cathode impedance and the change rate of the anode impedance, a second calculation formula is preset, which specifically includes the following formula:
the rate of change Δ of the cathode impedance or anode impedance (R)(x+N)－Rx)/Rx；
Wherein, x is the sum of the number of charging and discharging tests executed in a cycle in a preset system one-stage test carried out by the charging and discharging tests of a plurality of previous cycle stages including the charging and discharging test of the previous cycle stage, namely the total number of the charging and discharging tests of the plurality of previous cycle stages ending to the previous cycle stage;
n is the number of times of charge and discharge tests circularly executed in the test of the preset system in one stage in the charge and discharge test of the cycle stage, and is the number of times of charge and discharge tests in one cycle stage;
Rxobtaining the corresponding cathode impedance R + or anode impedance R- (obtained according to the third step) after the charge-discharge test at the previous cycle stage;
R(x+N)obtaining the corresponding cathode impedance R + or anode impedance R- (obtained according to the third step) after the charge-discharge test at the cycle stage;
in the fourth step, the change rate of the cathode impedance and the change rate of the anode impedance are calculated according to a preset second calculation formula, whether the cathode impedance or the anode impedance is stable is correspondingly judged according to whether the change rate of the cathode impedance or the anode impedance is smaller than a preset value (for example, 2.5%), and when the cathode impedance or the anode impedance is unstable, the cathode impedance or the anode impedance is a main cause of the cycle attenuation of the battery, for example, when the cathode impedance or the anode impedance is larger than or equal to the preset value, the cathode impedance or the anode impedance is judged to be unstable; and when the value is less than the preset value, the stability is judged.
Based on the technical scheme, the reference electrode is introduced into the battery, the electrode potentials of the cathode and the anode of the battery are monitored, and the impedance change of the cathode and the anode is further calculated, so that the main reason of the cycle attenuation of the battery can be monitored without disassembling the battery, and whether the main reason is caused by the impedance increase of the cathode or the impedance increase of the anode is accurately judged.
The invention relates to a method for nondestructively analyzing the stability of electrode impedance in the battery circulation process, which comprises the steps of firstly constructing a three-electrode battery system by using a reference electrode, monitoring the potential difference between a cathode and an anode relative to the reference electrode along with the change of battery pulse, and reflecting the cathode impedance and the anode impedance by using the ratio of the cathode electrode potential and the anode electrode potential to the applied pulse current. The main reason of the cycle failure of the battery is judged by analyzing the impedance changes of the cathode and the anode.
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.
Firstly, a three-electrode battery is manufactured. The specific manufacturing process of the three-electrode battery is as follows:
1. manufacturing a cathode plate: mixing a nickel-cobalt-manganese NCM ternary material, a conductive agent (such as carbon nano tube or carbon black) and polyvinylidene fluoride according to a mass ratio of 94: 2: and 4, homogenizing, coating, rolling and shearing to obtain the cathode sheet.
2. Manufacturing an anode sheet: mixing artificial graphite, a conductive agent (such as acetylene black), sodium carboxymethyl cellulose and a binder (such as styrene butadiene rubber) according to a mass ratio of 96.5: 1: 1: and 1.5, homogenizing, coating, rolling and shearing to obtain the anode sheet.
3. Preparing a three-electrode battery:
referring to fig. 2, a lithium ion three-electrode battery according to the present invention includes a battery case 1, a cathode 2, an anode 3, and a reference electrode 4. The cathode 2, the anode 3 and the reference electrode 4 are sequentially placed, assembled and packaged in the battery shell 1, the diaphragms 5 are respectively arranged between the cathode 2 and the anode 3 and between the anode 3 and the reference electrode 4, and the reference electrode tab 40 of the reference electrode 4, the cathode tab 20 of the cathode 2 and the anode tab 30 of the anode 3 are respectively led out of the battery shell 1.
The three-electrode battery requires a sufficient electrolyte, which may include a lithium salt, which may include lithium hexafluorophosphate LiPF, and an anhydrous organic solvent6Lithium hexafluorophosphate LiPF in the electrolyte6The molar concentration of (a) is 1.0 mol/L; the anhydrous organic solvent comprises propylene carbonate PC, ethylene carbonate EC and ethyl methyl carbonate EMC, and the volume ratio of the propylene carbonate PC to the ethylene carbonate EC to the ethyl methyl carbonate EMC 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.
And secondly, analyzing the impedance change of the cathode and the anode, wherein the capacity retention rate of the ternary/graphite soft package battery cell (model SP4360143) is 83% (figure 3) after 630 times of 1C/1C circulation.
1. And manufacturing a three-electrode battery cell, and carrying out a circulation and pulse 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 mode one-stage test (namely a circulating mode): charging to 4.2V at constant current of 1C, charging to 0.05C at constant voltage of 4.2V, standing for 10min, and discharging to 2.5V at constant current of 1C. Two-stage testing (namely pulse mode) of a preset mode: 5C discharge for 10 s.
The first step of the invention is carried out as follows:
first, a first substep is performed: executing a preset system two-stage test on the three-electrode cell to obtain the 0 th cycle pulse data of the three-electrode cell (namely the initial and original pulse data of the three-electrode cell when the test operation is not started, namely the cathode impedance and the anode impedance of the three-electrode cell at the initial stage when the test operation is not started), and recording the data as 0;
it should be noted that, specifically, the cathode electrode potential V before the pulse test in the preset system two-stage test can be recorded1+ and anode electrode potential V1And the cathode electrode potential V after the pulse test2+ and anode electrode potential V2-, and the pulse current I0Then, calculating to obtain cathode impedance R + and anode impedance R-according to a preset first calculation formula;
then, a second substep is performed: the method comprises the following specific steps:
(1) and carrying out a plurality of cycle stage charge and discharge tests: testing at one stage according to a preset standard, cycling to 50 weeks, and sleeping for 3 h. The charge and discharge were tested in two stages according to the preset standard, and the 50 th cycle pulse data (including the cathode impedance and the anode impedance) was obtained and recorded as data 1.
(2) And continuing to perform a plurality of cycle stage charge and discharge tests: and continuously performing a stage of test according to a preset standard, performing a cycle test, and sleeping for 3 hours after the cycle is performed to the 100 th week. And (3) carrying out charge and discharge according to a preset standard two-stage test to obtain pulse data (including cathode impedance and anode impedance) of the 100 th cycle, and recording the pulse data as data 2.
(3) And continuing to perform a plurality of cycle stage charge and discharge tests: and continuously performing a stage of test according to a preset standard, performing a cycle test, and sleeping for 3 hours after the cycle is circulated to the 150 th week. And (3) carrying out charging and discharging according to a preset standard two-stage test to obtain pulse data (including cathode impedance and anode impedance) of the 150 th cycle, and recording the pulse data as data 3.
(4) The cycle phase is continued for a plurality of times (each cycle phase includes a plurality of cycle phase charge and discharge tests), and pulse data 4, data 5, data 6 … … are collected to data 12 (including cathode impedance and anode impedance).
2. And (4) processing data of the pulse test.
First, electrode potentials and currents of the cathode, anode of data 0, data 1, data 2, data 3 … … to data 12 are extracted.
Next, when 0 week, 50 weeks, 100 weeks, 150 weeks … … -600 weeks were calculated, respectively, the cathode and anode impedances under the standard two-stage test were as shown in table 1, the cathode and anode impedance change rates were calculated, and the relationship curves between the cathode and anode impedance change rates and the cycle number were plotted as shown in fig. 4.
Table 1 is a schematic representation of the cathode impedance and anode impedance values during cycling in an embodiment of a method for non-destructive analysis of the stability of the electrode impedance during cycling of a battery according to the present invention.
Table 1:
and finally, qualitatively analyzing the main reasons of the cycle degradation of the battery according to the impedance change rates of the cathode and the anode.
Reference judgment basis: when a plurality of sets are formed by the change rates delta of the pulse electrode impedance (cathode impedance or anode impedance) in different cycle phases, if the element delta in each set is less than or equal to 2.5% (2.5% is set for the battery system in the embodiment and is an empirical value, specifically, a plurality of deltas with the number of all deltas being 95% are selected, and then an average value is obtained, for example, 95 deltas in 100 deltas are obtained, and the difference between any two deltas is less than 2% or other preset proportion), it is considered that no significant impedance increase occurs in the corresponding electrode material; otherwise, there is a significant impedance increase of the corresponding electrode material.
Referring to fig. 4, the cycle number is used as an abscissa, the pulse electrode impedance change rate (i.e., the cathode impedance change rate) Δ of the cathode is used as an ordinate, and a pulse electrode impedance change rate curve of the cathode is drawn, as can be seen from fig. 4, the change of the pulse electrode impedance change rate curve of the whole cathode is small, and Δ is less than or equal to 2.5%, which proves that the cathode maintains better stability in the cycle process.
Referring to fig. 4, in a similar manner, a pulse electrode impedance contrast analysis was performed on the anode to plot the rate of change of the pulse electrode impedance of the anode, and as seen from the graph in fig. 4, the rate of change of the pulse electrode impedance at week 350 relative to week 300 was 13.2%, which was greater than 2.5%, indicating that a significant impedance increase occurred at the anode, i.e., the cycling failure of the battery was caused by an excessive increase in the anode impedance.
In summary, compared with the prior art, the method for nondestructively analyzing the electrode impedance stability in the battery cycle process provided by the invention has scientific design, can conveniently, quickly and reliably judge the impedance change of the cathode and the anode in the battery cycle process without damaging the battery, quickly judge the reason of the battery cycle failure (namely the cycle attenuation reason of the battery), and accurately judge whether the impedance of the cathode or the anode is increased, namely judge the stability of the cathode impedance and the anode impedance, is favorable for determining the attenuation reason of the battery, indicates the direction for the improvement of the battery system in the next step, and has great guiding significance.
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 (7)
1. A method for nondestructively analyzing the stability of the impedance of an electrode in the cycling process of a battery is characterized by comprising the following steps:
first, a three-electrode cell is constructed using a reference electrode, and first, the first substep is performed: performing a first preset system two-stage test on the three-electrode battery to obtain cathode impedance R + and anode impedance R-of the three-electrode battery during the first preset system two-stage test;
then, a second substep is performed: performing a plurality of cycle stage charge and discharge tests, wherein each cycle stage charge and discharge test comprises a preset system one-stage test and a preset system two-stage test which are performed in sequence, the preset system one-stage test is a cycle test, and the preset system two-stage test is a pulse test;
in the first sub-step, in the first preset mode two-stage test of the three-electrode battery, the cathode electrode potential V before the pulse test in the preset mode two-stage test is recorded1+ and anode electrode potential V1And the cathode electrode potential V after the pulse test2+ and anode electrode potential V2-, and the pulse current I0Then, according to a preset first calculation formula, calculating to obtain the cathode impedance R + and the anode impedance R-of the three-electrode battery in the first preset mode two-stage test;
secondly, recording the cathode electrode potential V before the pulse test in the preset system two-stage test for each cycle stage charge-discharge test1+ and anode electrode potential V1And the cathode electrode potential V after the pulse test2+ and anode electrode potential V2-, and the pulse current I0；
Thirdly, calculating to obtain cathode impedance R + and anode impedance R-according to a preset first calculation formula for each cycle stage charge-discharge test;
fourthly, calculating and obtaining the change rate of the cathode impedance and the change rate of the anode impedance in the charge-discharge test at the first cycle stage; calculating and obtaining the change rate of cathode impedance and the change rate of anode impedance of each cycle phase charge-discharge test except the first cycle phase charge-discharge test;
fifthly, correspondingly judging whether the impedance of the cathode or the anode is stable or not according to whether the change rate of the impedance of the cathode or the anode is smaller than a preset value or not, and correspondingly judging the main reason of the cycle attenuation of the battery when the impedance of the cathode or the anode is unstable;
in the first substep and the third substep of the first step, the preset first calculation formula specifically includes the following formula:
cathode impedance R + (V)2+－V1+)/I0；
Anode impedance R ═ V2-－V1-)/I0；
In the fourth step, the change rate of the cathode impedance and the change rate of the anode impedance in the charge-discharge test in the first cycle stage are calculated and obtained, specifically: for the first cycle stage charge-discharge test, performing subtraction operation on corresponding cathode impedance R + and anode impedance R-obtained after the charge-discharge test in the cycle stage and cathode impedance R + and anode impedance R-obtained in the first preset system two-stage test respectively to obtain cathode impedance variation and anode impedance variation, dividing the obtained cathode impedance variation by cathode impedance R + obtained in the first preset system two-stage test, and dividing the obtained anode impedance variation by anode impedance R-obtained in the first preset system two-stage test, so as to obtain the change rate of cathode impedance and the change rate of anode impedance obtained in the first cycle stage charge-discharge test;
in the fourth step, the change rate of the cathode impedance and the change rate of the anode impedance of each cycle phase charging and discharging test except the first cycle phase charging and discharging test are calculated and obtained, specifically: for each cycle phase charge-discharge test except the first cycle phase charge-discharge test, calculating the change rate of the cathode impedance and the change rate of the anode impedance compared with the previous cycle phase charge-discharge test according to a preset second calculation formula;
presetting a second calculation formula, which specifically comprises the following formula:
impedance of cathodeOr the rate of change Δ of the anode impedance (R)(x+N)－Rx)/Rx；
Wherein, x is the sum of the number of charging and discharging tests executed in a cycle in a preset system one-stage test carried out by the charging and discharging tests of a plurality of previous cycle stages including the charging and discharging test of the previous cycle stage, namely the total number of the charging and discharging tests of the plurality of previous cycle stages ending to the previous cycle stage;
n is the number of times of charge and discharge tests circularly executed in the test of the preset system in one stage in the charge and discharge test of the cycle stage, and is the number of times of charge and discharge tests in one cycle stage;
Rxobtaining corresponding cathode impedance R + or anode impedance R-after the charge-discharge test in the previous cycle stage;
R(x+N)the obtained corresponding cathode impedance R + or anode impedance R-after the charge-discharge test in the cycle stage.
2. The method for non-destructive analysis of electrode impedance stability during battery cycling according to claim 1, wherein a three-electrode battery comprises a battery case (1), a cathode (2), an anode (3), and a reference electrode (4);
the cathode (2), the anode (3) and the reference electrode (4) are sequentially placed, assembled and packaged in the battery shell (1);
diaphragms (5) are respectively arranged between the cathode (2) and the anode (3) and between the anode (3) and the reference electrode (4);
a reference electrode tab (40) of the reference electrode (4), a cathode tab (20) of the cathode (2) and an anode tab (30) of the anode (3) are respectively led out of the battery shell (1);
and the reference electrode is one of a lithium sheet, a platinum electrode or a calomel electrode.
3. The method for the non-destructive analysis of the stability of the impedance of the electrodes during cycling of a battery according to claim 1, wherein in the first step, the charge-discharge test for each cycle phase comprises the following operations:
firstly, executing a preset system one-stage test: circularly executing preset n times of charge-discharge tests, wherein the value range of n is 10-100;
then, sleep is preset for a sleep duration t1，t1The value range is 2 h-5 h;
then, executing a preset system two-stage test: the discharge test is performed once in advance, and the number of discharge tests is not counted in the total number of cycles.
4. The method for the non-destructive analysis of the stability of the impedance of the electrode during the battery cycling process according to claim 3, wherein in the first step, each charge-discharge test in the standard one-stage test is preset, comprising the following operations:
firstly, the three-electrode battery is applied with a first current I with a preset magnitude1Charging to a preset upper limit cut-off voltage by constant current;
then, the three-electrode battery is charged to a current equal to a second current I with a preset magnitude at a preset upper limit cut-off voltage in a constant voltage mode2；
Then, after standing for a preset time, a first current I is applied1And discharging the constant current to a preset lower limit cut-off voltage.
5. The method for non-destructive analysis of the impedance stability of an electrode during battery cycling as recited in claim 4, wherein in the first step, a standard two-stage test is preset, comprising in particular the operations of:
continuously performing pulse test on the three-electrode battery subjected to the one-stage test of the preset system, namely, using a pulse current I with a preset magnitude0Constant current discharge preset pulse duration t2。
6. The method for the non-destructive analysis of the stability of the impedance of an electrode during battery cycling according to claim 5, wherein in the first step, the pulse current I in the standard two-stage test is preset0The value range is I1～50I1；
In the first step, in the preset mode two-stage testIs preset pulse duration t2The value range is 0.1 s-180 s.
7. A method for non-destructive analysis of the stability of the impedance of an electrode during cycling of a cell according to any one of claims 1 to 6, wherein, in the second step, the value of the cathode electrode potential is equal to the potential difference between the cathode and the reference electrode;
the anode electrode potential has a value equal to the potential difference between the anode and the reference electrode.
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