Lithium battery positive and negative electrode capacity decay rate analysis method and system

Abstract

The present invention belongs to the field of lithium battery testing technology, and discloses a method and system for analyzing the capacity decay rate of the positive and negative electrodes of a lithium battery, including: obtaining the voltage and capacity data of a fresh battery during the first charging process, and obtaining a first relationship curve corresponding to the differential of the voltage to the capacity and the capacity; obtaining the voltage and capacity data during the recharging process of an aged battery, and obtaining a second relationship curve corresponding to the differential of the voltage to the capacity and the capacity; comparing the completeness of the groove figure appearing on the rightmost side of the first relationship curve and the second relationship curve, and obtaining the size relationship between the capacity decay rate of the negative electrode of the lithium battery and the capacity decay rate of the positive electrode of the lithium battery. The method of the present invention has high accuracy in qualitatively judging the capacity decay rate of the positive and negative electrodes of the lithium battery, and the analysis operation process is simple, and can be widely used in the research of lithium batteries using high-nickel ternary positive electrode materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery testing, and in particular relates to a method and system for analyzing the capacity attenuation rate of positive and negative electrodes of a lithium battery. Background Art

[0002] Lithium batteries are composed of positive electrodes, negative electrodes and other auxiliary materials. As the battery is charged and discharged, the capacity of the positive and negative electrodes of the battery will gradually decrease. During the development of the battery, the positive or negative electrode with poor cycle performance needs to be replaced to improve the overall cycle performance of the battery. At this time, it is necessary not only to determine whether the capacity of the positive and negative electrodes in the battery has decayed, but also to be able to further determine the rate of capacity decay of the positive and negative electrodes. At present, it is usually necessary to disassemble the battery and measure the capacity of the positive and negative electrode materials to determine which of the positive and negative electrode capacities decays faster; this method is complicated to operate, inefficient, and difficult to achieve accurate analysis. Summary of the invention

[0003] The purpose of the present invention is to provide a method for analyzing the capacity decay rate of the positive and negative electrodes of a lithium battery, so as to accurately analyze the capacity decay rate of the positive and negative electrodes of a lithium battery without disassembling the battery.

[0004] The present invention is achieved through the following technical solutions:

[0005] The analysis method of capacity decay rate of positive and negative electrodes of lithium batteries includes:

[0006] Acquire voltage and capacity data of a fresh battery during a first charging process, and obtain a first relationship curve corresponding to the differential of voltage to capacity and capacity based on the acquired voltage and capacity data;

[0007] Acquiring voltage and capacity data of an aged battery during recharging, and obtaining a second relationship curve corresponding to the differential of voltage to capacity and capacity according to the acquired voltage and capacity data, wherein the aged battery is a battery discharged to a voltage lower than a set voltage after cyclic charge and discharge of a fresh battery;

[0008] By comparing the completeness of the groove pattern appearing on the rightmost side of the first relationship curve and the second relationship curve, the magnitude relationship between the capacity decay rate of the negative electrode of the lithium battery and the capacity decay rate of the positive electrode of the lithium battery is obtained.

[0009] In some embodiments, when the completeness of the groove pattern of the first relationship curve is higher than the completeness of the groove pattern of the second relationship curve, the capacity decay rate of the negative electrode of the lithium battery is greater than the capacity decay rate of the positive electrode; and / or

[0010] When the degree of integrity of the groove pattern of the second relationship curve is higher than that of the groove pattern of the first relationship curve, the capacity decay rate of the positive electrode of the lithium battery is greater than the capacity decay rate of the negative electrode; and / or

[0011] When the completeness of the groove patterns of the first relationship curve and the second relationship curve is the same or the difference in the completeness is within a set value range, the capacity decay rates of the positive electrode and the negative electrode of the lithium battery are the same;

[0012] The completeness of the groove pattern refers to the difference between the ordinates of the left end point and the right end point of the groove pattern. The smaller the difference between the ordinates of the groove pattern, the higher its completeness.

[0013] In some embodiments, the fresh battery uses a high-nickel ternary positive electrode material, and the content of Ni in the high-nickel ternary positive electrode material accounts for no less than 80% of the total of Ni, Co, and Mn in molar ratio.

[0014] In some embodiments, the charge cutoff voltage for charging a fresh battery for the first time and for charging an aged battery after discharge is the same, and the charge cutoff voltage is not less than 4.1V.

[0015] In some embodiments, the charging cut-off voltage is 4.2V-4.3V.

[0016] In some embodiments, the battery is discharged to less than 4V after the cyclic charge and discharge.

[0017] In some embodiments, when the voltage of the battery after cyclic charge and discharge is lower than a set voltage, the battery in the current state is regarded as an aged battery.

[0018] In some embodiments, the horizontal coordinate difference between the left end point and the right end point of the groove pattern is not less than 1% SOC, where SOC is a percentage of battery capacity.

[0019] In some embodiments, the charge rate used for charging the fresh battery for the first time and for charging the aged battery after discharge is the same, and the charge rate is less than 0.5C.

[0020] On the other hand, the present invention also provides a lithium battery positive and negative electrode capacity decay rate analysis system, comprising:

[0021] A first curve acquisition unit, the first curve acquisition unit is used to obtain a first relationship curve corresponding to the differential of voltage to capacity and the capacity according to the acquired voltage and capacity data of the fresh battery during the first charging process;

[0022] a second curve acquisition unit, the second curve acquisition unit being used to obtain a second relationship curve corresponding to the differential of voltage to capacity and capacity according to the acquired voltage and capacity data of the aged battery during the recharging process, wherein the aged battery is a battery discharged to a voltage lower than a set voltage after cyclic charge and discharge of a fresh battery;

[0023] The decay rate analysis unit is used to compare the completeness of the groove pattern appearing on the rightmost side of the first relationship curve and the second relationship curve, and analyze the capacity decay rate of the positive and negative electrodes of the lithium battery according to the comparison result.

[0024] In some embodiments, the decay rate analysis unit is used to respectively obtain the vertical coordinate difference between the left end point and the right end point of the groove graphics on the first relationship curve and the second relationship curve, and analyze the capacity decay rate of the positive and negative electrodes of the lithium battery based on the comparison result of the vertical coordinate difference of the groove graphics.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] When studying batteries using high-nickel ternary positive electrode materials, it was found that when the battery is charged to a certain voltage, a reaction platform will appear on the voltage-capacity curve. The reaction platform is reflected as a groove pattern on the corresponding voltage-capacity differential-capacity curve, and the completeness of the groove pattern is related to the decay rate of the battery's positive and negative electrode capacities. Based on this discovery, the present invention obtains the relationship curve between the voltage-capacity differential and capacity of fresh batteries and aging batteries after cycles during the charging process, and compares the groove patterns on the curves. Without disassembling the battery, the present invention realizes the analysis of the capacity decay rate of the positive and negative electrodes of the lithium battery, and can quickly determine which of the positive and negative electrodes of the lithium battery decays faster.

[0027] The experiment proves that the method of the present invention has high accuracy in qualitatively judging the capacity decay rate of the positive and negative electrodes of lithium batteries, and the analysis operation process is simple, and can be widely used in the research of lithium batteries using high-nickel ternary positive electrode materials and having similar characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1Schematic diagram of the completeness of the groove pattern in an embodiment of the present invention; in the figure, H1 is the height value of the left end point of the groove pattern, H2 is the height value of the right end point of the groove pattern, ∆H is the height difference between the left end point and the right end point, and A, B, C, and D correspond to the numbers of the groove patterns respectively.

[0030] Figure 2 is a schematic diagram of the first relationship curve in Example 1 of the present invention; in the figure, the ordinate It is the differential of voltage with respect to capacity, the horizontal axis is capacity Q, and the dotted box is the groove figure that appears at the far right end of the curve.

[0031] Figure 3 is a schematic diagram of the second relationship curve in Example 1 of the present invention; in the figure, the ordinate It is the differential of voltage with respect to capacity, the horizontal axis is capacity Q, and the dotted box is the groove figure that appears at the far right end of the curve.

[0032] Figure 4 is a schematic diagram of the first relationship curve in Example 2 of the present invention; in the figure, the ordinate It is the differential of voltage with respect to capacity, the horizontal axis is capacity Q, and the dotted box is the groove figure that appears at the far right end of the curve.

[0033] Figure 5 is a schematic diagram of the second relationship curve in Example 2 of the present invention; in the figure, the ordinate It is the differential of voltage with respect to capacity, the horizontal axis is capacity Q, and the dotted box is the groove figure that appears at the far right end of the curve. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0035] At present, when analyzing the capacity decay rate of the positive and negative electrodes of a battery, the battery is usually disassembled after cyclic charge and discharge, and the positive and negative electrodes are then remade into button-type half-cells. The capacities of the positive and negative electrodes are measured and compared with their initial capacities to obtain the decay rate, in order to determine which of the positive and negative electrodes decays faster.

[0036] Obviously, this testing method requires repeated disassembly, assembly and testing of the battery, which not only has low operating efficiency, but the quality of disassembly and assembly will affect the capacity measurement results, thereby affecting the accuracy of the test results.

[0037] The present invention provides a method that can be applied to analyzing the capacity decay rate of positive and negative electrodes of a lithium battery using a high-nickel positive electrode material. The capacity decay rate of the positive and negative electrodes can be analyzed and judged without disassembling the battery.

[0038] The high-nickel positive electrode material in the present invention refers to a material in which the molar ratio of nickel is not less than 80%.

[0039] The study found that when the above-mentioned lithium battery is charged to above 4.1V, a reaction platform will appear on the voltage and capacity curve. By differentiating the voltage with respect to the capacity, the relationship between the differential of the voltage with respect to the capacity and the capacity will appear as a groove shape on the far right of the curve.

[0040] Through further research on the groove pattern, it was found that when the battery uses different negative electrode materials, there will be certain differences in the groove patterns in the above relationship curve obtained by the fresh battery and the cycled battery. Through a large number of experiments, the rules and characteristics of the groove patterns on the above relationship curve were found.

[0041] It was found that when the decay rate of the positive electrode of the battery is greater than the decay rate of the negative electrode, the completeness of the groove figure in the relationship curve corresponding to the cycled battery is higher than the groove figure in the relationship curve corresponding to the fresh battery; and when the decay rate of the negative electrode of the battery is greater than the decay rate of the positive electrode, the completeness of the groove figure in the relationship curve corresponding to the fresh battery is higher than the groove figure in the relationship curve corresponding to the cycled battery.

[0042] Based on the above findings, the method for analyzing the capacity decay rate of the positive and negative electrodes of a lithium battery is obtained by applying the findings to the judgment of the capacity decay rate of the positive and negative electrodes of a lithium battery.

[0043] In some embodiments of the present invention, a method for analyzing the capacity decay rate of positive and negative electrodes of a lithium battery includes:

[0044] Charging a fresh battery for the first time, acquiring voltage and capacity data during the charging process, and obtaining a first relationship curve corresponding to the differential of voltage to capacity and the capacity based on the acquired voltage and capacity data;

[0045] The fresh battery is charged and discharged cyclically to obtain an aged battery;

[0046] Discharging the aged battery after cyclic charge and discharge to a voltage lower than a set voltage, recharging the discharged aged battery, acquiring voltage and capacity data during the recharging process, and obtaining a second relationship curve corresponding to the differential of voltage to capacity and capacity based on the acquired voltage and capacity data;

[0047] By comparing the completeness of the groove figures appearing on the far right of the first relationship curve and the second relationship curve, the relationship between the capacity decay rate of the negative electrode of the lithium battery and the capacity decay rate of the positive electrode of the lithium battery is obtained, and the capacity decay rates of the positive and negative electrodes of the lithium battery are analyzed.

[0048] The method of this embodiment is applicable to lithium batteries using high-nickel positive electrode materials, wherein the high-nickel positive electrode material refers to a high-nickel ternary positive electrode material in which the content of Ni relative to the total of Ni, Co, and Mn in molar ratio is not less than 80%.

[0049] The fresh battery here refers to the battery that has not been cycled.

[0050] When the battery is charged by a charger and discharger, as the charging progresses, the battery capacity gradually increases and the battery voltage also gradually increases. There is a continuous, one-to-one relationship between the battery capacity and the voltage. Therefore, the voltage can be differentiated with respect to the capacity to obtain a relationship curve corresponding to the differential of the voltage with respect to the capacity and the capacity.

[0051] The voltage-to-capacity differential here refers to the differential processing of the measured voltage to capacity, which can be expressed as , where V is voltage, Q is capacity, and λ represents the differential of voltage to capacity. is the differential of voltage with respect to capacity.

[0052] The first relationship curve and the second relationship curve are curves obtained by taking the differential λ of voltage to capacity as the ordinate and taking the capacity Q as the abscissa.

[0053] In some embodiments, by comparing the completeness of the groove pattern appearing on the rightmost side of the first relationship curve and the second relationship curve, the capacity decay rate of the positive and negative electrodes of the lithium battery is analyzed, and the method used is:

[0054] When the completeness of the groove pattern of the first relationship curve is higher than the completeness of the groove pattern of the second relationship curve, it is determined that the capacity decay rate of the negative electrode of the lithium battery is greater than the capacity decay rate of the positive electrode.

[0055] When the degree of completeness of the groove pattern of the second relationship curve is higher than the degree of completeness of the groove pattern of the first relationship curve, it is determined that the capacity decay rate of the positive electrode of the lithium battery is greater than the capacity decay rate of the negative electrode.

[0056] When the integrity of the groove patterns of the first relationship curve and the second relationship curve is the same or the difference in the integrity of the two groove patterns is within the set value range, that is, the difference in the integrity between the two is not obvious, it is determined that the capacity decay rate of the positive electrode and the negative electrode of the lithium battery is the same.

[0057] Reference Figure 2 and Figure 3The completeness of the groove pattern refers to the difference between the ordinates of the left and right endpoints of the groove pattern. The smaller the difference between the ordinates of the groove pattern, the higher its completeness. The setting value for judging whether there is a significant difference between the two completenesses can be set according to the situation. For example, it is set to 5% of the difference between the ordinates of the highest point and the lowest point in the groove pattern of the first relationship curve. When the difference between the ordinates of the left and right endpoints of the two groove patterns is within the setting value range, it is judged that the difference in the completeness of the two groove patterns is not obvious, that is, the completeness of the two groove patterns is the same.

[0058] Or, Figure 1 Take the groove pattern shown in as an example, in which H1 is the height value (ordinate value) of the left end point of the groove pattern, H2 is the height value (ordinate value) of the right end point of the groove pattern, and ∆H is the height difference (ordinate difference) between the left end point and the right end point. Compare the height difference ∆H between the left end point and the right end point of the groove pattern. When ∆H is smaller, the groove pattern is more complete, and when ∆H is larger, the groove pattern is less complete. Therefore, from Figure 1 It can be seen that Figure A has the highest degree of completeness, followed by Figure B, Figure C, and Figure D has the lowest degree of completeness.

[0059] In some embodiments, the charge cutoff voltage for charging a fresh battery for the first time and charging an aged battery after discharge is the same, and the charge cutoff voltage is not less than 4.1 V. For example, the charge cutoff voltage can be set to any voltage within the range of 4.2 V-4.3 V.

[0060] In some embodiments, the above method steps discharge the aged battery after cyclic charge and discharge to below 4 V. When the voltage of the battery after cyclic charge and discharge is lower than the set voltage, such as lower than 4 V, it is not necessary to discharge, and the battery can be directly charged again.

[0061] In some embodiments, the horizontal coordinate difference between the left end point and the right end point of the groove pattern selected on the far right side of the curve should be no less than the capacity corresponding to 1% SOC, so as to eliminate the influence of the abnormal groove pattern formed on the curve due to the test voltage fluctuation on the analysis. SOC is the percentage of battery capacity. For example, when the overall capacity of the battery is 1Ah, 1% SOC is expressed as 0.01 Ah.

[0062] In some embodiments, the charge rate used for the first charge of a fresh battery and the recharge of an aged battery after discharge is the same, and the charge rate is set to be less than 0.5C to ensure that the battery polarization during the charging process can be eliminated as much as possible.

[0063] The fresh battery and the battery after cyclic charge and discharge in the embodiment of the present invention are all full batteries. Generally, in battery design, when the full battery is charged to 4.3V, the positive electrode potential is about 4.3V, the negative electrode potential is about 0V, and the voltage of the full battery is the difference between the positive electrode potential and the negative electrode potential. At this time, the curve corresponding to the full battery has a relatively complete groove pattern of the positive electrode.

[0064] During the battery cycle, if the positive electrode capacity decays quickly, the lithium ions released from the positive electrode are not enough to fill all the lithium insertion vacancies in the negative electrode. At this time, the potential of the negative electrode will increase relatively. When the charging cut-off voltage of the whole battery is set to remain unchanged, the potential of the positive electrode will also increase. As the positive electrode potential increases, the completeness of the groove pattern on the curve will become more complete. Therefore, the more complete the groove pattern is, the greater the decay rate of the positive electrode is.

[0065] On the contrary, if the capacity of the negative electrode decays faster and the positive electrode has not yet released all the lithium ions, the negative electrode potential will drop to about 0. As charging progresses, the negative electrode potential may further drop to a negative value. When the charging cut-off voltage of the full battery is set to remain unchanged, the potential of the positive electrode will also decrease due to the decrease in the potential of the negative electrode, and the completeness of the groove pattern on the curve will be more incomplete. Therefore, the more incomplete the groove pattern is, the greater the decay rate of the negative electrode is.

[0066] Based on the above principles, more importantly, the present invention provides a new idea that can realize the analysis of the capacity decay rate of the positive and negative electrodes of lithium batteries. The method of the present invention is not only applicable to lithium batteries using high-nickel ternary positive electrode materials, but also applicable to lithium batteries using other positive / negative electrode materials and having similar characteristics to the above.

[0067] The method of the present invention is described in detail below with reference to specific embodiments.

[0068] Example 1

[0069] S01. Prepare a fresh battery A, wherein the positive electrode material of the fresh battery A is a 9-series ternary positive electrode material (the molar ratio of nickel metal to the sum of nickel, cobalt and manganese metals is above 90%), and the negative electrode material is graphite;

[0070] S02, charging the fresh battery A for the first time, with the charging cut-off voltage being 4.3V, and recording the voltage and capacity data during the charging process;

[0071] S03, performing a certain number of cycles of charge and discharge on the fresh battery A;

[0072] S04, discharging the battery A after the cyclic charge and discharge to 3V;

[0073] S05, recharging the battery A after being discharged in step S04, and recording the voltage and capacity data during the charging process;

[0074] S06, performing a differential process on the voltage versus capacity tested in step S02, and drawing a relationship curve with the differential of the voltage versus capacity as the ordinate and the capacity as the abscissa, to obtain a first relationship curve, such as Figure 2 As shown;

[0075] S07, performing a differential process on the voltage versus capacity tested in step S05, and drawing a relationship curve with the differential of the voltage versus capacity as the ordinate and the capacity as the abscissa, to obtain a second relationship curve, such as Figure 3 As shown;

[0076] S08. Comparison Figure 2 and Figure 3 The completeness of the groove pattern on the far right can be seen Figure 3 The completeness of the groove pattern in Figure 2 From the groove pattern in the figure, it can be judged that the positive electrode capacity decay rate of the battery is greater than the negative electrode capacity decay rate.

[0077] Based on this analysis result, if we want to further improve the cycle life of battery A during the subsequent research and development process, we need to replace the positive electrode material with a more stable one with a lower capacity decay rate.

[0078] Example 2

[0079] S01, prepare a fresh battery B, wherein the positive electrode material of the fresh battery B is a 9-series ternary positive electrode material (the molar ratio of nickel metal to the sum of nickel, cobalt and manganese metals is above 90%), and the negative electrode material is a silicon-carbon negative electrode;

[0080] S02, charging the fresh battery B for the first time, with the charging cut-off voltage being 4.3V, and recording the voltage and capacity data during the charging process;

[0081] S03, performing a certain number of cycles of charge and discharge on the fresh battery B;

[0082] S04, discharging the battery B after the cyclic charge and discharge to 3V;

[0083] S05, recharging the battery B after being discharged in step S04, and recording the voltage and capacity data during the charging process;

[0084] S06, performing a differential process on the voltage versus capacity tested in step S02, and drawing a relationship curve with the differential of the voltage versus capacity as the ordinate and the capacity as the abscissa, to obtain a first relationship curve, such as Figure 4 As shown;

[0085] S07, performing a differential process on the voltage versus capacity tested in step S05, and drawing a relationship curve with the differential of the voltage versus capacity as the ordinate and the capacity as the abscissa, to obtain a second relationship curve, such as Figure 5 As shown;

[0086] S08. Comparison Figure 4 and Figure 5 The completeness of the groove pattern on the far right can be seen Figure 4 The completeness of the groove pattern in Figure 5 From the groove pattern in the figure, it can be judged that the capacity decay rate of the negative electrode of the battery is greater than that of the positive electrode.

[0087] Based on this analysis result, if we want to further improve the cycle life of Battery B during the subsequent research and development process, we need to replace the negative electrode material with a more stable one with a lower capacity decay rate.

[0088] Some embodiments of the present invention also relate to a lithium battery positive and negative electrode capacity decay rate analysis system, comprising:

[0089] A first curve acquisition unit, the first curve acquisition unit is used to obtain a first relationship curve corresponding to the differential of voltage to capacity and the capacity according to the voltage and capacity data of the fresh battery in the first charging process;

[0090] a second curve acquisition unit, the second curve acquisition unit being used to obtain a second relationship curve corresponding to the differential of voltage with respect to capacity and the capacity according to the voltage and capacity data acquired during the recharging process of the battery, wherein the battery is a battery discharged to a voltage lower than a set voltage after cyclic charge and discharge of a fresh battery;

[0091] The decay rate analysis unit is used to compare the completeness of the groove pattern appearing on the rightmost side of the first relationship curve and the second relationship curve, and analyze the capacity decay rate of the positive and negative electrodes of the lithium battery based on the comparison results.

[0092] Accordingly, in some embodiments, the attenuation rate analysis unit is used to obtain the ordinate difference between the left end point and the right end point of the groove graphics on the first relationship curve and the second relationship curve, respectively, and compare the ordinate difference of the groove graphics, and analyze the capacity attenuation rate of the positive and negative electrodes of the lithium battery based on the comparison results.

[0093] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0094] The above description shows and describes several preferred embodiments of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not depart from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for analyzing the capacity decay rate of positive and negative electrodes of lithium batteries, characterized in that: Lithium batteries use high-nickel positive electrode materials. High-nickel positive electrode materials refer to high-nickel ternary positive electrode materials in which the content of Ni is not less than 80% relative to the sum of Ni, Co, and Mn in molar ratio; including: The voltage and capacity data of a fresh battery during the first charging process are obtained, and a first relationship curve corresponding to the differential of the voltage to the capacity and the capacity is obtained according to the obtained voltage and capacity data; the charging cut-off voltage for the first charging of the fresh battery and the recharging of the aged battery after discharge are the same, and the charging cut-off voltage is not less than 4.1V; the fresh battery refers to a battery that has not been cycled; The voltage and capacity data of the aged battery during the recharging process are obtained, and a second relationship curve corresponding to the differential of the voltage to the capacity and the capacity is obtained according to the obtained voltage and capacity data, wherein the aged battery is a battery discharged to a voltage lower than a set voltage after cyclic charge and discharge of a fresh battery; the first relationship curve and the second relationship curve are curves obtained by taking the differential of the voltage to the capacity as the ordinate and the capacity as the abscissa, respectively; Compare the completeness of the groove pattern appearing on the rightmost side of the first relationship curve and the second relationship curve to obtain the magnitude relationship between the capacity decay rate of the negative electrode of the lithium battery and the capacity decay rate of the positive electrode of the lithium battery; When the degree of integrity of the groove pattern of the first relationship curve is higher than that of the groove pattern of the second relationship curve, the capacity decay rate of the negative electrode of the lithium battery is greater than the capacity decay rate of the positive electrode; When the degree of integrity of the groove pattern of the second relationship curve is higher than that of the groove pattern of the first relationship curve, the capacity decay rate of the positive electrode of the lithium battery is greater than the capacity decay rate of the negative electrode; When the completeness of the groove patterns of the first relationship curve and the second relationship curve is the same or the difference in the completeness is within a set value range, the capacity decay rates of the positive electrode and the negative electrode of the lithium battery are the same; The completeness of the groove pattern refers to the difference between the ordinates of the left end point and the right end point of the groove pattern. The smaller the difference between the ordinates of the groove pattern, the higher its completeness.

2. The method for analyzing the capacity decay rate of the positive and negative electrodes of a lithium battery according to claim 1, characterized in that: The battery after cyclic charge and discharge is discharged to below 4V.

3. The method for analyzing the capacity decay rate of the positive and negative electrodes of a lithium battery according to claim 1, characterized in that: When the voltage of the battery after cyclic charge and discharge is lower than the set voltage, the battery in the current state is regarded as an aged battery.

4. The method for analyzing the capacity decay rate of the positive and negative electrodes of a lithium battery according to claim 1, characterized in that: The horizontal coordinate difference between the left end point and the right end point of the groove pattern is not less than 1% SOC, where SOC is the percentage of battery capacity.

5. The method for analyzing the capacity decay rate of the positive and negative electrodes of a lithium battery according to claim 1, characterized in that: The charge rate used for the first charge of a fresh battery is the same as the charge rate used for the recharge of an aged battery after discharge, and the charge rate is less than 0.5C.

6. Lithium battery positive and negative electrode capacity decay rate analysis system, characterized in that: Lithium batteries use high-nickel positive electrode materials. High-nickel positive electrode materials refer to high-nickel ternary positive electrode materials in which the content of Ni is not less than 80% relative to the sum of Ni, Co, and Mn in molar ratio; including: a first curve acquisition unit, the first curve acquisition unit being used to obtain a first relationship curve corresponding to the differential of voltage to capacity and capacity according to the voltage and capacity data of the fresh battery during the first charging process; the charging cut-off voltage for the first charging of the fresh battery and the charging cut-off voltage for the recharging of the aged battery after discharge are the same, and the charging cut-off voltage is not less than 4.1V; the fresh battery refers to a battery that has not been subjected to cyclic charge and discharge; a second curve acquisition unit, the second curve acquisition unit being used to obtain a second relationship curve corresponding to the differential of voltage to capacity and capacity according to the voltage and capacity data acquired during the recharging process of the aged battery, wherein the aged battery is a battery discharged to a voltage lower than a set voltage after cyclic charge and discharge of a fresh battery; the first relationship curve and the second relationship curve are curves obtained by taking the differential of voltage to capacity as the ordinate and taking the capacity as the abscissa respectively; A decay rate analysis unit, the decay rate analysis unit is used to compare the completeness of the groove pattern appearing on the rightmost side of the first relationship curve and the second relationship curve, and analyze the capacity decay rate of the positive and negative electrodes of the lithium battery according to the comparison result; When the degree of integrity of the groove pattern of the first relationship curve is higher than that of the groove pattern of the second relationship curve, the capacity decay rate of the negative electrode of the lithium battery is greater than the capacity decay rate of the positive electrode; When the degree of integrity of the groove pattern of the second relationship curve is higher than that of the groove pattern of the first relationship curve, the capacity decay rate of the positive electrode of the lithium battery is greater than the capacity decay rate of the negative electrode; When the completeness of the groove patterns of the first relationship curve and the second relationship curve is the same or the difference in the completeness is within a set value range, the capacity decay rates of the positive electrode and the negative electrode of the lithium battery are the same; The completeness of the groove pattern refers to the difference between the ordinates of the left end point and the right end point of the groove pattern. The smaller the difference between the ordinates of the groove pattern, the higher its completeness.

7. The lithium battery positive and negative electrode capacity decay rate analysis system according to claim 6, characterized in that: The decay rate analysis unit is used to obtain the ordinate difference between the left end point and the right end point of the groove graphics on the first relationship curve and the second relationship curve, respectively, and analyze the capacity decay rate of the positive and negative electrodes of the lithium battery based on the comparison result of the ordinate difference of the groove graphics.

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