Analysis method for judging whether battery is overcharged or not

Abstract

The invention discloses an analysis method for judging whether a battery is overcharged or not. The analysis method comprises the following steps: acquiring a to-be-detected sample of a to-be-detected battery and a reference sample of a reference battery; the polar powder scraped from the to-be-detected sample and the reference sample is subjected to digestion and constant volume, the content of the target elements in the solution with the constant volume is measured, and the content values of the target elements of the to-be-detected sample and the reference sample are obtained through calculation; and judging whether the to-be-detected battery is overcharged or not based on a comparison result of the target element content values of the to-be-detected sample and the reference sample. According to the invention, by integrating the content analysis of the positive and negative lithium elements and related main elements, whether the battery is overcharged can be judged with low detection cost, data support is provided for the use boundary analysis of the battery, and the hidden danger of larger safety accidents is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery analysis, and in particular to an analysis method for judging whether a battery is overcharged. Background Art

[0002] Lithium-ion power batteries are subject to a variety of electrical abuse conditions during use. Overcharging is a common electrical abuse condition. Overcharging means that during the charging process, the battery voltage exceeds its normal operating voltage range due to various reasons, which has a negative impact on the safety and life of the battery. Overcharging can cause the collapse of the positive electrode material structure, which not only affects the performance of the battery, but may also cause thermal runaway of the battery and even cause safety accidents. Therefore, effective overcharge detection and analysis of power batteries is of great significance to ensure the safety and reliability of the battery.

[0003] Existing overcharge detection and analysis methods are mainly achieved by measuring battery parameters such as voltage, current and temperature, as well as through a battery management system (BMS). When the voltage, current or temperature of the battery exceeds the set threshold, the battery management system will activate the overcharge protection mechanism and stop charging to prevent the battery from overcharging. Some other studies use electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and other technologies to analyze the microstructure and electrochemical properties of overcharged batteries to understand the impact of overcharging on batteries. The atomic and nanoscale structure and composition of the battery pole piece can also be analyzed and observed through a spherical aberration electron microscope (HAADF) to determine whether the battery is overcharged. When a severely overcharged battery is fully charged and dissected, a uniform layer of lithium precipitation can be observed on the negative electrode surface with the naked eye.

[0004] Existing overcharge detection methods have some problems and limitations. First, these methods mainly rely on battery parameters such as voltage, current and temperature, which may be affected by many factors, such as battery aging, ambient temperature, etc., and large lithium deposition at the negative electrode may also be due to the low ambient temperature of the battery operating conditions, so it may not accurately reflect the true state of the battery. Secondly, although spherical aberration electron microscopy observation can provide more accurate judgment, it is complicated to operate and has high cost, and is not suitable for large-scale application.

[0005] Therefore, how to simply and accurately determine whether a battery is overcharged is an urgent problem to be solved in the current field of battery safety technology. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings and defects of the prior art and to provide an analysis method for determining whether a battery is overcharged.

[0007] An analysis method for determining whether a battery has been overcharged, comprising:

[0008] Step 1: Obtain a test sample of the test battery and a reference sample of the reference battery;

[0009] Step 2: Digest and fix the volume of the powder scraped from the sample to be tested and the reference sample, determine the content of the target element in the solution after fixing the volume, and calculate the content value of the target element in the sample to be tested and the reference sample;

[0010] Step 3: Based on the comparison result of the target element content values ​​of the sample to be tested and the reference sample, determine whether the battery to be tested is overcharged.

[0011] The target element is one or more of the main elements in the positive electrode material, and the main elements in the positive electrode material include but are not limited to lithium, nickel, iron, manganese, cobalt, and aluminum.

[0012] The target element content values ​​of the sample to be tested and the reference sample are calculated based on the mass of the powder used in the digestion and volume determination process, the target element content determination data in the solution, the final volume of the volume and the dilution multiple.

[0013] The target element content values ​​of the sample to be tested and the reference sample are obtained by calculation using the following formula:

[0014] X1=n*X0*N / m;

[0015] Wherein, m is the sampling mass of the positive / negative electrode powder of the sample to be tested / reference sample, N is the final volume, n is the dilution factor, X0 is the target element content in the solution, and X1 is the calculated target element content value of the positive / negative electrode of the sample to be tested / reference sample.

[0016] Wherein, judging whether the battery to be tested is overcharged based on the comparison result of the target element content values ​​of the sample to be tested and the reference sample includes:

[0017] First, it is determined whether the battery under test is abused; when it is determined that the battery under test is abused, it is determined whether the battery under test is overcharged.

[0018] Wherein, the step of determining whether the battery under test is subjected to electrical abuse comprises:

[0019] When it is determined whether the lithium content of the negative electrode of the sample to be tested is greater than the lithium content of the negative electrode of the reference sample, it is determined that there is electrical abuse in the use of the battery to be tested.

[0020] Wherein, the step of determining whether the battery to be tested is overcharged includes:

[0021] When the lithium element content of the positive electrode of the sample to be tested is lower than the lithium element content of the positive electrode of the reference battery, the molar ratio of lithium / elements other than lithium of the positive electrode of the sample to be tested is smaller than the molar ratio of Li / elements other than lithium of the positive electrode of the reference battery, and the dissolution amount of elements other than lithium of the negative electrode of the sample to be tested is greater than the dissolution amount of elements other than lithium of the negative electrode of the reference battery, it is judged that the battery to be tested is overcharged.

[0022] The element other than lithium is one of the main elements in the positive electrode material other than lithium, including but not limited to one of nickel, iron, manganese, cobalt, and aluminum.

[0023] The step of obtaining a sample of the battery to be tested includes:

[0024] The battery to be tested is fully discharged according to the preset charge and discharge process, and then disassembled, and the positive and negative electrodes are taken as samples to be tested; a battery from the same batch as the battery to be tested and with the same remaining capacity after cycling is taken as a reference battery, which is fully discharged using the same discharge process and then disassembled, and the positive and negative electrodes are taken as reference samples.

[0025] The charging and discharging process includes: discharging at 0.5C-1C to a cut-off voltage, standing, then discharging at 0.2C-0.3C to a cut-off voltage, standing, and then discharging at 0.02-0.1C to a cut-off voltage.

[0026] The target element content in the solution after volume determination is carried out, and the element quantification equipment used may be an inductively coupled plasma emission spectrometer ICP, or an atomic absorption spectrometer (AAS) or other instruments, or other testing equipment that can accurately quantify the element content.

[0027] The powder scraped from the sample to be tested and the reference sample is digested and fixed in volume, and the acid dissolution method or other methods can be used.

[0028] Overcharging of lithium batteries will cause excessive lithium escaping from the positive electrode and cause structural collapse, while excessive lithium in the negative electrode cannot be completely embedded. In this way, the present invention can determine whether the battery is overcharged at a relatively low detection cost through comprehensive analysis of the content of lithium elements and related main elements in the positive and negative electrodes, thereby providing data support for battery usage boundary analysis and reducing the hidden dangers of major safety accidents.

[0029] The present invention adopts the testing and analysis idea of ​​testing the positive and negative lithium contents to analyze whether the battery is overcharged by adopting corresponding equipment. Compared with the existing electrochemical analysis technology and electron microscope observation, the present invention does not require complex equipment and professional equipment operators, takes less time, is conducive to large-scale application, improves the efficiency of battery overcharge detection, is not only suitable for power batteries, but also can be widely used in other types of batteries, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic flow chart of the analysis method for judging whether a battery has been overcharged according to the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] like Figure 1 As shown, an analysis method for determining whether a battery has been overcharged includes:

[0033] Step 1: Obtain a test sample of the test battery and a reference sample of the reference battery;

[0034] Step 2: Digest and fix the volume of the powder scraped from the sample to be tested and the reference sample, determine the content of the target element in the solution after fixing the volume, and calculate the content value of the target element in the sample to be tested and the reference sample;

[0035] Step 3: Based on the comparison result of the target element content values ​​of the sample to be tested and the reference sample, determine whether the battery to be tested is overcharged.

[0036] Wherein, the target element includes one or more of lithium, nickel, iron and manganese.

[0037] The target element content values ​​of the sample to be tested and the reference sample are calculated based on the mass of the powder used in the digestion and volume determination process, the target element content determination data in the solution, the final volume of the volume and the dilution multiple.

[0038] The target element content values ​​of the sample to be tested and the reference sample are obtained by calculation using the following formula:

[0039] X1=n*X0*N / m;

[0040] Wherein, m is the sampling mass of the positive / negative electrode powder of the sample to be tested / reference sample, N is the final volume, n is the dilution factor, X0 is the target element content in the solution, and X1 is the calculated target element content value of the positive / negative electrode of the sample to be tested / reference sample.

[0041] Wherein, judging whether the battery to be tested is overcharged based on the comparison result of the target element content values ​​of the sample to be tested and the reference sample includes:

[0042] First, it is determined whether the battery under test is abused; when it is determined that the battery under test is abused, it is determined whether the battery under test is overcharged.

[0043] Wherein, the step of determining whether the battery under test is subjected to electrical abuse comprises:

[0044] When it is determined whether the lithium content of the negative electrode of the sample to be tested is greater than the lithium content of the negative electrode of the reference sample, it is determined that there is electrical abuse in the use of the battery to be tested.

[0045] Wherein, the step of determining whether the battery to be tested is overcharged includes:

[0046] When the lithium element content of the positive electrode of the sample to be tested is lower than the lithium element content of the positive electrode of the reference battery, the molar ratio of lithium / elements other than lithium of the positive electrode of the sample to be tested is smaller than the molar ratio of Li / elements other than lithium of the positive electrode of the reference battery, and the dissolution amount of elements other than lithium of the negative electrode of the sample to be tested is greater than the dissolution amount of elements other than lithium of the negative electrode of the reference battery, it is judged that the battery to be tested is overcharged.

[0047] Wherein, the element other than lithium includes one of nickel, iron and manganese.

[0048] The step of obtaining a sample of the battery to be tested includes:

[0049] The battery to be tested is fully discharged according to the preset charge and discharge process, and then disassembled, and the positive and negative electrodes are taken as samples to be tested; a battery from the same batch as the battery to be tested and with the same remaining capacity after cycling is taken as a reference battery, which is fully discharged using the same discharge process and then disassembled, and the positive and negative electrodes are taken as reference samples.

[0050] The charging and discharging process includes: discharging at 0.5C-1C to a cut-off voltage, standing, then discharging at 0.2C-0.3C to a cut-off voltage, standing, and then discharging at 0.02-0.1C to a cut-off voltage.

[0051] Example 1

[0052] In this embodiment, the main material of the positive electrode of the test sample soft-pack lithium-ion experimental battery is NCM622, the 1C capacity is 3.8Ah, it is charged at a constant current of 1C=3.8A for 30min, and the constant current of 0.7C=2.7Ah is charged to 4.55V, and the capacity retention rate is 98%.

[0053] Step 1: Obtain the test sample and reference sample

[0054] Fully discharge the battery to be tested: discharge to 3V at 0.5C, let stand for 15-60min, then discharge to 3V at 0.2C-0.3C, let stand for 15-60min, then discharge to 3V at 0.02-0.1C. Then disassemble the battery and take 10cm positive and negative plates as the samples to be tested;

[0055] Take another battery from the same batch as the battery to be tested and with the same residual capacity after cycling, discharge it to 3V at 0.5C, let it stand for 15-60min, then discharge it to 3V at 0.2C-0.3C, let it stand for 15-60min, and then discharge it to 3V at 0.02-0.1C. Dissect it and take 10cm of positive and negative plates respectively as reference samples.

[0056] Step 2: Digestion of samples and ICP determination

[0057] Step 1) Scrape the test sample and reference sample obtained in the first step, mark the scraped positive and negative electrode powders respectively, weigh them in a clean beaker and record the masses, which are m1=0.410g, m2=0.400g, m3=0.400g, and m4=0.408g respectively.

[0058] Step 2) Sample digestion and volume determination:

[0059] In the above step 1), 5 mL of hydrochloric acid and deionized water were added to the sample beaker and heated to digest it. The positive electrode solution was filtered and fixed to volume in a 100 mL volumetric flask, and the negative electrode solution was filtered and fixed to volume in a 50 mL volumetric flask. After fixing to volume, the positive electrode was diluted 100 times and the negative electrode was diluted 20 times.

[0060] Step 3) Determine the content of relevant elements in the sample after digestion treatment by using ICP and external standard method to determine the content of elements in the solution after constant volume;

[0061] The test result is recorded as the positive electrode X of the battery under test. 1Li =2.3ppm, positive electrode X of the tested battery 1Ni =14.1ppm, positive electrode of reference battery X2 Li =2.6ppm, positive electrode of reference battery X2 Ni =14.9ppm; negative electrode Y1 of the battery under test Li =6.2ppm;

[0062] Negative pole Y of the battery to be tested 1Ni =0.134ppm, reference cell negative electrode Y2 Li =5.0ppm, reference cell negative electrode Y2 Ni =0.064ppm, converted to the element content in the positive and negative electrodes, as follows:

[0063] The positive electrode element content of the battery to be tested is X 1正Li =100*2.3*100 / 0.41=56097.5ppm1;

[0064] The positive electrode element content of the battery to be tested is X 1正Ni =100*14.1*100 / 0.41=343902.4ppm;

[0065] Reference battery positive electrode element content X 2正Li =100*2.6*100 / 0.4=65000ppm2;

[0066] Reference battery positive electrode element content X 2正Ni =100*14.9*100 / 0.4=372500ppm;

[0067] The negative electrode element content of the battery to be tested is Y 1负Li =20*6.2*50 / 0.4=15550ppm;

[0068] The negative electrode element content of the battery to be tested is Y 1负Ni =1*0.134*50 / 0.4=16.8ppm;

[0069] Reference battery negative electrode element content Y 2负Li =20*5*50 / 0.408=12254.9ppm;

[0070] Reference battery negative electrode element content Y 2负Ni =1*0.064*50 / 0.408=7.8ppm;

[0071] Step 3: Determine whether the battery under test is overcharged

[0072] Overcharging, fast charging and low temperature environment will cause lithium dendrites to precipitate on the surface of the negative electrode. However, when overcharging, the positive electrode material is severely de-lithiated, and excessive Li+ migrates to the negative electrode, which will not only cause lithium crystals to precipitate at the negative electrode, but also cause the crystal structure of the positive electrode to collapse, prompting the positive electrode material to directly react with the electrolyte and release oxygen and reaction heat. The main elements of the positive electrode will therefore accumulate excessively on the surface of the negative electrode. However, compared with the severe excessive release of lithium elements from the positive electrode material, the reduction of the main elements cannot affect the reduction of the positive electrode Li / Ni (Fe, Mn) molar ratio.

[0073] Based on this, the judgment of overcharge can be divided into two steps;

[0074] Step 1: When the lithium content of the negative electrode of the battery under test is greater than that of the reference battery, it can be determined that the battery is abused;

[0075] Step 2: When the following three conditions are met: (1) the lithium content of the positive electrode is lower than that of the reference battery; (2) the molar ratio of Li / Ni (Fe, Mn) of the positive electrode to be tested is less than that of the reference battery; and (3) the dissolution of nickel (iron, manganese) of the negative electrode to be tested is greater than that of the reference battery, it can be determined that the battery to be tested is overcharged.

[0076] That is, in the first step, when Y 1负Li =15550>Y 2负Li=12254.9, it can be judged that the battery has a history of abuse. Step 2: X 1正Li =56097.5<X 2正Li =65000,X 1正Li / X 1正Ni =1.39<X 2正Li / X 2正Ni =1.46, Y 1负Ni =16.8>Y 2负Ni =7.8When both conditions are met, it is judged that the battery under test is overcharged.

[0077] Table 1 Analysis of element contents in samples

[0078]

[0079] Example 2

[0080] In this embodiment, the main material of the positive electrode of the test sample soft-pack lithium-ion experimental battery is NCM622, the 1C capacity is 3.8Ah, it is charged at a constant current of 1C=3.8A for 30min, and the constant current of 0.7C=2.7Ah is charged to 4.45V, and the capacity retention rate is 98%.

[0081] Step 1: Obtain the sample to be tested and the reference sample

[0082] Fully discharge the battery to be tested: discharge to 3V at 0.5C, let stand for 15-60min, then discharge to 3V at 0.2C-0.3C, let stand for 15-60min, then discharge to 3V at 0.02-0.1C. Then disassemble the battery and take 10cm positive and negative plates as the samples to be tested;

[0083] Take another battery from the same batch as the battery to be tested and with the same residual capacity after cycling, discharge it to 3V at 0.5C, let it stand for 15-60min, then discharge it to 3V at 0.2C-0.3C, let it stand for 15-60min, and then discharge it to 3V at 0.02-0.1C. Dissect it and take 10cm of positive and negative plates respectively as reference samples.

[0084] Step 2: Digestion of samples and ICP determination

[0085] Step 1) Scrape the test sample and reference sample obtained in the first step, mark the scraped positive and negative electrode powders respectively, weigh them in a clean beaker and record the masses, which are m1=0.408g, m2=0.400g, m3=0.402g, and m4=0.408g respectively.

[0086] Step 2) Sample digestion and volume adjustment: Add 5 mL of hydrochloric acid and deionized water to the sample beaker in the above step 1) and heat and digest it. Filter the positive electrode solution and adjust the volume to a 100 mL volumetric flask, and filter the negative electrode solution and adjust the volume to a 50 mL volumetric flask. After adjusting the volume, the positive electrode is diluted 100 times and the negative electrode is diluted 20 times.

[0087] Step 3) Determine the content of relevant elements in the sample after digestion treatment by using ICP and external standard method to determine the content of elements in the solution after constant volume;

[0088] The test results are recorded as: positive electrode X 1Li =2.5ppm, positive electrode X of the battery to be tested 1Ni =14.6ppm, positive electrode of reference battery X2 Li =2.6ppm, positive electrode of reference battery X2 Ni =14.9ppm;

[0089] Negative electrode Y1 of the battery to be tested Li =5.9ppm, negative electrode Y of the tested battery 1Ni =0.091ppm, reference cell negative electrode Y2 Li =5.0ppm, reference cell negative electrode Y2 Ni =0.064ppm, converted to the element content in the positive and negative electrodes, as follows:

[0090] The positive electrode element content of the battery to be tested is X 1正Li =100*2.5*100 / 0.408=61274.51ppm1;

[0091] The positive electrode element content of the battery to be tested is X 1正Ni =100*14.6*100 / 0.408=357843.1ppm;

[0092] Reference battery positive electrode element content X 2正Li =100*2.6*100 / 0.4=65000ppm2;

[0093] Reference battery positive electrode element content X 2正Ni =100*14.9*100 / 0.4=372500ppm;

[0094] The negative electrode element content of the battery to be tested is Y 1负Li =20*5.9*50 / 0.402=14676.6ppm;

[0095] The negative electrode element content of the battery to be tested is Y 1负Ni =1*0.091*50 / 0.402=11.3ppm;

[0096] Reference battery negative electrode element content Y2负Li =20*5*50 / 0.408=12254.9ppm;

[0097] Reference battery negative electrode element content Y 2负Ni =1*0.064*50 / 0.408=7.8ppm;

[0098] Step 3: Determine whether the battery under test is overcharged

[0099] Overcharging, fast charging and low temperature environment will cause lithium dendrites to precipitate on the surface of the negative electrode. However, when overcharging, the positive electrode material is severely de-lithiated, and excessive Li+ migrates to the negative electrode, which will not only cause lithium crystals to precipitate at the negative electrode, but also cause the crystal structure of the positive electrode to collapse, prompting the positive electrode material to directly react with the electrolyte and release oxygen and reaction heat. The main elements of the positive electrode will therefore accumulate excessively on the surface of the negative electrode. However, compared with the severe excessive release of lithium from the positive electrode material, the reduction of the main elements cannot affect the reduction of the positive electrode Li / Ni (Fe, Mn) molar ratio.

[0100] Based on this, the judgment of overcharge can be divided into two steps:

[0101] Step 1: When the lithium content of the negative electrode of the battery under test is greater than that of the reference battery, it can be determined that the battery is abused;

[0102] Step 2: When the following three conditions are met: (1) the lithium content of the positive electrode is lower than that of the reference battery; (2) the molar ratio of Li / Ni (Fe, Mn) of the positive electrode to be tested is less than that of the reference battery; and (3) the dissolution of nickel (iron, manganese) of the negative electrode to be tested is greater than that of the reference battery, it can be determined that the battery to be tested is overcharged.

[0103] That is, in the first step, when Y 1负Li =14676.6>Y 2负Li =12254.9, it can be judged that the battery has a history of abuse. Step 2: X 1正Li =61247.5<X 2正Li =65000,X 1正Li / X 1正Ni) =1.43<X 2正Li / X 2正Ni =1.46, Y 1负Ni =11.3>Y 2负Ni =7.8When both conditions are met, it is judged that the battery under test is overcharged.

[0104] Table 2 Analysis of element contents in samples

[0105]

[0106] The present invention can accurately determine whether a battery is overcharged by a simple method. The overcharge degrees of the batteries in Examples 1 and 2 of the present invention are different, and no difference is found during dissection. By quickly obtaining results by analyzing the contents of lithium and nickel elements in the positive and negative electrodes, it can be determined that the battery is overcharged. By comparing Example 1 with Example 2, it can be seen that the positive electrode of a severely overcharged battery has a low lithium content, while the negative electrode has a higher lithium content and a higher nickel dissolution rate, and the positive electrode lithium-nickel ratio is lower. There is a regularity to be followed, and the battery usage boundary can be determined by this data, providing data support for research and development.

[0107] The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0108] Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is therefore intended that all changes falling within the meaning and range of equivalent elements of the claims are included in the present invention.

[0109] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An analytical method for determining whether a battery has been overcharged, characterized in that: include: Step 1: Obtain a test sample of the test battery and a reference sample of the reference battery; Step 2: Digest and fix the volume of the powder scraped from the sample to be tested and the reference sample, determine the content of the target element in the solution after fixing the volume, and calculate the content value of the target element in the sample to be tested and the reference sample; Step 3: Based on the comparison result of the target element content values ​​of the sample to be tested and the reference sample, determine whether the battery to be tested is overcharged.

2. The analysis method for determining whether a battery has been overcharged according to claim 1, characterized in that: The target element is one or more main elements in the positive electrode material.

3. The analysis method for determining whether a battery has been overcharged according to claim 1, characterized in that: The target element content values ​​of the sample to be tested and the reference sample are calculated based on the mass of the powder used in the digestion and volume determination process, the target element content determination data in the solution, the final volume of the volume and the dilution multiple.

4. The analysis method for determining whether a battery has been overcharged according to claim 3, characterized in that: The target element content values ​​of the sample to be tested and the reference sample are obtained by calculation using the following formula: X1=n*X0*N / m; Wherein, m is the sampling mass of the positive / negative electrode powder of the sample to be tested / reference sample, N is the final volume, n is the dilution factor, X0 is the target element content in the solution, and X1 is the calculated target element content value of the positive / negative electrode of the sample to be tested / reference sample.

5. The analysis method for determining whether a battery has been overcharged according to claim 1, characterized in that: The step of judging whether the battery to be tested is overcharged based on the comparison result of the target element content values ​​of the sample to be tested and the reference sample includes: First, it is determined whether the battery under test is abused; if it is determined that the battery under test is abused, it is determined whether the battery under test is overcharged.

6. The analysis method for determining whether a battery has been overcharged according to claim 5, characterized in that: The step of determining whether the battery under test is subjected to electrical abuse comprises: When it is determined whether the lithium content of the negative electrode of the sample to be tested is greater than the lithium content of the negative electrode of the reference sample, it is determined that there is electrical abuse in the use of the battery to be tested.

7. The analysis method for determining whether a battery has been overcharged according to claim 5, characterized in that: The step of determining whether the battery to be tested is overcharged comprises: When the lithium content of the positive electrode of the sample to be tested is lower than the lithium content of the positive electrode of the reference battery, the molar ratio of lithium / target elements other than lithium of the positive electrode of the sample to be tested is smaller than the molar ratio of Li / target elements other than lithium of the positive electrode of the reference battery, and the dissolution amount of target elements other than lithium of the negative electrode of the sample to be tested is greater than the dissolution amount of target elements other than lithium of the negative electrode of the reference battery, it is judged that the battery to be tested is overcharged.

8. The analysis method for determining whether a battery has been overcharged according to claim 7, characterized in that: The target element other than lithium is one of the main elements in the positive electrode material other than lithium.

9. The analysis method for determining whether a battery has been overcharged according to claim 1, characterized in that: The step of obtaining a test sample of a battery to be tested comprises: The battery to be tested is fully discharged according to the preset charge and discharge process, and then disassembled, and the positive and negative electrodes are taken as samples to be tested; a battery from the same batch as the battery to be tested and with the same remaining capacity after cycling is taken as a reference battery, which is fully discharged using the same discharge process and then disassembled, and the positive and negative electrodes are taken as reference samples.

10. The analysis method for determining whether a battery has been overcharged according to claim 1, characterized in that: The charging and discharging process includes: discharging at 0.5C-1C to a cut-off voltage, standing, then discharging at 0.2C-0.3C to a cut-off voltage, standing, and then discharging at 0.02-0.1C to a cut-off voltage.

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