Method for evaluating stability of nickel-containing positive electrode material

Abstract

The embodiment of the invention provides a method for evaluating the stability of a nickel-containing positive electrode material, and belongs to the technical field of batteries. According to the evaluation method, I (003) and I (104) are obtained through the step S1, I (003) / I (104) represents the Li / Ni mixed arrangement degree of a nickel-containing positive electrode material matrix, a t value is obtained through the step S2, and t represents the metal dissolution condition of the nickel-containing positive electrode material after circulation, so that k = (I (003) / I (104)) / t can be used as a structural stability factor of the nickel-containing positive electrode material in the step S3, and the stability of the nickel-containing positive electrode material is improved. The crystal structure and the metal dissolution amount of the nickel-containing positive electrode material after circulation are evaluated, so that the damage degree and the stability of the nickel-containing positive electrode material structure are measured. As k can represent the stability of the nickel-containing positive electrode material from the structural characteristics of the nickel-containing positive electrode material, the same evaluation index k can comprehensively evaluate the stability performance of the nickel-containing positive electrode material in multiple aspects such as cycle stability, storage stability, high-temperature stability and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a method for evaluating the stability of a nickel-containing positive electrode material. BACKGROUND

[0002] At present, the electric vehicle industry is developing rapidly, and the demand for power batteries is significantly increasing. As one of the four main materials of power batteries, positive electrode materials play a key role in electrical performance. Electric vehicles are developing towards long endurance and high safety, so improving energy density, prolonging service life and improving material safety and stability are the problems to be solved for the current positive electrode materials. Among them, the hexagonal system layered nickel-containing positive electrode material LiNi x Co y Mn z O2(wherein, 0

[0003] For fast-charging batteries, the kinetics and thermodynamic stability of nickel-containing positive electrode materials need to be balanced. The existing nickel-containing positive electrode material LiNi x Co y Mn z O2 cannot achieve good stability while ensuring low initial direct current resistance (DCR) performance. Doping in the nickel-containing positive electrode material body can change the crystal structure and improve the stability of the nickel-containing positive electrode material. In addition, doping on the surface of the nickel-containing positive electrode material to form a coating structure can also provide a channel for Li ion diffusion, while blocking the positive active material and the electrolyte, thereby protecting the nickel-containing positive electrode material body from the damage of electrolyte corrosion.

[0004] In research and development work, researchers need to use certain methods to evaluate the stability of the above various nickel-containing positive electrode materials. For example, testing the capacity retention rate of the battery after different cycles can be used to evaluate the cycle stability of the nickel-containing positive electrode material. Testing the capacity retention rate of the battery after different cycles at full charge can be used to evaluate the storage stability of the nickel-containing positive electrode material. For example, testing the capacity retention rate of the battery after different cycles at high temperature can be used to evaluate the high-temperature stability of the nickel-containing positive electrode material.

[0005] However, the stability of nickel-containing positive electrode materials includes but is not limited to the above. It can be seen that if you want to comprehensively evaluate the stability of nickel-containing positive electrode materials, such as a comprehensive evaluation of cycle stability, storage stability, high-temperature stability, etc., you need to test the capacity retention rate of multiple aspects separately, which is a large workload. In addition, when the capacity retention rate is used as an evaluation index to evaluate the stability of several nickel-containing positive electrode materials with similar structures and small stability differences, the differentiation is not enough, which is not conducive to making an accurate judgment. Therefore, it is necessary to design a method for evaluating the stability of nickel-containing positive electrode materials, which can more simply and accurately judge the pros and cons of the stability of nickel-containing positive electrode materials. Summary of the Invention

[0006] The present invention aims to solve, at least to a certain extent, one of the technical problems in the related art. To this end, an embodiment of the present invention provides a method for evaluating the stability of a nickel-containing positive electrode material. This evaluation method can indicate the stability of the positive electrode material based on its structural characteristics. The same evaluation result can simultaneously illustrate the stability performance of the nickel-containing positive electrode material in multiple aspects, such as cycle stability, storage stability, and high-temperature stability. In addition, the discrimination of the evaluation index is more representative than the capacity retention rate. When used to evaluate the stability of several nickel-containing positive electrode materials with similar structures and small differences in stability, the evaluation result is more accurate.

[0007] The embodiment of the present invention provides a method for evaluating the stability of a nickel-containing positive electrode material, comprising the following steps:

[0008] S1. Perform X-ray diffraction test on the nickel-containing positive electrode material to obtain the XRD pattern of the nickel-containing positive electrode material, and read the peak intensity I of the 003 peak in the XRD pattern. (003) and the peak intensity of peak 104 (104) ;

[0009] S2. Provide a battery cell comprising the nickel-containing positive electrode material, and test the battery cell after cycling to determine the mass fraction t of the total amount of transition metal Ni and / or Mn and Co dissolved from the negative electrode sheet, where the number of cycles of the battery cell is n, where n = 80 to 200;

[0010] S3. According to the I (003) 、The I (104) and t to calculate the structural stability factor k of the nickel-containing positive electrode material, wherein k=(I (003) / I (104) ) / t;

[0011] S4. When the k is above the critical value k0, the nickel-containing positive electrode material is judged to be a high-stability nickel-containing positive electrode material; when the k is less than the k0, the nickel-containing positive electrode material is judged to be a non-high-stability nickel-containing positive electrode material; the k0 = 3 to 6.

[0012] The evaluation method of the embodiment of the present application has the advantages and technical effects that:

[0013] (1) The preparation method of the embodiment of the present application obtains I (003) and I (104) , I (003) / I (104) represents the Li / Ni mixing degree of the nickel-containing positive electrode material matrix, the value t is obtained through step S2, t represents the metal dissolution of the nickel-containing positive electrode material after cycling, and therefore step S3 can use k=(I (003) / I (104) ) / t as a structure stability factor of the nickel-containing positive electrode material to evaluate the crystal structure and the metal dissolution of the nickel-containing positive electrode material after cycling, so as to measure the degree of destruction and stability of the structure of the nickel-containing positive electrode material.

[0014] (2) The evaluation method of the embodiment of the present application proposes a structure stability factor k of the nickel-containing positive electrode material, k=(I (003) / I (104) ) / t, and uses k as an evaluation index of stability, since k can represent the stability of the nickel-containing positive electrode material from the structure characteristics, the same evaluation index k can comprehensively evaluate the cycle stability, storage stability, high-temperature stability and other stability performances of the nickel-containing positive electrode material, and the evaluation process can be greatly simplified compared with the evaluation method in the prior art.

[0015] (3) In the step S2 of the evaluation method of the embodiment of the present application, the cycle number n of the battery cell is required to be 80-200 when the value t is tested, the value t obtained in this range has good distinguishability, so that the value k also has good distinguishability, which is convenient for judging whether the nickel-containing positive electrode material is a high-stability positive electrode material.

[0016] (4) In the evaluation method of the embodiment of the present application, the critical value of judging whether the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material is k0, and the critical value k0=3-6, the specific value of the critical value k0 can be adjusted according to the specific value of the cycle number n, and the critical value k0 in the above range can make the value k have good distinguishability, which is convenient for judging whether the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material.

[0017] (5) When the evaluation object contains not only Ni but also Co and / or Mn, the evaluation method of the embodiment of the present application tests the total mass fraction of the dissolved transition metals Ni and / or Mn and Co on the negative electrode sheet t, instead of testing only the mass fraction of the dissolved transition metal on the negative electrode sheet, because sometimes the dissolution of Ni and Mn does not change, but the dissolution of Co increases, and if only one kind of transition metal is evaluated, it may lead to misjudgment of the final evaluation result.

[0018] In some embodiments, when n = 80, k 0(n＝80) is 6.

[0019] In some embodiments, when n = 200, k 0(n＝200) is 3.

[0020] In some embodiments, the method used for testing t is ICP method.

[0021] In addition, the embodiment of the present application also provides an evaluation method for stability of nickel-containing positive electrode material, comprising the following steps:

[0022] S1. X-ray diffraction test is performed on different nickel-containing positive electrode materials to obtain XRD patterns of each of the nickel-containing positive electrode materials, and the peak intensity I (003) and the peak intensity I (104) of the 003 peak in each of the XRD patterns are read respectively.

[0023] S2. A plurality of battery cells are provided, each of the battery cells containing one of the nickel-containing positive electrode materials, the types of the nickel-containing positive electrode materials in each two of the battery cells being different, and the total amount of dissolved transition metals Ni and / or Mn and Co on the negative electrode tab after cycling of each of the battery cells is tested respectively, the number of cycles of the battery cells is n, and the number of cycles of each of the battery cells is the same.

[0024] S3. The structural stability factor k of each of the nickel-containing positive electrode materials is calculated according to the I (003) , the I (104) and the t, and the k = (I (003) / I (104) ) / t.

[0025] S4. The k values of different nickel-containing positive electrode materials are sorted, and the stability of different nickel-containing positive electrode materials is sorted according to the k, and the greater the k, the higher the stability of the nickel-containing positive electrode material.

[0026] The evaluation method of the embodiment of the present application has the following advantages and technical effects:

[0027] (1) The preparation method of the embodiment of the present application obtains I (003) and I (104) through step S1, I (003) / I (104) represents the Li / Ni mixing degree of the nickel-containing positive electrode material matrix, t value is obtained through step S2, and t represents the metal dissolution of the nickel-containing positive electrode material after cycling, so step S3 can utilize k = (I (003) / I (104)As a structural stability factor of the nickel-containing positive electrode material, k is used to evaluate the crystal structure and the amount of metal dissolution of different nickel-containing positive electrode materials after cycling, and measure the degree of destruction of the structure of different nickel-containing positive electrode materials and the stability thereof.

[0028] (2) The evaluation method of the embodiment of the present application proposes a structural stability factor k of the nickel-containing positive electrode material, k=(I (003) / I (104) ) / t, and uses k as an evaluation index of stability. Since k can represent the stability of the nickel-containing positive electrode material from the structural characteristics thereof, the same evaluation index k can comprehensively evaluate the stability performance of the nickel-containing positive electrode material in multiple aspects such as cycling stability, storage stability, and high-temperature stability, thereby greatly simplifying the evaluation process compared with the evaluation method in the prior art.

[0029] (3) The evaluation method of the embodiment of the present application uses the structural stability factor k as an evaluation index, which is more representative than the capacity retention rate used as an evaluation index in the prior art. When used to evaluate the relative stability of different nickel-containing positive electrode materials, the evaluation result is more accurate, especially when used to compare the stability of different nickel-containing positive electrode materials with similar structures and small differences in stability, the stability of the nickel-containing positive electrode materials can also be distinguished.

[0030] (4) In step S2 of the preparation method of the embodiment of the present application, the cycle number n of each battery is the same when the value t is tested, which can ensure that the k value corresponding to each nickel-containing positive electrode material is obtained at the same level, thereby realizing the evaluation of the relative stability of different nickel-containing positive electrode materials and ensuring the accuracy of the evaluation result.

[0031] In some embodiments, n is greater than or equal to 80.

[0032] In some embodiments, the method used to test t is ICP method.

[0033] In some embodiments, the different nickel-containing positive electrode materials contain the same type of transition metal.

[0034] In addition, the embodiment of the present application also provides an evaluation method for the stability of a nickel-containing positive electrode material, which comprises the following steps:

[0035] S1. X-ray diffraction test is performed on different nickel-containing positive electrode materials to obtain XRD patterns of each nickel-containing positive electrode material, and the peak intensity I (003) and the peak intensity I (104) of the 104 peak in each XRD pattern are read, respectively.

[0036] S2. providing a plurality of battery cells, each of the battery cells containing a kind of the nickel-containing positive electrode material, the kinds of the nickel-containing positive electrode material in each two of the battery cells being different, respectively testing a total amount of transition metals Ni and / or Mn and Co dissolved on a negative electrode tab after cycling of each of the battery cells accounts for a mass fraction t of the negative electrode tab, a number of cycles of the battery cells being n, the number of cycles of each of the battery cells being different;

[0037] S3. calculating a structure stability factor k of each of the nickel-containing positive electrode materials according to the I (003) , the I (104) and the t respectively, the k = (I (003) / I (104) ) / t;

[0038] S4. selecting the nickel-containing positive electrode materials with the same k, sorting the n of the nickel-containing positive electrode materials with the same k, obtaining a sorting of the stability of the nickel-containing positive electrode materials with the same k according to the sorting of the n, the larger the n is, the higher the stability of the nickel-containing positive electrode material is judged.

[0039] The evaluation method of the embodiment of the present application has the following advantages and technical effects:

[0040] (1) The evaluation method of the embodiment of the present application obtains I (003) and I (104) through step S1, I (003) / I (104) represents the Li / Ni mixing degree of the nickel-containing positive electrode material matrix, the t value is obtained through step S2, t represents the metal dissolution of the nickel-containing positive electrode material after cycling, therefore step S3 can use k = (I (003) / I (104) ) / t as the structure stability factor of the nickel-containing positive electrode material to evaluate the crystal structure and the metal dissolution of different nickel-containing positive electrode materials after cycling, and measure the degree of destruction and the pros and cons of the stability of the structure of different nickel-containing positive electrode materials.

[0041] (2) The evaluation method of the embodiment of the present application proposes the structure stability factor k of the nickel-containing positive electrode material, k = (I (003) / I (104) ) / t, and takes k as an evaluation index of stability, since k can represent the stability of the nickel-containing positive electrode material from the structure characteristics, therefore the same evaluation index k can comprehensively evaluate the cycle stability, storage stability, high-temperature stability and other stability performances of the nickel-containing positive electrode material, compared with the evaluation method in the prior art, the evaluation process can be greatly simplified.

[0042] (3) The preparation method of the embodiment of the present application is characterized in that, in step S2, the cycle number of each of the battery cells is different, so that the k value of at least part of the nickel-containing positive electrode materials can be the same, and then in step S4, the nickel-containing positive electrode materials with the same k value are selected, and the stability of different nickel-containing positive electrode materials is measured by comparing the cycle number n of the nickel-containing positive electrode materials when the t value is tested, that is, the greater the n, the higher the stability of the nickel-containing positive electrode material, and the evaluation process is simple and the evaluation result is accurate.

[0043] In some embodiments, the n is greater than or equal to 80.

[0044] In some embodiments, the method for testing the t is ICP method.

[0045] In some embodiments, the different nickel-containing positive electrode materials contain the same type of transition metal. DETAILED DESCRIPTION

[0046] Embodiments of the present application are described in detail below. The embodiments described below are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0047] The embodiment of the present application provides an evaluation method for the cycle stability of a nickel-containing positive electrode material, comprising the following steps:

[0048] S1. X-ray diffraction test is performed on the nickel-containing positive electrode material to obtain an XRD pattern of the nickel-containing positive electrode material, and the peak intensity I of the 003 peak in the XRD pattern is read (003) and the peak intensity I of the 104 peak (104) ;

[0049] S2. A battery cell comprising the nickel-containing positive electrode material is provided, and the total content of the dissolved transition metals Ni and / or Mn and Co on the negative electrode tab after the cycle is tested to be t, and the cycle number of the battery cell is n, and the n = 80-200.

[0050] S3. The structural stability factor k of the nickel-containing positive electrode material is calculated according to the I (003) , the I (104) and the t, and the k = (I (003) / I (104) ) / t.

[0051] S4. When the k is greater than or equal to a critical value k0, the nickel-containing positive electrode material is determined to be a high-stability nickel-containing positive electrode material; when the k is less than the k0, the nickel-containing positive electrode material is determined to be a non-high-stability nickel-containing positive electrode material; and the k0 = 3-6.

[0052] The preparation method of the embodiment of the present application is characterized in that, in step S1, the I (003) / I (104) ,I (003) / I (104) represents the Li / Ni mixing degree of the nickel-containing positive electrode material matrix, the t value is obtained by testing step S2, t represents the metal dissolution of the nickel-containing positive electrode material after cycling, and therefore step S3 can use k=(I (003) / I (104) ) / t as the structural stability factor of the nickel-containing positive electrode material to evaluate the crystal structure and the metal dissolution amount of the nickel-containing positive electrode material after cycling, so as to measure the degree of destruction and stability of the structure of the nickel-containing positive electrode material.

[0053] The evaluation method of the embodiment of the present application proposes a structural stability factor k of the nickel-containing positive electrode material, k=(I (003) / I (104) ) / t, and uses k as the evaluation index of stability, since k can indicate the stability of the nickel-containing positive electrode material from the structural characteristics of the nickel-containing positive electrode material, the same evaluation index k can indicate the stability performance of the nickel-containing positive electrode material in multiple aspects such as cycle stability, storage stability, and high-temperature stability. It is not necessary to test the cycle stability, storage stability, high-temperature stability, and other performances of the nickel-containing positive electrode material respectively as in the prior art, which greatly reduces the workload of the evaluation process.

[0054] It should be noted that the order of steps S1 and S2 in the evaluation method of the embodiment of the present application is not particularly limited, step S1 can be performed first and then step S2 can be performed, or step S2 can be performed first and then step S1 can be performed, or both steps can be performed simultaneously. However, it should be noted that the nickel-containing positive electrode material in step S1 is exactly the same as the nickel-containing positive electrode material included in the battery cell in step S2.

[0055] In the evaluation method of the embodiment of the present application, when testing the t value, the cycle number n of the battery cell needs to be 80-200, the t value obtained in this range has good distinguishability, so that the k value also has good distinguishability, which is convenient for judging whether the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material. In the evaluation method of the embodiment of the present application, the critical value for judging whether the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material is k0, and the critical value k0=3-6. The specific value of the critical value k0 can be adjusted according to the specific value of n, and the critical value k0 in the above range can make the k value have good distinguishability, which is convenient for judging whether the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material.

[0056] It should be noted that the evaluation object of the evaluation method of the embodiment of the present application is the nickel-containing positive electrode material, and the type of the nickel-containing positive electrode material is not particularly limited, which can be any Li b Ni x Co y Mn z Aa O2 type cathode material, wherein, 1≤b≤1.1, 0<x≤1, 0≤y≤1, 0≤z≤1, 0≤a≤0.2, x+y+z+a=1, A is selected from at least one of Ti, Al, Zr, Y, Sr, W, Sb, Ce, Mg, Co, Mo and V, that is, the nickel-containing cathode material can be a unary, binary, ternary, quaternary cathode material, etc., the nickel-containing cathode material can be doped with other elements or not doped with other elements in addition to containing Ni and optionally Co, Mn, the nickel-containing cathode material body can be coated with a coating layer material or not coated. It can be seen that the evaluation method of the embodiment of the present application has relatively wide applicability.

[0057] The stability of the nickel-containing cathode material can be measured in various ways, including but not limited to cycle stability, storage stability, high-temperature stability, safety performance, etc. The stability of the nickel-containing cathode material needs to be considered from multiple angles, and different types of batteries may need to focus on different factors in different application scenarios. Therefore, the stability of the nickel-containing cathode material to be investigated can be multi-faceted or a certain aspect, and the evaluation method of the embodiment of the present application can achieve the above evaluation purposes.

[0058] In the evaluation method of the embodiment of the present application, the peak intensity I (003) and the peak intensity I (104) of the 003 peak in the XRD pattern are selected, because the 003 peak and the 004 peak are the first two strong peaks in the XRD pattern of the nickel-containing cathode material, and are the most representative, I (003) / I (104) can fully indicate the Li / Ni mixing degree of the nickel-containing cathode material matrix.

[0059] In addition, the evaluation method of the embodiment of the present application selects the total amount of dissolved transition metal Ni and / or Mn and Co on the tested negative electrode sheet as the mass fraction t of the negative electrode sheet, because the metal dissolution will eventually be deposited on the surface of the negative electrode sheet, so as to characterize the metal dissolution on the negative electrode sheet. In addition, when the evaluation object is a unary positive electrode material, the amounts of dissolved Co and Mn are 0, and the evaluation method of the embodiment of the present application selects the total amount of dissolved transition metal Ni and / or Mn and Co on the tested negative electrode sheet as the mass fraction t of the negative electrode sheet, which is actually the total amount of dissolved transition metal Ni on the tested negative electrode sheet as the mass fraction t of the negative electrode sheet. When the evaluation object is a multi-element positive electrode material such as a binary, ternary or quaternary positive electrode material, Co and / or Mn are contained in addition to Ni, and the evaluation method of the embodiment of the present application selects the total amount of dissolved transition metal Ni and / or Mn and Co on the tested negative electrode sheet as the mass fraction t of the negative electrode sheet, rather than only testing the amount of dissolved transition metal as the mass fraction of the negative electrode sheet, because sometimes the dissolution of Ni and Mn does not change, but the dissolution of Co increases, and if only one kind of transition metal is evaluated, it may lead to misjudgment.

[0060] In some embodiments, the step S2 tests the total amount of dissolved transition metal Ni, Mn and Co on the negative electrode sheet of the battery cell after cycling as the mass fraction t of the negative electrode sheet. This is more conducive to improving the accuracy of the evaluation result than testing the total amount of dissolved transition metal Ni or Mn and Co on the negative electrode sheet of the battery cell after cycling as the mass fraction t of the negative electrode sheet.

[0061] The evaluation method is used to evaluate the stability of a certain nickel-containing positive electrode material, and therefore the evaluation result is measured by the absolute value of k. When testing the value of t, the cycle number n of the battery cell is set to 80-200, for example, 60, 80, 100, 120, 140, 160, 180, 200, etc., and then the t value is tested after disassembly, in order to ensure that there is enough transition metal Ni and / or Mn and Co deposited on the negative electrode sheet, so as to ensure that the evaluation result of dividing high-stability and non-high-stability positive electrode materials by k=k0 as the dividing line is accurate. It can be understood that if the cycle number of the battery cell is not limited when testing the value of t, the absolute value of k obtained is meaningless and cannot be used to evaluate the stability of the nickel-containing positive electrode material. When the cycle number n of the battery cell is too small, the discrimination of k is poor, and the judgment result is not accurate. When the cycle number n of the battery cell is too large, the accuracy of the judgment result is not significantly improved, but it is not conducive to improving the judgment speed.

[0062] Preferably, in some embodiments, when the n=80, the critical value k 0(n＝80) is 6. When the n=200, the critical value k 0(n＝200)The setting mode is helpful to further improve the accuracy of the evaluation result. It should be understood that the critical value k0 is determined according to the cycle number n. When n is a value between 80 and 200, k0 decreases with the increase of n.

[0063] Preferably, in some embodiments, the method for testing t is ICP method. The ICP method is inductively coupled plasma spectrometry test method, and the measured t value is more accurate, which is helpful to improve the accuracy of the stability judgment of the nickel-containing positive electrode material. The specific operation of the method for testing t is as follows: the battery after cycling is discharged to zero state, the negative electrode sheet is obtained by disassembling the battery, the negative electrode sheet is digested to obtain a digestion solution, the total mass of transition metals Ni and / or Mn and Co in the digestion solution is tested by ICP method, and the mass of the negative electrode sheet is divided to calculate the t.

[0064] In addition, the embodiment of the present application also provides a method for evaluating the stability of a nickel-containing positive electrode material, comprising the following steps:

[0065] S1. X-ray diffraction test is performed on different nickel-containing positive electrode materials to obtain XRD patterns of each of the nickel-containing positive electrode materials, and the peak intensity I (003) and the peak intensity I (104) of the 003 peak in each of the XRD patterns are read, respectively.

[0066] S2. A plurality of batteries are provided, each of which contains a nickel-containing positive electrode material, the types of the nickel-containing positive electrode materials in each two of the batteries are different, the total mass fraction t of the dissolved amounts of transition metals Ni and / or Mn and Co on the negative electrode sheet after cycling of each of the batteries is tested, the cycle number of the battery is n, and the cycle numbers of each of the batteries are the same.

[0067] S3. The structure stability factor k of each of the nickel-containing positive electrode materials is calculated according to the I (003) , the I (104) and the t, respectively, and the k = (I (003) / I (104) ) / t.

[0068] S4. The sizes of the k of different nickel-containing positive electrode materials are sorted, and the stability of the different nickel-containing positive electrode materials is sorted according to the k, and the greater the k, the higher the stability of the nickel-containing positive electrode material.

[0069] The preparation method of the embodiment of the present application obtains I (003) and I (104) , I (003) / I (104)Li / Ni mixed arrangement degree represented by Li / Ni positive electrode material matrix, t value obtained by step S2, t represents metal dissolution of nickel-containing positive electrode material after cycling, so step S3 can use k=(I (003) / I (104) ) / t as a structural stability factor of nickel-containing positive electrode material to evaluate different nickel-containing positive electrode material crystal structures and metal dissolution after cycling, measure the degree of destruction of different nickel-containing positive electrode material structures and the pros and cons of stability.

[0070] The evaluation method of the embodiment of the application proposes a structural stability factor k of the nickel-containing positive electrode material, k=(I (003) / I (104) ) / t, and takes k as an evaluation index of stability, since k can indicate the stability of the nickel-containing positive electrode material from the structural characteristics, therefore the same evaluation index k can indicate the stability performance of the nickel-containing positive electrode material in multiple aspects such as cycle stability, storage stability and high temperature stability, greatly simplifying the evaluation process.

[0071] The evaluation method of the embodiment of the application uses the structural stability factor k as an evaluation index, which is more representative than the evaluation index used in the prior art, i.e. capacity retention rate, and when used to evaluate the stability of different nickel-containing positive electrode materials, the evaluation result is more accurate, especially when used to compare the stability of different nickel-containing positive electrode materials with similar structures and small stability differences, it can also distinguish the stability.

[0072] In step S2 of the evaluation method of the embodiment of the application, the cycle number n of each said battery is the same when testing t value, which can ensure that the k value corresponding to each nickel-containing positive electrode material is obtained at the same level, and then realize the relative high and low evaluation of the stability of different nickel-containing positive electrode materials, and ensure the accuracy of the evaluation result.

[0073] It can be understood that the order of steps S1 and S2 is not important, and step S1 can be performed first and then step S2, or step S2 can be performed first and then step S1, or both can be performed at the same time. However, it should be noted that multiple batteries are provided in step S2, each of which contains one said nickel-containing positive electrode material, and the types of said nickel-containing positive electrode materials in each two said batteries are different, that is, the nickel-containing positive electrode materials contained in different batteries in step S2 correspond one-to-one to the nickel-containing positive electrode materials in step S1. For example, when there are m (m≥2) nickel-containing positive electrode materials to be evaluated in step S1, the m nickel-containing positive electrode materials can be assembled into m batteries in step S2, each of which contains one nickel-containing positive electrode material.

[0074] The evaluation method is used for evaluating the relative stability of different nickel-containing positive electrode materials, so as to determine the relative stability of different nickel-containing positive electrode materials by the relative k value as long as the test conditions are the same, and thus the cycle number n of the battery at the time of test t is not limited.

[0075] In some embodiments, the n is 80 or more, for example, 80, 100, 120, 140, 160, 180, 200, 300, 400, 500, etc. When the n is too small, the amount of transition metal Ni and / or Mn deposited on the negative electrode plate is too small, the k value of different nickel-containing positive electrode materials is too small, and it is not conducive to compare the stability of different nickel-containing positive electrode materials. Preferably, the n is 80-200. When the n is too large, the accuracy of the judgment result is not significantly improved, and it is not conducive to improve the judgment speed.

[0076] In some embodiments, the method used for testing the t is ICP method. The specific operation of the ICP method is as described above.

[0077] In some embodiments, the stability is at least one of cycle stability, storage stability and high-temperature stability.

[0078] It should be noted that the evaluation method of the embodiments of the present application is aimed at different nickel-containing positive electrode materials, and the type of nickel-containing positive electrode material is not particularly limited, as described above.

[0079] In some embodiments, the different nickel-containing positive electrode materials contain the same type of transition metal. When the evaluation object meets this condition, the evaluation result is more accurate. For example, the evaluation method for evaluating the stability of a ternary positive electrode material relative to a binary positive electrode material is more accurate when the evaluation object is a ternary positive electrode material.

[0080] In addition, the embodiments of the present application also provide an evaluation method for the stability of a nickel-containing positive electrode material, comprising the following steps:

[0081] S1. X-ray diffraction test is performed on different nickel-containing positive electrode materials to obtain the XRD pattern of each nickel-containing positive electrode material, and the peak intensity I (003) and the peak intensity I (104) of the 104 peak in each XRD pattern are read, respectively.

[0082] S2. providing a plurality of battery cells, each of the battery cells containing a kind of the nickel-containing cathode material, the kinds of the nickel-containing cathode material in each two of the battery cells being different, respectively testing a total amount of dissolved transition metal Ni and / or Mn and Co on a negative electrode tab of each of the battery cells after cycling, the number of cycles of the battery cells being n, the number of cycles of each of the battery cells being different;

[0083] S3. calculating a structure stability factor k of each of the nickel-containing cathode materials according to the I (003) , the I (104) and the t respectively, the k = (I (003) / I (104) ) / t;

[0084] S4. selecting the nickel-containing cathode materials with the same k, sorting the n of the nickel-containing cathode materials with the same k, obtaining a sorting of the stability of the nickel-containing cathode materials with the same k according to the sorting of the n, the larger the n is, the higher the stability of the nickel-containing cathode material is.

[0085] The preparation method of the embodiment of the application obtains I (003) and I (104) through step S1, I (003) / I (104) represents the Li / Ni mixing degree of the nickel-containing cathode material matrix, the t value is obtained through step S2, and the t represents the metal dissolution of the nickel-containing cathode material after cycling, so that step S3 can use k = (I (003) / I (104) ) / t as the structure stability factor of the nickel-containing cathode material to evaluate the crystal structure and the metal dissolution of the nickel-containing cathode material after cycling.

[0086] The preparation method of the embodiment of the application is different in the number of cycles of each of the battery cells when the t value is tested in step S2, so that the k value of at least a part of the nickel-containing cathode materials may be the same, and then the nickel-containing cathode materials with the same k value are selected in step S4, and the stability of the different nickel-containing cathode materials is measured by comparing the number of cycles n of the nickel-containing cathode materials when the t value is tested, the larger the n is, the higher the stability of the nickel-containing cathode material is, the evaluation process is simple and the evaluation result is accurate.

[0087] It can be understood that the order of steps S1 and S2 is not important, and step S1 can be performed first, or step S2 can be performed first, or both can be performed simultaneously. However, it should be noted that in step S2, a plurality of battery cells are provided, each of which contains a nickel-containing positive electrode material, and the types of nickel-containing positive electrode materials in each of the two battery cells are different, that is, the nickel-containing positive electrode materials contained in different battery cells in step S2 correspond one-to-one to the nickel-containing positive electrode materials in step S1.

[0088] The evaluation method is used to evaluate the relative stability of different nickel-containing positive electrode materials, so as long as the test conditions are the same, the relative stability of different nickel-containing positive electrode materials can be judged by the relative value of n, and therefore the number of cycles n of the battery cell at time t does not need to be limited.

[0089] In some embodiments, the n is 80 or more, such as 80, 100, 120, 140, 160, 180, 200, 300, 400, 500, etc. When n is too small, the amount of transition metal Ni and / or Mn deposited on the negative electrode plate is too small, and it is not easy to make the k of different nickel-containing positive electrode materials reach the same value, thereby affecting the comparison of the stability of different nickel-containing positive electrode materials. Preferably, the n is 80-200. When n is too large, the accuracy of the judgment result is not significantly improved, and the judgment speed is not improved.

[0090] In some embodiments, the method used to test t is ICP method. The specific operation of ICP method is as described above.

[0091] In some embodiments, the stability is at least one of cycle stability, storage stability, and high-temperature stability.

[0092] It should be noted that the evaluation method of the embodiments of the present application is aimed at different nickel-containing positive electrode materials, and the type of nickel-containing positive electrode material is not particularly limited, as described above.

[0093] In some embodiments, the different nickel-containing positive electrode materials contain the same type of transition metal. When the evaluation object satisfies this condition, the evaluation result is more accurate. For example, compared with the evaluation method of the stability of one evaluation object being a ternary positive electrode material and another evaluation object being a binary positive electrode material, the evaluation result of the evaluation method is more accurate when the evaluation objects are both ternary positive electrode materials.

[0094] The present application will be described in detail below with reference to the embodiments.

[0095] Embodiment 1

[0096] The evaluation object is a polycrystalline positive electrode material Li 1.05Ni 0.886 Co 0.05 Mn 0.05 Al 0.01 Ti 0.004 O2(Recorded as nickel-containing positive electrode material I), the nickel-containing positive electrode material is a core-shell structure, the chemical formula of the core is Li 1.05 Ni 0.89 Co 0.05 Mn 0.05 Al 0.01 O2, the first coating layer coated on the surface of the core is a lithium titanate fast ion conductor coating layer, and the second coating layer coated on the surface of the first coating layer is also a lithium titanate fast ion conductor coating layer.

[0097] Polycrystalline Li 1.05 Ni 0.886 Co 0.05 Mn 0.05 Al 0.01 Ti 0.004 O2 positive electrode material is prepared by the following method:

[0098] (1) The polycrystalline hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2is mixed with lithium hydroxide in a molar ratio of 1:1.05, and 1% mol Al2O3 accounting for the molar percentage of the polycrystalline hydroxide precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2is added, and sintered at 750°C for 8 hours under a pure oxygen atmosphere. After cooling, the polycrystalline primary sintered material Li 1.05 Ni 0.89 Co 0.05 Mn 0.05 Al 0.01 O2is obtained by crushing and sieving.

[0099] (2) The polycrystalline primary sintered material Li 1.05 Ni 0.89 Co 0.05 Mn 0.05 Al 0.01 O2of step (1) is mixed with 0.3 mol% TiO2 accounting for the molar percentage of the polycrystalline primary sintered material Li 1.05 Ni 0.89 Co 0.05 Mn 0.05 Al 0.01 O2, and sintered at 600°C for 8 hours under a pure oxygen atmosphere. After cooling, the polycrystalline secondary sintered material Li 1.05 Ni 0.887 Co 0.05 Mn 0.05Al 0.01 Ti 0.003 O2;

[0100] (3) The polycrystalline secondary sintered material Li in step (2) 1.05 Ni 0.887 Co 0.05 Mn 0.05 Al 0.01 Ti 0.003 O2 and Li in polycrystalline secondary sintering materials 1.05 Ni 0.887 Co 0.05 Mn 0.05 Al 0.01 Ti 0.003 The molar percentage of O2 is 0.1mol% TiO2, and the mixture is sintered at 400℃ for 6h in pure oxygen atmosphere. After cooling, the polycrystalline positive electrode material Li 1.05 Ni 0.886 Co 0.05 Mn 0.05 Al 0.01 Ti 0.004 O2.

[0101] A method for evaluating the stability of a nickel-containing positive electrode material, wherein the evaluation object is a nickel-containing positive electrode material I, and the evaluation method comprises the following steps:

[0102] S1. Perform X-ray diffraction test on the nickel-containing positive electrode material to obtain the XRD spectrum of the nickel-containing positive electrode material. The test is performed at an angle of 10 to 80 degrees and a scanning speed of 3 degrees / min. The peak intensity of the 003 peak in the full spectrum of the test results is read. (003) and the peak intensity of peak 104 (104) , I (003) / I (104) As shown in Table 1;

[0103] S2. The nickel-containing positive electrode material is assembled into a lithium-ion battery cell. After the lithium-ion battery cell is cycled for 80 cycles, the cycled lithium-ion battery cell is discharged to a zero-charge state, the lithium-ion battery cell is disassembled to obtain a negative electrode plate, the negative electrode plate is digested to obtain a digestion solution, and the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by the ICP method. The mass fraction t (in wt%) of the total amount of transition metals Ni, Co and Mn dissolved on the negative electrode plate is calculated. The results are shown in Table 1.

[0104] S3. According to I (003) , I (104) and t to calculate the structural stability factor k of the nickel-containing positive electrode material, k=(I (003) / I (104) ) / t, the results are shown in Table 1;

[0105] S4. k is above 6 (critical value k 0(n＝80) ), it is determined that the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material.

[0106] Example 2

[0107] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, and the only difference is that the polycrystalline hydroxide precursor in step (1) is replaced by Ni 0.83 Co 0.12 Mn 0.05 (OH)2, and the prepared positive electrode material is denoted as nickel-containing positive electrode material II.

[0108] An evaluation method for the stability of a nickel-containing positive electrode material, the evaluation object being nickel-containing positive electrode material II, the evaluation method comprising the following steps:

[0109] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material, the test is performed at an angle of 10-80° and a scanning speed of 3° / min, and the peak intensity I (003) and the peak intensity I (104) of the 104 peak in the full spectrum of the test result are read. (003) / I (104) As shown in Table 1;

[0110] S2. The nickel-containing positive electrode material is assembled into a lithium ion cell, after 80 cycles of the lithium ion cell, the cycled lithium ion cell is discharged to zero state, the lithium ion cell is disassembled to obtain a negative electrode sheet, the negative electrode sheet is digested to obtain a digestion solution, the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by ICP method, and the total mass fraction t (unit: wt%) of the total amount of transition metals Ni, Co and Mn dissolved out from the negative electrode sheet is calculated, and the results are shown in Table 1.

[0111] S3. The structural stability factor k of the nickel-containing positive electrode material is calculated according to I (003) , I (104) and t, k = (I (003) / I (104) ) / t, and the results are shown in Table 1.

[0112] S4. k is above 6 (critical value k 0(n＝80) ), it is determined that the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material.

[0113] Example 3

[0114] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, except that the amount of TiO2 added in step (2) accounts for 0.1 mol% of the molar percentage of the polycrystalline primary sintered material, and the prepared positive electrode material is recorded as nickel-containing positive electrode material III.

[0115] An evaluation method for the stability of a nickel-containing positive electrode material, the evaluation object being nickel-containing positive electrode material III, the evaluation method comprising the following steps:

[0116] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material, the test is carried out at an angle of 10-80° and a scanning speed of 3° / min, and the peak intensity I of the 003 peak in the full spectrum of the test result is read (003) and the peak intensity I of the 104 peak (104) , I (003) / I (104) as shown in Table 1.

[0117] S2. The positive electrode material is assembled into a lithium ion battery, after 80 cycles of the lithium ion battery, the cycled lithium ion battery is discharged to zero state, the negative electrode sheet is obtained by disassembling the lithium ion battery, the total mass of transition metals Ni, Co and Mn in the digestion solution obtained after digestion of the negative electrode sheet is tested by ICP method, and the total mass fraction t (unit: wt%) of the transition metals Ni, Co and Mn dissolved out on the negative electrode sheet is calculated. The results are shown in Table 1.

[0118] S3. According to I (003) , I (104) and t, the structural stability factor k of the nickel-containing positive electrode material is calculated, k=(I (003) / I (104) ) / t, and the results are shown in Table 1.

[0119] S4. If k is greater than 6 (critical value k 0(n＝80) ), the nickel-containing positive electrode material is determined to be a high-stability nickel-containing positive electrode material.

[0120] Example 4

[0121] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, except that the amount of TiO2 added in step (3) accounts for 0.05 mol% of the molar percentage of the polycrystalline primary sintered material, and the prepared positive electrode material is recorded as nickel-containing positive electrode material IV.

[0122] An evaluation method for the stability of a nickel-containing positive electrode material, the evaluation object being nickel-containing positive electrode material IV, the evaluation method comprising the following steps:

[0123] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material, the angle is selected as 10-80°, the scanning speed is 3° / min for testing, and the peak intensity I of the 003 peak in the test result full spectrum is read (003) and the peak intensity I of the 104 peak (104) , I (003) / I (104) as shown in Table 1.

[0124] S2. The nickel-containing positive electrode material is assembled into a lithium ion cell, after the lithium ion cell is cycled for 80 cycles, the cycled lithium ion cell is discharged to zero state, the negative electrode sheet is obtained by disassembling the lithium ion cell, the total mass of transition metals Ni, Co and Mn in the digestion solution obtained after digestion of the negative electrode sheet is tested by ICP method, and the total mass fraction t (unit: wt%) of the total amount of transition metals Ni, Co and Mn dissolved out on the negative electrode sheet is calculated, and the results are shown in Table 1.

[0125] S3. According to I (003) , I (104) and t, the structural stability factor k of the nickel-containing positive electrode material is calculated, k = (I (003) / I (104) ) / t, and the results are shown in Table 1.

[0126] S4. If k is greater than 6 (critical value k 0(n＝80) ), the nickel-containing positive electrode material is determined to be a high-stability nickel-containing positive electrode material.

[0127] Example 5

[0128] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, the only difference is that the amount of TiO2 added in step (2) accounts for 1 mol% of the molar percentage of the polycrystalline primary sintered material, and the prepared positive electrode material is recorded as nickel-containing positive electrode material V.

[0129] A method for evaluating the stability of a nickel-containing positive electrode material, the evaluation object is nickel-containing positive electrode material V, the evaluation method comprises the following steps:

[0130] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material, the angle is selected as 10-80°, the scanning speed is 3° / min for testing, and the peak intensity I of the 003 peak in the test result full spectrum is read (003) and the peak intensity I of the 104 peak (104) , I (003) / I (104) as shown in Table 1.

[0131] S2. Assemble the nickel-containing positive electrode material into a lithium ion battery cell, after 80 cycles of the lithium ion battery cell, discharge the cycled lithium ion battery cell to zero state of charge, disassemble the lithium ion battery cell to obtain a negative electrode sheet, after digestion of the negative electrode sheet, a digestion solution is obtained, the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by ICP method, the total mass fraction of the transition metals Ni, Co and Mn dissolved on the negative electrode sheet t (unit: wt%) is calculated, and the results are shown in Table 1.

[0132] S3. According to I (003) , I (104) and t, the structural stability factor k of the nickel-containing positive electrode material is calculated, k = (I (003) / I (104) ) / t, and the results are shown in Table 1.

[0133] S4. If k is greater than 6 (critical value k 0(n＝80) ), the nickel-containing positive electrode material is determined to be a high-stability nickel-containing positive electrode material.

[0134] Example 6

[0135] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, the only difference is that the amount of TiO2 added in step (3) is 0.5 mol% of the molar percentage of the polycrystalline secondary sintered material, and the prepared positive electrode material is recorded as positive electrode material VI.

[0136] A method for evaluating the stability of a nickel-containing positive electrode material, the evaluation object is nickel-containing positive electrode material VI, the method comprises the following steps:

[0137] S1. X-ray diffraction test is performed on the nickel-containing positive electrode material to obtain the XRD pattern of the nickel-containing positive electrode material, the angle is selected to be 10-80°, the scanning speed is 3° / min, the peak intensity I (003) and the peak intensity I (104) of the 104 peak in the full spectrum of the test results are read, I (003) / I (104) , and the results are shown in Table 1.

[0138] S2. Assemble the nickel-containing positive electrode material into a lithium ion battery cell, after 80 cycles of the lithium ion battery cell, discharge the cycled lithium ion battery cell to zero state of charge, disassemble the lithium ion battery cell to obtain a negative electrode sheet, after digestion of the negative electrode sheet, a digestion solution is obtained, the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by ICP method, the total mass fraction of the transition metals Ni, Co and Mn dissolved on the negative electrode sheet t (unit: wt%) is calculated, and the results are shown in Table 1.

[0139] S3. According to I (003) , I(104) and t to calculate the structural stability factor k of the nickel-containing positive electrode material, k = (I (003) / I (104) ), and the results are shown in Table 1.

[0140] S4. k is greater than 6 (critical value k 0(n＝80) ), it is judged that the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material.

[0141] Example 7

[0142] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, except that the addition of TiO2 in steps (2) and (3) is cancelled, and the prepared positive electrode material is denoted as positive electrode material VII.

[0143] An evaluation method for the stability of a nickel-containing positive electrode material, the evaluation object being the nickel-containing positive electrode material VII, the evaluation method comprising the following steps:

[0144] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material, the test is carried out at an angle of 10-80° and a scanning speed of 3° / min, and the peak intensity I (003) and the peak intensity I (104) of the 104 peak in the test result full spectrum are read. (003) / I (104) , as shown in Table 1.

[0145] S2. The nickel-containing positive electrode material is assembled into a lithium ion battery, after 80 cycles of the lithium ion battery, the cycled lithium ion battery is discharged to zero state, the negative electrode sheet is obtained by disassembling the lithium ion battery, the total mass of transition metals Ni, Co and Mn in the digestion solution obtained by digesting the negative electrode sheet is tested by ICP method, the total mass fraction t (unit: wt%) of the total amount of transition metals Ni, Co and Mn dissolved out of the negative electrode sheet is calculated, and the results are shown in Table 1.

[0146] S3. According to I (003) , I (104) and t, the structural stability factor k of the nickel-containing positive electrode material is calculated, k = (I (003) / I (104) ) / t, and the results are shown in Table 1.

[0147] S4. k is less than 6 (critical value k 0(n＝80) ), it is judged that the nickel-containing positive electrode material is a non-high-stability nickel-containing positive electrode material.

[0148] Example 8

[0149] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, except that TiO2 in step (3) is replaced by WO3, and the prepared positive electrode material is denoted as positive electrode material VIII.

[0150] An evaluation method of the stability of a nickel-containing positive electrode material, the evaluation object being the nickel-containing positive electrode material VIII, the evaluation method comprising the following steps:

[0151] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material, the test being performed at an angle of 10-80° and a scanning speed of 3° / min, and the peak intensity I of the 003 peak in the full spectrum of the test result is read. (003) and the peak intensity I of the 104 peak. (104) , I (003) / I (104) As shown in Table 1;

[0152] S2. The nickel-containing positive electrode material is assembled into a lithium ion battery, after 80 cycles of the lithium ion battery, the cycled lithium ion battery is discharged to zero state, the negative electrode sheet is obtained by disassembling the lithium ion battery, the total mass of transition metals Ni, Co and Mn in the digestion solution obtained by digesting the negative electrode sheet is tested by ICP method, and the total mass fraction t (unit: wt%) of the transition metals Ni, Co and Mn dissolved out of the negative electrode sheet is calculated. The results are shown in Table 1.

[0153] S3. The structural stability factor k of the nickel-containing positive electrode material is calculated according to I (003) , I (104) and t, k = (I (003) / I (104) ) / t, and the results are shown in Table 1;

[0154] S4. If k is less than 6 (critical value k 0(n＝80) ), it is judged that the nickel-containing positive electrode material is a non-high-stability nickel-containing positive electrode material.

[0155] Example 9

[0156] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, except that TiO2 in steps (2) and (3) is replaced by Al2O3, and the prepared positive electrode material is denoted as nickel-containing positive electrode material IX.

[0157] An evaluation method of the stability of a nickel-containing positive electrode material, the evaluation object being the nickel-containing positive electrode material IX, the evaluation method comprising the following steps:

[0158] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material, the angle is selected as 10-80°, the scanning speed is 3° / min for testing, and the peak intensity I of the 003 peak in the test result full spectrum is read (003) and the peak intensity I of the 104 peak (104) , I (003) / I (104) as shown in Table 1.

[0159] S2. The nickel-containing positive electrode material is assembled into a lithium ion cell, after the lithium ion cell is cycled for 80 cycles, the cycled lithium ion cell is discharged to zero state, the negative electrode sheet is obtained by disassembling the lithium ion cell, the negative electrode sheet is digested to obtain a digestion solution, the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by ICP method, the total mass fraction t (unit: wt%) of the total amount of transition metals Ni, Co and Mn dissolved out on the negative electrode sheet is calculated, and the results are shown in Table 1.

[0160] S3. The structure stability factor k of the nickel-containing positive electrode material is calculated according to I (003) , I (104) and t, k = (I (003) / I (104) ) / t, and the results are shown in Table 1.

[0161] S4. If k is less than 6 (critical value k 0(n＝80) ), it is judged that the nickel-containing positive electrode material is a non-high-stability nickel-containing positive electrode material.

[0162] Example 10

[0163] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, the only difference is that TiO2 is replaced by WO3 in steps (2) and (3), and the prepared positive electrode material is recorded as positive electrode material X.

[0164] An evaluation method for the stability of a nickel-containing positive electrode material, the evaluation object is a nickel-containing positive electrode material X, the evaluation method comprises the following steps:

[0165] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material, the angle is selected as 10-80°, the scanning speed is 3° / min for testing, and the peak intensity I of the 003 peak in the test result full spectrum is read (003) and the peak intensity I of the 104 peak (104) , I (003) / I (104) as shown in Table 1.

[0166] S2. Assemble the nickel-containing positive electrode material into a lithium ion battery cell, after the lithium ion battery cell is cycled for 80 cycles, discharge the cycled lithium ion battery cell to zero state of charge, disassemble the lithium ion battery cell to obtain a negative electrode sheet, and obtain a digestion solution after digesting the negative electrode sheet, test the total mass of transition metals Ni, Co and Mn in the digestion solution by ICP method, calculate the total mass fraction t (unit: wt%) of the transition metals Ni, Co and Mn dissolved from the negative electrode sheet to the mass of the negative electrode sheet, and the results are shown in Table 1.

[0167] S3. According to I (003) , I (104) and t, calculate the structure stability factor k of the nickel-containing positive electrode material, k = (I (003) / I (104) ) / t, and the results are shown in Table 1.

[0168] S4. If k is less than 6 (critical value k 0(n＝80) ), it is judged that the nickel-containing positive electrode material is a non-high-stability nickel-containing positive electrode material.

[0169] Example 11

[0170] The evaluation object is a polycrystalline positive electrode material Li 1.05 Ni 0.986 Al 0.01 Ti 0.004 O2 (denoted as nickel-containing positive electrode material XI), which is a core-shell structure, the chemical formula of the core is Li 1.05 Ni 0.99 Al 0.01 O2, the first coating layer coated on the surface of the core is a lithium titanate fast ion conductor coating layer, and the second coating layer coated on the surface of the first coating layer is also a lithium titanate fast ion conductor coating layer.

[0171] The preparation method of the evaluation object of this example is the same as that of the evaluation object of Example 1, the only difference is that the polycrystalline hydroxide precursor in step (1) is replaced by Ni(OH)2.

[0172] A method for evaluating the stability of a nickel-containing positive electrode material, the evaluation object is a nickel-containing positive electrode material I, the method comprising the following steps:

[0173] S1. Perform X-ray diffraction test on the nickel-containing positive electrode material to obtain the XRD pattern of the nickel-containing positive electrode material, select an angle of 10-80°, and test at a scanning speed of 3° / min to read the peak intensity I (003) and the peak intensity I (104) of the 104 peak in the test result full spectrum, I (003) / I (104) as shown in Table 1.

[0174] S2. The nickel-containing positive electrode material is assembled into a lithium-ion battery cell. After the lithium-ion battery cell is cycled for 80 cycles, the cycled lithium-ion battery cell is discharged to a zero-charge state, the lithium-ion battery cell is disassembled to obtain a negative electrode plate, the negative electrode plate is digested to obtain a digestion solution, and the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by the ICP method. The mass fraction t (in wt%) of the total amount of transition metals Ni, Co and Mn dissolved on the negative electrode plate is calculated. The results are shown in Table 1.

[0175] S3. According to I (003) , I (104) and t to calculate the structural stability factor k of the nickel-containing positive electrode material, k=(I (003) / I (104) ) / t, the results are shown in Table 1;

[0176] S4.k is less than 6 (critical value k 0(n＝80) ), it is judged that the nickel-containing positive electrode material is not a high-stability nickel-containing positive electrode material.

[0177] Example 12

[0178] A method for evaluating the stability of a nickel-containing positive electrode material, wherein the evaluation object is the same as the evaluation object in Example 1, that is, nickel-containing positive electrode material I, and the evaluation method comprises the following steps:

[0179] S1. Perform X-ray diffraction test on the nickel-containing positive electrode material to obtain the XRD spectrum of the nickel-containing positive electrode material. The test is performed at an angle of 10 to 80 degrees and a scanning speed of 3 degrees / min. The peak intensity of the 003 peak in the full spectrum of the test results is read. (003) and the peak intensity of peak 104 (104) , I (003) / I (104) As shown in Table 1;

[0180] S2. The nickel-containing positive electrode material is assembled into a lithium-ion battery cell. After the lithium-ion battery cell is cycled for 200 cycles, the cycled lithium-ion battery cell is discharged to a zero-charge state, the lithium-ion battery cell is disassembled to obtain a negative electrode plate, the negative electrode plate is digested to obtain a digestion solution, and the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by the ICP method. The mass fraction t (in wt%) of the total amount of transition metals Ni, Co and Mn dissolved on the negative electrode plate is calculated. The results are shown in Table 1.

[0181] S3. According to I (003) , I (104) and t to calculate the structural stability factor k of the nickel-containing positive electrode material, k=(I (003) / I (104) ) / t, the results are shown in Table 1;

[0182] S4. k is greater than or equal to 3 (critical value k 0(n＝200) ), it is determined that the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material.

[0183] Example 13

[0184] A method for evaluating the stability of a nickel-containing positive electrode material, the evaluation object is the same as that of Example 2, and is the nickel-containing positive electrode material II. The method comprises the following steps:

[0185] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material. The test is performed at an angle of 10-80° and a scanning speed of 3° / min. The peak intensity I (003) and the peak intensity I (104) of the 104 peak in the test result full spectrum are read. (003) (104) As shown in Table 1;

[0186] S2. The nickel-containing positive electrode material is assembled into a lithium ion battery. After the lithium ion battery is cycled for 200 cycles, the cycled lithium ion battery is discharged to zero state, the lithium ion battery is disassembled to obtain a negative electrode sheet, the negative electrode sheet is digested to obtain a digestion solution, the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by ICP method, and the total mass fraction t (unit: wt%) of the transition metals Ni, Co and Mn dissolved out of the negative electrode sheet is calculated. The results are shown in Table 1.

[0187] S3. The structural stability factor k of the nickel-containing positive electrode material is calculated according to I (003) , I (104) and t, k = (I (003) / I (104) ) / t. The results are shown in Table 1.

[0188] S4. k is greater than or equal to 3 (critical value k 0(n＝200) ), it is determined that the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material.

[0189] Example 14

[0190] A method for evaluating the stability of a nickel-containing positive electrode material, the evaluation object is the same as that of Example 3, and is the nickel-containing positive electrode material III. The method comprises the following steps:

[0191] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material. The test is performed at an angle of 10-80° and a scanning speed of 3° / min. The peak intensity I (003) and the peak intensity I (104) of the 104 peak in the test result full spectrum are read. (003) ​ / I (104) As shown in Table 1;

[0192] S2. The nickel-containing positive electrode material is assembled into a lithium ion battery cell, after 200 cycles of the lithium ion battery cell, the cycled lithium ion battery cell is discharged to zero state, the lithium ion battery cell is disassembled to obtain a negative electrode sheet, the negative electrode sheet is digested to obtain a digestion solution, the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by ICP method, the total mass fraction t (unit: wt%) of the total amount of transition metals Ni, Co and Mn dissolved on the negative electrode sheet is calculated, and the results are shown in Table 1.

[0193] S3. According to I (003) , I (104) and t, the structural stability factor k of the nickel-containing positive electrode material is calculated, k = (I (003) / I (104) ) / t, and the results are shown in Table 1;

[0194] S4. k is greater than 3 (critical value k 0(n＝200) ), it is judged that the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material.

[0195] Example 15

[0196] A method for evaluating the stability of a nickel-containing positive electrode material, the evaluation object is the same as that of Example 7, and is a nickel-containing positive electrode material VII. The evaluation method comprises the following steps:

[0197] S1. The nickel-containing positive electrode material is tested by X-ray diffraction to obtain the XRD pattern of the nickel-containing positive electrode material, the angle is selected to be 10-80°, the scanning speed is 3° / min, the peak intensity I (003) and the peak intensity I (104) of the 104 peak in the test result full spectrum are read, I (003) / I (104) As shown in Table 1;

[0198] S2. The nickel-containing positive electrode material is assembled into a lithium ion battery cell, after 200 cycles of the lithium ion battery cell, the cycled lithium ion battery cell is discharged to zero state, the lithium ion battery cell is disassembled to obtain a negative electrode sheet, the negative electrode sheet is digested to obtain a digestion solution, the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by ICP method, the total mass fraction t (unit: wt%) of the total amount of transition metals Ni, Co and Mn dissolved on the negative electrode sheet is calculated, and the results are shown in Table 1.

[0199] S3. According to I (003) , I (104) and t, the structural stability factor k of the nickel-containing positive electrode material is calculated, k = (I (003) / I(104) ) / t, the results are shown in Table 1;

[0200] S4. k is less than 3 (critical value k 0(n＝200) ), it is judged that the nickel-containing positive electrode material is a non-high-stability nickel-containing positive electrode material.

[0201] Example 16

[0202] A method for evaluating the stability of a nickel-containing positive electrode material, the evaluation object is the same as that of Example 8, both of which are nickel-containing positive electrode material VIII, and the evaluation method comprises the following steps:

[0203] S1. The nickel-containing positive electrode material is subjected to X-ray diffraction test to obtain the XRD pattern of the nickel-containing positive electrode material, the angle is selected to be 10-80°, the scanning speed is 3° / min, the peak intensity I of the 003 peak in the full spectrum of the test result is read (003) and the peak intensity I of the 104 peak (104) , I (003) / I (104) As shown in Table 1;

[0204] S2. The nickel-containing positive electrode material is assembled into a lithium ion battery, after 200 cycles of the lithium ion battery, the cycled lithium ion battery is discharged to zero state, the lithium ion battery is disassembled to obtain a negative electrode sheet, the negative electrode sheet is digested to obtain a digestion solution, the total mass of transition metals Ni, Co and Mn in the digestion solution is tested by ICP method, the total mass fraction t (unit: wt%) of the total amount of transition metals Ni, Co and Mn dissolved out from the negative electrode sheet is calculated, the results are shown in Table 1.

[0205] S3. The structural stability factor k of the nickel-containing positive electrode material is calculated according to I (003) , I (104) and t, k = (I (003) / I (104) ) / t, the results are shown in Table 1;

[0206] S4. k is less than 3 (critical value k 0(n＝200) ), it is judged that the nickel-containing positive electrode material is a non-high-stability nickel-containing positive electrode material.

[0207] It should be noted that in the above examples 1-11, the nickel-containing positive electrode material is assembled into a lithium ion cell in step S1, and the specific operation is as follows: take 92:5:3 mass ratio of nickel-containing positive electrode material, conductive carbon black and PVDF (polyvinylidene fluoride), add a certain amount of N-methyl pyrrolidone (NMP) and mix uniformly to obtain a positive electrode slurry with a solid content of 70wt%, coat on an aluminum foil, and then dry to form a positive electrode sheet (positive electrode active layer thickness is 100μm). Then, with the separator (24μm PP separator), electrolyte (volume ratio EC:PC:EMC=1:2:7, 1.1mol / L LiPF6), graphite negative electrode sheet, the full battery is assembled in the glove box, and then placed for 12h. When testing the t value, the full battery is cycled for 80 times under the conditions of temperature 45℃, charge-discharge voltage 3.0-4.3V, and charge-discharge current 1C.

[0208] The same assembly method as in step S1 is used to assemble each nickel-containing positive electrode material into a positive electrode sheet and a full battery, and then the following performance tests are carried out to verify the accuracy of the evaluation results of examples 1-11.

[0209] (1) The first discharge specific capacity: 0.1C constant current charging to 4.3V, then constant voltage charging to 4.3V, and then 0.1C discharging to 3.0V, the first discharge specific capacity is tested, and the results are shown in Table 1.

[0210] (2) 50% SOC-DCR (internal resistance at 50% state of charge): 1C CC-CV to 4.3V, 1C DC for 30min, 30min standing, 4C DC for 10s, 1C DC to 3V. DCR=(4C 10s end voltage-stationary end voltage) / 4C current, and the results are shown in Table 1.

[0211] (3) High temperature cycle stability: 80 cycles under the conditions of temperature 45℃, charge-discharge voltage 3.0-4.3V, and charge-discharge current 1C, the discharge specific capacity is tested, and the capacity retention rate is calculated, and the results are shown in Table 1.

[0212] (4) High temperature storage stability: 0.1C 4.3V CCCV full battery at room temperature, 15 days standing in 60℃ oven, and then testing 3.0-4.3V capacity at room temperature, and calculating the ratio of capacity before storage, which is the capacity retention rate of 60℃ storage for 15 days, and the results are shown in Table 1.

[0213] Table 1. Stability evaluation results of nickel-containing positive electrode materials of examples 1-11 and battery performance test results

[0214]

[0215]

[0216] Examples 1-11 are according to the absolute value of k and the critical value k0 comparison of the nickel-containing positive electrode material whether it is a high stability nickel-containing positive electrode material. From Table 1, the k value of nickel-containing positive electrode materials I-VI is greater than 6 (critical value k 0(n＝80) ), so it can be considered that the nickel-containing positive electrode materials I-VI are high stability nickel-containing positive electrode materials. The k value of nickel-containing positive electrode materials VII-XI is less than 6 (critical value k 0(n＝80) ), so it can be considered that the nickel-containing positive electrode materials VII-XI are non-high stability nickel-containing positive electrode materials.

[0217] The 45℃ cycle 80 times capacity retention and 60℃ storage 15 days capacity retention in Table 1 are evidence of whether the nickel-containing positive electrode material has high stability. Specifically, the 45℃ cycle 80 times capacity retention of nickel-containing positive electrode materials I-VI is above 98%, and the 60℃ storage 15 days capacity retention is above 94%, so it can be considered that the nickel-containing positive electrode materials I-VI have good cycle stability, storage stability and high temperature stability, and are indeed high stability nickel-containing positive electrode materials. The 45℃ cycle 80 times capacity retention of nickel-containing positive electrode materials VII-XI is below 98%, and the cycle 80 times capacity retention is below 94%, so it can be considered that the cycle stability, storage stability and high temperature stability of the nickel-containing positive electrode materials VII-XI are poor, and are indeed non-high stability nickel-containing positive electrode materials.

[0218] In summary, the evaluation method of the embodiment of the application uses k=(I (003) / I (104) ) / t as a structural stability factor of the nickel-containing positive electrode material, and can distinguish the stability of the nickel-containing positive electrode material according to the k value, and the judgment result is accurate; in addition, the evaluation method is universal, which is helpful for engineers to quickly screen the positive electrode materials.

[0219] In addition, the relative high and low of the nickel-containing positive electrode materials can also be judged according to the k value sorting of each nickel-containing positive electrode material, and the higher the k value of the nickel-containing positive electrode material, the higher its stability. The evaluation objects of Examples 1-10 are all nickel-cobalt-manganese positive electrode materials, and the comparability is strong. From the sorting of the capacity retention of the batteries in Examples 1-10 after 45℃ cycle 80 times and the capacity retention after 60℃ storage 15 days in Table 1, the sorting and the k value sorting of each example are consistent, which are all Example 2> Example 5> Example 6> Example 1> Example 4> Example 3> Example 10> Example 8> Example 9> Example 7, which shows that the evaluation method has accurate judgment result, and is helpful for engineers to quickly screen the nickel-containing positive electrode materials.

[0220] The nickel-containing positive electrode materials I, II, III, VII, and VIII were assembled into positive electrode sheets and button-type full cells using the same assembly method as the lithium ion cell in step S1, and the following performance tests were performed to verify the evaluation results of Examples 12-16.

[0221] (1) First discharge specific capacity: 0.1C constant current charging to 4.3V, then constant voltage charging to 4.3V, and then 0.1C discharging to 3.0V, testing the first discharge specific capacity, the results are shown in Table 2.

[0222] (2) 50% SOC-DCR (internal resistance at 50% state of charge): 1C CC-CV to 4.3V, 1C DC for 30min, stand for 30min, 4C DC for 10s, 1C DC to 3V. DCR = (4C 10s end voltage - stand end voltage) / 4C current, the results are shown in Table 2.

[0223] (3) High temperature cycle stability: under the conditions of temperature 45℃, charge and discharge voltage 3.0-4.3V, and charge and discharge current 1C, cycle for 200 times, test the discharge specific capacity, calculate the capacity retention rate, the results are shown in Table 2.

[0224] Table 2. Stability evaluation results of nickel-containing positive electrode materials of Examples 12-16 and battery performance test results

[0225]

[0226] Examples 12-16 are to determine whether the nickel-containing positive electrode material is a high-stability nickel-containing positive electrode material according to the comparison of the absolute value of k with the critical value k0. As can be seen from Table 2, the k value of the nickel-containing positive electrode materials I, II, and III is greater than 3 (the critical value k0), so it can be considered that the nickel-containing positive electrode materials I, II, and III are high-stability nickel-containing positive electrode materials. The k value of the nickel-containing positive electrode materials IV and V is less than 3 (the critical value k0), so it can be considered that the nickel-containing positive electrode materials IV and V are non-high-stability nickel-containing positive electrode materials. 0(n＝200) ) above, so it can be considered that the nickel-containing positive electrode materials I, II, and III are high-stability nickel-containing positive electrode materials. The k value of the nickel-containing positive electrode materials IV and V is less than 3 (the critical value k 0(n＝200) ) above, so it can be considered that the nickel-containing positive electrode materials I, II, and III are high-stability nickel-containing positive electrode materials. The k value of the nickel-containing positive electrode materials IV and V is less than 3 (the critical value k0), so it can be considered that the nickel-containing positive electrode materials IV and V are non-high-stability nickel-containing positive electrode materials.

[0227] The 45℃ cycle 200 times capacity retention rate in Table 2 is a proof of whether the nickel-containing positive electrode material has high stability. Specifically, as can be seen from Table 2, the nickel-containing positive electrode materials I, II, and III have a 45℃ cycle 200 times capacity retention rate of 93% or more, so it can be considered that the nickel-containing positive electrode materials I, II, and III have good cycle stability and high temperature stability, and are indeed high-stability nickel-containing positive electrode materials. The nickel-containing positive electrode materials IV and V have a 45℃ cycle 200 times capacity retention rate of less than 93%, so it can be considered that the cycle stability and high temperature stability of the nickel-containing positive electrode materials IV and V are poor, and are indeed non-high-stability nickel-containing positive electrode materials.

[0228] In summary, the evaluation method of the embodiment of the present application uses k=(I (003) / I (104) ) as a structural stability factor of the nickel-containing positive electrode material, the stability of different nickel-containing positive electrode materials can be ranked according to the order of k value, and the judgment result is accurate; in addition, the evaluation method is universal, which is helpful for engineers to quickly screen the nickel-containing positive electrode material.

[0229] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the skilled person in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0230] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A method for evaluating the stability of a nickel-containing positive electrode material, characterized in that: The following steps are involved: S1. Perform X-ray diffraction test on the nickel-containing positive electrode material to obtain the XRD pattern of the nickel-containing positive electrode material, and read the peak intensity I of the 003 peak in the XRD pattern. (003) and the peak intensity of peak 104 (104) ; S2. Provide a battery cell comprising the nickel-containing positive electrode material, and test the battery cell after cycling to determine the mass fraction t of the total amount of transition metal Ni and / or Mn and Co dissolved from the negative electrode sheet, where the number of cycles of the battery cell is n, where n = 80 to 200; S3. According to the I (003) 、The I (104) and t to calculate the structural stability factor k of the nickel-containing positive electrode material, wherein k=(I (003) / I (104) ) / t; S4. When the k is above the critical value k0, the nickel-containing positive electrode material is judged to be a high-stability nickel-containing positive electrode material; when the k is less than the k0, the nickel-containing positive electrode material is judged to be a non-high-stability nickel-containing positive electrode material; the k0 = 3 to 6.

2. The method for evaluating the stability of a nickel-containing positive electrode material according to claim 1, wherein: When n=80-200, the larger n is, the smaller k0 is.

3. The method for evaluating the stability of a nickel-containing positive electrode material according to claim 1, wherein: When n=80, the k 0(n＝80) is 6.

4. The method for evaluating the stability of a nickel-containing positive electrode material according to claim 1, wherein: When n=200, the k 0(n＝200) is 3.

5. The method for evaluating the stability of a nickel-containing positive electrode material according to any one of claims 1 to 4, wherein: The method used to test the t is the ICP method.

6. A method for evaluating the stability of a nickel-containing positive electrode material, characterized in that: The following steps are involved: S1. Perform X-ray diffraction tests on different nickel-containing cathode materials to obtain the XRD patterns of each nickel-containing cathode material, and read the peak intensity of the 003 peak in each XRD pattern. (003) and the peak intensity of peak 104 (104) ; S2. Provide a plurality of battery cells, each containing a nickel-containing positive electrode material, wherein the nickel-containing positive electrode materials in each two battery cells are of different types, and test the mass fraction t of the sum of the dissolution amount of transition metal Ni and / or Mn and Co on the negative electrode sheet of each battery cell after cycling, wherein the number of cycles of the battery cell is n, and the number of cycles of each battery cell is the same; S3. According to the I (003) 、The I (104) and t respectively calculate the structural stability factor k of each nickel-containing positive electrode material, wherein k=(I (003) / I (104) ) / t; S4. Sort the sizes of k of different nickel-containing positive electrode materials, and obtain a stability ranking of different nickel-containing positive electrode materials according to the ranking of k. The larger the k, the higher the stability of the nickel-containing positive electrode material.

7. A method for evaluating the stability of a nickel-containing positive electrode material, characterized in that: The following steps are involved: S1. Perform X-ray diffraction tests on different nickel-containing cathode materials to obtain the XRD patterns of each nickel-containing cathode material, and read the peak intensity of the 003 peak in each XRD pattern. (003) and the peak intensity of peak 104 (104) ; S2. Providing a plurality of battery cells, each containing a nickel-containing positive electrode material, wherein the nickel-containing positive electrode materials in each two battery cells are of different types, and testing the mass fraction t of the sum of the dissolution amount of transition metal Ni and / or Mn and Co on the negative electrode sheet of each battery cell after cycling, wherein the number of cycles of the battery cell is n, and the number of cycles of each battery cell is different; S3. According to the I (003) 、The I (104) and t respectively calculate the structural stability factor k of each nickel-containing positive electrode material, wherein k=(I (003) / I (104) ) / t; S4. Select the nickel-containing positive electrode materials with the same k, sort the sizes of n of the nickel-containing positive electrode materials with the same k, and obtain the stability ranking of the nickel-containing positive electrode materials with the same k according to the sorting of n. The larger the n, the higher the stability of the nickel-containing positive electrode material.

8. The method for evaluating the stability of a nickel-containing positive electrode material according to claim 6 or 7, wherein: The n is greater than or equal to 80.

9. The method for evaluating the stability of a nickel-containing positive electrode material according to claim 6 or 7, wherein: The method used to test the t is the ICP method.

10. The method for evaluating the stability of a nickel-containing positive electrode material according to claim 6 or 7, wherein: The different nickel-containing positive electrode materials contain the same type of transition metals.

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