Cascade utilization classification method for retired power lithium battery based on positive electrode material

Abstract

The invention discloses an ex-service power lithium battery echelon utilization classification method based on a positive electrode material. Comprising the following steps: extracting the positive electrode material of the retired power lithium battery with the appearance meeting the requirement, and obtaining the following parameters: the number a of cracks in the worst view field, the percentage a1 of the cracks in the view field area, the crack width a2, the solid electrolyte interface thickness b and the radius value c of a second semicircle; grading the aging degree of the positive electrode material and the grade of the retired power lithium battery according to the divided value ranges of a, b and c; part of the graded retired power lithium battery is extracted for a cyclic charge and discharge test, whether the charge and discharge performance of the graded retired power lithium battery meets the use requirement under the cyclic rate is judged, and if yes, the graded retired power lithium battery is put into an application scene under the working condition of the corresponding cyclic rate; and if not, increasing or decreasing the cycle rate, carrying out a charge-discharge experiment under the corresponding cycle rate, judging whether the charge-discharge performance meets the use requirement, and if not, continuing to carry out the charge-discharge experiment.

Description

Technical Field

[0001] The present invention relates to the technical field of cascade utilization of retired power lithium batteries, and in particular to a classification method for cascade utilization of retired power lithium batteries based on positive electrode materials. Background Art

[0002] At present, lithium batteries still dominate the field of power batteries. Generally, when the capacity of a power battery is less than 80% of its original capacity, it cannot be used in a car any longer, that is, it reaches the retirement standard. The service life of automotive power lithium batteries is generally five to ten years. After nearly ten years of vigorous development, most of the early power lithium batteries have reached the retirement age. If large-scale retired power lithium batteries are not properly disposed of, it will seriously pollute the environment, cause waste of resources, and hinder the sustainable development of the new energy vehicle industry.

[0003] There are two main ways to recycle retired power batteries: direct recycling and cascade utilization. Since the recycling value of lithium iron phosphate power batteries is relatively low, cascade utilization is generally adopted. The cascade utilization of retired power lithium batteries refers to the use of used power lithium batteries in new energy vehicles and other fields after testing, screening, and reorganization, so as to fully utilize the value of the batteries in other fields with lower requirements for battery performance. However, due to the large number of recycled retired power batteries, incomplete factory data preservation, and the complexity of previous service conditions, the performance of retired power lithium batteries often varies greatly and is difficult to trace, which has caused difficulties in the standardization and rationalization of cascade utilization.

[0004] Therefore, it is necessary to establish certain methods to conduct preliminary screening and classification of retired power lithium batteries in order to facilitate the subsequent cascade utilization process. The existing screening and rating methods mostly use the electrical performance of the battery as the main classification indicator, without combining the electrical performance of the battery with the changes in the positive electrode material of the battery. The electrical performance of the battery mainly refers to the voltage, capacity, internal resistance, charge and discharge performance, cycle life and self-discharge rate of the battery. The electrical performance of the battery is mainly related to the battery material, battery structure, manufacturing process and use conditions. The retired power battery has been used. The battery structure, manufacturing process and use conditions have been determined before the power battery is retired. The structure and chemical composition of the battery material will change during the battery charging and discharging process. After the power battery is retired, if the battery electrical performance is used as the main classification indicator for the cascade utilization of retired power batteries, without paying attention to the battery material itself, this will make the screening and classification of the cascade utilization of retired power batteries not rigorous and accurate. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a classification method for the cascade utilization of retired power lithium batteries based on positive electrode materials, so as to solve the problem that the existing retired power lithium batteries use a single classification indicator during the cascade utilization process, resulting in inaccurate cascade utilization screening and classification.

[0006] In view of the shortcomings of the prior art, the present invention provides a classification method for the cascade utilization of retired power lithium batteries based on positive electrode materials, and the classification method for the cascade utilization of retired power lithium batteries comprises the following steps:

[0007] S1. Perform appearance inspection on retired power lithium batteries and select retired power lithium batteries that meet the appearance requirements;

[0008] S2. Extracting positive electrode materials from the retired power lithium batteries screened in step S1, and obtaining the following parameters of the positive electrode materials of the retired power lithium batteries:

[0009] The number of cracks in the worst viewing field a, the percentage of the viewing field area occupied by the cracks a1, and the crack width a2;

[0010] Solid electrolyte interface thickness b;

[0011] The radius c of the second semicircle in the impedance test diagram;

[0012] S3, dividing the positive electrode material by the numerical ranges of the three parameters a, b, and c in step S2, and rating the aging degree of the positive electrode material according to the divided ranges, and rating the retired power lithium batteries for which the aging degree of the positive electrode material has been rated;

[0013] S4, extracting a certain number of retired power lithium batteries from the retired power lithium batteries that have obtained the grade rating in step S3 to perform cyclic charge and discharge tests at different cycle rates;

[0014] S5, performing the following evaluation operation on the retired power lithium battery subjected to the cyclic charge and discharge test in step S4: if the charge and discharge performance of the retired power lithium battery meets the use requirements under the cycle rate, the retired power lithium battery is put into the application scenario under the corresponding cycle rate condition;

[0015] If the charge and discharge performance of the retired power lithium battery does not meet the usage requirements at the cycle rate, increase or decrease the cycle rate, and perform the cyclic charge and discharge test again at the increased or decreased cycle rate, and repeat this step until the charge and discharge performance of the retired power lithium battery meets the usage requirements at the cycle rate for the cyclic charge and discharge test.

[0016] Preferably, the numerical ranges of the parameters a1, a2, b, and c in step S2 are:

[0017] a1: 0% to 50%, a2: 0 μm to 2 μm, b: 0 μm to 0.5 μm, c≥0.

[0018] Preferably, the number of retired power lithium batteries extracted from different rating levels in step S4 accounts for x% of the total number of retired power lithium batteries in the corresponding rating level;

[0019] Wherein, the value range of x is 10-20.

[0020] Preferably, the aging degree rating of the positive electrode material and the grade rating of the retired power lithium battery in step S3 include the following:

[0021] 0≤a1<10%, 0≤a2<0.4μm, 0≤b<0.1μm, c≥0, the positive electrode material aging rating is level 1, and the retired power lithium battery rating is level A;

[0022] 10≤a1<20%, ​​0.4≤a2<0.8μm, 0.1≤b<0.2μm, c≥0, the positive electrode material aging rating is level 2, and the retired power lithium battery rating is level B;

[0023] 20≤a1<30%, 0.8≤a2<1.2μm, 0.2≤b<0.3μm, c≥0, the positive electrode material aging rating is level 3, and the retired power lithium battery rating is level C;

[0024] 30≤a1<40%, 1.2≤a2<1.6μm, 0.3≤b<0.4μm, c≥0, the positive electrode material aging rating is level 4, and the retired power lithium battery rating is level D;

[0025] 40≤a1≤50%, 1.6≤a2≤2.0μm, 0.4≤b<0.5μm, c≥0, the positive electrode material aging rating is level 5, and the retired power lithium battery rating is level E.

[0026] Preferably, the appearance inspection of the retired power lithium battery in step S1 includes checking whether the retired power lithium battery has bulging and leakage, and the retired power lithium battery with bulging and leakage will no longer be subjected to step S2.

[0027] Preferably, in step S4, the cycle rate of the cyclic charge and discharge test of the retired power lithium battery is 0.1C to 0.5C.

[0028] The present invention provides a classification method for the cascade utilization of retired power lithium batteries based on positive electrode materials, which integrates the positive electrode materials of batteries into the classification of the cascade utilization of retired power lithium batteries. Because the changes in the positive electrode materials of batteries can more clearly reflect the electrical properties of the batteries, the electrical properties of the batteries are combined with the changes in the positive electrode materials of batteries as screening indicators for the cascade utilization of retired power lithium batteries, making the screening and classification process more rigorous and accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart of a classification method for recycling retired power lithium batteries provided in an embodiment of the present invention;

[0030] Figure 2 A 1000-fold scanning electron microscope (SEM) image of the retired power lithium battery positive electrode material provided in Example 1 of the present invention;

[0031] Figure 3 This is a 10,000-fold scanning electron microscope (SEM) image of the retired power lithium battery positive electrode material provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "top", "bottom", "top surface", "bottom surface", "inside", "outside", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0034] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood to exclude the number itself, and "above", "below", "within" etc. are understood to include the number itself. If the terms "first", "second", "third" are described, they are only used for the purpose of description and distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0035] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "set" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The following is an explanation of the embodiments of the present invention based on its overall structure.

[0036] Figure 1 A flowchart of the classification method for the cascade utilization of retired power lithium batteries provided in an embodiment of the present invention is provided in Figure 1 The classification method for the cascade utilization of retired power lithium batteries comprises the following steps:

[0037] S1. Perform appearance inspection on retired power lithium batteries and select retired power lithium batteries that meet the appearance requirements.

[0038] Specifically, the appearance inspection of the retired power lithium battery in step S1 includes checking whether the retired power lithium battery has bulging and leakage. The retired power lithium battery with bulging and leakage will not proceed to the next step.

[0039] For more details, see Figure 1 In a specific implementation scheme, N retired power lithium battery cells are visually inspected to check whether there are unqualified phenomena such as bulging and leakage. If so, the unqualified batteries are screened out to obtain M retired power lithium battery cells with normal appearance, where M≤N.

[0040] S2. Extracting positive electrode materials from the retired power lithium batteries selected in step S1, and obtaining the following parameters of the positive electrode materials of the retired power lithium batteries: the number of cracks a in the most degraded field of view, the percentage of the crack area in the field of view a1, and the crack width a2; the solid electrolyte interface degree b; and the radius value c of the second semicircle in the impedance test diagram.

[0041] Specifically, when disassembling the positive electrode materials of retired power lithium batteries, a purified glove box and an atmosphere furnace are generally used to first remove the outer shell of the battery, then separate the diaphragm, sort out the positive electrode of the battery, and then extract the positive electrode material.

[0042] Specifically, by observing the high-magnification morphology of retired power lithium batteries under a scanning electron microscope, the parameter values ​​of the number of cracks a in the most degraded field of view, the percentage of the crack area in the field of view a1, the crack width a2, and the solid electrolyte interface thickness b can be obtained. Usually, the scanning electron microscope magnification is 1000 times and 10000 times to obtain the parameter values ​​of parameters a, a1 and a2. Among them, the percentage of the crack area in the field of view a1 is specifically the percentage of the number of cracks a in the most degraded field of view to the most degraded field of view area, and the crack width a2 is specifically the width of the crack in the most degraded field of view.

[0043] The SEI film is the Solid Electrolyte Interphase. During the first charge and discharge process of a lithium-ion battery, the electrode material reacts with the electrolyte at the solid-liquid interface to form a passivation film covering the surface of the electrode. This is the SEI film. Specifically, when the battery is charged, lithium ions escape from the positive electrode, pass through the electrolyte, and embed into the negative electrode. On the surface of the negative electrode, lithium ions react with the components in the electrolyte to form an SEI film. This process is irreversible. Once formed, the SEI film will continue to evolve and stabilize during the subsequent charge and discharge process.

[0044] Among them, in the impedance test of the positive electrode material in the power lithium battery, a Nyquist diagram is usually obtained. Two semicircles may appear in the diagram. In the Nyquist diagram, the first semicircle can usually represent the following: For the positive electrode material, although the SEI film is mainly formed at the negative electrode, in some special cases, a similar interface film will also be formed on the positive electrode surface, or there will be some interface reaction products. This semicircle part reflects the impedance brought by this interface film or interface reaction on the positive electrode surface. In the Nyquist diagram, the second semicircle is usually related to the charge transfer process. The second semicircle can usually represent the following: 1. Charge transfer impedance: This semicircle reflects the impedance generated by the charge transfer process between the electrode material and the electrolyte. During the battery charging and discharging process, lithium ions undergo charge transfer at the interface between the positive electrode material and the electrolyte. This process is affected by many factors, such as the conductivity of the electrode material, the contact of the interface, and the ionic conductivity of the electrolyte. 2. Interface reaction: In addition to charge transfer, this semicircle is also related to some interface reactions, such as side reactions on the surface of the positive electrode material, the formation of SEI film (solid electrolyte interface film), etc. These reactions will affect the efficiency and speed of charge transfer, thus manifesting as specific impedance characteristics. Therefore, by measuring the impedance of the positive electrode material, the radius value c of the second semicircle can be obtained, and the radius value c of the second semicircle can characterize the thickness of the SEI film. Defining and evaluating retired power lithium batteries based on the thickness of the SEI film of the positive electrode material can more accurately screen the subsequent classification and utilization of retired power lithium batteries.

[0045] See also Figure 1 In a specific implementation scheme, M retired power lithium batteries are disassembled, positive electrode materials are extracted, and then the following tests are performed respectively:

[0046] The high-magnification morphologies of M retired power lithium batteries were observed under a SEM scanning electron microscope, and the main statistics were the number of cracks a in the most degraded field of view, the percentage of cracks in the field of view area a1, the crack width a2, and the solid electrolyte interface thickness b.

[0047] The impedance of the positive electrode materials of M retired power lithium batteries was measured, and the radius c of the second semicircle was statistically analyzed. In the cascade classification method, the radius c of the second semicircle and the thickness b of the solid electrolyte interface itself were used to generally characterize the thickness of the SEI film. Compared with the single use of the solid electrolyte interface thickness b to express the thickness of the SEI film, the radius c of the second semicircle combined with the solid electrolyte interface thickness b to characterize the thickness of the SEI film will be more accurate.

[0048] S3. Divide the positive electrode material by the numerical ranges of the three parameters a, b, and c in step S2, and rate the aging degree of the positive electrode material according to the divided ranges, and rate the retired power lithium batteries for which the aging degree of the positive electrode material has been rated.

[0049] Among them, in the preferred embodiment, the numerical ranges of the three parameters a, b, and c are: a1: 0% to 50%, a2: 0μm to 2μm, b: 0μm to 0.5μm, c≥0. All retired power lithium batteries are further divided into corresponding numerical ranges within the numerical ranges specified by the above parameters. The rating of the aging degree of the positive electrode material and the grade rating of retired power lithium batteries will be carried out on the basis of the corresponding numerical ranges that have been divided.

[0050] As a more preferred embodiment, the numerical ranges of parameters a, b, and c are divided as follows, and the aging degree rating of the positive electrode material and the grade rating of the retired power lithium battery are rated as follows according to the division results, specifically:

[0051] 0≤a1<10%, 0≤a2<0.4μm, 0≤b<0.1μm, c≥0, the positive electrode material aging rating is level 1, and the retired power lithium battery rating is level A.

[0052] 10≤a1<20%, ​​0.4≤a2<0.8μm, 0.1≤b<0.2μm, c≥0, the positive electrode material aging rating is level 2, and the retired power lithium battery rating is level B.

[0053] 20≤a1<30%, 0.8≤a2<1.2μm, 0.2≤b<0.3μm, c≥0, the positive electrode material aging rating is level 3, and the retired power lithium battery rating is level C.

[0054] 30≤a1<40%, 1.2≤a2<1.6μm, 0.3≤b<0.4μm, c≥0, the positive electrode material aging rating is level 4, and the retired power lithium battery rating is level D.

[0055] 40≤a1≤50%, 1.6≤a2≤2.0μm, 0.4≤b<0.5μm, c≥0, the positive electrode material aging rating is level 5, and the retired power lithium battery rating is level E.

[0056] See also Figure 1 In a specific implementation scheme, the aging degree of the positive electrode materials of M retired power lithium batteries is divided according to the obtained SEM scan and impedance spectrum test data, and the retired power lithium batteries are rated as A, B, C, D and E according to the aging degree of the positive electrode materials.

[0057] S4. Select a certain number of retired power lithium batteries from the retired power lithium batteries that have obtained the grade rating in step S3 to conduct cyclic charge and discharge tests at different cycle rates.

[0058] Specifically, the cycle rate of the cyclic charge and discharge test of retired power lithium batteries is 0.1C to 0.5C. Each grade of retired power lithium batteries corresponds to a cycle rate, and the cycle rates of retired power lithium batteries of different grades are different.

[0059] Among them, the number of retired power lithium batteries drawn from different grade ratings accounts for 10% to 20% of the total number of retired power lithium batteries in the corresponding grade rating.

[0060] See also Figure 1 In a specific implementation scheme, when performing a cyclic charge and discharge test, M retired power lithium batteries are graded as A, B, C, D and E. The cycle rate corresponding to A is A. When retired power lithium batteries are extracted from retired power lithium batteries in A for cyclic charge and discharge test, the number extracted accounts for 10% of the total number of retired power lithium batteries in A. Similarly, the cycle rate corresponding to B is B. When retired power lithium batteries are extracted from retired power lithium batteries in B for cyclic charge and discharge test, the number extracted accounts for 10% of the total number of retired power lithium batteries in B. The same is true for the cyclic charge and discharge test of the remaining rated retired power lithium batteries. When performing cyclic charge and discharge tests, cyclic charge and discharge tests at different cycle rates are required. For retired power lithium batteries extracted from A, in addition to performing cyclic charge and discharge tests at the cycle rate A corresponding to A, cyclic charge and discharge tests are also required at the cycle rates corresponding to other levels. By analogy, the same is true for retired power lithium batteries extracted from other levels.

[0061] S5. The retired power lithium battery subjected to the cyclic charge and discharge test in step S4 is evaluated as follows: if the charge and discharge performance of the retired power lithium battery meets the use requirements under the cycle rate, the retired power lithium battery is put into the application scenario under the corresponding cycle rate condition; if the charge and discharge performance of the retired power lithium battery does not meet the use requirements under the cycle rate, the cycle rate is increased or decreased, and the cyclic charge and discharge test is performed again at the increased or decreased cycle rate, and this step is repeated until the charge and discharge performance of the retired power lithium battery meets the use requirements under the cycle rate for the cyclic charge and discharge test.

[0062] See also Figure 1 In a specific implementation scheme, the charge and discharge performance of the sampled retired power lithium batteries that have completed the cyclic charge and discharge test among the retired power lithium batteries of Class A, Class B, Class C, Class D and Class E is judged to determine whether their charge and discharge performance meets the use requirements under the cycle rate. If so, they are put into the application scenario under the corresponding cycle rate condition; if not, the cycle rate is increased or decreased, and the charge and discharge experiment is carried out under the corresponding cycle rate to determine whether the charge and discharge performance meets the use requirements. If not, the above steps are repeated. For example: assuming that the charge and discharge performance of the retired power lithium battery sampled from Class A at the A cycle rate does not meet the usage requirements at the A cycle rate, the cycle rate will be increased, and the cycle charge and discharge test will continue using the B cycle rate. If it meets the requirements, the retired power lithium battery will be put into the application scenario under the B cycle rate conditions. If it still does not meet the usage requirements at the B cycle rate, the cycle rate can be reduced, and the cycle charge and discharge test will be carried out using a cycle rate smaller than the A cycle rate or a cycle rate larger than the B cycle rate, until the charge and discharge performance of the sampled retired power lithium battery meets the usage requirements at the corresponding cycle rate.

[0063] Among them, the impedance spectrum measurement and charge and discharge performance test of retired power lithium batteries are carried out using the Blue Electric battery testing system.

[0064] Among them, the rating standards of retired power lithium batteries can be obtained according to the relevant parameters of the retired power lithium batteries, as shown in Table 1 below:

[0065]

[0066] Table 1 Rating standards for retired power lithium batteries

[0067] As shown in Table 1, the classification method for the cascade utilization of retired power lithium batteries provided by the present invention classifies retired power lithium batteries in combination with the changes in positive electrode materials. In the actual cascade utilization of retired power lithium batteries, based on the above, retired power lithium batteries can be quickly and more accurately allocated to corresponding cycle rate conditions for use.

[0068] In the above-mentioned retired power lithium battery rating standard table, the values ​​of a1 and c are accurate to 1% and 1 respectively, and the values ​​of a2 and b are accurate to 0.1μm respectively; the aging level rating allows 0.5 levels.

[0069] Example 1

[0070] This embodiment 1 provides a classification method for the cascade utilization of retired power lithium batteries based on positive electrode materials, which is as follows:

[0071] (1) The three recycled retired lithium iron phosphate soft-pack batteries were numbered 1-1, 1-2, and 1-3, and the positive electrode materials of the three retired lithium iron phosphate soft-pack batteries were extracted.

[0072] (2) The extracted positive electrode material was placed under a scanning electron microscope for observation, and the magnification of the scanning electron microscope was 1000 times, and the Figure 2 The high-magnification morphology photo of the battery positive electrode material shown in the figure Figure 2 (a) in the figure represents a 1000 times scanning electron microscope (SEM) image of the lithium iron phosphate soft pack battery numbered 1-1. Figure 2 (b) in the figure shows a 1000x scanning electron microscope (SEM) image of the lithium iron phosphate soft pack battery numbered 1-2. Figure 2 (c) in the figure represents a 1000x scanning electron microscope (SEM) image of the lithium iron phosphate soft pack battery numbered 1-3. Through 1000x scanning electron microscope, the crack-related parameters of the lithium iron phosphate soft pack battery numbered 1-1 can be obtained: a1=50%, a2=2μm, the crack-related parameters of the lithium iron phosphate soft pack battery numbered 1-2: a1=1%, a2=0.4μm, and the crack-related parameters of the lithium iron phosphate soft pack battery numbered 1-3: a1=25%, a2=1μm.

[0073] (3) The extracted positive electrode material was placed under a scanning electron microscope again for observation at a magnification of 10,000 times to obtain Figure 3 The high-magnification morphology photo of the battery positive electrode material shown. Figure 3 (a) in the figure represents a 10000 times scanning electron microscope (SEM) image of the lithium iron phosphate soft pack battery numbered 1-1. Figure 3 (b) in the figure shows a 10,000x scanning electron microscope (SEM) image of a lithium iron phosphate soft-pack battery numbered 1-2. Figure 3(c) in the figure represents a 10,000x scanning electron microscope (SEM) image of the lithium iron phosphate soft pack battery numbered 1-3. Through the 10,000x scanning electron microscope, the value of the solid electrolyte interface degree b of the lithium iron phosphate soft pack battery numbered 1-1 can be obtained: b = 0.4μm, the value of the solid electrolyte interface degree b of the lithium iron phosphate soft pack battery numbered 1-2: b = 0.1μm, the value of the solid electrolyte interface degree b of the lithium iron phosphate soft pack battery numbered 1-3: b = 0.3μm,

[0074] (4) The impedance test of the positive electrode materials of the three numbered batteries was performed. In the corresponding impedance spectrum, the impedance parameter value of the lithium iron phosphate soft-pack battery numbered 1-1 was c=950, the impedance parameter value of the lithium iron phosphate soft-pack battery numbered 1-2 was c=70; the impedance parameter value of the lithium iron phosphate soft-pack battery numbered 1-3 was c=100. The parameter values ​​of the positive electrode materials of the three batteries were c≥0, which met the requirements.

[0075] (5) The three batteries were rated. Based on the above parameter values ​​and the above-mentioned retired power lithium battery rating standard table, for the three retired lithium iron phosphate soft-pack batteries, the positive electrode material aging of the lithium iron phosphate soft-pack battery numbered 1-1 was level 5, the positive electrode material aging of the lithium iron phosphate soft-pack battery numbered 1-2 was level 1.5, and the positive electrode material aging of the lithium iron phosphate soft-pack battery numbered 1-3 was level 3.5. Therefore, the lithium iron phosphate soft-pack battery numbered 1-1 was rated as E-level, with a cascade utilization cycle ratio of 0.5C, the lithium iron phosphate soft-pack battery numbered 1-2 was rated as A-level, with a cascade utilization cycle ratio of 0.1C, and the lithium iron phosphate soft-pack battery numbered 1-3 was rated as C-level, with a cascade utilization cycle ratio of 0.3C.

[0076] (6) The positive electrode materials of the three batteries were assembled into button batteries, and cyclic charge and discharge tests were carried out at their respective corresponding cycle rates. The lithium iron phosphate soft-pack battery numbered 1-1 was subjected to cyclic charge and discharge tests at a cycle rate of 0.5C, the lithium iron phosphate soft-pack battery numbered 1-2 was subjected to cyclic charge and discharge tests at a cycle rate of 0.1C, and the lithium iron phosphate soft-pack battery numbered 1-3 was subjected to cyclic charge and discharge tests at a cycle rate of 0.3C. Charge and discharge curves of the three batteries were obtained respectively. The following results can be obtained through the cyclic charge and discharge tests: the battery assembled with the positive electrode material of the lithium iron phosphate soft-pack battery numbered 1-1 reached the scrap standard after about 300 cycles (1200 hours), the battery assembled with the positive electrode material of the lithium iron phosphate soft-pack battery numbered 1-2 was scrapped after about 160 cycles (3200 hours), and the battery assembled with the positive electrode material of the lithium iron phosphate soft-pack battery numbered 1-3 was scrapped after about 280 cycles (1867 hours).

[0077] In summary, the present invention provides a classification method for the cascade utilization of retired power lithium batteries based on positive electrode materials, which integrates battery positive electrode materials into the classification of retired power lithium batteries for cascade utilization. By combining the electrical performance of the battery with the changes in the battery positive electrode materials as screening indicators for the cascade utilization of retired power lithium batteries, the screening and classification process is made more rigorous and accurate.

[0078] The above is only a specific implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A classification method for the cascade utilization of retired power lithium batteries based on positive electrode materials, characterized in that: The classification method for the cascade utilization of retired power lithium batteries comprises the following steps: S1. Perform appearance inspection on retired power lithium batteries and select retired power lithium batteries that meet the appearance requirements; S2. Extracting positive electrode materials from the retired power lithium batteries screened in step S1, and obtaining the following parameters of the positive electrode materials of the retired power lithium batteries: The number of cracks in the worst viewing field a, the percentage of the viewing field area occupied by the cracks a1, and the crack width a2; Solid electrolyte interface thickness b; The radius c of the second semicircle in the impedance test diagram; S3, dividing the positive electrode material by the numerical ranges of the three parameters a, b, and c in step S2, and rating the aging degree of the positive electrode material according to the divided ranges, and rating the retired power lithium batteries for which the aging degree of the positive electrode material has been rated; S4, extracting a certain number of retired power lithium batteries from the retired power lithium batteries that have obtained the grade rating in step S3 to perform cyclic charge and discharge tests at different cycle rates; S5, performing the following evaluation operation on the retired power lithium battery subjected to the cyclic charge and discharge test in step S4: if the charge and discharge performance of the retired power lithium battery meets the use requirements under the cycle rate, the retired power lithium battery is put into the application scenario under the corresponding cycle rate condition; If the charge and discharge performance of the retired power lithium battery does not meet the usage requirements at the cycle rate, increase or decrease the cycle rate, and perform the cyclic charge and discharge test again at the increased or decreased cycle rate, and repeat this step until the charge and discharge performance of the retired power lithium battery meets the usage requirements at the cycle rate for the cyclic charge and discharge test.

2. According to claim 1, a classification method for the cascade utilization of retired power lithium batteries based on positive electrode materials is characterized in that: The numerical ranges of the parameters a1, a2, b, and c in step S2 are: a1: 0% to 50%, a2: 0 μm to 2 μm, b: 0 μm to 0.5 μm, c≥0.

3. According to claim 1, a classification method for retired power lithium batteries based on positive electrode materials for cascade utilization is characterized in that: The number of retired power lithium batteries extracted from different rating levels in step S4 accounts for x% of the total number of retired power lithium batteries in the corresponding rating level; Wherein, the value range of x is 10-20.

4. According to claim 1, a classification method for the cascade utilization of retired power lithium batteries based on positive electrode materials is characterized in that: The aging rating of the positive electrode material and the grade rating of the retired power lithium battery in step S3 include the following: 0≤a1<10%, 0≤a2<0.4μm, 0≤b<0.1μm, c≥0, the positive electrode material aging rating is level 1, and the retired power lithium battery rating is level A; 10≤a1<20%, ​​0.4≤a2<0.8μm, 0.1≤b<0.2μm, c≥0, the positive electrode material aging rating is level 2, and the retired power lithium battery rating is level B; 20≤a1<30%, 0.8≤a2<1.2μm, 0.2≤b<0.3μm, c≥0, the positive electrode material aging rating is level 3, and the retired power lithium battery rating is level C; 30≤a1<40%, 1.2≤a2<1.6μm, 0.3≤b<0.4μm, c≥0, the positive electrode material aging rating is level 4, and the retired power lithium battery rating is level D; 40≤a1≤50%, 1.6≤a2≤2.0μm, 0.4≤b<0.5μm, c≥0, the positive electrode material aging rating is level 5, and the retired power lithium battery rating is level E.

5. According to claim 1, a classification method for the cascade utilization of retired power lithium batteries based on positive electrode materials is characterized in that: The appearance inspection of the retired power lithium battery in step S1 includes checking whether the retired power lithium battery has bulging and leakage. If the retired power lithium battery has bulging and leakage, step S2 will not be performed.

6. The method for classifying retired power lithium batteries for cascade utilization based on positive electrode materials according to claim 1 is characterized in that: In the step S4, the cycle rate of the cyclic charge and discharge test of the retired power lithium battery is 0.1C to 0.5C.

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