Compatibility evaluation method for lithium ion battery system material and cooling liquid

Abstract

The invention belongs to the field of lithium ion battery materials, and particularly discloses a compatibility evaluation method of a lithium ion battery system material and a cooling liquid. According to the evaluation method, the change rate of the physical and chemical properties of the cooling liquid and the lithium ion battery system material is taken as original data, the calculation method is improved on the basis of the Topsis method, and the Euclidean distance is replaced by the vertical distance of the ideal solution, so that the defects of the Euclidean distance are overcome; the calculation process for evaluating the compatibility of the cooling liquid and the lithium ion battery system material is simpler and more convenient, and the calculation result is more accurate.

Description

Technical Field

[0001] The invention belongs to the field of lithium-ion battery materials, and in particular relates to a method for evaluating the compatibility of lithium-ion battery system materials with a coolant. Background Art

[0002] During the operation of lithium-ion batteries, uneven temperature fields are easily generated in single cells and battery packs, and a battery thermal management system (BTMS) should be used to control the battery temperature at 15-35°C. As a battery thermal management system, immersion liquid cooling is gradually being used in new energy power stations, off-grid energy storage and other places that require larger battery capacity and higher system power density.

[0003] Compatibility is an indicator of whether several materials are suitable for combined use. When materials with good compatibility are combined into an insulation system, it is not easy for them to produce physical or chemical changes that seriously damage the performance of the insulation system. For immersion liquid cooling, the coolant is in direct contact with the components of the lithium battery system and connects almost all components. Chemical corrosion may occur, leading to a decrease in the electrochemical performance of the battery, electrolyte leakage, and other phenomena, thereby causing system failure. In addition, since the operation process of lithium-ion batteries is a multi-factor coupling effect such as electric-thermal fields, but because the structural materials used are different from those of transformers, the design of the cooling system and the transformer cannot be completely universal, and the compatibility standards of coolant and transformer materials may not be applicable to lithium-ion battery systems. Therefore, it is particularly important to understand the material composition of the lithium-ion battery system and the compatibility of its materials with the coolant.

[0004] Among the existing technologies, the Topsis method is used to comprehensively evaluate the compatibility of materials. It is simple to calculate and is suitable for the evaluation and analysis of multiple schemes and multiple indicators. However, it was found during use that it also has the following shortcomings: while the scheme indicators are close to the Euclidean distance of the positive ideal solution, there is also the possibility that they are close to the Euclidean distance of the negative ideal solution. The schemes are ranked only based on the relative degree of closeness, and sometimes the results obtained are not accurate.

[0005] The existing methods for evaluating the compatibility of lithium-ion battery system materials with coolant have problems such as complex process and low accuracy of results. Therefore, there is still a need to continue to develop a method for evaluating the compatibility of coolant with lithium-ion battery system materials. Summary of the invention

[0006] In view of the problems of the above-mentioned prior art methods for evaluating the compatibility of lithium-ion battery system materials and coolant, such as complex process and low accuracy of results, the present invention provides a method for evaluating the compatibility of lithium-ion battery system materials and coolant.

[0007] To achieve the above purpose, the following technical solutions are specifically included:

[0008] A method for evaluating the compatibility of lithium-ion battery system materials and coolant, comprising the following steps:

[0009] (1) performing a compatibility test on a mixture of lithium-ion battery system materials and coolant, and measuring the change rates of the physical and chemical properties of the lithium-ion battery system materials and coolant before and after the compatibility test;

[0010] (2) A matrix S is constructed based on the change rates of the physical and chemical properties of the lithium-ion battery system materials and the coolant before and after the compatibility test. In the matrix S, there are i lithium-ion battery system materials as evaluation objects and j physical and chemical property change rates as evaluation indicators. The expression of the matrix S is as follows:

[0011]

[0012] (3) According to the following expression, the evaluation index in the matrix S is maximized and normalized to obtain the normalized matrix S':

[0013]

[0014] Among them, S minj represents the minimum value of the jth evaluation index in the matrix S, S maxj Represents the maximum value of the jth evaluation index in the matrix S;

[0015] The forward matrix S' is expressed as follows:

[0016]

[0017] (4) Use the hierarchical analysis method to construct a hierarchical structure model and determine the weight vector w of each indicator; the specific steps include:

[0018] (4-1) constructing a hierarchical model, wherein the hierarchical model includes a target layer, a criterion layer, and a corresponding indicator layer, wherein the target layer includes compatibility between the coolant and the lithium-ion battery system materials, the criterion layer includes the coolant and the lithium-ion battery system materials; and the indicator layer includes physical and chemical performance indicators of the coolant and the lithium-ion battery system materials;

[0019] (4-2) The physical and chemical performance indicators corresponding to the criterion layer are compared and scored by the 1-9 scaling method, and a judgment matrix P is formed. The expression of the judgment matrix P is as follows:

[0020] P=(p ij ) n×n (4)

[0021] Wherein, i, j = 1, 2, 3, ..., n; and the values ​​in the judgment matrix P represent the importance of a certain indicator relative to another indicator in the hierarchical structure model;

[0022] (4-3) The judgment matrix P is vector normalized Get the weights w of various physical and chemical performance indicators i , and construct a weight vector w; the vector is normalized Weight of physical and chemical performance index w i , the expression of the weight vector w is as follows:

[0023]

[0024] w=[w 1 w 2 w 3 … w i ] (7);

[0025] (5) Calculate the weight matrix S″ using the forward matrix S′ described in step (3) and the weight vector w described in step (4-3) ij , the weight matrix S″ ij The expression is as follows:

[0026] S″ ij =S′×w (8);

[0027] (6) Calculate the vertical distance P of the i-th evaluation object in the matrix S by the following equations (9)-(13): i , and according to the vertical distance P i Evaluate the compatibility of lithium-ion battery system materials and coolants;

[0028]

[0029] t ij =S″ ij -S + (10)

[0030]

[0031] And t kj Satisfy|t kj |=|t ij | max (12)

[0032]

[0033] Among them, t ij is the weight matrix S i ′ j ′ TranslationS + The value of the i-th row and j-th column in the weighted decision matrix formed after t kjis the weight matrix S i ′ j ′ TranslationS + The value corresponding to the maximum absolute value of the i-th column in the weighted decision matrix formed later; is the weight matrix S i ′ j ′ TranslationS + The ideal solution in the weighted decision matrix formed later; P i is the vertical distance of the i-th evaluation object in the matrix S.

[0034] In the evaluation method of the present invention, a decision matrix is ​​first constructed based on the change rate of the physical and chemical properties of the lithium ion battery system material and the coolant before and after the compatibility test, and a forward matrix composed of evaluation indicators is calculated; then, the weight of each evaluation indicator is determined by using the hierarchical analysis method, including establishing a hierarchical model according to the structure of the lithium ion battery system, constructing a judgment matrix, and determining a final weight matrix; finally, based on the weight matrix of each material, a vertical distance is calculated; when the vertical distance is larger, the corresponding evaluation material is farther away from the optimal solution, and the score of the material is lower; when the vertical distance is smaller, the corresponding evaluation material is closer to the optimal solution, and the score of the material is higher, and according to the principle of the highest comprehensive evaluation score, the corresponding evaluation material is determined to be the most suitable material for the component, and the material with the best compatibility with the coolant in each component is determined.

[0035] In the evaluation method of the present invention, the change rate of the physical and chemical properties of the coolant and the material is used as the original data, and the calculation method is improved on the basis of the Topsis method, and the vertical distance of the ideal solution is used instead of the Euclidean distance to make up for the defects of the Euclidean distance, so that the calculation process of evaluating the compatibility of the coolant and the lithium-ion battery system materials is simpler and the calculation results are more accurate.

[0036] Preferably, in steps (1), (2), (4) and (6), the coolant comprises transformer oil.

[0037] Preferably, in steps (1), (2), (4) and (6), the lithium-ion battery system materials include battery materials and other structural materials, and the battery materials include at least one of a battery casing, an electrode material, a PCB board and an electrolyte.

[0038] Preferably, the battery casing includes at least one of an aluminum alloy, an insulating film, a pressure relief valve, and a pole.

[0039] Preferably, the electrode material includes at least one of lithium iron phosphate, graphite, an adhesive, a conductive agent, a layered oxide sodium ion positive electrode, a polyanion sodium ion positive electrode, and hard carbon.

[0040] Preferably, the PCB board includes at least one of copper foil and synthetic resin.

[0041] Preferably, the electrolyte includes a lithium ion battery electrolyte and a sodium ion battery electrolyte, and the electrolyte contains an organic solvent and an electrolyte salt.

[0042] Preferably, the other structural materials include at least one of metal parts, PET, injection molded parts, foam, insulating sheets, sealing rubber, and cable harnesses.

[0043] Preferably, the metal part includes at least one of a connecting strip, a sheet metal part, and a screw.

[0044] Further preferably, the connecting strip includes at least one of nickel and copper.

[0045] Preferably, the injection molded part comprises plastic.

[0046] Preferably, the foam and the insulating sheet include plastic and viscose.

[0047] Preferably, the sealing rubber includes at least one of nitrile rubber, fluororubber and acrylic rubber.

[0048] Preferably, the cable harness comprises polyvinyl chloride.

[0049] If the surface area of ​​lithium-ion battery system materials can be measured, then every 800 cm 3 The surface area of ​​the battery system material in the coolant is not less than 52cm 2 For example, for every 800 mL of coolant, the surface area of ​​the rubber material can be 65 cm 2 ; If the surface area of ​​the battery system material is not measurable, the mass of the battery system material is 0.5-1.5% of the mass of the coolant.

[0050] Preferably, in step (1), the lithium-ion battery system material is further subjected to a drying treatment, the drying treatment temperature is 100-110° C., and the drying treatment temperature is 12-24 hours.

[0051] Preferably, in step (1), the temperature of the compatibility test is 90-110° C., and the time of the compatibility test is >300 h, more preferably 450-550 h.

[0052] Preferably, in step (1), the compatibility test comprises the following steps:

[0053] (1) Test the physical and chemical properties of the coolant and the dried lithium-ion battery system materials respectively;

[0054] (2) placing the dried lithium-ion battery system materials and coolant in a glass container, and allowing the coolant to submerge the dried lithium-ion battery system materials, and conducting a compatibility test under closed conditions;

[0055] (3) After the compatibility test is completed, the lithium-ion battery system material is taken out from the coolant, and the physical and chemical properties of the coolant and the lithium-ion battery system material after the compatibility test are tested respectively. Finally, the change rate of the physical and chemical properties of the lithium-ion battery system material and the coolant before and after the compatibility test is calculated.

[0056] Preferably, the physical and chemical properties include at least one of the viscosity, acid value, dielectric loss factor, breakdown voltage, and interfacial tension of the coolant, and at least one of the tensile strength, hardness, and mass of the lithium-ion battery system material.

[0057] The present invention also provides an application of the compatibility evaluation method of the lithium ion battery system material and the coolant in the preparation of the lithium ion battery system.

[0058] The method of the present invention effectively and reasonably evaluates the compatibility of coolant and battery system materials according to the characteristics of lithium-ion battery liquid cooling technology, provides technical guidance for the design and material selection of lithium-ion battery liquid cooling technology, supplements the current gap in the compatibility evaluation method of coolant and lithium-ion battery system materials, is of great significance to the structural design and safe operation of lithium-ion battery liquid cooling systems, makes the calculation process of evaluating the compatibility of coolant and lithium-ion battery system materials simpler and the calculation results more accurate, and is more conducive to the construction of lithium-ion battery system components.

[0059] Compared with the prior art, the present invention has the following beneficial effects: in the evaluation method of the present invention, the change rate of the physical and chemical properties of the coolant and the material is used as the original data, and the calculation method is improved on the basis of the Topsis method, and the vertical distance of the ideal solution is used instead of the Euclidean distance to make up for the defects of the Euclidean distance, so that the calculation process of evaluating the compatibility of the coolant and the lithium-ion battery system materials is simpler and the calculation results are more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 The present invention is a flow chart of a method for evaluating the compatibility of lithium-ion battery system materials with a coolant.

[0061] Figure 2 This is a schematic diagram of the hierarchical structure model in Example 1. DETAILED DESCRIPTION

[0062] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0063] Example 1

[0064] A method for evaluating the compatibility of lithium-ion battery system materials and coolant, the flow chart is as follows Figure 1 As shown, the following steps are included:

[0065] (1) Classifying lithium-ion battery system materials according to component types, and performing compatibility tests on different materials of one component each time. In this embodiment, copper and nickel, which are commonly used metal materials for battery connectors, and transformer oil, which are commonly used as coolant for lithium battery immersion liquid cooling, are used as examples to perform compatibility tests; including the steps of pretreatment of experimental materials, sample compatibility testing, compatibility parameter measurement and calculation, and obtaining compatibility test results;

[0066] (1-1) Material pretreatment: The copper sheet and nickel sheet were processed to a suitable size and regular shape, and dried in an oven at 105°C ± 5°C for 16 h;

[0067] (1-2) Before the compatibility test, the physical and chemical properties of the materials were tested: the untested transformer oil was used as a blank oil sample, and its viscosity, acid value, dielectric loss factor, breakdown voltage, and interfacial tension were tested respectively; the tensile strength, hardness, and quality of the copper sheet and nickel sheet materials were measured respectively. The test results are shown in Table 1;

[0068] (1-3) Material compatibility test: The dried copper sheet and nickel sheet are placed in two 1L beakers respectively, and 800mL of transformer oil is added to each beaker to completely immerse the copper sheet and nickel sheet in the coolant, and then sealed with aluminum foil; thus, a blend of transformer oil and copper sheet or nickel sheet is obtained as a material oil sample, and the prepared material oil sample is placed in a circulating air supply oven, and the oven temperature is set to 100°C. A compatibility test is performed in the oven for 500 hours. After cooling to room temperature, the material oil sample is taken out of the oven, and the copper sheet and nickel sheet are taken out of the transformer oil with clean clips respectively. The copper sheet and nickel sheet after the compatibility test are cleaned with a solvent such as n-heptane;

[0069] (1-4) Compatibility parameter measurement: The transformer oil after the compatibility test was used as the test oil sample, and its viscosity, acid value, dielectric loss factor, breakdown voltage, and interfacial tension were tested respectively; the copper sheet and nickel sheet after the compatibility test were used as material test samples, and their tensile strength, hardness, and quality were tested respectively, and the change rate of each performance parameter was calculated. The results are shown in Table 1;

[0070] Among them, the corresponding physical and chemical properties are tested according to the following national standards: viscosity GB / T 265-1988, acid value GB / T28552-2012, dielectric loss factor GB / T 5654-2007, breakdown voltage GB / T 507-2002, interfacial tension GB / T6541-1986, tensile strength GB / T 1040.2:2006, and hardness GB / T 39693.7-2022.

[0071] Table 1

[0072]

[0073]

[0074] (2) A decision matrix S is constructed based on the change rate data of the physical and chemical properties of lithium-ion battery system materials and coolant before and after the compatibility test. In the matrix S, there are i lithium-ion battery system materials as evaluation objects and j physical and chemical property change rates as evaluation indicators. The expression of the matrix S is as follows:

[0075]

[0076] Then, in this embodiment, corresponding to the two evaluation objects of copper sheet and nickel sheet, the S of the coolant corresponding to the copper sheet or the nickel sheet is μ , S p , S tanδ , S BV , S σ , and S corresponding to the copper or nickel sheet Rm , S HB , S M There are 8 physical and chemical property change rates in total. According to the data in Table 1 above, the decision matrix S is as follows:

[0077]

[0078] (3) According to the following expression, the evaluation index in the matrix S is maximized and normalized to obtain the normalized matrix S':

[0079]

[0080] Among them, S minj represents the minimum value of the jth evaluation index in the decision matrix S, S maxj Represents the maximum value of the jth evaluation index in the decision matrix S;

[0081] The forward matrix S' is expressed as follows:

[0082]

[0083] The details are as follows:

[0084]

[0085] Similarly: S 1 ′ 2 =0, S 2 ′ 2 =1, S 3 ′ 1 =1, S 3 ′ 2 =0, S 4 ′ 1 =1, S 4 ′ 2 =0, S 5 ′ 1 =0, S 5 ′ 2 =1, S 6 ′ 1 =1, S 6 ′ 2 =0, S 7 ′ 1 =1, S 7 ′ 2 =0, S 8 ′ 1 =1, S 8 ′ 2 =0, and we get the forward matrix:

[0086]

[0087] (4) Determine the weight of each indicator using the hierarchical analysis method, including establishing a hierarchical model and constructing a judgment matrix based on the lithium-ion battery system structure:

[0088] (4-1) Establish a hierarchical model, as shown in the attached diagram Figure 2 As shown:

[0089] Target layer: compatibility of coolant and battery materials;

[0090] Criteria layer: Two criterion layers are formed with coolant and battery materials; under each criterion layer, an index layer is set respectively, and the index layer represents the eight indicators of the compatibility evaluation system of coolant and lithium-ion battery materials, wherein the index layer includes: viscosity of coolant, acid value of coolant, dielectric loss factor of coolant, breakdown voltage of coolant, interfacial tension of coolant, tensile strength of battery materials, hardness of battery materials, and quality of battery materials;

[0091] Based on the above, a compatibility evaluation system for coolant and lithium-ion battery materials is formed, which consists of 2 criterion layers and 8 indicator layers.

[0092] (4-2) Constructing the judgment matrix: Compare and score the indicators of the criterion layer using the 1-9 scaling method, and finally form the judgment matrix P;

[0093] P=(p ij ) n×n (4)

[0094] Among them, i, j = 1, 2, 3, ..., n; and the values ​​in the matrix P represent the importance of a certain indicator relative to another indicator in the hierarchical model. The relative importance is usually expressed on a scale of 1-9, where the judgment basis of the scale of 1-9 is as follows:

[0095] 1 means that both indicators are equally important;

[0096] 3 means one indicator is slightly more important than the other;

[0097] 5 means one indicator is significantly more important than the other;

[0098] 7 means one indicator is more important than another;

[0099] 9 means one indicator is extremely important than another;

[0100] Reverse judgment uses the inverse;

[0101] The indicators of this embodiment are expressed on a scale of 1-9 and the results are as follows:

[0102] Table 2

[0103] Indicator layer Viscosity Acid value Dielectric loss factor Breakdown voltage Interfacial tension tensile strength hardness quality Viscosity 1 1 / 5 1 / 5 1 / 5 3 1 / 3 3 3 Acid value 5 1 1 1 3 3 3 3 Dielectric loss factor 5 1 1 1 3 3 3 3 Breakdown voltage 5 1 1 1 3 3 3 3 Interfacial tension 1 / 3 1 / 3 1 / 3 1 / 3 1 1 1 1 tensile strength 3 1 / 3 1 / 3 1 / 3 1 1 1 1 hardness 1 / 3 1 / 3 1 / 3 1 / 3 1 1 1 1 quality 1 / 3 1 / 3 1 / 3 1 / 3 1 1 1 1

[0104] but

[0105] (4-3) Judgment matrix P is vector normalized Finally, the weight of each indicator w is obtained i :

[0106]

[0107] This embodiment has 8 indicators, n=8, and the weight calculation of each indicator is as follows:

[0108]

[0109]

[0110] (4-4) Construct the weight vector w:

[0111] w=[w 1 w 2 w 3 … w i ] (7);

[0112] Based on the above calculation, the weight vector in this embodiment is specifically:

[0113]

[0114] (5) Based on the forward matrix S′ in step (3) and the weight vector w in step (4-4), the weight matrix S″ is calculated according to the following expression:

[0115] S″ ij =S′×w (8);

[0116] The specific results of the weight matrix in this embodiment are as follows:

[0117]

[0118] (6) Calculate the vertical distance P of the i-th evaluation object in the matrix S by the following equations (9)-(13): i , and according to the vertical distance P i Evaluate the compatibility of lithium-ion battery system materials and coolants;

[0119]

[0120] t ij =S″ ij -S + (10)

[0121]

[0122] And t kj Satisfy|t kj |=|t ij | max (12)

[0123]

[0124] Among them, t ij is the weight matrix S″ij TranslationS + The value of the i-th row and j-th column in the weighted decision matrix formed after t kj is the weight matrix S″ ij TranslationS + The value corresponding to the maximum absolute value of the i-th column in the weighted decision matrix formed later; is the weight matrix S″ ij TranslationS + The ideal solution in the weighted decision matrix formed later; P i is the vertical distance of the i-th evaluation object in the matrix S;

[0125] In this embodiment, the ideal solution after translation is calculated,

[0126]

[0127] Vertical distance of copper sheet:

[0128]

[0129] Vertical distance of nickel sheet:

[0130]

[0131] When the vertical distance is larger, the corresponding material is farther from the optimal solution, and the score of the material is lower; when the vertical distance is smaller, the corresponding material is closer to the optimal solution, and the score of the material is higher. According to the principle of the highest comprehensive evaluation score, the corresponding material is determined to be the most suitable material for the component. According to the above calculation results, P 1 =0.231 <P 2 =0.3256, therefore, the copper sheet has better compatibility with the coolant. The method of the present invention is improved on the basis of the original Topsis method, replacing the Euclidean distance with the vertical distance of the ideal solution, and combining with specific data to demonstrate the feasibility and effectiveness of using the vertical distance as a method for evaluating the compatibility of the battery system material with the coolant, thereby making up for the defects of the Euclidean distance, making the calculation process simpler and the calculation result more accurate.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for evaluating the compatibility of lithium-ion battery system materials and coolant, characterized in that: The steps include: (1) performing a compatibility test on a mixture of lithium-ion battery system materials and coolant, and measuring the change rates of the physical and chemical properties of the lithium-ion battery system materials and coolant before and after the compatibility test; (2) A matrix S is constructed based on the change rates of the physical and chemical properties of the lithium-ion battery system materials and the coolant before and after the compatibility test. In the matrix S, there are i lithium-ion battery system materials as evaluation objects and j physical and chemical property change rates as evaluation indicators. The expression of the matrix S is as follows: (3) According to the following expression, the evaluation index in the matrix S is maximized and normalized to obtain the normalized matrix S': Among them, S minj represents the minimum value of the jth evaluation index in the matrix S, S maxj Represents the maximum value of the jth evaluation index in the matrix S; The forward matrix S' is expressed as follows: (4) Use the hierarchical analysis method to construct a hierarchical structure model and determine the weight vector w of each indicator; the specific steps include: (4-1) constructing a hierarchical model, wherein the hierarchical model includes a target layer, a criterion layer, and a corresponding indicator layer, wherein the target layer includes compatibility between the coolant and the lithium-ion battery system materials, the criterion layer includes the coolant and the lithium-ion battery system materials; and the indicator layer includes physical and chemical performance indicators of the coolant and the lithium-ion battery system materials; (4-2) The physical and chemical performance indicators corresponding to the criterion layer are compared and scored by the 1-9 scaling method, and a judgment matrix P is formed. The expression of the judgment matrix P is as follows: P=(p ij ) n×n (4), Wherein, i, j = 1, 2, 3, ..., n; and the values ​​in the judgment matrix P represent the importance of a certain indicator relative to another indicator in the hierarchical structure model; (4-3) The judgment matrix P is vector normalized Get the weights w of various physical and chemical performance indicators i , and construct a weight vector w; the vector is normalized Weight of physical and chemical performance index w i , the expression of the weight vector w is as follows: <h2 style=";text-align:left;direction:ltr">w=[w1 w2 w3…w<h2 style=";text-align:left;direction:ltr"> i <h2 style=";text-align:left;direction:ltr"> (7) (5) Calculate the weight matrix S by using the forward matrix S' described in step (3) and the weight vector w described in step (4-3) i ′ j ′ , the weight matrix S i ′ j ′ The expression is as follows: S i ′ j ′ =S ′ ×w(8); (6) Calculate the vertical distance P of the i-th evaluation object in the matrix S by the following equations (9)-(13): i , and according to the vertical distance P i Evaluate the compatibility of lithium-ion battery system materials and coolants; t ij =S i ′ j ′ -S + (10), And t kj Satisfy|t kj |=|t ij | max (12) Among them, t ij is the weight matrix S i ′ j ′ TranslationS + The value of the i-th row and j-th column in the weighted decision matrix formed after t kj is the weight matrix S i ′ j ′ TranslationS + The value corresponding to the maximum absolute value of the i-th column in the weighted decision matrix formed later; is the weight matrix S i ′ j ′ TranslationS + The ideal solution in the weighted decision matrix formed later; P i is the vertical distance of the i-th evaluation object in the matrix S.

2. The method for evaluating the compatibility of lithium-ion battery system materials and coolant according to claim 1, characterized in that: In steps (1), (2), (4) and (6), the coolant includes transformer oil, the lithium-ion battery system materials include battery materials and other structural materials, and the battery materials include at least one of a battery casing, an electrode material, a PCB board, and an electrolyte.

3. The method for evaluating the compatibility of lithium-ion battery system materials and coolant according to claim 2, characterized in that: Include at least one of the following: The battery shell includes at least one of an aluminum alloy, an insulating film, a pressure relief valve, and a pole; The electrode material includes at least one of lithium iron phosphate, graphite, a binder, a conductive agent, a layered oxide sodium ion positive electrode, a polyanion sodium ion positive electrode, and hard carbon; The PCB board includes at least one of copper foil and resin; The electrolyte contains an organic solvent and an electrolyte salt; The other structural materials include at least one of metal parts, PET, injection molded parts, foam, insulating sheets, sealing rubber, and cable harnesses.

4. The method for evaluating the compatibility of lithium-ion battery system materials and coolant according to claim 1, characterized in that: In step (1), the lithium-ion battery system material is further dried at a temperature of 100-110° C. for 12-24 hours.

5. The method for evaluating the compatibility of lithium-ion battery system materials and coolant according to claim 1, characterized in that: In step (1), the temperature of the compatibility test is 90-110° C., and the time of the compatibility test is >300 h.

6. The method for evaluating the compatibility of lithium-ion battery system materials and coolant according to claim 1, characterized in that: In step (1), the compatibility test includes the following steps: (1) Test the physical and chemical properties of the coolant and the dried lithium-ion battery system materials respectively; (2) placing the dried lithium-ion battery system materials and coolant in a glass container, and allowing the coolant to submerge the dried lithium-ion battery system materials, and conducting a compatibility test under closed conditions; (3) After the compatibility test is completed, the lithium-ion battery system material is taken out from the coolant, and the physical and chemical properties of the coolant and the lithium-ion battery system material after the compatibility test are tested respectively. Finally, the change rate of the physical and chemical properties of the lithium-ion battery system material and the coolant before and after the compatibility test is calculated.

7. The method for evaluating the compatibility of lithium-ion battery system materials and coolant according to claim 1, characterized in that: In steps (1), (2) and (4), the physical and chemical properties include at least one of the viscosity, acid value, dielectric loss factor, breakdown voltage and interfacial tension of the coolant, and at least one of the tensile strength, hardness and mass of the lithium-ion battery system material.

8. Use of the compatibility evaluation method for lithium-ion battery system materials and coolant according to any one of claims 1 to 7 in the preparation of lithium-ion battery systems.

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