Method for evaluating dynamic and thermodynamic matching performance of negative pole piece, design method of negative pole piece, negative pole piece and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and particularly provides a negative pole piece dynamic and thermodynamic matching performance evaluation method, a negative pole piece design method, a negative pole piece and a lithium ion battery. The evaluation method comprises the following steps: acquiring a dynamic failure characteristic parameter ZR and a thermodynamic failure characteristic parameter ZT of the negative pole piece of the lithium ion battery; the ratio K of the dynamic failure characteristic parameter ZR to the thermodynamic failure characteristic parameter ZT is calculated, and when K is larger than or equal to 0.65 and smaller than or equal to 0.73, the dynamic and thermodynamic matching performance of the negative pole piece is good. According to the invention, a method for evaluating the dynamic and thermodynamic matching performance of the negative pole piece is found, and the optimal dynamic and thermodynamic matching ratio of the negative pole piece under 35-DEG C 1P / 1P circulation is obtained, that is, K meets # imgabs 1 #, so that the dynamic and thermodynamic matching of the negative pole piece of the lithium ion battery can be achieved, and the requirement of 35-DEG C 1P / 1P charge-discharge circulation 8000cls at 70% SOH is met.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and specifically provides a method for evaluating the kinetic and thermodynamic matching of a negative electrode plate, a method for designing a negative electrode plate, a negative electrode plate, and a lithium-ion battery. Background Art

[0002] Electrochemical energy storage is an important form of energy storage, with lithium-ion batteries dominating the mainstream. New energy storage systems place high demands on the lifespan of lithium-ion batteries. Typically, household energy storage systems require a lifespan of at least 3,000 cycles (at 100% SOC), commercial energy storage systems require at least 6,000 cycles, and large-scale energy storage systems require at least 10,000 cycles. Long-life lithium-ion batteries have been a research hotspot in the battery field in recent years.

[0003] Among different types of lithium-ion batteries, lithium iron phosphate (LFP) batteries have always been a research hotspot due to their good safety and long cycle life. They are also the most widely used batteries in large-scale energy storage and electric vehicles, and are the first choice in the current energy storage field.

[0004] At present, the capacity decay of lithium iron phosphate batteries in room temperature cycles mainly comes from the loss of active lithium. The positive electrode lithium iron phosphate itself is relatively stable. The main reason for the decline in cycle performance is the loss of active lithium caused by negative electrode side reactions and the cycle deterioration caused by polarization and even lithium precipitation, which makes it difficult to achieve the requirement of 35℃ 1P / 1P charge and discharge cycle exceeding 8000cls@70% SOH.

[0005] Accordingly, this field requires a new technical solution to solve the above technical problems. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned technical problem, namely, to solve the problem in the prior art that it is difficult to achieve the 35°C 1P / 1P charge and discharge cycle requirement of more than 8000cls@70% SOH due to the loss of active lithium and polarization and even lithium precipitation caused by side reactions at the negative electrode of lithium-ion batteries.

[0007] In a first aspect, the present invention provides a method for evaluating the kinetic and thermodynamic matching of a negative electrode plate, wherein the evaluation method comprises:

[0008] Obtain the dynamic failure characteristic parameter Z of the negative electrode of the lithium-ion battery R and thermodynamic failure characteristic parameter Z T ;

[0009] Calculate the dynamic failure characteristic parameter Z Rand thermodynamic failure characteristic parameter Z T Ratio

[0010] When K satisfies 0.65≤K≤0.73, it indicates that the negative electrode plate has good kinetic and thermodynamic matching;

[0011] When K does not satisfy 0.65≤K≤0.73, it indicates that the kinetics and thermodynamics of the negative electrode are not well matched.

[0012] In the preferred technical solution of the above evaluation method, the dynamic failure characteristic parameter Z is obtained. R The methods include:

[0013] Establish the linear relationship between the capacity loss rate Y and the number of cycles n during the battery cycle: lnY-lnn;

[0014] Obtain the slope of the linear relationship lnY-lnn, which is the dynamic failure characteristic parameter Z R ;

[0015] And / or, obtaining the thermodynamic failure characteristic parameter Z T The methods include:

[0016] Establish the linear relationship between the capacity loss rate Y during the battery cycle and the single cycle capacity Q': lnY-lnQ';

[0017] Obtain the slope of the linear relationship lnY-lnQ', which is the thermodynamic failure characteristic parameter Z T .

[0018] In the preferred technical solution of the above evaluation method, the method of establishing the linear relationship lnY-lnn includes the following steps:

[0019] S1. According to the rate acceleration model, the capacity loss rate Y and the cycle time t satisfy the Arrhenius formula of the following formula (1):

[0020] In formula (1): T is the thermodynamic temperature, A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and Z is the power law factor;

[0021] S2. Based on the fact that T remains unchanged, transform the above formula into formula (2): lnY=lnA rate +Z R lnt formula (2)

[0022] S3. Combined with the relationship that the cycle time t is proportional to the number of cycles n at the same magnification, the above formula becomes formula (3): lnY=lnA rate +ZR lnn formula (3)

[0023] S4. The linear relationship lnY-lnn is obtained by fitting formula (3).

[0024] And / or, the method for establishing the linear relationship lnY-lnQ' comprises the following steps:

[0025] S1. According to the temperature acceleration model, the capacity loss rate Y and the cycle time t satisfy the Arrhenius formula of the following formula (1'):

[0026] In formula (1'): T is the thermodynamic temperature, A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and Z is the power law factor;

[0027] S2. Combining the relationship that the capacity Q output during the battery cycle is proportional to the cycle time t, the above formula is converted into formula (2'):

[0028] S3, based on the capacity Q output during the battery cycle is equal to the superposition of the single cycle capacity Q', the above formula becomes formula (3'):

[0029] S4. The linear relationship lnY-lnQ' is obtained by fitting formula (3').

[0030] In a second aspect, the present invention provides a method for designing a negative electrode plate, wherein the design method comprises:

[0031] The kinetic and thermodynamic matching of the negative electrode sheet is evaluated using the evaluation method described in the first aspect above;

[0032] If the kinetic and thermodynamic matching of the negative electrode plate is good, the design requirements are met;

[0033] If the evaluation shows that the kinetic and thermodynamic matching of the negative electrode plate is not good, the negative electrode active material of the negative electrode plate is adjusted to adjust the K value so that the kinetic and thermodynamic matching of the negative electrode plate meets the design requirements.

[0034] In a preferred technical solution of the above design method, the negative electrode active material includes amorphous carbon and crystalline carbon.

[0035] In the preferred technical solution of the above design method, the negative electrode active material of the negative electrode sheet is adjusted to be:

[0036] The mass ratio of the amorphous carbon to the crystalline carbon is regulated to be (1.0-2.5%): (97.5-99.0%).

[0037] In the preferred technical solution of the above design method, the negative electrode plate further includes a conductive agent, a binder and a thickener.

[0038] In the preferred technical solution of the above design method, the mass ratio of the negative electrode active material, the conductive agent, the binder and the thickener is (90-94%): (1-5%): (1-4%): (1-3%).

[0039] In a third aspect, the present invention provides a negative electrode plate, which is designed by the design method described in the second aspect.

[0040] In a fourth aspect, the present invention provides a lithium-ion battery comprising the aforementioned negative electrode plate.

[0041] The technical solution of the present invention has the following technical effects:

[0042] (1) The present invention has discovered a method for evaluating the kinetic and thermodynamic matching of negative electrode sheets, and obtained the optimal kinetic and thermodynamic matching of negative electrode sheets of lithium-ion batteries under 35°C 1P / 1P cycle, that is, when the kinetic failure characteristic parameter Z of the negative electrode sheet of the lithium-ion battery is R and thermodynamic failure characteristic parameter Z T The ratio K satisfies The lithium-ion battery can achieve 8000cls of charge and discharge cycles at 35°C 1P / 1P @ 70% SOH;

[0043] (2) The present invention achieves an optimal match between the kinetics and thermodynamics of the negative electrode of the lithium-ion battery by regulating the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material of the lithium-ion battery to meet the ratio of (1.0-2.5%): (97.5-99.0%), thereby achieving the requirement of 8000cls@70% SOH at 35°C 1P / 1P charge and discharge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0045] Figure 1 is the lnY-lnn fitting curve of the lithium ion battery of Example 1 under 35°C 1P / 1P cycle conditions;

[0046] Figure 2 is the lnY-lnQ' fitting curve of the lithium ion battery of Example 1 under 35°C 1P / 1P cycle conditions;

[0047] Figure 3 is the lnY-lnn fitting curve of the lithium ion battery of Example 2 under 35°C 1P / 1P cycle conditions;

[0048] Figure 4 is the lnY-lnQ' fitting curve of the lithium ion battery of Example 2 under 35°C 1P / 1P cycle conditions;

[0049] Figure 5 This is the lnY-lnn fitting curve of the lithium-ion battery of Comparative Example 1 under 35°C 1P / 1P cycle conditions;

[0050] Figure 6 This is the lnY-lnQ' fitting curve of the lithium-ion battery of Comparative Example 1 under 35°C 1P / 1P cycle conditions;

[0051] Figure 7 This is the lnY-lnn fitting curve of the lithium-ion battery of Comparative Example 2 under 35°C 1P / 1P cycle conditions;

[0052] Figure 8 This is the lnY-lnQ' fitting curve of the lithium-ion battery of Comparative Example 2 under 35°C 1P / 1P cycle conditions;

[0053] Figure 9 This is the lnY-lnn fitting curve of the lithium-ion battery of Comparative Example 3 under 35°C 1P / 1P cycle conditions;

[0054] Figure 10 This is the lnY-lnQ' fitting curve of the lithium-ion battery of Comparative Example 3 under 35°C 1P / 1P cycle conditions;

[0055] Figure 11 This is the lnY-lnn fitting curve of the lithium-ion battery of Comparative Example 4 under 35°C 1P / 1P cycle conditions;

[0056] Figure 12 This is the lnY-lnQ' fitting curve of the lithium-ion battery of Comparative Example 4 under 35°C 1P / 1P cycle conditions;

[0057] Figure 13 35°C 1P / 1P cycle trend diagram of the lithium-ion batteries of various embodiments and comparative examples. DETAILED DESCRIPTION

[0058] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0059] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0060] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0061] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0062] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0063] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass described in the examples of this application may be a mass unit known in the chemical industry, such as μg, mg, g, kg, etc.

[0064] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be understood to indicate or imply relative importance or to implicitly specify the quantity of the technical features being referred to. For example, without departing from the scope of the embodiments of this application, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0065] Dynamic failure characteristic parameter Z R : Refers to the cycle attenuation characteristics of different negative electrode materials caused by changes in internal resistance during a certain rate of charge and discharge.

[0066] Thermodynamic failure characteristic parameter Z T : Refers to the cycle attenuation characteristics of different negative electrodes at a certain temperature during the charge and discharge process due to the thermal stability of the material and the internal resistance heat-generating side reaction.

[0067] Linear relationship lnY-lnn: refers to the linear relationship between the capacity loss rate Y and the number of cycles n during the cycling of a lithium-ion battery under the 1P / 1P cycle condition at 35°C.

[0068] The linear relationship lnY-lnQ' refers to the linear relationship between the capacity loss rate Y during the lithium-ion battery cycle and the single cycle capacity Q' during the battery cycle under the 1P / 1P cycle condition at 35°C.

[0069] Energy storage cell cycle life: refers to the number of charge and discharge cycles a battery undergoes under a certain charge and discharge regime when the battery capacity drops to a specified value. For example, ≥8000 cycles@70% SOH means that when the health status of the energy storage cell drops to 70%, the number of charge and discharge cycles that have been completed exceeds 8000.

[0070] SOH is defined as follows:

[0071] Where: C aged is the current capacity of the battery; C rated is the rated capacity of the battery.

[0072] The experimental methods in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0073] Based on the problem pointed out in the background technology, in the prior art, due to the loss of active lithium caused by side reactions at the negative electrode of lithium-ion batteries, as well as polarization and even lithium plating leading to cycle deterioration, it is difficult to achieve the 35°C 1P / 1P charge and discharge cycle requirement of more than 8000cls@70% SOH.

[0074] In a first aspect, the present invention provides a method for evaluating the kinetic and thermodynamic matching of a negative electrode plate, wherein the evaluation method comprises:

[0075] Obtain the dynamic failure characteristic parameter Z of the negative electrode of the lithium-ion battery R and thermodynamic failure characteristic parameter Z T ;

[0076] Calculate the dynamic failure characteristic parameter Z R and thermodynamic failure characteristic parameter Z T Ratio

[0077] When K satisfies 0.65≤K≤0.73, it indicates that the negative electrode plate has good kinetic and thermodynamic matching;

[0078] When K does not satisfy 0.65≤K≤0.73, it indicates that the kinetics and thermodynamics of the negative electrode are not well matched.

[0079] At present, the capacity decay of lithium iron phosphate batteries in room temperature cycles mainly comes from the loss of active lithium. The positive electrode lithium iron phosphate itself is relatively stable. The main reason for the decline in cycle performance is the loss of active lithium caused by negative electrode side reactions and the cycle deterioration caused by polarization and even lithium precipitation, which makes it difficult to achieve the requirement of 35℃ 1P / 1P charge and discharge cycle exceeding 8000cls@70% SOH.

[0080] Through research, the present invention found that if the kinetic characteristics of the negative electrode sheet account for too high a proportion, it will lead to increased thermodynamic losses, intensified side reactions, increased active lithium loss, and accelerated cycle decay; if the thermodynamic characteristics of the negative electrode sheet account for too high a proportion, it will not be able to meet the 1P rate requirement, resulting in kinetic deterioration, increased polarization, and even the risk of lithium plating, leading to cycle deterioration; when the kinetic characteristics and thermodynamic characteristics of the negative electrode sheet of the lithium-ion battery are optimally matched, side reactions can be slowed down, active lithium loss can be reduced, cycle decay can be slowed down, and the risk of polarization and lithium plating can be reduced. Therefore, to achieve a 35°C 1P / 1P charge and discharge cycle of more than 8000cls@70% SOH, the kinetic characteristics and thermodynamic characteristics of the negative electrode sheet of the lithium-ion battery need to be optimally matched.

[0081] The present invention has discovered a method for evaluating the kinetic and thermodynamic matching of negative electrode sheets through experiments, and obtained the optimal kinetic and thermodynamic matching of negative electrode sheets of lithium-ion batteries under 35°C 1P / 1P cycle, that is, when the kinetic failure characteristic parameter Z of the negative electrode sheet of the lithium-ion battery is R and thermodynamic failure characteristic parameter Z T The ratio K satisfies The lithium-ion battery can achieve 8000cls@70% SOH at 35°C 1P / 1P charge and discharge cycles.

[0082] According to the technical solution of the present invention, the dynamic failure characteristic parameter Z is obtained. R The methods include:

[0083] Establish the linear relationship between the capacity loss rate Y and the number of cycles n during the battery cycle: lnY-lnn;

[0084] Obtain the slope of the linear relationship lnY-lnn, which is the dynamic failure characteristic parameter Z R ;

[0085] And / or, obtaining the thermodynamic failure characteristic parameter Z T The methods include:

[0086] Establish the linear relationship between the capacity loss rate Y during the battery cycle and the single cycle capacity Q': lnY-lnQ';

[0087] Obtain the slope of the linear relationship lnY-lnQ', which is the thermodynamic failure characteristic parameter Z T .

[0088] In some embodiments, the method for establishing the linear relationship lnY-lnn comprises the following steps:

[0089] S1. According to the rate acceleration model, the capacity loss rate Y and the cycle time t satisfy the Arrhenius formula of the following formula (1):

[0090] In formula (1): T is the thermodynamic temperature, A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and Z is the power law factor;

[0091] S2. Based on the fact that T remains unchanged, transform the above formula into formula (2): lnY=lnA rate +Z R lnt formula (2)

[0092] S3. Combined with the relationship that the cycle time t is proportional to the number of cycles n at the same magnification, the above formula becomes formula (3): lnY=lnA rate +Z R lnn formula (3)

[0093] S4. The linear relationship lnY-lnn is obtained by fitting formula (3).

[0094] In some embodiments, the method for establishing the linear relationship lnY-lnQ' comprises the following steps:

[0095] S1. According to the temperature acceleration model, the capacity loss rate Y and the cycle time t satisfy the Arrhenius formula of the following formula (1'):

[0096] In formula (1'): T is the thermodynamic temperature, A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and Z is the power law factor;

[0097] S2. Combining the relationship that the capacity Q output during the battery cycle is proportional to the cycle time t, the above formula is converted into formula (2'):

[0098] S3, based on the capacity Q output during the battery cycle is equal to the superposition of the single cycle capacity Q', the above formula becomes formula (3'):

[0099] S4. The linear relationship lnY-lnQ' is obtained by fitting formula (3').

[0100] In a second aspect, the present invention provides a method for designing a negative electrode sheet, wherein the design method comprises:

[0101] The kinetic and thermodynamic matching of the negative electrode sheet is evaluated using the evaluation method described in the first aspect above;

[0102] If the kinetic and thermodynamic matching of the negative electrode plate is good, the design requirements are met;

[0103] If the evaluation shows that the kinetic and thermodynamic matching of the negative electrode plate is not good, the negative electrode active material of the negative electrode plate is adjusted to adjust the K value so that the kinetic and thermodynamic matching of the negative electrode plate meets the design requirements.

[0104] In some embodiments, the negative electrode active material includes amorphous carbon and crystalline carbon.

[0105] In some specific embodiments, the negative electrode active material of the negative electrode sheet is adjusted to be:

[0106] The mass ratio of the amorphous carbon to the crystalline carbon is regulated to be (1.0-2.5%): (97.5-99.0%).

[0107] The present invention has found that if the proportion of amorphous carbon in the negative electrode active material is too high, thermodynamic aging losses will become dominant, side reactions will increase, and active lithium will be consumed; if the proportion of amorphous carbon in the negative electrode active material is too low, the electrode design will not be able to meet the 1P rate threshold, the kinetics will be insufficient, the active lithium deintercalation rate will be reduced, polarization will increase, reversible losses will increase, and there will even be a risk of lithium plating. That is, the ratio of amorphous carbon to crystalline carbon in the negative electrode active material will have a significant impact on thermodynamic properties, kinetic properties, cycle performance, etc. Based on this, the present invention has conducted a lot of research and found that when the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material is controlled within the range of (1.0-2.5%): (97.5-99.0%), the kinetic characteristics and thermodynamic characteristics of the negative electrode of the lithium-ion battery can be optimally matched, thereby achieving the requirement of 8000cls@70% SOH at 35°C 1P / 1P charge and discharge cycles. Therefore, in the design of the present invention, the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material is controlled within the range of (1.0-2.5%): (97.5-99.0%).

[0108] In some specific embodiments, the mass ratio of amorphous carbon to crystalline carbon is 2.5%:97.5%.

[0109] In some specific embodiments, the mass ratio of amorphous carbon to crystalline carbon is 1%:99.0%.

[0110] In some specific embodiments, the crystalline carbon is selected from natural graphite, artificial graphite, or a combination thereof; and / or the amorphous carbon is selected from soft carbon, hard carbon, mesophase pitch carbonization product, calcined coke, or a combination thereof.

[0111] It should be noted that this application does not impose any restrictions on the materials of crystalline carbon and amorphous carbon. In practical applications, those skilled in the art can select the specific materials of crystalline carbon and amorphous carbon according to actual needs. Any adjustments and changes to the specific materials of crystalline carbon and amorphous carbon do not deviate from the basic principles of this application and should be limited to the scope of protection of this application.

[0112] In some specific embodiments, the negative electrode plate further includes a conductive agent, a binder, and a thickener.

[0113] It should be noted that the present invention does not specifically limit the mass ratio of the negative electrode active material, the conductive agent, the binder and the thickener, and the commonly used ratio in the art can be adopted. For example, the mass ratio of the negative electrode active material, the conductive agent, the binder and the thickener can be (90-94%): (1-5%): (1-4%): (1-3%).

[0114] In some specific embodiments, the mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickener is 94%:3%:1.5%:1.5%.

[0115] It should be noted that the present invention does not impose specific limitations on the conductive agent, binder, and thickener, and commonly used materials in the art may be used. For example, the conductive agent may be one or more of carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene; the binder may be one or more of styrene-butadiene rubber, polyacrylic acid, polyimide, polyvinyl alcohol, and polyethyleneimine; and the thickener may be one or more of sodium carboxymethyl cellulose, polyacrylonitrile, and polyacrylate.

[0116] In some specific embodiments, the binder is a combination of styrene-butadiene rubber and polyacrylic acid.

[0117] It should be noted that when the binder is a combination of styrene-butadiene rubber and polyacrylic acid, the present invention does not specifically limit the mass ratio of the two, and the commonly used ratio in this field can be adopted. For example, the mass ratio of the styrene-butadiene rubber and polyacrylic acid can be (0.1-0.5):1.

[0118] In some specific embodiments, the mass ratio of the styrene-butadiene rubber to the polyacrylic acid is 0.5:1.

[0119] In some embodiments, the conductive agent is carbon black.

[0120] In some embodiments, the thickener is sodium carboxymethyl cellulose.

[0121] In a third aspect, the present invention provides a negative electrode plate, which is designed using the design method described in the second aspect.

[0122] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the aforementioned negative electrode plate.

[0123] The lithium-ion battery of the present invention achieves an optimal match between the kinetics and thermodynamics of the negative electrode of the lithium-ion battery by regulating the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material of the lithium-ion battery to meet the ratio of (1.0-2.5%): (97.5-99.0%), thereby achieving the requirement of 8000cls@70% SOH at 35°C 1P / 1P charge and discharge cycles.

[0124] The lithium-ion battery negative electrode sheet and the lithium-ion battery containing the same are described in detail below through several specific embodiments.

[0125] In the following examples and comparative examples, the amorphous carbon ratio test and 35°C 1P / 1P cycle test methods are as follows:

[0126] 1. Amorphous carbon ratio test method

[0127] ① Before testing, different graphite samples were dried in a vacuum drying oven at 100°C for 2 hours to eliminate the influence of moisture;

[0128] ②Then the crucible is treated to a constant weight;

[0129] ③ Open the knob of the oxygen cylinder and adjust the pressure reducing valve to a maximum of 0.2MPa, then turn on the power switch of the thermostatic bath and set the temperature to 20℃;

[0130] ④ Weigh about 10mg-20mg of sample into the sample crucible for later use;

[0131] ⑤ Edit the test program: temperature range 30-700℃, heating rate 10℃ / min, oxygen condition, flow rate 50mL / min;

[0132] ⑥After the test starts and the instrument reaches the sample placement temperature, place the sample in for testing;

[0133] ⑦ After the sample test is completed, wait until the temperature drops to the removal temperature, open the furnace door and take out the sample;

[0134] ⑧The amorphous carbon ratio is calculated as the weight loss rate of this process.

[0135] 2. 35℃ 1P / 1P cycle test method

[0136] ① Place the lithium-ion battery at 35 (± 2) ° C for 60 minutes;

[0137] ②1P rate discharge to 2.0V;

[0138] ③Stay still for 5 minutes;

[0139] ④1P rate charge to 3.65V;

[0140] ⑤Stay still for 5 minutes;

[0141] ⑥ Repeat steps ②-⑤ until the SOH reaches 70%.

[0142] Example 1

[0143] This embodiment provides a lithium-ion battery negative electrode plate and a lithium-ion battery. The lithium-ion battery negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on a surface of the negative electrode current collector, wherein the negative electrode material layer includes a negative electrode active material, the negative electrode active material includes amorphous carbon and crystalline carbon, and the mass ratio of the amorphous carbon to the crystalline carbon is 2.5%:97.5% (denoted as graphite 1).

[0144] The preparation method of the lithium ion battery negative electrode sheet and the lithium ion battery of this embodiment is as follows:

[0145] (1) Negative electrode

[0146] The negative electrode sheet was prepared using the above-mentioned graphite 1 as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber and polyacrylic acid as the binder, and sodium carboxymethyl cellulose as the thickener. The mass ratio of the negative electrode active material, conductive agent, binder and thickener in the negative electrode sheet was 94:3:1.5:1.5, the styrene-butadiene rubber and polyacrylic acid in the binder was 0.5:1, and the negative electrode current collector was copper foil.

[0147] (2) Positive electrode

[0148] The positive electrode sheet was prepared using lithium iron phosphate as the positive electrode active material, acetylene black as the conductive agent, and polyvinylidene fluoride as the binder. The mass ratio of lithium iron phosphate, acetylene black, and polyvinylidene fluoride in the positive electrode sheet was 96:2:2, and the positive electrode current collector was aluminum foil.

[0149] (3) Lithium-ion batteries

[0150] Using celegard2400 as the separator, the positive electrode sheet, separator, and negative electrode sheet are assembled into a battery cell in a winding manner, and then an electrolyte composed of lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) is injected into the battery cell (the solvent is EC, DEC and DMC in a volume ratio of 1:1:1, and the concentration of LiPF6 is 1.3 mol / L) and sealed to obtain a lithium-ion battery.

[0151] In this embodiment, the dynamic failure characteristic parameter Z of the negative electrode of the lithium ion battery is R Obtained by a method comprising the steps of:

[0152] S1. According to the rate acceleration model, the capacity loss rate Y and the cycle time t satisfy the Arrhenius formula of the following formula (1):

[0153] In formula (1): T is the thermodynamic temperature, A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and Z is the power law factor;

[0154] S2. Based on the fact that T remains unchanged, transform the above formula into formula (2): lnY=lnA rate +Z R lnt formula (2)

[0155] S3. Combined with the relationship that the cycle time t is proportional to the number of cycles n at the same magnification, the above formula becomes formula (3): lnY=lnA rate +Z R lnn formula (3)

[0156] S4. The linear relationship between the capacity loss rate Y and the number of cycles n during the lithium-ion battery cycle under the 35°C 1P / 1P cycle condition is obtained by fitting formula (3): lnY-lnn is y=0.7909x-8.1816, as shown in Figure 1 As shown, the slope of the linear relationship is 0.7909, which is the dynamic failure characteristic parameter Z R .

[0157] In this embodiment, the thermodynamic failure characteristic parameter Z of the negative electrode of the lithium ion battery is T Obtained by a method comprising the steps of:

[0158] S1. According to the temperature acceleration model, the capacity loss rate Y and the cycle time t satisfy the Arrhenius formula of the following formula (1'):

[0159] In formula (1'): T is the thermodynamic temperature, A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and Z is the power law factor;

[0160] S2. Combining the relationship that the capacity Q output during the battery cycle is proportional to the cycle time t, the above formula is converted into formula (2'):

[0161] S3, based on the capacity Q output during the battery cycle is equal to the superposition of the single cycle capacity Q', the above formula becomes formula (3'):

[0162] S4. The linear relationship between the capacity loss rate Y and the single cycle capacity Q' of lithium-ion batteries with different negative electrodes during cycling under 35°C 1P / 1P cycling conditions is obtained by fitting formula (3'): lnY-lnQ' is y=1.2183x+10.893, as shown in Figure 2 As shown, the slope of the linear relationship is 1.2183, which is the thermodynamic failure characteristic parameter Z. T .

[0163] The dynamic failure characteristic parameter Z of the negative electrode plate of the lithium ion battery of this embodiment R is 0.7909, and the thermodynamic failure characteristic parameter Z T is 1.2183, the ratio of the two is 0.65, satisfying The relationship formula.

[0164] After a 35°C 1P / 1P cycle test, the cycle life of the lithium-ion battery of this embodiment is predicted to be 8600 cls@70% SOH. Therefore, the lithium-ion battery of this embodiment can achieve the requirement of 8000 cls@70% SOH at 35°C 1P / 1P charge-discharge cycles.

[0165] Example 2

[0166] This embodiment provides a lithium ion battery negative electrode plate and a lithium ion battery. The preparation method thereof refers to that of Example 1. The difference from Example 1 is that the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material is 1.0%:99.0% (denoted as graphite 2).

[0167] The linear relationship between the capacity loss rate Y and the number of cycles n during the lithium ion battery cycle under the 35°C 1P / 1P cycle condition is obtained by fitting according to the method of Example 1: Figure 3 As shown) and the linear relationship between the capacity loss rate Y during the battery cycle and the single cycle capacity Q'lnY-lnQ' (as shown Figure 4As shown), the dynamic failure characteristic parameter Z is obtained according to the linear relationship R and thermodynamic failure characteristic parameter Z T The ratio of the two is shown in Table 1. The lithium ion battery of this embodiment was subjected to a 35° C. 1P / 1P cycle test. The test results are shown in Table 1.

[0168] Comparative Example 1

[0169] This comparative example provides a lithium ion battery negative electrode sheet and a lithium ion battery. The preparation method thereof refers to Example 1. The difference from Example 1 is that the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material is 0.7%:99.3% (denoted as graphite 1').

[0170] The linear relationship between the capacity loss rate Y and the number of cycles n during the lithium ion battery cycle under the 35°C 1P / 1P cycle condition is obtained by fitting according to the method of Example 1: Figure 5 As shown) and the linear relationship between the capacity loss rate Y during the battery cycle and the single cycle capacity Q'lnY-lnQ' (as shown Figure 6 As shown), the dynamic failure characteristic parameter Z is obtained according to the linear relationship R and thermodynamic failure characteristic parameter Z T The ratio of the two is shown in Table 1. The lithium ion battery of the comparative example was subjected to a 35°C 1P / 1P cycle test, and the test results are shown in Table 1.

[0171] Comparative Example 2

[0172] This comparative example provides a lithium ion battery negative electrode sheet and a lithium ion battery. The preparation method thereof refers to Example 1. The difference from Example 1 is that the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material is 2.8%:97.2% (denoted as graphite 2').

[0173] The linear relationship between the capacity loss rate Y and the number of cycles n during the lithium ion battery cycle under the 35°C 1P / 1P cycle condition is obtained by fitting according to the method of Example 1: Figure 7 As shown) and the linear relationship between the capacity loss rate Y during the battery cycle and the single cycle capacity Q'lnY-lnQ' (as shown Figure 8 As shown), the dynamic failure characteristic parameter Z is obtained according to the linear relationship R and thermodynamic failure characteristic parameter Z T The ratio of the two is shown in Table 1. The lithium ion battery of the comparative example was subjected to a 35°C 1P / 1P cycle test, and the test results are shown in Table 1.

[0174] Comparative Example 3

[0175] This comparative example provides a lithium ion battery negative electrode sheet and a lithium ion battery. The preparation method thereof refers to Example 1. The difference from Example 1 is that the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material is 0.5%:99.5% (denoted as graphite 3').

[0176] The linear relationship between the capacity loss rate Y and the number of cycles n during the lithium ion battery cycle under the 35°C 1P / 1P cycle condition is obtained by fitting according to the method of Example 1: Figure 9 As shown) and the linear relationship between the capacity loss rate Y during the battery cycle and the single cycle capacity Q'lnY-lnQ' (as shown Figure 10 As shown), the dynamic failure characteristic parameter Z is obtained according to the linear relationship R and thermodynamic failure characteristic parameter Z T The ratio of the two is shown in Table 1. The lithium ion battery of the comparative example was subjected to a 35°C 1P / 1P cycle test, and the test results are shown in Table 1.

[0177] Comparative Example 4

[0178] This comparative example provides a lithium ion battery negative electrode sheet and a lithium ion battery. The preparation method thereof refers to Example 1. The difference from Example 1 is that the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material is 6.3%:93.7% (denoted as graphite 4').

[0179] The linear relationship between the capacity loss rate Y and the number of cycles n during the lithium ion battery cycle under the 35°C 1P / 1P cycle condition is obtained by fitting according to the method of Example 1: Figure 11 As shown) and the linear relationship between the capacity loss rate Y and the single capacity Q' during the battery cycle is lnY-lnQ' (as shown Figure 12 As shown), the dynamic failure characteristic parameter Z is obtained according to the linear relationship R and thermodynamic failure characteristic parameter Z T The ratio K of the two is shown in Table 1. The lithium ion battery of the comparative example was subjected to a 35° C. 1P / 1P cycle test, and the test results are shown in Table 1.

[0180] The ratio of amorphous carbon to crystalline carbon and the dynamic failure characteristic parameter Z of each embodiment and comparative example R and thermodynamic failure characteristic parameter Z T The ratio K of the two and the results of 35℃ 1P / 1P cycle test are shown in Table 1. The trend diagram of 35℃ 1P / 1P cycle of lithium ion batteries of various embodiments and comparative examples is shown in Table 1. Figure 13 shown.

[0181] Table 1

[0182] From the results in Table 1, it can be seen that when the mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material of the lithium ion battery meets the ratio of (1.0-2.5%) to (97.5-99.0%), the dynamics and thermodynamics of the negative electrode of the lithium ion battery can be optimally matched, that is, the dynamic failure characteristic parameter Z R and thermodynamic failure characteristic parameter Z T The ratio K satisfies relationship, and achieve the requirement of 8000cls@70% SOH at 35℃ 1P / 1P charge and discharge cycle.

[0183] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A method for evaluating the kinetic and thermodynamic matching of a negative electrode plate, characterized in that: The evaluation methods include: Obtain the dynamic failure characteristic parameter Z of the negative electrode of the lithium-ion battery R and thermodynamic failure characteristic parameter Z T ; Calculate the dynamic failure characteristic parameter Z R and thermodynamic failure characteristic parameter Z T The ratio K, When K satisfies 0.65≤K≤0.73, it indicates that the negative electrode plate has good kinetic and thermodynamic matching; When K does not satisfy 0.65≤K≤0.73, it indicates that the kinetics and thermodynamics of the negative electrode are not well matched.

2. The evaluation method according to claim 1, wherein: Obtain the dynamic failure characteristic parameter Z R The methods include: Establish the linear relationship between the capacity loss rate Y and the number of cycles n during the battery cycle: lnY-lnn; Obtain the slope of the linear relationship lnY-lnn, which is the dynamic failure characteristic parameter Z R ; And / or, obtaining the thermodynamic failure characteristic parameter Z T The methods include: Establish the linear relationship between the capacity loss rate Y during the battery cycle and the single cycle capacity Q': lnY-lnQ'; Obtain the slope of the linear relationship lnY-lnQ', which is the thermodynamic failure characteristic parameter Z T .

3. The evaluation method according to claim 2, wherein: The method for establishing the linear relationship lnY-lnn includes the following steps: S1. According to the rate acceleration model, the capacity loss rate Y and the cycle time t satisfy the Arrhenius formula of the following formula (1): In formula (1): T is the thermodynamic temperature, A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and Z is the power law factor; S2. Based on the fact that T remains unchanged, transform the above formula into formula (2): lnY = lnA rate + Z R ln t Equation (2) S3. Combined with the relationship that the cycle time t is proportional to the number of cycles n at the same magnification, the above formula becomes formula (3): lnY=lnA rate +Z R lnn formula(3) S4, the linear relationship lnY-lnn is obtained by fitting formula (3); And / or, the method for establishing the linear relationship lnY-lnQ' comprises the following steps: S1. According to the temperature acceleration model, the capacity loss rate Y and the cycle time t satisfy the Arrhenius formula of the following formula (1'): In formula (1'): T is the thermodynamic temperature, A is the pre-exponential factor, Ea is the activation energy, R is the ideal gas constant, and Z is the power law factor; S2. Combining the relationship that the capacity Q output during the battery cycle is proportional to the cycle time t, the above formula is converted into formula (2'): S3, based on the capacity Q output during the battery cycle is equal to the superposition of the single cycle capacity Q', the above formula becomes formula (3'): S4. The linear relationship lnY-lnQ' is obtained by fitting formula (3').

4. A design method for a negative electrode plate, characterized in that: The design method includes: The evaluation method according to any one of claims 1 to 3 is used to evaluate the kinetic and thermodynamic matching of the negative electrode plate; If the kinetic and thermodynamic matching of the negative electrode plate is good, the design requirements are met; If the evaluation shows that the kinetic and thermodynamic matching of the negative electrode plate is not good, the negative electrode active material of the negative electrode plate is adjusted to adjust the K value so that the kinetic and thermodynamic matching of the negative electrode plate meets the design requirements.

5. The design method according to claim 4, characterized in that: The negative electrode active material includes amorphous carbon and crystalline carbon.

6. The design method according to claim 5, characterized in that: The negative electrode active material of the negative electrode plate is adjusted to be: The mass ratio of amorphous carbon to crystalline carbon in the negative electrode active material is regulated to be (1.0-2.5%): (97.5-99.0%).

7. The design method according to claim 6, characterized in that: The negative electrode plate further includes a conductive agent, a binder and a thickener.

8. The design method according to claim 7, characterized in that: The mass ratio of the negative electrode active material, the conductive agent, the binder and the thickener is (90-94%): (1-5%): (1-4%): (1-3%).

9. A negative electrode plate, characterized in that: The negative electrode plate is designed using the design method described in any one of claims 4 to 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 9.

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