Method for evaluating influence of lithium ion battery negative electrode material on thermodynamic property of lithium ion battery

Abstract

The invention provides a method for evaluating the influence of a lithium ion battery negative electrode material on the thermodynamic property of a lithium ion battery, and relates to the technical field of lithium ion batteries. According to the evaluation method, different negative electrode materials are prepared into half cells, a charging corresponding curve graph is drawn by utilizing the logarithms of the lithium removal potential and the specific capacity of the half cells under the same multiplying power, and a thermodynamic parameter K is calculated and established; the thermodynamic parameter K can be used for evaluating the safety performance of different negative electrodes under a normal-temperature adiabatic overcharge test, and the smaller the value of the thermodynamic parameter K is, the greater the influence of the negative electrode material to be evaluated on the overcharge performance of the lithium ion battery is, namely the poorer the safety performance of the lithium ion battery is. The evaluation method is simple in experimental process, high in practicability and capable of rapidly screening and evaluating the lithium ion battery negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method for evaluating the influence of lithium-ion battery anode materials on the thermodynamic properties of lithium-ion batteries. Background Technology

[0002] As a core technology for modern energy storage, the optimization of lithium-ion batteries' performance and lifespan is crucial for promoting clean energy applications and achieving sustainable energy development. Among the many factors affecting lithium-ion battery performance, kinetic and thermodynamic performance are two key dimensions. Kinetic performance mainly involves the migration rate of lithium ions in electrode materials and electrolytes, as well as interfacial reaction rates, directly determining the battery's instantaneous output capability, such as charge-discharge performance and power density at high rates. Thermodynamic performance, on the other hand, is related to the energy state, phase transition behavior, and thermal stability of the battery system. It fundamentally constrains the battery's cycle life, capacity retention, and safety margins, especially under extreme conditions such as high temperatures or overcharging, where thermodynamic runaway can lead to serious safety issues. Therefore, a deep understanding and synergistic optimization of kinetic and thermodynamic characteristics is the core path to improving the overall performance of lithium-ion batteries and extending their lifespan, which is of great significance for applications such as electric vehicles and large-scale energy storage.

[0003] In recent years, to alleviate the widespread "range anxiety" in power tools and electric vehicles, thick electrode (60~160µm) technology has become an important development direction in the lithium battery field due to its ability to significantly increase the loading of active materials on the electrode. This technology effectively improves the volumetric energy density of the battery by increasing the proportion of active material per unit area of ​​the electrode, enabling devices to run for longer periods or travel farther on a single charge, and is gradually becoming a research hotspot in high-energy battery design.

[0004] However, with the increase of electrode thickness, problems such as the elongation of internal ion transport paths and uneven reaction distribution become increasingly prominent. The influence of thermodynamic factors on the internal reaction behavior of thick electrodes (60~160µm) has long been neglected. Thermodynamic parameters such as entropy change, enthalpy change, and interfacial thermal stability during cycling not only affect the phase transition behavior and structural stability of the material but also directly relate to the safety performance of the electrode under extreme conditions such as high temperature and overcharge. Therefore, developing a method to rapidly and accurately evaluate the thermodynamic properties of anode materials and systematically compare the thermodynamic response characteristics of different anodes under overcharge testing is of significant theoretical and engineering guiding value for optimizing thick electrode design, improving overall battery safety, and accelerating the development of lithium-ion battery systems from the material to the integration level.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for evaluating the influence of lithium-ion battery anode materials on the thermodynamic performance of lithium-ion batteries. The evaluation method is simple in experimental process, highly practical, and can quickly screen and evaluate lithium-ion battery anode materials.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The present invention provides a method for evaluating the influence of lithium-ion battery anode materials on the thermodynamic properties of lithium-ion batteries, the evaluation method comprising: The negative electrode material to be evaluated was prepared as a negative electrode sheet and assembled into a half cell. The half cell was subjected to charge and discharge tests, and the charging voltage and capacity during the charging process were recorded. Then, the logarithm of the charging voltage was taken and differentiated. Using the data after differential processing as the Y-axis and the SOC value during the charging process as the X-axis, a charging curve is plotted; the SOC value is the percentage of remaining power to rated capacity. Record the X-axis value corresponding to the first peak of the negative electrode in the charging curve diagram when the SOC value is between 0 and 0.2, and denote it as F1; record the X-axis value corresponding to the first peak of the negative electrode in the charging curve diagram when the SOC value is between 0.2 and 0.6, and denote it as F2. The thermodynamic regulating parameter K is calculated using the formula: K = F2 - F1; 0.35 <K<0.41。

[0008] The smaller the value of the thermodynamic adjustment parameter K, the greater the impact of the negative electrode material to be evaluated on the thermodynamic performance of the lithium-ion battery, that is, the worse the thermodynamic performance of the lithium-ion battery.

[0009] Furthermore, the negative electrode material to be evaluated is a graphite material or a graphite-silicon-oxygen composite material; Preferably, the graphite material comprises: artificial graphite 1 (D50 particle size 14 μm, specific surface area 1.1 μm). 2 / g, discharge capacity 345mAh / g; artificial graphite 2 (D50 particle size 10um, specific surface area 1.4m) 2 / g, discharge capacity 345mAh / g; artificial graphite 3 (D50 particle size 13um, specific surface area 1.3m) 2 / g, discharge capacity 350mAh / g; artificial graphite 4 (D50 particle size 15um, specific surface area 3.0m) 2 / g, discharge capacity 355mAh / g; artificial graphite 5 (D50 particle size 16um, specific surface area 1.5m) 2 At least one of the following: / g, discharge capacity 358mAh / g.

[0010] Furthermore, the mass ratio of graphite to silicon oxide in the graphite-silicon-oxygen composite material is 99 to 1:10, preferably 70:30.

[0011] Furthermore, the negative electrode sheet contains the negative electrode material to be evaluated, a conductive agent, and a binder; Preferably, by mass percentage, the negative electrode sheet comprises: 95-96% of the negative electrode material to be evaluated, 2-3% of the conductive agent, and 2-4% of the binder.

[0012] Furthermore, the compaction density of the negative electrode sheet is 1.50~1.60 g / cm³. 3 .

[0013] Furthermore, methods for charging and discharging half-cells include: The negative electrode was discharged to 5mV at a constant current of 0.1C, and then discharged to 5mV at a constant current of 0.01C; it was left to stand for 10 minutes; then it was charged to 1.5V at a constant current of 0.1C, and the voltage and capacity during the charging process were recorded.

[0014] Furthermore, the differential process after taking the logarithm of the charging voltage includes: Take the logarithm of the charging voltage to obtain the data log10(V), denoted as Y1; then differentiate the Y1 data to obtain the data dlog10(V) / d(SOC), denoted as Y2.

[0015] Furthermore, the evaluation method also includes: The negative electrode sheet prepared from the negative electrode material to be evaluated is assembled into a full cell. Then, the full cell is subjected to formation and high-temperature aging processes, and then subjected to room temperature overcharge test and room temperature cycle test. The irreversible capacity loss rate is calculated based on the results of the room temperature cycling test. Then, the anode material to be evaluated is evaluated based on the highest temperature and irreversible capacity loss rate of the room temperature overcharge test.

[0016] The higher the maximum temperature and irreversible capacity loss rate of the room temperature overcharge test, the greater the impact of the negative electrode material to be evaluated on the thermodynamic performance of the lithium-ion battery, that is, the worse the thermodynamic performance of the lithium-ion battery.

[0017] Furthermore, the voltage range for the room temperature overcharge test is 2.5~5V, the charging and discharging current is 1C, and the room temperature is 25±2℃.

[0018] Furthermore, the voltage range of the ambient temperature cycling test is 2.5~3.65V, the charging and discharging current is 0.5C, and the charging and discharging is performed at 0.05C every 200 cycles, with the ambient temperature being 25±2℃.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a method for evaluating the influence of lithium-ion battery anode materials on the thermodynamic performance of lithium-ion batteries. This method involves plotting charging curves of the logarithm of the delithiation potential and specific capacity of different anode materials at the same rate, and calculating and establishing a thermodynamic parameter K. This thermodynamic parameter K can be used to evaluate the thermodynamic performance of different anodes under overcharge. The evaluation method described in this application is simple in experimental procedure, highly practical, and can quickly screen and evaluate lithium-ion battery anode materials. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 The charging curve of graphite 1 provided in Embodiment 1 of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] According to one aspect of the present invention, a method for evaluating the influence of lithium-ion battery anode materials on the thermodynamic properties of lithium-ion batteries, the evaluation method comprising: The negative electrode material to be evaluated was prepared as a negative electrode sheet and assembled into a half cell. The half cell was subjected to charge and discharge tests, and the charging voltage and capacity during the charging process were recorded. Then, the logarithm of the charging voltage was taken and differentiated. Using the data after differential processing as the Y-axis and the SOC value during the charging process as the X-axis, a charging curve is plotted; the SOC value is the percentage of remaining power to rated capacity. Record the X-axis value corresponding to the first peak of the negative electrode in the charging curve diagram when the SOC value is between 0 and 0.2, and denote it as F1; record the X-axis value corresponding to the first peak of the negative electrode in the charging curve diagram when the SOC value is between 0.2 and 0.6, and denote it as F2. The thermodynamic regulating parameter K is calculated using the formula: K = F2 - F1; 0.35 <K<0.41。

[0024] The smaller the value of the thermodynamic adjustment parameter K, the greater the impact of the negative electrode material to be evaluated on the overcharge performance of the lithium-ion battery, that is, the worse the safety performance of the lithium-ion battery.

[0025] The present invention provides a method for evaluating the influence of lithium-ion battery anode materials on the thermodynamic performance of lithium-ion batteries. This method involves plotting charging curves of the logarithm of the delithiation potential and specific capacity of different anode materials at the same rate, and calculating and establishing a thermodynamic parameter K. This thermodynamic parameter K can be used to evaluate the thermodynamic performance of different anodes under overcharge. The evaluation method described in this application is simple in experimental procedure, highly practical, and can quickly screen and evaluate lithium-ion battery anode materials.

[0026] The present invention provides a method for evaluating the influence of lithium-ion battery anode materials on the thermodynamic performance of lithium-ion batteries. This method involves plotting charging curves of the logarithm of delithiation potential and specific capacity of different anode materials at the same rate, and calculating and establishing a thermodynamic parameter K. This thermodynamic parameter K can be used to evaluate the thermodynamic performance of different anodes at the same rate. The evaluation method described in this application is simple in experimental procedure, highly practical, and can quickly screen and evaluate lithium-ion battery anode materials.

[0027] It should be noted that the "thermodynamic properties" mentioned in this invention refer to the uniformity of phase transition behavior and the stability of the microstructure of the negative electrode material during the lithium-ion intercalation / deintercalation process. Macroscopically, these properties are directly reflected in the battery's long-term cycle life, capacity retention rate, and the highest temperature during overcharge testing.

[0028] Specifically, the correlation principle between the thermodynamic adjustment parameter K of this invention and the battery overcharge performance can be explained as follows: For graphite-based anode materials, the delithiation process involves a series of phase transition reactions occurring in stages. The characteristic peaks (F1 and F2) obtained by performing specific logarithmic differentiation on the voltage-capacity curves likely correspond to the critical boundaries of key phase transition stages. The thermodynamic compatibility parameter K (i.e., the difference between F2 and F1), defined in this application, essentially reflects the degree of separation and orderliness of the staged phase transition process. Specifically: a larger K value indicates an orderly, clear, and distinct phase transition process, which is beneficial to the uniformity of the reaction inside the electrode and the stability of the structure; conversely, a smaller K value suggests that the phase transition process may overlap or tend towards disorder. This chaotic phase transition behavior may lead to uneven lithium ion insertion / extraction within the electrode, causing localized stress concentration and unstable growth of the SEI film, ultimately manifesting as a significant increase in the temperature during macroscopic battery overcharge testing.

[0029] It should also be noted that the evaluation method of the above-mentioned lithium-ion battery anode material on the thermodynamic performance of lithium-ion battery is particularly suitable for the rapid screening of anode materials used in thick electrodes (such as 60-160μm). Since thick electrodes are more sensitive to the uniformity of material reaction, the method of the present invention can predict and avoid rapid degradation caused by poor thermodynamic performance in advance.

[0030] In a preferred embodiment of the present invention, the negative electrode material to be evaluated is a graphite material or a graphite-silicon-oxygen composite material. Preferably, the graphite material includes at least one of the following: artificial graphite 1 (D50 particle size 14 μm, specific surface area 1.1 m² / g, discharge capacity 345 mAh / g); artificial graphite 2 (D50 particle size 10 μm, specific surface area 1.4 m² / g, discharge capacity 345 mAh / g); artificial graphite 3 (D50 particle size 13 μm, specific surface area 1.3 m² / g, discharge capacity 350 mAh / g); artificial graphite 4 (D50 particle size 15 μm, specific surface area 3.0 m² / g, discharge capacity 355 mAh / g); and artificial graphite 5 (D50 particle size 16 μm, specific surface area 1.5 m² / g, discharge capacity 358 mAh / g).

[0031] In a preferred embodiment of the present invention, the mass ratio of graphite to silicon oxide in the graphite-silicon-oxygen composite material is 99 to 1:10, preferably 70:30.

[0032] In a preferred embodiment of the present invention, the negative electrode sheet includes a negative electrode material to be evaluated, a conductive agent, and a binder; Preferably, by mass percentage, the negative electrode sheet comprises: 95-96% of the negative electrode material to be evaluated, 2-3% of the conductive agent, and 2-4% of the binder.

[0033] In a preferred embodiment of the present invention, the compaction density of the negative electrode sheet is 1.50~1.60 g / cm³. 3 .

[0034] In a preferred embodiment, the compaction density of the negative electrode sheet is 1.50~1.60 g / cm³. 3 When the compaction density is less than 1.50 g / cm³ 3 This can lead to excessive thickness of the negative electrode, affecting its conductivity and consequently causing abnormal thermodynamic capacity performance; while compaction greater than 1.60 g / cm³... 3 The electrode has poor wettability, resulting in a low thermodynamic capacity utilization.

[0035] In a preferred embodiment of the present invention, a method for charging and discharging a half-cell includes: The negative electrode was discharged to 5mV at a constant current of 0.1C, and then discharged to 5mV at a constant current of 0.01C; it was left to stand for 10 minutes; then it was charged to 1.5V at a constant current of 0.1C, and the voltage and capacity during the charging process were recorded.

[0036] In a preferred embodiment of the present invention, the differential processing after taking the logarithm of the charging voltage includes: Take the logarithm of the charging voltage to obtain the data log10(V), denoted as Y1; then differentiate the Y1 data, i.e., dlog10(V) / d(SOC), and the resulting data is denoted as Y2.

[0037] In a preferred embodiment, Y2 of this application establishes a thermodynamic parameter K based on the logarithmic ratio of the specific capacity at the same rate (delithiation potential) and specific capacity, i.e., dlog10(V) / d(SOC). This thermodynamic parameter K can be used to evaluate the thermodynamic performance of different negative electrodes at the same rate.

[0038] In a preferred embodiment of the present invention, the evaluation method further includes: The negative electrode sheet prepared from the negative electrode material to be evaluated is assembled into a full cell. Then, the full cell is subjected to formation and high-temperature aging processes, and then subjected to room temperature overcharge test and room temperature cycle test. The irreversible capacity loss rate is calculated based on the results of the room temperature cycling test. Then, the anode material to be evaluated is evaluated based on the highest temperature and irreversible capacity loss rate of the room temperature overcharge test.

[0039] The higher the maximum temperature and irreversible capacity loss rate of the room temperature overcharge test, the greater the impact of the negative electrode material to be evaluated on the thermodynamic performance of the lithium-ion battery, that is, the worse the thermodynamic performance of the lithium-ion battery.

[0040] In a preferred embodiment of the present invention, the voltage range of the room temperature overcharge test is 2.5~5V, the charging and discharging current is 1C, and the room temperature is 25±2℃.

[0041] In a preferred embodiment of the present invention, the voltage range of the room temperature cycling test is 2.5~3.65V, the charging and discharging current is 0.5C, and the charging and discharging is performed at 0.05C every 200 cycles, and the room temperature is 25±2℃.

[0042] Furthermore, the formula for calculating the irreversible capacity loss rate is as follows: Irreversible capacity loss (%) = (Late cycle (0.05C capacity) - Late cycle (0.5C discharge capacity)) / Fresh battery (0.5C discharge capacity).

[0043] The technical solution of the present invention will be further described below with reference to the embodiments.

[0044] Example 1 A method for evaluating the influence of different lithium-ion battery anode materials on the thermodynamic properties of lithium-ion batteries, the method comprising the following steps: (i) Different negative electrode materials to be tested are added to the same mass of deionized water at a ratio of 96:2:2 with conductive agent (super-P conductive carbon black) and binder (PAA polyacrylic acid) to prepare a negative electrode slurry with a solid content of 50%.

[0045] The negative electrode material to be tested in this embodiment includes: Table 1:

[0046] Note: Artificial graphite 1 (D50 particle size 14µm, specific surface area 1.1m² / g, discharge capacity 345mAh / g); Artificial graphite 2 (D50 particle size 10µm, specific surface area 1.4µm / g). 2 / g, discharge capacity 345mAh / g; artificial graphite 3 (D50 particle size 13um, specific surface area 1.3m) 2 / g, discharge capacity 350mAh / g; artificial graphite 4 (D50 particle size 15um, specific surface area 3.0m) 2 / g, discharge capacity 355mAh / g; artificial graphite 5 (D50 particle size 16um, specific surface area 1.5m) 2 / g, discharge capacity 358mAh / g).

[0047] Table 2:

[0048] Note: Silicon-oxygen 1 (D50 particle size 7µm, specific surface area 1.5µm) 2 / g, discharge capacity 1300mAh / g), silicon oxide 2 (D50 particle size 7um, specific surface area 1.0m) 2 / g, discharge capacity 1500mAh / g), silicon oxide 3 (D50 particle size 6um, specific surface area 1.6m) 2 / g, discharge capacity 1600mAh / g), silicon oxide 4 (D50 particle size 7um, specific surface area 1.5m) 2 / g, discharge capacity 1600mAh / g).

[0049] (II) The negative electrode slurry from each of the above experimental groups was prepared into negative electrode sheets and assembled into half-cells and full-cells, as detailed below: 1. Half-cell fabrication: The negative electrode paste of each experimental group was coated onto the surface of an 8µm copper foil, with a coating density of 8 mg / cm³. 2 , at 1.50g / cm 3The compaction density is rolled to achieve an electrode thickness of 62 μm, which is then assembled with lithium foil to form a half-cell. Ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of EC:EMC:DEC = 1:4:2:3. Then, fluoroethylene carbonate and vinylene carbonate are added, dissolved, and stirred thoroughly before lithium salt LiPF6 is added.

[0050] 2. Full battery construction: The negative electrode paste for each experimental group was coated onto the surface of copper foil, with a single-sided areal density of 8 mg / cm², and a density of 1.50 g / cm². 3 The compaction density was achieved through roller pressing, resulting in an electrode thickness of 115µm, which was then cut into 80µm pieces. 80mm; Commercial lithium iron phosphate, conductive agent SP, and binder PVDF were mixed at a mass ratio of 97:2:1 to form a slurry, which was then coated onto the surface of aluminum foil. The positive electrode surface density was calculated using N:P = 1.1, and was 2.5 g / cm³. 3 The positive electrode sheet is obtained by pressing with a compaction roller, and then cut into 76mm pieces. 77mm; together with the above negative electrode sheet, form a soft-pack stacked battery with a capacity of 2.5Ah, and add the electrolyte from step 1 above.

[0051] (III) Testing: 1. Half-cell test: Discharge to 5mV with a constant current of 0.1C, then discharge to 5mV with a constant current of 0.01C; let stand for 10 minutes; charge to 1.5V with a constant current of 0.1C, and record the voltage and capacity during the charging process; The charging voltage (i.e., the lithium removal potential) is logarithmically divided to obtain a new data log10(V), denoted as Y1. The capacity is normalized to SOC, and SOC is used as the X-axis. Then, the Y1 data is differentiated, i.e., dlog(V) / d(SOC), denoted as Y2. The SOC value is the percentage of remaining power to rated capacity. Using the differentiated data Y2 as the Y-axis and the SOC value during the charging process as the X-axis, a charging curve is plotted. Figure 1 The charging curve of graphite 1 provided in this embodiment is shown.

[0052] Record the X-axis value corresponding to the first peak of the negative electrode in the charging curve diagram when the SOC value is between 0 and 0.2, and denote it as F1; record the X-axis value corresponding to the first peak of the negative electrode in the charging curve diagram when the SOC value is between 0.2 and 0.6, and denote it as F2. Calculate the thermodynamic regulation parameter K, with the formula: K = F2 - F1, where 0.35 < K < 0.41; the smaller the value of the thermodynamic regulation parameter K, the greater the impact of the to-be-evaluated anode material on the thermodynamic performance of the lithium-ion battery, that is, the worse the thermodynamic performance of the lithium-ion battery.

[0053] 2. Full battery test: After subjecting the above full battery to the processes of formation and high-temperature aging, conduct a room-temperature overcharge test within the voltage range of 2.5 - 5.0V, with a charging current of 1C, and the room temperature is 25 ± 2°C; for the room-temperature cycle test, the voltage range is 2.5 - 3.65V, the charging and discharging currents are 0.5C, and every 200 cycles, conduct 0.05C charging and discharging, and the room temperature is 25 ± 2°C.

[0054] Then calculate the irreversible capacity loss rate based on the highest temperature during room-temperature overcharge and the cycle test results, and evaluate the to-be-evaluated anode material.

[0055] Calculate the irreversible capacity loss rate based on the temperature recorded during the overcharge test and the cycle test results, and evaluate the to-be-evaluated anode material. The higher the highest temperature, the greater the irreversible capacity loss rate, indicating that the to-be-evaluated anode material has worse thermodynamic performance for the lithium-ion battery. This reflects that there are significant energy dissipations, irreversible phase changes or interfacial side reactions during the lithium deintercalation / insertion process, which are all manifestations of thermodynamic instability. Therefore, this index can be directly related to the cycle life and safety life of the battery, providing a key thermodynamic criterion for quickly screening high-performance anode materials.

[0056] The calculation formula for the irreversible capacity loss rate is as follows: Irreversible capacity loss (%) = (Capacity at the later stage of the cycle (0.05C capacity) - Discharge capacity at the later stage of the cycle (0.5C discharge capacity)) / Fresh battery (0.5C discharge capacity).

[0057] (IV). The test results of the above different to-be-tested anode materials are shown in Table 3 and Table 4.

[0058] Table 3:

[0059] As can be seen from Table 3, in experimental groups 1 - 5, the effects of different types of artificial graphite materials on the thermodynamic performance of lithium-ion batteries were investigated. From artificial graphite 1 to artificial graphite 5, the K value gradually decreased from 0.405 to 0.391. Correspondingly, the highest overcharge temperature increased from 91.4°C to 98.8°C. This shows that the evaluation method of the present invention can effectively distinguish the internal thermodynamic performance of different graphite materials, providing a rapid basis for the screening of graphite materials. The smaller the value of the thermodynamic regulation parameter K, the greater the impact of the to-be-evaluated anode material on the overcharge performance of the lithium-ion battery, that is, the worse the safety performance of the lithium-ion battery.

[0060] Experimental groups 6-9 used artificial graphite 1 and different silicon-oxygen addition amounts of 1% to investigate the effects of different types of silicon-oxygen materials on the thermodynamic properties of lithium-ion batteries. From experimental group 6 to experimental group 9, the K value decreased from 0.379 to 0.359. The maximum overcharge temperature increased from 102.3℃ to 113.6℃. This indicates that, at the same addition amount, different silicon-oxygen materials have different degrees of influence on the thermodynamic properties of the composite material. The method of this invention can quickly screen out silicon-oxygen materials with better compatibility with graphite substrates and less negative impact on overall thermodynamic properties. For example, under these conditions, silicon-oxygen 1 performed better than silicon-oxygen 4. The smaller the value of the thermodynamic adjustment parameter K, the greater the impact of the negative electrode material under evaluation on the overcharge performance of the lithium-ion battery, that is, the worse the safety performance of the lithium-ion battery.

[0061] Compared to experimental group 6 (1% silicon-oxygen 1), when the silicon-oxygen content increased to 2% (comparison group 1) and 3% (comparison group 2), the K value decreased sharply (0.379→0.343→0.322); the performance deteriorated significantly simultaneously: the maximum overcharge temperature changed from 102.3℃→115.5℃→120.7℃. This indicates that increasing the silicon content exacerbates volume expansion during cycling, severely damaging the stability of the electrode structure. The precipitous drop in the K value in this application accurately captures this microscopic-level thermodynamic performance deterioration. The smaller the value of the thermodynamic adjustment parameter K, the greater the impact of the evaluated negative electrode material on the overcharge performance of the lithium-ion battery, i.e., the worse the safety performance of the lithium-ion battery.

[0062] Table 4:

[0063] Table 4 shows that experimental groups 1-5 investigated the effects of different types of artificial graphite materials on the thermodynamic performance of lithium-ion batteries. From artificial graphite 1 to artificial graphite 5, the K value gradually decreased from 0.405 to 0.391. Correspondingly, the irreversible capacity loss increased from 8.80% to 10.70%, and the capacity retention decreased from 92.20% to 90.50%. This demonstrates that the evaluation method of this invention can effectively distinguish the intrinsic thermodynamic properties of different graphite materials, providing a rapid basis for graphite material screening. The greater the irreversible capacity loss rate, the greater the impact of the evaluated negative electrode material on the thermodynamic performance of the lithium-ion battery, i.e., the worse the thermodynamic performance of the lithium-ion battery.

[0064] Experimental groups 6-9 used artificial graphite 1 and different silicon-oxygen addition amounts of 1% to investigate the effects of different types of silicon-oxygen materials on the thermodynamic properties of lithium-ion batteries. From experimental group 6 to experimental group 9, the K value decreased from 0.379 to 0.359. The irreversible capacity loss increased from 9.50% to 10.60%, and the capacity retention decreased from 88.60% to 86.60%. This indicates that, at the same addition amount, different silicon-oxygen materials have different degrees of influence on the thermodynamic properties of the composite material. The method of this invention can quickly screen out silicon-oxygen materials with better compatibility with graphite substrates and less negative impact on overall thermodynamic properties. For example, under these conditions, silicon-oxygen 1 performs better than silicon-oxygen 4. The greater the irreversible capacity loss rate, the greater the impact of the negative electrode material under evaluation on the thermodynamic properties of the lithium-ion battery, that is, the worse the thermodynamic properties of the lithium-ion battery.

[0065] Compared to experimental group 6 (1% silicon-oxygen 1), when the silicon-oxygen content increased to 2% (comparison group 1) and 3% (comparison group 2), the K value decreased sharply (0.379→0.343→0.322); the performance deteriorated significantly simultaneously: irreversible capacity loss increased sharply (9.50%→11.8%→12.7%), and capacity retention rate dropped sharply (88.60%→85.30%→84.30%). This indicates that increasing the silicon content exacerbates volume expansion during cycling, severely damaging the stability of the electrode structure. The precipitous drop in the K value in this application accurately captures this microscopic-level deterioration of thermodynamic performance. The greater the irreversible capacity loss rate, the greater the impact of the negative electrode material being evaluated on the thermodynamic performance of the lithium-ion battery, i.e., the worse the thermodynamic performance of the lithium-ion battery.

[0066] Furthermore, full-cell testing results validated the accuracy of the K-value prediction. This highlights a key technical advantage of this application: in the early stages of material screening and formulation design, a simple half-cell test is sufficient to effectively predict potential cycle life risks of high-silicon content solutions based on the K-value. This method can efficiently identify and eliminate problematic material solutions in the early stages, thereby helping researchers focus on more promising candidate systems, significantly saving the time and financial costs required for subsequent full-cell validation, and accelerating the development process of high-performance battery systems.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the influence of lithium-ion battery anode materials on the thermodynamic properties of lithium-ion batteries, characterized in that, The evaluation methods include: The negative electrode material to be evaluated was prepared as a negative electrode sheet and assembled into a half cell. The half cell was subjected to charge and discharge tests, and the charging voltage and capacity during the charging process were recorded. Then, the logarithm of the charging voltage was taken and differentiated. Using the data after differential processing as the Y-axis and the SOC value during the charging process as the X-axis, a charging curve is plotted; the SOC value is the percentage of remaining power to rated capacity. Record the X-axis value corresponding to the first peak of the negative electrode between 0 and 0.2 SOC in the charging curve, and denote it as F1; Record the X-axis value corresponding to the first peak of the negative electrode between 0.2 and 0.6 in the charging curve, and denote it as F2; The thermodynamic regulating parameter K is calculated using the formula: K = F2 - F1; 0.35 <K<0.41。 2. The evaluation method according to claim 1, characterized in that, The negative electrode material to be evaluated is a graphite material or a graphite-silicon-oxygen composite material.

3. The evaluation method according to claim 2, characterized in that, The mass ratio of graphite to silicon oxide in the graphite-silicon-oxygen composite material is 99 to 1:10, preferably 70:

30.

4. The evaluation method according to claim 1, characterized in that, The negative electrode sheet contains the negative electrode material to be evaluated, a conductive agent, and a binder; Preferably, by mass percentage, the negative electrode sheet comprises: 95-96% of the negative electrode material to be evaluated, 2-3% of the conductive agent, and 2-4% of the binder.

5. The evaluation method according to claim 1, characterized in that, The compaction density of the negative electrode sheet is 1.50~1.60 g / cm³. 3 .

6. The evaluation method according to claim 1, characterized in that, Methods for charging and discharging half-cells include: The negative electrode was discharged to 5mV at a constant current of 0.1C, and then discharged to 5mV at a constant current of 0.01C; it was left to stand for 10 minutes; then it was charged to 1.5V at a constant current of 0.1C, and the voltage and capacity during the charging process were recorded.

7. The evaluation method according to claim 1, characterized in that, Taking the logarithm of the charging voltage and then differentiating it includes: Take the logarithm of the charging voltage to obtain the data log10(V), denoted as Y1; then differentiate the Y1 data to obtain the data dlog10(V) / d(SOC), denoted as Y2.

8. The evaluation method according to claim 1, characterized in that, The evaluation method also includes: The negative electrode sheets prepared from the negative electrode material to be evaluated were assembled into a full cell. Then, the full cell was subjected to formation and high-temperature aging processes, and then subjected to room temperature overcharge test and room temperature cycle test. The irreversible capacity loss rate is calculated based on the results of the room temperature cycling test. Then, the anode material to be evaluated is evaluated based on the highest temperature and irreversible capacity loss rate of the room temperature overcharge test.

9. The evaluation method according to claim 8, characterized in that, The voltage range for the room temperature overcharge test is 2.5~5V, the charging and discharging current is 1C, and the room temperature is 25±2℃.

10. The evaluation method according to claim 8, characterized in that, The voltage range for the ambient temperature cycling test is 2.5~3.65V, the charging and discharging current is 0.5C, and the charging and discharging is performed at 0.05C every 200 cycles. The ambient temperature is 25±2℃.

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