Evaluation method for thermal instability of ternary cathode materials for lithium-ion batteries

Abstract

The application provides a kind of evaluation method of lithium ion battery ternary positive electrode material thermal instability, in-situ X-ray diffraction technique is used to evaluate lithium ion battery ternary positive electrode material thermal instability, comprising the following steps: providing lithium ion battery of ternary positive electrode material, the lithium ion battery is charged to different SOC state;After charging, the lithium ion battery is disassembled, and the ternary positive electrode material on the positive electrode sheet is collected;The ternary positive electrode material is placed on the sample stage of in-situ X-ray diffractometer, the sample is heated at a heating rate of 0.5-1.5 ℃ / min in a vacuum environment, the scanning speed of in-situ X-ray diffractometer is set to 2.8-4.8 ° / min, the scanning angle 2 theta is at least 15-72 °, the ternary positive electrode material is subjected to full scanning treatment, and a scanning spectrum is obtained;The thermal stability range of the ternary positive electrode material is determined according to the scanning spectrum.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a method for evaluating thermal instability of a ternary positive electrode material for a lithium-ion battery. Background Art

[0002] With the intensifying energy crisis and environmental degradation, there is an urgent need for clean energy to replace traditional fossil fuels. Lithium-ion batteries are gaining increasing attention due to their high capacity, long cycle life, and environmental friendliness. New energy vehicles (NEVs) that use lithium-ion batteries to replace internal combustion engines have become increasingly popular. However, with their widespread adoption and the pursuit of high energy density, safety issues have emerged. A major safety issue with lithium-ion power batteries is thermal runaway, typically manifested as fires in electric vehicles. Analysis reveals that, in addition to the normal charge and discharge reactions, lithium-ion batteries also experience numerous potential exothermic side reactions, such as thermal decomposition of the charged cathode, decomposition of the SEI film leading to the reduction and decomposition of the electrolyte on the exposed highly active carbon anode surface, and thermal decomposition of the electrolyte. These exothermic side reactions can all lead to thermal runaway. In particular, the ternary cathode materials of charged lithium-ion batteries undergo phase transitions at high temperatures, generating significant amounts of heat and oxygen. These heat and oxygen exacerbate these exothermic side reactions, making these phase transitions highly detrimental to the safety of lithium-ion batteries.

[0003] X-ray diffraction technology works by producing a regularly distributed diffraction pattern on a film on the back of a crystal structure when X-rays strike it from a specific direction. Ex situ X-ray diffraction patterns can be used to analyze the composition and relative elemental content of the sample, but this information is insufficient for evaluating the thermal stability of lithium-ion batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for evaluating the thermal instability of a ternary positive electrode material for a lithium-ion battery, aiming to solve the problem that the existing technology cannot effectively evaluate the thermal stability of lithium-ion batteries.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery, which uses an in-situ X-ray diffraction technique to evaluate thermal instability of a ternary cathode material for a lithium-ion battery, comprising the following steps:

[0007] Providing a lithium-ion battery with a ternary cathode material, and charging the lithium-ion battery to different SOC states;

[0008] Disassemble the charged lithium-ion battery and collect the ternary positive electrode material on the positive electrode sheet;

[0009] Placing the ternary cathode material on a sample stage of an in-situ X-ray diffractometer, heating the sample at a heating rate of 0.5°C to 1.5°C / min under a vacuum environment, setting the in-situ X-ray diffractometer to a scanning speed of 2.8 to 4.8° / min and a scanning angle 2θ of at least 15-72°, performing a full scan on the ternary cathode material to obtain a scan spectrum;

[0010] The thermal stability range of the ternary cathode material at the corresponding SOC state is determined based on the scanning spectrum.

[0011] Preferably, in the step of scanning the ternary cathode material to obtain a scanning spectrum, the preset scanning temperature range is 25°C to 500°C, and the actual scanning temperature range spans at least 300°C.

[0012] Preferably, in the step of scanning the ternary cathode material to obtain a scanning spectrum, the actual scanning temperature range is 25°C to 500°C.

[0013] Preferably, in the step of charging the lithium-ion battery to different SOC states, the lithium-ion battery is charged at a charge rate of 0.5C and cut-off voltages of 3.90V, 3.95V, 4.00V, 4.05V, 4.10V, 4.15V, 4.20V, 4.25V and 4.30V, respectively, to obtain different SOC states of the lithium-ion battery.

[0014] Preferably, in the step of disassembling the charged lithium-ion battery and collecting the ternary positive electrode material on the positive electrode plate, the positive electrode plate is soaked and cleaned with dimethyl carbonate, dried, and then wetted with N-methylpyrrolidone before collecting the ternary positive electrode material on the positive electrode plate.

[0015] Preferably, in the step of disassembling the charged lithium-ion battery and collecting the ternary positive electrode material on the positive electrode sheet, a scraper is used to scrape the ternary positive electrode material along one direction on the positive electrode sheet.

[0016] Preferably, after the step of collecting the ternary positive electrode material on the positive electrode sheet, the method further includes grinding the ternary positive electrode material.

[0017] Preferably, the lithium-ion battery is a cylindrical battery, and the step of disassembling the charged lithium-ion battery includes: removing the heat shrink sleeve from the negative end of the lithium-ion battery in an environment with a relative humidity of less than 10% RH; cutting the battery cell along the groove, pulling up the cap, straightening the tab, parallel to the battery direction, and cutting off the positive tab along the surface of the upper insulating gasket with pliers; spirally dissecting the steel shell along the edge of the shell opening, avoiding the disassembled shell part from puncturing the electrode group short circuit during the dissection process, and when dissecting to the lower part, pulling the steel shell along the axial direction of the electrode group to remove the tab, cutting off the negative electrode tab, and removing the electrode group; using a blade to cut the termination tape along the termination line of the electrode group diaphragm, unfolding the core, and tearing off the positive electrode sheet.

[0018] Preferably, in the step of performing a full scan on the ternary positive electrode material to obtain a scanning spectrum, the scanning speed of the in-situ X-ray diffractometer is set to 3.8° / min, the scanning angle 2θ is set to 15-72°, the sample temperature is increased from 25°C to 500°C at a heating rate of 1.2°C / min, and the scanning spectrum is collected.

[0019] The method for evaluating thermal instability of ternary cathode materials for lithium-ion batteries provided by the present invention has the following advantages:

[0020] First, during the sample heating process, the sample is subjected to a programmed in-situ X-ray diffraction scan to obtain all diffraction patterns of the ternary cathode material in the lithium-ion battery within the test temperature range. Then, by analyzing (using JADE software) the diffraction patterns of the lithium-ion battery ternary cathode material at different temperatures and comparing the changes in material composition and crystal structure, information such as the phase transition temperature of the lithium-ion battery ternary cathode material can be obtained, thereby effectively evaluating the thermal instability of the lithium-ion battery in a high-temperature environment and ultimately determining the thermal stability range of the ternary cathode material at the corresponding SOC state.

[0021] Secondly, in the present invention, the tested ternary positive electrode material is heated at a heating rate of 0.5°C to 1.5°C / min, and at the same time, the tested ternary positive electrode active material is subjected to in-situ X-ray diffraction scanning at a scanning speed of 2.8 to 4.8° / min. Under this condition, due to the slow heating rate, it is beneficial for the ternary positive electrode material to fully undergo phase change reaction in a high temperature environment; at the same time, the faster the scanning speed, the smaller the temperature difference between the high diffraction angle and the low diffraction angle of the X-ray diffraction spectrum, and it is easy to obtain a more refined diffraction pattern, and ultimately obtain a more accurate evaluation result. In addition, since the present invention sets the scanning angle 2θ to 15-72°, it is possible to obtain the overall diffraction situation of the ternary positive electrode active material within the range, and then better determine the phase change situation based on the diffraction peak intensity and diffraction peak position of the ternary positive electrode active material under different temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1The in-situ X-ray diffraction pattern obtained by performing a full scan process on the ternary positive electrode material NCM ternary positive electrode material at 4.20V provided by an embodiment of the present invention;

[0023] Figure 2 This is a 4.20V thermal instability diagram obtained by the thermal instability evaluation method of the lithium-ion battery ternary positive electrode material provided in Example 1 of the present invention;

[0024] Figure 3 This is a diagram showing the crystal structure and phase transition temperature of the thermal instability evaluation method for the ternary cathode material for lithium-ion batteries provided in Example 1 of the present invention;

[0025] Figure 4 This is a 4.20V thermal instability diagram obtained by the thermal instability evaluation method of the lithium-ion battery ternary cathode material provided in Example 2 of the present invention;

[0026] Figure 5 This is a 4.20V thermal instability diagram obtained by the thermal instability evaluation method of the lithium-ion battery ternary positive electrode material provided in Example 3 of the present invention;

[0027] Figure 6 This is a 4.20V thermal instability diagram obtained by the thermal instability evaluation method for lithium-ion battery ternary positive electrode materials provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0030] An embodiment of the present invention provides a method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery, which uses in-situ X-ray diffraction technology to evaluate thermal instability of a ternary cathode material for a lithium-ion battery, comprising the following steps:

[0031] S01 provides a lithium-ion battery of a ternary cathode material, charging the lithium-ion battery to different SOC states;

[0032] S02. Disassemble the charged lithium-ion battery and collect the ternary positive electrode material on the positive electrode sheet;

[0033] S03. Place the ternary positive electrode material on the sample stage of an in-situ X-ray diffractometer, heat the sample at a heating rate of 0.5°C to 1.5°C / min in a vacuum environment, set the scanning speed of the in-situ X-ray diffractometer to 2.8 to 4.8° / min, and the scanning angle 2θ to at least 15-72°, perform a full scan on the ternary positive electrode material to obtain a scanning spectrum; S04. Determine the thermal stability range of the ternary positive electrode material under the corresponding SOC state based on the scanning spectrum.

[0034] The method for evaluating thermal instability of ternary cathode materials for lithium-ion batteries provided by the embodiments of the present invention has the following advantages:

[0035] First, during the sample heating process, the sample is subjected to a programmed in-situ X-ray diffraction scan to obtain all diffraction patterns of the ternary cathode material in the lithium-ion battery within the test temperature range. Then, by analyzing (using JADE software) the diffraction patterns of the lithium-ion battery ternary cathode material at different temperatures and comparing the changes in material composition and crystal structure, information such as the phase transition temperature of the lithium-ion battery ternary cathode material can be obtained, thereby effectively evaluating the thermal instability of the lithium-ion battery in a high-temperature environment and ultimately determining the thermal stability range of the ternary cathode material at the corresponding SOC state.

[0036] Secondly, in an embodiment of the present invention, the tested ternary cathode material is heated at a heating rate of 0.5°C to 1.5°C / min, and at the same time, the tested ternary cathode material is subjected to in-situ X-ray diffraction scanning at a scanning speed of 2.8 to 4.8° / min. Under this condition, due to the slow heating rate, it is beneficial for the ternary cathode material to fully undergo phase change reaction in a high temperature environment; at the same time, the faster the scanning speed, the smaller the temperature difference between the high diffraction angle and the low diffraction angle of the X-ray diffraction spectrum, and it is easy to obtain a more refined diffraction pattern, and ultimately obtain a more accurate evaluation result. In addition, since the embodiment of the present invention sets the scanning angle 2θ to 15-72°, it is possible to obtain the overall diffraction situation of the ternary cathode material within the range, and then better determine the phase change situation based on the diffraction peak intensity and diffraction peak position of the ternary cathode material under different temperature conditions.

[0037] Specifically, in the above step S01, the lithium-ion battery is charged to different SOC states, and the SOC (state of charge) state is determined according to the working state of the lithium-ion battery with a specific ternary positive electrode material. For example, a lithium-ion battery with ternary positive electrode material A usually operates under the conditions of a charging rate of A1C and a cut-off voltage of A2V. Then, in order to evaluate the thermal stability of the lithium-ion battery in this working state, the lithium-ion battery can be charged under the conditions of a charging rate of A1C and a cut-off voltage of A2V. Of course, in order to obtain a uniform thermal stability of the battery under multiple different SOC states, parallel evaluation and detection of multiple different SOC states can be set.

[0038] In some embodiments, in the step of charging the lithium-ion battery to different SOC states, the lithium-ion battery is charged at a charge rate of 0.5C and cutoff voltages of 3.90V, 3.95V, 4.00V, 4.05V, 4.10V, 4.15V, 4.20V, 4.25V, and 4.30V, respectively, to obtain different SOC states of the lithium-ion battery. Under these charging conditions, the higher the SOC of the lithium-ion battery, the greater the possibility of thermal instability, and the more violent the reaction when thermal instability occurs, the greater the value of the assessment.

[0039] In some specific embodiments, before and after charging, the lithium-ion battery is placed on a charge and discharge tester for static treatment, and the static time is preferably greater than or equal to 30 minutes, so that the lithium-ion battery is charged under stable conditions and the positive electrode material is in a stable SOC state, providing a state basis for the subsequent use of in-situ X-ray diffraction technology to evaluate the thermal stability of the ternary positive electrode material.

[0040] In the above step S02, the charged lithium-ion battery is disassembled to obtain the positive electrode of the lithium-ion battery. Specifically, the method of disassembling the lithium-ion battery can be different depending on the specific type of lithium-ion battery.

[0041] In some embodiments, when the lithium-ion battery is a cylindrical lithium-ion battery, the step of disassembling the charged lithium-ion battery includes: removing the heat shrink sleeve from the negative end of the lithium-ion battery in an environment with a relative humidity of less than 10% RH; cutting the battery cell along the groove, pulling up the cap, straightening the tab, parallel to the battery direction, and cutting off the positive electrode tab along the surface of the upper insulating gasket with pliers; spirally dissecting the steel shell along the edge of the shell opening, preventing the disassembled shell part from puncturing the electrode group short circuit during the dissection process, and when dissecting to the lower part, pulling the steel shell along the axial direction of the electrode group to remove the tab, cutting off the negative electrode tab, and removing the electrode group; using a blade to cut the termination tape along the termination line of the electrode group separator, unwinding the core, and tearing off the positive electrode sheet. Specifically, the environment with a relative humidity of less than 10% RH is preferably a professional dissection room with a dehumidifier, which can prevent the influence of water vapor on the ternary positive electrode material of the lithium-ion battery. Cutting the battery cell along the grooves can be done with pipe-nosed pliers, while spirally dissecting the steel shell along the edges can be done with diagonal pliers. This method prevents damage to the positive electrode sheet during lithium-ion battery disassembly, ensuring its integrity. This, in turn, ensures the integrity of the ternary cathode material on the positive electrode sheet, thereby ensuring the accuracy of the phase transition temperature of the ternary cathode material determined using in-situ X-ray diffraction.

[0042] The collected positive electrode sheets must be sealed in a sealed environment and avoid contact with water vapor and oxygen.

[0043] Preferably, in the step of disassembling the charged lithium-ion battery and collecting the ternary positive electrode material on the positive electrode sheet, the positive electrode sheet is soaked and cleaned with dimethyl carbonate, dried, and then wetted with N-methylpyrrolidone before collecting the ternary positive electrode material on the positive electrode sheet. Soaking the positive electrode sheet in dimethyl carbonate can remove lithium-ion battery side reaction residues and electrolyte components; the soaking time is preferably 30 minutes or longer. After soaking, the positive electrode sheet is naturally dried. The positive electrode sheet is further wetted with N-methylpyrrolidone and then scraped to facilitate the detachment of the ternary positive electrode material from the current collector surface, thereby collecting the ternary positive electrode material on the positive electrode sheet.

[0044] Furthermore, during the step of disassembling the charged lithium-ion battery and collecting the ternary positive electrode material from the positive electrode sheet, a scraper is used to scrape and collect the ternary positive electrode material along a single direction on the positive electrode sheet. This method (single direction) can prevent the morphology of the ternary positive electrode material from being damaged, thereby ensuring the accuracy of the in-situ X-ray diffraction results.

[0045] Furthermore, after collecting the ternary positive electrode material from the positive electrode sheet, the step of grinding the ternary positive electrode material to uniformly disperse the ternary positive electrode material is further performed. The grinding is preferably performed in a mortar to uniformly disperse the ternary positive electrode material without damaging the material morphology.

[0046] In the above step S03, the ternary cathode material is placed on the sample stage of the in-situ X-ray diffractometer, and the environmental chamber where the sample stage is located is evacuated to place the test sample in a vacuum environment to prevent oxidation reaction of the sample in a high temperature environment.

[0047] In an embodiment of the present invention, the sample is heated at a heating rate of 0.5°C to 1.5°C / min, and the in-situ X-ray diffraction technique is used to scan the diffraction pattern of the sample within the heating temperature range. By comparing the diffraction peak intensity and position changes in the sample diffraction pattern, the changes in the material composition and crystal structure are obtained, and information such as the phase transition temperature of the lithium-ion battery ternary positive electrode material is obtained. The thermal instability of the lithium-ion battery in a high temperature environment is effectively evaluated through the collected information. Among them, the heating rate is controlled at 0.5°C to 1.5°C / min. The slower the heating rate, the more sufficient the reaction time of the ternary positive electrode material in the high temperature reaction area, the more sufficient the reaction, and the ternary positive electrode material can fully undergo a phase change reaction in a high temperature environment. When the heating rate is too fast, the reaction in this high temperature reaction area may be skipped due to lack of time to react, and the phase change reaction cannot occur. More preferably, the sample is heated at a heating rate of 1.2°C / min, and the temperature is slowly increased to allow the ternary positive electrode material to fully undergo a phase change reaction in a high-temperature environment, while obtaining a diffraction pattern with a smaller temperature difference, thereby obtaining more accurate information on changes in material composition and crystal structure, effectively evaluating the thermal instability of lithium-ion batteries in a high-temperature environment, and ultimately determining the thermal stability range of the ternary positive electrode material under the corresponding SOC state.

[0048] In an embodiment of the present invention, in the step of scanning the ternary positive electrode material to obtain a scanning spectrum, the preset scanning temperature range is 25°C to 500°C, that is, the scanning temperature range can be within the range of 25°C to 500°C, and the temperature starting point of the specific scanning range can be flexibly set, but the actual scanning temperature range spans at least 300°C, so that scanning spectra of more temperature points can be obtained, thereby obtaining a more refined scanning spectrum, thereby ensuring the accuracy and reliability of the spectrum analysis results.

[0049] In a specific preferred embodiment, in the step of scanning the ternary cathode material to obtain a scanning pattern, the actual scanning temperature range is 25°C to 500°C. That is, the tested ternary cathode material is heated from 25°C to 500°C at a heating rate of 0.5°C to 1.5°C / min, and the diffraction patterns within this temperature range are collected for comparative analysis. By comparing the changes in material composition and crystal structure, information such as the phase transition temperature of the lithium-ion battery ternary cathode material is obtained, thereby effectively assessing the thermal instability of the lithium-ion battery in a high-temperature environment.

[0050] In an embodiment of the present invention, the scanning speed of the in-situ X-ray diffractometer is 2.8 to 4.8° / min, and the scanning angle 2θ is at least 15-72°. Under this scanning condition, the scanning speed is fast, and the faster the scanning speed, the smaller the temperature difference between the high diffraction angle and the low diffraction angle of the X-ray diffraction spectrum, and the more accurate the evaluation; at the same time, since the scanning angle 2θ covers the range of 15-72°, the overall diffraction situation of the ternary positive electrode material within this range can be obtained, and then the overall diffraction situation of the ternary positive electrode material within the range can be obtained. Avoid the diffraction peak material from being offset or incomplete when scanning with a single scanning speed and a single scanning angle, resulting in the inability to obtain accurate derivative spectrum information, and thus the inability to obtain changes in material composition and crystal structure. Of course, it should be understood that the X-ray spectrum diffraction angle range can be 0-90°, but since the ternary positive electrode material has no diffraction characteristic peaks at lower or higher diffraction angles, the preferred scanning angle 2θ in the embodiment of the present invention is 15-72°.

[0051] In one embodiment, taking 4.20VNCM ternary cathode material as an example, this step performs a full scan on the ternary cathode material, and the obtained three-dimensional in-situ X-ray diffraction pattern is Figure 1 shown.

[0052] In a specific preferred embodiment, the ternary positive electrode material is subjected to a full scanning process, and in the step of obtaining a scanning spectrum, the scanning speed of the in-situ X-ray diffractometer is set to 3.8° / min, the scanning angle 2θ is set to 15-72°, the sample temperature is increased from 25°C to 500°C at a heating rate of 1.2°C / min, and the scanning spectrum is collected, which is conducive to obtaining more accurate evaluation results.

[0053] In the above step S04, based on the diffraction pattern obtained by scanning within the scanning temperature range in step S03, the changes in material composition and crystal structure are analyzed, and then information such as the phase transition temperature of the lithium-ion battery ternary positive electrode material is determined, thereby effectively evaluating the thermal instability of the lithium-ion battery in a high-temperature environment, and ultimately determining the thermal stability range, i.e., safety, of the ternary positive electrode material under the corresponding SOC state.

[0054] Compared with non-in-situ X-ray diffraction technology, in-situ X-ray diffraction technology can effectively analyze the changes in the material composition and crystal structure of the ternary cathode material of lithium-ion batteries with temperature changes. By analyzing the changes in the material composition and crystal structure of the ternary cathode material at different temperatures, the phase transition temperature, oxygen release temperature and other information of the ternary cathode material of lithium-ion batteries can be obtained, thereby effectively evaluating the thermal instability of lithium-ion batteries in high temperature environments. For example, the ternary cathode material Li 0.33 Ni 0.8 Co 0.15 Al 0.05 O2 cutoff voltage is 4.12VvsLi / Li + , the phase change reaction equation is and Ternary cathode material Li 0.33 Ni 0.8 Co 0.15 Al 0.05 When O2 undergoes a phase change, a large amount of heat and oxygen will be generated. A large amount of heat and oxygen will intensify the exothermic side reaction of the lithium-ion battery. The exothermic side reaction of the lithium-ion battery will lead to thermal runaway, which is extremely detrimental to the safety performance of the lithium-ion battery.

[0055] Using this method, we evaluated four ternary cathode materials with varying nickel contents and found that the phase transition temperatures from layered to spinel, and from spinel to rock salt, varied across the four materials. By analyzing the phase transition temperatures, we concluded that the thermal safety of the four ternary cathode materials follows the order: N1L > S85E > S800 > EO211. This is illustrated below with reference to specific examples.

[0056] Example 1

[0057] A method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery, using in-situ X-ray diffraction technology to evaluate thermal instability of a ternary cathode material for a lithium-ion battery, comprises the following steps:

[0058] Providing a lithium-ion battery S800, charging the lithium-ion battery at a charge rate of 0.5C and a cutoff voltage of 4.20V, and allowing the battery to rest on a charge-discharge tester for 30 minutes before and after charging;

[0059] Disassemble the charged lithium-ion battery and collect the ternary positive electrode material on the positive electrode sheet;

[0060] The ternary cathode material is placed on the sample stage of an in-situ X-ray diffractometer. Under a vacuum environment, the sample is heated from 25°C to 500°C at a heating rate of 0.5°C to 1.5°C / min. The scanning speed of the in-situ X-ray diffractometer is set to 3.8° / min and the scanning angle 2θ is set to 15-72°. The ternary cathode material is fully scanned to obtain a scanning spectrum;

[0061] The thermal stability range of the ternary cathode material at the corresponding SOC state is determined based on the scanning spectrum.

[0062] The evaluation method for thermal instability of the lithium-ion battery ternary positive electrode material provided in Example 1, the 4.20V thermal instability diagram obtained is as follows Figure 2 As shown in the figure, at 30℃, the (108) and (110) peaks split significantly, indicating that the crystal is a layered structure; at 84℃, the (108) and (110) peaks merge, and the (003) peak intensity decreases significantly, indicating that the layered structure has been destroyed and begins to transform into a spinel structure; at 156℃, the (021)(202)(111) diffraction peaks of rock salt structure NiO appear, indicating that the rock salt structure begins to form. The crystal structure and phase transition temperature of the layered phase, spinel phase and rock salt phase of the ternary positive electrode material are shown in Figure 2. Figure 3 As shown, Figure 2 The material compositions corresponding to the corresponding X-ray diffraction crystal planes are shown in Table 1 below.

[0063] Table 1

[0064]

[0065]

[0066] Example 2

[0067] A method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery, using in-situ X-ray diffraction technology to evaluate thermal instability of a ternary cathode material for a lithium-ion battery, comprises the following steps:

[0068] A lithium-ion battery N1L is provided, and the lithium-ion battery is charged at a charge rate of 0.5C and a cutoff voltage of 4.20V. The battery is left standing on a charge and discharge tester for 30 minutes before and after charging.

[0069] Disassemble the charged lithium-ion battery and collect the ternary positive electrode material on the positive electrode sheet;

[0070] The ternary positive electrode material is placed on a sample stage of an in-situ X-ray diffractometer, the sample is heated from 25℃ to 500℃ at a heating rate of 0.5℃-1.5℃ / min in a vacuum environment, the scanning speed of the in-situ X-ray diffractometer is set to 3.8° / min, the scanning angle 2θ is set to 15-72°, the ternary positive electrode material is subjected to full scanning treatment, and a scanning spectrum is obtained.

[0071] The thermal stability range of the ternary positive electrode material in the corresponding SOC state is determined according to the scanning spectrum.

[0072] The evaluation method of the thermal instability of the lithium ion battery ternary positive electrode material provided in Example 2 obtains a 4.20V thermal instability condition diagram as shown in Figure 4 As shown in the diagram, the (108) and (110) peaks are obviously split at 30℃ (108) and (110), indicating that the crystal is a layered structure; the (108) and (110) peaks are fused into one peak at 156℃, indicating that the layered structure has been destroyed, and this is a spinel structure; the (021) (202) (220) diffraction peaks of rock salt structure NiO appear at 372℃, indicating that the spinel structure changes to a rock salt structure at this time.

[0073] Example 3

[0074] An evaluation method of the thermal instability of a lithium ion battery ternary positive electrode material, which evaluates the thermal instability of the lithium ion battery ternary positive electrode material by using in-situ X-ray diffraction technology, comprises the following steps:

[0075] A lithium ion battery EO211 is provided, and the lithium ion battery is subjected to charging treatment under the condition that the charging rate is 0.5C and the cutoff voltage is 4.20V; the battery is placed on a charge-discharge tester for 30min before and after charging;

[0076] The charged lithium ion battery is disassembled, and the ternary positive electrode material on the positive electrode sheet is collected;

[0077] The ternary positive electrode material is placed on a sample stage of an in-situ X-ray diffractometer, the sample is heated from 25℃ to 500℃ at a heating rate of 0.5℃-1.5℃ / min in a vacuum environment, the scanning speed of the in-situ X-ray diffractometer is set to 3.8° / min, the scanning angle 2θ is set to 15-72°, the ternary positive electrode material is subjected to full scanning treatment, and a scanning spectrum is obtained;

[0078] The thermal stability range of the ternary positive electrode material in the corresponding SOC state is determined according to the scanning spectrum.

[0079] The evaluation method of the thermal instability of the lithium ion battery ternary positive electrode material provided in Example 3 obtains a 4.20V thermal instability condition diagram as shown in Figure 5As shown in the figure, it can be seen that at 30℃, the (108) and (110) peaks split significantly, and the crystal is a layered structure; at 120℃, the layered structure has been destroyed and begins to transform into a spinel structure; at 138℃, the (202)(104) diffraction peaks of rock salt structure NiO appear, indicating that the spinel structure is in phase transition to the rock salt structure.

[0080] Example 4

[0081] A method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery, using in-situ X-ray diffraction technology to evaluate thermal instability of a ternary cathode material for a lithium-ion battery, comprises the following steps:

[0082] A lithium-ion battery S85E is provided, and the lithium-ion battery is charged at a charge rate of 0.5C and a cutoff voltage of 4.20V. The battery is left standing on a charge and discharge tester for 30 minutes before and after charging.

[0083] Disassemble the charged lithium-ion battery and collect the ternary positive electrode material on the positive electrode sheet;

[0084] The ternary cathode material is placed on the sample stage of an in-situ X-ray diffractometer. Under a vacuum environment, the sample is heated from 25°C to 500°C at a heating rate of 0.5°C to 1.5°C / min. The scanning speed of the in-situ X-ray diffractometer is set to 3.8° / min and the scanning angle 2θ is set to 15-72°. The ternary cathode material is fully scanned to obtain a scanning spectrum;

[0085] The thermal stability range of the ternary cathode material at the corresponding SOC state is determined based on the scanning spectrum.

[0086] The evaluation method for thermal instability of lithium-ion battery ternary cathode materials provided in Example 4 is as follows: Figure 6 As shown in the figure, it can be seen that at 30℃, the (108) and (110) peaks split significantly, indicating that the crystal has a layered structure; at 138℃, the layered structure has begun to destroy and transform into a spinel structure; at 210℃, the (111) diffraction peak of the rock salt structure Ni6MnO8 appears, indicating that the spinel structure is in phase transition to the rock salt structure at this time; the main peak of the diffraction spectrum from 318℃ to 500℃ always has lithium compounds, indicating that it is not completely deactivated.

[0087] In summary, the types and thermal stability evaluation results of the four ternary cathode materials are shown in Table 2 below.

[0088] Table 2

[0089]

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery, characterized in that: The in-situ X-ray diffraction technique is used to evaluate the thermal instability of lithium-ion battery ternary cathode materials, including the following steps: Providing a lithium-ion battery with a ternary cathode material, and charging the lithium-ion battery to different SOC states, wherein the SOC state is determined according to the operating state of the lithium-ion battery with a specific ternary cathode material; Disassemble the charged lithium-ion battery and collect the ternary positive electrode material on the positive electrode sheet; The ternary cathode material is placed on the sample stage of an in-situ X-ray diffractometer, and the sample is heated at a heating rate of 0.5°C to 1.5°C / min under a vacuum environment. The scanning speed of the in-situ X-ray diffractometer is set to 2.8 to 4.8° / min and the scanning angle 2θ is set to 15-72°. The ternary cathode material is fully scanned to obtain a scanning spectrum; The thermal stability range of the ternary cathode material at the corresponding SOC state is determined based on the scanning spectrum.

2. The method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery according to claim 1, wherein: In the step of scanning the ternary cathode material to obtain a scanning spectrum, the preset scanning temperature range is 25° C. to 500° C., and the actual scanning temperature range spans at least 300° C.

3. The method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery according to claim 1 or 2, wherein: In the step of charging the lithium-ion battery to different SOC states, the lithium-ion battery is charged at a charge rate of 0.5C and cut-off voltages of 3.90V, 3.95V, 4.00V, 4.05V, 4.10V, 4.15V, 4.20V, 4.25V and 4.30V, respectively, to obtain different SOC states of the lithium-ion battery.

4. The method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery according to claim 1 or 2, wherein: In the step of disassembling the charged lithium-ion battery and collecting the ternary positive electrode material on the positive electrode plate, the positive electrode plate is soaked and cleaned with dimethyl carbonate, dried, and then wetted with N-methylpyrrolidone, and then the ternary positive electrode material on the positive electrode plate is collected.

5. The method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery according to claim 4, wherein: In the step of disassembling the charged lithium-ion battery and collecting the ternary positive electrode material on the positive electrode sheet, a scraper is used to scrape the ternary positive electrode material along one direction on the positive electrode sheet.

6. The method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery according to claim 5, wherein: After the step of collecting the ternary positive electrode material on the positive electrode sheet, the method further includes grinding the ternary positive electrode material.

7. The method for evaluating thermal instability of a ternary cathode material for a lithium-ion battery according to claim 1 or 2, wherein: The lithium-ion battery is a cylindrical battery, and the steps of disassembling the charged lithium-ion battery include: removing the heat shrink sleeve from the negative end of the lithium-ion battery in an environment with a relative humidity of less than 10% RH; cutting the battery cell along the groove, pulling up the cap, straightening the tab, parallel to the battery direction, and cutting off the positive tab along the surface of the upper insulating gasket with pliers; spirally dissecting the steel shell along the edge of the shell opening, preventing the disassembled shell part from puncturing the electrode group and short-circuiting during the dissection process; when dissecting to the lower part, pulling the steel shell along the axis of the electrode group to remove the tab, cutting off the negative tab, and removing the electrode group; cutting the termination tape along the termination line of the electrode group diaphragm with a blade, unfolding the winding core, and tearing off the positive electrode sheet.

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