Method for rapidly screening high-temperature stability of ternary layered positive electrode material of lithium battery
By testing the AC impedance change rate and SEI film thickness of the battery, combined with the charge-discharge cycle capacity decay, the high-temperature stability of ternary layered cathode materials for lithium batteries can be rapidly evaluated. This solves the problem of slow screening speed in existing technologies, improves R&D efficiency, and reduces costs.
Patent Information
- Application Number
- CN202511748535.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-03-06
AI Technical Summary
Existing technologies make it difficult to quickly screen for high-temperature stable ternary layered cathode materials for lithium batteries, resulting in high R&D costs and low efficiency.
By testing the AC impedance change rate of the battery at high temperature and observing the SEI film thickness using transmission electron microscopy, combined with the capacity decay during charge-discharge cycles, the high-temperature stability of ternary layered cathode materials can be rapidly evaluated.
This technology enables the rapid screening of high-temperature stable ternary layered cathode materials in a short period of time, reducing time and cost and improving R&D efficiency.
Smart Images
Figure CN121612936A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of materials testing technology, specifically relating to a method for rapidly screening the high-temperature stability of ternary layered cathode materials for lithium batteries. Background Technology
[0002] Lithium-ion batteries, also known as lithium-ion rechargeable batteries or lithium-ion storage batteries, are a new type of chemical power source that has been developed over the past 30 years. Since Sony Corporation of Japan commercialized lithium-ion batteries in 1991, they have been a hot topic of research and application worldwide. Due to their advantages such as high energy density, wide operating temperature range, low self-discharge rate, long storage time, and no memory effect, lithium-ion batteries have been widely used in 3C products, electric vehicles, and electrochemical energy storage.
[0003] Ternary layered cathode material (LiNi) x Co y Mn z O2 (where x+y+z=1) is currently a hot research topic due to its advantages such as high specific capacity and low cost (compared to cobalt acid), leading to its widespread application. However, there are many types of ternary layered cathode materials, and even slight differences in the proportion of transition metal atoms can have a significant impact on their high-temperature stability. Furthermore, the lifespan differences of many ternary layered cathode materials after short-term cycling after high-temperature exposure are not significant, often only becoming apparent after hundreds of weeks. Therefore, quickly identifying the most heat-resistant ternary material from a variety of candidate ternary layered cathode materials is one of the challenges in screening high-quality cathode materials.
[0004] As is well known, the speed of research and development directly determines the time cost invested. While increasing the number of R&D personnel and equipment can accelerate the process, the associated costs are high, and their effect on speeding up the screening of ternary layered cathode materials is limited. In the development of ternary layered cathode materials, sample testing consumes a significant amount of time, especially cycle testing, which often takes several weeks to determine the high-temperature stability of the material. If the high-temperature stability of the material could be inferred from changes in certain structural parameters at high temperatures within a short period, R&D efficiency would be greatly improved. Therefore, developing a method for rapidly screening the high-temperature stability of ternary layered cathode materials for lithium batteries is imperative. Summary of the Invention
[0005] To address the shortcomings of existing rapid screening technologies for electrode materials, the present invention aims to provide a method for rapidly screening the high-temperature stability of ternary layered cathode materials for lithium batteries. This method is designed to quickly screen the stability of materials under high-temperature environments, thereby overcoming the deficiencies of existing rapid screening technologies for battery materials, saving production costs, and improving production efficiency.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for rapidly screening the high-temperature stability of ternary layered cathode materials for lithium batteries includes the following steps: A ternary layered cathode material is used to form the cathode, and a matching anode is used to assemble the battery; preferably, the ternary layered cathode material is a nickel-cobalt-manganese ternary layered cathode material Li(Ni) x Co y Mn z O2, where: 0 ≤ x ≤1, 0≤ y ≤1, 0≤ z ≤1, x + y + z =1; The negative electrode is at least one of lithium metal, natural graphite, artificial graphite, graphene, mesophase carbon microspheres, amorphous carbon, soft carbon, hard carbon, silicon suboxide, silicon, and lithium titanate.
[0007] The AC impedance of the battery was analyzed after being placed at high temperature for different times, and the impedance change rate was calculated. The thickness of the SEI film on the surface of the ternary layered cathode material was tested by transmission electron microscopy. Preferably, the high temperature was 60~120 ℃ and the placement time at high temperature was 1-3 days.
[0008] The high-temperature stability of ternary layered cathode materials can be inferred from the impedance change rate combined with the SEI film thickness change; ternary layered cathode materials with small impedance change rate and small SEI film thickness change have good high-temperature stability.
[0009] Furthermore, the test also includes capacity testing of batteries after high-temperature storage through charge-discharge cycles. By observing the capacity decay, the high-temperature stability can be effectively determined. Preferably, the current density for the charge-discharge cycle test is 1 mA / g to 1000 mA / g, and the voltage range is 2 V to 4.5 V.
[0010] As a preferred technical solution, the battery is a button cell battery; a button cell battery includes, from bottom to top, a negative electrode shell, a negative electrode, a separator, a positive electrode, a gasket, a spring, and a positive electrode shell. Because button cells are small in size, low in cost, and require little space during testing, they are convenient for simulating real-world usage scenarios; therefore, they are chosen for assembly into button cells and performance testing.
[0011] The basic principle of this invention is as follows: When the battery is at rest, due to side reactions at the electrode / electrolyte interface and the decomposition of impurity phases on the material surface, this surface chemical evolution is more pronounced at high temperatures, leading to the gradual depletion of the electrolyte and the formation of a thick solid electrolyte film (SEI) on the material surface, composed of various side reaction products (mainly including LF, Li2CO3, Li2O, ROCOLi, MnF, etc.). Because the SEI film has poor Li... +Increased electron conductivity and interfacial impedance significantly hinder the kinetic processes during charge and discharge, ultimately leading to increased polarization and decreased capacity during cycling, resulting in battery instability at high temperatures. Different ternary layered cathode materials exhibit varying electrode / electrolyte interfacial side reactions due to differences in the proportions of nickel, cobalt, and manganese. These differences become increasingly apparent over time, resulting in varying SEI film thicknesses, specifically manifested as an increase in battery impedance over time. Therefore, by testing the AC impedance of ternary layered cathode materials placed at high temperatures for different periods and fitting multiple sets of data, the average daily impedance increase rate was determined. This rate was then correlated with the capacity decay of the ternary layered cathode material after high-temperature placement and charge-discharge cycles, effectively assessing its high-temperature stability. Furthermore, by observing the SEI film on the surface of the ternary layered cathode material using a transmission electron microscope, the thickness of the SEI film formed after the material has been placed at high temperature can be directly observed. The thicker the SEI film, the greater the interfacial impedance. Therefore, the thickness of the surface SEI film can correspond to the impedance increase rate, which can also be used to determine the high-temperature stability of the ternary layered cathode material.
[0012] The technical solution of the present invention has the following beneficial effects: (1) This invention is universal and can be applied to all known ternary layered cathode materials on the market; (2) This invention can quickly assess the high-temperature stability of ternary layered cathode materials. By rapidly screening materials based on impedance increase rate and SEI film thickness within a short time, it can solve the problem of incomparability caused by differences in the initial state of materials (such as crystallinity, morphology, etc.) and reduce the time cost of long-term testing, effectively accelerating the research and development speed. The method of this invention is stable and reliable, and can evaluate the high-temperature stability of ternary layered cathode materials in a short time, screening out high-quality materials. The method of this invention is simple, economical, fast, efficient, and easy to promote and use. Attached Figure Description
[0013] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This invention provides a comparison of the cycle life of five ternary layered cathode materials selected for high-temperature storage for two days at room temperature in an embodiment of the invention. Figure 3 Nyquist plots of five ternary layered cathode materials selected for embodiments of the present invention after being placed at a high temperature of 70 °C for 0 days, 1 day, and 2 days; Figure 4 Equivalent circuit diagram used for fitting AC impedance; Figure 5 The graph shows the linear relationship between the AC impedance of five ternary layered cathode materials selected in this embodiment of the invention and the number of days they are placed at high temperature, where the slope represents the impedance increase rate. Figure 6 This is a comparison chart of the impedance increase rate and the number of cycles when the discharge cycle capacity drops to 80% of the initial value for the five ternary layered cathode materials selected in the embodiments of the present invention. Figure 7 The surface SEI film images of five ternary layered cathode materials selected for embodiments of the present invention were observed by transmission electron microscopy after being placed at a high temperature of 70 °C for 2 days. Detailed Implementation
[0014] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.
[0015] In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail; the raw materials used in this invention are all commercially available products.
[0016] This embodiment provides a method for rapidly screening cyclically stable ternary layered cathode materials. Figure 1 This is a flowchart of the method of the present invention. The screening method is performed according to this flowchart and includes the following steps: Selecting ternary layered cathode material LiNi 0.55 Co 0.15 Mn 0.3 O2 (5515), LiNi 0.6 Co 0.1 Mn 0.3 O2 (613), LiNi 0.6 Co 0.2 Mn 0.2 O2 (622), LiNi 0.72 Co 0.05 Mn 0.23 O2 (7205), LiNi 0.74 Co 0.01 Mn 0.25O2 (7401) was used to fabricate positive electrode sheets, which were then assembled into button cells of the same type in a bottom-to-top stacking order and injected with electrolyte: negative electrode shell, lithium metal negative electrode, glass fiber filter paper separator, positive electrode sheet, gasket, spring sheet, and positive electrode shell. The button cells were then placed in a 70 °C high-temperature oven. The Nyquist plots of the button cells after 0, 1, and 2 days of high-temperature exposure were tested using an electrochemical workstation. The AC impedance was obtained by fitting the Nyquist plots using an equivalent circuit. A graph was plotted with the number of days the same material was exposed to high temperature as the horizontal axis and the corresponding AC impedance as the vertical axis. Linear fitting was performed on the three coordinate points, and the slope represents the impedance increase rate. This serves as a basis for quickly screening ternary layered positive electrode materials with high-temperature stability. A larger impedance increase rate indicates greater instability at high temperatures and a shorter cycle life. In this example, the order of the impedance increase rate of the five materials is 622>5515>7401>613>7205, which corresponds to the order of the number of cycles until the capacity decays to 80% of the initial value.
[0017] Figure 2 The cycling performance of five ternary layered cathode materials selected for this embodiment of the invention is shown. The test conditions were as follows: after placing the button cell at high temperature for two days, it was charged to 4.4 V and then discharged to 2.8 V weekly at 25 °C, cycling at a current density of 200 mA / g until the capacity decayed to 80% of the initial value. As shown in the figure, the cycle times for the five selected ternary layered cathode materials were 622 > 5515 > 7401 > 613 > 7205.
[0018] Figure 3 Nyquist plots of five ternary layered cathode materials selected for embodiments of the present invention, after being placed at a high temperature of 70 °C for 0 days, 1 day, and 2 days. The semicircle represents the charge transfer impedance R. ct The smaller the diameter of the semicircle, the smaller R. ct The smaller the value, the better. It can be seen that the Nyquist plot before high-temperature storage shows a relatively small semicircle. As the number of days of high-temperature storage increases, the diameter of the semicircle also increases.
[0019] Figure 4The equivalent circuit diagram used for fitting the AC impedance was fitted using Nova, as shown in Table 1. The AC impedances of 5515 after 0, 1, and 2 days of high-temperature storage were 52 Ω, 160 Ω, and 303 Ω, respectively; those of 613 after 0, 1, and 2 days were 92 Ω, 159 Ω, and 229 Ω, respectively; those of 622 after 0, 1, and 2 days were 109 Ω, 346 Ω, and 1034 Ω, respectively; those of 7205 after 0, 1, and 2 days were 98 Ω, 133 Ω, and 219 Ω, respectively; and those of 7401 after 0, 1, and 2 days were 103 Ω, 188 Ω, and 268 Ω, respectively. It can be seen that as the number of days of high-temperature storage increases, side reactions occur between the surface of different ternary materials and the electrolyte, leading to an increase in the SEI film on the material surface. Because the SEI film has poor lithium-ion and electronic conductivity, it greatly hinders the kinetic process during charging and discharging. As a result, the impedance of the material gradually increases, leading to increased polarization and decreased capacity during cycling.
[0020] Table 1. AC impedance of different ternary layered cathode materials
[0021] Figure 5 The figure shows the linear relationship between the AC impedance of five ternary layered cathode materials selected in this embodiment of the invention and the number of days they are placed at high temperature. The slope represents the impedance increase rate, indicating the average daily impedance increase. As shown in the figure, the impedance increase rates of the five selected ternary layered cathode materials are 622>5515>7401>613>7205.
[0022] Figure 6 This is a comparison of the impedance increase rate and the number of cycles when the discharge cycle capacity drops to 80% of the initial value for five ternary layered cathode materials selected in this embodiment of the invention. In ternary layered cathode materials, the side reactions at the electrode / electrolyte interface and the decomposition of impurity phases on the material surface are more pronounced at high temperatures, leading to the gradual depletion of the electrolyte and the formation of a thick SEI film composed of various side reaction products on the material surface. Because the SEI film has poor Li... + The increase in impedance due to electronic conductivity significantly hinders the kinetic processes during charging and discharging, ultimately leading to increased polarization and decreased capacity during cycling. Therefore, the average increase in impedance per cycle can be approximated as the average capacity decay per cycle. As shown in the figure, the distribution of the impedance increase rate of the ternary layered cathode material is consistent with the number of cycles of capacity decay, indicating that this method can be used for rapid screening of high-temperature stable ternary layered cathode materials.
[0023] Figure 7The images show the surface SEI film of five ternary layered cathode materials selected for this invention, observed using a transmission electron microscope (TEM) after being placed at 70 °C for two days. Due to the regular structure and large particle size (2-4 μm) of the cathode materials, the electron beam of the TEM has difficulty penetrating the cathode particles, resulting in a distinctly dark black color and a well-organized lattice. In contrast, the SEI film, composed of a mixture of various substances and relatively thin, is easily penetrated by the electron beam, exhibiting a gray, amorphous state. The images clearly show different SEI thicknesses on the surfaces of the different materials. Specifically, the SEI thickness of 5515 is 20 nm; that of 613 is 13 nm; that of 622 is 27 nm; that of 7205 is 12 nm; and that of 7401 is 25 nm. Therefore, the impedance growth rate of the five selected ternary layered cathode materials is 622 > 5515 > 7401 > 613 > 7205.
[0024] The above experiments show that the method provided by this invention can quickly evaluate the high-temperature stability of ternary layered cathode materials. By rapidly screening materials based on the impedance increase rate and SEI film thickness in a short time, it can solve the problem of incomparability caused by differences in the initial state of materials (such as crystallinity, morphology, etc.), and reduce the time cost of conducting long-term testing, effectively accelerating the research and development speed.
[0025] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.
Claims
1. A method for rapidly screening high-temperature stability of ternary layered cathode materials of lithium batteries, characterized in that, The method comprises the following steps: The ternary layered positive material is made into a positive electrode, and matched with a negative electrode to assemble a battery; The AC impedance of the battery placed at high temperature for different time is analyzed, and the impedance change rate is calculated; and the SEI film thickness on the surface of the ternary layered positive material is observed; The high temperature stability of the ternary layered positive material is inferred according to the impedance change rate combined with the SEI film thickness change; the ternary layered positive material with small impedance change rate and small SEI film thickness change has good high temperature stability. 2.The method for rapidly screening high-temperature stability of ternary layered cathode material of lithium battery of claim 1, characterized in that, The ternary layered cathode material is a nickel-cobalt-manganese ternary layered cathode material Li(Ni x Co y Mn z )O2, wherein: 0≤ x ≤1, 0≤ y ≤1, 0≤ z ≤1, x + y + z =1. 3.The method for rapidly screening high-temperature stability of ternary layered cathode material of lithium battery of claim 1, characterized in that, The negative electrode is at least one of lithium metal, natural graphite, artificial graphite, graphene, mesocarbon microbeads, amorphous carbon, soft carbon, hard carbon, silicon monoxide, silicon, and lithium titanate. 4.The method for rapidly screening high-temperature stability of ternary layered cathode material of lithium battery of claim 1, characterized in that, The battery is a button cell. 5.The method for rapidly screening high-temperature stability of ternary layered cathode material of lithium battery of claim 4, characterized in that, The button cell comprises, from bottom to top, a negative electrode shell, a negative electrode, a separator, a positive electrode, a gasket, a spring, and a positive electrode shell. 6.The method for rapidly screening high-temperature stability of ternary layered cathode material of lithium battery of claim 1, characterized in that, The temperature of the high temperature is 60-120 DEG C. 7.The method for rapidly screening high-temperature stability of ternary layered cathode material of lithium battery of claim 1, characterized in that, The time of placing at the high temperature is 1-3 days. 8.The method for rapidly screening high-temperature stability of ternary layered cathode material of lithium battery of claim 1, characterized in that, The SEI film thickness is obtained by transmission electron microscope test. 9.The method for rapidly screening high-temperature stability of ternary layered cathode material of lithium battery of claim 1, characterized in that, The capacity test of the battery after high temperature placement is also included, and the high temperature stability is effectively determined by observing the capacity attenuation. 10.The method for rapidly screening high-temperature stability of ternary layered cathode material of lithium battery of claim 9, characterized in that, The current density of the charge and discharge cycle test is 1 mA / g-1000 mA / g, and the voltage range is 2V-4.5V.