A surface nano-fluorinated scandium lithium layer modified and near-surface co-doped anode material of nickel-cobalt-manganese ternary and a preparation method thereof

Abstract

The application relates to a kind of surface nano fluorinated scandium lithium layer modification and near surface anion and cation co-doped nickel cobalt manganese ternary positive electrode material and its preparation method, belong to chemical energy storage battery technical field.According to the molar ratio of Li, Sc and F element 3:1:6, lithium salt, scandium salt and fluorine salt are weighed respectively, then ultrasonic is added in ethanol aqueous solution and is fully stirred to obtain mixed salt solution;Nickel cobalt manganese ternary positive electrode material is added to the mixed salt solution, heated and stirred until the suspension is dry, and then dried to obtain a powder;The powder is calcined in oxygen atmosphere to obtain a kind of surface nano fluorinated scandium lithium layer modification and near surface anion and cation co-doped modified nickel cobalt manganese ternary positive electrode material.The synergistic effect of Li3ScF6 surface coating and near surface lattice Sc, F co-doping improves the electrochemical performance and thermal stability of nickel cobalt manganese ternary positive electrode material.

Description

Technical Field

[0001] This invention relates to a nickel-cobalt-manganese ternary cathode material modified with a surface nano-lithium scandium fluoride layer and co-doped with anions and cations near the surface, and its preparation method. Specifically, it relates to a method for improving the performance of nickel-cobalt-manganese ternary materials by using a surface lithium scandium fluoride nano-coating layer to suppress interfacial side reactions and by using anions and cations near the surface to synergistically strengthen the lattice. This invention belongs to the field of chemical energy storage battery technology. Background Technology

[0002] Lithium-ion power batteries, as an interdisciplinary field within the three major areas of new energy, new energy vehicles, and new materials, are the core and key to the new energy vehicle industry. Nickel-cobalt-manganese ternary cathode materials, especially high-nickel ternary materials with nickel content further increased to over 60% of the total molar proportion of transition metals, have become the mainstream technology for long-range electric vehicle power batteries due to their advantages of high specific capacity, high operating voltage, and suitable cost. However, the cycle performance and safety performance of these materials rapidly decline with increasing nickel content, becoming an obstacle to their further large-scale application. The main reasons are: while increasing the nickel content can bring higher specific capacity, it exacerbates the side reactions between the cathode material and the electrolyte during cycling, affecting interfacial lithium-ion transport; repeated charge-discharge processes trigger irreversible phase transitions in the material, causing the material structure to easily degrade from the initial layered phase to a poorly conductive phase (such as spinel and rock salt phases), resulting in increased impedance and rapid capacity decay; in addition, the oxygen framework of the material is prone to instability and oxygen release at high temperatures, causing thermal decomposition or even thermal runaway, seriously affecting the battery's safety performance.

[0003] Modifying ternary materials can improve their properties. For example, surface coating strategies can suppress interfacial side reactions by isolating the cathode material from the electrolyte, thereby improving the material's electrochemical stability to some extent. The near-surface lattice of ternary materials, as the site of the most intense electrochemical reactions and phase transitions, is often the first to be affected when material performance degrades. Protecting this region is particularly important, but traditional single strategies are still insufficient and incomplete in protecting the material. Developing effective modification measures that, while suppressing interfacial side reactions, also strengthen the near-surface structure, especially the stability of lattice oxygen, can significantly improve the material's cycle performance and safety. Some researchers have used scandium and fluorine-containing materials to coat the surface of nickel-cobalt-manganese ternary cathode materials. For example, Chinese patent application 201811623152.1 discloses a method to generate an ScF3 coating layer on the surface of a high-nickel ternary cathode material by mixing scandium fluoride prepared from scandium oxide powder, ammonium fluoride, etc. with a high-nickel ternary precursor and a lithium source solid phase. This method alleviates the structural degradation of the material and improves its electrochemical performance, but it is limited to the coating effect and does not reflect the effect of ion doping. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a nickel-cobalt-manganese ternary cathode material modified with a surface nano-scandium lithium fluoride layer and near-surface cation and anion co-doping, and its preparation method. The synergistic effect of Li3ScF6 surface coating and near-surface lattice Sc and F co-doping improves the electrochemical performance and thermal stability of the nickel-cobalt-manganese ternary cathode material.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] A method for preparing a nickel-cobalt-manganese ternary cathode material with a surface-modified nano-scandium lithium fluoride layer and near-surface co-doped anions and cations, the method comprising the following steps:

[0007] (1) Weigh out lithium salt, scandium salt and fluorine salt according to the molar ratio of Li, Sc and F elements of 3:1:6, then add them to an ethanol aqueous solution, sonicate and stir thoroughly to obtain a mixed salt solution; wherein the volume ratio of anhydrous ethanol and deionized water in the ethanol aqueous solution is 0.5~5:1;

[0008] (2) Add nickel-cobalt-manganese ternary cathode material to the mixed salt solution, heat and stir until the suspension dries, and then dry to obtain powder; wherein, the molar ratio of scandium salt to nickel-cobalt-manganese ternary cathode material is 0.01~0.03; the solid-liquid ratio of nickel-cobalt-manganese ternary cathode material to ethanol aqueous solution is 0.02g~1g:1mL;

[0009] (3) The powder is calcined in an oxygen atmosphere at a temperature of 300-600°C for 3-5 hours. After calcination, a modified nickel-cobalt-manganese ternary cathode material with a surface nano-scandium lithium fluoride layer and near-surface anion and cation co-doped is obtained.

[0010] Preferably, in step (1), the lithium salt, scandium salt and fluoride salt are lithium nitrate (LiNO3), scandium nitrate (Sc(NO3)3) and ammonium fluoride (NH4F), respectively.

[0011] Preferably, in step (1), the ultrasound time is 1 to 3 hours.

[0012] Preferably, in step (2), the nickel-cobalt-manganese ternary material has the chemical formula LiNi. x Co y Mn 1-x-y O2, where 0.6≤x<1, 0<y≤0.2, 0<(1-xy)≤0.2.

[0013] Preferably, in step (2), the heating temperature is 60~80℃ and the stirring speed is 300~500r / min.

[0014] Preferably, in step (3), the heating rate during calcination is 0.5~3℃ / min.

[0015] A nickel-cobalt-manganese ternary cathode material with a surface-modified nano-scandium lithium fluoride layer and near-surface co-doped anions and cations is prepared by the above method.

[0016] A lithium-ion secondary battery, wherein the positive electrode material of the battery is a nickel-cobalt-manganese ternary positive electrode material modified with a surface nano-scandium lithium fluoride layer and co-doped with anions and cations near the surface, as described in this invention.

[0017] Beneficial effects

[0018] (1) The method described in this invention can apply a solid electrolyte coating layer to a nickel-cobalt-manganese ternary cathode material, and through the subsequent calcination process, drive a small number of anions and cations in the coating layer to enter the near-surface lattice of the material, ultimately forming a modified ternary material with a Li3ScF6 layer for surface modification and protection, and an ion-doped lattice for near-surface reinforcement. The electrochemical performance and safety performance of the material are improved. The method is feasible and effective, with multiple modification effects and simple process technology.

[0019] (2) The method of the present invention uses a mixed solution of anhydrous ethanol and deionized water. On the one hand, this promotes better dissolution and dispersion of the precursor salt ions in deionized water, which facilitates uniform adsorption onto the NCM surface during stirring. On the other hand, the introduction of anhydrous ethanol also reduces the potential destructive effect of deionized water on the NCM surface lattice, thus balancing the two aspects. This point is particularly important for materials with higher nickel content. In subsequent steps, by further controlling the stirring temperature and stirring rate, different proportions of solvent can be evaporated and removed at a relatively uniform rate, which is beneficial for the stable and uniform binding of the coating salt onto the material surface. In addition, by optimizing the secondary calcination process, sufficient thermochemical driving force can be provided to the pretreated material to drive the formation of the surface coating layer while simultaneously increasing the ions (Sc) contained in the coating layer. 3+ and F - It can also enter the crystal lattice to undergo effective doping.

[0020] (3) The surface modification layer, lithium scandium fluoride, is a unique halide solid electrolyte with a wide electrochemical window and high conductivity. It can accelerate lithium ion transport at the interface and improve the rate performance of the material. Due to its chemical inertness, the lithium scandium fluoride layer can suppress the side reactions at the electrode-electrolyte interface during the cycling process and improve the cycling stability of the material.

[0021] (4)Sc 3+ and F - It can penetrate near the surface of the material during the re-firing process, strengthening the crystal lattice. Among them, Sc 3+Doping can form stronger Sc-O bonds than the TM-O bonds in ternary materials, stabilizing the crystal structure, suppressing unfavorable phase transitions during cycling, and thus improving cycling performance. Meanwhile, F... - Doping replaces the O in the near-surface lattice 2- The TM-F bonds formed not only stabilize the structure but also increase the oxygen release barrier on the surface, which greatly enhances the thermal stability of the material and significantly improves the safety performance of the lithium-ion battery prepared accordingly. Attached Figure Description

[0022] Figure 1 The images are scanning electron microscope (SEM) images of the materials described in Comparative Example 1 and Example 1.

[0023] Figure 2 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the material described in Example 1.

[0024] Figure 3 The X-ray diffraction (XRD) patterns of the materials described in Comparative Example 1 and Example 1 are shown.

[0025] Figure 4 This is a comparison chart of the 1C electrochemical cycle test results of the materials described in Comparative Example 1 and Example 1.

[0026] Figure 5 This is a comparison chart of the rate performance test results of the materials described in Comparative Example 1 and Example 1. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments.

[0028] The material characterization and analysis methods used in the following examples or comparative examples are as follows:

[0029] (1) Scanning electron microscope (SEM) test: Scanning electron microscope, instrument model is FEI Quanta, Netherlands.

[0030] (2) High-resolution transmission electron microscopy (HR-TEM) test: Transmission electron microscope, instrument model is JEM-2100, Japan.

[0031] (3) X-ray photoelectron spectroscopy (XPS) test: X-ray photoelectron spectrometer, instrument model ThermoKalpha, USA.

[0032] (4) X-ray diffraction (XRD) test: X-ray diffractometer, instrument model: Rigaku Ultima IV, Japan.

[0033] (5) Differential scanning calorimetry (DSC) test: Differential scanning calorimeter, instrument model is DSC214 Polyma, Germany.

[0034] (6) Assembly and testing of CR2025 button batteries: A slurry was prepared from the positive electrode material (the final product obtained in the example), acetylene black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 and coated onto aluminum foil. The dried aluminum foil loaded with the slurry was cut into small circular pieces with a diameter of approximately 1 cm using a cutting machine to serve as the positive electrode. A lithium metal sheet was used as the negative electrode, Celgard 2500 as the separator, and a 1M carbonate solution as the electrolyte (wherein the solvent is a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1, and the solute is LiPF6). The CR2025 button batteries were assembled in an argon-atmosphere glove box. The charge / discharge current density was 1C = 200 mA / g, and the charge / discharge tester used was a Land CT2100A, manufactured in China.

[0035] Comparative Example 1

[0036] Weigh out 473.13 g of nickel sulfate hexahydrate, 28.11 g of cobalt sulfate monohydrate, and 16.90 g of manganese sulfate heptahydrate according to the molar ratio of Ni:Co:Mn = 90:5:5, and prepare 1 L of metal salt solution with a total metal ion concentration of 2 mol / L. Weigh out 160 g of NaOH powder and add it to deionized water to prepare 1 L of NaOH solution with a concentration of 4 mol / L. Take 50 mL of 30% ammonia solution and add it to deionized water to prepare 1 L of ammonia solution.

[0037] 1 L of deionized water was added to the co-precipitation reactor as the reaction base solution. The prepared metal salt solution, NaOH solution, and ammonia solution were continuously and slowly pumped into the reactor under Ar atmosphere at a rate of 200 mL / h using a peristaltic pump. The pH of the base solution was controlled at 11.2, the temperature at 55℃, and the stirring rate at 500 r / min. After feeding, the mixture was immediately aged for 10 h. After aging, the material was filtered, repeatedly washed with deionized water until neutral, and then dried in an oven at 80℃ for 10 h to obtain the precursor Ni. 0.90 Co 0.05 Mn 0.05 (OH)2. The precursor and LiOH·H2O were dispersed and mixed in anhydrous ethanol at a molar ratio of 1:1.02 until the ethanol was completely evaporated. The mixture was then transferred to a tube furnace under an O2 atmosphere and pre-calcined at 550℃ for 5 h, followed by heating to 720℃ and holding at that temperature for 15 h, and then naturally cooled to room temperature to obtain a nickel-cobalt-manganese ternary cathode material, LiNi. 0.90 Co 0.05 Mn 0.05 O2.

[0038] Example 1

[0039] Lithium nitrate (0.115 g), scandium nitrate (0.129 g), and ammonium fluoride (0.125 g) were weighed according to a Li:Sc:F molar ratio of 3:1:6. These were added to 10.8 mL of a 50 vol% (i.e., anhydrous ethanol and deionized water volume ratio of 1) ethanol-water solution and sonicated for 1 h. After thorough stirring, a uniformly dispersed solution was obtained. The LiNi synthesized in Comparative Example 1 was then taken... 0.90 Co 0.05 Mn 0.05 5.4 g of high-nickel ternary cathode material with O2 was added to the above solution (i.e., the molar ratio of Sc salt to NCM material was controlled at 1%). The solution was stirred at 60°C and stirred at a stirring speed of 500 r / min until it dried. After drying, it was transferred to a tube furnace and heated to 500°C at a heating rate of 2°C / min under a pure oxygen atmosphere and calcined for 5 h to obtain a nickel-cobalt-manganese ternary cathode material with a surface nano-scandium lithium fluoride layer and near-surface anion and cation co-doped.

[0040] The morphology and surface elemental composition of the materials prepared in Comparative Example 1 and this embodiment were analyzed using SEM technology, see [link to SEM]. Figure 1 .from Figure 1 Upon inspection, the surface morphology of the modified material particles changed significantly, with the primary particle gaps filled with the coating material and the surface coating layer adhering uniformly. HR-TEM technology revealed a representative (202) crystal plane of Li3ScF6 crystals on the surface. XPS analysis of the surface chemical state of the modified material in this embodiment is shown in the figure. Figure 2 Chemical signals of Sc and F were detected on the surface, while no corresponding signals were observed at the corresponding binding energies in the material of Comparative Example 1. The lattice changes of the materials in Comparative Example 1 and this embodiment were analyzed using XRD technology, see [link to XRD analysis]. Figure 3 It was found that compared with the unmodified material, the modified material, due to the doping of the near-surface lattice, had the (003) peak shifted to a lower angle, indicating that the lattice of the material modified by the method described in this invention expands along the c-axis, the lithium layer widens, and it can accelerate the insertion and extraction of lithium ions in the lattice, which is beneficial to improving rate performance; the electrochemical performance of the materials described in Comparative Example 1 and this embodiment at 80 cycles at 1C rate in the voltage range of 2.75~4.3V is compared in the figure. Figure 4 The unmodified material exhibits a 1C first-cycle discharge capacity of 205.5 mAh / g and an 80-cycle capacity retention of 70.6%. In contrast, the material in this embodiment demonstrates a first-cycle specific capacity of 204.1 mAh / g and an 80-cycle capacity retention of 90.2%, significantly higher than the unmodified material. The rate performance tests for the unmodified material and the material in this embodiment are shown in [link to relevant documentation]. Figure 5As can be seen, the discharge capacity of the material in this embodiment at a high rate of 10C is still higher than that of the unmodified material, proving that the method described in this embodiment can significantly improve the rate performance of the material. The thermal stability of the material was analyzed by DSC technology. The peak thermal decomposition temperature of the unmodified material was 202℃, and the heat release was 1251J / g, while the peak thermal decomposition temperature of the modified material was delayed to 231℃, and the heat release was 528J / g. The thermal stability of the modified material was effectively improved in this embodiment, and the safety performance was significantly improved.

[0041] Example 2

[0042] Lithium nitrate (0.115 g), scandium nitrate (0.129 g), and ammonium fluoride (0.125 g) were weighed according to a Li:Sc:F molar ratio of 3:1:6. These were added to 27 mL of a 50 vol% (i.e., anhydrous ethanol and deionized water volume ratio of 1) ethanol-water solution and sonicated for 1 h. After thorough stirring, a uniformly dispersed solution was obtained. The LiNi synthesized in Comparative Example 1 was then taken... 0.90 Co 0.05 Mn 0.05 5.4 g of high-nickel ternary cathode material with O2 was added to the above solution (i.e., the molar ratio of Sc salt to NCM material was controlled at 1%). The solution was stirred at 60°C and stirred at a stirring speed of 500 r / min until it dried. After drying, it was transferred to a tube furnace and heated to 500°C at a heating rate of 2°C / min under a pure oxygen atmosphere and calcined for 5 h to obtain a nickel-cobalt-manganese ternary cathode material with a surface nano-scandium lithium fluoride layer and near-surface anion and cation co-doped.

[0043] The morphology and surface elemental analysis of the materials prepared in Comparative Example 1 and this embodiment were performed using SEM technology. It was found that the surface morphology of the material particles changed significantly after modification. The gaps between the particles were filled with coating material, and the surface coating layer was uniformly attached. The representative (202) crystal plane of Li3ScF6 crystal material was found on the surface by HR-TEM technology. The chemical state of the surface of the modified material in this embodiment was analyzed by XPS technology. Chemical signals of Sc and F were detected on the surface, while no corresponding signals were found at the corresponding binding energy of the material in Comparative Example 1. The lattice changes of the materials in Comparative Example 1 and this embodiment were analyzed by XRD technology. It was found that compared with the unmodified material, the (003) peak of the modified material shifted to a lower angle direction due to the doping of the near-surface lattice. This indicates that the lattice of the material modified by the method of the present invention expands along the c-axis, the lithium layer is widened, which can accelerate the insertion and extraction of lithium ions in the lattice and is beneficial to improving the rate performance. Comparative Example 1 and this embodiment The comparison of the electrochemical performance of the materials described above at 80 cycles at a 1C rate within a voltage range of 2.75~4.3V shows that the unmodified material has a first-cycle discharge capacity of 205.5 mAh / g and an 80-cycle capacity retention of 70.6%. In contrast, the material in this embodiment has a first-cycle specific capacity of 201.5 mAh / g and an 80-cycle capacity retention of 85.3%, which is significantly higher than that of the unmodified material. Testing the rate performance of the unmodified material and the material in this embodiment shows that the material in this embodiment still has a higher discharge capacity at a high rate of 10C than the unmodified material, proving that the method described in this embodiment can significantly improve the rate performance of the material. The thermal stability of the materials was analyzed using DSC technology. The peak thermal decomposition temperature of the unmodified material is 202℃, with a heat release of 1251 J / g, while the peak thermal decomposition temperature of the modified material is delayed to 225℃, with a heat release of 820 J / g. This embodiment demonstrates that the modified material has effectively improved thermal stability and significantly enhanced safety performance.

[0044] Example 3

[0045] Lithium nitrate (0.115 g), scandium nitrate (0.129 g), and ammonium fluoride (0.125 g) were weighed according to a Li:Sc:F molar ratio of 3:1:6. These were added to 10.8 mL of a 50 vol% (i.e., anhydrous ethanol and deionized water volume ratio of 1) ethanol-water solution and sonicated for 1 h. After thorough stirring, a uniformly dispersed solution was obtained. The LiNi synthesized in Comparative Example 1 was then taken... 0.90 Co 0.05 Mn 0.055.4 g of high-nickel ternary cathode material with O2 was added to the above solution (i.e., the molar ratio of Sc salt to NCM material was controlled at 1%). The solution was stirred at 300 r / min at 80 °C until it dried. After drying, the solution was transferred to a tube furnace and heated to 600 °C at a heating rate of 0.5 °C / min under a pure oxygen atmosphere. The solution was then calcined for 3 h to obtain a nickel-cobalt-manganese ternary cathode material with a surface nano-scandium lithium fluoride layer and near-surface anion and cation co-doped.

[0046] The morphology and surface elemental analysis of the materials prepared in Comparative Example 1 and this embodiment were performed using SEM technology. It was found that the surface morphology of the material particles changed significantly after modification. The gaps between the particles were filled with coating material, and the surface coating layer was uniformly attached. The representative (202) crystal plane of Li3ScF6 crystal material was found on the surface by HR-TEM technology. The chemical state of the surface of the modified material in this embodiment was analyzed by XPS technology. Chemical signals of Sc and F were detected on the surface, while no corresponding signals were found at the corresponding binding energy of the material in Comparative Example 1. The lattice changes of the materials in Comparative Example 1 and this embodiment were analyzed by XRD technology. It was found that compared with the unmodified material, the (003) peak of the modified material shifted to a lower angle direction due to the doping of the near-surface lattice. This indicates that the lattice of the material modified by the method of the present invention expands along the c-axis, the lithium layer is widened, which can accelerate the insertion and extraction of lithium ions in the lattice and is beneficial to improving the rate performance. Comparative Example 1 and this embodiment The comparison of the electrochemical performance of the materials described above at 80 cycles at a 1C rate within a voltage range of 2.75~4.3V shows that the unmodified material has a first-cycle discharge capacity of 205.5 mAh / g and an 80-cycle capacity retention of 70.6%. In contrast, the material in this embodiment has a first-cycle specific capacity of 204.5 mAh / g and an 80-cycle capacity retention of 92.1%, which is significantly higher than that of the unmodified material. Testing the rate performance of the unmodified material and the material in this embodiment shows that the material in this embodiment still has a higher discharge capacity at a high rate of 10C than the unmodified material, proving that the method described in this embodiment can significantly improve the rate performance of the material. The thermal stability of the materials was analyzed using DSC technology. The peak thermal decomposition temperature of the unmodified material is 202℃, with a heat release of 1251 J / g, while the peak thermal decomposition temperature of the modified material is delayed to 235℃, with a heat release of 480 J / g. This embodiment demonstrates that the modified material has effectively improved thermal stability and significantly enhanced safety performance.

[0047] Example 4

[0048] Lithium nitrate (0.345 g), scandium nitrate (0.387 g), and ammonium fluoride (0.375 g) were weighed according to a Li:Sc:F molar ratio of 3:1:6. These were added to 10.8 mL of a 50 vol% (i.e., anhydrous ethanol and deionized water volume ratio of 1) ethanol-water solution and sonicated for 1 h. After thorough stirring, a uniformly dispersed solution was obtained. The LiNi synthesized in Comparative Example 1 was then used... 0.90 Co 0.05 Mn 0.05 5.4 g of high-nickel ternary cathode material with O2 was added to the above solution (i.e., the molar ratio of Sc salt to NCM material was controlled at 3%). The solution was stirred at 80 °C and stirred at a stirring speed of 300 r / min until it dried. After drying, it was transferred to a tube furnace and heated to 300 °C at a heating rate of 2 °C / min under a pure oxygen atmosphere and calcined for 5 h to obtain a nickel-cobalt-manganese ternary cathode material with a surface nano-scandium lithium fluoride layer and near-surface anion and cation co-doping.

[0049] The morphology and surface elemental analysis of the materials prepared in Comparative Example 1 and this embodiment were performed using SEM technology. It was found that the surface morphology of the material particles changed significantly after modification. The gaps between the particles were filled with coating material, and the surface coating layer was uniformly attached. The representative (202) crystal plane of Li3ScF6 crystal material was found on the surface by HR-TEM technology. The chemical state of the surface of the modified material in this embodiment was analyzed by XPS technology. Chemical signals of Sc and F were detected on the surface, while no corresponding signals were found at the corresponding binding energy of the material in Comparative Example 1. The lattice changes of the materials in Comparative Example 1 and this embodiment were analyzed by XRD technology. It was found that compared with the unmodified material, the (003) peak of the modified material shifted to a lower angle direction due to the doping of the near-surface lattice. This indicates that the lattice of the material modified by the method of the present invention expands along the c-axis, the lithium layer is widened, which can accelerate the insertion and extraction of lithium ions in the lattice and is beneficial to improving the rate performance. Comparative Example 1 and this embodiment The comparison of the electrochemical performance of the materials described above at 80 cycles at a 1C rate within a voltage range of 2.75~4.3V shows that the unmodified material has a first-cycle discharge capacity of 205.5 mAh / g and an 80-cycle capacity retention of 70.6%. In contrast, the material in this embodiment has a first-cycle specific capacity of 203.2 mAh / g and an 80-cycle capacity retention of 78.6%, which is significantly higher than that of the unmodified material. Testing the rate performance of the unmodified material and the material in this embodiment shows that the material in this embodiment still has a higher discharge capacity at a high rate of 10C than the unmodified material, proving that the method described in this embodiment can significantly improve the rate performance of the material. The thermal stability of the material was analyzed using DSC technology. The peak thermal decomposition temperature of the unmodified material is 202℃, with a heat release of 1251 J / g, while the peak thermal decomposition temperature of the modified material is delayed to 212℃, with a heat release of 755 J / g. This embodiment demonstrates that the modified material has effectively improved thermal stability and significantly enhanced safety performance.

[0050] Comparative Example 2

[0051] Lithium nitrate (0.115 g), scandium nitrate (0.129 g), and ammonium fluoride (0.125 g) were weighed according to a Li:Sc:F molar ratio of 3:1:6. These were added to 10.8 mL of a 10 vol% (i.e., anhydrous ethanol to deionized water volume ratio of 0.11) ethanol-water solution and sonicated for 1 h. After thorough stirring, a uniformly dispersed solution was obtained. The LiNi synthesized in Comparative Example 1 was then used... 0.90 Co 0.05 Mn 0.05 5.4 g of high-nickel ternary cathode material with O2 was added to the above solution (i.e., the molar ratio of Sc salt to NCM material was controlled at 1%). The solution was stirred at 60°C and 500 r / min until it dried. After drying, the solution was transferred to a tube furnace and heated to 500°C at a heating rate of 2°C / min under a pure oxygen atmosphere. The solution was then calcined for 5 h to obtain a modified nickel-cobalt-manganese ternary cathode material.

[0052] The morphology and surface elemental analysis of the materials prepared in Comparative Example 1 and this Comparative Example were performed using SEM technology. It was found that the surface morphology of the material particles changed significantly after modification. The gaps between the particles were filled with coating material, and the surface coating layer was uniformly attached. The representative (202) crystal plane of Li3ScF6 crystal material was found on the surface by HR-TEM technology, and a rock salt-like phase that is not conducive to lithium-ion transport appeared in the near-surface layer. The surface chemical state of the modified material in this Comparative Example was analyzed by XPS technology. Chemical signals of Sc and F were detected in the surface layer, while no corresponding signals were found in the material of Comparative Example 1 at the corresponding binding energy. The lattice changes of the materials in Comparative Example 1 and this Comparative Example were analyzed by XRD technology. It was found that compared with the unmodified material, the (003) peak of the modified material shifted to a lower angle direction due to the doping of the near-surface lattice. This indicates that the lattice of the material modified by the method of this invention expands along the c-axis direction, and the lithium layer is widened. The comparison of the electrochemical performance of the materials described in the comparative example at 1C rate within a voltage range of 2.75~4.3V shows that the unmodified material has a first-cycle discharge capacity of 205.5 mAh / g and an 80-cycle capacity retention of 70.6%. In contrast, the material in this comparative example has a first-cycle specific capacity of 202.2 mAh / g and an 80-cycle capacity retention of 65.5%, both lower than the unmodified material. Testing the rate performance of the unmodified and comparative materials shows that the material in this comparative example has a lower discharge specific capacity at a high rate of 10C than the unmodified material, proving that the method described in this comparative example cannot improve the rate performance of the materials. DSC analysis of the thermal stability of the materials shows that the peak thermal decomposition temperature of the unmodified material is 202℃ with a heat release of 1251 J / g, while the peak thermal decomposition temperature of the modified material is 205℃ with a heat release of 1180 J / g. This comparative example demonstrates that the modified material cannot significantly improve the thermal stability of the materials.

[0053] Comparative Example 3

[0054] Lithium nitrate (0.575 g), scandium nitrate (0.645 g), and ammonium fluoride (0.625 g) were weighed according to a Li:Sc:F molar ratio of 3:1:6. These were added to 10.8 mL of a 50 vol% (i.e., anhydrous ethanol and deionized water volume ratio of 1) ethanol-water solution and sonicated for 1 h. After thorough stirring, a uniformly dispersed solution was obtained. The LiNi synthesized in Comparative Example 1 was then taken... 0.90 Co 0.05 Mn 0.05 5.4 g of high-nickel ternary cathode material with O2 was added to the above solution (i.e., the molar ratio of Sc salt to NCM material was controlled at 5%). The solution was stirred at 60°C and 500 r / min until it dried. After drying, the solution was transferred to a tube furnace and heated to 500°C at a heating rate of 2°C / min under a pure oxygen atmosphere and calcined for 5 h to obtain a modified nickel-cobalt-manganese ternary cathode material.

[0055] The morphology and surface elemental analysis of the materials prepared in Comparative Example 1 and this Comparative Example were performed using SEM technology. It was found that the surface morphology of the material particles changed significantly after modification. The gaps between the particles were filled with coating material, but obvious agglomerates appeared on the surface. The representative (202) crystal plane of Li3ScF6 crystal material was found on the surface by HR-TEM technology, and a rock salt-like phase that is not conducive to lithium-ion transport appeared in the near-surface layer. The surface chemical state of the modified material in this Comparative Example was analyzed by XPS technology. Chemical signals of Sc and F were detected in the surface layer, while no corresponding signals were found in the material of Comparative Example 1 at the corresponding binding energy. The lattice changes of the materials in Comparative Example 1 and this Comparative Example were analyzed by XRD technology. It was found that compared with the unmodified material, the (003) peak of the modified material shifted to a lower angle direction due to the doping of the near-surface lattice. This indicates that the lattice of the material modified by the method of this invention expands along the c-axis direction, and the lithium layer is widened. The materials in Comparative Example 1 and this Comparative Example have a range of 2.75~4 A comparison of the electrochemical performance at 1C rate over 80 cycles within a 0.3V voltage range shows that the unmodified material has a first-cycle discharge capacity of 205.5 mAh / g and an 80-cycle capacity retention of 70.6%. In contrast, the material in this comparative example has a first-cycle specific capacity of 195.2 mAh / g and an 80-cycle capacity retention of 68%, both lower than the unmodified material. Testing the rate performance of the unmodified and comparative materials reveals that the material in this example has a lower discharge specific capacity at a high rate of 10C than the unmodified material, proving that the method described in this example cannot improve the rate performance. The comparative example's excessively thick surface coating hinders lithium-ion transport, thus worsening the rate performance. DSC analysis of the material's thermal stability shows that the unmodified material has a peak thermal decomposition temperature of 202℃ and an exothermic heat of 1251 J / g, while the modified material has a peak thermal decomposition temperature of 198℃ and an exothermic heat of 1005 J / g. This comparative example demonstrates that the modified material cannot significantly improve the material's thermal stability.

[0056] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A nickel-cobalt-manganese ternary cathode material with a surface-modified nano-scandium lithium fluoride layer and near-surface co-doped anions and cations, characterized in that: The material is prepared by the following method, which includes the following steps: Lithium nitrate (0.115 g), scandium nitrate (0.129 g), and ammonium fluoride (0.125 g) were weighed according to a Li:Sc:F molar ratio of 3:1:

6. These three components were added to 10.8 mL of 50 vol% ethanol aqueous solution and sonicated for 1 h. After thorough stirring, a uniformly dispersed solution was obtained. LiNi... 0.90 Co 0.05 Mn 0.05 5.4 g of high-nickel ternary cathode material with O2 was added to the above solution and stirred at 300 r / min at 80 °C until it dried. After drying, it was transferred to a tube furnace and heated to 600 °C at a heating rate of 0.5 °C / min under a pure oxygen atmosphere and calcined for 3 h to obtain nickel-cobalt-manganese ternary cathode material with surface nano-scandium lithium fluoride layer modification and near-surface anion and cation co-doping. Among them, the co-doped ion is Sc 3+ and F - .

2. A lithium-ion secondary battery, characterized in that: The positive electrode material of the battery is a nickel-cobalt-manganese ternary positive electrode material with surface nano-scandium lithium fluoride layer modification and near-surface anion and cation co-doping as described in claim 1.

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