Modified cathode material, method for preparing the same, cathode sheet comprising the same, secondary battery, and electronic device

Abstract

This application belongs to the field of electrochemical technology, and specifically relates to a modified cathode material, its preparation method, and a cathode sheet, secondary battery, and electronic device containing the material. The modified cathode material includes: a ternary cathode material; and an oxide coating on the surface of the ternary cathode material, wherein the coating is an island-like coating, and the general chemical formula of the oxide is: Li. 2‑x A (1+x) / 3 B2O6F, 0.7≤x≤0.8; wherein A includes La and at least one of Mg, Ca, Sr, Ba, Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, and Zn; wherein B includes Nb and at least one of Ti, Zr, V, Mo, W, Bi, Ta, and Hf; wherein the oxide content relative to the total mass of the modified cathode material is 0.6%~1.5%. The modified cathode material provided in this application has high capacity utilization, excellent rate performance, and good thermal safety properties. Applying the modified cathode material provided in this application to secondary batteries can effectively improve the energy density and heat resistance of secondary batteries.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a modified cathode material, its preparation method, and cathode sheets, secondary batteries, and electronic devices containing the material. Background Technology

[0002] Lithium-ion rechargeable batteries have become a key research focus in the new energy field due to their high energy density, stable charge-discharge platform, low self-discharge rate, and long cycle life. The cathode material is a crucial factor affecting battery performance in lithium-ion batteries. Currently, ternary cathode materials are a major type of cathode material; generally, the output specific capacity of ternary cathode materials can be improved by increasing the nickel content and the charging cutoff voltage.

[0003] LiNi ternary cathode material x Co y Mn 1-x-y O2 was developed by Professor Ohzuku in 1999. It can be viewed as a mixed solid solution of LiNiO2, LiCoO2, and LiMnO2 in different proportions, exhibiting a layered structure. Ni is the main variable-valence element, providing energy through redox reactions, thus enabling the cathode material to produce different output specific capacities. Co primarily provides electronic conductivity and maintains the stability of the layered structure. Mn does not undergo valence changes and its main role is to improve the material's thermal stability. (LiNi) x Co y Mn 1-x-y O2 combines the advantages of Ni, Co, and Mn to achieve optimal overall performance.

[0004] However, the high nickel content and charging cutoff voltage imply deep lithium intercalation / deintercalation and redox reactions, which not only exacerbate the Li-carboxylation process during cycling but also... + / Ni 2+ Disordered mixing hinders lithium-ion diffusion, leading to localized lattice distortion, inducing intracrystalline cracks, and causing greater volume expansion and contraction of layered structures, resulting in intergranular microcracks. After long-term cycling, this can even lead to particle fragmentation. Furthermore, deep redox reactions generate large amounts of highly reactive and unstable Ni. 4+ It will plunder electrons from nearby oxygen lattice and be reduced to Ni. 2+ This loss of oxygen at the interface causes lattice oxygen to lose electrons and recombine, forming O2 that leaks out. Simultaneously, this loss of interfacial lattice oxygen not only leads to harmful interfacial phase transitions, but the leaked oxygen also catalyzes the decomposition of the electrolyte, exacerbating the risk of battery thermal runaway and potentially causing fires and explosions. These problems severely impact the cycle stability, rate performance, and safety of high-voltage, high-nickel ternary cathode materials, hindering their commercial application. Summary of the Invention

[0005] The purpose of this application is to provide a modified cathode material, a method for preparing the same, and a cathode sheet, a secondary battery, and an electronic device containing the same material.

[0006] According to a first aspect of this application, this application provides a modified cathode material, the modified cathode material comprising: a ternary cathode material; and an oxide coated on the surface of the ternary cathode material, the coating being an island-like coating, the general chemical formula of the oxide being: Li 2-x A (1+x) / 3 B2O6F, 0.7≤x≤0.8; A includes La and at least one of Mg, Ca, Sr, Ba, Al, Cd, Co, Cr, Cu, Fe, Mn, Ni and Zn; B includes Nb and at least one of Ti, Zr, V, Mo, W, Bi, Ta and Hf; the content of the oxide relative to the total mass of the modified cathode material is 0.6%~1.5%.

[0007] In some specific embodiments, the particle size D50 of the modified cathode material ranges from 3.3 to 3.7 μm.

[0008] In some specific embodiments, the particle size of the oxide coating on the surface of the ternary cathode material is 0.4 μm to 0.6 μm.

[0009] In some specific embodiments, the A in the oxide includes La and Al; the content of Al relative to the total mass of the oxide is 1.8% to 2.2%.

[0010] In some specific embodiments, the B in the oxide includes Nb and Ta; the content of Ta relative to the total mass of the oxide is 1.3% to 1.7%.

[0011] According to a second aspect of this application, this application provides a method for preparing a modified cathode material, wherein the oxide is prepared by the following method: A source, B source, and LiF are prepared according to the general chemical formula Li 2-x A (1+x) / 3 The first mixture is obtained by uniformly mixing B2O6F according to the stoichiometric ratio shown. The first mixture is calcined at 800°C to 1200°C for 3 to 5 hours. After calcination, it is ground and then mixed with a second part of LiF to obtain a second mixture. The mass of the second part of LiF is 1 to 2 times the mass of LiF in the first mixture. The second mixture is dried under vacuum and then pressed into tablets. The tablets are sintered at 1000°C to 1200°C for 5 to 7 hours under a nitrogen atmosphere. The sintered material is then crushed and ground to obtain the oxide.

[0012] In some specific embodiments, the modified cathode material is prepared by the following method: the oxide and the ternary cathode material are mixed to obtain a third mixture, and the third mixture is placed in a nitrogen atmosphere and sintered at 400°C to 500°C for 10 to 12 hours to obtain the modified cathode material.

[0013] According to a third aspect of this application, this application provides a positive electrode sheet, the positive electrode sheet comprising the modified positive electrode material described in the first aspect or the modified positive electrode material prepared by the method described in the second aspect.

[0014] According to a fourth aspect of this application, this application provides a secondary battery comprising the modified cathode material as described in the third aspect.

[0015] According to a fifth aspect of this application, an electronic device is provided, the electronic device comprising a secondary battery as described in the fourth aspect.

[0016] The modified cathode material provided in this application has high specific capacity and ionic conductivity, as well as good thermal safety properties. Applying the modified cathode material provided in this application to secondary batteries can effectively improve the energy density and heat resistance of secondary batteries. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0018] Figure 1 The image shows a SEM image of the oxide prepared in Example 2.

[0019] Figure 2 The XRD pattern of the oxide prepared in Example 2;

[0020] Figure 3 SEM image of the oxide-coated modified cathode material NCM78@0.6%LMFO-Al&Ta prepared in Example 2;

[0021] Figure 4 SEM image of the coated and modified NCM78@0.9%LMFO-Al&Ta material obtained in Example 3;

[0022] Figure 5 SEM image of the coated and modified NCM78@1.2%LMFO-Al&Ta material obtained in Example 4;

[0023] Figure 6 SEM image of the coated and modified NCM78@1.5%LMFO-Al&Ta material obtained in Example 5;

[0024] Figure 7 The image shows a SEM image of the coated and modified NCM78@LATP material obtained in Example 6.

[0025] Figure 8 SEM image of the coated and modified NCM78@LLZO material obtained in Example 7;

[0026] Figure 9 The image shows the SEM image of the NCM78@Base material obtained in Comparative Example 1. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] The most common solution to the application challenges of high-nickel ternary cathode materials is surface coating. Common coating materials include metal oxides / fluorides, such as MgO, TiO2, ZrO, and AlF3, which are simple to prepare and inexpensive. However, as inert coating materials, metal oxides / fluorides often reduce the specific capacity and rate performance of the cathode material. This application introduces an aluminum-containing pyrochlore-structured solid electrolyte material and significantly improves the structural thermal stability and electrochemical performance of the ternary cathode material through surface coating technology.

[0029] The purpose of this application is to provide a modified cathode material, a method for preparing the same, and a cathode sheet, a secondary battery, and an electronic device containing the same material.

[0030] According to a first aspect of this application, this application provides a modified cathode material, the modified cathode material comprising: a ternary cathode material; and an oxide coated on the surface of the ternary cathode material, the coating being an island-like coating, the general chemical formula of the oxide being: Li 2-x A (1+x) / 3 B2O6F, 0.7≤x≤0.8; A includes La and at least one of Mg, Ca, Sr, Ba, Al, Cd, Co, Cr, Cu, Fe, Mn, Ni and Zn; B includes Nb and at least one of Ti, Zr, V, Mo, W, Bi, Ta and Hf; the content of the oxide relative to the total mass of the modified cathode material is 0.6%~1.5%.

[0031] In some specific embodiments, the value of x can be 0.70, 0.72, 0.74, 0.75, 0.76, 0.78, 0.80, or a value within the range of any two of these values.

[0032] In some specific embodiments, the content of the oxide relative to the total mass of the modified cathode material can be 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or a value within any two of these ranges.

[0033] In some specific embodiments, the particle size D50 of the modified cathode material ranges from 3.3 μm to 3.7 μm.

[0034] In some specific embodiments, the particle size D50 of the modified cathode material can be 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, or a value within any two of these ranges.

[0035] In some specific embodiments, the particle size of the oxide coating on the surface of the ternary cathode material is 0.4 μm to 0.6 μm.

[0036] In some specific embodiments, the A in the oxide includes La and Al; the content of Al relative to the total mass of the oxide is 1.8% to 2.2%.

[0037] In some specific embodiments, the content of Al relative to the total mass of oxides can be 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, or a value within the range of any two of these values.

[0038] In some specific embodiments, the B in the oxide includes Nb and Ta; the content of Ta relative to the total mass of the oxide is 1.3% to 1.7%.

[0039] In some specific embodiments, the content of Ta relative to the total mass of oxides can be 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, or a value within the range of any two of these values.

[0040] According to a second aspect of this application, this application provides a method for preparing a modified cathode material, wherein the oxide is prepared by the following method: A source, B source, and LiF are prepared according to the general chemical formula Li 2-x A (1+x) / 3The first mixture is obtained by uniformly mixing B2O6F according to the stoichiometric ratio shown. The first mixture is calcined at 800°C to 1200°C for 3 to 5 hours. After calcination, it is ground and then mixed with a second part of LiF to obtain a second mixture. The mass of the second part of LiF is 1 to 2 times the mass of LiF in the first mixture. The second mixture is dried under vacuum and then pressed into tablets. The tablets are sintered at 1000°C to 1200°C for 5 to 7 hours under a nitrogen atmosphere. The sintered material is then crushed and ground to obtain the oxide.

[0041] In some specific embodiments, the mass of the second portion of LiF is 1, 1.2, 1.4, 1.6, 1.8, or 2 times the mass of LiF in the first mixture, or a value within a range of any two of these values.

[0042] In some specific embodiments, the first mixture is calcined at a temperature of 800°C to 1200°C for 3 to 5 hours; wherein the calcination temperature can be 800°C, 900°C, 1000°C, 1100°C, or 1200°C, and the calcination time can be 3 hours, 4 hours, or 5 hours, or a value within any range of these values.

[0043] In some specific embodiments, the second mixture is dried and then compressed into tablets, and sintered in a nitrogen atmosphere at a temperature of 1000°C to 1200°C for 5 to 7 hours; wherein the sintering temperature can be 1000°C, 1050°C, 1100°C, 1150°C, or 1200°C, and the sintering time can be 5 hours, 6 hours, or 7 hours, or a value within any range of two of these values.

[0044] In some specific embodiments, the modified cathode material is prepared by the following method: the oxide and the ternary cathode material are mixed to obtain a third mixture, and the third mixture is placed in a nitrogen atmosphere and sintered at 400°C to 500°C for 10 to 12 hours to obtain the modified cathode material.

[0045] In some specific embodiments, the third mixture is placed in a nitrogen atmosphere and sintered at 400°C to 500°C for 10 to 12 hours; wherein the sintering temperature can be 400°C, 420°C, 440°C, 460°C, 480°C, or 500°C, and the sintering time can be 10 hours, 11 hours, or 12 hours, or a value within any two of these values.

[0046] In some specific embodiments, the ternary cathode material is prepared by hydroxide coprecipitation-controlled crystallization.

[0047] In some specific embodiments, the ternary cathode material is Li[Ni] 0.78 Co 0.11 Mn 0.11 O2].

[0048] In some specific embodiments, the ternary cathode material is prepared using the following method:

[0049] NiSO4•6H2O, CoSO4•7H2O and MnSO4•H2O were dissolved in deionized water in a molar ratio of 78:11:11 to prepare a 2 mol / L mixed solution. The mixed solution was then continuously pumped into a nitrogen-protected continuously stirred reactor using a peristaltic pump.

[0050] An 8 mol / L NaOH precipitant solution and an appropriate concentration of NH3•H2O complexing agent solution were pumped separately into the reactor. The pH value of the solution in the reactor was monitored using an online pH meter, and the pH value was maintained stable at 11-12 by controlling the amount of NaOH added. The total ammonia concentration in the reactor was controlled by adjusting the pumping rate of ammonia water. The reaction temperature was set at 60°C, the stirring speed at 1000 rpm / min, and the reaction time at 10 h. The mixture was then aged overnight with stirring without feeding. Finally, the obtained precursor material was repeatedly washed with deionized water, filtered until the pH value was neutral, and dried in an 80°C forced-air oven for 24 h to prepare Ni. 0.78 Co0. 11 Mn 0.11 (OH)2 precursor materials;

[0051] Ni 0.78 Co 0.11 Mn 0.11 The (OH)2 precursor material and LiOH•H2O lithium salt were uniformly mixed in a mortar at a molar ratio of 1:1.05, placed in a corundum crucible, and calcined at high temperature in a muffle furnace under an air atmosphere. The specific calcination process was as follows: first, calcination was carried out at a low temperature of 500°C for 3 hours, then the temperature was continuously increased to 850°C for sintering for 10 hours. After completion, the mixture was allowed to cool naturally to room temperature to obtain the ternary cathode material Ni. 0.78 Co 0.11 Mn 0.11 (OH)2.

[0052] In some specific embodiments, the oxide is prepared by the following method:

[0053] Source A, source B, and LiF were selected according to the general chemical formula Li 2-x A (1+x) / 3The first mixture is obtained by uniformly mixing B2O6F according to the stoichiometric ratio shown. The first mixture is calcined at 1000°C for 4 hours, then ground, and a second part of LiF is added and mixed evenly to obtain the second mixture. The mass of the second part of LiF is 1.91 times the mass of LiF in the first mixture. The second mixture is dried for 1 hour under vacuum and 22.5°C, then pressed into tablets under 76 MPa pressure. The tablets are wrapped with Pt foil and sintered at 1200°C for 6 hours under a nitrogen atmosphere. The sintered material is then crushed and ground to obtain the oxide.

[0054] According to a third aspect of this application, this application provides a positive electrode sheet, the positive electrode sheet comprising the modified positive electrode material described in the first aspect or the modified positive electrode material prepared by the method described in the second aspect.

[0055] According to a fourth aspect of this application, this application provides a secondary battery comprising the modified cathode material as described in the third aspect.

[0056] The secondary battery of this application includes a positive electrode, a negative electrode, and an electrolyte.

[0057] In one embodiment, the electrolyte comprises a lithium salt and a non-aqueous solvent. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as the purpose of this application is achieved.

[0058] The secondary battery of this application also includes a separator for separating the positive electrode and the negative electrode, preventing internal short circuits in the secondary battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the separator material can be, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separators based on polytetrafluoroethylene, polyester membranes (e.g., polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, or aramid membranes.

[0059] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0060] According to a fifth aspect of this application, an electronic device is provided, the electronic device comprising a secondary battery as described in the fourth aspect.

[0061] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0062] Example

[0063] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0064] The test methods and equipment used in the embodiments and comparative examples of this application are as follows:

[0065] 1. Scanning Electron Microscopy (SEM) Testing

[0066] The prepared negative electrode active material particles were observed using a scanning electron microscope (ZEISSSEM) and SEM images were taken. The porosity and circular pores of the particles were measured using the measurement function of the scanning electron microscope.

[0067] For cross-sectional testing, an ion polisher (instrument model IB-09010CP) was used to cut out a flat cross-section, which was then photographed by SEM. The principle of ion polishing is that under vacuum conditions, the ion source ionizes argon gas. After acceleration and focusing, the high-speed argon ions knock out atoms or molecules on the sample surface, thus achieving ion polishing.

[0068] The calculation / statistical method for the percentage of pore area in a single particle of negative electrode active material is as follows: using the measurement function of scanning electron microscope, the cross-sectional area S1 of a single particle is measured and calculated, and the pore area S2 in the cross-section of a single particle is measured and calculated. The percentage of pore area in a single particle is S2 / S1×100%.

[0069] For negative electrode active material particles, the diameter of the circular pores in the particles is calculated / statistically as follows: the diameter of the circular pores in the particles is measured and calculated using the measurement function of a scanning electron microscope.

[0070] 2. Particle size testing

[0071] The particle size distribution of the prepared negative electrode active material was tested using a Malvern particle size analyzer (Master Sizer 2000). In the volume-based particle size distribution of the material, starting from the smallest particle size, the particle size reaching 50% of the volume accumulation is defined as D50, and the particle size reaching 99% of the volume accumulation is defined as D99.

[0072] 3. X-ray diffraction analysis (XRD)

[0073] The composition and crystal structure of the material were characterized using X-ray powder diffraction (XRD) at an operating voltage of 40 kV and an operating current of 40 mA, with a copper target (Kα, incident wavelength λ = 0.154 nm). Sample preparation and testing conditions were as follows: the dry powder sample was placed on a background-free single-crystal silicon sample stage; the scan rate was 1° / min; and the scan range was 10°–80°. Phase analysis was performed on the XRD data using Jade software, and further refinement of the XRD data using GSAS software yielded more detailed information such as lattice parameters.

[0074] 4. Ionic conductivity test

[0075] The ionic conductivity of the solid electrolyte was characterized using EIS. First, the electrolyte powder sample was placed in a 10 mm diameter mold and cold-pressed at 360 MPa for 5 minutes to form a 10 mm diameter electrolyte sheet. Carbon paper was used as blocking electrodes on both sides of the electrolyte sheet. The test frequency range was 1 MHz to 100 mHz. The test temperature started at 20°C, and impedance values ​​were measured at 20°C increments. The ionic conductivity of the solid electrolyte ceramic sheet was calculated using the formula σ = L / (R*S), where L is the thickness of the ceramic sheet, R is the measured impedance, and S is the area of ​​the ceramic sheet.

[0076] 5. Differential Scanning Calorimetry (DSC)

[0077] The thermal stability of the sample is characterized using differential scanning calorimetry (DSC). A dry sample powder of 5–8 mg is placed in an Al₂O₃ crucible. The detection atmosphere is typically nitrogen, and the heating rate is 2°C / min. The phase transition process of the material at high temperatures is analyzed by observing the heat absorption and release of the sample.

[0078] 6. Electrochemical performance testing

[0079] The battery cycler is used to perform electrochemical measurements on assembled batteries. Each sample is pre-cycled three times with a constant current of 0.2C within a voltage range of 2.8–4.2V. In the current effect test, the battery is run at a constant current at various rates (0.2C, 0.33C, 1C, and 2C) by setting the cycling steps to obtain output capacity data at different current densities.

[0080] 7. DC Impedance Test (DCR)

[0081] The DC impedance change curve was tested using the current interruption method. The battery charging process was divided into several equal parts. During constant current charging, the current was intermittently interrupted for 1 minute, and the voltage change data before and after the current drop were recorded. The voltage change was then calculated using the formula R. dc =ΔV / ΔI can be used to calculate the corresponding impedance value (DCR) of the battery at different states of charge (SOC) and at low temperature during the charging process.

[0082] Example 1

[0083] Preparation of oxides:

[0084] S1) Obtain lanthanum oxide, niobium oxide and LiF powder, and mix them in a certain proportion;

[0085] S2) The mixture prepared in step S1 was calcined at 1000°C for 4 hours. After calcination, it was ground and 1.91 times the excess of LiF was added.

[0086] S3) The material prepared in step S2 was dried for 1 hour under vacuum and at 22.5°C, then pressed into tablets under a pressure of 76 MPa. The material was wrapped with Pt foil and sintered for 6 hours under a nitrogen atmosphere and at 1200°C. After crushing and grinding, the oxide LMFO:Li was obtained. 1.25 La 0.58 Nb2O6F.

[0087] Preparation of ternary cathode materials: Li[Ni] was prepared by hydroxide coprecipitation-controlled crystallization method. 0.78 Co 0.11 Mn 0.11 O2] includes the following steps:

[0088] S4) NiSO4•6H2O, CoSO4•7H2O and MnSO4•H2O are dissolved in secondary water in a molar ratio of 78:11:11 to prepare a 2 mol / L mixed solution. The mixed solution is then continuously pumped into a nitrogen-protected continuously stirred reactor using a peristaltic pump.

[0089] S5) An 8 mol / L NaOH precipitant solution and a suitable concentration of NH3•H2O complexing agent solution were pumped into the reactor separately. The pH value of the solution in the reactor was monitored using an online pH meter, and the pH value was maintained stable at 11-12 by controlling the amount of NaOH added. The total ammonia concentration in the reactor was controlled by adjusting the pumping rate of ammonia water. The reaction temperature was set to 60°C, the stirring speed to 1000 rpm / min, and the reaction time to 10 h. The mixture was then aged overnight with stirring without feeding. Finally, the obtained precursor material was repeatedly washed with deionized water, filtered until the pH value was neutral, and dried in an 80°C forced-air oven for 24 h to prepare Ni. 0.78 Co0. 11 Mn 0.11 (OH)2 precursor materials;

[0090] S6) Ni 0.78 Co 0.11 Mn 0.11 The (OH)2 precursor material and LiOH•H2O lithium salt were uniformly mixed in a mortar at a molar ratio of 1:1.05, placed in a corundum crucible, and calcined at high temperature in a muffle furnace under an air atmosphere. The specific calcination process was as follows: first, calcination was carried out at a low temperature of 500°C for 3 hours, then the temperature was continuously increased to 850°C for sintering for 10 hours. After completion, the mixture was allowed to cool naturally to room temperature to obtain the ternary cathode material Ni. 0.78 Co 0.11 Mn 0.11 (OH)2 was sieved through a 300-mesh screen and stored in a glove box for later use.

[0091] Preparation of modified cathode materials:

[0092] S7) The oxide and ternary cathode material are mixed in a high-speed mixer at a certain mass ratio. The speed is set to 850 rpm / min and the mixing time is 30 min. The mixed material is sintered in a nitrogen atmosphere at 400°C for 12 h to complete the preparation of the solid electrolyte coated cathode material. The mass content of the oxide, i.e., LMFO, relative to the ternary cathode material is 0.6%.

[0093] Example 2

[0094] In Example 1, LMFO was replaced with LMFO-Al&Ta, that is, aluminum source and tantalum source were added in S1, and the other steps were the same, to obtain LMFO containing aluminum and tantalum and denoted as LMFO-Al&Ta, wherein the content of aluminum relative to the total mass of oxides was 2.0% and the content of tantalum relative to the total mass of oxides was 1.5%.

[0095] Examples 3 to 5

[0096] Except for adjusting the preparation parameters according to Table 1, the remaining parameters of Examples 3 to 5 are the same as those of Example 2.

[0097] Example 6

[0098] This embodiment provides a ternary cathode material modified with a solid electrolyte coating of a NASICON-type oxide, denoted as NCM78@LATP, wherein the NASICON-type oxide is Li. 1.3 Al 0.3 Ti 1.7 (PO4)3 was obtained through market purchase. The preparation methods of the ternary cathode material and the modified cathode material are the same as in Example 1.

[0099] Example 7

[0100] This embodiment provides a ternary cathode material NCM78@LLZO modified with a solid electrolyte coating containing a garnet-type oxide, wherein the garnet-type oxide is Li7La3Zr2O. 12 The materials were obtained through market purchases, and the preparation methods for the ternary cathode material and the modified cathode material were the same as in Example 1.

[0101] Comparative Example 1

[0102] This comparative example provides a ternary cathode material without oxide coating modification. Its preparation method is the same as steps S4-S6 in Example 1. The cathode material obtained is denoted as NCM78@Base.

[0103] Table 1. Positive electrode materials obtained in Examples 1 to 7 and Comparative Example 1

[0104]

[0105] The relevant parameters and properties of the active materials prepared in the above embodiments and comparative examples were tested using the aforementioned test methods. The oxide solid electrolyte LMFO-Al&Ta prepared in Example 2 was analyzed by electron microscopy (SEM) as shown below. Figure 1 As shown, the XRD pattern is as follows Figure 2 As shown in Table 2, the basic physical property data are shown in Table 2; the SEM image of the coated modified NCM78@0.6%LMFO-Al&Ta material obtained in Example 2 is shown in Table 2. Figure 3 As shown. The SEM image of the coated and modified NCM78@0.9%LMFO-Al&Ta material obtained in Example 3 is shown below. Figure 4 As shown. The SEM image of the coated and modified NCM78@1.2%LMFO-Al&Ta material obtained in Example 4 is shown below. Figure 5As shown. The SEM image of the coated and modified NCM78@1.5%LMFO-Al&Ta material obtained in Example 5 is shown below. Figure 6 As shown. The SEM image of the coated / modified NCM78@LATP material obtained in Example 6 is shown below. Figure 7 As shown. The SEM image of the coated and modified NCM78@LLZO material obtained in Example 7 is shown below. Figure 8 As shown.

[0106] SEM images of the NCM78@Base material obtained in Comparative Example 1 are shown below. Figure 9 As shown.

[0107] Figure 3-6 In the middle, the large particles are ternary cathode materials, and the small particles on the surface are oxide-coated materials. It can be seen that the oxide is coated in an island-like manner on the surface of the ternary cathode material.

[0108] The XRD pattern of the solid electrolyte LMFO-Al&Ta is shown. The red peak at the bottom of the figure is the peak pattern of the standard card, and the black peak at the top is the peak pattern obtained in this application. The figure shows that the diffraction peaks of the material are consistent with those of the standard card PDF:97-042-1960, and there are no impurities.

[0109] The basic physical property data of the oxides LMFO and LMFO-Al&Ta in Examples 1 and 2 obtained in this application are shown in Table 2 below:

[0110] Table 2. Basic physical property data of LMFO and LMFO-Al&Ta

[0111]

[0112] As shown in Table 2, LMFO-Al&Ta has smaller particles and higher ionic conductivity compared to basic LMFO.

[0113] This application tested the thermal properties of the aforementioned embodiments and comparative examples, and the test results are shown in Table 3:

[0114] Table 3 Thermal properties of the modified cathode materials obtained in Examples 1 to 7 and the cathode material obtained in Comparative Example 1

[0115]

[0116] As shown in Table 3, in all embodiments with different contents of LMFO-Al&Ta, the peak temperature of differential scanning calorimetry (DSC) of the ternary cathode material was significantly increased (by about 5-10°C), indicating that its thermal performance was improved.

[0117] Examples 8 to 14

[0118] Examples 8 to 14 all provide a button cell, wherein the button cell is prepared by the following method:

[0119] Preparation of the positive electrode sheet: The positive active material of the electrode sheet is the solid electrolyte-coated modified ternary positive electrode material NCM78@0.6%LMFO prepared in Example 1. The preparation method of the positive electrode sheet includes: mixing the positive active material NCM78@0.6%LMFO, conductive agent, and binder P in a mass ratio of 96:2:2 with solvent NMP to form a uniform slurry, and uniformly coating it on the positive current collector aluminum foil to obtain the positive electrode sheet;

[0120] Assembly of coin cell battery: The aforementioned positive electrode, separator, electrolyte and lithium metal sheet are assembled, wherein the separator is a polyethylene film, the electrolyte is 1 mol / L LiPF6 dissolved in a solvent system with a volume ratio of EC:EMC=3:7, the negative electrode is a lithium metal sheet, the battery is a 2025 type coin cell, and performance testing is carried out in the voltage range of 2.8-4.45V.

[0121] Comparative Example 2

[0122] The positive electrode material prepared in Comparative Example 1 was used as the positive electrode active material, and lithium metal half-cells were prepared according to the methods shown in Examples 8 to 14.

[0123] Examples 15 to 18

[0124] Examples 15 to 18 all provide a pouch cell; the pouch cell is prepared using the following method:

[0125] The positive electrode sheet is prepared by means of the positive active material of the electrode sheet being the ternary positive electrode material NCM78@0.6%LMFO prepared in Example 1. The preparation method of the positive electrode sheet includes: mixing the positive active material NCM78@0.6%LMFO, conductive agent, and binder P in a mass ratio of 96:2:2 with solvent NMP to form a uniform slurry, and uniformly coating it on the positive current collector aluminum foil to obtain the positive electrode sheet.

[0126] Soft-pack full battery assembly: using the aforementioned positive electrode, separator, electrolyte, and silicon-carbon negative electrode, wherein the separator is a base film with a double-layer solid electrolyte coating, the electrolyte is 1 mol / L LiPF6 dissolved in a solvent system with a volume ratio of EC:EMC=3:7, and the negative electrode is a silicon-carbon negative electrode, which includes graphite, silicon-carbon, conductive agent, and binder, mixed in a certain proportion (75:17.5:2.5:5.0);

[0127] Comparative Example 3

[0128] Using the positive electrode material prepared in Comparative Example 1 as the positive electrode active material, soft-pack full cells were prepared according to the methods shown in Examples 15 to 18.

[0129] Table 4. Positive electrode active materials used in Examples 8 to 18

[0130]

[0131] The relevant parameters and properties of the active materials prepared in the above embodiments and comparative examples were tested using the above testing methods. The results are shown in Tables 5 and 6.

[0132] Table 5. Basic electrochemical performance test data of lithium metal half-cells in comparative examples and individual embodiments.

[0133]

[0134] Table 6. Basic electrochemical performance test data of pouch cells in comparative examples and embodiments.

[0135]

[0136] The results presented in Table 5 show that the button cells of Examples 9-12 provided in this application have better first-efficiency performance, capacity utilization, and rate performance than Comparative Example 2 and Examples 13 and 14.

[0137] The results presented in Table 6 show that the first-efficiency performance, capacity utilization, and rate performance of the pouch cell of Example 15 provided in this application are all superior to those of Comparative Example 3 and Examples 17 and 18.

[0138] The specific embodiments of this application have been described in detail above, but they are merely examples, and this application is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to this application are also within the scope of this application. Therefore, all equivalent changes and modifications made without departing from the spirit and scope of this application should be covered within the scope of this application.

Claims

1. A modified cathode material, characterized in that, The modified cathode material includes: Ternary cathode materials; An oxide coating on the surface of a ternary cathode material, wherein the coating is an island-like coating, and the general chemical formula of the oxide is: Li 2-x A (1+x) / 3 B2O6F, 0.7≤x≤0.8; the A includes La and Al; the content of Al relative to the total mass of the oxide is 1.8%~2.2%; The B includes Nb and Ta; the content of Ta relative to the total mass of the oxide is 1.3%~1.7%; The oxide content accounts for 0.6% to 1.5% of the total mass of the modified cathode material.

2. The modified cathode material according to claim 1, characterized in that, The particle size D50 of the modified cathode material ranges from 3.3 μm to 3.7 μm.

3. The modified cathode material according to claim 1, characterized in that, The particle size of the oxide coating on the surface of the ternary cathode material is 0.4 μm to 0.6 μm.

4. A method for preparing the modified cathode material as described in claim 1, characterized in that, The oxide was prepared by the following method: Source A, source B, and LiF were selected according to the general chemical formula Li 2-x A (1+x) / 3 The first mixture was obtained by uniformly mixing B2O6F according to the stoichiometric ratio shown. The first mixture was calcined at 800℃~1200℃ for 3h~5h, then ground, and the second part of LiF was added and mixed evenly to obtain the second mixture; the mass of the second part of LiF was 1~2 times the mass of LiF in the first mixture. The second mixture was dried under vacuum and then pressed into tablets. The tablets were then sintered at a nitrogen atmosphere and a temperature of 1000℃~1200℃ for 5h~7h. The sintered material was then crushed and ground to obtain the oxide.

5. The method for preparing the modified cathode material according to claim 4, characterized in that, The modified cathode material was prepared by the following method: The oxide and the ternary cathode material are mixed to obtain a third mixture. The third mixture is then placed in a nitrogen atmosphere and sintered at 400℃~500℃ for 10~12h to obtain the modified cathode material.

6. A positive electrode sheet for a battery, characterized in that, The modified cathode material includes the modified cathode material according to any one of claims 1 to 3 or the modified cathode material prepared by the method according to any one of claims 4 to 5.

7. A secondary battery, characterized in that, Including the modified cathode material as described in claim 6.

8. An electronic device, characterized in that, The electronic device includes the secondary battery as described in claim 7.

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