Nano single-crystal positive electrode material and preparation method thereof, solid-state battery and electric equipment

Abstract

The invention provides a nano single-crystal positive electrode material and a preparation method thereof, a solid-state battery and electric equipment, and relates to the field of solid-state batteries. The nano single crystal positive electrode material comprises an inner core, and a first coating layer, a second coating layer and a third coating layer which are sequentially stacked on the surface of the inner core, the chemical general formula of the inner core is LiaNixCoyMnzMwO2, a is more than or equal to 1.02 and less than or equal to 1.2, x is more than or equal to 0.8 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 0.2, z is more than or equal to 0 and less than or equal to 0.1, w is more than or equal to 0 and less than or equal to 0.03, x + y + z + w = 1, and M comprises one or more of Zr, Sr, Y, Sb, Al, W, Ta, Mg, Ca, Ti, Mo and Nb; the first coating layer comprises a transition metal compound; the second coating layer comprises a boron-containing compound; the third coating layer includes a sulfide. The three coating layers of the nano single-crystal positive electrode material are progressive layer by layer, so that the electrochemical performance of the nano single-crystal positive electrode material is improved.

Description

Technical Field

[0001] The present application relates to the field of solid-state batteries, and in particular to a nano single crystal positive electrode material and a preparation method thereof, a solid-state battery and an electrical device. Background Art

[0002] Currently, solid-state battery cathode materials still face problems such as small contact area, low contact quality, and poor interfacial circulation during use, which further limits the application of solid-state batteries. In order to further improve the energy density of solid-state batteries and the interfacial contact between the material and the solid electrolyte, nano-crystallization of cathode materials is a very suitable method. It can increase the contact area and contact quality between the material and the electrolyte, and can also improve the compaction density and energy density of the material by blending with other cathode materials through grading.

[0003] However, due to its small particle size, nano-single-crystal positive electrode material will inevitably agglomerate, and due to the increase in specific surface area, its sensitivity to air increases, which will lead to an increase in residual lithium; and nano-single-crystal positive electrode material is not easy to disperse, and there will be problems in its performance in solid-state batteries, resulting in poor capacity and many interfacial side reactions.

[0004] Based on this, there is an urgent need to provide a nano-single-crystal positive electrode material to solve the above problems. Summary of the Invention

[0005] The purpose of this application is to provide a nano single crystal positive electrode material and a preparation method thereof, a solid-state battery and an electrical device to solve the above problems.

[0006] To achieve the above objectives, the present application provides a nano single crystal positive electrode material in a first aspect, comprising a core and a first coating layer, a second coating layer and a third coating layer sequentially stacked on the surface of the core; The chemical formula of the core is Li a Ni x Co y Mn z M w O2, wherein 1.02≤a≤1.2, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.1, 0≤w≤0.03, x+y+z+w=1, and M includes one or more of Zr, Sr, Y, Sb, Al, W, Ta, Mg, Ca, Ti, Mo, and Nb; The first coating layer includes a transition metal compound; The second coating layer includes a boron-containing compound; The third coating layer includes a sulfur-containing compound.

[0007] Optionally, the nano single crystal cathode material satisfies at least one of the following conditions: (1) The nano single crystal cathode material comprises a polyhedral structure; (2) The average side length of the nano single crystal positive electrode material is 50-800 nm, and the average thickness is 20-400 nm; (3) The D50 of the nano single crystal positive electrode material is 0.3 μm-1.1 μm, and the D100 is 1.5 μm-3.5 μm; (4) The specific surface area of ​​the nano single crystal positive electrode material is 2.1m 2 / g-5.4m 2 / g; (5) The half-peak width of the nano single crystal positive electrode material is 0.205-0.425; (6) The relative surface energy of the 003 crystal plane of the nano single crystal positive electrode material is 2 J / m 2 -4J / m 2 ; (7) The relative surface energy of the 104 crystal face of the nano single crystal positive electrode material is 1.0 J / m 2 -1.5J / m 2 ; (8) The relative surface energy of the 101 crystal plane of the nano single crystal positive electrode material is 1.5 J / m 2 -2J / m 2 .

[0008] Optionally, the nano single crystal cathode material satisfies at least one of the following conditions: (1) In the general chemical formula of the core, 1.05≤a≤1.15, 0.8≤x≤0.98; (2) M includes one or more of Zr, Al, W, Ti and Nb; (3) The first coating layer Raw materials Including transition metal salts, the transition metal salts include ammonium tungstate, ammonium molybdate, tungsten trioxide, lithium tungstate, lithium molybdate, molybdenum trioxide, titanium dioxide, aluminum oxide, lithium phosphate, ammonium phosphate, lithium niobate, lithium zirconium phosphate, lithium aluminate, Li 1.3 Al 0.3 Ti 1.7 (PO4)3、Li 1.5 Al 0.5 Ge 1.5 One or more of (PO4)3, Li3YCl6, Li3YBr6, LiTaQ3, lithium silicate and lithium titanate; (4) The boron-containing compound includes one or more of boric acid, lithium borate, boron trioxide, LiBa(B3O3)3 (LBBO), niobium diboride, aluminum boride and titanium boride; (5) The sulfur-containing compound includes Li 10 GeP2S10 , Li3PS4, lithium sulfide, tungsten disulfide, molybdenum disulfide, iron sulfide, Li 10 GeP2S 12 、β-Li3PS4、Li 3.25 Ge 0.25 P 0.75 S4 and Li6PS5Cl x One or more of .

[0009] The second aspect of the present application provides a method for preparing the nano single crystal positive electrode material, comprising: Ni x Co y Mn z (OH)2, a dispersant, a lithium salt, a dopant containing M and a molten salt are first mixed to obtain a first mixture, and the first mixture is first sintered in an oxygen-containing atmosphere to obtain a first sintered product; performing a second mixing of the first sintered product and a transition metal salt to obtain a second mixture, and performing a second sintering of the second mixture in an oxygen-containing atmosphere to obtain a second sintered product; performing a third mixing of the second sintered product and a boron-containing compound to obtain a third mixture, and performing a third sintering of the third mixture under an oxygen-containing atmosphere to obtain a third sintered product; The third sintered product is mixed with a sulfur-containing compound for a fourth time to obtain a fourth mixture. The fourth mixture is sintered for a fourth time under an inert atmosphere to obtain a nano single crystal positive electrode material.

[0010] Optionally, the method for preparing the nano single crystal positive electrode material satisfies at least one of the following conditions: (1) The dispersant includes one or more of polyacrylate, polyvinyl pyrrolidone, sodium dodecylbenzene sulfonate, sodium hexametaphosphate, stearic acid, lecithin, fatty acid glyceride, polysorbate, sodium dioctyl sulfosuccinate, Span 20-80, Tween 20-80, polyoxyethylene fatty acid ester, oleic acid, alkaline earth metal soap, lauric acid, palmitic acid, alkali metal soap and organic amine soap; (2) The molten salt includes one or more of lithium chloride, potassium chloride, sodium chloride, sodium nitrate, potassium nitrate and lithium nitrate; (3) The M-containing dopant includes one or more of an oxide, hydroxide, nitrate, or carbonate containing M; (4) Ni x Co y Mn z The D50 of (OH)2 is 0.1μm-0.6μm, and the D100 is 0.7μm-2μm; (5) The lithium salt includes one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium oxide, lithium sulfide, lithium acetate and methyl lithium.

[0011] Optionally, the method for preparing the nano single crystal positive electrode material satisfies at least one of the following conditions: (1) The dispersant and the Ni x Co y Mn z The mass ratio of (OH)2 is 0.005-0.015:1; (2) The molten salt and the Ni x Co y Mn z The mass ratio of (OH)2 is 0.05-10:1; (3) Li in the lithium salt, M in the M-containing dopant, and Ni x Co y Mn z The molar ratio of (OH)2 is 1.02-1.6:0-0.03:1; (4) The concentration of the transition metal salt in the second mixture is 500 ppm to 1500 ppm; (5) The concentration of the boron-containing compound in the third mixture is 500 ppm to 2500 ppm; (6) The concentration of the sulfur-containing compound in the fourth mixture is 500 ppm to 2000 ppm; (7) Ni x Co y Mn z The D50 of (OH)2 is 0.3μm-0.5μm, and the D100 is 0.75μm-1.1μm; (8) The molten salt includes lithium chloride and / or potassium chloride.

[0012] Optionally, the method for preparing the nano single crystal positive electrode material satisfies at least one of the following conditions: (1) The first sintering includes low-temperature sintering and high-temperature sintering performed sequentially; The low-temperature sintering has a heating rate of 5°C / min-12°C / min, an end temperature of 250°C-550°C, and a constant temperature time of 1h-24h; The high temperature sintering has a heating rate of 2°C / min-15°C / min, an end temperature of 500°C-800°C, and a constant temperature time of 4h-16h; (2) The second sintering has a heating rate of 1°C / min-10°C / min, an end temperature of 250°C-700°C, and a constant temperature time of 1h-24h; (3) The third sintering has a heating rate of 1°C / min-10°C / min, an end temperature of 250°C-550°C, and a constant temperature time of 1h-24h; (4) The fourth sintering has a heating rate of 1°C / min-10°C / min, an end temperature of 250°C-350°C, and a constant temperature time of 1h-24h; (5) The cooling rates of the first sintering, the second sintering, the third sintering, and the fourth sintering are each independently 1°C / min to 8°C / min; (6) The first mixing includes two mixing steps: x Co y Mn z (OH)2 and a dispersant are mixed for a fifth time to obtain a fifth mixture, and the fifth mixture is sand-milled to obtain a sand-milled material; performing a sixth mixing of the sand-milled material, the lithium salt, the M-containing dopant, and the molten salt; (7) The first sintered product is further washed, crushed, and dried before the second mixing; (8) The oxygen mass content of the first sintering, the second sintering, and the third sintering is independently 90%-100%.

[0013] Optionally, the method for preparing the nano single crystal positive electrode material satisfies at least one of the following conditions: (1) The stirring speed of the sand mill is 1000 rpm-2500 rpm, the frequency is 10 Hz-50 Hz, the pumping time is 60 times / min-85 times / min, the solid content is 10%-80%, and the sand milling time is 0.1h-8h; (2) The water washing temperature is 2°C-15°C, the time is 0.5min-15min, and the solid-liquid ratio of the water washing is 0.5-2:1.

[0014] The third aspect of the present application provides a solid-state battery, comprising the nano single crystal positive electrode material or the nano single crystal positive electrode material prepared by the preparation method of the nano single crystal positive electrode material.

[0015] A fourth aspect of the present application provides an electrical device comprising the solid-state battery.

[0016] Compared with the prior art, the advantages of this application include: The nano single crystal positive electrode material provided by the present application has a core with a polyhedral nano single crystal structure, which reduces grain boundary fracture, reduces stress concentration and microcracks caused by anisotropic volume changes, and improves lithium ion diffusion kinetics by exposing specific active interfaces; the first coating layer is in close contact with the core matrix material, reducing interface impedance, optimizing interface contact and electrochemical stability, so that the ionic conductivity between particles is improved; the boron-containing compound of the second coating layer acts as a dielectric layer and a buffer layer, which can be in close contact with the inner transition metal compound layer and the outer sulfur-containing compound layer, and it has good contact with the first coating layer and the sulfur-containing compound layer, with small interface reaction. The glassy boron-containing compound has a certain deformation ability, which helps to maintain close contact of the interface, form a stable interface layer, and inhibit continuous interface side reactions; the sulfur-containing compound of the third coating layer has good contact with the electrolyte, optimizes the interface compatibility between the positive electrode material and the sulfur-containing compound electrolyte, increases the contact area between the positive electrode material particles and the electrolyte, and reduces the interface impedance; the three coating layers are progressively applied layer by layer to improve the electrochemical properties of the nano single crystal positive electrode material.

[0017] The preparation method of the nano single crystal positive electrode material provided by the present application, the introduction of composite molten salt during the sintering process improves the dispersibility between the positive electrode material particles, and the addition of dispersant and molten salt successfully prepares the nano single crystal core; a multi-layer coating structure is prepared by a multi-stage sintering coating process, the introduction of transition metal salt is to generate fast ion conductors or oxides on the surface of the nano single crystal, thereby improving the ionic conductivity between the nano single crystal particles; the coating of boron-containing compounds can reduce the direct contact between the active material and the electrolyte, inhibit the side reaction between the positive electrode and the sulfur-containing compound electrolyte, and improve the cycle performance; the introduction of sulfur-containing compounds optimizes the interface compatibility between the positive electrode and the sulfur-containing compound electrolyte, increases the contact area between the positive electrode particles and the electrolyte, and reduces the interface impedance. The technical solution of the present application combines the ionic conductivity improvement effect of the transition metal oxide layer, the side reaction inhibition effect of the boron coating layer, and the interface compatibility improvement effect of the sulfur coating layer and the sulfur-containing compound electrolyte, and plays a comprehensive synergistic effect, and finally obtains a nano single crystal positive electrode material with high dispersibility, stable interface structure, excellent first charge and discharge efficiency and cycle performance.

[0018] The solid-state battery and electrical equipment of the nano single crystal positive electrode material provided in this application have excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0020] Figure 1 This is an SEM image of the nano single crystal positive electrode material provided in Example 1; Figure 2 This is the XRD pattern of the nano single crystal positive electrode material provided in Example 1. DETAILED DESCRIPTION

[0021] First, the solution provided in this application is explained in more detail as follows: In a first aspect, the present application provides a nano single crystal positive electrode material, comprising a core and a first coating layer, a second coating layer and a third coating layer sequentially stacked on the surface of the core; The chemical formula of the core is Li a Ni x Co y Mn z M w O2, wherein 1.02≤a≤1.2, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.1, 0≤w≤0.03, x+y+z+w=1, and M includes one or more of Zr, Sr, Y, Sb, Al, W, Ta, Mg, Ca, Ti, Mo, and Nb; Optionally, the chemical formula of the core is Li a Ni x Co y Mn z M w In O2, a may be 1.02, 1.05, 1.1, 1.15, 1.2, or any value between 1.02 and 1.2; x may be 0.8, 0.85, 0.9, 0.95, 1, or any value between 0.8 and 1; y may be 0, 0.05, 0.1, 0.15, 0.2, or any value between 0 and 0.2; z may be 0, 0.05, 0.1, or any value between 0 and 0.1; and w may be 0, 0.001, 0.005, 0.01, 0.02, 0.03, or any value between 0 and 0.03; Preferably, 0.02≤y≤0.1, 0.01≤z≤0.06, 0.0005≤w≤0.015; The first coating layer includes a transition metal compound; The second coating layer includes a boron-containing compound; The third coating layer includes a sulfur-containing compound.

[0022] It should be noted that the third coating layer can optimize the interfacial compatibility between the nano-single crystal positive electrode material and the sulfur-containing compound electrolyte, increase the contact area between the nano-single crystal positive electrode material particles and the electrolyte, and reduce the interfacial impedance.

[0023] In some embodiments, the nano single crystal cathode material satisfies at least one of the following conditions: (1) The nano single crystal cathode material comprises a polyhedral structure; (2) The average side length of the nano single crystal positive electrode material is 50-800 nm, preferably 100-400 nm, and the average thickness is 20-400 nm, preferably 100-350 nm; Optionally, the average side length of the nano single crystal positive electrode material may be 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm or any value between 50 and 800 nm, and the average thickness may be 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm or any value between 20 and 400 nm; It should also be noted that the side length of the nano single crystal positive electrode material refers to the main geometric dimension of the single crystal particle on the two-dimensional plane (such as the side length of a square, rectangle or polygon), and the thickness (height) of the nano single crystal positive electrode material refers to the dimension of the single crystal particle in the direction perpendicular to the two-dimensional plane; and the average side length and average thickness of the primary particles refer to randomly selecting ≥30 primary particles with clear outlines, measuring their side lengths and thicknesses respectively, and calculating their average side lengths and average thicknesses respectively; (3) The D50 of the nano single crystal positive electrode material is 0.3 μm-1.1 μm, and the D100 is 1.5 μm-3.5 μm; Optionally, the D50 of the nano single crystal positive electrode material may be 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm or any value between 0.3 μm and 1.1 μm, and the D100 may be 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm or any value between 1.5 μm and 3.5 μm; (4) The specific surface area of ​​the nano single crystal positive electrode material is 2.1m 2 / g -5.4m 2 / g; Optionally, the specific surface area of ​​the nano single crystal cathode material can be 2.1m 2 / g, 2.5m 2 / g、3m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g, 5.4m 2 / g or 2.1m 2 / g -5.4m 2 Any value between / g; (5) The half-peak width of the nano single crystal positive electrode material is 0.205-0.425; Optionally, the half-value width of the nano single crystal positive electrode material can be 0.205, 0.25, 0.3, 0.35, 0.4, 0.425 or any value between 0.205 and 0.425; (6) The relative surface energy of the 003 crystal plane of the nano single crystal positive electrode material is 2 J / m 2 -4J / m 2 ; Optionally, the relative surface energy of the 003 crystal plane of the nano single crystal positive electrode material can be 2 J / m 2 、3J / m 2 , 4J / m 2 or 2J / m 2 -4J / m 2 Any value between It should be noted that the surface energy of the 003 crystal plane is significantly higher than that of the 104 crystal plane due to the charge imbalance and the large number of dangling bonds. This crystal plane has the highest surface energy because the exposed O 2- Ions lead to an imbalance in surface charge and strong electrostatic repulsion, resulting in a lack of strong TM-O bonds (transition metal-oxygen bonds) to stabilize the surface, leading to high surface energy. During the formation of cathode materials, in order to minimize the total surface energy, the crystals will preferentially grow rapidly in the direction perpendicular to the (003) plane, minimizing or even eliminating the high-energy 003 plane area (or not being exposed in the equilibrium state), ultimately forming a polyhedron; (7) The relative surface energy of the 104 crystal face of the nano single crystal positive electrode material is 1.0 J / m 2 -1.5J / m 2 ; Optionally, the relative surface energy of the 104 crystal plane of the nano single crystal positive electrode material can be 1.0 J / m 2 , 1.1J / m 2 , 1.2J / m 2 , 1.3J / m 2 , 1.4J / m 2 , 1.5J / m 2 or 1.0 J / m 2 -1.5J / m 2 Any value between It should be noted that the 104 crystal plane is the most stable low-energy plane. Theoretical calculations and experiments show that it has the lowest surface energy. + , TM ions and O 2- The 104 crystal face family is the most stable and most exposed crystal face because of its relatively low surface energy, which allows it to be retained under near-equilibrium growth conditions. The 104 crystal face is one of the main channels for lithium ion insertion / deinsertion, has high reactivity, and is also a key face for material structural stability. (8) The relative surface energy of the 101 crystal plane of the nano single crystal positive electrode material is 1.5 J / m 2 -2J / m 2 .

[0024] Optionally, the relative surface energy of the 101 crystal plane of the nano single crystal positive electrode material can be 1.5 J / m 2 , 1.6J / m 2 , 1.7J / m 2 , 1.8J / m 2 , 1.9J / m 2 , 2J / m 2 or 1.5 J / m 2 -2J / m 2 Any value in between.

[0025] It should be noted that the 101 crystal plane is mainly composed of transition metals and oxygen, and its thermodynamic stability is at a medium level.

[0026] In some embodiments, the nano single crystal cathode material satisfies at least one of the following conditions: (1) In the general chemical formula of the core, 1.05≤a≤1.15, 0.8≤x≤0.98; Optionally, in the chemical formula of the kernel, a may be 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, or any value between 1.05 and 1.15, and x may be 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, or any value between 0.8 and 0.98; (2) M includes one or more of Zr, Al, W, Ti and Nb; (3) The raw materials of the first coating layer include transition metal salts, and the transition metal salts include ammonium tungstate, ammonium molybdate, tungsten trioxide, lithium tungstate, lithium molybdate, molybdenum trioxide, titanium dioxide, aluminum oxide, lithium phosphate, ammonium phosphate, lithium niobate, lithium zirconium phosphate, lithium aluminate, Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (lithium aluminum titanium phosphate, referred to as LATP), Li 1.5 Al 0.5 Ge 1.5(PO4)3 (lithium aluminum germanium phosphate, abbreviated as LAGP), Li3YCl6, Li3YBr6, LiTaQ3, one or more of lithium silicate and lithium titanate, preferably including one or more of lithium tungstate, lithium molybdate and lithium phosphate; regarding the above-mentioned lithium tungstate, lithium molybdate and lithium phosphate, since they contain specific transition metals and lithium atoms at the same time, they are conducive to the fast ion conductivity on the surface of nano single crystal particles.

[0027] (4) The boron-containing compound includes one or more of boric acid, lithium borate, boron trioxide, LiBa(B3O3)3 (LBBO), niobium diboride, aluminum boride, and titanium boride, preferably one or more of niobium diboride, aluminum boride, and titanium boride. Niobium diboride, aluminum boride, and titanium boride, because they contain both boron and niobium or aluminum or titanium, have excellent interfacial adsorption and control properties, can anchor transition metal compounds and sulfides on both sides, and improve interfacial stability.

[0028] (5) The sulfur-containing compound includes Li 10 GeP2S 10 (abbreviated as LGPS), Li3PS4 (abbreviated as LPS), lithium sulfide, tungsten disulfide, molybdenum disulfide, iron sulfide, Li 10 GeP2S 12 、β-Li3PS4、Li 3.25 Ge 0.25 P 0.75 S4 and Li6PS5Cl x One or more of, preferably lithium sulfide, tungsten disulfide, molybdenum disulfide, iron sulfide, Li 10 GeP2S 12 、β-Li3PS4、Li 3.25 Ge 0.25 P 0.75 S4 and Li6PS5Cl x One or more of, more preferably including one or more of lithium sulfide, tungsten disulfide, molybdenum disulfide, and iron sulfide; by containing sulfur element and specific metal element, it can exert affinity with sulfide electrolyte material, increase the contact area between positive electrode particles and electrolyte, and reduce interface impedance.

[0029] The second aspect of the present application provides a method for preparing the nano single crystal positive electrode material, comprising: Ni x Co y Mn z (OH)2, a dispersant, a lithium salt, a dopant containing M and a molten salt are first mixed to obtain a first mixture, and the first mixture is first sintered in an oxygen-containing atmosphere to obtain a first sintered product; It should be noted that the introduction of molten salt during the sintering process can prevent the agglomeration and growth of the nano-single crystal during the sintering process, form a complete nano-single crystal morphology, and promote the formation of a complete lattice. The introduction of the composite molten salt can reduce the melting point and improve the thermal stability on the one hand, and improve the melting effect of the molten salt on the other hand. After the molten salt is melted, it is dispersed between the nano-precursor and the lithium salt, so that the positive electrode particles will not agglomerate together during the reaction between the precursor and the lithium salt. In addition, the crystal structure of the high nickel ternary material (layered oxide, space group R3m) is a hexagonal system. The viscosity and surface tension of the molten salt cause the crystal to move vertically along the 00 The 3-dimensional crystal face, i.e., the 001 direction, preferentially grows. Anions or cations in the molten salt can selectively adsorb on specific crystal faces during crystal growth. This adsorption can change the relative surface energy of different crystal faces or hinder the growth rate of certain crystal faces, thereby affecting the type of crystal face ultimately exposed and helping to form a specific polyhedral structure (such as promoting the exposure of the 104 crystal face). The molten salt may also provide a specific chemical environment to stabilize certain low-energy faces. In addition, the viscosity and ionic environment of the molten salt can act as a "soft template" to regulate the anisotropic growth of the crystals, thereby forming a polyhedral structure with more distinct particle edges. This can be understood as follows: during crystal growth, to minimize total surface energy, the crystal preferentially grows perpendicular to the 003 crystal plane, or 001 plane. The 003 crystal plane has the highest surface energy, and the crystal minimizes the area of ​​the high-energy 003 crystal plane by rapidly growing along the c-axis. Because of this rapid growth along the 001 crystal plane, the resulting crystal typically expands relative to the direction perpendicular to the c-axis (i.e., within the ab plane), forming a flat or plate-like polyhedron (e.g., a hexagonal plate, whose largest face is typically the 001 crystal plane). performing a second mixing of the first sintered product and a transition metal salt to obtain a second mixture, and performing a second sintering of the second mixture in an oxygen-containing atmosphere to obtain a second sintered product; It should be noted that the fast ion conductor is generated by the reaction of the transition metal salt and the residual lithium in the first sintered product, and is coated on the surface of the core nanoparticles, thereby reducing the interface impedance, optimizing the interface contact and electrochemical stability, and improving the ionic conductivity between the particles, thereby further improving the performance of the material in solid-state batteries. performing a third mixing of the second sintered product and a boron-containing compound to obtain a third mixture, and performing a third sintering of the third mixture under an oxygen-containing atmosphere to obtain a third sintered product; It is important to note that the boron compound interface layer generally has high thermal stability. The molten boron phase can wet the surfaces of the positive electrode particles and the solid electrolyte particles. After cooling, it forms a connecting bridge, significantly increasing the contact area between the particles. It can also melt during the high-temperature sintering process. The boron compound interface layer generally has high thermal stability.

[0030] The third sintered product is mixed with a sulfur-containing compound for a fourth time to obtain a fourth mixture. The fourth mixture is sintered for a fourth time under an inert atmosphere to obtain a nano single crystal positive electrode material.

[0031] In some embodiments, the method for preparing the nano single crystal cathode material satisfies at least one of the following conditions: (1) The dispersant includes one or more of polyacrylate, polyvinyl pyrrolidone, sodium dodecylbenzene sulfonate, sodium hexametaphosphate, stearic acid, lecithin, fatty acid glyceride, polysorbate, sodium dioctyl sulfosuccinate, Span 20-80, Tween 20-80, polyoxyethylene fatty acid ester, oleic acid, alkaline earth metal soap, lauric acid, palmitic acid, alkali metal soap and organic amine soap; (2) The molten salt includes one or more of lithium chloride, potassium chloride, sodium chloride, sodium nitrate, potassium nitrate and lithium nitrate; Preferably, the molten salt includes lithium chloride and potassium chloride; in some embodiments, the mass ratio of lithium chloride to potassium chloride is 0.2-0.8:0.2-0.8, and illustratively, the mass ratio of lithium chloride to potassium chloride can be 0.2:0.8, 0.4:0.6, 0.5:0.5, 0.6:0.4, 0.8:0.2 or any value between 0.2-0.8:0.2-0.8; it should be noted that when the mass ratio of lithium chloride to potassium chloride is not within the range of 0.2-0.8:0.2-0.8, too high or too low a ratio will result in poor melting effect; (3) The M-containing dopant includes one or more of an oxide, hydroxide, nitrate, or carbonate containing M; (4) Ni x Co y Mn z The D50 of (OH)2 is 0.1μm-0.6μm, and the D100 is 0.7μm-2μm; Optional, Ni x Co y Mn z The D50 of (OH)2 may be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, or any value between 0.1 μm and 0.6 μm, and the D100 may be 0.7 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, or any value between 0.7 μm and 2 μm; (5) The lithium salt includes one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium oxide, lithium sulfide, lithium acetate and methyl lithium.

[0032] In some embodiments, the method for preparing the nano single crystal cathode material satisfies at least one of the following conditions: (1) The dispersant and the precursor Ni x Co y Mn z The mass ratio of (OH)2 is 0.005-0.015:1; Optional, dispersant and Ni x Co y Mn z The mass ratio of (OH)2 can be 0.005:1, 0.01:1, 0.015:1 or any value between 0.005 and 0.015:1; It should be noted that if the dispersant content is too high, too much dispersant will remain between the precursor particles, which will be brought into the cathode material and affect the material performance. If the dispersant content is too low, the dispersion and deagglomeration effects will not be obvious. (2) The molten salt and the Ni x Co y Mn z The mass ratio of (OH)2 is 0.05-10:1; Optional, molten salt and Ni x Co y Mn z The mass ratio of (OH)2 can be 0.05:1, 0.5:1, 1:1, 2:1, 4:1, 6:1, 8:1, 10:1 or any value between 0.05-10:1; preferably 0.1-8:1, more preferably 0.5-2.0:1.

[0033] It should be noted that when the amount of molten salt is too low, the molten salt will not be able to completely infiltrate the mixture after melting, resulting in poor agglomeration effect, causing the nanoparticles to be unable to disperse and agglomerate severely; when the amount of molten salt is too high, the sintered material will be too hard to be post-processed, and it will hinder the reaction between the lithium salt and the precursor. (3) Li in the lithium salt, M in the M-containing dopant, and Ni x Co y Mn z The molar ratio of (OH)2 is 1.02-1.6:0-0.03:1; Optionally, Li in the lithium salt, M in the M-containing dopant and Ni x Co y Mn zThe molar ratio of (OH)2 can be 1.02:0:1, 1.1:0.01:1, 1.2:0.01:1, 1.3:0.01:1, 1.4:0.01:1, 1.5:0.01:1, 1.6:0.01:1, 1.1:0.02:1, 1.1:0.03:1 or any value between 1.02-1.6:0-0.03:1; (4) The concentration of the transition metal salt in the second mixture is 500 ppm to 1500 ppm; Optionally, the concentration of the transition metal salt in the second mixture may be 500 ppm, 1000 ppm, 1500 ppm, or any value between 500 ppm and 1500 ppm; It should be noted that when the concentration of the transition metal salt is too high, the coating agent content is too high, which increases the impedance and affects the capacity; when the concentration of the transition metal salt is too low, the coating effect will not be obvious. (5) The concentration of the boron-containing compound in the third mixture is 500 ppm to 2500 ppm; Optionally, the concentration of the boron-containing compound in the third mixture may be 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, or any value between 500 ppm and 2500 ppm; It should be noted that when the concentration of the boron-containing compound is too low, the particle surface cannot be effectively coated; when the concentration of the boron-containing compound is too high, too much boron-containing compound will be coated on the particle surface, reducing the capacity; (6) The concentration of the sulfur-containing compound in the fourth mixture is 500 ppm to 2000 ppm; Optionally, the concentration of the sulfur-containing compound in the fourth mixture may be 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, or any value between 500 ppm and 2000 ppm; It should be noted that when the concentration of sulfur-containing compounds is too low, no effective sulfur-containing compound coating can be formed on the surface of the material; when the concentration of sulfur-containing compounds is too high, a thick coating layer will be formed on the surface of the material, affecting the performance; (7) Ni x Co y Mn z The D50 of (OH)2 is 0.3μm-0.5μm, and the D100 is 0.75μm-1.1μm; Optional, Ni x Co y Mn zThe D50 of (OH)2 may be 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, or any value between 0.3 μm and 0.5 μm, and the D100 may be 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.05 μm, 1.1 μm, or any value between 0.75 μm and 1.1 μm; (8) The molten salt includes lithium chloride and / or potassium chloride.

[0034] In some embodiments, the method for preparing the nano single crystal cathode material satisfies at least one of the following conditions: (1) The first sintering includes low-temperature sintering and high-temperature sintering performed sequentially; The low-temperature sintering has a heating rate of 5°C / min-12°C / min, an end temperature of 250°C-550°C, and a constant temperature time of 1h-24h; Optionally, the heating rate of low-temperature sintering can be 5°C / min, 6°C / min, 8°C / min, 10°C / min, 12°C / min, or any value between 5°C / min and 12°C / min; the endpoint temperature can be 250°C, 300°C, 400°C, 500°C, 550°C, or any value between 250°C and 550°C; and the constant temperature time can be 1h, 4h, 8h, 12h, 16h, 20h, 24h, or any value between 1h and 24h. The high temperature sintering has a heating rate of 2°C / min-15°C / min, an end temperature of 500°C-800°C, and a constant temperature time of 4h-16h; Optionally, the heating rate of high-temperature sintering can be 2°C / min, 4°C / min, 5°C / min, 6°C / min, 8°C / min, 10°C / min, 12°C / min, 15°C / min or any value between 2°C / min and 15°C / min, the end temperature can be 500°C, 600°C, 700°C, 800°C or any value between 500°C and 800°C, and the constant temperature time can be 4h, 8h, 12h, 16h or any value between 4h and 16h; It should be noted that low-temperature sintering is to fully melt the lithium salt. When the temperature of low-temperature sintering is too low, the lithium salt has not yet fully melted, which will affect the subsequent reaction between the lithium salt and the precursor. When the temperature of low-temperature sintering is too high, the lithium salt may react with the precursor in an incompletely melted state in advance, resulting in agglomeration. When the temperature of high-temperature sintering is too low, the lithiation reaction cannot be fully carried out. When the temperature is too high, over-burning may occur, and serious lithium volatilization may occur. (2) The second sintering has a heating rate of 1°C / min-10°C / min, an end temperature of 250°C-700°C, and a constant temperature time of 1h-24h; Optionally, the heating rate of the second sintering may be 1°C / min, 2°C / min, 4°C / min, 6°C / min, 8°C / min, 10°C / min, or any value between 1°C / min and 10°C / min; the endpoint temperature may be 250°C, 300°C, 400°C, 500°C, 600°C, 700°C, or any value between 250°C and 700°C; and the constant temperature time may be 1h, 4h, 8h, 12h, 16h, 20h, 24h, or any value between 1h and 24h. It should be noted that if the end temperature of the second sintering is too high, the coating material will be sintered and melted into the material, and it will not be able to form an effective coating on the material surface; if the end temperature of the second sintering is too low, it will not be able to effectively coat the material surface. (3) The third sintering has a heating rate of 1°C / min-10°C / min, an end temperature of 250°C-550°C, and a constant temperature time of 1h-24h; Optionally, the heating rate of the third sintering can be 1°C / min, 2°C / min, 4°C / min, 6°C / min, 8°C / min, 10°C / min, or any value between 1°C / min and 10°C / min; the endpoint temperature can be 250°C, 300°C, 400°C, 500°C, or any value between 250°C and 500°C; and the constant temperature time can be 1h, 4h, 8h, 12h, 16h, 20h, 24h, or any value between 1h and 24h. It should be noted that if the end point temperature of the third sintering is too low, the boron-containing compound coating layer cannot be effectively formed; if the end point temperature is too high, the boron-containing compound may be severely bonded or even doped into the crystal lattice. (4) The fourth sintering has a heating rate of 1°C / min-10°C / min, an end temperature of 250°C-350°C, and a constant temperature time of 1h-24h; Optionally, the heating rate of the fourth sintering may be 1°C / min, 2°C / min, 4°C / min, 6°C / min, 8°C / min, 10°C / min, or any value between 1°C / min and 10°C / min; the endpoint temperature may be 250°C, 300°C, 350°C, or any value between 250°C and 350°C; and the constant temperature time may be 1h, 4h, 8h, 12h, 16h, 20h, 24h, or any value between 1h and 24h. It should be noted that if the final temperature of the fourth sintering is too low, the sulfur-containing compound coating layer cannot be effectively formed. If the final temperature of the fourth sintering is too high, it may cause severe adhesion of the sulfur-containing compound or even doping into the crystal lattice. (5) The cooling rates of the first sintering, the second sintering, the third sintering, and the fourth sintering are each independently 1°C / min to 8°C / min; Optionally, the cooling rates of the first sintering, the second sintering, the third sintering and the fourth sintering can be independently 1°C / min, 2°C / min, 4°C / min, 6°C / min, 8°C / min or any value between 1°C / min and 8°C / min; (6) The first mixing includes two mixing steps: x Co y Mn z (OH)2 and a dispersant are mixed for a fifth time to obtain a fifth mixture, and the fifth mixture is sand-milled to obtain a sand-milled material; performing a sixth mixing of the sand-milled material, the lithium salt, the M-containing dopant, and the molten salt; It should be noted that the introduction of the dispersant during the sand milling process can make the nanoparticles obtained by sand milling evenly dispersed. The dispersant forms a layer around the solid particles through the action of anchoring groups and soluble tails to prevent the dispersed particles from sticking together again; the dispersant is burned off during the subsequent sintering process.

[0035] In some embodiments, the sand-milled material is further dried, and the drying includes one or more of vacuum drying, blast drying, flash drying, spray drying, freeze drying, and low-temperature sintering drying. Among them, the drying methods such as vacuum drying, blast drying, flash drying, spray drying, and low-temperature sintering drying control the drying temperature to be 120°C-350°C, and the freeze drying controls the drying temperature to be -15°C---80°C. The drying time is 4h-40h. In addition, the drying in other steps of the present application can also adopt the above drying methods. It should also be noted that the sixth mixing includes one or more of grinding mixing, high-speed mixer mixing, and food processor mixing; the speed of the sixth mixing is controlled to be 300-1900 rpm, and the mixing time is 10 min-60 min; (7) The first sintered product is further washed, crushed, and dried before the second mixing; (8) The oxygen mass content of the first sintering, the second sintering, and the third sintering is independently 90%-100%.

[0036] Optionally, the oxygen mass content of the first sintering, the second sintering, and the third sintering can be independently 90%, 95%, 100%, or any value between 90% and 100%.

[0037] In some embodiments, the oxygen content is controlled by introducing oxygen-containing gas such as air and / or oxygen during the first sintering, the second sintering, and the third sintering, wherein the flow rate of the oxygen-containing gas is 5m / s. 3 / h-30m 3 / h; In some embodiments, the method for preparing the nano single crystal cathode material satisfies at least one of the following conditions: (1) The stirring speed of the sand mill is 1000 rpm-2500 rpm, the frequency is 10 Hz-50 Hz, the pumping time is 60 times / min-85 times / min, the solid content is 10%-80%, and the sand milling time is 0.1h-8h; Optionally, the stirring speed of the sand mill can be 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm or any value between 1000 rpm and 2500 rpm, the frequency can be 10 Hz, 20 Hz, 30 Hz, 40 Hz, 50 Hz or any value between 10 Hz and 50 Hz, the pump frequency can be 60 times / min, 65 times / min, 70 times / min, 75 times / min, 80 times / min, 85 times / min or any value between 60 times / min and 85 times / min, the solid content can be 10%, 20%, 40%, 60%, 80% or any value between 10% and 80%, and the sand milling time can be 0.1 h, 1 h, 2 h, 4 h, 6 h, 8 h or any value between 0.1 h and 8 h; (2) The water washing temperature is 2°C-15°C, the time is 0.5min-15min, and the solid-liquid ratio of the water washing is 0.5-2:1. Optionally, the water washing temperature can be 2°C, 5°C, 10°C, 15°C or any value between 2°C-15°C, preferably 8°C-15°C; the time can be 0.5min, 1min, 2min, 4min, 6min, 8min, 10min, 15min or any value between 0.5min-15min, preferably 8min-15min; the solid-liquid ratio of the water washing can be 0.5:1, 1:1, 1.5:1, 2:1 or any value between 0.5-2:1, preferably 0.5-1:1. It should be noted that the solid-liquid ratio of the water washing is the mass ratio of the solid phase to the liquid phase. For example, the solid-liquid ratio is 1g:1g.

[0038] The water washing step can fully remove the molten salt and residual lithium, avoid the introduction of impurities into the product, and recycle the molten salt. It is preferred to perform water washing more than twice.

[0039] The third aspect of the present application provides a solid-state battery, comprising the nano single crystal positive electrode material or the nano single crystal positive electrode material prepared by the preparation method of the nano single crystal positive electrode material.

[0040] A fourth aspect of the present application provides an electrical device comprising the solid-state battery.

[0041] It should be noted that electrical equipment may include but is not limited to mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.; among them, mobile devices may include but are not limited to at least one of mobile phones and laptops; electric vehicles may include but are not limited to at least one of pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0042] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0043] Example 1 The first aspect of this embodiment provides a nano single crystal positive electrode material, comprising a core and a first coating layer, a second coating layer and a third coating layer sequentially stacked on the surface of the core; the core has the general chemical formula of Li 1.02 Ni 0.95 Co 0.02 Mn 0.02 Al 0.01 O2, the first coating layer is lithium molybdate, the second coating layer is niobium diboride, and the third coating layer is lithium sulfide.

[0044] Nano single crystal cathode material has a polyhedral structure, and its SEM is as follows Figure 1 As shown, the surface of the nano single crystal positive electrode material particles is smooth, the edges are sharp, the grain boundaries are clear, and there is no obvious agglomeration or cracks.

[0045] XRD of nano single crystal cathode materials Figure 2 As shown, the half-peak width data from the XRD diagram is larger than the conventional one, indicating smaller primary particles, and I003 / 104 is also larger, indicating smaller lithium-nickel mixing.

[0046] A second aspect of this embodiment provides a method for preparing a nano single crystal positive electrode material, and the specific preparation steps are as follows: S1: Ni 0.96 Co 0.02 Mn 0.02The (OH)2 precursor, dispersant polyacrylate and pure water were mixed, and the sand mill stirring speed was controlled to be 1000 rpm, the sand mill frequency was 10 Hz, the pumping time was 60 times / min, the solid content was 30%, and the sand milling time was 4 h to obtain a precursor material with a D50 of 0.15 μm and a D100 of 0.7 μm; S2: The precursor material is dried by a vacuum dryer, the temperature of the vacuum drying oven is controlled at 120°C, the drying time is 4 hours, and then the precursor material, lithium salt, M-containing dopant and molten salt are mixed in a high-speed mixer according to the molar ratio of Li in the lithium salt (lithium hydroxide) to the precursor material of 1.06:1, the mass ratio of the molten salt (potassium chloride and lithium chloride mass ratio of 1:1) to the precursor material of 0.5:1, and the molar ratio of the dopant containing M (aluminum oxide, the molar ratio is calculated according to the aluminum element of aluminum oxide) to the precursor material of 0.01:1. The high-speed mixer speed is set to 300 rpm and the mixing time is 10 minutes; the obtained mixture is placed in a pure oxygen atmosphere for one sintering. The sintering system is divided into two stages. The pure oxygen flow rate introduced during the first sintering stage is 10m 3 / h, the oxygen content in the furnace is 90wt%, the heating rate is 5℃ / min, the temperature is raised to 510℃, the reaction is carried out for 4h, the temperature is then raised to 720℃ at a heating rate of 10℃ / min, the reaction is carried out for 12h, and then the temperature is lowered to room temperature at a cooling rate of 1℃ / min to obtain a burnt material; S3: The calcined material was mechanically crushed and passed through a 325-mesh sieve. The sieved material was washed twice with water at a solid-liquid ratio of 0.5g:1g. The water temperature was controlled at 8°C and the washing time was 15 minutes. The material was centrifuged and dried in a double-cone dryer at a drying temperature of 150°C and a drying time of 4 hours to obtain a dry material. S4: Mix the dry material and lithium molybdate to obtain a mixture with a lithium molybdate concentration of 2000ppm. Place the mixture in a pure oxygen atmosphere for secondary sintering at a pure oxygen flow rate of 15m 3 / h, the oxygen content in the furnace is 99%, the temperature is raised to 550℃ at a heating rate of 3℃ / min, and the reaction is carried out for 8h, and then cooled to room temperature at a cooling rate of 3℃ / min. The cooled material is subjected to air flow crushing and passed through a 325 mesh sieve to obtain a second-burned material; S5: Mix the sintered material and niobium diboride to obtain a mixture with a niobium diboride concentration of 1500ppm. Place the mixture in a pure oxygen atmosphere for three sinterings at a pure oxygen flow rate of 20m 3 / h, the oxygen content in the furnace is 99%, the temperature is raised to 460℃ at a heating rate of 3℃ / min, the reaction is carried out for 8h, and then cooled to room temperature at a cooling rate of 3℃ / min. The cooled material is subjected to air flow crushing and passed through a 325 mesh sieve to obtain a three-burned material; S6: The three-burned material and lithium sulfide are mixed to obtain a mixture with a lithium sulfide concentration of 1000 ppm. The mixture is placed in an argon atmosphere and sintered four times at a flow rate of 20 m 3 / h, heated to 350℃ at a heating rate of 3℃ / min, reacted for 6h, and then cooled to room temperature at a cooling rate of 3℃ / min. The cooled material was air flow crushed and passed through a 325-mesh sieve to obtain a nano single crystal positive electrode material.

[0047] Example 2 The first aspect of this embodiment provides a nano single crystal positive electrode material, comprising a core and a first coating layer, a second coating layer and a third coating layer sequentially stacked on the surface of the core; the core has the general chemical formula of Li 1.015 Ni 0.947 Co 0.04 Mn 0.01 Zr 0.00 3O2, the first coating layer is lithium tungstate, the second coating layer is titanium boride, and the third coating layer is tungsten disulfide.

[0048] A second aspect of this embodiment provides a method for preparing a nano single crystal positive electrode material, and the specific preparation steps are as follows: S1: Ni 0.95 Co 0.04 Mn 0.01 The (OH)2 precursor, dispersant stearic acid and pure water were mixed, and the sand mill stirring speed was controlled to 1800 rpm, the sand mill frequency was 30 Hz, the pumping time was 70 times / min, the solid content was 35%, and the sand milling time was 4 h to obtain a precursor material with a D50 of 0.6 μm and a D100 of 1.7 μm; S2: Dry the precursor material in a vacuum dryer, control the vacuum drying oven temperature at 130°C, and dry for 30 hours. Then, according to the molar ratio of Li in the lithium salt (lithium chloride) and the precursor material being 1.03:1, the mass ratio of the molten salt (sodium chloride and sodium nitrate mass ratio being 1:1) and the precursor material being 1:1, and the molar ratio of the M-containing dopant (ZrO2) and the precursor material being 0.003:1, the precursor material, lithium salt, the M-containing dopant and the molten salt are mixed in a high-speed mixer, the high-speed mixer speed is set to 1300 rpm, and the mixing time is 20 minutes; the obtained mixture is placed in a pure oxygen atmosphere for a single sintering. The sintering system is divided into two stages. The pure oxygen flow rate introduced during the first sintering stage is 18m 3 / h, the oxygen content in the furnace is 99wt%, the heating rate is 5℃ / min, the temperature is raised to 300℃, the reaction is carried out for 1h, the temperature is then raised to 730℃ at a heating rate of 2℃ / min, the reaction is carried out for 14h, and then the temperature is lowered to room temperature at a cooling rate of 2℃ / min to obtain a burnt material; S3: The calcined material was mechanically crushed and passed through a 200-mesh sieve. The sieved material was washed twice with water at a solid-liquid ratio of 0.5g:1g. The water temperature was controlled at 10°C and the washing time was 10 minutes. The material was centrifuged and dried in a double-cone dryer at a drying temperature of 120°C and a drying time of 8 hours to obtain a dry material. S4: Mix the dry material and ammonium tungstate to obtain a mixture with an ammonium tungstate concentration of 800ppm. Place the mixture in a pure oxygen atmosphere for secondary sintering at a pure oxygen flow rate of 20m 3 / h, the oxygen content in the furnace is 99%, the temperature is raised to 450℃ at a heating rate of 3℃ / min, the reaction is carried out for 8h, and then cooled to room temperature at a cooling rate of 3℃ / min. The cooled material is subjected to air flow crushing and passed through a 325 mesh sieve to obtain a second-burned material; S5: Mix the second sintered material and titanium boride to obtain a mixture with a titanium boride concentration of 1500ppm. Place the mixture in a pure oxygen atmosphere for three sinterings at a pure oxygen flow rate of 20m 3 / h, the oxygen content in the furnace is 99%, the temperature is raised to 400℃ at a heating rate of 3℃ / min, the reaction is carried out for 8h, and then cooled to room temperature at a cooling rate of 3℃ / min. The cooled material is subjected to air flow crushing and passed through a 325 mesh sieve to obtain a three-burned material; S6: Mix the three-sintered material and tungsten disulfide to obtain a mixture with a tungsten disulfide concentration of 1000ppm. Place the mixture in an argon atmosphere and sinter it four times at a flow rate of 20m 3 / h, heated to 350℃ at a heating rate of 3℃ / min, reacted for 6h, and then cooled to room temperature at a cooling rate of 3℃ / min. The cooled material was air flow crushed and passed through a 325-mesh sieve to obtain a nano single crystal positive electrode material.

[0049] Example 3 The first aspect of this embodiment provides a nano single crystal positive electrode material, comprising a core and a first coating layer, a second coating layer and a third coating layer sequentially stacked on the surface of the core; the core has the general chemical formula of Li 1.03 Ni 0.96 Co 0.01 Mn 0.01 Ti 0.02 O2, the first coating layer is lithium phosphate, the second coating layer is aluminum boride, and the third coating layer is iron sulfide.

[0050] Nano single crystal cathode material has a polyhedral structure, and its SEM is as follows Figure 1 shown.

[0051] A second aspect of this embodiment provides a method for preparing a nano single crystal positive electrode material, and the specific preparation steps are as follows: S1: Ni 0.98 Co 0.01 Mn0.01 The (OH)2 precursor, dispersant polyacrylate and pure water were mixed, and the sand mill stirring speed was controlled to 2500 rpm, the sand mill frequency was 50 Hz, the pumping time was 85 times / min, the solid content was 80%, and the sand milling time was 4 h to obtain a precursor material with a D50 of 0.6 μm and a D100 of 2 μm; S2: Dry the precursor by flash evaporator, control the flash evaporator temperature at 350 ° C, dry for 40 hours, and then according to the molar ratio of Li in lithium salt (lithium oxide) and precursor material of 1.55:1, the mass ratio of molten salt (potassium nitrate) and precursor material of 2:1, the molar ratio of M-containing dopant (TiO2) and precursor material of 0.02:1, mix the precursor material, lithium salt, M-containing dopant and molten salt in a high-speed mixer, set the high-speed mixer speed to 1900 rpm, and the mixing time to 60 minutes; place the obtained mixture in a pure oxygen atmosphere for one sintering. The sintering system is divided into two stages. The flow rate of oxygen and air introduced during the first sintering stage is 5m 3 / h, the oxygen content in the furnace is 95wt%, the heating rate is 10℃ / min, the temperature is raised to 500℃ for reaction for 1h, then the temperature is raised to 800℃ at a heating rate of 8℃ / min for reaction for 24h, and then the temperature is lowered to room temperature at a cooling rate of 8℃ / min to obtain a burnt material; S3: The calcined material was mechanically crushed and passed through a 500-mesh sieve. The sieved material was washed twice with water at a solid-liquid ratio of 0.5g:1g. The water temperature was controlled at 15°C and the washing time was 8 minutes. The material was centrifuged and dried in a double-cone dryer at a drying temperature of 120°C and a drying time of 40 hours to obtain a dry material. S4: Mix the dry material and ammonium phosphate to obtain a mixture with an ammonium phosphate concentration of 1500ppm. Place the mixture in a pure oxygen atmosphere for secondary sintering at a pure oxygen flow rate of 30m 3 / h, the oxygen content in the furnace is 90%, the temperature is raised to 700℃ at a heating rate of 10℃ / min, and the reaction is carried out for 24h, and then cooled to room temperature at a cooling rate of 8℃ / min. The cooled material is subjected to air flow crushing and passed through a 325 mesh sieve to obtain a second-burned material; S5: Mix the second sintered material and aluminum boride to obtain a mixture with an aluminum boride concentration of 1500ppm. Place the mixture in a pure oxygen atmosphere for three sinterings at a pure oxygen flow rate of 20m 3 / h, the oxygen content in the furnace is 99%, the temperature is raised to 460℃ at a heating rate of 3℃ / min, the reaction is carried out for 8h, and then cooled to room temperature at a cooling rate of 3℃ / min. The cooled material is subjected to air flow crushing and passed through a 325 mesh sieve to obtain a three-burned material; S6: Mix the three-burned material and iron sulfide to obtain a mixture with an iron sulfide concentration of 1000 ppm. Place the mixture in an argon atmosphere and sinter it four times at a flow rate of 20m 3 / h, heated to 350℃ at a heating rate of 3℃ / min, reacted for 6h, and then cooled to room temperature at a cooling rate of 3℃ / min. The cooled material was air flow crushed and passed through a 325-mesh sieve to obtain a nano single crystal positive electrode material.

[0052] Example 4 The difference from Example 1 is that the M-containing dopant is replaced by Nb2O5.

[0053] Example 5 The difference from Example 1 is that the molten salt is replaced by lithium chloride.

[0054] Example 6 The difference from Example 1 is that no M-containing dopant is added.

[0055] Comparative Example 1 The difference from Example 1 is that no molten salt is added.

[0056] Comparative Example 2 The difference from Example 1 is that the first coating layer is not provided.

[0057] Comparative Example 3 The difference from Example 1 is that the second coating layer is not provided.

[0058] Comparative Example 4 The difference from Example 1 is that the third coating layer is not provided.

[0059] Comparative Example 5 The difference from Example 1 is that the first cladding layer is arranged between the second cladding layer and the third cladding layer.

[0060] Comparative Example 6 The difference from Example 1 is that in step S2, the molar ratio of the dopant containing M (calculated as the aluminum element in aluminum oxide) to the precursor material is 0.04:1.

[0061] Comparative Example 7 The difference from Example 1 is that no dispersant is added.

[0062] The product parameters of the nano single crystal positive electrode materials prepared in the above examples and comparative examples are shown in Table 1.

[0063]

[0064] The product parameters of the nano single crystal positive electrode materials prepared in the above examples and comparative examples are shown in Table 2.

[0065]

[0066] The nano single crystal cathode materials prepared in the above examples and comparative examples are assembled into solid-state batteries, and the specific steps are as follows: According to the mass ratio of active material (nano single crystal cathode material): solid electrolyte (Li6PS5Cl): conductive agent (nano carbon fiber VGCF) = 70:30:3, these materials were added to a mortar and ground for 10 minutes to obtain a composite cathode material; Then, the solid electrolytes prepared in the above examples and comparative examples were weighed respectively, poured into the solid-state battery mold, manually rotated until uniform and flat, and pressurized for 1 minute; the composite positive electrode material (the ratio of composite positive electrode material to solid electrolyte was 1:5) was weighed, poured into the mold, manually rotated until uniform and flat, and pressurized for 1 minute; Add the indium sheet, lithium sheet and copper foil to the negative electrode side, apply pressure and maintain pressure for 30 seconds; place the mold into the metal kit, apply pressure and tighten the knob; let it stand for 120 minutes.

[0067] Then, electrochemical testing was performed using a blue electric test cabinet. The initial charge and discharge was performed at 0.1C, with a constant voltage cutoff current of 0.025C, upper and lower voltage limits of 1.9-3.7V, and a test temperature of 25°C. The initial charge and discharge capacity was recorded.

[0068] Then, a cyclic performance test was conducted, with 1C charge-discharge cycles performed at 1.9-3.7V, and the charge-discharge capacity at the 50th cycle was recorded. The specific results are shown in Table 3.

[0069]

[0070] analyze: From the above tests, it can be seen from Comparative Example 1 that the failure to introduce molten salt will cause the material to agglomerate during the sintering process, D50 and D100 will be too large, and a good single crystal morphology cannot be formed, which will further affect the performance of the solid-state battery capacity and the discharge capacity will be low.

[0071] According to Comparative Examples 2, 3 and 4, it can be seen that the three coating layers of the present application need to exist together to exert the synergistic coating effect of the three in order to obtain excellent electrochemical performance.

[0072] According to Comparative Example 5, it can be seen that the coating order of the three coating layers and the order of setting them from the inside to the outside need to be determined, otherwise it will be difficult to exert their synergistic effect, which will affect the performance of the solid-state battery.

[0073] From Comparative Example 6, we can know that excessive dopant content will change the lattice parameters, affect ion transport, and thus affect the performance of the solid-state battery.

[0074] From Comparative Example 7, it can be seen that the introduction of a dispersant is essential, otherwise the precursor material will be severely agglomerated, which will affect the subsequent sintering process, resulting in the inability to disperse the nano single crystal material well and unsatisfactory performance.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0076] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and to form different embodiments. For example, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this application and should not be construed as an admission or any implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A nano single crystal cathode material, characterized in that: It comprises an inner core and a first coating layer, a second coating layer and a third coating layer sequentially stacked on the surface of the inner core; The chemical formula of the core is Li a Ni x Co y Mn z M w O2, wherein 1.02≤a≤1.2, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.1, 0≤w≤0.03, x+y+z+w=1, and M includes one or more of Zr, Sr, Y, Sb, Al, W, Ta, Mg, Ca, Ti, Mo, and Nb; The first coating layer includes a transition metal compound; The second coating layer includes a boron-containing compound; The third coating layer includes a sulfur-containing compound.

2. The nano single crystal cathode material according to claim 1, characterized in that At least one of the following conditions is met: (1) The nano single crystal cathode material comprises a polyhedral structure; (2) The average side length of the nano single crystal positive electrode material is 50-800 nm, and the average thickness is 20-400 nm; (3) The D50 of the nano single crystal positive electrode material is 0.3 μm-1.1 μm, and the D100 is 1.5 μm-3.5 μm; (4) The specific surface area of ​​the nano single crystal positive electrode material is 2.1m 2 / g-5.4m 2 / g; (5) The half-peak width of the nano single crystal positive electrode material is 0.205-0.425; (6) The relative surface energy of the 003 crystal plane of the nano single crystal positive electrode material is 2 J / m 2 -4J / m 2 ; (7) The relative surface energy of the 104 crystal plane of the nano single crystal positive electrode material is 1.0 J / m 2 -1.5J / m 2 ; (8) The relative surface energy of the 101 crystal plane of the nano single crystal positive electrode material is 1.5 J / m 2 -2J / m 2 .

3. The nano single crystal cathode material according to claim 1 or 2, characterized in that: At least one of the following conditions is met: (1) In the general chemical formula of the core, 1.05≤a≤1.15, 0.8≤x≤0.98; (2) M includes one or more of Zr, Al, W, Ti and Nb; (3) The raw materials of the first coating layer include transition metal salts, and the transition metal salts include ammonium tungstate, ammonium molybdate, tungsten trioxide, lithium tungstate, lithium molybdate, molybdenum trioxide, titanium dioxide, aluminum oxide, lithium phosphate, ammonium phosphate, lithium niobate, lithium zirconium phosphate, lithium aluminate, Li 1.3 Al 0.3 Ti 1.7 (PO4)3、Li 1.5 Al 0.5 Ge 1.5 One or more of (PO4)3, Li3YCl6, Li3YBr6, LiTaQ3, lithium silicate and lithium titanate; (4) The boron-containing compound includes one or more of boric acid, lithium borate, boron trioxide, LiBa(B3O3)3 (LBBO), niobium diboride, aluminum boride and titanium boride; (5) The sulfur-containing compound includes Li 10 GeP2S 10 , Li3PS4, lithium sulfide, tungsten disulfide, molybdenum disulfide, iron sulfide, Li 10 GeP2S 12 、β-Li3PS4、Li 3.25 Ge 0.25 P 0.75 S4 and Li6PS5Cl x One or more of .

4. A method for preparing a nano single crystal positive electrode material according to any one of claims 1 to 3, characterized in that: include: Ni x Co y Mn z (OH)2, a dispersant, a lithium salt, a dopant containing M and a molten salt are first mixed to obtain a first mixture, and the first mixture is first sintered in an oxygen-containing atmosphere to obtain a first sintered product; performing a second mixing of the first sintered product and a transition metal salt to obtain a second mixture, and performing a second sintering of the second mixture in an oxygen-containing atmosphere to obtain a second sintered product; performing a third mixing of the second sintered product and a boron-containing compound to obtain a third mixture, and performing a third sintering of the third mixture under an oxygen-containing atmosphere to obtain a third sintered product; The third sintered product is mixed with a sulfur-containing compound for a fourth time to obtain a fourth mixture. The fourth mixture is sintered for a fourth time under an inert atmosphere to obtain a nano single crystal positive electrode material.

5. The method for preparing a nano single crystal cathode material according to claim 4, characterized in that: At least one of the following conditions is met: (1) The dispersant includes one or more of polyacrylate, polyvinyl pyrrolidone, sodium dodecylbenzene sulfonate, sodium hexametaphosphate, stearic acid, lecithin, fatty acid glyceride, polysorbate, sodium dioctyl sulfosuccinate, Span 20-80, Tween 20-80, polyoxyethylene fatty acid ester, oleic acid, alkaline earth metal soap, lauric acid, palmitic acid, alkali metal soap and organic amine soap; (2) The molten salt includes one or more of lithium chloride, potassium chloride, sodium chloride, sodium nitrate, potassium nitrate and lithium nitrate; (3) The M-containing dopant includes one or more of an oxide, hydroxide, nitrate, or carbonate containing M; (4) Ni x Co y Mn z The D50 of (OH)2 is 0.1μm-0.6μm, and the D100 is 0.7μm-2μm; (5) The lithium salt includes one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium oxide, lithium sulfide, lithium acetate and methyl lithium.

6. The method for preparing a nano single crystal cathode material according to claim 5, characterized in that: At least one of the following conditions is met: (1) The dispersant and the Ni x Co y Mn z The mass ratio of (OH)2 is 0.005-0.015:1; (2) The molten salt and the Ni x Co y Mn z The mass ratio of (OH)2 is 0.05-10:1; (3) Li in the lithium salt, M in the M-containing dopant, and Ni x Co y Mn z The molar ratio of (OH)2 is 1.02-1.6:0-0.03:1; (4) The concentration of the transition metal salt in the second mixture is 500 ppm to 1500 ppm; (5) The concentration of the boron-containing compound in the third mixture is 500 ppm to 2500 ppm; (6) The concentration of the sulfur-containing compound in the fourth mixture is 500 ppm to 2000 ppm; (7) Ni x Co y Mn z The D50 of (OH)2 is 0.3μm-0.5μm, and the D100 is 0.75μm-1.1μm; (8) The molten salt includes lithium chloride and / or potassium chloride.

7. The method for preparing a nano single crystal cathode material according to claim 4, characterized in that: At least one of the following conditions is met: (1) The first sintering includes low-temperature sintering and high-temperature sintering performed sequentially; The low-temperature sintering has a heating rate of 5°C / min-12°C / min, an end temperature of 250°C-550°C, and a constant temperature time of 1h-24h; The high temperature sintering has a heating rate of 2°C / min-15°C / min, an end temperature of 500°C-800°C, and a constant temperature time of 4h-16h; (2) The second sintering temperature rise rate is 1°C / min-10°C / min, the end temperature is 250°C-700°C, and the constant temperature time is 1h-24h; (3) The third sintering has a heating rate of 1°C / min-10°C / min, an end temperature of 250°C-550°C, and a constant temperature time of 1h-24h; (4) The fourth sintering has a heating rate of 1°C / min-10°C / min, an end temperature of 250°C-350°C, and a constant temperature time of 1h-24h; (5) The cooling rates of the first sintering, the second sintering, the third sintering, and the fourth sintering are each independently 1°C / min to 8°C / min; (6) The first mixing includes two mixing steps: x Co y Mn z (OH)2 and a dispersant are mixed for a fifth time to obtain a fifth mixture, and the fifth mixture is sand-milled to obtain a sand-milled material; performing a sixth mixing of the sand-milled material, the lithium salt, the M-containing dopant, and the molten salt; (7) The first sintered product is further washed, crushed, and dried before the second mixing; (8) The oxygen mass content of the first sintering, the second sintering, and the third sintering is independently 90%-100%.

8. The method for preparing a nano single crystal cathode material according to claim 7, characterized in that: At least one of the following conditions is met: (1) The stirring speed of the sand mill is 1000 rpm-2500 rpm, the frequency is 10 Hz-50 Hz, the pumping time is 60 times / min-85 times / min, the solid content is 10%-80%, and the sand milling time is 0.1h-8h; (2) The water washing temperature is 2°C-15°C, the time is 0.5min-15min, and the solid-liquid ratio of the water washing is 0.5-2:

1.

9. A solid-state battery, characterized in that: The invention comprises the nano single crystal positive electrode material according to any one of claims 1 to 3 or the nano single crystal positive electrode material prepared by the preparation method of the nano single crystal positive electrode material according to any one of claims 4 to 8.

10. An electrical device, characterized in that: Including the solid-state battery according to claim 9.

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