A nano-monocrystal positive electrode material, a preparation method thereof, a solid-state battery, and an electric device

Abstract

The application provides a nano single-crystal positive electrode material, a preparation method thereof, a solid-state battery and an electric device, and relates to the field of solid-state batteries. The nano single-crystal positive electrode material comprises a core and a first coating layer, a second coating layer and a third coating layer which are sequentially arranged 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 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, and the third coating layer comprises a sulfide. The three coating layers of the nano single-crystal positive electrode material are progressive, and 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, in particular to a nano-single-crystal positive electrode material, a preparation method thereof, a solid-state battery and an electric device. BACKGROUND

[0002] At present, the positive electrode material for solid-state batteries still has problems such as small contact area, low contact quality and poor interface cycle in the use process, which further limits the application of solid-state batteries. In order to further improve the energy density of the solid-state battery and the interface contact of the material and the solid-state electrolyte, nano-single-crystalization of the positive electrode material is a very suitable method, which can improve the contact area and contact quality of the material and the electrolyte, and can also improve the compaction density and energy density of the material by grading and mixing with other positive electrode materials.

[0003] However, the nano-single-crystal positive electrode material inevitably agglomerates due to its small particle size, and its air sensitivity increases due to the increase of specific surface area, which leads to the increase of residual lithium; and the nano-single-crystal positive electrode material is not easy to disperse, which causes problems in performance play in the solid-state battery, leading to poor capacity and more interface side reactions.

[0004] Therefore, there is an urgent need to provide a nano-single-crystal positive electrode material to solve the above problems. SUMMARY

[0005] The present application aims to provide a nano-single-crystal positive electrode material, a preparation method thereof, a solid-state battery and an electric device to solve the above problems.

[0006] To achieve the above purpose, the first aspect of the present application provides a nano-single-crystal positive electrode material, which comprises a core and a first coating layer, a second coating layer and a third coating layer successively stacked on the surface of the core.

[0007] 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.

[0008] The first coating layer comprises a transition metal compound.

[0009] The second coating layer comprises a boron-containing compound.

[0010] The third coating layer comprises a sulfur-containing compound.

[0011] Optionally, the nano-single-crystal cathode material satisfies at least one of the following conditions:

[0012] (1) the nano-single-crystal cathode material comprises a polyhedral structure;

[0013] (2) the nano-single-crystal cathode material has an average edge length of 50-800 nm and an average thickness of 20-400 nm;

[0014] (3) the nano-single-crystal cathode material has a D50 of 0.3 μm-1.1 μm and a D100 of 1.5 μm-3.5 μm;

[0015] (4) the nano-single-crystal cathode material has a specific surface area of 2.1 m 2 / g-5.4 m 2 / g;

[0016] (5) the nano-single-crystal cathode material has a half-peak width of 0.205-0.425;

[0017] (6) the nano-single-crystal cathode material has a relative surface energy of 2 J / m 2 -4 J / m 2 of the 003 crystal face;

[0018] (7) the nano-single-crystal cathode material has a relative surface energy of 1.0 J / m 2 -1.5 J / m 2 of the 104 crystal face;

[0019] (8) the nano-single-crystal cathode material has a relative surface energy of 1.5 J / m 2 -2 J / m 2 of the 101 crystal face.

[0020] Optionally, the nano-single-crystal cathode material satisfies at least one of the following conditions:

[0021] (1) in the chemical formula of the core, 1.05≤a≤1.15 and 0.8≤x≤0.98;

[0022] (2) M comprises one or more of Zr, Al, W, Ti and Nb;

[0023] (3) the first coating layer Starting materials of the formula comprises a transition metal salt, and the transition metal salt comprises 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 Al0.5 Ge 1.5 One or more of (PO4)3, Li3YCl6, Li3YBr6, LiTaQ3, lithium silicate and lithium titanate;

[0024] (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;

[0025] (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 .

[0026] The second aspect of the present application provides a method for preparing the nano single crystal positive electrode material, comprising:

[0027] 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;

[0028] 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;

[0029] 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;

[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] Optionally, the method for preparing the nano single crystal positive electrode material satisfies at least one of the following conditions:

[0032] (1) the dispersant comprises one or more of polyacrylate, polyvinylpyrrolidone, sodium dodecyl benzene sulfonate, sodium hexametaphosphate, stearic acid, lecithin, glycerol fatty acid ester, polysorbate, dioctyl sodium 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;

[0033] (2) the molten salt comprises one or more of lithium chloride, potassium chloride, sodium chloride, sodium nitrate, potassium nitrate and lithium nitrate;

[0034] (3) the M-containing dopant comprises one or more of M-containing oxide, hydroxide, nitrate and carbonate;

[0035] (4) the Ni x Co y Mn z (OH)2has a D50 of 0.1 μm-0.6 μm and a D100 of 0.7 μm-2 μm;

[0036] (5) the lithium salt comprises one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium oxide, lithium sulfide, lithium acetate and methyl lithium.

[0037] Optionally, the preparation method of the nano-single-crystal cathode material satisfies at least one of the following conditions:

[0038] (1) the mass ratio of the dispersant to the Ni x Co y Mn z (OH)2is 0.005-0.015:1;

[0039] (2) the mass ratio of the molten salt to the Ni x Co y Mn z (OH)2is 0.05-10:1;

[0040] (3) the molar ratio of Li in the lithium salt, M in the M-containing dopant and the Ni x Co y Mn z (OH)2is 1.02-1.6:0-0.03:1;

[0041] (4) the concentration of the transition metal salt in the second mixture is 500 ppm-1500 ppm;

[0042] (5) the concentration of the boron-containing compound in the third mixture is 500 ppm-2500 ppm;

[0043] (6) the concentration of the sulfur-containing compound in the fourth mixture is 500 ppm-2000 ppm;

[0044] (7) the Ni x Co y Mn z D50 of the (OH)2 is 0.3 μm-0.5 μm, and D100 is 0.75 μm-1.1 μm;

[0045] (8) the molten salt comprises lithium chloride and / or potassium chloride.

[0046] Optionally, the preparation method of the nanometer single-crystal positive electrode material satisfies at least one of the following conditions:

[0047] (1) the first sintering comprises low-temperature sintering and high-temperature sintering performed in sequence;

[0048] the heating rate of the low-temperature sintering is 5℃ / min-12℃ / min, the end point temperature is 250℃-550℃, and the constant temperature time is 1h-24h;

[0049] the heating rate of the high-temperature sintering is 2℃ / min-15℃ / min, the end point temperature is 500℃-800℃, and the constant temperature time is 4h-16h;

[0050] (2) the heating rate of the second sintering is 1℃ / min-10℃ / min, the end point temperature is 250℃-700℃, and the constant temperature time is 1h-24h;

[0051] (3) the heating rate of the third sintering is 1℃ / min-10℃ / min, the end point temperature is 250℃-550℃, and the constant temperature time is 1h-24h;

[0052] (4) the heating rate of the fourth sintering is 1℃ / min-10℃ / min, the end point temperature is 250℃-350℃, and the constant temperature time is 1h-24h;

[0053] (5) the cooling speed of the first sintering, the second sintering, the third sintering and the fourth sintering is independently 1℃ / min-8℃ / min;

[0054] (6) the first mixing comprises two times of mixing, namely: the Ni x Co y Mn z (OH)2 and a dispersant are subjected to fifth mixing to obtain a fifth mixture, and the fifth mixture is subjected to sand milling to obtain a sand-milled material;

[0055] the sand-milled material, the lithium salt, the M-containing dopant and the molten salt are subjected to sixth mixing;

[0056] (7) the first sintering product is further subjected to water washing, crushing, and drying before the second mixing;

[0057] (8) the oxygen mass content of the first sintering, the second sintering, and the third sintering is independently 90%-100%.

[0058] Optionally, the preparation method of the nanometer single-crystal positive electrode material satisfies at least one of the following conditions:

[0059] (1) the sanding stirring speed is 1000 rpm-2500 rpm, the frequency is 10 Hz-50 Hz, the pump frequency is 60 times / min-85 times / min, the solid content is 10%-80%, and the sanding time is 0.1 h-8 h;

[0060] (2) the water washing temperature is 2℃-15℃, the time is 0.5 min-15 min, and the solid-liquid ratio of water washing is 0.5-2:1.

[0061] The third aspect of the application provides a solid-state battery comprising the nanometer single-crystal positive electrode material or the nanometer single-crystal positive electrode material prepared by the preparation method.

[0062] The fourth aspect of the application provides an electric device comprising the solid-state battery.

[0063] Compared with the prior art, the beneficial effects of the application include:

[0064] The nanometer single-crystal positive electrode material provided by the application has a polyhedral nanometer single-crystal structure as the core, reduces the grain boundary fracture and the stress concentration and micro-cracks caused by the anisotropic volume change, and improves the lithium ion diffusion kinetics by exposing a specific active interface; the first coating layer is in close contact with the core matrix material, reduces the interface impedance, optimizes the interface contact and the electrochemical stability, and improves the ion conductivity between particles; the boron-containing compound in the second coating layer acts as a medium layer and a buffer layer, can be in close contact with the transition metal compound layer in the inner layer and the sulfur-containing compound layer outside, and is in 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, helps to maintain the close contact of the interface, forms a stable interface layer, and inhibits continuous interface side reactions; the sulfur-containing compound in the third coating layer is in good contact with the electrolyte, optimizes the interface compatibility of the positive electrode material and the sulfur-containing compound electrolyte, improves the contact area of the positive electrode material particles and the electrolyte, and reduces the interface impedance; the three-layer coating layer is progressive, and the electrochemical performance of the nanometer single-crystal positive electrode material is improved.

[0065] The preparation method of the nanometer single crystal positive electrode material provided in the application introduces composite molten salt to improve the dispersibility between the positive electrode material particles in the sintering process, and the addition of the dispersant and the molten salt successfully prepares a nanometer single crystal core; a multi-layer coating structure is prepared through a multi-stage sintering coating process, the introduction of the transition metal salt is to generate a fast ion conductor or an oxide on the surface of the nanometer single crystal to improve the ion conductivity between the nanometer single crystal particles; the coating of the boron-containing compound can reduce the direct contact between the active material and the electrolyte, inhibit the side reaction of the positive electrode and the sulfur-containing compound electrolyte, and improve the cycle performance; the introduction of the sulfur-containing compound optimizes the interfacial compatibility of the positive electrode and the sulfur-containing compound electrolyte, improves the contact area of the positive electrode particles and the electrolyte, and reduces the interfacial impedance. The technical scheme of the application combines the ion conductivity improvement effect of the transition metal oxide layer, the side reaction inhibition effect of the boron coating layer, and the interfacial compatibility improvement effect of the sulfur coating layer and the sulfur-containing compound electrolyte, and has a comprehensive synergistic effect, so that a nanometer single crystal positive electrode material with high dispersibility, stable interfacial structure, excellent first charge-discharge efficiency and cycle performance is finally obtained.

[0066] The solid-state battery and the electric device provided in the application have excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0067] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as limiting the scope of the application.

[0068] Figure 1 The SEM image of the nanometer single crystal positive electrode material provided for Example 1 is shown in FIG. 1.

[0069] Figure 2 The XRD image of the nanometer single crystal positive electrode material provided for Example 1 is shown in FIG. 2. DETAILED DESCRIPTION

[0070] First, the scheme provided in the application will be explained in more detail as follows:

[0071] The first aspect of the application provides a nanometer single crystal positive electrode material, which comprises a core and a first coating layer, a second coating layer and a third coating layer sequentially stacked on the surface of the core.

[0072] The chemical formula of the core is Li a Ni x Co y Mn z M wO2, 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 comprises one or more of Zr, Sr, Y, Sb, Al, W, Ta, Mg, Ca, Ti, Mo, and Nb;

[0073] Optionally, the chemical formula of the core is Li a Ni x Co y Mn z M w In O2, a can be 1.02, 1.05, 1.1, 1.15, 1.2, or any value between 1.02 and 1.2, x can be 0.8, 0.85, 0.9, 0.95, 1, or any value between 0.8 and 1, y can be 0, 0.05, 0.1, 0.15, 0.2, or any value between 0 and 0.2, z can be 0, 0.05, 0.1, or any value between 0 and 0.1, and w can be 0, 0.001, 0.005, 0.01, 0.02, 0.03, or any value between 0 and 0.03;

[0074] Preferably, 0.02≤y≤0.1, 0.01≤z≤0.06, and 0.0005≤w≤0.015;

[0075] The first coating layer comprises a transition metal compound;

[0076] The second coating layer comprises a boron-containing compound;

[0077] The third coating layer comprises a sulfur-containing compound.

[0078] It should be noted that the third coating layer can optimize the interface compatibility of the nano-single-crystal cathode material and the sulfur-containing compound electrolyte, increase the contact area of the nano-single-crystal cathode material particles and the electrolyte, and reduce the interface impedance.

[0079] In some embodiments, the nano-single-crystal cathode material satisfies at least one of the following conditions:

[0080] (1) The nano-single-crystal cathode material comprises a polyhedral structure;

[0081] (2) The average edge length of the nano-single-crystal cathode material is 50-800 nm, preferably 100-400 nm, and the average thickness is 20-400 nm, preferably 100-350 nm;

[0082] Optionally, the average edge length of the nanometer single-crystal cathode material can be 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, or any value between 50 nm and 800 nm, and the average thickness can be 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, or any value between 20 nm and 400 nm.

[0083] It should also be noted that the edge length of the nanometer single-crystal cathode material refers to the main geometric dimension (such as the edge length of a square, rectangle, or polygon) of the single-crystal particle in a two-dimensional plane, and the thickness (height) of the nanometer single-crystal cathode material refers to the dimension of the single-crystal particle in the direction perpendicular to the two-dimensional plane; and the average edge length and the average thickness of the primary particles refer to the average edge length and the average thickness, respectively, of ≥30 primary particles with clear outlines randomly selected, measured for their edge length and thickness, respectively, and calculated, respectively.

[0084] (3) The D50 of the nanometer single-crystal cathode material is 0.3 μm-1.1 μm, and the D100 is 1.5 μm-3.5 μm.

[0085] Optionally, the D50 of the nanometer single-crystal cathode material can 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 can 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.

[0086] (4) The specific surface area of the nanometer single-crystal cathode material is 2.1 m 2 / g -5.4 m 2 / g.

[0087] Optionally, the specific surface area of the nanometer single-crystal cathode material can be 2.1 m 2 / g, 2.5 m 2 / g, 3 m 2 / g, 3 m 2 / g, 3.5 m 2 / g, 4 m 2 / g, 4.5 m 2 / g, 5 m 2 / g, 5.4 m 2 / g, or any value between 2.1 m 2 / g and 5.4 m 2 / g.

[0088] (5) The half-height width of the nanometer single-crystal cathode material is 0.205-0.425.

[0089] Optionally, the half-peak width of the nanometer single-crystal cathode material can be 0.205, 0.25, 0.3, 0.35, 0.4, 0.425 or any value between 0.205 and 0.425.

[0090] (6) the relative surface energy of the 003 crystal plane of the nanometer single-crystal cathode material is 2 J / m 2 -4 J / m 2 .

[0091] Optionally, the relative surface energy of the 003 crystal plane of the nanometer single-crystal cathode material can be 2 J / m 2 , 3 J / m 2 , 4 J / m 2 or any value between 2 J / m 2 -4 J / m 2 .

[0092] It should be noted that the 003 crystal plane has a significantly higher surface energy than the 104 crystal plane due to charge imbalance and dangling bonds. This crystal plane has the highest surface energy because the exposed O 2- ions cause surface charge imbalance, strong electrostatic repulsion, and lack of strong TM-O bonds to stabilize the surface, resulting in high surface energy. During the generation of the cathode material, in order to minimize the total surface energy, the crystal will preferentially grow in the direction perpendicular to the (003) plane, minimizing or even eliminating the high-energy 003 plane (or not exposing it in the balanced form), and finally forming a polyhedron;

[0093] (7) the relative surface energy of the 104 crystal plane of the nanometer single-crystal cathode material is 1.0 J / m 2 -1.5 J / m 2 .

[0094] Optionally, the relative surface energy of the 104 crystal plane of the nanometer single-crystal cathode material can be 1.0 J / m 2 , 1.1 J / m 2 , 1.2 J / m 2 , 1.3 J / m 2 , 1.4 J / m 2 , 1.5 J / m 2 or any value between 1.0 J / m 2 -1.5 J / m 2 .

[0095] It should be noted that the 104 crystal plane is the most stable low-energy plane, and theoretical calculations and experiments show that its surface energy is the lowest, with mixed Li + , TM ions and O 2-The 104 crystal plane family is the most stable and the most main exposed crystal plane, because the surface energy of these planes is relatively low, and is retained under the growth conditions close to equilibrium. The 104 crystal plane is one of the main channels for lithium ion intercalation / deintercalation, has high reactivity, and is also a key plane for material structure stability;

[0096] (8) the relative surface energy of the 101 crystal plane of the nano-single-crystal cathode material is 1.5 J / m 2 -2 J / m 2 .

[0097] Optionally, the relative surface energy of the 101 crystal plane of the nano-single-crystal cathode material can be any value between 1.5 J / m 2 , 1.6 J / m 2 , 1.7 J / m 2 , 1.8 J / m 2 , 1.9 J / m 2 , 2 J / m 2 or 1.5 J / m 2 -2 J / m 2 .

[0098] It should be noted that the 101 crystal plane is mainly composed of transition metals and oxygen, and has medium thermodynamic stability.

[0099] In some embodiments, the nano-single-crystal cathode material satisfies at least one of the following conditions:

[0100] (1) in the chemical formula of the core, 1.05≤a≤1.15, 0.8≤x≤0.98;

[0101] Optionally, in the chemical formula of the core, a can 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 can 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;

[0102] (2) M includes one or more of Zr, Al, W, Ti and Nb;

[0103] (3) the raw material of the first coating layer includes a transition metal salt, and the transition metal salt includes 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, referred to as LAGP), Li3YCl6, Li3YBr6, LiTaO3, lithium silicate and lithium titanate, preferably including one or more of lithium tungstate, lithium molybdate, lithium phosphate; as to the above lithium tungstate, lithium molybdate, lithium phosphate, since specific transition metals and lithium atoms are contained at the same time, it is beneficial to exert fast ion conduction performance on the surface of the nano single crystal particles.

[0104] (4) the boron-containing compound includes one or more of boric acid, lithium borate, diboron trioxide, LiBa(B3O3)3 (LBBO), niobium diboride, aluminum boride and titanium boride, preferably including one or more of niobium diboride, aluminum boride and titanium boride. As to the above niobium diboride, aluminum boride and titanium boride, since boron and niobium or aluminum or titanium elements are contained at the same time, they have excellent interface adsorption and regulation performance, can anchor transition metal compounds and sulfides on both sides, and improve the interface stability.

[0105] (5) the sulfur-containing compound includes Li 10 GeP2S 10 (referred to as LGPS), Li3PS4 (referred to 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 , preferably including one or more of 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 , more preferably including one or more of lithium sulfide, tungsten disulfide, molybdenum disulfide and iron sulfide; by containing sulfur elements and specific metal elements, the affinity with sulfide electrolyte materials can be exerted, the contact area of the positive electrode particles and the electrolyte is increased, and the interface impedance is reduced.

[0106] The second aspect of the present application provides a preparation method of the nano single crystal positive electrode material, comprising:

[0107] mixing Ni x Co y Mn za first mixing of the (OH)2, dispersant, lithium salt, M-containing dopant, and molten salt to obtain a first mixture, a first sintering of the first mixture under an oxygen-containing atmosphere to obtain a first sintering product;

[0108] It should be noted that the molten salt is introduced in the sintering process to prevent agglomeration during sintering, form a complete nanocrystalline morphology, and promote the formation of a complete lattice. Through the introduction of composite molten salt, on the one hand, the melting point is reduced, and the thermal stability is improved. On the other hand, the melting effect of the molten salt is improved. 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 of the precursor and the lithium salt. In addition, the crystal structure of high-nickel ternary material (layered oxide, space group R3m) is hexagonal, and the viscosity and surface tension of the molten salt promote the preferential growth of the crystal along the direction perpendicular to the 003 crystal plane, i.e. the 001 direction. The anions or cations in the molten salt can selectively adsorb on the specific crystal plane of the crystal growth. This adsorption can change the relative surface energy of different crystal planes or hinder the growth rate of certain crystal planes, thereby affecting the type of crystal plane finally exposed, which helps to form a specific polyhedral structure (such as promoting the exposure of the 104 crystal plane). The molten salt can also provide a specific chemical environment to stabilize certain low-energy surfaces. Moreover, the viscosity and ionic environment of the molten salt can act as a "soft template" to regulate the anisotropic growth of the crystal to form a polyhedral structure with more distinct edges and corners.

[0109] It can be understood that, when the crystal grows, the crystal will preferentially grow along the direction perpendicular to the 003 crystal plane, i.e. the 001 plane, in order to minimize the total surface energy. 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 direction. It is precisely because of the rapid growth of the 001 crystal plane that the finally formed crystal is relatively expanded along the direction perpendicular to the c-axis (i.e. in the ab plane), presenting a flat or plate-like polyhedron (such as a hexagonal plate, whose large face is usually the 001 crystal plane).

[0110] a second mixing of the first sintering product and a transition metal salt to obtain a second mixture, a second sintering of the second mixture under an oxygen-containing atmosphere to obtain a second sintering product;

[0111] 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 sintering product, which is coated on the surface of the core nanoparticles, reduces the interface impedance, optimizes the interface contact and electrochemical stability, and improves the ionic conductivity between particles, further improving the performance of the material in solid-state batteries.

[0112] a third mixing of the second sintering product and a boron-containing compound to obtain a third mixture, a third sintering of the third mixture under an oxygen-containing atmosphere to obtain a third sintering product.

[0113] It is noted that the interface layer of boron-containing compound generally has high thermal stability, the molten boron phase can wet the surface of positive electrode particles and solid-state electrolyte particles, and form a connecting bridge after cooling, which significantly increases the contact area between particles and can be melted during high-temperature sintering. The interface layer of boron-containing compound generally has high thermal stability.

[0114] The third sintered product is mixed with a sulfur-containing compound to obtain a fourth mixture, and the fourth mixture is sintered under an inert atmosphere to obtain a nano-single-crystal positive electrode material.

[0115] In some embodiments, the preparation method of the nano-single-crystal positive electrode material satisfies at least one of the following conditions:

[0116] (1) the dispersant comprises one or more of polyacrylate, polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, sodium hexametaphosphate, stearic acid, lecithin, fatty acid glyceride, polysorbate, dioctyl sodium 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;

[0117] (2) the molten salt comprises one or more of lithium chloride, potassium chloride, sodium chloride, sodium nitrate, potassium nitrate, and lithium nitrate;

[0118] Preferably, the molten salt comprises 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; for example, 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 is 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 ratio will result in poor melting effect;

[0119] (3) the M-containing dopant comprises one or more of M-containing oxides, hydroxides, nitrates, and carbonates;

[0120] (4) the Ni x Co y Mn z (OH)2 has a D50 of 0.1 μm-0.6 μm and a D100 of 0.7 μm-2 μm;

[0121] Preferably, the Ni x Co y Mn zThe D50 of the (OH)2may 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;

[0122] (5) The lithium salt comprises one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium oxide, lithium sulfide, lithium acetate, and methyllithium.

[0123] In some embodiments, the preparation method of the nano-single-crystal cathode material satisfies at least one of the following conditions:

[0124] (1) The mass ratio of the dispersant and the precursor Ni x Co y Mn z (OH)2is 0.005-0.015:1;

[0125] Optionally, the mass ratio of the dispersant and the precursor Ni x Co y Mn z (OH)2may be 0.005:1, 0.01:1, 0.015:1, or any value between 0.005 and 0.015:1;

[0126] It should be noted that when the content of the dispersant is too large, the dispersant will be excessively left between the precursor particles, and then be brought into the cathode material, affecting the performance of the material. When the content of the dispersant is too small, the dispersing and de-agglomeration effects are not obvious.

[0127] (2) The mass ratio of the molten salt and the precursor Ni x Co y Mn z (OH)2is 0.05-10:1;

[0128] Optionally, the mass ratio of the molten salt and the precursor Ni x Co y Mn z (OH)2may 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 and 10:1; preferably 0.1-8:1, and more preferably 0.5-2.0:1.

[0129] It should be noted that when the amount of molten salt is too low, the molten salt cannot completely infiltrate the mixture after melting, the agglomeration effect is poor, the nanoparticles cannot be dispersed, and the agglomeration is serious; when the amount of molten salt is too high, the sintered material is too hard, cannot be post-processed, and hinders the reaction of lithium salt and the precursor;

[0130] (3) the molar ratio of Li in the lithium salt, M in the M-containing dopant and Ni x Co y Mn z (OH)2 is 1.02-1.6:0-0.03:1;

[0131] Optionally, the molar ratio of Li in the lithium salt, M in the M-containing dopant and Ni x Co y Mn z (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;

[0132] (4) the concentration of the transition metal salt in the second mixture is 500ppm-1500ppm;

[0133] Optionally, the concentration of the transition metal salt in the second mixture can be 500ppm, 1000ppm, 1500ppm or any value between 500ppm-1500ppm;

[0134] It should be noted that when the concentration of the transition metal salt is too high, the content of the coating agent introduced is too high, the impedance is increased, and the capacity is affected; when the concentration of the transition metal salt is too low, the coating effect is not obvious;

[0135] (5) the concentration of the boron-containing compound in the third mixture is 500ppm-2500ppm;

[0136] Optionally, the concentration of the boron-containing compound in the third mixture can be 500ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm or any value between 500ppm-2500ppm;

[0137] It should be noted that when the concentration of the boron-containing compound is too low, the surface of the coated particles cannot be effectively coated; when the concentration of the boron-containing compound is too high, too much boron-containing compound is coated on the surface of the particles, and the capacity is reduced;

[0138] (6) the concentration of the sulfur-containing compound in the fourth mixture is 500 ppm-2000 ppm;

[0139] Optionally, the concentration of the sulfur-containing compound in the fourth mixture can be 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, or any value between 500 ppm and 2000 ppm;

[0140] It should be noted that when the concentration of the sulfur-containing compound is too low, an effective sulfur-containing compound coating cannot be formed on the surface of the material; when the concentration of the sulfur-containing compound is too high, a relatively thick coating layer will be formed on the surface of the material, affecting the performance;

[0141] (7) the Ni x Co y Mn z (OH)2has a D50 of 0.3 μm-0.5 μm and a D100 of 0.75 μm-1.1 μm;

[0142] Optionally, the Ni x Co y Mn z (OH)2may have a D50 of 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 a D100 of 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;

[0143] (8) the molten salt comprises lithium chloride and / or potassium chloride.

[0144] In some embodiments, the preparation method of the nanometer single-crystal positive electrode material satisfies at least one of the following conditions:

[0145] (1) the first sintering comprises low-temperature sintering and high-temperature sintering performed in sequence;

[0146] The low-temperature sintering has a heating rate of 5 ℃ / min-12 ℃ / min, an end temperature of 250 ℃-550 ℃, and a constant temperature time of 1 h-24 h;

[0147] Optionally, the temperature rising rate of the low-temperature sintering can be 5℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, or any value between 5℃ / min and 12℃ / min, the end point temperature can be 250℃, 300℃, 400℃, 500℃, 550℃, or any value between 250℃ and 550℃, and the constant temperature time can be 1h, 4h, 8h, 12h, 16h, 20h, 24h, or any value between 1h and 24h;

[0148] The temperature rising rate of the high-temperature sintering is 2℃ / min-15℃ / min, the end point temperature is 500℃-800℃, and the constant temperature time is 4h-16h;

[0149] Optionally, the temperature rising rate of the high-temperature sintering can be 2℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, 15℃ / min, or any value between 2℃ / min and 15℃ / min, the end point temperature can be 500℃, 600℃, 700℃, 800℃, or any value between 500℃ and 800℃, and the constant temperature time can be 4h, 8h, 12h, 16h, or any value between 4h and 16h;

[0150] It should be noted that the low-temperature sintering is to make the lithium salt fully melt. When the temperature of the low-temperature sintering is too low, the lithium salt has not fully melted, which will affect the subsequent reaction of the lithium salt and the precursor. When the temperature of the low-temperature sintering is too high, the lithium salt may react with the precursor in a non-completely melted state, resulting in agglomeration. When the temperature of the high-temperature sintering is too low, the lithiation reaction cannot be fully carried out, and when the temperature is too high, over-burning and serious lithium volatilization may occur;

[0151] (2) The temperature rising rate of the second sintering is 1℃ / min-10℃ / min, the end point temperature is 250℃-700℃, and the constant temperature time is 1h-24h;

[0152] Optionally, the temperature rising rate of the second sintering can be 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, or any value between 1℃ / min and 10℃ / min, the end point temperature can be 250℃, 300℃, 400℃, 500℃, 600℃, 700℃, or any value between 250℃ and 700℃, and the constant temperature time can be 1h, 4h, 8h, 12h, 16h, 20h, 24h, or any value between 1h and 24h;

[0153] It should be noted that, if the end temperature of the second sintering is too high, the coating material will sinter and melt into the material, and cannot form an effective coating on the surface of the material; if the end temperature of the second sintering is too low, the coating material cannot effectively coat on the surface of the material;

[0154] (3) The heating rate of the third sintering is 1℃ / min-10℃ / min, the end temperature is 250℃-550℃, and the holding time is 1h-24h;

[0155] Optionally, the heating rate of the third sintering can be 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, or any value between 1℃ / min and 10℃ / min, the end temperature can be 250℃, 300℃, 400℃, 500℃, or any value between 250℃ and 500℃, and the holding time can be 1h, 4h, 8h, 12h, 16h, 20h, 24h, or any value between 1h and 24h;

[0156] It should be noted that, if the end temperature of the third sintering is too low, the boron-containing compound coating layer cannot be effectively formed; if the end temperature is too high, the boron-containing compound may be bonded seriously or even doped into the lattice;

[0157] (4) The heating rate of the fourth sintering is 1℃ / min-10℃ / min, the end temperature is 250℃-350℃, and the holding time is 1h-24h;

[0158] Optionally, the heating rate of the fourth sintering can be 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min, 10℃ / min, or any value between 1℃ / min and 10℃ / min, the end temperature can be 250℃, 300℃, 350℃, or any value between 250℃ and 350℃, and the holding time can be 1h, 4h, 8h, 12h, 16h, 20h, 24h, or any value between 1h and 24h;

[0159] It should be noted that, if the end temperature of the fourth sintering is too low, the sulfur-containing compound coating layer cannot be effectively formed, and if the end temperature of the fourth sintering is too high, the sulfur-containing compound may be bonded seriously or even doped into the lattice;

[0160] (5) The cooling rate of the first sintering, the second sintering, the third sintering, and the fourth sintering is independently 1℃ / min-8℃ / min;

[0161] Optionally, the cooling rate of the first sintering, the second sintering, the third sintering and the fourth sintering can be independently 1 ℃ / min, 2 ℃ / min, 4 ℃ / min, 6 ℃ / min, 8 ℃ / min or any value between 1 ℃ / min-8 ℃ / min;

[0162] (6) The first mixing includes two mixing, namely: the Ni x Co y Mn z (OH)2and the dispersant to obtain a fifth mixture, and the fifth mixture is sand milled to obtain a sand-milled material;

[0163] The sand-milled material is mixed with the lithium salt, the M-containing dopant and the molten salt to obtain a sixth mixture;

[0164] It should be noted that the dispersant is introduced in the sand milling process, which can make the nanoparticles obtained by sand milling uniformly dispersed. The dispersant forms a layer around the solid particles through the action of the anchoring group and the soluble tail, preventing the dispersed particles from adhering together again. The dispersant is burned off in the subsequent sintering process.

[0165] In some embodiments, the sand-milled material is further dried, and the drying includes one or more of vacuum drying, air blowing drying, flash drying, spray drying, freeze drying and low-temperature sintering drying; wherein the drying temperature of the vacuum drying, air blowing drying, flash drying, spray drying, low-temperature sintering drying and the like is controlled to be 120-350 ℃, and the drying temperature of the freeze drying is controlled to be -15- -80 ℃. The drying time is 4-40 h; in addition, the drying in other steps of the present application can also use the above drying methods;

[0166] It should also be noted that the sixth mixing includes one or more of grinding mixing, high-speed mixing, and blender mixing; the rotation speed of the sixth mixing is controlled to be 300-1900 rpm, and the mixing time is 10-60 min;

[0167] (7) The first sintering product is further washed with water, crushed and dried before the second mixing;

[0168] (8) The oxygen mass content of the first sintering, the second sintering and the third sintering is independently 90%-100%.

[0169] 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%-100%.

[0170] In some embodiments, the first sintering, the second sintering and the third sintering are controlled by introducing air and / or oxygen-containing gas such as oxygen to control the oxygen content, wherein the flow rate of the oxygen-containing gas is 5m 3 / h-30m 3 / h;

[0171] In some embodiments, the preparation method of the nano-single-crystal positive electrode material satisfies at least one of the following conditions:

[0172] (1) the sanding stirring speed is 1000 rpm-2500 rpm, the frequency is 10 Hz-50 Hz, the pump times are 60 times / min-85 times / min, the solid content is 10%-80%, and the sanding time is 0.1 h-8 h.

[0173] Optionally, the sanding stirring speed 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 times 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 sanding 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.

[0174] (2) the temperature of the water washing is 2℃-15℃, the time is 0.5min-15min, and the solid-liquid ratio of the water washing is 0.5-2:1. Optionally, the temperature of the water washing can be 2℃, 5℃, 10℃, 15℃, or any value between 2℃ and 15℃, preferably 8℃-15℃; the time can be 0.5min, 1min, 2min, 4min, 6min, 8min, 10min, 15min, or any value between 0.5min and 15min, preferably 8min-15min; and 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 and 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 and the liquid phase. For example, the solid-liquid ratio is 1g:1g.

[0175] Through the water washing step, the molten salt and residual lithium can be fully removed, impurities can be avoided to be introduced into the product, and the molten salt can be recycled and utilized. Preferably, the water washing is performed more than twice.

[0176] The third aspect of the present application provides a solid-state battery comprising the nanometer single-crystal positive electrode material or the nanometer single-crystal positive electrode material prepared by the preparation method of the nanometer single-crystal positive electrode material.

[0177] The fourth aspect of the present application provides a power-using device comprising the solid-state battery.

[0178] It should be noted that the power-using device can be, but is not limited to, a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc.; wherein the mobile device can include, but is not limited to, at least one of a mobile phone, a notebook computer, etc.; the electric vehicle can include, but is not limited to, at least one of a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.

[0179] The embodiments of the present application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0180] Example 1

[0181] The first aspect of the present embodiment provides a nanometer single-crystal positive electrode material, an inner core and a first coating layer, a second coating layer and a third coating layer successively stacked on the surface of the inner core; the chemical formula of the inner core is 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.

[0182] The nanometer single-crystal positive electrode material is a polyhedral structure, and the SEM thereof is as shown in Figure 1 The surface of the nanometer single-crystal positive electrode material particle is smooth, the edge is sharp, the grain boundary is clear, and there is no obvious agglomeration or crack.

[0183] The XRD of the nanometer single-crystal positive electrode material is as shown in Figure 2 The half-width data from the XRD graph is larger than that of the conventional one, which shows that the primary particle thereof is smaller, and I003 / 104 is also larger, which shows that the lithium-nickel disorder thereof is smaller.

[0184] The second aspect of the present embodiment provides a preparation method of a nanometer single-crystal positive electrode material, and the specific preparation steps are as follows:

[0185] S1: preparing a Ni 0.96 Co 0.02 Mn0.02 The precursor material is mixed with a dispersant polyacrylate and pure water, the sand mill stirring speed is controlled at 1000 rpm, the sand mill frequency is controlled at 10 Hz, the pump frequency is controlled at 60 times / min, the solid content is controlled at 30%, and the sand mill time is controlled at 4 h, to obtain a precursor material with a D50 of 0.15 μm and a D100 of 0.7 μm;

[0186] S2: The precursor material is dried by a vacuum drying machine, the temperature of the vacuum drying oven is controlled at 120℃, the drying time is controlled at 4 h, then the precursor material, lithium salt (lithium hydroxide), M-containing dopant (aluminum oxide, the molar ratio is calculated according to the aluminum element of aluminum oxide) and molten salt (potassium chloride and lithium chloride with a mass ratio of 1:1) are mixed in a high-speed mixer, the rotation speed of the high-speed mixer is set at 300 rpm, and the mixing time is set at 10 min; the obtained mixture is placed in a pure oxygen atmosphere for primary sintering, the sintering system is divided into two stages, the pure oxygen flow rate is 10 m 3 / h during the first stage of sintering, the oxygen content in the furnace is 90wt%, the heating rate is 5℃ / min, the temperature is raised to 510℃ and reacted for 4 h, then the temperature is raised to 720℃ at a heating rate of 10℃ / min and reacted for 12 h, then the temperature is lowered to room temperature at a cooling rate of 1℃ / min, to obtain a primary sintered material;

[0187] S3: The primary sintered material is mechanically crushed and then sieved through a 325 mesh sieve, the sieved material is washed twice with water at a solid-liquid ratio of 0.5g:1g, the water temperature is controlled at 8℃, the water washing time is 15 min, the material is collected by centrifugation, and dried by a double-cone dryer, the drying temperature is set at 150℃, and the drying time is set at 4 h, to obtain a dried material;

[0188] S4: The dried material is mixed with lithium molybdate, the concentration of lithium molybdate in the obtained mixture is 2000 ppm, the mixture is placed in a pure oxygen atmosphere for secondary sintering, the pure oxygen flow rate is 15 m 3 / h, the oxygen content in the furnace is 99%, the temperature is raised to 550℃ at a heating rate of 3℃ / min and reacted for 8 h, then the temperature is cooled to room temperature at a cooling rate of 3℃ / min, the cooled material is air-jet broken and sieved through a 325 mesh sieve, to obtain a secondary sintered material;

[0189] S5: The secondary sintered material is mixed with niobium diboride, the concentration of niobium diboride in the obtained mixture is 1500 ppm, the mixture is placed in a pure oxygen atmosphere for tertiary sintering, the pure oxygen flow rate is 20 m 3 / h, the oxygen content in the furnace is 99%, the temperature is raised to 460℃ at a rate of 3℃ / min, and the reaction is carried out for 8h, then the temperature is cooled to room temperature at a rate of 3℃ / min, the cooled material is subjected to air flow crushing, and is sieved through a 325 mesh screen to obtain the trisintered material;

[0190] S6: The trisintered material and lithium sulfide are mixed to obtain a mixture in which the concentration of lithium sulfide is 1000ppm, and the mixture is subjected to four times of sintering in an argon atmosphere, the flow rate is 20m 3 / h, the temperature is raised to 350℃ at a rate of 3℃ / min, and the reaction is carried out for 6h, then the temperature is cooled to room temperature at a rate of 3℃ / min, the cooled material is subjected to air flow crushing, and is sieved through a 325 mesh screen to obtain the nanometer single-crystal positive electrode material.

[0191] Embodiment 2

[0192] The first aspect of the embodiment provides a nanometer single-crystal positive electrode material, an inner core and a first coating layer, a second coating layer and a third coating layer are sequentially stacked on the surface of the inner core; the chemical formula of the inner core is 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.

[0193] The second aspect of the embodiment provides a preparation method of a nanometer single-crystal positive electrode material, and the specific preparation steps are as follows:

[0194] S1: A Ni 0.95 Co 0.04 Mn 0.01 (OH)2 precursor, a dispersant stearic acid and pure water are mixed, the sanding stirring speed is controlled to be 1800rpm, the sanding machine frequency is controlled to be 30Hz, the pump times are controlled to be 70 times / min, the solid content is controlled to be 35%, and the sanding time is controlled to be 4h to obtain a precursor material with a D50 of 0.6μm and a D100 of 1.7μm;

[0195] S2: The precursor material is dried by a vacuum drying machine, the temperature of the vacuum drying box is controlled to be 130℃, the drying time is controlled to be 30h, then the molar ratio of Li in the lithium salt (lithium chloride) to the precursor material is 1.03:1, the mass ratio of the molten salt (sodium chloride and sodium nitrate with a mass ratio of 1:1) to the precursor material is 1:1, and the molar ratio of the M-containing dopant (ZrO2) to the precursor material is 0.003:1, the precursor material, the lithium salt, the M-containing dopant and the molten salt are mixed in a high-speed mixer, the rotation speed of the high-speed mixer is set to be 1300rpm, and the mixing time is 20min; the obtained mixture is subjected to one time of sintering in a pure oxygen atmosphere, the sintering system is divided into two stages, the pure oxygen flow rate is 18m 3 / h, the oxygen content in the furnace is 99wt%, the heating rate is 5℃ / min, heated to 300℃ for 1h, then heated to 730℃ at a heating rate of 2℃ / min for 14h, then cooled to room temperature at a cooling rate of 2℃ / min, to obtain a calcined material;

[0196] S3: the calcined material is mechanically broken and sieved through a 200 mesh sieve, the sieved material is washed twice with water at a solid-liquid ratio of 0.5g:1g, the water temperature is controlled at 10℃, the water washing time is 10min, the material is collected by centrifugation, and dried by a double-cone dryer, the drying temperature is set at 120℃, and the drying time is set at 8h, to obtain a dried material;

[0197] S4: the dried material is mixed with ammonium tungstate, the concentration of ammonium tungstate in the obtained mixture is 800ppm, and the mixture is placed in a pure oxygen atmosphere for secondary sintering, the pure oxygen flow rate is 20m 3 / h, the oxygen content in the furnace is 99%, heated to 450℃ at a heating rate of 3℃ / min for 8h, then cooled to room temperature at a cooling rate of 3℃ / min, the cooled material is subjected to air flow breaking and sieved through a 325 mesh sieve, to obtain a secondary calcined material;

[0198] S5: the secondary calcined material is mixed with titanium boride, the concentration of titanium boride in the obtained mixture is 1500ppm, and the mixture is placed in a pure oxygen atmosphere for tertiary sintering, the pure oxygen flow rate is 20m 3 / h, the oxygen content in the furnace is 99%, heated to 400℃ at a heating rate of 3℃ / min for 8h, then cooled to room temperature at a cooling rate of 3℃ / min, the cooled material is subjected to air flow breaking and sieved through a 325 mesh sieve, to obtain a tertiary calcined material;

[0199] S6: the tertiary calcined material is mixed with tungsten disulfide, the concentration of tungsten disulfide in the obtained mixture is 1000ppm, and the mixture is placed in an argon atmosphere for quaternary sintering, the flow rate is 20m 3 / h, heated to 350℃ at a heating rate of 3℃ / min for 6h, then cooled to room temperature at a cooling rate of 3℃ / min, the cooled material is subjected to air flow breaking and sieved through a 325 mesh sieve, to obtain a nano single-crystal positive electrode material.

[0200] Example 3

[0201] The first aspect of the embodiment provides a nano single-crystal positive electrode material, an inner core and a first coating layer, a second coating layer and a third coating layer successively stacked on the surface of the inner core; the chemical formula of the inner core is 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.

[0202] The nano-single crystal cathode material is a polyhedral structure, and its SEM is shown in Figure 1 .

[0203] The second aspect of the embodiment provides a preparation method of the nano-single crystal cathode material, and the specific preparation steps are as follows:

[0204] S1: mixing the Ni 0.98 Co 0.01 Mn 0.01 (OH)2 precursor, the dispersant polyacrylate and pure water, controlling the sanding stirring speed to be 2500 rpm, the sanding machine frequency to be 50 Hz, the pump times to be 85 times / min, the solid content to be 80%, and the sanding time to be 4 h to obtain the precursor material with a D50 of 0.6 μm and a D100 of 2 μm;

[0205] S2: drying the precursor material by using a flash evaporator, controlling the flash evaporator temperature to be 350℃, the drying time to be 40 h, then mixing the precursor material, the lithium salt (lithium oxide), the M-containing dopant (TiO2) and the molten salt (potassium nitrate) according to the molar ratio of Li in the lithium salt to the precursor material being 1.55:1, the mass ratio of the molten salt (potassium nitrate) to the precursor material being 2:1, and the molar ratio of the M-containing dopant (TiO2) to the precursor material being 0.02:1, mixing the precursor material, the lithium salt and the molten salt in a high-speed mixer, setting the high-speed mixer rotating speed to be 1900 rpm and the mixing time to be 60 min; placing the obtained mixed material in a pure oxygen atmosphere to perform a first sintering, the sintering system is divided into two stages, the oxygen and air flow rate is 5 m 3 / h when the first stage sintering is performed, the oxygen content in the furnace is 95wt%, the temperature rising rate is 10℃ / min, the temperature is raised to 500℃ and reacted for 1 h, then the temperature is raised to 800℃ at a temperature rising rate of 8℃ / min and reacted for 24 h, then the temperature is lowered to room temperature at a temperature lowering rate of 8℃ / min, and the first sintered material is obtained;

[0206] S3: mechanically crushing the first sintered material and then passing it through a 500-mesh sieve, washing the sieved material twice according to the solid-liquid ratio of 0.5g:1g, controlling the water temperature to be 15℃, the water washing time to be 8 min, centrifuging the material, drying the material by using a double-cone dryer, setting the drying temperature to be 120℃ and the drying time to be 40 h, and obtaining the dried material;

[0207] S4: mixing the dried material and ammonium phosphate to obtain a mixture with the ammonium phosphate concentration of 1500ppm, placing the mixture in a pure oxygen atmosphere to perform a second sintering, the pure oxygen flow rate is 30 m 3 / h, the oxygen content in the furnace is 90%, the temperature is raised to 700℃ at a temperature rising rate of 10℃ / min and reacted for 24 h, then the temperature is lowered to room temperature at a cooling speed of 8℃ / min, the material after cooling is subjected to airflow crushing and then passed through a 325-mesh sieve, and the second sintered material is obtained;

[0208] S5: The mixture of the double-sintered material and aluminum boride is obtained, the concentration of aluminum boride in the mixture is 1500 ppm, and the mixture is placed in a pure oxygen atmosphere for three times of sintering, the flow rate of pure oxygen is 20 m 3 / h, the oxygen content in the furnace is 99%, the temperature is raised to 460℃ at a rate of 3℃ / min, and the reaction is carried out for 8h, then the temperature is cooled to room temperature at a rate of 3℃ / min, and the cooled material is subjected to air flow crushing and sieving through a 325 mesh sieve to obtain a triple-sintered material;

[0209] S6: The triple-sintered material and iron sulfide are mixed to obtain a mixture with a concentration of 1000 ppm of iron sulfide, and the mixture is placed in an argon atmosphere for four times of sintering, the flow rate is 20 m 3 / h, the temperature is raised to 350℃ at a rate of 3℃ / min, and the reaction is carried out for 6h, then the temperature is cooled to room temperature at a rate of 3℃ / min, and the cooled material is subjected to air flow crushing and sieving through a 325 mesh sieve to obtain a nano-single-crystal positive electrode material.

[0210] Example 4

[0211] The difference from Example 1 is that the M-containing dopant is replaced by Nb2O5.

[0212] Example 5

[0213] The difference from Example 1 is that the molten salt is replaced by lithium chloride.

[0214] Example 6

[0215] The difference from Example 1 is that no M-containing dopant is added.

[0216] Comparative Example 1

[0217] The difference from Example 1 is that no molten salt is added.

[0218] Comparative Example 2

[0219] The difference from Example 1 is that no first coating layer is provided.

[0220] Comparative Example 3

[0221] The difference from Example 1 is that no second coating layer is provided.

[0222] Comparative Example 4

[0223] The difference from Example 1 is that no third coating layer is provided.

[0224] Comparative Example 5

[0225] The difference from Example 1 is that the first coating layer is provided between the second coating layer and the third coating layer.

[0226] Comparative Example 6

[0227] The difference from Example 1 is that the molar ratio of the M-containing dopant (calculated according to the aluminum element of aluminum trioxide) and the precursor material in the S2 step is 0.04:1.

[0228] Comparative Example 7

[0229] The difference from Example 1 is that no dispersant is added.

[0230] The product parameters of the nano-single-crystal positive electrode materials prepared in the above examples and comparative examples are shown in Table 1.

[0231]

[0232] The product parameters of the nano-single-crystal positive electrode materials prepared in the above examples and comparative examples are shown in Table 2.

[0233]

[0234] The nano-single-crystal positive electrode materials prepared in the above examples and comparative examples are assembled into solid-state batteries, and the specific steps are as follows:

[0235] According to the mass ratio of active material (nano-single-crystal positive electrode material): solid-state electrolyte (Li6PS5Cl): conductive agent (nano-carbon fiber VGCF) = 70:30:3, these materials are added to a mortar and ground for 10 min to obtain a composite positive electrode material;

[0236] Then, the solid-state electrolyte prepared in the above examples and comparative examples is weighed and poured into a solid-state battery mold, and manually rotated to be uniform and flat, and pressure is maintained for 1 min; the composite positive electrode material (the ratio of the composite positive electrode material to the solid-state electrolyte is 1:5) is weighed and poured into the mold, and manually rotated to be uniform and flat, and pressure is maintained for 1 min;

[0237] Indium sheets, lithium sheets, and copper foils are added to the negative electrode side, and pressure is maintained for 30 s; the mold is placed in a metal sleeve, and the knob is tightened after pressure is applied; and the mold is left to stand for 120 min.

[0238] Then, electrochemical tests are performed using a blue light test cabinet. The first charge and discharge is performed at 0.1C, the charge constant voltage cutoff current is 0.025C; the upper and lower limit voltages are 1.9-3.7V, the test temperature is 25℃, and the first charge and discharge capacity is recorded.

[0239] Then, the cycle performance test is performed, and the 1C charge and discharge cycle is performed at 1.9-3.7V, and the charge and discharge capacity of the 50th week cycle is recorded. The specific results are shown in Table 3.

[0240]

[0241] Analysis:

[0242] From the above test, it can be known from Comparative Example 1 that the introduction of molten salt can cause the material to agglomerate during sintering, the D50 and D100 are large, and a better single crystal morphology cannot be formed, which further affects the capacity of the solid-state battery, and the discharge capacity is low.

[0243] According to Comparative Example 2, Comparative Example 3 and Comparative Example 4, it can be known that the three coating layers of the present application need to exist together to play a synergistic coating effect of the three, so as to obtain excellent electrochemical performance.

[0244] According to Comparative Example 5, it can be known that the coating sequence of the three coating layers and the sequential setting sequence from the inside to the outside need to be determined, otherwise it is difficult to play their synergistic effect, which will affect the performance of the solid-state battery.

[0245] From Comparative Example 6, it can be known that too much dopant content can change the lattice parameter, affect ion transmission, and further affect the performance of the solid-state battery.

[0246] From Comparative Example 7, it can be known that the introduction of a dispersant is essential, otherwise the precursor material will seriously agglomerate, which will affect the subsequent sintering process, so that the nano single crystal material cannot be well dispersed, and the performance is not ideal.

[0247] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0248] In addition, those skilled in the art can understand that although some embodiments herein include certain features included in other embodiments rather than other features, the combination of features of different embodiments means that it is within the scope of the present application and forms different embodiments. For example, any one of the claimed embodiments can be used in any combination. The information disclosed in the BACKGROUND section is only intended to deepen the understanding of the overall background of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A nanosized single-crystalline cathode material, characterized in that, The core and first, second and third cladding layers are 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, 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; a raw material of the first coating layer includes a transition metal salt, the transition metal salt includes ammonium tungstate, ammonium molybdate, tungsten trioxide, lithium tungstate, lithium molybdate, molybdenum trioxide, titanium dioxide, aluminum oxide, 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 lithium phosphate, Li3YCl6, Li3YBr6, lithium silicate, and lithium titanate. The second cladding layer comprises a boron-containing compound; The third cladding layer comprises a sulfur-containing compound.

2. The nanosized single-crystalline cathode material of claim 1, wherein, At least one of the following conditions is met: (1) The nano-single-crystal positive electrode material comprises a polyhedral structure; (2) The average edge 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 0.3-1.1 μm, and the D100 is 1.5-3.5 μm; (4) the specific surface area of the nano-monocrystal positive electrode material is 2.1 m 2 / g-5.4 m 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-monocrystal positive electrode material is 2 J / m 2 -4 J / m 2 ; (7) the relative surface energy of the 104 crystal plane of the nano-monocrystal positive electrode material is 1.0 J / m 2 -1.5 J / m 2 ; (8) the relative surface energy of the 101 crystal plane of the nano-monocrystal positive electrode material is 1.5 J / m 2 -2 J / m 2 .

3. The nanosized single-crystalline cathode material according to claim 1 or 2, characterized in that, At least one of the following conditions is met: (1) In the chemical formula of the core, 1.05≤a≤1.15, and 0.8≤x≤0.98; (2) M comprises one or more of Zr, Al, W, Ti and Nb; (3) The boron-containing compound comprises one or more of boric acid, lithium borate, diboron trioxide, niobium diboride, aluminum boride and titanium boride; (4) the sulfur-containing compound comprises 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 the following:

4. A method for preparing the nanosized single-crystalline cathode material according to any one of claims 1 to 3, characterized in that, The first, second and third cladding layers are sequentially stacked on the surface of the core; Ni x Co y Mn z a first mixture of Ni(OH)2, dispersant, lithium salt, M-containing dopant, and molten salt, to obtain a first mixture, and sintering the first mixture under an oxygen-containing atmosphere to obtain a first sintered product; The second mixture is subjected to second sintering in an oxygen-containing atmosphere to obtain a second sintering product; The third sintering product is subjected to fourth mixing with a sulfur-containing compound to obtain a fourth mixture, and the fourth mixture is subjected to fourth sintering in an inert atmosphere to obtain a nano-single-crystal positive electrode material. At least one of the following conditions is met:

5. The method for preparing a nano single crystal cathode material according to claim 4, characterized in that: (1) The dispersant comprises one or more of polyacrylate, polyvinylpyrrolidone, sodium dodecylbenzenesulfonate, sodium hexametaphosphate, stearic acid, lecithin, fatty acid glyceride, polysorbate, dioctyl sodium 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 comprises one or more of lithium chloride, potassium chloride, sodium chloride, sodium nitrate, potassium nitrate and lithium nitrate; (3) The M-containing dopant comprises one or more of M-containing oxides, hydroxides, nitrates and carbonates; (5) The lithium salt comprises one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium oxide, lithium sulfide, lithium acetate and methyl lithium. (4) the Ni x Co y Mn z D50 of the (OH)2is 0.1 pm - 0.6 pm, and D100 is 0.7 pm - 2 pm; At least one of the following conditions is met:

6. The method of claim 5, wherein the nanosized single-crystal cathode material is prepared by a process comprising: (4) The concentration of the transition metal salt in the second mixture is 500-1500 ppm; ​ (1) the dispersant and the Ni x Co y Mn z (OH)2is 0.005-0.015: 1; (2) the molten salt and the Ni x Co y Mn z 0.05-10: 1; (3) Li in the lithium salt, M in the M-containing dopant, and the Ni x Co y Mn z the molar ratio of Li2CO3:(NH4)2S: (NH4)2SO4:(NH4)2SO3:(NH4)2S2O3:(NH4)2S2O4:(NH4)2S2O5:(NH4)2S2O6:(NH4)2S2O7:(NH4)2S2O8:(NH4)2S2O9:(NH4)2S2O10:(NH4)2 (5) The concentration of the boron-containing compound in the third mixture is 500-2500 ppm; (6) The concentration of the sulfur-containing compound in the fourth mixture is 500-2000 ppm; (8) The molten salt comprises lithium chloride and / or potassium chloride. (7) the Ni x Co y Mn z D50 of the (OH)2is 0.3-0.5 pm, and D100 is 0.75-1.1 pm; At least one of the following conditions is met:

7. The method for preparing a nano single crystal cathode material according to claim 4, characterized in that: (1) The first sintering comprises low-temperature sintering and high-temperature sintering in sequence. ​ The temperature rising rate of the low-temperature sintering is 5℃ / min-12℃ / min, the end point temperature is 250℃-550℃, and the constant temperature time is 1h-24h; The temperature rising rate of the high-temperature sintering is 2℃ / min-15℃ / min, the end point temperature is 500℃-800℃, and the constant temperature time is 4h-16h; (2) The temperature rising rate of the second sintering is 1℃ / min-10℃ / min, the end point temperature is 250℃-700℃, and the constant temperature time is 1h-24h; (3) The temperature rising rate of the third sintering is 1℃ / min-10℃ / min, the end point temperature is 250℃-550℃, and the constant temperature time is 1h-24h; (4) The temperature rising rate of the fourth sintering is 1℃ / min-10℃ / min, the end point temperature is 250℃-350℃, and the constant temperature time is 1h-24h; (5) The cooling speed of the first sintering, the second sintering, the third sintering and the fourth sintering is independently 1℃ / min-8℃ / min; (6) the first mixing includes two times of mixing, i.e. mixing the Ni x Co y Mn z (OH)2and dispersant to obtain a fifth mixture, and sand milling the fifth mixture to obtain a sand-milled material; The sand-milled material, the lithium salt, the M-containing dopant and the molten salt are mixed for the sixth time; (7) The first sintering product is further subjected to water washing, crushing and drying 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-milling is 1000rpm-2500rpm, the frequency is 10Hz-50Hz, the pump times is 60times / min-85times / min, the mass solid content is 10%-80%, and the sand-milling time is 0.1h-8h; (2) The temperature of the water washing is 2℃-15℃, the time is 0.5min-15min, and the solid-liquid ratio of the water washing is 0.5g-2g:1g.

9. A solid state battery, characterized by The nano-single-crystal cathode material of any one of claims 1-3 or prepared by the preparation method of any one of claims 4-8.

10. An electric device, characterized by The solid-state battery of claim 9.

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