Positive electrode active material, method for producing same, composite positive electrode, solid-state battery, and electrical device

Abstract

The application provides a positive electrode active material and a preparation method thereof, a composite positive electrode, a solid-state battery and an electrical equipment, and relates to the field of solid-state batteries. The positive electrode active material comprises a core and a coating layer covering the outer surface of the core. The coating layer comprises, from inside to outside, a lithium halide layer, an ion conductive layer, a halide electrolyte layer and a boride layer. The positive electrode active material can effectively improve the energy density and cycle stability of the battery.

Description

Technical Field

[0001] This application relates to the field of solid-state batteries, and more particularly to a positive electrode active material and its preparation method, a composite positive electrode, a solid-state battery, and electrical equipment. Background Technology

[0002] Solid-state lithium batteries are considered an important development direction for the next generation of energy storage technology due to their high safety and high energy density.

[0003] To ensure ion conduction, traditional composite cathode preparation methods require combining the cathode active material with a solid electrolyte. This significantly dilutes the proportion of the cathode active material, resulting in a lower energy density for the composite cathode. Secondly, the solid-solid contact between the cathode active material and the solid electrolyte results in a small interfacial contact area and insufficient stability, making them prone to interfacial side reactions and contact failure during cycling, leading to a decline in cycle performance. In other words, current cathode active materials for solid-state batteries suffer from low energy density and poor cycle performance, which limits the application of solid-state batteries. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode active material and its preparation method, a composite positive electrode, a solid-state battery, and an electrical device to solve the above-mentioned problems.

[0005] To achieve the above objectives, this application adopts the following technical solution: A positive electrode active material includes a core and a coating layer covering the outer surface of the core. The coating layer includes a lithium halide layer, an ion-conducting layer, a halide electrolyte layer and a boride layer arranged sequentially from the inside to the outside.

[0006] According to an embodiment of this application, 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 at least one of Zr, Sr, Y, Sb, Al, W, Ta, Mg, Ca, Ti, Mo, Nb, and B; And / or, the lithium halide layer comprises LiX, where X contains at least one of F, Cl, Br, I, and At; And / or, the ion-conducting layer includes Li b M' c O d M' e O fAt least one of the following, wherein M' includes at least one of W, Mo, Ti, Co, B, Ta, Si, Nb, Zr, and P, 1≤b≤7, 1≤c≤5, 2≤d≤7, 1≤e≤3, and 2≤f≤5; And / or, the halide electrolyte layer comprises Li3M''X6, where M'' contains at least one of Y, Sc, Er, Ho, In, Ga, Al, Ti, V, Ta, and Nb; And / or, the boride layer includes at least one of lithium borate, lithium thioborate, lithium tetraborate, lithium metaborate, and lithium triborate.

[0007] According to an embodiment of this application, the Dv50 particle size of the core is 2.1µm to 2.9µm, preferably 2.2µm to 2.5µm; And / or, the thickness of the lithium halide layer is 10~60nm, preferably 20~40nm; And / or, the thickness of the ion-conducting layer is 50~150nm, preferably 60~90nm; And / or, the thickness of the halide electrolyte layer is 1~80nm, preferably 20~40nm; And / or, the thickness of the boride layer is 1~60nm, preferably 4~40nm.

[0008] And / or, the Dv50 of the positive electrode active material is 2.5µm to 5µm; And / or, the BET of the positive electrode active material is 0.8~1.4m. 2 / g.

[0009] This application also provides a method for preparing the positive electrode active material as described above, comprising: The positive electrode precursor is mixed with lithium salt, first lithium halide, and optional M-containing material, and subjected to first sintering to obtain the first sintering product. The first calcined product is mixed with a compound containing M' and subjected to a second sintering to obtain a second calcined product; The second sintering product is mixed with a second lithium halide and an M''-containing halide, and then subjected to a third sintering to obtain a third sintering product; The tertiary sintering product is mixed with a boron-containing substance and subjected to a fourth sintering to obtain a positive electrode active material.

[0010] According to an embodiment of this application, the chemical formula of the positive electrode precursor is Ni. x' Co y' Mn z' (OH)₂, where 0.8≤x'≤1, 0≤y'≤0.2, 0≤z'≤0.2; x'+ y'+ z'=1; And / or, the lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium oxide, lithium sulfide, lithium acetate, and lithium methyl. And / or, the substance containing M includes at least one of the following: oxides containing M, hydroxides containing M, nitrates containing M, and carbonates containing M; And / or, the first lithium halide includes at least one of lithium chloride, lithium fluoride, lithium bromide, and lithium iodide; And / or, the mass of the first lithium halide accounts for 500~3000 ppm of the mass of the cathode precursor; In some embodiments, the equipment used for mixing the cathode precursor with the lithium salt, the first lithium halide, and optionally the M-containing substance includes at least one of grinding and mixing, high-speed mixer mixing, and food processor mixing. Further, the cathode precursor is mixed with the lithium salt, the first lithium halide, and optionally the M-containing substance at a rotation speed of 300-1900 rpm for 10-60 minutes to achieve uniform mixing of the components.

[0011] And / or, the first sintering includes sequential low-temperature sintering and high-temperature sintering, wherein the temperature of the low-temperature sintering is lower than the temperature of the high-temperature sintering; And / or, the temperature of the low-temperature sintering is 250-550℃, preferably 450-500℃, the time of the low-temperature sintering is 1-24h, preferably 8-12h, and the heating rate of the low-temperature sintering is 1-10℃ / min, preferably 3-6℃ / min; And / or, the high-temperature sintering temperature is 660-900℃, preferably 690℃~850℃; the high-temperature sintering time is 4-24h, preferably 8-16h; and the high-temperature sintering heating rate is 1-8℃ / min, preferably 3~6℃ / min.

[0012] In some embodiments, the first sintering is carried out in an oxygen atmosphere with an oxygen flow rate of 5-30 m / s. 3 / h, the oxygen value inside the equipment used for the first sintering is controlled at 90%-100%.

[0013] In some embodiments, after the first sintering is completed, the method further includes cooling the sintered product at a cooling rate of 1-8°C / min.

[0014] In some embodiments, after obtaining the calcined product, the preparation method further includes: pulverizing the obtained calcined product, mixing the pulverized calcined product with a transition metal compound, and performing a second sintering. Further, the pulverization process of the calcined product includes at least one of grinding, airflow crushing, vibration crushing, and mechanical crushing, and the particle size of the pulverized calcined product is 100-500 mesh.

[0015] According to embodiments of this application, the M'-containing compound includes at least one of ammonium tungstate, tungsten trioxide, lithium tungstate, tungstic acid, molybdenum trioxide, ammonium molybdate, lithium molybdate, titanium dioxide, cobalt tetroxide, cobalt hydroxyl oxide, cobalt oxide, niobium pentoxide, niobic acid, lithium niobate, lithium borate, boric acid, lithium titanate, tantalum pentoxide, lithium tantalate, silicon dioxide, lithium silicate, lithium zirconate, lithium phosphate, and lithium zirconium phosphate. And / or, the mass of the M'-containing compound accounts for 500 to 20,000 ppm of the mass of the calcined product; In some embodiments, the method of mixing the product with the M'-containing compound includes at least one of grinding, high-speed mixer mixing, and food processor mixing.

[0016] In some embodiments, the calcined product and the M'-containing compound are mixed at a speed of 300-1900 rpm for 10-60 min to achieve uniform mixing of the calcined product and the M'-containing compound.

[0017] And / or, the temperature of the second sintering is 550-720℃, preferably 600℃~680℃; the time of the second sintering is 4-24h, preferably 6-12h; the heating rate of the second sintering is 1-8℃ / min, preferably 3~6℃ / min.

[0018] In some embodiments, the second sintering is carried out in an oxygen atmosphere with an oxygen flow rate of 5-30 m / s. 3 / h, the oxygen value inside the equipment during the second sintering is 90%-100%.

[0019] In some embodiments, after the second sintering is completed, the preparation method further includes: cooling the second sintering product at a cooling rate of 1-8°C / min.

[0020] According to an embodiment of this application, the second lithium halide includes at least one of lithium chloride, lithium fluoride, lithium bromide, and lithium iodide. And / or, the halogen in the M''-containing halide comprises at least one of F, Cl, Br, I, and At; And / or, the mass of the M'' halide accounts for 500~2000 ppm of the mass of the dicalcined product, and the molar ratio of the second lithium halide to the M'' halide is 3.03:1~3.1:1; And / or, the temperature of the third sintering is 250-700℃, preferably 250℃-605℃, the time of the third sintering is 1-24h, preferably 10-24h; the heating rate of the third sintering is 1-10℃ / min, preferably 2-4℃ / min; In some embodiments, the third sintering is carried out under an inert gas protection or under vacuum conditions, wherein the inert gas includes at least one of nitrogen and argon.

[0021] In some embodiments, after the third sintering is completed, the preparation method further includes cooling the sintered product at a cooling rate of 1-8 °C / min.

[0022] And / or, the boron-containing substance includes at least one of boric acid, lithium borate, boron oxide, lithium thioborate, lithium tetraborate, lithium metaborate, and lithium triborate; And / or, the mass of the boron-containing substance accounts for 500 to 2000 ppm of the mass of the tricalcined product; And / or, the temperature of the fourth sintering is 200-350℃, preferably 260℃~300℃; the time of the fourth sintering is 1-24h, preferably 6~10h; the heating rate of the fourth sintering is 1-10℃ / min, preferably 3~6℃ / min.

[0023] In some embodiments, the fourth sintering is carried out under an inert gas or under vacuum conditions, the inert gas including at least one of nitrogen and argon.

[0024] In some embodiments, after the fourth sintering is completed, the preparation method further includes cooling the product after the fourth sintering at a cooling rate of 1-8°C / min.

[0025] In some embodiments, after the fourth sintering is completed, the preparation method further includes pulverizing and sieving the product after the fourth sintering to obtain the positive electrode active material. Further, the sieving process controls the particle size to be 100-500 mesh.

[0026] This application also provides a composite positive electrode, comprising a positive electrode active material, a conductive agent, and a sulfide electrolyte; wherein the positive electrode active material is the positive electrode active material described above or a positive electrode active material prepared by the preparation method of the positive electrode active material described above; And / or, the sulfide electrolyte accounts for 5% to 30% of the mass of the composite cathode.

[0027] This application also provides a solid-state battery, including the composite cathode described above.

[0028] This application also provides an electrical device, including the solid-state battery described above.

[0029] Compared with the prior art, the beneficial effects of this application include: The positive electrode active material of this application includes a core and a coating layer. The coating layer includes a lithium halide layer, an ion-conducting layer, a halide electrolyte layer, and a boride layer. These coating layers work together to effectively improve the energy density and cycle stability of the material. Specifically, the lithium halide layer can weaken the grain boundary forces between single-crystal positive electrode material particles, improve dissociation performance, prevent particle agglomeration, and thus improve the material contact quality. Simultaneously, lithium halide can also improve the ionic conductivity of the material. The halogen anions in the lithium halide can stabilize oxygen in the material, thereby improving the material's safety. Furthermore, when in contact with the electrolyte, it can repair cracks caused by expansion during cycling. The ion-conducting layer has high ionic conductivity, which helps reduce residual lithium. The halide electrolyte layer is formed by the in-situ reaction of halides and lithium halide, and features high ionic conductivity, low interfacial impedance, and high stability. This reduces the amount of sulfide electrolyte used in the composite positive electrode, which is beneficial for constructing high-performance all-solid-state lithium batteries. The halide electrolyte layer can compensate for the deficiencies of sulfide electrolyte in terms of oxidation resistance and air stability, jointly stabilizing the positive electrode interface. In addition, halide electrolytes can absorb oxygen, inhibit the reaction between oxygen and sulfide electrolytes, and improve the safety performance of materials; the boride layer can further improve the stability of materials and interfacial contact performance. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0031] Figure 1 Here is an electron microscope image of the positive electrode active material in Example 1; Figure 2 This is a comparison graph of the charge-discharge curves of Example 4 and Comparative Example 2; Figure 3 This is a comparison graph of the cycle curves of Example 1 and Comparative Example 1. Detailed Implementation

[0032] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0033] The conjunction "composed of" excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of" appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0034] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0035] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0036] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0037] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0038] A positive electrode active material includes a core and a coating layer covering the outer surface of the core. The coating layer includes a lithium halide layer, an ion-conducting layer, a halide electrolyte layer and a boride layer arranged sequentially from the inside to the outside.

[0039] According to an embodiment of this application, 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 includes at least one of Zr, Sr, Y, Sb, Al, W, Ta, Mg, Ca, Ti, Mo, Nb, and B; And / or, the lithium halide layer comprises LiX, where X contains at least one of F, Cl, Br, I, and At; The ion-conducting layer includes Li b M' c O d M' e O f At least one of the following, wherein M' includes at least one of W, Mo, Ti, Co, B, Ta, Si, Nb, Zr, and P, 1≤b≤7, 1≤c≤5, 2≤d≤7, 1≤e≤3, and 2≤f≤5; The halide electrolyte layer comprises Li3M''X6, where M'' contains at least one of Y, Sc, Er, Ho, In, Ga, Al, Ti, V, Ta, and Nb, and X contains at least one of F, Cl, Br, I, and At. The boride layer includes lithium borate (Li3BO3) and lithium thioborate (Li9B). 19 S 33 It is at least one of lithium tetraborate (Li2B4O7), lithium metaborate (LiBO2), and lithium triborate (LiB3O5).

[0040] According to the embodiments of this application, the Dv50 particle size of the core is 2.1µm to 2.9µm, preferably 2.2µm to 2.5µm. When the Dv50 of the core is too small, the primary particles of the material are too small, the contact area between the cathode material and the electrolyte increases, which may aggravate the occurrence of side reactions. When the Dv50 of the core is too large, the contact area between the material and the electrolyte decreases, the matching with the electrolyte deteriorates, and the material capacity is lowered.

[0041] For example, the Dv50 grain size of the kernel can be 2.1µm, 2.2µm, 2.3µm, 2.4µm, 2.5µm, 2.6µm, 2.7µm, 2.8µm, 2.9µm or any value between 2.1µm and 2.9µm.

[0042] The thickness of the lithium halide layer is 10~60nm, preferably 20~40nm. When the thickness of the lithium halide layer is too small, it cannot effectively weaken the grain boundaries and cannot effectively improve the degree of dissociation and ionic conductivity. When the thickness of the lithium halide layer is too large, it may cause severe particle agglomeration and difficulty in dissociation. In addition, the increased impedance due to the increased coating layer cannot effectively improve the ionic conductivity.

[0043] For example, the thickness of the lithium halide layer can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm or any value between 10 and 60 nm.

[0044] The thickness of the ion-conducting layer is 50~150nm. When the thickness of the ion-conducting layer is too small, it may result in low ion conductivity and increased residual lithium. When the thickness of the ion-conducting layer is too large, it may result in uneven surface coating and significantly increased impedance.

[0045] For example, the thickness of the ion-conducting layer can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm or any value between 50 and 150 nm.

[0046] The thickness of the halide electrolyte layer is 1~80nm, preferably 20~40nm. When the thickness of the halide electrolyte layer is too thin, it cannot effectively improve the contact with the sulfide electrolyte, and the lack of ion conduction between the cathode materials leads to poor performance of the all-solid-state cathode. When the halide electrolyte layer is too thick, it will result in low material capacity.

[0047] For example, the thickness of the halide electrolyte layer can be 1 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm or any value between 1 and 80 nm.

[0048] The thickness of the boride layer is 1~60nm, preferably 4~40nm; when the thickness of the boride layer is too thick, it will cause the material surface to be covered with too much boride, affecting ion shuttle; when the thickness of the boride layer is too thin, it will reduce the material contact performance.

[0049] For example, the thickness of the boride layer can be 1 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm or any value between 1 and 60 nm.

[0050] The Dv50 particle size of the positive electrode active material is 2.5µm to 5µm, preferably 3µm to 3.9µm. When the Dv50 particle size of the positive electrode active material is too small, the primary particles are too small, the contact area between the positive electrode material and the electrolyte increases, which may aggravate the occurrence of side reactions. When the Dv50 particle size of the positive electrode active material is too large, the contact area between the material and the electrolyte decreases, the matching with the electrolyte deteriorates, and the material capacity is low.

[0051] For example, the Dv50 particle size of the positive electrode active material is 2.5µm, 3µm, 3.5µm, 4µm, 4.5µm, 5µm or any value between 2.5µm and 5µm.

[0052] The BET of the positive electrode active material is 0.8~1.4 m. 2 / g, preferably 0.9~1.2 m 2 / g. When the BET of the positive electrode active material is too small, the contact area between the material and the electrolyte decreases, resulting in a lower material capacity; when the BET of the positive electrode active material is too large, the contact area between the material and the electrolyte increases, which may exacerbate the occurrence of side reactions.

[0053] For example, the BET of the positive electrode active material is 0.8m. 2 / g, 0.9 m 2 / g、1 m 2 / g、1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.4 m 2 / g or 0.8~1.4 m 2 Any value between / g.

[0054] This application also provides a method for preparing the positive electrode active material as described above, comprising: The positive electrode precursor is mixed with lithium salt, first lithium halide, and optional M-containing material, and subjected to first sintering to obtain the first sintering product. The first calcined product is mixed with a compound containing M' and subjected to a second sintering to obtain a second calcined product; The second sintering product is mixed with a second lithium halide and an M''-containing halide, and then subjected to a third sintering to obtain a third sintering product; The tertiary sintering product is mixed with a boron-containing substance and subjected to a fourth sintering to obtain a positive electrode active material.

[0055] According to an embodiment of this application, the chemical formula of the positive electrode precursor is Ni. x' Co y' Mn z' (OH)2, where 0.8≤x'≤1, 0≤y'≤0.2, 0≤z'≤0.2; x'+y'+z'=1; The lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium oxide, lithium sulfide, lithium acetate, and lithium methyl. The substance containing M includes at least one of the following: oxides containing M, hydroxides containing M, nitrates containing M, and carbonates containing M; The first lithium halide includes at least one of lithium chloride, lithium fluoride, lithium bromide, and lithium iodide; The mass of the first lithium halide accounts for 500 to 3000 ppm of the mass of the cathode precursor; for example, the mass of the first lithium halide accounts for 500 ppm, 800 ppm, 1000 ppm, 1300 ppm, 1500 ppm, 1800 ppm, 2000 ppm, 2300 ppm, 2500 ppm, 2800 ppm, 3000 ppm or any value between 500 and 3000 ppm of the mass of the cathode precursor.

[0056] The first sintering includes sequential low-temperature sintering and high-temperature sintering, wherein the temperature of the low-temperature sintering is lower than the temperature of the high-temperature sintering; The low-temperature sintering temperature is 250-550℃, the low-temperature sintering time is 1-24h, and the low-temperature sintering heating rate is 1-10℃ / min. If the low-temperature sintering temperature is too low, the lithium salt may not melt completely; if the low-temperature sintering temperature is too high, over-sintering may occur.

[0057] For example, the temperature for low-temperature sintering is any value between 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, or 250-550℃; the time for low-temperature sintering is any value between 1h, 3h, 5h, 8h, 10h, 13h, 15h, 18h, 20h, 23h, 24h, or 1-24h; and the heating rate for low-temperature sintering is any value between 1℃ / min, 3℃ / min, 5℃ / min, 8℃ / min, 10℃ / min, or 1-10℃ / min.

[0058] The high-temperature sintering temperature is 660-900℃, the high-temperature sintering time is 4-24h, and the high-temperature sintering heating rate is 1-8℃ / min. If the high-temperature sintering temperature is too low, incomplete material crystallization may occur, resulting in low material capacity; if the high-temperature sintering temperature is too high, over-sintering may occur, leading to severe agglomeration of material particles.

[0059] For example, the high-temperature sintering temperature is any value between 660℃, 700℃, 800℃, 900℃ or 660-900℃; the high-temperature sintering time is any value between 4h, 5h, 8h, 10h, 13h, 15h, 18h, 20h, 23h, 24h or 4-24h; and the high-temperature sintering heating rate is any value between 1℃ / min, 3℃ / min, 5℃ / min, 8℃ / min or 1-8℃ / min.

[0060] According to embodiments of this application, the M'-containing compound includes at least one of ammonium tungstate, tungsten trioxide, lithium tungstate, tungstic acid, molybdenum trioxide, ammonium molybdate, lithium molybdate, titanium dioxide, cobalt tetroxide, cobalt hydroxyl oxide, cobalt oxide, niobium pentoxide, niobic acid, lithium niobate, lithium borate, boric acid, lithium titanate, tantalum pentoxide, lithium tantalate, silicon dioxide, lithium silicate, lithium zirconate, lithium phosphate, and lithium zirconium phosphate. The mass of the M'-containing compound accounts for 500-20000 ppm of the mass of the calcined product. If the amount of the M'-containing compound added is too low, the compound cannot form a continuous conductive network and cannot effectively improve ionic conductivity. If the amount of the M'-containing compound added is too high, it may cause particle agglomeration, affecting ion transport and capacity utilization.

[0061] For example, the mass of the compound containing M' as a percentage of the mass of the calcined product is 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, 11000 ppm, 12000 ppm, 13000 ppm, 14000 ppm, 15000 ppm, 16000 ppm, 17000 ppm, 18000 ppm, 19000 ppm, 20000 ppm, or any value between 500 and 20000 ppm.

[0062] The second sintering temperature is 550-720℃, the second sintering time is 4-24 hours, and the heating rate of the second sintering is 1-8℃ / min. If the second sintering temperature is too low, the coating agent may not be able to adhere strongly to the material surface, leading to rapid capacity decay in subsequent cycles; if the second sintering temperature is too high, the coating elements may enter the material interior, affecting the material's solid-state capacity. If the second sintering time is too short, the coating elements will not complete the decomposition and chemical reaction on the material surface and cannot effectively adhere to it; if the second sintering time is too long, the coating elements may be doped into the material interior.

[0063] For example, the temperature of the second sintering is any value between 550℃, 600℃, 650℃, 700℃, 720℃, or 550-720℃; the time of the second sintering is any value between 4h, 5h, 8h, 10h, 13h, 15h, 18h, 20h, 23h, 24h, or 4-24h; and the heating rate of the second sintering is any value between 1℃ / min, 3℃ / min, 5℃ / min, 8℃ / min, or 1-8℃ / min.

[0064] According to an embodiment of this application, the second lithium halide includes at least one of lithium chloride, lithium fluoride, lithium bromide, and lithium iodide. The halogen in the M''-containing halide includes at least one of F, Cl, Br, I, and At; The mass of the M'' halide comprises 500-2000 ppm of the dicalcined product, and the molar ratio of the second lithium halide to the M'' halide is 3.03:1-3.1:1. If the mass ratio of the M'' halide to the dicalcined product is too small, the halide electrolyte cannot form an effective coating on the surface. If the mass ratio of the M'' halide to the dicalcined product is too large, there will be too much halide electrolyte coating on the material surface, reducing the capacity of the solid cathode. If the molar ratio of the second lithium halide to the M'' halide is too small, it may be impossible to synthesize a halide solid electrolyte with the corresponding proportion. If the molar ratio of the second lithium halide to the M'' halide is too large, lithium halide residue may remain in the electrolyte, affecting ionic conductivity.

[0065] For example, the mass of the M'' halide as a percentage of the mass of the dicalcined product is 500 ppm, 800 ppm, 1000 ppm, 1300 ppm, 1500 ppm, 1800 ppm, 2000 ppm, or any value between 500 and 2000 ppm; the molar ratio of the second lithium halide to the M'' halide is 3.03:1, 3.04:1, 3.05:1, 3.06:1, 3.07:1, 3.08:1, 3.09:1, 3.1:1, or any value between 3.03:1 and 3.1:1.

[0066] The third sintering temperature is 250-700℃, the third sintering time is 1-24h, and the third sintering heating rate is 1-10℃ / min. If the third sintering temperature is too low, the reaction may be incomplete, resulting in poor crystallinity, which will hinder ion migration, reduce electrical conductivity, and cause impurity phases to appear, which cannot be uniformly coated on the material surface. If the third sintering temperature is too high, it may cause severe volatilization of the second lithium halide, resulting in a significant decrease in ionic conductivity and a deterioration in electrical performance.

[0067] For example, the temperature of the third sintering is any value between 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, or 250-700℃; the time of the third sintering is any value between 1h, 3h, 5h, 8h, 10h, 13h, 15h, 18h, 20h, 23h, 24h, or 1-24h; and the heating rate of the third sintering is any value between 1℃ / min, 3℃ / min, 5℃ / min, 8℃ / min, 10℃ / min, or 1-10℃ / min.

[0068] The boron-containing substance includes at least one of boric acid, lithium borate, boron oxide, lithium thioborate, lithium tetraborate, lithium metaborate, and lithium triborate. The boron-containing substance accounts for 500-2000 ppm of the mass of the calcined product. If the amount of boron-containing substance added is too low, it may cause the boron-containing substance to fail to form a uniform coating on the material surface, resulting in degradation of the material surface structure. If the amount of boron-containing substance added is too high, it may invade the crystal lattice, destroy the near-crystalline structure, and hinder lithium ion diffusion.

[0069] For example, the mass of the boron-containing substance accounts for any value between 500 ppm, 800 ppm, 1000 ppm, 1300 ppm, 1500 ppm, 1800 ppm, 2000 ppm, or 500 to 2000 ppm of the mass of the tricalcined product.

[0070] The fourth sintering temperature is 200-350℃, the fourth sintering time is 1-24h, and the fourth sintering heating rate is 1-10℃ / min. If the fourth sintering temperature is too low, problems such as uneven coating, poor crystallinity of the coating layer, and poor ionic conductivity may occur; if the fourth sintering temperature is too high, boron may diffuse into the bulk lattice of the cathode material, destroying the lattice structure.

[0071] For example, the temperature of the fourth sintering is any value between 200℃, 250℃, 300℃, 350℃, or 200-350℃; the time of the fourth sintering is any value between 1h, 3h, 5h, 8h, 10h, 13h, 15h, 18h, 20h, 23h, 24h, or 1-24h; and the heating rate of the fourth sintering is any value between 1℃ / min, 3℃ / min, 5℃ / min, 8℃ / min, 10℃ / min, or 1-10℃ / min.

[0072] This application also provides a composite positive electrode, comprising a positive electrode active material, a conductive agent, and a sulfide electrolyte; wherein the positive electrode active material is the positive electrode active material described above or a positive electrode active material prepared by the preparation method of the positive electrode active material described above.

[0073] In some embodiments, the sulfide electrolyte accounts for 5% to 30% of the mass of the composite cathode. For example, the mass percentage of the sulfide electrolyte in the composite cathode is 5%, 9.7%, 10%, 15%, 20%, 25%, 30%, or any value between 5% and 30%.

[0074] This application also provides a solid-state battery, including the composite cathode described above.

[0075] The positive electrode active material of this application contains a halide electrolyte layer, which improves the interfacial contact with the sulfide solid electrolyte, reduces the amount of sulfide electrolyte used in the composite positive electrode, and enhances material safety. The halide electrolyte layer in the positive electrode active material of this application can partially replace the sulfide solid electrolyte that would otherwise need to be added, reducing the amount of sulfide electrolyte added in the composite positive electrode for solid-state batteries. On the one hand, this increases the proportion of positive electrode active material in the composite positive electrode, which is beneficial for improving the energy density of solid-state batteries. On the other hand, the halide electrolyte has good high-voltage resistance, high stability, and plasticity, which can compensate for the deficiencies of sulfide electrolyte in terms of oxidation resistance and air stability. Specifically, the halide electrolyte is more stable than the sulfide electrolyte in the atmospheric environment and can be exposed to low-humidity air for a short time without causing severe gas production or toxic release, which greatly reduces the production threshold and cost; in addition, it has good compatibility with high-voltage positive electrodes. By combining the positive electrode active material with halide electrolyte and the sulfide electrolyte with high ionic conductivity, the advantages of both are complementary, and a high-performance all-solid-state lithium battery can be constructed together.

[0076] This application also provides an electrical device, including the solid-state battery described above.

[0077] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0078] I. Preparation of positive electrode active materials Example 1 The positive electrode active material includes a core and a coating layer covering the outer surface of the core. The coating layer includes, from the inside out, a lithium halide layer, an ion-conducting layer, a halide electrolyte layer, and a boride layer. The core has the chemical formula Li. 1.03 Ni 0.9167 Co 0.06 Mn 0.02 Zr 0.002 W 0.0013 The O2 layer is a lithium halide layer of LiCl, the ion-conducting layer includes Li2WO4, WO3, LiCoO2 and Co3O4, the halide electrolyte layer includes Li3YCl6, and the boride layer includes lithium borate.

[0079] Methods for preparing positive electrode active materials include: Step 1: Select Ni 0.92 Co 0.06 Mn 0.02(OH)₂ was used as the positive electrode precursor. Lithium hydroxide was added at a ratio of 1.03:1 (Li molar to total metal molar ratio in the positive electrode precursor). ZrO₂, WO₃, and lithium chloride were also added. The amount of ZrO₂ added was 2000 ppm of the positive electrode precursor mass, the amount of WO₃ added was 2500 ppm of the positive electrode precursor mass, and the mass of lithium chloride was 500 ppm of the positive electrode precursor mass. The high-speed mixer was set at 900 rpm for 20 min. The mixture was then subjected to a first sintering in a pure oxygen atmosphere to obtain the first-sintered product. The sintering process was divided into two stages, with a pure oxygen flow rate of 15 m³ / h. 3 / h, oxygen value in furnace is 99%, reaction is carried out at 470℃ for 6h with a heating rate of 4℃ / min, and then reaction is carried out at 730℃ for 14h with a heating rate of 4℃ / min and a cooling rate of 3℃ / min.

[0080] Step 2: After the product of the first burnt product is crushed by air jet, it is passed through a 325-mesh sieve.

[0081] Step 3: Mix the sieved first-calcination product with WO3 and Co3O4. The mass of WO3 should be 2000 ppm of the first-calcination product, and the mass of Co3O4 should be 10000 ppm of the first-calcination product. The high-speed mixer should be set at 800 rpm for 25 minutes. Place the mixture in a pure oxygen atmosphere for a second sintering, with a pure oxygen flow rate of 20 m³ / h. 3 / h, with an oxygen value of 99% in the furnace, the reaction was carried out at 650℃ for 8 hours, with a heating rate of 3℃ / min and a cooling rate of 3℃ / min, to obtain the second calcination product.

[0082] Step 4: Pass the secondary calcination product through a 325-mesh sieve. Mix the sieved secondary calcination product with lithium chloride and yttrium chloride. The molar ratio of lithium chloride to yttrium chloride is 3.05:1, and the mass of yttrium chloride accounts for 1500 ppm of the secondary calcination product. The high-speed mixer speed is 800 rpm, and the mixing time is 25 min. Place the mixture in a nitrogen atmosphere for a third sintering at 500℃ for 14 h, with a heating rate of 3℃ / min and a cooling rate of 3℃ / min, to obtain the tertiary calcination product.

[0083] Step 5: Pass the triple-burned product through a 325-mesh sieve. Mix the sieved triple-burned product with lithium borate, where the mass of lithium borate accounts for 1200 ppm of the triple-burned product. Use a high-speed mixer at 750 rpm for 20 min. Place the mixture in a nitrogen atmosphere for a fourth sintering at 300℃ for 10 h, with a heating rate of 5℃ / min and a cooling rate of 2.5℃ / min, to obtain the quadruple-burned product.

[0084] Step 6: After the product from the four-calcination process is passed through a 325-mesh sieve, the positive electrode active material is obtained.

[0085] Electron micrograph of the positive electrode active material in Example 1 is shown below. Figure 1As shown.

[0086] Example 2 The structure of the positive electrode active material in Example 2 is the same as that in Example 1.

[0087] The difference between Example 2 and Example 1 is that in step 4, the molar ratio of lithium chloride to yttrium chloride is 3.03:1, the mass of yttrium chloride accounts for 500 ppm of the mass of the second sintering product, and the temperature of the third sintering is 250°C. Everything else is the same as in Example 1.

[0088] Example 3 The structure of the positive electrode active material in Example 3 is the same as that in Example 1.

[0089] The difference between Example 3 and Example 1 is that in step 4, the molar ratio of lithium chloride to yttrium chloride is 3.1:1, the mass of yttrium chloride accounts for 2000 ppm of the mass of the second sintering product, and the temperature of the third sintering is 700°C. Everything else is the same as in Example 1.

[0090] Example 4 The structure of the positive electrode active material in Example 4 differs from that in Example 1 in that the halide electrolyte layer includes Li3YBr6.

[0091] The difference between Example 4 and Example 1 is that in step 4, lithium bromide is used instead of lithium chloride in Example 1 in an equal molar amount, and yttrium bromide is used instead of yttrium chloride in Example 1 in an equal mass. Everything else is the same as in Example 1.

[0092] Example 5 The structure of the positive electrode active material in Example 5 is the same as that in Example 1.

[0093] The difference between Example 5 and Example 1 is that in step 5, the mass of lithium borate accounts for 500 ppm of the mass of the triple-sintered product, and the fourth sintering temperature is 260°C. Everything else is the same as in Example 1.

[0094] Example 6 The structure of the positive electrode active material in Example 6 is the same as that in Example 1.

[0095] The difference between Example 6 and Example 1 is that in step 5, the mass of lithium borate accounts for 2000 ppm of the mass of the tricalcined product. Everything else is the same as in Example 1.

[0096] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that step 4 in Example 1 is omitted, and step 5 is performed directly using the product of step 3 after step 3. Everything else is the same as in Example 1.

[0097] The positive electrode active material prepared in Comparative Example 1 does not contain a halide electrolyte layer. Everything else is the same as in Example 1.

[0098] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step 4, the molar ratio of lithium chloride to yttrium chloride is 2.7:1, the mass of yttrium chloride accounts for 300 ppm of the mass of the second sintering product, the temperature of the third sintering is 750°C, and the time of the third sintering is 26 h. Everything else is the same as in Example 1.

[0099] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step 4, the mass of yttrium chloride accounts for 3500 ppm of the mass of the dicalcined product. Everything else is the same as in Example 1.

[0100] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that step 5 is omitted, and the product of step 4 is directly passed through a 325-mesh sieve, and the sieved product is used as the positive electrode active material.

[0101] The positive electrode active material of Comparative Example 4 does not contain a boride layer.

[0102] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in step 5, the mass of lithium borate accounts for 300 ppm of the mass of the triple-sintered product, and the fourth sintering temperature is 150°C. Everything else is the same as in Example 1.

[0103] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that in step 5, the mass of lithium borate accounts for 3400 ppm of the mass of the triple-sintered product, and the fourth sintering temperature is 400°C. Everything else is the same as in Example 1.

[0104] II. Performance Testing The physical properties of the positive electrode active materials prepared in the examples and comparative examples were characterized, including particle size distribution, BET, and SEM tests.

[0105] The test results are shown in Table 1.

[0106] Table 1. Physical properties of the positive electrode active materials prepared in the examples and comparative examples.

[0107] The positive electrode active materials prepared in the examples and comparative examples were assembled into batteries under the same conditions, specifically including: 1. Add the positive electrode active material and solid electrolytes Li6PS5Cl and VGCF in a mortar at a mass ratio of 90:10:3 and grind for 10 minutes to obtain the composite positive electrode material; 2. Weigh the electrolyte Li6PS5Cl, pour it into the solid-state battery mold, manually rotate it until it is even and flat, and pressurize and hold for 1 minute; 3. Weigh the composite cathode material (the mass ratio of composite cathode material to electrolyte is 1:5), pour it into the mold, manually rotate it until it is uniform and flat, and pressurize and hold for 1 minute; 4. Add indium sheet, lithium and copper foil to the negative electrode side, and apply pressure and hold for 30 seconds; 5. Place the mold into the metal assembly, apply pressure, and tighten the knob; 6. Let stand for 120 minutes, and then perform a charge and discharge test at a rate of 0.1C under the conditions of 25℃ and voltage range of 1.9-3.7 V. The constant voltage charging cutoff current is 0.025C.

[0108] Electrochemical performance tests were conducted on the battery by performing 0.1C charge-discharge cycles at 1.9–3.7V. The charge-discharge capacity of the first cycle and the charge-discharge capacity of the 250th cycle were recorded. The specific results are shown in Table 2.

[0109] Table 2. Comparison of electrochemical performance between the examples and comparative examples.

[0110] From Table 2, Figure 2 and Figure 3 It can be seen that Examples 1-6 have both high initial coulombic efficiency and high cycle stability, and their overall performance is significantly better than that of Comparative Examples 1-6.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0112] Furthermore, those skilled in the art will understand 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 form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A positive electrode active material, characterized in that, It includes a core and a coating layer covering the outer surface of the core. The coating layer includes a lithium halide layer, an ion-conducting layer, a halide electrolyte layer and a boride layer arranged sequentially from the inside to the outside.

2. The positive electrode active material according to claim 1, characterized in that, 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 at least one of Zr, Sr, Y, Sb, Al, W, Ta, Mg, Ca, Ti, Mo, Nb, and B; And / or, the lithium halide layer comprises LiX, where X contains at least one of F, Cl, Br, I, and At; And / or, the ion-conducting layer comprises Li b M' c O d M' e O f At least one of the following, wherein M' includes at least one of W, Mo, Ti, Co, B, Ta, Si, Nb, Zr, and P, 1≤b≤7, 1≤c≤5, 2≤d≤7, 1≤e≤3, and 2≤f≤5; And / or, the halide electrolyte layer comprises Li3M''X6, where M'' contains at least one of Y, Sc, Er, Ho, In, Ga, Al, Ti, V, Ta, and Nb; And / or, the boride layer includes at least one of lithium borate, lithium thioborate, lithium tetraborate, lithium metaborate, and lithium triborate.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The core's Dv50 particle size is 2.1µm~2.9µm; And / or, the thickness of the lithium halide layer is 10~60 nm; And / or, the thickness of the ion-conducting layer is 50~150nm; And / or, the thickness of the halide electrolyte layer is 1~80 nm; And / or, the thickness of the boride layer is 1~60 nm; And / or, the Dv50 of the positive electrode active material is 2.5µm to 5µm; And / or, the BET of the positive electrode active material is 0.8~1.4m. 2 / g.

4. A method for preparing a positive electrode active material as described in any one of claims 1-3, characterized in that, include: The positive electrode precursor is mixed with lithium salt, first lithium halide, and optional M-containing material, and subjected to first sintering to obtain the first sintering product. The first calcined product is mixed with a compound containing M' and subjected to a second sintering to obtain a second calcined product; The second sintering product is mixed with a second lithium halide and an M''-containing halide, and then subjected to a third sintering to obtain a third sintering product; The tertiary sintering product is mixed with a boron-containing substance and subjected to a fourth sintering to obtain a positive electrode active material.

5. The method for preparing the positive electrode active material according to claim 4, characterized in that, The chemical formula of the positive electrode precursor is Ni. x' Co y' Mn z' (OH)2, where 0.8≤x'≤1, 0≤y'≤0.2, 0≤z'≤0.2; x'+y'+z'=1; And / or, the lithium salt includes at least one of lithium carbonate, lithium hydroxide, lithium oxide, lithium sulfide, lithium acetate, and lithium methyl. And / or, the substance containing M includes at least one of the following: oxides containing M, hydroxides containing M, nitrates containing M, and carbonates containing M; And / or, the first lithium halide includes at least one of lithium chloride, lithium fluoride, lithium bromide, and lithium iodide; And / or, the mass of the first lithium halide accounts for 500 to 3000 ppm of the mass of the cathode precursor; And / or, the first sintering includes sequential low-temperature sintering and high-temperature sintering, wherein the temperature of the low-temperature sintering is lower than the temperature of the high-temperature sintering; And / or, the temperature of the low-temperature sintering is 250-550℃, the time of the low-temperature sintering is 1-24h, and the heating rate of the low-temperature sintering is 1-10℃ / min; And / or, the high-temperature sintering temperature is 660-900℃, the high-temperature sintering time is 4-24h, and the high-temperature sintering heating rate is 1-8℃ / min.

6. The method for preparing the positive electrode active material according to claim 4, characterized in that, The M'-containing compound includes at least one of the following: ammonium tungstate, tungsten trioxide, lithium tungstate, tungstic acid, molybdenum trioxide, ammonium molybdate, lithium molybdate, titanium dioxide, cobalt tetroxide, cobalt hydroxyl oxide, cobalt oxide, niobium pentoxide, niobic acid, lithium niobate, lithium borate, boric acid, lithium titanate, tantalum pentoxide, lithium tantalate, silicon dioxide, lithium silicate, lithium zirconate, lithium phosphate, and lithium zirconium phosphate. And / or, the mass of the M'-containing compound accounts for 500 to 20,000 ppm of the mass of the calcined product; And / or, the second sintering temperature is 550-720℃; the second sintering time is 4-24h; and the second sintering heating rate is 1-8℃ / min.

7. The method for preparing the positive electrode active material according to claim 4, characterized in that, The second lithium halide includes at least one of lithium chloride, lithium fluoride, lithium bromide, and lithium iodide; And / or, the halogen in the M''-containing halide includes at least one of F, Cl, Br, I, and At; And / or, the mass of the M'' halide accounts for 500~2000 ppm of the mass of the dicalcined product, and the molar ratio of the second lithium halide to the M'' halide is 3.03:1~3.1:1; And / or, the temperature of the third sintering is 250-700℃, the time of the third sintering is 1-24h, and the heating rate of the third sintering is 1-10℃ / min; And / or, the boron-containing substance includes at least one of boric acid, lithium borate, boron oxide, lithium thioborate, lithium tetraborate, lithium metaborate, and lithium triborate; And / or, the mass of the boron-containing substance accounts for 500 to 2000 ppm of the mass of the tricalcined product; And / or, the temperature of the fourth sintering is 200-350℃; the time of the fourth sintering is 1-24h; and the heating rate of the fourth sintering is 1-10℃ / min.

8. A composite positive electrode, characterized in that, It includes a positive electrode active material, a conductive agent, and a sulfide electrolyte; wherein the positive electrode active material is the positive electrode active material according to any one of claims 1-3 or is a positive electrode active material prepared by the preparation method of the positive electrode active material according to any one of claims 4-7; And / or, the sulfide electrolyte accounts for 5% to 30% of the mass of the composite cathode.

9. A solid-state battery, characterized in that, Includes the composite positive electrode as described in claim 8.

10. An electrical-related device, characterized in that, Includes the solid-state battery as described in claim 9.

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