Composite cathode active material, preparation method thereof, cathode, and full solid-state battery

Abstract

The application relates to a kind of composite positive electrode active material and its preparation method, positive electrode and full solid-state battery in lithium battery production technical field.The composite positive electrode active material is core-shell structure, the core material includes ternary positive electrode active material, the shell includes first coating layer and second coating layer;The first coating layer includes Ta, and the second coating layer includes La and F.Through the coordination of first coating layer and second coating layer, the composite positive electrode active material has high ion release rate and ion migration rate and good cycle stability and high voltage stability, and can also effectively improve the interface contact between positive electrode and solid-state electrolyte membrane, so that the prepared battery has good cycle performance and rate performance, and lower battery internal resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a composite positive electrode active material, a preparation method thereof, a positive electrode and a full solid-state battery. BACKGROUND

[0002] The ternary positive electrode active material includes three elements of nickel, cobalt and manganese or nickel, cobalt and aluminum, and is the most promising positive electrode material for full solid-state lithium batteries at present. It has a high energy density and is widely concerned. However, the ternary positive electrode is often accompanied by particle breakage, oxygen release of the positive electrode, and the strong oxidizing property of Ni 4+ will cause an increase in the interfacial side reaction and the cycle performance of the composite positive electrode will decline. Therefore, it is necessary to further optimize and improve the interfacial contact between the positive electrode and the sulfide or halide electrolyte, promote the transmission of lithium ions, reduce the side reaction, and improve the cycle performance of the battery. SUMMARY

[0003] The purpose of the present application is to provide a composite positive electrode active material, a preparation method thereof, a positive electrode and a full solid-state battery.

[0004] The technical solution of the present application is as follows:

[0005] The first aspect of the present application provides a composite positive electrode active material, which is a core-shell structure, the core of the core-shell structure includes a ternary positive electrode active material, and the shell of the core-shell structure includes a first coating layer and a second coating layer.

[0006] The first coating layer is formed on the surface of the ternary positive electrode active material particles.

[0007] The second coating layer is formed on the side surface of the first coating layer away from the ternary positive electrode active material particles.

[0008] The first coating layer includes Ta.

[0009] The second coating layer includes La and F.

[0010] In some embodiments, the content of Ta in the first coating layer is S, the content of La and F in the second coating layer is M and N respectively, and 0.6

[0011] In some embodiments, the ternary positive electrode active material is LiNi x Co y Mn 1-x-y O2, wherein x=0.5-1.0, y>0, and x+y<1.

[0012] In some embodiments, the thickness of the first coating layer is 5-20 nm.

[0013] In some embodiments, the second coating layer has a thickness of 1-15 nm.

[0014] In some embodiments, the first coating layer has a thickness greater than that of the second coating layer.

[0015] In a second aspect, the present application provides a preparation method of the composite cathode active material as described above, comprising the following steps:

[0016] S1, mixing a ternary cathode active material precursor, a lithium source and a Ta source, heat preservation, and then calcining to form an intermediate, the intermediate comprising a ternary cathode active material and a first coating layer formed on the surface of the ternary cathode active material;

[0017] S2, mixing the intermediate, a La source and LiF, dissolving in a solvent, stirring in a constant temperature environment, filtering, drying and secondary calcining to obtain a composite cathode active material.

[0018] In some embodiments, in the step S1, the molar ratio of the ternary cathode active material to the Ta source is 1:(0.008-0.05).

[0019] In some embodiments, in the step S2, the molar ratio of the intermediate, the La source and LiF is 1:(0.001-0.01):(0.003-0.015).

[0020] In a third aspect, the present application provides a cathode comprising the composite cathode active material as described in the first aspect.

[0021] In a fourth aspect, the present application provides an all-solid-state battery comprising the composite cathode active material as described in the first aspect and / or the cathode as described in the third aspect.

[0022] Compared with the prior art, the technical scheme of the present application has the beneficial technical effects that: the first coating layer containing Ta is formed on the surface of the ternary cathode active material, on the one hand, the Ta coating can form a coating layer with high ionic conductivity on the surface of the ternary cathode active material, on the other hand, Ta can react with Ni 4+ and residual lithium on the surface of the ternary cathode active material during sintering, which is conducive to the structural stability of the first coating layer and the improvement of the battery capacity, and improves the cycle performance of the battery.

[0023] The second coating layer contains La and F, on the one hand, which is conducive to improving the oxidation resistance of the cathode active material and improving the stability of the cathode active material at high voltage, on the other hand, the second coating layer also has good lithium ion transport capacity, which can improve the lithium ion conduction of the solid-solid interface between the cathode and the electrolyte.

[0024] The first coating layer and the second coating layer cooperate, so that the composite positive electrode active material has high ion release rate and ion migration rate, good cycle stability and high voltage stability, and can effectively improve the interface contact between the positive electrode and the solid electrolyte membrane, so that the prepared battery has good cycle performance and rate performance, and low battery internal resistance. DETAILED DESCRIPTION

[0025] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] Unless otherwise defined, all technical and scientific terms used in the present application have the same meanings as commonly understood by those skilled in the art to which the present application belongs; the terms used in the specific embodiments are only for the purpose of describing the specific embodiments, and are not intended to limit the present application; the terms in the specification and claims of the present application and the above description, such as "include" and "have", as well as any variations thereof, are intended to cover non-exclusive inclusion.

[0027] In the description of the specific embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0028] In the present application, the phrase "embodiment" means that the specific features, structures or properties described in combination with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the described embodiments of the present application can be combined with other embodiments.

[0029] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in the present application generally represents an "or" relationship between the front and rear associated objects.

[0030] Throughout this disclosure, numerical expressions are approximate measures of a range or limit to encompass minor deviations and embodiments having about the stated value as well as embodiments having the stated exact value. Except in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., amounts or conditions) in this specification (including the claims) are to be rea d as approximations of the numerical values that they represent, even though the numerical values are presented in a manner indicating a particular precision. The numerical values should be understood to be approximations that can vary from a slightly different numerical value in some instances. If the numerical value is preceded by the term "about" the numerical value indicates that the stated numerical value can vary from the value by a minor amount. If the inaccuracy provided by "about" is not otherwise understood in the art to have this ordinary meaning, then "about" as used in this disclosure indicates at least a variation that can be produced by the ordinary methods of measuring and using such parameters. For example, "about" can include a variation smaller than or equal to 5%, alternatively smaller than or equal to 4%, alternatively smaller than or equal to 3%, alternatively smaller than or equal to 2%, alternatively smaller than or equal to 1%, alternatively smaller than or equal to 0.5%, and in certain aspects, alternatively smaller than or equal to 0.1%.

[0031] In addition, the disclosure of ranges includes all values and further subdivisions between the stated ranges and the disclosure of ranges includes the endpoints and subdivisions of the ranges given.

[0032] The ternary cathode is often accompanied by particle breakage, oxygen release from the cathode, and strong oxidizing nature of Ni 4+ which can cause an increase in interfacial side reactions and deterioration of the cycle performance of the composite cathode. Therefore, it is necessary to further optimize and improve the interfacial contact between the cathode and the sulfide or halide electrolyte, promote lithium ion transmission, reduce side reactions, and improve the cycle performance of the battery.

[0033] To solve the above problems, the present application provides a technical scheme.

[0034] In a first aspect, the present application provides a composite cathode active material, the composite cathode active material is a core-shell structure, the core of the core-shell structure comprises a ternary cathode active material, and the shell of the core-shell structure comprises a first coating layer and a second coating layer.

[0035] The first coating layer is formed on the surface of the ternary cathode active material particles.

[0036] The second coating layer is formed on the side surface of the first coating layer away from the ternary cathode active material particles.

[0037] The first coating layer comprises Ta.

[0038] The second coating layer comprises La and F.

[0039] The first coating layer containing Ta is formed on the surface of the ternary positive electrode active material. On the one hand, the Ta coating can form a coating layer with high ionic conductivity on the surface of the ternary positive electrode active material. On the other hand, Ta can react with Ni 4+ and residual lithium on the surface of the ternary positive electrode active material during sintering, which is conducive to the structural stability of the first coating layer and the improvement of the battery capacity and the cycle performance of the battery.

[0040] The second coating layer contains La and F. On the one hand, it is conducive to improving the oxidation resistance of the positive electrode active material and the stability of the positive electrode active material at high voltage. On the other hand, the second coating layer also has good lithium ion transport capacity and can improve the lithium ion conduction of the solid-solid interface between the positive electrode and the electrolyte.

[0041] The first coating layer and the second coating layer cooperate with each other, so that the composite positive electrode active material has high ion extraction rate and ion migration rate, good cycle stability and high voltage stability, and can effectively improve the interface contact between the positive electrode and the solid-state electrolyte membrane, so that the prepared battery has good cycle performance and rate performance, and low battery internal resistance.

[0042] In some embodiments, the content of Ta in the first coating layer is S, and the content of La and F in the second coating layer is M and N, respectively, which satisfies: 0.6 < (N + S) / M < 1.2.

[0043] The positive electrode under this condition has good interface ion transport performance, significantly improves the side reaction of the positive electrode, and makes the battery have good rate performance and cycle performance.

[0044] In some embodiments, the ternary positive electrode active material is LiNi x Co y Mn 1-x-y O2, wherein x = 0.5-1.0, y > 0, and x + y < 1. The advantage of this setting is to improve the energy density of the battery. Ta in the coating layer can react with Ni 4+ to form a stable structure.

[0045] In some embodiments, the thickness of the first coating layer is 5-20 nm.

[0046] In specific applications, in addition to the range endpoints 5 nm and 20 nm, the specific thickness of the first coating layer can also be selected as 7 nm, 9 nm, 12 nm, 15 nm, 18 nm, or any value within the range. The present application does not make any limitation on this.

[0047] In some embodiments, the thickness of the second coating layer is 1-15 nm.

[0048] In specific applications, the thickness of the first coating layer can be selected from 1 nm, 3 nm, 5 nm, 7 nm, 9 nm, 12 nm, 14 nm or any value within the range, in addition to the range endpoints 1 nm and 15 nm. The present application does not make any limitation in this regard.

[0049] In some embodiments, the thickness of the first coating layer is greater than the thickness of the second coating layer.

[0050] The Ta coating can form a coating layer with high ionic conductivity on the surface of the ternary positive electrode active material. The thickness of the first coating layer being greater than the thickness of the second coating layer is beneficial to improving the lithium ion transmission rate of the composite positive electrode active material and improving the rate performance of the battery.

[0051] In a second aspect, the present application provides a preparation method of the composite positive electrode active material as above, comprising the following steps:

[0052] S1, mixing a ternary positive electrode active material precursor, a lithium source and a Ta source, heat preservation, and then calcining to form an intermediate, the intermediate comprising a ternary positive electrode active material and a first coating layer formed on the surface of the ternary positive electrode active material;

[0053] S2, mixing the intermediate, a La source and LiF, dissolving in a solvent, stirring in a constant temperature environment, filtering, drying and secondary calcining to obtain the composite positive electrode active material.

[0054] In some embodiments, in step S1, the molar ratio of the ternary positive electrode active material to the Ta source is 1:(0.008-0.05).

[0055] In some embodiments, in step S1, the heat preservation comprises the step of heat preservation at 400-500℃ for 4-6h.

[0056] In some embodiments, in step S1, the calcining comprises the step of calcining at a calcining temperature of 700-800℃ for 7-10h in an air atmosphere.

[0057] In some embodiments, after step S1, there is further sieving and iron removal. After sieving, the particle size D50 of the intermediate is 3-12μm.

[0058] In some embodiments, in step S2, the molar ratio of the intermediate, the La source and LiF is 1:(0.001-0.01):(0.003-0.015).

[0059] In some embodiments, in step S2, the solvent is anhydrous ethanol.

[0060] In some embodiments, in step S2, the constant temperature of the constant temperature environment is 30-60℃.

[0061] In some embodiments, in step S2, the stirring time is greater than 4 hours.

[0062] In some preferred embodiments, in step S2, the stirring time is 4-20 hours.

[0063] In some embodiments, in step S2, the stirring speed is 300-800 rpm.

[0064] In some embodiments, in step S2, the secondary calcination comprises calcination in an air atmosphere at a calcination temperature of 300-600°C for 3-5 hours.

[0065] In a third aspect, the present application provides a positive electrode, which comprises the composite positive electrode active material according to the first aspect.

[0066] In some embodiments, the positive electrode comprises a positive electrode material layer, which comprises the composite positive electrode active material according to the first aspect.

[0067] In some embodiments, the positive electrode material layer further comprises a binder. The binder improves the binding between the composite positive electrode active material particles and also improves the binding between the positive electrode material layer and the positive electrode current collector.

[0068] In some embodiments, non-limiting examples of the binder include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, and the like.

[0069] In some embodiments, the positive electrode material layer comprises a conductive agent, thereby imparting electrical conductivity to the electrode. The conductive agent can comprise any electrically conductive material, provided that it does not cause chemical changes. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, and the like), metal-based materials (e.g., metal powder, metal fibers, and the like, including, for example, copper, nickel, aluminum, silver, and the like), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0070] In some embodiments, the positive electrode tab comprises a positive electrode current collector, which can be, illustratively, aluminum (Al), but is not limited thereto.

[0071] In some embodiments, the mass percentage of the composite positive electrode active material particles in the positive electrode material layer is 80-99%, based on the total mass of the positive electrode material layer.

[0072] In some embodiments, the mass of the conductive agent accounts for 1-20% of the mass of the positive electrode material layer.

[0073] In some embodiments, the mass of the binder is 1-20% of the mass of the positive electrode material layer.

[0074] In some embodiments, the positive electrode tab provided by the present application further comprises a solid-state electrolyte powder for improving the ionic conductivity of the composite positive electrode. The present application does not limit the type of solid-state electrolyte powder, which can be an oxide solid-state electrolyte powder, a sulfide solid-state electrolyte powder, or a halide solid-state electrolyte powder. Optionally, the mass of the solid-state electrolyte powder is 1-20% of the mass of the positive electrode tab; preferably 5-20%.

[0075] In some embodiments, the thickness of the positive electrode material layer in the positive electrode tab provided by the present application is 30-400 μm, such as 30 μm, 40 μm, 50 μm, 80 μm, 110 μm, 200 μm, 300 μm, 400 μm, preferably 50-110 μm.

[0076] In a fourth aspect, the present application provides a full solid-state battery comprising the composite positive electrode active material of the first aspect and / or the positive electrode of the third aspect.

[0077] The full solid-state battery further comprises a negative electrode, wherein the negative electrode comprises a negative electrode tab.

[0078] The negative electrode tab comprises:

[0079] In some embodiments, the negative electrode tab comprises a current collector and a negative electrode active material layer disposed on the current collector.

[0080] In the present application, the specific type of negative electrode active material is not specifically limited and can be selected as needed. Specifically, the negative electrode active material is selected from one or more of natural graphite, artificial graphite, mesophase carbon microbeads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured Li4Ti5O12, and Li-Al alloy. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and mixtures thereof. The crystalline carbon can be amorphous or flaky, small flaky, spherical, or fibrous natural graphite or artificial graphite. The amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc. 12

[0081] In some embodiments, elemental metals and metal-based compounds can also be selected as negative electrode active materials, such as compounds containing Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, Zn, etc.

[0082] ​In some embodiments, the mass ratio of the negative active material included in the negative active material layer can be 80-99%, for example, 80%, 85%, 90%, 95%, 97%, 99%, etc., and preferably 95-97%.

[0083] In some embodiments, the negative material layer can include a binder; the binder improves the binding of the negative active material particles to each other and the binding of the negative active material to the current collector.

[0084] In some embodiments, non-limiting examples of the binder include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, nylon, etc.

[0085] In some embodiments, the negative active material layer can be obtained by coating a negative slurry on a negative current collector, and then performing drying and the like, the negative slurry including at least a negative active material and a negative binder. When an aqueous solvent is used as a liquid medium for forming the negative slurry, it is preferable to use a viscosity enhancer for slurry formation, which is generally used to adjust the viscosity of the slurry.

[0086] In some embodiments, the aforementioned viscosity enhancer can be one or more of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphated starch, casein and its salts, etc.

[0087] In some embodiments, the mass ratio of the viscosity enhancer in the negative slurry can be 0.1-5%, for example, 0.1%, 0.2%, 0.5%, 0.6%, 1%, 2%, 3%, 4%, 5%, etc., and preferably 0.5-3%, and further preferably 0.6-2%.

[0088] In some embodiments, the negative active material layer includes a conductive material, thereby making the electrode conductive. The conductive material can include any conductive material that does not cause chemical changes. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powder, metal fibers, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0089] In some embodiments, the negative current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, a polymer substrate coated with a conductive metal, and combinations thereof.

[0090] The all-solid-state battery further includes a solid-state electrolyte film.

[0091] The solid-state electrolyte film includes a solid-state electrolyte.

[0092] In some embodiments, the solid-state electrolyte can also be a sulfide solid-state electrolyte including any one of Li2S-P2S5, Li2S-P2S5-MSx (where M is Si, Ge and Sn and 0≤x≤2), Li3.4Si0.4P0.6S4, Li10GeP2S11.7O0.3, Li9.6P3S12, Li7P3S11, Li9P3S9O3, Li10.35Si1.35P1.65S12, Li9.81Sn0.81P2.19S12, Li10(Si0.5Ge0.5)P2S12, Li(Ge0.5Sn0.5)P2S12, Li(Si0.5Sn0.5)PsS12, Li10GeP2S12 (LGPS), Li6PS5X (where X is Cl, Br or I), Li7P2S8I, Li10.35Ge1.35P1.65S12, Li3.25Ge0.25P0.75S4, Li10SnP2S12, Li10SiP2S12, or a combination of at least two of Li9.54Si1.74P1.44S11.7Cl0.3, typical but non-limiting combinations include a combination of Li2S-P2S5 and Li2S-P2S5-MSx (where M is Si, Ge and Sn and 0≤x≤2), a combination of Li3.4Si0.4P0.6S4 and Li10GeP2S11.7O0.3, a combination of Li7P3S11, Li9P3S9O3 and Li10.35Si1.35P1.65S12, or a combination of Li9.81Sn0.81P2.19S12, Li10(Si0.5Ge0.5)P2S12, Li(Ge0.5Sn0.5)P2S12 and Li(Si0.5Sn0.5)PsS12.

[0093] In some embodiments, the solid-state electrolyte can also be a halide solid-state electrolyte having a general formula of Li x MX y N z wherein 1≤x≤4, 4≤y+nz≤8, n is an absolute value of a valence of N. The metal element M includes at least one of V, Cr, Mn, Zn, Cd, Fe, Pb, In, Y, Al, Sc, La, Lu, Ga, Zr or Hf. X includes at least one of halogen elements F, Cl, Br, I. N is at least one of non-metal elements O, S. Illustratively, the halide solid-state electrolyte includes Li3InBr 6-m Clm (0≤m≤6), LiInX4, Li3YX6, Li3ErX6, Li3ScX6, Li3LaX6, Li 3-m Er 1- m Zr m Cl6 (x≤0.6), Li 3-m Y 1-m Zr m Cl6 (m≤0.6), Li3Y 1-m In m Cl6(0 <m<1)、Li2ZrX6、Li2ZrX y Oz(0<z≤1,y+z=6)、Li2ZrX y A mixture of one or more of the following: Sz (0 < z ≤ 1, y + z = 6).

[0094] In some preferred embodiments, the halide solid electrolyte includes Li₂ZrCl₆, Li₂ZrCl₅F, and Li₂ZrCl₆. 5.5 O 0.25 Li3InCl6, Li3YCl6, Li2H f At least one of Cl6, LiInBr4, Li3InBr6, Li3LaI6, and Li3LuCl6.

[0095] The solid electrolyte includes at least one of sulfide solid electrolyte and halide solid electrolyte, and may also include oxide solid electrolyte.

[0096] In some embodiments, the oxide solid electrolyte includes any one or a combination of at least two of garnet ceramics, LISICON-type oxides, NASICON-type oxides, or perovskite ceramics. Typical but non-limiting combinations include combinations of garnet ceramics and LISICON-type oxides, combinations of LISICON-type oxides and NASICON-type oxides, or combinations of LISICON-type oxides, NASICON-type oxides, and perovskite ceramics.

[0097] In some embodiments, the garnet ceramic includes Li 6.5 La3Zr 1.75 Te 0.25 O 12 Li7La3Zr2O 12 Li 6.2 Ga 0.3 La 2.95 Rb 0.05 Zr2O 12 Li 6.85 La 2.9Ca 0.1 Zr 1.75 Nb 0.25 O 12 , Li 6.25 Al 0.25 La3Zr2O 12 , Li 6.75 La3Zr 1.75 Nb 0.25 O 12 or a combination of at least two of any of Li6.75La3Zr1.75Nb0.25O12, Li6.5La3Zr1.75Te0.25O12, Li7La3Zr2O12, Li6.85La2.9Ca0.1Zr1.75Nb0.25O12, Li6.25Al0.25La3Zr2O12, Li6.5La3Zr1.75Te0.25O12, and Li6.75La3Zr1.75Nb0.25O12, typical but non-limiting combinations include a combination of Li6.5La3Zr1.75Te0.25O12 and Li7La3Zr2O12, a combination of Li6.85La2.9Ca0.1Zr1.75Nb0.25O12 and Li6.25Al0.25La3Zr2O12, or a combination of Li6.25Al0.25La3Zr2O12, Li6.75La3Zr1.75Nb0.25O12, and Li6.75La3Zr1.75Nb0.25O12.

[0098] In some embodiments, the LISICON-type oxide includes any of Li14Zn(GeO4)4, Li3+x(P1-xSix)O4 (where 0 < x < 1), or Li3+xGexV1-xO4 (where 0 < x < 1), or a combination of at least two of any of Li14Zn(GeO4)4, Li3+x(P1-xSix)O4 (where 0 < x < 1), and Li3+xGexV1-xO4 (where 0 < x < 1), typical but non-limiting combinations include a combination of Li14Zn(GeO4)4 and Li3+x(P1-xSix)O4 (where 0 < x < 1), a combination of Li3+x(P1-xSix)O4 (where 0 < x < 1) and Li3+xGexV1-xO4 (where 0 < x < 1), or a combination of Li14Zn(GeO4)4, Li3+x(P1-xSix)O4 (where 0 < x < 1), and Li3+xGexV1-xO4 (where 0 < x < 1).

[0099] In some embodiments, the NASICON-type oxide can be defined by LiMM'(PO4)3, where M and M' are independently selected from the group consisting of Al, Ge, Ti, Sn, Hf, Zr, and La, for example, in certain variations, the NASICON-type oxide can be selected from any one or a combination of at least two of Li1+xAlxGe2-x(PO4)3(LAGP) where 0≤x≤2, Li1+xAlxTi2-x(PO4)3(LATP) where 0≤x≤2, Li1+xYxZr2-x(PO4)3(LYZP) where 0≤x≤2, Li1.3Al0.3Ti1.7(PO4)3, LiTi2(PO4)3, LiGeTi(PO4)3, LiGe2(PO4)3, LiHf2(PO4)3, typical but non-limiting combinations include a combination of LAGP and LATP, a combination of LYZP and Li1.3Al0.3Ti1.7(PO4)3, or a combination of LiTi2(PO4)3, LiGeTi(PO4)3, LiGe2(PO4)3, and LiHf2(PO4)3.

[0100] In some embodiments, the perovskite-type ceramic includes any one or a combination of at least two of Li3.3La0.53TiO3, LiSr1.65Zr1.3Ta1.7O9, Li2x-ySr1-xTayZr1-yO3 where x = 0.75y and 0.60 < y < 0.75, Li3 / 8Sr7 / 16Nb3 / 4Zr1 / 4O3, Li3xLa(2 / 3-x)TiO3 where 0 < x < 0.25, typical but non-limiting combinations include a combination of Li3.3La0.53TiO3 and LiSr1.65Zr1.3Ta1.7O9, a combination of Li2x-ySr1-xTayZr1-yO3 where x = 0.75y and 0.60 < y < 0.75 and Li3 / 8Sr7 / 16Nb3 / 4Zr1 / 4O3, or a combination of Li3.3La0.53TiO3, LiSr1.65Zr1.3Ta1.7O9, and Li3 / 8Sr7 / 16Nb3 / 4Zr1 / 4O3.

[0101] The method of preparation of the present application is described below in accordance with the technical content of the present application, but should not be limited to the following examples:

[0102] Example 1

[0103] Preparation of the composite cathode active material:

[0104] S1, Ni 0.9 Co 0.05 Mn 0.05The intermediate is obtained by mixing the precursor, lithium source LiOH, and tantalum ethoxide in a high-speed mixer at a molar ratio of 1:1.03:0.03, then incubating at 450°C for 5h, heating to 725°C at a heating rate of 3°C / min, and calcining at 725°C in an air atmosphere for 8h. After sieving and removing iron, the intermediate with a particle size D50 of 9μm is obtained. The intermediate includes a ternary positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 O2 and a first coating layer formed on the surface of the ternary positive electrode active material;

[0105] The first coating layer has a thickness of 10nm, and the content S of Ta in the first coating layer is 0.27%.

[0106] S2, the intermediate, nano-La2O3, and LiF are dissolved in anhydrous ethanol solution at a molar ratio of 1:0.005:0.01. After incubation at 50°C in a glove box for 5h with mechanical stirring at 500rpm, the mixture is filtered and dried, and then calcined at 350°C in an air atmosphere for 4h to obtain the composite positive electrode active material.

[0107] The second coating layer has a thickness of 8nm, and in the second coating layer, the content M of La is 0.48%, and the content N of F is 0.27%.

[0108] wherein (S+N) / M=1.125.

[0109] Example 2

[0110] Preparation of the composite positive electrode active material:

[0111] S1, the Ni 0.9 Co 0.05 Mn 0.05 The intermediate is obtained by mixing the precursor, lithium source LiOH, and tantalum ethoxide in a high-speed mixer at a molar ratio of 1:1.03:0.02, then incubating at 450°C for 5h, heating to 725°C at a heating rate of 3°C / min, and calcining at 725°C in an air atmosphere for 8h. After sieving and removing iron, the intermediate with a particle size D50 of 9μm is obtained. The intermediate includes a ternary positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 O2 and a first coating layer formed on the surface of the ternary positive electrode active material;

[0112] The first coating layer has a thickness of 8nm, and the content S of Ta in the first coating layer is 0.21%.

[0113] S2, the intermediate, nano La2O3, LiF are dissolved in anhydrous ethanol solution according to the molar ratio 1:0.007:0.006, 50℃ in a glove box, 500 rpm mechanical stirring for 5h, finally filter, dry, calcined at 350℃ in air atmosphere for 4h to obtain the composite positive electrode active material;

[0114] The thickness of the second coating layer is 6nm; in the second coating layer, the content M of La is 0.51%, and the content N of F is 0.25%.

[0115] Wherein, (S+N) / M=0.9.

[0116] Example 3

[0117] Preparation of the composite positive electrode active material:

[0118] S1, the Ni 0.9 Co 0.05 Mn 0.05 (OH)2precursor, lithium source LiOH, and ethanol tantalum are mixed in a high-speed mixer according to the molar ratio 1:1.03:0.015, then heated to 725℃ at a heating rate of 3℃ / min, and calcined at 725℃ in air atmosphere for 8h to obtain the intermediate, which is sieved and de-ironed to obtain the intermediate with a particle size D50=9μm, and the intermediate includes the ternary positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 O2 and a first coating layer formed on the surface of the ternary positive electrode active material;

[0119] The thickness of the first coating layer is 7nm, and the content S of Ta in the first coating layer is 0.14%.

[0120] S2, the intermediate, nano La2O3, LiF are dissolved in anhydrous ethanol solution according to the molar ratio 1:0.007:0.006, 50℃ in a glove box, 500 rpm mechanical stirring for 5h, finally filter, dry, calcined at 350℃ in air atmosphere for 4h to obtain the composite positive electrode active material;

[0121] The thickness of the second coating layer is 4nm; in the second coating layer, the content M of La is 0.55%, and the content N of F is 0.21%.

[0122] Wherein, (S+N) / M=0.64.

[0123] Example 4

[0124] Preparation of the composite positive electrode active material:

[0125] S1, the Ni 0.9 Co 0.05 Mn0.05 The (OH)₂ precursor, lithium source LiOH, and tantalum ethoxide were mixed in a high-speed mixer at a molar ratio of 1:1.03:0.008. The mixture was then held at 450°C for 5 hours, heated to 725°C at a rate of 3°C / min, and calcined at 725°C for 8 hours in air to obtain an intermediate. After sieving and iron removal, an intermediate with a particle size D50 of 9 μm was obtained. This intermediate includes the ternary cathode active material LiNi. 0.9 Co 0.05 Mn 0.05 O2 and a first coating layer formed on the surface of the ternary positive electrode active material;

[0126] The thickness of the first coating layer is 5 nm, and the Ta content (S) in the first coating layer is 0.05%.

[0127] S2. The intermediate, nano-La2O3, and LiF were dissolved in anhydrous ethanol solution at a molar ratio of 1:0.007:0.006. The mixture was kept at 50°C in a glove box and mechanically stirred at 500 rpm for 5 hours. Finally, the mixture was filtered, dried, and calcined at 350°C in air for 4 hours to obtain the composite positive electrode active material.

[0128] The thickness of the second coating layer is 4 nm; in the second coating layer, the La content (M) is 0.55% and the F content (N) is 0.21%.

[0129] Wherein, (S+N) / M=0.47.

[0130] Example 5

[0131] Preparation of composite positive electrode active materials:

[0132] S1, Ni 0.9 Co 0.05 Mn 0.05 The (OH)₂ precursor, lithium source LiOH, and tantalum ethoxide were mixed in a high-speed mixer at a molar ratio of 1:1.03:0.05. The mixture was then held at 450°C for 5 hours, heated to 725°C at a rate of 3°C / min, and calcined at 725°C for 8 hours in air to obtain an intermediate. After sieving and iron removal, an intermediate with a particle size D50 of 9 μm was obtained. This intermediate includes the ternary cathode active material LiNi. 0.9 Co 0.05 Mn 0.05 O2 and a first coating layer formed on the surface of the ternary positive electrode active material;

[0133] The thickness of the first coating layer is 14 nm, and the Ta content (S) in the first coating layer is 0.35%.

[0134] S2, the intermediate, nano-La2O3, LiF are dissolved in anhydrous ethanol solution according to a molar ratio of 1:0.001:0.008, and then the solution is kept at 50°C in a glove box with 500 rpm mechanical stirring for 5h. Finally, after filtration and drying, the composite positive electrode active material is obtained by calcining at 350°C in air for 4h.

[0135] The thickness of the second coating layer is 1nm; in the second coating layer, the content M of La is 0.35%, and the content N of F is 0.25%.

[0136] Wherein, (S+N) / M=1.71.

[0137] Comparative Example 1

[0138] Compared with Example 1, the different technical features of Comparative Example 1 are that the composite positive electrode active material only includes the ternary positive electrode active material and the second coating layer.

[0139] Comparative Example 2

[0140] Compared with Example 1, the different technical features of Comparative Example 2 are that the composite positive electrode active material only includes the ternary positive electrode active material and the first coating layer.

[0141] Comparative Example 3

[0142] Compared with Example 1, the different technical features of Comparative Example 3 are that the composite positive electrode active material only includes the ternary positive electrode active material.

[0143] Examples 1-5 and Comparative Examples 1-3 also include the preparation of a battery.

[0144] I. Preparation of the positive electrode

[0145] ① Preparation of the positive electrode: the composite positive electrode active material, PTFE, super-P, and sulfide solid electrolyte Li6PS5Cl are mixed uniformly according to a mass ratio of 70:3:2:25, and then put into a high-shear equipment mixer for fiberization treatment to form a first mixture. The first mixture is rolled to form a first positive electrode layer; the rolling temperature is 60°C, and the rolling time is 5min.

[0146] ② Preparation of the negative electrode: the negative electrode is selected to be an Ag-C alloy.

[0147] ③ Preparation of the solid electrolyte film: the sulfide solid electrolyte Li6PS5Cl and the binder PTFE are mixed according to a mass ratio of 65:35, and then pressed into a film.

[0148] ④ Preparation of the battery structure

[0149] The positive electrode current collector, the positive electrode layer, the solid electrolyte film, and the negative electrode layer are stacked to obtain the battery structure by hot pressing.

[0150] Performance test:

[0151] I. Cycle capacity retention rate:

[0152] Charged to a charge cut-off voltage of 4.25V at a current of 0.1C at a temperature of 45℃, converted to constant voltage charging to a cut-off current of 0.05C, rested for 0.5h, discharged to a cut-off voltage of 2.5V at a current of 0.1C, rested for 0.5h, entered the next charge-discharge cycle, and so on, a total of 100 charge-discharge cycles were performed.

[0153] II. First discharge capacity test:

[0154] The battery was discharged at a constant current of 0.1C to a cut-off voltage of 2.5V.

[0155] III. Rate performance test:

[0156] At room temperature (25℃), the fully charged battery was discharged to a cut-off voltage of 2.5V at a current of 0.1C, and the capacity obtained was C0.

[0157] At room temperature (25℃), the fully charged battery was discharged to a cut-off voltage of 2.5V at a current of 3C, and the capacity obtained was C1, and C1 / C0 was the 3C discharge capacity retention rate in the following.

[0158] IV. Ta element content determination: The Ta element content of the first coating layer was obtained by XPS etching time of 60-120s, and the atomic percentage of Ta was obtained by peak area calculation after background subtraction of XPS peak, and the content was recorded as mass percentage S%.

[0159] V. La and F element content determination: The La and F element content of the second coating layer was obtained by XPS etching time of 0-10s, and the atomic percentage of La and F was obtained by peak area calculation after background subtraction of XPS peak, and the content was recorded as mass percentage M% and N%, respectively.

[0160] The relevant test data are as follows:

[0161]

[0162] From Comparative Example 1 and Comparative Examples 1, 2 and 3, it can be seen that the first coating layer and the second coating layer cooperate to make the composite positive electrode active material have high ion release rate and ion migration rate, good cycle stability and high voltage stability, and can also effectively improve the interface contact between the positive electrode and the solid electrolyte membrane, so that the prepared battery has good cycle performance and rate performance.

[0163] From Comparative Example 1 and Examples 4 and 5, it can be seen that when 0.6 < (N + S) / M < 1.2 is satisfied, the battery has good rate performance and cycle performance.

[0164] Although the technical scheme and examples of the present application have been described in detail, the person skilled in the art of manufacturing lithium ion batteries and in the same field, inspired by the present application, can select or change technical features to obtain a technically equivalent scheme, and the lithium battery manufactured thereby shall fall within the protection scope of the present application.

Claims

1. A composite positive electrode active material, characterized in that, The composite positive electrode active material has a core-shell structure, wherein the core of the core-shell structure includes a ternary positive electrode active material, and the shell of the core-shell structure includes a first coating layer and a second coating layer; The first coating layer is formed on the surface of the ternary positive electrode active material particles; The second coating layer is formed on the surface of the first coating layer away from the ternary cathode active material particles; The first coating layer includes Ta; The second coating layer comprises La and F; If the mass percentage of Ta in the first coating layer is S, and the mass percentages of La and F in the second coating layer are M and N respectively, then the following condition is satisfied: 0.6 < (N + S) / M < 1.

2.

2. The composite positive electrode active material according to claim 1, characterized in that, The ternary cathode active material is LiNi. x Co y Mn 1-x-y O2, where x = 0.5~1.0, y > 0, and x + y < 1.

3. The composite positive electrode active material according to claim 1, characterized in that, The thickness of the first coating layer is 5~20 nm.

4. The composite positive electrode active material according to claim 3, characterized in that, The thickness of the second coating layer is 1~15 nm.

5. The composite positive electrode active material according to claim 1, characterized in that, The thickness of the first coating layer is greater than the thickness of the second coating layer.

6. A method for preparing the composite positive electrode active material as described in claim 1, characterized in that, Includes the following steps: S1. A ternary cathode active material precursor, a lithium source, and a Ta source are mixed, kept at a certain temperature, and then calcined to form an intermediate. The intermediate includes a ternary cathode active material and a first coating layer formed on the surface of the ternary cathode active material. S2. The intermediate, La source, and LiF are mixed and dissolved in a solvent. The mixture is stirred at a constant temperature, filtered, dried, and calcined a second time to obtain the composite positive electrode active material.

7. The method according to claim 6, characterized in that, In step S1, the molar ratio of the ternary cathode active material to the Ta source is 1:(0.008~0.05); and / or, In step S2, the molar ratio of the intermediate, La source, and LiF is 1:(0.001~0.01):(0.003~0.015).

8. Positive electrode, characterized in that, The positive electrode includes the composite positive electrode active material as described in claim 1.

9. An all-solid-state battery, characterized in that, The all-solid-state battery includes the composite positive electrode active material as described in claim 1 and / or the positive electrode as described in claim 8.

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