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, 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 material or lithium-rich manganese-based positive electrode material, the shell layer includes LiNbO2F.The application can effectively improve the high-voltage stability of the composite positive electrode active material by forming the shell layer of fluoride LiNbO2F on the surface of ternary positive electrode material or lithium-rich manganese-based positive electrode material, and then the cycle performance of the full solid-state battery can be effectively improved.On the other hand, by coating LiNbO2F, the solid-solid contact of the positive electrode and the solid-state electrolyte membrane can be effectively improved, the interface contact of the positive electrode and the solid-state electrolyte membrane is improved, and the polarization of the battery is reduced, the internal resistance of the battery is effectively reduced.

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] With the development of full solid-state batteries, people have higher requirements for energy density. At present, the application of ternary positive electrode materials and lithium-rich manganese-based positive electrode materials is the key to realizing high energy density of solid-state batteries. However, the ternary positive electrode materials and lithium-rich materials often have problems such as lattice oxygen release, metal dissolution and structure collapse, which will further aggravate the side reaction with sulfide and halide electrolyte, leading to the accumulation of interface by-products and rapid decline of cycle performance. Therefore, in order to further improve the interface side reaction between the positive electrode and the electrolyte, the positive electrode material needs to be coated. However, the current positive electrode material coating is mostly oxide coating, which often decomposes at high voltage and has poor high voltage resistance, and has little effect on the surface of the positive electrode.

[0003] Therefore, there is an urgent need for a good coating material to solve the above problems. SUMMARY

[0004] The purpose of the present application is to provide a composite positive electrode active material, a preparation method, a positive electrode and a battery.

[0005] The technical solution of the present application is as follows:

[0006] The first aspect of the present application provides a composite positive electrode active material, which is a core-shell structure, the core material comprises a ternary positive electrode material or a lithium-rich manganese-based positive electrode material, and the shell layer comprises LiNbO2F.

[0007] In some embodiments, the ternary positive electrode material is LiNi x Co y Mn 1-x-y O2, wherein x=0.5-1.0, y>0, and x+y<1.

[0008] In some embodiments, the thickness of the shell layer is 5-30 nm.

[0009] In some embodiments, the mass ratio of the core material to LiNbO2F is 1:(0.005-0.05).

[0010] In some embodiments, the particle size D50 of the core material is 3-12 μm.

[0011] The second aspect of the present application provides a preparation method of the composite positive electrode active material as described above, comprising the following steps:

[0012] 1) mixing the core material with LiNbO2F and a solvent to form a mixed solution;

[0013] 2) filtering the mixed solution and drying to obtain a precursor;

[0014] 3) calcining the precursor to obtain the composite cathode active material.

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

[0016] In some embodiments, the step 1) comprises: after mixing, stirring is performed, and the stirring time is ≥ 4 h.

[0017] In some embodiments, in the step 3), the calcining temperature is 350-450 ℃; and / or, the calcining time is 2-4 h.

[0018] In a third aspect, the application provides a cathode, which comprises the composite cathode active material as described in the first aspect.

[0019] In a fourth aspect, the application provides an all-solid-state battery, which comprises the composite cathode active material as described in the first aspect and / or the cathode as described in the third aspect.

[0020] Compared with the prior art, the technical scheme of the application has the beneficial technical effects that: by forming a shell layer of fluoride LiNbO2F on the surface of the ternary cathode material or the lithium-rich manganese-based cathode material, the high-voltage stability of the composite cathode active material can be effectively improved, and then the cycle performance of the all-solid-state battery can be effectively improved. On the other hand, by coating LiNbO2F, the solid-solid contact between the cathode and the solid-state electrolyte film can be effectively improved, the interface contact between the cathode and the solid-state electrolyte film can be improved, and the polarization of the battery can be reduced, thereby effectively reducing the internal resistance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 SEM image of Example 1 of the application.

[0022] Figure 2 dQ / dV curve of Example 1 and Comparative Example 1 of the application. DETAILED DESCRIPTION

[0023] The technical scheme of the application will be described in detail below with reference to the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the detailed description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising," "including," and "having," as well as variations thereof, are intended to cover a non-exclusive inclusion.

[0025] In the description 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 more than two, unless otherwise explicitly and specifically limited.

[0026] In the present application, the phrase "embodiments" means that the specific features, structures or properties described in conjunction with the embodiments 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 that is not mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present application can be combined with other embodiments.

[0027] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship between 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 a "or" relationship between the front and rear associated objects.

[0028] Throughout this disclosure, numerical expressions are approximate measures of quantities or limits to range of values to encompass minor variations of the given value and embodiments having about the recited value as well as embodiments having the recited 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 attached claims, are to be rea as modified by the term "about," whether or not "about" actually appears before the numerical value, except that the term "about" is not rea to modify a number of atoms of a molecule or a number of molecules in a composition. "About" means that slight deviations from the exact value are acceptable, up to a degree that is reasonable in the art. If the deviations from the exact value are not otherwise understood in the art to have the ordinary meaning, then "about" indicates at least the variations that can be produced by the ordinary methods of measurement and use of such parameters. For example, "about" can include variations less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.

[0029] 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.

[0030] The structure of ternary positive electrode material and lithium-rich manganese-based positive electrode material is easily destroyed at high voltage, resulting in the cycle performance of the battery being deteriorated, and when applied in a full solid-state battery, a side reaction with a solid-state electrolyte film containing a sulfide solid-state electrolyte and / or a halide solid-state electrolyte is easily caused, further affecting the cycle performance of the full solid-state battery at high voltage, and in the full solid-state battery, there is a technical problem of poor interface between the positive electrode and the solid-state electrolyte film due to solid-solid contact, resulting in a large internal resistance of the battery, which needs to be solved.

[0031] To solve the above problems, a technical solution is proposed in the present application.

[0032] The first aspect of the present application provides a composite positive electrode active material, the composite positive electrode active material is of a core-shell structure, the core material comprises a ternary positive electrode material or a lithium-rich manganese-based positive electrode material, and the shell layer comprises LiNbO2F.

[0033] The present application can effectively improve the high-voltage stability of the composite positive electrode active material by forming a shell layer of fluoride LiNbO2F on the surface of the ternary positive electrode material or the lithium-rich manganese-based positive electrode material, thereby effectively improving the cycle performance of the full solid-state battery. On the other hand, by coating LiNbO2F, the solid-solid contact between the positive electrode and the solid-state electrolyte film can be effectively improved, the interface contact between the positive electrode and the solid-state electrolyte film is improved, and the polarization of the battery is reduced, thereby effectively reducing the internal resistance of the battery.

[0034] In some embodiments, the ternary cathode 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 such a setting is to facilitate the improvement of the energy density of the battery.

[0035] In some embodiments, the lithium-rich manganese-based cathode material is Li a Ni b Mn c O2, wherein a > 1, and b + c = 1.

[0036] In some embodiments, the thickness of the shell layer is 5-30 nm. It can be understood that if the shell layer is too thin, it is easy to fail to be coated in the charge and discharge cycle, and if the shell layer is too thick, it is easy to affect the extraction and migration of lithium ions from the cathode active material.

[0037] Specifically, the thickness of the shell layer can be 5 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 20 nm, 25 nm, or 30 nm. Of course, it can also be any value within this range, and the present application does not make any limitation on this.

[0038] In some embodiments, the mass ratio of the core material to LiNbO2F is 1:(0.005-0.05). Specifically, the mass ratio of the cathode active material to LiNbO2F can be 1:0.005, 1:0.01, 1:0.015, 1:0.02, 1:0.025, 1:0.03, 1:0.035, 1:0.04, 1:0.045, or 1:0.05. Of course, it can also be any value within this range, and the present application does not make any limitation on this.

[0039] In some embodiments, the particle size D50 of the core material is 3-12 μm.

[0040] Specifically, it can be 3 μm, 4.5 μm, 5 μm, 6.2 μm, 7 μm, 8.6 μm, 9 μm, 10 μm, 11 μm, or 12 μm. Of course, it can also be any value within this range, and the present application does not make any limitation on this.

[0041] In a second aspect, the present application provides a preparation method of the above composite cathode active material, comprising the following steps:

[0042] 1) mixing the core material with LiNbO2F and a solvent to form a mixed solution;

[0043] 2) filtering the mixed solution and drying to obtain a precursor;

[0044] 3) calcining the precursor to obtain the cathode active material.

[0045] In a second aspect, the present application provides a method for preparing the composite cathode active material as above, comprising the following steps:

[0046] In some embodiments, step 1) comprises: after mixing, stirring is performed, and the stirring time is ≥ 4 h.

[0047] In some preferred embodiments, the stirring time is 4-20 h.

[0048] In some preferred embodiments, the stirring speed is 300-800 rpm.

[0049] In some preferred embodiments, in step 1), the solvent is anhydrous ethanol.

[0050] In some preferred embodiments, in step 1), the mixing comprises constant temperature mixing. The constant temperature is 20-50℃.

[0051] In some embodiments, in step 3), the calcination temperature is 350-450℃.

[0052] In some embodiments, in step 3), the calcination time is 2-4 h.

[0053] In some embodiments, in step 3), the calcination atmosphere is argon.

[0054] In some embodiments, before step 1), the method further comprises preparing LiNbO2F, comprising the following steps:

[0055] ①Li2O, Nb2O5, LiF powders are mixed according to a molar ratio of 0.51:1:1 to form a mixture;

[0056] ②The mixture is calcined, and after calcination, it is slowly cooled to room temperature to obtain a calcined product;

[0057] ③The calcined product is crushed and sieved to obtain LiNbO2F.

[0058] As one of the implementation manners, in step ①, the mixing is performed by ball milling, and the ball milling speed is 250-500 rpm.

[0059] As one of the implementation manners, in step ①, the mixing time is 4-8 h.

[0060] As one of the implementation manners, in step ②, the calcination temperature is 800-900℃.

[0061] As one of the implementation manners, in step ②, the calcination time is 5-12 h.

[0062] As one of the embodiments, in step ②, the calcination atmosphere is a mixed atmosphere of Ar and H2.

[0063] As one of the preferred embodiments, in step ②, the volume ratio of H2 in the calcination atmosphere is 3% to 10%.

[0064] As one of the embodiments, in step ③, the breaking is specifically carried out by putting the calcination product into a high-energy ball mill.

[0065] As one of the embodiments, in step ③, the rotation speed of the high-energy ball mill is 100 to 200 rpm.

[0066] As one of the embodiments, in step ③, the breaking time is 2 to 5 hours.

[0067] In a third aspect, the present application provides a positive electrode, which comprises the composite positive electrode active material according to the first aspect.

[0068] 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 of the present application.

[0069] 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.

[0070] 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, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resin, nylon, and the like.

[0071] 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.

[0072] In some embodiments, the positive electrode tab comprises a positive electrode current collector, which can be, illustratively, aluminum (Al), but is not limited thereto.

[0073] In some embodiments, the mass percentage of the composite positive electrode active material particles in the positive electrode material layer is 70% to 97%, based on the total mass of the positive electrode material layer.

[0074] In some embodiments, the mass of the conductive agent is 1-20% of the mass of the positive electrode material layer.

[0075] In some embodiments, the mass of the binder is 1-20% of the mass of the positive electrode material layer.

[0076] 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 1-30% of the mass of the positive electrode tab; preferably 5-20%.

[0077] 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, and preferably 50-110 μm.

[0078] 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.

[0079] The full solid-state battery further comprises a negative electrode, wherein the negative electrode comprises a negative electrode tab.

[0080] The negative electrode tab comprises:

[0081] In some embodiments, the negative electrode tab comprises a current collector and a negative electrode active material layer disposed on the current collector.

[0082] 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, Li-Al alloy, and Ag-C 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

[0083] ​In some embodiments, elemental metals and metal-based compounds can also be selected as negative active materials, such as compounds containing Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, Zn, and the like metals or metalloids.

[0084] In some embodiments, the mass ratio of the negative active material contained in the negative active material layer can be 80%-99%, such as 80%, 85%, 90%, 95%, 97%, 99%, and the like, preferably 95%-97%.

[0085] In some embodiments, the negative active material layer can include a binder; the binder improves the binding between the negative active material particles and the binding between the negative active material and the current collector.

[0086] 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 polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

[0087] In some embodiments, the negative active material layer can be obtained by coating a negative electrode slurry on a negative electrode current collector, and then performing drying and the like, the negative electrode 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 electrode slurry, it is preferable to use a viscosity enhancer for slurry formation, which is generally used to adjust the viscosity of the slurry.

[0088] In some embodiments, the aforementioned viscosity enhancer can be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphated starch, casein and its salts, and the like.

[0089] In some embodiments, the mass ratio of the viscosity enhancer in the negative electrode slurry can be 0.1%-5%, such as 0.1%, 0.2%, 0.5%, 0.6%, 1%, 2%, 3%, 4%, 5%, and the like, preferably 0.5%-3%, and further preferably 0.6%-2%.

[0090] In some embodiments, the negative active material layer includes a conductive material, thereby rendering the electrode electrically conductive. The conductive material can include any electrically conductive material that does not cause chemical changes. Non-limiting examples of conductive materials 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 powders, metal fibers, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0091] In some embodiments, the negative current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, polymer substrate coated with conductive metal, and combinations thereof.

[0092] The all-solid-state battery further includes a solid-state electrolyte film.

[0093] The solid-state electrolyte film includes a solid-state electrolyte.

[0094] In some embodiments, the solid-state electrolyte is a sulfide solid-state electrolyte including any one of or a combination of at least two 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 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.

[0095] In some embodiments, the solid-state electrolyte is a halide solid-state electrolyte with a general formula of Li x MX y N z wherein 1≤x≤4, 4≤y+nz≤8, n is the absolute value of the 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 Cl m (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 y Sz(0

[0096] In some preferred embodiments, the halide solid-state electrolyte includes at least one of Li2ZrCl6, Li2ZrCl5F, Li2ZrCl 5.5 O 0.25 , Li3InCl6, Li3YCl6, Li2H f Cl6, LiInBr 4、 Li3InBr6, Li3LaI6, Li3LuCl6.

[0097] The solid-state electrolyte includes at least one of a sulfide solid-state electrolyte and a halide solid-state electrolyte, and can further include an oxide solid-state electrolyte.

[0098] In some embodiments, the oxide solid state electrolyte comprises any one or a combination of at least two of garnet ceramic, LISICON-type oxide, NASICON-type oxide, or perovskite-type ceramic, typical but non-limiting combinations include a combination of garnet ceramic and LISICON-type oxide, a combination of LISICON-type oxide and NASICON-type oxide, or a combination of LISICON-type oxide, NASICON-type oxide, and perovskite-type ceramic.

[0099] In some embodiments, the garnet ceramic comprises 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 2.9 Ca 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 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 , typical but non-limiting combinations include a combination of Li 6.5 La3Zr 1.75 Te 0.25 O 12 and Li7La3Zr2O 12 , Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 and Li6.25Al0.25La3Zr2O12, or a combination of Li6.25Al0.25La3Zr2O12, Li6.75La3Zr1.75Nb0.25O12, and Li6.75La3Zr1.75Nb0.25O12.

[0100] In some embodiments, the LISICON-type oxide comprises any one or a combination of at least two of Li14Zn(Ge04)4, Li3+x(P1-xSix)04(where 0 < x < 1), or Li3+xGexV1-x04(where 0 < x < 1), typical but non-limiting combinations include a combination of Li14Zn(Ge04)4and Li3+x(P1-xSix)04(where 0 < x < 1), a combination of Li3+x(P1-xSix)04(where 0 < x < 1) and Li3+xGexV1-x04(where 0 < x < 1), or a combination of Li14Zn(Ge04)4, Li3+x(P1-xSix)04(where 0 < x < 1), and Li3+xGexV1-x04(where 0 < x < 1).

[0101] In some embodiments, the NASICON-type oxide can be defined by LiMM'(P04)3, where M and M' are independently selected from 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(P04)3(LAGP) (where 0 < x < 2), Li1+xAlxTi2-x(P04)3(LATP) (where 0 < x < 2), Li1+xYxZr2-x(P04)3(LYZP) (where 0 < x < 2), Li1.3Al0.3Ti1.7(P04)3, LiTi2(P04)3, LiGeTi(P04)3, LiGe2(P04)3, LiHf2(P04)3, typical but non-limiting combinations include a combination of LAGP and LATP, a combination of LYZP and Li1.3Al0.3Ti1.7(P04)3, or a combination of LiTi2(P04)3, LiGeTi(P04)3, LiGe2(P04)3, and LiHf2(P04)3.

[0102] In some embodiments, the perovskite ceramic comprises 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), with typical but non-limiting combinations including 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.

[0103] The preparation method of the present application is described below according to the technical content of the present application, but should not be limited to the following examples:

[0104] Example 1:

[0105] Preparation of the composite cathode active material:

[0106] I. Preparation of LiNbO2F

[0107] Li2O (purity 99.9%), Nb2O5 (purity 99%), LiF (purity 99.9%) powders were weighed according to the molar ratio of 0.51:1:1 and mixed in a planetary ball mill at a mixing speed of 300 rpm for 5 h. Subsequently, the mixture was calcined in a crucible at 850°C under an Ar / H2 (5% H2) mixed atmosphere for 8 h, and then slowly cooled to room temperature;

[0108] The obtained LiNbO2F powder was crushed by a high-energy ball mill at 150 rpm for 3 h, and finally sieved to obtain LiNbO2F nanoparticles with uniform particle size;

[0109] II. Preparation of the core material

[0110] The Ni 0.9 Co 0.05 Mn 0.05 (OH)2 precursor and lithium source LiOH were mixed in a high-speed mixer according to a molar ratio of 1:1.03, then heated to 725°C at a heating rate of 3°C / min, and calcined at 725°C in air for 8 h to obtain the ternary cathode material LiNi 0.9 Co 0.05 Mn0.05 O2, after sieving and removing iron, a ternary positive electrode material with a particle size D50 = 10 μm is obtained;

[0111] III. Preparation of the composite positive electrode active material

[0112] The obtained LiNi 0.9 Co 0.05 Mn 0.05 O2 and LiNbO2F are dissolved in anhydrous ethanol solution according to a mass ratio of 1:0.02, stirred in a glove box at a constant temperature of 30°C and a stirring speed of 500 rpm for 5 h, and finally filtered and dried to obtain a precursor. The precursor is calcined at 400°C under an argon atmosphere for 3 h to obtain a composite positive electrode active material.

[0113] The thickness of the shell layer is 10 nm.

[0114] Example 2:

[0115] Example 2 differs from Example 1 in that the mass ratio of LiNi 0.9 Co 0.05 Mn 0.05 O2 and LiNbO2F is 1:0.03, and the remaining technical features are the same.

[0116] The thickness of the shell layer is 17 nm.

[0117] Example 3:

[0118] Example 3 differs from Example 1 in that the mass ratio of LiNi 0.9 Co 0.05 Mn 0.05 O2 and LiNbO2F is 1:0.05, and the remaining technical features are the same.

[0119] The thickness of the shell layer is 30 nm.

[0120] Example 4:

[0121] Example 4 differs from Example 1 in that the mass ratio of LiNi 0.9 Co 0.05 Mn 0.05 O2 and LiNbO2F is 1:0.005, and the remaining technical features are the same.

[0122] The thickness of the shell layer is 6 nm.

[0123] Example 5:

[0124] Example 5 differs from Example 1 in that the mass ratio of LiNi 0.9 Co 0.05 Mn 0.05The mass ratio of O2 and LiNbO2F is 1:0.08, and the rest of the technical features are the same.

[0125] The thickness of the shell layer is 55 nm.

[0126] Example 6:

[0127] Example 6 is different from Example 1 in that the core material in Example 3 is a lithium-rich manganese-based positive electrode material Li 1.2 Ni 0.25 Mn 0.75 O2.

[0128] The thickness of the shell layer is 12 nm.

[0129] Comparative Example 1

[0130] Comparative Example 1 is different from Example 1 in that the composite positive electrode active material only includes the core material LiNi 0.9 Co 0.05 Mn 0.05 O2, and does not include a shell layer.

[0131] Comparative Example 2

[0132] Comparative Example 2 is different from Example 6 in that the composite positive electrode active material only includes the core material Li 1.2 Ni 0.25 Mn 0.75 O2, and does not include a shell layer.

[0133] Examples 1-6 and Comparative Examples 1-2 also include the preparation of a battery.

[0134] I. Preparation of the positive electrode

[0135] 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, placed in a high-shear equipment mixer, and fiberized 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 5 min.

[0136] ② Preparation of the negative electrode: the negative electrode is selected to be an Ag-C alloy.

[0137] 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.

[0138] ④ Preparation of the battery structure

[0139] The positive electrode current collector, the positive electrode layer, the solid electrolyte film, and the negative electrode layer are stacked and hot-pressed to obtain a battery structure.

[0140] Performance test:

[0141] I. Cycle capacity retention rate:

[0142] Charged to 4.25V at 0.3C, then constant voltage charged to 0.05C, rested for 0.5h, discharged to 2.5V at 0.3C, rested for 0.5h, and then entered the next charge-discharge cycle, and so on, for a total of 250 charge-discharge cycles.

[0143] II. Shell thickness test

[0144] The shell thickness was mainly observed by TEM, and the average thickness was calculated from ten positions.

[0145] III. Battery internal resistance test

[0146] The solid-state batteries prepared in Examples 1-6 and Comparative Examples 1-2 were measured for internal resistance by a voltage resistance meter at an ambient temperature of 30℃.

[0147] IV. dQ / dV curve

[0148] The solid-state batteries prepared in Examples 1-5 and Comparative Example 1 were subjected to electrochemical testing, with a voltage range of 2.5V-4.25V. Voltage and capacity data were obtained, and a dQ / dV curve was plotted. The difference between the highest peak and the lowest peak at a voltage of 4.2V was recorded as the redox peak difference.

[0149] The technical effects of the above examples are compared in the following table:

[0150]

[0151] By comparing Examples 1-5 and Comparative Example 1, and Example 6 and Comparative Example 2, it can be seen that by forming a shell of fluoride LiNbO2F on the surface of the ternary positive electrode material or the lithium-rich manganese-based positive electrode material, the high-voltage stability of the positive electrode active material can be effectively improved, and in turn the cycle performance of the solid-state battery can be effectively improved. On the other hand, by coating LiNbO2F, the solid-solid contact between the positive electrode and the solid-state electrolyte membrane can be effectively improved, the interface contact between the positive electrode and the solid-state electrolyte membrane can be improved, and the polarization of the battery can be reduced, effectively reducing the internal resistance of the battery.

[0152] Although the technical solutions and examples of the present application have been described in detail, the manufacturers of lithium-ion batteries and those skilled in the art will be inspired to select or modify technical features to obtain technically equivalent solutions, and the lithium batteries manufactured thereby shall fall within the scope of protection of the present application.

Claims

1. A composite positive electrode active material, characterized by, The composite positive electrode active material is a core-shell structure, the core material comprises a ternary positive electrode material or a lithium-rich manganese-based positive electrode material, and the shell layer comprises LiNbO2F. The thickness of the shell layer is 5-30 nm.

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

3. The composite cathode active material according to claim 1, characterized in that, The mass ratio of the core material to LiNbO2F is 1:(0.005-0.05).

4. The composite cathode active material according to claim 1, characterized in that, The particle size D50 of the core material is 3-12 μm.

5. A method of producing the composite positive electrode active material as claimed in claim 1, characterized by, The method comprises the following steps: 1) mixing the core material with LiNbO2F and a solvent to form a mixed solution; 2) filtering the mixed solution and drying to obtain a precursor; 3) calcining the precursor to obtain the composite positive electrode active material.

6. The method of claim 5, wherein, The step 1) comprises: after mixing, stirring for ≥4 h.

7. The method of claim 5, wherein, In the step 3), the calcining temperature is 350-450 ℃; And / or, the calcining time is 2-4 h.

8. A positive electrode characterized by comprising The positive electrode comprises the composite positive electrode active material according to claim 1.

9. An all-solid battery, characterized by The all-solid-state battery comprises the composite positive electrode active material according to claim 1 and / or the positive electrode according to claim 8.

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