Cobalt-free single crystal positive electrode material, preparation method thereof and solid-state battery

Abstract

The invention provides a cobalt-free single-crystal positive electrode material, a preparation method thereof and a solid-state battery. The cobalt-free single-crystal positive electrode material comprises a doped cobalt-free single-crystal inner core and a fast ion conductor coating layer arranged on the surface of the doped cobalt-free single-crystal inner core, doped elements in the doped cobalt-free single crystal core comprise cesium, titanium and sulfur. Through the synergistic effect of multi-element doping and fast ion conductor coating, the interlayer spacing of the cobalt-free single-crystal positive electrode material can be expanded, the lithium ion diffusion barrier is reduced, the structure of the material is stabilized, and the occurrence of harmful phase change of the material is reduced, so that the electrochemical performance of the cobalt-free single-crystal positive electrode material is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and relates to a cobalt-free single-crystal cathode material, its preparation method, and a solid-state battery. Background Technology

[0002] Solid-state batteries represent a revolutionary breakthrough in battery technology by replacing the liquid electrolyte in traditional liquid lithium batteries with a solid electrolyte. The high capacity of ultra-high nickel cathode materials, combined with silicon-based anodes, significantly improves the capacity of solid-state batteries. Furthermore, the safety shortcomings of ultra-high nickel cathodes are significantly mitigated in solid-state batteries, effectively addressing the safety hazards present in liquid batteries.

[0003] Ultra-high nickel single-crystal cathode materials have become the preferred material for solid-state battery cathode materials due to their high energy density and lack of grain boundary cracking. However, in the process of adapting their own characteristics to the solid-state battery system, there are still problems such as low cycle performance and low ion conduction efficiency caused by crystal structure collapse.

[0004] CN120817633A discloses a nanocrystalline single-crystal cathode material and its preparation method, a solid-state battery, and an electrical device, relating to the field of solid-state batteries. The nanocrystalline single-crystal cathode material includes a core and a first coating layer, a second coating layer, and a third coating layer sequentially stacked on the surface of the core; the core has the general chemical formula Li. a Ni x Co y Mn z M w O2, wherein 1.02≤a≤1.2, 0.8≤x≤1, 0≤y≤0.2, 0≤z≤0.1, 0≤w≤0.03, x+y+z+w=1, M includes one or more of Zr, Sr, Y, Sb, Al, W, Ta, Mg, Ca, Ti, Mo and Nb; the first coating layer includes a transition metal compound; the second coating layer includes a boron-containing compound; and the third coating layer includes a sulfide.

[0005] CN116799174A discloses a double-coated single-crystal cathode material, its preparation method and application. The method includes: (1) making a first contact between the single-crystal cathode material and a fast ion conductor to obtain cathode material I; (2) subjecting the cathode material I to a first heat treatment at 300-800°C in the presence of an oxygen-containing atmosphere to obtain cathode material II; (3) subjecting the cathode material II to a second heat treatment with oxalic acid powder at 300-800°C in the presence of a nitrogen-containing atmosphere to obtain a double-coated single-crystal cathode material.

[0006] While the above solutions can effectively improve structural stability, they cannot improve rate performance and energy density. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a cobalt-free single-crystal cathode material, its preparation method, and a solid-state battery. Through the synergistic effect of multi-element doping and fast ion conductor coating, the present invention can expand the interlayer spacing of the cobalt-free single-crystal cathode material, reduce the lithium-ion diffusion barrier, stabilize the material structure, reduce the occurrence of harmful phase transitions, and thus improve the electrochemical performance of the cobalt-free single-crystal cathode material.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a cobalt-free single-crystal cathode material, the cobalt-free single-crystal cathode material comprising a doped cobalt-free single-crystal core and a fast-ion conductor coating layer disposed on the surface of the doped cobalt-free single-crystal core;

[0010] The doping elements in the doped cobalt-free single crystal core include cesium, titanium, and sulfur.

[0011] This invention incorporates multiple doping elements into a cobalt-free single-crystal core. Cesium occupies lithium sites, and its ionic radius and bond energy with oxygen are significantly greater than those of lithium. Doping cesium at lithium sites effectively suppresses structural collapse and phase transitions during deep delithiation, reduces nickel-lithium mixing, and significantly improves lithium-ion transport efficiency. Titanium effectively enhances the stability of lattice oxygen, suppressing oxygen evolution and thus improving the material's cycle stability. Sulfur doping at oxygen sites weakens the bond energy between transition metals and oxygen, reducing oxygen activity and further suppressing oxygen evolution. Furthermore, because sulfur's ionic radius is larger than oxygen's, it expands the interlayer spacing, further improving lithium-ion insertion / extraction efficiency. Finally, a fast ion conductor is coated onto the material surface, increasing both ionic conductivity and structural stability, thereby enhancing the rate performance and cycle performance of the cobalt-free single-crystal cathode material.

[0012] Preferably, the chemical formula of the doped cobalt-free single crystal core is LiCs. u (Ni x Mn y Ti z )O 2-n S n Where 0.8 ≤ x < 1, 0 <y≤0.2,0<z≤0.1,0<u≤0.03,0<m≤0.05,0<n≤0.05。

[0013] Preferably, the material of the fast ion conductor coating layer includes LLZO (Li7La3Zr2O). 12 ), Li3PO4-Li2S complex phase or LATP (Li 1.3 Al 0.3 Ti 1.7Any one or at least two of (PO4)3) are combined, and typical but non-limiting combinations include combinations of LLZO and LATP, combinations of LLZO and Li3PO4-Li2S complex phases, or combinations of Li3PO4-Li2S complex phases and LATP, etc.

[0014] Preferably, the thickness of the fast ion conductor coating layer is 2.5nm to 8nm, for example: 2.5nm, 3nm, 5nm, 6nm or 8nm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] In a second aspect, the present invention provides a method for preparing a cobalt-free single-crystal cathode material as described in the first aspect, the method comprising the following steps:

[0016] A nickel-manganese mixed salt solution, a titanium salt solution, a precipitant solution, and a complexing agent solution were injected concurrently into a reaction apparatus to carry out a co-precipitation reaction, thereby obtaining a titanium-doped precursor.

[0017] A titanium-doped precursor, lithium salt, and cesium salt are mixed and subjected to a first sintering process to obtain a sintered material;

[0018] A doped cobalt-free single-crystal core material is obtained by mixing a calcined material with lithium sulfide and then heat-treating it.

[0019] After mixing the doped cobalt-free single crystal core material with a solvent, a fast ion conductor raw material is added, and the mixture is stirred and reacted. The solvent is then evaporated to obtain a solid material. The obtained solid material is subjected to a second sintering treatment to obtain the cobalt-free single crystal cathode material.

[0020] This invention prepares a doped cobalt-free single-crystal core material by a combination of bulk uniform wet doping and dry doping. Then, a fast ion conductor is coated on the surface of the doped cobalt-free single-crystal core material. By increasing the interlayer spacing of the battery material, the lithium-ion diffusion barrier is reduced, the material structure is stabilized, and the occurrence of harmful phase transitions is reduced, thereby synergistically regulating the electrochemical performance of the ultra-high nickel single-crystal cathode.

[0021] The fast ion conductor raw materials described in this invention are various raw materials weighed after elemental proportioning according to the chemical formula of the desired fast ion conductor.

[0022] Preferably, the solute in the nickel-manganese mixed salt solution includes sulfates and / or nitrates.

[0023] Preferably, the mass concentration of the nickel-manganese mixed salt solution is 50 g / L to 150 g / L, for example: 50 g / L, 80 g / L, 100 g / L, 120 g / L or 150 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the solute in the titanium salt solution includes titanium sulfate.

[0025] Preferably, the molar concentration of the titanium salt solution is 1 mol / L to 3 mol / L, for example: 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the precipitant solution comprises a sodium hydroxide solution.

[0027] Preferably, the mass percentage concentration of the precipitant solution is 20% to 40%, for example: 20%, 25%, 30%, 35% or 40%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the complexing agent solution comprises ammonia.

[0029] Preferably, the mass percentage concentration of the complexing agent solution is 10% to 20%, for example: 10%, 12%, 15%, 18% or 20%, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the pH of the coprecipitation reaction is 11 to 12, for example: 11, 11.2, 11.5, 11.8 or 12, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the temperature of the coprecipitation reaction is 55℃~60℃, for example: 55℃, 56℃, 58℃, 59℃ or 60℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the ammonia concentration in the coprecipitation reaction is 4 g / L to 5 g / L, for example: 4 g / L, 4.2 g / L, 4.5 g / L, 4.8 g / L or 5 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the coprecipitation reaction time is 40h to 80h, for example: 40h, 50h, 60h, 70h or 80h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the lithium salt comprises lithium hydroxide and / or lithium carbonate.

[0035] Preferably, the cesium salt includes cesium carbonate.

[0036] Preferably, the atmosphere of the first sintering treatment includes oxygen.

[0037] Preferably, the temperature of the first sintering treatment is 700℃~900℃, for example: 700℃, 750℃, 800℃, 850℃ or 900℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, the first sintering treatment time is 8h to 12h, for example: 8h, 9h, 10h, 11h or 12h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0039] Preferably, the temperature of the heat treatment is 100℃~150℃, for example: 100℃, 110℃, 120℃, 140℃ or 150℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the atmosphere for the heat treatment includes nitrogen and / or argon.

[0041] Preferably, the heat treatment time is 8h to 12h, for example: 8h, 9h, 10h, 11h or 12h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the temperature of the stirring reaction is 20℃~30℃, for example: 20℃, 22℃, 25℃, 28℃ or 30℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the stirring reaction time is 0.5h to 1.5h, for example: 0.5h, 0.8h, 1h, 1.2h or 1.5h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, the temperature of the evaporating solvent is 70℃~90℃, for example: 70℃, 75℃, 80℃, 85℃ or 90℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, the atmosphere for the second sintering treatment includes nitrogen and / or argon.

[0046] Preferably, the temperature of the second sintering treatment is 800℃~850℃, for example: 800℃, 810℃, 820℃, 840℃ or 850℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] Preferably, the second sintering treatment time is 8h to 12h, for example: 8h, 9h, 10h, 11h or 12h, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0048] Thirdly, the present invention provides a solid-state battery comprising the cobalt-free single-crystal cathode material as described in the first aspect.

[0049] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) The present invention can expand the interlayer spacing of cobalt-free single crystal cathode material, reduce the lithium ion diffusion barrier, stabilize the structure of the material, reduce the occurrence of harmful phase transitions of the material, and thus improve the electrochemical performance of cobalt-free single crystal cathode material through the synergistic effect of multi-element doping and fast ion conductor coating.

[0052] (2) In the cobalt-free single-crystal cathode material of the present invention, the fast ion conductor coating improves the first-cycle charge-discharge efficiency and cycle performance of the material to a certain extent. The fast ion conductor coating stabilizes the structure through Ti-O and Al-O bonds, restricts the oxidation reaction on the surface, protects the interface from electrolyte corrosion, reduces anisotropic strain, prevents the propagation of microcracks, thereby maintaining structural integrity and preserving lithium diffusion channels, thus improving the cycle performance of the material. Cs ions have a large ionic radius, and partial doping to replace Li sites can broaden the Li ion transport channels to a certain extent, playing a certain supporting role. Compared with dry doping, wet bulk doping of Ti can distribute Ti more uniformly in the bulk phase of the material. Strong Ti-O bonds stabilize the lattice oxygen inside the material and reduce the oxidation state of Ni, further reducing oxygen release and electrolyte decomposition. S doping fundamentally improves the cycle stability of the cathode material. S doping reduces the hindrance in the Li transport process by increasing the gap between Li channels.

[0053] (3) The battery made of the cobalt-free single crystal cathode material of the present invention can achieve a first-cycle discharge capacity of more than 183.8 mAh / g, a first-cycle charge-discharge coulombic efficiency of more than 81.5%, and a capacity retention rate of more than 69% after 100 cycles at 1C. By adjusting the preparation conditions, the battery made of the cobalt-free single crystal cathode material can achieve a first-cycle discharge capacity of more than 205.7 mAh / g, a first-cycle charge-discharge coulombic efficiency of more than 87.1%, and a capacity retention rate of more than 83.5% after 100 cycles at 1C. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0055] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0056] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0057] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0058] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0059] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0060] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0061] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0062] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0063] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0064] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0065] Example 1

[0066] This embodiment provides a cobalt-free single-crystal cathode material, which includes materials with the chemical formula LiCs. 0.002 Ni 0.9 Mn 0.1 Ti 0.001 O 1.998 S 0.002 The doped cobalt-free single crystal core and the LATP fast ion conductor coating layer disposed on the surface of the doped cobalt-free single crystal core, wherein the thickness of the LATP fast ion conductor coating layer is 5 nm;

[0067] The cobalt-free single-crystal cathode material is prepared by the following method:

[0068] A 100 g / L Ni:Mn = 90:10 transition metal solution, a 32% sodium hydroxide solution, a 16% ammonia solution, and a 2 mol / L titanium sulfate solution were prepared and injected into a 50 L continuous stirred tank. The reaction temperature was maintained at 58 °C, the pH was maintained at 11.4, and the ammonia concentration was 4.5 g / L. The reaction was carried out under these conditions for 60 h to obtain the titanium-doped precursor.

[0069] LiOH and cesium carbonate were weighed separately, and the titanium-doped precursor, LiOH and cesium carbonate were mixed evenly. The mixture was then calcined at 800°C for 10 hours in an oxygen atmosphere to obtain a calcined material.

[0070] After washing, filtering and drying the calcined material, it was uniformly mixed with Li2S and heat-treated at 120℃ for 10 hours in an argon atmosphere to obtain a doped cobalt-free single crystal core material.

[0071] A doped cobalt-free single-crystal core material was dispersed in deionized water at a mass ratio of 9:1. Al₂O₃, TiO₂, LiNO₃, and NH₄H₂PO₄, with a Li:Al:Ti:P stoichiometric ratio of 1.3:0.3:1.7:3, were added to the suspension, followed by vigorous stirring at 25°C for 1 hour. The mixture was then heated to 80°C until the solvent completely evaporated, dried, and sintered at 820°C for 10 hours under an inert atmosphere to obtain the cobalt-free single-crystal cathode material.

[0072] Example 2

[0073] This embodiment provides a cobalt-free single-crystal cathode material, which includes materials with the chemical formula LiCs. 0.002 Ni 0.9 Mn 0.1 Ti 0.001 O 1.998 S 0.002 The doped cobalt-free single crystal core and the LLZO fast ion conductor coating layer disposed on the surface of the doped cobalt-free single crystal core, wherein the thickness of the LLZO fast ion conductor coating layer is 2.5 nm;

[0074] The cobalt-free single-crystal cathode material is prepared by the following method:

[0075] A 100 g / L Ni:Mn=90:10 transition metal solution, a 20% sodium hydroxide solution, a 20% ammonia solution, and a 1 mol / L titanium sulfate solution were prepared and injected into a 50 L continuous stirred tank. The reaction temperature was maintained at 60 °C, the pH was maintained at 11, and the ammonia concentration was 5 g / L. The reaction was carried out under these conditions for 40 h to obtain the titanium-doped precursor.

[0076] LiOH and cesium carbonate were weighed separately, and the titanium-doped precursor, LiOH and cesium carbonate were mixed evenly. The mixture was then calcined at 700°C for 12 hours in an oxygen atmosphere to obtain a calcined material.

[0077] After washing, filtering and drying the calcined material, it was uniformly mixed with Li2S and heat-treated at 100℃ for 12 hours in an argon atmosphere to obtain a doped cobalt-free single crystal core material.

[0078] A doped cobalt-free single-crystal core material was dispersed in deionized water at a mass ratio of 9:1. Li₂CO₃, La₂O₃, and ZrO₂ with a stoichiometric ratio of Li:La:Zr:O of 7:3:2:12 were added to the suspension, followed by vigorous stirring at 25°C for 1 hour. The mixture was then heated at 70°C until the solvent completely evaporated, dried, and sintered at 800°C for 12 hours under an inert atmosphere to obtain the cobalt-free single-crystal cathode material.

[0079] Example 3

[0080] This embodiment provides a cobalt-free single-crystal cathode material, which includes materials with the chemical formula LiCs. 0.02 Ni 0.9 Mn 0.1 Ti 0.2 O 1.95 S 0.05 The doped cobalt-free single crystal core and the Li3PO4-Li2S composite fast ion conductor coating layer disposed on the surface of the doped cobalt-free single crystal core, wherein the thickness of the Li3PO4-Li2S composite fast ion conductor coating layer is 8 nm.

[0081] The cobalt-free single-crystal cathode material is prepared by the following method:

[0082] A 100 g / L Ni:Mn=90:10 transition metal solution, a 40% sodium hydroxide solution, a 10% ammonia solution, and a 3 mol / L titanium sulfate solution were prepared and injected into a 50 L continuous stirred tank. The reaction temperature was maintained at 55 °C, the pH was maintained at 12, and the ammonia concentration was 4 g / L. The reaction was carried out under these conditions for 80 h to obtain the titanium-doped precursor.

[0083] LiOH and cesium carbonate were weighed separately, and the titanium-doped precursor, LiOH and cesium carbonate were mixed evenly. The mixture was then calcined at 900°C for 8 hours in an oxygen atmosphere to obtain a calcined material.

[0084] After washing, filtering and drying the calcined material, it was uniformly mixed with Li2S and heat-treated at 150℃ for 8 hours in an argon atmosphere to obtain a doped cobalt-free single crystal core material.

[0085] The doped cobalt-free single-crystal core material was dispersed in deionized water at a mass ratio of 9:1. Li3PO4 and Li2S were added to the suspension, and the mixture was then vigorously stirred at 25°C for 1 hour. The mixture was heated at 90°C until the solvent was completely evaporated, dried, and then sintered at 850°C for 8 hours in an inert atmosphere to obtain the cobalt-free single-crystal cathode material.

[0086] Example 4

[0087] The only difference between this embodiment and Embodiment 1 is that the thickness of the fast ion conductor coating is 2 nm; all other conditions and parameters are exactly the same as in Embodiment 1.

[0088] Example 5

[0089] The only difference between this embodiment and Embodiment 1 is that the thickness of the fast ion conductor coating is 10 nm; all other conditions and parameters are exactly the same as in Embodiment 1.

[0090] Example 6

[0091] The only difference between this embodiment and Embodiment 1 is that the cesium content in the chemical formula of the doped cobalt-free single crystal core is 0.04 (i.e., LiCs). u (Ni x Mn y Ti z )O 2-n S n In this case, u=0.04), other conditions and parameters are exactly the same as in Example 1.

[0092] Example 7

[0093] The only difference between this embodiment and Embodiment 1 is that the titanium content in the chemical formula of the doped cobalt-free single crystal core is 0.15%, and the nickel content is (i.e., LiCs) u (Ni x Mn y Ti z )O 2-n S n In this case, z=0.15), other conditions and parameters are exactly the same as in Example 1.

[0094] Example 8

[0095] The only difference between this embodiment and Embodiment 1 is that the sulfur content in the chemical formula of the doped cobalt-free single crystal core is 0.08%, and the nickel content is (i.e., LiCs) u (Ni x Mn y Ti z )O 2-n S n In this case, n=0.08), other conditions and parameters are exactly the same as in Example 1.

[0096] Comparative Example 1

[0097] The only difference between this comparative example and Example 1 is that titanium is not doped in the cobalt-free doped single crystal core; all other conditions and parameters are exactly the same as in Example 1.

[0098] Comparative Example 2

[0099] The only difference between this comparative example and Example 1 is that cesium is not doped in the cobalt-free doped single crystal core; all other conditions and parameters are exactly the same as in Example 1.

[0100] Comparative Example 3

[0101] The only difference between this comparative example and Example 1 is that sulfur is not doped in the cobalt-free doped single crystal core; all other conditions and parameters are exactly the same as in Example 1.

[0102] Comparative Example 4

[0103] The only difference between this comparative example and Example 1 is that the fast ion conductor coating layer is not provided; all other conditions and parameters are exactly the same as in Example 1.

[0104] Comparative Example 5

[0105] This comparative example directly uses the chemical formula LiNi. 0.9 Mn 0.1 O2-free cobalt-free single-crystal cathode material.

[0106] Performance testing:

[0107] The above cathode materials were assembled into solid-state coin cells, and their electrochemical performance was tested. The 0.1C discharge capacity and charge-discharge coulombic efficiency were tested at an operating voltage of 3.0V-4.3V, and 100 charge-discharge cycles were performed at 1C. The test results are shown in Table 1.

[0108] Table 1

[0109]

[0110] As shown in Table 1, and based on Examples 1-8, the battery made from the cobalt-free single-crystal cathode material of the present invention can achieve a first-cycle discharge capacity of over 183.8 mAh / g, a first-cycle charge-discharge coulombic efficiency of over 81.5%, and a capacity retention rate of over 69% after 100 cycles at 1C. By adjusting the preparation conditions, the battery made from the cobalt-free single-crystal cathode material can achieve a first-cycle discharge capacity of over 205.7 mAh / g, a first-cycle charge-discharge coulombic efficiency of over 87.1%, and a capacity retention rate of over 83.5% after 100 cycles at 1C.

[0111] A comparison of Examples 1 and 4-5 shows that the thickness of the fast ion conductor coating layer in the cobalt-free single-crystal cathode material of the present invention affects its performance. When the thickness of the fast ion conductor coating layer is controlled between 2.5 nm and 8 nm, the performance of the cobalt-free single-crystal cathode material is better. If the thickness of the fast ion conductor coating layer is too thin, it cannot effectively suppress the volume change and stress of the single crystal particles under long-term cycling, especially at high rates, leading to coating layer cracking and failure. If the thickness of the fast ion conductor coating layer is too thick, it will increase the impedance of lithium ion diffusion, reduce the lithium ion transport efficiency, and decrease the rate performance.

[0112] A comparison of Examples 1 and 6 shows that the cesium content in the doped cobalt-free single crystal core of the cobalt-free single crystal cathode material of the present invention affects its performance. When the cesium content in the chemical formula of the doped cobalt-free single crystal core is controlled to be less than 0.03, the performance of the cobalt-free single crystal cathode material is better. If the cesium content is too high, the large ionic radius of cesium ions will cause the crystal lattice to be distorted, and the structural stability of the material will decrease.

[0113] A comparison of Examples 1 and 7 shows that the titanium content in the doped cobalt-free single crystal core of the cobalt-free single crystal cathode material of the present invention affects its performance. When the titanium content in the chemical formula of the doped cobalt-free single crystal core is controlled to be less than 0.1, the performance of the cobalt-free single crystal cathode material is better. If the titanium content is too high, it will reduce the active nickel content, resulting in a significant decrease in the material's capacity. Moreover, excessive titanium is more likely to generate impurity phases in the material, affecting ion / electron transport.

[0114] A comparison of Examples 1 and 8 shows that the sulfur content in the doped cobalt-free single crystal core of the cobalt-free single crystal cathode material of the present invention affects its performance. When the sulfur content in the chemical formula of the doped cobalt-free single crystal core is controlled to be less than 0.05, the performance of the cobalt-free single crystal cathode material is better. If the sulfur content is too high, the electrochemical performance of the material will decrease and impurity phases may be generated.

[0115] As can be seen from the comparison between Example 1 and Comparative Examples 1-5, the present invention incorporates multiple doping elements in the cobalt-free single-crystal core. Cesium occupies lithium sites, and its ionic radius and bond energy with oxygen are significantly greater than those of lithium. Doping to lithium sites effectively suppresses structural collapse and phase transitions during deep delithiation, reduces nickel-lithium mixing, and significantly improves lithium-ion transport efficiency. Titanium effectively enhances the stability of lattice oxygen, suppresses oxygen evolution, and thus improves the material's cycle stability. Sulfur doping at oxygen sites weakens the bond energy between transition metals and oxygen, reduces oxygen activity, and further suppresses oxygen evolution. Moreover, since the ionic radius of sulfur is greater than that of oxygen, it can expand the interlayer spacing, further improving the lithium-ion insertion / extraction efficiency. Coating the material surface with a fast ion conductor improves both the material's ionic conductivity and structural stability. Compared to conventional cobalt-free single-crystal cathode materials, the rate performance and cycle performance of the cobalt-free single-crystal cathode material of the present invention are significantly improved.

[0116] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A cobalt-free single-crystal cathode material, characterized in that, The cobalt-free single-crystal cathode material includes a doped cobalt-free single-crystal core and a fast-ion conductor coating layer disposed on the surface of the doped cobalt-free single-crystal core; The doping elements in the doped cobalt-free single crystal core include cesium, titanium, and sulfur.

2. The cobalt-free single-crystal cathode material as described in claim 1, characterized in that, The chemical formula of the doped cobalt-free single crystal core is LiCs. u (Ni x Mn y Ti z )O 2-n S n Where 0.8 ≤ x < 1, 0 <y≤0.2,0<z≤0.1,0<u≤0.03,0<m≤0.05,0<n≤0.05。 3. The cobalt-free single-crystal cathode material as described in claim 1 or 2, characterized in that, The material of the fast ion conductor coating layer includes any one or a combination of at least two of LLZO, Li3PO4-Li2S composite phase or LATP; Preferably, the thickness of the fast ion conductor coating layer is 2.5 nm to 8 nm.

4. A method for preparing a cobalt-free single-crystal cathode material as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: A nickel-manganese mixed salt solution, a titanium salt solution, a precipitant solution, and a complexing agent solution were injected concurrently into a reaction apparatus to carry out a co-precipitation reaction, thereby obtaining a titanium-doped precursor. A titanium-doped precursor, lithium salt, and cesium salt are mixed and subjected to a first sintering process to obtain a sintered material; A doped cobalt-free single-crystal core material is obtained by mixing a calcined material with lithium sulfide and then heat-treating it. After mixing the doped cobalt-free single crystal core material with a solvent, a fast ion conductor raw material is added, and the mixture is stirred and reacted. The solvent is then evaporated to obtain a solid material. The obtained solid material is subjected to a second sintering treatment to obtain the cobalt-free single crystal cathode material.

5. The preparation method according to claim 4, characterized in that, The solutes in the nickel-manganese mixed salt solution include sulfates and / or nitrates; Preferably, the mass concentration of the nickel-manganese mixed salt solution is 50 g / L to 150 g / L; Preferably, the solute in the titanium salt solution includes titanium sulfate; Preferably, the molar concentration of the titanium salt solution is 1 mol / L to 3 mol / L; Preferably, the precipitant solution comprises a sodium hydroxide solution; Preferably, the mass percentage concentration of the precipitant solution is 20% to 40%; Preferably, the complexing agent solution comprises ammonia; Preferably, the mass percentage concentration of the complexing agent solution is 10% to 20%.

6. The preparation method according to claim 4 or 5, characterized in that, The pH of the coprecipitation reaction is 11-12; Preferably, the temperature of the co-precipitation reaction is 55℃~60℃; Preferably, the ammonia concentration in the co-precipitation reaction is 4 g / L to 5 g / L; Preferably, the coprecipitation reaction takes 40 to 80 hours.

7. The preparation method according to claim 4 or 5, characterized in that, The lithium salt includes lithium hydroxide and / or lithium carbonate; Preferably, the cesium salt includes cesium carbonate; Preferably, the atmosphere of the first sintering treatment includes oxygen; Preferably, the temperature of the first sintering treatment is 700℃~900℃; Preferably, the first sintering treatment takes 8 to 12 hours.

8. The preparation method according to any one of claims 4-7, characterized in that, The heat treatment temperature is 100℃~150℃; Preferably, the atmosphere for the heat treatment includes nitrogen and / or argon; Preferably, the heat treatment time is 8h to 12h.

9. The preparation method according to any one of claims 4-8, characterized in that, The temperature of the stirring reaction is 20℃~30℃; Preferably, the stirring reaction time is 0.5h to 1.5h; Preferably, the temperature of the evaporating solvent is 70°C to 90°C; Preferably, the atmosphere for the second sintering treatment includes nitrogen and / or argon; Preferably, the temperature of the second sintering treatment is 800℃~850℃; Preferably, the second sintering treatment takes 8 to 12 hours.

10. A solid-state battery, characterized in that, The solid-state battery comprises the cobalt-free single-crystal cathode material as described in any one of claims 1-3.

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