Composite positive electrode material and preparation method and application thereof

Abstract

The invention provides a composite positive electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) providing a lithium-rich manganese-based precursor inner core, placing the lithium-rich manganese-based precursor inner core in a base solution, and injecting a metal salt solution, a precipitator solution and a complexing agent solution into the base solution in a parallel flow manner to obtain a lithium-rich manganese-based precursor inner core; carrying out coprecipitation reaction by taking the lithium-rich manganese-based precursor inner core as a crystal nucleus to obtain a composite precursor; and (2) mixing the composite precursor, an inorganic nano material and a lithium source, and calcining to obtain the composite positive electrode material. The method can be used for preparing the positive electrode material which is high in core-shell bonding strength, stable in interface, good in ion transmission effect and high in energy density, and the positive electrode material can improve the energy density and cycling stability of a solid-state battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state batteries, and relates to a composite cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of electric vehicles and renewable energy storage technologies, solid-state batteries have received extensive attention as the next-generation battery technology. Replacing the flammable liquid electrolyte with a non-flammable and more stable solid electrolyte can solve the safety problems of batteries. Developing all-solid-state lithium batteries with high energy density, long cycle life, low cost, and high safety is one of the important directions for the development of the next-generation lithium-ion batteries.

[0003] In solid-state batteries, the poor interfacial contact between the solid electrolyte and the cathode material and the low ion transport efficiency are also the key factors restricting the improvement of battery performance. There is often a large interfacial impedance between traditional cathode materials and solid electrolytes, which not only increases the internal resistance of the battery, reduces the charge and discharge efficiency of the battery, but also causes serious heating of the battery during the cycling process, further affecting the performance and safety of the battery.

[0004] CN119050309A discloses a cathode material for all-solid-state batteries and a preparation method thereof. The preparation method includes: first preparing a molybdenum-doped manganese-nickel-cobalt precipitate, and then preparing the cathode material by calcining the molybdenum-doped manganese-nickel-cobalt precipitate, a lithium salt, a surfactant, and a conductive agent.

[0005] CN119706967A discloses a lithium-rich manganese-based material for all-solid-state batteries, a preparation method thereof, and an application thereof. The preparation method includes: mixing and drying a lithium-rich manganese-based carbonate precursor, a dopant, and a first solvent to obtain a doped lithium-rich manganese-based carbonate precursor, and then performing sintering and washing to obtain a pretreated precursor; ball-milling the pretreated precursor and then mixing and calcining it with a lithium source to obtain a submicron single-crystalline lithium-rich manganese-based cathode material; mixing the single-crystalline lithium-rich manganese-based cathode material, a metal source coating agent, and a second solvent, and then removing the second solvent and calcining to obtain the lithium-rich manganese-based material for all-solid-state batteries.

[0006] The cathode materials prepared by the above-mentioned schemes have relatively low energy density, or problems such as capacity attenuation and poor stability will occur during long-term use, which affects their application in solid-state batteries. Summary of the Invention

[0007] The purpose of the present invention is to provide a composite cathode material, a preparation method thereof, and an application thereof. The method of the present invention can prepare a cathode material with a large core-shell binding strength, a stable interface, good ion transport effect, and high energy density. The cathode material can improve the energy density and cycle stability of solid-state batteries.

[0008] To achieve the object of the present invention, the following technical solutions are adopted in the present invention:

[0009] In a first aspect, the present invention provides a method for preparing a composite cathode material, and the preparation method comprises the following steps:

[0010] (1) Provide a lithium-rich manganese-based precursor core, place the lithium-rich manganese-based precursor core in a bottom liquid, and inject a metal salt solution, a precipitant solution, and a complexing agent solution into the bottom liquid in a co-current manner, and perform a coprecipitation reaction using the lithium-rich manganese-based precursor core as a crystal nucleus to obtain a composite precursor;

[0011] (2) Mix the composite precursor, an inorganic nanomaterial, and a lithium source, and obtain the composite cathode material through calcination treatment.

[0012] In the present invention, the lithium-rich manganese-based precursor is used as a crystal nucleus, and a coprecipitation reaction is carried out on its surface to prepare a coating layer to form a composite precursor, and then it is mixed and sintered with an inorganic nanomaterial and a lithium source to obtain the composite cathode material. In the present invention, a metal hydroxide is in-situ coated on the surface of the lithium-rich manganese-based precursor at the precursor stage, and the combination effect of the two is good, and the stability is greatly improved. During the process of mixing and sintering it with an inorganic nanomaterial and a lithium source, the coating layer will not fall off, and the inorganic nanomaterial can be uniformly doped into the interior of the composite precursor and dispersed in the lithium-rich core. By regulating the charge distribution of oxygen anions (O 2- ), irreversible oxygen release is inhibited. At the same time, the inorganic nanomaterial is preferentially distributed at the grain boundaries of the composite precursor, which can inhibit the expansion of grain boundary cracks and also inhibit the layered → spinel phase transformation of the lithium-rich core.

[0013] Preferably, the chemical formula of the lithium-rich manganese-based precursor core in step (1) is Ni x Mn 1-x (OH)2, 0 < x < 0.4.

[0014] The lithium-rich manganese-based precursor core in the present invention is prepared by a conventional coprecipitation method.

[0015] Preferably, the median particle size D50 of the lithium-rich manganese-based precursor core in step (1) is 2 μm to 4 μm, for example: 2 μm, 2.5 μm, 3 μm, 3.5 μm or 4 μm, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0016] Preferably, the metal salt solution in step (1) includes a ternary nickel cobalt manganese mixed salt solution and / or a cobalt salt solution.

[0017] In the present invention, a ternary nickel-cobalt-manganese mixed salt solution and / or a cobalt salt solution are used for coprecipitation to coat nickel-cobalt-manganese hydroxide and / or cobalt hydroxide on the surface of the core of the lithium-rich manganese-based precursor. After subsequent sintering, NCM and / or lithium cobaltate are formed. These materials have high stability and can inhibit the formation of the shell. At the same time, a composite cathode material with excellent electrochemical performance, stability, and long cycle life can be obtained, which is suitable for applications with high energy density such as solid-state batteries, and has low cost and application prospects.

[0018] Preferably, the total mass concentration of metal ions in the metal salt solution in step (1) is 50 g to 150 g / L, for example: 50 g / L, 80 g / L, 100 g / L, 120 g / L, or 150 g / L, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0019] Preferably, the precipitant solution in step (1) includes a sodium hydroxide solution.

[0020] Preferably, the mass concentration of the precipitant solution in step (1) is 20% to 50%, for example: 20%, 25%, 30%, 40%, or 50%, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0021] Preferably, the complexing agent solution in step (1) includes an ammonia water solution.

[0022] Preferably, the mass concentration of the complexing agent solution in step (1) is 10% to 30%, for example: 10%, 15%, 20%, 25%, or 30%, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0023] Preferably, the bottom liquid in step (1) includes ammonia water.

[0024] Preferably, the ammonia mass concentration in the bottom liquid in step (1) is 1 g / L to 10 g / L, for example: 1 g / L, 2 g / L, 5 g / L, 8 g / L, or 10 g / L, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0025] Preferably, the feeding rate of the nickel-cobalt-manganese mixed salt solution in step (1) is 6 L / h to 10 L / h, for example: 6 g / L, 7 g / L, 8 g / L, 9 g / L, or 10 g / L, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0026] Preferably, the feeding rate of the precipitant solution in step (1) is 2 L / h to 3 L / h, for example: 2 g / L, 2.2 g / L, 2.5 g / L, 2.8 g / L, or 3 g / L, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0027] Preferably, the feeding rate of the complexing agent solution in step (1) is 0.6 L / h to 1 L / h, for example: 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L, or 1 g / L, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0028] Preferably, the temperature of the coprecipitation reaction in step (1) is 40 °C to 80 °C, for example: 40 °C, 50 °C, 70 °C, or 80 °C, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0029] Preferably, the pH of the coprecipitation reaction in step (1) is 10 to 12, for example: 10, 10.5, 11, 11.5, or 12, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0030] Preferably, stirring is carried out during the coprecipitation reaction in step (1).

[0031] Preferably, the stirring speed is 200 rpm to 400 rpm, for example: 200 rpm, 300 rpm, or 400 rpm, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0032] Preferably, the composite precursor in step (1) includes a lithium-rich manganese-based precursor core and a coating layer provided on the surface of the lithium-rich manganese-based precursor core.

[0033] Preferably, the thickness of the coating layer is 5 μm to 10 μm, for example: 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, etc. It is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0034] Preferably, the inorganic nanomaterial in step (2) includes an inorganic nanomaterial with high dielectric properties.

[0035] The high-dielectric inorganic nanomaterial of the present invention can alleviate bottleneck problems such as limited ion transport, unstable interface, and mechanical stress concentration in the positive electrode of a solid-state battery, and a solid-state battery with high energy density and long cycle life can be obtained.

[0036] Preferably, the inorganic nanomaterial in step (2) includes any one or a combination of at least two of TiO2, SrTiO3, or BaTiO3. Typical but non-limiting combinations include the combination of TiO2 and BaTiO3, the combination of SrTiO3 and BaTiO3, or the combination of TiO2 and SrTiO3, etc.

[0037] Preferably, the lithium source in step (2) includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, or lithium acetate. Typical but non-limiting combinations include the combination of lithium hydroxide and lithium acetate, the combination of lithium hydrogencarbonate and lithium acetate, or the combination of lithium hydroxide and lithium carbonate, etc.

[0038] Preferably, the mass ratio of the inorganic nanomaterial to the composite precursor in step (2) is (0.1 - 0.4):100. For example: 0.1:100, 0.15:100, 0.2:100, 0.3:100, or 0.4:100, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] Preferably, the molar ratio of lithium element in the lithium source to the metal element in the composite precursor is (1.15 - 1.25):1. For example: 1.15:1, 1.18:1, 1.2:1, 1.22:1, or 1.25:1, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0040] Preferably, grinding is carried out during the mixing process in step (2).

[0041] Preferably, the mixing time in step (2) is 30 min - 40 min. For example: 30 min, 32 min, 35 min, 38 min, or 40 min, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] Preferably, the heating rate of the calcination treatment in step (2) is 4 °C / min - 6 °C / min. For example: 4 °C / min, 4.5 °C / min, 5 °C / min, 5.5 °C / min, or 6 °C / min, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] Preferably, the temperature of the calcination treatment in step (2) is 500 °C - 800 °C. For example: 500 °C, 550 °C, 600 °C, 700 °C, or 800 °C, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] Preferably, the calcination time in step (2) is 12 h to 20 h, for example, 12 h, 15 h, 16 h, 18 h or 20 h, etc., not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0045] In a second aspect, the present invention provides a composite positive electrode material, which is prepared by the preparation method described in the first aspect.

[0046] In the composite positive electrode material of the present invention, the surface of the lithium-rich manganese-based material is coated with a highly stable metal lithium acid compound as a shell, which can provide a larger energy storage capacity while having a higher specific capacity, improve the first coulomb efficiency of the battery, and also improve the cycle life and stability of the material. The addition of high-stability materials effectively overcomes the shortcomings of the rapid capacity decay, poor structural stability, and cycle performance of the lithium-rich manganese positive electrode material alone, and the existence of potential safety hazards. The doping of inorganic nanomaterials can weaken the Coulomb force between lithium ions and the lattice, reduce the activation energy of ion diffusion, and thus improve the lithium ion transmission efficiency inside the positive electrode. Moreover, the high specific surface area and interface effect of nanomaterials can form a continuous dielectric enhancement region between positive electrode particles, guide lithium ions to migrate along a low-resistance path, and especially alleviate the ion blocking problem at the interface between the solid electrolyte and the positive electrode. At the same time, inorganic nanomaterials can also serve as a physical barrier to reduce the direct contact between the positive electrode active material and the solid electrolyte, and inhibit the release of high-pressure oxygen at the interface or the decomposition of the sulfide electrolyte.

[0047] In a third aspect, the present invention provides a positive electrode plate, wherein the positive electrode plate comprises the composite positive electrode material as described in the second aspect.

[0048] In a fourth aspect, the present invention provides a solid-state battery, comprising the positive electrode plate as described in the third aspect.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The present invention uses a lithium-rich manganese-based precursor as a crystal core, and in situ prepares a coating layer on its surface to form a composite precursor. The core-shell bonding strength in the composite precursor is large and will not fall off during the subsequent sintering process. By mixing with inorganic nanomaterials and lithium sources, the inorganic nanomaterials can be doped into the inner core to stabilize its structure while improving the ion conductivity of the material. The composite positive electrode material has excellent electrochemical properties, stability and long cycle life, and can alleviate bottleneck problems such as limited ion transport, unstable interface, and mechanical stress concentration in the positive electrode of solid-state batteries, thereby obtaining a solid-state battery with high energy density and long cycle life.

[0051] (2) The initial discharge capacity of the solid-state battery made of the composite cathode material of the present invention can reach more than 212.9 mAh / g, and the capacity retention rate after 200 cycles can reach more than 75.9%. By adjusting the preparation conditions and parameters, the initial discharge capacity of the solid-state battery made of the composite cathode material can reach more than 217.7 mAh / g, and the capacity retention rate after 200 cycles can reach more than 82%. Detailed implementation mode

[0052] The technical solution of the present invention will be further described below through specific implementation modes. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0053] The lithium-rich manganese-based precursor core of the present invention is prepared by the following method: Nickel sulfate and manganese sulfate are weighed according to the molar ratio of nickel to manganese of 0.3:0.7, and they are dissolved in an appropriate amount of deionized water to prepare a mixed salt solution with a concentration of 0.5 mol / L. The mixed salt solution, 2 mol / L sodium hydroxide solution and 15% ammonia water by mass are co-fed into the bottom liquid, and a coprecipitation reaction is carried out under the conditions of pH = 10, stirring speed of 400 rpm and temperature of 60 °C. The reaction mixture is filtered, washed and dried to obtain Ni 0.3 Mn 0.7 (OH)2 lithium-rich manganese-based precursor core.

[0054] Example 1

[0055] This example provides a composite cathode material, which is prepared by the following method:

[0056] (1) Prepare a bottom liquid with a temperature of 60 °C, ammonia concentration of 5 g / L and pH of 11. Place the lithium-rich manganese-based precursor core with a median particle size D50 of 3 μm in the bottom liquid. A nickel-cobalt-manganese sulfate solution with a concentration of 100 g / L (Ni:Co:Mn = 60:20:20), a 30% sodium hydroxide solution by mass and a 20% ammonia water by mass are simultaneously co-fed into the bottom liquid at a feeding rate of 8 L / h, 2.5 L / h and 0.8 L / h respectively for coprecipitation reaction. During the reaction process, control the pH of the reaction system to be 11, ammonia concentration to be 5 g / L and temperature to be 60 °C until a composite precursor with a coating layer thickness of 8 μm (median particle size of 19 μm) is formed;

[0057] (2) Mix the composite precursor, inorganic nanomaterials, and lithium hydroxide, and grind them thoroughly in a mortar for 30 min to obtain a mixed material. Among them, the mass ratio of the composite precursor to the inorganic nanomaterials is 100:0.3. The inorganic nanomaterials include TiO₂ and BaTiO₃ with a particle size of 10 nm to 50 nm and a mass ratio of 1:1. The molar ratio of the metal elements in the composite precursor to the lithium element in the lithium source is 1:1.2. Under an oxygen atmosphere, heat from 20 °C to 600 °C at a heating rate of 5 °C / min, calcine and hold at this temperature for 18 h, and then cool naturally to 20 °C to obtain the composite cathode material.

[0058] Example 2

[0059] This example provides a composite cathode material, which is prepared by the following method:

[0060] (1) Prepare a bottom solution with a temperature of 60 °C, an ammonia concentration of 5 g / L, and a pH of 11. Place the lithium-rich manganese-based precursor core with a median particle size D50 of 2 μm in the bottom solution. Simultaneously and co-currently add a cobalt sulfate salt solution with a concentration of 100 g / L, a sodium hydroxide solution with a mass concentration of 30%, and an ammonia water solution with a mass concentration of 20% to the bottom solution at a feeding rate of 8 L / h, 2.5 L / h, and 0.8 L / h respectively for co-precipitation reaction. During the reaction process, control the pH of the reaction system to be 11, the ammonia concentration to be 5 g / L, and the temperature to be 60 °C until a composite precursor with a coating layer thickness of 5 μm (median particle size of 12 μm) is formed;

[0061] (2) Mix the composite precursor, inorganic nanomaterials, and lithium hydroxide, and grind them thoroughly in a mortar for 30 min to obtain a mixed material. Among them, the mass ratio of the composite precursor to the inorganic nanomaterials is 100:0.1. The inorganic nanomaterials include SrTiO₃ and BaTiO₃ with a particle size of 10 nm to 50 nm and a mass ratio of 1:1. The molar ratio of the metal elements in the composite precursor to the lithium element in the lithium source is 1:1.15. Under an oxygen atmosphere, heat from 20 °C to 500 °C at a heating rate of 4 °C / min, calcine and hold at this temperature for 20 h, and then cool naturally to 20 °C to obtain the composite cathode material.

[0062] Example 3

[0063] This example provides a composite cathode material, which is prepared by the following method:

[0064] (1) Prepare a base solution with a temperature of 60 °C, an ammonia concentration of 5 g / L, and a pH of 11. Place the core of the lithium-rich manganese-based precursor with a median particle size D50 of 4 μm in the base solution. Simultaneously add a nickel-cobalt-manganese sulfate solution (Ni:Co:Mn = 50:20:30) with a concentration of 100 g / L, a sodium hydroxide solution with a mass concentration of 30%, and an ammonia water solution with a mass concentration of 20% into the base solution at a feeding rate of 8 L / h, 2.5 L / h, and 0.8 L / h respectively in a co-current manner for coprecipitation reaction. During the reaction process, control the pH of the reaction system to be 11, the ammonia concentration to be 5 g / L, and the temperature to be 60 °C until a composite precursor with a coating layer thickness of 10 μm (median particle size of 24 μm) is formed;

[0065] (2) Mix the composite precursor, inorganic nanomaterials, and lithium hydroxide, and grind them thoroughly in a mortar for 30 min to obtain a mixed material. Among them, the mass ratio of the composite precursor to the inorganic nanomaterials is 100:0.4. The inorganic nanomaterials include SrTiO3 and BaTiO3 with a particle size of 10 nm - 50 nm and a mass ratio of 1:1. The molar ratio of the metal elements in the composite precursor to the lithium element in the lithium source is 1:1.25. Under an oxygen atmosphere, heat from 20 °C to 800 °C at a heating rate of 6 °C / min, calcine and hold at this temperature for 12 h, and then naturally cool to 20 °C to obtain the composite cathode material.

[0066] Example 4

[0067] The difference between this example and Example 1 is only that the thickness of the coating layer is 3 μm, and other conditions and parameters are exactly the same as those in Example 1.

[0068] Example 5

[0069] The difference between this example and Example 1 is only that the thickness of the coating layer is 12 μm, and other conditions and parameters are exactly the same as those in Example 1.

[0070] Example 6

[0071] The difference between this example and Example 1 is only that the mass ratio of the inorganic nanomaterials to the composite precursor is 0.05:100, and other conditions and parameters are exactly the same as those in Example 1.

[0072] Example 7

[0073] The difference between this example and Example 1 is only that the mass ratio of the inorganic nanomaterials to the composite precursor is 0.5:100, and other conditions and parameters are exactly the same as those in Example 1.

[0074] Comparative Example 1

[0075] The difference between this comparative example and Example 1 is only that the core only uses the lithium-rich manganese-based precursor and does not undergo coprecipitation treatment, and other conditions and parameters are exactly the same as those in Example 1.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 1 is only that a ternary nickel-cobalt-manganese precursor is used as a seed crystal, and a lithium-rich manganese-based precursor is coated on its surface without coprecipitation treatment, and other conditions and parameters are exactly the same as those in Example 1.

[0078] Comparative Example 3

[0079] The difference between this comparative example and Example 1 is only that inorganic nanomaterials are not added in step (2), and other conditions and parameters are exactly the same as those in Example 1.

[0080] Performance test:

[0081] The composite cathode material, conductive agent, and binder prepared in the examples and comparative examples are added to an appropriate amount of solvent (such as N-methylpyrrolidone NMP) according to a certain mass ratio (usually 8:1:1 or other optimized ratios), and a planetary ball mill or stirrer is used for sufficient stirring and grinding to form a uniform slurry. The prepared slurry is uniformly coated on an aluminum foil current collector with a coating thickness of 100 μm, and after drying, rolling, and punching, a positive electrode sheet for a solid-state battery is obtained. It is assembled into a solid-state battery with Li6PS5Cl as the solid electrolyte and a graphite negative electrode as the negative electrode. A battery test system is used to perform charge and discharge tests on the assembled solid-state battery to test its capacity density and cycling performance at 1C. The test results are shown in Table 1:

[0082] Table 1

[0083] Initial discharge capacity (mAh / g) Capacity retention rate after 200 cycles (%) Example 1 221.1 82.2 Example 2 220.5 83.8 Example 3 217.7 82 Example 4 215.6 75.9 Example 5 216.8 76 Example 6 212.9 80.8 Example 7 214.4 77.5 Comparative Example 1 190.6 73.9 Comparative Example 2 207.1 67.4 Comparative Example 3 197.5 70.7

[0084] As can be seen from Table 1, from Examples 1-7, it can be obtained that the initial discharge capacity of the solid-state battery made of the composite cathode material of the present invention can reach more than 212.9 mAh / g, and the capacity retention rate can reach more than 75.9% after 200 cycles. By adjusting the preparation conditions and parameters, the initial discharge capacity of the solid-state battery made of the composite cathode material can reach more than 217.7 mAh / g, and the capacity retention rate can reach more than 82% after 200 cycles.

[0085] It can be obtained by comparing Example 1 with Examples 4-5 that during the preparation process of the composite cathode material of the present invention, the thickness of the coating layer of the composite precursor affects its performance. Controlling the thickness of the coating layer within 5 μm to 10 μm results in better performance of the prepared composite cathode material. The coating layer is a stable NCM ternary material or LiCoO2, which itself serves as an active material. If the thickness of the coating layer is too small, the thin coating layer may partially participate in the reaction during charge and discharge, slightly increasing the total capacity, but the synergistic reaction between the core and the shell may be limited, and the overly thin ternary layer cannot completely isolate the direct contact between the lithium-rich manganese-based core and the solid electrolyte, leading to side reactions such as oxygen release and transition metal dissolution, and accelerating capacity decay during long-term cycling. If the thickness of the coating layer is too large, it will prolong the transmission path of lithium ions from the core to the electrolyte, resulting in increased polarization at high rates, and the difference in thermal expansion coefficients between the lithium-rich manganese-based material and the ternary material may cause microcracks to form in the thick coating layer during cycling, damaging the integrity of the core-shell structure.

[0086] It can be obtained by comparing Example 1 with Examples 6-7 that during the preparation process of the composite cathode material of the present invention, the addition amount of the inorganic nanomaterial affects its performance. Controlling the mass ratio of the inorganic nanomaterial to the composite precursor within 0.1 to 0.4:100 results in better performance of the prepared composite cathode material. The main role of the inorganic nanomaterial is to improve the ion transport ability and interface stability of the battery. If the doping amount is too small, its advantages may not be fully utilized, and it may not effectively improve the limited ion transport in the positive electrode of the solid-state battery or relieve the interface instability problem, resulting in insufficient performance improvement and affecting the service life and charge-discharge performance of the battery. If the doping amount of the inorganic nanomaterial is too large, it may cause the material structure to become overly complex, resulting in hindrance to the ion transport path, making the positive electrode / electrolyte interface unstable, thereby affecting the overall performance of the solid-state battery, increasing the interface resistance, and the excessive doping amount may cause aggregation of the inorganic nanomaterial, affecting its uniform distribution, and further affecting the charge-discharge efficiency and cycle stability of the battery.

[0087] It can be obtained by comparing Example 1 with Comparative Example 1 that in the composite cathode material of the present invention, a lithium metal oxide compound with high stability is coated on the surface of the lithium-rich manganese-based material as the outer shell. While having a relatively high specific capacity, it can provide a larger energy storage capacity, improve the first Coulomb efficiency of the battery, and also improve the cycle life and stability of the material. The addition of the high-stability material effectively overcomes the deficiencies of the lithium-rich manganese positive electrode material when used alone, such as fast capacity decay, poor structural stability, room for improvement in cycle performance, and potential safety hazards.

[0088] It can be seen from the comparison between Example 1 and Comparative Example 2 that using the lithium-rich manganese-based material as the core has better performance than using the ternary material as the core. Because placing the high-capacity material in the core can maximize the utilization rate of the active material, while the outer ternary material improves the cycle stability through structural protection, achieving a balance between energy density and lifespan. The stable layered structure of the outer ternary material can inhibit the oxygen loss and phase transformation of the core, and has high mechanical strength, which can effectively restrain the volume expansion of the core. At the same time, the toughness of the ternary material is used to disperse stress and avoid particle pulverization. If the ternary material is used as the core, the lithium-rich manganese-based outer shell is prone to uneven coating due to the difference in crystallization rate during the coprecipitation process, and cracks are likely to occur during calcination due to the difference in thermal expansion coefficient between the core and the outer shell, which will sacrifice the energy density and it is difficult to solve the problem of the instability of the outer shell structure. Therefore, the composite design of lithium-rich manganese-based core + ternary outer shell is the optimal solution that takes into account both performance and reliability.

[0089] It can be seen from the comparison between Example 1 and Comparative Example 3 that the doping of inorganic nanomaterials can weaken the Coulomb force between lithium ions and the lattice, reduce the activation energy of ion diffusion, thereby improving the lithium ion transport efficiency inside the cathode. Moreover, the high specific surface area and interfacial effect of the nanomaterials can form a continuous dielectric enhancement region between the cathode particles, guiding the lithium ions to migrate along the low-resistance path, especially alleviating the ion blocking problem at the interface between the solid electrolyte and the cathode. At the same time, the inorganic nanomaterials can also act as a physical barrier to reduce the direct contact between the cathode active material and the solid electrolyte, inhibiting the release of high-pressure oxygen or the decomposition of sulfide electrolyte at the interface.

[0090] The applicant declares that the above description is only the specific implementation manner 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 thought of within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a composite cathode material, characterized in that, The preparation method comprises the following steps: (1) Provide a lithium-rich manganese-based precursor core, place the lithium-rich manganese-based precursor core in a bottom liquid, and inject a metal salt solution, a precipitating agent solution, and a complexing agent solution into the bottom liquid in parallel, and perform a coprecipitation reaction using the lithium-rich manganese-based precursor core as a crystal nucleus to obtain a composite precursor; (2) Mix the composite precursor, an inorganic nanomaterial, and a lithium source, and obtain the composite cathode material through a calcination treatment.

2. The preparation method according to claim 1, characterized in that, The chemical formula of the lithium-rich manganese-based precursor inner core described in step (1) is Ni x Mn 1-x (OH)2, where 0 < x < 0.4; Preferably, the median particle size D50 of the lithium-rich manganese-based precursor core in step (1) is 2 μm to 4 μm.

3. The preparation method according to claim 1 or 2, characterized in that, The metal salt solution in step (1) includes a ternary nickel-cobalt-manganese mixed salt solution and / or a cobalt salt solution; Preferably, the precipitating agent solution in step (1) includes a sodium hydroxide solution; Preferably, the complexing agent solution in step (1) includes an ammonia water solution.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The composite precursor in step (1) includes a lithium-rich manganese-based precursor core and a coating layer provided on the surface of the lithium-rich manganese-based precursor core; Preferably, the thickness of the coating layer is 5 μm to 10 μm.

5. The preparation method according to any one of claims 1-4, characterized in that, The inorganic nanomaterial in step (2) includes an inorganic nanomaterial with high dielectric permittivity; Preferably, the inorganic nanomaterial in step (2) includes any one or a combination of at least two of TiO2, SrTiO3, or BaTiO3; Preferably, the lithium source in step (2) includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, or lithium acetate.

6. The preparation method according to any one of claims 1-5, characterized in that, The mass ratio of the inorganic nanomaterial to the composite precursor in step (2) is (0.1 to 0.4):100; Preferably, the molar ratio of lithium element in the lithium source to the metal element in the composite precursor is (1.15 to 1.25):

1.

7. The preparation method according to any one of claims 1-6, characterized in that, Grinding is performed during the mixing process in step (2); Preferably, the mixing time in step (2) is 30 min to 40 min; Preferably, the heating rate of the calcination treatment in step (2) is 4 °C / min to 6 °C / min; Preferably, the temperature of the calcination treatment in step (2) is 500 °C to 800 °C; Preferably, the time of the calcination treatment in step (2) is 12 h to 20 h.

8. A composite cathode material, characterized in that, The composite cathode material is prepared by the preparation method according to any one of claims 1-7.

9. A positive electrode sheet, characterized in that, The positive electrode sheet includes the composite cathode material according to claim 8.

10. A solid-state battery, characterized in that, The solid-state battery includes the positive electrode sheet according to claim 9.