A composite positive electrode material and preparation method thereof and all-solid-state lithium battery

Abstract

The present invention provides a composite cathode material, a preparation method thereof, and an all-solid-state lithium battery, belonging to the technical field of lithium battery cathode materials. The composite cathode material provided by the present invention includes a cathode active material and a fast ion conductor coated with MXene. In the present invention, a fast ion conductor is introduced into the cathode active material to improve the ion transport ability of the cathode material; MXene with high electronic conductivity is used to coat the fast ion conductor to improve the electronic conductivity and discharge specific capacity of the composite cathode material. At the same time, the long-term cycling stability of the cathode material is significantly improved. The ionic conductivity of the composite cathode material provided by the present invention can reach 7.555×10<supgt;‑3< / supgt; S / cm, and the electronic conductivity can reach 4.761×10<supgt;‑5< / supgt> S / cm; the first-cycle discharge specific capacity of the all-solid-state lithium battery prepared with the composite cathode material can reach 211.22 mAh / g, and the capacity retention rate can reach more than 96% after 150 cycles at 0.5C.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery positive electrode materials, and in particular to a composite positive electrode material and a preparation method thereof, and an all-solid-state lithium battery. Background Art

[0002] my country is currently in a critical transition period from non-renewable energy sources such as coal, oil, and natural gas to renewable energy sources such as solar energy, nuclear energy, and electricity. Lithium-ion batteries, with their high energy density, long cycle life, and environmental friendliness, are an important alternative to traditional non-renewable fossil fuels. Traditional liquid lithium-ion batteries, due to the use of organic liquid electrolytes to transport lithium ions, inevitably experience side reactions during the charge and discharge process. Furthermore, electrolyte volatilization and leakage may occur during the battery cycle. This not only causes irreversible degradation of the lithium-ion battery's discharge capacity, but also poses serious safety risks if certain flammable and explosive organic electrolytes leak.

[0003] All-solid-state lithium-ion batteries (SSLIBs), as a type of lithium-ion battery, have attracted widespread attention due to their characteristics of being leak-proof, non-flammable, having good mechanical properties, good electrochemical stability, high safety, and excellent thermal stability. However, it is difficult for SSLIBs to achieve high mass loading of cathode materials, and thus difficult to achieve practical applications with high energy density. This is because an increase in the loading will increase the thickness of the cathode sheet, and the side away from the electrolyte will be blocked by other particles when transmitting lithium ions, seriously affecting the stable output of lithium ions inside the cathode. As a result, only the part of the cathode in contact with the electrolyte can completely release lithium ions, ultimately reducing the battery's discharge capacity. Moreover, an increase in the loading will significantly increase the charge and discharge current, which indirectly accelerates the chemical side reactions between the cathode side and the electrolyte, accelerating the formation of the CEI layer. An excessively thick CEI will lead to a decline in battery performance, thereby reducing the battery's service life.

[0004] In order to improve the above problems, modifying the positive electrode material by blending or coating fast lithium ion conductors is an effective way to achieve high load of solid-state batteries. The filled fast ion conductor can not only build a fast and stable lithium ion channel to assist the positive electrode in the transmission of lithium ions, but also the formed coating layer can protect the positive electrode material and improve the cycle stability of the battery. However, the modified SSLIBs have a lower discharge capacity due to the reduction in the proportion of active materials, and they still have the problem of insufficient positive electrode electronic conductivity. Summary of the Invention

[0005] The present invention aims to provide a composite cathode material, a method for preparing the same, and an all-solid-state lithium battery. The composite cathode material provided by the present invention has high ionic and electronic conductivity, and a lithium battery prepared using the composite cathode material has high discharge capacity and high cycle stability.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a composite cathode material, comprising a cathode active material and a MXene-coated fast ion conductor.

[0008] Preferably, the mass ratio of the fast ion conductor to the positive electrode active material in the MXene-coated fast ion conductor is (0.01-5):100.

[0009] Preferably, the mass ratio of MXene to the positive electrode active material in the MXene-coated fast ion conductor is (0.01-5):100.

[0010] Preferably, the particle size of the fast ion conductor in the MXene-coated fast ion conductor is 0.1 to 10 μm.

[0011] Preferably, the positive electrode active material includes LiFePO4, LiNi 0.5 Co 0.3 Mn 0.2 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2 or LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0012] Preferably, the fast ion conductor in the MXene-coated fast ion conductor comprises Li 6.4 La3Zr 1.4 Ta 0.6 O 12 、Li3PO4、Li 1.4 Al 0.4 Ti 1.6 (PO4)3、LiTi 0.5 Zr 1.5 (PO4)3 or Li2AlZr(PO4)3.

[0013] The present invention also provides a method for preparing the composite positive electrode material described in the above technical solution, comprising the following steps:

[0014] (1) mixing a fast ion conductor and MXene with an organic solvent to obtain a fast ion conductor dispersion and a MXene dispersion;

[0015] (2) mixing the fast ion conductor dispersion obtained in step (1) with the MXene dispersion to obtain a mixed solution;

[0016] (3) Mixing the positive electrode active material with the mixed solution obtained in step (2) and drying the mixture to obtain a composite positive electrode material.

[0017] Preferably, the mass concentrations of the fast ion conductor dispersion and the MXene dispersion in step (1) are independently 1 to 100 mg / mL.

[0018] Preferably, the organic solvent in step (1) comprises anhydrous ethanol, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

[0019] The present invention also provides an all-solid-state lithium battery, wherein the positive electrode material in the all-solid-state lithium battery is the composite positive electrode material described in the above technical solution or the composite positive electrode material prepared by the preparation method described in the above technical solution.

[0020] The present invention provides a composite positive electrode material, comprising a positive electrode active material and a MXene-coated fast ion conductor. The present invention introduces a fast ion conductor into the positive electrode active material and utilizes the high lithium ion conductivity of the fast ion conductor to construct an efficient and stable ion transport network, thereby improving the ion transport capacity of the positive electrode material. By using MXene with high electronic conductivity to coat the fast ion conductor, the electronic conductivity and discharge specific capacity of the composite positive electrode material are improved. At the same time, the functional atoms or groups such as -F, -O and -OH present in MXene can prevent corrosion of the electrolyte, play a role in protecting the positive electrode active material, and significantly improve the long-term cycle stability of the positive electrode material. The results of the examples show that the ionic conductivity of the composite positive electrode material provided by the present invention is 7.555×10 -3 S / cm, and the electronic conductivity is 4.761×10 -5 S / cm, with high ionic conductivity and high electronic conductivity; the all-solid-state lithium battery prepared with the composite positive electrode material has a first-cycle discharge capacity of up to 211.22 mAh / g, and a capacity retention rate of over 96% after 150 cycles at 0.5C, showing high discharge capacity and high cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a SEM image of the LMN positive electrode sheet in Application Example 1 of the present invention;

[0022] Figure 2 This is a comparison chart of the first cycle charge and discharge curves of the all-solid-state lithium battery in Application Example 1 of the present invention and Comparative Application Example 1;

[0023] Figure 3 This is a comparison chart of the rate performance of the all-solid-state lithium battery in Application Example 1 of the present invention and Comparative Application Example 1;

[0024] Figure 4 This is a comparison chart of the long cycle curves of the all-solid-state lithium battery in Application Example 1 of the present invention and Comparative Application Example 1;

[0025] Figure 5 This is a SEM image of the LML positive electrode sheet in Application Example 2 of the present invention;

[0026] Figure 6 A comparison chart of the first cycle charge and discharge curves of the all-solid-state lithium battery in Application Example 2 of the present invention and Comparative Application Example 2;

[0027] Figure 7 This is a comparison chart of the rate performance of the all-solid-state lithium battery in Application Example 2 of the present invention and Comparative Application Example 2;

[0028] Figure 8 This is a comparison chart of the long cycle curves of the all-solid-state lithium batteries in Application Example 2 of the present invention and Comparative Application Example 2. DETAILED DESCRIPTION

[0029] The present invention provides a composite cathode material, comprising a cathode active material and a MXene-coated fast ion conductor.

[0030] In the present invention, the positive electrode active material preferably includes LiFePO4, LiNi 0.5 Co 0.3 Mn 0.2 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2 or LiNi 0.8 Co 0.1 Mn 0.1 The present invention limits the type of positive electrode active material to the above range to further improve the conductivity of the composite positive electrode material.

[0031] In the present invention, the fast ion conductor in the MXene-coated fast ion conductor preferably includes Li 6.4 La3Zr 1.4 Ta 0.6 O 12 、Li3PO4、Li 1.4 Al 0.4 Ti 1.6 (PO4)3、LiTi 0.5 Zr 1.5 (PO4)3 or Li2AlZr(PO4)3. In the present invention, the type of fast ion conductor in the MXene-coated fast ion conductor is limited to the above range, so that the composite cathode material can have good ionic conductivity.

[0032] In the present invention, the mass ratio of the fast ion conductor to the cathode active material in the MXene-coated fast ion conductor is preferably (0.01-5):100, more preferably (1-4):100, and even more preferably (2-3):100. By limiting the mass ratio of the fast ion conductor to the cathode active material in the MXene-coated fast ion conductor to the above range, the ionic conductivity of the composite cathode material can be further improved.

[0033] In the present invention, the MXene is specifically Ti3C2T x , where T x The MXene is a functional group such as -F, -O and -OH. In the present invention, MXene can improve the electronic conductivity of the composite cathode material.

[0034] In the present invention, the mass ratio of MXene in the MXene-coated fast ion conductor to the cathode active material is preferably (0.01-5):100, more preferably (1-4):100, and even more preferably (1-2):100. By limiting the mass ratio of MXene in the MXene-coated fast ion conductor to the cathode active material within the above range, the electronic conductivity of the composite cathode material can be further improved.

[0035] In the present invention, the particle size of the MXene-coated fast ion conductor is preferably 0.1 to 10 μm, more preferably 2 to 8 μm, and even more preferably 4 to 6 μm. Limiting the particle size of the MXene-coated fast ion conductor to the above range can further improve the ionic conductivity of the composite cathode material.

[0036] The present invention introduces a fast ion conductor into the positive electrode active material and utilizes the high lithium ion conductivity of the fast ion conductor to construct an efficient and stable ion transport network, thereby improving the ion transport capacity of the positive electrode material. By using MXene with high electronic conductivity to coat the fast ion conductor, the electronic conductivity and discharge specific capacity of the composite positive electrode material are improved. At the same time, the functional atoms or groups such as -F, -O and -OH present in MXene can prevent the corrosion of the electrolyte, play a role in protecting the positive electrode active material, and significantly improve the long-term cycle stability of the positive electrode material.

[0037] The present invention also provides a method for preparing the composite positive electrode material described in the above technical solution, comprising the following steps:

[0038] (1) mixing a fast ion conductor and MXene with an organic solvent to obtain a fast ion conductor dispersion and a MXene dispersion;

[0039] (2) mixing the fast ion conductor dispersion obtained in step (1) with the MXene dispersion to obtain a mixed solution;

[0040] (3) Mixing the positive electrode active material with the mixed solution obtained in step (2) and drying the mixture to obtain a composite positive electrode material.

[0041] The present invention mixes the fast ion conductor and MXene with an organic solvent to obtain a fast ion conductor dispersion and a MXene dispersion.

[0042] In the present invention, the mass concentration of the fast ion conductor dispersion is preferably 1 to 100 mg / mL, more preferably 5 to 50 mg / mL, and further preferably 5 to 10 mg / mL. In the present invention, the mass concentration of the MXene dispersion is preferably 1 to 100 mg / mL, more preferably 2 to 50 mg / mL, and further preferably 2 to 5 mg / mL. The present invention limits the mass concentrations of the fast ion conductor dispersion and the MXene dispersion to the above range, which can make the fast ion conductor and MXene more uniformly dispersed in the solvent and is conducive to the subsequent preparation of the composite positive electrode material.

[0043] In the present invention, the preparation method of the MXene preferably comprises the following steps:

[0044] (a) mixing LiF and concentrated hydrochloric acid to obtain a mixed solution 1;

[0045] (b) mixing Ti3AlC2 with the mixed solution 1 obtained in step (a) to perform an etching reaction to obtain a mixed solution 2;

[0046] (c) centrifuging, acid-washing, and water-washing the mixed solution 2 obtained in step (b) to obtain a precipitate;

[0047] (d) mixing the precipitate obtained in step (c) with water and sequentially performing sonication, centrifugation, and drying to obtain MXene.

[0048] In the present invention, LiF and concentrated hydrochloric acid are preferably mixed to obtain a mixed solution 1.

[0049] In the present invention, the ratio of the mass of LiF to the volume of concentrated hydrochloric acid is preferably (1-1.6) g: (10-20) mL; and the molar concentration of the concentrated hydrochloric acid is preferably 8-9 mol / L. Limiting the ratio of the mass of LiF to the volume of concentrated hydrochloric acid and the concentration of the concentrated hydrochloric acid to the above ranges ensures sufficient progress of subsequent reactions.

[0050] In the present invention, the mixing of LiF and concentrated hydrochloric acid is preferably performed in a polytetrafluoroethylene reactor; the mixing temperature is preferably room temperature; the mixing is preferably performed under stirring conditions; the stirring speed is preferably 450-500 rpm; and the stirring time is preferably 15-30 minutes. Limiting the mixing parameters to the above ranges can achieve more uniform mixing of the materials.

[0051] After obtaining the mixed solution 1, the present invention preferably mixes Ti3AlC2 with the mixed solution 1 to perform an etching reaction to obtain a mixed solution 2.

[0052] In the present invention, the ratio of the mass of Ti3AlC2 to the volume of the mixed solution 1 is preferably (1-2) g: (10-20) mL. Limiting the ratio of the mass of Ti3AlC2 to the volume of the mixed solution 1 to the above range can ensure the production of MXene with excellent performance.

[0053] In the present invention, the mixing temperature of the Ti3AlC2 and the mixed solution 1 is preferably 40-50°C; the mixing of the Ti3AlC2 and the mixed solution 1 is preferably carried out under stirring; the stirring speed is preferably 450-500 rpm; and the stirring time is preferably 24-48 hours. Setting the mixing parameters within the above ranges can produce MXene with excellent performance.

[0054] After obtaining the mixed solution 2, the present invention preferably centrifuges, acid-washes and water-washes the mixed solution 2 in sequence to obtain a precipitate.

[0055] In the present invention, the centrifugation is preferably performed in a centrifuge, and the rotation speed of the centrifugation is preferably 3500 to 5000 rpm. The present invention achieves solid-liquid separation of the mixed solution 2 by centrifugation.

[0056] In the present invention, the acid used in the pickling process is preferably hydrochloric acid; the concentration of the hydrochloric acid is preferably 0.5 to 1 mol / L; the number of pickling cycles is preferably 3 to 5; each pickling cycle is preferably followed by centrifugation; the centrifugation speed is preferably 3500 to 5000 rpm; and the centrifugation time is preferably 5 to 10 minutes. In the present invention, the water used in the water washing process is preferably deionized water; the number of water washing cycles is preferably 5 to 10; each water washing cycle is preferably followed by centrifugation; the centrifugation speed is preferably 3500 to 5000 rpm; and the centrifugation time is preferably 5 to 10 minutes. The present invention can remove impurities and acid from the precipitate through pickling and water washing.

[0057] After obtaining the precipitate, the present invention preferably mixes the precipitate with water and then sequentially performs sonication, centrifugation, and drying to obtain MXene.

[0058] In the present invention, the ultrasonic treatment is preferably performed in an ice-water bath; the ultrasonic treatment time is preferably 1 to 1.5 hours. The present invention can exfoliate the precipitate by ultrasonic treatment to obtain a single layer or a few layers of MXene.

[0059] In the present invention, the centrifugal speed is preferably 3500-5000 rpm, and the centrifugal time is preferably 1-1.5 hours. The present invention can fully remove the precipitate through centrifugation to obtain a monolayer / few-layer MXene dispersion.

[0060] In the present invention, the drying is preferably freeze drying. The present invention has no particular limitation on the temperature and time of the freeze drying, and parameters well known to those skilled in the art can be used to select them.

[0061] The MXene prepared by the above method in the present invention has a single-layer / few-layer structure, which can better improve the electronic conductivity of the composite positive electrode material.

[0062] In the present invention, the organic solvent preferably includes anhydrous ethanol, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide. Limiting the type of organic solvent to the above range ensures that the organic solvent can be completely evaporated at a lower temperature during the drying process of preparing the composite cathode material, thereby avoiding decomposition of MXene.

[0063] In the present invention, the fast ion conductor and MXene are preferably mixed with the organic solvent separately by ultrasonic mixing; the ultrasonic mixing time is preferably 5 to 10 minutes; and the ultrasonic mixing is preferably performed in an ice-water bath. The ultrasonic frequency is not particularly limited in the present invention; any ultrasonic frequency commonly used by those skilled in the art can be used. The present invention can obtain a fast ion conductor dispersion and a MXene dispersion through ultrasonic mixing.

[0064] After obtaining the fast ion conductor dispersion and the MXene dispersion, the present invention mixes the fast ion conductor dispersion and the MXene dispersion to obtain a mixed solution.

[0065] In the present invention, the mixing of the fast ion conductor dispersion and the MXene dispersion is preferably performed by ultrasonic mixing; the ultrasonic mixing time is preferably 30 to 60 minutes; and the ultrasonic mixing is preferably performed in an ice-water bath. The present invention does not particularly limit the ultrasonic frequency; any ultrasonic frequency commonly used by those skilled in the art can be used.

[0066] The present invention preferably performs manual shaking every 5-10 minutes during the ultrasonication process. Manual shaking can prevent some solids from settling to the bottom, resulting in a more evenly dispersed mixture. The secondary mixing can produce a more uniform mixture and allow the MXene to encapsulate the fast ion conductor.

[0067] After obtaining the mixed solution, the present invention mixes the positive electrode active material with the mixed solution and then dries the mixture to obtain a composite positive electrode material.

[0068] In the present invention, the mixing of the positive electrode active material and the mixed solution is preferably performed by stirring; the stirring time is preferably 1 to 5 hours. The present invention does not particularly limit the stirring operation or the stirring speed; stirring can be performed using an operation and speed well known to those skilled in the art. Stirring can achieve uniform mixing of the positive electrode active material and the mixed solution.

[0069] In the present invention, the drying is preferably performed under vacuum; the drying temperature is preferably 30 to 120°C, more preferably 40 to 100°C, and even more preferably 50°C. The present invention does not particularly limit the vacuum drying equipment and vacuum level; commonly used equipment and vacuum levels by those skilled in the art can be used. Drying can remove the organic solvent to obtain a composite positive electrode material.

[0070] The present invention prepares a fast ion conductor dispersion and a MXene dispersion separately, and then mixes the fast ion conductor dispersion and the MXene dispersion to uniformly coat the fast ion conductor with MXene, thereby further improving the electrical conductivity of the composite positive electrode material, thereby improving the discharge capacity and cycle stability of the all-solid-state lithium battery prepared from the composite positive electrode material.

[0071] The present invention also provides an all-solid-state lithium battery, wherein the positive electrode material in the all-solid-state lithium battery is the composite positive electrode material described in the above technical solution or the composite positive electrode material prepared by the preparation method described in the above technical solution.

[0072] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0073] Example 1

[0074] A composite positive electrode material composed of LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622) and MXene-coated Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO) composition; the Li 6.4 La3Zr 1.4 Ta0.6 O 12 and LiNi 0.6 Co 0.2 Mn 0.2 The mass ratio of O2 is 2:100; the MXene-coated Li 6.4 La3Zr 1.4 Ta 0.6 O 12 MXene and LiNi in 0.6 Co 0.2 Mn 0.2 The mass ratio of O2 is 1:100; the Li 6.4 La3Zr 1.4 Ta 0.6 O 12 The particle size of (LLZTO) is 5 μm;

[0075] The preparation method of the MXene comprises the following steps:

[0076] (a) LiF and concentrated hydrochloric acid were mixed in a polytetrafluoroethylene reactor at room temperature at 500 rpm for 20 min to obtain a mixed solution 1; the mass ratio of the LiF to the volume of the concentrated hydrochloric acid was 1.6 g:20 mL; and the molar concentration of the concentrated hydrochloric acid was 9 mol / L;

[0077] (b) Ti3AlC2 and the mixed solution 1 obtained in step (a) were mixed at a speed of 500 rpm and 50°C for 48 hours to perform an etching reaction to obtain a mixed solution 2; the mass ratio of the Ti3AlC2 to the volume of the mixed solution 1 was 1 g:20 mL;

[0078] (c) the mixed solution 2 obtained in step (b) was centrifuged at 3500 rpm to separate the solid, and the solid was pickled three times with 1 mol / L dilute hydrochloric acid, centrifuged at 3500 rpm for 5 min after each pickling, and then washed five times with deionized water, centrifuged at 3500 rpm for 5 min after each washing, to obtain a precipitate;

[0079] (d) mixing the precipitate obtained in step (c) with water, ultrasonicating the mixture in an ice-water bath for 1 hour, and then centrifuging the mixture at 3500 rpm for 1 hour to obtain a MXene dispersion, and freeze-drying the MXene dispersion to obtain MXene;

[0080] The preparation method of the composite positive electrode material comprises the following steps:

[0081] (1) Li 6.4 La3Zr 1.4 Ta 0.6 O12 (LLZTO) and MXene were mixed with anhydrous ethanol in an ice-water bath for 10 min by ultrasonication to obtain Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO) dispersion and MXene dispersion; the Li 6.4 La3Zr 1.4 Ta 0.6 O 12 The mass concentration of the (LLZTO) dispersion is 6.67 mg / mL; the mass concentration of the MXene dispersion is 3.33 mg / mL;

[0082] (2) Li obtained in step (1) 6.4 La3Zr 1.4 Ta 0.6 O 12 The (LLZTO) dispersion and the MXene dispersion were ultrasonically mixed in an ice-water bath for 30 min and manually shaken every 5 min to obtain a mixed solution;

[0083] (3) LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622) and the mixed solution obtained in step (2) were stirred for 3 hours and then dried in a vacuum oven at 50°C to obtain a composite positive electrode material, which was recorded as LMN.

[0084] Example 2

[0085] The only difference between Example 2 and Example 1 is that the positive electrode active material is LiFePO4 (LFP). Other steps are the same as Example 1, and a composite positive electrode material is obtained, which is recorded as LML.

[0086] Example 3

[0087] The only difference between Example 3 and Example 1 is that the positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), other parameters are the same as those in Example 1.

[0088] Example 4

[0089] The only difference between Example 4 and Example 1 is that the fast ion conductor in the MXene-coated fast ion conductor is Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP), and the rest are the same as in Example 1.

[0090] Example 5

[0091] The only difference between Example 5 and Example 2 is that the fast ion conductor in the MXene-coated fast ion conductor is Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP), and the rest are the same as in Example 2.

[0092] Example 6

[0093] The only difference between Example 6 and Example 3 is that the fast ion conductor in the MXene-coated fast ion conductor is Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP), and the rest are the same as in Example 3.

[0094] Example 7

[0095] The only difference between Example 7 and Example 1 is that the fast ion conductor in the MXene-coated fast ion conductor is Li2AlZr(PO4)3(LAZP), and the rest is the same as Example 1.

[0096] Example 8

[0097] The only difference between Example 8 and Example 2 is that the fast ion conductor in the MXene-coated fast ion conductor is Li2AlZr(PO4)3(LAZP), and the rest is the same as Example 2.

[0098] Example 9

[0099] The only difference between Example 9 and Example 3 is that the fast ion conductor in the MXene-coated fast ion conductor is Li2AlZr(PO4)3(LAZP), and the rest is the same as Example 3.

[0100] Example 10

[0101] The difference between Example 10 and Example 1 is that the anhydrous ethanol in step (1) is replaced by N-methylpyrrolidone; and the drying temperature in step (3) is 120°C.

[0102] Example 11

[0103] The difference between Example 11 and Example 1 is that the anhydrous ethanol in step (1) is replaced by N,N-dimethylformamide; and the drying temperature in step (3) is 70°C.

[0104] Example 12

[0105] The difference between Example 12 and Example 1 is that the anhydrous ethanol in step (1) is replaced by N,N-dimethylacetamide; and the drying temperature in step (3) is 70°C.

[0106] Application Examples 1-12

[0107] An all-solid-state lithium battery:

[0108] The composite positive electrode materials in Examples 1 to 12 were respectively mixed with SuperP and PVDF (polyvinylidene fluoride) in a mass ratio of 8:1:1 in NMP (N-methylpyrrolidone) and stirred for 12 hours to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on an aluminum foil with a scraper and placed in a vacuum oven at 120°C for 12 hours until the solvent was evaporated. The LMN positive electrode sheet with a diameter of 13 mm was cut with a cutter;

[0109] The 2025-type button-type all-solid-state lithium battery was assembled in an argon atmosphere glove box. The positive electrode of the all-solid-state lithium battery was an LMN positive electrode sheet, the electrolyte was a PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) electrolyte, and the negative electrode was a lithium sheet.

[0110] Comparative Application Example 1

[0111] The difference between the comparative application example 1 and the application example 1 is that the positive electrode material in the positive electrode sheet is LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), other parameters are the same as those in Application Example 1.

[0112] Comparative Application Example 2

[0113] The difference between comparative application example 2 and application example 2 is that the positive electrode material in the positive electrode sheet is LiFePO4 (LFP), and the rest is the same as application example 2.

[0114] The ionic conductivity and electronic conductivity of the composite cathode material were tested using an electrochemical workstation;

[0115] The micromorphology of the composite cathode sheet was observed using a scanning electron microscope (SEM, SU8000), and the operating voltage of the scanning electron microscope was 3KV;

[0116] The charge and discharge process, long cycle performance, and rate performance of the 2025 button battery were tested using the NEWARE test system. The charge and discharge voltage window was set to 2.8-4.3V, the current density for the long cycle test was set to 0.1C, and the current density for the rate performance test was set to 0.1C, 0.2C, 0.3C, 0.5C, 1C, and 2C, respectively. All tests were performed at room temperature of 25°C.

[0117] The electrochemical impedance spectroscopy (EIS) test frequency range of 2025 button battery is 0.01~100kHz, and the perturbation amplitude is 10mV.

[0118] The SEM of the LMN positive electrode sheet in Application Example 1 is as follows: Figure 1 As shown, from Figure 1 It can be seen that the MXene-coated LLZTO is evenly distributed in the positive electrode, which successfully fills the gaps between the positive electrode particles.

[0119] The comparison of the first cycle charge and discharge curves of the lithium battery in Application Example 1 and Comparative Application Example 1 is shown in the figure below. Figure 2 As shown, from Figure 2 It can be seen that the first cycle discharge capacity of the lithium battery prepared by LMN positive electrode is 166.4mAh / g, while LiNi 0.6 Co 0.2 Mn 0.2 The first-cycle discharge capacity of the lithium battery prepared with O2 (NCM622) positive electrode sheet is 151.9 mAh / g.

[0120] The comparison of the rate performance of lithium batteries in Application Example 1 and Comparative Application Example 1 is shown in the figure below: Figure 3 As shown, from Figure 3 It can be seen that compared with LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LMN can still maintain good capacity at high rates.

[0121] The comparison of the long cycle curves of lithium batteries in Application Example 1 and Comparative Application Example 1 is shown in the figure below. Figure 4 As shown, from Figure 4 As can be seen, the loading of both is 8.5 mg / cm 2 , LMN can still maintain good capacity after 30 cycles at 0.1C, while LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622) has decayed to 90% of its original value after 30 cycles at 0.1C.

[0122] The SEM of the LML positive electrode sheet in Application Example 2 is as follows: Figure 5 As shown, from Figure 5 It can be seen that the MXene-coated LLZTO is evenly distributed in the positive electrode, which successfully fills the gaps between the positive electrode particles.

[0123] The comparison of the first cycle charge and discharge curves of the lithium battery in Application Example 2 and Comparative Application Example 2 is shown in the figure below. Figure 6 As shown, from Figure 6 It can be seen that the first-cycle discharge capacity of the lithium battery prepared with the LML positive electrode sheet is 156.6 mAh / g, while the first-cycle discharge capacity of the lithium battery prepared with the LiFePO4 (LFP) positive electrode sheet is 134.9 mAh / g.

[0124] The comparison of the rate performance of lithium batteries in Application Example 2 and Comparative Application Example 2 is shown in the figure below: Figure 7 As shown, from Figure 7 It can be seen that compared with LiFePO4 (LFP), LML has a higher capacity at different rates.

[0125] The long cycle curve comparison of lithium batteries in Application Example 2 and Comparative Application Example 2 is shown in the figure below. Figure 8 As shown, from Figure 8 As can be seen, the loading of both is 10 mg / cm 2 , LML has a capacity retention rate of 96% after 150 cycles at 0.5C, while the capacity retention rate of LiFePO4 (LFP) is only 88%.

[0126] The ionic conductivity and electronic conductivity data of the composite positive electrode materials of Examples 1 to 12 are shown in Table 1.

[0127] Table 1 Ionic conductivity and electronic conductivity data of the composite positive electrode materials of Examples 1 to 12

[0128]

[0129]

[0130] The first-cycle discharge specific capacity and capacity retention rate data after 50 cycles at 0.1C of the all-solid-state lithium batteries in Application Examples 3 to 12 are shown in Table 2.

[0131] Table 2 First cycle discharge capacity and capacity retention rate after 50 cycles at 0.1C for all-solid-state lithium batteries in application examples 3 to 12

[0132] Application Examples First cycle discharge capacity (mAh / g) Capacity retention rate (%) Application Example 3 203.15 98.12 Application Example 4 161.31 99.50 Application Example 5 153.28 99.75 Application Example 6 211.22 99.31 Application Example 7 165.80 98.88 Application Example 8 150.87 99.18 Application Example 9 207.32 98.56 Application Example 10 164.90 99.34 Application Example 11 167.52 98.96 Application Example 12 163.22 98.55

[0133] The ionic conductivity of the composite cathode material provided by the present invention can reach 7.555×10 -3 S / cm, and the electronic conductivity can reach 4.761×10 -5 S / cm, with high ionic conductivity and high electronic conductivity; the all-solid-state lithium battery prepared with the composite positive electrode material has a first-cycle discharge capacity of up to 211.22 mAh / g, and a capacity retention rate of over 96% after 150 cycles at 0.5C, showing high discharge capacity and high cycle stability.

[0134] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A composite cathode material comprising a cathode active material and a MXene-coated fast ion conductor; The mass ratio of the fast ion conductor to the positive electrode active material in the MXene-coated fast ion conductor is (2-5):100; The mass ratio of MXene to the positive electrode active material in the MXene-coated fast ion conductor is (0.01-1):100; The fast ion conductor in the MXene-coated fast ion conductor includes Li 6.4 LqCy 1.4 Ta 0.6 O 12 , Li 1.4 Al 0.4 Ti 1.6 (PO4)3、LiTi 0.5 Zr 1.5 (PO4)3 or Li2AlZr(PO4)3.

2. The composite positive electrode material according to claim 1, characterized in that The particle size of the fast ion conductor in the MXene-coated fast ion conductor is 0.1 to 10 μm.

3. The composite positive electrode material according to claim 1, characterized in that: The positive electrode active material includes LiFePO4, LiNi 0.5 Co 0.3 Mn 0.2 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2 or LiNi 0.8 Co 0.1 Mn 0.1 O2.

4. The method for preparing the composite positive electrode material according to any one of claims 1 to 3, comprising the following steps: (1) mixing a fast ion conductor and MXene with an organic solvent respectively to obtain a fast ion conductor dispersion and a MXene dispersion; (2) mixing the fast ion conductor dispersion obtained in step (1) with the MXene dispersion to obtain a mixed solution; (3) Mixing the positive electrode active material with the mixed solution obtained in step (2) and drying the mixture to obtain a composite positive electrode material.

5. The preparation method according to claim 4, characterized in that: The mass concentrations of the fast ion conductor dispersion and the MXene dispersion in step (1) are independently 1 to 100 mg / mL.

6. The preparation method according to claim 4, characterized in that: The organic solvent in step (1) includes anhydrous ethanol, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

7. An all-solid-state lithium battery, characterized in that: The positive electrode material in the all-solid-state lithium battery is the composite positive electrode material according to any one of claims 1 to 3 or the composite positive electrode material prepared by the preparation method according to any one of claims 4 to 6.

Images