Half-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material, preparation method thereof and application thereof in solid-state battery

Abstract

The application discloses a kind of semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode materials and preparation method and application thereof, the material includes high-voltage positive electrode material, and its surface is coated with semi-cyclic polyacrylonitrile gel layer.Preparation method includes polyacrylonitrile, lithium salt and ion liquid are dispersed in solvent, high-voltage positive electrode material is added, stirring, sintering, to obtain above-mentioned material.Semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material in the application, with semi-cyclic polyacrylonitrile gel layer as coating layer, can optimize contact impedance and charge transfer resistance, while it can improve the kinetics transmission in composite positive electrode and can realize in-situ construction stable internal interface layer in electrochemical process, inhibit the occurrence of side reaction and improve the stability of positive electrode structure and the cycle stability of battery, so it can be widely used to construct solid-state battery, and its preparation method also has the advantages of simple process, process controllable, continuous production etc., suitable for large-scale preparation, convenient for industrial application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials and its preparation, and relates to a semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material, a preparation method thereof and application thereof in solid-state batteries. BACKGROUND

[0002] In the development of batteries with high energy density and high safety, lithium ion batteries gradually begin to develop from liquid to solid. The solid-state electrolyte system has high electrochemical stability and thermal stability, and can be used with high-nickel, lithium-rich positive electrode materials and metal lithium negative electrodes to improve the energy density of the battery. Among them, the application of nickel-cobalt-manganese ternary positive electrode material with high specific energy and high voltage in solid-state batteries plays a key role. However, the positive electrode side interface problem is a key problem hindering the practical development of ternary solid-state lithium batteries. A common modification method for the positive electrode side interface is to coat the surface of the positive electrode particles, which can alleviate the volume change of the positive electrode material and the contact resistance problem to some extent. However, most coating layers are inert and insulating to electrons and ions, and can be considered as a good physical barrier layer, so they are not effective in solving the physical contact between particles and improving the stability of the battery. And some nano-coatings are difficult to achieve uniform and continuous coating, which affects the capacity of the active material and the stability of the cycle. Therefore, how to design a continuous and uniform coating layer on the surface of the high-voltage positive electrode material, which can conduct electrons and ions at the same time, can effectively solve the above-mentioned problems, and finally endow the solid-state battery with excellent electrochemical stability. SUMMARY

[0003] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material with excellent performance, a preparation method thereof and application thereof in solid-state batteries.

[0004] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0005] The application discloses a semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material, which comprises a high-voltage positive electrode material, and a semi-cyclic polyacrylonitrile gel layer coated on the surface of the high-voltage positive electrode material; and the semi-cyclic polyacrylonitrile gel layer further contains an ionic liquid and a lithium salt.

[0006] The semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material is further improved, and the mass content of the semi-cyclic polyacrylonitrile gel layer in the semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material is 1% to 3%.

[0007] The semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material is further improved, and the mass content of the semi-cyclized polyacrylonitrile gel layer in the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material is 1.5% to 2.5%; and the high-voltage positive electrode material is at least one of a nickel-cobalt-manganese ternary positive electrode material, a lithium cobaltate ternary positive electrode material, and a lithium nickel-manganese oxide ternary positive electrode material.

[0008] As a general technical concept, the application also provides a preparation method of a semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material, comprising the following steps:

[0009] S1, dispersing polyacrylonitrile, lithium salt, and ionic liquid in a solvent, stirring to obtain a polymer solution;

[0010] S2, adding a high-voltage positive electrode material to the polymer solution, stirring until the solvent is completely volatilized, drying to obtain a polymer coated high-voltage positive electrode material;

[0011] S3, sintering the polymer coated high-voltage positive electrode material to obtain a semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material.

[0012] The preparation method is further improved, and the mass ratio of the polyacrylonitrile, lithium salt, and ionic liquid is 1:1:1.4; the mass ratio of the polyacrylonitrile to the high-voltage positive electrode material is 0.003 to 0.01:1; and the mass ratio of the solvent to the high-voltage positive electrode material is 4:3.

[0013] The preparation method is further improved, and the lithium salt is lithium difluoro(oxalato)borate, or a complex lithium salt of lithium difluoro(oxalato)borate and lithium bistrifluoromethanesulfonylimide, or a complex lithium salt of lithium difluoro(oxalato)borate and lithium bis(oxalato)borate.

[0014] The preparation method is further improved, and the ionic liquid is one or more of a piperidine ionic liquid, a quaternary ammonium ionic liquid, an imidazole ionic liquid, and a pyrrole ionic liquid.

[0015] The preparation method is further improved, and the solvent is N,N-dimethylformamide.

[0016] The preparation method is further improved, and the high-voltage positive electrode material is at least one of a nickel-cobalt-manganese ternary positive electrode material, a lithium cobaltate ternary positive electrode material, and a lithium nickel-manganese oxide ternary positive electrode material.

[0017] The preparation method is further improved, and the piperidine ionic liquid is N-methyl-N-propyl piperidine di(trifluoromethylsulfonyl) imide; the quaternary ammonium ionic liquid is N-methyl-N,N-diethyl-N-(2-methoxyethyl) ammonium di(trifluoromethylsulfonyl) imide; the imidazole ionic liquid is di(trifluoromethylsulfonyl) 1-ethyl-3-methyl imidazole; and the pyrrole ionic liquid is N-methyl-N-propyl pyrrole di(trifluoromethylsulfonyl) imide.

[0018] The preparation method is further improved, and in S1, the stirring is performed for 0.5h to 3h.

[0019] The preparation method is further improved, and in S2, the stirring is performed at 50℃ to 80℃, the stirring is performed for 5h to 10h, the drying is performed at 100℃ to 110℃, and the drying is performed for 12h to 24h.

[0020] The preparation method is further improved, and in S3, the heating rate in the sintering process is 5℃ / min, the sintering temperature is 210℃ to 290℃, and the sintering time is 0.5h. Further preferably, the sintering temperature is 240℃ to 280℃.

[0021] The preparation method is further improved, and the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material comprises a high-voltage positive electrode material, and a semi-cyclized polyacrylonitrile gel layer is coated on the surface of the high-voltage positive electrode material; the semi-cyclized polyacrylonitrile gel layer further contains an ionic liquid and a lithium salt; and the mass content of the semi-cyclized polyacrylonitrile gel layer in the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material is 1.5% to 2.5%.

[0022] As a general technical concept, the application also provides a semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material or a semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material prepared by the preparation method in the application, and application of the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material in a solid-state battery.

[0023] The application is further improved, and the solid-state battery is a lithium battery.

[0024] In the application, the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material is used to construct a solid-state battery (lithium battery), a semi-cyclized polyacrylonitrile gel layer is coated on a nickel-cobalt-manganese ternary positive electrode material as a positive electrode, lithium metal is used as a negative electrode, and the solid-state battery (lithium battery) is assembled by a composite electrolyte membrane.

[0025] Compared with the prior art, the application has the following advantages:

[0026] (1) In order to solve the problem that the prior art cannot effectively build a continuous and uniform coating of electron and ion double conductors on the surface of high-voltage positive electrode material, the application creatively proposes a semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material. The semi-cyclic polyacrylonitrile gel layer can be used as a coating layer, and the coordination between the high-polarity group-C≡N functional groups contained in the coating layer and transition metal ions can ensure the close contact between the coating layer and the high-voltage positive electrode material, realize continuous and uniform coating, and optimize the contact impedance between high-voltage positive electrode material active particles and the charge transfer resistance between the electrode and the electrolyte. In addition, the semi-cyclic polyacrylonitrile gel layer has ion and electron double transmission functions, which can effectively improve the kinetic transmission in the composite positive electrode, and based on the in-situ construction of stable internal interface layer (CEI) by lithium salt in the coating layer during the electrochemical process, further inhibit the occurrence of side reactions between the high-voltage positive electrode material and the electrolyte, and ultimately improve the stability of the positive electrode structure and the cycle stability of the battery.

[0027] (2) In the semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material of the application, the mass content of the semi-cyclic polyacrylonitrile gel layer is optimized to be 1% to 3%, and especially when the mass content is 1.5% to 2.5%, it is more conducive to effectively building an ion and electron double transmission layer. This is because: when the mass content of the semi-cyclic polyacrylonitrile gel layer is too low, it is difficult to achieve continuous and effective coating of the high-voltage positive electrode material; and when the mass content is too high, too much semi-cyclic polyacrylonitrile gel will weaken the ion and electron transmission effect of the coating layer, reduce the positive electrode material loading in the solid composite positive electrode, and is not conducive to improving the overall energy density of the solid-state battery.

[0028] (3) The preparation method of the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material of the present application first disperses polyacrylonitrile, lithium salt and ionic liquid in a solvent, stirs, thereby obtaining a polyacrylonitrile solution containing lithium salt and ionic liquid, which is conducive to the uniform coating of polyacrylonitrile, lithium salt and ionic liquid on the surface of the high-voltage positive electrode material, then adds the high-voltage positive electrode material to the polyacrylonitrile solution, at this time, the polyacrylonitrile, lithium salt and ionic liquid are uniformly coated on the surface of the high-voltage positive electrode material, after the solvent is completely volatilized and dried, a high-voltage positive electrode material uniformly coated with polyacrylonitrile, lithium salt and ionic liquid is formed, and finally, the high-voltage positive electrode material uniformly coated with polyacrylonitrile, lithium salt and ionic liquid is sintered, so that the polyacrylonitrile undergoes a cyclization reaction and is converted into semi-cyclized polyacrylonitrile gel, thereby forming a continuous and uniform coating layer on the surface of the high-voltage positive electrode material, which can simultaneously conduct electrons and ions. In particular, if polyacrylonitrile, lithium salt, ionic liquid and high-voltage positive electrode material are directly dispersed in a solvent, the incomplete dissolution of polyacrylonitrile in the solvent will make it difficult for polyacrylonitrile to effectively coat the surface of the high-voltage positive electrode material, and there will still be defects such as poor uniformity and discontinuity of the coating. In addition, the preparation method of the present application also has the advantages of simple process, controllable process, continuous production and the like, and is suitable for large-scale preparation and easy for industrial application.

[0029] (4) The preparation method of the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material of the present application also optimizes the sintering temperature to be 210-290°C, and in particular, when the sintering temperature is 240-280°C, the coating layer can be given the optimal electron and ion dual conduction characteristics, thereby being more conducive to obtaining a positive electrode material with excellent performance. This is because: when the temperature is too low, the semi-cyclization effect is poor, at this time, the coating layer only has high ion transmission but poor electron conductivity due to the large proportion of non-cyclized polyacrylonitrile; and when the temperature is too high, the polyacrylonitrile is completely cyclized, at this time, the coating layer only has electron conductivity. In addition, in the present application, using N,N-dimethylformamide as the solvent is more conducive to dissolving polyacrylonitrile, thereby being more conducive to forming a uniform and continuous coating layer on the surface of the high-voltage positive electrode material.

[0030] (5) The application of the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material in solid-state batteries, based on the ion and electron dual transmission of the coating layer, as well as the optimization and improvement of the solid-state composite positive electrode side interface, can make the solid-state battery exhibit more excellent cycle stability and rate performance. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application.

[0032] Figure 11 is the appearance of PAN samples after heat treatment at different temperatures in Example 1 of the present invention.

[0033] Figure 2 1 is the XRD spectrum of the PAN sample after heat treatment at different temperatures in Example 1 of the present invention.

[0034] Figure 3 FTIR images of PAN samples after heat treatment at different temperatures in Example 1 of the present invention.

[0035] Figure 4 These are Raman spectra of PAN samples after heat treatment at different temperatures in Example 1 of the present invention.

[0036] Figure 5 These are the SEM and TEM images of the semi-cyclized polyacrylonitrile gel-coated nickel-cobalt-manganese ternary positive electrode material (NCM@PAN260-2%) and the nickel-cobalt-manganese ternary positive electrode material (NCM) in Example 3 of the present invention.

[0037] Figure 6 This is the EDS graph of the semi-cyclized polyacrylonitrile gel-coated nickel-cobalt-manganese ternary positive electrode material (NCM@PAN260-2%) prepared in Example 3 of the present invention.

[0038] Figure 7 XRD patterns of the semi-cyclized polyacrylonitrile gel-coated nickel-cobalt-manganese ternary positive electrode materials (NCM@PAN260-1%, NCM@PAN260-2%, NCM@PAN260-3%) prepared in Examples 2-4 of the present invention, the semi-cyclized polyacrylonitrile polymer layer-coated nickel-cobalt-manganese ternary positive electrode material (NCM@PAN260) prepared in Comparative Example 1, the polyacrylonitrile polymer layer-coated nickel-cobalt-manganese ternary positive electrode material (NCM@PAN) prepared in Comparative Example 2, and the nickel-cobalt-manganese ternary positive electrode material (NCM).

[0039] Figure 8 This is a graph showing the change in interfacial impedance over time of a solid-state battery assembled from a semi-cyclized polyacrylonitrile gel-coated nickel-cobalt-manganese ternary positive electrode material (NCM@PAN260-2%) and an uncoated nickel-cobalt-manganese ternary positive electrode material (NCM) in Example 5 of the present invention.

[0040] Figure 9 This is a comparison chart of constant current charge and discharge tests at different rates for the NCM / lithium solid-state battery assembled with semi-cyclized polyacrylonitrile gel-coated nickel-cobalt-manganese ternary positive electrode materials (NCM@PAN260-1%, NCM@PAN260-2%, NCM@PAN260-3%) in Example 5 of the present invention. DETAILED DESCRIPTION

[0041] The application will be further described in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the application is not limited thereby.

[0042] In the following examples, the materials and instruments used are commercially available unless otherwise specified. The processes used are conventional processes, the equipment used is conventional equipment, and the data obtained are the average values of three or more repeated experiments.

[0043] Example 1

[0044] Investigation of the effect of different sintering temperatures on the cyclization of polyacrylonitrile

[0045] The preparation method of the semi-cyclized polyacrylonitrile of the present embodiment comprises the following steps: taking an appropriate amount (≥1 g) of polyacrylonitrile (PAN) sample, and calcining in a muffle furnace at 210℃, 220℃, 230℃, 260℃, 290℃ for 0.5 h, respectively. The muffle furnace parameters are set as follows: heating from room temperature to the target temperature at a rate of 5℃ / min, and maintaining the temperature for 0.5 h.

[0046] In the present embodiment, the products obtained by sintering at 210℃, 220℃, 230℃, 260℃, 290℃ are named as PAN210, PAN220, PAN230, PAN260, and PAN290, respectively.

[0047] Example 2

[0048] A semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material comprises a high-voltage positive electrode material, wherein the surface of the high-voltage positive electrode material is coated with a semi-cyclized polyacrylonitrile gel layer, and the semi-cyclized polyacrylonitrile gel layer further contains an ionic liquid and a lithium salt.

[0049] In the present embodiment, the mass content of the semi-cyclized polyacrylonitrile gel layer in the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material is 1%.

[0050] In the present embodiment, the high-voltage positive electrode material is a nickel-cobalt-manganese ternary positive electrode material.

[0051] A preparation method of the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material in the present embodiment, comprises the following steps: mixing LiNi 0.8 Co 0.1 Mn 0.1 O2 positive electrode active particles, polyacrylonitrile (PAN), lithium difluoro(oxalato)borate (LiDFOB), and N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide salt (PYR 14 TFSI) to obtain a mixture, and then mixing the mixture with a solvent to obtain a semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material.

[0052] S1, disperse polyacrylonitrile, lithium salt and ionic liquid in DMF solvent, stir uniformly to obtain a polymer solution, specifically:

[0053] Take 0.0178g polyacrylonitrile (PAN), 0.0178g lithium difluorooxalate borate (LiDFOB) and 0.025g N-methyl-N-butyl pyrrolidine (bis (trifluoromethylsulfonyl) imide salt (PYR 14 TFSI) is dispersed in 8g N, N-dimethylformamide (DMF), stirred at 30℃ for 0.5h to obtain a clear polymer solution.

[0054] S2, take NCM active particles as the core, add NCM active particles to the polymer solution, stir thoroughly until the solvent is completely volatilized and dried, and ensure that the surface of the NCM is uniformly coated, specifically:

[0055] Take 6g NCM active positive electrode material (LiNi 0.8 Co 0.1 Mn 0.1 O2 positive electrode active particles) is added to the polymer solution in step S1 and ultrasonically treated for 10min, then magnetically stirred at 50℃ for 4h until the DMF is completely volatilized, so that the surface of the NCM active particles is coated with a uniform polyacrylonitrile gel layer, and then vacuum dried at 100℃ for 24h to obtain a polyacrylonitrile gel layer coated NCM active positive electrode material.

[0056] S3, sinter the coated NCM and grind to obtain a semi-cyclized polyacrylonitrile gel layer coated nickel-cobalt-manganese ternary positive electrode material, specifically:

[0057] The polyacrylonitrile gel layer coated NCM active positive electrode material sample is calcined at a temperature increasing rate of 5℃ / min to 260℃ for 0.5h, and then ground into a fine powder to obtain a semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material (semi-cyclized polyacrylonitrile gel coated nickel-cobalt-manganese ternary positive electrode material), which can be represented as NCM@PAN260-1%.

[0058] Example 3

[0059] A semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material, comprising a high-voltage positive electrode material, wherein the surface of the high-voltage positive electrode material is coated with a semi-cyclized polyacrylonitrile gel layer, and the semi-cyclized polyacrylonitrile gel layer further contains an ionic liquid and a lithium salt.

[0060] In this embodiment, the mass content of the semi-cyclized polyacrylonitrile gel layer in the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material is 2%.

[0061] In this embodiment, the high-voltage positive electrode material is a nickel-cobalt-manganese ternary positive electrode material.

[0062] A preparation method of the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material in the above embodiment, prepared by LiNi 0.8 Co 0.1 Mn 0.1 O2 positive active particles, polyacrylonitrile (PAN), lithium difluoro(oxalato)borate (LiDFOB), and N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR 14 TFSI) is prepared, including the following steps:

[0063] S1, dispersing polyacrylonitrile, lithium salt and ionic liquid in DMF solvent, stirring uniformly to obtain a polymer solution, specifically:

[0064] Take 0.036g polyacrylonitrile (PAN), 0.036g lithium difluoro(oxalato)borate (LiDFOB) and 0.0504g N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR 14 TFSI) and disperse them in 8g N,N-dimethylformamide (DMF), stir at 30℃ for 0.5h to obtain a clear polymer solution.

[0065] S2, taking NCM active particles as the core, adding NCM active particles to the polymer solution, stirring thoroughly until the solvent is completely volatilized and dried, and ensuring that the NCM surface is uniformly coated, specifically:

[0066] Add 6g NCM active positive electrode material to the polymer solution and ultrasonically treat for 10min, then magnetically stir at 50℃ for 4h until the DMF is completely volatilized, so that the NCM active particles are coated with a uniform polyacrylonitrile gel layer, and then vacuum dry at 100℃ for 24h to obtain a polyacrylonitrile gel layer coated NCM active positive electrode material.

[0067] S3, sintering the coated NCM and grinding to obtain a semi-cyclized polyacrylonitrile gel layer coated nickel-cobalt-manganese ternary positive electrode material, specifically:

[0068] Take the polyacrylonitrile gel layer coated NCM active positive electrode material sample, heat to 260℃ at a heating rate of 5℃ / min and calcine for 0.5h, grind into a fine powder after taking out, to obtain a semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material (semi-cyclized polyacrylonitrile gel coated nickel-cobalt-manganese ternary positive electrode material), which can be represented as NCM@PAN260-2%.

[0069] Example 4

[0070] A high-voltage positive electrode material coated with semi-cyclic polyacrylonitrile gel, comprising a high-voltage positive electrode material, wherein the surface of the high-voltage positive electrode material is coated with a semi-cyclic polyacrylonitrile gel layer, and the semi-cyclic polyacrylonitrile gel layer further contains an ionic liquid and a lithium salt.

[0071] In this embodiment, the mass content of the semi-cyclic polyacrylonitrile gel layer in the semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material is 3%.

[0072] In this embodiment, the high-voltage positive electrode material is a nickel-cobalt-manganese ternary positive electrode material.

[0073] A preparation method of the semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material in the above embodiment, prepared from LiNi 0.8 Co 0.1 Mn 0.1 O2 positive electrode active particles, polyacrylonitrile (PAN), lithium difluoro(oxalato)borate (LiDFOB), and N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide salt (PYR 14 TFSI), comprising the following steps:

[0074] S1, dispersing polyacrylonitrile, lithium salt and ionic liquid in DMF solvent, stirring uniformly to obtain a polymer solution, specifically:

[0075] Taking 0.0546g of polyacrylonitrile (PAN), 0.0546g of lithium difluoro(oxalato)borate (LiDFOB) and 0.0764g of N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide salt (PYR 14 TFSI) and dispersing them in 8g of N,N-dimethylformamide (DMF), stirring at 30°C for 0.5h to obtain a clear polymer solution.

[0076] S2, taking NCM active particles as the core, adding NCM active particles to the polymer solution, stirring thoroughly until the solvent is completely volatilized, and then drying to ensure that the surface of NCM is uniformly coated, specifically:

[0077] Adding 6g of NCM active positive electrode material to the polymer solution and ultrasonic treatment for 10min, then magnetic stirring at 50°C for 4h until the DMF is completely volatilized, so that the surface of the NCM active particles is coated with a uniform polyacrylonitrile gel layer, and then vacuum drying at 100°C for 24h to obtain NCM active positive electrode material coated with a polyacrylonitrile gel layer.

[0078] S3, sintering the coated NCM and grinding to obtain a semi-cyclic polyacrylonitrile gel layer coated nickel-cobalt-manganese ternary positive electrode material, specifically:

[0079] S3, the NCM active positive electrode material sample coated with the polyacrylonitrile gel layer is calcined at a temperature increasing rate of 5 ℃ / min to 260 ℃ for 0.5 h, and then ground into fine powder after being taken out, to obtain a semi-cyclic polyacrylonitrile gel layer coated high-voltage positive electrode material (semi-cyclic polyacrylonitrile gel layer coated nickel-cobalt-manganese ternary positive electrode material), which can be expressed as NCM@PAN260-3%.

[0080] Comparative Example 1

[0081] A semi-cyclic polyacrylonitrile polymer layer coated nickel-cobalt-manganese ternary positive electrode material is prepared from LiNi 0.8 Co 0.1 Mn 0.1 O2 positive electrode active particles and polyacrylonitrile PAN, including the following steps:

[0082] S1, the polyacrylonitrile is dispersed in DMF solvent to obtain a polymer solution after being stirred uniformly, specifically as follows:

[0083] 0.1856 g of polyacrylonitrile PAN is dispersed in 8 g of DMF, and the mixture is stirred at 30 ℃ for 0.5 h to obtain a clear polymer solution.

[0084] S2, taking the NCM active particles as the core, the NCM active particles are added into the polymer solution, and the mixture is stirred thoroughly until the solvent is completely volatilized and then dried, to ensure that the surface of the NCM is uniformly coated, specifically as follows:

[0085] 6 g of NCM active positive electrode material is added into the polymer solution and ultrasonically treated for 10 min, and then the mixture is magnetically stirred at 50 ℃ for 4 h until the DMF is completely volatilized, so that the surface of the NCM active particles is coated with a uniform polyacrylonitrile gel layer, and then the mixture is vacuum dried at 100 ℃ for 3 h.

[0086] S3, the coated NCM is sintered and ground, to obtain a semi-cyclic polyacrylonitrile gel layer coated nickel-cobalt-manganese ternary positive electrode material, specifically as follows:

[0087] The polyacrylonitrile coated NCM sample is calcined at a temperature increasing rate of 5 ℃ / min to 260 ℃ for 0.5 h, and then ground into fine powder after being taken out, to obtain a semi-cyclic polyacrylonitrile gel layer coated nickel-cobalt-manganese ternary positive electrode material, which can be expressed as NCM@PAN260.

[0088] Comparative Example 2

[0089] A polyacrylonitrile polymer layer coated nickel-cobalt-manganese ternary positive electrode material is prepared from LiNi 0.8 Co 0.1 Mn 0.1 O2 positive electrode active particles and polyacrylonitrile PAN, including the following steps:

[0090] S1, disperse polyacrylonitrile in DMF solvent, stir evenly to obtain a polymer solution, specifically:

[0091] Take 0.1856g polyacrylonitrile PAN and disperse it in 8g DMF, stir at 30°C for 0.5h to obtain a clear polymer solution.

[0092] S2, take NCM active particles as the core, add NCM active particles to the polymer solution, dry after sufficient stirring until the solvent is completely volatilized, and ensure that the surface of the NCM is uniformly coated, specifically:

[0093] Add 6g NCM active positive electrode material to the polymer solution and ultrasonically treat for 10min, then magnetically stir at 50°C for 4h until the DMF is completely volatilized, so that the surface of the NCM active particles is coated with a uniform polyacrylonitrile gel layer, and then vacuum dry at 100°C for 24h.

[0094] S3, grind the coated NCM to obtain a polyacrylonitrile polymer layer coated nickel-cobalt-manganese ternary positive electrode material, denoted as NCM@PAN.

[0095] Example 5

[0096] A kind of semi-cyclic polyacrylonitrile gel coated high-voltage positive electrode material in solid-state battery, wherein the solid-state battery is NCM / lithium battery, using conventional technical means respectively with the semi-cyclic polyacrylonitrile gel layer coated nickel-cobalt-manganese ternary positive electrode material prepared in example 2-4 as positive electrode, lithium metal as negative electrode, composite electrolyte film is assembled.

[0097] In this embodiment, the compounding process of the composite electrolyte film is as follows:

[0098] A1, dissolve 0.5g PVDF-HFP in 8.5g butanone, magnetically stir at 50°C for 30min to obtain a 5.5% polymer clear solution.

[0099] A2, disperse 0.5g Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO) inorganic ceramic powder, lithium salt and ionic liquid are added to the polymer clear solution in the mass ratio of m PVDF-HFP :m LiDFOB :m LLZTO :m PYR14TFSI =1:1:1:1.4 under inert atmosphere, continuously stir for 3h to obtain a uniform casting solution. Pour the solution into a stainless steel mold and dry under vacuum drying conditions at 60°C for 24h to obtain a composite electrolyte film.

[0100] In this embodiment, the thickness of the composite electrolyte film is about 84 pm.

[0101] The NCM composite cathode in Comparative Example 1-2 was used as the cathode, a lithium metal anode, and a composite electrolyte film was assembled into an NCM / lithium battery using conventional technical means.

[0102] The cathode materials prepared in Example 1-5 and Comparative Example 1-2 were respectively characterized as follows, and the prepared composite cathodes were assembled into NCM / lithium solid-state batteries for the following tests:

[0103] (1) Scanning electron microscope (SEM) test: After gold spraying treatment of the sample to be tested, the surface and cross-sectional morphology of the sample were characterized by field emission scanning electron microscope.

[0104] (2) Transmission electron microscope (TEM) characterization: The sample was dispersed in water or ethanol under ultrasonic conditions, a small amount of dispersion was taken with a dropper and dropped on a carbon film supported on a copper net, and after drying, the sample was sent for characterization test.

[0105] (3) X-ray diffraction (XRD) test: The powder sample obtained in Example 1 was analyzed by X-ray diffraction pattern to obtain information such as composition and crystal structure of the material. The scanning range was 2 theta = 5-80°, and the scanning speed was 6° / min.

[0106] (4) Fourier infrared spectroscopy (FT-IR) test: The PAN samples at different sintering temperatures obtained in Example 1 were analyzed by FTIR technology, and the test conditions were: powder conventional tabletting absorption mode, wave number range 400-4000 cm -1 .

[0107] (5) Raman spectroscopy (Raman) test: The powder sample obtained in Example 1 was analyzed by a certain wavelength of light interacting with the internal structure of the sample to obtain Raman spectroscopy information, and the degree of semi-cyclization of PAN and the coating effect of PAN on NCM were analyzed. Test conditions: powder sample conventional test, wavelength of laser is 532 nm, wave number range is 300-1800 cm -1 .

[0108] (6) Constant current charge and discharge performance: The assembled NCM / lithium solid-state battery was tested for cycle performance. The test voltage range was 3.3 V-4.2 V, and the test temperature was 60°C.

[0109] The above test methods are all standard test methods in the art, and when non-disclosed parameters are involved, they are all selected according to the conventional operation in the art.

[0110] Figure 1 This is the appearance of the PAN sample after heat treatment at different temperatures in Example 1 of the present invention. Figure 1 As can be seen, as the calcination temperature increases, the PAN sample changes from white at room temperature to pale yellow, yellow, brown, and finally black at 260°C. This is because PAN undergoes cross-linking and cyclization during the heat treatment, gradually transforming its molecular structure from linear to heterocyclic, resulting in a corresponding color change. Furthermore, the PAN sample obtained at 290°C is black.

[0111] Figure 2 The XRD spectra of PAN samples after heat treatment at different temperatures in Example 1 of the present invention are shown in FIG. Figure 2 As can be seen in the figure, nearly all samples exhibit a distinct peak at a diffraction angle of 2θ = 17°. This peak represents the (100) plane of the hexagonal structure of the PAN molecule. As the heat treatment temperature increases, the peak intensity at 2θ = 17° gradually decreases, and at 290°C, it almost disappears, indicating that the degree of cyclization of PAN increases with increasing heat treatment temperature. Comparison of the diffraction intensities at other diffraction angles indicates that PAN molecules heat-treated at 260°C achieve the ideal degree of semi-cyclization.

[0112] Figure 3 FTIR images of PAN samples after heat treatment at different temperatures in Example 1 of the present invention are shown in FIG. Figure 3 It can be seen that the PAN molecules without heat treatment have a peak at 2245 cm -1 There is a characteristic peak at 1587cm, which is caused by the stretching vibration of -C≡N. As the heat treatment temperature increases, the peak intensity gradually decreases until it disappears at 290℃. At the same time, as the heat treatment process proceeds, the peak intensity at 1587cm -1 A broad absorption peak appears at 1369 cm -1 The peak intensities at 1587 cm-1 and 1597 cm-2 gradually weakened, which was attributed to the behaviors of -C=N / -C=C and -CH bonds during the heat treatment. The higher the heat treatment temperature, the stronger the peak at 1587 cm-1. -1 and 1369cm -1 The wider the peak at 2245cm, the greater the width of the peak. This is because during the heat treatment, the -C≡N triple bond gradually opens with the cross-linking and cyclization reaction of PAN molecules, and the molecular structure changes from a linear structure to a cyclic structure. In addition, when the temperature is too high, such as at 290℃, the molecule has not yet undergone cyclization and has already undergone thermal cracking, resulting in a peak at 2245cm -1 The peak intensity at is almost zero.

[0113] Figure 4Raman spectra of PAN samples after heat treatment at different temperatures in Example 1 of the present application. From Figure 4 It can be seen that the PAN molecules without heat treatment have no characteristic peaks, while the PAN after heat treatment has obvious characteristic peaks, especially at higher temperatures, such as 260℃ and 290℃, both at 1580cm -1 and 1355cm -1 Form a peak region with a certain width, which is due to the sp2π hybridization of carbon atoms and the formation of disordered structure, i.e. there are delocalized π electron bonds. These delocalized bonds can provide an environment rich in electronegativity, giving the sample good conductivity.

[0114] Figure 5 SEM and TEM images of nickel-cobalt-manganese ternary positive electrode material coated with semi-cyclized polyacrylonitrile gel (NCM@PAN260-2%) and nickel-cobalt-manganese ternary positive electrode material (NCM) in Example 3 of the present application. Figure 5 In the figure, a and b are SEM images of NCM, c is a SEM image of NCM@PAN260-2%, and d is a TEM image of NCM@PAN260-2%. From Figure 5 It can be seen that before coating, the surface of NCM spherical particles is rough, uniform and the spherical surface is clearly visible, composed of a large number of micro-nano structure primary particles, and the particle feeling is obvious. After coating, the basic shape of the NCM positive electrode particles remains unchanged, still spherical particles, but the positive electrode surface particle corners become blurred. At the same time, it can be seen from the TEM image that there is a coating film of about 10nm thickness on the surface of the positive electrode material after coating. The crystal lattice spacing of 0.24nm can be attributed to the (101) plane of NCM, which indicates that the PAN260-LiDFOB-PYR 14 TFSI constructed gel polymer layer is coated on the surface of NCM.

[0115] Figure 6 EDS image of nickel-cobalt-manganese ternary positive electrode material coated with semi-cyclized polyacrylonitrile gel (NCM@PAN260-2%) prepared in Example 3 of the present application. From Figure 6 It can be seen that in addition to the three elements Ni, Co and Mn that make up the positive electrode material, the elements C, N, F, O and S from the coating layer are uniformly distributed and overlap with Ni, Co and Mn, and the surface distribution of C, N, F, O and S elements is consistent with the size of NCM particles, indicating that the coating layer is uniformly distributed on the outer layer of the NCM positive electrode.

[0116] Figure 7XRD patterns of the semi-cyclized polyacrylonitrile gel coated nickel-cobalt-manganese ternary cathode material (NCM@PAN260-1%, NCM@PAN260-2%, NCM@PAN260-3%) prepared in Examples 2-4 of the present application, the semi-cyclized polyacrylonitrile polymer layer coated nickel-cobalt-manganese ternary cathode material (NCM@PAN260) prepared in Comparative Example 1, the polyacrylonitrile polymer layer coated nickel-cobalt-manganese ternary cathode material (NCM@PAN) prepared in Comparative Example 2, and the nickel-cobalt-manganese ternary cathode material (NCM). The results show that there is no significant difference between the XRD patterns of the original NCM active particles and the semi-cyclized polyacrylonitrile gel layer coated nickel-cobalt-manganese ternary cathode material, and there is no appearance of any identifiable second phase peaks and peak shifts, indicating that the semi-cyclized polyacrylonitrile gel layer has an amorphous structure and does not destroy the crystal structure of the main body NCM.

[0117] Figure 8 The interface impedance-time change graph of the solid-state battery assembled from the semi-cyclized polyacrylonitrile gel coated nickel-cobalt-manganese ternary cathode material (NCM@PAN260-2%) and the uncoated nickel-cobalt-manganese ternary cathode material (NCM) in Example 5 of the present application. Figure 8 In the figure, NCM-day1 represents the initial impedance of the solid-state battery composed of uncoated NCM, NCM@PAN-day1 represents the initial impedance of the solid-state battery composed of semi-cyclized polyacrylonitrile gel coated NCM, NCM-day4 represents the impedance value of the solid-state battery composed of uncoated NCM after being stored for 4 days, and NCM@PAN-day4 represents the impedance value of the solid-state battery composed of semi-cyclized polyacrylonitrile gel coated NCM after being stored for 4 days. It can be seen from the figure that the interface impedance of the solid-state battery assembled from the semi-cyclized polyacrylonitrile gel coated NCM is always lower than that of the uncoated NCM, and the increase amplitude is significantly smaller than that of the uncoated NCM. Figure 8 It can be seen that although the interface charge transfer impedance Rct of the battery presents a gradually increasing trend as the storage time increases, the interface impedance of the solid-state battery assembled from the coated cathode is always lower than that of the uncoated battery, and the increase amplitude is significantly smaller than that of the uncoated NCM solid-state battery. Specifically, the fitted charge transfer impedance of the uncoated NCM solid-state battery is 2667Ω on the first day, and this value reaches 8056Ω on the fourth day. The initial impedance of the solid-state battery after the gel coating layer coating treatment is 2396Ω, and the impedance value after being stored for 4 days is 4632Ω, which indicates that the semi-cyclized polyacrylonitrile gel layer can significantly reduce the interface impedance between the cathode and the solid-state electrolyte, and plays a role in maintaining the stability of the interface.

[0118] Figure 9 The constant current charge-discharge test under different rates of the NCM / lithium solid-state battery assembled from the semi-cyclized polyacrylonitrile gel coated nickel-cobalt-manganese ternary cathode material (NCM@PAN260-1%, NCM@PAN260-2%, NCM@PAN260-3%) in Example 5 of the present application. Figure 9In specific embodiments, NCM-1% is NCM@PAN260-1%, NCM-2% is NCM@PAN260-2%, and NCM-3% is NCM@PAN260-3%. In specific embodiments, NCM-1% is NCM@PAN260-1%, NCM-2% is NCM@PAN260-2%, and NCM-3% is NCM@PAN260-3%. Figure 9 It can be seen that different coating amounts of semi-cyclized polyacrylonitrile gel layers have different effects on the performance of NCM solid-state batteries. When the coating layer content is 1%, the capacity decreases rapidly. When the coating layer content is 2%, the NCM solid-state battery exhibits relatively excellent rate performance. At 0.1C, 0.2C and 0.5C rates, it can release 141.9 mAh·g -1 -1, 117.7 mAh·g -1 -1 and 93.6 mAh·g -1 -1, respectively. Therefore, for semi-cyclized polyacrylonitrile gel layers, the semi-cyclized polyacrylonitrile gel layer with a coating amount of 2% has better performance for coating nickel-cobalt-manganese ternary positive electrode materials.

[0119] Therefore, the semi-cyclized polyacrylonitrile gel layer coated nickel-cobalt-manganese ternary positive electrode material provided by the present application can ensure that the gel layer is uniformly coated on the surface of the NCM positive electrode material. In the cycle process, on the one hand, it improves the structural stability of the positive electrode material, and on the other hand, it effectively constructs the ion and electron double channels in the composite positive electrode, and optimizes the contact impedance between NCM active particles and the charge transfer resistance between the electrode and the electrolyte to improve the overall performance of the NCM solid-state battery.

[0120] In summary, the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material can utilize the coordination between the high-polarity group-C≡N functional groups contained in the coating layer and transition metal ions to ensure the close contact between the coating layer and the high-voltage positive electrode material, realize continuous and uniform coating, optimize the contact impedance between the active particles of the high-voltage positive electrode material and the charge transfer resistance between the electrode and the electrolyte, and effectively improve the kinetic transmission in the composite positive electrode by utilizing the dual ion and electron transmission of the semi-cyclized polyacrylonitrile gel layer. In addition, the lithium salt in the coating layer can realize in-situ construction of a stable inner interface layer (CEI) in the electrochemical process, further inhibiting the occurrence of side reactions between the high-voltage positive electrode material and the electrolyte, and ultimately improving the stability of the positive electrode structure and the cycle stability of the battery. At the same time, the preparation method of the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material of the application first disperses polyacrylonitrile, lithium salt and ionic liquid in a solvent, stirs, and thereby obtains a polyacrylonitrile solution containing lithium salt and ionic liquid, which is conducive to uniform coating of polyacrylonitrile, lithium salt and ionic liquid on the surface of the high-voltage positive electrode material. Then, the high-voltage positive electrode material is added to the polyacrylonitrile solution, at which time polyacrylonitrile, lithium salt and ionic liquid are uniformly coated on the surface of the high-voltage positive electrode material. After the solvent is completely volatilized and dried, a high-voltage positive electrode material uniformly coated with polyacrylonitrile, lithium salt and ionic liquid is formed. Finally, the high-voltage positive electrode material uniformly coated with polyacrylonitrile, lithium salt and ionic liquid is sintered to make polyacrylonitrile undergo a cyclization reaction and be converted into semi-cyclized polyacrylonitrile gel, thereby forming a continuous and uniform coating layer that can simultaneously conduct electrons and ions on the surface of the high-voltage positive electrode material. In addition, the preparation method has the advantages of simple process, controllable process, continuous production, etc., is suitable for large-scale preparation, and is convenient for industrial application. Therefore, when the semi-cyclized polyacrylonitrile gel coated high-voltage positive electrode material is used in a solid-state battery, the solid-state battery can exhibit more excellent cycle stability and rate performance.

[0121] The above is only the preferred embodiment of the present application, but not to limit the present application. Any skilled person in the art can make many possible changes and modifications to the technical solutions of the present application by using the above disclosed methods and technical contents. Therefore, any simple modification made to the above embodiments according to the technical essence of the present application, without departing from the technical solutions of the present application, still belongs to the protection scope of the technical solutions of the present application.

Claims

1. A semi-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material, characterized in that: The invention comprises a high-voltage positive electrode material, the surface of which is coated with a semi-cyclized polyacrylonitrile gel layer; the semi-cyclized polyacrylonitrile gel layer also contains ionic liquid and lithium salt; the mass content of the semi-cyclized polyacrylonitrile gel layer in the semi-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material is 1.5% to 2.5%.

2. The semi-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material according to claim 1, characterized in that: The high voltage positive electrode material is at least one of a nickel-cobalt-manganese ternary positive electrode material, a lithium cobalt oxide ternary positive electrode material, and a lithium nickel-manganese oxide ternary positive electrode material.

3. A method for preparing a semi-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material, characterized in that: The following steps are involved: S1, dispersing polyacrylonitrile, lithium salt and ionic liquid in a solvent, stirring to obtain a polymer solution; S2. Adding the high-voltage positive electrode material to the polymer solution, stirring until the solvent is completely volatilized, and drying to obtain the polymer-coated high-voltage positive electrode material; S3. Sintering the polymer-coated high-voltage positive electrode material to obtain a semi-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material; the semi-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material includes a high-voltage positive electrode material, and the surface of the high-voltage positive electrode material is coated with a semi-cyclized polyacrylonitrile gel layer; the semi-cyclized polyacrylonitrile gel layer also contains ionic liquid and lithium salt; the mass content of the semi-cyclized polyacrylonitrile gel layer in the semi-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material is 1.5% to 2.5%.

4. The preparation method according to claim 3, characterized in that The mass ratio of the polyacrylonitrile, lithium salt and ionic liquid is 1:1:1.4; the mass ratio of the polyacrylonitrile to the high-voltage positive electrode material is 0.003-0.01:1; and the mass ratio of the solvent to the high-voltage positive electrode material is 4:

3.

5. The preparation method according to claim 4, characterized in that The lithium salt is lithium difluorooxalatoborate, or a composite lithium salt of lithium difluorooxalatoborate and lithium bis(trifluoromethanesulfonyl)imide, or a composite lithium salt of lithium difluorooxalatoborate and lithium dioxalatoborate; The ionic liquid is one or more of piperidine ionic liquids, quaternary ammonium ionic liquids, imidazole ionic liquids and pyrrole ionic liquids; The solvent is N,N-dimethylformamide; The high voltage positive electrode material is at least one of a nickel-cobalt-manganese ternary positive electrode material, a lithium cobalt oxide ternary positive electrode material, and a lithium nickel-manganese oxide ternary positive electrode material.

6. The preparation method according to claim 5, characterized in that The piperidine ionic liquid is N-methyl-N-propylpiperidinium di(trifluoromethylsulfonyl)imide; the quaternary ammonium ionic liquid is N-methyl-N,N-diethyl-N-(2-methoxyethyl)ammonium di(trifluoromethylsulfonyl)imide; the imidazole ionic liquid is di(trifluoromethylsulfonyl)1-ethyl-3-methylimidazole; and the pyrrole ionic liquid is N-methyl-N-propylpyrrole di(trifluoromethylsulfonyl)imide.

7. The preparation method according to any one of claims 3 to 6, characterized in that In S1, the stirring time is 0.5h to 3h; In S2, the stirring is performed at a temperature of 50°C to 80°C; the stirring time is 5 hours to 10 hours; the drying is performed at a temperature of 100°C to 110°C; the drying time is 12 hours to 24 hours; In S3, the heating rate during the sintering process is 5°C / min; the sintering temperature is 210°C to 290°C; and the sintering time is 0.5 h.

8. Use of the semi-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material according to claim 1 or 2 or the semi-cyclized polyacrylonitrile gel-coated high-voltage positive electrode material prepared by the preparation method according to any one of claims 3 to 7 in a solid-state battery.

9. The use according to claim 8, characterized in that The solid-state battery is a lithium battery.

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