Positive electrode material for solid-state battery as well as preparation method and application of positive electrode material

Abstract

The invention discloses a positive electrode material for a solid-state battery as well as a preparation method and application of the positive electrode material. The positive electrode material for the solid-state battery comprises a niobium-doped positive electrode core and a three-dimensional network coating layer, wherein the three-dimensional network coating layer comprises polyaniline nanofibers and graphene. According to the invention, the positive electrode material is doped by using the niobium element, and the doped positive electrode material is coated by using the coating layer with a specific structure and components, so that the performance of the positive electrode material can be improved, and the capacity, the rate capability, the fast charge performance and the cycle performance of the solid-state battery applying the positive electrode material are further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a positive electrode material for solid-state batteries and a preparation method and application thereof. Background Art

[0002] As batteries are used more deeply and widely in various fields of life, people have higher requirements for battery performance, such as high energy density, high safety, and long service life. Batteries can be divided into liquid batteries and solid-state batteries according to the state of the electrolyte. Among them, solid-state batteries have obvious advantages in terms of safety performance. They are not easy to burn or leak, and are more suitable for scenarios with higher safety requirements. In addition, the electrochemical window of solid-state electrolytes is wider, which can adapt to higher voltage cathode materials, which is conducive to improving the energy density of the battery.

[0003] However, solid-state batteries also face some problems. Because the electrolyte in solid-state batteries is solid, the interface between the solid electrolyte and the electrode material is a solid-solid interface, resulting in weak contact and low ion transport kinetics. This increases the internal resistance of the battery and thus degrades battery performance. Therefore, it is difficult to directly apply the cathode materials used in traditional liquid batteries to solid-state batteries.

[0004] To address the above problems, relevant research has modified the positive electrode materials through coating and doping to better improve the performance of solid-state batteries.

[0005] CN118299560A discloses a method for coating lithium niobate on the surface by doping niobium. The method uses niobium pentoxide and residual alkali to in-situ construct a coating interface on the surface of the positive electrode material and simultaneously forms bulk doping. The method uses niobium pentoxide to consume the residual LiOH and Li2CO3 in the sintering process of the high-nickel ternary positive electrode material to form Li3NbO4 with high ionic conductivity and in-situ coat the surface of the high-nickel ternary positive electrode material. At the same time, the high-valent Nb 5+ Doping niobium into the bulk of high-nickel ternary cathode materials can effectively resolve the severe interfacial reactions between the cathode material and the electrolyte in solid-state batteries, while maintaining the stability of the cathode material during battery cycling. However, this method involves doping and coating niobium during the calcination of the cathode material, which is not an atomic-level reaction. This can lead to uneven niobium doping and affect the performance of the cathode material.

[0006] CN 104485443 A discloses a method for preparing a graphene polymer-coated niobium-doped lithium cobalt aluminate composite cathode material. The method comprises preparing a niobium-doped lithium cobalt aluminate cathode material through gel sol followed by calcination, and then preparing a graphene polymer-coated niobium-doped lithium cobalt aluminate cathode material through a spheroidal graphite process. This method consumes high energy during the preparation process, making it unsuitable for large-scale industrial production.

[0007] Therefore, providing a positive electrode material suitable for solid-state batteries that can effectively improve the performance of solid-state batteries and has the advantage of low-cost large-scale preparation is a technical problem that needs to be solved urgently. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the object of the present invention is to provide a positive electrode material for solid-state batteries and a preparation method and use thereof.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a positive electrode material for a solid-state battery, wherein the positive electrode material for a solid-state battery comprises a niobium-doped positive electrode core and a three-dimensional network coating layer, wherein the three-dimensional network coating layer comprises polyaniline nanofibers and graphene.

[0011] During the charge and discharge process, the crystal structure of the positive electrode material in a solid-state battery expands and contracts, reducing structural stability and interfacial contact, leading to a decrease in battery performance. The present invention improves the performance of the positive electrode material by doping it with niobium, which is beneficial to the performance of solid-state batteries. The main reasons are as follows: First, niobium occupies specific positions in the crystal lattice or replaces some other metal ions, forming more stable chemical bonds, preventing the collapse or distortion of the crystal structure, thereby enhancing the stability of the crystal structure and maintaining its integrity during the insertion and extraction of lithium ions. Second, after niobium atoms enter the crystal lattice of the positive electrode material, they change the energy state of the lattice, making it less likely for the material to transition from one phase to another during the charge and discharge process, thereby improving the cycle life of the battery. Third, niobium has a certain degree of electron conductivity. When doped into the positive electrode material, it can improve the overall electronic conductivity of the material. During the battery's electrode reaction, electrons can be transmitted more quickly within the positive electrode material, reducing electrode polarization and thus improving the battery's charge and discharge efficiency. Fourth, niobium doping can optimize the microstructure of the cathode material, making the diffusion path of lithium ions in the material smoother. This helps improve the battery's rate performance, allowing the battery to better utilize its capacity during high-rate charge and discharge, shortening the charge and discharge time. Fifth, niobium doping can also inhibit the interfacial reaction between the cathode material and the electrolyte, thereby improving the battery's cycle performance.

[0012] Furthermore, the present invention not only uses niobium as a doping agent, but also coats the niobium-doped positive electrode material with a coating layer. The polyaniline nanofibers in the coating layer have a one-dimensional morphology, while the graphene has a two-dimensional morphology. The two layers form a three-dimensional network structure. By introducing this coating layer, the performance of the positive electrode material can be effectively improved, thereby enhancing the electrochemical performance of the solid-state battery. The main advantages are as follows: First, the three-dimensional network coating layer constructed by graphene and polyaniline nanofibers has excellent conductivity, with extremely fast electron transfer speed and extremely low resistivity, allowing the battery to respond more quickly to changes in current during charge and discharge, thereby improving the battery's charge and discharge efficiency and overall performance. Second, because graphene has an extremely high specific surface area, the three-dimensional network constructed by it and the one-dimensional polyaniline nanofibers can provide more active sites for the adsorption and storage of lithium ions and facilitate the diffusion of lithium ions, which can significantly improve the energy storage capacity of the battery's positive electrode. Moreover, it allows lithium ions to be more easily embedded in and released from the material, allowing the battery to store more electricity, shorten the charge and discharge time, and improve the battery's rate performance. Third, the coating is much stronger than traditional battery materials. It acts as a support structure within the battery, helping to stabilize the electrode material's structure and preventing expansion and contraction caused by the insertion and extraction of lithium ions during charge and discharge, thereby extending the battery's lifespan. Fourth, the coating prevents agglomeration of particles in the positive electrode material, maintaining material uniformity and improving the battery's electrochemical performance.

[0013] Applying the positive electrode material of the present invention to solid-state batteries can improve the capacity, rate performance, fast charging performance and cycle performance of solid-state batteries.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] Preferably, based on the total mass of the positive electrode material for the solid-state battery as 100%, the content of the positive electrode core is 85%-95%, for example, it can be 85%, 86%, 87%, 88%, 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94% or 95%, etc.

[0016] Preferably, the doping amount of niobium is 500ppm-5000ppm based on the total mass of the positive electrode core, for example, 500ppm, 700ppm, 800ppm, 1000ppm, 1200ppm, 1500ppm, 1750ppm, 2000ppm, 2200ppm, 2400ppm, 2600ppm, 2800ppm, 3000ppm, 3300ppm, 3500ppm, 3800ppm, 4000ppm, 4250ppm, 4500ppm, 4700ppm, or 5000ppm. If the doping amount of niobium is too low, the improvement effect on the positive electrode material will be insignificant; if the doping amount of niobium is too high, the cost will increase and the positive electrode material will weaken the inhibitory effect of the electrolyte on the interface reaction.

[0017] Preferably, based on 100% of the total mass of the positive electrode material for the solid-state battery, the thickness of the coating layer is 0.1 μm-2 μm, for example, 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm or 2 μm, etc. Within this preferred thickness range, the coating layer can be better utilized to improve the performance of the positive electrode material, thereby improving the electrochemical performance of the battery prepared using the same.

[0018] Preferably, the mass ratio of polyaniline nanofibers to graphene in the coating layer is 1:(1-2), for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, or 1:2. If the content of polyaniline nanofibers is too high, the improvement in the conductive properties of the precursor material due to the coating of graphene will be weakened; if the content of polyaniline nanofibers is too low, the cross-linking effect on the graphene will be insignificant, and the graphene will not be significantly coated on the surface of the precursor material, resulting in a decrease in the improvement effect of the coating layer on the positive electrode material.

[0019] In a second aspect, the present invention provides a method for preparing a positive electrode material for a solid-state battery as described in the first aspect, the preparation method comprising the following steps:

[0020] (1) adding a metal mixed salt solution, a precipitant solution, a complexing agent solution, and a niobium source solution to a bottom solution in parallel to perform a coprecipitation reaction to obtain a niobium-doped positive electrode precursor core;

[0021] (2) calcining the niobium-doped cathode precursor core described in step (1) to obtain a niobium-doped oxide;

[0022] (3) mixing the niobium-doped oxide with a lithium salt and performing secondary calcination to obtain a niobium-doped positive electrode core;

[0023] (4) The niobium-doped positive electrode core described in step (3) is stirred and coated with a polyaniline-graphene composite to obtain the positive electrode material for a solid-state battery.

[0024] The present invention uses a coprecipitation method to dope niobium into the cathode material, achieving an atomic-level reaction and uniform niobium doping, effectively improving the performance of the cathode material. The niobium-doped cathode precursor core is mixed with a lithium salt and then calcined to obtain the cathode material core. This is then coated with a PANI-graphene film at room temperature to produce the cathode material.

[0025] Preferably, the metal elements in the metal mixed salt solution in step (1) are Ni, Co and Mn, and the molar ratio of each element is Ni:Co:Mn=(50-98):(1-30):(1-30), wherein the selection range of Ni is "50-98", for example, it can be 50, 52, 55, 58, 60, 65, 70, 75, 80, 85, 88, 90, 95 or 98, etc.; the selection range of Co is "1-30", for example, it can be 1, 3, 5, 7, 10, 13, 16, 18, 20, 22, 25, 26, 28 or 30, etc.; the selection range of Mn is "1-30", for example, it can be 1, 3, 5, 7, 10, 13, 16, 18, 20, 22, 25, 26, 28 or 30, etc.

[0026] The present invention does not specifically limit the source of the metal element in the metal mixed salt solution. For example, it can be a metal salt. For example, the metal salt can be one or more of acetate, nitrate, sulfate or chloride.

[0027] Preferably, the concentration of the metal mixed salt solution in step (1) is 1 mol / L-4 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L.

[0028] Preferably, the concentration of the precipitant solution in step (1) is 1 mol / L-5 mol / L, for example, it can be 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L or 5 mol / L.

[0029] Preferably, the concentration of the complexing agent solution in step (1) is 0.1 mol / L-2 mol / L, for example, it can be 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.7 mol / L, 1 mol / L, 1.5 mol / L, 1.8 mol / L or 2 mol / L.

[0030] Preferably, the base liquid in step (1) is made of water, liquid alkali and ammonia water, and the pH of the base liquid is 10.5-11, for example, it can be 10.5, 10.6, 10.7, 10.8, 10.9 or 11; the ammonia concentration in the base liquid is 0.2-2 mol / L, for example, it can be 0.2 mol / L, 0.5 mol / L, 0.7 mol / L, 1 mol / L, 1.5 mol / L, 1.8 mol / L or 2 mol / L.

[0031] Preferably, the temperature of the coprecipitation reaction in step (1) is 40°C-70°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C.

[0032] Preferably, during the coprecipitation reaction in step (1), the pH of the reaction system is 10.5-11, for example, 10.5, 10.6, 10.7, 10.8, 10.9 or 11, etc.; the concentration of aqueous ammonia in the reaction system is 0.2 mol / L-2 mol / L, for example, 0.2 mol / L, 0.5 mol / L, 0.7 mol / L, 1 mol / L, 1.5 mol / L, 1.8 mol / L or 2 mol / L, etc. By controlling the pH and aqueous ammonia concentration during the coprecipitation reaction, the particle size and diameter of the prepared hydroxide can be regulated.

[0033] Preferably, the coprecipitation reaction in step (1) is carried out under the conditions of protective gas and stirring. The stirring condition is conducive to improving the uniformity of the reaction, and the protection of the protective gas can prevent oxidation of the material.

[0034] The present invention does not specifically limit the type of protective gas, and it can be, for example, nitrogen or argon.

[0035] Preferably, the particle size D50 of the niobium-doped positive electrode precursor core in step (1) is 3 μm-8 μm, for example, it can be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm or 8 μm.

[0036] As a preferred technical solution of the method for preparing the positive electrode material for solid-state batteries described in the present invention, the temperature of the primary calcination in step (2) is 600°C-800°C, for example, it can be 600°C, 625°C, 650°C, 675°C, 700°C, 725°C, 750°C or 800°C, etc.

[0037] Preferably, the heating rate of the primary calcination in step (2) is 5°C / min-10°C / min, for example, it can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min.

[0038] Preferably, the holding time of the primary calcination in step (2) is 10 h to 14 h, for example, it can be 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h or 14 h.

[0039] Preferably, the temperature of the secondary calcination in step (3) is 600°C-800°C, for example, it can be 600°C, 625°C, 650°C, 675°C, 700°C, 725°C, 750°C or 800°C.

[0040] Preferably, the heating rate of the secondary calcination in step (3) is 5°C / min-10°C / min, for example, it can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min.

[0041] Preferably, the holding time of the secondary calcination in step (3) is 10 h to 14 h, for example, it can be 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h or 14 h.

[0042] Preferably, the mass ratio of the niobium-doped oxide to the lithium salt in step (3) is 1:(1.15-1.25), for example, it can be 1:1.15, 1:1.16, 1:1.17, 1:1.18, 1:1.19, 1:1.2, 1:1.21, 1:1.22, 1:1.23, 1:1.24 or 1:1.25, etc.

[0043] By controlling the ratio of the niobium-doped cathode precursor core to the lithium salt, as well as the parameters of the primary and secondary calcinations, the performance of the cathode material can be improved.

[0044] As a preferred technical solution of the method for preparing the positive electrode material for solid-state batteries according to the present invention, the method for preparing the polyaniline-graphene composite in step (4) comprises the following steps:

[0045] (a) preparing graphene oxide dispersion and polyaniline nanofiber dispersion respectively;

[0046] (b) mixing the graphene oxide dispersion and the polyaniline nanofiber dispersion described in step (a) and performing a hydrothermal reaction to obtain a polyaniline-graphene composite.

[0047] In this method, through the hydrothermal reaction, on the one hand, graphene oxide can be reduced to graphene, and on the other hand, the composite of two-dimensional sheet-like graphene and one-dimensional polyaniline nanofibers can be achieved to obtain a three-dimensional polyaniline-graphene composite.

[0048] The present invention does not specifically limit the source of the polyaniline nanofiber dispersion, and for example, the dispersion can be prepared according to the method in CN1786304A.

[0049] Preferably, the mass concentration of the graphene oxide dispersion in step (a) is 5%-10%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc.

[0050] Preferably, the mass concentration of the polyaniline nanofiber dispersion in step (a) is 5%-10%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%.

[0051] Preferably, the temperature of the hydrothermal reaction in step (b) is 145°C-180°C, for example, it can be 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C or 180°C.

[0052] Preferably, the stirring and coating time in step (4) is 8h-40h, for example, it can be 8h, 10h, 12h, 13h, 15h, 16h, 17h, 20h, 22h, 23h, 24h, 26h, 28h, 30h, 32h, 35h, 37h or 40h, etc.

[0053] In the present invention, coating of the positive electrode material can be achieved by stirring at room temperature. The method is simple and easy to operate, and the prepared positive electrode material has good performance.

[0054] In the present invention, room temperature refers to 20°C-30°C, for example, it can be 20°C, 22°C, 25°C, 28°C or 30°C.

[0055] Preferably, the method further comprises washing and drying the obtained product after the stirring and coating in step (4).

[0056] The present invention does not impose any particular limitation on the washing method. For example, the washing may be performed by centrifugation in a centrifuge under pure water conditions.

[0057] Preferably, the drying temperature is 100°C-155°C, for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C, 145°C, 150°C or 155°C.

[0058] In a third aspect, the present invention provides a positive electrode, which includes the positive electrode material for solid-state batteries described in the first aspect.

[0059] In a fourth aspect, the present invention provides a battery comprising the positive electrode described in the third aspect.

[0060] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] The present invention improves the performance of the positive electrode material by doping the positive electrode material with niobium and coating the doped positive electrode material with a coating layer of specific structure and composition, thereby enhancing the capacity, rate performance, fast charging performance and cycle performance of the solid-state battery using the positive electrode material. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0064] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. The following examples are convenient for better understanding of the present invention, but are not intended to limit the present invention. The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0065] Example 1

[0066] This embodiment provides a positive electrode material for a solid-state battery, wherein the positive electrode material for a solid-state battery comprises a niobium-doped positive electrode core and a three-dimensional network coating layer, wherein the three-dimensional network coating layer comprises polyaniline nanofibers and graphene;

[0067] Wherein, based on the total mass of the positive electrode material for the solid-state battery being 100%, the content of the positive electrode core is 93%;

[0068] Based on the total mass of the positive electrode core, the doping amount of niobium element is 2000ppm;

[0069] Based on the total mass of the positive electrode material for the solid-state battery as 100%, the thickness of the coating layer is 0.5 μm;

[0070] In the coating layer, the mass ratio of polyaniline nanofibers to graphene is 1:1.

[0071] This embodiment also provides a method for preparing the above-mentioned positive electrode material for solid-state batteries, comprising the following steps:

[0072] (1) Preparation of niobium-doped positive electrode core:

[0073] Weigh a certain amount of nickel nitrate, cobalt nitrate, and manganese nitrate, and thoroughly mix them in a molar ratio of Ni:Co:Mn=90:5:5 to prepare a metal mixed salt solution, wherein the concentration of the metal mixed salt solution is 2 mol / L;

[0074] Prepare 2 mol / L sodium hydroxide solution, 0.3 mol / L ammonia solution, and niobium oxalate solution;

[0075] Add half pure water to the reactor, add a certain amount of liquid alkali and ammonia water to make the pH reach 10.7 and the ammonia concentration reach 0.3 mol / L, keep the reactor at 50℃ and keep the temperature constant, turn on the stirring device, and introduce nitrogen as a protective gas in advance to prevent oxidation;

[0076] The prepared nickel-cobalt-manganese metal salt solution, sodium hydroxide solution, ammonia solution, and niobium salt solution are added to a reaction kettle in parallel. During this process, the pH of the reaction system is controlled within the range of 10.5-11, and the concentration of ammonia solution is controlled within the range of 0.2 mol / L-1 mol / L. After a certain reaction time, nickel-cobalt-manganese hydroxide with a particle size D50 of 5 μm and a niobium content of 2000 ppm is grown.

[0077] The nickel-cobalt-manganese hydroxide is subjected to a primary calcination, wherein the primary calcination comprises heating the nickel-cobalt-manganese hydroxide at a heating rate of 5° C. / min and maintaining the temperature at 650° C. for 10 hours to obtain a niobium-doped oxide.

[0078] The niobium-doped oxide was then mixed with lithium hydroxide in a mass ratio of 1:1.2. The mixture was placed in a rotary kiln and heated at a rate of 10°C / min. After being kept at 700°C for 12 hours, it was cooled to room temperature to obtain the niobium-doped positive electrode core.

[0079] (2) Preparation of coating material:

[0080] A 10 wt% graphene oxide solution is prepared and ultrasonically dispersed to obtain a first dispersion liquid. A 10 wt% polyaniline nanofiber solution is prepared and ultrasonically dispersed to obtain a second dispersion liquid. The first dispersion liquid and the second dispersion liquid are subjected to a hydrothermal reaction in a reactor at a temperature of 150° C. The hydrothermal reaction can convert the graphene oxide into graphene and simultaneously generate a polyaniline-graphene composite (abbreviated as PANI-graphene composite material). The PANI-graphene film is then washed with pure water in a centrifuge to obtain a PANI-graphene film.

[0081] (3) Coating:

[0082] The niobium-doped positive electrode core obtained in step (1) and the PANI-graphene film obtained in step (2) are added to a reactor and stirred at room temperature for 40 hours to allow the PANI-graphene film to fully coat the surface of the positive electrode material. The mixture is then washed three times with pure water using a centrifuge and then dried at 130° C. to obtain a PANI-graphene film-coated and niobium-doped positive electrode material, i.e., a positive electrode material for a solid-state battery.

[0083] Example 2

[0084] This embodiment provides a positive electrode material for a solid-state battery, wherein the positive electrode material for a solid-state battery comprises a niobium-doped positive electrode core and a three-dimensional network coating layer, wherein the three-dimensional network coating layer comprises polyaniline nanofibers and graphene;

[0085] Wherein, based on the total mass of the positive electrode material for the solid-state battery being 100%, the content of the positive electrode core is 90%;

[0086] Based on the total mass of the positive electrode core, the doping amount of niobium element is 1000ppm;

[0087] Based on the total mass of the positive electrode material for the solid-state battery as 100%, the thickness of the coating layer is 1.5 μm;

[0088] In the coating layer, the mass ratio of polyaniline nanofibers to graphene is 1:2.

[0089] This embodiment also provides a method for preparing the above-mentioned positive electrode material for solid-state batteries, comprising the following steps:

[0090] (1) Preparation of niobium-doped positive electrode core:

[0091] Weigh a certain amount of nickel sulfate, cobalt sulfate, and manganese sulfate, and thoroughly mix them in a molar ratio of Ni:Co:Mn=80:10:10 to prepare a metal mixed salt solution, wherein the concentration of the metal mixed salt solution is 3 mol / L;

[0092] Prepare 3 mol / L sodium hydroxide solution, 0.3 mol / L ammonia solution, and niobium chloride solution;

[0093] Add half pure water to the reactor, add a certain amount of liquid alkali and ammonia water to make the pH reach 10.9 and the ammonia concentration reach 0.5 mol / L, keep the reactor at 65℃ and keep the temperature constant, turn on the stirring device, and introduce nitrogen as a protective gas in advance to prevent oxidation;

[0094] The prepared nickel-cobalt-manganese metal salt solution, sodium hydroxide solution, ammonia solution, and niobium salt solution are added to a reaction kettle in parallel. During this process, the pH of the reaction system is controlled within the range of 10.5-10.8, and the concentration of ammonia solution is controlled within the range of 0.2 mol / L-0.8 mol / L. After a certain reaction time, nickel-cobalt-manganese hydroxide with a particle size D50 of 7 μm and a niobium content of 1000 ppm is grown.

[0095] The nickel-cobalt-manganese hydroxide is subjected to a primary calcination, wherein the primary calcination comprises heating the nickel-cobalt-manganese hydroxide at a heating rate of 8° C. / min and maintaining the temperature at 750° C. for 13 hours to obtain a niobium-doped oxide.

[0096] The niobium-doped oxide was then mixed with lithium hydroxide in a mass ratio of 1:1.2. The mixture was placed in a rotary kiln, heated at a rate of 5°C / min, calcined at 800°C, kept at that temperature for 10 hours, and then cooled to room temperature to obtain a niobium-doped positive electrode core.

[0097] (2) Preparation of coating material:

[0098] A 5wt% graphene oxide solution is prepared and ultrasonically dispersed to obtain a first dispersion liquid, a 10wt% polyaniline nanofiber solution is prepared and ultrasonically dispersed to obtain a second dispersion liquid, the first dispersion liquid and the second dispersion liquid are subjected to a hydrothermal reaction in a reactor at a temperature of 165°C. The hydrothermal reaction can convert the graphene oxide into graphene and simultaneously generate a polyaniline-graphene composite (abbreviated as PANI-graphene composite material), which is then washed with pure water in a centrifuge to obtain a PANI-graphene film.

[0099] (3) Coating:

[0100] The niobium-doped positive electrode core obtained in step (1) and the PANI-graphene film obtained in step (2) are added to a reactor and stirred at room temperature for 20 hours to allow the PANI-graphene film to fully coat the surface of the positive electrode material. The mixture is then washed three times with pure water using a centrifuge and then dried at 120° C. to obtain a PANI-graphene film-coated and niobium-doped positive electrode material, i.e., a positive electrode material for a solid-state battery.

[0101] Example 3

[0102] This embodiment provides a positive electrode material for a solid-state battery, wherein the positive electrode material for a solid-state battery comprises a niobium-doped positive electrode core and a three-dimensional network coating layer, wherein the three-dimensional network coating layer comprises polyaniline nanofibers and graphene;

[0103] Wherein, based on the total mass of the positive electrode material for the solid-state battery being 100%, the content of the positive electrode core is 95%;

[0104] Based on the total mass of the positive electrode core, the doping amount of niobium element is 4000ppm;

[0105] Based on the total mass of the positive electrode material for the solid-state battery as 100%, the thickness of the coating layer is 1 μm;

[0106] In the coating layer, the mass ratio of polyaniline nanofibers to graphene is 1:1.5.

[0107] This embodiment also provides a method for preparing the above-mentioned positive electrode material for solid-state batteries, comprising the following steps:

[0108] (1) Preparation of niobium-doped positive electrode core:

[0109] Weigh a certain amount of nickel nitrate, cobalt nitrate, and manganese nitrate, and thoroughly mix them in a molar ratio of Ni:Co:Mn=70:10:20 to prepare a metal mixed salt solution, wherein the concentration of the metal mixed salt solution is 1 mol / L;

[0110] Prepare 4 mol / L sodium hydroxide solution, 1 mol / L ammonia solution, and niobium salt solution;

[0111] Add half pure water to the reactor, add a certain amount of liquid alkali and ammonia water to make the pH reach 10.5 and the ammonia concentration reach 0.5 mol / L, keep the reactor at 70℃ and keep the temperature constant, turn on the stirring device, and introduce nitrogen as a protective gas in advance to prevent oxidation;

[0112] The prepared nickel-cobalt-manganese metal salt solution, sodium hydroxide solution, ammonia solution, and niobium salt solution are added to a reaction kettle in parallel. During this process, the pH of the reaction system is controlled within the range of 10.5-10.8, and the concentration of ammonia solution is controlled within the range of 0.2 mol / L-0.7 mol / L. After a certain reaction time, nickel-cobalt-manganese hydroxide with a particle size D50 of 5 μm and a niobium-doped content of 4000 ppm is grown.

[0113] The nickel-cobalt-manganese hydroxide is subjected to a primary calcination, wherein the primary calcination comprises heating the nickel-cobalt-manganese hydroxide at a heating rate of 10° C. / min and maintaining the temperature at 700° C. for 11 hours to obtain a niobium-doped oxide.

[0114] Niobium-doped nickel-cobalt-manganese hydroxide was then mixed with lithium hydroxide in a mass ratio of 1:1.2. The mixture was placed in a rotary kiln, heated at a rate of 7°C / min, calcined at 600°C, kept at that temperature for 14 hours, and then cooled to room temperature to obtain a niobium-doped positive electrode core.

[0115] (2) Preparation of coating material:

[0116] A 7wt% graphene oxide solution is prepared and ultrasonically dispersed to obtain a first dispersion liquid, and an 8wt% polyaniline nanofiber solution is prepared and ultrasonically dispersed to obtain a second dispersion liquid. The first dispersion liquid and the second dispersion liquid are subjected to a hydrothermal reaction in a reactor at a temperature of 180°C. The hydrothermal reaction can convert the graphene oxide into graphene and simultaneously generate a polyaniline-graphene composite (abbreviated as PANI-graphene composite material). The PANI-graphene film is then washed with pure water in a centrifuge.

[0117] (3) Coating:

[0118] The niobium-doped positive electrode core obtained in step (1) and the PANI-graphene film obtained in step (2) are added to a reactor and stirred at room temperature for 30 hours to allow the PANI-graphene film to fully coat the surface of the positive electrode material. The mixture is then washed three times with pure water using a centrifuge and then dried at 150° C. to obtain a PANI-graphene film-coated and niobium-doped positive electrode material, i.e., a positive electrode material for a solid-state battery.

[0119] Example 4

[0120] The difference between this embodiment and embodiment 1 is that, based on the total mass of the positive electrode core, the doping amount of niobium element is 5100 ppm.

[0121] Example 5

[0122] The difference between this embodiment and embodiment 1 is that the thickness of the coating layer is 1.5 coating layers.

[0123] Example 6

[0124] The difference between this embodiment and embodiment 1 is that in the coating layer, the mass ratio of polyaniline nanofibers to graphene is 1:4.

[0125] Example 7

[0126] The difference between this embodiment and embodiment 1 is that in the coating layer, the mass ratio of polyaniline nanofibers to graphene is 4:1.

[0127] Comparative Example 1

[0128] The difference between this comparative example and Example 1 is that niobium is not doped into the positive electrode material.

[0129] Comparative Example 2

[0130] The difference between this comparative example and Example 1 is that the positive electrode material does not contain a coating layer.

[0131] Comparative Example 3

[0132] The difference between this comparative example and Example 1 is that the coating layer does not contain graphene.

[0133] Comparative Example 4

[0134] The difference between this comparative example and Example 1 is that the coating layer does not contain polyaniline nanofibers.

[0135] Assembling lithium-ion batteries:

[0136] The positive electrode materials of Examples 1-7 and Comparative Examples 1-4 were prepared into positive electrode sheets by the following method: adding the positive electrode material, Super P and PVDF to NMP in a mass ratio of 95:2:3, mixing them evenly to obtain a positive electrode slurry, coating the positive electrode slurry on aluminum foil, and drying to obtain a positive electrode sheet.

[0137] A positive electrode sheet, a lithium sheet and a polypropylene separator are prepared into a battery core, and the battery core is placed in a battery shell and then injected with an electrolyte, wherein the electrolyte is a 1 mol / L lithium hexafluorophosphate electrolyte, to obtain a lithium-ion battery.

[0138] Electrochemical performance test:

[0139] (1) Discharge capacity test:

[0140] After fully charging the lithium-ion battery to a maximum voltage of 4.2V, let it stand for 4 hours and discharge it in constant current (CC) mode. Select a discharge rate of 0.5C, set the cut-off voltage to 3.0V, connect a constant current discharge instrument, start discharge and monitor the voltage in real time until the voltage drops to the cut-off value, record the discharge time, and calculate the actual capacity using the formula: Capacity (mAh) = Current (mA) × Time (h). Repeat 3 times and take the average value. Divide the actual capacity by the mass of the active material to obtain the discharge capacity in grams.

[0141] (2) Rate performance test: Discharge at 0.5C to the cutoff voltage and then let it stand. Then charge at 0.5C constant current to the upper limit voltage (4.2V) and maintain constant voltage until the current drops to 0.05C. Switch the target rate to 0.2C, 0.5C, 1C and 5C respectively. Each rate is cycled 10 times. The ratio of the last 5C discharge capacity to the last 0.5C discharge rate is recorded, which is the rate performance (%).

[0142] (3) Fast charging performance test: Charge at 5C to the target SOC (80% SOC) and record the time.

[0143] (4) Cycling performance test: After fully charging with a current of 1C, let it stand for 30 minutes, then discharge it at a constant current to the cut-off voltage (2.75V). After standing, recycle the battery with a charge rate of 5C and a discharge rate of 1C. The number of cycles until the capacity decays to 80% is recorded.

[0144] The test results are shown in the following table:

[0145] Table 1

[0146]

[0147]

[0148] As can be seen from Table 1, the present invention improves the performance of the positive electrode material by doping the positive electrode material with niobium and coating the doped positive electrode material with a coating layer of a specific structure and composition, thereby improving the capacity, rate performance, fast charging performance and cycle performance of the solid-state battery using the positive electrode material.

[0149] At the same time, by comparing Examples 1 and 5 with Comparative Example 1, it can be seen that there is an optimal range for the doping amount of niobium, and too little or too much niobium doping is not conducive to improving battery performance.

[0150] By comparing Example 1 with Example 7 and Comparative Example 2, it can be seen that if the coating layer is too thin, it is not conducive to improving the discharge capacity, rate performance, fast charging performance and cycle performance of the battery; if the coating layer is too thick, although the cycle performance is slightly improved, it will lead to a decrease in the discharge capacity, rate performance and fast charging performance.

[0151] By comparing Example 1 with Examples 8-9 and Comparative Examples 3-4, it can be seen that there is an optimal range for the mass ratio of polyaniline nanofibers to graphene, and a synergistic effect can be achieved by optimizing the ratio of the two.

[0152] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A positive electrode material for a solid-state battery, characterized in that: The positive electrode material for solid-state batteries includes a niobium-doped positive electrode core and a three-dimensional network coating layer, wherein the three-dimensional network coating layer includes polyaniline nanofibers and graphene.

2. The positive electrode material for solid-state batteries according to claim 1, characterized in that Based on the total mass of the positive electrode material for the solid-state battery as 100%, the content of the positive electrode core is 85%-95%; Preferably, based on the total mass of the positive electrode core, the doping amount of niobium element is 500ppm-5000ppm; Preferably, based on the total mass of the positive electrode material for the solid-state battery as 100%, the thickness of the coating layer is 0.1 μm-2 μm; Preferably, in the coating layer, the mass ratio of polyaniline nanofibers to graphene is 1:(1-2).

3. A method for preparing a positive electrode material for a solid-state battery according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) adding a metal mixed salt solution, a precipitant solution, a complexing agent solution, and a niobium source solution to a bottom solution in parallel to perform a coprecipitation reaction to obtain a niobium-doped positive electrode precursor core; (2) calcining the niobium-doped cathode precursor core described in step (1) to obtain a niobium-doped oxide; (3) mixing the niobium-doped oxide with a lithium salt and performing secondary calcination to obtain a niobium-doped positive electrode core; (4) The niobium-doped positive electrode core described in step (3) is stirred and coated with a polyaniline-graphene composite to obtain the positive electrode material for a solid-state battery.

4. The preparation method according to claim 3, characterized in that The metal elements in the metal mixed salt solution of step (1) are Ni, Co and Mn, and the molar ratio of each element is Ni:Co:Mn=(50-98):(1-30):(1-30); Preferably, the concentration of the metal mixed salt solution in step (1) is 1 mol / L-4 mol / L; Preferably, the concentration of the precipitant solution in step (1) is 1 mol / L-5 mol / L; Preferably, the concentration of the complexing agent solution in step (1) is 0.1 mol / L-2 mol / L; Preferably, the base liquid in step (1) is made of water, liquid alkali and ammonia water, the pH of the base liquid is 10.5-11, and the concentration of ammonia water in the base liquid is 0.2-2 mol / L; Preferably, the temperature of the coprecipitation reaction in step (1) is 40°C-70°C; Preferably, during the coprecipitation reaction in step (1), the pH of the reaction system is 10.5-11, and the concentration of aqueous ammonia in the reaction system is 0.2-2 mol / L; Preferably, the coprecipitation reaction in step (1) is carried out under the conditions of protective gas and stirring; Preferably, the particle size D50 of the niobium-doped positive electrode precursor core in step (1) is 3 μm-8 μm.

5. The preparation method according to claim 3 or 4, characterized in that The temperature of the primary calcination in step (2) is 600° C.-800° C.; Preferably, the heating rate of the primary calcination in step (2) is 5°C / min-10°C / min; Preferably, the holding time of the primary calcination in step (2) is 10h-14h; Preferably, the temperature of the secondary calcination in step (3) is 600° C.-800° C.; Preferably, the heating rate of the secondary calcination in step (3) is 5°C / min-10°C / min; Preferably, the holding time of the secondary calcination in step (3) is 10h-14h; preferably, the mass ratio of the niobium-doped oxide to the lithium salt in step (3) is 1:(1.15-1.25).

6. The preparation method according to any one of claims 3 to 5, characterized in that The preparation method of the polyaniline-graphene composite in step (4) comprises the following steps: (a) preparing graphene oxide dispersion and polyaniline nanofiber dispersion respectively; (b) mixing the graphene oxide dispersion and the polyaniline nanofiber dispersion described in step (a) and performing a hydrothermal reaction to obtain a polyaniline-graphene composite.

7. The preparation method according to claim 6, characterized in that The mass concentration of the graphene oxide dispersion in step (a) is 5%-10%; Preferably, the mass concentration of the polyaniline nanofiber dispersion in step (a) is 5%-10%; Preferably, the temperature of the hydrothermal reaction in step (b) is 145°C-180°C.

8. The preparation method according to any one of claims 3 to 7, characterized in that The stirring and coating time in step (4) is 8h-40h; Preferably, the method further comprises washing and drying the obtained product after the stirring and coating in step (4); Preferably, the drying temperature is 100°C-155°C.

9. A positive electrode, characterized in that The positive electrode includes the positive electrode material for solid-state batteries according to claim 1 or 2.

10. A battery, characterized in that: The battery includes the positive electrode according to claim 9.

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