Doped and coated lithium-rich compound as well as preparation method and application thereof

Abstract

The invention provides a doped and coated lithium-rich compound and a preparation method and application thereof, the doped and coated lithium-rich compound comprises an inner core and a coating layer on the surface of the inner core, the inner core comprises a rare earth element doped lithium-rich compound, and the coating layer comprises graphene oxide. According to the doped and coated lithium-rich compound, by doping rare earth elements, gas production of the lithium-rich compound in the cycle process can be inhibited, the cycle stability and the rate capability of a material are improved, meanwhile, the surface of the lithium-rich compound is coated with graphene oxide, and the conductivity and the air stability of the lithium-rich compound are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a doped and coated lithium-rich compound and a preparation method and application thereof. Background Art

[0002] With the widespread application of lithium-ion batteries in electric vehicles, renewable energy storage, and portable electronic devices, battery performance requirements continue to increase, especially in terms of capacity, energy density, charge and discharge rate, and cycle life. The positive electrode material of lithium-ion batteries plays a vital role in battery performance. However, during long-term charge and discharge, especially under high-rate or deep discharge conditions, lithium-ion batteries often experience irreversible lithium ion loss and battery capacity decay. This makes the actual battery life and performance unable to meet the requirements of high-performance applications.

[0003] Therefore, lithium replenishment technology has emerged to extend battery life and restore battery performance. Lithium replenishment materials can restore battery capacity and performance by effectively replenishing lost lithium ions. This is especially true after deep discharge, significantly slowing the capacity decay of lithium-ion batteries and improving their overall stability and cycle life. Lithium-rich compounds such as lithium-rich ferrite (Li5FeO4) and lithium-rich nickelate (LiNiO2) are widely used as lithium replenishers due to their low cost, good thermal stability, environmental friendliness, and long cycle life.

[0004] Lithium-rich compounds, a primary choice for lithium replenishment materials, still face technical bottlenecks. In particular, during high-rate charge and discharge, they are prone to gassing. This not only increases internal battery pressure, threatening safety, but also causes electrolyte volatilization, impacting battery performance and cycle life.

[0005] In order to solve the gas production problem of the above-mentioned lithium-rich compounds, it is necessary to develop efficient and stable lithium-supplementing materials to improve their stability and performance in practical applications. Summary of the Invention

[0006] The object of the present invention is to provide a doped and coated lithium-rich compound and its preparation method and application, wherein the doped and coated lithium-rich compound can inhibit the gas production of the lithium-rich compound during the circulation process, thereby solving the above-mentioned technical problems.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a doped and coated lithium-rich compound, comprising a core and a coating layer on the surface of the core, wherein the core comprises a rare earth element-doped lithium-rich compound, and the coating layer comprises graphene oxide.

[0009] In some embodiments, the rare earth element-doped lithium-rich compound includes rare earth element-doped lithium-rich lithium ferrite and / or rare earth element-doped lithium-rich lithium nickelate.

[0010] In some embodiments, the molar amount of the rare earth element doped in the core is 0.1 mol% to 0.3 mol% of the molar amount of the transition metal element in the lithium-rich compound.

[0011] In some embodiments, in the doped and coated lithium-rich compound, the content of the coating layer is 0.4 wt%-1 wt%.

[0012] In a second aspect, the present invention provides a method for preparing the doped and coated lithium-rich compound as described in the first aspect, the preparation method comprising the following steps:

[0013] A rare earth element doped lithium-rich compound is prepared by a sol-gel method; the rare earth element doped lithium-rich compound is then dispersed in a coating liquid for coating treatment, and finally heat treated to obtain the doped and coated lithium-rich compound.

[0014] The coating solution includes graphene oxide and an amine structure template.

[0015] In some embodiments, the coating process is performed using evaporation-induced self-assembly.

[0016] In some embodiments, the evaporation-induced self-assembly method is performed at a temperature of 70° C. to 90° C. for a time of 8 h to 12 h.

[0017] In some embodiments, the amine structural template includes any one of polyethyleneimine, polyacrylamine, or polyamide, or a combination of at least two thereof.

[0018] In some embodiments, the pH of the coating solution is 9-11.

[0019] In some embodiments, in the coating solution, the concentration of graphene oxide is 1 mg / mL-5 mg / mL, and the mass concentration of the amine structure template is 0.1 wt%-1 wt%.

[0020] In some embodiments, the heat treatment is performed at a temperature of 150° C. to 230° C. for a time of 3 h to 6 h in a protective atmosphere.

[0021] In some embodiments, the method for preparing the rare earth element-doped lithium-rich compound comprises the following steps:

[0022] A lithium source, a transition metal source, a rare earth metal source, a complexing agent and a solvent are mixed to prepare a sol, which is then dried to obtain a xerogel, wherein the transition metal source includes an iron source and / or a nickel source.

[0023] The dry gel is then subjected to ball milling, heat pretreatment and sintering treatment in sequence to obtain the rare earth element-doped lithium-rich compound.

[0024] In some embodiments, the mass ratio of the lithium source, transition metal source, complexing agent and solvent is (70-220):(50-280):(20-80):(250-800).

[0025] In some embodiments, the ball milling speed is 380 rpm-520 rpm, the ball milling time is 4 h-6 h, and the particle size of the ball milled powder is in the range of 500 nm-1 μm.

[0026] In some embodiments, the temperature of the heat pretreatment is 150° C.-300° C., and the time of the heat pretreatment is 2 h-10 h.

[0027] In some embodiments, the sintering temperature is 800° C.-1000° C., the sintering time is 20 h-28 h, and the sintering heating rate is 1° C. / min-5° C. / min.

[0028] In a third aspect, the present invention provides a positive electrode plate, which includes the doped and coated lithium-rich compound as described in the first aspect, or the doped and coated lithium-rich compound prepared by the preparation method described in the second aspect.

[0029] In a third aspect, the present invention provides a lithium-ion battery, comprising the doped and coated lithium-rich compound as described in the first aspect, or the doped and coated lithium-rich compound prepared by the preparation method described in the second aspect, or the positive electrode sheet as described in the third aspect.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention adopts dual modification of rare earth element doping and graphene oxide, which can effectively inhibit the generation of gas by lithium-rich compounds during the cycle process and reduce the battery performance degradation caused by gas production. When the lithium-rich compounds are used as lithium supplements, the stability and safety of the lithium-rich compounds during long-term use can be improved, ensuring the reliability of the battery in harsh working environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention provides a flow chart of the method for preparing the doped and coated lithium-rich compound.

[0033] Figure 2 This is an SEM image of the doped and coated lithium-rich compound described in Example 1 of the present invention.

[0034] Figure 3 This is a low-resolution TEM image (200 nm scale) of the doped and coated lithium-rich compound described in Example 1 of the present invention.

[0035] Figure 4 This is a high-resolution TEM image (2 nm scale) of the doped and coated lithium-rich compound described in Example 1 of the present invention.

[0036] Figure 5 This is the EDS element distribution image of the doped and coated lithium-rich compound described in Example 1 of the present invention.

[0037] Figure 6 The charge and discharge curves of a lithium-rich compound battery prepared using the doped and coated lithium-rich compound described in Example 1 of the present invention.

[0038] Figure 7 1 is a cycle performance diagram of lithium iron phosphate batteries prepared using the lithium-rich compounds described in Example 1 and Comparative Example 1 of the present invention, wherein Example 1 corresponds to the LFP-2% lithium supplement / Gr curve in the figure, and Comparative Example 1 corresponds to the LFP / Gr curve in the figure. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0040] In a first aspect, the present invention provides a doped and coated lithium-rich compound, comprising a core and a coating layer on the surface of the core, wherein the core comprises a rare earth element-doped lithium-rich compound, and the coating layer comprises graphene oxide.

[0041] The present invention uses dual modification of rare earth element doping and graphene oxide to effectively inhibit the generation of gas by lithium-rich compounds during the cycle process, reducing battery performance degradation caused by gas production. When the lithium-rich compounds are used as lithium supplements, the stability and safety of the lithium-rich compounds during long-term use can be improved, ensuring the reliability of the battery in harsh working environments.

[0042] In addition to the gas production problem, lithium-rich compounds, such as Li5FeO4, also face a more serious problem. During the charge and discharge process, the surface of these materials, such as Li5FeO4, easily reacts with oxygen and moisture in the air, generating a high-impedance surface layer. This surface layer reduces the material's electrical conductivity, thereby affecting the battery's charge and discharge efficiency and cycle stability. The present invention significantly improves the conductivity and cycle stability of lithium-rich compound materials by doping with rare earth elements and coating with graphene oxide. Rare earth element doping enhances the material's structural stability and reduces its volume expansion during charge and discharge, while the graphene oxide coating strengthens the material's electrical conductivity network, thereby improving the material's rate performance and cycle life. This allows lithium-ion batteries to exhibit better performance and a longer service life during high-rate discharge and prolonged use.

[0043] In a specific embodiment, the rare earth element-doped lithium-rich compound includes rare earth element-doped lithium-rich lithium ferrite and / or rare earth element-doped lithium-rich lithium nickelate.

[0044] In a specific embodiment, the molar amount of rare earth element doping in the core is 0.1 mol%-0.3 mol% of the molar amount of transition metal elements in the lithium-rich compound, for example, it can be 0.1 mol%, 0.15 mol%, 0.2 mol%, 0.25 mol% or 0.3 mol%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] The doping amount of the rare earth element described in the present invention will affect the stability and gas production of the material. If the doping amount of the rare earth element is too little, the improvement effect of the structural stability will not be obvious. If the doping amount of the rare earth element is too much, the excessive rare earth ions will replace the transition metal sites, causing lattice distortion, and will also form an insulating rare earth oxide impurity phase, which will hinder the diffusion of lithium ions.

[0046] In a specific embodiment, the rare earth element includes any one of La, Y, Sm or Ce, or a combination of at least two of them.

[0047] In a specific embodiment, in the doped and coated lithium-rich compound, the content of the coating layer is 0.4wt%-1wt%, for example, it can be 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 1wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] The content of the coating layer described in the present invention will affect the conductivity of the lithium-rich compound and the stability of the material to air and moisture. It is preferably within a specific range. If the content of the coating layer is too little, the improvement effect on the conductivity and stability is not obvious. However, if the content of the coating layer is too much, the overly thick coating layer will hinder the diffusion of lithium ions and will also cause the tap density of the material to decrease, affecting the processability of electrode preparation.

[0049] In a second aspect, the present invention provides a method for preparing the doped and coated lithium-rich compound as described in the first aspect, the flow chart of the preparation method is as follows Figure 1 As shown, the following steps are included:

[0050] S1: Rare earth element-doped lithium-rich compounds are prepared by a sol-gel method.

[0051] S2: dispersing the rare earth element-doped lithium-rich compound in a coating solution for coating, wherein the coating solution comprises graphene oxide and an amine structure template;

[0052] S3: Finally, heat treatment is performed to obtain the doped and coated lithium-rich compound.

[0053] The present invention first adopts a sol-gel method to prepare a rare earth element-doped lithium-rich compound, and then performs coating, wherein the coating liquid includes graphene oxide and an amine structure template agent, the graphene oxide contains a large number of oxygen-containing functional groups such as carboxyl and hydroxyl groups, and the amine structure template agent contains amino groups. The rich amino groups of the amine structure template agent can not only form hydrogen bonds with the oxygen-containing functional groups (-COOH / -OH) of graphene oxide, but also produce coordination effects with metal ions on the surface of the lithium-rich compound. Therefore, the amine structure template agent acts as a bridge to enhance the binding force between the graphene oxide and the surface of the lithium-rich compound. The amine structure template agent will be carbonized during subsequent heat treatment to form a nitrogen-doped carbon layer, which further enhances the interfacial bonding force between the core and the coating layer. Therefore, the core of the present invention and the coating layer on the surface of the core also include a nitrogen-doped carbon layer to enhance the interfacial bonding force between the core and the coating layer.

[0054] In one specific embodiment, the coating treatment is performed using an evaporation-induced self-assembly method.

[0055] The present invention uses an evaporation-induced self-assembly method to form a uniform graphene oxide coating layer, which not only improves the surface structure of the lithium-rich compound, but also gives it better hydrophobicity, which helps reduce the material's reaction with moisture in the air and improves its stability. At the same time, the conductivity of the coating layer enhances the overall conductivity of the battery, thereby improving the overall performance of the battery, especially in high-rate charge and discharge and high-temperature environments.

[0056] In a specific embodiment, the treatment temperature of the evaporation-induced self-assembly method is 70°C-90°C, for example, it can be 70°C, 80°C or 90°C, and the time is 8h-12h, for example, it can be 8h, 9h, 10h, 11h or 12h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0057] In a specific embodiment, the amine structural template includes any one of polyethyleneimine, polyacrylamine or polyamide, or a combination of at least two thereof.

[0058] In a specific embodiment, the pH of the coating solution is 9-11, for example, 9, 10 or 11, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0059] The present invention regulates the pH of the coating solution by using ammonia water, and makes the pH alkaline, preferably 9-11, so as to promote the amine structure template agent to play a role.

[0060] In a specific embodiment, in the coating solution, the concentration of graphene oxide is 1 mg / mL-5 mg / mL, for example, it can be 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL or 5 mg / mL, and the mass concentration of the amine structure template is 0.1 wt%-1 wt%, for example, it can be 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt% or 1 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] In one embodiment, the coating solution is obtained by dispersing graphene oxide in anhydrous ethanol, using ultrasonic vibration to ensure its uniform dispersion, adding an amine structural template thereto, and then adjusting the pH of the solution with ammonia water.

[0062] In a specific embodiment, the heat treatment temperature is 150°C-230°C, for example, it can be 150°C, 170°C, 190°C, 210°C or 230°C, and the heat treatment time is 3h-6h, for example, it can be 3h, 4h, 5h or 6h, and is carried out in a protective atmosphere, such as under nitrogen.

[0063] In one embodiment, the method for preparing the rare earth element-doped lithium-rich compound comprises the following steps:

[0064] A lithium source, a transition metal source, a rare earth metal source, a complexing agent and a solvent are mixed to prepare a sol, which is then dried to obtain a xerogel, wherein the transition metal source includes an iron source and / or a nickel source.

[0065] The dry gel is then subjected to ball milling, heat pretreatment and sintering treatment in sequence to obtain the rare earth element-doped lithium-rich compound.

[0066] In a specific embodiment, the mass ratio of the lithium source, transition metal source, complexing agent and solvent is (70-220):(50-280):(20-80):(250-800), for example, it can be 70:50:20:250, 100:100:50:400, 170:250:60:600 or 220:280:80:800, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] In a specific embodiment, the rare earth metal source includes any one of rare earth chloride, rare earth nitrate or rare earth fluoride, or a combination of at least two of them; the lithium source includes any one of LiOH, CH3COOLi, Li2O or Li2CO3, or a combination of at least two of them; the transition metal source includes any one of Fe(NO3)3, Ni(NO3)2 or Fe2O3, or a combination of at least two of them; the chelating agent includes citric acid or polyacrylic acid.

[0068] In a specific embodiment, mixing a lithium source, a transition metal source, a rare earth metal source, a complexing agent, and a solvent includes dispersing the rare earth metal source in anhydrous ethanol to obtain a rare earth metal source solution; dissolving the lithium source and the transition metal source in anhydrous ethanol, and adding a complexing agent to obtain a mixed solution, adding the rare earth metal source solution to the mixed solution and ultrasonically treating it, and adjusting the pH of the solution to 6-7 (for example, it can be 6, 6.5 or 7), and then letting it stand or stirring to form a sol.

[0069] In a specific embodiment, the concentration of the rare earth metal source solution is 0.01 mol / L-0.1 mol / L, for example, it can be 0.01 mol / L, 0.03 mol / L, 0.05 mol / L, 0.07 mol / L, 0.09 mol / L or 0.1 mol / L, and the volume ratio of the rare earth metal source solution to the mixed solution is (1-3):1, for example, it can be 1:1, 2:1 or 3:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0070] In a specific embodiment, the ball milling speed is 380rpm-520rpm, for example, it can be 380rpm, 400rpm, 500rpm or 520rpm, the ball milling time is 4h-6h, for example, it can be 6h, 5h or 6h, and the particle size range of the ball milled powder is between 500nm-1μm, for example, it can be 500nm, 600nm, 700nm, 800nm, 900nm or 1μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0071] In a specific embodiment, the temperature of the heating pretreatment is 150°C-300°C, for example, it can be 150°C, 200°C, 250°C or 300°C, and the time of the heating pretreatment is 2h-10h, for example, it can be 2h, 4h, 6h, 8h or 10, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0072] In a specific embodiment, the sintering temperature is 800°C-1000°C, for example, it can be 800°C, 900°C or 1000°C, the sintering time is 20h-28h, for example, it can be 20h, 22h, 24h, 26h or 28h, and the sintering heating rate is 1°C / min-5°C / min, for example, it can be 1°C / min, 2°C / min, 3°C / min, 4°C / min or 5°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0073] In a third aspect, the present invention provides a positive electrode plate, which includes the doped and coated lithium-rich compound as described in the first aspect, or the doped and coated lithium-rich compound prepared by the preparation method described in the second aspect.

[0074] In a specific embodiment, in the positive electrode plate, the added amount of the doped and coated lithium-rich compound is less than or equal to 2wt% of the mass of the positive electrode active material, for example, it can be 2wt%, 1.5wt% or 1wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0075] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the doped and coated lithium-rich compound as described in the first aspect, or the doped and coated lithium-rich compound prepared by the preparation method described in the second aspect, or the positive electrode sheet as described in the fourth aspect.

[0076] Example 1

[0077] This embodiment provides a doped and coated lithium-rich compound, comprising a core and a coating layer on the surface of the core, wherein the core comprises La-doped Li5FeO4, wherein the doping molar amount of La is 0.2 mol% of the molar amount of Fe;

[0078] The coating layer includes graphene oxide; the content of the coating layer in the doped and coated lithium-rich compound is 0.7 wt%;

[0079] The preparation method of the doped and coated lithium-rich compound comprises the following steps:

[0080] (1) LaCl3 was dissolved in anhydrous ethanol to obtain a rare earth metal source solution with a concentration of 0.05 mol / L, CH3COOLi, Fe2O3, citric acid and anhydrous ethanol were mixed in a weight ratio of 70:50:20:250 to obtain a mixed solution, the rare earth metal source solution and the mixed solution were mixed in a volume ratio of 1:1, the pH was adjusted to 6.5, and a sol was obtained by ultrasonic treatment, which was dried to form a xerogel.

[0081] Then, under inert gas protection, the dry gel was ball-milled at a speed of 520 rpm for 5 hours until the powder particle size was 500 nm. The ball-milled powder was heated at 200°C for 4 hours, and then heated to 900°C at a heating rate of 3°C / min and sintered at high temperature for 24 hours to obtain a rare earth-doped lithium-rich compound.

[0082] (2) dispersing graphene oxide in anhydrous ethanol and using ultrasonic vibration to ensure its uniform dispersion, adding polyethyleneimine to the graphene oxide solution to obtain a dispersion having a graphene oxide concentration of 3 mg / mL and a polyethyleneimine concentration of 0.6 wt%, adding the rare earth-doped lithium-rich compound described in step (1) to the dispersion, treating the dispersion at 80° C. for 8 hours using an evaporation-induced self-assembly method, and finally heat-treating the dispersion at a temperature of 220° C. for 5 hours under nitrogen protection to obtain the doped and coated lithium-rich compound.

[0083] The SEM image of the doped and coated lithium-rich compound described in this embodiment is as follows: Figure 2 As shown, the low-resolution TEM image is Figure 3 As shown, the outer layer has an obvious coating structure, and the high-resolution TEM image is shown in Figure 4 As shown, the lattice spacing of 0.187nm corresponding to the (202) crystal plane of the Li5FeO4 material and the amorphous phase structure corresponding to graphene can be seen. The EDS element distribution graph is shown in Figure 5 As shown, it can be seen that Fe, La and C elements are evenly distributed in the material.

[0084] Example 2

[0085] This embodiment provides a doped and coated lithium-rich compound, comprising a core and a coating layer on the surface of the core, wherein the core comprises Y-doped Li5FeO4, wherein the doping molar amount of Y is 0.3 mol% of the molar amount of Fe;

[0086] The coating layer includes graphene oxide; the content of the coating layer in the doped and coated lithium-rich compound is 0.5wt%;

[0087] The preparation method of the doped and coated lithium-rich compound comprises the following steps:

[0088] (1) Y(NO3)3 was dissolved in anhydrous ethanol to obtain a rare earth metal source solution with a concentration of 0.1 mol / L, Li2CO3, Fe2O3, polyacrylic acid and anhydrous ethanol were mixed in a weight ratio of 140:160:50:500 to obtain a mixed solution, the rare earth metal source solution and the mixed solution were mixed in a volume ratio of 3:1, the pH was adjusted to 6.8, and a sol was obtained by ultrasonic treatment, which was dried into a xerogel.

[0089] Then, under inert gas protection, the dry gel was ball-milled at a speed of 500 rpm for 6 hours to a powder particle size of 800 nm. The ball-milled powder was heated at 250°C for 6 hours, then heated to 800°C at a heating rate of 4°C / min and sintered at high temperature for 28 hours to obtain a rare earth-doped lithium-rich compound.

[0090] (2) dispersing graphene oxide in anhydrous ethanol and using ultrasonic vibration to ensure its uniform dispersion, adding polyethyleneimine to the graphene oxide solution to obtain a dispersion having a graphene oxide concentration of 2 mg / mL and a polyethyleneimine concentration of 0.1 wt%, adding the rare earth-doped lithium-rich compound described in step (1) to the dispersion, treating the dispersion at 70° C. for 12 hours using an evaporation-induced self-assembly method, and finally heat-treating the dispersion at 150° C. for 3 hours under nitrogen protection to obtain the doped and coated lithium-rich compound.

[0091] Example 3

[0092] This embodiment provides a doped and coated lithium-rich compound, comprising a core and a coating layer on the surface of the core, wherein the core comprises Sm-doped Li5FeO4, wherein the doping molar amount of Sm is 0.2 mol% of the molar amount of Fe;

[0093] The coating layer comprises graphene oxide; the content of the coating layer in the doped and coated lithium-rich compound is 0.4 wt%;

[0094] The preparation method of the doped and coated lithium-rich compound comprises the following steps:

[0095] (1) SmF3 was dissolved in anhydrous ethanol to obtain a rare earth metal source solution with a concentration of 0.05 mol / L, Li2CO3, Fe(NO3)3, citric acid and anhydrous ethanol were mixed in a weight ratio of 200:230:60:700 to obtain a mixed solution, the rare earth metal source solution and the mixed solution were mixed in a volume ratio of 2:1, citric acid was added to adjust the pH to 7, and a sol was obtained after ultrasonic treatment, which was dried into a xerogel.

[0096] Then, under inert gas protection, the dry gel was ball-milled at a speed of 380 rpm for 4 hours to a powder particle size of 700 nm. The ball-milled powder was pretreated by heating at 150°C for 10 hours, and then heated to 950°C at a heating rate of 5°C / min and sintered at high temperature for 26 hours to obtain a rare earth-doped lithium-rich compound.

[0097] (2) dispersing graphene oxide in anhydrous ethanol and using ultrasonic vibration to ensure its uniform dispersion, adding polyethyleneimine to the graphene oxide solution to obtain a dispersion having a graphene oxide concentration of 1 mg / mL and a polyethyleneimine concentration of 1 wt%, adding the rare earth-doped lithium-rich compound described in step (1) to the dispersion, treating the dispersion at 90° C. for 8 hours using an evaporation-induced self-assembly method, and finally heat-treating the dispersion at 180° C. for 4 hours under nitrogen protection to obtain the doped and coated lithium-rich compound.

[0098] Example 4

[0099] This embodiment provides a doped and coated lithium-rich compound, comprising a core and a coating layer on the surface of the core, wherein the core comprises Ce-doped Li5FeO4, wherein the doping molar amount of Ce is 0.1 mol% of the Fe molar amount;

[0100] The coating layer comprises graphene oxide; the content of the coating layer in the doped and coated lithium-rich compound is 1 wt%;

[0101] The preparation method of the doped and coated lithium-rich compound comprises the following steps:

[0102] (1) CeCl3 was dissolved in anhydrous ethanol to obtain a rare earth metal source solution with a concentration of 0.01 mol / L, Li2O, Fe2O3, citric acid and anhydrous ethanol were mixed in a weight ratio of 220:280:80:800 to obtain a mixed solution, the rare earth metal source solution and the mixed solution were mixed in a volume ratio of 1:1, citric acid was added to adjust the pH to 6, and a sol was obtained after ultrasonic treatment, which was dried to form a xerogel.

[0103] Then, under inert gas protection, the dry gel was ball-milled at 420 rpm for 5 hours until the powder particle size was 1 μm. The ball-milled powder was pretreated by heating at 300°C for 2 hours, then heated to 1000°C at a heating rate of 1°C / min and sintered at high temperature for 20 hours to obtain a rare earth-doped lithium-rich compound.

[0104] (2) dispersing graphene oxide in anhydrous ethanol and using ultrasonic vibration to ensure its uniform dispersion, adding polyethyleneimine to the graphene oxide solution to obtain a dispersion having a graphene oxide concentration of 5 mg / mL and a polyethyleneimine concentration of 0.5 wt%, adding the rare earth-doped lithium-rich compound described in step (1) to the dispersion, treating it at 75° C. for 8 hours using an evaporation-induced self-assembly method, and finally heat-treating it at a temperature of 230° C. for 3 hours under nitrogen protection to obtain the doped and coated lithium-rich compound.

[0105] Example 5

[0106] This embodiment provides a doped and coated lithium-rich compound, which is the same as that of Example 1 except that the core of the doped and coated lithium-rich compound includes La-doped LiNiO2 and the doping molar amount of La is 0.2 mol% of the molar amount of Ni.

[0107] The preparation method of the doped and coated lithium-rich compound described in this embodiment is the same as that of Example 1, except that Fe2O3 is replaced by nickel nitrate according to the formula amount.

[0108] Example 6

[0109] This embodiment provides a doped and coated lithium-rich compound, which is the same as that of Example 1 except that the doping molar amount of La is 0.05 mol% of the Fe molar amount;

[0110] The preparation method of the doped and coated lithium-rich compound is the same as that of Example 1 except that the formula amounts are changed.

[0111] Example 7

[0112] This embodiment provides a doped and coated lithium-rich compound, which is the same as that of Example 1 except that the doping molar amount of La is 0.5 mol% of the Fe molar amount;

[0113] The preparation method of the doped and coated lithium-rich compound is the same as that of Example 1 except that the formula amounts are changed.

[0114] Example 8

[0115] This embodiment provides a doped and coated lithium-rich compound. The doped and coated lithium-rich compound is the same as Example 1 except that in its preparation method, the evaporation-induced self-assembly method is not used to treat the compound at 80°C for 8 hours, but the compound is refluxed at 80°C for 8 hours to make the obtained doped and coated lithium-rich compound adaptable.

[0116] Example 9

[0117] This embodiment provides a doped and coated lithium-rich compound, which is the same as Example 1 except that polyethyleneimine is not added in the preparation method to adapt the obtained doped and coated lithium-rich compound.

[0118] Comparative Example 1

[0119] This comparative example provides a lithium-rich compound, which is Li5FeO4.

[0120] Comparative Example 2

[0121] This comparative example provides a lithium-rich compound, which is the same as Example 1 except that it does not contain a coating layer.

[0122] The preparation method of the lithium-rich compound described in this comparative example is the same as that of Example 1 except that step (2) is not performed.

[0123] Comparative Example 3

[0124] This comparative example provides a lithium-rich compound, which is the same as Example 1 except that it does not contain the La doping element.

[0125] The preparation method of the lithium-rich compound in this comparative example is the same as that in Example 1, except that no rare earth metal source is added during the preparation of the lithium-rich compound.

[0126] Lithium storage performance test of the lithium-rich compounds of the above examples and comparative examples:

[0127] The lithium-rich compounds of the above embodiments and comparative examples were uniformly mixed with conductive carbon black and a binder in a mass ratio of 8:1:1 to prepare a composite electrode as a working electrode, a metal lithium sheet was used as a counter electrode, and a LiPF6 solution with a concentration of 1 mol / L (ED, DMC, EMC volume ratio of 1:1:1) was used as an electrolyte to assemble into a lithium-rich compound battery. Then, a charge and discharge test was performed between 2.5 and 4.5 V. The 0.1C first cycle charge specific capacity, 0.1C first cycle discharge specific capacity, 0.1C first cycle irreversible capacity, 0.2C first cycle charge specific capacity, 0.2C first cycle discharge specific capacity, 0.2C first cycle irreversible capacity, 0.5C first cycle charge specific capacity, 0.5C first cycle discharge specific capacity and 0.5C first cycle irreversible capacity obtained by the test are shown in Table 1. The charge and discharge curves of the lithium-rich compound battery prepared from the lithium-rich compound of Example 1 are shown in Table 1. Figure 6 As shown by Figure 6 It can be seen that the lithium-rich compound battery prepared with the material of Example 1 has excellent lithium storage performance and rate performance.

[0128] Table 1

[0129]

[0130]

[0131] Lithium iron phosphate, the lithium-rich lithium ferrite material provided in the above embodiments and comparative examples, conductive carbon black, and a binder were uniformly mixed in a mass ratio of 78:2:10:10 to form a composite electrode as a working electrode, graphite was used as a counter electrode, N / P=1.1, and a LiPF6 solution with a concentration of 1 mol / L (ED, DMC, EMC volume ratio of 1:1:1) was used as an electrolyte to assemble a lithium iron phosphate battery. The charge and discharge test was carried out between 2.7 and 4.5 V in the first cycle, and the charge and discharge test was carried out between 2.8 and 3.65 V in the cycle stage. The capacity retention rate of 200 cycles obtained by the test is shown in Table 2. The cycle performance diagram of the lithium iron phosphate battery prepared by using the lithium-rich compounds of Example 1 and Comparative Example 1 as lithium supplements is shown in FIG. Figure 7 As shown by Figure 7 It can be seen that the lithium iron phosphate battery prepared by using the lithium-rich compound of Example 1 as a lithium supplement has excellent cycle performance.

[0132] The lithium iron phosphate battery prepared above was tested for its high-temperature storage performance. The testing method included storing the lithium iron phosphate battery at 25°C, 40°C, 50°C, and 60°C for 7 days, and measuring gas production using a needle-type gas collector. The gas production at different temperatures is shown in Table 2.

[0133] Table 2

[0134]

[0135]

[0136] The deterioration time of the lithium-rich compounds provided in the above examples and comparative examples under different air humidity conditions is compared. When the LiOH content in the material is greater than 5 mol% as measured by XRD, it indicates that the material has deteriorated. The stability time of the material obtained by the test is shown in Table 3:

[0137] Table 3

[0138]

[0139]

[0140] From Tables 1 to 3 we can see that:

[0141] It can be seen from Examples 1-4 and Comparative Examples 1-3 that the present invention dopes rare earth elements and coats graphene oxide in lithium-rich compounds, which can enhance the structural stability of the material, improve the cycle performance and rate performance of lithium-ion batteries, reduce high-temperature storage gas production, and ensure that the material is not easily deteriorated in air and humidity environments; it can be seen from Example 1 and Example 5 that the lithium-rich compound of the present invention can be lithium-rich lithium ferrite or lithium-rich lithium nickelate; it can be seen from Example 1 and Examples 6-7 that the doping amount of rare earth elements in the present invention will affect the stability and gas production of the material, thereby affecting the cycle performance and high-temperature storage performance of the battery; it can be seen from Example 1 and Example 8 that the present invention preferably adopts evaporation-induced self-assembly method to coat graphene oxide, which can improve the uniformity of the coating layer and the bonding strength with the core, thereby promoting the coating layer to exert excellent effects, which is beneficial to improving the comprehensive performance of the battery; it can be seen from Example 1 and Example 9 that the present invention preferably adds an amine structural template agent to the coating liquid, which is beneficial for it to act as a bridge, enhance the bonding strength between the core and the coating layer, and improve the performance of the battery.

[0142] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A doped and coated lithium-rich compound, characterized in that: The doped and coated lithium-rich compound comprises a core and a coating layer on the surface of the core, the core comprises a lithium-rich compound doped with a rare earth element, and the coating layer comprises graphene oxide.

2. The doped and coated lithium-rich compound according to claim 1, characterized in that The rare earth element doped lithium-rich compound includes rare earth element doped lithium-rich lithium ferrite and / or rare earth element doped lithium-rich lithium nickelate; And / or, in the core, the doping molar amount of the rare earth element is 0.1 mol% to 0.3 mol% of the molar amount of the transition metal element in the lithium-rich compound.

3. The doped and coated lithium-rich compound according to claim 1 or 2, characterized in that In the doped and coated lithium-rich compound, the content of the coating layer is 0.4 wt%-1 wt%.

4. A method for preparing a doped and coated lithium-rich compound according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: A rare earth element-doped lithium-rich compound is prepared by a sol-gel method; the rare earth element-doped lithium-rich compound is dispersed in a coating solution for coating, and finally heat-treated to obtain the doped and coated lithium-rich compound; The coating solution includes graphene oxide and an amine structure template.

5. The preparation method according to claim 4, characterized in that The coating treatment is performed using an evaporation-induced self-assembly method; The evaporation-induced self-assembly method has a processing temperature of 70° C.-90° C. and a processing time of 8 h-12 h.

6. The preparation method according to claim 4 or 5, characterized in that The amine structure template includes any one of polyethyleneimine, polyacrylamine or polyamide, or a combination of at least two thereof; and / or, the pH of the coating solution is 9-11; And / or, in the coating solution, the concentration of graphene oxide is 1 mg / mL-5 mg / mL, and the mass concentration of the amine structure template is 0.1 wt%-1 wt%; And / or, the heat treatment temperature is 150° C.-230° C., the heat treatment time is 3 h-6 h, and is performed in a protective atmosphere.

7. The preparation method according to claim 4 or 5, characterized in that The method for preparing the rare earth element-doped lithium-rich compound comprises the following steps: A lithium source, a transition metal source, a rare earth metal source, a complexing agent and a solvent are mixed to prepare a sol, and then dried to obtain a xerogel, wherein the transition metal source includes an iron source and / or a nickel source; The dry gel is then subjected to ball milling, heat pretreatment and sintering treatment in sequence to obtain the rare earth element-doped lithium-rich compound.

8. The preparation method according to claim 7, characterized in that The mass ratio of the lithium source, transition metal source, complexing agent and solvent is (70-220):(50-280):(20-80):(250-800); And / or, the ball milling speed is 380 rpm-520 rpm, the ball milling time is 4 h-6 h, and the particle size of the ball milled powder is in the range of 500 nm-1 μm; And / or, the temperature of the heating pretreatment is 150° C.-300° C., and the time of the heating pretreatment is 2 h-10 h; And / or, the sintering temperature is 800° C.-1000° C., the sintering time is 20 h-28 h, and the sintering heating rate is 1° C. / min-5° C. / min.

9. A positive electrode plate, characterized in that: The positive electrode plate comprises the doped and coated lithium-rich compound according to any one of claims 1 to 3, or the doped and coated lithium-rich compound prepared by the preparation method according to any one of claims 4 to 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the doped and coated lithium-rich compound according to any one of claims 1 to 3, or the doped and coated lithium-rich compound prepared by the preparation method according to any one of claims 4 to 8, or the positive electrode sheet according to claim 9.

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