Composite coated lithium-rich lithium ferrite material as well as preparation method and application thereof

Abstract

The invention provides a composite coated lithium-rich lithium ferrite material and a preparation method and application thereof.The composite coated lithium-rich lithium ferrite material comprises an inner core and a composite coating layer on the surface of the inner core, and the inner core comprises lithium-rich lithium ferrite; the composite coating layer comprises hydrophobic polymer layers and metal oxide layers which are alternately stacked, the coating layer closest to the inner core is the hydrophobic polymer layer or the metal oxide layer, and the coating layer farthest from the inner core is the hydrophobic polymer layer or the metal oxide layer; the number of the hydrophobic polymer layers is larger than or equal to 2, and the number of the metal oxide layers is larger than or equal to 2. According to the composite coated lithium-rich lithium ferrite material disclosed by the invention, the hydrophobic polymer layers and the metal oxide layers are alternately coated, so that the conductivity and the stability of the lithium-rich lithium ferrite material are improved, the lithium-rich lithium ferrite material is also endowed with hydrophobicity, the gelation phenomenon in the slurry stirring process is prevented, and the service life of the lithium-rich lithium ferrite material is prolonged. And the cycling stability and the rate capability of the lithium ion battery can be effectively improved.

Description

Technical Field

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

[0002] Lithium-ion batteries, with their high energy density, long cycle life, high efficiency, and safety, have become a core energy storage technology in modern electronic devices, electric vehicles, and large-scale energy storage systems. However, despite significant progress in the application of lithium-ion batteries in various fields, the problem of performance degradation during long-term use remains unresolved. In particular, challenges in the stability, capacity retention, and conductivity of battery anode and cathode materials have become bottlenecks affecting battery performance.

[0003] Lithium-rich ferrite (Li5FeO4), a lithium-supplementing material, is widely used in cathode mixing in lithium-ion batteries due to its high specific capacity and excellent pre-lithiation properties. It has the potential to extend battery life and increase energy density. However, the surface of Li5FeO4 readily reacts with oxygen and carbon dioxide in the air, forming a high-impedance surface film (such as Li2CO3 and LiOH), which affects its electrochemical activity, leading to capacity fading and shortened cycle life.

[0004] In order to solve the above problems, it is necessary to provide a lithium-rich lithium ferrite material, the coating layer of which has excellent performance and can effectively improve the cycle stability and rate performance of lithium-ion batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite-coated lithium-rich lithium ferrite material and its preparation method and application to solve the above problems.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a composite-coated lithium-rich ferrite material, which includes a core and a composite coating layer on the surface of the core, wherein the core includes lithium-rich ferrite, and the composite coating layer includes a hydrophobic polymer layer and a metal oxide layer alternately stacked.

[0008] In the composite coating layer, the coating layer closest to the core is a hydrophobic polymer layer or a metal oxide layer, and the coating layer farthest from the core is a hydrophobic polymer layer or a metal oxide layer.

[0009] In the composite coating layer, the number of the hydrophobic polymer layer is ≥2, and the number of the metal oxide layer is ≥2.

[0010] In some embodiments, the number of the hydrophobic polymer layer is 4-10 layers.

[0011] In some embodiments, the number of the metal oxide layers is 4 to 10.

[0012] In some embodiments, in the composite coating layer, the coating layer farthest from the core is a hydrophobic polymer layer.

[0013] In some embodiments, the thickness of a single layer of the hydrophobic polymer layer is 5 nm-10 nm.

[0014] In some embodiments, the thickness of a single metal oxide layer is 5 nm to 10 nm.

[0015] In some embodiments, the total thickness of the composite coating layer is 50 nm-100 nm.

[0016] In some embodiments, in the composite-coated lithium-rich lithium ferrite material, the total content of the composite coating layer is 0.6 wt %-1.5 wt %.

[0017] In some embodiments, in the composite coating layer, the mass ratio of the metal oxide layer to the hydrophobic polymer layer is (2-3):1.

[0018] In some embodiments, the hydrophobic polymer layer includes a hydrophobic polymer material and / or a cross-linked product of a hydrophobic polymer material, and the hydrophobic polymer material includes polystyrene and / or polytetrafluoroethylene.

[0019] In some embodiments, the metal oxide layer includes ZnO or TiO2.

[0020] In a second aspect, the present invention provides a method for preparing the composite-coated lithium-rich lithium ferrite material as described in the first aspect, the preparation method comprising the following steps:

[0021] The lithium-rich lithium ferrite is first cleaned and pretreated, then alternately coated with a hydrophobic polymer material and a metal oxide, and finally heat-treated to obtain the composite-coated lithium-rich lithium ferrite material.

[0022] The number of times the hydrophobic polymer material is coated is ≥2 times, and the number of times the metal oxide is coated is ≥2 times.

[0023] In the process of alternately coating the hydrophobic polymer material and the metal oxide, the first coating is the hydrophobic polymer material or the metal oxide, and the last coating is the hydrophobic polymer material or the metal oxide.

[0024] In some embodiments, in the process of alternating coating of the hydrophobic polymer material and the metal oxide, the last coating is the hydrophobic polymer material.

[0025] In some embodiments, during the process of alternately coating the hydrophobic polymer material and the metal oxide, solid-liquid separation and drying are performed after each coating, and then the next coating is performed.

[0026] In some embodiments, the hydrophobic polymer material and the metal oxide are coated by a liquid phase coating method, wherein the solvent used in the liquid phase coating method includes an anhydrous organic solvent.

[0027] In some embodiments, the method of coating the polymer material includes: dispersing the object to be coated in a solution of a hydrophobic polymer material for self-assembly coating the water-transporting polymer material, wherein the concentration of the solution of the hydrophobic polymer material is 10 mg / mL-25 mg / mL.

[0028] In some embodiments, the method of coating the metal oxide includes: dispersing the object to be coated in a metal oxide solution for self-assembly coating the metal oxide, wherein the concentration of the metal oxide solution is 0.5 mg / mL-2 mg / mL.

[0029] In some embodiments, the cleaning pretreatment comprises the following steps: dispersing the lithium-rich lithium ferrite in an anhydrous organic solvent, and then washing with the anhydrous organic solvent.

[0030] In some embodiments, the heat treatment temperature is 180° C.-220° C., and the heat treatment time is 3 h-6 h.

[0031] In a third aspect, the present invention provides a positive electrode plate, which includes the composite-coated lithium-rich lithium ferrite material as described in the first aspect, or the composite-coated lithium-rich lithium ferrite material prepared by the preparation method described in the second aspect.

[0032] In a fourth aspect, the present invention provides a lithium-ion battery, which includes the composite-coated lithium-rich ferrite material as described in the first aspect, or the composite-coated lithium-rich ferrite material prepared by the preparation method described in the second aspect, or the positive electrode sheet as described in the third aspect.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention can prevent the lithium-rich ferrite from reacting with oxygen and carbon dioxide in the air by alternately coating the surface of the lithium-rich ferrite with multiple layers of hydrophobic polymer layers and multiple layers of metal oxide layers, thereby forming a stable conductive network on the surface of the lithium-rich ferrite, promoting the transmission of lithium ions in the electrode, significantly improving the charge and discharge rate performance of the electrode, increasing the interface reaction area between the lithium-rich ferrite and the electrolyte, promoting ion transmission, and thus improving the charge and discharge performance of the battery, especially the performance under high-rate discharge conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a flow chart of the preparation method.

[0036] Figure 2 This is an SEM image of the composite-coated lithium-rich lithium ferrite material described in Example 1 of the present invention.

[0037] Figure 3 This is a low-magnification TEM image (200 nm scale) of the composite-coated lithium-rich lithium ferrite material described in Example 1 of the present invention.

[0038] Figure 4 This is a high-magnification TEM image (5 nm scale) of the composite-coated lithium-rich lithium ferrite material described in Example 1 of the present invention.

[0039] Figure 5 The charge and discharge curves of the lithium-rich lithium ferrite battery prepared using the lithium-rich lithium ferrite materials described in Example 1 and Comparative Example 1 of the present invention at 0.05C are shown, wherein Example 1 corresponds to the experimental group curve in the figure, and Comparative Example 1 corresponds to the blank group curve in the figure.

[0040] Figure 6 The graph is a cycle performance graph of a lithium iron phosphate battery prepared using the lithium-rich lithium ferrite material described in Example 1 and Comparative Example 1 of the present invention as a lithium supplement. The graph corresponds to the LFP-2% lithium supplement / Gr curve in Example 1, and the graph corresponds to the LFP / Gr curve in Comparative Example 1. DETAILED DESCRIPTION

[0041] 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 specific embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0042] In the first aspect, the present invention provides a composite-coated lithium-rich ferrite material, which includes a core and a composite coating layer on the surface of the core, wherein the core includes lithium-rich ferrite, and the composite coating layer includes a hydrophobic polymer layer and a metal oxide layer alternately stacked.

[0043] In the composite coating layer, the coating layer closest to the core is a hydrophobic polymer layer or a metal oxide layer, and the coating layer farthest from the core is a hydrophobic polymer layer or a metal oxide layer.

[0044] In the composite coating layer, the number of the hydrophobic polymer layer is ≥2, and the number of the metal oxide layer is ≥2.

[0045] The present invention alternately coats multiple layers of hydrophobic polymer layers and multiple layers of metal oxide layers. Compared with coating only one hydrophobic polymer layer and coating only one metal oxide layer, even if the total thickness of the coating layer is the same, the multi-layer alternating coating of the present invention effectively suppresses the phase change and volume expansion of lithium-rich lithium ferrite during charging and discharging by uniformly dispersing stress, and can construct a stable three-dimensional conductive channel on the surface of the material through alternating coating.

[0046] The present invention alternately coats the surface of the lithium-rich lithium ferrite with multiple layers of hydrophobic polymer layers and multiple layers of metal oxide layers, and has the following advantages: it can prevent the lithium-rich lithium ferrite from reacting with oxygen and carbon dioxide in the air, form a stable conductive network on the surface of the lithium-rich lithium ferrite, promote the transmission of lithium ions in the electrode, significantly improve the charge and discharge rate performance of the electrode, increase the interface reaction area between the lithium-rich lithium ferrite and the electrolyte, promote ion transmission, and thus improve the charge and discharge performance of the battery, especially the performance under high-rate discharge conditions.

[0047] In addition, during the initial charge and discharge process of the battery, lithium-rich lithium iron oxide may also cause gelation due to reasons such as surface water absorption and excessive surface alkalinity, further affecting the stability and efficiency of the battery. The present invention can reduce the gelation phenomenon of the slurry by alternating multiple layers of hydrophobic polymer and multiple layers of metal oxide. The composite coating layer can enhance the compatibility of lithium-rich lithium iron oxide particles with the electrolyte and other materials, reducing the gelation phenomenon in the slurry. This improvement can ensure the fluidity and uniformity of the slurry during the battery production process, avoid the manufacturing difficulty and performance instability caused by gelation, and thus improve production efficiency and product consistency.

[0048] The alternating multi-layer hydrophobic polymer layer and multi-layer metal oxide layer of the present invention can also improve the stability of lithium-rich lithium ferrite, effectively inhibit the phase change and structural instability of lithium-rich lithium ferrite during the cycle process, and improve the tolerance of lithium-rich lithium ferrite under high temperature conditions. It not only improves the thermal stability of the material, but also enhances the safety performance of the battery and reduces the risk of thermal runaway.

[0049] In summary, the present invention effectively solves the problems of poor stability of lithium-rich lithium ferrite, easy reaction with oxygen and carbon dioxide in the air, easy gelation of slurry, and poor conductivity of the coating layer.

[0050] In the composite coating layer described in the present invention, the coating layer closest to the core is a hydrophobic polymer layer or a metal oxide layer, which means that the coating layer first coated on the surface of the core can be a hydrophobic polymer layer or a metal oxide layer, and the coating layer farthest from the core is a hydrophobic polymer layer or a metal oxide layer, which means the last coated coating layer, that is, the outermost coating layer of the material can be a hydrophobic polymer layer or a metal oxide layer.

[0051] The chemical formula of the lithium-rich lithium ferrite of the present invention is Li5FeO4.

[0052] In the composite coating layer of the present invention, the number of layers of the hydrophobic polymer layer is ≥2 layers, for example, it can be 2 layers, 3 layers, 4 layers, 5 layers, 6 layers, 7 layers, 8 layers, 9 layers, 10 layers, 11 layers, 12 layers, 13 layers, 14 layers or 15 layers, and more preferably 4 layers to 10 layers.

[0053] The number of metal oxide layers of the present invention is ≥2 layers, for example, it can be 2 layers, 3 layers, 4 layers, 5 layers, 6 layers, 7 layers, 8 layers, 9 layers, 10 layers, 11 layers, 12 layers, 13 layers, 14 layers or 15 layers, and more preferably 4 layers to 10 layers.

[0054] The hydrophobic polymer layer and metal oxide layer of the present invention are preferably 4-10 layers respectively. If the number of layers is too small, the conductive network formed in the coating layer is discontinuous, ion transmission is limited, the barrier effect is insufficient, and the environmental stability is poor. If the number of layers is too large, the ion transmission resistance increases and the dynamic performance decreases.

[0055] In a specific embodiment, in the composite coating layer, the coating layer farthest from the core is a hydrophobic polymer layer.

[0056] The present invention preferably coats the outermost layer with a hydrophobic polymer layer. Since the metal oxide layer easily reacts with the electrolyte, especially at high temperatures, the outermost hydrophobic polymer layer can further enhance the stability of the lithium-rich lithium ferrite material.

[0057] In a specific embodiment, the thickness of the single-layer hydrophobic polymer layer is 5nm-10nm, for example, it can be 5nm, 6nm, 7nm, 8nm, 9nm or 10nm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0058] In a specific embodiment, the thickness of the single-layer metal oxide layer is 5nm-10nm, for example, it can be 5nm, 6nm, 7nm, 8nm, 9nm or 10nm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0059] In the present invention, when the total thickness of the composite coating layer is the same, the thickness of the single coating layer will affect the number of coating layers, and when the number of coating layers is the same, it will affect the total thickness of the composite coating layer. Therefore, when the total thickness of the composite coating layer is the same, if the thickness of the single hydrophobic polymer layer or the single metal oxide layer is too thin, the number of layers of the corresponding coating layer will be too many. If the thickness of the single hydrophobic polymer layer or the single metal oxide layer is too thick, the number of layers of the corresponding coating layer will be too few. When the number of coating layers is the same, if the thickness of the single hydrophobic polymer layer or the single metal oxide layer is too thin, the thickness of the composite coating layer will be too small, and the barrier effect of the coating layer will be weakened. If the thickness of the single hydrophobic polymer layer or the single metal oxide layer is too thick, the thickness of the composite coating layer will be too large, which will hinder ion transmission and concentrate mechanical stress, making the coating layer prone to cracking.

[0060] In a specific embodiment, the total thickness of the composite coating layer is 50nm-100nm, for example, it can be 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm or 100nm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0061] In a specific embodiment, in the composite-coated lithium-rich lithium ferrite material, the total content of the composite coating layer is 0.6wt%-1.5wt%, for example, it can be 0.6wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt% or 1.5wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] In a specific embodiment, in the composite coating layer, the mass ratio of the metal oxide layer to the hydrophobic polymer layer is (2-3):1, for example, it can be 2:1, 2.5:1 or 3:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0063] In a specific embodiment, the hydrophobic polymer layer includes a hydrophobic polymer material and / or a cross-linked product of a hydrophobic polymer material, and the hydrophobic polymer material includes polystyrene and / or polytetrafluoroethylene.

[0064] In one embodiment, the molecular weight of the polystyrene is 100,000-500,000, for example, 100,000, 200,000, 300,000, 400,000 or 500,000, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0065] In one specific embodiment, the metal oxide layer includes ZnO and / or TiO2.

[0066] In the second aspect, the present invention provides a method for preparing the composite coated lithium-rich ferrite material 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:

[0067] S1: First, the lithium-rich lithium ferrite is cleaned and pre-treated.

[0068] S2: Then alternately coating the hydrophobic polymer material and the metal oxide, the number of times the hydrophobic polymer material is coated is ≥2 times, the number of times the metal oxide is coated is ≥2 times, and the first coating is the hydrophobic polymer material or the metal oxide, and the last coating is the hydrophobic polymer material or the metal oxide.

[0069] S3: Finally, heat treatment is performed to obtain the composite-coated lithium-rich lithium ferrite material.

[0070] The present invention first pre-treats the lithium-rich lithium ferrite by cleaning to remove moisture, impurities and bubbles on the surface of the particles to ensure that there is no moisture in the material. It then alternately coats the particles with a hydrophobic polymer material and a metal oxide, and finally performs a heat treatment to further enhance the strength of the coating layer. At the same time, the surface of the hydrophobic polymer material is thermally stabilized to improve its hydrophobicity and heat resistance.

[0071] Corresponding to the composite-coated lithium-rich lithium ferrite material product of the present invention, the number of times the hydrophobic polymer material is coated is ≥2 times, and the number of times the metal oxide is coated is ≥2 times, forming a multi-layer alternatingly coated hydrophobic polymer layer and metal oxide layer, and the first coating is a hydrophobic polymer material, which can also be a metal oxide, and the last coating is a hydrophobic polymer material, which can also be a metal oxide.

[0072] In a specific embodiment, in the process of alternately coating the hydrophobic polymer material and the metal oxide, the last coating is the hydrophobic polymer material, so that the outermost coating layer is the hydrophobic polymer layer.

[0073] In a specific embodiment, during the process of alternately coating the hydrophobic polymer material and the metal oxide, solid-liquid separation and drying are performed after each coating, and then the next coating is performed.

[0074] In a specific embodiment, the hydrophobic polymer material and the metal oxide are coated by a liquid phase coating method, wherein the solvent used in the liquid phase coating method includes an anhydrous organic solvent.

[0075] In one specific embodiment, the method for coating the polymer material includes: dispersing the object to be coated in a solution of a hydrophobic polymer material for self-assembly to coat the water-transferring polymer material, wherein the concentration of the solution of the hydrophobic polymer material is 10 mg / mL-25 mg / mL, for example, it can be 10 mg / mL, 15 mg / mL, 20 mg / mL or 25 mg / mL, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0076] In one embodiment, an ultrasonic cleaner is used to disperse the object to be coated in a solution of a hydrophobic polymer material, and the dispersion time is 15 min to 30 min, for example, 15 min, 20 min, 25 min or 30 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0077] In one specific embodiment, the method for coating the metal oxide includes: dispersing the object to be coated in a metal oxide solution for self-assembly coating the metal oxide, wherein the concentration of the metal oxide solution is 0.5 mg / mL-2 mg / mL, for example, it can be 0.5 mg / mL, 1 mg / mL, 1.5 mg / mL or 2 mg / mL, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0078] The present invention dissolves a hydrophobic polymer material in an anhydrous organic solvent and stirs the solution until it is completely transparent to obtain a solution of the hydrophobic polymer material. A metal oxide is added to the same solvent as the solution of the hydrophobic polymer material to form a solution of the metal oxide. The solution is subjected to magnetic stirring and ultrasonic treatment under a nitrogen protective atmosphere to ensure the uniformity of the solution.

[0079] In one specific embodiment, an ultrasonic cleaner is used to disperse the object to be coated in a metal oxide solution, and the dispersion time is 15 min to 30 min, for example, 15 min, 20 min, 25 min or 30 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0080] In a specific embodiment, the cleaning pretreatment comprises the following steps: dispersing the lithium-rich lithium ferrite in an anhydrous organic solvent, and then washing with the anhydrous organic solvent.

[0081] The method involves adding lithium-rich lithium manganate particles to an anhydrous organic solvent and using an ultrasonic cleaner to remove moisture, impurities, and bubbles from the particle surface. The particles are then repeatedly washed with the anhydrous organic solvent at room temperature until the washing solution becomes completely transparent, ensuring the material is free of moisture.

[0082] In a specific embodiment, the anhydrous organic solvent includes any one of anhydrous cyclohexane, anhydrous n-hexane or anhydrous dichloromethane, or a combination of at least two thereof.

[0083] In a specific embodiment, the heat treatment temperature is 180° C.-220° C., and the heat treatment time is 3 h-6 h.

[0084] In one embodiment, the heat treatment is performed under a protective atmosphere, such as a nitrogen atmosphere.

[0085] The technical solution of the present invention is further illustrated below through specific embodiments.

[0086] Example 1

[0087] This embodiment provides a composite-coated lithium-rich lithium ferrite material, including a core and a composite coating layer on the surface of the core, the core includes Li5FeO4, and the composite coating layer includes alternatingly stacked hydrophobic polymer layers (made of polystyrene) and metal oxide layers (made of ZnO), wherein the coating layer closest to the core is the hydrophobic polymer layer, and the coating layer farthest from the core is the hydrophobic polymer layer.

[0088] The total thickness of the composite coating layer is 50 nm, the number of the hydrophobic polymer layer is 5, and the thickness of a single hydrophobic polymer layer is 5 nm, the number of the metal oxide layer is 4, and the thickness of a single metal oxide layer is 6.25 nm.

[0089] In the composite-coated lithium-rich lithium ferrite material, the total content of the composite coating layer is 0.6 wt %, and in the composite coating layer, the mass ratio of the metal oxide layer to the hydrophobic polymer layer is 2:1.

[0090] The preparation method of the composite coated lithium-rich lithium ferrite material comprises the following steps:

[0091] (1) 1 g of Li5FeO4 particles were added to 10 mL of anhydrous cyclohexane and treated with an ultrasonic cleaner for 30 min to remove moisture, impurities and bubbles on the surface of the particles. Then, the Li5FeO4 particles were repeatedly washed with anhydrous cyclohexane at room temperature until the washing liquid was completely transparent to ensure that the material was free of moisture, thereby obtaining pretreated Li5FeO4 particles.

[0092] (2) Polystyrene (molecular weight of 300,000) was dissolved in anhydrous cyclohexane to obtain a polymer solution with a concentration of 15 mg / mL, and ZnO powder was added to the anhydrous cyclohexane to form a ZnO solution with a concentration of 1 mg / mL.

[0093] (3) adding the pretreated Li5FeO4 particles in step (1) to the polymer solution in step (1), and treating them with an ultrasonic cleaner for 25 minutes to ensure that the polystyrene uniformly coats the particle surface; then, alternately dispersing the Li5FeO4 particles in the ZnO solution and the polymer solution, wherein the particles are dispersed in the polymer solution 5 times and in the ZnO solution 4 times; after each dispersion, the excess solvent is removed by centrifugation and dried; finally, the coated particles are placed in a high-temperature furnace protected by nitrogen for heat treatment at a temperature of 200°C for 4 hours to obtain the composite-coated lithium ferrite-rich material.

[0094] The SEM image of the composite coated lithium-rich lithium ferrite material of this embodiment is as follows: Figure 2 As shown, the low magnification TEM image is as follows Figure 3 As shown in the high magnification TEM image Figure 4 As shown, combined Figure 2-Figure 4 It can be seen that the outer layer has an obvious coating structure, and Figure 4 It can be seen that the ZnO (102) crystal plane corresponds to a lattice spacing of 0.19 nm, and the Li5FeO4 material (202) crystal plane corresponds to a lattice spacing of 0.187 nm, as well as the amorphous phase structure corresponding to the organic hydrophobicity.

[0095] Example 2

[0096] This embodiment provides a composite-coated lithium-rich lithium ferrite material, which includes a core and a composite coating layer on the surface of the core, wherein the core includes Li5FeO4, and the composite coating layer includes alternatingly stacked hydrophobic polymer layers (made of polytetrafluoroethylene) and metal oxide layers (made of TiO2), wherein the coating layer closest to the core is the hydrophobic polymer layer, and the coating layer farthest from the core is the hydrophobic polymer layer.

[0097] The total thickness of the composite coating layer is 80 nm, the number of the hydrophobic polymer layer is 6, the thickness of a single hydrophobic polymer layer is 7 nm, the number of the metal oxide layer is 5, and the thickness of a single metal oxide layer is 7.6 nm.

[0098] In the composite-coated lithium-rich lithium ferrite material, the total content of the composite coating layer is 1.1 wt %, and in the composite coating layer, the mass ratio of the metal oxide layer to the hydrophobic polymer layer is 2.5:1.

[0099] The preparation method of the composite coated lithium-rich lithium ferrite material comprises the following steps:

[0100] (1) 2 g of Li5FeO4 particles were added to 15 mL of anhydrous n-hexane and treated with an ultrasonic cleaner for 15 min to remove moisture, impurities and bubbles on the surface of the particles. Then, the Li5FeO4 particles were repeatedly washed with anhydrous n-hexane at room temperature until the washing liquid was completely transparent to ensure that the material was free of moisture, thereby obtaining pretreated Li5FeO4 particles.

[0101] (2) Dissolve polytetrafluoroethylene (molecular weight 2 million) in anhydrous n-hexane to obtain a polymer solution with a concentration of 10 mg / mL, and add TiO2 powder to anhydrous n-hexane to form a TiO2 solution with a concentration of 2 mg / mL.

[0102] (3) adding the pretreated Li5FeO4 particles in step (1) to the polymer solution in step (1), and treating them with an ultrasonic cleaner for 30 minutes to ensure that polytetrafluoroethylene evenly coats the surface of the particles; then, alternately dispersing the Li5FeO4 particles in the TiO2 solution and the polymer solution, wherein the particles are dispersed in the polymer solution for 6 times and in the TiO2 solution for 5 times; after each dispersion, the excess solvent is removed by centrifugation and dried; finally, the coated particles are placed in a high-temperature furnace protected by nitrogen for heat treatment at a temperature of 180°C for 6 hours to obtain the composite-coated lithium ferrite-rich material.

[0103] Example 3

[0104] This embodiment provides a composite-coated lithium-rich lithium ferrite material, which includes a core and a composite coating layer on the surface of the core, wherein the core includes Li5FeO4, and the composite coating layer includes a hydrophobic polymer layer (made of polystyrene) and a metal oxide layer (made of TiO2) alternately stacked, wherein the coating layer closest to the core is the hydrophobic polymer layer, and the coating layer farthest from the core is the metal oxide layer.

[0105] The total thickness of the composite coating layer is 60 nm, the number of the hydrophobic polymer layer is 4, and the thickness of a single hydrophobic polymer layer is 7.5 nm, and the number of the metal oxide layer is 4, and the thickness of a single metal oxide layer is 7.5 nm.

[0106] In the composite-coated lithium-rich lithium ferrite material, the total content of the composite coating layer is 0.9 wt %, and in the composite coating layer, the mass ratio of the metal oxide layer to the hydrophobic polymer layer is 2:1.

[0107] The preparation method of the composite coated lithium-rich lithium ferrite material comprises the following steps:

[0108] (1) 0.5 g of Li5FeO4 particles were added to 5 mL of anhydrous dichloromethane and treated with an ultrasonic cleaner for 20 min to remove moisture, impurities and bubbles on the surface of the particles. Then, the Li5FeO4 particles were repeatedly washed with anhydrous dichloromethane at room temperature until the washing liquid was completely transparent to ensure that the material was free of moisture, thereby obtaining pretreated Li5FeO4 particles.

[0109] (2) Dissolve polystyrene (molecular weight 300,000) in anhydrous dichloromethane to obtain a polymer solution with a concentration of 25 mg / mL, and add TiO2 powder to anhydrous dichloromethane to form a TiO2 solution with a concentration of 0.5 mg / mL.

[0110] (3) adding the pretreated Li5FeO4 particles in step (1) to the polymer solution in step (1), and treating them with an ultrasonic cleaner for 25 minutes to ensure that the polystyrene uniformly coats the particle surface, and then alternately dispersing the Li5FeO4 particles in the TiO2 solution and the polymer solution, wherein the particles are dispersed in the polymer solution 4 times and in the TiO2 solution 4 times. After each dispersion, the excess solvent is removed by centrifugation and the particles are dried. Finally, the coated particles are placed in a high-temperature furnace protected by nitrogen for heat treatment at a temperature of 210°C for 4 hours to obtain the composite coated lithium ferrite-rich material.

[0111] Example 4

[0112] This embodiment provides a composite-coated lithium-rich lithium iron ore material, which includes a core and a composite coating layer on the surface of the core, wherein the core includes Li5FeO4, and the composite coating layer includes a hydrophobic polymer layer (made of polystyrene) and a metal oxide layer (made of ZnO) alternately stacked, wherein the coating layer closest to the core is the metal oxide layer, and the coating layer farthest from the core is the hydrophobic polymer layer.

[0113] The total thickness of the composite coating layer is 100 nm, the number of the hydrophobic polymer layer is 10, and the thickness of a single hydrophobic polymer layer is 5 nm, and the number of the metal oxide layer is 10, and the thickness of a single metal oxide layer is 5 nm.

[0114] In the composite-coated lithium-rich lithium ferrite material, the total content of the composite coating layer is 1.5 wt %, and in the composite coating layer, the mass ratio of the metal oxide layer to the hydrophobic polymer layer is 2:1.

[0115] The preparation method of the composite coated lithium-rich lithium ferrite material comprises the following steps:

[0116] (1) 1 g of Li5FeO4 particles were added to 10 mL of anhydrous cyclohexane and treated with an ultrasonic cleaner for 30 min to remove moisture, impurities and bubbles on the surface of the particles. Then, the Li5FeO4 particles were repeatedly washed with anhydrous cyclohexane at room temperature until the washing liquid was completely transparent to ensure that the material was free of moisture, thereby obtaining pretreated Li5FeO4 particles.

[0117] (2) Polystyrene (molecular weight 400,000) was dissolved in anhydrous cyclohexane to obtain a polymer solution with a concentration of 15 mg / mL, and ZnO powder was added to the anhydrous cyclohexane to form a ZnO solution with a concentration of 1 mg / mL.

[0118] (3) Alternately dispersing the pretreated Li5FeO4 particles in the ZnO solution and the polymer solution, wherein the particles are dispersed in the polymer solution 10 times and in the ZnO solution 10 times. After each dispersion, the excess solvent is removed by centrifugation and the particles are dried. Finally, the coated particles are placed in a high-temperature furnace protected by nitrogen for heat treatment at a temperature of 220°C for 3 hours to obtain the composite-coated lithium ferrite-rich material.

[0119] Example 5

[0120] This embodiment provides a composite-coated lithium iron-rich material. The composite-coated lithium iron-rich material is the same as Example 1 except that the total thickness of the composite coating layer is 90 nm, the number of the hydrophobic polymer layer is 5 layers, the thickness of the single hydrophobic polymer layer is 10 nm, the number of the metal oxide layer is 4 layers, the thickness of the single metal oxide layer is 10 nm, and the mass ratio of the metal oxide layer and the hydrophobic polymer layer is adaptively changed.

[0121] The preparation method of the composite coated lithium ferrite-rich material described in this embodiment is the same as that in Example 1, except that the concentration of the polymer solution and the concentration of the ZnO solution are changed to change the thickness of the single hydrophobic polymer layer and the thickness of the single metal oxide layer, thereby changing the total thickness of the composite coating layer.

[0122] Example 6

[0123] This embodiment provides a composite-coated lithium-rich lithium iron oxide material. The composite-coated lithium-rich lithium iron oxide material is the same as Example 1 except that the coating layer farthest from the core is a metal oxide layer, the number of the metal oxide layers is 5, and the thickness of a single metal oxide layer is 5 nm.

[0124] The preparation method of the composite coated lithium-rich lithium ferrite material described in this embodiment is the same as that of Example 1 except that it is dispersed in the ZnO solution five times.

[0125] Example 7

[0126] This embodiment provides a composite-coated lithium iron-rich material. The composite-coated lithium iron-rich material is the same as Example 1 except that the total thickness of the composite coating layer is 150 nm, the number of hydrophobic polymer layers is 14, the thickness of a single hydrophobic polymer layer is 5 nm, the number of metal oxide layers is 13, the thickness of a single metal oxide layer is 6.15 nm, and the mass ratio of the metal oxide layer and the hydrophobic polymer layer is adaptively changed.

[0127] The preparation method of the composite coated lithium ferrite-rich lithium material described in this embodiment is the same as that of Example 1, except that the total thickness of the composite coating layer is changed by dispersing the material in the polymer solution 14 times and in the ZnO solution 13 times.

[0128] Example 8

[0129] This embodiment provides a composite-coated lithium iron-rich material. The composite-coated lithium iron-rich material is the same as Example 1 except that the total thickness of the composite coating layer is 50 nm, the number of the hydrophobic polymer layer is 3 layers, the thickness of the single hydrophobic polymer layer is 10 nm, the number of the metal oxide layer is 2 layers, the thickness of the single metal oxide layer is 10 nm, and the mass ratio of the metal oxide layer and the hydrophobic polymer layer is adaptively changed.

[0130] The preparation method of the composite coated lithium ferrite-rich material described in this embodiment is the same as that of Example 1, except that it is dispersed in a polymer solution three times and dispersed in a ZnO solution twice, and the concentration changes of the polymer solution and the metal oxide cause the thickness of the single layer to change.

[0131] Comparative Example 1

[0132] This comparative example provides a lithium-rich lithium ferrite material. The lithium-rich lithium ferrite material is the same as Example 1 except that it does not include a composite coating layer.

[0133] Comparative Example 2

[0134] This comparative example provides a composite-coated lithium-rich lithium ferrite material. The composite-coated lithium-rich lithium ferrite material is the same as Example 1 except that the composite coating layer is a metal oxide layer (the metal oxide layer is directly coated on the surface of the inner core) and a hydrophobic polymer layer stacked in sequence, the thickness of the single hydrophobic polymer layer is 25 nm, the thickness of the single metal oxide layer is 25 nm, and the mass ratio of the metal oxide layer and the hydrophobic polymer layer is adaptively changed.

[0135] The preparation method of the composite coated lithium ferrite-rich lithium material described in this comparative example is the same as that of Example 1, except that the pretreated Li5FeO4 particles are first dispersed once in a metal oxide solution and then dispersed once in a polymer solution, and the changes in the concentration of the polymer solution and the metal oxide cause the thickness of the single layer to change.

[0136] The lithium-rich lithium ferrite material provided in the above embodiments and comparative examples is uniformly mixed with conductive carbon black and a binder in a mass ratio of 8:1:1, and prepared into a composite electrode as a working electrode, a metal lithium sheet as a counter electrode, and a LiPF6 solution with a concentration of 1 mol / L (ED, DMC, EMC volume ratio of 1:1:1) as an electrolyte to assemble into a lithium-rich lithium ferrite battery, and then a charge and discharge test is carried out between 2.5 and 4.5 V. The 0.05C first cycle charge specific capacity, 0.05C first cycle discharge specific capacity, 0.05C first cycle irreversible capacity, 0.25C first cycle charge specific capacity, 0.25C first cycle discharge specific capacity and 0.25C first cycle irreversible capacity obtained by the test are shown in Table 1. The charge and discharge curves of the lithium-rich lithium ferrite battery prepared from the materials of Example 1 and Comparative Example 1 at 0.05C are as follows: Figure 5 As shown by Figure 5 It can be seen that the lithium-rich lithium iron oxide battery prepared using the material of Example 1 has excellent lithium storage performance.

[0137] 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 with a current of 1C. The capacity retention rate of 200 cycles obtained by the test is shown in Table 1. The cycle performance diagram of the lithium iron phosphate battery prepared by using the materials of Example 1 and Comparative Example 1 as lithium supplements is shown in FIG. Figure 6 As shown by Figure 6 It can be seen that the lithium iron phosphate battery prepared by using the material of Example 1 as a lithium supplement has excellent cycle performance.

[0138] Table 1

[0139]

[0140]

[0141] The deterioration time of the materials 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 detected by XRD, it indicates that the material has deteriorated. The material stability time obtained by the test is shown in Table 2:

[0142] Table 2

[0143]

[0144] From Tables 1 and 2, we can see the following:

[0145] It can be seen from Examples 1-5 and Comparative Examples 1-2 that the present invention alternately coats multiple layers of hydrophobic polymer layers and metal oxide layers on the surface of Li5FeO4, which can effectively improve the lithium storage performance and rate performance of Li5FeO4, improve the cycle performance of batteries using Li5FeO4 as a lithium supplement, and at the same time improve the stability of Li5FeO4 under different humidity environments; it can be seen from Examples 1 and 6 that the present invention preferably uses a hydrophobic polymer layer as the coating layer farthest from the core, that is, the outermost coating layer is a hydrophobic polymer layer, which can further improve the stability of Li5FeO4 and improve the electrochemical properties of the material; it can be seen from Examples 1 and 7-8 that the present invention preferably uses 4-10 layers of hydrophobic polymer layers and 4-10 layers of metal oxide layers, which can ensure the single layer thickness of each layer and the total thickness within a reasonable range, thereby improving the effect of alternating multi-layer coating and improving the electrochemical properties and stability of the material.

[0146] 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 composite coated lithium-rich lithium ferrite material, characterized in that: The composite coated lithium-rich ferrite material comprises a core and a composite coating layer on the surface of the core, wherein the core comprises lithium-rich ferrite, and the composite coating layer comprises a hydrophobic polymer layer and a metal oxide layer alternately stacked; In the composite coating layer, the coating layer closest to the core is a hydrophobic polymer layer or a metal oxide layer, and the coating layer farthest from the core is a hydrophobic polymer layer or a metal oxide layer; In the composite coating layer, the number of the hydrophobic polymer layer is ≥2, and the number of the metal oxide layer is ≥2.

2. The composite coated lithium-rich lithium ferrite material according to claim 1, characterized in that: The number of layers of the hydrophobic polymer layer is 4 to 10; And / or, the number of layers of the metal oxide layer is 4 to 10; And / or, in the composite coating layer, the coating layer farthest from the core is a hydrophobic polymer layer.

3. The composite coated lithium-rich lithium ferrite material according to claim 1 or 2, characterized in that: The thickness of the monolayer of the hydrophobic polymer layer is 5nm-10nm; And / or, the thickness of the single metal oxide layer is 5 nm to 10 nm; And / or, the total thickness of the composite coating layer is 50nm-100nm.

4. The composite coated lithium-rich lithium ferrite material according to claim 1 or 2, characterized in that: In the composite-coated lithium-rich lithium ferrite material, the total content of the composite coating layer is 0.6wt%-1.5wt%; And / or, in the composite coating layer, the mass ratio of the metal oxide layer to the hydrophobic polymer layer is (2-3):1; And / or, the hydrophobic polymer layer includes a hydrophobic polymer material and / or a cross-linked product of a hydrophobic polymer material, and the hydrophobic polymer material includes polystyrene and / or polytetrafluoroethylene.

5. A method for preparing the composite-coated lithium-rich lithium ferrite material according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: The lithium-rich lithium ferrite is first cleaned and pretreated, then alternately coated with a hydrophobic polymer material and a metal oxide, and finally heat-treated to obtain the composite-coated lithium-rich lithium ferrite material; The number of times the hydrophobic polymer material is coated is ≥2 times, and the number of times the metal oxide is coated is ≥2 times; In the process of alternately coating the hydrophobic polymer material and the metal oxide, the first coating is the hydrophobic polymer material or the metal oxide, and the last coating is the hydrophobic polymer material or the metal oxide.

6. The preparation method according to claim 5, characterized in that During the alternating coating process of the hydrophobic polymer material and the metal oxide, the last coating is the hydrophobic polymer material; And / or, during the process of alternately coating the hydrophobic polymer material and the metal oxide, solid-liquid separation and drying treatment are performed after each coating, and then the next coating is performed.

7. The preparation method according to claim 5 or 6, characterized in that: The hydrophobic polymer material and the metal oxide are coated by a liquid phase coating method, wherein the solvent used in the liquid phase coating method includes an anhydrous organic solvent; And / or, the method for coating the polymer material comprises: dispersing the object to be coated in a solution of a hydrophobic polymer material to carry out self-assembly coating the water-transporting polymer material, wherein the concentration of the solution of the hydrophobic polymer material is 10 mg / mL-25 mg / mL; And / or, the method for coating the metal oxide includes: dispersing the object to be coated in a metal oxide solution for self-assembly coating the metal oxide, wherein the concentration of the metal oxide solution is 0.5 mg / mL-2 mg / mL.

8. The preparation method according to claim 5 or 6, characterized in that: The cleaning pretreatment comprises the following steps: dispersing the lithium-rich lithium ferrite in an anhydrous organic solvent, and then washing with the anhydrous organic solvent; And / or, the temperature of the heat treatment is 180° C.-220° C., and the time of the heat treatment is 3 h-6 h.

9. A positive electrode plate, characterized in that: The positive electrode plate includes the composite-coated lithium-rich lithium ferrite material according to any one of claims 1 to 4, or the composite-coated lithium-rich lithium ferrite material prepared by the preparation method according to any one of claims 5 to 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the composite-coated lithium-rich lithium ferrite material as described in any one of claims 1 to 4, or the composite-coated lithium-rich lithium ferrite material prepared by the preparation method as described in any one of claims 5 to 8, or the positive electrode sheet as described in claim 9.

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