Composite coated lithium-excess lithium iron oxide material, method of preparation thereof, and use

Abstract

This invention provides a composite coated lithium-excess lithium iron oxide material, a method for preparing the same, and its use. [Solution] The composite coated lithium-rich lithium iron oxide material includes a core and a composite coating layer on the core surface. The core contains lithium-rich lithium iron oxide, and the composite coating layer includes hydrophobic polymer layers and metal oxide layers arranged alternately. The coating layer closest to the core is either a hydrophobic polymer layer or a metal oxide layer, and the coating layer furthest from the core is either a hydrophobic polymer layer or a metal oxide layer. The number of hydrophobic polymer layers is ≥ 2, and the number of metal oxide layers is ≥ 2. By alternately coating with hydrophobic polymer layers and metal oxide layers, not only is the conductivity and stability of the lithium-rich lithium iron oxide material improved, but hydrophobicity is also imparted to it, preventing the occurrence of gelation during the slurry stirring process, and effectively enhancing the circulation stability and rate performance of the lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the field of battery technology and relates to a lithium-excess lithium iron oxide material with a composite coating, a method for preparing the same, and its use.

Background Art

[0002] Lithium-ion batteries have become the core energy storage technology in modern electronic devices, electric vehicles, and large-scale energy storage systems due to their high energy density, long cycle life, high efficiency, and safety. However, despite the remarkable progress in the use of lithium-ion batteries in various fields, the problem of performance degradation during long-term use has not been fundamentally solved. In particular, issues such as the stability, capacity retention rate, and conductivity of battery anode materials and cathode materials have become bottlenecks affecting battery performance.

[0003] Lithium-excess lithium iron oxide (Li5FeO4), as a lithium-supplemental material, has a high specific capacity and good prelithiation characteristics, so it is widely used in the positive electrode agitation of lithium-ion batteries, which may extend the service life of the battery and increase the energy density. However, the surface of Li5FeO4 is prone to react with oxygen and carbon dioxide in the air to form a film with high impedance (such as Li2CO3, LiOH, etc.), which affects its electrochemical activity and causes capacity decay and shortening of the cycle life.

[0004] To solve the above problems, it is necessary to provide a lithium-excess lithium iron oxide material, and the coating layer of the lithium-excess lithium iron oxide material has excellent performance and can effectively improve the cycle stability and rate performance of lithium-ion batteries.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The object of the present invention is to provide a composite coated lithium-rich lithium iron oxide material, a method for preparing the same, and its use, in order to solve the above problems. [Means for solving the problem]

[0006] To achieve this objective, the present invention employs the following technical solutions. In a first aspect, the present invention provides a composite coated lithium-rich lithium iron oxide material, the composite coated lithium-rich lithium iron oxide material comprising an inner core containing lithium-rich lithium iron oxide, and a composite coating layer comprising hydrophobic polymer layers and metal oxide layers that are coated on the surface of the inner core and arranged alternately in layers, wherein the number of hydrophobic polymer layers in the composite coating layer is ≥ 2, and the number of metal oxide layers in the composite coating layer is ≥ 2.

[0007] Of the composite coating layers, the coating layer closest to the inner core is a hydrophobic polymer layer or a metal oxide layer, and the coating layer furthest from the inner core is a hydrophobic polymer layer or a metal oxide layer.

[0008] In some embodiments, the number of hydrophobic polymer layers ranges from 4 to 10.

[0009] In some embodiments, the number of metal oxide layers is 4 to 10.

[0010] In some embodiments, the coating layer furthest from the core of the composite coating layer is a hydrophobic polymer layer.

[0011] In some examples, the thickness of the single layer of hydrophobic polymer is 5 nm to 10 nm.

[0012] In some embodiments, the single layer of the metal oxide thing The layer thickness is 5nm-10nm.

[0013] In some embodiments, the total thickness of the composite coating layer is 50 nm to 100 nm.

[0014] In some embodiments, the total content of the composite coating layer in the composite coated lithium iron oxide material is 0.6 wt% to 1.5 wt%.

[0015] In some embodiments, the mass ratio of the metal oxide layer to the hydrophobic polymer layer in the composite coating layer is (2-3):1.

[0016] In some embodiments, the hydrophobic polymer layer includes a hydrophobic polymer material and / or a crosslinked product of the hydrophobic polymer material.

[0017] In some embodiments, the hydrophobic polymer material includes polystyrene and / or polytetrafluoroethylene.

[0018] In some embodiments, the metal oxide layer comprises ZnO or TiO2.

[0019] In a second aspect, the present invention provides a method for preparing a composite coated lithium-rich lithium iron oxide material as described in the first aspect, wherein the preparation method is A step of pre-treating lithium iron oxide with excess lithium, A step of alternately coating the lithium excess lithium iron oxide with a hydrophobic polymer layer and a metal oxide layer, wherein the number of coatings of the hydrophobic polymer layer is ≥ 2 and the number of coatings of the metal oxide layer is ≥ 2, and the layer first coated on the lithium excess lithium iron oxide is the hydrophobic polymer layer or the metal oxide layer, and the last layer coated on the lithium excess lithium iron oxide is the hydrophobic polymer layer or the metal oxide layer. The process includes the step of performing heat treatment to obtain the composite coated lithium-excess lithium iron oxide material.

[0020] In some embodiments, the final layer applied to the lithium-rich lithium iron oxide is a hydrophobic polymer layer.

[0021] In some embodiments, the step of alternately coating the lithium-excess lithium iron phosphate with a hydrophobic polymer layer and a metal oxide layer includes performing solid-liquid separation and drying treatment after each coating and before performing the next coating.

[0022] In some embodiments, the hydrophobic polymer layer and the metal oxide layer are coated by a liquid-phase coating method, and the solvent used in the liquid-phase coating method includes an anhydrous organic solvent.

[0023] 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 and coating the hydrophobic polymer material by self-assembly, and the concentration of the solution of the hydrophobic polymer material is 10 mg / mL - 25 mg / mL.

[0024] In some embodiments, the method of coating the metal oxide includes dispersing the object to be coated in a solution of a metal oxide and coating the metal oxide by self-assembly, and the concentration of the solution of the metal oxide is 0.5 mg / mL - 2 mg / mL.

[0025] In some embodiments, the step of performing a washing pretreatment on the lithium-excess lithium iron phosphate includes dispersing the lithium-excess lithium iron phosphate in an anhydrous organic solvent and washing the lithium-excess lithium iron phosphate with the anhydrous organic solvent.

[0026] In some embodiments, the temperature of the heat treatment is 180°C - 220°C, and the time of the heat treatment is 3 h - 6 h.

[0027] In a third aspect, the present invention provides a positive electrode plate, and the positive electrode plate includes the composite-coated lithium-excess lithium iron phosphate material described in the first aspect.

[0028] In a fourth aspect, the present invention provides a lithium-ion battery, and the lithium-ion battery includes the composite-coated lithium-excess lithium iron phosphate material described in the first aspect or the positive electrode plate described in the third aspect.

Advantages of the Invention

[0029] Compared to conventional technologies, the present invention has the following beneficial effects. This invention prevents lithium iron oxide from reacting with oxygen and carbon dioxide in the air by alternately coating the surface of lithium iron oxide with multiple layers of hydrophobic polymer and multiple layers of metal oxide. This forms a stable conductive network on the surface of lithium iron oxide, promotes the conduction of lithium ions within the electrode, significantly improves the charge-discharge rate characteristics of the electrode, expands the interfacial reaction area between lithium iron oxide and the electrolyte, promotes ion conduction, and further improves the charge-discharge performance of the battery, especially under high-rate discharge conditions. [Brief explanation of the drawing]

[0030] [Figure 1] This is a flowchart of the preparation method according to the present invention. [Figure 2] This is an SEM image of a composite-coated lithium-rich lithium iron oxide material according to Example 1 of the present invention. [Figure 3] This is a low-magnification TEM image (200 nm scale) of a composite-coated lithium-rich lithium iron oxide material according to Example 1 of the present invention. [Figure 4] This is a high-magnification TEM image (5 nm scale) of a composite-coated lithium-rich lithium iron oxide material according to Example 1 of the present invention. [Figure 5] These are the charge-discharge curves at 0.05C for lithium-rich lithium iron oxide batteries prepared using lithium-rich lithium iron oxide materials according to Example 1 and Comparative Example 1 of the present invention. Example 1 corresponds to the experimental group curve in the figure, and Comparative Example 1 corresponds to the blank group curve in the figure. [Figure 6] This figure shows the cycle performance of lithium iron phosphate batteries prepared using lithium-rich lithium iron oxide materials as supplemental lithium agents according to Example 1 and Comparative Example 1 of the present invention. Here, Example 1 corresponds to the LFP-2% supplemental lithium agent / Gr curve in the figure, and Comparative Example 1 corresponds to the LFP / Gr curve in the figure. [Modes for carrying out the invention]

[0031] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art will understand that the above-described embodiments are merely for the purpose of understanding the present invention and should not be considered as specific limitations of the present invention.

[0032] In a first aspect, the present invention provides a composite coated lithium-rich lithium iron oxide material comprising a core and a composite coating layer on the surface of the core, wherein the core contains lithium-rich lithium iron oxide, and the composite coating layer comprises hydrophobic polymer layers and metal oxide layers arranged alternately in layers.

[0033] Of the composite coating layers, the coating layer closest to the inner core is a hydrophobic polymer layer or a metal oxide layer, and the coating layer furthest from the inner core is a hydrophobic polymer layer or a metal oxide layer.

[0034] Of the composite coating layers, the number of hydrophobic polymer layers is ≥ 2, and the number of metal oxide layers is ≥ 2.

[0035] In this invention, multiple layers of hydrophobic polymer and multiple layers of metal oxide are alternately coated. Compared to the case where only one layer of hydrophobic polymer and one layer of metal oxide are used, the total thickness of the coating layer is the same. However, the present invention uniformly distributes stress through the alternating multilayer coating, effectively suppressing the phase transition and volume expansion of lithium-excess lithium iron oxide during the charge-discharge process, and the alternating coating allows for the construction of stable three-dimensional conductive channels on the surface of the material.

[0036] The present invention further offers the following advantages by alternately coating the surface of lithium iron oxide with multiple layers of hydrophobic polymer and multiple layers of metal oxide: it prevents lithium iron oxide from reacting with oxygen and carbon dioxide in the air, forms a stable conductive network on the surface of lithium iron oxide, promotes the conduction of lithium ions within the electrode, significantly improves the charge-discharge rate characteristics of the electrode, expands the interfacial reaction area between lithium iron oxide and the electrolyte, promotes ion conduction, and further improves the charge-discharge performance of the battery, especially under high-rate discharge conditions.

[0037] Furthermore, lithium iron oxide in excess lithium can cause aggregation during the initial charge-discharge process of the battery due to factors such as surface water absorption and excessive alkalinity, which further affects the battery's stability and efficiency. This invention reduces the gelation phenomenon of the slurry by alternately coating multiple layers of hydrophobic polymer and multiple layers of metal oxide. The composite coating layer enhances the compatibility between lithium iron oxide particles and the electrolyte and other materials, reducing gelation in the slurry. This improvement ensures the fluidity and uniformity of the slurry during the battery production process, avoiding manufacturing difficulties and performance instability caused by gelation, thus improving production efficiency and product consistency.

[0038] This invention enhances the stability of lithium iron oxide by alternately coating it with multiple layers of hydrophobic polymer and multiple layers of metal oxide. It effectively suppresses phase transitions and structural destabilization that occur during the recycling process of lithium iron oxide, improves its resistance to high-temperature conditions, enhances the thermal stability of the material, and increases the safety performance of the battery, thereby reducing the risk of thermal runaway.

[0039] As described above, the present invention effectively solves the problems of lithium excess lithium iron oxide having low stability, readily reacting with oxygen and carbon dioxide in the air, easily causing gelation of the slurry, and having low conductivity of the coating layer.

[0040] In the composite coating layer described in the present invention, the statement that the coating layer closest to the inner core is a hydrophobic polymer layer or a metal oxide layer means that the coating layer initially applied to the surface of the inner core may be either a hydrophobic polymer layer or a metal oxide layer, and the statement that the coating layer furthest from the inner core is a hydrophobic polymer layer or a metal oxide layer means that the last coating layer applied, i.e., the outermost coating layer of the material, may be either a hydrophobic polymer layer or a metal oxide layer.

[0041] The chemical formula of the lithium-rich lithium iron oxide described in the present invention is Li5FeO4.

[0042] In the composite coating layer described in the present invention, the number of hydrophobic polymer layers is ≥ 2, and may be, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 layers, and is further preferably 4 to 10 layers.

[0043] The number of metal oxide layers described in the present invention is ≥ 2 layers, and may be, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 layers, and is further preferably 4 to 10 layers.

[0044] The hydrophobic polymer layer and metal oxide layer described in the present invention are preferably each comprised of 4 to 10 layers. If the number of layers is too small, the conductive network formed within the coating layer becomes discontinuous, limiting ion conduction and resulting in insufficient barrier effect and reduced environmental stability. If the number of layers is too large, the ion conduction resistance increases, and the dynamic performance deteriorates.

[0045] In one specific embodiment, the coating layer furthest from the inner core among the composite coating layers is a hydrophobic polymer layer.

[0046] In this invention, it is preferable that the outermost layer is a hydrophobic polymer layer, as metal oxide layers are prone to side reactions with the electrolyte, especially at high temperatures. Therefore, in this invention, coating the outermost layer with a hydrophobic polymer layer can further improve the stability of lithium-rich lithium iron oxide material.

[0047] In one specific embodiment, the thickness of the single layer of hydrophobic polymer is 5 nm to 10 nm, and may be, for example, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, or 10 nm, but is not limited to the listed values, and other values ​​within the numerical range that are not listed are also applicable.

[0048] In one specific embodiment, the single layer of the metal oxide thing The layer thickness is 5nm-10nm, and may be, for example, 5nm, 6nm, 7nm, 8nm, 9nm, or 10nm, but is not limited to the listed numbers; other numbers within the range not listed also apply.

[0049] In this invention, when the total thickness of the composite coating layer is the same, the thickness of the single coating layer affects the number of coating layers, and when the number of coating layers is the same, it affects the total thickness of the composite coating layer. Therefore, when the total thickness of the composite coating layer is the same, a single hydrophobic polymer layer or a single metal oxide layer thing If the layer thickness is too thin, the number of corresponding coating layers will be excessive, resulting in a single layer of hydrophobic polymer or a single layer of metal oxide. thing If the layer thickness is too thick, the number of corresponding coating layers will be insufficient. If the number of coating layers is the same, a single hydrophobic polymer layer or a single metal oxide layer will be used. thing If the layer thickness is too thin, the thickness of the composite coating layer will decrease, reducing the barrier effect of the coating layer, resulting in a single layer of hydrophobic polymer or a single layer of metal oxide. thing If the layer thickness is too high, the composite coating layer becomes excessively thick, inhibiting ion conduction and causing mechanical stress to concentrate, making the coating layer prone to cracking.

[0050] In one specific embodiment, the total thickness of the composite coating layer is 50 nm to 100 nm, and may be, for example, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, or 100 nm, but is not limited to the listed values, and other values ​​within the numerical range that are not listed also apply.

[0051] In one specific embodiment, in the composite coated lithium-rich lithium iron oxide material, the total content of the composite coating layer is 0.6 wt% to 1.5 wt%, and may be, for example, 0.6 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.4 wt%, or 1.5 wt%, but is not limited to the listed values, and other values ​​within the numerical range that are not listed also apply.

[0052] In one specific embodiment, the mass ratio of the metal oxide layer to the hydrophobic polymer layer in the composite coating layer is (2-3):1, and may be, for example, 2:1, 2.5:1, or 3:1, but is not limited to the listed values, and other values ​​within the numerical range that are not listed are also applicable.

[0053] In one specific embodiment, the hydrophobic polymer layer contains a hydrophobic polymer material and / or a crosslinked product of the hydrophobic polymer material, wherein the hydrophobic polymer material includes polystyrene and / or polytetrafluoroethylene.

[0054] In one specific embodiment, the molecular weight of the polystyrene is between 100,000 and 500,000, and may be, for example, 100,000, 200,000, 300,000, 400,000, or 500,000, but is not limited to the listed numbers, and other numbers within the range not listed also apply.

[0055] In one specific embodiment, the metal oxide layer includes ZnO and / or TiO2.

[0056] In a second aspect, the present invention provides a method for preparing a composite coated lithium-rich lithium iron oxide material as described in the first aspect, the flowchart of which is shown in Figure 1. S1 is a pre-treatment for lithium iron oxide in excess lithium, S2 is a method of alternately coating the lithium-excess lithium iron oxide with a hydrophobic polymer layer and a metal oxide layer, wherein the number of coatings of the hydrophobic polymer layer is ≥ 2 and the number of coatings of the metal oxide layer is ≥ 2, and the first layer coated on the lithium-excess lithium iron oxide is the hydrophobic polymer layer or the metal oxide layer, and the last layer coated on the lithium-excess lithium iron oxide is the hydrophobic polymer layer or the metal oxide layer, The method includes S3, which involves heat treatment to obtain the composite coated lithium-excess lithium iron oxide material.

[0057] This invention first involves pre-treating lithium iron oxide with excess lithium by washing to remove moisture, impurities, and air bubbles from the particle surface, ensuring that no moisture is present in the material. Next, it alternately coats the material with a hydrophobic polymer material and a metal oxide, and finally performs a heat treatment to further increase the strength of the coating layer. Simultaneously, by performing a heat stabilization treatment on the surface of the hydrophobic polymer material, its hydrophobicity and heat resistance are enhanced.

[0058] In relation to the composite coated lithium-rich lithium iron oxide material product of the present invention, the number of coatings of the hydrophobic polymer material is ≥ 2, and the number of coatings of the metal oxide is ≥ 2, forming a multilayer alternating coating of hydrophobic polymer layers and metal oxide layers, wherein the first coating is a hydrophobic polymer material, which may be a metal oxide, and the last coating is a hydrophobic polymer material, which may be a metal oxide.

[0059] In one specific embodiment, in the process of alternately coating with a hydrophobic polymer material and a metal oxide, the last layer to be coated is the hydrophobic polymer material, and the outermost coating layer is the hydrophobic polymer layer.

[0060] In one specific embodiment, in the process of alternately coating a hydrophobic polymer material with a metal oxide, solid-liquid separation and drying treatment are performed after each coating is completed, and then the next coating is carried out.

[0061] In one specific embodiment, the hydrophobic polymer material and metal oxide are coated using a liquid-phase coating method, and the solvent used in the liquid-phase coating method includes an anhydrous organic solvent.

[0062] In one specific embodiment, the method for coating the polymer material includes the step of dispersing the object to be coated in a solution of the hydrophobic polymer material and coating it with the hydrophobic polymer material by self-assembly, wherein the concentration of the solution of the hydrophobic polymer material is 10 mg / mL to 25 mg / mL, and may be, for example, 10 mg / mL, 15 mg / mL, 20 mg / mL, or 25 mg / mL, but is not limited to the listed values, and other values ​​within the numerical range that are not listed are also applicable.

[0063] In one specific 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 ​​within the numerical range that are not listed are also applicable.

[0064] In one specific embodiment, the method of coating with the metal oxide includes the step of dispersing the object to be coated in a metal oxide solution and coating it with the metal oxide by self-assembly, wherein the concentration of the metal oxide solution is 0.5 mg / mL to 2 mg / mL, and may be, for example, 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 ​​within the numerical range that are not listed are also applicable.

[0065] In this invention, a hydrophobic polymer material is dissolved in an anhydrous organic solvent and stirred until completely transparent to obtain a solution of the hydrophobic polymer material. A metal oxide is added to the same solvent as the hydrophobic polymer material solution to form a metal oxide solution, and the solution is subjected to magnetic stirring and ultrasonic treatment under a nitrogen atmosphere to ensure the uniformity of the solution.

[0066] 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 ​​within the numerical range that are not listed are also applicable.

[0067] In one specific embodiment, the pre-washing treatment includes the steps of dispersing lithium excess lithium ironate in an anhydrous organic solvent, and then washing with the anhydrous organic solvent.

[0068] This invention involves adding lithium-rich lithium manganate particles to an anhydrous organic solvent and treating them using an ultrasonic cleaner to remove moisture, impurities, and air bubbles from the particle surface. The particles are repeatedly washed with the anhydrous organic solvent at room temperature until the cleaning solution is completely clear and the material is free of moisture.

[0069] In one specific embodiment, the anhydrous organic solvent includes one of anhydrous cyclohexane, anhydrous n-hexane, or anhydrous dichloromethane, or a combination of at least two of these.

[0070] In one specific embodiment, the heat treatment temperature is 180°C-220°C, and the heat treatment time is 3h-6h.

[0071] In one specific embodiment, the heat treatment is carried out under a protective atmosphere, for example, under a nitrogen atmosphere.

[0072] The technical solutions of the present invention will be further described below through specific examples.

[0073] Example 1

[0074] This embodiment provides a composite coated lithium-rich lithium iron oxide material comprising a core and a composite coating layer on the surface of the core, wherein the core contains Li5FeO4, and the composite coating layer comprises alternatingly stacked hydrophobic polymer layers (made of polystyrene) and metal oxide layers (made of ZnO), with the coating layer closest to the core being a hydrophobic polymer layer and the coating layer furthest from the core being a hydrophobic polymer layer.

[0075] The total thickness of the composite coating layer is 50 nm, the number of hydrophobic polymer layers is 5, the thickness of a single hydrophobic polymer layer is 5 nm, the number of metal oxide layers is 4, and the thickness of a single metal oxide layer is 6.25 nm.

[0076] In the composite coated lithium-rich lithium iron oxide material, the total content of the composite coating layer is 0.6 wt%, and the mass ratio of the metal oxide layer to the hydrophobic polymer layer in the composite coating layer is 2:1.

[0077] The method for preparing the composite coated lithium-excess lithium iron oxide material is as follows: Step (1) involves adding 1 g of Li5FeO4 particles to 10 mL of anhydrous cyclohexane and treating them with an ultrasonic cleaner for 30 minutes to remove moisture, impurities, and bubbles from the particle surface. Then, at room temperature, the Li5FeO4 particles are repeatedly washed with anhydrous cyclohexane until the washing solution is completely clear and the material is free of moisture, thereby obtaining the pre-treated Li5FeO4 particles. Step (2) involves dissolving polystyrene (molecular weight 300,000) in anhydrous cyclohexane to obtain a polymer solution with a concentration of 15 mg / mL, and adding ZnO powder to the anhydrous cyclohexane to form a ZnO solution with a concentration of 1 mg / mL. Step (3) comprises adding the pre-treated Li5FeO4 particles described in step (1) to the polymer solution described in step (1), and treating them with an ultrasonic cleaner for 25 minutes to ensure that polystyrene is uniformly coated on the surface of the particles, then dispersing the Li5FeO4 particles alternately in the ZnO solution and the polymer solution, dispersing them in the polymer solution 5 times and in the ZnO solution 4 times, removing excess solvent and drying after each dispersion using centrifugation, and finally heat-treating the coated particles in a high-temperature furnace under a nitrogen atmosphere at a temperature of 200°C for 4 hours to obtain the composite coated lithium-rich lithium iron oxide material.

[0078] The SEM image of the composite coated lithium-rich lithium iron oxide material described in this embodiment is shown in Figure 2, the low-magnification TEM image is shown in Figure 3, and the high-magnification TEM image is shown in Figure 4. Referring to Figures 2-4, a clear coating layer structure can be seen in the outer layer. Simultaneously, as can be seen from Figure 4, the ZnO(102) crystal planes correspond to a lattice spacing of 0.19 nm, the Li5FeO4(202) crystal planes correspond to a lattice spacing of 0.187 nm, and the organic hydrophobicity corresponds to an amorphous structure.

[0079] Example 2

[0080] This embodiment provides a composite coated lithium iron oxide material, the composite coated lithium iron oxide material comprising an inner core and a composite coating layer on the surface of the inner core, the inner core comprising Li5FeO4, and the composite coating layer comprising alternatingly stacked hydrophobic polymer layers (made of polytetrafluoroethylene) and metal oxide layers (made of TiO2), the coating layer closest to the inner core being a hydrophobic polymer layer and the coating layer furthest from the inner core being a hydrophobic polymer layer.

[0081] The total thickness of the composite coating layer is 80 nm, the number of hydrophobic polymer layers is 6, the thickness of a single hydrophobic polymer layer is 7 nm, the number of metal oxide layers is 5, and the thickness of a single metal oxide layer is 7.6 nm.

[0082] In the composite coated lithium-rich lithium iron oxide material, the total content of the composite coating layer is 1.1 wt%, and the mass ratio of the metal oxide layer to the hydrophobic polymer layer in the composite coating layer is 2.5:1.

[0083] The method for preparing the composite coated lithium-excess lithium iron oxide material is as follows: Step (1) involves adding 2 g of Li5FeO4 particles to 15 mL of anhydrous n-hexane and treating them with an ultrasonic cleaner for 15 min to remove moisture, impurities, and air bubbles from the particle surface, then repeatedly washing the Li5FeO4 particles with anhydrous n-hexane at room temperature until the washing solution is completely clear and the material is free of moisture, thereby obtaining the pre-treated Li5FeO4 particles. Step (2) involves dissolving polytetrafluoroethylene (molecular weight 2 million) in anhydrous n-hexane to obtain a polymer solution with a concentration of 10 mg / mL, and adding TiO2 powder to anhydrous n-hexane to form a TiO2 solution with a concentration of 2 mg / mL. Step (3) comprises adding the pre-treated Li5FeO4 particles described in step (1) to the polymer solution described in step (1), and treating them with an ultrasonic cleaner for 30 minutes to ensure that polytetrafluoroethylene is uniformly coated on the surface of the particles, then dispersing the Li5FeO4 particles alternately in the TiO2 solution and the polymer solution, dispersing them in the polymer solution 6 times and in the TiO2 solution 5 times, removing excess solvent and drying after each dispersion using centrifugation, and finally heat-treating the coated particles in a high-temperature furnace under a nitrogen atmosphere, with a heat treatment temperature of 180°C for 6 hours, to obtain the composite coated lithium-rich lithium iron oxide material.

[0084] Example 3

[0085] This embodiment provides a composite coated lithium iron oxide material, the composite coated lithium iron oxide material comprising a core and a composite coating layer on the surface of the core, the core comprising Li5FeO4, and the composite coating layer comprising alternatingly stacked hydrophobic polymer layers (made of polystyrene) and metal oxide layers (made of TiO2), the coating layer closest to the core being the hydrophobic polymer layer and the coating layer furthest from the core being the metal oxide layer.

[0086] The total thickness of the composite coating layer is 60 nm, the number of hydrophobic polymer layers is 4, the thickness of a single hydrophobic polymer layer is 7.5 nm, the number of metal oxide layers is 4, and the thickness of a single metal oxide layer is 7.5 nm.

[0087] In the composite coated lithium-rich lithium iron oxide material, the total content of the composite coating layer is 0.9 wt%, and the mass ratio of the metal oxide layer to the hydrophobic polymer layer in the composite coating layer is 2:1.

[0088] The method for preparing the composite coated lithium-excess lithium iron oxide material is Step (1) involves adding 0.5 g of Li5FeO4 particles to 5 mL of anhydrous dichloromethane, treating them with an ultrasonic cleaner for 20 minutes to remove moisture, impurities, and air bubbles from the particle surface, and then repeatedly washing the Li5FeO4 particles with anhydrous dichloromethane at room temperature until the washing solution is completely clear and the material is free of moisture, thereby obtaining the pre-treated Li5FeO4 particles. Step (2) involves dissolving polystyrene (molecular weight 300,000) in anhydrous dichloromethane to obtain a polymer solution with a concentration of 25 mg / mL, and adding TiO2 powder to the anhydrous dichloromethane to form a TiO2 solution with a concentration of 0.5 mg / mL. Step (3) comprises adding the pre-treated Li5FeO4 particles described in step (1) to the polymer solution described in step (1), and treating them with an ultrasonic cleaner for 25 minutes to ensure that polystyrene is uniformly coated on the surface of the particles, then dispersing the Li5FeO4 particles alternately in the TiO2 solution and the polymer solution, dispersing them in the polymer solution four times and dispersing them in the TiO2 solution four times, removing excess solvent and drying after each dispersion using centrifugation, and finally heat-treating the coated particles in a high-temperature furnace under a nitrogen atmosphere, with a heat treatment temperature of 210°C for 4 hours, to obtain the composite coated lithium-rich lithium iron oxide material.

[0089] Example 4

[0090] This embodiment provides a composite coated lithium iron oxide material, the composite coated lithium iron oxide material comprising a core and a composite coating layer on the surface of the core, the core comprising Li5FeO4, and the composite coating layer comprising alternatingly stacked hydrophobic polymer layers (made of polystyrene) and metal oxide layers (made of ZnO), the coating layer closest to the core being the metal oxide layer and the coating layer furthest from the core being the hydrophobic polymer layer.

[0091] The total thickness of the composite coating layer is 100 nm, the number of hydrophobic polymer layers is 10, the thickness of a single hydrophobic polymer layer is 5 nm, the number of metal oxide layers is 10, and the thickness of a single metal oxide layer is 5 nm.

[0092] In the composite coated lithium-rich lithium iron oxide material, the total content of the composite coating layer is 1.5 wt%, and the mass ratio of the metal oxide layer to the hydrophobic polymer layer in the composite coating layer is 2:1.

[0093] The method for preparing the composite coated lithium-excess lithium iron oxide material is as follows: Step (1) involves adding 1 g of Li5FeO4 particles to 10 mL of anhydrous cyclohexane and treating them with an ultrasonic cleaner for 30 minutes to remove moisture, impurities, and bubbles from the particle surface. Then, at room temperature, the Li5FeO4 particles are repeatedly washed with anhydrous cyclohexane until the washing solution is completely clear and the material is free of moisture, thereby obtaining the pre-treated Li5FeO4 particles. Step (2) involves dissolving polystyrene (molecular weight 400,000) in anhydrous cyclohexane to obtain a polymer solution with a concentration of 15 mg / mL, and adding ZnO powder to the anhydrous cyclohexane to form a ZnO solution with a concentration of 1 mg / mL. Step (3) comprises dispersing the pre-treated Li5FeO4 particles described in step (1) alternately in a ZnO solution and a polymer solution, dispersing them in the polymer solution 10 times and in the ZnO solution 10 times, removing excess solvent after each dispersion using centrifugation and drying, and finally heat-treating the coated particles in a high-temperature furnace under a nitrogen atmosphere at a temperature of 220°C for 3 hours to obtain the composite coated lithium-rich lithium iron oxide material.

[0094] Example 5

[0095] This embodiment provides a composite coated lithium iron oxide material, the composite coated lithium iron oxide material having a total thickness of 90 nm for the composite coating layer, 5 hydrophobic polymer layers, a thickness of 10 nm for each single hydrophobic polymer layer, 4 metal oxide layers, and a thickness of 10 nm for each single metal oxide layer, and is the same as in Example 1 except that the mass ratio of the metal oxide layer and the hydrophobic polymer layer changes adaptively.

[0096] The method for preparing the composite-coated lithium-rich lithium iron oxide material described in this embodiment is the same as in Example 1, except that the thickness of the single layer of hydrophobic polymer and the single layer of metal oxide are changed by varying the concentrations of the polymer solution and the ZnO solution, thereby changing the total thickness of the composite coating layer.

[0097] Example 6

[0098] This embodiment provides a composite coated lithium-rich lithium iron oxide material, which is the same as in Example 1 except that the coating layer furthest from the core is a metal oxide layer, the number of metal oxide layers is 5, and the thickness of a single metal oxide layer is 5 nm.

[0099] The method for preparing the composite coated lithium-rich lithium iron oxide material described in this example is the same as in Example 1, except that it is dispersed five times in a ZnO solution.

[0100] Example 7

[0101] This embodiment provides a composite coated lithium iron oxide material, the composite coated lithium iron oxide material having a total thickness of 150 nm for the composite coating layer, 14 hydrophobic polymer layers, a thickness of 5 nm for each single hydrophobic polymer layer, 13 metal oxide layers, and a thickness of 6.15 nm for each single metal oxide layer, and is the same as in Example 1 except that the mass ratio of the metal oxide layer and the hydrophobic polymer layer changes adaptively.

[0102] The method for preparing the composite-coated lithium-rich lithium iron oxide material described in this embodiment is the same as in Example 1, except that the material is dispersed 14 times in a polymer solution and 13 times in a ZnO solution, thereby changing the total thickness of the composite coating layer.

[0103] Example 8

[0104] This embodiment provides a composite coated lithium iron oxide material, the composite coated lithium iron oxide material having a total thickness of 50 nm for the composite coating layer, three hydrophobic polymer layers, a thickness of 10 nm for each single hydrophobic polymer layer, two metal oxide layers, and a thickness of 10 nm for each single metal oxide layer, and is the same as in Example 1 except that the mass ratio of the metal oxide layer and the hydrophobic polymer layer changes adaptively.

[0105] The method for preparing the composite-coated lithium-rich lithium iron oxide material described in this embodiment is the same as in Example 1, except that the material is dispersed three times in a polymer solution and twice in a ZnO solution, and the thickness of the single layer is changed by changing the concentration of the polymer solution and the concentration of the metal oxide.

[0106] Comparative Example 1

[0107] This comparative example provides a lithium-rich lithium iron oxide material, which is the same as in Example 1 except that it does not contain a composite coating layer.

[0108] Comparative Example 2

[0109] This comparative example provides a composite coated lithium-rich lithium iron oxide material, the composite coated lithium iron oxide material having a single layer of metal oxide (metal oxide) in which the composite coating layer is sequentially laminated. thing The layer is a single hydrophobic polymer layer (the layer is directly coated on the core surface), and 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 changes adaptively, except that it is the same as in Example 1.

[0110] The method for preparing the composite-coated lithium-rich lithium iron oxide material described in this comparative example is the same as in Example 1, except that the pre-treated Li5FeO4 particles are first dispersed once in a metal oxide solution, then dispersed once in a polymer solution, and the thickness of the single layer is changed by changing the concentration of the polymer solution and the concentration of the metal oxide.

[0111] The lithium iron oxide materials described in the above examples 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 the working electrode, a metallic lithium piece as the counter electrode, and a 1 mol / L LiPF6 (ED, DMC, EMC volume ratio 1:1:1) solution as the electrolyte to assemble a lithium iron oxide battery. Next, a charge-discharge test was performed at 2.5-4.5V, and the measured 0.05C initial charge ratio capacity, 0.05C initial discharge ratio capacity, 0.05C initial irreversible capacity, 0.25C initial charge ratio capacity, 0.25C initial discharge ratio capacity, and 0.25C initial irreversible capacity are shown in Table 1. Correspondingly, the charge-discharge curves at 0.05C for the lithium iron oxide batteries prepared with the materials of Example 1 and Comparative Example 1 are shown in Figure 5. As can be seen from Figure 5, the lithium iron oxide battery prepared with the material of Example 1 has excellent lithium storage performance.

[0112] Lithium iron phosphate, lithium-rich lithium iron oxide material provided in the above examples and comparative examples, conductive carbon black, and binder were uniformly mixed in a mass ratio of 78:2:10:10 to form a composite electrode as the working electrode, graphite was used as the counter electrode, and a 1 mol / L LiPF6 (ED, DMC, EMC volume ratio 1:1:1) solution with an N / P ratio of 1.1 was used as the electrolyte to assemble a lithium iron phosphate battery. Charge-discharge tests were performed between 2.7-4.5V in the initial stage of chemical formation, and between 2.8-3.65V in the cycle stage, with a current of 1C. The measured capacity retention rate after 200 cycles is shown in Table 1. The cycle performance diagram of lithium iron phosphate batteries prepared using the materials of Example 1 and Comparative Example 1 as supplemental lithium agents is shown in Figure 6. As can be seen from Figure 6, the lithium iron phosphate battery prepared using the material of Example 1 as supplemental lithium agent exhibits excellent cycle performance.

[0113] [Table 1]

[0114] The materials provided in the above examples and comparative examples were subjected to a comparison of their degradation times under different air humidity conditions. When the LiOH content in the material was detected to be >5 mol% by XRD, the material was deemed to have degraded, and the measured stability times of the materials are shown in Table 2.

[0115] [Table 2]

[0116] As can be seen from Tables 1 and 2, the following can be understood. As can be seen from Examples 1-5 and Comparative Examples 1-2, the present invention effectively enhances the lithium storage performance and rate performance of Li5FeO4 by alternately coating the surface of Li5FeO4 with multiple hydrophobic polymer layers and metal oxide layers, improving the battery's circulation performance as a lithium supplement, and simultaneously improving the stability of Li5FeO4 under different humidity environments. As can be seen from Examples 1 and 6, in the present invention, it is preferable that the coating layer furthest from the inner core is a hydrophobic polymer layer, i.e., the outermost coating layer is a hydrophobic polymer layer, which further improves the stability of Li5FeO4 and enhances the electrochemical performance of the material. As can be seen from Examples 1 and 7-8, in the present invention, it is preferable that the number of hydrophobic polymer layers is 4-10 layers and the number of metal oxide layers is 4-10 layers, which ensures the thickness of each layer and allows the total thickness to be within a reasonable range, thereby improving the effect of the multilayer alternating coating and enhancing the electrochemical performance and stability of the material.

[0117] The above are merely specific embodiments of the present invention, and the scope of protection of the present invention is not limited thereto. Those skilled in the art will understand that any changes or substitutions that can be easily conceived within the technical scope disclosed by the present invention are included within the scope of protection and disclosure of the present invention.

Claims

1. A composite coated lithium-excess lithium iron oxide material, The inner core contains lithium-rich lithium iron oxide, The inner core is covered with a composite coating layer comprising a hydrophobic polymer layer and a metal oxide layer, which are alternately stacked and provided on the surface of the inner core, The number of hydrophobic polymer layers in the composite coating layer is 2 to 14, and the number of metal oxide layers in the composite coating layer is 2 to 13. The aforementioned metal oxide layer is ZnO or TiO2. The thickness of the single layer of hydrophobic polymer is 5 nm to 10 nm. A composite coated lithium-excess lithium iron oxide material characterized in that the thickness of the single layer of metal oxide is 5 nm to 10 nm.

2. The composite coated lithium-excess lithium iron oxide material according to claim 1, characterized in that the number of hydrophobic polymer layers is 4 to 10 layers, and / or the number of metal oxide layers is 4 to 10 layers.

3. The composite coated lithium-rich lithium iron oxide material according to claim 1, characterized in that the coating layer furthest from the inner core among the composite coating layers is a hydrophobic polymer layer.

4. The composite coated lithium-excess lithium iron oxide material according to Claim 1, characterized in that the total thickness of the composite coating layer is 50 nm to 100 nm.

5. In the composite coated lithium-rich lithium iron oxide material, the total content of the composite coating layer is 0.6 wt% - 1.5 wt%. The composite coated lithium-rich lithium iron oxide material according to claim 1, characterized in that, and / or, the mass ratio of the metal oxide layer to the hydrophobic polymer layer in the composite coating layer is (2-3):

1.

6. The composite coated lithium-excess lithium iron oxide material according to claim 1, characterized in that the hydrophobic polymer layer contains a hydrophobic polymer material and / or a crosslinking product of the hydrophobic polymer material, and the hydrophobic polymer material contains polystyrene and / or polytetrafluoroethylene.

7. A method for preparing a composite coated lithium-excess lithium iron oxide material according to any one of claims 1 to 6, wherein the preparation method is: A step of pre-treating lithium iron oxide with excess lithium, A step of alternately coating the lithium excess lithium iron oxide with a hydrophobic polymer layer and a metal oxide layer, wherein the number of coatings of the hydrophobic polymer layer is ≥ 2 and the number of coatings of the metal oxide layer is ≥ 2, and the layer first coated on the lithium excess lithium iron oxide is the hydrophobic polymer layer or the metal oxide layer, and the last layer coated on the lithium excess lithium iron oxide is the hydrophobic polymer layer or the metal oxide layer. A preparation method characterized by comprising the step of performing heat treatment to obtain the composite coated lithium-excess lithium iron oxide material.

8. The preparation method according to claim 7, characterized in that the final layer applied to the lithium excess lithium iron oxide is a hydrophobic polymer layer.

9. The step of alternately coating the lithium-excess lithium iron oxide with a hydrophobic polymer layer and a metal oxide layer is, The preparation method according to claim 7, characterized in that it includes the step of performing solid-liquid separation and drying treatment after each coating and before performing the next coating.

10. The preparation method according to claim 7, characterized in that the hydrophobic polymer layer and the metal oxide layer are coated by a liquid phase coating method, and the solvent used in the liquid phase coating method includes an anhydrous organic solvent.

11. The method for coating the polymer material includes the steps of dispersing the object to be coated in a solution of the hydrophobic polymer material and coating it with the hydrophobic polymer material by self-assembly, wherein the concentration of the solution of the hydrophobic polymer material is 10 mg / mL to 25 mg / mL. The preparation method according to claim 7, wherein the method for coating with the metal oxide comprises the step of dispersing the object to be coated in a solution of metal oxide and coating it with the metal oxide by self-assembly, and the concentration of the metal oxide solution is 0.5 mg / mL to 2 mg / mL.

12. The step of pre-treating lithium iron oxide with excess lithium is: The step includes dispersing the lithium excess lithium iron oxide in an anhydrous organic solvent and washing the lithium excess lithium iron oxide with the anhydrous organic solvent. The preparation method according to claim 7, characterized in that the temperature of the heat treatment is 180°C to 220°C and the duration of the heat treatment is 3h to 6h.

13. A positive electrode plate, wherein the positive electrode plate comprises a composite coated lithium-excess lithium iron oxide material as described in any one of claims 1 to 6.

14. A lithium-ion battery, wherein the lithium-ion battery includes the positive electrode plate described in claim 13.

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