Composite lithium supplement material, preparation method thereof, positive plate and battery

Abstract

The invention relates to the technical field of batteries, in particular to a composite lithium supplement material, a preparation method thereof, a positive plate and a battery. The composite lithium supplement material comprises a base material and a coating layer at least partially coating the surface of the base material, the coating layer comprises a first coating layer and a second coating layer; the surface of the base material is coated with the first coating layer, and the surface of the first coating layer is coated with the second coating layer; the base material comprises lithium-rich lithium ferrite; the first coating layer is a Mg1-XZnXAl2O4 oxide, and x is equal to 0 to 1.0; and the second coating layer is a carbon material. The composite lithium supplement material can stabilize the material structure, prevent the lithium supplement particles from generating cracks in the charging and discharging process to generate a new interface, reduce the side reaction with an electrolyte, reduce the gas production rate in the cell circulation and storage process, and improve the high-temperature storage performance and the high-temperature cycle performance of the material; meanwhile, residual alkali on the surface of the lithium supplement agent can be prevented from reacting with a glue solution to form slurry gel, and the processability of the material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a composite lithium supplement material and a preparation method thereof, a positive electrode sheet and a battery. Background Art

[0002] Lithium-ion batteries have become a type of energy storage secondary battery with broad application prospects due to their advantages such as high discharge voltage, high specific energy density, long cycle life, and wide applicable temperature range. At present, both lithium iron phosphate batteries and ternary batteries have the demand for improved energy density and cycle life. Lithium replenishment technology is an effective way to meet this demand. Positive electrode lithium replenishment is the most commonly used and safest pre-lithium technology. In the existing technology, the positive electrode lithium replenishers that have been used mainly include lithium-rich lithium ferrite and lithium-rich lithium nickelate. Among them, lithium-rich lithium ferrite has a higher lithium replenishment efficiency and is more cost-effective. However, lithium-rich lithium ferrite also has some problems. First, it is difficult to process. During the homogenization process, due to the high residual alkali content of the material, the slurry viscosity rebounds quickly and gel is easily formed. Second, many cracks will be generated during the charge and discharge process, exposing new interfaces and producing side reactions with the electrolyte, resulting in the problem of continuous gas production during late cycles or high-temperature storage.

[0003] Therefore, how to improve the processing problem of easy gelation of lithium-rich lithium iron oxide lithium-supplementing slurry, and reduce or avoid the problem of continuous gas production during battery cell cycling or high-temperature storage, is crucial to the development of lithium-supplementing positive electrode materials.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite lithium supplement material and its preparation method, a positive electrode sheet and a battery, so as to solve the technical problems in the prior art that the lithium-rich lithium ferrite lithium supplement slurry is easy to gel and the battery cell prepared therefrom continues to produce high gas during cycling or high-temperature storage.

[0006] The present inventors discovered that while existing lithium supplementation technologies can address these issues, their optimization, primarily through the introduction of high-cost transition metals (such as manganese, titanium, vanadium, and scandium) or rare earth elements (such as lanthanide oxides), significantly increases raw material costs. For example, in CN 118782797 A, while doping the matrix with transition metals and coating it with lanthanide oxides (such as lanthanum oxide) improves slurry stability and suppresses battery gassing, the use of precious metal raw materials leads to increased costs, making large-scale production unsuitable. Therefore, the present inventors aim to develop a lithium supplementation agent that is more cost-effective while also improving battery performance.

[0007] Specifically, the present invention has the following technical solutions: In a first aspect, the present invention provides a composite lithium supplement material, comprising a base material and a coating layer at least partially coated on a surface of the base material; the coating layer comprises a first coating layer and a second coating layer; the first coating layer is coated on the surface of the base material, and the second coating layer is coated on the surface of the first coating layer; The matrix material includes lithium-rich lithium ferrite; The first coating layer is Mg 1-X Zn X Al2O4 oxide, x=0~1.0; the second coating layer is a carbon material.

[0008] In the composite lithium supplement material of the present invention, Mg 1-X Zn X The combination of the Al2O4 oxide coating and the carbon coating can stabilize the material structure, prevent the lithium supplement agent particles from cracking and forming new interfaces during charging and discharging, thereby reducing side reactions with the electrolyte, reducing gas production during battery cell cycling and storage, and improving the material's high-temperature storage performance and high-temperature cycling performance; at the same time, it can prevent the residual alkali on the lithium supplement agent surface from reacting with the glue to form slurry gel, thereby improving the material's processing performance.

[0009] In the present invention, x=0-1.0, for example, it can be any value among 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or a numerical range with any two of the above values ​​as endpoints.

[0010] In the present invention, the first coating layer and the second coating layer can be fully coated or partially coated, preferably fully coated. When partially coated, the coating rate is greater than 80%, preferably greater than 95%.

[0011] In the present invention, the chemical formula of the lithium-rich lithium ferrite in the matrix material is Li5FeO4; the carbon material of the second coating layer is chemical vapor deposited carbon, which is generated by high-temperature cracking of a gaseous carbon source, and the gaseous carbon source can be at least one of conventional methane, ethylene, propylene and propane.

[0012] According to the composite lithium supplement material provided by the present invention, the porosity of the first coating layer is 5% to 20%, for example, it can be any value among 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%, or a numerical range with any two of the above values ​​as endpoints.

[0013] The present invention has found that by controlling the porosity of the first coating layer to be within the above range, it is beneficial for it to work synergistically with the second coating layer, more effectively stabilize the material structure, avoid the material from generating more cracks during the charging and discharging process, generate new interfaces, and thus reduce side reactions with the electrolyte.

[0014] According to the composite lithium supplement material provided by the present invention, the thickness of the first coating layer is greater than that of the second coating layer, and the difference in thickness between the first coating layer and the second coating layer is 1 mm to 2.5 mm.

[0015] Preferably, the thickness of the first coating layer is 3nm~5nm, for example, it can be any value among 3nm, 4nm, 5nm, or a numerical range with any two of the above values ​​as endpoints; the thickness of the second coating layer is 1nm~3nm, for example, it can be any value among 1nm, 2nm, 3nm, or a numerical range with any two of the above values ​​as endpoints.

[0016] According to the composite lithium supplement material provided by the present invention, 0.3≤x≤0.7.

[0017] In a second aspect, the present invention provides a method for preparing the composite lithium supplement material, comprising coating the first coating layer on the surface of the base material using a sol-gel method.

[0018] Conventional coating methods in this field include sol-gel method, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), hydrothermal / solvothermal method, spray drying method, mechanical ball milling method, electrochemical deposition and solution impregnation method, etc. The present invention finds that compared with spray drying method and mechanical ball milling method, the use of sol-gel method is easier to obtain a uniform and dense first coating layer of nanometer thickness on the surface of the substrate material; compared with CVD, PVD, ALD and hydrothermal method, it has lower cost and is easier to industrialize.

[0019] According to the preparation method of the composite lithium supplement material provided by the present invention, the method of coating the first coating layer on the surface of the base material using a sol-gel method comprises the following steps: S1: dissolving zinc salt, magnesium salt and aluminum salt in water, adding a complexing agent and mixing to obtain a glue solution; S2: mixing the glue solution with a matrix material at 50° C. to 90° C. to obtain a clear sol precursor solution; heating the solution to evaporate the solvent in the sol precursor solution to obtain a xerogel; S3: crushing and grinding the dry gel, and annealing the obtained powder in an oxygen atmosphere at 600° C. to 1000° C.

[0020] In the specific implementation process, in S2, Li5FeO4 matrix material powder is slowly added to the glue solution, and the glue solution temperature is controlled to be 50~90 °C to obtain a clarified glue solution precursor; for example, it can be any value among 50°C, 60°C, 70°C, 80°C, 90°C, or a numerical range with any two of the above values ​​as endpoints; then the glue solution temperature is increased to 150~200°C, the sol precursor solution is evaporated, and continuous stirring is continued until the solvent in the wet gel is completely volatilized to obtain a dry gel; for example, it can be any value among 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, or a numerical range with any two of the above values ​​as endpoints.

[0021] In the specific implementation process, in S3, the dry gel obtained in S2 is crushed and ground, and the powder is placed in a porcelain boat and annealed at a high temperature in an oxygen atmosphere at a temperature of 600-1000°C, for example, any value among 600°C, 700°C, 800°C, 900°C, 1000°C or a numerical range with any two of the above values ​​as endpoints, to finally obtain Li5FeO4 / Mg 1- X Zn X Al2O4 (x=0~1.0).

[0022] In the present invention, the zinc salt can be zinc nitrate hexahydrate, zinc sulfate or other soluble zinc salts; the magnesium salt can be soluble magnesium salts such as magnesium nitrate hexahydrate and magnesium citrate; the aluminum salt can be aluminum nitrate nonahydrate, aluminum sulfate or other soluble aluminum salts.

[0023] In a specific implementation process, the complexing agent can be one of EDTA (ethylenediaminetetraacetic acid) and citric acid, or a combination in any proportion.

[0024] According to the preparation method of the composite lithium supplement material provided by the present invention, the preparation method of the composite lithium supplement material comprises: preparing a base material by a hydrothermal method, coating the surface of the base material with Mg by a sol-gel method 1- X Zn X Al2O4 oxide forms the first coating layer; and carbon material is deposited on the surface of the first coating layer to form the second coating layer.

[0025] Preferably, the hydrothermal method for preparing the matrix material comprises: heat-treating a mixture of a lithium source, an iron source and water to obtain a first mixture, performing solid-liquid separation on the first mixture, collecting the solid, washing, drying and sintering.

[0026] Preferably, the method for depositing carbon material on the surface of the first coating layer includes: introducing a gaseous carbon source into the reaction chamber for pulse deposition, then introducing an inert gas for a first purge treatment, and then introducing an oxygen source for pulse deposition, and then introducing an inert gas for a second purge treatment to complete one deposition coating, repeating 3 to 5 times to form a second coating layer.

[0027] According to the preparation method of the composite lithium supplement material provided by the present invention, the temperature of the heat treatment is 150°C to 300°C; and the temperature of the sintering is 700°C to 800°C.

[0028] In the present invention, during the preparation process of the matrix material, the heat treatment temperature is 150~300°C, for example, it can be any value among 150°C, 200°C, 250°C, 300°C, or a numerical range with any two of the above values ​​as endpoints; the heat treatment time is 5~12h, for example, it can be any value among 5h, 8h, 10h, 12h, or a numerical range with any two of the above values ​​as endpoints.

[0029] In the present invention, during the preparation process of the matrix material, the sintering temperature is 700~800℃, for example, it can be any value among 700℃, 720℃, 750℃, 780℃, 800℃, or a numerical range with any two of the above values ​​as endpoints; the sintering time is 3~8h, for example, it can be any value among 3h, 4h, 5h, 6h, 7h, 8h, or a numerical range with any two of the above values ​​as endpoints.

[0030] According to the method for preparing the composite lithium supplement material provided by the present invention, the gaseous carbon source includes at least one of methane, ethylene, propylene and propane.

[0031] According to the preparation method of the composite lithium supplement material provided by the present invention, the flow rate of the gaseous carbon source is 30 sccm~50 sccm, for example, it can be any value among 30 sccm, 40 sccm, 50 sccm, or a numerical range with any two of the above values ​​as endpoints, and the introduction time of the gaseous carbon source is 5s~10s, for example, any value among 5s, 6s, 7s, 8s, 9s, 10s, or a numerical range with any two of the above values ​​as endpoints.

[0032] According to the preparation method of the composite lithium supplement material provided by the present invention, the conditions of the first purge treatment and the second purge treatment are independently: the flow rate is 80 sccm~100 sccm, for example, it can be any value among 80 sccm, 90 sccm, 100 sccm or a numerical range with any two of the above values ​​as endpoints; the time is 30s~50s, for example, any value among 30s, 40s, 50s or a numerical range with any two of the above values ​​as endpoints.

[0033] In the present invention, the inert gas may be nitrogen, argon or helium.

[0034] According to the preparation method of the composite lithium supplement material provided by the present invention, the oxygen source includes water vapor; the flow rate of the oxygen source is 30 sccm to 50 sccm, for example, it can be any value among 30 sccm, 40 sccm, 50 sccm, or a numerical range with any two of the above values ​​as endpoints; the introduction time of the oxygen source is 1 s to 3 s, for example, any value among 1 s, 2 s, 3 s, or a numerical range with any two of the above values ​​as endpoints.

[0035] According to the preparation method of the composite lithium supplement material provided by the present invention, the deposition coating temperature is 200°C~300°C, for example, it can be any value among 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, or a numerical range with any two of the above values ​​as endpoints.

[0036] As a preferred embodiment of the present invention, the preparation method of the composite lithium supplement material includes: (1) Lithium-rich lithium ferrite is prepared by a hydrothermal method: a mixture of a lithium source, an iron source and water is heat-treated at 150°C to 300°C for 5 to 12 hours to obtain a first mixture; the first mixture is subjected to solid-liquid separation, and the solid is collected for washing, drying and sintering at a sintering temperature of 700 to 800°C for 3 to 8 hours.

[0037] (2) coating the first coating layer on the surface of the base material using a sol-gel method: Zinc salt, magnesium salt and aluminum salt are dissolved in water, and a complexing agent is added and mixed to obtain a glue solution; the glue solution is mixed with a matrix material at 50°C to 90°C to obtain a clarified sol precursor solution; the temperature is raised to 150°C to 200°C to evaporate the solvent in the sol precursor solution to obtain a dry gel; the dry gel is crushed and ground, and the obtained powder is annealed at 600°C to 1000°C in an oxygen atmosphere.

[0038] (3) Depositing carbon material on the surface of the first coating layer: introducing a gaseous carbon source into the reaction chamber for a first purge treatment, then introducing water vapor for a second purge treatment, completing a deposition coating, and repeating this process 3 to 5 times to form a second coating layer; wherein the flow rate of the gaseous carbon source is 30 sccm to 50 sccm, and the introduction time of the gaseous carbon source is 5 s to 10 s; the conditions of the first purge treatment and the second purge treatment are independently: the flow rate is 80 sccm to 100 sccm, and the time is 30 s to 50 s. The flow rate of the water vapor is 30 sccm to 50 sccm, and the introduction time of the water vapor is 1 s to 3 s. The temperature of the deposition coating is 200°C to 300°C.

[0039] In the present invention, the preparation method of the composite lithium supplement material is simple and easy, and the obtained lithium supplement material has excellent electrochemical properties and processing properties through the coordination of various steps.

[0040] In a third aspect, the present invention provides a positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer on the surface of the positive electrode current collector, wherein the positive electrode material layer comprises lithium iron phosphate material and the composite lithium supplement material.

[0041] Preferably, the mass content of the composite lithium supplement material in the positive electrode material layer is 1% to 5%, for example, it can be any value among 1%, 2%, 3%, 4%, 5%, or a numerical range with any two of the above values ​​as endpoints.

[0042] In a fourth aspect, the present invention provides a battery comprising the composite lithium supplement material or the positive electrode sheet.

[0043] The battery of the present invention has low or no gas production at high temperatures, excellent high-temperature cycle performance, good safety performance, and greatly reduced production costs, which is conducive to large-scale production.

[0044] Based on this, the technical solution of the present invention has the following beneficial effects: (1) In the composite lithium supplement material of the present invention, Mg 1-X Zn X The combination of the Al2O4 oxide coating and the carbon coating can stabilize the material structure, prevent the lithium supplement agent particles from cracking and forming new interfaces during charging and discharging, thereby reducing side reactions with the electrolyte, reducing gas production during battery cell cycling and storage, and improving the material's high-temperature storage performance and high-temperature cycling performance; at the same time, it can prevent the residual alkali on the lithium supplement agent surface from reacting with the glue to form slurry gel, thereby improving the material's processing performance.

[0045] (2) The preparation method of the composite lithium supplement material of the present invention is simple and easy. Through the coordination of various steps, the obtained lithium supplement material has excellent electrochemical properties and processing properties.

[0046] (3) The battery of the present invention has low gas production at high temperature and after multiple cycles, high high temperature cycle capacity retention rate, and good safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0048] Figure 1 This is a graph showing the capacity retention of soft-pack batteries prepared with the lithium supplement agents of Example 1 and Comparative Example 1 provided by the present invention at 45° C. and 1.68C / 1C for 1500 cycles. DETAILED DESCRIPTION

[0049] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0050] This embodiment provides a composite lithium supplement material, comprising a base material and a coating layer fully coated on the surface of the base material; the coating layer comprises a first coating layer and a second coating layer; the first coating layer is coated on the surface of the base material, and the second coating layer is coated on the surface of the first coating layer; the base material is lithium-rich lithium ferrite; the first coating layer is Mg 1-X Zn X The porosity of Al2O4 oxide is 5% to 20%, and 0.3≤x≤0.7; the second coating layer is a carbon material. 1-X Zn XThe combination of the Al2O4 oxide coating and the carbon coating stabilizes the material structure, preventing cracks in the lithium supplement particles during charge and discharge, which can lead to the formation of new interfaces. This reduces side reactions with the electrolyte, reduces gas production during battery cell cycling and storage, and improves the material's high-temperature storage and cycling performance. It also prevents residual alkali on the lithium supplement surface from reacting with the glue to form a slurry gel, improving the material's processing performance. Furthermore, when the thickness of the first coating layer is limited to 3nm to 5nm and the thickness of the second coating layer is limited to 2nm to 3nm, and the thickness difference between the first and second coating layers is controlled to be 1mm to 2.5mm within the above thickness ranges, this helps to enhance the synergistic effect of the first and second coating layers, further improving the material's high-temperature storage and cycling performance.

[0051] Unless otherwise specified, the various raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0052] Example 1 This embodiment provides a composite lithium supplement material, the preparation method of which includes the following steps: (1) Lithium hydroxide and ferric nitrate of corresponding mass were weighed according to the Li:Fe molar ratio of 5:1, dissolved in a reactor, and subjected to hydrothermal reaction at 250 °C for 6 h. LFO powder was then obtained by filtration, washing, and drying. The obtained LFO powder was then sintered at 800 °C in an oxygen atmosphere for 5 h to obtain LFO crystal particles (Li5FeO4 matrix material).

[0053] (2) According to the molar ratio of Zn:Mg:Al of 0.5:0.5:2, the corresponding mass of zinc nitrate hexahydrate, magnesium nitrate hexahydrate, and aluminum nitrate nonahydrate are weighed and fully dissolved in deionized water, and then EDTA complexing agent is slowly added thereto and stirred thoroughly, wherein the mass of EDTA is 1.5 times the total mass of the above nitrates; then Li5FeO4 matrix material powder is slowly added thereto, wherein the mass of Li5FeO4 is 1.5 times the total mass of Mg 0.5 Zn 0.5 The mass ratio of Al2O4 is 97:3, and the glue temperature is controlled at 80 °C to obtain a glue precursor; the glue temperature is increased to 180 °C, the sol precursor solution is evaporated, and stirring is continued until the solvent in the wet gel is completely evaporated to obtain a dry gel; the obtained dry gel is then crushed and ground, and placed in a porcelain boat, and annealed at 800 °C for 5 hours in an oxygen atmosphere. Finally, the thickness of the first coating layer is 4 nm and the porosity is 5%.

[0054] (3) The LFO with the first coating layer is placed in the ALD reaction chamber, and the gaseous carbon source methane is introduced into the ALD reaction chamber. The temperature in the reaction chamber is 260°C, the methane flow rate is 50 sccm, and the introduction time is 8 s; nitrogen is then introduced into the ALD reaction chamber for a second purge treatment, with a nitrogen flow rate of 80 sccm and a time of 30 s; water vapor is then introduced, with a water vapor flow rate of 30 sccm and an introduction time of 2 s; nitrogen is then introduced into the ALD reaction chamber for a third purge treatment, with a nitrogen flow rate of 80 sccm and a time of 30 s, to complete a second deposition coating; the above steps are repeated 4 times to form a second coating layer, and the thickness of the second coating layer is 2 nm.

[0055] Example 2 This embodiment provides a composite lithium supplement material. The preparation method differs from that of Example 1 in that, in step (2), corresponding amounts of zinc nitrate hexahydrate, magnesium nitrate hexahydrate, and aluminum nitrate nonahydrate are weighed and fully dissolved in deionized water in a Zn:Mg:Al molar ratio of 0.3:0.7:2. The resulting first coating layer has a thickness of 4 nm and a porosity of 10%.

[0056] Example 3 This embodiment provides a composite lithium supplement material. The preparation method differs from that of Example 1 in that, in step (2), corresponding amounts of zinc nitrate hexahydrate, magnesium nitrate hexahydrate, and aluminum nitrate nonahydrate are weighed and fully dissolved in deionized water in a Zn:Mg:Al molar ratio of 0.7:0.3:2. The resulting first coating layer has a thickness of 4 nm and a porosity of 10%.

[0057] Example 4 This embodiment provides a composite lithium supplement material, and its preparation method differs from that of Example 1 in that: in step (1), the sintering temperature of LFO is 900° C. and the sintering time is 4 h.

[0058] Example 5 This embodiment provides a composite lithium supplement material. The preparation method differs from that of Example 1 in that, in step (2), magnesium nitrate is not added, but the total amount of nitrate is controlled the same as in Example 1. Relevant amounts of zinc nitrate hexahydrate and aluminum nitrate nonahydrate are weighed and fully dissolved in deionized water at a Zn:Al molar ratio of 1:2. A first coating layer is prepared. The final first coating layer has a thickness of 4 nm and a porosity of 15%.

[0059] Example 6 This embodiment provides a composite lithium supplement material, and its preparation method differs from that of Example 1 in that: in step (2), zinc nitrate is not added, but the total amount of nitrate is controlled the same as in Example 1, and corresponding masses of magnesium nitrate hexahydrate and aluminum nitrate nonahydrate are weighed and fully dissolved in deionized water according to a Mg:Al molar ratio of 1:2 to prepare a first coating layer. The final thickness of the first coating layer is 4 nm and the porosity is 10%.

[0060] Example 7 This embodiment provides a composite lithium supplement material, and its preparation method differs from that of Example 1 in that: in step (3), LFO with a first coating layer is placed in an ALD reaction chamber, and gaseous carbon source methane is introduced into the ALD reaction chamber, the temperature in the reaction chamber is 260°C, the methane flow rate is 30 sccm, and the introduction time is 5 s; nitrogen is then introduced into the ALD reaction chamber for a second purge treatment, the nitrogen flow rate is 80 sccm, and the time is 30 s; then water vapor is introduced, the water vapor flow rate is 30 sccm, and the introduction time is 2 s; nitrogen is then introduced into the ALD reaction chamber for a third purge treatment, the nitrogen flow rate is 80 sccm, and the time is 30 s, to complete a second deposition coating; the above steps are repeated 3 times to form a second coating layer, and the final thickness of the second coating layer is 1 nm.

[0061] Example 8 This embodiment provides a composite lithium supplement material. The difference between its preparation method and that of embodiment 1 is that in step (2), the mass of the added Li5FeO4 matrix material powder is twice that of embodiment 1, that is, the mass of Li5FeO4 and Mg 0.5 Zn 0.5 The mass ratio of Al2O4 is 97:1.5, and the final thickness of the first coating layer is 2nm.

[0062] Example 9 This embodiment provides a composite lithium supplement material. The difference between its preparation method and that of embodiment 1 is that the first coating layer is prepared by mechanical ball milling. The specific preparation method is as follows: The corresponding mass of zinc oxide, magnesium oxide and aluminum oxide were weighed according to the Zn:Mg:Al molar ratio of 0.5:0.5:2 and placed in a ball mill. Then, Li5FeO4 matrix material powder was added and ethanol was added as the grinding medium for ball milling for 12 hours. After the ball milling was completed, the slurry was taken out and dried at 80°C for 2 hours, then placed in a porcelain boat and annealed at 800°C for 5 hours in an oxygen atmosphere. The final thickness of the first coating layer was 4nm and the porosity was 30%.

[0063] Comparative Example 1 This comparative example provides a lithium supplement material. The difference between its preparation method and that of Example 1 is that no coating is performed, and the Li5FeO4 matrix material is prepared according to the following method: According to the molar ratio of Li:Fe of 5:1, the corresponding mass of lithium hydroxide and ferric nitrate were weighed and dissolved in a reactor, and a hydrothermal reaction was carried out at 235°C for about 6.5 hours. Then, LFO powder was obtained through filtration, washing and drying steps. The obtained LFO powder was then sintered at 800°C in an oxygen atmosphere for 5 hours to obtain LFO crystals.

[0064] Comparative Example 2 This comparative example provides a lithium supplement material. The difference between its preparation method and that of Example 1 is that only carbon material is coated on the surface of the base material. The specific preparation method is as follows: According to the molar ratio of Li:Fe of 5:1, the corresponding mass of lithium hydroxide and ferric nitrate were weighed and dissolved in a reactor, and a hydrothermal reaction was carried out at 235°C for about 6.5 hours. Then, LFO powder was obtained through filtration, washing and drying steps. The obtained LFO powder was then solid-phase mixed with glucose and sintered at 800°C in an oxygen atmosphere for 5 hours to obtain solid-phase carbon-coated LFO crystal particles, wherein the mass ratio of LFO to glucose was 98.5:3.75.

[0065] Comparative Example 3 This comparative example provides a lithium supplement material. The difference between its preparation method and that of Example 1 is that the surface of the Li5FeO4 base material prepared in Example 1 is coated with a first coating layer, and the first coating layer contains only aluminum oxide. The preparation method is as follows: Aluminum nitrate nonahydrate is fully dissolved in deionized water, and then EDTA chelating agent is slowly added thereto and stirred thoroughly, wherein the mass of EDTA is 1.5 times the total mass of the above-mentioned nitrates; then Li5FeO4 matrix material powder is slowly added thereto, and the glue temperature is controlled to be 80 °C to obtain a glue precursor; the glue temperature is increased to 180 °C, the sol precursor solution is evaporated, and stirring is continued until the solvent in the wet gel is completely evaporated to obtain a dry gel; the obtained dry gel is then crushed and ground, and placed in a porcelain boat, and annealed at 800 °C for 5 hours in an oxygen atmosphere. Finally, the thickness of the first coating layer is 4 nm and the porosity is 5%.

[0066] Experimental example The lithium supplement materials obtained in each example and comparative example were prepared into 4Ah LFP lithium supplement soft pack batteries under the same conditions. The battery preparation method is as follows: The positive electrode main material LFP, lithium supplement agent, SP, CNT, and PVDF were added and homogenized in a mass ratio of 94.5%:2%:1%:0.5%:2%. The viscosity of the discharge material was controlled at 5500-7000 mPa·st. The positive electrode slurry was coated on carbon-coated aluminum foil with an area density of 20 mg / cm 2, after roller pressing, the compaction is 2.6g / cm 3 The main material of the negative electrode is artificial graphite, with a charge capacity of 380 mAh / g. Graphite, SP, CMC, and SBR are mixed uniformly in a mass ratio of 96%:1%:1.3%:1.7% to obtain a negative electrode slurry, which is then coated on a 6 μm thick copper foil with an area density of 9.75 mg / cm 2 , the charging N / P is 1.06, and the compaction after roller pressing is 1.5g / cm 3 ; Then assembled, the diaphragm uses Enjie's 9+1+1 diaphragm; in terms of mass percentage, the composition of the electrolyte is: LiFP613%, EC 30%, EMC 23.5%, DMC 30%, VC 3%, DTD 0.5%.

[0067] The prepared soft-pack battery was subjected to high-temperature storage and cycle performance tests after formation. The formation voltage range was 2.0V~4.2V, and the performance test voltage range was 2.0V~3.65V.

[0068] The viscosity change of the positive electrode slurry containing the lithium supplement was tested after standing for 12 hours, and the gas production and storage capacity retention rate of the battery during high temperature storage were tested. The test results are shown in Table 1 below. The gas production was calculated by measuring the battery volume before and after storage or before and after cycling using the drainage method and making the difference. The capacity retention rate of the soft-pack battery prepared with the lithium supplement of Example 1 and Comparative Example 1 at 45°C, 1.68C / 1C for 1500 cycles is shown in the figure below. Figure 1 shown.

[0069] Table 1 Test results

[0070] As can be seen from Table 1, the viscosity of the positive electrode slurry prepared with the composite lithium supplement material obtained in each embodiment changed little after standing for 12 hours, and the slurry had good stability; the positive electrode slurry prepared with the lithium supplement material obtained in the comparative example had a rapid increase in viscosity after standing for 12 hours, and the slurry had become jelly-like, with poor stability. It can be seen that the composite lithium supplement material of the present invention is beneficial to improving the stability of the positive electrode slurry and improving the processing performance.

[0071] The batteries obtained in each embodiment of the present invention have a low gas production of less than 1 mL when stored at 60°C for 30 days; the gas production after 1500 cycles at 45°C is less than 1 mL. It can be seen that the lithium supplement of the present invention can significantly improve the gas production problems of high-temperature storage and high-temperature cycling. This is because the first coating layer and the second coating layer can stabilize the material structure under the synergistic effect, avoiding the generation of cracks and new interfaces in the lithium supplement particles during the charge and discharge process, thereby reducing side reactions with the electrolyte, reducing the gas production during the battery cycle and storage process, and reducing the loss of active lithium, improving the high-temperature storage capacity retention rate of the lithium supplement battery, and the capacity retention rate after 30 days of storage at 60°C is above 93.5%. The composite lithium supplement material obtained by the method of the present invention can improve the stability of the slurry, reduce the high-temperature gas production of the battery, and improve the storage and cycle stability of the battery.

[0072] The lithium supplement material in the comparative example obtained a battery with high gas production when stored at 60°C for 30 days and high gas production after 1500 cycles at 45°C, and a relatively low capacity retention rate when stored at 60°C for 30 days.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A composite lithium supplement material, comprising a matrix material, characterized in that: The substrate further comprises a coating layer at least partially coated on the surface of the substrate; the coating layer comprises a first coating layer and a second coating layer; the first coating layer is coated on the surface of the substrate, and the second coating layer is coated on the surface of the first coating layer; The matrix material includes lithium-rich lithium ferrite; The first coating layer is Mg 1-X Zn X Al2O4 oxide, x=0~1.0; the second coating layer is a carbon material.

2. The composite lithium supplement material according to claim 1, characterized in that: The porosity of the first coating layer is 5% to 20%.

3. The composite lithium supplement material according to claim 1, characterized in that: The thickness of the first coating layer is greater than that of the second coating layer, and the difference in thickness between the first coating layer and the second coating layer is 1 mm to 2.5 mm; Preferably, the thickness of the first cladding layer is 3 nm to 5 nm; the thickness of the second cladding layer is 1 nm to 3 nm.

4. The composite lithium supplement material according to any one of claims 1 to 3, characterized in that: 0.3≤x≤0.7。 5. The method for preparing the composite lithium supplement material according to any one of claims 1 to 4, characterized in that: The method comprises coating the first coating layer on the surface of the base material by using a sol-gel method.

6. The method for preparing the composite lithium supplement material according to claim 5, characterized in that: The method for coating the first coating layer on the surface of the base material using a sol-gel method comprises the following steps: S1: dissolving zinc salt, magnesium salt and aluminum salt in water, adding a complexing agent and mixing to obtain a glue solution; S2: mixing the glue solution with a matrix material at 50° C. to 90° C. to obtain a clear sol precursor solution; heating the solution to evaporate the solvent in the sol precursor solution to obtain a xerogel; S3: crushing and grinding the dry gel, and annealing the obtained powder in an oxygen atmosphere at 600° C. to 1000° C.

7. The method for preparing the composite lithium supplement material according to claim 5, characterized in that: include: The base material is prepared by a hydrothermal method, and Mg is coated on the surface of the base material by a sol-gel method. 1-X Zn X Al2O4 oxide, forming the first coating layer; depositing a carbon material on the surface of the first coating layer to form the second coating layer; Preferably, the method for preparing the matrix material by a hydrothermal method comprises: heat-treating a mixture of a lithium source, an iron source and water to obtain a first mixture, performing solid-liquid separation on the first mixture, collecting the solid, washing, drying and sintering; Preferably, the method for depositing carbon material on the surface of the first coating layer includes: introducing a gaseous carbon source into the reaction chamber for pulse deposition, then introducing an inert gas for a first purge treatment, and then introducing an oxygen source for pulse deposition, and then introducing an inert gas for a second purge treatment to complete one deposition coating, repeating 3 to 5 times to form a second coating layer.

8. The method for preparing the composite lithium supplement material according to claim 7, characterized in that: The temperature of the heat treatment is 150°C to 300°C; the temperature of the sintering is 700°C to 800°C; Preferably, the gaseous carbon source includes at least one of methane, ethylene, propylene and propane; the oxygen source includes water vapor; Preferably, the flow rate of the gaseous carbon source is 30 sccm to 50 sccm, and the introduction time of the gaseous carbon source is 5 s to 10 s; Preferably, the conditions of the first purge process and the second purge process are independently: a flow rate of 80 sccm to 100 sccm, and a time of 30 s to 50 s; Preferably, the flow rate of the oxygen source is 30 sccm to 50 sccm, and the introduction time of the oxygen source is 1 s to 3 s; Preferably, the temperature of the deposition coating is 200°C to 300°C.

9. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode material layer on the surface of the positive electrode current collector, wherein the positive electrode material layer comprises a lithium iron phosphate material and the composite lithium supplement material according to any one of claims 1 to 4 or the composite lithium supplement material prepared by the preparation method according to any one of claims 5 to 8; preferably, the mass content of the composite lithium supplement material in the positive electrode material layer is 1% to 5%.

10. A battery, characterized in that: Contains any one or more of the following materials: a) The composite lithium supplement material according to any one of claims 1 to 4; b) the composite lithium supplement material prepared by the preparation method according to any one of claims 5 to 8; c) The positive electrode sheet according to claim 9.

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