Phosphate positive electrode active material, preparation method therefor, positive electrode sheet, battery cell and electrical apparatus

Abstract

A phosphate positive electrode active material, a preparation method therefor, a positive electrode sheet, a battery cell and an electrical apparatus. The method comprises: providing a mixed solution comprising a lithium source, a metal source, a phosphorus source and a surfactant, the metal source being an iron source and / or a manganese source; subjecting the mixed solution to a hydrothermal reaction to prepare reaction particles; mixing the reaction particles with a carbon source, and wet grinding same to obtain a paste; and performing heat treatment on the paste to prepare a phosphate positive electrode active material, the temperature of the heat treatment being 650℃ to 1300℃. The present method improves the conductivity and the capacity per gram of the carbon-coated phosphate positive electrode active material, increases the charge-discharge capacity and the cycle capacity retention rate of battery cells, and greatly enhances the continuity of production processes. The positive electrode sheet, battery cell and electrical apparatus having the beneficial effects of the positive electrode active material can be achieved.

Description

Phosphate cathode active material, preparation method thereof, cathode sheet, battery cell and electric device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese Patent Application No. 202410653401.0, filed on May 24, 2024, entitled “Phosphate cathode active material, preparation method thereof, cathode sheet, battery cell and electric device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application belongs to the technical field of batteries, and specifically relates to a phosphate cathode active material, a preparation method thereof, a cathode sheet, a battery cell and an electric device. BACKGROUND

[0004] The cathode active material of a lithium ion battery is crucial to the performance of the battery. At present, the most studied cathode active material is a phosphate cathode active material, such as LiFePO4, LiFe 0.5 Mn 0.5 PO4. It has the advantages of high structural stability, good reliability, moderate working voltage, good platform characteristics, and large theoretical capacity, and has gradually become a hot spot for battery researchers to compete.

[0005] However, the phosphate cathode active material has a relatively obvious disadvantage in the preparation process, and the lattice defects of the cathode active material are large, which directly leads to a small overall gram capacity of the material, hindering the practical application of the material. Therefore, it is necessary to improve the preparation method of the phosphate cathode active material.

[0006] SUMMARY

[0007] The purpose of the present application is to provide a preparation method of a phosphate cathode active material, to improve the sphericity of the phosphate cathode active material, to reduce the lattice defects in the cathode active material, and thus to improve the gram capacity of the cathode active material; the cathode sheet containing the cathode phosphate cathode active material obtains an improved gram capacity, the battery cell containing the cathode sheet obtains an improved battery energy density and cycle capacity retention rate; the present application also aims to provide an electric device capable of achieving the beneficial effects of the battery cell.

[0008] In a first aspect, an embodiment of the present application provides a preparation method of a phosphate cathode active material, which comprises:

[0009] providing a mixed solution comprising a lithium source, a metal source, a phosphorus source and a surfactant, the metal source being an iron source and / or a manganese source;

[0010] carrying out a hydrothermal reaction on the mixed solution to obtain reaction particles;

[0011] The reaction particles are mixed with a carbon source and wet ground to obtain a slurry;

[0012] The slurry is heat treated at a temperature of 650°C or higher to obtain the phosphate cathode active material.

[0013] In the present embodiment, the surfactant in the mixed solution plays a role in dispersing the lithium source, iron source and other particles. The surfactant has a certain surface activity, can improve the interaction between the particles and the solution and between the particles and the particles on the surface of the particles, reduce the degree of aggregation between the particles, keep uniform dispersion, and is not prone to precipitation or agglomeration. This facilitates the subsequent treatment of the mixed solution.

[0014] More importantly, the surfactant in the mixed solution is conducive to controlling the particle morphology of the product obtained by the subsequent hydrothermal reaction, improving the sphericity of the product, reducing the lattice defect rate of the cathode active material, and facilitating the preparation of reaction particles with higher sphericity, thereby facilitating the improvement of the capacity of the cathode active material.

[0015] In the present embodiment, the heat treatment is carried out at a temperature of 650°C or higher. On the one hand, this is conducive to improving the graphitization degree of the carbon source, improving the overall conductivity of the phosphate cathode active material, and improving the cycle performance in the battery; on the other hand, heat treatment at this temperature can further reduce the lattice defect rate of the phosphate cathode active material by promoting the thermal motion of defect site atoms and lattice self-repairing under high temperature conditions. In addition, heat treatment at this temperature reduces the heat treatment time, reduces energy consumption, improves production efficiency, and is conducive to batch industrial production.

[0016] In summary, the preparation method of the present embodiment solves the problem of poor cycle performance of the battery due to particle agglomeration and the like in the preparation of phosphate cathode active materials by hydrothermal / solvothermal method at a temperature of 650°C or higher. The reason may be that further heat treatment of the reaction particles at this temperature can promote the thermal motion of defect site atoms and lattice self-repairing under high temperature conditions, which can further reduce the lattice defect rate of the phosphate cathode active material, thereby improving the cycle performance of the battery. In addition, heat treatment at this temperature also completes the carbon coating modification of the material surface, so that the carbon has a higher graphitization degree, and the conductivity of the carbon-coated phosphate cathode active material is improved. In addition, the continuity of the production process is also greatly improved.

[0017] Due to the improved conductivity and specific capacity of the carbon-coated phosphate cathode active material, the battery containing the material has improved kinetic performance and cycle performance.

[0018] According to an embodiment of one aspect of the present application, the surfactant includes one or more of tartaric acid, propylene glycol, isopropyl alcohol, citric acid, glycerol, ethylenediamine, triethanolamine, ethylenediaminetetraacetic acid. The surfactant is of the above-mentioned kind, which is conducive to dispersing the particles of the lithium source, the iron source, and the like, controlling the particle morphology of the product obtained by the subsequent hydrothermal reaction, and improving the sphericity of the subsequent product,

[0019] According to an embodiment of one aspect of the present application, the ratio of the molar amount of the surfactant to the amount of substance of phosphorus in the phosphorus source is 1:(10-20). The ratio of the molar amount of the surfactant to the amount of substance of phosphorus in the phosphorus source is in the above-mentioned range, which can further improve the dispersing degree and stability of the phosphorus source in the solution and improve the sphericity of the product of the hydrothermal reaction,

[0020] According to an embodiment of one aspect of the present application, the lithium source includes one or more of lithium carbonate, lithium acetate, lithium citrate, lithium dihydrogen phosphate, lithium hydroxide, and lithium phosphate.

[0021] According to an embodiment of one aspect of the present application, the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0022] According to an embodiment of one aspect of the present application, the iron source includes one or more of ferrous sulfate, ferrous hydroxide, ferrous oxalate, ferrous acetate, and ferrous chloride.

[0023] According to an embodiment of one aspect of the present application, the carbon source includes one or more of glucose, sucrose, polyvinyl alcohol, polyethylene glycol, gelatin, and polyvinylpyrrolidone.

[0024] According to an embodiment of one aspect of the present application, the phosphate positive electrode active material is a lithium iron manganese phosphate positive electrode active material, and a mixed solution including a lithium source, a metal source, a phosphorus source, and a surfactant is provided, wherein the metal source is an iron source and / or a manganese source, and includes:

[0025] A mixed solution including a lithium source, an iron source, a phosphorus source, a manganese source, and a surfactant is provided.

[0026] According to an embodiment of one aspect of the present application, the mixed solution further includes a doping element source, and the doping element source includes one or more of a sulfate, a nitrate, a hydrochloride, and an acetate of an M element; the M element represents a doping element of a Mn site and / or a Fe site of the phosphate composite positive electrode active material.

[0027] According to an embodiment of one aspect of the present application, the M element includes one or more of Mg, Zn, Ti, Zr, V, Ni, Al, Cr, Nb, and W.

[0028] In the embodiment, the mixed solution further comprises a doping element source, and a metal element included in the doping element source can partially replace a position of iron in a lattice in the phosphate positive electrode active material, so that modification of the phosphate positive electrode active material is realized, and performance of the phosphate positive electrode active material is changed.

[0029] According to an embodiment of one aspect of the present application, a mixed solution comprising a lithium source, a metal source, a phosphorus source and a surfactant is provided, and the metal source is an iron source and / or a manganese source, which comprises:

[0030] A first mixed solution comprising a lithium source and a metal source is provided.

[0031] A second mixed solution comprising a phosphorus source and a surfactant is provided.

[0032] The first mixed solution is mixed with the second mixed solution to obtain a mixed solution comprising a lithium source, an iron source, a phosphorus source and a surfactant.

[0033] In the embodiment, the phosphorus source and the surfactant are independently mixed, the phosphorus source can be better dispersed, the phosphorus source and the surfactant can be dispersed into a stable complex, the sphericity of a subsequent product can be further controlled, the lattice defect of the phosphate positive electrode active material can be reduced, and thus the specific capacity of the phosphate positive electrode active material can be improved.

[0034] According to an embodiment of one aspect of the present application, the mixed solution is subjected to a hydrothermal reaction, which can specifically include: the mixed solution is heated to 160-240 ℃ and then is kept for a certain time, and the heating rate is 1-5 ℃ / min.

[0035] In the embodiment, the reaction temperature and the heating rate of the hydrothermal reaction are controlled, which is beneficial to control the morphology and the lattice defect rate of the reaction particles.

[0036] According to an embodiment of one aspect of the present application, the mixed solution is subjected to a hydrothermal reaction, which can specifically include: the mixed solution is placed in a hydrothermal reaction kettle for hydrothermal reaction, and the filling degree of the mixed solution in the hydrothermal reaction kettle is 50%-85%.

[0037] In the embodiment, the mixed solution in the hydrothermal reaction kettle is in a vacuum state at the initial moment of the reaction, and as the reaction proceeds, water vapor is evaporated, the mixed solution in the hydrothermal reaction kettle is in a high-temperature and high-pressure state, which is beneficial to the reaction, and the filling degree is in the above range, which is beneficial to improve the reaction efficiency and control the morphology and the lattice defect rate of the reaction particles under the premise of ensuring the safety of the experiment.

[0038] According to an embodiment of one aspect of the present application, the holding time of the hydrothermal reaction is 7-15 h.

[0039] In the embodiment, the heat preservation time is in the above range, which is beneficial to making the crystal growth of the phosphate cathode active material more complete and orderly; and can be helpful to the lattice rearrangement and stability of the crystal, thereby improving the crystallinity and the order degree of the crystal structure of the phosphate cathode active material, and improving the purity and the electrochemical performance of the phosphate cathode active material.

[0040] According to the embodiment of one aspect of the present application, before the heat treatment of the slurry, the method further comprises the step of: performing spray drying treatment on the slurry. In the embodiment, the spray drying treatment on the slurry can better realize the carbon coating, so as to perform high-temperature heat treatment and improve the performance of the carbon-coated phosphate cathode active material.

[0041] According to the embodiment of one aspect of the present application, the mass content of the carbon source is 0.5% to 16% based on the total dry weight of the reaction particles and the carbon source.

[0042] In the embodiment of the present application, the mass content of the carbon source in the total dry weight of the reaction particles and the carbon source is controlled in the above range, which is beneficial to improving the conductivity on the basis of taking into account the cycle performance, and is also beneficial to further improving the specific capacity of the phosphate cathode active material.

[0043] According to the embodiment of one aspect of the present application, the temperature of the heat treatment is 750°C to 1300°C.

[0044] In the embodiment of the present application, the heat treatment can be performed by using a specific boiler, such as a high-temperature reaction furnace. When the temperature of the heat treatment is in the above range, the graphitization degree of the carbon coating layer can be further improved, the conductivity of the carbon-coated phosphate cathode active material can be further improved, the lattice defect rate of the phosphate cathode active material can be further reduced, and the specific capacity of the cathode active material can be improved.

[0045] According to the embodiment of one aspect of the present application, the time of the heat treatment is 1h to 2h. In the embodiment of the present application, the time of the heat treatment is in the above range, which can improve the conductivity and the specific capacity of the phosphate cathode active material, and improve the production efficiency of the material.

[0046] In a second aspect, the embodiment of the present application provides a phosphate cathode active material, which is prepared by the preparation method of the first aspect. The graphitization degree of the carbon coating layer in the phosphate cathode active material of the embodiment is improved, the lattice defect degree is improved, and thus the phosphate cathode active material has improved conductivity and specific capacity, which is beneficial to improving the energy density, cycle performance and kinetic performance of a battery cell containing the phosphate cathode active material.

[0047] According to the embodiment of one aspect of the present application, the cathode active material comprises:

[0048] The core contains phosphate, and its chemical formula is: LiFe m Mn j M n PO4, m>0, j≥0, n≥0, M includes one or more of Mg, Zn, Ti, Zr, V, Ni, Al, Cr, Nb and W;

[0049] A carbon coating layer covers at least a portion of the surface of the core structure.

[0050] According to one embodiment of this application, the peak intensity I of the carbon-containing D peak in the Raman spectrum of the carbon coating layer is... D Peak intensity I of G peak G The following condition must be met: 1.5 ≤ I G / I D ≤4. In this embodiment, the graphitization degree of the carbon coating layer in the phosphate cathode active material is further improved, thus the phosphate cathode active material has improved conductivity, which is beneficial to improving the dynamic performance of the battery cell containing the phosphate cathode active material.

[0051] Thirdly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive active material film layer disposed on at least one side of the positive current collector. The positive active material film layer comprises a phosphate positive active material prepared by the preparation method of the first aspect or a phosphate positive active material prepared by the second aspect. The positive electrode sheet of this embodiment includes the phosphate positive active material, and therefore also has the above-mentioned beneficial effects.

[0052] Fourthly, embodiments of this application provide a battery cell including the positive electrode sheet of the third aspect. The battery cell of this embodiment includes the positive electrode sheet, and therefore also has the aforementioned beneficial effects.

[0053] Fifthly, embodiments of this application provide an electrical device including a battery cell from the fourth aspect. The electrical device of this embodiment includes this battery cell and therefore also has the aforementioned beneficial effects. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0055] Figure 1 shows a schematic flowchart of a method for preparing a phosphate positive electrode active material according to an embodiment of this application.

[0056] Fig. 2 shows a process flow diagram of a spray drying and heat treatment of a phosphate cathode active material according to an embodiment of the present application.

[0057] Fig. 3 shows a schematic diagram of an embodiment of a battery cell according to the present application.

[0058] Fig. 4 shows an exploded schematic diagram of the battery cell shown in Fig. 1.

[0059] Fig. 5 shows a schematic diagram of an embodiment of an electrical device comprising a battery cell according to the present application as a power source.

[0060] Fig. 6 shows a scanning electron microscope image of a phosphate cathode active material prepared according to Example 1 of the present application.

[0061] Fig. 7 shows an X-ray diffraction pattern of a phosphate cathode active material prepared according to Example 1 and Comparative Example 1 of the present application.

[0062] Fig. 8 shows a scanning electron microscope image of a phosphate cathode active material prepared according to Example 2 of the present application.

[0063] Fig. 9 shows an X-ray diffraction pattern of a phosphate cathode active material prepared according to Example 2 of the present application.

[0064] Fig. 10 shows a scanning electron microscope image of a phosphate cathode active material prepared according to Comparative Example 1 of the present application.

[0065] wherein 101, carrier gas source; 102, flow meter; 103, slurry container; 104, spray drying device; 105, reaction furnace; 106, material collector.

[0066] In the drawings, the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0067] Hereinafter, embodiments of an electrode assembly and a method of manufacturing the same, a battery cell, a battery module, a battery pack, and an electrical device according to the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters well known in the art, repeated descriptions of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0068] The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges are also intended to include any and all sub-ranges of the same, wherein each sub-range is inclusive of the end values. For example, if a range is from 1 to 10, then the range includes any and all sub-ranges between (and including) the minimum of 1 and the maximum of 10, that is, any of 1 to 3, 4 to 6, 7 to 9, etc. In other words, unless context dictates otherwise, each numerical range is intended to indicate the range including the minimum and maximum values, and any numerical sub-ranges falling within the minimum and maximum values.

[0069] Unless otherwise indicated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0070] Unless otherwise indicated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0071] Unless otherwise indicated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0072] Unless otherwise indicated, in the present application, the term "active ion" refers to an ion that can be reversibly intercalated and deintercalated between the positive and negative electrodes of a battery cell.

[0073] As appeared in the present application, "multiple" refers to two or more (including two). As appeared in the present application, "multiple", "several" refers to two or more (including two). As appeared in the present application, "multiple", "several" refers to two or more (including two).

[0074] As in the background art, the preparation method of the existing phosphate positive electrode active material has large lattice defects, which directly leads to small specific capacity of the whole material.

[0075] For example, the hydrothermal method is the mainstream choice for preparing high-performance and high-consistency phosphate positive electrode active materials. However, there are still great difficulties in controlling the particle morphology and particle size synthesized by the hydrothermal method, and the reaction temperature is low when preparing lithium iron phosphate by the hydrothermal / solvothermal method, which is easy to cause anti-site defects in the material lattice.

[0076] In addition, the high-temperature solid-phase method is used in industry to prepare phosphate positive electrode active materials. Although this method has a simple process route and is easy to mass-produce, it has high product production energy consumption, uneven material mixing, incomplete reaction, large primary particle size of finished products, uneven particle size distribution, and serious particle agglomeration, which results in poor product electrochemical performance, etc., which seriously restricts the charge and discharge performance of the battery cell.

[0077] Based on this, the present application provides a preparation method, which can continuously produce and prepare phosphate positive electrode active materials, and improve the lattice defect rate of the phosphate positive electrode active materials.

[0078] Preparation method of phosphate positive electrode active material

[0079] FIG. 1 is a flowchart of a preparation method of a phosphate positive electrode active material according to an embodiment of the present application. As shown in FIG. 1, the method comprises steps 101, 102, 103 and 104.

[0080] Step 101, a mixed solution comprising a lithium source, a metal source, a phosphorus source and a surfactant is provided, and the metal source is an iron source and / or a manganese source.

[0081] In this step, the lithium source, the iron source and the phosphorus source can be the raw materials commonly used for preparing the phosphate positive electrode active material.

[0082] In this step, the surfactant plays a role in dispersing the lithium source, the iron source and other particles in the mixed solution. The surfactant has good surface activity, can reduce the aggregation degree between particles through the interaction between the particle surface and the solution or between the particles, keep uniform dispersion, is not easy to precipitate or agglomerate, and is conducive to obtaining reaction particles with higher sphericity, thereby facilitating the subsequent treatment of the mixed solution.

[0083] More importantly, the surfactant in the mixed solution is conducive to controlling the particle morphology of the product obtained by the subsequent hydrothermal reaction, improving the sphericity of the product, and improving the capacity of the positive active material and reducing the lattice defect rate of the positive active material.

[0084] In step 102, the mixed solution is subjected to hydrothermal reaction to obtain reaction particles.

[0085] In this step, the mixed solution is subjected to hydrothermal reaction, i.e., the lithium source, iron source, and phosphorus source in the mixed solution are reacted. The reaction particles can be phosphate positive active materials or precursors of partial phosphate positive active materials. The reaction particles have good sphericity, which is conducive to improving the capacity of the positive active material and reducing the lattice defect rate of the positive active material.

[0086] In step 103, the reaction particles are mixed with a carbon source and subjected to wet grinding to obtain a slurry.

[0087] In this step, the reaction particles are mixed with the carbon source to directly prepare carbon-coated positive active materials. This continuous reaction reduces the complexity of the process and improves production efficiency.

[0088] In this step, the mixture containing the reaction particles and the carbon source is subjected to wet grinding, which improves the uniformity of the contact between the reaction particles and the carbon source, reduces the particle size of the reaction particles, and improves the consistency of the particle size of the reaction particles. This is conducive to more uniform doping of carbon in the phosphate positive active material during subsequent heat treatment and is also conducive to reducing the lattice defect rate of the phosphate positive active material.

[0089] In step 104, the slurry is subjected to heat treatment to obtain phosphate positive active materials, wherein the heat treatment temperature is greater than or equal to 650°C.

[0090] In this step, heat treatment is performed at a temperature greater than or equal to 650°C. On the one hand, this is conducive to improving the graphitization degree of the carbon source, improving the overall conductivity of the phosphate positive active material, and improving the cycle performance in the battery. On the other hand, heat treatment at this temperature can further reduce the lattice defect rate of the phosphate positive active material by promoting the thermal motion of defect point atoms and lattice self-repairing under high temperature conditions. In addition, heat treatment at this temperature reduces the heat treatment time, reduces energy consumption, improves production efficiency, and is conducive to batch industrial production. For example, the heat treatment temperature can be any value in the range of 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, or a range composed of any of these values.

[0091] In summary, the preparation method of the embodiments of the present application solves the problems of poor cycle performance and low energy density of the battery caused by particle agglomeration and the like of the phosphate positive electrode active material prepared by the hydrothermal / solvothermal method at a temperature greater than or equal to 650°C. The reason may be that further heat treatment of the reaction particles at this temperature can promote the thermal motion of defect point atoms and the self-repair of the crystal lattice under high temperature conditions, which can further reduce the lattice defect rate of the phosphate positive electrode active material, thereby improving the cycle performance and energy density of the battery cell. In addition, the heat treatment at this temperature also completes the carbon-coated modification of the material surface, so that the carbon has a higher graphitization degree, and the conductivity of the carbon-coated phosphate positive electrode active material is improved. In addition, the continuity of the production process is also greatly improved.

[0092] Due to the improved conductivity and specific capacity of the carbon-coated phosphate positive electrode active material, the battery containing the material has improved kinetic performance and cycle performance.

[0093] In some optional embodiments, in order to disperse the particles of the lithium source, the iron source and the like, control the particle morphology of the product obtained by the subsequent hydrothermal reaction, and improve the sphericity of the subsequent product, the surface active agent includes one or more of tartaric acid, propylene glycol, isopropyl alcohol, citric acid, glycerol, ethylenediamine, triethanolamine, and ethylenediaminetetraacetic acid. The surface active agent in this step can be a substance with the above-mentioned properties, such as an organic acid, an organic alcohol or an organic amine substance.

[0094] In some embodiments, in order to further disperse the particles of the lithium source, the iron source and the like, control the particle morphology of the product obtained by the subsequent hydrothermal reaction, and improve the sphericity of the subsequent product, the surface active agent is an amine surface active agent. The amine surface active agent includes one or more of ethylenediamine, triethanolamine, and ethylenediaminetetraacetic acid.

[0095] The reason why the amine surface active agent can further improve the sphericity of the subsequent product may be that the amine surface active agent forms a stable complex with the phosphorus source, which is beneficial to the nucleation of the crystal grains in the subsequent hydrothermal reaction, thereby improving the morphology and sphericity of the product of the hydrothermal reaction, and improving the specific capacity of the phosphate positive electrode active material.

[0096] In some optional embodiments, in order to further improve the dispersion degree and stability of the phosphorus source in the solution and improve the sphericity of the product of the hydrothermal reaction, the molar ratio of the surface active agent to the amount of substance of phosphorus in the phosphorus source is 1:(10-20).

[0097] Optionally, the ratio of the molar amount of the surfactant to the amount of substance of the phosphorus element in the phosphorus source can be any value in the range consisting of 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20 or a range composed thereof.

[0098] In some optional embodiments, in order to obtain the phosphate positive electrode active material, the lithium source comprises one or more of lithium carbonate, lithium acetate, lithium citrate, lithium dihydrogen phosphate, lithium hydroxide, lithium phosphate.

[0099] In some optional embodiments, in order to obtain the phosphate positive electrode active material, the phosphorus source comprises one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate.

[0100] In some optional embodiments, in order to obtain the phosphate positive electrode active material, the iron source comprises one or more of ferrous sulfate, ferrous hydroxide, ferrous oxalate, ferrous acetate, ferrous chloride, ferrous nitrate.

[0101] In some optional embodiments, the molar amount M of the phosphorus element in the phosphorus source is 0.3-2 mol / L. p The ratio of the molar amount of the phosphorus element to the molar amount of the iron source and the metal source is (1-1.05):1. In some optional embodiments, the molar concentration of the phosphorus element in the mixed solution is 0.3-2 mol / L.

[0102] In some optional embodiments, in order to obtain the carbon-coated phosphate positive electrode active material, the carbon source comprises one or more of glucose, sucrose, polyvinyl alcohol, polyethylene glycol, gelatin, polyvinylpyrrolidone.

[0103] Generally, the phosphate positive electrode active material comprises lithium iron phosphate positive electrode active material, lithium manganese iron phosphate positive electrode active material, and metal element modified lithium manganese iron phosphate positive electrode active material.

[0104] In some optional embodiments, the phosphate positive electrode active material is a lithium manganese iron phosphate positive electrode active material, and in step 101, the mixed solution comprising the lithium source, the metal source, the phosphorus source and the surfactant is provided, and the metal source comprises the iron source and the manganese source, and the iron source comprises:

[0105] The mixed solution comprising the lithium source, the iron source, the phosphorus source, the manganese source and the surfactant is provided.

[0106] In some optional embodiments, in step 101, according to an embodiment of the aspect of the application, the mixed solution further comprises a doping element source, and the doping element source comprises one or more of a sulfate, a nitrate, a hydrochloride and an acetate of an M element; the M element represents a doping element of the Mn site and / or the Fe site of the phosphate composite positive electrode active material.

[0107] In some optional embodiments, the M element comprises one or more of Mg, Zn, Ti, Zr, V, Ni, Al, Cr, Nb, and W.

[0108] In the present embodiment, the mixed solution further comprises a doping element source, and a metal element included in the doping element source can partially replace the position of iron in the lattice of the phosphate positive electrode active material, so as to realize modification of the phosphate positive electrode active material and facilitate change of the performance of the phosphate positive electrode active material.

[0109] In some optional embodiments, the step 101 of providing the mixed solution comprising the lithium source, the metal source, the phosphorus source, and the surfactant comprises:

[0110] The first mixed solution comprising the lithium source and the metal source is provided.

[0111] The second mixed solution comprising the phosphorus source and the surfactant is provided.

[0112] The first mixed solution is mixed with the second mixed solution to obtain the mixed solution comprising the lithium source, the iron source, the phosphorus source, and the surfactant.

[0113] In the present embodiment, the phosphorus source and the surfactant are independently mixed, which can better disperse the phosphorus source, disperse the phosphorus source and the surfactant into a stable complex, further control the sphericity of the subsequent product, reduce the lattice defects of the phosphate positive electrode active material, and thus improve the specific capacity of the phosphate positive electrode active material.

[0114] In some optional embodiments, the step 102 of performing the hydrothermal reaction on the mixed solution can specifically comprise: after the mixed solution is warmed to 160-240℃, the mixed solution is kept warm, and the warming rate is 1-5℃ / min.

[0115] In the present embodiment, the reaction temperature and the warming rate of the hydrothermal reaction are controlled, which is beneficial to control the morphology and the lattice defect rate of the reaction particles. Exemplarily, the target temperature of the warming can be any value or a range composed of any values in 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, and 240℃; and the warming rate can be any value or a range composed of any values in 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, and 5℃ / min.

[0116] In some optional embodiments, the step 102 of performing the hydrothermal reaction on the mixed solution can specifically comprise: the mixed solution is placed in a hydrothermal reaction kettle to perform the hydrothermal reaction, and the filling degree of the mixed solution in the hydrothermal reaction kettle is 50%-85%.

[0117] In the present embodiment, the mixed solution in the hydrothermal reactor is in a vacuum state at the initial moment of the reaction, and as the reaction proceeds, water vapor evaporates, and the mixed solution is in a high-temperature and high-pressure state, which is conducive to the reaction; and the filling degree is in the above range, which is conducive to improving the reaction efficiency and controlling the morphology and lattice defect rate of the reaction particles under the premise of ensuring the safety of the experiment. For example, the filling degree of the mixed solution in the hydrothermal reactor can be any value or a range composed of any values in 50%, 55%, 60%, 65%, 70%, 75%, 80%, and 85%.

[0118] In some optional embodiments, the holding time of the hydrothermal reaction is 7-15 h. Alternatively, the holding time can be any value or a range composed of any values in 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, and 15 h.

[0119] In the present embodiment, the holding time is in the above range, which is conducive to making the crystal growth of the phosphate positive electrode active material more complete and orderly; and can help the crystal lattice rearrangement and stability, thereby improving the crystallinity and the order degree of the crystal structure of the phosphate positive electrode active material, and improving the purity and the electrochemical performance of the phosphate positive electrode active material.

[0120] In some optional embodiments, in order to better realize the carbon coating and improve the performance of the carbon-coated phosphate positive electrode active material, the slurry is further subjected to a spray drying treatment before being subjected to the heat treatment.

[0121] In some optional embodiments, the inlet temperature of the spray drying treatment is 200-280°C, and the outlet temperature is 100-120°C.

[0122] In some optional embodiments, the speed of the spray drying treatment is 0.05-0.2 L / min.

[0123] In some optional embodiments, the spray drying treatment can be carried out in an air atmosphere. The product after the spray drying treatment can be conveyed to a high-temperature furnace by using a carrier gas. The carrier gas used is an inert gas, and the flow rate of the inert gas is 10-40 L / min. The carrier gas can be any one of nitrogen, hydrogen, helium, neon, argon, and carbon dioxide.

[0124] In some optional embodiments, the step 102 of subjecting the mixed solution to a hydrothermal reaction to prepare reaction particles can specifically include:

[0125] subjecting the mixed solution to a hydrothermal reaction to prepare reaction particles,

[0126] The reaction particles are washed and dried.

[0127] In some alternative embodiments, step 103, the reaction particles are mixed with the carbon source and wet ground to obtain the slurry;

[0128] The reaction particles are mixed with the carbon source and wet ground in the presence of a solvent to obtain the slurry; the solvent can be one or more of water, ethanol, acetone, and butanone, and is preferably deionized water. The mass fraction of the solvent in the slurry is 40wt% to 80wt%.

[0129] The reaction particles are mixed with the carbon source and wet ground to achieve continuity in the production process, and the same batch of reaction particles and carbon source can continuously enter the next reaction stage, avoiding additional storage of the reaction particles before carbon coating or carbon doping.

[0130] In some alternative embodiments, step 103, the mass content of the carbon source is 0.5% to 16% based on the total dry weight of the reaction particles and the carbon source. Alternatively, the mass content of the carbon source can be any of 0.5%, 1.5%, 2.5%, 3.5%, 4.5%, 5.5%, 6.5%, 7.5%, 8.5%, 9.5%, 10.5%, 11.5%, 12.5%, 13.5%, 14.5%, 15.5% or a range consisting of any of these values.

[0131] In the embodiments of the present application, the total dry weight of the reaction particles and the carbon source refers to the mass of the solid portion after removing the water from the mixed solution containing the reaction particles and the carbon source. The mass of the solid portion refers to the mass after removing the water from the mixed solution to reach a constant weight. The sample (mixed solution) is dried at a specific temperature (generally around 90-105 degrees), until the difference in mass between two consecutive weighings is not more than 0.1% of the mass of the sample before drying, i.e. the constant weight is reached. This mass is the total dry weight of the reaction particles and the carbon source. In some embodiments, the carbon source includes carbon source. The carbon source can also include other carbon sources such as Ketjen black, carbon nanotubes, graphene, etc.

[0132] In some alternative embodiments, step 104, the temperature of the heat treatment is 750°C to 1300°C.

[0133] In the embodiments of the present application, the heat treatment can be performed using a specific boiler, such as a high-temperature reaction furnace. When the temperature of the heat treatment is in the above range, the graphitization degree of the carbon coating layer can be further improved, the electrical conductivity of the carbon-coated phosphate positive active material can be further improved, and the lattice defect rate of the further phosphate positive active material can be reduced, thereby improving the specific capacity of the positive active material.

[0134] In some alternative embodiments, in order to improve the conductivity and gram capacity of the phosphate positive electrode active material, and to improve the production efficiency of the material, the heat treatment time is 1 h to 2 h.

[0135] Alternatively, the heat treatment time can be any value in the range of 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, 2.0 h or a range composed of the above values.

[0136] In some alternative embodiments, after step 104, the phosphate positive electrode active material is subjected to crushing and sieving, iron removal, and the phosphate positive electrode active material is prepared. The crushing method can be air jet milling or other crushing methods commonly used in the art.

[0137] FIG. 2 is a process flow diagram of a spray drying and heat treatment process of a phosphate positive electrode active material according to an embodiment of the present application. The ball-mixed slurry is contained in the slurry container 103, and after being atomized by the spray drying device 104, the atomized material is sent into the reaction furnace 105 under the action of the protective carrier gas from the carrier gas source 101, the flow rate of which is controlled by the flow meter 102. The atomized material moves in a spiral track in the reaction furnace under the action of the protective gas, and under the action of the high temperature of the reaction furnace 105, the crystallinity of the nanoparticles is improved, and the carbon source is cracked and carbonized at high temperature, completing the coating modification of the particle surface. The temperature of the reaction furnace 105 is controlled to be 750-1300°C, and by adjusting the carrier gas flow rate and the effective size of the furnace body, the processing time of the material in the reaction furnace can be controlled, and the material is prepared, which is then loaded into the material collector 106.

[0138] In the embodiment of the present application, the hydrothermal product is compounded with a carbon source and then subjected to continuous heat treatment, and the spray drying and heat treatment process can realize continuous production, improve the crystallinity of the phosphate positive electrode active material, reduce the production cost, and promote the graphitization degree of carbon in the phosphate positive electrode active material.

[0139] Phosphate positive electrode active material

[0140] In a second aspect, the present application provides a phosphate positive electrode active material prepared by the preparation method of the first aspect.

[0141] In the embodiment, the phosphate positive electrode active material has improved conductivity and gram capacity, and in a battery containing the material, the battery has improved battery cell capacity and cycle capacity stability.

[0142] In some alternative embodiments, the phosphate positive electrode active material comprises:

[0143] The core comprises a phosphate with a chemical formula of LiFe m Mnj M n PO4, m>0, j≥0, n≥0, M includes one or more of Mg, Zn, Ti, Zr, V, Ni, Al, Cr, Nb and W;

[0144] A carbon coating layer covers at least a portion of the surface of the core structure.

[0145] In this embodiment, the phosphate cathode active material has a carbon coating layer with a high degree of graphitization; and the phosphate cathode active material has high sphericity and low lattice defect rate, which improves the conductivity and specific capacity of the carbon-coated phosphate cathode active material. In the battery containing this material, the battery achieves improved kinetic performance and cycle performance.

[0146] In some alternative implementations, m+j+n=1. In some alternative implementations, m+2j+n=。 In some alternative implementations, m+j+2n=1.

[0147] In some alternative embodiments, the carbon coating layer exhibits a peak intensity I of the D peak in the Raman spectrum. D Peak intensity I of G peak G The following condition must be met: 1.5 ≤ I G / I D ≤4. In this embodiment, the graphitization degree of the carbon coating layer in the phosphate cathode active material is further improved, thus the phosphate cathode active material has improved conductivity, which is beneficial to improving the dynamic performance of the battery cell containing the phosphate cathode active material.

[0148] Positive electrode sheet

[0149] Thirdly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive active material film layer disposed on at least one side of the positive current collector, wherein the positive active material film layer comprises a phosphate positive active material prepared by the preparation method of the first aspect or a phosphate positive active material of the second aspect.

[0150] The presence of phosphate-based positive electrode active materials in the positive electrode active material film layer is beneficial for improving battery capacity and energy density, thereby comprehensively changing battery performance.

[0151] In some alternative embodiments, the positive electrode active material film layer comprises 85% to 99% phosphate positive electrode active material.

[0152] In some alternative embodiments, the positive electrode active material film layer includes a binder and a conductive agent. In some embodiments, the positive electrode active material film layer includes 0.1% to 5% binder and 0.1% to 5% conductive agent.

[0153] When the positive active material film layer has the conductive agent or the binder, the positive active material film layer has certain cohesive strength, the flexibility of the positive active material film layer can be improved, the probability of breakage or cracking of the positive active material film layer during winding or folding can be reduced, and the conductivity of the positive electrode sheet is improved, and the internal resistance of the positive electrode sheet is reduced.

[0154] In some optional embodiments, the positive active material film layer includes 0.4% to 10% of the conductive agent, and the conductive agent can be 0.7% to 5% based on the total mass of the positive active material film layer.

[0155] The content of the conductive agent in the positive active material film layer is in the above range, which is beneficial to reduce the internal resistance of the positive electrode sheet, reduce the internal resistance of the battery, facilitate the transfer of electrons, and improve the charge and discharge efficiency of the battery.

[0156] In some embodiments, the compaction density of the positive active material film layer is 1.5 to 4 g / cm 3 .

[0157] According to the embodiments of the present application, the compaction density of the positive active material film layer is controlled, which can effectively enhance the mixing uniformity and contact of the high dielectric material and the positive active material, and is beneficial to the electrochemical performance of the positive electrode sheet in the battery.

[0158] The present application does not have special restrictions on the type of positive conductive agent. As an example, the positive conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0159] In some embodiments, the positive active material film layer can also optionally include a positive binder. The present application does not have special restrictions on the type of positive binder. As an example, the positive binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic ester resin.

[0160] In some embodiments, the positive current collector can adopt a metal foil or a composite current collector. As an example of the metal foil, an aluminum foil can be adopted. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0161] The positive electrode active material film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector, drying, and cold-pressing. The positive electrode slurry is usually formed by dispersing and stirring positive electrode active material particles, an optional conductive agent, an optional binder, and any other components in a solvent. The solvent can be N-methyl pyrrolidone (NMP), but is not limited thereto.

[0162] As an example, the total amount of the binder is preferably 1 wt% to 2.5 wt%, for example, 1 wt%, 1.5 wt%, 2 wt%, or 2.5 wt%, based on the total mass of the positive electrode active material, the conductive agent, and the binder. If the amount of the polymer or the binder is too low, too little binder cannot support the strength of the positive electrode active material film layer, and thus cannot satisfy the roll-pressing and thinning. If the amount of the binder is too large, the positive electrode active material film layer can be too sticky, and thus can easily stick to the roll during the roll-pressing of the film, and thus cannot be thinned and current collector-combined.

[0163] Battery cell

[0164] In a fourth aspect, an embodiment of the present application provides a battery cell, including the positive electrode sheet of the third aspect.

[0165] In some embodiments, the battery cell includes a negative electrode sheet, a separator, and an electrolyte.

[0166] [Negative electrode sheet]

[0167] The specific composition and structure of the negative electrode sheet can be selected according to the type of the battery cell, and the present application is not limited thereto.

[0168] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer including a negative electrode active material and disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two opposite surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0169] The negative electrode active material is a material capable of releasing and intercalating active ions, and the negative electrode active material can be a material known in the art. As an example, the negative electrode active material includes but is not limited to one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. The silicon-based material can include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material can include one or more of elemental tin, tin oxide, and tin alloy material. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials can also be used.

[0170] In some embodiments, the negative electrode film layer can also optionally include a negative electrode conductive agent. The present application does not have a particular limitation on the kind of the negative electrode conductive agent, and as an example, the negative electrode conductive agent can include one or more of super conductive carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0171] In some embodiments, the negative electrode film layer can also optionally include a negative electrode binder. The present application does not have a particular limitation on the kind of the negative electrode binder, and as an example, the negative electrode binder can include one or more of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethylacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0172] In some embodiments, the negative electrode film layer can also optionally include other auxiliary agents. As an example, the other auxiliary agents can include a thickening agent, e.g., sodium carboxymethyl cellulose (CMC-Na), PTC thermistor material, etc.

[0173] In some embodiments, the negative electrode current collector can employ a metal foil or a composite current collector. As an example of the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0174] The negative electrode film layer is typically formed by coating a negative electrode slurry on a negative electrode current collector, drying, and cold-pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional auxiliary agents in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP) or deionized water, but is not limited thereto.

[0175] The negative electrode tab does not exclude other additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode tab of the present application can also include a conductive primer layer (e.g., composed of a conductive agent and a binder) interposed between the negative electrode current collector and the negative electrode film layer, disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode tab of the present application can also include a protective layer covering the surface of the negative electrode film layer.

[0176] When the battery cell is a sodium metal battery cell, the negative electrode tab can not include a negative active material capable of deintercalating and intercalating active ions. For example, in some embodiments, the negative electrode tab can include a sodium sheet or a sodium alloy sheet; in other embodiments, the negative electrode tab includes a mesh or foam-like three-dimensional skeleton layer, for example, a foam copper or copper alloy, a foam nickel or nickel alloy, a foam aluminum or aluminum alloy, a copper or copper alloy mesh, a nickel or nickel alloy mesh, an aluminum or aluminum alloy mesh, and the like.

[0177] [Separator]

[0178] The separator is disposed between the positive electrode tab and the negative electrode tab and mainly functions to prevent the positive electrode and the negative electrode from shorting. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be selected.

[0179] In some embodiments, the material of the separator can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of the layers can be the same or different.

[0180] [Electrolyte]

[0181] In some embodiments, the battery cell includes an electrolyte. The electrolyte functions to conduct active ions between the positive electrode tab and the negative electrode tab. The type of the electrolyte is not particularly limited in the present application and can be selected as needed. For example, the electrolyte can be selected from at least one of a solid-state electrolyte and a liquid-state electrolyte (i.e., electrolyte solution).

[0182] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0183] The type of the electrolyte salt is not particularly limited and can be selected as needed.

[0184] For example, the electrolyte salt includes one or more selected from lithium salts for lithium-ion batteries, sodium salts for sodium-ion batteries. As an example, the lithium salt includes one or more selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium difluorophosphate bisoxalate (LiDFOP), lithium tetrafluorophosphate oxalate (LiTFOP). The kind of solvent is not particularly limited, and can be selected according to actual needs. In some embodiments, as an example, the solvent can include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0185] In some embodiments, the electrolyte can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, can also include a positive electrode film-forming additive, and can also include an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature performance of the battery, an additive capable of improving low-temperature power performance of the battery, etc.

[0186] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0187] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0188] [Preparation method]

[0189] The method for preparing the battery cell of the present application is known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form the battery cell. As an example, the positive electrode sheet, the separator and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a stacking process, the electrode assembly can be placed in an outer package, the electrolyte can be injected after drying, and the battery cell can be obtained through processes such as packaging, standing, formation, shaping, etc.

[0190] The shape of the battery cell of the present application is not particularly limited, and it can be a flat body, a cuboid or other shapes. As an example, FIG. 3 is a battery cell 5 in a cuboid structure.

[0191] In some embodiments, as shown in FIG. 4, the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate jointly form a containing cavity. The shell 51 has an opening communicating with the containing cavity, and the cover plate 53 is used to cover the opening to close the containing cavity. The electrode assembly 52 of the first aspect of the present application or the electrode assembly 52 prepared according to the method of the second aspect of the present application is packaged in the containing cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or several, which can be adjusted according to requirements.

[0192] In some embodiments of the present application, the battery cell according to the present application can be assembled into a battery or a battery module, and the number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0193] Optionally, the battery module can further include a housing having a containing space, and a plurality of battery cells are contained in the containing space.

[0194] In some embodiments, a plurality of battery modules can also be connected in series or in parallel or in a hybrid manner to form a battery pack. In some embodiments, a plurality of battery cells can also directly constitute a battery pack. The above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0195] Electric device

[0196] In a fifth aspect, the embodiments of the present application provide an electric device, which includes the battery cell of the fourth aspect.

[0197] The battery cell can be used as a power source of an electric device or as an energy storage unit of an electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0198] FIG. 5 is a schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the demand of the electric device for high power and high energy density, a battery pack or a battery module can be used.

[0199] The electric device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The electric device usually requires thinning, and a battery monomer can be used as a power source.

[0200] Embodiments

[0201] The following examples more specifically describe the present disclosure, which are merely illustrative and not restrictive, since various modifications and changes in the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further purification, and the instruments used in the examples are commercially available.

[0202] Example 1

[0203] Preparation of positive active material particles:

[0204] Step 1.1, preparation of solution A, lithium hydroxide and ferrous sulfate were mixed in deionized water at a molar ratio of 1:1, and a homogeneous solution A was obtained. The concentration of lithium element in the mixed solution was controlled to be 1 mol / L;

[0205] Step 1.2, preparation of solution B, phosphoric acid was dissolved in deionized water and stirred to obtain a 1 mol / L phosphoric acid solution; then ethylenediamine was added to the phosphoric acid solution at a material amount ratio of 1:10, and the mixture was stirred to obtain a mixed solution B;

[0206] Step 1.3, solution A was added to solution B at a uniform speed, and the mixture was stirred to obtain a homogeneous solution C;

[0207] Step 1.4, the homogeneous solution C was transferred to a high-temperature reaction kettle, the filling degree of the reaction kettle was controlled to be 65%, and the reaction kettle was sealed after the air inside the reaction kettle was exhausted. The reaction kettle was heated to 180°C at a rate of 5°C / min and then kept at this temperature, and the hydrothermal reaction was treated for 10 h;

[0208] Step 1.5, the hydrothermal reaction product obtained in step 1.4 was washed with deionized water until it was neutral, and then it was placed in an oven and dried at 100°C for 10 h;

[0209] Step 1.6, collect the dried material, take 10wt% of the mass of the dried material sucrose, mix the dried material with sucrose with deionized water, and then ball mill for 6h, control the mass ratio of deionized water in the ball mill slurry to be 60wt%;

[0210] Step 1.7, the slurry after ball milling is sequentially subjected to spray drying treatment and heat treatment, wherein the slurry atomization inlet temperature is 260℃, the outlet temperature is 115℃, the spray drying treatment is selected in an air atmosphere, the product is transported to a high-temperature furnace for heat treatment with a carrier gas, the carrier gas used is nitrogen, the carrier gas flow is 30L / min, the reaction furnace has an inner diameter of 1m and an effective length of 6m, the reaction furnace temperature is 900℃, and the reaction time is 1.5h.

[0211] Step 1.8, the material collected in step 1.7 is subjected to air flow dispersion, and after iron removal, a nanoscale carbon-coated lithium iron phosphate positive electrode active material is obtained, and the powder compaction density of the material is shown in Table 1.

[0212] Preparation of lithium ion battery:

[0213] The carbon-coated lithium iron phosphate positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride prepared are mixed uniformly in a mass ratio of 95:3:2 in an N-methylpyrrolidone solvent system, and then the positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 13μm at a coating density of 13.6mg / cm 2 After drying, cold pressing, and cutting, the positive electrode sheet of Example 1 is obtained.

[0214] Preparation of negative electrode sheet: lithium sheet with a thickness of 1.5mm is used as negative electrode sheet.

[0215] Electrolyte: LiPF6 is dispersed in a solvent, and the solvent is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethylene dimethyl carbonate (1:1:1 by volume), and the concentration of LiPF6 is 1mol / L.

[0216] Separator: polypropylene microporous membrane with a thickness of 7μm is used as a separator.

[0217] Assembly: the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive and negative electrodes to isolate the positive and negative electrodes, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the above-mentioned electrolyte is injected and packaged, and a lithium ion battery is obtained.

[0218] SEM detection was performed on the carbon-coated lithium iron phosphate positive electrode active material prepared in Example 1, and FIG. 6 was obtained. FIG. 7 shows the XRD pattern of the carbon-coated lithium iron phosphate positive electrode active material prepared in this example. As can be seen from the figure, the positive electrode active material prepared in this example has a single phase, the particle size of the primary particles is less than 100 nm, the particles have high sphericity, and the dispersion is good.

[0219] Examples 2-1 to 2-6

[0220] The difference between this example and Example 1 is that the heat treatment temperature of the reaction furnace is different, as shown in Table 1.

[0221] Example 3

[0222] The difference between this example and Example 1 is that the preparation of the positive electrode active material particles:

[0223] Step 3.1, preparation of solution A, lithium hydroxide, manganese sulfate, and ferrous sulfate were put into deionized water in a molar ratio of 1:0.6:0.4 and mixed and stirred to obtain homogeneous solution A. The concentration of lithium element in the mixed solution was controlled to be 1.1 mol / L;

[0224] Step 3.2, preparation of solution B, phosphoric acid was dissolved in deionized water and stirred to obtain a 1.1 mol / L phosphoric acid solution; then triethanolamine was added to the phosphoric acid solution in a substance amount ratio of 1:10 to the phosphoric acid, and stirred to obtain a mixed solution B;

[0225] Step 3.3, solution A was added to solution B at a uniform speed, and mixed and stirred to obtain a homogeneous solution C;

[0226] Step 3.4, the homogeneous solution C was transferred to a high-temperature reaction kettle, the filling degree of the reaction kettle was controlled to be 70%, and the inside of the reaction kettle was evacuated and sealed after the air was removed. The reaction kettle was heated to 220°C at a rate of 3°C / min and then held at temperature, and the hydrothermal reaction was treated for 12 h;

[0227] Step 3.5, the hydrothermal reaction product obtained in step 2.4 was washed with deionized water until it was neutral, and then placed in an oven and dried at 105°C for 10 h;

[0228] Step 3.6, the dried material was collected, 15wt% of the mass of the dried material was glucose, and the dried material and the glucose were mixed with deionized water and ball milled for 6 h, and the mass fraction of deionized water in the ball milled slurry was controlled to be 65wt%;

[0229] Step 3.7, the ball-milled slurry was subjected to spray drying and heat treatment, the slurry was atomized at an inlet temperature of 240°C and an outlet temperature of 120°C, argon was used as the carrier gas at a flow rate of 25 L / min, the reaction furnace had an inner diameter of 1 m and an effective length of 6 m, the furnace temperature was 1050°C, and the reaction time was 1.2 h.

[0230] Step 3.8, the material collected in step 2.7 was subjected to air flow dispersion, and after screening for iron, a nanoscale spherical carbon-coated lithium iron manganese phosphate positive electrode active material was obtained.

[0231] The carbon-coated lithium iron manganese phosphate positive electrode active material prepared in Example 2 was subjected to SEM detection, and Figure 8 was obtained, Figure 9 shows the XRD pattern of the carbon-coated lithium iron phosphate positive electrode active material prepared in this example, and the diffraction peaks of the JCPDS #74-0375 in Figure 9 are the diffraction peaks of the commonly used card during X-ray extension. As can be seen from the above figure, the positive electrode active material prepared in this example has a single phase, the primary particle size is less than 100 nm, the particle sphericity is high, and the dispersion is good.

[0232] Examples 4-1 to 4-3

[0233] The difference between this example and Example 3 is that the types of surfactants are different, as shown in Table 1.

[0234] Example 5

[0235] The difference between this example and Example 1 is that the preparation of the positive electrode active material particles: the operations of steps 1.1 to 1.3 are replaced by: mixing lithium hydroxide, ferrous sulfate, phosphoric acid and ethylenediamine in deionized water, wherein the molar ratio of lithium hydroxide to ferrous sulfate is 1:1, and the amount-of-substance ratio of phosphoric acid to ethylenediamine is 1:10, after mixing, stirring to obtain a homogeneous solution C.

[0236] Examples 6-1 to 6-3

[0237] The difference between this example and Example 1 is that the content of the surfactant is different, as shown in Table 1.

[0238] Comparative Example 1

[0239] The difference between this comparative example and Example 1 is that in step 1.2, no ethylenediamine is added to the phosphoric acid solution.

[0240] Figure 10 is an SEM image of the positive electrode active material prepared in Comparative Example 1, and Figure 7 shows an XRD image of the positive electrode active material prepared in Comparative Example 1. As can be seen from the figures, the positive electrode active material prepared in Comparative Example 1 has no impurity diffraction peak, the primary particle size is larger than that of Example 1, and the particle morphology is irregular, the sphericity is low, and the particle dispersibility is poorer than that of Example 1. This shows that the addition of the surfactant in the example plays an important role in adjusting the morphology, size and dispersibility of the crystal particles in the hydrothermal reaction.

[0241] Comparative Example 2

[0242] The difference between this comparative example and Example 1 is that the furnace temperature of the reaction furnace is 600°C.

[0243] Comparative Example 3

[0244] The difference between this comparative example and Example 1 is that the furnace temperature of the reaction furnace is 600°C. In Step 1.2, ethylenediamine is not added to the phosphoric acid solution.

[0245] Test Section

[0246] The lithium ion battery cells prepared in the examples and comparative examples were subjected to electrochemical performance testing. The test voltage range of the lithium iron phosphate was 2.0-3.7V, and the test voltage range of the lithium iron manganese phosphate was 2.0-4.6V, at a temperature of 25°C. The specific test method is as follows.

[0247] 1) The powder compaction density of the phosphate positive electrode active material prepared in the examples and comparative examples was detected. The detection method referred to the national standard GB / T 24533-2009 Appendix L "Test method of powder compaction density". The compaction density was determined by a compaction density instrument. The exemplary test method is as follows: 1g of the above positive electrode active material was weighed, added into a metal cylindrical sleeve with a cross-sectional area of 1.298cm 2 The pressure was increased to 300kg (equivalent to 3kN) in the metal cylindrical sleeve, and the pressure was maintained for 30s, then the pressure was released, the change in the height of the top column exposed outside the sleeve before and after compaction was recorded, and then the powder compaction density of the active material under a pressure of 3kN was calculated.

[0248] 2) The battery prepared in the examples and comparative examples was subjected to charge capacity and discharge capacity detection by constant current discharge method at a rate of 1C. The test battery was installed on the test instrument and placed in a test environment of (25±1) °C. The following program was set: static 10min; constant current charging to 3.7V or 4.6V at 1.0C current, then constant voltage charging until the current decreased to 0.05C, charging stopped; static 5min; then constant current discharging to 2.0V at 1.0C current, recording the charge and discharge capacity, the ratio of discharge capacity to charge capacity multiplied by 100% is the charge-discharge efficiency.

[0249] 3) The capacity retention of the batteries prepared in the examples and comparative examples was detected after 200 cycles at 1C / 1C. The detection method was as follows: the battery was placed in the test channel of a Chenhua electrochemical workstation, and was charged at a rate of 1C to a charge cut-off voltage of 3.7V or 4.6V, and was then allowed to stand for 5 min, and was discharged at a rate of 1C to a discharge cut-off voltage of 2.0V, and the discharge capacity was recorded, and the battery was allowed to stand for another 5 min. The cycle was repeated, and the cycle capacity retention was calculated according to the formula: cycle capacity retention = (discharge capacity of the battery after 200 cycles / discharge capacity of the battery in the first cycle) x 100%.

[0250] The detection results are shown in Table 1.

[0251] As can be seen from the test results in Table 1, the charge specific capacity and discharge specific capacity of the lithium iron phosphate positive electrode active material prepared in the examples are higher than those of the comparative examples, which indicates that the specific capacity of the phosphate positive electrode active material prepared by the method of the examples is higher. The reason may be that the addition of the surfactant and the higher heat treatment temperature can improve the lattice defect rate of the positive electrode active material.

[0252] As can be seen from the IG / ID values of the carbon in the phosphate positive electrode active materials of Examples 1 and 2-1 to 2-6, the graphitization degree of the carbon in the phosphate positive electrode active material is higher at a higher temperature.

[0253] As can be seen from the comparison between Example 1 and Example 5, first mixing the phosphorus source with the surfactant, and then mixing with other raw materials for preparing the positive electrode active material, can improve the specific capacity and cycle capacity stability of the phosphate positive electrode active material.

[0254] As can be seen from Examples 3 and 4-1 to 4-4, different types of surfactants have different effects on the specific capacity and cycle capacity stability of the phosphate positive electrode active material. Substances with basicity or amine substances, such as triethanolamine, ethylenediamine and ethylenediaminetetraacetic acid, have a better effect on improving the specific capacity and cycle capacity stability of the phosphate positive electrode active material. The reason may be that: such surfactants form stable complexes with the phosphorus source, which is beneficial to the nucleation of the crystal grains in the subsequent hydrothermal reaction, thereby improving the morphology of the hydrothermal reaction product, such as sphericity.

[0255] As can be seen from Examples 1 and 6-1 to 6-3, the ratio of the amount of the surfactant to the amount of the phosphoric acid substance can affect the specific capacity and cycle capacity stability of the phosphate positive electrode active material.

[0256] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art, without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A method for preparing a phosphate cathode active material, comprising: providing a mixed solution comprising a lithium source, a metal source, a phosphorus source, and a surfactant, the metal source being an iron source and / or a manganese source; subjecting the mixed solution to a hydrothermal reaction to obtain reaction particles; mixing the reaction particles with a carbon source and performing wet grinding to obtain a slurry; and subjecting the slurry to a heat treatment to obtain the phosphate cathode active material, wherein the heat treatment is performed at a temperature of 650 ℃ or higher. The heat treatment is performed at a temperature of 750 ℃ to 1300 ℃. The heat treatment is performed for 1 h to 2 h. The surfactant comprises one or more of tartaric acid, propylene glycol, isopropyl alcohol, citric acid, glycerol, ethylenediamine, and triethanolamine. The ratio of the molar amount of the surfactant to the amount of substance of phosphorus in the phosphorus source is 1: (10-20).

2. The production method according to claim 1, wherein The method satisfies one or more of the following conditions:

3. The production method according to claim 1 or 2, wherein 1) the lithium source comprises one or more of lithium carbonate, lithium acetate, lithium citrate, lithium dihydrogen phosphate, lithium hydroxide, and lithium phosphate; 4. The production method according to any one of claims 1 to 3, wherein 2) the phosphorus source comprises one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate; 5. The production method according to any one of claims 1 to 4, wherein 3) the iron source comprises one or more of ferrous sulfate, ferrous hydroxide, ferrous oxalate, ferrous acetate, and ferrous chloride; 6. The production method according to any one of claims 1 to 5, wherein 4) the manganese source comprises one or more of manganese nitrate, manganous nitrate, manganous acetate, and manganous formate; 5) the carbon source comprises one or more of glucose, sucrose, polyvinyl alcohol, polyethylene glycol, gelatin, and polyvinylpyrrolidone; 6) the mass content of the carbon source is 0.5% to 16% based on the total dry weight of the reaction particles and the carbon source. The providing of the mixed solution comprising the lithium source, the metal source, the phosphorus source, and the surfactant comprises: providing a first mixed solution comprising the lithium source and the metal source; providing a second mixed solution comprising the phosphorus source and the surfactant; and mixing the first mixed solution with the second mixed solution to obtain the mixed solution comprising the lithium source, the metal source, the phosphorus source, and the surfactant.

7. The production method according to any one of claims 1 to 6, wherein The mixed solution further comprises a dopant element source, the dopant element source comprising one or more of a sulfate, a nitrate, a hydrochloride, and an acetate of an M element, the M element representing a doping element of Mn sites and / or Fe sites of the phosphate composite cathode active material. The M element comprises one or more of Mg, Zn, Ti, Zr, V, Ni, Al, Cr, Nb, and W. The subjecting of the mixed solution to the hydrothermal reaction satisfies one or more of the following conditions: 1) the mixed solution is warmed to 160 ℃ to 240 ℃ and then held at the temperature, the warming rate being 1 ℃ / min to 5 ℃ / min; 8. The production method according to any one of claims 1 to 7, wherein 2) the mixed solution is placed in a hydrothermal reactor for the hydrothermal reaction, the filling degree of the mixed solution in the hydrothermal reactor being 50% to 85%.

9. The production method according to claim 8, wherein The holding time of the hydrothermal reaction is 7 h to 15 h.

10. The production method according to any one of claims 1 to 9, wherein The method further comprises, before the subjecting of the slurry to the heat treatment, a step of subjecting the slurry to a spray drying treatment. The phosphate cathode active material is prepared by the method of any one of claims 1 to 10. The phosphate cathode active material comprises:

11. The production method according to any one of claims 1 to 10, wherein ​ 12. The production method according to any one of claims 1 to 11, wherein ​ 13. A phosphate cathode active material, wherein, ​ 14. The phosphate cathode active material according to claim 13, wherein, ​ LiFe m Mn j M n PO4, m > 0, j > 0, n > 0, M comprises one or more of Mg, Zn, Ti, Zr, V, Ni, Al, Cr, Nb and W; A carbon coating layer is coated on at least part of the surface of the core structure.

15. The phosphate cathode active material according to claim 13 or 14, wherein The peak intensity I D of the carbon in the Raman spectrum of the carbon-coated layer including a D peak G satisfies: 1.5 ≤ I G / I D ≤ 4.

16. A positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material film layer provided on at least one side of the positive electrode current collector, wherein the positive electrode active material film layer comprises a phosphate positive electrode active material prepared by the method according to any one of claims 1 to 12 or the phosphate positive electrode active material according to any one of claims 13 to 15.

17. A battery cell, wherein, A battery comprising the positive electrode sheet according to claim 16.

18. An electrical device, comprising: A battery cell comprising the battery according to claim 17.

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