A carbon-coated LiMn x Fe 1-x PO4 material and its preparation method and application

Abstract

This application relates to a carbon-coated LiMn x Fe 1‑x PO4 material and its preparation method and application, the preparation method comprises the following steps: (1) introducing reaction gas to LiMn x Fe 1‑x PO4 is heated, and the surface material reacts with the reaction gas to obtain LiMn which eliminates the surface material. x Fe 1‑x PO4; (2) introducing a carbon source gas to eliminate the surface material LiMn obtained in step (1) x Fe 1‑x PO4 is chemically vapor deposited to obtain the carbon-coated LiMn x Fe 1‑x PO4 material, where 0≤x≤1. The surface material is removed by chemical vapor deposition and carbon-coated, so that the obtained coated carbon layer is uniform and dense, and the final positive electrode material has the characteristics of high compaction density, low specific surface area and excellent electrochemical performance.

Description

Technical Field

[0001] This application belongs to LiMn x Fe 1-x In the field of PO4 cathode material manufacturing technology, for example, a carbon-coated LiMn x Fe 1-x PO4 material, preparation method and application thereof. Background Art

[0002] Olivine-structured LiMn x Fe 1-x The crystal structure of PO4 (0≤x≤1) material is very stable, and a large amount of lithium ions are continuously intercalated and deintercalated during the charge and discharge process. Compared with ternary cathode materials, its structure is more stable and safer. And because it has a stable charge and discharge platform at around 2.5~4.5V, it has attracted extensive attention from relevant scientific researchers. However, compared with ternary materials, LiMn x Fe 1-x The compaction density of PO4 positive electrode materials is relatively low, which limits their application in a wider range of fields.

[0003] Increasing the compaction density can effectively increase the volume energy density of the material.

[0004] Generally speaking, within the material's allowable compaction range, the greater the electrode's compaction density, the higher the battery's capacity. Therefore, compaction density is also considered a reference indicator for measuring a material's energy density. Increasing the material's compaction density can be achieved through a rational distribution of spheres of varying particle sizes, increasing the primary particle size of the cathode material, or reducing the carbon coating content. However, increasing the primary particle size and reducing the carbon coating content both reduce the material's lithium-ion conductivity. Achieving both good lithium-ion conductivity and excellent compaction density is a key development direction for cathode materials.

[0005] CN 112436120A discloses a lithium iron manganese phosphate composite, a method for manufacturing the same, and a positive electrode for a lithium ion battery. The lithium iron manganese phosphate composite material comprises, by weight: a) 50-90% large-particle lithium iron manganese phosphate, having a primary particle size of 80-500 nm and a secondary particle size of 5-20 μm, wherein the manganese content of the lithium iron manganese phosphate material is 20-80%, based on the total molar number of transition metal elements in the lithium iron manganese phosphate material; and b) 10-50% small-particle lithium iron manganese phosphate, having a primary particle size of 30-200 nm and a secondary particle size of 0.5-4 μm, wherein the manganese content of the lithium iron manganese phosphate material is 50-90%, based on the total molar number of transition metal elements in the lithium iron manganese phosphate material. The manganese content of the large-particle lithium iron manganese phosphate is lower than that of the small-particle lithium iron manganese phosphate.

[0006] CN 113072051A discloses a post-treatment method for phosphate-based cathode materials. The method involves oxidatively calcining the synthesized lithium iron phosphate cathode material to burn off the loose carbon layer, adding a carbon source and a lithium supplement, and then grinding and calcining it again to form a high-density, low-specific-surface-area cathode material. However, during the oxidative calcination to burn off the loose carbon layer, ferrous ions are inevitably oxidized, and when carbon coating is performed again after calcination, the coating layer still exhibits unevenness and pores.

[0007] In view of the above technical problems, how to balance lithium ion conductivity and compaction density and improve the unevenness and porosity in the carbon coating process are urgent issues to be solved in the field of lithium manganese iron phosphate positive electrode material manufacturing technology. Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] In order to solve the above technical problems, the present application provides a carbon-coated LiMn x Fe 1-x PO4 material and its preparation method and application, adopt the method of chemical vapor deposition to carbon-coat the surface material, so that the obtained carbon coating layer is uniform and dense, and the final LiMn x Fe 1-x PO4 positive electrode material has the characteristics of high compaction density, low specific surface area and excellent electrochemical performance.

[0010] To achieve this goal, this application adopts the following technical solutions:

[0011] In the first aspect, the present invention provides a carbon-coated LiMn x Fe 1-x A method for preparing PO4 material, comprising the following steps:

[0012] (1) Introduce reaction gas to LiMn x Fe 1-x PO4 is heated, and the surface material reacts with the reaction gas to obtain LiMn which eliminates the surface material. x Fe 1-x PO4;

[0013] (2) introducing carbon source gas to remove the surface material of LiMn obtained in step (1) x Fe 1-x PO4 is chemically vapor deposited to obtain the carbon-coated LiMn x Fe 1-xPO4 material, wherein 0≤x≤1, for example, can be 0, 0.2, 0.4, 0.6, 0.8, 0.9 or 1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] In the embodiment of the present application, the chemical vapor deposition method is used to carbon-coat the removed surface material, so that the obtained coated carbon layer is uniform and dense, and the final formed LiMn x Fe 1-x PO4 positive electrode material has the characteristics of high compaction density, low specific surface area and excellent electrochemical performance.

[0015] Elimination of surface material, referring to LiMn x Fe 1-x Non-LiMn on the PO4 surface x Fe 1-x During the preparation process, a loose coating layer easily forms on the surface of the material. This loose structure increases the specific surface area of ​​the positive electrode material and reduces the compaction density, thereby affecting battery performance. In the embodiment of the present application, the reaction gas is introduced under heating conditions, and the reaction gas reacts with the surface material, thereby eliminating the loose surface material.

[0016] In one embodiment, the LiMn x Fe 1-x PO4 was prepared by the following method:

[0017] (a) mixing a manganese source, an iron source, a lithium source, a phosphorus source, and a carbon source, ball-milling the mixture, and drying the mixture to obtain a precursor;

[0018] (b) calcining the obtained precursor to obtain the LiMn x Fe 1-x PO4.

[0019] In one embodiment, the manganese source in step (a) comprises any one of manganese carbonate, manganese acetate, manganese phosphate, manganous phosphate, manganese dioxide, manganese trioxide or trimanganese tetraoxide, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of manganese carbonate and manganese acetate, a combination of manganese acetate and manganese phosphate, a combination of manganese phosphate and manganous phosphate, a combination of manganous phosphate and manganese dioxide, a combination of manganese dioxide and manganese trioxide, a combination of manganese trioxide and trimanganese tetraoxide, a combination of manganese carbonate, manganese acetate and manganese phosphate, a combination of manganese acetate, manganese phosphate and manganous phosphate, a combination of manganese phosphate, manganous phosphate and manganese dioxide, a combination of manganous phosphate, manganese dioxide and manganese trioxide, and a combination of manganese dioxide, manganese trioxide and trimanganese tetraoxide.

[0020] In one embodiment, the iron source in step (a) comprises any one of ferric nitrate, ferric oxide, ferric phosphate, ferrous acetate or ferric oxide, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of ferric nitrate and ferric oxide, a combination of ferric oxide and ferric phosphate, a combination of ferric phosphate and ferrous acetate, a combination of ferrous acetate and ferric oxide, a combination of ferric nitrate, ferric oxide and ferric phosphate, a combination of ferric oxide, ferrous phosphate and ferrous acetate, and a combination of ferric phosphate, ferrous acetate and ferric oxide.

[0021] In one embodiment, the lithium source in step (a) comprises lithium carbonate and / or lithium hydroxide.

[0022] In one embodiment, the phosphorus source in step (a) comprises any one or a combination of at least two of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, ferric phosphate, manganese phosphate or manganous phosphate. Typical but non-limiting combinations include a combination of diammonium hydrogen phosphate and ammonium dihydrogen phosphate, a combination of ammonium dihydrogen phosphate and sodium dihydrogen phosphate, a combination of sodium dihydrogen phosphate and ferric phosphate, a combination of ferric phosphate and manganese phosphate, a combination of manganese phosphate and manganous phosphate, a combination of diammonium hydrogen phosphate and ammonium dihydrogen phosphate and sodium dihydrogen phosphate, a combination of ammonium dihydrogen phosphate and sodium dihydrogen phosphate and ferric phosphate, a combination of sodium dihydrogen phosphate and ferric phosphate and manganous phosphate, and a combination of ferric phosphate and manganous phosphate or manganous phosphate.

[0023] In one embodiment, the carbon source in step (a) comprises any one or a combination of at least two of citric acid, glucose, carbon nanotubes or polyethylene glycol. Typical but non-limiting combinations include a combination of citric acid and glucose, a combination of glucose and carbon nanotubes, a combination of carbon nanotubes and polyethylene glycol, a combination of citric acid, glucose and carbon nanotubes, and a combination of glucose, carbon nanotubes and polyethylene glycol.

[0024] In one embodiment, the molar ratio of the manganese source, iron source, lithium source and phosphorus source in step (a) satisfies LiMn x Fe 1- x PO4, chemical dosage ratio of 0≤x≤1.

[0025] In one embodiment, based on the sum of the masses of the manganese source, iron source, lithium source, phosphorus source and carbon source in step (a) as the total mass, the mass proportion of the carbon source is 8 to 12 wt%, for example, it can be 8 wt%, 9 wt%, 10 wt%, 11 wt% or 12 wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In the embodiment of this application, LiMn x Fe 1-x During the preparation of PO4, an excess of carbon source is added to ensure that the iron or manganese ions are fully reduced.x Fe 1-x A loose carbon layer will form on the surface of PO4, which will be eliminated by reacting with the reaction gas.

[0027] In one embodiment, the solvent for the ball milling in step (a) is water.

[0028] In one embodiment, the calcination in step (b) is performed under a protective gas atmosphere.

[0029] In one embodiment, the protective gas includes any one of nitrogen, argon or helium, or a combination of at least two of them. Typical but non-limiting combinations include a combination of nitrogen and argon, a combination of argon and helium, and a combination of nitrogen and helium.

[0030] In one embodiment, the calcination temperature in step (b) is 600-900°C, for example, 600°C, 650°C, 700°C, 800°C or 900°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] In one embodiment, the calcination time in step (b) is 8 to 20 hours, for example, 8 hours, 10 hours, 12 hours, 15 hours or 20 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] In one embodiment, the reaction gas in step (1) includes water vapor and / or carbon dioxide.

[0033] In the embodiment of the present application, water vapor or carbon dioxide reacts with the carbon layer on the surface of the material under heating conditions, thereby removing the loose carbon layer on the surface of the positive electrode material during the preparation process, avoiding the problem of low compaction density of the positive electrode material due to sufficient carbon source during synthesis, and also avoiding the problem of other metal elements being oxidized when the material is decarbonized under oxidizing atmosphere conditions.

[0034] In one embodiment, the heating reaction in step (1) is carried out in a water-gas furnace.

[0035] In one embodiment, the flow rate of the reaction gas in step (1) is 3 to 8 L / min, for example, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min or 8 L / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] In one embodiment, the heating temperature in step (1) is 800-1300°C, for example, 800°C, 900°C, 1000°C, 1100°C, 1200°C or 1300°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] In one embodiment, the heating time in step (1) is 60 to 80 minutes, for example, 60 minutes, 65 minutes, 70 minutes, 75 minutes or 80 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] In one embodiment, the heating rate of step (1) is 15 to 30°C / min, for example, 15°C / min, 20°C / min, 25°C / min, 28°C / min or 30°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] In one embodiment, the carbon source gas in step (2) is any one of methane, ethane, ethylene, acetylene, benzene or toluene, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of methane and ethane, a combination of ethane and ethylene, a combination of ethylene and acetylene, a combination of acetylene and benzene, a combination of benzene and toluene, a combination of methane, ethane and ethylene, a combination of ethane, ethylene and acetylene, a combination of ethylene, acetylene and benzene, and a combination of acetylene, benzene and toluene.

[0040] In one embodiment, the flow rate of the carbon source gas in step (2) is 0.4 to 6 L / min, for example, it can be 0.6 L / min, 1 L / min, 2 L / min, 3 L / min, 4 L / min or 5 L / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In one embodiment, the gas introduced in step (2) further includes a protective gas.

[0042] In one embodiment, the protective gas includes any one of nitrogen, argon or helium, or a combination of at least two of them. Typical but non-limiting combinations include a combination of nitrogen and argon, a combination of argon and helium, a combination of nitrogen and helium, or a combination of nitrogen, argon and helium.

[0043] In one embodiment, the chemical vapor deposition in step (2) is performed at 500-850°C, for example, 500°C, 600°C, 700°C, 800°C or 850°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] In one embodiment, the chemical vapor deposition in step (2) is performed for 30 to 400 minutes, for example, 30 minutes, 100 minutes, 200 minutes, 300 minutes or 400 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] In one embodiment, the chemical vapor deposition step (2) further includes removing the surface material of LiMn x Fe 1-x PO4 is crushed.

[0046] In one embodiment, the particle size after crushing is 0.2 to 0.4 μm, for example, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm or 0.4 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] As an optional technical solution of the preparation method described in the first aspect of the present application, the preparation method comprises the following steps:

[0048] (1) In a water gas furnace, water vapor and / or carbon dioxide reaction gas is introduced at a flow rate of 3 to 8 L / min. LiMn x Fe 1-x PO4 is heated at 800-1300℃ for 60-80min, and the reaction gas reacts with the surface material, wherein the heating rate is 15-30℃ / min, and LiMn is obtained by eliminating the surface material. x Fe 1-x PO4;

[0049] (2) Eliminate the surface layer of LiMn obtained in step (1) x Fe 1-x After PO4 is crushed to a particle size of 0.2-0.4 μm, protective gas and carbon source gas are introduced, the flow rate of the carbon source gas is 0.4-6 L / min, and chemical vapor deposition is carried out at 500-850 ° C for 30-400 min to obtain the carbon-coated LiMn x Fe 1-x PO4 material, where 0≤x≤1;

[0050] Step (1) LiMn x Fe 1-x PO4 is prepared by the following method:

[0051] (a) According to lithium manganese iron phosphate LiMn x Fe 1-x A manganese source, an iron source, a lithium source, and a phosphorus source are mixed in a chemical dosage ratio of PO4, and a carbon source is added with a mass proportion of 8 to 12 wt% based on the sum of the mass of the manganese source, the iron source, the lithium source, the phosphorus source, and the carbon source as the total mass, and the mixture is ball-milled in water as a solvent and then dried and ground to obtain a precursor;

[0052] (b) calcining the obtained precursor at 600-900° C. for 8-20 h under a protective gas atmosphere to obtain the LiMnx Fe 1-x PO4.

[0053] In the second aspect, the present invention provides a carbon-coated LiMn x Fe 1-x PO4 material, the carbon-coated LiMn x Fe 1-x The PO4 material is obtained by the preparation method as described in the first aspect, wherein 0≤x≤1.

[0054] In a third aspect, the embodiment of the present application provides a carbon-coated LiMn according to the second aspect. x Fe 1-x Application of PO4 materials, the carbon-coated LiMn x Fe 1-x PO4 material is used in positive electrode sheets or batteries, where 0≤x≤1.

[0055] Compared with the related art, this application has at least the following beneficial effects:

[0056] In this application, the chemical vapor deposition method is used to carbon-coat the removed surface material, so that the obtained coated carbon layer is uniform and dense, and the final LiMn x Fe 1-x PO4 positive electrode material has the characteristics of high compaction density, low specific surface area and excellent electrochemical performance.

[0057] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0058] To facilitate understanding of the present application, the present application lists the following examples. Those skilled in the art should understand that the examples are only provided to help understand the present application and should not be considered as specific limitations of the present application.

[0059] Example 1

[0060] This embodiment provides a carbon-coated LiMn 0.5 Fe 0.5 A method for preparing PO4 material, comprising the following steps:

[0061] (1) In the water gas furnace, the reaction gas of carbon dioxide is introduced at a flow rate of 5L / min, and LiMn 0.5 Fe 0.5 PO4 is heated at 1000℃ for 70min, and the reaction gas reacts with the surface material. The heating rate is 20℃ / min, and LiMn is obtained by eliminating the surface material. 0.5 Fe 0.5 PO4;

[0062] (2) Eliminate the surface layer of LiMn obtained in step (1) 0.5 Fe 0.5 After PO4 was crushed to a particle size of 0.3 μm, nitrogen and methane were introduced, with a methane flow rate of 3 L / min, and chemical vapor deposition was performed at 650°C for 200 min to obtain the carbon-coated LiMn 0.5 Fe 0.5 PO4 material;

[0063] Step (1) LiMn 0.5 Fe 0.5 PO4 is prepared by the following method:

[0064] (a) According to LiMn 0.5 Fe 0.5 Manganese carbonate, ferric nitrate, lithium carbonate and diammonium phosphate are mixed in a chemical dosage ratio of PO4, and citric acid is added with a mass proportion of 10 wt% based on the sum of the mass of manganese carbonate, ferric nitrate, lithium carbonate, diammonium phosphate and citric acid as the total mass, and the mixture is ball-milled in water as a solvent and then dried and ground to obtain a precursor;

[0065] (b) The obtained precursor was calcined at 750°C for 10 h under nitrogen atmosphere to obtain the LiMn 0.5 Fe 0.5 PO4.

[0066] Example 2

[0067] This embodiment provides a method for preparing a carbon-coated LiFePO4 material, the preparation method comprising the following steps:

[0068] (1) In a water gas furnace, water vapor is introduced as a reaction gas at a flow rate of 3 L / min, and LiFePO4 is heated at 800°C for 80 min. The reaction gas reacts with the surface material, wherein the heating rate is 15°C / min, and LiFePO4 with the surface material eliminated is obtained;

[0069] (2) The LiFePO4 obtained in step (1) with the surface layer removed was crushed to a particle size of 0.2 μm, and then argon and ethane gases were introduced, with the ethane gas flow rate being 0.4 L / min, and chemical vapor deposition was performed at 500° C. for 400 min to obtain the carbon-coated LiFePO4 material;

[0070] The LiFePO4 described in step (1) is prepared by the following method:

[0071] (a) mixing iron oxide, lithium hydroxide, and ammonium dihydrogen phosphate according to a stoichiometric ratio of LiFePO4, adding glucose in an amount of 8 wt% based on the sum of the weight of the iron oxide, lithium hydroxide, ammonium dihydrogen phosphate, and glucose, ball milling the mixture in water, and then drying and grinding the mixture to obtain a precursor;

[0072] (b) Under an argon atmosphere, the obtained precursor was calcined at 600° C. for 20 h to obtain the LiFePO 4 .

[0073] Example 3

[0074] This embodiment provides a method for preparing a carbon-coated LiMnPO4 material, the preparation method comprising the following steps:

[0075] (1) In a water gas furnace, carbon dioxide reaction gas is introduced at a flow rate of 8 L / min, and LiMnPO4 is heated at 1300°C for 60 min. The reaction gas reacts with the surface material, wherein the heating rate is 30°C / min, and LiMnPO4 with the surface material eliminated is obtained;

[0076] (2) The LiMnPO4 obtained in step (1) with the surface layer removed was crushed to a particle size of 0.4 μm, and then helium and ethylene gases were introduced, with the ethylene gas flow rate being 6 L / min, and chemical vapor deposition was performed at 850° C. for 30 min to obtain the carbon-coated LiMnPO4 material;

[0077] The LiMnPO4 in step (1) is prepared by the following method:

[0078] (a) mixing manganese dioxide, lithium carbonate, and sodium dihydrogen phosphate in a stoichiometric ratio of LiMnPO4, and adding carbon nanotubes in an amount of 12 wt% by weight based on the sum of the mass of manganese dioxide, lithium carbonate, sodium dihydrogen phosphate, and carbon nanotubes, ball milling the mixture in water, and then drying and grinding the mixture to obtain a precursor;

[0079] (b) The obtained precursor was calcined at 900° C. for 8 h under a helium atmosphere to obtain the LiMnPO 4 .

[0080] Example 4

[0081] This embodiment provides a carbon-coated LiMn 0.5 Fe 0.5 The method for preparing PO4 material is different from that of Example 1 in that the reaction gas in step (1) is water vapor.

[0082] Example 5

[0083] This embodiment provides a carbon-coated LiMn 0.5 Fe0.5 The method for preparing PO4 material is different from that in Example 1 in that the flow rate of the reaction gas in step (1) is 2 L / min.

[0084] Example 6

[0085] This embodiment provides a carbon-coated LiMn 0.5 Fe 0.5 The method for preparing PO4 material is different from that of Example 1 in that the flow rate of the reaction gas in step (1) is 10 L / min.

[0086] Example 7

[0087] This embodiment provides a carbon-coated LiMn 0.5 Fe 0.5 The method for preparing PO4 material is different from that in Example 1 in that the mass proportion of the carbon source in step (a) is 6 wt%.

[0088] Example 8

[0089] This embodiment provides a carbon-coated LiMn 0.5 Fe 0.5 The method for preparing PO4 material is different from that in Example 1 in that the mass proportion of the carbon source in step (a) is 15 wt%.

[0090] Example 9

[0091] This embodiment provides a carbon-coated LiMn 0.5 Fe 0.5 The method for preparing PO4 material is different from that of Example 1 in that the heating temperature in step (1) is 700°C.

[0092] Example 10

[0093] This embodiment provides a carbon-coated LiMn 0.5 Fe 0.5 The preparation method of PO4 material is different from that of Example 1 in that the heating temperature in step (1) is 1400°C.

[0094] Comparative Example 1

[0095] This comparative example provides a LiMn 0.5 Fe 0.5 A method for preparing a PO4 material, the method comprising:

[0096] (a) According to LiMn 0.5 Fe 0.5Manganese carbonate, ferric nitrate, lithium carbonate and diammonium phosphate are mixed in a chemical dosage ratio of PO4, and citric acid is added with a mass proportion of 10 wt% based on the sum of the mass of manganese carbonate, ferric nitrate, lithium carbonate, diammonium phosphate and citric acid as the total mass, and the mixture is ball-milled in water as a solvent and then dried and ground to obtain a precursor;

[0097] (b) The obtained precursor was calcined at 750°C for 10 h under nitrogen atmosphere to obtain the LiMn 0.5 Fe 0.5 PO4.

[0098] Comparative Example 2

[0099] This comparative example provides a method for preparing a LiFePO4 material, which comprises:

[0100] (a) mixing iron oxide, lithium hydroxide, and ammonium dihydrogen phosphate according to a chemical dosage ratio of LFePO4, adding citric acid in an amount of 10 wt% based on the sum of the mass of the iron oxide, lithium hydroxide, ammonium dihydrogen phosphate, and citric acid as the total mass, ball milling in water, and then drying and grinding to obtain a precursor;

[0101] (b) Under an argon atmosphere, the obtained precursor was calcined at 600° C. for 20 h to obtain the LiFePO 4 .

[0102] Comparative Example 3

[0103] This comparative example provides a preparation method of LiMnPO4 material, which comprises:

[0104] (a) mixing manganese dioxide, lithium carbonate, and sodium dihydrogen phosphate in a stoichiometric ratio of LiMnPO4, and adding carbon nanotubes in an amount of 12 wt% by weight based on the sum of the mass of manganese dioxide, lithium carbonate, sodium dihydrogen phosphate, and carbon nanotubes, ball milling the mixture in water, and then drying and grinding the mixture to obtain a precursor;

[0105] (b) The obtained precursor was calcined at 900° C. for 8 h under a helium atmosphere to obtain the LiMnPO 4 .

[0106] Comparative Example 4

[0107] This comparative example provides a carbon-coated LiMn 0.5 Fe 0.5 The method for preparing PO4 material is different from that in Example 1 in that step (1) is not performed.

[0108] Comparative Example 5

[0109] This comparative example provides a carbon-coated LiMn 0.5 Fe0.5 The method for preparing PO4 material is different from that in Example 1 in that step (2) is not performed.

[0110] The above-obtained materials were assembled into simulated batteries for testing, and the test results are shown in Table 1 below.

[0111] Test conditions: Ambient temperature controlled at +25±1°C. Test voltage range: 2.5-4.3V (vs. Li / Li).

[0112] Table 1

[0113] Test number <![CDATA[Compaction density (g / cm 3 )]]> 0.1C gram capacity (mAh / g) Example 1 2.43 158.1 Example 2 2.51 162.3 Example 3 2.43 158.6 Example 4 2.45 158.2 Example 5 2.35 154.7 Example 6 2.48 159.3 Example 7 2.54 155.4 Example 8 2.32 148.3 Example 9 2.29 145.3 Example 10 2.50 135.9 Comparative Example 1 2.30 146.0 Comparative Example 2 2.34 149.8 Comparative Example 3 2.15 135.0 Comparative Example 4 2.20 138.2 Comparative Example 5 2.58 114.4

[0114] The following conclusions can be drawn from Table 1:

[0115] (1) From the comparison between Examples 1-3 and 4 and Comparative Examples 1-3, it can be seen that the present application adopts the chemical vapor deposition method to carbon-coat the removed surface material, so that the obtained coated carbon layer is uniform and dense, and the final formed LiMn x Fe 1-x PO4 positive electrode material has the characteristics of high compaction density, low specific surface area and excellent electrochemical performance.

[0116] (2) Comparison of Examples 5 and 6 with Example 1 shows that the flow rate of the reaction gas will affect the reaction process and effect of removing the surface material. When the flow rate is too large, it will not promote the reaction but will increase the cost. When the flow rate is too small, it may result in too little reactive gas being provided.

[0117] (3) From the comparison between Examples 7 and 8 and Example 1, it can be seen that in LiMn x Fe 1-x During the preparation of PO4 positive electrode materials, sufficient carbon source is added to ensure that manganese and iron ions are fully reduced. When the carbon source is insufficient, trivalent manganese and trivalent iron ions are not fully reduced, resulting in a decrease in gram capacity; when the carbon source is excessive, the reactive gas is not enough to remove all carbon coatings, resulting in a decrease in compaction density.

[0118] (4) From the comparison between Examples 9 and 10 and Example 1, it can be seen that the heating temperature of the reaction process will affect the reaction progress and effect of eliminating the surface material. When the heating temperature is too high, although the carbon coating on the surface can be fully eliminated, it will also damage the positive electrode material. When the heating temperature is too low, the carbon coating on the surface cannot be fully eliminated.

[0119] (5) From the comparison of Comparative Examples 4 and 5 with Example 1, it can be seen that when the material with loose surface structure is directly carbon-coated without eliminating it, the quality of the subsequent carbon coating is affected, and the compaction density and gram capacity of the material are reduced; when carbon coating is not performed, the electrochemical performance of the positive electrode material is poor.

[0120] In summary, the present invention adopts the method of chemical vapor deposition to carbon-coat the removed surface material, so that the obtained coated carbon layer is uniform and dense, and the final formed LiMn x Fe 1-x PO4 positive electrode material has the characteristics of high compaction density, low specific surface area and excellent electrochemical performance.

Claims

1. A carbon-coated LiMn x Fe 1-x A method for preparing PO4 material, comprising the following steps: (1) Introduce reaction gas to LiMn x Fe 1-x PO4 is heated, and the surface material reacts with the reaction gas to obtain LiMn which eliminates the surface material. x Fe 1-x PO4; The reaction gas in step (1) includes water vapor and / or carbon dioxide; The heating reaction in step (1) is carried out in a water-gas furnace; The flow rate of the reaction gas in step (1) is 3 to 8 L / min; The heating rate of step (1) is 15-30°C / min, the heating temperature is 800-1300°C, and the heating time is 60-80min; (2) introducing carbon source gas to remove the surface material of LiMn obtained in step (1) x Fe 1-x PO4 is chemically vapor deposited to obtain the carbon-coated LiMn x Fe 1-x PO4 material, where 0≤x≤1.

2. The preparation method according to claim 1, wherein Step (1) LiMn x Fe 1-x PO4 was prepared by the following method: (a) mixing a manganese source, an iron source, a lithium source, a phosphorus source, and a carbon source, ball-milling the mixture, and drying the mixture to obtain a precursor; (b) calcining the obtained precursor to obtain the LiMn x Fe 1-x PO4.

3. The preparation method according to claim 2, wherein The manganese source in step (a) includes any one of manganese carbonate, manganese acetate, manganese phosphate, manganous phosphate, manganese dioxide, manganese trioxide or manganese tetraoxide, or a combination of at least two thereof.

4. The preparation method according to claim 2, wherein The iron source in step (a) includes any one of ferric nitrate, ferric oxide, ferric phosphate, ferrous acetate or ferrosoferric oxide, or a combination of at least two thereof.

5. The preparation method according to claim 2, wherein The lithium source in step (a) includes lithium carbonate and / or lithium hydroxide.

6. The preparation method according to claim 2, wherein The phosphorus source in step (a) includes any one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, ferric phosphate, manganese phosphate or manganous phosphate, or a combination of at least two thereof.

7. The preparation method according to claim 2, wherein The carbon source in step (a) comprises any one of citric acid, glucose, carbon nanotubes or polyethylene glycol, or a combination of at least two thereof.

8. The preparation method according to claim 2, wherein The molar ratio of the manganese source, iron source, lithium source and phosphorus source in step (a) satisfies LiMn x Fe 1-x PO4, chemical dosage ratio of 0≤x≤1.

9. The preparation method according to claim 2, wherein Taking the sum of the masses of the manganese source, iron source, lithium source, phosphorus source and carbon source in step (a) as the total mass, the mass proportion of the carbon source is 8 to 12 wt%.

10. The preparation method according to claim 2, wherein The solvent for the ball milling in step (a) is water.

11. The preparation method according to claim 2, wherein The calcination in step (b) is carried out under a protective gas atmosphere.

12. The preparation method according to claim 11, wherein The protective gas includes any one of nitrogen, argon or helium, or a combination of at least two of them.

13. The preparation method according to claim 2, wherein The calcination temperature in step (b) is 600-900°C.

14. The preparation method according to claim 2, wherein The calcination time in step (b) is 8 to 20 hours.

15. The preparation method according to claim 1, wherein The carbon source gas in step (2) is any one of methane, ethane, ethylene, acetylene, benzene or toluene, or a combination of at least two of them.

16. The preparation method according to claim 1, wherein The flow rate of the carbon source gas in step (2) is 0.4 to 6 L / min.

17. The preparation method according to claim 1, wherein The gas introduced in step (2) also includes protective gas.

18. The preparation method according to claim 17, wherein The protective gas includes any one of nitrogen, argon or helium, or a combination of at least two of them.

19. The preparation method according to claim 1, wherein The chemical vapor deposition in step (2) is carried out at 500-850°C.

20. The preparation method according to claim 1, wherein The chemical vapor deposition in step (2) is carried out for 30 to 400 minutes.

21. The preparation method according to claim 1, wherein Step (2) also includes removing the surface material of LiMn before the chemical vapor deposition. x Fe 1-x PO4 is crushed.

22. The preparation method according to claim 21, wherein The particle size after the pulverization is 0.2 to 0.4 μm.

23. The preparation method according to claim 1, wherein The preparation method comprises the following steps: (1) In a water gas furnace, water vapor and / or carbon dioxide reaction gas is introduced at a flow rate of 3 to 8 L / min. LiMn x Fe 1-x PO4 is heated at 800-1300℃ for 60-80min, and the reaction gas reacts with the surface material, wherein the heating rate is 15-30℃ / min, and LiMn is obtained by eliminating the surface material. x Fe 1-x PO4; (2) Eliminate the surface layer of LiMn obtained in step (1) x Fe 1-x After PO4 is crushed to a particle size of 0.2-0.4 μm, protective gas and carbon source gas are introduced, the flow rate of the carbon source gas is 0.4-6 L / min, and chemical vapor deposition is carried out at 500-850 ° C for 30-400 min to obtain the carbon-coated LiMn x Fe 1-x PO4 material, where 0≤x≤1; Step (1) LiMn x Fe 1-x PO4 is prepared by the following method: (a) According to LiMn x Fe 1-x A manganese source, an iron source, a lithium source, and a phosphorus source are mixed in a chemical dosage ratio of PO4, and a carbon source is added with a mass proportion of 8 to 12 wt% based on the sum of the mass of the manganese source, the iron source, the lithium source, the phosphorus source, and the carbon source as the total mass, and the mixture is ball-milled in water as a solvent and then dried and ground to obtain a precursor; (b) calcining the obtained precursor at 600-900° C. for 8-20 h under a protective gas atmosphere to obtain the LiMn x Fe 1-x PO4.

24. A carbon-coated LiMn x Fe 1-x PO4 material, the carbon-coated LiMn x Fe 1-x The PO4 material is obtained by the preparation method according to any one of claims 1 to 23, wherein 0≤x≤1.

25. A carbon-coated LiMn according to claim 24 x Fe 1-x Application of PO4 materials, the carbon-coated LiMn x Fe 1- x PO4 material is used in positive electrode sheets or batteries, where 0≤x≤1.