Phosphate-graphene composite positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a phosphate-graphene composite positive electrode material and a preparation method and a lithium ion battery, and the method comprises the following steps: (1) mixing raw materials of a phosphate-based positive electrode material, an acid solution and graphite powder to obtain a mixed solution; (2) the mixed solution is subjected to a first reaction and drying to obtain a phosphate-oxidized graphene composite precursor; and (3) the phosphate-oxidized graphene composite precursor is subjected to calcination and crushing to obtain the phosphate-graphene composite positive electrode material. In the process of preparing the phosphate-based positive electrode material by a liquid phase method, the raw materials are usually dissolved by using acid and subsequent neutralization or removal is needed, and a large amount of acid is also needed for preparing graphene by using the graphite oxidation method. In the application, the acid used for preparing the phosphate-based positive electrode material by the liquid phase method is simultaneously used for preparing graphene by graphite intercalation oxidation, and is in-situ coated on the surface of the phosphate positive electrode material, and then the composite material is obtained by calcination reduction, and the composite material has good capacity and rate performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery cathode material, and particularly relates to a phosphate-graphene composite cathode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Polyanion cathode material represented by lithium iron phosphate is a kind of lithium ion battery cathode material with excellent performance and green safety, but the electronic conductivity of lithium iron phosphate is very low, so that lithium iron phosphate cannot play electrochemical performance alone.

[0003] Carbon coating and carbon material compounding is a classic and efficient method to improve the electronic conductivity of lithium iron phosphate, and graphene is a carbon material with outstanding thermal, mechanical and electrical properties, and its preparation and application research in various fields are in full swing, so in recent years, as a carbon source for coating lithium iron phosphate and a conductive agent, graphene has become a lithium iron phosphate carbon coating material with excellent performance and broad prospects.

[0004] However, conventional graphene is difficult to prepare and expensive, and there are problems of graphene agglomeration in the process of separate preparation of graphene, complicated steps due to the need for separation, and wastewater generation, and there is also a problem of particle agglomeration in the process of separate preparation of the cathode material, which ultimately leads to a complex overall preparation process of the existing composite material and relatively low capacity and rate performance of the product.

[0005] Therefore, it is necessary to develop a method and a cathode material capable of shortening the preparation process and further improving the capacity and rate performance of the composite material. SUMMARY

[0006] In view of the problems in the prior art, the present application provides a phosphate-graphene composite cathode material, a preparation method thereof and a lithium ion battery, and the present application innovatively combines the preparation of phosphate-based cathode material and graphene together to realize the synchronous preparation and in-situ compounding of the two, greatly simplifying the process of separate preparation of graphene and phosphate-based cathode material and compounding thereof, and improving the capacity and rate performance of the composite material.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a method for synchronous synthesis and in-situ compounding of phosphate-based cathode material and graphene, which comprises:

[0009] (1) mixing raw materials of phosphate-based cathode material, an acidic solution and graphite powder to obtain a mixed solution;

[0010] (2) the mixed solution is subjected to a first reaction and dried to obtain a phosphate-oxidized graphene composite precursor;

[0011] (3) the phosphate-graphene oxide composite precursor is calcined and pulverized to obtain a phosphate-graphene composite positive electrode material.

[0012] The method provided by the application combines the synthesis of the phosphate-based positive electrode material and the synthesis of graphene and synchronously performs in situ. The acid commonly used in the preparation of the phosphate-based positive electrode material by the liquid phase method and needed to be removed subsequently is simultaneously used for intercalation of graphite, so that the interlayer force of graphite crystals is weakened and then the graphite crystals are easily peeled to form graphene. The graphene obtained in the process does not need complicated operations such as separation, impurity removal, cleaning, drying, recombination with the phosphate-based positive electrode material and the like, but is coated on the surface of the phosphate-based positive electrode material in situ to form a composite material. The obtained graphene is also spaced by the precursor or the phosphate-based positive electrode material, so that the agglomeration of graphene is avoided. The application shortens the process, avoids the need for subsequent treatment of a large amount of waste acid and heavy metals in the preparation process of the oxidized graphene, the agglomeration of graphene and the need for re-dispersion and the like, greatly reduces the cost of the graphene in the application of carbon coating of the phosphate-based positive electrode material, and makes the phosphate-based positive electrode material / graphene composite material have higher capacity and rate performance.

[0013] In the application, the acid is simultaneously used for intercalation, oxidation and dissolution of the raw material of the phosphate-based positive electrode material, and KMnO4, KClO3, NaClO and other oxidation intercalation agents are not used compared with the separate preparation of graphene, graphene oxide or multilayer graphene oxide in the prior art, so that the generation of subsequent by-product waste and the operations such as cleaning, impurity ion pollution / removal and the like are avoided.

[0014] Preferably, the raw material of the phosphate-based positive electrode material in step (1) comprises a lithium source, a phosphorus source and an iron source.

[0015] Preferably, the lithium source comprises any one or a combination of at least two of metallic lithium, lithium oxide, lithium peroxide, lithium hydroxide, lithium nitrate, lithium nitrite, lithium oxalate, lithium carbonate, lithium acetate, lithium phosphate, lithium oleate, lithium stearate, lithium permanganate, lithium ferrate, lithium dihydrogen phosphate or lithium hydrogen phosphate, wherein a typical but non-limiting combination is a combination of lithium oxide and lithium hydroxide, a combination of lithium nitrate and lithium hydroxide, a combination of lithium oxide and lithium nitrate, a combination of lithium ferrate and lithium hydroxide and the like, preferably containing lithium oxide and / or lithium ferrate.

[0016] The application preferably uses raw materials containing strong oxidizing properties, which is more conducive to the oxidation intercalation of graphite, and further preferably uses a combination of raw materials with strong oxidizing properties and other raw materials to reduce the cost.

[0017] Preferably, the phosphorus source comprises any one or a combination of at least two of diphosphorus pentoxide, phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, ferric phosphate, lithium phosphate or lithium dihydrogen phosphate, wherein typical but non-limiting combinations are a combination of phosphoric acid and diammonium hydrogen phosphate, a combination of ammonium dihydrogen phosphate and diammonium hydrogen phosphate, a combination of ammonium phosphate and diammonium hydrogen phosphate, a combination of lithium dihydrogen phosphate and lithium phosphate.

[0018] Preferably, the iron source comprises any one or a combination of at least two of metallic iron, iron oxide, iron hydroxide, iron sulfate, iron nitrate, iron acetate, iron citrate, iron phosphate, iron pyrophosphate, ferrous pyrophosphate, ferrous sulfate, ferrocene, ferrous phosphate or ferrous oxalate, wherein typical but non-limiting combinations are a combination of iron oxide and iron hydroxide, a combination of ferrous sulfate and iron nitrate, a combination of iron acetate and iron hydroxide, a combination of iron citrate and ferrocene.

[0019] Preferably, the lithium source, phosphorus source, iron source and graphite powder are configured in elemental molar ratios of Li:Fe:P:C as (0.90-1.10):(0.90-1.10):(0.90-1.10):(0.1-5), such as 0.98:1:0.99:0.1, 1.02:0.98:0.99:0.5, 1.08:0.98:1.03:0.3, 1.05:0.98:1.02:4.5, 0.98:0.99:1.01:5, 1.1:1.1:1.1:5 or 1.0:1.0:1.0:3.5, etc.

[0020] Preferably, the raw material further comprises a manganese source for replacing part of the iron source.

[0021] Preferably, the manganese source comprises any one or a combination of at least two of metallic manganese, manganese-iron alloy, manganese carbonate, manganese sulfate, manganese nitrate, manganese oxalate, lithium permanganate or lithium ferrate, preferably comprising lithium permanganate.

[0022] Preferably, the lithium source, phosphorus source, iron source, manganese source and graphite powder are configured in elemental molar ratios of Li:(Fe+Mn):P:C as (0.90-1.10):(0.90-1.10):(0.90-1.10):(0.1-5), such as 0.98:1:0.99:0.1, 1.02:0.98:0.99:0.5, 1.08:0.98:1.03:0.3, 1.05:0.98:1.02:4.5, 0.98:0.99:1.01:5, 1.1:1.1:1.1:5 or 1.0:1.0:1.0:3.5, etc.

[0023] Preferably, the molar ratio of Fe:Mn in the iron source and the manganese source is 1:(0-20), such as 1:0, 1:0.1, 1:0.5, 1:0.75, 1:1, 1:2, 1:3, 1:5, 1:7, 1:8, 1:10, 1:12, 1:15, 1:18, or 1:20, etc.

[0024] Preferably, the particle size of the graphite powder is in the range of 0.5-100 μm, such as 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 55 μm, 60 μm, 80 μm, or 100 μm, etc.

[0025] Preferably, the mixing in step (1) comprises: mixing the acid solution and the graphite powder first, then adding the raw material of the phosphate-based positive electrode material, and performing shearing dispersion to obtain a mixed solution.

[0026] Preferably, the acid solution comprises any one or a combination of at least two of nitric acid, sulfuric acid, acetic acid, or phosphoric acid, wherein a typical but non-limiting combination is a combination of nitric acid and sulfuric acid, a combination of nitric acid and phosphoric acid, a combination of phosphoric acid and sulfuric acid, a combination of acetic acid and nitric acid, preferably nitric acid, a combination of nitric acid and acetic acid, a combination of nitric acid and phosphoric acid, or a combination of nitric acid and phosphoric acid and acetic acid.

[0027] Preferably, the phosphorus source contains phosphorus pentoxide. The phosphorus pentoxide can generate phosphoric acid, thereby increasing the concentration of dehydrated acid in the system, which is more conducive to intercalation. The phosphorus source preferably contains phosphorus pentoxide, which can contain only phosphorus pentoxide or a combination of phosphorus pentoxide and other phosphorus sources.

[0028] Preferably, when the raw material of the phosphate-based positive electrode material does not contain a strong oxidizing substance, hydrogen peroxide is added to the acid solution.

[0029] Preferably, the concentration of hydrogen peroxide in the acid solution is 1-20 wt%, such as 1 wt%, 2 wt%, 5 wt%, 7 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, or 20 wt%, etc.

[0030] Preferably, the strong oxidizing substance comprises any one or a combination of at least two of lithium permanganate, lithium peroxide, or lithium ferrate.

[0031] The present application preferably uses a raw material of a phosphate-based positive electrode material with oxidizing property or an oxidizing agent hydrogen peroxide to perform synergistic oxidation stripping on graphite, thereby avoiding the addition of intercalation agents such as potassium permanganate, potassium chlorate, or sodium hypochlorite, wherein the raw material of the phosphate-based positive electrode material with oxidizing property can be used in combination with other raw materials of the phosphate-based positive electrode material.

[0032] Preferably, the temperature is controlled at 0-100℃ before the shearing dispersion, for example, it can be 0℃, 10℃, 15℃, 20℃, 25℃, 30℃, 45℃, 50℃, 60℃, 70℃, 80℃ or 100℃, etc.

[0033] Preferably, the method of shearing dispersion comprises any one of ultrasonic dispersion, high-speed shearing dispersion or wet milling.

[0034] Preferably, the power of ultrasonic dispersion is 10-5000W, for example, it can be 10W, 20W, 50W, 100W, 400W, 500W, 800W, 1000W, 1500W, 2000W, 3000W or 5000W, etc.

[0035] Preferably, the time of ultrasonic dispersion is 10min-6h, for example, it can be 10min, 20min, 30min, 40min, 50min, 1h, 2h, 3h, 4h, 5h or 6h, etc.

[0036] Preferably, the rotation speed of high-speed shearing dispersion is 500-50000r / min, for example, it can be 500r / min, 600r / min, 1000r / min, 2000r / min, 5000r / min, 10000r / min, 20000r / min, 30000r / min, 40000r / min or 50000r / min, etc.

[0037] Preferably, the time length of high-speed shearing dispersion is 5min-6h, for example, it can be 5min, 20min, 30min, 40min, 50min, 1h, 2h, 3h, 4h, 5h or 6h, etc.

[0038] Preferably, the method of wet milling comprises sand milling and / or ball milling.

[0039] Preferably, the time of wet milling is 1-12h, for example, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, etc.

[0040] Preferably, the carbon source is added for mixing after the shearing dispersion.

[0041] Preferably, acid intercalation of graphite powder occurs in the shearing dispersion.

[0042] Preferably, any one or a combination of at least two of oxidation, exfoliation or expansion of graphite powder occurs in the shearing dispersion, preferably, acid intercalation, oxidation, exfoliation and expansion occur simultaneously.

[0043] In the mixing, part of the graphite powder is oxidized, exfoliated and expanded. The graphite powder that is not completely exfoliated will generate gas in the calcination, and then continue to expand and exfoliate.

[0044] Preferably, before the first reaction of the mixed solution in step (2), a carbon source other than the graphite powder is added.

[0045] Preferably, the carbon source includes any one or a combination of at least two of sucrose, starch, dextrin, glucose, fructose, amino acid, citric acid, malic acid, oleic acid, stearic acid, oleylamine, octadecylamine, polyvinyl alcohol, polyvinyl pyrrolidone or polyacrylic acid, and a typical but non-limiting combination is a combination of sucrose and starch, a combination of dextrin and starch, a combination of stearic acid and dextrin, a combination of glucose and amino acid, a combination of oleylamine and octadecylamine, and a combination of polyvinyl alcohol and amino acid.

[0046] Preferably, the amount of the carbon source added accounts for 0.1-20% of the total mass of the mixed solution, for example, it can be 0.1%, 1%, 1.2%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15%, 18% or 20%, etc.

[0047] Preferably, the first reaction in step (2) includes any one of a self-heating evaporation reaction, a coprecipitation reaction, a sol-gel reaction or a solvothermal reaction.

[0048] Preferably, the solvothermal reaction includes an organic solvothermal reaction or a hydrothermal reaction.

[0049] Preferably, the temperature of the calcination in step (3) is 500-850℃, for example, it can be 500℃, 550℃, 600℃, 620℃, 650℃, 700℃, 720℃, 750℃, 800℃ or 850℃, etc.

[0050] Preferably, the calcination includes at least one calcination or at least one temperature zone of the calcination.

[0051] Preferably, the holding time of each of the calcination or each temperature zone of the calcination is 2-20h, for example, it can be 2h, 3h, 5h, 7h, 8h, 9h, 10h, 12h, 14h, 15h, 18h or 20h, etc. Preferably, the calcination is carried out in a protective atmosphere or a reducing atmosphere.

[0052] Preferably, the particle size distribution of the crushed graphite is D10≥0.1μm and D99≤15μm, wherein D10 can be, for example, 0.1μm, 0.2μm, 0.5μm, 1μm, 1.2μm or 1.5μm, etc., and D99 can be, for example, 15μm, 14μm, 13μm, 12μm or 10μm, etc.

[0053] Preferably, the protective atmosphere comprises nitrogen and / or argon.

[0054] Preferably, the reducing atmosphere comprises any one or a combination of at least two of CO, H2, gaseous hydrocarbons or gaseous hydrocarbon derivatives, such as a combination of CO and H2, natural gas or water gas, etc.

[0055] Preferably, the graphene oxide in the phosphate-graphene oxide composite precursor is reduced synchronously with the positive electrode material precursor during the calcination process to form a phosphate-graphene composite positive electrode material.

[0056] In the present application, the phosphate positive electrode material precursor is reduced and converted into a phosphate positive electrode material, and at the same time, the graphene oxide is also reduced to graphene, and the system forms a conductive network, and the electrical resistivity sharply decreases.

[0057] As a preferred technical solution of the present application, the method comprises the following steps:

[0058] (1) mixing an acidic solution and graphite powder with a particle size range of 0.5-100 μm, then adding raw materials of the phosphate-based positive electrode material, controlling the temperature at 0-100 ℃, performing shear dispersion, and then adding a carbon source other than the graphite powder to obtain a mixed solution;

[0059] The raw materials of the phosphate-based positive electrode material comprise a lithium source, a phosphorus source and an iron source; the lithium source, the phosphorus source, the iron source and the graphite powder are configured in an elemental molar ratio of Li:Fe:P:C as (0.90-1.10):(0.90-1.10):(0.90-1.10):(0.1-5);

[0060] Optionally, the raw materials further comprise a manganese source, and the lithium source, the phosphorus source, the iron source, the manganese source and the graphite powder are configured in an elemental molar ratio of Li:(Fe+Mn):P:C as (0.90-1.10):(0.90-1.10):(0.90-1.10):(0.1-5); and the molar ratio of Fe:Mn in the iron source and the manganese source is 1:(0-20);

[0061] (2) the mixed solution is subjected to a first reaction and dried to obtain a phosphate-graphene oxide composite precursor;

[0062] (3) the phosphate-graphene oxide composite precursor is calcined at 500-850 ℃ under a protective atmosphere or a reducing atmosphere for 2-20 h and pulverized to obtain a phosphate-graphene composite positive electrode material.

[0063] Compared with the present application using graphite powder as raw material, the preparation process of the multi-layer graphene still needs to be treated by acid intercalation, cleaning and drying through graphite powder, which will cause the agglomeration of the multi-layer graphene in the drying process, and the compounding effect is poor when the multi-layer graphene is compounded with the phosphate positive electrode material, and the preparation process of the multi-layer graphene itself is complex, which means that an additional acid intercalation treatment, cleaning and drying process is needed, and the excess wastewater needs to be treated. The present application can directly use graphite powder as raw material, which has short process and low cost.

[0064] Moreover, the method provided by the present application does not use oxidants such as sodium hypochlorite and intercalation agents, and can avoid the influence of subsequent impurity ions such as chloride ions and sodium ions on the battery.

[0065] The drying in the above process is not particularly limited, and any device and mode that can be used for drying known to those skilled in the art can be used, and the actual process can also be adjusted, for example, air drying, vacuum drying, drying or freeze drying, etc., or a combination of different modes.

[0066] The crushing in the above process is also not particularly limited, and any device and mode that can be used for crushing known to those skilled in the art can be used, and the actual process can also be adjusted, for example, grinding, extrusion crushing, splitting crushing or impact crushing, etc., or a combination of different modes.

[0067] In the second aspect, the present application provides a phosphate-graphene composite positive electrode material, which is prepared by the method for synchronous synthesis and in-situ compounding of a phosphate-based positive electrode material and graphene according to the first aspect.

[0068] The phosphate-graphene composite positive electrode material provided in the second aspect of the present application is prepared by the method according to the first aspect, and the graphene and the phosphate-based positive electrode material are spaced from each other, avoiding the agglomeration when they are prepared separately, and the capacity and rate performance of the obtained composite material are both high.

[0069] Preferably, the content of graphene in the phosphate-graphene composite positive electrode material is 0.5-10wt%, for example, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt% or 10wt%, etc.

[0070] Preferably, the phosphate-graphene composite positive electrode material includes graphene wrapped on the surface of the phosphate-based positive electrode material particles and graphene extending to the outside of the phosphate-based positive electrode material particles.

[0071] The graphene in the phosphate-graphene composite positive electrode material provided by the application not only wraps the surface of the phosphate-based positive electrode material particles, but also extends to the outside of the particles, and is more likely to contact the adjacent phosphate-based positive electrode material particles to form a graphene conductive network.

[0072] Preferably, the thickness of the carbon layer in the graphene phosphate-graphene composite positive electrode material is 1-10 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, etc.

[0073] Preferably, the particle size D10 of the phosphate-graphene composite positive electrode material is 0.3-0.55 μm, for example, 0.3 μm, 0.35 μm, 0.38 μm, 0.4 μm, 0.41 μm, 0.44 μm, 0.45 μm, 0.46 μm, 0.49 μm, 0.5 μm or 0.55 μm, etc.

[0074] Preferably, the particle size D50 of the phosphate-graphene composite positive electrode material is 1.0-2.0 μm, for example, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2.0 μm, etc.

[0075] Preferably, the particle size D90 of the phosphate-graphene composite positive electrode material is 3.5-9.0 μm, for example, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm or 9.0 μm, etc.

[0076] Preferably, the particle size D99 of the phosphate-graphene composite positive electrode material is 7.5-15 μm, for example, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 10 μm, 10.5 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc.

[0077] In a third aspect, the application provides a lithium ion battery comprising the phosphate-graphene composite positive electrode material according to the first aspect.

[0078] The lithium ion battery according to the third aspect of the application contains the phosphate-graphene composite positive electrode material according to the second aspect, and the capacity and rate performance of the battery are improved, and the production cost is low.

[0079] Compared with the prior art, the application has at least the following beneficial effects:

[0080] (1) The method for synchronously synthesizing and in-situ compounding the phosphate-based positive electrode material and graphene directly combines the preparation of graphene and the phosphate-based positive electrode material together, saves the operations of separately preparing and impurity removing, drying and compounding, shortens the process of original preparation, reduces the cost, and uses the acid originally used for preparing the phosphate-based positive electrode material as the intercalation solution of graphene, reduces the use of intercalation agent and the generation of waste liquid, and reduces the preparation cost.

[0081] (2) The composite material of the phosphate-based positive electrode material and graphene reduces the agglomeration of graphene and the positive electrode material, the lithium ion battery prepared from the composite material has high rate performance and capacity, the 0.1C charge / discharge capacity of the lithium ion battery assembled from the composite material is ≥155 mAh / g, the 1C charge / discharge capacity is ≥139 mAh / g, the 3C charge / discharge capacity is ≥121 mAh / g, preferably ≥140 mAh / g, the 5C charge / discharge capacity is ≥105 mAh / g, preferably ≥121 mAh / g. BRIEF DESCRIPTION OF DRAWINGS

[0082] Figure 1 FIG. 1 is a TEM diagram of the composite material prepared in Example 1. DETAILED DESCRIPTION

[0083] The technical solutions of the present application will be further described in combination with the drawings and through specific embodiments.

[0084] The present application will be further described in detail below. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims.

[0085] Example 1

[0086] The present embodiment provides a method for synchronously synthesizing and in-situ compounding a phosphate-based positive electrode material and graphene, which comprises the following steps:

[0087] (1) mixing a concentrated nitric acid solution (concentration of 68 wt%) and graphite powder with an average particle size of 30 μm, then adding raw materials of a lithium iron manganese phosphate positive electrode material, heating to 80℃ for ultrasonic dispersion, the power of ultrasonic dispersion is 3000 W, and the time is 2 h to obtain a mixed solution, lithium carbonate, diammonium hydrogen phosphate, iron nitrate, lithium permanganate and graphite powder are configured according to the element molar ratio of Li:(Fe+Mn):P:C of 1.05:1:1.02:0.5, wherein the molar ratio of Fe:Mn is 1:0.3;

[0088] (2) adding a carbon source other than graphite powder into the mixed solution, the carbon source being glucose, the added amount of the carbon source accounting for 12% of the total mass of the mixed solution, uniformly mixing, self-heating evaporation reaction of the system, drying to no obvious moisture, obtaining a phosphate-oxidized graphene composite precursor;

[0089] (3) calcining the phosphate-oxidized graphene composite precursor at 750℃ for 15h under an argon atmosphere and airflow pulverizing to D10≥0.1μm and D99≤15μm, obtaining a phosphate-graphene composite positive electrode material.

[0090] The TEM image of the phosphate-graphene composite positive electrode material prepared in this example is shown in FIG. 1. Figure 1 As can be seen from FIG. 1, the thin gauze-like objects are graphenes, part of which is wrapped on the surface of lithium manganese iron phosphate particles, and part of which extends out of the surface of the lithium manganese iron phosphate particles, can be connected with other lithium manganese iron phosphate particles, and is easier to form a conductive network between the lithium manganese iron phosphate particles, enhancing the overall conductivity of the material, and further ensuring the charge and discharge capacity and improving the rate performance. Figure 1 Example 2

[0091] This example provides a method for synchronous synthesis and in-situ compounding of a phosphate-based positive electrode material and graphene, which comprises the following steps:

[0092] (1) mixing a combined solution of concentrated nitric acid and glacial acetic acid (the concentration of the nitric acid is 68wt%, the volume ratio of the concentrated nitric acid to the glacial acetic acid is 3:1) and graphite powder with an average particle size of 10μm, then adding raw materials of a lithium manganese iron phosphate positive electrode material, heating to 80℃ and performing high-speed shearing dispersion, the rotation speed of the high-speed shearing dispersion being 20000r / min, the time being 2h, obtaining a mixed solution; lithium oxide, iron phosphate, iron oxide, lithium permanganate and graphite powder are configured according to the element molar ratio of Li:(Fe+Mn):P:C being 1.02:1:1.03:1, wherein the molar ratio of Fe:Mn is 1:2;

[0093] (2) adding a carbon source other than graphite powder into the mixed solution, the carbon source being fructose, the added amount of the carbon source accounting for 8% of the total mass of the mixed solution, the system undergoing self-heating evaporation reaction, drying to no obvious moisture, obtaining a phosphate-oxidized graphene composite precursor;

[0094] (3) twice calcining and reducing the phosphate-oxidized graphene composite precursor, the first time being calcined at 400℃ for 3h, then heating to 720℃ for 10h, after cooling, pulverizing to D10≥0.1μm and D99≤15μm, obtaining a phosphate-graphene composite positive electrode material.

[0095] Example 3

[0096]

[0097] ​The embodiment provides a method for synchronous synthesis and in-situ compounding of a phosphate-based positive electrode material and graphene, and the method comprises the following steps:

[0098] (1) a combined solution of concentrated sulfuric acid and hydrogen peroxide (the concentration of sulfuric acid is 98 wt%, the concentration of hydrogen peroxide is 20 wt%, and the volume ratio of sulfuric acid to hydrogen peroxide is 5:1) and graphite powder with an average particle size of 5 μm are mixed first, then raw materials of a lithium iron manganese phosphate positive electrode material are added, wet grinding is carried out at 60 ℃, the wet grinding is ball milling, the rotating speed of the ball milling is 2000 r / min, and the time is 12 h, so that a mixed solution is obtained; lithium peroxide, diaphosphorus pentoxide, iron acetate, manganese sulfate and graphite powder are configured according to the element molar ratio of Li:(Fe+Mn):P:C as 1.08:1:1.05:10, wherein the molar ratio of Fe:Mn is 1:0.5;

[0099] (2) a carbon source except the graphite powder is added to the mixed solution, the carbon source is sucrose, the adding amount of the carbon source accounts for 10% of the total mass of the mixed solution, a self-heating evaporation reaction occurs in the system, and the system is dried until no obvious moisture is observed, so that a phosphate-oxidized graphene composite precursor is obtained;

[0100] (3) the phosphate-oxidized graphene composite precursor is calcined at 650 ℃ for 10 h under a nitrogen atmosphere, airflow crushing is carried out until D10 is greater than or equal to 0.2 μm and D99 is less than or equal to 15 μm, so that a phosphate-graphene composite positive electrode material is obtained.

[0101] Embodiment 4

[0102] The embodiment provides a method for synchronous synthesis and in-situ compounding of a phosphate-based positive electrode material and graphene, and the method comprises the following steps:

[0103] (1) a combined solution of nitric acid, phosphoric acid and glacial acetic acid (the concentration of nitric acid in the combined solution is 63 wt%, and the concentration of phosphoric acid is 85 wt%) and graphite powder with an average particle size of 5 μm are mixed first, then raw materials of a lithium iron manganese phosphate positive electrode material are added, wet grinding is carried out at 20 ℃, the wet grinding is ball milling, the rotating speed of the ball milling is 3000 r / min, and the time is 2 h, so that a mixed solution is obtained; lithium peroxide, diaminium hydrogen phosphate, iron nitrate, lithium permanganate and graphite powder are configured according to the element molar ratio of Li:(Fe+Mn):P:C as 1:1:0.95:8, wherein the molar ratio of Fe:Mn is 1:2;

[0104] (2) a carbon source except the graphite powder is added to the mixed solution, the carbon source is octadecylamine, the adding amount of the carbon source accounts for 5% of the total mass of the mixed solution, a self-heating evaporation reaction occurs in the system, and the system is dried until no obvious moisture is observed, so that a phosphate-oxidized graphene composite precursor is obtained;

[0105] (3) the phosphate-graphene oxide composite precursor is calcined at 800 DEG C under a nitrogen atmosphere for 12 hours each time and airflow pulverized to D10 >= 0.2 microns and D99 <= 8 microns, to obtain a phosphate-graphene composite positive electrode material.

[0106] Example 5

[0107] The embodiment provides a method for synchronous synthesis and in-situ compounding of a phosphate-based positive electrode material and graphene, and the method comprises the following steps:

[0108] (1) first mix concentrated nitric acid solution (concentration is 68 wt%) and graphite powder with an average particle size of about 20 microns, then add raw materials of a lithium iron phosphate positive electrode material, and perform ultrasonic dispersion at 0 DEG C, the ultrasonic dispersion peeling power is 1000 W, and the time is 5 hours, to obtain a mixed solution; lithium superoxide, diaphosphine, iron nitrate, lithium nitrate, graphite powder are configured according to an element molar ratio of Li:Fe:P:C of 1.01:1:1.03:2;

[0109] (2) add a carbon source other than the graphite powder to the mixed solution, the carbon source is polyvinyl alcohol, the addition amount of the carbon source accounts for 3% of the total mass of the mixed solution, the system undergoes a self-heating evaporation reaction, and is dried until no obvious moisture is present, to obtain a phosphate-oxidized graphene composite precursor;

[0110] (3) the phosphate-oxidized graphene composite precursor is calcined at 700 DEG C under an argon atmosphere for 15 hours and airflow pulverized to D10 >= 0.1 microns and D99 <= 10 microns, to obtain a phosphate-graphene composite positive electrode material.

[0111] Example 6

[0112] The embodiment provides a method for synchronous synthesis and in-situ compounding of a phosphate-based positive electrode material and graphene, and the method comprises the following steps:

[0113] (1) first mix concentrated nitric acid solution (concentration is 68 wt%) and graphite powder with an average particle size of about 20 microns, then add raw materials of a lithium iron phosphate positive electrode material, and perform ultrasonic dispersion at 0 DEG C, the ultrasonic dispersion peeling power is 1000 W, and the time is 5 hours, to obtain a mixed solution; lithium superoxide, diaphosphine, iron nitrate, lithium nitrate, graphite powder are configured according to an element molar ratio of Li:Fe:P:C of 1.01:1:1.03:2;

[0114] (2) add a carbon source other than the graphite powder to the mixed solution, the carbon source is polyvinyl alcohol, the addition amount of the carbon source accounts for 3% of the total mass of the mixed solution, the system undergoes a self-heating evaporation reaction, and is dried until no obvious moisture is present, to obtain a phosphate-oxidized graphene composite precursor;

[0115] (3) The phosphate-graphene oxide composite precursor is calcined at 550 DEG C for 5h, 700 DEG C for 8h under argon atmosphere, and is pulverized by airflow to obtain a phosphate-graphene composite positive electrode material with D10≥0.1 μm and D99≤15 μm.

[0116] Comparative Example 1

[0117] The present comparative example provides a method for synchronous synthesis and in-situ compounding of a phosphate-based positive electrode material and graphene, which replaces the acid solution in Example 1 with water, and the rest is the same as Example 1.

[0118] The present comparative example uses water as the solution, which cannot intercalate the graphite powder, and finally it is difficult to obtain a positive electrode material of intercalated and compounded lithium manganese iron phosphate and graphene.

[0119] The particle size of the phosphate-based positive electrode material and the agglomeration of graphene in the composite material prepared in the above examples are measured by a laser particle size analyzer, and the specific data are shown in Table 1.

[0120] Table 1

[0121] D10 (pm) D50 (pm) D90 (pm) D99 (pm) Example 1 0.46 1.39 7.21 14.55 Example 2 0.40 1.21 4.53 9.23 Example 3 0.38 1.14 3.85 14.68 Example 4 0.44 1.32 5.65 7.89 Example 5 0.41 1.18 4.92 9.16 Example 6 0.41 1.08 6.87 13.91

[0122] The present application takes Example 1 as an example to prepare a lithium battery and test the rate performance. The present application does not have special limitations on the actual application of the positive electrode material, and only the preparation and testing process of the detailed button cell is given here for performance testing. The specific process is as follows:

[0123] Test method: button cell production: the phosphate-graphene composite positive electrode material (90%) prepared in the above examples, conductive agent acetylene black (3%), and binder polyvinylidene fluoride (PVDF, 7%) are added to an appropriate amount of N-methyl pyrrolidone solution (NMP solution), stirred in a vacuum stirrer for 2h, and a positive electrode slurry is prepared; the slurry is uniformly coated on an aluminum foil, then placed in a vacuum drying oven at 130 DEG C for 12h, and then rolled and cut into a circular piece with a diameter of 14mm as a positive electrode sheet. The positive electrode sheet, negative electrode sheet (metal lithium sheet with a diameter of 14.5mm), separator (Celgard2400 microporous polypropylene film), and electrolyte (1mol / L LiPF6 / EC+DMC (volume ratio 1:1)) are assembled into a CR2025 type button lithium ion battery in a hydrogen-filled glove box.

[0124] Charge-discharge test: the prepared test battery is subjected to charge-discharge test at 25±0.5 DEG C using a lithium ion battery charge-discharge test system, and the charge-discharge conditions are as follows: charge termination voltage 3.75V; discharge termination voltage 2.00V; charge-discharge current density: 0.1C, 1C, 3C and 5C.

[0125] The test methods of application examples 2-6 (using the composite materials prepared in examples 2-6 respectively) refer to the test method of application example 1, and the test results are shown in Table 2.

[0126] Table 2

[0127]

[0128] As can be seen from Table 1 and Table 2: in combination of application examples 1-6, it can be seen that the composite material obtained by the method for synchronous synthesis and in-situ compounding of the phosphate-based positive electrode material and graphene has excellent particle size, and the agglomeration phenomenon between the composite materials is less, wherein D50 is controlled between 1.0-2.0 μm, D90 is controlled between 3.5-9.0 μm, and D99 is controlled between 7.5-15 μm; due to the in-situ introduction of graphene in the composite material, the preparation process is shortened and the production cost is reduced, and the final obtained composite material has high rate performance, and after being assembled into a lithium ion battery, the 0.1C charge / discharge capacity is ≥155 mAh / g, the 1C charge / discharge capacity is ≥139 mAh / g, the 3C charge / discharge capacity is ≥121 mAh / g, preferably ≥140 mAh / g, and the 5C charge / discharge capacity is ≥105 mAh / g.

[0129] The above examples are used to illustrate the detailed structural features of the present application, but the present application is not limited to the above detailed structural features, i.e. it does not mean that the present application must rely on the above detailed structural features to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the components selected by the present application, addition of auxiliary components, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for the simultaneous synthesis and in-situ composite of phosphate-based cathode materials and graphene, characterized in that, The method includes: (1) First, mix the acidic solution and graphite powder, then add the raw materials of the phosphate-based cathode material, and perform shear dispersion to obtain a mixture; the raw materials of the phosphate-based cathode material include lithium source, phosphorus source and iron source; the acidic solution includes any one or at least two of nitric acid, sulfuric acid, acetic acid or phosphoric acid. (2) The mixture is subjected to a first reaction and dried to obtain a phosphate-graphene oxide composite precursor; (3) The phosphate-graphene oxide composite precursor is calcined and pulverized to obtain phosphate-graphene composite cathode material; The phosphate-graphene composite cathode material includes graphene coated on the surface of phosphate-based cathode material particles and graphene extending beyond the phosphate-based cathode material particles. The particle size D10 of the phosphate-graphene composite cathode material is 0.3~0.55μm; The particle size D99 of the phosphate-graphene composite cathode material is 7.5~15μm.

2. The method according to claim 1, characterized in that, The lithium source includes any one or a combination of at least two of the following: lithium metal, lithium oxide, lithium peroxide, lithium hydroxide, lithium nitrate, lithium nitrite, lithium oxalate, lithium carbonate, lithium acetate, lithium phosphate, lithium oleate, lithium stearate, lithium permanganate, lithium ferrate, lithium dihydrogen phosphate, or lithium hydrogen phosphate. The phosphorus source includes any one or a combination of at least two of phosphorus pentoxide, phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, iron phosphate, lithium phosphate, or lithium dihydrogen phosphate. The iron source includes any one or a combination of at least two of the following: metallic iron, iron oxide, iron hydroxide, iron sulfate, iron nitrate, iron acetate, iron citrate, iron phosphate, iron pyrophosphate, ferrous pyrophosphate, ferrous sulfate, ferrocene, ferrous phosphate, or ferrous oxalate.

3. The method according to claim 1, characterized in that, The lithium source, phosphorus source, iron source and graphite powder are configured with an elemental molar ratio of Li:Fe:P:C of (0.90~1.10):(0.90~1.10):(0.90~1.10):(0.1~5).

4. The method according to claim 2, characterized in that, The lithium source includes lithium peroxide and / or lithium ferrate.

5. The method according to claim 1, characterized in that, The raw materials for the phosphate-based cathode material also include a manganese source to replace part of the iron source; The manganese source includes any one or a combination of at least two of the following: metallic manganese, ferromanganese alloy, manganese carbonate, manganese sulfate, manganese nitrate, manganese oxalate, or lithium permanganate.

6. The method according to claim 5, characterized in that, The manganese source includes lithium permanganate; And / or, the lithium source, phosphorus source, iron source, manganese source and graphite powder are configured in an elemental molar ratio of (0.90~1.10):(0.90~1.10):(0.90~1.10):(0.1~5) for Li:(Fe+Mn):P:C.

7. The method according to claim 6, characterized in that, The molar ratio of Fe:Mn in the iron source and manganese source is 1:(0~20); And / or, the particle size range of the graphite powder is 0.5~100μm.

8. The method according to claim 7, characterized in that, The phosphorus source contains phosphorus pentoxide.

9. The method according to claim 8, characterized in that, The acidic solution includes nitric acid; And / or, when the raw materials of the phosphate-based cathode material do not contain strong oxidizing substances, hydrogen peroxide is added to the acidic solution; wherein, the strong oxidizing substances include any one or a combination of at least two of lithium permanganate, lithium peroxide, or lithium ferrate.

10. The method according to claim 9, characterized in that, The concentration of hydrogen peroxide in the acidic solution is 1~20 wt%; Before performing the shearing and dispersion, the temperature is controlled at 0~100℃; The shear dispersion method includes any one of ultrasonic dispersion, high-speed shear dispersion, or wet grinding.

11. The method according to claim 10, characterized in that, The power of the ultrasonic dispersion is 10~5000W; The ultrasonic dispersion time is 10 min to 6 h; The rotational speed of the high-speed shear dispersion is 500~50000 r / min; The duration of the high-speed shear dispersion is 5 min to 6 h; The wet grinding method includes sand milling and / or ball milling; The wet grinding time is 1~12 hours.

12. The method according to claim 1, characterized in that, During the shear dispersion, the graphite powder undergoes acid intercalation; And / or, the graphite powder in the shear dispersion also undergoes any one or a combination of at least two of oxidation, exfoliation, or expansion.

13. The method according to claim 1, characterized in that, Before the first reaction of the mixture described in step (2), a carbon source other than graphite powder is added.

14. The method according to claim 13, characterized in that, The carbon source includes any one or a combination of at least two of the following: sucrose, starch, dextrin, glucose, fructose, amino acids, citric acid, malic acid, oleic acid, stearic acid, oleylamine, octadecylamine, polyvinyl alcohol, polyvinylpyrrolidone, or polyacrylic acid. And / or, the amount of carbon source added accounts for 0.1 to 20% of the total mass of the mixture.

15. The method according to claim 1, characterized in that, The first reaction in step (2) includes any one of the following: self-heating evaporation reaction, co-precipitation reaction, sol-gel reaction or solvothermal reaction.

16. The method according to claim 1, characterized in that, The calcination temperature in step (3) is 500~850℃; And / or, the calcination includes at least one calcination or calcination in at least one temperature zone; The holding time for each calcination or each temperature zone calcination is 2 to 20 hours.

17. The method according to claim 1, characterized in that, The calcination described in step (3) is carried out in a protective atmosphere or a reducing atmosphere; The protective atmosphere includes nitrogen and / or argon. The reducing atmosphere includes any one or a combination of at least two of CO, H2, gaseous hydrocarbons or gaseous hydrocarbon derivatives; The particle size distribution after pulverization is D10≥0.1μm and D99≤15μm; During the calcination process, graphene oxide and cathode material precursor in the phosphate-graphene oxide composite precursor are simultaneously reduced to form phosphate-graphene composite cathode material.

18. A phosphate-graphene composite cathode material, characterized in that, The phosphate-graphene composite cathode material is prepared by the method described in any one of claims 1 to 17, which involves the simultaneous synthesis and in-situ composite of phosphate-based cathode materials and graphene. The phosphate-graphene composite cathode material includes graphene coated on the surface of phosphate-based cathode material particles and graphene extending beyond the phosphate-based cathode material particles. The particle size D10 of the phosphate-graphene composite cathode material is 0.3~0.55μm; The particle size D99 of the phosphate-graphene composite cathode material is 7.5~15μm.

19. The phosphate-graphene composite cathode material according to claim 18, characterized in that, The graphene content in the phosphate-graphene composite cathode material is 0.5~10 wt%. The thickness of the carbon layer in the graphene phosphate-graphene composite cathode material is 1~10 nm; The particle size D50 of the phosphate-graphene composite cathode material is 1.0~2.0 μm; The particle size D90 of the phosphate-graphene composite cathode material is 3.5~9.0 μm.

20. A lithium-ion battery, characterized in that, The lithium-ion battery includes the phosphate-graphene composite cathode material as described in claim 18 or 19.

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