A method for preparing a self-synthesized graphene-coated manganese iron precursor, lithium manganese iron phosphate cathode material, its preparation method and application

Abstract

This invention discloses a method for preparing a self-synthesized graphene-coated manganese-iron precursor, a lithium manganese iron phosphate cathode material, its preparation method, and its application, relating to the field of battery materials technology. The method for preparing the self-synthesized graphene-coated manganese-iron precursor includes: mixing a manganese source, an iron source, a nickel source, graphite powder, perchloric acid, and potassium chlorate; stirring and reacting the mixture at 200–400°C for 7–12 hours under inert gas protection; and washing and drying to obtain the self-synthesized graphene-coated manganese-iron precursor. This invention improves the uniformity of manganese-iron element distribution and carbon coating at the microscopic level by first reacting iron, manganese, and graphite to generate a graphene-coated manganese-iron precursor, and then mixing the resulting precursor with a phosphorus source, a lithium source, and a carbon source through sand milling. The metal-catalyzed synthesis of graphene and the double carbon coating process result in more uniform carbon coating, improving the purity and conductivity of the material, while simultaneously reducing the specific surface area and increasing the capacity.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a method for preparing a self-synthesized graphene-coated manganese iron precursor, lithium manganese iron phosphate cathode material, its preparation method, and its application. Background Technology

[0002] With the increasing global demand for clean energy, lithium-ion batteries (LIBs), as high-efficiency energy storage devices, are widely used in electric vehicles, portable electronic devices, and grid energy storage systems. As a key component of lithium-ion batteries, the performance of the cathode material directly affects the battery's energy density, cycle life, and safety. LiMnFePO4 combines the advantages of lithium iron phosphate and lithium manganese phosphate, resulting in a higher theoretical capacity. However, due to the uneven distribution of Mn and Fe in the crystal lattice and the poor conductivity of LiMnFePO4, the uniform distribution of Mn and Fe elements in LiMnFePO4 is crucial to its electrochemical performance. Uneven elemental distribution leads to material instability and affects the battery's charge-discharge efficiency. To improve the conductivity of LiMnFePO4, carbon coating technology is commonly used. However, uneven carbon coating leads to differences in material conductivity, affecting its overall performance. Currently, methods for preparing LiMnFePO4 cathode materials with uniform Mn and Fe distribution and uniform carbon coating mainly include solution co-precipitation, solid-state reaction, and spray drying. These methods have solved the problem of uniform distribution of Mn and Fe to some extent, but there is still considerable room for improvement in terms of the uniformity of carbon coating and the controllability of the process.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a self-synthesized graphene-coated manganese iron precursor, a lithium manganese iron phosphate cathode material, its preparation method, and its application.

[0005] This invention is implemented as follows:

[0006] In a first aspect, the present invention provides a method for preparing a self-synthesized graphene-coated manganese-iron precursor, comprising: mixing a manganese source, an iron source, a nickel source, graphite powder, perchloric acid and potassium chlorate, stirring and reacting at 200~400℃ for 7~12h under inert gas protection, and washing and drying to obtain the self-synthesized graphene-coated manganese-iron precursor.

[0007] In an optional embodiment, the molar ratio of the manganese source to the iron source is (2~8):(8~2);

[0008] And / or, the mass of the graphite powder is 0.5 wt% to 3.5 wt% of the total mass of the manganese source and the iron source;

[0009] And / or, the mass of the nickel source is 0.5 wt% to 4.5 wt% of the total mass of the manganese source and the iron source;

[0010] And / or, the mass of the perchloric acid is 0.03 wt% to 0.09 wt% of the total mass of the manganese source and the iron source;

[0011] And / or, the mass of the potassium chlorate is 9.5 wt% to 16.8 wt% of the total mass of the manganese source and the iron source.

[0012] In an optional embodiment, the manganese source includes at least one of manganese carbonate, manganese oxalate, and manganese phosphate;

[0013] And / or, the iron source includes at least one of ferric phosphate, ferrous oxalate, ferrous sulfate, ferric oxide, ferrous oxide and magnetite;

[0014] And / or, the nickel source includes nickel sulfate.

[0015] Secondly, the present invention provides a method for preparing lithium manganese iron phosphate cathode material, comprising mixing and crushing a self-synthesized graphene-coated manganese iron precursor obtained by the preparation method of the self-synthesized graphene-coated manganese iron precursor described in any of the foregoing embodiments with a phosphorus source, a lithium source, a carbon source and water to obtain a slurry, drying to obtain a calcination precursor; and calcining the calcination precursor to obtain lithium manganese iron phosphate cathode material.

[0016] In an optional embodiment, the slurry has a molar ratio of (Mn+Fe):P = (0.94~1.02):1, and Li:P = (1.01~1.10):1; the mass of the carbon source is 2.5wt%~12.5wt% of the mass of the self-synthesized graphene-coated manganese-iron precursor.

[0017] Preferably, the phosphorus source includes at least one of phosphoric acid and ammonium dihydrogen phosphate;

[0018] Preferably, the lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate;

[0019] Preferably, the carbon source includes at least one of glucose, sucrose, polyethylene glycol, starch, ethyl cellulose, and citric acid.

[0020] In an optional embodiment, the slurry further includes an additive, wherein the amount of the additive is 100 ppm to 5000 ppm;

[0021] Preferably, the additive includes at least one of Ti source, Mo source, Mg source, Al source, Sb source, Cu source, Zr source, and Zn source.

[0022] In an optional embodiment, the Dv50 of the crushed particle size is 0.1~0.8 μm;

[0023] Preferably, the calcination is carried out under a nitrogen atmosphere at 650-800°C for 6-15 hours.

[0024] Thirdly, the present invention provides a lithium manganese iron phosphate cathode material, which is prepared by the method for preparing lithium manganese iron phosphate cathode material as described in any of the foregoing embodiments; the compaction density of the lithium manganese iron phosphate cathode material at a pressure of 3000 kg is 2.15 g / cm³. 3 ~2.6 g / cm 3 ;

[0025] And / or, the BET of the lithium manganese iron phosphate cathode material is 5 m. 2 / g~15 m 2 / g;

[0026] And / or, the powder resistivity of the lithium manganese iron phosphate cathode material at a pressure of 12 MPa is 10 Ω·cm to 700 Ω·cm;

[0027] And / or, the residual lithium content on the surface of the lithium manganese iron phosphate cathode material is less than 700 ppm;

[0028] And / or, the Dv50 of the lithium manganese iron phosphate cathode material is 0.4~1.5 μm.

[0029] Fourthly, the present invention provides a positive electrode sheet comprising the lithium manganese iron phosphate positive electrode material as described in the foregoing embodiments.

[0030] Fifthly, the present invention provides the application of lithium manganese iron phosphate cathode material as described in the foregoing embodiments or cathode sheet as described in the foregoing embodiments in the preparation of lithium-ion batteries.

[0031] The present invention has the following beneficial effects:

[0032] The lithium manganese iron phosphate cathode material provided by this invention involves first reacting iron, manganese, and graphite in a reactor to generate a graphene-coated manganese iron precursor. The resulting precursor is then mixed with a phosphorus source, a lithium source, and a carbon source through sand milling, which improves the uniformity of manganese iron element distribution and carbon coating at the microscopic level. The metal-catalyzed graphene synthesis and double carbon coating process further enhance the uniformity of carbon coating, improving material purity and conductivity while reducing specific surface area and increasing capacity. The process of this invention is simple, highly controllable, and requires minimal reaction conditions and equipment, making it easy to achieve large-scale industrial production. The raw materials do not contain toxic, radioactive, or other harmful substances, making it environmentally friendly. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a SEM image of the self-synthesized graphene-coated manganese-iron precursor provided in Example 1 of the present invention;

[0035] Figure 2 This is a SEM image of the lithium iron phosphate cathode material provided in Example 1 of the present invention;

[0036] Figure 3 This is a SEM image of the lithium iron phosphate cathode material provided in Comparative Example 1 of this invention;

[0037] Figure 4 The XRD patterns of lithium manganese iron phosphate cathode materials provided in Embodiment 1 and Comparative Example 1 of the present invention are shown below.

[0038] Figure 5 The elemental EMPA diagram of the lithium iron phosphate cathode material provided in Embodiment 1 of the present invention;

[0039] Figure 6 The elemental EMPA diagram of the lithium iron phosphate cathode material provided in Comparative Example 1 of this invention;

[0040] Figure 7 The charge and discharge capacity diagrams of CR2016 batteries prepared from the lithium manganese iron phosphate cathode material provided in Example 1 and Comparative Example 1 of the present invention are shown.

[0041] Figure 8 This is a SEM image of the self-synthesized graphene-coated manganese-iron precursor provided in Comparative Example 2 of this invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0043] In the description of this invention, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, or product that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, or products.

[0044] When a numerical range is disclosed in this invention, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Further, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed in this invention should be understood to include any and all subranges to which they are incorporated.

[0045] Unless otherwise specified, the chemical formula provided in this invention is calculated based on the feeding ratio. In reality, considering factors such as lithium source burn-out, the atomic ratio in the actual obtained cathode material may not be exactly the same as the ratio in the chemical formula.

[0046] This invention provides a method for preparing a self-synthesized graphene-coated manganese-iron precursor, comprising: mixing a manganese source, an iron source, a nickel source, graphite powder, perchloric acid and potassium chlorate, stirring and reacting at 200~400℃ for 7~12h under inert gas protection, and washing and drying to obtain the self-synthesized graphene-coated manganese-iron precursor.

[0047] In this invention, the mixing of manganese source, iron source, nickel source, graphite powder, perchloric acid, and potassium chlorate allows for a more uniform distribution of ferromanganese. Simultaneously, the graphite powder, under the oxidation of perchloric acid and potassium chlorate, first synthesizes graphene oxide, which is then converted to graphene under the catalytic reduction of the nickel source. The graphene can then uniformly coat the surface of the ferromanganese precursor. Inert gases include, but are not limited to, nitrogen and helium.

[0048] In some embodiments of the present invention, the molar ratio of manganese source to iron source is (2~8):(8~2); for example, it can be any one of 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 or a range between any two. The manganese source includes, but is not limited to, at least one of manganese carbonate, manganese oxalate, and manganese phosphate; the iron source includes, but is not limited to, at least one of ferric phosphate, ferrous oxalate, ferrous sulfate, ferric oxide, ferrous oxide, and magnetite.

[0049] In some embodiments of the present invention, the mass of graphite powder is 0.5 wt% to 3.5 wt% of the total mass of the manganese source and the iron source; for example, it can be any one of 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt% or a range between any two.

[0050] In some embodiments of the present invention, the mass of the nickel source is 0.5 wt% to 4.5 wt% of the total mass of the manganese and iron sources; for example, it can be any one or a range between any two of 0.5 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, 3.5 wt%, 4 wt%, and 4.5 wt%. The nickel source includes, but is not limited to, nickel sulfate.

[0051] In some embodiments of the present invention, the mass of perchloric acid is 0.03 wt% to 0.09 wt% of the total mass of the manganese source and the iron source; for example, it can be any one of 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt% or a range between any two.

[0052] In some embodiments of the present invention, the mass of potassium chlorate is 9.5 wt% to 16.8 wt% of the total mass of the manganese and iron sources. For example, it can be any one of 9.5 wt%, 9.8 wt%, 10 wt%, 10.5 wt%, 10.8 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 15.5 wt%, 16 wt%, 16.5 wt%, 16.8 wt%, or a range between any two.

[0053] This invention synthesizes a graphene-coated manganese-iron precursor structure, which, compared to the conventional method of directly using graphene or graphene oxide for coating, exhibits better uniformity and yields a more effective precursor.

[0054] Furthermore, the present invention provides a method for preparing lithium manganese iron phosphate cathode material, which includes mixing and crushing the above-mentioned self-synthesized graphene-coated manganese iron precursor with a phosphorus source, a lithium source, a carbon source and water to obtain a slurry, drying it to obtain a calcination precursor; and calcining the calcination precursor to obtain lithium manganese iron phosphate cathode material.

[0055] Specifically, it includes the following steps:

[0056] S1, Mixed.

[0057] The above-mentioned self-synthesized graphene-coated manganese-iron precursor was mixed with phosphorus source, lithium source, carbon source and water, crushed to obtain slurry, and dried to obtain calcined precursor.

[0058] In the slurry, the molar ratio of (Mn+Fe):P = (0.94~1.02):1, and the molar ratio of Li:P = (1.01~1.10):1; the mass of the carbon source is 2.5wt%~12.5wt% of the mass of the self-synthesized graphene-coated manganese-iron precursor.

[0059] In some embodiments of the present invention, (Mn+Fe):P is a range of 0.94:1, 0.95:1, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1.0:1, 1.01:1, or 1.02:1, or any two of these values. Li:P is a range of 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, or 1.10:1, or any two of these values. The mass of the carbon source is any one or any two of the following values: 2.5 wt%, 3.5 wt%, 4.5 wt%, 5.0 wt%, 6.5 wt%, 7.5 wt%, 8.5 wt%, 9.5 wt%, 10.5 wt%, 11.5 wt%, or 12.5 wt% of the mass of the self-synthesized graphene-coated manganese-iron precursor.

[0060] The phosphorus source includes, but is not limited to, at least one of phosphoric acid and ammonium dihydrogen phosphate; the lithium source includes, but is not limited to, at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; and the carbon source includes, but is not limited to, at least one of glucose, sucrose, polyethylene glycol (PEG), starch, ethyl cellulose, and citric acid. The molecular weight of the polyethylene glycol is 100 to 10,000.

[0061] Furthermore, the slurry also includes additives. The additives in this invention are metal ion sources. Metal ions can increase the diffusion rate of Li+, thereby increasing the rate and capacity of the lithium manganese iron phosphate cathode material.

[0062] The amount of additive added is 100 ppm to 5000 ppm; for example, it can be any one of 100 ppm, 200 ppm, 300 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm or 5000 ppm or a range between any two.

[0063] Preferably, the additive includes at least one of the following: Ti source, Mo source, Mg source, Al source, Sb source, Cu source, Zr source, and Zn source. Specifically, the Ti source includes, but is not limited to, at least one of titanium dioxide and titanium sulfate; the Mo source includes, but is not limited to, at least one of molybdenum trioxide and ammonium molybdate; the Mg source includes, but is not limited to, at least one of magnesium oxide, magnesium chloride, and magnesium acetate; the Al source includes, but is not limited to, at least one of aluminum acetate and aluminum oxide; the Sb source includes, but is not limited to, at least one of antimony trioxide and antimony pentoxide; the Cu source includes, but is not limited to, at least one of copper carbonate, copper hydroxide, and copper oxide; the Zr source includes, but is not limited to, at least one of zirconium dioxide, zirconium hydroxide, and zirconium sulfate; and the Zn source includes, but is not limited to, at least one of zinc oxide and zinc chloride.

[0064] The Dv50 of the crushed particle size is 0.1~0.8 μm, for example, it can be any one of 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm or 0.8 μm or any two of them.

[0065] S2, roasting.

[0066] Calcination includes calcination at 650–800°C for 6–15 hours under a nitrogen atmosphere. The calcination temperature can be any one of 650°C, 700°C, 725°C, 750°C, or 800°C, or a range between any two. The calcination time can be any one of 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 13 hours, 14 hours, or 15 hours, or a range between any two.

[0067] This invention provides a lithium manganese iron phosphate cathode material, which is prepared by the above-mentioned method for preparing lithium manganese iron phosphate cathode materials.

[0068] The lithium manganese iron phosphate cathode material provided by this invention has high capacity, high compaction density, good elemental uniformity, excellent structural stability and outstanding electrochemical performance; it also has good energy density and cycle performance.

[0069] The molecular formula of lithium manganese iron phosphate cathode material is LiMn. 1-x Fe x A z PO4; wherein 0.2≤x≤0.8, 0≤z≤0.05, and A includes at least one of Ti, Mo, Mg, Al, Sb, Cu, Zr, and Zn.

[0070] In some embodiments of the present invention, the residual lithium content on the surface of the lithium manganese iron phosphate cathode material is less than 700 ppm.

[0071] In some embodiments of the present invention, the residual lithium content on the surface of the lithium manganese iron phosphate cathode material is 100 ppm to 660 ppm. For example, it can be any one of 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 400 ppm, 500 ppm or 600 ppm or a range between any two.

[0072] In some embodiments of the present invention, the specific surface area (BET) of the lithium manganese iron phosphate cathode material is 5 m². 2 / g~15m 2 / g. For example: it can be 5 m. 2 / g、6 m 2 / g、7 m 2 / g、8 m 2 / g、9 m 2 / g、10 m 2 / g、11 m 2 / g、12 m 2 / g、13m 2 / g、14 m 2 / g and 15 m 2 The range of values ​​in / g, either one or both.

[0073] In some embodiments of the present invention, the powder resistivity of the lithium manganese iron phosphate cathode material at a pressure of 12 MPa is 10 Ω·cm to 700 Ω·cm. For example, it can be any one of 10 Ω·cm, 30 Ω·cm, 50 Ω·cm, 100 Ω·cm, 150 Ω·cm, 200 Ω·cm, 300 Ω·cm, 400 Ω·cm, 500 Ω·cm, 600 Ω·cm, or 700 Ω·cm, or a range between any two.

[0074] In some embodiments of the present invention, the compaction density of the lithium manganese iron phosphate cathode material under a pressure of 3000 kg is 2.15 g / cm³. 3 ~2.6 g / cm 3 For example: it can be 2.15 g / cm³. 3 2.2 g / cm 3 2.25 g / cm 3 2.3 g / cm 3 2.35 g / cm 3 2.4 g / cm 3 2.45 g / cm 3 2.5 g / cm 3 Or 2.6 g / cm3 The range of values ​​between any one or any two of them.

[0075] In some embodiments of the present invention, the Dv50 of the lithium manganese iron phosphate cathode material particle size is 0.4~1.5 μm, for example, it can be any one or any two of 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm or 1.5 μm.

[0076] Furthermore, the present invention provides a positive electrode sheet comprising the aforementioned lithium manganese iron phosphate positive electrode material. The present invention also provides the application of the aforementioned lithium manganese iron phosphate positive electrode material or positive electrode sheet in the preparation of lithium-ion batteries.

[0077] The positive electrode includes a current collector and a positive active layer disposed on the current collector. The positive active layer contains the aforementioned lithium manganese iron phosphate positive electrode material. In addition, the positive active layer also contains conventional binders, modifiers, and conductive agents. The specific amounts of the lithium manganese iron phosphate positive electrode material, binders, modifiers, and conductive agents are not specifically limited in this invention and can be adjusted according to actual conditions. The binders, modifiers, and conductive agents can also be conventional binders, modifiers, and conductive agents. For example, the modifier can be at least one of sodium polyacrylate, polyrotaxane, polyacrylamide, and polyethyleneimine. The conductive agent is selected from at least one of conductive carbon black, acetylene black, graphite, and graphene. The binder is selected from at least one of guar gum, sodium alginate, sodium carboxymethyl cellulose, gum arabic, carrageenan, styrene-butadiene rubber, and polyvinylidene fluoride.

[0078] The above-mentioned lithium manganese iron phosphate cathode material or cathode sheet can be used in the preparation of lithium-ion batteries. For example, a lithium-ion battery may include the above-mentioned cathode sheet, as well as conventional cathode sheets, electrolytes, separators, etc., thereby forming a complete lithium battery structure.

[0079] Furthermore, the present invention may also provide an electrical device, including the aforementioned lithium battery, and may also include electrical equipment, the specific type of which is not limited.

[0080] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0081] Example 1

[0082] This example provides a method for preparing lithium iron phosphate cathode material, the steps of which are as follows:

[0083] 1) Take 5kg of pure water, add 800g of potassium chlorate, 5g of perchloric acid (72wt%), 116.0g of graphite powder, and 58g of nickel sulfate. Stir well and pour into the reaction vessel.

[0084] The graphite powder content is 2 wt% of the mass of the manganese and iron sources, and the nickel sulfate content is 1 wt% of the mass of the manganese and iron sources.

[0085] 2) Weigh 3093g (about 26.9mol) of manganese carbonate and 2705.6g (about 17.94mol) of ferric phosphate, mix them evenly with a high-speed mixer and add them to the reaction vessel of step 1). Under nitrogen protection, stir and react at 250℃ for 10h. Then wash with pure water 6 times and dry in an oven at 100℃ for 24h to obtain the self-synthesized graphene-coated manganese iron precursor.

[0086] The molar ratio of Fe to Mn was 4:6; the Fe content in the synthesized graphene-coated manganese-iron precursor was 18.02 wt%, the Mn content was 26.59 wt%, and the P content was 9.98 wt%.

[0087] 3) Take 5500g of the self-synthesized graphene-coated manganese-iron precursor from step 1) and add it to 18L of water. Then, add 3064.8g of ammonium dihydrogen phosphate, 1770.3g of lithium carbonate, 31.93g of molybdenum trioxide, 137.5g of glucose, 401.5g of PEG4000, and 66g of citric acid in sequence. After mixing evenly, mill the slurry to a particle size Dv50 = 0.8 μm. After the particle size meets the standard, spray dry to obtain the calcined precursor.

[0088] In terms of molar ratio, (Mn+Fe) / P=1.0; Li / P=1.08; and the amount of carbon source used is 11 wt% of the self-synthesized graphene-coated manganese-iron precursor.

[0089] 4) Under a nitrogen atmosphere, the calcination precursor was calcined at 785℃ for 12 h, with a heating time of 155 min; after natural cooling to room temperature, the material was crushed to a Dv50 of 0.7 μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.6 Fe 0.4 Mo 0.005 PO4 / C.

[0090] Example 2

[0091] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 2) of this example, the molar ratio is Fe:Mn=2:8.

[0092] Example 3

[0093] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 2) of this example, the molar ratio is Fe:Mn=5:5.

[0094] Example 4

[0095] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 2) of this example, the molar ratio is Fe:Mn=6:4.

[0096] Example 5

[0097] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 2) of this example, the molar ratio is Fe:Mn=8:2.

[0098] Example 6

[0099] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 2) of this example, the reaction temperature for self-synthesizing graphene-coated manganese iron precursor is 200℃.

[0100] Example 7

[0101] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 2) of this example, the reaction temperature for self-synthesizing graphene-coated manganese iron precursor is 400℃.

[0102] Example 8

[0103] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 1), the graphite powder content is replaced by 3.5 wt% instead of 2 wt%.

[0104] Example 9

[0105] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 1), the graphite powder content is replaced from 2wt% to 0.5wt%.

[0106] Example 10

[0107] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 3), the grinding particle size Dv50 is replaced from 0.8 μm to 0.3 μm.

[0108] Example 11

[0109] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 3), the grinding particle size Dv50 is replaced from 0.8 μm to 1.1 μm.

[0110] Example 12

[0111] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 3), (Mn+Fe) / P=1.0 and Li / P=1.08 are replaced with (Mn+Fe) / P=1.02 and Li / P=1.10.

[0112] Example 13

[0113] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 3), (Mn+Fe) / P=1.0 and Li / P=1.08 are replaced with (Mn+Fe) / P=0.94 and Li / P=1.01.

[0114] Example 14

[0115] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 1), the nickel sulfate content is replaced by 4.5 wt% instead of 1 wt%.

[0116] Example 15

[0117] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 1), the nickel sulfate content is replaced by 0.5 wt% instead of 1 wt%.

[0118] Comparative Example 1

[0119] This comparative example is basically the same as Example 1, except that graphene coating was not performed in this comparative example, and manganese, iron, phosphorus, and lithium sources were directly mixed. Specifically, the steps include:

[0120] 1) Take 15 kg of water, then add 3095.3 g of ammonium dihydrogen phosphate, 3093 g of manganese carbonate, 2705.6 g of ferric phosphate, 1789.5 g of lithium carbonate, 32.28 g of molybdenum trioxide, 145.0 g of glucose, 423.3 g of PEG4000, and 69.6 g of citric acid in sequence. After mixing evenly, mill the slurry to a particle size Dv50 = 0.8 μm. After the particle size meets the standard, spray dry to obtain the calcination precursor.

[0121] In terms of molar ratio, (Mn+Fe) / P=1.0; Li / P=1.08; and the amount of carbon source used is 11 wt% of the amount of manganese and iron sources.

[0122] 2) Under a nitrogen atmosphere, the calcination precursor was calcined at 785℃ for 12 h, with a heating time of 155 min; after natural cooling to room temperature, the material was crushed to a Dv50 of 0.7 μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.6 Fe 0.4 Mo 0.005 PO4 / C.

[0123] Comparative Example 2

[0124] This comparative example is essentially the same as Example 1, except that soluble raw materials are used for both the manganese and iron sources. Specifically, it includes the following steps:

[0125] 1) Take 5kg of pure water, add 800g of potassium chlorate, 5g of perchloric acid (72wt% purity), 119.9g of graphite powder, and 60g of nickel sulfate. Stir well and pour into the reaction vessel.

[0126] The graphite powder content is 2 wt% of the mass of the manganese and iron sources, and the nickel sulfate content is 1 wt% of the mass of the manganese and iron sources.

[0127] 2) Weigh 3481g of manganese sulfate and 2317.8g of ferrous sulfate, mix them evenly with a high-speed mixer and add them to the reaction vessel of step 1). Under nitrogen protection, stir and react at 250℃ for 10h. After washing with pure water 6 times, dry in an oven at 100℃ for 24h to obtain the self-synthesized graphene-coated manganese-iron precursor.

[0128] The molar ratio of Fe to Mn was 4:6; the Fe content in the synthesized graphene-coated manganese-iron precursor was 15.33 wt%, and the Mn content was 22.61 wt%.

[0129] 3) Take 5500g of the self-synthesized graphene-coated manganese-iron precursor from step 1) and add it to 18L of water. Then, add 4340.4g of ammonium dihydrogen phosphate, 1505.6g of lithium carbonate, 27.15g of molybdenum trioxide, 137.5g of glucose, 401.5g of PEG4000, and 66g of citric acid in sequence. After mixing evenly, mill the slurry to a particle size Dv50 = 0.8 μm. After the particle size meets the standard, spray dry to obtain the calcined precursor.

[0130] In terms of molar ratio, (Mn+Fe) / P=1.0; Li / P=1.08; and the amount of carbon source used is 11 wt% of the self-synthesized graphene-coated manganese-iron precursor.

[0131] 4) Under a nitrogen atmosphere, the calcination precursor was calcined at 785℃ for 12 h, with a heating time of 155 min; after natural cooling to room temperature, the material was crushed to a Dv50 of 0.7 μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.6 Fe0.4 Mo 0.005 PO4 / C;

[0132] Comparative Example 3

[0133] This comparative example is basically the same as Example 1, except that graphene coating was not performed in this comparative example, and only the manganese-iron precursor was prepared first.

[0134] 1) Weigh 3093g of manganese carbonate and 2705.6g of ferric phosphate, mix them evenly with a high-speed mixer, and add them to a reactor containing 10kg of pure water. Under a nitrogen atmosphere, react at 250℃ for 10h in the reactor. After washing with pure water 6 times, dry in an oven at 100℃ for 24h to obtain the manganese-iron precursor.

[0135] The molar ratio of Fe to Mn was 4:6; the Fe content in the manganese-iron precursor was 18.01 wt%, the Mn content was 26.56 wt%, and the P content was 9.96 wt%.

[0136] 2) Take 5500g of the manganese-iron precursor from step 1) and add it to 18L of water. Then, add 3060.2g of ammonium dihydrogen phosphate, 1768.7g of lithium carbonate, 31.89g of molybdenum trioxide, 137.5g of glucose, 401.5g of PEG4000, and 66g of citric acid in sequence. After mixing evenly, mill the slurry to a particle size Dv50 = 0.8 μm. After the particle size meets the standard, spray dry to obtain the calcined precursor.

[0137] In terms of molar ratio, (Mn+Fe) / P=1.0; Li / P=1.08; and the amount of carbon source used is 11 wt% of the manganese-iron precursor.

[0138] 3) Under a nitrogen atmosphere, the calcination precursor was calcined at 785℃ for 12 h, with a heating time of 155 min; after natural cooling to room temperature, the material was crushed to a Dv50 of 0.7 μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.6 Fe 0.4 Mo 0.005 PO4 / C;

[0139] Comparative Example 4

[0140] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 1) of this example, the graphite powder content is 5 wt% of the mass of the manganese source and the iron source.

[0141] Comparative Example 5

[0142] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 1, except that in step 1) of this example, the graphite powder content is 10 wt% of the mass of the manganese source and the iron source.

[0143] Comparative Example 6

[0144] 1) Weigh 3093g of manganese carbonate, 2705.6g of iron phosphate, and 116.0g of graphene oxide powder. Mix them evenly with a high-speed mixer and add them to a reactor containing 10kg of pure water. React at 250℃ for 10h under a nitrogen atmosphere. Wash with pure water 6 times and dry in an oven at 100℃ for 24h to obtain the main precursor A.

[0145] The molar ratio Fe:Mn = 4:6; the Fe content in the main precursor A was found to be 18.02 wt%, the Mn content was 26.59 wt%, and the P content was 9.97 wt%.

[0146] 2) Take 5500g of the main precursor A from step 1) and add it to 18L of water. Then, add 3064.8g of ammonium dihydrogen phosphate, 1770.3g of lithium carbonate, 31.93g of molybdenum trioxide, 137.5g of glucose, 401.5g of PEG4000, and 66g of citric acid in sequence. After mixing evenly, mill the slurry to a particle size Dv50 = 0.8 μm. After the particle size meets the standard, spray dry to obtain the calcined precursor.

[0147] Among them, in terms of molar ratio, (Mn+Fe) / P=1.0; Li / P=1.08; and the carbon source content is mainly 11wt% of precursor A.

[0148] 3) Under a nitrogen atmosphere, the calcination precursor was calcined at 785℃ for 12 h, with a heating time of 155 min; after natural cooling to room temperature, the material was crushed to a Dv50 of 0.7 μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.6 Fe 0.4 Mo 0.005 PO4 / C;

[0149] Comparative Example 7

[0150] This comparative example is basically the same as Example 1, except that in this comparative example, the reaction temperature of the self-synthesized graphene-coated manganese-iron precursor in step 2) is 150°C.

[0151] Experimental Example 1

[0152] The powder resistivity, specific surface area, compaction density, and residual lithium of the lithium manganese iron phosphate cathode materials prepared in Examples 1-15 and Comparative Examples 1-7 were measured. The test methods are as follows:

[0153] (1) Powder resistivity:

[0154] The powder resistivity of lithium manganese iron phosphate cathode material was tested using a Suzhou Jinglü ST-2722 powder resistivity meter. 1.20 g of lithium manganese iron phosphate cathode material was weighed and placed into a mold, the height was adjusted to 20 mm, and compacted using a pressure of 12 MPa. The resistivity data was then read from the resistivity display window.

[0155] (2) BET:

[0156] The specific surface area of ​​lithium manganese iron phosphate cathode material was tested using a Microtonic TriStar II 3020 instrument. The mass of the empty tube was weighed, and then 10.00 g of lithium manganese iron phosphate cathode material was added. After degassing at 150°C for 1.5 h, the tube containing the sample was placed in the test station for about 90 min, and the experimental data were recorded.

[0157] (3) Compacted density:

[0158] The compaction density of lithium manganese iron phosphate cathode material was tested using a powder compaction density meter. 5.50 g of lithium manganese iron phosphate cathode material was weighed and placed into a mold, and a pressure of 3000 kg was applied. After the test, the material was demolded and the data was collected.

[0159] (4) Residual lithium:

[0160] Residual lithium was tested using a Mettler T5 automatic potentiometric titrator. 30.00 g of lithium manganese iron phosphate cathode material was weighed and placed in a 250 mL stoppered conical flask containing 100 g of deionized water. After stirring for 30 min, the mixture was filtered under reduced pressure (filter membrane pore size: 0.45 μm). 20 mL of the filtrate was taken and titrated with 0.05 mol / L HCl and NaCO3 standard solutions. The data was recorded after titration.

[0161] The test results are shown in Table 1.

[0162] Table 1. Performance Test Statistics of Lithium Manganese Iron Phosphate Cathode Materials of Different Groups

[0163]

[0164] Experimental Example 2

[0165] The lithium manganese iron phosphate cathode materials prepared in Examples 1-15 and Comparative Examples 1-7 were used to prepare CR2016 batteries, and their electrical performance was tested.

[0166] (1) The preparation method of CR2016 battery is as follows: 19.2g of lithium manganese iron phosphate cathode material, 0.4g of acetylene black, and 0.4g of polyvinylidene fluoride (PVDF) are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2, and mixed and stirred to obtain cathode material slurry. The cathode material slurry is uniformly coated on aluminum foil with a coating amount of 1.45 g / cm². 2 The material is then placed in a drying oven at 85°C for 1 hour, hot-pressed, cooled, and cut into 12 cm positive electrode sheets using a punching machine. In a glove box, the positive electrode, separator (12 μm thick polypropylene), negative lithium electrode sheet, and LiPF6 electrolyte are assembled to form a CR2016 battery.

[0167] (2) The electrical performance test method is as follows: Under a constant temperature environment of 25℃, charge at 0.1 C to 4.3 V at 2 V to 4.2 V, then charge at 4.3 V at constant voltage until the current is ≤0.05 mA, let stand for 5 min, and then discharge at 0.1 C to 2 V. Record the battery capacity. Under a constant temperature environment of 25℃, charge at 1 C and 4.3 V at constant current and constant voltage to full charge, let stand for 5 min, then discharge at 1 C at constant current to 2 V, let stand for 5 min, and repeat the same charge and discharge cycle for 100 cycles. Record the battery capacity at different cycle numbers and take the average value. Calculate the average battery capacity and capacity retention rate.

[0168] The test results are shown in Table 2.

[0169] Table 2. Statistical table of electrical properties of lithium manganese iron phosphate cathode materials of different groups

[0170]

[0171] Comparing Examples 1-5, Tables 1 and 2 show that a higher Fe content results in better powder performance. Comparing Examples 1, 6, and 7, a higher reaction temperature for the self-synthesized graphene-coated manganese-iron precursor leads to higher compaction, lower BET, and a slight decrease in capacity, but it is still significantly better than the comparative example. Comparing Examples 1 and 8-9, Tables 1 and 2 show that increasing the amount of graphite powder increases the specific surface area of ​​the lithium manganese-iron phosphate cathode material and decreases the compaction density, but has little effect on capacity. Comparing Examples 1 and 10-11, Tables 1 and 2 show that reducing the particle size of the grinding media increases BET and capacity, but reduces cycle retention. Comparing Examples 1 and 12-13, Tables 1 and 2 show that reducing the ratio of metal to phosphorus and the ratio of lithium to phosphorus can decrease the specific surface area and increase the compaction density, but it deteriorates the capacity. By comparing Examples 1 and 14-15, and as shown in Tables 1 and 2, it can be seen that both excessively high and low nickel sulfate content affect the powder properties of the material. Excessive nickel content can break the crystal lattice of the material; insufficient nickel content will prevent complete catalytic formation of graphene. Examples 1-15 and Comparative Examples 1-7 demonstrate that the lithium manganese iron phosphate cathode material obtained within the dosage range of this invention still exhibits superior performance, significantly better than the comparative examples.

[0172] By comparing Example 1 and Comparative Example 1, as shown in Tables 1 and 2, it can be seen that after the manganese and iron sources are coated with graphene, the capacity of the LMFP product in Example 1 is improved, the BET is significantly reduced, and the compaction is significantly improved. Figure 2 and Figure 3 It can be seen that the finished particles of Example 1 are more rounded and have better uniformity than those of Comparative Example 1. Figure 4 It can be seen that the peak shapes of Example 1 and Comparative Example 1 are consistent with those of LFP-PDF#40-1499 and LMP-PDF#77-0178, indicating that LMFP was successfully synthesized in both cases. Figure 5 and Figure 6 It can be seen that the distribution of Mn and Fe in the material in Example 1 is more uniform than that in Comparative Example 1. From... Figure 7 It can be seen that the specific capacity of Example 1 is significantly better than that of Comparative Example 1.

[0173] By comparing Example 1 and Comparative Example 2, from Table 1, Figure 1 and Figure 8 It can be seen that the main precursors prepared from water-soluble manganese and iron sources have unstable particle size and poor powder properties.

[0174] By comparing Example 1 and Comparative Example 3, it can be seen that the precursor, which was not coated with self-synthesized graphene, has significantly reduced electrical performance, possibly due to poor uniformity of carbon coating.

[0175] By comparing Example 1 with Comparative Examples 4 and 5, it can be seen that during the generation of self-synthesized graphene-coated manganese-iron precursor, excessive graphite addition will affect the performance of LMFP. This may be because excessive coating may affect crystal growth and reduce compaction density.

[0176] By comparing Example 1 and Comparative Example 6, it can be seen that directly adding graphene oxide did not improve the performance, possibly due to uneven coating.

[0177] By comparing Example 1 and Comparative Example 7, it can be seen that when the synthesis temperature of the precursor is reduced, there is no significant deterioration in electrical properties, but the compaction density of the material is reduced, possibly because the particle growth of the precursor is limited at low temperatures.

[0178] In summary, the lithium manganese iron phosphate cathode material provided by this invention involves first reacting iron, manganese, and graphite in a reactor to generate a graphene-coated manganese iron precursor. The resulting precursor is then mixed with a phosphorus source, a lithium source, and a carbon source through sand milling, which improves the uniformity of manganese iron element distribution and carbon coating at the microscopic level. The metal-catalyzed graphene synthesis and double carbon coating process result in more uniform carbon coating, improving material purity and conductivity, while simultaneously reducing specific surface area and increasing capacity. The process of this invention is simple, highly controllable, and requires only basic reaction conditions and equipment, making it easy to achieve large-scale industrial production. The raw materials do not contain toxic, radioactive, or other harmful substances, making it environmentally friendly.

[0179] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a self-synthesized graphene-coated manganese-iron precursor, characterized in that, The process includes: mixing a manganese source, an iron source, a nickel source, graphite powder, perchloric acid, and potassium chlorate; stirring and reacting the mixture at 200-400°C for 7-12 hours under inert gas protection; washing with water and drying to obtain a self-synthesized graphene-coated manganese-iron precursor; the mass of the graphite powder is 0.5 wt% to 3.5 wt% of the total mass of the manganese source and the iron source; the manganese source includes at least one of manganese carbonate, manganese oxalate, and manganese phosphate; the iron source includes at least one of ferric phosphate, ferrous oxalate, ferrous sulfate, ferric oxide, ferrous oxide, and magnetite.

2. The method for preparing a self-synthesized graphene-coated manganese-iron precursor according to claim 1, characterized in that, The molar ratio of the manganese source to the iron source is (2~8):(8~2); And / or, the mass of the nickel source is 0.5 wt% to 4.5 wt% of the total mass of the manganese source and the iron source; And / or, the mass of the perchloric acid is 0.03 wt% to 0.09 wt% of the total mass of the manganese source and the iron source; And / or, the mass of the potassium chlorate is 9.5 wt% to 16.8 wt% of the total mass of the manganese source and the iron source.

3. The method for preparing a self-synthesized graphene-coated manganese-iron precursor according to claim 1 or 2, characterized in that, The nickel source includes nickel sulfate.

4. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, It includes preparing a self-synthesized graphene-coated manganese-iron precursor by the method of any one of claims 1-3, mixing the self-synthesized graphene-coated manganese-iron precursor with a phosphorus source, a lithium source, a carbon source and water, crushing it to obtain a slurry, drying it to obtain a calcining precursor; and calcining the calcining precursor to obtain a lithium manganese-iron phosphate cathode material.

5. The method for preparing lithium manganese iron phosphate cathode material according to claim 4, characterized in that, In the slurry, the molar ratio of (Mn+Fe):P is (0.94~1.02):1, and the molar ratio of Li:P is (1.01~1.10):1; the mass of the carbon source is 2.5wt%~12.5wt% of the mass of the self-synthesized graphene-coated manganese-iron precursor.

6. The method for preparing lithium manganese iron phosphate cathode material according to claim 4, characterized in that, The phosphorus source includes at least one of phosphoric acid and ammonium dihydrogen phosphate.

7. The method for preparing lithium manganese iron phosphate cathode material according to claim 4, characterized in that, The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

8. The method for preparing lithium manganese iron phosphate cathode material according to claim 4, characterized in that, The carbon source includes at least one of glucose, sucrose, polyethylene glycol, starch, ethyl cellulose, and citric acid.

9. The method for preparing lithium manganese iron phosphate cathode material according to claim 4, characterized in that, The slurry also includes additives, and the amount of additives added is 100 ppm to 5000 ppm.

10. The method for preparing lithium manganese iron phosphate cathode material according to claim 9, characterized in that, The additives include at least one of the following: Ti source, Mo source, Mg source, Al source, Sb source, Cu source, Zr source, and Zn source.

11. The method for preparing lithium manganese iron phosphate cathode material according to claim 4, characterized in that, The particle size of the crushed material has a Dv50 of 0.1~0.8 μm.

12. The method for preparing lithium manganese iron phosphate cathode material according to claim 4, characterized in that, The calcination includes calcination at 650~800℃ for 6~15 hours under a nitrogen atmosphere.

13. A lithium iron phosphate cathode material, characterized in that, It is prepared using the method for preparing lithium manganese iron phosphate cathode material as described in any one of claims 4-12; the compaction density of the lithium manganese iron phosphate cathode material at a pressure of 3000 kg is 2.15 g / cm³. 3 ~2.6 g / cm 3 ; And / or, the BET of the lithium manganese iron phosphate cathode material is 5 m. 2 / g~15 m 2 / g; And / or, the powder resistivity of the lithium manganese iron phosphate cathode material at a pressure of 12 MPa is 10 Ω·cm to 700 Ω·cm; And / or, the residual lithium content on the surface of the lithium manganese iron phosphate cathode material is less than 700 ppm; And / or, the Dv50 of the lithium manganese iron phosphate cathode material is 0.4~1.5 μm.

14. A positive electrode plate, characterized in that, It includes the lithium manganese iron phosphate cathode material as described in claim 13.

15. The application of the lithium manganese iron phosphate cathode material as described in claim 13 or the cathode sheet as described in claim 14 in the preparation of lithium-ion batteries.

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