Positive electrode material and preparation method therefor, lithium-ion battery, and electric device

Abstract

The present disclosure belongs to the technical field of batteries. Specifically disclosed are a positive electrode material and a preparation method therefor, a lithium-ion battery, and an electric device. The positive electrode material comprises lithium manganese iron phosphate, and the unit cell volume of the lithium manganese iron phosphate is (I). Therefore, the positive electrode material has a relatively high compaction density, electronic conductivity and ionic conductivity, and using the positive electrode material can improve the energy density and cycle stability of a battery comprising the positive electrode material.

Description

Cathode materials and their preparation methods, lithium-ion batteries and electrical devices

[0001] Priority information

[0002] This application claims priority and benefits to patent application No. 202411961136.9, filed with the China National Intellectual Property Administration on December 27, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure belongs to the field of battery technology, specifically relating to a cathode material and its preparation method, a lithium-ion battery, and an electrical device. Background Technology

[0004] In recent years, driven by market demand for improved overall performance of lithium-ion batteries, phosphate-based batteries are undergoing an upgrade from lithium iron phosphate (LFP) to lithium manganese iron phosphate (LMFP). LMFP is created by doping LFP with manganese and adjusting the ratio of manganese to iron atoms to increase the voltage platform. LMFP has a higher voltage platform than LFP, and its theoretical energy density is expected to be 15-20% higher, thus overcoming the energy density bottleneck faced by LFP to some extent. It not only boasts a higher voltage platform, higher energy density, and better low-temperature performance, but also retains the high safety and low-cost advantages of LFP. However, its compaction density, electronic conductivity, and lithium-ion conductivity are relatively low. Therefore, improving the compaction density and electrochemical performance of LMFP has received continuous attention from those skilled in the art.

[0005] To improve the electrochemical performance of lithium manganese iron phosphate (LMFP) cathode materials, researchers typically employ modification techniques such as nano-sizing, carbon coating, and ion doping. For example, one method involves adding manganese, iron, and surfactants to an acidic hydrogen peroxide solution, then transferring the mixture to a high-temperature, high-pressure reactor for reaction, followed by filtration and sintering to obtain the LMFP material. However, this method utilizes acidic hydrogen peroxide, a potentially explosive and hazardous substance, and requires a high-temperature, high-pressure reactor, raising significant cost and safety concerns. Therefore, the preparation method for LMFP cathode materials still requires further improvement. Summary of the Invention

[0006] This disclosure is based on the inventors' discoveries and understanding of the following facts and problems:

[0007] The inventors discovered that the cell volume and grain size of LMFP materials are closely related to the material's capacity and compaction density. Through adjustments to the manufacturing process, LMFP materials with specific microstructures, cell volumes, and grain sizes were prepared, resulting in lithium-ion batteries with high compaction density and excellent electrochemical performance.

[0008] This disclosure aims to at least partially address one of the technical problems in the related art. To this end, this disclosure proposes a cathode material with high energy density or excellent cycle stability, a method for preparing the same, and a lithium-ion battery.

[0009] The first aspect of this disclosure proposes a cathode material, including lithium manganese iron phosphate, wherein the cell volume of the lithium manganese iron phosphate is [missing information]. Therefore, this cathode material has high compaction density, electronic conductivity, and ionic conductivity.

[0010] In some embodiments, the cell volume of the lithium manganese iron phosphate is In other embodiments, the cell volume is This facilitates lithium-ion insertion / extraction, thereby improving the cycle life of lithium-ion batteries.

[0011] In some embodiments, the lithium manganese iron phosphate has the composition shown in Formula I: Li a Mn x Fe y M 1-x-y (PO4) b Formula I

[0012] Wherein, 0.90≤a≤1.20, 0.30≤x≤0.95, 0.05≤y≤0.70, and 0.95≤b≤1.10;

[0013] M is selected from at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, and Si; 1.03 ≤ b / (x+y) ≤ 1.15.

[0014] With the above composition, this lithium manganese iron phosphate cathode material not only has a higher voltage platform, higher energy density, and better low-temperature performance, but also has higher compaction density, electronic conductivity, and ionic conductivity.

[0015] In some implementations, 0.95 ≤ a ≤ 1.15; in other implementations, 1.00 ≤ a ≤ 1.10; and in some specific examples, 1.02 ≤ a ≤ 1.08.

[0016] In some implementations, 1.00 ≤ b ≤ 1.09; in other implementations, 1.01 ≤ b ≤ 1.07.

[0017] In some implementations, 0.90 ≤ x + y ≤ 1.00; in other implementations, 0.95 ≤ x + y < 1.00.

[0018] In some implementations, 1.05 ≤ b / (x+y) ≤ 1.10.

[0019] In some embodiments, the lithium manganese iron phosphate satisfies: 80nm ≤ L 10 ≤200nm; in other embodiments, 100nm≤L 10 ≤180nm.

[0020] In some embodiments, the lithium manganese iron phosphate satisfies: 150nm ≤ L 50 ≤300nm; in other embodiments, 160nm≤L 50 ≤260nm.

[0021] In some embodiments, the lithium manganese iron phosphate satisfies: 200nm ≤ L 90 ≤500nm; in other embodiments, 220nm≤L 90 ≤480nm.

[0022] Among them, L 10 L 50 L 90 These are the grain sizes corresponding to the cumulative volume percentage of the lithium manganese iron phosphate grain size Ln reaching 10%, 50%, and 90%, respectively. Grain sizes within these ranges are beneficial for shortening the migration path of lithium ions in the cathode material, increasing the lithium ion diffusion rate, i.e., resulting in better material kinetics. Simultaneously, suitable grain sizes can increase the compaction density of the cathode material.

[0023] In some embodiments, the compacted density of the lithium manganese iron phosphate is 2.3 g / cm³. 3 ~2.6g / cm 3 This is beneficial for improving the energy density of lithium-ion batteries.

[0024] The second aspect of this disclosure discloses a method for preparing a cathode material, comprising:

[0025] A first mixture containing lithium source, M source, phosphorus source, manganese source and iron source is sintered once to obtain a primary sintered material. The primary sintered material includes secondary particles, which are formed by the agglomeration of multiple primary particles. The primary particle size P of the primary particles satisfies 100nm≤P≤500nm.

[0026] The first sintered material is mixed with a carbon source in a solvent and then subjected to a second grinding process to obtain a second mixture.

[0027] The second mixture is subjected to a second spray drying process to obtain a second spray-dried material;

[0028] The second spray-dried material is subjected to secondary sintering to obtain the lithium manganese iron phosphate.

[0029] This disclosure achieves a suitable primary particle size by controlling the conditions of the primary sintering process, thereby increasing the compaction density of the cathode material. Furthermore, this preparation method is simple and suitable for large-scale industrial production.

[0030] In some embodiments, the first mixture is subjected to a first spray drying to obtain a first spray-dried material; the first spray-dried material is then heated to 400°C to 700°C under an inert atmosphere at a heating rate of 1°C / min to 5°C / min, held at that temperature for 3 hours to 15 hours, and subjected to a first sintering to obtain a first sintered material. This can promote the reaction and is beneficial to the growth of primary particle crystals.

[0031] In some embodiments, the molar ratio of phosphorus in the phosphorus source to manganese in the manganese source and iron in the iron source, n(P) / n(Mn+Fe), is 1.03:1 to 1.15:1. This allows for a more complete phosphating reaction and increases the compaction density of the cathode material.

[0032] In some embodiments, the D of the first mixture 50 The thickness ranges from 0.1 μm to 0.5 μm. This is beneficial for improving the rate performance of lithium-ion batteries.

[0033] In some embodiments, the D of the second mixture 50 The micrometer size ranges from 0.2 μm to 0.6 μm. This is beneficial for improving the rate performance of lithium-ion batteries.

[0034] In some embodiments, the mass ratio of the carbon source to the primary sintering material is 2:100 to 20:100. This facilitates the reaction and improves sintering efficiency.

[0035] In some embodiments, the manganese source includes at least one of manganese sulfate, manganese carbonate, manganese nitrate, and manganese tetroxide. Therefore, the material is widely available and the cost is low.

[0036] In some embodiments, the iron source includes at least one of ferric phosphate, ferric nitrate, ferric sulfate, ferrous oxalate, ferrous carbonate, and ferric oxide. Therefore, the material is widely available and the cost is low.

[0037] In some embodiments, the phosphorus source includes at least one selected from phosphoric acid, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate. Therefore, the material is widely available and has a low cost.

[0038] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium nitrate. Therefore, the material is widely available and the cost is low.

[0039] In some embodiments, the M source includes at least one of oxides, hydroxides, and carbonates containing the M element. Therefore, the materials are widely available and the cost is low.

[0040] In some embodiments, the carbon source includes at least one of glucose, sucrose, and organic polymers. Therefore, the materials are widely available and inexpensive.

[0041] In some embodiments, the secondary sintering of the second spray-dried material includes heating it to 600°C to 800°C at a heating rate of 1°C / min to 3°C / min under an inert atmosphere and holding it at that temperature for 5 hours to 20 hours. This can promote the reaction and improve the reaction efficiency.

[0042] This disclosure provides a third aspect of a lithium-ion battery, comprising the cathode material described in the first aspect of the disclosure or the cathode material prepared by the method described in the second aspect of the disclosure. Consequently, this lithium-ion battery exhibits high energy density and excellent cycle stability.

[0043] This fourth aspect of the disclosure provides an electrical device comprising the lithium-ion battery described in the third aspect of the disclosure. Therefore, the electrical device has a long service life. Attached Figure Description

[0044] Figure 1 is an SEM image of the primary sintering material of Embodiment 1 of this disclosure.

[0045] Figure 2 is a SEM image of the cathode material of Embodiment 1 of this disclosure.

[0046] Figure 3 is a grain size distribution diagram of the cathode materials of Embodiments 1-2 and Comparative Examples 1-2 of this disclosure.

[0047] Figure 4 is a SEM image of the primary sintering material of Comparative Example 1 of this disclosure.

[0048] Figure 5 is a SEM image of the cathode material of Comparative Example 2 of this disclosure. Detailed Implementation

[0049] The embodiments of this disclosure are described in detail below, with examples of the embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this disclosure, and should not be construed as limiting this disclosure.

[0050] The first aspect of this disclosure proposes a cathode material, including lithium manganese iron phosphate, wherein the cell volume of the lithium manganese iron phosphate is [missing information]. Therefore, this cathode material has high compaction density, electronic conductivity, and ionic conductivity.

[0051] In some embodiments, the cell volume of the lithium manganese iron phosphate is For example, it can be... or etc.; in other embodiments, the cell volume is This is beneficial for further improving the compaction density, electronic conductivity, and ionic conductivity of the cathode material.

[0052] In some embodiments, the lithium manganese iron phosphate has the composition shown in Formula I: Li a Mn x Fe y M 1-x-y (PO4) b Formula I

[0053] Wherein, 0.90≤a≤1.20, 0.30≤x≤0.95, 0.05≤y≤0.70, and 0.95≤b≤1.10;

[0054] M is selected from at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, and Si; 1.03 ≤ b / (x+y) ≤ 1.15.

[0055] With the above composition, this lithium manganese iron phosphate cathode material not only has a higher voltage platform, higher energy density, and better low-temperature performance, but also has higher compaction density, electronic conductivity, and ionic conductivity.

[0056] In some implementations, 0.95≤a≤1.15, for example, it can be 0.95, 0.98, 1, 1.05, 1.08, 1.1 or 1.15, etc.; in other implementations, 1.00≤a≤1.10; in some specific implementations, 1.02≤a≤1.08.

[0057] In some implementations, 1.00≤b≤1.09, for example, it can be 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08 or 1.09, etc.; in other implementations, 1.01≤b≤1.07.

[0058] In some implementations, 0.90 ≤ x + y ≤ 1.00, for example, it can be 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or 1.00; in other implementations, 0.95 ≤ x + y < 1.00.

[0059] In some implementations, 1.05 ≤ b / (x+y) ≤ 1.10, for example, it can be 1.05, 1.06, 1.07, 1.08, 1.09 or 1.10, etc.

[0060] In some embodiments, the lithium manganese iron phosphate satisfies: 80nm ≤ L 10 ≤200nm, for example, it can be 80nm, 100nm, 120nm, 140nm, 160nm, 180nm or 200nm, etc.; in other embodiments, 100nm≤L 10 ≤180nm.

[0061] In some embodiments, the lithium manganese iron phosphate satisfies: 150nm ≤ L 50 ≤300nm, for example, can be 150nm, 170nm, 190nm, 210nm, 230nm, 250nm, 270nm, or 300nm, etc.; in other embodiments, 160nm≤L 50 ≤260nm.

[0062] In some embodiments, the lithium manganese iron phosphate satisfies: 200nm ≤ L 90 ≤500nm, for example, it can be 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, or 500nm, etc.; in other embodiments, 220nm≤L 90 ≤480nm.

[0063] Among them, L 10 L 50 L 90 These are the grain sizes Ln corresponding to the cumulative volume percentages of the lithium manganese iron phosphate grain size when they reach 10%, 50%, and 90%, respectively. It should be noted that the grain size Ln is obtained by statistically analyzing the size of the powder X-ray diffraction pattern obtained using CuKα rays and a Fundamental Parameter fitting algorithm. Wherein, L... 50 As a physical quantity representing the median of volume distribution, grain size is a key indicator. Smaller grain sizes result in shorter migration paths and higher diffusion rates for lithium ions in the cathode material, indicating better material kinetics. However, excessively small grain sizes can also lead to lower compaction density. Grain size L 10 L 50 L 90 Meeting the above ranges results in superior compaction density and electrochemical specific capacity compared to other ranges.

[0064] In some embodiments, the compacted density of the lithium manganese iron phosphate is 2.3 g / cm³. 3 ~2.6g / cm 3 For example, it can be 2.3 g / cm³. 3 2.4g / cm 3 2.5g / cm 3Or 2.6g / cm 3 This is beneficial for improving the energy density of lithium-ion batteries.

[0065] The second aspect of this disclosure discloses a method for preparing a cathode material, comprising:

[0066] S1: A first mixture containing lithium source, M source, phosphorus source, manganese source and iron source is sintered once to obtain a primary sintered material. The primary sintered material includes secondary particles, which are formed by the agglomeration of multiple primary particles. The primary particle size P of the primary particles satisfies 100nm≤P≤500nm.

[0067] Specifically, the size P of the primary particles can be 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, or 500nm, etc. A larger primary particle size in the primary sintered material is beneficial for forming grains with the desired size L during the second grinding and sintering process. n Secondary particulate materials of lithium manganese iron phosphate with required distribution.

[0068] In this step, there are no particular restrictions on the specific method of mixing the lithium source, M source, phosphorus source, manganese source, and iron source; for example, a mixer (such as a ball mill) can be used. After mixing, the first mixture can be dispersed in a solvent with a certain solid content, and then subjected to the first grinding until the particle size D of the material is achieved. 50 When the particle size is 0.1μm to 0.5μm, the first spray drying treatment is performed.

[0069] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium nitrate. Therefore, the material is widely available and the cost is low.

[0070] In some embodiments, the M source includes at least one of oxides, hydroxides, and carbonates containing the M element. Therefore, the materials are widely available and the cost is low.

[0071] In some embodiments, the phosphorus source includes at least one selected from phosphoric acid, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate. Therefore, the material is widely available and has a low cost.

[0072] In some embodiments, the manganese source includes at least one of manganese sulfate, manganese carbonate, manganese nitrate, and manganese tetroxide. Therefore, the material is widely available and the cost is low.

[0073] In some embodiments, the iron source includes at least one of ferric phosphate, ferric nitrate, ferric sulfate, ferrous oxalate, ferrous carbonate, and ferric oxide. Therefore, the material is widely available and the cost is low.

[0074] It should be noted that the phosphorus source, manganese source, and iron source are selected from commercially available raw materials. This disclosure does not impose specific limitations; they can be independent raw materials of phosphorus, manganese, and iron, or combined raw materials of phosphorus + manganese, phosphorus + iron, manganese + iron, or phosphorus + manganese + iron. Those skilled in the art can choose according to their needs. As an example, combined raw materials of phosphorus + manganese, phosphorus + iron, manganese + iron, or phosphorus + manganese + iron can be selected from manganese phosphate, ferric phosphate, ferric manganese oxide, ferric manganese hydroxide, ferric manganese carbonate, ferric manganese phosphate, ferric manganese pyrophosphate, etc.

[0075] In some embodiments, the molar ratio of phosphorus in the phosphorus source to manganese in the manganese source and iron in the iron source, n(P) / n(Mn+Fe), is 1.03:1 to 1.15:1, for example, 1.03:1, 1.05:1, 1.08:1, 1.1:1, 1.13:1, or 1.15:1. This allows for a more complete phosphating reaction and increases the compaction density of the cathode material.

[0076] In this paper, a suitable P / (Mn+Fe) molar ratio allows for a more complete phosphating reaction, while appropriate primary sintering temperature and holding time promote the reaction and facilitate the growth of primary particle crystals. If the P / (Mn+Fe) molar ratio is too high, the primary sintering temperature is too high, and the holding time is too long, the primary particle size will be too large, affecting not only the efficiency of secondary grinding and increasing grinding energy consumption, but also the capacity of the finished lithium manganese iron phosphate cathode material. Conversely, if the P / (Mn+Fe) molar ratio is too low, the primary sintering temperature is too low, and the holding time is too short, the primary particle size of the obtained primary sintered material will be smaller. After secondary grinding and sintering, the grain size will be smaller, thus affecting the compaction density of the finished lithium manganese iron phosphate cathode material. The P / (Mn+Fe) molar ratio, primary sintering temperature, and holding time meet the ranges described in this disclosure, exhibiting superior compaction density and capacity compared to other ranges.

[0077] In some embodiments, the first mixture is subjected to a first spray drying to obtain a first spray-dried material; the first spray-dried material is then heated to 400℃~700℃ (e.g., 400℃, 500℃, 600℃, or 700℃) at a heating rate of 1℃ / min~5℃ / min (e.g., 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min) under an inert atmosphere, and held at that temperature for 3h~15h (e.g., 3h, 5h, 8h, 10h, 12h, or 15h) for a first sintering to obtain a first sintered material. This promotes the reaction and is beneficial to the growth of primary particle crystals.

[0078] In some embodiments, the D of the first mixture 50The micrometer size is between 0.1 μm and 0.5 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, or 0.5 μm. This is beneficial for improving the rate performance of lithium-ion batteries.

[0079] In particle size distribution, D 50 Also known as the median particle size, it means that the particle size of 50% of the volume is less than or equal to this value, and can be measured by a Malvern particle size analyzer: disperse the cathode material in a dispersant (ethanol, acetone or other surfactant), sonicate for 30 minutes, add the sample into the Malvern particle size analyzer, and start the test.

[0080] S2: The first sintering material is mixed with the carbon source in a solvent and then subjected to a second grinding to obtain a second mixture.

[0081] In some embodiments, the carbon source includes at least one selected from glucose, sucrose, and organic polymers. The carbon source accounts for 1% to 20% of the theoretical yield of lithium manganese iron phosphate.

[0082] In some embodiments, the mass ratio of the carbon source to the primary sintering material is 2:100 to 20:100, for example, 2:100, 5:100, 8:100, 10:100, 12:100, 15:100, 18:100, or 20:100. This facilitates the reaction and improves sintering efficiency.

[0083] In some embodiments, the D of the second mixture 50 The micrometer size ranges from 0.2μm to 0.6μm, for example, it can be 0.2μm, 0.3μm, 0.4μm, 0.5μm, or 0.6μm. This is beneficial for improving the rate performance of lithium-ion batteries.

[0084] This disclosure does not limit the solvent and solid content used in the first and second grinding processes, as long as they can achieve sufficient dispersion and do not chemically react with phosphorus, manganese, iron, lithium, or M sources. For manufacturing cost considerations, the solvent described in this disclosure can be deionized water, and the solid content can be ≥30%.

[0085] This disclosure does not limit the parameters of grinding and spray drying processes in principle, as long as they can meet the requirements of D. 50 The slurry with the required particle size is dried into spherical powder. Those skilled in the art can set the parameters according to the equipment.

[0086] S3: The second mixture is subjected to a second spray drying to obtain a second spray-dried material.

[0087] Specifically, the particle size D of the second mixture can be... 50When the material is ground to a thickness of 0.2 μm to 0.6 μm, a second spray drying process is performed.

[0088] S4: The second spray-dried material is sintered a second time to obtain the lithium manganese iron phosphate.

[0089] In some embodiments, the secondary sintering of the second spray-dried material includes: heating to 600℃~800℃ (e.g., 600℃, 650℃, 700℃, 750℃, or 800℃) at a heating rate of 1℃ / min~3℃ / min (e.g., 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, or 3℃ / min, etc.) under an inert atmosphere, and holding at that temperature for 5h~20h (e.g., 5h, 8h, 10h, 12h, 15h, 18h, or 20h, etc.). This can promote the reaction and improve the reaction efficiency.

[0090] The method disclosed herein has at least the following technical effects:

[0091] (1) The cathode material preparation process of lithium manganese iron phosphate provided in this disclosure has a higher degree of crystallinity. It can obtain secondary particles of different sizes without mixing of large and small particles, so as to achieve a higher compaction density while also taking into account better electrochemical performance.

[0092] (2) The preparation process of the lithium manganese iron phosphate cathode material provided in this disclosure is simple, the cost is relatively low, and it is suitable for industrialization.

[0093] This disclosure provides a third aspect of a lithium-ion battery, comprising the cathode material described in the first aspect of the disclosure or the cathode material prepared by the method described in the second aspect of the disclosure. Consequently, this lithium-ion battery exhibits high energy density and excellent cycle stability.

[0094] It is understood that there are no particular restrictions on the specific type of lithium-ion battery; it can be a primary battery or a secondary battery. The shape of the lithium-ion battery can be cylindrical, square, or any other shape. According to the outer packaging, it can be a hard-shell battery or a soft-pack battery.

[0095] Typically, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode, negative electrode, and separator are fabricated into electrode assemblies using winding or stacking processes. The electrode assemblies and electrolyte are housed in an outer package. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor for active ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through.

[0096] In some embodiments, the positive electrode sheet may include a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes the lithium manganese iron phosphate positive electrode material described in this disclosure, a conductive agent, and a binder. The positive current collector may include a metal foil, for example, aluminum foil. The conductive agent may include acetylene black, single-walled carbon nanotubes, and other materials conventional in the art. The binder may be polyvinylidene fluoride (PVDF) and other materials conventional in the art.

[0097] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a layer of negative electrode active material disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material, a thickener, a conductive agent, and a binder. The negative electrode current collector may be a metal foil, for example, copper foil. The negative electrode active material may include artificial graphite, natural graphite, silicon-carbon based composite materials, lithium metal composite materials, lithium metal materials, and other commonly used negative electrode active materials in the art. The thickener may be sodium carboxymethyl cellulose (CMC-Na) and other conventional materials in the art. The conductive agent may be acetylene black and other conventional materials in the art. The binder may be styrene-butadiene rubber and other conventional materials in the art.

[0098] In some embodiments, the separator may be a separator known in the art that can be used in batteries and is stable to the electrolyte used, such as a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene composite separator, etc.

[0099] This fourth aspect of the disclosure provides an electrical device comprising the lithium-ion battery described in the third aspect of the disclosure. Therefore, the electrical device has a long service life.

[0100] In some embodiments, the lithium-ion battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0101] The embodiments of this disclosure are described in detail below.

[0102] Example 1

[0103] Step S1: Weigh and mix lithium carbonate, iron phosphate, manganese tetroxide, magnesium oxide, and lithium dihydrogen phosphate according to the molar ratio of Li, Mn, Fe, Mg, and P of 1.050:0.581:0.387:0.032:1.035. Add glucose (5.0% of the theoretical yield of lithium manganese iron phosphate) to deionized water as the solvent, controlling the solid content at 40 wt%. Then, use a ball mill (2000 rpm) to... 50 The machine is stopped when the particle size reaches 0.25μm to obtain secondary ground material;

[0104] Step S2: The material obtained in step S1 is fed into the inlet of a centrifugal atomizing dryer (inlet temperature set to 225℃, outlet temperature controlled at 100±5℃) with a solid content of 40% for spray drying to obtain primary spray-dried material. The dried material is heated to 600℃ at a heating rate of 2℃ / min under N2 atmosphere, held at that temperature for 6h, and then cooled with the furnace to obtain primary sintered material (its SEM is shown in Figure 1).

[0105] Step S3: Weigh and mix the primary sintered material obtained in step S2 with glucose and polyethylene glycol at a mass ratio of 100:5:5, disperse in deionized water, control the solid content at 50 wt%, and grind using a ball mill (2000 rpm). 50 The machine is stopped when the particle size reaches 0.35μm to obtain secondary ground material;

[0106] Step S4: The material obtained in step S3 is fed into the inlet of a centrifugal atomizing dryer (inlet temperature set to 225℃, outlet temperature controlled at 100±5℃) with a solid content of 40% for spray drying. The secondary spray-dried material is heated to 750℃ at a heating rate of 1.5℃ / min under N2 atmosphere, held at that temperature for 15h, and then cooled with the furnace to obtain the lithium manganese iron phosphate cathode material A1. Its SEM is shown in Figure 2. The mixed morphology of primary particles of different sizes can be seen in the field of view. The grain size distribution calculated by XRD is shown in Figure 3.

[0107] Example 2

[0108] The method of Example 1 is followed, except that in step S1, the molar ratio of Li, Mn, Fe, Mg and P is 1.050:0.581:0.387:0.032:1.030, and all other parameters are the same. The lithium manganese iron phosphate cathode material A2 is obtained, and the grain size distribution calculated by XRD is shown in Figure 3.

[0109] Example 3

[0110] The method of Example 1 is followed, except that in step S1, the molar ratio of Li, Mn, Fe, Mg and P is 1.050:0.581:0.387:0.032:1.080, while the rest are the same, to obtain the lithium manganese iron phosphate cathode material A3.

[0111] Example 4

[0112] The method of Example 1 is followed, except that in step S1, the molar ratio of Li, Mn, Fe, Mg, and P is 1.050:0.581:0.387:0.032:1.010, while the rest are the same, to obtain the lithium manganese iron phosphate cathode material A4.

[0113] Example 5

[0114] The method of Example 1 is followed, except that in step S1, the molar ratio of Li, Mn, Fe, Mg, and P is 1.050:0.775:0.194:0.031:1.035, while the rest are the same, to obtain the lithium manganese iron phosphate cathode material A5.

[0115] Example 6

[0116] The method of Example 1 is followed, except that in step S1, the molar ratio of Li, Mn, Fe, Mg, and P is 1.050:0.581:0.387:0.032:1.000, while the rest are the same, to obtain the lithium manganese iron phosphate cathode material A6.

[0117] Example 7

[0118] The method of Example 1 is the same, except that in step S2, the primary drying material is heated to 400°C at a heating rate of 2°C / min under N2 atmosphere and held at that temperature for 6 hours. The rest are the same, and the lithium manganese iron phosphate cathode material A7 is obtained.

[0119] Example 8

[0120] The method of Example 1 is the same, except that in step S2, the primary drying material is heated to 750°C at a heating rate of 2°C / min under N2 atmosphere and held at that temperature for 6 hours. The rest are the same, and the lithium manganese iron phosphate cathode material A8 is obtained.

[0121] Example 9

[0122] The method of Example 1 is the same, except that in step S4, the secondary spray-dried material is heated to 600°C at a heating rate of 1.5°C / min under N2 atmosphere and kept at that temperature for 15 hours. The rest are the same, and the lithium manganese iron phosphate cathode material A9 is obtained.

[0123] Comparative Example 1

[0124] Following the method of Example 1, except that in step S1, the molar ratio of Li, Mn, Fe, Mg, and P is 1.050:0.581:0.387:0.032:0.930, while all other parameters remain the same, the lithium manganese iron phosphate cathode material D1 is obtained. The SEM image of the primary sintered material is shown in Figure 4, and the SEM image of the finished product is shown in Figure 5. The grain size distribution of the finished product, calculated by XRD, is shown in Figure 3.

[0125] Comparative Example 2

[0126] The method of Example 1 was followed, except that in step S2, the dried material was heated to 380°C at a heating rate of 2°C / min under a N2 atmosphere and held at that temperature for 6 hours. All other steps were the same to obtain the lithium manganese iron phosphate cathode material D2. The grain size distribution of the finished product, calculated by XRD, is shown in Figure 3.

[0127] The relevant parameters of the above embodiments and comparative examples were obtained through testing using the following methods:

[0128] (1) SEM test: The results were obtained using a Hitachi S-4800 scanning electron microscope from Japan.

[0129] (2) Primary particle size P: The projected area of ​​each single crystal particle in the electron microscope is statistically analyzed, and then its particle size is calculated. The specific method is: the average diameter is obtained by converting the projected area of ​​300 random primary particles in the scanning electron microscope image into a standard circle with equal area, which is the primary particle size P of the primary sintering material in the preparation process of lithium manganese iron phosphate cathode material.

[0130] (3) Unit volume measurement: The measurement was performed using a Rigaku Smartlab 9KW rotating target diffractometer, with a range of 10-80°, a voltage of 40kV, a current of 200mA, a step size of 0.02°, and a scan time of 2° / min. The test results were refined and calculated using the WPPF method in SmartLab Studio II software to obtain the unit volume.

[0131] (4) Grain size L 10 L 50 L 90 The results were measured using a Rigaku Smartlab 9KW rotating target diffractometer, with a range of 10-80°, a voltage of 40kV, a current of 200mA, a step size of 0.02°, and a scan time of 2° / min. The grain size distribution was calculated using the WPPF grain size distribution function of SmartLab Studio II software according to the Fundamental Parameter (FP) method. The grain size distribution diagrams of the cathode materials of Examples 1, 10, and Comparative Example 1 are shown in Figure 3.

[0132] (5) Compacted density test: The compacted density was measured using a compacted density tester of MCP-PD51 model from Mitsubishi Chemical Corporation of Japan. 1±0.01g of sample was weighed and the test was conducted at a pressure of 3T.

[0133] (6) Electrochemical Performance Testing: In the following examples and comparative examples, the Shenzhen Xinwei Battery Testing System was used to test the electrochemical performance of the R2025 coin cells. The initial charge-discharge capacity test conditions were: 25℃, 0.1C charge-discharge, voltage range 2.5-4.35V, and charging constant voltage cutoff current of 0.05C. The battery preparation process is as follows:

[0134] Electrode preparation: The positive electrode material, conductive agent SuperP and polyvinylidene fluoride (PVDF) are thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 90:5:5 to form a uniform slurry. The slurry is coated on aluminum foil and dried at 120°C for 12 hours. Then, it is stamped with a pressure of 100 MPa to form a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm.

[0135] Battery Assembly: In an argon-filled glove box with both water and oxygen content less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into an R2025 coin cell and then left to stand for 6 hours. The negative electrode used a 15.6 mm diameter, 0.45 mm thick lithium metal sheet; the separator used a 25 μm polypropylene microporous membrane (Celgard 2325); and the electrolyte used was a 1 mol / L mixture of equal parts LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0136] The test results above show that, compared with the comparative example, the lithium manganese iron phosphate cathode material prepared by the method described in this disclosure has a higher degree of crystallinity, a larger primary particle size and a suitable grain size distribution in the primary sintered material, and higher compaction density and electrochemical capacity. The molar ratio of P / (Mn+Fe) and the sintering conditions are crucial for preparing specific primary sintered materials and specific lithium manganese iron phosphate cathode material products. Specifically, compared with Example 1, the P content in Example 3 is increased, which is outside the preferred range of this disclosure, resulting in increased compaction density but decreased capacity; the P content in Example 4 is decreased, which is outside the preferred range of this disclosure, resulting in decreased compaction density and capacity; the P content in Example 6 is too low, which is outside the preferred range of this disclosure, resulting in a greater decrease in compaction density and capacity; the primary sintering temperature in step S2 of Example 7 is relatively low, resulting in smaller grain size, leading to decreased compaction density and capacity; the primary sintering temperature in step S2 of Example 8 is relatively high, resulting in larger grain size, leading to decreased capacity; the secondary sintering temperature in step S4 of Example 9 is relatively low, resulting in smaller cell volume and grain size, leading to decreased compaction density and capacity; while in Comparative Example 1, the P content is too low, which is outside the range of this disclosure, resulting in smaller primary particle size, smaller cell volume and grain size, leading to poor compaction density and capacity; in Comparative Example 2, the primary sintering temperature in step S2 is too low, resulting in smaller cell volume and grain size, leading to poor compaction density and capacity. In summary, the preparation process provided in this disclosure can effectively improve the compaction density and electrochemical capacity of lithium manganese iron phosphate cathode materials.

[0137] In the description of this disclosure, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0138] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific embodiment," or "some embodiments," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0139] Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A cathode material, wherein, This includes lithium manganese iron phosphate, wherein the cell volume of the lithium manganese iron phosphate is...

2. The cathode material according to claim 1, wherein, The cell volume of the lithium manganese iron phosphate is 3. The cathode material according to claim 1 or 2, wherein, The cell volume of the lithium manganese iron phosphate is 4. The cathode material according to any one of claims 1 to 3, wherein, The lithium manganese iron phosphate has the composition shown in Formula I: Li a Mn x Fe y M 1-x-y (PO4) b Formula I Wherein, 0.90≤a≤1.20, 0.30≤x≤0.95, 0.05≤y≤0.70, and 0.95≤b≤1.10; M is selected from at least one of Ti, Mg, Zn, Cu, Sr, Al, Zr, Y, Co, W, Ca, Nb, Sn, Sb, Mo, V, B, and Si; 1.03≤b / (x+y)≤1.

15.

5. The cathode material according to claim 4, wherein, At least one of the following conditions must be met: 0.95≤a≤1.15; 1.00≤b≤1.09; 0.90≤x+y≤1.00; 1.05≤b / (x+y)≤1.

10.

6. The cathode material according to claim 5, wherein, At least one of the following conditions must be met: 1.00≤a≤1.10; 1.01≤b≤1.07; 0.95≤x+y<1.

00.

7. The cathode material according to claim 5 or 6, wherein, 1.02≤a≤1.08。 8. The cathode material according to claim 1, wherein, The lithium manganese iron phosphate satisfies: 80nm ≤ L 10 ≤200nm, 150nm≤L 50 ≤300nm, 200nm≤L 90 ≤500nm; Among them, L 10 L 50 L 90 The grain size Ln is the grain size corresponding to the cumulative volume percentage of the lithium manganese iron phosphate grain size Ln reaching 10%, 50%, and 90%, respectively.

9. The cathode material according to claim 8, wherein, The lithium manganese iron phosphate satisfies: 100nm≤L 10 ≤180nm,160nm≤L 50 ≤260nm,220nm≤L 90 ≤480nm。 10. The cathode material according to claim 1, wherein, The compacted density of the lithium manganese iron phosphate is 2.3 g / cm³. 3 ~2.6g / cm 3 .

11. A method for preparing the cathode material according to any one of claims 1 to 10, wherein, include: A first mixture containing lithium source, M source, phosphorus source, manganese source and iron source is sintered once to obtain a primary sintered material. The primary sintered material includes secondary particles, which are formed by the agglomeration of multiple primary particles. The primary particle size P of the primary particles satisfies 100nm≤P≤500nm. The first sintered material is mixed with a carbon source in a solvent and then subjected to a second grinding process to obtain a second mixture. The second mixture is subjected to a second spray drying process to obtain a second spray-dried material; The second spray-dried material is subjected to secondary sintering to obtain the lithium manganese iron phosphate.

12. The method according to claim 11, wherein, The first mixture is subjected to a first spray drying process to obtain a first spray-dried material; The first spray-dried material is heated to 400℃~700℃ under an inert atmosphere at a heating rate of 1℃ / min~5℃ / min, and held at that temperature for 3h~15h to undergo a first sintering process to obtain a first sintered material.

13. The method according to claim 11, wherein, The molar ratio of phosphorus in the phosphorus source to manganese in the manganese source and iron in the iron source, n(P) / n(Mn+Fe), is 1.03:1 to 1.15:

1.

14. The method according to claim 11, wherein, D of the first mixture 50 The thickness is 0.1 μm to 0.5 μm; and / or D of the second mixture 50 The range is 0.2μm to 0.6μm.

15. The method according to claim 11, wherein, The mass ratio of the carbon source to the primary sintering material is 2:100 to 20:

100.

16. The method according to claim 11, wherein, At least one of the following conditions must be met: The manganese source includes at least one of manganese sulfate, manganese carbonate, manganese nitrate, and manganese tetroxide; The iron source includes at least one of ferric phosphate, ferric nitrate, ferric sulfate, ferrous oxalate, ferrous carbonate, and ferric oxide. The phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate. The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium nitrate; The M source includes at least one of oxides, hydroxides, and carbonates containing the M element; The carbon source includes at least one of glucose, sucrose, and organic polymers.

17. The method according to claim 11, wherein, The second spray-dried material is subjected to secondary sintering, which includes heating to 600℃~800℃ at a heating rate of 1℃ / min~3℃ / min under an inert atmosphere and holding at that temperature for 5h~20h.

18. A lithium-ion battery, wherein, The cathode material includes any one of claims 1 to 10 or the cathode material prepared by any one of claims 11 to 17.

19. An electrical appliance, wherein, Including the lithium-ion battery as described in claim 18.

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