A lithium manganese iron phosphate positive electrode material, a preparation method and application thereof

Abstract

The application discloses a lithium manganese iron phosphate positive material and a preparation method and application thereof, and relates to the technical field of battery material preparation. The preparation method uses manganese iron hydroxide as a precursor to prepare the lithium manganese iron phosphate positive material, and through condition control such as pre-sintering treatment, the lithium manganese iron phosphate positive material with more uniform element distribution, more stable structure and better electrical performance can be obtained. The method has the advantages of simple process, high element utilization rate, low cost, environmental friendliness, easy realization of large-scale industrial production and wide industrialization prospect.

Description

Technical Field

[0001] This disclosure relates to the field of battery material preparation technology, and in particular to a lithium manganese iron phosphate cathode material, its preparation method and application. Background Technology

[0002] With the increasing severity of the energy crisis, lithium-ion secondary batteries have long been considered the most promising energy conversion and storage devices, among which lithium manganese iron phosphate (LiMn) is a prime example. x Fe 1-x PO4 (LMFP) is widely used in the cathode of lithium-ion batteries due to its advantages such as low cost, high safety and long cycle life.

[0003] In related technologies, some studies have involved dissolving lithium, iron, manganese, and phosphorus sources in water and mixing them before sintering. However, the resulting lithium manganese iron phosphate (LMFP) exhibits uneven distribution of Fe and Li elements and contains residual impurities, resulting in low element utilization. Other studies have shown that adding iron and manganese sources during the grinding process leads to Fe and Mn interdiffusion during solid-state sintering, forming a solid solution that hinders uniform distribution of iron and manganese, resulting in uneven proportions and affecting structural stability. Therefore, improving the elemental uniformity in lithium manganese iron phosphate materials while simultaneously ensuring their electrical performance is a pressing issue that needs to be addressed. Summary of the Invention

[0004] This disclosure aims to address at least one of the technical problems existing in the prior art. To this end, this disclosure proposes a method for preparing lithium manganese iron phosphate cathode material.

[0005] This disclosure also proposes a lithium manganese iron phosphate cathode material prepared by the above preparation method.

[0006] This disclosure also proposes a positive electrode sheet comprising the above-mentioned lithium manganese iron phosphate positive electrode material.

[0007] This disclosure also proposes the application of the above-mentioned lithium manganese iron phosphate cathode material or the above-mentioned cathode sheet in the field of lithium-ion batteries.

[0008] A method for preparing a lithium manganese iron phosphate cathode material according to a first aspect embodiment of the present disclosure includes the following steps:

[0009] 1) Under an inert gas atmosphere, manganese iron hydroxide is pre-calcined to obtain manganese iron oxide;

[0010] 2) Prepare a slurry containing manganese iron oxide, phosphorus source, lithium source and carbon source, dry it to obtain the calcination precursor;

[0011] The carbon source content is 15wt% to 40wt% of the manganese iron oxide;

[0012] 3) The calcination precursor is calcined and crushed under an inert gas atmosphere to obtain the lithium manganese iron phosphate cathode material.

[0013] The particle size Dv50 of the lithium manganese iron phosphate cathode material is 0.2 μm to 0.8 μm.

[0014] The preparation method according to the embodiments of this disclosure has at least the following beneficial effects:

[0015] The preparation method described in this embodiment yields lithium manganese iron phosphate cathode materials with more uniform elemental distribution and more stable structure, exhibiting high element utilization. This preparation method is simple, uses widely available raw materials, is low-cost, and does not require expensive or complex equipment or harsh reaction conditions, making it easy to achieve large-scale industrial production and possessing broad industrialization prospects. The raw materials are free of harmful substances, are environmentally friendly, and demonstrate excellent environmental performance.

[0016] The carbon source content is 15wt% to 40wt% of the manganese iron oxide. For example, it can be 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, or 40wt%. If the carbon source content is too high, more carbon molecules will remain on the material surface, resulting in a larger BET of the lithium manganese iron phosphate cathode material.

[0017] According to some embodiments of this disclosure, the particle size Dv50 of the slurry is 0.3 μm to 0.9 μm. For example, it can be 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm.

[0018] According to some embodiments of this disclosure, the manganese iron hydroxide is Fe m Mn 1-m (OH)2;0.2≤m≤0.8.

[0019] According to some embodiments of this disclosure, the manganese iron hydroxide includes Fe 0.2 Mn 0.8 (OH)2, Fe 0.3 Mn 0.7 (OH)2, Fe 0.4 Mn 0.6 (OH)2, Fe 0.5 Mn 0.5 (OH)2, Fe 0.6 Mn 0.4 (OH)2, Fe 0.7 Mn 0.3 (OH)2, Fe 0.8 Mn 0.2 At least one of (OH)2.

[0020] According to some embodiments of this disclosure, the method for preparing the manganese iron hydroxide includes the following steps:

[0021] Under the action of antioxidants, alkaline precipitants, and complexing agents, Fe 2+ With Mn 2+ The reaction yields the manganese iron hydroxide;

[0022] Fe 2+ With Mn 2+ The molar ratio is m:1-m; 0.2≤m≤0.8.

[0023] According to some embodiments of this disclosure, the antioxidant includes at least one of sodium isoascorbate, ascorbic acid, sodium ascorbate, and isoascorbic acid.

[0024] According to some embodiments of this disclosure, the concentration of the antioxidant is 1 mol / L to 3 mol / L. For example, it can be 1 mol / L, 1.25 mol / L, 1.5 mol / L, 1.75 mol / L, 2 mol / L, 2.25 mol / L, 2.5 mol / L, 2.75 mol / L, or 3 mol / L.

[0025] According to some embodiments of this disclosure, the alkaline precipitant includes sodium hydroxide.

[0026] According to some embodiments of this disclosure, the concentration of the alkaline precipitant is 0.25 mol / L to 1 mol / L. For example, it can be 0.25 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, or 1 mol / L.

[0027] According to some embodiments of this disclosure, the complexing agent includes at least one selected from ethylenediaminetetraacetic acid, citric acid, oxalic acid, acetic acid, polyacrylic acid, and tartaric acid.

[0028] According to some embodiments of this disclosure, the concentration of the complexing agent is 0.5 mol / L to 2 mol / L. For example, it can be 0.5 mol / L, 0.75 mol / L, 1 mol / L, 1.25 mol / L, 1.5 mol / L, 1.75 mol / L, or 2 mol / L.

[0029] According to some embodiments of this disclosure, the Fe 2+ Sources include ferrous sulfate.

[0030] According to some embodiments of this disclosure, the Fe 2+The concentration ranges from 0.5 mol / L to 2.5 mol / L. For example, it can be 0.5 mol / L, 0.75 mol / L, 1 mol / L, 1.25 mol / L, 1.5 mol / L, 1.75 mol / L, 2 mol / L, 2.25 mol / L, or 2.5 mol / L.

[0031] According to some embodiments of this disclosure, the Mn 2+ The sources include at least one of manganese sulfate, manganese nitrate, and manganese chloride.

[0032] According to some embodiments of this disclosure, the Mn 2+ The concentration ranges from 0.75 mol / L to 3 mol / L. For example, it can be 0.75 mol / L, 1 mol / L, 1.25 mol / L, 1.5 mol / L, 1.75 mol / L, 2 mol / L, 2.25 mol / L, 2.5 mol / L, 2.75 mol / L, or 3 mol / L.

[0033] According to some embodiments of this disclosure, the pH of the reaction is 10 to 13. For example, it can be 10, 10.5, 11, 11.5, 12, 12.5, or 13.

[0034] According to some embodiments of this disclosure, the reaction temperature is 50°C to 70°C. For example, it can be 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C, or 70°C.

[0035] According to some embodiments of this disclosure, the reaction time is 60 min to 100 min. For example, it can be 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min, or 100 min.

[0036] According to some embodiments of this disclosure, the reaction is carried out in an inert gas atmosphere.

[0037] According to some embodiments of this disclosure, the inert gas includes at least one of nitrogen, helium, neon, argon, krypton, xenon, and radon.

[0038] According to some embodiments of this disclosure, the solvent for the reaction is water.

[0039] According to some embodiments of this disclosure, the temperature of the pre-firing treatment is 350°C to 750°C. For example, it can be 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, or 750°C.

[0040] According to some embodiments of this disclosure, the pre-burning treatment time is 3h to 8h. For example, it can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h.

[0041] According to some embodiments of this disclosure, in the slurry, the molar ratio of P:(Mn+Fe) is (1.01~1.1):1. For example, it can be 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 1.1:1.

[0042] According to some embodiments of this disclosure, in the slurry, the Li:P ratio is (1.01 to 1.1):1, in molar ratio. For example, it can be 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 1.1:1.

[0043] According to some embodiments of this disclosure, the phosphorus source includes at least one of phosphoric acid, lithium dihydrogen phosphate, lithium phosphate, and potassium dihydrogen phosphate.

[0044] According to some embodiments of this disclosure, the lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, and lithium hydroxide.

[0045] According to some embodiments of this disclosure, the carbon source includes at least one selected from glucose, sucrose, polyethylene glycol (PEG), soybean lecithin, and citric acid.

[0046] According to some embodiments of this disclosure, the molecular weight of the polyethylene glycol is 1500 to 10000.

[0047] According to some embodiments of this disclosure, in step S2, the slurry further includes a metal ion source. Metal ions can enhance the Li... + This increases the diffusion rate, thereby improving the rate capability and capacity of lithium manganese iron phosphate cathode materials.

[0048] According to some embodiments of this disclosure, the metal ion source includes at least one of Ti source, V source, Ni source, Mg source, Al source, Sb source, Cu source, Zr source, and Zn source.

[0049] According to some embodiments of this disclosure, the Ti source includes titanium dioxide.

[0050] According to some embodiments of this disclosure, the V source includes at least one of vanadium oxalate, ammonium metavanadate, and vanadium pentoxide.

[0051] According to some embodiments of this disclosure, the Ni source includes at least one of nickel oxide, nickel hydroxide, nickel dioxide, nickel trioxide, nickel nitrate, and nickel sulfate.

[0052] According to some embodiments of this disclosure, the Mg source includes at least one of magnesium oxide and magnesium chloride.

[0053] According to some embodiments of this disclosure, the Al source includes at least one of aluminum acetate and aluminum oxide.

[0054] According to some embodiments of this disclosure, the Sb source includes at least one of antimony trioxide and antimony pentoxide.

[0055] According to some embodiments of this disclosure, the Cu source includes at least one of copper carbonate, copper hydroxide, and copper oxide.

[0056] According to some embodiments of this disclosure, the Zr source includes at least one of zirconium dioxide and zirconium hydroxide.

[0057] According to some embodiments of this disclosure, the Zn source includes at least one of zinc oxide and zinc chloride.

[0058] According to some embodiments of this disclosure, the doping amount of metal ions in the slurry is 300ppm to 5000ppm. For example, it can be 300ppm, 500ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm or 5000ppm.

[0059] According to some embodiments of this disclosure, at least one of Ti, V, Ni, Mg, Al, Sb, Cu, Zr, and Zn is distributed on the surface of the calcined precursor or at adjacent grain boundaries.

[0060] According to some embodiments of this disclosure, the solvent for the slurry is water.

[0061] According to some embodiments of this disclosure, the preparation of a slurry containing the aforementioned manganese iron oxide, phosphorus source, lithium source, and carbon source includes:

[0062] After preparing a slurry containing the manganese iron oxide and phosphorus source, it is mixed with the lithium source and the carbon source.

[0063] According to some embodiments of this disclosure, the preparation of a slurry containing the aforementioned manganese iron oxide, phosphorus source, lithium source, carbon source, and metal ion source includes:

[0064] After preparing a slurry containing the manganese iron oxide and phosphorus source, it is mixed with the lithium source, the carbon source, and the metal ion source.

[0065] According to some embodiments of this disclosure, the calcination temperature is 550℃ to 750℃. For example, it can be 550℃, 575℃, 600℃, 625℃, 650℃, 675℃, 700℃, 725℃, or 750℃.

[0066] According to some embodiments of this disclosure, the calcination treatment time is 5h to 12h. For example, it can be 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h.

[0067] According to some embodiments of this disclosure, the heating rate of the calcination treatment is 1 to 6 °C / min. For example, it can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, or 6 °C / min.

[0068] According to some embodiments of this disclosure, step 2) further includes a second crushing of the slurry.

[0069] According to some embodiments of this disclosure, the first crushing and the second crushing each independently include at least one of sand milling, ball milling, roller milling, and pulverizing.

[0070] According to some embodiments of this disclosure, the drying includes spray drying.

[0071] A lithium manganese iron phosphate cathode material according to a second aspect of this disclosure is prepared by the above-described preparation method.

[0072] The preparation method according to the embodiments of this disclosure has at least the following beneficial effects:

[0073] The lithium manganese iron phosphate cathode material in the embodiments exhibits good elemental uniformity, excellent structural stability, and outstanding electrochemical performance; it also demonstrates good energy density and cycle performance.

[0074] According to some embodiments of this disclosure, the molecular formula of the lithium manganese iron phosphate cathode material is LiMn. 1-x Fe x A z PO4;

[0075] Wherein, 0.2≤x≤0.8, 0≤z≤0.05, and A includes at least one of Ti, V, Ni, Mg, Al, Sb, Cu, Zr, and Zn.

[0076] According to some embodiments of this disclosure, the residual lithium content on the surface of the lithium manganese iron phosphate cathode material is less than 700 ppm.

[0077] According to some embodiments of this disclosure, the residual lithium content on the surface of the lithium manganese iron phosphate cathode material is 100ppm to 660ppm. For example, it can be 100ppm, 150ppm, 200ppm, 250ppm, 300ppm, 400ppm, 500ppm, or 600ppm.

[0078] According to some embodiments of this disclosure, the specific surface area (BET) of the lithium manganese iron phosphate cathode material is 5 m². 2 / g~20m 2 / g. For example: it can be 5m. 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g or 20m 2 / g.

[0079] According to some embodiments of this disclosure, 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 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.

[0080] According to some embodiments of this disclosure, the compaction density of the lithium manganese iron phosphate cathode material under a pressure of 3000 kg is 1.9 g / m³. 3 ~2.5g / m 3 For example: it can be 1.9g / m³ 3 1.95g / m 3 2.0g / m 3 2.05g / m 3 2.1g / m 3 2.15g / m 3 2.2g / m 3 2.25g / m 3 2.3g / m 3 2.35g / m 32.4g / m 3 2.45g / m 3 Or 2.5g / m 3 .

[0081] A positive electrode sheet according to a third aspect embodiment of the present disclosure includes the above-described lithium manganese iron phosphate positive electrode material.

[0082] Application of the above-described lithium manganese iron phosphate cathode material or cathode sheet according to the fourth aspect embodiment of this disclosure in the field of lithium-ion batteries.

[0083] Other features and advantages of this disclosure will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing this disclosure. Attached Figure Description

[0084] Figure 1A manganese iron hydroxide Fe 0.4 Mn 0.6 SEM image of (OH)2 before pre-calcination treatment;

[0085] Figure 1B manganese iron hydroxide Fe 0.4 Mn 0.6 SEM image of (OH)2 after pre-calcination treatment;

[0086] Figure 2 The XRD patterns of the lithium iron phosphate cathode materials prepared in Example 1 and Comparative Example 1 are shown.

[0087] Figure 3A SEM image of the lithium iron phosphate cathode material prepared in Example 1;

[0088] Figure 3B Here is a SEM image of the lithium iron phosphate cathode material prepared in Comparative Example 1;

[0089] Figure 4A The elemental EDS diagram of the lithium iron phosphate cathode material prepared in Example 1 is shown below.

[0090] Figure 4B The elemental EDS diagram of the lithium iron phosphate cathode material prepared in Comparative Example 1 is shown.

[0091] Figure 5 The charge / discharge capacity diagrams of CR2016 batteries prepared from lithium manganese iron phosphate cathode materials in Example 1 and Comparative Example 1 are shown. Detailed Implementation

[0092] The following will describe the concept and technical effects of this disclosure clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of this disclosure.

[0093] Unless otherwise specified, all reagents used are commercially available products.

[0094] In the description of this disclosure, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, or product that includes a series of steps or units is not necessarily limited to those steps or units that are expressly listed, but may include other steps or units that are not expressly listed or that are inherent to such processes, methods, or products.

[0095] When a numerical range is disclosed in this disclosure, 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. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, 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 disclosure should be understood to include any and all subranges to which they are incorporated.

[0096] Unless otherwise specified, the chemical formulas provided in this disclosure are calculated based on the feeding ratio. In reality, considering factors such as lithium source burn-off, the atomic ratios in the actual manganese iron hydroxide or cathode material may not be exactly the same as those in the chemical formula.

[0097] In the embodiments of this disclosure, manganese iron hydroxide Fe 0.4 Mn 0.6 The preparation method of (OH)2 is as follows:

[0098] 1) Mix ferrous sulfate (final concentration 2.4 mol / L) and manganese sulfate (final concentration 3.6 mol / L) in water, Fe 2+ With Mn 2+ The molar ratio is 4:6. Stir until dissolved to obtain mixture I;

[0099] 2) Add antioxidant (sodium isoascorbate, final concentration 4 mol / L), alkaline precipitant (sodium hydroxide, final concentration 1 mol / L) and complexing agent (ethylenediaminetetraacetic acid, final concentration 2 mol / L) to water, stir and mix evenly to obtain mixture II;

[0100] 3) Pour 1000 mL of mixture II into the reactor while stirring at 600 rpm. Purge the reactor with nitrogen to maintain oxygen levels below 100 ppm. Then, slowly add 1000 mL of mixture I. Maintain the pH of the reactor solution at 12.0 and the temperature at 60℃. React for 80 min. Wash and dry the reactants to obtain manganese iron hydroxide (Fe). 0.4 Mn0.6 (OH)2.

[0101] manganese iron hydroxide Fe 0.2 Mn 0.8 (OH)2, Fe 0.3 Mn 0.7 (OH)2, Fe 0.5 Mn 0.5 (OH)2, Fe 0.6 Mn 0.4 (OH)2, Fe 0.7 Mn 0.3 (OH)2, Fe 0.8 Mn 0.2 The preparation of (OH)2 refers to the above-mentioned manganese iron hydroxide Fe 0.4 Mn 0.6 The preparation method of (OH)2 is adapted to adjust the Fe content in mixed solution I. 2+ With Mn 2+ The molar ratio is sufficient.

[0102] Example 1

[0103] This example provides a method for preparing lithium iron phosphate cathode material, the steps of which are as follows:

[0104] 1) Under a nitrogen atmosphere, manganese iron hydroxide Fe 0.4 Mn 0.6 (OH)2 was pre-calcined at 650℃ for 5 hours to obtain manganese iron oxide, and the Fe content was found to be 28.12 wt% and the Mn content was 40.45 wt%.

[0105] 2) Weigh 1500g of the manganese iron oxide from step 1) and add it to 6L of water. Then, add 1972.29g of lithium dihydrogen phosphate, 21.03g of lithium carbonate, 14.71g of titanium dioxide, 150g of PEG 6000, and 90g of glucose in sequence. After mixing evenly, mill the slurry until the particle size Dv50 is 0.38μm. After the particle size meets the standard, spray dry to obtain the calcined precursor.

[0106] In terms of molar ratio, P:(Mn+Fe)=1.02:1; Li:P=1.03:1;

[0107] The carbon source was 16 wt% of manganese iron oxide.

[0108] 3) Under a nitrogen atmosphere, the calcination precursor was calcined at 680℃ for 7 hours, with a heating time of 328 minutes and a heating rate of 2℃ / min. After natural cooling to room temperature, the material was crushed to a Dv50 of 0.4μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.6 Fe 0.4 Ti 0.01PO4 / C.

[0109] Example 2

[0110] 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 P:(Mn+Fe)=1.01:1.

[0111] Example 3

[0112] 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 P:(Mn+Fe)=1.05:1.

[0113] Example 4

[0114] 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 P:(Mn+Fe)=1.1:1.

[0115] Example 5

[0116] 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), the grinding particle size Dv50 is replaced from 0.38 μm to 0.1 μm.

[0117] Example 6

[0118] 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), the grinding particle size Dv50 is replaced from 0.38 μm to 1.0 μm.

[0119] Example 7

[0120] 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), the grinding particle size Dv50 is replaced from 0.38 μm to 1.5 μm.

[0121] Example 8

[0122] 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 particle size Dv50 is replaced by 0.2 μm instead of 0.4 μm.

[0123] Example 9

[0124] This example provides a method for preparing lithium iron phosphate cathode material, the steps of which are as follows:

[0125] 1) Under a nitrogen atmosphere, manganese iron hydroxide Fe 0.2 Mn 0.8 (OH)2 was pre-calcined at 350℃ for 8 hours to obtain manganese iron oxide, and the Fe content was found to be 14.82 wt% and the Mn content was 56.64 wt%.

[0126] 2) Weigh 1257.52g of phosphoric acid and add it to 6L of water. Then, add 1500g of manganese iron oxide (from step 1), 788.42g of lithium phosphate, 15.58g of magnesium oxide, 14.44g of nickel oxide, 120g of PEG 1500, 80g of glucose, and 40g of citric acid in sequence. After mixing evenly, mill the slurry until the particle size Dv50 is 0.1μm. After the particle size meets the standard, spray dry to obtain the calcination precursor.

[0127] In terms of molar ratio, P:(Mn+Fe)=1.01:1; Li:P=1.04:1;

[0128] The carbon source content is 16 wt% of manganese iron oxide.

[0129] 3) Under a nitrogen atmosphere, the calcination precursor was calcined at 550℃ for 12 h, with a heating time of 106 min and a heating rate of 5℃ / min. After natural cooling to room temperature, the material was crushed to a Dv50 of 0.4 μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.8 Fe 0.2 PO4Mg 0.02 Ni 0.01 / C.

[0130] Example 10

[0131] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 9, except that in step 2) of this example, the molar ratio of Li:P is 1.03:1.

[0132] Example 11

[0133] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 9, except that in step 2) of this example, the molar ratio of Li:P is 1.1:1.

[0134] Example 12

[0135] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 9, except that in step 2) of this example, the molar ratio of Li:P is 1.01:1.

[0136] Example 13

[0137] This example provides a method for preparing lithium iron phosphate cathode material, the steps of which are as follows:

[0138] 1) Under a nitrogen atmosphere, manganese iron hydroxide Fe 0.6 Mn 0.4 (OH)2 was pre-calcined at 750℃ for 3 hours to obtain manganese iron oxide, with a measured Fe content of 40.6 wt% and a Mn content of 26.97 wt%.

[0139] 2) Weigh 1826.87g of phosphoric acid and add it to 6L of water. Then, add 1500g of manganese iron oxide (from step 1), 28.53g of vanadium oxalate, 708.41g of lithium carbonate, 200g of PEG 10000, 100g of soybean lecithin, and 75g of glucose in sequence. After mixing evenly, take 25wt% of the slurry and mill it to a particle size Dv50 of 1.5μm, and take 75wt% of the slurry and mill it to a particle size Dv50 of 0.4μm. After the particle size of the material meets the standard, spray dry it to obtain the calcination precursor.

[0140] In terms of molar ratio, P:(Mn+Fe)=1.02:1; Li:P=1.03:1;

[0141] The carbon source content is 25 wt% of manganese iron oxide.

[0142] 3) Under a nitrogen atmosphere, the calcination precursor was calcined at 750℃ for 5 hours, with a heating time of 120 minutes and a heating rate of 6℃ / min. After natural cooling to room temperature, the material was crushed to a Dv50 of 0.4μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.4 Fe 0.6 PO4V 0.01 / C.

[0143] Example 14

[0144] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 13, except that in step 3), the calcination temperature of 750°C is replaced with 680°C.

[0145] Example 15

[0146] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 13, except that in step 3), the calcination temperature of 750°C is replaced with 550°C.

[0147] Example 16

[0148] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 13, except that in step 3), the calcination time of 5h is replaced with 8h.

[0149] Example 17

[0150] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 13, except that in step 3), the calcination time of 5h is replaced with 12h.

[0151] Example 18

[0152] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 13, except that in step 3), the heating rate of 6℃ / min is replaced with 4℃ / min.

[0153] Example 19

[0154] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 13, except that in step 3), the heating rate of 6℃ / min is replaced with 1℃ / min.

[0155] Example 20

[0156] This example provides a method for preparing lithium iron phosphate cathode material, the steps of which are as follows:

[0157] 1) Under a nitrogen atmosphere, manganese iron hydroxide Fe 0.8 Mn 0.2 (OH)2 was pre-calcined at 650℃ for 5 hours to obtain manganese iron oxide, and the Fe content was found to be 58.63 wt% and the Mn content was 14.81 wt%.

[0158] 2) Weigh 1959.20g of phosphoric acid and add it to 6L of water. Then, add 1500g of manganese iron oxide (from step 1), 760.80g of lithium carbonate, 160g of PEG 6000, and 80g of glucose in sequence. After mixing evenly, mill the slurry until the particle size Dv50 is 0.5μm. Once the particle size of the material meets the standard, spray dry it to obtain the calcination precursor.

[0159] In terms of molar ratio, P:(Mn+Fe)=1.01:1; Li:P=1.03:1;

[0160] The carbon source content is 16 wt% of manganese iron oxide.

[0161] 3) Under a nitrogen atmosphere, the calcination precursor was calcined at 680℃ for 8 hours, with a heating time of 328 minutes and a heating rate of 2℃ / min. After natural cooling to room temperature, the material was crushed to a Dv50 of 0.8μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.8 Fe 0.2 PO4 / C.

[0162] Example 21

[0163] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 20, except that in step 2), the carbon source content of 16 wt% is replaced with 30 wt%.

[0164] Example 22

[0165] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 20, except that in step 2), the carbon source content of 16wt% is replaced with 40wt%.

[0166] Example 23

[0167] This example provides a method for preparing lithium iron phosphate cathode material. The steps are basically the same as those in Example 20, except that in this example, the order of adding raw materials in step 2) is S-iron manganese hydroxide, lithium carbonate, phosphoric acid, PEG 6000, and glucose.

[0168] Comparative Example 1

[0169] This example provides a method for preparing lithium iron phosphate cathode material, the steps of which are as follows:

[0170] 1) Weigh 825g of manganese carbonate and add it to 6L of water. Then, add 688.32g of ferrous oxalate, 1268.55g of lithium dihydrogen phosphate, 13.53g of lithium carbonate, 14.71g of titanium dioxide, 151.3g of PEG 6000, and 90.9g of glucose in sequence. After mixing evenly, mill the slurry to a particle size of 0.38μm. Once the particle size meets the standard, spray dry to obtain the calcination precursor.

[0171] In terms of molar ratio, P:(Mn+Fe)=1.02:1; Li:P=1.03:1;

[0172] The carbon source content is 16 wt% of Mn and Fe sources.

[0173] 2) Under a nitrogen atmosphere, the calcination precursor was calcined at 680℃ for 7 hours, with a heating time of 328 minutes and a heating rate of 2℃ / min. After natural cooling to room temperature, the material was crushed to a Dv50 of 0.4μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.6 Fe 0.4 Ti 0.01 PO4 / C.

[0174] Comparative Example 2

[0175] This example provides a method for preparing lithium iron phosphate cathode material, the steps of which are as follows:

[0176] 1) Weigh 1200g of manganese oxalate and add it to 6L of water. Then, add 316.48g of ferric phosphate, 832.94g of phosphoric acid, 407.22g of lithium carbonate, 15.58g of magnesium oxide, 14.44g of nickel oxide, 121.32g of PEG 1500, 80.87g of glucose, and 40.43g of citric acid in sequence. After mixing evenly, mill the slurry until the Dv50 is 0.1μm. After the particle size meets the standard, spray dry to obtain the calcination precursor.

[0177] In terms of molar ratio, P:(Mn+Fe)=1.01:1; Li:P=1.04:1;

[0178] The carbon source content is 16 wt% of Mn and Fe sources.

[0179] 2) Under a nitrogen atmosphere, the calcination precursor was calcined at 550℃ for 12 hours, with a heating time of 106 minutes and a heating rate of 5℃ / min. After natural cooling to room temperature, the material was crushed to a Dv50 of 0.4μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.8 Fe 0.2 PO4Mg 0.02 Ni 0.01 / C.

[0180] Comparative Example 3

[0181] This example provides a method for preparing lithium iron phosphate cathode material, the steps of which are as follows:

[0182] 1) Weigh 513.14g of phosphoric acid and add it to 6L of water. Then, add 380g of manganese tetroxide, 1127.10g of ferric phosphate, 483.65g of lithium carbonate, 28.53g of vanadium oxalate, 200.95g of PEG 10000, 100.476g of soybean lecithin, and 75.35g of glucose in sequence. After mixing evenly, take 25wt% of the slurry and mill it to a particle size of 1.5μm, and take 75wt% of the slurry and mill it to a particle size of 0.4μm. After the particle size meets the standard, spray dry to obtain the calcination precursor.

[0183] In terms of molar ratio, P:(Mn+Fe)=1.02:1; Li:P=1.03:1;

[0184] The carbon source content, consisting of Mn and Fe sources, is 25 wt%.

[0185] 2) Under a nitrogen atmosphere, the calcination precursor was calcined at 750℃ for 5 hours, with a heating time of 120 minutes and a heating rate of 6℃ / min. After natural cooling to room temperature, the material was crushed to a Dv50 of 1.8 μm to obtain the lithium manganese iron phosphate cathode material LiMn. 0.4 Fe 0.6 PO4V0.01 / C.

[0186] Comparative Example 4

[0187] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as in Example 1, except that step 1 is omitted.

[0188] Comparative Example 5

[0189] 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 nitrogen atmosphere is replaced with an air atmosphere.

[0190] Comparative Example 6

[0191] 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 particle size Dv50 is replaced by 1.0 μm instead of 0.4 μm.

[0192] Comparative Example 7

[0193] 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 particle size Dv50 is replaced by 1.8 μm instead of 0.4 μm.

[0194] Comparative Example 8

[0195] This example provides a method for preparing lithium manganese iron phosphate cathode material. The steps are basically the same as those in Example 20, except that in step 2), the carbon source content of 16wt% is replaced with 10wt%.

[0196] Detection example

[0197] 1. The powder resistivity, specific surface area, compaction density, and residual lithium of the lithium manganese iron phosphate cathode materials prepared in Examples 1 to 23 and Comparative Examples 1 to 8 were tested. The test methods are as follows:

[0198] (1) Powder resistivity:

[0199] The powder resistivity of lithium manganese iron phosphate cathode material was tested using a powder resistivity meter with a four-probe method. 2.40 g of lithium manganese iron phosphate cathode material was weighed and placed into a mold, adjusted to a height of 20 mm, and compacted using a pressure of 12 MPa. Data was then collected. The formula for calculating powder resistivity is as follows:

[0200]

[0201] In the formula: ρ1 is the powder resistivity, and C is the probe spacing correction coefficient. This is a height correction factor (determined based on the values ​​of W and S). W is the shape and position correction factor (determined based on the values ​​of d and S), S is the powder compaction height, S is the distance between two adjacent probes of the four probes, and d is the cross-sectional area of ​​the powder cavity.

[0202] (2) BET:

[0203] 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 and measured for about 90 min. The experimental data were recorded.

[0204] (3) Compacted density:

[0205] 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. The formula for calculating compaction density is as follows:

[0206]

[0207] In the formula: ρ2 is the compaction density, m is the sample mass, D is the mold diameter, and h is the compaction height.

[0208] (4) Residual lithium:

[0209] 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.

[0210] The detection principle is as follows:

[0211] OHˉ+H+=H2O;CO3 2- +H + =HCO3 - HCO3 - +H + =H2O + CO2↑.

[0212] The abrupt change in electrode potential indicates the titration endpoint: Before and after the titration reaches the endpoint, the concentration of the analyte ion in the titrant will change continuously by n orders of magnitude, causing a sudden change in potential. The content of the analyte is calculated by the amount of titrant consumed.

[0213] The test results are shown in Table 1.

[0214] Table 1

[0215]

[0216]

[0217] 2. CR2016 batteries were prepared using the lithium manganese iron phosphate cathode materials obtained in Examples 1 to 23 and Comparative Examples 1 to 8, respectively, and their electrical performance was tested. The preparation method of the CR2016 battery is as follows:

[0218] 19.2g of lithium manganese iron phosphate cathode material, 0.4g of acetylene black, and 0.4g of polyvinylidene fluoride (PVDF) were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2, and the mixture was stirred to obtain a cathode material slurry. The cathode material slurry was then uniformly coated onto aluminum foil with a coating amount of 1.45g / cm². 2 The material is then placed in a drying oven at 85°C for 1 hour, hot-pressed, cooled, and cut into 12cm positive electrode sheets using a punching machine. In a glove box, the positive electrode, separator (12μm thick polypropylene), negative lithium electrode sheet, and LiPF6 electrolyte are assembled to form a CR2016 battery.

[0219] The electrical performance testing methods are as follows:

[0220] Under constant temperature conditions of 25℃, the battery was charged at 0.1C to 4.3V at a voltage of 2V to 4.2V, then charged at 4.3V at a constant voltage until the current was ≤0.05mA. After standing for 5 minutes, the battery was discharged at 0.1C to 2V, and the battery capacity was recorded.

[0221] Under a constant temperature environment of 25℃, the battery was charged to full capacity at a constant current and constant voltage of 1C and 4.3V, left to stand for 5 minutes, and then discharged to 2V at a constant current of 1C, left to stand for 5 minutes. The same charging and discharging process was repeated for the next cycle until 100 cycles were completed. The battery capacity at different cycle counts was recorded and the average value was taken. The average battery capacity and capacity retention rate were calculated.

[0222] The test results are shown in Table 2.

[0223] Table 2

[0224]

[0225]

[0226] The prepared manganese-iron hydroxide is mainly in the form of burred granules with tight internal connections, consisting of disordered stacking of thin, lamellar grains. This effectively alleviates the problem of easily broken spherical particles during subsequent sintering, resulting in a cathode material with higher structural stability, energy density, and cycle performance. Furthermore, after pre-calcination, the burrs on the surface of the manganese-iron hydroxide are significantly reduced and become smoother, which helps to reduce the specific surface area of ​​the final product. Figure 1A and Figure 1B As shown, the lithium manganese iron phosphate cathode material prepared from pre-calcined manganese iron hydroxide (Example 1) has a higher specific capacity than the lithium manganese iron phosphate cathode material prepared from un-calcined manganese iron hydroxide (Comparative Example 4), and a lower BET.

[0227] The lithium iron phosphate cathode material obtained by pre-calcining iron-manganese hydroxide in nitrogen (Example 1) outperformed the lithium iron phosphate cathode material obtained by pre-calcining in air (Comparative Example 5). This may be because pre-calcination in air easily generates Mn2O3 and Fe2O3, rather than the manganese-iron polymer FeMnO3, thus affecting the performance of the cathode material. Within the P:(Mn+Fe) = (1–1.05):1 range (Examples 1–4), the specific capacity of the lithium iron phosphate cathode material first increases and then decreases with increasing P content, and it also reduces BET. Within the Li:P = (1.01–1.1) range, BET deteriorates with increasing Li content, but capacity increases. With increasing carbon content, the capacity and first-time efficiency of the lithium iron phosphate cathode material improve, but BET deteriorates. The higher the sintering temperature and the longer the sintering time of the lithium iron phosphate cathode material, the lower the powder resistivity.

[0228] XRD results showed that lithium manganese iron phosphate (e.g., in Comparative Example 1 and Example 1) was successfully synthesized. Figure 2 (As shown). SEM and EDS images of Comparative Example 1 and Comparative Example 1 (as shown). Figure 3A , Figure 3B , Figure 4A and Figure 4B At the same sintering temperature, the lithium manganese iron phosphate cathode material prepared with manganese iron oxide as a precursor has better crystallinity, more uniform particle distribution, regular elliptical particle shape, and more uniform element distribution; while the lithium manganese iron phosphate cathode material of Comparative Example 1 has different particle shapes, and the Mn element distribution is generally more concentrated.

Claims

1. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: 1) Under an inert gas atmosphere, manganese iron hydroxide is pre-calcined to obtain manganese iron oxide; the pre-calcination temperature is 350℃~750℃; the pre-calcination time is 3 h~8 h. 2) Prepare a slurry composed of manganese iron oxide, phosphorus source, lithium source and carbon source, dry it to obtain the calcination precursor; The carbon source content is 15wt%~40wt% of the manganese iron oxide; the manganese iron hydroxide is Fe m Mn 1-m (OH)₂; 0.2≤m≤0.8; In the slurry, the molar ratio of Li:P is (1.01~1.1):1; 3) The calcination precursor is calcined and crushed under an inert gas atmosphere to obtain the lithium manganese iron phosphate cathode material. The particle size Dv50 of the lithium manganese iron phosphate cathode material is 0.2 μm to 0.8 μm.

2. The preparation method according to claim 1, characterized in that, The phosphorus source includes at least one of phosphoric acid, lithium dihydrogen phosphate, lithium phosphate, and potassium dihydrogen phosphate. And / or, the lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, and lithium hydroxide; And / or, the carbon source includes at least one of glucose, sucrose, polyethylene glycol, soybean lecithin, and citric acid.

3. The preparation method according to claim 1, characterized in that, In the slurry, the molar ratio is P:(Mn+Fe)=(1.01~1.1):

1.

4. The preparation method according to claim 1, characterized in that, The calcination temperature is 550℃~750℃.

5. The preparation method according to claim 1, characterized in that, The calcination treatment time is 5 h to 12 h.

6. The preparation method according to claim 1, characterized in that, In step 2), the slurry also includes a metal ion source.

7. The preparation method according to claim 6, characterized in that, The metal ion source includes at least one of the following: Ti source, V source, Ni source, Mg source, Al source, Sb source, Cu source, Zr source, and Zn source.

8. The preparation method according to claim 1, characterized in that, The preparation of a slurry containing the aforementioned manganese iron oxide, phosphorus source, lithium source, and carbon source includes: After preparing a slurry containing the manganese iron oxide and phosphorus source, it is mixed with the lithium source and the carbon source.

9. The preparation method according to claim 1, characterized in that, The heating rate of the calcination treatment is 1~6℃ / min.

Images