Lithium manganese iron phosphate positive electrode material, and preparation method therefor and use thereof

Abstract

The present application relates to the technical field of battery material preparation, and discloses a lithium manganese iron phosphate positive electrode material, and a preparation method therefor and a use thereof. In the preparation method, a manganese iron hydroxide is used as a precursor to prepare a lithium manganese iron phosphate positive electrode material. A lithium manganese iron phosphate positive electrode material having a more uniform element distribution, a more stable structure, and better electrical performance can be obtained by means of conditional controls such as pre-sintering treatment. The present application has a simple process, a high element utilization rate and low costs, is environmentally-friendly and easy to realize large-scale industrial production, and has broad industrialization prospects.

Description

A lithium manganese iron phosphate positive electrode material and its preparation method and application Technical Field

[0001] The present disclosure relates to the technical field of battery material preparation, and in particular to a lithium manganese iron phosphate positive electrode material and a preparation method and application thereof. Background Art

[0002] As the energy crisis becomes increasingly serious, lithium-ion secondary batteries have been considered the most promising energy conversion and energy storage devices. x Fe 1-x PO4, LMFP) is widely used in the positive electrode 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 dissolved lithium, iron, manganese, and phosphorus sources in water and mixed them for subsequent sintering. The resulting LMFP has uneven distribution of Fe and Li elements, and other impurities remain, resulting in low element utilization. Other studies have also found that when adding iron and manganese sources during the grinding process, Fe and Mn diffuse into each other during the solid-phase sintering process to form a solid solution, making it difficult for the iron and manganese elements to be evenly distributed, resulting in an uneven ratio and affecting the stability of the structure. Therefore, how to improve the element uniformity in lithium manganese iron phosphate materials while ensuring their electrical properties is an urgent problem that needs to be solved.

[0004] Summary of the Invention

[0005] The present disclosure aims to solve at least one of the technical problems existing in the prior art. To this end, the present disclosure provides a method for preparing a lithium manganese iron phosphate positive electrode material.

[0006] The present disclosure also provides a lithium manganese iron phosphate positive electrode material prepared by the above preparation method.

[0007] The present disclosure also provides a positive electrode sheet comprising the above-mentioned lithium iron manganese phosphate positive electrode material.

[0008] The present disclosure also proposes the application of the above-mentioned lithium iron manganese phosphate positive electrode material or the above-mentioned positive electrode plate in the field of lithium-ion batteries.

[0009] According to the first embodiment of the present disclosure, a method for preparing a lithium manganese iron phosphate positive electrode material includes the following steps:

[0010] 1) pre-calcining ferromanganese hydroxide under an inert gas atmosphere to obtain ferromanganese oxide;

[0011] 2) preparing a slurry containing manganese iron oxide, a phosphorus source, a lithium source, and a carbon source, and drying the slurry to obtain a calcined precursor;

[0012] The carbon source has a content of 15 wt% to 40 wt% of the manganese iron oxide;

[0013] 3) calcining the calcined precursor under an inert gas atmosphere and first crushing it to obtain the lithium manganese iron phosphate positive electrode material;

[0014] The particle size Dv50 of the lithium manganese iron phosphate positive electrode material is 0.2 μm to 0.8 μm.

[0015] The preparation method according to the embodiment of the present disclosure has at least the following beneficial effects:

[0016] The preparation method of the embodiment can produce a lithium manganese iron phosphate cathode material with a more uniform element distribution and a more stable structure, and has a high element utilization rate. This preparation method is simple, uses a wide range of raw materials, is low-cost, does not require expensive and complex equipment or harsh reaction conditions, and is easily achievable for large-scale industrial production, thus having broad prospects for industrialization. The raw materials do not contain harmful substances, are environmentally friendly, and have excellent environmental performance.

[0017] The carbon source content is 15 wt% to 40 wt% of the manganese iron oxide. For example, it can be 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%. If the carbon source content is too high, more carbon molecules will remain on the material surface, resulting in an increased BET value for the lithium manganese iron phosphate cathode material.

[0018] According to some embodiments of the present disclosure, the particle size Dv50 of the slurry is 0.3 μm to 0.9 μm, for example, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm.

[0019] According to some embodiments of the present disclosure, the manganese iron hydroxide is Fe m Mn 1-m (OH)2;0.2≤m≤0.8.

[0020] According to some embodiments of the present disclosure, the ferromanganese 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 0.2At least one of (OH)2.

[0021] According to some embodiments of the present disclosure, the method for preparing manganese iron hydroxide comprises the following steps:

[0022] Under the action of antioxidants, alkaline precipitants and complexing agents, Fe 2+ With Mn 2+ Reaction to obtain the manganese iron hydroxide;

[0023] Fe 2+ With Mn 2+ The molar ratio is m:1-m; 0.2≤m≤0.8.

[0024] According to some embodiments of the present disclosure, the antioxidant includes at least one of sodium erythorbate, ascorbic acid, sodium ascorbate, and erythorbate.

[0025] According to some embodiments of the present disclosure, the concentration of the antioxidant is 1 mol / L to 3 mol / L, for example, 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.

[0026] According to some embodiments of the present disclosure, the alkaline precipitant includes sodium hydroxide.

[0027] According to some embodiments of the present disclosure, the concentration of the alkaline precipitant is 0.25 mol / L to 1 mol / L, for example, 0.25 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L or 1 mol / L.

[0028] According to some embodiments of the present disclosure, the complexing agent includes at least one of ethylenediaminetetraacetic acid, citric acid, oxalic acid, acetic acid, polyacrylic acid, and tartaric acid.

[0029] According to some embodiments of the present disclosure, the concentration of the complexing agent is 0.5 mol / L to 2 mol / L, for example, 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.

[0030] According to some embodiments of the present disclosure, the Fe 2+ Sources include ferrous sulfate.

[0031] According to some embodiments of the present disclosure, the Fe 2+The concentration is 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.

[0032] According to some embodiments of the present disclosure, the Mn 2+ The source includes at least one of manganese sulfate, manganese nitrate, and manganese chloride.

[0033] According to some embodiments of the present disclosure, the Mn 2+ The concentration is 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.

[0034] According to some embodiments of the present 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.

[0035] According to some embodiments of the present 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.

[0036] According to some embodiments of the present disclosure, the reaction time is 60 min to 100 min, for example, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min or 100 min.

[0037] According to some embodiments of the present disclosure, the reaction is carried out in an inert gas atmosphere.

[0038] According to some embodiments of the present disclosure, the inert gas includes at least one of nitrogen, helium, neon, argon, krypton, xenon, and radon.

[0039] According to some embodiments of the present disclosure, the solvent of the reaction is water.

[0040] According to some embodiments of the present 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.

[0041] According to some embodiments of the present disclosure, the pre-burning treatment time is 3 hours to 8 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours.

[0042] According to some embodiments of the present disclosure, in the slurry, the molar ratio of P:(Mn+Fe)=(1.01-1.1):1. For example, the molar ratio may 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 the present disclosure, in the slurry, the molar ratio of Li:P is (1.01-1.1):1. For example, the molar ratio may 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.

[0044] According to some embodiments of the present disclosure, the phosphorus source includes at least one of phosphoric acid, lithium dihydrogen phosphate, lithium phosphate, and potassium dihydrogen phosphate.

[0045] According to some embodiments of the present disclosure, the lithium source includes at least one of lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, and lithium hydroxide.

[0046] According to some embodiments of the present disclosure, the carbon source includes at least one of glucose, sucrose, polyethylene glycol (PEG), soy lecithin, and citric acid.

[0047] According to some embodiments of the present disclosure, the molecular weight of the polyethylene glycol is 1500 to 10000.

[0048] According to some embodiments of the present disclosure, in step S2, the slurry further includes a metal ion source. Metal ions can increase the + The diffusion rate of lithium manganese iron phosphate cathode material is improved.

[0049] According to some embodiments of the present disclosure, the metal ion source includes at least one of a Ti source, a V source, a Ni source, a Mg source, an Al source, a Sb source, a Cu source, a Zr source, and a Zn source.

[0050] According to some embodiments of the present disclosure, the Ti source includes titanium dioxide.

[0051] According to some embodiments of the present disclosure, the V source includes at least one of vanadyl oxalate, ammonium metavanadate, and vanadium pentoxide.

[0052] According to some embodiments of the present disclosure, the Ni source includes at least one of nickel oxide, nickel hydroxide, nickel dioxide, nickel trioxide, nickel nitrate, and nickel sulfate.

[0053] According to some embodiments of the present disclosure, the Mg source includes at least one of magnesium oxide and magnesium chloride.

[0054] According to some embodiments of the present disclosure, the Al source includes at least one of aluminum acetate and aluminum oxide.

[0055] According to some embodiments of the present disclosure, the Sb source includes at least one of antimony trioxide and antimony pentoxide.

[0056] According to some embodiments of the present disclosure, the Cu source includes at least one of copper carbonate, copper hydroxide, and copper oxide.

[0057] According to some embodiments of the present disclosure, the Zr source includes at least one of zirconium dioxide and zirconium hydroxide.

[0058] According to some embodiments of the present disclosure, the Zn source includes at least one of zinc oxide and zinc chloride.

[0059] According to some embodiments of the present disclosure, the doping amount of metal ions in the slurry is 300 ppm to 5000 ppm, for example, 300 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm or 5000 ppm.

[0060] According to some embodiments of the present disclosure, at least one of Ti, V, Ni, Mg, Al, Sb, Cu, Zr, and Zn is distributed on the surface or adjacent grain boundaries of the calcined precursor.

[0061] According to some embodiments of the present disclosure, the solvent of the slurry is water.

[0062] According to some embodiments of the present disclosure, preparing a slurry containing the ferromanganese oxide, a phosphorus source, a lithium source, and a carbon source includes:

[0063] After preparing a slurry containing the manganese iron oxide and the phosphorus source, the slurry is mixed with the lithium source and the carbon source.

[0064] According to some embodiments of the present disclosure, preparing a slurry containing the ferromanganese oxide, a phosphorus source, a lithium source, a carbon source, and a metal ion source includes:

[0065] After preparing a slurry containing the manganese iron oxide and the phosphorus source, the slurry is mixed with the lithium source, the carbon source and the metal ion source.

[0066] According to some embodiments of the present disclosure, the calcination temperature is 550°C to 750°C. For example, it may be 550°C, 575°C, 600°C, 625°C, 650°C, 675°C, 700°C, 725°C or 750°C.

[0067] According to some embodiments of the present disclosure, the calcination treatment time is 5 hours to 12 hours, for example, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours or 12 hours.

[0068] According to some embodiments of the present disclosure, the heating rate of the calcination process is 1-6°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, or 6°C / min.

[0069] According to some embodiments of the present disclosure, step 2) further includes performing a second crushing on the slurry.

[0070] According to some embodiments of the present disclosure, the first crushing and the second crushing each independently include at least one of sand milling, ball milling, roller milling, and pulverizing.

[0071] According to some embodiments of the present disclosure, the drying comprises spray drying.

[0072] A lithium manganese iron phosphate positive electrode material according to an embodiment of the second aspect of the present disclosure is prepared by the above preparation method.

[0073] The preparation method according to the embodiment of the present disclosure has at least the following beneficial effects:

[0074] The lithium manganese iron phosphate positive electrode material of the embodiment has good element distribution uniformity, excellent structural stability and outstanding electrochemical performance; and good energy density and cycle performance.

[0075] According to some embodiments of the present disclosure, the molecular formula of the lithium manganese iron phosphate positive electrode material is LiMn 1-x Fe x A z PO4;

[0076] Among them, 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.

[0077] According to some embodiments of the present disclosure, the residual lithium content on the surface of the lithium manganese iron phosphate positive electrode material is less than 700 ppm.

[0078] According to some embodiments of the present disclosure, the residual lithium content on the surface of the lithium iron manganese phosphate positive electrode material is 100 ppm to 660 ppm, for example, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 400 ppm, 500 ppm, or 600 ppm.

[0079] According to some embodiments of the present disclosure, the specific surface area (BET) of the lithium manganese iron phosphate cathode material is 5m 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.

[0080] According to some embodiments of the present disclosure, the powder resistivity of the lithium iron manganese phosphate cathode material at a pressure of 12 MPa is 10 Ω·cm to 700 Ω·cm. For example, the powder resistivity may 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.

[0081] According to some embodiments of the present disclosure, the compaction density of the lithium manganese iron phosphate positive electrode material under a pressure of 3000 kg is 1.9 g / m 3 ~2.5g / m 3 For example: it can be 1.9g / m 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 3, 2.4g / m 3 , 2.45g / m 3 or 2.5g / m 3 .

[0082] A positive electrode plate according to an embodiment of the third aspect of the present disclosure includes the above-mentioned lithium manganese iron phosphate positive electrode material.

[0083] According to the fourth aspect of the present disclosure, the lithium manganese iron phosphate positive electrode material or positive electrode plate is used in the field of lithium-ion batteries.

[0084] Other features and advantages of the present disclosure will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1A is a diagram of ferromanganese hydroxide Fe 0.4 Mn 0.6 SEM image of (OH)2 before calcination treatment;

[0086] Figure 1B shows the manganese iron hydroxide Fe 0.4 Mn 0.6 SEM image of (OH)2 after pre-calcination;

[0087] FIG2 is an XRD pattern of the lithium manganese iron phosphate positive electrode materials prepared in Example 1 and Comparative Example 1;

[0088] FIG3A is a SEM image of the lithium manganese iron phosphate positive electrode material prepared in Example 1;

[0089] FIG3B is a SEM image of the lithium manganese iron phosphate positive electrode material prepared in Comparative Example 1;

[0090] FIG4A is an elemental EDS diagram of the lithium manganese iron phosphate cathode material prepared in Example 1;

[0091] FIG4B is an elemental EDS diagram of the lithium manganese iron phosphate cathode material prepared in Comparative Example 1;

[0092] FIG5 is a graph showing the charge and discharge capacities of CR2016 batteries prepared using the lithium manganese iron phosphate positive electrode materials of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0093] The following will clearly and completely describe the concept and technical effects of the present disclosure in conjunction with embodiments to fully understand the purpose, features and effects of the present disclosure.

[0094] All reagents used without manufacturer indication are commercially available conventional products.

[0095] In the description of the present disclosure, the terms "comprises" and "has" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, or product that includes a series of steps or units is not necessarily limited to those steps or units expressly listed, but may include other steps or units not expressly listed or inherent to the process, method, or product.

[0096] 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 such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed in this disclosure are understood to include any and all subranges subsumed therein.

[0097] Unless otherwise specified, the chemical formula provided in the present disclosure is a chemical formula calculated based on the feed ratio. In fact, considering factors such as the burn-off of the lithium source, the atomic ratio in the actual manganese iron hydroxide or positive electrode material obtained may not be exactly the same as the ratio in the chemical formula.

[0098] In the embodiment of the present disclosure, manganese iron hydroxide Fe 0.4 Mn 0.6 The preparation method of (OH)2 is as follows:

[0099] 1) Mix ferrous sulfate (final concentration of 2.4 mol / L) and manganese sulfate (final concentration of 3.6 mol / L) in water. 2+ With Mn 2+ The molar ratio of is 4:6, and the mixture is stirred until dissolved to obtain a mixed solution I;

[0100] 2) adding an antioxidant (sodium isoascorbate, final concentration of 4 mol / L), an alkaline precipitant (sodium hydroxide, final concentration of 1 mol / L), and a complexing agent (ethylenediaminetetraacetic acid, final concentration of 2 mol / L) to water, stirring and mixing to obtain a mixed solution II;

[0101] 3) Pour 1000 mL of mixed solution II into the reactor under the stirring speed of 600 rpm, introduce nitrogen into the reactor to maintain the oxygen concentration below 100 ppm, and then slowly add 1000 mL of mixed solution I; maintain the pH value of the reactor liquid at 12.0 and the temperature at 60°C, react for 80 minutes, wash the reactants, and dry them to obtain manganese iron hydroxide Fe 0.4 Mn 0.6 (OH)2.

[0102] Manganese iron hydroxide Fe 0.2 Mn0.8 (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 Preparation method of (OH)2, adapting to adjust Fe in mixed solution I 2+ With Mn 2+ The molar ratio can be.

[0103] Example 1

[0104] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material, the steps are as follows:

[0105] 1) Under nitrogen atmosphere, manganese iron hydroxide Fe 0.4 Mn 0.6 (OH)2 was pre-calcined at 650℃ for 5h to obtain manganese iron oxide, and the Fe content was detected to be 28.12wt% and the Mn content was 40.45wt%.

[0106] 2) Weigh 1500 g of the manganese iron oxide from step 1) and add it to 6 L of water. Then, add 1972.29 g of lithium dihydrogen phosphate, 21.03 g of lithium carbonate, 14.71 g of titanium dioxide, 150 g of PEG 6000, and 90 g of glucose in that order. After mixing evenly, the slurry is sand-milled to a particle size Dv50 of 0.38 μm. After reaching the required particle size, spray drying is performed to obtain a calcined precursor.

[0107] Wherein, in terms of molar ratio, P:(Mn+Fe)=1.02:1; Li:P=1.03:1;

[0108] The amount of carbon source used is 16 wt% of the manganese iron oxide.

[0109] 3) Under nitrogen atmosphere, the precursor was calcined at 680 ° C for 7 h, with a heating time of 328 min and a heating rate of 2 ° C / min; after cooling naturally to room temperature, the material was crushed to a Dv50 of 0.4 μm to obtain lithium manganese iron phosphate positive electrode material LiMn 0.6 Fe 0.4 Ti 0.01 PO4 / C.

[0110] Example 2

[0111] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that in step 2) of this example, the molar ratio is P:(Mn+Fe)=1.01:1.

[0112] Example 3

[0113] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that in step 2) of this example, the molar ratio is P:(Mn+Fe)=1.05:1.

[0114] Example 4

[0115] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that in step 2) of this example, the molar ratio is P:(Mn+Fe)=1.1:1.

[0116] Example 5

[0117] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that in step 2), the sanding particle size Dv50 is replaced from 0.38 μm to 0.1 μm.

[0118] Example 6

[0119] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that: in step 2), the sanding particle size Dv50 is changed from 0.38 μm to 1.0 μm.

[0120] Example 7

[0121] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that in step 2), the sanding particle size Dv50 is replaced from 0.38 μm to 1.5 μm.

[0122] Example 8

[0123] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that in step 3), the crushing particle size Dv50 is replaced from 0.4 μm to 0.2 μm.

[0124] Example 9

[0125] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material, the steps are as follows:

[0126] 1) Under nitrogen atmosphere, manganese iron hydroxide Fe 0.2 Mn 0.8(OH)2 was pre-calcined at 350℃ for 8h to obtain manganese iron oxide, and the Fe content was detected to be 14.82wt% and the Mn content was 56.64wt%.

[0127] 2) Weigh 1257.52 g of phosphoric acid and add it to 6 L of water. Then, add 1500 g of the manganese iron oxide from step 1), 788.42 g of lithium phosphate, 15.58 g of magnesium oxide, 14.44 g of nickel oxide, 120 g of PEG 1500, 80 g of glucose, and 40 g of citric acid in that order. After mixing thoroughly, the slurry is sand-milled to a particle size Dv50 of 0.1 μm. After reaching the required particle size, the slurry is spray-dried to obtain a calcined precursor.

[0128] Wherein, in terms of molar ratio, P:(Mn+Fe)=1.01:1; Li:P=1.04:1;

[0129] The carbon source content is 16 wt% of the manganese iron oxide.

[0130] 3) Under nitrogen atmosphere, the precursor was calcined at 550 ° C for 12 h, with a heating time of 106 min and a heating rate of 5 ° C / min; after cooling naturally to room temperature, the material was crushed to a Dv50 of 0.4 μm to obtain lithium manganese iron phosphate positive electrode material LiMn 0.8 Fe 0.2 PO4Mg 0.02 Ni 0.01 / C.

[0131] Example 10

[0132] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 9, with the only difference being that in step 2) of this example, the molar ratio of Li:P is 1.03:1.

[0133] Example 11

[0134] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 9, with the only difference being that in step 2) of this example, the molar ratio of Li:P is 1.1:1.

[0135] Example 12

[0136] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 9, with the only difference being that in step 2) of this example, the molar ratio of Li:P is 1.01:1.

[0137] Example 13

[0138] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material, the steps are as follows:

[0139] 1) Under nitrogen atmosphere, manganese iron hydroxide Fe 0.6 Mn 0.4 (OH)2 was pre-calcined at 750℃ for 3h to obtain manganese iron oxide, with the measured Fe content being 40.6wt% and the Mn content being 26.97wt%.

[0140] 2) 1826.87 g of phosphoric acid was weighed and added to 6 L of water. Then, 1500 g of the manganese iron oxide from step 1), 28.53 g of vanadyl oxalate, 708.41 g of lithium carbonate, 200 g of PEG 10000, 100 g of soy lecithin, and 75 g of glucose were added in that order. After uniform mixing, 25 wt% of the slurry was sand-milled to a particle size Dv50 of 1.5 μm, and 75 wt% of the slurry was sand-milled to a particle size Dv50 of 0.4 μm. After the material reached the required particle size, it was spray-dried to obtain a calcined precursor.

[0141] Wherein, in terms of molar ratio, P:(Mn+Fe)=1.02:1; Li:P=1.0.3:1;

[0142] The carbon source content is 25 wt% of the manganese iron oxide.

[0143] 3) Under nitrogen atmosphere, the calcined precursor was calcined at 750 ° C for 5 h, with a heating time of 120 min and a heating rate of 6 ° C / min; after cooling naturally to room temperature, the material was crushed to a Dv50 of 0.4 μm to obtain lithium manganese iron phosphate positive electrode material LiMn 0.4 Fe 0.6 PO4V 0.01 / C.

[0144] Example 14

[0145] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 13, with the only difference being that in step 3), the calcination temperature of 750°C is replaced with 680°C.

[0146] Example 15

[0147] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 13, with the only difference being that in step 3), the calcination temperature of 750°C is replaced with 550°C.

[0148] Example 16

[0149] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 13, with the only difference being that in step 3), the calcination time of 5 h is replaced with 8 h.

[0150] Example 17

[0151] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 13, with the only difference being that in step 3), the calcination time of 5 h is replaced with 12 h.

[0152] Example 18

[0153] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 13, with the only difference being that in step 3), the heating rate of 6°C / min is replaced with 4°C / min.

[0154] Example 19

[0155] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 13, with the only difference being that in step 3), the heating rate of 6°C / min is replaced with 1°C / min.

[0156] Example 20

[0157] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material, the steps are as follows:

[0158] 1) Under nitrogen atmosphere, manganese iron hydroxide Fe 0.8 Mn 0.2 (OH)2 was pre-calcined at 650℃ for 5h to obtain manganese iron oxide, and the Fe content was detected to be 58.63wt% and the Mn content was 14.81wt%.

[0159] 2) Weigh 1959.20 g of phosphoric acid and add it to 6 L of water. Then, add 1500 g of the manganese iron oxide from step 1), 760.80 g of lithium carbonate, 160 g of PEG 6000, and 80 g of glucose in that order. After mixing thoroughly, the slurry is sand-milled to a particle size Dv50 of 0.5 μm. After the particle size reaches the specified value, the material is spray-dried to obtain a calcined precursor.

[0160] Wherein, in terms of molar ratio, P:(Mn+Fe)=1.01:1; Li:P=1.03:1;

[0161] The carbon source content is 16 wt% of the manganese iron oxide.

[0162] 3) Under nitrogen atmosphere, the precursor was calcined at 680 ° C for 8 h, with a heating time of 328 min and a heating rate of 2 ° C / min; after cooling naturally to room temperature, the material was crushed to a Dv50 of 0.8 μm to obtain lithium manganese iron phosphate positive electrode material LiMn 0.8 Fe 0.2 PO4 / C.

[0163] Example 21

[0164] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 20, with the only difference being that in step 2), the carbon source content of 16 wt% is replaced with 30 wt%.

[0165] Example 22

[0166] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 20, with the only difference being that in step 2), the carbon source content of 16 wt% is replaced with 40 wt%.

[0167] Example 23

[0168] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 20, with the only difference being that in this example, the order of adding the raw materials in step 2) is S-iron manganese hydroxide, lithium carbonate, phosphoric acid, PEG 6000, and glucose.

[0169] Comparative Example 1

[0170] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material, the steps are as follows:

[0171] 1) 825 g of manganese carbonate was weighed and added to 6 L of water. 688.32 g of ferrous oxalate, 1268.55 g of lithium dihydrogen phosphate, 13.53 g of lithium carbonate, 14.71 g of titanium dioxide, 151.3 g of PEG 6000, and 90.9 g of glucose were then added in that order. After mixing thoroughly, the slurry was sand-milled to a particle size of 0.38 μm. After reaching the required particle size, the slurry was spray-dried to obtain a calcined precursor.

[0172] Wherein, in terms of molar ratio, P:(Mn+Fe)=1.02:1; Li:P=1.03:1;

[0173] The carbon source content is 16 wt % of the Mn source and the Fe source.

[0174] 2) Under nitrogen atmosphere, the precursor was calcined at 680 ° C for 7 h, with a heating time of 328 min and a heating rate of 2 ° C / min; after cooling naturally to room temperature, the material was crushed to a Dv50 of 0.4 μm to obtain lithium manganese iron phosphate positive electrode material LiMn 0.6 Fe 0.4 Ti 0.01 PO4 / C.

[0175] Comparative Example 2

[0176] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material, the steps are as follows:

[0177] 1) 1200 g of manganese oxalate was weighed and added to 6 L of water. 316.48 g of ferric phosphate, 832.94 g of phosphoric acid, 407.22 g of lithium carbonate, 15.58 g of magnesium oxide, 14.44 g of nickel oxide, 121.32 g of PEG 1500, 80.87 g of glucose, and 40.43 g of citric acid were then added in sequence. After uniform mixing, the slurry was sand-milled to a Dv50 of 0.1 μm. After reaching the required particle size, the slurry was spray-dried to obtain a calcined precursor.

[0178] Wherein, in terms of molar ratio, P:(Mn+Fe)=1.01:1; Li:P=1.04:1;

[0179] The carbon source content is 16 wt % of the Mn source and the Fe source.

[0180] 2) Under nitrogen atmosphere, the precursor was calcined at 550 ° C for 12 hours, with a heating time of 106 minutes and a heating rate of 5 ° C / min; after cooling naturally to room temperature, the material was crushed to a Dv50 of 0.4 μm to obtain lithium manganese iron phosphate positive electrode material LiMn 0.8 Fe 0.2 PO4Mg 0.02 Ni 0.01 / C.

[0181] Comparative Example 3

[0182] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material, the steps are as follows:

[0183] 1) 513.14 g of phosphoric acid was weighed and added to 6 L of water. 380 g of manganese tetraoxide, 1127.10 g of ferric phosphate, 483.65 g of lithium carbonate, 28.53 g of vanadyl oxalate, 200.95 g of PEG 10000, 100.476 g of soy lecithin, and 75.35 g of glucose were then added in that order. After uniform mixing, 25 wt% of the slurry was sand-milled to a particle size of 1.5 μm, and 75 wt% of the slurry was sand-milled to a particle size of 0.4 μm. After the particle size reached the required standard, the slurry was spray-dried to obtain a calcined precursor.

[0184] Wherein, in terms of molar ratio, P:(Mn+Fe)=1.02:1; Li:P=1.0.3:1;

[0185] The content of carbon source, Mn source and Fe source is 25 wt%.

[0186] 2) Under nitrogen atmosphere, the precursor was calcined at 750 ° C for 5 h, with a heating time of 120 min and a heating rate of 6 ° C / min; after cooling naturally to room temperature, the material was crushed to a Dv50 of 1.8 μm to obtain lithium manganese iron phosphate positive electrode material LiMn 0.4 Fe 0.6 PO4V0.01 / C.

[0187] Comparative Example 4

[0188] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that step 1 is omitted.

[0189] Comparative Example 5

[0190] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that in step 1), the nitrogen atmosphere is replaced with an air atmosphere.

[0191] Comparative Example 6

[0192] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that in step 3), the crushing particle size Dv50 is replaced from 0.4 μm to 1.0 μm.

[0193] Comparative Example 7

[0194] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 1, with the only difference being that: in step 3), the crushing particle size Dv50 is replaced from 0.4 μm to 1.8 μm.

[0195] Comparative Example 8

[0196] This example provides a method for preparing a lithium manganese iron phosphate positive electrode material. The steps are basically the same as those in Example 20, with the only difference being that in step 2), the carbon source content of 16 wt% is replaced with 10 wt%.

[0197] Test example

[0198] 1. The powder resistivity, specific surface area, compacted density, and residual lithium of the lithium manganese iron phosphate positive electrode materials prepared in Examples 1 to 23 and Comparative Examples 1 to 8 were tested. The test methods are as follows:

[0199] (1) Powder resistivity:

[0200] The powder resistivity of the lithium iron phosphate cathode material was measured using a four-probe powder resistivity meter. 2.40g of lithium iron phosphate cathode material was weighed and placed in a mold. The mold was adjusted to a height of 20mm and compacted using a pressure of 12MPa. The data was then collected. The formula for calculating the powder resistivity is as follows:

[0201] Where: ρ1 is the powder resistivity, C is the probe spacing correction factor, is the height correction coefficient (determined according to the values ​​of W and S), is the shape and position correction coefficient (determined according to the values ​​of d and S), W is the powder compaction height, S is the distance between two adjacent needles of the four-probe, and d is the cross-sectional area of ​​the powder cavity.

[0202] (2)BET:

[0203] The specific surface area of ​​lithium iron manganese phosphate cathode material was measured using a Micromeritics TriStar II 3020 instrument. An empty tube was weighed, then loaded with 10.00g of lithium iron manganese phosphate cathode material. After degassing at 150°C for 1.5 hours, the tube containing the sample was placed in the test station and measured for approximately 90 minutes, with the experimental data recorded.

[0204] (3) Compacted density:

[0205] The compaction density of the lithium manganese iron phosphate cathode material was tested using a powder compaction density meter. 5.50g of lithium manganese iron phosphate cathode material was weighed and placed in a mold. A pressure of 3000kg was applied. After the test, the mold was removed and data was collected. The compaction density was calculated as follows:

[0206] Where: ρ2 is the compaction density, m is the sample mass, D is the mold diameter, and h is the compaction height.

[0207] (4) Residual lithium:

[0208] Residual lithium was tested using a Mettler T5 automatic potentiometric titrator. 30.00g of lithium iron manganese phosphate cathode material was weighed and placed into a 250mL stoppered conical flask containing 100g of deionized water. After stirring for 30 minutes, the mixture was filtered under reduced pressure (with a 0.45μm pore size filter membrane). 20mL of the filtrate was titrated with 0.05mol / L HCl and NaCO3 standard solutions. After the titration, the data was read. The detection principle is as follows:

[0209] OH - +H + =H2O;CO3 2- +H + =HCO3 - ;HCO3 - +H + =H2O+CO2↑.

[0210] The sudden jump of electrode potential indicates the endpoint of titration: before and after the titration reaches the endpoint, the concentration of the ion to be measured in the droplet will continuously change by n orders of magnitude, causing a sudden jump in potential. The content of the measured component is calculated by the amount of titrant consumed.

[0211] The test results are shown in Table 1.

[0212] Table 1

[0213] 2. The lithium manganese iron phosphate cathode materials prepared in Examples 1 to 23 and Comparative Examples 1 to 8 were used to prepare CR2016 batteries, and their electrical properties were tested. The CR2016 battery preparation method is as follows:

[0214] Dissolve 19.2g of lithium manganese iron phosphate positive electrode material, 0.4g of acetylene black, and 0.4g of polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) in a mass ratio of 96:2:2, mix and stir to obtain a positive electrode material slurry. Apply the positive electrode material slurry evenly on aluminum foil with a coating amount of 1.45g / cm 2 The sample was then dried in a drying oven at 85°C for 1 hour, hot-pressed, cooled, and cut into 12 cm long positive electrode sheets using a sheet puncher. In a glove box, the positive electrode, separator (12 μm thick polypropylene), negative lithium sheet, and LiPF6 electrolyte were assembled into a CR2016 battery.

[0215] The electrical performance test method is as follows:

[0216] At a constant temperature of 25°C, charge the battery at 2V to 4.2V at 0.1C to 4.3V, then charge at 4.3V at a constant voltage until the current is ≤ 0.05mA, let it stand for 5 minutes, and then discharge it at 0.1C to 2V, and record the battery capacity.

[0217] Under a constant temperature environment of 25℃, charge the battery to full charge at a constant current and constant voltage of 1C and 4.3V, let it stand for 5 minutes, then discharge it to 2V at a constant current of 1C, let it stand for 5 minutes, and perform the next cycle charge and discharge process in the same way. After 100 cycles, record the battery capacity at different cycle numbers and take the average value to calculate the average battery capacity and capacity retention rate.

[0218] The test results are shown in Table 2.

[0219] Table 2

[0220] The prepared manganese iron hydroxide is mainly granular with burrs, and the internal connection of the particles is tight, and the flaky grains are disorderly stacked, which can effectively alleviate the shortcomings of the spherical particles that are easily broken during the latter sintering process, thereby making the prepared positive electrode material have higher structural stability, energy density and cycle performance. After the manganese iron hydroxide is pre-burned, the burrs on the surface of the material are significantly reduced and become smoother, which is conducive to reducing the specific surface area of ​​the subsequent finished product. As shown in Figures 1A and 1B. The specific capacity of the lithium manganese iron phosphate positive electrode material (Example 1) prepared from the pre-burned manganese iron hydroxide is higher than that of the lithium manganese iron phosphate positive electrode material (Comparative Example 4) prepared from the manganese iron hydroxide that has not been pre-burned, and the BET is lower.

[0221] The performance of the lithium iron manganese phosphate positive electrode material (Example 1) obtained by pre-calcining iron manganese hydroxide in nitrogen is better than that of the lithium iron manganese phosphate positive electrode material (Comparative Example 5) obtained by pre-calcining in air. This may be because pre-calcining in air easily generates Mn2O3 and Fe2O3, rather than manganese-iron polymers of FeMnO3, which affects the performance of the positive electrode material. In the range of P:(Mn+Fe)=(1~1.05):1 (Examples 1~4), with the increase of P content, the specific capacity of the lithium iron manganese phosphate positive electrode material first increases and then decreases, and the BET can be reduced. In the range of Li:P=(1.01~1.1), with the increase of Li content, BET will deteriorate, but the capacity will increase. With the increase of carbon content, the capacity and first effect of the lithium iron manganese phosphate positive electrode material will improve, but the BET will be deteriorated. The higher the sintering temperature and time of the lithium iron manganese phosphate positive electrode material, the lower the powder resistivity.

[0222] XRD results show that both Comparative Example 1 and Example 1 successfully synthesized lithium manganese iron phosphate (as shown in Figure 2). Comparing the SEM and EDS images of Example 1 and Comparative Example 1 (Figures 3A, 3B, 4A, and 4B), at the same sintering temperature, the lithium manganese iron phosphate positive electrode 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 positive electrode material of Comparative Example 1 has different particle shapes, and the overall distribution of Mn element is relatively concentrated.

Claims

1. A preparation method of a lithium iron manganese phosphate cathode material, characterized in that, It includes the following steps: 1) Under an inert gas atmosphere, pre-calcine manganese iron hydroxide to obtain manganese iron oxide; 2) Prepare a slurry containing manganese iron oxide, phosphorus source, lithium source, and carbon source, and dry it to obtain a calcination precursor; The content of the carbon source is 15wt% - 40wt% of the manganese iron oxide; 3) Under an inert gas atmosphere, calcine the calcination precursor, and perform the first crushing to obtain the lithium iron phosphate manganese cathode material; The particle size Dv50 of the lithium iron phosphate manganese cathode material is 0.2μm - 0.8μm.

2. The preparation method according to claim 1, characterized in that, The manganese iron hydroxide is Fe m Mn 1-m (OH)2; 0.2 ≤ m ≤ 0.8; And / or, 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, The temperature of the pre-calcination treatment is 350°C - 750°C.

4. The preparation method according to claim 1, wherein The time of the pre-calcination treatment is 3h - 8h.

5. The preparation method according to claim 1, wherein In the slurry, in terms of molar ratio, P:(Mn + Fe) = (1.01 - 1.1):1; And / or, in the slurry, in terms of molar ratio, Li:P = (1.01 - 1.1):

1.

6. The preparation method according to claim 1, wherein, The temperature of the calcination treatment is 550°C - 750°C.

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

8. The preparation method according to claim 1, characterized in that In the step S2, the slurry further includes a metal ion source.

9. The preparation method according to claim 8, wherein 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.

10. The preparation method according to claim 1, characterized in that, Preparing the slurry containing the manganese iron oxide, phosphorus source, lithium source, and carbon source includes: After preparing the slurry containing the manganese iron oxide and phosphorus source, mix it with the lithium source and the carbon source.

11. The preparation method according to claim 1, characterized in that, The heating rate of the calcination treatment is 1 - 6°C / min.

12. A lithium iron manganese phosphate cathode material, characterized in that, Prepared by the preparation method according to any one of claims 1 to 11.

13. The lithium iron manganese phosphate cathode material according to claim 12, wherein The residual lithium content on the surface of the lithium iron phosphate manganese cathode material is less than 700ppm; and / or, the BET of the lithium iron manganese phosphate cathode material is 5 m 2 / g to 20 m 2 / g; And / or, the powder resistivity of the lithium iron phosphate manganese cathode material under a pressure of 12MPa is 10Ω·cm - 700Ω·cm; And / or, the tap density of the lithium iron manganese phosphate cathode material under a pressure of 3000 kg is 1.9 g / m 3 ~2.5 g / m 3 .

14. A positive electrode plate, characterized in that, It includes the lithium iron phosphate manganese cathode material according to claim 12 or 13.

15. The application of the lithium iron phosphate manganese cathode material according to claim 12 or 13, or the positive electrode sheet according to claim 14 in the field of lithium ion batteries.

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