High-performance lithium manganese iron phosphate precursor, preparation method of lithium manganese iron phosphate cathode material and battery using this cathode material

Abstract

A high-performance lithium manganese iron phosphate precursor, a method for preparing lithium manganese iron phosphate cathode material, and a battery using the cathode material are disclosed. The precursor has the formula MnxFe. 1‑x (HPO4) y (P2O7) (1‑y) / 2 Where 0.5≤x<1, 0≤y≤1, it is obtained by pre-sintering manganese iron ammonium phosphate monohydrate at 300~800℃ under an inert atmosphere. The preparation method of lithium manganese iron phosphate cathode material is as follows: the pre-sintered precursor is mixed with lithium source, carbon source and dopant element, and sintered at high temperature under an inert atmosphere to obtain carbon-coated lithium manganese iron phosphate cathode material. In this invention, after pre-sintering manganese iron ammonium phosphate monohydrate, ammonia and water of crystallization are removed, so that a porous structure is formed inside the pre-sintered product, which is conducive to the diffusion of lithium during mixed lithium sintering, thereby improving the lithium ion insertion / extraction rate in lithium manganese iron phosphate cathode material, so that the cathode material has the characteristics of high capacity and excellent rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a high-performance lithium manganese iron phosphate precursor, a method for preparing lithium manganese iron phosphate cathode material, and a battery using the cathode material. Background Technology

[0002] Lithium manganese iron phosphate (LMFP) is a solid solution of lithium manganese phosphate (LFP) and lithium manganese phosphate (LiMnPO4, LMP). LMFP can maintain the discharge time of LFP (171 mAh / g) while increasing the discharge voltage (from 3.4V to about 4.1V), thereby improving the energy density (up to 21%). Currently, LMFP has entered the market for small-powered two-wheeled and three-wheeled vehicles, mainly for use in ternary lithium batteries to improve the safety performance and reduce the cost of ternary batteries. In the future, if the voltage instability of LMFP batteries can be fundamentally resolved, LMFP batteries are expected to be widely used in electric vehicles, and may even replace LFP batteries in the future.

[0003] While LMFPs offer higher energy density and higher operating voltage compared to LFPs, they suffer from lower electronic conductivity, lower lithium-ion diffusion rate, lower compaction density, and reduced energy density utilization. 3+ The John-Teller effect leads to manganese leaching and other issues. The conductivity of LMFP cathode materials is relatively simple, and most companies in the industry have already solved it. Other issues such as dual voltage, specific capacity, and cycle life have been addressed by some leading companies in the industry. The manganese precipitation problem caused by the John-Teller effect is the biggest challenge, and the industry is working on breakthroughs, with a few companies making progress. The performance of LMFP cathode materials is highly dependent on their overall properties, mainly including phase transition, lattice distortion, point defects, Mn / Fe ratio, particle morphology, and elemental doping. To obtain high-performance LMFP cathode materials, in-depth exploration of how material properties affect electrical properties is of great significance.

[0004] The main methods for industrial-scale production of LMFP include solid-state methods, co-precipitation methods, and hydrothermal methods. Solid-state methods suffer from poor material stability and limited performance improvement due to the inability to achieve atomic-level homogeneous mixing. Hydrothermal methods require sophisticated equipment and suffer from cumbersome operations, high energy consumption, and low production capacity. The co-precipitation method first synthesizes the manganese iron phosphate precursor using a wet process, and then mixes and sintersects it with a lithium source. This route achieves atomic-level homogeneous mixing of manganese, iron, and phosphorus elements, while also offering mild synthesis conditions, simple operation, high production capacity, and stable product quality. Currently, the main precursor for preparing manganese iron phosphate using the co-precipitation method is manganese iron phosphate (Mn). x Fe 1-x PO4·H2O and ferric ammonium manganese phosphate NH4Mn x Fe1-x There are two forms, PO4·H2O, in which manganese iron phosphate (Mn) is produced. x Fe 1-x In the PO4·H2O precursor, both Mn and Fe are trivalent. Since +3 valent Mn is extremely unstable, during the drying and decrystalline water process, +3 valent Mn decomposes into +2 valent Mn, while +3 valent Fe remains stable, resulting in phase separation and a decrease in the performance of the cathode sintering material. (The last part, "manganese iron ammonium phosphate NH4Mn," appears to be an unrelated fragment and is omitted from the translation.) x Fe 1-x In PO4·H2O, both Mn and Fe are in the +2 oxidation state, which is stable. During decrystallization, the transformation of these two elements is simultaneous, and phase separation does not occur. However, in ammonium manganese phosphate (NH4Mn),... x Fe 1-x PO4.H2O contains ammonium ions. When used directly as a precursor, it releases a large amount of ammonia gas during the mixing and milling process with lithium source. This not only causes waste gas treatment problems for cathode material manufacturers, but also leads to a decrease in the compaction density and electrical performance of cathode materials.

[0005] Therefore, how to overcome the shortcomings of the existing technology is the subject of this invention. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance lithium manganese iron phosphate precursor, a method for preparing lithium manganese iron phosphate cathode material, and a battery using the cathode material.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A high-performance lithium manganese iron phosphate precursor, with the formula Mn x Fe 1-x (HPO4) y (P2O7) (1-y) / 2 , where 0.5≤x<1, 0≤y≤1, is prepared by sintering manganese iron ammonium phosphate monohydrate at 300~800℃.

[0009] A further technical solution, the preparation method of which includes:

[0010] Step 1: Add the phosphorus source solution, the mixed salt solution containing metallic manganese and iron, and the ammonia solution to the reaction vessel to obtain the manganese iron ammonium monohydrate precipitate.

[0011] Step 2: The prepared manganese iron ammonium phosphate monohydrate precipitate is subjected to solid-liquid separation, washing and drying to obtain manganese iron ammonium phosphate monohydrate powder;

[0012] Step 3: Place the manganese iron ammonium phosphate monohydrate powder obtained in Step 2 into a sintering furnace for sintering to obtain the high-performance manganese iron lithium phosphate precursor.

[0013] A further technical solution is that the expression for the manganese iron ammonium phosphate monohydrate is NH4Mn x Fe 1-x PO4·H2O, and 0.5≤x<1, wherein the molar ratio of the metal element (Mn+Fe) to the element P is 0.95~1.05.

[0014] In a further technical solution, in step one, inert gas or nitrogen is continuously introduced into the reaction vessel, the reaction temperature is 20-70℃, the stirring speed is 300-900 rpm, and the pH value of the reaction process is adjusted by controlling the flow rate of ammonia water to maintain the pH at 4-7.

[0015] In a further technical solution, in step one, the concentration of the phosphorus source solution is 1-4 mol / L, and the phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate, and trisodium phosphate.

[0016] The concentration of the mixed manganese and iron salt solution is 0.5–3 mol / L. The manganese source is at least one of manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride; the iron source is at least one of ferrous sulfate, ferric nitrate, ferric acetate, and ferric chloride.

[0017] A further technical solution involves drying at a temperature of 60–150°C in step two.

[0018] In a further technical solution, the sintering time in step three is 4–15 hours.

[0019] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0020] A method for preparing lithium manganese iron phosphate cathode material involves mixing the precursor with a lithium source, a carbon source, and doping elements, and then sintering the mixture at high temperature under an inert atmosphere to obtain carbon-coated lithium manganese iron phosphate cathode material.

[0021] In a further technical solution, the lithium source is at least one of lithium hydroxide and lithium carbonate; the coated carbon source is one or more of sucrose, glucose, polyethylene glycol, carbon black, graphene, polyvinyl alcohol, polyacryl alcohol, citric acid, cellulose, starch, dextrin, fructose, lactose, maltose, oxalic acid, and ascorbic acid.

[0022] A further technical solution is to use at least one of nitrogen or argon as the inert atmosphere, the high-temperature sintering temperature as 400–1000℃, and the sintering time as 6–20h.

[0023] A further technical solution is proposed, where the cathode material is expressed as Li. y Mn x-z Fe 1-x M zPO4 / C; where 0.5≤x<1, 0.99≤y≤1.10, 0.1≤z≤1, and M is the dopant element.

[0024] In a further technical solution, the doping element M is at least one of Mg, Ni, Co, Cu, Zn, and Ti.

[0025] The present invention further protects a battery made using the above-mentioned carbon-coated lithium manganese iron phosphate cathode material, wherein the carbon-coated lithium manganese iron phosphate cathode material uses a lithium manganese iron phosphate precursor prepared by the above method as a manganese iron source material.

[0026] The working principle and advantages of this invention are as follows:

[0027] This invention removes ammonia and water of crystallization after pre-sintering manganese iron ammonium phosphate monohydrate. The removal of ammonium ions and water of crystallization creates a porous structure inside the pre-sintered product, which facilitates lithium diffusion during mixed lithium sintering. This improves the lithium ion insertion / extraction rate in the lithium manganese iron ammonium phosphate cathode material, resulting in cathode materials with high capacity and excellent rate performance.

[0028] This invention involves pre-calcining manganese iron ammonium phosphate monohydrate to remove ammonium and water of crystallization, and then further increasing the degree of pre-calcination to form a new phase as a precursor. The new phase product is pyrophosphate, whose elemental composition is consistent with that of lithium manganese iron phosphate except for lithium, and it contains no other impurity elements. This invention can prepare high-purity and high-performance lithium manganese iron phosphate cathode materials.

[0029] Pre-sintering manganese iron ammonium phosphate monohydrate completely removes impurity elements N and H, increasing the metal content in the precursor by more than 9%, which can effectively improve the production capacity of lithium manganese iron phosphate cathode materials. Attached Figure Description

[0030] Figure 1A The unsintered NH4Mn of this invention 0.6 Fe 0.4 SEM image 1 of PO4.H2O precursor (raw material);

[0031] Figure 1B The unsintered NH4Mn of this invention 0.6 Fe 0.4 SEM of PO4.H2O precursor (raw material) Figure 2 ;

[0032] Figure 2 The unsintered NH4Mn of this invention 0.6 Fe 0.4 XRD pattern of PO4.H2O precursor (raw material);

[0033] Figure 3AThe amorphous Mn after pre-sintering in Example 1 of this invention 0.6 Fe 0.4 SEM image of HPO4 precursor 1;

[0034] Figure 3B The amorphous Mn after pre-sintering in Example 1 of this invention 0.6 Fe 0.4 SEM of HPO4 precursor Figure 2 ;

[0035] Figure 4 The amorphous Mn after pre-sintering in Example 1 of this invention 0.6 Fe 0.4 XRD pattern of HPO4 precursor;

[0036] Figure 5A The (Mn) after pre-sintering in Example 2 of this invention 0.6 Fe 0.4 SEM image of the 2P2O7 precursor;

[0037] Figure 5B The (Mn) after pre-sintering in Example 2 of this invention 0.6 Fe 0.4 SEM of 2P2O7 precursor Figure 2 ;

[0038] Figure 6 The (Mn) after pre-sintering in Example 2 of this invention 0.6 Fe 0.4 XRD pattern of the 2P2O7 precursor;

[0039] Figure 7A Here is a SEM image of the lithium iron phosphate cathode material prepared in Example 1 of this invention;

[0040] Figure 7B SEM image of the lithium manganese iron phosphate cathode material prepared in Example 1 of this invention. Figure 2 . Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0042] The present invention will be clearly described below with illustrations and detailed description. Any person skilled in the art who understands the embodiments of the present invention can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0043] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” and “having,” as used herein, are open-ended, meaning they include, but are not limited to, specific embodiments of the same.

[0044] Unless otherwise specified, the terms used herein generally have their ordinary meaning in the context of the art, the subject matter, and the specific context. Certain terms used to describe this case will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing this case.

[0045] Example 1:

[0046] Step 1: Take 1 kg of NH4Mn 0.6 Fe 0.4 The PO4·H2O precursor was sintered in a box furnace at 300°C for 6 hours, with a small amount of compressed air continuously introduced during the sintering process, yielding 810 g of amorphous Mn. 0.6 Fe 0.4 HPO4 precursor.

[0047] Step 2: Pre-sinter the material from Step 1 to obtain 810g of amorphous Mn. 0.6 Fe 0.4 HPO4 precursor, 206g lithium carbonate, 13.4g PEG8000 and 83.7g glucose were added to 1500g deionized water and ground for 2-6 hours. After the particle size was less than 0.5 microns, the slurry was spray-dried. After drying, the sprayed material was placed in a nitrogen atmosphere furnace and heated to 700℃ at a heating rate of 5℃ / min and calcined at a constant temperature for 12 hours. Then it was cooled to room temperature to obtain sintered material. The sintered material was crushed to obtain carbon-coated lithium manganese iron phosphate cathode material.

[0048] In Example 1, the compaction density of the carbon-coated lithium manganese iron phosphate cathode material powder is 2.1 g / cm³. 3 The coin cell has a discharge capacity of 150.7 mAh / g at 0.1C and 146.9 mAh / g at 1.0C.

[0049] Example 2:

[0050] Step 1: Take 1 kg of NH4Mn 0.6 Fe 0.4 The PO4·H2O precursor was sintered in a box furnace at 800℃ for 6 hours, with nitrogen continuously introduced during the sintering process, yielding 760g of (Mn) 0.6 Fe 0.4 )2P2O7 precursor.

[0051] Step 2: Pre-sinter the material from Step 1 to obtain 760g (Mn) 0.6 Fe 0.42P2O7 precursor, 206g lithium carbonate, 13.4g PEG8000 and 83.7g glucose were added to 1500g deionized water and ground for 2-6 hours. After the particle size was less than 0.5 micrometers, the slurry was spray-dried. After drying, the sprayed material was placed in a nitrogen atmosphere furnace and heated to 700℃ at a heating rate of 5℃ / min and calcined at a constant temperature for 12 hours. Then it was cooled to room temperature to obtain sintered material. The sintered material was crushed to obtain carbon-coated lithium manganese iron phosphate cathode material.

[0052] In Example 2, the carbon-coated lithium manganese iron phosphate cathode material powder was compacted to 2.07 g / cm³. 3 The button cell has a 0.1C discharge capacity of 153.2 mAh / g and a 1.0C discharge capacity of 151.4 mAh / g.

[0053] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-performance lithium manganese iron phosphate precursor, characterized in that: The expression is Mn x Fe 1-x (HPO4) y (P2O7) (1-y) / 2 wherein 0.5≤x<1, 0≤y<1, is prepared by sintering manganese iron ammonium phosphate monohydrate at 300-800℃; Its preparation methods include: Step 1: Add the phosphorus source solution, the mixed salt solution containing metallic manganese and iron, and the ammonia solution to the reaction vessel to obtain the manganese iron ammonium monohydrate precipitate. Step 2: The prepared manganese iron ammonium phosphate monohydrate precipitate is subjected to solid-liquid separation, washing and drying to obtain manganese iron ammonium phosphate monohydrate powder; Step 3: Place the manganese iron ammonium phosphate monohydrate powder obtained in Step 2 into a sintering furnace for sintering to obtain the high-performance manganese iron lithium phosphate precursor; The ammonium manganese iron phosphate monohydrate has a formula of NH4Mn x Fe 1-x PO4·H2O, and 0.5≤x<1, wherein the molar ratio of metal elements (Mn+Fe) to element P is 0.95-1.05; In step three, the sintering time is 6~15 hours.

2. The high-performance lithium manganese iron phosphate precursor according to claim 1, characterized in that: In step one, inert gas or nitrogen is continuously introduced into the reaction vessel, the reaction temperature is 20-70℃, the stirring speed is 300-900 rpm, and the pH value of the reaction process is adjusted by controlling the flow rate of ammonia water to maintain the pH at 4-7.

3. The high-performance lithium manganese iron phosphate precursor according to claim 1, characterized in that: In step one, the concentration of the phosphorus source solution is 1~4 mol / L, and the phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate, and trisodium phosphate. The concentration of the mixed manganese and iron salt solution is 0.5~3 mol / L. The manganese source is at least one of manganese sulfate, manganese nitrate, manganese acetate and manganese chloride; the iron source is at least one of ferrous sulfate, ferric nitrate, ferric acetate and ferric chloride.

4. The high-performance lithium manganese iron phosphate precursor according to claim 1, characterized in that: The drying temperature in step two is 60~150℃.

5. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that: The precursor of any one of claims 1 to 4 is mixed with a lithium source, a carbon source and a doping element, and then sintered at high temperature under an inert atmosphere to obtain a carbon-coated lithium manganese iron phosphate cathode material.

6. The method for preparing the cathode material according to claim 5, characterized in that: The lithium source is at least one of lithium hydroxide and lithium carbonate; the coated carbon source is one or more of sucrose, glucose, polyethylene glycol, carbon black, graphene, polyvinyl alcohol, polyacryl alcohol, citric acid, cellulose, starch, dextrin, fructose, lactose, maltose, oxalic acid, and ascorbic acid.

7. The method for preparing the cathode material according to claim 5, characterized in that: The inert atmosphere is at least one of nitrogen or argon, the high-temperature sintering temperature is 400~1000℃, and the sintering time is 6~20h.

8. The method for preparing the cathode material according to claim 5, characterized in that: The positive electrode material has a formula of Li y Mn x-z Fe 1-x M z PO4 / C; wherein, 0.5≤x<1, 0.99≤y≤1.10, 0.1≤z≤1, and M is a doping element.

9. The method for preparing the cathode material according to claim 5, characterized in that: The dopant element M is at least one of Mg, Ni, Co, Cu, Zn, and Ti.

10. A battery, characterized in that: The battery is prepared using carbon-coated lithium manganese iron phosphate cathode material prepared by any one of claims 5 to 9.

Images