CN117525317A - Manganese-assisted carbon-coated lithium iron manganese phosphate material and preparation method thereof - Google Patents

Manganese-assisted carbon-coated lithium iron manganese phosphate material and preparation method thereof Download PDF

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CN117525317A
CN117525317A CN202311448181.XA CN202311448181A CN117525317A CN 117525317 A CN117525317 A CN 117525317A CN 202311448181 A CN202311448181 A CN 202311448181A CN 117525317 A CN117525317 A CN 117525317A
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manganese
organic acid
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ferrous
lithium
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吴永青
黄耀博
黄碧英
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Tianneng Battery Group Co Ltd
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Abstract

The invention discloses a manganese-assisted carbon-coated lithium iron manganese phosphate material and a preparation method thereof. According to the invention, the organic acid is directly adopted as a complexing agent, a modifier and a carbon source, and the organic acid has rich carboxyl groups, so that the uniform distribution of ferrous ions and manganous ions at a molecular level in the coprecipitation process is more facilitated; the organic acid can react with excessive manganese source to generate organic acid manganese, when the organic acid manganese after grinding and dispersing is calcined at high temperature, carbon monoxide can be released during decomposition, ferrous ions and manganous ions can be effectively prevented from being oxidized into iron ions and manganese ions in the synthesis process, the mixing degree of transition metals in the carbon-coated LMFP is effectively reduced, meanwhile, a carbon coating layer which is uniformly distributed and contains a certain amount of Mn is formed on the surface of the LMFP in the decomposition process of the organic acid manganese, and Mn in the carbon coating layer can effectively inhibit the dissolution of the manganous ions in the circulation process of the LMFP, and the rate performance and stability of the battery are improved.

Description

Manganese-assisted carbon-coated lithium iron manganese phosphate material and preparation method thereof
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a manganese-assisted carbon-coated lithium iron manganese phosphate material and a preparation method thereof.
Background
LiFePO in recent years 4 The (LMFP) is used as a positive electrode material of the lithium ion battery, and is widely applied to the commercial fields of electric automobiles, electric tools, energy storage and the like by virtue of the advantages of abundant natural resources, safety, stability, low cost, no toxicity, long cycle life and the like. However, the discharge voltage plateau is relatively low (-3.4V vs Li) + Li) and electrical/ionic insulation, greatly limiting its application in advanced energy storage fields of high energy density, high power, fast response.
Currently, liFePO is aimed at 4 The main treatment modes are as follows: (1) particle nano crystallization, (2) element doping to realize high energy density, and (3) electron/ion conductive network construction.
Patent No. CN115043387B discloses a preparation method of ammonium ferromanganese phosphate, lithium ferromanganese phosphate and application thereof. Firstly preparing manganese ferric ammonium phosphate by adopting a coprecipitation method, and then mixing and calcining the manganese ferric ammonium phosphate with a lithium source and a carbon source to prepare manganese-assisted carbon-coated lithium manganese ferric phosphate large particles. Preparing ferricyanide solution, manganese salt solution and mixed solution of phosphoric acid and perchloric acid respectively, adding ferricyanide solution, manganese salt solution, mixed solution and alkali liquor into base solution in parallel flow for reaction to obtain precipitate which is ferromanganese phosphate, and then mixing and calcining the precipitate with lithium hydroxide and glucose to obtain manganese-assisted carbon-coated ferromanganese phosphate particles.
The patent application with publication number of CN116374981A discloses a preparation method and application of in-situ growth of lithium iron manganese phosphate on the surface of conductive carbon microspheres to form a three-dimensional conductive network, wherein the preparation method comprises the following steps: firstly, preparing conductive carbon microspheres and mixing a lithium iron manganese phosphate precursor solution, and performing a hydrothermal reaction in the next step to obtain a lithium iron manganese phosphate precursor; and (3) carrying out high-temperature sintering on the lithium iron manganese phosphate precursor to obtain the lithium iron manganese phosphate anode material.
According to the scheme, a coprecipitation method and a hydrothermal method are adopted respectively, a lithium iron manganese phosphate precursor is synthesized firstly, and then manganese-assisted carbon-coated lithium iron manganese phosphate particles are synthesized through high-temperature calcination. The coprecipitation method requires the additional introduction of a modifier for controlling the morphology of the particles, so that impurities are introduced and the synthesis cost is increased; although the hydrothermal method does not need to introduce modifier, the hydrothermal method needs higher equipment cost and longer synthesis time, which is not beneficial to large-scale industrialized production.
The patent application with publication number of CN115057426A discloses a method for preparing lithium iron manganese phosphate by a liquid phase method, which comprises the following steps: the organic acid and/or organic acid salt solution is prepared according to the mole ratio of 1.00: dripping 0.95-1.05 into a solution containing ferrous ions and manganous ions for reaction, washing and suction filtering to obtain an organic acid ferrous manganese ammonium filter cake; and (3) dropwise adding the ammonium phosphate salt solution into the organic acid ferrous manganese ammonium according to the molar ratio of 1.00:0.95-1.00 for reaction to obtain ferrous manganese ammonium phosphate and organic acid and/or organic acid salt solution, mixing and drying the ferrous manganese ammonium phosphate, lithium carbonate, doping agent and carbon source according to the molar ratio of 1.00:0.50-0.55:0.005-0.02:0.25-0.50 to obtain a precursor, preserving heat in an anaerobic environment at 160-250 ℃, and preserving heat in an anaerobic environment at 300-500 ℃ and 600-800 ℃ in sequence after rolling to obtain the high-magnification and high-compaction lithium manganese iron phosphate. The addition of the dopant improves the rate capability of the lithium manganese iron phosphate, because the dopant selects a lithium source containing nonmetallic elements, the nonmetallic elements are doped at the O position, the bond energy of Li-O bonds is reduced, and LiFePO is stabilized 4 Is also Li + The transmission provides a wider channel.
Disclosure of Invention
Aiming at the defects of the scheme, the invention aims to provide a manganese-assisted carbon-coated lithium iron manganese phosphate material and a preparation method thereof. The method synthesizes the organic acid ferromanganese precursor firstly by a coprecipitation method, and then carries out high-temperature sintering on the organic acid ferromanganese, a lithium source and a phosphorus source to prepare the LiMn 0.6 Fe 0.4 PO 4 Mn/C positive electrode material.
In order to achieve this, specific embodiments are as follows:
the preparation method of the manganese-assisted carbon-coated lithium iron manganese phosphate material comprises the following steps of:
(1) Adding a manganous source and a ferrous source into an organic acid aqueous solution to carry out mixed reaction to obtain an organic acid ferrous-manganese mixed solution;
(2) Adjusting the pH value of the organic acid ferrous manganese mixed solution obtained in the step (1) to be 2-5 by using ammonia water, reacting to obtain a reactant, washing and drying the reactant to obtain the organic acid ferrous manganese;
(3) The manganese ferrous organic acid, the lithium source and the phosphorus source obtained in the step (2) are mixed according to the mass ratio of n (Mn) l-x Fe x )∶n(Li)∶n(PO 4 3- ) Weighing and mixing the materials in the ratio of (1:1.1) - (1.5:1.01) - (1.03), adding the organic acid and the manganous source, mixing, and fully grinding to obtain mixed slurry;
wherein x is more than 0.3 and less than 0.7; the organic acid accounts for 3-8wt% of the total mass of the organic acid ferrous manganese, the lithium source and the phosphorus source, and the manganous source accounts for 0.1-0.5wt% of the total mass of the organic acid ferrous manganese, the lithium source and the phosphorus source;
(4) And (3) drying the mixed slurry obtained in the step (3), calcining under inert gas, and obtaining the manganese-assisted carbon-coated lithium iron manganese phosphate material after the calcining is finished.
In this patent, manganese ion (Mn) 2+ ) Manganese is used to form manganese carboxylate through the reaction of manganese and carboxyl, a protective film is constructed on the surface of particles, and a carbon coating layer containing a certain amount of Mn is formed on the surface of LMFP in a uniform distribution manner in the decomposition process by matching with organic acid manganese, so that Mn in the carbon coating layer can effectively inhibit the dissolution of manganous ions of LMFP in the circulation process, slow down the aggravation of side reactions of electrodes and electrolyte, weaken the thickening (consumption of active lithium) trend of SEI films, and improve the rate performance and stability of the battery.
Specifically, the manganous source is at least one of manganese sulfate, manganese nitrate, manganese carbonate and manganese acetate,
in the step (1), the ferrous source is at least one of ferrous oxalate, ferrous sulfate, ferrous oxide, ferrous chloride and ferrous hydroxide,
in the step (1), the molar ratio of manganese element in the manganous source to iron element in the ferrous source is 6:4.
In the step (1), the organic acid aqueous solution is obtained by mixing organic acid and water, wherein the mass ratio of the organic acid to the water is 1:2-4, and the organic acid is at least one of ethylenediamine tetraacetic acid, polyacrylic acid, tartaric acid, citric acid and oxalic acid.
In the step (2), the reaction temperature is 55-70 ℃ and the reaction time is 2-6h;
the drying temperature is 60-90 ℃ and the drying time is 6-12 h.
In the step (3), the phosphorus source is at least one of ammonium dihydrogen phosphate, phosphoric acid, lithium phosphate, lithium dihydrogen phosphate and ferric phosphate,
the lithium source is at least one of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide and lithium phosphate,
the mixed components before grinding also comprise a dispersing agent, wherein the dispersing agent is polyethylene glycol.
The grinding conditions are as follows: the grinding speed is 350-450 rpm, and the grinding time is 5-8 h.
In the step (4), the drying temperature is 60-85 ℃ and the drying time is 4-8 hours,
the calcination temperature is 600-800 ℃, and the calcination time is 3-10 hours.
The method comprises the following specific steps:
1. preparing organic acid ferromanganese powder:
weighing and mixing according to the mass ratio of the organic acid to the deionized water of 1:2-4, continuously stirring to form an organic acid aqueous solution, and then adding MnCO 3 And FeC 2 O 4 ·H 2 O is weighed according to the mol ratio of Mn to Fe=6 to 4 and is respectively added into the organic acid aqueous solution to form solution A;
adjusting the PH value of the solution to 2-5 by adding a proper amount of ammonia water into the solution A, controlling the reaction temperature to 55-70 ℃ and the reaction time to 2-6h;
after the reaction is finished, obtaining a precipitate, filtering the precipitate, cleaning the precipitate for a plurality of times by using deionized water and ethanol, and then placing the precipitate in a drying oven at 60-90 ℃ for drying for 6-12 h;
and after the drying is finished, obtaining the organic acid ferromanganese powder.
2. Preparation of manganese-assisted carbon-coated lithium iron manganese phosphate (LMFP/Mn/C) composite:
mixing the dried organic acid ferromanganese powder with Li 2 CO 3 And NH 4 H 2 PO 4 According to the mass ratio of n (Mn l-x Fe x )∶n(Li)∶n(PO 4 3- ) The method comprises the steps of (1:1.1-1.5:1.01-1.03) weighing, simultaneously weighing 3-8wt% of organic acid and 0.1-0.5wt% of manganese salt, mixing the weighed mixture with polyethylene glycol (PEG) aqueous solution to prepare slurry, and ball milling for 5-8 hours at 350-450 rpm;
placing the ground slurry in a drying oven at 60-85 ℃ for 4-8 h, and placing the dried powder in a box-type furnace, wherein the sintering temperature is as follows: the room temperature is 600-800 ℃; naturally cooling to room temperature. The sintering atmosphere is nitrogen, and LMFP/Mn/C powder is obtained. The calcined LMFP/Mn/C powder was thoroughly ground.
The invention also provides the manganese-assisted carbon-coated lithium iron manganese phosphate material prepared by the preparation method.
The invention also provides a lithium ion battery anode, which comprises the manganese-assisted carbon-coated lithium iron manganese phosphate material.
3. Preparing a lithium ion battery anode material:
weighing and mixing the ground LMFP/Mn/C, SP, PVDF according to the mass ratio of 8:1:1, and grinding uniformly;
dripping 1-5wt% NMP into the mixture after grinding, and grinding while dripping to homogenize;
uniformly coating the grinded slurry on an aluminum foil to prepare an electrode plate;
and (3) putting the coated electrode plate into a vacuum environment at 60-90 ℃ and drying for 8-12 h to obtain the anode of the lithium ion battery.
The invention also provides a lithium ion battery, which comprises the positive electrode of the lithium ion battery.
The invention has the beneficial effects that:
the inventionBy directly adopting organic acid as complexing agent, modifier and carbon source, the organic acid has rich carboxyl group, which is more beneficial to Fe 2+ And Mn of 2+ Achieving a uniform distribution of molecular levels during co-precipitation; the organic acid can react with excessive manganese source to generate organic acid manganese, and when the organic acid manganese after grinding and dispersing is calcined at high temperature, carbon monoxide can be released during decomposition, so that Fe in the synthesis process can be effectively prevented 2+ And Mn of 2+ Oxidation to Fe 3+ And Mn of 3+ Effectively reduce LiMn 0.6 Fe 0.4 PO 4 The mixing degree of transition metal in the/C, and simultaneously, a layer of evenly distributed carbon coating layer containing a certain amount of Mn is formed on the surface of the LMFP in the decomposition process of the organic acid manganese, and Mn in the carbon coating layer can effectively inhibit Mn of the LMFP in the circulation process 2+ And improves the rate performance and stability of the battery.
Drawings
Fig. 1 is a graph showing discharge capacities of a battery fabricated from the positive electrode material prepared in example 1 at current densities of 0.1C, 0.2C, 0.5C, 1C and 2C in a voltage range of 2.0V to 4.5V.
Detailed Description
Example 1
1. Preparing ferromanganese ethylenediamine tetraacetate powder:
weighing and mixing ethylenediamine tetraacetic acid and deionized water according to the mass ratio of 1:2, continuously stirring to form ethylenediamine tetraacetic acid aqueous solution, and then weighing 17.5g and 17.9g of MnCO respectively 3 And FeC 2 O 4 ·H 2 O, and respectively adding the two solutions into an ethylenediamine tetraacetic acid aqueous solution to form a solution A;
adjusting the PH value of the solution to 2 by adding a proper amount of ammonia water into the solution A, controlling the reaction temperature to 55 ℃ and the reaction time to 2 hours;
after the reaction is finished, obtaining a precipitate, filtering the precipitate, cleaning the precipitate for a plurality of times by using deionized water and ethanol, and then placing the precipitate in a drying oven at 60 ℃ for drying for 12 hours;
and after the drying is finished, obtaining the ferromanganese ethylenediamine tetraacetate powder.
2. Preparation of manganese-assisted carbon-coated lithium iron manganese phosphate (LMFP/Mn/C) composite:
drying the dried ferromanganese ethylenediamine tetraacetate powder and Li 2 CO 3 And NH 4 H 2 PO 4 According to the mass ratio of n (Mn l- x Fe x )∶n(Li)∶n(PO 4 3- ) The method comprises the steps of weighing the mixture in a ratio of 1:1.1:1.02, and simultaneously weighing manganese iron ethylenediamine tetraacetate powder and Li 2 CO 3 And NH 4 H 2 PO 4 3wt% of ethylenediamine tetraacetic acid and 0.1wt% of manganese sulfate, and mixing the weighed mixture with polyethylene glycol (PEG) aqueous solution to prepare slurry, and ball milling for 8 hours at 350 rpm;
placing the ground slurry in a drying oven at 85 ℃ for 4 hours, and placing the dried powder in a box-type furnace, wherein the sintering temperature is as follows: room temperature to 600 ℃; naturally cooling to room temperature. The sintering atmosphere is nitrogen, and the LMFP/Mn/C powder is obtained after the sintering is finished.
Fully grinding the calcined LMFP/Mn/C powder;
3. preparing a lithium ion battery anode material:
weighing and mixing the ground LMFP/Mn/C, SP, PVDF according to the mass ratio of 8:1:1, and grinding uniformly;
1wt% NMP was added dropwise to the mixture after the uniform grinding, followed by grinding to homogenize the mixture;
uniformly coating the grinded slurry on an aluminum foil to prepare an electrode plate;
and (5) putting the coated electrode plate into a vacuum environment at 60 ℃ and drying for 12 hours to obtain the anode of the lithium ion battery.
Example 2
1. Preparing a poly (ferromanganese acrylate) powder:
weighing and mixing polyacrylic acid and deionized water according to the mass ratio of 1:3.2, continuously stirring to form polyacrylic acid aqueous solution, and then weighing 17.8g and 18g of MnCO respectively 3 And FeC 2 O 4 ·H 2 O, and respectively adding the two components into polyacrylic acid aqueous solutions to form solution A;
adjusting the PH value of the solution to 2.5 by adding a proper amount of ammonia water into the solution A, controlling the reaction temperature to 65 ℃ and the reaction time to 4 hours;
after the reaction is finished, obtaining a precipitate, filtering the precipitate, cleaning the precipitate for a plurality of times by using deionized water and ethanol, and then placing the precipitate in a drying oven at 75 ℃ for drying for 9 hours;
and after the drying is finished, obtaining the poly (ferromanganese acrylate) powder.
2. Preparation of manganese-assisted carbon-coated lithium iron manganese phosphate (LMFP/Mn/C) composite:
drying the dried manganese iron polyacrylate powder and Li 2 CO 3 And NH 4 H 2 PO 4 According to the mass ratio of n (Mn l-x Fe x )∶n(Li)∶n(PO 4 3- ) The method comprises the steps of weighing (1:1.3:1.01), and simultaneously weighing manganese iron ethylenediamine tetraacetate powder and Li 2 CO 3 And NH 4 H 2 PO 4 Polyacrylic acid and 0.3wt% of manganese carbonate, and mixing the weighed mixture with polyethylene glycol aqueous solution to prepare slurry, and ball milling for 6.5 hours at 400 rpm;
placing the ground slurry in a drying oven at 75 ℃ for 6 hours, and placing the dried powder in a box-type furnace, wherein the sintering temperature is as follows: room temperature to 700 ℃; naturally cooling to room temperature. The sintering atmosphere is nitrogen, and LMFP/Mn/C powder is obtained.
Fully grinding the calcined LMFP/Mn/C powder;
3. preparing a lithium ion battery anode material:
weighing and mixing the ground LMFP/Mn/C, SP, PVDF according to the mass ratio of 8:1:1, and grinding uniformly;
dropping 3wt% NMP into the mixture after being ground, and grinding while dropping to homogenize;
uniformly coating the grinded slurry on an aluminum foil to prepare an electrode plate;
and (5) putting the coated electrode plate into a vacuum environment at 90 ℃ and drying for 8 hours to obtain the anode of the lithium ion battery.
Example 3
Weighing and mixing tartaric acid and deionized water according to the mass ratio of 1:4, continuously stirring to form tartaric acid aqueous solution, and then17.5g and 18.3g MnCO are weighed respectively 3 And FeC 2 O 4 ·H 2 O, and respectively adding the two solutions into tartaric acid aqueous solution to form solution A;
adjusting the PH value of the solution to 5 by adding a proper amount of ammonia water into the solution A, controlling the reaction temperature to 70 ℃ and the reaction time to 6 hours;
after the reaction is finished, obtaining a precipitate, filtering the precipitate, cleaning the precipitate for a plurality of times by using deionized water and ethanol, and then placing the precipitate in a drying oven at 90 ℃ for drying for 6 hours;
and after the drying is finished, obtaining the ferromanganese tartrate powder.
2. Preparation of manganese-assisted carbon-coated lithium iron manganese phosphate (LMFP/Mn/C) composite:
drying the dried ferromanganese tartrate powder and Li 2 CO 3 And NH 4 H 2 PO 4 According to the mass ratio of n (Mn l-x Fe x )∶n(Li)∶n(PO 4 3- ) The method comprises the steps of weighing the mixture in a ratio of 1:1.5:1.03, and simultaneously weighing manganese iron ethylenediamine tetraacetate powder and Li 2 CO 3 And NH 4 H 2 PO 4 8wt% of tartaric acid and 0.5wt% of manganese acetate, mixing the weighed mixture with an aqueous solution of polyethylene glycol to prepare slurry, and ball-milling for 5 hours at 450 rpm/min;
placing the ground slurry in a drying oven at 85 ℃ for 4 hours, and placing the dried powder in a box-type furnace, wherein the sintering temperature is as follows: room temperature to 800 ℃; naturally cooling to room temperature. The sintering atmosphere is nitrogen, and LMFP/Mn/C powder is obtained.
Fully grinding the calcined LMFP/Mn/C powder;
3. preparing a lithium ion battery anode material:
weighing and mixing the ground LMFP/Mn/C, SP, PVDF according to the mass ratio of 8:1:1, and grinding uniformly;
dropwise adding 5wt% NMP to the mixture after uniform grinding, and grinding while dropwise adding to carry out homogenization;
uniformly coating the grinded slurry on an aluminum foil to prepare an electrode plate;
and (5) putting the coated electrode plate into a vacuum environment at 90 ℃ and drying for 8 hours to obtain the anode of the lithium ion battery.
Comparative example 1
1. Preparing ferromanganese ethylenediamine tetraacetate powder:
weighing and mixing ethylenediamine tetraacetic acid and deionized water according to the mass ratio of 1:2, continuously stirring to form ethylenediamine tetraacetic acid aqueous solution, and then weighing 17.5g and 17.9g of MnCO respectively 3 And FeC 2 O 4 ·H 2 O, and respectively adding the two solutions into an ethylenediamine tetraacetic acid aqueous solution to form a solution A;
adjusting the PH value of the solution to 2 by adding a proper amount of ammonia water into the solution A, controlling the reaction temperature to 55 ℃ and the reaction time to 2 hours;
after the reaction is finished, obtaining a precipitate, filtering the precipitate, cleaning the precipitate for a plurality of times by using deionized water and ethanol, and then placing the precipitate in a drying oven at 60 ℃ for drying for 12 hours;
and after the drying is finished, obtaining the ferromanganese ethylenediamine tetraacetate powder.
2. Preparing a carbon-coated lithium iron manganese phosphate (LMFP/C) composite:
drying the dried ferromanganese ethylenediamine tetraacetate powder and Li 2 CO 3 And NH 4 H 2 PO 4 According to the mass ratio of n (Mn l- x Fe x )∶n(Li)∶n(PO 4 3- ) Weighing the materials in a ratio of (1:1.1:1.02), mixing the weighed mixture with polyethylene glycol (PEG) aqueous solution to prepare slurry, and ball milling the slurry for 8 hours at a speed of 350 rpm;
placing the ground slurry in a drying oven at 85 ℃ for 4 hours, and placing the dried powder in a box-type furnace, wherein the sintering temperature is as follows: room temperature to 600 ℃; naturally cooling to room temperature. The sintering atmosphere is nitrogen, and the LMFP/C powder is obtained after the sintering is finished.
Fully grinding the calcined LMFP/C powder;
3. preparing a lithium ion battery anode material:
weighing and mixing the ground LMFP/C, SP, PVDF according to the mass ratio of 8:1:1, and grinding uniformly;
1wt% NMP was added dropwise to the mixture after the uniform grinding, followed by grinding to homogenize the mixture;
uniformly coating the grinded slurry on an aluminum foil to prepare an electrode plate;
and (5) putting the coated electrode plate into a vacuum environment at 60 ℃ and drying for 12 hours to obtain the anode of the lithium ion battery.
Comparative example 2
1. Preparing a poly (ferromanganese acrylate) powder:
weighing and mixing polyacrylic acid and deionized water according to the mass ratio of 1:3.2, continuously stirring to form polyacrylic acid aqueous solution, and then weighing 17.8g and 18g of MnCO respectively 3 And FeC 2 O 4 ·H 2 O, and respectively adding the two components into polyacrylic acid aqueous solutions to form solution A;
adjusting the PH value of the solution to 2.5 by adding a proper amount of ammonia water into the solution A, controlling the reaction temperature to 65 ℃ and the reaction time to 4 hours;
after the reaction is finished, obtaining a precipitate, filtering the precipitate, cleaning the precipitate for a plurality of times by using deionized water and ethanol, and then placing the precipitate in a drying oven at 75 ℃ for drying for 9 hours;
and after the drying is finished, obtaining the poly (ferromanganese acrylate) powder.
2. Preparing a carbon-coated lithium iron manganese phosphate (LMFP/Mn/C) composite:
drying the dried manganese iron polyacrylate powder and Li 2 CO 3 And NH 4 H 2 PO 4 According to the mass ratio of n (Mn l-x Fe x )∶n(Li)∶n(PO 4 3- ) The method comprises the steps of weighing the manganese iron powder, the lithium iron powder and the lithium iron powder, wherein the weight of the manganese iron powder is 1:1.3:1.01 2 CO 3 And NH 4 H 2 PO 4 Polyacrylic acid of 5.8wt%, and mixing the weighed mixture with polyethylene glycol aqueous solution to prepare slurry, and ball milling for 6.5 hours at 400 rpm;
placing the ground slurry in a drying oven at 75 ℃ for 6 hours, and placing the dried powder in a box-type furnace, wherein the sintering temperature is as follows: room temperature to 700 ℃; naturally cooling to room temperature. The sintering atmosphere is nitrogen, and LMFP/C powder is obtained.
Fully grinding the calcined LMFP/C powder;
3. preparing a lithium ion battery anode material:
weighing and mixing the ground LMFP/C, SP, PVDF according to the mass ratio of 8:1:1, and grinding uniformly;
dropping 3wt% NMP into the mixture after being ground, and grinding while dropping to homogenize;
uniformly coating the grinded slurry on an aluminum foil to prepare an electrode plate;
and (5) putting the coated electrode plate into a vacuum environment at 90 ℃ and drying for 8 hours to obtain the anode of the lithium ion battery.
Comparative example 3
Weighing and mixing tartaric acid and deionized water according to the mass ratio of 1:4, and continuously stirring
An aqueous tartaric acid solution was formed, followed by weighing 17.5g and 18.3g of MnCO, respectively 3 And FeC 2 O 4 ·H 2 O, and respectively adding the two solutions into tartaric acid aqueous solution to form solution A;
adjusting the PH value of the solution to 5 by adding a proper amount of ammonia water into the solution A, controlling the reaction temperature to 70 ℃ and the reaction time to 6 hours;
after the reaction is finished, obtaining a precipitate, filtering the precipitate, cleaning the precipitate for a plurality of times by using deionized water and ethanol, and then placing the precipitate in a drying oven at 90 ℃ for drying for 6 hours;
and after the drying is finished, obtaining the ferromanganese tartrate powder.
2. Preparation of manganese-assisted carbon-coated lithium iron manganese phosphate (LMFP/Mn/C) composite:
drying the dried ferromanganese tartrate powder and Li 2 CO 3 And NH 4 H 2 PO 4 According to the mass ratio of n (Mn l-x Fe x )∶n(Li)∶n(PO 4 3- ) The method comprises the steps of weighing the manganese iron tartrate powder and the Li at the same time, wherein the weight ratio is 1:1.5:1.03 2 CO 3 And NH 4 H 2 PO 4 Manganese acetate of 0.5wt%, mixing the weighed mixture with polyethylene glycol aqueous solution to prepare slurry, and ball milling for 5h at 450 rpm;
placing the ground slurry in a drying oven at 85 ℃ for 4 hours, and placing the dried powder in a box-type furnace, wherein the sintering temperature is as follows: room temperature to 800 ℃; naturally cooling to room temperature. The sintering atmosphere is nitrogen, and LMFP/Mn/C powder is obtained.
Fully grinding the calcined LMFP/Mn/C powder;
3. preparing a lithium ion battery anode material:
weighing and mixing the ground LMFP/Mn/C, SP, PVDF according to the mass ratio of 8:1:1, and grinding uniformly;
dropwise adding 5wt% NMP to the mixture after uniform grinding, and grinding while dropwise adding to carry out homogenization;
uniformly coating the grinded slurry on an aluminum foil to prepare an electrode plate;
and (5) putting the coated electrode plate into a vacuum environment at 90 ℃ and drying for 8 hours to obtain the anode of the lithium ion battery.
Test example 1
The positive electrodes prepared in examples 1 to 3 and comparative examples 1 to 3 were used as positive electrodes, and metallic lithium sheets were used as negative electrodes; the separator is a Celgard2400 polypropylene porous membrane; the electrolyte is a solution composed of EC, DMC and EMC according to the mass ratio of 1:1:1, and the solute is LiPF 6 ，LiPF 6 The concentration of (2) is 1.0mol/L; inside the glove box, 2023 type button cell was assembled. The battery was subjected to a charge-discharge cycle performance test, in which continuous charge and discharge were performed at current densities of 0.1C, 0.2C, 0.5C, 1C and 2C in the cutoff voltage range of 2.0 to 4.5V, electrochemical performance test results were shown in table 1 for discharge capacities at different rates, and electrochemical performance test results for the battery assembled in example 1 are shown in fig. 1.
As can be seen from the data in Table 1, by adopting organic acid as complexing agent, modifier and carbon source and using coordination of carboxyl and manganese ion as bridge for connecting organic acid molecules, multiple organic acid molecules can be polymerized and connected to form organic acid manganese protective film, and the discharge capacity of example 1 with excessive manganese ion distribution doped manganese for auxiliary carbon coating under different multiplying power of 0.1C, 0.2C, 0.5C, 1C and 2C is obviously improved compared with the comparative example, and the specific discharge capacity is 155.2mAh/g, 154.8mAh/g, 151.9mAh/g, 146.5mAh/g and 133.4mAh/g respectively.
Table 1 discharge capacities (mAh/g) of examples and comparative examples at different magnifications
As can be seen from the data in Table 2, the Mn element content in the electrolyte after the products prepared in examples 1-3 and comparative examples 1-3 are circulated for 200 weeks at 2C ratio is obviously reduced compared with the comparative example by using organic acid as complexing agent, modifier and carbon source and using the coordination of carboxyl and manganese ion as bridge for connecting organic acid molecules during preparation of lithium iron manganese phosphate precursor, polymerizing and connecting a plurality of organic acid molecules to form a protective film of organic acid manganese, and adding excessive manganese ion distribution doped manganese for auxiliary carbon coating in example 1 after being circulated for 200 weeks at 2C ratio.
Table 2 content of Mn element in electrolyte after 200 weeks of circulation at 5C magnification in examples and comparative examples
From the above data, it can be seen that the manganese-assisted carbon-coated lithium manganese iron phosphate material contains the organic acid ferromanganese precursor, the size of the precursor particles can be adjusted by adjusting the amount of the organic acid, ferrous ions and manganous ions can be uniformly distributed at the molecular level in the coprecipitation process, and meanwhile, a carbon coating layer containing a certain amount of Mn can be uniformly distributed on the surface of the LMFP (Mn is contained in the electrolyte, so that the stability of the structure is improved (the lower the content of Mn ions in the electrolyte is determined, the more stable the structure is indicated), and Mn of the LMFP in the charge-discharge cycle process can be effectively inhibited 2+ The organic acid structure promotes the conductivity rate, thereby promoting the ferromanganese phosphateHigh rate performance and structural stability of lithium composites.

Claims (10)

1. The preparation method of the manganese-assisted carbon-coated lithium iron manganese phosphate material is characterized by comprising the following steps of:
(1) Adding a manganous source and a ferrous source into an organic acid aqueous solution to carry out mixed reaction to obtain an organic acid ferrous-manganese mixed solution;
(2) Adjusting the pH value of the organic acid ferrous manganese mixed solution obtained in the step (1) to be 2-5 by using ammonia water, reacting to obtain a reactant, washing and drying the reactant to obtain the organic acid ferrous manganese;
(3) The organic acid ferrous manganese, lithium source and phosphorus source obtained in the step (2) are mixed according to the mass ratio of n (Mn) 1-x Fe x )∶n(Li)∶n(PO 4 3- ) Weighing and mixing the materials in the ratio of (1:1.1) - (1.5:1.01) - (1.03), adding the organic acid and the manganous source, mixing, and fully grinding to obtain mixed slurry;
wherein x is more than 0.3 and less than 0.7; the organic acid accounts for 3-8wt% of the total mass of the organic acid ferrous manganese, the lithium source and the phosphorus source, and the manganous source accounts for 0.1-0.5wt% of the total mass of the organic acid ferrous manganese, the lithium source and the phosphorus source;
(4) And (3) drying the mixed slurry obtained in the step (3), calcining under inert gas, and obtaining the manganese-assisted carbon-coated lithium iron manganese phosphate material after the calcining is finished.
2. The method for preparing a manganese-assisted carbon-coated lithium iron phosphate material according to claim 1, wherein the manganous source is at least one of manganese sulfate, manganese nitrate, manganese carbonate and manganese acetate,
in the step (1), the ferrous source is at least one of ferrous oxalate, ferrous sulfate, ferrous oxide, ferrous chloride and ferrous hydroxide,
in the step (1), the molar ratio of manganese element in the manganous source to iron element in the ferrous source is 6:4.
3. The method for preparing the manganese-assisted carbon-coated lithium iron phosphate material according to claim 1, wherein in the step (1), an organic acid aqueous solution is obtained by mixing an organic acid and water, wherein the mass ratio of the organic acid to the water is 1:2-4, and the organic acid is at least one of ethylenediamine tetraacetic acid, polyacrylic acid, tartaric acid, citric acid and oxalic acid.
4. The method for preparing a manganese-assisted carbon-coated lithium iron manganese phosphate material according to claim 1, wherein in the step (2), the reaction temperature is 55-70 ℃ and the reaction time is 2-6h;
the drying temperature is 60-90 ℃ and the drying time is 6-12 h.
5. The method for preparing a manganese-assisted carbon-coated lithium iron manganese phosphate material according to claim 1, wherein in the step (3), the phosphorus source is at least one of phosphoric acid, monoammonium phosphate, lithium dihydrogen phosphate and iron phosphate,
the lithium source is at least one of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide and lithium phosphate, and the mixed components before grinding also comprise a dispersing agent, wherein the dispersing agent is polyethylene glycol.
6. The method for preparing the manganese-assisted carbon-coated lithium iron manganese phosphate material according to claim 1, wherein the grinding conditions are as follows: the grinding speed is 350-450 rpm, and the grinding time is 5-8 h.
7. The method for preparing manganese-assisted carbon-coated lithium iron phosphate material according to claim 1, wherein in the step (4), the drying temperature is 60-85 ℃ and the drying time is 4-8 h,
the calcination temperature is 600-800 ℃, and the calcination time is 3-10 hours.
8. The manganese-assisted carbon-coated lithium iron manganese phosphate material prepared by the preparation method according to any one of claims 1 to 7.
9. A lithium ion battery positive electrode comprising the manganese-assisted carbon-coated lithium iron manganese phosphate material of claim 8.
10. A lithium ion battery comprising the positive electrode of the lithium ion battery of claim 9.
CN202311448181.XA 2023-11-01 2023-11-01 Manganese-assisted carbon-coated lithium iron manganese phosphate material and preparation method thereof Pending CN117525317A (en)

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