Multi-composite metal oxide coated lithium iron phosphate material and method for preparing the same

Abstract

The application belongs to the technical field of battery materials, and discloses a lithium iron phosphate material coated with a multi-composite metal oxide layer. After activation treatment, mixed metal powder of lithium, magnesium, niobium, titanium and lanthanum is reacted with water at a temperature of 80-120 DEG C to generate Mg(OH)2, Nb(OH)5, Ti(OH)4 and La(OH)3, and the hydroxide surface will adsorb Li + xLi + ·Mg(OH)2·Nb(OH)5·Ti(OH)4·La(OH)3·yH2O, a uniform coating layer is formed on the surface of the positive electrode material, and the coating layer is dehydrated at high temperature to generate a multi-composite metal oxide Li2O·MgO·Nb2O5·TiO2·La2O3 coating layer. The battery assembled by the lithium iron phosphate material coated with the multi-composite metal oxide layer has good capacity retention rate and rate performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a lithium iron phosphate material and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have many advantages such as high energy density, long cycle life, no memory effect, etc., and are widely favored. Vigorously promoting the development, production and sales of lithium ion batteries is in line with the policy of energy technology innovation and development in China, and is conducive to energy saving, emission reduction and energy transformation.

[0003] In the selection of positive electrode materials of lithium ion energy storage batteries or power batteries, lithium iron phosphate has low cost, no toxicity and good safety stability. However, the lithium iron phosphate has poor ion and electronic conductivity, and has low specific capacity when large current charging and discharging. In addition, the lithium iron phosphate has low compaction density, cannot exert greater energy density, and has poor low-temperature performance in low-temperature environment. Battery manufacturers have higher requirements for the compaction density of lithium iron phosphate, hoping to reach 2.5g / cm 3 , and have high capacity. SUMMARY

[0004] In view of the problems in the prior art, the application aims to provide a lithium iron phosphate material with high compaction density and high rate, and a preparation method thereof.

[0005] To achieve the above-mentioned purpose, the application provides the following specific technical solutions.

[0006] Firstly, the application provides a lithium iron phosphate material, and a multi-composite metal oxide layer is coated on the surface of the material.

[0007] Further, the multi-composite metal oxide is a composite oxide of lithium, magnesium, niobium, titanium and lanthanum, i.e. Li2O·MgO·Nb2O5·TiO2·La2O3.

[0008] Further, the compaction density of the lithium iron phosphate material is 2.4-2.6g / cm 3 .

[0009] In addition, the application provides a preparation method of the above-mentioned lithium iron phosphate material, comprising the following steps.

[0010] Step S1, pre-activating mixed metal powder of lithium, magnesium, niobium, titanium and lanthanum: adding the mixed metal powder into hydrochloric acid, sulfuric acid or nitric acid with a concentration of 0.2mol / L-0.5mol / L and a temperature of 60-80℃ for acid corrosion, and then vacuum drying at a temperature of 90-110℃ to obtain pre-activated mixed metal powder;

[0011] Step S2, the pre-activated mixed metal powder, the polymer compound are added into water according to the mass ratio ((0.4-1.2):1) to react; after the reaction is completed, the dispersion slurry is obtained, the slurry is sieved and dried to obtain the multi-composite metal oxide;

[0012] Step S3, the lithium source, the iron source, the phosphorus source, the multi-composite metal oxide, the carbon source and the solvent are mixed to form the slurry K, the slurry K is sand-milled and dried;

[0013] Step S4, the material obtained after drying in step S3 is sintered in a protective atmosphere to obtain the lithium iron phosphate material.

[0014] Further, in some preferred embodiments of the present application, the mixed metal powder is composed of lithium, magnesium, niobium, titanium and lanthanum metal powder, and the molar ratio of lithium, magnesium, niobium, titanium and lanthanum is n(Li):n(Mg):n(Nb):n(Ti):n(La)=(0.3-0.5):(0.02-0.05):(0.2-0.5):(0.2-0.6):(0.3-0.5).

[0015] Further, in some preferred embodiments of the present application, the polymer compound is urea-formaldehyde resin or phenol-formaldehyde resin, and the addition amount is 0.05%-0.1% of the mass of the lithium iron phosphate material. The resin will be thermally decomposed to produce gas during heating, and a uniform pore metal oxide framework is formed in the coating layer.

[0016] Further, in some preferred embodiments of the present application, the temperature of the reaction in step S2 is 70-110°C, and the time is 2-6h.

[0017] Further, in some preferred embodiments of the present application, the solvent is at least one of water, ethanol or ethylene glycol. Typical but non-limiting combinations include: a combination of water and ethanol, a combination of ethanol and ethylene glycol, etc., and water is preferred.

[0018] Further, in some preferred embodiments of the present application, the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium dihydrogen phosphate or lithium nitrate. Typical but non-limiting combinations include: a combination of lithium nitrate and lithium carbonate, a combination of lithium carbonate and lithium hydroxide, a combination of lithium oxalate and lithium dihydrogen phosphate, etc., and lithium carbonate is preferred.

[0019] Further, in some preferred embodiments of the present application, the iron source is at least one of an iron salt, a ferrous salt or an iron oxide, preferably any one or a combination of at least two of iron phosphate, ferroferric oxide, iron acetate, iron nitrate or ferrous oxalate, typically but not limitedly a combination of iron phosphate and ferrous oxalate, a combination of iron acetate and iron nitrate, a combination of ferroferric oxide, iron nitrate and ferrous oxalate, and the like, and further preferably iron phosphate or ferroferric oxide.

[0020] Further, in some preferred embodiments of the present application, the phosphorus source is at least one of ammonium dihydrogen phosphate, ammonium phosphate, iron phosphate, lithium dihydrogen phosphate or phosphoric acid, typically but not limitedly a combination of iron phosphate and lithium dihydrogen phosphate, a combination of phosphoric acid and ammonium dihydrogen phosphate, and the like, and preferably iron phosphate.

[0021] Further, in some preferred embodiments of the present application, the carbon source is any one or a combination of at least two of a sugar, an acid or an alcohol, preferably any one or a combination of at least two of glucose, sucrose, starch, graphite conductive liquid, ascorbic acid or polyethylene glycol, typically but not limitedly a combination of sucrose and glucose, a combination of sucrose and polyethylene glycol, a combination of starch, glucose and polyethylene glycol, and the like, and further preferably glucose or polyethylene glycol.

[0022] Further, in some preferred embodiments of the present application, in step S3, the amount of the solvent added is 35-70% of the total mass of the substances added.

[0023] Further, in some preferred embodiments of the present application, in step S3, the molar ratio of the lithium source, the iron source and the phosphorus source is (1-1.05):(1-1.05):1.

[0024] Further, in some preferred embodiments of the present application, in step S3, the amount of the carbon source added is 2-18% of the total mass of the solid materials other than the carbon source.

[0025] Further, in some preferred embodiments of the present application, in step S3, the molar ratio of the phosphorus source to the multi-composite metal oxide is 1:(0-0.01).

[0026] Further, in some preferred embodiments of the present application, in step S3, the drying method is spray drying.

[0027] Further, in some preferred embodiments of the present application, in step S4, the protective atmosphere includes any one or a combination of at least two of a nitrogen atmosphere, a helium atmosphere and an argon atmosphere, typically but not limitedly a combination of a nitrogen atmosphere and a helium atmosphere, a combination of a helium atmosphere and an argon atmosphere, and the like.

[0028] Further, in some preferred embodiments of the present application, the sintering temperature in step S4 is 600-750°C.

[0029] Further, in some preferred embodiments of the present application, the sintering time in step S4 is 4-7h, preferably 4.5-5.5h.

[0030] Further, in some preferred embodiments of the present application, the step of jet milling the lithium iron phosphate material is included.

[0031] Further, in some preferred embodiments of the present application, the particle size of the sanding slurry K in step S3 is 0.4-1μm.

[0032] In the present application, the mixed metal powder of lithium, magnesium, niobium, titanium and lanthanum is activated and then reacted with water at a temperature of 80-120°C to form Mg(OH)2, Nb(OH)5, Ti(OH)4 and La(OH)3. The surface of these hydroxides will adsorb Li + xLi + Mg(OH)2·Nb(OH)5·Ti(OH)4·La(OH)3·yH2O, forming a uniform coating layer on the surface of the positive electrode material, which dehydrates at high temperature to form a Li2O·MgO·Nb2O5·TiO2·La2O3 multi-composite metal oxide coating layer.

[0033] The Li2O·MgO·Nb2O5·TiO2·La2O3 multi-composite metal oxide as the modification material is amphoteric and can act as a barrier to HF and H2O after the positive electrode material is assembled into a battery, reducing the corrosion of the positive electrode material. Meanwhile, the two oxides MgO and La2O3 can neutralize the acidic electrolyte and inhibit side reactions. The ion conductivity of the modification material Li2O·MgO·Nb2O5·TiO2·La2O3 composite compound at room temperature is 8.2×10 -4 S / cm, which belongs to fast ion conductors and can improve the rate performance of the material. Therefore, the battery assembled from the positive electrode material modified with the multi-composite metal oxide has good capacity retention and rate performance.

[0034] Compared with the prior art, the present application has the following obvious beneficial technical effects:

[0035] (1) The Li2O·MgO·Nb2O5·TiO2·La2O3 multi-composite metal oxide modifies the lithium iron phosphate material, so that the battery containing the material has good capacity retention and rate performance;

[0036] (2) Through the composite oxidation of multiple metals, a coating layer is formed, and the coating layer is a fast ion conductor, which provides a new technical idea for the coating modification of lithium iron phosphate material;

[0037] (3) The coating modification process of lithium iron phosphate is simple, easy to operate, and very convenient for industrialization and application. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the drawings needed to be used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0039] Figure 1 SEM image of the positive electrode material provided for Example 1 of the present application;

[0040] Figure 2 SEM image of the positive electrode material provided for Example 2 of the present application;

[0041] Figure 3 SEM image of the positive electrode material provided for Example 3 of the present application;

[0042] Figure 4 SEM image of the positive electrode material provided for Comparative Example 1 of the present application;

[0043] Figure 5 SEM image of the positive electrode material provided for Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0044] In order to facilitate the understanding of the present application, the present application will be described more fully below in conjunction with the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0045] Unless otherwise defined, all the professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used in this paper are only for the purpose of describing the specific embodiments and are not intended to limit the scope of protection of the present application.

[0046] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0047] Example 1

[0048] In this embodiment, the lithium iron phosphate material modified by multiple composite metal oxides is prepared according to the following method:

[0049] (1) The mixed metal powder of lithium, magnesium, niobium, titanium and lanthanum (n(Li):n(Mg):n(Nb):n(Ti):n(La) = 0.3:0.02:0.3:0.3:0.5) is added into sulfuric acid with a concentration of 0.2 mol / L for pre-activation at a temperature of 70°C; and then vacuum drying is performed at a drying temperature of 100°C;

[0050] (2) The pre-activated mixed metal powder 24 g and urea-formaldehyde resin 60 g are added into an aqueous solution for reaction; after the reaction is completed, the mixed solution is dispersed by using an ultrasonic cell disruptor, and then sieving and drying are performed to obtain a multi-composite metal oxide;

[0051] (3) 6000 g of iron phosphate, 2000 g of iron oxide, 2355 g of lithium phosphate, 978 g of glucose, 342 g of polyethylene glycol and 45 g of the multi-composite metal oxide are weighed and added into a ball mill, wherein the molar ratio of total iron elements to total phosphorus elements is 0.96:1; the molar ratio of total iron elements to lithium elements is 1:1.02; then 60% of the total mass of water is added, and the mixture is ground, and the grinding is stopped when the slurry particle size D50 is 0.5 μm; the ground slurry is subjected to spray drying to obtain a precursor;

[0052] (4) The precursor is sintered at a high temperature of 600°C for 5 h in a nitrogen environment, and the sintered lithium iron phosphate is crushed to obtain a lithium iron phosphate product.

[0053] Example 2

[0054] In this example, a high-compaction lithium iron phosphate material is prepared according to the following method:

[0055] (1) The mixed metal powder of lithium, magnesium, niobium, titanium and lanthanum (n(Li):n(Mg):n(Nb):n(Ti):n(La) = 0.4:0.03:0.2:0.5:0.3) is added into hydrochloric acid with a concentration of 0.4 mol / L for pre-activation at a temperature of 80°C; and then vacuum drying is performed at a temperature of 90°C;

[0056] (2) The pre-activated mixed metal powder 30 g and phenol-formaldehyde resin 30 g are added into an aqueous solution for reaction; after the reaction is completed, the mixed solution is dispersed by using an ultrasonic cell disruptor, and then sieving and drying are performed to obtain a multi-composite metal oxide;

[0057] (3) Weigh 6000 g of iron phosphate, 2000 g of iron oxide, 2332 g of lithium carbonate, 978 g of glucose, 342 g of polyethylene glycol, and 27 g of multi-composite metal oxide into a ball mill, wherein the molar ratio of total iron elements to total phosphorus elements is 0.98:1; the molar ratio of total iron elements to lithium elements is 1:1.03; then add 60% of the total mass of water, mix and grind, stop grinding when the slurry particle size D50 is 0.55 μm, spray dry the ground slurry to obtain a precursor;

[0058] (4) The precursor is sintered at 650°C for 4h under a nitrogen atmosphere, and the sintered lithium iron phosphate is crushed to obtain a lithium iron phosphate product.

[0059] Example 3

[0060] In this example, a high-density lithium iron phosphate material is prepared according to the following method:

[0061] (1) The mixed metal powder of lithium, magnesium, niobium, titanium, and lanthanum (n(Li):n(Mg):n(Nb):n(Ti):n(La) = 0.5:0.05:0.5:0.2:0.5) is added to 0.5 mol / L nitric acid for pre-activation at a temperature of 60°C; then vacuum drying is performed at a temperature of 110°C;

[0062] (2) The pre-activated mixed metal powder 24 g and phenolic resin 40 g are added to an aqueous solution for reaction; after the reaction is completed, the mixed solution is dispersed using an ultrasonic cell disruptor, then sieved and dried to obtain a multi-composite metal oxide;

[0063] (3) Weigh 6000 g of iron phosphate, 2000 g of iron oxide, 2332 g of lithium carbonate, 1275 g of glucose, and 35 g of multi-composite metal oxide into a ball mill, wherein the molar ratio of total iron elements to total phosphorus elements is 0.98:1; the molar ratio of total iron elements to lithium elements is 1:1.03; then add 60% of the total mass of water, mix and grind, stop grinding when the slurry particle size D50 is 0.55 μm, spray dry the ground slurry to obtain a precursor;

[0064] (4) The precursor is sintered at 630°C for 4h under a mixed nitrogen atmosphere, and the sintered lithium iron phosphate is crushed to obtain a lithium iron phosphate product.

[0065] Comparative Example 1

[0066] In this example, a lithium iron phosphate material is prepared according to the following method:

[0067] (1) Take 1000 kg of iron phosphate, 249 kg of lithium carbonate, 110 kg of glucose monohydrate and 5 kg of polyethylene glycol as a dispersant together into 1500 L of pure water, stir for 0.5 h, and then obtain a mixed solution; the mixed solution is ground by a sand mill to D50 = 0.2-0.25 μm to obtain a slurry; the ground slurry is spray dried to obtain a precursor;

[0068] (2) The precursor is sintered at 740°C for 10 h under a nitrogen atmosphere, and the sintered lithium iron phosphate is crushed to obtain a lithium iron phosphate product.

[0069] Comparative Example 2

[0070] The lithium iron phosphate material in the present comparative example is prepared according to the following method:

[0071] (1) Take 1000 kg of iron phosphate, 249 kg of lithium carbonate, 110 kg of glucose monohydrate together into 1500 L of pure water, stir for 0.5 h, and then obtain a mixed solution; the mixed solution is ground by a sand mill to D50 = 0.2-0.25 μm to obtain a slurry; the ground slurry is spray dried to obtain a precursor;

[0072] (2) The precursor is sintered at 760°C for 8 h under a nitrogen atmosphere, and the sintered lithium iron phosphate is crushed to obtain a lithium iron phosphate product.

[0073] Comparative Example 1 and Comparative Example 2 are the current industrial process for producing lithium iron phosphate.

[0074] Figures 1-5 The SEM images of the lithium iron phosphate materials prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 are shown in the figures. As can be seen from the figures, the lithium iron phosphate materials prepared in Examples 1-3 have no obvious large particle substances on the surface, and the coating of the composite metal oxides can well maintain the structure of the materials themselves, which is conducive to the performance of the materials. The lithium iron phosphate materials prepared in Comparative Example 1 and Comparative Example 2 have obvious large particle substances on the surface, and the damage degree of the materials is more serious.

[0075] The tap density of the lithium iron phosphate materials obtained in Examples 1, 2, 3 and Comparative Examples 1, 2 is tested. In addition, the lithium iron phosphate materials obtained in Examples 1, 2, 3 and Comparative Examples 1, 2 are assembled into button cells according to the same method commonly used in the art, i.e., the prepared lithium iron phosphate materials are used as positive electrode materials, lithium sheets are used as negative electrode materials to prepare CR2025 button cells. The specific preparation process is as follows: the positive electrode material, carbon black and polytetrafluoroethylene are dissolved in N-methyl pyrrolidone at a proper ratio, ground thoroughly and coated on an aluminum foil, then the foil is dried and knocked into pieces, and the assembly is completed in a glove box in the order of positive electrode shell→positive electrode piece→separator→lithium piece→gasket→negative electrode shell. The discharge specific capacity of the battery is tested. The results are shown in Table 1.

[0076] Table 1 Comparison of properties of lithium iron phosphate materials

[0077]

[0078] As can be seen from Table 1, the lithium iron phosphate materials obtained in Examples 1-3 have higher tap densities than the lithium iron phosphate materials obtained in Comparative Examples 1 and 2.

[0079] Batteries using the lithium iron phosphate materials obtained in Examples 1-3 as positive electrode materials have better discharge specific capacities.

[0080] The above description is merely preferred embodiments of the present application, and it is to be noted that, for the ordinary skilled in the art, certain improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A lithium iron phosphate material, characterized in that, The lithium iron phosphate material is coated with a multi-composite metal oxide layer on the surface; the compaction density of the lithium iron phosphate material is 2.4-2.6 g / cm 3 ; The multi-composite metal oxide is Li2O·MgO·Nb2O5·TiO2·La2O3; the molar ratio of lithium, magnesium, niobium, titanium and lanthanum in the multi-composite metal oxide is n(Li):n(Mg):n(Nb):n(Ti):n(La)=(0.3-0.5):(0.02-0.05):(0.2-0.5):(0.2-0.6):(0.3-0.5).

2. The method of claim 1, wherein the lithium iron phosphate material is prepared by the steps of: mixing a lithium source, an iron source, and a phosphate source; and heating the mixture to a temperature of 600-800°C for 1-10 hours. The method comprises the following steps: In step S1, the mixed metal powder of lithium, magnesium, niobium, titanium and lanthanum is pre-activated: the mixed metal powder is added into hydrochloric acid, sulfuric acid or nitric acid with a concentration of 0.2-0.5 mol / L and a temperature of 60-80℃ for acid etching, and then vacuum dried at a temperature of 90-110℃ to obtain the pre-activated mixed metal powder; The mixed metal powder is composed of metal powders of lithium, magnesium, niobium, titanium and lanthanum, and the molar ratio of lithium, magnesium, niobium, titanium and lanthanum is n(Li):n(Mg):n(Nb):n(Ti):n(La)=(0.3-0.5):(0.02-0.05):(0.2-0.5):(0.2-0.6):(0.3-0.5); In step S2, the pre-activated mixed metal powder and the high molecular compound are added into water according to a mass ratio of (0.4-1.2):1 for reaction; after the reaction is completed, the slurry is dispersed, sieved and dried to obtain the multi-composite metal oxide; In step S3, the lithium source, the iron source, the phosphorus source, the multi-composite metal oxide, the carbon source and the solvent are mixed to form a slurry K, which is sand-milled and dried; In step S4, the material obtained after drying in step S3 is sintered in a protective atmosphere to obtain the lithium iron phosphate material.

3. The production method according to claim 2, wherein The high molecular compound is urea-formaldehyde resin or phenol-formaldehyde resin; and the addition amount of the high molecular compound is 0.05%-0.1% of the mass of the lithium iron phosphate material.

4. The production method according to claim 2, wherein The reaction in step S2 is carried out at a temperature of 70-110℃ for 2-6h.

5. The production method according to claim 2, wherein In step S3, the solvent is at least one of water, ethanol or ethylene glycol, and the addition amount of the solvent is 35-70% of the total mass of the added substances; the molar ratio of the lithium source, the iron source and the phosphorus source is (1-1.05):(1-1.05):1; the addition amount of the carbon source is 2-18% of the total mass of the solid materials other than the carbon source; and the molar ratio of the phosphorus source to the multi-composite metal oxide is 1:(0-0.01).

6. The production method according to claim 5, wherein In step S3, the particle size of the sand-milled slurry K is 0.4-1μm.

7. The production method according to claim 2, wherein In step S4, the sintering is carried out at a temperature of 600-750℃ for 4-7h.

8. The production method according to any one of claims 2 to 7, wherein The method further comprises a step of jet milling the lithium iron phosphate material.

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