CN106602024A - In-situ surface-modified lithium-rich material and preparation method thereof - Google Patents

Abstract

The invention discloses a lithium-rich material with in-situ modification of the surface. The raw materials include a coating layer and a lithium-rich material precursor. The coating layer is metal phosphate, and the lithium-rich material precursor is MnMA oxide, hydroxide A mixture of at least one of compound, carbonate, oxalate and lithium source, wherein M is a metal element, and A is at least one of S, P, B and F. A preparation method is also disclosed, wherein metal phosphate compounds are coated on the lithium-rich material precursor particles, and then sintered at a high temperature to form an in-situ modified lithium-rich material. The advantage of the present invention is that the in-situ modified structure of the present invention greatly improves the surface stability and electrical conductivity of the lithium-rich material, and significantly improves the charge-discharge specific capacity, efficiency, rate and cycle performance of the material; The invention has simple preparation process, low cost, good result reproducibility and is suitable for large-scale popularization.

Description

A kind of surface in-situ modified lithium-rich material and preparation method thereof

technical field

The invention belongs to the technical field of lithium ion batteries, in particular to a surface in-situ modified lithium-rich material and a preparation method thereof.

Background technique

Due to the characteristics of high energy density, long cycle life, environmental protection, and low cost, lithium-ion batteries have developed rapidly in more than 20 years, and their applications involve communications, transportation, military, medical, entertainment, and many other fields. In recent years, with the rapid development of electric vehicles, high specific energy and high power lithium-ion batteries have become an inevitable direction for the development of lithium-ion batteries in the future. The current commercial cathode materials, such as LiCoO ₂ , LiFePO ₄ , LiMn ₂ O ₄ , and ternary materials, all have low specific capacities (<200mAh/g). The cathode material is the main factor limiting the specific energy of the battery. Therefore, in order to develop a high specific energy battery, it is urgent to find a cathode material with a higher specific capacity.

In recent years, lithium-rich materials have attracted widespread attention due to their high specific capacity, good safety, and low cost. Its specific capacity generally exceeds 250mAh/g, and even reaches 300mAh/g in some reports (NanoLett., 2008, 8(3):957-961). Although lithium-rich materials have high capacity, their cycle performance is poor, and there is a serious problem of voltage attenuation, which restricts their commercial application. Therefore, it is necessary to modify Li-rich materials to improve their specific capacity and voltage retention during cycling.

At present, the main methods to improve the electrochemical performance of lithium-rich materials are coating and doping (Adv. Mater. 2012, 24, 1192–1196; Adv. Funct. Mater. 2014, 1-7). The most common coating method is to use Al(OH) ₃ , Al ₂ O ₃ , TiO ₂ and other inert materials to coat the surface of lithium-rich materials (Electrochimica Acta 50 (2005) 4784-4791, Journal of Power Sources 159 (2006) 1334-1339), these coatings usually protect the surface structure of lithium-rich materials, prevent the material from contacting with the electrolyte and cause negative reactions, and improve the initial charge-discharge efficiency and cycle performance of lithium-rich materials to a certain extent. The patent with the publication number CN 103035906 A uses a wet method to coat the surface of Li[Li _(1-2x)/3 M _x Mn _(2-x)/3 ]O ₂ with 3-10wt% LiMnPO ₄ . It is beneficial to the improvement of the rate performance of the material, and the PO ₄ ^3- in LiMnPO ₄ can effectively inhibit the dissolution of the electrode material in the electrolyte, prevent the hydrofluoric acid in the electrolyte from corroding the surface of the active material, and improve the thermodynamic stability of the material. The technical solution disclosed in the patent with the publication number CN101859887 is to coat the positive electrode material with phosphate, which can protect the material and improve the capacity and rate performance. The technical solution disclosed in the patent with the publication number CN 103904311A is to coat a layer of lithium iron phosphate on the surface of the finished lithium-rich material, wherein the lithium source used for the lithium iron phosphate comes from the lithium in the lithium-rich material. The "surplus" lithium is conducive to the stability of the material structure, but this kind of post-coating on the finished lithium-rich material by the liquid phase method needs to first immerse the finished lithium-rich material in the solution, and then undergo precipitation and filtration. , washing, drying, heat treatment and a series of treatment processes, the method is more complicated. In addition, there are problems such as uneven coating layer and insufficient bonding degree of coating layer and lithium-rich material. Therefore, it cannot fundamentally reduce or inhibit the precipitation of oxygen and the migration of transition metals, so it cannot effectively solve the problems of poor cycle performance and voltage attenuation of materials.

Although the above-mentioned studies on improving the structural stability and electrochemical performance of lithium-rich materials have achieved the beneficial effect of improving capacity and rate performance to a certain extent, considering the overall market, while improving lithium-rich materials, the preparation of The method is simple and the cost of the selected materials is low, which is a method that can be promoted in the market. In the field of lithium batteries, the technical problem to be solved is to establish a simple, effective and easy-to-scale promotion of lithium-rich materials. The method of surface modification and coating can obtain lithium battery products with high cycle life, specific capacity and high rate performance.

Contents of the invention

In order to solve the above technical problems, the present invention provides a surface in-situ modified lithium-rich material and its preparation method, which realizes the improvement of the surface stability and electrical conductivity of the lithium-rich material, and makes the charge-discharge specific capacity, efficiency, and rate of the material and cycle performance are significantly improved.

In order to achieve the above purpose, the technical solution disclosed in the present invention is: a surface in-situ modified lithium-rich material developed by the present invention, the raw material includes a coating layer and a lithium-rich material precursor, and the coating layer is a metal phosphate , the lithium-rich material precursor is a mixture of at least one of MnMA oxides, hydroxides, carbonates, oxalates and a lithium source, where M is a metal element, and A is S, P, B and F at least one of . Metal phosphates are used to coat the lithium-rich material precursor, the coating layer is uniform, and the bonding degree is high, and the coating layer and the raw material of the lithium-rich material will undergo interfacial reaction to form a lithium-containing intermediate layer (inter layer), thereby improving the ionic conductivity and electrochemical performance of the material.

Further, the metal phosphate is at least one of phosphates corresponding to Ti, Mg, Zr, Zn, Cr, Cu, V, Fe, Mn, Al, Co, Ni and Mo. The selected metal phosphate can coat the lithium-rich material precursor to obtain a lithium-rich material with high charge-discharge specific capacity, efficiency, rate and cycle performance.

Further, the metal M in the lithium-rich material precursor is at least one of Ni, Co, Al, Mg, Ti, Fe, Cu, Cr, Mo, Zr, Ru and Sn.

Further, the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate, wherein the molar ratio of Li to MnMA is 1-2.5:1.

Further, the molar percentage of the cladding layer in the raw material is 0.01%-12%, and the molar percentage of the lithium-rich material precursor is 88%-99.99%. The selected coating molar percentage takes into account the thickness of the material coating layer and the performance of the material. After verification of the lithium-rich material obtained in the subsequent steps, a material with high charge-discharge specific capacity, efficiency, rate and cycle performance can be obtained. At the same time The amount of raw materials used is minimal and the cost is low.

Further, the chemical formula of the in-situ modified lithium-rich material obtained in the present invention is (1-a) Li _{1+ x Mny} M _z A _w O _r -aLi _b Me _c PO ₄ , where 0.0001≤a≤ 0.12, 0≤b≤3, 0≤c≤1.5, 0<x≤1, 0<y≤1, 0≤z<1, 0≤w≤0.2, 1.8≤r≤3.

The invention also discloses a method for preparing the lithium-rich material. The lithium-rich material precursor particles are coated with metal phosphate compounds, and then sintered at high temperature to form an in-situ modified lithium-rich material. The coating layer of the in-situ coated lithium-rich material obtained by this coating method is uniform, and the coating layer and the lithium-rich material have a good combination and stability, which effectively prevents the lithium-rich material from interacting with the electrolyte. Negative reaction due to contact; at the same time, the "excess" lithium source in the lithium-rich precursor is used to "in-situ" chemically react with the cladding material to form a lithium-containing high-conductivity layer. As a result, the discharge capacity, initial charge-discharge efficiency, and rate performance of the lithium-rich material are significantly improved, and the cycle performance and voltage decay of the material are effectively improved.

Further, the method includes the following steps, (1) adding soluble phosphates into the lithium-rich material precursor, and adding the soluble metal salt solution dropwise while stirring; wherein the molar weight of the soluble phosphate is 1-1 of the soluble metal salt 3 times, the molar ratio of soluble metal salt to lithium-rich material precursor is 0.0001-0.12:0.9999-0.88.

(2) Continue stirring the mixed solution obtained in step (1), and then carry out drying treatment;

(3) Insulating the dried material in step (2) for two times to obtain a lithium-rich material with in-situ surface modification.

Further, the concentration of the soluble metal salt solution in the step (1) in the step (1) is 0.001-10mol/L, the concentration of the soluble phosphate solution is 0.001-10mol/L, and the selected mass concentration is convenient for dissolving , After the verification of lithium-rich materials in subsequent steps, materials with high charge-discharge specific capacity, efficiency, rate and cycle performance can be obtained, and the amount of raw materials used while obtaining beneficial effects is the lowest and the cost is low.

Further, the soluble phosphate in the step (1) includes at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and potassium phosphate.

Further, the soluble metal salt in the step (1) is at least one of soluble salts of Ti, Mg, Zr, Zn, Cr, Cu, V, Fe, Mn, Al, Co, Ni and Mo.

Further, in the step (2), the mixed solution obtained in the step (1) is continuously stirred for 10 min-12 h, and then dried. The drying here includes any form of drying in the prior art, for example, heat drying, blast drying, vacuum drying, spray drying, microwave drying and centrifugal drying are all possible.

In the step (1), the concentration of the soluble metal salt solution is 0.001-10 mol/L, and the concentration of the soluble phosphate solution is 0.001-10 mol/L.

Further, in the step (2), the mixed solution obtained in the step (1) is continuously stirred for 10 min-12 h, and then dried.

Further, the two heat preservation operations in the step (3) refer to the operations of heat preservation at 400-600° C. for 2-8 hours and heat preservation at 700-1000° C. for 3-36 hours.

The selection of temperature and other parameter conditions in the above method steps is beneficial to the uniformity of the coating layer; on the other hand, because the coating layer and the lithium-rich material are sintered at the same time, the bonding degree of the coating layer and the lithium-rich material is increased, and the The stability of the cladding layer; and the cladding layer and the raw material of the lithium-rich material will also undergo interfacial reactions during the sintering process to form a lithium-containing interlayer with high conductivity, thereby improving the ionic conductivity of the material and electrochemical performance.

The positive progress effect of the present invention lies in: the in-situ modified structure of the present invention greatly improves the surface stability and electrical conductivity of the lithium-rich material, so that the charge-discharge specific capacity, efficiency, rate and cycle performance of the material are all significantly improved ; The preparation process of the present invention is simple, the cost is low, the result is reproducible, and is suitable for large-scale promotion.

Description of drawings

Fig. 1 is the X-ray diffraction (XRD) spectrum of the positive electrode materials synthesized in the present invention in Comparative Example 1, Example 1 and Example 2.

Fig. 2 is the comparative example 1 of the present invention synthesis, embodiment 1 and embodiment 2 anode material charge-discharge curve contrast graph for the first time, in the figure, curve 1 is comparative example 1, curve 2 is embodiment 1, and curve 3 is embodiment 2.

Fig. 3 is a comparison chart of discharge curves at different current densities of the cathode materials synthesized in Comparative Example 1, Example 1 and Example 2 of the present invention.

Fig. 4 is a graph comparing cycle performance curves of the positive electrode materials synthesized in Comparative Example 1, Example 1 and Example 2 of the present invention.

detailed description

The present invention will be described in further detail below through specific examples.

Example 1: A lithium-rich material with in-situ surface modification developed by the present invention. The raw material includes a coating layer and a lithium-rich material precursor. The coating layer is metal phosphate, specifically iron phosphate, and the Iron phosphate is made from diammonium hydrogen phosphate and iron nitrate nonahydrate. The lithium-rich material precursor is a mixture of Ni _0.13 Co _0.13 Mn _0.54 O ₂ and lithium hydroxide. The molar ratio of the coating layer to the raw material is 0.01%. The lithium-rich material precursor is 99.99%, and the molar ratio of Li to Ni _0.13 Co _0.13 Mn _0.54 is 1.5:1, and the chemical formula of the in-situ modified lithium-rich material is 0.9999Li _1.5 Mn _0.54 Ni _0.13 Co _0.13 O ₂ -0.0001 FePO ₄ .

The precursor of the lithium-rich material can be prepared by using the existing technology, and the in-situ modified lithium-rich material coated with metal phosphate in the above embodiment can also be prepared by using the method for preparing the lithium-rich material in the prior art.

Example 2: A lithium-rich material with in-situ surface modification developed by the present invention. The raw material includes a coating layer and a lithium-rich material precursor. The coating layer is a metal phosphate, specifically manganese phosphate. Manganese phosphate is made from ammonium dihydrogen phosphate and manganese acetate. The precursor of the lithium-rich material is a mixture of AlCr _0.5 Mn hydroxide and lithium carbonate. The molar weight of the coating layer accounts for 12% of the raw material. The lithium-rich material The precursor is 88%, the molar ratio of AlCr _0.5 Mn to Li is 1:2.5, and the obtained surface in situ modified lithium-rich material has a chemical formula of 0.88Li ₂ MnAlCr _0.5 O ₃ -0.12LiMnPO ₄ .

The method for preparing the in-situ modified lithium-rich material is to coat the precursor particles of the lithium-rich material with metal phosphate compounds, and then sinter at high temperature to form the in-situ modified lithium-rich material.

The temperature and other specific parameters adopted are subject to the realization of the final product.

Example 3: A lithium-rich material with in-situ surface modification developed by the present invention. The raw material includes a coating layer and a lithium-rich material precursor. The coating layer is metal phosphate, specifically nickel phosphate. Nickel phosphate is made from ammonium dihydrogen phosphate and nickel nitrate hexahydrate. The lithium-rich material precursor is a mixture of carbonate and lithium acetate of Mg _0.13 Mo _0.13 Mn _0.54 S _0.2 , Li and Mg _0.13 Mo _0.13 Mn _0.54 S _0.2 The molar ratio is 1:1, the molar weight of the coating layer accounts for 0.01% of the raw material, and the lithium-rich material precursor is 99.99%. The chemical formula of the in-situ modified lithium-rich material is 0.9999LiMn _0.54 Mg _0.13 Mo _0.13 S _0.2 O _1.8 -0.0001LiNiPO ₄ .

The method for preparing the in-situ modified lithium-rich material is to coat the precursor particles of the lithium-rich material with metal phosphate compounds, and then sinter at high temperature to form the in-situ modified lithium-rich material.

The specific preparation method includes the following steps, (1) adding soluble phosphates into the lithium-rich material precursor, and adding the soluble metal salt solution dropwise while stirring; the concentration of the soluble metal salt solution is 0.001mol/L, and the selected soluble The concentration of the phosphate solution is 0.001mol/L; the molar amount of soluble phosphate is twice that of soluble metal salt, and the molar ratio of soluble metal salt to lithium-rich material precursor is 0.0001:0.9999.

(2) Continue stirring the mixed solution obtained in step (1) for 10 min, and then carry out spray drying of the mixed solution;

(3) The material dried in step (2) is kept for two times. After the heat preservation, the in-situ modified lithium-rich material is obtained. The two heat preservation operations refer to the operation of holding at 600°C for 2 hours and holding at 1000°C for 3 hours. .

Example 4: A lithium-rich material with in-situ surface modification developed by the present invention. The raw material includes a coating layer and a lithium-rich material precursor. The coating layer is a metal phosphate, specifically cobalt phosphate. Cobalt phosphate is prepared from sodium phosphate and cobalt nitrate hexahydrate. The lithium-rich material precursor is a mixture of Ti _0.13 Zr _0.13 Mn _0.54 P _0.1 oxalate and lithium nitrate. The mole of the coating layer accounts for 0.01% of the raw material, and the remaining It is a lithium-rich material precursor, in which the molar ratio of Li to Ti _0.13 Zr _0.13 Mn _0.54 P _0.1 is 1.2:1, and the chemical formula of the in-situ modified lithium-rich material obtained is 0.9999Li _1.2 Mn _0.54 Ti _0.13 Zr _0.13 P _0.1 O ₂ -0.0001 LiCoPO ₄ .

The method for preparing the in-situ modified lithium-rich material is to coat the precursor particles of the lithium-rich material with metal phosphate compounds, and then sinter at high temperature to form the in-situ modified lithium-rich material.

The specific preparation method includes the following steps, (1) adding soluble phosphates into the lithium-rich material precursor, and adding the soluble metal salt solution dropwise while stirring; the concentration of the soluble metal salt solution is 10mol/L, and the selected soluble phosphoric acid The concentration of the salt solution is 10mol/L; the molar amount of the soluble phosphate is three times that of the soluble metal salt, and the molar ratio of the soluble metal salt to the lithium-rich material precursor is 0.0001:0.9999.

(2) Continue stirring the mixed solution obtained in step (1) for 12h, then filter and wash the mixed solution, and then dry it;

(3) The material dried in step (2) is kept warm twice, and the surface in situ modified lithium-rich material is obtained after the heat preservation. The two heat preservation operations refer to the operation of holding at 400°C for 8 hours and holding at 700°C for 36 hours. .

Example 5: A lithium-rich material with in-situ surface modification developed by the present invention. The raw material includes a coating layer and a lithium-rich material precursor. The coating layer is a metal phosphate, specifically aluminum phosphate, and the Aluminum phosphate is made from potassium phosphate and aluminum nitrate. The lithium-rich material precursor is a mixture of Fe _0.1 Ru _0.1 Mn _0.54 B _0.1 O ₂ and lithium hydroxide. Lithium-rich material precursor, in which the molar ratio of Li to Fe _0.1 Ru _0.1 Mn _0.54 B _0.1 is 1.5:1, and the chemical formula of the in-situ modified lithium-rich material is 0.88Li _1.23 Mn _0.5 Fe _0.1 Ru _0.14 B _0.1 O ₂ -0.12 AlPO ₄ .

The method for preparing the in-situ modified lithium-rich material is to coat the precursor particles of the lithium-rich material with metal phosphate compounds, and then sinter at high temperature to form the in-situ modified lithium-rich material.

The specific preparation method includes the following steps, (1) adding soluble phosphates into the lithium-rich material precursor, and adding the soluble metal salt solution dropwise while stirring; the concentration of the soluble metal salt solution is 1mol/L, and the selected soluble phosphoric acid The concentration of the salt solution is 1mol/L; the molar amount of the soluble phosphate is twice that of the soluble metal salt, and the molar ratio of the soluble metal salt to the lithium-rich material precursor is 0.12:0.88.

(2) Continue stirring the mixed solution obtained in step (1) for 1 h, then filter and wash the mixed solution, and then dry it;

(3) The material dried in step (2) is kept warm twice, and the surface in situ modified lithium-rich material is obtained after the heat preservation. The two heat preservation operations refer to the operation of holding at 450°C for 5 hours and holding at 800°C for 25 hours. .

Example 6: A lithium-rich material with in-situ surface modification developed by the present invention. The raw materials include a coating layer and a lithium-rich material precursor. The coating layer is metal phosphate, specifically zirconium phosphate. Zirconium phosphate is made from ammonium dihydrogen phosphate and zirconium isopropoxide. The lithium-rich material precursor is a mixture of Cu _0.1 Sn _0.1 Mn _0.54 F _0.1 O ₂ and lithium hydroxide, in which Li and Cu _0.1 Sn _0.1 Mn _0.54 F The molar ratio of _0.1 is 1.5:1, the molar weight of the cladding layer accounts for 0.01% of the raw material, and the rest is the precursor of the lithium-rich material. The chemical formula of the in-situ modified lithium-rich material obtained is 0.9999Li _1.23 Mn _0.54 Cu _0.1 Sn _0.1 F _0.1 O ₂ -0.0001 LiZr _0.5 PO ₄ .

The method for preparing the in-situ modified lithium-rich material is to coat the precursor particles of the lithium-rich material with metal phosphate compounds, and then sinter at high temperature to form the in-situ modified lithium-rich material.

The specific preparation method includes the following steps, (1) adding soluble phosphates into the lithium-rich material precursor, and adding the soluble metal salt solution dropwise while stirring; the concentration of the soluble metal salt solution is 2mol/L, and the selected soluble phosphoric acid The concentration of the salt solution is 2mol/L; the molar amount of the soluble phosphate is twice that of the soluble metal salt, and the molar ratio of the soluble metal salt to the lithium-rich material precursor is 0.0001:0.9999.

(2) Continue stirring the mixed solution obtained in step (1) for 1 h, and then spray-dry the mixed solution;

(3) The material dried in step (2) is kept for two times. After the heat preservation, the in-situ modified lithium-rich material is obtained. The two heat preservation operations refer to the operation of holding at 500°C for 2 hours and holding at 850°C for 20 hours. .

Example 7: A lithium-rich material with in-situ surface modification developed by the present invention. The raw material includes a coating layer and a lithium-rich material precursor. The coating layer is metal phosphate, specifically titanium phosphate. Titanium phosphate is produced from phosphoric acid and tetrabutyl titanate. The lithium-rich material precursor is a mixture of Ni _0.10 Co _0.10 Mn _0.57 O ₂ and lithium hydroxide, wherein the molar ratio of Li to Ni _0.10 Co _0.10 Mn _0.57 is 1.3: 1. The molar weight of the coating layer accounts for 12% of the raw material, and the rest is the precursor of the lithium-rich material. The chemical formula of the in-situ modified lithium-rich material obtained is 0.88Li _1.23 Mn _0.57 Ni _0.10 Co _0.10 O ₂ -0.12Ti _0.75 PO ₄ .

The method for preparing the in-situ modified lithium-rich material is to coat the precursor particles of the lithium-rich material with metal phosphate compounds, and then sinter at high temperature to form the in-situ modified lithium-rich material.

The specific preparation method includes the following steps, (1) adding soluble phosphates into the lithium-rich material precursor, and adding the soluble metal salt solution dropwise while stirring; the concentration of the soluble metal salt solution is 3mol/L, and the selected soluble phosphoric acid The concentration of the salt solution is 3mol/L; the molar amount of soluble phosphate is 1-3 times that of soluble metal salt, and the molar ratio of soluble metal salt to lithium-rich material precursor is 0.12:0.88.

(2) Continue to stir the mixed solution obtained in step (1) for 2h, and then spray dry the mixed solution;

(3) The material dried in step (2) is kept for two times. After the heat preservation, the in-situ modified lithium-rich material is obtained. The two heat preservation operations refer to the operation of holding at 500°C for 2 hours and holding at 850°C for 20 hours. .

Embodiment 8: A surface in situ modified lithium-rich material developed by the present invention. The raw material includes a coating layer and a lithium-rich material precursor. The coating layer is a metal phosphate, specifically magnesium phosphate. Magnesium phosphate is made from diammonium hydrogen phosphate and magnesium sulfate. The lithium-rich material precursor is a mixture of Ni _0.30 Mn _0.48 Fe _0.08 O ₂ and lithium hydroxide. The mass percentage of the coating layer is 12% of the mass percentage of the raw material. The rest is the lithium-rich material precursor, in which the molar ratio of Li to Ni _0.30 Mn _0.48 Fe _0.08 is 1.7:1, and the chemical formula of the obtained surface in-situ modified lithium-rich material is 0.88Li _1.13 Mn _0.48 Ni _0.30 Fe _0.08 O ₂ -0.12LiMgPO ₄ .

The method for preparing the in-situ modified lithium-rich material is to coat the precursor particles of the lithium-rich material with metal phosphate compounds, and then sinter at high temperature to form the in-situ modified lithium-rich material.

The specific preparation method includes the following steps, (1) adding soluble phosphates into the lithium-rich material precursor, and adding the soluble metal salt solution dropwise while stirring; the concentration of the soluble metal salt solution is 4mol/L, and the selected soluble phosphoric acid The concentration of the salt solution is 4mol/L; the molar amount of the soluble phosphate is three times that of the soluble metal salt, and the molar ratio of the soluble metal salt to the lithium-rich material precursor is 0.12:0.88.

(2) Continue stirring the mixed solution obtained in step (1) for 6h, and then spray dry the mixed solution;

(3) The material dried in step (2) is kept warm twice, and the surface in situ modified lithium-rich material is obtained after the heat preservation. The two heat preservation operations refer to the operation of holding at 600°C for 4 hours and holding at 860°C for 16 hours. .

Embodiment 9: A lithium-rich material with surface in-situ modification developed by the present invention. The raw material includes a coating layer and a lithium-rich material precursor. The coating layer is a metal phosphate, specifically zinc phosphate, and the Zinc phosphate is made from potassium phosphate and zinc sulfate. The lithium-rich material precursor is a mixture of Ni _0.30 Mn _0.48 Fe _0.08 O ₂ and lithium hydroxide. The molar weight of the coating layer accounts for 0.01% of the raw material, and the rest is Lithium-rich material precursor, in which the molar ratio of Li to Ni _0.30 Mn _0.48 Fe _0.08 is 1.3:1, and the chemical formula of the obtained surface in-situ modified lithium-rich material is 0.9999Li _1.13 Mn _0.48 Ni _0.30 Fe _0.08 O ₂ -0.0001 LiZnPO ₄ .

The method for preparing the in-situ modified lithium-rich material is to coat the precursor particles of the lithium-rich material with metal phosphate compounds, and then sinter at high temperature to form the in-situ modified lithium-rich material.

The specific preparation method includes the following steps, (1) adding soluble phosphates into the lithium-rich material precursor, and adding the soluble metal salt solution dropwise while stirring; the concentration of the soluble metal salt solution is 5mol/L, and the selected soluble phosphoric acid The concentration of the salt solution is 5 mol/L; the molar amount of the soluble phosphate is three times that of the soluble metal salt, and the molar ratio of the soluble metal salt to the lithium-rich material precursor is 0.0001:0.9999.

(2) Continue stirring the mixed solution obtained in step (1) for 6h, then filter and wash the mixed solution, and then carry out drying treatment;

(3) The material dried in step (2) is kept warm twice, and the surface in situ modified lithium-rich material is obtained after the heat preservation. The two heat preservation operations refer to the operation of holding at 600°C for 4 hours and holding at 860°C for 16 hours. .

Example 10: A lithium-rich material with surface in-situ modification developed by the present invention. The raw material includes a coating layer and a lithium-rich material precursor. The coating layer is metal phosphate, specifically copper phosphate. Copper phosphate is made from ammonium phosphate and copper sulfate. The precursor of the lithium-rich material is a mixture of Ni _0.30 Mn _0.48 Fe _0.08 O ₂ and lithium hydroxide. It is a lithium-rich material precursor, in which the molar ratio of Li to Ni _0.30 Mn _0.48 Fe _0.08 is 1.12:1, and the chemical formula of the in-situ modified lithium-rich material obtained is 0.9999Li _1.1 Mn _0.48 Ni _0.30 Fe _0.08 O ₂ -0.00001 CuPO ₄ .

The method for preparing the in-situ modified lithium-rich material is to coat the precursor particles of the lithium-rich material with metal phosphate compounds, and then sinter at high temperature to form the in-situ modified lithium-rich material.

The specific preparation method includes the following steps, (1) adding soluble phosphates into the lithium-rich material precursor, and adding the soluble metal salt solution dropwise while stirring; the concentration of the soluble metal salt solution is 6mol/L, and the selected soluble phosphoric acid The concentration of the salt solution is 6mol/L; the molar amount of the soluble phosphate is three times that of the soluble metal salt, and the molar ratio of the soluble metal salt to the lithium-rich material precursor is 0.0001:0.9999.

(2) Continue stirring the mixed solution obtained in step (1) for 6h, then filter and wash the mixed solution, and then carry out drying treatment;

(3) The material dried in step (2) is kept warm twice, and the surface in situ modified lithium-rich material is obtained after the heat preservation. The two heat preservation operations refer to the operation of holding at 600°C for 4 hours and holding at 860°C for 16 hours. .

The following is the test data of the surface in-situ modified lithium-rich material obtained in the present invention:

First of all, comparative examples 1-3 are set, and comparative examples 1-3 are all lithium-rich materials obtained by the prior art. Comparative example 1: step 1, precursor synthesis

According to the ratio of the amount of substance (Li:Ni:Co:Mn=1.24:0.13:0.13:0.54), take by weighing nickelous oxide, cobalt oxide, manganese dioxide and lithium carbonate, wherein lithium carbonate is excessive 3%, in the blender After mixing in medium for 12 hours, add deionized water according to the proportion of solid content of 20wt%, and then pour the slurry into a ball mill to grind until the medium particle size is less than 0.3 microns. Finally, the obtained slurry is spray-dried to obtain the precursor of Li[Li _0.20 Ni _0.13 Co _0.13 Mn _0.54 ]O ₂ .

Step 2. High temperature sintering

The precursor was kept at 450°C for 5 hours, then continued to heat up to 800°C, and held for 25 hours; finally, the temperature was naturally cooled to room temperature, and the Li[Li _0.20 Ni _0.13 Co _0.13 Mn _0.54 ]O ₂ material was obtained.

Comparative example 2: Step 1, precursor synthesis

According to the ratio of the amount of substance (Li:Ni:Co:Mn=1.27:0.10:0.10:0.57), take by weighing nickelous oxide, cobalt oxide, manganese dioxide and lithium carbonate, wherein lithium carbonate is excessive 3%, in the blender After mixing in medium for 12 hours, add deionized water according to the proportion of solid content of 20wt%, and then pour the slurry into a ball mill to grind until the medium particle size is less than 0.3 microns. Finally, the obtained slurry was stirred on a water bath at 60°C until dry, and then dried in a vacuum oven at 100°C for 12 hours to obtain a precursor of Li[Li _0.23 Ni _0.10 Co _0.10 Mn _0.57 ]O ₂ .

Step 2. High temperature sintering

The precursor was kept at 500°C for 2 hours, then continued to heat up to 850°C, and held for 20 hours; finally, the temperature was naturally cooled to room temperature, and the Li[Li _0.23 Ni _0.10 Co _0.10 Mn _0.57 ]O ₂ material was obtained.

Comparative example 3: Step 1, precursor synthesis

According to the ratio of the amount of substance (Li:Ni:Fe:Mn=1.16:0.30:0.08:0.48) take by weighing nickelous oxide, ferric nitrate, manganese dioxide and lithium carbonate, wherein lithium carbonate is excessive 3%, in mixer After mixing in medium for 12 hours, add deionized water according to the proportion of solid content of 20wt%, and then pour the slurry into a ball mill to grind until the medium particle size is less than 0.3 microns. Finally, the obtained slurry was filtered, washed thoroughly, and dried in a blast oven at 100°C for 6 hours to obtain a precursor of Li[Li _0.13 Ni _0.30 Mn _0.48 Fe _0.08 ]O ₂ .

Step 2. High temperature sintering

The precursor was kept at 600°C for 4 hours, then continued to heat up to 860°C, and held for 16 hours; finally, the temperature was naturally cooled to room temperature, and the Li[Li _0.13 Ni _0.30 Mn _0.48 Fe _0.08 ]O ₂ material was obtained.

In order to test the electrochemical properties of the materials of Examples 1-10 of the present invention and Comparative Examples 1-3, the above-mentioned prepared materials were used as positive electrode materials, assembled into button batteries, and charged and discharged experiments were carried out. The specific experimental steps were as follows:

1) Mix the above active material, conductive carbon black (Supper P) and polyvinylidene fluoride (PVDF) at a ratio of 80:10:10, add N-methyl-2-pyrrolidone (NMP) to make a slurry, and Coated on aluminum foil, dried and cut into circular pole pieces with a diameter of 1.4 cm.

2) After the above-mentioned pole pieces are rolled, they are dried in a vacuum drying oven at 120 degrees for 12 hours, and then in a glove box filled with argon, with pure lithium sheets as the negative electrode material, 1mol/L LiPF6-EC+DEC+DMC ( The volume ratio is 1:1:1) as the electrolyte, with Celgard2300 as the diaphragm, and packed into a CR2032 button battery.

3) Carry out the charge and discharge test on the assembled button experimental battery on the charge and discharge tester. The charge and discharge voltage range is: 2 to 4.8V, and the current density of 200mA/g is defined as 1C. The charge and discharge system of the rate performance test is: Charge and discharge at a constant current density of 0.1C, 0.2C, 0.5C, 1C, and 3C for 3 weeks each. The charging and discharging system for the cycle performance test is: first charge and discharge at a constant current density of 0.1C in the voltage range of 2-4.8V for 3 weeks, and then perform constant current charging and discharging at a current density of 1C in the voltage range of 2-4.6V.

The test results of the 0.1C initial discharge specific capacity, 3C discharge specific capacity and 200-cycle capacity retention rate of the experimental battery prepared according to the above method are listed in Table 1.

From the results of charge and discharge tests, compared with the lithium-rich material without surface coating in the comparative example, the composite lithium-rich material with in-situ coating on the surface of Examples 1-10 of the present invention has better initial discharge capacity, 3C discharge Capacity and cycle performance are improved to varying degrees.

The electrochemical performance test data sheet of the material prepared in the embodiment of the present invention and comparative example in table 1

Fig. 1 is the X-ray diffraction spectrum of the material prepared by comparative example 1, embodiment 1 and embodiment 2 (the XRD spectrum of the material prepared by other specific examples is similar, omitted), as can be seen from the figure the XRD of the material before and after coating The graphs all show the layered structure of α-NaFeO ₂ , which shows that the coating has no obvious influence on the basic layered structure of the lithium-rich material. In the graph after coating, the diffraction peak of the Li ₃ PO ₄ structure can be seen, indicating that This Li ₃ PO ₄ -like structure exists in the coated material, which is beneficial to improve the electrical conductivity of the material.

Fig. 2, Fig. 3 and Fig. 4 are respectively the first charge and discharge comparison chart, rate discharge capacity comparison chart and cycle performance comparison chart of Example 1, Example 2 and Comparative Example 1. It can be seen from the figure that the initial discharge capacity, rate performance and cycle capacity retention rate of Examples 1 and 2 after surface in-situ coating are all significantly improved.

The composite lithium-rich material coated in situ on the surface provided by the invention has high specific capacity, good rate performance and cycle performance, and can be used as a positive electrode material of a power lithium ion battery for pure electric vehicles and plug-in hybrid vehicles. Moreover, the preparation is simple and the industrial production is easy.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (13)

1. a kind of surface in situ modification type richness lithium material, it is characterised in that raw material includes clad, rich lithium material presoma, The clad is metal phosphate, and rich lithium material presoma is in oxide, hydroxide, carbonate, the oxalates of MnMA At least one mixture with lithium source, wherein M is metallic element, and A is at least one in S, P, B and F.

2. in-situ modification type according to claim 1 richness lithium material, it is characterised in that the metal phosphate be Ti, Mg, At least one of Zr, Zn, Cr, Cu, V, Fe, Mn, Al, Co, Ni corresponding with Mo phosphate.

3. in-situ modification type according to claim 1 richness lithium material, it is characterised in that in the rich lithium material presoma Metal M is at least one in Ni, Co, Al, Mg, Ti, Fe, Cu, Cr, Mo, Zr, Ru and Sn.

4. in-situ modification type according to claim 1 richness lithium material, it is characterised in that the lithium source is Lithium hydrate, carbon At least one in sour lithium, lithium acetate, lithium nitrate, wherein Li are 1-2.5 with the mol ratio of MnMA：1.

5. in-situ modification type according to claim 1 richness lithium material, it is characterised in that clad mole in the raw material Amount percentage ratio is 0.01%-12%, and the mole percentage ratio of the rich lithium material presoma is 88%-99.99%.

6. in-situ modification type according to claim 1 richness lithium material, it is characterised in that the in-situ modification type richness lithium material Chemical formula be (1-a) Li_1+xMn_yM_zA_wO_r-aLi_bMe_cPO₄, wherein, 0.0001≤a≤0.12,0≤b≤3,0≤c≤1.5, 0 ＜ x≤1,0 ＜ y≤1,0≤z ＜ 1,0≤w≤0.2,1.8≤r≤3.

7. it is a kind of prepare described in claim 1-6 any one in-situ modification type richness lithium material method, it is characterised in that should Method is included in rich lithium material precursor particle and coats metal phosphate compounds, and then Jing high temperature sinterings form in-situ modification Type richness lithium material.

8. it is according to claim 7 prepare in-situ modification type richness lithium material method, it is characterised in that the method include as Lower step, (1) is added into soluble phosphate in rich lithium material presoma, while stirring Deca soluble metal salt solution, The mole of wherein soluble phosphate is 1-3 times of soluble metallic salt, and soluble metallic salt rubs with rich lithium material presoma You are than being 0.0001-0.12：0.9999-0.88.

(2) mixed solution for obtaining step (1) continues to stir, and is then dried process；

(3) the dried material of step (2) is incubated twice, surface in situ modification type richness lithium material is obtained after insulation.

9. it is according to claim 8 prepare in-situ modification type richness lithium material method, it is characterised in that the step (1) Middle soluble phosphate includes at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, diammonium phosphate, sodium phosphate, potassium phosphate.

10. it is according to claim 8 prepare in-situ modification type richness lithium material method, it is characterised in that the step (1) Middle soluble metallic salt is at least one in the soluble-salt of Ti, Mg, Zr, Zn, Cr, Cu, V, Fe, Mn, Al, Co, Ni and Mo.

11. methods for preparing in-situ modification type richness lithium material according to claim 8, it is characterised in that the step (1) Middle soluble metal salt solution concentration is 0.001-10mol/L, and the concentration of soluble phosphoric acid salt solution is 0.001-10mol/ L。

12. methods for preparing in-situ modification type richness lithium material according to claim 8, it is characterised in that the step (2) The middle mixed solution for obtaining step (1) continues to stir after 10min-12h, is being dried process.

13. methods for preparing in-situ modification type richness lithium material according to claim 8, it is characterised in that the step (3) In twice insulation operation refer to successively 400-600 DEG C be incubated 2-8h, 700-1000 DEG C be incubated 3-36h operation.