阅读说明：本技术 一种金属掺杂和Mxene包覆双重改性磷酸铁锂复合材料及制备方法与应用 (Metal-doped and Mxene-coated double-modified lithium iron phosphate composite material, and preparation method and application thereof ) 是由 吴其修 于 2019-08-15 设计创作，主要内容包括：一种金属掺杂和Mxene包覆双重改性磷酸铁锂复合材料的制备方法,包括以下步骤：S1.制备磷酸铁锂/Mxene前驱体：将铁盐溶液、磷酸或其盐溶液、锂盐溶液依次置于反应釜,搅拌均匀后加入Mxene,调节溶液pH至7～10,通入保护气体进行反应后,冷却到室温,离心分离、干燥,得到前驱体产物；S2.将步骤S1的前驱体产物置于高温炉中,在惰性气氛下高温烧结,冷却到室温得到金属掺杂和Mxene包覆双重改性磷酸铁锂复合材料。通过掺杂和MXene表面包覆对磷酸铁锂进行双重改性,有效提高了电极材料的导电性,制备的复合材料表现出优异的大倍率性能和循环性能。(A preparation method of a metal-doped and Mxene-coated dual-modified lithium iron phosphate composite material comprises the following steps: s1, preparing a lithium iron phosphate/Mxene precursor: sequentially placing an iron salt solution, a phosphoric acid or a salt solution thereof and a lithium salt solution in a reaction kettle, uniformly stirring, adding Mxene, adjusting the pH value of the solution to 7-10, introducing a protective gas for reaction, cooling to room temperature, performing centrifugal separation, and drying to obtain a precursor product; s2, placing the precursor product obtained in the step S1 in a high-temperature furnace, sintering at high temperature in an inert atmosphere, and cooling to room temperature to obtain the metal-doped and Mxene-coated double-modified lithium iron phosphate composite material. The lithium iron phosphate is subjected to double modification through doping and MXene surface coating, so that the conductivity of the electrode material is effectively improved, and the prepared composite material has excellent high-rate performance and cycle performance.)

1. A preparation method of a metal-doped and Mxene-coated double-modified lithium iron phosphate composite material is characterized by comprising the following steps of:

s1, preparing a lithium iron phosphate/Mxene precursor: sequentially placing an iron salt solution, a phosphoric acid or a salt solution thereof and a lithium salt solution in a reaction kettle, uniformly stirring, adding Mxene, adjusting the pH value of the solution to 7-10, introducing a protective gas for reaction, cooling to room temperature, performing centrifugal separation, and drying to obtain a precursor product;

s2, placing the precursor product obtained in the step S1 in a high-temperature furnace, sintering at high temperature in an inert atmosphere, and cooling to room temperature to obtain the metal-doped and Mxene-coated double-modified lithium iron phosphate composite material.

2. The method of claim 1, wherein the MXene has a molecular formula of M in step S1_a+1X_aWherein, M atomic layers are packed in a hexagonal close packing manner, X atoms are filled in octahedral vacancies to form an MX layer, and M is selected from one or a mixture of more than two of Ti, Zr, Cr, Mo, V and Ta; x is C or N;

preferably, theMXene is selected from Ti₃C₂、Zr₃C₂、Ti₄C₃Or V₄C₃。

3. The preparation method according to claim 1 or 2, wherein in step S1, MXene is heated in air at 150-250 ℃ for reaction for 0.5-30 mins and then cooled to room temperature to obtain MO before preparing the lithium iron phosphate/Mxene precursor₂Mxene composite material, MO in composite material₂The mass ratio is 8-15%.

4. The method according to any one of claims 1 to 3, wherein the lithium salt in step S1 is Li₂CO₃At least one of LiOH, lithium acetate and lithium nitrate; the iron salt is ferrous phosphate, ferrous oxalate or ferrous sulfate; the phosphoric acid or the salt thereof is phosphoric acid or ammonium dihydrogen phosphate.

5. The method according to any one of claims 1 to 4, wherein the concentrations of the iron salt solution and the phosphoric acid or its salt solution in step S1 are the same or different and are 0.4 to 3.0mol/L and the lithium salt solution is 2.5 to 4mol/L, independently of each other.

6. The method according to any one of claims 1 to 5, wherein the iron salt solution, the phosphoric acid or a salt solution thereof, and the lithium salt solution in step S1 are prepared in such a manner that the molar ratio of the iron element, the phosphate group, and the lithium element is 1 (1-1.5) to (1-1.2);

preferably, the iron salt described in step S1: the molar ratio of Mxene is 1 (0.01-0.6).

7. The production method according to any one of claims 1 to 6, wherein the temperature of the high-temperature sintering in step S2 is 500 ℃ to 750 ℃.

8. The metal-doped and Mxene-coated dual modified lithium iron phosphate composite prepared by the preparation method of any one of claims 1 to 7.

9. The metal-doped and Mxene-coated dual modified lithium iron phosphate composite material according to claim 8, wherein the particle size of the composite material is 50-300 nm;

preferably, the mass content of MXene in the metal-doped and Mxene-coated double-modified lithium iron phosphate composite material is 1-30.0 wt%;

preferably, the mass content of M in the metal-doped and Mxene-coated dual-modified lithium iron phosphate composite material is 0.1-8.0 wt%.

10. A lithium ion battery comprising the metal-doped and Mxene-coated dual modified lithium iron phosphate composite prepared by the preparation method according to any one of claims 1 to 7.

Technical Field

The invention relates to the technical field of lithium ion battery materials, in particular to a metal-doped and Mxene-coated double-modified lithium iron phosphate composite material for a lithium ion battery, and a preparation method and application thereof.

Background

The lithium ion battery has a series of advantages of high specific capacity, high working voltage, good safety, no memory effect and the like, and is widely applied to various portable electronic instruments and equipment such as notebook computers, mobile phones and instrument and meter lamps. Meanwhile, the lithium ion battery has good application prospect in the fields of electric vehicles, electric tools, energy storage power stations and the like. Therefore, with the continuous widening of the application field of the lithium ion battery and the continuous upgrading and updating of corresponding products, higher and higher requirements are certainly put forward on the lithium ion battery, and the most direct method for improving the comprehensive performance of the battery is to improve the performance of the battery material.

The positive electrode material is used as one of the core components of the battery and plays a critical role in the comprehensive performance of the battery. The most studied lithium ion battery positive electrode materials in the market at present mainly comprise lithium cobaltate, lithium nickelate, lithium manganate, ternary materials and lithium iron phosphate. The lithium iron phosphate anode material has the advantages of rich raw materials, low price, no pollution, good safety, obvious charge and discharge platform, appropriate capacity and the like, and is very suitable for being used as the anode material of the lithium ion battery. However, the conductivity of the lithium iron phosphate is low, and the lithium iron phosphate is an important factor for restricting the rate capability and cycle performance improvement. The conductivity of lithium iron phosphate is improved mainly by two ways: one is doping modification, and the other is surface carbon coating modification, wherein the surface coating is a modification means which is relatively commonly used in industrialization. However, the existing modification method can only improve the conductivity and the cycle performance of the lithium iron phosphate material to a certain extent.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a metal-doped and Mxene-coated dual-modified lithium iron phosphate composite material, and a preparation method and application thereof. The lithium ion battery mainly solves the problems that in the prior art, the electronic conductivity and the ionic conductivity of lithium iron phosphate in the lithium ion battery are poor, and the diffusion coefficient of lithium ions is small during charging and discharging, so that the discharge capacity of the material at room temperature is small, and the cycle performance and the rate performance are poor.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a metal-doped and Mxene-coated dual-modified lithium iron phosphate composite material comprises the following steps:

s1, preparing a lithium iron phosphate/Mxene precursor: sequentially placing an iron salt solution, a phosphoric acid or a salt solution thereof and a lithium salt solution in a reaction kettle, uniformly stirring, adding Mxene, adjusting the pH value of the solution to 7-10, introducing a protective gas for reaction, cooling to room temperature, performing centrifugal separation, and drying to obtain a precursor product;

s2, placing the precursor product obtained in the step S1 in a high-temperature furnace, sintering at high temperature in an inert atmosphere, and cooling to room temperature to obtain the metal-doped and Mxene-coated double-modified lithium iron phosphate composite material.

According to the embodiment of the invention, in the step S1, the molecular formula of MXene is M_a+1X_aWherein, M atomic layers are packed in a hexagonal close packing manner, X atoms are filled in octahedral vacancies to form an MX layer, and M is selected from one or a mixture of more than two of Ti, Zr, Cr, Mo, V and Ta; x is C or N.

Preferably, the MXene is selected from Ti₃C₂、Zr₃C₂、Ti₄C₃Or V₄C₃The MXene is commercially available or prepared according to the prior art.

According to an embodiment of the present invention, in step S1, the lithium iron phosphate/Mxene precursor is first preparedHeating MXene in air at 150-250 ℃, reacting for 0.5-30 mins, and cooling to room temperature to obtain MO₂Mxene composite material, MO in composite material₂The mass ratio is 8-15%;

according to an embodiment of the present invention, the lithium salt described in step S1 is Li₂CO₃At least one of LiOH, lithium acetate and lithium nitrate; the iron salt is ferrous phosphate, ferrous oxalate or ferrous sulfate; the phosphoric acid or the salt thereof is phosphoric acid or ammonium dihydrogen phosphate.

According to an embodiment of the present invention, the concentrations of the iron salt solution and the phosphoric acid or a salt solution thereof described in step S1 are the same or different, and are 0.4 to 3.0mol/L and the concentration of the lithium salt solution is 2.5 to 4mol/L, independently of each other;

according to an embodiment of the invention, the iron salt solution, the phosphoric acid or a salt solution thereof, and the lithium salt solution described in step S1 are (1-1.5) to (1-1.2) in a molar ratio of the iron element, the phosphate radical, and the lithium element;

according to an embodiment of the present invention, the iron salt described in step S1: the molar ratio of Mxene is 1 (0.01-0.6);

according to the embodiment of the invention, the reaction temperature in the step S1 is 100-160 ℃;

according to an embodiment of the present invention, the shielding gas in step S1 is nitrogen or carbon dioxide;

according to the embodiment of the present invention, the flow rate of the shielding gas in step S1 is 0.1 to 10L/min, and more preferably 0.5 to 5L/min;

according to the embodiment of the present invention, the stirring rotation speed in step S1 is 30 to 200r/min, and more preferably 50 to 150 r/min;

according to the embodiment of the present invention, the reaction time in step S1 is 1 to 24 hours, and more preferably 1 to 8 hours;

according to an embodiment of the present invention, the temperature of the high temperature sintering is 500 to 750 ℃, preferably 550 to 700 ℃ in step S2.

According to the embodiment of the present invention, in the step S2, the sintering time is 0.5 to 12 hours, preferably 1 to 8 hours, and further preferably 2 to 6 hours.

According to an embodiment of the present invention, in step S2, the inert gas atmosphere is nitrogen or argon.

According to the embodiment of the present invention, the flow rate of the shielding gas in the step S2 is 0.2 to 10L/min, and more preferably 0.5 to 5L/min;

the invention also provides the metal-doped and Mxene-coated dual-modified lithium iron phosphate composite material prepared by the method.

Preferably, the particle size of the metal-doped and Mxene-coated dual-modified lithium iron phosphate composite material is 50-300 nm.

Preferably, the mass content of MXene in the metal-doped and Mxene-coated dual-modified lithium iron phosphate composite material is 1-30.0 wt%, and more preferably 1-15.0 wt%.

Preferably, the mass content of M in the metal-doped and Mxene-coated dual-modified lithium iron phosphate composite material is 0.1-8.0 wt%, and more preferably 0.2-5.0 wt%.

The invention also provides a lithium ion battery, which comprises the metal-doped and Mxene-coated double-modified lithium iron phosphate composite material.

The invention has the following advantages:

1. the two-dimensional layered transition metal carbide nanosheet (MXene) material used in the invention is a novel two-dimensional crystal compound with a graphene-like structure, has high specific surface area, good conductivity and hydrophilicity, and is easy to react with Li¹⁺、PO₄ ^3-、Fe²⁺And (4) combining. In the hydrothermal reaction process, the growth of the lithium iron phosphate nanocrystal and the MXene coating process are synchronously performed, and the uniformity of the obtained lithium iron phosphate/Mxene precursor is better.

2. In the preparation method, MXene is heated and oxidized to form uniformly distributed nano MO on the surface in situ₂In the high-temperature sintering process, M enters the crystal lattice of the lithium iron phosphate to realize the doping of metal ions, and MXene with excellent conductivity is coated on the surface of the lithium iron phosphate to effectively control the growth of crystal grains. Preparation ofThe crystal grains in the composite material are orderly arranged and are densely stacked, so that the structural stability of the electrode material is maintained; the lithium iron phosphate is subjected to double modification through doping and MXene surface coating, so that the conductivity of the electrode material is effectively improved, and the composite material has excellent high-rate performance and cycle performance.

Detailed Description

The technical solution of the present invention will be further described in detail with reference to specific embodiments. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

Unless otherwise indicated, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.