CN103746094A - C-LiFePO4/PTPAn composite material, its application and lithium battery prepared from it - Google Patents

Abstract

The invention provides a C-LiFePO4/PTPAn composite material, its application and a lithium battery produced by the composite material thereof. The C-LiFePO4/PTPAn composite material is characterized by taking a carbon-coated LiFePO4 material and PTPAn as raw materials and prepared by a solution blending method. The C-LiFePO4/PTPAn composite material which is taken as a lithium ion batteries cathode material has good charge and discharge performances, cycle stability and high magnification performance.

Description

C-LiFePO4/PTPAn composite material, its application and lithium battery prepared from it

technical field

The invention belongs to the technical field of lithium ion batteries, and in particular relates to a C-LiFePO ₄ /PTPAn composite material and its application as a lithium battery positive electrode material and the lithium ion battery prepared therefrom.

Background technique

With the further development of human society, the energy problems, resource problems and environmental problems facing the world are becoming more and more serious. Since the current energy structure is basically based on petrochemical fuels (petroleum, coal, natural gas), this not only causes resource depletion but also pollutes the environment. Electric energy will play an increasingly important role in the future due to its cleanliness, safety and convenience. Therefore, in the future, lithium-ion batteries with good mobility and convenient storage and power supply will play a pivotal role in a society based on electric energy. the

Traditional lithium-ion battery cathode materials mainly use transition metal oxides, such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide and vanadium oxide, etc. These materials are mainly precious metals, which often have limited mineral resources, high prices, Defects such as polluting the environment and high preparation costs. Therefore, for the sustainable development of human society, the research and development of new high-performance electrochemical power sources and materials has become particularly critical. Although LiFePO ₄ cathode material has great advantages compared with other materials, it still has many defects, such as low electronic conductivity and ion diffusion rate of the material, resulting in poor high-rate charge and discharge performance, so it needs to be Conduct modification studies. At present, there are two main ways to solve the above problems: the research on improving the electronic conductivity of LiFePO ₄ mainly focuses on metal doping, metal ion doping, carbon coating and organic conductive polymer surface coating; improving the ion diffusion rate mainly focuses on By controlling the synthesis conditions, it is possible to obtain LiFePO ₄ with complete crystal form, single structure and fine particles.

Conductive polymers have attracted extensive attention due to their good electrical conductivity and electrochemical activity. In recent years, with the advances in the molecular design and fabrication of conductive polymers, the application of conductive polymers as cathode materials in lithium-ion batteries has aroused great interest. Polytriphenylamine (PTPAn) not only has a high electronic conductivity framework similar to polyparaphenylene (PPP), but also has a high energy density of polyaniline (PAn) units. The porous framework structure of polytriphenylamine makes polytriphenylamine ultrafast. Electron transfer rate constant and excellent ion transport ability, so polytriphenylamine shows stable cycle performance as anode material; at the same time, the free redox center inside polytriphenylamine is stable and protected by the framework inside the polymer, making polytriphenylamine Aniline still exhibits superior charge-discharge performance even under high-rate charge-discharge conditions, but its application as a lithium battery cathode material is limited due to its low theoretical capacity (109mAh/g). the

As a cathode material, the low diffusion and transport rate of electrons and Li ⁺ inside and outside the inorganic nano- _LiFePO4 cathode material is the main problem affecting the performance of lithium batteries. The organic conductive polymer polytriphenylamine has a stable charge-discharge voltage platform similar to _LiFePO4 at 3.5V as a positive electrode material, and its porous structure is more conducive to the diffusion of Li ⁺ , which shows superior cycle stability as a lithium-ion battery material. performance and high rate charge and discharge performance. Comprehensively considering the advantages and disadvantages of LiFePO ₄ and polytriphenylamine, the present invention uses a small amount of polytriphenylamine to modify the surface of C-LiFePO ₄ through the solution blending method, hoping to use the unique porous framework of polytriphenylamine to transform the C-LiFePO ₄ material Build an electronic network structure, make up for the defects of LiFePO ₄ as a positive electrode material, and increase the lithium ion migration rate of the material, thereby improving the electrochemical performance of LiFePO ₄ as a positive electrode material.

Contents of the invention

The first object of the present invention is to provide a C-LiFePO ₄ /PTPAn composite material, which has good charge and discharge performance, cycle stability and high rate performance.

The second object of the present invention is to provide the application of the C-LiFePO ₄ /PTPAn composite material as the positive electrode material of lithium ion battery.

The third object of the present invention is to provide a lithium ion battery made of the C-LiFePO ₄ /PTPAn composite material as the positive electrode material.

In order to realize the above-mentioned purpose of the invention, the present invention adopts following technical scheme:

The invention provides a C-LiFePO ₄ /PTPAn composite material. The C-LiFePO ₄ /PTPAn composite material is prepared by a solution blending method using carbon-coated LiFePO ₄ material and polytriphenylamine as raw materials.

In the present invention, the carbon-coated LiFePO ₄ material is obtained by mixing LiFePO ₄ with a certain amount of sucrose by using sucrose as the carbon source, and performing heat treatment in N ₂ . The heat treatment conditions are as follows: 5°C/min) from room temperature to 250-400°C (preferably 350°C), keep warm for 0.5-2h (preferably 1h), and then increase the temperature at a rate of 2-10°C/min (preferably 5°C/min) To 500-700 (preferably 650) ℃, sintering for 2-10 hours (preferably 5 hours). Preferably, the mass of sucrose is 2-10% of the mass of LiFePO ₄ , more preferably 8%.

In the present invention, polytriphenylamine is prepared according to a conventional chemical oxidation method, wherein the oxidizing agent is ferric chloride. the

Furthermore, the mass content of polytriphenylamine in the C-LiFePO ₄ /PTPAn composite material is ≤20%, preferably 3-20%, more preferably 5-15%, and more preferably 10%.

Further, the solution blending method is specifically: fully dispersing the carbon-coated LiFePO ₄ material and polytriphenylamine in the solvent, then evaporating the solvent to dryness, and drying to obtain the C-LiFePO ₄ /PTPAn composite material; the solvent Choose from halogenated hydrocarbon solvents or phenolic reagents.

Furthermore, the solvent is preferably chloroform or cresol. the

The present invention also provides the application of the C-LiFePO ₄ /PTPAn composite material as a lithium battery positive electrode material, and the specific application method adopts conventional operations.

Compared with the prior art, the present invention has the following technical effects:

(1) Compared with other inorganic cathode materials, the discharge specific capacity of the C-LiFePO ₄ /PTPAn composite material described in the present invention can reach 140-155mAh/g; after 50 cycles, the discharge specific capacity remains above 90%; high The charging and discharging performance is excellent at the rate of 10C, and the discharge specific capacity can reach 90~115mAh/g at the rate of 10C.

(2) Compared with the existing lithium batteries using other inorganic materials as positive electrode materials (pure LiFePO ₄ , LiMnPO ₄ ), the lithium battery prepared by the present invention has higher charge-discharge specific capacity, superior cycle stability and Excellent fast charge and discharge performance and other advantages.

Description of drawings

The present invention will be described in detail below in conjunction with the accompanying drawings. the

Figure 1 is the scanning electron micrographs of (a) C-LiFePO ₄ , (b) C-LiFePO ₄ /3%PTPAn, (c) C-LiFePO ₄ /10%PTPAn, (d) C-LiFePO ₄ /20%PTPAn ;(e) Transmission electron micrograph of C-LiFePO ₄ /10%PTPAn; (f) High magnification transmission electron micrograph of C-LiFePO ₄ /10%PTPAn.

Figure 2 respectively shows the positive electrode materials with PTPAn, LiFePO ₄ , C-LiFePO ₄ , and C-LiFePO ₄ /PTPAn composites as active materials at a charge-discharge rate of 0.1C, LiPF ₆ EC/DMC (V/V,1: 1) In the electrolyte, the first charge and discharge curve in the voltage range of 2.5-4.2V.

Figure 3 shows the positive electrode materials with C-LiFePO ₄ and C-LiFePO ₄ /PTPAn composites as active materials at a charge-discharge rate of 0.1C, in LiPF ₆ EC/DMC (V/V, 1:1) electrolyte, Cycling performance graph over the voltage range of 2.5-4.2V.

Figure 4 shows the positive electrode materials with C-LiFePO ₄ and C-LiFePO ₄ /PTPAn composites as active materials at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and _10C . In EC/DMC (V/V, 1:1) electrolyte, the first charge and discharge curve in the voltage range of 2.5-4.2V.

Figure ₅ shows the _{LiPF 6} Cycle performance diagram in the voltage range of 2.5-4.2V in EC/DMC (V/V, 1:1) electrolyte.

Detailed ways

The present invention is further illustrated by the following examples. the

Example

First add 0.045mol of LiOH·H ₂ O into 120mL of ethylene glycol, stir at a constant speed, then prepare a mixed solution (H ₂ O 30mL) with 0.015mol of H ₃ PO ₄ and 0.015mol of FeSO ₄ ·7H ₂ O Add it dropwise to the above solution, and heat the system to 120°C for 20 hours after the feeding is completed. After the reaction, cool to room temperature, centrifuge, wash with deionized water, and dry the precipitate to constant weight to obtain the precursor of LiFePO ₄ , which is mixed with a certain amount of sucrose (the mass of sucrose is 8% of the mass of LiFePO ₄ ), and placed in a tube. Sintering in the flow of high-purity _N2 in the furnace with program temperature control, the heat treatment conditions are as follows: firstly, the temperature is raised from room temperature to 350°C at the rate of 5°C/min, kept for 1h, and then the temperature is raised to 650°C at the rate of 5°C/min , keep it warm for 5h, then cool to room temperature, finally get C-LiFePO ₄ , its scanning electron microscope photo is shown in Figure 1.

Add 0.5g of triphenylamine (TPA) monomer, 1.9282g of ferric chloride and 20mL of chloroform into the reaction vessel, and carry out polymerization reaction at normal temperature and pressure under the protection of _N2 . After 24 hours of reaction, add a large amount of methanol to make the product Precipitate, then filter, and vacuum-dry the filter cake in an oven at 60° C. overnight to obtain off-white solid powder of PTPAn.

Preparation of inorganic-organic nanocomposite C-LiFePO ₄ /PTPAn by solution blending method: the prepared PTPAn with porous structure was dissolved in chloroform, and then C-LiFePO ₄ nanomaterials were put into it in proportion, ultrasonically dispersed , ultrasonic dispersion frequency 53KHz, power 100%, time 15min, finally the solvent chloroform was evaporated to dryness, vacuum drying to obtain C-LiFePO ₄ /x%PTPAn composite material, where x% represents the mass percentage of PTPAn in the composite material. Three kinds of composite materials including C-LiFePO ₄ /3%PTPAn, C-LiFePO ₄ /10%PTPAn and C-LiFePO ₄ /20%PTPAn were prepared in the experiment.

Among them, the scanning electron microscope images of C-LiFePO ₄ /3%PTPAn, the scanning electron microscope images of C-LiFePO ₄ /10%PTPAn, the transmission electron microscope images, the high-power transmission electron microscope images and the scanning electron microscope images of C-LiFePO ₄ /20%PTPAn are all see picture 1.

Electrical performance test:

The prepared PTPAn, LiFePO ₄ , C-LiFePO ₄ , C-LiFePO ₄ /3%PTPAn composites, C-LiFePO ₄ /10%PTPAn composites, and C-LiFePO ₄ /20%PTPAn composites were used as cathode materials , prepare a lithium-ion battery as follows:

a) Weigh 1 part of binder powder, 2 parts of acetylene black, and 7 parts of prepared cathode material powder, and mix them evenly;

b) Disperse the mixture in a) in N-methylpyrrolidone solvent, grind and disperse evenly;

c) Apply the slurry in b) evenly on the aluminum foil, and place it in an oven at 60°C for 24 hours in vacuum to obtain a positive electrode sheet;

d) Using the positive electrode sheet prepared in c) as the positive electrode, the lithium metal sheet as the negative electrode, 1mol/L LiPF ₆ EC/DMC (V/V, 1:1) as the electrolyte, and the PP film as the diaphragm, in an argon-filled atmosphere Assemble the button cell in the glove box.

The electrical properties of PTPAn, LiFePO ₄ , C-LiFePO ₄ , C-LiFePO ₄ /3%PTPAn composites, C-LiFePO ₄ /10%PTPAn composites, and C-LiFePO ₄ /20%PTPAn composites are shown in Figure 2-figure 5, it can be seen from Fig. 2-Fig. 5 that the C-LiFePO ₄ /PTPAn composite material prepared by the present invention has high charge-discharge specific capacity, excellent cycle stability and very good fast charge-discharge performance.

Claims (10)

1. a C-LiFePO ₄/ PTPAn composite material, described C-LiFePO ₄/ PTPAn composite material is with the coated LiFePO of carbon ₄material and poly-triphenylamine are raw material, by solution blended process, make.

2. C-LiFePO as claimed in claim 1 ₄/ PTPAn composite material, is characterized in that: described C-LiFePO ₄mass content≤20% of poly-triphenylamine in/PTPAn composite material.

3. C-LiFePO as claimed in claim 1 ₄/ PTPAn composite material, is characterized in that: described C-LiFePO ₄in/PTPAn composite material, the mass content of poly-triphenylamine is 3～20%.

4. C-LiFePO as claimed in claim 1 ₄/ PTPAn composite material, is characterized in that: described C-LiFePO ₄in/PTPAn composite material, the mass content of poly-triphenylamine is 5～15%.

5. C-LiFePO as claimed in claim 1 ₄/ PTPAn composite material, is characterized in that: described C-LiFePO ₄in/PTPAn composite material, the mass content of poly-triphenylamine is 10%.

6. the C-LiFePO as described in one of claim 1～5 ₄/ PTPAn composite material, is characterized in that: the LiFePO that carbon is coated ₄material is to take sucrose as carbon source, makes LiFePO ₄mix with sucrose, at N ₂in heat-treat and obtain, heat-treat condition is: first the speed with 2-10 ℃/min rises to 250-400 ℃ by room temperature, insulation 0.5～2h, then be warming up to 500-700 ℃ with the speed of 2-10 ℃/min, sintering 2～10 hours; Sucrose quality is LiFePO ₄2～10% of quality.

7. the C-LiFePO as described in one of claim 1～5 ₄/ PTPAn composite material, is characterized in that: described solution blended process is specially: make the coated LiFePO of carbon ₄material and poly-triphenylamine fully disperse in solvent, and then solvent evaporated, is drying to obtain C-LiFePO ₄/ PTPAn composite material; Described solvent is selected from halogenated hydrocarbon solvent or phenols reagent.

8. C-LiFePO as claimed in claim 7 ₄/ PTPAn composite material, is characterized in that: described solvent is chloroform or cresols.

9. C-LiFePO as claimed in claim 1 ₄/ PTPAn composite material is as the application of anode material of lithium battery.

10. with C-LiFePO claimed in claim 1 ₄the lithium battery that/PTPAn composite material makes as positive electrode.

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