CN102569803A - Lithium iron phosphate/PpyPy composite cathode material for boron-doped modification lithium ion battery and preparation method therefor - Google Patents

Abstract

The invention discloses a lithium iron phosphate/polypyridine composite cathode material for a boron-doped modified lithium ion battery and a preparation method thereof. The method is to mix lithium source compound, phosphorus source compound, iron source compound, boron source compound, coating material conductive polymer polypyridine or conductive polymer pyrolysis precursor polyacrylonitrile, etc., at 250-400 ° C Heating under low temperature for 5-20 hours, cooling and ball milling to obtain a reaction precursor; calcining the reaction precursor at 500-800°C for 10-40 hours, and obtaining a boron-doped modified lithium-ion battery composite cathode material after cooling. The invention effectively controls the chemical composition, structure and particle size of the composite doped modified positive electrode material, improves the electronic conductivity of the material and the diffusion rate of lithium ions, improves the electrochemical performance of the material; The synthesis process is convenient for industrialized large-scale production.

Description

Lithium iron phosphate/polypyridine composite positive electrode material for boron-doped modified lithium ion battery and preparation method thereof

technical field

The invention relates to a positive electrode material for a lithium ion battery, in particular to a lithium iron phosphate/polypyridine composite positive electrode material for a boron-doped modified lithium ion battery and a preparation method thereof.

Background technique

Lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ) and lithium iron phosphate (LiFePO ₄ ) are all used as cathode materials for lithium-ion batteries. Among them, LiCoO ₂ is relatively expensive, expensive, resource-poor, and highly toxic; LiNiO ₂ is difficult to prepare. Poor thermal stability and poor safety; although LiMn ₂ O ₄ has good safety performance, its capacity decays significantly and its cycle reversibility is poor; LiFePO ₄ with olivine crystal structure has large discharge specific capacity, long cycle life and safety performance Good, cheap, non-toxic and non-environmental pollution and other outstanding advantages, so it has a wide range of application prospects.

However, LiFePO ₄ also has some significant disadvantages, that is, its lithium ion mobility and electronic conductivity are low, and the charge and discharge process is controlled by the diffusion rate of Li ⁺ between LiFePO ₄ -FePO ₄ phases, resulting in It can only work with extremely small currents, which greatly limits its practical application. Therefore, the research so far has mainly focused on improving its electronic conductivity and ion conductivity. One is to obtain a fine and uniform material by controlling the growth rate of the material grains in the material process, so as to reduce the migration path of lithium ions in it and increase the migration rate of lithium ions; The method of doping is to introduce a conductive agent between the grains (such as conductive carbon black or crystal phase doping method to introduce other metal heteroatoms inside the crystal to improve the electronic conductivity of the material. Such as Yang et al. [Electrochemistry Communications, 505 ～508(3), 2001] adopt hydrothermal synthesis method, Park etc. [Electrochemistry Communications, 839～842(5), 2003] adopt liquid phase coprecipitation method, Croce etc. [Electrochemical and Solid State Letters, A47～A50(5 ), 2002] used the sol-gel method to synthesize lithium iron phosphate materials with fine and uniform particle size, which improved the electrical properties of the materials; such as Shin et al [Journal of PowerSources, 1383-1388 (2), 2006] used acetylene black as carbon The charge transfer impedance of the LiFePO ₄ /C material prepared by the source decreased from 493.3 ohms of the carbon-free coating material to 9.253 ohms, and the impedance remained basically unchanged after 30 cycles; Park [Solid State Communications, 311～314 (5 ), 2004] etc. first uniformly disperse the pure LiFePO ₄ powder in the AgNO ₃ aqueous solution to make a suspension, and then use ascorbic acid to reduce Ag ⁺ to metal Ag to prepare the LiFePO ₄ material coated with Ag on the surface, and improve the LiFePO ₄ material electrochemical performance; Wu et al [Journal of PowerSources, 440-444(2), 2004] used Ti ⁴⁺ for iron-site doping to obtain LiFe _1-x Ti _x PO ₄ (x ranged from 0.01 to 0.09) materials, showing excellent cycle performance and rate performance. The above methods and approaches can significantly improve the electrochemical performance of _LiFePO4 materials to varying degrees, but each has defects that directly restrict its wide application:

1. Although the liquid phase synthesis method can synthesize material powders with uniform particle size and fine particle size, which reduces the diffusion path of lithium ions, the improvement of the electronic conductivity of the material is not obvious, and the above method still has requirements for equipment High or complicated process, etc., it is difficult to carry out industrialized large-scale production;

2. The method of simply coating carbon or metal powder can only effectively improve the electronic conductivity of the material, but the structure of pyrolytic carbon, the thickness of the carbon layer, the distribution of carbon on the surface and the concentration gradient of the metal powder will affect the coating effect. Moreover, the addition of too much carbon will significantly reduce the true density of the material and the volume specific energy of the material, and too much metal powder will reduce the mass specific capacity of the material;

3. Doping metal (M) elements such as Ti or Co to form Li(M _y Fe _1-y )PO4 will reduce the stability of the crystal structure of the material, thereby affecting the electrical properties of the material.

Contents of the invention

The purpose of the present invention is to solve the shortcomings of the above-mentioned prior art, to provide a boron-doped modified polymer with cheap and easy-to-obtain raw materials, which is suitable for large-scale production and has high ion conductivity and electronic conductivity. A composite material (LiFe(PO ₄ ) _1-X (BO ₃ ) _x /PPyPy) coated with pyridine and a preparation method thereof.

In the present invention, polyacrylonitrile (commonly known as acrylic fiber, PAN) with a relatively high degree of industrialization is used as a conductive polymer polypyridine (PPyPy) prepared by pyrolysis as a coating conductive material, and LiFePO ₄ /PPyPy composite positive electrode material can effectively control the chemical composition, structure and particle size of the composite doped modified positive electrode material, improve the electrical conductivity of the material, and improve the electrochemical performance of the material; at the same time, it also simplifies the synthesis process of the material, The consistency of material preparation is guaranteed to a greater extent, and it is convenient for industrialized mass production.

The purpose of the present invention is achieved through the following technical solutions:

The preparation method of lithium iron phosphate/polypyridine composite cathode material for boron-doped modified lithium ion battery is characterized in that it comprises the following steps:

In the first step, the lithium source compound, the phosphorus source compound, the iron source compound, and the boron source compound are mixed according to the molar ratio of Li:Fe:P:B in a ratio of 1:1:(0.98～0.90):(0.02～0.10), Then add polypyridine conductive polymer or polyacrylonitrile, and wet ball mill in ethanol or acetone medium for 2-12 hours; the amount of polypyridine conductive polymer is 1.5g-60g per mole of Li ⁺ ; the amount of polyacrylonitrile is Molar Li ⁺ added 2.0g ~ 80g;

The lithium source compound is one or more of lithium nitrate, lithium carbonate, lithium acetate and lithium fluoride;

The phosphorus source compound is one or more of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and iron phosphate;

The iron source compound is one or more of ferrous oxalate, ferrous acetate, ferric phosphate, ferric oxide and ferric citrate;

The boron source compound is one or more of boric acid, diboron trioxide and triethyl borate;

In the second step, the mixed raw materials are heated to 250-400°C under the protection of a nitrogen or argon atmosphere, heated at a constant temperature for 5-20 hours, cooled and ground to obtain a reaction precursor;

In the third step, the temperature of the reaction precursor is raised to 500-800°C under the protection of nitrogen or argon atmosphere, and it is calcined at a constant temperature for 10-40 hours. After cooling, the lithium iron phosphate/polypyridine for boron-doped modified lithium-ion batteries is obtained. Composite cathode material.

In order to further realize the purpose of the present invention, the polypyridine conductive polymer is prepared by the following method: polyacrylonitrile is thermally decomposed in the range of 200-1100 ° C under the protection of nitrogen or argon atmosphere, and the heating rate is 1-40 °C/min, the obtained material is washed, dried and pulverized to obtain a polypyridine conductive polymer.

The polyacrylonitrile is placed in a high-temperature furnace with automatic temperature control.

The first step of wet ball milling is carried out in a planetary ball mill.

The temperature is raised to 250-400° C. in the second step and 500-800° C. in the third step at a rate of 1° C.-20° C./min.

A lithium iron phosphate/polypyridine composite positive electrode material for a boron-doped modified lithium ion battery is prepared by the above method.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The conductive polymer polypyridine (PPyPy) prepared by thermal cracking of polyacrylonitrile (PAN) has good electrical conductivity, and the coating effect of PPyPy produced by high temperature thermal cracking is good, the distribution is quite uniform, and it can be used in boron-doped During the process, the strong electron-attracting boron atoms will attract the electrons of the carbon atoms, causing the covalent bonds between the carbon atoms to break, resulting in the rearrangement of the carbon skeleton structure, and the boron atoms preferentially occupy the position of the carbon atoms to accelerate the formation of the graphite layered structure , effectively improving the degree of graphitization of PPyPy, and jointly improving the electronic conductivity of LiFe(PO ₄ ) _1-X (BO ₃ ) _x /PPyPy composite cathode materials;

2. The reducing substances produced by the thermal cracking of PAN effectively inhibit the growth of LiFePO ₄ crystals and reduce the particle size of LiFePO ₄ , and after boron is doped and modified at the phosphorus site, the BO ₃ atomic group has a higher density than the PO ₄ atomic group. The strong inductive effect causes the shrinkage of the unit cell volume, and also refines the grains, improving the lithium ion conductivity of the LiFe(PO ₄ ) _1-X (BO ₃ ) _x /PPyPy composite cathode material;

3. The PPyPy used in the coating of the present invention has reversible electrochemical redox characteristics and strong charge storage capacity. The LiFeBO ₃ produced by doping modification also has an redox potential between 2.9 and 3.1V, and a theoretical specific capacity of 220mAh/g, will not reduce the discharge specific capacity of the composite cathode material;

4. The high-temperature solid-phase synthesis process of the composite positive electrode material of the present invention is simple, which is conducive to large-scale industrial production.

5. The composite cathode material of the present invention is mainly applied in power batteries and energy storage batteries, and has broad application prospects

Description of drawings

Fig. 1 is the X-ray diffraction pattern of the Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy composite cathode material prepared according to Example 1.

Figure 2 is the rate discharge curve after the Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy composite cathode material prepared in Example 1 is assembled into an experimental battery, the charge and discharge voltage range is 2.5-4.2V, and the electrolyte is 1mol/LLiPF ₆ /ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), the charge and discharge rates are 0.2C, 0.5C, 1.0C, 2.0C, respectively.

Fig. 3 is the cycle performance curve of the Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy composite cathode material prepared according to Example 2 after being assembled into an experimental battery, the charge and discharge voltage range is 2.5-4.2V, and the electrolyte is 1mol/LLiPF ₆ /ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), the charge and discharge rates are 0.2C, 2..0C, respectively.

specific implementation plan

In order to better understand the present invention, the present invention will be further described below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

Example 1

The first step is to weigh 10g of polyacrylonitrile powder, put it in a high-temperature furnace connected with automatic temperature control, and carry out thermal cracking at 650°C under the protection of argon atmosphere, with a heating rate of 3°C/min, and pulverize the obtained material Grind and sieve to finally obtain a black polypyridine conductive polymer material (PPyPy) with metallic luster;

In the second step, in order to produce 0.1mol lithium iron phosphate material, take by weighing 0.05mol lithium carbonate, 0.1mol ferrous oxalate, 0.095mol diammonium hydrogen phosphate and 0.05mol boric acid respectively, then add 0.45gPPyPy, and use ethanol as a dispersant (the The amount of addition is 1/2 of the total mass of raw materials), and it is wet-milled with a planetary ball mill for 6 hours; mix well;

The third step is to raise the temperature of the mixed raw materials to 300°C at a heating rate of 2°C per minute in a nitrogen atmosphere protection, keep heating at a constant temperature of 300°C for 10 hours, cool and grind to obtain a reaction precursor;

The fourth step is to raise the temperature of the reaction precursor to 650°C at a rate of 2°C per minute under the protection of a nitrogen atmosphere, and keep it at a constant temperature of 650°C for calcination for 24 hours. After cooling, boron-doped phosphoric acid for lithium-ion batteries can be obtained. Lithium iron/polypyridine composite cathode material (Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy). The X-ray diffraction pattern of Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy composite cathode material is shown in Figure 1, and the reference standard card is olivine lithium iron phosphate with intact crystal form.

The composite coated and modified positive electrode material prepared above at 650°C was used as the positive electrode active material to make the positive electrode film, and the positive electrode film was composed of Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy with a mass ratio of 85:10:5 The positive electrode material is composed of active material, acetylene black and polytetrafluoroethylene emulsion (solid content), thickness ≤ 0.1mm, the positive electrode film is rolled on the stainless steel mesh to make the positive electrode sheet; metal lithium sheet is used as the negative electrode; the separator is polypropylene microporous Membrane (Celgard2300); electrolyte is 1mol/L LiPF6/ethylene carbonate (EC) + dimethyl carbonate (DMC) (volume ratio 1:1), assembled into an experimental battery in an argon-filled glove box, at room temperature The rate charge and discharge test is carried out under the following conditions, and the charge and discharge voltage range is 2.5~4.2V. As shown in Figure 2, when discharged at rates of 0.2C, 0.5C, 1.0C, and 2.0C, the first discharge specific capacities are 146.8mAh/g, 133.4mAh/g, 127.4mAh/g, and 117.3mAh/g, respectively. The small capacity fading indicates that the Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy composite cathode material prepared by this method has excellent rate performance.

Example 2

The first step is to prepare 0.1mol lithium iron phosphate material, respectively weigh 0.0495mol lithium carbonate, 0.1mol ferrous oxalate, 0.095mol diammonium hydrogen phosphate/0.05, 0.05mol boric acid, then add 1.0g polyacrylonitrile powder , with ethanol as a dispersant (its addition is 1/2 of the total mass of the raw material), uniformly mixed through high-speed ball milling;

In the second step, the mixed raw materials are heated to 350°C at a heating rate of 5°C per minute in a nitrogen atmosphere protection, heated at a constant temperature for 10 hours, cooled and ground to contain the reaction precursor;

In the third step, the temperature of the reaction precursor is raised to 650°C at a rate of 5°C per minute under the protection of a nitrogen atmosphere, and it is calcined at a constant temperature for 25 hours. Pyridine composite cathode material (Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy).

The composite coated and modified positive electrode material prepared above at 650°C was used as the positive electrode active material to make the positive electrode film, and the positive electrode film was composed of Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy with a mass ratio of 85:10:5 The positive electrode material is composed of active material, acetylene black and polytetrafluoroethylene (solid content), the thickness is ≤0.1mm, the positive electrode film is rolled on the stainless steel mesh to make the positive electrode sheet; the metal lithium sheet is used as the negative electrode; the diaphragm is polypropylene microporous membrane (Celgard2300); the electrolyte is 1mol/L LiPF6/ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), assembled into an experimental battery in an argon-filled glove box, at room temperature Carry out cycle performance charge and discharge test, the charge and discharge voltage range is 2.5 ~ 4.2V. As shown in Figure 3, the capacity fading is small and the rate performance is relatively good.

Example 3

The first step is to weigh 10 g of polyacrylonitrile powder heated for 2 hours in an air atmosphere at 250°C for pre-oxidation, place it in a high-temperature furnace connected with automatic temperature control, and carry out thermal cracking at 900°C under an argon atmosphere, with a heating rate of 10°C/min, the obtained material was pulverized, ground and sieved to finally obtain a black polypyridine conductive polymer material (PPyPy) with metallic luster;

In the second step, in order to prepare 0.1mol lithium iron phosphate material, weigh 0.05mol lithium hydroxide, 0.1mol ferrous oxalate, 0.0.092mol ammonium dihydrogen phosphate/0.04mol diboron trioxide, and then add 0.15gPPyPy, with ethanol As a dispersant (the amount added is 1/2 of the total mass of raw materials), wet ball milling with a planetary ball mill for 6 hours; mix well;

The third step is to raise the temperature of the mixed raw materials to 400°C at a heating rate of 15°C per minute in an argon atmosphere protection, keep heating at a constant temperature of 400°C for 20 hours, cool and grind to obtain a reaction precursor;

In the fourth step, the reaction precursor is heated up to 600°C at a rate of 15°C per minute under the protection of an argon atmosphere, calcined at a constant temperature for 10 hours, and after cooling, the boron-doped lithium iron phosphate/polymer lithium ion battery is obtained. Pyridine composite cathode material (Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy).

The composite coated and modified positive electrode material prepared above at 650°C was used as the positive electrode active material to make the positive electrode film, and the positive electrode film was composed of Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy with a mass ratio of 85:10:5 The positive electrode material is composed of active material, acetylene black and polytetrafluoroethylene (solid content), the thickness is ≤0.1mm, the positive electrode film is rolled on the stainless steel mesh to make the positive electrode sheet; the metal lithium sheet is used as the negative electrode; the diaphragm is polypropylene microporous membrane (Celgard2300); the electrolyte is 1mol/L LiPF6/ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), assembled into an experimental battery in an argon-filled glove box, at room temperature Carry out the charge and discharge test, the charge and discharge voltage range is 2.5 ~ 4.2V. When the material prepared in this example is charged and discharged at a rate of 0.1C, its initial discharge specific capacity reaches 137.1 mAh/g.

Example 4

The first step is to prepare 0.1mol lithium iron phosphate material, respectively weigh 0.06mol lithium fluoride, 0.04mol lithium acetate, 0.1mol ferrous acetate, 0.09mol ammonium phosphate, 0.01mol triethyl borate, and then add 0.2g polyacrylonitrile powder, with acetone as a dispersant (its addition is 1/2 of the total mass of raw materials), mixed uniformly through high-speed ball milling for 12 hours;

In the second step, the mixed raw materials are heated to 350°C at a rate of 1°C per minute in an argon atmosphere protection, heated at a constant temperature for 5 hours, cooled and ground to contain the reaction precursor;

In the third step, the temperature of the reaction precursor is raised to 700°C at a rate of 20°C per minute under the protection of nitrogen atmosphere, and it is calcined at a constant temperature for 40 hours. Pyridine composite cathode material (Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy).

The composite coated and modified positive electrode material prepared above at 700°C was used as the positive electrode active material to make the positive electrode film, and the positive electrode film was composed of Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy with a mass ratio of 85:10:5 The positive electrode material is composed of active material, acetylene black and polytetrafluoroethylene (solid content), the thickness is ≤0.1mm, the positive electrode film is rolled on the stainless steel mesh to make the positive electrode sheet; the metal lithium sheet is used as the negative electrode; the diaphragm is polypropylene microporous membrane (Celgard2300); the electrolyte is 1mol/L LiPF6/ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), assembled into an experimental battery in an argon-filled glove box, at room temperature Carry out the charge and discharge test, the charge and discharge voltage range is 2.5 ~ 4.2V. When the material is charged and discharged at a rate of 0.1C, its initial discharge specific capacity reaches 151.2mAh/g.

Example 5

The first step is to weigh 10 g of polyacrylonitrile powder heated for 2 hours in an air atmosphere at 250°C for pre-oxidation, place it in a high-temperature furnace connected with automatic temperature control, and carry out thermal cracking at 900°C under an argon atmosphere, with a heating rate of 10°C/min, the obtained material was pulverized, ground and sieved to obtain a black polypyridine conductive polymer material (PPyPy) with metallic luster

In the second step, in order to prepare 0.1 mol of lithium iron phosphate material, 0.1 mol of lithium nitrate, 0.95 mol of iron phosphate, 0.05 mol of ammonium dihydrogen phosphate, 0.05 mol of ferrous oxalate, and 0.05 mol of boric acid were weighed respectively. Add 6gPPyPy again, with acetone as dispersant (its addition is 1/2 of the total mass of raw materials), wet ball milling with planetary ball mill for 2 hours; mix well;

The third step is to heat the mixed raw materials to 300°C at a rate of 10°C per minute in an argon atmosphere protection, heat at a constant temperature for 10 hours, cool and grind to obtain a reaction precursor;

The fourth step is to raise the temperature of the reaction precursor to 800°C at a rate of 20°C per minute under the protection of an argon atmosphere, calcine at a constant temperature for 30 hours, and obtain boron-doped lithium iron phosphate for modified lithium-ion batteries after cooling. Polypyridine composite cathode material (Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy).

The composite coating modified positive electrode material prepared above at 800°C was used as the positive electrode active material to make the positive electrode film, and the positive electrode film was composed of Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy composite with a mass ratio of 85:10:5 The positive electrode material is composed of active material, acetylene black and polytetrafluoroethylene (solid content), the thickness is ≤0.1mm, the positive electrode film is rolled on the stainless steel mesh to make the positive electrode sheet; the metal lithium sheet is used as the negative electrode; the diaphragm is polypropylene microporous membrane (Celgard2300); the electrolyte is 1mol/L LiPF6/ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), assembled into an experimental battery in an argon-filled glove box, at room temperature Carry out the charge and discharge test, the charge and discharge voltage range is 2.5 ~ 4.2V. When the material prepared in this example is charged and discharged at a rate of 0.1C, its initial discharge specific capacity reaches 128.4mAh/g.

Example 6

The first step is to prepare 0.1mol lithium iron phosphate material, respectively weigh 0.1mol lithium hydroxide, 0.6mol iron citrate, 0.02mol oxidation, 0.09mol ammonium dihydrogen phosphate, 0.01mol triethyl borate, and then add 2.0g Polyacrylonitrile powder, with acetone as a dispersant (its addition is 1/2 of the total mass of raw materials), wet ball milling with a planetary ball mill for 6 hours; mix uniformly;

In the second step, the mixed raw materials are heated to 300°C at a heating rate of 10°C per minute in a nitrogen atmosphere protection, heated at a constant temperature for 10 hours, cooled and ground to obtain a reaction precursor;

In the third step, the temperature of the reaction precursor is raised to 800°C at a rate of 10°C per minute under the protection of a nitrogen atmosphere, and it is calcined at a constant temperature for 30 hours. After cooling, the boron-doped lithium iron phosphate/poly Pyridine composite cathode material (Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy).

The composite coating modified positive electrode material prepared above at 800°C was used as the positive electrode active material to make the positive electrode film, and the positive electrode film was composed of Li(FePO ₄ ) _1-X (BO ₃ ) _x /PPyPy composite with a mass ratio of 85:10:5 The positive electrode material is composed of active material, acetylene black and polytetrafluoroethylene (solid content), the thickness is ≤0.1mm, the positive electrode film is rolled on the stainless steel mesh to make the positive electrode sheet; the metal lithium sheet is used as the negative electrode; the diaphragm is polypropylene microporous membrane (Celgard2300); the electrolyte is 1mol/L LiPF6/ethylene carbonate (EC)+dimethyl carbonate (DMC) (volume ratio 1:1), assembled into an experimental battery in an argon-filled glove box, at room temperature Carry out the charge and discharge test, the charge and discharge voltage range is 2.5 ~ 4.2V. When the material prepared in this example is charged and discharged at a rate of 0.1C, its initial discharge specific capacity reaches 108.3mAh/g.

Claims (6)

1. the boron-doping modification lithium-ion battery is characterized in that comprising the steps: with the preparation method of LiFePO4/coalescence pyridine composite positive pole

The first step is 1: 1 with Li source compound, P source compound, Fe source compound, boron source compound according to the mol ratio of Li: Fe: P: B: (0.98～0.90): the mixed of (0.02～0.10); Add coalescence pyridine conducting polymer or polyacrylonitrile again, in ethanol or medium-acetone wet ball grinding 2-12 hour; Every mole of Li of coalescence pyridine conducting polymer consumption ⁺Add 1.5g～60g; The polyacrylonitrile consumption is every mole of Li ⁺Add 2.0g～80g;

Said Li source compound is one or more in lithium nitrate, lithium carbonate, lithium acetate and the lithium fluoride;

Said P source compound is one or more in ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and the ferric phosphate;

Said Fe source compound is one or more in ferrous oxalate, ferrous acetate, ferric phosphate, di-iron trioxide and the ironic citrate;

Said boron source compound is one or more in boric acid, diboron trioxide and the triethyl borate;

Second step was warming up to 250～400 ℃ with mixed raw material under nitrogen or argon gas atmosphere protection, heated at constant temperature 5～20 hours obtains the reaction precursor body after cooling, the grinding;

The 3rd step had been warming up to 500～800 ℃ with the reaction precursor body under the protection of nitrogen or argon gas atmosphere, calcining at constant temperature 10～40 hours promptly gets the boron-doping modification lithium-ion battery with LiFePO4/coalescence pyridine composite positive pole after the cooling.

2. according to the preparation method of the said boron-doping modification lithium-ion battery of claim 1 with LiFePO4/coalescence pyridine composite positive pole; It is characterized in that; Said coalescence pyridine conducting polymer prepares through following method: polyacrylonitrile under nitrogen or argon gas atmosphere protection, is carried out thermal cracking in 200-1100 ℃ of scope, heating rate is 1-40 ℃/min; The gained material is carried out washing and drying pulverize, obtain coalescence pyridine conducting polymer.

3. according to the preparation method of the said boron-doping modification lithium-ion battery of claim 2, it is characterized in that said polyacrylonitrile is to place in the temperature automatically controlled high temperature furnace with LiFePO4/coalescence pyridine composite positive pole.

4. according to the preparation method of the said boron-doping modification lithium-ion battery of claim 1, it is characterized in that the wet ball grinding of the first step is in planetary ball mill, to carry out with LiFePO4/coalescence pyridine composite positive pole.

5. according to the preparation method of the said boron-doping modification lithium-ion battery of claim 1 with LiFePO4/coalescence pyridine composite positive pole; It is characterized in that second step was warming up to 250～400 ℃, and to be warming up to 500～800 ℃ with the 3rd step be with the intensification of the heating rate of 1 ℃ of-20 ℃/min.

6. a boron-doping modification lithium-ion battery is characterized in that each said method preparation by claim 1-5 with LiFePO4/coalescence pyridine composite positive pole.

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