CN102013489A - Metallic titanium doped carbon-coating lithium iron phosphate and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of battery material preparation, and relates to a titanium-doped carbon-coated lithium iron phosphate and a preparation method thereof. The chemical expression of the substance is: LiFe _1-x Ti _x PO ₄ /C, wherein 0<x≤0.2, and the mass percentage of C is 10%. Its preparation method comprises the following steps: weighing lithium source, Fe ₂ O ₃ , TiO ₂ and NH ₄ H ₂ PO ₄ in molar ratio lithium:iron:titanium:phosphorus=1:1-x:x:1 For batching, where 0<x≤0.2; then add acetone, grind, dry, add a saturated aqueous solution of citric acid to make a rheological phase precursor, and then grind it at a constant temperature of 400 ° C for 3-6 hours under an inert atmosphere and press it into a compact cylinder; finally, the temperature is raised to 500-900°C and roasted at a constant temperature for 5-15 hours to obtain the product. The material prepared by the invention has the characteristics of high capacity and high tap density, the preparation method of the material is simple, the cost is low, and the material is suitable for industrial production.

Description

A kind of metal titanium-doped carbon-coated lithium iron phosphate and preparation method thereof

technical field

The invention relates to the technical field of battery material preparation, in particular to metal titanium-doped carbon-coated lithium iron phosphate and a preparation method thereof.

Background technique

Lithium-ion battery, as a high-performance green power source, has been widely used in various portable electronic products and communication tools in recent years, and has been gradually developed as a power source for electric vehicles, thus promoting it to a safe, environmentally friendly, low-cost Development in the direction of cost and high specific energy.

Cathode material is a key part that determines the performance of lithium-ion batteries. Today, with more emphasis on safety and environmental protection, lithium iron phosphate has become a research hotspot in various countries. Lithium iron phosphate material is non-toxic, environmentally friendly, rich in raw materials, low in price, good in high temperature stability, safe in use, good in power storage performance, and has many advantages such as a charge and discharge life of more than 2,000 times.

So far, there have been many reports on the synthesis methods of materials. The most researched and most likely to realize industrialization is the high-temperature solid-phase method, but lithium iron phosphate has its inherent shortcomings, such as low lithium ion diffusion coefficient and poor conductivity. etc. Therefore, the materials prepared by conventional methods have disadvantages such as poor electrochemical performance, uneven particle size distribution, and low tap density. In order to improve the performance of the material, it is generally doped or coated, such as C coating (CN101172599, CN101442117, CN101764205A, CN101777636A), transition metal doping (CN1785799), rare earth doping (CN1830764, CN101630738), etc., The above methods can improve the performance of lithium iron phosphate to a certain extent, but the performance improvement is not too significant.

Invention content:

Aiming at the shortage of current materials, the present invention provides a metal titanium-doped carbon-coated lithium iron phosphate and a preparation method thereof. The material prepared by this method has excellent electrochemical performance, especially at a high current density with extremely small capacity decay, and the product The tap density is relatively high. The synthesis method of the material is simple, the cost is low, and the material is suitable for industrial production.

Technical scheme of the present invention is:

A metal titanium-doped carbon-coated lithium iron phosphate, the chemical expression of which is: LiFe _1-x Ti _x PO ₄ /C, wherein 0<x≤0.2, and the mass percentage of C is 10%.

The preparation method of the metal titanium-doped carbon-coated lithium iron phosphate comprises the following steps:

(1) Lithium source, Fe ₂ O ₃ , TiO ₂ and NH ₄ H ₂ PO ₄ are weighed in molar ratio lithium:iron:titanium:phosphorus=1:1-x:x:1 ratio, where 0 <x≤0.2;

(2) Add acetone to the prepared powder and place it in a ball mill to rotate for 2-10 hours at a rate of 200-500rpm/min. The amount of acetone is 3 to 5 times the volume of the powder;

(3) Dry the ground slurry in an oven at 100-110°C, then add a saturated aqueous solution of citric acid to make a rheological phase precursor, wherein the quality of citric acid is the raw material in step (1) according to its carbon content Calculation of 20% of the mass sum of lithium source, Fe ₂ O ₃ , TiO ₂ , NH ₄ H ₂ PO ₄ ;

(4) Heat the above precursor at a heating rate of 1°C/min under an inert atmosphere, keep the temperature at 100°C for 2-5 hours, then raise the temperature to 400°C for 3-6 hours, take it out and grind it after cooling down in the furnace, and grind it at 100-200MPa Under pressure, press it into a compact cylinder;

(5) Heat the pressed cylinder to 500-900° C. for 5-15 hours in an inert atmosphere, and roast it at a constant temperature for 5-15 hours, then cool down to room temperature with the furnace to obtain titanium-doped carbon-coated lithium iron phosphate, a positive electrode material for lithium-ion batteries.

The lithium source is lithium carbonate, lithium dihydrogen phosphate or lithium fluoride.

The beneficial effects of the invention are: the material prepared by the invention has the characteristics of high capacity and high tap density, and the preparation method of the material is simple, the cost is low, and it is suitable for industrial production.

The titanium-doped carbon-coated LiFe _0.9 Ti _0.1 PO ₄ /C material prepared by the formula of the present invention has a discharge specific capacity higher than 150mAh/g at 0.2C, and the discharge specific capacity of this material is still as high as 98.8mAh/g at a high rate of 5C. g, the capacity decay after 20 cycles is 96.2mAh/g, and the capacity decay rate is only 2.6%, while the specific capacity of the undoped material decays from 84.3mAh/g to 43.4mAh/g after 20 cycles at a high rate of 5C , the capacity fading rate is 48.5%, and the tap density of this material reaches 1.62g/ml.

The preparation of the material in the present invention uses ferric oxide as the iron source, the conductive agent is added in the material precursor, a part is used to reduce the ferric iron, and the excess reduced carbon is directly coated on the LiFePO ₄ particles, without the need for later coating The conductivity of the material can be improved by coating treatment, the cost is low, and it is suitable for industrial production. In order to better illustrate the scientific significance and practical value of the present invention, the following will be described in detail in conjunction with the embodiments and accompanying drawings.

Description of drawings:

Accompanying drawing 1 is the XRD curve of four kinds of products LiFePO ₄ /C, LiFe _0.93 Ti _0.07 PO ₄ /C, LiFe _0.9 Ti _0.1 PO ₄ /C, LiFe _0.83 Ti _0.17 PO ₄ /C obtained in Example 1, can see The products are all lithium iron phosphate with olivine structure, and the doping of metal titanium element does not change the structure of the material.

Accompanying drawing 2 is the four kinds of products LiFePO ₄ /C, LiFe _0.93 Ti _0.03 PO ₄ /C, LiFe _0.9 Ti _0.1 PO ₄ /C, LiFe _0.83 Ti _0.17 PO ₄ /C obtained in Example 1 at a rate of 0.2C The first charge and discharge curve.

Figure 3 is the cycle performance curves of LiFe _0.9 Ti _0.1 PO ₄ /C materials prepared in Examples 1, 2, and 3 at 0.2C, 0.5C, 2C, and 5C rates.

Figure 4 is the cycle performance curves of LiFePO ₄ /C and LiFe _0.9 Ti _0.1 PO ₄ /C materials at 0.2C, 0.5C, 2C, 5C rates.

Detailed ways:

Example 1

(1) Accurately weigh 0.025molLi ₂ CO ₃ , 0.0225molFe ₂ O ₃ , 0.005molTiO ₂ and 0.05molNH ₄ H ₂ PO ₄ and put them into the ball mill tank for batching;

(2) Add the prepared powder into acetone which is 4 times the volume of the powder, and then place it in a ball mill and rotate it at a rate of 250rpm/min for 5h;

(3) Dry the ground slurry in an oven at 110° C., and then add a saturated aqueous solution containing 2.2 g of citric acid to make a rheological phase precursor;

(4) Heat the above precursor at a heating rate of 1°C/min under an inert atmosphere, keep the temperature at 100°C for 2 hours, then raise the temperature to 400°C for 5 hours, take it out and grind it after cooling down in the furnace, and press it under a pressure of 200MPa into a compact cylinder;

(5) Heat up the pressed cylinder to 850°C for 12 hours at a constant temperature in a high-purity nitrogen atmosphere, and then cool down to room temperature with the furnace to obtain 8.7g of titanium-doped carbon-coated lithium iron phosphate, the positive electrode material for lithium-ion batteries, wherein the mass of carbon is 0.87g (mass of carbon remaining after citric acid participates in reduction reaction and decomposition).

A titanium-doped carbon-coated lithium iron phosphate material was prepared, in which the theoretical ratio of iron and titanium elements was Fe:Ti=0.9:0.1 (expressed as LiFe _0.9 Ti _0.1 PO ₄ , the same below).

The electrochemical performance test of the material is carried out according to the following method. First, the positive electrode material is coated into an electrode sheet, and the adhesive used in the preparation of the electrode sheet is 0.02mol/L PVDF NMP solution, which is weighed according to the mass ratio of 85:8:7. Grind the active material, acetylene black and the corresponding amount of binder solution evenly, add a certain amount of binder solution dropwise, stir and coat evenly on the aluminum foil, dry at 100°C for 24 hours, punch the electrode plate coated with the positive electrode material Form a disc with a diameter of about 10mm, control the active material content of the positive electrode sheet between 8 and 10mg, use metal lithium sheet as the counter electrode, Celgard2400 as the diaphragm, 1mol/LLiPF6/EC+DMC+EMC (volume ratio 1:1: 1) Electrolyte, assembled into a button battery in a glove box with dry air (relative humidity ≤ 4%), and let it stand for 24 hours after the battery is assembled.

Example 2

(1) Accurately weigh 0.025molLi ₂ CO ₃ , 0.025molFe ₂ O ₃ and 0.05molNH ₄ H ₂ PO ₄ and put them into the ball mill tank for batching;

(2) Add the prepared powder into acetone which is 4 times the volume of the powder, and then place it in a ball mill and rotate it at a rate of 250rpm/min for 5h;

(3) Dry the ground slurry in an oven at 110° C., and then add a saturated aqueous solution containing 2.2 g of citric acid to make a rheological phase precursor;

(4) Heat the above precursor at a heating rate of 1°C/min under an inert atmosphere, keep the temperature at 100°C for 2 hours, then raise the temperature to 400°C for 5 hours, take it out and grind it after cooling down in the furnace, and press it under a pressure of 200MPa into a compact cylinder;

(5) The pressed cylinder was heated to 850° C. for 12 h at a constant temperature in an inert atmosphere, and the temperature was lowered to room temperature with the furnace to obtain 8.7 g of titanium-doped carbon-coated lithium iron phosphate, a positive electrode material for lithium-ion batteries.

A carbon-coated lithium iron phosphate material is prepared, wherein the theoretical ratio of each element is LiFePO ₄ .

Example 3

(1) Accurately weigh 0.025molLi ₂ CO ₃ , 0.02325molFe ₂ O ₃ , 0.0035molTiO ₂ and 0.05molNH ₄ H ₂ PO ₄ and put them into the ball mill tank for batching;

(2) Add the prepared powder into acetone which is 4 times the volume of the powder, and then place it in a ball mill and rotate it at a rate of 250rpm/min for 5h;

(3) Dry the ground slurry in an oven at 110° C., and then add a saturated aqueous solution containing 2.2 g of citric acid to make a rheological phase precursor;

(4) Heat the above precursor at a heating rate of 1°C/min under an inert atmosphere, keep the temperature at 100°C for 2 hours, then raise the temperature to 400°C for 5 hours, take it out and grind it after cooling down in the furnace, and press it under a pressure of 200MPa into a compact cylinder;

(5) The pressed cylinder was heated to 850° C. for 12 h at a constant temperature in an inert atmosphere, and the temperature was lowered to room temperature with the furnace to obtain 8.7 g of titanium-doped carbon-coated lithium iron phosphate, a positive electrode material for lithium-ion batteries.

A titanium-doped carbon-coated lithium iron phosphate material was prepared, in which the theoretical ratio of each element was LiFe _0.93 Ti _0.07 PO ₄ .

Example 4

(1) Accurately weigh 0.025molLi ₂ CO ₃ , 0.02175molFe ₂ O ₃ , 0.0085molTiO ₂ and 0.05molNH ₄ H ₂ PO ₄ and put them into the ball mill tank for batching;

(2) Add the prepared powder into acetone which is 4 times the volume of the powder, and then place it in a ball mill and rotate it at a rate of 250rpm/min for 5h;

(3) Dry the ground slurry in an oven at 110° C., and then add a saturated aqueous solution containing 2.2 g of citric acid to make a rheological phase precursor;

(4) Heat the above precursor at a heating rate of 1°C/min under an inert atmosphere, keep the temperature at 100°C for 2 hours, then raise the temperature to 400°C for 5 hours, take it out and grind it after cooling down in the furnace, and press it under a pressure of 200MPa into a compact cylinder;

(5) The pressed cylinder was heated to 850° C. for 12 h at a constant temperature in an inert atmosphere, and the temperature was lowered to room temperature with the furnace to obtain 8.7 g of titanium-doped carbon-coated lithium iron phosphate, a positive electrode material for lithium-ion batteries.

A titanium-doped carbon-coated lithium iron phosphate material is prepared, wherein the theoretical ratio of each element is LiFe _0.87 Ti _0.13 PO ₄ .

Table 1 Example 1, 2, 3 and 4 prepare the unit cell parameter data of four kinds of materials

The above table is the unit cell parameter data of the four materials prepared in Examples 1, 2, 3 and 4. This data is obtained from the XRD data in accompanying drawing 1. It can be seen from the table that LiFe _0.9 Ti _0.1 PO ₄ /C material The value of a is smaller, the value of c is larger, that is, the value of c/a is larger, and the diffusion of lithium ions in this material is easier, that is, the conductivity of the material is better.

The charge and discharge performance test of the battery is carried out at room temperature, and the constant current charge and discharge test is carried out with Wuhan Jinnuo battery tester. The four materials prepared in Examples 1, 2, 3 and 4 are charged and discharged for the first time at a rate of 0.2C. When the voltage range is 2.4-4.2V, the capacity reaches 151mAh/g, 142mAh/g, 146mAh/g and 121mAh/g respectively, as shown in Figure 2, it can be seen that the LiFe _0.9 Ti _0.1 PO ₄ /C material prepared in Example 1 The first discharge specific capacity is larger. Figure 4 is the cycle performance curves of Examples 1 and 2 at different discharge currents. It can be seen that the discharge specific capacity of the material LiFe _0.9 Ti _0.1 PO ₄ /C in Example 1 is large and attenuated no matter whether it is a small current or a high current. Small, especially at a high rate of 5C, the discharge specific capacity of the LiFe _0.9 Ti _0.1 PO ₄ /C material is still 98.1mAh/g, after 20 cycles, the capacity decay is 96.2mAh/g, and the capacity decay rate is only 1.9%. Much lower than the undoped material in Example 2.

Example 5

(1) Accurately weigh 0.05mol LiH ₂ PO ₄ , 0.0225mol Fe ₂ O ₃ and 0.005mol TiO ₂ into a ball mill tank for batching;

(2) Add the prepared powder into acetone which is 4 times the volume of the powder, and then place it in a ball mill and rotate it at a rate of 250rpm/min for 5h;

(3) Dry the ground slurry in an oven at 110° C., and then add a saturated aqueous solution containing 1.8 g of citric acid to make a rheological phase precursor;

(4) Heat the above precursor at a heating rate of 1°C/min under an inert atmosphere, keep the temperature at 100°C for 2 hours, then raise the temperature to 400°C for 5 hours, take it out and grind it after cooling down in the furnace, and press it under a pressure of 200MPa into a compact cylinder;

(5) The pressed cylinder was heated to 850° C. for 12 h at a constant temperature in an inert atmosphere, and the temperature was lowered to room temperature with the furnace to obtain 8.7 g of titanium-doped carbon-coated lithium iron phosphate, a positive electrode material for lithium-ion batteries.

A titanium-doped carbon-coated lithium iron phosphate material is prepared, wherein the theoretical ratio of each element is LiFe _0.9 Ti _0.1 PO ₄ .

Example 6

(1) Accurately weigh 0.05mol LiF, 0.0225mol Fe ₂ O ₃ , 0.005mol TiO ₂ and 0.05mol NH ₄ H ₂ PO ₄ and put them into the ball mill tank for batching;

(2) Add the prepared powder into acetone which is 4 times the volume of the powder, and then place it in a ball mill and rotate it at a rate of 250rpm/min for 5h;

(3) Dry the ground slurry in an oven at 110° C., and then add a saturated aqueous solution containing 2.1 g of citric acid to make a rheological phase precursor;

(4) Heat the above precursor at a heating rate of 1°C/min under an inert atmosphere, keep the temperature at 100°C for 2 hours, then raise the temperature to 400°C for 5 hours, take it out and grind it after cooling down in the furnace, and press it under a pressure of 200MPa into a compact cylinder;

(5) The pressed cylinder was heated to 850° C. for 12 h at a constant temperature in an inert atmosphere, and the temperature was lowered to room temperature with the furnace to obtain 8.7 g of titanium-doped carbon-coated lithium iron phosphate, a positive electrode material for lithium-ion batteries.

A titanium-doped carbon-coated lithium iron phosphate material is prepared, wherein the theoretical ratio of each element is LiFe _0.9 Ti _0.1 PO ₄ .

From the cycle performance curves of the three materials prepared in Examples 1, 5 and 6, i.e. accompanying drawing 3, it can be seen that with Li ₂ CO ₃ , the electrochemical performance of the lithium source synthetic material is better, and the capacity is higher at different rates and Attenuation is minimal at high magnification 5C.

Claims (3)

1. A metal titanium-doped carbon-coated lithium iron phosphate and a preparation method thereof, characterized in that the chemical expression of the substance prepared by the method is: LiFe _1-x Ti _x PO ₄ /C, wherein 0<x≤0.2, C The mass percentage is 10%. 2. a kind of metal titanium-doped carbon-coated lithium iron phosphate and preparation method thereof as claimed in claim 1, comprising the steps of: (1) Lithium source, Fe ₂ O ₃ , TiO ₂ and NH ₄ H ₂ PO ₄ are weighed in molar ratio lithium:iron:titanium:phosphorus=1:1-x:x:1 ratio, where 0 <x≤0.2; (2) Add acetone to the prepared powder and place it in a ball mill to rotate for 2-10 hours at a rate of 200-500rpm/min. The amount of acetone is 3 to 5 times the volume of the powder; (3) Dry the ground slurry in an oven at 100-110°C, then add a saturated aqueous solution of citric acid to make a rheological phase precursor, wherein the amount of citric acid is the raw material in step (1) according to its carbon content Calculation of 20% of the mass sum of lithium source, Fe ₂ O ₃ , TiO ₂ and NH ₄ H ₂ PO ₄ ; (4) Heat the above precursor at a heating rate of 1°C/min under an inert atmosphere, keep the temperature at 100°C for 2-5 hours, then raise the temperature to 400°C for 3-6 hours, take it out and grind it after cooling down in the furnace, and grind it at 100-200MPa Under pressure, press it into a compact cylinder; (5) The pressed cylinder is heated to 500-900° C. for 5-15 h at a constant temperature in an inert atmosphere, and the temperature is lowered to room temperature with the furnace to obtain titanium-doped carbon-coated lithium iron phosphate, a positive electrode material for lithium-ion batteries. 3. A metal titanium-doped carbon-coated lithium iron phosphate and a preparation method thereof as claimed in claim 2, characterized in that said lithium source is lithium carbonate, lithium dihydrogen phosphate or lithium fluoride.

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