CN102074690A

CN102074690A - Method for synthesizing battery anode material LiFePO4 by using controllable carbon clad FePO4

Info

Publication number: CN102074690A
Application number: CN2010106040837A
Authority: CN
Inventors: 夏永姚; 王明娥
Original assignee: Fudan University
Current assignee: Nanjing hongbaoli Group Li Tai Energy Technology Co Ltd
Priority date: 2010-12-24
Filing date: 2010-12-24
Publication date: 2011-05-25
Anticipated expiration: 2030-12-24
Also published as: CN102074690B

Abstract

The invention belongs to the technical field of battery materials, and particularly discloses a method for synthesizing battery anode material LiFePO4 by using controllable carbon clad FePO4. The method comprises the following steps of: synthesizing carbon clad ferric phosphate, mixing the clad ferric phosphate and lithium hydroxide in a ratio, performing pretreatment at the temperature of between 200 and 500 DEG C, and performing high-temperature calcination for 6 to 15 hours at the temperature of between 600 and 900 DEG C to obtain carbon clad nano lithium ferrous phosphate. The carbon is clad on the surface of the ferric phosphate precursor so as to avoid agglomeration in the high-temperature calcination process; and the charge capacity and the discharge capacity of the first ring are close to the theoretical capacity (170mAh/g) of the lithium ferrous phosphate. The carbon clad ferric phosphate is used as a raw material in the method, so the synthesized sample has small granules and high capacity, the raw material cost is low, the process is simple, and the method is suitable for mass production.

Description

The controlled carbon of a kind of usefulness coats FePO 4Synthetic cell positive material LiFePO 4Method

Technical field

The invention belongs to the battery material technical field, be specifically related to the controlled carbon of a kind of usefulness and coat FePO ₄Synthetic cell positive material LiFePO ₄Method.

Background technology

In United States Patent (USP), at first mentioned NASICON type phosphate material Li at J. Barker in 1996 etc. ₃V ₂(PO ₄) ₃Application as positive electrode material of lithium secondary cell.Goodenough group reported first in 1997 have a LiFePO 4 (LiFePO of olivine structural ₄) can be reversible embedding or deviate from ion, be considered to the desirable positive electrode of lithium ion battery.LiFePO ₄Theoretical capacity be 170mAh/g, relatively the electrode potential of lithium is 3.5V.Under little electric current, LiFePO ₄Smooth discharge voltage profile is arranged, and its voltage curve can match in excellence or beauty with stabilized voltage power supply.But electronics and ionic conductance that it is bad make at Li ⁺Embedding and the process of deviating from, electronics can not import and derive timely, makes its active material utilization reduce the capacity partial loss.The low shortcoming of its electronic conductivity can be by reducing phosphate material granularity and coat in its surface carbon, mechanical lapping avoids.

Invented a kind of preparation method who is used for the phosphate material having mesoporous structure of lithium secondary battery in the Chinese patent 200810102098.6.The mesoporous material of mentioning the second particle with mesoporous sphere or elliposoidal that is formed by the primary particle reunion in the invention can improve the high rate performance and the energy density of current material.Mention the LiFePO 4 that coats with the synthetic carbon of ferric phosphate in the Chinese patent 200610025223.9.It is to adopt reducing agent that the ferric iron in the ferric phosphate is reduced into ferrous iron, simultaneously with solution in the ammonium ion reaction, form amorphous ferrous ammonium phosphate, ferrous ammonium phosphate and lithium acetate reaction then, obtain LiFePO 4, coat through carbon again and handle, obtain the LiFePO 4 that carbon coats.The method does not coat ferric phosphate earlier with carbon, reunite in the easily middle high-temperature sintering process, can not obtain the nano-lithium iron phosphate that carbon coats.

Summary of the invention

The object of the present invention is to provide a kind of cost of material low, process route is simple, and the controlled carbon of usefulness that is fit to large-scale production coats FePO ₄Synthetic LiFePO ₄Method.

The controlled carbon of the usefulness that the present invention proposes coats FePO ₄Synthetic LiFePO ₄Method, be that organic carbon source is at FePO under the catalysis of lithium hydroxide alkali condition ₄Surface aggregate, the FePO that synthetic carbon coats ₄, again with FePO ₄After/RF and the lithium salts mixing and ball milling,,, obtain the LiFePO 4 (LiFePO of 1nm～5 μ m again through 600～900 ℃ of high-temperature process through 200～500 ℃ of preliminary treatment ₄).

The controlled carbon of a kind of usefulness coats FePO ₄Synthetic cell positive material LiFePO ₄Method, the synthetic sample particle is little, capacity is big, cost of material is low, process route is simple, is fit to large-scale production.

The concrete operations step of the inventive method is as follows:

(1) the synthetic 1--100g of the taking by weighing granular size of carbon coating ferric phosphate is 1nm～5 μ m ferric phosphates, after the ultrasonic dispersion of the distilled water of 80--120ml 15--30min, the adding mol ratio is 0.001～1 organic carbon source: P-hydroxybenzoic acid, septichen or m-hydroxybenzoic acid, ultrasonic again 15--30min, add lithium hydroxide, mol ratio LiOH:FePO ₄=1:1 is heated to 40～50 ℃, stirs 15--30min, adds the formalin of 1～100ml, be warmed up to 70～250 ℃, reaction 2～24h is cooled to room temperature and regulates PH to 6.8-7.2 with acid later on, evaporate to dryness, the reproducibility carbon of adding precursor quality 1～25%, ball milling;

(2) the synthetic mixture that above-mentioned ball milling is good of carbon cladded ferrous lithium phosphate, under the protection of gas, 200～500 ℃ of preliminary treatment 2～6h, ball milling, 600～900 ℃ of high-temperature process 6～15h obtain the LiFePO 4 that carbon coats again.

Among the present invention, FePO ₄In Fe also can be Mn, Ti, Mg, V, Co, Ni.

Among the present invention, carbon-coating thickness is 2 nm--10nm.

Among the present invention, it is P-hydroxybenzoic acid that carbon coats precursor, septichen or P-hydroxybenzoic acid.

Protective gas is a nitrogen among the present invention, argon gas, or hydrogen-argon-mixed, the volume content of wherein hydrogen-argon-mixed middle hydrogen is 2%-10%.

The acid of regulating pH among the present invention is oxalic acid, acetic acid, citric acid.

Advantage of the present invention is to synthesize the carbon coating ferric phosphate that the surface coats 2nm--10nm thickness, avoid because high-temperature process causes the reunion of LiFePO 4, thereby improve the electronic conductivity of LiFePO 4, obtain LiFePO 4 near theoretical capacity 170mAh/g.This method cost of material is low, and process route is simple, and the particle of LiFePO 4 is controlled, is fit to large-scale production.

Description of drawings

Fig. 1 is that the synthetic carbon cladded ferrous lithium phosphate of the inventive method is positive pole, and the lithium sheet is the charging and discharging curve of negative pole.

Fig. 2 and Fig. 3 are respectively the TEM and the SEM photos of carbon cladded ferrous lithium phosphate.

Embodiment

Can further understand the present invention from following examples, but the present invention not only is confined to following examples.

Embodiment 1

(1) carbon coats the synthetic of ferric phosphate.

Taking by weighing 1 g granular size is the ferric phosphate of 100nm, joins in the beaker that fills 200ml distilled water, ultrasonic dispersion 20min, the adding mol ratio is 0.05 m-hydroxybenzoic acid, and mol ratio is the lithium hydroxide of 1:1, is heated to 40 ℃, after the stirring and dissolving, add the formalin of 5ml, be warming up to 70 ℃, reaction 12h, be cooled to room temperature, regulate PH to 7 with hydrochloric acid,, add 15% sucrose ball milling the water evaporate to dryness.

(2) carbon cladded ferrous lithium phosphate is synthetic

The mixture that ball milling is good, under the protection of gas, through 400 degree preliminary treatment 5h, the high-temperature process 8h of 650 degree obtains the LiFePO 4 that carbon coats again.Charging and discharging capacity is 156mAh/g under 0.1 C situation, and circulation 200 circles only decay 3%.

Embodiment 2

(1) carbon coats the synthetic of ferric phosphate

Take by weighing the ferric phosphate that the 5g granular size is 250nm, join in the beaker that fills 250ml distilled water, ultrasonic dispersion 20min, the adding mol ratio is 0.1 m-hydroxybenzoic acid, mol ratio is the lithium hydroxide of 1:1, is heated to 40 ℃, adds the formalin of 15ml, be warming up to 100 ℃, reaction 5h is cooled to room temperature, regulates PH to 7 with sulfuric acid, with the water evaporate to dryness, add 10% sucrose ball milling.

(2) the synthetic mixture that ball milling is good of carbon cladded ferrous lithium phosphate, under the protection of gas, through 300 degree preliminary treatment 5h, the high-temperature process 15h of 600 degree obtains the LiFePO 4 that carbon coats again.Charging and discharging capacity is 130mAh/g under the 0.5C situation, and circulation 200 circles only decay 5%.

Embodiment 3

(1) carbon coats the synthetic of ferric phosphate

Take by weighing the ferric phosphate that the 10g granular size is 1000nm, join in the beaker that fills 500ml distilled water, ultrasonic dispersion 20min, the adding mol ratio is 0.5 m-hydroxybenzoic acid, and mol ratio is the lithium hydroxide of 1:1, is heated to 50 ℃, after the stirring and dissolving, add the formalin of 20ml, be warming up to 250 ℃, reaction 8h, be cooled to room temperature, regulate PH to 7 with phosphoric acid,, add 5% sucrose ball milling the water evaporate to dryness.

(2) carbon cladded ferrous lithium phosphate is synthetic

The mixture that ball milling is good, under the protection of gas, through 350 degree preliminary treatment 3h, the high-temperature process 15h of 600 degree obtains the LiFePO 4 that carbon coats again.Charging and discharging capacity is 80mAh/g under the situation of 15C, and enclosed pasture efficient is up to 99%.

Claims

1. one kind coats FePO with controlled carbon ₄Synthetic cell positive material LiFePO ₄Method, it is characterized in that concrete steps are as follows:

(1) the synthetic 1--100g of the taking by weighing granular size of carbon coating ferric phosphate is 1nm～5 μ m ferric phosphates, after the ultrasonic dispersion of the distilled water of 80--120ml 15--30min, the adding mol ratio is 0.001～1 organic carbon source P-hydroxybenzoic acid, septichen or m-hydroxybenzoic acid, ultrasonic again 15--30min, add lithium hydroxide, mol ratio LiOH:FePO ₄=1:1 is heated to 40～50 ℃, stirs 15--30min, adds the formalin of 1～100ml, be warmed up to 70～250 ℃, reaction 2～24h is cooled to room temperature and regulates PH to 6.8-7.2 with acid later on, evaporate to dryness, the reproducibility carbon of adding precursor quality 1～25%, ball milling;

2. method according to claim 1 is characterized in that Fe is changed to Mn, Ti, Mg, V, Co, or Ni.

3. method according to claim 1 is characterized in that carbon-coating thickness is 2～10nm.

4. method according to claim 1 is characterized in that protective gas is a nitrogen, argon gas, or hydrogen-argon-mixed, the volume content of wherein hydrogen-argon-mixed middle hydrogen is 2%～10%.

5. method according to claim 1, the acid that it is characterized in that regulating pH is oxalic acid, acetic acid or citric acid.