Method of preparing positive electrode composite material of Lithium ion cell contg, ferrous phosphate lithium salt-carbon

[0017] Example 1

[0018] Mix 0.5 mol of lithium hydroxide and 0.5 mol of iron phosphate, put them in a nylon tank, and add 80 ml of alcohol. After mixing for 2 hours on a ball mill, the mixture is mixed into 14 grams of polypropylene and placed in a tube furnace. Under a nitrogen atmosphere of 1 liter/min, the temperature was increased to 700° C. at a rate of 5° C./min, and the temperature was kept constant for 10 hours, and then the temperature was lowered to room temperature.

[0019] The carbon content of the obtained composite material is 2.5%, and the XRD spectrum is shown in figure 1 , Compared with the standard card, it is olivine LiFePO with intact crystal form 4 , And no diffraction peak of carbon is observed.

[0020] The composite material obtained in Example 1 was used to prepare electrodes in the following manner.

[0021] Weigh the composite material obtained in Example 1 at a mass ratio of 80:10:10: carbon black: polytetrafluoroethylene, grind uniformly to make an electrode, with a pure lithium sheet as the negative electrode to dissolve in ethyl carbonate + carbonic acid 1.0mol/L LiPF in a mixed solvent of dimethyl ester (1∶1 by volume) 6 It is the electrolyte, and the polypropylene microporous film is the diaphragm, assembled into a simulated lithium-ion battery. figure 2 For the first charge-discharge curve of the corresponding battery at a cut-off voltage of 4.2V-2.5V at a rate of 0.1C, indicating that the tested battery has a stable charge-discharge voltage platform of about 3.4V, the reversible specific capacity of the composite material in Example 1 can be calculated It is 164mAh/g. image 3 Is the discharge curve of the corresponding battery at different charge and discharge rates. In the discharge rate range of 0.1C-0.5C, the reversible capacity of the positive electrode active material is between 4145-164 mAh/g. Figure 4 It is the cycle performance of the corresponding battery at a rate of 0.2C. Among them, the specific capacity is LiFePO 4 Mass calculation instead of LiFePO 4 -The quality of the carbon composite is the same in the following examples.

[0022] Example 2:

[0023] Mix 0.5 mol of lithium hydroxide, 0.25 mol of ferric oxide and 0.5 mol of ammonium dihydrogen phosphate into a nylon tank, add 80 ml of alcohol, mix thoroughly on a ball mill for 2 hours, and mix the mixture into 20 grams The polypropylene was put into a tube furnace, and under a nitrogen atmosphere of 5 liters/minute, the temperature was raised to 700°C at a rate of 5°C/minute, and the temperature was kept constant for 20 hours, and then the temperature was lowered to room temperature. The carbon content of the obtained composite material was measured to be 4.6%. The electrode sheet was also prepared according to the method of Example 1. After being assembled into a battery, it was charged and discharged at a rate of 0.2C, and the reversible capacity was determined to be 157mAh/g.

[0024] Example 3:

[0025] Mix 0.5 mol of lithium hydroxide and 0.5 mol of iron phosphate, put them in a nylon tank, and add 80 ml of alcohol. After mixing on a ball mill for 1 hour, the mixture is mixed with 25 grams of polyethylene and placed in a tube furnace. Under a nitrogen atmosphere of 1 liter/min, the temperature was increased to 500° C. at a rate of 5° C./min, and the temperature was kept constant for 24 hours, and then the temperature was lowered to room temperature. The carbon content of the obtained composite material was measured to be 3.1%, and the electrode sheet was prepared according to the method of Example 1. After being assembled into a battery, the battery was charged and discharged at a rate of 0.5C, and the reversible capacity was determined to be 148mAh/g.