Synthesis Of Polyaniline-coated CF_x Cathode Materials And Application For Lithium Battery

Nowadays CF_x, which act as a cathode material, has the highest theoretical specific capacity in primary lithium batteries. Its theoretical specific capacity reach up to 865 mAh/g, which is much higher than the commercial MnO2 material（theoretical discharge specific capacity is 308 mAh/g）. Because Li-CF_x battery has the outstanding advantages of high and low temperature performance and high theoretical specific capacity, so the battery can be widely used in aerospace, military equipment, medical and health care, wearable devices. But the conductivity of CF_x reduced rapidly with the increase of fluorine. When the x = 1, the conductivity of CF_x becomes poor, thus this influence the electrochemical properties the CF_x.In this paper, in order to increase the the electrical conductivity of CF_x material, we coated a layer of conductive PANI on the surface of CF_x by in-situ chemical oxidative polymerization. By this way, we get PANI/CF_x composite material. This paper studied the influence of oxidant species and the PANI layer thickness on the PANI/CF_x composite material electrochemical performance and obtained the optimal electrochemical properties of materials corresponds to the thickness of PANI coating layer to improve the electrochemical properties. The main contents and conclusions of this paper are as follows:（1） By in-situ chemical oxidative polymerization, we used three different kinds of oxidants, FeCl₃, H2O2,（NH₄）₂S₂O₈, successfully prepared the PANI/CF_x composite materials. And the PANI/CF_x composite materials were carried out SEM, TEM measurements and discharge performance testing. Test results show that with the increase of oxidizer oxidizing, surface coating of PANI layer thicker. FeCl₃, H2O2 and（NH₄）₂S₂O₈ oxidant prepared PANI layer thickness is about 230 nm, 300 nm, 300 nm respectively. The discharge performance of PANI/CF_x composite material which was synthesised by FeCl₃ oxidizing agent is better than the other two kinds of PANI/CF_x composite materials discharge performance.（2） In order to get the best PANI layer thickness when FeCl₃ as oxidant, we changed CF_x and aniline monomer proportion and got the PANI/CF_x composite materials with different thickness of the PANI layers. Through the study of the TEM, discharge performance and some other tests of PANI/CF_x composite materials, we get the following conclusions: When CF_x and aniline monomer mass ratio is 4:1, 2:1, 4:3, all the three synthetic PANI/CF_x composite materials discharge rate can reach 8 C; all composite materials discharge specific capacity are above 800 mAh/g at 0.1 C, which is close to the theoretical specific capacity; the two materials, when CF_x and aniline monomer mass ratio is 2:1, 4:3 respectively, discharge performance is best. In accordance with the TEM analysis, the best thickness of PANI layer is about 160 nm to 180 nm.（3） In order to get the best PANI layer thickness when（NH₄）₂S₂O₈ as oxidant, we changed CF_x and aniline monomer proportion and got the PANI/CF_x composite materials with different thickness of the PANI layers. Through the study of discharge performance of PANI/CF_x composite materials, we get the following conclusions: When CF_x and aniline monomer mass ratio is 4:1, 8:1, 16:1, all the three synthetic PANI/CF_x composite materials discharge rate can reach 6 C; all composite materials discharge specific capacity are above 700 mAh/g at 0.1 C, which is close to the theoretical specific capacity; the synthetic PANI/CF_x composite material, when CF_x and aniline monomer mass ratio is 8:1, discharge performance is best. In accordance with the TEM analysis, the best thickness of PANI layer is about 150 nm to 170 nm.（4） Through comparison and analysis of discharge performance of PANI/CF_x composite materials in part（2） and（3）, the PANI/CF_x composite material, which was prepared by FeCl₃ when CF_x:aniline monomer = 4:3, is best. So we selected this material and CF_x raw material for high and low temperature performance test. Through the discharge test, the synthetic PANI/CF_x composite material has preferably excellent high and low temperature performance compared with CF_x. When the battery discharge at 0.1 C, the battery can discharge at-30 ℃ and discharge platform is about 1.91 V, discharge specific capacity can reach 657 mAh/g. discharge. The discharge platform of the battery is about 2.62 V at 100 ℃. When the battery discharge at 0.5 C, the lowest temperature can only reach to-20 ℃. The discharge platform is about 1.80 V and discharge specific capacity can reach 547 mAh/g; When the battery discharge at high temperature, the battery can discharge at 100 ℃.A layer of conductive PANI was coated on the surface of CF_x successfully by in-situ chemical oxidative polymerization. PANI/CF_x composite materials electrochemical performance has obvious improvement compared to the original CF_x. This laid a good foundation for our country Li-CF_x battery commercialization.