The Performance Of Electrode Materials Of Lithium-ion Capacitors Based On The System Of Lithium Iron Phosphate/Porous Carbon

As a type of energy storage device with excellent performance,lithium-ion capacitor has many outstanding properties in energy density and power density, so its application is explored widely. Followed by, the researches about its electrode materials are becoming more and more. In this paper, to obtain the electrode materials of lithium-ion capacitor with high performance is the purpose. Through modification of different materials, we tried to assemble lithium ion capacitors with high-performance. The cathode material used LiFePO4 which was modified by carbon coating and cobalt doping. And the anode materials used GRF, NGRF and polymer of intrinsic microporous (PIM-1), which were activated by CO2 in different temperature. Then the electrochemical properties of half-cell and the applications in lithium-ion capacitor of cathode materials and anode materials were researched. The main researches contained three aspects.1. We synthesized LiFePO4/C by co-precipitation method, and determined the optimum conditions of it. The electrochemical performance of LiFe0.96Co0.04PO4/C synthesized under these conditions was the best. It had the morphology of nano-lamellar, and the discharge specific capacity of its half-cell was up to 141.2mAh·g-1 with a current density of 0.1C. After the 100 cycles, it can still maintain 98.2%. When the current density increased to 1C, the discharge specific capacity was 112.3mAh·g-1. It was better than LiFeP04/C. For lithium-ion hybrid capacitors, (LiFeP04/C)/AC provided a maximum energy density of 47.6Wh·kg-1 and a maximum power density of 1004.7W·kg-1. But(LiFe0.96Co0.04PO4/C)/AC provided a higher and maximum energy density of 51 Wh·kg-1, and a higher and maximum power density of 1050.5 W·kg-1.2. We synthesized GRF and NGRF by sol-gel method, and activated them by CO2 in different temperature. Then GRF-A-x and NGRF-A-x were obtained. They had the different sizes of flaky distribution, and graphene served as the support to form a three-dimensional structure.CO2 activation had produced a large number of microporous and mesoporous, which made the surface area increase and the pore structure more abundant. With the temperature of CO2 activation increasing, the discharge specific capacity of GRF-A-x was also increased, and the addition of N element increased the discharge specific capacity of the corresponding materials. Among these, the discharge specific capacity of GRF-A-10 and NGRF-A-10 were 917.1mAh·g-1 and 1077.2mAh·g-1 with a current density of 0.1A·g-1. For lithium-ion hybrid capacitors,L4A6/GRF-A-10 obtained a maximum energy density of 30.7Wh·kg-1 and a maximum power density of 1182W·kg-1. And L4A6/NGRF-A-10 obtained the maximum energy density of 33.4Wh·kg-1, the maximum power density of 2392.6W·kg-1.3. After organic synthesis, high-temperature carbonization and CO2 activation, we got PIM-1-C and PIM-1-A. PIM-1-A was of the distribution with micrometer spherical. And CO2 activation made a large number of heteroatoms removed from PIM-1-A, then the pore structure became more abundant. It also made the specific surface area increase to 965.3m2·g-1. In addition, the discharge specific capacity was 1158.4 mAh-g-1 with a current density of 0.1A·g-1, which was 5.1 times of PIM-1-C. For lithium-ion hybrid capacitors, L4A6/PIM-1-A had a maximum energy density of 18.5Wh·kg-1 and a maximum power density of 2412 W·kg-1.