Fabrication And Performance Investigation Of Graphene-based Cathode Catalysts

Lithium-air battery is a kind of environmentally friendly new-type energy storage device with high specific energy. However, its practical process is restricted by some disadvantages such as low actual specific capacity and bad cycle performance. In order to optimize the cathode structure and improve the catalytic performance, this research prepared the cathode materials with high dispersion and high catalytic activity.Firstly, graphene was prepared by microwave-assisted glycol method, then combined with Co3O4. The research results presented that the initial discharge specific capacity of the lithium-air batteries with Co3O4-XC-72 and Co3O4-graphene as cathode materials are 1926 m Ah/g and 5205 m Ah/g, respectively. The discharge voltage are both about 2.5 V. This result indicated that the addition of graphene can enhance the catalytic performance of Co3O4. When the discharge specific capacity was limited to a certain degree, we can get a very stable discharge platform, and with the decrease of the discharge specific capacity, the batteries’ discharge platform gradually improved. The cycle performance of batteries also improved. When the initial discharge specific capacity was 1000 m Ah/g, the discharge voltage of the cattery was 2.8 V and can be recycled 5 times. Co3O4-graphene was prepared by mechanical mixing method and in-situ carbonized sucrose method respectively. Test results showed that the initial discharge specific capacity can both reach 5200 m Ah/g. The discharge voltage can reach 2.65 V with the cathode materials prepared by in-situ carbonized sucrose method, which is higher than 2.55 V prepared by mechanical mixing method. However the in-situ carbonized sucrose method is not stable.Pt/graphene was prepared by microwave-assisted glycol method. The particle size of Pt is about 2.5 nm, and its dispersion on the surface of graphene is very uniform with no reunion. The layer structure of graphene was obvious, and the graphene prepared was mixture of single layer and multilayer. The surface and edge of graphene is rough and there were many defects, which is beneficial to the diffusion of oxygen, and can promote the electrode reaction. The initial discharge specific capacity of lithium-air batteries with Pt/graphene as cathode material is 8878 m Ah/g, and the discharge voltage is 2.6 V. As the amount of Pt in Pt/graphene improved, the discharge specific capacity of the battery gradually increased, and discharge voltage is 2.6 V. When the content of Pt was 20 wt.%, the rise of specific capacity is small, so the best content of Pt was 20 wt.%.Co3O4-Pt/graphene was prepared by combining Co3O4 and Pt/graphene. The initial discharge specific capacity of the battery with Co3O4-Pt/graphene as cathode materials can reach 8869 m Ah/g, and the discharge voltage is 2.7 V. The catalytic performance of Co3O4-Pt/graphene is close to Pt/graphene, and the addition of Co3O4 can lower the cost of catalysts. As the amount of Pt in Co3O4-Pt/graphene improved, the discharge specific capacity and the discharge voltage of the battery gradually increased. When the content of Pt was 20 wt.%, the rise of battery performance is small, so the best content of Pt was 20 wt.%. The test results showed that the discharge specific capacity of the battery reduced gradually with the increase of current density, and the cycle performance improved. The initial discharge specific capacity of the battery can reach 10000 m Ah/g when replenishing electrolytes or drying the oxygen during the testing process. When the discharge specific capacity is limited to 1000 m Ah/g, the batteries can cycle 15 and 19 times, respectively.