Preparation And Performance Of Macroprous/Mesoporous Carbon Materials For Lithium Air Batteries

Lithium-air batteries have ultra-high theoretical specific energy and discharge capacity. Nonaqueous Li-air batteries are of great potential in the fields of electric vehicles, military and other fields. However, lithium-air batteries are still in the stage of basic research currently and many problems need to be further studied and resolved. In this paper, the hierarchical ordered macroporous/ultrathin mesoporous carbon architecture as cathode material and further functionalization by amorphous Ru nanoclusters were studied.First, formaldehyde and phenol were used to prepare phenolic resin by condensation polymerization and then triblock copolymer F127 was dissolved as the soft template. Uniform and close-packed Si O2（size is about 250nm） solid nanospheres as hard template were firstly prepared by the classic Sto?ber method. They were subsequently immersed into the mixture of phenolic resin and triblock copolymer F127, and kept quiescence for 10 h. After the mixture was calcinated under inert atmosphere, the hierarchical carbon architecture was finally obtained by removing the close-packed silica template. Then the porous carbon was studied as a cathode material for lithium-air battery performance. The N2 adsorption-desorption plots of the macroporous/mesoporous hierarchical porous carbon architecture showed a type â…¢ isotherm with a steep increase of nitrogen absorption at a relatively high pressure（P/P0 = 0.70⁰.99）, indicating that the majority of pore volume was contributed by the mesoporous structure. The mesopore size of macroporous/mesoporous architecture was mainly distributed around 6.595 nm, 8.878 nm and 18.528 nm, respectively. Meanwhile, the BET revealed that the hierarchical macroporous/mesoporous architecture had a surface area of 451.247 m2 g-1 and a large pore volume of 1.881 cm3 g-1. The ordered macropores and ultrathin mesporous walls remarkably enhanced the access capability of O2 or Li+ to the numerous three-phase reaction sites, and the large pore volume easily could accommodate the discharge products. Electrochemical performance results also showed that the hierarchical macroporous/mesoporous porous carbon ha d obvious catalytic discharge voltage platform of up to 2.79 V in ORR process of lithium-air battery. Furthermore, the hierarchical macroporous/mesoporous porous carbon performed an outstanding cycling performance up to over 100 and 200 cycles at the current of 1000 m A g-1 and 2000 m A g-1, respectively. But the discharge cutoff voltage droped to less than 1.0V.The hierarchical macroporous/mesoporous porous carbon was dispersed in Ru（NO3）3 solution in ethylene glycol, which was subject to heating at 160 °C for 3 h to obtain the Ru functionalized carbon architecture. Additionally, the uniformly dispersed amorphous Ru nanoclusters with diameter of 1² nm efficiently reduc ed the charge polarization（about 0.3V） and increased the cycling stability. The Ru functionalized hierarchical macroporous/mesoporous porous carbon performed an outstanding cycling performance up to over 100 cycles at the current of 1000 m A g-1 and 2000 m A g-1, respectively. And the discharge cutoff voltage droped to more than 1.0V.The morphologies of Ketjen carbon black and the hierarchical macroporous/mesoporous carbon after discharging to 2.0 V were observed by SEM. The discharge products for the hierarchical macroporous/mesoporous carbon cathodes looked like a bouquet of flowers consisting of numerous nanosheets. In contrast, the Ketjen carbon black cathode was completely covered by the dense discharge products, which would certainly restrain the transport processes and deactivate the catalytic sites for subsequent ORR and OER processes. Meanwhile, discharge products by three dimensional growth routes could significantly improve the discharge capacity.Finally,g-C₃N₄ graphite was applied as catalyst in lithium/air batteries. The g-C₃N₄ and macroprous/mesoporous hierarchical porous carbon were mixed with a ratio of 1:1, which can effectively improve the performance of lithium/air batteries: on the one hand, it can effectively reduce the OER overpotential, on the other hand, it can promote cycling performance.