Structure Designing And Interface Evolution Of Cathode Materials For Li-O₂ Batteries

Among different types of“beyond lithium-ion”batteries,lithium-oxygen battery?LOB?is regarded as a promising candidate of the next generation energy storage device due to the highest theoretical energy density(?3500 W h kg^-1)and inexhaustible cathode active matter—oxygen.However,the development of LOB is still in its early stage.There are still a lot of problems to be solved:?1?low transportation efficiency of oxygen and ions;?2?serious parasitic reactions,which result in poor cycle stability;?3?evaporation of electrolyte and subsequential safety issues.To overcome these problems,this paper focuses on structure designing and interface evolution of cathode materials.The achievements are as follows:?1?A novel oxygen cathode is fabricated by stacking,rolling and slicing the CNT films and cotton pieces to facilitate the multiphase electrochemical reaction in LOB.In such configuration,the CNT film is sandwiched between cotton layers with fluffy fibers.The cotton layer?partially wetted?is gas/electrolyte bicontinuous,forming vertical oxygen/ion diffusion expressways.The unique configuration greatly enlarges the reactive zone and efficiency.The multiphase electrochemical reaction can proceed smoothly,resulting in remarkably improved capacity.Besides,gel polymer electrolyte?GPE?with good mechanical stability and flexibility is employed to suppress Li dendrite growth and electrolyte evaporation.The good ionic conductivity and electrochemical of GPE ensure efficient charge transfer and stable interface resistance.Due to the synergistic effect of the rolled configuration and GPE,the cathode exhibits enhanced discharge capacity of13564 mA h g^-1 and cycle life of 262 cycles(with a limited capacity of 500 mA h g^-1),which is 2.5 and 5.5 times larger than that of conventional parallel aligned CNT film.?2?Mo₂C nano-flower is synthesized by mixing,centrifuging,lyophilizing and annealing.Carbon particles are closely attached to Mo₂C nano-flower to get a composite cathode.Such cathode ensures good electronic conductivity and catalytic efficiency.Therefore,the battery reactions are greatly boosted.Amorphous MoO₃ film is detected on the surface of Mo₂C.Such material is a good OER catalyst,which can significantly reduce charge overpotential as well as suppress the decomposition of cathode?carbon material?and electrolyte.Consequently,the cycle stability is greatly improved.Compared with pure carbon cathode,Mo₂C cathode obviously reduces the overpotential,and enhances the specific capacity and rate capability.As the result,the cell is able to charge/discharge stably at high performance level.Owing to the synergistic effect of Mo₂C and MoO₃,the cell exhibits high discharge capacity of 7992 mA h g^-1 and long cycle life of 135 cycles(with a limited capacity of 500 mA hg^-1).