Carbon Microspheres Composites As Cathode Materials For Lithium-air Batteries

Lithium-ion batteries have been widely used as energy storage in the past decades.But,recently,with the development with the development of the new material,Lithium-ion batteries with low current density cannot meet the needs of the new market of the electric cars.Thus,the electrochemical systems with high energy density are urgently needed.Metal-air cells are widely researched for their high energy density.Among them,the most representative one is the Li-air battery.This paper studies the Li-O2 battery with the CMs 、 boron doped carbon microspheres(B-CMs)and the cobalt,boron co-doped carbon microspheres as air cathode materials to find the best remarkable air cathode catalyst material.The carbon microspheres synthesized by a reflux-calcination method show large BET surface area and full of nanosized pores.The CMs which were employed as an air cathode without the addition of any metal particles,not only provide reaction sites but also acte as a cathode carbon support in the non-aqueous system of Li–O2 batteries.At the current density of 200 mA g-1,the CMs as the air cathode material of the Li-O2 battery deliver an initial discharge capacity of 12081.0 mAh g-1.Little capacity loss is shown after 20 full discharge–charge cycles under a current density of 300 mA g-1.60 cycles of continuous discharge and charge are achieved with no capacity loss with a cut-off capacity of 1000 mAh g-1,at 200 mA g-1.A series of different mass fraction of boron doped carbon microspheres are prepared by impregnating-calcinations method.When the mass ratio of the carbon microspheres and the boron acid is 1:15(the virtual loaded mass is 8.07% confirmed by the EDX),the composite catalyst owns the best activity when used in Li-O2 battery.Boron doped carbon microspheres own larger BET surface area and larger pore size.Via TEM,SEM and Raman tests,we can see that boron atoms are homogeneously doped on the carbon microspheres.The existence of B doped on the CMs is B3 C and BC2 O revealed by the typical Fourier transform IR(FTIR)spectra.The Li-O2 batteries with B-CMs air cathode delivered a first discharge capacity of 13757.2 mAh g-1,with a lower charge potential(4.05 V)and a higher discharge potential(2.62 V).And the columbic efficiency of the B-CMs was 90.1%.The battery based on B-CMs as air cathode material can sustain 15 cycles with a cut off capacity of 3000 mAh g-1,at 100 m A g-1.We test the life of the battery with B-CMs at 200 mA g-1;the battery can cycle up to 151 cycles with a cut-off capacity of 1000 mAh g-1.We prepared a series of CCoB air cathode catalyst with different raw material ration by a one-step and two-step synthesized methods.The battery show the best performance with the mass ratio of C:Co:B(4:2:60)via the impregnating-calcinations method as well as the mass ratio of C:Co:B(4:8:12)via the one-step synthesized method.The batteries with the CCoB air cathode material show low charge potential,1.6 V lower than the one with B-CMs cathode catalyst,for the addition of cobalt.But the cell life of the battery with CCoB cathode material has decayed for the easily falling off of the cobalt atoms during the cycling.