A gradient porous cathode for non-aqueous lithium-air batteries leading to a high capacity

In conventional porous cathodes of non-aqueous lithium-air batteries, the higher discharge reaction rate in the oxygen richer region will result in a gradient distribution of the solid product, Li2O2, decreasing from the air side to the separator side. Such a distribution of the solid product means that although the pores toward the separator side remain open, the pores at the air side will be blocked first with an increase in the discharge capacity, terminating the discharge process and resulting in a low discharge capacity. In this work, we design and fabricate a cathode structure with a stepwise gradient pore distribution (pore size reducing from 500 to 300 and 100 nm) by mixing carbon powder and nanotubes. The gradient porous cathode enables the capacity of a non-aqueous lithium-air battery discharging at 0.1 mA/cm(2) to be 19.2% higher than that by a uniform porous cathode (-100 nm in pore size) and 82.3% higher than that by a uniform porous cathode (-500 nm in pore size). The SEM image analysis suggests that the increased discharge capacity can be mainly attributed to the fact that the gradient cathode can not only increase oxygen transport pathways but also retain a sufficiently large specific surface area. (C) 2014 Elsevier B.V. All rights reserved.