Tuning the Carbon Crystallinity for Highly Stable Li-O2 Batteries

Abstract

The increasing demands for emerging high-energy-density applications, such as electric vehicles, have prompted considerable efforts to design a new type of innovative, sustainable battery. Li–O2 batteries can deliver much higher energy densities than current Li-ion batteries and have thus attracted much attention; however, their poor cyclic stability remains a major obstacle to their use in high-energy-density applications. The carbon-based cathode materials (CCMs) used for Li–O2 batteries are considered one of the origins of this cycle-life degradation, which has led to the development of several alternative types of cathode materials, such as Au or TiC.1,2,3 However, there is currently no practical substitute for CCMs, which exhibit desirable properties such as high specific surface area, high electrical conductivity, light weight, and chemical stability and involve the use of well-known technologies with low processing and raw material costs. This study provides a new perspective on Li–O2 batteries, for which the cyclic stability can be dramatically increased using well-ordered graphitic CCMs. Through a systematic investigation on the controlled carbon, we demonstrate that the graphitic crystallinity of carbon is an important factor in determining the stability of not only the cathode but also the electrolyte. To discern the degradation factors affecting the cathode from those affecting the electrolyte, we used carbon isotope (13C)-based air electrodes with various degrees of graphitic crystallinity. Furthermore, in situ differential electrochemical mass spectroscopy analysis clearly demonstrates that as the crystallinity of the carbon increases, the CO2 evolution from the cell is reduced, which leads to a three-fold enhancement in the cycle stability of the cell. Reference 1. Thotiyl, M. M. O. et al., J. Am. Chem. Soc. 2012, 135, 494 2. Peng, Z et al., Science 2012, 337, 5633. Thotiyl, M. M. O. et al., Nat. Mater. 2013, 12, 1050