Although silicon is a very attractive anode material because of its higher energy density, its huge volume change over repeated charge−discharge cycles rapidly degrades cycle life. As an alternative approach to mitigate the well-known drawbacks of silicon while retaining the energy density advantages, silicon monoxide (SiOx, x ≈ 1) has become attractive as well (e.g., earlier post).
SiOx offers high reversible specific capacity and improved cyclic performance; however, it still suffers from inevitable volumetric changes and poor electrical conductivity. A number of research efforts have tackled those challenges as well. Now, separate research teams in China and the US report two new approaches toward a commercially viable SiOx electrode.
A team at the University of Kentucky (Chen et al.) has synthesized a high performance binder-free SiOx/C composite electrode for Li-ion batteries by mixing SiOx particles and Kraft lignin. After a heat treatment, the lignin formed a conductive matrix hosting SiOx particles, ensuring electronic conductivity, connectivity, and accommodation of volume changes during lithiation/delithiation. No conventional binder or conductive agent was necessary.
The composite electrode showed excellent performance, maintaining ∼900 mAh g−1 after 250 cycles at a rate of 200 mA g−1, and good rate capability.
They attributed the excellent electrochemical performance to the comparatively small volume change of SiOx-based electrodes (160%) and the flexibility of the lignin-derived carbon matrix to accommodate the volume change. A paper on their work is published in the Journal of Power Sources.
The team in China (Zhang et al.) developed a mild and efficient method to prepare a micro-sized SiOx/C core–shell composite. By mixing citric acid and ball-milled SiOx and subjecting them to carbonization, they obtained a uniform SiOx/C core–shell composite with a micro-sized SiOx core and conformal carbon shell.
The carbon shell effectively enhanced the electrical conductivity of SiOx and mitigated the volume changes of SiOx during lithiation and delithiation. The SiOx/C composite electrode delivered a reversible specific capacity of 1296.3 mAh g–1; coulombic efficiency of as high as 99.8%; and capacity retention of 65.1% (843.5 mAh g–1) after 200 cycles.
The composite also exhibited excellent rate capability. The approach is mild, mass-productive, and cost-effective and, thus, can be employed in large-scale production of high-performance SiOx/C composite anode material, the team said. A paper on their work is published in the ACS journal Energy & Fuels.
Tao Chen, Jiazhi Hu, Long Zhang, Jie Pan, Yiyang Liu, Yang-Tse Cheng (2017) “High performance binder-free SiOx/C composite LIB electrode made of SiOx and lignin,” Journal of Power Sources, Volume 362, Pages 236-242 doi: 10.1016/j.jpowsour.2017.07.049
Junying Zhang, Xiaoming Zhang, Chunqian Zhang, Zhi Liu, Jun Zheng, Yuhua Zuo, Chunlai Xue, Chuanbo Li, and Buwen Cheng (2017) “Facile and Efficient Synthesis of a Microsized SiOx/C Core–Shell Composite as Anode Material for Lithium Ion Batteries” Energy & Fuels doi: 10.1021/acs.energyfuels.7b00775