Batteries: Two-material interface

Adv. Energy Mater. http://doi.org/f3qdmb (2016)

Both ionic and electronic conductors are often required in batteries to facilitate the transport of ions and electrons through the active materials. In solid-state batteries, however, the continuous volume changes of the solid active materials can cause severe contact loss with the conductors and consequently break the diffusion pathways, leading to deterioration in performance. This is known as ‘active material isolation’ in heterogeneous electrode designs, which involve a three-material interface. Kyu Hwan Oh, Se-Hee Lee and colleagues at the University of Colorado at Boulder and Seoul National University have now reported an electrode design with a two-material interface by pairing a mixed ionic and electronic conductor (LiTiS₂) with an insulating active material (FeS₂), eliminating the need to have separate ionic and electronic conductors.

Prepared by ball-milling FeS₂, TiS₂ and Li₃N, the FeS₂–LiTiS₂ cathode features nanodomains of FeS₂ in amorphous LiTiS₂ matrices, maximizing the contact between the active material and the conductor. Compared to a standard FeS₂ cathode, the transport properties are significantly improved in the FeS₂–LiTiS₂ system, as manifested by the charge transfer resistance being more than halved. The researchers also showed that the cathode design enables a capacity retention of 62% and an average Coulombic efficiency of 99.8% for 500 cycles. Importantly, the work suggests that it is possible to remove the solid electrolyte (the ionic conductor) and other conductive additives by using just a mixed ionic–electronic conducting matrix.