TiH2-based anode: In situ formation of solid electrolyte for high volumetric energy density with minimal content of conducting agent

Herein, we report the fabrication of an electrode composite with an ultra-high active material content (90 wt%). This composite was possible because of the utilization of TiH2 as an anode active material that forms a solid electrolyte (LiH) in situ and functions as an electronic conductor, enabling a substantial reduction of the amount of conductor additive in the electrodes. The electrochemical performance of the TiH2-based electrodes with a high active material content was comparable to that of electrode composites that include a solid electrolyte because of sufficient Li+-ion conduction pathways provided by the LiH formed in situ. To further increase the capacity of the TiH2-based electrode, MgH2 (theoretical capacity: 2036 mAh/g) was mixed with TiH2 to function as an active material. TiH2, which is known to exhibit high electron conductivity and a high density, is expected to be used as a partial substitute for low-density carbon additives to increase the volumetric energy density of batteries and their active material content. Hence, the xMgH2-(1 − x)TiH2-AB (AB: acetylene black) electrode composite exhibited a high active material content (90 wt%) and improved volumetric energy density (1687 Wh/L, based on the anode) compared with a MgH2-AB (70:30 wt%) electrode composite (1157 Wh/L), even when the AB content of the xMgH2-(1 − x)TiH2-AB composite was 10 wt%. In addition, a MgH2-TiH2-VGCF (VGCF: vapor-grown carbon fiber) based electrode composite exhibited the highest volumetric and gravimetric energy density (2154 Wh/L, 1888 Wh/kg) among the investigated composites, facilitated by sufficient electron pathways provided by VGCF.