A Ternary Composite with Medium Adsorption Confirms Good Reversibility of Li-Se Batteries.

For Li-Se batteries, cathode using carbonaceous hosts to accommodate Se performed modestly, whereas those applying metallic compounds with stronger chemical adsorption exhibited even more rapid capacity decay, the intrinsic reasons for which are still not clear. Herein, it is found that Se tends to precipitate on the surface of the electrode during cycling, and the precipitation speed depends on the polarization degree of the host. A further enhanced adsorption does not certainly generate better electrochemical activity, since hosts with overhigh adsorption ability are hard to desorb polyselenides, leading to catalyst passivation and rapid capacity decay. These findings encourage us to design a ternary anatase/rutile/titanium nitride (aTiO2 /rTiO2 /TiN@C) composite host, integrating good adsorption of TiO2 and rapid electron transport ability of TiN, and introducing rutile to weaken overall adsorption. The aTiO2 /rTiO2 /TiN@C composite with medium adsorption not only avoids rapid loss of active substances in electrolyte but also slows down the precipitation speed of Se. As a result, the aTiO2 /rTiO2 /TiN@C/Se electrode delivered good rate capability(154 mA h g-1 at 20 C) and good cycling stability(a low decay of 0.024% per cycle within 500 cycles at 2 C).