Amorphous anion-rich titanium polysulfides for aluminum-ion batteries

The strong electrostatic interaction between Al3+ and close-packed crystalline structures, and the single-electron transfer ability of traditional cationic redox cathodes, pose challenged for the development of high-performance rechargeable aluminum batteries. Here, to break the confinement of fixed lattice spacing on the diffusion and storage of Al-ion, we developed a previously unexplored family of amorphous anion-rich titanium polysulfides (a-TiSx, x = 2, 3, and 4) (AATPs) with a high concentration of defects and a large number of anionic redox centers. The AATP cathodes, especially a-TiS4, achieved a high reversible capacity of 206 mAh/g with a long duration of 1000 cycles. Further, the spectroscopy and molecular dynamics simulations revealed that sulfur anions in the AATP cathodes act as the main redox centers to reach local electroneutrality. Simultaneously, titanium cations serve as the supporting frameworks, undergoing the evolution of coordination numbers in the local structure.

Automated summary

A previously unexplored family of amorphous anion-rich titanium polysulfides was developed, achieving high reversible capacity and long cycle life by breaking the constraint of fixed lattice spacing on the diffusion and storage of Al-ion. Spectroscopy and molecular dynamics simulations revealed the sulfur anions in the cathodes act as main redox centers while titanium cations serve as supporting frameworks in the local structure.