“Quasi-Zero-Strain” TiO_2–x as an Ultra-Long-Life Anode for Li-Ion Batteries

Zero-strain electrodes are rather attractive as they exhibit no deformation during lithiation and can withstand long-term cycles. However, this property relies on a loosely packed lattice, which limits zero-strain anodes to a few materials like Li4Ti5O12. Therefore, although titanium dioxide has a higher dielectric constant and Li+ diffusion rate, its tight Ti/O packing results in ∼4% volume expansion after lithiation and leads to poor stability. Herein, to alleviate the volume expansion of TiO2, we take advantage of the fact that the lattice parameters of ionic crystals increase as their size decreases and construct a unique “quasi-zero-strain” anode by introducing abundant mesopores. Specifically, layered K2Ti2O5 was deliberately selected as a precursor, and the K+ ions between Ti–O layers were then exchanged by H+. After removing H2O through a heat treatment, a large number of mesopores were introduced within the Ti–O layer, which expanded the lattice parameter by 4.1%. Thus, this quasi-zero-strainTiO2–x showed impressive rate performance and excellent stability, with a capacity retention of 98.6% even after 35 000 cycles at 100C. We believe that this strategy can greatly expand the types of zero-strain materials and pave a solid pathway for the development of LIBs.