Revealing the underlying mechanism for the good low-temperature Li+-storage performance of titanium niobates

Titanium niobates with shear ReO 3 crystal structures have emerged as promising candidates for environmental-friendly lithium-ion batteries due to their excellent low-temperature electrochemical performance. However, the underlying mechanism of this merit at low temperatures remains unclear. In this work, through in-situ powder X-ray diffraction examination, we identify that TiNb 2 O 7 and Ti 2 Nb 10 O 29 own negative thermal expansion (NTE) behavior along the b axis (−6.29 × 10 −7  K −1 for TiNb 2 O 7 and −4.8 × 10 −6  K −1 for Ti 2 Nb 10 O 29 ) for the first time, which significantly benefits their low-temperature performance. This NTE behavior in TiNb 2 O 7 //Ti 2 Nb 10 O 29 enables wider Li  +  diffusion channels and larger embedding sites at low temperatures, leading to good −10 °C performance with a high reversible capacity (78 %//84 % of that at 25 °C), rapid Li + diffusion (63 %//32 % of that at 25 °C), and good rate capability (1C vs. 0.1C retention of 70 %//64 %). In addition, the more open low-temperature crystal structure in TiNb 2 O 7 //Ti 2 Nb 10 O 2 reduces unit-cell-volume expansion during lithiation at low temperatures, enhancing the −10 °C cycling stability (101.3 %//93.9 % capacity retention after 1000 cycles at 10C). Therefore, TiNb 2 O 7 and Ti 2 Nb 10 O 29 are very suitable for low-temperature energy storage.