[Nanosized Insertion Materials for Li-Ion Batteries]Spinel Li4Ti5O12

The disadvantage of a high voltage of∼1.55 V versus Li metal compared with anode materials like graphite is compensated by the material's safe operation, high rate capability, low cost, and excellent recyclability

 in micrometer sized Li_4+xTi₅O₁₂ two-phase separation is unstable above 80 K and domains of 16c occupation and 8a occupation intimately mix at a nanometer length scale. This appears as a solid solution for diffraction and the open circuit potential

 - The very low interface and strain energy imposed by the coexisting phases facilitates mixing of the two phases on a small scale. This leads to a solid solution electrochemical response at relative low temperatures (above 80 K)

(c) Li occupancy of the 8a (closed symbols) and 16c (open symbols) sublattices in spinel Li₄þxTi₅O₁₂. 

  - additional lithium incorporation was predicted to lead to a negative and therefore impossible to achieve intercalation potential - directly observation indicates an increased capacity at positive potential with decreasing particle size, exceeding Li7Ti5O12. Neutron diffraction proved simultaneous occupation of both 8a and 16c, which explains the additional capacity.Furthermore, the additional capacity was suggested to reside mainly near the surface, explaining the increasing capacity with decreasing particle size

 oxygen-terminated surface (oxygen-rich surfaces) would explain the relative high voltages of the first inserted capacity as well as the additional capacity at low potential that scales with the particle surface. However, too high surface lithium storage was found to result in irreversible capacity loss, most likely due to surface reconstruction, creating a thin layer of inactive material