Supplying precise power is a significant factor in many electric devices to secure optimized performance, energy efficiency and device protection. For example, in OLEDs, the energy efficiency is highly dependent on the applied potential. However, most of electrode materials for batteries have its unique thermodynamic value, which is almost impossible to be adjusted. Therefore, tunability of the electrochemical property of materials is highly desirable for improving the performance of electric devices.

MLi₂Ti₆O₁₄ (MLTO, M = 2 Na, Sr, Pb, Ca, Ba etc.) have been paid attention for the next-generation anode material for lithium-ion batteries (LIB) because of its lower working voltage than that of Li₄Ti₅O₁₂ (LTO). Also, they shows flat potential plateau as well as LTO. Their operating potential and equivalent amount of intercalatible lithium ions varies depend on the M species. However, all of their crystal structures are analogous, except minor differences. Based on these observations, we achieved precise tuning of the electrochemical properties of MLTO with two coexisting M species by modulating stoichiometry of M species.

In this research, we used Na, Sr-coexisting MLTO (Na_2-2xSr_xLi₂Ti₆O₁₄, NaSrLTO). Na₂Li₂Ti₆O₁₄ (NaLTO) has the lowest working potential (1.25 V) as well as the lowest reversibly intercalatible Li⁺ (2.0 equiv.^-1) among the MLTOs, and SrLi₂Ti₆O₁₄ (SrLTO) is diametrical of NaLTO (1.4 V and 2.5 equiv.^-1). In NaSrLTO, operating potential gradually rises and equivalent inserted Li⁺ increases as higher ratio of Sr exists. Ab initio calculations revealed that the gradual potential change is originated from the gradual change of electron density of Ti³⁺/Ti⁴⁺ redox center. Also, Because SrLTO has half-vacant 8f Wyckoff position, SrLTO is able to store more Li⁺ than NaLTO, which all of Na atoms fully occupy the 8f Wyckoff position.