A solid solution of spinel (2/3)Li(Li1/3Ti5/3)O4–(1/3)Li(Ni1/2Ti3/2)O4 was prepared, and its structural/electrochemical properties were compared with Li(Li1/3Ti5/3)O4 to identify the effect of doping to the structural invariance of Li(Li1/3Ti5/3)O4. The solid solution retained the zero strain characteristic of Li(Li1/3Ti5/3)O4 during discharge/charge with an excellent cycle stability, while the rate capability was notably improved. However, a reversible broadening of the XRD peak was observed at the end of discharge, indicating some structural changes. XANES measurements showed that the oxidation state of Ti was +4 and that of Ni was +2 in the solid solution.