Abstract: Lithium-ion batteries, which have played important role in the extraordinary expansion of the electronic products market, are still under intensive study for applications in sustainable transportation and energy storages. To obtain lithium ion batteries with specific energy > 200 W•h/kg at cell-level, LiNi0.5Mn1.5O4 (LNMO) is one of the most promising candidates for the cathode. It has many advantages, e.g. high operating voltage [ca. 4.7 V (vs. Li/Li+)], reasonable practical capacity (ca. 135 mA•h/g), excellent rate capability, relatively low cost. In this paper, the structural differences of LNMO with two space groups (disordered Fd-3m and ordered P4332) and its associated electrochemical performances are presented. The atomic-level structure, especially in the surface region, of LNMO during the first charge/discharge cycle (3.5—4.9V) is reported in detail. The preparation and modification of LNMO, e.g. synthesis methods, effects of coating and doping are then reviewed. We also propose surface modification of LNMO, which is different from conventional coating and doping. Surface modified LNMO with TiO2 shows that the surface is covered by oxide particles and the few nanometer surface structure is also doped with Ti ions. The influence of surface modification on the electrochemical cycling performance of LNMO at 25 ℃ and 55 ℃ is reported.

Key words: lithium-ion batteries, LiNi0.5Mn1.5O4, atomic-scale structure, electrochemical performance, surface modification