Suppressing detrimental phase transitions via tungsten doping of LiNiO 2 cathode for next-generation lithium-ion batteries

A series of W-doped (1.0, 1.5, and 2.0 mol%) LiNiO 2 cathodes was synthesized to systematically investigate the stabilization effect of W doping. The 2 mol% W-LiNiO 2 cathode delivered 195.6 mA h g −1 even after 100 cycles at 0.5C, which was 95.5% of its initial capacity. The capacity retention of LiNiO 2 cycled under the same conditions was 73.7%. In situ X-ray diffraction analysis of the cathodes during charging showed that the W doping protracted the deleterious phase transition to the extent that the two-phase reaction (H2 → H3) merged into a single phase; thus, the phase transition proceeded through a solid-solution-like reaction. The significantly enhanced cycling stability due to W doping largely originated from the reduction of the structural stress associated with the repetitive phase transition caused by the reduction of the abrupt lattice collapse/expansion. The effect of the reduced lattice distortion together with the W-rich surface phase and cation ordering greatly stabilized the LiNiO 2 structure during cycling, making W-doped LiNiO 2 a candidate material for practical high-energy density cathodes.