Unraveling structural evolution of LiNi_0.5Mn_1.5O ₄ by in situ neutron diffraction

The electrochemical properties of the spinel LiNi_0.5Mn _1.5O₄ cathode material are influenced by the synthesis processes, which determines the impurity phase and the distribution of Ni and Mn in the spinel structure. Taking advantage of neutron's high sensitivity to Ni and Mn, in situ neutron diffraction has been employed to quantify the phase formation/structural evolution process under continuous heating/cooling and isothermal annealing conditions. The results show that the subtle Ni and Mn ordering process occurs slowly at 700°C and the degree of ordering can be controlled by the annealing time. At temperatures above 750°C, the LiNi _0.5Mn_1.5O₄ spinel phase starts to decompose into the rock-salt impurity phase accompanied by the release of O₂. The rock-salt phase reverts back to the spinel phase upon cooling along with the oxygen uptake. The dynamic process of structural evolution of LiNi _0.5Mn_1.5O₄ that was unraveled by in situ neutron diffraction is valuable for guiding the synthesis of cathode materials with desirable properties.