Abstract
LiNiO2 (LNO) represents the end member in the compositional space of the LiNi1-x-yMnxCoyO2 (as x and y approach zero) cathode system. Despite its high theoretical specific capacity (275 mAh/g), LNO suffers from phase transitions with large volume change and unfavorable reactions upon electrochemical cycling, which restricts its practical use in the application of lithium-ion batteries. While the contributing factor to the structural instability is commonly linked to the undesired volume collapse associated with the H2-H3 phase transition, detailed analysis of structural evolution following the entire route of phase transitions (H1-M-H2-H3) in real time under battery operating conditions remains a challenging task. In this work, we employ operando neutron diffraction to study the structural changes (crystal lattice, Li/Ni−O bond length, O−Ni−O bond angles, and LiO2/NiO2 layer thickness) of LNO cathode in a home-built LixNiO2||graphite full cell during Li+ de-/intercalation. In particular, the anomalous increase(decrease) of Ni−O(Li−O) bond length at high SOC (>∼85 %) in the H3 phase is discussed in the context of O2− (2p)→Ni4+(3d) negative charge transfer.
