UC Berkeley

Disordered rock-salt (DRX) cathodes within the Li–Mn–Ti–O (LMTO) composition space have recently been extensively studied, as they promise to deliver exceptional energy density at low cost in Li-ion batteries. Disordered rock-salt (DRX) cathodes within the Li–Mn–Ti–O (LMTO) composition space have recently been extensively studied, as they promise to deliver exceptional energy density at low cost in Li-ion batteries. The development of LMTO DRX with improved electrochemical performance requires optimization of the composition and particle size/morphology, which are determined by synthesis conditions such as annealing temperature. These challenges motivate an investigation of the LMTO rock-salt phase diagram, with a focus on understanding the stability of DRX by quantifying the order-disorder transition temperature ( T disord ) as a function of composition. First-principles calculations and X-ray diffraction experiments are applied to establish the LMTO phase diagram, which lies within the LiMnO 2 –Li 2 MnO 3 –Li 2 TiO 3 pseudo-ternary. The T disord decreases significantly as off-stoichiometry is introduced to the end-point compositions, resulting in a eutectoid phase diagram. Importantly, a significant range of LMTO compositions containing small to moderate fractions of Li-excess and Ti 4+ doping (relative to LiMnO 2 ) have T disord spanning 700–900 °C. These temperatures are substantially lower than conventional DRX synthesis temperatures, suggesting the promise of decreasing synthesis temperatures for specific DRX compositions. The compositions containing moderate to high fractions of Mn 4+ instead have greater T disord and phase separation to layered Li 2 MnO 3 becomes highly favored.