There is a growing appreciation for the role of surface reactivity and subsequent reconstruction affecting the performance of high-voltage, high-capacity Li-ion cathode materials. In particular, the promising Li-excess materials are known to exhibit significant vulnerability toward oxygen release, which can cause surface densification and impede Li intercalation. Here we focus on the end member, Li2MnO3, as a Li-excess, Mn-rich representative of this class of materials and systematically elucidate all possible stoichiometric low Miller index surfaces with various cation ordering on each surface. We apply surface cation reconstruction rules that depend on the local environment, including target Mn–Li site exchanges, and optimize the resulting surface Li configurations using metadynamics. The equilibrium Wulff shape shows dominant (001), (010) surface facets, and almost all facets exhibit favorable Mn reconstruction. Most importantly, we find that while all equilibrium LixMnO3 surfaces become unstable toward oxygen release for x < 1.7, some facets are consistently more resistant than others which may provide a design metric for more stable particle morphologies and enhanced surface oxygen retention.
BT - ACS Applied Materials & Interfaces DA - 09/2016 DO - 10.1021/acsami.6b07259 IS - 38 LA - eng N2 -There is a growing appreciation for the role of surface reactivity and subsequent reconstruction affecting the performance of high-voltage, high-capacity Li-ion cathode materials. In particular, the promising Li-excess materials are known to exhibit significant vulnerability toward oxygen release, which can cause surface densification and impede Li intercalation. Here we focus on the end member, Li2MnO3, as a Li-excess, Mn-rich representative of this class of materials and systematically elucidate all possible stoichiometric low Miller index surfaces with various cation ordering on each surface. We apply surface cation reconstruction rules that depend on the local environment, including target Mn–Li site exchanges, and optimize the resulting surface Li configurations using metadynamics. The equilibrium Wulff shape shows dominant (001), (010) surface facets, and almost all facets exhibit favorable Mn reconstruction. Most importantly, we find that while all equilibrium LixMnO3 surfaces become unstable toward oxygen release for x < 1.7, some facets are consistently more resistant than others which may provide a design metric for more stable particle morphologies and enhanced surface oxygen retention.
PY - 2016 SP - 25595 EP - 25602 ST - ACS Appl. Mater. Interfaces T2 - ACS Applied Materials & Interfaces TI - Surface Morphology and Surface Stability against Oxygen Loss of the Lithium-Excess Li 2 MnO 3 Cathode Material as a Function of Lithium Concentration VL - 8 SN - 1944-8244 ER -