Toward High Specific Energy and Long Cycle Life Li/Mn-Rich Layered Oxide || Graphite Lithium-Ion Batteries via Optimization of Voltage Window

Abstract

Li/Mn-rich layered oxide (LMR) cathode active materials promise exceptionally high practical specific discharge capacity (>250 mAh g⁻¹) as a result of both conventional cationic and anionic oxygen redox. The latter requires electrochemical activation at high cathode potential (>4.5 V vs Li|Li⁺), though it is accompanied by capacity and voltage fade in the course of continuous release of lattice oxygen, layered-to-spinel phase transformation, redox couple shift, as well as transition metal dissolution, whereas the latter is particularly detrimental for graphite-based anodes due to electrode crosstalk. Herein, the degradation is investigated in LMR || graphite full cells by systematically varying the voltage windows, analyzing electrochemical data and changes at the anode surface. Based on this, the optimal operational voltage window, i.e., upper and lower cutoff voltage (UCV and LCV), is elaborated to finally solve the dilemma of decent cycle life (at high UCVs) and insufficient LMR activation/capacity (at low UCV) and is shown to be superior via distinguishing between formation and postformation cycles of 4.5 and 4.3 V, respectively.