High-voltage stability of ethylene carbonate (EC) and an EC-based electrolyte for 5 V-class LiNi_0.5Mn_1.5O₄ batteries

LiNi_0.5Mn_1.5O₄ (LNMO) is a promising high-energy cathode material for lithium-ion batteries due to its high operating voltage (~5 V vs. Li⁺/Li) which leads to a high energy density. However, the high voltage also induces unstable LNMO/electrolyte interface when cycled in regular electrolytes. In this work, we present a high-voltage ethylene carbonate (EC)/1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) electrolyte that is highly compatible with LiNi_0.5Mn_1.5O₄ batteries. Through the use of the electrolyte, we uncover two insights that go against conventional understanding. Contrary to the common belief that EC decomposes readily under high voltage, we demonstrate the outstanding high-voltage stability of both EC and the EC/TTE electrolyte. Moreover, we find that LNMO cycles in this electrolyte without forming a typical cathode/electrolyte interphase (CEI), experiencing instead a unique surface restructuring. Under the conditions of the high-voltage stability of the electrolyte and of surface restructuring, the dissolution of nickel and manganese from LNMO is also mitigated. These features lead to long-term cyclability of LNMO batteries with an average CE of 99.86%. By challenging the perceived instability of EC and revealing a CEI-free surface restructuring process, this work offers both a practical electrolyte design and a fresh interfacial stabilization concept for high-voltage batteries.