‘Breathing-crystals’ the origin of electrochemical activity of mesoporous Li–MnO2

Abstract

Akin to Le Chatalier's principle, we show that a mesoporous material can mitigate the effect of stress by expanding or contracting elastically into the pore space; we simulate this ‘breathing-crystal’ phenomenon using MD simulation. In particular, our simulations reveal that mesoporous Li–MnO₂ is electrochemically active because the stress, associated with charge cycling, does not influence the structure or dimensions of the (unlithiated) 1 × 1 tunnels in which the lithium ions intercalate and reside. Conversely, the parent bulk material suffers structural collapse and blockage of the 1 × 1 tunnels under stress. The mechanism associated with Li deintercalation is presented together with the activation energy barriers, which are calculated to be 0.4 eV – irrespective of whether the mesoporous host is unstrained or under considerable (1.6 GPa) tensile or compressive stress.