‘Breathing-Crystals’ The Origin of Electrochemical Activity of Mesoporous Li-MnO2

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) 1x1 tunnels in which the lithium ions intercalate and reside. Conversely, the parent bulk material suffers structural collapse and blockage of the 1x1 tunnels under stress. The mechanism associated with Li deintercalation is presented together with the activation energy barriers, which are calculated to be 0.4eV - irrespective of whether the mesoporous host is un-strained or under considerable (1.6 GPa) tensile or compressive stress.