Strain engineering has transformed applications in the semiconductor electronics industry, but has not been widely explored as a tool for electrochemical applications. Our early studies have demonstrated for the first time that mechanical strain applied across interfaces of engineered 2-D nanomaterials or externally applied to pseudocapacitive electrodes can result in deviations in the energetics and kinetics of Faradaic charge storage reactions [1-2]. Here, we present results that extend this idea to vanadium pentoxide (V₂O₅) due to its well-known capability to function as a cathode for the intercalation of lithium ions. To characterize the role of strain in modulating the lithium insertion properties, we use atomic layer deposition (ALD) to prepare ultrathin coatings of crystalline V₂O₅ on the surface of superelastic NiTi shape memory alloy surfaces. As a key challenge in characterizing the role of strain is the ability to assess electrochemical properties in a fixed strain state, we exploit the capability of NiTi to "lock-in" strain in the elastic regime, which extends up to ~ 15% strain. This enables us to directly measure the average strain transferred to the V₂O₅ material, and correlate this to the observed electrochemical properties. Through electrochemical tests, we observe over 50 mV shift in the electrochemical potential that is correlated to strain, and over 2X change in the diffusion coefficient of lithium ions. We further build a semi-quantitative model for strain modulated battery performance that is supported by density functional theory calculations. Overall, this work demonstrates new degrees of freedom to design or engineer electrodes for energy storage by using pre-strained or strain-engineered electrode materials.

References:

[1]. N. Muralidharan, R. Carter, L. Oakes, A.P. Cohn, and C.L. Pint*, "Strain engineering to modify the electrochemistry of energy storage electrodes," Sci. Rep. 6, 27542 (2016).

[2]. L. Oakes, R. Carter, T. Hanken, A.P. Cohn, K. Share, B. Schmidt, and C.L. Pint*, "Interface strain in vertically stacked two-dimensional heterostructured carbon-MoS₂ nanosheets controls electrochemical reactivity," Nat. Commun. 7, 11796 (2016).