Stable cycling performance with high power density in lithium ion battery (LIBs) is required to meet the criteria for the power source such as electric vehicles. But generally, high power density is hindered by slow diffusion of lithium ions in micrometric electrode materials. [1] From this perspective, nanoparticle electrode materials can enhance the rate of lithium ions because of shortened diffusion pathway of lithium ion. Besides, high surface area of electrode induces facile access of charge via large contact area with electrolyte and conducting additives like carbon. In contrast, chemical degradation at electrode-electrolyte interface is also facilitated by large contact area with nanoparticle electrode. Unfavorable interfacial reactions such as dissolution of cathode species and decomposition of electrolyte mainly occur through energetically unstable surfaces of the active material. [2] In order to minimize side reactions that can negatively affect electrochemical performance, introducing electrochemically inactive ions on the surface of active materials can improve the interfacial stability. However, this substitution should take place as thin passivating layers on individual particles to preserve storage capacity. [3] A strategy toward the stabilization of electrode-electrolyte interfaces has been devised by introducing core-shell nanocrystals, consisting of electroactive lithium transition metal oxide cores and ultra-thin inactive epitaxial oxide shells on the surface. Spinel Li_1+xMn_2-xO₄ nanocrystals were used as a core component, with an Al-rich shell as passivation layers to minimize unfavorable reaction on the surface of cathode particles. The electrochemical performance shows that Spinel Li_1+xMn_2-xO₄ nanoparticle with conformal shell reveals improved capacity retention and rate capability even at elevated temperature, compared to a bare counterpart.

Reference

1. Isaac D. Scott, Yoon Seok Jung, Andrew S. Cavanagh, Yanfa Yan, Anne C. Dillon, Steven M. George, and Se-Hee Lee, Nano Letters, 414–418, 11 (2011).

2. Peter G. Bruce, Bruno Scrosati, and Jean-Marie Tarascon, Angew. Chem. Int. Ed, 2930-2946, 47 (2008).

3. Chunjoong Kim, Patrick J. Phillips, Linping Xu, Angang Dong, Raffaella Buonsanti, Robert F. Klie, and Jordi Cabana, Chem. Matter, 394-399, 27 (2014).