Developing Li-Metal Alloy Batteries with High Cyclability and Rate Capability

Abstract

The development of high-energy density and high-power density lithium ion batteries (LIBs) for portable electronics, electric vehicles, and other large-scale energy storage devices over the last decade has led to continual search on new electrode candidates. The cost-effective, chemically stable (safe), and highly conductive metal as anode electrode that is capable of high capacity due to the large Li stoichiometric ratio, has recently stimulated enormous attention. There have been many efforts to increase the capacity using group IV elements Sn, Ge, Pb, Si and Mg, Al, Ga, Zn, and Bi thus far. Sn, another group IV element, is a promising alternative anode material, as its bulk phase is known to have a higher theoretical capacity of 990 mAh/g (Li4.4Sn) compared to 370 mAh/g of commercial graphite. Sn is also less toxic and less expensive, but huge volume changes up to 300% during Li insertion and extraction limit the energy capacity and cycle lifetime in LIBs. In addition to the volume factor, another obstacle lies in the naturally formed oxide layer, which introduces a non-reversible capacity, although some researchers have found that an ultrathin coating on electrodes could enhance the performance of lithium-ion batteries. To maximize the electrochemical performance of Sn, a well-desired configuration that can efficiently prevent the chemo-mechanical failure must be developed. Here we present a novel sub-100nm Sn nano-cage (Sn-NC) comprising an industrially available, pure metal Sn and a conductive oxide surface (not SnOx). The protection of the rigid oxide surface and the adjustable interspace can prevent the pulverization and oxidation of the metal while supplying a fast Li+/e- pathway. The coin/punch cell assembled using Sn-NCs as anode provides a high capacity (>600 mAh/g) with a long cyclability (>500 cycles) at a high charge/discharge rate. The synthesis of Sn-NCs is scalable thus indicating a potential on industrial commercialization.