Anodes that undergo alloying reactions with lithium are attractive substitutes for graphite in lithium ion batteries for their high capacities. However, these high-capacity alloy type anodes suffer from short lifetimes associated with severe volume changes upon lithiation. It is well-recognized that nanoporous architectures can help accommodate these large volume changes, but this mechanism is not well understood. To improve the lifetime of high-capacity nanoporous anode materials, a fundamental understanding of the structural changes upon cycling is necessary. We utilize nanoporous tin (NP-Sn), synthesized by the selective removal of magnesium from a magnesium-tin alloy, as a platform to study the deleterious effects of volume change in these alloying-type anodes (Fig. 1A).<br/>Transmission X-ray microscopy utilizing hard X-ray’s enables imaging of thick samples during battery operation with a large field of view. Imaging of this type is more representative of the actual electrode environment. The resolution of the final image at the Stanford Synchrotron Research Laboratory beam line 6-2 is ~30 nm, and is well matched to the morphology of the NP-Sn as previously shown in Fig.1A. <i>Operando</i> transmission X-ray microscopy was used to directly observe a significant volume change suppression in the NP-Sn compared to dense tin. (Fig. 1B). In figure 1C, the areal expansion in NP-Sn is limited to only 20% while in dense tin it is calculated to be 130% or six-fold larger. As a result of the supressed volume change in NP-Sn, the material can be cycled hundred’s of times with minimal degradation to the capacity. This improvement compared to dense tin strongly suggests that the volume expansion during lithiation is significantly accommodated by the porous structure.

Reducing the large volume change in alloy anodes through porous nanoscale architecture

251st National Meeting (2016)

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