Lithium ion batteries with significantly higher energy and power density desired for new personal electronic devices, electric vehicles, and large-scale energy storage, require new materials. This review focuses on the replacement of the graphite anode with silicon or germanium. Si and Ge both have significantly higher Li storage capacities than graphite, but also undergo significant volumetric expansion and contraction during lithiation and delithiation. Si and Ge nanomaterials can tolerate these mechanical stresses, but solvent decomposition and loss of electrical contact with the current collector tend to lead to failure. Si and Ge anodes must therefore be formulated with appropriate binder, conductive carbon, and stabilizing additives in the electrolyte solvent to achieve stable cycling and high capacity, as described herein.
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