Pulsed laser deposition and chemical vapor deposition were used to deposit very thin silicon on multilayer graphene (MLG) on a nickel foam substrate for application as an anode material for lithium ion batteries. The as-grown material was directly fabricated into an anode without a binder, and tested in a half-cell configuration. Even under stressful voltage limits that accelerate degradation, the Si-MLG films displayed higher stability than Si-only electrodes. Post-cycling images of the anodes reveal the differences between the two material systems and emphasize the role of the graphene layers in improving adhesion and electrochemical stability of the Si.

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Imbalance between the voltage or state-of-charge of individual cells in batteries can seriously degrade their performance. A brief review of the range of mechanisms that can contribute to such imbalance in NiCd and NiH, batteries is provided, and a new process that can contribute to cell imbalance is presented. Detailed electrical, calorimetric, and modeling data are presented to demonstrate that the nickel electrode in these battery cells can exist in two distinct states, which are differentiated by significant variations in charge voltage, charge efficiency, and heat generation. The distinct states are attributed to surface area changes in the discharged nickel electrode active material arising from a combination of particle fracturing and ripening processes: Different combinations of these nickel electrode states can explain much of the history-dependent performance variability often observed for these battery types.