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A method is described in which crystalline silicon can be used as a practical anode material for lithium-ion batteries. Commercial lithium-ion cells are typically charged at a constant current to a fixed voltage and then are held by the charger at constant voltage until the current decreases to a certain value ͑also known as constant current/constant voltage or CCCV charging͒. It is first shown that CCCV charging can be used to reversibly cycle crystalline silicon and limit its capacity. A cycling method is then demonstrated in which crystalline silicon is first partially converted to amorphous silicon, in situ, during conditioning cycles. After the conditioning cycles the silicon can be cycled normally, using CCCV cycling limits, with good coulombic efficiency and little overlithiation during the first cycle.

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A set of guidelines is proposed for designing high-energy-density alloy anode materials. It is first shown that the molar volume of lithium is about 9 mL/mol in a wide variety of lithium alloys and is independent of lithium content. Using this property of lithium alloys, simple relationships between the volumetric energy density and the volumetric expansion of an alloy are derived. These relationships are extremely powerful for designing alloys with the maximum possible energy density for a given electrode-coating performance.