A New Strategy to Mitigate the Initial Capacity Loss of Lithium Ion Batteries

Electrode materials and electrolyte choices largely dictate the design parameters and the type of lithium-ion battery (LIB) that can be optimized and eventually utilized. Certainly all three components (anode, electrolyte, and cathode) must work in harmony to produce the highest possible energy density achievable for an LIB-based energy storage device. Balancing the electrochemical performance characteristics of the cathode and anode active materials is critical for maximizing the power/energy density of a LIB. Hard carbon (non-graphitizable) anode materials, like tin, tin oxide, silicon and silicon oxide, have a high theoretical capacity (>550 mAh/g depending on their structural and chemical properties) but unfortunately they also exhibit a large initial capacity loss (ICL), which overrides the true reversible capacity in a full cell. Overcoming the large ICL of hard carbon in a full-cell lithium-ion battery (LIB) necessitates a new strategy wherein a sacrificial lithium source additive such as Li5FeO4 (LFO) is used on the cathode side. Full batteries using hard carbon coupled with LFO/LiCoO2 (LCO) are currently under development at our laboratory. We find that the reversible capacity of a cathode containing LFO can be increased by 24%. Furthermore, the cycle performance of full cells with LFO additive is improved from <90% to >95%. We believe that the LFO can not only address the irreversible capacity loss of the anode, but can also provide the additional lithium ion source required to mitigate the lithium loss caused by side reactions. In addition, we have explored the possiblity to achieve higher capacity on hard carbon, whereby the energy density of full cells can be increased from ca. 300 Wh/kg to >400 Wh/kg .