This technology can be applied to lithium-ion batteries to increase energy capacity.
Current phosphate-based lithium-ion batteries typically store one lithium ion per transition metal in the cathode, which intrinsically limits the cathode's maximum energy density. Multi-electron cathodes, where more than one lithium ion can be cycled per transition metal, would drastically increase battery capacity. Many transition metals have multiple stable oxidation states and could, in theory,
be used as multi-electron cathodes. However, activating the additional redox reactions in the metal typically require voltages that are not suitable for
commercial batteries. This technology uses two different metals to create stable multi-electron cathodes that operate within voltage ranges that are practical for commercial applications.
Lithium ion batteries operate by reversibly inserting and removing lithium ions from the cathode
material. In theory, many cathode structures can accommodate metal
cations with reduction states of +2, +3, and +4 so each metal can
participate in multiple redox reactions, creating multi-electron
cathodes. However, there is no transition metal where both the +2/+3
and the +3/+4 redox couple are active within the appropriate voltage
range for commercial batteries so, currently, only one redox couple can
be used in the battery operation. This technology mixes molybdenum or
vanadium with another transition metal using the overall formula LiaMxM'yX,
where M is one or more transition metals, M' is molybdenum and/or
vanadium, and X is a chemical group that contains phosphate. Mixing a
transition metal M that has a high +2/+3 redox voltage with molybdenum or
vanadium combines the redox couples of the different metals and allows more than one lithium ion to be stored per metal, which
increases the cathode capacity over using any of the metals alone.
- Higher capacity lithium-ion batteries
- Compatible with current commercially used electrolytes