Since the introduction of intercalation cathodes in the 1970s the energy stored has not significantly increased above 600 Wh per kg of active material [1]. Although conversion reactions can lead to higher initial capacities, there is still no convincing experimental evidence that batteries based on such reactions have energy efficiencies close to approaching the 90% of intercalation systems for hundreds of cycles. Thus there is a need to improve the energy stored in cells in intercalation based reactions above the around 20% of the theoretical value. Two possible approaches will be described: attaining 2 e per redox center by intercalating 2 Li (as opposed to 1 Mg), and attaining closer to 1 Li cycling in the layered oxides. The latter is a challenge because the thermal instability of the oxides is directly proportional to the charging voltage, i.e. to the oxidation level of the oxygen in the lattice. One of the challenges in inserting 2 Li is the stability of the lattice over hundreds of insertions and removals; the reactions of Li with VOPO₄ will be used as an example. It should be possible to attain energy densities in full cells of 350 Wh/kg and 1 kWh/liter.  This work is supported by DOE BES EFRC NECCES under award #  DE-SC0012583.

[1] Chem. Rev. 114, 11414, 2014