Revisiting the energy efficiency and (potential) full-cell performance of lithium-ion batteries employing conversion/alloying-type negative electrodes

The energy efficiency of new lithium-ion chemistries is a very important, but frequently not provided performance measure for new alternative active materials for application as negative and positive lithium-ion battery (LIB) electrodes. This is particularly true for those active materials, not hosting lithium cations via insertion mechanisms, but via alloying and/or conversion reactions. Herein, the energy efficiency of alternative negative electrode active materials hosting lithium via combined conversion and alloying processes and the impact factors on the energy efficiency of such compounds in complete battery cells (full-cells) is revisited. Specifically, the effect of (i) varying the relative contribution of the conversion and alloying reaction, (ii) limiting the specific capacity, (iii) pre-cycling and pre-lithiating the anode, as well as (iv) the choice of the active material for the positive electrode, is investigated. The results show that a proper combination of these measures may enable lithium-ion cells based on conversion/alloying anodes that provide energy efficiencies of >95%, accompanied by gravimetric energy densities that might outperform graphite-based lithium-ion cells.