(Invited) Advances in Cathode Materials for High Energy Density Lithium-Ion Batteries

Advances in high energy density of lithium-ion technology hinges upon the development of next generation high capacity cathode materials. Current state-of-the-art cathodes like NMC have capacity in the range of 180 mAh/g within a voltage window of 2.5-4.2 V. This is a factor of two less than the capacity of the most commonly used anode material, carbon (372 mAh/g). Current high voltage cathode chemistries such as lithium-manganese rich NMC (LMR-NMC) cathodes though promise capacities > 270 mAh/g when cycled to 4.7 V but has a number of stability issues including phase transition and TM dissolution.  Mn-Ni high voltage spinel although structurally stable and more robust has relatively lower capacity 147 mAh/g.  More than anything these high voltage cathodes need to be cycled at voltages > 4.6 volts that is clearly above the electrochemical stability window for the most commonly used electrolytes (LiPF₆ in carbonates). 

The talk will review the research progress made in the area of high voltage cathodes for lithium-ion namely, lithium-magnanese rich NMC and high voltage spinel, and the remaining challenges there-in. Topics include other alternative high capacity, 4 V cathodes chemistries that utilize multiple redox states of the host transition metals and thereby intercalate two or more lithium ions per formula unit of the TM.  To this effect, we report our recent work on solid-solution compositions of nickel-stabilized two lithium copper oxides having generic formula, Li₂Cu_xNi_1-xO₂, where x = 0.4-0.6. Optimized composition of this family of cathodes show reversible capacities in excess of 200 mAh/g with good capacity retention but further work is needed to stablize the structure.