Tailoring a fluorophosphate as a novel 4 V cathode for lithium-ion batteries.

Lithium-ion batteries, which have been widely used to power portable electronic devices, are on the verge of being applied to new automobile applications. To expand this emerging market, however, an electrode that combines fast charging capability, long-term cycle stability, and high energy density is needed. Herein, we report a novel layered lithium vanadium fluorophosphate, Li(1.1)Na(0.4)VPO(4.8)F(0.7), as a promising positive electrode contender. This new material has two-dimensional lithium pathways and is capable of reversibly releasing and reinserting ~1.1 Li(+) ions at an ideal 4 V (versus Li(+)/Li) to give a capacity of ~156 mAh g(-1) (energy density of 624 Wh kg(-1)). Moreover, outstanding capacity retentions of 98% and 96% after 100 cycles were achieved at 60°C and room temperature, respectively. Unexpectedly high rate capability was delivered for both charge and discharge despite the large particle size (a few microns), which promises further enhancement of power density with proper nano-engineering.