A Low-Strain Phosphate Cathode for High-Rate and Ultralong Cycle-Life Potassium-Ion Batteries.

Most potassium-ion battery (PIB) cathode materials have deficient structural stability because of the huge radius of potassium ion, leading to inferior cycling performance. We report the controllable synthesis of a novel low-strain phosphate material K3 (VO)(HV2 O3 )(PO4 )2 (HPO4 ) (denoted KVP) nanorulers as an efficient cathode for PIBs. The as-synthesized KVP nanoruler cathode exhibits an initial reversible capacity of 80.6 mAh g-1 under 20 mA g-1 , with a large average working potential of 4.11 V. It also manifests an excellent rate property of 54.4 mAh g-1 under 5 A g-1 , with a high capacity preservation of 92.1 % over 2500 cycles. The outstanding potassium storage capability of KVP nanoruler cathode originates from a low-strain K+ uptake/removal mechanism, inherent semiconductor characteristic, and small K+ migration energy barrier. The high energy density and prolonged cyclic stability of KVP nanorulers//polyaniline-intercalated layered titanate full battery verifies the superiority of KVP nanoruler cathode in PIBs.