KTiOPO 4 (KTP) microblocks, which were prepared using a simple solid state method, have been used as novel anode materials for sodium ion batteries (SIBs). The as-prepared KTP microblocks with size distribution of 300–500 nm delivered high performance of electrochemical storage of sodium, such as an initial charge capacity of 108.7 mAh g −1 at 200 mA g −1 with almost no capacity loss in 1000 cycles, and good rate capability of 80.3 mAh g −1 even at the current density of 1000 mA g −1 . Ex situ XPS and in situ XRD showed an irreversible phase reaction mechanism during the insertion/extraction of Na + . Dendrite formation at lower potential could be suppressed at the average potential of 1.3 V. This work indicated that KTP microblocks are low-cost and safe anode materials for SIBs.
The development of high-energy-density and high-power cathode materials represents a critical requirement for advancing practical sodium-ion battery (SIB) technologies. In this work, a high-entropy-doped KTiOPO 4 (KTP)-type NaV 0.95 (Fe, Mn, Ni, Al, Ca) 0.05 PO 4 F (HE-NVPF) cathode material is presented, designed to enhance reaction kinetics, operation voltage, and energy density through single-crystal phase formation and improved electronic/ionic conductivity. The high-entropy doping strategy enables the elimination of inductive nucleation agents while promoting single-crystal growth of HE-NVPF during low-temperature hydrothermal synthesis. The KTP-type crystal structure facilitates complete Na ion utilization and enables a solid-solution Na storage mechanism in HE-NVPF cathodes, accompanied by minimal lattice volume changes (4%). When tested in half cells in combination with Na metal anode, the HE-NVPF cathodes exhibit a remarkably high energy density of 532 Wh kg −1 with an average operating voltage of 4.0 V, an exceptional long cycle life of 3 000 cycles, and high capacity retentions at 30 C (2 min per charge). Its practical feasibility is demonstrated in graphite//HE-NVPF full cells, which present power densities of above 10 000 W kg −1 and energy densities of over 342 Wh kg −1 for 1000 cycles. This work offers new insights into designing high-entropy doped cathode materials for long-life and fast-charging SIBs.
Searching for low-cost, high-capacity, high-power, high-stability, high-tap-density, and inherently safe materials for developing cheap, safe, and high-performance batteries has always been a research hotspot. Herein, an inherently safe, low-cost, and low-strain KTiOPO 4 (KTOP) submicron single crystals with a uniform thin layer carbon coating are developed using a ball-mill assisted solid-state method. Uniform solid electrolyte interphase, carbon coating, and inherently stable structure synergistically help compact KTOP submicron single crystals achieve an exceptional anodic K-ion storage performance. The carbon-coated KTOP single crystals obtained under the carbonization temperature of 400°C (KTOP-C-400) can deliver an exceptional potassium ion storage performance of 253.3, 224.0, 175.5, and 131.1 mA h g −1 at the current density of 100, 200, 500, and 1000 mA g −1 , respectively, in the electrolyte of 5 M potassium bis(fluorosulfonyl)imide (KFSI) in DIGLYME electrolytes. Even after being cycled at 1000 mA g −1 for 1000 cycles, the capacity was maintained at 182.5 mA h g −1 with a coulombic efficiency of 99.9%.
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