Pomegranate‐Like KVPO₄F@C Microspheres as High‐Volumetric‐Energy‐Density Cathode for Potassium‐Ion Batteries

Abstract

KVPO4F is one of the most competitive cathode candidates for potassium‐ion batteries (KIBs) because of its high output voltage and energy density. Although the gravimetric energy density of KIBs is intensively discussed in literature, little attention is paid to the volumetric energy density. In view of this, pomegranate‐like carbon‐coated KVPO4F microspheres with a high volumetric energy density are designed in this work. The nano‐sized primary particles with carbon sheets in KVPO4F microspheres enable promis rate capability by enhancing the K+ diffusion kinetics, while the micro‐sized spheres guarantee the improvement of cycling stability. Owing to the dense hierarchical microspheres, the volumetric energy density of cells is greatly improved compared to bulk materials. This cathode delivers a reversible capacity of 101.5 mA h g−1 at 0.3 C with an average output voltage of 4.0 V and a capacity retention of 85.1% after 200 cycles. The KVPO4F@C microspheres have a compact density of 2.45 g cm−3 and further offer a high volumetric energy density up to 891.3 Wh L−1. The overcharge behavior of KVPO4F in the first three cycles is also revealed. The presented KVPO4F@C microspheres cathode provides a new sight for developing KIBs with large volumetric energy density.

Low‐Temperature Preparation Copper‐Doped Nickel Chloride Cathode for Thermal Battery Overcomes the Energy‐Power Trade‐Off

“…2 and other cathode materials for secondary batteries. [45,[51][52][53][54][55][56][57][58][59][60][61][62][63] by adding CuCl 2 •2H 2 O. The fabricating temperature is reduced from 600 to 400 °C, which is caused by the spontaneous adsorption of NiCl 2 •2H 2 O toward dissociative copper ions during preparation process, weakening the bonding strength of Ni─O bond.…”

“…b) Voltage-specific capacity graph and c) rate-specific capacity graph of Ni 0.95 Cu 0.05 Cl. 2 and other cathode materials for secondary batteries [45,[51][52][53][54][55][56][57][58][59][60][61][62][63].…”

Ligand Engineering Enables Fast Kinetics of KVPO4F Cathode for Potassium-Ion Batteries

“…To address this issue, the strategy of carbon coating is commonly used. − Liao et al developed a simple one-step sintering method to synthesize carbon-coated KVPO 4 F nanoplates with enhanced K + migration and electronic conductivity . Xie et al improved the rate capability of KVPO 4 F by carbon coating combined with nanoscale structural design . However, few researchers have proposed effective solutions to the tough challenge from the fundamental perspective of the intrinsic electronic structure in the material. , Based on the molecular orbital theory (MOT) of complexes, each atomic orbital in a polyhedron constitutes a molecular orbital via symmetry adapted linear combinations. , For KVPO 4 F (KVPF) polyanionic material, the V 3+ 3d orbital interacts with the p orbital of six symmetry matched ligands in the form of π-bonds to constitute the molecular orbital of the V octahedrons .…”

Low-Dimensional Vanadium-Based High-Voltage Cathode Materials for Promising Rechargeable Alkali-Ion Batteries

“…Xie et al fabricated a kind of pomegranatestructured carbon-coated KVPF microspheres comprised of nanosized primary particles and carbon sheets, which simultaneously improve the K + diffusion kinetics and cycling stability. Also the dense hierarchical structure endows it with a higher compact density of 2.45 g cm −3 and a high volumetric energy density of up to 891 W h L −1 , along with an excellent capacity retention of 85% over 200 cycles, a high capacity of 102 mA h g −1 at 0.3C and significantly enhanced rate capabilities (Figure 21d,e) [129]. And the performances, including rate capabilities, ICE, and cycling performance, could be further enhanced by in situ carbon coating (e.g., the porous single-crystalline KVPO 4 F/C nanoplates) [130].…”