No abstract

Phosphate cathode materials with a stable and open framework structure are expected to be one of the favorable cathode materials for aqueous zinc-ion batteries (AZIBs). However, the slow migration rate of Zn2+ and complex mechanism in aqueous electrolyte are serious problems that limit their application at the present. Here, a new rocking-chair-type cathode material Zn3V4(PO4)6@C (ZVP@C) for AZIBs is synthesized for the first time and evaluated using a composite carbon coating to improve the electronic conductivity. Benefiting from the two-electron reaction of vanadium and the cointercalation of Zn2+/H+, ZVP@C/30%BP delivers a specific capacity as high as 120 mAh·g–1 at 0.04 A·g–1. A good capacity retention of 80% after 400 cycles at 1 A·g–1 is also obtained, which is attributed to the stable crystal structure and the cointercalation reaction of Zn2+/H+. The reaction mechanism is investigated by in situ X-ray diffraction (XRD), ex situ XRD, ex situ X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS). This work not only provides a new phosphate cathode material for AZIBs but also gives a new strategy for improving the specific capacity of phosphate cathode material.

A cathode material, Na 2 [(VO) 2 (HPO 4 ) 2 (C 2 O 4 )]•2H 2 O, for aqueous zinc-ion batteries is synthesized by a hydrothermal method. Na 2 [(VO) 2 (HPO 4 ) 2 (C 2 O 4 )]•2H 2 O presents a two-dimensional layered structure and sheetlike morphology, which provide fast and reversible Zn 2+ insertion/extraction. Na 2 [(VO) 2 (HPO 4 ) 2 (C 2 O 4 )]•2H 2 O delivers a high average voltage plateau (∼1.3 V), a moderate specific capacity (90 mA h g −1 ), and good cycle stability (100% after 100 cycles). The Zn 2+ storage mechanism is investigated by in situ XRD and ex situ XPS.