Layered VOPO₄ as a Cathode Material for Rechargeable Zinc-Ion Battery: Effect of Polypyrrole Intercalation in the Host and Water Concentration in the Electrolyte

Abstract

Rechargeable zinc-ion batteries (RZIB) present an interesting alternative to rechargeable Li-ion batteries. Among the active materials, layered vanadium-based oxides show a poor cell voltage but modifying this structure by attaching a phosphate group to the vanadium redox center can drastically enhance the cathode voltage. With this layered VOPO4 material, we demonstrate that preintercalating polypyrrole between crystallographic layers and using electrolyte with controlled water amounts are two absolutely essential conditions for easy and reversible Zn2+ (de)­intercalation, thus vastly improving battery outputs and long-term capacity retention. We establish that the rational design of open-layered structures hinges imperatively on factors like host structural integrity and electrode–electrolyte compatibility in delivering the performance of multivalent-ion batteries.

VOPO4⋅2H2O Nanosheet Cathode for Enhanced Sodium Storage

“…Recently, two-dimensional (2D) layer electrodes have shown the promising electrochemical property due to their unique 2D ion transport corridor, short ion diffusion distance and adjustable interlayer space, which are beneficial to promote the Na-ion insertion/extraction reactions (Huang et al, 2014;Shi et al, 2019;Verma et al, 2019). Among them, 2D hydrated vanadium oxyphosphate (VOPO 4 •2H 2 O) has received considerable attention as the promising cathode materials for SIBs because of its high redox reaction potential (∼3.5 V), high theoretical specific capacity (166 mAh g −1 ), and various valences reactions (e.g., V 5+…”

An In Situ Cross‐Linked Nonaqueous Polymer Electrolyte for Zinc‐Metal Polymer Batteries and Hybrid Supercapacitors

“…[ 33,38 ] The high‐voltage operability of VOPO 4 in ZMBs is recently receiving attention owing to the presence of the phosphate group linked to the vanadium‐ion center, which is reported to expand the cation intercalation voltage (due to inductive effect) compared to oxides. [ 40–42 ] Here, the synthesis of VOPO 4 is performed using a simple reflux method. The scheme adopted for the synthesis of VOPO 4 is presented in Figure S2 (Supporting Information).…”

“…2H 2 O phase. [ 40,43 ] Field emission scanning electron microscope (FESEM) images of the as‐synthesized VOPO 4 . 2H 2 O samples are shown in Figure 1d,e).…”

“…The peaks at 519.1 (V2p 3/2 ) and 526.5 eV (V2p 1/2 ) correspond to the V 5+ oxidation state, and if one closely observes, a small quantity of V 4+ can also be observed (peak at 517.2 eV). [ 40,44 ] Similarly, the peak at 134.2 eV is associated with the P2p energy level indicating a pentavalent tetra‐bonded P. [ 44 ] The peak originating from the oxygen O2p energy level at 531.9 eV is also visible. [ 45 ]…”

“…The cell displayed a high specific capacity of 78 mAh g −1 (at 0.05 Ag −1 ), which is comparable with several other nonaqueous liquid electrolyte‐based ZMBs (summarized in Table S2, Supporting Information). [ 19,28,29,40,50–52 ] At the same current density of 0.05 Ag −1 , the cell delivers an E av of 1.2 V with a specific energy density of 96 Wh kg −1 (calculation of E av is provided in Figure S13 (Supporting Information) followed by relevant explanations). The specific energy density values at other current densities are also presented in Figure 4b.…”