Computational discovery of cathode materials for rechargeable aqueous zinc-ion batteries

TL;DR

The paper addresses the limited availability of high-performance cathodes for rechargeable aqueous zinc-ion batteries (RAZIBs) by implementing a high-throughput computational screening of >$2000$ synthesized materials to evaluate Zn$^{2+}$ percolation paths, aqueous stability via Pourbaix diagrams, and transition-metal redox feasibility. The study computes intercalation energetics $H_{Zn}$ and $E_{Zn}$, using MD and DFT-derived metrics, and identifies 131 viable candidates, with 56 showing feasible Zn intercalation potentials within the aqueous window; 10 novel materials are proposed for experimental testing, including $ ext{FePO}_4$ polymorphs that achieve $E_{Zn} > 1.3$ V vs Zn/Zn$^{2+}$. A key finding is the strong correlation between higher average metal oxidation state and favorable Zn$^{2+}$ coordination environments with higher $E_{Zn}$, guiding future material design. The authors provide an open, generalizable framework and data to accelerate RAZIB cathode discovery, supporting grid-scale energy storage deployment.

Abstract

Rechargeable aqueous zinc-ion batteries (RAZIBs) attract considerable scientific and commercial interest for deployment in grid-scale energy storage due to higher safety and lower manufacturing cost when compared to lithium-ion batteries. However, currently studied cathode materials suffer from severe capacity fade when cycling at rates appropriate for grid-scale applications ($<$ C/2), which hampers the commercialization of RAZIBs. To address the present limitation on cathode material availability, more than 2000 previously synthesized oxides, chalcogenides, Prussian blue analogues, and polyanion materials were computationally screened for the discovery of highly stable RAZIB cathode materials. The structural, electrochemical, and chemical properties of the materials were respectively evaluated through an investigation of the available Zn$^{2+}$ percolation paths in the crystal structure, the stability of the material in aqueous media under RAZIB operation conditions, and the attained transition metal oxidation state during cycling. The transition metal oxidation state and intercalating ion coordination environment were determined to govern the magnitude of the calculated intercalation potential, with this finding directly supporting the development of batteries with high operation potentials. Finally, 10 previously unexplored materials were identified with leading metrics for operation as RAZIB cathode materials, such as high Zn$^{2+}$ (de)intercalation potential, electrochemical stability, theoretical gravimetric capacity, and energy density, being here proposed for experimental testing. The materials identified in this study demonstrate a guide for advancing the available cathode materials for RAZIB, and help expedite the establishment of RAZIB as a commercially viable technology for grid-scale energy storage.

Figures (5)

• Figure 1: (a) Result for the void search in the $\alpha$-FePO4 structure, with the regions in the crystal which are at least 1.90 $\text{\AA}$ from an atom being presented. (b) Percolation path associated with the percdistmax for $\alpha$-FePO4, calculated to be equal to 1.87 $\text{\AA}$ with an associated percdisp of 0.99 $\text{\AA}$. (c) Calculated Pourbaix diagram for the Fe-P-H2O system, alongside a heatmap highlighting the calculated dGpbx for $\alpha$-FePO4. The region of interest for RAZIB operation is delimited by the orange dashed lines.
• Figure 2: (a) percdistmax as a function of the avgdGpbx for all materials considered. (b) percdistmax for a percdisp of less than 0.7 $\text{\AA}$ (percdistmax(percdisp $<$ 0.7 $\text{\AA}$)) and avgdGpbx results for materials considered for EZn calculation.
• Figure 3: Parameters utilized for the screening of novel RAZIB cathode materials, with number of remaining candidate materials after each screening parameter also presented.
• Figure 4: Calculated EZn results for all materials plotted (a) in the order of increasing potential and (b) with respect to the material avgdGpbx. Materials that have been previously experimentally investigated are highlighted in the graphs with an outer black line on their markers. The dashed lines represent the HER and OER reversible potentials calculated at a pH = 5 and [Zn^2+] = 1 M.
• Figure 5: (a) Complete EZn profile predicted for $\alpha$-FePO4. The dashed black lines represent the HER and OER potential calculated at a pH = 5 and [Zn^2+] = 1 M. (b) DOS and PDOS results for $\alpha$-FePO4 with the associated pCOHP analysis results for the Fe-O bond in the structure. Energy is shifted so the Ef is at 0 eV.