Abstract
Symmetric batteries, in which the same active material is used for the positive and the negative electrode, simplifying the manufacture process and reducing the fabrication cost, have attracted extensive interest for large-scale stationary energy storage. In this paper, we propose a symmetric battery based on titanium hexacyanoferrate (TiHCF) with two well-separated redox peaks of Fe3+/Fe2+ and Ti4+/Ti3+ and tested it in aqueous Na-ion/ K-ion/Mg-ion electrolytes. The result shows that all the symmetric batteries exhibit a voltage plateau centered at around 0.6 V, with discharge capacity around 30 mAhg−1 at C/5. Compared to a Mg-ion electrolyte, the TiHCF symmetric batteries in Na-ion and K-ion electrolytes have better stability. The calculated diffusion coefficient of Na+, K+, and Mg2+ are in the same order of magnitude, which indicates that the three-dimensional ionic channels and interstices in the lattice of TiHCF are large enough for an efficient Na+, K+ and Mg2+ insertion and extraction.
Highlights
The widespread development and deployment of renewable energy sources (RES) has highlighted the necessity of energy conversion and storage devices to integrate the intermittent renewable energy from the solar and wind power, etc., into the energy grid [1]
We propose a symmetric battery based on titanium hexacyanoferrate (TiHCF) with two well-separated redox peaks of Fe3+/Fe2+ and Ti4+/Ti3+ and tested it in aqueous Na-ion/ K-ion/Mg-ion electrolytes
From the linear sweep voltammetry (LSV) curves, we found that the overall electrochemical stability window of all three electrolytes gave almost the same potential range, and compared with 1 M and 10 M NaNO3 electrolyte, 0.1 M NaNO3 electrolyte had even better performance, as shown in Figure S1b,c
Summary
The widespread development and deployment of renewable energy sources (RES) has highlighted the necessity of energy conversion and storage devices to integrate the intermittent renewable energy from the solar and wind power, etc., into the energy grid [1]. Symmetric batteries have recently gained attention for their energy storage capabilities, because they utilize the same active materials in both electrodes of a battery, the positive and the negative, which in turn leads to a simplified manufacturing process with a clearly reduced cost. The practical utilization of symmetric energy storage systems is hindered by the limited choice of available electrode materials, as well as the lower discharge potential, especially in aqueous electrolyte. Yang et al [24] reported a symmetric aqueous Na-ion battery based on PB material, and the as-obtained full batteries exhibit good cycling stability and rate capacity. They were able to deliver a capacity of 32 mAhg−1 at 20 C, and 97% of initial capacity was maintained after 200 cycles at 2 C. Compared to the most phosphate materials, metal hexacyanometalates can be synthesized, and no high temperature calcinations are required
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