Metal-ion batteries based on aqueous electrolyte are attracting widespread attention in the field of large-scale energy storage due to the low cost, high safety and environmental friendliness. However, the development of the most studied aqueous Li⁺ and Na⁺ batteries are plagued by the low energy density, which mainly derived from the low capacity of electrode materials (<150 mAh g^-1) and the limited voltage window of aqueous electrolyte (<1.8 V). The latter could be conquered by the water-in-salt electrolyte, and the operating voltage > 3V could be obtained¹. But the capacity of electrode materials still needs to be enhanced.

Due to the high capacity of metal zinc anode (820 mAh g^-1), aqueous Zinc-ion battery based on Zn²⁺ storage cathode and metal Zn anode holds immense potential to achieve high capacity. But the capacity of cathode still has much room for improvement. As the most used cathode materials for zinc-ion battery, manganese oxides exhibit high theoretical capacity (308 mAh g^-1), low cost and low toxicity. Various manganese dioxides, including the α-MnO₂, β-MnO₂, γ-MnO₂, δ-MnO₂, etc. have been reported as host materials for Zn²⁺/H⁺ insertion in the mild aqueous electrolyte. However, all the crystalline form of manganese oxides undergo structure transformation to layered structure with interlaminar water molecules during zinc-ion insertion, leading to capacity fading of the cell. And the cycling stability of manganese oxides decreases dramatically when cycled at high depth of discharge².

In this work, we proposed novel polyaniline-intercalated MnO₂ nanolayers as a high performance cathode material for zinc-ion battery, which is prepared by a simple one-step inorganic/organic interface reaction³. With the typical nano-size (approximately 10 nm), expanded interlayer space, uniform meso-structure and polymer-reinforced layered structure, the polyaniline-intercalated MnO₂ nanolayers show a high rate performance and excellent cycle stability at high charge/discharge depth (200 stable cycles with capacity of 280 mAh g^-1, corresponding 90.9% utilization of theoretical capacity of 308 mAh g^-1), which is much superior to previous reports. The polyaniline-reinforced layered structure efficiently eliminate the hydrated H⁺/Zn²⁺-insertion-induced phase transformation and the subsequent structure collapse, which is important to achieve long cycle life and high utilization simultaneously. In addition, a H⁺/Zn²⁺ co-insertion process in the layered MnO₂ was proposed, and a self-regulating mechanism of electrolyte involving generation/dissolution of flake-like zinc hydroxide sulfate was clarified.

Reference:

1 C. Yang, J. Chen, T. Qing, X. Fan, W. Sun, A. von Cresce, M.S. Ding, O. Borodin, J. Vatamanu, M.A. Schroeder, N. Eidson, C. Wang, and K. Xu, Joule, 1, 122 (2017).

2 J. Huang, Z. Guo, Y. Ma, D. Bin, Y. Wang, and Y. Xia, Small methods, 1800272 (2018).

3 J. Huang, Z. Wang, M. Hou, X. Dong, Y. Liu, Y. Wang, and Y. Xia, Nature Communications, 9, 2906 (2018).