Due to its low toxicity, abundant resources, stable chemical properties and high theoretical capacity, zinc metal has broad prospects in aqueous energy storage applications. However, a series of side reactions such as water splitting and zinc corrosion caused by the thermodynamic reaction between the zinc metal anode and the aqueous electrolyte and zinc dendrite growth problems hindered its further development. The construction of an artificial protective layer on the surface of the zinc anode can effectively inhibit the side reactions and regulate the Zn2+ deposition behavior, and improve the utilization rate of the zinc metal anode. Therefore, it is still challenging to construct a multifunctional thin protective layer with strong adhesion, good water resistance and high ion diffusivity for the development of artificial SEI layers.
Based on this, the research team of Wu Peiyi/Jiao Yucong of Donghua University proposed to construct an artificial protective layer (LPL) with zinc-hydrophobic bifunctional properties by using lysozyme conformational transformation in situ by simple immersion method to improve the stability of the zinc anode and achieve high zinc utilization rate of the zinc anode. The Zn/Zn battery assembled based on LPL can run stably for more than 1200 h under 77.7% DOD, and even when the DOD reaches 93.2%, it can still run stably for more than 120 h, the Zn/AC capacitor can run stably for more than 80,000 times, and the assembled Zn/Zn0.25V2O5 full cell still has high capacity and stability under low N/P ratio (2.1) and high zinc utilization rate (48%), and its pouch battery capacity can be as high as 100 mA h and stable operation for more than 150 times, proving the application potential of LPL in zinc-based energy storage systems. His results were published in the internationally renowned journal Advanced Materials under the title "Constructing Lysozyme Protective Layer via Conformational Transition for Aqueous Zn Batteries". The first author of this paper is Pan Yifan, a 2022 doctoral student of Donghua University, the corresponding authors are Prof. Jiao Yucong and Professor Wu Peiyi, and the corresponding unit is the School of Chemistry and Chemical Engineering, Donghua University.
Conformational transition process and structural stability of lysozyme
Lysozyme can form a stable 2D film on the zinc surface due to the hydrophobic induced aggregation effect, and during the conformational transition, the disulfide bond is broken, and the lysozyme conformation changes from α-helix to β-sheet, exposing a large number of hydrophilic and hydrophobic functional groups.
Fig.1 Schematic diagram of lysozyme conformational transition, regulation of EDL on zinc anode surface, and characterization of LPL conformational transition and adhesion properties, the authors proved that the lysozyme conformational transition was successfully transformed by CD and FTIR, and proved that the β-sheet structure was still stable after immersion in 2 M ZnSO4 for 72 h. The XPS results showed that the lysozyme after conformational transition exposed abundant functional groups, which was conducive to enhancing the interaction between LPL, zinc anode and Zn2+. The 180° peel test showed that the peel strength of LPL was significantly higher than that of bare zinc, and even after immersion in 2 M ZnSO4 for 72 h, it still had a higher peel strength, which further verified the strong adhesion performance of LPL. The electrostatic interaction between the positively charged lysozyme and the negatively charged zinc anode can significantly enhance the adhesion of LPL on the zinc anode, which is conducive to improving the long-term cycling stability. Zinc plating/stripping performance evaluation is based on LPL-assembled Zn/Zn symmetrical cells with an operating life of more than 1200 h at 1 mA cm-2 and 10 mA h cm-2 (zinc sheet thickness: 22 μm, DOD: 77.7%). The operating life is also more than 120 h at a high DOD of 93.2%. The Zn/Zn symmetrical battery can run stably for more than 2800, 1500 and 650 h under the conditions of intermittent, shelving for 30 days, or even electrode immersion for 7 days, and the Coulomb efficiency test further proves that the Zn/Zn2+ cycle reversibility is good, showing high practical application potential.
Fig.2 Zn/Zn2+ reversibility characterization of EDL structure regulation mechanismElectrical bilayer (EDL) structure is a key factor affecting ion diffusion and zinc deposition behavior, which can directly affect the cycling performance of zinc-ion batteries. Therefore, the authors further studied the regulatory mechanism of LPL on EDL structure. The results of the electrical bilayer capacitance test and calculation show that LPL makes the zinc surface have a thinner EDL layer, which can be attributed to the interaction between LPL and zinc ions, which weakens the interaction between SO42- and Zn2+, which is conducive to faster charge transfer kinetics and lower Zn2+ desolvation energy barrier. At the same time, due to the less H2O and SO42- in the EDL structure, the side reactions are better inhibited, and the zinc surface with LPL also obtains a more stable electrode/electrolyte interface, which further proves that LPL has good static anti-corrosion ability by quantifying the corrosion rate.
Fig.3 EDL structure regulation, characterization of zinc deposition and side reaction inhibition behavior, the authors observed the inhibition behavior of LPL on side reactions during electroplating by in-situ light microscopy. In-situ Raman testing can be further used to visualize the change in zinc ion concentration at the electrode/electrolyte interface during zinc deposition. At the same time, 3D CLMS characterized the surface structure of zinc after electroplating, which further demonstrated that LPL can effectively inhibit side reactions. Theoretical calculations show that the functional groups on the surface of LPL have strong binding energy to zinc ions, which is conducive to improving the solvation environment of zinc ions and inducing uniform deposition of zinc ions.
Fig.4 Zinc deposition behavior and side reaction inhibition characterization of whole cell performance evaluation, the authors further compared the performance of Zn/Zn0.25V2O5, Zn/MnO2 whole cell and Zn/AC supercapacitors based on LPL assembly. Thanks to the good side reaction and dendrite inhibition ability of LPL during cycling, the assembled Zn/Zn0.25V2O5 cell can also run stably for more than 300 times under the conditions of low N/P ratio (2.1) and high zinc utilization rate (48%), and the cycling performance exceeds that of most reported work. The Zn/AC capacitors assembled based on LPL have a cycle life of more than 80,000 cycles. The authors further tested the performance of LPL pouch batteries, which have a high capacity of 100 mA h and can run stably for more than 150 times, proving their practical application potential.
Fig.5 Summary of performance characterization of whole cells and capacitors: In this work, an artificial protective layer with zinc-philic-hydrophobic bifunctional characteristics was constructed in situ by simple immersion method to achieve high zinc utilization rate of zinc anode. Lysozyme can form a stable 2D film on the zinc surface due to the hydrophobic induced aggregation effect, and during the conformational transition, the disulfide bond is broken, and the lysozyme conformation changes from α-helix to β-sheet, exposing a large number of hydrophilic and hydrophobic functional groups. Among them, the hydrophilic group can adjust the solvation structure of Zn2+, modify the EDL structure, and improve the deposition behavior of Zn2+. The hydrophobic functional group can prevent the water from coming into direct contact with the zinc surface to form a dense water-blocking barrier layer, which can effectively inhibit side reactions and dendrite growth. The zinc-zinc symmetrical battery assembled based on lysozyme protective layer can run stably for more than 1200 h at a high discharge depth of 77.7%, and even when the DOD reaches 93.2%, it can still run stably for more than 120 h, the assembled Zn/Zn0.25V2O5 whole battery can run stably for more than 300 times under low N/P ratio (2.1) and high zinc utilization rate (48%), and the corresponding pouch battery can also be stably cycled for 150 times at 100 mA h. This work proposes a new way to construct an artificial protective layer in situ to achieve the high performance of zinc-based energy storage devices. Original link: https://doi.org/10.1002/adma.202314144 Source: Frontiers of Polymer Science