Electrochemical and Transport Properties of Non-Aqueous Zn Electrolytes and Reversible Intercalation Chemistry for Zn/V2O5 and Zn/MnO2 Batteries
Authors: Han Sang-Don , Senguttuvan Premkumar , Tepavcevic Sanja , Rajput Nav Nidhi , Qu Xiaohui , Persson Kristin A , Johnson Christopher , Burrell Anthony K. 
Published: February 2020

A non-aqueous multivalent metal cell, one of the potential candidates for a post-lithium-ion battery, provides an attractive opportunity in energy storage research due to higher theoretical volumetric capacity of a metal anode coupled with the limited dendrite formation at the metal anode.1 The development of compatible electrolytes and reversible multivalent intercalation cathodes, however, is a significant challenge:1 in the case of Ca metal cells there is recently developed electrolytes possibly compatible with reversible chemistry at a Ca metal anode, which need much more improvement.2 In Mg metal cells various halide, BH4 and their derivatives electrolytes are known to be compatible with Mg metal anode, but correlation between speciation and functionality is still under debate.3-7 The compatibility of glyme-Mg(TFSI)2 electrolyte with Mg metal is also controversial and generally low Coulombic efficiency and high overpotential are observed in cell cycling.6,7 However, it appears that non-aqueous Zn2+ ion chemistry in Zn metal cells with a reversible intercalation cathode provides an exception among multivalent metals with a number of promising features: high volumetric capacity,1 similar ionic radius compared with Li+ and Mg2+ ions,8 relatively lower activation barrier energy for diffusion in cathode materials (e.g., FePO4, CoO2 and V2O5)9 and highly-efficient reversible Zn deposition behavior on a Zn metal anode with wide electrochemical window.7 In addition, the non-aqueous Zn system provides an opportunity to delve into the mechanisms in multivalent cell chemistry (e.g., reversible deposition on a metal anode and (de)intercalation into(from) a cathode material) and furthermore possibly solve the present issues in multivalent cell design and prototyping.7

In this study, the electrochemical and transport properties (e.g., reversible Zn deposition behavior, Coulombic efficiency, anodic stability, ionic conductivity and diffusion coefficient) of a variety of non-aqueous Zn electrolytes have been examined in detail.7 Classical molecular dynamics and DFT calculations have been utilized to complement the experimental work and to provide insights into the molecular-level solvation structure and dynamics of the bulk electrolytes and a prediction of the electrochemical stability window.7 Based upon the experimental analysis and the simulation studies of the range of different electrolytes, we have selected promising electrolytes and instituted electrochemically testing with a cell consisting of a Zn metal anode and a variety of cathodes materials. Among them, the Zn metal cell consisting of an acetonitrile-Zn(TFSI)2 electrolyte and a synthesized nanostructured bilayered-hydrated V2O5
10 demonstrates good reversibility and stability for 120 cycles with nearly 100% coulombic efficiency and ~180 mAhg-1 of gravimetric capacity, albeit operating at a relatively low cell voltage of 0.9 V. On the other hand, λ-MnO2 (spinel) host material represents no intercalation behavior even in all selected electrolytes, while nanostructured and low crystalline α-, γ-, and δ-MnO2(tunnel or layer) show possible intercalation behavior.

Acknowledgments

This work was supported as part of the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. The submitted abstract has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract no. DE-AC02-06CH11357.

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