Recently, new energy storage chemistries based on nonaqueous electrolytes and multivalent metals (e.g., Mg, Zn, Ca and Al) have drawn the attention of the researchers as a promising advanced energy storage technology due to their higher theoretical volumetric capacity, limited dendrite formation and low cost.¹ A major developmental need for these systems is the identification of electrolytes compatible with both electrodes while showing reversible deposition/dissolution on an anode and multivalent intercalation into a cathode.^1,2 In the case of nonaqueous Mg or Ca ion-based systems, electrolyte compatibility issues (e.g., low Coulombic efficiency, a high overpotential and corrosion) have held back the development of Mg or Ca metal batteries.³ However, the nonaqueous Zn²⁺ ion chemistry utilized in a Zn metal cells with a reversible intercalation cathode is an exception with a number of promising features including highly-efficient reversible Zn deposition/dissolution on a Zn metal anode with a wide electrochemical window,³ similar ionic radius compared with Li⁺ and Mg²⁺ ions,⁴ relatively lower activation barrier energy for diffusion in cathode materials (e.g., FePO₄, CoO₂ and V₂O₅)⁵ and high volumetric capacity.¹ Considering these advantages, a nonaqueous Zn system provides an opportunity to delve into the mechanisms in multivalent-ion cell chemistry and solve the present issues in multivalent cell design and prototyping.³

In this study, the intercalation chemistry on a variety of cathodes materials (e.g., V₂O₅, Mn₂O₄ and FePO₄) have been investigated in various nonaqueous Zn electrolytes. The electrochemical and transport properties of the electrolytes (e.g., reversible Zn deposition, anodic/cathodic stability, ionic conductivity and diffusion coefficient) were characterized utilizing the experimental and computational analysis.³ Among various Zn metal cells, a Zn/nanostructured bilayered V₂O₅ cell with a selected acetonitrile(AN)-Zn(TFSI)₂ electrolyte demonstrates good reversibility and stability for 120+ cycles with nearly 100% Coulombic efficiency and ~170 mAhg^-1 of gravimetric capacity, albeit operating at a cell voltage of 0.7 V vs. Zn/Zn²⁺.⁶ A Zn/nanostructured layered δ-MnO₂ cell with an AN-Zn(TFSI)₂ electrolyte also shows good reversibility (~100% Coulombic efficiency) and stability for 50+ cycles with ~100 mAhg^-1 capacity with an operating voltage of 1.2 V vs. Zn/Zn²⁺.⁷ By utilizing a combination of analytical tools, we address numerous factors affecting capacity fade, and issues associated with the second phase formation including Mn dissolution in Zn/δ-MnO₂ cells that have been extensively cycled.⁷

References

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2. H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour and D. Aurbach, Energy Environ. Sci. 2013, 6, 2265-2279.

3. S.-D. Han, N. N. Rajput, X. Qu, B. Pan, M. He, M. S. Ferrandon, C. Liao, K. A. Persson and A. K. Burrell, ACS Appl. Mater. Inter. 2016, 8, 3021-3031.

4. R. D. Shannon, Acta Cryst. 1976, A32, 751-767.

5. Z. Rong, R. Malik, P. Canepa, G. Gautam, M. Liu, A. Jain, K. Persson and G. Ceder, Chem. Mater. 2015, 27, 6016-6021.

6. P. Senguttuvan, S.-D. Han, S. Kim, A. L. Lipson, S. Tepavcevic, T. T. Fister, I. D. Bloom, A. K. Burrell and C. S. Johnson, Adv. Energy Mater. 2016, 6, 1600826.

7. S.-D. Han, S. Kim, D. Li, V. Petkov, H. D. Yoo, P. J. Phillips, H. Wang, J. J. Kim, K. L. More, B. Key, R. F. Klie, J. Cabana, V. Stamenkovic, T. T. Fister, N. M. Markovic, A. K. Burrell, S. Tepavcevic, J. T. Vaughey, 2017, in revision.