Aluminum salt electrolyte additives with anion insertion/extraction for high-voltage zinc and nickel metal batteries at ultra-low temperatures

Abstract

Compared with divalent metal cations, trivalent Al³⁺ has a higher hydrolysis constant and exhibits stronger proton dissociation ability, which provides new opportunities for low-temperature energy storage devices. Unfortunately, the high charge density and strong Coulomb interaction of Al³⁺ limit this application. To address the challenge, this work innovatively used aluminum salt as an electrolyte additive and achieved efficient operation of zinc and nickel metal batteries at ultra-low temperatures by synergistically utilizing the advantages of anions and cations. XPS and in-situ Raman spectroscopy reveal that anions (Cl⁻ and ClO₄⁻) can achieve effective insertion/extraction in the cathode, significantly improving the redox kinetics of the metal battery. Meanwhile, Al³⁺, which offers a low binding energy of -9.12 eV with water molecules, achieves excellent deposition/stripping reversibility on the metallic Zn and Ni surface. This synergistic effect of anions and cations not only improves the open circuit voltage of the battery, but also significantly reduces the ion diffusion resistance at low temperatures. Consequently, Zn//Zn and Ni//Ni symmetric cells can operate for more than 400 h at -30°C, and the polarization voltage remains highly stable. Impressively, zinc and nickel metal batteries with 2 m AlCl₃ as the electrolyte additive are able to maintain voltages of 1.28 V and 0.55 V, respectively, after 550 h of standing at -30°C. The zinc metal battery still has a discharge specific capacity of 118.5 mAh g⁻¹ and a Coulombic efficiency of 96.9 % after 2400 cycles at -50°C. Even under temperature fluctuations from -15 to 5°C, the battery can still maintain a discharge specific capacity of 168.8 mAh g⁻¹. This electrolyte design strategy based on aluminum salt additives is expected to promote the application of energy storage devices in extreme environments.