Magnesium–Antimony Liquid Metal Battery for Stationary Energy Storage

Abstract

Batteries are an attractive option for gridscale energy storage applications because of their small footprint and flexible siting. A high-temperature (700°C) magnesium−antimony (Mg||Sb) liquid metal battery comprising a negative electrode of Mg, a molten salt electrolyte (MgCl 2 −KCl−NaCl), and a positive electrode of Sb is proposed and characterized. Because of the immiscibility of the contiguous salt and metal phases, they stratify by density into three distinct layers. Cells were cycled at rates ranging from 50 to 200 mA/cm 2 and demonstrated up to 69% DC−DC energy efficiency. The self-segregating nature of the battery components and the use of low-cost materials results in a promising technology for stationary energy storage applications.L arge-scale energy storage is poised to play a critical role in enhancing the stability, security, and reliability of tomorrow's electrical power grid, including the support of intermittent renewable resources. 1 Batteries are appealing because of their small footprint and flexible siting; however, conventional battery technologies are unable to meet the demanding low-cost and long-lifespan requirements of this application.A high-temperature (700°C) magnesium−antimony (Mg||Sb) liquid metal battery comprising a negative electrode of Mg, a molten salt electrolyte (MgCl 2 −KCl−NaCl), and a positive electrode of Sb is proposed (Figure 1). Because of density differences and immiscibility, the salt and metal phases stratify into three distinct layers. During discharge, at the negative electrode Mg is oxidized to Mg 2+ (Mg → Mg 2+ + 2e − ), which dissolves into the electrolyte while the electrons are released into the external circuit. Simultaneously, at the positive electrode Mg 2+ ions in the electrolyte are reduced to Mg (Mg 2+ + 2e − → Mg Sb ), which is deposited into the Sb electrode to form a liquid metal alloy (Mg−Sb) with attendant electron consumption from the external circuit (Figure 2 where R is the gas constant, T is temperature in Kelvins, F is the Faraday constant, a Mg(in Sb) is the activity of Mg dissolved in Sb, and a Mg is the activity of pure Mg.Recent work on self-healing Li−Ga electrodes for lithium ion batteries has demonstrated the appeal of liquid components. 2 While solid electrodes are susceptible to mechanical failure by mechanisms such as electrode particle cracking, 3 these are inoperative in liquid electrodes, potentially endowing cells with unprecedented lifespans. The self-segregating nature of liquid electrodes and electrolytes could also facilitate inexpensive manufacturing of a battery so constructed. However, there do not appear to be economical materials options that exist as liquids at or near room temperature.Previous work with elevated-temperature liquid batteries demonstrated impressive current density capabilities (>1000 mA/cm 2 when discharged at 0 V) with a variety of chemistries. 4−7 However, that work generally used prohibitively expensive metalloids (such as Bi and Te) as the positive electrode. The resulting cells exhibited...

Electrolytes for electrochemical energy storage

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