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The ability to store energy on the electric grid would greatly improve its efficiency and reliability while enabling the integration of intermittent renewable energy technologies (such as wind and solar) into baseload supply. Batteries have long been considered strong candidate solutions owing to their small spatial footprint, mechanical simplicity and flexibility in siting. However, the barrier to widespread adoption of batteries is their high cost. Here we describe a lithium-antimony-lead liquid metal battery that potentially meets the performance specifications for stationary energy storage applications. This Li||Sb-Pb battery comprises a liquid lithium negative electrode, a molten salt electrolyte, and a liquid antimony-lead alloy positive electrode, which self-segregate by density into three distinct layers owing to the immiscibility of the contiguous salt and metal phases. The all-liquid construction confers the advantages of higher current density, longer cycle life and simpler manufacturing of large-scale storage systems (because no membranes or separators are involved) relative to those of conventional batteries. At charge-discharge current densities of 275 milliamperes per square centimetre, the cells cycled at 450 degrees Celsius with 98 per cent Coulombic efficiency and 73 per cent round-trip energy efficiency. To provide evidence of their high power capability, the cells were discharged and charged at current densities as high as 1,000 milliamperes per square centimetre. Measured capacity loss after operation for 1,800 hours (more than 450 charge-discharge cycles at 100 per cent depth of discharge) projects retention of over 85 per cent of initial capacity after ten years of daily cycling. Our results demonstrate that alloying a high-melting-point, high-voltage metal (antimony) with a low-melting-point, low-cost metal (lead) advantageously decreases the operating temperature while maintaining a high cell voltage. Apart from the fact that this finding puts us on a desirable cost trajectory, this approach may well be more broadly applicable to other battery chemistries.

h i g h l i g h t s g r a p h i c a l a b s t r a c t Electrochemical behavior of the LieBi system was investigated for liquid metal cells. Lithium insertion kinetics in liquid bismuth were studied in a threeelectrode cell. LijLiCleLiBrjBi cells showed long life, high efficiency, and low fade rate. System scalability demonstrated in prototypes with 10 and 100 times original capacity. Robustness shown by cooling to solidify cell, followed by heating and recycling. a b s t r a c tIn an assessment of the performance of a LijLiCleLiFjBi liquid metal battery, increasing the current density from 200 to 1250 mA cm À2 results in a less than 30% loss in specific discharge capacity at 550 C. The charge and discharge voltage profiles exhibit two distinct regions: one corresponding to a LieBi liquid alloy and one corresponding to the two-phase mixture of LieBi liquid alloy and the intermetallic solid compound, Li 3 Bi. Full cell prototypes of 0.1 Ah nameplate capacity have been assembled and cycled at 3 C rate for over a 1000 cycles with only 0.004% capacity fade per cycle. This is tantamount to retention of over 85% of original capacity after 10 years of daily cycling. With minimal changes in design, cells of 44.8 Ah and 134 Ah capacity have been fabricated and cycled at C/3 rate. After a hundred cycles and over a month of testing, no capacity fade is observed. The coulombic efficiency of 99% and energy efficiency of 70% validate the ease of scalability of this battery chemistry. Post mortem cross sections of the cells in various states of charge demonstrate the total reversibility of the Li 3 Bi solid phase formed at high degrees of lithiation.

No abstract

The liquid metal battery (LMB) is attractive due to its simple construction, its circumvention of solid-state failure mechanisms and resultantly long lifetimes, and its particularly low levelized cost of energy. Here, we provide a study of a unique binary electrolyte, NaOH-NaI, in order to pursue a low-cost and low-temperature sodium-based liquid metal battery (LMB) for grid-scale electricity storage. Thermodynamic studies have confirmed a low eutectic melting temperature (220 • C) as well as provided data to complete the phase diagram of this system. X-ray diffraction has further supported the existence of a recently discovered compound, Na 7 (OH) 5 I 2 , as well as offered initial evidence toward a NaI-rich compound displaying Pm-3m symmetry. These phase equilibrium data have then been used to optimize parameters from a two-sublattice thermodynamic solution model to provide a starting point for study of higher order systems. Further, a detailed electrochemical study has identified the voltage window and related oxidation/reduction reactions and found greatly improved stability of the pure sodium electrode against the electrolyte. Finally, an Na|NaOH-NaI|Pb-Bi proof-of-concept cell was assembled. This cell achieved over 100 cycles and displayed leakage currents below 0.40 mA/cm 2 . These results highlight an exciting class of low-melting molten salt electrolytes that may enable low cost grid-scale storage. The pressing need for highly scalable and economically viable battery systems for grid-storage has prompted many researchers to pursue entirely new electrochemical approaches. One such technology that has recently grown from the university lab bench to the commercial production floor is the liquid metal battery (LMB) 1,2 -a system that takes advantage of a three liquid-layer design to store and deliver large quantities of energy at particularly low levelized costs.The LMB is designed with an electropositive liquid metal anode, A, separated from an electronegative liquid metal cathode, B, by a molten salt electrolyte. Upon discharge, the anode, A, oxidizes, transports across the A-itinerant electrolyte, and reduces at the cathode interface to form an A-B alloy. The reaction is driven by the partial free energy difference of A in the high activity negative electrode environment versus that of the alloyed metal A (in B) in the positive electrode.Because all three active battery components are liquid phase, the system is able to operate at high current densities with minimal overpotential losses. In addition, because the cell is restored to its virgin liquid state upon each recharge, the device is immune to solid-state failure mechanisms common in lithium-ion batteries 3 and, as a result, is expected to provide exceptionally long amortizable service lifetimes.In spite of the benefits of the LMB system, the high temperatures required to achieve a fully molten state present challenges when scaling the battery to production. Higher temperatures drive costs due to issues associated with device sealing, expensive wiri...