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What is Liquid Metal Battery?

The liquid-metal battery is composed of two liquid metal electrodes which are being separated by a molten salt electrolyte—being self-segregate into three layers based upon density and immiscibility. This battery is considered an innovative approach to solve problems regarding grid-scale electricity storage. Its capabilities enable an improved integration of renewable resources into the electric grid. Furthermore, the battery is expected to improve the overall reliability of an ageing power grid and it can offset the need to build additional generation, transmission, and distribution assets. 

With all these potentials, the majority of start-ups and companies are targeting utility-scale energy storage with innovative systems that can help in utilizing iron flow batteries, compressed air, saltwater batteries, and other electrochemical processes. These liquid-metal batteries are made for grid energy storage to balance out intermittent renewable power sources such as solar panels and wind turbines. Aside from that, it can also be used for electric vehicles.

The liquid metal battery is based on research conducted by co-founder Donald Sadoway at the Massachusetts Institute of Technology. Unlike the other storage options on the market, this battery system is quite different as it is the only battery where all three active components are in liquid form when the battery operates. Two liquid electrodes—magnesium and antimony, are being separated by a molten salt electrolyte, while the liquid layers float on top of each other based on density differences and immiscibility. 

The system is also being operated at an elevated temperature maintained by self-heating during its charging and discharging, which is the reason why it is in a low-cost and long-lasting storage system.

Ambri as one of the startups manufacturing the liquid metal battery is still continuing to improve the performance and longevity of its batteries—some of its test cells have been running and being offered for almost four years without showing any signs of degradation. The company is also experimenting with other elemental combinations, including lithium, calcium and lead. Because of the simple design and easy-to-source materials, the manufacturing process of the battery will cost far less than other storage technologies for an equivalent amount of storage. 

History of Liquid Metal Batteries

Professor Donald Sadoway at the Massachusetts Institute of Technology has conducted research about the liquid-metal rechargeable batteries. Magnesium–antimony and lead-antimony were both used in the experiments at MIT. Upon experiments, both the electrode and electrolyte layers were heated until they became liquid and self-segregate due to density and immiscibility. These batteries may have a longer lifespan as compared to conventional batteries, due to a cycle of creation and destruction where the electrodes undergo during the charge-discharge cycle. Thus, making them immune to degradation affecting conventional battery electrodes.

The technology was initially proposed in 2009 which is based on magnesium and antimony separated by molten salt. Magnesium was selected to be the negative electrode due to its low cost and low solubility in the molten-salt electrolyte. Whereas, Antimony was chosen to be the positive electrode for it is low cost and has a higher anticipated discharge voltage.

In 2011, the researchers managed to demonstrate the cell with a lithium anode and a lead-antimony cathode, which have higher ionic conductivity and lower melting points between 350 to 430 °C. The downside of Li chemistry is it has a higher cost. A-Li/LiF plus LiCl and LiI/Pb-Sb cell with about 0.9 V open-circuit potential operating at 450 °C had electroactive material that costs about US$100 per kilowatt-hour and US$100 per kilowatt with 25 years projected lifespan. Its discharge power at 1.1 A/cm2 is only 44 percent while 88 percent at 0.14 A/cm2.

The experimental data indicated that about 69 percent of storage efficiency, has a good storage capacity of over 1000 mAh/cm2, has low leakage of about < 1 mA/cm2 and a high maximal discharge capacity of over 200 mA/cm2. Furthermore, by October 2014, the MIT team managed to achieve operational efficiency of approximately 70 percent at high charge and discharge rates of 275 mA/cm2, which is similar to the pumped-storage of hydroelectricity systems and higher efficiencies at lower currents. Tests showed that the system would retain about 85 percent of its initial capacity after a 10-year regular use. 

Whereas, by September 2014, a study illustrated a disposition using a molten alloy of lead and antimony as the positive electrode, liquid lithium as the negative electrode; and a molten mixture of lithium salts as the electrolyte.

Prior to that, the Liquid Metal Battery Corporation (LMBC) was established to commercialize and market the liquid-metal battery technology in 2010. In 2012, LMBC was renamed as Ambri. The name “Ambri” is derived from “cAMBRIdge” Massachusetts, where the LMBC company is headquartered and where MIT is located at the same time. 

In 2012 and 2014, Ambri received $40 million funds from Bill Gates, GVB, Khosla Ventures and Total S.A. 

Moreover, Ambri made an announcement in September 2015 about the layoff and pushing back of commercial sales. But they also announced a return to the battery business along with a redesigned battery in the year 2016.

A recent innovation is the PbBi alloy which allows a very low melting point lithium-based battery. This battery uses a molten salt electrolyte based on LiCl-LiI and operates at 410 °C.

Voltage Inefficiencies of Liquid Metal Battery

Liquidity provides liquid metal batteries with superior transport properties and kinetics. The operating voltage of an electrochemical cell or Ecell differs from the equilibrium cell potential, Ecell, eq, depending on the current density, dependent losses or voltage inefficiencies.

Typical voltage inefficiencies include:

  1. Charge transfer losses – which result from the sluggish electrode kinetics.
  2. Ohmic losses – that happened to arise from the electrical resistivity of the cell electrolyte electrodes, and current collectors.
  3.  Mass transport – in which the losses are caused by slow diffusion of reactants to and products away from the electrode−electrolyte interface. 

Advantages and Disadvantages of Liquid Metal Batteries

Advantages of Liquid Metal Battery 

Liquid metal batteries can boast an ultrafast electrode charge which transfers kinetics because of the liquid to liquid electrode to electrolyte interfaces, high rate capability, as well as low ohmic losses that are being enabled by highly conductive molten salt electrolytes reaching up to 3 S cm−1. This is also followed by the active mass transport of reactants and products to and from the interface of the electrode−electrolyte by liquid-state diffusion. Entirely, these properties enable liquid metal batteries to operate with relatively high voltage efficiencies at high current densities.

Liquid metal batteries have a very low cost, too because most of the electrode materials being used are earth-abundant and cheaper than other materials. Moreover, the natural self-segregation of the active liquid components enables simpler and lower-cost cell fabrication as compared with other conventional batteries. 

Whereas, the most considered feature of these liquid metal batteries is the continuous creation and annihilation of the liquid metal electrodes during the charge−discharge cycles. This feature allows liquid metal batteries the potential for modern life cycle by rendering them to be immune to microstructural electrode degradation mechanisms that can limit the life cycle of a conventional battery. Aside from being modular in design that can be customized in order to meet some specific needs of customers,  the liquid material batteries can also respond to grid signals in milliseconds, store energy up to 12 hours and can discharge slowly over time. Plus, it is indeed easy to install without moving parts in the operation. 

All in all, the low cost of materials, simple and easy assemble, and the potential for the long lifetimes’ position of liquid metal batteries are all good features of liquid metal batteries to compete in the grid-storage market. 

Disadvantages of Liquid Metal Battery 

Despite all the advantages, liquid metal batteries also have some disadvantages, which make them inappropriate to use in portable applications and works. These include elevated operating temperatures which are generally less than 200 °C, it also has low theoretical specific energy density which is typically less than 200 Wh kg−1, and has comparatively low equilibrium cell voltages which are usually less than 1.0 volts. Aside from that, these batteries have highly corrosive active cell components and high self-discharge rates for some chemistries because of the metallic solubility of the electrode species in the molten salt electrolyte. Additionally, there are three liquid layers that make the operation of battery more sensitive to motion and potentially dangerous when the liquid electrodes are touch, thus leading to a short-circuited cell and fleeting heat generation.

Future Ahead: Liquid Metal Battery

Ambri together with NEC Energy Solutions (NEC) made an announcement regarding the signed joint development agreement (JDA) wherein NEC will develop and design an energy storage system based on the liquid metal battery technology of Ambri. NEC will also employ its proprietary AEROS energy storage operating system and controls in order to optimize the system performance of the Ambri-based energy storage systems for the NEC customers that could possibly include utilities, independent power producers (IPPs) and other project developers.

Reviews on the Liquid Metal Battery

Are Liquid-Metal Batteries The Future Of Energy? | Startups | NBC News

Bill Nye Explains Liquid Metal Batteries

Don Sadoway and the Future of the Liquid Metal Battery

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