Page 52 - ESJ – ENERGY STORAGE JOURNAL

ALTERNATIVE BATTERY TECHNOLOGIES

With its dream of developing the next generation of batteries, Ambri invent-
ed the liquid metal battery. But the big question is whether it can make the
jump from kWh laboratory testing to MWh energy storage systems.

Liquid metal: the hottest

topic in energy storage

In 2005, the committee planning the uid metal battery chemistries, not just
new Massachusetts Institute of Tech- magnesium and antimony. Following
nology’s Energy Initiative was looking this success they were able to build a
to develop a new battery. 20Wh, 200Wh and a 1kWh cell.
At the time the institute was focused The process that inspired Sadoway
on lithium ion batteries, but Donald — aluminium smelting using the Hall-
Sadoway, the institution’s professor of Héroult process — has a reputation
materials chemistry, had another idea of consuming massive amounts of
after talking with his colleague pro- electrical energy, with some smelters
fessor Ceder, who was engaged with consuming GWhs of electricity every
MIT’s Energy Initiative. day. It is even, sometimes, disparag-
Sadoway had 40 years working with ingly referred to as ‘congealed electric-
extreme electrochemical processes, ity’.
ranging from aluminium smelting to In fact CSIRO, the Commonwealth
lithium polymer batteries. He had a Scientific and Industrial Research Or-
team of students and post-doctoral ganization, calculates the embodied
fellows, chief among them David energy (the overall energy required to
Bradwell, who played a pivotal role in make the material) for aluminium is
advancing the technology. They began 211GJ per tonne, compared to 22.7
to work on a liquid metal battery. GJ per tonne for steel.
Five years later, Bradwell and Sa- In 2016, after spending several years
doway, along with Luis Ortiz, co- Sadoway and Bradwell: wanted to developing other critical cell and sys-
founded Ambri with the goal of com- invent a technology that could meet tem components, such as a high tem-
mercializing the technology they had a price point, and not just invent a perature seal for each cell, Ambri built
invented. ‘nice new technology’. its first in-house prototype system that
Before spinning out Ambri, while at proved critical performance metrics of
MIT, Sadoway and Bradwell worked ously releasing electrical current from the technology, such as questions that
on this novel battery platform, with the magnesium atoms in the negative were previously faced by the alumini-
all three active components in liquid electrode, which causes them to lose um smelting process.
form as the battery operates. two electrons to make magnesium “A common question we get is
The two liquid metal electrodes are ions (Mg2+), which then dissolve into ‘doesn’t your battery require a lot of
separated by a molten salt electrolyte. the molten salt electrolyte. energy to stay hot’,” says Bradwell,
These liquid layers float on top of each These magnesium ions migrate now Ambri’s senior vice president of
other based on density differences and across the electrolyte and accept two commercialization and chief technol-
immiscibility. electrons at the surface of the antimo- ogy officer. “But it only needs energy
The original cell chemistry had the ny positive electrode, which then mix to take it up to the operating tem-
negative electrode (anode) floating as together to form an Mg-Sb alloy. perature of 500°C. For a 1MWh scale
the top liquid layer in the cell made During this process, electrons flow battery you will need about 3MWh to
of low density, low-cost, lightweight through a circuit connected to both heat it.
liquid magnesium. The positive elec- electrodes, providing electrical power. “Once at operating temperature the
trode (cathode), pooled as the bottom In order to keep the electrodes and current passing between the electrodes
liquid layer in the cell, was made of electrolyte in a liquid state, the cells generates enough heat to keep it at its
high-density liquid antimony. must operate above 500°C. To charge optimum operating temperature.
Sadoway and Bradwell came up the battery, the current is reversed and “The battery runs at 80%-85% ef-
with these two metals when searching this forces the magnesium to de-alloy ficiency and the rest of that energy
the periodic table for a pair of metals and return to the upper electrode, re- is released as heat by the cells. Our
that would meet the constraints of be- storing the initial constitution of the thermally insulated containers retain
ing earth abundant, low cost, suitably battery. that heat to keep the cells warm, so
low melting points, have sufficient as long as the battery is cycled once
density differences and a high mutual Powered from within every one to two days, the system
reactivity. Sadoway and his team initially built is self-heated, and requires no extra
The magnesium-antimony liquid a 1Wh cell. They operated hundreds energy input to stay hot,” says Brad-
metal battery discharges by spontane- of cells to test out a plurality of liq- well.

50 • Energy Storage Journal • Summer 2019 www.energystoragejournal.com