POWER January 2021 - 38

ENERGY STORAGE
Zinc-ion Batteries Are a Scalable
Alternative to Lithium-ion
Lithium-ion batteries are the most popular battery storage option today, controlling
more than 90% of the global grid battery storage market, according to some
estimates. However, the lithium-ion supply chain is becoming constrained. Zinc-ion
batteries may offer a safer, and ultimately cheaper, energy storage option.
Ryan Brown
L
are the key enabling
ithium-ion batteries have emerged
as an important technology in the
fight against climate change. They
technology for
continued improvements in electric vehicles
(EVs), and for renewable energy
storage installations.
However, lithium-ion raw materials
are not produced in sufficient quantities
to meet the imminent demand
from both of those markets, and a quick
comparison between projections for
adoption of these technologies and investments
made by miners show that
lithium-ion's supply chain will soon be
very constrained. This shortage will
become even more severe as governments
around the world pass legislation
that accelerates the transition to EVs
and renewables.
New battery technologies are sorely
needed to address this shortage. The
need for light batteries means that lithium
is unlikely to be replaced for EVs;
lithium's position on the periodic table
all but guarantees that it will remain the
king of energy density.
Renewable energy storage, on the
other hand, really only requires a low
lifetime cost. Here lithium's advantage
is primarily due to its position as the
incumbent. In fact, lithium-ion's safety
risks make it a poor fit for a market that
seeks to place massive battery packs in
people's homes and businesses. Nonlithium
batteries are far more likely to
succeed in energy storage for renewables.
The question then becomes,
what technologies can beat lithium-ion
for energy storage, while being able to
scale at the rate demanded by climate
change?
Many companies have tried to build
new energy storage batteries over the
past decades. None have really succeeded.
Even for technologies that
made it out of the lab, the rapidly decreasing
manufacturing costs for
38
lithium-ion eroded their competitive position
before they could scale up.
It has become increasingly clear that
any alternative to lithium-ion batteries
needs to adopt standard manufacturing
processes to allow for a rapid and
low-cost scale-up. So far, the zinc-ion
battery (Figure 1) is the only non-lithium
technology that can adopt lithium-ion's
manufacturing process to make an attractive
solution for renewable energy
storage, particularly for its compatibility
along with other advantages.
How Lithium-ion Batteries Are Made
To appreciate lithium-ion batteries, one
has to start with the science. Lithiumion
batteries are what is referred to as
an intercalation battery. This means that
the same ion (lithium) reacts at both the
anode and the cathode, traveling between
the two through a liquid electrolyte.
When the battery is discharged, the
graphite anode releases a lithium ion into
the electrolyte at the same time that the
cathode absorbs one. During charge, the
process is reversed.
Importantly, the electrolyte does not
need to store large amounts of ions,
it only needs to serve as a conduit between
the electrodes. Most other battery
chemistries do not use intercalation,
depending instead on each electrode
reacting with the electrolyte. This means
they typically require a large quantity of
electrolyte to store reactants. By needing
a minimal amount of electrolyte, lithium-ion
batteries can be very compact.
Another key feature of lithium-ion
batteries is their ability to store a large
amount of energy in a small amount of
material. This means that lithium-ion
electrodes can be built with relatively
thin coatings of active material (that is,
the materials at each electrode that react),
with total electrode thickness of
less than 0.1 millimeters. This is in contrast
to lead-acid batteries, whose electrodes
are multiple millimeters thick. The
www.powermag.com
1. Salient Energy's zinc-ion battery cell has
various components, as shown here. The zincion
battery, like a lithium-ion battery, functions
using intercalation. Zinc ions react at both
electrodes and travel between them through
a water-based electrolyte. During discharge,
zinc metal at the anode is dissolved into the
electrolyte as zinc ions. At the same time, zinc
ions are absorbed into the cathode from the
electrolyte. This process is reversed during
charge. Courtesy: Salient Energy
use of thin coatings allows for higher energy
efficiency and better performance
in high-power applications.
The combination of these two traits, low
electrolyte volume and thin electrodes,
drives the lithium-ion manufacturing process.
Electrodes are made by applying thin
coatings to thin metal substrates. These
thin coatings allow for fairly rapid application
and in-line drying in a continuous, rollto-roll
production process.
A separator, which can be quite thin
since it does not need to store excess
electrolyte, is placed between the electrodes
before they are (typically) wound
together and placed in a container. Electrolyte
is injected into the cell before it is
sealed and sent off for initial cycling. This
carefully controlled cycling, called formation
cycling, causes reactions to happen
within the cell that protect its longevity.
Conditions for Lithium-ion
Manufacturing Compatibility
This understanding of lithium-ion manufacturing
reveals the requirements for
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