Grid-scale batteries: They’re not just lithium

When size and weight don't matter, lots of other battery chemistries can work.

As power utilities and industrial companies seek to use more renewable energy, the market for grid-scale batteries is expanding rapidly. Alternatives to lithium-ion technology may provide environmental, labor, and safety benefits. And these new chemistries can work in markets like the electric grid and industrial applications that lithium doesn't address well.

“I think the market for longer-duration storage is just now emerging,” said Mark Higgins, chief commercial officer and president of North America at Redflow. “We have a lot of… very rapid scale-up in the types of projects that we’re working on and the size of projects that we’re working on. We’ve deployed about 270 projects around the world. Most of them have been small off-grid or remote-grid systems. What we’re seeing today is much more grid-connected types of projects.”

“Demand… seems to be increasing every day,” said Giovanni Damato, president of CMBlu Energy. Media projections of growth in this space are huge. “We're really excited about the opportunity to… just be able to play in that space and provide as much capacity as possible.”

New industrial markets are also becoming active. Chemical plants, steel plants, and metal processing plants have not been able to deploy renewable energy well so far due to batteries’ fire hazards, said Mukesh Chatter, co-founder and CEO of Alsym Energy. “When you already are generating a lot of heat in these plants and there’s a risk of fire to begin with, you don’t want to deploy any battery that’s flammable.”

Chatter said that the definition of long-duration energy storage is not agreed upon by industry organizations. Still, there are a number of potential contenders developing storage for this market. Here, we’ll look at Redflow, CMBlu Energy, and BASF Stationary Energy Storage.

Zinc-bromine batteries

Redflow has been manufacturing zinc-bromine flow batteries since 2010, Higgins said. These batteries do not require the critical minerals that lithium-ion batteries need, which are sometimes from parts of the world that have unsafe labor practices or geopolitical risks. The minerals for these zinc-bromine batteries are affordable and easy to obtain.

Flow batteries contain liquid or gaseous electrolytes that flow through cells from tanks, according to the International Flow Battery Forum website:

The interconversion of energy between electrical and stored chemical energy takes place in the electrochemical cell. This consists of two half cells separated by a porous or an ion-exchange membrane. The battery can be constructed of low-cost and readily available materials, such as thermoplastics and carbon-based materials. Many parts of the battery can be recycled. Electrolytes can be recovered and reused, leading to low cost of ownership.

Building these can be quite different from other batteries. “I would say that our manufacturing process is much more akin to… an automotive manufacturing process than to [an] electronics manufacturing process… like [a] lithium-ion battery,” Higgins said. “Essentially, it is assembling batteries that are made out of plastic tanks, pumps, fans, [and] tubing. It’s a flow battery, so it’s a liquid that flows through the system that goes through an electrical stack that has cells in it, which is where most of Redflow’s intellectual property resides. The rest of the battery is all… parts that we can obtain just about anywhere.”

The charging and discharging happen inside an electrical stack. In the stack, zinc is plated onto a carbon surface during the charging process. It is then dissolved into the liquid during the discharging process, Higgins said.

The zinc-bromine electrolyte is derived from an industrial chemical that has been used in the oil and gas sector for a long time, Higgins added.

This battery cannot catch fire, and all of its parts are recyclable, Higgins told Ars. “You don’t have any of the toxic materials that you do in a lithium-ion battery.” The electrolyte liquid can be reused in other batteries. If it’s contaminated, it can be used by the oil and gas industry. If the battery leaks, the contents can be neutralized quickly and are subsequently not hazardous.

“Right now, we manufacture our batteries in Thailand,” Higgins said. “The process and wages are all fair wages and we follow all relevant environmental and labor standards.” The largest sources of bromine come from the Dead Sea or within the United States. The zinc comes from Northern Europe, the United States, or Canada.

The batteries typically use an annual maintenance program to replace components that wear out or fail, something that’s not possible with many other battery types. Higgins estimated that two to four years down the road, this technology will be “completely competitive with lithium-ion” from a cost perspective. Some government grants have helped with the commercialization process.

Redox-flow batteries go Blu

A second company, CMBlu Energy, is now starting to take commercial orders for its Organic SolidFlow batteries, Damato, its president, told Ars. It has already deployed several smaller systems in Europe. And it recently announced that it is partnering with Argonne National Laboratory and Idaho National Laboratory to study how these batteries can be used in microgrids.

Organic SolidFlow batteries are redox-flow batteries with a twist, Damato said. They have stationary solids in their tanks, which increases their energy-storage capacity compared to conventional flow batteries. They use organic (carbon-based) polymers that hold and transfer charge, which can be sourced from anywhere. This means that they do not require any materials that come from conflict countries that have unsafe working conditions.

The batteries are designed in modular units that are around the same size as standing desks at their highest position, Damato said, with four battery stacks connected in series. The modules contain storage tanks and cell stacks. Each cell in the stack has a membrane that separates its two electrodes. The number of cells in a stack can be customized. A module weighs around two tons and supplies power for five to 10 hours.

Thermal runaway is a non-issue with this redox-flow battery because of its inherent chemistry and the fact that it uses an aqueous solution, Damato said.

For maintenance, CMBlu Energy recommends regular visual inspections, including checking the pumps and valves and looking for leaks—the maintenance requirements are relatively minimal. Some of the performance monitoring for leaks is automated, along with data collection on pressure and temperature. The electrolyte needs to be rejuvenated approximately every 10 years, depending on the environmental conditions of the installation.

Since the batteries are made of plastic, they can be recycled similarly to other plastics. Damato said this is cost-effective. The support structures and copper wiring are also recyclable, as are the solid and liquid electrolytes.

Sulfur-sodium batteries are hot

A third company, BASF SES, is selling a battery made by Japanese manufacturer NGK Insulators, the NAS Battery, that has sulfur as the positive electrode and sodium as the negative one. The electrolyte is a beta-alumina ceramic tube. While the battery discharges, the sulfur is reduced to polysulfide, and the sodium is oxidized; this process is reversed during charging. When the battery is in use, it runs at around 300° C, with both the sodium and the sulfur in their liquid state.

According to Justin Williams, senior account executive at Trevi Communications, “Beta-alumina solid electrolyte (BASE) is sodium polyaluminate. The material has a specific crystal structure [that] enables very fast ion transport. It is used as an ion conductor with high selectivity.”

There have been over 250 projects utilizing these batteries, according to Caroline Brannock, senior battery technology sales manager at BASF SES.

The batteries are packaged in 20-foot-long shipping containers that has six modules that collectively provide 1.45 megawatt-hours, Brannock said. The shipping containers are usually used in groups of four.

This technology does not make use of any of the critical minerals that are problematic in lithium-ion batteries. In addition to sodium and sulfur, NGK Insulators uses oxygen, steel, carbon, and silica-based materials, all of which are inexpensive and widely available. Brannock said the details of how these are combined during manufacturing is confidential.

The safety tests for the NAS Battery included short-circuiting the modules, putting the modules in fires, and submerging them, none of which caused leakage or fires in the modules. Lighting an individual cell on fire resulted in similarly safe results. A drop test showed that only the enclosure was damaged, and no fire or leaks occurred.

“When we're talking about climate resiliency, the battery can withstand a great deal,” Brannock said. She mentioned that it tolerates heat and cold as well as high-salinity environments. The container also gives it a layer of protection.

In Japan, NGK Insulators partners with companies that recycle end-of-life batteries. Installations outside Japan are only just reaching end-of-life, and the company is currently identifying local recycling partners.

Kat Friedrich is a former mechanical engineer who started out as an applied mathematics, engineering, and physics major at the University of Wisconsin-Madison. She has completed a graduate degree focusing on science and environmental journalism and has edited seven news publications, two of which she co-founded. She is the editor-in-chief of the energy magazine Solar Today.