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137-Year-Old Battery Technology Could be Key to Future Energy Storage

As amazing as lithium-ion batteries are, they have limitations and issues, but there are lots of battery alternatives. The chemistry of flow batteries alone is complex enough to make your head spin. One promising candidate is zinc-bromine batteries... When you realize they've been there for 137 years, calling them up and coming sounds strange... but they could be the future of energy storage. And why now, for such an old idea?

There is little doubt that building efficient energy storage devices will make or break our progress in the utilization of intermittent renewable energy. When it isn't sunny enough to use solar or windy enough to turn turbines, batteries full of previously generated renewable energy can keep systems running. When it's bright and sunny or the wind is blowing, it can store excess energy for when it's needed the most. In the chemical battery field, lithium-ion batteries are the reigning champions, but a 137-year-old concept could knock them out. This is because the usage of lithium-ion batteries is somewhat paradoxical in the drive for sustainable energy. They're fantastic for electric vehicles, but recycling lithium-ion batteries has historically proven tricky and dangerous, though several firms are working on it. The mining process is also extremely harmful to the environment, needing around 500,000 gallons of water for each metric ton produced.

Despite this, lithium-ion batteries continue to dominate the market due to their low cost and great energy density. Nonetheless, the cost of lithium is rising. Between early 2021 and February 2022, the cost of battery-grade carbonate lithium surged by more than 700% in China, one of the world's top producers of lithium2.

Given the prevalence of li-ion, that doesn't bode well. Rising lithium prices complicate the task of manufacturing even more energy-dense versions, such as lithium metal and solid-state electrolyte batteries, the latter of which has yet to hit the market. There is an obvious need to reduce our dependency on lithium. Alternative types of batteries are gaining attention as the need for EVs and renewable energy storage grows. It seems like there's a new one every week, but in this instance... it's an old one.

Gelion and Redflow, two Australian businesses, have stepped up to the mark with zinc-bromine batteries that promise safer, more reliable, and more robust designs. In July, Redflow began production of the third generation of their zinc-bromine flow battery, the ZBM3, at its Thai manufacturer. In September, the company announced an official partnership with Empower Energies to introduce their 10 kWh battery to North America. The same month, Gelion began producing Endure, their non-flow zinc-bromide battery, in Sydney at an existing lead-acid battery factory.

So, what distinguishes zinc-bromine from other battery chemistries?

Before we get into the worth of zinc-bromine batteries in comparison to their competitors, let's go through how they work. Zinc-bromine batteries are a type of redox-flow battery, or RFB. RFBs, like all batteries, have a cathode, an anode, and a separator.

Flow batteries differ from others in that they use tanks full of liquid electrolyte on either side of the battery, one for catholyte and one for anolyte, rather than the solid components found in contemporary batteries. Each side includes a chemical in a different oxidation state. A cell stack is housed in a compartment between the two tanks and is separated by an ion-selective membrane.

When you drain a flow battery, the chemical energy contained inside it is transformed into electrical energy via reduction-oxidation (AKA "redox"). Ions in the anolyte oxidize, or lose electrons. These electrons then pass through the battery's circuit and past the membrane. On the other hand, ions in the catholyte absorb these electrons, lowering their oxidation state. As the battery charges, the procedure is reversed.

Because the traditional RFB construction of tanks and pumps translates into a lot of bulk, they're best suited for stationary applications. Consider storage for an EV charging station, not an EV battery. Because of the versatility of their design, they are extremely helpful at the home or grid scale. If you want more power, simply add more stacks; if you want more storage capacity, simply add more electrolytes and storage tanks.

Gelion goes a step farther because their battery, the Endure, isn't an RFB. Instead, it employs the same plate format and housing design as a lead-acid battery. 8 The distinction is that it replaces lead and sulphuric acid with a bromide-positive plate and a zinc-negative plate, with a layer of gel acting as an electrode in the center. The "gel" in "Gelion" refers to gel-based electrolytes rather than liquid-based electrolytes.

This implies that, unlike RFBs, the Endure does not utilize pumps or tanks, allowing for a considerably more compact design. The plate design not only reduces space but also eliminates the need for specialist maintenance, an auxiliary power source, and a secondary backup system.

However, the chemical process inside remains constant. When the battery charges, zinc ions migrate to the negative electrode, accept electrons, and reduce to zinc. Bromide ions migrate to the positive electrode, lose electrons, and oxidize to bromine. When you discharge, the opposite happens.

The depth of discharge of flow batteries (including the Endure) is a significant advantage. It is possible to discharge flow batteries, including those manufactured by Redflow, all the way to zero without hurting them. 129 In contrast, certain lithium-ion batteries have an intrinsic capacity limitation since they degrade when depleted to less than 20%.

In terms of safety, RFBs offer a significant advantage over lithium-ion batteries. To avoid catastrophic failures, lithium-ion batteries must be carefully managed. When mishandled, damaged, or overheated, they are prone to thermal runaway, which can result in fires. They're also renowned for exploding. Fires caused by lithium-ion batteries are extremely dangerous since they are difficult to extinguish and can re-ignite.

To put this in context, a Tesla lithium-ion battery pack caught fire last year while being tested at the Victoria Big Battery in Australia. It burnt for three days. Another Tesla Megapack energy storage installation, this time in California, caught fire last September. Similar to the fire in Australia, neighboring people were advised to close their windows to protect themselves from the harmful smoke.

While these occurrences are uncommon and lithium-ion batteries are normally quite safe, when they occur, there are major safety issues. Flow batteries address this issue by employing non-flammable materials and water-based electrolytes rather than organic ones. This significantly minimizes the likelihood of a fire.

Vanadium RFBs are now the most popular, although there are many other chemistries to choose from, including all-iron, uranium, and even copper. However, zinc-bromine is by far the oldest of the group. A zinc-bromine battery was first patented in 1885 by a New Yorker named C.S. Bradley.

So, why are they significant now?

For one thing, the astounding simplicity. Another advantage is that bromine is a natural fire retardant, which is appealing given the volatility of some lithium chemistries. Gelion claims that its bromine gel may "significantly lessen or even extinguish a fire."

Other flow batteries can also give a minimal fire danger, with vanadium having an advantage due to its specific properties. Vanadium can live in numerous oxidation states, and according to a study published last month by the US Department of Energy, VRFBs have a nearly infinite cycle life. In fact, we recently reviewed a new vanadium redox flow battery chemistry in a video.

Despite its utility, vanadium has a number of drawbacks.

Cost is a major consideration. The metal itself, which is largely utilized to reinforce and toughen steel alloys, is notorious for its price instability. In comparison, the components of zinc-bromine batteries are substantially less expensive. Because ocean water contains the majority of the earth's bromine, we're actually swimming in it.

It's clear to see how much of a difference that makes. According to a 2017 study, the chemical cost of storing a vanadium RFB is approximately $124.4/kWh. This is roughly 15 and a half times the cost of a zinc-bromine system at $8/kWh.

A 2021 study looked into the materials costs of vanadium, zinc-bromine, and all-iron batteries. Zinc-bromine batteries were the least expensive of the three, at $153/kWh, significantly less than vanadium's $491/kWh.

Researchers also evaluated the effects of each type of battery on human and environmental health, showing another risk with VRFBs: toxicity. Because vanadium oxides are highly poisonous, VRFB production poses a greater risk to human health than zinc-bromine production. Vanadium can also be dissolved in sulfuric acid, which is caustic and dangerous to both humans and the environment.

To be clear, all of these difficulties can and are addressed by competent engineering and design.

These findings do not suggest that zinc-bromine is completely risk-free. Because of its carcinogenic nature, bromine remains a concern to human health in electrolyte form. Nonetheless, Sandia National Laboratories claims that the chemical reactivity and evaporation rate of bromine in electrolyte is far lower than pure bromine - and the chemical smells so terrible that a spill would be detected fast.

Sure, zinc-bromine may be less expensive and have a lower environmental impact than vanadium. But does it stink in compared to li-ion?

To be clear, zinc-bromine batteries are not as energy-dense. On a grid scale, Gelion's batteries have an energy density of 120 Wh/kg. In a 2021 presentation, Redflow's Systems Integration Architect, Simon Hackett, stated that the company's batteries are "more energy-dense than lead-acid, but far less energy-dense than lithium."

However, in terms of round-trip efficiency, zinc-bromine batteries can potentially compete with lithium-ion batteries. Gelion's Endure battery has an RTE of 85 to 90%. This is comparable to the 82 to 90% RTE for lithium-ion batteries revealed in a September U.S. Department of Energy research.

That study, which evaluated the cost and performance of grid energy storage technology, also demonstrates how the capital cost of zinc-bromine batteries can be less expensive than either li-ion or vanadium. In the instance of a 10 MW battery holding energy for four hours, li-ion batteries are the cheapest when considering the storage block itself, which includes the cost of battery modules, racks, flow battery stacks, electrolyte, and tanks. Their HVAC and plumbing systems are likewise less expensive.

However, both Gelion and Redflow claim that their zinc-bromine batteries do not require air conditioning in the first place.

Gelion's founder, Thomas Maschmeyer, claimed to The Guardian in 2021 that their operating costs will be 25% lower than lithium's since their batteries do not require air conditioning or fire suppression equipment. Furthermore, the Endure battery does not employ tanks. There is no fluid to hold.

The cost of system integration, which includes shipping and installing the batteries, is estimated by the Department of Energy to be between $46 and $52/kWh for lithium and vanadium. Zinc-bromine costs between $10 and $18/kWh. In addition, zinc-bromine is significantly less expensive in terms of engineering, building equipment, connecting to the grid, and transformers.

Gelion believes that its production process lowers costs even further. A RFB usually necessitates the establishment of a new production line. However, the Endure's casing is the same type used in lead-acid batteries, and 18 of the 22 phases of its production process can be accomplished within an existing lead-acid battery facility.

Gelion estimated in a presentation to investors earlier this year that it would cost around $16 million to convert a lead-acid battery facility to make 1Gwh of its batteries, while establishing a new 1Gwh li-ion battery facility from scratch would cost roughly $130 million.

Zinc-bromine batteries also have a longer lifespan than lithium batteries. This is due in part to their durability and depth of discharge, like with other flow batteries. This is also true in the context of their life cycle. According to the Department of Energy, lithium phosphate batteries have a cycle life of approximately 2,400 cycles, whereas lithium nickel manganese cobalt batteries have a cycle life of approximately 1,500 cycles. Zinc-bromine flow batteries, on the other hand, have a lifespan of around 4,500 cycles, and zinc-bromine non-flow batteries have a lifespan of around 5,000. 20

Both Gelion and Redflow highlight the toughness of their batteries. Gelion describes the Endure as "abuse-tolerant," and in one test, it managed to stay running while "burning and charring" over a hotplate heated to 700 degrees Celsius. The two products have similar levels of resistance to high temperatures, with the Endure's highest limit being 50 C and the ZBM3's being 45 C. 9 32

In terms of design advancements, zinc-bromine batteries appear to be on fire. And, given Australia's bushfires and overall hot temperature, the country's association with zinc-bromine batteries makes perfect sense. Indeed, the blackouts caused by bushfires encouraged Australian state and federal governments to invest in rechargeable batteries for domestic battery energy storage systems and rural telecommunications stations. According to the company's Systems Integration Architect, Redflow's battery is particularly well-suited for use in telecom stations due to its compact size in comparison to other flow batteries.

When zinc-bromine batteries approach the end of their useful lives, they are also easier to recycle than lithium-ion batteries. Because zinc-bromine electrolyte is dense, it is frequently recycled by the oil and gas industry. Because the Endure's casing is identical to that of a lead-acid battery, it can be recycled in the same manner, but with the extra benefit of what the business refers to as more "benign" components, such as non-toxic lead or caustic sulfuric acid.

Zinc-bromine batteries aren't perfect. In general, zinc dendrite growth threatens to poke through the separator of zinc-bromine batteries. As a result, zinc-bromine RFBs typically require maintenance in the form of "strip cycles" to remove zinc buildup. It's worth noting, though, that Redflow says that thoroughly discharging its batteries removes the zinc. And Gelion's solution to dendrites is a porous barrier that separates the zinc and bromide, which clearly hinders their growth.

However, zinc-bromine batteries, like any other technology, are not the be-all and end-all. They're designed for specific applications such as large-scale grids, long-term storage, remote places, and harsh temperatures. It's pointless to compare them to solid-state batteries, for example, because they're designed to solve distinct problems. Solid-state batteries are thin and tiny, but zinc-bromine batteries are (relatively) large and heavy. Solid-state drives are garnering interest due of their possible use in EVs. Zinc-bromine batteries, on the other hand, are designed to provide electricity to your home, solar or wind farms, or isolated places. Overall, zinc-bromine batteries may function well in fixed sites but are far too big for mobile or portable applications.

The most significant distinction, however, is that the fabrication of solid-state batteries is now too expensive to adapt to uses in EVs and consumer devices.

Zinc-bromine batteries have already arrived.

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