The fervour surrounding energy storage devices is driving significant developments in battery chemistry and technology, causing a diverse marketplace to emerge. Jacob Harris explains.

The ability to affordably store energy in large quantities for both residential and grid applications is set to redefine energy consumption, production and grid operation. With batteries set to become a requisite part of residential power systems, it should come as no surprise that development in the energy storage sector has gone into overdrive.

Li-Ion batteries are the current forerunners in this booming industry, and with their high energy density and compact footprint it’s easy to see why. Indeed, a host of lithium alternatives to Tesla’s now famous Powerwall are beginning to come out of the woodwork. American company Enphase Energy’s recent unveiling of a compact 25kg, 1.2kWh modular option that will allow users to fine tune their storage capacity by adding or subtracting units is one such example.

Advancements in lithium battery technology are also progressing with US body, the National Institute of Standards and Technology (NIST), University of Arizona and Seoul National University jointly developing an inexpensive method for fabricating lithium – sulphur batteries.

Through a process coined ‘inverse vulcanisation’ researchers have produced a stable plasticised sulphur cathode that is cheap (sulphur is a petroleum bi-product) and easy to produce. The resulting battery was touted to retain over 50% of its capacity after 500 cycles.

Their ability to deliver in power intensive situations means lithium batteries can perform well in a range of applications, but the alkali metal’s inherent instability and the battery’s consequential incendiary potential will always dissuade a considerable portion of the market.

To fill this gap there is a host of emergent battery chemistries and technologies that have the potential to deliver some very stiff competition to lithium and make the energy storage market extremely competitive in the near future.

Redflow’s ZBM

A relatively small, modular zinc-bromine flow battery that can also be containerised to form large scale storage systems has been developed by Brisbane-based company Redflow. The batteries, or zinc-bromide modules (ZBMs), range from 8 – 11kWh and have a footprint of just 0.34m².

Flow batteries operate by continuously pumping an electrolyte between a storage compartment and a reaction chamber containing the electrodes. This action means flow batteries contain more moving parts than most other batteries and while this can be seen as a disadvantage, the separation of compartments also allows for the replacement of the electrode stack while retaining the battery’s other elements.

The nominal 48V batteries have a 100% depth of discharge and operate at near linear voltage and current levels across all charge states, making them well suited to energy applications as opposed to power applications.

While the company’s key target market is telecommunication base transceiver sites, Redflow also focuses on transmission and distribution deferral over smart grids and micro grids, renewables integration, on and off grid remote power and residential energy storage.

The batteries can be kept at low or zero state of charge for long periods of time without degradation and can use their full capacity for deep day-in day-out cycling. ZBMs can also be stored uncharged and have an indefinite shelf life.

“We have a longer base life than Li-Ion and when factoring in the ZBM’s capacity for 100% depth of discharge and its indefinite shelf life, Redflow’s battery life can be seen to significantly increase. Our ZBM3 (11kWh) has an expected life of more than 44,000kWh, and this can be extended further with a stack replacement,” says Redflow’s marketing manager Sciobhan Leahy.

ZBMs are built from a commonly sourced plastic and contain no rare earth elements. Their electrolyte (a water based solution of zinc-bromide salt) is fire retardant and because of the separation of the stack and tank there is no chance of thermal runaway.

ZBMs are managed by an on-board Module Management System (MMS) that controls battery operations while providing access to battery status, real-time data, event logs, warnings and alarms. This allows the battery to self-manage and protect against potential risks.

Ambri’s liquid metal battery

American company Ambri is in the process of fine tuning a liquid metal battery. Originally developed by MIT professor Don Sadoway, the technology is touted to fundamentally change the way power grids are operated. Unfortunately, dates for the first commercial sales have recently been pushed back due to an issue with one of the battery’s seals, but the company is still progressing with development – albeit at a reduced pace.

The battery’s cells are made of three simple components, a salt electrolyte which separates two metal (electrode) layers of magnesium (Mg) and antimony (Sb). Because of their different densities these components naturally form three layers when in a liquid state. As the battery discharges, Mg electrons move across the electrolyte to form an Mg-Sb alloy, when the battery is recharged the metals separate again and return to their original compositions.

Because the battery is all liquid, the electrodes will not degrade in the same way as their solid counterparts. This means the battery could potentially last many years without losing much of its storage capacity. The batteries are also incredibly scalable and can range in size from 100kWh to hundreds of mWhs.

The cells are housed in steel containers and are assembled in systems using basic components such as steel racking. Because of this, Ambri’s manufacturing strategy involves steel workers on a production line that is similar to an aluminium smelter. This relatively simple manufacturing process and the technology’s use of cheap, earth abundant materials, means the batteries promise to be extremely affordable to build and maintain.

Aquion Energy’s aqueous hybrid ion battery

Commercial shipments of Aquion Energy’s AHI batteries began in mid-2014 and are rapidly increasing because, according to Aquion’s VP of product management Matthew Maroon, they satisfy several unmet market requirements.

Being saltwater batteries that use no heavy metals, they are a clean, non-toxic energy storage solution based on abundant, low-cost materials. AHI batteries are modular and scalable for various power/energy ratio applications up to mW scale and are easily manufactured, providing economical, long-duration storage for high-energy applications such as renewable energy storage and time shifting.

“AHI batteries are optimised for daily deep cycling (defined as 4 to 20+ hour charge and discharge cycles) for residential solar. Being adept at long duration cycling and because they’re not damaged by long stands at partial state of charge, they are high performing under solar cycling profiles and are the cleanest and safest storage solution available. In fact, Aquion batteries are the only ones that are Cradle-to-Cradle certified and we’ve found that their inherent safety really resonates with customers,” says Matthew.

As the energy storage market grows, we can expect new innovations in battery technology to come to light increasingly frequently. There is room for multiple players in battery manufacturing as different battery chemistries will play a role in meeting the needs of different customer types and applications.