The extent of human activity’s contribution may still raise arguments but there can be no doubt that the globe’s environment and climate is changing, and a significant contributor is the generation of electricity via fossil fuels – which despite the advent of renewable power sources like wind and solar, remain entrenched in the power mix of most countries.
The drive to develop more environment-friendly energy sources such as solar cell and wind electricity has gained momentum, but their use is affected by both their intermittent production of power and the existing grid’s inability to store energy efficiently.
Energy needs to be stored to be able to meet the demand of the grid when the sun isn’t shining or the wind blowing. So, the switch to renewable power requires the widespread deployment of long lasting, safe, and affordable energy storage systems.
How quickly the UK and other nations move to net zero will be determined by how soon a new electricity infrastructure can be put in place. New pylons, connectors and cables will be required that can hook up renewable energy sources to national power grids, while the use of renewables will also require the development and installation of reliable electrical energy storage (EES) solutions.
Consequently, a lot of research is being undertaken into new energy technologies, especially rechargeable batteries.
Among the battery technologies being studied are solid-state batteries, which use a solid material instead of a liquid electrolyte to transport charge between the electrodes. They can offer higher energy density, faster charging, and better safety than conventional lithium-ion batteries.
Other technologies being researched include silicon and lithium-metal anodes, lithium-sulfur batteries, sodium-ion batteries and redox flow batteries.
All of these technologies certainly have benefits – higher energy densities in many cases than lithium-ion – and are more environmentally friendly. In some cases, they also have the additional benefit of being more scalable, flexible, longer-lasting, and safer when used in large-scale energy storage applications.
That’s certainly the case with redox flow batteries (RFB). According to a new report from IDTechEx, RFB manufacturers claim that their systems have a much higher cycle life - in some cases 20,000+ cycles - which means that RFBs can dispatch more energy over their lifetime, resulting in lower costs of storage (LCOS) compared to Li-ion batteries.
As greater volumes of renewable energy sources penetrate electricity grids, so energy storage technologies that can provide longer durations of storage, such as RFBs, will be needed to dispatch energy over these longer timeframes.
Lithium alternatives
A cheap, safe alternative battery technology to lithium is seen as key to moving the ‘needle’ to a completely renewable power sector.
Energy storage, the capture and storage of energy for later use, is a market that’s now worth between $44bn and $55bn and is expected to reach up to $150bn by 2030.
It does face major economic and supply challenges, as already indicated, whether that’s using scarce and price volatile materials – lithium - which have led to more concentrated supply chains which, in turn, pose a huge risk to energy security, access and sustainability.
With the focus on lithium-ion batteries a report commissioned by Eurometaux found that to meet clean energy goals, Europe would need up to 21 times more lithium in 2050 compared with today – suggesting that demand for lithium would far exceed supply.
While rechargeable batteries, such as nickel zinc, nickel metal hydride, and lithium-ion batteries (LIBs) have been around for decades, in terms of commercial energy storage devices, the focus has tended to be on LIBs as they offer high efficiency in delivering energy, high voltage, and long cycling life.
However, lithium-ion batteries are both costly and have serious safety issues – so efforts have begun to focus on developing alternatives - zinc-ion batteries (ZIBs), for example - that are lower cost.
In terms of zinc there are plentiful supplies of the metal, and it offers high chemical/physical stability, it is more environmentally friendly, and much safer that lithium. As a result, zinc metal has been applied in various batteries, such as Ni–Zn batteries, MnO2–Zn batteries, Zn-ion batteries, and Zn–air batteries.
Another promising candidate in terms of energy storage is a rechargeable solid-state zinc-ion storage system which has attracted research interest as they offer high stability, excellent zinc-ion conductivity, superior mechanical properties, and easy fabrication. All of these attributes will be required for the development of flexible and safe rechargeable zinc-ion based energy storage devices.
However, for this technology to be deployed developers will need to effectively address electrolyte leakage issues and seek to deliver scale in terms of the industrial production of these forms of batteries.
Despite numerous technical challenges, zinc-ion batteries are seen by many as being an essential component in powering and maintaining future electric grids that can use renewable sources of power.
“Emerging within the last 10 years, zinc-ion batteries offer many advantages over lithium,” according to Dr Mylad Chamoun the founder and CTO of Enerpoly, a Swedish company that’s using patented technology to develop zinc-ion batteries that allow for sustainable energy storage. “Zinc offers significant material cost savings, increased safety and provide for much easier recycling options.”
Its potential ability to deliver grid-scale energy storage at a considerably cheaper cost would help to integrate renewables into energy infrastructure and aid countries looking to reach decarbonisation targets, according to Dr. Chamoun.
Enerpoly uses a proprietary battery chemistry that came out of research conducted by Dr. Chamoun during his PhD at Stockholm University and work at Princeton University, along with the sustainability expertise of co-founder Dr. Samer Nameer (CSO), who conducted research at Stanford University.
“Our focus is on developing sustainable zinc-ion batteries for large-scale stationary applications such as grid-scale storage or industrial standby, while addressing the safety and environmental concerns of traditional energy storage technologies,” explained Dr. Chamoun.
By using abundant sources of zinc and manganese to create these batteries they are not only cheaper to produce but lowers the risk from supply chain disruptions or material shortages that can affect lithium-ion materials such as lithium and cobalt.
“Today the annual production of zinc globally is over 100 times that of lithium. Not to mention that demand for lithium and cobalt is anticipated to outweigh the supply within the next decade,” said Dr Chamoun.
Zinc-ion batteries also address the requirement for more rigorous safety standards that are being created for batteries used in homes, factories or within the electrical grid.
The flammable and toxic solvent-based electrolyte of lithium-ion batteries is also being replaced with a water-based alternative, removing the risk of fire and explosion, while the disposal of lithium-ion batteries which can be challenging due to the toxic compounds they contain, can be replaced with a much simpler and far safer end of life treatment for zinc-ion batteries.
Iron for energy storage
Stationary energy storage systems will play a central role for the success of the energy transition and another company, VARTA AG, is currently involved in two research projects that are using alternatives to lithium.
One project is researching the use of iron for energy storage, in the form of a so-called iron slurry/air storage. A slurry is a viscous mass in which iron is dissolved in an electrolyte as a storage medium.
During operation, this mass is pumped from an external container, the reservoir, through the actual battery cell and back again. In the cell, the mass reacts with air and releases stored energy. Charging also takes place in this way.
The system offers many advantages. Iron is readily available, non-hazardous and can easily be recycled, while the power of the cell can be changed by the size of the reservoir. The larger the container, the more energy can be stored.
According to Cornelia Wiedemann, Project Manager Product Development, who is leading the technical side of the "FeEnCap" project at VARTA, "While the iron accumulator is quite an old technology – as a solid-state cell in which iron is used as the electrode material, it is even obsolete - what is new is that iron is used as a slurry.”
The project’s name "FeEnCap" is composed of the chemical name of the element iron "Fe", the abbreviation "En" for "energy" and "Cap" for "capsuled".
The research project is looking to make the technology more powerful, and this will be done by increasing the conductivity of the slurry.
"In previous iron batteries, the components were pressed into a tablet, which resulted in very good contact between the particles and good conductivity. In the slurry, the particles are free, they don't bind directly to each other and therefore don't always touch, so the conductivity of the slurry is worse."
In a previous project, the conductivity was improved with material such as graphite. "FeEnCap now aims to improve the conductivity by encapsulating the slurry components so that the system has good charging and discharging capability," said Wiedemann.
It’s not a replacement for lithium-ion batteries, according to Wiedemann. "But it's a very interesting technology for stationary electricity storage, precisely because of its low cost, good availability and good recyclability."
In another project VARTA is working on developing its own zinc-ion batteries (ZIB).
According to Nicolas Bucher, Head of Funded Projects at VARTA AG, "Although ZIB systems have already reached a high level of technological maturity, the technology has not yet been able to establish itself across broad fields of application compared to the lithium-ion battery (LIB). The main problem with ZIB so far is its low efficiency and short service life."
This is where its research project comes in, in which VARTA is collaborating with three companies and two research institutions.
"Modern zinc-ion concepts actually belong to the type of zinc-metal batteries, but on the positive electrode they consist of materials such as manganese oxides, vanadium oxides or Prussian blue analogues (PBA) such as copper hexacyanoferrate, which enable reversible ion intercalation. Added to this is the use of aqueous electrolyte, which increases the safety of the ZIB system immensely."
The PBA cathode materials deliver low energy losses and can charge and discharge quickly. This makes them particularly relevant for an application in the stationary energy storage sector, because it is necessary to react quickly to any load peaks in the power grid in to be able to avoid widespread power outages.
Another advantage of PBA cathode materials is their simple, scalable and cost-effective synthesis. In the course of rapid commercialisation, correspondingly large quantities of electrodes can be produced and thus cells can be produced correspondingly quickly.
The major disadvantage of PBA systems so far has been their short service life of only 300 cycles (charging and discharging). However, VARTA has managed to raise the number of cycles to over 800 by modifying the respective PBA structure.
In the end if we are to deliver a successful energy transition then delivering a decentralised energy storage system will be critical, and those systems will need to provide good availability, with low costs and good reusability.
A variety of different chemistries are being developed which aim to deliver the reliability and scalability required for power grids based in renewables, enabling the shift to net zero.
