BATTERY TECHNOLOGY
Anolyte tank
Pump
Current collector
The EU has recognised the problems arising from the need to import lithium and cobalt into the bloc for LIBs , elements which cannot be sourced in Europe . One aim of the EU ’ s new battery regulation is to help secure a sustainable supply of these elements by promoting recycling . However a move to sodium-ion technology would remove the need to import these elements and European businesses have recognised this advantage . Tiamat , a spin-off of the French National Centre for Scientific Research ( CNRS ), is accelerating the commercialisation of sodium-ion , with a plan to bring a battery to market in 2023 and ramp up to 6 GWh / year by 2030 .
Redox flow
When it comes to stationary energy storage applications , redox flow technology offers an exciting alternative to LIBs . Redox flow batteries ( RFBs ) are already in use for stationary storage , with 0.25 GWh being installed in 2019 . This pales in comparison with the 8.8 GWh of LIBs installed the same year , but the poor safety and high maintenance cost of Li-ion , coupled with the scarcity of lithium , is fostering a bigger swing towards alternative stationary energy storage solutions . The front-runner in the redox flow area is the vanadium redox flow battery
Ion-selective membrane
Porous electrode Catholyte tank
Vanadium reflux flow battery
( VRB ). The VRB includes two large storage tanks , one holding a ‘ positive electrolyte ’ mixture of VO 2
+ and VO 2 + ions and the other holding a ‘ negative electrolyte ’ mixture of V 3
+ and V 2
+ ions . The respective electrolyte solutions are pumped into a cell on either side of an ion-permeable membrane . When the battery is charging , VO 2 + ions in the positive electrolyte are oxidised to VO 2
+ ions and electrons leave the positive terminal of the battery . At the same time electrons enter the negative terminal and reduce the V 3
+ to V 2
+. The process is reversed during discharge , providing an electrical power supply from the battery . VRBs are already deployed globally for stationary energy storage . The largest installation is the Minami Hayakita Substation in Japan , delivering 15 MW of power and having a 60 MWh storage capacity . A much larger installation in China , developed by the Dalian Institute of Chemical Physics , has recently completed construction and entered its single module commissioning stage . Scottish Water has also completed construction on a 0.8 MWh installation at a water treatment facility , as part of the country ’ s drive towards net zero emissions by 2040 . The technology is thus relatively mature , but nevertheless improvements are being made . Research has focussed on improving the electrolytes , aiming to pack more active material ions into the liquids to increase energy density , and developing membranes which can more efficiently transport the hydrogen ions generated during the redox process . RFBs offer a number of benefits . Although vanadium metal is a scarce resource , there is no vanadium consumption by the battery . They have good cyclability and can be recharged many times during their lifetime . Crucially , RFBs offer complete decoupling of power and energy : the energy storage capacity of an RFB depends only on the total amount of active chemical species contained in the storage tanks , while the deliverable power , a product of the cell voltage and current , depends on the number of cells in the stack . Thus a given installation can be tailored to focus on supplying high power , high energy ( capacity ) or both . Exact and independent control over power and energy can be achieved , a feat which is not possible for LIBs . Control over energy supply from the battery is much greater for an RFB , where the solution flow can be easily stopped if needed .
Looking forward
This is just a taste of the range of challenger technologies that may threaten the dominance of LIBs over the coming years . It will not be straightforward or cheap to shift our existing manufacturing capabilities and supply chains away from lithium ion , but such a paradigm shift looks increasingly likely as the ethical and safety concerns around LIBs gain momentum . •
Callum McGuinn
PARTNER
MEWBURN ELLIS k + 44 20 7776 5300 J callum . mcguinn @ mewburn . com j www . mewburn . com
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