BATTERY TECHNOLOGY
Battery technology innovation :
Where are we now ?
Callum McGuinn , partner and patent attorney at Mewburn Ellis , looks at the growing alternatives to lithium-ion batteries
Despite its dominance of the secondary battery market , lithium-ion technology has some serious and unavoidable drawbacks . For one , the manufacture of lithium-ion batteries ( LIBs ) tends to require a steady stream of expensive , scarce and often environmentally damaging raw materials , such as lithium , nickel and cobalt . Aside from this , the finished batteries themselves present safety issues , which are accepted as a tradeoff against the many benefits of Li-ion technology . There are a number of contenders offering an alternative to LIBs , but how likely are they to replace the clear market leader and when can we expect to see commercialisation ?
Lithium-sulfur
The relative low energy density of LIBs is most keenly felt in the electric vehicle ( EV ) sector . For an EV to have a sufficiently long range , or for aerial vehicles , manned or unmanned , to be able to remain aloft efficiently , the battery should be as light as possible . Batteries of high energy density ( the energy deliverable per unit weight of the battery ) will therefore be crucial to future EV applications . Enter the lithium-sulfur ( Li-S ) battery . Li-S batteries in theory are cheap , with a large specific capacity ( up to 1675 mAhg -1 , compared with only 155 mAhg -1 for Li-ion ), high specific energy ( up to 2567 Wh kg -1 vs . 387 Wh kg -1 for Li-ion ) and lower environmental impact than existing Li-ion batteries . Sulfur is a naturally abundant element , very safe and non-toxic . A Li-S battery reacts lithium with sulfur ( S 8
) to form lithium sulfide ( Li 2
S ), generating electrical energy along the way . This reaction is a source of very high levels of electrical energy . This is five times as much as the reactions in a Li-ion battery , hence the very high specific energy for a Li-S battery . Before we see Li-S technology replace fossil fuels or other battery technologies in our phones , cars and helicopters , there are some important problems , which researchers are currently working hard to solve . However , some exciting breakthroughs have already been made . The reaction to form Li 2
S in the battery first forms long-chain lithium polysulfides , such as Li 2
S 8 and Li 2
S 6
, as intermediates . These can dissolve in the electrolyte within the battery and diffuse between electrodes . This ‘ polysulfide shuttle ’ effect can ultimately cause a layer of Li 2
S to form on the anode . This in turn blocks the passage of lithium , causing ageing of the battery and loss of capacity over time . There is also a large change in volume of the electrode during the reaction that forms Li 2
S . This volume change can cause physical degradation of the electrodes , which again leads to capacity fade and ultimately failure of the battery . Some research has focussed on various types of carbon-sulfur conductive matrix materials for use in the cathode of the battery to address some of these problems . Some of these rely on embedding the sulfur within carbon nanopores , which
Sodium-ion batteries are poised to take on lithium-ion
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