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The course of science rarely runs smoothly, but new research from Rice University shows that experimentation with an everyday object such as sticky tape can deliver an energy-technology breakthrough.
A sticky problem hinders the development of lithium metal anode (LMA) batteries. Short circuits, thermal runaway and loss of efficiency can be caused by the build-up of inactive lithium and lithium ‘dendrites’ — spiky protrusions that can short-circuit a battery — during the battery’s lifecycle.
Now researchers from Rice University may have found a novel solution for such problems. The team has found a way to turn adhesive tape into a silicon oxide film that could solve these problems by protecting the lithium anode, the element creating the issues. The technique used by the team is similar to that used to produce graphene sheets.
The team utilized a standard industrial infrared laser cutter to transform a commercially available silicone-based adhesive tape into a porous silicon oxide coating. The researchers added a tiny amount of laser-induced graphene derived from the tape’s backing of polyimide. The silicon oxide layer is deposited directly on to the battery’s current collector, offering it protection, preserving efficiency and suppressing the formation of unwanted lithium.
Research detailing the Rice University crew’s findings are published in the journal Advanced Materials.
In addition to preserving the efficiency of the lithium battery, forming the silicon oxide film with a laser avoids the use of toxic organic solvents and the need for long drying times.
The development could be a significant boost to the lithium battery market. These batteries are already renowned for their long life, providing a much higher power-density than alternative batteries. The fact that lithium is highly reactive means that this type of cell has gradually been replaced in many areas by lithium-ion technology. However, this development could turn that switch full-cycle, bringing lithium metal batteries back to the forefront.
A downside with lithium-ion batteries is that dosing them with graphite, the process that distinguishes them from lithium-metal batteries, makes them quite heavy. This means a battery with pure lithium metal stands to be much lighter, a boon for use in technology as wide-ranging as phones and other compact technology, as well as cars and other vehicles.
The Technique that Introduces Sticky Tape to Lithium Metal Batteries
The researchers’ inspiration for adapting sticky tape with lasers to fulfill a role in lithium metal batteries arose from previous attempts to produce a free-standing film of laser-induced graphene using commercially available tape.
During the experiments, material scientists found that not only could they produce graphene, but they also recovered a foamy, translucent film from the side of the tape that had held the adhesive.
This layer formed after the team stuck the tape to the current collector and blasted it multiple times with a laser. This laser exposure had the effect of raising the temperature of the tape to around 2000 ⁰C, resulting in a porous coating of mainly silicon and oxygen around the conductor. A small amount of carbon was also present.
The team realized that the foamy by-product that they had created could be applied to lithium-metal batteries, as it soaked up and released lithium without the formation of dendrites. These dendrites can be a significant problem for lithium-metal batteries and, in extreme circumstances, can cause fires , presenting a major safety hazard. Therefore, any method of eliminating them is an essential breakthrough for this technology.
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Another issue present in lithium-metal batteries and in lithium-ion batteries is the disintegration of the lithium anode during the charge/recharge cycle. This leads to lithium clustering at the cathode, severely limiting the life-span of the battery. Rice University researchers found that when the current collector was coated with their laser-induced silicon oxide, the breakdown did not occur.
Lithium Anodes — The Future of Battery Technology
The main difference between the batteries that the team suggests this breakthrough could improve — lithium-metal batteries — and widely used lithium-ion batteries, is that in the latter lithium ions are inserted into layers of graphite with six carbon atoms sealing a single lithium-ion. As the battery charges and recharges, they are freed from this graphite structure.
Lithium-metal batteries eliminate the need for graphite, allowing lithium-ions to shuttle directly from the anode. This results in a capacity that is up to 10 times higher than graphite-lithium ion batteries.
The lack of graphite means more lithium must be added to the anode to compensate for the degradation, meaning the resultant battery is lightweight with high-performance, but with a shorter life-span. The team’s film also takes away any safety issues.
The use of the silicon oxide film seems to have negated the use of excess lithium and increased the lifetime of the lithium-metal battery by about three times. They found that the silicon-oxide system resulted in a lithium-metal cell that could undergo 60 charge/recharge cycles, losing only 30% capacity. The team believes the system they have pioneered could be ideal for outdoor expeditions or short-term demands in rural areas.
Silicon oxide films can be manufactured with standard industrial lasers, which means that scaling up its production is relatively straightforward. The laser-technique involves no toxic solvents and can be performed at room temperature in an area with a normal atmosphere belaying safety concerns.
The team proposes that the system used to produce the film can also be applied to create films that can produce coatings and filters for metal nanoparticles.
The research provides an example of how scientific developments and breakthroughs can arise from the most unexpected sources, such as household objects.
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References and Further Reading
Chen. W., Salvatierra. R, Ren. M, et al. (2020) Laser‐Induced Silicon Oxide for Anode‐Free Lithium Metal Batteries. Advanced Materials. https://doi.org/10.1002/adma.202002850.
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