Current lithium metal batteries with solid electrolytes, found in our phones, laptops and electric cars, are lightweight, inflammable, pack a lot of energy, and can be recharged very quickly. In recent times though, developments in the technology have been slow due to mysterious short circuiting and failure.
Following new research it appears that the failure comes down to one thing - stress. To be more precise, mechanical stress, occurring most prominently during potent recharging.
It has been found that even modest indentation, bending or twisting of the batteries can cause nanoscopic fissures in the materials to open and lithium to intrude into the solid electrolyte causing the batteries to short circuit. Further, it has been found that even dust or other impurities introduced in manufacturing can generate enough stress to cause failure.
If the issue of damage causing the short-circuiting phenomenon in batteries were to be resolved, energy-dense, fast-charging, non-flammable lithium metal batteries that last a long time could be produced, potentially overcoming the main barriers to the widespread adoption of electric vehicles, among numerous other benefits.
The significance of this discovery is down to the fact that many of today's leading solid electrolytes are ceramic. Ceramics enable fast transport of lithium ions and physically separate the two electrodes that store energy; and most importantly, they are fireproof. Like ceramics in our homes though, they can develop tiny cracks on their surface.
It has been found that ceramics are often imbued with nanoscopic cracks, dents, and fissures, many less than 20 nanometers wide; and during fast charging, these inherent fractures open, allowing lithium to intrude.
In the real world, a solid-state battery is made of layers upon layers of cathode-electrolyte-anode sheets stacked one atop another. The electrolyte's role is to physically separate the cathode from the anode, yet allow lithium ions to travel freely between the two. If cathode and anode touch or are connected electrically in any way, as by a tunnel of metallic lithium, a short circuit occurs. If even a subtle bend, slight twist, or speck of dust occurs between the electrolyte and the lithium anode, it will cause imperceptible crevices, ultimately leading to failure of the battery.
An analogy of this phenomenon is the way a pothole appears in otherwise flawless pavement. From rain and snow, cars eventually pound water into the tiny, pre-existing imperfections in the pavement producing ever-widening cracks that grow over time.
Now that it is known how such imperfections are formed, and how the short-circuiting issues arise, mechanical forces may now intentionally be used to toughen the battery material during manufacturing, much like a blacksmith anneals a blade during production, ultimately eliminating the problems which cause batteries to unexpectedly short-circuit. Additionally, ways of coating the electrolyte surface to prevent cracks or repair them if they emerge are also being explored now the root cause of the problem is known.
By creating more reliable batteries, consumer faith in battery powered technologies will likely be increased, further helping the public move to technologies (such as electric vehicles) that align with bringing the world to net zero status. Further, given that such discoveries will likely produce longer lasting and higher performing batteries, the lifespan of battery powered technologies may be increased, with this being hugely beneficial from a sustainability point of view.
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