YOU OFTEN find rechargeable lithium-ion batteries in phones, laptops, hoverboards and even planes and electric cars. They are light-weight, highly efficient and rechargeable; this makes them ideal for all sorts of gadgets.
In comparison to nickel-cadmium batteries, lithium-ion batteries are more reliable, hold charge for longer and can be built to be much smaller and thinner. The components of a lithium-ion battery are much less toxic than those of other battery types, which may contain lead or cadmium. The iron, copper, nickel and cobalt of a lithium-ion battery are safe for landfill or incinerators. Yet, 25 years after their introduction to the market, there are still occasional reports of lithium-ion batteries causing fires in all sorts of devices, including a fire on-board a Boeing 747 flight in 2010 which killed two people.
In 2016 2.5m Samsung Galaxy Note 7 smartphones were recalled due to a problem with their batteries, causing fires and injuries to many users. The recall of the Samsung phones was due to an engineering fault, the theory being that one part inside the battery
was coiled incorrectly leading to an excess of stress on another single part. As more demands are made on the battery in any given device, engineers try to pack more power in to smaller spaces.
Within a lithium-ion battery, there are three main components: the positively charged cathode (a metal oxide), the negatively charged anode (graphite) and the liquid electrolyte, a solvent of lithium ions. The cathode and anode must be physically separated by a permeable wall and in very slim batteries this can be done by a polymer as thin as ten microns.If this wall is breached, it can lead to a process called thermal runaway. The battery gets hotter, leading to further degradation of the polymer, which causes the battery to heat even more. The flammable electrolyte can reach 500°C at which point it may ignite or even explode.
Simply adding flame retardant to the electrolyte solution would lessen the chance of fire but at the same time massively reduces the efficiency of the battery. To reduce the risk of a catastrophic fire, researchers at Stanford University have devised an automatic fire extinguisher for lithium-ion batteries. Yi Cui and this team have produced a thin polymer capsule that contains a fire retardant. If the battery overheats to the point that the polymer shell melts, the miniature fire extinguisher is automatically set off and the fire retardant released into the battery.
If these safety devices can be shown to work on a large-scale in a real world setting then it opens lithium-ion batteries to more widespread use in electric cars and aircraft. Currently a safer alternative to lithium-ion batteries is the solid state battery, where the liquid electrolyte is replaced with a solid which is far less flammable. However the inherent problem with the solid state battery is that it takes an incredibly long time to charge – negating most of its useful potential in cars and electronic devices.
Still, it is important to note that lithium-ion batteries are generally extremely safe. The probability of the lithium-ion battery in your phone failing is less than one in a million – whereas the probability of you being stuck by lighting stands at around 1 in 13 000 – meaning that lithium-ion batteries remain a relatively safe and efficient option.