Lithium Battery Flaws
Lithium batteries are now more popular than ever, from cell phones to cordless power tools. They have a high energy density, which means they can pack a lot of energy into a small package.
They contain an insulating separator sheet that keeps the positive and negative electrodes apart, while still allowing lithium ions to pass through. If the separator fails, it can cause the battery to heat up and burn.
Lithium-ion batteries
These are the batteries you’re likely to find in most cell phones, digital cameras and laptops. Pound for pound, they have the greatest energy density of all lithium rechargeable battery chemistries. Unfortunately, they have a tendency to burst into flames occasionally, which can cause a lot of expensive damage in a very short amount of time.
The cells in a lithium-ion battery have a thin sheet of microperforated plastic between the positive and negative electrodes that allow lithium ions to pass through. The anode is made of lithium cobalt oxide and the cathode is made of carbon, both of which are materials that can easily bind with lithium ions and store them inside their structures. During charging, lithium ions move from the LiCoO2 to the carbon and back again during discharge cycles. Each movement of ions provides one volt of electric current.
The electrolyte in a lithium-ion battery is typically an organic solvent, like diethyl carbonate or dimethyl carbonate, that helps conduct the ions. When a separator fails, the lithium ions can then move too freely between the anode and cathode, making the anode overheat and decompose. This produces oxygen, which reacts with the carbon of the cathode to produce more heat and start a fire. It only takes a small spark to set the whole battery on fire.
Button-cell or coin batteries
Button batteries or coin cells are small round primary disposable lithium batteries that are used to power devices like wrist watches, key fobs, calculators, LED accessories and hearing aids. Their size and shape, along with their long battery life and low self-discharge rate makes them ideal for powering portable electronics. Button cell batteries are available in a wide variety of anode and cathode materials, including alkaline, silver oxide, lithium, and zinc air.
Depending on their size, button batteries can present serious lithium battery hazards for children and pets. Children under 5 years are especially at risk of swallowing these batteries, which may cause esophageal injuries such as burning or tearing, and can even get lodged in the throat. Three such cases in Australia involving a child under the age of five have resulted in death.
Sizing for coin battery codes (CR2016, CR2032, etc) is similar to that of other lithium batteries. The first two letters indicate the chemical composition and the last four indicate the battery’s dimensions, with the first number indicating diameter in millimeters, and the second two indicating height in tenths of a millimeter. For example, CR2032 indicates a 20mm diameter and 3.2mm tall 3V button battery.
Fires
Lithium-ion batteries are a technological and commercial success story, powering everything from cell phones to electric cars. Unfortunately, they are not without their flaws, one of which is the tendency to catch fire. While it is rare – a few batteries per million are reported to catch fire – it is still a major concern, particularly as the fires can spread quickly and create massive safety hazards.
A lithium battery consists of two electrodes that are separated by an electrolyte, which is typically an organic solvent with lithium salts. When the battery charges, the lithium ions move between the electrodes through insertion or extraction reactions. When the battery reaches full charge, these reactions are no longer reversible and they produce heat, which can be very intense. If a metal fragment punctures the partition that keeps the electrodes separate or the battery is overheated, this can trigger a chain reaction of thermal runaway.
Often, these battery fires are caused by short circuits. If the negative terminal of a lithium battery touches metal, the battery will generate high levels of heat that can melt the plastic casing. If this happens, the battery will then explode, which is a very dangerous event.
In addition to this, the chemistry of lithium-ion batteries can be affected by their environment. Temperature, the state of charge (SOC), and the composition of the battery’s electrolyte can affect the rate of the reaction that produces the highly flammable hydrogen gas, fluoride. To understand this, researchers have conducted multiple fire tests of different battery types and SOC-levels to study the combustion process. In some of these experiments, water mist was added to the battery during the firing to see how this would affect the production of HF gases.
Rechargeable batteries
Rechargeable lithium batteries power many new smart phones, tablets and laptops. They also drive electric cars and provide storage for renewable wind and solar power. They deliver a tremendous amount of energy for their size and weight. However, they can have issues that require special attention.
During normal use, the battery chemically undergoes a series of oxidation-reduction reactions between its positive and negative electrodes. This creates positively charged ions that move from the cathode to the anode, and negative electrons that flow through the wires. The electrochemical oxidation-reduction reactions must be completely reversible to achieve a long life. Unfortunately, this is not always the case.
When a rechargeable battery overheats, it can rupture or explode. This is because the organic solvent used in the battery electrolyte breaks down and lithium battery generates flammable hydrocarbon gases. The battery may also hiss, bulge and leak flammable liquid electrolyte. The rupture, explosion or fire releases a burst of electric energy that can cause serious injury or death.
Some of these problems can be prevented by following good handling practices. Batteries should be stored in a cool, dry place away from heat sources, never block a fire escape or exit route and should only be charged using the charger that came with the battery. Also, a BMS (battery management system) is needed to monitor the condition of the batteries and ensure they only charge when conditions are safe.
