What is a Lithium Battery?
Lithium batteries are used in a wide variety of electronic devices including cell phones and laptops. They are known for their light weight, high energy density and rechargeability.
Batteries are composed of an anode, cathode, separator, and electrolyte. The chemistry of lithium batteries involves oxidation-reduction reactions. During discharge electrons move from the negative cathode to the positive anode.
A lithium battery consists of two electrodes, an electrolyte medium and a separator to keep the cathode and anode apart. When the battery is charged, an oxidation reaction occurs in the cathode, releasing lithium ions into the electrolyte. These ions then jump to the anode, where they create an electric current. To facilitate this process, the cathode and anode are coated with binders that help them withstand the oxidation reactions.
Electrode coatings are just a small percentage of the total weight of a lithium battery, but they play an important role in its performance. They provide a variety of benefits, including safety enhancements and increased energy density.
Researchers have been exploring different materials for the cathode of lithium batteries. Silicon (Si) is attractive because it can alloy with Li, resulting in high theoretical capacity. However, Si anodes suffer from huge volume changes during charging/discharging cycles. These changes result in Si pulverization, continuous rupture and regeneration of the solid electrolyte interface (SEI), and an electrical disconnection between the Si and current collectors. These issues lead to short cycle life and low reversible capacity.
Every cell in your body functions via electrical currents. These currents are carried by electrolytes – chemicals that conduct electric charges. Batteries require an electrolyte medium to carry the electric charge between anode and cathode atoms. The electrolyte also acts as a separator between the two electrodes to keep them apart.
Lithium metal reacts vigorously with water to form lithium hydroxide and hydrogen gas, so the battery requires a non-aqueous electrolyte and a sealed container that rigidly excludes moisture. Electrolytes used in batteries typically are a mixture of organic carbonates such as ethylene carbonate and propylene carbonate.
The researchers found that using fluorinated solvents such as difluoroethylene carbonate and 1,1,2,2-tetrafluoroethyl-2,3,3,3-tetrafluoropropane ether (F-EPE) resulted in significantly higher cycling performance. These solvents, as well as ionic liquids with a high melting point and a low boiling point, can better withstand the extreme temperatures needed for safe operation of lithium batteries.
The research team also studied the surface chemistry of the various types of cathode materials and found that the use of fluorinated solvents can help reduce unwanted side reactions lithium battery in these batteries. These solvents can bind with the cathode material and form protective surface films.
The cathode is a key component of lithium batteries that determines its energy density through cell voltage and capacity. Lithium ions are intercalated into and extracted from the cathode by the action of the electrolyte.
Nickel, cobalt and manganese are the most common cathode materials for lithium batteries. Adding nickel to the mix increases the battery’s capacity while cobalt reduces its internal resistance. The addition of manganese creates a very stable manganese spinel structure which enables high discharge rates and long cycle life.
Electrons from the circuit flow one way when using your impact driver or other device and back the other way when charging. During the lithium battery recharging process an oxidation reaction occurs at the cathode while a reduction reaction takes place in the anode. This results in lithium ions flowing through the separator and into the anode where they recombine with their electrons. This process allows the battery to be recharged over and over again. In a regular battery, these lithium ions are stored in the anode as potential energy. In a rechargeable battery, the polarity switches between the cathode (positive) and anode (negative). This is what gives the battery its reversible chemistry.
In battery cells, a cathode and anode facilitate the flow of electric charge. The cathode is the positive electrode, which reduces (gains electrons) while the anode loses electrons (oxidizes).
Graphite is used as the anode in conventional lithium batteries because it provides the highest energy density. Graphite’s molecular structure naturally creates gaps that allow lithium to nestle inside it when charged, a process called intercalation. This allows the battery to cycle without the formation of lithium dendrites, the roots-like structures that can grow and eventually pierce the separator and cause internal short circuiting leading to heat, fire and explosion.
Alternative anode materials include silicon alloys and carbon nanowires. These alternatives have higher voltages, which limits their energy density. To improve their energy density, anodes are typically coated with binders and solvents. Using recycled material for anode and cathode production conserves natural resources and minimizes the environmental impact of mining and processing raw materials. It also reduces waste from end-of-life batteries and manufacturing scraps. This makes it a crucial step towards achieving electrification and clean energy goals on a global scale.
It’s important that all users of lithium batteries are aware of the specificities and risks that they pose. While they can be safely used in a range of devices, if they are charged incorrectly or stored at the wrong temperature they may overheat and explode.
During normal operation, lithium batteries are safe and heat related failures are rare. However, a thermal runaway in just one cell can cause the surrounding cells to heat up, vaporise the electrolyte fluid and create highly flammable gases. This can cause fires that are difficult to control.
If a lithium battery powered device is in a fire, it should be immediately turned off and placed in a non-flammable surface such as a metal desk. The battery should then be isolated within a fire-rated building to prevent it from affecting other properties and to allow fire crews to identify the battery location quickly.