What is a Lithium Ion Battery?
Lithium batteries are used in many things that you use everyday like mobile devices, electric cars and forklift trucks. They are also more energy-efficient and sustainable than lead-acid, saving your business money in the long run.
The battery’s electrodes are made from materials that intercalate lithium ions. These materials are rare and require mining, which can cause health issues, human rights violations and generational legacies of environmental degradation for local communities.
What is a Lithium Ion Battery?
Lithium ion batteries are rechargeable cells that contain lithium and an electrolyte solution. An oxidation reaction occurs in the anode of the battery, which releases lithium ions that move through the electrolyte solution to the cathode. The anode and cathode are separated by a separator with microscopic holes that allow lithium ions to pass through while preventing electrons from moving in either direction.
When the battery is plugged into a charger, the anode and cathode start an oxidation and reduction reaction that creates new lithium ions in the anode and removes electrons from the cathode. This completes the circuit, which allows electricity to flow from the cathode through the electrolyte and into the anode. The battery then charges up, and the positive and negative electrodes are separated by the separator again.
The separator is the key to what makes lithium-ion batteries so useful. It can handle large amounts of energy and is capable of holding a charge for a long time. Those traits make these batteries ideal for use in electric vehicles and renewable energy storage systems.
They can also be found in consumer devices, including cellphones and power tools. They have a much higher voltage than standard alkaline cells (3.7 volts) and are smaller, which helps them fit into small spaces like cell phone cases and digital cameras.
Lithium Ion Battery Structure
The lithium ion battery is made up of two electrodes, an anode and a cathode. The anode is typically made of carbon while the cathode is made of a material that stores lithium ions. When the battery is discharging, positively-charged lithium ions move from the anode to the cathode through a process called intercalation. The cathode then releases electrons to the anode, creating a flow of electricity from one end of the cell to the other.
A separator is placed between the anode and cathode to Lithium Ion Battery prevent direct contact between these materials. The separator also allows lithium ions to pass through while keeping electrons away from each other. The electrolyte used is a chemical compound that meets very stringent safety requirements.
Lithium-manganese spinel is a popular choice for the cathode in lithium batteries because it has excellent thermal stability, making it ideal for high-performance applications. Its AB2O4 structure gives it unique chemical properties that improve the battery’s performance.
Cylindrical lithium cells are the form factor most people associate with traditional household batteries such as AA batteries. These cells come in varying widths and lengths and can be used to build battery packs with a range of amp-hours and voltages. They are often used to power electric vehicles (EVs), drones, children’s toys, and portable medical devices where weight is a concern. These batteries are typically stored at a partial charge (between 30% and 50%) to extend their lifespan and maintain high performance.
Lithium Ion Battery Applications
Lithium ion batteries are used in many applications including portable electronics such as cell Lithium Ion Battery phones and tablets, electric vehicles, power tools, and backup systems. The batteries have very high energy density compared to nickel metal hydride cells which allows them to hold more charge for the same size and weight.
Battery manufacturers optimize the design for cost and energy density depending on their specific application. Generally, UPS solutions use lower cost batteries that are less capable of fast discharges. The tradeoff is longer runtime with limited energy density.
Among lithium ion battery chemistries, Li-FePO4 (LiFePO4) is very safe and has an excellent Depth of Discharge (DoD). It also operates well over a wide temperature range with no thermal or mechanical stress and offers high cycle and calendar life. Its higher initial cost, however, makes it less economical than other lithium ion technologies.
Most lithium ion batteries are sensitive to overcharging and under-discharging. They also experience ageing over time, which is dependent on the number of cycles and can affect performance. It is important to monitor the State of Health (SoH) to ensure that the battery is operating at its best. In addition, lithium ion batteries should be stored in a cool environment to reduce ageing and to maintain the highest levels of energy density possible.
Lithium Ion Battery Degradation
In a battery, ions flow freely between the cathode and anode. Using the battery causes the ions to flow in one direction, while charging the battery reverses the direction of ion flow. Over time, this causes the battery to lose capacity. Erratic charging, over-discharge, and heat can speed up the degradation process. Scientists from SLAC National Accelerator Laboratory used X-ray tomography to study the gradual degradation of nickel-manganese-cobalt, or NMC, cathodes in LiBs.
NMC cathodes degrade due to non-uniform ion distribution within the cell, which reduces the capacity of the battery. The researchers discovered that the cathode surface becomes rough, causing a decrease in ion transfer between the cathode and electrolyte. This causes the impedance of the battery to increase, leading to capacity fade.
The team also found that NMC cathodes can develop a solid-electrolyte interphase, or SEI layer, which reduces the rate of lithium plating from the cathode. The SEI layer growth leads to pore blockage, which increases the rate of cyclic degradation.
It’s important to understand the progression of each degradation mechanism, as it can help us predict when a battery will stop working. However, most studies are isolated, looking at each degradation mechanism in isolation, with little consideration for how they interact with each other. In order to accurately model degradation, it is necessary to understand how each degradation mechanism influences each other, and this is known as path dependence.
