Lithium Ion Battery Capacity
Lithium ion batteries are used in many items that need long battery life, from laptops and cell phones to emergency power backups, solar power storage and alarm systems. They are also great for electric cars and hybrids.
A lithium ion battery has an anode, cathode, separator and electrolyte. The electrolyte carries the positive lithium ions between the anode and cathode through the separator.
Capacity
A lithium battery’s capacity is the amount of energy it can store and deliver. It is typically expressed in ampere-hours (Ah) or milliampere-hours (mAh). The capacity of a lithium battery is important for many applications, such as providing electrical power to run lights or charging mobile phones.
The capacity of a lithium battery depends on a number of factors. These include the chemical and physical processes occurring within the electrodes, the electrolyte, and the battery’s structure. The chemical reactions that occur during discharging and charging can be characterized by insertion (intercalation) and extraction (deintercalation). The amount of energy stored in the battery is proportional to these interactions and to the cell’s volume.
During charging, an external circuit applies an overvoltage to the battery that forces electrons into the negative electrode and into the electrolyte. The battery’s internal impedance increases during the charge and discharge cycles, reducing its capacity.
The capacity of a battery is also affected by its age. It will begin to lose its ability to deliver power after a year, even when it is not in use. This phenomenon is known as aging and affects all batteries, including other types such as nickel-metal hydride. However, battery manufacturers are constantly improving lithium-ion chemistry and developing new battery designs that will increase capacity over time. They are also working to prevent the aging process.
Voltage
A lithium battery’s voltage changes as the cell is charged and discharged. During charging, an external electrical circuit applies a voltage greater than the cell’s own to force electrons into the negative electrode where they bind to lithium ions in a process called intercalation. The resulting chemical energy is stored as electric charge in the electrolyte. During discharging, the same process occurs in reverse. The result is that the battery gradually loses its electric energy.
The type of cathode material that a battery uses determines the shape of its voltage curve. Early Li ion batteries used coke (a coal product) as the anode, but since 1997 ion lithium battery most manufacturers have switched to graphite to attain a flatter discharge curve. Researchers are also looking at options like carbon nanotubes that are one atom thick and promise to improve performance even more.
The high working voltage of lithium ion batteries makes them useful in a wide range of portable devices. They also have a much lower self-discharge rate than nickel-based systems. This allows for simplification of device design and cost reductions. In addition, it is possible to charge them at low temperatures, which helps reduce permanent capacity loss over long storage periods. This makes them a good choice for things like power tools and electric vehicles, as well as home and office appliances.
Discharge
Lithium-ion batteries require little maintenance compared to nickel-cadmium or nickel-metal hydride cells. They don’t have a memory effect and don’t need to be cycled regularly, and their self-discharge rate is less than half that of nickel-cadmium batteries. They also produce less greenhouse gas when disposed of.
During discharge, an electrical current from the external power source causes electrons to flow from the cathode through the electrolyte toward the positive terminal of the battery. The flow of electrons lowers the chemical potential of the battery, causing lithium ions to migrate from the anode to the cathode and then through the electrolyte toward the negative electrode where they’re embedded in the porous electrolyte surface.
Discharging also reduces the capacity of a lithium-ion battery, which may be an issue in EVs where fast charging is a requirement for long drive times. If a cell is frequently discharged and recharged, the SEI grows thicker and degrades cycling capacity by blocking ionic movement in the anode and electrolyte.
To avoid this, most lithium-ion battery packs include a protection circuit that limits peak voltage Portable lifepo4 battery during charge and prevents the cell from reaching a too low state of charge during discharge. The circuit consists of IC’s and MOSFET’s that regulate current, detect short circuits, reverse polarity, temperature, and cell imbalances in multi-cell packs. The protection circuit is a key element in the safety of lithium-ion batteries and helps ensure they don’t experience overcharging, over-discharging, or internal short circuits that could lead to fire.
Safety
Lithium-ion batteries are used in electronic devices such as cellphones, laptop computers and tablets, e-scooters and other devices that use plug-in charging. When these batteries are improperly used, stored or charged, they can overheat, catch fire and explode. Fire agencies across the country continue to respond to battery-related fires. These battery fires can occur in the devices that contain them, at the battery recycling and disposal facilities or during transport and processing of discarded batteries by municipal waste and recycling services.
A major cause of lithium-ion battery fires is contamination of the cell’s electrolyte by microscopic metallic particles that get into contact with other battery components. This can trigger the battery’s internal short circuit and thermal runaway mode, which is essentially an uncontrolled, self-perpetuating cycle of disintegration and explosions. Attempts to eliminate this risk by changing the battery’s design have been unsuccessful.
Other safety hazards are caused by improper use, charging and storage. Attempting to disassemble a lithium-ion battery can damage the internal circuitry and expose the flammable electrolyte. The use of non-approved chargers can overcharge the battery, causing overheating and potentially resulting in the generation of sparks and/or explosive venting. Batteries that are stored at high temperatures degrade more rapidly, resulting in reduced cycling capacity. In addition, long-term storage at higher cell voltages may result in lithium plating on the anode current collectors, which also reduces capacity. To avoid this, battery cells should be discharged to 40% SoC periodically to prevent irreversible degradation.