Lithium-ion batteries power the lives of millions of people each day. From laptops and cell phones to hybrids, electric cars, and golf cart, these rechargeable batteries are also making an impact powering material handling and airport ground support equipment due to its light weight, high energy density, and ability to recharge. The technology behind lithium-ion batteries make them a great choice because of their distinct advantages and environmentally-friendly benefits.
So how exactly do lithium-ion batteries work? And, what makes them so popular in so many applications?
THE BASICS
A battery is made up of an anode, cathode, separator, electrolyte, and two current collectors (positive and negative). Electrodes are the two battery ends. One is the anode and the other is the cathode. The anode stores the lithium and is typically made from carbon, while the cathode also stores the lithium and is made from a chemical compound that is a metal oxide. The separator blocks the flow of negative and positive electrons inside the battery but allows for ions to pass through. The electrolyte carries positively charged lithium ions from the anode to the cathode and vice versa through the separator. The movement of the lithium ions creates free electrons in the anode which creates a charge at the positive current collector. The electrical current then flows from the current collector through a device being powered (cell phone, computer, etc.) to the negative current collector.
THE BATTERY PACK
The battery pack, which holds the lithium-ion cells, operates much like a computer. It contains the following: at least one temperature sensor to monitor the battery’s temperature. A voltage converter and regulator circuit that focuses on keeping the voltage and current at safe levels. A Euro connector, which allows power and information to move in and out of the battery pack. The cell tap, which oversees the cells’ voltages in the battery pack. A battery monitoring system, a small computer that oversees the whole battery and ensures safety to the user.
ENERGY DENSITY VS. POWER DENSITY
The two most common concepts associated with batteries are energy density and power density. Energy density is measured in watt-hours per kilogram (Wh/kg) and is the amount of energy the battery can store with respect to its mass. Power density is measured in watts per kilogram (W/kg) and is the amount of power that can be generated by the battery with respect to its mass. To draw a clearer picture, think of draining a pool. Energy density is similar to the size of the pool, while power density is comparable to draining the pool as quickly as possible.
BATTERY MANAGEMENT SYSTEM (BMS)
The management system plays an integral role in making sure the battery cell works at its highest levels. It also impacts how the battery functions, offering several protections and features.
The BMS maintains cell temperatures in the ideal operating range to prevent overheating or freezing. The BMS monitors currents and voltage to keep both at safe levels. Dendrites begin to form in the cell if voltages drop too low which can short the cell, so it is important that a lithium-ion battery pack has a system to monitor this.There is no “memory” built into the pack, so partial discharges do not hurt the battery. Lithium-ion batteries can charge and discharge during the times that are most convenient for equipment operators. Built-in controllers prevent overcharging, in order to prevent from forming that can cause significant damage to lithium-ion batteries. Cell balancing is monitored so that equalization charges are never needed. Because lithium-ion batteries do not need equalization charges, they do not release dangerous gasses. The battery management system also allows managers to track the battery health of their fleet through onboard computers that send vital data to through cloud-based services.