Batteries

Batteries are devices that store chemical energy and convert it to electrical energy via electrochemical reactions. A typical battery consists of one or more electrochemical cells, each containing an anode, a cathode, an electrolyte, and a separator that prevents short circuits while allowing ion flow. Batteries are classified as primary (non-rechargeable) or secondary (rechargeable). Common chemistries include lead-acid (used in vehicles and backup power), nickel-based systems such as nickel-cadmium and nickel-metal hydride, lithium-based systems such as lithium-ion and lithium-polymer, alkaline manganese, zinc-carbon, and redox flow batteries for large-scale storage.

In operation, ions move between electrodes through the electrolyte while electrons travel through an external circuit, delivering power when the battery discharges and storing energy when it is charged. Performance is described by energy capacity (charged energy stored), energy density (capacity per mass or volume), power density (rate of delivering energy), cycle life (number of charge-discharge cycles), calendar life, and efficiency. Primary cells prioritize energy density and simplicity, while secondary cells emphasize cyclability and rechargeability.

Applications range from portable electronics and consumer devices to electric vehicles and stationary grid storage. Safety considerations include the risk of internal short circuits, overheating, flammability, and gas buildup; proper design, protective hardware, and management systems mitigate hazards. Batteries also present environmental concerns, such as mining impacts and end-of-life disposal; recycling and responsible collection programs aim to recover materials and reduce pollution.

Research focuses on increasing energy and power density, improving safety and charging speed, reducing cost and reliance on scarce materials, and developing solid-state and flow technologies. Advances include lithium metal and solid-state chemistries, cobalt-free chemistries, and enhanced recycling processes.