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Batteries

Devices that chemically store energy.
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Batteries convert chemical energy into electrical energy through the use of two electrodes, the cathode (positive terminal) and anode (negative terminal), and an electrolyte, which permits the transfer of ions between the two electrodes. In rechargeable batteries, electrical current acts to reverse the chemical reaction that happens during discharging.

Batteries have a long history: primitive batteries made of copper, iron, vinegar, and clay pots have been discovered in the Middle East that date to around 200 B.C. Modern electrochemical batteries date to 1799, when physicist Alessandro Volta stacked layers of zinc, copper, and brine-soaked paper or cloth to create a voltaic pile. In 1836, chemist John Frederick Daniell placed a copper plate at the bottom of a glass jar containing a copper sulfate solution. A zinc plate was suspended in the jar, with a zinc sulfate solution surrounding it by floating on the copper sulfate. This became the Daniell cell.

Lithium-ion is the dominant rechargeable battery chemistry used today, found in virtually every portable consumer device. Developed by John Goodenough, Rachid Yazami, and Akira Yoshino in the early 1980s and commercialized by Sony and Asahi Kasei in 1991, lithium-ion batteries replaced nickel-cadmium batteries and provide about twice the energy density.

There are a number of different compounds used for lithium-ion batteries, but a lithium cobalt oxide cathode and a carbon anode are the most common.

Lithium-ion batteries require a protection circuit to limit the peak voltage. They also suffer from instability and capacity degradation over long term use due to the formation of dendrites, thin metallic structures that form from the battery’s electrode. When dendrites grow to puncture the battery’s electrolyte, it can cause fires. Limiting dendrite growth is a major focus of battery research.

Another concern for lithium-ion batteries are the materials used to make them: both lithium and cobalt are often sourced from conflict regions, making supply unreliable.

Lithium-metal, lithium-oxygen, lithium-sulfur, and sulfur-ion batteries are among the many battery chemistries being researched as potential replacements for lithium-ion. While some of these promise greater capacity or lighter weight, they still have major problems to overcome, typically related to dendrite growth and instability.

For grid-scale storage, redox flow batteries are considered a possible contender. Rather than solid electrodes, these batteries can use large tanks filled with liquid electrolytes and allow energy storage in the range of kilowatt-hours to tens of megawatt-hours.