Batteries

Batteries are devices that store energy to later be converted into electricity using chemical reactions. During discharge of a battery, the anode undergoes an oxidation reaction, which produces electrons, and the cathode undergoes a reduction reaction, which absorbs electrons. These processes, when organized in a device with an electrolyte and separator, produce electric current. Because batteries are so commonly used in all aspects of modern life, many types have been developed using a wide range of materials.

TYPES AND MATERIALS

  • Zinc-Carbon Batteries use zinc metal as the anode and magnesium dioxide as the cathode. Common electrolytes are ammonium chloride and zinc chloride. This type of battery is considered a “dry cell” because the electrolyte has the consistency of a paste, which cannot flow or leak in the manner of liquid electrolytes. These batteries are often designed with a zinc anode as the outer container and an inner graphite rod mixed with magnesium oxide powder for the cathode. Paper separators and steel casings are also typical.
  • Alkaline Batteries use zinc powder as the anode and manganese dioxide as the cathode. The electrolyte, potassium hydroxide, is an alkaline solution that has the potential to cause health and safety issues if this “wet cell” battery leaks. However, this type of battery exhibits high energy density. The cell construction is typically similar to zinc-carbon batteries, using a cylindrical structure with a steel casing. Common separators include polymer and cellulose films.
  • Lead-Acid Batteries, unlike most zinc-carbon and alkaline batteries, are rechargeable. The anode is lead metal and the cathode is lead oxide with sulfuric acid for the electrolyte. Antimony and calcium are sometimes alloyed with the electrodes to increase mechanical stability.

These electrodes are often structured as porous grids, which are then filled with an electrolyte paste of sulfuric acid mixed with lead powder. The paste can also contain a number of materials such as carbon black, barium sulfate, lignosulfonate, and sulfonated naphthalene. These promote the electrochemical reaction in the cell and prevent short circuiting.

Rubber, PVC, polyethylene, or cellulose can be chosen for a separator and the paste-filled lead plates will then be stacked. This type of battery is relatively easy and inexpensive to make, leading to its popularity despite drawbacks of low energy density.

  • Lithium-ion Batteries typically use graphite as the anode and lithium cobalt oxide as the cathode. Electrolytes consist of lithium salts such as LiPF6 or LiClO4 dispersed in organic solvents like ethylene carbonate or diethyl carbonate. Common separators include polypropylene and polyethylene films. These battery components can be arranged into cylinders, pouches, or prisms.

These batteries are also rechargeable, as lithium ions can intercalate back and forth between the layered structures of the electrodes. As the ions move from anode to the cathode, the battery discharges and electrons flow, creating electricity to power a device. Due to their high energy density and ease of charge/discharge, lithium-ion batteries have become widely used and increasingly popular to study.

Solid State Batteries have gained tremendous attention in the past few decades due to their increased safety and mechanical properties. By using a solid-state electrolyte along with two solid electrodes, this type of battery eliminates the danger of flammable liquid leakage. These batteries also have the potential to withstand extreme temperature changes which would otherwise cause liquid electrolytes to freeze or boil.

Although solid-state batteries remove the need for a separator, they also require careful attention to ionic transport across solid-solid interfaces. Many ceramic, polymer, and hybrid materials have been explored for the design of solid-state battery electrolytes. Some of these have achieved ionic conductivities comparable to liquid electrolytes and are beginning to appear in battery production, although liquid electrolytes remain the standard.

APPLICATIONS

Batteries are essential to technology in today’s world. Besides the mountains of disposable batteries each household uses for small electronics and everyday living, lead-acid batteries start our cars and provide emergency power supply. Lithium-ion battery usage has had the most rapid increase recently as laptops, cell phones, and other portable electronics have become central to modern culture.

References

  1. http://storage4.eu/2013/03/rechargeable-battery-diagram-convention/
  2. http://www.brighthubengineering.com/marine-engines-machinery/49635-batteries-used-on-ships/
  3. Thackeray, M.; Wolverton, C.; Isaacs,E. Energy Environ. Sci., 2012, 5, 7854-7863