Battery technology is continually being developed to enable higher energy density and greater efficiency, thereby permitting the use of batteries as power sources for more applications. For example, there is currently a great drive toward the use of batteries for electric vehicle propulsion. Current battery technologies, such as lead-acid and lithium ion batteries, have a lower gravimetric energy density (e.g., expressed as watt-hours per kilogram; Wh/kg) than is desired for use in extended range electric vehicles. Other applications for battery technology may also benefit from battery technologies that provide a higher energy density.
A rechargeable lithium-oxygen (Li—O2) battery can store, theoretically, about 5-10 times more energy than current lithium ion batteries. The high energy density makes the Li—O2 battery very attractive as an emerging energy storage system for a wide range of applications, including the propulsion of electric vehicles. A Li—O2 battery is composed of a Li anode, an air cathode, where oxygen is accessed from the external environment, and an electrolyte containing Li salts, which is in contact with both the anode and cathode. In some examples, oxygen may be provided from air, in which case, the battery may be referred to as a Li-air battery.
Some configurations of Li—O2 batteries employ an aprotic, nonaqueous electrolyte to impart ionic conductivity between a Li-bearing anode and a porous cathode. The porous nature of the cathode allows oxygen harvested from air to diffuse into the battery and react electrochemically with Li ions. The electrolyte may include a lithium salt (e.g., trifluoromethanesulfonimide, triflate, perchlorate, etc.) dissolved in a liquid organic solvent (e.g., an ether, an amide, a carbonate, etc.).
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