Lithium-Ion Batteries: Fundamentals and Safety

Rechargeable batteries with lithium metal on the anode can in principle provide extraordinarily high energy densities, but it was discovered in the mid-1980s that cycling such batteries produced unwanted dendrites on the anode. The inherent instability of lithium metal, especially during charging, shifted research to a nonmetallic platform using lithium ions (Li+). Li-ion batteries come in many varieties but differ most often in the cathode materials; common examples include lithium cobalt oxide (lithium cobaltate), lithium manganese oxide (also known as spinel or lithium manganate), lithium iron phosphate, as well as lithium nickel manganese cobalt (or NMC), and lithium nickel cobalt aluminum oxide (or NCA). Originally, coal-derived coke was used as the anode, but since 1997, most Li-ion manufacturers have shifted to graphite to attain a flatter discharge curve; graphite stores lithium ions well when the battery is charged and has long-term cycle stability. Although lower in specific energy than lithium-metal, Li-ion technology is safe, provided cell manufacturers and battery packers follow appropriate measures in keeping voltage and currents to secure levels. Li-ion is a low-maintenance battery type, an advantage many other chemistries cannot claim. The nominal cell voltage of 3.60 V can directly power cell phones and digital cameras, offering simplifications and economic efficiencies over multicell designs. Cost reduction, increase in specific energy, and the absence of toxic material have served to make Li-ion the universally accepted battery for portable applications, first in the consumer industry and now increasingly also in heavy industry, including electric powertrains for vehicles. Keywords: battery; electrode; electrolyte; graphite; lithium; lithium-ion; protection circuit; spinel; thermal runaway; titanate