Lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy density per weight. Rechargeable batteries using lithium metal anodes (negative electrodes) are capable of providing both high voltage and excellent capacity, resulting in an extraordinary high energy density.
After much research on rechargeable lithium ion batteries during the 1980s, it was found that cycling causes changes on the lithium electrode. These transformations, which are part of normal wear and tear, reduce the thermal stability, causing potential thermal runaway conditions. When this occurs, the cell temperature quickly approaches the melting point of lithium, resulting in a violent reaction called "venting with flame". A large quantity of rechargeable lithium batteries sent to Japan had to be recalled in 1991 after a battery in a mobile phone released flaming gases and inflicted burns to a person's face.