BACKGROUND: HISTORICAL ADVANCES IN BATTERY TECHNOLOGY
Advancements in rechargeable batteries have enabled the development of mobile electronic devices, from cordless phones, to laptops, to the mobile phone – which now as a ubiquitous smartphone is now essentially a handheld computer and communicator and a whole host of sensors. Previously, major battery capacity innovations have required a change in the chemistry of the battery, which necessitated whole ecosystem changes of manufacturing, power management ICs, charging electronics, and the device platforms in order to take advantage of the new battery chemistry. In the 1960-70’s, rechargeable batteries were based on NiCd chemistry, which enabled the growth of cordless phones. NiCd batteries were fairly heavy and also exhibited a “memory effect” which ultimately affected performance.
NiMH batteries started being used in the 1980’s, and had advantages of higher capacity and no “memory effect”. The new chemistry batteries required all new charging and management circuits. In the 1990’s, rechargeable batteries based on Li-ion chemistry came on the market enabled by the scientific work and innovations of Dr. John Goodenough. This was a more substantial change compared to the change from NiCd to NiMH because the fundamental voltage of the cell jumped from 1.2V to 3.7V for Li-ion batteries. Li-ion batteries had substantial increases in energy density over NiMH, (40% smaller and lighter) and could be recharged in any condition. Once again, all new charging and power management electronics had to be developed, as well as new battery manufacturing processes and factories. Li-ion batteries historically have shown an average of 3-5% improvement per year in energy density.