Page - 155 - in Water, Energy, and Environment - A Primer

memory effect (removing the need to fully discharge the battery before recharging), can handle hundreds to thousands of charge–recharge cycles, and have good round-trip electrical efficiency. Li-ionbatteriesdohaveadownside: theyare sensitive toheat, can’t be fully discharged, are still costly (although costs are coming down rapidly), and battery cells with certain chemical formulations can occasionally burst into flame if damaged or otherwise overstressed. The term ‘lithium-ion’ refers not to a single chemistry but to a number of chemical combinations where lithium ions are transferred between the electrodes during the charge–discharge cycles. The lithium ions are derived from electrodematerials that contain lithium compounds, and different compounds present different cell voltages, energy densities, lifetime, and safety characteristics. Battery management systems are required – Li-ion batteries lack the ability to dissipate overcharge energy – and safety characteristics are a function of system design and control algorithms, regardless of battery cell chemistry. 9.2.1.5 Supercapacitors Supercapacitors, also a relatively new battery technology, store energy in electric fields created by stored electric charge. They fill a gap between ordinary capacitors and rechargeable batteries. Because the charge is stored physically, with no chemical or phase change occurring, the charge–discharge processes are fast andhighly reversible. They can be repeated over and over again, with virtually no limit, at high round-trip efficiency. Depending on the design, supercapacitors (also called ultracapacitors) canhave reasonably high energy densities and can deliver quick bursts of energy during peak power demands. Because of these characteristics they are now widely used as low-current power sources for computer memories, medical devices, and in cars, buses, trains, cranes and elevators, including energy recovery from Energystorage 155