Advances in Lithium and Nickel-Metal Hydride Battery Performance
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of large lithium batteries has been the Standard 14650 cylindrical lithium cell. Its diameter is 14 mm and its height is 65 mm. This cell is in mass production for cellular telephones and laptop Com puters. Its observed deficiencies for other uses are ■ Low power Output. Computers and telephones don't need much power, so the current flowing through the thin electrodes doesn't create much voltage drop. ■ Narrow operating temperature. Below 0°C, Output drops severely. ■ Short life w h e n subjected to deep discharges. ■ Irreversible capacity loss under some conditions. ■ Sensitivity to overcharge. A cell in a series-connected string can be damaged if it reaches füll charge and then is overcharged before the other cells reach füll Charge. A m o n g the options for i m p r o v i n g lithium cells are changing the processing and composition of electrolytes. Armand evaluated dozens of new salts for polymer electrolytes. His basis of merit included conductivity, phase diagrams, concentration gradients, solid-electrolyteinterphase (SEI) film buildup and the film's properties, plus corrosion and stability Windows. Armand's conclusions were ■ The solid-polymer-electrolyte battery has a nonunique chemistry, in contrast to conventional nickel-cadmium and lithium-ion chemistries. ■ "Neoclassical" salts, like LiTFSl (trifluoromethanesulfonylimide), perfectly meet the requirements of specific power, energy, and safety. ■ Lithium-ion Systems are still in search of a replacement for LiPF6, for improved safety and reduced aluminum corrosion. ■ A whole panoply of new salts, based on different principles and chemistries, has been found.
Lithium Batteries: 1999 Status
Solid-Gel Electrolytes
A r m a n d from t h e U n i v e r s i t e de Montreal described today's Status of l i t h i u m batteries at the 1999 Second Hawaii Battery Conference. 1 Lithium batteries have surpassed other batteries in energy content as measured by watthours per kilogram of battery weight or watt-hours per liter of battery volume (Figure 1). He also described an automated process for manufacturing lithium cells (Figure 2). Inputs in the process are lithium salts, polymers, solvents, and lithium ingots. The Outputs are cells that are ready for spraying of metal contacts. The starting point for the development
Today's high-production lithium-ion cells use a liquid-organic electrolyte and a Polyethylene microporous electronseparating membrane. An alternative cell has a dry-polymer electrolyte, but the cell needs to withstand temperatures of 60-80°C, so that it can be used as a power source for electric vehicies. A sec ond alternative lithium-ion cell, de scribed by Huang, uses a gel-polymer electrolyte (GPE).2 These cells presently require three- to fourfold excess lithium, and have a cycle life of fewer t h a n 100 charges/discharges. Huang showed that GPE lithium-ion
Advances in Lithium and Nickel-Metal Hydride Battery Performance* Henry Oman Traditional batteries stored energy in thick plates made f rom heavy metals like lead, nickel, and zinc. They deli
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