Lithium-ion batteries are typically charged using constant current that is applied until the cell voltage reaches about 4.2 V, at which time, charging continues at a constant voltage until the full battery capacity is attained. This process is slow, typically requiring 2-4 h. Empirically selected pulse-charging sequences have been shown to provide enhanced charging; however, no model exists to explain and optimize the pulse-charging protocols. Modeling the lithium diffusion into a homogeneous intercalant layer indicates that the lithium concentration reaches saturation at the graphite/electrolyte interface after about 1 h under conventional constant current charging, mandating the shift to the lower rate constant voltage charging. It is shown here that charging the lithium battery using non-dc waveforms with properly selected parameters may circumvent this lithium saturation, enabling charging at significantly higher rates. A nonlinearly decreasing current density profile which conforms to the mass transfer coefficient variation was shown to provide complete charging in less than 3 4 of an hour, faster than any other pulse-charging profile studied.Lithium is particularly advantageous as the negative electrode material in batteries because of its very negative standard potential ͑−3.04 V͒, low specific gravity, and wide availability. However, lithium metal cannot be safely used in rechargeable batteries because of dendritic deposition, 1 which may lead to shorting and as a consequence to thermal runaway. 2 Furthermore, the highly active lithium reacts with the electrolyte. Nonlevel deposition accompanied by reaction with the electrolyte often leads to electrically isolated regions containing the active material ͑lithium͒ resulting in lower capacity. To overcome this, lithium is being intercalated into a carbon or graphite matrix on the negative electrode, 3 still maintaining a high voltage ͑0.2 to 0.4 V vs Li/Li + ͒, high capacity ͑ϳ372 Ah/Kg of graphite mass͒, and high energy density ͑ϳ150 Wh/Kg͒.Conventional lithium-ion battery charging is typically done in two stages, as shown in Fig. 1. The battery is first charged at a constant current until the cell voltage reaches the upper voltage limit of 4.1 to 4.2 V. This is followed by a second, constant voltage charging stage until the current drops to about 3% of its rated value. The charging time for the first stage ͑constant current͒ is typically 1 h, during which time about 88% of the battery capacity is charged. The second stage ͑constant voltage͒ takes about 1.5 to 2 h, extending significantly the charging time of the battery. 4 Charging the battery at higher voltages ͑i.e., exceeding ϳ4.2 V͒ or at higher current densities typically leads to decreased cycle life 5 and rapid buildup of internal resistance, probably due to excessive buildup of the film forming at the solid electrolyte interface ͑SEI͒. 6-9 The underlying reason for these phenomena is the formation of metallic lithium at the electrode-electrolyte interface. This buildup is due to imbalance between t...

The application of periodic current or potential pulses in electrochemical systems has attracted much attention [1-4], principally with the objective of controlling the concentration of the electroactive species at the electrode/electrolyte interphase.

An attenuated total reflectance (ATR) infrared (IR) cell was designed using a boron-doped silicon wafer as the optically transparent electrode to simultaneously perform ATR-IR spectroscopic and electrochemical impedance measurements. The degradation of industrial lubricants was investigated by monitoring the near-surface concentration of hydrocarbons, detergents and anti-wear additives and the formation of degradation products, while polarizing the cell using electrochemical impedance spectroscopy (EIS). The detergent and the anti-wear agent concentration on and near the silicon surface, based on the IR spectra, and the sum of bulk solution and charge transfer resistance, based on the impedance spectra, were all at a maximum for 30 h drain oil, and then decreased for later drain oils. These results agree with other independent measurements, such as oil viscosity, total acid number (TAN), and total base number (TBN) to indicate that the lubricant is significantly degraded after 30 h in the engine test. These data demonstrate the potential use of the ATR silicon-based electrochemical cell as a monitoring device for lubricant degradation, and as an effective analytical tool capable of studying interfacial kinetics, surface interactions of the additives, and performance of silicon-based spectroelectrochemical devices.

A sub-atmospheric pressure nickel hydrogen (Ni-H2) battery with metal hydride for hydrogen storage is developed for implantable neuroprosthetic devices. Pressure variations during charge and discharge of the cell are analyzed at different states of charge and are found to follow the desorption curve of the pressure composition isotherm (PCI) of the metal hydride. The measured pressure agreed well with the calculated theoretical pressure based on the PCI and is used to predict the state of charge of the battery. Hydrogen equilibration with the metal hydride during charge/discharge cycling is fast when the pressure is in the range from 8 to 13 psia and slower in the range from 6 to 8 psia. The time constant for the slower hydrogen equilibration, 1.37h, is similar to the time constant for oxygen recombination and therefore pressure changes due to different mechanisms are difficult to estimate. The self-discharge rate of the cell with metal hydride is two times lower in comparison to the cell with gaseous hydrogen storage alone and is a result of the lower pressure in the cell when the metal hydride is used.