Rapid Charging of Lithium-Ion Batteries Using Pulsed Currents

Abstract

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...

Linear Stability Analysis of Transient Electrodeposition in Charged Porous Media: Suppression of Dendritic Growth by Surface Conduction

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Optimal charging strategies in lithium-ion battery

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