Li-ion Cell Charging Time Cut

Philips Research has found a way to cut charging time in lithium-ion cells without compromising cycle life.

Following research at its Eindhoven labs, Professor Peter Notten and his team have added a high-current initial charge to the standard CC CV scheme to achieve 60% charge from empty in 10 minutes and almost complete charge in 20 minutes with no significant cycle-life deterioration. Conventional techniques achieve under 40% in 20 minutes, claims the labs. Adding an initial CV phase cuts charge time.

Boostcharging’, as Notten calls it, can only be applied to empty cells and springs from experiments with, and modeling of, unlimited-current constant voltage charging, which can achieve 30% shorter charge time and a very fast initial fill compared with CC CV charging, at the expense of reduced cycle life from 300 to 220 cycles (to 20% capacity lost) for the 18500-size cells.

When currents are above normal, cell damage increases with level of charge. “Our experience is, up to 50% of charge, it’s not a problem,” said Notten.

By applying 4.3V with no current limit to an empty cell, up to 8A is forced in. Stopping this unlimited-current boost after five minutes puts around 30% charge in, but avoids cell damage. It is this head start, followed by a standard CC CV scheme, which cuts charge time.

Li-ion cells are conventionally charged by a constant-current constant-voltage scheme, or ‘CC CV’.

This consists of applying a constant current, usually equal to the capacity in Amp-hours (known as the 1C rate, for example 2A for a 2Ah cell) until the cell voltage reaches 4.1V or 4.2V for some graphite electrode cells.

This is followed by a constant voltage charge at that voltage, until charge is terminated when current drops to C/10 or a similar figure.

Both phases last about the same time and the whole procedure lasts between one and a half and two hours.

Some ‘fast chargers’ terminate charge at the end of the CC phase, but only achieve around 70 %charge. Other methods achieve 100% fill, but cut cell life.