How is it possible? Every Li battery manufacturer under the sun wants to create fast-chargeable batteries, so it's a hot research topic.
There is no standard definition for high-drain-rate cells, but basic design guidelines dictate that standard cobalt-oxide-based cells can support a 2-C or maybe a 3-C rate, continuous current. High-drain cells based on cobalt-oxide support roughly double those currents, but only for seconds. The new high-drain cells support 20 C continuous.
Given that a high-discharge-rate cell can support high-current discharges over a very short period, in theory, a battery charger could fully charge that cell in an equally short amount of time. But to take advantage of this possibility, the conventional battery-charger design must be modified. For the sake of simplicity, these changes can be illustrated with the example of a single-bay charger supporting a single-cell battery pack.
Cell Characteristics
On the surface, fast-charging Li-ion cells seem straightforward. It seems that one could simply increase the current delivered during the constant-current phase of the charge cycle. However, as shown in the table, the overall charge time is not significantly decreased when the current is increased from 1 C to higher rates.
The difference in charge time with a 2-C rate versus a 3-C rate is only about one minute, regardless of the cell vendor. Essentially, the cells will just reach the upper-voltage cutoff faster, but the time in the constant-voltage charge mode will be much longer. Obviously, this increases the potential for damage to the battery due to overvoltage. The resistance of traditional Li-ion cells will cause them to heat up more during faster charges, so the cells will begin to break down. Fast charging significantly reduces the battery life cycle.
Designing a cell that can accommodate high-discharge and high-charge rates is an effort to reduce the path length and resistance for the transport of ions and electrons. Fig. 1 shows a cross section of a typical Li-ion cylindrical cell. Changes start with the battery's active materials. Traditional Li-ion cells are based on a lithium-cobalt-oxide (LiCoO2) cathode compound. In this material, Li-ions, which diffuse in and out of the cathode, can only be inserted through 2-D paths in the crystal structure.
The path length can be shortened by changing the physical morphology of the battery's active material or changing the material's chemical structure, or by doing both. One approach to addressing the problem physically is to decrease the particle size of the materials to as small as nano-scale. New chemistries such as manganese spinel (LiMn2O4) offer 3-D pathways for ion insertion.
In addition to these changes, the resistance of the cells must be lowered by using thin materials, increasing the amount of current collectors, and increasing the electrolyte concentration and reducing its viscosity with solvents. Many of these changes suggest that Li-polymer cells, which can be very thin, lend themselves for use in designing for high rates.
Li-ion cell manufacturers have been experimenting with their formulations in order to implement designs specific to high-rate applications. A few manufacturers have come up with solutions. E-One Moli Energy introduced a high-discharge-rate cell based on a manganese-spinel cathode material for cordless power tools.
Best Answer
LiIon is usually charged at constant current until a max allowed voltage is reached and then is held at that voltage while current tails off under "control" of chemistry of battery until Ichg = k% of Imax where k% is chosen according to longevity or max energy concerns.50% or 25% of Imax gives longer life. 10% or 5% tail gives max capacity but lower life.
Lowering Vpedesatl by 0.1V greatly assists battery life.
Discharging to higher cutoff voltage aids cycle life.
LiIon also has calendar life and starts self destructing from day one so a lightly used battery still dies.
Best cycle life is achieved by stopping charge when Vpedestal is reached and systen changes from CC to Cv. By monitoring voltage this point can be observed. You could even do a "dumb" system that simply watched delta Vbat and declared constant V when delta fell to zero. Only slightly more than a comparator and an RC delay in one input would achieve that.(While Vin is ramping a delayed vin is lower. When Vin pedestals the delayed Vin almost catches up. An offset voltage is needed to allow comparator towork).
LiIon cells mechanically flex the cell as metallic Lithium is "plated" in and out of the cell*. Cycle life is in large part due to battery beating itself to death mechanically.(This is why LiFePO4 lasts much longer and has lower capacity - the material is held in an Olivine matrix that maintains constant shape as active material is moved in/out BUT it takes up some space. )
Charge to CV level as often and as soon as possible.
If charging all the way their "disconnect message" is a sign of bad ethos. They are probably trying to minimise the risk of fire without telling you.
For longest storage life (as opposed to long life in regular use) storing at a lower voltage than Vmax is in order. Probably at about 3.6 V and only about 30% state of charge. The various Mars Rovers use LiIon batteries and have a design life of about 8000 cycles - but charge to about 3.6 - 3.7 V maximum.
8000 / 365(~=) ~= 22 Terran years.