"Gee are they 400volt batteries like a Tesla."
No, they are referring there to the AC power supplying the charger.
"The thing that intrigues me is the 220v DC technology."
I'm assuming it is the charging supply to the battery, which will be different to the output voltage from it, and in principle could even be AC rather than DC. I'm not sure what they are using ATM, but DC can be used more efficiently than AC by the internal battery changing circuitry (less heat dissipation), and higher voltage means lower current handling requirements in the charging station, and charging connections to the battery. I'm pretty sure all charging stations provide a DC output to the batteries, so the improvement offered by the "220V DC technology" will be a higher voltage than previously. The battery will have to be compatible with existing VMT machines, so I'm picking it is still 60V output, and a drop-in substitute for the battery type currently used in the CPx, VS2 etc.
This should hopefully all become clearer after reading the discussion below.
"Do you know how they can fast charge without overheating the battery."
Batteries are lot different to what they used to be. Technically a battery is 2 or more cells connected in series. Back when we were kids, 12V lead-acid batteries were true batteries, being 6 lead-acid cells contained in a single assembly, and internally connected in series. However, the things we put into our torches and transistor radios were not batteries, but in fact single alkaline dry cells. They only constituted a battery once they were installed (2 or more in series).
So colloquially we have always incorrectly referred to single cells as batteries. Nowadays we have a further misnomer occurring, where EV batteries and grid level storage batteries are not batteries in the technical sense, but in fact complex battery systems. They consist of large series/parallel arrangements of cells complete with charging control, output current control, protection circuitry (over voltage, over current, over temperature, lightning protection etc), and cooling systems. All this circuitry needs it's own power supply, so these 'batteries' need to be 'turned on' (powered up from their own power supply - often a separate dedicated battery) before becoming available for use.
So getting to your question, the limiting factor in charging times of Li ion batteries is usually the current handling capacity of the circuitry (either the AC power supply, the charging station, or the internal charging circuitry in the battery). However, the ultimate maximum charge rate for an individual cell is determined by it's chemistry, physical construction, desired service life, and yes, heat dissipation. In a nutshell, how much current it can take without excessive damage. The charging time can be less than 20 minutes.
I think the half hour charge time of the new VMT battery (system) was probably determined by the maximum heat dissipation they could reasonably achieve. It would not surprise me if the fast charging stations have forced air cooling. The charging station and internal battery circuitry will have then been designed to handle the required current (considerably beefed up compared to the standard 60V/45Ahr battery). The "220V DC technology" probably helps in this regard, reducing the current requirement relative to a lower voltage, and increasing efficiency, but requiring higher voltage rated components in the charging station and internal charging circuitry of the battery.
This equation of higher voltage leading to lower current and higher efficiency (also lower weight) is a common theme running through the EV industry ATM. It is being made possible by advancements in high voltage semiconductor devices made from wide bandgap semiconductor materials such as GaN and SiC.
All IMO.
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