True rapid charging takes more than just better cells

A question we get a lot about our 15-min EV charging technology is, “What happens when Chinese manufacturers make faster cells?” i.e. great if we can charge batteries 0-100% in 15 minutes flat today, but new cells be able to do that without our tech?

They’re already starting to roll out—companies have announced 5C and 6C cells in recent months. And that’s actually great for us.

Firstly, there’s a lot of misconceptions about how long it takes to charge a battery with a certain C-rating. Cells or batteries are marketed as being rated for 4C/5C/6C to show their maximum charging speed.?

The simple explanation for this number thrown about in EV forums and blogs is that 1C means the battery can charge in 1 hour, 2C means 30 minutes (1/2 hour) and 4C means 15 minutes (1/4 hour). 1 hour divided by the C-rate. That’s not entirely right.

A 5C rated battery takes 35 mins to charge fully—not 12 mins.

This is because when we talk about C-rates and charging, we’re really talking about how much current a battery can take in at a time (amps, A), relative to how much charge is stored (ampere-hours, Ah). Like this ??

400 amps of current sounds like it should charge a 100 Ah battery in just 15 minutes. But for a battery rated for 4C or 5C, that’s usually the maximum current it can accept. In practice, that peak current can’t be sustained for a meaningful period, even harder in real world conditions (cell ageing, temp, etc). Which we saw in the 5C battery charging graph.

That’s where we come in.

A cell is basically a can of chemicals. Fairly “dumb”. It will behave however you make it behave. Today the industry depends on the cell chemistry to manage itself—this is fairly limiting. A CC-CV charge profile basically provides a fixed amount of current (CC) for X minutes/hours and then in CV (constant voltage mode) just oversaturates the cell until the cell has had enough. Basically you apply constant voltage across the cell tabs and wait for the cell to get to full absorption and saturation (where current decays down) and then you switch off charging.

So basically you let the cell decide how much to eat. But remember—cells are dumb and this kind of charging has limitations on how fast you can charge.

Our approach is fundamentally different—through active management (BMS + software) we figure out how to sustain peak performance throughout while taking strategic breaks. Our system decides how to quick feed cells without damaging them. That along with our thermal management allows us to push peak performance for longer durations on regular cells. Result: 0-100% in 15 mins. And we’re doing this on cells with 1C rating.

We believe material science alone is limiting. Everything in life has gotten smart (engines, to watches, to heart monitoring)—why not energy? Even with charging and batteries, electronics and software will be the differentiator.?

The cell is just one part of what you need to make rapid charging work. Everything else is equally important (I would argue even more so). Remember cells are a commodity and everyone will have access to the same cell (give or take). So the differentiation will come long-term in energy management. How to extract maximum life and performance. Counterintuitively that has nothing to do with the cell. But everything with energy management.?

If we can get faster-charging cells, we’re the happiest. We’re quite excited to push boundaries even further when core material structures improve. That multiplied with our core tech will amplify performance. To a world with 5 minute charging.?

And as charge times on average keep coming down (i.e. a lot more energy being transferred in much less time) the overall chaos is more. Which means everything about the BMS, the software, control loops, connector, charger and network need to be rethought and redesigned for a rapid charging future.