Featured Gigafactory batteries might have a Prius application

Source: Next Big Future: Gigafactory batteries and factory productivity

The basis of the energy storage system of Tesla products are lithium-ion cells in the 18650 form factor. These cylindrical cells have a diameter of 18 mm and are 65 mm in length, a size used for the batteries of laptops. Cylindrical cells are generally less expensive (costing 190–200 dollars per kWh as of 2014) than large format cells whose active layers are stacked or folded (approximately 240–250 dollars per kWh).

The battery cells that will be produced at the Gigafactory are of a new form factor, larger than the 18650 cells used in the Model S and Model X automobiles. While the cells were originally expected to be at least 20 mm in diameter and 70 mm in length,revised specifications for the optimized form factor are 21 mm (0.83 in) by 70 mm (2.8 in). The new battery cells themselves will be bigger than the ones currently used (18650 to 20700), the battery packs will be smaller thanks to better packaging and cooling.​

Clever, sad to say, I'd thought they would have been making pouch cells. One excellent innovation is use of serial strings operating in parallel. With dedicated serial string managers working together at the parallel buss bars, a marginal string can be protected from thermal runaway and more robust than serial-only strings.
This might provide a path forward for Prius traction battery rebuild.

Back of the envelope:

• 14 cells * 3.7V = 51.8V :: modules
  • Interior 2 strings for capacity and battery management
• 51.8V * 4 modules = 207.2V :: Gen-2, Gen-3, and Gen-4
  
• 51.8V * 7 modules = 362.6V :: Gen-1

The Gen-1 version requires a resistor array and variable power supply to trick the existing battery controller to properly charge the battery. The 19 resistors are driven by a variable voltage power supply to keep the voltages and currents within safe range for the LiON modules.

Bob Wilson

 

I was looking at the voltages needed to match Prius pack voltages. There is a little more engineering to apply including power, packaging, and cooling. Back of the envelope suggests each module be 14 cells with at least 2 strings for reliability. However, I didn't include Si voltage drop, 1.2V.

Now I've done a lot of NHW11 testing its maximum currents are 50A/75A. So I'm pretty sure multiple strings can handle these values for the durations typically found.

Like most engineering projects, a set of successive designs to refine the approach and identify technical risks.

Bob Wilson