Published on January 28th, 2019 | by Kyle Field0
Tesla Model 3 Battery Pack & Battery Cell Teardown Highlights Performance Improvements
January 28th, 2019 by Kyle Field
Electric vehicle expert Jack Rickard recently took to the Tesla Model 3 battery pack with his unique combination of “stoic heroism” and battery know-how, in order to shed some light on the battery setup in the Tesla Model 3. Why heroism? Jack tore down a nearly fully charged 2170 battery, defying battery handling best practices and common sense, for your benefit. But I digress.
The explainer (which lasts 2 hours) starts with a discussion about the Tesla Model 3 battery pack design and how it deviates from the pack design of the Tesla Model S and X. The Tesla Model 3 battery pack represents a bottom-up redesign of the battery pack, starting first and foremost with the battery cells used in the pack. With the design of its early vehicles, Tesla was not a big enough player in the battery market to be able to design the ideal battery cell and instead used the next best thing — standard 18650 lithium-ion batteries.
The good thing about 18650 batteries was that these were commodity lithium-ion battery cells and allowed Tesla to purchase reliable cells from its battery supplier, Panasonic, at the scale it needed to build high volumes of the Model S and X. Tesla’s aspirations for Model 3 production volumes changed all of that and led to the development of a cylindrical battery that represented the ideal balance between surface area for cooling, the amount of energy stored in a given volume, and price. The result was the 2170 lithium-ion cell, which stretched the length of the cell from 65 mm to 70 mm and increased the diameter of the cell from 18 mm to 21 mm.
Panasonic’s battery cell production lines in Tesla’s Gigafactory in Sparks, Nevada, produce the 2170 cells exclusively. They are then fed directly into battery packs for the Tesla Model 3.
Back to Jack’s teardown of the Model 3: Jack noted that Tesla changed the cooling design for the Model 3. The Model S and X used a serpentine cooling system that routed cooling fluids through the battery pack, but in the Model 3, Tesla switched to a manifold-based system that runs dedicated cooling channels between each row of battery cells. The new design allows for better cooling of the cells in the Model 3 compared to the packs in Tesla’s other vehicles.
The battery cells in the Tesla Model 3 battery pack are sealed together with a unique epoxy that makes removing, replacing, or reusing individual cells much more difficult. Jack opines that the plastic between the cells is there to pad the cells, as a structural support which also serves to keep them from rattling around in the pack. As with other Tesla Model 3 battery pack teardowns we’ve seen, he also said that the stuff is extremely difficult to remove and put it in the same category as the universal fix-all epoxy JB Weld.
That didn’t stop Jack and he moved straight on into tearing down a battery cell — a nearly fully charged one at that. Jack proceeded to unroll the “jelly roll” of the cell and walked through some very interesting details about the anode and cathode from the 2170 cell, and how Tesla has improved the battery from the 18650s.
Notably, Jack details how charging and discharging the battery is not a chemical reaction, but rather, a flow of electrons from the cathode material to the anode material and back (as the battery is charged and discharged).
First and foremost in that improvement, Tesla was able to cram a significantly larger surface area of battery material in the 2170 compared to the 18650. Surface area is interesting and all, but in practical terms, the increase in internal battery surface in the 2170 cells combined with the improved design of the Tesla Model 3 pack translates into an increase in the amount of energy stored in the same volume, and at a lower weight to boot. Check out the tale of the tape:
Model 3 2170 Cell:
- Weight: 70 grams
- Volume: 970 mm3
- Capacity: 4.8Ah / 17.3 Wh
- Density: 247 Wh/kg
Model S/X 18650 Cell:
- Weight: 45 grams
- Volume: 660 mm3
- Capacity: 3.0 Ah / 10.8 Wh
- Density: 240 Wh/kg
It’s clear right off the bat that moving to the slightly larger exterior dimensions results in a surge in interior volume, as the cell increases nearly 50% in volume. Combined with improvements in the chemistry, that translates to an overall storage capacity improvement of more than 50%. Density at the cellular level also improves slightly, from 240 Wh/kg to 247 Wh/kg, according to Jack.
His analysis found that the improvements Tesla made with Model 3’s battery were not only made at the cellular level, but even more impressively at the pack level. The improved design of the Model 3 pack translates to an improved energy density at the pack level, from 126.7 Wh/kg in the Model S to 159.5 Wh/kg in the Model 3.
These improvements demonstrate that Tesla continues to push the envelope with pack design and vehicle design as its vehicles continue to push the limits of what is possible in an electric vehicle. In practical terms, Tesla’s innovations in battery cell and pack design continue to enable it to lead the industry in range for the price and performance.
Jack dove into the constituents of Tesla’s batteries and expressed his opinion that graphite was the critical material to watch, as sourcing for the other components has largely been resolved for Tesla. Tesla continues to work to reduce the amount of cobalt in its batteries, and with its sourcing in Canada this is largely a non-issue from a supply chain standpoint. Having said that, the toxicity of cobalt is a real issue and is one of the main reasons Tesla plans to phase out the use of cobalt in its batteries over the next few years.
The change in form factor of its battery cells isn’t all good news, though, according to Jack, as the new chemistry results in a flammability temperature of just 150–180°F due to the higher energy density of its cells — compared to a flammability point of 350°F with the 18650 cells. The increased risk of flammability of the new cell design is likely why Tesla chose to upgrade the cooling system of the Model 3 pack, mitigating the increased risk at the cellular level.
Efficiencies in the pack design for the Model 3 translate to manufacturing as well, as Jack noted that Tesla has made significant improvements in the time required to assemble a Model 3 battery pack since kicking off production of the car back in June 2017. The battery pack initially required 7 hours to assemble and has since been improved to the point that today it only takes 17 minutes to assemble a battery pack. Those improvements do not translate to improvements in vehicle efficiency. However, they show that Tesla has made progress in manufacturing to reach the price point targeted for the Model 3 when it was first unveiled — or nearly so.
Thanks to the folks over at Reddit, I took the suggestion to listen to the talk at 1.75× and it worked out great. Jack takes his time unpacking the vast store of details filed away in his brain as he works, which tends to be on the slower side for most listeners. Have a look at the full 2 hour (!!) video above for the full details from his unpacking of the Tesla Model 3 battery pack.