Key requirements for a vehicle battery include:
- Excellent power density
- Longevity with minimal degradation
- Works well at all encountered temperatures
- Ability to quickly charge without reducing battery life
- Handle harsh environments – high vibration, shock & humidity
- Avoidance of materials in limited supply
- Reproducibility – each cell should produce the same voltage and current in high volume manufacturing
It’s easy to understand that most battery breakthroughs improve one item on this list. What is often unstated are the other criteria that are not met. A cell that has 10 times the power density of existing cells, but only lasts for 5 charge cycles is not practical for a vehicle.
Tesla has succeeded in offering one of the fastest charging practical systems to date, offering up to 250 kWh charging.
While faster charging is a desirable feature, even if a new cell can be charged at a faster rate, as a practical matter, this causes a whole set of other issues that are often ignored at first glance.
Battery Temperature – Cells generate heat while charging. If the cell gets too hot, it can be damaged or worse, may catastrophically fail. Vehicle manufacturers solve this by cooling the pack while charging. To double the maximum charging speed, the car’s battery cooling system must handle double the heat load in worst-case conditions. This means doubling the radiator size, having a larger HVAC compressor, adding more fans and other components.
Internal HV Components – More power requires thicker wires and larger contactors. This increases costs, requires some additional space and adds to the vehicle weight.
Connector – The connector must get larger to accommodate either more current or higher insulation if using higher voltages.
Cable – To supply more charging power requires a larger diameter cable. If the same voltages are used in a Tesla, then the wire size must be increased to handle the added current. If an entirely new high voltage design, such as 800v as suggested by a Porsche prototype, then much thicker insulation is needed. In either case, the cable gets much thicker and heavier. At some point, it will be beyond the ability of owners to lift and connect!
Tesla and its battery partner, Panasonic, continue to do basic cell research. Tesla is also funding the battery research group at Dalhousie University, headed up by the renowned battery researcher, Jeff Dahn.
Tesla maintains a significant group of engineers and researchers at its Palo Alto headquarters. Since Tesla is one of the largest consumers of Lithium Batteries in the world, many new technologies are brought to them first, where they can evaluate new designs.
In summer 2019, Tesla started rolling out the new version 3 Supercharger, with up to 250 kWh charging power. Currently, only the Tesla Model 3 can charge at this rate. The Model S and X made in Spring 2019 get 200 kW charging, and others up to 150 kW.
For more on Tesla’s Supercharging, check out our Supercharger Superguide.
Kurt Kelty, Tesla’s Directory of Battery Technology gave a nice talk on Battery design and Gigafactory production in March 2017 at the International Battery Seminar. You can watch the video here (41 minutes):