Electric car batteries
What attributes do we need to know to rate a battery for an electric vehicle?
- kWh price
- Durability, how many charge/discharge cycles can it handle without losing much capacity?
- Power density, by weight and volume (W/kg and W/L)
- Energy density, by weight and volume (Wh/kg and Wh/L)
Let’s focus on those attributes.
- For the price go down, we can use cheaper materials, but what really cut the costs is the manufacturing process. Building a lithium cell is a time and energy consuming task, specially because we still use liquid electrolytes. This will change with the introduction of solid state cells. For now, there isn’t a cell maker that has a big advantage regarding price.
- For battery life cathode and anode chemistries are very important. For the cathode the most popular chemistry is NMC (Nickel Manganese Cobalt) which has a great durability. The most notable exceptions is Nissan Leaf’s 24 kWh battery with LMO (Lithium Manganese Oxide) which has a bad lifespan. The 30 kWh NMC battery in the MY2016 will be a lot more durable. The other notable exception to the NMC chemistry is Tesla Motors, that uses NCA (Nickel Cobalt Aluminum) as cathode in the batteries of their electric cars, Model S and Model X. NCA has a good lifespan but has safety problems, yet Tesla Motors did a great job making the battery as safe as possible. For the anode, graphite had been used almost exclusivity, but recently more silicon is been added to the blend. A good battery also has a TMS (thermal management system), because high temperature reduces the lithium cells lifespan.
- For hybrids is very important the power density, because they have little batteries that still have to deliver high power. For electric cars is more important energy density.
- I left energy density to the end because this is where you can see if the automakers are interested in selling electric cars by providing good electric range or not. In electric cars because of the limited space available for the battery, Wh/L is more important than Wh/kg. Tesla Motors is the car company that is using batteries with the best Wh/L value. With the introduction of a bit of silicon to the graphite mixture used in the cathode, the cells in the Model S 90D have an energy density of about 700 Wh/L which is more than the double of the old 24 kWh Nissan Leaf’s battery (317 Wh/L). If Nissan wanted they could already be selling an electric car with twice the range of the Nissan Leaf.
Besides Panasonic for Tesla Motors, there is an battery manufacturer that is already selling high density batteries with silicon-graphite anodes. Amprius already sells 700 Wh/L batteries for tablets and smartphones. One example is the Chinese android smartphone Bluboo X550 that has its 5.300 mAh battery made by the California-based company Amprius.
The ugly truth is that there are batteries available that can at least double the range of current electric cars, but unfortunately only Tesla Motors is using them.