Innovative Features of Tesla Batteries

 

When Tesla began development on the Roadster, the engineers needed to figure out how to design a battery that was durable, long lasting, and heat resistant. At the time, most Lithium Ion batteries were meant for use in small appliances, such as Laptop computers. As a result, the longevity of these cells way too short, and the cells lacked the durability and power that Tesla needed. Additionally, the 18650 cells themselves were too expensive per cell to justify the cost of an electric vehicle. In response, Tesla designed their own version of the Panasonic NCR18650B battery. A range of different alloys were integrated into the battery to make it safer, increase its lifespan by 5 times, and increase the power output.

  • Lifespan

Panasonic cell capacity cycle tests

Tesla cell capacity cycle tests

 

 

 

 

 

 

 

 

 

 

 

Pictured above are the cycle tests for Panasonic and Tesla cells. Tesla cells can Last up to 6 times longer than panasonic cells. Unlike standard 18650’s, Tesla 18650’s have a much lower capacity loss over time. Panasonic batteries normally last 2-3 years before loosing too much capacity. On the other hand, Tesla cells can last for up to 20 years before needing to be replaced.

  • Durability

Quote from Tesla CIO:
We use a nickel-cobalt-aluminum (LiNiCoAlO2) lithium-ion chemistry for our battery cathode material. We don’t use a titanate, which has about half the energy density but is generally good at high charge rates. Some start-ups are using metal oxides; we fall broadly in that category. At this point we really have heavily customized that cell. We’ve totally custom-engineered that cell working jointly with Panasonic to create. It’s an automotive cell, tested to automotive standards. It doesn’t go into laptops anywhere.

Since the Tesla cells weren’t designed for laptops, they have a much stronger durability than standard 18650’s. During the early days of Tesla, the engineers decided to test the Tesla cell durability by discharging an entire car battery. Remarkably, only the plastic casing of the battery melted — all of the cells were fine.

Capture

Tesla cells are known for having very little loss in capacity over their lifespan. Most Tesla EVs will drastically outlive their gas-powered counterparts before the battery pack needs to be replaced. 

Even when excess strain is put on Tesla cells (due to aggressive driving…etc), the capacity loss still remains minimal. With the exception of a few data points, most  Tesla cars follow the steady downward curve. In more recent models, we can expect the rate of capacity loss to decrease even sooner as battery technology improves.

 

  • Supercharging

A key characteristic of Tesla cell durability is their ability to be supercharged. A Tesla cell can be charged in less than an hour. This makes Tesla cells very useful since you don’t have to wait up to 3 hours (in the case of Panasonic cells) for your cells to charge. Charging a Tesla battery is like filling up a cup with water. At first you can pour very fast since the water level is very far away from the cup rim. When A Tesla cell, or any other 18650 is charged, the same scenario occurs. The battery starts off charging from 0% at the max amperage. Then, once the Voltage hits 4.20 Volts, the amperage begins to taper off (the battery is being “topped off” at this point). Tesla cells can be charged at twice the amperage as normal Lithium Ions because they have different chemistry and alloys that allows a 2000 mah charging current.

Battery Charging Graph over time

The first 75% of a battery’s charge is the fast charge time. The last 25% of the charge is the trickle charging phase where the cells are “topped off” 

The problem with most Lithium Ions is that the last 25% of the battery’s charge can talk about 1.5 times longer than the first 75% of the battery’s charge. This means that it can take up to 3 hours for one 18650 to charge.

tesla supercharge graph

The charge rate graph for Tesla Lithium Ion cells; the faster rate of charge allows the cells to be charged in just over an hour.

Tesla sought to improve the charging characteristics my increasing the charging current during the first 80% of the battery’s charge. As the graph shows, Tesla was able to shorten the fast charging cycle to just 40 minutes. By contrast, standard 18650’s generally take about 100 minutes to reach 75% charge. By that time, a Tesla battery will have finished charging.

More steps are being taken to increase charge rates in the future. Some of the new supercharging V3 stations will have a much higher charging output.

Elon Musk Supercharger V3

Elon is suggesting that the supercharger V3, which will be used with the new Tesla Lithium Ion cells, more than 2X the current amp charge. At this rate, a Lithium Ion cell could be charged in 20 minutes or less (Tesla’s goal is to get to 5 minutes charging time, since this is the average amount of time it takes to refuel a gas powered car).

There are, however, some disadvantages with supercharging. If used often, Supercharging 18650 cells can cause them to loose cell life faster. For this reason, we recommend charging at 1000 mah whenever possible, as this will maintain the life of the Tesla cell.

We currently have some Tesla cells available here.