Cylindrical Li-ion batteries are Tesla’s battery of choice, but understanding their structure is important before delving into their use in Elon Musk’s vehicles. Cylindrical Li-ion cells have a significantly different shape from prismatic cells, but their internal design is similar to that of wound prismatic cells. The positive electrode is ~178.0μm thick due to its being coated on each side with ~12g total of LiCoO2. The negative electrode typically contains ~6.5g of carbon (1).
The construction of a typical cylindrical cell, as seen in Figure 35.30, is very close to that of a wound prismatic cell. A PTC device is an example of a device that disconnects the cell under certain pressures and temperatures that could cause malfunctions (1). Most cells also contain charge interrupt devices, which prevent overcharging (overcharging leads to a loss of cell performance) (2).
Figure 35.33 shows the mass distribution in two 18650 Li-ion batteries. The 18650 Li-ion battery is one of the most common sizes of cylindrical Li-ion batteries. As seen in the diagram, the two electrodes account for the bulk of the cell’s mass, with the positive electrode accounting for slightly more. This makes sense given that the mass of LiCoO2 used to coat the positive electrode is almost twice that of the graphite present at the negative electrode (1).
The rest of the cells’ characteristics vary little from those of wound Li-ion cells, which are analyzed here. Having covered the design and configuration of cylindrical Li-ion cells, we will look at their applications in the next post.
- Linden, David and Thomas B. Reddy, Handbook of Batteries, Third Edition, McGraw Hill, New York, 2002.