Engineers Analyzed Batteries from Tesla and China’s Leading EV Manufacturer

The electric vehicle (EV) market is dominated by Tesla, which is most popular in Europe and North America, and BYD, which is most popular in the Chinese market. Both manufacturers have released limited data about their batteries, so the mechanical structure and characteristics of these battery cells remain a mystery.

To provide design guidance for the development of next-generation batteries, Jonas Gorsch, RWTH Aachen University, Germany, and colleagues have analyzed two commercial lithium-ion batteries—the Tesla 4680 cell and the BYD Blade cell—by taking them apart. The team compared the electrical, mechanical, material, and process designs of the batteries, highlighting key differences in energy density, electrode materials, and manufacturing techniques.

The BYD cell uses a large prismatic cell format, while the Tesla 4680 cell is a large cylindrical cell with a much smaller volume. Both cells demonstrate the trend towards increasing cell sizes and the cell-to-pack approach, a battery design that eliminates the need for traditional battery modules, where individual cells are grouped into modules, and integrates individual cells directly into the battery pack. This reduces weight, increases energy density and simplifies manufacturing, resulting in better performance and cost efficiency.

Lithium iron phosphate (LFP; BYD Blade cell) and Li(Ni,Mn,Co)O2 (NMC811; Tesla 4680 cell) are used as cathode materials, resulting in cell-level energy densities of 160 Wh/kg and 355.26 Wh/l, and 241.01 Wh/kg and 643.3 Wh/l, respectively. The team found that Tesla’s batteries prioritize high energy density and performance, while BYD’s batteries prioritize volume efficiency and lower-cost materials. Tesla’s tabless cell design aims for high thermal conductivity, enabling efficient cooling, especially during fast charging. Therefore, it is not intended for direct comparison but rather for learning and improvement. However, the team found that this high-current design is not consistent throughout the cell, leading to higher thermal losses compared to the BYD cell, indicating unrealized optimization potential in Tesla’s first mass-produced version of the cell.

Both cells use graphite anodes. The team was surprised to find no silicon in the anodes of either cell, especially Tesla’s, as silicon is widely considered in research to be a key material for increasing energy density.

The researchers also discovered that the BYD Blade uses a different method to hold the electrode plates in place, using an electrode stack with a novel processing step to laminate the edges of the separator that sits between the anode and cathode.

The Tesla battery uses a novel binder—a substance that holds the active materials in the electrodes together—compared to those used by most manufacturers in industry. Polyacrylic acid (PAA) and polyethylene oxide (PEO) are the binders used on the anode side of the Tesla 4680 cell.

The Tesla 4680 cell uses laser welding and the BYD Blade cell uses laser and ultrasonic welding as electrode contacting technologies. Ultrasonic welding is used by many others in the industry to connect the thin electrode foils.
Although the BYD cell is much larger than the Tesla cell, the proportion of passive cell components—such as current collectors, housing, and busbars—is similar.

Further studies are needed to determine the impact of mechanical cell design choices on electrode performance in EV batteries, as well as the lifetime of the Tesla and BYD cells, the researchers say. As both Tesla and BYD continue to innovate and improve their battery technologies, the findings will serve as a benchmark for future developments in automotive battery design.