Tesla's batteries: a five-year reality check

The Battery Day 2020: what worked and what didn’t

Welcome to Lithium Horizons! This newsletter explores the latest developments, companies, and ideas at the frontiers of energy materials. Subscribe below to get the next article delivered straight to your inbox.

---

In September 2020, Tesla hosted its highly anticipated Battery Day. Led by Elon Musk and Drew Baglino, the event outlined a grand plan to rewrite the economics of lithium-ion batteries and unlock a 25,000 USD electric vehicle (Figure 1).

Five years after Battery Day, Tesla’s vision proved directionally right but far harder to manufacture than its timelines suggested. While Tesla successfully industrialized certain manufacturing innovations, many core breakthroughs in materials and cell design remain difficult to scale.

Figure 1. Drew Baglino and Elon Musk on stage at the Battery Day 2020. Source: Tesla

This article examines what Tesla’s Battery Day got right, where execution fell short, and what those outcomes reveal about the battery industry.

NOTE: You can watch the full Battery Day event on Youtube. The transcript of the event can be read here and here.

The original promise

Tesla’s thesis was straightforward: to build a truly affordable EV, battery manufacturing had to be vertically integrated and radically redesigned.

The Battery Day set two headline targets:

1. Scale: 100 GWh of battery production by the mid-2020s and 3 TWh by 2030.

2. Cost: A 56% reduction in pack-level costs.

To achieve this, Tesla presented five interconnected innovations:

1. The 4680 ‘‘tabless’’ format

Shifting from a standard 2170 cylindrical cell to a larger 4680 format (i.e., 46 mm diameter, 80 mm height), Tesla could use fewer cells per pack and larger electrodes, resulting in cheaper assembly. The claim was that this format could deliver 5x more energy and 6x more power per cell.

To solve the heat issues, which are common in larger cells, Tesla introduced a ‘‘tabless’’ design (Figure 2), where the electrode’s entire edge conducts current, lowering resistance and improving thermal dissipation.¹ This was also supposed to help in achieving a higher production throughput, since there would be no stopping for traditional tab welding steps.

Figure 2. Top view of a Tesla 4680 cell showing fringed ‘‘tabs’’ in a ‘‘tabless’’ cell design. Source: Institute of Physics

The cell form factor change was expected to allow for a 14% USD/kWh reduction at the battery-pack level.

2. Dry electrode manufacturing

Conventional electrode coating relies on liquid solvent-based slurries (i.e., wet process or coating) and massive drying ovens to evaporate said solvents after coating (Figure 3). By using a dry powder-to-film process (i.e., dry process or coating), Tesla aimed to eliminate solvents, cut factory footprint tenfold and lower energy consumption.

The end goal was a high-speed continuous-motion production line capable of ~20 GWh/year; a massive increase in production output considering that state-of-the-art wet process lines offer ~3 GWh/year per line.

Figure 3. Wet versus dry coating. Source: InfinityPV

This manufacturing innovation was supposed to enable an additional 18% USD/kWh reduction at the battery pack level.

3. Silicon-rich anode

To boost energy density, Tesla proposed replacing most graphite with raw metallurgical silicon, which would help increase the range by 20% at a cost of only 1.20 USD/kWh of anode material. Since silicon changes its volume by up to 400% during charge-discharge cycles, its particles crack and lose electrical contact with each other. To mitigate this, Tesla proposed wrapping silicon in an ion-conductive polymer and using ‘‘elastic’’ binders (Figure 4).