The Ultracapacitors, Electrodes, & Battery Manufacturing Tech Tesla Gets with Maxwell Technologies
As reported … Monday, Tesla has nearly acquired Maxwell Technologies, a San Diego–based energy storage products and research business, for $218 million, with the transaction expected to complete in Q2 2019. Is this a stationary storage play or an EV play for Tesla … or both?
Maxwell is Best Known for its Ultracapacitors — What are They?
Ultracapacitors store electrical energy, like batteries, but rather than electro-chemically (batteries), they store the energy electro-statically. There’s also a notable difference in balance between energy density and power density. Lithium-ion batteries have energy density typically in the 150–250 Wh/kg range, and power density in the 250–350 W/kg range. Maxwell’s current commercial ultracapacitors, such as the DuraBlue range pictured above, have much lower energy density of 8–10 Wh/kg (around 5% that of lithium-ion), yet much higher power density of 12–14 kW/kg (around 45× that of lithium-ion).
In the context of EV applications, this means that a 50 kg array of ultracapacitors could potentially input or output 650 kW of burst power (although, at 0.18 kWh, this would last just a second or so). Lower power levels would obviously be sustained for proportionately longer. For context, that’s about twice the power that the Tesla Model 3 Performance’s 480 kg battery pack is currently tuned to provide (331 kW).
If the economics made sense, a modest ultracapacitor array could work alongside the battery pack as a cache of energy, to reduce the load on (and/or work in parallel with) the main battery during short bursts of hard acceleration or strong regenerative braking. Since ultracapacitors can perform reliably over hundreds of thousands of cycles, this could also reduce the cycling load on the lithium-ion pack, and potentially allow it to have a chemistry that prioritizes energy density over power density. The round-trip energy efficiency of Maxwell’s ultracapacitors is in the 80% efficiency range, which is pretty decent (lithium-ion is 80 to 90%). In a mid-2018 conversation with the San Diego Business Journal, Maxwell reported having already sold 6.1 million ultracapacitors to automakers.
With their extremely fast response, high power density, and high cycle durability, ultracapacitors also have applications in fast-response stationary storage applications and grid load balancing (read more about Maxwell’s case studies of these).
Dry Battery Electrodes
Another interesting technology that Maxwell has developed is its dry battery electrode manufacturing process. Maxwell believes it has potential to lower traditional battery manufacturing costs:
“We believe that our patent-protected, proprietary manufacturing process, which has been utilized through many years of ultracapacitor production, can be applied to the manufacturing of battery electrode without the use of solvents to produce a highly reliable electrode material with uniform characteristics resulting in enhanced product performance, long-term durability, and lower manufacturing cost.” (Maxwell Annual Report, 2017)