Seeo, a quiet lithium-ion battery startup backed by greentech investor Vinod Khosla, has moved into a new home and installed a pilot production line that can produce 4 megawatt hours worth of battery cells per year. Mohit Singh, Seeo co-founder, gave us an update on the company during a recent exclusive tour of Seeo’s new headquarters in Hayward, Calif.
The pilot line is a critical step to help Seeo move toward commercializing its technology. The startup was founded in 2007 and formerly based in Berkeley, which is home to Lawrence Berkeley National Laboratory, where Singh and his fellow co-founders, Hany Eitouni and Nitash Balsara, first developed the technology concept to produce batteries that are unlike the lithium-ion batteries found in consumer electronics, electric cars and energy storage systems today.
A conventional lithium-ion battery cell uses a liquid electrolyte – which is typically made up of a lithium salt in an organic solvent –as the medium to shuttle lithium ions back and forth between the cathode and the anode to charge and discharge the cell. Liquid electrolytes can be very conductive, but can also be flammable and can react with other components of the cell that ends up shorten the life span of the cell.
In contrast Seeo is using a dry polymer electrolyte, which forgoes the use of solvent and feels like plastic to the touch, Singh explained to me. Making a solid state electrolyte to be nearly as conductive as liquid electrolytes is a big challenge that Seeo is working on. In Seeo’s electrolyte, lithium will move across chains of an ionically conducting polymer in order to travel back and forth from the anode and the cathode during discharge and charge. Singh declined to divulge the makeup of the polymer material.
Using polymer electrolytes can lead to a longer battery life because it’s not flammable like the liquid electrolyte and sustains virtually no loss of capacity under prolonged exposures to high temperatures. Overheating is a significant problem for today’s lithium-ion batteries and requires complex and costly cooling systems.
Nissan and General Motors say the batteries in their electric vehicles are good for 100,000 miles today. Seeo’s goal is to double that mileage, Singh said.
Using polymer electrolyte also makes it possible to use lithium metal as the anode material. Graphite has historically been the anode material of choice, but it’s bulky and can’t hold as much energy as lithium metal. Lithium metal has 4-5 times higher practical capacity than graphite while silicon nano wires – another option being explored by many companies – have 2-3 times.
But lithium metal can grow dendrites during the charging process and that causes short circuits and therefore limits the battery cell’s longevity. The use of polymer electrolyte can prevent dendrite growth, though achieving this is difficult and has stumbled past efforts to commercialize lithium metal polymer cells.
Seeo has built its core technology to overcome this big challenge, Singh said. He noted that research has shown that lithium metal polymer battery cells can easily achieve 250 Wh/kg (a measure of energy density), compared with the less than 200 Wh/kg commonly found in lithium-ion cells today.
Solid state electrolytes have received more attention in recent years because battery and car makers are seeking better materials and recipes for making batteries that can last more than just a few years. Lithium-ion batteries have long been used in consumer electronics, but they tend to wear out quickly after a few years.
“We didn’t talk a lot about the life of batteries until electric vehicles came into the market. Solid state wasn’t a sexy topic before, but it is now,” Singh said. Seeo wants to make its own batteries and will be looking for commercial manufacturing sites in a year or so.
The U.S. Department of Energy in August announced a $4.9 million grant to Seeo to expand its research and development work on lithium metal polymer cells. The company is now hiring chemists for the project. Seeo also raised at least $25 million from private investors.
Seeo isn’t alone is trying to improve the electrolyte in order to prolong a battery’s life. Sakti3 is another startup, based in Michigan, that is developing battery cells with a solid-state electrolyte, and is also backed by Khosla Ventures.
Leyden Energy in Fremont, Calif., meanwhile, is using a different type of lithium-ion containing salt in the liquid electrolyte in order to build more high temperature-tolerant and longer-lasting batteries.