Typical lithium batteries being used right now to power the first generation of electric vehicles have limitations based upon their technologies in how far one can go on a daily basis. A number of promising start ups, such as PolyPlus, are trying to address this issue through the development of next generation EV battery technology.
PolyPlus is developing what are known as lithium-oxygen batteries that reportedly offer up to ten times the energy density of current battery technologies, meaning down the road electric cars might be able to go farther longer on one charge. To learn more about its technology, we recently interviewed the company.
What exactly does PolyPlus develop? PolyPlus is developing lithium-oxygen batteries; oxygen can be scavenged from water or air, and thus we are developing both lithium-water and lithium-air batteries. These types of batteries are potential game-changers in their respective industries because they have unprecedented energy densities: from two to ten times the energy density of competing batteries.
How do the batteries PolyPlus make differ from other types of lithium batteries? PolyPlus lithium-oxygen batteries use a fundamentally different chemistry based on a breakthrough discovery at PolyPlus, which led to the invention of water-stable lithium metal electrodes. We call these protected lithium electrodes or PLEs. The invention of the PLE enables the development of lithium-water and lithium-air batteries with unprecedented energy densities leading to vastly improved performance and safety.
There are two types of lithium batteries with which most people are familiar: lithium metal primary (single-use) batteries that go into wrist watches and cameras, and lithium-ion secondary (rechargeable) batteries that go into cell phones, laptops, and many other devices. Li-ion batteries are based on the use of lithiated carbon which is heavy compared to lithium metal, 375 milliamp hours per gram for LiC6 compared to 3785 milliamp hours per gram for lithium metal. So, using a lithium metal negative electrode rather than a lithiated carbon electrode represents a significant improvement in the weight of the battery.
Li-ion batteries also use relatively heavy positive electrode materials such as cobalt, nickel, and/or manganese oxides. Lithium-air and lithium-water batteries are effectively the Holy Grails of the battery field since the positive electrode is essentially weightless (you do not carry the air or water positive electrode in the cell, it is provided for “free” from the environment).
Scientists have theorized about lithium-air batteries for many years, but had never been able to protect lithium metal from water and humidity while keeping it electrochemically active. PolyPlus’ core invention is a way to physically isolate lithium metal from the environment while keeping it electrochemically active. This opens the door to lithium-oxygen batteries, which can store a great deal of energy in a small, lightweight package.
Where and when will consumers most likely come across PolyPlus technology? PolyPlus’ first products will likely be lithium-water batteries that will power unmanned underwater vehicles, sensors, and many undersea devices. Next, we’ll release a lithium-air battery for the military to help troops in the field.
What are the commercial applications for your technology? In about five years, the first rechargeable lithium-air batteries will start appearing in consumer electronics devices. A few years after that, we hope to commercialize rechargeable lithium-air batteries for electric vehicles. Our target is to design a battery that is one-third the weight and half the size of current lithium-ion batteries.
Where does PolyPlus see the future of electric vehicle battery development heading? Right now, most battery companies are incrementally refining lithium-ion batteries. Though lithium-ion is a mature chemistry (Sony released it 20 years ago), we anticipate that improvements of 15% to 20% in weight and size is possible. Still, it is not clear that the fundamental chemistry can be improved more than that amount from its performance today.
A hurdle to mass electric car adoption is range anxiety. With a 20% battery range improvement on the Nissan Leaf, for example, it could travel 100 to 150 miles per charge. While attractive to a niche market, the mass market demands a range of 250 to 300 miles or more. The only way batteries will store enough energy for that type of range is if there is a step-change improvement in energy density, which will very likely require a new battery chemistry. Lithium-air batteries are the most promising of the new chemistries.
Our opinion is that battery energy density and widespread electric vehicle adoption may be tightly correlated; only with advances in batteries will electric vehicles reduce or eliminate range anxiety, which will open the door to the mass auto market.