Qichao Hu, co-inventor of the battery and CEO of SolidEnergy said: “This battery is half of the weight and the volume but you still keep the same capacity and that’s why you can achieve twice the energy density. What that means is, in the same volume and the same mass you can have twice the battery capacity, or you can have the same battery capacity but now its half the volume and half the mass.”
The company has shrunk the size of the battery by half by swapping a graphite anode for thin, high-energy lithium foil, which can hold more ions and which is about one-fifth the thickness of a traditional lithium anode, as well as several times thinner and lighter than traditional graphite, carbon, or silicon anodes.
Solid Energy had to address a number of technical issues. Lithium tends to reacts poorly with the electrolyte and forms compounds that increase both resistance in the battery and reduce cycle life. This reaction also creates dendrites on the anode, which lead to short circuits, generating high heat that can ignite the flammable electrolyte, and make the battery non rechargeable. Another major setback was that the battery only worked at 80°C or higher.
These problems were addressed by developing a solid and liquid hybrid electrolyte solution.
Hu explained: “The cathode is a standard lithium-ion cathode. Then we have our own ionic liquid electrolyte consisting of a new type of lithium salt, solvents and additives, then we have a separator, and then on the anode side we have a solid electrolyte that consists of polymer and ceramic materials, and finally a lithium-metal anode. So it’s a hybrid system in that it’s not pure liquid or pure solid, it has a liquid electrolyte on the cathode side and a solid electrolyte coated on the anode side.”
According to Hu, the combination of polymer and ceramics in the solid electrolyte acts like a blanket that suppresses the porous dendrites and it doesn’t need to be heated to function.
Hu argues the battery is just as safe as a lithium-ion battery. “Ordinary lithium-ion batteries have a very inflammable and volatile electrolyte but in our system, the electrolyte in non-flammable so even if there is an accident and the cell gets shorted, there will not be an explosion.”
SolidEnergy plans to bring the batteries first to drones in November, smartphones and wearables in early 2017, and to electric cars in 2018.
