Scientists at Stanford University have revealed a novel electrolyte design they claim will boost the performance of lithium metal batteries.
The team from the US institution added fluorine atoms onto the electrolyte molecule to make the liquid more stable and create a new molecule that allows the lithium metal anode to function well in the electrolyte.
The novel synthetic compound, abbreviated to FDMB, can be readily produced in bulk and ‘reasonably cheap’, say the scientists.
The study was published on 22 June in the journal Nature Energy.
In tests, the Stanford team found the lithium metal battery retained 90% of its initial charge after 420 cycles. In laboratories, typical lithium metal batteries stop working after about 30 cycles.
The researchers also found the coulombic efficiency of the battery reached 99.52% in the half-cells and 99.98% in full cells. This means the full cells are close to the 99.9% coulombic efficiency required to become commercially viable.
An anode-free battery using FDMB achieved about 325 watt-hours per kilogram specific energy in the team’s laboratory.
Study co-author Yi Cui, professor of materials science and engineering and of photon science at the SLAC National Accelerator Laboratory, said: “Most electric cars run on lithium-ion batteries, which are rapidly approaching their theoretical limit on energy density.
“Our study focused on lithium metal batteries, which are lighter than lithium-ion batteries and can potentially deliver more energy per unit weight and volume.”
In the study researchers used organic chemistry to rationally design and create new, stable electrolytes for the batteries.
For potential use in consumer electronics, the Stanford team also tested the FDMB electrolyte in anode-free lithium metal pouch cells.
“The idea is to only use lithium on the cathode side to reduce weight,” said co-lead author Hansen Wang, a graduate student in materials science and engineering.
“The anode-free battery ran 100 cycles before its capacity dropped to 80% – not as good as an equivalent lithium-ion battery, which can go for 500 to 1,000 cycles, but still one of the best performing anode-free cells,” he said.
Image: A conventional (clear) electrolyte on the left and the novel Stanford electrolyte on the right. (Image credit: Zhiao Yu)