US researchers have found a solution to polysulphide crossover and shuttling in lithium-sulphur batteries, which has previously reduced battery efficiency and lifetime.
Scientists at the Lawrence Berkeley National Laboratory in California say they have solved a problem with the membranes that separate the electrodes, which have until now allowed unwanted ions such as polysulphide ions (Li2Sx) to pass through, or cross over, reducing battery efficiency and life.
Now they have developed a membrane made from PIMs (polymer intrinsic microporosity), which have pore sizes of less than one nanometer in diameter, compared with the 17-nm pore size of typical membrane separators.
The substantially smaller pore size provides selective control over the ions transported through the membrane, allowing smaller ions like lithium and sodium to pass through while larger polysulphides are blocked.
When integrated into lithium-sulphur cells, the scientists found the PIM membranes were 500 times more effective at blocking unwanted crossover than conventional membranes.
Leading the research, Brett Helms said the PIMs’ unique features meant they were amorphous but still exhibited high intrinsic microporosity and a high surface area.
“Given that the pore size, pore chemistry and overall porosity for PIM membranes are tunable using molecular engineering and polymer processing, the membrane’s transport characteristics can be tailored to suit a broad spectrum of electrochemical devices, from batteries to fuel cells,” he said.