Researchers at the University of Leeds have developed a material and a process that could simplify the manufacture of lithium-ion cells, claiming that it could cut production cost with no loss of cell performance.
The process has already been licensed to US cell maker Polystor, and now the university is looking to build a collaborative venture between Leeds, Polystor and one other, as well as to find further licensees.
The material replaces the separator and liquid electrolyte of traditional Li-ion cells.
"The conventional way of making rechargeable lithium-ion cells is to use a polymer mesh separator and to assemble the two electrodes either side and then introduce a liquid electrolyte," Professor Ian Ward of the University of Leeds told Electronics Weekly.
The separator keeps the electrodes apart, preventing current flow, and the electrolyte conducts ions between them during charge ad discharge.
Ward's invention is a gel that both separates and conducts ions.
"We make a thermo-reversible gel. We mix a liquid lithium salt electrolyte into PVDF [poly(vinylidene fluoride)] to make a homogeneous melt," he said. "When you extrude it, it looks exactly like a polymer film and before it is completely frozen, you roll it between the electrodes."
In practice, the melt is extruded directly onto rollers press strips of anode and cathode material together - at up to 10m/minute.
The gel is tacky, so it sticks the electrodes together, removing the need to bind the structure together by other means.
Once rolled in "it then cools and freezes, undergoing a phase-change separation to become just like a porous rubber at the micron level with liquid electrolyte to conduct ions", said Ward.
The polymer gel contains about 70% of liquid electrolyte, he added. The resulting cell will perform exactly as it would with conventional construction.
Cell makers might not want to retrofit the equipment, but compared with the traditional way "it is a neater process if you are starting from scratch", said Ward.
With a thermal-reversible gel, does this mean heat could cause electrodes to short out inside a cell and cause thermal run-away?
Ward replied that health and safety rules forbid thermal run-away testing at the University, and that the melt temperature is around 140°C.
Safety devices within traditional Li-ion cells, which can run-away if abused thermally, cut current well below this temperature.
