Toray Industries has developed a resin film for use in the anode current collector of lithium-ion batteries, replacing the copper foil that conventionally does the job. The company says it is the first film substrate to meet all four requirements of the anode environment, and has begun supplying samples.

Copper reduction is the point for anyone building at scale. A film collector carries a copper layer of around one micron on a 4.5 micron substrate, against copper foil of six microns or more, cutting collector weight by 50% to 60% and cell weight by roughly 10%.

Figure 1: Comparison of conventional copper foil anode current collector and film current collectorFigure 2: Comparison of copper foil and film current collectors for anode applicationsFigure 3. Toray assessment of capacity retention during battery cycling tests (using single-layer laminate cell with battery capacity of 30 milliampere-hours)

The range claim needs reading carefully. Toray estimates up to 10% more electric vehicle range, but only if the weight saved is spent on additional active material rather than taken as a lighter pack, and under conditions it does not fully specify.

The obstacle has always been chemistry rather than cost. Polyethylene terephthalate film works on the cathode side but breaks down in the strongly reducing conditions at the anode, and no substrate had previously combined reduction resistance with adhesion, strength and thermal stability.

Automotive is not the first target. Toray plans to commercialise the film for small and medium batteries in mobile devices, drones and electric vertical take-off and landing aircraft, while it considers larger applications in vehicles and energy storage.

Source: Toray