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Toshiba has achieved a dramatic 20% increase in the capacity and input/output power of its SCiB™ lithium-ion rechargeable battery by developing a new structure that replaces the insulating separator between the battery’s anode and cathode.

By deploying a skin-coated electrode (SCdE), which is an electrode covered with an extremely thin nanofiber membrane of resin, Toshiba has realized a separator-free design that brings the anode and cathode as close together as possible. The new design not only boosts battery performance but also reduces the cost of the insulator by approximately half. Details of the new Li-ion rechargeable battery will be unveiled on June 7, 2018, at the International Nanofiber Symposium in Tokyo.

The nanofiber membrane for the SCdE is fabricated by electrospinning, which is a nanofiber production technique, where a high voltage is applied to a polymer solution at a normal ambient temperature. Electrospinning can produce a non-woven fabric from a wide range of materials selected for various characteristics such as high heat resistance or high corrosion resistance. Electrospinning also allows the fabrication of fibers with diameters in the range from tens of nanometers to micrometers, and can be used to create structures through which ions can move smoothly. This allows the realization of a non-woven fabric that can function as a separator in a lithium-ion battery.

Toshiba applied electrospinning to the fabrication of a highly insulating and highly heat resistant resin membrane that coats both sides of an electrode to obtain an SCdE. This new structure removes the need for a free-standing separator between the anode and cathode, while simultaneously coating both sides of the electrode maintains the same safety level as that of a current SCiB™ with a separator. Because the extremely thin insulating nanofiber membrane is integrated with the electrode, it is now possible to realize a thin membrane without any of the difficulties associated with introducing a thin separator into the production process. Toshiba’s new SCiB™ with the SCdE realizes a high performance that cannot be achieved even with an expensive thin separator.

In a demonstration, Toshiba showed that, the SCdE lowers the internal resistance of its SCiB™ by achieving higher ion conductance at a given energy density. For a high-output-power 10Ah SCiB™, the SCiB™ with the SCdE boosts the output power from 1,800W to 2,200W. Improving the input/output power will promote the application of its SCiBTM at low temperatures, accelerating the replacement of lead-acid battery. In another demonstration, the SCiB™ with SCdE realized energy density improvement from 2.9Ah to 3.8Ah keeping the same input/output power at the same can size. The test also showed that the new battery maintains over 95% of its capacity after 8,000 charge-discharge cycles. The long life property is another advantage of the SCiB™.

Toshiba intends to refine the new technology and introduce it into lithium-ion batteries for cars and batteries for stationary devices, putting it into practical use in FY2019.

This new development makes use of results developed with funding from Japan’s New Energy and Industrial Technology Development Organization (NEDO).