Photo ①: The separator developed this time. Combination of PVDF nanofiber and PET microfiber has greatly improved the heat resistance, strength and ion permeability as compared with conventional separator.

Dr. Kim Ick Soo (Associate Professor of Division of Frontier Fibers of Institute for Fiber Engineering, Interdisciplinary Cluster for Cutting Edge Research) succeeded in realizing substantial high heat resistance, high performance, and simultaneous mass production of "separators (* 2)", which is used for lithium ion secondary batteries (* 1) using nanofibers (see photo ①). On July 28th, he had a joint press conference with a research collaborator Distinguished Professor Kenji Hyodo and Kei Watanabe, Representative Director of Nafias Co., Ltd (see photo ②, ③).

"Separator" is a component that plays an important role in separating the positive electrode and the negative electrode of a lithium ion secondary battery. The separator announced this time is based on a nanofiber nonwoven fabric compounded of polyvinylidene fluoride (PVDF) nanofiber and polyethylene terephthalate (PET) microfiber (Photo 2, Photo 3). It is characterized by very high heat resistance compared with separator using conventional polyethylene and polypropylene.
Combination of PVDF-PET also has greatly improved the strength and improved reactivity between the positive electrode and the negative electrode, and became a revolutionary material to contribute to further miniaturization, higher output and larger capacity of the battery by making the ultra-thin separator. In addition, while making full use of the characteristics of nanofibers, we improved the durability by compositing PET, at the same time realized higher functionality and lower cost of materials.

This achievement is based on industry-academic collaborative research between Shinshu University which has core technology of nanofiber mass production and TENTOK PAPER Co., Ltd. (Fuji City, Shizuoka prefecture), NafiaS Inc. (Shinshu University-based start up company), N2Cell (financial aid). It is also decided to be published in the famous International Journal magazine "ACS Applied Materials & Interfaces" (Impact factor : 7,504).

*1 Lithium ion secondary battery : A secondary battery (a battery that can be used many times by charging) that performs charging and discharging by moving lithium ions between the positive electrode and the negative electrode. It is used for mobile phones, computers, electric cars, etc., and is spread all over the world.
*2 Separator : It is between the positive electrode and the negative electrode of the lithium ion secondary battery and insulates the active material at each electrode. Numerous pinholes are on the surface, and only ions can pass through to generate electric power. In this research, by using nanofibers as a separator material, we succeeded in keeping the pore ratio on the surface to 90% or more (about 40% for the conventional product) and to distributing with a uniform pore size.

Photo ②: From the left: Dr. Masayuki Takatera, Director of IFES, Associate Professor Kim Ick Soo, Distinguished Professor of Kenji Hyodo, Mr. Keiji Watanabe, Representative Director of Nafias Co., Ltd.

Photo ③: Associate Professor Kim Ick Soo, Distinguished Professor Kenji Hyodo, and Representative Director Kei Watanabe with the real developed separator in their hands.