A Semi-IPN Polymeric Binder for High Performance Silicone Negative Electrodes in Lithium Ion Batteries

As applications of rechargeable lithium ion batteries are gradually increasing from small electronic devices to automobiles or power storages, there is increasing demand for electrode materials for use in rechargeable batteries having various advantageous characteristics including high safety, extended cycle life, high energy density and high output characteristic.

To develop rechargeable lithium ion batteries with high energy density, intensive studies have focused on silicone anode materials due to their high theoretical capacity (4200mAh/g). However, the commercial use of Si-based material is still hindered because of severe volume expansion by up to 300% during the repeated charge and discharge cycles, which results in pulverization and capacity fading.

In order to alleviate the volume changes, various nanostructured Si electrodes have drawn attention. Although the pulverization issue can be resolved by using the nanometer-scale materials, an effective low-cost solution to the volume-change problem remains elusive.

In the past, polymeric binder has played only passive roles in the performance of lithium ion batteries. But recent works show that the choice of binder is very important to stabilize the cycling performance of Si-based negative electrodes for LIB, and the functions of binders have become critical.

So we synthesized the new semi-interpenetrating network (semi-IPN) binder that can endure expansion of the Si-based active material. The term semi-IPN refers to a network structure of a linear polymer and a cross-linking polymer. Such a semi-IPN polymeric binder includes two kinds of polymers in a chain shape to form a network structure, and has high mechanical strength and excellent stability in the liquid electrolyte compared with general polymer. Accordingly, a rechargeable lithium ion battery including this binder can effectively control the expansion of a Si-based active material and exhibit improved cycling performance.