Parameters Affecting Lithium Ion Conductivity of Carboxymethyl Cellulose Binders
Authors: Lobato de Faria Marco , Kuss Christian 
Published: November 2022

In an effort to minimize green house gas emissions, the development of renewable energy storage has become important, especially for the transportation industry.(I) Currently, the most effective energy storage solution is Li-ion batteries due to their long cycle life and high energy density.(I) However, this current technology uses highly reactive and flammable liquid electrolytes which are both limited by their limited charging speed through a liquid medium and their unsafe nature.(II) For this reason, many large companies such as Hyundai and Samsung have heavily invested in the development of all-solid-state batteries (ASSB), seen as the next step in safe fast-charging energy storage.(III)
However, problems remain that need to be solved before ASSBs can become commercially viable. One of these problems is cycling stability, where battery performance significantly drops after a few charge/discharge cycles, notably through mechanical degradation and interfacial contact issues caused by volume changes of the active material against a rigid solid electrolyte.(I) For this reason, there is growing interest in increasing the system’s mechanical flexibility thus preventing degradation by the use of ionically conductive polymers as soft binders and volume buffers.(IV) One potential choice for such materials are environmentally friendly natural biopolymers such as cellulose derivatives like carboxymethyl cellulose (CMC), whose functional groups coordinate cations during transport. CMC has already been shown to act as a binder that increases mechanical stability for electrodes of current Li-ion technology and exhibits proton conductivity in fuel cell applications. It is also being investigated for its potential in ASSBs, Na-ion, and Zn batteries where it has been shown to have high durability and that it combines well with a variety of other polymers when used as binders or as a solid electrolyte in these batteries.(IV-VII)
To further our understanding of incorporating this biopolymer in batteries, we are studying the effects of various aspects of CMC film preparation on their ionic conductivity such as salt concentration and film homogeneity. In addition, to the preparation parameters, we investigated the activation energy of ion transport for CMC films of differing concentrations through temperature dependence measurements. Furthermore, we investigated the structure of these materials with infrared spectroscopy and differential scanning calorimetry to see the effects of salt concentration on the microstructure. This data is of importance in assessing the impact of CMC binders and will lay a foundation for optimizing binder choice for cheap and biodegradable components in both current and next-generation battery technology.

References

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