Effects of Different Manufacturing Processes on TEMPO-oxidized CNF Performance as binder for Flexible Lithium-ion Batteries

Huiran Lu, Valentina Guccini, Hyeyun Kim, German Salazar-Alvarez, Göran Lindbergh, and Ann Cornell*

ACS Appl. Mater. Interfaces (2017)
DOI: 10.1021/acsami.7b10307

Abstract:
Carboxylated cellulose nanofibers (CNF) prepared using the TEMPO-route are good binders of electrode components in flexible lithium-ion batteries (LIB). However, the different parameters employed for the defibrillation of CNF, such as charge density and degree of homogenization, affect its properties when used as binder. This work presents a systematic study of CNF prepared with different surface charge densities and various degrees of homogenization and their performance as binder for flexible LiFePO4 electrodes. The results show that the CNF with high charge density had shorter fiber lengths compared with the CNF with low charge density, as observed with atomic force microscope (AFM). Also, CNF processed with a large number of passes in the homogenizer showed a better fiber dispersibility, as observed with rheological measurements. The electrodes fabricated with highly charged CNF exhibited the best mechanical and electrochemical properties. The CNF at the highest charge density (1550 µmol g-1) and lowest degree of homogenization (3+3 passes in the homogenizer) achieved the overall best performance, including a high Young’s modulus of approximately 311 MPa and a good rate capability with a stable specific capacity of 116 mAh g-1 even up to 1C. This work allows a better understanding of the influence of the processing parameters of CNF on their performance as binder for flexible electrodes. The results can also contribute to the understanding of the optimal processing parameters of CNF to fabricate other materials, e.g., membranes or separators.

Controlled molecular reorientation enables strong cellulose fibers regenerated from ionic liquid solutions

Johan Sundberg, Valentina Guccini, Karl M.O. Håkansson, German Salazar-Alvarez, Guillermo Toriz, Paul Gatenholm

Polymer 75 (2015) 119-124.
DOI: 10.1016/j.polymer.2015.08.035

Highlights:
• Strong cellulose fibers spun from ionic liquid solution.
• Extrusion process simulated in silica based upon rheological measurements.
• Increased DO for fibers regenerated with ethanol stretched at high RH.
• Significant improvement of mechanical properties for re-oriented fibers.
• Mechanical properties comparable to commercially available fibers.

Abstract:
Cellulose is difficult to solubilize and undergoes thermal decomposition prior to melting. In recent years ionic liquids have been evaluated as solvents of cellulose. In the regeneration process the non-solvent governs the resulting material's crystallinity. Water adsorbs to amorphous cellulose, acts as plasticizer and lowers the Tg, hence the degree of crystallinity will affect the potential strain induced reorientation. We prepared regenerated cellulose fibers form ionic liquid using different non-solvents. The influence of shear forces upon cellulose chain alignment during extrusion was simulated in silica based upon rheological measurements. The regenerated fibers had different physical, morphological and mechanical properties. Molecular re-orientation in fibers induced by mechanical strain, at humidities above the Tg, resulted in much improved mechanical properties with the Young's modulus reaching 23.4 ± 0.8 GPa and the stress at break 504.6 ± 51.9 MPa, which is comparable to commercially available cellulose fibers.