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  • 1. Kim, Jong Min
    et al.
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Seong, Kwang-dong
    Oh, Jiseop
    Salazar-Alvarez, Germán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Piao, Yuanzhe
    Extensively interconnected silicon nanoparticles via carbon network derived from ultrathin cellulose nanofibers as high performance lithium ion battery anodes2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 118, p. 8-17Article in journal (Refereed)
    Abstract [en]

    Silicon is a good alternative to conventional graphite anode but it has bad cycling and rate performance. To overcome these severe problems, extensively interconnected silicon nanoparticles using carbon network derived from ultrathin cellulose nanofibers were synthesized. Ultrathin cellulose nanofibers, an abundant and sustainable material, entangle each silicon nanoparticle and become extensively interconnected carbon network after pyrolysis. This wide range interconnection provides an efficient electron path by decreasing the likelihood that electrons experience contact resistivity and also suppresses the volume expansion of silicon during lithiation. In addition, Ultrathin cellulose nanofibers are carboxylated and therefore adhesive to silicon nanoparticles through hydrogen bonding. This property makes ultrathin cellulose the perfect carbon source when making silicon composites. As a consequence, it exhibits 808 mAh g(-1) of the reversible capacity after 500 cycles at high current density of 2 A g(-1) with a coulombic efficiency of 99.8%. Even at high current density of 8 A g(-1), it shows a high reversible discharge capacity of 464 mAh g(-1). Moreover, extensively interconnected carbon network prevents the formation of a brittle electrode with a water-based binder. Therefore, this remarkable material has a huge potential for LIBs applications.

  • 2. Lu, Huiran
    et al.
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH Royal Institute of Technology, Sweden.
    Kim, Hyeyun
    Salazar-Alyarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH Royal Institute of Technology, Sweden.
    Lindbergh, Göran
    Cornell, Ann
    Effects of Different Manufacturing Processes on TEMPO-Oxidized Carboxylated Cellulose Nanofiber Performance as Binder for Flexible Lithium-Ion Batteries2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 43, p. 37712-37720Article in journal (Refereed)
    Abstract [en]

    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 varying 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 those of CNF with low charge density, as observed with atomic force microscopy. Also, CNF processed with a large number of passes in the homogenizer showed a better fiber dispersibility, as observed from rheological measurements. The electrodes fabricated with highly charged CNF exhibited the best mechanical and electrochemical properties. The CNF at the highest charge density (ISSO mu mol 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 1 C. 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 also contribute to the understanding of the optimal processing parameters of CNF to fabricate other materials, e.g., membranes or separators.

  • 3.
    Schütz, Christina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Agthe, Michael
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fall, Andreas B.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gordeyeva, Korneliya
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Salajkova, Michaela
    Plivelic, Tomas S.
    Lagerwall, Jan P. F.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Rod Packing in Chiral Nematic Cellulose Nanocrystal Dispersions Studied by Small-Angle X-ray Scattering and Laser Diffraction2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 23, p. 6507-6513Article in journal (Refereed)
    Abstract [en]

    The packing of cellulose nanocrystals (CNC) in the anisotropic chiral nematic phase has been investigated over a wide concentration range by small-angle X-ray scattering (SAXS) and laser diffraction. The average separation distance between the CNCs and the average pitch of the chiral nematic phase have been determined over the entire isotropic-anisotropic biphasic region. The average separation distances range from 51 nm, at the onset of the anisotropic phase formation, to 25 nm above 6 vol % (fully liquid crystalline phase) whereas the average pitch varies from approximate to 15 mu m down to approximate to 2 mu m as phi increases from 2.5 up to 6.5 vol %. Using the cholesteric order, we determine that the twist angle between neighboring CNCs increases from about 1 degrees up to 4 degrees as phi increases from 2.5 up to 6.5 vol %. The dependence of the twisting on the volume fraction was related to the increase in the magnitude of the repulsive interactions between the charged rods as the average separation distance decreases.

  • 4. Sundberg, Johan
    et al.
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Håkansson, Karl M. O.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Toriz, Guillermo
    Gatenholm, Paul
    Controlled molecular reorientation enables strong cellulose fibers regenerated from ionic liquid solutions2015In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 75, p. 119-124Article in journal (Refereed)
    Abstract [en]

    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 T-g, 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.

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