Dynamic Networks of Cellulose Nanofibrils Enable Highly Conductive and Strong Polymer Gel Electrolytes for Lithium‐Ion Batteries

Abstract

Tunable dynamic networks of cellulose nanofibrils (CNFs) are utilized to prepare high‐performance polymer gel electrolytes. By swelling an anisotropically dewatered, but never dried, CNF gel in acidic salt solutions, a highly sparse network is constructed with a fraction of CNFs as low as 0.9%, taking advantage of the very high aspect ratio and the ultra‐thin thickness of the CNFs (micrometers long and 2–4 nm thick). These CNF networks expose high interfacial areas and can accommodate massive amounts of the ionic conductive liquid polyethylene glycol‐based electrolyte into strong homogeneous gel electrolytes. In addition to the reinforced mechanical properties, the presence of the CNFs simultaneously enhances the ionic conductivity due to their excellent strong water‐binding capacity according to computational simulations. This strategy renders the electrolyte a room‐temperature ionic conductivity of 0.61 ± 0.12 mS cm−1 which is one of the highest among polymer gel electrolytes. The electrolyte shows superior performances as a separator for lithium iron phosphate half‐cells in high specific capacity (161 mAh g−1 at 0.1C), excellent rate capability (5C), and cycling stability (94% capacity retention after 300 cycles at 1C) at 60 °C, as well as stable room temperature cycling performance and considerably improved safety compared with commercial liquid electrolyte systems.

An Ultrahigh Modulus Gel Electrolytes Reforming the Growing Pattern of Li Dendrites for Interfacially Stable Lithium‐Metal Batteries

“…The ionic conductivity and elastic modulus of the as‐proposed PLF@GPE were compared with the state‐of‐the‐art values reported for gel electrolytes. [ 12,13,24–30 ] As presented in Figure 3b, the PLF@GPE shows a competitive ionic conductivity and the highest elastic modulus among the mentioned GPEs.…”

“…Figure 5e compares the room‐temperature cycling stability of LFP||Li cells assembled with gel electrolytes which are reported in recently published works. [ 17,24,25,27–29,32–40 ] Relying on the exquisite topology of the supporting skeleton, the PLF@GPE rendered the best‐in‐class capacity retention after long‐term cycling tests.…”

Recent Advances in Biopolymer-Based Hydrogel Electrolytes for Flexible Supercapacitors

“…Fortunately, biopolymer-based materials show unique advantages in terms of regulation of porous microstructure. For instance, tunable dynamic networks of cellulose nanofibrils (CNFs) are fabricated by swelling an anisotropically dewatered CNF gel in acidic salt solutions . A network is created by taking advantage of the extremely high aspect ratio of ultrathin CNFs.…”

“…For instance, tunable dynamic networks of cellulose nanofibrils (CNFs) are fabricated by swelling an anisotropically dewatered CNF gel in acidic salt solutions. 67 A network is created by taking advantage of the extremely high aspect ratio of ultrathin CNFs. Modulation of the pore structure by using different concentrations of salt ions leads to a sharp increase in conductivity from 0.05 to 0.6 mS cm –1 .…”

Superstrong Ionogel Enabled by Coacervation-Induced Nanofibril Assembly for Sustainable Moisture Energy Harvesting

“…Consequently, judicious selection and modification of the polymer matrix of ionogels are crucial to imparting ionogels with excellent properties in many aspects. Cellulose, as the most abundant renewable biopolymer, is a promising substitute of petroleum-based polymers from the perspective of environmental sustainability due to its biodegradability and low cost. , Especially, nanocellulose has special morphologies and characteristics, such as outstanding strength, low density, and high specific surface area, which make it an ideal building block for flexible functional composites like ionogels. , However, there are numerous obstacles to hinder nanocellulose-based ionogels from exploiting the advantages of nanocellulose comprehensively . For instance, low compatibility between ILs and cellulose results in the risk of IL leakage when IL content is high, ILs inevitably make a serious deterioration of the mechanical properties of nanocellulose and the loss of the microstructural integrity due to the solvent effect of ILs, , and complex ingredients and complicated multistep processing increase costs .…”