Conductive Cellulose Nanofiber Enabled Thick Electrode for Compact and Flexible Energy Storage Devices

Abstract

the current collector. Recently, progresses have been made in thick electrode architecture design by incorporating external magnetic fields and carbon templates for fast charge transfer kinetics, but the complicated producing processes and fragile electrode mechanical properties limit their ability for practical applications. [10][11][12][13][14][15] Fiber like carbon materials with large aspect ratio, such as carbon nanotubes (CNT), can significantly improve electrode mechanical strength and energy density due to its excellent electron conductivity and good compatibility to form continuous network with lower electrical percolation threshold. [16][17][18][19] Nonetheless, CNT is still constrained to complicated syntheses by expensive or low throughput methods which limits their application in bunch commercial products.Cellulose nanofiber (CNF) as an emerging biomass binder shows great potential in field of flexible and freestanding electrode fabrication due to its 1D nanostructure, excellent electrochemical stability, and robust mechanical property. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] However, conventional CNFbased electrodes are characterized by low energy density owing to inadequate conductivity arising from the poor compatibility between CNF and conductive agents. Here, we report a conductive nanofiber network with decoupled electron and ion transfer pathways based on neutral carbon black (CB) nanoparticles and negatively charged CNF for high-loading thick electrode (up to 60 mg cm −2 ). This unique conductive CNF is achieved by a spontaneous electrostatic self-assembly technology as shown in Figure 1a. Microsize cellulose pulp was pretreated by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidization, which selectively oxidized the C6-hydroxyl group to a carboxyl group, leading to a strong negatively charged surface of the cellulose fibers. Negatively charged CNF was then obtained by disintegrating the microsized cellulose fiber down to the nanoscale by a probe sonication process for 1 h (Figures S1-S5, Supporting Information). Such negatively charged CNF can firmly absorb neutral CB nanoparticles by electrostatic attraction, forming a conformal conductive nanofiber. The conductive CNF can further assemble into an interconnected 3D network and tightly wrap the active electrode materials such as lithium iron phosphate (LFP) during the freeze-drying process (Figure 1b).Thick electrodes are appealing for high energy density devices but succumb to sluggish charge transfer kinetics and poor mechanical stability. Nanomaterials with large aspect ratio, such as carbon nanotubes, can help improve the charge transfer and strength of thick electrodes but represent a costly solution which hinders their utility outside of "lab scale production." Here, a conductive nanofiber network with decoupled electron and ion transfer pathways by the conformal electrostatic assembly of neutral carbon black particles on negatively charged cellulose nanofibers is reported. After integrating with ...

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“…From the view point of production cost and capacity, cellulose, the most abundant natural polymer on earth, is highly competitive and attractive as a 1D building block for constructing thick electrodes . Recently, Kuang et al reported a highly conductive hybrid fiber based on abundantly available cellulose nanofibers (CNFs) and commercialized CBs as a 1D building block for constructing free‐standing thick electrodes ( Figure 8 a) . The hybrid fibers were readily prepared by the conformal electrostatic assembly of neutral CBs on negatively charged CNFs, ensuring and efficient space packing of the CBs with low interface resistance.…”

“…e) Areal and volumetric capacity comparisons of the nanopaper electrode and the conventional electrode under different active mass loadings. Reproduced with permission . Copyright 2018, John Wiley and Sons.…”

Safety Issues in Lithium Ion Batteries: Materials and Cell Design

“…However, the optimized free-standing electrode exhibit lower energy density and inferior rate capability than conventional electrode. Kuang et al (2018) prepared a nanopaper electrode with compact structure and high mass loading (up to 60 mg/cm 2 ), in which conductive nanofiber (CNF) network is designed with decoupled electron and ion transfer pathways via electrostatic assembly of neutral CB particles on negatively charged CNF. Wang et al (2018a) made a folded GR high areal capacity composite electrode by a water-facilitated folding method.…”