Chitin and Chitosan—Structurally Related Precursors of Dissimilar Hard Carbons for Na-Ion Battery

Abstract

Hard carbons (HCs) prepared from renewable precursors are promising cost-effective electrodematerial candidates for the application in Na-ion battery. Usually these materials are derived from cellulose. Here, however, we demonstrate that other polysaccharides, such as chitin and chitosan, can be as well up-and-coming parent materials of HCs. Despite structural similarities, thermal decomposition of these two biopolymers proceeds differently, contributing to the discrepancies in physicochemical properties of resulting HCs. Although chitin-and chitosan-derived HCs have comparable d-spacings and crystallite sizes, solid state pyrolysis of the former biopolymer leads to micro-mesoporous material with significant specific surface area, while that of chitosan yields non-porous carbon. Despite that, both materials deliver similar initial specific charge of 280 mAh g-1 (at C/10 rate) and their electrochemical performance starts to diverge only upon longer cycling at higher rate. With time, inorganic contaminants present in chitosan-derived HC presumably delay the diffusion of Na-ions to and within the electrode, and slow down the rate of electrochemical reactions, eventually triggering polarization build-up. Further optimization of the chitosan-derived HC through acid-treatment enables unblocking some of the micropores and increasing the carbon content in this material, therefore enhancing its active surface area and suppressing continuous fading of the specific charge.

Impact of biomass inorganic impurities on hard carbon properties and performance in Na-ion batteries

“…2 and Table S3, SI) showed that the C content increases and reaches 80 wt% for HC-P, 68 wt% for HC-A while HC-G, has the lowest carbon percentage, ~64 wt%. Overall, these values are significantly lower than other hard carbons originating from lignin [28] or chitosan [35]. Moreover, the O content significantly decreases after pyrolysis, but for HC-G is still high, ~24 wt% compared to the other carbons (16.3 wt% for HC-A and 11.7…”

“…It was reported before that such impurities react with the O2 and CO2 from the atmosphere, while exposed to air, forming metallic oxides and/or metallic carbonates [28], which may also explain the large amount of oxygen. Such impurities (metals + heteroatoms) may have different negative impacts on the electrochemical performance such as a decrease of the overall material conductivity or electrolyte decomposition with formation of SEI layer causing an initial irreversibility and/or fading capacity, as reported before [28,35].…”

“…As result, the N2 specific surface area (SSA) decreased considerably (from 180 to ~10 m 2 g -1 ), the d-spacing slightly diminished, as well, while the electrochemical performance was improved (both reversible capacity and stability over cycling). In another study, [35] chitosan precursor was washed after the heat treatment at 1300°C with an acidic solution (20% HCl) to remove the Ca-based impurities coming from its extraction from sea food shells. Although efficient, washing does not significantly alter the texture or structure of the hard carbon, but an increase in active surface area (ASA) could be observed (from 1.8 to 5.2 m 2 g -1 ).…”

“…The resulting data were converted via PowDLL [43] and then treated with the profile peaks fitting option in Winplotr [44]. The refined peaks positions led to calculated d-spacing for the pristine materials of 3.819(13) Å for HC-A, 3.788(7) Å for HC-G and 3.977(15) Å for HC-P, values wide enough to allow Na + insertion-extraction, as reported in literature [35,45]. The presence of impurities is indicated by several sharp peaks visibles for all three pristine materials ( Fig.…”

Unraveling the Properties of Biomass-Derived Hard Carbons upon Thermal Treatment for a Practical Application in Na-Ion Batteries

“…They observed that the lignin-rich peanut shell hard carbon showed the best electrochemical performance because of its favorable surface area, degree of graphitization, and elemental composition, which was correlated with its high lignin content. Conder et al [39] also explored the role of the biomass composition in the performance of hard carbon by preparing chitin and chitosan derived materials. Even if the parent biomolecules were very similar, the derived hard carbons presented different physicochemical and electrochemical properties.…”