Abstract
AbstractSodium‐ion batteries (SIBs) and potassium‐ion batteries (PIBs) are prospective candidates for large‐scale energy storage systems cause of their abundant resources. However, unsatisfactory rate and cycling performance of carbon‐based anodes present a bottleneck for the applications of SIBs/PIBs due to the large sizes of sodium/potassium ions. Herein, oxygen‐doped vertically aligned carbon aerogels (VCAs) with hierarchically tailored channels are synthesized as anodes in SIBs/PIBs via a controllable unidirectional ice‐templating technique. VCA‐3 (cooling rate of 3 K min−1) delivers the highest reversible capacity of ≈298 mAh g−1 at 0.1 C with an excellent cycling performance over 2000 cycles at 0.5 C for SIBs, while VCA‐5 manifests a superior capacity of ≈258 mAh g−1 at 0.1 C with an 82.7% retention over 1000 cycles at 0.5 C for PIBs. Moreover, their full cells demonstrate the promising potential of VCAs in applications. This novel controllable ice‐templating strategy opens unique avenues to tune the construction of hollow aligned channels for shortening ion‐transport pathways and ensuring structural integrity. New insights into structure‐performance correlations regulated by the cooling rates of an ice‐templating strategy and design guidelines for electrodes applicable in multiple energy storage technologies are reported.
Highlights
vertically aligned carbon aerogels (VCAs)-3 delivers the highest reversible capacity of ≈298 mAh g−1 at 0.1 C with an excellent cycling performance over 2000 cycles at 0.5 C for SIBs, while VCA-5 manifests a superior capacity of ≈258 mAh g−1 at 0.1 C
We innovatively develop a controllable unidirectional ice-templating strategy (Scheme 1) to tailor lowcost cellulose nanocrystals (CNCs)/polyethylene oxide (PEO)-derived, vertically aligned carbon aerogels (VCAs) anodes with desirable features for the large-scale practical applications of SIBs/potassium-ion batteries (PIBs)
By gently controlling the cooling rate of the unidirectional ice-templating technique, the oxygenfunctionality, ordered structures, defect densities, channel widths, as well as interlayer spacings of graphitic domains for VCAs have been tuned gradually to modulate the Na+/K+ storage behavior, thereby ensuring optimized ice-templated carbon micro/nanostructures suited for their application as stable SIB or PIB anode materials
Summary
VCA-U has the 24% and 71% capacitance contribution at 0.1 and 5.0 mV s−1, respectively (Figure S11d, Supporting Information) Such a higher proportion of capacitive contribution along with the faster electrochemical kinetic account for the superior rate performance and structural stability of the VCA-5 electrode in PIBs. Figure 6d shows the Nyquist plots of VCA electrodes from EIS analysis, where VCA-5 displays the smallest Rct in comparison with VCA-3, VCA-7, and VCA-U (Table S3, Supporting Information) in half cells of PIBs. Figure 6d shows the Nyquist plots of VCA electrodes from EIS analysis, where VCA-5 displays the smallest Rct in comparison with VCA-3, VCA-7, and VCA-U (Table S3, Supporting Information) in half cells of PIBs It demonstrates that the VCA-5 electrode possesses the lowest charge-transfer resistance at the electrode/electrolyte interface during the potassiation/depotassiation process, which can be attributed to the enhanced number of short-range ordered nanodomains with an expanded interlayer spacing, the appropriate number of defective sites and well-developed hollow channels.[35] To further illustrate the K+ ion diffusion kinetics of VCA electrodes, GITT measurements were conducted as well (Figure 6e,f; Figure S12, Supporting Information). The energy density of VCA-5//K2PTCDA full-cell was estimated ≈118 Wh kg−1, which is comparatively higher among some reported PIB full cells (see Table S5, Supporting Information)
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