Polyvinylidene Fluoride-Derived Carbon-Confined Microcrystalline Graphite with Improved Cycling Life and Rate Performance for Potassium Ion Batteries

Abstract

The practical application of the state-of-art graphite anode materials for potassium ion batteries (KIBs) is currently frustrated by their poor cycling life and unsatisfactory rate performance. Herein, a bifunctional carbon coating derived from polyvinylidene fluoride is developed not only to create a confinement effect for suppressing the enormous c-axis volume expansion of graphite host during the potassiation/depotassiation process but also to tune the electrode surface condition through an increased specific surface, enriched mesopores, and F-doping. After the coverage with the featured carbon coating, the charge transfer/K ion diffusion kinetics is enhanced prominently, which is verified through systematic kinetics analyses, including determining the capacitive contribution, the calculation of the K ion diffusion coefficient, and investigating the impedance spectroscopy. The hybridized electrode exhibits substantially improved cycling stability (especially long-term ability) and rate capability. Typically, a high charge capacity of 191 mAh g–1 is well-retained after 120 cycles at 0.1 A g–1, and a favorable rate capacity retention of 42.2% is still maintained under the large current density of 1.0 A g–1. This study demonstrates that the confinement strategy with a well-designed robust carbon coating is feasible to solve the deficiency of graphite materials when used in KIBs and sheds light on the further exploration of high-performance graphite electrodes for practical KIBs.

Surface Modification with F-Doped Carbon Layer Coating on Natural Graphite Anode for Improving Interface Compatibility and Electrochemical Performance of Lithium-Ion Capacitors

“…To investigate the surface chemical composition and state of the materials, XPS analysis was conducted, focusing on the target elements C and F. Owing to the high electronegativity of F, three types of C−F bonds can exist (ionic, semi-ionic, and covalent bonds) with different bond lengths and energies. 35,58 In the F 1s spectra shown in Figure 3a, the C−F bonds were observed in semi-ionic bonds (687.1 eV) predominantly and covalent bonds (688.2 eV), consistent with the previous studies. 37,43 The C atoms on the coating layer change the electronic configuration from sp 2 (the semi-ionic C−F bonds) to sp 3 (the covalent C−F bonds) through the coating process.…”

Promoting the Normal- and Low-Temperature Performances of Natural Graphite by the F-Doping Derived from PVDF Modification

“…In addition, C–F bonds (C 1s at 290.0 eV and F 1s at 690.0 eV , ) were also distinguished in PG180-1 (Figures c,f), possibly because the molten PVDF interacted strongly with NG during sintering to realize the F-doping adjacent to the NG surface. The superficial F-doping could not only improve the electron conductance and Li-ion transfer in graphite but also boost the structural stability and cycling stability of the graphite anode. − …”

Advancements and Prospects of Graphite Anode for Potassium‐Ion Batteries

“…Reproduced with permission. [ 112 ] Copyright 2021, American Chemical Society. i) SEM image of G@PSC and j) schematic diagram showing the formed structure; k) The detailed K‐storage process and K‐storage sites of G@PSC at the second discharge process.…”

“…Here, Yang et al. [ 112 ] prepared a fluorine‐doped carbon‐coating‐protected natural microcrystalline graphite (FC@NMG‐3) utilizing PVDF as a carbon source. HRTEM images in Figure 10f reveal the turbostratic morphology of carbon coating with a thickness of ≈2 nm, which was consistent with the PVDF‐derived pyrolytic carbon.…”

“…Polyvinylidene fluoride (PVDF) with high fluorine content and pore-rich nature in the resulting product is considered as a potential precursor choice for forming effective fluorine-doped carbon coatings. Here, Yang et al [112] prepared a fluorine-doped carboncoating-protected natural microcrystalline graphite (FC@NMG-3) utilizing PVDF as a carbon source. HRTEM images in Figure 10f reveal the turbostratic morphology of carbon coating with a thickness of ≈2 nm, which was consistent with the PVDF-derived pyrolytic carbon.…”