| Author: | Yu, Zhenlu |
| Title: | Building stable electrode/electrolyte interfaces for advanced potassium-ion batteries |
| Advisors: | Zhang, Biao (AP) Huang, Haitao (AP) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Subject: | Electrodes, Carbon Potassium-ion batteries Electric batteries -- Electrodes Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Physics |
| Pages: | xvii, 170 pages : color illustrations |
| Language: | English |
| Abstract: | Potassiumion batteries (PIBs) are considered promising complements to prevailing Li-ion batteries for large-scale energy storage. Stable cycling of PIBs relies on not only the development of advanced electrode materials but also the building of robust electrode/electrolyte interfaces on both anode and cathode sides. This thesis first explores the K ion storage mechanism in carbon anodes and then investigates the effect of the anode/electrolyte interface on the charge/discharge kinetics. The carbon-based interfacial chemistry regulation strategy is further extended to high-capacity potassium metal anodes. Along with the anodes, this thesis is also committed to constructing cathode/electrolyte interfaces at a high voltage to realize a competitive energy density. Hard carbon is among the most attractive anodes for PIBs, but the inexplicit charge storage mechanism at the low voltage region impedes the rational structural design. Systematic studies demonstrate the presence of quasi-potassium nanoclusters after deep discharging, evidencing that the K ion pore-filling, in addition to intercalation, contributes to the low-voltage capacity. To improve the rate performance of hard carbons, cyclic ether tetrahydrofuran (THF) as a weak solvent is applied to regulate the interfacial chemistry and boost the de-solvation process. An inorganic-rich solid electrolyte interphase (SEI) resulting from enhanced anion decomposition benefits the charge transfer for superior rate capability and cyclic performance even at 0 °C. Besides severing as anodes, carbon-based materials have been widely utilized as the host for potassium metal anodes. Carbon nanofibers are adopted as a model system to explore the surface functionality of carbon in determining interfacial behavior. Because of the lower Fermi level than commercial Al, the CNFs modified Al prevents excessive electrolyte consumption and promotes the formation of thin inorganic-rich SEI. The performance is further improved by incorporating nickel species to provide abundant active sites for K-embryo nucleation and induce planar growth of K metal. Consequently, the decorated Al current collector enables a 4.4 V anode-free full cell with 89% capacity retained after 50 cycles. To achieve a high-voltage potassium metal battery, we extend the terminal alkyl chain of ether solvent to alleviate the electrolyte decomposition at high voltages. The high viscosity accompanied by the long alkyl groups could be effectively mitigated by introducing an S-containing additive, which further enhances the oxidative stability to 4.6 V. Additionally, the additive aids in forming S-rich organic species at the interphases, which prevents the cathode's metal dissolution and facilitate uniform K deposition by enhancing the kinetics. Thanks to the stable interphases and minimized side reactions, the dilute non-fluorinated ether-based electrolyte allows the full cell to cycle stably for more than 200 cycles, achieving a high Coulombic efficiency of over 99.4% with a negative/positive capacity ratio of 4. |
| Rights: | All rights reserved |
| Access: | open access |
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