Three VO2 polymorphs, namely monoclinic VO2 (B), monoclinic VO2 (M), and tetragonal VO2 (A), are synthesized, and their microstructures and electrochemical properties are studied for application in Zn-ion batteries (ZIBs). A cost-effective ZnSO4-based aqueous electrolyte with various concentrations (3 − 7 m) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) additive is developed. The optimal ZnSO4/LiTFSI ratio in the electrolyte for superior Zn//VO2 battery properties is examined. The coordination structures of various electrolytes are investigated using wide-angle X-ray scattering. The incorporation of LiTFSI impairs the hydrogen-bonded network of H2O molecules and causes solvated-TFSI and TFSI‧‧‧TFSI structures to form, altering the electrolyte properties (such as electrochemical stability window, ionic conductivity, and Zn(OH)2)3(ZnSO4)·xH2O byproduct formation tendency). It is found that an excessive LiTFSI concentration leads to the formation of ion aggregates in the electrolyte and thus deterioration of electrode specific capacity and rate capability. Operando transmission X-ray microscopy observations confirm the high dimensional stability of the VO2 cathode during charging and discharging; the length variation of the VO2 (B) rods is approximately 10 %. The electrolyte composition also affects the Zn2+/Zn redox behavior at the anode side. The incorporation of LiTFSI into the electrolyte affects the Zn plating/stripping Coulombic efficiency, morphology of the deposited Zn, dead Zn amount, and anode cycle life. The constructed Zn//VO2 (B) cell with 1 m ZnSO4/5 m LiTFSI dual-salt electrolyte shows 90 % capacity retention after 1000 cycles. The proposed electrode material and electrolyte composition have great potential for applications in high-performance and high-stability rechargeable ZIBs.
High entropy oxide (HEO) materials have recently emerged as promising anodes for lithium-ion batteries (LIBs). In this study, we conduct the first comparative analysis to investigate the influence of various electrode binders on electrochemical properties of (CrMnFeNiCu)3O4 HEO anodes. The organic-solvent-soluble polyvinylidene fluoride and water-soluble polyvinyl formamide, sodium carboxymethyl cellulose, sodium alginate, and sodium polyacrylate (NaPAA) binders are examined. Notably, the NaPAA binder leads to a significant enhancement in the HEO performance. The NaPAA coating on (CrMnFeNiCu)3O4 effectively improves the electrode charged discharge Coulombic efficiency and mitigates the electrode deterioration. Binder adhesion strength and stability toward electrolyte are assessed. The charge-transfer resistance and apparent Li+ diffusion of the HEO electrodes with various binders, accompanied by the post-cycling analyses, are examined. By employing the NaPAA binder, exceptional electrode capacities of 800 and 495 mAh g–1 are attained at charge-discharge rates of 50 and 2000 mA g–1, respectively, without noticeable capacity degradation after 300 cycles. The thermal reactivity of the lithiated electrodes is investigated using differential scanning calorimetry, and the impact of binders on the electrode exothermic onset temperature and total heat released is studied. Our findings provide valuable insights for enhancing the performance and safety of HEO anodes for LIBs.
A cost-effective chemical prelithiation solution, which consists of Li+, polyaromatic hydrocarbon (PAH), and solvent, is developed for a model hard carbon (HC) electrode. Naphthalene and methyl-substituted naphthalene PAHs, namely 2-methylnaphthalene and 1-methylnaphthalene, are first compared. Grafting an electron-donating methyl group onto the benzene ring can decrease electron affinity and thus reduce the redox potential, which is validated by density functional theory calculations. Ethylene glycol dimethyl ether (G1), diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether solvents are then compared. The G1 solution has the highest conductivity and least steric hindrance, and thus the 1-methylnaphthalene/G1 solution shows superior prelithiation capability. In addition, the effects of the interaction time between Li+ and 1-methylnaphthalene in G1 solvent on the electrochemical properties of a prelithiated HC electrode are investigated. Nuclear magnetic resonance data confirm that 10-h aging is needed to achieve a stable solution coordination state and thus optimal prelithiation efficacy. It is also found that appropriate prelithiation creates a more Li+-conducing and robust solid-electrolyte interphase, improving the rate capability and cycling stability of the HC electrode.
