O3-type layered oxide materials are attractive materials for cathode fabrication for commercial sodium-ion batteries (SIBs). However, their electrochemical performance and practical viability are hindered by rapid capacity decay—driven by severe phase transitions and air/moisture sensitivity. Herein, multielement codoped O3-type layered oxide materials NaLi0.05Ni0.3Mn0.5₋xCu0.1Mg0.05SnxO2 (x = 0, 0.01, 0.03, 0.05) were synthesized using a simple spray-drying method. These materials were used for fabricating cathodes for SIBs. The incorporation of Sn formed strong Sn–O bonds, effectively enhancing the structural stability. Enhanced cycling stability and rate performance were achieved, benefiting from the medium entropy–derived stabilization, disordered elemental distribution, and large interlayer spacing after Sn doping. The optimized NaLi0.05Ni0.3Mn0.47Cu0.1Mg0.05Sn0.03O2 (x = 0.03; Sn0.03) cathode demonstrated a reversible capacity reaching 142 mAh g−1 within a potential window of 2.0–4.2 V Na/Na+, while exhibiting excellent cycling endurance (retaining 83% of the initial capacity after 500 cycles at 1C) and rate capability (98 mAh g−1 at 30 C). The underlying mechanism was investigated via operando synchrotron X-ray diffraction and X-ray absorption spectroscopy to monitor the lattice evolution and charge compensation behavior during cycling. Sn doping facilitated a solid solution–dominated phase transition, effectively mitigating lattice distortion and complex phase transition, and enhancing the cycling performance. The reversible redox reactions of Ni2+/Ni4+ and Cu2+/Cu3+ compensated the charges, while Mn4+ and Sn4+ remained electrochemically inactive, further stabilizing the structure. Sn doping improved the structural integrity, maintaining electrochemical performance after water immersion and air exposure. A Sn0.03//hard carbon full cell exhibited a competitively high energy density of 261.89 Wh kg−1. Density functional theory results corroborated delayed phase transitions and enhanced air/moisture stability with Sn incorporation. These findings underscore the effects of multielement codoping medium entropy and Sn incorporation in O3-type layered oxides, establishing Sn0.03 as an efficient candidate cathode material for practical SIB applications.
Silicon suboxide (SiOx) is a promising anode material for next-generation lithium-ion batteries because of its high capacity and structural stability. However, its practical application is severely limited by substantial irreversible lithium consumption during the first cycle, making effective prelithiation essential for improving the initial Coulombic efficiency (ICE). Although direct-contact prelithiation provides a simple approach for lithium compensation, controlling lithium transfer at the electrode/Li interface remains a major challenge. Herein, Ni/Ag bilayer thin films with identical nominal total metal thickness but different stacking sequences were introduced onto SiOx electrodes to regulate direct-contact prelithiation. Single-layer Ni and Ag coatings together with Ni/Ag bilayers of opposite stacking sequences were systematically investigated to examine the influence of the SiOx-facing and Li-facing metal layers. Among them, the SiOx/Ni/Ag electrode exhibited the most efficient prelithiation behavior, achieving an ICE of 96.9% after only 7 min of direct contact, whereas the SiOx/Ag/Ni electrode reached only 87.7% even after 10 min of prelithiation. Structural and depth-resolved chemical analyses revealed that the optimized stacking sequence promoted more complete conversion toward Li-rich silicate species while suppressing electrode expansion. Consequently, the SiOx/Ni/Ag electrode exhibited lower interfacial resistance and faster electrochemical stabilization while maintaining stable cycling performance. These findings demonstrate that the arrangement of functional metal layers, rather than metal composition alone, strongly influences lithium transfer during direct-contact prelithiation, establishing stacking-sequence engineering as a useful thin-film design strategy for efficient prelithiation of high-capacity Si-based anodes.
The practical viability of small-molecule organic anodes is often limited by active material dissolution and the accompanying interfacial instability in liquid electrolytes. Herein, we investigate how functional group chemistry influences Li/Li+ interactions, dissolution behavior, interfacial evolution, and electrochemical accessibility in naphthalene-derived organic anodes. Using naphthalene as a model framework, we systematically compare hydroxylated and carboxylated derivatives through combined computational, electrochemical, spectroscopic, and morphological analyses. Density functional theory (DFT) calculations reveal stronger localized Li+ interactions at the vicinal dihydroxyl groups of 2,3-dihydroxynaphthalene (DHN) and the carboxyl group of 2-naphthoic acid (NPA) than in Naph and the monohydroxylated derivatives. However, this enhanced local affinity does not translate into improved electrochemical reversibility. Naphthalene and the monohydroxylated derivatives exhibit limited dissolution, relatively stable interfacial behavior, and sustained cycling performance over 1000 cycles. In contrast, DHN and NPA exhibit greater active material dissolution and more extensive interfacial reconstruction, resulting in reduced electrochemical accessibility and inferior reversibility. This work highlights the importance of balancing favorable Li/Li+ interactions with resistance to dissolution and interfacial reconstruction to presere electrochemically accessible active material in small-molecule organic anodes.
