Various hetero-element doping strategies have been widely investigated and have improved the cycle life of Ni-rich cathode materials. However, these approaches primarily focus on enhancing structural stability or controlling particle morphology to reduce microcrack formation, while overlooking the detrimental effects of the increased surface area. This provides additional reactive sites for residual lithium compounds, thereby exacerbating side reactions with the electrolyte and promoting extensive gas evolution. Consequently, suppressing parasitic reactions during the high-temperature operation of Ni-rich cathodes remains challenging. In this study, we employed a synergistic surface modification strategy comprising a washing process and an additional fluorine coating to develop an F-coated cathode material based on Nb-treated Li[Ni0.921Co0.040Mn0.020Al0.014Nb0.005]O2. The proposed strategy effectively passivates both grain boundaries and particle surfaces by forming lithium niobate and a stable lithium fluoride coating layer. Accordingly, the pouch-type full cell incorporating the developed cathode exhibited an excellent cycling retention of 81.5% after 1400 cycles at 45 °C, even at a charging C-rate of 2 C. Notably, isothermal microcalorimetry analysis revealed a significant reduction in heat generation for the modified cathode, clearly demonstrating the effectiveness of the proposed strategy. Overall, this synergistic surface engineering strategy overcomes the inherent limitations of Ni-rich cathode materials, providing a viable pathway for the development of stable, high-energy lithium-ion batteries operating at elevated temperatures.
Hexagonal boron nitride (h-BN) is chemically robust but intrinsically insulating, which limits its direct use as an electrochemically active electrode material. Here, Mn-doped h-BN powders were synthesized via high-energy ball milling, followed by solution-assisted mixing with an Mn precursor, and annealing under N2 at 700–900 °C. Structural and defect evolution were investigated using XRD, Raman spectroscopy, photoluminescence (PL), and electron paramagnetic resonance (EPR). Increasing annealing temperature and Mn content induce measurable lattice modifications and phonon softening, as evidenced by a redshift of the E2g Raman mode and the emergence of additional defect-activated bands. PL reveals a systematic enhancement of blue emission with increasing processing severity, consistent with the creation of dopant- and defect-related radiative recombination pathways and concomitant band-structure perturbation. EPR directly confirms Mn incorporation through the Mn2+ hyperfine sextet and shows temperature-dependent linewidth broadening, indicating stronger Mn–Mn interactions and partial clustering at higher annealing temperatures, while a carbon-related signal near g≈2.005 is suppressed upon annealing. Electrochemical testing in symmetric supercapacitor cells demonstrates a transition from predominantly electric double-layer behavior at 700 °C to a pronounced pseudocapacitive response at higher temperatures, with the best overall performance achieved at intermediate thermal activation (800 °C) and moderate Mn loading (∼3%). For this best-performing composition, the maximum specific capacitance reaches 566.73 F/g at a scan rate of 10 mV/s, and the Ragone plot yields an energy density of 78.7 Wh/kg at a power density of 15.7 kW/kg. These results show that Mn-assisted defect engineering provides a viable route to activate h-BN and tailor its charge-storage mechanism for energy-storage applications.
Complex hydrides offer high H2 storage capacities but suffer from kinetic degradation and microstructural coarsening, requiring operations at elevated temperatures, typically above 180°C. Here, we demonstrate grain boundary complexion-mediated structural stabilization using ultra-low loading of Zr-based metal-organic frameworks (Zr-MOFs; 1 at.% Zr; UiO-66 vs. MIP-206) in the reactive hydride composite system 6Mg(NH2)2-9LiH-2LiBH4 (6.9.2-RHC). Incorporation of microporous Zr-UiO-66 significantly lowers the hydrogen absorption onset temperature from 162°C to 81°C, enables measurable hydrogen uptake at 35°C (1.07 wt.% under 80 bar H2). In addition, UiO-66 accelerates desorption by more than threefold at 140°C, increases reversible capacity from 3.2 to 4.1 wt.%, and maintains the capacity over 15 cycles compared with the pristine 6.9.2-RHC. In situ synchrotron radiation X-ray diffraction confirms that the intrinsic amide–imide reaction pathway remains unchanged, suggesting that structural stabilization plays a dominant role in the enhanced hydrogen storage performance. SAXS reveals stabilized nanoscale domains (≈2.4–3.3 nm), while SANS/USANS demonstrates suppression of hierarchical aggregation relative to pristine 6.9.2-RHC. Ball-milling of UiO-66 preserves short-range tetrahedral structural units (≈0.76 nm) that are proposed to stabilize grain-boundary complexions capable of accommodating the large (20–30 per cent) volume changes associated with hydrogen cycling. The performance hierarchy (UiO-66 > MIP-206 > pristine) demonstrates that MOF-derived short-range structural motifs suppress coarsening by promoting grain-boundary complexions, enabling practical low-temperature hydride operation through stabilized reactive interfaces.
