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.
LiFePO4 batteries suffer from sluggish charge transfer, severe polarization, and reaction heterogeneity at low temperatures. In this work, a Joule-Heating-Driven Riveting strategy constructs a Zn-mediated surface-bulk coupled architecture for low-temperature electrochemical modulation. Mechanically assisted surface assembly followed by ultrafast Joule heating integrates anchored Zn-containing domains with near-surface lattice reconstruction, creating a built-in electric field and a favorable electronic environment for Li+ extraction/insertion. The modified LiFePO4 exhibits at −20°C across a broad rate range higher reversible capacity, reduced voltage hysteresis, and superior cycling durability. Mechanistic studies reveal accelerated kinetics, enhanced solid-solution behavior, and suppressed structural fluctuation, alleviating polarization-induced phase heterogeneity. In pouch full cells, the cathode shows lower resistance increase, stable output, and uniform stress evolution. Post-cycling and simulation analyses confirm reduced side reactions, mitigated local stress, and homogeneous lithium distribution. This work presents an effective cathode-engineering strategy for low-temperature LiFePO4 batteries and a scalable route for cold-tolerant polyanion cathodes.
Tuning the electronic structure and redox-active-site distribution of organic cathodes is crucial for achieving high-capacity, fast-charging, durable, and wide-temperature adaptable sodium-ion batteries (SIBs). Herein, two bipolar porous organic polymers (POPs) (denoted as HATN-TPA and QPDO-TPA) were rationally designed and synthesized to explore how molecular-level structural differences govern sodium-storage behavior. Compared with QPDO-TPA, HATN-TPA features a narrower band gap and more uniformly distributed redox-active sites, enabling accelerated sodium-ion diffusion kinetics and highly reversible multi-electron redox processes. As a result, the HATN-TPA cathode for SIBs delivers a high reversible specific capacity of 242.6 mAh g-1 at 0.1 A g-1, an exceptional rate capability of 123.5 mAh g-1 at an ultra-high current density of 30 A g-1 (≈100 C), and outstanding cycling stability with approximately 91% capacity retention over 25,000 cycles at 2 A g-1. Notably, the HATN-TPA cathode maintains robust sodium-ion storage performance over a wide temperature range, retaining 172.2 mAh g-1 after 850 cycles at -20°C and 200.8 mAh g-1 after 500 cycles at 60°C. Moreover, a HATN-TPA cathode with a high mass loading (>6 mg cm-2) also delivers high specific capacity, underscoring its practical potential. Comprehensive in situ FT-IR and ex situ XPS/EPR characterizations, combined with theoretical simulations, elucidate the dual-ion storage mechanism during the charge/discharge process. Furthermore, a hard carbon//HATN-TPA full cell demonstrates excellent rate performance and long-term cycling stability. This work establishes a molecular-engineering strategy for constructing next-generation bipolar POPs toward high-performance electrochemical storage systems.
