Nickel sulfide/nickel phosphide heterostructures anchored on porous carbon nanosheets with rapid electron/ion transport dynamics for sodium-ion half/full batteries

Construction of three-dimensional hierarchical nest-like NiS2 with efficient stress dissipation for superior sodium storage

Transitional metal sulfides (TMSs) with high theoretical capacities are promising anode materials for sodium-ion batteries (SIBs). However, the low conductivity and large volume change during charge/discharge processes lead to poor rate capability and inferior cycling stability. In this work, we constructed three-dimensional hierarchical NiS2 microspheres by hydrothermal method followed by sulfurization. With polyvinylpyrrolidone (PVP) as a directing agent, NiS2 nanosheets orderly stack concentrically with an opening in the center, giving rise to a nest-like structure. By using PVP with different molecular weight, different morphologies of flower-like or solid NiS2 microspheres can be obtained. Finite element analysis (FEA) suggests that the unique nest-like structure can effectively dissipate the stress and suppress the volume variation during sodium insertion, thus giving rise to greatly enhanced reversible capacity and cycling stability for sodium storage, as compared to the other two samples with different organized structure.

Crystal Field Stabilization Energy Asymmetrically Constructed Built-in Electric Fields for Efficient Water Cracking

Efficient bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) play crucial roles in water electrolysis. However, the discrepancy in binding affinities of catalytic sites to O/H-contained intermediates makes it difficult to achieve OER and HER bifunctional catalysis simultaneously. Multi-component heterostructures have been demonstrated to be an effective solution to realize bifunctional electrocatalysts, but the division of labor and action mechanism of each component are not fully elucidated. Therefore, based on asymmetrical crystal field stabilization energy (CFSE) between NiS and Ni2P, the heterogeneous catalyst (NiS/Ni2P@NF) with built-in electric field (BEF) is constructed in this paper, which showed efficient bifocal water cracking. DFT calculation has confirmed that BEF causes the directional movement of electrons in the material, thus optimizing the OER/HER reaction path. Further control experiments indicated that NiS and Ni2P serves as the active species for the corresponding OER and HER, thus NiS/Ni2P@NF delivers a remarkably reduced cell voltage of 1.62 V (10 mA cm-2) within a H-type electrolyzer as both anode and cathode electrodes. The strategy of constructing BEF based on asymmetrical CFSE has the potential to precisely induce the local electron flow of the catalytic site and accurately design multifunctional catalysts with composition-function contrast.

Heterogeneous Engineering Strategy Derived In Situ Carbon-Encased Nickel Selenides Enabling Superior LIBs/SIBs with High Thermal Safety

Nowadays, the extended usage of lithium/sodium ion batteries (LIBs/SIBs) encounters nerve-wracking issues, including a lack of suitable reservoirs and high thermal runaway hazards. Although using TiO2 and Li4Ti5O12 has been confirmed to be effective in improving battery safety, their low theoretical capacities inevitably cause damage to the electrochemical performance of the battery. Achieving win-win results has become an urgent necessity. This study designed a metal-organic framework (MOF)-derived in situ carbon-coated metal selenide (Ni-Se@G@C) as the anode. When the current density is 0.1-0.3 A g-1, the initial capacity of LIBs reaches 993.2 mAh g-1, which increases to 1478.9 mAh g-1 after running 800 cycles. When running at 2 A g-1, the cell also offers a relatively high capacity of 458.3 mAh g-1 after 1500 cycles. After the replacement of graphite with Ni-Se@G@C, the self-heating temperature (T0) and thermal runaway triggering temperature (T1) of half and full cells are significantly increased. Meanwhile, the maximum thermal runaway temperature (T2) and maximal heating release rate (HRRmax) are significantly reduced. Of note, the usage of Ni-Se@G@C enables the battery with superior cycling and rate performance. When used in SIBs, the cell gives an initial discharge capacity of 624.9 mAh g-1, which still remains at 269.4 mAh g-1 after running 200 cycles at 1 A g-1. Notably, Ea of the Ni-Se@G@C cell is 5.6 times higher than that of the graphite cell, corroborating the promoted safety performance. This work provides a new paradigm for MOF-derived micro/nanostructures, enabling the battery with an excellent electrochemical and safety performance portfolio.

Vacancy-Defect Ternary Topological Insulators Bi2Se2Te Encapsulated in Mesoporous Carbon Spheres for High Performance Sodium Ion Batteries and Hybrid Capacitors

Ternary topological insulators have attracted worldwide attention because of their broad application prospects in fields such as magnetism, optics, electronics, and quantum computing. However, their potential and electrochemical mechanisms in sodium ion batteries (SIBs) and hybrid capacitors (SIHCs) have not been fully studied. Herein, a composite material comprising vacancy-defects ternary topological insulator Bi2Se2Te encapsulated in mesoporous carbon spheres (Bi2Se2Te@C) is designed. Bi2Se2Te with ample vacancy-defects has a wide interlayer spacing to enable frequent insertion/extraction of Na+ and boost reaction kinetics within the electrode. Meanwhile, the Bi2Se2Te@C with optimized yolk-shell structure can buffer the volume variation without breaking the outer protective carbon shell, ensuring structural stability and integrity. As expected, the Bi2Se2Te@C electrode delivers high reversible capacity and excellent rate capability in half SIB cells. Various electrochemical analyses and theoretical calculations manifest that Bi2Se2Te@C anode confirms the synergistic effect of ternary chalcogenide systems and suitable void space yolk-shell structure. Consequently, the full cells of SIB and SIHC coupled with Bi2Se2Te@C anode exhibit good performance and high energy/power density, indicating its widespread practical applications. This design is expected to offer a reliable strategy for further exploring advanced topological insulators in Na+-based storage systems.

Micro-mesoporous cobalt phosphosulfide (Co3S4/CoP/NC) nanowires for ultrahigh rate capacity and ultrastable sodium ion battery

The construction of heterostructure materials has been demonstrated as the promising approach to design high-performance anode materials for sodium ion batteries (SIBs). Herein, micro-mesoporous cobalt phosphosulfide nanowires (Co3S4/CoP/NC) with Co3S4/CoP hetero-nanocrystals encapsulating into N-doped carbon frameworks were successfully synthesized via hydrothermal reaction and subsequent phosphosulfidation process. The obtained micro-mesoporous nanowires greatly improve the charge transport kinetics from the facilitation of the charge transport into the inner part of nanowire. When evaluated as SIBs anode material, the Co3S4/CoP/NC presents outstanding electrochemical performance and battery properties owing to the synergistic effect between Co3S4 and CoP nanocrystals and the conductive carbon frameworks. The electrode material delivers outstanding reversible rate capacity (722.33 mAh/g at 0.1 A/g) and excellent cycle stability with 522.22 mAh/g after 570 cycles at 5.0 A/g. Besides, the Ex-situ characterizations including XRD, XPS, and EIS further revealed and demonstrated the outstanding sodium ion storage mechanism of Co3S4/CoP/NC electrode. These findings pave a promising way for the development of novel metal phosphosulfide anodes with unexpected performance for SIBs and other alkali ion batteries.

Synthesis of multi-cavity mesoporous carbon nanospheres through solvent-induced self-assembly: Anode material for sodium-ion batteries with long-term cycle stability

Mesoporous carbon nanospheres (MCSs) are extensively employed in energy storage applications due to their ordered pore size, large specific surface area (SSA), and abundant active sites, resulting in excellent electrochemical performance for sodium storage. However, challenges persist in achieving precise structural control and stable synthesis reactions for these MCSs. Additionally, employing MCSs with a larger SSA in sodium storage applications can lead to increased side reactions and potential structural instability. To address these issues, we propose a solvent-induced self-assembly method for obtaining high nitrogen-containing multi-cavity MCSs with reduced SSA. The morphology and SSA of the nanospheres can be precisely adjusted by regulating the reaction time. Introducing an amine-phenol bridging structure into the polymer system significantly bolsters the structural and morphological stability of the mesoporous materials. The performance of these novel nanospheres in sodium-ion batteries (SIBs) is remarkable, exhibiting excellent sodium storage capability and exceptional ultra-long cycle stability. At a rate of 0.1 A g-1, the nanospheres achieved a high reversible capacity of 252 mAh g-1, and even after 20,000 cycles at 5 A g-1, a specific capacity of 136 mAh g-1 was retained. In summary, our study presents a novel approach for synthesizing mesoporous carbon materials and offers valuable insights for sodium storage research, opening new possibilities for enhancing energy storage applications.

Cu/Ti co-doping boosting P2-type Fe/Mn-based layered oxide cathodes for high-performance sodium storage

Environmentally friendly P2-type layered iron manganese oxides appear to be one of the most potential cathode materials for sodium-ion batteries (SIBs). However, their practical application is hindered by the unfavorable phase transitions, dissolution of transition metals, and poor air stability. One effective strategy by either single-cation doping or high-cost Li involved co-doping is used to alleviate the problems. Here, low-cost Cu/Ti co-doping is introduced to boost P2-Na0.7Cu0.2Fe0.2Mn0.5Ti0.1O2 as an air and electrochemical stable cathode material for SIBs. The resulting electrode delivers an initial capacity of 130 mAh g-1 at 0.1C within 2.0-4.2 V, a reversible discharge capacity of 61.0 mAh g-1 at a high rate of 5C and a capacity retention ratio exceeding 71.1% after 300 cycles. In particular, the co-doped crystal structure is well-maintained after 1 month of exposure to air, and even 3 days of soaking in water. Furthermore, the enhancement is elucidated by the effectively mitigated P2-Z and the completely suppressed P2-P'2 phase transitions, the decreased volume variation proved by in-situ X-ray diffraction (XRD), as well as the lowered transition-metal dissolution evidenced by inductively coupled plasma optical emission spectrometer (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The low-lost Cu/Ti doping strategy could thus be effective for designing and preparing environmentally friendly and high-performance cathode materials for SIBs.