Flower-like Spherical α-Ni(OH)2 Derived NiP2 as Superior Anode Material of Sodium-Ion Batteries

Transition metal phosphides (TMPs) are promising anode candidates for sodium-ion batteries, due to their high theoretical specific capacity and working potential. However, the low conductivity and excessive volume variation of TMPs during insertion/extraction of sodium ions result in a poor rate performance and long-term cycling stability, largely limiting their practical application. In this paper, NiP₂ nanoparticles encapsulated in three-dimensional graphene (NiP₂@rGO) were obtained from the flower-like spherical α-Ni(OH)₂ by phosphating and carbon encapsulation processes. When used as a sodium-ion batteries anode material, the NiP₂@rGO composite shows an excellent cycling performance (117 mA h g⁻¹ at 10 A g⁻¹ after 8000 cycles). The outstanding electrochemical performance of NiP₂@rGO is ascribed to the synergistic effect of the rGO and NiP₂. The rGO wrapped on the NiP₂ nanoparticles build a conductive way, improving ionic and electronic conductivity. The effective combination of NiP₂ nanoparticles with graphene greatly reduces the aggregation and pulverization of NiP₂ nanoparticles during the discharge/charge process. This study may shed light on the construction of high-performance anode materials for sodium-ion batteries and to other electrode materials.     

Wintersweet‐Flower‐Like CoFe2O4/MWCNTs Hybrid Material for High‐Capacity Reversible Lithium Storage

CoFe₂O₄/multiwalled carbon nanotubes (MWCNTs) hybrid materials were synthesized by a hydrothermal method. Field emission scanning electron microscopy and transmission electron microscopy analysis confirmed the morphology of the as‐prepared hybrid material resembling wintersweet flower “buds on branches”, in which CoFe₂O₄ nanoclusters, consisting of nanocrystals with a size of 5–10 nm, are anchored along carbon nanotubes. When applied as an anode material in lithium ion batteries, the CoFe₂O₄/MWCNTs hybrid material exhibited a high performance for reversible lithium storage. In particular, the hybrid anode material delivered reversible lithium storage capacities of 809, 765, 539, and 359 mA h g^?1 at current densities of 180, 450, 900, and 1800 mA g^?1, respectively. The superior performance of CoFe₂O₄/MWCNTs hybrid materials could be ascribed to the synergistic pinning effect of the wintersweet‐flower‐like nanoarchitecture. This strategy could also be applied to synthesize other metal oxide/CNTs hybrid materials as high‐capacity anode materials for lithium ion batteries.     

Bismuth Nanoparticles Anchored on Ti3C2Tx MXene Nanosheets for High-Performance Sodium-Ion Batteries

Sodium-ion batteries are promising energy-storage systems, but they are facing huge challenges for developing fast-charging anode materials. Bismuth (Bi)-based anode materials are considered as candidates for fast-charging anodes of sodium-ion batteries due to their excellent rate performance. Herein, we designed a two-dimensional Bi/MXene anode material based on a hydrogen thermal reduction strategy. Benefitting from microstructure advantages, Bi/MXene anodes exhibited an excellent rate capability and superior cycle performance in Na//Bi/MXene half-batteries and Na₃V₂(PO₄)₃/C//Bi/MXene full-batteries. Moreover, full-batteries can complete a charge/discharge cycle in 7 min and maintain an excellent cycle life (over 7000 cycles). The electrochemical test results showed that Bi/MXene is a promising anode material with fast charge/discharge capability for sodium-ion batteries.     

Synthesis of Porous Ni-Doped CoSe2/C Nanospheres towards High-Rate and Long-Term Sodium-Ion Half/Full Batteries

Carbon-layer-coated porous Ni-doped CoSe₂ (Ni-CoSe₂/C) nanospheres have been fabricated by a facile hydrothermal method followed by a new selenization strategy. The porous structure of Ni-CoSe₂/C is formed by the aggregation of many small particles (20–40 nm), which are not tightly packed together, but are interspersed with gaps. Moreover, the surfaces of these small particles are covered with a thin carbon layer. Ni-CoSe₂/C delivers superior rate performance (314.0 mA h g⁻¹ at 20 A g⁻¹), ultra-long cycle life (316.1 mA h g⁻¹ at 10 A g⁻¹ after 8000 cycles), and excellent full-cell performance (208.3 mA h g⁻¹ at 0.5 A g⁻¹ after 70 cycles) when used as an anode material for half/full sodium-ion batteries. The Na storage mechanism and kinetics have been confirmed by ex situ X-ray diffraction analysis, assessment of capacitance performance, and a galvanostatic intermittent titration technique (GITT). GITT shows that Na⁺ diffusion in the electrode material is a dynamic change process, which is associated with a phase transition during charge and discharge. The excellent electrochemical performance suggests that the porous Ni-CoSe₂/C nanospheres have great potential to serve as an electrode material for sodium-ion batteries.     

NiSe2 nanoparticles encapsulated in CNTs covered and N-doped TiN/carbon nanofibers as a binder-free anode for advanced sodium-ion batteries

Metal selenides are promising anodes for sodium-ion batteries (SIBs) due to the high theoretical capacity through conversion reaction mechanism. However, developing metal selenides with superior electrochemical sodium-ion storage performance is still a great challenge. In this work, a novel composite material of free-standing NiSe₂ nanoparticles encapsulated in N-doped TiN/carbon composite nanofibers with carbon nanotubes (CNTs) in-situ grown on the surface (NiSe₂@N-TCF/CNTs) is prepared by electrospinning and pyrolysis technique. In this composite materials, NiSe₂ nanoparticles on the surface of carbon nanofibers were encapsulated into CNTs, thus avoiding aggregation. The in-situ grown CNTs not only improve the conductivity but also act as a buffer to accommodate the volume expansion. TiN inside the nanofibers further enhances the conductivity and structural stability of carbon-based nanofibers. When directly used as anode for SIBs, the NiSe₂@N-TCF/CNT electrode delivered a reversible capacity of 392.1 mAh/g after 1000 cycles and still maintained 334.4 mAh/g even at a high rate of 2 A/g. The excellent sodium-ion storage performance can be attributed to the fast Na⁺ diffusion and transfer rate and the pseudocapacitance dominated charge storage mechanism, as is evidenced by kinetic analysis. The work provides a novel approach to the fabrication of high-performance anode materials for other batteries.     

Tin oxide–based anodes for both lithium-ion and sodium-ion batteries

Tin oxide, SnO₂, is a suitable anode for both lithium-ion and sodium-ion batteries (LIBs and SIBs) unlike graphite and silicon, which are only suitable anodes for LIB. SnO₂ has garnered much attention because of its high theoretical capacities (LIB = 1494 mA h g^?1 and SIB = 1378 mA h g^?1). However, the commercialization of SnO₂ anodes is still hugely challenged because these anodes suffer from large volume expansion caused by lithiation/delithiation or sodiation/desodiation during cycling, leading to severe capacity fading. The adopted strategies to solve these problems are nanosizing that greatly improves the structural stability of the material and helps to have fast reaction kinetics. Synthesizing nanocomposite of SnO₂ nanoparticles with nanoporous carbonaceous materials to buffer the volume expansion, enhance cycling stability; create oxygen deficiency to improve intrinsic conductivity. In this review, the recent research trends on SnO₂ as anode for both LIB and SIB systems are presented.     

Determination of Electron and Hole Mobility of Regioregular Poly(3‐hexylthiophene) by the Time of Flight Method

Time of flight method (TOF) is used to measure the electron and hole mobility of a spin coated regioregular poly(3‐hexylthiophene) (P3HT) film. We find that both electron and hole have the same mobility (about 3.8～3.9×10^?4 cm²/Vs) at an applied field of 120 kV/cm. It is demonstrated in this paper that the electron‐hole recombination process may prevent the electron transport in the material due to the fact that the carrier recombination time is much shorter than the transit time.     

Improving Na+ transport kinetics and Na+ storage of hierarchical rhenium-nickel sulfide (ReS2@NiS2) hollow architecture by assembling layered 2D-3D heterostructures

Mixed metal sulfides have been widely used as anode material of sodium-ion batteries (SIBs) because of their excellent conductivity and sodium ion storage performance. Herein, ReS₂@NiS₂ heterostructures have been triumphantly designed and prepared through anchoring ReS₂ nanosheet arrays on the surface of NiS₂ hollow nanosphere. Specifically, the carbon nanospheres was used as hard template to synthesize NiS₂ hollow spheres as the substrate and then the ultrathin two-dimensional ReS₂ nanosheet arrays were uniformly grown on the surface of NiS₂. The internal hollow property provides sufficient space to relieve the volume expansion, and the outer two-dimensional nanosheet realizes the rapid electron transport and insertion/extraction of Na⁺. Owing to the great improvement of the transport kinetics of Na⁺, NiS₂@ReS₂ heterostructure electrode can achieve a high specific capacity of 400 mAh/g at the high current density of 1 A/g and still maintain a stable cycle stability even after 220 cycles. This hard template method not only paves a new way for the design and construct binary metal sulfide heterostructure electrode materials with outstanding electrochemical performance for Na⁺ batteries but also open up the potential applications of anode materials of SIBs.     

Titanium Trisulfide Monolayer: Theoretical Prediction of a New Direct‐Gap Semiconductor with High and Anisotropic Carrier Mobility

A new two‐dimensional (2D) layered material, namely, titanium trisulfide (TiS₃) monolayer, is predicted to possess novel electronic properties. Ab initio calculations show that the perfect TiS₃ monolayer is a direct‐gap semiconductor with a bandgap of 1.02 eV, close to that of bulk silicon, and with high carrier mobility. More remarkably, the in‐plane electron mobility of the 2D TiS₃ is highly anisotropic, amounting to about 10 000 cm² V^?1 s^?1 in the b direction, which is higher than that of the MoS₂ monolayer, whereas the hole mobility is about two orders of magnitude lower. Furthermore, TiS₃ possesses lower cleavage energy than graphite, suggesting easy exfoliation for TiS₃. Both dynamical and thermal stability of the TiS₃ monolayer is examined by phonon‐spectrum calculation and Born–Oppenheimer molecular dynamics simulation. The desired electronic properties render the TiS₃ monolayer a promising 2D atomic‐layer material for applications in future nanoelectronics.     

Sn Anodes Protected by Intermetallic FeSn2 Layers for Long-lifespan Sodium-ion Batteries with High Initial Coulombic Efficiency of 93.8 %

With a theoretical capacity of 847 mAh g⁻¹, Sn has emerged as promising anode material for sodium-ion batteries (SIBs). However, enormous volume expansion and agglomeration of nano Sn lead to low Coulombic efficiency and poor cycling stability. Herein, an intermetallic FeSn₂ layer is designed via thermal reduction of polymer-Fe₂O₃ coated hollow SnO₂ spheres to construct a yolk-shell structured Sn/FeSn₂@C. The FeSn₂ layer can relieve internal stress, avoid the agglomeration of Sn to accelerate the Na⁺ transport, and enable fast electronic conduction, which endows quick electrochemical dynamics and long-term stability. As a result, the Sn/FeSn₂@C anode exhibits high initial Coulombic efficiency (ICE=93.8 %) and a high reversible capacity of 409 mAh g⁻¹ at 1 A g⁻¹ after 1500 cycles, corresponding to an 80 % capacity retention. In addition, NVP//Sn/FeSn₂@C sodium-ion full cell shows outstanding cycle stability (capacity retaining rate of 89.7 % after 200 cycles at 1 C).     

Dual-Function Presodiation with Sodium Diphenyl Ketone towards Ultra-stable Hard Carbon Anodes for Sodium-Ion Batteries

Hard carbon (HC) is a promising anode material for sodium-ion batteries, yet still suffers from low initial Coulombic efficiency (ICE) and unstable solid electrolyte interphase (SEI). Herein, sodium diphenyl ketone (Na-DK) is applied to realize dual-function presodiation for HC anodes. It compensates the irreversible Na uptake at the oxygen-containing functional groups and reacts with carbon defects of five/seven-membered rings for quasi-metallic sodium in HC. The as-formed sodium induces robust NaF-rich SEI on HC in 1.0 M NaPF₆ in diglyme, favoring the interfacial reaction kinetics and stable Na⁺ insertion and extraction. This renders the presodiated HC (pHC) with high ICE of ≈100 % and capacity retention of 82.4 % after 6800 cycles. It is demonstrated to couple with Na₃V₂(PO₄)₃ cathodes in full cells to show high capacity retention of ≈100 % after 700 cycles. This work provides in-depth understanding of chemical presodiation and a new strategy for highly stable sodium-ion batteries.     

SCF-Xα MO studies of the x-ray spectra of CuO and ZnO

SCF-Xα scattered wave cluster MO calculations for the oxyanions CuO^?6₄ (D_4h symmetry) and ZnO^?6₄ (Td symmetry) yield results in good agreement with the X-ray photoelectron and X-ray emission spectra of CuO and ZnO, respectively. Agreement of the calculations with optical data is fair. Calculations of the valence electron and core electron hole states of these oxyanions support the assignment of photoelectron shakeup satellites to valence band to conduction band transitions. Calculated shakeup energies for the Cu2p core spectrum in CuO are 7.4 and 9.9 eV (cf. experimental values of 7.5 and 10.0 eV) while shakeup peaks in the valence region spectrum are predicted at 6.1 and 8.0 eV. (Cf. a broad peak with maximum at 8.1 eV observed experimentally.) The absence of intense low energy satellites in the spectra of ZnO is explained by the small amount of electron reorganization in the outer valence levels attendant upon hole formation.     

Green Template‐Free Synthesis of Hierarchical Shuttle‐Shaped Mesoporous ZnFe2O4 Microrods with Enhanced Lithium Storage for Advanced Li‐Ion Batteries

In the work, a facile and green two‐step synthetic strategy was purposefully developed to efficiently fabricate hierarchical shuttle‐shaped mesoporous ZnFe₂O₄ microrods (MRs) with a high tap density of ～0.85 g cm³, which were assembled by 1D nanofiber (NF) subunits, and further utilized as a long‐life anode for advanced Li‐ion batteries. The significant role of the mixed solvent of glycerin and water in the formation of such hierarchical mesoporous MRs was systematically investigated. After 488 cycles at a large current rate of 1000 mA g^?1, the resulting ZnFe₂O₄ MRs with high loading of ～1.4 mg per electrode still preserved a reversible capacity as large as ～542 mAh g^?1. Furthermore, an initial charge capacity of ～1150 mAh g^?1 is delivered by the ZnFe₂O₄ anode at 100 mA g^?1, resulting in a high Coulombic efficiency of ～76 % for the first cycle. The superior Li‐storage properties of the as‐obtained ZnFe₂O₄ were rationally associated with its mesoprous micro‐/nanostructures and 1D nanoscaled building blocks, which accelerated the electron transportation, facilitated Li⁺ transfer rate, buffered the large volume variations during repeated discharge/charge processes, and provided rich electrode–electrolyte sur‐/interfaces for efficient lithium storage, particularly at high rates.     

Mesoporous MnCo2O4 with a Flake‐Like Structure as Advanced Electrode Materials for Lithium‐Ion Batteries and Supercapacitors

A mesoporous flake‐like manganese‐cobalt composite oxide (MnCo₂O₄) is synthesized successfully through the hydrothermal method. The crystalline phase and morphology of the materials are characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller methods. The flake‐like MnCo₂O₄ is evaluated as the anode material for lithium‐ion batteries. Owing to its mesoporous nature, it exhibits a high reversible capacity of 1066 mA h g^?1, good rate capability, and superior cycling stability. As an electrode material for supercapacitors, the flake‐like MnCo₂O₄ also demonstrates a high supercapacitance of 1487 F g^?1 at a current density of 1 A g^?1, and an exceptional cycling performance over 2000 charge/discharge cycles.     

Pyrrolic nitrogen-doped carbon sandwiched monolayer MoS<Subscript>2</Subscript> vertically anchored on graphene oxide for high-performance sodium-ion battery anodes

In this work, a novel pyrrolic nitrogen-doped carbon sandwiched monolayer MoS₂ hybrid was prepared. This sandwiched hybrid vertically anchors on graphene oxide as anode materials for sodium-ion batteries. Such electrode was fabricated by facile ionic liquid-assisted reflux and annealing methods. Owing to rational structure and enhancement from pyrrolic nitrogen dopant, this unique MoS₂/C-graphene hybrid exhibits reversible specific capacity of 486 mAh g^?1 after 1000 cycles with a low average fading capacity of 0.15 mAh g^?1 (fading cyclic rate of ca. 0.03% per cycle). A capacity of 330 mAh g^?1 is remained at the current densities of 10.0 A g^?1. The proposed strategy provides a convenient way to create new pyrrolic nitrogen-doped hybrids for energy field and other related applications.     

Electrical and optical properties of high-purity p-type single crystals of GeFe2O4

Single crystals of the spinel GeFe₂O₄, grown by the chemical vapor transport technique, are p-type semiconductors with an acceptor ionization energy of 0.39 eV. The material is a heavily compensated band-type semiconductor, with a typical hole concentration of 10¹⁴ cm^?3 near room temperature, and a temperature-independent Hall mobility of 2 cm²/V·sec. Optical absorption measurements show the optical band gap to be ?2.3 eV; the octahedral field splitting of the Fe²⁺d-levels is 10 200 cm^?1. Magnetic measurements show that n_eff is 5.26, from which a trigonal field splitting of 950 cm^?1 is derived.     

Hole transport of trans-1,2-biscarbazolylcyclobutane-doped poly(bisphenol A carbonate) film

The hole transport of trans-1,2-biscarbazolylcyclobutane (CB) doped poly(bisphenol A carbonate) (PC) film has been investigated in the CB concentration range of 3.8 × 10^?4 mol cm^?3 (12 wt%) to 1.6 × 10^?3 mol cm^?3 (51 wt%). The hole mobility increased drastically with increasing CB concentration. The hole mobility was analyzed by a random hopping model. The localization radius ρ₀ of the CB/PC system was 1.9 Å, which is larger than that obtained for the N-isopropyl-carbazole-doped PC system. This suggests that the larger localization radius of the CB/PC system is related to the larger spatial extent of the CB molecule. The highest hole mobility of 2.9 × 10^?6 cm² V^?1 s^?1 was obtained when the CB concentration was 1.6 × 10^?3 mol cm^?3 (51 wt%) at E = 1.6 × 10⁵ V cm^?1 and T = 298 K. This mobility is about 10 times higher than that of poly(N-vinylcarbazole) (PVCz). The activation energy of hole mobility for the CB/PC system decreased with increasing CB concentration and was 0.31 eV at 51 wt% of CB, which is lower than the 0.45 eV for PVCz. The low activation energy for the CB/PC system is ascribed to the absence of an excimer-forming site that works as a multiple-trapping site for hole carriers.     

Non‐Conjugated Dicarboxylate Anode Materials for Electrochemical Cells

Classical organic anode materials for Na‐ion batteries are mostly based on conjugated carboxylate compounds, which can stabilize added electrons by the double‐bond reformation mechanism. Now, 1,4‐cyclohexanedicarboxylic acid (C₈H₁₂O₄, CHDA) with a non‐conjugated ring (?C₆H₁₀?) connected with carboxylates is shown to undergo electrochemical reactions with two Na ions, delivering a high charge specific capacity of 284 mA h g^?1 (249 mA h g^?1 after 100 cycles), and good rate performance. First‐principles calculations indicate that hydrogen‐transfer‐mediated orbital conversion from antibonding π* to bonding σ stabilize two added electrons, and reactive intermediate with unpaired electron is suppressed by localization of σ‐bonds and steric hindrance. An advantage of CHDA as an anode material is good reversibility and relatively constant voltage. A large variety of organic non‐conjugated compounds are predicted to be promising anode materials for sodium‐ion batteries.     

Co2P/Sn4P3 particle encapsulated in N,P codoped carbon nanocubes for efficient sodium storage

Phosphorus-based materials as the anode for sodium-ion batteries have drawn extensive attention because of their high theoretical capacity and low insertion potential. Nevertheless, the severe volume variation and low electric conductivity hindered their further practical applications. Herein, a novel Co₂P/Sn₄P₃ hybrid encapsulated in carbon nanocubes was fabricated by a coprecipitation method followed by phosphating progress. Accompanying with the N, P codoping and abundant grain boundaries, which facilitates electric transport and provides rich active sites, the as-synthesized Co₂P/Sn₄P₃@C anode delivered a high charge specific capacity of 185.6 mA h g^?1 after 400 cycles at the current density of 1000 mA g^?1 and outstanding cycling stability with a high capacity retention of 86.9%. Kinetics exploration indicated that the capacity was governed by the surface pseudo-capacitive controlled process due to the abundant defects originated from heteroatom doping and grain boundaries.     

Carbonyl-rich Poly(pyrene-4,5,9,10-tetraone Sulfide) as Anode Materials for High-Performance Li and Na-Ion Batteries

Organic carbonyl electrode materials are widely employed for alkali metal-ion secondary batteries in terms of their sustainability, structure designability and abundant resources. As a typical redox-active organic electrode materials, pyrene-4, 5, 9, 10-tetraone (PT) shows high theoretical capacity due to the rich carbonyl active sites. But its electrochemical behavior in secondary batteries still needs further exploration. Herein, PT-based linear polymers (PPTS) is synthesized with thioether bond as bridging group and then employed as an anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). As expected, PPTS shows improved conductivity and insolubility in the non-aqueous electrolyte. When used as an anode material for LIBs, PPTS delivers a high reversible specific capacity of 697.1 mAh g⁻¹ at 0.1 A g⁻¹ and good rate performance (335.4 mAh g⁻¹ at 1 A g⁻¹). Moreover, a reversible specific capacity of 205.2 mAh g⁻¹ at 0.05 A g⁻¹ could be obtained as an anode material for SIBs.