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Li and Zn metal batteries are the most promising candidates to replace conventional Li-ion batteries. However, a series of issues, especially dendrites caused by uneven deposition of cations during charge-discharge cycles, hinder their practical application. Here, we proposed a facile separator modification method which combines physical and chemical forces to regulate uniform and rapid deposition of both Li

Aqueous zinc energy storage devices, holding various merits such as high specific capacity and low costs, have attracted extensive attention in recent years. Nevertheless, Zn metal anodes still suffer from a short lifespan and low Coulombic efficiency due to corrosion and side reactions in aqueous electrolytes. In this paper, we construct an artificial Sn inorganic layer on Zn metal anode through a facile strategy of atoms exchange. The Sn layer suppresses Zn dendrite growth by facilitating homogeneous Zn plating and stripping during charge and discharge processes. Meanwhile, the Sn protective layer also serves as a physical barrier to decrease Zn corrosion and hydrogen generation. As a result, The Sn-coated anode (Sn|Zn) exhibits a low polarization voltage (∼34 mV at 0.5 mAh/cm2) after 800 testing hours and displays a smooth and an even surface without corrosion. Moreover, the zinc ion capacitor (Sn|Zn|| activated carbon) is assembled with an enhanced capacity of 42 mAh/g and a capacity retention of 95% after 10000 cycles at 5 A/g. This work demonstrates a feasible approach for the commercialization of aqueous Zn-based energy storage devices.

A fundamental understanding of the nucleation and growth behaviors of Zn metal anodes over a wide range of temperatures is of great value for suppressing Zn dendrite growth. However, work focused on the early nucleation and growth behavior of Zn metal at various temperatures is still absent. Here, we study the effect of cycling temperature on Zn nuclei size and areal density and find that low temperature induces a smaller and dense nucleus, which prevents the formation of dendrites. Based on this finding, a cooling-treatment-based self-healing strategy is developed to in situ eliminate dendrites, which effectively prolongs the lifespan of the Zn anode by 520%. This novel self-healing strategy could be employed as a reliable strategy for restoring batteries in situ to reach a longer lifespan.

Dendrite growth and side reactions of Zn metal anodes remain unresolved obstacles for practical application of aqueous Zn ion batteries. Herein, a two-dimensional (2D) organic-inorganic heterostructure with controlled thickness was constructed as a protective layer for a Zn metal anode. The reduction of uniformly distributed polyoxometalate in the layer causes a negative charge density gradient, which can accelerate zinc ion transfer, homogenize zinc deposition, and shield sulfates at the electrode interface, while the exposed hydrophobic alkyl chain of the layer can isolate the direct contact of water with the Zn anode. As a result of the synergetic effect, this 2D organic-inorganic heterostructure enables high Zn plating/stripping reversibility, with high average Coulombic efficiencies of 99.97% for 3700 cycles at 2 mA cm(-2). Under high Zn utilization conditions, a high areal-capacity full cell with hundreds of cycles was demonstrated.

Aqueous zinc metal batteries with mild acidic electrolytes are considered promising candidates for large-scale energy storage. However, the Zn anode suffers from severe Zn dendrite growth and side reactions due to the unstable interfacial pH and the absence of a solid electrolyte interphase (SEI) protective layer. Herein, a novel and simple mixed electrolyte strategy is proposed to address these problems. The mixed electrolytes of 2 M ZnSO

Transition metal oxychlorides (TMOCl) have attracted great attention as promising cathode materials for chloride ion batteries (CIBs). However, current research on TMOCl has been mainly focused on FeOCl and VOCl. On the other hand, the theoretical study of anionic rechargeable batteries faces the difficulty of predicting the discharge voltage of the electrode materials based on the half-cell system. Herein, a reliable theoretical voltage formula for CIBs is proposed based on a full-cell system with Li/LiCl as the reference anode. A high throughput screening method for TMOCl is applied among 16 transition metals. After the screening according to energetic and dynamic stability, Co is identified, which can form a new cathode material of CoOCl. Compared to FeOCl and VOCl, CoOCl has a higher discharge voltage, which is beneficial for achieving a larger energy density. The small crystal field splitting energy and exchange splitting energy of Co3+ result in higher electronic conductivity. In addition, the uniform Cl− binding environment leads to a low Cl− diffusion barrier of 0.37 eV, which is much smaller than that of VOCl (0.65 eV) and FeOCl (0.58 eV).

The unique properties of MXenes that arise from terminating functional groups and oxidation of MXenes make them attractive for application in photovoltaic devices like perovskite solar cells (PSCs). Here, oxidation of Ti3C2Tx hydrocolloid was carried out to tune its properties desirable for an electron transport layer (ETL) in low-temperature processed PSCs. The calculations of the energy levels were carried out using the Vienna ab initio simulation package (VASP) code based on density functional theory (DFT). Oxidation of Ti3C2Tx can generate Ti–O bonds and effectively reduce the macroscopic defects of the film fabricated by spin-coating, while a transition from metallic material to semiconductor occurred after heavy oxidation. A better matching of energy levels between perovskite and ETL layer in the case of a hybrid of oxidized and pristine Ti3C2Tx renders a champion power conversion efficiency (PCE) of 18.29%. The improvement in PCE can be attributed to the increased electron mobility in the ETL, which promotes electron transport and reduces the electron–hole recombination. Hence, by presenting a simple method for high performance in PSCs by MXene-derived materials, this work demonstrates the great potential of these materials for applications in low-temperature processed PSCs and other photovoltaic technologies.

Controlling morphology, adopting metal cations and introducing crystal water are three effective strategies to improve the electrochemical performance of various battery electrodes. However, the effects of simultaneously applying these three strategies to aqueous rechargeable zinc batteries (ARZBs) are rarely demonstrated. Herein, hierarchical H11 Al2 V6 O23.2 (HAVO) microspheres were successfully prepared using a simple hydrothermal method, and used as cathode material for ARZBs. The as-prepared HAVO microspheres exhibited superior electrochemical performance than the dehydrated AlV3 O9 (AVO) microspheres, i. e. they have a larger specific capacity of 390.4 mA h g-1 at 100 mA g-1 , a better rate capability of 191.4 mA h g-1 at 5000 mA g-1 and a higher cycling stability of up to 1000 cycles with a capacity retention of 80.9 %. The excellent electrochemical performance of HAVO is due to the synergistic effects of the shortened ion diffusion distance in primary HAVO nanosheets, the improved electronic conductivity, and structural stability by adopting Al3+ into the lattice, the enhanced charge transfer properties and ion diffusion coefficient of the electrode due to the existence of crystal water. Therefore, this work may offer a new route for the design and synthesis of more advanced electrode materials for ARZBs.

Titanium-substituted LiTix Fe1-2x SO4 F (x=0, 0.01, 0.02, 0.03) cathode materials were synthesized by a solvothermal method. X-ray diffraction, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy were used to investigate the effects of Ti substitution on the structure of LiFeSO4 F, and it was shown that Ti substitutes the Fe(2) site. First-principles calculations and UV-visible spectroscopy demonstrate that Ti substitution reduces the bandgap of LiFeSO4 F which improves the electronic conductivity from 8.3×10-12 S cm-1 to 3.9×10-11 S cm-1 . CI-NEB and BV calculations show that the Li diffusion energy barriers along the (100), (010) and (101) directions are decreased after Ti substitution, and the Li diffusion coefficient is increased from 4.99×10-11 cm2 S-1 to 1.59×10-10 cm2 S-1 . The improved electronic conductivity and ionic diffusivity mean that the Ti-substituted material shows improved electrochemical properties compared to the pristine LiFeSO4 F.

The ORR and OER properties of a series of recombinant single atom catalysts (SACs) prepared by recombining Pt single atoms on 26 representative MXenes were comprehensively studied by first-principles calculations. The stability of Pt atoms on the MXene surface was studied using formation energies and diffusion energy barriers. Charge transfer analysis showed that the Pt atoms not only acted as the catalytic center of the SACs but also behaved as a charge transfer medium between the MXene substrate and the reactants. The catalytic properties of the recombinant SACs were dependent on several interacting factors including the Pt-5d states, the work functions of the recombinant systems, the electronegativity of the submetals, and the vacant electron orbitals of the C/N and O/F elements of the MXenes. In all the recombinant SACs under investigation, V-, Ti-, Nb-, and Cr-based MXenes, including Ti2CF2-VF-Pt, Ti3C2F2-VF-Pt, V2CO2-VO-Pt, Nb2CF2-VF-Pt, Nb4C3F2-VF-Pt, Cr2TiC2F2-VF-Pt, Ti3(C,N)2-CO2-VO-Pt, and Ti3(C,N)2-NO2-VO-Pt, were screened as promising ORR catalysts. In particular, three F-terminated ones (Nb2CF2-VF-Pt, Nb4C3F2-VF-Pt, and Cr2TiC2F2-VF-Pt) were proposed as effective ORR/OER bifunctional catalysts. The results revealed the highly active nature of the selected SACs and highlighted the great potential of MXenes as efficient ORR and OER catalysts.

NASICON-structured Na4MnV(PO4)3 has been recognized as a potential positive electrode material for sodium-ion batteries, but its electrochemical mechanism during de(sodiation) has not been well understood. In this work, the structural transformation, charge transfer, and ionic diffusion properties of Na4MnV(PO4)3 were comprehensively studied by first-principles calculations combined with experimental studies. The results revealed two independent Na sites, Na(1) and Na(2), in the structure of Na4MnV(PO4)3, but only Na(2) can be extracted between 2.5 and 3.8 V. Extraction of the first Na+ caused charge transfer on V3+ and was associated with a solid-solution reaction. In addition, Na+ migrated along the 3D channels in the NASICON structure with low energy barriers of

Lithium metal batteries are promising next generation energy storage devices. However, uncontrolled lithium dendrite growth and inevitable side reactions of traditional organic liquid electrolytes with electrodes are obstacles to their practical applications. Herein, a new ionogel electrolyte with an organic–inorganic semi-interpenetrating network is designed by the confinement of ionic liquid within a NH2 pendent group optimized cross-linked poly(ionic liquid) copolymer backbone and glass fiber scaffold. The ionogel electrolyte shows superior physicochemical properties, including improved lithium ion transmission, high mechanical strength, wide electrochemical window, non-leakage, non-volatility and fire resistance. In Li//Li symmetric cells fabricated with this ionogel electrolyte, repeated Li plating/stripping could last over 1800 h without significant dendrite formation. Besides, the full cells paired with a high-voltage Li3V2(PO4)3 cathode present excellent cycling stability with a capacity retention of 83% after 1000 cycles (0.5C rate, 3.0–4.3 V) and 91% after 100 cycles (0.2C rate, 3.0–4.8 V). This study presents a new strategy for the use of organic–inorganic semi-interpenetrating networks for designing new composite ionogel electrolytes with desirable properties for high-voltage LMBs.

Developing highly active, stable, and conductive bifunctional oxygen reduction (ORR) and oxygen evolution (OER) catalysts is a key step for fuel cells and metal–air batteries. Herein, an effective idea for designing bifunctional catalysts is presented by regulating the surface electronic structures of Nb2CT2 (T = O, F, and OH) using Pt/Pd single atoms. The results indicated that Pt-doped systems (Nb2CO2–VO–Pt, Nb2CF2–VF–Pt) were the most promising bifunctional ORR/OER catalysts. In particular, Nb2CF2–VF–Pt was even better than landmark Pt(111) and IrO2(110) catalysts, with relatively low overpotentials of 0.40 V and 0.37 V for ORR and OER, respectively. The high catalytic nature of Nb2CF2–VF–Pt was explained by electronic structures, volcano plots, and charge transfer mechanisms, which mainly depended on the electron donor capacity and synergistic effects from F-terminated groups and Pt noble metals. Moreover, 100% utilization of Pt was achieved for the designed bifunctional catalysts with a minimum radius between two adjacent active centers. This was the first design of a bifunctional ORR/OER catalyst based on Nb2CT2 and highlighted a new perspective on the application of MXenes.

An artificial organic/inorganic composite protecting film for lithium metal anode with one-side surface pits structure was prepared by poly(vinylidene fluoride-co-hexafluoropropylene) and Al2O3+LiNO3 inorganic additives. Due to the unique surface structure, the composite film can not only serve as an artificial protective film, but also act as an additional lithium plating host, which synergistically enabled the lithium metal anode to adapt to high current densities meanwhile maintain dendrite-free during long-term cycling. As a result, the protected lithium metal anode can operate stably for 1000 h at a high current density of 10.0 mA cm-2. When paired with a LiFePO4 or sulfur cathode, the full cells with unflooded electrolyte showed significantly improved cycling performance, demonstrating great potential of this artificial protecting film in lithium metal batteries.

Due to the high discharge voltage and a favorable theoretical capacity, Na2FePO4F have been attracted much attention as the viable cathode materials for sodium-ion storage. However, the low intrinsic electronic conductivity of Na2FePO4F suppresses its practical applications. Herein, ion doping strategy is employed to improve the electrochemical performance of Na2FePO4F as the cathode of sodium ion batteries. We first used density functional theory (DFT) calculation to screen the optimum dopants by evaluating the structural, electronic and electrochemical properties of metal-doped Na2FePO4F. Our calculation results indicate that the Co-doped Na2FePO4F is the most promising candidate for practical applications. To further prove the validity of metal doping, Na2Fe0.94Co0.06PO4F/C was synthesized by sol-gel method and showed superior electrochemical performance compared with the pristine material. The specific capacity of the Na2Fe0.94Co0.06PO4F/C is 99.93 mAh g−1 at 0.2 C and the discharge capacity retention is 62.1% after 400 cycles at 1 C.

The insufficient charge extraction in chlorophyll-based solid-state solar cells (CSSCs) limits the photovoltaic performance, resulting in low photon-to-electron conversion efficiency. In this work, we employ poly(3-hexylthiophene) (P3HT) as a hole transporter to improve the charge extraction in CSSCs with a carboxylated chlorophyll sensitizer (H2Chl-1) adsorbed on mesoporous TiO2 as an electron acceptor and self-aggregates of a zinc chlorophyll derivative (ZnChl-2) as an electron donor. P3HT enhances the photon-to-electron conversion in both 300–540 nm and 660–725 nm wavelength regions. The charge recombination of CSSCs was suppressed by addition of P3HT to the ZnChl-2 aggregate layer that is spin-coated on H2Chl-1 adsorbed TiO2, as evidenced by the increased recombination resistance in the electrochemical impedance spectroscopy. As a result, the incident photon-to-electron conversion efficiency of the redmost peak of CSSCs with P3HT layer achieves a maximum value of 70.8%, and the power conversion efficiency is substantially enhanced from 2.1% to 3.1%.

VC2, a new two-dimensional transition metal carbide containing C2 dimers, was predicted by the swarm-intelligent global-structure search method. The structural properties and Li+ storage ability of VC2 monolayers and stacked VC2 multilayers were systematically investigated by first-principles calculations, and the high structural stability and electronic conductivity of the materials suggested promising Li+ storage properties. VC2 monolayers showed a theoretical capacity of 1073 mA h g−1 based on multilayer Li+ adsorption, while stacked VC2 showed an even larger theoretical capacity of 1430 mA h g−1. Intercalated Li+ formed ordered arrangements between VC2 layers, retaining a well-ordered layered structure. Li+ near the VC2 layer formed ionic bonds with the host material, while Li in middle layers formed metallic Li–Li bonds. All Li+ was stored in the interlayer space with low diffusion barriers, which demonstrated high rate capability of the material for lithium ion batteries. Remarkably, the predicted VC2 carbide achieved more than 1000 mA h g−1 capacity irrespective of being in monolayer or stacked layer structures, which rendered them very convenient for practical material preparation and battery applications.

Identifying high performance electrode materials particularly with a large capacity and appropriate working voltage is one of the most promising approaches for improving the energy density of rechargeable batteries. Herein, a tetra-VN2 monolayer with intrinsic thermal/dynamic stability and excellent electronic conductivity is described that was identified using energy and stability directed screening as a potential electrode material for rechargeable alkali ion batteries. The maximum alkali ion storage was found for Li2VN2, Na4VN2 and K4VN2, which corresponded to specific capacities of 679, 1358 and 1358 mA h g−1. The average working voltages of tetra-VN2 in Li-, Na-, and K-ion batteries were 2.59, 1.59, and 1.62 V, which produced specific energies of 1761, 2162, and 2206 W h kg−1, which were much larger than those of most well-known cathode materials. This suggested that the tetra-VN2 monolayer could be a promising alkali ion storage material for high energy rechargeable batteries. Interestingly, different from intercalation-type cathode materials, alkali ions were stored in the tetra-VN2 monolayer via an adsorption/desorption process. With this surface storage mechanism, the alkali ions could migrate in the electrode with low energy barriers, which were found to be 0.237, 0.018, and 0.075 eV for Li+, Na+, and K+, respectively. This feature was representative of the excellent rate capability of tetra-VN2 in rechargeable batteries.

Journal of materials chemistry / A 8(19), 9567 - 9578 (2020). doi:10.1039/D0TA00858C, Monoclinic VO$_2$(B) nanoflakes prepared by a hydrothermal method displayed superior electrochemical performance in 1 M ZnSO$_4$ electrolyte. The reaction mechanisms of VO$_2$(B) and the essential causes of byproduct formation in aqueous rechargeable zinc batteries (ARZBs) were comprehensively studied by electrochemical measurements combined with in operando synchrotron techniques and first-principles calculations. During the electrochemical processes, the electrode underwent a reversible solid-solution reaction between VO$_2$(B) and Zn$_{0.44}$VO$_2$ with the simultaneous formation/decomposition of the (Zn(OH)$_2$)$_3$(ZnSO$_4$)��5H$_2$O byproduct. Importantly, the formation of the byproduct was attributed to [Zn(H$_2$O)$_6$]$^{2+}$ dehydration, where the byproduct could protect the electrode material from the corrosion of H$_3$O$^+$ and facilitate the dehydration process of Zn$^{2+}$ on the electrode���electrolyte interface. The byproducts could facilitate the migration of Zn$^{2+}$ on the electrode surface due to their three-dimensional pathways. In addition, the electrochemical performance of VO$_2$(B) and the byproduct in ZnSO$_4$ electrolyte were compared with those in Zn(CF$_3$SO$_3$)$_2$ and Zn(NO$_3$)$_2$. An appropriate electrolyte (1 M Zn(CF$_3$SO$_3$)$_2$) to form a byproduct with largely expanded ionic pathways was proven to further improve the electrochemical performance of VO$_2$(B). This work not only provides a deep understanding of the Zn$^{2+}$ storage mechanism in VO$_2$(B) but also establishes a clear relationship between the byproducts and electrochemical performance of vanadium-based electrode materials in ARZBs., Published by RSC, London ��[u.a.]��

Nanostructures can improve battery capacity and cycle life, especially with sulfide electrodes. In this work, a freestanding flexible electrode, consisting of MnS nanoparticles embedded onto carbon nanofibers, was prepared by electrospinning. The produced hybrid was used as an electrode for lithium-ion and sodium-ion batteries. MnS nanoparticles have a size of about 5 nm and the particles are evenly distributed in the carbon nanofibers. Carbon nanofibers act as electronic conductors and buffer the volume change, while MnS nanoparticles react through rapid electrochemical reaction. As a Li-ion battery anode, this hybrid electrode exhibits specific capacities from 240 mAh g-1 at a high current density of 5 A g-1 , up to 600 mAh g-1 at 200 mA g-1 .

Chlorophylls are the most abundant bipolar organic semiconductor found in nature. We demonstrated novel bulk-heterojunction organic-inorganic solar cells (OISCs) in which a carboxylated chlorophyll derivative (H2Chl-1) sensitizing mesoporous TiO2 functioned as an n-type electron acceptor and self-aggregates of zinc chlorophyll (ZnChl-2) functioned as a p-type electron donor. In this work, we employed chloroform (CF), chlorobenzene (CB), and their mixtures as processing solvents to manage the morphology of ZnChl-2 aggregates and the pore-filling of ZnChl-2 into mesoporous TiO2. ZnChl-2 aggregates generated from a mixed solvents (CF:CB = 2:1) exhibited the smallest surface roughness and most efficient charge separation and the power conversion efficiency of OISCs was substantially improved to 2.13%. Importantly, the incident photon-to-current conversion efficiency profiles of these OISCs consisted of the spectral components of both TiO2-attached H2Chl-1 and self-aggregated ZnChl-2, indicating that efficient charge separation can occur at the interface between these two chlorophyll species.

The hole transport layer (HTL) plays an important role in perovskite solar cells (PSCs). We demonstrate the cupper iodide (CuI)/poly (3,4-ethylenedioxythiophene) poly (styrenesulphonate) (PEDOT:PSS) double layers as the anode buffer layer for efficient hole transport in PSCs. An obvious enhancement of open-circuit voltage and power conversion efficiency (PCE) is observed, and a final PCE of 14.3% is achieved. While the single PEDOT:PSS based device’s PCE is 12.9%. The inorganic CuI buffer layer significantly enhanced the hole extraction from the perovskite film, as revealed from the photoluminescence spectra. The average exciton lifetime is reduced to 2.7 ns. Moreover, the devices with double HTLs structure exhibit better long time stability. The PCE remains 88% of the initial value after 720 h’ storage.

First-principles calculations based on density functional theory were performed to investigate the electrochemical properties of K1−xVOPO4 in potassium-ion batteries (KIBs). The material showed multiple phase transitions during K ion extraction, which began with a two-phase transition (0 ≤ x ≤ 0.5), followed by a solid-solution transition (0.5 < x ≤ 0.625), another two-phase transition (0.625 < x ≤ 0.75), and finally a solid-solution transition (0.75 < x ≤ 1). These processes resulted in a small total unit cell volume variation of 6.6%, which was beneficial for the cycle stability of KIBs. Density of states and Bader charge analysis revealed that both V and O participated in the charge transfer process, where V acted as the redox center of KVOPO4 contributing to the K storage capacity, and O acted as a charge transfer medium between V and K. The stepwise increased repulsion between V cations caused three voltage plateaus for K1−xVOPO4. In addition, the one-dimensional diffusion pathway for K ions with low energy barriers of 0.214–0.491 eV ensured high K ion mobility resulting in superior high rate capability.

Although lithium–sulfur batteries are expected to be the promising next generation of energy storage systems, the shuttle effect of polysulfides severely hampers their practical application. In this study, we introduce mesoporous titanium nitride microspheres to decorate the commercial separator and effectively suppress the shuttle effect. Specifically, titanium nitride improves the utilization of sulfur as an upper current collector through its strong chemical adsorption for polysulfides and high conductivity. In addition, its mesoporous spherical structure also forms a favorable physical barrier to block the diffusion of polysulfides. With this titanium nitride modified separator, the cell exhibits an excellent capacity retention ratio of 76% after 200 cycles at 0.5C. A relatively high capacity of 672 mA h g−1 is obtained even at a high current density of 3C. These results suggest that the design of separators modified with transition metal nitride-based materials is a promising approach for developing high performance lithium–sulfur batteries.

Two-dimensional transition metal disulfides have attracted great attention as anode materials for sodium ion batteries (SIBs) due to their high capacities and long cycle life, but knowledge of the mechanisms for phase transitions, charge-transfer reactions, and ionic diffusion kinetics during Na+ insertion has been lacking. These properties were systematically investigated in this work via experimental testing and first-principles calculations using VS2 nanosheets as an example material. The material showed a stable discharge capacity of 386 mA h g−1 in the 0.3–3.0 V voltage window which then increased to 657 mA h g−1 with further discharging to 0.01 V. It was discovered that Na+ first intercalated into octahedral interstitial sites of NaxVS2, with 0 < x ≤ 1.0, accompanied by partial reduction of S anions. Afterwards, Na+ intercalated into tetrahedral interstitial sites of NaxVS2, with 1.0 < x ≤ 2.0, causing partial reduction of both V cations and S anions. The electrode was finally converted into a V/Na2S nanocomposite after insertion of 3.0 mol of Na+, giving rise to a large specific capacity. This work not only revealed the structural transformation and mixed anionic/cationic redox reactions of VS2 during Na+ intercalation, but also helped us to understand the electrochemical reaction mechanisms of transition metal disulfides in SIBs.

Discovering effective bifunctional catalysts to facilitate Li2O2 oxidation and prolong the discharge life to ease the “sudden death” of batteries is a key task for developing high performance Li–O2 batteries. Herein, an advanced aprotic Li–O2 battery is designed using Co9S8@carbon porous nanocages as a bifunctional catalyst derived from a metal–organic framework. It achieves superior electrocatalytic activity, resulting in a high-energy efficiency of 72.7% and a long cycle life of up to 110 cycles at 100 mA g−1 current density. Combined experimental studies and density functional theory calculations reveal that the promising electrochemical performance observed here could be attributed to the high catalytic activity of Co9S8. In addition, the open-framework porous structure of these carbon porous nanocages provides a facile mass transport pathway and fast charge transfer kinetics for the oxygen reduction/evolution reactions.

Li3V2(PO4)3 (LVP) has been highlighted as a promising cathode material for lithium ion batteries, but it suffers from poor rate capability and rapid capacity decay due to sluggish electrode kinetics and vigorous electrode/electrolyte side reactions at high voltage. In this study, an inexpensive aqueous lithium poly-acrylic acid (LiPAA) binder was developed to deftly solve the shortcomings of the LVP material by tailoring the functional groups in the binder. The good adhesion and cohesion properties of the LiPAA binder ensured a close linkage between the active LVP particles, conductive additives and current collector, which formed a stable and conductive network in the electrode. In addition, the reversible H+/Li+ exchange in LiPAA effectively assisted the transport of Li+ ions at the electrode interface, which allowed the establishment of a Li+ conductive pathway without considerable degradation of the electrolyte. Due to these advantages, the LVP electrode containing the LiPAA binder exhibited significantly improved electrochemical performance compared to the electrode that employed the traditional polyvinylidene fluoride binder. The new electrode configuration showed a large specific capacity of 107 mA h g−1 at 70C rate and a high capacity retention of 91% was obtained after 1400 cycles at 10C rate, showcasing the great potential of this aqueous binder in lithium ion batteries.

Li+/Mg2+ hybrid-ion batteries (LMIBs) have attracted intensive attention because they can circumvent some serious drawbacks of Li- and Mg-rechargeable batteries. In this work, a novel LMIB was proposed that uses a VS2 nanosheet-based cathode and an all-phenyl complex + LiCl/tetrahydrofuran hybrid electrolyte. Combined spectroscopic analysis and theoretical simulations revealed that (phenyl)2Mg and tetrahydrofuran inserted into the nanosheets at an early battery-cycling stage. The interlayer spacing of VS2 was expanded from 5.78 to 8.76 A by the inserted organic species, which significantly reduced the diffusion barrier of Li+. As a result, the LMIBs showed remarkable battery performance with a large discharge capacity (181 mA h g−1 at 50 mA g−1), high rate capability (93 mA h g−1 at 5 A g−1), and long cycle stability (0.04% capacity fading per cycle in 500 cycles).

Slow diffusion kinetics of Na+ in electrode is a major obstacle for the rate capability of Na-ion batteries. In this work, super-fast Na+ diffusion in a VS2 anode was achieved by creating ordered (OSV-VS2-x) or disordered S vacancies (DSV-VS2-x) in VS2 nanosheets under a H2/Ar reduction atmosphere. Both the disordered and ordered S vacancies can improve the Na+ diffusion kinetics in VS2. Especially, disordered S vacancies provided an extra ion diffusion pathway perpendicular to the VS2 plane, which significantly reduced the Na+ diffusion barrier of DSV-VS2-x to 0.229 eV, much smaller than the 0.473 eV for VS2 and 0.401 eV for OSV-VS2-x. Taking this advantage, the DSV-VS2-x nanosheets exhibited impressive rate capability (117 mA·h·g−1 at 100 C) and ultra-long cycle life (~100% capacity retention after 5000 cycles at 50 C) in the 1.0–3.0 V voltage window. About 95% of the capacity was attributed to a pseudocapacitive process. The vacancy engineering strategy proposed in this work could significantly improve the rate capability of VS2 and other transition metal dichalcogenides. This technology that combines the high rate performance of supercapacitors with the high energy density of rechargeable batteries would promote the development of high power energy storage devices.

A micro-emulsion method has been introduced to synthesize spinel ZnMn 2 O 4 . By means of a simple adjustment of the reaction solvent or added surfactant, we successfully gain distinct micro-shapes as porous hexahedron, porous microsphere and porous core-shell microsphere. XRD test results validate the phase purity of resulting ZnMn 2 O 4 materials. Interestingly, the different structural characteristics result in significant disparate electrochemical performances. The porous core-shell microsphere (PCMZ) exerts surprisingly remarkable specific capacity and excellent rate performance. The observed enormous discharge capacity of synthesized PCMZ (∼1600 mAh g −1 for the 100th cycle) is the highest among the ever reported ZnMn 2 O 4 -based material. The long cycle performance at high current rate (1208 mAh g −1 after 250 cycles at 500 mA g −1 ) is also the best. Large amount of experimental results demonstrate that the resulted high specific capacity is mainly assigned to the generation of higher valence Mn during cycling and extra interfacial Li storage caused by its unique architecture.

Spinel ZnMn 2 O 4 is considered as a potentially high-capacity anode material for Li-ion batteries. However, its low conductivity causes poor rate capability and insufficient cyclability, thus turning into a challenge for battery applications. Hybrid inorganic/ordered mesoporous carbon (CMK-3) nanostructure represents a promising material platform for next-generation energy storage due to the presence of a large surface area, which facilitates ion transport and storage, and improves electron transport. Here we report a convenient and advanced architecture design of ultrathin 2D ZnMn 2 O 4 nanosheets integrated on 3D CMK-3 framework. Benefiting from the sufficient electrochemically available interfaces and abundant electronic/ionic pathways provided by the ultrathin ZnMn 2 O 4 and the interconnected channels of CMK-3 network, this ZnMn 2 O 4 @CMK-3 material provides a high reversible capacity of 997 mAh g −1 at 100 mA g −1 after 100 cycles, a strong rate capability with 693 mAh g −1 at 2 A g −1 , and a remarkable long-term cyclability with a capacity retention of 94% over 1600 cycles.

An integrated WS2@CMK-3 nanocomposite has been prepared by a one-step hydrothermal method and then used as the anode material for lithium-ion and sodium-ion batteries. Ultrathin WS2 nanosheets have been successfully embedded into the ordered mesoporous carbon (CMK-3) framework. Owing to the few-layered nanostructure of WS2, as well as the high electronic conductivity and the volume confinement effect of CMK-3, the material shows larger discharge capacity, better rate capability, and improved cycle stability than pristine WS2. When tested in lithium-ion batteries, the material delivers a reversible capacity of 720 mA h g−1 after 100 cycles at a current density of 100 mA g−1. A large discharge capacity of 307 mA h g−1 is obtained at a current density of 2 A g−1. When used in sodium-ion batteries, the material exhibits a capacity of 333 mA h g−1 at 100 mA g−1 without capacity fading after 70 cycles. A discharge capacity of 230 mA h g−1 is obtained at 2 A g−1. This excellent performance demonstrates that the WS2@CMK-3 nanocomposite has great potential as a high-performance anode material for next-generation rechargeable batteries.

Ag2 Mo2 O7 micro-rods are prepared by one-step hydrothermal method and their lithium electrochemical properties, as the anode for lithium-ion batteries, are comprehensively studied in terms of galvanostatic charge-discharge cycling, cyclic voltammetry, and rate performance measurements. The electrode delivers a high reversible capacity of 825 mAh g-1 at a current density of 100 mA g-1 and a superior rate capability with a discharge capacity of 263 mAh g-1 under the high current density of 2 Ag-1 . The structural transition and phase evolution of Ag2 Mo2 O7 were investigated by using ex situ XRD and TEM. The Ag2 Mo2 O7 electrode is likely to be decomposed into amorphous molybdenum, Li2 O, and metallic silver based on the conversion reaction. Silver nanoparticles are not involved in the subsequent electrochemical cycles to form a homogeneous conducting network. Such in situ decomposition behavior provides an insight into the mechanism of the electrochemical reaction for the anode materials and would contribute to the design of new electrode materials in future.

Chloride ion adsorption on Ti2C monolayers was theoretically investigated. Electrochemical parameters, including specific capacity, chloride ion (Cl−) diffusion barrier, and discharge voltage profile, were studied via first-principles calculations. The most favorable Cl− adsorption configuration was identified using a partial particle swarm optimization algorithm and the results showed that Cl− adsorption onto Ti2C monolayers achieved a large theoretical capacity (331 mA h g−1), high working voltage (4.0–3.5 V), and low diffusion barrier (0.22 eV). This resulted in excellent rate capability and a large specific energy of 1269 W h kg−1 at the material level. The effects of terminal O, F, and OH groups on Cl− adsorption onto Ti2C monolayer were also studied, which showed that Cl− could not be adsorbed onto O and F terminated Ti2C monolayers. In comparison, Cl− adsorption onto OH terminated Ti2C was allowed but generated a smaller specific capacity (126 mA h g−1) and lower working voltage (3.5–1.5 V) than a bare Ti2C monolayer.

The practical uses of magnesium-ion batteries are hindered by their poor rate capability and fast capacity decay. Moreover, traditional sodium ion batteries suffer from serious safety problems resulting from the sodium dendrites formed on the anode. In order to circumvent these problems, we designed a highly reversible Na+/Mg2+ hybrid-ion battery composed of a metallic Mg anode, a TiS2 derived titanium sulfide cathode and a 1.0 M NaBH4 + 0.1 M Mg(BH4)2/diglyme hybrid electrolyte. The battery showed remarkable electrochemical performances with a large discharge capacity (200 mA h g−1 at the 1C rate), high rate capability (75 mA h g−1 at the 20C rate) and long cycle life (90% capacity retention after 3000 cycles). Moreover, it exhibited excellent safety properties due to dendrite-free Mg deposition of the anode and the high thermal stability of the cathode. These merits demonstrate the great potential of the reported Na+/Mg2+ hybrid-ion battery for large-scale energy storage.

We report for the first time one-dimensional (1D) wurtzite (WZ) MnSe nanoconveyors with a single-crystalline configuration fabricated by a solution-processed colloidal method. High-resolution transmission electron microscopy (HRTEM) measurements show that the stem of MnSe nanoconveyors grows along the [100] direction, while the teeth grow along the [0001] direction. We find that the initial WZ nanobelts with the [100] growth direction are crucial to the formation of nanoconveyors, whereas the teeth are a result of a self-catalyzed growth process induced by the Mn-terminated (0001) surface. The magnetic measurements suggest that 1D WZ MnSe nanoconveyors consist of an antiferromagnetic core and a ferromagnetic shell below the blocking temperature. Furthermore, the hysteresis measurements indicate that these nanoconveyors have 300 Oe coercive fields, which is attributed to the high surface-to-volume ratio of the nanoconveyors. This facile solution-based strategy can be anticipated to synthesize WZ metal chalcogenide nanomaterials with 1D hierarchical structures, for potential applications from spintronics to photocatalysis.

TiO2 has poor photocatalytic performance when synthesised using traditional processes under visible light, which has limited its practical applications. In this work, titanium sulfate and hydrazine hydrate were used as raw materials to fabricate highly mesoporous honeycomb TiO2via a two-step hydrothermal and calcination method. The formation mechanism of the highly mesoporous TiO2 was analyzed based on experiments and theories. The parameters were flexible using the preparation method. Samples with high photocatalytic performance can be obtained without strictly controlling the process parameters such as hydrazine hydrate dosage, the hydrothermal temperature and so on. The preparation process was as follows: the raw materials were prepared at 180 °C for 48 h in the first hydrothermal stage, and then synthesized at 150 °C for 48 h in the second hydrothermal process. The hydrazine hydrate dosage was 10 ml in the second process. The prepared grain sizes were about 16.4 nm and the specific surface areas were approximately 105.12 m2 g−1 after the samples were heated at 450 °C for 4 h. Their degradation rate was 1.8 times that of P25. The improved performances are ascribed to the unique point defects because of nitrogen atom doping in the TiO2 and the highly mesoporous structure increased by adding hydrazine hydrate.

A graphene@MoS2@TiO2 hybrid material was successfully prepared by a multi-step solution chemistry method. Few-layered MoS2 nanosheets were impregnated into the nanovoids of mesoporous TiO2 microspheres and the composite was further encapsulated by a graphene layer. When used as a negative electrode material for lithium ion batteries, the nanovoids of TiO2 reduced aggregation of MoS2 and suppressed the large volume change of the active material. Moreover, the dissolution and shuttle of polysulfides were effectively suppressed by the hybrid bonding between MoS2 and TiO2. The nano-sized MoS2 and TiO2 particles encapsulated by a high electronic conductive graphene layer improved the charge transfer reaction of the electrode. Due to these merits, the graphene@MoS2@TiO2 showed a large discharge capacity of 980 mA h g−1 at 0.1 A g−1 current density with a capacity retention of 89% after 200 cycles. Moreover, the material delivered 602 mA h g−1 at 2 A g−1 current density, much larger than 91 mA h g−1 for the pristine MoS2. This demonstrated that the hybrid graphene@MoS2@TiO2 microspheres have great potential as a high-performance negative electrode material for lithium ion batteries.

First-principles calculations based on density functional theory were carried out to investigate the electrochemical performance of monolayer VS2 for Li-, K-, Mg- and Al-ion batteries. A VS2 monolayer shows differential storage ability for various cations, able to adsorb three layers of Li, two layers of Mg, one layer of K, and 1/9 layer of Al on both sides of the monolayer, producing theoretical capacities of 1397, 1863, 466, and 78 mA h g−1 for Li, Mg, K, and Al, respectively. The average working voltages of VS2 monolayers for Li+, K+ and Mg2+ are close to those of metallic Li, K, and Mg, suggesting that they can be used as anode materials in these rechargeable batteries. The adsorbed cations form a honeycomb-stacking lattice on VS2 monolayers, similar to the plating process of Li, K, and Mg metal anodes. More interestingly, the honeycomb Li lattice is different from the body-centered cubic lattice of a Li metal anode, which provides very small diffusion barriers, resulting in the high rate capability of VS2 monolayer in Li-ion batteries.

In this study, Ge0.90Ga0.10 nano-twists were prepared by an in situ Ga-alloying method to inhibit the fractal growth of Ge. The mobility of Li+ in the Ge0.90Ga0.10 nano-twists was two orders higher than that in Ge. This advantage promotes fast charging of Li-ion batteries with the rate capability of 819 mA h g-1 at 16 A g-1.

Large overpotential in oxygen reduction and evolution reactions is the intractable obstruction of Li-O2 batteries, causing inferior round-trip efficiency and diminished cycle life. Modulating the reaction mechanism of Li2O2 is of crucial importance for a high-performance Li-O2 battery. Herein, we report a composite of amorphous RuO2 nanoparticles decorated carbon nanotubes (A-RuO2@CNT) as an efficient catalyst for Li-O2 batteries. The amorphous catalyst contains abundant defects and vacancies as well as distorted atom arrangements, which provide sufficient active sites for reactions and enhance the affinity for LiO2 intermediates. As a result, the formation/decomposition mechanisms of Li2O2 are reasonably regulated. An amorphous film-like Li2O2 product forms and uniformly deposits on the surface of A-RuO2@CNT, thus achieving faster redox kinetics and smaller overpotential. When used in Li-O2 batteries, the amorphous catalyst affords remarkably decreased charge overpotential and enhanced cyclic stability, which is superior to its crystalline counterpart.

Rechargeable aqueous zinc-ion batteries (AZIBs) are emerging as promising candidates for large-scale energy storage systems because of their low cost and high safety. However, the slow migration rate and strong electrostatic repulsion of divalent Zn2+ put forward many requirements for the properties of cathode materials. Herein, we present an aluminium pre-intercalated orthorhombic V2O5 (Al0.2V2O5) as a new cathode material for AZIBs. The analyses of GITT, ex-situ XRD, TEM and XPS indicate that the Al0.2V2O5 electrode possesses a higher Zn2+ diffusion coefficient than V2O5. And, the pre-intercalated Al3+ can stabilize the crystal structure and prevent Zn2+ from being trapped in the lattice. Because of the above advantages, Al0.2V2O5 shows much-enhanced electrochemical performance including a high capacity of 448.4 mA h g−1 at 0.1 A g−1, excellent rate capability of 143.9 mA h g−1 at 10 A g−1 and impressive long-term cycling stability with a capacity retention of 61.4% after 5000 cycles at 5 A g−1. Furthermore, the Al0.2V2O5/Zn battery can provide a high energy density of 327.1 W h kg−1 at 0.1 A g−1 and a high power density of 5491.8 W kg−1 at 10 A g−1, which shows great potential in the applications of large-scale energy storage.

Two-dimensional transition metal dichalcogenides (TMDs) have been intensively studied as electrode materials for lithium-ion batteries. But, most of TMDs are low electronic conductors, and there is lack of research on the distinct electrochemical mechanisms of monolayer and bulk TMDs. In this work, the Li+ storage properties of monolayer and bulk TiSe2 are studied by first-principles calculations based on the density functional theory. Calculations showed that bulk TiSe2 works on the intercalation mechanism, which results in a theoretical capacity of 260 mA·h·g−1 in the voltage window of 1.14–2.09 V. In comparison, monolayer TiSe2 works on the adsorption mechanism which gives a theoretical capacity of 780 mA·h·g−1 in 0.18–1.43 V. A two-stage redox process was revealed for both TiSe2 forms. In the initial stage, Se acted as the main redox species; then both Ti and Se participated in the redox reaction. In addition, the material possesses low Li+ diffusion barriers. Especially, a very small diffusion barrier of 163 meV at high Li+ concentration and 39 meV at low Li+ concentration was obtained for monolayer TiSe2, which provide great potential as a high rate anode material for lithium ion batteries.