Spontaneous Built-In Electric Field in C3 N4 -CoSe2 Modified Multifunctional Separator with Accelerating Sulfur Evolution Kinetics and Li Deposition for Lithium-Sulfur Batteries.

The discovery of the heterostructures that is combining two materials with different properties has brought new opportunities for the development of lithium sulfur batteries (LSBs). Here, C3 N4 -CoSe2 composite is elaborately designed and used as a functional coating on the LSBs separator. The abundant chemisorption sites of C3 N4 -CoSe2 form chemical bonding with polysulfides, provides suitable adsorption energy for lithium polysulfides (LiPSs). More importantly, the spontaneously formed internal electric field accelerates the charge flow in the C3 N4 -CoSe2 interface, thus facilitating the transport of LiPSs and electrons and promoting the bidirectional conversion of sulfur. Meanwhile, the lithiophilic C3 N4 -CoSe2 sample with catalytic activity can effectively regulate the uniform distribution of lithium when Li+ penetrates the separator, avoiding the formation of lithium dendrites in the lithium (Li) metal anode. Therefore, LSBs based on C3 N4 -CoSe2 functionalized membranes exhibit a stable long cycle life at 1C (with capacity decay of 0.0819% per cycle) and a large areal capacity of 10.30 mAh cm-2 at 0.1C (sulfur load: 8.26 mg cm-2 , lean electrolyte 5.4 µL mgs -1 ). Even under high-temperature conditions of 60 °C, a capacity retention rate of 81.8% after 100 cycles at 1 C current density is maintained.

Construction of the Fast Potassiation Path in Sbx Bi1-x @NC Anode with Ultrahigh Cycling Stability for Potassium-Ion Batteries.

Due to the scarce of lithium resources, potassium-ion batteries (PIBs) have attracted extensive attention due to their similar electrochemical properties to lithium-ion batteries (LIBs) and more abundant potassium resources. Even though there is considerable progress in SbBi alloy anode for LIBs and PIBs, most studies are focused on the morphology/structure tuning, while the inherent physical features of alloy composition's effect on the electrochemical performance are rarely investigated. Herein, combined the nanonization, carbon compounding, and alloying with composition regulation, the anode of nitrogen-doped carbon-coated Sbx Bi1-x (Sbx Bi1-x @NC) with a series of tuned chemical compositions is designed as an ideal model. The density functional theory (DFT) calculation and experimental investigation results show that the K+ diffusion barrier is lower and the path is easier to carry out when element Bi dominates the potassiation reaction, which is also the reason for better circulation. The optimized Sb0.25 Bi0.75 @NC shows an excellent cycling performance with a reversible specific capacity of 301.9 mA h g-1 after 500 cycles at 0.1 A g-1 . Meanwhile, the charge-discharge mechanism is intuitively invetigated and analyzed by in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) in detail. Such an alloy-type anode synthesis approach and in situ observation method provide an adjustable strategy for the designing and investigating of PIB anodes.

Origin of oxygen-redox and transition metals dissolution in Ni-rich LixNi0.8Co0.1Mn0.1O2 cathode.

Recently, Ni-rich LiNixCoyMn1-x-yO2 (x ≥ 0.8) draw significant research attention as cathode materials in lithium-ion batteries due to their superiority in energy density. However, the oxygen release and the transition metals (TMs) dissolution during the (dis)charging process lead to serious safety issues and capacity loss, which highly prevent its application. In this work, we systematically explored the stability of lattice oxygen and TM sites in LiNi0.8Co0.1Mn0.1O2(NCM811) cathode via investigating various vacancy formations during lithiation/delithiation, and properties such as the number of unpaired spins (NUS), net charges, and d band center were comprehensively studied. In the process of delithiation (x = 1 → 0.75 → 0), the vacancy formation energy of lattice oxygen [Evac(O)] has been identified to follow the order of Evac(O-Mn) > Evac(O-Co) > Evac(O-Ni), and Evac(TMs) shows a consistent trend with the sequence of Evac(Mn) > Evac(Co) > Evac(Ni), demonstrating the importance of Mn to stabilize the structural skeleton. Furthermore, the |NUS| and net charge are proved to be good descriptors for measuring Evac(O/TMs), which show linear correlations with Evac(O) and Evac(TMs), respectively. Li vacancy plays a pivotal role on Evac(O/TMs). Evac(O/TMs) at x = 0.75 vary extremely between the NiCoMnO layer (NCM layer) and the NiO layer (Ni layer), which correlates well with |NUS| and net charge in the NCM layer but aggregates in a small region in the Ni layer due to the effect of Li vacancies. In general, this work provides an in-depth understanding of the instability of lattice oxygen and transition metal sites on the (104) surface of Ni-rich NCM811, which might give new insights into oxygen release and transition metal dissolution in this system.

Alkaline Tolerant Antifreezing Additive Enabling Aqueous Zn||Ni Battery Operating at -60 °C.

Alkaline aqueous batteries such as the Zn||Ni batteries have attracted substantial interests due to their merits of high energy density, high safety and low cost. However, the freeze of aqueous electrolyte and the poor cycling stability in alkaline condition have hindered their operation in subzero conditions. Herein, we construct a stable aqueous electrolyte with lowest freezing point down to -90 °C by adding dimethyl sulfoxide (DMSO) as alkaline tolerant antifreezing additive into 1 M KOH solution. Meanwhile, we find the DMSO can also retard Zn anode corrosion and prevent Zn dendrite formation in alkaline condition, which enables the Zn plating/stripping over 700 h cycle at 1 mA cm-2 and 0.5 mAh cm-2 . The fabricated Zn||Ni battery can endure low working temperature even down to -60 °C and its dischage capacity retains 84.1 % at -40 °C, 60.6 % at -60 °C at 0.5 C. Meanwhile, it can maintain 600 cycles with a specific capacity retention of 86.5 % at -40 °C at 2 C.

State of the Art in Crystallization of LiNbO3 and Their Applications.

Lithium niobate (LiNbO3) crystals are important dielectric and ferroelectric materials, which are widely used in acoustics, optic, and optoelectrical devices. The physical and chemical properties of LiNbO3 are dependent on microstructures, defects, compositions, and dimensions. In this review, we first discussed the crystal and defect structures of LiNbO3, then the crystallization of LiNbO3 single crystal, and the measuring methods of Li content were introduced to reveal reason of growing congruent LiNbO3 and variable Li/Nb ratios. Afterwards, this review provides a summary about traditional and non-traditional applications of LiNbO3 crystals. The development of rare earth doped LiNbO3 used in illumination, and fluorescence temperature sensing was reviewed. In addition to radio-frequency applications, surface acoustic wave devices applied in high temperature sensor and solid-state physics were discussed. Thanks to its properties of spontaneous ferroelectric polarization, and high chemical stability, LiNbO3 crystals showed enhanced performances in photoelectric detection, electrocatalysis, and battery. Furthermore, domain engineering, memristors, sensors, and harvesters with the use of LiNbO3 crystals were formulated. The review is concluded with an outlook of challenges and potential payoff for finding novel LiNbO3 applications.

Ce(OH)3 as a novel negative electrode material for supercapacitors.

Novel electrode materials with desired specific capacitances are needed for supercapacitors. Rare-earth (RE)-based materials are fascinating in the field of catalysis and energy. Herein, a series of hydroxides including La, Ce, Pr and Nd was synthesized via in situ precipitation. Interestingly, only Ce(OH)3 showed a redox peak in both positive and negative ranges. The other RE hydroxides exhibited a redox peak only in the positive range. Therefore, in order to certify that Ce(OH)3 can be used as a negative electrode, symmetrical supercapacitors consisting of Ce(OH)3 as both positive and negative electrodes were assembled, and showed a voltage window of 1.3 V. Moreover, asymmetrical supercapacitors were successfully fabricated, in which the positive electrode was composed of La(OH)3, Pr(OH)3 or Nd(OH)3. These results may pave the way to novel negative electrode materials.

High areal capacitance of manganese oxide electrodes with cerium as rare earth modification.

Manganese oxides have attracted wide attention as promising electrode materials for high-energy density supercapacitors. However, the electrochemical performance of the manganese oxide materials deteriorates considerably with the increase in mass loading due to their moderate electronic and ionic conductivities. This phenomenon leads to low areal capacitance, which limits the practical application of these materials. Herein, we perform a potentiostatic electrodeposition of manganese oxides with Ce as rare earth (RE) modification on a nickel (Ni) foam substrate to achieve high areal capacitance. Under optimum conditions, manganese oxide nanosheets are axially grown on Ni foam to form a hierarchically porous network nanostructure, which ensures facile ionic and electric transport. The Ce-modified manganese oxide with the Mn:Ce molar ratio of 1:0.1 yields an outstanding areal capacitance of 3.67 F cm-2 at 2 mA cm-2 and a good rate capability compared with the capacitance of 2.59 F cm-2 at 2 mA cm-2 of pure manganese oxide without the addition of Ce. This result verifies the importance of Ce modification to manganese oxides. Our results suggest the important role played by the RE element Ce in enhancing the electrochemical performance of high areal capacitance manganese oxide electrodes, which is essential to bringing them one step toward further practical applications.

High specific capacitance of manganese-based colloidal system with rare earth modification.

Ever-increasing global energy consumption has increased aggregate demand on electrochemical energy storage devices with high energy density. Over the past few decades, manganese oxides have attracted wide attention due to their abundant reserves, low cost, environmental friendliness, and high theoretical capacity. However, most reported manganese-based materials have exhibited capacity far below the theoretical capacity, which was only on the basis of Mn3+/Mn4+ couple. The rich chemistry of manganese enables it to exist in various valence states, such as Mn0, Mn2+, Mn3+, Mn4+, and Mn7+, providing great opportunity for discovering new manganese-based electrode systems. Herein, we formed a Mn2+/Mn4+ couple from a manganese-based colloidal system with rare earth (RE) modification, which was formed in-situ on nickel (Ni) foam in KOH electrolyte under an electric field assistance. The Mn-based colloidal electrode, with Mn:Ce mass ratio of 1:0.5, achieved a high specific capacitance of 2985 F g-1 at 3 A g-1, which was higher than the theoretical capacity of 2193 F g-1 on the basis of the Mn3+/Mn4+ couple. After the addition of Ce3+, the prepared sample exhibited improved rate capability performance. Our manganese-based colloidal electrode with RE modification delivered a high specific capacitance of 1223 F g-1 at 20 A g-1, with 54.5% retention of 2243 F g-1 at 3 A g-1 at Mn:Ce mass ratio of 1:0.05. Colloidal electrode systems involving Mn-based colloids are a novel way to engineer the electrochemical performance of inorganic materials.

Electronegativity principles in metal oxides based supercapacitors.

To meet growing demands for energy consumptions in modern society, it is necessary to develop different energy sources. Renewable energy such as wind and solar sources are intermittent, therefore, energy storage devices become more and more important to store energy for use when no wind or no light. Supercapacitors play a key role in energy storage, mainly due to their high power density and long cycling life. However, supercapacitors are facing the obstacle of low energy density, one of the most intensive approaches is to rationally design new electrode materials. In this review, we focus on metal oxides-based materials and present an electronegativity criterion for the design and appropriate selection of new electrode chemical compositions. Metal elements with proper electronegativity scale have the potential to transfer electron for energy storage. Suitable positive and negative electrodes matching can enhance many properties of supercapacitors, which may overcome many related obstacles. Furthermore, electronegativity scale may also help people to find novel metal oxides based supercapacitors.

Geo-inspired crystallization engineering: multifunctional materials design and fabrication at nanoscale and beyond.

Crystallization engineering aims to design and develop solutions for the optimum conversion of natural resources for use by humans, by using crystallization. Crystallization is a cross-scale process, from atoms, ions and molecules in microscale to bulk crystals in macroscale. Fabricating nanomaterials with desired performances is an open issue with multiscale challenges during crystallization. For innovation in crystallization engineering, geology may provide various sources of inspiration such as structures, compositions and formation conditions, if mineral materials can be regarded as novel artificial materials. This review shows us some geo-inspirations that enable people to create and engineer novel materials with satisfactory performance.

Toward materials-by-design: achieving functional materials with physical and chemical effects.

Advances in renewable and sustainable energy technologies critically depend on our ability to rationally design and process target materials with optimized performances. Advanced material design and discovery are ideally involved in material prediction, synthesis and characterization. Control of material crystallization enables the rational design and discovery of novel functional inorganic materials in multi-scale. Material processing can be adjusted by various physical fields and chemical effects at different energy states. Material microstructure, architecture and functionality can thus be modified by multiple design methodologies. In this review, we show typical examples using physical and chemical methods to shape inorganic functional materials and evaluate their specific applications in Na-air batteries, Li-ion batteries and supercapacitors. Furthermore, this review also provides insight into the understanding of synthesis-structure relationship of inorganic functional materials.

Challenges and perspectives of NASICON-type solid electrolytes for all-solid-state lithium batteries.

NASICON-type (lithium super ionic conductor) solid electrolyte is of great interest because of its high ionic conductivity, wide potential window, and good chemical stability. In this paper, the key problems and challenges of NASICON-type solid electrolyte are described from the aspects of ionic conductivity, electrode interface, and electrochemical stability. Firstly, the migration mechanism of lithium ion is analyzed from the three-dimensional structure of NASICON-type solid electrolyte, and progress in the research of conductivity and stability is summarized. Then, the effective methods to reduce interface impedance and improve the cycle stability of all-solid-state lithium batteries (ASSLBs) with NASICON-type solid electrolyte are introduced. Finally, solutions to improve the conductivity of electrolytes and deal with electrode/electrolyte interface problems are summarized, and the development prospects of ASSLBs are discussed.

Colloidal Supercapattery: Redox Ions in Electrode and Electrolyte.

Redox chemistry is the cornerstone of various electrochemical energy conversion and storage systems, associated with ion diffusion process. To actualize both high energy and power density in energy storage devices, both multiple electron transfer reaction and fast ion diffusion occurred in one electrode material are prerequisite. The existence forms of redox ions can lead to different electrochemical thermodynamic and kinetic properties. Here, we introduce novel colloid system, which includes multiple varying ion forms, multi-interaction and abundant redox active sites. Unlike redox cations in solution and crystal materials, colloid system has specific reactivity-structure relationship. In the colloidal ionic electrode, the occurrence of multiple-electron redox reactions and fast ion diffusion leaded to ultrahigh specific capacitance and fast charge rate. The colloidal ionic supercapattery coupled with redox electrolyte provides a new potential technique for the comprehensive use of redox ions including cations and anions in electrode and electrolyte and a guiding design for the development of next-generation high performance energy storage devices.

Colloidal paradigm in supercapattery electrode systems.

Among decades of development, electrochemical energy storage systems are now sorely in need of a new design paradigm at the nano size and ion level to satisfy the higher energy and power demands. In this review paper, we introduce a new colloidal electrode paradigm for supercapattery that integrates multiple-scale forms of matter, i.e. ion clusters, colloidal ions, and nanosized materials, into one colloid system, coupled with multiple interactions, i.e. electrostatic, van der Waals forces, and chemical bonding, thus leading to the formation of many redox reactive centers. This colloidal electrode not only keeps the original ionic nature in colloidal materials, but also creates a new attribute of high electroactivity. Colloidal supercapattery is a perfect application example of the novel colloidal electrode, leading to higher specific capacitance than traditional electrode materials. The high electroactivity of the colloidal electrode mainly comes from the contribution of exposed reactive centers, owing to the confinement effect of carbon and a binder matrix. Systematic and thorough research on the colloidal system will significantly promote the development of fundamental science and the progress of advanced energy storage technology.

Crystal growth: an anisotropic mass transfer process at the interface.

Crystal growth is a dynamic physicochemical process, which depends on the multi-parameter synergetic control and directly determines the crystal features such as geometry and size. In this study, both thermodynamic and kinetic factors that determine inorganic single crystal growth are integrated by focusing on the mass transfer process at an interface. For the specific growth system, the integrated parameter is then classified to extract the critical control factors in anisotropic growth. The driving force of mass transfer essentially depends on the anisotropic chemical bonding architectures, leading to different concentration gradients along various [uvw] directions. Exquisitely controlling the chemical bonding architecture can therefore be used to regulate the mass transfer process of a compound in a straightforward manner, encompassing the origin of anisotropic growth as well as a variety of geometries in the formation of a multicomponent crystal.

Nucleation-dependant chemical bonding paradigm: the effect of rare earth ions on the nucleation of urea in aqueous solution.

Rare earth ions can be used to construct a variety of novel structures and are favorable to chemical bonding regulation and design. In this study, the chemical bonding paradigm between rare earth ions (Ln3+) and urea molecules in an aqueous solution can be tracked by the evolution of C[double bond, length as m-dash]O, NH2, and CN vibration bands during the urea nucleation stage. Rare earth ions such as La3+, Gd3+, and Lu3+ can manipulate the nucleation time of urea via regulating the nucleation-dependant N-C[double bond, length as m-dash]OH-N hydrogen-bonding between urea molecules. Two types of chemical bondings between Ln3+ and urea molecules have been confirmed, which are Ln3+O[double bond, length as m-dash]C-N and Ln3+NH2-C. Compared with Ln3+NH2-C, Ln3+ prefers to coordinate with the O[double bond, length as m-dash]C bond in urea. With a higher concentration of rare earth ions in the solution, some N-C[double bond, length as m-dash]OH-N hydrogen bonds are broken as a consequence of the incorporation of Ln3+ into the lattice, resulting in the decreased symmetry of local urea molecules in the crystalline nuclei and the consequent Ln3+ concentration-dependent nucleation time of urea. Moreover, using the ionic electronegativity scale of Ln3+, the different effects of La3+, Gd3+, and Lu3+ on urea nucleation can be further distinguished. The present study provides basic data for unrevealing the chemical bonding regulation role of rare earth ions in the formation of hydrogen bonded materials, which may give insight into the design and fabrication of novel materials utilizing rare earth ions to adjust the chemical bonding process.

Crystallization-Dependent Luminescence Properties of Ce:LuPO4.

The luminescence properties of Ce:LuPO4 depend on both the Ce(3+) center and the host lattice. In this article, we studied the dependence of the luminescence properties of Ce:LuPO4 on both the doping concentration of Ce(3+) and the size and morphology of the LuPO4 matrix at micro- and nanosize regimes. The crystalline behavior of Ce:LuPO4, including its size and shape, was investigated via precursor transformation crystallization. On the basis of this crystallization approach, Ce:LuPO4 hollow nanospheres, nanorods, and regular tetrahedrons were obtained. For micro- and nanostructured Ce:LuPO4, the surface-induced chemical bonding architecture can be effectively varied by controlling the size of the crystalline material and its geometry. Our experimental observations demonstrate that one-dimensional Ce:LuPO4 nanorods doped with 0.1 mol % Ce(3+) possess the best performance among the as-prepared samples. The significant anisotropy of Ce:LuPO4 nanorods can result in a larger specific surface area and enhanced luminescence properties. Moreover, the improved luminescence property of Ce:LuPO4 nanostructures can also be optimized by increasing the preferential anisotropic chemical bonding architecture to regulate the 5d level of Ce(3+). Our work also shows that the photoluminescence emission intensity of Ce:LuPO4 nanorods is increased as the surface area normal to their axial direction increases. From the standpoint of crystallization, the luminescence properties of Ce(3+) in nano- and microsize matrixes can be well-optimized by controlling the crystalline behavior of the host lattice under proper synthesis conditions.

Luminescence Mechanistic Study of BaLaGa3O7:Nd Using Density Functional Theory Calculations.

BaLaGa3O7:Nd (BLGO:Nd) has been investigated as a laser crystal material for about three decades. In the present work, the luminescence mechanism of BLGO:Nd is clarified by density functional theory (DFT) calculations. Structural optimization was first performed on the constructed supercell to obtain the equilibrium geometry. On the basis of the optimized crystal, the electronic structures of the BLGO host (without and with single defects) and the BLGO:Nd phosphor (without and with neighboring defects) were comprehensively investigated. Three important features are revealed by theoretical analyses. First, single defects in BLGO have little effect on the light emission, although the impurity levels appeared within the band gap. Second, luminescence can be realized by the introduction of Nd ions. Calculations of optical properties demonstrated that parity-forbidden transitions among the 4f levels are partially allowed because the mixing of 4f and 5d configurations occurs at higher empty 4f levels. It is thus clear that the electronic transitions between occupied 4f and empty 4f-5d states are electric-dipole-allowed. Therefore, light emission in BLGO:Nd can be achieved in the electronic transition process of Nd 4f electrons → empty 4f-5d levels → empty 5d levels → Nd 4f levels. The neighboring intrinsic defects play only an auxiliary role in prolonging the decay time. Third, co-doping of Tb in BLGO:Nd is considered to be beneficial to luminescence in theory because of its shallow to deep distribution of impurity orbitals in the band gap. Therefore, BLGO:Nd co-doped with other lanthanide ions will offer guidelines in the search for the best luminescent materials.

Structural design of graphene for use in electrochemical energy storage devices.

There are many practical challenges in the use of graphene materials as active components in electrochemical energy storage devices. Graphene has a much lower capacitance than the theoretical capacitance of 550 F g(-1) for supercapacitors and 744 mA h g(-1) for lithium ion batteries. The macroporous nature of graphene limits its volumetric energy density and the low packing density of graphene-based electrodes prevents its use in commercial applications. Increases in the capacity, energy density and power density of electroactive graphene materials are strongly dependent on their microstructural properties, such as the number of defects, stacking, the use of composite materials, conductivity, the specific surface area and the packing density. The structural design of graphene electrode materials is achieved via six main strategies: the design of non-stacking and three-dimensional graphene; the synthesis of highly packed graphene; the production of graphene with a high specific surface area and high conductivity; the control of defects; functionalization with O, N, B or P heteroatoms; and the formation of graphene composites. These methodologies of structural design are needed for fast electrical charge storage/transfer and the transport of electrolyte ions (Li(+), H(+), K(+), Na(+)) in graphene electrodes. We critically review state-of-the-art progress in the optimization of the electrochemical performance of graphene-based electrode materials. The structure of graphene needs to be designed to develop novel electrochemical energy storage devices that approach the theoretical charge limit of graphene and to deliver electrical energy rapidly and efficiently.

Morphology engineering of high performance binary oxide electrodes.

Advances in materials have preceded almost every major technological leap since the beginning of civilization. On the nanoscale and microscale, mastery over the morphology, size, and structure of a material enables control of its properties and enhancement of its usefulness for a given application, such as energy storage. In this review paper, our aim is to present a review of morphology engineering of high performance oxide electrode materials for electrochemical energy storage. We begin with the chemical bonding theory of single crystal growth to direct the growth of morphology-controllable materials. We then focus on the growth of various morphologies of binary oxides and their electrochemical performances for lithium ion batteries and supercapacitors. The morphology-performance relationships are elaborated by selecting examples in which there is already reasonable understanding for this relationship. Based on these comprehensive analyses, we proposed colloidal supercapacitor systems beyond morphology control on the basis of system- and ion-level design. We conclude this article with personal perspectives on the directions toward which future research in this field might take.