One-Pot synthesized bicontinuous hierarchical Li3V2(PO4)3/C mesoporous nanowires for high-rate and ultralong-life lithium-ion batteries

The design and synthesis of spinel one-dimensional multi-shelled nanostructures for Li-ion batteries

The rational design, synthesis, and massive production of one-dimensional (1D) spinel composite oxides with multi-shelled nanostructures are critical for the realization of highly efficient energy conversion and storage. However, owing to the limitations of the synthetic methods, the 1D multi-shelled nanostructures, especially for multi-element oxides and binary-metal oxides, have been rarely fabricated. Herein, we design a facile and general method to fabricate 1D spinel composite oxides with complex architectures. It is found that the concentration of the precursor polymer PAN can control the structures of the products at optimal heating rate, including hollow nanofibers, wire-in-tube nanofibers, and tube-in-tube nanofibers. This technique could be extended to various inorganic multi-element oxides and binary-metal oxides. Moreover, numerous twin boundaries (TBs) are found to form in the Co_0.5Ni_0.5Fe₂O₄ tube-in-tube nanofibers. Benefiting from both large porosity and TBs structures, the tube-in-tube hollow nanostructures are measured to possess superior electrochemical performances with high energy and stability in lithium-ion storage.

Precise surface control of cathode materials for stable lithium-ion batteries

The increasing demand for high-energy Li-ion batteries (LIBs) continues to push the development of electrode materials, particularly cathode materials, towards their capacity limits. Despite the enormous success, the stability and reliability of LIBs are becoming a serious concern due to the much-aggravated side reactions between electrode materials and organic electrolytes. How to stabilize the cathode/electrolyte interface is therefore an imperative and urgent task drawing considerable attention from both academia and industry. An active treatment on the surface of cathode materials, usually by introducing an inert protection layer, to diminish their side reaction with electrolytes turns out to be a reasonable and effective strategy. This Feature Article firstly outlines our synthesis efforts for the construction of a uniform surface nanocoating on various cathode materials. Different wet chemical routes have been designed to facilitate the control of growth kinetics of targeted coating species so that a precise surface coating could be achieved with nanometer accuracy. Furthermore, we showed the possibility to transform the outer coating layer into a surface doping effect through surface solid reaction at high temperature. A detailed discussion on the structure-performance relationship of these surface-controlled cathode materials is introduced to probe the stabilization mechanism. Finally, perspectives on the development tendency of high-energy cathodes for stable LIBs are provided.

Rational Design and Engineering of One-Dimensional Hollow Nanostructures for Efficient Electrochemical Energy Storage

The unique structural characteristics of one-dimensional (1D) hollow nanostructures result in intriguing physicochemical properties and wide applications, especially for electrochemical energy storage applications. In this Minireview, we give an overview of recent developments in the rational design and engineering of various kinds of 1D hollow nanostructures with well-designed architectures, structural/compositional complexity, controllable morphologies, and enhanced electrochemical properties for different kinds of electrochemical energy storage applications (i.e. lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-selenium sulfur batteries, lithium metal anodes, metal-air batteries, supercapacitors). We conclude with prospects on some critical challenges and possible future research directions in this field. It is anticipated that further innovative studies on the structural and compositional design of functional 1D nanostructured electrodes for energy storage applications will be stimulated.

Micro/Nano Na3V2(PO4)3/N-Doped Carbon Composites with a Hierarchical Porous Structure for High-Rate Pouch-Type Sodium-Ion Full-Cell Performance

Polyanion-type Na₃V₂(PO₄)₃ (NVP) is an overwhelmingly attractive cathode material for sodium-ion batteries (SIBs) because of its high structural stability and fast Na⁺ mobility. However, its practical application is strongly plagued by either nanoscale particle size or poor rate performance. Herein, a micro/nanocomposite NVP cathode with a hierarchical porous structure is proposed to solve the problem. The microscale NVP material assembled by interconnected nanoflakes with N-doped carbon coating that is capable of simultaneously providing fast carrier transmission dynamics and outstanding structural integrity exhibits precedent sodium-storage behavior. It delivers a superior rate capability (79.1 mAh g^-1 at 200C) and excellent long-life cycling (capacity retention of 73.4% after 10 000 cycles at 100C). Remarkably, a pouch-type sodium-ion full cell consisting of the as-obtained NVP cathode and a hard carbon anode demonstrates the gravimetric energy density as high as 212 Wh kg^-1 and an exceptional rate performance (71.8 mAh g^-1 at 10C). Such structural design of fabricating micro/nanocomposite electrode materials is expected to accelerate the practical applications of SIBs for large-scale energy storage.

Stabilized covalent interfacial coupling design of Li3V2(PO4)3 with carbon framework for boosting lithium storage kinetics

LVP@C with stabilized electronic conductive layer is prepared by a facile organic–inorganic hybrid hydrogel-enabled methodology, in which LVP is chemically interacting with carbon framework via P–C and P–O–C bonds.

Flexible All-Solid-State Li-Ion Battery Manufacturable in Ambient Atmosphere

The rational design and exploration of safe, robust, and inexpensive energy storage systems with high flexibility are greatly desired for integrated wearable electronic devices. Herein, a flexible all-solid-state battery possessing competitive electrochemical performance and mechanical stability has been realized by easy manufacture processes using carbon nanotube enhanced phosphate electrodes of LiTi₂(PO₄)₃ and Li₃V₂(PO₄)₃ and a highly conductive solid polymer electrolyte made of polyphosphazene/PVDF-HFP/LiBOB [PVDF-HFP, poly(vinylidene fluoride-co-hexafluoropropylene)]. The components were chosen based on their low toxicity, systematic manufacturability, and (electro-)chemical matching in order to ensure ambient atmosphere battery assembly and to reach high flexibility, good safety, effective interfacial contacts, and high chemical and mechanical stability for the battery while in operation. The high energy density of the electrodes was enabled by a novel design of the self-standing anode and cathode in a way that a large amount of active particles are embedded in the carbon nanotube (CNT) bunches and on the surface of CNT fabric, without binder additive, additional carbon, or a large metallic current collector. The electrodes showed outstanding performance individually in half-cells with liquid and polymer electrolyte, respectively. The prepared flexible all-solid-state battery exhibited good rate capability, and more than half of its theoretical capacity can be delivered even at 1C at 30 °C. Moreover, the capacity retentions are higher than 75% after 200 cycles at different current rates, and the battery showed smaller capacity fading after cycling at 50 °C. Furthermore, the promising practical possibilities of the battery concept and fabrication method were demonstrated by a prototype laminated flexible cell.

The bead-like Li3V2(PO4)3/NC nanofibers based on the nanocellulose from waste reed for long-life Li-ion batteries

In this work, we firstly synthesized the high-quality nanocellulose from the waste reed, a low-cost biomass, and designed the nanostructure for energy applications. We successfully constructed the bead-like Lithium vanadium phosphate/nanofiber carbon (LVP/NC) multi-structure by self-assembly based on the nanocellulose framework. During the carbonization process, the nanocellulose turn into porous carbon nanofiber into which LVP nanoparticles can be embedded to form a bead-like structure. The unique structure can endow the effective electron contacts and ions transportation. As cathode for Li ion batteries, the composite exhibits the discharge specific capacity of 131.6 mA h/g, which is close to the theoretical specific capacity. Moreover, the composites reveal an excellent long-cycle performance. At 10 C, the capacity retention is near 90 % after 1000 cycles. With the excellent performance, this bead-like composite shows great application value and the facile synthesis strategy can be used for preparing other cathode with high performance.

Ultralong cycle stability of aqueous zinc-ion batteries with zinc vanadium oxide cathodes

Rechargeable aqueous zinc-ion batteries are promising candidates for large-scale energy storage but are plagued by the lack of cathode materials with both excellent rate capability and adequate cycle life span. We overcome this barrier by designing a novel hierarchically porous structure of Zn-vanadium oxide material. This Zn_0.3V₂O₅·1.5H₂O cathode delivers a high specific capacity of 426 mA·h g^-1 at 0.2 A g^-1 and exhibits an unprecedented superlong-term cyclic stability with a capacity retention of 96% over 20,000 cycles at 10 A g^-1. Its electrochemical mechanism is elucidated. The lattice contraction induced by zinc intercalation and the expansion caused by hydronium intercalation cancel each other and allow the lattice to remain constant during charge/discharge, favoring cyclic stability. The hierarchically porous structure provides abundant contact with electrolyte, shortens ion diffusion path, and provides cushion for relieving strain generated during electrochemical processes, facilitating both fast kinetics and long-term stability.

Engineering a High-Energy-Density and Long Lifespan Aqueous Zinc Battery via Ammonium Vanadium Bronze

Aqueous rechargeable zinc batteries (ARZBs) are desirable for energy storage devices owing to their low cost and abundance of the Zn anode, but their further development is limited by a dearth of ideal cathode materials that can simultaneously possess high capacity and stability. Herein, we employ a layered structure of ammonium vanadium bronze (NH₄)_0.5V₂O₅ as the cathode material for ARZBs. The large interlayer distance supported by the NH₄⁺ insertion not only facilitates the Zn²⁺-ion intercalation/deintercalation but also improves the electrochemical stability in ARZBs. As a result, the layered structural (NH₄)_0.5V₂O₅ cathode delivers a high capacity up to 418.4 mA h g^-1 at a current density of 0.1 A g^-1. A reversible capacity of 248.8 mA h g^-1 is still retained after 2000 cycles and a capacity retention of 91.4% was maintained at 5 A g^-1. Furthermore, in comparison with previously reported Zn-ion batteries, the Zn/(NH₄)_0.5V₂O₅ battery achieves a prominent high energy density of 418.4 W h kg^-1 while delivering a high power density of 100 W kg^-1. The results would enlighten and push the ammonium vanadium compounds to a brand new stage for the application of aqueous batteries.

Superior Li-ion storage of VS4 nanowires anchored on reduced graphene

Research on VS4 is lagging due to the difficulty in its tailored synthesis. Herein, unique architecture design of one-dimensional VS4 nanowires anchored on reduced graphene oxide is demonstrated via a facile solvothermal synthesis. Different amounts of reduced graphene oxide with VS4 are synthesized and compared regarding their rate capability and cycling stability. Among them, VS4 nanowires@15 wt% reduced graphene oxide present the best electrochemical performance. The superior performance is attributed to the optimal amount of reduced graphene oxide and one-dimensional VS4 nanowires based on (i) the large surface area that could accommodate volume changes, (ii) enhanced accessibility of the electrolyte, and (iii) improvement in electrical conductivity. In addition, kinetic parameters derived from electrochemical impedance spectroscopy spectra and sweep rate dependent cyclic voltammetry curves such as charge transfer resistances and Li+ ion apparent diffusion coefficients both support this claim. The diffusion coefficient is calculated to be 1.694 × 10-12 cm2 s-1 for VS4 nanowires/15 wt% reduced graphene oxide, highest among all samples.

Synergetic effect of Na-doping and carbon coating on the electrochemical performances of Li3-x Na x V2(PO4)3/C as cathode for lithium-ion batteries

Carbon coated Li_3-x Na _x V₂(PO₄)₃/C (x = 0.04, 0.06, 0.10, 0.12, 0.18) cathode materials for lithium-ion batteries were synthesized via a simple carbothermal reduction reaction route using methyl orange as the reducing agent, which also acted as the Na and carbon sources. The influence of various Na-doping levels on the structure and electrochemical performance of the Li_3-x Na _x V₂(PO₄)₃/C composites was investigated. The valence state of vanadium, the form of residual carbon and the overall morphology of the Li_2.90Na_0.10V₂(PO₄)₃/C, which showed the highest initial specific discharge capacity of 128 mA h g^-1 at the current density of 0.1C (1C = 132 mA g^-1) among this series of composites, were further examined by X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and high-resolution transmission electron microscopy, respectively. The results indicated that a well crystallized structure of Na-doped Li_2.90Na_0.10V₂(PO₄)₃ coated by a carbon matrix is obtained. In the further electrochemical measurements, the Li_2.90Na_0.10V₂(PO₄)₃/C cathode material shows superior discharge capacities of 124, 118, 113, 106 and 98 mA h g^-1 at 0.3, 0.5, 1, 2 and 5C, respectively. High capacity retention of 97% was obtained after 1100 cycles in long-term cyclic performance tests at 5C. The reason for such a promising electrochemical performance of the as-prepared Li_2.90Na_0.10V₂(PO₄)₃/C has also been explored, which revealed that the synergetic effect of the Na-doping and carbon coating provide enlarged Li⁺ diffusion channels and the increased electronic conductivity.

F-Doping effects on carbon-coated Li3V2(PO4)3 as a cathode for high performance lithium rechargeable batteries: combined experimental and DFT studies

F-Doping effects on polyaniline-derived carbon coated Li3V2(PO4)3 (Li3V2(PO4)3-xFx@C) as a cathode for high performance Li rechargeable batteries are systematically investigated with a combined experimental and DFT theoretical calculation approach. The results clearly indicate that the doping amount has a significant impact on the rate capability and long cycle life. The optimal material (Li3V2(PO4)2.88F0.12@C) delivers 123.16 mA h g-1@2C, which is close to the theoretical value (133 mA h g-1), while showing a greatly improved cycle stability. Rietveld refinements show that the F- doping does not obey Vegard's Law, which may be attributed to the generated lower valence of V ions. AC impedance spectroscopy shows that the F-doping can achieve faster interfacial charge transfer for higher reaction reversibility. DFT calculations confirm that the lower V2+ (t2g↑)3 does exist in Li3V2(PO4)2.88F0.12, and the mean nearest neighbor Li-O bond length also increases for faster electrochemical kinetics, and further reveal that there is a tendency for a transition from the insulator to the n-type semiconductor due to the F dopant. The combined experimental and calculated results suggest that F-doping indeed greatly facilitates the charge transfer rate of the Li+ insertion/de-insertion process for better reversibility and enhances the Li+ diffusion rate to access the reaction sites, thus resulting in high rate capacity and cycling stability. This work not only offers a facile and effective approach to synthesize high performance Li-ion battery material for very promising practical applications, but also discloses scientific insights on element coating and doping to guide the electrode material design for fast electrode kinetics in energy storage devices.

Nanostructured Li3 V2 (PO4 )3 Cathodes

To further increase the energy and power densities of lithium-ion batteries (LIBs), monoclinic Li₃ V₂ (PO₄ )₃ attracts much attention. However, the intrinsic low electrical conductivity (2.4 × 10^-7 S cm^-1 ) and sluggish kinetics become major drawbacks that keep Li₃ V₂ (PO₄ )₃ away from meeting its full potential in high rate performance. Recently, significant breakthroughs in electrochemical performance (e.g., rate capability and cycling stability) have been achieved by utilizing advanced nanotechnologies. The nanostructured Li₃ V₂ (PO₄ )₃ hybrid cathodes not only improve the electrical conductivity, but also provide high electrode/electrolyte contact interfaces, favorable electron and Li⁺ transport properties, and good accommodation of strain upon Li⁺ insertion/extraction. In this Review, light is shed on recent developments in the application of 0D (nanoparticles), 1D (nanowires and nanobelts), 2D (nanoplates and nanosheets), and 3D (nanospheres) Li₃ V₂ (PO₄ )₃ for high-performance LIBs, especially highlighting their synthetic strategies and promising electrochemical properties. Finally, the future prospects of nanostructured Li₃ V₂ (PO₄ )₃ cathodes are discussed.

One-Dimensional Hetero-Nanostructures for Rechargeable Batteries

Rechargeable batteries are regarded as one of the most practical electrochemical energy storage devices that are able to convert and store the electrical energy generated from renewable resources, and they function as the key power sources for electric vehicles and portable electronics. The ultimate goals for electrochemical energy storage devices are high power and energy density, long lifetime, and high safety. To achieve the above goals, researchers have tried to apply various morphologies of nanomaterials as the electrodes to enhance the electrochemical performance. Among them, one-dimensional (1D) materials show unique superiorities, such as cross-linked structures for external stress buffering and large draw ratios for internal stress dispersion. However, a homogeneous single-component electrode material can hardly have the characteristics of high electronic/ionic conductivity and high stability in the electrochemical environment simultaneously. Therefore, designing well-defined functional 1D hetero-nanostructures that combine the advantages and overcome the limitations of different electrochemically active materials is of great significance. This Account summarizes fabrication strategies for 1D hetero-nanostructures, including nucleation and growth, deposition, and melt-casting and electrospinning. Besides, the chemical principles for each strategy are discussed. The nucleation and growth strategy is suitable for growing and constructing 1D hetero-nanostructures of partial transition metal compounds, and the experimental conditions for this strategy are relatively accessible. Deposition is a reliable strategy to synthesize 1D hetero-nanostructures by decorating functional layers on 1D substrate materials, on the condition that the preobtained substrate materials must be stable in the following deposition process. The melt-casting strategy, in which 1D hetero-nanostructures are synthesizes via a melting and molding process, is also widely used. Additionally, the main functions of 1D hetero-nanostructures are summarized into four aspects and reviewed in detail. Appropriate surface modification can effectively restrain the structure deterioration and the regeneration of the solid-electrolyte interphase layer caused by the volume change. A porous or semihollow external conducting material coating provides advanced electron/ion bicontinuous transmission. Suitable atomic heterogeneity in the crystal structure is beneficial to the expansion and stabilization of the ion diffusion channels. Multiphase-assisted structural design is also an accessible way for the sulfur electrode material restriction. Moreover, some outlooks about the further industrial production, more effective and cheaper fabrication strategies, and new heterostructures with smaller-scale composition are given in the last part. By providing an overview of fabrication methods and performance-enhancing mechanisms of 1D hetero-nanostructured electrode materials, we hope to pave a new way to facile and efficient construction of 1D hetero-nanostructures with practical utility.

Remarkable Effect of Sodium Alginate Aqueous Binder on Anatase TiO2 as High-Performance Anode in Sodium Ion Batteries

Sodium alginate (SA) is investigated as the aqueous binder to fabricate high-performance, low-cost, environmentally friendly, and durable TiO₂ anodes in sodium-ion batteries (SIBs) for the first time. Compared to the conventional polyvinylidene difluoride (PVDF) binder, electrodes using SA as the binder exhibit significant promotion of electrochemical performances. The initial Coulombic efficiency is as high as 62% at 0.1 C. A remarkable capacity of 180 mAh g^-1 is achieved with no decay after 500 cycles at 1 C. Even at 10 C (3.4 A g^-1), it remains 82 mAh g^-1 after 3600 cycles with approximate 100% Coulombic efficiency. TiO₂ electrodes with SA binder display less electrolyte decomposition, fewer side reactions, high electrochemistry reaction activity, effective suppression of polarization, and good electrode morphology, which is ascribed to the rich carboxylic groups, high Young's modulus, and good electrochemical stability of SA binder.

Li0.93V2.07BO5: a new nano-rod cathode material for lithium ion batteries

The compound Li_0.93V_2.07BO₅ (LVBO) has been successfully designed and used for the first time as a cathode material for lithium ion batteries (LIBs). It belongs to a new family of lithium transition metal borates, namely LiMBO₃ (M = Mn, Fe or Co), which are regarded as good alternatives to phosphates because of their comparably lower molecular weights, which can lead to a larger theoretical specific capacity than those of phosphate-based LiMPO₄. LVBO crystallizes in the space group Pbam with V atom and Li atom occupying the same sites, which makes the structure more stable and brings a disorder effect. Further structure and components of the promising cathode material have been characterized based on the results of X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and inductively coupled plasma mass spectrometry. The synthesized LVBO/C material displays a nanorod morphology with a size of 20-100 nm and shows good electrochemical activity. When used as cathode material in LIBs, LVBO/C delivers an initial discharge specific capacity of 125 mA h g^-1 and exhibits relatively good cycle stability. These results are of great interest for further study of its electrochemical behaviors, which is of significance in exploring new borate cathode materials for LIBs.

1D Nanomaterials: Design, Synthesis, and Applications in Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have received extensive attention as ideal candidates for large-scale energy storage systems (ESSs) owing to the rich resources and low cost of sodium (Na). However, the larger size of Na⁺ and the less negative redox potential of Na⁺ /Na result in low energy densities, short cycling life, and the sluggish kinetics of SIBs. Therefore, it is necessary to develop appropriate Na storage electrode materials with the capability to host larger Na⁺ and fast ion diffusion kinetics. 1D materials such as nanofibers, nanotubes, nanorods, and nanowires, are generally considered to be high-capacity and stable electrode materials, due to their uniform structure, orientated electronic and ionic transport, and strong tolerance to stress change. Here, the synthesis of 1D nanomaterials and their applications in SIBs are reviewed. In addition, the prospects of 1D nanomaterials on energy conversion and storage as well as the development and application orientation of SIBs are presented.

Magnesium/chloride co-doping of lithium vanadium phosphate cathodes for enhanced stable lifetime in lithium-ion batteries

Combining XRD with ³¹P NMR, it is demonstrated that the Mg and Cl atoms of the new Mg and Cl co-doped Li₃V₂(PO₄)₃/C material occupy V and O sites in its structure, respectively.

Anthracite-Derived Dual-Phase Carbon-Coated Li3V2(PO4)3 as High-Performance Cathode Material for Lithium Ion Batteries

In this study, low cost anthracite-derived dual-phase carbon-coated Li₃V₂(PO₄)₃ composites have been successfully prepared via a traditional solid-phase method. XRD results show that the as-prepared samples have high crystallinity and anthracite introduction has no influence on the LVP crystal structure. The LVP/C particles are uniformly covered with a dual-phase carbon layer composed of amorphous carbon and graphitic carbon. The effect of the amount of anthracite on the battery performance of LVP as a cathode material has also been studied. The LVP/C composite obtained with 10 wt % anthracite (LVP/C-10) delivers the highest initial charge/discharge capacities of 186.1/168.2 mAh g^-1 at 1 C and still retains the highest discharge capacity of 134.0 mAh g^-1 even after 100 cycles. LVP/C-10 also displays an outstanding average capacity of 140.8 mAh g^-1 at 5 C. The superior rate capability and cycling stability of LVP/C-10 is ascribed to the reduced particle size, decreased charge-transfer resistance, and improved lithium ion diffusion coefficient. Our results demonstrate that using anthracite as a carbon source opens up a new strategy for larger-scale synthesis of LVP and other electrode materials with poor electronic conductivity for lithium ion batteries.

Bicontinuous Spider Network Architecture of Free-Standing MnCoO X @NCNF Anode for Li-Ion Battery

Herein, a smart strategy is proposed to tailor unique interwoven nanocable architecture consisting of MnCoO _x nanoparticles embedded in one-dimensional (1D) mesoporous N-doped carbon nanofibers (NCNFs) by using electrospinning technique. The as-prepared network mat of N-doped carbon nanofibers with embedded MnCoO _x nanoparticles (MnCoO _x @NCNFs) is tested as a current collector-free and binder-free flexible anode, which eliminates slurry preparation process during electrode fabrication in the Li-ion battery (LIB). The MnCoO _x @NCNFs possess versatile structural characteristics that can address simultaneously different issues such as poor conductivity, low cycling stability, volume variation, flexibility, and binder issue associate with the metal oxide. The free-standing mat electrode shows not only high initial discharge and charge capacities but also reversible discharge cycling stability of almost 80% retention up to 100 cycles and 60% retention up to 500 cycles at 1.0 A/g. Such high Li storage capacity and excellent cycling stability are attributed to the unique flexible and free-standing spider network-like architecture of the 1D MnCoO _x @NCNFs that provides the platform for bicontinuous electron/ion pathways for superior electrochemical performance. Along with excellent electrochemical performance, simple synthesis procedure of unique binder-free MnCoO _x @NCNFs can achieve cost-effective scalable mass production for practical use in a flexible mode, not merely in LIBs but also in a wide spectrum of energy storage fields.

Carbon Nanofibers Heavy Laden with Li3V2(PO4)3 Particles Featuring Superb Kinetics for High-Power Lithium Ion Battery

Fast lithium ion and electron transport inside electrode materials are essential to realize its superb electrochemical performances for lithium rechargeable batteries. Herein, a distinctive structure of cathode material is proposed, which can simultaneously satisfy these requirements. Nanosized Li3V2(PO4)3 (LVP) particles can be successfully grown up on the carbon nanofiber via electrospinning method followed by a controlled heat-treatment. Herein, LVP particles are anchored onto the surface of carbon nanofiber, and with this growing process, the size of LVP particles as well as the thickness of carbon nanofiber can be regulated together. The morphological features of this composite structure enable not only direct contact between electrolytes and LVP particles that can enhance lithium ion diffusivity, but also fast electron transport through 1D carbon network along nanofibers simultaneously. Finally, it is demonstrated that this unique structure is an ideal one to realize high electron transport and ion diffusivity together, which are essential for enhancing the electrochemical performances of electrode materials.

Porous One-Dimensional Nanomaterials: Design, Fabrication and Applications in Electrochemical Energy Storage

Electrochemical energy storage technology is of critical importance for portable electronics, transportation and large-scale energy storage systems. There is a growing demand for energy storage devices with high energy and high power densities, long-term stability, safety and low cost. To achieve these requirements, novel design structures and high performance electrode materials are needed. Porous 1D nanomaterials which combine the advantages of 1D nanoarchitectures and porous structures have had a significant impact in the field of electrochemical energy storage. This review presents an overview of porous 1D nanostructure research, from the synthesis by bottom-up and top-down approaches with rational and controllable structures, to several important electrochemical energy storage applications including lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-oxygen batteries and supercapacitors. Highlights of porous 1D nanostructures are described throughout the review and directions for future research in the field are discussed at the end.

NASICON-Structured Materials for Energy Storage

The demand for electrical energy storage (EES) is ever increasing, which calls for better batteries. NASICON-structured materials represent a family of important electrodes due to its superior ionic conductivity and stable structures. A wide range of materials have been considered, where both vanadium-based and titanium-based materials are recommended as being of great interest. NASICON-structured materials are suitable for both the cathode and the anode, where the operation potential can be easily tuned by the choice of transition metal and/or polyanion group in the structure. NASICON-structured materials also represent a class of solid electrolytes, which are widely employed in all-solid-state ion batteries, all-solid-state air batteries, and hybrid batteries. NASICON-structured materials are reviewed with a focus on both electrode materials and solid-state electrolytes.

Pillared Structure Design of MXene with Ultralarge Interlayer Spacing for High-Performance Lithium-Ion Capacitors

Two-dimensional transition-metal carbide materials (termed MXene) have attracted huge attention in the field of electrochemical energy storage due to their excellent electrical conductivity, high volumetric capacity, etc. Herein, with inspiration from the interesting structure of pillared interlayered clays, we attempt to fabricate pillared Ti₃C₂ MXene (CTAB-Sn(IV)@Ti₃C₂) via a facile liquid-phase cetyltrimethylammonium bromide (CTAB) prepillaring and Sn⁴⁺ pillaring method. The interlayer spacing of Ti₃C₂ MXene can be controlled according to the size of the intercalated prepillaring agent (cationic surfactant) and can reach 2.708 nm with 177% increase compared with the original spacing of 0.977 nm, which is currently the maximum value according to our knowledge. Because of the pillar effect, the assembled LIC exhibits a superior energy density of 239.50 Wh kg^-1 based on the weight of CTAB-Sn(IV)@Ti₃C₂ even under higher power density of 10.8 kW kg^-1. When CTAB-Sn(IV)@Ti₃C₂ anode couples with commercial AC cathode, LIC reveals higher energy density and power density compared with conventional MXene materials.

NASICON-Type Mg0.5Ti2(PO4)3 Negative Electrode Material Exhibits Different Electrochemical Energy Storage Mechanisms in Na-Ion and Li-Ion Batteries

A carbon-coated Mg_0.5Ti₂(PO₄)₃ polyanion material was prepared by the sol-gel method and then studied as the negative electrode materials for lithium-ion and sodium-ion batteries. The material showed a specific capacity of 268.6 mAh g^-1 in the voltage window of 0.01-3.0 V vs Na⁺/Na⁰. Due to the fast diffusion of Na⁺ in the NASICON framework, the material exhibited superior rate capability with a specific capacity of 94.4 mAh g^-1 at a current density of 5A g^-1. Additionally, 99.1% capacity retention was achieved after 300 cycles, demonstrating excellent cycle stability. By comparison, Mg_0.5Ti₂(PO₄)₃ delivered 629.2 mAh g^-1 in 0.01-3.0 V vs Li⁺/Li⁰, much higher than that of the sodium-ion cells. During the first discharge, the material decomposed to Ti/Mg nanoparticles, which were encapsulated in an amorphous SEI and Li₃PO₄ matrix. Li⁺ ions were stored in the Li₃PO₄ matrix and the SEI film formed/decomposed in subsequent cycles, contributing to the large Li⁺ capacity of Mg_0.5Ti₂(PO₄)₃. However, the lithium-ion cells exhibited inferior rate capability and cycle stability compared to the sodium-ion cells due to the sluggish electrochemical kinetics of the electrode.

Investigations on Zr incorporation into Li3V2(PO4)3/C cathode materials for lithium ion batteries

Zr-modified Li₃V₂(PO₄)₃/C composites (LVZrP/C and LVP/C-Zr) obtained from different ways exhibit enhanced performance, in which Zr exists not only in the LVP lattice but also on the LVP surface.

Synthesizing nonstoichiometric Li3−3xV2+x(PO4)3/C as cathode materials for high-performance lithium-ion batteries by solid state reaction

A simple solid state reaction method has been developed to synthesize nonstoichiometric Li_3−3xV_2+x(PO₄)₃/C (x = 0–0.15) nanocomposites.

Core–shell-structured Li3V2(PO4)3–LiVOPO4 nanocomposites cathode for high-rate and long-life lithium-ion batteries

A facile strategy has been developed to construct unique core–shell-structured Li_2.7V_2.1(PO₄)₃ nanocomposites with a Li₃V₂(PO₄)₃ core and LiVOPO₄ shell by using nonstoichiometric design and high-energy ball milling (HEBM) treatment.

Nanoporous carbon leading to the high performance of a Na3V2O2(PO4)2F@carbon/graphene cathode in a sodium ion battery

The Na₃V₂O₂(PO₄)₂F/graphene sandwich cathode has attracted great attention as a potential candidate for sodium-ion batteries in view of its high capacity and good cycling ability.

Large-scale synthesis of Li3V2(PO4)3@C composites by a modified carbothermal reduction method as cathode material for lithium-ion batteries

Carbon coated Li₃V₂(PO₄)₃composites were prepared by a modified carbothermal reduction method.

Improved rate capability and cycling stability of bicontinuous hierarchical mesoporous LiFePO4/C microbelts for lithium-ion batteries

Bicontinuous hierarchical mesoporous LiFePO₄/C microbelts have been synthesized using a simple dual-solvent electrospinning method for the first time. The sample exhibits a high reversible capacity (153 mA h g⁻¹ at 0.5C), and an excellent high rate cycling performance.

Nanorod-Nanoflake Interconnected LiMnPO4·Li3V2(PO4)3/C Composite for High-Rate and Long-Life Lithium-Ion Batteries

Olivine-type structured LiMnPO₄ has been extensively studied as a high-energy density cathode material for lithium-ion batteries. However, preparation of high-performance LiMnPO₄ is still a large obstacle due to its intrinsically sluggish electrochemical kinetics. Recently, making the composites from both active components has been proven to be a good proposal to improve the electrochemical properties of cathode materials. The composite materials can combine the advantages of each phase and improve the comprehensive properties. Herein, a LiMnPO₄·Li₃V₂(PO₄)₃/C composite with interconnected nanorods and nanoflakes has been synthesized via a one-pot, solid-state reaction in molten hydrocarbon, where the oleic acid functions as a surfactant. With a highly uniform hybrid architecture, conductive carbon coating, and mutual cross-doping, the LiMnPO₄·Li₃V₂(PO₄)₃/C composite manifests high capacity, good rate capability, and excellent cyclic stability in lithium-ion batteries. The composite electrodes deliver a high reversible capacity of 101.3 mAh g^-1 at the rate up to 16 C. After 4000 long-term cycles, the electrodes can still retain 79.39% and 72.74% of its maximum specific discharge capacities at the rates of 4C and 8C, respectively. The results demonstrate that the nanorod-nanoflake interconnected LiMnPO₄·Li₃V₂(PO₄)₃/C composite is a promising cathode material for high-performance lithium ion batteries.

Advanced High Energy Density Secondary Batteries with Multi-Electron Reaction Materials

Secondary batteries have become important for smart grid and electric vehicle applications, and massive effort has been dedicated to optimizing the current generation and improving their energy density. Multi-electron chemistry has paved a new path for the breaking of the barriers that exist in traditional battery research and applications, and provided new ideas for developing new battery systems that meet energy density requirements. An in-depth understanding of multi-electron chemistries in terms of the charge transfer mechanisms occuring during their electrochemical processes is necessary and urgent for the modification of secondary battery materials and development of secondary battery systems. In this Review, multi-electron chemistry for high energy density electrode materials and the corresponding secondary battery systems are discussed. Specifically, four battery systems based on multi-electron reactions are classified in this review: lithium- and sodium-ion batteries based on monovalent cations; rechargeable batteries based on the insertion of polyvalent cations beyond those of alkali metals; metal-air batteries, and Li-S batteries. It is noted that challenges still exist in the development of multi-electron chemistries that must be overcome to meet the energy density requirements of different battery systems, and much effort has more effort to be devoted to this.

Carbon wrapped hierarchical Li3V2(PO4)3 microspheres for high performance lithium ion batteries

Nanomaterials are extensively studied in electrochemical energy storage and conversion systems because of their structural advantages. However, their volumetric energy density still needs improvement due to the high surface area, especially the carbon based nanocomposites. Constructing hierarchical micro-scaled materials from closely stacked subunits is proposed as an effective way to solve the problem. In this work, Li₃V₂(PO₄)₃@carbon hierarchical microspheres are prepared by a solvothermal reaction and subsequent annealing. Hierarchical Li₃V₂(PO₄)₃ structures with different subunits are obtained with the aid of polyvinyl pyrrolidone (PVP). Moreover, excessive PVP interconnect and form PVP-based hydrogels, which later convert into conductive carbon layer on the surface of Li₃V₂(PO₄)₃ microspheres during the annealing process. As a cathode material for lithium ion batteries, the 3D carbon wrapped Li₃V₂(PO₄)₃ hierarchical microspheres exhibit high rate capability and excellent cycling stability. The electrode has the capacity retention of 80% after 5000 cycles even at 50C.