Architectural Engineering Achieves High-Performance Alloying Anodes for Lithium and Sodium Ion Batteries.

Tremendous efforts have been dedicated to the development of high-performance electrochemical energy storage devices. The development of lithium- and sodium-ion batteries (LIBs and SIBs) with high energy densities is urgently needed to meet the growing demands for portable electronic devices, electric vehicles, and large-scale smart grids. Anode materials with high theoretical capacities that are based on alloying storage mechanisms are at the forefront of research geared towards high-energy-density LIBs or SIBs. However, they often suffer from severe pulverization and rapid capacity decay due to their huge volume change upon cycling. So far, a wide variety of advanced materials and electrode structures are developed to improve the long-term cyclability of alloying-type materials. This review provides fundamentals of anti-pulverization and cutting-edge concepts that aim to achieve high-performance alloying anodes for LIBs/SIBs from the viewpoint of architectural engineering. The recent progress on the effective strategies of nanostructuring, incorporation of carbon, intermetallics design, and binder engineering is systematically summarized. After that, the relationship between architectural design and electrochemical performance as well as the related charge-storage mechanisms is discussed. Finally, challenges and perspectives of alloying-type anode materials for further development in LIB/SIB applications are proposed.

Mesopore-Induced Ultrafast Na+ -Storage in T-Nb2 O5 /Carbon Nanofiber Films toward Flexible High-Power Na-Ion Capacitors.

Hybrid Na-ion capacitors (NICs) are receiving considerable interest because they combine the merits of both batteries and supercapacitors and because of the low-cost of sodium resources. However, further large-scale deployment of NICs is impeded by the sluggish diffusion of Na+ in the anode. To achieve rapid redox kinetics, herein the controlled fabrication of mesoporous orthorhombic-Nb2 O5 (T-Nb2 O5 )/carbon nanofiber (CNF) networks is demonstrated via in situ SiO2 -etching. The as-obtained mesoporous T-Nb2 O5 (m-Nb2 O5 )/CNF membranes are mechanically flexible without using any additives, binders, or current collectors. The in situ formed mesopores can efficiently increase Na+ -storage performances of the m-Nb2 O5 /CNF electrode, such as excellent rate capability (up to 150 C) and outstanding cyclability (94% retention after 10 000 cycles at 100 C). A flexible NIC device based on the m-Nb2 O5 /CNF anode and the graphene framework (GF)/mesoporous carbon nanofiber (mCNF) cathode, is further constructed, and delivers an ultrahigh power density of 60 kW kg-1 at 55 Wh kg-1 (based on the total weight of m-Nb2 O5 /CNF and GF/mCNF). More importantly, owing to the free-standing flexible electrode configuration, the m-Nb2 O5 /CNF//GF/mCNF NIC exhibits high volumetric energy and power densities (11.2 mWh cm-3 , 5.4 W cm-3 ) based on the full device, which holds great promise in a wide variety of flexible electronics.

Scalable Synthesis of Fe/N-Doped Porous Carbon Nanotube Frameworks for Aqueous Zn-Air Batteries.

Aqueous Zn-air batteries are emerging to be ideal next-generation energy-storage devices with high safety and high energy/power densities. However, the rational design and fabrication of low-cost, highly efficient, and durable electrocatalysts on the cathode side remain highly desired. Herein, template-assisted, scalable Fe-implanted N-doped porous carbon nanotube networks (Fe-N-CNNs) have been synthesized based on an environmentally friendly template hydroxyapatite nanowires (HAP NWs). Thanks to the hierarchical meso/micropores, high specific surface area, and abundant active sites, the optimized Fe-N-CNNs exhibit excellent oxygen reduction activity. Furthermore, the Zn-air batteries based on the Fe-N-CNNs cathode deliver a high discharge voltage of 1.27 V at a current density of 20 mA cm-2 and a large peak power density of 202.2 mW cm-2 . More far-reaching, this HAP-based template strategy opens a new avenue toward the mass production of efficient, cost-effective electrocatalysts, and the Fe-N-CNNs with hollow interiors are expected to extend their other potential uses in energy storage, molecular sieves, adsorbents, and biomedical engineering.

Microwave-Assisted Rapid Synthesis of Self-Assembled T-Nb2 O5 Nanowires for High-Energy Hybrid Supercapacitors.

Recently ion-intercalation hybrid supercapacitors, with high energy density at high power density, have been widely investigated to meet ever-increasing practical demands. Here, a unique hybrid supercapacitor has been designed and fabricated using self-assembled orthorhombic-phase niobium oxide@carbon (T-Nb2 O5 @C) nanowires as an anode and commercially available activated carbon as a cathode. The 3D-interconnected T-Nb2 O5 @C nanowires have been synthesized through a highly efficient microwave-solvothermal method, combined with subsequent thermal treatment. The experimental parameters (e.g., time and temperature) can be easily programmed, and the synthesis time can be significantly shortened, thus enabling the buildup of abundant recipes for the engineering of scaled-up production. The Li-ion intercalation pseudocapacitance electrode, made from the as-formed self-assembled T-Nb2 O5 @C nanowires, shows excellent charge storage and transfer capability. When assembled into a hybrid supercapacitor with a cathode of activated carbon, a high energy density of 60.6 Wh kg-1 and a high power density of 8.5 kW kg-1 with outstanding stability are achieved. In virtue of easy optimization and programmability of the synthetic strategy, and the remarkable electrochemical performance, the self-assembled T-Nb2 O5 @C nanowires offer a promising anode for asymmetric hybrid supercapacitors.

Constructing Hierarchical Tectorum-like α-Fe2 O3 /PPy Nanoarrays on Carbon Cloth for Solid-State Asymmetric Supercapacitors.

The design of complex heterostructured electrode materials that deliver superior electrochemical performances to their individual counterparts has stimulated intensive research on configuring supercapacitors with high energy and power densities. Herein we fabricate hierarchical tectorum-like α-Fe2 O3 /polypyrrole (PPy) nanoarrays (T-Fe2 O3 /PPy NAs). The 3D, and interconnected T-Fe2 O3 /PPy NAs are successfully grown on conductive carbon cloth through an easy self-sacrificing template and in situ vapor-phase polymerization route under mild conditions. The electrode made of the T-Fe2 O3 /PPy NAs exhibits a high areal capacitance of 382.4 mF cm-2 at a current density of 0.5 mA cm-2 and excellent reversibility. The solid-state asymmetric supercapacitor consisting of T-Fe2 O3 /PPy NAs and MnO2 electrodes achieves a high energy density of 0.22 mWh cm-3 at a power density of 165.6 mW cm-3 .

Mass Production and Pore Size Control of Holey Carbon Microcages.

Architectural control of porous solids, such as porous carbon cages, has received considerable attention for versatile applications because of their ability to interact with liquids and gases not only at the surface, but throughout the bulk. Herein we report a scalable, facile spray-pyrolysis route to synthesize holey carbon microcages with mosquito-net-like shells. Using the surfaces of water droplets as the growth templates, styrene-butadiene rubber macromolecules are controllably cross-linked, and size-controllable holes on the carbon shells are generated. The as-formed carbon microcages encapsulating Si nanoparticles exhibit enhanced lithium-storage performances for lithium-ion batteries. The scalable, inexpensive synthesis of porous carbon microcages with controlled porosity and the demonstration of outstanding electrochemical properties are expected to extend their uses in energy storage, molecular sieves, catalysis, adsorbents, water/air filters, and biomedical engineering.

Direct planting of ultrafine MoO2+δ nanoparticles in carbon nanofibers by electrospinning: self-supported mats as binder-free and long-life anodes for lithium-ion batteries.

Three-dimensional (3D) interconnected carbon nanofibrous mats containing well-dispersed MoO2+δ nanocrystals are fabricated through a facile electrospinning route followed by thermal treatment in N2. The resulting nanostructured monolithic hybrid mat made of C/MoO2+δ nanofibers exhibits superior Li-storage performances, when evaluated as a free-standing anode material. At a current density of 200 mA g(-1), a reversible capacity as high as 876.9 mA h g(-1) is achieved after 250 cycles. A capacity of 447.9 mA h g(-1) could still be maintained after 1000 cycles even at a high current density of 2000 mA g(-1), indicating high rate capability and cyclability. The attractive electrochemical performances of the as-obtained 3D C/MoO2+δ networks may benefit from the synergistic effects of the unique nanoarchitectures and the integrity of the electrodes. Monodispersed MoO2+δ nanocrystals encapsulated in carbon nanofibers not only provide interfacial storage but also improve the transport kinetics of electrons and lithium ions.

Nanostructured Mo-based electrode materials for electrochemical energy storage.

The development of advanced energy storage devices is at the forefront of research geared towards a sustainable future. Nanostructured materials are advantageous in offering huge surface to volume ratios, favorable transport features, and attractive physicochemical properties. They have been extensively explored in various fields of energy storage and conversion. This review is focused largely on the recent progress in nanostructured Mo-based electrode materials including molybdenum oxides (MoO(x), 2 ≤ x ≤ 3), dichalconides (MoX2, X = S, Se), and oxysalts for rechargeable lithium/sodium-ion batteries, Mg batteries, and supercapacitors. Mo-based compounds including MoO2, MoO3, MoO(3-y) (0 < y < 1), MMo(x)O(y) (M = Fe, Co, Ni, Ca, Mn, Zn, Mg, or Cd; x = 1, y = 4; x = 3, y = 8), MoS2, MoSe2, (MoO2)2P2O7, LiMoO2, Li2MoO3, etc. possess multiple valence states and exhibit rich chemistry. They are very attractive candidates for efficient electrochemical energy storage systems because of their unique physicochemical properties, such as conductivity, mechanical and thermal stability, and cyclability. In this review, we aim to provide a systematic summary of the synthesis, modification, and electrochemical performance of nanostructured Mo-based compounds, as well as their energy storage applications in lithium/sodium-ion batteries, Mg batteries, and pseudocapacitors. The relationship between nanoarchitectures and electrochemical performances as well as the related charge-storage mechanism is discussed. Moreover, remarks on the challenges and perspectives of Mo-containing compounds for further development in electrochemical energy storage applications are proposed. This review sheds light on the sustainable development of advanced rechargeable batteries and supercapacitors with nanostructured Mo-based electrode materials.

A Bamboo-Inspired Nanostructure Design for Flexible, Foldable, and Twistable Energy Storage Devices.

Flexible energy storage devices are critical components for emerging flexible electronics. Electrode design is key in the development of all-solid-state supercapacitors with superior electrochemical performances and mechanical durability. Herein, we propose a bamboo-like graphitic carbon nanofiber with a well-balanced macro-, meso-, and microporosity, enabling excellent mechanical flexibility, foldability, and electrochemical performances. Our design is inspired by the structure of bamboos, where a periodic distribution of interior holes along the length and graded pore structure at the cross section not only enhance their stability under different mechanical deformation conditions but also provide a high surface area accessible to the electrolyte and low ion-transport resistance. The prepared nanofiber network electrode recovers its initial state easily after 3-folded manipulation. The mechanically robust membrane is explored as a free-standing electrode for a flexible all-solid-state supercapacitor. Without the need for extra support, the volumetric energy and power densities based on the whole device are greatly improved compared to the state-of-the-art devices. Even under continuous dynamic operations of forceful bending (90°) and twisting (180°), the as-designed device still exhibits stable electrochemical performances with 100% capacitance retention. Such a unique supercapacitor holds great promise for high-performance flexible electronics.

Flexible and Binder-Free Electrodes of Sb/rGO and Na3V2(PO4)3/rGO Nanocomposites for Sodium-Ion Batteries.

Flexible power sources have shown great promise in next-generation bendable, implantable, and wearable electronic systems. Here, flexible and binder-free electrodes of Na3V2(PO4)3/reduced graphene oxide (NVP/rGO) and Sb/rGO nanocomposites for sodium-ion batteries are reported. The Sb/rGO and NVP/rGO paper electrodes with high flexibility and tailorability can be easily fabricated. Sb and NVP nanoparticles are embedded homogenously in the interconnected framework of rGO nanosheets, which provides structurally stable hosts for Na-ion intercalation and deintercalation. The NVP/rGO paper-like cathode delivers a reversible capacity of 113 mAh g(-1) at 100 mA g(-1) and high capacity retention of ≈96.6% after 120 cycles. The Sb/rGO paper-like anode gives a highly reversible capacity of 612 mAh g(-1) at 100 mA g(-1) , an excellent rate capacity up to 30 C, and a good cycle performance. Moreover, the sodium-ion full cell of NVP/rGO//Sb/rGO has been fabricated, delivering a highly reversible capacity of ≈400 mAh g(-1) at a current density of 100 mA g(-1) after 100 charge/discharge cycles. This work may provide promising electrode candidates for developing next-generation energy-storage devices with high capacity and long cycle life.

TiO2-B nanosheets/anatase nanocrystals co-anchored on nanoporous graphene: in situ reduction-hydrolysis synthesis and their superior rate performance as an anode material.

A unique hybrid, TiO2-B nanosheets/anatase nanocrystals co-anchored on nanoporous graphene sheets, can be synthesized by a facile microwave-induced in situ reduction-hydrolysis route. The as-formed nanohybrid has a hierarchically porous structure, involving both mesopores of approximately 4 nm and meso-/macropores of 30-60 nm in the graphene sheets, and a large surface area. Importantly, electrodes composed of the nanohybrid exhibit superior rate capability (160 mA h g(-1) at ca. 36 C; 154 mA h g(-1) at ca. 72 C) and excellent cyclability. The synergistic effects of conductive graphene with numerous nanopores and the pseudocapacitive effect of ultrafine TiO2-B nanosheets and anatase nanocrystals endow the hybrid a superior rate capability.

Microwave-Induced in†situ synthesis of Zn2GeO4/N-doped graphene nanocomposites and their lithium-storage properties.

Zn2GeO4/N-doped graphene nanocomposites have been synthesized through a fast microwave-assisted route on a large scale. The resulting nanohybrids are comprised of Zn2GeO4 nanorods that are well-embedded in N-doped graphene sheets by in situ reducing and doping. Importantly, the N-doped graphene sheets serve as elastic networks to disperse and electrically wire together the Zn2GeO4 nanorods, thereby effectively relieving the volume-expansion/contraction and aggregation of the nanoparticles during charge and discharge processes. We demonstrate that an electrode that is made of the as-formed Zn2GeO4/N-doped graphene nanocomposite exhibits high capacity (1463 mA h g(-1) at a current density of 100 mA g(-1)), good cyclability, and excellent rate capability (531 mA h g(-1) at a current density of 3200 mA g(-1)). Its superior lithium-storage performance could be related to a synergistic effect of the unique nanostructured hybrid, in which the Zn2GeO4 nanorods are well-stabilized by the high electronic conduction and flexibility of N-doped graphene sheets. This work offers an effective strategy for the fabrication of functionalized ternary-oxide-based composites as high-performance electrode materials that involve structural conversion and transformation.

Hollow 0.3Li2MnO3·0.7LiNi(0.5)Mn(0.5)O2 microspheres as a high-performance cathode material for lithium-ion batteries.

Hollow 0.3Li(2)MnO(3)·0.7LiNi(0.5)Mn(0.5)O(2) microspheres are synthesized on a large scale through a simple in situ template-sacrificial route. Starting from porous MnO(2) microspheres, the hollow microspheres assembled with 0.3Li(2)MnO(3)·0.7LiNi(0.5)Mn(0.5)O(2) nanocrystals are formed by a nanoscale Kirkendall effect. The nanocrystal-assembled hollow 0.3Li(2)MnO(3)·0.7LiNi(0.5)Mn(0.5)O(2) microspheres exhibit a highly reversible capacity as high as 295 mAh g(-1) over 100 cycles and excellent rate capability (125 mAh g(-1) at 1000 mA g(-1)). Benefitting from a unique hollow and nanocrystalline architecture, the as-formed hollow microspheres show much enhanced high-temperature (55 °C) electrochemical performances, compared with the products obtained by conventional sol-gel/solid-state reaction methods. This work demonstrates that a fabrication strategy based on the present in situ template-sacrificial approach offers a new method for the design of high-performance cathode materials with hollow interiors for Li-ion battery applications.

Electrospun sillenite Bi12MO20 (M = Ti, Ge, Si) nanofibers: general synthesis, band structure, and photocatalytic activity.

Sillenite Bi12MO20 (M = Ti, Ge, Si) nanofibers have been fabricated through a facile electrospinning route for photocatalytic applications. Uniform Bi12MO20 (M = Ti, Ge, Si) nanofibers with diameters of 100-200 nm and lengths of up to several millimeters can be readily obtained by thermally treating the electrospun precursors. The photocatalytic activities of these nanofibers for degradation of rhodamine B (RhB) were explored under UV-visible light. The band structure and the degradation mechanisms were also discussed. The fibrous photocatalysts of Bi12TiO20, Bi12SiO20 and Bi12GeO20 exhibit different photocatalytic behaviours, which are attributed to the microstructure, band gap, and electronic structures.

A Safer High-Energy Lithium-Ion Capacitor Using Fast-Charging and Stable ω-Li3 V2 O5 Anode.

Lithium-ion capacitors (LICs) are flourishing toward high energy density and high safety, which depend significantly on the performance of the intercalation-type anodes used in LICs. However, commercially available graphite and Li4 Ti5 O12 anodes in LICs suffer from inferior electrochemical performance and safety risks due to limited rate capability, energy density, thermal decomposition, and gassing issues. Here a safer high-energy LIC based on a fast-charging ω-Li3 V2 O5 (ω-LVO) anode with a stable bulk/interface structure is reported. The electrochemical performance, thermal safety, and gassing behavior of the ω-LVO-based LIC device are investigated, followed by the exploration of the stability of the ω-LVO anode. The ω-LVO anode exhibits fast lithium-ion transport kinetics at room/elevated temperatures. Paired with an active carbon (AC) cathode, the AC||ω-LVO LIC with high energy density and long-term endurability is achieved. The accelerating rate calorimetry, in situ gas assessment, and ultrasonic scanning imaging technologies further verify the high safety of the as-fabricated LIC device. Theoretical and experimental results unveil that the high safety originates from the high structure/interface stability of the ω-LVO anode. This work provides important insights into electrochemical/thermochemical behaviors of ω-LVO-based anodes within LICs and offers new opportunities to develop safer high-energy LIC devices.

High-Safety Lithium-Ion Batteries with Silicon-Based Anodes Enabled by Electrolyte Design.

High-energy-density lithium-ion batteries (LIBs) with high safety have long been pursued for extending the cruise range of electric vehicles. Owing to the high gravimetric capacity, silicon is a promising alternative to the convention graphite anode for high-energy LIBs. However, it suffers from intrinsic poor interfacial stability with liquid electrolytes, inevitably increasing the risk of thermal runaway and posing serious safety challenges. In this review, we will focus on mitigating thermal runaway of silicon anodes-based LIBs from the perspective of electrolyte design. First, the thermal runaway mechanism of LIBs is briefly introduced, while the specific thermal failure reactions associated with silicon anodes and electrolytes are discussed in detail. We then summarize the safety countermeasures (e. g., thermally stable solid electrolyte interphase, nonflammable electrolytes, highly stable lithium salts, mitigating electrode crosstalk, and solid-state electrolytes) enabled by customized electrolyte design to address these triggers of thermal runaway. Finally, the remaining unanswered questions regarding the thermal runaway mechanism are presented, and future directions to achieve intrinsically safe electrolytes for silicon-based anodes are prospected. This review is expected to provide insightful knowledge for improving the safety of LIBs with silicon-based anodes.

Ionogel-Based Membranes for Safe Lithium/Sodium Batteries.

Alkali (lithium, sodium)-based second batteries are considered one of the brightest candidates for energy-storage applications in order to utilize the random and intermittent renewable energy to achieve carbon neutrality. Conventional lithium/sodium batteries containing liquid organic electrolytes are vulnerable to electrolytes leakage and even combustion, which hinders their large-scale and reliable application. All-solid-state electrolytes which are considered to have better safety have been developed in recent years. However, most of them suffer from low ionic conductivity and large interfacial resistance with the electrode. Ionogel-electrolyte membranes composed of ionic liquids and solid matrices, have attracted much attention because of their nonvolatility, nonflammability, and superior chemical and electrochemical properties. This review focuses on the most recent advances of ionogel electrolytes that sprang up with the emerging demand and progress of safe lithium/sodium batteries. The ionogel-electrolyte membranes are discussed based on the framework components and preparation methods. Their structure and properties, including ionic conductivity, mechanical strength, electrochemical stabilities, and so on, are demonstrated in combination with their applications. The current challenges and insights on the future development of ionogel electrolytes for advanced safe lithium/sodium batteries are also proposed.

Interface Engineering to Boost Thermal Safety of Microsized Silicon Anodes in Lithium-Ion Batteries.

Battery safety is vital to the application of lithium-ion batteries (LIBs), especially for high energy density cells applied in electric vehicles. As an anode material with high theoretical capacity and natural abundance, Si has received extensive attention for LIBs. However, it suffers from severe electrode pulverization during cycling due to large volume changes and an unstable solid electrolyte interphase (SEI), resulting in accelerated capacity fading and even safety hazards. Therefore, safe and long-term cycling of Si-based anodes, especially under high-temperature cycling, is highly challenging for state-of-the-art high-energy LIBs. The thermal behavior of SEI is crucial for a high safety battery as the decomposition of SEI is the first step in thermal runaway. Here, highly reversible and thermotolerant microsized Si anodes for safe LIBs are demonstrated. Comprehensive electrochemical/mechanical/thermochemical behaviors of the SEI are systematically investigated. The rational design of robust SEI endows the Si-based cells with long-term durability at elevated temperatures and superior thermal safety. This work paves the way for designing industrial-scale, low-cost, microsized Si anodes with applications in next-generation LIBs with high energy densities and high safety.

Hybrid Ionogel Electrolytes for Advanced Lithium Secondary Batteries: Developments and Challenges.

Incidents in the use of lithium-ion batteries are usually caused by the malfunction of flammable organic liquid electrolytes with poor thermal stability. Therefore, the development of noncombustible electrolytes is regarded as one of the most effective means to prevent the safety hazards of lithium-ion batteries. Ionic liquids have attracted much interest recently, mainly due to their high ionic conductivity, low volatility, and incombustibility. The application of ionic liquids to the preparation of quasi-solid-state gel electrolytes combines the advantages of ionic liquids and avoids the risks of organic liquid electrolytes. Therefore, the solid-state ionogels have been considered as a promising alternative electrolyte system, especially for the much-desired energy storage devices with higher energy density and flexibility. This review focuses on the recent progress of ionogel electrolytes for lithium-ion batteries. The preparation strategies for ionogel electrolytes based on different frameworks, namely inorganic matrix, organic matrix, and organic-inorganic hybrid matrix, are discussed. Subsequently, efforts to improve the properties of the ionogel electrolytes, including the ionic conductivity, mechanical properties, and lithium-ion transfer number, are summarized. Besides, the applications of ionogel electrolytes in high-voltage lithium-ion batteries and lithium metal batteries as well as the batteries under extreme environments are outlined. Finally, the perspectives on studying and improving the performances of ionogel electrolytes for advanced lithium-ion batteries are provided.

Efficient removal of heavy metal ions from aqueous systems with the assembly of anisotropic layered double hydroxide nanocrystals@carbon nanosphere.

We report on the efficient removal of heavy metal ions from simulated wastewater with a nanostructured assembly. The nanoassembly was obtained via direct assembling the performed anisotropic layered double hydroxide nanocrystals (LDH-NCs) onto the surface of carbon nanospheres (labeled as LDH-NCs@CNs). It was found that the maximum adsorption capacity of the nanoassembly toward Cu(2+) was ∼ 19.93 mg g(-1) when the initial Cu(2+) concentration was 10.0 mg L(-1), displaying a high efficiency for the removal of heavy metal ions. The Freundlich adsorption isotherm was applicable to describe the removal processes. Kinetics of the Cu(2+) removal was found to follow pseudo-second-order rate equation. Furthermore, the as-prepared building unit of the assembly, including LDH-NCs, CNs, and the assembly, as well as Cu(2+)-adsorbed assembly, were carefully examined by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), nitrogen sorption measurements, and X-ray photoelectron spectroscopy (XPS). Based on the characterization results, a possible mechanism of Cu(2+) removal with the assembly of LDH-NCs@CNs was proposed. Comparison experiments show that the adsorption capacity of the resulting LDH-NCs@CNs assembly was much higher than its any building unit alone (CNs or LDH-NCs), exhibiting the deliberation of the assembly on water decontamination. This work provides a very efficient, fast and convenient approach for exploring promising nanoassembly materials for water treatment.