A hyperaccumulation pathway to three-dimensional hierarchical porous nanocomposites for highly robust high-power electrodes

Biomass-Derived Materials for Advanced Rechargeable Batteries

Biomass-derived materials generally exhibit uniform and highly-stable hierarchical porous structures that can hardly be achieved by conventional chemical synthesis and artificial design. When used as electrodes for rechargeable batteries, these structural and compositional advantages often endow the batteries with superior electrochemical performances. This review systematically introduces the innate merits of biomass-derived materials and their applications as the electrode for advanced rechargeable batteries, including lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, and metal-sulfur batteries. In addition, biomass-derived materials as catalyst supports for metal-air batteries, fuel cells, and redox-flow batteries are also included. The major challenges for specific batteries and the strategies for utilizing biomass-derived materials are detailly introduced. Finally, the future development of biomass-derived materials for advanced rechargeable batteries is prospected. This review aims to promote the development of biomass-derived materials in the field of energy storage and provides effective suggestions for building advanced rechargeable batteries.

New Emerging Fast Charging Microscale Electrode Materials

Fast charging lithium (Li)-ion batteries are intensively pursued for next-generation energy storage devices, whose electrochemical performance is largely determined by their constituent electrode materials. While nanosizing of electrode materials enhances high-rate capability in academic research, it presents practical limitations like volumetric packing density and high synthetic cost. As an alternative to nanosizing, microscale electrode materials cannot only effectively overcome the limitations of the nanosizing strategy but also satisfy the requirement of fast-charging batteries. Therefore, this review summarizes the new emerging microscale electrode materials for fast charging from the commercialization perspective. First, the fundamental theory of electronic/ionic motion in both individual active particles and the whole electrode is proposed. Then, based on these theories, the corresponding optimization strategies are summarized toward fast-charging microscale electrode materials. In addition, advanced functional design to tackle the mechanical degradation problems related to next generation high capacity alloy- and conversion-type electrode materials (Li, S, Si et al.) for achieving fast charging and stable cycling batteries. Finally, general conclusions and the future perspective on the potential research directions of microscale electrode materials are proposed. It is anticipated that this review will provide the basic guidelines for both fundamental research and practical applications of fast-charging batteries.

Analyzing synthesis routes for BaCuPO4: implications for hydrogen evolution and supercapattery performance

In recent years, energy storage and conversion tools have evolved significantly in response to rising energy demands. Owing to their large surface area, superior electric and chemical stabilities, and thermal conductivities, barium copper phosphate (BaCuPO4) materials are promising electrode materials for electrochemical energy storage systems. In this study, the synthesis of nanostructures (NSs) using hydrothermal and chemical precipitation methods and exploring the electrochemical characteristics of BaCuPO4 in asymmetric supercapacitors provides a comparative investigation. Systematic characterization shows that nanomaterials prepared by applying the hydrothermal method have a more crystalline and large surface area than chemical precipitation. In the three cell arrangements, the hydrothermally prepared BaCuPO4 NSs delivered a high specific capacity (764.4 C g-1) compared to the chemical precipitation route (660 C g-1). Additionally, the supercapattery associated with the two electrode assemblages delivers an optimum specific capacity of 77 C g-1. The energy and power density of BaCuPO4//AC NSs were 52.13 W h kg-1 and 950 W kg-1, respectively. A durability test was also performed with BaCuPO4//AC NSs for 5000 consecutive cycles. Further, the coulombic efficiency and capacity retention of BaCuPO4//AC after 5000 cycles were 81% and 92%, respectively. Bimetallic phosphate is comparatively suggested for future perspectives towards HER to overcome the performance of single metal phosphate materials. This is the first approach, we are aware of, for investigating the electrochemical behavior of BaCuPO4, and our results suggest that it may be useful as an electrode material in electrochemical systems requiring high energy and rate capabilities.

Cell-like-carbon-micro-spheres for robust potassium anode

Large-scale low-cost synthesis methods for potassium ion battery (PIB) anodes with long cycle life and high capacity have remained challenging. Here, inspired by the structure of a biological cell, biomimetic carbon cells (BCCs) were synthesized and used as PIB anodes. The protruding carbon nanotubes across the BCC wall mimicked the ion-transporting channels present in the cell membrane, and enhanced the rate performance of PIBs. In addition, the robust carbon shell of the BCC could protect its overall structure, and the open space inside the BCC could accommodate the volume changes caused by K+ insertion, which greatly improved the stability of PIBs. For the first time, a stable solid electrolyte interphase layer is formed on the surface of amorphous carbon. Collectively, the unique structural characteristics of the BCCs resulted in PIBs that showed a high reversible capacity (302 mAh g-1 at 100 mA g-1 and 248 mAh g-1 at 500 mA g-1), excellent cycle stability (reversible capacity of 226 mAh g-1 after 2100 cycles and a continuous running time of more than 15 months at a current density of 100 mA g-1), and an excellent rate performance (160 mAh g-1 at 1 A g-1). This study represents a new strategy for boosting battery performance, and could pave the way for the next generation of battery-powered applications.

3D Carbon Networks: Design and Applications in Sodium Ion Batteries

As the key component of a new generation for low-cost energy storage systems, sodium-ion batteries (SIBs) have attracted enormous attention and research due to its promising potentiality in large-scale electrochemical energy storage. For practical application of SIBs, carbonaceous materials have been considered to be one of the best choices for electrodes in virtue of their abundant reserves, low cost, easy availability, and environmental friendliness. 3D carbon network (3D-carbon) is of particular interests, which has displayed outstanding features, including abundant active sites, interconnected multi-level pore structures, high electronic conductivity, and excellent mechanical stability. Herein, we review the structural advantages of 3D-carbon and its preparation methods, and then discuss recent progress in 3D carbon materials and their composites for SIBs. The superior functionalities of 3D-carbon are emphasized as support templates or encapsulation shell membranes. Finally, we summarize and outline the challenges and future prospects of 3D-carbon in SIBs.

Low-Frequency Dielectric Relaxation in Structures Based on Macroporous Silicon with Meso-Macroporous Skin-Layer

The spectra of dielectric relaxation of macroporous silicon with a mesoporous skin layer in the frequency range 1-106 Hz during cooling (up to 293-173 K) and heating (293-333 K) are presented. Macroporous silicon (pore diameter ≈ 2.2-2.7 μm) with a meso-macroporous skin layer was obtained by the method of electrochemical anodic dissolution of monocrystalline silicon in a Unno-Imai cell. A mesoporous skin layer with a thickness of about 100-200 nm in the form of cone-shaped nanostructures with pore diameters near 13-25 nm and sizes of skeletal part about 35-40 nm by ion-electron microscopy was observed. The temperature dependence of the relaxation of the most probable relaxation time is characterized by two linear sections with different slope values; the change in the slope character is observed at T ≈ 250 K. The features of the distribution of relaxation times in meso-macroporous silicon at temperatures of 223, 273, and 293 K are revealed. The Havriliak-Negami approach was used for approximation of the relaxation curves ε″ = f(ν). The existence of a symmetric distribution of relaxers for all temperatures was found (Cole-Cole model). A discussion of results is provided, taking into account the structure of the studied object.

Hyperaccumulation Route to Ca-Rich Hard Carbon Materials with Cation Self-Incorporation and Interlayer Spacing Optimization for High-Performance Sodium-Ion Batteries

The hard carbon (HC) has been emerging as one of the most promising anode materials for sodium-ion batteries (SIBs). Incorporation of cations into the HC lattice proved to be effective to regulate their d-interlayer spacing with a modified SIB performance. However, the complexity and high cost of current synthetic processes limited its large-scale application in SIBs. Through the natural hyperaccumulation process, a cost-effective and scale-up-driven procedure to produce Ca-ion self-incorporated HC materials was proposed by applying tamarind fruits as the precursor with the enrichment of Ca ions. In virtue of one-step pyrolysis, the self-incorporated and well-distributed Ca ions in tamarind fruits had successfully served as the buffer layer to expand the d-interlayer spacing of HC materials. Furthermore, the natural porosity hierarchy could be largely preserved by the optimization of calcination temperature. As a result, the Ca-rich HC material had exhibited the optimized cycling performance (326.7 mA h g^-1 at 50 mA g^-1 and capacity retention rate of 89.40% after 250 cycles) with a high initial Coulombic efficiency of 70.39%. This work provided insight into applying the hyperaccumulation effect of biomass precursors to produce doped HC materials with ion self-incorporation and the optimized d-interlayer spacing, navigating its large-scale application for high-performance SIBs.

Bioinspired networks consisting of spongy carbon wrapped by graphene sheath for flexible transparent supercapacitors

Hierarchically ordered structures with low tortuosity, excellent mechanical flexibility, high optical transparency, and outstanding electrical conductivity are critically important in developing flexible transparent supercapacitor electrodes for innovative applications in electronics and displays. Here a CVD process is employed to fabricate leaf-skeleton inspired electrodes, which are reticulated monolithic networks consisting of carbon nanostructures serving as a 3D spongy core and graphene-based films as a protective/conductive shell. The network electrodes show optical transmittance of 85–88%, an electrical sheet resistance of ~1.8 Ω/sq, and an areal capacitance of 7.06 mF cm−2 (at 0.78 mA cm−2 in a three-electrode cell) in Na2SO4 aqueous electrolyte. Flexible transparent and symmetric supercapacitors, based on PVA/H3PO4 gel and the network electrodes, possess a stable working voltage of 1.6 V, energy and power density of 0.068 μWh cm−2 and 47.08 μW cm−2 at an optical transparency of ~80%, and no capacitance loss over 30,000 flat-bend-release cycles.

Ultra-high Areal Capacity Realized in Three-Dimensional Holey Graphene/SnO2 Composite Anodes

Nanostructured alloy-type electrode materials and its composites have shown extraordinary promise for lithium-ion batteries (LIBs) with exceptional gravimetric capacity. However, studies to date are usually limited to laboratory cells with too low mass loading (and thus too low areal capacity) to exert significant practical impact. Herein, by impregnating micrometer-sized SnO₂/graphene composites into 3D holey graphene frameworks (HGF), we show that a well-designed 3D-HGF/SnO₂ composite anode with a high mass loading of 12 mg cm⁻² can deliver an ultra-high areal capacity up to 14.5 mAh cm⁻² under current density of 0.2 mA cm⁻² and stable areal capacity of 9.5 mAh cm⁻² under current density of 2.4 mA cm⁻², considerably outperforming those in the state-of-art research devices or commercial devices. This robust realization of high areal capacity defines a critical step to capturing the full potential of high-capacity alloy-type electrode materials in practical LIBs.

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3D holey graphene framework/SnO₂ composite electrode was designed and prepared

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Micrometer-sized SnO₂/graphene was impregnated into 3D holey graphene frameworks

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The 3D composite anode can deliver an ultra-high areal capacity up to 14.5 mAh cm⁻²

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This study defines a critical step in exploring the alloy-type electrode for LIBs

Hydrangea-Shaped 3D Hierarchical Porous Magnesium Hydride-Carbon Framework with High Rate Performance for Lithium Storage

Magnesium hydride (MgH₂) is a promising anode material for lithium-ion batteries (LIBs) by virtue of its high theoretical specific capacity, suitable potential, and abundant source. However, the electrochemical performance of the MgH₂ electrode is still far from satisfactory due to its poor electronic conductivity and fast capacity decay. In this paper, a hydrangea-shaped three-dimensional (3D) hierarchical magnesium hydride-carbon framework (MH@HyC) comprising MgH₂ nanoparticles (NPs) uniformly self-assembled on hierarchical porous carbon (HyC) is fabricated for advanced lithium storage. Featuring high surface area and a well-defined macro-meso-micropore structure, HyC plays an ideal structure-directing role for the growth of MgH₂ NPs with size control, high loading, and a hydrangea-shape array. Taking advantage of the robust 3D hierarchical porous structure and the derived interactions, MH@HyC not only provides sufficient electrochemically active sites and enhances the electronic conductivity and channels for rapid transfer of electrons/Li ions but also relieves the agglomeration and accommodates the volumetric effects during cycling, leading to high capacity utilization, fast electrochemical kinetics, and well-sustained structural integrity. As a result, MH@HyC delivers a high reversible capacity of 554 mAh g^-1 after 1000 cycles at a high current rate of 2 A g^-1, enabling it a potential anode candidate for LIBs.

Bacteria-Derived Biological Carbon Building Robust Li-S Batteries

Lithium sulfur (Li-S) batteries are attracting increasing interest for high-density energy storage. However, the practical application is limited by the rapid capacity fading over repeated charge/discharge cycles which is largely attributed to the formation and shuttling of soluble polysulfide species. To address these issues, we develop a hierarchical structure composite with triple protection strategy via graphene, organic conductor PEDOT, and nitrogen and phosphorus codoped biological carbon to encapsulate sulfur species (GOC@NPBCS). This unique hierarchical structure can effectively immobilize the sulfur species while at the same time improve the electrical conductivity and ensure efficient lithium ion transport to enable excellent Li-S battery performance. In particular, the biological carbon derived from natural bacteria features inherent nitrogen and phosphorus codoping with a strong absorption to lithium polysulfides, which can greatly suppress the dissolution and shuttling of polysulfides that are responsible for rapid capacity fading. With these synergistic effects, the GOC@NPBCS cathode exhibits exceptionally stable cycling stability (an ultralow capacity fading rate of 0.045% per cycle during 1000 cycles at the current rate of 5 C), high specific capacity (1193.8 mAh g^-1 at 0.5 C based on sulfur weight), and excellent rate capability.

Fungi-Enabled Synthesis of Ultrahigh-Surface-Area Porous Carbon

The growth of white-rot fungi is related to the superior infiltrability and biodegradability of hyphae on a lignocellulosic substrate. The superior biodegradability of fungi toward plant substrates affords tailored microstructures, which benefits subsequently high efficient carbonization and chemical activation. Here, the mechanism underlying the direct growth of mushrooms toward the lignocellulosic substrate is elucidated and a fungi-enabled method for the preparation of porous carbons with ultrahigh specific surface area (3439 m² g^-1 ) is developed. Such porous carbons could have potential applications in energy storage, environment treatment, and electrocatalysis. The present study reveals a novel pore formation mechanism in root-colonizing fungi and anticipates a valuable function for fungi in developing the useful porous carbons with a high specific surface area.

Facile and scalable preparation of 3D SnO2/holey graphene composite frameworks for stable lithium storage at a high mass loading level

A binder-free 3D SnO₂/holey graphene composite framework electrode with high mass loading shows superior Li⁺ storage performance.

Nanohybrid structured RuO2/Mn2O3/CNF as a catalyst for Na-O2 batteries

A 3D RuO₂/Mn₂O₃/carbon nanofiber (CNF) composite has been prepared in this study by a facile two step microwave synthesis, as a bi-functional electrocatalyst towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). RuO₂ nanoparticles with the mean size of 1.57 nm are uniformly distributed on Mn₂O₃ nano-rods grown on electrospun CNFs. The electrocatalytic activity of the composites are investigated towards ORR/OER under alkaline condition. The ternary RuO₂/Mn₂O₃/CNF composite showed superior ORR activity in terms of onset potential (0.95 V versus RHE) and Tafel slope (121 mV dec^-1) compared to its RuO₂/CNF and Mn₂O₃/CNF counterparts. In the case of OER, the RuO₂/Mn₂O₃/CNF exhibited 0.34 V over-potential value measured at 10 mA cm^-2 and 52 mV dec^-1 Tafel slope which are lower than those of the other synthesized samples and as compared to state of the art RuO₂ and IrO _x type materials. RuO₂/Mn₂O₃/CNF also exhibited higher specific capacity (9352 mAh [Formula: see text]) than CNF (1395 mAh [Formula: see text]), Mn₂O₃/CNF (3108 mAh [Formula: see text]) and RuO₂/CNF (4859 mAh g _carbon ^-1) as the cathode material in Na-O₂ battery, which indicates the validity of the results in non-aqueous medium. Taking the benefit of RuO₂ and Mn₂O₃ synergistic effect, the decomposition of inevitable side products at the end of charge occurs at 3.838 V versus Na/Na⁺ by using RuO₂/Mn₂O₃/CNF, which is 388 mV more cathodic compared with CNF.

N-Doped Dual Carbon-Confined 3D Architecture rGO/Fe3O4/AC Nanocomposite for High-Performance Lithium-Ion Batteries

To address the issues of low electrical conductivity, sluggish lithiation kinetics and dramatic volume variation in Fe₃O₄ anodes of lithium ion battery, herein, a double carbon-confined three-dimensional (3D) nanocomposite architecture was synthesized by an electrostatically assisted self-assembly strategy. In the constructed architecture, the ultrafine Fe₃O₄ subunits (∼10 nm) self-organize to form nanospheres (NSs) that are fully coated by amorphous carbon (AC), formatting core-shell structural Fe₃O₄/AC NSs. By further encapsulation by reduced graphene oxide (rGO) layers, a constructed 3D architecture was built as dual carbon-confined rGO/Fe₃O₄/AC. Such structure restrains the adverse reaction of the electrolyte, improves the electronic conductivity and buffers the mechanical stress of the entire electrode, thus performing excellent long-term cycling stability (99.4% capacity retention after 465 cycles relevant to the second cycle at 5 A g^-1). Kinetic analysis reveals that a dual lithium storage mechanism including a diffusion reaction mechanism and a surface capacitive behavior mechanism coexists in the composites. Consequently, the resulting rGO/Fe₃O₄/AC nanocomposite delivers a high reversible capacity (835.8 mA h g^-1 for 300 cycles at 1 A g^-1), as well as remarkable rate capability (436.7 mA h g^-1 at 10 A g^-1).

Scalable 2D Hierarchical Porous Carbon Nanosheets for Flexible Supercapacitors with Ultrahigh Energy Density

2D carbon nanomaterials such as graphene and its derivatives, have gained tremendous research interests in energy storage because of their high capacitance and chemical stability. However, scalable synthesis of ultrathin carbon nanosheets with well-defined pore architectures remains a great challenge. Herein, the first synthesis of 2D hierarchical porous carbon nanosheets (2D-HPCs) with rich nitrogen dopants is reported, which is prepared with high scalability through a rapid polymerization of a nitrogen-containing thermoset and a subsequent one-step pyrolysis and activation into 2D porous nanosheets. 2D-HPCs, which are typically 1.5 nm thick and 1-3 µm wide, show a high surface area (2406 m² g^-1 ) and with hierarchical micro-, meso-, and macropores. This 2D and hierarchical porous structure leads to robust flexibility and good energy-storage capability, being 139 Wh kg^-1 for a symmetric supercapacitor. Flexible supercapacitor devices fabricated by these 2D-HPCs also present an ultrahigh volumetric energy density of 8.4 mWh cm^-3 at a power density of 24.9 mW cm^-3 , which is retained at 80% even when the power density is increased by 20-fold. The devices show very high electrochemical life (96% retention after 10000 charge/discharge cycles) and excellent mechanical flexibility.

Hierarchically Nanostructured Transition Metal Oxides for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been widely used in the field of portable electric devices because of their high energy density and long cycling life. To further improve the performance of LIBs, it is of great importance to develop new electrode materials. Various transition metal oxides (TMOs) have been extensively investigated as electrode materials for LIBs. According to the reaction mechanism, there are mainly two kinds of TMOs, one is based on conversion reaction and the other is based on intercalation/deintercalation reaction. Recently, hierarchically nanostructured TMOs have become a hot research area in the field of LIBs. Hierarchical architecture can provide numerous accessible electroactive sites for redox reactions, shorten the diffusion distance of Li-ion during the reaction, and accommodate volume expansion during cycling. With rapid research progress in this field, a timely account of this advanced technology is highly necessary. Here, the research progress on the synthesis methods, morphological characteristics, and electrochemical performances of hierarchically nanostructured TMOs for LIBs is summarized and discussed. Some relevant prospects are also proposed.

Energy storage mechanism in aqueous fiber-shaped Li-ion capacitors based on aligned hydrogenated-Li4Ti5O12 nanowires

It is reported that Li ions can contribute a lot to the capacitance of aqueous Li-ion capacitors (LICs), which might be due to the intercalation/de-intercalation processes of Li⁺ ions that also occur at the anodes. However the energy storage mechanism in the aqueous LIC system still requires further proof. In this work, a type of aqueous fiber-shaped LIC has been designed and developed using hydrogenated Li₄Ti₅O₁₂ (H-LTO) anodes, active carbon (AC) cathodes, and LiCl/PVA gel electrolytes with a double-helical structure. The obtained single LTO wire electrode exhibits a high specific capacitance in volume (34.1 F cm^-3) and superior cycling stabilities (∼100% over 100 000 cycles), both of which are due to the formed amorphous layers at the surface of the electrodes. Moreover, it is found via sweep voltammetry analysis that most of the energy stored in an aqueous fiber-shaped capacitor electrode is attributed to the Li ions' intercalation, whose content exceeds 85% at a low scan rate and gradually decreases with increasing scan rate; while the energy stored by the double electric layers remains almost unchanged with different scan rates. Furthermore, the well-matched wearable fiber-shaped LICs show high capacitive behaviors (18.44 μW h cm^-2) and superior static/dynamic cycling stabilities. This research would provide some insight into the charge storage mechanism in electrodes in the aqueous system, and give more suggestions to develop high-energy-density fiber-shaped energy storage devices.