Nitrogen self-doped carbon with super high-rate and long cycle life as anode materials for lithium-ion batteries

Nitrogen self-doped carbon was synthesized by hydrothermal and microwave calcination using polyacrylonitrile as a carbon source and nitrogen source. This method dramatically reduces the material preparation time while improving the electrochemical performance of amorphous carbon. X-ray photoelectron spectroscopy (XPS) analyses reveal that the pyridine nitrogen content is increased and the graphitized nitrogen disappeared in an amorphous carbon block. This indicates that the nitrogen doping sites of the amorphous carbon block can be modulated by the hydrothermal method. Microscopic observations show that the nitrogen self-doped carbon is nano-carbon spheres and carbon micron block. The self-doped nitrogen micron carbon block exhibits excellent cyclability and ultra-high rate capacity. When cycled at 0.5 A g⁻¹, the discharge capacity remains 356.6 mA h g⁻¹ after 1000 cycles. Even cycled at 5 A g⁻¹, the rate capacity was maintained at 183.3 mA h g⁻¹ after 300 cycles. The defects produced by self-doped pyridine nitrogen, not only improved the reactivity and electronic conductivity but also enhanced lithium-ion diffusion kinetics.

Nitrogen doping sites can be modulated by the hydrothermal method. The defects produced by self-doped pyridine nitrogen, not only improved the reactivity and electronic conductivity but also enhanced lithium-ion diffusion kinetics.     

From grass to battery anode: agricultural biomass hemp-derived carbon for lithium storage

Biomass-derived carbon, as a low-cost material source, is an attractive choice to prepare carbon materials, thus providing an alternative to by-product and waste management. Herein, we report the preparation of carbon from hemp stem as a biomass precursor through a simple, low-cost, and environment-friendly method with using steam as the activating agent. The hemp-derived carbon with a hierarchically porous structure and a partial graphitization in amorphous domains was developed, and for the first time, it was applied as an anode material for lithium-ion battery. Natural hemp itself delivers a reversible capacity of 190 mA h g⁻¹ at a rate of 300 mA g⁻¹ after 100 cycles. Ball-milling of hemp-derived carbon is further designed to control the physical properties, and consequently, the capacity of milled hemp increases to 300 mA h g⁻¹ along with excellent rate capability of 210 mA h g⁻¹ even at 1.5 A g⁻¹. The milled hemp with increased graphitization and well-developed meso-porosity is advantageous for lithium diffusion, thus enhancing electrochemical performance via both diffusion-controlled intercalation/deintercalation and surface-limited adsorption/desorption. This study not only demonstrates the application of hemp-derived carbon in energy storage devices, but also guides a desirable structural design for lithium storage and transport.

Hemp-derived carbon was prepared by physical activation using only steam, and directly applied as an electrode for lithium storage.     

Investigation of Cu doped flake-NiO as an anode material for lithium ion batteries

Cu foil is widely used in commercial lithium ion batteries as the current collector of anode materials with excellent conductivity and stability. In this research, commercial Cu foil was chosen as the current collector and substrate for the synthesis of Cu doped flake-NiO via a traditional hydrothermal method. The effect of the ratio of Cu and the calcination temperature on the electrochemical performance of NiO was investigated. The structure and phase composition of the Cu doped flake-NiO electrode were studied through X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and inductive coupled plasma emission spectrometry (ICP). The electrochemical properties of the Cu doped flake-NiO electrode were studied through cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and a galvanostatic charge–discharge cycling technique. According to the results, the Cu-doped NiO electrode, calcined at 400 °C with a molar ratio of Cu : Ni = 1 : 8, exhibited a high reversible charge capacity. The good cycling stability and rate performance indicate that the as-prepared electrode can be applied as a potential anode for lithium ion batteries.

Cu doped flake-NiO shows excellent electrochemical performance as anode materials for lithium ion batteries.     

Flexible C–Mo2C fiber film with self-fused junctions as a long cyclability anode material for sodium-ion battery

Electrospun carbon fiber films have high contact resistance at the fiber junctions, which causes poor cycling stability and limits their further improvement in energy storage performances. To eliminate the contact resistance of the film, we provide a new strategy to fuse the fiber junctions by introducing MoO₂ in the fibers, which replaces the C–C interface by a more active C–MoO₂–C interface at the fiber junction to promote mass transfer. MoO₂ reacts with C matrix to generate Mo₂C and form self-fused junctions during the carbonization process. Due to much lower charge transfer and sodium diffusion resistance, the C–Mo₂C fiber film with self-fused junctions shows much better cyclability with capacity retention of 90% after 2000 cycles at a constant current density of 1 A g⁻¹. Moreover, the Mo₂C particles provide many electrochemically active sites, leading to additional improvement in sodium storage. The C–Mo₂C fiber film has a capacity of 134 mA h g⁻¹ at 1 A g⁻¹ and a high capacity of 99 mA h g⁻¹ even at 5 A g⁻¹.

Fiber junctions were fused by introducing MoO₂, that eliminates the contact resistance at fiber junctions, and significantly improves the cyclability.     

Study on low-temperature cycle failure mechanism of a ternary lithium ion battery

This study is focused on the changes in parameters such as discharge capacity, and the possible failure mechanism of a 25 Ah ternary lithium ion battery during cycling at −10 °C. A new battery and a battery after 500 cycles were disassembled. The morphology and structure of the cathode and anode electrodes were characterized. Transmission electron microscopy (TEM) and X-ray photoelectron absorption spectroscopy (XPS) were used to analyze the changes in the microstructure and chemical environment of the anode electrode interface. The results show that after 500 cycles at −10 °C, the capacity of the battery is only 18.3 Ah, and there is a large irreversible capacity loss. The battery samples after low-temperature cycling produced gas during storage at 25 °C. It is found that a large amount of lithium plating on the anode surface is an important factor for the reduction in battery capacity. The dissolution of transition metal elements in the cathode electrode and deposition on the anode electrode, and the catalytic decomposition of electrolyte at the anode interface are the main reasons for the gassing of the battery.

The failure of low-temperature performance of ternary lithium-ion battery is the result of side reactions such as lithium deposition, positive material transition metal ion dissolution and electrolyte decomposition.     

Crystal-seeds induced construction of ZnO–ZnFe2O4 micro-cubic composites as excellent anode materials for lithium ion battery

This work aims at designing a fine assembly of two different transition metal oxides with a distinct band-gap energy into a bi-component-active hetero-structure to enhance the hetero-interface interactions and synergetic functionalities of bi-components to improve electrochemical performance. Herein, a facile marriage of crystal-seeds induction and hydrothermal reactions has been utilized to fabricate ZnO–ZnFe₂O₄ micro-cubic composites. Benefiting from the synergetic effects of the bi-functional components and their unique hetero-junction structure, the ZnO–ZnFe₂O₄ micro-cubic composites exhibit a significant improvement in lithium storage performance. The reversible capacity is retained at a value of 811 mA h g⁻¹ after 200 cycles at a current density of 100 mA g⁻¹. Even at high current densities of 1 and 5 A g⁻¹, the electrodes are still able to deliver capacities of 584 and 430 mA h g⁻¹ after 200 cycles, respectively.

This work aims at designing a fine assembly of two different transition metal oxides with a distinct band-gap energy into a bi-component-active hetero-structure to improve electrochemical performance.     

Electrochemical characteristics of amorphous silicon carbide film as a lithium-ion battery anode

The electrochemical reactions of SiC film with Li⁺ have been investigated by electrochemical characterization and X-ray photoelectron spectroscopy. The SiC film is prepared by inductively-coupled-plasma chemical-vapor-deposition (ICP-CVD) technique and displays an amorphous state due to the low processing temperature (∼350 °C). An irreversible reaction of SiC with Li⁺ occurs with the formation of lithium silicon carbide (Li_xSi_yC) and elemental Si, followed by a reversible alloying/dealloying reaction of the elemental Si with Li⁺. The 500 nm SiC film shows an initial reversible specific capacity of 917 mA h g⁻¹ with a capacity retention of 41.0% after 100 cycles at 0.3C charge/discharge current, and displays much better capacity retention than the Si film (5.2%). It is found that decreasing the SiC thickness effectively improves the specific capacity by enhancing the reaction kinetics but also degrades the capacity retention (for 250 nm SiC, its initial capacity is 1427 mA h g⁻¹ with a capacity retention of 25.7% after 100 cycles). The better capacity retention of the 500 nm SiC anode is mainly because residual SiC exists in the film due to its incomplete reaction caused by its lower reaction kinetics, and it has high hardness and can act as a buffer matrix to alleviate the anode volume change, thus improving the mechanical stability and capacity retention of the SiC anode.

The electrochemical reactions of SiC film with Li⁺ have been investigated by electrochemical characterization and X-ray photoelectron spectroscopy.     

Graphitic carbon-wrapped NiO embedded three dimensional nitrogen doped aligned carbon nanotube arrays with long cycle life for lithium ion batteries

In this work, a three-dimensional nitrogen doped aligned carbon nanotube array (NACNTs)@NiO@graphitic carbon composite was fabricated by an effective strategy involving nebulized ethanol assisted infiltration, In this structure, the NiO nanoparticles were wrapped by graphitic carbon layers and NiO@graphitic carbon core–shell nanoparticles adhered strictly to the surface of NACNTs to form a highly ordered 3D structure. When this composite was used as an anode for lithium ion batteries, the well-ordered pore of its NACNTs can facilitate the electrolyte to penetrate and improve electronic conductivity. At the same time, the graphitic layers can promote the stability of a solid electrolyte interface film. Therefore, the NACNTs@NiO@graphitic carbon composite containing 68.1 wt% NiO delivers excellent capacity retention of 91.6% after 200 cycles at 0.2C.

NACNTs@NiO@graphitic carbon composites were synthesized with the help of nebulizing. The outstanding performances are attributed to the original structure of NACNTs@NiO@graphitic carbon.     

Facile synthesis of a high electrical and ion conductivity junction-less 3D carbon sponge electrode for self-standing lithium ion battery anode

Lithium ion batteries (LIB) are the most extensively researched and developed batteries. Currently, LIBs are used in various applications such as electric vehicles (EV), hybrid EVs (HEV), plug-in HEVs, and energy storage systems. However, their energy density is insufficient and further improvement is required. In this study, we propose the facile synthesis of a self-standing, junction-less 3D carbon sponge electrode (3DCS) for improving the energy density. A self-standing structure can improve the energy density by reducing non-active materials such as binders and current collectors, in electrodes. We use a kitchenware melamine sponge as the carbon precursor. The utilization of materials mass-produced by existing facilities is crucial for ensuring availability and low costs. Such characteristics are imperative for industrialization. These self-standing 3DCS electrodes, fabricated using available low-cost melamine sponges, demonstrate high charge-rate characteristics with a capacity retention of 81.8% at 4000 mA g⁻¹ and cycle durability with 95.4% capacity retention after 500 cycles, without current collector, binder, and conductive additives. This high availability, low-cost material with excellent characteristics is beneficial for research institutions and companies that do not have facilities.

Conceptual diagram of junction-less 3D carbon sponge electrode.     

UIO-66-NH2-derived mesoporous carbon used as a high-performance anode for the potassium-ion battery

As potassium is abundant and has an electronic potential similar to lithium''s, potassium-ion batteries (KIBs) are considered as prospective alternatives to lithium-ion batteries (LIBs). However, the much larger radius of the K ion poses challenges for the potassiation and depotassiation processes when the typical graphite-based anode is used, resulting in poor electrochemical performance. Thus, there is an urgent need to develop novel anode materials that are suitable for K ions. Herein, we develop a porous carbon material with high surface area derived from UIO-66-NH₂ metal–organic frameworks as an anode material instead of a graphite-based anode. The material is prepared using a double-solvent diffusion-pyrolysis method, which increased mesopore volume and average pore size, and to a certain extent, slightly improved the nitrogen content of the production. The material exhibits a high capacity as well as excellent rate performance and cycling stability. A potassium battery with our porous carbon as the anode delivers a high reversible capacity of 346 mA h g⁻¹ at 100 mA g⁻¹ (compared to 279 mA h g⁻¹ with a graphite-based anode), and 214 mA h g⁻¹ at a discharge rate of up to 2 A g⁻¹. After 800 cycles, the capacity is still 187 mA h g⁻¹ at 0.1 A g⁻¹. Qualitative and quantitative kinetics analyses demonstrated that the battery''s high K storage performance was principally dominated by a surface-driven capacitive mechanism, and the potassiation and depotassiation processes may have occurred on the surface of the porous carbon instead of in the interlayer space, as is the case with a graphite anode. This work may provide a basis for developing other carbonaceous materials to use in KIBs.

The N-doped mesoporous carbon material prepared by a double-solvent diffusion pyrolysis method with UIO-66-NH₂ as a precursor can deliver a high reversible capacity of 346 mA h g⁻¹ at 100 mA g⁻¹ when used as an anode for non-aqueous KIBs.     

Application of soot discharged from the combustion of marine gas oil as an anode material for lithium ion batteries

Many studies have recently investigated the characteristics of combustion products emitted from ships and onshore plant facilities for use as energy sources. Most combustion products that have been reported until now are from heavy oils, however, no studies on those from light oils have been published. This study attempted to use the combustion products from the light oils from naval ships as anode materials for lithium ion batteries (LIBs). These products have a carbon black morphology and were transformed into highly crystalline carbon structures through a simple heat treatment. These new structured materials showed reversible capacities of 544, 538, 510, 485, 451 and 395 mA h g⁻¹ at C-rates of 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0C, respectively, and excellent rate performance. These findings were the result of a combination hierarchical pores ranging from the meso- to macroscale and the high capacitive charge storage behavior of the soot. The results of this study prove that annealed soot with a unique multilayer graphite structure shows promising electrochemical performance suitable for the production of low-cost, high-performance LIB anode materials.

Many studies have recently investigated the characteristics of combustion products emitted from ships and onshore plant facilities for use as energy sources.     

Amorphous red phosphorus incorporated with pyrolyzed bacterial cellulose as a free-standing anode for high-performance lithium ion batteries

Amorphous red phosphorus/pyrolyzed bacterial cellulose (P-PBC) free-standing films are prepared by thermal carbonization and a subsequent vaporization-condensation process. The distinctive bundle-like structure of the flexible pyrolyzed bacterial cellulose (PBC) matrix not only provides sufficient volume to accommodate amorphous red-phosphorus (P) but also restricts the pulverization of red-P during the alternate lithiation/delithiation process. When the mass ratio of raw materials, red-P to PBC, is 70 : 1, the free-standing P-PBC film anode exhibits high reversible capacity based on the mass of the P-PBC film (1039.7 mA h g⁻¹ after 100 cycle at 0.1C, 1C = 2600 mA g⁻¹) and good cycling stability at high current density (capacity retention of 82.84% after 1000 cycles at 2C), indicating its superior electrochemical performances.

A novel freestanding anode was prepared by combining amorphous red-P with a pyrolyzed bacterial cellulose (PBC) matrix for the first time.     

In situ fabrication of a graphene-coated three-dimensional nickel oxide anode for high-capacity lithium-ion batteries

The high theoretical specific capacity of nickel oxide (NiO) makes it attractive as a high-efficiency electrode material for electrochemical energy storage. However, its application is limited due to its inferior electrochemical performance and complicated electrode fabrication process. Here, we developed an in situ fabrication of a graphene-coated, three-dimensional (3D) NiO–Ni structure by simple chemical vapor deposition (CVD). We synthesized NiO layers on Ni foam through a thermal oxidation process; subsequently, we grew graphene layers directly on the surface of NiO after a hydrogen-assisted reduction process. The uniform graphene coating renders high electrical conductivity, structural flexibility and high elastic modulus at atomic thickness. The graphene-coated 3D NiO–Ni structure delivered a high areal density of ∼23 mg cm⁻². It also exhibits a high areal capacity of 1.2 mA h cm⁻² at 0.1 mA cm⁻² for its Li-ion battery performance. The high capacity is attributed to the high surface area of the 3D structure and the unique properties of the graphene layers on the NiO anode. Since the entire process is carried out in one CVD system, the fabrication of such a graphene-coated 3D NiO–Ni anode is simple and scalable for practical applications.

The processing of graphene coated NiO–Ni anode using one CVD system delivered high Li-ion battery performance.     

Electroless plating of a Sn–Ni/graphite sheet composite with improved cyclability as an anode material for lithium ion batteries

A Sn–Ni/graphite sheet composite is synthesized by a simple electroless plating method as an anode material for lithium ion batteries (LIBs). The microstructure and electrochemical properties of the composite are characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), and AC impedance spectroscopy. The results show that the as-prepared composite has Sn–Ni nanoparticles around 100 nm in size, where metallic Ni acts as an “anchor” to fix metallic Sn. The reunion phenomenon of Sn is alleviated by adding metallic Ni between the metallic Sn and graphite sheets. The Sn–Ni/graphite sheet electrode exhibits a good rate performance with a capability of 637.4, 586.3, 466.7, 371.5, 273.6, 165.3 and 97.3 mA h g⁻¹ at a current density of 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 and 10 A g⁻¹, respectively. The good electrical conductivity of Ni, high specific capacity of Sn and excellent cycling capability of the graphite sheets have a synergistic effect and are the main reasons behind the superior electrochemical performance. Furthermore, the as-prepared composite exhibits excellent lithium storage capacity and the reversible capacity increased as the cycle number increased.

A Sn–Ni/graphite sheet composite is synthesized by a simple electroless plating method as an anode material for lithium ion batteries (LIBs).     

A bidirectional growth mechanism for a stable lithium anode by a platinum nanolayer sputtered on a polypropylene separator

The issue of uncontrollable Li dendrite growth, caused by irregular lithium deposition, restricts the wide applications of Li metal based high energy batteries. In this paper, a polypropylene separator with a sputtered platinum nanolayer has been developed to improve the stability of the Li metal anodes. It was found that cells using the modified separators resulted in a smooth Li surface and a stable “electrode–electrolyte” interface. On the one hand, platinum nanolayers can enhance the mechanical properties and micro-structures of commercial polypropylene separators. On the other hand, platinum nanolayers provide stable Li deposition during repeated charging/discharging by a bidirectional growth mechanism. After long-time cycling, the dendrites from opposite directions and dead Li are integrated into a flat and dense new-formed Li anode, decreasing the risk of low Coulombic efficiency and cycling instability that may end in cell failure. This design may provide new ideas in next-generation energy storage systems for advanced stable metallic battery technologies.

Stable Li nucleation and deposition were achieved by applying a platinum-modified-separator with a bidirectional lithium growth mechanism.     

Glucose hydrothermal encapsulation of carbonized silicone polyester to prepare anode materials for lithium batteries with improved cycle stability

A silicon polyester (Si-PET) was synthesized with ethylene glycol and phthalic anhydride, and then it was carbonized and hydrothermally coated with glucose. The formed SiO_x with layered graphene as the 3D network had an amorphous carbon layer. The graphene oxide (rGO) after carbothermal reduction was completely retained in SiO_x, which improved the conductivity of the SiO_x anode material. SiO_x were encapsulated with a flexible amorphous carbon layer on the surface, which can not only improve the electrical performance, but also effectively relieve the huge volume changes of the compound. Further, the key point is that, the solid electrolyte interphase (SEI) film was mainly formed on the surface carbon layer. This would keep a stable SEI film during volume pulverization, and result in a good cycle stability. The SiO_x/C-rGO material maintained a reversible capacity of 660 mA h g⁻¹ at a current density of 100 mA g⁻¹ for 100 cycles, a reversible capacity of 469.7 mA h g⁻¹ at a current density of 200 mA g⁻¹ for 300 cycles. The Coulomb efficiency was maintained at 98% except for the first cycle. After long cycling, the electrode expansion was 16%, which was much lower than those of silicon based materials. Therefore, this article provides a cheap, simple, and commercially valuable anode material for lithium batteries.

Silicon polyester (Si-PET) was synthesized with ethylene glycol and phthalic anhydride, and then it was carbonized and hydrothermally coated with glucose. The forming SiO_x with layered graphene as the 3D network had amorphous carbon layer.     

A first-principles study on Si24 as an anode material for rechargeable batteries

Due to its intriguing geometry, possessing an open-channel structure, Si₂₄ demonstrates potential for storing and/or transporting Li/Na ions in rechargeable batteries. In this work, first-principles calculations were employed to investigate the phase stability and Li/Na storage and transport properties of the Si₂₄ anode to evaluate its electrochemical performance for batteries. The intercalation of Li and Na into the Si₂₄ structure could deliver a capacity of 159 mA h g⁻¹ (Li₄Si₂₄ and Na₄Si₂₄), and the average intercalation potentials were 0.17 V (vs. Li) and 0.34 V (vs. Na). Moreover, the volume change of Si₂₄ upon intercalation proved very small (0.09% for Li, 2.81% for Na), indicating its “zero-strain” properties with stable cycling performance. Li⁺ and Na⁺ can diffuse along the channels inside the Si₂₄ structure with barrier energies of 0.14 and 0.80 eV respectively, and the ionic conductivity of Li_2.66Si₂₄ was calculated to be as high as 1.03 × 10⁻¹ S cm⁻¹ at 300 K. Our calculations indicate that the fast Li-ionic conductivity properties make the Si₂₄ structure a novel anode material for both lithium and sodium ion batteries.

Systematic investigation of Si₂₄ for Li/Na ion batteries using first-principles methods.     

Sodium insertion/extraction investigations into zinc ferrite nanospheres as a high performance anode material

Electrode materials with high fast charging and high capacity are urgently required for the realization of sodium-ion batteries (SIBs). In this work, zinc ferrite (ZnFe₂O₄) nanospheres have been prepared by the simple hydrothermal route and the structural analysis of ZnFe₂O₄ was evaluated by using X-ray diffraction. The morphology and microstructural characterizations are obtained using scanning electron microscopy and transmission electron microscopy. The results indicate that a single phase material was obtained with uniform sphere-like morphology and high crystallinity. The Brunauer–Emmett–Teller method was employed to determine the specific surface area of the ZnFe₂O₄ nanospheres which has been calculated to be 32 m² g⁻¹. The electrochemical results indicate that the composite possesses high sodium storage capability (478 mA h g⁻¹), and good cycling stability (284 mA h g⁻¹ at 100^th cycle) and rate capability (78 mA h g⁻¹ at 2 A g⁻¹). The high sodium storage performance of the ZnFe₂O₄ electrode is ascribed to the mesoporous nature of the ZnFe₂O₄ nanospheres. Further, sodium kinetics and the reaction mechanism in ZnFe₂O₄ nanospheres have been elucidated using electrochemical impedance spectroscopy, galvanostatic intermittent titration technique, ex situ TEM, and XAS. The acquired results indicate sluggish kinetics, reversibility of the material, and the stable structure of ZnFe₂O₄. Therefore, such a structure can be considered to be an attractive contender as a low cost anode for SIBs.

Electrode materials with high fast charging and high capacity are urgently required for the realization of sodium-ion batteries (SIBs).     

The effect of compressive stresses on a silicon electrode’s cycle life in a Li-ion battery

Lithium-ion cells are currently very promising electrochemical power sources. New high-capacity electrodes made from silicon are currently under intensive study. As well as its high capacity, silicon undergoes a significant volume increase (up to 300%) during lithiation. This leads to the generation of internal stresses and fast cell degradation due to active material pulverization and separation from the current collector. Stress formation and its effect on silicon lithiation has been theoretically investigated by many researchers. It has been shown that internal compressive stress can slow down or stop silicon lithiation. In our study we applied external stress to an electrode active layer and measured the cell electrochemical parameters: capacity, cycle life, and charge transfer resistance. In contrast with theoretical estimations we observed an increase in capacity and cycle life when high compressive stress was applied. We believe this behavior is related to stress-induced lithiation front slowdown, which entails a longer stress relaxation period and as a consequence improves the cell parameters.

We have investigated the effect of applying external pressure during cell preparation and its further electrochemical behavior as a Li-ion battery electrode.     

Three-dimensional TiNb2O7 anchored on carbon nanofiber core–shell arrays as an anode for high-rate lithium ion storage

The control of structure and morphology in an electrode design for the development of large-power lithium ion batteries is crucial to create efficient transport pathways for ions and electrons. Herein, we report a powerful combinational strategy to build omnibearing conductive networks composed of titanium niobium oxide nanorods and carbon nanofibers (TNO/CNFs) via an electrostatic spinning method and a hydrothermal method into free-standing arrays with a three-dimensional heterostructure core/shell structure. TNO/CNF electrode exhibits significantly superior electrochemical performance and high-rate capability (241 mA h g⁻¹ at 10C, and 208 mA h g⁻¹ at 20C). The capacity of the TNO/CNF electrode is 257 mA h g⁻¹ after 2000 cycles at 20C, which is much higher than that of the TNO electrode. In particular, the TNO/CNF electrode delivers a reversible capacity of 153.6 mA h g⁻¹ with a capacity retention of 95% after 5000 cycles at ultrahigh current density. Superior electrochemical performances of the TNO/CNF electrode are attributed to the unique composite structure.

The control of structure and morphology in an electrode design for the development of large-power lithium ion batteries is crucial to create efficient transport pathways for ions and electrons.