Rice husk-derived SiOx@carbon nanocomposites as a high-performance bifunctional electrode for rechargeable batteries

This paper we use ZnCl₂ to activates and reduces rice husks to produce SiO_x@N-doped carbon core-shell nanocomposites with inner voids is a facile and effective strategy to improve the electrochemical performance. As an anode material for the lithium-ion batteries, the composites exhibit a high reversible capacity (1315 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹) and long-term stability (584 mAh g⁻¹ after 500 cycles at 500 mA g⁻¹). Such outstanding cycling stability is attributed to the small size of the SiO_x particles with inner voids and the carbon layer coating can guarantee good structural integrity for long cycle stability. As a cathode material for Li–S batteries, the composite displays a high capacity and good stability (675 mAh g⁻¹ after 100 cycles at 0.1C). Its good performance and facile preparation will improve the utilization of rice husk waste.     

One-step microwave-assisted synthesis of Sb2O3/reduced graphene oxide composites as advanced anode materials for sodium-ion batteries

Sb₂O₃/reduced graphene oxide (RGO) composites were prepared through a facile microwave-assisted reduction of graphite oxide in SbCl₃ precursor solution, and investigated as anode material for sodium-ion batteries (SIBs). The experimental results show that a maximum specific capacity of 503 mA h g⁻¹ is achieved after 50 galvanostatic charge/discharge cycles at a current density of 100 mA g⁻¹ by optimizing the RGO content in the composites and an excellent rate performance is also obtained due to the synergistic effect between Sb₂O₃ and RGO. The high capacity, superior rate capability and excellent cycling performance of Sb₂O₃/RGO composites demonstrate their excellent sodium-ion storage ability and show their great potential as electrode materials for SIBs.     

Investigation the sodium storage kinetics of H1.07Ti1.73O4@rGO composites for high rate and long cycle performance

Insertion type material has been attracted plenty of attentions as the anode of sodium ion batteries (SIBs) due to the low volume change induced long cycle stability. H_1.07Ti_1.73O₄ (HTO), a two-dimensional layered material, is a new insertion type anode material for SIBs reported in this study. Layered HTO composites were decorated with rGO nanosheets via an electrostatic assembly method followed by hydrothermal treatment. When adapted as the anode material of SIBs, HTO@rGO composite exhibits an enhanced sodium ion storage behavior, including high rate capability and long cycle stability. It can deliver high capacities of 142.8 and 66.7 mA h g⁻¹ at 100 and 10 000 mA g⁻¹, respectively. Moreover, it can keep a capacity of 75.1 mA h g⁻¹ at 5 A g⁻¹ after even 5000 cycles, corresponding to a high capacity retention of 70.8% (0.0058% capacity decay per cycle). HTO exhibits a small volume expansion of 19.6% by in-situ transmission electron microscopy (in-situ TEM). The diffusion coefficient of sodium ions is increased from 1.77 × 10⁻¹⁴ cm² s⁻¹ in HTO composites to 4.80 × 10⁻¹⁴ cm² s⁻¹ in HTO@rGO composites. Our designed and synthesized HTO@rGO provides a new route for high rate and long cycle stable SIBs anode materials.     

Enhanced anode performance of micro/meso-porous reduced graphene oxide prepared from carbide-derived carbon for energy storage devices

Micro/meso-porous reduced graphite oxide (MMRGO) nanosheets were produced using precursor carbide-derived carbon (CDC), which was produced at a high temperature of 1200 °C, through a massive wet chemistry synthetic route involving graphite oxidation and microwave reduction. X-ray diffraction (XRD) and transmission electron microscopy (TEM) show that the MMRGO nanosheets were fabricated with 2–3 layers and ripple-like corrugations. N₂ sorption isotherms confirmed that micro/meso-pores coexisted in the RGO sample from CDC. In the anode application of Li-ion batteries, this RGO sample had an enhanced capacity performance at the 0.1 C rate and 1 C rate, with ∼1200 mAh g⁻¹ at the 100th cycle and ∼1000 mAh g⁻¹ at the 200th cycle, respectively.     

A ternary MnO/MnTiO3@C composite anode with greatly enhanced cycle stability for Li-ion batteries

Manganese monoxide (MnO) has been widely studied as a potential anode material of Li-ion batteries because of its high specific capacity and abundant raw materials. However, the poor cycling stability of MnO associating to its large volume change during the repeated conversion reaction with Li⁺ has restricted its practical applications. Herein, ternary MnO/MnTiO₃@C composite anode materials are prepared by in situ capturing TiO₂ nanoparticles into sea urchin-like MnO₂ in a mild hydrothermal reaction, followed by resorcinol-formaldehyde (RF) resin coating and thermal treatment. With the strong stabilization effect of the MnTiO₃ component, the optimized ternary MnO/MnTiO₃@C composite anode exhibits greatly enhanced cycling performance as compared to MnO@C. A reversible capacity of 383 mAh g^?1 is preserved after 500 cycles at 1000 mA g^?1. This improved cycle performance can be originated from the stable TiO crystals and the highly reversible amorphous Li_xMnTiO₃ phase generated in the first lithiation process. The reasonably high specific capacity and robust cycle stability enable the ternary MnO/MnTiO₃@C composites to be promising alternative anode materials to graphite for Li-ion batteries.     

Piezoelectric-driven self-accelerated anion migration for SiOX-C/PbZr0.52Ti0.48O3 with durable lithium storage performance

Silicon oxides (SiO_X) based materials with great specific capacity and suitable working potential have caused widespread concern. During alloying process, the volume expansion of SiO_X is approximately 200%, which limits its practical application for lithium-ion batteries (LIBs). For the purpose of surmounting the shortcomings of large volume change, a lot of efforts have been made, such as regulating the structure and morphology of active materials, incorporating with other conductive materials, and matching the suitable battery systems. However, to date, the volume expansion of SiO_X anode in the cycle process cannot be absolutely avoided due to its intrinsic characteristics. In this work, these seeming drawback is creatively exploited to increase the electrochemical performance of SiO_X materials. PbZr_0.52Ti_0.48O₃ (PZT) is taken advantage as functional addition agent, which is based on piezoelectric effect elicited by volume expansion of SiO_X. Specifically, the large volume change of SiO_X-C could be transmitted to PZT particles, thus resulting in a polarization process. Then the piezoelectric potential is generated, so as to promote Li ⁺ mobility. SiO_X-C/PZT was synthesized via a sol-gel method and high energy ball-milling procedure. Accordingly, SiO_X-C/PZT anode exhibits excellent the superior cycling capability, it retains 570 mA h g^-1 after 200 cycles at 400 mA g^-1. Besides, it also has stable long-cycling life (430 mA h g^-1 after 500 cycles at 500 mA g^-1 with a retention of 75%). The relevant results demonstrate that PZT piezoelectric material can favorably increase the electrochemical property of SiO_X anode materials.     

Electrochemical performance of Li4Ti5O12 anode materials synthesized using a spray-drying method

In this study, spinel lithium titanate (Li₄Ti₅O₁₂, LTO) anode materials were synthesized from two titanium sources (P25 TiO₂, 100% anatase TiO₂) using a spray-drying method and subsequent calcination at various temperatures. The electrochemical performance of both a Li/LTO half cell and a LiNi_0.5Mn_1.5O₄/LTO (LNMO/LTO) full cell were investigated. The electrochemical performance of the LTO material prepared from P25 TiO₂ was superior to that of the LTO prepared from 100% anatase TiO₂. After modification of LTO material with AlPO₄, the LTO coated with 2 wt% of AlPO₄ (denoted “2%AlPO₄-LTO”) provided the best performances. The specific (delithiation) capacities of the 2%AlPO₄-LTO anode material was 189.7 mA h g⁻¹ at 0.1C/0.1C, 184.5 mA h g⁻¹ at 1C/1C, 178.8 mA h g⁻¹ at 5C/5C, and 173.1 mA h g⁻¹ at 10C/10C. From long-term cycling stability tests, the specific capacity at the first cycle and the capacity retention after cycling were 185.5 mA h g⁻¹ and 98.06%, respectively, after 200 cycles at 1C/1C and 182.1 mA h g⁻¹ and 99.18%, respectively, after 100 cycles at 1C/10C. For the LNMO/2%AlPO₄-LTO full cell, the average specific capacity (delithiation) and coulombic efficiency after the first five cycles were 164.8 mA h g⁻¹ and 93.30%, respectively, at 0.1C/0.1C. The specific capacities at higher C-rates were 156.1 mA h g⁻¹ at 0.2C/0.2C, 135.7 mA h g⁻¹ at 1C/1C, 97.5 mA h g⁻¹ at 3C/3C, and 46.5 mA h g⁻¹ at 5C/5C. After twenty-five cycles, the C-rate returned to 1C/1C and the specific capacity, coulombic efficiency, and capacity retention were maintained at 134.1 mA h g⁻¹, 99.17%, and 98.82%, respectively.     

Wrapping mesoporous Fe2O3 nanoparticles by reduced graphene oxide: Enhancement of cycling stability and capacity of lithium ion batteries by mesoscopic engineering

The fast capacity fading at high current density turns out to be one of the key challenges limiting the broad applications of transition metal oxide-based electrodes. Herein, Fe₂O₃ nanoparticles with well-defined mesopores wrapped by reduced graphene oxide (RGO) have been synthesized via a facile hydrothermal strategy. The as-prepared nanocomposites were systematically characterized. XPS and Raman analyses confirm the co-existence of Fe₂O₃ and RGO in the nanocomposite system. SEM and TEM reveal that the mesoporous Fe₂O₃ nanoparticles have a size of 20–60?nm and are uniformly dispersed and tightly wrapped by RGO. When used as the anode in lithium ion batteries, the mesoporous-Fe₂O₃/RGO electrode exhibits excellent cycling stability (1098?mA?h?g^?1 after 500 cycles at 1?A?g^?1) and superior rate capability (574?mA?h?g^?1 at 5?A?g^?1). The excellent electrochemical performance can be mainly ascribed to the unique mesoscopic architecture that serves as a cushion to alleviate volume change of Fe₂O₃ during discharge/charge cycles, provides a sustainably large contact area with the electrolyte, and improves electrical conductivity. This unique nanocomposite electrode holds great potential as an anode material for advanced lithium ion batteries.     

Nitrogen-doped carbon-coated hierarchical Li4Ti5O12-TiO2 hybrid microspheres as excellent high rate anode of Li-ion battery

Nitrogen-doped carbon-coated Li₄Ti₅O₁₂-TiO₂ (LTO-TO) hybrid microspheres were prepared by heat treating the dry mixture of urea and chemically lithiated dandelion-like TiO₂ microspheres in a stainless steel autoclave at 550 °C for 5 h. The hybrid materials were tested as anode of Li-ion batteries. As compared to the pristine sample, the N-doped carbon-coated LTO-TO microspheres exhibited higher specific capacity at both low and high current rates. Discharge capacities of 184 and 123 mAh g⁻¹ were obtained at 0.2 C and 20 C, respectively. Moreover, the LTO-TO/C electrode showed excellent cycle performance, with a discharge capacity of 121.3 mAh g⁻¹ remained after 300 cycles at 5 C, corresponding to an average capacity degradation rate of 0.073% per cycle. These high specific capacity, excellent rate capability and cycle performance demonstrated the high potentiality of the N-doped carbon-coated LTO-TO microspheres as anode material of both energy storage-type and power-type Li-ion batteries.     

In-situ synthesis of reduced graphene oxide wrapped Mn3O4 nanocomposite as anode materials for high-performance lithium-ion batteries

We report a novel in-situ symbiosis method to prepare reduced graphene oxide wrapped Mn₃O₄ nanoparticles (rGO/Mn₃O₄) with uniform size about 50 nm as anodes for lithium-ion batteries (LIBs), which can simplify the preparation process and effectively reduce pollution. The rGO/Mn₃O₄ nanocomposite exhibited a reversible specific capacity of 795.5 mAh g^?1 at 100 mA g^?1 after 200 cycles (capacity retention: 87.4%), which benefits from the unique structural advantages and the synergistic effect of rGO and Mn₃O₄. The Mn₃O₄ nanoparticles encapsulated among the rGO nanosheets exhibited good electrochemical activity, and the multilayer wrinkled rGO sheets provided a stable 3D conduction channel for Li⁺/e^? transport. The rGO/Mn₃O₄ nanocomposite is a promising anode candidate for advanced LIBs with excellent cycling performance and rate performance. Furthermore, this new preparation method can be extended to green and economical synthesis of advanced graphene/manganese-based nanocomposites.     

Flower-like hierarchical Li1.2Ni0.13Co0.13Mn0.54O2 by architectural design for lithium-ion batteries with superior capacity retention

In this work, hierarchical flower-like Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ (LNCM) with exposed {010} planes assembled and double-sphere Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ without {010} planes as a comparison were successfully synthesized via a simple solvothermal method. The diffusion of Li⁺ could be enhanced in the flower-like LNCM with exposed {010} active planes, and the cathode exhibits a superior electrochemical performance especially in long-term cycling stability even at high current densities. The initial discharge capacity of this sample is 274 mA h g⁻¹ at 0.1C (25 mA g⁻¹), with corresponding initial coulombic efficiencies of 77%. Especially, the capacity retention reaches up to 98% at 1250 mA g⁻¹ current density after 100 cycles. By comparing with other LNCM materials reported recently, our optimal cathode has a pretty outstanding electrochemical performance, which is promising for the next generation lithium ion batteries.     

Reduced graphene oxide anchored with δ-MnO2 nanoscrolls as anode materials for enhanced Li-ion storage

We developed a one-pot in situ synthesis procedure to form nanocomposite of reduced graphene oxide (RGO) sheets anchored with 1D δ-MnO₂ nanoscrolls for Li-ion batteries. The as-prepared products were characterized by X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The electrochemical performance of the δ-MnO₂ nanoscrolls/RGO composite was measured by galvanostatic charge/discharge cycling and electrochemical impedance spectroscopy. The results show that the δ-MnO₂ nanoscrolls/RGO composite displays superior Li-ion battery performance with large reversible capacity and high rate capability. The first discharge and charge capacities are 1520 and 810 mAh g⁻¹, respectively. After 50 cycles, the reversible discharge capacity is still maintained at 528 mAh g⁻¹ at the current density of 100 mAh g⁻¹. The excellent electrochemical performance is attributed to the unique nanostructure of the δ-MnO₂ nanoscrolls/RGO composite, the high capacity of MnO₂ and superior electrical conductivity of RGO.     

Electrochemical performance of SiOC anodes prepared by a different silicone

SiOC is one of the most promising anodes for lithium-ion batteries, which shows the good structural stability and high capacity comparing to commercial graphite anode. In this paper, different SiOC anodes (SiOC-217, SiOC-H44, and SiOC-MK) were prepared from polymer precursors with different side groups (phenyl, methyl-phenyl, methyl) to investigate the effects of free carbon on the electrochemical performance of SiOC anodes. The results of X-ray photoelectron spectroscopy presented that SiOC was composed by different SiO_xC_4−x units and free carbon phase. The initial discharge capacity of SiOC-217 was 742.67 mA h g⁻¹. After 100 cycles, the reversible capacity of SiOC-217 reached 450.65 mA h g⁻¹ at 0.2 C, indicating a capacity retention rate of 60.68%. After cycling at high current densities, SiOC-217 exhibited a high discharge capacity of 592.88 mA h g⁻¹ at 0.1 C. SiOC-217 exhibited excellent electrochemical performance due to the high content of free carbon phase. Furthermore, the high contents of SiO₂C₂ and SiO₃C units further enhanced the improvement of electrochemical performance.     

Sn-based glass–graphite-composite as a high capacity anode for lithium-ion batteries

Sn-based anode has been widely studied because of its high theoretical specific capacity. However, the capacity of Sn-based anode decreases sharply during the cycle, which hinders its application in commercial batteries. In this paper, Sn-based glass was successfully obtained by melt quenching method. Sn-based glass and graphite were combined by the ball milling method as anode materials. The Sn-based glass–graphite-composite anode can still maintain the capacity of 700 mA h g⁻¹ after 500 cycles at 500 mA g⁻¹, which is about 2.7 times that of the Sn glass anode (260 mA h g⁻¹) under the same test conditions. The addition of graphite can effectively inhibit the accumulation of Sn particles in the discharge process of Sn-based glass anode, which improves the capacity of Sn-based glass anode, and the addition of graphite can effectively reduce the resistance of Sn-based glass anode. Therefore, the Sn-based glass–graphite-composite anode has excellent Li⁺ ions storage properties.     

Micro/nanostructured Bi2Mn4O10 with hierarchical spindle morphology as a highly efficient anode material for lithium-ion batteries

Mullite-type compound Bi₂Mn₄O₁₀ has shown the feasibility as anodes of next lithium-ion batteries (LIBs). Herein micro/nano-Bi₂Mn₄O₁₀ with hierarchical spindle-like architectures has been successfully synthesized using a one-step hydrothermal method without any no surfactant or template. A time-dependent experiment is carried out to observe the morphology evolution, suggesting a nucleation–aggregation/growth–dissolution–recrystallization process. As anode of LIBs, the as-prepared spindle-shaped micro/nano Bi₂Mn₄O₁₀ harvests a significantly high initial discharge capacity of 1022 mA h g⁻¹ at 1 C, an excellent cyclability performance (563.8 mA h g⁻¹ after 400 cycles), a better high-rate capability (100 mA h g⁻¹ at 10 C), quick diffusion kinetics (1.8 × 10⁻¹² cm² s⁻¹), and low active energy (19.5 kJ mol⁻¹), which are significantly superior to that of its bulk counterparts and the previous reports. The encouraging lithium storage performance largely stems from the synergistic effect of the unique spindle-shaped micro/nanostructure.     

Electrospinning-derived ZnCo2O4@carbon nanofiber composite for high-performance lithium ion storage

The degradation of the cobalt-zinc oxide structure and its poor conductivity during the charge and discharge limit their further applications for lithium ion storage. Herein, ZnCo₂O₄@carbon nanofiber composite with nano-fibrous structure is obtained by electrospinning, annealing in argon and low-temperature oxidation to effectively overcome the above issue. The active sites of ZnCo₂O₄ are evenly dispersed inside the carbon nanofibers, which can effectively avoid its aggregation and improve electrical conductivity. Additionally, the stable nanofibrous structure can maintain structural stability. The composite exhibits superior lithium ion storage capacity when being served as anode electrode. The ZnCo₂O₄@carbon nanofiber electrode possesses a high capacity of 1071 mA h g⁻¹ at 0.1 A g⁻¹. Besides, the electrode shows an outstanding rate capability of 505 mA h g⁻¹ at 3 A g⁻¹ and maintain 714 mA h g⁻¹ after 250 cycles when current density is adjusted to 0.2 A g⁻¹ again. Additionally, the electrode has an outstanding long-cycle performance, which remains a capacity of 447.165 mA h g⁻¹ at 0.5 A g⁻¹ after 500 cycles and 421.477 mA h g⁻¹ at 1 A g⁻¹ after 518 cycles. This result demonstrates that ZnCo₂O₄@carbon nanofiber composite has potential application prospects in the fields of advanced energy storage.     

Electrochemical performance of Bi2Te3/GO composite anode for LIB application

Present investigation deals with the study of electrochemical properties of Bi₂Te₃/GO composite for its use as anode material in Li-ion batteries. The Bi₂Te₃/GO composite has been synthesized via polyol route. The surface morphology and structural properties of the as-prepared samples have been studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy techniques. The phase of as-synthesized composite was found out to be rhombohedral as has been characterized by X-ray diffractometer. The presence of GO in the Bi₂Te₃ matrix has been confirmed by the presence of characteristic D and G bands in the Raman spectra. The as-synthesized composite showed the first cycle discharge/charge capacity of 752/514 mAh g⁻¹ at the current density of 0.1 Ag⁻¹, superior rate capability (~50 mAh g⁻¹ at 2 Ag⁻¹), and excellent cycling stability over 500 cycles at 0.1 Ag⁻¹. The presence of GO in the matrix helps to enhance the electronic conductivity due to the rapid Li-ion diffusion and helps to shield the changes in volume during the cycling processes.     

Stable composite electrolytes of PVDF modified by inorganic particles for solid-state lithium batteries

Polymer electrolytes have been attracting much attention because of their flexibility and easy follow-up processing, but their Li⁺ conductivity in lithium-metal batteries (LIBs) is unsatisfactory. Stable composite electrolytes of poly (vinylidene fluoride) (PVDF) polymer with high lithium-ion conductivity have been prepared by a trigger structural modification of Li_6.5La₃Zr_1.5Nb_0.25Ta_0.25O₁₂ (LLZNTO) garnet ceramic and TiO₂ oxide. The influences of various amounts of TiO₂ and LLZNTO on electrochemical performance were systematically examined. These composite electrolytes exhibited maximal Li⁺ conductivity of 2.89 × 10⁻⁴ S cm⁻¹, which is consistent with the value of pure ceramic electrolytes. Furthermore, it possessed the stable long-term Li cycling and the wide electrochemical window, involving repeated Li plating/stripping at 0.2 mA cm⁻² over 280 h without failure. The discharge specific capacity and Coulomb efficiency for all-solid-state LIBs assembled with these membranes delivered outstanding cycling stability with high discharge capacities (117.9 mA h g⁻¹) at 0.1 C rate and Coulomb efficiency reached 99.9% after 25 cycles. The high Li⁺ conduction capability can be ascribed function of introducing TiO₂ and LLZNTO to restrain tremendously the crystalline behavior of the polymer. Furthermore, the LLZNTO can be complex with PVDF for dehydrofluorination, and it can also offer a burst transportation route for lithium ions. This system might serve as an attractive use for polymer solid electrolytes and open up new possibilities for safe all-solid-state LIBs.     

Effect of graphene nanosheets on electrochemical performance of Li4Ti5O12 in lithium-ion capacitors

In order to improve the electrochemical performance of lithium titanium oxide, Li₄Ti₅O₁₂ (LTO), for the use in the lithium-ion capacitors (LICs) application, LTO/graphene composites were synthesized through a solid state reaction. The composite exhibited an interwoven structure with LTO particles dispersed into graphene nanosheets network rather than an agglomerated state pristine LTO particles. It was found that there is an optimum percentage of graphene additives for the formation of pure LTO phase during the solid state synthesis of LTO/graphene composite. The effect of graphene nanosheets addition on electrochemical performance of LTO was investigated by a systemic characterization of galvanostatic cycling in lithium and lithium-ion cell configuration. The optimized composite exhibited a decreased polarization upon cycling and delivered a specific capacity of 173 mA h g⁻¹ at 0.1 C and a well maintained capacity of 65 mA h g⁻¹ even at 20 C. The energy density of 14 Wh kg⁻¹ at a power density of 2700 W kg⁻¹ was exhibited by a LIC full cell with a balanced mass ratio of anode to cathode along with a superior capacitance retention of 97% after 3000 cycles at a current density of 0.4 A g⁻¹. This boost in reversible capacity, rate capability and cycling performance was attributed to a synergistic effect of graphene nanosheets, which provided a short lithium ion diffusion path as well as facile electron conduction channels.     

Simple fabrication of strongly coupled cobalt ferrite/carbon nanotube composite based on deoxygenation for improving lithium storage

An easy method to synthesize a strongly coupled cobalt ferrite/carbon nanotube (CoFe₂O₄/CNT) composite with oxygen bridges between CoFe₂O₄ and reduced carbon nanotubes (CNTs) by calcining the precursor material was reported. The precursor was prepared by an electrostatic self-assembly of the exfoliated Co(II)Fe(II)Fe(III)-layered double hydroxide (CoFeFe-LDH) nanosheets and acid treated CNTs. The deoxygenation effect of ferrous ion (Fe²⁺) in CoFeFe-LDH nanosheets on the oxygen-containing groups of acid treated CNTs was investigated by X-ray photoelectron spectroscopy (XPS) measurement. After thermal conversion, the obtained CoFe₂O₄ was bonded to the reduced CNTs through Metal–O–C (oxygen bridge), which was characterized by XPS, Fourier transform infrared spectroscopy, and Raman spectroscopy. When applied as an anode for lithium-ion battery, the CoFe₂O₄/CNT composite exhibited a low resistance of charge transfer and Li-ion diffusion, good cycle performance, and high rate capability. At a lower current density of 0.15 A·g⁻¹, a specific discharge capacity of 910 mA·h·g⁻¹ was achieved up to 50 cycles. When current density was increased to 8.8 A·g⁻¹, the CoFe₂O₄/CNT composite still delivered 500 mA·h·g⁻¹.