A tin(iv) oxides/carbon nanotubes composite with core-tubule structure as an anode material for high electrochemistry performance LIBs

SnO₂/CNTs composites with core-tubule structure are prepared by a facile wet chemical method. The investigation of electrochemical characteristics of the SnO₂/CNTs composites shows that the composites exhibit some advantages, such as stable core-tubule structure, small particle size of SnO₂, low electron-transfer resistance and faster lithium ion migration speed. The final product synthesized under optimized conditions can release a stable capacity of about 743 mA h g⁻¹ after 100 cycles at the current density of 0.4 A g⁻¹, 598 mA h g⁻¹ after 500 cycles at the current density of 4 A g⁻¹. Even at a super high current density of 8 A g⁻¹, the composite can still deliver a steady capacity of 457 mA h g⁻¹, and the discharge capacity can be restored to 998 mA h g⁻¹ when current density is decreased to 0.4 A g⁻¹.

SnO₂/CNTs composites with core-tubule structure are prepared by a facile wet chemical method.     

The synthesis of triazine–thiophene–thiophene conjugated porous polymers and their composites with carbon as anode materials in lithium-ion batteries

The polymers based on thiophene armed triazine and different thiophene derivatives including thiophene (Th), thieno[3,2-b]thiophene (TT), dithieno[3,2-b:2′,3′-d]thiophene (DTT) or thieno[2′,3'':4,5]thieno[3,2-b]thieno[2,3-d]thiophene (TTTT) are synthesized through a Stille coupling reaction. By introducing thiophene derivatives with increasing sizes as the linkage units (from thiophene, DT to DTT, TTTT), the band gaps (E_g) of the resultant polymers decrease continuously. Then the composite materials (polymer@C) between polymers and Vulcan XC-72 carbon are prepared by in situ polymerization to test their electrochemical performances in lithium ion batteries. The synthesized composites show distinct morphologies due to the different linkage units of thiophene or fused cyclothiophene derivatives and the cross-linked structure can be found in composites with the longer thiophene derivatives (bridging molecules) like PTT-3@C and PTT-4@C, which are expected to be beneficial to improve the performances of the electrode materials. The specific capacities of the composites are 495 mA h g⁻¹, 671 mA h g⁻¹, 707 mA h g⁻¹, and 772 mA h g⁻¹ for PTT-1@C, PTT-2@C, PTT-3@C and PTT-4@C at a current density of 100 mA g⁻¹, respectively. In particular, benefiting from the enlarged conjugation length and planarity of the linkage units, the conjugated microporous polymers could deliver continuously improved capacities.

Four different kinds of conjugated porous polymers PTTs were synthesized and their composites with carbon material were used as the electrode materials for LIBs.     

Mesopore-dominant nitrogen-doped carbon with a large defect degree and high conductivity via inherent hydroxyapatite-induced self-activation for lithium-ion batteries

In this study, N-doped mesopore-dominant carbon (NMC) materials were prepared using bio-waste tortoise shells as a carbon source via a one-step self-activation process. With intrinsic hydroxyapatites (HAPs) as natural templates to fulfill the synchronous carbonization and activation of the precursor, this highly efficient and time-saving method provides N-doped carbon materials that represent a large mesopore volume proportion of 74.59%, a high conductivity of 4382 m S⁻¹, as well as larger defects, as demonstrated by Raman and XRD studies. These features make the NMC exhibit a high reversible lithium-storage capacity of 970 mA h g⁻¹ at 0.1 A g⁻¹, a strong rate capability of 818 mA h g⁻¹ at 2 A g⁻¹, and a good capacity of 831 mA h g⁻¹ after 500 cycles at 1 A g⁻¹. This study provides a highly efficient and feasible method to prepare renewable biomass-derived carbons as advanced electrode materials for the application of energy storage.

A hydroxyapatite-induced self-activation method has been used to prepare nitrogen-doped mesopore-dominant carbon. The carbon has abundant macro/mesopores, high conductivity, and favorable defects and exhibited high-performance in LIBs.     

The influence of different Si : C ratios on the electrochemical performance of silicon/carbon layered film anodes for lithium-ion batteries

With a high specific capacity (4200 mA h g⁻¹), silicon based materials have become the most promising anode materials in lithium-ions batteries. However, the large volume expansion makes the capacity reduce rapidly. In this work, a periodic silicon/carbon (Si/C) multilayer thin film was synthesized by magnetron sputtering method on copper foil. The titanium (Ti) film (about 20 nm) as the transition layer was deposited on the copper foil prior to the deposition of the multilayer film. Superior electrochemical lithium storage performance was obtained by the multilayer thin film. The initial discharge and charge specific capacity of the Si (15 nm)/C (5 nm) multilayer film anode are 2640 mA h g⁻¹ and 2560 mA h g⁻¹ with an initial coulombic efficiency of ∼97%. The retention specific capacity is about 2300 mA h g⁻¹ and there is ∼87% capacity retention after 200 cycles.

With a high specific capacity (4200 mA h g⁻¹), silicon based materials have become the most promising anode materials in lithium-ions batteries.     

Dual-doped hierarchical porous carbon derived from biomass for advanced supercapacitors and lithium ion batteries

Nowadays, designing heteroatom-doped porous carbons from inexpensive biomass raw materials is a very attractive topic. Herein, we propose a simple approach to prepare heteroatom-doped porous carbons by using nettle leaves as the precursor and KOH as the activating agent. The nettle leaf derived porous carbons possess high specific surface area (up to 1951 m² g⁻¹), large total pore volume (up to 1.374 cm³ g⁻¹), and high content of nitrogen and oxygen heteroatom doping (up to 17.85 at% combined). The obtained carbon as an electrode for symmetric supercapacitors with an ionic liquid electrolyte can offer a superior specific capacitance of 163 F g⁻¹ at 0.5 A g⁻¹ with a capacitance retention ratio as high as 67.5% at 100 A g⁻¹, and a low capacitance loss of 8% after 10 000 cycles. Besides, the as-built supercapacitor demonstrates a high specific energy of 50 W h kg⁻¹ at a specific power of 372 W kg⁻¹, and maintains 21 W h kg⁻¹ at the high power of 40 kW kg⁻¹. Moreover, the resultant carbon as a Li-ion battery anode delivers a high reversible capacity of 1262 mA h g⁻¹ at 0.1 A g⁻¹ and 730 mA h g⁻¹ at 0.5 A g⁻¹, and maintains a high capacity of 439 mA h g⁻¹ after 500 cycles at 1 A g⁻¹. These results demonstrate that the nettle leaf derived porous carbons offer great potential as electrodes for advanced supercapacitors and lithium ion batteries.

Nettle leaf derived nitrogen and oxygen dual-doped porous carbons exhibit great potential as anodes for high performance supercapacitors and lithium ion batteries.     

Hard carbon spheres prepared by a modified Stöber method as anode material for high-performance potassium-ion batteries

The Stöber method is a highly efficient synthesis strategy for homogeneous monodisperse polymer colloidal spheres and carbon spheres. This work delivers an extended Stöber method and investigates the synthesis process. By calcining the precursor under appropriate conditions, solid secondary particles of amorphous carbon (SSAC) and hollow secondary particles of graphitized carbon (HSGC) can be directly synthesized. The two materials have a nano-primary particle structure and a closely-packed sub-micron secondary particle structure, which can be used in energy storage. We find that SSAC and HSGC have high potassium-ion storage capacity with reversible capacities of 274 mA h g⁻¹ and 283 mA h g⁻¹ at 20 mA g⁻¹ respectively. Significantly, SSAC has better rate performance with a specific capacity of 107 mA h g⁻¹ at 1 A g⁻¹.

A modified Stöber method synthesizes resorcinol-formaldehyde resin-based secondary particle hard carbon spheres as anode material for high-performance potassium-ion batteries.     

Performance optimization of freestanding MWCNT-LiFePO4 sheets as cathodes for improved specific capacity of lithium-ion batteries

The typical lithium-ion-battery positive electrode of “lithium-iron phosphate (LiFePO₄) on aluminum foil” contains a relatively large amount of inactive materials of 29 wt% (22 wt% aluminum foil + 7 wt% polymeric binder and graphitic conductor) which limits its maximum specific capacity to 120.7 mA h g⁻¹ (71 wt% LiFePO₄) instead of 170 mA h g⁻¹ (100 wt% LiFePO₄). We replaced the aluminum current-collector with a multi-walled carbon nanotube (MWCNT) network. We optimized the specific capacity of the “freestanding MWCNT-LiFePO₄” positive electrode. Through the optimization of our unique surface-engineered tape-cast fabrication method, we demonstrated the amount of LiFePO₄ active materials can be as high as 90 wt% with a small amount of inactive material of 10 wt% MWCNTs. This translated to a maximum specific capacity of 153 mA h g⁻¹ instead of 120.7 mA h g⁻¹, which is a significant 26.7% gain in specific capacity compared to conventional cathode design. Experimental data of the freestanding MWCNT-LiFePO₄ at a low discharge rate of 17 mA g⁻¹ show an excellent specific capacity of 144.9 mA h g⁻¹ which is close to its maximum specific capacity of 153 mA h g⁻¹. Furthermore, the freestanding MWCNT-LiFePO₄ has an excellent specific capacity of 126.7 mA h g⁻¹ after 100 cycles at a relatively high discharge rate of 170 mA g⁻¹ rate.

We optimized the specific capacity of freestanding MWCNT-LiFePO₄ positive electrode. We demonstrated as high (low) as 90 wt% LiFePO₄ active material (10 wt% MWCNTs inactive material). This corresponded to a maximum specific capacity of 153 mA h g⁻¹.     

Synthesis of hierarchical Sn/SnO nanosheets assembled by carbon-coated hollow nanospheres as anode materials for lithium/sodium ion batteries

Tin-based anode materials have aroused interest due to their high capacities. Nevertheless, the volume expansion problem during lithium insertion/extraction processes has severely hindered their practical application. In particular, nano–micro hierarchical structure is attractive with the integrated advantages of nano-effect and high thermal stability of the microstructure. Herein, hierarchical Sn/SnO nanosheets assembled by carbon-coated hollow nanospheres were successfully synthesized by a facile glucose-assisted hydrothermal method, in which the glucose served as both morphology-control agent and carbon source. The hierarchical Sn/SnO nanosheets exhibit excellent electrochemical performances owing to the unique configuration and carbon coating. Specifically, a reversible high capacity of 2072.2 mA h g⁻¹ was observed at 100 mA g⁻¹. Further, 964.1 mA h g⁻¹ after 100 cycles at 100 mA g⁻¹ and 820.4 mA h g⁻¹ at 1000 mA g⁻¹ after 300 cycles could be obtained. Encouragingly, the Sn/SnO also presents certain sodium ion storage properties. This facile synthetic strategy may provide new insight into fabricating high-performance Sn-based anode materials combining the advantages of both structure and carbon coating.

Hierarchical Sn/SnO nanosheets assembled by carbon-coated hollow nanospheres with promising lithium and sodium storage performances.     

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.     

Nanostructured diatom earth SiO2 negative electrodes with superior electrochemical performance for lithium ion batteries

Diatomaceous earth (DE) is a naturally occurring silica source constituted by fossilized remains of diatoms, a type of hard-shelled algae, which exhibits a complex hierarchically nanostructured porous silica network. In this work, we analyze the positive effects of reducing DE SiO₂ particles to the sub-micrometer level and implementing an optimized carbon coating treatment to obtain DE SiO₂ anodes with superior electrochemical performance for Li-ion batteries. Pristine DE with an average particle size of 17 μm is able to deliver a specific capacity of 575 mA h g⁻¹ after 100 cycles at a constant current of 100 mA g⁻¹, and reducing the particle size to 470 nm enhanced the reversible specific capacity to 740 mA h g⁻¹. Ball-milled DE particles were later subjected to a carbon coating treatment involving the thermal decomposition of a carbohydrate precursor at the surface of the particles. Coated ball-milled silica particles reached stable specific capacities of 840 mA h g⁻¹ after 100 cycles and displayed significantly improved rate capability, with discharge specific capacities increasing from 220 mA h g⁻¹ (uncoated ball-milled SiO₂) to 450 mA h g⁻¹ (carbon coated ball-milled SiO₂) at 2 A g⁻¹. In order to trigger SiO₂ reactivity towards lithium, all samples were subjected to an electrochemical activation procedure prior to electrochemical testing. XRD measurements on the activated electrodes revealed that the initial crystalline silica was completely converted to amorphous phases with short range ordering, therefore evidencing the effective role of the activation procedure.

Diatomaceous earth SiO₂ anodes with superior electrochemical performance are obtained by ball milling, carbon coating and electrochemical activation of SiO₂ particles.     

The synthesis of alternating donor–acceptor polymers based on pyrene-4,5,9,10-tetraone and thiophene derivatives,their composites with carbon,and their lithium storage performances as anode materials

Two conjugated polymer@activated carbon composites were synthesized by the in situ polymerization of two donor–acceptor type polymers including poly[(thiophene-2,5-yl)-((pyrene-4,5,9,10-tetraone)-2,7-yl)] (PTPT) and poly[((2,3-dihydrothieno[3,4-b][1,4]dioxine)-5,7-yl)-((pyrene-4,5,9,10-tetraone)-2,7-yl)] (POTPT) on activated carbon (AC) by one-step cross-coupling reaction catalyzed by an organometallic catalyst. Cyclic voltammetry showed that both polymers exhibited ambipolar properties, low bandgaps, and low electrode potentials, which could be useful for their application as anodes in lithium-ion battery cells (LIBs). For PTPT@AC and POTPT@AC anodes, they showed a high capacity of 253.9 and 370.5 mA h g⁻¹ at 100 mA g⁻¹. Besides, the capacities of pure polymers were calculated to be 693.5 and 1276.5 mA h g⁻¹ for PTPT and POTPT, respectively, at 100 mA g⁻¹. Compared with PTPT, the introduction of the 3,4-ethylenedioxy unit into the side chain of the thiophene unit leads to substantially improved performance of POTPT due to the lowered LUMO energy levels of POTPT and the electron-rich feature of the EDOT unit. It is suggested that the structure-tuning strategy might be an effective method to prepare the new polymer-based anode for next generation LIBs with high performance and high safety.

The preparation procedure and cycling performance of the two polymer composites.     

Improved pseudocapacitive charge storage in highly ordered mesoporous TiO2/carbon nanocomposites as high-performance Li-ion hybrid supercapacitor anodes

A Li-ion hybrid supercapacitor (Li-HSCs), an integrated system of a Li-ion battery and a supercapacitor, is an important energy-storage device because of its outstanding energy and power as well as long-term cycle life. In this work, we propose an attractive material (a mesoporous anatase titanium dioxide/carbon hybrid material, m-TiO₂-C) as a rapid and stable Li⁺ storage anode material for Li-HSCs. m-TiO₂-C exhibits high specific capacity (∼198 mA h g⁻¹ at 0.05 A g⁻¹) and promising rate performance (∼90 mA h g⁻¹ at 5 A g⁻¹) with stable cyclability, resulting from the well-designed porous structure with nanocrystalline anatase TiO₂ and conductive carbon. Thereby, it is demonstrated that a Li-HSC system using a m-TiO₂-C anode provides high energy and power (∼63 W h kg⁻¹, and ∼4044 W kg⁻¹).

A mesoporous TiO₂/carbon nanocomposite prepared by block copolymer self-assembly improves pseudocapacitive behavior and achieves high energy/power density Li-ion hybrid supercapacitors.     

Heterogeneous synthesis and electrochemical performance of LiMnPO4/C composites as cathode materials of lithium ion batteries

In this study, a facile yet efficient interfacial hydrothermal process was successfully developed to fabricate LiMnPO₄/C composites. In this strategy, the walls of carbon nanotubes were employed as heterogeneous nucleation interfaces and biomass of phytic acid (PA) as an eco-friendly phosphorus source. By comparing the experimental results, a reasonable nucleation-growth mechanism was proposed, suggesting the advantages of interfacial effects. Meanwhile, the as-synthesized LiMnPO₄/C samples exhibited superior rate performances with discharge capacities reaching 161 mA h g⁻¹ at C/20, 134 mA h g⁻¹ at 1C, and 100 mA h g⁻¹ at 5C. The composites also displayed excellent cycling stabilities by maintaining 95% of the initial capacity over 100 continuous cycles at 1C. Electrochemical impedance spectroscopy showed that the superior electrochemical performances were attributed to the low charge-transfer resistance and elevated diffusion coefficient of lithium ions. In sum, the proposed approach for the preparation of LiMnPO₄/C composites looks promising for future production of composite electrode materials for high-performance lithium-ion batteries.

A heterogeneous nucleation technique was used to prepare LiMnPO₄/C. The walls of carbon nanotubes were employed as nucleation interfaces and phytic acid as an eco-friendly phosphorus source. The product exhibits superior electrochemical performance.     

Structure and conductivity enhanced treble-shelled porous silicon as an anode for high-performance lithium-ion batteries

Silicon is regarded as the next generation anode material for lithium-ion batteries because of its high specific capacity, low intercalation potential and abundant reserves. However, huge volume changes during the lithiation and delithiation processes and low electrical conductivity obstruct the practical applications of silicon anodes. In this study, a treble-shelled porous silicon (TS-P-Si) structure was synthesized via a three-step approach. The TS-P-Si anode delivered a capacity of 858.94 mA h g⁻¹ and a capacity retention of 87.8% (753.99 mA h g⁻¹) after being subjected to 400 cycles at a current density of 400 mA g⁻¹. The good cycling performance was due to the unique structure of the inner silicon oxide layer, middle silver nano-particle layer and outer carbon layer, leading to a good conductivity and a decreased volume change of this silicon-based anode.

In this paper, a treble-shelled porous silicon structure is synthesized through three-step approach to enhance the structural stability and conductivity.     

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.     

Polyimide-derived carbon nanofiber membranes as free-standing anodes for lithium-ion batteries

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies. The influence of carbonization temperature on the physical-chemical characteristics of CNMs was investigated in detail. The electrochemical performances of CNMs as free-standing electrodes without any binder or conducting materials for lithium-ion batteries were also discussed. Furthermore, the surface state and internal carbon structure had an important effect on the nitrogen state, electrical conductivity, and wettability of CNMs, and then further affected the electrochemical performances. The CNMs/Li metal half-cells exhibited a satisfying charge–discharge cycle performance and excellent rate performance. They showed that the reversible specific capacity of CNMs carbonized at 700 °C could reach as high as 430 mA h g⁻¹ at 50 mA g⁻¹, and the value of the specific capacity remained at 206 mA h g⁻¹ after 500 cycles at a high current density of 1 A g⁻¹. Overall, the newly developed carbon nanofiber membranes will be a promising candidate for flexible electrodes used in high-power lithium-ion batteries, supercapacitors and sodium-ion batteries.

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies.     

Enhanced stability of nitrogen doped porous carbon fiber on cathode materials for high performance lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are considered to be one of the candidates for high-energy density storage systems due to their ultra-high theoretical specific capacity of 1675 mA h g⁻¹. However, problems of rapid capacity decay, sharp expansion in volume of the active material, and the shuttle effect have severely restricted their subsequent development and utilization. Herein, we design a nitrogen-doped porous carbon nanofiber (NPCNF) network as a sulfur host by the template method. The NPCNF shows a feather-like structure. After loading sulfur, the NPCNF/S composite can maintain a hierarchically porous structure. A high discharge capacity of 1301 mA h g⁻¹ is delivered for the NPCNT/S composite at 0.1C. The reversible charge/discharge capacity at 2C is 576 mA h g⁻¹, and 700 mA h g⁻¹ is maintained after 500 cycles at 0.5C. The high electrochemical performance of this NPCNT/S composite is attributed to the synergy effects of abundant N active sites and high electrical conductivity of the material.

The conductive network of nitrogen-doped porous carbon nanofibers was successfully prepared by the template method. The doping of nitrogen and the synergistic effect of mesopores and micropores reduce the energy barrier of Li⁺ migration in the material.     

Ultradispersed titanium dioxide nanoparticles embedded in a three-dimensional graphene aerogel for high performance sulfur cathodes

Lithium–sulfur (Li–S) batteries are regarded as one of the most promising energy storage technologies, however, their practical application is greatly limited by a series of sulfur cathode challenges such as the notorious “shuttle effect”, low conductivity and large volume change. Here, we develop a facile hydrothermal method for the large scale synthesis of sulfur hosts consisting of three-dimensional graphene aerogel with tiny TiO₂ nanoparticles (5–10 nm) uniformly dispersed on the graphene sheet (GA–TiO₂). The obtained GA–TiO₂ composites have a high surface area of ∼360 m² g⁻¹ and a hierarchical porous structure, which facilitates the encapsulation of sulfur in the carbon matrix. The resultant GA–TiO₂/S composites exhibit a high initial discharge capacity of 810 mA h g⁻¹ with an ultralow capacity fading of 0.054% per cycle over 700 cycles at 2C, and a high rate (5C) performance (396 mA h g⁻¹). Such architecture design paves a new way to synthesize well-defined sulfur hosts to tackle the challenges for high performance Li–S batteries.

GA–TiO₂ composites as a cathode material realize an excellent electrochemical performance in Li–S batteries.     

Facile thermochemical conversion of FeOOH nanorods to ZnFe2O4 nanorods for high-rate lithium storage

We successfully prepared ZnFe₂O₄ nanorods (ZFO-NRs) by a simple thermochemical reaction of FeOOH nanorods with Zn(NO₃)₂ to use as an anode material in lithium-ion batteries. The FeOOH nanorod shape was well maintained after conversion into ZFO-NR with the formation of porous structures. The nanorod structure and porous morphology facilitate Li⁺ transport, improve the reaction rates owing to the larger contact area with the electrolyte, and reduce the mechanical stress during lithiation/delithiation. The ZFO-NR electrode exhibited a reversible capacity of 725 mA h g⁻¹ at 1 A g⁻¹ and maintained a capacity of 668 mA h g⁻¹ at 2 A g⁻¹; these capacities are much higher and more stable than those of ZFO nanoparticles prepared by a hydrothermal method (ZFO-HT) (216 and 117 mA h g⁻¹ at 1 and 2 A g⁻¹, respectively). Although ZFO-NRs exhibited high, stable capacities at moderate current densities for charging and discharging, the capacity rapidly decreased under fast charging/discharging conditions (>4 A g⁻¹). However, carbonized ZFO-NR (C/ZFO-NR) exhibited an improved reversible capacity and rate capability resulting from an increased conductivity compared with ZFO-NRs. The specific capacity of C/ZFO-NRs at 1 A g⁻¹ was 765 mA h g⁻¹; notably, a capacity of 680 mA h g⁻¹ was maintained at 6 A g⁻¹.

ZnFe₂O₄ nanorods were prepared by a simple thermochemical conversion of FeOOH nanorods, and exhibited an improved reversible capacity and rate capability.     

Preparation of cobalt sulfide@reduced graphene oxide nanocomposites with outstanding electrochemical behavior for lithium-ion batteries

Cobalt sulfide@reduced graphene oxide composites were prepared through a simple solvothermal method. The cobalt sulfide@reduced graphene oxide composites are composed of cobalt sulfide nanoparticles uniformly attached on both sides of reduced graphene oxide. Some favorable electrochemical performances in specific capacity, cycling performance, and rate capability are achieved using the porous nanocomposites as an anode for lithium-ion batteries. In a half-cell, it exhibits a high specific capacity of 1253.9 mA h g⁻¹ at 500 mA g⁻¹ after 100 cycles. A full cell consists of the cobalt sulfide@reduced graphene oxide nanocomposite anode and a commercial LiCoO₂ cathode, and is able to hold a high capacity of 574.7 mA h g⁻¹ at 200 mA g⁻¹ after 200 cycles. The reduced graphene oxide plays a key role in enhancing the electrical conductivity of the electrode materials; and it effectively prevents the cobalt sulfide nanoparticles from dropping off the electrode and buffers the volume variation during the discharge–charge process. The cobalt sulfide@reduced graphene oxide nanocomposites present great potential to be a promising anode material for lithium-ion batteries.

Cobalt sulfide@reduced graphene oxide nanocomposites obtained through a dipping and hydrothermal process, exhibit ascendant lithium-ion storage properties.