A high performance silicon/carbon composite anode with carbon nanofiber for lithium-ion batteries

The electrochemical performance of a composite of nano-Si powder and a pyrolytic carbon of polyvinyl chloride (PVC) with carbon nanofiber (CNF) was examined as an anode for lithium-ion batteries. CNF was incorporated into the composite by two methods; direct mixing of CNF with the nano-Si powder coated with carbon produced by pyrolysis of PVC (referred to as Si/C/CNF-1) and mixing of CNF, nano-Si powder, and PVC with subsequent firing (referred to as Si/C/CNF-2). The external Brunauer-Emmett-Teller (BET) surface area of Si/C/CNF-1 was comparable to that of Si/C/CNF-2. The micropore BET surface area of Si/C/CNF-2 (73.86 m² g⁻¹) was extremely higher than that of Si/C/CNF-1 (0.74 m² g⁻¹). The composites prepared by both methods exhibited high capacity and excellent cycling stability for lithium insertion and extraction. A capacity of more than 900 mA h g⁻¹ was maintained after 30 cycles. The coulombic efficiency of the first cycle for Si/C/CNF-1 was as low as 53%, compared with 73% for Si/C/CNF-2. Impedance analysis of cells containing these anode materials suggested that the charge transfer resistance for Si/C/CNF-1 was not changed by cycling, but that Si/C/CNF-2 had high charge transfer resistance after cycling. A composite electrode prepared by mixing Si/C/CNF-2 and CNF exhibited a high reversible capacity at high rate, excellent cycling performance, and a high coulombic efficiency during the first lithium insertion and extraction cycles.     

High performance Si/C@CNF composite anode for solid-polymer lithium-ion batteries

The electrochemical performance of a composite of nano-Si powder and a pyrolytic carbon of polyvinyl chloride (PVC) with carbon nanofiber (CNF) was examined as an anode for solid-polymer lithium-ion batteries. Nano-Si powder was firstly coated with carbon by pyrolysis of PVC and then mixed with CNF (referred to as Si/C@CNF) using a rotation mixer. The composite exhibited good cycling performance, but suffered from a large irreversible capacity loss of which the retention was less than 60%. In order to reduce the loss, a thin lithium sheet was attached to the Si/C@CNF electrode surface as a reducing agent. The irreversible capacity of the first cycle was lowered to as much as 0 mAh g⁻¹ and after the third cycle, the lithium insertion and extraction efficiency was almost 100%. A reversible capacity of more than 1000 mAh g⁻¹ was still maintained after 40 cycles.     

Novel carbon nanofiber-cobalt oxide composites for lithium storage with large capacity and high reversibility

Carbon nanofiber (CNF)-Co₃O₄ composites were prepared by the calcination of CNF-Co(OH)₂ composite precursors under argon atmosphere. SEM and TEM observations revealed that Co₃O₄ particles in the size of ca. 30–50 nm were highly dispersed and attached on the surface of the reticular CNF and all around. As for electrode materials, the CNF-Co₃O₄ composite demonstrated very high reversible capacity (more than 900 mAh g⁻¹ in the initial 50 cycles) and excellent electrochemical cycling stability. The improved cycle performance of the CNF-Co₃O₄ composite can be attributed to its unique reticular and morphology-stable composite texture with high dispersion of Co₃O₄ nanoparticles on the CNF that provides excellent electronic and ionic conduction pathway for the electrochemical processes.     

Improvement of cycle behaviour of SiO/C anode composite by thermochemically generated Li4SiO4 inert phase for lithium batteries

A new anode composite material is prepared by thermal treatment of a blend made of silicon monoxide (SiO) and lithium hydroxide (LiOH) at 550 °C followed by ball milling with graphite. X-ray diffraction pattern confirms the presence of Li₄SiO₄ in the thermally treated (SiO + LiOH) material. The electrode appears to be smooth and glassy as evident from observation with a scanning electron microscope (SEM), possibly due to the presence of nano-silicon and Li₄SiO₄ particles, and exhibits superior performance with a charge capacity of ∼333 mAh g⁻¹ at the 100th cycle with a low-capacity fade on cycling. Cyclic voltammograms of the electrode predict high power capability. On the other hand, the electrode comprising of only SiO and C prepared through ball milling, devoid of Li₄SiO_4, shows hard crust particulates in the electrode exhibiting low charge–discharge capacities with cycling.     

High-rate nano-crystalline Li4Ti5O12 attached on carbon nano-fibers for hybrid supercapacitors

A lithium titanate (Li₄Ti₅O₁₂)-based electrode which can operate at unusually high current density (300 C) was developed as negative electrode for hybrid capacitors. The high-rate Li₄Ti₅O₁₂ electrode has a unique nano-structure consisting of unusually small nano-crystalline Li₄Ti₅O₁₂ (ca. 5-20 nm) grafted onto carbon nano-fiber anchors (nc-Li₄Ti₅O₁₂/CNF). This nano-structured nc-Li₄Ti₅O₁₂/CNF composite are prepared by simple sol-gel method under ultra-centrifugal force (65,000 N) followed by instantaneous annealing at 900 °C for 3 min. A model hybrid capacitor cell consisting of a negative nc-Li₄Ti₅O₁₂/CNF composite electrode and a positive activated carbon electrode showed high energy density of 40 Wh L⁻¹ and high power density of 7.5 kW L⁻¹ comparable to conventional EDLCs.     

High reversible capacities of graphite and SiO/graphite with solvent-free solid polymer electrolyte for lithium-ion batteries

The combination of graphite or silicon monoxide (SiO)/graphite = 1/1 mixture with a solvent-free solid polymer electrolyte (SPE) was fabricated using a new preparation process, involving precoating the electrode with vapor-grown carbon fiber (VGCF) and binders (polyvinyl difluoride: PVdF or polyimide: PI), followed by the overcoating of the SPE. The reversible capacity of [graphite | SPE | Li] and [SiO/graphite | SPE | Li] cells were >360 and >1000 mAh g⁻¹ with 78% and 77% for the 1st Coulombic efficiency, respectively. The reversible capacities were 75% at the 250th cycle for [graphite | SPE | Li] and 72% at the 100th cycle for [SiO/graphite | SPE | Li]. The electrode used was compatible with that of the conventional liquid electrolyte system, and the SPE film could be formed on the electrode by the continuous overcoating process, which will lead to a low-cost electrodes and low-cost battery production. The solid-state lithium-ion polymer battery (SSLiPB) developed in this study, which consisted of [LiFePO₄ | SPE | graphite], showed the reversible capacity of 128 mAh g⁻¹ (based on the LiFePO₄ capacity) with favorable cycle performance.     

Microstructural controls of titanate nanosheet composites using carbon fibers and high-rate electrode properties for lithium ion secondary batteries

Composite electrodes of reassembled titanate and two kinds of carbon fibers were prepared and their high-rate electrode properties were examined. Multi-walled carbon nanotubes (MWNT) and vapor-grown carbon fibers (VGCF) were used for preparing the composites. The electronic conductivity of the MWNT composites increased with increasing contents of MWNT and exhibited a typical insulator-conductor transition. The MWNT composite with a MWNT content of 50 wt.% showed a capacity of 150 ± 5 mAh (g titanate)⁻¹ at a discharge rate of 0.67 C, and did not show a good high-rate capability due to the large content of hydrated water. The effect of the porous structure of the electrodes was revealed in the high-rate electrode properties of the microstructurally controlled composites with both MWNT and VGCF. The composites with 50 wt.% VGCF and 10 wt.% MWNT showed a reversible capacity of approximately 160 mAh (g titanate)⁻¹ at a discharge rate of 0.63 C and almost no capacity fading at relatively large discharge rate up to 19 C. A composite electrode with excellent high-rate capability was obtained by the microstructural control with carbon fibers.     

Anode properties of thick-film electrodes prepared by gas deposition of Ni-coated Si particles

Thick-film electrodes of Si particles coated with Ni, Ni-Sn, and Ni-P were fabricated by electroless deposition followed by gas deposition to form the anode of a Li-ion battery. The electrode of Ni-coated Si showed remarkably improved cycling performance with a discharge capacity of 580 mA h g⁻¹ at the 1000th cycle, which is possibly caused by its higher elastic modulus than that of the uncoated Si electrode. The electrode of Si coated with Ni-P, which consisted of Ni₃P, with the lower coating amount exhibited a higher initial capacity and excellent cycling performance with a capacity of 790 mA h g⁻¹ at the 1000th cycle, whereas poor performance was obtained for the electrode of Si coated with Ni-Sn. The excellent performance in the case of Ni-P coating is attributed to the smaller amount of coating, the high elastic modulus, and the lower reactivity of Ni₃P with Li ions in comparison with Ni₃Sn in Ni-Sn.     

Nickel hydroxide/activated carbon composite electrodes for electrochemical capacitors

In this paper, a nickel hydroxide/activated carbon (AC) composite electrode for use in an electrochemical capacitor was prepared by a simple chemical precipitation method. The structure and morphology of nickel hydroxide/AC were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that nano-sized nickel hydroxide was loading on the surface of activated carbon. Electrochemical performance of the composite electrodes with different loading amount was studied by cyclic voltammetry and galvanostatic charge/discharge measurements. It was demonstrated that the introduction of a small amount of nickel hydroxide to activated carbon could promote the specific capacitance of a composite electrode. The composite electrodes have good electrochemical performance and high charge–discharge properties. Moreover, when the loading amount of nickel hydroxide was 6 wt.%, the composite electrode showed a high specific capacitance of 314.5 F g⁻¹, which is 23.3% higher than pure activated carbon (255.1 F g⁻¹). Also, the composite electrochemical capacitor exhibits a stable cyclic life in the potential range of 0–1.0 V.     

Nanosized tin and tin oxides loaded expanded mesocarbon microbeads as negative electrode material for lithium-ion batteries

Tin-based composites using expanded mesocarbon microbeads (EMCMB) as matrix were prepared by impregnating tin chloride and the following reduction under hydrogen atmosphere at different temperatures. The morphologies and structural characteristics of the composites were investigated by FE-SEM, EDS and XRD measurements. It was found that tin exists inside EMCMB in the form of oxidation states (Sn(II) and Sn(IV)) after reduction at lower temperature (below 350 °C), and metallic tin exists both outside EMCMB and between carbon layers after reduction at higher temperature (450 °C). The electrochemical properties of the composites as negative electrode material for lithium-ion batteries were systematically investigated by cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy tests. The results showed that loading amount of tin or tin oxides and reduction temperature had large influences on the reversible capacity and cycle performance of these composites. Among them, the composite reduced at 230 °C with appropriate loading amount of tin oxides not only exhibited the high first reversible gravimetric capacity of 401 mAh g⁻¹ and an excellent cyclability with only 0.2% capacity loss/cycle at lower current density, but also showed a stable cycle performance at higher current density due to its lower resistance.     

Carbon nanofiber activated by molybdenum disulfide as an effective binder-free composite anode for highly reversible lithium storage

Carbon nanofiber film (CNF) as anode material for lithium-ion batteries (LIBs) draws attention for its excellent cyclic stability, but its practical application is limited due to low specific capacity. Considering the advantages of pure CNF and MoS₂, a flexible film which CNF covered by MoS₂ (MoS₂/CNF) is successfully produced and evaluated as a binder-free electrode for LIBs without mixing with carbon black and polymer binder. MoS₂ nanoflakes (8.91 wt% of the composite sample) covering on CNF (MoS₂/CNF-B sample) plays the key role in activating the electrochemical properties of CNF, but dense MoS₂ nanoflakes (39.4 wt%) on CNF (MoS₂/CNF-A) seriously limit the electrochemical properties of CNF. At 0.1 and 1.0 A g⁻¹, MoS₂/CNF-B sample delivers 967.1 and 605.7 mA h g⁻¹, the capacities are almost twice as much as those of pure CNF. The initial columbic efficiency of MoS₂/CNF-B sample of 76.4% is much higher than that of pure CNF sample of 62.1%. Moreover, MoS₂/CNF-B sample presents no capacity decay till 100 cycles, and the cycled electrode at the 100th cycle still maintains a stable composite structure of MoS₂ nanoflakes covering on CNF.     

Rechargeable lithium sulfide electrode for a polymer tin/sulfur lithium-ion battery

In this work we investigate the electrochemical behavior of a new type of carbon-lithium sulfide composite electrode. Results based on cyclic voltammetry, charge (lithium removal)-discharge (lithium acceptance) demonstrate that this electrode has a good performance in terms of reversibility, cycle life and coulombic efficiency. XRD analysis performed in situ in a lithium cell shows that lithium sulfide can be converted into sulfur during charge and re-converted back into sulfide during the following discharge process. We also show that this electrochemical process can be efficiently carried out in polymer electrolyte lithium cells and thus, that the Li₂S-C composite can be successfully used as cathode for the development of novel types of rechargeable lithium-ion sulfur batteries where the reactive and unsafe lithium metal anode is replaced by a reliable, high capacity tin-carbon composite and the unstable organic electrolyte solution is replaced by a composite gel polymer membrane that is safe, highly conductive and able to control dendrite growth across the cell. This new Sn-C/Li₂S polymer battery operates with a capacity of 600 mAh g⁻¹ and with an average voltage of 2 V, this leading to a value of energy density amounting to 1200 Wh kg⁻¹.     

Electrochemical performance of a tin-coated carbon fibre electrode for rechargeable lithium-ion batteries

An Sn-carbon fibre composite electrode is fabricated by electrodepositing a thin film (0.5 ± 0.1 μm) of Sn with an ultrafine grain size (350 ± 50 nm) on the 7.5 ± 1.5 μm diameter fibres of a carbon fibre paper (CFP). The electrochemical performance of the Sn-CFP composite being considered as an anode material for rechargeable Li-ion batteries is evaluated by conducting galvanostatic charge-discharge cycling tests. The Sn-CFP electrode displays a reversible planar capacity of 2.96 mAh cm⁻² with a capacity retention of 50% after twenty cycles, compared to the 23% measured for a 2.2 ± 0.2 μm thick Sn coating deposited on a Cu foil. The enhanced cycling performance of the Sn-CFP electrode is attributed to the double role played by carbon fibres, which act as randomly oriented current collectors in addition to being an active material. The small thickness and large surface area of the Sn coating on the carbon fibres enhances the coating's chemical reactivity and tolerance for volume change. It is suggested that transforming Sn to Sn oxides in Sn-CFP electrodes may improve the cycling performance of these composites as anode materials for rechargeable Li-ion batteries.     

Carbon-supported,nano-structured,manganese oxide composite electrode for electrochemical supercapacitor

Carbon-supported MnO₂ nanorods are synthesized using a microemulsion process and a manganese oxide/carbon (MnO₂/C) composite is investigated for use in a supercapacitor. As shown by high-resolution transmission electron microscopy the 2 nm × 10 nm MnO₂ nanorods are uniformly dispersed on the carbon surface. Cyclic voltammograms recorded for the MnO₂/C composite electrode display ideal capacitive behaviour between −0.1 and 0.8 V (vs. saturated calomel electrode) with high reversibility. The specific capacitance of the MnO₂/C composite electrode found to be 165 F g⁻¹ and is estimated to be as high as 458 F g⁻¹ for the MnO₂. Based on cyclic voltammetric life-cycle tests, the MnO₂/C composite electrode gives a highly stable and reversible performance for up to 10,000 cycles.     

Preparation and characterization of a new nanosized silicon–nickel–graphite composite as anode material for lithium ion batteries

A new type of nanosized silicon–nickel–graphite (Si–Ni–G) composite was prepared by high energy mechanical milling (HEMM) and pyrolysis using SiO as the precursor of Si for the first time. X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) and scanning electron microscopy (SEM) were used to determine the phases obtained and to observe the microstructure and distribution of the composite. The composite powders consisted of Si, Ni, SiO₂, NiO and a series of Si–Ni alloys. The formation of the inactive SiO₂ and Si–Ni alloy phases could accommodate the large volume changes of the active particles during cycling. In addition, cyclic voltammetry (CV) and galvanostatic discharge/charge tests were carried out to characterize the electrochemical properties of the composite. The composite electrodes exhibited an initial discharge and charge capacity of 1450.3 and 956.4 mAh g⁻¹, respectively, maintaining a reversible capacity of above 900 mAh g⁻¹ for nearly 60 cycles.     

Supercapacitive properties of polyaniline/Nafion/hydrous RuO2 composite electrodes

Chemically prepared polyaniline is tested for its supercapacitive behaviour in an aqueous electrolyte of 1.0 M H₂SO₄. In order to improve the cycleability of the polyaniline electrode, it is made into a composite with Nafion. This composite electrode shows improved cycleability and higher specific capacitance compared with a pure polyaniline electrode. It is therefore used as a matrix for the electrochemical deposition of hydrous RuO₂. The resulting ternary composite electrode has a high specific capacitance of 475 F g⁻¹ at 100 mV s⁻¹ and 375 F g⁻¹ at 1000 mV s⁻¹ in the voltage range of −0.2 to 0.8 V versus Ag/AgCl. All three types of electrode are characterized by cyclic voltammetry and impedance anaylsis.     

Electroless-plated tin compounds on carbonaceous mixture as anode for lithium-ion battery

A composite anode materials was prepared that contained tin compounds of Sn₆O₄(OH)₄, SnO₂ and Sn₃PO₄ on the surface of carbonaceous mixture mesophase graphite particles (MGP) and nature graphite (NG). The nanosize tin compounds were electrolessly plated from aqueous solutions onto the carbonaceous mixture. The morphology and structure of tin compounds were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the tin compounds particle size was a crucial factor to improve Sn compounds/Carbon composite anodes for cyclability and reversible capacity. The homogeneous dispersion and smaller particle size of tin compounds was attributed to the additive of NG. As the carbonaceous substrate was C-C mixture carbon, the particle size of Sn compounds was about 20-30 nm. However, the particle size was 100-200 nm, as the carbon substrate was singular MGP. Electrochemical performance test of the Sn compounds/C-C composite electrode shows the maximum specific charge capacity of 583 mAh g⁻¹ at the 5th cycle. The charge capacity retention of Sn compounds/C-C electrode was 85% after 20 cycles. The reversible capacity of Sn compounds/C-C electrode increased 292 and 97 mAh g⁻¹ more than pristine (NG + MGP) electrode and Sn compounds/C electrode at the 5th cycle, respectively.     

Anode properties of Ru-coated Si thick film electrodes prepared by gas-deposition

Thick film electrodes consisting of Ru and Ru-coated Si particles were fabricated by a gas-deposition method and their electrochemical properties of anodes for Li rechargeable battery were evaluated. The discharge capacity of the Ru electrode at 1000th cycle is approximately 400 mAh g⁻¹. The result showed that the electrode reaction is based on the redox reaction of RuO₂ which was formed on the Ru surface during the charge-discharge processes. By coating Si particles with Ru using an electroless deposition technique, we obtained an electrode with remarkable discharge capacity of 570 mAh g⁻¹ at 1000th cycle. The reason for the improvement in the electrode performance appears to result from the fact that the Ru electrode exhibits excellent cycleability itself and the Ru coated on Si reduces the stress generated by the immense volumetric changes occurring in the Si particles.     

Synthesis and characterization of the iron/copper composite as an electrode material for the rechargeable alkaline battery

Iron/copper composite particles were synthesized by a chemical reduction method and then used as the anode material for a rechargeable alkaline battery. The particle size and structure of the samples were characterized by SEM and XRD. Their electrochemical performance was also studied. The results showed that the iron/copper composite prepared by this method is nanosized. Copper improves the electron transfer between particles, and the nanosized iron/copper composite not only has a high electrochemical capacity of up to 800 mAh g⁻¹(Fe to Fe(III)), but also has an excellent rate-capacity performance at a current density of 3200 mA g⁻¹. Compared with the iron nanoparticle without copper, the iron/copper composite sample maintains a smaller particle size during electrochemical cycling, and therefore improves the cycling stability of the iron electrode.     

Long cycle-life LiFePO4/Cu-Sn lithium ion battery using foam-type three-dimensional current collector

To improve the cycle-life performance of LiFePO₄/Cu-Sn lithium ion battery, a new methodology using a foam-type three-dimensional current collector was investigated. By applying the three-dimensional nickel substrate for the negative electrode, instead of conventional copper foil, the cycle performance of the Cu-Sn electrode was improved. In addition, a heat treatment of the electrode was revealed to suppress the capacity decline drastically: the heat treated electrode showed the capacity above 400 mAh g⁻¹ even after 50 cycles. A full-cell which combined the developed negative electrode and a positive electrode based on LiFePO₄ also showed a favorable cycle performance. Furthermore, a full-cell using aqueous slurry was prepared, and the cell exhibited an excellent cycle-life performance in which it maintained above 90% of the maximum capacity even at the 200th cycle.