Electrochemical properties of carbon-coated Si/B composite anode for lithium ion batteries

Carbon-coated Si and Si/B composite powders prepared by hydrocarbon gas (argon + 10 mol% propylene) pyrolysis were investigated as the anodes for lithium-ion batteries. Carbon-coated silicon anode demonstrated the first discharge and charge capacity as 1568 mAh g⁻¹ and 1242 mAh g⁻¹, respectively, with good capacity retention for 10 cycles. The capacity fading rate of carbon-coated Si/B composite anode decreased as the amounts of boron increased. In addition, the cycle life of carbon-coated Si/B/graphite composite anode has been significantly improved by using sodium carboxymethyl cellulose (NaCMC) and styrene butadiene rubber (SBR)/NaCMC mixture binders compared to the poly(vinylidene fluoride, PVdF) binder. A reversible capacity of about 550 mAh g⁻¹ has been achieved at 0.05 mAm g⁻¹ rate and its capacity could be maintained up to 450 mAh g⁻¹ at high rate of 0.2 mAm g⁻¹ even after 30 cycles. The improvement of the cycling performance is attributed to the lower interfacial resistance due to good electric contact between silicon particles and copper substrate.     

Application of bis(fluorosulfonyl)imide-based ionic liquid electrolyte to silicon-nickel-carbon composite anode for lithium-ion batteries

An ionic liquid electrolyte containing bis(fluorosulfonyl)imide (FSI) anion without any solvent is applied to a silicon-nickel-carbon (Si-Ni-carbon) composite anode for rechargeable lithium (Li)-ion batteries. The FSI-based ionic liquid electrolyte successfully provides a stable, reversible capacity for the Si-Ni-carbon anode, which is comparable to the performance observed in a typical commercialized solvent-based electrolyte, while a common ionic liquid electrolyte containing bis(trifluoromethanesulfonyl)imide (TFSI) anion without FSI presents no reversible capacity to the anode at all. Ac impedance analysis reveals that the FSI-based electrolyte provides very low interfacial and charge-transfer resistances at the Si-based composite anode, even when compared to the corresponding resistances observed in a typical solvent-based electrolyte. Galvanostatic cycling of the Si-based composite anode in the FSI-based electrolyte with a charge limitation of 800 mAh g⁻¹ is stable and provides a discharge capacity of 790 mAh g⁻¹ at the 50th cycle, corresponding to a cycle efficiency of 98.8%.     

Nanocone-arrays supported tin-based anode materials for lithium-ion battery

The electrodeposited nickel nanocone-arrays without any template are introduced to Sn-based anode materials as current collector for lithium ion battery. Nickel nanocone-arrays are tightly wedged in the electrodeposited Sn film, and thereby enhance the interfacial strength between active materials and substrate. Furthermore, annealing is conducted to form Sn-Ni alloy, in which Ni renders an inactive matrix to buffer volume change during cyclic lithiation/delithiation. The nanocone-arrays supported Sn-Ni alloy anode shows satisfactory Li⁺ storage properties with the first reversible capacity of 807 mAh g⁻¹. The charge capacity for the 50th cycle is 678 mAh g⁻¹, delivering good retention rate of 99.6% per cycle. These improved performances of nickel nanocone-arrays supported Sn-Ni alloy anodes indicate the potential of their application as electrode materials for high performance energy storage.     

Preparation and electrochemical properties of carbon-doped TiO2 nanotubes as an anode material for lithium-ion batteries

Carbon-doped TiO₂ nanotubes were synthesized through a sol–gel and subsequent hydrothermal process. Transmission electron microscopy and X-ray diffraction showed that the products are uniformly straight tubes with the diameter around 10 nm in anatase-type. The electrochemical performances of the nanotubes were tested by constant current discharge/charge, cyclic voltammetry, and electrochemical impedance spectroscopy. The initial discharge capacity reaches 291.7 mAh g⁻¹ with a coulombic efficiency of 91.7% at a current density of 70 mA g⁻¹. There is a distinct potential plateau near 1.75 and 1.89 V (versus Li⁺/Li) in the lithium intercalation and extraction processes, respectively, and the lithium insertion capacity is about 204 mAh g⁻¹ over the plateau of 1.75 V region in the first cycle. From the 2nd to the 30th cycles, the average reversible capacity loss is less than 1.73 mAh g⁻¹ per cycle. After 30 cycles, the reversible capacity still remains 211 mAh g⁻¹ with a coulombic efficiency larger than 99.7%, implying a perfect reversibility and cycling stability.     

Carbothermal synthesis of Sn-based composites as negative electrode for lithium-ion batteries

The composite [Sn-BPO₄/xC] to be used as negative electrode material for the storage of electrochemical energy was obtained by dispersing electroactive tin species onto a BPO₄ buffer matrix by carbothermal reduction of a mixture of SnO₂ and nanosized BPO₄. This composite material was thoroughly characterized by X-ray diffraction, Scanning Electron Microscopy, ¹¹⁹Sn Mössbauer spectroscopy and Raman spectroscopy. The electrochemical tests of this new material highlight its very interesting electrochemical properties, i.e., a discharge capacity of 850 mAh g⁻¹ for the first cycle and reversible capacity around 585 mAh g⁻¹ at C/5 rate. These electrochemical performances are attributed to the very high dispersion and stabilisation of tin metal particles onto the BPO₄ matrix. The irreversible capacity observed for the first charge/discharge cycle is due the reduction of interfacial Sn^II species and to the passivation of the anode surface by liquid electrolyte decomposition (formation of the SEI layer).     

Cycleable graphite/FeSi6 alloy composite as a high capacity anode material for Li-ion batteries

FeSi₆/graphite composite was prepared by mechanical ball milling. The FeSi₆ alloy particles consist of an electrochemically active silicon phase and inactive phases FeSi₂, distributed uniformly in the graphite matrix. The composite anode offers a large reversible capacity (about 800 mAh g⁻¹) and good cycleability, due to the buffering effect of the inactive FeSi₂ phase and graphite layers on the volumetric changes of Si phase during lithium–Si alloying reaction. Since FeSi₆ alloy is a low-cost industrial material, this alloy compound provides a possible alternative for development of high capacity lithium-ion batteries.     

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.     

Silicon-coated carbon nanofiber hierarchical nanostructures for improved lithium-ion battery anodes

Silicon-coated carbon nanofibers (CNFs) are a viable method of exploiting silicon's capacity in a battery anode while ameliorating the complications of silicon expansion as it alloys with lithium. Silicon-coated CNFs were fabricated through chemical vapor deposition and deposited onto a carbon fiber mesh. This novel anode material demonstrated a capacity of 954 mAh g⁻¹ in the first cycle, but faded to 766 mAh g⁻¹ after 20 cycles. Structural characterization of the samples before and after cycling was carried out using field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results suggest that a portion of the fade may be due to separation of the silicon coating from the CNFs. Enough silicon remains in contact with the conductive network of CNFs to allow a usable reversible capacity that well exceeds that of graphite. An anode of this material can double the capacity of a lithium-ion battery or allow a 14% weight reduction.     

Temperature-controlled microwave solid-state synthesis of Li3V2(PO4)3 as cathode materials for lithium batteries

Monoclinic Li₃V₂(PO₄)₃ can be rapidly synthesized at 750 °C for 5 min (MW5m) by using temperature-controlled microwave solid-state synthesis method (TCMS). The carbon-free sample MW5m presents well electrochemical properties. In the cut-off voltage 3.0-4.3, MW5m presents a charge capacity 132 mAh g⁻¹, almost equivalent to the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹), and discharge capacity 126.4 mAh g⁻¹. In the cut-off voltage 3.0-4.8 V, MW5m shows an initial discharge capacity of 183.4 mAh g⁻¹, near to the theoretical discharge capacity. In the cycle performance, the capacity fade of Li₃V₂(PO₄)₃ is dependent on the cut-off voltage and the preparation method.     

Reduced graphene oxide/tin oxide composite as an enhanced anode material for lithium ion batteries prepared by homogenous coprecipitation

Reduced graphene oxide/tin oxide composite is prepared by homogenous coprecipitation. Characterizations show that tin oxide particles are anchored uniformly on the surface of reduced graphene oxide platelets. As an anode material for Li ion batteries, it has 2140 mAh g⁻¹ and 1080 mAh g⁻¹ capacities for the first discharge and charge, respectively, which is more than the theoretical capacity of tin oxide, and has good capacity retention with a capacity of 649 mAh g⁻¹ after 30 cycles. The simple synthesis method can be readily adapted to prepare other composites containing reduced graphene oxide as a conducting additive that, in addition to supporting metal oxide nanoparticles, can also provide additional Li binding sites to, perhaps, further enhance capacity.     

Catalytically graphitized glass-like carbon examined as anode for lithium-ion cell performing at high charge/discharge rates

The influence of a long-time heat treatment of hard carbon in the presence of iron catalyst on its structural properties and electrochemical performance is concerned in terms of potential application as anode material for lithium-ion cell. Glass-like carbon spheres obtained by carbonization of phenol resin were catalytically graphitized by heat treatment at temperature 1000 °C in argon atmosphere for 20 h and 100 h. After this process iron was completely removed from the product of reaction. The original carbon was entirely useless as anode for Li-ion cell because of its extremely poor reversible capacity (54 mAh g⁻¹). Due to heat treatment composite materials consisting of microcrystalline graphite admixed with turbostratic carbon were produced. Modified carbons were tested as anode materials using gradually increasing current density. Based on electrochemical measurements a mixed intercalation/insertion mechanism for storage of lithium ions was concluded. Discharge capacity of carbon heat treated for 100 h attained value of 276 mAh g⁻¹ and its reversible capacity appeared to be better than that of flaky graphite upon discharging at current density in the range 50-250 mA g⁻¹.     

Improvement of cyclic behavior of a ball-milled SiO and carbon nanofiber composite anode for lithium-ion batteries

The cyclic performance of a composite SiO and carbon nanofiber (CNF) anode was examined for lithium-ion batteries. SiO powder of several micrometers was pulverized using high energy mechanical milling. The SiO was ball-milled for 12 h with CNF to produce a composite electrode material that exhibited excellent cycling performance. A reversible capacity of approximately 700 mAh g⁻¹ was observed after 200 cycles. The excellent cyclic performance was discussed with respect to the change of the valence state of Si by ball-milling. A large irreversible capacity at the first cycle for the SiO/CNF composite electrode was reduced to 2% by chemically pre-charging with a lithium film attached to the rim of the electrode.     

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.     

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.     

Co-doped NiO nanoflake arrays toward superior anode materials for lithium ion batteries

Co-doped NiO nanoflake arrays with a cellular-like morphology are fabricated by low temperature chemical bath deposition. As anode material for lithium ion batteries (LIBs), the array film shows a capacity of 600 mAh g⁻¹ after 50 discharge/charge cycles at low current density of 100 mA g⁻¹, and it retains 471 mAh g⁻¹ when the current density is increased to 2 A g⁻¹. Appropriate electrode configuration possesses some unique features, including high electrode-electrolyte contact area, direct contact between each naonflake and current collector, fast Li⁺ diffusion. The Co²⁺ partially substitutes Ni³⁺, resulting in an increase of holes concentration, and therefore improved p-type conductivity, which is useful to reduce charge transfer resistance during the charge/discharge process. The synergetic effect of these two parts can account for the improved electrochemical performance.     

Autogenic reactions for preparing carbon-encapsulated, nanoparticulate TiO2 electrodes for lithium-ion batteries

We report an anhydrous, autogenic technique for synthesizing electronically interconnected, carbon-encapsulated, nanoparticulate anatase anode materials (TiO₂-C) for lithium-ion batteries. The TiO₂-C nanoparticles provide a reversible capacity of ∼200 mAh g⁻¹, which exceeds the theoretical capacity of the commercially attractive spinel anode, Li₄Ti₅O₁₂ (175 mAh g⁻¹) and is competitive with the capacity reported for other TiO₂ products. The processing method is extremely versatile and has implications for preparing, in a single step, a wide variety of electrochemically active compounds that are coated, in situ, with carbon.     

Morphology effect on the electrochemical performance of NiO films as anodes for lithium ion batteries

NiO films were prepared by chemical bath deposition and electrodeposition method, respectively, using nickel foam as the substrate. The films were characterized by scanning electron microscopy (SEM) and the images showed that their morphologies were distinct. The NiO film prepared by chemical bath deposition was highly porous, while the film prepared by electrodeposition was dense, and both of their thickness was about 1 μm. As anode materials for lithium ion batteries, the porous NiO film prepared by chemical bath deposition exhibited higher coulombic efficiency and weaker polarization and its specific capacity after 50 cycles was 490 mAh g⁻¹ at the discharge–charge current density of 0.5 A g⁻¹, and 350 mAh g⁻¹ at 1.5 A g⁻¹, higher than the electrodeposited film (230 mAh g⁻¹ at 0.5 A g⁻¹, and 170 mAh g⁻¹ at 1.5 A g⁻¹). The better electrochemical performances of the film prepared by chemical bath deposition are attributed to its highly porous morphology, which shorted diffusion length of lithium ions, and relaxed the volume change caused by the reaction between NiO and Li⁺.     

Reversible high capacity nanocomposite anodes of Si/C/SWNTs for rechargeable Li-ion batteries

Nanocomposites comprising silicon (Si), graphite (C) and single-walled carbon nanotubes (SWNTs), denoted as Si/C/SWNTs, have been synthesized by dispersing SWNTs via high power ultrasonication into a pre-milled Si/C composite mixture, followed by subsequent thermal treatment. The Si/C composite powder was prepared by high-energy mechanical milling (HEMM) of elemental Si and graphite using polymethacrylonitrile (PMAN) as a diffusion barrier suppressing the possible mechanochemical reaction between silicon and graphite to form SiC, and further prevent the amorphization of graphite during extended milling. A nanocomposite with nominal composition of Si-35 wt.% SWNTs-37 wt.% exhibits a reversible discharge capacity of ∼900 mAh g⁻¹ with an excellent capacity retention of capacity loss of 0.3% per cycle up to 30 cycles. Functionalization of the SWNTs with LiOH significantly improves the cyclability of the nanocomposite containing Si-45 wt.% SWNTs-28 wt.% exhibiting a reversible capacity of 1066 mAh g⁻¹ and displaying almost no fade in capacity up to 30 cycles. The improved electrochemical performance is hypothesized to be attributed to the formation of a nanoscale conductive network by the dispersed SWNTs which leads to successful maintenance of good electrical contact between the electrochemically active particles during cycling.     

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.     

Preparation and electrochemical properties of Li4Ti5O12 thin film electrodes by pulsed laser deposition

Spinel Li₄Ti₅O₁₂ thin film anode material for lithium-ion batteries is prepared by pulsed laser deposition. Thin film anodes are deposited at ambient temperature, then annealed at three different temperatures under an argon gas flow and the influence of annealing temperatures on their electrochemical performances is studied. The microstructure and morphology of the films are characterized by XRD, SEM and AFM. Electrochemical properties of the films are evaluated by using galvanostatic discharge/charge tests, cyclic voltammetry and a.c. impedance spectroscopy. The results reveal that all annealed films crystallize and exhibit good cycle performance. The optimum annealing temperature is about 700 °C. The steady-state discharge capacity of the films is about 157 mAh g⁻¹ at a medium discharge/charge current density of 10 μA cm⁻². At a considerably higher discharge/charge current density of 60 μA cm⁻² (about 3.45 C) the discharge capacity of the films remains steady at a relative high value (146 mAh g⁻¹). The cycleability of the films is excellent. This implies that such films are suitable for electrodes to be used at high discharge/charge current density.