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.     

A study on the electrochemical characteristics of LiFePO4 cathode for lithium polymer batteries by hydrothermal method

Phospho-olivine LiFePO₄ cathode materials were prepared by hydrothermal reaction at 150 °C. Carbon black was added to enhance the electrical conductivity of LiFePO₄. LiFePO₄-C powders (0, 3, 5 and 10 wt.%) were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). LiFePO₄-C/solid polymer electrolyte (SPE)/Li cells were characterized electrochemically by charge/discharge experiments at a constant current density of 0.1 mA cm⁻² in a range between 2.5 and 4.3 V vs. Li/Li⁺, cyclic voltammetry (CV) and ac impedance spectroscopy. The results showed that initial discharge capacity of LiFePO₄ was 104 mAh g⁻¹. The discharge capacity of LiFePO₄-C/SPE/Li cell with 5 wt.% carbon black was 128 mAh g⁻¹ at the first cycle and 127 mAh g⁻¹ after 30 cycles, respectively. It was demonstrated that cycling performance of LiFePO₄-C/SPE/Li cells was better than that of LiFePO₄/SPE/Li cells.     

Spray-pyrolyzed silicon/disordered carbon nanocomposites for lithium-ion battery anodes

A new and effective approach to prepare carbon-coated Si nanocomposites as high capacity anode materials for lithium-ion batteries with markedly improved electrochemical performance is described. Initially, nanosized Si particles (<100 nm) were mixed with different concentrations of the carbon source precursor, citric acid in ethanol solution via ultrasonication. Spray pyrolysis of these mixtures at 400 °C in air resulted in an amorphous carbon coating on the spherical Si nanoparticles. High-resolution transmission electron microscopy (HRTEM) analysis confirms a homogeneous layer of amorphous carbon coating of ∼10 nm. These resultant nanocomposites show excellent cycling performance, especially when the disordered carbon (DC) content is above 50 wt.%. The 44Si/56DC nanocomposite shows the highest specific capacity retention of 1120 mAh g⁻¹ after 100 cycles. The carbon-coating on the nanocrystalline Si particles appears to be the main reason for the good cyclability, suggesting the excellent potential of these Si/DC-based nanocomposites for use as alternative anodes for lithium-ion batteries.     

C-rate performance of silicon oxycarbide anodes for Li+ batteries enhanced by carbon nanotubes

We show that employing single wall carbon nanotubes (CNTs) as the conducting agent significantly increases the capacity of silicon oxycarbide anodes at high C-rates. In these anodes 515 mAh g⁻¹ can be extracted in just over 3 min. The capacity decreases to 300 mAh g⁻¹ at the same extraction rate when carbon black is used as the conducting agent. The CNT anodes have good cyclic stability, retaining 89.2% of initial capacity after 40 cycles. The coulombic efficiency ranges from 95% to 100%.     

Silicon,graphite and resin based hard carbon nanocomposite anodes for lithium ion batteries

Nanocomposite based on graphite (C), silicon (Si) and poly[(o-cresyl glycidyl ether)-co-formaldehyde] resin based amorphous hard carbon (HC), denoted as Si/C/HC, have been synthesized by thermal treatment of mechanically milled graphite, silicon and resin of nominal composition C–18 wt.% Si–40 wt.% resin at 973 K, 1073 K and 1173 K in ultrahigh purity argon atmosphere. The formation of the electrochemically inactive SiC is bypassed as well as the amorphization kinetics of graphite is reduced during prolonged milling of graphite and Si in the presence of the resin. Microstructural analysis has confirmed that the Si nanoparticle gets embedded, and is homogeneously dispersed and distributed on the graphite matrix after mechanical milling as well as after thermal treatment. Electrochemical studies have revealed that the Si/C/HC based nanocomposite, tested as a lithium ion anode, synthesized after thermal treatment at 1173 K exhibits a stable capacity of ∼640 mAh g⁻¹ with an excellent capacity retention when cycled at a rate of ∼160 mA g⁻¹. The nanocomposite anode also shows a moderate rate capability when cycled at different discharge/charge rates. Scanning electron microscopy analysis indicates that the structural integrity and the microstructural stability of the nanocomposite during the alloying/dealloying process contribute to the good cyclability observed in the above nanocomposites.     

Carboxymethylcellulose and carboxymethylcellulose-formate as binders in MgH2-carbon composites negative electrode for lithium-ion batteries

Influence of carboxymethylcellulose sodium salt (CMC) and carboxymethylcellulose-formate (CMC-f) binders on the cyclability of a MgH₂-33.3% CMC type binder-33.3%C_t,x electrodes has been investigated for the first time. These electrodes show a large reversible capacity of 1800-1900 mAh g⁻¹ at an average voltage of 0.5 V vs. Li⁺/Li° which is suitable for the negative electrode in lithium-ion batteries. Moreover, addition of CMC or CMC-f binder with C_t,x carbon leads to an improved capacity retention with 240 mAh g⁻¹ and 542 mAh g⁻¹, respectively, compare to 174 mAh g⁻¹ for MgH₂-18%C_t,x after 40 cycles.     

Porous micro-spherical aggregates of LiFePO4/C nanocomposites: A novel and simple template-free concept and synthesis via sol-gel-spray drying method

Porous micro-spherical aggregates of LiFePO₄/C nanocomposites were prepared with a process of spray drying at 200 °C and subsequent heat treatment at 700 °C for 12 h by a novel and simple template-free sol-gel-SD method independent of surfactants or templates. The results indicate that the as-obtained LiFePO₄ porous microspheres have the mean diameter of 19.8 μm, average pore size of 45 nm, and large specific surface area (20.2 m² g⁻¹) with evenly distributed carbon (4.5 wt.%). The particles can be easily brought into contact with electrolyte, facilitating electric and lithium ion diffusion. They present large reversible discharge capacity of 137.5 mAh g⁻¹ at the current density of 0.1 C, good rate capacity of 53.8 mAh g⁻¹ at 10 C, and excellent capacity retention rate closed to 100% after various current densities in the region of 2.0-4.3 V.     

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.     

All-solid-state lithium secondary batteries with high capacity using black phosphorus negative electrode

Black phosphorus was prepared from red phosphorus by using mixer mill and planetary ball-mill apparatuses. The composites with black phosphorus and acetylene black (AB) were also prepared by using the mixer mill apparatus. The mechanical milling of black phosphorus and AB brought about a decrease in size of secondary particles of the composites. The all-solid-state lithium cells with the composite and the Li₂S-P₂S₅ glass-ceramic electrolyte exhibited the first discharge capacity of 1962 mAh g⁻¹ and the coulombic efficiency of 89% at the current density of 0.064 mA cm⁻² (24 mA g⁻¹). The all-solid-state cells worked at 3.8 mA cm⁻² (1.47 A g⁻¹) at 25 °C and showed the excellent cycle performance with a high capacity of over 500 mAh g⁻¹ for 150 cycles. Black phosphorus is one of the most attractive negative electrodes with both high capacity and high-rate performance in all-solid-state lithium rechargeable batteries with sulfide electrolytes.     

Significant effects of poly(3,4-ethylenedioxythiophene) additive on redox responses of poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) cathode for rechargeable Li batteries

Redox behaviors of the poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM)-coated electrodes composited with carbon black (CB) or poly(3,4-ethylenedioxy-thiophene) (PEDOT) are presented. Effects of PEDOT additive on the redox activity of PDBM were investigated to apply their composite materials as candidates of cathodes for rechargeable lithium batteries. The film having a PEDOT/PDBM with weight ratio of 1/1 shows a gravimetric capacity of 129 mAh g⁻¹ (corresponding to 188 mAh g⁻¹ for PDBM and 70 mAh g⁻¹ for PEDOT). The highest energy density observed was 140 mAh g⁻¹ (406 mWh g⁻¹) for the composite cathode. Good cycle-ability over 100 cycles was attained with a PEDOT/PDBM composite cathode.     

Electrochemical characterizations of multi-layer and composite silicon-germanium anodes for Li-ion batteries using magnetron sputtering

To improve the electrochemical performance of Si film, we investigate the addition of two film forms of Ge. Si/Ge multi-layered and Si-Ge composite electrodes that are fabricated by magnetron sputtering onto Cu current collector substrates are investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and extended X-ray absorption fine structure (EXAFS) are employed to analyze the structures of the Si-Ge electrodes. When used as an anode electrode for a lithium ion battery, the first discharge capacity of a Si/Ge 150 multi-layer cell with a ratio of Si 15 nm/Ge 3 nm is 2099 mAh g⁻¹ between 1.1 and 0.01 V. A stable reversible capacity of 1559 mAh g⁻¹ is maintained after 100 cycles with a capacity retention rate of 74.25%. Additionally, the Si_0.84Ge_0.16 composite has an initial discharge capacity of 1915 mAh g⁻¹ and a capacity retention of 74.25%. In full cell tests of Si-Ge electrodes, the Si_0.84Ge_0.16/LiCoO₂ cell delivers a specific capacity of approximatly 160 mAh g⁻¹ and a capacity retention of 52.4% after 100 cycles. The results reveal that these two systems of sputtered Si-Ge electrodes can be used as anodes in lithium ion batteries with higher energy densities.     

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.     

Silicon and silicon-copper composite nanorods for anodes of Li-ion rechargeable batteries

We investigate the anode performance of Si-based nanorods by tuning its composition using an oblique (co)deposition technique. Our results show that pure Si nanorods have a higher initial anodic capacity of 1500 mAh g⁻¹, but the capacity diminishes after 50 cycles due to the morphological change and pulverization. By introducing approximately 70 at.% Cu into Si nanorods, the Si-Cu composite nanorods demonstrate 500 mAh g⁻¹ of capacity sustainable in 100 cycles, which is attributed to the flexibility and improved toughness of Si-Cu composite nanorods.     

Synthesis and characterization of Carbon Nano Fiber/LiFePO4 composites for Li-ion batteries

Carbon Nano Fibers (CNFs) coated with LiFePO₄ particles have been prepared by a non-aqueous sol–gel technique. The functionalization of the CNFs by HNO₃ acid treatment has been confirmed by Raman and XPS analyses. The samples pure LiFePO₄ and LiFePO₄–CNF have been characterized by XRD, SEM, RAMAN, XPS and electrochemical analysis. The LiFePO₄–CNF sample shows better electrochemical performance compared to as-prepared LiFePO₄. LiFePO₄–CNF (10 wt.%) delivers a higher specific capacity (∼140 mAh g⁻¹) than LiFePO₄ with carbon black (25 wt.%) added after synthesis (∼120 mAh g⁻¹) at 0.1C.     

Polyaniline and polyaniline–carbon nanotube composite fibres as battery materials in ionic liquid electrolyte

New battery materials are presented that consist of either a solid polyaniline (PANi) fibre or the same fibre containing carbon nanotubes (CNTs). An ionic liquid ethylmethyl imidazolium bis(trifluoromethanesulfonyl) amide (EMI.TFSA) is used as electrolyte. The electrochemical properties of PANi and PANi/CNT fibres are investigated by means of cyclic voltammetry, a.c. impedance and galvanostatic charge–discharge techniques. A PANi fibre with a CNT content of 0.25 wt.% exhibits a discharge capacity of 12.1 mAh g⁻¹.     

Vertically aligned carbon nanotube electrodes for lithium-ion batteries

As portable electronics become more advanced and alternative energy demands become more prevalent, the development of advanced energy storage technologies is becoming ever more critical in today's society. In order to develop higher power and energy density batteries, innovative electrode materials that provide increased storage capacity, greater rate capabilities, and good cyclability must be developed. Nanostructured materials are gaining increased attention because of their potential to mitigate current electrode limitations. Here we report on the use of vertically aligned multi-walled carbon nanotubes (VA-MWNTs) as the active electrode material in lithium-ion batteries. At low specific currents, these VA-MWNTs have shown high reversible specific capacities (up to 782 mAh g⁻¹ at 57 mA g⁻¹). This value is twice that of the theoretical maximum for graphite and ten times more than their non-aligned equivalent. Interestingly, at very high discharge rates, the VA-MWNT electrodes retain a moderate specific capacity due to their aligned nature (166 mAh g⁻¹ at 26 A g⁻¹). These results suggest that VA-MWNTs are good candidates for lithium-ion battery electrodes which require high rate capability and capacity.     

All solid-state battery with sulfur electrode and thio-LISICON electrolyte

A high-capacity type of all solid-state battery was developed using sulfur electrode and the thio-LISICON electrolyte. New nano-composite of sulfur and acetylene black (AB) with an average particle size of 1–10 nm was fabricated by gas-phase mixing and showed a reversible capacity of 900 mAh g⁻¹ at a current density of 0.013 mA cm⁻².     

Preparation and electrochemical characterization of ionic-conducting lithium lanthanum titanate oxide/polyacrylonitrile submicron composite fiber-based lithium-ion battery separators

Lithium lanthanum titanate oxide (LLTO)/polyacrylonitrile (PAN) submicron composite fiber-based membranes were prepared by electrospinning dispersions of LLTO ceramic particles in PAN solutions. These ionic-conducting LLTO/PAN composite fiber-based membranes can be directly used as lithium-ion battery separators due to their unique porous structure. Ionic conductivities were evaluated after soaking the electrospun LLTO/PAN composite fiber-based membranes in a liquid electrolyte, 1 M lithium hexafluorophosphate (LiPF₆) in ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (1:1 vol). It was found that, among membranes with various LLTO contents, 15 wt.% LLTO/PAN composite fiber-based membranes provided the highest ionic conductivity, 1.95 × 10⁻³ S cm⁻¹. Compared with pure PAN fiber membranes, LLTO/PAN composite fiber-based membranes had greater liquid electrolyte uptake, higher electrochemical stability window, and lower interfacial resistance with lithium. In addition, lithium//1 M LiPF₆/EC/EMC//lithium iron phosphate cells containing LLTO/PAN composite fiber-based membranes as the separator exhibited high discharge specific capacity of 162 mAh g⁻¹ and good cycling performance at 0.2 C rate at room temperature.     

CoO-loaded graphitable carbon hollow spheres as anode materials for lithium-ion battery

A new type of CoO nanoparticles encapsulated by graphitable hollow carbon sphere (GHCS) composite material was synthesized. The core–shell structure CoO/GHCS composite shows the improved cyclability as an anodic material in Li-ion battery. The core–shell composite containing 50 wt% CoO exhibits a reversible capacity of 584 mAh g⁻¹ at a constant current density of 100 mA g⁻¹ between 0 and 3.0 V (vs. Li⁺/Li), and remains a capacity retention of 95% after 50th cycle. The improvement could be attributed to that the GHCS with a good electronic conductivity and high surface severs as dispersing medium to prevent CoO nanoparticles from aggregating, and provide the enough space to buffer the volume change during the Li-ion insertion and extraction reactions in CoO nanoparticles.     

Enhancement of electrochemical performance of lithium dry polymer battery with LiFePO4/carbon composite cathode

LiFePO₄/carbon composite electrode was prepared and applied to the dry polymer electrolyte. Enhanced low-temperature performance of LiFePO₄ was achieved by modifying the interface between LiFePO₄ and polymer electrolyte. The molecular weight of the polymer and the salt concentration as the Li/O ratio were optimized at 3 × 10⁵ and 1/10, respectively. Impedance analysis revealed that a small resistive component occurred in the frequency range of the charge transfer process. The reversible capacity of the laminate cell was 140 mAh g⁻¹ (C/20) and 110 mAh g⁻¹ (C/2) at 40 °C, which is comparable to the performance in the liquid electrolyte system.