Strategic dispersion of carbon black and its application to ink-jet-printed lithium cobalt oxide electrodes for lithium ion batteries

The effects of surface-modified carbon black induced by UV/ozone and triethylenetetramine on the microstructure and electrochemical properties of ink-jet-printed LiCoO₂ electrodes for lithium ion batteries are observed. The dispersion properties of surface-modified carbon black and LiCoO₂ ink are evaluated using particle size distribution measurements, surface pressure calculations, and scanning electron microscopy. Modifications to the surface of carbon black result in improved dispersion properties, which in turn enhance the compactness and homogeneity of the microstructure of ink-jet-printed LiCoO₂ electrodes compared to those printed with as-received carbon black. Electrochemical experiments indicate that LiCoO₂ electrodes ink-jet-printed with surface-modified carbon black exhibit improved initial specific discharge capacities compared to those printed with as-received carbon black due to the better electrical contact between the carbon black and the LiCoO₂, as evidenced by the analysis of the area-specific impedance of the electrode as a function of the depth of discharge.     

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.     

Crystal chemistry modification of lithium nickel cobalt oxide cathodes for lithium ion rechargeable batteries

As a cathode material for lithium ion rechargeable batteries, LiNi_0.8Co_0.2O₂ (LNCO) is one of the most attractive candidates for high power electronic devices. In the present work, we have synthesized LNCO powder by solid-state route. The discharge capacity and the capacity retention of LNCO cathode are found to be 100 mAh g⁻¹ and 63%, respectively. Molybdenum doping, replacing parts of cobalt ion in LNCO lattice increases the discharge capacity (157 mAh g⁻¹) and improve its capacity retention characteristics. Through X-ray Rietveld analyses, we have found that Mo doping increases the inter-slab spacing between the (Co,Ni)O₂ octahedral layers which provides easier Li¹⁺ intercalation leading to improved electrochemical properties in the modified cathode.     

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⁺.     

Structural characterization and electrochemical properties of non-graphitizable carbons for a lithium ion battery

Structural characteristics and electrochemical properties of non-graphitizable carbons were investigated. The carbons were obtained by heat-treating the oxidized graphitizable carbon precursors with various molar ratios of aromatic compounds and cross-linking agent. The discharge profiles of the non-graphitizable carbons heat-treated at 600°C had one plateau discharge region at 1.0 V vs. Li/Li⁺, which is similar to graphitizable ones heat-treated at the temperature. However, the discharge profiles of the non-graphitizable carbons heat-treated above 800°C exhibited two plateau discharge regions at 0.2 and 1.0 V vs. Li/Li⁺. The discharge capacities of the non-graphitizable carbons increased with an increase of cavity volume, which was controlled by molar ratios of aromatic compound and cross-linking agent. The structural parameters proposed were measured to compare with each other, and it was found that they showed good correlation.     

Improving electrochemical properties and structural stability of lithium manganese silicates as cathode materials for lithium ion batteries via introducing lithium excess

The serious capacity decay caused by structural amorphization is still a major issue for polyanion-type lithium manganese silicates (Li₂MnSiO₄) as cathode material for lithium ion batteries. In this work, a new strategy for alleviating the structural instability via the introduction of excess lithium into the host crystal lattice is provided. A comprehensive study demonstrates that the required energy for the extraction/insertion of lithium ions into host crystal lattice was decreased as a result of changed local environment of cations in the compound after the excess lithium occupancy in lattice. Importantly, it was found that Li-rich samples deliver higher reversible capacity and increased average potential than pristine sample, indicating the improved energy density of polyanion-type Li_{2 + 2x}Mn_{1 − x}SiO₄/C_. Additionally, the structure of Li2.2 sample was kept intact, while the Li2.0 sample was transformed to amorphous state at 200 mA h g⁻¹ during the initial charging process by controlling the charge cut-off potential. As expected, the introduction of a certain amount of excess lithium into Li₂MnSiO₄ is explored as a route to achieving increased capacity with more movable lithium, while maintaining its structural stability and cyclic stability.     

New strategy to prepare nitrogen self-doped graphene nanosheets by magnesiothermic reduction and its application in lithium ion batteries

Nitrogen self-doped graphene (N/G) nanosheets were prepared through magnesiothermic reduction of melamine. The obtained N/G features porous structure consisting of multi-layer nanosheets. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectra and X-ray diffraction (XRD). As anode of lithium ion batteries (LIBs), it exhibits excellent reversible specific capacity of 1753 mAh g⁻¹ at 0.1 A g^-1 after 200 cycles. The reversible capacity can maintain at 1322 mAh g⁻¹ after 500 cycles at 2 A g⁻¹. At the same time, all results indicate remarkable cycle stability and rate performance as anode materials. Furthermore, this study demonstrates an economical, clean and facile strategy to synthesize N/G nanosheets from cheap chemicals with excellent electrochemical performance in LIBs.     

Preparation and application of bamboo-like carbon nanotubes in lithium ion batteries

CNTs with bamboo-like structure (B-CNTs) has been prepared via a CVD process with novel carbon precursor. The potential application of B-CNTs as electric conductive additive and anode materials for lithium ion batteries was explored. The EIS spectra prove that it is better electric conductive additive than multiwalled CNTs and traditional carbon black (CB). The electric resistance of the electrode is decreased around 20 Ω when B-CNTs is used instead of CB. The cycle stability is also enhanced. However, the test cell with B-CNTs as anode material shows low reversible capacity of 135 mAh g⁻¹ and very low initial cycle efficiency of 17.3%, which indicates that so-prepared B-CNTs is not suitable for anode material.     

Synthesis of SnO2 nanorods and hollow spheres and their electrochemical properties as anode materials for lithium ion batteries

Abstract

SnO₂ nanorods and hollow spheres were conducted via a surfactant assisted hydrothermal reaction with the hydrothermal temperature. The crystalline structure and morphologies of the as prepared samples were characterised by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the products are hollow spheres with diameters of approximately 400–800 nm and shell thicknesses of 60–70 nm via hydrothermal treating at 160°C for 42 h and rod-like nanostructures with diameters of ～30 nm and lengths of 100–300 nm via hydrothermal treating at 200°C for 42 h respectively. The as prepared samples were used as anode materials for lithium ion battery, whose charge–discharge properties and cycle performance were examined. The results show that the initial discharge capacities of SnO₂ hollow spheres and SnO₂ nanorods samples are 1303 and 1426 mA h g^?1 at 0·2C rate, and still retain charge capacities of 518 and 578 mA h g^?1 respectively. Its good cycling behaviour and charge capacities make it a promising cathode material for advanced electrochemical devices for lithium ion batteries.     

Synthesis and electrochemical performance of Li2CoSiO4 as cathode material for lithium ion batteries

Li₂CoSiO₄ has been prepared successfully by a solution route or hydrothermal reaction for the first time, and its electrochemical performance has been investigated primarily. Reversible extraction and insertion of lithium from and into Li₂CoSiO₄ at 4.1 V versus lithium have shown that this material is a potential candidate for the cathode in lithium ion batteries. At this stage reversible electrochemical extraction was limited to 0.46 lithium per formula unit for the Li₂CoSiO₄/C composite materials, with a charge capacity of 234 mAh g⁻¹ and a discharge capacity of 75 mAh g⁻¹.     

A novel CuO-nanotube/SnO2 composite as the anode material for lithium ion batteries

A novel CuO-nanotubes/SnO₂ composite was prepared by a facile solution method and its electrochemical properties were investigated as the anode material for Li-ion battery. The as-prepared composite consisted of monoclinic-phase CuO-nanotubes and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were dramatically decorated on the CuO-nanotubes. The composite showed higher reversible capacity, better durability and high rate performance than the pure SnO₂. The better electrochemical performance could be attributed to the introducing of the CuO-nanotubes. It was found that the CuO-nanotubes were reduced to metallic Cu in the first discharge cycle, which can retain tube structure of the CuO-nanotubes as a tube buffer to alleviate the volume expansion of SnO₂ during cycling and act as a good conductor to improve the electrical conductivity of the electrodes.     

Electrochemical properties of cross-linked polymer electrolyte by electron beam irradiation and application to lithium ion batteries

A polymer electrolyte was successfully fabricated for a room temperature operation lithium battery by cross-linking the mixture of oligomeric poly (ethylene glycol) dimethylether (PEGDME) and poly (ethylene glycol) diacrylate (PEGDA) with Li(CF₃SO₂)₂N using electron beam irradiation. The maximum ionic conductivity achieved for the cross-linked solid polymer electrolyte (c-SPE) at room temperature was 2.1 × 10⁻⁴ S cm⁻¹ and the lithium transport number of the electrolyte was around 0.2. The c-SPE showed no reaction heat with lithium metal up to 300 °C. The interface resistance of Li/c-SPE/Li at room temperature was about 45 Ω cm², which is considerable lower than that of 210 Ω cm² for Li/PEO₁₀Li(CF₃SO₂)₂N/Li. The electrochemical window of the polymer electrolyte was above 4 V (versus Li⁺/Li). The initial discharge capacity for the Li/SPE/LiFePO₄-C cell was approximately 90 mAh g⁻¹ for LiFePO₄-C at 1/10 °C rate at room temperature and showed a good cyclability and a high coulombic efficiency of 99.2%.     

Development and characterization of a bilayer separator for lithium ion batteries

A battery separator is placed between the positive and negative electrodes to prevent electric contact of the electrodes while maintaining good ionic flow. The most commonly used separators for lithium-ion batteries are porous polyolefin membranes. However, they generally do not have good dimentional stability at elevated temperatures. In this study, a bilayer separator has been formed directly on an anode. This bilayer separator comprised a ceramic layer and a porous polyvinylidene fluoride (PVDF) layer. Coin cells with this type of separators showed stable cycling performance at room temperature. They also showed significantly improved rate capabilities compared to the reference cell with a conventional polyolefin separator. An oven test has been used to characterize the cells thermal stability. Charged cells were kept in an oven at 150 °C and their voltage drop was recorded. The reference cell with a conventioal separator failed within about 50 min, while no noticeable voltage drop was observed for the cells with the new bilayer separator within the measured 2 h.     

Self-assembled synthesis of hierarchical nanostructured CuO with various morphologies and their application as anodes for lithium ion batteries

We report a simple self-assembled synthesis of hierarchical CuO particles with various morphologies such as leaf, shuttle, flower, dandelion, and caddice clew. The morphologies can be easily tailored by adjusting the pH value. The synthesis is based on dehydration and re-crystallization of precursor Cu(OH)₂ nanowires. [Cu(NH₃)₄]²⁺ and OH⁻ in the solutions are considered as the key factors to influence the assembling manner of CuO. The obtained hierarchical CuO particles serve as a good model system for the study as anodes for lithium ion batteries. Various morphologies of CuO particles result in different electrochemical performances of electrodes. Compared to others, dandelion-like and caddice clew-like CuO exhibit reversible discharge capacities of 385 mAh g⁻¹ and 400 mAh g⁻¹ at 0.1 C, 340 mAh g⁻¹ and 374 mAh g⁻¹ at 0.5 C after 50 cycles, respectively. The higher discharge capacities and better cycling performances are attributed to their larger surface area and porosity, leading to better contact between CuO and electrolyte and shorter diffusion length of lithium ions.     

A novel flame retardant and film-forming electrolyte additive for lithium ion batteries

Allyl tris(2,2,2-trifluoroethyl) carbonate (ATFEC) was synthesized as a bi-functional additive of flame retardant and film former in electrolytes for lithium ion batteries (LIBs). The flame retardancy of the additive was characterized with differential scanning calorimetry (DSC) and self-extinguishing time (SET). It is shown that adding 1 vol.% ATFEC in 1 M LiPF₆/propylene carbonate (PC) can effectively enhance the thermal stability of the electrolyte and suppress the co-intercalation of PC into the graphitic anode. Further evaluation indicates that the additive hardly affect the conductivity of electrolyte. These support the feasibility of using ATFEC as an additive on formulating an electrolyte with multiple functions such as film-forming enhancement, high thermal stability and high ionic conductivity.     

Surface structure and electrochemical characteristics of plasma-fluorinated petroleum cokes for lithium ion battery

Plasma-fluorination of petroleum coke and those heat-treated at 1860, 2300 and 2800 °C (abbreviated to PC, PC1860, PC2300 and PC2800) was conducted for 15, 30 and 60 min using CF₄ gas at 90 °C. Fluorine contents obtained by elemental analysis were negligible except PC fluorinated for 60 min (0.7 at.%). Fluorine concentration on the surface decreased with increasing heat-treatment temperature of petroleum coke, i.e. from PC to PC2800 when plasma-fluorination was made for 30 and 60 min. Transmission electron microscopic observation revealed that the closed edges of PC2800 were destroyed and opened by plasma-treatment. Plasma-fluorination increased surface disorder of heat-treated petroleum cokes, however, slightly reduced surface areas. These surface structure changes increased first coulombic efficiencies of PC2300 and PC2800 by 6–8 and 8–10% at both 60 and 150 mA g⁻¹, respectively.     

Synthesis by Spark Plasma Sintering: A new way to obtain electrode materials for lithium ion batteries

In the search of high-performance materials for lithium ion batteries, Li₂CoPO₄F offers many advantages like high theoretical capacity and high operating potential. The synthesis of Li₂CoPO₄F has been reinvestigated considering a conventional solid state reaction and an unconventional way. Due to the long heat-treatments required by the conventional approach, a beginning of grains coalescence is observed. Limiting particles growth has been allowed by a shorter reaction done by SPS (Spark Plasma Sintering). By this method, the synthesis of Li₂CoPO₄F was greatly shortened (from 10 h to 9 min), which favours the getting of submicrometric particles. The comparison of the electrochemical properties of the Li₂CoPO₄F obtained by the different ways confirms the advantages of SPS synthesis in performance enhancement.     

Enhancing the electrochemical properties of NiFe2O4 anode for lithium ion battery through a simple hydrogenation modification

Nanocrystal NiFe₂O₄ (NFO) octahedron with a spinel structure has been successfully synthesized by a one-step hydrothermal method. The effects of hydrogenation on the crystal structure, morphology, surface structure, and the electrochemical performance of NFO are comprehensively investigated for the first time. After hydrogenation, the well-defined octahedron morphology of NFO disappears and a small fraction of metallic Ni and some oxygen vacancies are generated after hydrogenation which has been characterized by X-ray diffraction (XRD), X-ray photoelectronic spectrometer (XPS) and Positron annihilation lifetime spectroscopy (PALS). Compared to the pristine NFO or the annealed NFO in air, the hydrogenated samples exhibit much better capacity retention (60% higher than un-hydrogenated NFO at 50th cycle) and rate capability (3 times higher at 1 A/g), which can be largely attributed to the synergetic effect of the conductive metallic Ni and oxygen vacancies resulting from H₂ reduction. Furthermore, this facile hydrogenation modification method may also be applied to improve the electrochemical performances of other transition metal oxides electrodes.     

Analysis and improvement of high temperature floating charge performance for high voltage lithium ion batteries

为研究高电压体系锂离子电池浮充性能的影响因素,对浮充失效电池的产气成分、正负极材料的结构变化、金属溶出情况、隔膜形貌及Gurley值变化等进行了深入分析研究,结果表明：电池在长时间高温浮充过程中,正极材料发生相变,金属元素溶出,同时释放O₂造成电解液的氧化分解;高温高电压状态下负极SEI膜也会破坏,并发生不断的重整及修复反应,这些反应产物沉积到负极表面及隔膜孔隙内,导致靠近负极侧的隔膜孔隙堵塞甚至贯穿,即引起正负极微短路,释放出大量气体。通过提高正极材料的结构稳定性、优化电解液形成稳定的CEI和SEI,改善增加隔膜的穿刺强度都能明显改善电池的高温浮充性能。