Enhanced electrochemical performance of Lithium-ion batteries by conformal coating of polymer electrolyte

This work reports the conformal coating of poly(poly(ethylene glycol) methyl ether methacrylate) (P(MePEGMA)) polymer electrolyte on highly organized titania nanotubes (TiO₂nts) fabricated by electrochemical anodization of Ti foil. The conformal coating was achieved by electropolymerization using cyclic voltammetry technique. The characterization of the polymer electrolyte by proton nuclear magnetic resonance (¹H NMR) and size-exclusion chromatography (SEC) shows the formation of short polymer chains, mainly trimers. X-ray photoelectron spectroscopy (XPS) results confirm the presence of the polymer and LiTFSI salt. The galvanostatic tests at 1C show that the performance of the half cell against metallic Li foil is improved by 33% when TiO₂nts are conformally coated with the polymer electrolyte.     

Nano silicon for lithium-ion batteries

New results for two types of nano-size silicon, prepared via thermal vapour deposition either with or without a graphite substrate are presented. Their superior reversible charge capacity and cycle life as negative electrode material for lithium-ion batteries have already been shown in previous work. Here the lithiation reaction of the materials is investigated more closely via different electrochemical in situ techniques: Raman spectroscopy, dilatometry and differential electrochemical mass spectrometry (DEMS). The Si/graphite compound material shows relatively high kinetics upon discharge. The moderate relative volume change and low gas evolution of the nano silicon based electrode, both being important points for a possible future use in real batteries, are discussed with respect to a standard graphite electrode.     

Gel electrolyte for lithium-ion batteries

The electrochemical performance of gel electrolytes based on crosslinked poly[ethyleneoxide-co-2-(2-methoxyethyoxy)ethyl glycidyl ether-co-allyl glycidyl ether] was investigated using graphite/Li_1.1[Ni_1/3Mn_1/3Co_1/3]_0.9O₂ lithium-ion cells. It was found that the conductivity of the crosslinked gel electrolytes was as high as 5.9 mS/cm at room temperature, which is very similar to that of the conventional organic carbonate liquid electrolytes. Moreover, the capacity retention of lithium-ion cells comprising gel electrolytes was also similar to that of cells with conventional electrolytes. Despite of the high conductivity of the gel electrolytes, the rate capability of lithium-ion cells comprising gel electrolytes is inferior to that of the conventional cells. The difference was believed to be caused by the poor wettability of gel electrolytes on the electrode surfaces.     

A biomass-derived biochar-supported NiS/C anode material for lithium-ion batteries

Nickel sulfides are perfect anode materials for high-capacity and low-cost lithium-ion batteries (LIBs); however, with the shortcoming of polysulfide intermediate dissolution, volume expansion exceeding the limit during cycling also restricts their development. Herein, NiS/C composite materials are successfully anchored on chestnut shell fluff (CSF)-derived biochar by a glucose-auxiliary hydrothermal method along with an annealing treatment. The CSF biochar acts as an effective electron transmission channel for the rapid lithiation/delithiation of NiS and as a fixed sulfur carrier for inhibiting the dissolution of polysulfide. Glucose restrains the accumulation of NiS particles and then transforms into uniform amorphous carbon during annealing, which is more effective in buffering for rapid volume variation. Moreover, the CSF-NiS/C electrode exhibits a remarkable specific capacity of 1522.8 mAh g^-1 (0.1 A g^-1) and distinguished rate performance with 295 mAh g^-1 capacity (3 A g^-1), which are better than those of the pure NiS/C anode material displays. Researchers may be inspired by both of these reasonable design and synthesis strategies that are beneficial for the development of high-performance nickel-based sulfide anode materials for LIBs.     

Three-dimensional porous Sn-Cu alloy anode for lithium-ion batteries

A binder-free three-dimensional (3D) porous Cu₆Sn₅ anode was prepared for lithium-ion batteries. In this novel approach, tin was deposited by electroless-plating on copper foam which was served as anode current collector as well as the source of copper for Cu₆Sn₅ alloy formation. With optimized post-treatment condition, Cu₆Sn₅ alloy with thickness of 1.2 μm was formed on the surface of copper foam network. 3D porous Sn-Cu₆Sn₅ and Cu₃Sn-Cu₁₀Sn₃-Cu₆Sn₅ composite anodes were also prepared for comparison. Electrochemical tests showed that 3D porous Cu₆Sn₅ anode exhibits the best electrochemical performance in terms of specific capacitance and cycleability, which delivers a rechargeable capacity of 404 mAh g⁻¹ over 100 cycles.     

Nanometer copper-tin alloy anode material for lithium-ion batteries

Nanometer copper-tin alloy anode materials with amorphous structure were prepared by a reverse microemulsion technique for lithium-ion batteries. It was found that the electrochemical performance of alloy was influenced by its particle size, which was controlled by appropriate surfactant content. The nanometer copper-tin alloy with particle size of 50-60 nm presented the best performance, showing a reversible specific capacity of 300 mA h/g over the full voltage range 0.0-1.2 V and capacity retention of 93.3% at 50 cycles. A great irreversible capacity was caused by the formation of a SEI layer on the surface of nanometer alloy. The contact resistance between nanometer particles resulted in the poor electric conductivity and the match of particle size and conductive agent content had a great impact on the electrochemical performance of the nanometer copper-tin alloy anode.     

High flash point electrolyte for use in lithium-ion batteries

The high flash point solvent adiponitrile (ADN) was investigated as co-solvent with ethylene carbonate (EC) for use as lithium-ion battery electrolyte. The flash point of this solvent mixture was more than 110 °C higher than that of conventional electrolyte solutions involving volatile linear carbonate components, such as diethyl carbonate (DEC) or dimethyl carbonate (DMC). The electrolyte based on EC:ADN (1:1 wt) with lithium tetrafluoroborate (LiBF₄) displayed a conductivity of 2.6 mS cm⁻¹ and no aluminum corrosion. In addition, it showed higher anodic stability on a Pt electrode than the standard electrolyte 1 M lithium hexafluorophosphate (LiPF₆) in EC:DEC (3:7 wt). Graphite/Li half cells using this electrolyte showed excellent rate capability up to 5C and good cycling stability (more than 98% capacity retention after 50 cycles at 1C). Additionally, the electrolyte was investigated in NCM/Li half cells. The cells were able to reach a capacity of 104 mAh g⁻¹ at 5C and capacity retention of more than 97% after 50 cycles. These results show that an electrolyte with a considerably increased flash point with respect to common electrolyte systems comprising linear carbonates, could be realized without any negative effects on the electrochemical performance in Li-half cells.     

A novel perspective on the formation of the solid electrolyte interphase on the graphite electrode for lithium-ion batteries

In this paper, we describe how the mechanism of formation of a protective film [the solid electrolyte interphase (or interface) (SEI)] on a graphite electrode for Li-ion batteries was investigated from the novel perspective of precipitation of the final decomposition products that arise from the reduction of a nonaqueous electrolyte solution in contact with the graphite electrode. Within the framework of this new perspective, we can elegantly account for the compositional and structural differences between the basal-plane and edge-plane SEIs and for the origins of the multi-layer structure and the parabolic growth law of the SEIs on both the edge-plane and basal-plane surfaces of the graphite electrode.     

Improving the performance of soft carbon for lithium-ion batteries

A novel technique for designing a robust solid electrolyte interface (SEI) on the negative electrodes of lithium-ion batteries has been developed using a silane coating. Two silane compounds, 3,3,3-trifluoropropyltrimethoxysilane (TFPTMS) and dimethoxybis(2-(2-(2-mothoxyethoxy)ethoxy)ethoxy)silane (1ND3(MeO)), have been investigated with respect to improving the capacity retention of lithium manganese oxide spinel/soft carbon cells. The impact of the silane coating on the soft carbon electrode will be attributed to (1) changes in surface functional groups, (2) compositional change of the SEI, and (3) changes in the kinetics of manganese deposition. The impact of the upper cutoff voltage on the capacity retention of the cell was also discussed.     

Synthesis of novel CuS with hierarchical structures and its application in lithium-ion batteries

Novel sphere-like CuS hierarchical structures are fabricated by solvothermal approach without any surfactant and template. SEM and TEM characterizations show that the CuS sphere-like structures are composed of tens to hundreds of well-arranged and self-assembled nanoplates with a thickness of about 20 nm. The effects of dosage of CuCl₂•6H₂O, temperature and reaction time on the morphology of the products are systematically investigated and the results indicate that the CuS sphere-like hierarchical structures can only be obtained under certain experimental conditions. The possible formation mechanism of the CuS hierarchical structures is proposed. In addition, the possibility of using CuS as the electrode material for lithium ion batteries is studied.     

Bismuth sulfide and its carbon nanocomposite for rechargeable lithium-ion batteries

Bi₂S₃ and Bi₂S₃/C nanocomposites prepared by high-energy mechanical milling were evaluated as electrode materials in lithium secondary batteries. For a Bi₂S₃/C nanocomposite, Bi₂S₃ nanocrystallites were well distributed in an amorphous carbon matrix. The reaction mechanism of the Bi₂S₃/C electrode was also examined during the first cycle. The Bi₂S₃/C nanocomposite anode showed superior electrochemical performance (ca. 500 mAh g⁻¹ and 85% of the capacity retention over 100 cycles).     

Nano-porous Si/C composites for anode material of lithium-ion batteries

Nano-porous silicon composite incorporated with graphite and pyrolyzed carbon was synthesized and investigated as a promising anode material for lithium-ion batteries. The nano-porous Si/graphite composite was prepared via two-step ball-milling followed by etching process. Then carbon was incorporated by using different approaches. The nano-porous Si/graphite/C composite exhibits a reversible capacity of about 700 mAh/g with no capacity loss up to the 120th cycle at a constant current density of 0.2 mA/cm². The superior electrochemical characteristics are attributed to the nanosized pores in Si particles, which suppress the volume effect, and buffering action as well as excellent electronic and ionic conductivity of carbon materials.     

锂离子二次电池5V正极材料的研究进展

综述了近年来有关锂离子二次电池5V高电位正极材料的研究进展,对高电位(>4.5V)正极材料特别是尖晶石类正极材料的放电机理、材料结构和性能之间的关系进行了评述。5V电位可以在非掺杂其它过渡金属离子和掺杂其它过渡金属离子两种条件下产生,与此对应的氧化还原电对种类有所不同;表现出的电化学性能也有所不同。性能优良的材料的得到不但取决于对掺杂元素的正确选择,同样也取决于适宜的合成路线和制备方法与工艺。     

Coaxial MnO/C nanotubes as anodes for lithium-ion batteries

Coaxial MnO/C nanotubes with an average diameter of about 450 nm, a wall thickness of about 150 nm, a length of 1–5 μm and a 10 nm thick carbon layer have been prepared using β-MnO₂ nanotubes as self-templates in acetylene at 600 °C. The microstructure of the product has been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The electrochemical performance of the product has been evaluated by galvanostatic charge/discharge cycling. It is found that the product exhibits a reversible capacity of nearly 500 mAh g⁻¹ at a current density of 188.9 mA g⁻¹, and 83.9% of capacity retention, higher than bare MnO nanotubes (58.2%) and MnO nanoparticles (25.8%). The results reveal that coaxial MnO/C nanotubes would be a promising anode material for next-generation lithium-ion batteries.     

Impedance spectroscopy on porous materials: A general model and application to graphite electrodes of lithium-ion batteries

Electrochemical impedance spectroscopy (EIS) was applied to porous negative graphite electrodes for lithium-ion batteries in the EC:DMC, 1 M LiPF₆ electrolyte. The effect of porosity on the electrode response time was studied and a theoretical model was developed, based on free path of the current lines between subsequent reaction sites. The effect of porosity on the electrode response is evidenced by the impedance spectra in which the high frequency capacitive semicircle is distorted. Fresh electrodes (before the formation of the solid electrolyte interphase, SEI) and cycled electrodes have different shapes of the impedance spectra indicating a change of processes at the surface. In particular, the shape of the spectrum for a fresh electrode can be related to an adsorption process. Impedance spectra of fresh electrodes were fitted using a simple model that considers porosity and the assumed electrochemical processes, giving good agreement between model and data. A correlation was found between adsorption sites and irreversible charge capacity in the first cycle.     

Preparation and electrochemical performance of flower-like hematite for lithium-ion batteries

Flower-like hematite (α-Fe₂O₃) has been successfully prepared by heat-treatment from the iron(III)-oxyhydroxide precursor, which is obtained by the hydrolysis of FeCl₃ solution in the presence of NaClO. In this process, no templates or catalysts are required. SEM and TEM characterizations confirm that micro-flowers are composed of several dozen self-assembled nanopetals with the thickness of about 20 nm. On the basis of the morphology investigations in time-dependent experiments, the possible growth mechanism of the flower-like α-Fe₂O₃ is proposed, which is similar to a two-stage growth process. Furthermore, as an anode electrode material for rechargeable lithium-ion batteries, the flower-like α-Fe₂O₃ exhibits excellent electrochemical performance, which can be attributed to the high surface area induced by the flower-like structure, the short lithium diffusion length and the restriction of volume change of the Li⁺ insertion/extraction.     

Hematite nanoflakes as anode electrode materials for rechargeable lithium-ion batteries

Hematite (α-Fe₂O₃) nanoflakes and nanocubes were synthesized by liquid-solid-solution method and their properties as anode electrode materials for rechargeable Li⁺-ion batteries were measured. When changing the water to ethanol volume ratio in the synthesis system, the nanocrystals can be changed from α-Fe₂O₃ to α-FeOOH, with shapes being tuned from nanoflakes to nanocubes, non-uniform particles and nanowires. When assembled as the anode electrode materials in rechargeable Li⁺-ion batteries, the hematite nanoflakes showed one more plateau in the first discharge progress of the voltage-composition curves than hematite nanocrystals with other shapes in the literature. X-ray diffraction, high-resolution transmission electron microscope and electrochemical data showed that this extra plateau came from the formation of Li₂Fe₃O₄ nanoclusters and amorphous Li₂O. This experiment showed that like sizes, shapes of nanocrystals may also affect the detailed electrochemical progress.     

Nano-alumina@cellulose-coated separators with the reinforced-concrete-like structure for high-safety lithium-ion batteries

Separators play a critical role in the safety and performance of lithium-ion batteries.However,commercial polyolefin separators are limited by their poor affinity with electrolytes and low melting points.In this work,we constructed a reinforced-concrete-like structure by homogeneously dispersing nanoAl₂O₃ and cellulose on the separators to improve their stability and performance.In this reinforcedconcrete-like structure,the cellulose is a reinforcing mesh,and the nano-Al₂O₃ acts as concrete to support the separator.After constructing the reinforced-concrete-like structure,the separators exhibit good stability even at 200℃（thermal shrinkage of 0.3%）,enhanced tensile strain（tensile stress of133.4 MPa and tensile strains of 62%）,and better electrolyte wettability（a contact angle of 6.5°）.Combining these advantages,the cells with nano-Al₂O₃@cellulose-coated separators exhibit stable cycling performance and good rate performance.Therefore,the construction of the reinforced-concretelike structure is a promising technology to promote the application of lithium-ion batteries in extreme environments.     

Additives-containing functional electrolytes for suppressing electrolyte decomposition in lithium-ion batteries

Several olefinic compounds such as vinyl acetate, divinyl adipate and allyl methyl carbonate were studied as additives for propylene carbonate (PC)-based electrolytes in lithium-ion battery, which kind of electrolytes always exfoliate graphitic carbon and decompose drastically to liberate organic gas. Three kinds of graphitic carbons commonly used in lithium-ion batteries, namely, natural graphite, MCMB 6-28 and MCF were chosen to test the decomposition-suppressing ability of additives. The effects of the type of graphitic anodes and the structure of additives on the electrolyte decomposition have been investigated in the terms solid electrolyte interface (SEI) formation, which was characterized by cyclic voltammetry (CV), ac impedance, SEM, XPS analyses, and auger electron spectroscopy (AES). The electrochemical performance of the additives-containing electrolytes in combination with LiCoO₂ cathode and graphitic carbon anode was also tested in coin cells.