Reason analysis for Graphite-Si/SiOx/C composite anode cycle fading and cycle improvement with PI binder

Designed Graphite-Si/SiO_x/C composite electrodes for rechargeable lithium-ion batteries are prepared with different binder of carboxymethyl cellulose-styrene butadiene rubber (CMC-SBR) and polyimide (PI). Electrode performance of composites highly depends on the selection of binder. The Si-based/graphite composite electrode containing PI binder shows very stable cycle stability with the retention higher than 95 % after 30 cycles; however, the capacity of composite electrode with CMC-SBR binder fades to less than 80 % after 20 cycles. The improvement mechanism of PI binder is characterized by SEM, EDS mapping, adhesive strength test, and electric performance test. The surface of anode film does not show crack after several cycles, and the SEI on the surface of Si/SiO_x/C particle is characterized. It is found that anode film peeing off strength matches well with the composite cycle stability. This result is further supported with cell disassembly result. We believe that improvement of anode film adhesion strength is an effective way to get stable long cycle life.     

Improving electrochemical performance of poly(vinyl butyral)-based electrolyte by reinforcement with network of ceramic nanofillers

This study has concerned the development of polymer composite electrolytes based on poly(vinyl butyral) (PVB) reinforced with calcinated Li/titania (CLT) for use as an electrolyte in electrochemical devices. The primary aim of this work was to verify our concept of applying CLT-based fillers in a form of nano-backbone to enhance the performance of a solid electrolyte system. To introduce the network of CLT into the PVB matrix, gelatin was used as a sacrificial polymer matrix for the implementation of in situ sol–gel reactions. The gelatin/Li/titania nanofiber films with various lithium perchlorate (LiClO₄) and titanium isopropoxide proportions were initially fabricated via electrospinning, and ionic conductivities of electrospun nanofibers were then examined at 25 °C. In this regard, the highest ionic conductivity of 2.55 × 10⁻⁶ S/cm was achieved when 10 wt% and 7.5 wt% loadings of LiClO₄ and titania precursor were used, respectively. The nanofiber film was then calcined at 400 °C to remove gelatin, and the obtained CLT film was then re-dispersed in solvated PVB-lithium bis(trifluoromethanesulfonyl)imide (PVB-LiTFSI) solution before casting to obtain reinforced composite solid electrolyte film. The reinforced composite PVB polymer electrolyte film shows high ionic conductivity of 2.22 × 10⁻⁴ S/cm with a wider electrochemical stability window in comparison to the one without nanofillers.

     

Preparation of tough cellulose II nanofibers with high thermal stability from wood

Well-dispersed cellulose II nanofibers with high purity of 92 % and uniform width of 15–40 nm were isolated from wood and compared to cellulose I nanofibers. First, ground wood powder was purified by series of chemical treatments. The resulting purified pulp was treated with 17.5 wt% sodium hydroxide (NaOH) solution to mercerize the cellulose. The mercerized pulp was further mechanically nanofibrillated to isolate the nanofibers. X-ray diffraction patterns revealed that the purified pulp had been transformed into the cellulose II crystal structure after treatment with 17.5 wt% NaOH, and the cellulose II polymorph was retained after nanofibrillation. The cellulose II nanofiber sheet exhibited a decrease in Young’s modulus (8.6 GPa) and an increase in fracture strain (13.6 %) compared to the values for a cellulose I nanofiber sheet (11.8 GPa and 7.5 %, respectively), which translated into improved toughness. The cellulose II nanofiber sheet also showed a very low thermal expansion coefficient of 15.9 ppm/K in the range of 20–150 °C. Thermogravimetric analysis indicated that the cellulose II nanofiber sheet had better thermal stability than the cellulose I nanofiber sheet, which was likely due to the stronger hydrogen bonds in cellulose II crystal structure, as well as the higher purity of the cellulose II nanofibers.     

Reversible Immobilization of Urease by Using Bacterial Cellulose Nanofibers

In this work, bacterial cellulose nanofibers were produced by using the Gluconacetobacter hansenii HE1 strain. These nanofibers were derivatized with dye affinity ligand Reactive Green 5, and these newly synthesized dye-attached nanofibers were used for affinity adsorption of urease. Reactive Green 5-attached nanofibers were characterized by Fourier transform infrared spectroscopy, SEM, and energy-dispersive x-ray spectroscopy analysis. Some adsorption conditions which significantly affect the adsorption efficiency were investigated. The maximum urease adsorption capacity was found to be 240 mg/g nanofiber in pH 6.0 and at room temperature. Dye-free plain nanofibers also used for studying nonspecific urease adsorption onto plain nanofibers and nonspecific adsorption were found to be negligible (3.5 mg/g nanofiber). Prepared dye-attached nanofibers can be used in five successive adsorption/desorption steps without any decrease in their urease adsorption capacity. The desorption rate of the adsorbed urease was found to be 98.9 %. The activity of the urease was also investigated, and it was found that free and desorbed urease from the dye-attached nanofibers showed similar specific activity.     

Manganese oxide nanoparticle-loaded porous carbon nanofibers as anode materials for high-performance lithium-ion batteries

Mn-based oxide-loaded porous carbon nanofiber anodes, exhibiting large reversible capacity, excellent capacity retention, and good rate capability, are fabricated by carbonizing electrospun polymer/Mn(CH₃COO)₂ composite nanofibers without adding any polymer binder or electronic conductor. The excellent electrochemical performance of these organic/inorganic nanocomposites is a result of the unique combinative effects of nano-sized Mn-based oxides and carbon matrices as well as the highly-developed porous composite nanofiber structure, which make them promising anode candidates for high-performance rechargeable lithium-ion batteries.     

Fabrication of porous carbon/Si composite nanofibers as high-capacity battery electrodes

Carbon/Si composite nanofibers with porous structures are prepared by electrospinning and subsequent carbonization processes. It is found that these porous composite nanofibers can be used as anode materials for rechargeable lithium-ion batteries (LIBs) without adding any binding or conducting additive. The resultant anodes exhibit good electrochemical performance; for example, a large discharge capacity of 1100 mAh g^?1 at a high current density of 200 mA g^?1.     

Polythiophene-coated nano-silicon composite anodes with enhanced performance for lithium-ion batteries

Herein, a new polythiophene-coated silicon composite anode material was prepared by in situ chemical oxidation polymerization method. The structure of this material was characterized by infrared spectroscopy, which proved that the oxidative polymerization of thiophene occurred mainly in α position. The polythiophene can provide the better electric contact between silicon particles. Therefore, the as-prepared Si/polythiophene composite electrodes achieve better cycling performance than the bare Si anode. The specific capacity of the composite electrode retains 478 mA h g^?1 after 50 cycles.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

担载纳米硅的锂-碳复合微球作为锂二次电池负极

金属锂由于其极高的理论比容量(3860mAh·g~(-1),2061mAh·cm~(-3))和低的还原电势(相对于标准氢电极(SHE)为-3.04 V)等特点,成为了高能量密度锂电池负极材料的极佳选择之一。从上个世纪七十年代开始,科研工作者便开始了金属锂负极的研究,然而,由于金属锂与电解液反应严重,镀锂过程体积膨胀大,且在循环中易生成枝晶,以金属锂为负极的电池循环稳定性差,而且容易短路从而带来安全隐患。因此金属锂做为锂电池负极的商业化推广最终没有成功。在本工作中,我们在前期设计的锂-碳纳米管复合微球(Li-CNT)中引入了纳米硅颗粒制备了硅颗粒担载的锂-碳复合球(LiCNT-Si)。实验发现,纳米硅颗粒的加入不仅提高了锂-碳复合微球的载锂量(10%(质量百分含量)的硅添加量使得比容量从2000 mAh·g~(-1)提高到2600 mAh·g~(-1)),降低了锂的沉积/溶解过电势,有利于引导锂离子回到复合微球内部沉积,大大提高了材料的循环稳定性。同时,担载了纳米硅颗粒的锂-碳复合球也继承了锂-碳复合微球循环过程中体积膨胀小,不长枝晶的优点。而且添加的纳米硅颗粒还填充了Li-CNT微球中的孔隙,减少了电解液渗入复合微球内部腐蚀里面的金属锂,进一步提高了材料的库仑效率。以添加10%硅的锂碳复合材料作为负极,与商用磷酸铁锂正极组成全电池,在常规酯类电解液中1C (0.7 mA·cm~(-2))条件下能稳定循环900圈以上,库仑效率为96.7%,大大高于同样条件下测得的Li-CNT复合材料(90.1%)和金属锂片(79.3%)的库仑效率。因此,这种通过简单的熔融浸渍法即可制备的,具有高的比容量和长的循环稳定性的锂硅-碳复合材料具有较大的潜能成为高能量密度电池的负极材料,尤其适用于锂硫、锂氧这种正极不含锂源的电池体系。     

Porous Si coated with S-doped carbon as anode material for lithium ion batteries

A novel porous Si/S-doped carbon composite was prepared by a magnesiothermic reaction of mesoporous SiO₂, subsequently coating with a sulfur-containing polymer-poly(3,4-ethylene dioxythiophene), and a post-carbonization process. The as-prepared Si composite was homogeneously coated with disordered S-doped carbon with 2.6 wt.%?S in the composite and retained a high surface area of 58.8 m²?g^?1. The Si/S-doped carbon composite exhibited superior electrochemical performance and long cycle life as an anode material in lithium ion cells, showing a stable reversible capacity of 450 mAh g^?1 even at a high current rate of 6,000 mA?g^?1.     

Titanium dioxide/graphene oxide composite and its application as an anode material in non-flammable electrolyte based on ionic liquid and sulfolane

A composite of aminosilane-grafted TiO₂ (TA) and graphene oxide (GO) was prepared via a hydrothermal process. The TiO₂/graphene oxide-based (TA/GO) anode was investigated in an ionic liquid electrolyte (0.7 M lithium bis(trifluoromethanesulfonyl)imide (LiNTf₂)) in ionic liquid (N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (MPPyrNTf₂)) at room temperature and in sulfolane (1 M lithium hexafluorophosphate (LiPF₆) in tetramethylene sulfolane (TMS)). Scanning and transmission electron microscopy (SEM and TEM) observations of the anode materials suggested that the electrochemical intercalation/deintercalation process in the ionic liquid electrolyte with vinylene carbonate (VC) leads to small changes on the surface of TA/GO particles. The addition of VC to the electrolyte (0.7 M LiNTf₂ in MPPyrNTf₂ + 10 wt.% VC) considerably increases the anode capacity. Electrodes were tested at different current regimes in the range 5–50 mA g^?1. The capacity of the anode, working at a low current regime of 5 mA g^?1, was ca. 245 mA g^?1, while a current of 50 mA g^?1 resulted in a capacity of 170 mA g^?1. The decrease in anode capacity with increasing current rate was interpreted as the result of kinetic limits of electrode operation. A much lower capacity was observed for the system TA/GO│1 M LiPF₆ in TMS + 10 wt.% VC│Li.     

Preparation and electrochemical properties of Si0.8Sb/C nanofiber composite anode materials for lithium-ion batteries

Journal of Solid State Electrochemistry - The Si0.8Sb/C nanofiber composite anode materials were synthesized with the method of high-energy ball milling combined with electrospinning. The...     

Capacity fade of LiFePO4/graphite cell at elevated temperature

18650-type lithium iron phosphate/graphite cells are cycled at 25 and 55 °C in order to investigate cycle performance and diagnostics for capacity fading. The cell losses more than 30 % of its initial capacity after 600 cycles when cycled at 55 °C compared to a 5 % loss for the cell cycled at 25 °C. There is no evident difference appeared between cathode and anode capacities before and after cycling, but only part of the cathode capacity could be recovered on the first charge after cycling. The loss of cycleable lithium is supposed to be the reason for the capacity fade. And both catalytic reaction of iron deposited on graphite surface and damage of solid–electrolyte interface layer by volume change play important roles in capacity fade.     

Mesoporous Carbon Nanofibers Embedded with MoS2 Nanocrystals for Extraordinary Li‐Ion Storage

MoS₂ nanocrystals embedded in mesoporous carbon nanofibers are synthesized through an electrospinning process followed by calcination. The resultant nanofibers are 100–150 nm in diameter and constructed from MoS₂ nanocrystals with a lateral diameter of around 7 nm with specific surface areas of 135.9 m² g^?1. The MoS₂@C nanofibers are treated at 450 °C in H₂ and comparison samples annealed at 800 °C in N₂. The heat treatments are designed to achieve good crystallinity and desired mesoporous microstructure, resulting in enhanced electrochemical performance. The small amount of oxygen in the nanofibers annealed in H₂ contributes to obtaining a lower internal resistance, and thus, improving the conductivity. The results show that the nanofibers obtained at 450 °C in H₂ deliver an extraordinary capacity of 1022 mA h g^?1 and improved cyclic stability, with only 2.3 % capacity loss after 165 cycles at a current density of 100 mA g^?1, as well as an outstanding rate capability. The greatly improved kinetics and cycling stability of the mesoporous MoS₂@C nanofibers can be attributed to the crosslinked conductive carbon nanofibers, the large specific surface area, the good crystallinity of MoS₂, and the robust mesoporous microstructure. The resulting nanofiber electrodes, with short mass‐ and charge‐transport pathways, improved electrical conductivity, and large contact area exposed to electrolyte, permitting fast diffusional flux of Li ions, explains the improved kinetics of the interfacial charge‐transfer reaction and the diffusivity of the MoS₂@C mesoporous nanofibers. It is believed that the integration of MoS₂ nanocrystals and mesoporous carbon nanofibers may have a synergistic effect, giving a promising anode, and widening the applicability range into high performance and mass production in the Li‐ion battery market.     

Polyaniline encapsulated silicon nanocomposite as high-performance anode materials for lithium ion batteries

Polyaniline encapsulated silicon (Si/PANI) nanocomposite as anode materials for high-capacity lithium ion batteries has been prepared by an in situ chemical polymerization of aniline monomer in the suspension of Si nanoparticles. The obtained Si/PANI nanocomposite demonstrates a reversible specific capacity of 840 mAh g^?1 after 100 cycles at a rate of 100 mA g^?1 and excellent cycling stability. The enhanced electrochemical performance can be due to that the polyaniline (PANI) matrix offers a continuous electrically conductive network as well as enhances the compatibility of electrode materials and electrolyte as a result of suppressing volume stress of Si during cycles and preventing the agglomeration of Si nanoparticles.     

Facile synthesized Cu-SnO2 anode materials with three-dimensional metal cluster conducting architecture for high performance lithium-ion batteries

A novel Cu-SnO₂ anode material derived from Cu₆Sn₅ alloy, retaining high conductivity of Cu and high theoretical capacity of SnO₂ with a facile synthesizing process by oxidation and reduction method. The novel Cu structure penetrates in the composite particles inducing high conductivity and spaceconfined SnO₂, which restrict the pulverization of SnO₂ during lithiation/delithiation process.     

Multilayered separator based on porous polyethylene layer,Al2O3 layer,and electro-spun PVdF nanofiber layer for lithium batteries

With an aim to enhance the thermal stability and electrolyte wetting of a polyethylene porous separator, an Al₂O₃ nano-powder layer and an electro-spun PVdF nanofiber layer were successively formed on both sides of the polyethylene separator. The Al₂O₃ layer provides excellent thermal stability as indicated by thermal shrinkage of only 7.8 % in area at 180 °C and absence of a meltdown up to 200 °C. The electrolyte uptake of the multilayer separator was increased with the thickness of the nanofiber layer. As a result, discharge capacity, rate capability, and cycle life of the lithium ion batteries employing the PVdF nanofiber layers were improved, overcompensating for a loss of performance caused by the Al₂O₃ layer. Therefore, the multilayer approach is highly effective in improving both the performance and safety of lithium ion batteries.     

Nanocrystalline cellulose-reinforced composite mats for lithium-ion batteries: electrochemical and thermomechanical performance

Nanocrystalline cellulose (NCC)-reinforced poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) composite mats have been prepared by electrospinning method. Polymer electrolytes formed by activating the composite mats with 1 M lithium bis(trifluoromethanesulfonyl)imide/1-butyl-3-methypyrrolidinium bis(trifluoromethanesulfonyl)imide electrolyte solution. The addition of 2 wt% NCC in PVdF-HFP improved the electrolyte retention and storage modulus of the separator by 63 and 15 %, respectively. The developed electrolyte demonstrated high value of ionic conductivity viz. 4?×?10^?4?S?cm^?1 at 30 °C. Linear scan voltammetry revealed a wide electrochemical stability of the composite mat separator up to 5 V (vs. Li⁺/Li). Cyclic voltammetry of the polymer electrolyte with a graphite electrode in 2.5 to 0 V (vs. Li⁺/Li) potential range showed a reversible intercalation/de-intercalation of Li⁺ ions in the graphite. No peaks were observed related to the reduction of the electrolyte on the anode.     

Dual template method to prepare hierarchical porous carbon nanofibers for high-power supercapacitors

Hierarchical porous carbon nanofibers serving as electrode materials are prepared through carbonization and hydrofluoric acid treatment of polyacrylonitrile-based electrospinning involving dual templates. The hierarchical porous structures are synergistically tailored by varying template contents in the spinning solution. The carbon nanofibers prepared from the electrospinning of polyacrylonitrile containing 15/15 wt.% polymethylmethacrylate/tetraethyl orthosilicate exhibit the largest specific surface area (699 m² g^?1) and microporous volume (0.196 cm³ g^?1). In 6 M KOH electrolyte, a symmetrical supercapacitor equipped with the hierarchical porous carbon nanofibers demonstrates its high-end specific capacitance of 170 F g^?1, superior rate capability, and high-power density output up to 14.7 kW kg^?1. Cycling evolution indicates capacitance fading is only 5.8 % of initial capacitance at a current density of 1 A g^?1 even after 8,000 cycles. The excellent electrochemical performances of the carbon nanofiber are mainly ascribed to the optimized pore size distributions of both micropores and mesopores and the unique hierarchical pore structures possessed by abundant micropores.     

A novel polyacrylonitrile-based porous structure gel polymer electrolyte composited by incorporating polyhedral oligomeric silsesquioxane by phase inversion method

A novel polyhedral oligomeric silsesquioxane (POSS) composite polyacrylonitrile (PAN)-based porous structure gel polymer electrolyte (GPE) is prepared by phase inversion method. The POSS additive filler is firstly obtained in the dehydration condensation reaction of vinyltrimethoxysilane (VTMS) and 3-methacryloxypropyltrimethoxysilane (MPTMS). The composition and structure of synthetic POSS and the prepared POSS composite PAN-based GPEs are investigated. It is found that compared with pure PAN-based GPE, the POSS composite PAN-based GPE with 8 wt.% POSS presents the homogeneous pore distribution and abundant electrolyte uptake (540.4 wt.%), which endows GPE-8% with the excellent comprehensive performances: the highest ionic conductivity of 2.62?×?10^?3 S cm^?1 at room temperature, the higher lithium ion transference number of 0.38, the good compatibility with lithium anode, and the higher electrochemical stability window of 5.7 V (vs. Li/Li⁺). At 0.2 C, the GPE-8%-based lithium ion battery produces a satisfactory discharge capacity of 140 mAh g^?1.

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