Sn/carbon nanotube composite anode with improved cycle performance for lithium-ion battery

Anode material for lithium-ion battery based on Sn/carbon nanotube (CNT) composite is synthesized via a chemical reduction method. The Sn/CNT composite is characterized by thermogravimetry, X-ray diffraction, and transition electron microscopy. The Sn/CNT composite delivers high initial reversible capacity of 630.5 mAh g^?1 and exhibits stable cycling performance with a reversible capacity of 413 mAh g^?1 at the 100th cycle. The enhanced electrochemical performance of the Sn/CNT composite could be mainly attributed to the well dispersion of Sn nanoparticles on CNT and partially filling Sn nanoparticles inside the CNT. It is proposed that the chemical treatment of CNT with concentrated nitric acid, which cuts carbon nanotube into short pieces and increases the amount of oxygen-functional groups on the surface, plays an important role in the anchoring of Sn nanoparticles on carbon nanotube and inhibiting the agglomeration of Sn nanoparticles during the charge–discharge process.     

Hydroxyl terminated Poly(dimethylsiloxane) as an electrolyte additive to enhance the cycle performance of lithium-ion batteries

Hydroxyl terminated poly(dimethylsiloxane) (PDMS-HT) is used as an electrolyte additive in electrolyte systems containing 1 M LiPF₆ in EC:DMC (ratios 1:9; 3:7; 4:6 and 1:1 v/v) to enhance the cycle performance of lithium-ion batteries. Adding a small amount of PDMS-HT to the standard LIB electrolyte leads to improved specific capacity as well as improved capacity retention over prolonged cycles. There is also a slight increase in Li⁺ ion conductivity when PDMS-HT is added. Also, the PDMS-HT additive allows the formation of a more stable solid electrolyte interface (SEI) layer that enables the LIB cells to be cycled for longer cycles with minimal capacity fading. This combination of improved ionic conductivity and stable SEI layer formation due to the PDMS-HT additive, makes it an excellent candidate for an electrolyte additive for lithium ion batteries.     

Influence of fluoroethylene carbonate on the solid electrolyte interphase of silicon anode for Li-ion batteries:A scanning force spectroscopy study

Silicon is an important high capacity anode material for the next generation Li-ion batteries.The electrochemical performances of the Si anode are influenced strongly by the properties of the solid electrolyte interphase(SEI).It is well known that the addition of flouroethylene carbonate(FEC)in the carbonate electrolyte is helpful to improve the cyclic performance of the Si anode.The possible origin is suggested to relate to the modification of the SEI.However,detailed information is still absent.In this work,the structural and mechanical properties of the SEI on Si thin film anode in the ethylene-carbonate-based(EC-based)and FEC-based electrolytes at different discharging and charging states have been investigated using a scanning atomic force microscopy force spectroscopy(AFMFS)method.Single-layered,double-layered,and multi-layered SEI structures with various Young’s moduli have been visualized three dimensionally at nanoscale based on the hundreds of force curves in certain scanned area.The coverage of the SEI can be obtained quantitatively from the two-dimensional(2D)project plots.The related analysis indicates that more soft SEI layers are covered on the Si anode,and this could explain the benefits of the FEC additive.     

Tea polyphenols as a novel reaction-type electrolyte additive in lithium-ion batteries

In this study, we reported tea polyphenols (TP) as a novel, cheap, environment-friendly and easy dissolution in common electrolytes reaction-type electrolyte additive for the graphite anode of the lithium-ion batteries. The TP can capture less stable radical anions that are harmful to oxidation stability of ethylene carbonate (EC) to form stable polymer. To a certain extent, it improved the electrochemical performance of the graphite electrode such as reversible capacity and cyclic stability by charge-discharge test, cyclic voltammetry (CV), scanning electron microscope (SEM), and electrochemical impedance microscope (EIS). The first charge capacities of the graphite electrodes in electrolytes without and with TP were 327.1 and 349.1 mAh g^?1, respectively. The charge capacities were 306.8 and 344.2 mAh g^?1 after 100 cycles and the capacity retention were 93.79 and 98.60%, respectively. The improvement was benefited from the effective scavenging the less stable radical anions and improvement the oxidation stability of EC and formation of a stable, compact and thin solid electrolyte interface (SEI) film with lower resistance.     

Effect of pyrolytic polyacrylonitrile on electrochemical performance of Si/graphite composite anode for lithium-ion batteries

The silicon/graphite (Si/G) composite was prepared using pyrolytic polyacrylonitrile (PAN) as carbon precursor, which is a nitrogen-doped carbon that provides efficient pathway for electron transfer. The combination of flake graphite and pyrolytic carbon layer accommodates the large volume expansion of Si during discharge-charge process. The Si/G composite was synthesized via cost-effective liquid solidification followed by carbonization process. The effect of PAN content on electrochemical performance of composites was investigated. The composite containing 40 wt% PAN exhibits a relatively better rate capability and cycle performance than others. It exhibits initial reversible specific capacity of 793.6 mAh g^?1 at a current density of 100 mA g^?1. High capacity of 661 mAh g^?1 can be reached after 50 cycles at current density of 500 mA g^?1.     

Optimal concentration of electrolyte additive for cyclic stability improvement of high-voltage cathode of lithium-ion battery

Additives that can be oxidized preferentially to the baseline electrolyte are possible of forming a protective cathode interphase, but less attention has been paid to the effect of the additive concentration. Herein, this issue is addressed by evaluating the effect of an easily oxidizable electrolyte additive, tripropyl borate (TPB), on the cyclic stability of high-voltage cathode, LiNi_0.5Mn_1.5O₄. It is found that the optimal concentration of TPB is 1 wt.% for the best cyclic stability of LiNi_0.5Mn_1.5O₄ and the discharge capacity of LiNi_0.5Mn_1.5O₄ will decrease when TPB concentration is lower or higher than this concentration. This effect is related to the resulting interphase from TPB, which cannot provide sufficient protection for the structural integrity of LiNi_0.5Mn_1.5O₄ when it is formed in the electrolyte with lower concentrations of TPB, while shows an increased interfacial impedance of LiNi_0.5Mn_1.5O₄/electrolyte when it is formed from higher concentrations of TPB.     

Facile preparation of SGC composite as anode for lithium-ion batteries

The silicon/graphite/carbon (SGC) composite was successfully prepared by ball-milling combined with pyrolysis technology using nanosilicon, graphite, and phenolic resin as raw materials. The structure and morphology of the as-prepared materials are characterized by X–ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). Meanwhile, the electrochemical performance is tested by constant current charge–discharge technique, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements. The electrodes exhibit not only high initial specific capacity at a current density of 100 mA g^?1, but also good capacity retention in the following 50 cycles. The EIS results indicate that the electrodes show low charge transfer impedance R_sf?+?R_ct. The results promote the as-prepared SGC material as a promising anode for commercial use.     

Controllable synthesis of spherical silicon and its performance as an anode for lithium-ion batteries

Spherical silicon is controllably synthesized by the hydrolysis of tetraethylorthosilicate (TEOS) with the addition of different contents of ammonia to form SiO₂, then reduced by magnesium powder in argon atmosphere at 900 °C for 3 h. The experimental results show that the electrochemical performance of the as-prepared silicon anode is much affected by the morphology of silicon, and the spherical silicon with a particle size of 250–300 nm shows a reversible capacity of 1,345.8 mAh g^?1 with the capacity retention of 83.2 % after 20 cycles. The relationship between the electrochemical performance of the spherical silicon and the diameters of silicon sphere makes it possible to control the performance of the silicon anode by adjusting the hydrolysis conditions of TEOS.     

Electrochemical properties of SnO2 nanorods as anode materials in lithium-ion battery

Well-dispersed SnO2 nanorods with diameter of 4-15 nm and length of 100-200 nm are synthesised through a hydrothermal route and their potential as anode materials in lithium-ion batteries is investigated. The observed initial discharge capacity is as high as 1778 mA·h/g, much higher than the theoretical value of the bulk SnO2 (1494 mA·h/g). During the following 15 cycles, the reversible capacity decreases from 929 to 576 mA·h/g with a fading rate of 3.5% per cycle. The fading mechanism is discussed. Serious capacity fading can be avoided by reducing the cycling voltages from 0.05-3.0 to 0.4-1.2 V. At the end, SnO2 nanorods with much smaller size are synthesized and their performance as anode materials is studied. The size effect on the electrochemical properties is briefly discussed.     

Allyl cyanide as a new functional additive in propylene carbonate-based electrolyte for lithium-ion batteries

Allyl cyanide (AC) was investigated as a film-forming additive in propylene carbonate (PC)-based electrolytes for graphite anode in lithium-ion batteries. The film-forming behavior of AC was characterized with cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. By adding 2 wt% AC in the electrolyte of 1 M LiPF₆-PC/DMC (1:1, in vol), the exfoliation of graphite anode was effectively suppressed over cycling. Graphite/Li half-cell showed an initial coulombic efficiency of 75 % and a specific capacity of 300 mAh/g after 48 cycles. A possible reductive polymerization mechanism of AC on the surface of graphite was proposed.     

Improving the rate performance and stability of LiNi<Subscript>0.6</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.2</Subscript>O<Subscript>2</Subscript> in high voltage lithium-ion battery by using fluoroethylene carbonate as electrolyte additive

Fluoroethylene carbonate (FEC) is investigated as the electrolyte additive to improve the electrochemical performance of high voltage LiNi_0.6Co_0.2Mn_0.2O₂ cathode material. Compared to LiNi_0.6Co_0.2Mn_0.2O₂/Li cells in blank electrolyte, the capacity retention of the cells with 5 wt% FEC in electrolytes after 80 times charge-discharge cycle between 3.0 and 4.5 V significantly improve from 82.0 to 89.7%. Besides, the capacity of LiNi_0.6Co_0.2Mn_0.2O₂/Li only obtains 12.6 mAh g^?1 at 5 C in base electrolyte, while the 5 wt% FEC in electrolyte can reach a high capacity of 71.3 mAh g^?1 at the same rate. The oxidative stability of the electrolyte with 5 wt% FEC is evaluated by linear sweep voltammetry and potentiostatic data. The LSV results show that the oxidation potential of the electrolytes with FEC is higher than 4.5 V vs. Li/Li⁺, while the oxidation peaks begin to appear near 4.3 V in the electrolyte without FEC. In addition, the effect of FEC on surface of LiNi_0.6Co_0.2Mn_0.2O₂ is elucidated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The analysis result indicates that FEC facilitates the formation of a more stable surface film on the LiNi_0.6Co_0.2Mn_0.2O₂ cathode. The electrochemical impedance spectroscopy (EIS) result evidences that the stable surface film could improve cathode electrolyte interfacial resistance. These results demonstrate that the FEC can apply as an additive for 4.5 V high voltage electrolyte system in LiNi_0.6Co_0.2Mn_0.2O₂/Li cells.     

Synthesis of three-dimensional cross-linked MnO@C composite as high-performance anode material for lithium-ion batteries

MnO@C composites with three-dimensional cross-linked structure were designed and fabricated through hydrothermal treatment. Cation exchange resin was used as the precursor to create a three-dimensional cross-linked porous carbon structure, which was evenly decorated by nanosized MnO particles. When compared with pristine MnO, those MnO@C composites showed much better stability during charge-discharge cycling, retaining a specific capacity of 615 mAh g^?1 (62.5 wt% MnO) after 100 cycles at a current density of 0.2 A g^?1. This could be ascribed to the special three-dimensional cross-linked porous carbon that not only accelerated the transport of Li⁺ ions but also buffered the volume change and prevented agglomeration of MnO particles during the repeated lithiation and delithiation process.     

Ethylene sulfate as film formation additive to improve the compatibility of graphite electrode for lithium-ion battery

Ethylene sulfate (DTD) is investigated as a novel film formation electrolyte additive for graphite anode material in lithium-ion battery. The CV results reveal that DTD is reduced prior to ethylene carbonate (EC) at the interface between graphite and electrolyte, while it cannot prevent the sustained reduction of propylene carbonate (PC) when the amount of DTD is lesser than 3 wt% in the PC-based electrolyte. XPS analyses demonstrate that the reduction products of DTD, Li₂SO₃, and ROSO₂Li are formed at the surface of graphite in the EC-based electrolyte, which is beneficial to lower the interfacial resistance as suggested by the EIS results. In addition, SEM images show a smoother and homogeneous surface film at the surface of graphite when DTD is incorporated into the electrolyte. Consequently, the Li/graphite half cells cycled in EC-based electrolyte containing DTD exhibit higher specific capacity and improved cycling capability than that without DTD.     

Effect of carbon coating on the electrochemical performance of LiFePO<Subscript>4</Subscript>/C as cathode materials for aqueous electrolyte lithium-ion battery

Organic electrolyte is widely used for lithium-ion rechargeable batteries but might cause flammable fumes or fire due to improper use such as overcharge or short circuit. That weakness encourages the development of tools and materials which are cheap and environmental friendly for rechargeable lithium-ion batteries with aqueous electrolyte. Lithium iron phosphate (LiFePO₄) with olivine structure is a potential candidate to be used as the cathode in aqueous electrolyte lithium-ion battery. However, LiFePO₄ has a low electronic conductivity compared to other cathodes. Conductive coating of LiFePO₄ was applied to improve the conductivity using sucrose as carbon source by heating to 600 °C for 3 h on an Argon atmosphere. The carbon-coated LiFePO₄ (LiFePO₄/C) was successfully prepared with three variations of the weight percentage of carbon. From the cyclic voltammetry, the addition of carbon coatings could improve the stability of cell battery in aqueous electrolyte. The result of galvanostatic charge/discharge shows that 9 % carbon exhibits the best result with the first specific discharge capacity of 13.3 mAh g^?1 and capacity fading by 2.2 % after 100 cycles. Although carbon coating enhances the conductivity of LiFePO₄, excessive addition of carbon could degrade the capacity of LiFePO₄.     

Synthesis of PAN/SnCl2 composite as Li-ion battery anode material

A novel process was proposed to synthesize the pyrolytic polyacrylonitrile (PAN)/SnCl₂ composite anode material for Li-ion batteries. The preparation started with the dissolution of PAN and SnCl₂ in dimethylformamide (DMF), followed by drying of the solution and pyrolysis of the dried mixture of PAN and SnCl₂ at 300 °C, leading to homogenous dispersal of SnCl₂ in pyrolytic PAN, which becomes conducting polymer matrix. The composite presented stable cycling capacity of about 490 mAh/g. It is demonstrated that SnCl₂, which has been considered to be an inactive electrode material, can become active by the proposed composite technique. This paves the promising way to prepare electrode materials for Li-ion batteries.     

Novel silicon nanowire film on copper foil as high performance anode for lithium-ion batteries

A novel silicon nanowire film anode was successfully prepared by a combination of magnetron sputtering deposition and metal-catalyzed electroless etching technology. Scanning electron microscopy revealed the formation of a Si film composed of nanowires with a diameter of ~70 nm and lengths of ~3.5 μm. As-prepared Si nanowire film is directly grown on current collectors without binders and carbon additives, which provides a good contact and adhesion of them to current collector. Furthermore, the defined spacing of nanoscale Si nanowire allows Si to undergo large volume change during the alloying/dealloying process without loss of its integrity. These structural features of the resulting Si nanowire make it a promising anode for lithium-ion batteries with remarkably improved electrochemical performance compared with the Si film-based electrode prepared without metal-catalyzed electroless etching process.     

Preparation of Si-PPy-Ag composites and their electrochemical performance as anode for lithium-ion batteries

The nanosilicon connected by polypyrrole (PPy) and silver (Ag) particles was simply synthesized by a chemical polymerization process in order to prepare Si-based anodes for Li-ion batteries. The phase structure, surface morphology, and electrochemical properties of the as-synthesized powders were analyzed by X-ray diffraction, FT-IR, scanning electron microscopy, and galvanostatic charge/discharge measurements. The cycle stability of the Si-PPy-Ag composites was greatly enhanced compared with the pure nanosilicon. A high capacity of more than 823 mA h g^?1 was maintained after 100 cycles. The improved electrochemical characteristics are attributed to the volume buffering effect as well as effective electronic conductivity of the polypyrrole and silver in the composite electrode.     

Development of monodispersed MnCO<Subscript>3</Subscript>/graphene nanosheet composite as anode for lithium-ion battery by hydrothermal synthesis

A unique monodispersed MnCO₃/graphene nanosheet composite is synthesized by a simple one-step hydrothermal method and used as anode of lithium-ion battery. X-ray diffraction patterns show the typical rhombohedral structure of MnCO₃. A transmission electron micrograph reveals that MnCO₃ is evenly distributed on the graphene nanosheet surface with a uniform diameter of 100 nm. Electrochemical performance results show that the specific discharge capacities of MnCO₃/graphene nanosheet composite remain above 1015.9 mAh g^?1 at a rate of 0.2 C after 85 cycles in the potential window of 0.01–2.0 V and even at a high rate of 1.0 C this parameter remains at 683.5 mAh g^?1 after 100 cycles. Thus, the composite also exhibits favorable rate performance. The excellent reversible capacities are attributed to the highly dispersed and large nanosheet structure of the composite, which may not only facilitate the fast transport of Li⁺ ions between the electrode and electrolyte but also provide enough surfaces to accommodate extra Li⁺ ions that contribute to partial interfacial storage capacities. Additionally, graphene nanosheet can effectively improve electrical conductivity of the composite. Therefore, MnCO₃/graphene nanosheet composite can be a great potential anode material for lithium-ion batteries.     

Preparation and electrochemical performance of bramble-like ZnO array as anode materials for lithium-ion batteries

A bramble-like ZnO array with a special three-dimensional (3D) nanostructure was successfully fabricated on Zn foil through a facile two-step hydrothermal process. A possible growth mechanism of the bramble-like ZnO array was proposed. In the first step of hydrothermal process, the crystal nucleus of Zn(OH) ₄ ^2? generated by the zinc atoms and OH^? ions fold together preferentially along the positive polar (0001) to form the needle-like ZnO array. In the second step of hydrothermal process, the crystal nuclei of Zn(OH) ₄ ^2? adjust their posture to keep their c-axes vertical to the perching sites due to the sufficient environmental force and further grow preferentially along the (0001) direction so as to form bramble-like ZnO array. The electrochemical properties of the needle- and bramble-like ZnO arrays as anode materials for lithium-ion batteries were investigated and compared. The results show that the bramble-like ZnO material exhibits much better lithium storage properties than the needle-like ZnO sample. Reasons for the enhanced electrochemical performance of the bramble-like ZnO material were investigated.