Three-dimensional reticular tin-manganese oxide composite anode materials for lithium ion batteries

Tin-manganese oxide film with three-dimensional (3D) reticular structure has been prepared by electrostatic spray deposition (ESD). X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that the film is amorphous. X-ray-photoemission spectroscopy (XPS) demonstrates that the 3D grid is composed of tin-manganese oxide. As an anode electrode for the lithium ion battery, the tin-manganese oxide film has 1188.3 mAh g⁻¹ of initial discharge capacity and very good capacity retention of 656.2 mAh g⁻¹ up to the 30th cycle. Such a composite film can be used as an anode for lithium ion batteries with higher energy densities.     

Effects of heteroatoms on electrochemical performance of electrode materials for lithium ion batteries

Recent studies of lithium ion batteries focus on improving electrochemical performance of electrode materials and/or lowering cost. Doping of active materials with heteroatoms is one promising method. This paper reviews the effects of heteroatoms on anode materials such as carbon- and tin-based materials, and cathode materials such as LiCoO₂, LiNiO₂, LiMn₂O₄ and V₂O₅. There are favorable and unfavorable effects, which depend on the species and physicochemical states of heteroatoms and the parent electrode materials. In the application of lithium ion batteries advantageous factors should be exploited, unwelcome side effects should be avoided as far as possible. Considerable gains towards improved electrochemical performance of the electrode materials have been achieved. Nevertheless, there are still problems needing further investigation including theoretical aspects, which will in the meanwhile stimulate the investigation for better electrode materials.     

Pitch carbon and LiF co-modified Si-based anode material for lithium ion batteries

To improve the electrochemical performance of silicon-based anode material, lithium fluoride (LiF) and pitch carbon were introduced to co-modify a silicon/graphite composite (SG), in which the graphite acts as a dispersion matrix. The pitch carbon helps to improve the electronic conductivity and lithium ion transport of the material. LiF is one of the main components of the solid electrolyte interphase (SEI) formed on the silicon surface, helping to tolerate the large volume changes of Si during lithiation/delithiation. The modified SG sample delivered a capacity of over 500 mA h g⁻¹, whereas unmodified SG delivered a capacity of lower than 50 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹. When performed at 4 A g⁻¹, the reversible capacity of the modified SG was 346 mAh g⁻¹, much higher than that of SG (only 37 mA h g⁻¹). The enhanced cycling and rate properties of the modified SG can be attributed to the synergetic contribution of the pitch carbon and LiF which help accommodate the volume change, reduce the side reaction, and form a stable solid electrolyte interface layer.     

Facile synthesis of CuO mesocrystal/MWCNT composites as anode materials for high areal capacity lithium ion batteries

CuO mesocrystal entangled with multi-wall carbon nanotube (MWCNT) composites are synthesized through a facile scalable precipitation and a followed oriented aggregation process. When evaluated as anode materials for lithium ion batteries, the CuO-MWCNT composites exhibit high areal capacity and good cycling stability (1.11 mA h cm⁻² after 400 cycles at the current density of 0.39 mA cm⁻²). The excellent electrochemical performance can be ascribed to the synergy effect of the unique structure of defect-rich CuO mesocrystals and the flexible conductive MWCNTs. The assembled architecture of CuO mesocrystals can favor the Li-ion transport and accommodate the volume change effectively, as well as possess the structural and chemical stability of bulk materials, while the entangled MWCNTs can maintain the structural and electrical integrity of the electrode during the cycles.     

Cathode materials modified by surface coating for lithium ion batteries

Recent research results confirm the importance of structural surface features of cathode materials for their electrochemical performance. Modification by coating is an important method to achieve improved electrochemical performance, and the latest progress was reviewed here. When the surface of cathode materials including LiCoO₂, LiNiO₂, LiMn₂O₄ and LiMnO₂ is coated with oxides such as MgO, Al₂O₃, SiO₂, TiO₂, ZnO, SnO₂, ZrO₂, Li₂O·2B₂O₃-glass and other materials, the coatings prevent the direct contact with the electrolyte solution, suppress phase transition, improve the structural stability, and decrease the disorder of cations in crystal sites. As a result, side reactions and heat generation during cycling are decreased. Accompanying actions such as suppression of Mn²⁺ dissolution, increase in conductivity and removal of HF in electrolyte solutions have been observed. Consequently, marked improvement of electrochemical performance of electrode materials including reversible capacity, coulomb efficiency in the first cycle, cycling behavior, rate capability and overcharge tolerance has been achieved. In conclusion, further directions are suggested for the surface modification of electrode materials. With further understanding of the effects of the surface structure of cathode materials on lithium intercalation and de-intercalation, better and/or cheaper cathode materials from surface modification will come up in the near future.     

Carbon-coated silicon as anode material for lithium ion batteries: advantages and limitations

Carbon coating of silicon powder was studied as a means of preparation of silicon-based anode material for lithium ion batteries. Carbon-coated silicon has been investigated at various cycling modes vs. lithium metal. Ex situ X-ray data suggest that there is irreversible reduction of crystallinity of the silicon content. Since carbon layer preserving the integrity of the particle, the reversibility of the structural changes in the amorphous state Li-Si alloy provides the reversible capacity. The progressively decreased Coulomb efficiency with cycling indicates that more and more lithium ions are trapped in some form of Li-Si alloy and become unavailable for extraction. This is the main factor for the capacity fading during cycling. Qualitative studies of the impedance spectra of the electrode material at the first cycle for the fresh anode and at the last cycle after the anode capacity faded considerably and provide further support for this model of fading mechanism.     

An urchin-like graphite-based anode material for lithium ion batteries

In situ preparation of carbon nanotubes on the surface of spherical graphite particles is made by chemical vapor deposition, resulting in an “urchin-like” hybrid material. TEM and SEM images show that carbon nanotubes are herringbone with turbulent layered structure, less than 100 nm in diameter and several micrometers in length in the average. The hybrid's use as an anode material in lithium ion batteries is examined using constant current charge-discharge tests, which prove that carbon nanotubes oriented on the surface effectively improve the reversible capacity. Cyclic voltammogram shows that there is no cathodic peak for the reaction of the Fe catalyst with Li⁺ in the charge-charge process in 0.0-1.6 V vs. Li/Li⁺ potential range.     

Advanced structures in electrodeposited tin base anodes for lithium ion batteries

A novel composite anode material consisted of electrodeposited Sn dispersing in a conductive micro-porous carbon membrane, which was directly coated on Cu current collector, was investigated. The composite material was prepared by: (1) casting a polyacrylonitrile (PAN)/dimethylformamide (DMF) solution that contained silica particles on a copper foil, (2) removing the solvent by evaporation, (3) dissolving the silica particles by immersing the copper foil into an alkaline solution, (4) drying the copper foil coated by micro-porous membrane, (5) electrodepositing Sn onto the copper foil through the micro-pores in the micro-porous membrane, and (6) annealing as-obtained composite material. This method provided the composite material with high decentralization of Sn and supporting medium purpose of conductive carbon membrane deriving from pyrolysis of PAN. SEM, XRD and EDS analysis confirmed this structure. The characteristic structure was beneficial to inhibit the aggregation between Sn micro-particles, to relax the volume expansion during cycling, and to improve the cycleability of electrode. Galvanostatic tests indicated the discharge capacity of the composite material remained over 550 mAh g⁻¹ and 71.4% of charge retention after 30 cycles, while that of the electrode prepared by electrodepositing Sn on a bare Cu foil decreased seriously to 82.5 mAh g⁻¹ and 13%. These results show that the composite material is a promising anode material with larger specific capacity and long cycle life for lithium ion batteries.     

A hierarchical porous carbon material for high power, lithium ion batteries

We synthesize a carbon anode material with unique nanostructure for high power lithium ion batteries. The carbon material is composed of numerous clusters of carbon nanobeads, and shows a macro-meso-micro hierarchical porous structure. This unique nanostructure appears to facilitate the rapid transfer of lithium ions and a very large ion adsorption. It exhibits a reversible capacity of 407.4 mAh g⁻¹ and its rate performance is drastically improved in comparison with that of the commercial graphite. The unique structure enables the anode to combine the advantages of both lithium ion batteries and electrochemical double layer capacitors, resulting in the good electrochemical performance.     

Electrochemical reaction of the SiMn/C composite for anode in lithium ion batteries

The SiMn-graphite composite powder was prepared by mechanical ball milling and its electrochemical performances were evaluated as the candidate anode materials for lithium ion batteries. It is found that the cyclic performance of the composite materials is improved significantly compared to SiMn alloy and pure silicon. The heat treatment of the electrodes is beneficial for enhancing the cyclic stabilities. The SiMn-20 wt.% graphite composite electrode after annealing at 200 °C has an initial reversible capacity of 463 mAh g⁻¹ and a charge-discharge efficiency of 70%. Moreover, the reversible capacity maintains 426 mAh g⁻¹ after 30 cycles with a coulomb efficiency of over 97%. The phase structure and morphology of the composite were analyzed by X-ray diffraction (XRD) and scanning electron microscopy. The lithiation/delithiation behavior was investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The composite materials appear to be promising candidates as negative electrodes for lithium rechargeable batteries.     

Pyrolytic polyurea encapsulated natural graphite as anode material for lithium ion batteries

Carbon encapsulated graphite was prepared by coating polyurea on the surface of natural graphite particles via interfacial polymerization followed by a pre-oxidation at 250 °C in air and a heat treatment at 850 °C in nitrogen. FT-IR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to investigate the structure of the graphite before and after the surface modification. Galvanostatic cycling, dc impedance spectroscopy, and cyclic voltammetry were used to investigate the electrochemical properties of the modified graphite as the anode material of lithium cells. The modified graphite shows a large improvement in electrochemical performance such as higher reversible capacity and better cycleability compared with the natural graphite. It can work stably in a PC-based electrolyte with the PC content up to 25 vol.% because the encapsulated carbon can depress the co-intercalation of solvated lithium ion. The initial coulombic efficiency of C-NG and NG in non-PC electrolyte is 74.9 and 88.5%, respectively.     

CuO/C microspheres as anode materials for lithium ion batteries

CuO/C microspheres are prepared by calcining CuCl₂/resorcinol-formaldehyde (RF) gel in argon atmosphere followed by a subsequent oxidation process using H₂O₂ solution. The microstructure and morphology of materials are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transition electron microscopy (TEM). Carbon microspheres have an average diameter of about 2 μm, and CuO particles with the sizes of 50–200 nm disperse in these microspheres. The electrochemical properties of CuO/C microspheres as anode materials for lithium ion batteries are investigated by galvanostatic discharge–charge and cyclic voltammetry (CV) tests. The results show that CuO/C microspheres deliver discharge and charge capacities of 470 and 440 mAh g⁻¹ after 50 cycles, and they also exhibit better rate capability than that of pure CuO. It is believed that the carbon microspheres play an important role in their electrochemical properties.     

Rheological properties and stability of NMP based cathode slurries for lithium ion batteries

Slurries for the manufacturing of cathodes for lithium ion batteries are compared regarding to their colloidal stability by means of rheology. Model formulations with nanoscaled LiFePO₄ (LFP) and micron scaled Li(Ni,Mn,Co)O₂ (NMC) were prepared by using N-methyl-2-pyrrolidone (NMP) as solvent. Polyvinylidene difluoride (PVDF) binder and carbon black (CB) conducting additive were added at typical amounts of a few weight percent. The influence of these inactive electrode components on the physical stability of the dispersions was investigated by steady state and oscillation experiments. It is demonstrated that the addition of a high molecular weight PVDF binder is sufficient to establish gel formation by bridging flocculation in case of the nanoscaled cathode material. For the larger micron scaled particles, the formation of a stable coagulated state is also feasible but it requires the combination of a particulate CB gel and a strengthening PVDF polymer network.     

Anodic titania films as anode materials for lithium ion batteries

Titania thin films were prepared through the anodisation of titanium metal in a 1.0 M sulphuric acid solution at 80 °C utilising a series of pulsed dc constant currents of increasing magnitude. Films were then tested as a potential anode material for lithium batteries using a variety of techniques. Electrochemical testing revealed that the films (3.8 cm²) offered good rate capabilities affording a constant capacity of 48 μAh for a constant current of 10 μA which decreased to 25 μAh on increasing the current to 1250 μA. Cyclic voltammetry was conducted over a range of scan rates from which capacitive currents were examined and rate constants, transfer coefficients and diffusion coefficients calculated. Electrochemical impedance spectroscopy was conducted over six potentials in the range 0.1-2.7 V with the experimental data successfully modelled using an equivalent circuit with the notation R(Q(RW))C. TEM observation of focussed ion beam milled cross-sections showed significant structural differences between the as-anodised film and those cycled in a lithium battery. Raman spectroscopy showed that the films had an anatase character that transformed into an unidentified lithium-containing, titanate phase on cycling. Based on a film thickness of 100 nm, and assuming density of 4 g cm⁻³ such films offered a stable capacity of 316 mAh g⁻¹.     

Low-cost carbon-silicon nanocomposite anodes for lithium ion batteries

The specific energy of the existing lithium ion battery cells is limited because intercalation electrodes made of activated carbon (AC) materials have limited lithium ion storage capacities. Carbon nanotubes, graphene, and carbon nanofibers are the most sought alternatives to replace AC materials but their synthesis cost makes them highly prohibitive. Silicon has recently emerged as a strong candidate to replace existing graphite anodes due to its inherently large specific capacity and low working potential. However, pure silicon electrodes have shown poor mechanical integrity due to the dramatic expansion of the material during battery operation. This results in high irreversible capacity and short cycle life. We report on the synthesis and use of carbon and hybrid carbon-silicon nanostructures made by a simplified thermo-mechanical milling process to produce low-cost high-energy lithium ion battery anodes. Our work is based on an abundant, cost-effective, and easy-to-launch source of carbon soot having amorphous nature in combination with scrap silicon with crystalline nature. The carbon soot is transformed in situ into graphene and graphitic carbon during mechanical milling leading to superior elastic properties. Micro-Raman mapping shows a well-dispersed microstructure for both carbon and silicon. The fabricated composites are used for battery anodes, and the results are compared with commercial anodes from MTI Corporation. The anodes are integrated in batteries and tested; the results are compared to those seen in commercial batteries. For quick laboratory assessment, all electrochemical cells were fabricated under available environment conditions and they were tested at room temperature. Initial electrochemical analysis results on specific capacity, efficiency, and cyclability in comparison to currently available AC counterpart are promising to advance cost-effective commercial lithium ion battery technology. The electrochemical performance observed for carbon soot material is very interesting given the fact that its production cost is away cheaper than activated carbon. The cost of activated carbon is about $15/kg whereas the cost to manufacture carbon soot as a by-product from large-scale milling of abundant graphite is about $1/kg. Additionally, here, we propose a method that is environmentally friendly with strong potential for industrialization.     

Enhanced electrochemical performance of ZrO2 modified LiNi0.6Co0.2Mn0.2O2 cathode material for lithium ion batteries

LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode has been modified by incorporating ZrO₂ nanoparticles to improve its electrochemical performance. Compared to the pristine electrode, the cycling stability and rate capability of 0.5 wt% ZrO₂ modified-NCM622 have been improved significantly. The 0.5 wt% ZrO₂ modified-NCM622 cathode shows a capacity retention of 83.8% after 100 cycles at 0.1 C between 2.8 and 4.3 V, while that of the pristine NCM622 electrode is only 75.6%. When the current rate is set as 5C, the capacity retention of the 0.5 wt% ZrO₂-modified NCM622 is 10% higher than that of the pristine NCM622. Also, the rate capability of 0.5 wt% ZrO₂-modified NCM622 is better than that of the pristine NCM622 at various C-rates in a voltage range of 2.8–4.3 V. The enhanced electrochemical performances of the ZrO₂-modified NCM622 cathodes can be attributed to their high Li-ion conductivity and structural stability.     

Nanoscale SnS with and without carbon-coatings as an anode material for lithium ion batteries

SnS nanoparticles were mechnochemical synthesized and then co-heated with polyvinyl alcohol (PVA) at various temperatures to obtain carbon coating. All amorphous carbon-coated SnS particles had average particle size of about 20-30 nm, revealed by transmission electron microscopy (TEM). During discharge-charge, ex situ XRD results indicated that SnS firstly decomposed to Sn, then lithium ions intercalated into Sn. The reaction of Li⁺ and Sn was responsible for the reversible capacity in cycling process. The lithium ion insertion and extraction mechanism of SnS anode was similar to that of Sn-based oxide. Electrochemical capacity retention of carbon-coated SnS obtained at 700 °C was superior to that of other prepared SnS anodes and especially the rate capability was obviously enhanced due to good electric conductivity and buffering matrix effects of carbon coating.     

锂离子电池正极材料LiFePO4的改性研究进展

橄榄石型结构的磷酸亚铁锂( LiFePO4)作为备受关注的锂离子电池正极材料,可望成为新一代首选的可代替钴酸锂的锂离子二次电池正极材料.详细地叙述了近年来国内外对LiFePO4改性所做的研究,着重介绍了导电剂掺杂包覆、金属离子掺杂和合成方法对LiFePO4电化学性能的影响,以及这些改性方法存在的问题.     

Flower-like CuO film-electrode for lithium ion batteries and the effect of surface morphology on electrochemical performance

Nanostructured CuO films with flower-like architectures were fabricated by immersing copper foils in an aqueous solution of sodium hydroxide and sodium dodecylsulfate, and subsequent heat treatment at low temperature. The as-prepared CuO films exhibited not only higher reversible capacity but also better rate capability than those of network-like counterpart as negative-electrodes of lithium ion batteries. The effect of surface morphology on the electrochemical performance of the CuO electrodes was discussed. It was confirmed that the unique flower-like structures are mainly responsible for the difference in electrochemical performance between the two kinds of electrodes. The result of this study provides an attractive electrode with high energy-density for lithium ion batteries via a simple and green procedure.     

Composite silicon film with connected silicon nanowires for lithium ion batteries

Composite silicon film, which is composed of silicon nanowires, Si-Au eutectic and Si particles as the melding spots, was prepared as anode for lithium ion batteries by a special secondary deposition process with vapor-liquid-solid (VLS) mechanism. Au-Si eutectic particles act as the melding spots between silicon nanowires. An attractive electrochemical performance with 88% of the coulombic efficiency in the first cycle was obtained in the charge-discharge tests. The connection among silicon nanowires by dispersed Si-Au particles is the key factor for the enhancement of its electrochemical reversibility.