A new ternary Li4FeSb2 structure formed upon discharge of the FeSb2/Li cell

We report here the performance of FeSb₂ used as negative electrode for Li-ions batteries. A capacity of 400 mAh g⁻¹ and 3500 mAh cm⁻³ can be retained after 10 cycles at a C/10 cycling rate. We studied in particular the electrochemical mechanism during the first discharge of the FeSb₂/Li battery. Both Mössbauer spectroscopy (⁵⁷Fe and ¹²¹Sb) and in situ XRD studies show the formation of an unknown fcc-phase during the first step. A second step shows the conversion process leading to Li₃Sb at the end of the discharge. The structure of the intermediate new phase Li₄FeSb₂ is isotype to the face-centered-cubic Li₃Sb phase in which one Fe atom is substituted by two Li atoms.     

Vanadium diphosphides as negative electrodes for secondary Li-ion batteries

We report on the Li electrochemical reactivity of amorphous and crystalline VP₂, synthesized by ball-milling and by 600 °C heat treatment of a ball-milled sample, respectively. The amorphous sample can reversibly react with 3.5 Li per formula unit as compared to solely 2.5 for the crystalline one. However in both cases there is a rapid capacity decay upon cycling that is more pronounced in the case of the crystalline sample. Complementary X-rays, HTREM and NMR tend to show that the Li reactivity mechanism differs from the classical conversion reactions since neither V nanoparticles nor the formation of Li₃P were detected, as opposed to some of the other MP₂ compounds (M = Ni or Cu). Besides structural phase variations within the 3d metal-based binary phosphide series, the possibility of a change in the nature of the redox centre upon lithiation from cation (M) to anion (P) is evoked.     

Pyroxene LiVSi2O6 as an electrode material for Li-ion batteries

Lithium vanadium metasilicate (LiVSi₂O₆) with pyroxene structure has been exploited as an electrode material for Li-ion batteries. Galvanostatic charge and discharge tests show that LiVSi₂O₆ is able to deliver a capacity of 85 mAh g⁻¹ at 30 °C, and a high capacity of 181 mAh g⁻¹ at 60 °C. The high capacity is believed to be due to the reactions of V³⁺/V⁴⁺ and V²⁺/V³⁺redox couples, accompanied by the excess 0.42 Li⁺ insertion into the lattice forming a Li-rich phase Li_1.42VSi₂O₆. High-energy synchrotron XRD combined with the Rietveld refinement analysis confirms that the electrochemical delithiation-lithiation reaction proceeds by a single phase redox mechanism with an overall volume variation of 1.9% between LiVSi₂O₆ and its delithiated state, indicating a very stable framework of LiVSi₂O₆ for Li⁺ ions extraction-insertion.     

2LiH + M (M = Mg, Ti): New concept of negative electrode for rechargeable lithium-ion batteries

xLiH + M composites, where M = Mg or Ti, are suggested as new candidates for negative electrode for Li-ion batteries. For this purpose, the xLiH + M electrode is prepared using the mechanochemical reaction: MH_x + xLi → xLiH + M or by simply grinding a xLiH + M mixture. The most promising electrochemical behaviour is obtained with the (2LiH + Mg) composite prepared via a mechanochemical reaction between MgH₂ and metallic Li leading to a very divided composite in which Mg crystallites of 20 nm size are embedded in a LiH matrix. Reversible capacities of 1064 mAh g⁻¹ (three times as much as the one of graphite) and 600 mAh g⁻¹ are reached for these phase mixtures after 1 and 28 h of grinding in vertical and planetary mill, respectively. The (2LiH + Ti) mixture prepared via the mechanochemical reaction between TiH₂ and Li exhibits a reversible capacity of 428 mAh g⁻¹. From X-ray diffraction measurements, the performances of the electrodes are attributed to the electrochemical conversion reaction: M + xLiH ↔ MH_x + xLi⁺ + xe⁻ (M = Mg, Ti) followed for M = Mg by an alloying process where M reacts with lithium ions to form Mg_1−xLi_x alloys.     

Electrochemical evaluation of rutile TiO2 nanoparticles as negative electrode for Li-ion batteries

Nanosized rutile TiO₂ has been prepared by sol–gel chemistry from a glycerol-modified titanium precursor in the presence of an anionic surfactant. The sample has been characterized by X-ray diffraction, nitrogen sorption, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and electrochemical tests. Nanosized rutile TiO₂ has been electrochemically investigated using two potential windows: 1.2–3 V and 1–3 V. It exhibits excellent high rates capabilities and good cycling stability.     

Electrochemical performances of BiSbO4 as electrode material for lithium batteries

We present an electrochemical study of BiSbO₄, an opened layered oxide having a structure related to Aurivillius phases. Li//BiSbO₄ cells show a large specific capacity as high as 1250 mAh g⁻¹ during reduction down to 0.5 V. This reaction involves 18Li atoms per formula unit, pointing it towards a very promising cathode material for primary lithium batteries, in particular for ICD devices. The characterization of the reduction products indicates that the reduction of BiSbO₄ with lithium presumably goes along firstly with the formation of metallic Sb and Bi to follow the formation of the alloys Li₃Bi and Li₃Sb dispersed in a lithium oxide matrix. In situ X-ray diffraction experiments proved the amorphous nature of both metals and final alloys. On the other hand when Li//BiSbO₄ cells are limited to discharge down to 1.2 V, BiSbO₄ reacts with 5Li atoms. After the first discharge, that develops a specific capacity of 350 mAh g⁻¹, high cyclability has been observed.     

Reactivity of complex hydrides Mg2FeH6, Mg2CoH5 and Mg2NiH4 with lithium ion: Far from equilibrium electrochemically driven conversion reactions

The electrochemical reaction of lithium ion with Mg₂FeH₆, Mg₂CoH₅ and Mg₂NiH₄ complex hydrides prepared by reactive grinding is studied here. Plateaus at an average potential of 0.25 V, 0.24 V and 0.27 V corresponding to discharge capacities of 6.6, 5.5 and 3.6 Li can be achieved respectively for Mg₂FeH₆, Mg₂CoH₅ and Mg₂NiH₄. From in situ X-ray diffraction (XRD) characterizations of complex hydride based electrodes, dehydrogenation leads to a decrease of the intensities of the diffraction peaks suggesting a strong loss of crystallinity since formation of Mg and M (M = Fe, Co, Ni) peaks is not observed. ⁵⁷Fe Mössbauer spectroscopy confirms the formation of nanoscale Fe or an amorphous Mg–Fe alloy during the decomposition of Mg₂FeH_6. Interestingly, lattice parameter variations suggest phase transitions in the Mg₂NiH₄ system involving the formation of low hydrogen content hydride Mg₂NiH, while an increase of lattice parameters of Mg₂CoH₅ hydride could be attributed to the formation of a Mg₂CoH₅Li_x solid solution compound up to x = 1.     

Double core-shell of Si@PANI@TiO2 nanocomposite as anode for lithium-ion batteries with enhanced electrochemical performance

A unique double core-shell structure of Si@PANI@TiO₂ nanocomposite is synthesized by a simple in-situ growth method. The two shells of polyaniline (PANI) and TiO₂, hand in hand, play a key role to improve the electrochemical performance: First, the flexible properties of polyaniline (PANI) effectively accommodate the volume change of Si during the cycling. Second, the good mechanical feature of TiO₂ can maintain the structural integrity and attenuate the volume expansion of Si cores. Finally, both of polyaniline and the lithiated TiO₂ enhance the conductivity of Si, which promotes the electrons transport. Resulting in the Si@PANI@TiO₂ double core-shell nanocomposite exhibits remarkable synergy in large, reversible lithium storage, delivering a reversible capacity as high as 1027 mAh g^?1 after 500 cycles and a superior rate capacity of 640 mAh g^?1, at a current of 500 and 4000 mA g^?1, respectively. This excellent cycling and high-rate capability can be ascribed to the unique and well-designed double core-shell structure with the synergistic effect between polyaniline (PANI) and TiO₂.     

Mesoporous carbon-encapsulated NiO nanocomposite negative electrode materials for high-rate Li-ion battery

In this study, a novel mesoporous carbon-encapsulated NiO nanocomposite is proposed and demonstrated for Li-ion battery negative electrode. The nanostructure of the electrode composes of an ordered mesoporous CMK-3 as a 3D nanostructured current collector with micorporous channels for Li⁺ transportation. In addition, exclusive formation of NiO nanoparticles in the confined space of the ordered mesoporous carbon is achieved using the hydrophobic encapsulation route. The half-cell assembled with the synthesized NiO/CMK-3 nanocomposite is able to deliver a high charge capacity of 812 mAh g⁻¹ at the first cycle at a C-rate of 1000 mA g⁻¹ and retained throughout the test with only 0.236% decay per cycle. Even the C-rate as high as 3200 mA g⁻¹, a charge capacity of 808 mAh g⁻¹ contributed by the NiO nanoparticles in CMK-Ni is obtained, which shows excellent rate capability for NiO with utilization close to 100%. The result suggests fast kinetics of conversion reaction for NiO with Li⁺. It also indicates the blockage of the pore channels by NiO nanoparticles does not take place in the synthesized NiO/CMK-3.     

Nickel foam supported Sn-Co alloy film as anode for lithium ion batteries

Sn-Co alloy films are deposited electrochemically directly onto nickel foam in an aqueous solution. The influence of electrochemical current density and heat treatment on the structure and morphology of the electrodeposited films is studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the Sn-Co alloy films are further investigated by galvanostatic charge-discharge tests. As anodes for lithium ion batteries, the Sn-Co alloy-film anodes, after further heat treatment at 200 °C for 30 min, delivers a specific capacity of 663 mAh g⁻¹ after 60 cycles. This high capacity retention is attributed to the unique electrode configuration with an enhanced interface strength between the active material and the current collector formed in the heat-treatment process.     

Nanostructured Si/Sn-Ni/C composite as negative electrode for Li-ion batteries

A nanostructured composite with overall atomic composition Ni_0.14Sn_0.17Si_0.32Al_0.037C_0.346 has been prepared combining powder metallurgy and mechanical milling techniques for being used as anode material in Li-ion battery. Chemical and structural properties of the nanocomposite have been determined by X-ray diffraction (XRD), ¹¹⁹Sn Transmission Mössbauer Spectroscopy (TMS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite consists of Si particles with typical size ∼150 nm embedded in a poorly crystallized and complex multielemental matrix. The matrix is composed mostly by Ni_3.4Sn₄, and disordered carbon. Electrochemical evaluation shows a high reversible capacity of 920 mAh g⁻¹, with reasonable reversible capacity retention (∼0.1% loss/cycle) over 280 cycles.     

Solvothermal synthesis of hierarchical LiFePO4 microflowers as cathode materials for lithium ion batteries

Hierarchical LiFePO₄ microflowers have been successfully synthesized via a solvothermal reaction in ethanol solvent with the self-prepared ammonium iron phosphate rectangular nanoplates as a precursor, which is obtained by a simple water evaporation method beforehand. The hierarchical LiFePO₄ microflowers are self-assemblies of a number of stacked rectangular nanoplates with length of 6-8 μm, width of 1-2 μm and thickness of around 50 nm. When ethanol is replaced with the water-ethanol mixed solvent in the solvothermal reaction, LiFePO₄ micro-octahedrons instead of hierarchical microflowers can be prepared. Then both of them are respectively modified with carbon coating through a post-heat treatment and their morphologies are retained. As a cathode material for rechargeable lithium ion batteries, the carbon-coated hierarchical LiFePO₄ microflowers deliver high initial discharge capacity (162 mAh g⁻¹ at 0.1 C), excellent high-rate discharge capability (101 mAh g⁻¹ at 10 C), and cycling stability, which exhibits better electrochemical performances than carbon-coated LiFePO₄ micro-octahedrons. These enhanced electrochemical properties can be attributed to the hierarchical micro/nanostructures, which can take advantage of structure stability of micromaterials for long-term cycling. Furthermore the rectangular nanoplates as the building blocks can improve the electrochemical reaction kinetics and finally promote the rate performance.     

Carbon-coated SiO2 nanoparticles as anode material for lithium ion batteries

A simple approach is proposed to prepare C-SiO₂ composites as anode materials for lithium ion batteries. In this novel approach, nano-sized silica is soaked in sucrose solution and then heat treated at 900 °C under nitrogen atmosphere. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis shows that SiO₂ is embedded in amorphous carbon matrix. The electrochemical test results indicate that the electrochemical performance of the C-SiO₂ composites relates to the SiO₂ content of the composite. The C-SiO₂ composite with 50.1% SiO₂ shows the best reversible lithium storage performance. It delivers an initial discharge capacity of 536 mAh g⁻¹ and good cyclability with the capacity of above 500 mAh g⁻¹ at 50th cycle. Electrochemical impedance spectra (EIS) indicates that the carbon layer coated on SiO₂ particles can diminish interfacial impedance, which leads to its good electrochemical performance.     

A new form of manganese carbonate for the negative electrode of lithium-ion batteries

A reverse micelles method is used in the synthesis of manganese carbonate. The use of cetyl-trimethylammonium bromide surfactant and hexanol cosurfactant allows the preparation of a new monodispersed form of MnCO₃. Particles with a regular shape and ca. 200 nm edges are observed by electron microscopy. The electrochemical reaction with lithium of the manganese carbonate leads to the formation of the manganese metal and lithium carbonate as the main side product, which yields higher capacity than graphite and good capacity retention. Submicron MnCO₃ could replace other more toxic and expensive anodes used in recent commercial Li-ion products.     

Electrochemical performance of VOMoO4 as negative electrode material for Li ion batteries

Polycrystalline samples of VOMoO₄ are prepared by a solid-state reaction method and their electrochemical properties are examined in the voltage window 0.005–3 V versus lithium. The reaction mechanism of a VOMoO₄ electrode for Li insertion/extraction is followed by ex situ X-ray diffraction analysis. During initial discharge, a large capacity (1280 mAh g⁻¹) is observed and corresponds to the reaction of ∼10.3 Li. The ex situ XRD patterns indicate the formation of the crystalline phase Li₄MoO₅ during the initial stages of discharge, which transforms irreversibly to amorphous phases on further discharge to 0.005 V. On cycling, the reversible capacity is due to the extraction/insertion of lithium from the amorphous phases. A discharge capacity of 320 mAh g⁻¹ is obtained after 80 cycles when cycling is performed at a current density of 120 mA g⁻¹.     

Synthesis of plate-like Li3V2(PO4)3/C as a cathode material for Li-ion batteries

Plate-like Li₃V₂(PO₄)₃/C composite is synthesized via a solution route followed by solid-state reaction. The Li₃V₂(PO₄)₃/C plates are 40-100 nm in thicknesses and 2-10 μm in lengths. TEM images show that a uniform carbon layer with a thickness of 5.3 nm presents on the surfaces of Li₃V₂(PO₄)₃ plates. The apparent Li-ion diffusion coefficient of the plate-like Li₃V₂(PO₄)₃/C is calculated to be 2.7 × 10⁻⁸ cm² s⁻¹. At a charge-discharge rate of 3 C, the plate-like Li₃V₂(PO₄)₃/C exhibits an initial discharge capacity of 125.2 and 133.1 mAh g⁻¹ in the voltage ranges of 3.0-4.3 and 3.0-4.8 V, respectively. After 500 cycles, the electrodes still can deliver a discharge capacity of 111.8 and 97.8 mAh g⁻¹ correspondingly, showing a good cycling stability.     

Microstructure and electrochemical performance of Si-SiO2-C composites as the negative material for Li-ion batteries

Si-SiO₂-C composites are synthesized by ball milling the mixture of SiO, graphite and coal pitch, and subsequent heat treatment at 900 °C in inert atmosphere. The electrochemical performance and microstructure of the composites are investigated. XRD and TEM tests indicate that the carbon-coating structure of Si-SiO₂-C composites form in pyrolysis process, which can remarkably improve the electrochemical cycling performance. The coal pitch as carbon precursor and graphite demonstrate the same important effect on the Li-alloying/de-alloying property of the Si-SiO₂-C composites. The Si-SiO₂-C composites exhibit the electrochemical reversible Li-alloying/de-alloying capacity of 700 mAh g⁻¹ and excellent cyclic stability even at about the 90th cycle.     

Nanostructured Fe2O3 and CuO composite electrodes for Li ion batteries synthesized and deposited in one step

Nanostructured composite electrodes based on iron and copper oxides for applications in Li-ion batteries are produced by Electrostatic spray pyrolysis (ESP). The electrodes are directly formed by electrospraying precursor solutions containing either iron or copper salts dissolved in N-methylpyrrolidone (NMP) together with polyvinylidene fluoride (PVdF) as binder. The morphology and the structure of the deposited electrodes are investigated by X-ray diffraction (XRD) and Transmission electron microscopy (TEM), which show that sub-micrometric deposits are formed as a composite of oxide nanoparticles of a few nanometers in a PVdF polymer matrix. Electrochemical characterization by cyclic voltammetry (CV) and galvanostatic charge-discharge tests demonstrate that the conversion reactions in these electrodes enable initial discharge capacities of about 800 mAh g⁻¹ and 1550 mAh g⁻¹ for CuO and Fe₂O₃, respectively. The capacity retention in both cases needs further improvements.     

Synthesis and performance of carbon-coated Li3V2(PO4)3 cathode materials by a low temperature solid-state reaction

The carbon-coated monoclinic Li₃V₂(PO₄)₃ (LVP) cathode materials can be synthesized by a low temperature solid-state reaction route. The influences of different heat treatments on the LVP have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical methods. In the range of 3.0-4.3 V, both LVP/C electrodes present good rate capability and excellent cyclic performance. It is found that the sample (LVP1/C) prepared by the two-step heat treatment with pre-sintering at 350 °C delivers the initial discharge capacity of 99.8 mAh g⁻¹ at 10 C charge-discharge rate and still retains 95.8 mAh g⁻¹ after 300 cycles. For the sample (LVP2/C) synthesized by the one-step heat treatment, 95.9 and 90.0 mAh g⁻¹ are obtained in the 1st and 300th cycles at 10 C rate, respectively. Our results based on the XRD patterns and the SEM images suggest that the good rate capability and cyclic performance may be owing to the pure phases, small particles, large specific surface areas and residual carbon. In the range of 3.0-4.8 V, compared with the LVP2/C, the LVP1/C also exhibits better performance.     

Fe and Ni impurity distribution and electrochemical performance of LiCoO2 electrode materials for lithium ion batteries

The distribution of Fe³⁺ and Ni³⁺ impurities and the electrochemical performance of LiCoO₂ electrodes were examined. Commercial LiCoO₂ powders supplied by Aldrich were used. The electrochemical performance of LiCoO₂ was modified by rotor blade grinding of LiCoO₂ followed by thermal treatment. Structural information on Fe³⁺ and Ni³⁺ impurities was obtained using both conventional X-band and high-frequency electron paramagnetic resonance spectroscopy (EPR). It was found that Fe³⁺ occupies a Co-site having a higher extent of rhombic distortion, while Ni³⁺ is in a trigonally distorted site. After rotor blade grinding of LiCoO₂, isolated Fe³⁺ ions display a tendency to form clusters, while isolated Ni³⁺ ions remain intact. Re-annealing of ground LiCoO₂ at 850 °C leads to disappearance of iron clusters; isolated Fe³⁺ ions are recovered. The electrochemical performance of LiCoO₂ was discussed on the basis of isolated and clustered ions.