Novel organic–inorganic poly (3,4-ethylenedioxythiophene) based nanohybrid materials for rechargeable lithium batteries and supercapacitors

Synthesis and characterization of poly (3,4-ethylenedioxythiophene) (PEDOT) interleaved between the layers of crystalline oxides of V and Mo is discussed with special emphasis on their application potential as electrodes for rechargeable Li batteries and supercapacitors. The expansion of the interlayer spacing of crystalline oxides (for example, V₂O₅ causes expansion from 0.43 to 1.41 nm) is consistent with a random layer stacking structure. These hybrid nanocomposites when coupled with a large-area Li foil electrode in 1 M LiClO₄ in a mixture of ethylene and dimethylcarbonate (1:1, v/v), give enhanced discharge capacity compared to pristine oxides. For example a discharge capacity of ∼350 mAh g⁻¹, in the potential range 4.2–2.1 V (versus Li⁺/Li) is obtained for PEDOT–V₂O₅ hybrid which is significantly large compared to that for simple Li-intercalated V₂O_5. The improvement of electrochemical performance compared with that of pristine oxides is attributed to higher electric conductivity, enhanced bi-dimensionality and increased structural disorder. Although these conducting polymer-oxide hybrids delivered more than 300 mAh g⁻¹ in the potential range 1.3–4.3 V, their cycle life needs further improvements to realize their commercial potential. Similarly, the double layer capacitance of MoO₃ increases from ∼40 mF g⁻¹ to ∼300 F g⁻¹ after PEDOT incorporation in the interlayer gap of MoO₃ under similar experimental conditions and the nanocomposite displays intriguing effects with respect to electrochemical Li⁺ insertion. The PEDOT–MoO₃ nanocomposite appears to be a promising electrode material for non-aqueous type supercapacitors.     

Electrochemical properties of the Li-ion polymer batteries with P(VdF-co-HFP)-based gel polymer electrolyte

Gel polymer electrolytes consisting of 25 wt.% P(VdF-co-HFP), 65 wt.% ethylene carbonate + propylene carbonate and 10 wt.% LiN(CF₃SO₂)₂ are prepared using by a solvent-casting technique. The electrodes are for use in lithium-ion polymer batteries. The electrochemical characteristics of the gel polymer electrolytes are evaluated by means of ac impedance and cyclic voltammetry. The charge–discharge performance of lithium polymer and lithium-ion polymer batteries is examined. A LiCoO₂ | gel polymer electrolyte (GPE) | mesocarbon microbeads (MCMB) cell delivers a discharge capacity of 146.8 and 144.5 mAh g⁻¹ on the first and the 20th cycle, respectively. The specific discharge capacity is greater than 140 mAh g⁻¹ for up to 20 cycle at all the current densities examined.     

LiMn2O4 cathode materials synthesized by the cellulose–citric acid method for lithium ion batteries

A new technique was employed to synthesize spinel LiMn₂O₄ cathode materials by adding cellulose and citric acid to an aqueous solution of lithium and manganese salts. Various synthesis conditions such as the calcination temperature and the citric acid-to-metal ion molar ratio (R) were investigated to determine the ideal conditions for preparing LiMn₂O₄ with the best electrochemical characteristics. The optimal synthesis conditions were found to be R = 1/3 and a calcination temperature of 800 °C. The initial discharge capacity of the material synthesized using the optimal conditions was 134 mAh g⁻¹, and the discharge capacity after 40 cycles was 125 mAh g⁻¹, at a current density of 0.15 mA cm⁻² between 3.0 and 4.35 V. Details of how the initial synthesis conditions affected the capacity and cycling performance of LiMn₂O₄ are discussed.     

Electrochemical behavior of Sn/SnO2 mixtures for use as anode in lithium rechargeable batteries

Anodes derived from oxides of tin have, of late, been of considerable interest because, in principle, they can store over twice as much lithium as graphite. A nanometric matrix of Li₂O generated in situ by the electrochemical reduction of SnO₂ can provide a facile environment for the reversible alloying of lithium with tin to a maximum stoichiometry of Li_4.4Sn. However, the generation of the matrix leads to a high first-cycle irreversible capacity. With a view to increasing the reversible capacity as well as to reduce the irreversible capacity and capacity fade upon cycling, tin–tin oxide mixtures were investigated. SnO₂, synthesized by a chemical precipitation method, was mixed with tin powder at two compositions, viz., 1:2 and 2:1, ball-milled and subjected to cycling studies. A mixture of composition Sn:SnO₂ = 1:2 exhibited a specific capacity of 549 mAh g⁻¹ (13% higher than that for SnO₂) with an irreversible capacity, which was 7% lower than that for SnO₂ and a capacity fade of 1.4 mAh g⁻¹ cycle⁻¹. Electrodes with this composition also exhibited a coulombic efficiency of 99% in the 40 cycles. It appears that a matrix in which tin can be distributed without aggregation is essential for realizing tin oxide anodes with high cyclability.     

Tin–graphite materials prepared by reduction of SnCl4 in organic medium: Synthesis,characterization and electrochemical lithiation

Tin–graphite materials were prepared by chemical reduction of SnCl₄ by t-BuONa-activated NaH. TEM imaging showed that the crude material is composed of an amorphous organic matrix containing tin present either as nanosized particles deposited on the graphite surface or as free aggregates. Subsequent washings with ethanol and water allow removal of side products as well as most part of the organic matrix. Electrochemical insertion of lithium occurred in graphite and in tin. The initial reversible massic capacity of 630 mAh g⁻¹ decayed to a stable value of 415 mAh g⁻¹ after 12 cycles. This capacity value was lower than the expected maximum one of 650 mAh g⁻¹ corresponding to a Sn/12C molar composition and assuming the formation of LiC₆ and Li₂₂Sn₅. Even if this massic capacity is not much improved by comparison with that of graphite, it must be pointed out that the volume capacity of this graphite/Sn material is much larger (2137 mAh cm⁻³) than that corresponding to graphite (837 mAh cm⁻³). It was hypothesized that the part of tin bound to graphite could be responsible for the stable reversible capacity. To the contrary, graphite unsupported tin aggregates would contribute to the observed gradual decline in the storage capacity. Therefore, the improvement in cycleability, compared to that of massive metals, could be attributed both to the nanoscale dimension of the metal particles and to interactions between graphite and metal the nature of which remaining to be precised.     

Properties of containing Sn nanoparticles activated carbon fiber for a negative electrode in lithium batteries

Activated carbon fiber (ACF) containing Sn nanoparticles were prepared by impregnation and were investigated as a negative electrode material in lithium batteries. The tin particle size was controlled by selecting an ACF with an adequate surface structure. This Sn/ACF composite cycled versus Li metal showed a first discharge capacity as high as 200 mAh g⁻¹ compared to the pristine ACF which showed only 87 mAh g⁻¹. Excellent cyclability with these composites was obtained with ACF BET SSA as large as 2000 m² g⁻¹ and 30 wt.% Sn.     

Effects of ball-milling on lithium insertion into multi-walled carbon nanotubes synthesized by thermal chemical vapour deposition

The effects of ball-milling on Li insertion into multi-walled carbon nanotubes (MWNTs) are presented. The MWNTs are synthesized on supported catalysts by thermal chemical vapour deposition, purified, and mechanically ball-milled by the high energy ball-milling. The purified MWNTs and the ball-milled MWNTs were electrochemically inserted with Li. Structural and chemical modifications in the ball-milled MWNTs change the insertion–extraction properties of Li ions into/from the ball-milled MWNTs. The reversible capacity (C_rev) increases with increasing ball-milling time, namely, from 351 mAh g⁻¹ (Li_0.9C₆) for the purified MWNTs to 641 mAh g⁻¹ (Li_1.7C₆) for the ball-milled MWNTs. The undesirable irreversible capacity (C_irr) decreases continuously with increase in the ball-milling time, namely, from 1012 mAh g⁻¹ (Li_2.7C₆) for the purified MWNTs to 518 mAh g⁻¹ (Li_1.4C₆) for the ball-milled MWNTs. The decrease in C_irr of the ball-milled samples results in an increase in the coulombic efficiency from 25% for the purified samples to 50% for the ball-milled samples. In addition, the ball-milled samples maintain a more stable capacity than the purified samples during charge–discharge cycling.     

Electrochemical lithium insertion into a poly(3,4-ethylenedioxythiophene)PEDOT/V2O5 nanocomposite

A nanocomposite comprised of conductive poly(3,4-ethylene dioxythiophene)PEDOT chains interleaved between the layers of crystalline V₂O₅ powder has been synthesized by direct in situ oxidation. The interlayer spacing of V₂O₅ expands from 4.32 to 13.84 Å and this interlayer separation is consistent with the existence of a monolayer of PEDOT in the V₂O₅ framework. The nanocomposite is coupled with a large-area Li foil counter electrode and a Li wire reference electrode in 1 M LiClO₄ in a mixture of ethylene and dimethylcorbonate (50/50 by volume), the discharge capacity is ≥300 m Ah g⁻¹ which is larger than that of pristine V₂O₅. The significant difference in capacity is explained on the basis of lithium ions insertion/de-insertion between the layers of V₂O₅.     

Cracking causing cyclic instability of LiFePO4 cathode material

The capacity of pure LiFePO₄ faded gradually from initial 149 mAh g⁻¹–117 mAh g⁻¹ under current density of 30 mA g⁻¹ at room temperature after 60 cycles. Some obvious cracks are observed in LiFePO₄ particles after cycling. The formation of cracks would lead to poor electric contact and capacity fading. A possible mechanism is proposed for the appearance of the cracks.     

Nanoparticled Li(Ni1/3Co1/3Mn1/3)O2 as cathode material for high-rate lithium-ion batteries

Nanoparticle of Li(Ni_1/3Co_1/3Mn_1/3)O₂ with size smaller than 40 nm was obtained by non-aqueous system co-precipitation method. The particle morphology and crystal plane orientation were observed by TEM and HRTEM. Electrochemical properties of this nanostructued material were studied with experiment cells. The results show that the material has high capacity of 160 mAh g⁻¹ and excellent rate capability for charge and discharge. For the 50C and 100C rate, its capacity remains above 100 mAh g⁻¹ after tens of cycles.     

Electrochemical characteristics of room temperature Li/FeS2 batteries with natural pyrite cathode

Electrochemical characteristics of Li/FeS₂ batteries having natural pyrite as cathode and liquid electrolytes have been studied at room temperature. The organic electrolytes used were 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in tetra(ethylene glycol) dimethyl ether (TEGDME) or a mixture of TEGDME and 1,3-dioxolane (DOX), and 1 M LiPF₆ in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). The pyrite powder and FeS₂ cathode were characterized by SEM, EDS, XRD and charge/discharge cycling. The discharge capacities of Li/FeS₂ cells with 1 M LiTFSI dissolved in TEGDME were 772 mAh g⁻¹ at the 1st cycle and 313 mAh g⁻¹ at the 25th cycle at 0.1C. The cycling performance could be improved by using a mixture of TEGDME and DOX as the electrolyte. It was found that TEGDME contributed to high initial discharge capacity, whereas, DOX contributed to better stabilization of the performance. The first discharge capacities of Li/FeS₂ cells showed a decreasing trend with higher current densities (615 and 534 mAh g⁻¹, respectively, at 0.5C and 1.0C). Li/FeS₂ cells with the battery grade electrolyte 1 M LiPF₆ in EC/DMC had lower initial discharge capacity and cycling capability compared to the TEGDME system. The natural pyrite cathode with 1 M LiTFSI dissolved in a mixture of TEGDME and DOX showed reasonably good first discharge capacity and overall cycling performance, suitable for application in room temperature lithium batteries.     

Nonflammable gel electrolyte containing alkyl phosphate for rechargeable lithium batteries

A nonflammable polymeric gel electrolyte has been developed for rechargeable lithium battery systems. The gel film consists of poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) swollen with lithium hexafluorophosphate (LiPF₆) solution in ternary solvent containing trimethyl phosphate (TMP). High ionic conductivity of 6.2 mS cm⁻¹ at 20 °C was obtained for the gel electrolyte consisting of 0.8 M LiPF₆/EC + DEC + TMP (55:25:20) with PVdF-HFP, which is comparable to that of the liquid electrolyte containing the same electrolytic salt. Addition of a small amount of vinylene carbonate (VC) in the gel electrolyte improved the rechargeability of a graphite electrode. The rechargeable capacity of the graphite in the gel containing VC was ca. 300 mAh g⁻¹, which is almost the same as that in a conventional liquid electrolyte system.     

Improvement of electrochemical properties of LiNi0.5Mn1.5O4 spinel

LiNi_0.5Mn_1.5O₄ material with a spinel structure is prepared by a sol–gel method. The material is initially fired at 850 °C and then subjected to a post-reaction annealing at 600 °C in order to minimize the nickel deficiency. The elevated firing temperature produces materials with a small surface-area which is beneficial for good capacity retention. Indeed, the spinel LiNi_0.5Mn_1.5O₄ not only shows a good cycle performance, but exhibits an excellent discharge capacity, i.e. 114 mAh g⁻¹ at 4.66 V plateau and 127 mAh g⁻¹ in total. Cyclic voltammetry and ac impedance spectroscopy are employed to characterize the reactions of lithium insertion and extraction in the LiNi_0.5Mn_1.5O₄ electrode. Excellent electrochemical performance and low material cost make this compound an attractive cathode for advanced lithium batteries.     

Electrochemical cycling behavior of LiCoO2 cathode prepared by mechanical alloying of hydroxides

Well-ordered high-temperature LiCoO₂ (HT-LiCoO₂) is synthesized by mechanical alloying (MA) of LiOH·H₂O and Co(OH)₂ powders and subsequent firing. Its electrochemical properties are investigated. The maximum discharge capacity of a sample mechanically alloyed and fired at 600 °C for 2 h is 152 mAh g⁻¹ at the C/40 rate, which is comparable to that obtained from a sample made by conventional solid state reactions. The cycleability is inferior, however, due to a relatively low crystallinity. When the firing temperature is increased to 850 °C, the first discharge capacity of 142 mAh g⁻¹ at the C/5 rate is increased by more than 10%, and retains 93% of its maximum value after 30 cycles. These cycling properties are about the same, or slightly higher, than those synthesized by firing a sample mixture of the same starting materials at 600 °C for 8 h and then at 850 °C for 24 h. Consequently, given the lower firing temperature and/or reduced reaction time, MA could prove a promising synthetic process for cathode materials used in rechargeable lithium batteries.     

Preparation of LiMn2O4 at the low temperature of 250 °C using eutectic self-mixing method

Spinel LiMn₂O₄ as a cathode material for lithium rechargeable batteries is prepared at the low temperature of 250 °C without any artificial mixing procedures of reactants. The phase transitions of lithium manganese oxide are found three times on heating at 250 °C. The prepared material exhibits the initial discharge capacity of 85.5 mAh g⁻¹ and the discharge capacity retention of 91.5% after 50 cycles.     

All-solid-state lithium secondary batteries using a layer-structured LiNi0.5Mn0.5O2 cathode material

All-solid-state cells of In/LiNi_0.5Mn_0.5O₂ using a superionic oxysulfide glass with high conductivity at room temperature of 10⁻³ S cm⁻¹ as a solid electrolyte were fabricated and the cell performance was investigated. Although a large irreversible capacity was observed at the 1st cycle, the solid-state cells worked as lithium secondary batteries and exhibited excellent cycling performance after the 2nd cycle; the cells kept charge–discharge capacities around 70 mAh g⁻¹ and its efficiency was almost 100%. This is the first case to confirm that all-solid-state cells using manganese-based layer-structured cathode materials work as lithium secondary batteries.     

Porous olivine composites synthesized by sol–gel technique

Porous LiMPO₄/C composites (where M stands for Fe and/or Mn) with micro-sized particles were synthesised by sol–gel technique. Particles porosity is discussed in terms of qualitative results obtained from SEM micrographs and in terms of quantitative results obtained from N₂ adsorption isotherms. Porous particles could be described as an inverse picture of nanoparticulate arrangement, where the pores serve as channels for lithium supply and the distance between the pores determines the materials kinetics. Tests show that the electrochemical behaviour of porous LiMPO₄/C composite is comparable with the results from the literature. The best electrochemical results were obtained with a LiFePO₄/C composite (over 140 mAh g⁻¹ at C/2 rate during continuous cycling). The capacity obtained with LiMnPO₄/C composite is much lower (40 mAh g⁻¹ at C/20 rate), although the textural properties are similar to those observed in the LiFePO₄/C composite.     

Co-doped Mn3O4: a possible anode material for lithium batteries

Undoped Mn₃O₄ shows relatively poor performance as a possible anode material on reversible reaction with lithium. A dramatic increase in cyclability is obtained on partial substitution of Mn by Co. Data are presented for the composition Mn_2.6Co_0.4O₄, which, after the first cycle, shows essentially constant capacity of 400 mAh g⁻¹ at ∼0.6 V.     

Polymeric gel electrolytes reinforced with glass-fibre cloth for lithium secondary batteries

Polymeric gel electrolytes (PGE), based on polyacrylonitrile blended with poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-co-HFP)), which are reinforced with glass-fibre cloth (GFC) to increase the mechanical strength, are prepared for the practical use in lithium secondary batteries. The resulting electrolytes exhibit electrochemical stability at 4.5 V against lithium metal and a conductivity value of (2.0–2.1)×10⁻³ S cm⁻¹ at room temperature. The GFC–PGE electrolytes show excellent strength and flexibility when used in batteries even if they contain a plasticiser. A test cell with LiCoO₂ as a positive electrode and mesophase pich-based carbon fibre (MCF) as a negative electrode display a capacity of 110 mAh g⁻¹ based on the positive electrode weight at the 0.2 C rate at room temperature. Over 80% of the initial capacity is retained after 400 cycles. This indicates that GFC is suitable as a reinforcing material to increase the mechanical strength of gel-based electrolytes for lithium secondary batteries.     

Novel architecture of composite electrode for optimization of lithium battery performance

We show that the polymeric binder of the composite electrode may have an important role on the lithium trivanadate Li_1.2V₃O₈ electrode performance. We describe a new tailored polymeric binder combination with controlled polymer–filler (carbon black) interactions that allows the preparation of new and more efficient electrode architecture. Using this polymeric binder, composite electrodes based on Li_1.2V₃O₈ display a room temperature cycling capacity of 280 mAh g⁻¹ (C/5 rate, 3.3–2 V) instead of 150 mAh g⁻¹ using a standard-type (poly(vinylidene fluoride)–hexafluoropropylene (PVdF–HFP) binder) composite electrode. We have coupled scanning electron microscopy (SEM) observations, galvanostatic cycling and electrochemical impedance spectroscopy in order to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance. Derived from these studies, the main key factors that provide efficient charge carrier collection within the composite electrode complex medium are discussed.