Use In Rechargeable Lithium Batteries Research Articles

Li2SnO3 as a Cathode Material for Lithium-ion Batteries: Defects, Lithium Ion Diffusion and Dopants

Tin-based oxide Li2SnO3 has attracted considerable interest as a promising cathode material for potential use in rechargeable lithium batteries due to its high- capacity. Static atomistic scale simulations are employed to provide insights into the defect chemistry, doping behaviour and lithium diffusion paths in Li2SnO3. The most favourable intrinsic defect type is Li Frenkel (0.75 eV/defect). The formation of anti-site defect, in which Li and Sn ions exchange their positions is 0.78 eV/defect, very close to the Li Frenkel. The present calculations confirm the cation intermixing found experimentally in Li2SnO3. Long range lithium diffusion paths via vacancy mechanisms were examined and it is confirmed that the lowest activation energy migration path is along the c-axis plane with the overall activation energy of 0.61 eV. Subvalent doping by Al on the Sn site is energetically favourable and is proposed to be an efficient way to increase the Li content in Li2SnO3. The electronic structure calculations show that the introduction of Al will not introduce levels in the band gap.

Defects, Dopants and Lithium Mobility in Li9V3(P2O7)3(PO4)2

Layered Li9V3(P2O7)3(PO4)2 has attracted considerable interest as a novel cathode material for potential use in rechargeable lithium batteries. The defect chemistry, doping behavior and lithium diffusion paths in Li9V3(P2O7)3(PO4)2 are investigated using atomistic scale simulations. Here we show that the activation energy for Li migration via the vacancy mechanism is 0.72 eV along the c-axis. Additionally, the most favourable intrinsic defect type is Li Frenkel (0.44 eV/defect) ensuring the formation of Li vacancies that are required for Li diffusion via the vacancy mechanism. The only other intrinsic defect mechanism that is close in energy is the formation of anti-site defect, in which Li and V ions exchange their positions (1.02 eV/defect) and this can play a role at higher temperatures. Considering the solution of tetravalent dopants it is calculated that they require considerable solution energies, however, the solution of GeO2 will reduce the activation energy of migration to 0.66 eV.

Combining electrospinning and sputtering to improve rechargeable lithium battery cathodes: coating carbon fibre felt with nickel sulfide

Various nickel sulfide nanostructures have been developed for the fabrication of high surface area electrodes for rechargeable lithium batteries. In this study, we fabricated a nickel sulfide covered carbon fibre felt with high uniformity, high density, and large area for cathode materials for use in rechargeable lithium batteries, by using a combined electrospinning and sputtering deposition technique. In particular, the nickel sulfide/carbon fibre felt is a multi-functional material that can act as a conducting electrode itself without the use of binders and conductive materials owing to the high conductivity of the interlinked carbon fibre structures. A Li/nickel sulfide cell with current density of 100 mA g−1 exhibits good cycle performance and high first discharge capacity (970.46 mAh g−1) and good coulombic efficiency of 99% at 20 cycles. This electrode has good structural and electrochemical properties and has a potential to be commercialized when the properties are matured.

Polycyclic Quinone Fused by a Sulfur-containing Ring as an Organic Positive-electrode Material for Use in Rechargeable Lithium Batteries

As a minor-metal free positive-electrode active material for use in rechargeable lithium batteries, a polycyclic quinone fused by a sulfur-containing dithiin ring, dibenzo[b,i]thianthrene-5,7,12,14-tetrone (SPT), was investigated. The prepared electrode in which the SPT was incorporated shows an initial discharge capacity of 231 mAh/g which corresponds to a four-electron transfer reaction of the SPT molecule. The average discharge potential of 2.6V vs. Li+/Li for the SPT-electrode is 0.4V higher than that of a previously reported cyclic quinone fused by a benzo-ring, i.e., 5,7,12,14-pentacenetetrone (PT). The effect of introducing saturated sulfur atoms into a polycyclic quinone skeleton is discussed along with the results of the DFT calculation, and a guide for designing an organic molecule which can satisfy both a high discharge potential and long cycle-life requirement is suggested.

Redox Active Oligomers Synthesized from Anthraquinone for Use in Rechargeable Lithium Batteries

Using redox active organic materials, that contain no scarce metal resources, as a positive-electrode active material instead of conventionally used rare-metal oxides can be a solution to the resource problem of the current rechargeable lithium batteries. Several types of organic positive-electrode materials have been proposed. Among them, low-molecular-weight crystalline organic compounds have been drawing attentions recently, since these compounds tend to show high utilization ratios during the charge/discharge processes. 9,10-Anthraquinone (AQ) (Fig. 1a), one of those low-molecular-weight crystalline organic compounds, also shows a capacity close to its theoretical value [1,2]; however, the electrode using AQ tends to seriously degrade upon cycling because of the dissolution of the redox-related molecules into the electrolyte solution during cycling.To suppress the dissolution and to improve their cycle stability, we focused our attention on the oligomerization technique. In this study, an anthraquinone dimer and a trimer connected by the -C≡C- bonds (Figs. 1b and 1c) were newly synthesized using the Sonogashira cross-coupling reaction; and their performances as positive-electrode active materials were compared with the AQ-monomer. The positive electrodes using the dimer and trimer as active materials showed initial discharge capacities of about 200 mAh/g, with the average voltages of 2.2-2.3 V vs. Li+/Li. These values are close to those of the AQ monomer, suggesting the two-electron redox reaction per AQ unit. Fig. 2 compares the cycle-life performances of the electrode using the AQ-monomer, dimer, and trimer. While the capacity of the AQ-monomer electrode rapidly decreased, the synthesized dimer and trimer showed better cycle stabilities. In particular, the trimer retained almost a constant capacity during 50 cycles without drastic decay. The oligomerization of the AQ units effectively reduces the solubility. The present study revealed that oligomerization of the redox active molecular units was an effective way to extend the cycle-life without losing the discharge capacity.

Novel cross-linked copolymer gel electrolyte supported by hydrophilic polytetrafluoroethylene for rechargeable lithium batteries

A novel hydrophilic polytetrafluoroethylene (PTFE)-supported gel polymer electrolyte (GPE) membrane based on the cross-linked poly(ethylene glycol) and poly(glycidyl methacrylate) block copolymer (PEG–b–PGMA) is successfully prepared by cationic ring-opening polymerization and followed by in situ cross-linking process. The poly(ethylene glycol) side chains of PEG–b–PGMA interact with the liquid electrolyte and hold it inside the membrane, while the hydrophilic and highly-porous PTFE membrane offers mechanical support for the cross-linked GPE. The ionic conductivity of the optimized GPE-3 reaches 1.30×10−3Scm−1 at 25°C and is high enough to be applied in lithium secondary batteries. The GPE is electrochemically stable up to 4.5V versus Li/Li+. Moreover, the optimized GPE membrane demonstrates non-flammability and good dimensional stability at elevated temperature, which can improve the safety of the cell. The Li/LiFePO4 cell using the GPE-3 exhibits stable cycling behavior and superior rate performance comparable to the cell based on conventional liquid electrolyte. Therefore, the reported GPE is very promising for the use in rechargeable lithium batteries.

Wrinkled-graphene enriched MoO3 nanobelts with increased conductivity and reduced stress for enhanced electrochemical performance

MoO3 has long suffered from poor conductivity and cyclability, which limit its high rate performance and ultralong cycling ability. Increasing the electronic conductivity with electron pathways of cathode materials can effectively enhance the lithium storage properties with stable cyclability and rate capability theoretically. Here the MoO3-reduced graphene oxide (rGO) hybrid nanobelts were designed and prepared and were tested as cathode materials for lithium batteries. It is demonstrated that the rGO is wrinkled and twisted around MoO3 nanobelts after reacting under high temperature and pressure conditions. The unique morphology of rGO, which has continuous electron pathways and stress buffering effects, endows the MoO3-rGO hybrid nanobelts with significantly increased rate capability and cycling ability. Meanwhile, it is demonstrated that MoO3-rGO hybrid nanobelts are promising cathode materials for use in rechargeable lithium batteries and our synthesis strategy is also versatile for exploiting advanced materials for Li-ion batteries.

Crystalline polycyclic quinone derivatives as organic positive-electrode materials for use in rechargeable lithium batteries

Abstract The performance of 9,10-anthraquinone (AQ), and 5,7,12,14-pentacenetetrone (PT) as active materials for rechargeable lithium batteries was investigated. Positive-electrodes in which AQ and PT were incorporated showed initial discharge capacities of greater than 200 mAh/g (AQ or PT) . The obtained discharge capacities suggest that a multi-electron redox reaction takes place in each derivative. The discharge capacity of the positive-electrode with AQ rapidly decreased during the charge/discharge cycles; however, the positive-electrode with PT showed a relatively good cycle-life performance; it maintained about 80% of the initial capacity even after 100 cycles.

Redox active poly( N-vinylcarbazole) for use in rechargeable lithium batteries

The performance of poly( N-vinylcarbazole) (PVK) for use in rechargeable lithium batteries was investigated. The positive-electrode (cathode) using PVK as an active material exhibited a discharge capacity of more than 120 mAh g −1 (PVK) with a mean potential of 3.7 V vs. Li +/Li. The PVK-electrode showed a stable cycle-life performance. In addition, the application of this polymer as a redox active binder material was also examined using a composite electrode with lithium iron phosphate (LiFePO 4). The LiFePO 4–PVK composite electrode showed a higher total discharge capacity than the conventional LiFePO 4–PVDF electrode.

Organic Positive-Electrode Materials Based on Dialkoxybenzoquinone Derivatives for Use in Rechargeable Lithium Batteries

The performance of 2,5-dialkoxy-1,4-benzoquinone derivatives as positive-electrode active materials for use in rechargeable lithium batteries was investigated. These derivatives showed stepwise two-electron redox behaviors in cyclic voltammetry, and also exhibited high initial discharge capacities of more than 200 mAh g-1 in charge/discharge tests. In particular, a positive-electrode that used a methoxy derivative showed the largest discharge capacity (close to 300 mAh g-1) among the dialkoxy derivatives tested. These discharge curves imply benzoquinone-based two-electron redox behavior. Theoretical quantum calculations based on the density functional theory (DFT) were also performed to discuss the electrochemical properties of these materials, and supported the experimental results.

High-capacity organic positive-electrode material based on a benzoquinone derivative for use in rechargeable lithium batteries

The performance of 2,5-dimethoxy-1,4-benzoquinone (DMBQ) as an active material for rechargeable lithium batteries was investigated. A positive-electrode that incorporated DMBQ showed an initial discharge capacity of 312 mAh g −1 with an average voltage of 2.6 V vs. Li +/Li. This discharge capacity corresponds to a benzoquinone-based two-electron redox behavior, and is more than twice that of the conventional positive-electrode material lithium cobalt oxide (LiCoO 2). Furthermore, the positive-electrode with DMBQ showed fair cycle-life performance. Theoretical quantum calculations based on the density functional theory (DFT) were also performed to clarify the mechanism of the electrochemical properties of the solid state of DMBQ.

Preparation of Lithium Sulfide-Carbon Composites Using Spark-Plasma-Sintering Process and their Electrochemical Properties

Lithium sulfide (Li2S)-carbon composite positive electrodes were prepared by the spark-plasma-sintering (SPS) process for use in rechargeable lithium batteries. By the SPS treatment of Li2S and acetylene black (AB) blended powder, the strong binding between the active materials and the carbon powders were formed. Such contact effect improved the electrochemical performance of the cells with liquid electrolytes (1M LiFP6/(EC+DMC)), probably due to the increase in conductivity of the positive electrodes, though the samples prepared by the ball-milling process showed no significant capacity in the electrochemical tests.

Li2MnSiO4 Lithium Battery Material: Atomic-Scale Study of Defects, Lithium Mobility, and Trivalent Dopants

A new family of silicate materials has attracted interest for potential use in rechargeable lithium batteries. The defect chemistry, doping behavior, and lithium diffusion paths in the Li2MnSiO4 cathode material are investigated by advanced modeling techniques. Our simulations show good reproduction of both monoclinic and orthorhombic structures of Li2MnSiO4. The most favorable intrinsic defect type is found to be the cation anti-site defect, in which Li and Mn ions exchange positions. The migration energies suggest differences in intrinsic Li mobility between the monoclinic and orthorhombic polymorphs, which would affect their rate capability as rechargeable electrodes. The results indicate curved Li diffusion paths and confirm the anisotropic nature of Li transport, which is probably general for the Li2MSiO4 (M = Mn, Fe, Co) family of compounds. Subvalent doping by Al on the Si site is energetically favorable and could be a synthesis strategy to increase the Li content.

Reversible Lithium Intercalation in Teardrop‐Shaped Ultrafine SnP0.94 Particles: An Anode Material for Lithium‐Ion Batteries.

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Advanced, lithium batteries based on high-performance composite polymer electrolytes

Progress in lithium battery technology may be achieved by passing from a conventional liquid electrolyte structure to a solid-state, polymer configuration. In this prospect, great R&D effort has been devoted to the development of suitable lithium conducting polymer electrolytes. In previous papers [F. Croce, L. Settimi, B. Scrosati, Electrochem. Commun. 8 (2006) 364 [1]; F. Croce, S. Sacchetti, B. Scrosati, J. Power Sources, in press [2]], we have shown that composite membranes based on blends between poly(ethylene oxide) and lithium salts with the dispersion of functionalized ZrO 2 ceramic filler, have unique transport and interfacial properties. In this paper, we complete the study of these advanced polymer electrolytes by evaluating their use in rechargeable lithium batteries. The results confirm the practical interest of these electrolytes which appear to be suitable for the fabrication of batteries directed to application in emerging technologies, such as those associated to hybrid and electric vehicles.

New sulfone electrolytes for rechargeable lithium batteries.: Part I. Oligoether-containing sulfones

Sulfones with different length of oligo ethylene glycol segments have been synthesized and tested for use in rechargeable lithium batteries. Relative to the model compound ethylmethyl sulfone (EMS), which has a melting point of 36.5 °C, the new sulfones have low melting points, mostly depressed below room temperature. Their conductivities are lower than that of EMS. The highest ambient temperature conductivity of 10 −2.58 S cm −1 was obtained for 0.7 M LiTFSI/MEMS solution (MEMS is methoxyethylmethylsulfone). The sulfones showed wide electrochemical stability windows, in excess of 5.0 V vs. Li/Li +, increasing with decreasing length of the oligoether chains. Unlike their fluorinated analogs, the present sulfones prove incompatible with graphite anode hosts, but a cell with lithium metal anode and manganate cathode performed well, maintaining good coulomb efficiency over 200 cycles.

A positive-temperature-coefficient electrode with thermal cut-off mechanism for use in rechargeable lithium batteries

A novel positive-temperature-coefficient (PTC) electrode was prepared by coating a thin layer of epoxy-carbon PTC material in between the electroactive LiCoO 2 layer and the electrode substrate and used for self-actuating thermal cut-off of Li-ion batteries when the batteries are overheated. Experimental results from cyclic voltammetry, impedance spectrometry and charge–discharge measurements demonstrate that the PTC electrode exhibits normal electrochemical behaviors at ambient temperature, but shows an enormous increase in the resistance at the temperature range of 100–130 °C. This PTC behavior of the electrode provides a current-limiting effect, acting as a reversible thermal shutdown switch for rechargeable lithium batteries.

Improved cyclability of Na-birnessite partially substituted by cobalt

We measured the electrode performance of Na-birnessite, which is layered manganese dioxide with sodium ions and water in the interlayer, for use in rechargeable lithium batteries. We focused on the effects of water on the electrode performance. X-ray diffraction (XRD) measurement and thermogravimetric (TG) analysis indicated that the weight loss on heating the material at 100 °C corresponded to the removal of surface water with no structural change, while that at 150 °C was associated with the removal of lattice water, leading to the layer shrinkage. According to this result, we prepared three kinds of electrode samples with different drying conditions, and examined the effect on the electrode performance. Furthermore, to improve the cyclability, we synthesized samples in which cobalt was substituted for some of the manganese. Even with a large substitution ratio of over 30%, we obtained the same initial capacity as the non-substituted sample, and the cyclability was improved. We assume that the substituted cobalt fixed sodium ions in the interlayer in the form of pillars that stabilized the layer structure.

Experimental and theoretical analysis of LiMn 2O 4 cathodes for use in rechargeable lithium batteries by electrochemical impedance spectroscopy (EIS)

A comparative study of the impedance response measured with composite electrodes and thin film electrodes of LiMn 2O 4 was conducted. The electrodes were prepared on different current collectors (i.e. aluminium, carbonised aluminium and gold) and the experiments were run at various state-of-discharge (SOD) and liquid electrolyte compositions. The impedance response was shown to be strongly dependent on the current collector used. It was demonstrated that the high-to-medium frequency semicircle can be attributed to the contact resistance between the current collector and the active electrode material and that the medium-to-low frequency semicircle can be ascribed to the active electrode material. For the analysis, a mathematical model based on a resistance between the current collector and the active electrode material, interfacial-charge transfer coupled to the double-layer charging and solid-phase diffusion was developed. Potential distribution due to porous electrode effects was also considered. Fitting the model to experimental data enabled reasonable values of the exchange-current density, the double-layer capacitance and the solid-phase diffusion coefficient. However, the very low fitted value of the effective conductivity in the liquid phase indicates that this model does not give a satisfying description of the intercalation process of LiMn 2O 4.

Investigation of LiMn 2O 4 cathodes for use in rechargeable lithium batteries by linear sweep voltammetry (LSV) : Part II. Experimental study using thin films, single particles and composite electrodes

Thin films, single particles and a composite electrode of the cathode material LiMn 2O 4 in the lithium battery system were investigated by linear sweep voltammetry (LSV) in 1 M LiClO 4+PC:EC. The experimental data were compared to and analysed by mathematical models described in Part I of this work. Analysis of the measured peak potential, E p, showed clearly that the larger the characteristic length, the larger is the potential peak shift, at a given sweep rate. From the observations of the measured peak current behaviour, I p, it seems that the composite electrode and the single particles are semi-infinite diffusion limited at all sweep rates applied. For the thin films, when increasing the sweep rate, a transition from finite to semi-infinite mass transfer limitation is indicated. A model based on solid-phase diffusion, interfacial charge transfer and an external IR-drop could fairly well be fitted to the experimental data measured on a single electrode system at a given sweep rate. It was found that the determined parameter values, i.e. solid-phase diffusion coefficient and the IR-drop, vary greatly with sweep rate and characteristic length. These results indicate that the physical description used is an oversimplification for describing the reaction mechanism in LiMn 2O 4.