Search

Abstract: The stability of various polymer binders was systematically investigated in the oxygen-rich environment required for the operation of Li–O2 batteries. Due to the coverage on air electrode surface by the discharge products and decomposition products of the electrolyte during the discharge process of Li–O2 batteries, the binder in the air electrode is hard to be detected making the evaluation of its stability problematic. Therefore, stability of the binder polymers against the reduced oxygen species generated during the discharge process was investigated by ball milling the polymers with KO2 and Li2O2, respectively. Most of the studied polymers are unstable under these conditions and their decomposition mechanisms are proposed according to the analyzed products. Polyethylene was found to exhibit excellent stability when exposed to superoxide and peroxide species and is suggested as a robust binder for air electrodes. In addition, the binding strength of the polymer significantly affects the discharge performance of Li–O2 batteries. [Copyright &y& Elsevier]

Abstract: The commercial Li4Ti5O12 (LTO) is successfully modified by AlF3 via a low temperature process. After being calcined at 400 °C for 5 h, AlF3 reacts with LTO to form a composite material which mainly consists of Al3+ and F− co-doped LTO with small amounts of anatase TiO2. Al3+ and F− co-doped LTO demonstrates ultrahigh rate capability comparing to the pristine LTO. Since the amount of the byproduct TiO2 is relatively small, the modified LTO electrodes retain the main voltage characteristics of LTO with a minor feature similar to those of anatase TiO2. The doped LTO anodes deliver slightly higher discharge capacity and maintain the excellent long-term cycling stability when compared to the pristine LTO anode. Therefore, Al3+ and F− co-doped LTO composite material synthesized at low temperature is an excellent anode for stable and ultra-high power lithium-ion batteries. [Copyright &y& Elsevier]

Abstract: The effects of six types of aprotic organic solvents on the discharge performance and discharge products in Li-O2 batteries are systematically investigated. A large amount of Li2O2 is identified in the air electrodes discharged in glyme-based electrolytes, while only a small amount of Li2O2 is detected in the air electrodes discharged in the electrolytes of nitrile, ionic liquid, phosphate, and sulfoxide. Li2CO3 and LiF are also found as byproducts whose compositions are related to the solvents. Li2CO3 is produced from oxidation and decomposition of the solvent, not from the oxidation of the carbon-based air electrode, as revealed by using a 13C-labeled carbon electrode and the solid-state 13C-magic angle spinning nuclear magnetic resonance technique. LiF in the discharge products can be attributed to the attack of superoxide radical anions to the Teflon binder and/or the F-containing imide salt. The formation of these byproducts will significantly reduce the Coulombic efficiency and cycle life of the Li-air batteries. Among the studied solvents, dibutyl diglyme is the suitable solvent for Li-O2 batteries based on its overall properties. However, better electrolytes that can ensure the formation of Li2O2 but minimize other reaction products need to be further investigated for long cycling rechargeable Li-air batteries. [Copyright &y& Elsevier]

Abstract: It is well known that LATP (Li1+x+y Al x Ti2−x Si y P3−y O12) glass is a good lithium (Li)-ion conductor. However, the interaction between LATP glass and H+ ions in aqueous electrolytes (including the diffusion and surface adsorption of H+ ions) needs to be well understood before the long-term application of LATP glass in an aqueous electrolyte can be realized. In this work, we investigate H+-ion diffusion in LATP glass and their interactions with the glass surface using both experimental and modeling approaches. Our results indicate that the apparent H+-related current observed in the initial cyclic voltammetry scan should be attributed to the adsorption of H+ ions on the LATP glass rather than the bulk diffusion of H+ ions. Furthermore, density functional theory calculations indicate that the H+-ion diffusion energy barrier (3.21 eV) is much higher than that for Li+ ions (0.79 eV) and Na+ ions (0.79 eV) in a NASICON-type LiTi2(PO4)3 material. As a result, H+-ion conductivity in LATP glass is negligible at room temperature. However, significant surface corrosion was found after the LATP glass in a strong alkaline electrolyte. Therefore, to prevent LATP glass from corrosion, appropriate electrolytes must be developed for long-term operation of LATP in aqueous Li–air batteries. [Copyright &y& Elsevier]

Abstract: The Li–O2 chemistry in nonaqueous liquid carbonate electrolytes and the underlying reason for its limited reversibility was systematically investigated. X-ray diffraction data showed that regardless of discharge depth lithium alkylcarbonates (lithium propylenedicarbonate (LPDC), or lithium ethylenedicarbonate (LEDC), with other related derivatives) and lithium carbonate (Li2CO3) are constantly the main discharge products, while lithium peroxide (Li2O2) or lithium oxide (Li2O) is hardly detected. These lithium alkylcarbonates are generated from the reductive decomposition of the corresponding carbonate solvents initiated by the attack of superoxide radical anions. More significantly, in situ gas chromatography/mass spectroscopy analysis revealed that Li2CO3 and Li2O cannot be oxidized even when charged to 4.6V vs. Li/Li+, while LPDC, LEDC and Li2O2 are readily oxidized, with CO2 and CO released from LPDC and LEDC and O2 evolved from Li2O2. Therefore, the apparent reversibility of Li–O2 chemistry in an organic carbonate-based electrolyte is actually an unsustainable process that consists of (1) the formation of lithium alkylcarbonates through the reductive decomposition of carbonate solvents during discharging and (2) the subsequent oxidation of these same alkylcarbonates during charging. Therefore, a stable electrolyte that does not lead to an irreversible by-product formation during discharging and charging is necessary for truly rechargeable Li–O2 batteries. [Copyright &y& Elsevier]

Abstract: The charging process of Li2O2-based air electrodes in Li–O2 batteries with organic carbonate electrolytes was investigated using in situ gas chromatography/mass spectroscopy (GC/MS) to analyze gas evolution. A mixture of Li2O2/Fe3O4/Super P carbon/polyvinylidene fluoride (PVDF) was used as the starting air electrode material, and 1-M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in carbonate-based solvents was used as the electrolyte. We found that Li2O2 was actively reactive to 1-methyl-2-pyrrolidinone and PVDF that were used to prepare the electrode. During the first charging (up to 4.6V), O2 was the main component in the gases released. The amount of O2 measured by GC/MS was consistent with the amount of Li2O2 that decomposed during the electrochemical process as measured by the charge capacity, which is indicative of the good chargeability of Li2O2. However, after the cell was discharged to 2.0V in an O2 atmosphere and then recharged to ∼4.6V, CO2 was dominant in the released gases. Further analysis of the discharged air electrodes by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy indicated that lithium-containing carbonate species (lithium alkyl carbonates and/or Li2CO3) were the main discharge products. Therefore, compatible electrolytes and electrodes, as well as the electrode-preparation procedures, need to be developed for rechargeable Li-air batteries for long term operation. [Copyright &y& Elsevier]

Abstract: A three-dimensional macroporous Cu/SnO2 composite anode sheet for lithium ion batteries was prepared via a novel method that is based on selective reduction of metal oxides at appropriate temperatures. SnO2 particles were imbedded on the Cu particles within the three-dimensionally interconnected Cu substrate, and the whole composite sheet was used directly as an electrode without adding extra conductive carbons and binders. Compared with the SnO2-based electrode prepared via the conventional tape-casting method on Cu foil, the porous Cu/SnO2 composite electrode shows significantly improved battery performance. This methodology produces limited wastes and is also adaptable to many other materials. It is a promising approach to make macroporous electrode for Li-ion batteries. [Copyright &y& Elsevier]

Abstract: In this article, two-dimensional, Co3O4 hexagonal nanodiscs are prepared using a hydrothermal method without surfactants. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been employed to characterize the structural properties. As revealed by the SEM and TEM experiments, the thickness of our as-fabricated Co3O4 hexagonal nanodiscs is about 20 nm, and the pore diameters range from several nanometers to 30 nm. As an anode for lithium-ion batteries, porous Co3O4 nanodiscs exhibit an average discharge voltage of ∼1 V (vs. Li/Li+) and a high specific charge capacity of 1161 mAh g−1 after 100 cycles. They also demonstrate excellent rate performance and high Columbic efficiency at various rates. These results indicate that porous Co3O4 nanodiscs are good candidates as anode materials for lithium-ion batteries. [Copyright &y& Elsevier]

Abstract: In this paper, we report the electrochemical characteristics of a novel cathode material, Li2CoPO4F, prepared by solid-state reactions. The solid-state reaction mechanism involved in synthesizing the Li2CoPO4F also is analyzed in this paper. When cycled between 2.0V and 5.0V during cyclic voltammetry measurements, the Li2CoPO4F samples present one, fully reversible anodic reaction at 4.81V. When cycled between 2.0V and 5.5V, peaks occurring at 4.81V and 5.12V in the first anodic scan evolved to one broad oxidative, mound-like pattern in subsequent cycles. Correspondingly, the X-ray diffraction (XRD) pattern of the Li2CoPO4F electrode discharged from 5.5V to 2.0V is slightly different from the patterns exhibited by a fresh sample and the sample discharged from 5.0V to 2.0V. This difference may correspond to a structural relaxation that appears above 5V. In the constant current cycling measurements, the Li2CoPO4F samples exhibited a capacity as high as 109mAhg−1 and maintained a good cyclability between 2.0V and 5.5V vs. Li/Li+. XRD measurements confirmed that the discharged state is Li2CoPO4F. Combining these XRD results and electrochemical data proved that up to 1mol Li+ is extractable when charged to 5.5V. [ABSTRACT FROM AUTHOR]

Abstract: To understand the limited cycle life performance and poor energy efficiency associated with rechargeable lithium–oxygen (Li–O2) batteries, the discharge products of primary Li–O2 cells at different depths of discharge (DOD) were systematically analyzed using XRD, FTIR and Ultra-high field MAS NMR. When discharged to 2.0V, the reaction products of Li–O2 cells include a small amount of Li2O2 along with Li2CO3 and RO–(C;OLi in the alkyl carbonate-based electrolyte. However, regardless of the DOD, there is no Li2O detected in the discharge products in the alkyl-carbonate electrolyte. For the first time it was revealed that in an oxygen atmosphere the high surface area carbon significantly reduces the electrochemical operation window of the electrolyte, and leads to plating of insoluble Li salts on the electrode at the end of the charging process. Therefore, the impedance of the Li–O2 cell continues to increase after each discharge and recharge process. After only a few cycles, the carbon air electrode is completely insulated by the accumulated Li salt terminating the cycling. [Copyright &y& Elsevier]