Search

Mixed ionic–electronic conductors (MIECs) can play a pivotal role in achieving high energies and power densities in rechargeable batteries owing to their ability to simultaneously conduct ions and electrons. Herein, a new strategy is proposed wherein late 3d transition metals (TMs) are substituted into a perovskite Li‐ion conductor to transform it into a Li‐containing MIEC. First‐principles calculations show that perovskite LixLayMO3 with late 3d TMs have a low oxygen vacancy formation energy, implying high electron carrier concentrations corresponding to high electronic conductivity. The activation barriers for Li diffusion in LixLayMO3 (M = Ti, Cr, Mn, Fe, and Co) are below 0.411 eV, resulting in high Li‐ion conductivity. The designed perovskites of Li0.34La0.55MnO3−δ experimentally prove to have high electronic (2.04 × 10−3 S cm−1) and Li‐ion (8.53 × 10−5 S cm−1) conductivities, and when applied in a carbon‐free cathode of a Li–air cell, they deliver superior reversibility at 0.21 mAh cm−2 over 100 charge/discharge cycles while avoiding the degradation associated with carbonaceous materials. This strategy enables the effective design of Li‐conducting MIEC and reversible Li–air batteries. [ABSTRACT FROM AUTHOR]

Achieving the high theoretical energy density (∼3500 W h kg−1) of Li–O2 batteries involves maximizing the electrochemically active surface area (EASA) of the electrodes. Carbon nanotubes (CNTs) have been widely adopted for Li–O2 electrodes but their EASA is limited by their electrolyte-phobic surface nature and the strong van der Waals interaction between CNTs. To increase the affinity between CNT-based electrodes and the electrolyte without decreasing CNT chemical stability, CNT buckypapers are functionalized with 3,5-bis(trifluoromethyl)phenylmaleimide. The solubility parameters of the electrolyte and CNTs are considered so that the maleimide groups increase the affinity between the electrode and electrolyte and the 3,5-bis(trifluoromethyl)phenyl groups protect the maleimide groups from decomposition. The functionalized CNT cathode exhibits a 58% greater discharge capacity and a 50% increased cyclability compared to the pristine CNT cathode when a 1 : 2.5 weight ratio of CNT to electrolyte was used due to an increased EASA and steric hindrance effect. Finally, a 3D folded Li–O2 cell is fabricated using the functionalized CNT-based cathode and demonstrated 30 cycles at 100 W h kgcell−1 cutoff. These results clearly show that high energy density and long cycling performance of Li–O2 batteries can be achieved even with a much reduced amount of electrolyte by increasing the affinity between CNT-based electrodes and the electrolyte. [ABSTRACT FROM AUTHOR]

Morphological characteristics and electrical conductivity of polyamide 6,6/poly( p-phenylene ether)/multi-walled carbon nanotube (PA66/PPE/MWCNT) ternary nanocomposites were investigated. The MWCNTs were modified by Co gamma ray (γ-ray) irradiation under a dry condition and O atmosphere, which introduces oxygen-containing functional groups on the surfaces of the MWCNTs and thereby provides better compatibility with the hydrophilic PA66 phase. It was observed that the MWCNTs are preferentially positioned in the continuous PA66 matrix, whereas PPE domains are almost free of MWCNTs. Since PA66 consists of a continuous phase and the MWCNTs are preferentially positioned in the PA66 phase, electrical conductivity of PA66/PPE/MWCNT ternary composites is higher than that of PA66/MWCNT binary composites at the same MWCNT content. It was observed that raising the processing temperature and increasing the mixing time were effective means of improving the electrical conductivity of the composites, via enhancement of MWCNT dispersion. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Li-O 2 batteries have attracted considerable attention for several decades due to their high theoretical energy density (>3400 Wh/kg). However, it has not been clearly demonstrated that their actual volumetric and gravimetric energy densities are higher than those of Li-ion batteries. In previous studies, a considerable quantity of electrolyte was usually employed in preparing Li-O 2 cells. In general, the electrolyte was considerably heavier than the carbon materials in the cathode, rendering the practical energy density of the Li-O 2 battery lower than that of the Li-ion battery. Therefore, air cathodes with significantly smaller electrolyte quantities need to be developed to achieve a high specific energy density in Li-O 2 batteries. In this study, we propose a core-shell-structured cathode material with a gel-polymer electrolyte layer covering the carbon nanotubes (CNTs). The CNTs are synthesized using the floating catalyst chemical vapor deposition method. The polymeric layer corresponding to the shell is prepared by the layer-by-layer (LbL) coating method, utilizing Li-Nafion along with PDDA-Cl [poly(diallyldimethylammonium chloride)]. Several bilayers of Li-Nafion and PDDA, on the CNT surface, are successfully prepared and characterized via X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The porous structure of the CNTs is retained after the LbL process, as confirmed by the nitrogen adsorption-desorption profile and BJH pore-size distribution analysis. This porous structure can function as an oxygen channel for facilitating the transport of oxygen molecules for reacting with the Li ions on the cathode surface. These polymeric bilayers can provide an Li-ion pathway, after absorbing a small quantity of an ionic liquid electrolyte, 0.5 M LiTFSI EMI-TFSI [1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide]. Compared to a typical cathode, where only liquid electrolytes are employed, the total quantity of electrolyte in the cathode can be significantly reduced; thereby, the overall cell energy density can be increased. A Li-O 2 battery with this core-shell-structured cathode exhibited a high energy density of approximately 390 Wh/kg, which was assessed by directly weighing all of the cell components together, including the gas diffusion layer, the interlayer [a separator containing a mixture of LiTFSI, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR-14), and PDDA-TFSI], the lithium anode, and the LbL-CNT cathode. The cycle life of the LbL-CNT-based cathode was found to be 31 cycles at a limited capacity of 500 mAh/g carbon . Although this is not an excellent performance, it is almost 2 times better than that of a CNT cathode without a polymer coating.