Operando Observation of the De-Evolution/Evolution Process of Hydrated LiOH in Moisture-Assisted Li-O2 Batteries.

All-solid-state Li-O2 batteries that use ceramic electrolytes have been suggested to overcome the limitations posed by the decomposition of organic electrolytes. However, these systems show a low discharge capacity and high overpotential because the discharge product Li2O2 has low electronic conductivity. In this study, all-solid-state planar-type Li-O2 cells were constructed using a lithium anode, a Li1·3Al0·3Ti1·7(PO4) (LATP) inorganic solid electrolyte, and an air electrode composed of a Pt grid pattern. The discharge/charge process was observed in real time in a humidified O2 environment for the first time, which clarified both the hydration process of the discharge products and the charging process of the hydrated discharge products. The discharge product (LiOH) could be easily hydrated in water, which would facilitate ion transport, thereby increasing the discharge capacity and discharge voltage (vs Li/Li+; from 2.96 to 3.4 V). Thus, Li-O2 cells with a high energy density and a capacity of 3600 mAh/gcathode were achieved using a planar Pt-patterned electrode in a humidified O2 environment. This study is the first to demonstrate the hydration of the discharge products of a Li-O2 cell in humidified O2. Based on a thorough understanding of the hydration phenomenon/mechanism, our findings suggest new strategies for developing high-energy-density all-solid-state Li-O2 batteries using a simple, easy-to-manufacture planar Pt-patterned cathode.

Surface engineering of inorganic solid-state electrolytes via interlayers strategy for developing long-cycling quasi-all-solid-state lithium batteries.

Lithium metal batteries (LMBs) with inorganic solid-state electrolytes are considered promising secondary battery systems because of their higher energy content than their Li-ion counterpart. However, the LMB performance remains unsatisfactory for commercialization, primarily owing to the inability of the inorganic solid-state electrolytes to hinder lithium dendrite propagation. Here, using an Ag-coated Li6.4La3Zr1.7Ta0.3O12 (LLZTO) inorganic solid electrolyte in combination with a silver-carbon interlayer, we demonstrate the production of stable interfacially engineered lab-scale LMBs. Via experimental measurements and computational modelling, we prove that the interlayers strategy effectively regulates lithium stripping/plating and prevents dendrite penetration in the solid-state electrolyte pellet. By coupling the surface-engineered LLZTO with a lithium metal negative electrode, a high-voltage positive electrode with an ionic liquid-based liquid electrolyte solution in pouch cell configuration, we report 800 cycles at 1.6 mA/cm2 and 25 °C without applying external pressure. This cell enables an initial discharge capacity of about 3 mAh/cm2 and a discharge capacity retention of about 85%.

Lithium superionic conductors with corner-sharing frameworks.

Superionic lithium conductivity has only been discovered in a few classes of materials, mostly found in thiophosphates and rarely in oxides. Herein, we reveal that corner-sharing connectivity of the oxide crystal structure framework promotes superionic conductivity, which we rationalize from the distorted lithium environment and reduced interaction between lithium and non-lithium cations. By performing a high-throughput search for materials with this feature, we discover ten new oxide frameworks predicted to exhibit superionic conductivity-from which we experimentally demonstrate LiGa(SeO3)2 with a bulk ionic conductivity of 0.11 mS cm-1 and an activation energy of 0.17 eV. Our findings provide insight into the factors that govern fast lithium mobility in oxide materials and will accelerate the development of new oxide electrolytes for all-solid-state batteries.

Carbon-free high-performance cathode for solid-state Li-O2 battery.

The development of a cathode for solid-state lithium-oxygen batteries has been hindered in practice by a low capacity and limited cycle life despite their potential for high energy density. Here, a previously unexplored strategy is proposed wherein the cathode delivers a specific capacity of 200 milliampere hour per gram over 665 discharge/charge cycles, while existing cathodes achieve only ~50 milliampere hour per gram and ~100 cycles. A highly conductive ruthenium-based composite is designed as a carbon-free cathode by first-principles calculations to avoid the degradation associated with carbonaceous materials, implying an improvement in stability during the electrochemical cycling. In addition, water vapor is added into the main oxygen gas as an additive to change the discharge product from growth-restricted lithium peroxide to easily grown lithium hydroxide, resulting in a notable increase in capacity. Thus, the proposed strategy is effective for developing reversible solid-state lithium-oxygen batteries with high energy density.

High-energy and durable lithium metal batteries using garnet-type solid electrolytes with tailored lithium-metal compatibility.

Lithium metal batteries using solid electrolytes are considered to be the next-generation lithium batteries due to their enhanced energy density and safety. However, interfacial instabilities between Li-metal and solid electrolytes limit their implementation in practical batteries. Herein, Li-metal batteries using tailored garnet-type Li7-xLa3-aZr2-bO12 (LLZO) solid electrolytes is reported, which shows remarkable stability and energy density, meeting the lifespan requirements of commercial applications. We demonstrate that the compatibility between LLZO and lithium metal is crucial for long-term stability, which is accomplished by bulk dopant regulating and dopant-specific interfacial treatment using protonation/etching. An all-solid-state with 5 mAh cm-2 cathode delivers a cumulative capacity of over 4000 mAh cm-2 at 3 mA cm-2, which to the best of our knowledge, is the highest cycling parameter reported for Li-metal batteries with LLZOs. These findings are expected to promote the development of solid-state Li-metal batteries by highlighting the efficacy of the coupled bulk and interface doping of solid electrolytes.

High-Energy Density Li-O2 Battery with a Polymer Electrolyte-Coated CNT Electrode via the Layer-by-Layer Method.

Li-O2 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-O2 cells. In general, the electrolyte was considerably heavier than the carbon materials in the cathode, rendering the practical energy density of the Li-O2 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-O2 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-O2 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/gcarbon. Although this is not an excellent performance, it is almost 2 times better than that of a CNT cathode without a polymer coating.

A safe and sustainable bacterial cellulose nanofiber separator for lithium rechargeable batteries.

Bacterial cellulose nanofiber (BCNF) with high thermal stability produced by an ecofriendly process has emerged as a promising solution to realize safe and sustainable materials in the large-scale battery. However, an understanding of the actual thermal behavior of the BCNF in the full-cell battery has been lacking, and the yield is still limited for commercialization. Here, we report the entire process of BCNF production and battery manufacture. We systematically constructed a strain with the highest yield (31.5%) by increasing metabolic flux and improved safety by introducing a Lewis base to overcome thermochemical degradation in the battery. This report will open ways of exploiting the BCNF as a "single-layer" separator, a good alternative to the existing chemical-derived one, and thus can greatly contribute to solving the environmental and safety issues.

Ion-channel aligned gas-blocking membrane for lithium-air batteries.

Lithium-metal-based batteries, owing to the extremely high specific energy, have been attracting intense interests as post-Li-ion batteries. However, their main drawback is that consumption/de-activation of lithium metal can be accelerated when O2 or S used in the cathode crosses over to the metal, reducing the lifetime of the batteries. In use of ceramic solid state electrolyte (SSE) separator, despite the capability of gas blocking, thick and heavy plates (~0.3 mm) are necessitated to compensate its mechanical fragility, which ruin the high specific energy of the batteries. Here, we demonstrate fabrication of a new membrane made of micron-sized SSE particles as Li-ion channels embedded in polymer matrix, which enable both high Li-ion conduction and gas-impermeability. Bimodal surface-modification was used to control the energy of the particle/polymer interface, which consequently allowed channel formation via a simple one-step solution process. The practical cell with the new membrane provides a cell-specific energy of over 500 Wh kg-1, which is the highest values ever reported.

A search map for organic additives and solvents applicable in high-voltage rechargeable batteries.

Chemical databases store information such as molecular formulas, chemical structures, and the physical and chemical properties of compounds. Although the massive databases of organic compounds exist, the search of target materials is constrained by a lack of physical and chemical properties necessary for specific applications. With increasing interest in the development of energy storage systems such as high-voltage rechargeable batteries, it is critical to find new electrolytes efficiently. Here we build a search map to screen organic additives and solvents with novel core and functional groups, and thus establish a database of electrolytes to identify the most promising electrolyte for high-voltage rechargeable batteries. This search map is generated from MAssive Molecular Map BUilder (MAMMBU) by combining a high-throughput quantum chemical simulation with an artificial neural network algorithm. MAMMBU is designed for predicting the oxidation and reduction potentials of organic compounds existing in the massive organic compound database, PubChem. We develop a search map composed of ∼1 000 000 redox potentials and elucidate the quantitative relationship between the redox potentials and functional groups. Finally, we screen a quinoxaline compound for an anode additive and apply it to electrolytes and improve the capacity retention from 64.3% to 80.8% near 200 cycles for a lithium ion battery in experiments.

Enhanced Electrochemical Stability of Quasi-Solid-State Electrolyte Containing SiO2 Nanoparticles for Li-O2 Battery Applications.

A stable electrolyte is required for use in the open-packing environment of a Li-O2 battery system. Herein, a gelled quasi-solid-state electrolyte containing SiO2 nanoparticles was designed, in order to obtain a solidified electrolyte with a high discharge capacity and long cyclability. We successfully fabricated an organic-inorganic hybrid matrix with a gelled structure, which exhibited high ionic conductivity, thereby enhancing the discharge capacity of the Li-O2 battery. In particular, the improved electrochemical stability of the gelled cathode led to long-term cyclability. The organic-inorganic hybrid matrix with the gelled structure played a beneficial role in improving the ionic conductivity and long-term cyclability and diminished electrolyte evaporation. The experimental and theoretical findings both suggest that the preferential binding between amorphous SiO2 and polyethylene glycol dimethyl ether (PEGDME) solvent led to the formation of the solidified gelled electrolyte and improved electrochemical stability during cycling, while enhancing the stability of the quasi-solid state Li-O2 battery.

Design of novel additives and nonaqueous solvents for lithium-ion batteries through screening of cyclic organic molecules: an ab initio study of redox potentials.

We have screened 142 cyclic organic compounds in search of novel functional additives and nonaqueous solvents for use in lithium-ion batteries through the use of ab initio calculations, and have determined redox potentials for all molecules. We have estimated the range of variation in oxidation potentials through heteroatom replacement and structure modification. By analyzing the oxidative properties of these compounds, we have shown that substituted heteroatoms and isomers in cyclic organic molecules can induce large variations of oxidation potentials more than 2.3 V. Calculations of reduction potentials show that the substituted heteroatoms, isomers, and the number of double bonds in cyclic organic molecules can change reduction potentials more than 1.7 V. Additionally, we have identified seventeen and twelve compounds that could serve as additives in eliciting film formation on cathodes and anodes, respectively. We have also identified five compounds that could function in the overcharge protection of over-lithiated layered oxide cathodes. Finally, we have identified five compounds that could serve as electrochemically stable solvents for high-voltage (>6 V vs. Li/Li(+)) applications. These inductive screenings and their analyses and findings extend our empirical knowledge into quantitative estimation in the design of materials.

A highly reversible lithium metal anode.

Lithium metal has shown a lot of promise for use as an anode material in rechargeable batteries owing to its high theoretical capacity. However, it does not meet the cycle life and safety requirements of rechargeable batteries owing to electrolyte decomposition and dendrite formation on the surfaces of the lithium anodes during electrochemical cycling. Here, we propose a novel electrolyte system that is relatively stable against lithium metal and mitigates dendritic growth. Systematic design methods that combined simulations, model-based experiments, and in situ analyses were employed to design the system. The reduction potential of the solvent, the size of the salt anions, and the viscosity of the electrolyte were found to be critical parameters determining the rate of dendritic growth. A lithium metal anode in contact with the designed electrolyte exhibited remarkable cyclability (more than 100 cycles) at a high areal capacity of 12 mAh cm(-2).

Interface Properties between Lithium Metal and a Composite Polymer Electrolyte of PEO18Li(CF3SO2)2N-Tetraethylene Glycol Dimethyl Ether.

The electrochemical properties of a composite solid polymer electrolyte, consisting of poly(ethylene oxide) (PEO)-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and tetraethylene glycol dimethyl ether (TEGDME) was examined as a protective layer between lithium metal and a water-stable lithium ion-conducting glass ceramic of Li1+x+y(Ti,Ge)2-xAlxP3-ySiyO12 (LTAP). The lithium ion conductivity and salt diffusion coefficient of PEO18LiTFSI were dramatically enhanced by the addition of TEGDME. The water-stable lithium electrode with PEO18LiTFSI-2TEGDME, as the protective layer, exhibited a low and stable electrode resistance of 85 Ω·cm2 at 60 °C, after 28 days, and low overpotentials of 0.3 V for lithium plating and 0.4 V for lithium stripping at 4.0 mA·cm-2 and 60 °C. A Li/PEO18LiTFSI-2TEGDME/LTAP/saturated LiCl aqueous solution/Pt, air cell showed excellent cyclability up to 100 cycles at 2.0 mAh·cm-2.

The effects of Mo doping on 0.3Li[Li0.33Mn0.67]O2·0.7Li[Ni0.5Co0.2Mn0.3]O2 cathode material.

Mo doped Li excess transition metal oxides formulated as 0.3Li[Li(0.33)Mn(0.67)]O(2)·0.7Li[Ni(0.5-x)Co(0.2)Mn(0.3-x)Mo(2x)]O(2) were synthesized using the co-precipitation process. The effects of the substitution of Ni and Mn with Mo were investigated for the density of the states, the structure, cycling stability, rate performance and thermal stability by tools such as first principle calculations, synchrotron X-ray diffraction, field-emission SEM, solid state (7)Li MAS nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), elemental mapping by scanning TEM (STEM), inductively coupled plasma atomic emission spectrometry (ICP-AES) and a differential scanning calorimeter (DSC). It was confirmed that high valence Mo(6+) doping of the Li-excess manganese-nickel-cobalt layered oxide in the transition metal enhanced the structural stability and electrochemical performance. This increase was due to strong Mo-O hybridization inducing weak Ni-O hybridization, which may reduce O(2) evolution, and metallic behavior resulting in a diminishing cell resistance.

Suppression of O2 evolution from oxide cathode for lithium-ion batteries: VO(x)-impregnated 0.5Li2MnO3-0.5LiNi(0.4)Co(0.2)Mn(0.4)O2 cathode.

A VO(x)-impregnated oxide cathode for lithium ion batteries exhibits a substantial drop in oxygen evolution during high voltage operation. An electrolyte was found to catalyze the gas evolution, and the VO(x) layer could protect the cathode oxide surface from the electrolyte and stabilize the surface oxide ions during their electrochemical oxidation.

Fabrication of thermally stable and cost-effective polymeric waveguide for optical printed-circuit board.

A thermally stable polymeric optical waveguide has been fabricated using ultraviolet (UV)-curable epoxy resins for the core and clad materials. A simple and cost-effective fabrication method that uses reusable polydimethylsiloxane (PDMS) masters has been developed. The 12-channel under-clad layer of the UV-cured epoxy was prepared using a PDMS master whose embossed channels had been fabricated by a polycarbonate (PC) secondary master. The thermal stability of the fabricated waveguide was tested at 200 degrees C for one hour. The optical waveguide was not damaged physically by thermal stress. Propagation losses detected by a cut-back method were 0.16 dB/cm and 0.26 dB/cm, respectively, before and after the thermal stability test at 850 nm. Loss increase after the thermal treatment can be attributed to the formation of the absorbing and scattering sources. This waveguide can be applied for areas that require thermal stability such as an optical printed-circuit board.