Advanced materials for sodium-beta alumina batteries: Status, challenges and perspectives

The increasing penetration of renewable energy and the trend toward clean, efficient transportation have spurred growing interests in sodium-beta alumina batteries that store electrical energy via sodium ion transport across a β″-Al₂O₃ solid electrolyte at elevated temperatures (typically 300-350 °C). Currently, the negative electrode or anode is metallic sodium in molten state during battery operation; the positive electrode or cathode can be molten sulfur (Na-S battery) or solid transition metal halides plus a liquid phase secondary electrolyte (e.g., ZEBRA battery). Since the groundbreaking works in the sodium-beta alumina batteries a few decades ago, encouraging progress has been achieved in improving battery performance, along with cost reduction. However, there remain issues that hinder broad applications and market penetration of the technologies. To better the Na-beta alumina technologies require further advancement in materials along with component and system design and engineering. This paper offers a comprehensive review on materials of electrodes and electrolytes for the Na-beta alumina batteries and discusses the challenges ahead for further technology improvement.     

Studies on the enhancement of solid electrolyte interphase formation on graphitized anodes in LiX-carbonate based electrolytes using Lewis acid additives for lithium-ion batteries

The new electrolyte systems utilizing one type of Lewis acids, the boron based anion receptors (BBARs) with LiF, Li₂O, or Li₂O₂ in carbonate solutions have been developed and reported by us. These systems open up a new approach in developing non-aqueous electrolytes with higher operating voltage and less moisture sensitivity for lithium-ion batteries. However, the formation of a stable solid electrolyte interphase (SEI) layer on the graphitized anodes is a serious problem needs to be solved for these new electrolyte systems, especially when propylene carbonate (PC) is used as a co-solvent. Using lithium bis(oxalato)borate (LiBOB) as an additives, the SEI layer formation on mesophase carbon microbeads (MCMB) anode is significantly enhanced in these new electrolytes containing boron-based anion receptors, such as tris(pentafluorophenyl) borane, and lithium salt such as LiF, or lithium oxides such as Li₂O or Li₂O₂ in PC and dimethyl carbonate (DMC) solvents. The cells using these electrolytes and MCMB anodes cycled very well and the PC co-intercalation was suppressed. Fourier transform infrared spectroscopy (FTIR) studies show that one of the electrochemical decomposition products of LiBOB, lithium carbonate (Li₂CO₃), plays a quite important role in the stablizing SEI layer formation.     

Ceramic and polymeric solid electrolytes for lithium-ion batteries

Lithium-ion batteries are important for energy storage in a wide variety of applications including consumer electronics, transportation and large-scale energy production. The performance of lithium-ion batteries depends on the materials used. One critical component is the electrolyte, which is the focus of this paper. In particular, inorganic ceramic and organic polymer solid-electrolyte materials are reviewed. Solid electrolytes provide advantages in terms of simplicity of design and operational safety, but typically have conductivities that are lower than those of organic liquid electrolytes. This paper provides a comparison of the conductivities of solid-electrolyte materials being used or developed for use in lithium-ion batteries.     

Electrochemical properties of lithium sulfur cells using PEO polymer electrolytes prepared under three different mixing conditions

Lithium sulfur cells were prepared by composing with sulfur cathode (PEO)₆LiBF₄ polymer electrolyte and lithium anode. (PEO)₆LiBF₄ polymer electrolyte was prepared under three different mixing conditions: stirred polymer electrolyte (SPE), ball-milled polymer electrolyte (BPE) and ball-milled polymer electrolyte with 10 wt%Al₂O₃ (BCPE). The effects of ball milling and additive were investigated by discharge test according to depth of discharge. The initial discharge capacity of lithium sulfur cell using BCPE was 1670 mAh g⁻¹-sulfur, which was better than those of SPE and BPE, and approximately equal to the theoretical capacity. The cycle performance of Li/(PEO)₆LiBF₄/S cell was remarkably improved by the addition of Al₂O_3.     

LiBF3Cl as an alternative salt for the electrolyte of Li-ion batteries

LiBF₃Cl was synthesized by reacting BF₃ etherate and LiCl in an organic media, and evaluated as a salt for the electrolyte of Li-ion batteries. XRD results showed that LiBF₃Cl has the same crystallographic structure as LiBF₄ except for little difference in the lattice parameter. With a 3:7 (w/w) solvent blend of ethylene carbonate and ethyl methyl carbonate, LiBF₃Cl electrolyte was found to have lower liquidus temperature than LiBF₄ analogue either due to its higher solubility or due to its higher tendency in forming a super-cooling solution, which was related to the less symmetry of BF₃Cl⁻ anion. Meanwhile, LiBF₃Cl electrolyte displayed excellent ability in passivating Al at high potentials due to the similar chemical composition of LiBF₃Cl and LiBF₄. Most importantly, the LiBF₃Cl electrolyte was superior to the LiBF₄ electrolyte in facilitating the formation of solid electrolyte interphase (SEI) on graphite electrode, which not only increased Coulombic efficiencies of the SEI formation, but also prolonged cycle life of the Li-ion batteries. The merits above make LiBF₃Cl very promising as an alternative lithium salt for the electrolyte of Li-ion batteries.     

Investigation on the charging process of Li2O2-based air electrodes in Li-O2 batteries with organic carbonate electrolytes

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 4.6 V), 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 2.0 V in an O₂ atmosphere and then recharged to ∼4.6 V, 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.     

Development and utility of manganese oxides as cathodes in lithium batteries

Manganese oxides have a long history of serving as a cathode in charge storage applications. Electrolytic manganese dioxide (EMD) is widely used in alkaline batteries and MnO₂ originally was part of the Leclanché wet cell patented in 1866. Leclanché wet cells used a naturally occurring MnO₂ ore with Zn metal as anode and ammonium chloride electrolyte. While there are a vast number of topics to discuss on manganese oxides, in this short paper, two topics researched at Argonne over the last 12 years are highlighted. First, the addition of lithia (Li₂O) as a stabilizing component in 3 V alpha-MnO₂ is examined. Second, an overview of the evolution of layered–layered composite-structured electrodes derived from the lithium-manganese oxide (Li₂MnO₃) layered rock-salt phase is presented.     

Effect of Al2O3 content on the adsorptive properties of Cu/ZnO/Al2O3 for removal of odorant sulfur compounds

Cu/ZnO/Al₂O₃ adsorbents for removal of odorant sulfur compounds were prepared with various Al/Cu molar ratios by co-precipitation method. The sulfur removing ability as a function of Al/Cu molar ratio of the adsorbents for t-butyl mercaptan (TBM), tetrahydro thiophene (THT), dimethyl disulfide (DMS) and H₂S were investigated at 250 °C and 6000 h⁻¹ space velocity. Based on the results of adsorption capacity and characterization by various techniques, the optimum Al/Cu ratio for maximum sulfur removal capacity is found to be at Al/Cu molar ratio of 0.15 which possesses the well-dispersed Cu species with high reducibility. The adsorption capacity is highest for H₂S followed by TBM, DMS and THT. The main role of Al₂O₃ component is to provide the dispersion of CuO species homogeneously with small particle formation and high reducibility.     

Electrochemical insertion/deinsertion of sodium on NaV6O15 nanorods as cathode material of rechargeable sodium-based batteries

A well defined nano-structured material, NaV₆O₁₅ nanorods, was synthesized by a facile low temperature hydrothermal method. It can perform well as the cathode material of rechargeable sodium batteries. It was found that the NaV₆O₁₅ nanorods exhibited stable sodium-ion insertion/deinsertion reversibility and delivered 142 mAh g⁻¹ sodium ions when worked at a current density of 0.02 A g⁻¹. In galvanostatic cycling test, a specific discharge capacity of around 75 mAh g⁻¹ could be obtained after 30 cycles under 0.05 A g⁻¹ current density. Concerned to its good electrochemical performance for reversible delivery of sodium ions, it is thus expected that NaV₆O₁₅ may be used as cathode material for rechargeable sodium batteries with highly environmental friendship and low cost.     

A study on the electrochemical characteristics of LiFePO4 cathode for lithium polymer batteries by hydrothermal method

Phospho-olivine LiFePO₄ cathode materials were prepared by hydrothermal reaction at 150 °C. Carbon black was added to enhance the electrical conductivity of LiFePO₄. LiFePO₄-C powders (0, 3, 5 and 10 wt.%) were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). LiFePO₄-C/solid polymer electrolyte (SPE)/Li cells were characterized electrochemically by charge/discharge experiments at a constant current density of 0.1 mA cm⁻² in a range between 2.5 and 4.3 V vs. Li/Li⁺, cyclic voltammetry (CV) and ac impedance spectroscopy. The results showed that initial discharge capacity of LiFePO₄ was 104 mAh g⁻¹. The discharge capacity of LiFePO₄-C/SPE/Li cell with 5 wt.% carbon black was 128 mAh g⁻¹ at the first cycle and 127 mAh g⁻¹ after 30 cycles, respectively. It was demonstrated that cycling performance of LiFePO₄-C/SPE/Li cells was better than that of LiFePO₄/SPE/Li cells.     

High power and high capacity cathode material LiNi0.5Mn0.5O2 for advanced lithium-ion batteries

Single-phase lithium nickel manganese oxide, LiNi_0.5Mn_0.5O₂, was successfully synthesized from a solid solution of Ni_1.5Mn_1.5O₄ that was prepared by means of the solid reaction between Mn(CH₃COO)₂·4H₂O and Ni(CH₃COO)₂·4H₂O. XRD pattern shows that the product is well crystallized with a high degree of Li–M (Ni, Mn) order in their respective layers, and no diffraction peak of Li₂MnO₃ can be detected. Electrochemical performance of as-prepared LiNi_0.5Mn_0.5O₂ was examined in the test battery by charge–discharge cycling with different rate, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The cycling behavior between 2.5 and 4.4 V at a current rate of 21.7 mA g⁻¹ shows a reversible capacity of about 190 mAh g⁻¹ with little capacity loss after 100 cycles. High-rate capability test shows that even at a rate of 6C, stable capacity about 120 mAh g⁻¹ is retained. Cyclic voltammetry (CV) profile shows that the cathode material has better electrochemical reversibility. EIS analysis indicates that the resistance of charge transfer (R_ct) is small in fully charged state at 4.4 V and fully discharged state at 2.5 V versus Li⁺/Li. The favorable electrochemical performance was primarily attributed to regular and stable crystal structure with little intra-layer disordering.     

Investigations on cellulose-based high voltage composite cathodes for lithium ion batteries

Carboxymethyl cellulose (CMC), a green and low-cost binder, is used to make lithium-ion battery composite electrodes containing the high voltage cathode material Li₂MnO₃-LiMO₂. This combination of materials results in a homogeneous electrode, which is proved by electron microscopy. The results of the electrochemical investigation indicate that CMC operates well at very high voltages (4.8 V). Compared to the PVDF binder, the CMC-based electrode shows an improved cycling stability as well as a very promising rate capability.     

A new low-temperature synthesis and electrochemical properties of LiV3O8 hydrate as cathode material for lithium-ion batteries

LiV₃O₈, synthesized from V₂O₅ and LiOH, by heating of a suspension of V₂O₅ in a LiOH solution at a low-temperature (100-200 °C), exhibits a high discharge capacity and excellent cyclic stability at a high current density as a cathode material of lithium-ion battery. The charge-discharge curve shows a maximum discharge capacity of 228.6 mAh g⁻¹ at a current density of 150 mA g⁻¹ (0.5 C rate) and the 100 cycles discharge capacity remains 215 mAh g⁻¹. X-ray diffraction indicates the low degree of crystallinity and expanding of inter-plane distance of the LiV₃O₈ phase, and scanning electronic microscopy reveals the formation of nano-domain structures in the products, which account for the enhanced electrochemical performance. In contrast, the LiV₃O₈ phase formed at a higher temperature (300 °C) consists of well-developed crystal phases, and coherently, results in a distinct reduction of discharge capacity with cycle numbers. Thus, an enhanced electrochemical performance has been achieved for LiV₃O₈ by the soft chemical method via a low-temperature heating process.     

Fabrication of all solid-state lithium-ion batteries with three-dimensionally ordered composite electrode consisting of Li0.35La0.55TiO3 and LiMn2O4

A composite electrode between three-dimensionally ordered macroporous (3DOM) Li_0.35La_0.55TiO₃ (LLT) and LiMn₂O₄ was fabricated by colloidal crystal templating method and sol–gel process. A close-packed PS beads with the opal structure was prepared by filtration of a suspension containing PS beads. Li–La–Ti–O sol was injected by vacuum impregnation process into the voids between PS beads, and then was heated to form 3DOM-LLT. Three-dimensionally ordered composite material consisting of LiMn₂O₄ and LLT was prepared by sol–gel process. The prepared composite was characterized with SEM and XRD. All solid-state Li-ion battery was fabricated with the LLT–LiMn₂O₄ composite electrode as a cathode, dry polymer electrolyte and Li metal anode. The prepared all solid-state cathode exhibited a volumetric discharge capacity of 220 mAh cm⁻³.     

Kinetics of N-ethylcarbazole hydrogenation over a supported Ru catalyst for hydrogen storage

The hydrogenation kinetics of N-ethylcarbazole over Ru/γ-Al₂O₃ was investigated to find the rate of controlling step on the mass transfer-reaction processes. The results showed that the kinetics of reaction was controlled by the hydrogenation reaction on the catalyst surfaces. This reaction followed first-order kinetics with an apparent activation energy of 30.94 kJ/mol. The apparent kinetics model of the hydrogenation was established.     

Preparation and characterization of nanocrystalline Ce0.8Sm0.2O1.9 for low temperature solid oxide fuel cells based on composite electrolyte

Nanocrystalline Ce_0.8Sm_0.2O_1.9 (SDC) has been synthesized by a combined EDTA–citrate complexing sol–gel process for low temperature solid oxide fuel cells (SOFCs) based on composite electrolyte. A range of techniques including X-ray diffraction (XRD), and electron microscopy (SEM and TEM) have been employed to characterize the SDC and the composite electrolyte. The influence of pH values and citric acid-to-metal ions ratios (C/M) on lattice constant, crystallite size and conductivity has been investigated. Composite electrolyte consisting of SDC derived from different synthesis conditions and binary carbonates (Li₂CO₃–Na₂CO₃) has been prepared and conduction mechanism is discussed. Water was observed on both anode and cathode side during the fuel cell operation, indicating the composite electrolyte is co-ionic conductor possessing H⁺ and O²⁻ conduction. The variation of composite electrolyte conductivity and fuel cell power output with different synthesis conditions was in accordance with that of the SDC originated from different precursors, demonstrating O²⁻ conduction is predominant in the conduction process. A maximum power density of 817 mW cm⁻² at 600 °C and 605 mW cm⁻² at 500 °C was achieved for fuel cell based on composite electrolyte.     

Synthesis and characterization of nano-sized γ-Al2O3 for investigation the effect of temperature on catalytic dehydration of methanol to dimethyl ether

The new high surface area and high active nano-sized porous γ-Al₂O₃ catalyst was produced by a co-precipitation method. The synthesized catalyst was characterized by X-ray diffraction, Fourier transform infrared, NH₃-temperature programmed desorption, and Brunauer-Emmett-Teller techniques. The results of characterization tests showed excellent textural and acidic properties of the synthesized catalyst for the methanol dehydration reaction. Catalytic dehydration of methanol to dimethyl ether was performed in an adiabatic fixed bed reactor using the new nano-sized catalyst at different operating temperatures. The results showed that the highest methanol conversion occurs in the temperature range of 300–350°C. Finally, a new correlation was developed to predict methanol conversion from operating temperature.     

The influence of sodium on the properties of CuInS2 thin films and solar cells

The controlled incorporation of sodium into the absorber layer of CuInS₂ solar cells improved cell performance remarkably. Without toxic KCN treatment, conversion efficiencies of over 6% were achieved by sulfurization of sodium-containing precursors. We also investigated the characteristics of the sodium-incorporated CuInS₂ films by intentional addition and diffusion from a soda-lime glass. The ternary compound semiconductor of NaInS₂ was found to form mainly on the surface of each of the CuInS₂ films.     

Synthesis and characterization of Nd doped LiMn2O4 cathode for Li-ion rechargeable batteries

Spinel powders of LiMn_1.99Nd_0.01O₄ have been synthesized by chemical synthesis route to prepare cathodes for Li-ion coin cells. The structural and electrochemical properties of these cathodes were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry, and charge-discharge studies. The cyclic voltammetry of the cathodes revealed the reversible nature of Li-ion intercalation and deintercalation in the electrochemical cell. The charge-discharge characteristics for LiMn_1.99Nd_0.01O₄ cathode materials were obtained in 3.4–4.3 V voltage range and the initial discharge capacity of this material were found to be about 149 mAh g⁻¹. The coin cells were tested for up to 25 charge-discharge cycles. The results show that by doping with small concentration of rare-earth element Nd, the capacity fading is considerably reduced as compared to the pure LiMn₂O₄ cathodes, making it suitable for Li-ion battery applications.