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A mathematical model of flow cell operation incorporating hydrodynamic and electrochemical effects in three dimensions is developed. The model and resulting simulations apply to recently demonstrated high energy-density semi-solid flow cells. In particular, state of charge gradients that develop during low flow rate operation and their effects on the spatial non-uniformity of current density within flow cells are quantified. A one-dimensional scaling model is also developed and compared to the full three-dimensional simulation. The models are used to demonstrate the impact of the choice of electrochemical couple on flow cell performance. For semi-solid flow electrodes, which can use solid active materials with a wide variety of voltage–capacity responses, we find that cell efficiency is maximized for electrochemical couples that have a relatively flat voltage vs. capacity curve, operated under slow flow conditions. For example, in flow electrodes limited by macroscopic charge transport, an LiFePO4-based system requires one-third the polarization to reach the same cycling rate as an LiCoO2-based system, all else being equal. Our conclusions are generally applicable to high energy density flow battery systems, in which flow rates can be comparatively low for a given required power.
In this work, we investigate a facile modification approach for depositing novel electrocatalyst of chromium oxide on graphite felt via impregnation in conjunction with unltrasonication in order to improve the electrochemical performance of the positive electrode in the vanadium redox flow battery (VRFB). The modified graphite felt with an ultra-thin coating layer of Cr2O3 not only promotes the activity and reversibility of VO2+/VO2 + redox reactions, but also exhibits excellent stability in repetitive cyclic voltammetry. The flow cell employing the modified graphite felt electrodes demonstrates enhanced performance with voltage efficiency and energy efficiency of 75.9% and 67.6% at a high current density of 150 mA cm−2, which are much higher than that of 66.9% and 56.8% obtained from the cell employing pristine graphite felt. Moreover, the utilization depth of the cell is significantly enhanced as the discharge capacity increases by 83.6%. The cycling test demonstrates the stability of the Cr2O3 coating layer on graphite felt, where no significant decay in efficiencies was observed. The results verify stable and significantly enhanced catalytic effect of chromium oxide in providing active sites and promoting the electrochemical performance of graphite felt in the VRFB.
The effects of water concentration (C H2O ) on the coulombic efficiency (CE) of lithium (Li) deposition/dissolution reactions in tetraglyme-based electrolytes are examined. The CE increases from approximately 50% to 80% with increasing C H2O to 1000 ppm, but decreases with further increase in C H2O . X-ray photoelectron spectroscopy analyses of the formed Li deposits reveal that the increase in CE at C H2O values of <1000 ppm is associated with the increase in the composition ratio of lithium oxide in the deposits. In contrast, the reduction of the CE at C H2O > 1000 ppm is associated with the formation of resistive lithium hydroxide (LiOH). In addition, scanning electron microscopic analysis of the deposits reveals that large Li-aggregates with the size of several tens of μm are formed when the C H2O exceeds 1000 ppm. Taken together, these results indicate that optimized amount of water is beneficial for reversible Li deposition/dissolution reactions.
A high-capacity and high-rate-capability anode material for lithium-ion batteries, silicon-doped iron oxyhydroxide or 2-line ferrihydrite (2Fh), was prepared by mixing iron nitrate powder, tetraethyl orthosilicate, 2-propanol, and ammonium hydrogen carbonate powder at room temperature. The design of this material was inspired by a bacteriogenic product, a nanometric amorphous iron-based oxide material containing small amounts of structural Si. The atomistic structure of the prepared Si-doped 2Fh was strongly affected by the Si molar ratio [x = Si/(Fe + Si)]. Its crystallinity gradually decreased as the Si molar ratio increased, with a structural variation from nanocrystalline to amorphous at x = 0.25. The sample with x = 0.20 demonstrated the best Li storage performance. The developed material exhibited a high capacity of ∼400 mAh g−1 at the 25th cycle in the voltage range of 0.3–3.0 V and at a current rate of 9 A g−1, which was three times greater than that of the Si-free 2Fh. This indicates that Si-doping into the 2Fh structure realizes good rate capability, which are presumably because of the specific nanocomposite structure of iron-based electrochemical centers embedded in the Si-based amorphous matrix, generated by reversible Li insertion/deinsertion process.
Solid-state 13C and 15N CP-MAS NMR data adequately reflected the presence of four nonequivalent PrDtc ligands in the tetranuclear lead(II) N,N-dipropyldithiocarbamate (PrDtc), [Pb4{S2CN(C3H7)2}8] (I); the spin–spin coupling constants 3J(15N–207Pb) for the ligands were estimated. It was shown by 13C MAS NMR that the chemisorption binding of AuCl3 from a solution in 2M HCl using lead(II) dipropyldithiocarbamate is accompanied by complete redistribution of the PrDtc ligands from Pb(II) to Au(III) coordination sphere; this gives the double complex of [Au{S2CN(C3H7)2}2][PbCl3] (II). Upon crystallization from an acetone–toluene mixture (3 : 1), this complex was isolated as the solvated form ([Au{S2CN(C3H7)2}2][PbCl3] ⋅ 1/2CH3C6H5)n (IIa), which was characterized by X-ray diffraction (CIF file CCDC no. 1978947). The cationic part of the complex is represented by non-centrosymmetric gold(III) complex ions, [Au{S2CN(C3H7)2}2]+, which are combined by pairs of nonequivalent Au···S secondary bonds, thus forming supramolecular pseudo-polymer chain ([Au{S2CN(C3H7)2}2]+)n. The 1D polymeric trichloroplumbate(II) anion, {[Pb(μ2-Cl)3]–}n, acts as the counter-ion. The C–H···Cl hydrogen bonds between the anionic and cationic chains lead to formation of channels in the crystal lattice, which are occupied by solvating toluene molecules.
A porous membrane of carboxymethyl cellulose (CMC) from natural macromolecule as a host of a gel polymer electrolyte for lithium ion batteries is reported. It is prepared, for the first time, by a simple non-solvent evaporation method and its porous structure is fine-adjusted by varying the composition ratio of the solvent and non-solvent mixture. The electrolyte uptake of the porous membrane based on CMC is 75.9%. The ionic conductivity of the as-prepared gel membrane saturated with 1 mol L−1 LiPF6 electrolyte at room temperature can be up to 0.48 mS cm−1. Moreover, the lithium ion transference in the gel membrane at room temperature is as high as 0.46, much higher than 0.27 for the commercial separator Celgard 2730. When evaluated by using LiFePO4 cathode, the prepared gel membrane exhibits very good electrochemical performance including higher reversible capacity, better rate capability and good cycling behaviour. The obtained results suggest that this porous polymer membrane shows great attraction to the lithium ion batteries requiring high safety, low cost and environmental friendliness.
This study reports a systematic investigation of electrolytes based on new salts consisting of various cations and the bis(oxalate)borate (BOB) anion for use in electrical double layer capacitors. The quaternary ammonium salts—tetraethylammonium tetrafluoroborate (TEABF4), spiro-(1,1ʹ)-bipyrrolidinium tetrafluoroborate (SBPBF4), 1,1-dimethylpyrrolidinium tetrafluoroborate (DMPBF4), tetraethylammonium bis(oxalato)borate (TEABOB), spiro-(1,1ʹ)-bipyrrolidinium bis(oxalato)borate (SBPBOB), and 1,1-dimethylpyrrolidinium bis(oxalato)borate (DMPBOB)—were successfully prepared in high purity and dissolved in acetonitrile (ACN) at a concentration of 1.0 M. The successful synthesis of the salts was confirmed by nuclear magnetic resonance, ultraviolet–visible, and Fourier-transform infrared spectroscopies. The physicochemical properties and electrochemical performance of the prepared electrolytes, namely, thermal stability, ionic conductivity, viscosity, electrochemical stability window, specific capacitance, and durability, were investigated. Compared to the BF4-containing electrolytes, the new electrolytes based on the BOB anion, particularly the DMPBOB salt, showed dramatically enhanced high-voltage performance at elevated temperature. Electrical double layer capacitors based on 1 M DMPBOB in ACN exhibited a capacitance retention of 55.9% and a coulombic efficiency of >99% after 2000 cycles at a working voltage of 4.0 V and 45 °C. Moreover, X-ray photoelectron spectroscopy suggested that a highly stable protective layer induced by the BOB-containing electrolyte was formed on the negative electrode of the capacitor, inhibiting acute electrolyte decomposition during the cycling test.
Publisher Summary This chapter discusses several types of high-temperature thermally activated primary batteries: calcium anode-based thermal batteries, lithium anode thermal batteries, and lithium alloy thermal batteries. In calcium-calcium chromate thermal batteries the overall reaction for the calcium-calcium chromate system is dependent on the discharge parameters. Thermal batteries are manufactured in a wide range of configurations to suit various types of application. The two principal pyrotechnic heat sources used in thermal batteries are a paper-type composition of zirconium and barium chromate powders supported on inorganic fibers and a pressed tablet made up of iron powder and potassium perchlorate, commonly known as a heat pellet. The zirconium-barium chromate heat paper is manufactured from pyrotechnic-grade zirconium and barium chromate; with a particle size of about 1-10μm. Thermal batteries are initiated by either mechanical action using a percussion-type primer or an electrical pulse to an integral electric match (squib). In lithium anode thermal batteries lithium metal is molten at thermal battery discharge temperatures and is retained on high surface area metals by immersion of the metal matrix in molten lithium to form anodes. Often this structure is contained within a metal cup to prevent leakage during cell operation. Another method is the fabrication of lithium alloy anodes, such as lithium-boron, lithium-aluminium and lithium-silicon, which are solid at battery discharge temperatures and thus offer the possibility of simpler construction.
Electrochemical properties of TiNb2O7 (TNO) electrodes during lithium storage have been studied in order to develop an alternative anode with high-capacity, fast-charging, and long-life to Li4Ti5O12 (LTO) in lithium-ion batteries. High-density TNO (HD-TNO) composite electrode consisting of micro-size spherical TNO secondary particles coated with carbon exhibited high-rate capability, long cycle-life, and a high volumetric capacity of more than twice that of LTO composite anodes. Large-size lithium-ion batteries using the HD-TNO anode and a LiNi0.6Co0.2Mn0.2O2 (NCM) cathode with a capacity of 49 A h were fabricated for automotive applications, and were found to have a high energy density of 350 W h L−1, a high input-power density of 10 kW L−1 for 10 s at 50% state of charge (SOC), and fast-charging from 0% to 90% SOC in less than 6 min. The capacity retention at 7000 cycles was 86% by full charge-discharge cycling at 1C rate. Cycle life was predicted to be 14000 cycles at 80% capacity retention. It was demonstrated that the TNO/NCM batteries have high energy-density, fast-charging, and long cycle-life for automotive applications such as electric vehicles with long driving ranges by fast-charging.
In order to restrain the decomposition and conductivity degradation of perovskite-type conductive material in the presence of chromia, manganese oxide modification of lanthanum strontium cobaltite has been studied. La0.7Sr0.3CoO3−δ (LSC) and MnO2-modified LSC coatings are applied onto Ni–Cr alloy and exposed to long-term oxidation text to examine their chemical stability. In a LSC coating, chromium species migrating from the Ni–Cr alloy could induce the decomposition of LSC and produce SrCrO4 and Co–Cr spinel oxides. In contrast, in the MnO2-modified LSC, Sr is stable and the low-conductivity phase SrCrO4 phase is rarely seen even the coated alloy has gone through 1000 h of oxidation tests at 800 °C. It highlights that MnO2 modification could greatly improve the stability of LSC under Cr-rich conditions. The study of solid state reactions reveals that the influence of MnO2 is mainly due to the reaction between MnO2 and LSC, instead of the direct reaction between MnO2 and chromium oxides.
The effect of the amorphous structure and nanocrystalline nature of metal oxide on its anode performance in lithium ion batteries is investigated with two nanocrystalline and one well-crystallized layered manganese oxides. X-ray amorphous manganese oxide nanocrystals are synthesized by soft-chemical redox reactions using reducing agents of KBH4 and LiI at room temperature, whereas well-crystallized layered manganese oxide is obtained by solid state reaction at elevated temperature. Although both of the amorphous manganese oxides lack a long-range structural order, they are crystallized with a layered MnO2-type local structure, which is nearly identical to the crystal structure of the well-crystallized K0.45MnO2. In comparison with the well-crystallized K0.45MnO2, both the amorphous manganese oxides commonly possess smaller particle sizes with larger surface areas and better homogeneity of composite structure. The amorphous manganese oxide nanocrystals show better anode performance with greater discharge capacity for lithium ion batteries than does the well-crystallized K0.45MnO2, which is attributable to the greater surface area, higher structural and electrochemical stability, more homogeneous composite structure, and better charge-transfer characteristics of the amorphous materials. This result highlights the merit of the nanocrystalline and amorphous nature for optimizing the electrode performance of manganese oxide. The present solution-based redox reaction can provide a facile, economic, and scalable route for synthesizing efficient manganese-based anode materials for lithium ion batteries.
We report a family of flame-retardant electrolytes for lithium batteries based on ionic nanocomposites. The nanocomposites are synthesized in one pot by dispersing SiO2 nanoparticles charge-balanced by both Li ions and mono-amino-terminated polyether (PEO-b-PPO-NH3 +) in an oligomeric PEO matrix. The Li+ and PEO-b-PPO-NH3 + ions lead to enhanced Li+ transference number and compatibility with the PEO matrix, respectively. The nanocomposite electrolyte containing 40% mass fraction of silica shows a notable electrochemical stability window of more than 6 V in contact with Lithium and high Li+ transference number over 0.5. Rheology measurements demonstrate the tunability of the system from liquid to gel-like as the silica mass fraction percentage increases from 0 to 40% while the conductivity remains almost constant. Thermal gravimetric and microscale combustion calorimeter measurements of the nanocomposites show decreased rate of mass loss and heat release rate compared to neat electrolyte. Finally, the fire retardancy of the nanocomposites measured by directly observing the formation and sustainability of flame, when exposed to direct fire, make them promising candidates in the ever-growing quest for safe lithium batteries.
Sodium ion batteries (SIBs) have been revived as important alternative energy storage devices for large-scale energy storage, which requires SIBs to have a long cycling life and high power density. However, the scarcity of suitable anode materials hinders their application. Herein, we report a bismuth intercalated graphite (Bi@Graphite) anode material, which is substantially different from the previously reported metal@Graphene. In Bi@Graphite, the Bi nanoparticles between graphite interlayers enhance the capacity, while the graphite sheath provides a robust fast electronic connection for long cycling stability. The Bi@Graphite possesses a safe average storage potential of approximately 0.5 V vs. Na/Na+, delivers a capacity of ∼160 mA h g−1 at 1C (160 mA g−1), exhibits outstanding cycling stability (ca. 90% capacity retention for 10000 cycles at 20C), and can maintain 70% capacity at 300C (∼110 mA h g−1 at 48 A g−1), which is equivalent to full charge/discharge in 12 s. Bi@Graphite demonstrates the highest rate-capability ever reported among all anodes for SIBs. Detailed characterization results indicate that the unique Bi nanoparticle-in-graphite structure and the fast kinetics of ether co-intercalation into graphite are responsible for these significant improvements, which could translate into SIBs with excellent power densities.
This work mainly emphasizes the development of new materials and design for a bipolar/end plate in a direct methanol fuel cell (DMFC). According to the DOE requirements, preliminary studies show that SS 316 (Stainless Steel 316) is a suitable candidate. Several flow field designs were studied and a modified serpentine design was proposed. SS 316 end plates were fabricated with an intricate modified serpentine flow field design on it. The performance of a single stack DMFC with SS 316 end plates were studied with different operational parameters. A long-term test was carried out for 100h with recycling the methanol and the contaminants in the MEA were characterized. The stack efficiency is found to be 51% and polarization losses are discussed. SS 316 with low permeability resulted in an increased pressure drop across the flow field, which increased the fuel cell performance. The use of SS 316 as bipolar plate material will reduce the machining cost as well as volume of the fuel cell stack.
A truncated octahedral structure spinel cathode material with a nominal composition of Li1.08Al0.08Mn1.85Co0.05O3.9F0.1 (LAMCOF) and an Al-rich surface layer is successfully prepared by a sol-gel route combined with a temperature-controlled heat-treatment process. Concentration gradient of Mn4+ ions is found to decrease through the surface to the interior of the as-prepared sample. As the consequence, the LAMCOF sample delivers high rate capability and excellent cycling stability at elevated temperature, showing an initial discharge capacity of 111.1mAhg−1 and capacity retention of 70.5% over 850 cycles at 1C rate under 55°C. Even at 5C rate under 55°C, it also displays a high capacity of 102.5mAhg−1 with capacity retention of 80.0% over 850 cycles. These results reveal the importance of an off-stoichiometric strategy and a temperature-controlled heat-treatment process for the preparation of LiMn2O4-based spinel cathode material with unique crystal orientation and Mn4+-rich surface layer, which both decrease the Mn dissolution and provide interfacial stability while preserving fast Li+ diffusion, resulting in improvement of cycle performance and rate capability of the as-prepared material. This proposed synthesis method does not need a supplementary coating process and is likely suitable to prepare other high performance cathode materials.
Flexible, transparent and self-supporting electrolyte films based on poly(trimethylene carbonate)/poly(ethylene oxide) (p(TMC)/PEO) interpenetrating networks doped with LiClO4 were prepared by the solvent casting technique. These novel solid polymer electrolyte (SPE) systems were characterized by measurements of conductivity, cyclic voltammetry, differential scanning calorimetry and thermogravimetry. The incorporation of solid electrolytes as components of electrochromic devices can offer certain operational advantages in real-world applications. In this study, all-solid-state electrochromic cells were characterized, using Prussian blue (PB) and poly-(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT) as complementary electrochromic compounds on poly(ethyleneterphthalate) (PET) coated with indium tin oxide (ITO) as flexible electrodes. Assembled devices with PET/ITO/PB/SPE/PEDOT/ITO/PET “sandwich-like” structure were assembled and successfully cycled between light and dark blue, corresponding to the additive optical transitions for PB and PEDOT electrochromic layers. The cells required long cycle times (>600s) to reach full color switch and have modest stability towards prolonged cycling tests. The use of short duration cycling permitted the observation of changes in the coloration–bleaching performance in cells with different electrolyte compositions.
Na0.6[Li0.2Mn0.8]O2 has been synthesized at different calcination temperatures by a solid state method. Its phase structure and electrochemical properties are investigated and discussed. Na0.6[Li0.2Mn0.8]O2 prepared at 600 °C shows a complicated structure and wonderful electrochemical performance. In the voltage range of 2.0 and 4.8 V, Na0.6[Li0.2Mn0.8]O2/Li cell delivers an initial discharge capacity of 247 mAh g−1 with an average voltage of 3.52 V, which demonstrates a very high energy density of 869 Wh kg−1. Furthermore, the material displays a stable capacity greater than 240 mAh g−1 over 30 cycles.
Sulfation at the negative electrode is one of the major failure modes of lead-acid batteries. To overcome the issues of sulfation, we herein report solvothermal synthesis of titanium dioxide- reduced graphene oxide hybrid as negative electrode additive in lead acid cell. The presence of titanium dioxide-reduced graphene oxide hybrid additive (0.5 wt. %) provides high interfacial stability, slows down hard sulfation, high active material utilization by occupying pores on the negative plate. 0.5 wt. % of titanium dioxide-reduced graphene oxide hybrid (3:1 wt. ratio) additive to the negative active mass delivers 85% increase in capacity during the first formation cycle, and thereby increases the formation efficiency from 3 cycles to 1 cycle; >20% and ∼200% increase in capacity at low discharge rates of C/20 and high rates of discharge (2C), respectively as compare to conventional lead acid cell. Besides, 3:1 wt. ratio titanium dioxide-reduced graphene oxide hybrid additive cells show ∼200% increase in high rate partial state of charge cycle life in relation to conventional cell. Titanium dioxide-reduced graphene oxide hybrid additives to the negative active mass provides increase in conductivity, controls the crystallization of lead sulphate growth, acts as a capacitor, decreases the hydrogen evolution and hence enhances the electrochemical performance.
Well-organized TiO2 nanotube arrays are synthesized by anodic oxidation and then modified with MoO3 via facile electrodeposition for their improved Li-ion intercalation property. All the bare and MoO3-deposited TiO2 nanotubes are cycled at a current of 50 or 200 μA cm−2. The deposited nanotubes surprisingly deliver twice or even triple areal capacity of the bare ones, as well as better rate capability. For example, the bare nanotubes exhibit an initial capacity of 81.2 μAh cm−2 and a final capacity of 59.6 μAh cm−2 over 48 electrochemical cycles, while the ones coated by MoO3 using only one deposition cycle displays a nearly doubled initial capacity of 154.9 μAh cm−2 and a final capacity of 116.6 μAh cm−2. More deposition cycles yield TiO2 nanotubes with higher capacities up to 204.7 μAh cm−2. Such improvement could be further optimized by tuning the dimensions of TiO2 nanotubes. An eight-fold increase in the capacity of MoO3/TiO2 nanotube composite anode is achieved easily with larger nanotubes for MoO3 coating. This is attributed to the combination of MoO3 with a high specific capacity and TiO2 nanotubes with large surface area allowing efficient MoO3 deposition and ionic transport inside the anode.