Lithium-containing Electrolyte Research Articles

Deferred-Action Lithium-Based Batteries

Deferred-action batteries, also known as reserve batteries, fulfill a unique role among energy storage technologies in which long-term shelf life (years, decades) is required while ensuring optimal performance upon activation. This objective is typically achieved through isolation of the electroactive components until battery operation is desired. Commonly, the electrolyte is isolated from one or both electrodes, and thus, limiting premature degradation and parasitic side-reactions until battery power is needed. During the reserve battery activation process, electrolyte is delivered to the electrode(s), which enable ionic conduction between the anode and cathode, and thus permitting normal operations analogous to a non-reserve design – which is ubiquitous among off-the-shelf batteries.The feasible activation mechanisms are largely determined by battery chemistries and material properties, which give rise to several classifications including: thermal, spin-activated, and gas-activated reserve type batteries. Reserve battery activation under these various classifications require ancillary components and specific conditions which contribute excess complexity, weight, and volume towards the overall battery design and thus, significant penalties in reliability, specific and volumetric densities are incurred. Improvements in reserve battery technology must include strategies for limiting these penalties through innovated electrolyte delivery designs tailored for modern, high-energy, high-power density lithium-based batteries.Herein, we report a novel electrolyte delivery mechanism facilitated by an electrochemical aperture. The electrochemical aperture serves as a physical barrier, isolating the liquid, lithium-containing electrolyte. Reserve battery activation proceeds via lithium transport, inducing physical transformations via the electrochemical aperture, which permit liquid electrolyte injection into the appropriate compartment(s). Accordingly, ionic conduction between the anode and cathode is established, and ultimately resulting in battery activation and enabling typical battery operation. Strategies for quantifying and reducing activation time via material optimization will be explored.Acknowledgements: Faraday Technology acknowledges the technical assistance of Dr. Joseph P. Fellner at the Air Force Research Laboratory, Wright-Patterson AFB (Dayton, OH) under Air Force Contract No. FA8650-19-P2024 (Phase I SBIR) and FA8650-21-C-2300 (Phase II SBIR). Figure 1

Electrochemical Aperture Optimization for Rapid Activation of Lithium-Ion Reserve Batteries

Reserve batteries fulfill a unique role among energy storage technologies in which long-term shelf life (years, decades) is required while ensuring optimal performance upon activation. This is typically achieved through isolation of the electroactive components until battery operation is desired. Commonly, the electrolyte is isolated from one or both electrodes, and thus, limiting premature degradation and parasitic side-reactions until battery activation is desired. During the reserve battery activation process, electrolyte is delivered to the electrode(s), which enable ionic conduction between the anode and cathode, and thus permitting normal operations analogous to a non-reserve design.The feasible activation mechanisms are largely determined by battery chemistries and material properties, which give rise to several classifications including: thermal, spin-activated, and gas-activated reserve type batteries. Reserve battery activation under these various classifications require ancillary components and/or specific conditions which contribute excess complexity, weight, and/or volume towards the overall battery design and thus, significant penalties in reliability, specific and/or volumetric densities are incurred. Improvements in reserve battery technology must include strategies for limiting these penalties through innovated electrolyte delivery designs tailored for modern, high-energy, high-power density lithium-based batteries.Herein, we report a novel electrolyte delivery mechanism facilitated by an electrochemical aperture. The electrochemical aperture exists as a physical barrier, isolating the liquid, lithium-containing electrolyte. Reserve battery activation proceeds via lithium transport to/from the electrochemical aperture, thus inducing physical transformations which permit liquid electrolyte permeation and delivery through the aperture and into the appropriate compartment, thus establishing ionic conduction between the anode and cathode. The accompanying figure highlights two embodiments of the lithium electrochemical aperture (LiECA) concept, specifically Li-containing Aperture and Li-host Aperture. During the inactive period, liquid electrolyte is isolated by the LiECA and stored within the cathode compartment. Electrochemical transport of lithium between the LiECA and cathode induce aperture openings, injecting electrolyte into the anode compartment, and ultimately resulting in battery activation and enabling battery operation.Acknowledgements: Faraday Technology acknowledges the technical assistance of Dr. Joseph P. Fellner at the Air Force Research Laboratory, Wright-Patterson AFB (Dayton, OH) under Air Force Contract No. FA8650-19-P2024 (Phase I SBIR program). Figure 1

Evaluation of Li Electrodeposition into Al from LiCl–KCl Electrolyte

This study investigated the effects of temperature and the current density on the production of an Al–Li master alloy using electrolysis. The current efficiency and the specific energy consumption were calculated according to Faraday’s law to determine optimal conditions for production of the Al–Li master alloy. Solid aluminum and graphite were used as the cathode and the anode, respectively. The LiCl–KCl eutectic molten salt was used as a lithium-containing electrolyte. Different current densities were applied to obtain the optimum condition. In addition, different temperatures were investigated at the optimum current density during the deposition of lithium. Scanning electron microscopy, optical microscopy, and the X-ray diffraction analysis were used to investigate the microstructure and phase compositions. Atomic absorption spectroscopy was used to measure the existing lithium. The results showed that electrolysis at 620°C and a current density of 0.9 A/cm2 at 4 V for 3 h leads to the formation of an Al–17.43 wt % Li master alloy. The current efficiency and the specific energy consumption for the optimum conditions were found to be 96% and 16.08 kWh/kg, respectively.

MeV-SIMS measurement of lithium-containing electrolyte

Secondary ion mass spectrometry (SIMS) is a method with high surface sensitivity that allows both elemental and molecular analysis. The MeV-SIMS technique uses heavy ion beams with energy in the MeV range, and samples can be measured under ambient conditions because of the high transmission capability of these ions at low vacuum pressures. Ambient MeV-SIMS is a suitable method for investigating the reactions at the electrode–electrolyte interface. In contrast, however, in this method, chemical noise originating from ionized residual gases can be found with high intensity. Under the conditions, signals from the surface have to be distinguished from the chemical noise. In this paper, MeV-SIMS measurements of a Li-containing electrolyte were performed and a method was established for separating out chemical noise and signals from the sample surface. The detection of a number of Li-containing electrolytic compounds from the sample surface by an ambient MeV-SIMS system was successful.

Electrochemical Aperture Enabling Rapid Delivery of Liquid Electrolyte for Lithium-Ion Reserve Batteries

Reserve batteries fulfill a unique role among energy storage technologies in which long-term shelf life (years, decades) is required while ensuring optimal performance upon activation. This is typically achieved through isolation of the electroactive components until battery operation is required. Commonly, the electrolyte is isolated from one or both electrodes, and thus, limiting premature degradation and parasitic side-reactions until battery activation is desired. During the reserve battery activation process, electrolyte is delivered to the electrode(s), which enable ionic conduction between the anode and cathode, and thus permitting normal operations analogous to a non-reserve design. The feasible activation mechanisms are largely determined by battery chemistries and material properties, which give rise to several classifications including: thermal, spin-activated, and gas-activated reserve type batteries. Reserve battery activation under these various classifications require ancillary components and/or specific conditions which contribute excess complexity, weight, and/or volume towards the overall battery design and thus, significant penalties in reliability, specific and/or volumetric densities are incurred. Improvements in reserve battery technology must include strategies for limiting these penalties through innovated electrolyte delivery designs tailored for modern, high-energy, high-power density lithium-based batteries. Herein, we report a novel electrolyte delivery mechanism facilitated by an electrochemical aperture. The electrochemical aperture exists as a physical barrier, isolating the liquid, lithium-containing electrolyte. Reserve battery activation proceeds via lithium transport to/from the electrochemical aperture, thus inducing physical transformations which permit liquid electrolyte permeation and delivery through the aperture and into the appropriate compartment, thus establishing ionic conduction between the anode and cathode. The accompanying figure highlights the lithium electrochemical aperture (LiECA) in a 3-electrode cell. During the inactive period (a), liquid electrolyte is isolated by the LiECA and stored within the cathode compartment. Electrochemical transport of lithium between the LiECA (b) and cathode induces aperture opening and injecting electrolyte into the anode compartment (c), and ultimately resulting in battery activation and operation. Acknowledgements: Faraday Technology acknowledges the technical assistance of Dr. Joseph P. Fellner at the Air Force Research Laboratory, Wright-Patterson AFB (Dayton, OH) under Air Force Contract No. FA8650-19-P2024 (Phase I SBIR program). Figure 1

Formation of the Solid Electrolyte Interphase on the Graphite Anode in Lithium-Ion Batteries – an Operando Neutron Depth Profiling Study

To date, commercial LIB cells are mostly based on graphite as anode material. During the first inter­calation of lithium into graphite, the electrolyte gets reduced at the anode, forming a nm-thick surface layer, the so-called solid electrolyte interphase (SEI). The SEI stops further electrolyte reduction, but as it consumes lithium during its formation, there is a loss of active lithium inventory, which causes the irreversible capacity loss during the first cycle of an LIB.[1] Neutron depth profiling (NDP) is a non-destructive technique and a suitable tool to measure lithium concentrations as a function of depth.[2,3] When irradiating the sample with a cold neutron beam, 6Li nuclides emit charged particles after neutron capture. The residual energy and the signal rate of the emitted 3H particles are correlated to depth and amount of lithium, respectively. Thus, SEI growth and lithium (de-)intercalation in graphite anodes can be studied up to a depth of ca. 30 µm. So far, in-situ NDP measurements in LIBs have been limited to thin solid-state cells or to cells with sub-mm thick anodes.[4,5] Here, we present operando NDP data for the first charge/discharge cycle of a 14 mm thick graphite anode (4 mm particles) vs. a capacitively over­sized LiFePO4 cathode, using a custom-designed coin-cell casing with 0.5 mm diameter holes which are sealed with a 7.5 µm-thick Kapton® window. Fig. 1 shows the voltage profile during cycling, demonstrating that the operando cell yields the expected first-cycle discharge capacity of 350 mAh/ggraphite. The higher irreversible capacity of ca. 98 mAh/g (ca. 22%) compared to conventional graphite used in commercial cells (ca. 10%) is due to the very high BET area of ca. 14 m2/g of the 4 µm sized graphite particles. Fig. 2 shows the NDP signals at three different states-of-charge (SOC): i) for the pristine graphite anode (0 h, black line), reflecting the lithium-containing electrolyte (1 M LiPF6 in EC/EMC 3:7 v:v) within the electrode pores; ii) for 100% SOC at the end of the first charge (16 h, red line); and, iii) at the end of the first discharge at again 0% SOC (32 h, blue line). The difference between the red and the blue line indicates that ca. ¼ of the active lithium has been consumed irreversibly for the SEI formation, in good agreement with the electrochemical data.

Lithium-Incorporated Nanoporous Coating Formed by Micro Arc Oxidation (MAO) on Magnesium Alloy with Improved Corrosion Resistance, Angiogenesis and Osseointegration.

Magnesium is an attractive candidate for orthopedic implants due to its similar mechanical properties to human bone and biodegradability. However, the high corrosion rate of magnesium accompanying with high pH value and poor osteogenic activity hinder its further application. In this study, we employed micro arc oxidation (MAO) to improve corrosion resistance by introduce nanoporous coating on AZ91 magnesium. Meanwhile, we added lithium, an angiogenic and osteogenic element, to the coating (named as Li-MAO) by reaction in a lithium-containing electrolyte to simultaneously enhance angiogenic and osteogenic activity of AZ91. The favorable corrosion resistance of Li-MAO was verified by electrochemical and immersion test in vitro. Better biocompatibility was observed in Li-MAO samples by cell counting kit-8 (CCK-8) and live/dead assay. The in vitro results of immunofluorescence staining, Alizarin red staining and osteogenic-related genes expression indicated better osteogenic ability of Li-MAO group, which may result from the activation the Wnt/β-catenin pathway. In vitro angiogenic tests also demonstrated better angiogenesis in Li-MAO group. A bone defect repair model was built to evaluate the in vivo osseointegration of samples. The outcomes of micro-computed tomography (Micro-CT) scanning, sequential fluorochrome labeling and Van Gieson staining suggested better in vivo bone repair ability of Li-MAO than other groups. Our promising results both in vitro and in vivo demonstrated that lithium-containing nanoporous coating can improve corrosion resistance, angiogenesis and osseointegration of magnesium alloy, which may forward the clinic application of Li-MAO magnesium.

Influences from solvents on charge storage in titanium carbide MXenes

Pseudocapacitive energy storage in supercapacitor electrodes differs significantly from the electrical double-layer mechanism of porous carbon materials, which requires a change from conventional thinking when choosing appropriate electrolytes. Here we show how simply changing the solvent of an electrolyte system can drastically influence the pseudocapacitive charge storage of the two-dimensional titanium carbide, Ti3C2 (a representative member of the MXene family). Measurements of the charge stored by Ti3C2 in lithium-containing electrolytes with nitrile-, carbonate- and sulfoxide-based solvents show that the use of a carbonate solvent doubles the charge stored by Ti3C2 when compared with the other solvent systems. We find that the chemical nature of the electrolyte solvent has a profound effect on the arrangement of molecules/ions in Ti3C2, which correlates directly to the total charge being stored. Having nearly completely desolvated lithium ions in Ti3C2 for the carbonate-based electrolyte leads to high volumetric capacitance at high charge–discharge rates, demonstrating the importance of considering all aspects of an electrochemical system during development.

Investigating the Distribution of Electrolyte Decomposition Products (SEI) in Silicon Electrodes By Neutron Depth Profiling

The electrochemical performance of silicon-based anodes in lithium-ion batteries is largely determined by the ongoing decomposition of electrolyte compounds at the silicon particle surface and the subsequent formation of a solid-electrolyte-interphase (SEI).1 Yet, the significant extent of electrolyte decomposition products which accumulate in the anodes as a result of the severe morphological changes of the silicon particles upon cycling requires to rethink the concept of a conformal SEI layer as it was proposed for state-of-the-art graphite anodes.2,3 Based on previous studies,4,5 our current characterization is concerned with the relation of the morphological changes and the resulting electrochemical performance of practical silicon-graphite electrodes. Hence, we apply ex-situ neutron depth profiling (NDP) to monitor the distribution of the lithium-containing electrolyte decomposition products across the thickness of silicon-graphite electrodes as a function of the cycle number. In contrast to conventional analytical techniques, NDP is a non-destructive method with a very high sensitivity to lithium, which allows to determine lithium concentration gradients across the thickness of the entire electrode.6 For our investigation, we prepared silicon-graphite (SiG) electrodes with a practical areal capacity of ~1.8 mAh cm-2 (initial thickness: ~19 µm), consisting of 35 wt% nanometer-sized silicon (~200 nm diameter) and 45 wt% graphite (~20 µm diameter). Vapor grown carbon fibers and lithiated poly(acrylic acid) binder accounted for the remaining 20 wt%.4 Utilizing SiG//LiFePO4 coin-cells with a capacitively oversized positive electrode (~3.5 mAh cm-2) and a relatively stable reference potential of ~3.45 V vs. Li/Li+, the silicon-graphite electrodes were aged by galvanostatic charge-discharge cycling at C/2 (~0.9 mA cm-2) up to 140 cycles. In the next step, we fully delithiated the active materials in the electrodes by applying a very slow C-rate of C/50 (~0.04 mA cm-2) and a high delithiation cutoff potential of ~2.0 V vs. Li/Li+. As a result, any residual lithium in these electrodes either originates from lithium-containing electrolyte decomposition products or the LiPAA binder. Based on the NDP spectra of the silicon-graphite electrodes after a different number of cycles, we demonstrate that the irreversible capacity obtained from charge-discharge cycling is directly proportional to the total amount of lithium-containing electrolyte decomposition products that accumulated in the electrodes during the same period. Further, we show that this accumulation is also reflected by the increase of the entire mass loading (coating + SEI) and the significant swelling of the electrodes (+140% in the delithiated state), thus following the two major degradation phenomena of silicon-graphite electrodes, which we discussed in our previous publication.4 In addition, we support our analysis by complementing the NDP spectra with high-resolution cross-sectional scanning electron microscopy (SEM) images of the silicon-graphite electrodes after different numbers of cycles. Finally, we analyze the energy loss of the 3H particles emitted by the nuclear reaction of 6Li with thermal neutrons as a function of the electrode depth, determining the evolution of the lithium concentration gradients across the thickness of the electrodes and discussing the implications on the utilization of the active materials near the separator/anode and the anode/current collector interface. Our analysis allows to shape a refined explanation of the accumulation of electrolyte decomposition products in silicon-graphite electrodes and its implication both on the changes in electrode morphology and the resulting electrochemical performance.

Quantifying the Distribution of Electrolyte Decomposition Products in Silicon-Graphite Electrodes by Neutron Depth Profiling

Silicon-based anodes for lithium-ion batteries exhibit severe volumetric changes of the active material particles during (de-)lithiation, resulting in continuously occurring side reactions at the silicon/electrolyte interface over extended charge/discharge cycling. The thus formed and accumulating electrolyte decomposition products lead to a growth of the solid-electrolyte-interphase (SEI) on the silicon particles. This results not only in an ongoing loss of electrolyte but also in a significant swelling and impedance increase of silicon-based anodes which significantly compromises their cycle-life. In the present study, neutron depth profiling (NDP) is used post mortem as a non-destructive, highly lithium-sensitive technique to (i) quantify the amount of lithium-containing electrolyte decomposition products in silicon-graphite (SiG) electrodes (35 wt% silicon, areal capacity ∼1.7 mAh cm−2), (ii) monitor their distribution across the SiG electrode thickness, and (iii) determine the active material utilization across the electrode over 140 cycles. Hence, SiG negative electrodes are aged and characterized by means of galvanostatic cycling in SiG//LiFePO4 pseudo-full cells, using a capacitively oversized positive electrode and an electrolyte mixture consisting of 1 M LiPF6 in EC:EMC with 5 wt% FEC. High-resolution cross-sectional SEM images and post-mortem characterization of the SiG electrodes with respect to changes in electrode mass thickness complement the analysis.

Tailored Mesoporous Carbon/Vanadium Pentoxide Hybrid Electrodes for High Power Pseudocapacitive Lithium and Sodium Intercalation

In this study, atomic layer deposition (ALD) is employed to synthesize hybrid electrode materials of especially tailored mesoporous carbon and vanadium oxide. The highly conformal and precise character of ALD allowed for depositing up to 65 mass % of vanadium oxide inside the 5–20 nm mesopores of the carbon particles, without substantially obstructing internal surface area. The deposited phase was identified as orthorhombic V2O5, and an increasing crystalline order was detected for higher mass loadings. Employing the hybrid material as lithium and sodium intercalation hosts at a rate of 0.5C yielded specific capacities of 310 and 250 mAh/g per V2O5, respectively, while showing predominantly pseudocapacitive behavior, that is, capacitor-like voltage profiles. C-rate benchmarking revealed a retention of about 50% of the maximum capacity for both lithium and sodium at a high rate of 100C. When testing for longevity in lithium-containing electrolyte, a steadily increasing capacity was observed to 116% of the initial value after 2000 cycles. In sodium electrolyte, the capacity faded to 75% after 2000 cycles, which represents one of the most stable performances for sodium intercalation in the literature. Homogeneously distributed vanadium oxide that is locally confined in the tailored carbon mesopores was identified as the reason for enhanced cyclability and rate behavior of the hybrid material.

Lithium-Ion Capacitor Based on LiFePO4 and Nanostructured Carbon By Electrostatic Spray Deposition

Many efforts have demonstrated the practicability of power units based on electrical double-layer capacitors (EDLCs) to replace or complement batteries, generally because of their ability to deliver higher power density, faster charge and discharge rate as wells as longer operational life cycle. However, EDLCs exhibit relatively poor energy density. This limitation is revealed in portable electronic systems whose functions demand high energy and power density at the same time. In order to overcome the low energy density limitation of EDLCs, lithium-ion capacitors have gained much interest. Lithium-ion capacitors are hybrid electrochemical charge storage devices that combine the high energy density capability of lithium-ion batteries and the high power density in EDLCs. This is typically achieved by using electrodes based on battery-type lithium intercalating material as the high energy density source, and a capacitor-type material as the high power density source, in a lithium-containing electrolyte. In this work, we evaluated the electrochemical performance of lithium-ion capacitor comprising lithium iron phosphate (LiFePO4) battery-type cathode and reduced graphene oxide-carbon nanotube (RGO-CNT) composite as capacitor-type anode for half and full cells. The electrodes were prepared via electrostatic spray deposition (ESD) method, a thin-film deposition method capable of operating in ambient conditions. The choice of LiFePO4 is mainly because it is relatively inexpensive and exhibit attractive electrochemical properties such as good cycling stability, high intercalating potential of ~3.5 V versus Li+/Li as well as flat voltage plateaus. On the other hand, among a variety of nanostructured carbon materials, RGO-CNT composite has been shown as a good double-layer electrode material in EDLCs with high power density capability. Material characterization of the electrodes was carried out using scanning electron microscopy (SEM) and X-Ray diffractometry (XRD) respectively. Detailed results will be presented at the meeting.

Lithium-ion capacitors using carbide-derived carbon as the positive electrode – A comparison of cells with graphite and Li4Ti5O12 as the negative electrode

Abstract The use of carbide-derived carbon (CDC) as the positive electrode material for lithium-ion capacitors (LICs) is investigated. CDC based LIC cells are studied utilizing two different negative electrode materials: graphite and lithium titanate Li 4 Ti 5 O 12 (LTO). The graphite electrodes are prelithiated before assembling the LICs, and LTO containing cells are studied with and without prelithiation. The rate capability and cycle life stability during 1000 cycles are evaluated by galvanostatic cycling at current densities of 0.4–4 mA cm −2 . The CDC shows a specific capacitance of 120 F g −1 in the organic lithium-containing electrolyte, and the LICs demonstrate a good stability over 1000 charge-discharge cycles. The choice of the negative electrode is found to have an effect on the utilization of the CDC positive electrode during cycling and on the specific energy of the device. The graphite/CDC cell delivers a maximum specific discharge energy of 90 Wh kg −1 based on the total mass of active material in the cell. Both the prelithiated and non-prelithiated LTO/CDC cells show a specific energy of around 30 Wh kg −1 .

Lithium-Ion Capacitor Based on Electrodes Constructed Via Electrostatic Spray Deposition

Conventional Electrochemical double-layer capacitors (EDLCs) are well suited as power devices that can provide large bursts of energy in short time periods. However, their relatively poor energy densities hinder their application in devices that require a simultaneous supply of both high energy and high power. In the wake of addressing this shortcoming of EDLCs, the concept of hybridization of lithium-ion batteries (LIBs) and EDLCs has gained significant scientific interest in past few years. Such a device, generally referred to as the “lithium-ion capacitor” typically utilizes a lithium intercalating electrode along with a fast charging capacitor electrode in a lithium-containing electrolyte. Herein we have constructed a lithium ion capacitor comprising a Li4Ti5O12 –TiO2 (LTO-TiO2) anode and a graphene and carbon nanotube (G-CNT) composite cathode using electrostatic spray deposition (ESD). The morphology and material properties were studied using scanning and transmission electron microscopy and X-ray diffraction studies, respectively. Electrochemical characterization was thereafter carried out for both the half cells as well as full cells.

Lithium-Ion Capacitor Based on Electrodes Constructed Via Electrochemical Spray Deposition

Conventional Electrochemical double-layer capacitors (EDLCs) are well suited as power devices that can provide large bursts of energy in short time periods. However, their relatively poor energy densities hinder their application in devices that require simultaneous supplies of both high energy and high power. In the wake of addressing this shortcoming of EDLCs, the concept of hybridization of lithium-ion batteries (LIBs) and EDLCs has started to gain popularity in recent years. Such a device, generally referred to as the “lithium-ion capacitor” typically utilizes a lithium intercalating electrode along with a fast charging capacitor electrode in a lithium-containing electrolyte. Herein we have constructed a lithium ion capacitor comprising a Li4Ti5O12 (LTO) anode and a graphene and carbon nanotube (G-CNT) composite cathode using electrostatic spray deposition (ESD). The morphology and material properties were studied scanning electron microscopy and X-ray diffraction studies, respectively. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements were carried out to evaluate the electrochemical performance of both half cells and full cells. The details will be presented at the conference.

Ion Solvation and the Search for a Correlation with Electrode Passivation

ABSTRACTThe solvation of cations and anions in a lithium-containing electrolyte was studied using electrospray ionization mass spectrometry (ESI-MS) combined with nuclear magnetic resonance (NMR) and electrochemical testing. The purpose of these experiments was to develop an understanding of the solvation of the small, hard Li+ cation and the more cryptic nature of the solvation of poorly-coordinating anions such as PF6- and BF4-. It has long been held that the passivation of graphitic anodes in lithium ion batteries is a solvation-driven process, meaning that whatever solvent molecules surround the Li+ cation will provide the raw material for the formation of the solid electrolyte interphase (SEI) layer. Because the SEI is a critical component, and because a binary solvent system is normally used in lithium batteries, it is necessary to understand the competitive nature of lithium solvation. Conversely, the anion can be chemically active even if poorly coordinating; therefore, it was desired to see if a competitive solvation condition exists for the anion as well. Results indicate that Li+ has a strong preference for cyclic carbonates like ethylene carbonate (EC) over linear carbonates, where the anions had a mixed preference. It is thought that anion solvent preference might dictate oxidative chemistry that occurs on the cathode, while the anion also significantly participates in the formation of SEI on the anode.

Mixed bi-material electrodes based on LiMn 2O 4 and activated carbon for hybrid electrochemical energy storage devices

The performance of mixed bi-material electrodes composed of the battery material, LiMn 2O 4, and the electrochemical capacitor material, activated carbon, for hybrid electrochemical energy storage devices is investigated by galvanostatic charge/discharge and pulsed discharge experiments. Both, a high and a low conductivity lithium-containing electrolyte are used. The specific charge of the bi-material electrode is the linear combination of the specific charges of LiMn 2O 4 and activated carbon according to the electrode composition at low discharge rates. Thus, the specific charge of the bi-material electrode falls between the specific charge of the activated carbon electrode and the LiMn 2O 4 battery electrode. The bi-material electrodes have better rate capability than the LiMn 2O 4 battery electrode. For high current pulsed applications the bi-material electrodes typically outperform both the battery and the capacitor electrode.

Enhancement of the Performance of Dye-Sensitized Solar Cell by Formation of Shallow Transport Levels under Visible Light Illumination

The performance enhancement of dye-sensitized solar cells (DSCs) in lithium-free and lithium-containing electrolytes under visible light-soaking was examined by impedance spectroscopy and photovoltage transient decay measurements. The improvement was found to arise from the formation of electronic transport levels close to the conduction band, resulting most likely from photoinduced proton intercalation in the TiO2 nanoparticles. These shallow trapping states accelerate the charge carrier transport within the nanocrystalline films without deteriorating the open circuit photovoltage. Subjecting the cells to forward bias in the dark produces a similar effect, whereas the introduction of lithium ions in the electrolyte suppresses the phenomena due to prevailing lithium ion intercalation. The redistribution of localized states in the band gap of TiO2 and the resulting conduction band edge movement appears to play a significant role in the performance of the DSC.

Electrostatic Layer-by-Layer Deposition and Electrochemical Characterization of Thin Films Composed of MnO2 Nanoparticles in a Room-Temperature Ionic Liquid

Thin films of MnO(2) nanoparticles were grown using the layer-by-layer method with poly(diallyldimetylammonium) as the intercalated layer. The film growth was followed by UV-vis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy. Linear growth due to electrostatic immobilization of layers was observed up to 30 bilayers, but electrical connectivity was maintained only for 12 MnO(2)/PPDA bilayers. The electrochemical characterization of this film in 1-butyl-2,3-dimethyl-imidazolium (BMMI) bis(trifluoromethanesulfonyl)imide (TFSI) (BMMITFSI) with and without addition of a lithium salt indicated a higher electrochemical response of the nanostructured electrode in the lithium-containing electrolyte. On the basis of EQCM experiments, it was possible to confirm that the charge compensation process is achieved mainly by the TFSI anion at short times (<2 s) and by BMMI and lithium cations at longer times. The fact that large ions like TFSI and BMMI participate in the electroneutrality is attributed to the redox reaction that occurs at the superficial sites and to the high concentration of these species compared to that of lithium cations.

Electrochemistry of NaK 2C 12 in lithium-containing electrolytes and its use in lithium-ion cells ☆

The electrochemistry of NaK 2C 12 in 1 M LiClO 4 EC-DMC solutions has been studied. The results show that, upon oxidation, NaK 2C 12 irreversibly releases one mole of potassium ions. The resulting composite electrode, that appears to be a mixture of graphite and Na–K alloy, is capable to reversibly intercalate lithium up to LiC 6 with fast rate. The compound can be used in lithium-ion cells with partially lithiated cathodes such as LiMn 2O 4, resulting in a two plateaus cell operating in the Li 1+ x Mn 2O 4 and Li 1− x Mn 2O 4 regions.