Propylene Carbonate Electrolyte Research Articles

Correlations Between Electrolyte Concentration and Solid Electrolyte Interphase Composition in Electrodeposited Lithium.

This study examined the electrochemical deposition and dissolution of lithium on nickel electrodes in propylene carbonate (PC) electrolytes containing different concentrations of lithium salts, including LiN(SO2C2F5)2 or LiPF6. The electrode reactions were significantly affected by the electrolyte concentration. The cyclability of the electrodes was considerably improved by increasing the electrolyte concentration. X-ray photoelectron spectroscopy (XPS) showed that the composition of the solid electrolyte interphase (SEI) was also affected by the electrolyte concentration. The SEI formed in the 1st cycle consisted mainly of LiF in 1 and 2.15 M LiN(SO2C2F5)2/PC solutions. After the 30th cycle in the former solution, there was a large decrease in the amount of LiF and a large increase in the amount of LiOH. On the other hand, in the latter solution there was a smaller decrease and a smaller increase in the amount of LiF and LiOH, respectively, as compared to the former solution after the 30th cycle.

Synthesis of samarium telluride thin films by successive ionic layer adsorption and reaction (SILAR) method for supercapacitor application

The present paper deals with synthesis of samarium telluride (Sm2Te3) thin films using simple and low cost successive ionic layer adsorption and reaction (SILAR) method for supercapacitor application. The Sm2Te3 thin films are characterized by X-ray diffraction (XRD) for structural determination, energy dispersive analysis of X-ray (EDAX) for elemental composition, field emission scanning electron microscopy (FE-SEM) for surface morphological study and contact angle measurement for wettability study. The Sm2Te3 exhibits orthorhombic crystal structure with cloud like surface morphology. The film surface showed lyophilic behavior with contact angle of 5.7° for propylene carbonate (PC). Further, electrochemical measurements are carried out in LiClO4–PC electrolyte using cyclic voltammetry (CV), galvanostatic charge discharge and electrochemical impedance spectroscopy (EIS) techniques. The Sm2Te3 film showed maximum specific capacitance and energy density of 144Fg−1 and 10Whkg−1 respectively. The EIS study showed negligible change in resistive parameters after 1000 electrochemical cycles.

D-Glucose Derived Nanospheric Hard Carbon Electrodes for Room-Temperature Sodium-Ion Batteries

Electrochemical performance of nanospheric glucose derived hard carbon based electrodes, specially derived from D-glucose via hydrothermal carbonization and subsequent pyrolysis at 1100°C, has been studied in 1 M NaClO4 propylene carbonate electrolyte. High Na+ electroreduction and Na oxidation peaks were observed in cyclic voltammograms. Galvanostatic charge/discharge measurements demonstrated high specific capacity, over 300 mAh g−1 for the first cycle. After 200th cycle, a specific capacity of 160 mAh g−1 (at 50 mA g−1 cycling rate) has been calculated for the nanospheric hard carbon based half-cells. Raman spectroscopy, inductively coupled plasma mass spectrometry and energy-dispersive X-ray spectroscopy data indicated accumulation (adsorption/absorption) of Na onto/into the electrochemically polarized porous nanospheric hard carbon material. Impedance data demonstrated that electrode potential has a noticeable influence on the total polarization, and charge transfer resistance as well as on the mass transfer characteristics at the carbon|(1 M NaClO4 + propylene carbonate) electrolyte interface.

One-step chemical synthesis of samarium telluride thin films and their supercapacitive properties

The letter reports synthesis of samarium telluride (Sm2Te3) thin films through a one-step chemical route. The formation of Sm2Te3 is confirmed by X-ray diffraction and X-ray photoelectron spectroscopy studies. The surface morphological study is carried out using field emission scanning electron microscopy and contact angle measurement techniques. The film shows barley-like microstructure with an average length of barley of about 5μm and diameter of about 300nm. The Sm2Te3 film surface exhibits lyophilic nature with contact angle of 21.3° for propylene carbonate electrolyte. Cyclic voltammetry results revealed specific capacitance of 207Fg−1 with power density of 14.18kWkg−1 in LiClO4-propylene carbonate electrolyte.

Exfoliation of Electrolyte-Intercalated Graphene: Molecular Dynamics Simulation Study

Ethylene carbonate (EC) is one of the most common electrolyte for lithium ion batteries, but it has a narrow working temperature range. Despite the structural similarity, propylene carbonate (PC) has a wider working temperature range as an electrolyte, but it induces exfoliation of the graphite anode. To understand the different behavior of EC and PC electrolytes at the atomistic level, we performed molecular dynamics (MD) simulations of electrolyte intercalated graphene sheets. We observed no diffusion of electrolyte between graphene sheets when interlayer distance is less than 6 A, but both of EC and PC form monolayer between graphene sheets with comparable density when interlayer distance is 7–8 A. Because of the size difference, the intercalated PC molecules induce a longer separation distance between graphene sheets compared to that of EC. The longer separation with PC intercalant induces more frequent sliding-exfoliation movement. We found that the exfoliation diffusion coefficient of the graphene s...

Electrochemical behavior of multifunctional graphene–polyimide nanocomposite film in two different electrolyte solutions

ABSTRACTThe effect of solvent on specific capacitance, bulk resistance, and charge/discharge capacity of graphene/polyimide composite films is studied by electrochemical methods. Composite films are synthesized by in situ condensation polymerization of poly (amic acid) in the presence of 50 wt % partly exfoliated graphene sheets followed by thermal curing at 250°C. Raman spectrum of the exfoliated graphene sheets show an increase in the ratio of ID to IG peak intensities from 0.167 to 0.222, suggesting increased defects in graphene basal planes. Electrochemical measurements carried out by using 0.4M potassium hexafluorophosphate (KPF6) dissolved in propylene carbonate and N‐methylpyrrolidone at 25°C show that the composite system exhibits both pseudocapacitance and supercapacitance behaviors, with an average capacitance of 40 and 36.5 F g−1, respectively. Bulk resistance of the composite obtained by using KPF6–propylene carbonate electrolyte solution is 300% lower than that obtained in KPF6–N‐methylpyrrolidone solution, with a fairly stable specific capacity of 85 μAhr g−1, with 80% retention observed after 30 charge–discharge cycles. Fourier transform infrared spectroscopy measurements show shifts in the cyclic imide carbonyl peak from 1778 to 1774 cm−1, which suggests that some form of interaction exists between the graphene and polyimide. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42673.

Quantification of Electrochemical Nanoscale Processes in Lithium Batteries By Operando EC-(S)TEM

Lithium (Li)-ion batteries are currently used for a wide variety of portable electronic devices, electric vehicles and renewable energy applications [1,2]. In addition, extensive worldwide research efforts are now being devoted to more advanced “beyond Li-ion” battery chemistries - such as lithium-sulfur (Li-S) [3] and lithium-air (Li-O2) [4] - in which the carbon anode is replaced with Li metal. However, the practical application of Li metal anode systems has been highly problematic. The main challenges involve controlling the formation of a solid-electrolyte interphase (SEI) layer and the suppression of Li dendrite growth during the charge/discharge process (achieving “dendrite-free” cycling). The SEI layer formation continuously consumes the electrolyte components creating highly resistive layer, which leads to the rapid decrease of cycling performance and degradation of the Li anode [5]. The growth of Li metal dendrites at the anode contributes to rapid capacity fading (the presence of “dead Li” created during the discharge leads to an increased overpotential) and, in the case of continuous growth, leads to internal short circuits and extreme safety issues [6]. Here we demonstrate the application of an operando electrochemical scanning transmission electron microscopy (ec-(S)TEM) cell to study the SEI layer formation and the initial stages of Li dendrite growth - the goal is to develop a mechanism for mitigating the degradation processes and increasing safety. Bright field (BF) STEM images in Figure 1 A-C show Li metal deposition and dissolution processes at the interface between the Pt working electrode and the lithium hexafluorophosphate (LiPF6) in propylene carbonate (PC) electrolyte during three charge/discharge cycles. A contrast reversal caused by Li metal being lighter/less dense than surrounding electrolyte (Li appears brighter than the background in BF STEM images) allows Li to be uniquely identified from the other components in the system - the only solid material that is less dense than the electrolyte is Li metal. Using these images, we can precisely quantify the total volume of Li deposition, the thickness of the SEI layer (observed as a ring of positive contrast around the electrode) and alloy formation due to Li+ ion insertion during each cycle. Furthermore, at the end of each discharge cycle we can quantify the presence of “dead Li” detached from the Pt electrode, thereby demonstrating the degree of irreversibility (and degradation of Pt electrode) associated with insertion/removal of Li+during this process with direct correlation to electrochemical performance. Such analyses provide significant insights into Li metal dendrite growth, which is critical to understand the complex interfacial reactions needed to be controlled for future Li-based and next generation energy storage systems. [7]

Electrochemically formed α’-NaV2O5: A new sodium intercalation compound

In this work the electrochemical behavior of α-V2O5 at RT, in a 1M NaClO4/PC (propylene carbonate) electrolyte is investigated for the first time. The irreversible formation of a sodiated layered compound is shown from the first electrochemical discharge step. This electrochemically formed compound, with highly stable structure close to that of the high temperature α’-NaV2O5 orthorhombic bronze, is demonstrated to be a genuine sodium intercalation compound. This material exhibits a high capacity of 120mAhg−1 available near 1.6V at C/10 rate with a promising cycling behaviour. X-ray diffraction and Raman spectroscopy show zero strain structural behaviour during Na+ insertion/extraction in this large interlayer spacing material.

Design of Electrochemcial Interface Between Cathode/Solid Electrolyte By Using Liquid Type Li+ Conducting Materials

Lithium ion secondary batteries have been used widely as power sources of various electric devices, and recently used for larger applications such as electric vehicles. According to this movement, the safety of battery becomes more important. However, it is difficult to realize high safety in current batteries using liquid electrolytes containing flammable organic solvents. Thus, all-solid-state batteries using ceramics electrolytes have been focused in recent years. We have studied about the all-solid-state batteries using Li7La3Zr2O12 (LLZ), which has Li+ conductivity higher than 10-4 S cm-1 at room temperature and chemical stability against lithium metal. Thus, LLZ is a promising solid electrolyte to realize the all-solid-state batteries with high safety and energy density. However, new insights and technologies are needed to form an electrochemical electrolyte/electrode interface in all-solid-state batteries since solid electrolytes have no fluidity. In this study, formation of an appropriate electrochemical interface for all-solid-state batteries is investigated by applying various Li+ conducting materials to the composite cathode formed on a LLZ pellet. LLZ powder was synthesized by solid state reaction and pelletized. LiFePO4 was used as cathode and its slurry containing acetylene black and polyvinilidene difluoride in a weight ratio of 80: 10: 10 in N-methylpyrrolidone was coated on LLZ pellet. After vacuum drying at 85 oC, a small amount of electrolyte materials was impregnated in to the cathode. Then, lithium-metal was attached onto the back side of LLZ pellet as anode. As the electrolyte materials, 1 mol dm-3 LiPF6 in propylene carbonate and lithium bisfluorosulfonylimide-tetraglyme complex (LiFSI-G4) were used. Fig. 1 shows a cross-sectional SEM image of the LLZ pellet with LiFePO4 composite cathode. The composite cathode with a thickness of about 10 μm was well attached onto the LLZ pellet. Fig. 2 shows the cyclic voltammogram of the cell without liquid electrolyte impregnation to the cathode. A couple of oxidation and reduction peaks corresponding to the charge and discharge of LiFePO4 were observed with a relatively high symmetry, centered at around 3.5 V, which agrees with the operating potential of LiFePO4. However, those peak currents were as low as 1 μA, suggesting that only a small amount of LiFePO4 near the LLZ/cathode interface worked. Fig. 3 shows cyclic voltammograms of the cells with LiFePO4 composite cathodes impregnated with (a) 1 mol dm-3 LiPF6 in propylene carbonate and (b) LiFSI-G4. In the case of 1 mol dm-3 LiPF6 in propylene carbonate, the oxidation and reduction peaks corresponding to the charge and discharge of LiFePO4 were observed, and those currents were increased compared with the cell without the electrolyte impregnation (Fig. 2). This improvement can be understood by the formation of Li+ conducting pathways between LiFePO4 in the cathode and LLZ pellet. Similarly, the currents were increased by applying LiFSI-G4. However, the charge and discharge peaks became broader and shifted to positive and negative, respectively. This difference may be due to the lower ionic conductivity and higher viscosity of LiFSI-G4 than those of propylene carbonate electrolyte solution. Further optimization on LLZ/LiFePO4 cathode interface is now underway and the details will be discussed in the meeting. Figure 1

Electrolyte and solvent effects in PPy/DBS linear actuators

An important question with conducting polymer linear actuators concerns the processes that occur once the electrolyte is changed. To address this question, a series of electro-chemo-mechanical deformation (ECMD) measurements on electrochemically prepared free-standing films of polypyrrole doped with dodecylbenzenesulfonate (DBS) were investigated under isometric (constant force) conditions in an organic solvent- and in aqueous based-electrolytes during cyclic voltammetric and square wave potential step experiments. The same film was actuated first in propylene carbonate electrolyte (0.1M TBACF3SO3), where cation-driven actuation (12% strain) was observed. The film was then exposed to an aqueous electrolyte (0.2M TMACl) where the actuation changed to anion-driven (7% strain). The same film was then returned to the propylene carbonate electrolyte, where anion-driven actuation (10% strain) was observed rather than the original cation-driven actuation. Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and scanning ionic conductance microscopy were applied to evaluate changes in morphology and electrochemical properties before and after the actuation cycles to examine changes in the actuation mode. The mechanism and reasons for the observed behaviour are proposed.

Development of glucose biosensors based on nanostructured graphene-conducting polyaniline composite.

A biosensor was fabricated by immobilizing glucose oxidase (GOD) into nanostructured graphene (GRA)-conducting polyaniline (PANI) nanocomposite, which was based on electrochemical polymerization of aniline in GRA synthesized by using electrochemical expansion of graphite in propylene carbonate electrolyte. Scanning electron spectroscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the morphology and performance of the as-prepared biosensor, respectively. Amperometric measurements were carried out to optimize test conditions (pH and applied potential) of the biosensor. Under the optimal conditions, the biosensor showed a linear range from 10.0 μM to 1.48 mM (R(2)=0.9988) with a sensitivity of 22.1 μA mM(-1) cm(-2), and a detection limit of 2.769 μM (S/N=3). The apparent Michaelis-Menten constant (KM(a)) was estimated to be 3.26 mM. The interference from glycine (Gly), D-galactose (D-Gal), urea (Urea), L-phenylalanine (L-Phe), ascorbic acid (AA), and L-tyrosine (L-Tyr) was also investigated. The results indicated that the biosensor exhibit high sensitivity and superior selectivity, providing a hopeful candidate for glucose biosensing.

Porous network of samarium sulfide thin films for supercapacitive application

In the present letter, a novel aqueous chemical method is employed to prepare thin film of Sm2S3 material containing porous network of interconnected nanoparticles for supercapacitive application. The orthorhombic phase formation of Sm2S3 film is concluded from X–ray diffraction study. The chemical states of samarium and sulfur are determined using X–ray photoelectron spectroscopy study. The pseudocapacitive behavior of Sm2S3 showed a maximum specific capacitance of 248Fg−1 in 1.5M LiClO4 electrolyte prepared in propylene carbonate electrolyte. The nature of charge and discharge curves confirmed pseudocapacitive behavior of film electrode. The highest power and energy densities of 15.6kWhkg−1 and 54.6Whkg−1, respectively are obtained. An electrochemical stability of 94% is retained after 1500 cycles.

Understanding the Interaction of the Carbonates and Binder in Na-Ion Batteries: A Combined Bulk and Surface Study

Organic carbonates are the predominant electrolyte base used in the best Li- and Na-ion battery systems. However, to date, their precise interactions with the electrode are not fully understood. Here, we elucidate the role of a prototypical electrolyte additive, fluoroethylene carbonate (FEC), in Na-ion batteries and illustrate its influence on the solid electrolyte interphase (SEI) composition. Through the use of bulk and surface analytical techniques, we find that early FEC decomposition forms a surface-passivating constituent (Na2CO3), reduces the rate of decomposition of the propylene carbonate electrolyte, and supports the preservation of the polyvinylidene difluoride (PVDF) binder. Furthermore, we observe that NaF is formed by the decomposing PVDF binder when no additive is present, resulting in the early degradation of battery performance. This new understanding of the SEI offers greater chemical insight into the selection of binder and electrolyte combinations, allowing better targeted use of thes...

Electrochemical behavior of MgO-templated mesoporous carbons in the propylene carbonate solution of sodium hexafluorophosphate

MgO-templated mesoporous carbons annealed from 900 to 1,500 °C were examined as active materials for negative electrodes in a propylene carbonate electrolyte containing 1 M sodium hexafluorophosphate. The carbons annealed at 1,000 °C exhibited 180 mAh g−1 at a rate of 0.1 A g−1 in a potential range of 2.00–0.01 V versus Na+/Na. The carbons showed good rate capability as well as cyclability. It is considered that mesopores plays a role of easy diffusion pathway for ions, and also significantly relates to both electric double layer capacitance and faradaic reactions involving Na ions. X-ray diffraction patterns, nuclear magnetic resonance spectra and Raman spectra were discussed for characterization of the carbons. Raman spectra indicated a reversible interaction of reduced Na with carbons. However, Na intercalation in the carbon layers was not confirmed for the carbon annealed at 1,000 °C. This is because the Na intercalation sites in the carbon layers are very few due to the disordered structure caused by the relatively low temperature annealing.

Suspensions of carbon nanofibers in organic medium: rheo-electrical properties.

The nonaqueous suspensions of carbon nanofibers (CNFs) in 1 M lithium bis(trifluoromethanesulfonaimide) in propylene carbonate electrolyte reveal unique structural evolution and shear-induced transition due to the high aspect ratio. The rheo-electrical behavior elucidates a microstructural transition from entangled-to-aggregated networks above a distinct percolation threshold. Under shear flow, both networks show a three-regime flow curve and an inverted-bell-like conductivity curve as a consequence of shear-induced alignment (entangled network) and shear-induced breaking up (aggregated network). The different particle morphology of carbon nanofibers (anisometric) and carbon black (CB; isometric) causes different aggregation mechanisms (aggregate vs. particulate) and then varied microstructure for their suspensions in the same electrolyte. This fact explains the higher rigidity and lower electric conductivity of CNFs than CB suspensions. Interestingly, the suspension of hybrid carbons at the optimum mixing ratio merges the advantages of both carbons to operate efficiently as precursors in the formulation of electrodes for energy storage systems.

Contribution of mesopores in MgO-templated mesoporous carbons to capacitance in non-aqueous electrolytes

MgO-templated mesoporous carbons were fabricated by annealing trimagnesium dicitrate nonahydrate at various temperatures from 700 to 1000 °C with subsequent acid leaching of MgO. The obtained carbons contained a large amount of mesopores. Performances of electric double-layer capacitors using these carbons were examined for propylene carbonate electrolyte containing 1 M tetraethylammonium tetrafluoroborate. The mesoporous carbons synthesized at higher temperatures showed better rate capabilities. AC impedance measurements indicated that high-temperature annealing of the carbon precursors and the presence of mesopores were important for high rate performance. In addition, the contribution of mesopores to capacitance was more significant at higher current densities of 30 A g−1.

Manganese hexacyanomanganate open framework as a high-capacity positive electrode material for sodium-ion batteries.

Potential applications of sodium-ion batteries in grid-scale energy storage, portable electronics and electric vehicles have revitalized research interest in these batteries. However, the performance of sodium-ion electrode materials has not been competitive with that of lithium-ion electrode materials. Here we present sodium manganese hexacyanomanganate (Na2MnII[MnII(CN)6]), an open-framework crystal structure material, as a viable positive electrode for sodium-ion batteries. We demonstrate a high discharge capacity of 209 mAh g(-1) at C/5 (40 mA g(-1)) and excellent capacity retention at high rates in a propylene carbonate electrolyte. We provide chemical and structural evidence for the unprecedented storage of 50% more sodium cations than previously thought possible during electrochemical cycling. These results represent a step forward in the development of sodium-ion batteries.

Electrochemical Characteristics of Cyclic Structure Additives in EDLCs

Introduction Electrochemical double-layer capacitor (EDLC) is on a rise as a kind of Energy storage system (ESS), nowadays.[1] EDLCs work by physical charge and discharge electrons at double-layer (also known as Helmholtz layer). Therefore, EDLCs have high power density and long cycle life, but energy density is very low.[2] The internal structure of EDLCs are consist of cathodic/anodic electrode, electrolyte and separator for prevention of short. Among of them, electrolyte is influence at internal resistance of EDLCs. Because of electrolytes were composed solvent and electrolytic salts.[3] So, we need to consider characteristics of solvent and salts. Characteristics of electrolyte are those; electrical stability, ion conductivity, viscosity, high temperature work, cell application.[4] Before papers are almost suggest cyclic structure carbonate as additives in PC, EC or AN-based electrolyte like DEC, DMC, etc. But GBL and PC addition can affirmative affects ion conductivity and potential stability. In this study, we experiment additives for electrolyte in EDLCs. Especially, we focused on the cyclic structure solvents addition. The additive was used Tetrahydrofuran(THF), γ-butyrolactone (GBL) and Propylene Carbonate(PC). Furthermore, we applied electrolyte samples to EDLC cell. Experiment First of all, 1M TEABF4 in PC as reference, THF and GBL is added at propylene carbonate 0 to 30% by volume. In this process, whole salt concentration kept as 1M. Each concentration of sample was 5% interval.Next, we approach PC addition to 1M SBPBF4 in AN. PC addition experiment goes same condition with upper experiment(0~30%, 5% interval).As Electrochemical properties, Ion Conductivity and LSV were accepted. Ion conductivity determines almost specification of electrolyte. LSV shows electrical stability. Apply to EDLC unit cell, those examine was measured; CV, impedance, charge/dis-charge Result& Discussion THF and GBL addition shows low viscosity than pristine PC. By using THF and GBL, PC-based electrolyte can decrease viscosity. But THF has not enough electrical stability. In LSV results, yield point was decreased by THF addition. Theoretically, boiling point of GBL is 206°C and flash point is over 80°C. So, GBL addition is enlarge non-flammable properties.Ion conductivity was observed by impedance. To suggest colligate property, the temperature range set 20°C to 80°C, and the interval is 10°C. By measuring LSV, current plateau area was detected that the area is stable potential range. GBL and PC addition gives electrical stability to Cell application shows overall effects at the electrolyte in EDLCs.

Towards Safer Sodium-Ion Batteries Via Ionic Liquids As Electrolyte Additives

Our society is in urgent need of more efficient, affordable and environmentally friendly energy storage technologies. While lithium-ion batteries (LIB) is undeniably the main track of development and outstanding at present, complementary technologies are needed for managing applications such as renewable energy integration. One particularly appealing alternative is to explore the feasibility of a technology analogous to LIB – sodium ion batteries (SIB) – using the basic LIB know-how and with sodium being more abundant and less expensive. As in any battery technology, the electrolyte choice is as important as that of the electrodes to ensure successful operation. Considering both safety and “environmental impact” ionic liquids (ILs) have emerged as an interesting option for LIB. ILs exhibit both non-volatility and non-flammability, but unfortunately their high viscosities and comparatively low conductivities are expected to considerably limit the rate performance. Mixed electrolytes, i.e. with ILs as additives to an organic electrolyte, are a compromise suggested to improve the safety – while still providing an appreciable conductivity. Here, the possibility of expanding this strategy also to the SIB technology has been explored.We here present a systematic study of several electrolytes consisting of a sodium salt (NaTFSI) dissolved in mixtures of ILs and organic solvents, using electrochemical techniques (cyclic voltammetry, chronopotentiometry) coupled to various safety tests (e.g. self-extinguishing time (SET) and flash point (FP)). Imidazolium (BMImTFSI/EMImTFSI) and pyrrolidinium (PYR13TFSI) ILs were used as additives to optimized ethylene carbonate: propylene carbonate (EC:PC) electrolytes, while Hard Carbon (HC) and Na3V2(PO4)3 (NVP) were used as anode and cathode, respectively. Electrochemical tests were performed on half cells to evaluate the cycling abilities and the electrochemical stability of each electrolyte/electrode combination. HC tested with the BMImTFSI-EC:PC electrolytes exhibit specific capacities of ca 250 mAhg-1 and 140 mAhg-1 at C/5 and 1C rates with capacity retentions of 95% and 98%, respectively. For PYR13TFSI-EC:PC ~150 mAhg-1 at C/10 rate a Coulombic efficiency of ca 98% was achieved. The NVP electrode, exhibits capacities of ~80 mAhg-1 with the BMImTFSI-EC:PC electrolytes at C/10 rate, and of 80, 75 and 46 mAhg-1 at C/10, C/5 and C, respectively with the PYR13TFSI-EC:PC electrolyte. A successful full SIB cell was assembled based on the best choices of the above materials as a proof of concept. As a major argument for the use of ILs is an increased safety, it was encouraging that the safety tests, carried out in air for many different compositions, unambiguously proved the addition of ILs to decrease the SET, as well as the flame intensity, and simultaneously raise the FP.

New Analytical Tool for Electrochemical Interfaces – in Situ Neutron Reflectometry

Interfacial reactions between intercalation electrodes and electrolyte have attracted much attention to achieve high current drain and long-term stability of lithium batteries, fuel cells, and metal-air batteries. However, there is no common strategy for the design of materials produced under an electrochemical potential field. Neutron reflectometry (NR) is a new experimental technique that gives useful information of the concentration gradient of diffusing species from the electrode to the electrolyte on battery operation [1]. Here we have detected a defect-rich phase in the 10–20 nm region from the surface of lithium intercalation electrodes, Li4Ti5O12, LiMn1/3Co1/3Ni1/3O2, and LiFePO4. The defective phase formation has been directly related to the electrochemical activity of nanosized electrode materials. Epitaxial films of each electrode material were grown on Nb:SrTiO3(111) substrates using a pulsed laser deposition apparatus [1-2]. Thicknesses of the films were 25 to 45 nm. NR measurements were performed on SOFIA (BL-16, J-PARC), which is a time-of-flight reflectometer [3]. A deuterated propylene carbonate electrolyte containing 1 M LiPF6 was used as an electrolyte solution to prevent incoherent scattering of 1H. The neutron reflectivity spectra were collected at pristine and at open circuit voltage condition. The models of interfacial structure were refined by the Parratt32 data analysis program using roughness, thickness, and scattering length density (SLD) of each layer as parameters. The SLD in the surface region of Li4Ti5O12(111) increased from the pristine to the cell-construction conditions. As nLi ions have a negative coherent scattering length of -1.9 fm, the increase in the SLD indicated a formation of lithium vacancies in the surface region prior to electrochemical cycling. The lithium vacancy-type (VLi') defect formation was confirmed by lattice contraction observed by surface X-ray diffraction [4]. Similar to Li4Ti5O12, a lithium vacancy-type defect phase was detected for LiMn1/3Co1/3Ni1/3O2(1-18). In contrast, LiFePO4(100) films showed a decrease in the SLD value at the electrochemical interface formation, indicating a defect phase of interstitial lithium type (Lii .). The type of defects generated may be related to the electrochemical potentials of the electrode and the electrolyte. The difference in electrochemical potential causes a gradual change in the structure at the interfacial region to equilibrate the potentials of the two materials. Lithium is the mobile species in these electrodes; therefore, lithium may participate in charge compensation with formation of the defect phase. The defective phase was related to an extremely high lithium storage capacity of nanosized Li4Ti5O12[5] and an isotropic lithium diffusion in nanosized LiFePO4. The results suggest how to create a defect phase at the electrochemical interface and the concept of interfacial defect phase control is extended to nanosize material control for next-generation battery materials. References M. Hirayama, et al., Electrochemistry, 78 (2010) 413.M. Hirayama, et al., Dalton Trans., 40 (2011) 2882.M. Koji et al., J. Phys.: Conf. Ser., 272 (2011) 012017.M. Hirayama, et al., J. Am. Chem. Soc., 132, (2010) 15268; K. Sakamoto, et al., Phys. Chem. Chem. Phys., 12 (2010) 3815; K. Sakamoto, et al., Chem. Mater., 21 (2009) 2632.Wagemaker, et al., J. Am. Chem. Soc., 131 (2009) 17786.