Solvent Decomposition Research Articles

Thiophene derivatives as novel functional additives for high-voltage LiCoO2 operations in lithium ion batteries

Thiophene derivatives (THs) are examined as novel functional additives for improving the cycling performance of high-voltage LiCoO2. Our investigation reveals that 2,2′-Bithiophene (2TH) and 2,2′:5′,2′′-Terthiophene (3TH) can be electrochemically polymerize prior to the electrolyte solvent decomposition to form a protective layer of conducting polymer film on the cathode surface, which blocks off severe electrolyte decomposition at high voltages and, therefore, improves the cycling stability of high voltage LiCoO2 cathode. After 100 cycles at a high cutoff voltage of 4.4V, the discharge capacity retention is 50% in the base electrolyte, in contrast, the LiCoO2 cathode cycled in the electrolyte containing 0.1 wt% 3TH displays a high capacity retention of 84.8% at 0.25C rate. This work demonstrates that these thiophene derivatives have considerable potential as functional additives for the applications in high-voltage lithium-ion batteries.

Cationic copper(I) complexes as highly efficient catalysts for single and double A(3) -coupling Mannich reactions of terminal alkynes: mechanistic insights and comparative studies with analogous gold(I) complexes.

Cationic CuL complexes (L=Buchwald-type phosphane) with N co-ligands have been characterised by structural and spectroscopic properties. These copper(I) complexes are extremely active catalysts, far more active than analogous gold(I) complexes, to promote the single and double A(3) coupling of terminal alkynes, pyrrolidine and formaldehyde. The activity data show the possible ways in which the solvent can influence the catalytic performance by limiting complex solubility, by solvent decomposition or instability of the copper(I) redox state. Isolation of copper(I) complexes that are likely to be the key catalytic species has allowed light to be shed on the reaction mechanism.

Lithium carbonate as an electrolyte additive for enhancing the high-temperature performance of lithium manganese oxide spinel cathode

The effect of lithium carbonate (Li2CO3) as an additive on the stability of the electrolyte and cycling performance of lithium manganese oxide spinel (LiMn2O4) batteries at elevated temperature was studied. The addition of Li2CO3 to the electrolyte can suppress the capacity fading of LiMn2O4 batteries. The linear sweep voltammetry (LSV) and the cyclic voltammetry (CV) indicate that Li2CO3 has a lower oxidation potential in the mixed solvents of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), participating in the formation process of the stable cathode electrolyte interface (CEI) film. In addition, the results of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrate that the stable CEI film of the cells with Li2CO3 can be formed, which can effectively reduce the dissolution of Mn2+ from LiMn2O4 into the electrolyte at elevated temperature. It is concluded that the addition of Li2CO3 to a solution of 1M LiPF6–EC/EMC/DEC=1/1/1 (weight ratio) may decrease solvent decomposition and change the structure of the passivation film on the LiMn2O4 cathode.

Deposition and Dissolution of Lithium through Lithium Phosphorus Oxynitride Thin Film in Some Ionic Liquids

Aprotic ionic liquids have been studied as alternative electrolytes for rechargeable lithium batteries because of non-volatility, which is expected to improve safety of the batteries. However, most of the organic cations giving room-temperature ionic liquids are instable against metallic lithium. In case of carbonate-based organic electrolytes, a passivation film, so called solid-electrolyte interphase (SEI) film, is known to form as a result of reductive decomposition of organic solvents. The SEI film is considered as a lithium ion conductor, though its nature has not been clarified yet. On the other hand, the reductive decomposition of the organic cations of ionic liquids hardly leads to formation of good SEI film. In the present study, electrochemical deposition and dissolution of lithium were investigated in some aprotic ionic liquids through a typical inorganic lithium ion conductor, lithium phosphorus oxynitraide (LiPON), thin film. Reversible deposition and dissolution of lithium were possible on a nickel electrode covered with LiPON thin film in bis(trifluoromethylsulfonyl)amide (TFSA–) based ionic liquids consisting of 1-butyl-1-methylpyrrolidinium (BMP+) and 1-ethyl-3-methyl imidazolium (EMI+). No cathodic current attributable to reductive decomposition of these cations was observed on the LiPON-coated electrodes, indicating that LiPON thin film acted as an artificial SEI film and that lithium ions were transported between the ionic liquids and LiPON. The deposition of lithium between the nickel electrode and LiPON thin film was confirmed by electrochemical quartz crystal microbalance (EQCM) measurements and X-ray photoelectron spectroscopy.

Enhancing the Stability of Non-Aqueous Electrolytes for Li-O2 Batteries

Li-O2 cells have been the subject of intense investigation in the last few years. The first step in the discharge reaction (oxygen reduction reaction or ORR) is thought to be a 1 e- process that forms the highly reactive intermediate superoxide, O2 -/LiO2. This superoxide species is responsible for the decomposition of most common non-aqueous electrolyte solvents.1 Finding a stable electrolyte for the non-aqueous Li-O2battery is a significant challenge. While allowing conduction of lithium ions between the electrodes, the electrolyte must be stable to nucleophilic attack on discharge, to oxidative decomposition on charge, and inert to the negative electrode. No such solution has been reported to date, and the understanding of the properties that confer stability is lacking. We will present a novel synthesized electrolyte, a chelate ionic liquid (IL), which is stable with respect to metallic lithium and also to superoxide-initiated attack. Figure 1a displays the 1H-NMR spectra of the by-products on cathodes discharged in the chelate IL as well as in the reference standard electrolyte, 1,2-dimethoxyethane (DME). Lithium formate (δ = 8.46 ppm) and dimethyl oxalate (δ = 3.92 ppm) are the two main proton-containing decomposition products formed from the DME molecule. These products are not observed for the new electrolyte. Moreover, when employed in a Li-O2 battery, 8-fold less CO2 evolution occurs on charge than for DME. CO2 is known to evolve during charge of the battery due to the oxidation of lithium carbonates/carboxylates which are formed as side-products by decomposition of electrolytes on discharge.2 This is shown by the results of differential electrochemical mass spectrometry (DEMS) in Figure 1b. Many other cell components besides the electrolyte suffer from instabilities in the non-aqueous Li-O2 battery, including binders and cathode materials.3,4 In particular, alternatives to carbon-based cathodes must be developed. By switching the positive electrode support to non-carbonaceous materials, cells utilizing the new chelate IL electrolyte have been cycled for over 300 hours with no capacity fading and little increase in polarization.5 In comparison, cells with the DME electrolyte, had a cycle life of less than 130 hours. This is displayed in Figure 2a and a comparison of the voltage profiles on the 10th cycle is shown in Figure 2b. The current causes of electrolyte instabilities will be discussed as well as pathways toward the development of new electrolyte/electrode systems with enhanced stabilities. References S. A. Freunberger, Y. Chen, N. E. Drewett, L. J. Hardwick, F. Bardé, P. G. Bruce, Angew. Chem. Int. Ed. 2011, 50, 1-6.B. D. McCloskey, A. Speidel, R. Scheffler, D. C. Miller, V. Viswanathan, J. S. Hummelshoj, J. K. Norskov, A. C. Luntz, J. Phys. Chem. Lett. 2012, 3, 997-1001.R. Black, S. H. Oh, J.-H. Lee, T. Yim, B. Adams, L. F. Nazar, J. Am. Chem. Soc. 2012, 134, 2902-2905.M. M. O. Thotiyl, S. A. Freunberger, Z. Peng, Y. Chen, Z. Liu, P. G. Bruce, Nature Mat. 2013 , 12, 1050-1056.B.D. Adams, R. Black, Z. Williams, R. Fernandes, M. Cuisinier, E. Jaemstorp Berg, P. Novak, G.K. Murphy, L.F. Nazar, Submitted.

High catalytic activity of anatase titanium dioxide for decomposition of electrolyte solution in lithium ion battery

It has been indicated that anatase TiO2 is a promising anode material for lithium ion power battery from many previous researches. Whereas, in this work, we find that the anatase TiO2, when used as an anode for lithium ion battery, has high catalytic activity to initiate the decarboxylation reaction of electrolyte solution, resulting in the large generation of sole gaseous component, CO2. The ROLi species and the new phase of flake-like Li2TiF6 material are the main reaction products between anatase TiO2 and LiPF6 based electrolyte solution. This work provides important and urgent information that the surface chemistry of anatase TiO2 used as the anode material of lithium ion battery must be modified to suppress its catalytic activity for the decomposition of solvents.

Reactivity of Amide Based Solutions in Lithium–Oxygen Cells

The stability of electrolyte solutions during lithium–oxygen cells operation is of great importance and interest. This is because oxides formed during reduction are strong nucleophiles which can initiate solvent decomposition. The highly polar amide based solvents have come to the fore as possible candidates for Li–O2 applications. They show typical cycling behavior as compared to other solvents; however, their stability toward lithium oxides is shrouded in doubt. The present study has focused on Li–O2 cells containing electrolyte solutions based on DMA/LiNO3. We have used various analytical tools, to explore the discharge–charge processes and related side reactions. The data obtained from FTIR, NMR, XPS, and EQCM all support a rational decomposition mechanism. The formation of various side products during the course the first discharge, leads to the conclusion that amide based solvents are not suitable for Li–O2 applications; however, electrolyte solution decomposition reduces the OER overpotential by forming oxidation mediators.

Pure Silicon Nano-Flake Powder As a High Capacity Anode in Lithium-Ion Batteries

Li-Si alloy is a promising high capacity anode; however, the poor cycleability should be improved for commercial applications. The poor cycleability has been attributed to a large volume during the charge/discharge cycling, resulting fracture and pulverization of Si particles. Therefore, relaxation of the physical stress is important to attain a good cycleability. It has been well recognized that Si nano-particles effectively reduces the stress by the expansion and shrinkage, which gives a good cycleability. However, the use of nano-particles results in a low packing density of the electrode. We designed Si nano-flakes called Si Leaf-Powder®(LP), which enables us to reduce the stress by the expansion and shrinkage and to make highly dense electrode composites. We prepared Si nano-flakes of different thickness (50-400 nm, Fig. 1) by a vapor phase deposition, and have investigated their charge and discharge characteristics [1-3]. Here we discuss the cycleability, the irreversible capacity, and the surface film (SEI) growth during cycling of the Si nano-flakes.The cycleability of Si-LPs of different thicknesses at C/6 in 1 M LiPF6/EC+DEC(1:1) +10 wt% VC is shown in Fig. 2 [1]. The cycleability of Si-LPs greatly depended on the thickness. Thinner samples (50-200 nm) showed relatively good cycleability, while thicker samples (300 and 400 nm) showed poor cycleability. For the thinner samples, the diffusion of metallic Li in the Si flakes is facile. The resulting uniform distribution of Li within the nano-flake during charging and discharging suppressed the physical stress and resulted in good cycleability.The large irreversible capacity (Q irr) of Si anodes is a serious problem for use in practical lithium-ion cells. The addition of VC does not reduce Q irr. The origin of the large Q irr has been attributed to the reduction of surface SiOx and solvent decomposition (and the following SEI formation), but such an extremely large Q irr of > 1000 mAh g-1is most probably owing to the latter phenomenon.We found that coating of Si-LPs with thin carbon layer is effective for reducing Q irr [2]. However, crack formation of the carbon layer decreased the Coulombic efficiency the initial cycles, and we concluded that further remarkable reduction of Q irr cannot be expected. To reduce Q irr, we also found that a pre-doping technique is effective. We can reduce Q irr practically to zero by the pre-doping technique, and we obtained good cycleability similar to that without pre-doping [3]. Figure 3 shows the variations of the discharge capacity and Coulombic efficiency of Si-LP (100 nm) upon a long-term cycle test. The Si-LP sample showed good cycleability up to the 500th cycle. The initial capacity was ca. 2000 mAh g-1, and gradually decreased to ca. 1500 mAh g-1at the 500 cycle. Unfortunately, the capacity suddenly dropped after the 560 cycle, the reason of which is not clear at present. Though Si-LP (100 nm) showed good cycleability in the long-term cycle test, we found another serious problem. The Coulombic efficiency was initially low and gradually increased to 98% at the 9th cycle and to 99% at the 80th cycle. It did not reach 100% even at the 500th cycle (99.8%). This fact indicates that solvent decomposition (and SEI growth) slowly proceeds and does not stop even at the 500thcycle. It is therefore important to completely suppress the solvent decomposition, e.g. by a good additive, for use in practical lithium-ion cells. Acknowledgment:This work was supported by JST (ALCA), Japan.

Identifying Descriptors for Solvent Stability in Non-Aqueous Li-O2 Batteries

A crucial challenge in developing rechargeable Li-O2 batteries is the identification of stable solvents that are resistant to decomposition in the electrochemical environment of Li-O2 discharge products. Recent theoretical studies using higher order quantum chemical methods have offered excellent insights into various possible degradation mechanisms such as nucleophilic attack/substitution and hydrogen atom abstraction in the presence of O2, O2 − and O2 2− anions [1-2]. Similarly, some experimental studies have analyzed various classes of solvents based on the reversibility of the O2 ↔ O2 − ↔ O2 2− oxygen reduction reactions in them [3-4]. These investigations, however, do not explicitly take into account either the effect of the electrode potential, or any direct electrochemical interaction of the solvent with the deposited Li-O2 discharge products. In this work, we attempt to identify suitable descriptor that can be used to test for solvent stability by building a unified picture of the energy levels of the solvent molecules, Li-O2 discharge products and the electrode potential. Based on recent experimental results [5-7], we first hypothesize that although solvent degradation affects the yield of Li2O2 during discharge, the majority of solvent degradation occurs via a process of decomposition of solvent into its oxidized products during charging, which eventually leads to CO2 evolution at higher potentials in non-aqueous Li-O2 batteries. Detailed analyses of these findings lead us to conclude the presence of a near universal mechanism of solvent degradation during charging. Further, we create the case for number of electrons per O2 evolved during the charging process to be the marker of cell performance, the ideal being 2e-/O2. Based on these concepts, we propose that the HOMO level would be a good descriptor for solvent stability and demonstrate that this correlates well the degree of rechargeability. Taking this analysis a step further, we demonstrate that Gutmann donor number is also a good empirical descriptor for solvent stability, which has been explained earlier in terms of Hard Soft Acid Base Theory. Employing these descriptors, we identify several solvents which could enhance the rechargeability of non-aqueous Li-O2 batteries.

CO2 and O2 Evolution at High Voltage Cathode Materials of Li-Ion Batteries: A Differential Electrochemical Mass Spectrometry Study

A three-electrode differential electrochemical mass spectrometry (DEMS) cell has been developed to study the oxidative decomposition of electrolytes at high voltage cathode materials of Li-ion batteries. In this DEMS cell, the working electrode used was the same as the cathode electrode in real Li-ion batteries, i.e., a lithium metal oxide deposited on a porous aluminum foil current collector. A charged LiCoO2 or LiMn2O4 was used as the reference electrode, because of their insensitivity to air, when compared to lithium. A lithium sheet was used as the counter electrode. This DEMS cell closely approaches real Li-ion battery conditions, and thus the results obtained can be readily correlated with reactions occurring in real Li-ion batteries. Using DEMS, the oxidative stability of three electrolytes (1 M LiPF6 in EC/DEC, EC/DMC, and PC) at three cathode materials including LiCoO2, LiMn2O4, and LiNi(0.5)Mn(1.5)O4 were studied. We found that 1 M LiPF6 + EC/DMC electrolyte is quite stable up to 5.0 V, when LiNi(0.5)Mn(1.5)O4 is used as the cathode material. The EC/DMC solvent mixture was found to be the most stable for the three cathode materials, while EC/DEC was the least stable. The oxidative decomposition of the EC/DEC mixture solvent could be readily observed under operating conditions in our cell even at potentials as low as 4.4 V in 1 M LiPF6 + EC/DEC electrolyte on a LiCoO2 cathode, as indicated by CO2 and O2 evolution. The features of this DEMS cell to unveil solvent and electrolyte decomposition pathways are also described.

Chemistry of the β-Thiolactones: Substituent and Solvent Effects on Thermal Decomposition and Comparison with the β-Lactones.

The synthesis of a series of di-, tri-, and tetraalkyl β-thiolactones and β-lactones is described as well as their thermal decomposition with extrusion of carbon oxysulfide and carbon dioxide in two solvents of opposite polarities. The β-thiolactones are considerably more thermally stable than the β-lactones and require higher temperatures for efficient decomposition in both solvents, whatever the degree of substitution. The results are interpreted in terms of a zwitterionic mechanism for fragmentation with a change in the rate-determining step between the two series.

The Effect of Battery Potential and Charge Rate on the Decomposition Reaction on the Anode Electrode of Lithium Ion Polymer Battery

The formation of the solid electrolyte interface (SEI) layer on the surface of the anode electrode prevents further electrolyte decomposition reaction. However, certain battery operating parameters initiate electrolyte solvent and salts decomposition reaction with lithium on the surface to the anode electrode. This decomposition reaction results in the formation of an insoluble reaction products that is non-uniform, electronically insulating, and unstable on the surface of the graphite particles. The loss/consumption of recyclable lithium ions at the anode by this passivation layer is one of the causes of major reversible capacity loss in the lithium ion battery. Understanding the potential and the charge rate that initiates the formation of the surface film layer is critical to effectively controlling/limiting these operational parameters in order to extend the calendar life performance of the battery. This paper seeks to investigate the effect of the state of charge and charge rate on the electrolyte decomposition reaction resulting in the formation of the surface film deposit. An image based quantitative analysis of the thickness of the surface film will be conducted to collaborate the observed changes in the electrochemical properties of the battery.

Schiff base bridged biporphyrin: Synthesis, characterization and spectral properties

Chromophoric molecules with mono-aminophenyl, 5-aminophenyl-10, 15, 20-triphenyl porphyrin, were chemically reduced from the precursors of 5-nitrophenyl-10, 15, 20-triphenyl porphyrin. The titled Schiff base bridged biporphyrins were furthermore prepared by condensation of 5-aminophenyl-10, 15, 20-triphenyl porphyrin with terephthalaldehyde. This novel conjugated Schiff base biporphyrin was well characterized by spectral determinations. Experimental results indicated that the titled compound possessed fluorescence enhancement in near infrared region. Compared with tetraphenyl porphyrin, both ultraviolet–visible absorption and fluorescence spectra of the titled compound appeared with slightly red shift. Photo experiments revealed that, after violet irradiation, the color of a chloroform solution with the titled compound changed sharply from pale green to dark green along with sensitively spectral variation during ultraviolet–visible absorption and electron paramagnetic resonance determinations. This sensitively photochromic mechanism was well explained by molecular recognition of the titled compound towards hydrogen chloride from the decomposition of the chloroform solvent. The titled compound was sensitive in recognizing towards hydrogen chloride.

Ab initio calculations of polycyclic aromatic hydrocarbons adsorbed on graphite edge for molecular-scale surface coatings of lithium-ion battery anodes

We have investigated the atomic configurations and electronic structures of graphite edges adsorbed by polycyclic aromatic hydrocarbons, aiming for application to lithium-ion-battery anodes, where thin and robust coating layers are required for fast charge/discharge processes and long lifetime. In particular, we examined the adsorption of a perylene molecule on an edge of graphite. We considered that the edge of perylene connects two layers of graphite with σ-bonds. We found that the optimized atomic structures are stable and the planar surface of perylene is parallel to the insertion direction of lithium ions similar to the original graphite edges. Therefore, the coating does not disturb the diffusion of lithium ions during charge/discharge processes. Furthermore, there is no hybridization between the graphite edge and the perylene molecule near the Fermi level, even though they have chemical bonds between them. Thus, the electronic states of the chemisorbed perylene molecule are insensitive to the change in the electric potential of the graphite. Consequently, we expect them to suppress the electrochemical decomposition of electrolytes and solvents on the anode surface. Hence, polycyclic aromatic hydrocarbons are one of the best candidates for the coating materials of graphite anodes for realizing a higher charge/discharge rate and longer lifetime.

A catalyst-free multicomponent domino sequence for the diastereoselective synthesis of (E)-3-[2-arylcarbonyl-3-(arylamino)allyl]chromen-4-ones

The three-component domino reactions of (E)-3-(dimethylamino)-1-arylprop-2-en-1-ones, 3-formylchromone and anilines under catalyst-free conditions afforded a library of novel (E)-3-(2-arylcarbonyl-3-(arylamino)allyl)-4H-chromen-4-ones in good to excellent yields and in a diastereoselective transformation. This transformation generates one C–C and one C–N bond and presumably proceeds via a reaction sequence comprising a Michael-type addition–elimination reaction, a nucleophilic attack of an enamine to a carbonyl reminiscent of one of the steps of the Bayllis–Hilman condensation, and a final deoxygenation. The deoxygenation is assumed to be induced by carbon monoxide resulting from the thermal decomposition of the dimethylformamide solvent.

Insights into the Thermal Decomposition of Co(II) Oleate for the Shape-Controlled Synthesis of Wurtzite-Type CoO Nanocrystals

Fatty acid salts of transition metals are known to undergo thermal decomposition in high-boiling organic solvents. Although it is a straightforward, promising approach for generating colloidal metal oxide nanocrystals in high yield, its widespread implementation is hindered by irreproducibility. Subtle structural variations and impurities are often introduced during preparation of the carboxylate precursors, which exhibit strong influence on thermal decomposition, and the resulting nucleation and growth of oxide nanocrystals. Here, we studied the colloidal synthesis of wurtzite-type CoO (wz-CoO) nanostructures via thermal decomposition of Co(II) oleate complex [Co(OL)]2. Using Fourier transform infrared spectroscopy, we discovered that the conventional method for preparing [Co(OL)]2 gives rise to an isolable impurity containing a free hydroxide moiety. Furthermore, [Co(OL)]2 did not thermally decompose within the expected temperature range when the impurity was removed. In contrast, pencil-shaped wz-CoO nanorods were synthesized when no measures were taken to remove the impurity, suggesting that the hydroxide functionality may facilitate the thermal decomposition. These insights enabled us to prepare size-and shape-controlled wz-CoO nanocrystals using purified [Co(OL)]2 solutions, by incorporating additives that mimic the action of the hydroxide impurity. We also demonstrate a simplified pathway to wz-CoO nanocrystals that does not require chemical additives for thermolysis.

Performance Improvement of Li Ion Battery with Non-Flammable TMP Mixed Electrolyte by Optimization of Lithium Salt Concentration and SEI Preformation Technique on Graphite Anode

We fabricated a lithium ion battery with a non-flammable trimethyl phosphate (TMP) electrolyte, which has sufficient cycle properties (capacity retention was 97% at 50 cycles) and safety improvement due to the optimization of lithium salt concentration and a graphite anode with pre-formed solid electrolyte interphase (SEI). By dissolving highly concentrated LiPF6, i.e., above 2 M, into the TMP mixed electrolyte, lithium ion easily intercalated into the graphite anode. This was because the solvation number of TMP molecule to the lithium ion decreased. When a SEI film was formed using ethylene carbonate and diethyl carbonate solvents in advance without TMP, the decomposition of the non-carbonate solvent, such as TMP, was suppressed. Eventually, we found that a safe and high-performance lithium ion battery could be fabricated only with a combination of controlling the solvation number in the electrolyte and SEI pre-forming technology on the graphite anode

Thermal Decomposition of Diethylketone Cyclic Triperoxide in Polar Solvents

The thermolysis of diethylketone cyclic triperoxide (3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane, DEKTP) was studied in different polar solvents (ethanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, and acetonitrile). The rate constant values (kd) are higher for reactions performed in secondary alcohols probably because of the possibility to form a cyclic adduct with the participation of the hydrogen atom bonded to the secondary carbon. The kinetic parameters were correlated with the physicochemical properties of the selected solvents. The products of the DEKTP thermal decomposition in different polar solvents support a radical-based decomposition mechanism.

On-Line Electrochemical Mass Spectrometry Investigations on the Gassing Behavior of Li4Ti5O12 Electrodes and Its Origins

Lithium ion batteries containing lithium titanate (LTO), Li4Ti5O12, as anode material are promising energy storage systems for their safety and long cycle-life. However, while there are few studies that demonstrate very long cycle-life of LTO-anode based batteries, a significant number report extensive evolution of hydrogen during cycling or storage of LTO cells (“gassing”), accompanied by strong capacity fading and poor cycling performance. Here, we analyzed LTO cells in-operando with on-line electrochemical mass spectrometry (OEMS) and determined the real-time concentration of evolved gases. With this method, we were able to determine a direct correlation between the amount of evolved hydrogen and the water content of the electrolyte upon charge and discharge. Our analysis suggests that the one-electron reduction reaction of water leads to hydrogen evolution and to the formation of hydroxide anions. The latter trigger a ring-opening reaction of cyclic carbonates and lead to solvent decomposition into CO2 and carbonate oligomers (detected by ex-situ ATR-FTIR). The deposition of the latter on the electrodes is likely responsible for the performance and capacity loss over a longer time period. We propose that the gassing of LTO batteries reported in some studies is caused by water intrusion during cell assembly or by water contained in improperly dried electrodes.

AFM study of oxygen reduction products on HOPG in the LiPF6–DMSO electrolyte

Ex situ atomic force microscopy (AFM) has been used to study the morphology of oxygen reduction products in the LiPF6-dimethyl sulfoxide (DMSO) electrolyte, i.e. Li2O2 on a highly oriented pyrolytic graphite (HOPG) surface. Both cyclic voltammetry and chronoamperometry have shown that at low cathodic polarization the initial deposits decorate the edge steps of HOPG. At higher overpotentials a massive deposit covers the terraces. Upon charging the battery cathode Li2O2 oxidation and dissolution do not take place until high overpotentials are reached at which solvent decomposition has been demonstrated by in situ FTIR studies.