Formation Of Solid Electrolyte Interphase Film Research Articles

Morphology of the Solid Electrolyte Interphase on Graphite in Dependency on the Formation Current

In this study, detailed insights in the solid electrolyte interphase (SEI) properties and its formation kinetics on different graphite types and in electrolyte mixtures based on ethylene carbonate as well as on propylene carbonate are presented. The competing most important reactions of (i) SEI formation and (ii) solvent cointercalation leading to exfoliation could be controlled by adjusting the specific current in the first cycle; in some cases it was possible to suppress the exfoliation completely and the electrode could be stably cycled. Post mortem scanning electron microscopy clearly revealed differences in the SEI film morphology on graphite particles after electrochemical cycling, depending on the formation conditions. By means of differential electrochemical mass spectrometry (DEMS) the solvent cointercalation prevailing over SEI film formation could be detected in propylene carbonate based electrolytes.

Effects of current densities on the formation of LiCoO2/graphite lithium ion battery

The activation characteristics and the effects of current densities on the formation of a separate LiCoO2 and graphite electrode were investigated and the behavior also was compared with that of the full LiCoO2/graphite batteries using various electrochemical techniques. The results showed that the formation current densities obviously influenced the electrochemical impedance spectrum of Li/graphite, LiCoO2/Li, and LiCoO2/graphite cells. The electrolyte was reduced on the surface of graphite anode between 2.5 and 3.6 V to form a preliminary solid electrolyte interphase (SEI) film of anode during the formation of the LiCoO2/graphite batteries. The electrolyte was oxidized from 3.95 V vs Li+/Li on the surface of LiCoO2 to form a SEI film of cathode. A highly conducting SEI film could be formed gradually on the surface of graphite anode, whereas the SEI film of LiCoO2 cathode had high resistance. The LiCoO2 cathode could be activated completely at the first cycle, while the activation of the graphite anode needed several cycles. The columbic efficiency of the first cycle increased, but that of the second decreased with the increase in the formation current of LiCoO2/graphite batteries. The formation current influenced the cycling performance of batteries, especially the high-temperature cycling performance. Therefore, the batteries should be activated with proper current densities to ensure an excellent formation of SEI film on the anode surface.

Thermal Behavior of Lithiated Graphite with Electrolyte in Lithium-Ion Batteries

A C80 calorimeter was used to study the thermal behaviors of and in electrolyte. C80 results show that alone shows one exothermic peak, which is attributed to the solid electrolyte interphase (SEI) decomposition. Four exothermic peaks were detected in electrolyte samples. These four peaks are attributed to SEI decomposition, Li-electrolyte reaction as well as new SEI film formation, new SEI film decomposition, and Li with PVDF/other products reactions. The apparent activation energy of and -electrolyte at different states of charge was calculated, and it was found that with intercalated lithium increasing, the activation energy shows a decreasing trend.

Formation and Influence Factors of Solid Electrolyte Interphase Film on the Negative Electrode Surface in Lithium-Ion Batteries

The electrochemical performance of a lithium ion battery depends basically on the characteristics of the solid electrolyte interphase (SEI) film that is formed on the negative electrode surface of the battery during its first charge-discharge process. The formation mechanism of the SEI film on surface of a MCF (mesophase-pitch-based carbon fiber) negative electrode was studied in the present paper. The studies have demonstrated the influence of some typical impurities on the formation of SEI film, and characterized the morphology and the composing of the SEI films using scanning electron microscopy and X-ray photoemission spectroscopy. The shape of SEI films overlaid on MCF has been observed distinctly.

In situ electrochemical impedance spectroscopy to investigate negative electrode of lithium-ion rechargeable batteries

The in situ electrochemical impedance spectroscopy (in situ EIS) in which the impedance spectra are measured simultaneously with the charge (intercalation)—discharge (deintercalation) sequence of lithium-ion rechargeable batteries has been developed. This method was applied to the investigation of the graphite electrode of lithium-ion rechargeable batteries. The resistance Rsei for lithium-ion permeation in the solid electrolyte interphase (SEI) film were determined, and the formation mechanisms of SEI was discussed. Moreover, the role of vinylene carbonate (VC) as an additive to LiPF6–ethylene carbonate/ethyl methyl carbonate electrolyte solution was investigated. It was clarified that Rsei decreases by the addition of VC, indicating the formation of a high quality SEI film.

Electrochemical properties of Co3O4, Ni?Co3O4 mixture and Ni?Co3O4 composite as anode materials for Li ion secondary batteries

By varying the synthetic temperature and time, Co3O4 with highly optimized electrochemical properties was obtained from the solid state reaction of CoCO3. As a result, Co3O4 showed a high capacity around 700 mAh/g and stable capacity retention during cycling (93.4% of initial capacity was retained after 100 cycles). However, its initial irreversible capacity reached about 30% of capacity. Several phenomenological examinations in our previous results told us that the main causes of low initial coulombic efficiency, that is, large initial irreversible capacity, were solid electrolyte interphase (SEI) film formation on surface and incomplete decomposition of Li2O during the first discharge process. SEI film formation cannot be restrained without the development of a special electrolyte, and there has been little research on the proper electrolyte composition, whereas in our research, Ni had the catalytic activity to facilitate Li2O decomposition. Thus, in order to improve the low initial coulombic efficiency of Co3O4 (69%), Ni was added to Co3O4 using two methods like physical mixing and mechanical milling. When adding the same amount of Ni, the mechanical milling showed the improvement in initial coulombic efficiency, 79%, but physical mixing had no effect. Finally, when the charge–discharge mechanism of Co3O4 was considered and the morphologies of Ni–Co3O4 mixture obtained by physical mixing and Ni–Co3O4 composite prepared by mechanical milling were compared, it was revealed that the initial coulombic efficiency of Ni–Co3O4 composite depends on the contact area between the Ni and the Co3O4.

Electrochemical properties of Co3O4, Ni–Co3O4 mixture and Ni–Co3O4 composite as anode materials for Li ion secondary batteries

Abstract By varying the synthetic temperature and time, Co 3 O 4 with highly optimized electrochemical properties was obtained from the solid state reaction of CoCO 3 . As a result, Co 3 O 4 showed a high capacity around 700 mAh/g and stable capacity retention during cycling (93.4% of initial capacity was retained after 100 cycles). However, its initial irreversible capacity reached about 30% of capacity. Several phenomenological examinations in our previous results told us that the main causes of low initial coulombic efficiency, that is, large initial irreversible capacity, were solid electrolyte interphase (SEI) film formation on surface and incomplete decomposition of Li 2 O during the first discharge process. SEI film formation cannot be restrained without the development of a special electrolyte, and there has been little research on the proper electrolyte composition, whereas in our research, Ni had the catalytic activity to facilitate Li 2 O decomposition. Thus, in order to improve the low initial coulombic efficiency of Co 3 O 4 (69%), Ni was added to Co 3 O 4 using two methods like physical mixing and mechanical milling. When adding the same amount of Ni, the mechanical milling showed the improvement in initial coulombic efficiency, 79%, but physical mixing had no effect. Finally, when the charge–discharge mechanism of Co 3 O 4 was considered and the morphologies of Ni–Co 3 O 4 mixture obtained by physical mixing and Ni–Co 3 O 4 composite prepared by mechanical milling were compared, it was revealed that the initial coulombic efficiency of Ni–Co 3 O 4 composite depends on the contact area between the Ni and the Co 3 O 4 .

Interaction of Poly(vinylidene fluoride) with Graphite Particles. 2. Effect of Solvent Evaporation Kinetics and Chemical Properties of PVDF on the Surface Morphology of a Composite Film and Its Relation to Electrochemical Performance

We have determined the dependence of the surface distribution of poly(vinylidene fluoride) (PVDF) on molecular weight and functionality of PVDF and solvent evaporation kinetics in a graphite composite film analogous to that used as an anode in a lithium ion battery. The homogeneity of the PVDF surface distribution on the graphite particles is determined from fluorine dot mappings, which are detected using energy-dispersive spectroscopy and electron probe X-ray microanalysis. The results are quantified with a standard deviation method and a spatial autocorrelation function approach, which yield consistent results. We have also examined the electrochemical performance of the anodes with cyclic voltammetry and impedance spectroscopy and correlated the electrochemical properties with the homogeneity of PVDF distribution in the final film. Hydroxyl-modified PVDF shows more homogeneous distribution compared to unmodified PVDF. Furthermore, the homogeneity of PVDF distribution on the graphite increases as the solvent evaporation rate increases. Samples with homogeneous PVDF distribution show higher electrochemical capacity and lower resistance, which can be explained in terms of solid electrolyte interphase film formation, binding capability, binder swelling, and electrochemically active sites of the modified PVDF.

The complex electrochemistry of graphite electrodes in lithium-ion batteries

This paper discusses the interrelated phenomena of solid electrolyte interphase (SEI) formation and the irreversible charge consumption which occurs during the first cycle of a graphite electrode, as well as their relevance to the cycling stability of lithium-ion batteries. Thus, results from relevant characterization methods, namely, in situ mass spectrometry, in situ infrared spectroscopy, in situ Raman and video microscopy, in situ scanning probe microscopy, in situ quartz crystal microbalance, and differential scanning calorimetry were combined for a more thorough understanding of observations made in cycling experiments. From electrochemical cycling tests, we have learned that a high specific charge (∼360 Ah/kg of carbon), satisfactory cycle life of the graphite electrodes (1000 deep cycles), and an irreversible charge of <7% during SEI formation can only be obtained when water contamination of the cell is avoided. Under such conditions, a good-quality SEI film is formed on the carbon surface. We conclude that during SEI film formation, at first the carbonate solvent(s) are reduced, forming ethylene gas, organic radicals, oligomers, and polymers. Then a SEI film is precipitated on the surface via a nucleation and growth mechanism. The irreversible charge consumption due to SEI formation is proportional to the BET specific surface area of the graphite and rapidly increases with increasing water content in the cell.

In-situ Electrochemical AFM Observations of SEI Film Formation on Graphite Anodes

Solid Electrolyte Interphase (SEI) films play an important role in lithium ion battery. SEI films form ongraphite anode surfaces during early lithium intercalation process. SEI films prevent further solvent decompositionduring charge and discharge in the battery. Morphological study of SEI film formation is very important to understandthe function of SEI film in lithium ion battery system. Simultaneous in-situ electrochemical Atomic Force Microscopy (AFM) and Friction Force Microscopy (FFM) were successfully introduced to monitor SEI film formation in realtime. Topographic and frictional changes on the surface of a Highly Oriented Pyrolytic Graphite (HOPG) electrodein 1 mol/dm3 LiClO4 EC/EMC (1:1) electrolyte were examined during charge and discharge. SEI film formationcommenced at approximately 2V vs. Li/Li+ and stable film formation with an island-like morphology was observedbelow approximately 0.9V vs. Li/Li+. Further experiments on a composite electrode made of synthetic graphite powderand polyvinylidene difluoride (PVDF) binder showed similar phenomena.

In Situ Electrochemical Atomic Force Microscope Study on Graphite Electrodes

Topographic and frictional changes on the surface of a highly oriented pyrolytic graphite electrode in ethylene carbonate/ethylmethyl carbonate (1:1) electrolyte were examined during charge and discharge by in situ electrochemical atomic force microscopy and friction force microscopy simultaneously in real‐time. Solid electrolyte interphase film formation commenced at approximately 2 V vs. and stable film formation with an island‐like morphology was observed below approximately 0.9 V vs. . Further experiments on a KS‐44 graphite/polyvinylidene difluoride binder composite electrode showed similar phenomena.