Carbonate Electrolyte System Research Articles

Enhancing the Cathode/Electrolyte interface in Ni-Rich Lithium-Ion batteries through homogeneous oxynitridation enabled by NO3− dominated clusters

To meet the demand for higher energy density in lithium-ion batteries, extensive research has focused on advanced cathodes and metallic lithium anodes. However, Ni-rich cathodes suffer from the inactive phase-transition and side reactions at the cathode-electrolyte interfaces (CEI). In this study, we propose a novel approach to enhance the solubility of LiNO3 in carbonate electrolyte systems using a local high-concentrated addition strategy with triethyl phosphate as a co-solvent. Rather than the traditional solvent-dominated solvation clusters, the NO3− dominated electrolyte is examined to elucidate unique complexation phenomena. Two distinct clusters in NO3− dominated electrolyte arising from as a consequence of intramolecular interactions intrinsic to the constituents. This promotes the formation of a homogeneous oxynitride interphase and facilitates more expeditious lithium ion diffusion kinetics. Hence, the less stress fragmentation and irreversible phase transformation occur on the cathode surface with the homogeneous oxynitridation interface. This innovative design enables efficient cycling of the Li || NCM811 cell, offering a promising strategy to improve lithium-ion batteries performance.

Converting LiNO3 additive to single nitrogenous component Li2N2O2 SEI layer on Li metal anode in carbonate-based electrolyte

With the increasing demand for high energy density energy storage device, Li metal has received intensive attention for its ultrahigh capacity and the lowest redox potential. LiNO3 is widely used as electrolyte additive for ether electrolyte, which can improve the cycle performance of Li metal anode. Compared to ethers, carbonates are more suitable for Li metal batteries with high voltage cathode because they have a wider electrochemical window. However, LiNO3 performs poor solubility in carbonate electrolyte, restricting its application in high voltage Li battery. Herein, we presented a facile method to introduce abundant LiNO3 additive to carbonate electrolyte system by introducing LiNO3-PAN es as the interlayer of the cell. LiNO3-PAN es is in sufficient contact with the electrolyte so that it can continuously releases LiNO3 to assist the formation of Li2N2O2-rich single nitrogenous component SEI layer on Li surface. With the help of LiNO3-PAN es, Li metal anode shows excellent cycle stability even at a high current density of 4 mA/cm2, so that the cycle performance of the full cells was significantly improved, whether in the anode-free Cu||LFP cell or the Li||NCM622 cell.

Highly reversible and safe lithium metal batteries enabled by Non-flammable All-fluorinated carbonate electrolyte conjugated with 3D flexible MXene-based lithium anode

Recognized as the most attractive and promising anode, Li metal has been pursued for its high specific capacity and lowest standard potential. However, the hazardous Li dendrite growth is one of the most challenging issues for LMB, which brings about fragile SEI formation, low CE, large volume change and even safety issues. To tackle these problems, we design a 3D flexible MXene based lithium metal anode to accommodate the volume changes, accelerate the charge transport and lower the specific current density. Moreover, nonflammable ternary all-fluorinated carbonate electrolyte system is proposed to construct stable interface by introducing LiF-rich SEI and address the safety concerns. With these synergetic effects, 3D Li-MXene anode in ternary all-fluorinated electrolyte shows significantly improved reversibility with high average CE at 94.5 % after 200 cycles. Full Li metal cell with LFP cathode, composited 3D anode and nonflammable electrolyte delivers high-capacity retention of 95.7 % at 300 mAh g−1 after 200 cycles and excellent rate ability. These results pave a new direction for developing high safety and high-performance Li metal batteries and can also be extended to other rechargeable metal-anode-based batteries such as Na/K/Mg/Ca et al.

Silicon micropillar electrodes of lithiumion batteries used for characterizing electrolyte additives* *Project supported by the National Key R&D Program of China (Grant Nos. 2016YFB0100500 and 2016YFB0100100) and the National Natural Science Foundation of China (Grant Nos. 11674387, 11574385, 22005332, 115674368, and 62065005).

The 〈 100 〉 crystal-oriented silicon micropillar array platforms were prepared by microfabrication processes for the purpose of electrolyte additive identification. The silicon micropillar array platform was used for the study of fluorinated vinyl carbonate (FEC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), and vinyl carbonate (VC) electrolyte additives in the LiPF6 dissolved in a mixture of ethylene carbonate and diethyl carbonate electrolyte system using charge/discharge cycles, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The results show that the silicon pillar morphology displays cross-shaped expansion after lithiation/delithiation, the inorganic lithium salt keeps the silicon pillar morphology intact, and the organic lithium salt content promotes a rougher silicon pillar surface. The presence of poly-(VC) components on the surface of FEC and VC electrodes allows the silicon pillar to accommodate greater volume expansion while remaining intact. This work provides a standard, fast, and effective test method for the performance analysis of electrolyte additives and provides guidance for the development of new electrolyte additives.

Unraveling the Nature of Excellent Potassium Storage in Small-Molecule Se@Peapod-Like N-Doped Carbon Nanofibers.

The potassium-selenium (K-Se) battery is considered as an alternative solution for stationary energy storage because of abundant resource of K. However, the detailed mechanism of the energy storage process is yet to be unraveled. Herein, the findings in probing the working mechanism of the K-ion storage in Se cathode are reported using both experimental and computational approaches. A flexible K-Se battery is prepared by employing the small-molecule Se embedded in freestanding N -doped porous carbon nanofibers thin film (Se@NPCFs) as cathode. The reaction mechanisms are elucidated by identifying the existence of short-chain molecular Se encapsulated inside the microporous host, which transforms to K2 Se by a two-step conversion reaction via an "all-solid-state" electrochemical process in the carbonate electrolyte system. Through the whole reaction, the generation of polyselenides (K2 Sen , 3≤n≤8) is effectively suppressed by electrochemical reaction dominated by Se2 molecules, thus significantly enhancing the utilization of Se and effecting the voltage platform of the K-Se battery. This work offers a practical pathway to optimize the K-Se battery performance through structure engineering and manipulation of selenium chemistry for the formation of selective species and reveal its internal reaction mechanism in the carbonate electrolyte.

Highly Concentrated Electrolyte towards Enhanced Energy Density and Cycling Life of Dual‐Ion Battery

AbstractDual‐ion batteries (DIBs) have attracted much attention owing to their low cost, high voltage, and environmental friendliness. As the source of active ions during the charging/discharging process, the electrolyte plays a critical role in the performance of DIBs, including capacity, energy density, and cycling life. However, most used electrolyte systems based on the LiPF6 salt demonstrate unsatisfactory performance in DIBs. We have successfully developed a 7.5 mol kg−1 lithium bis(fluorosulfonyl)imide (LiFSI) in a carbonate electrolyte system. Compared with diluted electrolytes, this highly concentrated electrolyte exhibits several advantages: 1) enhanced intercalation capacity and cycling stability of the graphite cathode, 2) optimized structural stability of the Al anode, and 3) significantly increased battery energy density. A proof‐of‐concept DIB based on this concentrated electrolyte exhibits a discharge capacity of 94.0 mAh g−1 at 200 mA g−1 and 96.8 % capacity retention after 500 cycles. By counting both the electrode materials and electrolyte, the energy density of this DIB reaches up to ≈180 Wh kg−1, which is among the best performances of DIBs reported to date.

Insight into the Effect of LiNO3 Additive in High‐Voltage NCA Cathode with a Cylindrical 18650 Lithium-Metal Battery

Lithium metal is an attractive anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA h g−1) and low density (0.59 g cm−3). Unfortunately, lithium metal itself faces huge problems including inhomogeneous lithium deposition, infinite volume expansion, increased polarization, and dendrite formation. To overcome these drawbacks, many researchers have employed LiNO3 additive in the ether-based electrolyte to modify the properties of the solid electrolyte interface (SEI) film formed on the lithium metal surface. The LiNO3 can improve an ionically conductive, dense, and stable SEI formation through Li stripping and plating. However, LiNO3 has low solubility in carbonate based. Thus, LiNO3 was applied as an additive in carbonate electrolyte using CuF2 as a dissolution promoter. Herein, we demonstrate carbonate electrolyte system using LiNO3 and CuF2 with different ratios in high‐voltage Ni‐rich cathode with a cylindrical shape (18650). To achieve fundamental understanding of the effect of electrolyte additive molecules on the SEI formation at the lithium anode, reactive molecular dynamic simulation (Reaxff) has been used to investigate the mechanism and property of the SEI layer on the lithium anode.

Dynamic behavior in lithium ion/graphene/propylene carbonate electrolyte systems through molecular dynamics simulation

The dynamic behavior of lithium ions in Li+/graphene/propylene carbonate (PC) electrolyte system was investigated by molecular dynamics (MD) simulation. The simulated system is composed of Li+, PC and graphene sheets (Gr). The radial distribution function and distribution of carboxyl oxygen atoms around Li+ indicate Li+ and PC can form coordination complexes, and the coordination number can be up to 5, which accords well with the experimental and density functional theory calculation results from literatures. The interaction energies and conductivity were obtained from the trajectories of MD simulation. The graphites were exfoliated into few-layer graphene and the dispersed graphene flakes system can keep stable because of the strong interaction between PC and Gr. The conductivity of the Li+/PC system increases with addition of Gr, which agrees well with the experimental observations. The results obtained in the current work are useful for the future design of PC-based electrolyte systems.

Performance Enhancement of Rechargeable Lithium-Sulfur Battery Utilizing High Mass-Loading Cathodes of Azulmic Carbon Composite

A sulfur (S) cathode has a high theoretical capacity (1,672 mAh g-1). However, a major problem is the behavior of Li polysulfide (Li2Sn) intermediates, which may dissolve into an electrolyte. If dissolution of Li2Sn occurs, this should lead to a rapid capacity decay. We have investigated microporous activated carbon as matrix stabilizing S and realized stable cycling performance.1-2 However, the S content (ca.30 wt.%) and S loading were relatively low, which remains to be improved. To enhance them, in this study we applied azulmic carbon(AZC)3 with a large pore volume and also a porous 3-D Al current collector. Using these materials together with our fluorinated electrolyte, we have successfully realized stable and high capacity of the S-based cathode. Methods: azulmic carbon (AZC) used in this study was an alkaline-activated type with basically micropores with some meso pores more than 2 nm in diameter. The AZC-S composite was prepared by mixing AZC with S at a weight ratio of AZC: S = 45:55, and then applying heat treatment: 155°C for 5 h, then 300°C for 2 h. The AZC-S composite cathode was prepared by mixing the AZC-S composite, acetylene black, and alginate binder at a respective weight ratio of 90:5:5 and loading the resulting slurry into a 3-D Al current collector, “celmet (Sumitomo Electric Industries)”. The electrolyte was 1.0 mol dm-3 LiTFSI/FEC:HFE(1:1) +VC [9+1] (by vol.). All the cell components were installed into a pouch cell with a Li anode. A typical charge-discharge cycling test was carried out at 167.2 mA g-1 (0.1 C) with cutoff voltages of 3.0 and 1.0 V at 25°C. Major results and conclusion: we carried out the thermogravimetric analysis of elemental S and the AZC. The weight loss of AZC-S corresponds to the S content: 55 wt.%. The resulting S mass loading into the 3-D collector was 8.2 mg cm-2. We also investigated the discharge capacities in 1.0 mol dm-3 /FEC: HEF+VC (vinylene carbonate) electrolyte and also 2.0 mol dm-3/EC: DMC+VC electrolyte during cycling. The present fluorinated electrolyte contributed to stable discharge capacity showing 505 mAh (g-S)-1 at the 300th cycle. We found that there was a reduction at the surface of the sulfur at the first discharge, and excellent SEI was formed. It protected from direct contact with the electrolyte. The fluorinated electrolyte is, therefore, applicable to AZC even including the meso pores more than 2 nm as pore size. On the other hand, the carbonate electrolyte system showed two plateaus in the discharge curve at the first cycle. The carbonate electrolyte penetrated into the meso pores and the dissolution of Li2Sn occurred. As a result, the discharge capacity showed only 317 mAh (g-S)-1 at the 170th cycle. Thus, using the fluorinated electrolyte enabled the present activated carbon to cycle, as the meso porous carbon containing a large amount of sulfur. We will also report other results in the improvement of discharge capacity by ball-milling and heat treatment for AZC. This work was supported by “Advanced Low Carbon Technology Research and Development Program, Specially Promoted Research for Innovative Next Generation Batteries (ALCA-SPRING)” from JST.[1] T. Takahashi et al., Prog. Nat. Sci., 25 (2015) 612. [2] S. Okabe et al., Electrochemistry, 85 (2017) 671.[3] S. Usuki et al., Electrochemistry, 85 (2017) 650. Figure 1

Reduced graphene oxide aerogel as stable host for dendrite-free sodium metal anode

Sodium (Na) metal has attracted great attention as a promising anode for next-generation energy storage systems because of its abundant resources, potentially low cost, and high theoretical capacity. However, severe dendrite growth, large volume expansion during plating/stripping lead to poor cycle performance and limit the practical application of sodium metal anodes. Here, oriented freeze-drying and molten infusion are used to synthesize a Na-infused reduced graphene oxide aerogel (Na@rGa) composite anode using a reduced graphene oxide aerogel (rGa) as a stable host. This unique host shows ultra-light weight which guarantees high capacity (1064 mAh g−1), and the large specific surface area and uniform pores effectively lower the local current density and uniform electrolyte distribution from the inner to the outside of electrode. The Na@rGa anode exhibits low overpotential (50 mV) and stable cycle performance for 1000 cycles at 5 mA cm−2 in carbonate electrolyte system. The electrochemical performance of a full cell using the Na@rGa composite anode is clearly superior to that of a reference cell. This work provides a new horizon for construction of three-dimensional stable hosts and safe sodium metal anodes.

A high-energy sulfur cathode in carbonate electrolyte by eliminating polysulfides via solid-phase lithium-sulfur transformation

Carbonate-based electrolytes demonstrate safe and stable electrochemical performance in lithium-sulfur batteries. However, only a few types of sulfur cathodes with low loadings can be employed and the underlying electrochemical mechanism of lithium-sulfur batteries with carbonate-based electrolytes is not well understood. Here, we employ in operando X-ray absorption near edge spectroscopy to shed light on a solid-phase lithium-sulfur reaction mechanism in carbonate electrolyte systems in which sulfur directly transfers to Li2S without the formation of linear polysulfides. Based on this, we demonstrate the cyclability of conventional cyclo-S8 based sulfur cathodes in carbonate-based electrolyte across a wide temperature range, from −20 °C to 55 °C. Remarkably, the developed sulfur cathode architecture has high sulfur content (>65 wt%) with an areal loading of 4.0 mg cm−2. This research demonstrates promising performance of lithium-sulfur pouch cells in a carbonate-based electrolyte, indicating potential application in the future.

Phase Diagram, Conductivity, and Glass Transition of LiTFSI–H2O Binary Electrolytes

The aqueous electrolyte system of lithium bis(trifluoromethanesulfonyl)imide, LiTFSI–H2O, was systematically and accurately measured for a complete liquid–solid phase diagram and an extensive set of data on electrolytic conductivity and glass-transition temperature. The conductivity data set was fitted with a VFT-based function (VFT: Vogel–Fulcher–Tammann), of which the three parameters were set to Laurent polynomial functions of composition. The fitting results were correlated with other quantities, and comparisons were made between the results of this study and those of other aqueous and carbonate electrolyte systems. The results of these measurements, correlations, and comparisons strongly suggest a decoupling of cationic conduction from the movement of the bulk solution, in sharp contrast to what has been observed in any nonaqueous electrolytes so far.

Understanding the Behavior of LiCoO2 Cathodes at Extended Potentials in Ionic Liquid–Alkyl Carbonate Hybrid Electrolytes

The current electrolyte compositions makes it hard to achieve a high energy density lithium-ion battery based on LiCoO2 chemistry due to the destabilization of the LiCoO2 crystal structure beyond 4.2 V vs Li/Li+ leading to oxygen evolution and electrolyte decomposition. Therefore, electrolyte developments may hold promise for improved performance, for example, if some of the advantageous properties of ionic liquids can be introduced into a carbonate electrolyte system. Here, we report the use of a hybrid electrolyte (HE) system with a LiCoO2 cathode and have observed an excellent electrochemical performance when cycled to 4.4 V vs Li/Li+. This extended potential range produces higher capacity via greater ion insertion/extraction and better structural stability. A discharge capacity of 161 mAh/g (0.7 lithium extraction) was observed in the HE as compared to 128 mAh/g in conventional electrolyte, after 60 cycles. The charge–discharge studies at extended potentials also indicate better capacity retention in ...

Encapsulation of Metallic Na in an Electrically Conductive Host with Porous Channels as a Highly Stable Na Metal Anode.

Room-temperature Na ion batteries (NIBs) have attracted great attention because of the widely available, abundant sodium resources and potentially low cost. Currently, the challenge of the NIB development is due primarily to the lack of a high-performance anode, while the Na metal anode holds great promise considering its highest specific capacity of 1165 mA h/g and lowest anodic potential. However, an uneven deposit, relatively infinite volume change, and dendritic growth upon plating/stripping cycles cause a low Coulombic efficiency, poor cycling performance, and severe safety concerns. Here, a stable Na carbonized wood (Na-wood) composite anode was fabricated via a rapid melt infusion (about 5 s) into channels of carbonized wood by capillary action. The channels function as a high-surface-area, conductive, mechanically stable skeleton, which lowers the effective current density, ensures a uniform Na nucleation, and restricts the volume change over cycles. As a result, the Na-wood composite anode exhibited flat plating/stripping profiles with smaller overpotentials and stable cycling performance over 500 h at 1.0 mA/cm2 in a common carbonate electrolyte system. In sharp comparison, the planar Na metal electrode showed a much shorter cycle life of 100 h under the same test conditions.

Microwave (MW) Assisted Electro-Active Tempo Functionalized Single Walled Carbon Nanotube (SWNT) Electrodes for Li-Ion Batteries

The ever-increasing demand for high-performing, light weight, economical, and safe power storage for high–tech portable devices and electric vehicles leads to augmented research efforts in the field of organic or organic/hybrid materials for energy storage devices.With the aim of performing a balance between battery (charge producing system) and capacitor (charge storing system), Carbon Nanotubes (CNTs) can work as a template that can be functionalized with stable electro-active redox group. Since both capacitors and batteries can provide limited usability, an electrode material that hosts both properties will be more rewarding for the development of battery technology. Owing to the electrical and physical properties, CNTs are challenging material for the energy storage devices. There are some noticeable works about producing Carbon Nanotube thin electrodes to fabricate paper battery [1-3]In the light of these investigations, rapid microwave (MW) assisted functionalization of Single Walled Carbon Nanotubes (SWNTs) with electro-active TEMPO group was successfully performed with one step nitrene insertion reaction without using any harshly oxidative methods which are uncontrollable and destructive for SWNT. Their role of Functionalized SWNT samples (f-SWNTs) were characterized as a host for Li storage and their performance as electro-active cathode material were investigated.f-SWNTs were easily dispersed in solvents and they can form stable dispersions during 1 month where as non-functionalized SWNTs coagulate immediately. This can be considered as an indication of a successful surface functionalization. Depending on the degree of functionalization of SWNTs (without losing its electrical properties) their dispersibility in H2O and NMP (N-Methyl-2-pyrrolidone) and free standing paper electrode forming possibilities increase (Fig.1). Output Open Circuit Voltage (O.C.V) of cells with SWNT and functionalized SWNT (f-SWNT) samples changes between 2.5-3.0V vs. Li metal. The Cyclic Voltammetry study of the TEMPO functionalized f- SWNT 1 sample vs. Li metal is seen in Fig. 2.The constructed 2016-size button cell of f-SWNT 1 displayed an initial specific capacity of 441 mAh/g which decreased to 127 mAh/g in the second cycle of charge- discharge (Fig. 3). This large first cycle irreversible capacity loss could be attributed to various causes such as the irreversible reduction of oxygenated functional groups that may be originally present on the CNT surface as well as the attached nitroxide radical functional group to its amine oxide form. This electrochemical reduction was known to be an irreversible process in non-aqueous carbonate electrolyte systems and may be responsible for the reduction in the charge capacity. In the fifth cycle it dropped to 54 mA/g and after tenth and fifteenth cycles this value was reduced to 35 and 28 mAh/g, repectively. The reversibility of nitroxide radical group of TEMPO under basic conditions may provide an opportunity for battery systems which is under investigation.The f-SWNT 1 was subjected to charge and discharge cycles between 3 and 4V vs. Li (Figure 4). The charge curve plateau between 3.6 and 3.7 V can be ascribed to irreversible electrochemical oxidation of nitroxide radicals to oxoammonium species. The charging capacity suddenly faded from 140 mAh/g to 20 mAh/g in 15 charge discharge cycles.

Electrokinetic and Impedimetric Dynamics of FeCo-Nanoparticles on Glassy Carbon Electrode

The electrochemical dynamics of a film of FeCo nanoparticles were studied on a glassy carbon electrode (GCE). The film was found to be electroactive in 1 M LiClO4 containing 1:1 v/v ethylene carbonate dimethyl carbonate electrolyte system. Cyclic voltammetric experiments revealed a diffusion-controlled electron transfer process on the GCE/FeCo electrode surface. Further interrogation on the electrochemical properties of the FeCo nanoelectrode in an oxygen saturated 1 M LiClO4 containing 1:1 v/v ethylene-carbonate-dimethyl carbonate revealed that the nanoelectrode showed good response towards the electro-catalytic reduction of molecular oxygen with a Tafel slope of about 120 mV which is close to the theoretical 118 mV for a single electron transfer process in the rate limiting step; and a transfer coefficient (α) of 0.49. The heterogeneous rate constant of electron transfer (ket), exchange current density (io) and time constant (τ) were calculated from data obtained from electrochemical impedance spectroscopy and found to have values of 2.3 x 10-5 cm s-1, 1.6 x 10-4 A cm-2 and 2.4 x 10-4 s rad-1, respectively.

Overpotentials and solid electrolyte interphase formation at porous graphite electrodes in mixed ethylene carbonate–propylene carbonate electrolyte systems

The first electrochemical lithium insertion was characterized for several graphite materials with high degree of crystallinity, different particle size distributions and surface morphologies in an ethylene carbonate (EC)/propylene carbonate (PC) electrolyte. For coarser graphite materials and graphites with a low superficial defect concentration, an irreversible process was observed which correlated with the electrochemical exfoliation of graphite. Different natural and synthetic graphites with similar particle size distribution and active surface area showed differences in the passivation behavior during the first electrochemical reduction. The fraction of graphite particles exfoliating during the first galvanostatic lithium insertion linearly increased with length of the irreversible plateau, which concomitantly moved to more positive potentials. This behavior can be rationalized when considering, besides the surface structure, local overpotentials for the solid electrolyte interphase formation process, and especially the overpotential distribution through the graphite electrode. These overpotentials cause a distribution of the local current density attributed to the passivation process. Optimizing the particle contacts in the electrode by applying mechanical pressure or by selecting the proper binder decreased the overpotentials and suppressed the graphite exfoliation in the EC/PC electrolyte. Therefore, both graphite surface structure and electrode engineering aspects have to be considered for successful passivation against exfoliation.

Surface reactivity of graphite materials and their surface passivation during the first electrochemical lithium insertion

The surface passivation of TIMREX ® SLX50 graphite powder was studied as received and after heat treatment at 2500 °C in an inert gas atmosphere by differential electrochemical mass spectrometry in electrochemical lithium half-cells. 1 M LiPF 6 in ethylene carbonate and either a dimethyl carbonate, propylene carbonate or 1-fluoro ethylene carbonate co-solvent was used as electrolyte systems in these half-cells. The SEI-film formation properties of both graphite materials were correlated with their active surface area (ASA), being responsible for the interactions between the carbon and the electrolyte system. The active surface area was determined from the amount of CO and CO 2 gas desorbed at temperatures up to 950 °C from the graphite material surface after chemisorption of oxygen at 300 °C. The structural ordering at the graphite surface increased significantly during the heat treatment of the SLX50 graphite material as indicated by the significant decrease of the ASA value. The increased surface crystallinity was confirmed by krypton gas adsorption, Raman spectroscopy as well as temperature-programmed desorption. This increased structural ordering seemed to be the parameter being responsible for a hindered passivation of the heat-treated SLX50 causing partial exfoliation of the graphite structure during the first electrochemical lithium insertion in the ethylene carbonate/dimethyl carbonate electrolyte. In the case of the ethylene carbonate/1-fluoro ethylene carbonate electrolyte system, primarily the fluoro compound is responsible for the graphite passivation. In this electrolyte system, pristine SLX50 and the less reactive, heat-treated SLX50 graphite showed significantly different SEI-film formation mechanisms. In contrast, no difference in the passivation mechanism could be identified for different graphite surfaces in the ethylene carbonate electrolyte system with propylene carbonate as co-solvent.

Exfoliation of Graphite during Electrochemical Lithium Insertion in Ethylene Carbonate-Containing Electrolytes

Post mortem scanning electron microscopy, X-ray diffraction analysis, and Raman spectroscopy were applied to study the exfoliation tendency of a high temperature-treated graphite negative electrode material during the first electrochemical lithium insertion in various carbonate electrolyte systems. Exfoliation of the heat-treated graphite electrode material was observed in propylene carbonate (PC)- and ethylene carbonate (EC)-containing electrolytes. Using acyclic carbonates and 1-fluoro ethylene carbonate, exfoliation of the graphite structure could be avoided. used as a conducting salt in the EC-based electrolyte increased the exfoliation tendency of the graphite material. Differential electrochemical mass spectrometry was performed to study the passivation of the untreated and heat-treated graphite surface during the first electrochemical insertion. The heat-treated graphite surface showed a reduced reactivity towards EC, which hindered the graphite surface passivation in EC-based electrolyte systems and led to the exfoliation of the graphite structure so far known only for PC-containing electrolytes. © 2004 The Electrochemical Society. All rights reserved.