Li4Ti5O12 Electrode Research Articles

Understanding the Capacity Loss in LiNi0.5Mn1.5O4–Li4Ti5O12 Lithium-Ion Cells at Ambient and Elevated Temperatures

The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is an attractive positive electrode because of its operating voltage around 4.7 V (vs Li/Li+) and high power capability. However, problems including electrolyte decomposition at high voltage and transition metal dissolution, especially at elevated temperatures, have limited its potential use in practical full cells. In this paper, a fundamental study for LNMO∥Li4Ti5O12 (LTO) full cells has been performed to understand the effect of different capacity fading mechanisms contributing to overall cell failure. Electrochemical characterization of cells in different configurations (regular full cells, back-to-back pseudo-full cells, and 3-electrode full cells) combined with an intermittent current interruption technique have been performed. Capacity fade in the full cell configuration was mainly due to progressively limited lithiation of electrodes caused by a more severe degree of parasitic reactions at the LTO electrode, while the contributions from active mass los...

Heating Effect on Manufacturing Li4Ti5O12 Electrode Sheet with PTFE Binder on Battery Cell Performance

The synthesis of Li4Ti5O12 (LTO) and study of the heating effect on the manufacturing process of LTO sheet on the electrochemical performance have been investigated. LTO anode material composed with LiOH.H2O, TiO2 as raw materials were synthesized by the solid-state process. All raw materials were stoichiometrically mixed and milled with a planetary ball mill for 4 h to become the precursor of LTO. The precursor was characterized by Simultaneous Thermal Analyzer (STA) to determine sintering temperature. The STA analysis revealed that the minimum temperature to sinter the precursor was 600 °C. The precursor was sintered by using high-temperature furnace at 900 °C for 2 h in air atmosphere. The final product was ground and sieved with a screen to get finer and more homogenous particles. The final product was characterized by X-ray Diffraction (XRD) to determined crystal structure and phases. LTO sheet was prepared by mixing LTO powders with PTFE and AB in ratio 85:10:5 wt% by varrying heating process with 40 °C, 50 °C and 70 °C to become slurry. The slurry was coated on Cu foil with doctor blade method and dried at 80 °C for 1 h. LTO sheet was characterized by FTIR to analyze functional groups. LTO sheet was cut into circular discs with 16 mm in diameter. LTO sheet was arranged with a separator, metallic lithium and electrolyte become coin cell in a glove box. Automatic battery cycler was used to measure electrochemical performance and specific capacity of the cell. From the XRD analysis showed that single phase of LTO phase with a cubic crystal structure is formed. FTIR testing showed that there are stretching vibrations of Ti-O and H-F from tetrahedral TiO6 and PTFE respectively. Increasing temperature on LTO sheet manufacturing doesn’t change the structure of LTO. Cyclic voltammetry analysis showed that sample with heating of 40 °C showed better redox process than others. Charge-discharge test also showed that sample with heating of 40 °C has higher specific capacity than other samples with 53 mAh·g-1.

Electrochemical Oscillation in Li-Ion Batteries

Summary Two-phase reactions are prevalent in Li-ion batteries, whereas the underlying dynamics of phase separation in a real electrode still remain elusive, since numerous electrode particles constitute a formidably complex system for existing experimental techniques. Here we present an intriguing oscillatory phenomenon in the typical phase-separating electrode material Li 4 Ti 5 O 12 . During galvanostatic processes, the voltage oscillates due to the discrete nature of multi-particle phase-separating reactions, and the subtle oscillatory signals allow us to evaluate the fraction of actively phase-separating particles in real time. Through the analysis of oscillatory phenomena, we unveil the dependence of the active fraction on the depth of charge/discharge, cycling current, and working temperature, considerably deepening our understanding of the multi-particle phase-separation reaction. Moreover, it is the first time that electrochemical oscillations have been identified in rechargeable battery systems, opening up a new frontier for both theoretical and experimental researchers.

Development of Electrolyte for Negative-Limited LiNi0.5Mn1.5O4 / Li4Ti5O12 Li Ion Cells

Spinel Li4Ti5O12 (LTO) is an attractive candidate for negative electrode materials of lithium ion battery because the LTO anode shows the high rate capability, long cycle life, outstanding safety characteristics, and a flat insertion/extraction potential of at 1.5 V vs. Li+/Li. The 4V-class cathode (such as LiCoO2, LiNi1/3Mn1/3Co1/3O2, and LiMn2O4) / LTO battery has a low working voltage of about 2.5 V, leading to its low energy density. Some researchers have studied the LiNi0.5Mn1.5O4 (LNMO) / LTO battery system, because LNMO cathode offers a high operating potential at 4.7 V, which increases the working voltage of the battery using the LTO anode to 3.1 V [1] [2] [3]. Amine et al. reported that the negative limited LNMO / LTO cell showed a high rate capability and long cycle life at room temperature [1]. However, we found that the negative-limited LNMO /LTO battery showed a poor cycle characteristic at 50 ℃ (figure1-a). In this presentation, we aim to clarify the degradation mechanism of the negative-limited LNMO / LTO battery in order to improve the cycle life at a high temperature. For this purpose, we disassembled the LNMO / LTO cells after the cycle test at 50 ℃ and extracted the electrodes and electrolyte. The extracted LNMO / Li-metal half-cell and the extracted LTO / Li-metal half-cell were assembled and tested. It was found that the capacity of the LNMO electrode did not decrease. On the other hand, the capacity of the LTO electrode decreased. It is revealed that the degradation of the negative-limited LNMO/LTO battery was caused by the decline of the LTO anode capacity. The XPS spectra of the LTO electrode indicated that LiF covered around the LTO materials and caused its capacity degradation. To reveal the generation pathway of LiF, the extracted electrolyte was analyzed by GC-MS, LC-MS/MS and 19F-NMR. The results revealed that the reduction reaction of the chain-like carbonate such as dimethyl carbonate and the ring-opening reaction of the cyclic carbonate such as ethylene carbonate caused the LiF generation. Especially, the lithium alkoxide generated by the ring-opening reaction of the cyclic carbonate accelerated the LiF generation reaction. The use of the electrolyte containing only chain-like carbonate as a solvent significantly improved the cycle characteristics at 50 ℃ (figure1-b).

Toward Optimal Performance and In‐Depth Understanding of Spinel Li4Ti5O12 Electrodes through Phase Field Modeling

AbstractComputational modeling is vital for the fundamental understanding of processes in Li‐ion batteries. However, capturing nanoscopic to mesoscopic phase thermodynamics and kinetics in the solid electrode particles embedded in realistic electrode morphologies is challenging. In particular for electrode materials displaying a first order phase transition, such as LiFePO4, graphite, and spinel Li4Ti5O12, predicting the macroscopic electrochemical behavior requires an accurate physical model. Herein, a thermodynamic phase field model is presented for Li‐ion insertion in spinel Li4Ti5O12 which captures the performance limitations presented in literature as a function of all relevant electrode parameters. The phase stability in the model is based on ab initio density functional theory calculations and the Li‐ion diffusion parameters on nanoscopic nuclear magnetic resonance (NMR) measurements of Li‐ion mobility, resulting in a parameter free model. The direct comparison with prepared electrodes shows good agreement over three orders of magnitude in the discharge current. Overpotentials associated with the various charge transport processes, as well as the active particle fraction relevant for local hotspots in batteries, are analyzed. It is demonstrated which process limits the electrode performance under a variety of realistic conditions, providing comprehensive understanding of the nanoscopic to microscopic properties. These results provide concrete directions toward the design of optimally performing Li4Ti5O12 electrodes.

Lithium-Ion Batteries: Charged by Triboelectric Nanogenerators with Pulsed Output Based on the Enhanced Cycling Stability.

The triboelectric nanogenerator (TENG) has been used to store its generated energy into lithium-ion batteries (LIBs); however, the influences of its pulse current and high voltage on LIB polarization and dynamic behaviors have not been investigated yet. In this paper, it is found that LIBs based on the phase transition reaction of the lithium storage mechanism [LiFePO4 (LFP) and Li4Ti5O12 (LTO) electrodes] are more suitable for charging by TENGs. Thus, the enhanced cycling capacity, Coulombic efficiency (nearly 100% for LTO electrode), and energy storage efficiency (85.3% for the LFP-LTO electrode) are successfully achieved. Moreover, the pulse current has a positive effect on the increase of the Li-ion extraction, reducing the charge-transfer resistance ( Rct) for all studied electrodes as well (LFP, LiNi0.6Co0.2Mn0.2O2, LTO, and graphite). The excellent cyclability, high Coulombic, and energy storage efficiencies demonstrated the availability of storing pulsed energy generated by TENGs. This research has provided a promising analysis to obtain an enhanced charging methodology, which provides significant guidance for the scientific research of the LIBs.

Electrospinning preparation of one-dimensional Co2+-doped Li4Ti5O12 nanofibers for high-performance lithium ion battery

One-dimensional Co2+-doped Li4Ti5O12 nanofibers with a diameter of approximately 500 nm have been synthesized via a one-step controllable electrospinning method. The Co2+-doped Li4Ti5O12 nanofibers were systematically characterized by XRD, ICP, TEM, SEM, BET, EDS mapping, and XPS. Based on the cubic spinel structure and one-dimensional effect of Li4Ti5O12, Co2+-doped Li4Ti5O12 nanofibers exhibit the enlarged lattice volume, reduced particle size and enhanced electrical conductivity. More importantly, Co2+-doped Li4Ti5O12 nanofibers as a lithium ion battery anode electrode performs superior electrochemical performance than undoped Li4Ti5O12 electrode in terms of electrochemical measurements. Particularly, the reversible capacity of Co2+-doped Li4Ti5O12 electrode reaches up to 140.1 mAh g−1 and still maintains 136.5 mAh g−1 after 200 cycles at a current rate of 5 C. Therefore, one-dimensional Co2+-doped Li4Ti5O12 nanofiber electrodes, showing high reversible capacity and remarkable recycling property, could be a potential candidate as an anode material.

In Situ Real-Time Mechanical and Morphological Characterization of Electrodes for Electrochemical Energy Storage and Conversion by Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring.

Quartz crystal microbalance with dissipation monitoring (QCM-D) generates surface-acoustic waves in quartz crystal plates that can effectively probe the structure of films, particulate composite electrodes of complex geometry rigidly attached to quartz crystal surface on one side and contacting a gas or liquid phase on the other side. The output QCM-D characteristics consist of the resonance frequency (MHz frequency range) and resonance bandwidth measured with extra-ordinary precision of a few tenths of Hz. Depending on the electrodes stiffness/softness, QCM-D operates either as a gravimetric or complex mechanical probe of their intrinsic structure. For at least 20 years, QCM-D has been successfully used in biochemical and environmental science and technology for its ability to probe the structure of soft solvated interfaces. Practical battery and supercapacitor electrodes appear frequently as porous solids with their stiffness changing due to interactions with electrolyte solutions or as a result of ion intercalation/adsorption and long-term electrode cycling. Unfortunately, most QCM measurements with electrochemical systems are carried out based on a single (fundamental) frequency and, as such, provided that the resonance bandwidth remains constant, are suitable for only gravimetric sensing. The multiharmonic measurements have been carried out mainly on conducting/redox polymer films rather than on typical composite battery/supercapacitor electrodes. Here, we summarize the most recent publications devoted to the development of electrochemical QCM-D (EQCM-D)-based methodology for systematic characterization of mechanical properties of operating battery/supercapacitor electrodes. By varying the electrodes' composition and structure (thin/thick layers, small/large particles, binders with different mechanical properties, etc.), nature of the electrolyte solutions and charging/cycling conditions, the method is shown to be operated in different application modes. A variety of useful electrode-material properties are assessed noninvasively, in situ, and in real time frames of ion intercalation into the electrodes of interest. A detailed algorithm for the mechanical characterization of battery electrodes kept in the gas phase and immersed into the electrolyte solutions has been developed for fast recognition of stiff and viscoelastic materials in terms of EQCM-D signatures treated by the hydrodynamic and viscoelastic models. Working examples of the use of in situ hydrodynamic spectroscopy to characterize stiff rough/porous solids of complex geometry and viscoelastic characterization of soft electrodes are presented. The most demonstrative example relates to the formation of solid electrolyte interphase on Li4Ti5O12 electrodes in the presence of different electrolyte solutions and additives: only a few cycles (an experiment during ∼30 min) were required for screening the electrolyte systems for their ability to form high-quality surface films in experimental EQCM-D cells as compared to 100 cycles (200 h cycling) in conventional coin cells. Thin/small-mass electrodes required for the EQCM-D analysis enable accelerated cycling tests for ultrafast mechanical characterization of these electrodes in different electrolyte solutions. Hence, this methodology can be easily implemented as a highly effective in situ analytical tool in the field of energy storage and conversion.

Smart Construction of Integrated CNTs/Li4Ti5O12 Core/Shell Arrays with Superior High-Rate Performance for Application in Lithium-Ion Batteries.

Exploring advanced high‐rate anodes is of great importance for the development of next‐generation high‐power lithium‐ion batteries (LIBs). Here, novel carbon nanotubes (CNTs)/Li4Ti5O12 (LTO) core/shell arrays on carbon cloth (CC) as integrated high‐quality anode are constructed via a facile combined chemical vapor deposition–atomic layer deposition (ALD) method. ALD‐synthesized LTO is strongly anchored on the CNTs' skeleton forming core/shell structures with diameters of 70–80 nm the combined advantages including highly conductive network, large surface area, and strong adhesion are obtained in the CC‐LTO@CNTs core/shell arrays. The electrochemical performance of the CC‐CNTs/LTO electrode is completely studied as the anode of LIBs and it shows noticeable high‐rate capability (a capacity of 169 mA h g−1 at 1 C and 112 mA h g−1 at 20 C), as well as a stable cycle life with a capacity retention of 86% after 5000 cycles at 10 C, which is much better than the CC‐LTO counterpart. Meanwhile, excellent cycling stability is also demonstrated for the full cell with LiFePO4 cathode and CC‐CNTs/LTO anode (87% capacity retention after 1500 cycles at 10 C). These positive features suggest their promising application in high‐power energy storage areas.

Influence of the Positive Electrode on Li4Ti5O12 (LTO) Electrode/Electrolyte Interfaces in Li-Ion Batteries

Li4Ti5O12(LTO)-based negative electrode for lithium-ion batteries is of interest for electrical vehicles due to its safety, low cost and cycling stability. In this study, the effect of the positive electrode on the electrochemical performances of LTO electrodes, in relation with the Solid Electrolyte Interphase (SEI) properties, has been investigated. Full cells LTO/LiNi3/5Co1/5Mn1/5O2 (NMC) and LTO/LiMn2O4 (LMO) were cycled at 40°C over 100 cycles and the electrodes were analyzed by XPS and Scanning Auger Microscopy (SAM) after one and 100 cycles. For both systems, LTO electrodes are homogeneously covered by surface layers since the first cycle which induces an irreversible capacity loss. This latter is more important for LTO/LMO compared to LTO/NMC. Both SEI layers are composed of organic (polyethylene oxides, oxalates) and inorganic species (LiF, phosphates and fluorophosphates) but in different proportions: more fluorine species are detected for LTO/LMO for instance. Moreover, the SEI is thicker on the LTO electrode when cycled versus LMO compared to NMC and contains small amounts of manganese, homogeneously spread over the surface. In conclusion, a thick SEI associated with the presence of metallic species could alter the passivating role of the SEI and explain the less efficient electrochemical performance of LTO/LMO cells.

Thermal Stability of Pyrrolidinium-FSI Ionic Liquid Electrolyte and Lithium-Ion Electrodes at Elevated Temperatures

Ionic liquids are an alternative electrolyte for lithium-ion batteries which are expected to increase thermal stability of the device. The thermal stability of lithium bis(fluorosulfonyl)imide salt (LiFSI) in 1-methyl-3-propylpyrrolidinium bis(fluorosulfonyl)imide (P13FSI) ionic liquid electrolyte was investigated at elevated temperatures after cycling in contact with commercially available electrode materials. Six commercial electrodes were investigated; LiFePO4, Li1.2Ni0.15Co0.1Mn0.55O2, LiMn1.5Ni0.5O4, Li4Ti5O12, LiCoO2 and graphite. Differential scanning calorimetry was performed on electrode | electrolyte combinations in high pressure hermetically sealed crucibles from 25 to 600°C. Of the electrodes studied here, LiFePO4 showed the lowest heat release and Li4Ti5O12 showed the highest onset temperature under the conditions used. Additionally, the ionic liquid electrolyte showed superior thermal stability as compared to the conventional electrolyte when used with LiMn1.5Ni0.5O4 and Li4Ti5O12 electrodes. Incremental state of charge investigations with both LiFePO4 and Li4Ti5O12 half cells showed that thermal stability varies with state of charge of the electrode. The thermal stability advantage provided by P13FSI electrolyte with each electrode should be considered to determine if the benefits of higher decomposition temperatures are outweighed by the higher energy released during ionic liquid decomposition.

Continuous and Conformal Lithium Titanate Spinel Thin Films by Solid State Reaction

In this work, we report on the fabrication of continuous and uniform thin films by a solid state reaction. The fabrication of spinel Li4Ti5O12 thin films was demonstrated by solid state reaction between TiO2 and Li2CO3 stacked-layers upon thermal annealing. The TiO2 layer was prepared by physical vapor deposition or atomic layer deposition, whereas the Li2CO3 layer was deposited by chemical solution deposition or atomic layer deposition. The solid state reaction and obtained material properties were investigated on planar substrates. It was found that continuous films with crystalline and stoichiometric Li4Ti5O12 can be formed by solid state reaction at temperatures higher than 650°C. The prepared films exhibited Li-ion intercalation characteristics for Li4Ti5O12 spinel with the typical flat plateau at 1.55 V (vs Li+/Li) for both charging and discharging. The theoretical capacity of 612 mAh cm−3 was obtained at slow charging rate of 0.1 C with still 45% capacity attainable at 20 C. Interestingly, it was found that the kinetics is strongly dependent on the current collector substrate used. A TiN substrate provided faster Li4Ti5O12 electrode kinetics than a Pt substrate, despite a thin anatase interlayer at the TiN/TiO2/ Li4Ti5O12 interface, showing the importance of interface or work function matching for high rate lithiation/delithiation performance. In addition, the potential of conformal Li4Ti5O12 thin films on high aspect ratio structures was demonstrated.

Bamboo-Shaped Zn2+-Doped Li4Ti5O12 Nanofibers: One-Step Controllable Synthesis and High-Performance Lithium-Ion Batteries

Bamboo-shaped Zn2+-doped Li4Ti5O12 nanofibers with the diameter of approximately 300 nm have been synthesized via a one-step controllable electrospinning method in this work. The structure and morphology of the as-prepared materials have been characterized by XRD, TEM, SEM, EDS-mapping, BET, ICP-OES and XPS. Fortunately, the introduction of Zn2+ ions cannot interrupt the original cubic spinel structure and one-dimentional bamboo-shaped nanostructure of Li4Ti5O12. The effects of two different kinds of Zn doping behaviors: substitutional doping and interstitial doping on the properties of bamboo-shaped Li4Ti5O12 nanofibers have been studied in detail. The comparative experiments prove that interstitial doping bamboo-shaped Li4Ti5O12 nanofibers exhibit the biggest lattice volume and best electrochemical performances than substitutional doping and undoped bamboo-shaped Li4Ti5O12 nanofibers. Particularly, the reversible capacity of interstitial doping Li4Ti5O12 electrode is up to 142.8 mA h g−1 and still remains at 141.7 mAh g−1 after 1000 cycles at a current rate of 5 C.

Lithium Metal Anodes: A Recipe for Protection

Effective stabilization of lithium metal anode is the key to the development of next-generation high-energy rechargeable batteries. In this issue of Joule, Linda Nazar and colleagues demonstrated a rationally designed electrolyte additive that can form a robust, single-ion-conducting protective layer on lithium metal surface while the battery operates, promoting uniform lithium deposition with high cycling efficiency.

Electrospinning preparation of one-dimensional Ce3+-doped Li4Ti5O12 sub-microbelts for high-performance lithium-ion batteries

One-dimensional Ce3+-doped Li4Ti5O12 (Li4Ti5−x Ce x O12, x = 0, 0.01, 0.02, and 0.05) sub-microbelts with the width of approximately 500 nm and thickness of about 200 nm have been synthesized via the facile electrospinning method. The structure and morphology of the as-prepared samples are characterized by XRD, TEM, SEM, BET, HRTEM, XPS, and AFM. Importantly, one-dimensional Li4Ti5O12 sub-microbelts can be well preserved with the introduction of Ce3+ ions, while CeO2 impurity is obtained when x is greater than or equal to 0.02. The comparative experiments prove that Ce3+-doped Li4Ti5O12 electrodes exhibit the brilliant electrochemical performance than undoped counterpart. Particularly, the reversible capacity of Li4Ti4.98Ce0.02O12 electrode reaches up to 139.9 mAh g−1 and still maintains at 132.6 mAh g−1 even after 100 cycles under the current rate of 4 C. The superior lithium storage properties of Li4Ti4.98Ce0.02O12 electrode could be attributed to their intrinsic structure advantage as well as enhanced overall conductivity.

Study of the Hydrate-Melt/Li4Ti5O12 Interphase by Scanning Electron Microscopy-Based Spectroscopy.

To develop safe and low-cost Li-ion batteries (LIBs), recently, an aqueous-based electrolyte so-called "hydrate-melt" (HDM) electrolyte is proposed. Li4Ti5O12 is a promising negative electrode material for a LIB with such a HDM electrolyte because of its unexpected reversible Li insertion and extraction properties without usually inevitable water reduction. The solid-electrolyte interphase formation is one of the reasons for this stable reaction, although a detailed analysis is not yet performed. Here, a Li4Ti5O12 electrode surface reacted in a HDM electrolyte is investigated by scanning electron microscopy-based analysis. Surface reaction products are clearly observed on the Li4Ti5O12 surface after the Li insertion reaction in a HDM electrolyte. Energy-dispersive X-ray spectroscopy and Auger electron spectroscopy indicated that the products do not contain any components originated from Li salts, whereas anion-derived passivation films seem to cover a bare surface below the products. Further, the surface products are identified as Li2O by the feature of Li-K-edge reflection electron energy-loss spectrum. The Li2O formation would be one of the key issues for stable Li insertion and extraction of a Li4Ti5O12 electrode in a HDM electrolyte.

Binder-induced surface structure evolution effects on Li-ion battery performance

A comparative investigation on binder induced chemical and morphological evolution of Li4Ti5O12 electrodes was performed via X-ray photoemission spectroscopy, scanning electron microscopy, and electrochemical measurements. Composite electrodes were obtained using three different binders (PAA, PVdF, and CMC) with 80:10:10 ratio of active material:carbon:binder. The electrochemical performances of the electrodes, were found to be intimately correlated with the evolution of the microstructure of the electrodes, probed by XPS and SEM analysis. Our analysis shows that the surface chemistry, thickness of the passivation layers and the morphology of the electrodes are strongly dependent on the type of binders that significantly influence the electrochemical properties of the electrodes. These results point to a key role played by binders in optimization of the battery performance and improve our understanding of the previously observed and unexplained electrochemical properties of these electrodes.

Mechanisms of the decrease in low-temperature electrochemical performance of Li4Ti5O12-based anode materials

The electrochemical performances of Li4Ti5O12 (LTO) and Li4Ti5O12-rutile TiO2 (LTO–RTO) composite electrodes at low temperatures were evaluated. The electrochemical performance of both electrodes decreased at low temperatures; regardless, the LTO–RTO electrode performed better than the LTO electrode. First, high viscosity and low ion conductivity of liquid electrolytes at low temperatures significantly reduce electrochemical performance. Second, cycling at low temperatures changes the crystal structure of LTO–based electrodes, impeding lithium ion diffusion and even causing the diffusion path to change from easy to difficult. However, changes in the crystal structure of the LTO–RTO electrode were not sufficient to change this path; thus, diffusion continued along the 8a-16c-8a pathway. Finally, from the perspective of dynamics, aggravation of a side reaction, increase in charge transfer resistance and polarization, and decrease in lithium ion diffusion at low temperatures reduce the electrochemical performance of LTO–based anode materials. However, the activation energy based on lithium ion diffusion is lower in the LTO–RTO electrode than the LTO electrode. The results confirmed that the electrochemical performance of the LTO–RTO electrode was better than that of the LTO electrode at low temperatures.

In situ real-time gravimetric and viscoelastic probing of surface films formation on lithium batteries electrodes

It is generally accepted that solid–electrolyte interphase formed on the surface of lithium-battery electrodes play a key role in controlling their cycling performance. Although a large variety of surface-sensitive spectroscopies and microscopies were used for their characterization, the focus was on surface species nature rather than on the mechanical properties of the surface films. Here we report a highly sensitive method of gravimetric and viscoelastic probing of the formation of surface films on composite Li4Ti5O12 electrode coupled with lithium ions intercalation into this electrode. Electrochemical quartz-crystal microbalance with dissipation monitoring measurements were performed with LiTFSI, LiPF6, and LiPF6 + 2% vinylene carbonate solutions from which structural parameters of the surface films were returned by fitting to a multilayer viscoelastic model. Only a few fast cycles are required to qualify surface films on Li4Ti5O12 anode improving in the sequence LiPF6 < LiPF6 + 2% vinylene carbonate << LiTFSI.

Large-scale production of high-quality graphene sheets by a non-electrified electrochemical exfoliation method

Graphene materials have recently experienced rapid developments, but large-scale production of high-quality graphene is still desired. Electrochemical exfoliation method is considered as a promising approach to meet this requirement. Here we demonstrate a non-electrified electrochemical exfoliation method to produce high-quality graphene (NEEG) sheets. By direct electrochemical reaction between graphite powders and metallic Li in 1 M LiPF6/propylene carbonate electrolyte, continuous graphite exfoliation is achieved with a high yield of excess 80% without any consumption of electric energy. The as-prepared NEEG has high quality with few defects (ID/IG = 0.45), a high C/O ratio of 27.74 and excellent electronic conductivity of 102.5 S cm−1. As conductive additives in Li4Ti5O12 electrode for lithium ion batteries, NEEG contributes to higher capacity and initial coulombic efficiency than common thermally reduced graphene oxide. Given the advantages of NEEG, the non-electrified electrochemical exfoliation method is promising for the large-scale preparation of high-quality graphene sheets.