LiPF6 Electrolyte Research Articles

Diffusion of ions and solvent in propylene carbonate solutions for lithium-ion battery applications

Diffusion of lithium ions in organic solvent solutions is important to the performance of lithium ion batteries. In this article, fully atomistic molecular dynamics (MD) simulations were employed to study the diffusive behavior of LiPF6 electrolyte salt and propylene carbonate in solutions at different temperatures in direct comparison to experimental diffusivity data. Organic solutions at 1 M concentrations were considered at the operational conditions of Lithium ion batteries. We show that non-polarizable scaled charge force fields can predict, quantitatively, the diffusion of Li+ and PC solvent in a range of operational temperatures. Such type of force fields are much less computational demanding than polarizable or ReaxFF models. Diffusion follows an Arrhenius type of behavior. van Hove autocorrelation functions show a nonGaussian type of movement for ions and PC solvent. The Li+ is moving by a mixed-vehicular mechanism. Moreover, the nearest neighbour distances of the Li+- carbonyl oxygen in these PC solutions is predicted accurately using the scaled charges GAFF, in agreement to experiments. Furthermore, quantitative prediction of modeled ionic conductivity in comparison to experiments can be achieved in a range of temperatures.

Fire-Preventing LiPF6 and Ethylene Carbonate-Based Organic Liquid Electrolyte System for Safer and Outperforming Lithium-Ion Batteries.

Battery safety is an ever-increasing significance to guarantee consumer's safety. Reducing or preventing the risk of battery fire and explosion is a must for battery manufacturers. Major reason for the occurrence of fire in commercial lithium-ion batteries is the flammability of conventional organic liquid electrolyte, which is typically composed of 1 M LiPF6 salt and ethylene carbonate (EC)-based organic solvents. Herein, we report the designed 1 M LiPF6 and EC-based nonflammable electrolyte including methyl(2,2,2-trifluoroethyl)carbonate, which breaks the conventional perception that EC-based liquid electrolyte is always flammable. The designed electrolyte also provides high anodic stability beyond the conventional charge cut-off voltage of 4.2 V. A graphite∥LiNi0.6Co0.2Mn0.2O2 lithium-ion full cell with our designed EC-based nonflammable electrolyte with a small fraction of vinylene carbonate additive under an aggressive condition of 4.5 V charge cut-off voltage, 0.5C rate, and 45 °C exhibits increased capacity, reduced interfacial resistance, and improved performance and rate capability. A basic understanding of how a high-voltage cathode-electrolyte interface and anode-electrolyte interface are stabilized and how failure modes are mitigated by fire-preventing electrolyte is discussed.

Study Performance of LiFePO4/Graphite Cylindrical Pouch Cell

Cylindrical cell Lithium ion battery with a pouch casing has been made at the Integrated Battery Laboratory, BATAN. LiFePO4 double sided coated aluminum foil with a thickness of 180 μm is used as a cathode sheet. The anode sheet is made from two-sided artificial graphite coated on copper foil with a thickness of 197 μm. The composition, crystal structure, of the coated LiFePO4 was measured by XRD. Battery cells are built by rolling thin layers of cathode, separator, and anode material into cylindrical shape using a rolling machine. The cylindrical cell is inserted into an aluminum bag and then sealed at 175°C. Cylindrical cell-bag inserted into the Glove Box then filled with ∼ 2.5 ml of LiPF6 electrolyte liquid. A vacuum sealing machine is used to seal the remainder of the bag set at 175 oC. The performance of lithium ion batteries is characterized by using a battery analyzer. LiFePO4 shows a release capacity of 250.00 mAh, with a specific capacity of 124.10 mAh/g in the 1st cycle and 100.20 mAh/g after 100th cycle, at a rate of 0.3C. The cell shows good performance after 100 cycles with 80.74% retention.

Electrochemically Active Red P/BaTiO3‐Based Protective Layers Suppressing Li Dendrite Growth for Li Metal Batteries

AbstractLi metal has been considered a promising anode for high‐energy density batteries because of its high specific capacity. However, uncontrolled Li dendrite growth and severe electrolyte decomposition are detrimental obstacles hindering the practical applications of lithium metal batteries. Herein, electrochemically active red P‐based protective layers are introduced to suppress Li dendrite growth during cycling. Red P particles confined in the protective layer react with Li dendrites, forming Li3P, as Li dendrites are penetrating through the protective layer. As a result, Li metal is no longer plated on the Li3P surface because Li3P is electrically insulating, eventually leading to suppressing Li dendrite growth. Moreover, the red P‐based protective layer is functionalized with dielectric BaTiO3 nanoparticles to scavenge radicals generated from electrolyte decomposition as well as to improve the mechanical strength of protective layers. The synergy effect of electrochemically active red P and inactive BaTiO3 gives rise to the improved short‐circuit time of Li metal and the excellent cycle performance and Coulombic efficiency of Li/Li symmetric and Li/LiFePO4 full cells over 200 cycles, despite the fact that the cell performances are examined with the conventional electrolyte of LiPF6 in ethylene carbonate/diethyl carbonate that is highly unstable against Li metal.

High-value utilization of graphite electrodes in spent lithium-ion batteries: From 3D waste graphite to 2D graphene oxide

The graphite electrodes of spent lithium-ion batteries (LIBs) have a good crystalline composition and layered structure, and the recovery potential is promising. However, the internal and external surfaces of the waste graphite are often polluted with various organic and inorganic impurities, which seriously restrict its high-value utilization. Herein, the microstructure and surface analysis of waste graphite at variable scales were carried out systematically to reveal the types and occurrence status of impurities and their influence on the preparation of graphene oxide (GO) using a modified Hummers method. The results show that the graphite surface contaminants are polyvinylidene fluoride binder, LiPF6 electrolyte and LiF residue from the solid electrolyte interface, while residual lithium (Li2CO3) and CuO were found to have invaded the crystal structure of graphite. Fortunately, the modified Hummers method can effectively remove these complicated associated impurities and prevent their re-contamination on the GO surface. More importantly, the modified Hummers method can not only destroy the longitudinal molecular bonds between graphite layers, but also splice them horizontally to form 2D GO, which is verified by high-resolution transmission electron microscope (HR-TEM) images. This paper provides theoretical support and practical guidance for the high-value utilization of waste graphite in spent LIBs.

Effect of plasticizer on the ion-conductive and dielectric behavior of poly(ethylene carbonate)-based Li electrolytes

Solid polymer electrolytes consisting of CO2-derived poly(ethylene carbonate) (PEC), LiPF6, and plasticizers (glycerol or 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide, EMImTFSI) were prepared by a simple casting method, and their dielectric relaxation behavior was evaluated using broadband electric spectroscopy (BES), which clarified the correlation between the polymer motion and ionic conduction. From the DSC and BES results, it was revealed that the addition of plasticizer decreased the glass transition temperature and increased the dc conductivity (σdc) of the PEC electrolyte. The BES results also revealed that the plasticizer increased the segmental motion of PEC and improved σdc, and the plasticizing effect of EMImTFSI on the PEC electrolyte was larger than that of glycerol. From the results of the Walden plot and fragility analysis, it was expected that the degree of decoupling e and fragility m would increase with the addition of plasticizer because these plasticizers weaken the interactions between the PEC chains and Li ions in the electrolyte. Plasticized poly(ethylene carbonate) (PEC)/LiPF6 electrolytes were prepared and evaluated their ion-conductive and dielectric relaxation behavior using broadband electric spectroscopy (BES). The BES results indicated that the plasticizer accelerates segmental motion of PEC and improve the dc conductivity, and the plasticizing effect of ionic liquid (EMImTFSI) on the PEC electrolyte is larger than that of glycerol. From the results of the Walden plot and fragility analysis, it was revealed that the degree of decoupling and the value of fragility increase by the addition of plasticizer, and these plasticizers weaken interactions between PEC chains and Li ions in the electrolyte.

High stable rate cycling performances of microporous carbon spheres/selenium composite (MPCS/Se) cathode as lithium–selenium battery

Loading selenium (Se) into microporous carbon spheres (MPCS) for the use as a cathode material is an efficient method for reducing the volume expansion and dissolution of polyselenides in the lithium-selenium (Li–Se) batteries during cycling. In this study, we produced MPCSs from glucose using a simple and efficient hydrothermal synthesis method, followed by activation of the MPCS with KOH. Selenium particles were homodispersed in the micropores of MPCS by a typical melt-diffusion process. The obtained MPCS/Se composites used as a cathode of Li–Se batteries show high Se loading of nearly 45%, and high capacities as well as stable cycling performance in both carbonate-based LiPF6 electrolyte (565 mAh g−1 at 1 C after 500 cycles) and ether-based LiTFSI electrolyte (480 mAh g−1 at 1 C after 500 cycles). Notably, an outstanding rate capability in the carbonate-based electrolyte and a coulombic efficiency of nearly 100% in both types of electrolytes were observed. The microporous structure of the MPCS material with high conductivity contributes to the excellent electrochemical properties and rate capability, effectively alleviating volume expansion and suppressing dissolution of polyselenides.

Fast-Charging Cathodes from Polymer-Templated Mesoporous LiVPO4F.

Fast-charging cathodes with high operating voltages are critical to the development of high energy and power density lithium-ion batteries. One route to fast-charging battery materials is through the formation of nanoporous networks, but these methods are often limited by the high calcination temperatures required for synthesis. Here, we report the synthesis of carbon-coated nanoporous LiVPO4F with excellent rate capabilities that can be stably cycled up to 4.6 V in standard LiPF6 electrolytes. During charge and discharge at 30C, 110 mAh/g (70% of theoretical capacity) was obtained, and only 9% of capacity was lost after 2000 cycles at 20C. These materials also showed excellent stability, with little self-discharge, an open-circuit voltage of 4.2 V, and a discharge capacity of 139 mAh/g obtained after holding for 12 h. Rate capabilities were further demonstrated in a proof-of-concept full cell made with a nanostructured Nb2O5. These devices were able to deliver 200 mAh/g at 1C and 100 mAh/g at 30C. Finally, operando X-ray diffraction and electrochemical kinetics were further used to provide insight into the nature of fast charging in these materials.

Modification of Li- and Mn-Rich Cathode Materials via Formation of the Rock-Salt and Spinel Surface Layers for Steady and High-Rate Electrochemical Performances.

We demonstrate a novel surface modification of Li- and Mn-rich cathode materials 0.33Li2MnO3·0.67LiNi0.4Co0.2Mn0.4O2 for lithium-ion batteries (high-energy Ni-Co-Mn oxides, HE-NCM) via their heat treatment with trimesic acid (TA) or terephthalic acid at 600 °C under argon. We established the optimal regimes of the treatment-the amounts of HE-NCM, acid, temperature, and time-resulting in a significant improvement of the electrochemical behavior of cathodes in Li cells. It was shown that upon treatment, some lithium is leached out from the surface, leading to the formation of a surface layer comprising rock-salt-like phase Li0.4Ni1.6O2. The analysis of the structural and surface studies by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy confirmed the formation of the above surface layer. We discuss the possible reactions of HE-NCM with the acids and the mechanism of the formation of the new phases, Li0.4Ni1.6O2 and spinel. The electrochemical characterizations were performed by testing the materials versus Li anodes at 30 °C. Importantly, the electrochemical results disclose significantly improved cycling stability (much lower capacity fading) and high-rate performance for the treated materials compared to the untreated ones. We established a lower evolution of the voltage hysteresis with cycling for the treated cathodes compared to that for the untreated ones. Thermal studies by differential scanning calorimetry also demonstrated lower (by ∼32%) total heat released in the reactions of the materials treated with fluoroethylene carbonate (FEC)-dimethyl carbonate (DEC)/LiPF6 electrolyte solutions, thus implying their significant surface stabilization because of the surface treatment. It was established by a postmortem analysis after 400 cycles that a lower amount of transition-metal cations dissolved (especially Ni) and a reduced number of surface cracks were formed for the 2 wt % TA-treated HE-NCMs compared to the untreated ones. We consider the proposed method of surface modification as a simple, cheap, and scalable approach to achieve a steady and superior electrochemical performance of HE-NCM cathodes.

Properties of Thin Lithium Metal Electrodes in Carbonate Electrolytes with Realistic Parameters.

To understand the baseline performance of lithium (Li) anode in liquid electrolytes, the electrochemical and physical properties of the Li anode are studied with realistic parameters, including thin thickness (50 μm), practical areal capacity (1-4 mA h cm-2), practical areal current (0.5-2 mA cm-2), and low electrolyte/capacity ratio. Two different Li salts, lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), are used to probe the effects of the electrolyte chemistry and concentration. The cycling of Li/Li symmetric cells, combined with the scanning electron microscopic investigation, demonstrates that the soft-short of Li/Li cells is induced by the continuous volume expansion of Li electrodes during cycling instead of dendrites. The volume change of a Li electrode is dictated by the depth of deposition and stripping (i.e., areal capacity) and the electrolyte/capacity ratio, with no strong correlation with the type of Li salt and concentration. On the other hand, the average Coulombic efficiency (CE) measurement demonstrates inherent correlation with the type of Li salt and its concentration in the electrolyte. Li electrode surface chemical analysis indicates that the fluoride-rich surface layer formed in the LiPF6 electrolyte can be detrimental to both CE and Li deposition-stripping overpotential.

Efficient and Facile Electrochemical Process for the Production of High-Quality Lithium Hexafluorophosphate Electrolyte.

The global consumption for lithium hexafluorophosphate (LiPF6) has increased dramatically with the rapid growth of Li-ion batteries (LIBs) for large-scale electric energy storage applications. Conventional LiPF6 production has a high cost and high energy consumption due to complicated separation and purification processes. Here, based on the electrode materials of LiMn2O4 and polyaniline (PANI), we propose a facile electrochemical extraction/release process for LiPF6 electrolyte production. This new technology consists of two independent steps: a PF6-- and Li+-extracting step using a PANI/LixMn2O4 cell in aqueous solution (an ion extraction step) and a LiPF6 electrolyte production step from the charged LiMn2O4/PANI+PF6- cell in an organic electrolyte (an ion release step). This new process can effectively avoid the contamination of HF residue in the final product, providing a great possibility to create a facile, energy-efficient, and low-cost LiPF6 electrolyte production.

Nonwoven rGO Fiber‐Aramid Separator for High‐Speed Charging and Discharging of Li Metal Anode

AbstractLi metal, which has a high theoretical specific capacity and low redox potential, is considered to the most promising anode material for next‐generation Li ion‐based batteries. However, it also exhibits a disadvantageous solid electrolyte interphase (SEI) layer problem that needs to be resolved. Herein, an advanced separator composed of reduced graphene oxide fiber attached to aramid paper (rGOF‐A) is introduced. When rGOF‐A is applied, F− anions, generated from the decomposition of the LiPF6 electrolyte during the SEI layer formation process form semi‐ionic CF bonds along the surface of rGOF. As Li+ ions are plated, the “F‐doped” rGO surface induces the formation of LiF, which is known as a component of a chemically stable SEI, therefore it helps the Li metal anode to operate stably at a high current of 20 mA cm−2 with a high capacity of 20 mAh cm−2. The proposed rGOF‐A separator successfully achieves a stable SEI layer that could resolve the interfacial issues of the Li metal anode.

Dual-Functional Electrolyte Additives toward Long-Cycling Lithium-Ion Batteries: Ecofriendly Designed Carbonate Derivatives.

Long-term stability of the solid electrolyte interphase (SEI) and cathode-electrolyte interface (CEI) layers formed on anodes and cathodes is imperative to mitigate the interfacial degradation of electrodes and enhance the cycle life of lithium-ion batteries (LIBs). However, the SEI on the anode and CEI on the cathode are vulnerable to the reactive species of PF5 and HF produced by the decomposition and hydrolysis of the conventional LiPF6 electrolyte in a battery inevitably containing a trace amount of water. Here, we report a new class of cyclic carbonate-based electrolyte additives to preserve the integrity of SEI and CEI in LIBs. This new class of additives is designed and synthesized by an ecofriendly approach that involves fixing CO2 with functional epoxides bearing various reactive side chains. It was found that the cyclic carbonates of 3-(1-ethoxyethoxy)-1,2-propylene carbonate and 3-trimethoxysilylpropyloxy-1,2-propylene carbonate, possessing high capability for the stabilization of Lewis-acidic PF5, exhibit a capacity retention of 79.0% after 1000 cycles, which is superior to that of the pristine electrolyte of 54.7%. Moreover, TMSPC has HF-scavenging capability, which, along with PF5 stabilization, results in enhanced rate capability of commercial LiNi0.6Mn0.2Co0.2O2 (NCM622)/graphite full cells, posing a significant potential for high-energy-density LIBs with long cycle stability.

Direct Operando Observation of Double Layer Charging and Early Solid Electrolyte Interphase Formation in Li-Ion Battery Electrolytes.

The solid electrolyte interphase (SEI) is the most critical yet least understood component to guarantee stable and safe operation of a Li-ion cell. Herein, the early stages of SEI formation in a typical LiPF6 and organic carbonate-based Li-ion electrolyte are explored by operando surface-enhanced Raman spectroscopy, on-line electrochemical mass spectrometry, and electrochemical quartz crystal microbalance. The electric double layer is directly observed to charge as Li+ solvated by ethylene carbonate (EC) progressively accumulates at the negatively charged electrode surface. Further negative polarization triggers SEI formation, as evidenced by H2 evolution and electrode mass deposition. Electrolyte impurities, HF and H2O, are reduced early and contribute in a multistep (electro)chemical process to an inorganic SEI layer rich in LiF and Li2CO3. This study is a model example of how a combination of highly surface-sensitive operando characterization techniques offers a step forward to understand interfacial phenomena in Li-ion batteries.

Tailored Architectures to Stabilize Electrode-Electrolyte Interfaces in Cathode Materials for Li-Ion Batteries

The market for electric vehicles has increased significantly in the recent decade. Thus lithium-ion batteries with high energy and power density, with the ability to withstand extreme cycling environments are necessary to compete with the flexibility of the fossil fuel reliant combustion engine. The main instabilities in the Li-ion battery can be traced to the electrode-electrolyte interface, here electroactive transition metals react with the electrolyte resulting in irreversible transitions forming insulating layers, or solid cathode electrolyte interfaces (CEI), that inhibit ion transport. Cathode material dissolution may also occur at the surface due to acidic attack from the HF byproduct from the decomposition of the LiPF6 electrolyte. During electrochemical cycling, uneven lithium diffusion causes the surface to become more reduced than the core which leads to structural changes which impedes ion transport. These structural changes cause nonuniform contraction and expansion of the lattice loosening connections between the transition metal oxide layers eventually leading to severe macroscopic cracking. This effect has been seen at lower cycling rates when particle size is increased. The cracks allow the electrolyte to permeate the particle allowing CEI formation within the particle greatly decreasing the cathode life.A solution to these detrimental surface interactions is by replacing the electroactive transition metal content at the surface with inactive ions improving the interfacial stability. To prevent significant decreases in storage capacity the coating is a thin passivating barrier. Previously our group has introduced a strategy toward stabilizing the electrode-electrolyte interface using Ni0.25Mn0.25Co0.50O nanocrystals (NC) of active material. Each individual NC is passivated by an epitaxial grown conformal ultrathin Al2O3 shell with a final composition of LiCo0.5Ni0.25Mn0.25O2 with a concentration gradient of Al3+ ions toward the outer layers after high temperature lithiation. This material showed increased cycling stability under harsh conditions of increased cycle rate and temperature. While this research had promising results, industrial methods are currently better suited to produce well defined dense secondary particle structures with a spherical morphology, made up of agglomerated nanoparticles. While many coating methods being researched on these secondary structures require coating materials to be deposited on as-made, pre-lithiated cathode material, this method makes it difficult to completely coat all surfaces, while losing the ability to control surface chemistry and homogeneity. Here an optimized systematic study was performed to form an aluminum shell in the same process of growth of NixMnzCoy(OH)2 (NMC) precursors. This procedure affords precise control over shell thickness and concentration gradient architectures. The core-shell precursors are reacted with LiOH in a high-temperature solid-state reaction, allowing the aluminum shell to diffuse into the surface lattice which will further suppress phase distortion in the bulk. The higher concentration of Al3+ at the surface protects against side reactions with the electrolyte. These secondary structured LiNi0.25Mn0.25Co0.50O2 were electrochemically tested using both Li-metal half cells and graphite anode full cells and the results were compared to nanocrystalline primary particles of a similar composition.While aluminum coatings have been studied on cathode material previously, it is still a challenge to determine finite spatial changes in distribution of elements within individual particles in 3D with current conventional methods available, such as SEM-EDS analysis. In this study, synchrotron-based imaging methods of X-ray fluorescence (XRF) nanoprobe cross-sectional mapping, XRF tomography, and transmission X-ray elemental tomography were used to evaluate aluminum coated gradient NMC material and other stabilized architectures of interest such as full concentration gradient NMC material. For tomographic measurements particles were loaded into 50-micron capillaries allowing for high throughput imaging. These techniques allowed for little sample manipulation which preserved sample morphology in pristine state. Increased resolution offered further insight into elemental distribution and extent of aluminum migration after high temperature lithiation. Advancements in these imaging techniques can better inform the future of stabilized cathode architecture design. Figure 1

2-Fluoropyridine: A novel electrolyte additive for lithium metal batteries with high areal capacity as well as high cycling stability

Abstract Development of high energy density lithium metal batteries (LMBs) with high cycling stability is becoming more and more important. In this study, a novel and reliable electrolyte additive, 2-Fluoropyridine (2-FP), was successfully applied to enhance the stability of different commercial liquid electrolytes and effectively improve the performance of LMBs for the first time. The 2-FP additive was found to play a critical role in the decrease of Li nucleation as well as deposition overpotential, and finally supressing the Li-dendrites. As a result, the high-voltage LiNi1/3Mn1/3Co1/3O2 cathode (1.5 mAh cm−2)|Li metal cell using the commercial carbonate-based LiPF6 electrolyte with 2% of 2-FP additive exhibited a stable capacity retention of 67.6% even after 300-cycle test with a coulombic efficiency as high as 99.89% at 0.75 mA cm−2. Meanwhile, in the case using another commercial ether-based LiTFSI electrolyte with it, the LiFePO4 cathode (1.5 mAh cm−2)|Li metal cell also maintained long-term stability with high coulombic efficiency and the discharge capacity even with a small electrolyte amount and a high current density of 1.5 mA cm−2. By combining the surface analysis with quantum chemistry calculations, it is verified that the stabilization effect by introduction of this additive at the extreme condition was resulted from the formation of a robust and stable solid electrolyte interphase (SEI), in which the LiF and Li3N components could play a synergistic role in the improvement of SEI layer performance. Such a fluoropyridine molecule with good compatibility in the LMBs is expected to be a promising electrolyte additive for the next generation of LMBs.

Analysis of Charging/Discharging Supercapacitor Active Carbon/rGO Based on Natural Materials

Active carbon/rGO based on natural materials as coconut shell has been assembled with a coin cell in shape of prototype supercapacitor. The physical feature of active carbon/rGO electrode were characterized by FTIR, and FESEM. The Electrochemical performance of supercapacitor in 1 M LiPF6 electrolyte solution with density current of 12 mA/g until 163 mA/g were analyzed by galvanostatic charge-discharge test. The result showed that active carbon/rGO had absorption peaks at wave numbers 1592.27 cm−1 and 1288.45 cm−1 which were functional groups as C = C and C-O. The morphology of activated carbon has been covered by the presence of rGO that determines the agglomeration of rGO around the pore of activated carbon so that it affects the performance of supercapacitors. Supercapacitor has a specific capacitance charging of 20.5 F/g, and discharging of 19 F/g in density current 12 mA/g.

Mixed Lithium Salts Electrolyte Improves the High-Temperature Performance of Nickel-Rich Based Lithium-Ion Batteries

The long-term cycle performance of NCM811/Li batteries at high temperature was achieved by mixing LiDFOB and LiPF6 salts into the ethylene carbonate (EC) and ethyl methyl carbonate (EMC) solution (EC/EMC = 3:7 by volume). The differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) tests indicate 0.8 M LiPF6/0.2 M LiDFOB electrolyte system could improve thermal stability. The NCM811 cell with the mixed lithium salts electrolyte shows superior high temperature cycling performance, as demonstrated by the high capacity retention (89.00%) after 100 cycles at 0.5 C, which is much better than that of the 1.0 M LiPF6 electrolyte (51.34%). Inductively coupled plasma (ICP), Scanning electron microscopy (SEM) and other spectroscopic analyses reveal that adding LiDFOB salt could suppress Ni/Co/Mn dissolution into the electrolyte, due to the LiDFOB salt can be decomposed to produce a protective CEI layer on NCM811 surface. These results show that mixed lithium salts (LiDFOB and LiPF6) is an efficient solution to enhance the high temperature performance of nickel-rich based lithium-ion batteries.

Assessing the Oxidation Behavior of EC:DMC Based Electrolyte on Non-Catalytically Active Surface

The race for developing Li-ion batteries positive electrodes with always greater energy density has recently renewed interest towards understanding the formation of the so-called cathode electrolyte interface (CEI) forming upon cycling at high potential. In this work, we used an approach combining electrochemical measurements with physical characterizations to study the different anodic events occurring for the state-of-the-art EC:DMC 1M LiPF6 (LP30) electrolyte. Doing so, we could find that EC-related species are first oxidized before the oxidation of DMC-related species at greater potential which forms a film relatively rich in organic polycarbonates species. Using a soluble redox probe, we could then demonstrate that while this organic layer is partially passivating, it is unstable with time and cycling. In fact, only reaching a potential as high as 5.4 V vs Li+/Li for several hours leads to the formation of a perfectly stable and passivating CEI.

Facile fabrication of thin metal oxide films on porous carbon for high density charge storage

In an effort to minimize the usage of non-renewable materials and to enhance the functionality of the renewable materials, we have developed thin metal oxide coated porous carbon derived from a highly abundant non-edible bio resource, i.e., palm kernel shell, using a one-step activation-coating procedure and demonstrated their superiority as a supercapacitive energy storage electrode. In a typical experiment, an optimized composition contained ~10 wt% of Mn2O3 on activated carbon (AC); a supercapacitor electrode fabricated using this electrode showed higher rate capability and more than twice specific capacitance than pure carbon electrode and could be cycled over 5000 cycles without any appreciable capacity loss in 1 M Na2SO4 electrolyte. A symmetric supercapacitor prototype developed using the optimum electrode showed nearly four times higher energy density than the pure carbon owing to the enhancements in voltage window and capacitance. A lithium ion capacitor fabricated in half-cell configuration using 1 M LiPF6 electrolyte showed larger voltage window, superior capacitance and rate capability in the ~10 wt% Mn2O3 @AC than the pure analogue. These results demonstrate that the current protocol allows fabrication of superior charge storing electrodes using renewable materials functionalized by minimum quantity of earthborn materials.