Commercial Graphite Electrodes Research Articles

Micron-sized secondary Si/C composite with in situ crosslinked polymeric binder for high-energy-density lithium-ion battery anode

Nanonization has been proven to be an effective approach in countering the drawbacks associated with volume change of silicon anodes. Considering the demand from practical applications, which not only involves high capacity and good cycling stability, but also includes facile process, high tap density, etc., it is highly desirable to fully take advantage of nano-sized silicon, while circumvent the side effects arisen from nanonization. We have successfully synthesized a micron-sized spherical composite (∼1–6 μm) via a facile spray-drying process, with nano-sized silicon embedded in a conductive matrix consisted of crosslinked binder and carbon. Volume change of silicon is largely buffered by the voids inside the structure, which secures silicon on its conductive network. More importantly, tap density of the secondary particle is three times that of the primary silicon nanoparticles, favoring its practical application in a lithium-ion battery. The composite displays a specific capacity of 1353 mAh g−1 after 500 cycles at 0.5C, which represents an 87% retention of its initial capacity. Full-cell lithium-ion batteries with the secondary composite and commercial cathode displays a high areal energy density of 10 mWh cm−2, while the thickness of the anode is only 1/3 that of commercial graphite electrode delivering the same areal energy density, which can be translated to a 39% increase in volumetric energy density in multi-stack batteries.

Design of Red Phosphorus Nanostructured Electrode for Fast-Charging Lithium-Ion Batteries with High Energy Density

Summary We propose that red phosphorus (P) is an ideal anode material for fast-charging lithium-ion batteries (LIBs) because of the combined advantages of high capacity (6,075 mAh cm−3) and relatively low yet safe lithiation potential (∼0.7 V versus Li/Li+). A red P/C nanocomposite has been fabricated, featuring amorphous red P nanodomains embedded in the nanopores of micrometer-scale porous conductive carbon with interior nanoscale void spaces, a conductive P-free carbon superficial layer, and a high tap density of 1.0 g cm−3. At an industrial-level areal capacity (3 mAh cm−2 or higher), a P/C electrode shows considerably better fast-charging capability than commercial graphite and Li4Ti5O12 electrodes, as well as much higher volumetric capacity and specific capacity based on the whole electrode. Meanwhile, our P/C electrode shows excellent long-term cycling stability with Coulombic efficiency of 100.0% (±0.1%) and 90% capacity retention from the 5th to 500th cycles.

Monolayer Zr2B2: A promising two-dimensional anode material for Li-ion batteries

Aiming to find an excellent anode material for Li-ion batteries, we report the two-dimensional Zr2B2 monolayer combining the density functional theory and crystal structure prediction techniques. We find that the monolayer Zr2B2 has initial metallicity and good stability, and keeps excellent electrical conductivity during the whole process of lithiation. The adsorption energy of lithium is −0.628 eV, which is enough to make sure the stability of the processing of lithiation. Furthermore, the ultralow diffusion energy barrier of Li ion on the surface of the monolayer Zr2B2 (17 meV) indicates an excellent charge-discharge rate. The theoretical specific capacity of 526 mA h g−1 is larger than that of the commercial graphite electrode. All these results propose the hexagonal monolayer Zr2B2 as an excellent anode material for Li-ion batteries.

Chitosan complements entrapment of silicon inside nitrogen doped carbon to improve and stabilize the capacity of Li-ion batteries

A facile strategy to entrap milled silicon (m-Si) particles using nitrogen-doped-carbon (N-C@m-Si) to overcome the dramatic volume changes in Si during intercalation of lithium ions and to improve its electronic conductivity is reported here. The only natural nitrogen containing biomaterial alkaline polysaccharide, i.e., chitosan, is used as the carbon source. Simple hydrothermal technique followed by a subsequent carbonization process is used to synthesize N-C and N-C@m-Si particles. N-C@m-Si exhibited significantly improved electrochemical performance as compared to bare m-Si, which is confirmed by the obtained discharge capacity of 942.4 mAh g−1 and columbic efficiency of 97% after 50 cycles at 0.1C rate. With regard to the N-C electrodes, the obtained discharge capacity of 485.34 mAh g−1 and columbic efficiency of 99.78%, after 50 cycles at 0.1C rate is superior to the commercial graphite electrodes. The solid electrolyte interphase (SEI) layer that formed over m-Si and N-C@m-Si electrodes is characterized using X-ray photoelectron spectroscopy. Compared to the SEI layer that formed over m-Si electrode after 10 charge-discharge cycles, the N-C@m-Si electrode had a stable lithium fluoride and carbonate species. Brief reaction mechanisms, representing the formation of different species in the SEI layer, is derived to explain its behavior during the electrochemical processes.

Effect of Defects on Diffusion Behaviors of Lithium-Ion Battery Electrodes: In Situ Optical Observation and Simulation.

Lithium-ion batteries (LIBs) with high energy efficiency are urgently needed in various fields. For the LIBs electrodes, defects would be generated during the manufacturing processes and mechanical degradation and significantly impact the stability and performance of the LIBs. However, the effects of electrode defects on the electrochemical processes are still not clear. Herein, an in situ optical observation system is developed for monitoring the Li diffusion around the preintroduced defects in the commercial graphite electrodes. The experiments show that the gas-filled defects vertical to the direction of the Li diffusion would obviously decelerate the Li diffusion, whereas the electrolyte-filled defects parallel to the direction of the Li diffusion would accelerate the Li diffusion. In addition, finite element analysis (FEA) suggests, consistent with the experiments, a nonuniform distribution of local Li concentration around the defect. The equivalent diffusivity obtained by the FEA is also dependent on the configuration of the defects. The diffusivities of the electrolyte-filled parallel defect and gas-filled vertical defect are 12.6 and 11.0%, respectively. For the gas-filled defects, the size-effect calculation manifests that the equivalent diffusivity would decrease with the enlarged defect size, and the shape of the defects would substantially impact the decrease rate. The results directly reveal the mechanisms of the defect-induced diffusion behavior change in the electrodes by the new equivalent two-dimensional experiments, and the equivalent diffusivity would be useful for optimizing the electrode designs in LIBs.

Planar Lithium Battery Cell Development to Advance in-Operando Nano-CT Imaging of Graphite Electrodes

In-operando nano-scale resolution X-ray computed tomography (nano-CT) imaging provides an excellent new possibility to investigate a wide variety of phenomena in the electrodes of Li-ion batteries. The 3D X-ray imaging provides direct observation of internal morphological changes in electrodes with up to 50 nm resolution regarding standard materials and electrolyte, which is difficult or impossible to achieve by electron microscopy. Such fine resolution enables the possibility to observe detailed structural changes like the deposition of electrolyte decomposition products within the electrode, transition from Li intercalation to electroplating on graphite, and lithium dendrite formation and growth. One task for applying in-situ nano-CT imaging on Li-ion battery imaging is to develop special lithium battery cells compatible with both the nano-CT instrument’s sample size constraint and X-ray attenuation length limits of higher atomic number materials. Herein, we have developed a planar cell design that allows us to use commercial electrode, separator, and electrolyte. Successful charging and discharging has been achieved with this planar cell design using commercial graphite, LiMn2O4, and lithium foil electrodes. In-operando nano-CT imaging is performed on planar cell lithium battery with focus on graphite anodes. The experimental methodology developed in this study has applicability to test wide ranges of electrolyte, separators and other electrode materials in Li-ion batteries.

Physics-Based Modeling of Aging in NMC/Graphite Cell Under High Voltage Operation at Different Temperatures

The high demand on specific capacity and occasionally harsh environment in electric vehicles has detrimental effects on electrochemical, mechanical and thermal properties of NMC/graphite Li-ion batteries. The battery lifetime is reduced at high voltage and high temperature, both in terms of capacity fade and impedance increase. At the graphite electrode, the notion of SEI layer formation and growth leading to battery aging is widely accepted. On the other hand, aging effects on the NMC electrode needs to be investigated more thoroughly. Xiong et al. [1] reported that Li-ion cells could experience rapid failure due to impedance rise at the NMC electrode when cycled at an elevated temperature or a cut-off voltage above 4.2 V. A surface film formation for transition metal oxides, the growth of which accelerates upon high temperature and charge voltages, has been reported [2,3]. Literature also shows that the interaction between the positive and negative electrodes in full lithium-ion cells contribute to declined cell performance [4]. However, these aging mechanisms are not independently distinguishable. Therefore, it is important to be able to quantify each contribution and to decouple different aging mechanisms occurring on each electrode at different temperatures under high voltage condition. This study focuses on impedance behavior of commercial NMC111 (LiNi1/3Mn1/3Co1/3O2) and graphite electrodes in a small laboratory pouch cells. The NMC111/graphite in full-cell configuration are calendar aged and cycle aged between +3.8 V and +4.6 V vs. Li at 25 °C and 40 °C until 50% capacity fade is reached. Capacity and impedance behavior of the full cells are measured periodically in order to track the performance changes with aging. Each electrode is harvested at specific intervals of cycling stages and electrochemically characterized in symmetric cells by means of electrochemical impedance spectroscopy (EIS). A physics-based model is employed to parameterize aging parameters by fitting the EIS results from the symmetric cells using a least square fitting tool in COMSOL Multiphysics. The pseudo two-dimensional (P2D) model is an extension to the work of Doyle et al. [5] incorporating intercalation kinetics, mass and charge transport based on concentrated solution porous electrode theory. From the preliminary EIS results on NMC111 symmetric cells in Fig. 1, impedance increases at a small magnitude at 25 °C at the end of life (EOL) compared to the beginning of life (BOL). At 40 °C, however, large impedance rise at EOL is seen. On the other hand, it had been shown that capacity fade occurs at both temperatures during slow cycling on half-cells. The model optimization is firstly done for cells at BOL to deduce the aging-independent parameters. Towards EOL, the quantification of intrinsic physical aging properties such as the particle sizes, porosity, local contact resistance and surface film resistance which are the causes of impedance rise or capacity fade can be made. The potential effects of calendar aging on cell degradation is separated from the effects of cycle aging. The comparison with experimental capacity loss and impedance rise will further validate the model. The extraction of the parameters from the model enables deduction of different aging-induced mechanisms at each electrode. This quantitative analysis of aging behavior will contribute to improved lifetime predictive model for NMC111/graphite lithium-ion batteries. [1] D. J. Xiong, R. Petibon, M. Nie, L. Ma, J. Xia, J.R. Dahn, J. Electrochem. Soc. 163 (2016), 3, A546-A551 [2] P. Niehoff, M. Winter, Langmuir 29 (2013), 51, 15813-15821 [3] M. Wohlfahrt-Mehrens, C. Vogler, J. Garche, J. Power Sources 127 (2004) 58-64 [4] K. Xu, Chem. Rev. 114 (2014) 11503-11618 [5] M. Doyle, J. Newman, A. C. Gozdz, C. N. Schmutz, J.-M. Tarascon, J. Electrochem. Soc. 143 (1996) 1890–1903. Figure 1

Lithium Ion Carbon Electrodes from Virtual Cathode Deposition

Commercial graphite electrodes exhibit insufficient energy density to meet future automotive battery targets. Herein we explore the electrochemical characteristics of a stable high energy density carbon battery anode layer directly prepared by PVD related Virtual Cathode Deposition technique. The novel form of carbon prepared by VCD enables access to a specific capacity much higher than the graphite theoretical value of 375mAhg-1 while having high coulombic efficiency and lifetime. Lithium ion diffusion was derived from a range of electrochemical methods and compared with ex-situ results. Our ex-situ analysis provides further insight into the differences between VCD prepared carbon and conventional graphite anodes.

Contribution of Combined Surface Analysis to the Understanding of Degradation Mechanisms of Li-Ion Negative Electrodes

Li-ion technology is among the most commercially viable solutions for electrochemical storage, particularly for the electric vehicle (VE) market. The fading of such systems is often related to the degradation of the electrode active materials in various ageing conditions; it is thus mandatory to better understand the causes of these failures. It is well known that the nature and amount of the solid electrolyte interphase (SEI) which forms at the surface of the active material during cycling, can be one of the main issues preventing durability of the cells. For that purpose, our lab is actively working on the characterization of such degradation mechanisms, trying to understand some fundamental aspects of lithiation or lithiation loss mechanisms, nature and dynamics of the SEI etc. Previous works allowed us to describe some fundamental aspects of silicon electrodes degradation in various configurations by using XPS, AES and ToF-SIMS combined with in situ FIB (known as FIB-ToF-SIMS) cross analysis [1-3]. This has recently been applied to the study of commercial graphite electrodes [4]. In this study, the electrodes have been cycled (vs NMC positive electrodes) at 5°C following 2 end-of-voltage windows strategies: 2.70V-4.20V (0%SOC-100%SOC), 3.42V-4.08V (10%SOC-90%SOC).The relationship between the end-of-voltage windows and the SOC limits were measured in the beginning of life at 25°C, and so these voltage ranges do not correspond strictly to specified SOC ranges for other temperatures, C-rates, or after ageing. It is observed that the former are fading a lot faster than the latter (cycled in the limited 3.42-4.08 V potential range). The relationship between the end-of-voltage windows and the SOC limits were measured in the beginning of life at 25°C, and so these voltage ranges do not correspond strictly to specified SOC ranges for other temperatures, C-rates, or after ageing. It is observed that the former are fading a lot faster than the latter (cycled in the limited 3.42-4.08 V potential range). ). A complete characterization study, involving also XRD and NMR, showed that the generation of SEI is much more important between 90 and 100% SOC, inducing lithium trapping in the graphite particles while also favoring some lithium plating. A scheme (Fig.1) has been proposed to explain the evolution of such electrodes in these particular cycling conditions. These results show the high impact of cycling policy on the integrity of Li-ion cells. They also emphasize the ability of FIB-ToF-SIMS, used in combination with XPS (as used in [2] and [4] but applied in this study to graphite electrodes), to unveil the underlying ageing mechanisms of Li-ion negative electrodes. [1] E. Radvanyi et al, Phys. Chem. Chem. Phys., 2014,16, 17142-17153 [2] A. Bordes et al, Chem. Mater., 2016, 28 (5), 1566-1573 [3] N. Dupré et al, Chem. Mater., 2016, 28 (8), 2557-2572 [4] B. Pilipili Matadi et al, J. Electrochem. Soc., 2017, 164 (12), A2374-A2389 Figure 1

3D Porous Cu–Zn Alloys as Alternative Anode Materials for Li‐Ion Batteries with Superior Low T Performance

AbstractZinc is recently gaining interest in the battery community as potential alternative anode material, because of its large natural abundance and potentially larger volumetric density than graphite. Nevertheless, pure Zn anodes have shown so far very poor cycling performance. Here, the electrochemical performance of Zn‐rich porous Cu–Zn alloys electrodeposited by an environmentally friendly (aqueous) dynamic hydrogen bubble template method is reported. The lithiation/delithiation mechanism is studied in detail by both in situ and ex situ X‐ray diffraction, indicating the reversible displacement of Zn from the Cu–Zn alloy upon reaction with Li. The influence of the alloy composition on the performance of carbon‐ and binder‐free electrodes is also investigated. The optimal Cu:Zn atomic ratio is found to be 18:82, which provides impressive rate capability up to 10 A g−1 (≈30C), and promising capacity retention upon more than 500 cycles. The high electronic conductivity provided by Cu, and the porous electrode morphology also enable superior lithium storage capability at low temperature. Cu18Zn82 can indeed steadily deliver ≈200 mAh g−1 at −20 °C, whereas an analogous commercial graphite electrode rapidly fades to only 12 mAh g−1.

Computational and Experimental Observation of Li‐Ion Concentration Distribution and Diffusion‐Induced Stress in Porous Battery Electrodes

AbstractA multiscale model of porous electrodes based on the Gibbs free energy is developed, in which the Li ion diffusion, diffusion‐induced stress (DIS), and polydispersities of electrode particle sizes are considered. The relationships between the size polydispersities and the concentration profiles and DIS evolution are investigated numerically. Li ion distributions are verified by in situ observation of color changes in a commercial porous graphite electrode. Simulations show small particles exhibit higher charge/discharge degrees and more rapid charge/discharge rates than large particles at the same macroscopic state of charge (SOC)/depth of discharge (DOD). Moreover, DIS is different in different size particles at a specific SOC and DOD, that is, there is a nonuniformly distributed stress field within porous electrodes during the charge/discharge processes. For SOC and DOD, which represent the macroscopic average states of charge and discharge, the influence of the microscopic SOC values and mass fractions of differently sized particles in porous electrodes should, therefore, be considered. Additionally, the fracture of particles in porous electrodes is likely caused by varied amplitude tensile‐compressive DISs during charge/discharge cycles. Reduced sizes and size polydispersities of electrode particles are prone to alleviate these stresses and thus improve battery performance.

Hierarchical MoS2-Carbon Microspheres: A Robust Anode for High Performance Lithium Ion Battery

With higher theoretical lithium ion capacity of 670 mAh g–1 comparing with commercial graphite electrodes, molybdenum disulfide (MoS2) may be a promising alternative for lithium ion batteries (LIBs) because it offers unique layered crystal structure with Mo atoms sandwiched between two layers of closely packed S atoms and the MoS2 layers are linked by weak van der Waals interaction. The large and tunable distance between layers enables the anticipated excellent rate and cycling stability because they can promote the reversible lithium ion intercalation and de-intercalation without huge volume change and consequently prevents the pulverization of active materials during the repeated charge and discharge processes. However, either bulk or nanoscale MoS2 delivers poor conductivity for the electron/ion transfer, thus leading to obvious capacity loss after several cycles. Moreover, the MoS2 based electrodes provide high capacity through similar electrochemical redox reactions with lithium sulfide batteries in essence, which may also lead to their degradation by the polysulfide shuttling effect. To overcome these barriers, numerous efforts have been devoted into the engineering of MoS2 nanostructures with optimized electrochemical performances. One effective strategy is to make the MoS2 into a few expanded layers, which provides a larger surface area, shorter lithium ions diffusion path and thus improved kinetics. On the other hand, combining conductive materials such as carbon or polymer with MoS2 will necessarily enhance the electron transport, cycling stability, structural integrity during the lithium-ion insertion/extraction processes. Herein, we prepared hierarchical MoS2-carbon microspheres via continuous and scalable ultrasonic nebulization route. The structure, composition, electrochemical properties are investigated in detail. The MoS2-carbon microspheres consist of MoS2 nanosheets with a few layers bridged by carbon (15 wt%), which separates the exfoliated MoS2 layers and prevents their aggregation and restacking. The novel architecture offers additional merits such as overall large size, high packing density, which promote their practical applications. The MoS2-C microspheres have been demonstrated to deliver excellent electrochemical performances in terms of low resistance, high capacity even at large current density, stable cycling performances, etc. The electrodes exhibited 800 mAh g–1 at 1000 mA g–1 over 170 cycles. At higher current density of 3200 mA g–1, a capacity of 730 mAh g–1 can be also maintained. The MoS2-C microspheres are practically applicable not only because of the continuous and large scale synthesis via current strategy, but also the robust and integrated architecture which ensures the excellent electrochemical properties.

Hierarchical Molybedenum Sulfide - Carbon Microspheres for High Performance Lithium Ion Battery Anode

With higher theoretical lithium ion capacity of 670 mAh g–1 comparing with commercial graphite electrodes, molybdenum disulfide (MoS2) may be a promising alternative for lithium ion batteries (LIBs) because it offers unique layered crystal structure with Mo atoms sandwiched between two layers of closely packed S atoms and the MoS2 layers are linked by weak van der Waals interaction. Either bulk or nanoscale MoS2 delivers poor conductivity for the electron/ion transfer, thus leading to obvious capacity loss after several cycles. To overcome these barriers, numerous efforts have been devoted into the engineering of MoS2 nanostructures with optimized electrochemical performances. Herein, we prepared hierarchical MoS2-carbon microspheres via continuous and scalable ultrasonic nebulization route. The structure, composition, electrochemical properties are investigated in detail. The MoS2-carbon microspheres consist of MoS2 nanosheets with a few layers bridged by carbon (15 wt%), which separates the exfoliated MoS2 layers and prevents their aggregation and restacking. The novel architecture offers additional merits such as overall large size, high packing density, which promote their practical applications. The MoS2-carbon microspheres have been demonstrated to deliver excellent electrochemical performances in terms of low resistance, high capacity even at large current density, ultrastable cycling over hundreds of cycles, etc. Specifically, the electrodes exhibited over 900, 800 mAh g–1 at 200, 1600 mA g–1 over 500 cycles, respectively. At higher current density of 3200 mA g–1, a capacity of 730 mAh g–1 can be also maintained. The MoS2-carbon microspheres are practically applicable not only because of the continuous and large scale synthesis via current strategy, but also the robust and integrated architecture which ensures the excellent electrochemical properties.

Effect of Pressure on Lithium-Ion Battery Ageing

Lithium-ion batteries can age non-uniformly posing additional challenge in managing larger battery cells. For instance, a non-uniform distribution of solid electrolyte interphase (SEI) or plated lithium has been observed in cylindrical cells along the jelly roll length (1-2). The authors have suggested pressure distribution as a cause of this non-uniform ageing. This necessitates investigation of the effect of pressure on ageing. With different goals in mind, the effect of pressure on the rate of lithium-ion battery ageing has been studied previously (3-4).The work by Rubino et al.(3) indicates that the higher capacity fade in prismatic cells as compared to cylindrical cells of the same chemistry is due to the lower pressure in the former. However, the pressure was not a directly controlled parameter in this study. In contrast, the work by Arnold et al. (4) on commercial pouch cells shows that high stack pressure causes higher capacity fade, and that a small stack pressure is important to extend the life-time. However, the pouch cells were constrained along the thickness inducing non-uniform pressure on the different electrode layers and varying amplitudes of cyclic stack pressure during charge and discharge that is proportional to the external pressure. Hence, the above discrepancy of the effect of pressure calls for further investigation on ageing of model systems with single layer cells subjected to different levels of constant pressure. As an additional contribution, postmortem analysis is performed in order to understand how pressure level affects ageing mechanism.Here we present a study on commercial NMC positive and graphite negative electrodes in small laboratory pouch cells. The pouch cells are subjected to different stack pressure levels at controlled temperature using spring loaded stainless steel plates. Additionally, in order to monitor any differences in current distribution due to pressure and ageing, groups of cells are connected in parallel as the current distribution is measured using high precision shunt resistors and a Keithly differential multimeter. Capacity and impedance are measured periodically in order to track the performance changes with aging. A preliminary result indicates higher capacity fade in cells subjected to lower stack pressure. Results from EIS test indicate an increased ohmic resistance for high stack pressure cells, while low stack pressure cells show an increase in charge transfer resistance. Furthermore, different stack pressure on the cells of a parallel connected cell configuration results in current distribution with the cell subjected lower pressure taking slightly larger share of current. Details of the experimental techniques, and results from electrochemical and post mortem analysis will be presented and discussed during the meeting. Conclusions from this study will contribute to better understanding of the causes of non-uniform aging and suggestion for solutions to this problem through better cell design.

Graphene Based Yolk-Shell Free-Standing Tin Anode Electrodes for High Capacity Li-Ion Batteries

The research on graphene has become one of the most attractive scientific topics at present, because this new carbon material possesses unique physicochemical properties which impart it with great potentials in various application areas. The application of graphene in energy storage materials, such as electrode active materials in Li ion battery, is believed to be a promising field with a huge market. The ultra-thin graphene layers with graphitic basal structure may favor a higher accommodation sites and a faster migration rate of Li ions during charge-discharge processes while keeping high electron conductivity, comparing with conventional graphite anodes. Therefore, graphene offers a new option to carbon-based anode materials in Li ion batteries. Since 2008, several research groups have studied the electrochemical properties of graphene anode materials. It was found that graphene powders could deliver a higher specific capacity than graphite, which was suitable for high-capacity Li ion batteries. On the contrary, graphene paper with a much denser stacking of graphene sheets comparing with powders shows apparently lower storage capacity. Accordingly, it is speculated that the morphology and the 3D construction manner of graphene is crucial to its charge-discharge characteristics. It is also well known that novel electrode materials with low cost, high capacity and easy to be produced at large scale is needed in order to meet the increasing energy storage demand. Metallic structures such as Sn, Ge, Si, Al, Sb and etc. have higher specific capacity than commercial graphite anode electrodes. Among these electrodes tin anodes have attracted much attention because it delivers a capacity up to three times higher than that of graphite. Theoretically, one tin atom can maximally react with 4.4 lithium atoms to form Li4.4Sn alloy, reaching a capacity of 993 mAh/g. However, the large amount of lithium insertion/extraction into/from Sn causes a large volume change (about 300%), which causes pulverization of tin particles and loss of contact with current collector, resulting in poor electrochemical performance. In this study, a “yolk-shell” structure for a stabilized and scalable tin anode is designed. Tin nanoparticles (∼8-20 nm) as the “yolk” were produced through a facile chemical reduction synthesis method. The surfaces of the tin nanoparticles firstly coated with a SiO2 sacrificial layer and the obtained composite nano tin/SiO2 particles were subjected to microwave hydrothermal carburization in order to obtain the shell structure. The as-synthesized nanocomposite particles were then subsequently treated with hydrofluoric acid in order to selectively remove the SiO2sacrificial layer and the tin/C yolk shell structure is obtained. As synthesized graphene oxide and carbon coated Sn was dispersed in 50 mL bidistilled water by the aid of 80 mg of SDS (Sodium dodecyl sulfate) surfactant and sonicated to form a well-dispersed suspension. In order to produce Sn/graphene paper, the as-synthesized graphene oxide paper was chemically reduced immediately after filtration by hydrazine solution. 2.0 M, 50 mL hydrazine solution slowly poured on to membrane supported graphene oxide paper and filtered via vacuum technique. The surface and cross-section morphologies of the produced sample electrodes were observed by scanning electron microscopy (SEM, Jeol 6060 LV). The phase structures of the samples were investigated by X-ray diffraction (XRD) (Rigaku D/MAX 2000 with thin film attachment) with CuKa radiation. Coin type CR2016 cells were assembled in an argon-filled glove box. The electrolyte solution was 1 M LiPF6 in EC/DMC (1:1 by volume). The electrochemical performance of the tin-C/Graphene nanocomposites was evaluated by galvanostatic discharge–charge measurement using a computer-controlled battery tester between 0.02 and 2.5 V using metallic lithium as the counter electrode. The cells were cyclically tested on a MTI Model BST8-MA electrochemical analyzer using 1C (18 mA/dm2) current density over a voltage range of 0.02–2.5 V. After being cycled for 50 cycles, electrochemical impedance spectroscopy (EIS) was conducted on coin cells using an electrochemical workstation (Gamry Instruments Reference 3000) over a frequency range from 100 kHz to 0.001 Hz with an ac amplitude of 5 mV. The measured voltage was about 0.2V after the cells were relaxed for 1 h. The data has been normalized and referred per unit of mass for the purpose of comparison. Cyclic voltammograms (CVs) were recorded on an electrochemical workstation (Gamry Instruments Reference 3000) at a scan rate of 0.5 mVs−1 between 0.02 and 2.5 V. All the potentials indicated here were referred to the Li/Li+ electrode potential. All electrochemistry tests were carried out at room temperature (25 °C). Keywords: Yolk-Shell, Tin/C/Graphene, Free-standing, Anode Electrode, Li-ion.

Electrochemical Modeling of Commercial LiFePO4 and Graphite Electrodes: Kinetic and Transport Properties and Their Temperature Dependence

Based on the variable solid-state diffusivity concept, a semi-physical model is developed to simulate the electrochemical performance of commercial LiFePO4 (LFP) and graphite electrodes. Although the developed model is not accurately describing the phase change process within the active material, it is reliable for engineering applications such as battery management, thermal analysis and management, and aging studies. The developed LFP and graphite models extend previous works by validating the models against galvanostatic charge/discharge experiments conducted at various currents (C/5 to 5C) and temperatures (10°C, 23°C, 35°C, and 45°C). The fidelity of the model is confirmed by the satisfactory fit of the model to the experimental data for two different materials over a wide range of operating conditions. Temperature dependency of transport and kinetic properties of LFP and graphite is analyzed, and yields the activation energies of 86 kJ mol−1 and 20 kJ mol−1 for diffusion of intercalated species in LFP and graphite particles, respectively. The activation energies for charge transfer reaction at the surface of LFP and graphite particles are also found to be 9 kJ mol−1 and 20 kJ mol−1, respectively. The estimated kinetic and transport parameters and their temperature dependencies can be reliably used in thermal, electrochemical, or aging modeling of batteries involving these two materials.

Borophene as an extremely high capacity electrode material for Li-ion and Na-ion batteries.

"Two-dimensional (2D) materials as electrodes" is believed to be the trend for future Li-ion and Na-ion battery technologies. Here, by using first-principles methods, we predict that the recently reported borophene (2D boron sheets) can serve as an ideal electrode material with high electrochemical performance for both Li-ion and Na-ion batteries. The calculations are performed on two experimentally stable borophene structures, namely β12 and χ3 structures. The optimized Li and Na adsorption sites are identified, and the host materials are found to maintain good electric conductivity before and after adsorption. Besides advantages including small diffusion barriers and low average open-circuit voltages, most remarkably, the storage capacity can be as high as 1984 mA h g(-1) in β12 borophene and 1240 mA h g(-1) in χ3 borophene for both Li and Na, which are several times higher than the commercial graphite electrode and are the highest among all the 2D materials discovered to date. Our results highly support that borophenes can be appealing anode materials for both Li-ion and Na-ion batteries with extremely high power density.

High-performance characteristics of silicon inverse opal synthesized by the simple magnesium reduction as anodes for lithium-ion batteries

Inverse silicon opal (ISi) and carbon-coated inverse Si opal (C–ISi) structures are prepared from the simple thermal reduction method using magnesium and investigated as the anode materials in lithium-ion batteries. The ISi and C–ISi samples comprise continuously arranged inverse opal structures, constructed by Si nanoparticles. The macroporous structures in ∼1 μm range are favourable for lithium-ion transport and more importantly for absorbing volumetric change in the silicon nanoparticles. Moreover, the carbon coating on the inverse Si opal improves the electrical conductivity and acts as a mechanical buffer for the volume change. C–ISi sample shows a high capacity of 1550 mAh g−1 at the 100th cycle with very stable cycle retention, whereas the ISi and pristine Si samples show 1146.4 mAh g−1 and approximately zero, respectively, at the 100th cycle with rapid capacity fading. Surprisingly, the volumetric expansion of C–ISi electrode after 100th cycles is only 16.1%, which is as low as that for commercial graphite electrodes.

Catalyst Ni-assisted synthesis of interweaved SiO/G/CNTs&CNFs composite as anode material for lithium-ion batteries

An interweaved silicon monoxide/graphite/carbon nanotubes&carbon nanofibers (SiO/G/CNTs&CNFs) composite has been easily synthesized by using high-energy wet ball milling, spray drying in combination with a subsequent chemical vapor deposition method. CNTs&CNFs grow on the interface and the internal interspace of the spherical composite composed of SiO and graphite during the calcination process. The existence of CNTs&CNFs and graphite not only provides a buffer medium to accommodate the volume expansion of SiO during the electrochemical reaction process, but also provides high electrical conductivity for electrode material. When used as an anode material, a reversible specific capacity is approximate 672.3 mAh g−1 after 100 cycles at a current density of 100 mA g−1, which is about 1.8 times larger than that of the commercial graphite electrode (372 mA g−1). Due to the facile synthesis process of the composite and excellent performance of the as-prepared electrode, great commercial potential is envisioned.

Electrochemical Performance of Commercial Carbon Fibers Towards Usage As Electrodes in Structural Li-Ion Batteries

There is a continuing and growing demand for new and improved battery technologies. Extensive research is dedicated to pushing the limits of Li-ion batteries in terms of safety, environmental aspects, cost, lifetime and performance. A lot of the focus lies on improving graphite and other types of carbon-based electrodes [1-2] and extensive research has been on going since the beginning of the 90’s. Another possible route is improving technologies on a system level by introducing multifunctional materials. One way to do this is with structural batteries, where a battery can replace a load-bearing component in an electric or a hybrid electric vehicle for instance, and still maintaining the battery function. This way the weight is reduced (as well as freeing up space) on a system level and the overall performance is increased. A trade off between mechanical and electrochemical properties is expected, however, to increase overall effectiveness the performance of the battery does not need to be on par with a state of the art Li-ion battery. This concept of utilizing multifunctional materials in battery applications for instance has previously been studied with various methods and results [3-5]. This work focuses on investigating the electrochemical properties of commercial PAN based carbon fibers as electrodes for a future structural application. The cycleability and lifetime of the battery are two important factors for this concept to be realized. The focus is on evaluating the coulombic efficiency of carbon fibers which previous studies [6-8] has shown to have a good capacity as well as mechanical properties. The capacity was determined to be around 80% of the theoretical capacity of commercial graphite electrodes when cycled at a C/10 rate (fully charged in ten hours). One of the most promising carbon fibers is IMS65, which is an intermediate modulus fiber with a high strength and stiffness. The combination of good mechanical and electrochemical properties makes this fiber (and other similar) a very promising candidate for a structural battery application, which is the background to the work currently being done. The goal of this work is thus to thoroughly examine the electrochemical properties, in particular the coulombic efficiency, of commercially available carbon fibers to find a good candidate for usage in a structural battery application in terms of lifetime, power and capacity. The methodology utilizes a half-cell setup where the carbon fibers are used as working electrode and lithium foil as counter electrode. A glass-microfiber filter is used as a separator and the liquid electrolyte is 1.0 M LiPf6in EC/DEC (1:1 by weight, Selectilyte LP40) with and without VC (Vinylene Carbonate) added as an electrolyte additive. The cell is placed in a heat box with a controlled temperature and cycled in a high precision charger setup to accurately determine the coulombic efficiency and capacity of the carbon fibers. In a final concept, a liquid electrolyte cannot be used if the battery is to have structural properties as well. Instead, utilizing a solid polymer electrolyte is proposed. The effect of the solid polymer electrolyte on the electrochemical performance will therefore also be presented. Other important parameters studied are the surface coating (normally a sizing of epoxy or polyurethane) and epoxy tabbing (for tensile testing) of the fibers and its effect on the electrochemical properties. [1] T. Iijima, K. Suzuki and Y. Matsuda, Synthetic metals, 73, 9-20 (1995) [2] J. S. Kim, W. Y. Yoon, K. Soo Yoo, G. S. Park, C. W. Lee, Y. Murakamia and D. Shindo, Journal of power sources, 104, 175-180 (2002) [3] J. F. Snyder, E. L. Wong, C. W. Hubbard, Journal of The Electrochemical Society, 156, A215-A224 (2009) [4] P. Liu, E. Sherman and A. Jacob, Journal of Power Sources, 189, 646-650 (2009) [5] S. M. Shalouf, J. Zhang and C. H. Wang, Plastics, Rubber and Composites, 43, 98-104 (2014) [6] M. h. Kjell, E. Jacques, D. Zenkert, M. Behm and G. Lindbergh, Journal of The Electrochemical Society, 158 (12), A1455-A1460 (2011) [7] E. Jacques, M. H. Kjell, D. Zenkert, G. Lindbergh and M. Behm, Carbon, 59, 246-254 (2013) [8] E. Jacques, M. Kjell, D. Zenkert and G. Lindbergh, Carbon, 68, 725-733 (2014)