Lithium Extraction Process Research Articles

Li2MnO3/Graphene Composite Anode Material for Lithium Ion Battery

Lithium ion batteries have been popularly used as the rechargeable power sources in consumer electronics due to their high energy storage density since the first commercial lithium ion battery launched by Sony in 1991. Graphite is still commonly used as anode material for commercial Lithium ion batteries due to its low redox potential close to Li+/Li, good cycling stability, low cost, and environmental friendliness.[1] However, the performance of current lithium ion batteries, which use graphite as the anode material, cannot satisfy requirements of fast charge Lithium ion batteries. The volume expansion/contraction of the graphite associated with the lithium insertion and extraction process, which results in loss of inter-particle electronic contract, consequently, lead to poor cycling stability. Another consideration of graphite is their safety caused from lithium dendrite formation due to its low Lithium intercalation potential at about 0 V (vs. Li/Li+). [2] The search for new anode materials for lithium ion batteries has been an important way to satisfy the ever-growing demands for better performance with higher energy/power densities, improved safety and longer cycle life. Recently, Li2MnO3 was investigated as an anode material for lithium ion battery.[3] Li2MnO3 exhibits much higher capacity than conventional carbon-based materials and a very stable cycling performance. In this work, as-prepared Li2MnO3/graphene composite material shows the enhanced reversible specific capacity and the rate performance compared with that of pristine Li2MnO3 . It was found that the conductivity of Li2MnO3/graphene was significantly improved by forming a conductive graphene network throughout the insulating Li2MnO3.

Sandwich-structured graphene sheets@LiNi0.5Mn1.5O4@graphene sheets composites as cathode materials for lithium ion batteries with high rate performance

Sandwich-structured graphene sheets@LiNi0.5Mn1.5O4@graphene sheets (GNRs@LNMO@GNRs) composites have been synthesized by growing graphene sheets(GNRs) on the surface of LiNi0.5Mn1.5O4 (LNMO) via an in-situ method of graphitizing organic compounds. The microstructure, surface morphology and electrochemical performances of GNRs@LNMO@GNRs composites have been examined by X-ray diffraction(XRD), transmission electron microscope(TEM) and different electrochemical tests. The TEM results show that the LNMO nanoparticles are homogeneously dispersed and attached on the GNRs surface. Electrochemical tests demonstrate that the GNRs@LNMO@GNRs electrode exhibits higher discharge capacity, higher coulombic efficiency, better cycling performance and rate capability than the pristine LNMO electrode. These findings reveal that distributing LNMO nanoparticles uniformly on the GNRs might not only provide a plenty of accessible active sites for the fast diffusion of lithium ions, decrease the electrochemical reaction resistance and improve the electronic conductivity, but also suppress the volume changes associated with lithium ion insertion and extraction processes, which result in the improved electrochemical performance of the GNRs@LNMO@GNRs. This study offers an effective way to obtain LNMO cathode materials of lithium ion batteries with high rate performance.

Rietveld Relaxation Analysis on LixNi0.5Mn1.5O4 (x = 0.1, 0.2) 5V Cathode Material

Introduction We have investigated the structural variation of γ-Fe2O3 after the termination of lithium insertion, and revealed the relaxation process from the discharging state to thermodynamically stable state [1-3]. We named this technique as “Relaxation analysis” and conducted this technique to various types of cathode or anode materials, such as LiMn2O4[4], LiFePO4[5], LiCoO2[6], or graphite [7] to clarify the insertion/extraction process as well as relaxation mechanism. In the present study, relaxation analysis has been made on the LixNi0.5Mn1.5O4 (x = 0.1, 0.2) after Li-extraction. LiNi0.5Mn1.5O4 with spinel-type structure is a promising cathode material because it operates at a higher voltage of ~4.7V [8] in comparison with the spinel cathode LiMn2O4. In the lithium extraction process, it has been reported that LixNi0.5Mn1.5O4 exhibits two existing phases (Li-rich and Li-lean phases) below x = 0.5 [9]. We investigated the structural relaxation of LixNi0.5Mn1.5O4 (x = 0.1, 0.2) by means of X-ray diffraction and the Rietveld analysis focusing on the change in molar ratio and structure parameter of two phases. Experiment Working electrode was prepared by LiNi0.5Mn1.5O4 powder (TOSHIMA Manufacturing Co.,Ltd) with Acetylene Black (AB) as a supplemental conductor and PVdF powder as an adhesive agent with ratio of 80 : 10 : 10 (weight ratio). Lithium foil was employed as the counter electrode and 1 mol·dm-3 LiPF6 in EC/EMC (3:7 v/v%, Kishida chemical Corp.,Ltd) was used as the electrolyte. Lithium was electrochemically extracted from LiNi0.5Mn1.5O4 using two electrode cell (Hohsen Corp.) at a constant current of 0.3C rate to obtain the sample of LixNi0.5Mn1.5O4 (x = 0.1,0.2). After the termination of Li extraction, we immediately removed the working electrode from the cell in a glove box to avoid the local cell reaction between the electrode material and the current collector. XRD data were collected from 10° to 120° in 2θ by using CuKα radiation (UltimaIV, Rigaku corp., Japan) at various relaxation time up to 70 hours. XRD data were analyzed by the Rietveld method using RIEVEC program [10]. Lattice constants and scale factors were obtained. Results and discussion Fig.1(a) and (b) show the X-ray diffraction patterns of x = 0.1 and x = 0.2 for LixNi0.5Mn1.5O4 measured after the termination of lithium extraction for 3h to 68h. Diffraction pattern gradually evolves with increasing relaxation time, i.e. the intensity of 400 peak of Li-rich phase develops while that of Li-lean phase does not change largely during relaxation. Each XRD profile can be well fitted with the Rietveld calculation. Fig.2 shows mole fraction changes of Li-rich phase. The mole fraction of Li-rich phase increases while that of Li-lean phase decreases with the relaxation time after lithium extraction. Fig.3 shows the variation of distance between oxygen and lithium for both phases. The O-Li distance of Li-lean phase is larger than that of Li-rich phase for both compositions. With the relaxation time up to 300-600 hours, Li-lean phase shrinks the O-Li distance, while Li-rich phase stretches it. It is found that, during the lithium extraction process, Li-lean phase is formed with excess amount of lithium ions, and it separates the Li-lean and Li-rich phases during the relaxation process. At the lithium extraction process, Li-lean phase with larger number of vacancy is favorable for lithium diffusion, while the ratio of Li-rich/Li-lean get into the equilibrium at the relaxation process. The decrease of the amount of lithium ion in Li-lean phase appears as the changes in the distance of oxygen and lithium. This phenomenon appears more clearly than when lithium extracted at a current of 0.1C rate.

Evidence of reversible oxygen participation in anomalously high capacity Li- and Mn-rich cathodes for Li-ion batteries

The reaction mechanism of a high capacity lithium- and manganese-rich metal oxide, 0.4Li2MnO3–0.6LiMn0.5Ni0.5O2, has been investigated at the atomic level. High-resolution synchrotron X-ray powder diffraction (HRPD) and X-ray absorption spectroscopy (XAS) were used, respectively, to evaluate the electrochemical charge and discharge reactions in terms of local and bulk structural changes, and variations in the oxidation states of the transition metal ions. Ni K-edge XAS data indicate the participation of nickel in reversible redox reactions, whereas Mn K-edge absorption spectra show that the manganese ions do not participate in the electrochemical reactions. Rietveld refinements of the oxygen occupancy during charge and discharge provide evidence of reversible oxygen release and re-accommodation by the host structure; this unique oxygen participation is likely the main reason for the anomalously high capacity of these electrodes. The HRPD data also show that during the early cycles, characteristic peaks of the Li2MnO3 component disappear when charged to 4.7V, but reappear on discharge to 2.5V, consistent with a reversible lithium and oxygen extraction process. The results provide new insights into the charge compensation mechanisms that occur when high capacity, lithium- and manganese-rich electrode materials are electrochemically cycled – a topic that is currently being hotly debated in the literature.

NiCo2S4 nanotube arrays grown on flexible nitrogen-doped carbon foams as three-dimensional binder-free integrated anodes for high-performance lithium-ion batteries.

Binary metal sulfides, especially NiCo2S4, hold great promise as anode materials for high-performance lithium-ion batteries because of their excellent electronic conductivity and high capacity compared to mono-metal sulfides and oxides. Here, NiCo2S4 nanotube arrays are successfully grown on flexible nitrogen-doped carbon foam (NDCF) substrates with robust adhesion via a facile surfactant-assisted hydrothermal route and the subsequent sulfurization treatment. The obtained NiCo2S4/NDCF composites show unique three-dimensional architectures, in which NiCo2S4 nanotubes of ∼5 μm in length and 100 nm in width are uniformly grown on the NDCF skeletons to form arrays. When used directly as integrated anodes for lithium-ion batteries without any conductive additives and binders, the NiCo2S4/NDCF composites exhibit a high reversible capacity of 1721 mA h g(-1) at a high current density of 500 mA g(-1), enhanced cycling performance with the capacity maintained at 1182 mA h g(-1) after 100 cycles, and a remarkable rate capability. The excellent lithium storage performances of the composites could be attributed to the unique material composition, a rationally designed hollow nanostructure and an integrated smart architecture, which offer fast electron transport and ion diffusion, enhanced material/-electrolyte contact area and facile accommodation of strains during the lithium insertion and extraction process.

Engineering of multi-shelled SnO2 hollow microspheres for highly stable lithium-ion batteries

Triple-shelled SnO2 hollow microspheres not only maintain a hierarchical structure during lithium insertion and extraction processes, but also improve the capacity of lithium-ion batteries.

Hierarchical structured graphene/metal oxide/porous carbon composites as anode materials for lithium-ion batteries

As a novel anode material for lithium-ion batteries, CeO2 displays imperceptible volumetric and morphological changes during the lithium insertion and extraction processes, and thereby exhibits good cycling stability. However, the low theoretical capacity and poor electronic conductivity of CeO2 hinder its practical application. In contrast, Co3O4 possesses high theoretical capacity, but undergoes huge volume change during cycling. To overcome these issues, CeO2 and Co3O4 nanoparticles are formed inside the pores of CMK-3 and display various electrochemical behaviors due to the different morphological structures of CeO2 and Co3O4 within CMK-3. Moreover, the graphene/metal oxide/CMK-3 composites with a hierarchical structure are then prepared and exhibit better electrochemical performances than metal oxides with or without CMK-3. This novel synthesis strategy is hopefully employed in the electrode materials design for Li-ion batteries or other energy conversion and storage devices.

Relaxation Structure Analysis of LixNiO2 (x=0.09) after Li-Extraction

Introduction We have investigated the structural variation of γ-Fe2O3 after the termination of lithium insertion, and revealed the transition of electrode material from kinetic state to equilibrium state clear [1,2]. We named this technique as “Relaxation analysis” and conducted this technique to various types of cathode or anode materials, such as LiMn2O4[3], LiFePO4[4], LiCoO2[5], or graphite [6] to clarify the insertion/extraction process as well as relaxation mechanism . LiNiO2 is one of the major cathode materials with low cost and low toxic nature in comparison with the widely used LiCoO2. LiNiO2 shows the rock-salt type structure with the space group, . When lithium is electrochemically extracted from the sample, two phases with similar structures (Li-rich and Li-lean phases) coexist below x = 0.32 of LixNiO2 [7,8]. In the present study, relaxation analysis has been performed on LixNiO2 (x = 0.09) after Li-extraction. We have investigated the structural relaxation of LixNiO2 (x = 0.09) by means of X-ray diffraction and the Rietveld analysis focusing on both the change of molar ratio and structure parameter in each phase. Experiment Working electrode was prepared by mixing LiNiO2 powder (Sumitomo Metal Mining Co., Ltd.) with Acetylene Black (AB) as a supplemental conductor and PVdF powder as an adhesive agent with the weight ratio of 80:10:10. Lithium foil was employed as the counter electrode and 1 mol∙dm-3 LiPF6 in EC/DMC (2:1 v/v%, Kishida chemical Co., Ltd) was used as the electrolyte. Lithium was electrochemically extracted from LiNiO2 using two electrode cell (Hohsen Co.) at a constant current of 0.01C rate to obtain the sample of Li0.09NiO2. After the termination of Li extraction, we immediately removed the working electrode from the cell in a glove box to avoid the local cell reaction between the electrode material and the current collector. XRD data were collected from 15 ° to 75° in 2θ for CuKα radiaton (RINT-TTR, Rigaku Co., Japan) at various relaxation time and were served for Rietveld structure analysis using RIEVEC program [9]. Results and discussion Fig.1 shows X-ray diffraction patterns of two phases of Li0.09NiO2 at various relaxation time after the termination of lithium extraction. Diffraction pattern gradually evolves with increasing relaxation time, i.e. the intensity of 003rich peak decreases and 003lean shifts toward the higher angle as observed in the inset. Each XRD profile can be well fitted with the Rietveld calculation. Fig.2 shows mole fraction changes of Li-lean phase. The mole fraction of Li-lean phase decreases while that of Li-rich phase increases with the relaxation time after lithium extraction. Fig.3 shows the variation of lattice constant (c-axis) for both phases. The Li-rich phase retains the c-length almost constant during the relaxation time, while Li-lean phase shrinks the c-axis. It is found that, during the lithium extraction process, Li-lean phase is formed with excess amount of lithium ions, and it separates the Li-lean phase without excess lithium ion and Li-rich phase during the relaxation process. At the lithium extraction process, Li-lean phase with larger number of vacancy is favorable for lithium diffusion, while the ratio of Li-rich/Li-lean get into the equilibrium with relaxation time.

Improving the Anode Performance of WS2 through a Self-Assembled Double Carbon Coating

Tungsten disulfide, which possesses a well-defined layered structure, has been intensively studied as an anode material for lithium ion batteries, but it usually suffers from poor cycling stability because of its large volume changes during lithium insertion and extraction processes. Herein, we develop a self-assembled double carbon coating to enhance the anode performance of WS2 via a self-assembly process between oleylamine-coated WS2 nanosheets and graphene oxide and subsequent pyrolysis treatment. When employed as an anode material for lithium ion batteries, the as-prepared WS2@C/reduced graphene oxide (WS2@C/RGO) composite exhibits excellent cycling stability and rate capability when compared to WS2@C nanosheets. A reversible capacity of 486 mA h g–1 and around 90% capacity retention were obtained after 200 cycles at a current density of 0.5 A g–1. Even under 10 A g–1, a high reversible capacity of 126 mA h g–1 can be retained. The good electrochemical performance could be attributed to the external ...

Hollow nanospheres composed of titanium dioxide nanocrystals modified with carbon and gold for high performance lithium ion batteries

Herein, we reported a facile route to fabricate carbon and Au treated TiO2 mesoporous hollow spheres (MHTiO2@C–Au) as high performance anode materials for lithium ion batteries. The high porosity of the hollow spheres, together with the inner carbon supporting and superficial Au coating, enhanced the cycling stability and rate performance of the MHTiO2@C–Au electrode significantly. The MHTiO2@C–Au composite exhibits a high reversible specific capacity of 186.6 mA h g−1 after 200 cycles at the current density of 1.0C, superior rate performances of around 151.0 mA h g−1 at the current rate of 5.0C. The outstanding electrochemical property is attributed to the overall structural features of the MHTiO2@C–Au, which can not only shorten the diffusion path of lithium ions and electrons, but also improve the stability of the hollow structures during the lithium ion insertion and extraction process.

Crystal Structural Changes and Charge Compensation Mechanism during Two Lithium Extraction/Insertion between Li2FeSiO4 and FeSiO4

Li2FeSiO4 is a promising cathode material for lithium ion batteries because of its theoretically high capacity if two lithium ions can be extracted/inserted per formula unit; however, the extraction/insertion of two lithium ions from Li2FeSiO4 remains a challenge. Herein, we successfully synthesized carbon-coated Li2FeSiO4 nanoparticles which exhibit a capacity commensurate to a reversible two-lithium extraction/insertion at elevated temperature. This study investigates the mechanism underlying a two lithium ion extraction/insertion in Li2FeSiO4 using synchrotron X-ray absorption spectroscopy and X-ray diffraction. Our results reveal that the contribution of the Fe-3d band is dominant for the first lithium extraction process from Li2FeSiO4 to LiFeSiO4. During the second lithium extraction process from LiFeSiO4 to FeSiO4, however, ligand holes are formed in the O-2p band rather than further oxidation of Fe3+. Structural analyses further reveal a phase transformation between Li2FeSiO4 and LiFeSiO4, while a ...

Graphene Folding in Si Rich Carbon Nanofibers for Highly Stable, High Capacity Li-Ion Battery Anodes

Silicon has received tremendous attention as lithium ion battery anode due to its high theoretical capacity) and low working potential versus Li+/Li. The major problems associated with Si are its poor conductivity and large volume change during the lithium insertion and extraction process. Previously, we prepared Si/carbon nanofibers with improved electrochemical performance of Si via environmental-friendly and cost-effective water-based electrospinning procedure [1]. In this work, we continued our effort to further improve the system. Graphene, possessing excellent mechanical property, high conductivity, and good stability, has been widely applied in the energy storage field. Herein, graphene was introduced to the Si/C nanofibers for the first time. It was found increasing graphene amount helps keep the fibers morphology after carbonization. And the fiber cross section images reveal that micrometer graphene is heavily folded into the nanometer fibers during electrospinning, while Si NPs are incorporated into the folds with nanospace inbetween. When applied as the anode material in LIBs, the composites show a high reversible capacity of ~1600 mAh g-1 at a charging rate of 100 mA/g and a stable capacity of 890 mAh g-1 at 1A/g after 50 cycles with 98% capacity retention. The interconnected graphene network not only ensures excellent conductivity, but also serves as a buffering matrix for the mechanic stress caused by volume change; the nanospace between Si NPs and graphene provides the space needed for volume expansion. 1. Y.S. Kim, K.W. Kim, D. Cho, N.S. Hansen, J. Lee, and Y.L. Joo, "Silicon-Rich Carbon Hybrid Nanofibers from Water-Based Spinning: The Synergy Between Silicon and Carbon for Li-ion Battery Anode Application", ChemElectroChem 1, 220-226 (2014).

Extracting the redox orbitals in Li battery materials with high-resolution x-ray compton scattering spectroscopy.

We present an incisive spectroscopic technique for directly probing redox orbitals based on bulk electron momentum density measurements via high-resolution x-ray Compton scattering. Application of our method to spinel Li_{x}Mn_{2}O_{4}, a lithium ion battery cathode material, is discussed. The orbital involved in the lithium insertion and extraction process is shown to mainly be the oxygen 2p orbital. Moreover, the manganese 3d states are shown to experience spatial delocalization involving 0.16±0.05 electrons per Mn site during the battery operation. Our analysis provides a clear understanding of the fundamental redox process involved in the working of a lithium ion battery.

Controllable Fabrication of Nanostructured Sn-TiO2 Composite Films on Cu Sheets as Anode Materials for Lithium-Ion Battery

Introduction. Lithium-ion batteries (LiB) have been widely used as power sources in many electric/electronic products such as cellular phones, digital cameras, portable computers, etc. Currently, most commercial lithium-ion batteries utilize carbon-based materials as anodic active substance and Cu foils as electric collectors. However, technologies related to LiB have been sophisticated to be close to the theoretical capacitance of carbon-based materials (LiC6: 372 mAh g-1). Considering on the applications in automobile industry for electric vehicles (EVs), it is highly desirable to explore some new anode materials with higher powder density and satisfied lifetime cycles to meet expanding needs for lithium-ion battery industry. To obtain higher gravimetric and volumetric capacity, Sn-based materials have attracted much interest as replacements for the conventional carbonaceous anode materials of Li-ion batteries, because the Sn materials has higher theoretical capacitance (Li4.4Sn: 994 mAh g-1) than that of graphite mentioned above. Pure Sn metal, however, exhibits poor cyclic lifetime due to its mechanical scalability from volume expansion and contraction of the pure Sn metal during lithium insertion and extraction processes. During the charge-discharge cycles, this mechanical scalability will crack and deteriorate the electrode, significantly affecting the mechanical stability and cyclic lifetime of the battery. In this study, we will report porous Sn-TiO2composite films fabricated on Cu sheets, to provide space for the volume change of Sn in the charge-discharge actions as anode materials for Li-ion batteries. Experimental. Various nanoporous Sn-TiO2 composite films were coated on Cu sheets by a hybrid electroplating, i.e., combining electro-deposition with electrophoric deposition, using an EtOH-H2O mixed bath mainly containing SnCl2 and TiCl3.The effects of ratios of Sn2+/Ti3+ and EtOH/H2O, current density, and operating temperature on the formation and electrochemical behaviors of the films were investigated. Moreover, in order to remove water absorbed in the films and improve the adhesion between the films and Cu substrates, the Sn-SnO2-TiO2anodes were heated at 423 – 473 K for 2 – 4 h in air. The morphology, chemical composition, chemical state, and crystalline structure of the electrodeposited films before and after heat treatment were investigated by a field emission scanning electron microscopy (FE-SEM) attached with an energy dispersive X-ray (EDX) analyzer, transmission electron microscopy (TEM) with x-ray energy-dispersive analysis (EDS), and x-ray diffractometer (XRD), and x-ray photoelectron spectroscopy (XPS). Electrochemical charge-discharge performances of the Sn2-TiO2 films electrodeposited on Cu sheets as binder-free anodes were investigated using home-made pouch cells assembled in an Ar-filled glove box. The cathode was utilized with a lithium metal foil, and the electrolyte solution was made of 1M LiPF6 in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) with a volumetric ratio of 1:1:1, respectively. The cells were charged and discharged at 0.1 A g-1 by a battery test system, and the cut-off voltage range was 0.01 – 2.0 V (vs. Li/Li+) at 303 K. Results and Discussion. Figs. 1a-1c show the representative FESEM images of as-deposited porous Sn-TiO2 films on Cu sheets, which were fabricated in plating baths with different ethanol/water ratios. It can be seen that the films composed of nano-flakes or nano-needles, thus making a networked nanoporous structure. The morphologies of the electrodeposited films were depended predominantly on ratios of Sn2+/Ti3+ and EtOH/H2O in electroplating baths, as well as the current density and operating temperatures. After heat treatment at 473 K for 2h (Fig.1d), the Sn nano-crystals grew into nano-sheets with micrometer sizes in across while remaining the nanoporous structure. Moreover, according to EDX and XPS analysis, the electrodeposited films consisted of Sn, SnO2, and a small amount of TiO2in 1–6 at%, irrespective of heat treatment. XRD measurement confirmed that the Sn is polycrystalline with a preferential in Sn (200) facet, which is different from the conventional Sn electrodeposits from a sulfuric-based bath that has a preferential Sn (220) facet. Furthermore, it is found that the Sn-SnO2-TiO2 composite films after heating exhibited good performance in charge-discharge Furthermore, it is found that the Sn-SnO2-TiO2 composite films exhibited a high initial discharge capacity of 1069 mAh g-1 and good cycle-life stability in charge-discharge evaluation, indicating a promising future as binder-free anode material for Li-ion batteries.

Study of the structural and thermal stability of Li0.3Co2/3Ni1/6Mn1/6O2

Thermal and structural stabilities of the delithiated positive electrode material LixCo2/3Ni1/6Mn1/6O2were studied by X-ray diffraction, magnetic and thermogravimetric analysis. In the opposite to the classical electrode materials LiNiO2 and LiCoO2, the structural symmetry (S.G. R-3m) of the starting material LiCo2/3Ni1/6Mn1/6O2 is preserved during the electrochemical cycling with a small variation of the unit cell parameters. Squid measurements evidenced that practically no Ni2+ ions were present in the lithium slab even after the lithium extraction process. For the thermal stability, the highly oxidized phase Li0.3Co2/3Ni1/6Mn1/6O2 was tested. This delithiated phase undergoes only 5.16% weight loss after heating up to 600°C. This weight loss has no effect on the structure symmetry as the starting α-NaFeO2 type structure was preserved during the thermal treatment. The obtained results coupled to the excellent electrochemical features of LiCo2/3Ni1/6Mn1/6O2clearly showits ability to compete with the commercialized cathode materials

The influence of carrier density and doping type on lithium insertion and extraction processes at silicon surfaces

The Li+ insertion and extraction characteristics at n-type and p-type Si(100) electrodes with different carrier density and doping type are investigated by cyclic voltammetry and constant current measurements. The insertion and extraction potentials are demonstrated to vary with cycling and the occurrence of an activation effect is shown in n-type electrodes where the charge capacity and voltammetric currents are found to be much higher than p-type electrodes. A rate-dependent redox process influenced by the surface region electronic density, which influences the magnitude of cyclic voltammetry current is found at Si(100) surface regions during Li insertion and extraction. At p-type Si(100) surface regions, a thin, uniform film forms at lower currents, while also showing a consistently high (>70%) Coulombic efficiency for Li extraction. The p-type Si(100) surface region does not undergo crack formation after deintercalation and the amorphization was demonstrated using transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and Raman scattering demonstrate that highly doped n-type Si(100) retains Li as a silicide and converts to an amorphous phase as a two-step phase conversion process. The findings show the succinct dependence of Li insertion and extraction processes for uniformly doped Si(100) single crystals and how the doping type and its effect on the semiconductor-solution interface dominate Li insertion and extraction, composition, crystallinity changes and charge capacity.

Micro-Sized Silicon-Carbon Composite Composed of Carbon-Coated Sub-10 Nm Si Primary Particles As High-Performance Anode Materials for Lithium-Ion Batteries

Recently, silicon has attracted considerable interest as a high-capacity anode material owing to its highest known capacity of 3580 mAh/g at room temperature, which is about 10 times larger than that of commercial graphite anodes (~370mAh/g). Despite promising advantages, practical application of silicon anodes in high performance Li-ion batteries is seriously hindered by its rapid capacity fading as a result of dramatic volume changes (>400 %) during lithium insertion and extraction processes. The huge volume changes of Si cause pulverization and loss of electrical contact between Si particles and conductive additives, as well as an unstable solid electrolyte interphase (SEI) layer, which in effect results in severe capacity fading. Constructing nanostructured silicon is a promising strategy and has been demonstrated to improve battery performance.1,2 However, there are some challenges involved in introducing these nanomaterials into electrode fabrication for practical application. One is the lower tap density of the nanoparticles, in contrast to commercially used micro-sized electrode materials, resulting in a lower volumetric energy density; the other is the difficulty with handling the chemicals, such as inhalation and explosion risks, arising from these nanoparticles in fabrication of electrodes.Thus, Control of primary particle sizes of Si below critical diameter (around 10 nm) in the micro-sized composite is more important in achieving good cycling stability as micro-sized aggregated structures of Si can expedite the capacity fading.3,4 Herein, we report a synthesis of micro-sized Si-C composites composed of carbon-coated sub-10 nm Si primary particles interconnected into secondary micro-sized particles, and its use as high-performance Li-ion anodes. This synthesis process involves facile thermal annealing of silsesquioxane with size-controlled formation of Si primary particles and subsequent carbon coating steps. The as-prepared Si-C composites anode material shows stabilized capacity of ~1600 mAh/g with excellent capacity retention (90% after 150 cycles). Moreover, the volumetric capacity can reach 1088 mAh/cm3 attributed to a high tap density (0.68 g/cm3) of micro-sized Si-C composites. Taking the facile synthesis and excellent performance of Si-C composites into account, it would be of significant interest for scalable fabrication for rechargeable lithium batteries. Furthermore, the silicon nanoparticles with controllable size are also easily used in other applications, such as light-emitting diodes, and high efficiency photovoltaic devices. Acknowledgements This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, Subcontract NO. 6951378 under the Batteries for Advanced Transportation Technologies (BATT) Program

A Novel synthesis of MgS and its application as electrode material for lithium-ion batteries

MgS was firstly investigated as an anode material for lithium-ion batteries (LIBs). A novel method for the synthesis of nano-sized MgS was conducted, i.e., by means of a reaction of MgH2 of S via ball milling. Acetylene black (AB) was used as electron conductive agent and introduced by two approaches to the MgS anode material: the one is ball milling AB with the as-prepared MgS derived from MgH2 and S; the other is pre-milling AB with S and then further milling the mixture with MgH2. X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM analyses show that MgS/AB composites with MgS nanocrystallites embedded in the AB matrix are formed via either of the approaches. The MgS anode derived from MgH2 and the pre-milled S/AB mixture shows high capacity. Capacity fading occurs mainly in the initial several cycles. A capacity of 630mAh/g is retained after 80cycles. The electrochemical property is much better than that of the MgS/AB derived from MgS and AB, due to the much homogenous microstructure of the former. The mechanism of the lithium insertion and extraction process of MgS is primarily discussed. The work is considered helpful in developing new synthesis method for MgS and new electrode material for LIBs.

Tin Nanoparticles Impregnated in Nitrogen-Doped Graphene for Lithium-Ion Battery Anodes

Tin possesses a high theoretical specific capacity as anode materials for Li-ion batteries, and considerable efforts have been contributed to mitigating the capacity fading along with its huge volume expansion during lithium insertion and extraction processes, mainly through nanostructured material design. Herein, we present Sn nanoparticles encapsulated in nitrogen-doped graphene sheets through heat-treatment of the SnO2 nanocrystals/nitrogen-doped graphene hybrid. The specific architecture of the as-prepared Sn@N-RGO involves three advantages, including a continuous graphene conducting network, coating Sn surface through Sn–N and Sn–O bonding generated between Sn nanoparticles and graphene, and porous and flexible structure for accommodating the large volume changes of Sn nanoparticles. As an anode material for lithium-ion batteries, the hybrid exhibits a reversible capacity of 481 mA h g–1 after 100 cycles under 0.1 A g–1 and a charge capacity as high as 307 mA h g–1 under 2 A g–1.

Relaxation analysis of LiMnPO4-based olivine-type material

Abstract In this study, we investigated the relaxation processes of LiMnPO 4 -based material after the termination of electrochemical insertion or extraction of lithium by using X-ray diffraction (XRD) and the Rietveld method. It was found that the relative mole fraction of Li-rich phase just after lithium insertion increased as the lithium insertion rate increased and the amount of Li-rich phase increased and that of Li-lean phase decreased with the relaxation time. It is considered that the Li-rich phase was preferable for lithium diffusion. Further, it is considered that Li-lean phase with excess lithium was formed and it changed to Li-rich phase with a low rate due to a high energy barrier at the lithium insertion process, and that Li-lean phase with excess lithium changed to Li-rich phase at the relaxation process. For lithium extraction, Li-rich phase increased and Li-lean phase decreased after lithium extraction. It is considered that the volume reduction transition from Li-rich phase to Li-lean phase even including excess lithium increased the lithium diffusion path outside the crystal and the transition was promoted for faster lithium diffusion at the lithium extraction process, and that Li-lean phase including excess lithium changed to Li-rich phase at the relaxation process.