Average Discharge Potential Research Articles

Layered Na-Ion Cathodes with Outstanding Performance Resulting from the Synergetic Effect of Mixed P- and O-Type Phases.

Herein, the synthesis of new quaternary layered Na‐based oxides of the type NaxMnyNizFe0.1Mg0.1O2 (0.67≤ x ≤ 1.0; 0.5≤ y ≤ 0.7; 0.1≤ z ≤ 0.3) is described. The synthesis can be tuned to obtain P2‐ and O3‐type as well as mixed P‐/O‐type phases as demonstrated by structural, morphological, and electrochemical properties characterization. Although all materials show good electrochemical performance, the simultaneous presence of the P‐ and O‐type phases is found to have a synergetic effect resulting in outstanding performance of the mixed phase material as a sodium‐ion cathode. The mixed P3/P2/O3‐type material, having an average elemental composition of Na0.76Mn0.5Ni0.3Fe0.1Mg0.1O2, overcomes the specific drawbacks associated with the P2‐ and O3‐type materials, allowing the outstanding electrochemical performance. In detail, the mixed phase material is able to deliver specific discharge capacities of up to 155 mAh g−1 (18 mA g−1) in the potential range of 2.0–4.3 V. In the narrower potential range of 2.5–4.3 V the material exhibits high average discharge potential (3.4 V versus Na/Na+), exceptional average coulombic efficiencies (>99.9%), and extraordinary capacity retention (90.2% after 601 cycles). The unexplored class of P‐/O‐type mixed phases introduces new perspectives for the development of layered positive electrode materials and powerful Na‐ion batteries.

Influence of cerium on microstructures and electrochemical properties of Al-Mg-Sn-Hg anode materials for seawater battery

Aluminum is an innovative anode material for seawater battery. But large polarization and low electrochemical activity restrict its application. In this research, Al-Mg-Sn-Hg-Ce anode materials were prepared and the microstructures were investigated by scanning electron microscopy (SEM). The electrochemical properties of Al-Mg-Sn-Hg-Ce anode materials were measured by potentiodynamic polarization and potential-time discharge in a 4.5 wt.%NaOH solution at 353 K. The results indicated that the increasing content of cerium addition refined the grain structure of Al-Mg-Sn-Hg alloy and promoted the uniform distribution of Sn and Hg elements in Al matrix. The morphology of second phases changed from disperse granular to intergranulate strip with the increasing content of cerium addition in Al-Mg-Sn-Hg alloy. During the half-cell tests at a 650 mA/cm3 current density, the discharge activity of Al-Mg-Sn-Hg-Ce alloy was improved with the increasing content of cerium addition. The average discharge potential of Al-Mg-Sn-Hg-0.3 wt.%Ce alloy was −1.721 V (vs. SCE), which was more negative than −1.406 V (vs. SCE) in AZ91D. The best corrosion resistance occurred in Al-Mg-Sn-Hg-0.05 wt.%Ce alloy with the corrosion current density, 18.84± 2.21 mA/cm2. The corrosion behaviours of Al-Mg-Sn-Hg-Ce alloys were also analyzed.

Lithium-Rich Core-Shell Cathodes with Low Irreversible Capacity and Mitigated Voltage Fade

Lithium-rich layered Ni-Mn-Co oxide materials have been intensely studied in the last decade. Mn-rich materials have serious voltage fade issues and the Ni-rich materials have poor thermal stability and readily oxidize the organic carbonate-based electrolyte.1 Core-shell (CS) strategies that use Ni-rich material as the core and Mn-rich materials as the shell can balance the pros and cons of these materials in a hybrid system.2 The lithium-rich CS materials synthesized through co-precipitation method introduced here showed much improved overall electrochemical performance compared to the core-only (Ni-rich) and shell-only (Mn-rich) samples. In this work, CS samples with 67 mol% of core with the composition Li1+x(Ni0.67Mn0.33)1-xO2 (C) and 33 mol% of shell with the compositions Li1+x(Ni0.2Mn0.6Co0.2)1-xO2 (S1) or Li1+x(Ni0.4Mn0.5Co0.1)1-xO2 (S2) with varied lithium content were synthesized and studied. Figure 1 shows the energy dispersive spectroscopy results of the CS precursor and lithiated samples. Figure 1 shows that there was diffusion of transition metals between the core and shell phases after sintering at 900oC compared to the prepared hydroxide precursors. A Mn-rich shell was still maintained whereas the Co which was only in the shell in the precursor was approximately homogeneous throughout the particles. The CS samples with optimal lithium content showed low irreversible capacity (IRC), as well as high capacity and excellent capacity retention. Sample CS2-3 had a reversible capacity of ~218 mAh/g with 12.3% (~30 mAh/g) IRC and 98% capacity retention after 40 cycles to 4.6 V at 30oC at a rate of ~C/20. Figure 2 shows the average discharge potential (a) and the difference between the average charge and discharge potentials, delta V (b), of cells with the core-only (C), CS and shell-only (S) samples. Figure 2 shows that cells of the CS samples have stable impedance (delta V is stable) as well as a very stable average voltage as compared to cells of the core-only and shell-only samples. Ultra-high precision coulometry (UHPC) measurements confirmed that the CS samples with optimal lithium content had distinctively better columbic efficiency. Apparently, the Mn-rich shell can effectively protect the Ni-rich core from reactions with the electrolyte while the Ni-rich core renders a high and stable average voltage. Reference 1. E.-J. Lee, H.-J. Noh, C. S. Yoon, and Y.-K. Sun, J. Power Sources, 273, 663–669 (2015). 2. J. Camardese, J. Li, D. W. Abarbanel, a. T. B. Wright, and J. R. Dahn, J. Electrochem. Soc., 162, A269–A277 (2014). Figure 1

Design & Development of Powerful Next Generation Layered Cathode Materials for Na-Ion Batteries

Sodium-Ion Batteries (SIBs) have established themselves as possible low-cost alternative to the common lithium-ion battery (LIB). The cost advantage is underlined by a powerful electrochemical performance, superior to any other secondary battery except for LIBs. Consequently, this has led to a rapidly increasing scientific interest within the last five years. In accordance with the economical concept of diversification SIBs are discussed to be promising alternative for applications, in which cost-efficient energy storage (in terms of $/kWh) is the most important criterion. In order to boost SIBs into such applications (e.g. for the decentralized and fragmented power grid of the future) new, powerful but also rather cheap materials composed of abundant and environmentally friendly elements, need to be used in order to cover the lower electrochemical performance. In fact, research community and research efforts are, currently, focusing on the material screening and development. [1-3] With respect to layered materials strong progress in terms of their understanding, characterization and their performance has been achieved. In this presentation we will focus on the design and development of layered cathode materials for powerful next generation SIBs. In the past, we have synthesized and characterized layered P2- NaxNi0.22Co0.11Mn0.66O2material. [4-6] In this presentation we will show how the composition of this material can be modified and reveal the effect on the electrochemical performance.[7-9] Final intention of the presentation is to: -illustrate the influence of the composition on the electrochemical performance, -illustrate how layered cathode materials can be designed, -demonstrate the feasibility of these principals via a new layered Na- based oxide. The final material delivers a stable capacity of about 110 mAh g-1 (3.4 V average discharge potential) at a high current rate of 1C (180 mA g-1) between 4.3-2.5 V (vs. Na/Na+) in conventional organic carbonate based electrolyte. This performance is among the best reported for layered Na-based oxides so far and certainly is promising for the application in future Na-based electrochemical energy storage devices. [1] S.-W. Kim et al. Adv. Energy Mater. 2 (2012), 710. [2] J.M. Tarascon Nature Chemistry 2 (2010), 510. [3] N. Yabuuchi et al. Chem. Rev. 114 (2014), 11636. [4] D. Buchholz et al. Chem. Mater. 25 (2013), 142. [5] D. Buchholz et al. J. Mater. Chem. A 2 (2014), 13415. [6] L.G. Chagas et al. J. Mater. Chem. A 2 (2014) 20263. [7] I. Hasa et al. Adv. Energy Mater. 4 (2014), 140083. [8] I. Hasa et al. ACS Appl. Mater. Interfaces 7 (2015), 5206. [9] D. Buchholz et al. J. Power Sources 282 (2015), 581.

Phosphite as Polyanion-Based Cathode for Li-Ion Battery: Synthesis, Structure, and Electrochemistry of LiFe(HPO3)2.

A new lithium containing iron(III) phosphite, LiFe(HPO3)2, has been synthesized via a solvent-free, low temperature, solid-state synthesis route. The crystal structure of this material has been determined employing single-crystal X-ray diffraction, which indicates that the compound has a three-dimensional structure formed by isolated FeO6 octahedral units joined together via bridging HPO3 pseudopyramidal moieties. This arrangement leads to the formation of channels along all the three crystallographic directions, where channels along the a- and b-axes host Li(+) ions. The compound was further characterized by TGA, IR, and Mössbauer spectroscopic techniques. Additionally, it has been demonstrated that this phase is electrochemically active toward reversible intercalation of Li(+) ions and thus can be used as a cathode material in Li-ion cells. An average discharge potential of 2.8 V and a practical capacity of 70 mAh·g(-1) has been achieved as indicated by the results of cyclic voltammetry and galvanostatic charge-discharge tests.

Vanadium-based polyoxometalate as new material for sodium-ion battery anodes

Affordable energy storage is crucial for a variety of technologies. One option is sodium-ion batteries (NIBs) for which, however, suitable anode materials are still a problem. We report on the application of a promising new class of materials, polyoxometalates (POMs), as an anode in NIBs. Specifically, Na6[V10O28]·16H2O is being synthesized and characterized. Galvanostatic tests reveal a reversible capacity of approximately 276 mA h g−1 with an average discharge potential of 0.4 V vs. Na/Na+, as well as a high cycling stability. The underlying mechanism is rationalized to be an insertion of Na+ in between the [V10O28]6− anions rather than an intercalation into a crystal structure; the accompanying reduction of V+V to V+IV is confirmed by X-ray Photoelectron Spectroscopy. Finally, a working full-cell set-up is presented with the POM as the anode, substantiating the claim that Na6[V10O28]·16H2O is a promising option for future high-performing sodium-ion batteries.

Sensitivity and Intricacy of Cationic Substitutions on the First Charge/Discharge Cycle of Lithium-Rich Layered Oxide Cathodes

The effects of various cationic substitutions in lithium-rich layered Li[Li0.2Mn0.4Co0.4-xMx]O2 (M = Cr, Fe, and Ni) on the electrochemical behavior and oxygen loss have been systematically investigated. Fe substitution dramatically decreases the reversible capacity of Li[Li0.2Mn0.4Co0.4-xFex]O2 due to the reduced oxygen loss from the lattice caused by a decrease in the metal-oxygen covalence and an irreversible migration of Fe3+ ions. With increasing Cr substitution, the reversible capacity of Li[Li0.2Mn0.4Co0.4-xCrx]O2 first increases due to the multi-electron transfer reaction of the Cr3+/6+ redox couple and then decreases due to reduced oxygen loss and irreversible migration of the smaller Cr6+ ions from octahedral to tetrahedral sites. With increasing Ni substitution, the reversible capacity of Li[Li0.2Mn0.4Co0.4-xNix]O2 also first increases because Ni3+ can be fully oxidized to Ni4+ before the oxygen loss begins while Co3+ can be oxidized only to around Co3.6+ and then decreases due to suppressed oxygen loss caused by the decrease in metal-oxygen covalence. Also, the Ni substitution raises the average discharge potential as Ni3+ ions will be reduced to Ni2+ before the Mn4+ ions are reduced to Mn3+. The study demonstrates the sensitivity and intricacies associated with the nature of the cations in lithium-rich layered oxide cathodes.

Study of the Failure Mechanisms of LiNi0.8Mn0.1Co0.1O2 Cathode Material for Lithium Ion Batteries

LiNi0.8Mn0.1Co0.1O2 (NMC811) can deliver a high capacity of ∼200 mAh/g with an average discharge potential of ∼3.8 V (vs. Li+/Li), making it a promising positive electrode material for high energy density lithium ion batteries. However, electrochemical tests from half cells and full cells show poor cycling performance when charged to potentials above 4.2 V. The calendar and cycle lifetimes of cells are affected by the structural stability of the active electrode materials as well as the parasitic reactions that occur in lithium ion batteries. In order to explore the major failure mechanisms of the material, half cells (coin cells) with control electrolyte and full cells (pouch cells) with control electrolyte and with selected electrolyte additives were tested over four different potential ranges. Isothermal microcalorimetry was used to explore the parasitic reactions and their potential dependence. In-situ and ex-situ X-ray diffraction and scanning electron microscopy were used to investigate the structural and morphological degradation of the materials over cycling. It was found that the dramatic c-axis change of the active material during charge and discharge may not be the major problem for cells that are cycled to higher potentials. The parasitic reactions that arise from the interactions between the electrolyte and the highly reactive delithiated cathode surface at high potentials are suggested as the main reason for the failure of cells cycled above 4.2 V. It should be possible to further improve the performance of NMC811 at high potentials by modifying the cathode surface and/or identifying and using electrolyte blends which reduce parasitic reactions.

Influence of the Electrode Morphology on Lithium-Ion Battery Performance

In the future the application of lithium ion batteries as an energy carrier for electric and hybrid electric vehicles will become important field in automotive industry. To achieve this aim, the power density, energy density and long term stability of a battery have to be increased. Sophisticated mixing processes as well as the calendaring process (electrode compression) are known to significantly affect the above mentioned criteria, in particular the electrochemical cell performance [1-3]. However, the underlying cause-effect relationships are to a large extend still unclear.The presented work investigates the influence of the electrode morphology on the electrochemical performance of the lithium ion battery, aiming at a model which correlates the intrinsic electrode design with characteristics, influence and dependencies of the electrode conductive paths. The performed experiments focused on the observation of changes in the electrode morphology upon external compression force using a novel analytical method, “quasi in-situ” compression scanning electron microscopy. For instance, direct insight into changes of particle-particle distances or pore volumes and their distribution may be obtained. Apart from electrode morphology analysis the electronic conductivity at the same compression pressure is investigated. Exemplary, figure 1a illustrates the changes of the electronic conductivity of the electrode as a function of pressure, as measured with the setup shown in figure 1b. While the porosity of the coating is decreased from initially 45% to 40%, the electronic conductivity increases significantly. Additional determination of the electrode compound performance in an electrochemical half cell (discharge rate test, average discharge potential and lifetime) for different compression forces is made. From the entire data set, a model is derived which correlates the morphological changes e.g., conductive additive network change with the resulting electrochemical performance. Fig.1: (a) Measurement of electrode conductivity for varying force and a schematic illustration of compressed and uncompressed electrode (b)Experimental setup of conductivity measurements for varying force F; a small current (10 mA) is applied to the system, the response in voltage is recorded.

All Solid State Lithium–Sulfur Battery Using a Glass-Type P2S5–Li2s Electrolyte

Introduction Lithium-sulfur battery has attracted great attention since its electrochemical process, i.e. 16Li + S8 = 8Li2S, theoretically provides a specific energy of 2500 Wh Kg-1 much larger than the 650 Wh Kg-1 of the conventional lithium battery presently offered by the market and largely used in the electronic devices. However, to realize the practical battery based on the sulfur cathode, its red-ox shuttle of polysulfide originated in the dissolution into the organic electrolyte is strongly required to prevent for improving the charge/discharge cycle ability. On the contrary, solid state sulfide electrolytes are of considerable practical concern in these days. Application of a solid-state ion conductor is one of promising candidates for avoiding the red-ox shuttle due to the dissolution of polysulfide in Li-S battery. Its applicability of Li2S-P2S5 based solid electrolyte to the sulfur cathode has been reported using Li-In alloy for the anode1). To obtain higher energy density, we adopted pure Li and verified its applicability to the all solid-state Li-S battery. Experimental A solid state lithium ion conductor was prepared by using high energy ball milling method. Li2S:P2S5=80:20 mol% (SE) was adopted. A coin cell, 2032 was prepared by stacking and compressing Li foil, SE, and sulfur/MCMB(50:50wt%) mixture. The loading level of net sulfur was approximately 0.9mgcm-2. Another cell configuration, a compression metal cell was also used for verifying the electrochemical performances. The electrochemical measurements were mostly performed at 80 oC. The details are given in our previous paper2). Results and Discussion The Li/Li2S–P2S5/S-MCMB cell was prepared and its electrochemical characteristics were evaluated by Galvanostatic charge discharge cycle at 80 °C. The average discharge potential was approximately 2.1 V and a cycling capacity of 400 mAh g−1 at a C/20 rate was observed. The cycling tests show ca.100% Coulombic efficiency and stable capacity. However, only 25% of the theoretical capacity of the sulfur electrode was obtained in this system, because of the high resistance of the solid–solid interface at the cathode side and the associated ohmic polarization during cycling. Nevertheless, the very stable capacity of 400 mAh g−1 at a working voltage of 2.1 V results in a theoretical energy density of 840 Wh kg−1, In addition, the solid cell here reported is characterized by very high safety level, since the cell is completely based on solid-state. The details of the electrochemical characteristics on anode and cathode including recent progress are given in the poster.1) M. Nagao, A. Hayashi, M. Tatsumisago, J. Mater. Chem. 22 (2012) 10015–100202) M. Agostini, Y. Aihara, T. Yamada, B. Scrosati, J. Hassoun, Solid State Ionics 244 (2013) 48–51

A study of lithium ion batteries cycle aging by thermodynamics techniques

Lithium ion batteries (LiB) are cycled under a galvanostatic regime (∼C/2-rate) between 2.75 V and 4.2 V for up to 1000 cycles. After each completed 100 cycles, the discharge capacity, capacity loss, average discharge potential were determined under the same C/2 rate. Then cells undergo an additional charge and discharge cycle at C/6 rate followed by a thermodynamics measurements test. This enables open-circuit potential (OCP), entropy (ΔS) and enthalpy (ΔH) data to be assessed.It is found that with increasing cycle number, the entropy and enthalpy profiles show more significant changes than those observed in the discharge and the OCP curves especially at particular SOC and OCP values. These differences are attributed to the higher sensitivity of entropy and enthalpy state functions to changes in the crystal structure of the graphite anode and the lithiated cobalt oxide (LCO) induced by cycle aging compared to the free energy ΔG (OCP) alone. The thermodynamics data are supported by post-mortem X-ray diffractometry (XRD) and Raman scattering (RS) analyses on the electrode materials. The results show important LCO crystal structure degradation, whereas, surprisingly, the graphite anode remains almost unaffected by heavy cycling, if not improved.

Performance study of magnesium-polyaniline rechargeable battery in 1-ethyl-3-methylimidazolium ethyl sulfate electrolyte

A novel electrolyte system for the magnesium-polyaniline rechargeable battery containing 0.025M magnesium sulfate (MgSO4) in 1-ethyl-3-methylimidazolium ethyl sulfate (EMIES) has been developed. The electrochemical properties of magnesium and polyaniline electrodes in the MgSO4–EMIES solution are investigated, respectively. The results show that the corrosion potential of magnesium is −1.55V (vs. SCE) in 0.025M MgSO4–EMIES and magnesium has high dissolution and deposition reversibility in the solution. Polyaniline shows good oxidation and reduction reversibility in 0.025M MgSO4–EMIES and the loose and porous structure of polyaniline is helpful to the doping and de-doping of anions as well as electron transfer. The study of the effect of current density on discharge capacity shows that the magnesium-polyaniline battery has higher discharge capacity at lower current density. At 667mAg−1, magnesium-polyaniline battery has an average discharge potential of 2.10V and the first cycle discharge capacity could be 116mAhg−1. The magnesium-polyaniline battery has good cycle performance and the coulombic efficiency of the 60th cycle can be nearly 95%. The new cheap and simple magnesium-polyaniline battery is of great significance in the future rechargeable battery.

Synthesis and lithium intercalation properties of Li3VO4 as a new anode material for secondary lithium batteries

Lithium intercalation properties of Li3VO4 are investigated for a possible application as a new anode material for lithium-ion batteries. A single phase Li3VO4 powders are successfully synthesized in an oxygen atmosphere by a two-step heating process and solution-based method. A structure with corner-shared VO4 and LiO4 tetrahedrons can reversibly intercalate lithium ions and exhibits a stable frame structure after cycling. The average discharge potential is lower than Li4Ti5O12. While the sample obtained from the solid-state reaction shows initial instability and stabilizes by the continuous cycling, the sample synthesized by precipitation exhibits excellent cyclability. 190 mAh g−1 of charge capacity is observed after 100th cycle at 1.0 C-rate.

Manufacturing process and electrochemical properties of an Mg–Ga–Hg anode sheet

Abstract The manufacturing process, electrochemical property, and microstructure evolution of as-cast, rolled, and annealed Mg-4.1% Ga-2.2% Hg anode sheet are studied in this investigation. The results show that the Mg-4.1% Ga-2.2% Hg anode sheet obtains an average discharge potential of −1.7924 V (vs. saturated calomel electrode) with an electric current density of 100 mA · cm−2 and a rapid activation time of less than 10 s in a half-cell test. The Mg–Ga–Hg sheet can be used as an anode material for seawater activated batteries. The Mg3Hg and Mg21Hg5Ga3 phases in the anode influence the electrochemical corrosion of the Mg–Ga–Hg anode sheet and provide a stable corrosion potential during discharge.

Electrochemical characteristics of rechargeable polyaniline/lead dioxide cell

Electrochemically synthesized polyaniline (PANI) and lead dioxide have been investigated as electrode materials for PANI/1.1 M H2SO4; 0.5 M (NH4)2SO4/PbO2 rechargeable cell. At constant current charge/discharge of the cell, the average discharge potential of 1.1 V, specific capacity of 50 mA h g−1, specific energy of 55 W h kg−1, and self discharge rate of 2.2% per day have been obtained.

Influence of zinc on electrochemical discharge activity of Mg-6%Al-5%Pb anode

Mg-6%Al-5%Pb (mass fraction) anodes with different contents of zinc were prepared by melting and casting. The electrochemical discharge behavior of these anodes in 3.5% NaCl solutions was investigated by galvanostatic test and electrochemical impedance spectroscopy (EIS). The microstructures and the corroded surfaces of these anodes were studied by scanning electron microscopy (SEM) and emission spectrum analysis (ESA). The phase structures and the corrosion products of the anodes were analyzed by X-ray diffraction (XRD). The results show that zinc promotes the grain refinement of Mg-6%Al-5%Pb anode and makes the average discharge potential of Mg-6%Al-5%Pb anode more negative during galvanostatic test. Mg-6%Al-5%Pb anode with the addition of 1% (mass fraction) zinc has the best electrochemical performance. The activation mechanism of zinc to Mg-6%Al-5%Pb anode is as follows: The hydrolyzation of dissolved Zn2+ ions reduces the pH value of the solution near the surface of the anode and accelerates the dissolution of Mg(OH)2 film; The precipitated Zn(OH)2 with similar structure as Mg(OH)2 combines with Mg(OH)2 film easily and makes it break down.

Nano-phase tin hollandites, K2(M2Sn6)O16(M = Co, In) as anodes for Li-ion batteries

The nano-phase tin hollandites, K2(M2Sn6)O16 (M = Co, In) of particle size <10 nm are prepared by high energy ball-milling of pre-synthesized compounds and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-cycling behavior of M = Co (nano-(K–Co)) and M = In (nano-(K–In)) is evaluated by galvanostatic cycling and cyclic voltammetry (CV) with Li-metal as counter electrode in the voltage range, 0.005–0.8 V (or 1.0 V). When cycled at 60 mA g−1 (0.12 C) in the voltage range, 0.005–0.8 V, a stable capacity of 500 (±5) mA h g−1 up to 60 cycles is noticed for nano-(K–Co), whereas nano-(K–In) showed an initial capacity of 570 (±5) mA h g−1, which dropped to 485 (±5) mA h g−1 (15% loss) at the end of 60 cycles. At 1 C-rate, the nano-(K–Co) showed a capacity of 410 (±5) mA h g−1 stable up to at least 100 cycles. Under similar cyclic conditions, the heat-treated electrode (300 °C, 12 h, Ar) of nano-(K–In) showed a significant improvement and gave a stable capacity of 570 (±5) mA h g−1 in the range of 5–50 cycles. The Coulombic efficiencies in both the compounds increased to 96–98% in the range of 10–60 cycles. For both the nano-phases, the average discharge potential is 0.13 V and average charge potential is 0.5 V vs.Li, as determined by the galvanostatic and CV data. Electrochemical impedance spectroscopy (EIS) data on nano-(K–Co) as a function of voltage are presented and discussed. The apparent Li-diffusion co-efficient (DLi+), estimated from EIS data, is 2.0–2.6 (±0.2) × 10−14 cm2s−1 between 0.25 and 0.45 V during the first-cycle. The observed Li-cycling data have been interpreted in terms of the alloying–de-alloying reaction of Sn in the nano-composite, ‘Sn–K2O–Co/In–Li2O’.

Nano-composites SnO(VO x ) as anodes for lithium ion batteries

Nano-composites of SnO(V2O3) x (x = 0, 0.25, and 0.5) and SnO(VO)0.5 are prepared from SnO and V2O3/VO by high-energy ball milling (HEB) and are characterized by X-ray diffraction (XRD), scanning electron microscopy, and high-resolution transmission electron microscopy techniques. Interestingly, SnO and SnO(VO)0.5 are unstable to HEB and disproportionate to Sn and SnO2, whereas HEB of SnO(V2O3) x gives rise to SnO2.VO x . Galvanostatic cycling of the phases is carried out at 60 mA g−1 (0.12 C) in the voltage range 0.005–0.8 V vs. Li. The nano-SnO(V2O3)0.5 showed a first-charge capacity of 435 (±5) mAh g−1 which stabilized to 380 (±5) mAh g−1 with no noticeable fading in the range of 10–60 cycles. Under similar cycling conditions, nano-SnO (x = 0), nano-SnO(V2O3)0.25, and nano-SnO(VO)0.5 showed initial reversible capacities between 630 and 390 (±5) mAh g−1. Between 10 and 50 cycles, nano-SnO showed a capacity fade as high as 59%, whereas the above two VO x -containing composites showed capacity fade ranging from 10% to 28%. In all the nano-composites, the average discharge potential is 0.2–0.3 V and average charge potential is 0.5–0.6 V vs. Li, and the coulombic efficiency is 96–98% after 10 cycles. The observed galvanostatic cycling, cyclic voltammetry, and ex situ XRD data are interpreted in terms of the alloying–de-alloying reaction of Sn in the nano-composite “Sn-VO x -Li2O” with VO x acting as an electronically conducting matrix.

Li-storage and cycling properties of spinel, CdFe2O4, as an anode for lithium ion batteries

Cadmium ferrite, CdFe2O4, is synthesized by urea combustion method followed by calcination at 900°C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-storage and cycling behaviour are examined by galvanostatic cycling, cyclic voltammetry (CV) and impedance spectroscopy in the voltage range, 0·005–3·0 V vs Li at room temperature. CdFe2O4 shows a first cycle reversible capacity of 870 (± 10) mAhg−1 at 0·07C-rate, but the capacity degrades at 4 mAhg−1 per cycle and retains only 680 (± 10) mAhg−1 after 50 cycles. Heat-treated electrode of CdFe2O4 (300°C; 12 h, Ar) shows a significantly improved cycling performance under the above cycling conditions and a stable capacity of 810 (± 10) mAhg−1 corresponding to 8·7 moles of Li per mole of CdFe2O4 (vs theoretical, 9·0 moles of Li) is maintained up to 60 cycles, with a coulombic efficiency, 96–98%. Rate capability of heat-treated CdFe2O4 is also good: reversible capacities of 650 (± 10) and 450 (± 10) mAhg−1 at 0·5 C and 1·4 C (1 C = 840 mAg−1) are observed, respectively. The reasons for the improved cycling performance are discussed. From the CV data in 2–15 cycles, the average discharge potential is measured to be ∼0·9 V, whereas the charge potential is ∼2·1 V. Based on the galvanostatic and CV data, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed. The impedance parameters as a function of voltage during the 1st cycle have been evaluated and interpreted.

Electrochemical performance of low temperature fluorinated graphites used as cathode in primary lithium batteries

The present study highlights the electrochemical performance of two series of fluorinated graphites used as the cathode in primary lithium batteries. These compounds were prepared under fluorine gas at room temperature using a catalytic atmosphere made of boron or chlorine fluoride, and then thermally treated between 100 and 600 °C. The electrochemical properties are correlated to a complete physico-chemical characterization, already performed by XRD, NMR, FT-IR and EPR. In particular, important parameters are taken into account: C–F bonding, carbon hybridization, fluorine content (i.e. F/C ratio) and amount of intercalated catalyst residues. It is shown that the average discharge potential of fluorinated graphite used in primary lithium batteries can be predicted owing to the chemical shift values ( δ C–F) obtained by solid 13C NMR. On the other hand, the higher capacity values are achieved for low temperature fluorinated graphite treated at the highest temperatures, i.e. for high fluorination level. The electrochemical performance study of these materials is completed by the study of the effect of simulated storage. The differences between the various samples during electrochemical tests and those observed using different electrolytes are discussed. Fluorinated graphites obtained with a chlorine catalyst or post-treated at temperatures higher than 450 °C are unaffected by ageing.