Lithium Counter Electrode Research Articles

Anisotropic Swelling and Fracture of Silicon Nanowires during Lithiation

We report direct observation of an unexpected anisotropic swelling of Si nanowires during lithiation against either a solid electrolyte with a lithium counter-electrode or a liquid electrolyte with a LiCoO(2) counter-electrode. Such anisotropic expansion is attributed to the interfacial processes of accommodating large volumetric strains at the lithiation reaction front that depend sensitively on the crystallographic orientation. This anisotropic swelling results in lithiated Si nanowires with a remarkable dumbbell-shaped cross section, which develops due to plastic flow and an ensuing necking instability that is induced by the tensile hoop stress buildup in the lithiated shell. The plasticity-driven morphological instabilities often lead to fracture in lithiated nanowires, now captured in video. These results provide important insight into the battery degradation mechanisms.

Comparison of Cycling Performance of Lithium Ion Cell Anode Graphites

Battery grade graphite products from major suppliers to the battery industry were evaluated in 2325 coin cells with lithium counter electrodes. First and ongoing cycle efficiency, total and reversible capacity, cycle life and discharge rate performance were measured to compare these anode materials. We then ranked the graphites using a formula which incorporates these performance measures to estimate the cost of the overall system, relative to the cost of a system using MCMB. This analysis indicates that replacing MCMB with CCP-G8 (Conoco Phillips) would add little to no cost, whereas each of the other graphites would lead to a more costly system. Therefore we chose CCP-G8 as the new baseline graphite for the BATT program.

Implementing Realistic Geometry and Measured Diffusion Coefficients into Single Particle Electrode Modeling Based on Experiments with Single LiMn2O4 Spinel Particles

Realistic geometry and diffusion coefficients were measured from a single particle LiMn2O4 electrode and implemented into a three-dimensional multiphysics simulation of a single particle, in order to demonstrate a novel approach to electrode material study. Dispersed particles were used, and electrochemical techniques and atomic force microscopy were performed on isolated single particles. Diffusion coefficients measured from both cyclic voltammetry and the potentiostatic intermittent titration technique ranged between 3.2 × 10−12 and 1.2 × 10−11 cm2/s, which was similar to values measured from thin film LiMn2O4 electrodes. The trend of diffusivity change over potential (versus lithium counter electrode) was similar to those observed from both composite cells and thin film electrodes. The measured diffusion coefficients were then used in simulation of discharge of the irregular particle, by importing the particle morphology into a finite element simulation, in order to simulate intercalation-induced stress generation. Simulation results showed a higher maximum stress generation due to altering diffusivity around the peak current potentials and high local stress concentration on the sharply indented surface area, suggesting that particle irregularities are important in studying both electrochemical performance and local failure mechanisms in cathode materials.

Comparative study on surface behaviors of copper current collector in electrolyte for lithium-ion batteries

The chemical and electrochemical stability of Cu current collectors in electrolyte for lithium-ion batteries is investigated. During long-term storage, the surface section of Cu foil is oxidized to copper compounds along with the reduction reaction of electrolyte. A continuous surface film can be formed on the Cu current collector after the foil is immersed in electrolyte for lithium ion batteries at room temperature for 30 days. This surface film is composed of inorganic compounds located in the inner layer and organic/inorganic mixed components stayed outside. It comes from the spontaneous reaction at the interface between Cu foil and electrolyte for the existence of trace water in electrolyte. Different from SEI film spontaneous formation during storage, surface film generated on Cu foil during electrochemical process shows different characteristic and mechanism. By using metal lithium as counter electrode, SEI film on Cu foil in Cu foil/metal Li battery is formed from surface chemical species floating from lithium counter electrode and electrochemical oxidation/reduction process. In contrast, thinner SEI film can be generated merely from electrochemical electrolyte decomposition and precipitation. All the evidences reveal that the structure of SEI film from different conditions is similar, which shows inorganic fluorides located in the inner layer and organic/inorganic mixed lied in the outer layer.

Self-Supported Three-Dimensional Nanoelectrodes for Microbattery Applications

A nanostructured three-dimensional (3D) microbattery has been produced and cycled in a Li-ion battery. It consists of a current collector of aluminum nanorods, a uniform layer of 17 nm TiO(2) covering the nanorods made using ALD, an electrolyte and metallic lithium counter electrode. The battery is electrochemically cycled more than 50 times. The increase in total capacity is 10 times when using a 3D architecture compared to a 2D system for the same footprint area.

Paper-like free-standing polypyrrole and polypyrrole–LiFePO 4 composite films for flexible and bendable rechargeable battery

Highly flexible, paper-like, free-standing polypyrrole and polypyrrole–LiFePO 4 composite films were prepared using the electropolymerization method. The films are soft, lightweight, mechanically robust and highly electrically conductivity. The electrochemical behavior of the free-standing films was examined against lithium counter electrode. The electrochemical performance of the free-standing pure PPy electrode was improved by incorporating the most promising cathode material, LiFePO 4, into the PPy films. The cell with PPy–LiFePO 4 composite film had a higher discharge capacity beyond 50 cycles (80 mA h/g) than that of the cell with pure PPy (60 mA h/g). The free-standing films can be used as electrode materials to satisfy the new market demand for flexible and bendable batteries that are suitable for the various types of design and power needs of soft portable electronic equipment.

XRD evidence of macroscopic composition inhomogeneities in the graphite–lithium electrode

In situ and ex situ X-ray diffraction (XRD) measurements were carried out on lithiated graphite electrodes at different states of charge. Data were collected from both sides of electrode. We found macroscopic inhomogeneities in the lithium concentration along the electrode thickness even when the electrode was allowed to rest for 24 h. The electrode side facing the lithium counter electrode in the coin type half-cell displays higher lithium concentration as compared to the side opposed to the XRD window. Residual stage 2 compound is found in the supposedly fully lithiated and fully delithiated electrode. It seems that the differences in the chemical potential between stage 2 and stage 1 is too small to average the lithium composition through chemical diffusion at ambient temperature in reasonable times.

Properties of amorphous Si thin film anodes prepared by pulsed laser deposition

Amorphous Si (a-Si) thin film anodes were prepared by pulsed laser deposition (PLD) at room temperature. Structures and properties of the thin films were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and electrochemical measurements. Galvanostatic charge/discharge tests of half cells using lithium counter electrode were conducted at a constant current density of 100 μA/cm 2 in different voltage windows. Cyclic voltammetry (CV) was obtained between 0 and 1.5 V at various scan rates from 0.1 to 2 mV/s. The apparent diffusion coefficient ( D Li) calculated from the CV measurements was about ∼10 −13 cm 2/s. The Si thin film anode was also successfully coupled with LiCoO 2 thin film cathode. The a-Si/LiCoO 2 full cell showed stable cycle performance between 1 and 4 V.

Nanostructured Columnar Tin Oxide Thin Film Electrode for Lithium Ion Batteries

Nanostructured tin oxide thin films with columnar grains were deposited on gold-coated silicon substrates using the combustion chemical vapor deposition method. Microscopy revealed that the columnar grains were covered by nanoparticles of less than 20 nm. The electrochemical behavior of the as-prepared thin film electrodes was examined against a lithium counter electrode. These thin film electrodes exhibited high specific capacity and good capacity retention. The capacity increased from an initial value of about 353 (μA h)/(cm2 μm) gradually to a maximum value of ∼490 (μA h)/(cm2 μm) during cycling. The reversible capacity was about 460 (μA h)/(cm2 μm) after 80 cycles at a charge/discharge rate of 0.3 mA/cm2. When the electrodes were discharged at 0.9 mA/cm2, the capacity retention obtained was about 64% of the capacity at 0.3 mA/cm2. The good electrochemical performance is attributed to the unique nanostructure with longitudinal and radial connectivity of active materials.

The study of LiNi 0.5Mn 1.5O 4 5-V cathodes for Li-ion batteries

In this work, we studied cycling and storage behavior at elevated temperatures of substituted spinel–nickel electrodes LiNi x Mn 2− x O 4 ( x = 0.5) that can operate as cathodes in 5-V advanced lithium-ion batteries. A stable electrochemical performance and low capacity fading were found upon cycling and storage (charged state) of LiNi 0.5Mn 1.5O 4 electrodes in DMC-EC/LiPF 6 solutions at elevated temperatures (60 °C). It was established that cycling/storage of these electrodes led to dissolution of manganese and nickel and reduction of Mn 2+ and Ni 2+ on the lithium counter electrode. These phenomena were studied by solution analysis (ICP) and surface chemistry and morphological measurements (ex situ X-ray photoelectron and Raman spectroscopies, and SEM) of the lithium and LiNi 0.5Mn 1.5O 4 electrodes. Since these electrodes perform well during prolonged cycling, it is clear that the above changes relate to surface phenomena and not changes in the bulk of the active mass.

Nanocrystalline Ag—Fe—Sn Anode Materials for Li‐Ion Batteries.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Nanocrystalline Ag-Fe-Sn Anode Materials for Li-Ion Batteries

The Ag-Fe-Sn alloy powders prepared by mechanical alloying technique have been studied as anode material for lithium-ion batteries. The half-cell tests with lithium counter electrode revealed that a suitable substitution of Fe for Ag led to a significant improvement of the cycling performance of the electrodes. Among these electrodes, the electrode was found to be capable of keeping a rechargeable capacity of about 280 mAh/g over 300 cycles, which was better than that of the Fe-free electrode. Typically, the structural changes of the electrode during Li insertion and/or extraction were characterized using the combined techniques involving X-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, and energy dispersive X-ray spectrometry. It is considered that the electrochemical properties of these electrodes are associated with their microstructure and morphology, such as the distribution of intermetallic compound in Sn matrix, the ratio as well as the presence of inactive Fe. © 2004 The Electrochemical Society. All rights reserved.

High Capacity, Reversible Silicon Thin-Film Anodes for Lithium-Ion Batteries

The properties of amorphous 250 nm and 1 μm silicon films deposited by radio-frequency (rf) magnetron sputtering on copper foil are investigated using X-ray diffractιon, scanning electron microscopy (SEM), and electrochemical methods. Galvanostatic half-cell electrochemical measurements conducted between 0.02 and 1.2 V using a lithium counter electrode have shown that the 250 nm Si thin films exhibit an excellent reversible specific capacity of nearly 3500 mAh/g when tested for 30 cycles. The high reversible capacity and excellent cyclability of the 250 nm sputtered silicon thin films suggest excellent adhesion between Si and Cu leading to high capacity retention. SEM analysis conducted on the 250 nm Si films after the 30th charge suggests the good adhesion of the ∼2 μm diam plates of silicon to the copper substrate.

Comparative studies of MCMB and CC composite as anodes for lithium-ion battery systems

Mesocarbon microbead (MCMB 2528) and CC composite have been investigated as anodes for lithium-ion batteries using half-cells with lithium counter electrode and three electrode cell systems containing LiCoO 2 cathode and lithium reference electrodes in 1 M LiPF 6 electrolyte (EC/DMC 1:1 v/v). The test results show that the practical capacity of CC composite anode is 50% higher than that of MCMB-based anode (based on total anode weight). The irreversible capacity loss of CC composite is significantly lower than that of MCMB carbon. Lithium-ion cells made with CC composite anode can accept repeated overdischarge without performance deterioration. The extra capacity of CC composite can be utilized to improve energy density and safety issues related to overcharge of lithium-ion cells. Differential scanning calorimetry (DSC) results indicates that the thermal stability of fully charged CC composite anode (lithiated anode) is much better than that of fully charged MCMB anode.

7Li NMR study of intercalated lithium in curved carbon lattices

A device was invented that permits nuclear magnetic resonance (NMR) analysis of the internal elements of a coin cell battery. The Coin Cell Battery Imager was used to record wideline 7Li NMR spectra of the lithium ions that were electrochemically intercalated into three different types of carbon-based materials. The samples included graphite, corannulene, and carbon derived from sepiolite clay. All samples were excised from 2032-size coin cells that were cycled multiple times and left in a discharged state (i.e., fully lithiated). A comparison of the 7Li NMR spectra recorded for the three carbons revealed that the curved carbon lattice derived from sepiolite affected the lithium resonances in a manner similar to that observed for the curved molecule corannulene, while both differed from the flat lattice of graphite. In addition, it was possible to observe lithium dendrites on the surface of a hard carbon electrode even in the presence of a large lithium counter electrode using NMR imaging techniques.

Three Electrode Electrochemical Voltage Spectroscopy (TEVS): evaluation of a model lithium ion system

Lithium ion cells incorporate two intercalation type electrodes which each demonstrate voltage profiles which are directly dependent on their relative states-of-charge. A new electrochemical technique, Three Electrode Electrochemical Voltage Spectroscopy (TEVS) is described which allows detailed information to be derived for both intercalation electrodes within a single experiment. Only minor modifications to conventional two electrode electrochemical cell designs are necessary for implementation of this technique. During the experimental procedure, both the pseudo-open circuit voltage ( ocv) profiles and the corresponding differential capacity plots for the two electrodes can be collected. A model lithium ion cell, namely the Li 1 − xMn 2O 4 Li 1 + xMn 2O 4 system, has been initially investigated using the new technique. This system can be cycled utilizing the approximate 3 V and 4 V vs. Li Li + voltage ranges. Around x = 0.68 in Li 1 − x Mn 2O 4 and Li 1 + x Mn 2O 4 was cycled in the cell under the prevailing TEVS test conditions. The collected TEVS data is directly compared to previously reported findings on two-electrode cells which utilized lithium counter electrodes.

The interfacial impedance variation of V 6O 13 composite electrodes during lithium insertion and extraction

Composite V 6O 13 electrodes were characterized in cells having metallic lithium counter and reference electrodes. The overall impedance changes closely follow the variation of the V 6O 13 unit cell volume. An abrupt change in unit cell volume if reflected in a corresponding abrupt change in the interfacial impedance. The variation of the interface impedance implies that the integrity of the electrode structure changes during the lithium insertion and extraction processes.

Electrochemistry of sulphur adsorbed on carbon

The modification of various carbonaceous materials by sulphur vapor was studied. The electrochemical properties of the products were measured in cells with a lithium counter electrode and either a liquid or a solid electrolyte. It was found that only physically adsorbed sulphur on the carbon surface is electrochemically active. Chemisorbed sulphur, which cannot be extracted with CS 2 or desorbed in vacuum at 300°C, is not electrochemically active. Sulphur is reduced in cells with a liquid electrolyte to polysulphides soluble in the electrolyte, causing irreversibility of the process. In cells with a solid polymeric electrolyte, P(EO) 8.LiClO 4, the sulphur-modified carbon can be cycled with a coulombic capacity decreasing from 175 mA h g −1 in the first to appreciably lower values in further cycles.

The Reduction of Sulfuryl Chloride at Teflon‐Bonded Carbon Cathodes

Polarization and discharge curves were measured for sulfuryl chloride reduction at Teflon‐bonded carbon cathodes fabricated using a number of different carbon powders. Lithium chloroaluminate was utilized as electrolyte solute. At moderate current densities cathode polarization tends to normalize with respect to Brunauer, Emmett, Teller (BET) surface area of the carbon. Cathode life increases with increased porosity of the electrode. The porosity is required for good accommodation of product . A formulation incorporating both high BET area and porosity was developed and found to provide good electrochemical performance against lithium counterelectrodes. When sulfuryl chloride is reduced at the optimized cathode (against a lithium anode), the main products of reaction are (which is quantitatively deposited within the electrode's pores) and . This suggests the overall cell reaction: . The addition of or to the electrolyte causes decrease or increase of cathode polarization, respectively. This may be taken as evidence that the reduction, at moderate current densities, occurs through a intermediate resulting from heterogeneous decomposition of . Reduction of undissociated may occur at high current densities or after the active area of the electrode is significantly reduced through deposition of product .