Function Of Li Concentration Research Articles

Redox Mechanisms, Structural Changes, and Electrochemistry of the Wadsley-Roth LixTiNb2O7 Electrode Material.

The TiNb2O7 Wadsley-Roth phase is a promising anode material for Li-ion batteries, enabling fast cycling and high capacities. While already used in commercial batteries, many fundamental electronic and thermodynamic properties of LixTiNb2O7 remain poorly understood. We report on an in-depth first-principles study of the redox mechanisms, structural changes, and electrochemical properties of LixTiNb2O7 as a function of Li concentration. First-principles electronic structure calculations reveal an unconventional redox mechanism upon Li insertion that results in the formation of metal-metal bonds. This metal dimer redox mechanism has important structural consequences as it results in a shortening of cation-pair distances, which in turn affects lattice parameters of the host and thereby alters Li site preferences as the Li concentration is varied. The new insights about redox mechanisms in TiNb2O7 and their effect on the structure and Li site preferences provide guidance on how the electrochemical properties of a promising class of anode materials can be tailored by exploiting the tremendous structural and chemical diversity of Wadsley-Roth phases.

First principles investigation into the interwoven nature of voltage and mechanical properties of the LixNMC-811 cathode

Density functional theory has been used to investigate the electrochemical and mechanical properties of the well-known cathode material Li x Ni 0.833 Mn 0.083 Co 0.083 O 2 (Li x -NMC-811) as a function of Li concentration. We used the PBE functional with dispersion corrections to calculate a voltage in good agreement with experiment, which gradually changes from 3.3 to 4.2 V during the charging process. A similar profile trend can be found without dispersion, though voltages were lower by ∼ 0.4 V and the known NMC lattice collapse was not captured as it was with dispersion. We compare calculated quantities such as Young’s modulus ( E ) to better understand the mechanical response of the material to outside forces with varying Li concentration. We also compare Poisson’s ratio ( ν ) and the Pugh ratio ( γ ), which are used as metrics of ductility, for each of these lithiation concentrations. We have shown that as the concentration of Li reaches x = 0 . 25 , the material transitions from ductile to brittle based on both ductility metrics. It is near this concentration that we also see the largest change in voltage from our calculations. We propose that this transition between ductile and brittle provides additional insight and understanding into structural failure and, consequently, capacity loss during normal cycling for cathode materials. Furthermore, it demonstrates a mechanism for reversibly controlling mechanical properties by electrochemical means. • DFT is used to examine the electrochemical and mechanical properties of Li-NMC-811. • The cathode experiences a transition from ductile to brittle. • The ductile/brittle transition corresponds to jumps in the voltage profile.

Role of Electronic Structure in Li Ordering and Chemical Strain in the Fast Charging Wadsley–Roth Phase PNb9O25

Wadsley–Roth crystallographic shear phases are a family of transition-metal oxides that show tremendous promise as electrode materials in Li-ion batteries. Despite their ability to intercalate lithium at high rates, little is known about their structural, thermodynamic, and electronic properties as a function of Li concentration. In this study, we use first-principles statistical mechanics methods to explore the lithium-site preference, lithiation strain, and electronic structure of PNb9O25, a Wadsley–Roth phase that has been shown to reversibly cycle at a rate of 60 C and that can accommodate more than one Li per Nb. We find that Li ions can occupy five symmetrically distinct interstitial sites within the PNb9O25 crystal structure, with three being pyramidal sites coordinated by five oxygen and two being window sites with square-planar oxygen coordination. The insertion of Li into PNb9O25 leads to a complex site filling sequence, with pyramidal sites preferred at low Li concentrations, followed by the filling of window sites at higher Li concentrations. Our findings are aided by neutron diffraction where pyramidal sites are found to be filled at low compositions. The order in which sites are filled is strongly influenced by the chemical strain due to Li insertion. The strain arises from the delocalization of donated electrons over the d orbitals of the structure’s edge-sharing niobium, which leads to a tetragonal distortion along the c-axis, thereby making vertical window sites favorable for Li occupancy at intermediate to high Li concentrations. Given the crystallographic similarities among different shear phases, we expect that the results of this study will also shed light on the electrochemical properties of other Wadsley–Roth chemistries.

The lithiation process and Li diffusion in amorphous [formula omitted] and Si from first-principles

Silicon is considered the next-generation, high-capacity anode for Li-ion energy storage applications, however, despite significant effort, there are still uncertainties regarding the bulk Si and surface SiO2 structural and chemical evolution as it undergoes lithiation and amorphization. In this paper, we present first-principles calculations of the evolution of the amorphous Si anode, including its oxide surface layer, as a function of Li concentration. We benchmark our methodology by comparing the results for the Si bulk to existing experimental evidence of local structure evolution, ionic diffusivity as well as electrochemical activity. Recognizing the important role of the surface Si oxide (either native or artificially grown), we undertake the same calculations for amorphous SiO2, analyzing its potential impact on the activity of Si anode materials. Derived voltage curves for the amorphous phases compare well to experimental results, highlighting that SiO2 lithiates at approximately 0.7 V higher than Si in the low Li concentration regime, which provides an important electrochemical fingerprint. The combined evidence suggests that i) the inherent diffusivity of amorphous Si is high (in the order 10−9cm2s−1 - 10−7cm2s−1), ii) SiO2 is thermodynamically driven to lithiate, such that Li–O local environments are increasingly favored as compared to Si–O bonding, iii) the ionic diffusivity of Li in LiySiO2 is initially two orders of magnitude lower than that of LiySi at low Li concentrations but increases rapidly with increasing Li content and iv) the final lithiation product of SiO2 is Li2O and highly lithiated silicides. Hence, this work suggests that - excluding explicit interactions with the electrolyte - the SiO2 surface layer presents a kinetic impediment for the lithiation of Si and a sink for Li inventory, resulting in non-reversible capacity loss through strong local Li–O bond formation.

In Situ Experimental Measurement of the Mechanical Properties of Carbon-Based Electrodes during the Electrochemical Process

The mechanics of battery electrodes are crucial for determining the cycling performance and battery lifetime. In this study, we investigated the fundamental important material properties of commercial carbon electrodes that strongly depend on the Li concentration. An optical system is used to perform in situ measurements of a mesocarbon microbead (MCMB) composite electrode during the electrochemical process in a homemade cell with a glass window. The deformation vs. capacity during the second lithiation is given and, combined with a built elastic modulus equation, the elastic modulus of carbon composite electrode is directly quantitatively characterized herein as a function of Li concentration by in situ experiments. It is found that the mechanical responses of the MCMB composite electrode somewhat depend on the graphite intercalation compound stage behavior. The material stiffening of the MCMB composite electrode is experimentally observed herein. Further, the elastic modulus varies nonlinearly with Li concentration. It initially increases, decreases, and then increases again from an initial value of 98 to a maximum of 194 MPa, which is a stiffening factor of two rather than the expected values of three. This experimental data are useful for understanding the relationship between the mechanics and the electrochemistry.

Modeling and in situ characterization of lithiation-induced stress in electrodes during the coupled mechano-electro-chemical process

Abstract Stress is one of the key factors leading to capacity fading and triggering safety issues in lithium-ion batteries. In this paper, the stress in layered electrodes during the electrochemical process is investigated. Considering the electrochemically induced changes in the elastic modulus of the electrode material, a stress model is established to obtain a modified Stoney stress equation. In addition, in situ bending deformation of the Si composite electrode during lithiation and delithiation is measured to be determined as a function of Li concentration. Combined with the established stress model, the lithiation-induced stress in the Si composite electrode material is quantitatively characterized. It is shown that the maximum compressive stress is 8.53 MPa. Furthermore, the differences between the established stress model and the classical Stoney stress equation are compared and discussed. Lithiation results in softening of the Si composite electrode material, which affects the stress during lithiation. The experimental results clearly demonstrate that softening of the Si composite electrode material significantly decreases and alleviates the stress.

Mechanical properties of Li–Sn alloys for Li-ion battery anodes: A first-principles perspective

Fracture and pulverization induced by large stress during charging and discharging may lead to the loss of electrical contact and capacity fading in Sn anode materials. A good understanding of mechanical properties is necessary for their optimal design under different lithiation states. On the basis of first-principles calculations, we investigate the stress-strain relationships of Li–Sn alloys under tension. The results show that the ideal tensile strengths of Li–Sn alloys vary as a function of Li concentration, and with the increase of Li+ concentration, the lowest tensile strength decreases from 4.51 GPa (Sn) to 1.27 GPa (Li7Sn2). This implies that lithiation weakens the fracture resistance of Li–Sn alloys.

Evaluation of thermal conductivity for liquid lead lithium alloys at various Li concentrations based on measurement and evaluation of density, thermal diffusivity and specific heat of alloys

The thermophysical properties of lead lithium alloy (Pb–Li) are essential for the design of liquid Pb–Li blanket system. The purpose of the present study is to make clear the density, the thermal diffusivity and the heat conductivity of the alloys as functions of temperature and Li concentration. The densities of the solid alloys were measured by means of the Archimedean method. The densities of the alloys at 300K as a function of Li concentration (0at%<χLi<28at%) were obtained in the equation as ρ(300K)[g/cm3]=−6.02×10−2×χLi+11.3. The density of the liquid alloys was formulated as functions of temperature and Li concentration (0at%<χLi<30at%), and expressed in the equation as ρ[g/cm3]=(9.00×10−6×T−7.01×10−2)×χLi+11.4−1.19×10−3T. The thermal diffusivity of Pb, Pb–5Li, Pb–11Li and Pb–17Li were measured by means of laser flash method. The thermal diffusivity of Pb–17Li was obtained in the equation as αPb–17Li[cm2/s]=3.46×10−4T+1.05×10−1 for the temperature range between 573K and 773K. The thermal conductivity of the Pb–17Li at the temperature of 773K was newly obtained and expressed in the equation as λ[W/mK]=4.47×10−2χLi2−0.08χLi+14.9. The dependence of Li concentration on the thermal diffusivities of the alloys was larger at higher temperature. The temperature dependence of the thermal conductivities of the alloys was larger when the Li concentration in the alloys was higher.

A Tale of Two Sites: On Defining the Carrier Concentration in Garnet‐Based Ionic Conductors for Advanced Li Batteries

Solid electrolytes based on the garnet crystal structure have recently been identified as a promising material to enable advance Li battery cell chemistries because of the unprecedented combination of high ionic conductivity and electrochemical stability against metallic Li. To better understand the mechanisms that give rise to high conductivity, the goal of this work is to correlate Li site occupancy with Li‐ion transport. Toward this goal, the Li site occupancy is studied in cubic garnet as a function of Li concentration over the compositions range: Li7−xLa3Zr2−xTaxO12 (x = 0.5, 0.75, and 1.5). The distribution of Li between the two interstitial sites (24d and 96h) is determined using neutron and synchrotron diffraction. The bulk conductivity is measured on &gt;97% relative density polycrystalline specimens to correlate Li‐ion transport as a function of Li site occupancy. It is determined that the conductivity changes nonlinearly with the occupancy of the octahedral (96h) Li site. It is shown that the effective carrier concentration is dependent on the Li site occupancy and suggests that this is a consequence of significant carrier–carrier coulombic interactions. Furthermore, the observation of maximum conductivity near Li = 6.5 mol is explained.

Multiscale Analysis of Lithiation of Si Anode of Li-Ion Batteries: First Principle Calculation and Finite Element Analysis

Silicon is known to have large Li storage capacity up to 4.4 Li atoms per Si atom in Li22Si5 compounds, but the large volume change and the mechanical stress during the charge-discharge cycles have damaged the electrode structures leading to rapid capacity fade.Recently, Cui et al. have applied the silicon nanowire structures to avoid the mechanical stresses induced by the volume change and demonstrated promising capacity of the silicon nanowire anode for Li ion batteries. However, there are many issues on the lithiation in silicon anode to understand its physics of mechanism.The kinetics of Li diffusion in Si anode is a main issue because the mechanical failure of Si active material significantly affects the stress state during cycles. In this presentation, we analyze the Li diffusivity in bulk-Si and LixSi (x>1) systems using first principle calculation and obtain the Li diffusion coefficient as function of Li concentration using kinetic Monte Carlo simulation. We also study the difference of lithiation between crystalline silicon and amorphous silicon.Based on the first principle calculation, we check the mechanical stability of Si anode in various shape and charged condition using the diffusion-induced macroscopic model based on finite element method. Our multiscale analysis can provide reliable predictions on the stability with respect to the stress deviation according to size and shape of Si nanowire including charge rates. We also construct a non-dimensional design criteria equation for allowable stresses based on Buckingham-Pi theorem. Moreover, we analyze stress of more complex Si nanowire called Si nanotube and explain why pre-lithiated Si nanowire could have better cycle-ability compared to pristine one.The multiscale approaches of Si anode from atomic scale to continuum scales help understand the mechanical failure of the Si anode in terms of the microstructure variations, and suggest a guideline to improve the Si anode performance for LIBs. ACKNOWLEDGEMENT This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MEST) (No. 2012R1A3A2048841) and by the Industrial Strategic technology development program (10041589) funded by the Ministry of Knowledge Economy (MKE, Korea)

Measurement and modeling of the mechanical and electrochemical response of amorphous Si thin film electrodes during cyclic lithiation

A combination of experimental measurements and numerical simulations are used to characterize the mechanical and electrochemical response of thin film amorphous Si electrodes during cyclic lithiation. Parameters extracted from the experiment include the variation of elastic modulus and the flow stress as functions of Li concentration; the strain rate sensitivity; the diffusion coefficient for Li transport in the electrode; the free energy of mixing as a function of Li concentration in the electrode; the exchange current density for the Lithium insertion reaction; as well as reaction rates and diffusion coefficients characterizing the rate of formation of solid-electrolyte interphase layer at the electrode surface. Model predictions are compared with experimental measurements; and the implications for practical Si based electrodes are discussed.

Understanding Li Diffusion in Li-Intercalation Compounds

Intercalation compounds, used as electrodes in Li-ion batteries, are a fascinating class of materials that exhibit a wide variety of electronic, crystallographic, thermodynamic, and kinetic properties. With open structures that allow for the easy insertion and removal of Li ions, the properties of these materials strongly depend on the interplay of the host chemistry and crystal structure, the Li concentration, and electrode particle morphology. The large variations in Li concentration within electrodes during each charge and discharge cycle of a Li battery are often accompanied by phase transformations. These transformations include order-disorder transitions, two-phase reactions that require the passage of an interface through the electrode particles, and structural phase transitions, in which the host undergoes a crystallographic change. Although the chemistry of an electrode material determines the voltage range in which it is electrochemically active, the crystal structure of the compound often plays a crucial role in determining the shape of the voltage profile as a function of Li concentration. While the relationship between the voltage profile and crystal structure of transition metal oxide and sulfide intercalation compounds is well characterized, far less is known about the kinetic behavior of these materials. For example, because these processes are especially difficult to isolate experimentally, solid-state Li diffusion, phase transformation mechanisms, and interface reactions remain poorly understood. In this respect, first-principles statistical mechanical approaches can elucidate the effect of chemistry and crystal structure on kinetic properties. In this Account, we review the key factors that govern Li diffusion in intercalation compounds and illustrate how the complexity of Li diffusion mechanisms correlates with the crystal structure of the compound. A variety of important diffusion mechanisms and associated migration barriers are sensitive to the overall Li concentration, resulting in diffusion coefficients that can vary by several orders of magnitude with changes in the lithium content. Vacancy clusters, groupings of vacancies within the crystal lattice, provide a common mechanism that mediates Li diffusion in important intercalation compounds. This mechanism emerges from specific crystallographic features of the host and results in a strong decrease of the Li diffusion coefficient as Li is added to an already Li rich host. Other crystallographic and electronic factors, such as the proximity of transition metal ions to activated states of hops and the occurrence of electronically induced distortions, can result in a strong dependence of the Li mobility on the overall Li concentration. The insights obtained from fundamental studies of ionic diffusion in electrode materials will be instrumental for physical chemists, chemical engineers, synthetic chemists, and materials and device designers who are developing these technologies.

Elastic behavior of crystalline Li–Sn phases with increasing Li concentration

We have studied the elastic properties of Li–Sn alloys as a function of Li concentration using first principle calculations. Here, we present the anisotropic elastic tensors as well as the orientation-averaged bulk, Young's and shear moduli and the Poisson's ratios for crystalline alloys. Our results demonstrate that crystal anisotropy has a significant effect on the stiffness of the material. We suggest that the bulk, shear and Young's moduli of isotropic LixSn alloys decrease monotonically with increasing Li concentration, resulting in elastic softening. On the other hand, highly anisotropic structures of very similar Li contents deviate from linearity indicating either elastic hardening or softening of the material. In addition to the significant role of anisotropy, our results also underscore the importance of including the concentration dependence of the elastic constants in the analysis of deformation during lithiation/delithiation of Sn anodes.

Structural and electrochemical properties of LiMoO 2

In this paper, we revisit the structural and electrochemical properties of lithium molybdenate, LiMoO 2, synthesized by a carbothermal method using citric acid as a chelating agent. Free-impurity microcrystalline powders were grown by a two-step synthesis with a final thermal treatment at 800 °C for 72 h in air. LiMoO 2 was characterized by means of X-ray diffractometry (XRD), Fourier transform infrared (FTIR) and Raman scattering (RS) spectroscopy and by nuclear magnetic resonance (NMR). Analyzing the data from the above experiments, we determine that LiMoO 2 crystallizes in the monoclinic system ( C2/ m S.G.) instead of the rhombohedral structure ( R 3 ¯ m S.G.) such as reported previously. The electrochemical performance of the synthesized products was evaluated in Li cells using non-aqueous solution 1 mol L −1 LiPF 6 in EC–DMC as electrolyte. The charge–discharge profiles of the monoclinic-phase LiMoO 2 display two plateaus and show the suitability of this electrode for electrochemical applications delivering a specific capacity 185 mAh g −1 in the potential range 3.7–2.0 V vs. Li 0/Li +. The chemical diffusion coefficient of Li + ions into the LiMoO 2 framework has been studied as a function of Li concentration; results show values in the range 10 −11–10 −12 cm 2 s −1.

Elastic softening of amorphous and crystalline Li–Si Phases with increasing Li concentration: A first-principles study

Knowledge of the elastic properties of Li–Si alloys as a function of Li concentration is crucial in the development of reliable deformation and fracture mechanics models for Si anodes in Li-ion batteries. Here, we have studied these properties using first-principles calculations for both amorphous and crystalline phases observed during lithiation of Si anodes. In the case of crystalline alloys, we present the anisotropic elastic tensors as well as the homogenized Young's, shear, and bulk moduli and the Poisson's ratios. We find that while these moduli decrease in an approximately linear manner with increasing Li concentration leading to significant elastic softening (by about one order of magnitude) in both crystalline and amorphous systems, the Poisson's ratios remain in the range of 0.05–0.20 and 0.20–0.30 in the case of crystalline and amorphous systems, respectively. Further, for a given Li concentration, we find that the amorphous structures are elastically somewhat softer than their crystalline counterparts, the difference being more significant (about 30–40%) in Li-poor phases. Our results underscore the importance of including the concentration dependence of elastic constants in the analysis of stress and deformation fields during lithiation and de-lithiation of Si anodes.

Cosmogenic 3He production rates in apatite, zircon and pyroxene inferred from Bonneville flood erosional surfaces

3He concentrations were measured in zircon, apatite and pyroxene separates from rhyolite surfaces along the Snake River near Twin Falls, Idaho. These fluted and potholed surfaces were presumably scoured by the Bonneville outburst flood ∼17.5 ka. Several of the samples contain inherited 3He from prior exposure, reflecting the complex incision history of the Snake River canyon and suggesting earlier flood events. Each individual mineral from the remaining surfaces yielded 3He concentrations that are within error of each other. 3He produced by neutron capture on 6Li was established from shielded samples and a simple neutron production model. The remaining 3He is spallogenic and was used to calibrate the production rate of cosmogenic 3He in zircon, apatite and pyroxene by assuming minimal erosion since the Bonneville flood. In all three phases the resulting production rates are ∼7–12% lower than previous 3He production rate estimates obtained by reference to various production rates for 10Be in quartz. This disagreement is partially reconciled here by recalculating previous results with a 10Be production rate of 4.51 at g −1 a −1 in quartz. Adopting this revised rate brings three independent 3He production rate estimates for zircon and apatite into agreement within 5%, with grand means of 103 ± 3 at g −1 a −1 in zircon and 133 ± 6 at g −1 a −1 in apatite. The major source of uncertainty in cosmogenic 3He dating of these phases is now correction for 3He produced by neutron capture on 6Li. Calculations are presented for assessing the amount of uncertainty introduced by this correction as a function of Li concentration, cosmic-ray exposure age, and He closure age.

Nondilute diffusion from first principles: Li diffusion inLixTiS2

We investigate Li diffusion in the favorable intercalation compound ${\text{Li}}_{x}{\text{TiS}}_{2}$ as a function of Li concentration, $x$, from first principles. We find that Li ions hop between neighboring octahedral interstitial sites of the ${\text{TiS}}_{2}$ host by passing through an adjacent tetrahedral site. The migration barriers for these hops are significantly reduced when the end points belong to a divacancy. We use a cluster expansion within kinetic Monte Carlo simulations to describe the configuration dependence of the migration barriers and predict a diffusion coefficient that varies by several orders of magnitude with Li concentration, exhibiting a maximum close to $x=0.5$. The kinetic Monte Carlo simulations predict that diffusion is mediated predominantly by divacancies. We also find that the migration barriers depend strongly on the $c$-lattice parameter, which decreases as Li ions are removed from ${\text{Li}}_{x}{\text{TiS}}_{2}$.

Synthesis, Structure, and Magnetic Properties of Li-Doped Manganese-Phthalocyanine, Lix[MnPc] (0 ⩽x⩽ 4)

We report on the first synthesis of Li-intercalated manganese-phthalocyanine (MnPc) in the bulk form and on the evolution of the structural and magnetic properties as a function of Li concentration, x. We find that solid beta-MnPc, which comprises rodlike assemblies of individual planar molecules, is best described as a glassy one-dimensional ferromagnet without three-dimensional ordering and that it can be quasi-continuously intercalated with Li up to x = 4, forming an isosymmetrical series of Li(x)[MnPc] phases. Inserted Li+ ions strongly bond to pyrrole-bridging nitrogen atoms of the Pc rings, thereby disrupting the ferromagnetic Mn-N(a)...Mn superexchange pathways. This gradually induces a crossover of the intrachain exchange interactions from ferromagnetic to antiferromagnetic as the doping level, x, increases coupled with a spin-state transition of the Mn2+ ions from intermediate spin, S = 3/2, to high spin, S = 5/2.

Effect of Li substitution on dielectric and ferroelectric properties of ZnO thin films grown by pulsed-laser ablation

Li-doped ZnO thin films (Zn1−xLixO, x=0.05–0.15) were grown by pulsed-laser ablation technique. Highly c-axis-oriented films were obtained at a growth temperature of 500 °C. Ferroelectricity in Zn1−xLixO was found from the temperature-dependent dielectric constant and from the polarization hysteresis loop. The transition temperature (Tc) varied from 290 to 330 K as the Li concentration increased from 0.05 to 0.15. It was found that the maximum value of the dielectric constant at Tc is a function of Li concentration. A symmetric increase in memory window with the applied gate voltage is observed for the ferroelectric thin films on a p-type Si substrate. A ferroelectric P-E hysteresis loop was observed for all the compositions. The spontaneous polarization (Ps) and coercive field (Ec) of 0.6μC∕cm2 and 45kV∕cm were obtained for Zn0.85Li0.15O thin films. These observations reveal that partial replacement of host Zn by Li ions induces a ferroelectric phase in the wurtzite-ZnO semiconductor. The dc transport studies revealed an Ohmic behavior in the lower-voltage region and space-charge-limited conduction prevailed at higher voltages. The optical constants were evaluated from the transmission spectrum and it was found that Li substitution in ZnO enhances the dielectric constant.

The role of structural and electronic alterations on the lithium diffusion in LixCo0.5Ni0.5O2

The mechanisms for lithium diffusion in LixCo0.5Ni0.5O2 were investigated using the galvanostatic intermittent titration technique (GITT). Membrane electrodes prepared with poly(vinylidene fluoride) and carbon black were employed in this study. The measured Brunauer–Emmett–Teller (BET) area of the LixCo0.5Ni0.5O2 powder was combined with the GITT data to obtain the lithium chemical diffusion coefficient (ĎLi+), the lithium self-diffusion coefficient (DLi+) and the thermodynamic factor (Φ) as a function of Li concentration (x). All three parameters vary non-monotonically with x. A minimum in ĎLi+ and DLi+ at x=0.5, along with structural changes, suggests the formation of a lithium superlattice at that concentration. The behavior of ĎLi+ is complex but for x<0.34 it eventually undergoes a continuous decrease due to the metallic character of LixCo0.5Ni0.5O2. We attribute the limitation of the specific reversible capacity of LixCo0.5Ni0.5O2 to this decrease in ĎLi+ and to elevated electrode voltages. Li transport in LixCo0.5Ni0.5O2 is analyzed taking the variations in the cell parameters and the oxidation states of the Ni, Co and O ions into account.