Chemical Diffusion Coefficient Of Lithium Research Articles

The Effects of Small Amounts of Cobalt in LiNi1-XCoxO2 on Lithium Diffusion

Lithium-ion batteries with Co-free Ni-rich cathodes have attracted interest due to lower cost and supply chain issues compared to cobalt-containing cathodes1. However, cobalt is thought to provide some benefits in cycling stability and rate performance. In this work, cobalt substitution for nickel in the positive electrode material LiNi1-xCoxO2 at 0 ≤ x ≤ 0.10 is systematically investigated to determine the impact of Co and material synthesis conditions on Li diffusivity, measured using the Atlung Method for Intercalant Diffusion (AMID)2,3 in coin cells vs Li metal negative electrodes. Cobalt was found to have no impact on Li diffusivity in the intermediate voltage range (4.2 V to 3.7 V), while cation mixing (%Ni in Li layer) was found to have a strong correlation to slow Li diffusivity. At high voltage (4.3 V to 4.2 V), 0 to 10% cobalt incrementally suppresses the H2-H3 phase transition4,5 enabling significantly faster lithium diffusion. Cation mixing can be minimized through synthesis conditions, improving Li diffusivity for the low and intermediate voltage regions, without using Co. In summary, with optimal positive electrode material synthesis conditions and limiting cell upper cutoff voltage to 4.2 V, Co-free Ni-rich materials can be made with similar rate performance as 10% Cobalt-containing materials. Additionally, cobalt was found to have minimal impact on the following material properties: crystallinity of LiNi1-xCoxO2, surface impurities, particle size, and electronic conductivity. Cobalt substituted for nickel from 0% to 10% was found to decrease first cycle discharge capacity in the voltage range between 3.0 V and 4.3 V and improve capacity retention in coin cell cycling vs Li metal negative electrodes. The capacity retention improvement is most likely due to the suppression of the H2-H3 phase transition as Co is added5. Figure 1. (a), (b) shows %Ni in Li layer vs Cobalt content, obtained from powder XRD Rietveld refinement from a series of LiNi1-xCoxO2 materials. (a), (b) were synthesized under two different O2 flow velocities, both at 700oC for 20 hours, with a Li:TM ratio of 1.02:1. (c), (d) Show the lithium chemical diffusion coefficient vs cell voltage for the materials from (a), (b), respectively, measured using the Atlung Method for Intercalant Diffusion (AMID), in coin cells at 30oC. The protocol consists of 2C to C/160-rate discharge steps per voltage interval (0.1V), with OCV relaxation in between discharge steps. Figure 1

(Digital Presentation) Recycled Cathode Materials Enabled Superior Performance for Lithium-Ion Batteries

With the widely equipped Lithium-ion batteries (LIBs) in electronics and electric vehicles, proper handle spent LIBs has been the subject of increasing concern. Significantly raised concerns about resource constraints and environmental issues are brought by spent LIBs. Therefore, properly handling spent LIBs is urgent and necessary.[1] However, until now, getting manufacturers to recruit recycled materials has been a hard sell because recycled materials are deemed as inferior to commercial materials, which limits the development of recycling. Although previous publications stated that their recovered materials had a comparable performance as commercial materials, the results, based on coin cells and low electrode loading, cannot convince manufacturers to employ recycled materials in the new LIBs.[2] Here, we demonstrate that recycled cathode materials with optimized microstructure have the best industrial relevant testing results (up to 11Ah cells) so far and compare them with state-of-the-art commercial equivalent. Interestingly, the recycled materials not only pass all the aggressive industrial plug-in hybrid electric vehicle (PHEV) battery tests, but also outperform control counterparts in some tests. Specifically, 1 Ah cells with the recycled LiNi1/3Mn1/3Co1/3O2 have the best cycle life result reported for recycled materials and enable 4,200 cycles and 11,600 cycles at 80% and 70% capacity retention, which is 33% and 53% better than the state-of-the-art, commercial LiNi1/3Mn1/3Co1/3O2. Meanwhile, its rate performance is 88.6% better than commercial powders at 5C. Through detailed experimental and modeling analysis of pristine and cycled materials, we discover that the unique porous and larger inside void microstructure enables the superior rate and cycle performance and less phase transformation. Compared with the control sample, the surface area of the recycled LiNi1/3Mn1/3Co1/3O2 is 82.14% larger and the cumulative pore volume is 61.25% larger. Even some recycled particles have an outer diameter of the void space equal to 40% to 60% of the particle diameter. The unique microstructure can reduce 16% hoop stress during the discharge/charge process compared to control materials, and improve the lithium chemical diffusion coefficient, enabling the superior performance of cycle life and rate performance and less phase transformation. The results pave the way to re-introduce recycled materials into new batteries.[3] [1] M. Chen, X. Ma, B. Chen, R. Arsenault, P. Karlson, N. Simon, Y. Wang, Recycling End-of-Life Electric Vehicle Lithium-Ion Batteries, Joule 2019, 3, 2622.10.1016/j.joule.2019.09.014[2] X. Ma, L. Azhari, Y. Wang, Li-ion battery recycling challenges, Chem 2021.10.1016/j.chempr.2021.09.013[3] X. Ma, M. Chen, Z. Zheng, D. Bullen, J. Wang, C. Harrison, E. Gratz, Y. Lin, Z. Yang, Y. Zhang, F. Wang, D. Robertson, S.-B. Son, I. Bloom, J. Wen, M. Ge, X. Xiao, W.-K. Lee, M. Tang, Q. Wang, J. Fu, Y. Zhang, B. C. Sousa, R. Arsenault, P. Karlson, N. Simon, Y. Wang, Recycled cathode materials enabled superior performance for lithium-ion batteries, Joule 2021.10.1016/j.joule.2021.09.005

Determination of Lithium Diffusion Coefficient in FeS2 through Improved Galvanostatic Intermittent Titration Technique (GITT) Modeling

Significant, recent efforts have been directed towards modeling lithium-ion batteries to optimize their performance and design. These models depend highly on physical parameters that must be evaluated experimentally for the system of interest. One of the most critical of these parameters is the chemical diffusion coefficient for lithium inside the active cathode material. Galvanostatic Intermittent Titration Technique (GITT) is a commonly used technique that can evaluate the diffusion coefficient, as well as other important information about the cell such as the reaction rate constant and open circuit potential. Despite its popularity, there remain several issues with the existing method of analyzing GITT data. Notably, the conventional method for extracting diffusion coefficients from GITT data relies on numerous assumptions, applies only at short discharge times, and lacks evidence validating the obtained coefficients.In this work, we describe a new method of extracting diffusion coefficients from GITT data. This method involves directly fitting a GITT pulse to a one-dimensional, single particle electrochemical model and can be applied for both ideal and non-ideal solution theory. We apply this approach to experimental measurements at two temperatures for the intercalation regime of FeS2, a conversion cathode material. Results are compared to the conventional method of evaluating diffusion coefficients from GITT data as well as diffusion coefficients obtained from electrochemical impedance spectroscopy. Diffusion coefficients are found to be higher for direct fitting, and more than an order of magnitude difference is observed between ideal and non-ideal diffusion coefficients. The modeling is also extended to a distribution of particles, and we show that the distribution behaves as a single particle with an effective particle radius proportional to the total volume to surface area ratio. Finally, the new diffusion coefficients are validated against discharge data for the cell, and it is shown that a reasonable prediction to the experimental data can be achieved using a single particle model. However, this is only possible with a non-ideal diffusion model, and high variation is observed across predictions obtained using other diffusion coefficient evaluation methods. This work demonstrates the susceptibility of electrochemical modeling to transport parameters and offers a simple, yet improved, method for evaluating diffusion coefficients from experimental GITT measurements.Supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

Polycrystalline and Single Crystalline NCM Cathode Materials—Quantifying Particle Cracking, Active Surface Area, and Lithium Diffusion

AbstractRepresentatives of the LixNi1−y−zCoyMnzO2 (NCM) family of cathode active materials (CAMs) with high nickel content are becoming the CAM of choice for high performance lithium‐ion batteries. In addition to high specific capacities, these layered oxides offer high specific energy, power, and long cycle life. Recently, the development of single crystalline particles of NCM has enabled even longer lifetimes due to achieving higher Coulomb efficiencies. In this work, the performance of NCM materials with different particle size and morphology is explored in terms of key parameters such as the charge‐transfer resistance and the chemical diffusion coefficient of lithium. Cracking of secondary particles leads to liquid electrolyte infiltration in the CAM, lowering the charge‐transfer resistance and increasing the apparent diffusion coefficient by more than one order of magnitude. In contrast, these effects are not observed with single‐crystalline NCM, which is mostly free of cracks after cycling. Consequently, severe kinetic limitations are observed when cycling large “uncracked” secondary particles at low potential and capacity. These results demonstrate that cracking of polycrystalline particles of NCM is not solely detrimental but helps to achieve high reversible capacities and rate capability. Thus, optimization of CAMs size and morphology is decisive to achieve good rate capability with high‐nickel NCMs.

Lithium insertion in α′-NaV2O5: Na-pillaring effect on the structural and electrochemical properties

Electrochemically formed α′-NaV2O5 bronze is investigated here as cathode material for rechargeable lithium batteries. We show that the layered structure of this compound, with Na ions located between the V2O5 layers, allows the reversible insertion of 1 lithium/mole of bronze at an average voltage of 2.1 V vs. Li+/Li. The Li insertion-extraction mechanism in α′-LixNaV2O5 is revealed thanks to ex situ XRD and Raman spectroscopy investigations. A narrow one-phase region occurs in the 0 < x ≤ 0.2 composition range while a two-phase mechanism prevails for 0.2 < x < 1. Also, we show that 0.3 additional Li ions can be inserted according to a second solid solution domain, leading to the fully lithiated α′-Li1.3NaV2O5 material. The structure of the α′-LiNaV2O5 is isomorphic to the pristine material. It is remarkable that only limited structural changes are found in the 0 < x ≤ 1.2 lithium composition range, consisting mainly in a 7% increase in the interlayer c parameter. A high structural reversibility is evidenced, which accounts for the remarkable stable capacities achieved whatever the C rate, near 120 mAh g−1 and 60 mAh g−1 at C/10 and 1C, respectively after 60 cycles. The lithium chemical diffusion coefficient DLi, in the range 10−9 – 10−10 cm2 s−1 in the 0.03 ≤ x ≤ 1.1 composition domain, is little affected by the Li concentration. The high mobility revealed for lithium ions is also supported by BVEL analysis, while a significant activation energy for Na-ions migration ascertains their immobility in the α′-NaV2O5 lattice. These results demonstrate the interest of large interlayer 2D host lattices stabilized by pillaring species such as Na to achieve a stable cycling behavior, a facile guest cation insertion and to promote the ionic diffusion.

Thin-film lithium batteries with 0.3–30 μm thick LiCoO2 films fabricated by high-rate pulsed laser deposition

High-rate pulsed laser deposition was applied to the preparation of thick LiCoO2 cathode films, which were then used in the fabrication of thin-film batteries. The deposition rate of the LiCoO2 films was 2–3 μm/h. The thin-film batteries showed an increase in capacity up to 470 μAh/cm2 with increasing cathode film thickness. The rate dependence of discharge capacity was analyzed using a diffusion model in which the chemical diffusion coefficient of lithium in the cathode determines the dynamic capacity. For the initial stage of discharge, the chemical diffusion coefficient was estimated to be 10−10 cm2/s. Conversely, the chemical diffusion coefficient decreases to ~10−12 cm2/s at the end of discharge. From the diffusion model, the available capacity was estimated as a function of cathode thickness. Crack formation inside the LiCoO2 film is also suggested as a cause of capacity limitation.

Elevated electrochemical property of LiMn2O4 originated from nano-sized Mn3O4

By employment of nano-sized pre-prepared Mn3O4 as precursor, LiMn2O4 particles have been successfully prepared by facile solid state method and sol-gel route, respectively. And the reaction mechanism of the used precursors of Mn3O4 is studied. The structure, morphology, and element distribution of the as-synthesized LiMn2O4 samples are characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Compared with LiMn2O4 synthesized by facile solid state method (SS-LMO), LiMn2O4 synthesized by modified sol-gel route (SG-LMO) possesses higher crystallinity, smaller average particle size (~175 nm), higher lithium chemical diffusion coefficient (1.17 × 10−11 cm2 s−1), as well as superior electrochemical performance. For example, the cell based on SG-LMO can deliver a capacity of 85.5 mAh g−1 at a high rate of 5 °C, and manifests 88.3% capacity retention after 100 cycles at 0.5 °C when cycling at 45 °C. The good electrochemical performance of the cell based on SG-LMO is ascribed mainly to its small particle size, high degree of dispersion, and uniform element distribution in bulk material. In addition, the lower polarization potential accelerates Li+ ion migration, and the lower atom location confused degree maintains integrity of crystal structure, both of which can effectively improve the rate capability and cyclability of SG-LMO.

Guidelines for the Analysis of Data from the Potentiostatic Intermittent Titration Technique on Battery Electrodes

The Li-ion battery (LIB) modeling community needs to rely on a vast bank of measured Li-ion cell parameters. Most of them are determined by routine experiments but some can solely be estimated by fitting a model to a well-designed experiment. For instance, the determination of the lithium chemical diffusion coefficient has been the focus of numerous studies. Specific techniques have been proposed for its estimation, e.g., the potentiostatic intermittent titration technique (PITT), the galvanostatic intermittent titration technique (GITT), the cyclic voltammetry (CV), and the electrochemical impedance spectroscopy (EIS). Our study focuses on the PITT so as to provide guidelines for experimental measurements and corresponding data analysis. The validity of underlying assumptions of published analytic solutions used to fit PITT data is assessed using a pseudo-2D (P2D) model. Among the tested assumptions are the drop of the porous-electrode effect, of the particle size distribution and of the finite kinetics of Li insertion/de-insertion. Tests are also conducted to assess the error made on the chemical diffusion coefficient and reaction-rate constant determination by fitting 2-electrode simulated data with a 3-electrode P2D model. An example of the P2D model fitting of PITT data obtained on a thin graphite electrode is provided.

Epitaxial LiCoO2 Film As a Model System for Fundamental Electrochemical Studies

Introduction LiCoO2 (LCO) is layered oxide material that is used as a positive electrode material in lithium ion batteries. Structural anisotropy of LCO is expected to have an effect on lithium ion transfer at the electrode/electrolyte interface. In order to understand the effect of the anisotropy on electrochemical properties, we utilized epitaxial growth of the following materials: SrTiO3 (STO) substrate covered with deposited SrRuO3(SRO), followed by deposition of LCO. Conductive SRO on STO maintains epitaxial growth and serves as a current collector [2]. We used three different orientations for the STO substrate, (100), (110), and (111), which induces (001), (110) and (108), and (104) LCO out of plane orientation. The morphology of the epitaxial film was studied using scanning electron microscope (SEM) and transmission electron microscope (TEM). Lithium ion transfer at the electrode/electrolyte interface, which can be studied with electrochemical measurements, should depend on the films’ surface morphology. Here we report a correlation between electrochemical properties and surface morphology studied by electron microscopy. Experimental LCO/SRO/STO (100), (110), and (111) samples were prepared by pulsed laser deposition in 200 mTorr oxygen pressure using a KrF laser at 650 oC for SRO and 600 oC for LCO. Samples will be referred as LCO/STO (100), (110), and (111), based on the orientation of the STO substrate. Phases and orientation of the films were studied by X-ray diffraction and scanning transmission electron microscopy (STEM). Thin lamellas of the samples for cross sectional TEM studies were prepared by focused ion beam. The lamellas were studied with a TEM operated at 300 kV. Electrochemical measurements were carried out in a three-electrode cell. The working electrode was the LCO/SRO/STO film, which was connected to the current collector with Ag paste on the sides the sample, not in contact with the electrolyte. Lithium metal served as both counter and reference electrodes. All of the potentials are referenced to Li/Li+. Cyclic voltammetry and impedance spectroscopy were carried out in 1 mol dm-3 LiClO4/propylene carbonate (PC). The area of the electrode exposed to electrolyte was defined by an O-ring. Cyclic voltammetry was carried out at 0.1 mV sec-1scan rate, and the potential range was from open circuit voltage to 4.2 V. Impedance spectroscopy was carried out in the frequency range of 100 k – 10 m Hz with amplitude of 10 mV. Results and discussions A cyclic voltammogram of LCO/ STO (100) is shown in Fig. 1. There was prominent redox peak around 3.94 V, followed by small peaks around 4.06 and 4.19 V. The other orientations, LCO/ STO (110) and (111) also showed similar peaks at the same potentials. From the TEM study, we observed that all of the films grew epitaxially, and the orientation was well controlled. These studies show that we have obtained well structured, electrochemically measurable LCO thin film with three different orientations. Figure 2 shows electrochemical impedance spectra of LCO/STO (100), (110) and (111) at 3.94 V. The high frequency (left side) intercept of the semi-circles onto the real axis are set at the same position for comparison. A modified Randles circuit was used to extract the charge transfer resistance of lithium ions at the LCO/electrolyte interface (Rct), the double layer capacitance, and the Warburg coefficient. The obtained values of Rct (normalized to geometric surface area) were 139, 97, and 235 W cm2, for LCO/STO (100), (110) and (111), respectively. In our study, we assume that lithium ion transfer takes place at the LCO {104} plane, which has open access to (001) plain layers with high lithium ion diffusivity [2], and not through the (001) plane. From TEM observation, the area of LCO {104} plains were 100 % of the geometric area for LCO/SRO/STO (100), 141 % for LCO/SRO/STO (110), and 54 % for LCO/STO/STO (100). By considering the percentage of {104} area of the samples, Rct is normalized as 139, 137, 126 W cm2, for LCO/STO (100), (110) and (111), respectively. The values are similar to each other, and support our assumption that lithium ion transfer takes place at the LCO {104} /electrolyte interface. In addition to the lithium charge transfer kinetics, surface film formation and the chemical diffusion coefficient of lithium in LCO will be discussed in the talk. Reference [1] K. Suzuki, K. Kim, S. Taminato, M. Hirayama, R. Kanno, J. Power Sources, 226(2003) 340 [2] A. Van der Ven, G. Ceder, Electrochem. Solid State Lett., 3 (2000) 301 Figure 1

Investigation of β/γ-MnO2 in composite electrodes with carbon nanotubes in a redox reaction with lithium in a model accumulator

Balastless thin-layer MnO2/Al electrodes without an electroconducting carbon additive in combination with multiwalled carbon nanotubes (MWCNT) MnO2/Al-MWCNT, as well as bulk-modified paste electrodes MnO2 (MWCNT) F4/18H12X9T stainless steel electrodes, have been studied in the redox reaction with lithium in a model accumulator on the basis of propylene carbonate (PC), dimetoxiethane (DME), and 1MLiClO4 and ethyl carbonate (EC), dimethylcarbonate (DMC), and 1M LiClO4 electrolytes. The window of the electrochemical stability of the anode oxidation on MnO2-Al/electrodes in the work range of the potentials for the electrolytes under study is 2.0–4.1 and 2.0–4.2 V, respectively. Because of the high contact resistance between the particles of the thin-layer β/γ-MnO2/Al electrode, its discharge capacity cannot exceed 110–120 mA h/g; however, it is stable through 180 cycles. The discharge capacity volume paste MnO2, F4/18H12X9T electrodes during the first cycle reaches 265–280 mA h/g and that of the reversible capacity ranges up to 185–250 mA h/g during the first 50 cycles. The role of the aluminum collector in the electrochemical transformation of MnO2 has been discussed in thin-layer MnO2/Al electrodes obtained by the mechanical rubbing of the active component into the aluminum matrix. The lithium chemical diffusion coefficient DLi established in the redox reaction of MnO2 with lithium has been estimated in thin-layer composite MnO2 MWCNT/Al electrodes at the current peak values (around 10−12 cm2/s) by slow cyclic voltammetry.

Microsized single-crystal spinel LAMO for high-power lithium ion batteries synthesized via polyvinylpyrrolidone combustion method

Microsized single-crystal Li1.08Mn1.89Al0.03O4 (LAMO) was synthesized via polyvinylpyrrolidone (PVP) combustion method. X-ray diffraction (XRD), scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM) characterization results indicate that the as-prepared LAMO has good crystallinity, uniform and smooth-surfaced morphology, and very low specific surface area. Galvanostatic charge-discharge tests demonstrate its excellent electrochemical performance. The capacity retentions at 30 °C and 55 °C are 98.8% and 93.3% respectively after 200 cycles at 1 C charge/discharge rate. Moreover, the LAMO exhibits excellent rate and low temperature performance. Even at high rates of 40 C and 60 C, the as-prepared LAMO are still able to deliver 91.2% and 85.6% capacity relative to the discharge capacity at C/5. The specific discharge capacity at −20 °C is 97.9 mAh g−1 which is 93.7% of the capacity discharging at 25 °C. To study the reason of the excellent rate performance, the potential intermittent titration technique (PITT) tests and cyclic voltammetry (CV) measurements were conducted and the lithium chemical diffusion coefficient (DLi+) was calculated.

Toward elucidation of delithiation mechanism of zinc-substituted LiFePO4

Results of research on the mechanism of delithiation of LiFe0.75Zn0.25PO4 cathode material having olivine structure are presented. Introduction of zinc into Fe-sublattice of LiFePO4 caused a decrease of unit cell volume, however, shrinkage of unit cell parameters a and b was accompanied by an increase of parameter c. Analysis of phase composition during delithiation process indicated presence of single phase in the range of lithium content from 1 to 0.5 in LixFe0.75Zn0.25PO4. This effect is accompanied by observed sloping shape of charge/discharge curves and results of Mössbauer studies. Introduction of zinc increased electrical conductivity of the material, as well as caused increase of chemical diffusion coefficient of lithium D, comparing to pure LiFePO4. Surface activated material exhibited discharge capacity of 88mAhg−1 at C/10 rate (70% of the theoretical value for LiFe0.75Zn0.25PO4). Cyclic voltammetry studies showed single oxidation and reduction peaks with mean potential value of 3.47V, and peak current vs. scan potential dependence characteristic for diffusional limitation of the electrode reaction. Determination of D, based on GITT method is presented. Additionally, results of PITT-type measurements are given, which allowed to simultaneously determine D and surface exchange reaction coefficient K. The measured values of chemical diffusion coefficient of lithium are of the order of 10−13 to 10−10cm2s−1, depending on an assumption about effective diffusion length.

Gel-combustion synthesis of LiFePO4/C composite with improved capacity retention in aerated aqueous electrolyte solution

The LiFePO4/C composite containing 13.4wt.% of carbon was synthesized by combustion of a metal salt–(glycine+malonic acid) gel, followed by an isothermal heat-treatment of combustion product at 750°C in reducing atmosphere. By a brief test in 1M LiClO4–propylene carbonate solution at a rate of C/10, the discharge capacity was proven to be equal to the theoretical one. In aqueous LiNO3 solution equilibrated with air, at a rate C/3, initial discharge capacity of 106mAhg−1 was measured, being among the highest ones observed for various Li-ion intercalation materials in aqueous solutions. In addition, significant prolongation of cycle life was achieved, illustrated by the fact that upon 120 charging/discharging cycles at various rates, the capacity remained as high as 80% of initial value. The chemical diffusion coefficient of lithium in this composite was measured by cyclic voltammetry. The obtained values were compared to the existing literature data, and the reasons of high scatter of reported values were considered.

ChemInform Abstract: Material Problems and Prospects of Li‐Ion Batteries for Vehicles Applications

AbstractReview: 35 refs.

Lithium diffusion in sputter-deposited Li4Ti5O12 thin films

Li4Ti5O12 (LTO) thin films are deposited by dc-ion beam sputtering at different oxygen partial pressures and different substrate temperatures. In order to investigate, how these two parameters influence the atomic structure, the specimens are characterized by X-ray diffraction and transmission electron microscopy. Electrochemical characterization of the films is done by cyclic voltammetry and chrono-potentiometry. To determine an averaged chemical diffusion coefficient of lithium, a method is developed, evaluating c-rate tests. The results obtained by this method are compared to results obtained by the well established galvanostatic intermittent titration technique (GITT), which is used to determine a concentration dependent diffusion coefficient of lithium in LTO.

A kinetic study of electrochemical lithium insertion in nanosized rutile β-MnO2 by impedance spectroscopy

The kinetics of the electrochemical lithium insertion reaction in nano-sized rutile β-MnO2 has been investigated using ac impedance spectroscopy. The experimental kinetic data are obtained for a rutile compound synthesized by ball-milling the powder produced from the heat treatment of manganese nitrate salts. The results are discussed as a function of the Li content for 0<x<0.6 and the number of cycles in the 4.1–2V window. From a comparison with data obtained on the micro-sized oxide, an improved kinetics is found with DLi values for the apparent chemical diffusion coefficient of lithium much higher by one order of magnitude than in microsized oxide. Impedance behaviour of the ball-milled rutile β-MnO2vs cycles demonstrates a new system takes place from the second cycle, characterized by a significant improvement of Li diffusion by a factor 5 and a cathode impedance which decreases by a factor 2, remaining thereafter unchanged during cycling.

A Study on the Electrochemical Properties of LiFePO&lt;sub&gt;4&lt;/sub&gt; Doping with Different Diameter MWCNTs

The LiFePO4/MWCNTs composite used as cathode was synthesized by ball milling. XRD and SEM experiments demonstrated that MWCNTs didn’t change the olivine structure of LiFePO4and that MWCNTs decentralized into the grains of LiFePO4and working as electric bridge improving the electrochemical properties of LiFePO4. The electrochemical performance of the composite electrodes with different MWNTs in diameter were studied by button cell. The result indicated that the composite with largest diameter MWNTs exhibited best electrochemical performance. The first charge-discharge specific capacity of the composite with MWNTs of 60-100nm in diameter were 136mAh/g-1 and 129 mAh/g-1 respectively at 0.1C rate under room temperature. The difference between charge-discharge platforms of the composite electrode was the least compared to the others. This phenomenon showed that the material had the largest chemical diffusion coefficient of lithium. At the same time, the capacity of the composite only lost 4.0％ after 10 cycles and kept constant after 20 cycles.

Li7PS6 and Li6PS5X (X: Cl, Br, I): Possible Three‐dimensional Diffusion Pathways for Lithium Ions and Temperature Dependence of the Ionic Conductivity by Impedance Measurements

AbstractPossible three‐dimensional diffusion pathways of lithium ions in crystalline lithium argyrodites are discussed based on earlier studies of local dynamics and site preferences. The specific Li‐ionic conductivities of the lithium argyrodites Li7PS6 and Li6PS5X (X: Cl, Br, I) and their temperature dependences are measured by impedance spectroscopy using different electron‐blocking and ion‐blocking electrode systems. Measurements were carried out between 160 K and 550 K depending on the respective sample. Bulk and grain boundary contributions and the influence of sample preparation are discussed. Typical values for the ionic conductivities at room temperature are in the range 10–7 to 10–5 S· cm–1 and at 500 K between 10–6 and 10–3 S· cm–1. Thermal activation energies are in the range 0.16 to 0.56 eV. The electronic conductivity at room temperature was measured by polarization measurements for the samples Li6PS5X (X: Cl, Br) and was shown to be in the order of magnitude of 10–8 S· cm–1. Chemical diffusion coefficients of lithium were calculated based on the polarization measurements. For Li6PS5Br a high value of 3.5 × 10–6 cm2·s–1 was found.

MATERIAL PROBLEMS AND PROSPECTS OF Li-ION BATTERIES FOR VEHICLES APPLICATIONS

This paper reviews material issues of development of Li -ion batteries for vehicles application. The most important of them is safety, which is related to application of nonflammable electrolyte with large electrochemical window and possibility of forming protective SEI (solid/electrolyte interface) to prevent plating of lithium on carbon anode during fast charge of the batteries. The amount of electrical energy, which a battery is able to deliver, depend on the electromotive power of the cell as well as on its capacity — both these factors are related to the chemistry of electrode materials. Nanotechnology applied to electrode materials may be a breakthrough for Li -batteries performance due to extreme reactivity of nanoparticles in relation to lithium. The electrode-electrolyte interface phenomena are decisive for a cell lifetime. Review of physicochemical properties of intercalated transition metal compounds with layered, spinel or olivine-type structure is provided in order to correlate their microscopic electronic properties, i.e. the nature of electronic states, with the efficiency of lithium intercalation process, which is controlled by the chemical diffusion coefficient of lithium. Data concerning cell voltage and character of discharge curves for various materials are correlated with the nature of chemical bonding and electronic structure. Proposed electronic model of the intercalation process allow for prediction and design of operational properties of intercalated electrode materials. Proposed method of measuring the Li x M a X b potential on the basis of the measurement of the electromotive force of the Li / Li +/ Li x M a X b electrochemical cell is a powerful tool of solid state physics allowing for direct observation of the Fermi level changes in such systems as a function of lithium content.

Kinetic analysis on LiFePO 4 thin films by CV, GITT, and EIS

LiFePO 4 thin films were deposited on Ti substrates by pulsed laser deposition (PLD). The apparent chemical diffusion coefficients of lithium in the films, D ˜ Li , were measured by cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS). The average D ˜ Li values calculated from CV results were in the order of 10 −14 cm 2 s –1. The D ˜ Li values obtained by GITT, and EIS techniques were in the range of 10 –14–10 –18 cm 2 s –1, 10 –14–10 –18 cm 2 s –1, respectively. The D ˜ Li values obtained by the two methods show a minimum point at x ∼ 0.5 for Li 1− x FePO 4. However, the overpotential values of the LiFePO 4 thin film electrodes obtained from the GITT results and the diffusion impedance deduced from the impedance spectra also show the minimum values at x ∼ 0.5 for Li 1– x FePO 4. This contradict could be caused by the improper use of GITT and EIS techniques for measuring the chemical diffusion coefficient of Li in Li 1– x FePO 4 which constitutes two phase, i.e., LiFePO 4 and FePO 4 in this region.