Apparent Chemical Diffusion Coefficient Research Articles

Brittle star-like nanoweb modified carbon cloth synthesized by self-templated hollow zeolitic imidazolate framework-8 for stable Li metal anodes

Li metal anode possesses the highest energy density among all anode candidates, but the dendrite growth impedes its application. Herein, a carbon cloth-assisted two-step self-template method was introduced to the synthesis of hollow zeolitic imidazolate framework-8, which exhibited a brittle star-like ZnO–N co-doped nano carbon web after annealing and acted as a promising stable Li metal anode (h-ZNCC-Li). The ZnO and N species are lithiophilic spots, which lead to a 4100 h stable Li plating/stripping process at a high current density and capacity of 10 mA/cm2 and 10 mAh/cm2, respectively. Moreover, at the end of the cycling, the brittle star-like h-ZNCC-Li anode displays a low-voltage hysteresis of 68 mV. The apparent chemical diffusion coefficient was calculated based on the impedance and cyclic voltammetry supporting the rapid diffusion mechanism. This work develops a unique and effective strategy of hollow metal-organic framework-derived carbon for lithium metal anode.

In-situ grown Li-Ti-O layer derived by atomic layer deposition to improve the Li storage performance of Li2TiSiO5 anode materials

Li2TiSiO5 (LTSO) fibers coated by an in-situ grown Li-Ti-O layer are synthesized through ALD and post thermal treatment. Due to the ALD coating technique, precise thickness control and conformal coating layer can be realized. Through post-heating treatment, the ALD-coated TiOx layer can react with lithium residues in the host materials, forming the Li-Ti-O coating layer. Benefiting from the Li-ion conductive feature of the Li-Ti-O phase, Li-Ti-O coated LTSO fibers exhibit a high reversible capacity of 229 mA h g−1 at a current density of 0.5 A g−1 after 400 cycles in the potential range of 0.1–3 V (vs. Li+/Li). Even at a high current density of 5 A g−1, a reversible capacity of 154 mA h g−1 can be achieved. Electrochemical impedance spectra (EIS) demonstrate that the Li-Ti-O coated LTSO fibers have an apparent chemical Li-ion diffusion coefficient of 1.43 × 10−15 cm2 s−1 and decreased charge transfer resistance compared to that of pristine LTSO fibers, leading to faster Li-ion transfer kinetics and improved electrochemical performances.

Kinetic insight into the electrochemical sodium insertion-extraction mechanism of the puckered γ′-V2O5 polymorph

The kinetics of the electrochemical Na reaction in the γ′-V2O5 polymorph prepared by the carboreduction route is investigated by electrochemical impedance spectroscopy. This cathode material with puckered layer structure is capable of delivering a high discharge capacity of 143 mAh g−1 at a relatively high operating voltage of 3.3 V vs. Na+/Na. In spite of a good cyclability, a low efficiency of the first charge process limits yet the value of the stable capacity of this material upon cycling. The present study intends to give further insight into the sodium insertion-extraction mechanism in γ′-V2O5 by achieving a picture of the main kinetic parameters as a function of Na uptake in γ-NaxV2O5 electrodes (0 ≤ x ≤ 0.97). We show that the evolution of cathode impedance, charge transfer resistance, double layer capacity and apparent chemical Na diffusion coefficient are highly correlated to the structural changes induced upon sodiation. A faster Na diffusion is revealed in the richest 0.6 < x ≤ 0.97 solid solution region while electron transport is slowed down in that composition domain due to the highly localized electron character of the sodiated phase. A significant modification of the surface area is also underlined, undoubtedly caused by the high volume expansion experienced during sodiation. The low efficiency of the first cycle, characterized by an important polarization at the end of the charge, is explained by a huge increase in the electrode impedance.

Li+ Insertion/Extraction Properties for TiNb2O7 Single Particle Characterized by a Particle-Current Collector Integrated Microelectrode

In this study, we evaluate the electrochemical properties of TiNb2O7 (TNO) single particle using a particle-current collector integrated microelectrode, in which TNO single particle with the size of approximately 10 μm was bonded on the tip of a tungsten microelectrode by platinum deposition using a focused ion beam process unit (FIB). Cyclic voltammogram of TNO single particle showed the reversible redox peaks at around 1.6−1.7 V vs. Li/Li+. Anodic peak current is higher than cathodic one at a fixed scan rate, indicating faster reaction during Li+ extraction (i.e. discharge) than Li+ insertion (i.e. charge) of TNO particle. This tendency was also confirmed in C-rate dependence of charge and discharge capacities. From the results for galvanostatic intermittent titration testing (GITT), we confirmed that at the equilibrium potential vs. Li/Li+ below 1.5 V, apparent chemical diffusion coefficient of Li+ in TNO at Li+ extraction process is much larger than at Li+ insertion process. Furthermore, the capacity retention of TNO single particle tested at current of 10C after 2000 cycles was above 99%, indicating excellent intrinsic stability of TNO single particle for Li+ insertion and extraction reaction.

Rational design of a high-energy LiNi0.8Co0.15Al0.05O2 cathode for Li-ion batteries

The energy density of lithium ion batteries heavily relies on the loading of electrochemically active materials in their cathode. LiNi0.8Co0.15Al0.05O2 (NCA) as a promising high-energy cathode material has a practical specific capacity of about 200 mAh g−1 which, however, is often compromised by the additives in the electrode, such as the conductive carbon and binder. To harvest a higher energy density NCA electrode, cyclic voltammetry and galvanostatic intermittent titration techniques are employed herein to evaluate the apparent chemical diffusion coefficient of Li+ and maximize the loading of NCA. Our results show that the carbon content can be reduced to 0.2 wt% (with 97.8 wt% of NCA), making a high-energy cathode for Li-ion batteries. This protocol would also set a precedent for the energy density optimization of other cathodes.

Large lithium storage in highly crystalline TiNb2O7 nanoparticles synthesized by a hydrothermal method as anodes for lithium-ion batteries

Lithium storage in hydrothermally synthesized TiNb2O7 (H-TNO) nanoparticles has been investigated by electrochemical and structural analysis and compared with that in solid-state synthesized TiNb2O7 (S-TNO) particles. The H-TNO was characterized to be highly crystallized primary particles having a single-crystal-like structure with a uniform face orientation. Cyclic voltammogram and charge-discharge potential characteristics of the H-TNO showed that additional lithium storage occurred for x > 4.0 in LixTiNb2O7 between 0.9 and 0.75 vs. Li/Li+. The H-TNO used as the anodes for lithium-ion batteries had highly reversible capacities of 341 mAh g−1 and 1480 mAh cm−3, performance superior to that in the case of S-TNO. Ex-situ X-ray absorption fine structure (XAFS) analysis exhibited simultaneous changes in the charge compensation in Ti and Nb with an increase of Li+ ion amounts in H-TNO for x > 4.0. Apparent chemical diffusion coefficient (Dapp) values of lithium in the H-TNO for x > 3.5 were one order of magnitude larger than those in the S-TNO from the results of galvanostatic intermittent titration technique (GITT) analysis. The additional lithium storage in H-TNO was attributed to the enhancement of lithium diffusivity in the highly crystallized primary particles with the short lithium diffusion length. The H-TNO exhibited high capacity, high-rate charge capability, and long-cycle-life performance.

One-dimensional Co3O4 nanonet with enhanced rate performance for lithium ion batteries: Carbonyl-β-cyclodextrin inducing and kinetic analysis

Kinetics-limited solid-state diffusion rate results in low rate capacity, retarding the practical applications of Co3O4 anode materials. Construction of nanonet can introduce sufficient interior transport pathways for rapid charging-discharging. Here, we fabricate one-dimensional Co3O4 nanonet (1D-NN) through a facile hydrothermal method with subsequent heat treatment. The construction of nanonet is achieved by employing carbonyl-β-cyclodextrin (C-β-CD) as a crosslinking agent. With the absence of C-β-CD, 1D Co3O4 is also fabricated, while the constructing blocks are independent nanoparticles (1D-NP). Evaluated as anodes for lithium ion batteries, 1D-NN exhibits better rate capacity than 1D-NP. Furthermore, to extract the key reason of outstanding rate capacity, the kinetic properties with different time constants are studied by EIS, GITT and CV simultaneously. The charge transfer resistance and the apparent chemical diffusion coefficient of 1D-NN are more superior to that of 1D-NP. The results of this work show that the C-β-CD induced 1D nanonet structure is conducive to Li+ transport for enhanced rate performance.

Lithium Diffusion in Cation-Mixing-Free LiMn1-xFexPO4 Synthesized by Hydrothermal Process

Lithium diffusion properties of LiMn1-xFexPO4 synthesized by hydrothermal methods were characterized from electrochemical and structural analysis. Structural defects such as cation mixing in LiMn1-xFexPO4 impede the lithium-ion diffusion. Therefore, it is important to understand effects of cation mixing in LiMn1-xFexPO4 on lithium diffusivity of LiMn1-xFexPO4. The amount of cation mixing of lithium and Mn/Fe in LiMn1-xFexPO4 was obtained by means of neutron diffraction measurements. Rietveld refinements indicated that cation mixing in the prepared LiMn1-xFexPO4 was negligible. Apparent chemical diffusion coefficients (Dapp) of lithium of LiMn1-xFexPO4 dependent on the Mn/Fe ratio were obtained by potential-step chronoamperometry (PSCA) measurements of thin composite electrodes. Dapp of lithium insertion or extraction reaction of LiMn1-xFexPO4 for Mn2+/Mn3+ increased with Fe content. Dapp for Fe2+/Fe3+ slightly increased with decreasing Fe content. The difference of Dapp value was attributed to the activation energies (Ea) of lithium diffusion process of LiMn1-xFexPO4. The Ea of LiMn1-xFexPO4 for Mn2+/Mn3+ and Fe2+/Fe3+ was determined by the energy barrier of lithium hopping at the interphase between Li-rich and Li-poor phase under electrochemical kinetic conditions.

Simulation of oxygen diffusion process on electrical conductivity relaxation

Abstract Finite element method (FEM) simulations were carried out for modeling the electrical conductivity relaxation (ECR) process of a mixed ionic electronic conductor upon abrupt change of oxygen partial pressure. Oxygen diffusion pathway was simulated considering enhanced surface exchange rate on the current and voltage terminals formed on the specimen. The results suggested that the vacancy diffusion coefficient, DV, ECR, obtained from ECR method appears to be dependent on vacancy concentration, δ, even though the true DV is constant. The effects of the following parameters were investigated; degree of catalytic effect, surface reaction rate constant and sample dimension. Change in the sample dimension in a realistic range did not effectively suppress the modification of diffusion paths, and the change of apparent chemical diffusion coefficient, Dchem, app, was inevitable when surface reaction rate constant, kchem, and Dchem are in the same range. The results of the FEM simulation were confirmed by ECR experiments with catalytic active (Pt) and inactive (Au) electrodes.

Determination of Chemical Diffusion Coefficient of Lithium Ions in Ceramics Derived from Pyrolysed Poly(1,2-dimethylsilazane) and Starch

The apparent chemical diffusion coefficient Li+ (DappLI+) in pyrolysed poly(1,2-dimethylsilazane)/starch (PSN/S) (weight ratio: 30/70) ceramic anode composite is determined by galvanostatic intermittent titration technique (GITT). The electrode material composition is C6.00N0.14H0.47O0.12Si0.13. The calculated values of DappLI+, depend on the applied potential, vary from 10-14 to 10-9 [cm2/s]. The diffusion coefficient of lithium ions calculated in this work are similar with the values reported by other authors for carbonaceous anodes.

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.

Lithium Diffusion in Li4/3Ti5/3O4 Particles during Insertion and Extraction

Lithium diffusion in a small Li4/3Ti5/3O4 (LTO) particle was investigated from kinetic viewpoints of two-phase transition process based on a core-shell model by means of galvanostatic and potentiostatic measurements of thin LTO composite electrodes. High-rate galvanostatic charge (insertion) – discharge (extraction) properties of the thin LTO composite electrode showed that the insertion into the LTO particle was significantly slower than the extraction. An apparent chemical diffusion coefficient (Dapp ) of lithium in the LTO particle during the insertion and extraction was evaluated from the results of potential step chronoamperometry (PSCA) with a spherical finite diffusion model. The phase-boundary movements between the two phases in the cathodic and the anodic potential steps for a long-time region were controlled by lithium diffusion through Li7/3Ti5/3O4 rock-salt (LTO-rock-salt) and Li4/3Ti5/3O4 spinel (LTO-spinel) shell, respectively. Dapp in the LTO-rock-salt and the LTO-spinel phase were estimated to be approximately 1 × 10−12 cm2/s and 1.6 × 10−11 cm2/s, respectively. The slower insertion was mainly due to a Dapp value one order of magnitude smaller in the LTO-rock-salt than that in the LTO-spinel phase. Electrochemical kinetic properties of the LTO particle with the core-shell structure were interpreted by lithium diffusion through the LTO-rock-salt shell during the insertion and the LTO-spinel shell with the low electron conductivity during the extraction.

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.

Determination of the chemical diffusion coefficient of Li + in intercalation-type Li 3V 2(PO 4) 3 anode material

The chemical diffusion coefficients of lithium ion ( D Li + ) in intercalation-type Li 3V 2(PO 4) 3 (LVP) anode material as a function of cell voltage between 3.0 and 0.0 V are systematically determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). The true chemical diffusion coefficients ( D Li + true) obtained from EIS and GITT for the single-phase region (1.6–0.0 V vs. Li +/Li) are in the range of 10 −10 to 10 −9 cm 2 s −1 and 10 −11 to 10 −10 cm 2 s −1, respectively, and exhibit a decreasing trend of the change of D Li + true vs. voltage as the discharge and charge proceeded. The apparent chemical diffusion coefficients ( D Li + app) measured from CV and GITT for the two-phase regions (around 2.5–1.6 V) are in the range of 10 −10 cm 2 s −1 and 10 −12 to 10 −10 cm 2 s −1, respectively. For GITT, D Li + app vs. voltage plots display a characteristic of “W” shape due to the strong interactions of Li + with surrounding ions. Finally, the D Li + values of LVP anode are compared with other anode materials, illustrating that LVP can also be used as a potential anode material to achieve high rate capability.

A comparative study on the low-temperature performance of LiFePO 4/C and Li 3V 2(PO 4) 3/C cathodes for lithium-ion batteries

The electrochemical properties of the LiFePO 4/C (LFP/C) and Li 3V 2(PO 4) 3/C (LVP/C) samples are investigated using Li-ion half cells at various low temperatures of 23, 0, -10 and -20 °C in the electrolyte 1.0 M LiPF 6/EC + DMC (1:1 w/w). In the voltage range of 2.5-4.3 V at 0.3C rate, the LFP/C electrode shows a stable reversible discharge capacity of 45.4 mAh g −1 at -20 °C, which is 31.5% of the capacity obtained at 23 °C. In the voltage range of 3.0-4.3 V at 0.3C rate, the LVP/C electrode delivers a high stable reversible discharge capacity of 108.1 mAh g −1 at -20 °C, being 86.7% of the capacity at 23 °C. The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements illustrate that the resistance and cell polarization of LFP/C at various low temperatures are larger than those of LVP/C. In addition, using CV method, the apparent chemical diffusion coefficient of lithium ions ( D L i + app ) in LFP and LVP at various low temperatures are in the magnitude of 10 −11 and 10 −10 cm 2 s −1, respectively, and the D L i + app decreasing rate of LFP as the temperature is much larger than LVP, meaning that the kinetics of the LFP electrode is relatively slow. The activation energies of LFP and LVP are calculated to be 47.48 and 6.57 kJ mol −1, respectively, which further indicates that the extraction/intercalation of Li + in LVP is much easier than in LFP. The high reversible capacity of LVP/C at -20 °C makes it an attractive cathode for low-temperature lithium ion batteries.

Lithium-storage and cycleability of nano-CdSnO3 as an anode material for lithium-ion batteries

Nano-CdSnO3 is prepared by thermal decomposition of the precursor, CdSn(OH)6 at 600 °C for 6 h in air. The material is characterized physically by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM) and selected-area electron diffraction (SAED) techniques. Nano-CdSnO3 exhibits a reversible and stable capacity of 475(±5) mAh g−1 (∼5 mol of cycleable Li per mole of CdSnO3) for at least 40 cycles between 0.005 and 1.0 V at a current rate of 0.13 C. Extensive capacity fading is found when cycling in the range 0.005–1.3 V. Cyclic voltammetry studies complement galvanostatic cycling data and reveal average discharge and charge potentials of 0.2 and 0.4 V, respectively. The proposed reaction mechanism is supported by ex situ XRD, TEM and SAED studies. The electrochemical impedance spectra taken during 1st and 10th cycle are fitted with an equivalent circuit to evaluate impedance parameters and the apparent chemical diffusion coefficient (DLi+) of Li. The bulk impedance, Rb, dominates at low voltages (≤0.25 V), whereas the combined surface film and charge-transfer impedance (R(sf+ct)) and the Warburg impedance dominate at higher voltages, ≥0.25 V. The DLi+ is in the range of (0.5–0.9) × 10−13 cm2 s−1 at V = 0.5–1.0 V during the 10th cycle.

Li diffusion in LiNi 0.5Mn 0.5O 2 thin film electrodes prepared by pulsed laser deposition

Kinetic and transport parameters of Li ion during its extraction/insertion into thin film LiNi 0.5Mn 0.5O 2 free of binder and conductive additive were provided in this work. LiNi 0.5Mn 0.5O 2 thin film electrodes were grown on Au substrates by pulsed laser deposition (PLD) and post-annealed. The annealed films exhibit a pure layered phase with a high degree of crystallinity. Surface morphology and thin film thickness were investigated by field emission scanning electron microscopy (FESEM). The charge/discharge behavior and rate capability of the thin film electrodes were investigated on Li/LiNi 0.5Mn 0.5O 2 cells at different current densities. The kinetics of Li diffusion in these thin film electrodes were investigated by cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). CV was measured between 2.5 and 4.5 V at different scan rates from 0.1 to 2 mV/s. The apparent chemical diffusion coefficients of Li in the thin film electrode were calculated to be 3.13 × 10 −13 cm 2/s for Li intercalation and 7.44 × 10 −14 cm 2/s for Li deintercalation. The chemical diffusion coefficients of Li in the thin film electrode were determined to be in the range of 10 −12–10 −16 cm 2/s at different cell potentials by GITT. It is found that the Li diffusivity is highly dependent on the cell potential.

Cathode having high rate performance for a secondary Li-ion cell surface-modified by aluminum oxide nanoparticles

In order to enhance the electrochemical properties, the spinel LiMn 2O 4 electrode surface was modified with amorphous Al 2O 3 nanoparticle as heterogeneous phase. LiMn 2O 4 was in preparation based on a conventional solid-state reaction. The LiMn 2O 4 procedure was soaked in aluminum tri 2-propoxide solution. The LiMn 2O 4 whose surface was modified by aluminum oxide was obtained through the heat treatment at 400 °C for 4 h. The Al 2O 3-modified LiMn 2O 4 electrode exhibits a capacity higher than that of the unmodified LiMn 2O 4 electrode. On the other hand, no variation was shown with open circuit potential and apparent chemical diffusion coefficient of Li ion for LiMn 2O 4 before and after the surface modification. The charge-transfer resistance of Al 2O 3-modified LiMn 2O 4 decreased significantly in comparison with the unmodified LiMn 2O 4. The improved charge-transfer kinetics was largely attributed to Al 2O 3 which plays an important role of increasing the chemical potential at the electrode/electrolyte interface.

Li-storage in LiFe 1/4Mn 1/4Co 1/4Ni 1/4PO 4 solid solution

Olivine structured LiFe 1/4Mn 1/4Co 1/4Ni 1/4PO 4 in pure solid solution single phase was obtained using solid-state reaction. For the carbon-coated material, in a voltage range of 3.0–5.1 V (vs. Li/Li +), three voltage plateaus were observed clearly in both galvanostatic discharging and galvanostatic intermittent titration technique (GITT) curves. These three plateaus are corresponding to Co 3+/Co 2+, Mn 3+/Mn 2+ and Fe 3+/Fe 2+ redox couples. No definite plateau can be assigned to Ni 3+/Ni 2+ redox couple in this voltage range. The overpotentials show the maximum when the redox reaction shifts from one redox couple to another couple. The apparent chemical diffusion coefficients of lithium ( D ˜ Li ) are in the same order of magnitude 10 −15 cm 2 s −1 for all transition reactions.

Li-ion diffusion in highly (0 0 3) oriented LiCoO 2 thin film cathode prepared by pulsed laser deposition

A pure, well crystallized and highly (0 0 3) oriented LiCoO 2 thin film was deposited on stainless steel substrates by pulsed laser deposition. The overall diffusion coefficients of lithium-ion in the potential range between 3.85 and 4.2 V were measured by three different electrochemical methods namely, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration technique (PITT). From CV, the apparent chemical diffusion coefficient of lithium-ion was estimated to be 2 × 10 −13 cm 2/s. EIS revealed that the charge-transfer resistance obviously decreased above 3.90 V and changed little up to 4.22 V. The diffusion coefficients obtained from EIS were in the order of 10 −12 cm 2/s while they were in the range of 6 × 10 −13 and 8 × 10 −12 cm 2/s from PITT, depending on the potentials.