Lithium Diffusion Coefficient Research Articles

MXene-mediated regulation of local electric field surrounding polyoxometalate nanoparticles for improved lithium storage

Due to their capability of reversibly accepting multi lithium ions, polyoxometalates (POMs) have been widely regarded as promising candidates for electrochemical lithium storage. Nevertheless, the insulating nature of POMs hinders fast migration kinetics of lithium within the bulk of these materials. Herein, we propose the introduction of a local electric field surrounding the POM nanoparticles consisting of Mn and V where the concomitant Coulomb forces can accelerate the migration of lithium ions. After rationally hybridizing POMs with MXene nanosheets, the imbalanced charge distribution emerging at their interface produces the local electric field, thereby leading to a 250-fold increase of lithium diffusion coefficient. In this regard, a capacitive contribution as high as 81.7% at 1.0 mV s−1 is observed. Moreover, the POM nanoparticles could densely assemble on the surface of MXene nanosheets, offering highly packed electrodes and thus high volumetric capacities. Due to the improved lithiumion transfer kinetics, the POMs/MXenes composites are paired with activated carbon to produce lithium-ion capacitors which could offer a high energy density of 195.5 W h kg−1 and a large power capability of 3800 W kg−1. The findings in this work could build a clear relationship between materials with different conductivities for designing electrode materials.

Is Closed-Loop Recycling of Lithium-Ion Batteries Feasible ?

Rechargeable Li-ion batteries have been developed and marketed over the past 30 years and are used today in different fields like electric vehicles, portable electronics, etc. In a few years, the development of this technology has been exponential, and it has quickly imposed on the energy storage market. However, it is important to note that this technology is very dependent on metals (Co, Ni, Cu, Al, Li ...). These metals are rare, expensive and non-renewable. In addition, they are unevenly distributed in the earth's crust and their production is often very polluting. Thus, the massive use of this technology is creating an imbalance between the needs for metals and the existing primary resources, leading irrevocably to environmental and economic problems.Recycling this waste is therefore essential to both limit the overexploitation of primary metal resources and reduce their ecological impact.In terms of batteries recycling, two main families of processes can be distinguished. The first, known as pyrometallurgy, is based on the high-temperature treatment of waste. In contrast, hydrometallurgical processes are processes with significantly lower energy costs, as these processes are carried out at near ambient temperatures. The principle is to dissolve metals in their ionic form. Toxic acids (and their mixtures) are very often used, but other methods are possible (bases, complexing agents, oxidants). Once in solution, the metals can be recovered in the form of salts, hydroxides or in their metallic form by conventional chemical processes (precipitation, crystallization, etc.) or electrochemical processes (electro-deposition). Several separation / purification steps are sometimes necessary. Relatively few studies have looked at closed-loop recycling, i.e. the resynthesis and reuse of recycled materials in batteries.Thus, the objective of this project is to test the feasibility of closed-loop recycling of cathode materials from Li-ion batteries based on the use of innovative and less toxic recycling routes, and to verify the electrochemical performance of recycled materials at the end of the recycling process.To build this green cycle, the present study has been carried out using both model cathode materials (LCO, NMC) and real cathodes from spent drone batteries, that have been discharged, opened and dismantled in a glove box. All materials have, of course, been characterised (X-ray diffraction, SEM) and the present metals content has been quantified (wet digestion followed by AAS analyses) in order to be able to establish reliable material balances at the end of the recycling process.The developed closed-loop recycling process was composed of three subsequent steps:1) The cathode materials recovered have been leached in a deep eutectic solvent medium (DES) composed of ethylene glycol – choline chloride mixture, replacing the concentrated acids traditionally used. DES is a new class of green solvents, that is, non-harmful to human health and the environment compared to conventional organic solvents. They consist of a mixture of products (solids) which, at a given ratio, become liquid (eutectic), and which have the combined properties of the different constituents of the mixture.2) Synthesis of recycling active material from the DES media by precipitation and calcination.3) Assembly of button cells, followed by electrochemical tests and batteries post-mortem analyses (X-ray diffraction, SEM) have been carried-out at the last step.Composite electrodes made of recycled active materials, polymer binder and carbon have been formulated and assembled into button cells with a Li counter-electrode and a conventional separator (e.g. Celgard impregnated with liquid electrolyte). The prepared batteries were then recycled by electrochemical methods coupled with impedance measurements. The aging of the cells was carried out through one hundred charge / discharge cycles and a specified «fast charging» test developed in our laboratory, allowing to calculate the lithium diffusion coefficient in the cathode material.The results have shown that the recycling of metals has been successfully carried out using a deep eutectic solvent (DES), in a closed-loop manner. The leaching protocol have been optimized at the optimum conditions: ChCl: EG (1:2) with 0.8 mol.L-1 of HCl, with a ratio(wt.) S/L of 1/50, heated to 87.5 °C, for 2 h. After being completely dissolved, the metals have been then recovered from the DES by precipitation, calcined and reused as active materials. Using this method, the DES solvent has also been recovered and reused in a closed-loop without suffering any damage. This work has also shown that the recovered battery materials can be reused into the battery manufacturing cycle without changing their electrochemical performance. Indeed, this process allowed to obtain a homogeneous powder with a morphology similar to the initial materials (particle size <1 μm), presenting good capacities (154 mAh.g-1). Figure 1

Dry Particle Fusion Assisted Ceramic Coatings for High Nickel Cathode for Scalable 18650 Lithium-Ion Batteries

Over the last several decades, energy storage has become one of the central tools for facilitating energy transformation from (electro)chemical reactions to electricity. Rechargeable lithium-ion batteries (LIBs) are among the most popular and promising mature technologies for portable electronics, grids, and transportation. The cathode, a working horse, mainly determines the overall capacity among the various components. Off-late layered Li-rich or Ni-rich material plays a vital role, especially Ni-rich LiNixMnyCo1-x-yO2; x ≥ 0.8 (NMC) get significant attention. However, it is unfortunate that such Ni-rich cathode materials encountered severe capacity degradation and poor thermal instability concerning the Ni-concentration. Several strategies have already been proposed to mitigate those issues, including electrolyte additive, cation doping, and coating or surface modification. Among them, the modification of the cathode surface, like core-shell construction, is a practical approach. Herein, a core-shell architecture was achieved by employing the cost-effective dry particle fusion method over Ni-rich (LiNi0.8Mn0.1Co0.1O2 (NMC811), where the nano aluminum oxide was used as a shell material with an average thickness of 150-200 nm. Such NMC@alumina core-shell exhibits excellent cycling stability compared with pristine NMC811. The chemical lithium diffusion coefficient was calculated using galvanostatic (GITT) and the potentio-dynamics process. Additionally, the control of parasitic reaction between the delithiated cathode and electrolyte was analyzed using the in-situ Differential Electrochemical Mass Spectrometry (DEMs) technique, where the onset potential and the amount of gas generated are compared with pristine material.

(Digital Presentation) Accelerated Degradation Mechanism of Ni-Rich Ncm Cathode Materials at High and Low Voltage Range Combined Cycling for Li-Ion Batteries

Lithium-ion batteries are widely used as power sources in electric buses, railways, ferries, and other mass transportation systems. To meet the energy needs of these infrastructure systems, it is important to realize battery control that enables high-energy operation for long periods of time. The high-capacity Ni-rich cathode material NCM811 (LiNi0.8Co0.1Mn0.1O2) has attracted research interest as a candidate high-energy-density cathode material. However, NCM811 has been reported to have some degradation problems, especially when operating at potential above 4.2 V versus Li/Li+1).Furthermore, the safety of NCM811 becomes compromised with time. Therefore, understanding the aging mechanism and predicting battery aging behavior are required for effective battery control. We have found that operating NCM811 cathodes at the combination of the potential higher than 4.2 V and lower potential less than 3.6 V that accelerates aging, leading to substantial capacity loss and increased resistance. However, aging was mitigated when NCM811 batteries were operated at a higher or lower potential range. Electrochemical and chemical analyses were performed to clarify the aging mechanism. We prepared 1-Ah LTO/NCM811 pouch cells. Charge/discharge cycling tests were carried out using various state-of-charge (SOC) ranges (SOC0-100%, SOC20-100%, and SOC0-70%) at a 3C rate at 65°C. When the cell was charged at SOC100% and SOC0%, the cathode potential was set to above 4.2 V and to below 3.6 V. The capacity retention and DC resistance (DCR: SOC50%, 0.2 sec) for these cells are shown in Figure1a. The capacity retention of the cell after 1000 cycles at SOC0-100% cycling test was about 75% for the initial capacity. However, a high capacity retention of 93% was obtained at SOC20-100% cycling, despite the cell was charged at SOC100% of 1000 times. The capacity retention of SOC0-70% cycling was nearly 100%. DCR increased 2.5-times after 1000 cycles at SOC0-100% cycling, which was higher increase than that of SOC20-100% cycling and SOC0-70% cycling. To clarify the mechanism, the cathode was removed from the deteriorated pouch cells and its electrochemical properties were investigated using a three-electrode glass beaker cell. The cell was assembled using the cathode and lithium metal as a counter electrode, and a reference electrode was also prepared. The lithium-diffusion coefficient of NCM811 at the time of preparation and after 1000 cycles was measured using the galvanostatic intermittent titration technique method. In the case of a NCM811 cathode operated at SOC0-100% for 1000 cycles, there was little change for the lithium-diffusion coefficient of x < 0.8 in LixNi0.8Co0.1Mn0.1O2, but that of x > 0.8 decreased to less than 1/10. Changes in the crystal structure of the NCM811 particle surface were analyzed by scanning transmission electron microscopy–electron energy loss spectroscopy (STEM-EELS). The thickness of the surface structural change layer was calculated from the EELS spectrum. Also, the thickness and composition of surface film was analyzed by hard X-ray photoelectron spectroscopy (HAX-PES). This measurement was performed at the SPring-8 synchrotron radiation facility. From the STEM-EELS analyses, in the case of SOC0-100% cycling, the surface crystal structure of NCM811 changed from the layered type to the rock-salt or spinel-layer type. The thickness of this transition layer increased by 7 nm compared from beginning. In the case of SOC0-70% cycling, the thickness increased by only 2 nm. It is expected that the cathode operated above 4.2 V at SOC0-100% cycling. From the HAX-PES analysis, the film thickness increased by 20 nm from the initial condition after SOC0-100% cycling. But, after SOC20-100% cycling and SOC0-70% cycling, the film thickness increased was suppressed than that. Based on the results of these analyses, we proposed the following model. In the first step, the structure change of NCM811 was accelerated at high potential. As the rock-salt layer disturbed lithium diffusion, the diffusional resistance increased and the capacity during discharge decreased. In the second step, when NCM811 subjected to a higher potential was discharged to a lower potential, the lithium can’t be intercalated smoothly at the surface x > 0.8 in LixNi0.8Co0.1Mn0.1O2. As a result, the lithium near the surface reacts with electrolyte, forming a film on the NCM811 surface. As the lithium was consumed by the film-growth reaction, the cathode operating potential increased, which accelerated the first step mechanism. The combination of the first and second steps accelerated aging. But this aging can be minimized by controlling the operating voltage. Understanding of the aging mechanism will enable accurate prediction of deterioration.[1]F. Friedrich, B. Strehle, etc, Journal of The Electrochemical Society, 166, A3760-A3774 (2019) Figure 1

A second nearest-neighbor modified embedded-atom method combined with a charge equilibration interatomic potential for the Li–Ni–O ternary system and Li diffusion in lithium-ion battery cathode structure

Ni is a key element, especially in layered cathodes, to achieve a large capacity and a reduced cost. To analyze and gain insight into such cathode materials, large-scale atomistic simulations such as molecular dynamics (MD) are a suitable method. In this paper, a Li–Ni–O interatomic potential has been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NNMEAM) formalism combined with a charge equilibration (Qeq) concept. This potential reproduces fundamental properties (thermodynamic, structural, elastic) of lithium-nickel and nickel oxide binary systems as well as the lithium-nickel oxide ternary system in good agreement with experiments and first-principles calculations. Lithium diffusion properties such as the activation energy for lithium migration and diffusion coefficients in Li1-xNiO2 layered structures are also calculated by a MD simulation and found to show the same tendency as observed in experiments. The potential can be utilized for simulating various material phenomena in the Li-ion battery (LIB) system and can be easily extended to the mainly used Li-[Ni,Mn,Co]-O quinary system, in combination with already developed Li–Mn–O and Li–Co–O ternary potentials based on the same formalism.

Kinetic insights into LixNi0.67N (1.67 ≤ x ≤ 2.17), a quasi “zero-strain” negative electrode material for Li-ion battery

The kinetics of the electrochemical lithium intercalation in the nitridonickelate LixNi0.67N (1.67 ≤ x ≤ 2.17) is investigated by electrochemical impedance spectroscopy during a full reduction-oxidation cycle in a two-electrode cell. The layered structure of this anode material delivers a reversible and stable specific capacity of 200 mAh g−1 over 100 cycles at C/10 near 0.5 V vs Li+/Li. The equivalent electric circuit simulation allows a full assignment of the impedance spectra, with different contributions including the SEI layers on each electrode, charge transfer and Li diffusion. The calculated lithium diffusion coefficient value of approximately 5 × 10−9 cm 2 s−1 almost does not vary with the lithium content in LixNi0.67N (1.67 ≤ x ≤ 2.17). Conversely, the charge transfer resistance (Rct) is found to strongly depend on the depth of reduction to be maximum for the fully reduced electrode, with a totally reversible behavior during oxidation. The overall impedance of the cell remains stable upon long cycling, which indicates a good chemical stability of the SEI on LixNi0.67N as well as remarkable structural and chemical stability of the nitridonickelate upon cycles. The present kinetic findings shed light on the remarkable “zero-strain” behavior of this negative electrode material presenting numerous Li vacancies.

Effect of Mechanical Activation and Carbon Coating on Electrochemistry of TiNb2O7 Anodes for Lithium-Ion Batteries

TiNb2O7 anode material with a Wadsley–Roth crystallographic shear structure was prepared by solid-state synthesis at a relatively low temperature (1000 °C) and a short calcination time (4 h) using preliminary mechanical activation of the reagent mixture. The as-prepared final product was then ball milled in a planetary mill with and without carbon black. The crystal structure and morphology of the samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical performance was studied in a galvanostatic mode in varied voltage intervals and at different cycling rates in combination with in situ electrochemical impedance spectroscopy (EIS) measurements. The resistance measured using in situ EIS had the highest values at the end of the discharge and the lowest when charging. The lithium diffusion coefficient, determined by galvanostatic intermittent titration technique (GITT), in samples milled with and without carbon black was an order of magnitude higher than that for the pristine sample. It was shown that improved electrochemical performance of the carbon composite TiNb2O7/C (reversible capacity of 250 mAh g−1 at C/10 with Coulomb efficiency of ~99%) was associated with improved conductivity due to the formation of a conductive carbon matrix and uniform distribution of submicron particles by size.

Melt Synthesis of Lithium Manganese Iron Phosphate: Part II. Particle Size, Electrochemical Performance, and Solid-State Lithium Diffusion

Melt synthesis is a fast and simple process to make dense LiMnyFe1−yPO4 (LMFP with 0 ≤ y ≤ 1) from all-dry, low-cost precursors with zero waste. Part one of this study confirmed that highly crystalline and phase pure LMFP materials can be made by melt synthesis. This part shows that planetary milling can reduce the primary particle size of melt LMFP (0%–75% Mn) to ∼200 nm, which is smaller than the primary particles in commercial LFP reference material (0% Mn). However, further particle size reduction is needed to reach particle sizes below 70 nm observed in reference LMFP (79% Mn). Melt LFP shows almost identical specific capacity and charge/discharge voltage as reference LFP. Melt LMFP materials show a high voltage Mn plateau at ∼4 V associated with the Mn2+/3+ redox, the length of which scales with Mn content. The Mn plateau raises the average discharge voltage of LMFP; hence a minimum specific discharge capacity between 160 mAh g−1 (0% Mn) and 145 mAh g−1 (80% Mn) is sufficient to match the volumetric energy density of LFP. The Atlung Method for Intercalant Diffusion shows that the lithium diffusion coefficient in LMFP is ∼1 order of magnitude higher in the voltage region of the Fe2+/3+ redox couple (3.75–3.1 V vs Li+/Li) than in the voltage region of the Mn2+/3+ redox couple (4.3–3.75 V vs Li+/Li). This emphasizes the need for very small primary particles when making LMFP with relatively high Mn content.

Melt Synthesis of Lithium Manganese Iron Phosphate: Part I. Composition, Physical Properties, Structural Analysis, and Charge/Discharge Cycling

Melt synthesis is a fast and simple process to make dense LiMnyFe1-yPO4 (LMFP with 0 ≤ y ≤ 1) from all-dry, low-cost precursors with zero waste. This study characterizes melt LMFP materials with 0%–100% Mn after particle size reduction by planetary milling and carbon coating with glucose. The melt LMFP samples show higher electrical conductivity at similar pellet density than LFP (0% Mn) and LMFP (79% Mn) reference samples made by traditional methods. The melt LMFP samples exhibit higher crystallinity than the reference samples and show no crystalline impurities. Their unit cell volume and crystallographic density scale with Mn content; the percentage of Fe and/or Mn in Li positions is below 1.5%, which is comparable to reference samples. Crystallite sizes of at least 100 to 175 nm are observed for melt LMFP, which is larger than the fine ∼50 nm crystallites of reference LMFP. Melt LFP shows specific discharge capacity and cycling stability comparable to reference LFP, but the melt LMFP samples with 25%–100% Mn shows worse performance than reference LMFP (79% Mn). Part two of this study will quantify the solid-state lithium diffusion coefficient in melt LMFP materials and correlate it to their electrochemical performance.

Phase Evolution and Li Diffusion in LATP Solid‐State Electrolyte Synthesized via a Direct Heat‐Cycling Method

Herein, the direct synthesis of phase‐pure lithium aluminum titanium phosphate (Li1.3Al0.3Ti1.7(PO4)3, LATP) solid‐electrolyte powder in 220 min and relatively low temperatures (850 °C) is achieved via a new (cyclic) fast heat treatment (c‐FHT) route. The complex structural evolution highlights rate‐limited lithium incorporation of intermediate metal phosphates formed prior to the final phase‐pure LATP. The prepared LATP product powder displays similar bulk (2 × 10−10 cm2 s−1) and local (3 × 10−10 cm2 s−1) values for lithium diffusion coefficients (DLi) characterized by electrochemical impedance spectroscopy and muon spin relaxation (μSR), respectively. The similarity between both DLi values suggests excellent retention of inter‐ and intraparticle lithium diffusion, which is attributed to the absence of deleterious surface impurities such as AlPO4. A low‐energy barrier (Ea = 73 meV) of lithium diffusion is also estimated from the μSR data.

Nucleation of Helium in Liquid Lithium at 843 K and High Pressures

Fusion energy stands out as a promising alternative for a future decarbonised energy system. In order to be sustainable, future fusion nuclear reactors will have to produce their own tritium. In the so-called breeding blanket of a reactor, the neutron bombardment of lithium will produce the desired tritium, but also helium, which can trigger nucleation mechanisms owing to the very low solubility of helium in liquid metals. An understanding of the underlying microscopic processes is important for improving the efficiency, sustainability and reliability of the fusion energy conversion process. The spontaneous creation of helium droplets or bubbles in the liquid metal used as breeding material in some designs may be a serious issue for the performance of the breeding blankets. This phenomenon has yet to be fully studied and understood. This work aims to provide some insight on the behaviour of lithium and helium mixtures at experimentally corresponding operating conditions (843 K and pressures between and 10 Pa). We report a microscopic study of the thermodynamic, structural and dynamical properties of lithium–helium mixtures, as a first step to the simulation of the environment in a nuclear fusion power plant. We introduce a new microscopic model devised to describe the formation of helium droplets in the thermodynamic range considered. Our model predicts the formation of helium droplets at pressures around 10 Pa, with radii between 1 and 2 Å. The diffusion coefficient of lithium (2 Å/ps) is in excellent agreement with reference experimental data, whereas the diffusion coefficient of helium is in the range of 1 Å/ps and tends to decrease as pressure increases.

Stable lithium anode enabled by biphasic hybrid SEI layer toward high-performance lithium metal batteries

Lithium (Li) metal has been proposed as the most promising anode for secondary lithium batteries with high energy density due to its considerable theoretical capacity (3860 mAh g−1) and lowest electrochemical potential (-3.04 V vs standard hydrogen electrode). However, the uncontrollable dendrite Li issues over repeated plating/stripping process results in huge volume change, low Coulombic efficiencies (CEs), and poor cycling performance. Here, a solid electrolyte interphase (SEI) layer mainly consisting of biphasic hybrid Li3Sb and LiF has been successfully in situ constructed on Li surface by spontaneous chemical reaction between Li and SbF3. The modified SEI can induce Li ions depositing on the linked-particle layer resulting from the relative low lithium diffusion coefficient of SEI layer component. The Li/Li symmetric cells with SbF3-modified Li (SF-Li) anodes show stable cycling over 400 h at 3.0 mA cm−2 for 3.0 mAh cm−2. The Li-S batteries with SF-Li anodes and ether-based electrolyte can achieve steady long-term cycling performance and high CEs. Particularly, the high voltage LiCoO2 (LCO)/Li batteries with SF-Li anodes and carbonate-based electrolyte also deliver excellent electrochemical properties even at harsh conditions. This work offers a new strategy to regulate Li ion deposition and benefits for the further development of safe Li metal batteries (LMBs).

Emcoating Architecture Construction via CO2 /H2 Coupling Treatment Doubles Reversible Capacity of NbO2 /C Anode.

As a promising alternative as lithium-ion anode, niobium dioxide appeals to researchers due to high theoretical capacity and good electron conductivity. However, rarely work about NbO2 based high performance anode is reported. Here, NbO2 nanoparticles emcoated in continuous carbon matrix is constructed through CO2 /H2 coupling treatment. CO2 activation introduces unique carbon emcoating structure, which builds interconnected electron conductive network with low carbon content. Furthermore, crystallographic phase of NbO2 is enhanced during H2 treatment, which increases the lithium storage ability. Electrochemical performance of NbO2 anodes is significantly improved based on the carbon emcoating structure. A high reversible capacity of 391 mAh g-1 is retained after 350 cycles at 0.2 C. Additionally, at a current density of 1 A g-1 , the reversible capacity reaches 139 mAh g-1 . Compared with conventional NbO2 /C nanohybrids, the lithium diffusion coefficient of carbon-emcoated sample shows improvement of three orders of magnitude. Moreover, the in situ XRD investigation shows a reversible lithium insertion behaviour with a limited volume change.

Optimization of LIB Electrolyte and Exploration of Novel Compounds via the Molecular Dynamics Method

Due to great interest in the development of electric vehicles and other applications, improving the performances of lithium-ion batteries (LIBs) is crucial. Specifically, components of electrolytes for LIBs should be adequately chosen from hundreds of thousands of candidate compounds. In this study, we aimed to evaluate some physical properties expected for combinations of molecules for electrolytes by microscopic simulations. That is, the viscosity, ionic conductivity, degree of dissociation, diffusion coefficient, and conformation of each molecule were analyzed via molecular dynamics (MD) simulations. We aimed to understand how molecular-sized structures and properties collaboratively affect the behavior of electrolytes. The practical models of molecules we used were ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL), γ-valerolactone (GVL), dimethyl carbonate (DMC), ethyl-methyl carbonate (EMC), diethyl carbonate (DEC), and lithium hexafluorophosphate (LiPF6). Many molecular systems of electrolytes were simulated, in which one molar LiPF6 was mixed into a single or combined solvent. It was found that small solvent molecules diffused with relative ease, and they contributed to the higher ionic conductivity of electrolytes. It was clarified that the diffusion coefficient of lithium (Li) ions is greatly affected by the surrounding solvent molecules. We can conclude that high-permittivity solvents can be selectively coordinated around Li ions, and Li salts are sufficiently dissociated, even when there is only a small content of high-permittivity solvent. Thus, we can confirm solely by MD simulation that one of the better candidates for solvent molecules, formamide (F), will exhibit higher performance than the current solvents.

Influence of Lithium Ion Kinetics, Particle Morphology and Voids on the Electrochemical Performance of Composite Cathodes for All-Solid-State Batteries

With the ongoing transformation to e-mobility, lithium all-solid-state batteries are promising candidates for advanced mobile energy storage. Other than in conventional lithium ion cells, the rigid solid electrolyte entails its own morphology and does not wet residual voids in composite electrodes, which can limit the cell performance. We therefore take a closer look at the influence of microstructural characteristics on different scales in composite cathodes by means of electrochemical simulation using the finite element method. Cathode active material particle arrangements are constructed to validate the model against experimental data. We highlight the significance of the active material particle size distribution and state-of-charge dependent input parameters, such as the lithium diffusion coefficient in NCM811 and the exchange current density at the interface of NCM811 and Li6PS5Cl. We zoom in on that interface under the presence of void space that can result from manufacturing or arise from inter-particle contact loss upon volume changes. In a 1-particle-void model, the impact of the active surface area covered by voids is studied as well as the influence of the void distribution and the void size on the electrochemical performance. Beyond that, we simulate a tortuosity-optimized structured electrode and provide first guidelines for laser-patterned all-solid-state cathodes.

Electrodeposition of Silicon from Molten KCl-K2SiF6 for Lithium-Ion Batteries

In this paper we report characteristics and electrochemical properties of silicon fibers used as lithium-ion battery anode. All samples were synthesized by potentiostatic electrodeposition from molten KCl–K2SiF6. From molten KCl–CsCl–K2SiF6 deposition was carried out in galvanostatic mode. Despite the synthesis in inert atmosphere and absence of oxygen containing compounds in the melt resulting silicon after washing contains at least 15 at% oxygen. Silicon fibers synthesized at −250 mV (vs Si) were the thinnest with diameter as small as 100 nm; average fiber length increased with increasing overvoltage. Addition of CsCl to the melt results in decrease of the average fibers diameter. Silicon fibers synthesized at −250 mV (vs Si) in KCl–K2SiF6 melt showed the best cycling performance with capacity of 1030 mAh·g−1 at 0.2 A·g−1 discharge current and capacity of 715 mAh·g−1 after 10 cycles. Lithium diffusion coefficients calculated from galvanostatic intermittent titration technique (GITT) are common for silicon-based anode. The highest initial diffusion coefficient value of 6.68·10−11 cm2·s−1 was achieved for silicon synthesized from melt with addition of CsCl. Low capacity and rapid capacity fading for all samples can be caused by high silicon dioxide content, further treatment of synthesized silicon is necessary to achieve higher performance.

High performance all-solid-state lithium battery: Assessment of the temperature dependence of Li diffusion

All-solid-state silicon/LiPON/lithium model batteries are assembled via magnetron sputtering followed by a lithium evaporation process. The cells were characterized via cyclic voltammetry, linear sweep voltammetry and impedance spectroscopy. Cyclic voltammetry confirms a long-term stability and high coulombic efficiency of the solid cells. Also, the assembled batteries were tested at extraordinary high scan rates, showing remarkably high output currents and an exceptional fast-cycling capability. Further rate-dependent investigations via linear sweep voltammetry indicate clearly two different ion-transport mechanisms in the silicon electrode at low and high scan rates. While a diffusion-controlled mechanism is suggested at high scan rates, a homogenous concentration profile is expected at extremely low rates. As a decisive advantage of solid-state cells, electrochemical cycling can be performed at elevated temperatures. This is used to determine the temperature dependence of the diffusion coefficients of lithium in the silicon electrode from room temperature to 165 °C. The effective activation energy of the lithium-ion migration in silicon is obtained to 0.1 eV, which is remarkably lower than that of inside LiPON, i.e. 0.55 eV. Complementary impedance data reveal that the kinetics of transport in the solid-state setup at very high output currents and low temperatures is controlled by lithium-ion migration in the LiPON film. • High rate capability and temperature durability of solid-state battery are shown. • Long-term stability and high coulombic efficiency are demonstrated. • Lithiation of silicon exhibits different kinetic regimes at low and high scan rates. • Temperature dependence of diffusion coefficients of lithium in Si was determined.

Зависимость электрохимических параметров композитных SiO/C-анодов для литий-ионных аккумуляторов от состава и температуры синтеза

The results of a study of anodes obtained by carbonization of silicon monoxide by means of a reaction with solid-phase fluorocarbon CF0.8 are presented. Charge/discharge voltage profiles were studied at different currents depending on the composition and temperature of the synthesis of composites. The irreversible losses of the 1st cycle and the contribution to them of intrinsic losses due to the formation of lithium oxide and its silicates and losses associated with the formation of SEI are analyzed. A difference has been established in the behavior of anodes made of SiO carbonized by annealing with CF0.8 at T=800°C (SiO/C composite) and silicon monoxide annealed with CF0.8 at T&gt;1000°C, at which disproportionation occurs simultaneously with the carbonization of SiO (d-SiO/C composite). The difference consisting in a higher discharge capacity, a higher Coulomb efficiency, and better rate capability of d-SiO/C is explained by a change in the composition of the SiOx matrix that occurs during the disproportionation process. The effect of the formation of d-SiO/C anodes by preliminary lithiation with a low current, after which the electrodes can be charged and discharged with much higher currents, has been discovered. The effect is explained by the amorphization of silicon crystallites and the increasing diffusion coefficient of lithium

Dependence of the electrochemical parameters of composite SiO/C anodes for lithium-ion batteries on the composition and synthesis temperature

The results of a study of anodes obtained by carbonization of silicon monoxide by means of a reaction with solid-phase fluorocarbon CF0.8 are presented. Charge/discharge voltage profiles were studied at different currents depending on the composition and temperature of the synthesis of composites. The irreversible losses of the 1st cycle and the contribution to them of intrinsic losses due to the formation of lithium oxide and its silicates and losses associated with the formation of SEI are analyzed. A difference has been established in the behavior of anodes made of SiO carbonized by annealing with CF0.8 at T=800oC (SiO/C composite) and silicon monoxide annealed with CF0.8 at T&amp;gt;1000oC at which disproportionation occurs simultaneously with the carbonization of SiO (d-SiO/C composite). The difference consisting in a higher discharge capacity, a higher Coulomb efficiency, and better rate capability of d-SiO/C is explained by a change in the composition of the SiOx matrix that occurs during the disproportionation process. The effect of the formation of d-SiO/C anodes by preliminary lithiation with a low current, after which the electrodes can be charged and discharged with much higher currents, has been discovered. The effect is explained by the amorphization of silicon crystallites and the increasing diffusion coefficient of lithium. Keywords: composite anodes SiO/C, lithium-ion batteries, disproportionation silicon monoxide, carbonization with fluorocarbon.

Electrochemical model analysis of bulk-type all-solid-state lithium-ion battery

This paper presents a numerical analysis of bulk-type all-solid-state lithium-ion batteries. The electrochemical modeling for analyzing all-solid-state batteries (ASSBs) is described, in which a single-ion conducting electrolyte theory is presented and coupled with the pseudo-two-dimensional (P2D) battery model used for lithium intercalation reactions in the porous electrodes. The benchmark study for an all-solid-state cell of Li/Li9.6P3S12/LiNbO3-coated LiCoO2 is performed using COMSOL Multiphysics®. The calculated charge-discharge curves agree well with the available experimental data. The modeling for the lithium diffusion coefficient in electrode active material particles, which is represented as a function of lithium stoichiometry, is also examined.