Initial Cycle Research Articles

Understanding the Origin of Unreliable Low-Resistance State During Initialization Process

The main factor hindering the massive employment for resistive random access memory (RRAM) can be ascribed to reliability issues. It has been reported that resistive switching (RS) characteristics were unstable during initial <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}-{V}$ </tex-math></inline-formula> cycles; however, the reason has not been studied yet. In this article, the mechanism for a significant increase in a low-resistance state (LRS) value during the initial cycles has been investigated. In this article, we suggest that the initialization process is actually the formation process of a stable TaOx interface layer between the RS layer and the top electrode (TE). Furthermore, a co-regulation model of the filament-type and the interface-type switching mechanisms on RS behavior is proposed, which explains the complete working process of devices. By reducing the size of the device and increasing the positive stop voltage, the initialization process of the device has been greatly shortened. This article may promote the development of advanced and reliable RRAM devices.

The Evolution Tracking of Tribasic Lead Sulfates Features in Lead-Acid Battery Positive Electrode using Design of Experiments

The positive electrode of lead-acid battery (LAB) still limits battery performance. Several approaches have been attempted to remedy this problem either with the incorporation of additives or by electrode modification. However initial performance and cycling of the LAB is determined by the kind and content of basic lead sulfate in the paste. As a result, it is critical to comprehend the mechanisms that take place during paste manufacture and how they affect the properties of the active materials. In this work, the experimental design methodology was applied to track the crystallite size and content of tribasic lead sulfates (3BS), and specific surface area of cured paste, using the AZURAD® software. The effect of two quantitative factors (water/LO ratio and acid/LO ratio) and one qualitative factor (curing program) were studied. SEM, XRD and BET were used to characterize the cured pastes. The acid/LO ratio plays an important role in determining the 3BS phase content reaching 78% for crystalline phase. At high temperatures, the acid/LO ratio shows, more influence on the 3BS crystallites size attaining a maximum value of 58 nm. The temperature in the curing step mitigates the effect of both ratios on the crystallites size of 3BS and SSA of cured paste. Results reveals two zones of nanostructured paste material evolution delimited at 10% of acid/LO ratio.

Boosting high initial coulombic efficiency of hard carbon by in-situ electrochemical presodiation

Hard carbon (HC) is a promising anode material for sodium ion batteries (SIBs), whereas inferior initial coulombic efficiency (ICE) severely limits its practical application. In the present work, we propose an in situ electrochemical presodiation approach to improve ICE by mixing sodium biphenyl (Na-Bp) dimethoxyethane (DME) solution with DME-based ether electrolyte. A solid electrolyte interface (SEI) could be formed beforehand on the HC electrode and Na+ was absorbed to nanopores and graphene stacks, compensating for the sodium loss and preventing electrolyte decomposition during the initial charge and discharge cycle. By this way, the ICE of half-cells was increased to nearly 100 % and that of full-cells from 45% to 96% with energy density from 132.9 to 230.5 W h kg−1. Our work provides an efficient and facile method for improving ICE, which can potentially promote the practical application of HC-based materials.

A numerical study on the battery thermal management system with mini-channel cold plate considering battery aging effect

Battery aging is critical for the batteries in electric vehicles, significantly affecting both thermal characteristics and electrochemical performance. In this research, a more realistic and generic model combining the electrochemistry, capacity fade and heat transfer is developed for the design of battery thermal management system (BTMS) to ensure efficient and durable operation of batteries. The thermal behaviors and electrochemical characteristics in different working cycles of BTMSs with X direction and Y direction mini-channels are analyzed and compared. It is found that BTMSs only provide effective cooling to batteries in their initial working cycles but fail to control the battery temperature after 1000 cycles due to the higher heat generation rate of aged battery caused by solid electrolyte interphase (SEI) formation. In addition, BTMS with Y direction mini-channels always provides more effective cooling to batteries to achieve good electrochemical performance with acceptable higher pressure loss during battery cycling. Furthermore, the optimization schemes are proposed for BTMS with Y direction mini-channels to further enhance cooling of the battery for high performance and durable operation of the batteries. The results show that optimizing mini-channel arrangement, arranging circular pin fins (CPF) and dispersing nanoparticles into coolant can be helpful for BTMS to provide effective thermal manage, achieve higher average potential and prevent SEI formation and capacity fade even after 1000 cycles, although the pressure loss is also higher.

Multilayer redox-based HfOx/Al2O3/TiO2 memristive structures for neuromorphic computing

Redox-based memristive devices have shown great potential for application in neuromorphic computing systems. However, the demands on the device characteristics depend on the implemented computational scheme and unifying the desired properties in one stable device is still challenging. Understanding how and to what extend the device characteristics can be tuned and stabilized is crucial for developing application specific designs. Here, we present memristive devices with a functional trilayer of HfOx/Al2O3/TiO2 tailored by the stoichiometry of HfOx (x = 1.8, 2) and the operating conditions. The device properties are experimentally analyzed, and a physics-based device model is developed to provide a microscopic interpretation and explain the role of the Al2O3 layer for a stable performance. Our results demonstrate that the resistive switching mechanism can be tuned from area type to filament type in the same device, which is well explained by the model: the Al2O3 layer stabilizes the area-type switching mechanism by controlling the formation of oxygen vacancies at the Al2O3/HfOx interface with an estimated formation energy of ≈ 1.65 ± 0.05 eV. Such stabilized area-type devices combine multi-level analog switching, linear resistance change, and long retention times (≈ 107–108 s) without external current compliance and initial electroforming cycles. This combination is a significant improvement compared to previous bilayer devices and makes the devices potentially interesting for future integration into memristive circuits for neuromorphic applications.

Low cycle fatigue properties of refractory high-entropy HfNbTiZr alloy

Considerable effort has been applied toward developing refractory high-entropy alloys (RHEAs) with both high strength and good ductility. However, the deformation and fatigue failure mechanisms of these alloys under cyclic loading remain poorly understood. The present work addresses this issue by investigating the low-cycle deformation behavior and microstructural evolution of an HfNbTiZr RHEA with a nominal composition of 25 mol% each of Hf, Nb, and Ti, and Zr forming the balance under symmetric tension-compression conditions at room temperature. Analysis of the cyclic stress responses of the alloy reveals a variety of internal stress trends at different strain amplitudes (Δεa), which implies the operations of a variety of cyclic deformation mechanisms. Further analysis demonstrates that cyclic softening is mainly caused by a rapid decrease in frictional stress during the initial cycles representing roughly 10% of the total number of cycles to failure. In general, the microstructural characteristics of the alloy observed with an increasing number of cycles under various values of Δεa demonstrate that softening occurs due to the formation of slip bands (SBs) caused by high-density dislocations arising in conjunction with increasing plastic strain accumulation. Specifically, dislocation structures forming at a low value of Δεa = 0.8% mainly consist of planar SBs (PSBs), while low-density cross SBs (CSBs) form at Δεa = 1.1%, and the density of the CSBs increases with further increasing Δεa. In addition, a fatigue lifetime prediction model was presented that obtained good prediction accuracy for the HfNbTiZr RHEA investigated herein. Accordingly, the present study can be expected to provide a fundamental basis for understanding the deformation mechanisms of other RHEAs.

Ultra-long cycle life organic-sodium batteries enabled by thiophene-based porphyrin in-situ electropolymerization

Organic-sodium batteries have attracted extensive attention due to the abundance of sodium resource and the molecular tunability of organic materials. However, the dissolution of organic materials in electrolytes and low electronic conductivity limit its development. Here, a porphyrin complex of [5,15-di(thiophen-2-yl) porphinato] M(II) (MTP, M = Cu, Ni) is proposed as highly stable cathode material for organic-sodium batteries. Benefiting from the multiple electron transfer of metal porphyrin complex and in-situ polymerization of thiophene groups of porphyrin complex in initial cycles, the CuTP cathode delivers a reversible capacity of 203 mAh/g at 100 mA g−1 and long-term cycling stability up to 11,000 cycles at a high current density of 5 A/g owing to the enhanced conjugated structure induced by in situ polymerization process. A specific energy density of 508 Wh kg−1 and a power density of 18 KW kg−1 are achieved for metal porphyrin-based cathode. The charge storage sites and in-situ polymerization mechanism of MTP cathode are systematically evaluated by both experimental and simulated studies. This study would provide a new strategy to address the dissolution issue of organic cathode and improve cycling stability of the organic-sodium batteries.

Genotyping marker density and prediction models effects in long-term breeding schemes of cross-pollinated crops.

In genomic recurrent selection, the more markers, the better because they buffer the linkage disequilibrium losses caused by recombination over cycles, and consequently, provide higher responses to selection. Reductions of genotyping marker density have been extensively evaluated as potential strategies to reduce the genotyping costs of genomic selection (GS). Low-density marker panels are appealing in GS because they entail lower multicollinearity and computing time and allow more individuals to be genotyped for the same cost. However, statistical models used in GS are usually evaluated with empirical data, using "static" training sets and populations. This may be adequate for making predictions during a breeding program's initial cycles but not for the long-term. Moreover, studies that focus on long selective breeding cycles generally do not consider GS models with the effect of dominance, which is particularly important for breeding outcomes in cross-pollinated crops. Hence, dominance effects are important and unexplored in GS for long-term programs involving allogamous species. To address it, we employed two approaches: analysis of empirical maize datasets and simulations of long-term breeding applying phenotypic and genomic recurrent selection (intrapopulation and reciprocal schemes). In both schemes, we simulated twenty breeding cycles and assessed the effect of marker density reduction on the population mean, the best crosses, additive variance, selective accuracy, and response to selection with models [additive, additive-dominant, general (GCA), and this plus specific combining ability (GCA + SCA)]. Our results indicate that marker reduction based on linkage disequilibrium levels provides useful predictions only within a cycle, as accuracy significantly decreases over cycles. In the long-term, without training set updating, high-marker density provides the best responses to selection. The model to be used depends on the breeding scheme: additive for intrapopulation and additive-dominant or GCA + SCA for reciprocal.

Evaluation of the Stability of Diamine-Appended Mg2(dobpdc) Frameworks to Sulfur Dioxide.

Diamine-appended Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) metal-organic frameworks are a promising class of CO2 adsorbents, although their stability to SO2─a trace component of industrially relevant exhaust streams─remains largely untested. Here, we investigate the impact of SO2 on the stability and CO2 capture performance of dmpn-Mg2(dobpdc) (dmpn = 2,2-dimethyl-1,3-propanediamine), a candidate material for carbon capture from coal flue gas. Using SO2 breakthrough experiments and CO2 isobar measurements, we find that the material retains 91% of its CO2 capacity after saturation with a wet simulated flue gas containing representative levels of CO2 and SO2, highlighting the robustness of this framework to SO2 under realistic CO2 capture conditions. Initial SO2 cycling experiments suggest dmpn-Mg2(dobpdc) may achieve a stable operating capacity in the presence of SO2 after initial passivation. Evaluation of several other diamine-Mg2(dobpdc) variants reveals that those with primary,primary (1°,1°) diamines, including dmpn-Mg2(dobpdc), are more robust to humid SO2 than those featuring primary,secondary (1°,2°) or primary,tertiary (1°,3°) diamines. Based on the solid-state 15N NMR spectra and density functional theory calculations, we find that under humid conditions, SO2 reacts with the metal-bound primary amine in 1°,2° and 1°,3° diamine-appended Mg2(dobpdc) to form a metal-bound bisulfite species that is charge balanced by a primary ammonium cation, thereby facilitating material degradation. In contrast, humid SO2 reacts with the free end of 1°,1° diamines to form ammonium bisulfite, leaving the metal-diamine bond intact. This structure-property relationship can be used to guide further optimization of these materials for CO2 capture applications.

Multiple performance enhancements with one effect: Improving the electrochemical performance of SiOx coated with specific aromatic compounds

In this study, modification is performed with pyrolyzed fuel oil to analyze the constituent components of petroleum residue oil (PRO), and carbon coating are performed on SiOx surfaces through vapor deposition to determine the effects of the aromatic compounds from the PRO. The effects of the carbon-coating from PRO on the electrochemical performance of a lithium-ion battery are also examined. Carbon-coating layers with amorphous structures and thicknesses of 13.8 to 24.6 nm are obtained depending on the deposition temperature. After 50cycles, the coulombic efficiency of the sample is 99.8 %, the initial cycle capacity is 1095.4 mAh/g at a current density of 1.0C. The rate test results for this sample showing a capacity of 417.4 mAh/g at a current density of 2.0C. This is attributing to the formation of a thick carbon-coating layer on the sample’s surface, which maintaining the stability of the sample’s structure and suppressing volume expansion. The impedance of this sample also shows the lowest resistance at 189.2 Ω, indicating a better electrochemical performance compared to those of the others. Since 250 PRO contains more 2,3-cycle aromatic compounds than other samples, it is much easier to form the poly-aromatic compound when forming the carbon coating layer of SiOx, thereby improving electrical conductivity and lithium ion diffusion.

An experimental study on residual stress relaxation in low‐cycle fatigue of Inconel 718Plus

AbstractResidual stress relaxation induced by the application of mechanical loads is determined by the nature of residual stress, the elasto‐plastic material properties, and the type of applied load. Despite the importance of the first load cycle, analytical models available in the literature generally assumed residual stress relaxation as a continuous process. Residual stress induced by machining on Inconel 718Plus superalloy cylindrical specimens was measured before and after the application of load cycles under strain control. Low‐cycle fatigue tests were carried out at room temperature for different strain amplitudes, and X‐ray diffraction measurements were performed before and after 10 and 100 cycles. A comprehensive analytical model was derived to describe the relaxation process associated with the initial cycles and that associated with the continuous application of load cycle, which is based on the plastic strain energy per cycle W and requires the evaluation of parameters that are only dependent on the material and not on the strain amplitude.

Is There a Ready Recipe for Hard Carbon Electrode Engineering to Enhance Na-Ion Battery Performance?

Hard carbon (HC) materials are commonly used as anode materials in Na-ion batteries. In most of the cases, their electrochemical performance is correlated only to their physicochemical properties, and the impact of the electrode additives (binders–conductive agent) and electrolyte is often neglected. In this work, a systematic study is performed to understand the role of electrode/electrolyte engineering on HC initial Coulombic efficiency (iCE), specific capacity, and cycle stability. Four HCs obtained by pyrolysis of several biopolymers, i.e., cellulose (HC-Cell), chitosan (HC-Chs), chitin (HC-Cht), and lignin (HC-Lig), are used. The binder was found to have an important impact on the electrochemical performance, with PVDF resulting in better performance than CMC. The carbon black additive had no significant impact on CMC-based electrochemical performance while it boosted the electrochemical performance of PVDF-based electrodes. For an optimized formulation (PVDF/carbon black), the best HC performance in NaPF6 in 1 EC:DEC was delivered by HC-Cell (83% iCE, 332 mAh g–1 at C/10, and 97% retention). This was attributed to its large graphene interlayer space, high purity, and low surface area. HC-Cht and HC-Chs exhibited similar good electrochemical performance (∼280 mAh g–1) whereas the use of HC-Lig resulted in low iCE and capacity fading overcycling due to the high level of impurities in its structure. This could be overcome by changing the electrolyte salt, by using NaClO4 (76% retention) instead of NaPF6 (52% retention). Based on the obtained results, the electrochemical performance could be correlated with the HC physicochemical properties and binder/conductive additive. It could be demonstrated that careful electrode engineering combined with proper electrolyte selection and tuned HC properties allowed all investigated materials achieving reasonable iCE (up to 83%), high specific capacity (∼280 to 332 mAh g–1), and high-capacity retention (72–97% after 50 cycles).

Soft‐Rigid Sandwich‐Structured Hybrid Electrolytes Based on Polymer‐in‐Ceramic Electrolytes for Stable‐Cycle Solid‐State Lithium‐Metal Batteries

AbstractSolid‐state lithium (Li) batteries are regarded as a promising candidate for next‐generation energy storage because of their high capacity and the intrinsic safety of solid‐state electrolytes (SSEs). Building an improved solid‐state battery has two main challenges, namely, to improve the ionic conductivity of solid electrolytes and to reduce interfacial problems. In particular, interfacial issues between SSEs and electrodes are critical factors that affect the performance of SSEs. Accordingly, a soft‐rigid sandwich‐structured hybrid electrolyte, wherein polymer‐in‐ceramic electrolytes (rigid inner structure) are sandwiched in between Celgard separator membranes (soft outer structure), was used to meet the above‐mentioned requirements. Results show that the hybrid electrolyte exhibits high ionic conductivity (4.76×10−4 S cm−1 at room temperature), low interfacial resistance (below 300 Ω for two sides), high thermal stability, and effective inhibition of Li dendrite growth due to its distinct structural advantages. Moreover, the solid‐state LiFePO4||Li battery that used this sandwich‐structured hybrid electrolyte has an initial discharge capacity of 125.8 mAh g−1, a high capacity retention of 94.9 % after 200 cycles, a good rate capability, and excellent Coulombic efficiency (close to 100 % except for the value of the initial cycle, which is 84 %) of 0.2 C at room temperature. Hence, the as‐synthesized sandwich‐structured hybrid electrolyte has great potential for practical application of solid‐state Li‐metal batteries.

Li Morphology Evolution during Initial Cycling in a Gel Composite Electrolyte

Li metal anodes are the potential solution for high-energy batteries. One of the challenges of applying such a high-energy anode is Li dendrite growth, which results in short-circuit and thermal runaway. Current battery research focuses on developing solid electrolytes to serve as a physical barrier to prevent dendrite growth. However, the Li morphology change during plating and stripping, and the mechanisms of how Li dendrite grows and propagates into a complex composite solid electrolyte are poorly understood. Understanding and controlling Li morphology evolution, dendrite formation, and growth during cycling are crucial to developing dendrite suppression strategies for solid electrolytes and enabling high-energy lithium metal batteries.In this work, Li morphology evolution during initial cycling in a crosslinked PEO-based gel composite electrolyte full cell with NMC 811 cathode is monitored via post-mortem SEM. The results show that severe surface pitting occurs as early as the second stripping cycle. Pit formation and continuous dissolution is the main cause of Li surface roughening and dendrite growth mechanism in the model gel composite electrolyte. Comparing Li dendrite growth mechanisms in liquid, polymer, and solid electrolytes, the observed dendrite growth mechanism resembles that of the liquid electrolyte the most. This study suggests that strategies to improve the electrochemical reversibility of electrodeposited Li reported in liquid electrolytes to control Li morphology and prevent dendrite growth may be transferrable in a gel electrolyte.This work is sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. Part of the measurements was performed at the Center for Nanophase Materials Sciences (CNMS), which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences.

Effects of Catalyst Composition, Loading, and Spray Parameters on the Performance of Unitized Regenerative Fuel Cell Membrane Electrode Assemblies

Proton exchange membrane unitized regenerative fuel cells (PEM-URFCs) combine the ability to both produce power (in fuel cell mode) and generate fuel and oxidant (in electrolysis mode) from the same cell. Compared with discrete fuel cell and electrolyzer systems, URFCs provide the potential for lower mass, volume, and cost. The composition and structure of the bifunctional oxygen catalyst layer (CL), which facilitates the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the same electrode, significantly affects performance and stability, particularly given the wide potential differences and different mass transport phenomena involved under operation in fuel cell or electrolysis mode. We previously showed bimetallic nanoframes provide bifunctional oxygen electrocatalysts with significantly higher activity compared with monometallic structures, evaluated using a rotating disk electrode configuration.1 Here, we investigated the effects of the oxygen CL composition, loading, and spray parameters on the performance of URFC membrane electrode assemblies (MEAs). Pt black and IrO2 catalysts were combined at different ratios and deposited at different mass loadings. Catalyst layers were sprayed directly onto membranes using an ultrasonic spray system. Within ultrasonically sprayed catalyst layers, higher spray rates resulted in improved fuel cell performance. Higher catalyst loadings improved both fuel cell and electrolyzer performance, but reached a region of diminishing returns at higher loadings. The ratio of the ORR catalyst (Pt) to the OER catalyst (IrO2) modulated the performance in both fuel cell and electrolyzer modes. Different catalyst ratios influence the catalyst utilization at higher loadings. The comparison of URFC performance at same Pt or IrO2 loadings indicates that in addition to the active catalyst itself, the non-catalytically active component influences MEA performance. This result is in line with our previous evaluation of synergistic effects of Pt and IrO2 within rotating disk electrode measurements1 and supports that in addition to the significant effects of catalyst material structure on performance, the electrode structure plays a critical role in fuel cell and electrolyzer performance in URFC MEAs. Repeated switching of URFC MEAs between fuel cell and electrolysis modes indicates that reasonable performance is maintained over the initial cycles within our single cell test configuration. References Godínez-Salomón, F.; Albiter, L.; Mendoza-Cruz, R.; Rhodes, C.P. Bimetallic Two-dimensional Nanoframes: High Activity Acidic Bifunctional Oxygen Reduction and Evolution Electrocatalysts. ACS Appl. Energy Mater. 2020, 3, 2404-2421. http://dx.doi.org/10.1021/acsaem.9b02051

Impact of Data Window on Prediction of Battery Aging and Swelling

Lithium-ion batteries degrade over time, based on their usage and these changes can be observed in the terminal voltage and cell expansion curves with respect to SOC. Physics-based battery models augmented with degradation modes can describe the changes in battery electrical and mechanical response as the battery ages and can be tuned to predict the observed rate of change. Tuning these models is computationally intensive, because it requires multiple simulations of the battery aging process over the entire lifetime. Accelerated simulations that use an adaptive inter-cycle extrapolation algorithm [1] can reduce simulation time and thus enable use of optimization algorithms to automatically tune degradation models [2].In this work, we investigate how the amount of aging data used to train the model impacts the prediction of future battery aging assuming the battery continues to operate under the same conditions. The electrode-specific state of health (eSOH) parameters are computed from the reference performance testing performed at periodic intervals throughout the battery's lifetime. These four parameters include the capacities of positive and negative electrodes Cp and Cn, and the corresponding electrode stoichiometric windows y0 and x100. These 4 parameters extracted from a cell aged at C/5 constant current charging rate were used for training the model.The aging model includes SEI growth in the negative electrodes which causes a loss of cyclable lithium/loss of lithium inventory (LLI) and loss of electrode active material (LAM) due to particle cracking at both the negative and positive electrodes. Simulation results show us that a shorter training window of three eSOH reference points (every 25 cycles) over (Cycles 41 to 98) over-predicts battery degradation because the rate of degradation during these initial cycles is larger than the degradation which happens later in the battery's life. The battery degradation parameters that are predicted (and shown in the figure) include battery capacity, maximum reversible swelling in the battery, loss of active material in the negative electrode and loss of lithium inventory. If we increase the model training window to five eSOH data points (Cycles 41 to 175), the prediction of battery degradation is much better because the model now accounts for both the initial higher rate of degradation and subsequent lower rate of degradation.

Li Pre-Doping of SiO Electrodes Using Li-Naphthalenide Solution for Next-Generation Batteries

SiO is regarded to be one of the promising anode materials to replace graphite in lithium-ion batteries (LIB) because of its higher specific capacity than graphite and better cycle stability than Si [1]. However, the large irreversible capacity is a serious problem which consumes charged capacity in vain during initial cycles. Therefore, Li pre-dope to dose Li to SiO beforehand has been proposed. In this study, our previous achievement on Li pre-doping to Si electrodes was much helpful. The highlights of the achievement are as follows [2, 3]. Li-naphthalenide (Li-NTL) was selected as a Li pre-doping agent.Li pre-doped capacity was much dependent on the solvent of Li-NTL solution.2-methyltetrahydrofuran (MeTHF) delivered the largest pre-doped capacity. Hence, we conducted this study on Li pre-doping to SiO electrodes by referring to the achievement on Si electrodes.SiO electrodes coated on Cu foil consisted of SiO, Ketjen Black, and polyimide binder in the ratio of 80 : 5 : 15 (m/m). Two types of SiO powder with an average particle size of 5 μmφwere used: carbon-coated SiO denoted as C-SiO and bare SiO which were purchased from OSAKA Titanium technologies Co., Ltd. We adopted 0.5 M NTL/MeTHF as a standard pre-doping solution based on our result of Li pre-doping to Si. SiO electrodes were confined in an air-tight cells with the pre-doping solution for 24 h to be pre-doped. The electrodes were taken out of the cells, rinsed in DMC, and used to assemble coin cells with Li counter electrodes, separators and electrolyte solution of 1.0 M LiPF6 / EC + DMC (1:1, v/v) + 10 wt% FEC. All of these processes were conducted in an Ar-filled glove box. Discharge/charge cycle test mode was constant-curent at 0.1 mA cm−2 between 0.02 and 1.5 V at 30 °C. Figure 1 shows charge/discharge performance of C-SiO electrodes with and without Li pre-doping. In Figure 1a, the OCV of the Li pre-doped electrode was as low as 0.2 V, which was much lower than that of the electrode without pre-doping, exceeding 2.0 V, and the charge capacity was nearly missing. However, the discharge capacity was not less than that of the electrode without pre-doping. This result reveals that SiO can be pre-doped effectively by Li-NTL/MeTHF, which is the same as Si. Figure 1b shows dQ/dV analysis results, in which the anodic curves for the with and without pre-doping are nearly identical. However, almost no cathodic curve is observed for the with pre-doping as shown in Figure 1a, while a sharp peak at 0.46 V assigned to formation of L x SiO y is observed for the without pre-doping [4]. A dashed curve inserted in the Figure 1b is the cathodic curve for the second cycle of the with pre-doping to complement the missing first cycle one. This curve shows no peak at 0.46 V and suggests formation of L x SiO y during pre-doping. We further analyzed the pre-doping reaction to elucidate the mechanism based on the result shown above. The detail of the results will be shown and discussed in our presentation.[1] M. N. Obrovac, V. L. Chevrier, Chem. Rev., 114, 11444 (2014).[2] M. Saito et al., s of PRiME 2020, A02-0410 (2020).[3] M. Saito et al., J. Electrochem. Soc., 166, A5174 (2019).[4] C. P. Grey et al., J. Am. Chem. Soc., 141, 7014 (2019). Figure 1

Evaluating Contributions of Pitch-Carbon Coating to Improved Stability of Si Anodes through Voltage-Resolved Multi-Phase Characterization

Silicon nanoparticles have emerged as a promising alternative to graphite to improve the energy density of next-generation lithium-ion battery anodes. Nano-sized Si domains facilitate rapid ion transport and minimize particle-scale mechanical degradation, but also exhibit increased (electro)chemical reactivity with Li-ion electrolyte components due to their high surface area. We have previously demonstrated that surface modification of Si nanoparticles with pitch-carbon is an effective strategy to reduce these parasitic reactions. In the present work, we holistically evaluate the mechanistic contribution of pitch-carbon coating to the observed stability improvement over uncoated Si. We utilize coupled in situ and ex situ methods to probe changes to solid-surface, volatile headspace, and gas-phase chemistry occurring during initial cycling. Measurements taken at targeted potentials associated with electrolyte species reduction enables the decoupling of specific reaction pathways tied to interfacial stability. Further, we demonstrate the non-trivial role of gas reconsumption in dictating the nature of the passivating surface layer evolved on both uncoated and pitch-coated Si. This multi-phase analysis offers insights into the mechanism of effective surface passivation, which may be applied to inform future Si material development. Figure 1

Soh Prediction of Li-Ion Batteries with Machine Learning-Based Method

As fossil fuel-driven society has brought environmental pollution and climate crisis, environmentally friendly alternative energy has been in the spotlight. In particular, electric vehicles receive attention as a next-generation transportation method. The most core technology for electric vehicles is the lithium-ion battery and the battery management system (BMS). However, due to the long lifespan of lithium-ion batteries, it is very time-consuming to measure and improve performance over time. In addition, since the batteries are driven under various conditions, it is not easy to measure the SOC and SOH in real-time because there are many variables. With the recent development of prediction technology through machine learning, it has become possible to predict with high accuracy without complex physical knowledge through high-quality data. In this study, machine learning technology was applied by utilizing charge/discharge data of lithium ion batteries. The measured values in the initial charge/discharge cycles were selected as independent variable, and the number of cycles remaining until the end of the life was selected as a dependent variable, and then a regression algorithm was applied. After that, model tuning was performed to increase accuracy by reducing overfitting of the data. This study used machine learning technology to predict the SOH of a lithium ion battery with high accuracy with only the initial cycles, thereby contributing to real-time data of BMS and raising the time efficiency of the study.

Dynamic Impedance Spectroscopy of Lithium Plating from Next Generation Electrolytes

The anode-free cells have emerged due to the need to maximize Li metal batteries' energy density. However, anode-free Li batteries suffer from short cycle life because of the lack of Li inventory at the anode. Freshly deposited Li metal anodes usually take hundreds of cycles to reach initial SEI stabilization optimum coulombic efficiency (CE) due to initial SEI stabilization and electrode activation. The anode-free cell design requires high Li metal CE over the whole cycling life, particularly during the initial activation cycles. A holistic approach to electrolyte design, mechanism understanding, and battery engineering is needed to fulfill these requirements. Here, we present a mechanistic study on lithium plating and stripping from next generation electrolytes.We conducted dynamic impedance spectroscopy (dEIS) to probe the formation and evolution of the SEI during Li plating and stripping on copper current collectors. dEIS superimposes a multisine waveform atop the dc stimulus signal, as shown by the lightly shaded curves in Fig 1 (top left). We applied a sliding window FFT protocol that takes the complex ratio of the measured potential and current signals obtained from Fig 1 (top right) and transforms it into complex impedance. We will discuss two Li platting systems, Lipon (an amorphous ceramic) and a liquid electrolyte with stabilizing additives. We observed drastic changes in the cells' impedance during plating and stripping, Figure 1 (bottom plots). We will show how the passivation layer's impedance continues to evolve during Li cycling and accounts for a significant amount of the overall cell resistance.The US Department of Energy’s Energy Efficiency and Renewable Energy Vehicles Technologies Office provided funding for this work under the US-German Cooperation on Energy Storage: Lithium-Solid-Electrolyte Interfaces program. Figure 1