Operational Window Research Articles

ITER NBI operational window and power availability constraints due to shine-through losses

Abstract This paper explores the operational boundaries and power availability of the neutral beam injection (NBI) system in ITER, with a specific focus on shine-through loss prevention. Shine-through, a phenomenon where part of the injected neutral beam remains un-ionized in the plasma and directly impacts the first wall components, poses a significant risk to the lifetime of ITER’s plasma-facing components. The operational window for NBI is consequently constrained by these losses, which are influenced by factors such as plasma density, beam energy, and injection geometry. Leveraging advanced numerical simulations, we investigate these dependencies across various ITER plasma scenarios, particularly for the DT-1 phase, which will mark the first NBI operations. In light of recent ITER blanket design changes, our analysis refines previous estimates of the maximum acceptable shine-through power on plasma-facing components. We then present a new heuristic formula which permits the calculation of the shine-through fraction and the minimum plasma density that permits ITER NBI operations as a function of global variables. This allows for establishing operational limits for Hydrogen and Deuterium NBI in Hydrogen, Deuterium, and Deuterium-Tritium plasmas. Additionally, we compare commonly used beam ionisation codes for ITER and tokamak simulations, evaluating their reliability in the investigated parameter space. The findings of this study are crucial for ensuring the efficient operation of the NBI system during ITER's experimental phases. They define the conditions under which beam power can be fully utilised without compromising operational lifetime, thereby informing future plasma operation plans and contributing to the success of ITER's scientific objectives.

Stable magnetocaloric effect over an ultrawide temperature range of 146–320 K via hydrostatic pressure in kagome magnets

Solid-state refrigeration leveraging the magnetocaloric effect (MCE) presents a sustainable and energy-efficient alternative to traditional gas compression refrigeration technologies. However, the practical utility of most magnetocaloric materials is restricted by their narrow operational temperature window. In this work, a stable magnetocaloric effect across an ultrawide temperature range of 146–320 K was achieved in Hf0.85Ta0.15Fe2 magnet via the hydrostatic pressure manipulation. Furthermore, the underlying mechanism for the extended and stable MCEs under hydrostatic pressure has been revealed by magnetization measurements and first-principles calculations. The material systems characterized by strong spin–lattice coupling exhibit considerable potential for externally manipulated hybrid-field-tuned magnetic properties and magnetocaloric performance, providing a convenient and practical approach for advancing applications in magnetic refrigeration technologies.

RL-BASED EVENT-TRIGGERED MODEL PREDICTIVE CONTROL FOR ELECTRIC VEHICLE ACTIVE BATTERY CELL BALANCING

Abstract To extend the operation window of batteries, active cell balancing has been studied in literature. However, such advancement presents significant computational challenges on real-time optimal control, especially when the number of cells in a battery increases. This paper investigates the use of reinforcement learning (RL) and model predictive control (MPC) to effectively balance battery cells while at the same time keeping the computational load at minimum. Specifically, event-triggered MPC is introduced as a way to reduce real-time computation. Different from existing literature where rule-based or threshold-based event-trigger policies are used to determine the event instances, deep RL is explored to learn and optimize the event-trigger policy. Simulation results demonstrate that the proposed framework can keep the cell state-of-charge variation under 1%, while using less than 1% computational resources compared to conventional MPC.

Dynamic adhesion measurement of powders using the drop testing method: Defining a window of operation

Dynamic adhesion measurement of powders using the drop testing method: Defining a window of operation

Optimizing CO preferential oxidation pathways via active-site engineering: A case study on MgO nano-sheets supported ultrasmall PtNi alloys

Active-sites play a pivotal role in catalyzing reactions at surfaces, yet engineering these active sites still remains a significant challenge. In this work, hydroxylated MgO nanosheets supported ultrasmall PtNi alloys approximately 2.6(1) nm (xPt-yNi/MgOhydr) has been investigated via active-site engineering. Experimental results and DFT calculations reveal that electron transfers from Ni to Pt and from hydroxyl groups to Pt 5d-orbitals generate active sites NiPt-(OH)x. In the preferential CO oxidation (CO-PROX) reaction, these active sites on xPt-yNi/MgOhydr switch the bicarbonates reaction pathway depending on temperature range. Consequently, the optimal catalyst, 5%Pt-0.5%Ni/MgOhydr, achieves 100% CO conversion at 100 °C, demonstrating a broad temperature operation window (100–200 °C) and excellent durability. The active site engineering approach presented in this study can promote the discovery of more excellent catalysts with the optimal reaction route for various applications.

Weakening Coulomb interactions in ionic liquid via hydrogen bonds enables ultrafast supercapacitors.

The application of ionic liquid electrolytes in ultrafast supercapacitors to achieve wide electrochemical operating windows and high electrochemical stability is highly applauded. However, the strong Coulomb interaction between ions leads to the overscreening effect and slow establishment process of the electrical double layer (EDL), which deteriorates the rate performance of supercapacitors. Herein, inspired by Coulomb's law and EDL transient dynamics, we introduce competitive hydrogen bond interactions into typical ionic-liquid electrolytes to weaken the Coulomb interaction between ions. Density functional theory calculations, nuclear magnetic resonance spectroscopy, and Fourier infrared spectrum, combined with differential capacitance, suggest that the introduction of competitive hydrogen bonds is responsible for the suppression of Coulomb interaction between ions. The existence of appropriate hydrogen bonds effectively improves the ion coordination and the interface model of the electrode surface, thus enhancing the response kinetics of ions. Based on this hybrid electrolyte design, the fabricated supercapacitor delivers an outstanding capacity of 100.0 mF g-1 at 120Hz with a cut-off frequency of 1842.4Hz and a relaxation time of 0.62ms. This work opens a pathway towards the design of electrolytes for ultrafast supercapacitors.

Optimising medium chain carboxylate production in xylan mixed-culture monofermentation.

This work investigates the optimization of medium-chain carboxylate (MCC) production through xylan mixed-culture monofermentation. The pH screening in batch assays showed that the hydrolysis stage and selectivity towards MCC precursors were optimised at pH 6. Subsequently, a continuous stirred tank reactor (CSTR) and a Sequential Batch Reactor (SBR) were operated at different Hydraulic Retention Times (HRT), revealing that the SBR at HRT 2 days yielded the highest caproic acid since lactic acid availability and chain elongation process were balanced. An enriched medium with yeast extract and vitamins favoured the growth of chain elongators, and therefore, the MCC production. Moreover, cross-feeding interaction between bacteria in xylan fermentation was observed, and Pseudoramibacter was present in the highest caproic acid yields. This work highlights the impact of selecting the proper operational window to optimise one-stage MCC production.

Enhanced Synaptic Memory Window and Linearity in Planar In2Se3 Ferroelectric Junctions.

A synaptic memristor using 2D ferroelectric junctions is a promising candidate for future neuromorphic computing with ultra-low power consumption, parallel computing, and adaptive scalable computing technologies. However, its utilization is restricted due to the limited operational voltage memory window and low on/off current (ION/OFF) ratio of the memristor devices. Here, it is demonstrated that synaptic operations of 2D In2Se3 ferroelectric junctions in a planar memristor architecture can reach a voltage memory window as high as 16V (±8 V) and ION/OFF ratio of 108, significantly higher than the current literature values. The power consumption is 10-5W at the on state, demonstrating low power usage while maintaining a large ION/OFF ratio of 108 compared to other ferroelectric devices. Moreover, the developed ferroelectric junction mimicked synaptic plasticity through pulses in the pre-synapse. The nonlinearity factors are obtained 1.25 for LTP, -0.25 for LTD, respectively. The single-layer perceptron (SLP) and convolutional neural network (CNN) on-chip training results in an accuracy of up to 90%, compared to the 91% in an ideal synapse device. Furthermore, the incorporation of a 3nm thick SiO2 interface between the α-In2Se3 and the Au electrode resulted in ultrahigh performance among other 2D ferroelectric junction devices to date.

Accelerated Continuous Flow Depolymerization of Poly(Methyl Methacrylate).

A continuous flow setup comprising an inline dialysis unit for immediate monomer removal is used for the depolymerization of poly(methyl methacrylate) (pMMA), synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The approach used allows one to carry out solution depolymerizations at much higher polymer content compared to batch processes while maintaining high depolymerization conversions. pMMA is efficiently depolymerized in the flow reactor, yielding up to 68% monomer recovery under catalyst-free reaction conditions at 160 °C, starting from a 1 molar repeat unit concentration, which is a 20-fold improvement compared to previous batch studies. This was achieved by using the inline dialysis to continuously remove monomer from the depolymerization solution and hence continuously shifting of the depolymerization equilibrium to the recycling side. Depolymerizations at various temperatures, starting polymer concentrations, and reactor setup modifications are investigated, clearly showing the highly advantageous effect of the monomer removal on the reaction. The employed approach represents a significant advancement toward the industrial feasibility of depolymerization of methacrylates by lowering the solvent use, expanding its temperature operation window, and bringing polymer contents to a practically relevant level.

Scalable production of ultraflat and ultraflexible diamond membrane.

Diamond is an exceptional material with great potential across various fields owing to its interesting properties1,2. However, despite extensive efforts over the past decades3-5, producing large quantities of desired ultrathin diamond membranes for widespread use remains challenging. Here we demonstrate that edge-exposed exfoliation using sticky tape is a simple, scalable and reliable method for producing ultrathin and transferable polycrystalline diamond membranes. Our approach enables the mass production of large-area (2-inch wafer), ultrathin (sub-micrometre thickness), ultraflat (sub-nano surface roughness) and ultraflexible (360° bendable) diamond membranes. These high-quality membranes, which have a flat workable surface, support standard micromanufacturing techniques, and their ultraflexible nature allows for direct elastic strain engineering and deformation sensing applications, which is not possible with their bulky counterpart. Systematic experimental and theoretical studies reveal that the quality of the exfoliated membranes depends on the peeling angle and membrane thickness, for which largely intact diamond membranes can be robustly produced within an optimal operation window. This single-step method, which opens up new avenues for the mass production of high-figure-of-merit diamond membranes, is expected to accelerate the commercialization and arrival of the diamond era in electronics, photonics and other related fields.

Continuous preparation of alkaline hydrogen peroxide solution by micromixing device: Experiment and theoretical analysis

AbstractIn the context of achieving continuous synthesis of acyl peroxides using microreactors, continuous preparation of alkaline hydrogen peroxide (AHP) solution is required. However, two key issues, Na2O2 precipitation and H2O2 decomposition, need to be considered or addressed. For the precipitation of Na2O2 during NaOH and H2O2 mixing, experiments revealed that precipitation could be avoided by appropriate selection of operation window. For the risk of violent H2O2 decomposition when NaOH and H2O2 solutions are one‐step mixed, theoretical approaches were adopted. Simulation‐derived mixing time is combined with decomposition kinetics to find a direct relationship between operation‐structure parameters and percentage of decomposed H2O2. This percentage is estimated to be in the order of 10−4 for micromixing devices, which indicates that micromixing devices can be used to one‐step mix NaOH and H2O2 solution without causing violent H2O2 decomposition. This work provides insights into the preparation of AHP solution and facilitates its continuous preparation.

In situ crosslinked gel polymer electrolytes for Li-ion capacitors using sacrificial salt pre-lithiation, enabling high-temperature operation

In this work the effect of encapsulating a standard liquid electrolyte (1 M LiFSI in EC:DMC) into a polymer matrix for Li-ion capacitors pre-lithiated using Li2C4O4 sacrificial salt is presented. The polymer precursor is added in liquid state, which facilitates the integration in already existing cell manufacturing lines and is polymerized in situ at 60 °C after cell assembly. The application of a gel polymer electrolyte (GPE) is demonstrated to have many benefits such as lowered risk of electrolyte leakage, reduced flammability, improved high-temperature stability and high-temperature performance. The introduction of the polymer component is suggested to improve the stability of the solid electrolyte interface (SEI), enabling capacity retention of >95 % after 1200 h floating at 60 °C first (600 h) and 70 °C after (600 h). The increased performance at higher temperatures over room temperature is explained by an increased capacity of the hard carbon (HC) negative electrode together with an improved ionic conductivity of the GPE. Further increasing the operational temperature window of the LIC to 80 °C enables additional 600 h floating, demonstrating the feasibility of the GPE concept to improve high temperature stability and performance of commercial Li-ion capacitors, importantly, without sacrificing room temperature operation.

Towards the definition of treatment wetland pathogen log reduction credits.

Treatment wetlands have the potential to treat a range of water and wastewater pollutants while using less energy and chemicals than conventional treatment processes, making them a viable option for improving the sustainability of water treatment systems. However, water treatment systems used for water reuse must also be protective of human health. To date, the human health protection benefits of treatment wetlands have not been rigorously quantified in the context of current human health risk frameworks. This study presents a comprehensive review of the ability of treatment wetlands to provide reliable pathogen reduction to meet risk-based treatment targets for water reuse. Following an existing protocol for establishing log reduction credits, we systematically reviewed the documented pathogen reduction performance of major treatment wetland types in terms of core components of that protocol, including pathogen removal mechanisms, identification of target pathogens, and influencing factors. Results of the review point to design and operational conditions under which treatment wetlands could likely be credited with a log reduction value of approximately 0.5 or greater for virus, protozoa and bacteria. These conditions are specified in terms of preliminary operating envelopes, or design and operational parameter windows associated with optimal performance. Important caveats are noted, as are specific and tractable recommendations for future research and data collection efforts that would help refine operating envelopes and define log reduction credits for these promising water treatment technologies. As a resource to other practitioners, we have also included the detailed performance characterization database as Supplemental Information. This database includes a detailed tracking of log reduction values as well as design and operational parameters reported in the literature.

Effect of Fast-Charging and Cycling Window on Lithium-Ion Battery Performance and Aging

Aggressive charging practices and extreme usage patterns of electric vehicle batteries pose safety risks, including fire hazards. Beyond fast charging, battery health is influenced by dynamic factors like temperature, state-of-charge (SoC) window of operation, and driving conditions relative to charging events1,2. Given that electric vehicles (EVs) rarely operate in their full SoC range (0–100%)3, understanding battery cell degradation across different SoC swing ranges and fast-charging effects becomes critical. This understanding not only optimizes battery usage and extends cell lifespan but also enhances lifetime economics and mitigates environmental consequences tied to raw material extraction and manufacturing2.This study explores the impact of SoC swing ranges and fast charging on the performance and aging of commercially available 18650 cells equipped with graphite-NCA electrodes. Departing from the conventional constant-current constant-voltage (CC-CV) fast charging protocol, we adopted a scaled-down version of the 150-kW real-world battery electric vehicle (BEV) fast charging profile. Unlike the broader SoC range of high current charging typical in CC-CV protocol, the real-world BEV fast-charging profile charges the battery at peak power or peak current only in a narrow SoC range between 10% and 40% SoC and then tapers down. Cycling experiments were conducted for two sets of SoC ranges: 0%-50% and 0%-100%. Both cycling experiments exhibited similar trends in overall capacity fade, yet the underlying causes differed. The DV-IC analysis revealed that the loss of active negative electrode material (LAMNE) was pivotal in capacity fade for both cycling experiments. Notably, during 0%-100% SoC cycling, loss of positive electrode material was observed alongside LAMNE. Additionally, variations in the homogeneity of lithium distribution within the negative electrode and kinetic rate degradation of the negative electrode were evident.This research underscores the critical role of SoC swing ranges and fast charging protocols in battery degradation, with differential voltage and incremental capacity analysis revealing distinct degradation pathways. It highlights the need for optimized battery usage strategies to extend cell lifespan, enhance lifetime economics, and mitigate environmental impact, thereby contributing to the sustainable growth of the EV market.

Molecular Design of Redox-Copolymers for Selective Electrochemical PGM Recovery

Platinum group metals (PGMs) are of vital importance to various industries such as manufacturing, transportation, and energy economy. To secure the supply chain of PGMs, it is important to selectively extract target species from the mining ores and recycle spent automobile catalytic converters or e-waste. However, PGMs are challenging species to separate due to very similar physical and chemical properties and low concentration and complex speciation depending on pH or type of electrolyte used.1 Electrochemical separation is environmentally benign with good modularity and scalability. The development of next-generation electrodes with selective interactions for metal-binding and recovery is critical for innovating sustainable mining processes.Redox electrodes were also shown to be efficient in controlling the operational voltage windows in aqueous-phase electrochemical systems, by increasing the Faradaic efficiency towards ion-binding and suppressing side reactions that would otherwise increase energetic costs. At the same time, polymer-functionalized electrodes have been shown to facilitate selective electrodeposition and regeneration of metals, thus providing an alternative approach for energy-efficient metal recovery. Redox-active polymers containing ferrocene have shown high selectivity towards anionic species such as metal oxyanions of arsenic and chromium.2 By modulating functional groups of redox polymers, charge-transfer behavior can be changed, and it can also provide new binding sites for target ions. We investigated a series of ferrocene-containing redox polymers to understand the kinetic and equilibrium uptake of PGM chloroanions. Different functional groups such as amide, alkyl, amine, and ester, respectively can modulate different redox potential within metallopolymers due to electron donating or electron withdrawing effects. The effect of these homopolymers was evaluated, with high uptake and regeneration being achieved for a range of PGMs. Going further than individual monomers, PGM-specific ligands were designed and incorporated into redox polymer by copolymerization. By leveraging heteroatom ligands as metal-specific functionality, the selectivity of the redox-copolymers in different pairs of PGM binary mixtures was tuned beyond the original homopolymers. The effect of ligand binding strength, ratio between redox group to ligand, and releasing solution on selectivity and uptake was investigated in detail.(1) Kim, K.; Candeago, R.; Rim, G.; Raymond, D.; Park, A. H. A.; Su, X. Electrochemical approaches for selective recovery of critical elements in hydrometallurgical processes of complex feedstocks. iScience 2021, 24 (5), 31, Review. DOI: 10.1016/j.isci.2021.102374.(2) Su, X.; Kushima, A.; Halliday, C.; Zhou, J.; Li, J.; Hatton, T. A. Electrochemically-mediated selective capture of heavy metal chromium and arsenic oxyanions from water. Nat. Commun. 2018, 9 (1), 4701. DOI: 10.1038/s41467-018-07159-0.

Quantitative Non-Destructive Morphological Characterization of All-Solid-State Batteries

In recent years, all-solid-state batteries (ASSBs) have attracted considerable attention within the scientific community owing to their potential for achieving high energy density, enhanced safety characteristics, and a broader operational temperature window. Specifically, sulfide-based solid-state electrolytes (SSEs) demonstrated the most promising ASSB chemistry with their room-temperature Li+ ionic conductivity comparable or exceeding to that of conventional liquid electrolytes (~10 mS cm-1). Our previous works showcased the superior cyclability of ASSB implementing sulfide-SSEs and carbon-free silicon anode with phenomenal stable cycling for 500 cycles1. Recently, we further demonstrated the scalability of carbon-free Si anode at the pouch cell level with cell capacity reaching 100 mAh under significantly low stacking pressure of 5 MPa2-3, showing promise to accelerate the development and commercialization of ASSBs.Characterizing ASSBs during and after operation is critical for their further development. Crucially, scaling up ASSBs to pouch-cell level introduces new challenges as characterizing the internal microstructure and morphological evolution at a larger scale becomes difficult and time-consuming. Previous works using destructive focus-ion beam-scanning electron microscope (FIB-SEM) can only visualize several tens of micrometers with long imaging times for 3D reconstruction up to hours. Thus, techniques with larger field of view (FOV) and shorter imaging time are inevitably needed to have a better statistical analysis. This study leverages the non-destructive nature of synchrotron X-ray micro-computed tomography (CT) to visualize the morphology and microstructure of each component within an ASSB pouch cell. Leveraging the large FOV of X-ray micro-CT, up to several millimeters and shorter imaging time, we are able to perform a quantitative analysis of the extracted microstructural information, including porosity, loss of contact, and tortuosity. These findings will provide a broader understanding of the structural evolution in ASSB pouch cells, bridging the gap between lab-level research and application-level production.Reference: Tan, D. H. S.; Chen, Y. T.; Yang, H.; Bao, W.; Sreenarayanan, B.; Doux, J. M.; Li, W.; Lu, B.; Ham, S. Y.; Sayahpour, B.; Scharf, J.; Wu, E. A.; Deysher, G.; Han, H. E.; Hah, H. J.; Jeong, H.; Lee, J. B.; Chen, Z.; Meng, Y. S., Carbon-free high-loading silicon anodes enabled by sulfide solid electrolytes. Science 2021, 373(6562), 1494-1499. Tan, D. H. S.; Meng, Y. S.; Jang, J., Scaling up high-energy-density sulfidic solid-state batteries: A lab-to-pilot perspective. Joule 2022, 6 (8), 1755-1769. Chen, Y.-T.; Jang, J.; Oh, J. A. S.; Ham, S.-Y.; Yang, H.; Lee, D.-J.; Vicencio, M.; Lee, J. B.; Tan, D. H. S.; Chouchane, M.; Cronk, A.; Song, M.-S.; Yin, Y.; Qian, J.; Chen, Z.; Meng, Y. S., Enabling Uniform and Accurate Control of Cycling Pressure for All-Solid-State Batteries. 2023.

Synthesis and Characterization of Novel Polymerizable Boronium Ionic Liquids

Boronium ionic liquids (BILs) are an emergent class of zwitterionic materials that have great potential as electrolytes for electrochemical energy storage. Their high electrochemical stability, afforded by charge delocalization across the cation, and thermal stability make them attractive electrolytes for supercapacitors. In this work, a series of novel polymerizable BIL (polyBIL) cations were paired with bis(trifluoromethane)sulfonimide, [TFSI]-, creating stable ILs with low melting points. These BILs were applied as electrolytes to symmetric double layer capacitors comprised of carbon nanofoam paper (CNP) electrodes. Monomeric polyBILs were characterized using cyclic voltammetry, differential scanning calorimetry, thermal gravimetric analysis, broadband dielectric spectroscopy and compared to previously reported non-polymerizable analogs. Their operational voltage windows were studied in a two-electrode configuration using cyclic voltammetry. Then, galvanostatic charge/discharge cycling was performed to assess the performance and long-term stability of the cells.

(Invited) Optimized Conditioning and Performance of PEM Fuel Cell Stacks

The fuel cell market is maturing, and the production volumes are increasing. In parallel, expectations on performance, lifetime and operational range for fuel cell stacks are growing. As fuel cell technology matures, more fuel cell stacks are used in real life applications instead of laboratory environment. These positive developments bring with them new challenges and opportunities to learn.Several of these challenges and their impact on stack design and validation will be discussed. The focus will be on optimization of useful stack power density, fuel cell stack conditioning, enlarging the LT-PEM fuel cell operation range and on durability testing.This talk addresses why conditioning and durability testing are closely connected and illustrates how this can impact stack platform and fuel cell development. In addition, the interactions between power density, stack integration and stack operational window are illustrated showing how each of these parameters could be optimized utilizing a current distribution plate and what trade-offs are relevant for optimized fuel cell stack and system performance.Powercell is active in various market segments and has developed stacks and stack components for ~20 years. The optimizations and trade-offs described hinge heavily on key PEM stack requirements which can be widely different in different PEM fuel cell market sectors, as illustrated by the emerging usage of fuel cells in aviation.

Degradation and Safety Analysis of Large Format LiFePO4/Graphite Battery

Large format LiFePO4/Graphite (LFP/Gr) Lithium-ion battery (LIB) have been developed for electric vehicles (EV) and stationary use. In case of large surface electrodes, intrinsic two-phase reaction of LFP has a risk to induce inhomogeneous reaction in planar electrode surface. We applied >200 Ah class LFP/Gr LIBs and cycled them around 80-65 % SOH levels. Among them, we applied non-destructive differential voltage analysis (dV/dQ) to three cells (Cell1:SOH 80.9 %, Cell2:SOH 73.5 %, Cell3:SOH 68.4 %), and determined the degree of inhomogeneity of the electrodes by disassembly of the cell in the Ar-filled glove box.We could obtain dV/dQ peak corresponds to Gr 2nd stage single phase by charge curve analysis between SOC 0 and 100 % at C/20. Based on the assumption that Gr capacity is twice of the Gr 2nd stage peak capacity, Gr capacity was sufficiently larger than cell capacity. Therefore, cell capacity fade was not related to the capacity fade of Gr but caused by the shift of the cathode / anode operation window (SOW) due to loss of lithium inventory (LLI) and/or capacity fade of LFP.After dV/dQ analysis with capacity check, cells were disassembled at 2.5 V, and confirmed LFP and Gr capacity by reassembling coin cells with Li counter electrode. Reassembled LFP/Li cells was discharged to 2 V, and Gr/Li cells were deintercalated to 2.5 V. The subtracted value of these residual capacities, we could estimate SOW capacity. The obtained estimated cell capacity by LFP-SOW showed strong correlation with SOH of cells before disassembly (R=0.98). Therefore, we confirmed that capacity fade of the cell was due to increase in SOW and/or capacity fade of LFP.To determine the degree of inhomogeneity in electrode planar, we applied XRD to LFP. As LFP reaction proceeds typical two-phase reaction, we can indirectly estimate Li content by estimating ratio of LFP and FePO4(FP). The LFP/FP ratio was optimized by Rietveld refinement of the diffraction peaks in various sampling points of the electrode sheet. We confirmed several macroscale inhomogeneous Li distributions in planar LFP electrode. Li poor area was observed at the beginning and the final edge of the roll electrode. The correlation details between cell SOH and degree of inhomogeneity will be discussed in the presentation.In addition, we applied two kinds of abuse test, overcharge and forced internal short circuit test by laser spot heating to three cells with different SOH. In case of overcharge, cell was charged at 0.78 C from SOC 100 %. In case of laser heating, pulse laser with 0.5 sec supply / 0.1 sec rest at 2000 W applied to the cell. The difference of the obtained parameters, and correlation with SOH will be discussed in the presentation.

State of Charge When Cycling LiFeO4/Graphite Cells Affects Lifetime

Lithium iron phosphate (LFP) battery cells are used ubiquitously in electric vehicles and stationary energy storage because they are cheap and have a relatively long lifetime, but they have low energy and power density1. This work compares the LFP / Graphite pouch cells undergoing charge-discharge cycles over three state of charge (SOC) windows: 0 – 25%, 0 – 100%, and 75 – 100%. Cycling LFP cells across a lower average SOC provides longer cell lifetime than a higher average SOC, regardless of depth of discharge. There are two capacity fade degradation mechanisms that are prominent at high SOC: iron dissolution and deposition onto the negative electrode, and lithiated graphite reactivity with electrolyte increasing incrementally with SOC and with the amount of deposited Fe. It is commonly known that cell voltage and depth of discharge should be minimized to improve lifetime, but this is based on cell types that operate at higher voltages than 3.65 V in LFP/AG cells. Our results show that even low voltage LFP systems have this trade-off between state of charge and lifetime. We show that the average SOC of operation is more critical for capacity fade than the variables of electrolyte salt choice (LiPF6 vs LiFSI), graphite choice or temperature (40°C vs 55°C). This work employed isothermal microcalorimetry to investigate the heat flow from lithiated graphite-electrolyte reactivity2, scanning micro-xray fluorescence to quantify iron deposition on the negative electrodes3, and liquid electrolyte analysis techniques NMR and GC-MS to investigate electrolyte degradation products.Figure 1: LFP/AG pouch cell cycling capacity fade across different SOC ranges in long term cycling over 2500 hours. For best comparison, only the C/20 checkup cycles are plotted, where all cells cycle 0-100% every 100 cycles or every ~300 hours. The regular cycles are at C/3 rate, and only 60 mAh out of 240 mAh nominal are cycled. Discharge capacity vs cycling time is plotted for (a) 40°C and (b) 55°C testing of LFP/AG cells with LiPF6 and LiFSI electrolyte salts at various SOC operation windows. The cell barcode IDs are indicated in the legends. The normalized discharge capacity fade per hour at (c) 40°C and (d) 55°C is summarized after 2500 hours of cycling for the different SOC windows cycled. Electrolyte is EC:DMC 3:7 2VC 1.5M LiFSI or LiPF6.