Charge Throughput Research Articles

Effect of Mechanical Pressure on Rate Capability, Lifetime, and Expansion in Multilayer Pouch Cells with Silicon-Dominant Anodes

Microscale silicon particles have a higher specific capacity but larger volume expansion than graphite particles, leading to particle decoupling and lifetime limitations. This study investigates a wide range of external mechanical pressures from zero (ZP - 0.00 MPa) to high (HP - 0.50 MPa) pressure to determine the optimal pressure for high rate capability, cyclic lifetime, energy density, low temperature rise, and low cell thickness gain. The cells are characterized by rate tests and impedance spectroscopy, and are aged until 70% state of health (SoH). The post-mortem analysis after 70% SoH and thickness measurements over 360 cycles in a compression test bench offer insights into the thickness gain. Electrochemical results reveal an immediate reduction in discharge capacity upon transitioning from normal pressure (NP - 0.20 MPa) to ZP, with NP and HP exhibiting superior performance over aging. The impedance was reduced initially and over aging for higher mechanical pressures, especially the cathode contact resistance, resulting in lower temperature rises during the rate tests. Overall, applying higher pressures reduced the anode and cell thickness gain. Moreover, the porosity decreased with increasing pressure, as determined by mercury intrusion porosimetry and pycnometer measurements. The increase of the anode mass correlates to the total charge throughput, which is pressure-dependent and the highest for NP.

Correlating Gas Composition and Electrochemical Data from First Formation Cycle of Lithium-Ion Batteries

The solid electrolyte interface (SEI) plays a crucial role for the performance and lifetime of lithium-ion batteries. It consists of decomposition products from electrolyte components (salt, solvent and additives) and is initially formed during the first charging process called the formation cycle. The chemical processes creating the SEI are a matter of current research. A better understanding of these reactions and their implications on cell performance can provide new ways to optimise the formation process. This can help reducing costs while increasing lifetime and performance of lithium-ion batteries.In this contribution we apply statistical correlation analysis on a large set of cells to gain new insights on the connection between formation and cell-performance. Cells (NMC622|Graphite, 1 Ah, ordered from LiFun) are divided in three groups. The groups differ only by the electrolyte. An electrolyte solution with EC:EMC (3:7 by wt.) and 1 M LiPF6 serves as a baseline. The other two groups use the same solvent and salt concentration but contain an additional 5% fluor ethylene carbonate and vinylene carbonate, respectively.All cells underwent the same formation procedure. It consists of a formation cycle with C/5 at 80°C, followed by a degassing-step and 9 subsequent cycles with the same current rate at 45°C. After these ten cycles a reference performance test (RPT) is conducted, including qOCV, capacity and pulse-resistance tests. During the degassing step gas samples from half of the cells were analysed using GC-MS.An incremental capacity analysis of the formation cycle shows clear distinctions between the three different electrolytes. Distinct peaks below 3 V are found for each group. The gas composition demonstrates that cells containing additives contain a higher share of carbondioxide and carbonmonoxid amid a substantially lower share of ethylene, compared to the cells without additives.The large number of over 100 cells in total enables a systematic correlation analysis. We investigated the correlation between features extracted from the first formation cycle and the RPT. In addition, correlations between electrical data from the first cycle and the relative amount of carbon-containing gasses in the samples are analysed.Correlations differ for the three groups of cells, however some common trends were observed. We found a negative correlation between the average voltage during formation and the difference between the capacity of the first discharge and the capacity measured in the RPT. This difference represents the loss over the 9 cycles at 45°C. It is positively correlated with the first discharge capacity indicating that lower lithium-losses in the first cycle are countered by higher losses in subsequent cycles.Correlations between gasses and electrical data from the formation cycle provide new insights into the chemical processes. If the shares of two gasses are positively correlated, we assume that the reactions producing these gasses are linked. We found such strong positive correlations for the shares of CH4, C2H6, C2H4 and CO in the case of VC-containing electrolyte. In this group the share of carbondioxide is negatively correlated to these gas-shares.Correlating the different gas-shares with the charge throughput in different voltage windows (during wetting at 1.5V, during the formation charge cycles from 1.5 to 3V, 3 to 3.8V, and 3.8 to 4.2 V, respectively), we found very different patterns for the three groups. VC-containing cells show weak or very weak correlations with all four charge-throughput values, with the exception of a moderate negative correlation between CO. Cells without additives show a moderate correlation between the wetting charge and the CO2-share. Cells containing FEC exhibit a moderate positive correlation between the share of CO2 and the charge throughput between 1.5 and 3.8 V.The combination of electrical data with the gas composition and statistical analysis provides a new way to improve our understanding of the SEI formation and the complex chemical reactions. Our results indicate that gasses generated by the decomposition of VC are not influenced by small changes of charge throughput during formation, whereas a higher charge-throughput at lower voltages in cells containing FEC correlates with an increased share of CO2.

Effect of Mechanical Pressure on Rate Capability, Lifetime, and Expansion of Multilayer Pouch Cells with Silicon-Dominant Anodes

Silicon-dominant (Si) anodes with microscale silicon particles meet the requirements of high energy density and low costs due to its ten times higher theoretical electrochemical capacity of 3579 mAh/gSi (Li15Si4) compared to graphite,1 lifetime extension due to partial lithiation,1-2 and high abundance and economic availability due to existing industrial infrastructure.1-2 The major drawback of silicon is the large volume expansion of nearly 300% upon full lithiation. This hinders the broad application of silicon as an active anode material due to continuous SEI (re-) formation and electrochemical milling of particles. Additionally, the volume expansion impacts the overall electrode stability, leading to thickness changes, the disruption of the electronic pathways, and the decoupling of particles. Although the approach of partial lithiation of microscale1 Si eases these effects by lowering the overall volume expansion, these problems still exist.2,3 In this work, the effect of different mechanical cell pressures on lithium-ion batteries with partially lithiated silicon-dominant anodes is investigated with 5.4 Ah multilayer pouch cells as a follow-up study of our previous work with laboratory T-Cells.3 Methodologically, a novel cell holder and pressure device were developed and validated to apply different mechanical cell pressures. Our investigation covers a pressure range from uncompressed as zero (ZP, 0.00 MPa) to high (HP, 0.50 MPa) external cell pressure to determine the optimal pressure for high rate capacity, cyclic lifetime, energy density, and low thickness gain. The cells were tested by checkup cycles at C/10, rate tests up to 3C, and cycled at C/2 until 70% state of health (SoH). Electrochemical impedance spectroscopy was conducted at different SoHs to quantify the effect of mechanical pressures on the impedance response.4 The post-mortem analysis after reaching 70% SoH and operando thickness measurements in a compression test5 bench give insights into the electrode and cell thickness gain.In the electrochemical results, the discharge capacity Q DCH was immediately reduced by decreasing the mechanical pressure from 0.20 MPa to 0.00 MPa or 0.05 MPa, both for the cells in the cell holder (see inset in Figure 1a) and the compression test bench (not shown). This pressure change was also quantified by an increased charge-averaged full cell potential during charging and a decreased charge-averaged full cell potential during discharging. The impedance was reduced for higher mechanical pressure, especially the cathode contact resistance initially and over aging, resulting in lower temperature increases during the rate tests. The capacity retention Q DCH and the total charge throughput were increased to 360 cycles until 70% SoH for higher mechanical pressures at NP (normal pressure, 0.20 MPa) and HP (see Figure 1) compared to 181 cycles for ZP. Overall, applying higher mechanical pressures reduced the thickness increase, as shown by operando thickness measurements and the post-mortem analysis. A dependency of the reversible thickness on the charged capacity was found. Moreover, the porosity decreased with increasing pressure, which was measured with mercury intrusion porosimetry (MIP) and pycnometry. The anode mass increase correlates to the total charge throughput, which is pressure-dependent and the highest for NP.Our findings demonstrate that applying the optimal mechanical cell pressure is significant when using microscale silicon-dominant anodes. We recommend a mechanical pressure of 0.50 MPa for increased rate capacity, minimizing impedance, heat evolution, and thickness gain, and 0.20 MPa for increased energy density. Acknowledgments: S.F. gratefully acknowledges the financial support from the BMBF (Federal Ministry of Education and Research, Germany) under the auspices of the ExZellTUM III project (grant number 03XP0255). The authors want to thank the research battery production team of iwb at TUM for the multi-layer pouch cell production. We also thank Wacker Chemie for kindly providing the microscale silicon material.

Influence of Cycling in Different State-of Charge Windows on Lifetime and Electrode Expansion of Microscale Silicon-Dominant Lithium-Ion Batteries

Silicon (Si) is a promising active anode material for next-generation lithium-ion batteries due to its high theoretical electrochemical capacity of 3579 mAh/gSi (Li15Si4) and low costs using microscale Si particles.1,2 However, the wide usage of Si as an active anode material is hindered due to its lower lifetime compared to graphite anodes. The degradation in silicon-containing batteries can be suppressed by partial lithiation strategies,2,3,4 with applications for automotive cells leading to improved lifetime.5 However, the lifetime problem still exists in partially lithiated microscale Si particles with lower volume expansion2,3 with ≈200 cycles for one-third silicon utilization, i.e., 1200 mAh/gSi 2. Moreover, we confirmed in our previous study6 as reported by Wetjen et al.4 and Haufe et al.2 that lower cell discharge cut-off voltages and thus higher silicon delithiation potentials versus Li+/Li led to accerlated aging and should be avoided.Thus, the motivation for this study is to avoid these high anode delithiation potentials by operating the cells in a high full cell state of charge (SoC) and to investigate the influence of different SoC windows on lifetime with laboratory 182.1 ± 0.7 mAh/gNCA Swagelok T-cells comprising a microscale silicon-dominant anode and a NCA cathode. The electrode-specific aging is monitored with the lithium metal reference electrode based on the anode and cathode potentials and pulse tests. To investigate the aging in different SOC regimes, three cycling conditions were chosen in the low (LV), middle (MV) and high voltage (HV) window and compared to cells cycled between 2.8 and 4.2 V as full voltage6. The voltage window of LV, MV and HV were chosen to represent cycling between 0-50%, 25-75%, and 50-100% SOC, respectively. Formation and checkups were the same for all cells with 2.80 V to 4.20 V. After reaching the end-of-life criterion of 55% state of health (SoH), the cells were disassembled and anode and cathodes were re-assembled in half-cells for a post-mortem analysis to reveal loss of lithium inventory (LLI) and loss of active material of the anode LAMAn, and the cathode LAMCat of the respective full-cells. Complementary to the electrochemical aging, dilatometer measurements7 were conducted to quantify the electrode expansion for the different silicon anode SoC windows since particle decoupling is expected to be one of the major aging mechanisms for microscale silicon2, which is expected for high electrode expansions.For the electrochemical results, the lifetime can be drastically increased from ≈230 to ≈560 equivalent full cycles (EFCs) for operating the full cell in the HV compared to the FV window, as shown in Fig. 1a. One EFCs is defined as the total charge throughput for charging and discharging one cycle normalized to the capacity of the initial checkup cycle. Over aging, the full cell degradation correlates very well with the end of discharge potential of the silicon anodes. Moreover, the electrode-specific pulse results show strong anode degradation while the cathode remains intact. The post-mortem results reveal LLI as most dominenat aging mode, which was very similar for all voltage windows. The HV cells showed both the highest LAMNE and LAMPE, whereas LAMNE was more dominant compared to LAMPE. The silicon amorphization was the lowest for the LV anodes and the highest for the HV anodes at the same SoH. The dilatometer results show that the silicon electrode expansion is the lowest for the low lithiation, i.e., LV, and the highest for the highest lithiation, i.e., HV. From the dilatometry results, we conclude that the mechanical electrode stability does not limit lifetime.Our results demonstrate that lifetime can be significantly improved by a factor of ≈2.4 based on the EFCs if operating cells with silicon dominant anodes in high SoCs and that low SoCs should be avoided. Acknowledgments: S. F. gratefully acknowledges the financial support from the BMBF (Federal Ministry of Education and Research, Germany) under the auspices of the ExZellTUM III project (grant number 03XP0255). The authors want to thank our student worker, Maximilian Reichl, for the fabrication of the NCA coatings. We also thank Wacker Chemie AG for kindly providing the microscale silicon material.

Active Material Lithiation in Gr/SiOx Blend Anodes at Increased C-Rates

The energy density of lithium-ion batteries can be improved by adding silicon as a secondary active anode material alongside graphite. However, accurate state estimation of batteries with blend electrodes requires detailed knowledge of the interplay between the active materials during lithiation. Challenges arise from the current split between the active materials and the overlap of their working potentials. This study examines the lithiation behavior of blend anodes using a setup consisting of a pure graphite and a pure SiOx half-cell connected in parallel. The setup allows for current measurements of both active materials, the determination of the state of lithiation throughout the entire charging process and measurements of balancing effects between the active materials during relaxation periods. Analysis of the behavior at increased charge rates results in greater SiOx lithiation after similar charge throughput indicating better kinetics for SiOx compared to graphite. A Doyle-Fuller-Newman model of a blend anode is used to further investigate the experimental findings on the lithiation behavior and transfer them to blend electrodes. Simulation-based variations of the silicon content show that an increased SiOx content in blend anodes leads to improved rate capability.

Matched micro-geometrical configuration leading to hetero-interfacial intimate contact of MoS2@UiO-66-NH2 Z-scheme heterojunction for efficient photocatalytic CO2 reduction

Z-scheme heterojunction is an effective strategy in photocatalysis, when hetero-interfacial intimate contact is the center of high-performance Z-scheme heterojunction structure. Here, x-MoS2 [x = plate (p), flower (f), and solid sphere (s)] with extensive optical absorption and high conductivity and stable UiO-66-NH2(y) (y = 100, 300, and 500 nm) with rich Lewis's acid sites were integrated to a series of x-MoS2@UiO-66-NH2(y) Z-scheme heterojunctions, which were fully characterized and used for photocatalytic reduction of CO2 (pCO2RR) into CH4 and CO. In response to the difficult modification of MoS2 and loose contact of composite bulk materials, the micro-geometric configurations on the size of UiO-66-NH2 and the morphology of MoS2 were optimized to achieve an intimate contact. The Z-scheme heterojunction f-MoS2@UiO-66-NH2 (100 nm) with perfectly matched micro-geometric configuration exhibited an excellent electron consumption rate (Rele) of 263.78 μmol g–1 h–1 and a high CH4 yield of 27.18 μmol g–1 h–1 with a selectivity of 82.44%, being far superior to most MoS2- and MOFs-based heterojunctions. Comprehensive investigations with extensive photoelectric characterizations, control experiments, and density functional theory (DFT) calculations demonstrate that the excellent photocatalytic performance of f-MoS2@UiO-66-NH2 (100 nm) could be attributed to that (i) the low size of UiO-66-NH2 strengthens mutual alignment and increases outer surface to maximize heterointerface contact with MoS2, accelerating the interfacial charge transfer; (ii) the hierarchical structure of f-MoS2 with optimal basal plane curvature greatly reduces contact barriers to present a high charge throughput with a charge excitation rate of 1.967 mV, smooth initiating the 8-electron CO2 methanation. Additionally, the durability of f-MoS2@UiO-66-NH2 (100 nm) was also investigated.

How Cell Design Affects the Aging Behavior: Comparing Electrode-Individual Aging Processes of High-Energy and High-Power Lithium-Ion Batteries Using High Precision Coulometry

The aging behavior of lithium-ion batteries is crucial for the development of electric vehicles and many other battery-powered devices. The cells can be generally classified into two types: high-energy (HE) and high-power (HP) cells. The cell type used depends on the field of application. As these cells differ in their electrical behavior, this work investigates whether both cell types also show different aging behavior. More precisely, the occurring capacity loss and internal side reactions are analyzed via the charge throughput. For comparison, aging tests are carried out with a high-precision battery tester, allowing the application of High Precision Coulometry (HPC). This enables early detection of aging effects and also allows us to break down the capacity loss into electrode-individual processes. A total of two sub-studies are performed: (1) a cyclic study focusing on lithium plating; and (2) an accelerated calendar aging study. It is found that HE cells exhibit stronger cyclic aging effects (lithium plating) and HP cells exhibit stronger calendar aging effects. The higher lithium plating can be explained by the higher diffusion resistance of the lithium ions within the electrodes of HE Cell. The higher calendar aging fits to the larger electrode surfaces of the HP cell. These results give deep insights into the proceeding aging in a novel way and are interesting for the selection of the appropriate cell type in the context of battery development. In a next step, the measured capacity losses could also be used for a simple parameterization of battery aging models.

An application-oriented lithium-ion battery degradation modelling framework for ageing prediction

In battery-powered applications with high energy demands, the battery is one of the most expensive single components. Since electrochemical storages such as lithium-ion batteries are prone to a slow but steady degradation process, at some point the battery will not be able to fulfil the application’s requirements any more. Due to the high component costs, predicting the battery’s end-of-life is essential for economic operations. Generally, degradation models parametrised from laboratory ageing studies are the solution to predicting the batteries’ lifetime if the loads are known. In this work, we introduce a degradation modelling framework, which has been parametrised to depict the ageing influences of different cycle depths and state-of-charges for the calendar and cyclic degradation. It models the non-linear degradation trajectories, including variances, evaluated in a laboratory ageing study. The ageing framework deploys the degradation model to simulate the expected time, cycles and charge throughput until a given end-of-life criterion. The model and the ageing framework achieve good accuracy with almost zero verification error for the cyclic ageing degradation rate when using interval estimation with the ageing variance confidence intervals. For the point estimation, neglecting the cell’s ageing variance, we achieved MAPE=10.88% and MAPE=22.97% for the degradation rates, respectively.

Lithium-Ion Battery Degradation: Measuring Rapid Loss of Active Silicon in Silicon-Graphite Composite Electrodes.

To increase the specific energy of commercial lithium-ion batteries, silicon is often blended into the graphite negative electrode. However, due to large volumetric expansion of silicon upon lithiation, these silicon-graphite (Si-Gr) composites are prone to faster rates of degradation than conventional graphite electrodes. Understanding the effect of this difference is key to controlling degradation and improving cell lifetimes. Here, the effects of state-of-charge and temperature on the aging of a commercial cylindrical cell with a Si-Gr electrode (LG M50T) are investigated. The use of degradation mode analysis enables quantification of separate rates of degradation for silicon and graphite and requires only simple in situ electrochemical data, removing the need for destructive cell teardown analyses. Loss of active silicon is shown to be worse than graphite under all operating conditions, especially at low state-of-charge and high temperature. Cycling the cell over 0-30% state-of-charge at 40 °C resulted in an 80% loss in silicon capacity after 4 kA h of charge throughput (∼400 equiv full cycles) compared to just a 10% loss in graphite capacity. The results indicate that the additional capacity conferred by silicon comes at the expense of reduced lifetime. Conversely, reducing the utilization of silicon by limiting the depth-of-discharge of cells containing Si-Gr will extend their lifetime. The degradation mode analysis methods described here provide valuable insight into the causes of cell aging by separately quantifying capacity loss for the two active materials in the composite electrode. These methods provide a suitable framework for any experimental investigations involving composite electrodes.

Effects of Tab Design in 21700 Li‐Ion Cells: Improvements of Cell Impedance, Rate Capability, and Cycling Aging

Li‐ion cells of the industrially relevant 21700 format are investigated experimentally by systematic variation of their tab design. To observe the effects of the tab design only, the cells are built on pilot scale using the same electrodes, electrolyte, and separator. Tabs are varied regarding 1) conventionally welded tabs and 2) tabs made from the electrodes’ foils (“foil tabs”), as well as the tab number. Conclusions are drawn on cell impedances, rate capability (0.5C–3C), heating behavior, and cycling aging. Cells with a multitab design show a reduced impedance (1 kHz) by 62%, an improved charging rate capability by ≈17% for 3C, an improved cycle stability by 26.5%, and charge throughput by 22.8%. For the check‐ups at C/10, improvements in cycle life and charge throughput of 51.1% and 42.4% are observed, respectively. The improved cycle life is due to the reduction of inhomogeneities in the jellyrolls as observed by X‐ray computed tomography. The data are put into context with cells from other studies to conclude the order of magnitude of the effects of tab design variation. Based on experimental findings, estimations are made for 46800 format cells regarding energy content and impedance.

CETS: Enabling Sustainable IoT with Cooperative Energy Transfer Schedule towards 6G Era.

The large scale of the Internet of Things necessitates using long-lasting physical layer devices for data collection. Deploying large numbers of Wi-Fi-enabled devices is expensive, so the Internet of Everything (IoE) is equipped with multiple communication modules to collect data where Wi-Fi is unavailable. However, because of their extended communication capabilities, IoE devices face energy limitations. As a result, IoE devices must be provided with the necessary energy resources. This paper introduces a novel multi-hop cooperation communication mechanism for Wireless Energy Transfer (WET) in the Wireless Powered-Internet of Everything (WP-IoE). IoE devices are outfitted here with various communication devices such as RF, Bluetooth, and Wi-Fi. This research proposes a two-phase energy transmission schedule to address the energy requirements. For data collection, the first phase provides a distributed tree-based data communication plan. The proposed model’s second phase used the reverse data collection protocol to implement wireless energy transmission. By combining these two phases, an optimized WET framework was created without unmanned aerial vehicles or robots. The experimental findings show that the proposed method in this research increases the average lifetime of the network and has a more significant charge latency and average charge throughput than other models.

Impact of micro-cycles on the lifetime of lithium-ion batteries: An experimental study

Experimental aging studies are commonly conducted on lithium-ion batteries by full charge and discharge cycles. However, such profiles may differ from the actual operation of batteries in electric vehicles and stationary applications, where they are subjected to different partial charges and discharges. These partial cycles, which take place during a main charge or discharge process, are called micro-cycles if their depth of discharge is <2 %. A number of authors have pointed out the relevance of the time resolution to estimate the energy throughput of a battery due to these micro-cycles in applications such as renewable microgrids. However, to the best of our knowledge, there are no experimental studies in the literature that assess the impact of these micro-cycles on battery degradation. In this article, the impact of micro-cycles on the loss of performance of a lithium-ion battery is experimentally studied. The results show that micro-cycles have a negligible, or even positive effect on the aging of lithium-ion cells compared to the aging caused by full cycles. In fact, if charge throughput or equivalent full cycles are used to measure the use of a battery, then cells subjected to micro-cycles exhibit a 50 % extended lifetime compared to cells only subjected to full cycles. More precisely, cells including micro-cycles with depth of discharge of 0.5 % lasted for nearly 3000 equivalent full cycles, whereas cells aged under standard deep cycles lasted for no >1500. Nevertheless, if the number of deep cycles, disregarding micro-cycles, is the unit to measure battery use, then the degradation of cells with and without micro-cycles is similar. Based on this result, the number of cycles can be identified as a more accurate variable to measure the use of a cell, in comparison to charge throughput.

Impact of high-amplitude alternating current on LiFePO4 battery life performance: Investigation of AC-preheating and microcycling effects

Superimposed Alternating Current (AC) imposed by electric machines and power electronics components in renewable energy systems and electric vehicles (EVs) exposes Li-ion batteries (LIBs) to high-amplitude AC harmonics (i.e., ripple currents). These AC perturbations make LIBs experience shallow charge-discharge cycles or microcycles, resulting in significantly increased battery charge throughput. Recently high amplitude AC-only waveforms have also attracted significant attention as they can be used to warm up/preheat EV batteries in low-temperature environments. To understand what happens when the amplitude of AC-bearing duty cycles is pushed to higher levels, beyond the recommended constant current value set by the manufacturer, a set of fresh LiFePO4 (LFP) cells were subjected to high-amplitude AC-only profiles at low and high frequencies for extended periods. Subsequently, LFP cells were cycled on dynamic current profiles (superimposed AC profiles) for ∼ 200 days, representing real situations encountered by LIBs in renewable energy and electromobility systems. Long-term aging results revealed that as long as the AC current induces a voltage oscillation that remains below the calculated threshold polarization overpotential, the cycle-life of LFP cells is not significantly affected for AC duties as high as the recommended constant current values. Furthermore, for high-frequency AC, a significant amount of microcycling is effectively filtered out by the battery’s double-layer capacitance. However, for low-frequency superimposed AC, for which most of the AC current flows through the charge-transfer resistance, higher charge throughput induced by microcycles causes accelerated degradation.

Electrothermal Aging Model of Li-Ion Batteries for Vehicle-to-Grid Services Evaluation

The growing interest in Electrical Vehicles (EVs) opens new possibilities in the use of Li-ion batteries in order to provide ancillary grid services while they are plugged to recharging stations. Indeed, Vehicle-to-Grid (V2G), Vehicle-to-Building (V2B), Vehicle-to-Home (V2H) as well as Vehicle-to-Vehicle (V2V) services can be carried out depending on the particular installation and on the connection to the distribution grid of the considered recharging station. Even if these are interesting and challenging opportunities, the additional charging/discharging cycles necessary to provide these services could decrease the expected life of EV batteries. For this reason, it is of paramount importance to study and develop reliable models of the batteries, which take the aging phenomena affecting the reliability of the Li-ion cells into account to evaluate the best charging/discharging strategy and the economic revenues. To this aim, this paper focuses on a battery pack made up with Li-ion nickel–manganese–cobalt (NMC) cells and proposes a semiempirical Electrothermal Aging Model, which accounts for both calendar and cycle aging. This modeling phase is supported by several experimental data recorded for many charge and discharge cycles at different C-rates and for several temperatures. Thus, it is possible to analyze and compare scenarios considering V2G services or not. Results show that the considered battery is subjected to a life reduction of about 2 years, which is a consequence of the increased Ah charge throughput, which moves from 120,000 Ah over 10 years (scenario without V2G services) to almost 230,000 Ah over 8 years (scenario with V2G services).

Variable DC-Link Voltage Regulation of Single-Phase MMC Battery Energy-Storage System for Reducing Additional Charge Throughput

Battery energy-storage system (BESS) based on the modular multilevel converter (MMC) can flexibly manage the battery packs integrated into submodules, where the battery pack can directly or through a small capacitor connect to the rear-end half-bridge circuit for reducing cost and volume caused by an additional dc-dc converter. But the alternating current ripples will cause substantial additional charge throughput for battery packs and, consequently, reduce the battery lifetime in theory. Therefore, this article proposes a variable dc-link voltage regulation method for a single-phase MMC-BESS. In specific, the phase disposition (PD) modulation scheme is improved to properly bypass the gating signals with unnecessary conduction during operation and the modified gating signals will be rearranged for balancing the states-of-charge and states-of-health. Doing so, the additional charge throughput could be significantly reduced compared with the traditional phase-shift modulation and PD modulation. Even comparing with the ideal dc current charging/discharging, the proposed method will only increase slight additional charge throughput and nearly negligible capacity loss. The experimental results of a 6.6 kW/6.6 kWh single-phase MMC-BESS prototype verified the performance of the proposed method.

Increase of Cycling Stability in Pilot-Scale 21700 Format Li-Ion Cells by Foil Tab Design

Li-ion cells of the industrially-relevant 21700 format were built on pilot-scale with tabs made from (a) the electrodes’ current collecting foils (Al and Cu, “foil tabs”) in comparison with (b) conventional tabs (Al and Ni) welded to the electrodes’ current collecting foils (“welded tabs”). Both cell types use the same anode (graphite), cathode (NMC622), separator, electrolyte, as well as the same tab positions. This allows a direct comparison of welded tabs and foil tabs regarding formation, C-rate capability, cell electrical resistance, and long-term cycling stability tests. Our data reproducibly shows 14.4% longer cycling stability and 11.2% increased total charge throughput in the case of the cells with foil tabs until 80% SOH, which is likely due to less inhomogeneities in the case of the foil tab design.

Lead Batteries for Dash-Cam Applications: Experiences and Lab Test Development

In modern road vehicles, one of the major energy consuming devices is the dash-cam, which is becoming more popular in many markets for several reasons. This dash-cam device is also operated during vehicle stand-still, therefore the energy demand usually is covered by the car's lead starter battery. In this paper, the influence of dash-cams on vehicle electrical systems in two different vehicles was investigated on the road and on the roller dynamometer. In both vehicles, similar strategies for battery operation and SoC maintenance were observed, but significant differences were found in Start/Stop characteristics and low-temperature operation. Vehicle A allowed for a higher DoD range during discharge, while vehicle B allowed for Start/Stop operation also at lower temperature conditions. In particular, the Start-Stop system was investigated in terms of average SoC, but also missed engine stop opportunities and premature engine restart events. Based on this knowledge, battery laboratory tests were developed that represent the operating mode of a vehicle with an activated dash-cam under controlled conditions. One test was an accelerated life test that was focused on the maximum charge throughput of the test batteries, and another test was focused on the reaction mechanism, which was found to be sulfation. These tests were validated with lead batteries of different technologies: AGM batteries (absorbent glass mat) turned out to be superior over flooded batteries in this vehicle application.

Industrial Tests of Technology For Smelting Sulfide-Copper Concentrate at the Pobeda Oxygen Blast Smelter using Bottom Tuyeres

The results of industrial tests of smelting sulfide copper concentrates on industrial oxygen using side and bottom tuyeres with a protective gas layer in the Pobeda smelting unit (PSU) at the Mednogorskiy Medno-Sernyy Kombinat (MMSK) are presented. Based on the analysis of the operating conditions of the PSU, the main results of the experimental meltings are discussed. The possibility of achieving the maximum charge throughput up to 475 ton/day with a specific oxygen consumption for the bottom tuyeres of 3250–3450 m3 /h is demonstrated. The copper content in slags varies in the range of 2.5–3.0%, the copper concentration in the matte comprises 38.68%, and the SO2 content in the exhaust gases equals 12.24 vol. %. The campaign duration of the bottom tuyeres was 4.6 days.

Calendar and cycle aging study of a commercial LiMn2O4 cell under consideration of influences by cell progress

Abstract Aging characteristics of lithium-ion cells are investigated on the basis of commercially available LiMn2O4 cells. The effects of time, cell state of charge (SOC), and temperature are examined for the case of calendar aging. Likewise, charge throughput, depth of discharge (DOD), average SOC, charge rate, and realistic discharge profiles are analyzed for cycle aging based on a thorough aging test campaign. Aging properties are described by means of capacity, resistance, and differential voltage analysis (DVA). In addition to the square root-like capacity decrease over time and charge throughput, a significantly lower capacity loss is observed for low SOC scenarios. The influence of continuous cell chemistry improvement and a change of the cell chemistry from LMO to LMO-NMC is investigated over a period of 3 years. Initial characterization tests show a decrease in resistance and increase in capacity over the years. DVA and incremental capacity analysis (ICA) help to reconstruct the cell development progress by observing the rise of the NMC-induced ICA peak at about 3.5 V. A comparison of the three cell batches which were purchased over a period of three years indicates that, although the ICA changes, the capacity and resistance characteristics vary only slightly.

A Numerical Study on Effects of Electrolyte Dry-out in Separators of Lithium-Ion Batteries

A variety of strategies to deal with the Lithium-ion batteries (LIBs) reaching the end-of-life (EOL) is being proposed, one of which is the secondary use applications such as the grid distribution system or the off-grid system. [1] It is reported that within the EOL range, the capacity fade generally represents linear dependence on charge throughput and that SEI layer growth is the dominant factor. After prolonged cycling, however, the transition point to the nonlinearity of aging is observed and the LIBs capacity dropped suddenly, indicating that some other aging mechanisms. [2] This rapid capacity drop phenomenon has been reported by experimental tests of other groups. [3-5] Among many phenomena related to the rapid drops, electrolyte dry-out including decomposition of additives has been considered as one of the major factors.In this work, we employ an electrochemical physical model for 20Ah NCM pouch-type cell, which describes both solid and liquid phase behavior through a concentrated solution and porous electrodes. A pseudo-two-dimensional (P2D) electrochemical physical model calculates lithium concentrations and electric potentials in the electrolyte and the active materials and allows them to expand to additional physical phenomena. Saturation in the porous media is defined to account for the dry-out of the electrolyte. Because electrodes have higher wettability than separators, if the decreases of saturation occur in the LIBs, the problem area is more likely to be a porous separator than a composite electrode. [6] For this reason, we assumed that saturation reduction occurs only at separators as the electrolytes are decreased in the cell. Reduced saturation in a separator can be followed by a block of ionic transport through separator pores, and result in the sudden death of LIBs battery.The P2D model cannot solve non-uniform phenomena appearing along the electrode area because of a one-dimensional calculation in the electrode thickness direction. Therefore, an expanded pseudo-three-dimensional (P3D) model was used to examine how dry-out in the separator affects the physics of the LIBs quantitatively. The P3D model is possible to simulate the imbalance in LIBs cells as well as the end-of-life of LIBs. Also, parametric studies about area and saturation of the dry-out we conducted by the model. The model results show that there is a critical saturation of the dry-out leading a sharp performance drop. This model can account for the sudden degradation of LIBs and the loss of ionic path and the internal imbalance caused by electrolyte dry-out.