Shallow Cycles Research Articles

Perturbation of the deep-Earth carbon cycle in response to the Cambrian Explosion.

Earth’s carbon cycle is strongly influenced by subduction of sedimentary material into the mantle. The composition of the sedimentary subduction flux has changed considerably over Earth’s history, but the impact of these changes on the mantle carbon cycle is unclear. Here, we show that the carbon isotopes of kimberlite magmas record a fundamental change in their deep-mantle source compositions during the Phanerozoic Eon. The 13C/12C of kimberlites before ~250 Ma preserves typical mantle values, whereas younger kimberlites exhibit lower and more variable ratios—a switch coincident with a recognized surge in kimberlite magmatism. We attribute these changes to increased deep subduction of organic carbon with low 13C/12C following the Cambrian Explosion when organic carbon deposition in marine sediments increased significantly. These observations demonstrate that biogeochemical processes at Earth’s surface have a profound influence on the deep mantle, revealing an integral link between the deep and shallow carbon cycles.

Diagenetic controls on porosity evolution and reservoir quality of an outcrop analogue of the Jurassic carbonate reservoirs in the Arabian Plate: An example from the Middle Jurassic Tuwaiq Mountain Formation, Central Saudi Arabia

The Middle Jurassic Tuwaiq Mountain Formation (TMF; formed of three members, from bottom to top T1, T2, and T3) represents one of the primary conventional and unconventional reservoirs to be assessed in Saudi Arabia. It is considered as a tight carbonate reservoir in the Jafurah Basin and conventional reservoir in the Arabian Basin. Here, we investigate the depositional, diagenetic, and stratigraphic impact on reservoir quality and porosity evolution of the TMF through an integrated petrographical, geochemical and petrophysical analyses on outcrop samples. The TMF has a complex diagenetic history including micritization, dissolution, recrystallization and neomorphism, meteoric cementation, evaporite precipitation, dolomitization, silicification, dolomite dissolution and calcitization. Dolomitization occurred via a hypersaline fluid mechanism, based on texture, association with evaporites, and Sr concentration. X-ray diffraction results support chert replacing evaporite as the mechanism of the two chert beds in the T3 member due to the presence of anhydrite relics in their samples. This replacement formed the necessary Ca 2+ rich fluid for dolomite dissolution and calcitization. Therefore, dolomite calcitization occurs locally and is stratigraphically controlled based on its position relative to chert beds in T3. T3 and the upper part of the T2 member contain calcitized dolomites, while the lower part of T2 and T1 contain only dissolved dolomite. As the fluid went deeper in the TMF, it became weaker. Therefore, the fluid was too weak to develop dolomite calcitization process and instead only affected T1 and the lower part of T2 by dolomite dissolution. Overall, dolomite dissolution and dolomite calcitization didn't have a high impact on porosity evolution as the TMF isn't a highly dolomitized formation. The distribution of porosity (ø), permeability (K), and reservoir-quality-index (RQI) of the TMF are stratigraphically controlled. The TMF represents the regressive system tract of a 3rd order depositional sequence, which is composed of seven 4th order cycles (i.e. deep lagoon cycles (DLC) and shallow lagoon cycles (SLC)). RQI, Ø, and K plots showed great fitting with the 4th order depositional-cycles as DLC has very poor reservoir properties (average ø = 7.7%, average K = 0.17 mD, average RQI = 0.03), while SLC has fair reservoir properties (average ø = 15.4%, average K = 2.64 mD, average RQI = 0.11). Reservoir quality contrast is controlled by two factors: (1) the reduced mud-content and increased grain-content in SLC compared with DLC resulted in increased primary interparticle porosity, and is governed by depositional energy; and (2) the higher primary interparticle porosity in SLCs compared with DLCs preferentially facilitated more infiltration of undersaturated meteoric fluids, resulting in enhanced grain dissolution. This is reflected on the higher proportion of moldic and vuggy porosity in SLCs compared with DLCs. The accurate assessment of the TMF micro-scale attributes and controls on reservoir quality in an outcrop analogue that occurs in close proximity to subsurface hydrocarbon producing intervals can provide important input for oilfield appraisal and enhanced oil recovery performance. • Cementation was the main destructive diagenetic feature of the reservoir quality. • Depositional texture controlled primary porosity and dissolution related secondary porosity. • Dolomite-Calcitization and meteoric-dissolution had a stratigraphically controlled distribution. • Dolomitization happened through hypersaline fluids like many Jurassic carbonates in the Arabian Plate. • Dedolomitization mechanism was related to the process of chert replacing evaporites.

An In-Depth Analysis of the Transformation of Tin Foil Anodes during Electrochemical Cycling in Lithium-Ion Batteries

Tin foils have an impressive lithium-storage capacity more than triple that of graphite anodes, and their adoption could facilitate a drastic improvement in battery energy density. However, implementation of a dense foil electrode architecture represents a significant departure from the standard blade-cast geometry with a distinct electrochemical environment, and this has led to confusion with regards to the first cycle efficiency of the system. In this work, we investigate the unique behavior of a tin active material in a foil architecture to understand its performance as an anode. We find shallow cycling of the foil results in an irreversible formation (< 40%) due to diffusional trapping, but intermediate and complete utilization allows for a remarkably reversible formation reaction (> 90%). This striking nonlinearity stems from an in situ transformation from bulk metal to porous electrode that occurs during formation cycles and defines electrode-level lithium-transport on subsequent cycles. An alternative cycling procedure for assessing the stability of foils is proposed to account for this chemomechanical effect.

The Effects of Electrolytes and Cycling Protocols on Bi-Birnessite Cathode for Alkaline Batteries

Stationary batteries need to be low-cost, highly energy-dense, safe, reliable, and made with abundant materials using simple manufacturing methods. MnO2 is abundant, low-cost, non-flammable, non-toxic, & has a high theoretical capacity of 617 mAh g-1. The phase changes of MnO2 during cycling are a significant determinant of the system’s reversibility. Electrolytic manganese dioxide, or γ-MnO2, is the most commonly used polymorph, frequently paired with Zn anodes in commercial primary batteries.1 In secondary batteries, long-lasting reversibility of γ-MnO2 cathodes requires limiting depth-of-discharge (DoD) to 5-10% of capacity to prevent the formation of additional MnO2 polymorphs. Alternatively, layered δ-MnO2, or birnessite, can deliver 60-80% of theoretical capacity but usually requires low active mass loading and has a low cycle-life due to the irreversible formation of Mn3O4. The use of copper and Bi2O3 additives was recently found to mitigate many birnessite problems, resulting in a cathode with high active mass loading that delivered full theoretical capacity for thousands of cycles.2 Furthermore, the birnessite was electrochemically synthesized from γ-MnO2 in situ, making the system even more attractive for commercialization. However, eliminating copper and replacing KOH with NaOH would make the system much more economically favorable. In this work, we investigated the sensitivity of Bi-birnessite’s cycle life to electrolyte type and cycling protocols. We compared the cycle life of Cu-intercalated Bi-birnessite in KOH to that of Bi-birnessite, with and without copper, in NaOH. We also evaluated the influence of depth-of-discharge on the capacity fade behavior of the cathode in NaOH. Finally, we assessed the performance of the cathode under a slow, shallow cycling protocol that simulates seasonal, long-term energy storage behavior. X-ray diffraction (XRD) was used at various points in the cathode’s cycle life to determine the phase evolution of the material. By extrapolating from the XRD and cycling data, we will compare the roles of KOH to NaOH and Cu2+ to Na+ in the system, respectively.References Shin, J., Seo, J. K., Yaylian, R., Huang, A. & Meng, Y. S. A review on mechanistic understanding of MnO2 in aqueous electrolyte for electrical energy storage systems. Int. Mater. Rev. 65, 356–387 (2020).10.1080/09506608.2019.1653520. Yadav, G. G. et al. Regenerable Cu-intercalated MnO2 layered cathode for highly cyclable energy dense batteries. Nat. Commun. 8, 14424 (2017). 10.1038/ncomms14424.

Energy requirement of hybrid vehicles

Increase in energy requirement has lead to the development of new energy storage devices for the movement of vehicles. This paper categorises the various types of vehicles with different intensities of hybrids based on degree of hybridisation. The parameters which depend on the performance of the battery are shallow cycle life, high dynamic charge acceptance for sturdy for regenerative braking and sturdy life of the battery. Lead Acid battery either liquid or absorptive glass fibre is expected to work with 14 V systems for micro hybrids with low cost battery maintenance system for increasing applications.. Advanced latest batteries are considered for mild or medium hybrid once they have proven the worthiness under real operating conditions under dynamic responses. NiMH and Li-ion batteries are dominating current and potential battery for high functionality HEVs. Li -ion offers an attractive opportunity for improvement in performance and cost. Super capacitors are considered for power applications where in the variation of signal is in the pulse form. Specific attention is given to system integration of the battery and advance technology during vehicle integration. In this paper there are various opportunities and challenges in obtaining a potential battery pack.

Comparing CO2 emissions impacts of electricity storage across applications and energy systems

Summary Electricity storage systems can support the decarbonization of energy systems. However, the effect of electricity storage use on greenhouse gas emissions is complex because of roundtrip efficiency losses of the storage and its effects on the dispatch of different electricity-generation technologies. The limited literature examining this issue focus on individual electricity storage applications and the geographies where they are applied. Here, we systematically compare the effects of electricity storage on CO2 emissions across four applications in electricity systems resembling seven European countries. Our findings reveal large emission impact differences between applications and countries. Among other findings, we find that when compared with wholesale arbitrage, storing electricity in other applications exhibits much lower effects on CO2 emissions. We also investigate different policy options to reduce CO2 emissions from storing electricity. We find that although a higher carbon price can have a substantial effect on reducing the CO2 emissions from wholesale arbitrage, other applications require alternative approaches.

Isotopic fingerprinting of biogeochemical processes and iron sources in the iron-limited surface Southern Ocean

Iron (Fe) is an essential micronutrient that limits primary productivity throughout the surface of the Southern Ocean. Here, we present the first high-resolution depth profiles for dissolved Fe and Fe isotope ratios (δ56Fe) from all major zones of the Southern Ocean, collected during the Antarctic Circumnavigation Expedition in austral summer 2017. Open-ocean surface waters are characterized by remarkably high δ56Fe values (up to +1.6‰) and very low Fe concentrations (<0.05 nmolkg−1). We attribute the elevated δ56Fe values above the ferricline to the effect of continuous shallow cycling processes (uptake, recycling, and binding of Fe to organic ligands), with only a very limited resupply of Fe from below. Below the ferricline, δ56Fe values approach ∼0‰ and remain constant down to our deepest samples at 1000 m, with no obvious isotope signal from regeneration. This overall pattern in δ56Fe is modified near islands, continental shelves and hydrothermal vents, where distinct δ56Fe signatures are associated with different Fe sources. Near the volcanic Balleny Islands, elevated surface Fe concentrations associated with low δ56Fe are indicative of reductive release of isotopically light Fe from sediments. Elevated δ56Fe values at depth near the Balleny seamount chain and near the East Scotia Arc may reflect distal hydrothermal influences, caused by fractionation associated with precipitation or the loss of specific phases of Fe during long-range transport. Sedimentary sources of isotopically light Fe on the Antarctic Peninsula are important for shelf waters. Long-distance transport of this sediment-derived Fe and its influence on surface waters are strongly dependent on the regional circulation, and may ultimately be the source of light Fe previously observed within Antarctic Intermediate Water in the Atlantic sector of the Southern Ocean.

OFx: A method of 4D image construction from free-breathing non-gated MRI slice acquisitions of the thorax via optical flux.

Since real-time 4D dynamic magnetic resonance imaging (dMRI) methods with adequate spatial and temporal resolution for imaging the pediatric thorax are currently not available, free-breathing slice acquisitions followed by appropriate 4D construction methods are currently employed. Self-gating methods, which extract breathing signals only from image information without any external gating technology, have much potential for this purpose, such as for use in studying pediatric thoracic insufficiency syndrome (TIS). Patients with TIS frequently suffer from extreme malformations of the chest wall, diaphragm, and spine, leading to breathing that is very complex, including deep or shallow respiratory cycles. Existing 4D construction methods cannot perform satisfactorily in this scenario, and most are not fully automatic, requiring manual interactive operations. In this paper, we propose a novel fully automatic 4D image construction method based on an image-derived concept called flux to address these challenges. We utilized 25 dMRI data sets from 25 pediatric subjects with no known thoracic anomalies and 58 dMRI data sets from 29 patients with TIS where each patient had a dMRI scan before and after surgery. A time sequence of 80 slices are acquired at each sagittal location continuously at a rate of ~480ms per slice under free-breathing conditions, with 30-40 sagittal locations across the chest for each subject depending on the thoracic size. In our approach, we first extract the breathing signal for each sagittal location based on the flux of the optical flow vector field of the body region from the image time series. Here, for each time point of respiratory phase, the net flux of the body region can be regarded as the flux going into or out of the body region, which we term Optical Flux (OFx). OFx provides a very robust representation of the real breathing motion of the thorax. OFx allows us to perform a full analysis of all respiratory cycles, extract only normal cycles in a robust manner, and map all extracted normal cycles on to one cosine respiration model for each sagittal location. Subsequently, we re-sample one normal cycle from the respiration model for each location independently. The normal cycle models associated with the different sagittal locations are finally composited to form the final constructed 4D image. We employ several metrics to evaluate the quality of the 4D construction results: Eie - error in locating time instants corresponding to end inspiration and end expiration; Eto - deviation from correct temporal order in each detected normal cycle; Ess - deviation in spatial smoothness; and Esc - deviation from spatial continuity as scored by a reader. The means and standard deviations of these metrics for normal subjects and TIS patients are found to be, respectively: Eie: 0.25±0.05 and 0.38±0.16 in units of time instance (ideal value=0); Eto: 2.7% ± 2.3% and 1.8%±2% (ideal value=0%); Ess: 0.5±0.17 and 0.54±0.25 in pixel units (ideal value=0); Esc: 4.6±0.48 and 4.56±0.98 (score range: best=5, worst=1). The results show that the OFx method achieves excellent spatial and temporal continuity and its yield was 100% meaning that it successfully performed 4D construction on every data set tested. Compared to a recently published method, OFx is fully automatic requiring about 5min of computational time per study starting from acquired dMRI scans. The method achieves high temporal and spatial continuity even on complex TIS data sets that include many abnormal respiratory cycles. A new 4D dMRI construction method based on the concept of optical flux is presented which is fully automatic and very robust in deriving respiratory signals purely from dynamic image sequences even when presented with complex breathing patterns due to severe disease conditions like TIS. Evaluations show that its accuracy is comparable to the variations found in manual annotations. An important characteristic of the method is that it is independent of the number of sagittal locations used in the construction process, which suggests that it is applicable to imaging techniques where data are acquired at only a few sagittal locations instead of the full width of the thorax. The method is not tied to any specific imaging modality, as demonstrated in this paper on not just dMRI but dynamic computed tomography (CT) as well.

The largest negative carbon isotope excursions in Neoproterozoic carbonates caused by recycled carbonatite volcanic ash

The late Ediacaran Shuram Excursion (SE) records the most prominent negative δ13C excursions (δ13C = −12‰) during Earth’s history. It has been hypothesized to have resulted from oxidation of dissolved organic matter, diagenetic or authigenic precipitates. However, the origin of the SE remains enigmatic; current models face challenges regarding the significant amount of atmospheric oxygen needed to balance such extensive oxidation and sustained inputs of light carbon with extremely negative C isotope compositions. Here, we show that the Doushantuo Formation at the Jiulongwan section in South China, a key stratum recording the SE event, contains mineralogical and geochemical signatures related to igneous processes. Both the occurrence of ankerite, feldspar, moissanite and euhedral quartz in the SE samples and the relatively consistent Ce anomalies of carbonate and O isotopes of quartz indicate a contribution from an igneous source. In particular, the SE samples have trace element and C isotope compositions similar to those of recycled carbonatites formed by decarbonation and melting of sedimentary carbonate rocks. These observations suggest that the deep cycle of ancient carbonate rocks, which were subjected to decarbonation during subduction, melting and eruption related to the breakup of the Rodinia supercontinent, contributed to the SE. This igneous model for the SE may provide a connection between the deep and shallow carbon cycles of the Earth.

Variations in Mid‐ to Late Holocene Nitrogen Supply to Northern Great Barrier Reef Halimeda Macroalgal Bioherms

AbstractThe northern Great Barrier Reef (GBR) Halimeda bioherms have accumulated on the outer continental shelf from calcium carbonate algal sediments over the past ∼10,000 years and cover &gt;6,000 km2 of shelf area. As such, Halimeda bioherms play a key role in the shallow marine carbon cycle over millennial timescales. The main source of nitrogen (N) to these bioherms is thought to be westward transport of upwelled NO3‐‐rich water from the Coral Sea. However, the primary N source has not been traced geochemically, and we have no understanding of any temporal variation. Here, we reconstruct patterns of N supply to Halimeda bioherms in the GBR since the mid‐Holocene using the 15N/14N ratio of skeletal‐bound organic N (δ15N‐skeletal organic material [SOM]) in modern and fossil Halimeda sediment cores. Average Halimeda skeletal δ15N‐SOM was 6.28 ± 0.26‰, consistent with δ15N‐NO3‐ from western tropical South Pacific (WTSP) thermocline waters. Thus, geochemically validating shelf‐break upwelling of an oceanic N source that regulates bioherm spatial distribution. Halimeda δ15N‐SOM decreased by 1‰–2‰ from 5,000 to 2,000 cal. yr BP, reaching a minima of 5.5‰ that persisted for almost 1,000 years. The Halimeda δ15N‐SOM variation reflects mid‐ to late Holocene changes in regional climate and intensified El Niño activity that likely facilitated elevated N2 fixation in the WTSP, thereby lowering thermocline δ15N‐NO3‐. Thus, Halimeda skeletal material provides a valuable high‐resolution geochemical archive of past oceanographic and climatic processes over centennial to millennial timescales, complementing existing paleoclimate proxy records.

Rationally design lithiophilic surfaces toward high−energy Lithium metal battery

The practical application of lithium (Li) metal anode has been hindered by the fast Li depletion and shallow cycling conditions. Herein, a universal and scalable approach for current collectors combining an enhanced lithiophilic surface and a conductive inner core enables a promising pathway for high−performance Li metal battery (LMB). The interface between anode and electrolyte accelerates Li ions self−concentration and enhances the electrokinetic surface conduction with suppressed Li concentration polarization. With Cu@Cu3N as an example, a fast Li plating/stripping at 20 mA cm−2 for 10,000 cycles and a stable full cell under the near realistic conditions with a high active material loading (19.1 mg cm−2), a low electrolyte/active materials ratio (2.3), and a limited Li resource (10.24 mAh cm−2: equivalent to 50 µm Li foil) are achieved for broadening the commercialization of LMB.

Reversible Capacity Losses in LiFePO4 / Graphite Cells

This investigation focuses on significant capacity losses that have been found to occur in commercial lithium-iron phosphate (LFP) / graphite cells after repeated shallow cycling around medium states of charge (SOCs). Many combinations of cycle depth, medium SOC and temperature are examined over up to 10,000 full cycle equivalents. Up to 1000 full cycle equivalents, the capacity loss rate is four times higher when the cells are cycled between 40% and 60% state of charge than it is with full cycles. It is shown that these extraordinary losses occur in three different lithium-iron phosphate / graphite cell models, two 26650-type and one 18650-type, but do not occur in a nickel-manganese-oxide / graphite 18650-type cell. Most of the apparently lost capacity is shown to be recoverable by holding the cells at either 0 % or 100 % state of charge over a period of several days. Differential voltage analysis and visual post-mortem inspection as well as coin cell experiments with harvested electrode material suggest that these capacity losses are caused by strongly non-uniform lithium distributions in the electrodes. Hypothetical mechanisms are presented and discussed that could lead to such non-uniform distributions of lithium forming preferentially in lithium-iron phosphate based cells. The findings presented in this study are believed to be particularly relevant for grid applications like primary control reserve or in other scenarios where the battery mainly serves as a peak power buffer, e. g. in hybrid drivetrains.The graph shows the capacity evolution of LFP / graphite cells cycled with full cycles and with 20 % cycle depth around three different medium SOCs. Capacity loss is largest when cycling between 40 % and 60 % SOC. The photographs show post-mortem views of the graphite anodes of three different LFP / graphite cell models that were cycled using this procedure until reaching ca. 80 % remaining capacity. Gold colored stripes at the top and the bottom of the electrodes indicate a non-uniform distribution of intercalated lithium. Figure 1

Extensive aging analysis of high-power lithium titanate oxide batteries: Impact of the passive electrode effect

Partial electrification of vehicle drive trains, for example by the usage of 48 V systems, require high-power batteries with extreme robustness to temperatures, current rates and energy throughputs. In this study, the application-relevant lifetime performance of 33 state-of-the-art high-power lithium titanate oxide nickel manganese cobalt oxide (LTO|NMC) cells is measured under cyclic, calendar, and drive cyclic aging regimes. Regular extended check-ups reveal the cell performance in terms of capacity loss and internal resistance increase, which allows for the identification of critical operating conditions. For the first time a passive electrode effect is identified in calendar aging tests of LTO cells in which the cathode is geometrically and capacitively oversized. Passive electrode areas lead to a change in cell balancing, which can be illustrated by the shift of the half-cell voltage curves. Generally, the investigated cells show an excellent cycle stability for shallow cycles, even at high ambient temperatures and high current rates. Only large cycle depths greater than 70% at elevated temperatures reduce the battery life significantly. Furthermore, the results show that cells cycled in areas of low state of charge age faster than in areas of high state of charge. The rise in internal resistance under calendar aging has the most detrimental influence on lifetime in a 48 V battery.

Evaluation of shallow cycling on two types of uncompressed automotive Li(Ni1/3Mn1/3Co1/3)O2-Graphite pouch cells

Abstract For this contribution, two generations of uncompressed pouch cells are investigated in cyclic aging tests. The results are analyzed for the key influence factors by opposing the results of both cell setup strategies with results of compressed cells reported in literature. The cells are evaluated with respect to pulse resistance, anode overhang, dV/dQ-analysis, capacity difference analysis, homogeneity of lithium distribution (HLD) and irreversible capacity losses. It is shown, that uncompressed cells reveal, in contrast to compressed cells, a higher HLD, which is demonstrated in the missing dV/dQ flattening over aging. The trends of peak heights in dV/dQ depend mainly on the graphite voltage and expansion characteristics and are therefore different for both cell generations due to different degrees of utilization of the anode. The trends are comparable to calendric aging test results. The irreversible losses for uncompressed cycled cells increase with cell potential while compressed cells show higher losses to lower and higher SOCs caused by low HLD. Therefore, uncompressed cells have a lower risk of developing lithium plating for inhomogeneous distributed active lithium during accelerated aging tests performing a full charge. Comparing both cell generations, the lifetimes show strong deviations and the largest impact is associated with n/p ratio of the anode to the cathode.

4D image construction from free-breathing MRI slice acquisitions of the thorax based on a concept of flux.

Retrospective 4D image construction from continuously acquired 2D slices is a necessary step to achieve high-quality 4D images. Self-gating methods, which extract breathing signals only from image information without any external gating technology, have much potential, such as in pediatric patients with thoracic insufficiency syndrome (TIS) who suffer from extreme malformations of the chest wall, diaphragm, and spine, leading to breathing that is very complex with lots of abnormal respiration cycles, including very deep or shallow cycles. Existing methods do not work well in this clinical scenario and most are not fully automatic, requiring some manual interactive operations. In this paper, we propose a fully automatic 4D dMRI construction method based on the concept of flux to address the 4D image construction from 2D slices of subjects with complex respiration. Firstly, we extract the breathing signal for each location based on the flux of the optical flow vector field of the body region from the image series. Then, we give a full analysis for all cycles and extract several normal ones and map them to one cosine respiration model for each location. After that, we re-sample one normal cycle from the respiration model for each location independently. All of these resampled normal cycles form the final constructed 4D image. Qualitative and quantitative evaluations on 25 subjects show that the proposed method can handle datasets from subjects with more complex respiration and achieves good self-consistency results while maintaining time and space continuity.

Capacity fading of a LiFePO4/graphite cell during shallow cycling due to planar inhomogeneity in LiFePO4

The capacity fading mechanism of a LiFePO4/graphite cell (nominal capacity 3 Ah) was investigated. We report that capacity fading resulted from the centimeter-scale planar inhomogeneous reaction on the LiFePO4 cathode after operation at a shallow state of charge (SOC), operated between SOC 40% and 60%. It was confirmed by (i) wide variations of electrode capacities of the disassembled electrode and by (ii) the two-dimensional X-ray diffraction (XRD) analysis. Li-ion content could be estimated by (i) comparing the residual capacities of several electrode regions of the LiFePO4 sheet after disassembly of the cell and (ii) the intensity ratio variations of the typical XRD peaks of LiFePO4 and FePO4 at 5 mm × 5 mm grids. The inhomogeneity was induced by using only the two-phase region in the LiFePO4. Electrode reversible capacities are not a dominant factor for capacity fading, and we found the inhomogeneity has a possibility for restoration. Therefore, we should consider a suitable operating procedure of the storage system for electricity grid use with long-term service life.

Analysis and modeling of cycle aging of a commercial LiFePO4/graphite cell

This paper presents cycle aging results of a commercial lithium-ion cell from a comprehensive, 29 month aging study and follows up on calendar aging results published previously [1]. We use a widely used commercial LiFePO4/graphite cell from Sony/Murata, which promises long calendar and cycle lifetime, that would make it suitable for stationary battery applications. The evolution of the cells’ capacity and impedance are shown in a static cycle aging study for 19 test points with different combinations of temperature, C-rate, depth of discharge and state of charge. Based on the measurement data shown herein and the calendar aging model presented in the previous paper, a semi-empirical combined aging model is presented for the capacity loss and resistance increase. Two dynamic load profiles are used to experimentally validate the combined aging model. Absolute model errors below 1% for the capacity loss and below 2% for the resistance increase in both dynamic load profiles demonstrate that the combined aging model can predict the lifetime of LiFePO4/graphite battery cells for different applications and varying operation conditions adequately. In the cycle experiments, an unexpectedly strong, but partly reversible capacity loss is observed with shallow cycles at medium states of charge.

Restructured rimous copper foam as robust lithium host

Uncontrollable growth of lithium (Li) dendrites and infinite volume change during cycling limit the practical implementation of Li metal anode in batteries. Three-dimensional (3D) porous materials with interconnected conductive skeleton are expected as ideal hosts to boost uniform Li deposition by reducing the local current density and Li nucleation barrier. However, surface modifications for the 3D conductive frameworks are complicated and costly, and most of these host materials can only afford shallow cycling at smaller current densities. Herein, a new strategy is proposed to fabricate rimous Cu foam (RCF) with ant-nest-like porous skeleton via a novel polysulfide-assisted reconstruction approach. The interconnected conducting Cu network with a larger and lithiophilic surface enables uniform and deep Li deposition into the interior space of RCF. The unique ant-nest-like interior channel not only endows a high intake capacity for Li, but also abstains volume fluctuation of Li anode during cycling. Therefore, the RCF-modified Li anode delivers excellent cycling stability with high Coulombic efficiency of 99% after 660 cycles at 1 ​mA ​cm−2 and small overpotential of 30 ​mV over 200 ​h under a high plating/stripping rate of 3 ​mA ​cm−2. More importantly, full cells paired with practical-level LiFePO4 cathode exhibit exceptional performance under high current densities.

Capacity Recovery Effect in Commercial LiFePO4 / Graphite Cells

We report a significant capacity recovery effect of more than 10% after continuous shallow cycling of commercial LiFePO4/Graphite cells. In a previous study on a LiFePO4/Graphite cell, we observed that capacity losses were more severe with shallow cycles than with full cycles. Herein, the effects of shallow cycling on aging are investigated in detail using three different LiFePO4/Graphite cell models, two 26650-type and one 18650-type. It is shown that a large portion of the capacity losses that occur with shallow cycling can be recovered by holding the cells at 0% or 100% state of charge. Differential voltage analysis and post-mortem experiments suggest that these capacity losses are caused by strongly non-uniform lithium distributions in the electrodes. Hypothetical mechanisms are presented and discussed that could lead to such non-uniform distributions of lithium.

High Performance Na-O2 Batteries and Printed Microsupercapacitors Based on Water-Processable, Biomolecule-Assisted Anodic Graphene.

Integrated approaches that expedite the production and processing of graphene into useful structures and devices, particularly through simple and environmentally friendly strategies, are highly desirable in the efforts to implement this two-dimensional material in state-of-the-art electrochemical energy storage technologies. Here, we introduce natural nucleotides (e.g., adenosine monophosphate) as bifunctional agents for the electrochemical exfoliation and dispersion of graphene nanosheets in water. Acting both as exfoliating electrolytes and colloidal stabilizers, these biomolecules facilitated access to aqueous graphene bio-inks that could be readily processed into aerogels and inkjet-printed interdigitated patterns. Na-O2 batteries assembled with the graphene-derived aerogels as the cathode and a glyme-based electrolyte exhibited a full discharge capacity of ∼3.8 mAh cm–2 at a current density of 0.2 mA cm–2. Moreover, shallow cycling experiments (0.5 mAh cm–2) boasted a capacity retention of 94% after 50 cycles, which outperformed the cycle life of prior graphene-based cathodes for this type of battery. The positive effect of the nucleotide-adsorbed nanosheets on the battery performance is discussed and related to the presence of the phosphate group in these biomolecules. Microsupercapacitors made from the interdigitated graphene patterns as the electrodes also displayed a competitive performance, affording areal and volumetric energy densities of 0.03 μWh cm–2 and 1.2 mWh cm–3 at power densities of 0.003 mW cm–2 and 0.1 W cm–3, respectively. Taken together, by offering a green and straightforward route to different types of functional graphene-based materials, the present results are expected to ease the development of novel energy storage technologies that exploit the attractions of graphene.