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The high volatility of the price of cobalt and the geopolitical limitations of cobalt mining have made the elimination of Co a pressing need for the automotive industry

Enabling extreme fast charging (XFC, ≤10–15 min charging) requires a comprehensive understanding of its implications. While lithium plating is a key bottleneck for the anode, the full extent of limitations for the cathode are not well-understood, particularly in extended-cycle settings with well-defined battery designs and conditions. This article presents cycle-life implications of XFC on cathodes at multiple length scales, combining electrochemical analyses, degradation modeling, and post-test characterizations. The comprehensive test matrix includes 41 well-defined gr/NMC pouch cells under varied fast-charge rates (1–9C) and state-of-charges cycled up to 1000 times. Cathode issues remain minimal in early cycling, but begin to accelerate in later life, when distinct cracking is found and identified as a fatigue mechanism. The bulk structure of cathodes remains intact, but distinct particle surface reconstruction is observed; however, this shows less pronounced effect on cathode aging than does cracking.

The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal (TM) oxide studies in various fields, especially on the fervent topic of oxygen redox states in battery electrodes. However, critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions, which has been a popular practice in the battery field. This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements, structures and electrochemical states through combined experimental and theoretical analyses. It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states. Furthermore, the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window, leading to a summary map of the relative energy positions of the low-lying TM states, with higher TM oxidation states at lower energies, corresponding to higher electrochemical potentials. The results naturally clarify some unusual redox reactions, such as Cr3+/6+. This work provides a critical clarification on O-K pre-edge interpretation and more importantly, a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.

Extreme fast charging (XFC) of commercial lithium-ion batteries (LIBs) in ≤10-15 minutes will significantly advance the deployment of electric vehicles globally. However, XFC leads to considerable capacity fade, mainly due to graphite anode degradation. Non-destructive three-dimensional (3D) investigation of XFC-cycled anodes is crucial to connect degradation with capacity loss. Here, we demonstrate the viability of simultaneous neutron and X-ray tomography (NeXT) for ex-situ 3D visualization of graphite anode degradation. NeXT is advantageous because of the sensitivity of neutrons to Li and H and X-rays to Cu. We combine the neutron and X-ray tomography with micron resolution for material identification and segmentation on one pristine and one XFC-cycled graphite anode, thereby underscoring the benefits of the simultaneous nature of NeXT. Our ex-situ results pave the way for the design of NeXT-friendly LIB geometries that will allow operando and/or in-situ 3D visualization of graphite anode degradation during XFC.

In composite battery electrode architectures, local limitations in ionic and electronic transport can result in nonuniform energy storage reactions. Understanding such reaction heterogeneity is important to optimizing battery performance, including rate capability and mitigating degradation and failure. Here, we use spatially resolved X-ray diffraction computed tomography to map the reaction in a composite electrode based on the LiFePO

To improve electric vehicle market acceptance, the charge time of their batteries should be reduced to 10–15 minutes. However, achieving 4C to 6C charge rates with today's batteries is only possible for cells with thin electrodes coming at the expense of low energy density and high battery manufacturing cost. An electrochemical model is validated versus high rate charge data for cells with several loadings. The model elucidates that the main limitations for high energy density cells are poor electrolyte transport resulting in salt depletion within the anode and Li plating at the graphite/separator interface. Next, the model is used to understand what future electrode and electrolyte properties can help enable 4C and 6C charging. Ideally, future electrolytes would be identified with 2X conductivity, 3–4X diffusivity, and transference number of 0.5–0.6. Alternatively charging at elevated temperatures enhances electrolyte transport by 1.5X conductivity and 2–3X diffusivity with a negligible effect on transference number. Another effective strategy to enable 4C and 6C charging is reducing electrode tortuosity. Conversely, increasing electrode porosity and negative/positive ratio are ineffective strategies to improve fast charge capability.

Summary Broad use of global or spatially averaging measurements over a cell to characterize highly localized Li plating phenomena in lithium-ion batteries during fast charging has created a disconnect between measurements and the underlying causes. Consequently, the field is missing a clear path to implementing fast charging as well as to expand into extreme fast charging (XFC). Aiming to bridge these gaps, we present a detailed look into local detection of Li plating and the consequent cycle life implications for electrodes and cells under XFC by utilizing electrochemistry and high-energy X-ray diffraction. Significant heterogeneity in Li plating during XFC results in accelerated and non-uniform cycle life losses, in contrast to the prevailing acceptance that C rate is correlated to Li plating for XFC. This behavior is triggered by local electrode heterogeneity, which has yet to be identified and is not apparent in volume-averaged quantifications. A better understanding of these multiscale local electrode heterogeneities is crucial for identifying pathways to enable XFC.

The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal (TM) oxide studies in various fields, especially on the fervent topic of oxygen redox states in battery electrodes. However, critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions, which has been a popular practice in the battery field. This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements, structures and electrochemical states through combined experimental and theoretical analyses. It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states. Furthermore, the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window, leading to a summary map of the relative energy positions of the low-lying TM states, with higher TM oxidation states at lower energies, corresponding to higher electrochemical potentials. The results naturally clarify some unusual redox reactions, such as Cr3+/6+. This work provides a critical clarification on O-K pre-edge interpretation and more importantly, a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.

Emerging nondestructive (direct) recycling techniques for lithium-ion batteries may introduce metallic impurities into recycled electrodes. In the present work, the impact of such nonionic contaminants on the practical performance of both anode and cathode materials is evaluated using a synergistic combination of electrochemical and thermal analysis. The impurities under study have been selected through evaluation of industrially shredded batteries, and include Fe0, Al0, Mg0, Cu0, and Si0. The electrochemical behavior of materials containing each individual contaminant at either the anode or the cathode is evaluated in both half-cell and full-cell format. Further, the first-cycle thermal signatures of full cells are used to validate and complement electrochemical signatures, and the two techniques are used in conjunction to suggest distinct mechanisms of electrochemical reactivity for the various impurities. At the anode, metallic contaminants are found to disrupt performance through direct reaction with Li and may serve as weak catalysts to accelerate electrolyte degradation. At the cathode, metallic contaminants show evidence of crossover during formation cycling to disrupt SEI formation. We suggest that coupled electrochemical and thermal analysis may be used to both identify the presence of contaminants and to elucidate specific mechanisms of reactivity for metallic impurities under anodic and cathodic conditions.

The potential for operating automotive battery packs at high upper cutoff voltages (UCV) has been explored using preliminary data on eight cathode materials. The pack level energy density, specific energy, and battery cost are calculated using the spreadsheet tool BatPaC. The tool used experimental data for some cathode materials such as the lithiated oxides of nickel manganese cobalt (NMC), nickel cobalt aluminum (NCA), layered lithium- and manganese-rich nickel manganese cobalt (LMRNMC). The half-cell data were obtained at UCVs between 4.2 and 4.7 V vs. Li/Li+. The experimental data showed LMRNMC with the highest lithiation capacity gain, increasing from 176 mAh·g−1 at 4.2 V to 260 mAh·g−1 at 4.7 V; this advantage is partly offset by its lower average voltage. Assuming optimized cell materials/design and an area-specific impedance of 12 Ω⋅cm2 for all the materials, the BatPaC results indicate that the specific energies or energy densities of the battery electric vehicle (BEV) and plug-in hybrid electric vehicle (PHEV) battery packs with the LMRNMC and NMC cathodes can exceed 180 (BEV) and 160 (PHEV) Wh·kg−1 at UCV>4.6 V vs. Li/Li+. The costs of these battery packs are lowest at UCV = 4.7 V (vs. Li/Li+); estimated at 135–145 and 210–220 $·kWh−1 for BEV and PHEV packs, respectively.

Increasing lithium-ion battery gravimetric energy density to > 300 Wh/kg, while simultaneously meeting a cost target of $80/kWh, is of paramount importance to increasing the driving range and affordability of electric vehicles. One way to address this goal is to reduce inactive components by increasing electrode areal capacities, but conventional thick electrode designs typically perform poorly at high discharge rates due to Li+ mass transport limitations. Here we compare the rate capability and cycle life of NMC 532/graphite pouch cells made with five different thick cathode and anode designs paired together in 25 combinations. We find that using different particle sizes to structure both the cathode and anode architectures in two-layer configurations results in a 2X capacity improvement over the worst-performing combination at high discharge rates (97 vs. 46 mAh/g at 2C). These different cathode/anode designs also translate to different cycle life performance, with many cells cycled at C/2 achieving ∼80% capacity retention after 1000 cycles, and cells cycled at 2C showing different degrees of capacity fade. Overall, these results demonstrate that simple, scalable changes in electrode design can significantly improve the performance of thick electrodes for high energy density batteries.

The capacity degradation mechanism in lithium nickel–manganese–cobalt oxide (NMC) cathodes (LiNi1/3Mn1/3Co1/3O2 (NMC333) and LiNi0.4Mn0.4Co0.2O2 (NMC442)) during high-voltage (cut-off of 4.8 V) operation has been investigated. In contrast to NMC442, NMC333 exhibits rapid structural changes including severe micro-crack formation and phase transformation from a layered to a disordered rock-salt structure, as well as interfacial degradation during high-voltage cycling, leading to a rapid increase of the electrode resistance and fast capacity decline. The fundamental reason behind the poor structural and interfacial stability of NMC333 was found to be correlated to its high Co content and the significant overlap between the Co3+/4+ t2g and O2− 2p bands, resulting in oxygen removal and consequent structural changes at high voltages. In addition, oxidation of the electrolyte solvents by the extracted oxygen species generates acidic species, which then attack the electrode surface and form highly resistive LiF. These findings highlight that both the structural and interfacial stability should be taken into account when tailoring cathode materials for high voltage battery systems.

The work herein reports on studies aimed at exploring the correlation between electrolyte volume and electrochemical performance of full cell, pouch-cells consisting of graphite/ Li1.02Ni0.50Mn0.29Co0.19O2 (NMC-532) as the electrodes and 1.2 M LiPF6 in ethylene carbonate:ethylmethyl carbonate (EC:EMC) as the electrolyte. It is demonstrated that a minimum electrolyte volume factor of 1.9 times the total pore volume of cell components (cathode, anode, and separator) is needed for long-term cyclability and low impedance. Less electrolyte results in an increase of the measured ohmic resistances. Increased resistance ratios for charge transfer and passivation layers at cathode, relative to initial values, were 1.5–2.0 after 100 cycles. At the cathode, the resistance from charge transfer was 2–3 times higher than for passivation layers. Differential voltage analysis showed that anodes were less delithiated after discharging as the cells were cycled.

Li-ion battery (LIB) research has continuing importance for the entire range of applications from consumer products to vehicle electrification and grid stabilization. In many cases, standard electrochemical methods only provide an overall voltage or specific capacity, giving an inadequate description of parallel redox processes or chemical gradients at the particle and pack level. X-ray absorption fine structure (XAFS) is frequently used to augment bulk electrochemical data, as it provides element-specific changes in oxidation state and local atomic structure. Such microscopic descriptors are crucial for elucidating charge transfer and structural changes associated with bonding or site mixing, two key factors in evaluating state of charge and modes of cell failure. However, the impact of XAFS on LIB research has been significantly constrained by a logistical barrier: contemporary XAFS work is performed almost exclusively at synchrotron x-ray light sources, where beamtime is infrequent and experiment time-frames are limited. Here we show that modern laboratory based XAFS can not only be applied to, e.g., characterization of ex situ LIB electrode materials, but can also be used for operando studies at industrially-relevant charging rates in a standard pouch cell preparation. Such capability enables accelerated discovery of new materials and improved operation modes for LIBs.

Silicon has been extensively studied as an anode material in lithium-ion batteries due to its extremely high theoretical specific capacity of 3578 mAh/g (assuming Li15Si4 as intermediate product). However, silicon undergoes huge volume variations during repeated discharge and charge, leading to poor electrode mechanical integrity, continual electrolyte decomposition and fast capacity decay. Developing high strength binders in silicon anodes have been considered as an efficient pathway to alleviate various capacity decay pathways. Currently, lithiated poly acrylic acid (LiPAA) is mostly used as the binder for silicon electrodes due to its strong binding capability and (electro)chemical compatibility with Si and electrolyte. However, cracks at the electrode level can still be observed for the cycled electrodes, which suggests that a stronger binder is required to mitigate volume expansion of Si electrode and hold the particles together. Herein we study the polyimide (PI) materials as the binders for Si anode in an attempt to achieve stable cycling performance. With PI binder, the silicon electrode exhibits a higher tensile strength than that of conventional PAA binder. The strong adhesion of the PI binder suppresses the structural collapse of the Si negative electrode during lithiation/delithiation, enabling high capacity retention and stable cycle life. However, the PI crosslinking process requires high temperature and inert atmosphere, which is a challenge for its practical application. In this work, we explore various PI crosslinking conditions and their effects on electrochemical performance. This work offers us an alternative binder material with high tensile strength for the Si electrode. Acknowledgement We gratefully acknowledge the support from the U.S. Department of Energy's Vehicle Technologies Office. This work is conducted under the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory. Argonne National Laboratory is operated for DOE office of Science by UChicago Argonne, LLC, under contract number DE-AC02-06CH11357.

Energy density of full cells containing layered-oxide positive electrodes can be increased by raising the upper cutoff voltage above the present 4.2 V limit. In this article we examine aging behavior of cells, containing LiNi0.5Co0.2Mn0.3O2 (NCM523)-based positive and graphite-based negative electrodes, which underwent up to ~400 cycles in the 3–4.4 V range. Electrochemistry results from electrodes harvested from the cycled cells were obtained to identify causes of cell performance loss; these results were complemented with data from X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) measurements. Our experiments indicate that the full cell capacity fade increases linearly with cycle number and results from irreversible lithium loss in the negative electrode solid electrolyte interphase (SEI) layer. The accompanying electrode potential shift reduces utilization of active material in both electrodes and causes the positive electrode to cycle at higher states-of-charge. Full cell impedance rise on aging arises primarily at the positive electrode and results mainly from changes at the electrode-electrolyte interface; the small growth in negative electrode impedance reflects changes in the SEI layer. Our results indicate that cell performance loss could be mitigated by modifying the electrode-electrolyte interfaces through use of appropriate electrode coatings and/or electrolyte additives.

The effects of propylene carbonate (PC) content in CsPF6-containing electrolytes on the performances of graphite electrode in lithium half cells and in graphite∥LiNi0.80Co0.15Al0.05O2 (NCA) full cells are investigated. It is found that the performance of graphite electrode is significantly affected by PC content in the CsPF6-containing electrolytes. An optimal PC content of 20% by weight in the solvent mixtures is identified. The enhanced electrochemical performance of graphite electrode can be attributed to the synergistic effects of the PC solvent and the Cs+ additive. The synergistic effects of Cs+ additive and appropriate amount of PC enable the formation of a robust, ultrathin, and compact solid electrolyte interphase (SEI) layer on the surface of graphite electrode, which is only permeable for desolvated Li+ ions and allows fast Li+ ion transport through it. Therefore, this SEI layer effectively suppresses the PC cointercalation and largely alleviates the Li dendrite formation on graphite electrode ...

Coin-cells are often the test format of choice for laboratories engaged in battery research and development as they provide a convenient platform for rapid testing of new materials on a small scale. However, reliable, reproducible data via the coin-cell format is inherently difficult, particularly in the full-cell configuration. In addition, statistical evaluation to prove the consistency and reliability of such data is often neglected. Herein we report on several studies aimed at formalizing physical process parameters and coin-cell construction related to full cells. Statistical analysis and performance benchmarking approaches are advocated as a means to more confidently track changes in cell performance. We show that trends in the electrochemical data obtained from coin-cells can be reliable and informative when standardized approaches are implemented in a consistent manner.

Commercial Li-ion batteries are typically cycled between 3.0 and 4.2 V. These voltages limits are chosen based on the characteristics of the cathode (e.g. lithium cobalt oxide) and anode (e.g. graphite). When alternative anode/cathode chemistries are studied the same cut-off voltages are often, mistakenly, used. Silicon (Si) based anodes are widely studied as a high capacity alternative to graphite for Lithium-ion batteries. When silicon-based anodes are paired with high capacity cathodes (e.g. Lithium Nickel Cobalt Aluminium Oxide; NCA) the cell typically suffers from rapid capacity fade. The purpose of this communication is to understand how the choice of upper cut-off voltage affects cell performance in Si/NCA cells. A careful study of three-electrode cell data will show that capacity fade in Si/NCA cells is due to an ever-evolving silicon voltage profile that pushes the upper voltage at the cathode to >4.4 V (vs. Li/Li+). This behaviour initially improves cycle efficiency, due to liberation of new lithium, but ultimately reduces cycling efficiency, resulting in rapid capacity fade.

Separation of cathode materials from the current collector remains a challenging task for the recycling of both spent lithium-ion batteries and cathode scraps. Dissolving the organic binder polyvinylidene difluoride (PVDF) with an organic solvent to recover both cathode materials and Al foils is an efficient and promising method. However, the use of toxic solvents limits their practical application in recycling large amounts of cathode scraps generated during the manufacturing process. Cyrene, a bioderived green solvent, is proposed here for a solvent-based separation process. This study investigated a closed-loop recovery process to reclaim cathode materials, Al foils, and PVDF binder from cathode scraps. Additionally, the reuse of the Cyrene solvent led to a circular recycling process. The Cyrene-based separation process embraces a sustainable electrode recovery and reuse platform and paves the way for battery recycling.

A combination of cell testing and electrochemical-thermal modeling is used to investigate extreme fast charging (XFC) performance for cells with a low loading of 1.5 mAh.cm−2 and moderate loading of 2.5 mAh.cm−2. Cells with a low loading of 1.5 mAh.cm−2 withstand XFC performance remarkably well even up to 9C constant current (CC) charging with high charge capacity, high coulombic efficiency and very little apparent lithium plating. For a moderate loading of 2.5 mAh.cm−2, the 6C CC charge capacity is poor with significant amounts of visually observed lithium plating. Simulated electrolyte transport properties are revealed to be insufficient and majorly set limitations for XFC performance in case of the moderate and the only simulated higher loadings (>2.5 mAh.cm-2). Charging at elevated temperature is shown to be an effective strategy for moderate loading cells enabling good 10-min charge capacity, high coulombic efficiency, and mitigating lithium plating. Lastly, an electrochemical model is used to investigate strategies for enabling 4–6C CC charging for cells incorporating loading beyond 3 mAh.cm−2. As a result, the combination of an increased cell temperature, reduced electrode tortuosity, and enhanced ion-transport in the electrolyte are most likely required to facilitate XFC for state of the art and future high energy lithium-ion batteries.

Increasing the areal capacity or electrode thickness in lithium ion batteries is one possible means to increase pack level energy density while simultaneously lowering cost. The physics that limit use of high areal capacity as a function of battery power to energy ratio are poorly understood and thus most currently produced automotive lithium ion cells utilize modest loadings to ensure long life over the vehicle battery operation. Here we show electrolyte transport limits the utilization of the positive electrode at critical C-rates during discharge; whereas, a combination of electrolyte transport and polarization lead to lithium plating in the graphite electrode during charge. Experimental measurements are compared with theoretical predictions based on concentrated solution and porous electrode theories. An analytical expression is derived to provide design criteria for long lived operation based on the physical properties of the electrode and electrolyte. Finally, a guideline is proposed that graphite cells should avoid charge current densities near or above 4 mA/cm2 unless additional precautions have been made to avoid deleterious side reaction.

This study aims to explore the correlations between electrolyte volume, electrochemical performance, and properties of the solid electrolyte interphase in pouch cells with Si-graphite composite anodes. The electrolyte is 1.2 M LiPF6 in ethylene carbonate:ethylmethyl carbonate with 10 wt % fluoroethylene carbonate. Single layer pouch cells (100 mA h) were constructed with 15 wt % Si-graphite/LiNi0.5Mn0.3CO0.2O2 electrodes. It is found that a minimum electrolyte volume factor of 3.1 times to the total pore volume of cell components (cathode, anode, and separator) is needed for better cycling stability. Less electrolyte causes increases in ohmic and charge transfer resistances. Lithium dendrites are observed when the electrolyte volume factor is low. The resistances from the anodes become significant as the cells are discharged. Solid electrolyte interphase thickness grows as the electrolyte volume factor increases and is nonuniform after cycling.

Batteries using lithium (Li) metal as anodes are considered promising energy storage systems because of their high energy densities. However, safety concerns associated with dendrite growth along with limited cycle life, especially at high charge current densities, hinder their practical uses. Here we report that an optimal amount (0.05 M) of LiPF6 as an additive in LiTFSI–LiBOB dual-salt/carbonate-solvent-based electrolytes significantly enhances the charging capability and cycling stability of Li metal batteries. In a Li metal battery using a 4-V Li-ion cathode at a moderately high loading of 1.75 mAh cm−2, a cyclability of 97.1% capacity retention after 500 cycles along with very limited increase in electrode overpotential is accomplished at a charge/discharge current density up to 1.75 mA cm−2. The fast charging and stable cycling performances are ascribed to the generation of a robust and conductive solid electrolyte interphase at the Li metal surface and stabilization of the Al cathode current collector. Deployment of rechargeable Li metal batteries requires fast charging capability and long-term cycling stability. Here the authors demonstrate the battery application potential of using a small amount of LiPF6 in a dual-salt electrolyte.

Li-ion batteries (LIB) have been successfully commercialized after the identification of ethylene-carbonate (EC)-containing electrolyte that can form a stable solid electrolyte interphase (SEI) on carbon anode surface to passivate further side reactions but still enable the transportation of the Li+ cation. These electrolytes are still utilized, with only minor changes, after three decades. However, the long-term cycling of LIB leads to continuous consumption of electrolyte and growth of SEI layer on the electrode surface, which limits the battery’s life and performance. Herein, a new anode protection mechanism is reported in which, upon changing of the cell potential, the electrolyte components at the electrode–electrolyte interface reorganize reversibly to form a transient protective surface layers on the anode. This layer will disappear after the applied potential is removed so that no permanent SEI layer is required to protect the carbon anode. This phenomenon minimizes the need for a permanent SEI la...

We report systematic studies of the microstructural changes of uncoated and AlF3-coated Li-rich Mn-rich (LMR) cathode materials (Li1.2Ni0.15Co0.10Mn0.55O2) before and after cycling using a combination of aberration-corrected scanning/transmission electron microscopy (S/TEM) and electron energy loss spectroscopy (EELS). TEM coupled with EELS provides detailed information about the crystallographic and electronic structure changes that occur after cycling, thus revealing the fundamental improvement mechanism of surface coating. The results demonstrate that the surface coating reduces oxidation of the electrolyte at high voltage, suppressing the accumulation of a thick solid electrolyte interface (SEI) layer on electrode particle surface. Surface coating significantly enhances the stability of the surface structure and protects the electrode from severe etching/corrosion by the acidic species in the electrolyte, reducing the formation of etched surfaces and corrosion pits. Moreover, surface coating alleviate...

Post-test analyses of cells consisting of a layered-layered cathode, a graphite anode and an organic carbonate-based electrolyte were performed. Many changes in the cell components were visible. Gas analysis revealed possible evidence of oxygen evolution from cathode and electrolyte degradation, including likely reaction products between electrolyte solvents and salt or binder. The anode surface was highly inhomogeneous and was comprised of a surface film of varying thickness, white precipitates, and dendritic growth of metallic Li and/or deliquescent salts. Manganese was incorporated into the anode and P, C, and O were preferentially incorporated into some areas of the anode surface. Analysis of the composition of the SEI layer shows that, unsurprisingly, it was complex.

In this article we describe efforts to improve performance and cycle life of cells containing Li1.2Ni0.15Mn0.55Co0.1O2-based positive and graphite-based negative electrodes. Initial work to identify high-performing materials, compositions, fabrication variables, and cycling conditions is conducted in coin cells. The resulting information is then used for the preparation of double-sided electrodes, assembly of pouch cells, and electrochemical testing. We report the cycling performance of cells with electrodes prepared under various conditions. Our data indicate that cells with positive electrodes containing 92 wt.% Li1.2Ni0.15Mn0.55Co0.1O2, 4 wt.% carbons (no graphite), and 4 wt.% PVdF (92–4–4) show ∼20% capacity fade after 1000 cycles in the 2.5–4.4 V range, significantly better than our baseline cells that show the same fade after only 450 cycles. Our analyses indicate that the major contributors to cell energy fade are capacity loss and impedance rise. Therefore incorporating approaches that minimize capacity fade and impedance rise, such as electrode coatings and electrolyte additives, can significantly enhance calendar and cycle life of this promising cell chemistry.

Lithium-ion batteries in electric and hybrid-electric vehicles are just now starting to reach their end-of-life. There are several options to address these end-of-life batteries, landfilling or recycling. Recycling is a desirable option because of the benefits it can bring, including reductions in life-cycle costs, reduced energy usage, lower environmental impacts, and decreased dependence on scarce or imported materials. The options available now for recycling of lithium-ion batteries are not optimal, so research and development (R&D) is needed to make economic processes available for use by the time large volumes of batteries from electric vehicles and other uses go out of service. By then these battery materials could be 20 year-old formulations with little residual value from its structure or contained elements. In particular, cathode formulations are evolving towards varied morphologies, emphasizing formulations that contain reduced quantities of cobalt (the valuable element sought in most current recycling operations), reducing the incentive for recycling with standard pyrometallurgical or hydrometallurgical methods. Several key questions must be addressed by R&D. Most of these focus on the cathode, which is the most valuable form of material that can be recovered. How can the cathode get separated from the other cell components? Can they be recovered? How can optimum cathode function get restored? Can we separate one cathode type from another? Can we modify the cathode composition or morphology to update it for reuse? This presentation will provide a summary of Argonne’s work to create a feasible battery recycling system.

The U.S. Department of Energy (DOE) has acknowledged extreme fast charging as one of the remaining challenges in enabling wide spread adoption of electric vehicles (EVs). The current DOE goal is to enable a 10-15 minute recharge time for high energy density cells with at least 200-250 Wh/kg. There are existing lithium-ion batteries that can be charged at very high rates (>5C), but these typically have prohibitively low energy density from use of thin electrodes and high cost. The charging time of EV type cells is limited by lithium plating, rapid temperature rise, and particle cracking. Through a combination of experimental data and Newman pseudo 2-D (P2D) modeling, this presentation will discuss physical properties needed to enable extreme fast charging of high energy density graphite/NMC 532 cells while avoiding lithium plating. The ANL team fabricated graphite/NMC 532 coin cells with loadings of 1.5, 2.7, 4.3 and 5 mAh/cm2 with similar electrode porosities and N/P ratio. The cells used standard “Generation 2” electrolyte consisting of 1.2 M LiPF6 in EC/EMC (3:7 by weight). After formation cycling, cells where charged at 6C with CC-CV protocol up to 4.1 V with a total charge time of 10 minutes at a temperature of 30 °C. At the lowest loading of 1.5 mAh/cm2, the cell achieved 90% SOC during 6C charging and almost all the capacity occurred during the CC portion. For this loading, cells could be 6C charged/C/2 discharged for 800 cycles and retain 70-80% of the initial capacity. However, at the higher loadings the achieved SOC during 6C charging rapidly fell off to less than 60% SOC and most of the capacity occurred during the CV portion. Further, the capacity fade is dramatically higher for thicker cells during continued 6C/C/2 cycling. For instance, cells with a loading of 4.3 and 5 mAh/cm2 capacity faded by 20% in only 5 cycles. A macro-homogeneous P2D model is used to investigate the poor 6C performance of thick-electrode cells and explore options from enabling 6C charging of high energy density cells. The model has been previously tuned to this chemistry under the DOE Computer-Aided Engineering for Electric-Drive Vehicle Batteries (CAEBAT) program. For loadings of 2.7, 4.3, and 5 mAh/cm2, the model predicts severe electrolyte depletion in the anode and saturation in the cathode are limiting high rate charging. The model and data seem to indicate solid-state diffusion and intercalation chemistry are sufficient to enable 6C charging. Based on this, the model is used to explore how the following might enable extreme fast charging of high energy density cells: Reducing electrode tortuosity Improving electrolyte properties Increasing electrode porosity Increasing charging temperature Increasing N/P ratio A combination of increased temperature, reduced electrode tortuosity, and improved electrolyte properties should enable 6C charging for cells with a loading of 4 mAh/cm2 and high energy density. Figure 1

Advanced x-ray spectroscopies permit the interrogation of a material’s local electronic structure in an element-specific manner. In particular, these techniques reveal the speciation and ligand environment of an electroactive element and can provide direct insight into the state-of-charge and state-of-health of a battery. Despite their utility, the scientific impact of advanced x-ray spectroscopies is necessarily constrained by the availability of instrumentation. For x-ray absorption fine structure (XAFS) and x-ray emission spectroscopy (XES), studies are traditionally performed at synchrotron x-ray facilities. These facilities frequently serve to push the forefront of science and, as a result, necessarily operate under an access model which excludes projects which require routine analytical characterization, rapid feedback, or regular access. Over the last four years, our group at the University of Washington has developed several families of laboratory-based instruments to expand the accessibility of advanced x-ray spectroscopies. For the study of transition metal chemistry, we have constructed two Rowland circle spectrometers based upon related designs. Both spectrometers provide energy resolutions comparable to that observed at a synchrotron endstation. Their designs are also highly efficient, allowing studies to be completed with commercial x-ray tube sources in time scales relevant for materials research programs. For many such studies, the instrumentation can generate satisfactory spectra in a matter of minutes, permitting operando studies of battery materials at charge rates in excess of 1C. From the standpoint of instrumentation, a brief review of the present designs is presented with emphasis on recent advances in extended-XAFS capabilities. Differences between the spectrometer designs and the advantages of each will also be highlighted. Regarding materials inquiry, a survey of the above instrument’s application to energy storage research is provided. This will include XAFS analyses of two systems of nanoparticle compounds which were engineered to be catalysts or pseudocapacitors. These results will facilitate a review of the information attainable from the underlying technique. The rich electronic structure of vanadyl phosphate cathode materials, as well a suite of vanadium oxides, is probed via valence-to-core XES (VTC-XES). Finally, operando x-ray absorption near-edge structure (XANES) results obtained from a pouch cell containing a nickel-rich NMC cathode at a variety of charge rates are presented.

The effects of propylene carbonate (PC) content in CsPF6-containing electrolytes on the performances of graphite electrode in lithium half cells and in graphite∥LiNi0.80Co0.15Al0.05O2 (NCA) full cells are investigated. It is found that the performance of graphite electrode is significantly affected by PC content in the CsPF6-containing electrolytes. An optimal PC content of 20% by weight in the solvent mixtures is identified. The enhanced electrochemical performance of graphite electrode can be attributed to the synergistic effects of the PC solvent and the Cs(+) additive. The synergistic effects of Cs(+) additive and appropriate amount of PC enable the formation of a robust, ultrathin, and compact solid electrolyte interphase (SEI) layer on the surface of graphite electrode, which is only permeable for desolvated Li(+) ions and allows fast Li(+) ion transport through it. Therefore, this SEI layer effectively suppresses the PC cointercalation and largely alleviates the Li dendrite formation on graphite electrode during lithiation even at relatively high current densities. The presence of low-melting-point PC solvent improves the sustainable operation of graphite∥NCA full cells under a wide temperature range. The fundamental findings also shed light on the importance of manipulating/maintaining the electrode/electrolyte interphasial stability in various energy-storage devices.

Thick electrodes have attracted considerable interest due to their potential role in achieving high energy density Li-ion batteries for electric vehicle applications. Incorporating thick electrodes eliminates many of the inactive separator and current collector layers that add cost, weight, and volume to the battery. However, mass transport of Li ions becomes a limiting factor at these dimensions and leads to poor rate capability at high charge and discharge rates. Different electrode architectures have been proposed to facilitate Li ion transport throughout the entirety of the electrodes, but the connection between structure and performance remains unclear. We used two different active material particle sizes to create thick anodes and cathodes (~4 mAh/cm2) with different structures and pore size distributions to determine the effect of architecture on electrochemical performance. Seven graphite anodes and seven NMC 532 cathodes were coated in various single- and double-layer configurations and assembled into single-layer pouch cells in forty-nine different cathode/anode combinations. These cells were then subjected to charge and discharge rate performance testing. We found that both particle size and structural arrangement have significant impacts on the resulting rate performance. Mercury porosimetry was performed on all electrodes to help correlate pore size distribution with performance. In addition, the best- and worst-performing cells were selected for post-mortem analysis to further understand the nature of the observed electrochemical differences. Our results demonstrate that the rate performance of thick electrodes can be improved by altering the electrode architecture. More precise control over the structure could lead to further improvements and enable the implementation of thick electrode Li-ion battery designs for cheaper, long-range electric vehicles. Figure 1

In the pursuit of next-generation high energy density lithium-ion batteries, practically incorporating silicon into the negative electrode without sacrificing cycle life, continues to headline many energy storage research and development programs including the DOE-EERE-VTO Next Generation Anodes project. Silicon has the ability to store approximately ten times the number of lithium-ions than the current standard negative electrode material, graphite, and would transform the battery market if successfully implemented into lithium-ion batteries. However, the electrochemical performance of silicon-containing electrodes continues to be afflicted by the continual SEI growth during electrochemical cycling. The development of high-performance silicon-containing electrodes is an important focus area for the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory. The scalability of the electrode fabrication process is almost as important as its electrochemical performance; here, we note a potential safety concern during the silicon-electrode slurry preparation process. Recent work has shown that significant quantities of gasses are generated when silicon particles are mixed in an aqueous medium using binders such as partially-lithiated polyacrylic acid (Li-PAA).¹,² Because hydrogen is the main gas generated, the uncontrolled chemical reactions and the resulting pressure buildup could pose a hazard for large industrial-scale processes. In order to better understand the chemical reactions we have developed a method to quantify the volume of gasses generated using the Archimedes principle. We show that the gas volumes are affected by various factors, which include the pH of the electrode slurry and characteristics of the silicon powders. Negligible gas generation is observed in electrode slurries containing the n-methyl-2-pyrrolidone (NMP) solvent, which could be considered as an alternative to the water-based processes presently under consideration. Other electrode preparation factors, such as the silicon powder type, solvents used for slurry dispersion, pH, binders, etc., and the concomitant effects on electrode electrochemical performance will also be discussed during the presentation. Support from David Howell, Brian Cunningham, and Peter Faguy of the U.S. Department of Energy’s Office of Vehicle Technologies is gratefully acknowledged. This work was performed under the auspices of the US Department of Energy, Office of Vehicle Technologies, Hybrid and Electric Systems, under Contract No. DE-AC02-06CH11357 Zhang, Y. Liu, B. Key, S. E. Trask, Z. Yang, W. Lu, “Silicon Nanoparticles: Stability in Aqueous Slurries and the Optimization of the Oxide Layer Thickness for Optimal Electrochemical Performance”, ACS Appl. Mater. & Interfaces (2017), p. 32727. A. Hays, G. M Veith, B. Key, J. Li, Y. Sheng, D. L Wood III, “Considerations in Electrode Preparation of Si-Based Slurries for Commercial Li-Ion Batteries”, 232nd ECS Meeting, Abstract MA2017-02 395 National Harbor, MD (October 2017).

Despite the potential advantages it brings, such as wider liquid range and lower cost, propylene carbonate (PC) is seldom used in lithium-ion batteries because of its sustained cointercalation into the graphene structure and the eventual graphite exfoliation. Here, we report that cesium cation (Cs(+)) directs the formation of solid electrolyte interphase on graphite anode in PC-rich electrolytes through its preferential solvation by ethylene carbonate (EC) and the subsequent higher reduction potential of the complex cation. Effective suppression of PC-decomposition and graphite-exfoliation is achieved by adjusting the EC/PC ratio in electrolytes to allow a reductive decomposition of Cs(+)-(EC)m (1 ≤ m ≤ 2) complex preceding that of Li(+)-(PC)n (3 ≤ n ≤ 5). Such Cs(+)-directed interphase is stable, ultrathin, and compact, leading to significant improvement in battery performances. In a broader context, the accurate tailoring of interphasial chemistry by introducing a new solvation center represents a fundamental breakthrough in manipulating interfacial reactions that once were elusive to control.

The unstable interface of lithium metal in high energy density Li sulfur (Li-S) batteries raises concerns of poor cycling, low efficiency and safety issues, which may be addressed by using intercalation types of anode. Herein, a new prototype of Li-ion sulfur battery with high performance has been demonstrated by coupling a graphite anode with a sulfur cathode (2 mA h cm(-2)) after successfully addressing the interface issue of graphite in an ether based electrolyte.