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Using a unique combination of advanced characterization techniques, we identify specific degradation mechanisms and quantify degradative species formed during fast charge cycling of lithium-ion battery pouch cells.

Selection, testing and validation of electrolyte candidates for Li-ion cells are discussed, based on a 10-minute target for extreme fast charge (XFC). A combination of modeling and laboratory measurements create a timely and synergistic approach to identifying candidate electrolyte formulations. Multi-solvent systems provide a balanced set of properties, wherein lower molecular-weight solvents offer reduced viscosity, increased species diffusivity, and mitigation of concentration polarization at high charge rates. Carefully selected formulations can exhibit peak conductivity and usable conductivity range of two to three times that of the baseline EC-EMC (3:7, wt.) + LiPF6. Candidates are also chosen based on stability and longevity within the cell environment. Lab testing coincides with property predictions from the Advanced Electrolyte Model (AEM) and a macro-scale cell model. Cell testing utilized coin and pouch cells having NMC532 or NMC811 cathodes with graphite electrodes. Results indicate combinations of low-molecular weight solvents are key for fast-charge electrolytes as they extend the useful conductivity range to both low and higher salt concentrations, and possess higher self-diffusivities compared to conventional solvents. This reduces impacts from concentration polarization. The choice of electrolyte also influences the tendency for lithium metal deposition at the anode, as showcased by experimental and modeling results herein.

Extreme fast charging (XFC, ≤15 min charging time) of Li-ion batteries (LIBs) has been proposed as an immediate target to increase the commercial appeal of electric vehicles. However, XFC of LIBs i...

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.

Li-M-Si ternary Zintl phases have gained attention recently due to their high structural stability, which can improve the cycling stability compared to a bulk Si electrode. Adding multivalent cation salts (such as Mg

Small amounts of high-capacity silicon-based materials are already used in the anode of commercial Li-ion batteries, helping increase their energy density. Despite their remarkable storage capability, silicon continuously reacts with the electrolyte, accelerating time-dependent cell performance fade. Nevertheless, very limited information is available on the specific consequences of this reactivity for the calendar aging of Li-ion cells. Here, we analyze aging effects on 450 mAh pouch cells containing 15 wt% of Si (and 73 wt% graphite) after storage at 21 oC for four years. We show that severe losses of Si capacity occurred due to particle isolation when cells were stored at high states of charge (SOC), but not when cells were fully discharged prior to storage. Impedance rise was also significantly higher when cells were kept at high SOCs and was mostly due to phenomena taking place at the cathode; the continuous electrolyte reduction at the anode did not lead to a major increase in bulk electrode resistance. A series of post-test characterization provided additional information on the effects of time and SOC on the calendar aging of Si-containing cells. Our study highlights the many challenges posed by Si during calendar aging and can inform future studies in the field.

A barrier to the widespread adoption of electric vehicles is enabling fast charging lithium-ion batteries. At normal charging rates, lithium ions intercalate into the graphite electrode. At high charging rates, lithiation is inhomogeneous, and metallic lithium can plate on the graphite particles, reducing capacity and causing safety concerns. We have built a cell for conducting high-resolution in situ X-ray microtomography experiments to quantify three-dimensional lithiation inhomogeneity and lithium plating. Our studies reveal an unexpected correlation between these two phenomena. During fast charging, a layer of mossy lithium metal plates at the graphite electrode-separator interface. The transport bottlenecks resulting from this layer lead to underlithiated graphite particles well-removed from the separator, near the current collector. These underlithiated particles lie directly underneath the mossy lithium, suggesting that lithium plating inhibits further lithiation of the underlying electrode.

Li4Ti5O12/LiMn2O4 (LTO/LMO) chemistry was evaluated as a potential candidate for behind-the-meter storage (BTMS) applications. Its long-term cycle performance at 45 °C was tested using ethylene carbonate (EC) and propylene carbonate (PC) solvent electrolytes. Over 1000 cycles, LTO/LMO cells exhibited ~80% capacity retention and Coulombic efficiency higher than 99.96%. Electrochemical test results showed the major degradation mode of LTO/LMO cells arises from continuous electrolyte decomposition at the LTO anode and loss of Li inventory. EC and PC electrolytes created distinct surface layers, where the EC reduction products were more effective in passivating the LTO electrode surface. Dissolution and migration of Mn from the cathode was probed as Mn2+ species distributed throughout the surface layer at the anode. By utilizing a prelithiated LTO electrode, the LTO/LMO cell performance was significantly enhanced with EC electrolyte. On the other hand, PC electrolyte resulted in accelerated electrolyte decomposition at the lithiated LTO surface due to the lack of surface passivation. Thus, mitigating parasitic reactions at the LTO electrode is the key to developing successful LTO/LMO cells.

Li4Ti5O12/LiMn2O4 (LTO/LMO) system is a promising candidate for behind-the-meter storage (BTMS) applications due to its critical-material-free chemistry exhibiting good safety and long lifetime. Here, we design LTO/LMO cells to mitigate their major degradation mechanism, loss of Li inventory, and improve their long-term cyclability. First, LMO electrodes with different loadings (2.61, 3.29, and 4.26 mAh cm−2) are paired with an LTO electrode (3.35 mAh cm−2) to create varying negative-to-positive ratios (N/P>1, =1, and + ion transport. For systems that suffer from limited transport properties, prelithiating the anode will be more effective since LTO (∼165 mAh g−1 LTO) can store the same amount of capacity using less material compared to LMO (∼100 mAh g−1 LMO). In this work, we demonstrate how the electrolyte properties and the electrode thickness of LTO/LMO cells can be designed to enhance their performance.

Crosstalk between the cathode and the anode in Li-ion batteries has a great impact on performance, safety and cycle lifetime. However, a systematic investigation of crosstalk behavior in silicon (Si)-based cells with various cathode materials has not been reported. We investigated the crosstalk behavior of a Si anode coupled with one of the following cathodes—LiCoO2 (LCO), LiNi0.5Mn0.3Co0.2 (NMC532), and LiFePO4 (LFP)—in a full cell. For each electrochemical couple, we compared electrolyte decomposition products, solid electrolyte interphase (SEI) chemistry, and degradation mechanisms during cycling. From a very early stage of cycling, each couple showed different crosstalk behavior; different electrolyte decomposition products and SEI chemistry on the Si anodes were seen. Specifically, the formation and growth mechanism of Si SEI differ depending on cathode materials. For the LFP system, the Si SEI rich in LiF and inorganic species, which is stable and robust. It forms at an early stage of cycle. As a result, mechanical failure of the Si electrode and Li loss are well suppressed in the LFP system, resulting in stable cycle life.

Realization of extreme fast charging (XFC, ≤15 minutes) of lithium-ion batteries is imperative for the widespread adoption of electric vehicles. However, dramatic capacity fading is associated with XFC, limiting its implementation. To quantitatively elucidate the effects of irreversible lithium plating and other degradation mechanisms on the cell capacity, it is important to understand the links between lithium plating and cell degradation at both the local and global (over the full cell) scales. Here, we study the nature of local lithium plating after hundreds of XFC cycles (charging C-rates ranging from 4C to 9C) in industrially-relevant pouch cells using spatially resolved X-ray diffraction. Our results reveal a spatial correlation at the mm scale between irreversible lithium plating on the anode, inactive lithiated graphite phases, and local state-of-charge of the cathode. In regions of plated lithium, additional lithium is locally and irreversibly trapped as lithiated graphite, contributing to the loss of lithium inventory (LLI) and to a local loss of active anode material. The total LLI in the cell from irreversibly plated lithium is linearly correlated to the capacity loss in the batteries after XFC cycling, with a non-zero offset originating from other parasitic side reactions. Finally, at the global (cell) scale, LLI drives the capacity fade, rather than electrode degradation. We anticipate that the understanding of lithium plating and other degradation mechanisms during XFC gained in this work will help lead to new approaches towards designing high-rate batteries in which irreversible lithium plating is minimized.

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.

With an increasing demand for intermittent renewable energy and electric vehicles, it is imperative to develop lithium-ion batteries with Earth-abundant cathode materials. Cobalt (Co) is preferred to be kept at a minimum because of its high cost and limited mining options, yet it has played an essential role in the high-performance transition metal oxides (TMOs). Herein, we report work from Argonne National Laboratory, conducted under the U.S. DoE’s Vehicle Technologies Office, Deep Dive consortium on Next-Generation Cathodes, to optimize electrolytes for LiNi0.9Mn0.05Co0.05O2. LiNi0.9Mn0.05Co0.05O2 is a high-Ni TMO benchmark as it outperforms most other TMOs under standard cycling conditions. In this study, we use the figure-of-merit approach to optimize electrolytes for this novel cathode material. Dual-salt carbonate electrolytes containing lithium difluorooxyphosphate and hexafluorophosphates were found to be the best for capacity retention and slowing the impedance rise. Transition metal dissolution and lithium inventory losses in the solid electrolyte interface were found to be the major causes for capacity fade.

Enabling extreme fast charging (XFC, charging in 10 to 15 minutes) in a lithium-ion battery (LiB) could play a key role in subsiding consumer’s range anxiety and spur the widespread adoption of electric vehicles (EVs).1,2 Such a high rate of charging induces unique aging modes in LiBs, thereby requiring a comprehensive understanding to enable effective solution strategies to minimize the negative effects of life and performance. This presentation will present a comprehensive understanding of the dominating aging modes and mechanisms of XFC in low- and moderate-loading Gr/NMC LiBs. We will discuss the major limitations of XFC in LiBs by first using experimental and modeling results followed by a comprehensive electrochemical analysis of cycle life aging implications for different charging conditions (e.g., 1C to 9C rate conditions). We will then discuss the aging mechanisms using comprehensive post-testing as well as multimodal and multi-scale microscopy techniques. Solid state diffusion in the negative electrode is not a key limiting factor for the fast charge conditions evaluated. Inadequate Li+ transport through the electrolyte primarily causes performance and distinct aging phenomena in LiBs. Eliminating the Li+ transport limitation within the electrolyte can offer a distinct increase in material utilization, avoiding Li deposition. Under such circumstances, the cathode could degrade in distinct ways depending on the particular NMC (e.g., NMC532 vs. NMC811) variants. NMC811 experiences a greater subsurface crystallographic degradation and interfacial degradation and displays similar extents of sub-particle cracking as compared to NMC532 under comparable charging conditions. Surprisingly, the NMC811 maintains superior electrochemical performance despite the more aggressive degradations. We found the better cycle life performance of NMC811 to be related to its inherently better solid state diffusion, electronic conduction, and radially oriented grain architecture. References S. Ahmed et al., J. Power Sources, 367, 250–262 (2017). Y. Liu, Y. Zhu, and Y. Cui, Nat. Energy, 4, 540–550 (2019).

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.

Battery performance is strongly correlated with electrode microstructure and weight loading of the electrode components. Among them are the carbon-black and binder additives that enhance effective conductivity and provide mechanical integrity. However, these both reduce effective ionic transport in the electrolyte phase and reduce energy density. Therefore, an optimal additive loading is required to maximize performance, especially for fast charging where ionic transport is essential. Such optimization analysis is however challenging due to the nanoscale imaging limitations that prevent characterizing this additive phase and thus quantifying its impact on performance. Herein, an additive-phase generation algorithm has been developed to remedy this limitation and identify percolation threshold used to define a minimal additive loading. Improved ionic transport coefficients from reducing additive loading has been then quantified through homogenization calculation, macroscale model fitting, and experimental symmetric cell measurement, with good agreement between the methods. Rate capability test demonstrates capacity improvement at fast charge at the beginning of life, from 37% to 55%, respectively for high and low additive loading during 6C CC charging, in agreement with macroscale model, and attributed to a combination of lower cathode impedance, reduced electrode tortuosity and cathode thickness.

Batteries capable of extreme fast-charging (XFC) are a necessity for the deployment of electric vehicles. Material properties of electrodes and electrolytes along with cell parameters such as stack pressure and temperature have coupled, synergistic, and sometimes deleterious effects on fast-charging performance. We develop a new experimental testbed that allows precise and conformal application of electrode stack pressure. We focus on cell capacity degradation using single-layer pouch cells with graphite anodes, LiNi0.5Mn0.3Co0.2O2 (NMC532) cathodes, and carbonate-based electrolyte. In the tested range (10–125 psi), cells cycled at higher pressure show higher capacity and less capacity fading. Additionally, Li plating decreases with increasing pressure as observed with scanning electron microscopy (SEM) and optical imaging. While the loss of Li inventory from Li plating is the largest contributor to capacity fade, electrochemical and SEM examination of the NMC cathodes after XFC experiments show increased secondary particle damage at lower pressure. We infer that the better performance at higher pressure is due to more homogeneous reactions of active materials across the electrode and less polarization through the electrode thickness. Our study emphasizes the importance of electrode stack pressure in XFC batteries and highlights its subtle role in cell conditions.

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 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.

The capacity fading phenomenon of high energy lithium-ion batteries (LIBs) using a silicon monoxide (SiO) anode and a nickel-rich transition metal oxide cathode were investigated during life test. The capacity loss of this electrode couple was found to increase not only with cycles (cycle life), but also with rest time (calendar life). The capacity fading rate for this type of LIB using SiO as the anode was found to be time-dependent, rather than cycle-count-dependent. Further detailed investigation revealed that the capacity loss of this electrode couple during rest was caused by the parasitic reactions on the anode, which consumed the lithium ions and lead to less cyclable lithium in the battery system.

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.

Growing demand for stationary energy storage systems requires the development of low cost, long cycle life, safe batteries. Lithium-ion batteries (LiBs) utilizing Li4Ti5O12 (LTO) anode and LiMn2O4 (LMO) cathode are promising candidates providing critical-material-free chemistry, high power capability, and long lifespan. However, their low energy density is a major drawback. In this work, we evaluate the rate performance of LTO/LMO cells fabricated with electrode loadings from 1.7 to 4.2 mAh cm−2 toward the development of high energy density and low cost LTO/LMO cells. The operating temperature is varied from 30 °C to 55 °C to evaluate the impact of electrode thickness vs temperature limitations on the electrode utilization. In addition, Newman modeling is performed to provide detailed understandings of the cell performance. Combining experimental and simulated results, we show the rate capability of the thicker electrodes is limited by the electrolyte transport. When the cells are discharged by applying pulsed current, Li+ ion depletion is mitigated and the discharge capacity increases. Thus, high energy density LTO/LMO cells for BTMS applications can operate more efficiently when intermittent rest is applied. Finally, overcoming electrolyte transport limitations will be the key to enabling the development of high energy density LTO/LMO cells using thick electrodes.

Heterogeneous battery performance is a critical issue for maximization of cell lifetime capacity and safety. Using high energy synchrotron X-ray diffraction, the influence of charge rate, voltage limit, uneven stack pressure, and gas generation on the lithium transport properties was quantified in single-layer graphite/LiNi0.5Mn0.3Co0.2O2 pouch cells. A freshly formatted cell tracked in operando during initial fast charge cycles indicated variable position-dependent performances, while lateral mapping showed a significant fast charge (6C) heterogeneity compared to slow charge (C/2). Pressure effects were non-dominant compared to charge rate. Maps of previously aged and rested cells indicate that lateral heterogeneity slowly equilibrates at rest, but regenerates upon further cycling at fast charge rate. Furthermore, an unformatted cell was mapped at charge and discharge during its first formation cycle to analyze the effect of byproduct gases on the heterogeneous lithium transport. Gas was observed as randomly interspersed “bubbles” which locally hindered lithium intercalation and caused significant heterogeneity. Electrode architectures and charging protocols that promote homogeneous intercalation are critical for predictable high-performance and long-life batteries.

The battery technology literature is reviewed, with an emphasis on key elements that limit extreme fast charging. Key gaps in existing elements of the technology are presented as well as developmental needs. Among these needs are advanced models and methods to detect and prevent lithium plating; new positive-electrode materials which are less prone to stress-induced failure; better electrode designs to accommodate very rapid diffusion in and out of the electrode; measure temperature distributions during fast charge to enable/validate models; and develop thermal management and pack designs to accommodate the higher operating voltage.

The ability to charge battery electric vehicles (BEVs) on a time scale that is on par with the time to fuel an internal combustion engine vehicle (ICEV) would remove a significant barrier to the adoption of BEVs. However, for viability, fast charging at this time scale needs to also occur at a price that is acceptable to consumers. Therefore, the cost drivers for both BEV owners and charging station providers are analyzed. In addition, key infrastructure considerations are examined, including grid stability and delivery of power, the design of fast charging stations and the design and use of electric vehicle service equipment. Each of these aspects have technical barriers that need to be addressed, and are directly linked to economic impacts to use and implementation. This discussion focuses on both the economic and infrastructure issues which exist and need to be addressed for the effective implementation of fast charging at 400 kW and above. In so doing, it has been found that there is a distinct need to effectively manage the intermittent, high power demand of fast charging, strategically plan infrastructure corridors, and to further understand the cost of operation of charging infrastructure and BEVs.

To achieve a successful increase in the plug-in battery electric vehicle (BEV) market, it is anticipated that a significant improvement in battery performance is required to increase the range that BEVs can travel and the rate at which they can be recharged. While the range that BEVs can travel on a single recharge is improving, the recharge rate is still much slower than the refueling rate of conventional internal combustion engine vehicles. To achieve comparable recharge times, we explore the vehicle considerations of charge rates of at least 400 kW. Faster recharge is expected to significantly mitigate the perceived deficiencies for long-distance transportation, to provide alternative charging in densely populated areas where overnight charging at home may not be possible, and to reduce range anxiety for travel within a city when unplanned charging may be required. This substantial increase in charging rate is expected to create technical issues in the design of the battery system and the vehicle's electrical architecture that must be resolved. This work focuses on vehicle system design and total recharge time to meet the goals of implementing improved charge rates and the impacts of these expected increases on system voltage and vehicle components.

Battery thermal barriers are reviewed with regards to extreme fast charging. Present-day thermal management systems for battery electric vehicles are inadequate in limiting the maximum temperature rise of the battery during extreme fast charging. If the battery thermal management system is not designed correctly, the temperature of the cells could reach abuse temperatures and potentially send the cells into thermal runaway. Furthermore, the cell and battery interconnect design needs to be improved to meet the lifetime expectations of the consumer. Each of these aspects is explored and addressed as well as outlining where the heat is generated in a cell, the efficiencies of power and energy cells, and what type of battery thermal management solutions are available in today's market. Thermal management is not a limiting condition with regard to extreme fast charging, but many factors need to be addressed especially for future high specific energy density cells to meet U.S. Department of Energy cost and volume goals.

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.

Correction for ‘Quantification of heterogeneous, irreversible lithium plating in extreme fast charging of lithium-ion batteries’ by Partha P. Paul et al., Energy Environ. Sci., 2021, DOI: 10.1039/d1ee01216a.

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.

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.

There is an ever-increasing demand for rechargeable batteries for electric vehicles, which primarily use lithium-ion batteries (LIB). One of the major proposed improvements in using LIBs for vehicles is in reducing the long recharging times (order of hours), to make it comparable to the 5-10 minute refueling times in gasoline-powered vehicles. Therefore, extreme fast charging (XFC) has been defined for LIBs, with a target to bring the charging time down to 15 minutes or less [1]. However, XFC of LIB is associated with several problems, the most prominent of which are a large loss of battery capacity over cycling and safety issues [2]. Therefore, an understanding of the how local, irreversibly plated lithium affects the local SOC of the cathode and anode, as well as tying the contributions from individual loss mechanisms quantitatively over the cell to the overall capacity fade of the cell during fast charging is necessary to design the battery for better safety and consistent performance. Towards addressing this issue, high energy X-ray diffraction (XRD) is employed, which helps build on the existing understanding of lithium plating in two ways. Firstly, XRD provides a way to quantify the amount of Li plating, as well as other loss mechanisms, and tie them to the global cell performance after XFC cycling. Second, XRD is an in-situ technique, allowing to characterize the entire battery in the fully assembled condition. Thus, local heterogeneities in the cathode and anode can be studied and correlated to heterogeneities in Li plating. In this work, sub-mm-scale XRD is used to quantify Li plating across different single layer pouch cells (3 mAh/cm2 specic capacity, with graphite anode and NMC cathode), where the charging rate and protocol are systematically varied (4C to 9C). The cells are cycled through hundreds of XFC cycles and studied in the discharged state. At the local level, the characteristics of plated lithium crystallites such as the preferred crystallographic orientations and size of plated Li on graphite are studied. Additionally, the regions with local lithium plating are correlated with the local SOC (lithium occupancy) and loss of active surface area in the cathode and anode, in the discharged state. Finally, the capacity fade of the cycled cells is correlated to the amount of dead Li, with separated contributions from irreversibly plated Li, Li trapped in graphite as LixC (which cannot be reversibly extracted from the anode) and reaction of plated Li with the electrolyte. Based on this knowledge of the properties of lithium plating and the conditions that favor it, as well as it's effect on overall battery performance, new approaches towards designing batteries can be realized, such that irreversible Li plating is minimized. This step will in turn help to guide the rational design of the next generation of XFC capable LIBs with a consistent and safe performance. References [1] T. R. Tanim, E. J. Dufek, M. Evans, C. Dickerson, A. N. Jansen, B. J. Polzin, A. R. Dunlop, S. E. Trask, R. Jackman, I. Bloom, et al. Extreme fast charge challenges for lithium-ion battery: Variability and positive electrode issues. Journal of The Electrochemical Society, 166(10):A1926{A1938, 2019. [2] A. Tomaszewska, Z. Chu, X. Feng, S. O'Kane, X. Liu, J. Chen, C. Ji, E. Endler, R. Li, L. Liu, et al. Lithium-ion battery fast charging: A review. eTransportation, 1:100011, 2019.

Lithium-ion batteries (LIBs) capable of fast-charging are essential in the popularization of electric vehicles. Typical fast-charge requirements are charging to 80% state of charge within 10 mins. However, such high rates cause active material degradation and undesired lithium plating, leading to capacity fading and safety hazards. These issues are impacted by charging conditions, e.g. charging protocol, temperature, external pressure, etc. Here, we focus on the pressure-dependence of fast-charge batteries using an in-house designed gas bladder cell configuration. Through a systematic study, we revealed correlations between externally applied electrode stack pressure and capacity fade. Additionally, we propose possible capacity fade mechanisms during fast charge and a way to mitigate it. We utilized single-layer pouch cell batteries with a graphite anode, LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode, and organic liquid electrolyte solution. Electrode stack pressure is achieved by opposing pairs of external flexible gas bladders. These gas bladders are formed by airtight sealing of a Kapton dome against each side of the flexible battery pouch. (Fig. (a)). By controlling the gas pressure within the bladders, the external pressure is precisely set and the flexible bladders locally conform to provide uniform pressure across the electrode stack. This combination bypasses issues with rigid plates where electrode thickness variations and internal electrical connections prevent uniform pressure. Additionally, the pressure is stable during battery cycling process regardless of material expansion/contraction or gassing. Furthermore, the X-ray transparent Kapton domes allow operando X-ray characterization. Using external pressures of 10, 50, and 125 psi, and on a control group with pressure applied by rigid plates, we performed a series of electrochemical experiments. All batteries were charged at 6C using CC-CV protocol and discharged at C/2 at room temperature for 140 cycles with a voltage range of 3 – 4.1 V. We found that the capacity fade decreases with increasing pressure (Fig. (b)); the capacity fade of rigid-plate cells is larger than gas-bladder cells. Additionally, the fast charge capacity increases with increasing pressure, indicating that the depth of charge/discharge in the entire cell is greater with higher external pressure (Fig. (c)). In contrast, the difference between the open circuit voltages at the end of charge and discharge is smaller at higher pressure. These two observations imply that the depth of reaction within the active material decreases with increasing pressure (Fig. (d)). Combining these two findings, we infer that there is more active material loss with lower external pressure, which is the main reason for capacity fading. The active material loss may come from the loss of electrical contact when particles crack or pulverize during fast charge, while higher external pressure can help preserve the electrical contact. Our study sheds new light on the influence of external pressure on fast-charge performance of LIBs. The use of gas-bladder cells helps to eliminate non-reproducibility in non-uniform cell thickness and material expansion/contraction. We plan to conduct operando X-ray diffraction experiments using the X-ray transparent AP cell to monitor the evolution of anode and cathode materials and Li plating during fast charge to investigate the underlying mechanism of the pressure-dependent behaviors. Figure 1

Silicon monoxide (SiO) is a very promising anode material for the next generation high energy lithium ion batteries due to its high theoretical specific capacity of 1710 mAh/g and volumetric capacity of 1547 Ah/L.[1] Compared to commercially used graphite, SiO can offer 18% cell stack level improvement in volumetric energy density and 11% in gravimetric energy density (calculated based on the same cell stack model), enabling utilization of smaller and lighter batteries. It also offers more stable cycle performance compared to Si due to less volume change (134% initial volume expansion and 117% reversible volume expansion), making it a more practical choice for lithium ion batteries in the near future. SiO is composed of Si nanodomains in a SiO2 matrix. An interphase region of transitional stoichiometry (SiOx, 0 < x < 2) is also present between Si and SiO2 and takes up 20-25 at.% of the entire composition.[2] During the lithiation and delithiation, the Si nanodomains react reversibly with lithium, similar to amorphous silicon, to give the reversible capacity. The SiO2 matrix reacts irreversibly with lithium to form lithium silicates and lithium oxide. Therefore, the Si domain size and interphase suboxide between Si and SiO2 have effect on the electrochemical performance of SiO. In this study, we gradually changed the microstructure of SiO via annealing treatment and thoroughly studied the change of the SiO microstructure and its impact on the electrochemical performance of the SiO. Together with electrode formulation optimization, up to 99% capacity retention during 50 cycles was obtained in full cells when using pure SiO as anode and LiNi0.5Mn0.3Co0.2O2 as cathode. Acknowledgement We gratefully acknowledge the support from Peter Faguy at the U.S. Department of Energy’s (DOE) office of Energy Efficiency & Renewable Energy (EERE) - Vehicle Technologies Office. This work is conducted under the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory. Argonne National Laboratory is a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357. Reference: Obrovac, M. N.; Chevrier, V. L., Alloy Negative Electrodes for Li-Ion Batteries. Chemical Reviews 2014, 114 (23), 11444-11502. Hirata, A.; Kohara, S.; Asada, T.; Arao, M.; Yogi, C.; Imai, H.; Tan, Y.; Fujita, T.; Chen, M., Atomic-scale disproportionation in amorphous silicon monoxide. Nature Communications 2016, 7, 11591.

The stability of silicon-containing anodes can, in principle, be extended by constraining these electrodes to limited states of lithiation. Partial utilization of the anode lessens the volume changes experienced by silicon particles during cycling, which can mitigate mechanisms of performance degradation. In full-cells, anode utilization can be modulated by adjusting the relative capacities of the negative and positive electrodes – the N/P ratio. Here, we examine how the N/P ratio affects the long-term stability of Si-based full-cells, and investigate how this parameter would impact the cost and energy of realistic Li-ion cells. We show that, for some configurations, cell failure due to rapid anode degradation can only by avoided at higher N/P ratios. The price of this enhanced stability is accelerated impedance rise at the cathode. Surprisingly, when electrode expansion is taken into account, increasing N/P ratio can actually increase the specific energy and energy density of silicon-rich Li-ion cells.