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The severe capacity fade of lithium-ion cells with silicon-dominant anodes has hindered their widescale commercialization. In this work, we link cell capacity fade to the heterogeneous physicochemical evolution of silicon anodes during battery cycling. Through a multilength scale characterization approach, we demonstrate that silicon particles near the anode surface react differently from those near the copper current collector. In particular, near the anode surface we find an amorphized wispy silicon encased in a highly fluorinated matrix of electrolyte-reduction products. In contrast, closer to the current collector, the silicon retains more of its initial morphology and structure, suggesting the presence of isolated particles. The results show that the accessibility of active silicon to lithium ions varies across the anode matrix. Material and cell designs, which minimize electrode expansion resulting from the in-filling of pores with the solid electrolyte interphase (SEI), are needed to enhance anode homogeneity during the electrochemical cycling.

Conductive paints are colloidal solutions, which are water-based, non-toxic and electrically conductive. In this work, we draw multiple semi-circles of different radii and breaths with conductive paint. We take two probes and fix one at 0° while the other is free to rotate between 0° to 180°. These probes are connected to the multimeter to measure the resistance of the conductive paint. Linearity between the resistance of the paint and the angle made by both the probes is verified. A relation between angle and resistance is formulated for each semi-circular specimen by linear regression based on the experimentally obtained data. The combination with appropriate accuracy and linearity of semi-circular dimension is chosen and the relation between angle and resistance is again formulated based on liner piecewise interpolation. The obtained relation based on the liner piecewise interpolation is compared with the experimental data to find the accuracy of the chosen semi-circular conductive paint dimension. The results obtained from the python simulation were compared with the experimental data and the accuracy was calculated and was found to be 94% accurate. Metal-based paints may oxidize with moisture content in the atmosphere, hence graphite is preferred in conductive paints.

High-energy batteries for automotive applications require cells to endure well over a decade of constant use, making their long-term stability paramount. This is particularly challenging for emerging cell chemistries containing silicon, for which extended testing information is scarce. While much of the research on silicon anodes has focused on mitigating the consequences of volume changes during cycling, comparatively little is known about the time-dependent degradation of silicon-containing batteries. Here we discuss a series of studies on the reactivity of silicon that, collectively, paint a picture of how the chemistry of silicon exacerbates the calendar aging of lithium-ion cells. Assessing and mitigating this shortcoming should be the focus of future research to fully realize the benefits of this battery technology. Silicon-containing batteries are increasingly becoming a reality in the mass market, but their calendar aging behaviours have received comparatively little attention. Researchers from the Silicon Consortium Project discuss the issues surrounding the calendar lifetime of silicon anodes for lithium-ion batteries.

Simply mixing several lithium salts in one electrolyte to obtain blended salt electrolytes has been demonstrated as a promising strategy to formulate advanced electrolytes for lithium metal batteries (LMBs) and lithium-ion batteries (LIBs). In this study, we report the use of dual-salt electrolytes containing lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiDFP) in ethylene carbonate/ethyl methyl carbonate (EC/EMC) mixture and tested them in layered high-nickel LIB cells. LiNi0.94Co0.06O2 was synthesized through a coprecipitation method and was used as a representative high-nickel cathode for the U.S. DOE realizing next-generation cathode (RNGC) deep dive program. The ionic conductivity of dual-salt electrolytes can be maintained by controlling the amount of LiDFP. Techniques including 1H Nuclear Magnetic Resonance (NMR), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-mass spectrometry (ICP-MS), and differential voltage analysis (DVA) were used to understand the improved performance. The multifaceted benefits of using the dual-salt electrolytes include (1) reduced transesterification, (2) formation of a stable cathode electrolyte interface, and (3) mitigation of cathode degradation at high voltages, especially stabilization of oxide particles during the H2 ↔ H3 transformation.

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.

Fast-charge protocols that prevent lithium plating are needed to extend the life span of lithium-ion batteries. Here, we describe a simple experimental method to estimate the minimum charging time ...

Nanometer-thick reconstruction layers on layered cathode surfaces have been widely observed on both pristine and cycled materials. However, the mechanisms of reconstruction and the role that these ...

Mechanical integrity of the solid electrolyte interphase (SEI) plays an essential role in determining the life and performance of lithium-ion batteries. Fracture and continued formation of the SEI contribute to consumption of lithium, drying of electrolyte, increase in impedance, and growth of dendrites resulting in capacity fade and premature failure. Electrolyte additives such as fluoroethylene carbonate (FEC) have been known to improve performance, but the underlying reasons have been elusive. Despite its importance, reliable methods for mechanical characterization of SEI have been lacking. Here, we present a new experimental technique that combines atomic force microscopy and membrane-bulge configuration to accurately measure the stress-strain behavior of SEI, including the onset of inelastic response and evolution of fracture. We characterize the SEI formed with two ethylene carbonate-based electrolytes, without and with fluoroethylene carbonate (FEC) additive. The measurements show a striking contrast; SEI with FEC additive has 80% higher elastic modulus and a vastly higher resistance to fracture. These findings offer a mechanical-behavior based rationale to understand how SEI controls battery performance. Moreover, the experimental technique offers a robust diagnostic tool to design electrolytes that can form SEI with the desired mechanical properties for optimal battery performance.

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.

The collaborative evaluation of electrode materials across multiple research entities requires standardized electrochemical testing protocols to produce reliable, one-to-one comparisons between different systems of interest. Similar to the work done by Long et al. on protocol standardization for coin-cell testing with graphite anodes [J. Electrochem. Soc., 163, A2999, (2016)], we introduce two standardized testing protocols designed to quickly evaluate important electrochemical properties of cathode materials using lithium-metal anodes. The two protocols measure kinetic and thermodynamic capacity losses, rate- and voltage-dependent cycling capacities, instabilities at high voltage and high cycling rate, and overpotentials at various states of charge. We then apply these protocols to four commercially available cathode materials to establish benchmark performance metrics that can be used to screen and evaluate new cathode materials.

Coin cells are used extensively as test devices in battery research for evaluation of new materials and optimization of cycling protocols. In this study, in situ X-ray diffraction profilometry is used to characterize spatial distribution of the active materials, lithiation, and phase distribution in electrodes of NCM523/graphite coin cells. The X-ray data indicate uneven areal compression of the electrode assembly in such cells, which we trace to a specific design feature that leads to elastic deformation of a metal spacer. Steep lithiation gradients observed in the electrodes imply radially-dependent resistivity, for which uneven compression of the separator is a likely cause. Electrochemical model calculations suggest that variable porosity of the polymer separator would account for the salient features of spatial profiles observed in these coin cells.

Instability of nickel-rich layered oxides at high voltages is an impediment to their wider use in Li-ion batteries. HF generated via LiPF6 hydrolysis accelerates corrosion, further destabilizing th...

Increasing the energy densities of Li-ion batteries necessitates operation of layered lithiated oxide cathodes at potentials exceeding 4 V vs Li/Li+. When continually exposed to such high potential...

Since its discovery, the high-voltage spinel oxide LiNi0.5Mn1.5O4 (LNMO, sg: Fd-3m) has been widely pursued as a promising cathode for next generation Li-ion batteries due to advantages that include the following: high operating voltage, excellent rate capability and low manufacturing cost (1, 2). However, the LNMO cathode when paired with graphite shows poor capacity retention and increased cell impedance due to oxidation of the organic liquid electrolyte and Mn2+ migration onto the anode (2, 3). Herein, we aim to understand the causes of poor capacity retention in LNMO/graphite full cells and systematically address those issues with various electrode modification strategies. Cycling performance of cells with carbon-nanotube (CNTs) in the LNMO electrode (LNMO-CNT), and with a thin layer of Al2O3 on the graphite electrode (Gr-Al2O3), is examined in half, full and three-electrode cell configurations. The cells with LNMO-CNT electrode show significantly lower cell impedance than cells with LNMO electrodes (without the CNT). Additionally, cells with the Al2O3-coated graphite electrode show improved capacity retention compared to cells with the uncoated graphite. Furthermore, cells containing Li4Ti5O12 anodes display the best capacity retention. We investigate and compare the physiochemical changes in electrodes and electrolyte using various diagnostic techniques; data from these experiments will be reported during the presentation. References : M. M. Thackeray, W. I. F. David, P. G. Bruce and J. B. Goodenough, Materials Research Bulletin, 18, 461 (1983). S. Patoux, L. Daniel, C. Bourbon, H. Lignier, C. Pagano, F. Le Cras, S. Jouanneau and S. Martinet, J Power Sources, 189, 344 (2009). F. Zou, H. C. Nallan, A. Dolocan, Q. Xie, J. Y. Li, B. M. Coffey, J. G. Ekerdt and A. Manthiram, Energy Storage Materials, 43, 499 (2021). Acknowledgements: This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

We have shown different strategies1, 2 in improving capacity retention and reducing impedance rise in modifying additives: in situ electrolyte additives to synthesize the beneficial lithium tetrafluorophosphate components3, 4 or dual-salt electrolytes1 for reducing cathodic impedance. The cathodes we have tested have a LiNiO2 structure with an ultra-low amount of Co/Mn. An improved structural stability compared to that of LiNiO2 can be achieved while maintaining the high Ni content and high specific capacity. Using an optimal ratio of Ni/Mn/Co of 90/5/5 for a LiNi90Mn5Co5O2 cathodes,5 we here report the reduced reactivity of electrolytes using a combinatorial approach of reducing EC and introducing effective additives, targeting both a more robust SEI formation and a less resistive cathode electrolyte interface. Multifaceted posttest analytical methods were used to understand the failure mechanism of the baseline cells and how additives/solvents approaches help the performance. For example, the new electrolytes prevent the transesterification reactions on anode surface, form a stable cathode interface, and mitigate structural damage on the cathode surface. Further analysis also investigated the how electrolytes protect the cathode bulk structure. [1] J. Yang, M.-T. Fonseca Rodrigues, S.-B. Son, J. C. Garcia, K. Liu, J. Gim, H. Iddir, D. P. Abraham, Z. Zhang and C. Liao, ACS Applied Materials & Interfaces, 2021. [2] J. Yang, I. Shkrob, K. Liu, J. Connell, N. L. Dietz Rago, Z. Zhang and C. Liao, Journal of The Electrochemical Society, 2020, 167, 070533. [3] J. Yang, I. Shkrob, Q. Liu, N. L. Dietz Rago, Y. Liu, K. Liu, Z. Zhang and C. Liao, Journal of Power Sources, 2019, 438, 227039. [4] I. A. Shkrob, B. Han, R. Sahore, A. P. Tornheim, L. Zhang, D. P. Abraham, F. Dogan, Z. Zhang and C. Liao, Chemistry of Materials, 2019, 31, 2459-2468. [5] C. S. Yoon, M. H. Choi, B.-B. Lim, E.-J. Lee and Y.-K. Sun, Journal of The Electrochemical Society, 2015, 162, A2483-A2489.

Calendar and cycle life of lithium-ion batteries (LIBs) are predominantly dictated by the passivating nature of the solid electrolyte interphase (SEI) film growth on battery anodes. Graphitic anodes exhibit stable SEI growth which enables ubiquitous commercialization of LIBs. In contrast, silicon anodes exhibit poorly passivating SEI characteristics including rapid thickness and composition changes during cycling (“breathing”) and sensitivity to electrolyte composition and surface functionalization. In this work, we develop a chemically complex continuum-level multicomponent, multiphase coupled thermodynamics-reaction-transport SEI model to unravel the mechanisms of SEI growth in LIB anodes. Atomistic calculations in conjunction with experimental datasets are utilized to ascertain the dominant decomposition pathways towards predominant SEI components like Li2EDC, Li2O, Li2CO3, LiMC, LiF etc. and inform the continuum model predictions. Furthermore, experimental voltage-hold measurements are utilized to validate the SEI model parasitic currents/composition evolution profiles enabling prediction of voltage regimes for stable SEI growth with favorable SEI composition. The development of such chemically complex SEI models will aid predictive electrolyte screening for the growth of stable and passivating SEI layers on next generation anodes like silicon. Figure 1(a) shows a schematic of the detailed SEI model incorporating species and charge transport through the pore and solid phases of the SEI for LEDC formation. Figure (b) showcases experimental leakage currents during V-hold at 100 mV and 250 mV for Li-Si half cells and the detailed SEI model fits. Figure (c) shows the SEI composition profiles predicted by the model and the formation of inner inorganic (Li2CO3, Li2O) - outer organic (LEDC) bilayer SEI. Interestingly, inorganic LiF from FEC decomposition is predicted to form throughout the SEI. Figure 1

While cycle-life parity between graphite and silicon (Si) based lithium-ion batteries (LIBs) is being reached, calendar lifetime of Si anodes remains disappointing compared to its graphite counterpart1. Silicon anode, owing to its intrinsic high (electro)chemical reactivity, exhibits poorly passivating solid electrolyte interphase (SEI) characteristics in common electrolyte formulations optimized for graphitic systems like LiPF6 salt in EC:EMC solvents. Rapid electrolyte screening for calendar lifetime optimization is essential for enabling silicon anodes, as standardized calendar lifetime estimation with the USABC open circuit voltage reference performance test (OCV-RPT) requires long-duration experiments (~years) for accuracy2. In this work, we perform calendar lifetime screening of novel electrolytes for Si anodes utilizing voltage-hold (V-hold) experiments. The V-hold protocol with shortened runtime (~weeks) affords faster testing as compared to the conventional OCV-RPT protocol. Composite silicon anodes with low (15 wt.% Si) and high contents of silicon (70 wt. %Si) are tested with fluorine-free electrolyte systems (e.g. LiBOB in EC:EMC) and EC free electrolytes (e.g. LiPF6 in FEC:EMC) respectively. Capacity during the V-hold has reversible anode lithiation and irreversible SEI growth contributions; consequently, a physics-based capacity deconvolution algorithm is devised to accurately split the parasitic currents for quantitative calendar lifetime estimation. The development of this synergistic experiment-modeling testing paradigm aids in the identification of electrolyte compositions that form stable, passivating SEI films on the silicon-based anodes. Figure 1 shows the voltage-hold cycle data for (a) fluorine-free and (b) fluorine-rich (right) electrolytes with 15% Si composite anodes collected in a 3-electrode cell. The corresponding normalized capacity and current profiles for 4.1V hold portion are shown in (c) and (d) respectively. Accurate deconvolution of irreversible capacity from the hold capacity is needed to obtain SEI stability information for calendar lifetime. 1McBrayer, J.D., Rodrigues, M.T.F., Schulze, M.C., Abraham, D.P., Apblett, C.A., Bloom, I., Carroll, G.M., Colclasure, A.M., Fang, C., Harrison, K.L. and Liu, G., 2021. Calendar aging of silicon-containing batteries. Nature Energy, 6(9), pp.866-872. 2U.S. Department of Energy Vehicle Technologies Program, United States Advanced Battery Consortium Battery Test Manual For Electric Vehicles, Revision 3.1, October 2020 http://www.uscar.org/guest/article_view.php?articles_id=86 Figure 1

Development of highly-active, durable and cost-effective oxygen reduction electrocatalyst for proton exchange membrane fuel cell is crucial and greatly desired to enable fuel cell powered vehicles that are competitive with internal combustion engine automobiles. The support’s structure is known to strongly influence the performance of Pt particles. Here, we present a new catalyst containing PtCo core-shell nanoparticle supported over hierarchical tailored porous carbon nanofibers with densely populated single-atomic Co-Nx sites embedded in N-doped graphene. In a fuel cell with a total Pt loading (anode + cathode) of 0.091 mg cm-2, the new catalyst delivered unprecedented mass activity of 2.28 A mgPt-1 at 0.9 ViR-free, Pt utilization of 11.1 kW gPt-1 at 150 kPaabs, and high durability with 80% retention of initial mass activity after 30,000 accelerated-stress-test cycles, significantly higher than that of the state-of-the-art Pt3Co/C. In-situ X-ray absorption spectroscopy revealed structure reversibility of the catalyst during oxygen reduction reaction and indicated that the enhanced activity can be attributed to simultaneous PtCo and Co-Nx contributions.

The development of longer lasting and faster charging lithium-ion batteries (LIBs) remains a critical engineering priority for the U.S. Department of Energy. To enable the next-generation technology, it is essential to understand the nature and extent of materials failure during battery operation. Under fast-charging conditions, it has been shown that graphite particles, which comprise the active material of the LIB anode, suffer irreversible material degradation that limits ultimate battery performance. This damage to the graphite manifests as turbostratic lattice disorder, severe morphological roughening, and anode swelling [1]. While these findings are essential to understand the nature of damage to the anode under fast-charge conditions, it remains to be seen whether such damage occurs at slower rates or is instead accelerated by extreme rate conditions and aging. In this regard, the recent advances in high-resolution electron microscopy (HREM) and four-dimensional scanning transmission electron microscopy (4D-STEM) methods provide the essential tools to enable nanoscopic quantification of battery degradation [2], [3]. In this work, we use advanced analytical electron microscopy and diffraction strategies to analyze nanoscopic degradation of graphite anode material under different cycling rate and aging conditions. The results of this work will demonstrate novel strategies for identifying nanoscale structural disorder that arise in battery materials as well as provide key understanding of graphite material failure to aid in the development of high-performance anode materials. We study (in post-mortem) the graphite particle cross-sections harvested from LIBs at different aging conditions for both C/2 (i.e., 2 hours to full charge) and 6C (i.e., 10 minutes to full charge) rate. At the nano- to atomic-scale, we rely primarily on aberration-corrected STEM for imaging and diffraction acquisition for each sample (see Figure 1 for the results). High resolution imaging reveals the extent of lattice disorder and amorphous character localized at graphite pore edges. The 4D-STEM data helps to further quantify the extent and distribution of nanoscale structural disorder (including permanent strain and turbostratic disorder). The experimental methods employed to acquire the datasets and the strategies employed to interpret the data to understand the nature of the resulting damage, including recent progress into Cepstral STEM, will be discussed. Additional supporting evidences of graphite disorder from Raman spectroscopy studies and rate-dependent anode swelling from scanning electron microscopy will also be presented. References : [1] S. Pidaparthy, M.-T. F. Rodrigues, J.-M. Zuo, and D. P. Abraham, “Increased Disorder at Graphite Particle Edges Revealed by Multi-length Scale Characterization of Anodes from Fast-Charged Lithium-Ion Cells,” J. Electrochem. Soc., vol. 168, no. 10, p. 100509, 2021. [2] J.-M. Zuo et al., “Data-Driven Electron Microscopy: Electron Diffraction Imaging of Materials Structural Properties,” arXiv Prepr. arXiv2110.02070, 2021. [3] E. Padgett et al., “The exit-wave power-cepstrum transform for scanning nanobeam electron diffraction: robust strain mapping at subnanometer resolution and subpicometer precision,” Ultramicroscopy, vol. 214, p. 112994, 2020. Acknowledgements: SP acknowledges support from the U. S. Department of Energy Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the U. S. Department of Energy under contract number DE‐SC0014664. This work was carried out in part in the Materials Research Laboratory Central Research Facilities, University of Illinois. DA and MTFR acknowledge support from DOE’s Vehicle Technologies Office. This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. Figure 1

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.

Safe, fast, and energy efficient cycling of lithium ion batteries is desired in many practical applications. However, modeling studies predict steep Li+ ion gradients in the electrodes during cycling at the higher currents. Such gradients introduce heterogeneities in the electrodes, which make it difficult to predict cell lifetimes as different portions of the cell age at different rates. There is a dearth of experimental methods to probe these concentration gradients across the depth of the electrode. Here we use spatially resolved energy dispersive X-ray diffraction to obtain a “movie” of lithiation and delithiation in different sections of the cell and quantify lithium gradients that develop in a porous graphite electrode during cycling at a 1C rate. Inhomogeneity in the total Li content, and in the individual ordered LixC6 phases formed during lithium insertion into (and extraction from) the graphite, has been observed in an operando fashion. The complex dynamics of lithium-staging in graphite with the distinct front propagation of phase changes have been characterized and new features of these dynamics are highlighted here. As large Li+ ion gradients contribute to cell polarization, our results suggest that Li plating conditions can be met near the graphite electrode surface, even when the cell is charged at a moderate (1C) rate.

Fast charging of Li-ion batteries would ease consumer concerns regarding refueling time of electric vehicles. In this series of articles, we are systematically examining the effects of high currents flowing through the cell. Here we consider open-circuit relaxation dynamics for cell voltage and individual electrode potentials after abrupt termination of steady-state charging currents (1-6C) or short current pulses (< 30 s) of either polarity (to 16C). We demonstrate that dispersive kinetics observed after these current perturbations become faster for higher currents applied before the rest period. Our observations indicate that the voltage relaxation behaviors (i) depend on the current during charge, and less so on the state of charge, (ii) display universal stretched-exponential kinetics, (iii) can be induced by a short current pulse, (iv) require a minimum amount of charge transfer during the pulse, and (v) originate mainly from the oxide cathode. Trap controlled Li+ ion transport through a partially disordered oxygen-depleted subsurface layer in the cathode is suggested as a possible origin for the relaxation behavior. The slow multidecadal responses to high currents can cause the nonlinearities observed during rapid charging of the electrochemical cells, reported in Part 2 of this series.

Li-ion batteries will lose both capacity and power over time due to calendar aging caused by slow parasitic processes that consume Li+ ions. Studying and mitigating these processes is traditionally an equally slow venture, which is especially taxing for the validation of new active materials and electrolyte additives. Here, we evaluate whether potentiostatic holds can be used to accelerate the diagnosis of Li+ loss during calendar aging. The technique is based on the idea that, under the right conditions, the current measured as the cell voltage is held constant can be correlated with the instantaneous rate of side reactions. Thus, in principle, these measurements could capture the rate of capacity fade in real time. In practice, we show that this method is incapable of quantitatively forecasting calendar aging trends. Instead, our study demonstrates that potentiostatic holds can be applied for initial qualitative screening of systems that exhibit promising long-term stability, which can be useful to shrink the parameter space for calendar aging studies. By facilitating the identification of improved formulations, this approach can help accelerate innovation in the battery industry.

Lithiated nickel-cobalt-manganese oxides, such as NCM523, are used in the positive electrode (cathode) of Li-ion cells. Using operando X-ray diffraction profilometry, lithiation gradients in the cathode matrix can be observed and quantified by expansion into Legendre polynomials with time-dependent weights. These weights (referred to as gradients) increase in magnitude when electric current flows through the cell, decrease during potentiostatic hold and finally relax to zero when the current is interrupted during open circuit rest. Both physics-based electrochemical models and operando X-ray experiments suggest that the time constants for gradient growth and abatement are primarily determined by ionic diffusion in the oxide particles, which in turn depends on their lithium content. In contrast, the magnitude of gradients depends mainly on the applied current. The X-ray profilometry provides a way of directly probing the formation and disappearance of Li gradients across the cathode during fast cycling, which can help to diagnose the effects of material degradation in the cells.

Difficulties with sourcing cobalt and the interest in increasing cell energy have motivated the development of Ni-rich oxide materials for lithium-ion battery cathodes. Despite the intense research on the topic, there is limited information available on the long-term performance of novel cathode formulations. Here, we evaluate the stability of LiNi0.9Mn0.05Co0.05O2 in full-cells tested for over five months, assessing how cycling, voltage and electrolyte additives impact cathode aging. We use differential voltage analysis to extract insights about the cathode from the full-cell data and identify the isolation of cathode particles in the delithiated (charged) state as a relevant mode of aging. Importantly, this particular mechanism of cathode aging does not cause immediate cell capacity fade, causing the simple analysis of cell capacity retention to overestimate the cathode stability under the investigated conditions. Our observations serve as cautionary tale indicating that careful analysis of data from extended testing may be required for assessing the performance of Ni-rich cathodes and for evaluating how these materials are affected by electrolyte additives.

Rapid charging of lithium-ion batteries being developed for electric vehicles is a formidable challenge. Electrochemical polarization of cells during fast charging favors deposition of metallic Li onto the surface of the graphite electrode, and this Li plating compromises safety and accelerates performance degradation. Observing the onset of Li nucleation is essential for elucidation of mechanisms and defining conditions favoring this Li plating, but presently available methods are not sufficiently sensitive and selective while also allowing satisfactory spatial resolution. Here we demonstrate the use of Raman spectroscopy as a sensitive means to identify Li nucleation and map Li deposition. Metallic Li is detected indirectly by probing the vibrations in an acetylide species (represented as Li—C≡C—X) that is formed on the exposed surface of Li nuclei in contact with the solid electrolyte interphase on graphite. Surface-enhanced Raman scattering (SERS) involving this species on Li nuclei appears to dramati...

The high capacity of silicon motivates its use as anode material for Li-ion batteries. While such Si-based electrodes are typically processed from aqueous slurries, elemental silicon is highly susceptible to hydrolysis, yielding flammable hydrogen gas as a byproduct. This gassing can present numerous safety and quality concerns for scaling up of the production. In this study we describe a method to quantify the volume of gases generated using the Archimedes principle. We show that the gas volumes are affected by various factors, which include the characteristics of the electrode slurry and attributes (particle size, surface coatings) of the silicon powders. A catalytic effect on gas evolution is observed when a lithiated polycarboxylate binder is present in the solution. On the other hand, 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. Our study can be used as a guide for the development of slurry mixtures that can mitigate the safety concerns associated with the silicon-electrode fabrication process.

The use of high-voltage, high-capacity positive electrodes in lithium ion batteries presents a challenge, given their tendency to degrade organic electrolytes. To prevent this damage, electrolyte additives modifying the cathode surface are required. Tris(trimethylsilyl) phosphite (TMSPi) is one such electrolyte additive. However, the mechanism for its protective action (similar to other phosphite, borate, and boroxane compounds) remains not completely understood. In LiPF6 containing carbonate electrolytes, TMSPi undergoes reactions yielding numerous products. Here we demonstrate that one of these products, PF2OSiMe3, is responsible for mitigation of the impedance rise that occurs in aged cells during charge/discharge cycling. This same agent can also be responsible for reducing parasitic oxidation currents and transition metal loss during prolonged cell cycling. Mechanistic underpinnings of this protective action are examined using computational methods. Our study suggests that this beneficial action orig...

Lithiated transition metal oxides serve as active materials in the positive electrode (cathode) of lithium-ion cells. During electrochemical cycling, lithium ions intercalate and deintercalate into these oxide particles. This behavior causes two types of lithiation gradients to emerge: (i) a bulk gradient across the depth of the cathode matrix (averaged over individual oxide particles) and (ii) a microscopic gradient across the particles themselves, which also depends on their location in the electrode. Here we show how both gradients can be studied using operando X-ray diffraction during 4C charge and 4C discharge. The oxide (de)lithiation is estimated from the unit cell parameters by indexing the X-ray diffraction spectra. By fitting the lithiation profiles with orthogonal polynomials, the bulk gradients across the electrode thickness are quantified. These gradients develop as the current flows through the cell and dissipate during open-circuit and potentiostatic-hold periods. Further details of lithiation dynamics can be obtained through shape analysis of the Bragg peaks. In particular, from electrochemical model simulations, we show that the width and skewness of the (003) peak track (de)lithiation fronts moving across the individual oxide particles.

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.

In this study, Auger electron spectroscopy (AES) combined with ion sputtering depth profiling, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) have been used in a complementary fashion to examine chemical and microstructural changes in graphite (Gr) and silicon/graphite (Si/Gr) blends contained in the negative electrodes of lithium-ion cells. We demonstrate how AES depth profiling can be used to characterize morphology of the solid electrolyte interphase (SEI) deposits in such heterogeneous media, complementing well-established methods, such as XPS and SEM. In this way we demonstrate that the SEI does not consist of uniformly thick layers on the graphite and silicon; the thickness of the SEI layers in cycle life aged electrodes follows an exponential distribution with a mean of ca. 13 nm for the graphite and ca. 20–25 nm for the silicon nanoparticles (with a crystalline core of 50–70 nm in diameter). A “sticky-sphere” model, in which Si nanoparticles are covered with a layer...

Electrolyte additives are known to improve the performance of lithium-ion cells. In this work we examine the performance of Li 1.03 Ni 0.5 Mn 0.3 Co 0.3 O 2 -graphite (NMC532/Gr) cells containing combinations of lithium bis(oxalate)borate (LiBOB), vinylene carbonate (VC), trivinylcyclotriboroxane (tVCBO), prop-1-ene-1,3-sultone (PES), phenyl boronic acid ethylene glycol ester (PBE), tris(trimethylsilyl) phosphite (TMSPi), triethyl phosphite (TEPi), and lithium difluoro(oxalate)borate (LiDFOB) added to our baseline (1.2 M LiPF 6 in EC:EMC, 3:7 w/w) electrolyte. In order to rank performance of the various electrolytes, we developed two separate figures of merit (FOM), which are based on the energy retention and power retention of the cells. Using these two metrics in conjunction, we show that only one of the fifteen electrolyte formulations tested significantly outperforms the baseline electrolyte: this electrolyte contains the 0.25 wt% tVCBO + 1 wt% TMSPi additive mix. Little correlation was observed between the FOMs for energy retention and power retention, which indicates that the mechanisms that govern these performance parameters are likely independent of each other. Our FOM approach has general applicability and can be used to develop electrolyte and electrode formulations that prolong the life of lithium-ion batteries.

Silicon-graphite (Si-Gr) electrodes typically contain lithiated carboxylates as polymer binders that are introduced through aqueous processing. Li-ion cells with such electrodes show significantly faster capacity fade than cells with graphite (Gr) electrodes. Here we examine the causes for capacity loss in Si-Gr cells containing LiPF6-based electrolytes. The presence of SiOxFy in the Si-Gr electrode, fluorophosphate species in the electrolyte, and silica on the positive electrode indicates the crucial role of the hydrolytic cycle. In particular, HF acid that is generated through LiPF6 hydrolysis corrodes Si particles. As it reacts, the released water re-enters the cycle. We trace the moisture initiating this detrimental cycle to the hydration water in the lithiated binders that cannot be fully removed by thermal treatment. The rate of HF corrosion can be reduced through the use of electrolyte additives. For the fluoroethylene carbonate (FEC) additive, the improved performance arises from changes to the so...

Li 1.03 (Ni 0.5 Mn 0.3 Co 0.2 ) 0.97 O 2 (NMC)-based coin cells containing the electrolyte additives vinylene carbonate (VC) and tris(trimethylsilyl)phosphite (TMSPi) in the range of 0–2 wt% were cycled between 3.0 and 4.4 V. The changes in capacity at rates of C/10 and C/1 and resistance at 60% state of charge were found to follow linear-with-time kinetic rate laws. Further, the C/10 capacity and resistance data were amenable to modeling by a statistics of mixtures approach. Applying physical meaning to the terms in the empirical models indicated that the interactions between the electrolyte and additives were not simple. For example, there were strong, synergistic interactions between VC and TMSPi affecting C/10 capacity loss, as expected, but there were other, more subtle interactions between the electrolyte components. The interactions between these components controlled the C/10 capacity decline and resistance increase.

Silicon has been investigated for decades, as an alternative to the graphite used in lithium-ion battery anodes, because of its high theoretical capacity. However, the large volume change of Si during electrochemical cycling (cycle-aging) deteriorates the solid electrolyte interphase (SEI) layer on the particles, resulting in increased electrolyte reduction reactions and associated capacity decay. Capacity fade is also observed in cells that are not cycled but simply held at voltage for extended periods of time (calendar-aging). [1] Here we report the calendar and cycle-aging behavior of cells with a Si anode that is paired with a NMC532 cathode (Figure 1). The tests were conducted in coin cells and in cells with a reference electrode (prepared by in-situ lithiation of a 25 mm Cu wire). This reference electrode allowed us to determine changes in the individual electrode profiles during aging and to examine impedance changes that were monitored via hybrid pulse power characterization (HPPC) tests. [2] Our various experiments have revealed the following: (i) capacity-fade is greater during cycle-aging than during calendar-aging; (ii) the capacity fade is associated with shifts in both positive and negative electrode potentials; (iii) parasitic currents are observed during the calendar-life hold, which indicate ongoing electrolyte reduction reactions at the silicon electrode; (iv)both electrodes contribute to the significant impedance rise observed during cell aging. To further examine sources of the observed performance degradation we conducted experiments with cells with the Si paired with LiFePO4. These data, along with the probable mechanisms of cell aging, will also be discussed during the presentation. References Kalaga et al., Acta 2018, 280, 221-228. Klett et al., Electrochem. Soc. 163 (2016) p. A875. Acknowledgments: M.L. acknowledges the generous grants from the U.S. National Science Foundation with the award numbers of CMMI-1660572 and IIP-1918991 that enabled her research at Argonne National Laboratory. The electrodes and electrolytes used in this study are from Argonne’s Cell Analysis, Modeling and Prototyping (CAMP) Facility. We are grateful to Andrew Jansen, Bryant Polzin, and Steve Trask for their assistance during this study. Figure 1

Lithium-ion batteries (LIBs) capable of safe and reliable cycling at a fast-charge rate (i.e., >2C or Our strategies to study the graphite anode degradation are based on advanced analytical electron microscopy and diffraction. We focus on the modifications that occur in the material when subjected to charging rates up to 6C (i.e., 10 minutes to full charge). The characterization is performed post-mortem across different length-scales on as-prepared electrodes and electrodes harvested from cycled cells (represented in Figure 1). At the bulk-scale, we use scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to probe the morphological and chemical changes in cross-sections of the graphite anode samples. At the nano- and atomic-scale, we use advanced transmission electron microscopy (TEM) and diffraction techniques to reveal changes in both the nano-scale chemistry and the graphite microstructure. Key findings from this investigation include the morphological changes to the graphite particles at the micron-scale and the partial-filling of the inter- and intra-particle gaps with solid electrolyte interphase (SEI) compounds at the meso-scale. Further, at the nano- to atomic-scale, we observe greater disorder and amorphous character in the graphite near the internal pore surfaces when compared to that of the bulk graphite regions. The nature of the lattice disorder, and the characterization methods employed to examine this disorder, will be discussed. Additional supporting evidences of graphite disorder and phase change from Raman spectroscopy and X-ray diffraction studies will also be presented. Acknowledgements: SP acknowledges support from the U.S. Department of Energy Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the U. S. Department of Energy under contract number DE‐SC0014664. This work was carried out in part in the Materials Research Laboratory Central Research Facilities, University of Illinois. DA and MTFR acknowledge support from DOE’s Vehicle Technologies Office. This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. References : [1] C. Heubner, K. Nikolowski, S. Reuber, M. Schneider, M. Wolter, and A. Michaelis, “Recent Insights into Rate Performance Limitations of Li-ion Batteries,” Batter. Supercaps, Nov. 2020. [2] M.-T. Fonseca Rodrigues et al., “Lithium Acetylide: A Spectroscopic Marker for Lithium Deposition During Fast Charging of Li-Ion Cells,” ACS Appl. Energy Mater., vol. 2, no. 1, pp. 873–881, Jan. 2019. [3] Y. Yang et al., “Quantification of Heterogeneous Degradation in Li-Ion Batteries,” Adv. Energy Mater., vol. 9, no. 25, p. 1900674, Jul. 2019. Figure 1

We previously reported1-4 the in situ electrolyte additives to selectively synthesize the beneficial lithium tetrafluorophosphate components in high yield (> 98%) and maximize the battery performance. The in situ method is particularly of interest to scale up electrolyte preparation since it would alleviate any requirements of extra separation and purification of the desired additives. Here we used a new strategy of change both the composition and materials in the standard electrolyte to formulate advanced electrolytes for lithium ion batteries (LIBs). New electrolytes for high voltage LIBs were demonstrated to be more effective than the previous additives. The LIBs containing Ni-rich cathodes cycled with the new electrolytes in optimal composition rendered better electrochemical performance than cells cycled with the start-of-art Gen2 electrolyte when cycled between 3.0 to 4.2 V, exhibiting effective suppression of the impedance rise during aging. 1H Nuclear Magnetic Resonance spectra of cycled new electrolyte suggested their capabilities in preventing the transesterification reactions on anode surface, while X-ray photoelectron spectroscopy and inductively coupled plasma mass spectrometry analysis indicated its ability to form a stable cathode interface and mitigate structural damage on the cathode surface. Further analysis also indicated the benefits of the new composition electrolyte in protecting the cathode bulk structure. [1] J. Yang, I. Shkrob, K. Liu, J. Connell, N. L. Dietz Rago, Z. Zhang and C. Liao, Journal of The Electrochemical Society, 2020, 167, 070533. [2] C. Liao, eTransportation, 2020, 5, 100068. [3] J. Yang, I. Shkrob, Q. Liu, N. L. Dietz Rago, Y. Liu, K. Liu, Z. Zhang and C. Liao, Journal of Power Sources, 2019, 438, 227039. [4] I. A. Shkrob, B. Han, R. Sahore, A. P. Tornheim, L. Zhang, D. P. Abraham, F. Dogan, Z. Zhang and C. Liao, Chemistry of Materials, 2019, 31, 2459-2468.