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

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.

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.

This work probes the slurry architecture of a high silicon content electrode slurry with and without low molecular weight polymeric dispersants as a function of shear rate to mimic electrode casting conditions for poly(acrylic acid) (PAA) and lithium neutralized poly(acrylic acid) (LiPAA) based electrodes. Rheology coupled ultra-small angle neutron scattering (rheo-USANS) was used to examine the aggregation and agglomeration behavior of each slurry as well as the overall shape of the aggregates. The addition of dispersant has opposing effects on slurries made with PAA or LiPAA binder. With a dispersant, there are fewer aggregates and agglomerates in the PAA based silicon slurries, while LiPAA based silicon slurries become orders of magnitude more aggregated and agglomerated at all shear rates. The reorganization of the PAA and LiPAA binder in the presence of dispersant leads to a more homogeneous slurry and a more heterogeneous slurry, respectively. This reorganization ripples through to the cast electrode architecture and is reflected in the electrochemical cycling of these electrodes.

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.

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 ...

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.

Owing to their high specific capacity and suitably low operating potential, silicon-based anodes are an attractive alternative to graphite in next-generation lithium-ion batteries. However, silicon anodes suffer from low initial coulombic efficiency and fast capacity decay, limiting their widespread application. Pre-lithiation strategies are highly appealing to compensate for irreversible active lithium loss and to boost the cell energy density. In this work, we maximize the cell energy density by direct pre-lithiation of the NMC (LiNi0.5Mn0.3Co0.2O2) cathode to Li1+xNMCO2 without introducing inactive deadweight to either electrode. First, we demonstrate that Li1+xNMCO2 can be synthesized chemically, via reaction between NMC and lithium napthalide, and electrochemically. The NMC cathode is tolerant of a one-time over-lithiation up to 60 mA h gNMC−1, giving capacity retention on par with untreated NMC in half cell electrochemical cycling. Using synchrotron X-ray absorption spectroscopy (ex situ) and diffraction (in situ), we demonstrate that higher amounts of over-lithiation lead to local structure distortion – driven by transition metal reduction to Jahn–Teller active Mn3+ and Co2+ – as well as bulk structural hysteresis during over-lithiation and layer “buckling” that increases the amount of lithium extracted from the structure in the charged state. The Li1+xNMCO2 with low-to-moderate over-lithiation capacity (23, 46, and 70 mA h gNMC−1) is proven to be a highly effective dual-purpose lithium source and cathode material in full cell tests with a commercially relevant Si–graphite anode. These cells show higher capacity, superior cycle life, and improved coulombic efficiencies when compared to those with stoichiometric NMC cathodes. This study introduces a new and simple method to pre-lithiate layered transition metal oxide cathodes, opening up new possibilities for the development of high energy density lithium-ion batteries with next-generation anodes.

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.

We investigated the effect of the Si/graphite weight ratio in half-cells on the solid electrolyte interphase (SEI) layer's chemistry. The nominal concentrations of active materials were (wt % Si/wt % Gr) 15/73, 30/58, 60/28, and 80/0. The electrolyte in the cells consisted of either 1.2 M LiPF

Extreme fast charging (XFC) is a key requirement for the adoption of battery-based electric vehicles by the transportation sector. However, XFC has been shown to accelerate degradation, causing the capacity, life, and safety of batteries to deteriorate. We tested cells containing five positive electrode chemistries, LFP (olivine structure), LMO (spinel), LCO (layered), NMC811 (layered) and NCA (layered), using fast-charging protocols. After testing, the negative electrodes from cells containing positive electrodes crystallizing with a layered structure were found to have more lithium deposited on their surfaces. Those crystallizing with a layered structure also tended to have a larger increase in impedance than those crystallizing with a spinel or olivine structure. Characterization of the negative electrodes by X-ray photoelectron spectroscopy showed that using the concentrations of LiF and LixPOyFz as metrics, the concentration of LiF in the SEI from the cell with different positive electrodes is LFP > LMO > LCO ∼ NMC811 > NCA; and for LixPOyFz, the order is LMO > LFP > NCA > NMC811 > LCO. Clearly, the positive-electrode material was influencing the amounts of these materials formed.

Porous electrodes for Li-ion batteries are composed of energy storing active material particles, carbon-binder networks, and electrolyte filled pores 1. The carbon-binder networks improve the electronic conduction through the porous electrode, and are expected to improve electrode performance at finite currents. Accordingly, the porous electrode designs treat carbon-binder networks as a positive influence. In this talk, by using systematic experiments of electrochemical performance for different electrode compositions, we will show that the carbon-binder networks also exhibit negative effects 2. These negative effects deteriorate performance by decreasing the area available for intercalation reaction as well as increasing the resistance to ion transport. These effects are prominent for electrodes even with low carbon-binder content, e.g., 5%wt (of dry electrode). We will discuss the implications of these results in the context of predicting porous electrode performance 3, and in turn, designing these electrodes for different operations. Liu et al. (2012) Particles and Polymer Binder Interaction: A Controlling Factor in Lithium-ion Electrode Performance, J. Electrochem. Soc. 159(3), pp. A214-A221, https://doi.org/10.1149/2.024203jes Mistry et al. (2021) Quantifying Negative Effects of Carbon-binder Networks from Electrochemical Performance of Porous Li-ion Electrodes, J. Electrochem. Soc. 168(7), 070536, https://doi.org/10.1149/1945-7111/ac1033 Doyle, Fuller & Newman (1993) Modeling of Galvanostatic Charge and Discharge of Lithium/Polymer/Insertion Cell, J. Electrochem. Soc. 140(6), pp. 1526-1533, https://doi.org/10.1149/1.2221597 Figure 1

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.

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

Replacing traditional graphite anode by Si anode can greatly improve the energy density of lithium-ion batteries. However, the large volume expansion and the formation of highly reactive lithium silicides during charging cause the continuous lithium and electrolyte consumption as well as the fast decay of Si anodes. In this work, by adding 0.1 M M(TFSI)x (M = Mg, Zn, Al and Ca) as a second salt into the electrolyte, we stabilize the anode chemistry through the in situ formation of Li–M–Si ternary phases during the charging process. First, lithium silicides and magnesium lithium silicides were synthesized as model compounds to investigate the influence of metal doping on the reactivity of lithiated Si. Using solid-state nuclear magnetic resonance spectroscopy, we show that Mg doping can dramatically suppress the chemical reactions between the lithium silicide compounds and common electrolyte solvents. New mixed salt electrolytes were prepared containing M(TFSI)x as a second salt to LiPF6 and tested in comm...

Ni-rich LiNi1–x–yMnxCoyO2 (NMC) cathode materials are being aggressively developed for high-voltage applications such as electric vehicles. These materials are desirable because of their high volum...

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.

Li-ion battery electrode electronic properties, including bulk conductivity and contact resistance, are critical parameters affecting cell performance and fast-charge capability. Contact resistance between the coating and current collector is often the largest electronic resistance in an electrode and is affected by chemical, microstructural, and interfacial variations. Direct measurements of contact resistance and bulk conductivity have proven to be challenging. In their absence, a mechanical electrode peel test is often used to compare adhesion and electrical contact resistance. However, using a micro-flexible-surface probe, contact resistance can be directly determined. This work compares contact resistance and mechanical peel strength of multiple commercial-grade HE5050 and NCM523 cathodes and graphite and silicon anodes. It was found that peel strength correlates well with contact resistance in a carefully curated data set (p < 0.05) and in some situations may be a good metric to estimate electrical properties. However, there were distinct outliers in the data set, indicating that peel strength may not accurately reflect electrical properties when there is significant variation in electrode composition. These results illustrate the value of the micro-flexible-surface probe in quantifying contact resistance and bulk conductivity to better understand how battery composition and processing steps affect microstructure and resulting cell performance.

Unstable electrode/electrolyte interface is the major cause of degradation for silicon (Si)-based anodes for lithium (Li)-ion batteries. Development of functional electrolyte additives can provide a viable path toward stabilizing the dynamic Si/electrolyte interface, which will benefit the development of high energy density Li-ion batteries. Here, we evaluate polymerizable electrolyte additives with varying functional groups (fluorocarbon, thiophosphate, and fluorophosphazene). The additives are examined using LiNi0.6Mn0.2Co0.2O2/Si full cells where the cycle performance and impedance are measured. Electrochemical tests show that the fluorine-containing additives provide better passivation at the Si electrode, leading to enhanced full cell performance. Among the three additives examined, best electrochemical performance is observed from the fluorocarbon-containing compound, followed by fluorophosphazene- and thiophosphate-containing compounds. Characterization of the solid electrolyte interphase (SEI) on cycled electrodes using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) reveal that higher concentration of fluorine and lithium oxide, and lower concentration of carbonate and organic species correlate with enhanced electrochemical performance.

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.

Calculations and modeling have shown that replacing the traditional graphite anode with silicon can greatly improve the energy density of lithium-ion batteries. However, the large volume change of silicon particles and high reactivity of lithiated silicon when in contact with the electrolyte lead to rapid capacity fading during charging/discharging processes. In this report, we use specific lithium silicides (LS) as model compounds to systematically study the reaction between lithiated Si and different electrolyte solvents, which provides a powerful platform to deconvolute and evaluate the degradation of various organic solvents in contact with the active lithiated Si-electrode surface after lithiation. Nuclear Magnetic Resonance (NMR) characterization results show that a cyclic carbonate such as ethylene carbonate is chemically less stable than a linear carbonate such as ethylmethyl carbonate, fluoroethylene carbonate, and triglyme as they are found to be more stable when mixed with LS model compounds. Guided by the experimental results, two ethylene carbonate (EC)-free electrolytes are studied, and the electrochemical results show improvements with graphite-free Si electrodes relative to the traditional ethylene-carbonate-based electrolytes. More importantly, the study contributes to our understanding of the significant fundamental chemical and electrochemical stability differences between silicon and traditional graphite lithium-ion battery (LIB) anodes and suggests a focused development of electrolytes with specific chemical stability vs lithiated silicon which can passivate the surface more effectively.

The solid electrolyte interphase (SEI) layer on a silicon anode is investigated by SERS. Gold electrodeposition on a silicon electrode is confirmed by SEM, and Raman enhancement is proved, allowing determination of the partial composition of its SEI. For the first time, organophosphate-derivatives seem to be detected by Raman.

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.

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.

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.