Large-format Li-ion battery cells tend to exhibit spatial heterogeneity in terms of material degradation, which in extreme cases can contribute to the initiation and propagation of severe degradation mechanisms such as Li plating. Studying large cells poses a challenge in terms of sample statistics and effort required for an analysis which covers a large fraction of the electrode surface area. This necessitates high-throughput, quantitative techniques capable of increased surface coverage and in a time-efficient manner. In this study we present a novel method we refer to as “OLSA” (Open-circuit potential based Local State of health Assessment), that maps the local state of health (SoH) within the cell by measurement of local electrode potential combined with a fitting procedure to estimate states of charge and subsequently offsets in lithium inventory, which enables an estimation of SoH. The technique is validated and then demonstrated by mapping aged electrodes from large format prismatic cell. The results show heterogeneous distribution of local SoH and increased LLI in areas of Li plating. We also present image analysis as a complementary method for conveniently evaluating and quantifying visible degradation on the negative electrode with 100% surface coverage. In this work, we show that the regions of lithium plating coincide with lower local SoH and higher LLI. We find that although image analysis provides limited predictive capacity to predict SoH, it is a convenient and powerful tool to assist in understanding the root causes of heterogeneous degradation.

Polyacrylic acid (PAA) is here studied as a binder material for LiNi0.5Mn1.5O4 (LNMO) cathodes for lithium-ion batteries. When the LNMO electrodes are fabricated with an active mass loading of ∼10 mg cm−2 (∼1.5 mA h cm−2), poor discharge capacity and short cycle life is obtained in full-cells with graphite electrodes. The electrochemical results with PAA are compared with a commonly used water-based binder, sodium carboxymethyl cellulose (CMC), which shows better electrochemical performance. The main cause for these problems in PAA based cells is identified to be the high internal resistance in the initial cycles, caused by factors such as contact resistance, inhomogeneous binder distribution and poor electrolyte wetting of the active material.

In this study, Synchrotron X-ray diffraction (XRD) radiography was utilized to investigate the ageing heterogeneity in 48 Ah prismatic lithium-ion cells with Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) as the positive electrode active material and graphite as the negative electrode active material after similar to 2800 cycles. The study revealed that the area closest to the positive electrode tab is most vulnerable to degradation, particularly impacting the NMC material. Application of principal component analysis allowed to differentiate and visualize part of positive electrode material that has a different degradation due to the lithium plating. A comparison of non-destructive X-ray diffraction-based methods and electrochemical characterization method which was performed on the opened cell has shown an importance of a complementary approach. Our results highlight the feasibility of employing non-destructive techniques to study large prismatic cells, thereby presenting extensive opportunities for advancements in battery research and industry.

Advances in methodologies for real-time analysis of batteries have come a long way, especially with the development of Operando Electrochemical Mass Spectrometry (OEMS). These approaches allow for the determination of side reactions during battery cycling with unprecedented selectivity and sensitivity, providing vital information necessary for determination of lifetime-limiting processes. However, the work thus far has primarily been carried out on model battery systems, where cell atmospheres are largely altered (through open flow, closed cell, and intermittent sampling approaches) and operation conditions are therefore not comparable with real-life situations. Herein, the development and validation of an intermittently closed OEMS system adapted for readily available commercial batteries is showcased. We provide a detailed description of a unique analysis design for large-format PHEV2 cells, with subsequent pressure and gassing data. A qualitative analysis of the results shows that side reactions brought on by structural transitions within both electrodes can be clearly observed. Transitions causing large volume changes in graphite induce H2 and C2H4 as SEI reformation products while the c lattice collapse in NMC induces CO2 evolution (through O2 release). OEMS can therefore be used for the quick and effective study of commercially available rechargeable batteries without influencing the internal battery chemistry.

Lithium ion batteries (LIB) have become a cornerstone of the shift to electric transportation. In an attempt to decrease the production load and prolong battery life, understanding different degradation mechanisms in state-of-the-art LIBs is essential. Here, we analyze how operational temperature and state-of-charge (SoC) range in cycling influence the ageing of automotive grade 21700 batteries, extracted from a Tesla 3 Long Range 2018 battery pack with positive electrode containing LiNixCoyAlzO2 (NCA) and negative electrode containing SiOx-C. In the given study we use a combination of electrochemical and material analysis to understand degradation sources in the cell. Herein we show that loss of lithium inventory is the main degradation mode in the cells, with loss of material on the negative electrode as there is a significant contributor when cycled in the low SoC range. Degradation of NCA dominates at elevated temperatures with combination of cycling to high SoC (beyond 50%).

Conditions such as the temperature and pressure experienced by lithium-ion battery components are dependent on cell geometry and can vary widely within a large cell. The resulting uneven degradation is challenging to study at the full cell level but can be revealed upon disassembly and post mortem analysis. In this work, we report localized lithium plating in automotive-grade, prismatic lithium-ion cells, also under cycling conditions generally considered to be mild (e.g., 5-65 %SOC, 23 degrees C, 0.5C cycle rate). Dead lithium content is quantified using 7Li nuclear magnetic resonance spectroscopy in both electrode and separator samples, corresponding to substantial capacity fade (26-46%) of the full cells. Severe lithium plating is typically initiated in regions near the positive tab, in which both the separators and negative electrodes are ultimately deactivated. High pressure arises during cycling, and we propose a deactivation mechanism based on high local stress due to electrode expansion and external constraint. Further, we develop a model to demonstrate that component deactivation can result in lithium plating even under mild cycling conditions. Notably, components harvested from regions with no detected lithium plating maintained adequate electrochemical performance.

The galvanostatic intermittent titration technique (GITT) is considered the go-to method for determining the Li+ diffusion coefficients in insertion electrode materials. However, GITT-based methods are either time-consuming, prone to analysis pitfalls or require sophisticated interpretation models. Here, we propose the intermittent current interruption (ICI) method as a reliable, accurate and faster alternative to GITT-based methods. Using Fick's laws, we prove that the ICI method renders the same information as the GITT within a certain duration of time since the current interruption. Via experimental measurements, we also demonstrate that the results from ICI and GITT methods match where the assumption of semi-infinite diffusion applies. Moreover, the benefit of the non-disruptive ICI method to operando materials characterization is exhibited by correlating the continuously monitored diffusion coefficient of Li+ in a LiNi0.8Mn0.1Co0.1O2-based electrode to its structural changes captured by operando X-ray diffraction measurements.

LixNi0.90Co0.05Al0.05O2 (NCA) extracted from an automotive battery cell is studied using a combination of in-house operando techniques to understand the correlation between gas evolution and structural collapse when NCA is cycled to high potentials in a lithium-ion battery configuration. The operando techniques comprise X-ray diffraction (XRD) and online electrochemical mass spectrometry (OEMS), and cycled using intermittent current interruption (ICI). The ICI cycling protocol is used to assess the dynamic change in resistance as well as to provide a validation of the operando setups. Both gas evolution and structural collapse have previously been observed as degradation mechanisms of Ni-rich electrodes including NCA, however, their causal link is still under debate. Here our presented results show a correlation between the decrease of the interlayer distance in NCA with both an increase in CO(2 )evolution and diffusion resistance above 4.1 V. Additionally, particle cracking, which is a mechanism often correlated with gas evolution, was found to be reversible and visible before gas evolution and Li diffusion resistance increase. The ICI technique is shown to be useful for the correlation of operando experiments on parallel setups and evaluation of mass transport dependent processes.

In the search for high-energy density Li-ion battery electrode materials which are also comparatively sustainanble, LiNi0.5Mn1.5O4 (LNMO) is often targeted as a promising next-generation alternative. While the capacity of LNMO is limited, it has a high operating voltage around 4.7 V vs. Li+/Li, and the spinel structure of the materials renders useful power capacilities. Moreover, it is a cobalt-free cathode. However, fabricating functional electrodes have shown problematic due to inherent instabilities at both bulk and surfaces, where especially operation at elevated temperatures has shown to cause capacity degradation. Problems comprise structural changes, loss of oxygen, and Mn dissolution, often interconnected with each other. One strategy to improve stabilization would be through coatings of the LNMO particles, either inorganic or organic. The polymer binder used for battery processing is inherently an organic coating layer, since it wraps around the particles of the electrodes. Thereby, binders has been shown to being able to add functionalities to electrode materials, e.g. to improve electronic conductivity, add storage capacity or mitigate side-reactions. The binder is at interplay with the reactions causing interphase layer formation. Thereby, changing or taioring the binder can cause direct improvements in cell performance. Poly(vinylidene difluoride) (PVdF) and its many derviates is since long time the standard for Li-ion battery electrodes, despite not being particular sustainable and being dependent on toxic solvents such as N-methyl-2-pyrrolidone (NMP). LNMO is, in this context, no exception. Nevertheless, while PVdF is chemically intert, it provides little other capabilities to the battery electrodes, and other binder systems could improve in this context: either through electochemica performance or through being more sustainable. Here, two other binder systems for LNMO are discussed: polyacrylonitrile (PAN) and polyacrylic acid (PAA). Polynitriles are often promoted as being comparatively stable at higher potentials, while also being ionically conductive, and should therefore in principle add functionalities into the resulting electrodes. PAA, on the other hand, has shown good adhesion and adherence to oxide surfaces, and can thereby form more robust interfacial layers on the cathode. We show here, however, that challenges remain for these alternative binder systems, not least due to the high operating potential of LNMO electrodes which cause side-reactions of both types of alternative binders. These side-reactions are their products are analyzed through a range of methods, e.g. photoelectron spectroscopy, electron microscopy and electroanalytical techniques, thereby providing guidance to the development of novel binders for high-voltage electrodes.

This is the dataset of electrochemical and operando X-ray diffraction experiments for our publication "Rapid determination of solid-state diffusion coefficients in Li-based batteries via intermittent current interruption method". This archive contains the raw data and scripts written in R used in the analysis and presentation of the results in this manuscript. Abstract of the manuscript: The galvanostatic intermittent titration technique (GITT) is considered the go-to method for determining the Li+diffusion coefficients in insertion electrode materials. However, GITT-based methods are either time-consuming, prone to analysis pitfalls or require sophisticated interpretation models. Here, we propose the intermittent current interruption (ICI) method as a reliable, accurate and faster alternative to GITT-based methods. Using Fick’s laws, we prove that the ICI method renders the same information as the GITT within a certain duration of time since the current interruption. Via experimental measurements, we also demonstrate that the results from ICI and GITT methods match where the assumption of semi-infinite diffusion applies. Moreover, the benefit of the non-disruptive ICI method to operando materials characterization is exhibited by correlating the continuously monitored diffusion coefficient of Li+ in a LiNi0.8Mn0.1Co0.1O2-based electrode to its structural changes captured by operando X-ray diffraction measurements.

In the field of lithium-based batteries, there is often a substantial divide between academic research and industrial market needs. This is in part driven by a lack of peer-reviewed publications from industry. Here we present a non-academic view on applied research in lithium-based batteries to sharpen the focus and help bridge the gap between academic and industrial research. We focus our discussion on key metrics and challenges to be considered when developing new technologies in this industry. We also explore the need to consider various performance aspects in unison when developing a new material/technology. Moreover, we also investigate the suitability of supply chains, sustainability of materials and the impact on system-level cost as factors that need to be accounted for when working on new technologies. With these considerations in mind, we then assess the latest developments in the lithium-based battery industry, providing our views on the challenges and prospects of various technologies.

An ethylene carbonate-free electrolyte composed of 1 M lithium bis(fluorosulfonyl) imide (LiFSI) in sulfolane (SL) is studied here for LiNi0.5Mn1.5O4-graphite full-cells. An important focus on the evaluation of the anodic stability of the SL electrolyte and the passivation layers formed on LiNi0.5Mn1.5O4 (LNMO) and graphite is being analysed along with intermittent current interruption (ICI) technique to observe the resistance while cycling. The results show that the sulfolane electrolyte shows more degradation at higher potentials unlike previous reports which suggested higher oxidative stability. However, the passivation layers formed due to this electrolyte degradation prevents further degradation. The resistance measurements show that major resistance arises from the cathode. The pressure evolution during the formation cycles suggests that there is lower gas evolution with sulfolane electrolyte than in the conventional electrolyte. The study opens a new outlook on the sulfolane based electrolyte especially on its oxidative/anodic stability.

The complex reaction mechanism of the lithium-sulfur battery system consists of repetitive dissolution and precipitation of the sulfur-containing species in the positive electrode. In particular, the precipitation of lithium sulfide (Li2S) during discharge has been considered a crucial factor for obtaining a high degree of active material utilization. Here, the influence of electrolyte amount, electrode thickness, applied current, and electrolyte salt on the formation of Li2S is systematically investigated in a series of operando X-ray diffraction experiments. Through a combination of simultaneous diffraction and resistance measurements, the evolution of Li2S is directly correlated to the variation in internal resistance and transport properties inside the positive electrode. The correlation indicates that at different stages the Li2S precipitation both facilitates and impedes the discharge process. This information about the kinetics of Li2S formation offers mechanistic explanations for the strong impact of different electrochemical cell parameters on the cell performance and, thus, directions for holistic optimizations to achieve high sulfur utilization.

Binders are electrochemically inactive components that have a crucial impact on battery aging although being present in only small amounts, typically 1-3% w/w in commercial products. The electrochemical performance of a battery can be tailored via these inactive materials by optimizing the electrode integrity and surface chemistry. Polyacrylonitrile (PAN) for LiNi0.5Mn1.5O4 (LNMO) half-cells is here investigated as a binder material to enable a stable electrode-electrolyte interface. Despite being previously described in the literature as an oxidatively stable polymer, it is shown that PAN degrades and develops resistive layers within the LNMO cathode. We demonstrate continuous internal resistance increase in LNMO-based cells during battery operation using the intermittent current interruption (ICI) technique. Through a combination of on-line electrochemical mass spectrometry (OEMS) and X-ray photoelectron spectroscopy (XPS) characterization techniques, the degradation products can be identified as solid on the LNMO electrode surface, and no excessive gas formation is seen. The increased resistance and parasitic processes are correlated to side-reactions of the PAN, possibly intramolecular cyclization, which can be identified as the main cause of the comparatively fast capacity fade.

The energy density and lifetime of lithium-ion cells for automotive applications have both substantially improved in recent years. This enables electric vehicles in both the consumer and commercial sectors that have greater range, better reliability, and longer service lives [1]. These factors all contribute to the widespread adoption of electric vehicles. However, inhomogeneities exist within cells that contribute to uneven internal degradation and, when severe, can trigger rapid failure. These inhomogeneities can be related to manufacturing tolerances or distributions of component parameters [2], as well as gradients in internal or external conditions. As such, the reality of heterogeneous aging is a complex, multivariate problem to solve. In this latest work, we cycle automotive-grade prismatic cells for several thousand cycles (until 10-30 % capacity fade) and harvest components for post mortem aging characterization and experimental parameter identification. The constituent electrodes are a Ni-rich layered oxide (approximately LiNi0.76Mn0.15Co0.09O2) and graphite. In addition to microscopy and electrochemical testing on harvested electrodes, we quantify local lithium plating on graphite with our recently developed method utilizing ex-situ, 7Li nuclear magnetic resonance spectroscopy [3]. We believe this to be the first report of spatially-resolved lithium plating quantification in commercial lithium-ion cells. Clear patterns emerge (see Figure 1), reflecting the geometry of the cell and showing reproducible heterogeneity that cannot be attributed solely to defects in manufacture. Several tests even confirm local lithium plating and unusually rapid degradation at comparatively mild cycle conditions (slow charge/discharge, low state-of-charge, and room temperature). The wound jellyroll design in contemporary prismatic cells enables very high packing efficiency and energy density, but includes inherently weak points from where lithium plating and internal stresses [4] can propagate. In some cases, cells achieve satisfactory lifetimes without accelerated aging. In others, heterogeneities cause extreme local degradation that triggers end-of-life even though other regions may remain relatively intact. We explore the causes of these patterns and question how such damage can occur, even under cycling conditions usually considered safe. References [1] P. Svens et al., IEEE Trans. Transp. Electrif., (2022), doi:10.1109/TTE.2022.3158838. [2] D. Beck et al., Energies, 14 (2022), 3276, doi:10.3390/en14113276. [3] Y. Fang et al., manuscript submitted, (2022). [4] P. Gupta and P. Gudmundson, J. Power Sources, 511 (2021), 230465, doi:10.1016/j.jpowsour.2021.230465. Figure 1

While lithium-sulfur batteries theoretically have both high gravimetric specific energy and volumetric energy density, only its specific energy has been experimentally demonstrated to surpass that of the state-of-the-art lithium-ion systems at cell level. One major reason for the unrealized energy density is the low capacity density of the highly porous sulfur/carbon composite as the positive electrode. In this work, mechanical compression at elevated temperature is demonstrated to be an effective method to increase the capacity density of the electrode by at least 90 % and moreover extends its cycle life. Distinct impacts of compression on the resistance profiles of electrodes with different thickness are investigated by tortuosity factors derived from both electrochemical impedance spectroscopy, X-ray computed tomography and kinetic analysis based on operando X-ray diffraction. The results highlights the importance of a homogeneous electrode structure highlight lithium-sulfur system.

Sulfur electrodes for lithium-sulfur batteries necessarily contain a conductive additive, typically carbon, to enable the electrochemical reactions, since sulfur and the discharge product, Li2S, are insulators. Consequently, the full passivation of carbon, by deposition of sulfur and/or Li2S, would necessarily produce the death of the battery. However, here we demonstrate that for high-performance lithium-sulfur batteries operated under lean electrolyte conditions (electrolyte to sulfur ratio of 6 mu L mg(S)(-1) in Li-S coin cells), the extent of passivation of carbon is not severe enough to limit performance. This is shown by performing impedance measurements of fully charged lithium-sulfur batteries, from which we demonstrate that we can evaluate the specific surface area of carbon, and we find that the capacity fade with cycling is not due to a decrease in the electrochemically active surface area of carbon. These results show that introducing a higher surface area carbon in the sulfur electrode formulation is not needed to prevent passivation, and that the focus of lithium-sulfur development should be directed towards other issues, such as mitigating undesirable reactions at the lithium electrode and achieving robust sulfur electrode structures enabling fast transport of electrolyte species and, thus, more homogeneous reactions. (c) 2021 Elsevier Ltd. All rights reserved.

AbstractTwo water‐soluble binders of carboxymethyl cellulose (CMC) and sodium alginate (SA) have been studied in comparison with N‐methylpyrrolidone‐soluble poly(vinylidene difluoride–co‐hexafluoropropylene) (PVdF‐HFP) to understand their effect on the electrochemical performance of a high‐voltage lithium nickel manganese oxide (LNMO) cathode. The electrochemical performance has been investigated in full cells using a Li4Ti5O12 (LTO) anode. At room temperature, LNMO cathodes prepared with aqueous binders provided a similar electrochemical performance as those prepared with PVdF‐HFP. However, at 55 °C, the full cells containing LNMO with the aqueous binders showed higher cycling stability. The results are supported by intermittent current interruption resistance measurements, wherein the electrodes with SA showed lower resistance. The surface layer formed on the electrodes after cycling has been characterized by X‐ray photoelectron spectroscopy. The amount of transition metal dissolutions was comparable for all three cells. However, the amount of hydrogen fluoride (HF) content in the electrolyte cycled at 55 °C is lower in the cell with the SA binder. These results suggest that use of water‐soluble binders could provide a practical and more sustainable alternative to PVdF‐based binders for the fabrication of LNMO electrodes.

Ni-rich oxide cathode active materials are today key components in Li-ion batteries used for electric vehicles (EV). The high capacity of LiNi x Co y Mn z O 2 and LiNi x Co y Al z O 2 (NCA) with x≥0.6 has enabled a continued increase in energy density and decrease in cost at the pack level, enabling the rapid growth of the EV market in recent years. Despite a wide use, rather fast material ageing results in the batteries being a source of considerable environmental impact [1]. Various degradation sources are highlighted in the literature, these include transition metal dissolution, surface layer reconstruction, particle cracking, etc [2]. However, when extrapolating the knowledge from a model cell to a commercial battery the relevance and the degree of degradation impact can drastically change [3]. The importance of approaching real conditions is a key to a full understanding of the ageing processes occurring in commercial cells. In the given work, we analyse commercial state-of-art 2170 cylindrical cells. The cells were aged at various temperatures and state of charge windows, targeting divergent usage scenarios. The degradation processes were accessed with a wide range of analytical techniques applied to extracted electrodes (x-ray diffraction, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, cycling voltammetry, incremental capacity analysis, electrochemical impedance spectroscopy and intermittent current interruption). In the current work we show that depending on the operating conditions, influence of ageing sources varies. Additionally, ageing mapping within cell geometry is presented highlighting “hot spots” of the cell [4]. References [1] W. Liu et al., “Nickel-Rich Layered Lithium Transition-Metal Oxide for High-Energy Lithium-Ion Batteries,” Angew. Chemie Int. Ed., vol. 54, no. 15, pp. 4440–4457, Apr. 2015. [2] T. Li, X.-Z. Yuan, L. Zhang, D. Song, K. Shi, and C. Bock, Degradation Mechanisms and Mitigation Strategies of Nickel-Rich NMC-Based Lithium-Ion Batteries, vol. 2018, no. January 2017. Springer Singapore, 2019. [3] M. Lucu et al., “Data-driven nonparametric Li-ion battery ageing model aiming at learning from real operation data – Part A: Storage operation,” J. Energy Storage, vol. 30, p. 101409, Aug. 2020. [4] Mikheenkova et al., in manuscript .

A comprehensive description of electrochemical processes in the positive electrode of lithium-sulfur batteries is crucial for the utilization of active material. However, the discharge mechanisms are complicated due to various reactions in multiple phases and the tortuosity of the highly porous carbon matrix. In this work, simultaneous measurements of small-angle and wide-angle scattering and cell resistance are performed on operating lithium-sulfur cells. Results indicate that precipitates grow mostly in number, not in size, and that the structure of the carbon matrix is not affected. The comparison of the small-angle and wide-angle scattering reveals the amorphous discharge products found at a low discharge rate. Further analysis demonstrates the correlation between the diffusion resistance and the compositional change of electrolyte in the mesopores at the end of discharge, which suggests that Li-ion deficiency is the limiting factor for sulfur utilization at a medium discharge rate.