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Multi-layer coating of electrodes with different material compositions helps unlock the full potential of high-loaded electrodes. Within this work, LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes with an areal capacity of >8.5 mA h cm−2 and tuned binder concentrations were fabricated by using an industrially relevant roll-to-roll process. Rate capability tests revealed an increase in practical specific discharge capacity independent from the C-rate for cathodes with reduced binder concentration in the top layer. At high current densities (C-rate of 1C) an improved performance of up to 27% was achieved. Additionally, at lower C-rates, binder gradients perpendicular to the current collector have beneficial effects on thick electrodes. However, surface analysis and electrochemical impedance spectroscopy revealed that without an adequate connection between the active material particles through a carbon-binder domain, charge transfer resistance limits cycling performance at high current densities.

Coating conducting polymers onto active cathode materials has been proven to mitigate issues at high current densities stemming from the limited conducting abilities of the metal-oxides. In the present study, a carbon coating was applied onto nickel-rich NMC622 via polymerisation of furfuryl alcohol, followed by calcination, for the first time. The formation of a uniform amorphous carbon layer was observed with scanning- and transmission-electron microscopy (SEM and TEM) and X-ray photoelectron spectroscopy (XPS). The stability of the coated active material was confirmed and the electrochemical behaviour as well as the cycling stability was evaluated. The impact of the heat treatment on the electrochemical performance was studied systematically and was shown to improve cycling and high current performance alike. In-depth investigations of polymer coated samples show that the improved performance can be correlated with the calcination temperatures. In particular, a heat treatment at 400 °C leads to enhanced reversibility and capacity retention even after 400 cycles. At 10C, the discharge capacity for carbon coated NMC increases by nearly 50% compared to uncoated samples. This study clearly shows for the first time the synergetic effects of a furfuryl polymer coating and subsequent calcination leading to improved electrochemical performance of nickel-rich NMC622.

The chemical diffusion coefficient in LiNi1/3Mn1/3Co1/3O2 was determined via the galvanostatic intermittent titration technique in the voltage range 3 to 4.2 V. Calculated diffusion coefficients in these layered oxide cathodes during charging and discharging reach a minimum at the open-circuit voltage of 3.8 V and 3.7 V vs. Li/Li+, respectively. The observed minima of the chemical diffusion coefficients indicate a phase transition in this voltage range. The unit cell parameters of LiNi1/3Mn1/3Co1/3O2 cathodes were determined at different lithiation states using ex situ crystallographic analysis. It was shown that the unit cell parameter variation correlates well with the observed values for chemical diffusion in NMC cathodes; with a notable change in absolute values in the same voltage range. We relate the observed variation in unit cell parameters to the nickel conversion into the trivalent state, which is Jahn-Teller active, and to the re-arrangement of lithium ions and vacancies., Graphical Abstract

The end-of-life event of the battery system of an electric vehicle is defined by a fixed end-of-life threshold value. However, this kind of end-of-life threshold does not capture the application and battery characteristics and, consequently, it has a low accuracy in describing the real end-of-life event. This paper proposes a systematic methodology to determine the end-of-life threshold that describes accurately the end-of-life event. The proposed methodology can be divided into three phases. In the first phase, the health indicators that represent the aging behavior of the battery are defined. In the second phase, the application specifications and battery characteristics are evaluated to generate the end-of-life criteria. Finally, in the third phase, the simulation environment used to calculate the end-of-life threshold is designed. In this third phase, the electric-thermal behavior of the battery at different aging conditions is simulated using an electro-thermal equivalent circuit model. The proposed methodology is applied to a high-energy electric vehicle application and to a high-power electric vehicle application. The stated hypotheses and the calculated end-of-life threshold of the high-energy application are empirically validated. The study shows that commonly assumed 80 or 70% EOL thresholds could lead to mayor under or over lifespan estimations. The iModBatt project has received funding from the European Union’s Horizon 2020 Programme for research and innovation under Grant Agreement No. 770054.

The paper reports the investigations performed in the course of the ESA TRP activity (Contract No. 4000123997/18/NL/HK) on the use of solid polymer electrolytes for safe lithium ion batteries for clean space. The objective is to develop 1Ah prototype pouch cells without using any volatile liquid component. The exchange of conventional, highly flammable electrolytes with solid Li+-conducting polymers significantly improves the electrochemical and thermal stability range of the battery cells. Thereby fragmentation events, and thus propagation of space debris, caused by battery malfunction can be mitigated. In the presented work, filled polymer electrolytes were investigated for potential use in all-solid-state lithium-ion batteries. The polyethylene oxide-based polymer phase was either mixed with a lithium-ion conducting glass-ceramic (active) or BaTiO 3 (passive) filler resulting in self-sustaining solid electrolyte membranes. Furthermore, carbon anodes and NMC622 cathodes were optimized to enable the assembly of full cells with enhanced safety properties.

Tin (IV) sulfide is a promising anode active material for lithium ion batteries due to its relatively high reversible capacity of 644 mAh/g, which is more than one and a half times that of graphite. During lithiation of tin (IV) sulfide, an inert Li2S matrix is formed in the first discharge cycle, which serves to accommodate the mechanical stresses associated with the volume expansion of tin during the successive LixSn alloying and de-alloying reactions. In order to improve the electrochemical performance of tin (IV) sulfide further, fundamental understanding and insights into the thermodynamics, phase formation, and driving forces for the lithiation reactions are still required. Therefore, in this work, a computational thermodynamics approach was combined with ex-situ XRD investigations of electrodes during the discharge reaction as well as galvanostatic intermittent titration technique (GITT) experiments in order to clarify the lithiation thermodynamics of tin (IV) sulfide. Based on the experimental data, a one-phase mechanism was suggested for the intercalation of lithium into SnS2, a thermodynamic model was developed to describe the intercalation reaction and the expected open circuit voltages were calculated.

Due to its theoretical capacity of 960 mAh/g, which is approximately two and a half times that of graphite (372 mAh/g), as well as its natural abundance, Sn is as an interesting anode active material to replace the currently used graphite in lithium ion batteries. However, Sn-based anodes have not been commercialized because they suffer from prohibitively large volume expansions due to the formation of brittle LixSn alloys during lithiation (>185 % for full lithiation to Li17Sn4). These volume changes lead to extensive crack formation, loss of electrical contact between particles, pulverization of the electrode during cycling, lithium trapping, and the growth of an unstable SEI. One way to take advantage of the high capacity of Sn and simultaneously overcome its degradation mechanisms is to use Sn-based chalcogenide compounds such as SnS2 and SnS as anode active materials. During lithiation of these compounds, a composite electrode structure consisting of active Sn particles embedded in an inactive Li2S buffer matrix is formed, which is expected to accommodate the mechanical stress of the alloying and de-alloying reactions during cycling. Although several authors have studied the lithiation of SnS2 via in-situ electron microscopy techniques, there are still many open questions regarding 1) the amount of lithium which can be intercalated into the layered structure of SnS2, 2) the structural changes of SnS2 during lithiation, and 3) if the reaction occurs via a one-phase or a two-phase process. Additionally, there are no published phase diagrams of the Li–Sn–S system at room temperature, which could be used to explore the changes in the electrode constitution during lithiation and de-lithiation. In fact, only Hwang et al. [1] modelled the phase equilibria in the Li–Sn–S at 0 K using density functional theory (DFT) calculations, but their data are incomplete since they omitted the Sn2S3, Li7Sn3 and Li5Sn2 phases and did not take into account the electrochemically and chemically observed solubility of lithium in SnS2. Therefore, in this work, the CALPHAD (CALculation of PHAse Diagrams) and computational thermodynamics methods were combined with key experiments to 1) understand the electrochemical lithiation of SnS2, 2) model the phase development during the equilibrium and non-equilibrium lithiation of the SnxSy tin sulfide compounds, and 3) evaluate the energetics of the competing lithiation reactions for the first time. Firstly, a thermodynamic description for the ternary Li–Sn–S system was developed by combining the descriptions of the Li–Sn system from Reichmann et al. [2] with that for the Sn–S system from Lindwall et al. [3] and the Gibbs free energy function for Li2S from the Scientific Group Thermodata Europe (SGTE) [4]. The ternary database was used to calculate the Li–Sn–S phase diagram at room temperature and simulate the titration curves for the equilibrium lithiation of the tin sulfide compounds. At the same time, homogeneous and heterogeneous Sn–S powder samples were processed as slurries, coated onto copper-foil substrates and subjected to electrochemical testing vs Li+/Li. The galvanostatic intermittent titration technique was used to characterize the quasi-equilibrium open circuit potentials of the electrodes during full and partial de-/lithiation in the potential range of 0.01-2.5 V. Additionally, a full profile, Rietveld refinement of the ex-situ XRD patterns of selected electrodes was performed in order to assess the phase development and structural changes of the electrode active materials during titration. These data were used to suggest a one-phase mechanism for the equilibrium lithiation of SnS2 after voltage relaxation. Finally, the electrochemical and crystallographic data were used to develop a new thermodynamic model to describe the intercalation of lithium ions into the layered SnS2 structure and calculate the measured open circuit voltage values. Using this description, it could be shown that lithiated SnS2 is indeed a metastable phase, which forms due to the energetic feasibility of the intercalation mechanism compared to the equilibrium conversion reaction. References [1] S. Hwang, et al., ACS Nano, 12, (2018), 3638-3645. [2] T.L Reichmann, D.J. Li, D.M. Cupid, Phys. Chem. Chem. Phys. 20 (2018), 22856-22866 [3] G. Lindwall, S.L. Shang, N.R. Kelly, T. Anderson, Z.K. Liu, Solar Energy (2016) 314-323 [4] SGTE Substance Database SGSUB, Version 4, 2008