The original version of this article contained errors in Figure 3a and Figure 3f. In Figure 3a, the activation energies (Ea) were calculated using a log scale instead of a logarithm ln scale. In Figure 3f, the y-axis interval was not properly selected. The correct y-axis interval in Figure 3f and the numerical values of the activation energy are now provided in Figure 3a and the main text. These errors have been corrected in the HTML and PDF versions of the article.

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Conformal coating of silicon (Si) anode particles is a common strategy for improving their mechanical integrity, to mitigate battery capacity fading due to particle volume expansion, which can result in particle crumbling due to lithiation induced strain and excessive solid-electrolyte interface formation. Here, we use operando transmission electron microscopy in an open cell to show that TiO2 coatings on Si/SiO2 particles undergo thickness dependent rupture on battery cycling where thicker coatings crumble more readily than thinner (∼5 nm) coatings, which corroborates the difference in their capacities.

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A key challenge for solid-state-batteries development is to design electrode-electrolyte interfaces that combine (electro)chemical and mechanical stability with facile Li-ion transport. However, while the solid-electrolyte/electrode interfacial area should be maximized to facilitate the transport of high electrical currents on the one hand, on the other hand, this area should be minimized to reduce the parasitic interfacial reactions and promote the overall cell stability. To improve these aspects simultaneously, we report the use of an interfacial inorganic coating and the study of its impact on the local Li-ion transport over the grain boundaries. Via exchange-NMR measurements, we quantify the equilibrium between the various phases present at the interface between an S-based positive electrode and an inorganic solid-electrolyte. We also demonstrate the beneficial effect of the LiI coating on the all-solid-state cell performances, which leads to efficient sulfur activation and prevention of solid-electrolyte decomposition. Finally, we report 200 cycles with a stable capacity of around 600 mAh g⁻¹ at 0.264 mA cm⁻² for a full lab-scale cell comprising of LiI-coated Li₂S-based cathode, Li-In alloy anode and Li₆PS₅Cl solid electrolyte.

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Batteries gained a lot of attention due to a raising demand for energy storage, as required for renewable energy generation systems, portable electronics and transport applications. For the development of new battery materials understanding of fundamental processes is essential, which often relies on the development of new characterisation techniques and tools that enable to study the underlying electrochemical processes at the relevant length scales, i.e. from an atomistic to a macroscopic level. Future batteries should be able to store more energy (per unit mass and or volume) and should be safer. Battery material solutions to achieve this are in principle known, where this thesis focusses on: (1) Si being one of the most promising negative electrode based on its large Li storage capacity (ten times higher than current graphite) and (2) solid electrolytes, replacing liquid electrolytes, which would practically annihilate safety concerns of Li batteries. However, for these new battery materials the challenge is to achieve a long cycle life by slowing down, or even preventing degradation reactions at the interfaces between the electrode and the electrolyte. This is the binding theme, and the topic of the main research questions of this thesis are thus: What are these degradation mechanisms and what is the impact of strategies to prevent it and achieve a long cycle life. The focus in this thesis is on Si negative electrodes in combination with liquid electrolytes in general, and for solid electrolytes in particular@en

All-solid-state Li-ion batteries promise safer electrochemical energy storage with larger volumetric and gravimetric energy densities. A major concern is the limited electrochemical stability of solid electrolytes and related detrimental electrochemical reactions, especially because of our restricted understanding. Here we demonstrate for the argyrodite-, garnet- and NASICON-type solid electrolytes that the favourable decomposition pathway is indirect rather than direct, via (de)lithiated states of the solid electrolyte, into the thermodynamically stable decomposition products. The consequence is that the electrochemical stability window of the solid electrolyte is notably larger than predicted for direct decomposition, rationalizing the observed stability window. The observed argyrodite metastable (de)lithiated solid electrolyte phases contribute to the (ir)reversible cycling capacity of all-solid-state batteries, in addition to the contribution of the decomposition products, comprehensively explaining solid electrolyte redox activity. The fundamental nature of the proposed mechanism suggests this is a key aspect for solid electrolytes in general, guiding interface and material design for all-solid-state batteries.

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With operando transmission electron microscopy visualizing the solid-solid electrode-electrolyte interface of silicon active particles and lithium oxide solid electrolyte as a model system, we show that (de)lithiation (battery cycling) does not require all particles to be in direct contact with electrolytes across length scales of a few hundred nanometers. A facile lithium redistribution that occurs between interconnected active particles indicates that lithium does not necessarily become isolated in individual particles due to loss of a direct contact. Our results have implications for the design of all-solid-state battery electrodes with improved capacity retention and cyclability. ©

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