To realize the full potential of solid-state batteries, the use of high-capacity negative electrodes such as lithium metal or silicon is needed. Silicon represents a safer alternative to lithium metal due to its higher lithiation potential, reducing the risk of dendrite formation. Silicon is challenging to operate at industry-relevant areal capacities with high capacity retention because of its volume change upon de-/lithiation. Furthermore, the insufficient reductive stability of commonly used Li 6 PS 5 Cl electrolyte limits the electrode design to pure silicon electrodes with a 2D interface to the electrolyte, because the electrode-electrolyte surface area needs to be minimized. These 2D silicon electrodes typically require unrealistically high stack pressures of 50 MPa for reliable operation. 1-3 Hydroborate solid electrolytes present an attractive alternative since they combine many attractive characteristics such as high ionic conductivity, high thermal stability, soft mechanical properties, and non-toxicity. We recently showed that hydroborates are compatible with high-voltage LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) positive electrodes. 4 In this work, we demonstrate that the hydroborate electrolyte Li 3 (CB 11 H 12 ) 2 (CB 9 H 10 ) also offers excellent kinetic stability against reduction in contact with lithiated silicon. 5 This property enables stable cycling of 3D silicon composite electrodes, even when using nano-sized silicon particles and conductive carbon additives. The lithiated 3D silicon composite electrodes feature a low interface resistance growth rate of ~ 0.3 Ω cm 2 h −0.5 at room temperature, in contrast to the rapid interface resistance growth rate of ~ 10 Ω cm 2 h −0.5 observed for the Li 6 PS 5 Cl electrolyte. 1, 2 An excellent initial coulombic efficiency of 96% is reached in half-cells at 60 °C, at a high reversible capacity of 3100 mAh g Si −1 , corresponding to an areal capacity of 8.9 mAh cm −2 . Owing to its high room-temperature conductivity of 1.5 mS cm −1 and wide electrochemical stability window, Li 3 (CB 11 H 12 ) 2 (CB 9 H 10 ) further enables successful integration of the 3D silicon composite electrode with the previously reported composite NMC811 electrode in a zero-lithium-excess full cell with an areal capacity of 3 mAh cm −2 . This NMC811/silicon full cell achieves a remarkable capacity retention of 66% after 100 cycles and respectable rate capability of 2 mAh cm −2 at 1 mA cm −2 at room temperature and under 50 MPa stack pressure. Importantly, a capacity of 2.8 mAh cm −2 is retained under moderate stack pressure of 8 MPa, highlighting the benefits of the 3D composite electrode design. References: H. Huo, Y. Bai, S. L. Benz, T. Weintraut, S. Wang, A. Henss, D. Raabe and J. Janek, Advanced Materials , 2024, 37 , 2415006. H. Huo, M. Jiang, Y. Bai, S. Ahmed, K. Volz, H. Hartmann, A. Henss, C. V. Singh, D. Raabe and J. Janek, Nature Materials , 2024, 23 , 543-551. D. H. S. Tan, Y.-T. Chen, H. Yang, W. Bao, B. Sreenarayanan, J.-M. Doux, W. Li, B. Lu, S.-Y. Ham, B. Sayahpour, J. Scharf, E. A. Wu, G. Deysher, H. E. Han, H. J. Hah, H. Jeong, J. B. Lee, Z. Chen and Y. S. Meng, Science , 2021, 373 , 1494-1499. H. Braun, R. Asakura, A. Remhof and C. Battaglia, ACS Energy Letters , 2024, 9 , 707-714. H. Braun, C. Bürgel, E. Quérel, A. Remhof, C. Battaglia, under review.

The hydroborate electrolyte Li 3 (CB 11 H 12 ) 2 (CB 9 H 10 ) enables 3D silicon composite electrodes with exceptionally low interfacial resistance growth, unlocking room-temperature NMC811/silicon solid-state batteries operated under moderate stack pressure.

Dry coating of battery electrodes is a promising technology for reducing the environmental footprint and the cost of lithium-ion battery cell manufacturing. However, obtaining a homogeneous electrode microstructure without a solvent is a key challenge. Here, we demonstrate the potential of twin-screw extrusion as a solvent-free, continuous dry-mixing method enabling precise polytetrafluoroethylene (PTFE) fibrillation and carbon black dispersion during NMC electrode production. Through in-depth microstructural characterization, we reveal a strong correlation between the microstructure of the extrudates and the calendered electrodes, underscoring the crucial role of mixing in controlling microstructure. Electrochemical cycling of high-areal-capacity (5.9 mAh cm-2) dry-coated NMC622 electrodes paired with graphite in coin cells yields 150 mAh g-1 upon discharge at C/2 with 79% capacity retention after 500 cycles. Our results highlight the industrial potential of twin-screw extrusion for continuous dry coating of battery electrodes.

Alternative conductive additives for lithium-ion batteries, such as carbon nanotubes and graphene, are academically well-established with pursued industrial opportunities while carbon black represents the global standard. However, further advancements are necessary to improve battery performance beyond current industrial metrics. Herein, a mixed-dimensional carbon material is introduced, featuring a network of 1D multi-walled nanotubes with 2D sheetlets, synthesized through a cost-effective process separating methane - a potent greenhouse gas - into carbon and low carbon intensity hydrogen. With proper slurry mixing, this material forms an expansive 3D conductive network within the electrode, enhancing electrical transport and thermal conductivity compared to carbon black electrodes. With only one-third of the carbon content (1 wt%), the electrical conductivity of a LiNi0.5Mn0.3Co0.2O2 cathode is 13 times higher than a carbon black reference, increasing both energy density and rate performance. The thermal conductivity is further improved by 40% (through-plane) and 200% (in-plane), promoting better heat dissipation. This carbon network also effectively retains transition metals during electrochemical cycling, limiting their migration to the anode, and thus reducing overall impedance build-up. The excellent compatibility of this conductive additive with state-of-the-art nickel-rich (85% nickel) layered oxides is also demonstrated, where 11.5 Ah pouch cells display >88% capacity retention after 1000 cycles at C/3.

To harness all the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals makes them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quantitative information about the interphase chemical composition and rate of formation are challenging to obtain because the reaction occurs at a buried interface. In this study, a thin layer of Na metal (Na0) is plated on the surface of a SE of the NaSICON family (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside a commercial XPS system whilst continuously analysing the composition of the interphase operando. We identify the existence of an interphase at the Na0|NZSP interface, and more importantly, we demonstrate for the first time that this protocol can be used to study the kinetics of interphase formation. A second important outcome of this article is that the surface chemistry of NZSP samples can be tuned to improve their stability against Na0. It is demonstrated by XPS and time-resolved electrochemical impedance spectroscopy (EIS) that a native Na3PO4 layer present on the surface of as-sintered NZSP samples protects their surface against decomposition.

Dry coating of battery electrodes is emerging as a promising alternative technology to the prevailing slurry coating and drying process widely adopted in the lithium-ion battery industry. 1,2,3 To date, the most energy-intensive step in cell manufacturing is the drying of slurry-coated electrodes, 1 and the adoption of dry coating aims to reduce both the environmental impact and production costs associated with electrode production. Beyond environmental and economic concerns, producing higher mass-loading electrodes, a crucial aspect for increasing cell energy density, would be greatly facilitated with a dry-coating approach. Bühler and Empa have collaboratively developed and are in the process of scaling up a dry-coating manufacturing method. 4 Our process centers around the extrusion mixing of electrode components, followed by calendering of the dry mixture to produce a free standing electrode which is laminated onto a current collector. In this presentation, we showcase the adaptability of extrusion mixing in inducing the shear fibrillation of polytetrafluoroethylene (PTFE) binder, crucial for achieving the desired electrode microstructures (see Figure 1a and 1b). Furthermore, our dry-coating technology demonstrates the capability to produce high-mass loading electrodes with areal capacities of 5 mAh cm -2 or more (see Figure 1c). The presentation encompasses a thorough characterization of dry-coated electrodes, including their microstructure and electrochemical performance in lab-scale batteries. Key aspects, such as the impact of carbon black dispersion on the rate capability and capacity retention, are evaluated. A comprehensive comparison with slurry-coated electrodes, fabricated using identical active electrode materials, mass fractions, and mass loading, reveals that our dry-coated electrodes exhibit comparable performance to their slurry-coated counterparts. 5 The scalability of our dry-coating technology is underscored, highlighting the achievable throughputs necessary for gigafactory-scale production with a single extruder. References: 1 F. Degen, M. Schütte, Journal of Cleaner Production, 2022 , 330, 129798 2 B. Schumm, S. Kaskel, Next Energy, 2023 , 100009 3 Y. Lu, C.Z. Zhao, H. Yuan, J.K. Hu, J.Q. Huang, Q. Zhang, Matter , 2022 , 5 , 876–898 4 InnoSuisse Flagship project CircuBat http://circubat.ch 5 E. Querel, V. Dolder, C. Hänsel, P. Stössel, C. Battaglia, in preparation

Battery research often encounters the challenge of determining chemical information, such as composition and elemental oxidation states, of a layer buried within a cell stack in a non-destructive manner. Spectroscopic techniques based on X-ray emission or absorption are well-suited and commonly employed to reveal this information. However, the attenuation of X-rays as they travel through matter creates a challenge when trying to analyze layers buried at depths exceeding hundred micrometers from the sample's surface. In the context of battery research, the limited escape depth of X-rays often necessitates the design of experiment-specific cells with thinner inner layers, despite the risk that these tailored cells may not exactly replicate the cycling behavior of larger commercial cells. Muon-induced X-ray emission (MIXE) is a non-destructive spectroscopic technique that involves implanting negative muons into a sample and detecting the highly energetic muonic X-rays generated when these muons are captured by the sample's atoms. By virtue of the high energy of muonic X-rays, the depth of analysis of MIXE greatly exceeds that of other X-ray based techniques. In this article, we introduce the technique and lay the groundwork for employing MIXE in future in situ/operando analyses of batteries. We demonstrate that MIXE can detect nearly all elements, including low atomic number ones such as Li. Additionally, we establish the quantitative nature of MIXE through the precise determination of LiNi x Mn y Co1-x-y O2 (NMC) electrode stoichiometries. Finally, we demonstrate that MIXE enables the acquisition of depth-resolved chemical information from a 700 μm thick cell, in good agreement with simulation results.

Dry coating of battery electrodes is emerging as a promising alternative technology to the prevailing slurry coating and drying process widely adopted in the lithium-ion battery industry. 1,2,3 To date, the most energy-intensive step in cell manufacturing is the drying of slurry-coated electrodes, 1 and the adoption of dry coating aims to mitigate both the environmental impact and production costs associated with electrode production. Beyond environmental and economic concerns, producing higher mass-loading electrodes, a crucial aspect for increasing cell energy density, faces inherent challenges with the slurry-coating process: the drying of thick coatings often leads to issues such as electrode cracking and the formation of inhomogeneous electrode microstructures. Bühler and Empa have collaboratively developed and are in the process of scaling up a dry-coating manufacturing method. 4 Our process centers around the extrusion mixing of electrode components, followed by calendering of the dry mixture to produce the final electrode and direct lamination onto a current collector. In this presentation, we showcase the adaptability of extrusion mixing in inducing shear fibrillation of polytetrafluoroethylene (PTFE) binder, crucial for achieving the desired electrode microstructures (see Figure 1a and 1b). Furthermore, we demonstrate the capability of our dry-coating technology to produce high-mass loading electrodes with areal capacities of 5 mAh cm -2 or more (see Figure 1c). The presentation encompasses a thorough characterization of dry-coated electrodes, including their microstructure and electrochemical performance in lab-scale batteries. Key aspects, such as rate capability and capacity retention, are evaluated. A comprehensive comparison with slurry-coated electrodes, fabricated using identical active electrode materials, mass fractions, and mass loading, reveals that our dry-coated electrodes exhibit comparable performance to their slurry-coated counterparts. 5 The scalability of our dry-coating technology is underscored, highlighting the achievable throughputs necessary for gigafactory-scale production with a single extruder. References: 1 F. Degen, M. Schütte, Journal of Cleaner Production, 2022 , 330, 129798 2 B. Schumm, S. Kaskel, Next Energy, 2023 , 100009 3 Y. Lu, C.Z. Zhao, H. Yuan, J.K. Hu, J.Q. Huang, Q. Zhang, Matter , 2022 , 5 , 876–898 4 InnoSuisse Flagship project CircuBat 5 E. Quérel, V. Dolder, C. Hänsel, P. Stössel, C. Battaglia, in preparation Figure 1

High performance alkali metal anode solid-state batteries require solid/solid interfaces with fast ion transfer that are morphologically and chemically stable upon electrochemical cycling. Void formation at the alkali metal/solid-state electrolyte interface during alkali metal stripping is responsible for constriction resistances and hotspots that can facilitate dendrite propagation and failure. Both externally applied pressures (35-400 MPa) and temperatures above the melting point of the alkali metal have been shown to improve the interfacial contact with the solid electrolyte, preventing the formation of voids. However, the extreme pressure and temperature conditions required can be difficult to meet for commercial solid-state battery applications. In this review, we highlight the importance of interfacial adhesion or 'wetting' at alkali metal/solid electrolyte interfaces for achieving solid-state batteries that can withstand high current densities without cell failure. The intrinsically poor adhesion at metal/ceramic interfaces poses fundamental limitations on many inorganics solid-state electrolyte systems in the absence of applied pressure. Suppression of alkali metal voids can only be achieved for systems with high interfacial adhesion (i. e. 'perfect wetting') where the contact angle between the alkali metal and the solid-state electrolyte surface goes to theta = 0 degrees. We identify key strategies to improve interfacial adhesion and suppress void formation including the adoption of interlayers, alloy anodes and 3D scaffolds. Computational modeling techniques have been invaluable for understanding the structure, stability and adhesion of solid-state battery interfaces and we provide an overview of key techniques. Although focused on alkali metal solid-state batteries, the fundamental understanding of interfacial adhesion discussed in this review has broader applications across the field of chemistry and material science from corrosion to biomaterials development.

LiNi1-x-yMnxCoyO2 (NMC) with a nickel content of ≥80% is currently considered one of the most promising lithium-ion battery cathode materials for applications that require both a high energy density and reasonable costs. However, its widespread use has so far been limited by its inherently lower structural stability and higher surface reactivity compared to NMC materials with a lower nickel content. Here, we explore wet-chemical titanium-based bulk and surface modifications to improve the cycling and high-voltage stability of NMC811. We find that both doping and coating with titanium improve cycling stability. For example, the capacity retention of graphite/NMC811 full cells cycled for 200 cycles between 2.8 and 4.4 V at C/3 improves from 86.1% for the pristine NMC811 to 89.4% and 91.5% for the doped and coated samples, respectively. Combining doping and coating in a two-step process results in a material with the most balanced properties in terms of capacity, cycling stability, rate performance, and high-voltage stability.

Understanding the interfacial dynamics of batteries is crucial to control degradation and increase electrochemical performance and cycling life. If the chemical potential of a negative electrode material lies outside of the stability window of an electrolyte (either solid or liquid), a decomposition layer (interphase) will form at the interface. To better understand and control degradation at interfaces in batteries, theoretical models describing the rate of formation of these interphases are required. This study focuses on the growth kinetics of the interphase forming between solid electrolytes and metallic negative electrodes in solid-state batteries. More specifically, we demonstrate that the rate of interphase formation and metal plating during charge can be accurately described by adapting the theory of coupled ion-electron transfer (CIET). The model is validated by fitting experimental data presented in the first part of this study. The data was collected operando as a Na metal layer was plated on top of a NaSICON solid electrolyte (Na(3.4)Zr(2)Si(2.4)P0.6O(12) or NZSP) inside an XPS chamber. This study highlights the depth of information which can be extracted from this single operando experiment and is widely applicable to other solid-state electrolyte systems.

To harness all the benefits of solid-state battery (SSB) architectures in terms of energy density, their negative electrode should be an alkali metal. However, the high chemical potential of alkali metals make them prone to reduce most solid electrolytes (SE), resulting in a decomposition layer called an interphase at the metal|SE interface. Quantitative information about the interphase chemical composition and rate of formation are challenging to obtain because the reaction occurs at a buried interface. In this study, a thin layer of Na metal (Na0) is plated on the surface of a SE of the NaSICON family (Na3.4Zr2Si2.4P0.6O12 or NZSP) inside a commercial XPS system whilst continuously analysing the composition of the interphase operando. We identify the existence of an interphase at the Na0|NZSP interface, and more importantly, we demonstrate for the first time that this protocol can be used to study the kinetics of interphase formation. A second important outcome of this article is that the surface chemistry of NZSP samples can be tuned to improve their stability against Na0. It is demonstrated by XPS and time-resolved electrochemical impedance spectroscopy (EIS) that a native Na3PO4 layer present on the surface of as-sintered NZSP samples protects their surface against decomposition.

Understanding the interfacial dynamics of batteries is crucial to control degradation and increase electrochemical performance and cycling life. If the chemical potential of a negative electrode material lies outside of the stability window of an electrolyte (either solid or liquid), a decomposition layer (interphase) will form at the interface. To better understand and control degradation at interfaces in batteries, theoretical models describing the rate of formation of these interphases are required. Yet, experimental data which could support these models are challenging to obtain considering that the decomposition reaction is dynamic in nature and occurs at a deeply buried interface making it inaccessible to quantitative non-destructive techniques such as X-ray photoelectron spectroscopy (XPS) which has a limited depth of analysis. In the first article of this two-parts study, an experiment was designed to study the formation of an interphase at the interface between a Na metal negative electrode and a NaSICON solid electrolyte (Na3.4Zr2Si2.4P0.6O12 or NZSP) using a recent XPS protocol. Data was collected operando as a Na metal layer was plated on top of the NZSP electrolyte inside the XPS chamber. It was demonstrated that an interphase forms at the Na0|NZSP interface but that a native Na3PO4 layer present on thermally activated NZSP samples can minimize the extent of decomposition. In this second article, it is demonstrated that the rate of plating and interphase formation at the Na0|NZSP interface can be accurately described by adapting the theory of coupled ion-electron transfer (CIET). Models are fitted using experimental data from the first part of this study (in particular, the peak positions and peak areas as a function of Na0 plating time). This second part of the study therefore highlights the depth of information which can be extracted from this single operando experiment.

Solid-state batteries (SSBs) with alkali metal anodes hold great promise as energetically dense and safe alternatives to conventional Li-ion cells. Whilst, in principle, SSBs have the additional advantage of offering virtually unlimited plating current densities, fast charges have so far only been achieved through sophisticated interface engineering strategies. Here, we reveal that such interface engineering can be easily achieved by tuning the chemistry of NaSICON solid electrolytes (Na3.4Zr2Si2.4P0.6O12) and taking advantage of the thermodynamic stabilization of a Na3PO4 layer on their surface upon thermal activation. The optimized planar Na|NZSP interfaces are characterized by their exceptionally low interface resistances (down to 0.1 Ω cm2 at room temperature) and, more importantly, by their tolerance to large plating current densities (up to 10 mA cm-2) even for extended cycling periods of 30 minutes (corresponding to an areal capacity 5 mAh cm-2).

Solid-state batteries (SSBs) with alkali metal anodes hold great promise as energetically dense and safe alternatives to conventional Li-ion cells. Whilst, in principle, SSBs have the additional advantage of offering virtually unlimited plating current densities, fast charges have so far only been achieved through sophisticated interface engineering strategies. With a combination of surface sensitive analysis, we reveal that such sophisticated engineering is not necessary in NaSICON solid electrolytes (Na3.4Zr2Si2.4P0.6O12) since optimised performances can be achieved by simple thermal treatments that allow the thermodynamic stabilization of a nanometric Na3PO4 protective surface layer. The optimized surface chemistry leads to stabilized Na|NZSP interfaces with exceptionally low interface resistances (down to 0.1 Ω cm2 at room temperature) and high tolerance to large plating current densities (up to 10 mA cm−2) even for extended cycling periods of 30 min (corresponding to an areal capacity 5 mAh cm−2). The created Na|NZSP interfaces show great stability with increment of only up to 5 Ω cm2 after four months of cell assembly.