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Understanding the chemical structure of the solid electrolyte interphase that forms and evolves during lithium-ion battery cycling is critical for advancing battery technology. This complex task often requires the use of postmortem protocols to extract the electrodes in controlled states of charge and prepare them for further characterization and analysis. Over decades of research and optimization, the scientific community has established and shared post-mortem workflow protocols tailored to specific techniques. However, numerous sources of artifacts can disturb this workflow, introducing experimental uncertainties at various stages, from electrode manufacturing to data interpretation. Here we present the results of a round-robin inter-laboratory study using post-mortem X-ray photoemission spectroscopy to characterize the solid electrolyte interphase formed on graphite electrode after cycling in two different electrolytes. Several leading European research teams, expert in battery manufacturing and characterization by X-ray photoemission spectroscopy, participated in a meticulously designed post-mortem workflow. The goal was to identify the sources of consistency and disparity in the results and their impact on the scientific conclusions. Moreover, human-induced bias and errors were quantified throughout key steps, from cell assembly to photoemission core level peak fitting and interpretation. Based on our findings, we offer key recommendations for identifying and minimizing sources of artifacts in the analysis of the solid electrolyte interphase chemical composition. Effectively addressing these challenges is essential for improving both the performance and longevity of batteries.

The development of high-energy density solid-state batteries is critical for the achievement of carbon neutrality goals and the advancement of clean energy. Still, the fundamental understanding of lithium transport mechanisms and degradation processes remains limited. Current characterisation methods face significant challenges in studying these complex systems, particularly due to the difficulty of detecting lithium dynamics in three-dimensional battery architectures in operando conditions. Here we present the ANISSA (Advanced Neutron Imaging for Solid-State batteries in Action) project, an integrated experimental framework combining high-resolution neutron and X-ray imaging techniques to research coupled electro-chemo-mechanical processes in lithium-based energy storage systems.

Despite being promoted as a superior Li-ion conductor, lithium lanthanum zirconium oxide (LLZO) still suffers from a number of shortcomings when employed as an active ceramic filler in composite polymer–ceramic solid electrolytes for rechargeable all-solid-state lithium metal batteries. One of the main limitations is the detrimental presence of Li₂CO₃ on the surface of LLZO particles, restricting Li-ion transport at the polymer–ceramic interfaces. In this work, a facile way to improve this interface is presented, by purposely engineering the LLZO particle surfaces for a better compatibility with a PEO:LiTFSI solid polymer electrolyte matrix. It is shown that a surface treatment based on immersing LLZO particles in a boric acid solution can improve the LLZO surface chemistry, resulting in an enhancement in the ionic conductivity and cation transference number of the CPE with 20 wt % of boron-treated LLZO particles compared to the analogous CPE with non-treated LLZO. Ultimately, an improved cycling performance and stability in Li//LiFePO₄ cells was also demonstrated for the modified material.

Poor ionic conductivity, low Li+ transference number, and limited electrochemical stability plague all-solid-state Li-metal batteries based on solid polymer electrolytes (SPEs). One strategy to overcome these hurdles is the insertion of ceramic fillers to generate composite polymer electrolytes (CPEs). These are based either on active (ion-conductive) fillers like Li7La3Zr2O12 or passive (non-conductive) fillers like Al2O3. In this work, the effect of passive Li-containing fillers is showcased, exemplified by a CPE platform of poly(trimethylene carbonate) (PTMC:LiTFSI) with LiAlO2 particles. The inclusion of such fillers shows a strikingly positive effect. The ionic conductivity is greatly improved by one order of magnitude at 20 wt% of LiAlO2 compared to the pristine PTMC SPE. Moreover, the Li+ transference number is significantly boosted and reaches values close to unity (T + = 0.97 at 20 wt% of LiAlO2), effectively rendering the material a single-ion conductor. The CPEs show outstanding cycling stability vs Li-metal, and electrochemical stability of up to 5 V vs Li+/Li. When implemented in a solid-state battery cell with LiNi0.33Mn0.33Co0.33O2 (NMC111) and Li-metal, a stable cycling performance for over 100 cycles is observed. This demonstrates the potential of using microsized and cost-effective LiAlO2 fillers in CPEs for applications in all-solid-state Li-metal batteries.

Solid composite polymer electrolytes (CPEs) are complex mixtures of ceramics, polymers, and lithium salts, where the interfaces between the different phases play an important role for stability, conductivity, and compatibility with electrode materials. In this study, two interfacial phenomena of CPEs consisting of lithium lanthanum zirconium oxide (LLZO) ceramic fillers in poly(trimethylene carbonate) (PTMC) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt are studied. First, the LLZO-polymer electrolyte interfaces are investigated. Second, the stability of this CPE material vs a Li-metal electrode is explored, by employing soft X-ray photoelectron spectroscopy (PES) in combination with in situ deposition of Li. Three different LLZO loadings in PTMC are investigated: 30, 50, and 70 wt %. The concentration of LiTFSI follows that of the particle concentration at the surface of the samples, where the CPE with 50 wt % bulk content of LLZO exhibits the highest surface concentrations of both salt and ceramic. This shows an affinity for the salt at the LLZO surface. Furthermore, the stability of the CPEs against Li is studied after in situ Li deposition and shows that PTMC can decompose, potentially forming polypropylene at the CPE|Li interface, with the CPE at 50 wt % of LLZO showing the most pronounced PTMC and TFSI breakdown. This is in agreement with the observed properties for the polymer-ceramic interfaces and highlights the decisive role of LiTFSI accumulation on the surface of the ceramic particles, both for ionic transport and chemical stability.

While polymer-based solid-state sodium batteries promise both safe operation and utilization of sustainable materials, they are held back by the insufficient ionic conductivity of the involved solid polymer electrolytes (SPEs). In this study, the conductivity and cation transference number are significantly improved through the construction of a composite polymer electrolyte (CPE) system based on poly(trimethylene carbonate) (PTMC) with sodium bis(trifluorosulfonylimide) (NaTFSI), combined with NaAlO₂ (NAO) ceramic filler at loadings ranging from 10 to 40 wt%. The NAO-based CPEs show the highest conductivity at 20 wt% NAO, with a Na⁺ transference number of ∼0.9 at 60 °C also being obtained for the same material, which is notably higher than that for the NAO-free SPE. Solid-state batteries composed of a Prussian white cathode and a Na metal anode and employing these CPEs reach a cycling performance of ∼100–150 mA h g⁻¹ at C/10 and 55 °C for more than 200 cycles without additives or plasticizers, thus opening the door to the potential exploration of CPEs for Na-based battery chemistries.

Two different types of electrolytes (co-solvent and multi-salt) are tested for use in high voltage LiNi_0.5Mn_1.5O₄||Si/graphite full cells and compared against a carbonate-based standard LiPF₆ containing electrolyte (baseline). Ex situ postmortem XPS analysis on both anodes and cathodes over the life span of the cells reveals a continuously growing SEI and CEI for the baseline electrolyte. The cells cycled in the co-solvent electrolyte exhibited a relatively thick and long-term stable CEI (on LNMO), while a slowly growing SEI was determined to form on the Si/graphite. The multi-salt electrolyte offers more inorganic-rich SEI/CEI while also forming the thinnest SEI/CEI observed in this study. Cross-talk is identified in the baseline electrolyte cell, where Si is detected on the cathode, and Mn is detected on the anode. Both the multi-salt and co-solvent electrolytes are observed to substantially reduce this cross-talk, where the co-solvent is found to be the most effective. In addition, Al corrosion is detected for the multi-salt electrolyte mainly at its end-of-life stage, where Al can be found on both the anode and cathode. Although the co-solvent electrolyte offers superior interface properties in terms of the limitation of cross-talk, the multi-salt electrolyte offers the best overall performance, suggesting that interface thickness plays a superior role compared to cross-talk. Together with their electrochemical cycling performance, the results suggest that multi-salt electrolyte provides a better long-term passivation of the electrodes for high-voltage cells.

Advanced manufacturing research for sustainable battery life cycles is of utmost importance to reach net zero carbon emissions (European Commission, 2023a) as well as several of the United Nations Sustainable Development Goals (UNSDGs), for example: 30% reduction of CO2 emission, 10 million job opportunities and access to electricity for 600 million people (World Economic Forum, 2019). This editorial paper highlights international motivations for pursuing more sustainable manufacturing practices and discusses key research topics in battery manufacturing. Batteries will be central to our sustainable future as generation and storage become key components to on-demand energy supply. Four underlying themes are identified to address industrial needs in this field: 1. Digitalizing and automating production capabilities: data-driven solutions for production quality, smart maintenance, automation, and human factors, 2. Human-centric production: extended reality for operator support and skills development, 3. Circular battery life cycles: circular battery systems supported by service-based and other novel business models, 4. Future topics for battery value chains: increased industrial resilience and transparency with digital product passports, and next-generation battery chemistries. Challenges and opportunities along these themes are highlighted for transforming battery value chains through circularity and more sustainable production, with a particular emphasis on lithium-ion batteries (LIB). The paper concludes with directions for further research to advance a circular and sustainable battery value chain through utilizing the full potential of digitalization realising a cleaner, more energy-efficient society.

An electrolyte destined for use in a dual-ion battery (DIB) must be stable at the inherently high potential required for anion intercalation in the graphite electrode, while also protecting the Al current collector from anodic dissolution. A higher salt concentration is needed in the electrolyte, in comparison to typical battery electrolytes, to maximize energy density, while ensuring acceptable ionic conductivity and operational safety. In recent years, studies have demonstrated that highly concentrated organic electrolytes, ionic liquids, gel polymer electrolytes (GPEs), ionogels, and water-in-salt electrolytes can potentially be used in DIBs. GPEs can help reduce the use of solvents and thus lead to a substantial change in the Coulombic efficiency, energy density, and long-term cycle life of DIBs. Furthermore, GPEs are suited to manufacture compact DIB designs without separators by virtue of their mechanical strength and electrical performance. In this review, we highlight the latest advances in the application of different electrolytes in DIBs, with particular emphasis on GPEs.

The spinel oxide LiNi_0.5Mn_1.5O₄ (LNMO) currently competes to replace the conventional layered transition metal oxide active material in Li-ion batteries. The high average operating potential (4.8 V vs Li⁺/Li) challenges the stability of the electrolyte, which, in turn, compromises the lifetime of the Li-ion cell. Online electrochemical mass spectrometry (OEMS) is herein implemented to study the degradation processes occurring at the cathode surface. Gases continuously evolve across subsequent cycles as a result of electrolyte oxidation, a process that is found to be only potentially activated and independent of electrode surface composition. The subsequent formation of protic species autocatalyzes electrolyte salt degradation, which in turn triggers the corrosion of active material, current collector, and conductive carbons. The effectiveness of several well-known electrolyte additives, previously claimed to act as cathode electrolyte interphase (CEI) formers, was explored, revealing the efficacy of phosphorus-based additives. Our study provides a rapid and quantifiable approach to tackle the major challenge of high-voltage cathode materials, namely, their stabilization toward the electrolyte and how to identify and develop an efficient passivating CEI.