The Faraday Institution

Empirical battery models have many uses, including pack design, charge estimation, and cell selection. An accurate model requires accurate parameters, however there are a range of subtleties in parameter fitting that are often missed in the literature. This work presents a best-practice guide for parameterisation, covering design of appropriate experiments; using numerical optimisers to fit model parameters to the experimental data; and building a suitable interpolation of the fitted model parameters, to get the required parameter-functions for a model. Key novelties include the importance of using timescales in place of capacitances for numerical stability; the design of a multi-step parameterisation process where model complexity is gradually increased to give more accurate parameter estimates; and a combined numerical and experimental design, so that the right experiments, data, and fitting methods are chosen for the target application. Our method is presented as a general recipe, so that users can easily choose the right setup for their needs. Scripts are provided which implement the method and reproduce the provided examples. Additionally, a full set of experimental data, model scripts, and fitted parameters are provided, both for testing the described method and for re-use in modelling studies.

Abstract Na-ion batteries (NIBs) have gained attention as a cost-effective option for large-scale energy storage, offering electrochemical properties similar to lithium-ion batteries (LIBs). To improve safety and energy density, solid-state electrolytes (SSEs) are being incorporated into NIBs, paving the way for high-performance all-solid-state sodium-ion batteries (ASSNIBs). This review summarises recent progress in Na-based SSEs, categorised into oxides, sulfides, and halides, with particular emphasis on their crystal structures, ion conduction mechanisms, and electrochemical performance. We then critically examine the key challenges facing ASSNIBs, including low ionic conductivity, unstable electrode/electrolyte interfaces, and the reliance on rare or costly materials. To gain deeper insights into these issues, we highlight advanced characterisation and modelling techniques, including cryogenic electron microscopy, in-situ/operando characterisation, and machine learning approaches—all of which contribute to understanding Na-ion transport mechanisms and interfacial dynamics more comprehensively, and comparing with conventional electrochemical tests, structural characterisation and modelling methods. Building on these insights, we explore promising strategies such as microstructural design, mixed-ion approaches, and interface engineering to overcome the current limitations in Na SSEs. Finally, we offer perspectives on future research directions to support the rational design and optimisation of Na SSEs, ultimately advancing the development of next-generation ASSNIBs. The advanced characterisation and machine learning methodologies emphasised herein will also prove valuable for broader applications in electrochemical energy storage systems. Graphical abstract

The pursuit of high-energy lithium-ion batteries (LIBs) has driven the adoption of Ni-rich layered oxides such as NMC811, but their reactivity with conventional ethylene carbonate (EC)-based electrolytes leads to interfacial instability and performance loss. Here, we systematically investigate how electrolyte composition and additives influence the formation and stability of the solid electrolyte interphase (SEI) in graphite||single-crystal NMC811 cells. Using commercial-grade pouch cells under a consistent formation protocol, we combine operando acoustic emission (AE) and electrochemical atomic force microscopy (EC-AFM) with complementary electrochemical and structural characterisation to probe SEI formation in real time. We first assess common additives in EC-containing electrolytes, then progressively reduce EC content, and finally introduce SEI-forming additives into EC-free electrolytes. While EC promotes SEI growth on graphite, it also accelerates parasitic reactions at the Ni-rich cathode, resulting in limited gains in cycling stability. By contrast, EC-free electrolytes with targeted additives, particularly 10% fluoroethylene carbonate (FEC), form more uniform SEI layers, suppress gas evolution, and significantly enhance cycling stability, achieving 95.5% capacity retention after 300 cycles. This work demonstrates the dual role of EC in Ni-rich systems and highlights how correlative operando methods can guide rational electrolyte design for long-lived, high-energy LIBs.

<h2>Summary</h2> Thermal runaway (TR), characterized by rapid exothermic reactions, presents a serious safety risk in lithium-ion batteries (LiBs). External triggers such as high temperatures, mechanical abuse, or internal short circuits (ISCs) can initiate TR, often resulting in sidewall rupture, which may escalate to catastrophic battery pack failure. In this study, we developed and applied high-speed synchrotron imaging techniques to investigate sidewall rupture mechanisms in LiBs subjected to different triggering scenarios. Using <i>in situ</i> 4D tomographic imaging, we visualized the dynamic evolution of sidewall rupture with high spatial and temporal resolution. The results revealed distinct failure behaviors linked to each trigger, underscoring the complex and condition-specific nature of sidewall breach and battery failure. These insights highlight the critical importance of implementing tailored safety strategies across diverse applications. Our findings demonstrate the powerful potential of synchrotron high-speed tomography as a diagnostic tool for advanced safety testing and cell qualification.

ABSTRACT O3‐type layered cathodes for sodium‐ion batteries (NIBs) are promising cathodes, yet they are limited by irreversible phase transitions at high voltages, structural strain, and sluggish Na + transport, which compromise their cycling and rate performance. Here, a particle engineering strategy using boron oxide to simultaneously stabilize lattice framework, and regulate the crystal facet exposure is proposed. Boron oxide acts as a dual‐function additive, serving as both a flux that governs anisotropic crystal growth and a dopant that reinforces the metal–oxygen network through strong B─O bonding. This dual role drives the formation of submicron hexagonal platelets with a dominant (003) facet orientation and an enlarged Na‐layer spacing, resulting in fast in‐plane Na⁺ diffusion and exceptional structural integrity. Contrary to the conventional view that (003) planes are electrochemically inactive, controlled exposure of these facets suppresses interfacial degradation while maintaining high‐rate kinetics. The optimized boron‐modified cathode achieves excellent cycling stability, with 82.6% capacity retention after 400 cycles at 2C in full cells, together with superior high‐rate performance (92.0 mAh g −1 at 10C). This work illustrates facet engineering via boron modification as an effective and scalable route to reconcile the long‐standing durability–power trade‐off in O3‐type sodium layered oxides.

With the growing demand for sustainable lithium-ion battery (LIB) technologies, the development of efficient recycling processes for electrode materials is critical. TiNb2O7 (TNO) is gaining increasing attention as a promising anode material for high power Li ion batteries due to its high rate capability, excellent structural stability, and safer operating voltage compared to conventional graphite. However, recycling strategies for TNO remain underdeveloped. This study presents a direct recycling approach for TNO anodes recovered from a cycled TiNb2O7/LiNi0.6Mn0.2Co0.2O2 (TNO/NMC622) cell. A full range of procedural steps including electrochemical cycling of the TNO/NMC622 pouch cell, cell dismantling, electrode delamination, materials recovery and repair, and lastly cell remanufacturing and electrochemical evaluation, were investigated. The results showed that residual lithium in the TNO can lead to a rutile-type impurity, which is detrimental to performance. Advanced characterisation of this sample was carried out using the DIAD beamline at the Diamond Light Source, as well as lab X-ray powder diffraction and scanning electron microscopy. The elemental composition of the rutile phase, and the corresponding formation of Ti2Nb10O29 found in the same sample without Li removal were analysed and a recycling approach was developed, combining hydrothermal lithium removal with a further heat treatment, which prevented the formation of these additional phases. Electrochemical testing of the recovered TNO highlighted that lithium removal is crucial as the recovered material without Li removal showed poor performance, while recycled TNO after Li removal exhibited high capacity and excellent rate capability and stability at high current densities, 279(5) and 261(10) mA h g-1 at 2 and 4 A g-1, respectively, comparable with commercial TNO.

Lithium‐ion batteries are the leading rechargeable battery technology. 1 M lithium hexafluorophosphate (LiPF6) dissolved in carbonate solvents is commonly used as the electrolyte; however, LiPF6 is hygroscopic and forms toxic HF in the presence of water. This work presents the synthesis of lithium bis(perfluorinated pinacolato)borate salts Li[B(pp)2]·xDME (x = 0 or 1, pp = perfluorinated pinacolato, O2C2(CF3)4), which exhibit superior air tolerance and have higher thermal stability than LiPF6. Lithium‐ion cycling using 1 M Li[B(pp)2]·DME and 0.2 M Li[B(pp)2] electrolyte salts was performed, where 0.2 M Li[B(pp)2] cycled with higher capacity than 1 M Li[B(pp)2]·DME. X‐ray photoelectron spectroscopy on the post‐cycled NMC cathode found a thicker cathode electrolyte interphase with less LiF when using Li[B(pp)2]·DME than for LiPF6 based electrolyte.

Among various electrode materials for supercapacitors, manganese oxide–carbon composites offer a promising balance of cost, performance, and environmental sustainability. Yet while these electrode structures can offer significant overall capacitance, the total capacitance is generally much lower than the theoretically achievable value, highlighting that the manganese oxide is in fact greatly underutilized. This study presents a novel one‐pot metal‐ammonia synthesis method for fabricating manganese oxide–activated carbon (MnAC) nanocomposites, designed to maximize manganese utilization in supercapacitor electrodes. By leveraging a thermodynamically driven deposition process, Mn 3 O 4 nanoparticles are uniformly anchored onto activated carbon, overcoming limitations of conventional synthesis routes such as poor conductivity and underutilized active materials. The resulting MnAC composites exhibit high specific capacitance (120 F g −1 ) and 94% capacity retention after 1000 cycles, along with exceptional manganese efficiency (1044 F g −1 relative to Mn content), approaching theoretical limits. Structural and electrochemical analyses confirm the formation of a well‐integrated, crystalline Mn 3 O 4 phase with enhanced redox activity and conductivity. This scalable synthesis eliminates toxic solvents and enables ammonia recovery, offering a sustainable pathway for high‐performance energy storage materials. The findings highlight the potential of MnAC composites for next‐generation supercapacitors and establish a foundation for further optimization of metal oxide–carbon hybrid electrodes.