Probing Mechanism of Lithium Extraction within a Solid-State Battery in Real Time

Sreelakshmi Anil Kumar ᵃᵇ, Dhanush Shanbhag ᵇᶜ, Ove Korjus ᵃ, Prashanth Sivakumar ᵇᵈᵉ, Laurence Croguennec ᵈᶠ, Christian Masquelier ᵇᶠᵍ, Jean-Noël Chotard ᵇᶠᵍ, Emmanuelle Suard ᵃ

ᵃ Institut Laue-Langevin (ILL), Grenoble, France

ᵇ Laboratoire de Réactivité et de Chimie des Solides (LRCS), UMR CNRS 7314, Université de Picardie Jules Verne, Amiens, France

ᶜ Umicore, Brussels, Belgium

ᵈ Univ. Bordeaux, CNRS, Bordeaux INP, ICMCB UMR 5026, Pessac, France

ᵉ TIAMAT, Amiens, France

ᶠ RS2E, Réseau Français sur le Stockage Electrochimique de l’Energie, FR CNRS 3459, Amiens, France

ᵍ Institut Universitaire de France, Paris, France

Anil Kumar et al., Advanced Energy Materials, 2026, e06600

https://doi.org/10.1002/aenm.202506600

All-solid-state batteries (ASSBs) are widely seen as the next generation of energy storage devices. By replacing the liquid electrolyte of conventional lithium-ion batteries with a solid material, they promise greater safety, higher energy density, and the ability to operate at extreme temperatures. However, understanding exactly what happens inside these batteries during charge and discharge at the atomic scale is a significant scientific challenge.

A team of researchers from the Institut Laue-Langevin (ILL), the LRCS (Amiens) and ICMCB (Bordeaux) has now achieved a key milestone: performing operando neutron powder diffraction (NPD) on a working all-solid-state battery, meaning they could track structural changes in real time, while the battery was actually cycling.

Why Neutrons?

Neutrons are uniquely suited to this type of study. Unlike X-rays, which interact with electrons and are poorly sensitive to light elements, neutrons interact directly with atomic nuclei. This makes them particularly sensitive to lithium, the very element responsible for the charge transfer, and also enable us to distinguish elements of closer atomic numbers such as the transition metals commonly present in positive electrode materials. Moreover, neutrons penetrate deeply into matter, allowing researchers to probe the full bulk of a thick battery pellet, without any beam damage to the sample.

The Battery System and the Challenge

The battery studied comprised LiNiO_0.6Mn_0.2Co_0.2O₂ (NMC622) as the positive electrode, a mixed-halide argyrodite solid electrolyte (Li_5.4PS_4.4BrCl_0.6), and a Li_0.5In alloy as the negative electrode. One of the main experimental obstacles was the need for a large quantity of active material, at least 140 mg, to generate a sufficient neutron diffraction signal. This required building a 2.5 mm thick battery pellet, which introduced new electrochemical challenges, notably increased internal resistance.

The key to overcoming this was the use of a newly developed high-conductivity electrolyte (Li_5.4PS_4.4BrCl_0.6), with an ionic conductivity six times higher than conventional Li₆PS₅Cl. This allowed the team to extract approximately 55% of the lithium from the active material, comparable to what is achieved in standard lab-scale cells.

Key Findings

Using the newly designed ILLBAT#5 electrochemical cell on the D20 diffractometer at ILL, the team collected neutron diffraction patterns every hour throughout the first charge-discharge cycle at room temperature. These operando measurements, combined with ex situ diffraction data, revealed several important results:

• During charging, two distinct structural phases of NMC622 (H1 and H2) were found to coexist throughout most of the charge. This was unexpected at such a slow cycling rate (C/60), where a single-phase, solid-solution behaviour would normally be expected.
• This coexistence was attributed to non-uniform current distribution across the thick electrode, causing different regions to reach different states of charge simultaneously.
• When the same experiment was repeated at 100°C, the two-phase behavior disappeared entirely, and the system followed a clean, single-phase pathway, confirming that improved ionic conductivity at higher temperature homogenizes the lithiation.
• Throughout the entire first cycle, the solid electrolyte remained structurally stable, with no change in peak positions or intensities in the NPD patterns, a reassuring result for the viability of sulfide-based ASSBs.

These results highlight how operando neutron diffraction provides insight that ex situ measurements alone cannot capture, including the real-time evolution of phase fractions, lattice parameters, and lithium occupancy throughout cycling.

[1] S. Anil Kumar et al., Advanced Energy Materials, 2026, e06600. DOI: 10.1002/aenm.202506600

[2] O. Korjus et al., ACS Materials Letters, 7 (2025) 2725–2731.

[3] D. Shanbhag et al., Journal of Power Sources, 657 (2025) 238175.

[4] J. Janek and W. G. Zeier, Nature Energy, 8 (2023) 230–240.