Ashok Sreekumar Menon

Surface oxygen loss driven degradation has restricted voltage operating windows and hindered the adoption of ever-increasing Ni-rich cathodes leading to cathode-engineering designs. Often overlooked in academic studies is the influence of electrode engineering through calendering on cell longevity. Here, we perform a systematic calendering study of industrially relevant single-crystal NMC811//graphite single-layer pouch cells cycled within conventional (3.0–4.2V) and O-loss degradation (2.5–4.4V) voltage windows to investigate cell performance and longevity without modifying the cathode chemistry. Single-crystal particles withstand aggressive calendering and are embedded within the aluminium current collector, substantially reducing interfacial contact resistance. Aggressive calendering suppresses contact-resistance growth during cycling, enabling prolonged utilisation of the additional high-voltage capacity and delaying the crossover between conventional and extended-voltage operation from approximately 40 to 300 cycles, without chemical modification. Furthermore, application of 1 MPa stack pressure further reduces contact resistance and suppresses its build-up during cycling, providing by 4-fold lifetime enhancement at 1C cycling rates.

Operando diffraction experiments enable real-time, nondestructive correlation of the electrochemical behavior of battery cells with the physicochemical changes occurring in their internal components. These experiments can now be directly performed on standard cell formats, identical to those used for electrochemical testing, at unprecedented scattering, temporal, and spatial resolutions. This can generate significant volumes of new multimodal datasets, opening exciting possibilities for probing and parameterizing complex battery performance and degradation mechanisms. To fully leverage the wealth of data produced by such experiments via data-driven machine learning methods, the open sharing of data via standardized, machine-readable formats, in line with FAIR principles, is essential. Currently, this is hindered by differences in the cell design, experimental protocols, and data-processing workflows. In this perspective, we discuss the need for standardizing operando battery diffraction experiments, the associated challenges, and propose a NeXus-based application definition for the standardized exchange of experimental metadata and results as a pathway toward reproducible research practices and transparent analytical workflows.

The electrochemical performance of single‐crystalline (SC) Ni‐rich layered oxide cathodes is fundamentally limited by bulk Li ⁺ diffusion within micrometre‐sized particles. During high‐voltage cycling—necessary for high‐energy applications—intraparticle Li ⁺ diffusion is further impeded by oxygen‐loss‐induced surface reconstruction from the layered phase to spinel/rock‐salt structures. Therefore, to fully understand how bulk Li ⁺ transport kinetics influences electrochemical degradation, it is necessary to establish the correlation between surface reconstruction and bulk delithiation during the anisotropic structural evolution (i.e., expansion of the layers followed by their contraction) of the cathode particles during long‐term cycling. In this work, we accomplish this using multi‐rate operando X‐ray diffraction studies of SC Ni‐rich layered oxide cathodes aged under different voltage windows in single‐layer pouch full cells. We quantify how increased surface reconstruction leads to greater heterogeneity in bulk delithiation, thereby promoting phase separation and exacerbating electrochemical capacity fade. These results provide a direct mechanistic link between surface degradation and bulk delithiation in such cathodes and offer a framework for non‐destructively probing kinetics‐dependent degradation under practically relevant conditions to guide strategies for improved cycling stability.

A macro-indentation technique is used to measure the hardness of polycrystalline lithium nickel oxide (LNO) particles in the composite cathode of a Li ion battery. The LNO particles are prepared at selected states of delithiation and are either uncoated or coated with amorphous alumina by particle atomic layer deposition (P-ALD): the P-ALD alumina coating enhances the electrochemical performance of the LNO cathode particles. A Vickers pyramidal indenter is used to indent the LNO cathode layer on a soft metallic substrate; the LNO layer thickness is much less than the indent depth, and consequently the indentation pressure is dictated by the hardness of the substrate. The average contact hardness of the LNO particles against the pyramidal indenter exceeds that of the substrate and is calculated from the true area of contact of the LNO particles, as measured by a scanning electron microscope (SEM). Additionally, high-throughput 3D profiling of the deformed cathode surfaces by an optical microscope is used to measure the true area of contact between LNO particles and indenter; the two techniques give excellent agreement. The average contact hardness of LNO particles is independent of both indent depth and hardness of the substrate. The contact hardness of the polycrystalline LNO particles is also independent of the presence of the P-ALD coating. A contact hardness of 345 +/- 22 MPa is measured for uncycled polycrystalline LNO particles in the initial, lithiated state; this hardness approximately halves when the LNO is delithiated.

The electrochemical performance of single-crystalline Ni-rich layered oxide cathodes is fundamentally limited by bulk Li⁺ diffusion within micrometre-sized particles. During high-voltage cycling—necessary for high-energy applications—intraparticle Li⁺ diffusion is further impeded by oxygen-loss-induced surface reconstruction from the layered phase to spinel/rock-salt structures. Therefore, to fully understand how bulk Li⁺ transport kinetics influences electrochemical degradation, it is necessary to establish the correlation between surface reconstruction and bulk delithiation during the anisotropic structural evolution (i.e., expansion of the layers followed by their contraction) of the cathode particles during long-term cycling. In this work, we accomplish this using multi-rate operando X-ray diffraction studies of single-crystalline Ni-rich layered oxide cathodes aged under different voltage windows in single-layer pouch full cells. We quantify how increased surface reconstruction leads to greater heterogeneity in bulk delithiation, thereby promoting phase separation and exacerbating electrochemical capacity fade. These results provide a direct mechanistic link between surface degradation and bulk delithiation in such cathodes and offer a framework for non-destructively probing kinetics-dependent degradation under practically relevant conditions to guide strategies for improved cycling stability.

Nickel-rich layered oxides are leading materials for high-energy lithium-ion batteries. During cycling, structural transformation at the surface impedes Li+ transport and degrades the performance. However, the evolution of the near-surface structure during cycling remains poorly understood. Here we use depth-resolved X-ray absorption spectroscopy (XAS) to characterise the changes in the electronic structure of transition metals (TMs) near the surface and in the bulk of cycled LiNi0.8Mn0.1Co0.1O2 (NMC811). Consistent changes in the O K-edge and metal L-edge spectra of discharged and charged electrodes reveal that TMs in the reduced surface layer (RSL) are redox active, even after extended cycling. The dynamic behaviour of the RSL – the degree of TM reduction and redox activity vs. inactivity – is shown to depend on the particle morphology and cycling protocol. These insights are helpful to understand the structural and electrochemical properties of the RSL and will guide future efforts to mitigate surface degradation and improve cycling performance.

The first application of disordered rocksalt (DRX) materials in aqueous zinc-ion batteries (ZIBs) demonstrates DRX ZnMnO ₂ as a versatile cathode for anode-free configurations, overcoming zinc anode degradation challenges.

The effect of dual cation magnesium/tungsten substitution in ultra-Ni-rich LiNiO ₂ cathodes was investigated. Combined bulk and surface stabilisation afforded through this coat-doping method improved the cyclability of these cathode materials.