Xuekun Lu

The fast‐charging capability of phase‐separating graphite electrodes is largely constrained by heterogeneous reaction kinetics and sluggish mass transport at both the particle and electrode scales, which increase the risk of parasitic lithium plating and associated safety concerns. A deeper mechanistic understanding of the interplay among phase‐separation dynamics, electrode microstructure, and lithium‐plating propensity is therefore essential for guiding the rational design of advanced electrode architectures and fast‐charging protocols. Here, we combine operando optical microscopy with three‐dimensional microstructure‐resolved phase‐field modeling to resolve the interplay between phase separation and lithium plating. Microscopy captures stages evolution, phase mode transitions and structural dynamics across the particle population and at the single‐particle level, which is driven by the slow interfacial reactions. Non‐equilibrium phase‐field simulations elucidate the kinetic control mechanisms governing phase transitions as the current varies. Importantly, a new mechanism of lithium plating associated with interfacial ohmic resistance is identified. Based on these insights, we evaluate particle‐size‐distribution design and use thermal activation as a mechanistic probe to resolve how temperature alters phase‐separation pathways and lithium‐plating behavior. These results may serve as a foundation for improving the physical understanding and driving optimization of fast charging protocols for lithium‐ion batteries.

Phase transitions in sodium layered transition metal (TM) oxides often induce microstrain and TM ion migration, leading to structural degradation and poor cycling stability. However, a rational design approach for optimizing phase transitions is still lacking. Here we introduce phase transition potential (Φ _phase ) as a rational descriptor to predict and control phase evolution in these cathodes. A lower Φ _phase enables smoother Na ⁺ migration and slower slab sliding during Na extraction, thereby facilitating a continuous phase transformation rather than abrupt phase changes. Guided by this concept, we design a calcium‐substituted layered oxide, Na _0.96 Ca _0.02 Ni _0.33 Fe _0.33 Mn _0.33 O ₂ (NCNFMO), which delivers a specific capacity of 140 mAh g ⁻¹ at 0.1 C and retains 84.2% of its initial capacity after 500 cycles at 1 C, compared to only 26.4% retention for NaNi _0.33 Fe _0.33 Mn _0.33 O ₂ . Moreover, the NCNFMO||Al@C full cell maintains a high‐capacity retention of 82.5% after 100 cycles, and 6.1 Ah full cell demonstrates an energy density of 192 Wh kg ⁻¹ _{entire cell} . These findings offer fundamental insights into phase behavior‐induced microstrain and a promising path toward high‐energy, long‐life sodium‐ion batteries.

Silicon is a promising negative electrode material for high-energy batteries, but its volume changes during cell cycling cause rapid degradation, limiting its loading to about 10 wt.% in conventional graphite/Si composite electrodes. Overcoming this threshold requires evidence-based design for the formulation of advanced electrodes. Here we combine multimodal operando imaging techniques, assisted by structural and electrochemical characterizations, to elucidate the multiscale electro-chemo-mechanical processes in graphite/Si composite negative electrodes. We demonstrate that the electrochemical cycling stability of Si particles strongly depends on the design of intraparticle nanoscale porous structures, and the encapsulation and loss of active Si particles result in excessive charging current being directed to the graphite particles, increasing the risk of lithium plating. We also show that heterogeneous strains are present between graphite and Si particles, in the carbon-binder domain and the electrode’s porous structures. Focusing on the volume expansion of the electrode during electrochemical cycling, we prove that the rate performance and Si utilization are heavily influenced by the expansion of the carbon-binder domain and the decrease in porosity. Based on this acquired knowledge, we propose a tailored double-layer graphite/Si composite electrode design that exhibits lower polarization and capacity decay compared with conventional graphite/Si electrode formulations.

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) offer solutions to challenges intrinsic to low-temperature PEMFCs, such as complex water management, fuel inflexibility, and thermal integration. However, they are hindered by phosphoric acid (PA) leaching and catalyst migration, which destabilize the critical three-phase interface within the membrane electrode assembly (MEA). This study presents an innovative approach to enhance HT-PEMFC performance through membrane modification using picosecond laser scribing, which optimises the three-phase interface by forming a graphene-like structure that mitigates PA leaching. Our results demonstrate that laser-induced modification of PA-doped membranes, particularly on the cathode side, significantly enhances the performance and durability of HT-PEMFCs, achieving a peak power density of 817.2 mW cm⁻² after accelerated stress testing, representing a notable 58.2% increase compared to untreated membranes. Furthermore, a comprehensive three-dimensional multi-physics model, based on X-ray micro-computed tomography data, was employed to visualise and quantify the impact of this laser treatment on the dynamic electrochemical processes within the MEA. Hence, this work provides both a scalable methodology to stabilise an important future membrane technology, and a clear mechanistic understanding of how this targeted laser modification acts to optimise the three-phase interface of HT-PEMFCs, which can have impact across a wide array of applications.

A nature-inspired solution for water management in flow fields for electrochemical devices.

The phase separation dynamics in graphitic anodes significantly affects lithium plating propensity, which is the major degradation mechanism that impairs the safety and fast charge capabilities of automotive lithium-ion batteries. In this study, we present comprehensive investigation employing operando high-resolution optical microscopy combined with non-equilibrium thermodynamics implemented in a multi-dimensional (1D+1D to 3D) phase-field modeling framework to reveal the rate-dependent spatial dynamics of phase separation and plating in graphite electrodes. Here we visualize and provide mechanistic understanding of the multistage phase separation, plating, inter/intra-particle lithium exchange and plated lithium back-intercalation phenomena. A strong dependence of intra-particle lithiation heterogeneity on the particle size, shape, orientation, surface condition and C-rate at the particle level is observed, which leads to early onset of plating spatially resolved by a 3D image-based phase-field model. Moreover, we highlight the distinct relaxation processes at different state-of-charges (SOCs), wherein thermodynamically unstable graphite particles undergo a drastic intra-particle lithium redistribution and inter-particle lithium exchange at intermediate SOCs, whereas the electrode equilibrates much slower at low and high SOCs. These physics-based insights into the distinct SOC-dependent relaxation efficiency provide new perspective towards developing advanced fast charge protocols to suppress plating and shorten the constant voltage regime.

Sodium (Na) is the most appealing alternative to lithium as an anode material for cost‐effective, high‐energy‐density energy‐storage systems by virtue of its high theoretical capacity and abundance as a resource. However, the uncontrolled growth of Na dendrites and the limited cell cycle life impede the large‐scale practical implementation of Na‐metal batteries (SMBs) in commonly used and low‐cost carbonate electrolytes. Herein, the employment of a novel bifunctional electrospun nanofibrous separator comprising well‐ordered, uniaxially aligned arrays, and abundant sodiophilic functional groups is presented for SMBs. By tailoring the alignment degree, this unique separator integrates with the merits of serving as highly aligned ion‐redistributors to self‐orientate/homogenize the flux of Na‐ions from a chemical molecule level and physically suppressing Na dendrite puncture at a mechanical structure level. Remarkably, unprecedented long‐term cycling performances at high current densities (≥1000 h at 1 and 3 mA cm⁻², ≥700 h at 5 mA cm⁻²) of symmetric cells are achieved in additive‐free carbonate electrolytes. Moreover, the corresponding sodium–organic battery demonstrates a high energy density and prolonged cyclability over 1000 cycles. This work opens up a new and facile avenue for the development of stable, low‐cost, and safe‐credible SMBs, which could be readily extended to other alkali‐metal batteries.

The assumption of a highly corrosive potential at the anode bipolar plate (BPP) and porous transport layer (PTL) in a proton exchange membrane water electrolyser (PEMWE) stack often leads to selection of expensive materials such as platinum–coated titanium. Here, we develop a physicochemical model of electrochemical potential distribution in a PTL and validate it by in situ and ex situ electrochemical potential measurement. Model predictions suggest that, under typical PEMWE operating conditions, the corrosive zone associated with the anode polarisation extends only ≈200 μm into the PTL from the catalyst layer, obviating the need for highly corrosion-resistant materials through the bulk of the PTL and at the BPP. Guided by this observation, we present single cell PEMWE tests using anode current collectors fabricated from carbon-coated 316L stainless steel. The material is shown to be tolerant to potentials up to 1.2 V vs. RHE and when tested in situ for 30 days at 2 A cm⁻² showed no evidence of degradation. These results strongly suggest that much of the titanium in PEMWEs may be substituted with cheaper, more abundant materials with no loss of electrolyser performance or lifetime, which would significantly reduce the cost of green hydrogen. The combined modelling and experimental approach developed here shows great promise for design optimisation of PEMWEs and other electrochemical energy conversion devices.

The performance of lithium-ion batteries is determined by the architecture and properties of electrodes formed during manufacturing, particularly in the drying process when solvent is removed and the electrode structure is formed. Temperature is one of the most dominant parameters that influences the process, and therefore a comparison of temperature effects on both NMC622-based cathodes (PVDF-based binder) and graphite-based anodes (water-based binder) dried at RT, 60, 80, 100 and 120 °C has been undertaken. X-ray computed tomography showed that NMC622 particles concentrated at the surface of the cathode coating except when dried at 60 °C. However, anodes showed similar graphite distributions at all temperatures. The discharge capacities for the cathodes dried at 60, 80, 100 and 120 °C displayed the following trend: 60 °C < 80 °C < 100 °C < 120 °C as C-rate was increased which was consistent with the trends found in adhesion testing between 60 and 120 °C. Focused-ion beam scanning electrode microscopy and energy-dispersive X-ray spectroscopy suggested that the F-rich binder distribution was largely insensitive to temperature for cathodes. In contrast, conductivity enhancing fine carbon agglomerated on the upper surface of the active NMC particles in the cathode as temperature increased. The cathode dried at RT had the highest adhesion force of 0.015 N mm⁻¹ and the best electrochemical rate performance. Conversely, drying temperature had no significant effect on the electrochemical performance of the anode, which was consistent with only a relatively small change in the adhesion, related to the use of lower adhesion water-based binders.

There is a growing need for lithium-ion batteries that possess increased energy storage capabilities, with a simultaneous requirement for fast charging and improved rate performance. Thick electrodes provide proportionately more active material and thus better storage capabilities, while having the unavoidable characteristic of an increased diffusion length that adversely affects the high rate performance of an electrode. Here, advanced X-ray nano-computed tomography (CT) imaging, morphological image processing techniques, and a coupled electrochemical model are combined to carry out an extensive parametric study in which the specific capacity of an electrode is assessed as a function of thickness, porosity and discharge rate. The study quantifies the extent to which thick electrodes are affected by the porosity, and examines their poor high-rate performance. In broad terms, the model shows significant heterogeneities in lithium, lithium-ion, and current density distributions across the electrode that give rise to the significant and inextricable link between thickness, porosity and discharge rate. The modelling methodology presented in this work provides a foundation for the design of novel thick battery electrodes, and an example of such a design is presented here.