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Abstract Atomic-resolution imaging of battery materials is critical for identification of local defects and structural variations, which are tied to battery performance. However, since battery materials are, by design, optimized to allow ion motion in response to an applied electric field, they are also very sensitive to radiation damage by an electron beam. Image resolution is therefore severely constrained by the dose applied. Here, we show that multislice electron ptychography (MEP) can provide sub-ångström lateral resolution images of both light and heavy elements of a Li-ion battery cathode, along with nanometer-scale depth information and greater dose efficiency than conventional electron microscopy methods. Using the depth-sectioning capability of MEP, we have been able to obtain direct visualizations of Li vacancy clusters, atom column by atom column, in LixNi0.33Mn0.33Co0.33O2 (NMC111) cathodes. This capability to track Li distributions will be valuable in understanding, informing, and optimizing electrode material design for ion storage and transfer. 

Abstract Electron ptychography has recently achieved unprecedented resolution, offering valuable insights across diverse material systems, including in three dimensions. However, high-quality ptychographic reconstruction is computationally expensive and time consuming, requiring a significant amount of manually tuning even for experts. Additionally, essential tools for ptychographic analysis are often scattered across multiple software packages, with some advanced features available only in costly commercial software like MATLAB. To address these challenges, we introduce PtyRAD (Ptychographic Reconstruction with Automatic Differentiation), an open-source software framework offers a comprehensive, flexible, and computationally efficient solution for electron ptychography. PtyRAD provides seamless optimization of multiple parameters—such as sample thickness, local tilts, probe positions, and mixed probe and object modes—using gradient-based methods with automatic differentiation. By utilizing PyTorch’s highly optimized tensor operations, PtyRAD achieves up to a 24× speedup in reconstruction time compared to existing packages without compromising image quality. In addition, we propose a real-space depth regularization, which avoids wrap-around artifacts and can be useful for twisted two-dimensional material datasets and vertical heterostructures. Moreover, PtyRAD integrates a Bayesian optimization workflow that streamlines hyperparameter selection. We hope the open-source nature of PtyRAD will foster reproducibility and community-driven development for future advances in ptychographic imaging. 

Strain engineering of electrocatalysts has been an extensively studied field in recent years, but there has been limited investigation of strain and ligand effects in the catalysts of heterostructured oxides. Such studies could have significant impacts as the localized changes in the electronic structure of metal oxide shells may induce enhanced catalytic activity, complementing those from the well-studied metallic systems. Here, we developed a colloidal synthesis route to monodisperse core–shell spinel oxide nanocrystals with tunable shell thickness for the oxygen reduction reaction (ORR) in alkaline media. We compare the activity of these heterostructured particles, finding a higher activity for smaller shell thicknesses. The smallest shell thickness aligns with the highest shell strain. The best-performing core–shell sample achieved a half-wave potential of 0.893 V versus RHE in 1.0 M KOH, making it one of the best-reported values for a spinel oxide electrocatalyst for alkaline ORR with a PGM-free catalyst. In addition, this value is within 11 mV of that of the Pt/C reference material. Though a Pt/C reference sample has an overall higher mass activity at 0.9 V vs RHE, when cost is considered, the strained spinel outperforms the Pt/C by over 600-fold at this potential. Our results provide an impetus for exploring the deliberate and controlled use of strain engineering in metal oxides as high-performance, low-cost electrocatalysts. 

A novel synthesis route torwards small (<5 nm), low-dispersity (<20%) high entropy and multi-metal rock-salt oxide nanoparticles is described.