Gang Chen

Stress critically influences the cycling and safety of lithium metal batteries, especially in pouch cell or pack configurations. However, intrinsic coupling between stress and swelling persistently obscures the fundamental understanding of stress-strain effects. Herein, through real-time stress control, we identify that electro-chemo-mechanical responses of industrial-level cells are directly linked to stress relief principles of Li negative electrode. Li dendrites can hardly penetrate separators due to the plastic collapse of porous Li deposits. While densification of collapsed deposits occurs at 0.1 ~ 0.2 MPa, the dense architecture necessitates stress relief through creep or plastic deformation. Crucially, the separator penetration-induced short circuit originates from plastic deformation of densified Li, under stress exceeding its bulk yield strength (~1 MPa). These stress relief principles enlighten us achieving the stress-optimized 27 Ah, 402 Wh kg⁻¹ module with nondeteriorative cycling performance compared to single cell, providing a scalable framework for addressing key challenges in high-energy battery systems.

Heterogeneous grain structured design has emerged as an effective strategy to overcome the limitations of mechanical properties in structural materials. Core–shell heterogeneous grain structured materials exhibit a good strength-ductility synergy owing to their continuously networked grain topology. However, controlling the grain size and fraction in core–shell structures through mechanical milling and powder metallurgy remains challenging. Therefore, the effects of grain structure topology on mechanical behavior remain unclear. This study establishes a crystal plastic finite element (CPFE) model of a core–shell structure and discusses the effects of core–shell topological characteristics, i.e., core–shell fraction (S_f = 15% to 65%), the core–shell interface gradient (θ = 63° to 90°), and the coarse grain/ultrafine grain size ratio (CG/UFG = 8/2 to 8/1), on tensile strength and hetero-deformation induced (HDI) hardening. The results indicate that the tensile strength is strongly correlated with the core–shell fraction and CG/UFG size ratio. The tensile strength is enhanced with increasing core–shell fraction and CG/UFG size ratio, which can be attributed to the increased fraction of ultrafine grains and their reduced grain size. The tensile strength increases by approximately 30% when the core–shell fraction increases from 15% to 65%, and increases by approximately 12% when the CG/UFG size ratio changes from 8/2 to 8/1. However, these two parameters exhibit a negligible influence on HDI hardening. In contrast, compared to θ = 63°, the HDI hardening at θ = 90° increases by approximately 20%, thus it indicates the sharp core–shell interface gradient markedly promotes HDI hardening, thereby improving the tensile strength through an increased hardening rate. Collectively, this study provides useful information for the microstructure design of core–shell heterogeneous grain structured materials.