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Self-discharge and chemically induced mechanical effects degrade calendar and cycle life in intercalation-based electrochromic and electrochemical energy storage devices. In rechargeable lithium-ion batteries, self-discharge in cathodes causes voltage and capacity loss over time. The prevailing self-discharge model centers on the diffusion of lithium ions from the electrolyte into the cathode. We demonstrate an alternative pathway, where hydrogenation of layered transition metal oxide cathodes induces self-discharge through hydrogen transfer from carbonate solvents to delithiated oxides. In self-discharged cathodes, we further observe opposing proton and lithium ion concentration gradients, which contribute to chemical and structural heterogeneities within delithiated cathodes, accelerating degradation. Hydrogenation occurring in delithiated cathodes may affect the chemo-mechanical coupling of layered cathodes as well as the calendar life of lithium-ion batteries. 

Abstract One of the most challenging aspects of developing high-energy lithium-based batteries is the structural and (electro)chemical stability of Ni-rich active cathode materials at thermally-abused and prolonged cell cycling conditions. Here, we report in situ physicochemical characterizations to improve the fundamental understanding of the degradation mechanism of charged polycrystalline Ni-rich cathodes at elevated temperatures (e.g., ≥ 40 °C). Using multiple microscopy, scattering, thermal, and electrochemical probes, we decouple the major contributors for the thermal instability from intertwined factors. Our research work demonstrates that the grain microstructures play an essential role in the thermal stability of polycrystalline lithium-based positive battery electrodes. We also show that the oxygen release, a crucial process during battery thermal runaway, can be regulated by engineering grain arrangements. Furthermore, the grain arrangements can also modulate the macroscopic crystallographic transformation pattern and oxygen diffusion length in layered oxide cathode materials. 

Abstract Mn‐rich cathodes balance performance and sustainability but suffer from limited cyclability due to Mn dissolution and cathode‐to‐anode crosstalk. The Jahn‐Teller (J‐T) effect of Mn³⁺is often linked to the above phenomena, such as in spinel LiMn₂O₄. However, in typical voltage ranges, significant Mn³⁺only appears near the end of discharge, highlighting the need to reassess its role in driving Mn dissolution, structural degradation, and battery performance. Here, the spinel cathode's degree of disorder is tailored to expand the Mn redox range, enabling segmentation into J‐T active and less active voltage ranges. Cycling at segmented voltage windows reveals surface degradation mechanisms with and without the major J‐T effect. Despite a stronger J‐T effect below 3.6 V vs. Li/Li⁺, Mn dissolution is less significant than above 3.6 V. Expanding the cycling window to 2.0–4.3 V causes severe degradation as the J‐T active range induces a tetragonal phase and Mn²⁺‐rich surface, driving Mn dissolution and consuming Li‐ion inventory in full cells. Reducing electrolyte acidity minimizes Mn³⁺disproportionation, enabling a stable dopant‐free Mn‐only cathode with a 250 mAh g⁻¹specific capacity. These findings demonstrate that full cells using Mn‐rich cathodes have the potential to avoid the notorious crosstalk problem through electrolyte engineering.