High‐Voltage Stability of Small‐Size Single Crystal Ni‐Rich Layered Cathode for Sulfide‐Based All‐Solid‐State Lithium Battery at 4.5 V

Abstract Mechanical damage of NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ), severe interfacial side reactions, and physical contact failure of cathode and solid electrolyte (SE) are the main obstacles for it to achieve high‐voltage stability in all‐solid‐state batteries (ASSLBs). The cathode morphology effects on the structural integrity are directly related to the electrochemical performance of ASSLBs. In this work, small‐size single crystal NCM811 (S‐SC) is synthesized for sulfide‐based ASSLBs to solve mechanical damage and contact failure issues. In addition, the interfacial stability is improved by a Li 2 O pre‐lithiation strategy. Cross section polisher‐scanning electron microscopy (CP‐SEM) is applied to reveal the mechanical structure evolution behavior of NCM811 cathodes with different morphology. Electrochemical impedance spectroscopy (EIS), time of flight secondary ion mass spectrometry (TOF‐SIMS), and X‐ray photoelectron spectroscopy (XPS) technologies are applied to characterize the interfacial stability among cycling. As a result, with a high mass loading of 35.67 mg cm −2 and high current density of 7.13 mA cm −2 , the Li 2 O pre‐lithiated S‐SC (S‐SC‐PL) cathode delivers extraordinarily high‐voltage stability of 100% after 500 cycles at 2.72–4.4 V and 100% after 200 cycles at 2.72–4.5 V in ASSLBs. This work provides an effective cathode morphological design strategy to improve high‐voltage stability of Ni‐rich layered cathodes for sulfide‐based ASSLBs.