The garnet Li 7 La 3 Zr 2 O 12 solid electrolyte presents promising potential in application of solid-state lithium batteries because of its high ionic conductivity and stability. However, the critical interfacial issues between cathodes and garnet electrolytes severely restrict capacity and cycling stability of solid batteries. In this work, the partially cyclized polyacrylonitrile (cPAN) nanolayer is coated on high-voltage LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM) cathode particles enabling interface-friendly solid-state garnet batteries. Through controlling cyclized temperature and time, the cyclized part of polyacrylonitrile equipped with delocalized sp 2 π bond presents good capability for electronic transfer, while the residual part not involved in cyclization leaves the coating with certain feature for ionic transfer. In this way, such hybrid-conductivity coating facilitates the transport of both ions and electrons inside the cathode. In addition, the moderate cyclization condition retains the elasticity of polymers, contributing to protection of NCM cathode and suppression of side reactions at NCM/garnet interface during cycling. Therefore, the resultant solid NCM/garnet/Li cell based on the proposed interface engineering strategy delivers a discharge capacity of 176 mAh g −1 with a capacity retention of 82.4 % after 400 cycles. This work puts forwards an attractive strategy to modulate the cathodic interfaces toward solid-state garnet batteries via introducing partially cyclized polyacrylonitrile protective layer with hybrid conductivity.
The complicated interfacial problems of poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) at high voltages severely hinder its practical applications for high-energy-density all-solid-state lithium batteries (ASSLBs). Herein, the failure mechanisms of ASSLBs with LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM)-PEO are studied. It is found that the ASSLBs after charge generates a sharp drop of 0.62 V at the cut-off voltage of 4.30 V, and induce a high interfacial resistance due to forming an uneven thick cathode electrolyte interface on the NCM surface, as well as cause the destruction of NCM surface structure during storage, leading to serious performance degradation. Constructing the interfacial nanolayer with aromatic polyamide (APA) on the surface of NCM active particles (NCM@APA) can mitigate interfacial side reactions between NCM and SPE. Robust interfacial nanolayers not only effectively protect the crystal structure of NCM but also provide a steady interfacial environment for Li + diffusion kinetics. Accordingly, NCM@APA||SPE||Li ASSLBs exhibit an acceptable voltage drop of 0.27 V after 10 days storage and a substantially improved electrochemical performance with an average coulombic efficiency of 99.1% and capacity retention of 76.7% at 30 mA g −1 after 80 cycles.
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