Lithium metal batteries are being explored in meeting ever-increasing energy density needs. Because of serious dendritic lithium issues in liquid-state electrolytes, it is generally thought that solid-state electrolytes are potential alternatives for lithium metal batteries. Herein, we design a new single lithium-ion conducting lithium poly­[(cyano)­(4-styrenesulfonyl)­imide] (LiPCSI) to replace the conventional dual-ion conducting salt for use in solid polymer electrolytes (SPEs) that successfully suppress the growth of lithium dendrites. Owing to highly delocalized anion moiety and oxidation-resistant cyano group, the tailored PEO8–LiPCSI SPE exhibits extremely high Li+ transference number (0.84) as well as oxidation potential (5.53 V vs Li+/Li). The symmetric Li/PEO8–LiPCSI/Li cell runs for 1000 h at 60 °C without a short circuit. The rechargeable solid-state Li/PEO8–LiPCSI/LiFePO4 cell discharges a capacity of 141 mAh g–1 with retention over 85% during 80 cycles. These merits enable the proposed PEO8–LiPCSI SPE to be very promising for solid-state lithium metal battery applications.

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The hybrid P3/P2-structured Na 0.5 Ni 0.3 Mn 0.7 O 2 as a cathode material for sodium-ion batteries (SIBs) demonstrates high initial discharge capacity. However, the existence of an unstable P3 phase leads to a fast capacity fade that is adverse to engineering applications. Herein, the introduction of inactive magnesium to partially replace electrochemically active nickel of Na 0.5 Ni 0.3 Mn 0.7 O 2 is proposed to reinforce the structural stability of the material. It is found that magnesium incorporation can suppress the growth of the P3 phase, and proper substitution of magnesium for nickel can even harvest pure P2 phase material. The X-ray diffraction (XRD) pattern reveals that the prepared Na 0.5 Ni 0.2 Mg 0.1 Mn 0.7 O 2 (Mg-0.1) is a structure-stable P2-type material. The fabricated Na 0.5 Ni 0.2 Mg 0.1 Mn 0.7 O 2 SIB cathode exhibits acceptable initial discharge capacity, tunable rate capability, and satisfactory cycling stability. These superior electrochemical properties account for low electrochemical resistances, fast Na + diffusion kinetics, and the extremely stable structure of the P2-Na 0.5 Ni 0.2 Mg 0.1 Mn 0.7 O 2 material, which are revealed by means of electrochemical impedance spectra and ex situ XRD technologies.

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