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Abstract2D magnetic materials have aroused widespread research interest owing to their promising application in spintronic devices. However, exploring new kinds of 2D magnetic materials with better stability and realizing their batch synthesis remain challenging. Herein, the synthesis of air‐stable 2D Cr5Te8 ultrathin crystals with tunable thickness via tube‐in‐tube chemical vapor deposition (CVD) growth technology is reported. The importance of tube‐in‐tube CVD growth, which can significantly suppress the equilibrium shift to the decomposition direction and facilitate that to the synthesis reaction direction, for the synthesis of high‐quality Cr5Te8 with accurate composition, is highlighted. By precisely adjusting the growth temperature, the thickness of Cr5Te8 nanosheets is tuned from ≈1.2 nm to tens of nanometers, with the morphology changing from triangles to hexagons. Furthermore, magneto‐optical Kerr effect measurements reveal that the Cr5Te8 nanosheet is ferromagnetic with strong out‐of‐plane spin polarization. The Curie temperature exhibits a monotonic increase from 100 to 160 K as the Cr5Te8 thickness increases from 10 to 30 nm and no apparent variation in surface roughness or magnetic properties after months of exposure to air. This study provides a robust method for the controllable synthesis of high‐quality 2D ferromagnetic materials, which will facilitate research progress in spintronics.

Despite of the good stability with Li‐metal, Li6.75La3Zr1.75Ta0.25O12(LLZTO) suffers from large interfacial resistance and severe Li‐metal penetration. Herein, a dual layer ceramic electrolyte of Ti‐doped LLZTO(Ti‐LLZTO)/LLZTO was developed, with the reducible Ti‐LLZTO layer contacting Li‐metal and the LLZTO layer contacting cathode. The identical crystal structures of Ti‐LLZTO and LLZTO enables a seamless contact and a barrierless Li+ transport between them. The densities of Ti‐LLZTO pellets are higher than that of LLZTO. With an in situ reduction of Ti‐LLZTO by Li‐metal, the interfacial wettability was improved and a mixed ion‐electron conducting layer was created. Both features help to reduce defects/pores on interface and homogenize the interfacial ionic/electronic flux, facilitating the reduction of interfacial resistance and suppression of dendrites. With the help of Ti‐LLZTO layer, long‐term stable lithium plating/stripping was reached in an areal capacity of 3.0 mAh cm−2.