Lithium‐ion batteries with polymer electrolytes (PEs) are promising candidates for high safety performance batteries. However, conventional PEs suffer from poor compatibility and high impedance of electrolyte–electrode interfaces. Herein, we present a method of the interfacial modification for PEs to inhibit lithium dendrites based on the solution to the interfacial compatibility. Our strategy is to improve the interfacial properties and inhibit the dendrite generation by coating a modified layer on PEs of the anode side with acetylene black (AB) and MXene. The mixed conductive layer (MCL) can promote the generation of Li3N and LiF with a uniform arrangement of electrons to form a dense solid electrolyte interphase layer and the even lithium‐ion deposition for improving the performance and stability of the battery during cycling. After adding the MCL, the discharge capacity of solid lithium‐ion batteries (SLIBs) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/organic modified montmorillonite (OMMT)/soybean isolate protein (SPI)/poly(vinylidene fluoride) (PVDF) (LOSP) PE from 74.2 mAh g−1 up to 111.1 mAh g−1 (AB‐LiTFSI/OMMT/SPI/PVDF (AB‐LOSP)) and 111.6 mAh g−1 (AB/MXene‐LiTFSI/OMMT/SPI/PVDF (AB/MXene‐LOSP)). The polarization voltage dropped by 0.06 and 0.12 V, respectively. This work represents a milestone in the dendrite‐free SLIBs with good performances.