Effect of graphene sheet and toluene-soluble component of pitch on the preparation, structure, and performance of LiMn0.8Fe0.2PO4@C@GNs

The graphene sheets (GNs) and toluene-soluble component of pitch (TS) are used as the mixed carbon source in the synthesis of LiMn 0.8 Fe 0.2 PO 4 @C@GNs through different carbon-coating methods. The results show that the ball–milling (BM) method is more favorable for the uniform dispersion of GNs and reduction of agglomeration compared to mechanical agitation (MA). The bridging effect of GNs and the pyrolytic carbon of TS with a high graphitization degree constructs an intact carbon skeleton on the surface of LiMn 0.8 Fe 0.2 PO 4 crystal, thus greatly improving the structural stability and electronic conductivity. Sample BM–1.5 containing 1.5 wt.% GNs prepared by ball–milling has a small (111) grain size, large specific surface area (48.32 m 2 ·g −1 ), and mesoporous volume (0.099 cm 3 ·g −1 ). Cathode BM–1.5 delivers the discharge-specific capacity of 150.9, 150.4, and 115.7 mAh·g −1 at the rate of 0.1 , 1, and 5 C, respectively, which are the optimal values of all samples. Moreover, the capacity in BM–1.5 at 1 C is well maintained at the retention of 95.7% after 100 cycles. And no obvious crack appears in the cathode film, showing excellent structural stability. Graphical abstract LiMn 0.8 Fe 0.2 PO 4 @C@GNs prepared by ball-milling with the toluene-soluble component of pitch and graphene sheet as the mixed carbon source has excellent electrochemical performance.