**4. Conclusions**

In this study, low crystalline MoO3/carbon composite microspheres in which MoO3 nanocrystals were distributed homogeneously in the amorphous C matrix, were directly prepared by a one-step spray pyrolysis within several seconds. The MoO3/carbon composite was spherical, with diameters on the order of microns, because they were formed from one droplet with several tens of micrometers by a series of drying, decomposition, and crystallization processes inside the hot-wall reactor during spray pyrolysis. The amorphous C matrix of the MoO3/C composite microspheres effectively buffered the large volume change of the MoO3 active material during the fast charging–discharging process. Therefore, a better cycling of the MoO3/C composite microspheres could be achieved because of the improved structural stability of the MoO3. Additionally, the small MoO3 nanograins imbedded within the C matrix decreased the diffusion distance and increased the diffusion rate of Li+ ions, thus accelerating the rate of the MoO3/C composite microspheres. The superior Li+-ion storage properties of the MoO3/C composite microspheres compared to those of the bare MoO3 were supported by an EIS analysis and by observing the morphologies of the samples obtained after 100 cycles. The simple process introduced in this study is expected to be useful for the large-scale synthesis of TMOs/carbon composite microspheres for a wide variety of applications including energy storage.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-4991/9/4/539/s1, Figure S1: Schematic diagram of spray pyrolysis system applied in the preparation of MoO3/C composite microspheres, Figure S2: N2 adsorption-desorption isotherms measured at 77 K for the MoO3/C composite microspheres and bare MoO3 powders, Figure S3: Cycle properties of the MoO3/C composite microspheres and the bare MoO3 powders, Figure S4: TGA curve of the bare MoO3 powders, Table S1: Fitted data obtained from the equivalent circuit for Nyquist plots.

**Funding:** This work was supported by the National Research Foundation of Korea (NRF) gran<sup>t</sup> funded by the Korea governmen<sup>t</sup> (MSIP) (NRF-2018R1A4A1024691, NRF-2017M1A2A2087577, and NRF-2018R1D1A3B07042514).

**Conflicts of Interest:** The authors declare no conflict of interest.
