Mesoporous TiO2-B/anatase microparticles have been in-situ synthesized from K2Ti2O5 without template. The TiO2-B phase around the particle surface accelerates the diffusion of charges through the interface, while the anatase phase in the core maintains the capacity stability. The heterojunction interface between the main polymorph of anatase and the trace of TiO2-B exhibits promising lithium ion battery performance. This trace of 5% (by mass) TiO2-B determined by Raman spectra brings the first discharge capacity of this material to 247 mA·h·g− 1, giving 20% improvement compared to the anatase counterpart. Stability testing at 1 C reveals that the capacity maintains at 171 mA·h·g− 1, which is better than 162 mA·h·g− 1 for single phase anatase or 159 mA·h·g− 1 for TiO2-B. The mesoporous TiO2-B/anatase microparticles also show superior rate performance with 100 mA·h·g− 1 at 40 C, increased by nearly 25% as compared to pure anatase. This opens a possibility of a general design route, which can be applied to other metal oxide electrode materials for rechargeable batteries and supercapacitors.