Electrospinning as a relatively mature method for preparing nanomaterials has been widely used for the preparation of one-dimensional nanofibres and related materials. In this paper, we found that two-dimensional flat filaments can be also obtained by careful design related parameters during electrospinning. Such two-dimensional nano-flat fiber (TDFF) has rather large aspect ratio, and thickness as low as 20-30 nm, while the length in the other two directions can reach micrometer level. This indicates that these materials can be regarded as two-dimensional nano-materials. The morphology of TDFF can be completely preserved after high-temperature calcination, achieving a inorganic two-dimensional sheet materials (TDFF-TiO2). The resulted TDFF-TiO2 not only have 2D structure, but also can be utilized as excellent two-dimensional dielectric filler. They can greatly improve the breakdown strength of the final polymer composites based on PVDF/TiO2 comparing with its 1D competitor, thereby improving the energy storage density of these materials. By adjusting the content of titanium dioxide nanofiller in the composite, a composite film (3vol%-TiO2/PVDF) was obtained with a maximum energy density of 12.45 J/cm3 (467 kV/mm). Since no conductive filler is added, the dielectric loss of the film is only 0.03 at the frequency 103-104 Hz. According to the energy density calculation formula, the substantial increase in the breakdown strength causes the energy density of the composite material to be significantly increased, which is 350% of the original pure polymer PVDF. More importantly, this method has universality and extensiveness and is expected to become a general method for preparing two-dimensional inorganic materials in the future.