Introduction Global energy crisis has sparked unprecedented momentum for renewable energy sources. Energy storage systems such as electrochemical capacitors, batteries, fuel cells, and dielectric capacitors are considered as the most important technologies to address rapidly growing energy demands and environmental concerns. In comparison with batteries or fuel cells, dielectric capacitors possess high power density resulting from their faster charging/discharging characteristics, which are advantageous for power electronics and pulse power applications. The majority of materials used for fabrication of dielectric capacitors consist of linear dielectrics, ferroelectrics, relaxor ferroelectrics, and anti-ferroelectrics. Among these materials, relaxor ferroelectrics are the most popular choice for capacitor applications because of their lack of long-range order ferroelectric domains. (1-x)Pb(Mg1/3Nb2/3)O3- xPbTiO3 (PMNT) as the typical representative of relaxor ferroelectrics, which possesses small remanent polarization and low coercive electric field, enjoys promising prospects in dielectric capacitor application. Nevertheless, limited by its low Eb, the energy storage density and efficiency for pure PMNT film are not yet ideal. Moreover, it is difficult for traditional PMNT film to be bendable due to limitations of rigid substrates, which lead to descend of flexibility and cannot meet modern flexible electronic production requirements. In this paper, to overcoming the bottlenecks of inflexibility and inferior energy storage performance of the pure PMNT films, rare-earth element of Sm and promising LaNiO3 (LNO) buffer layer were introduced into PMNT thin film. To obtain extraordinary flexibility, two-dimensional mica substrate was used to prepare the modified PMNT film via a simple sol-gel method. The microstructure, dielectric, ferroelectric and energy storage properties of the flexible Pb0.99Sm0.01(Mg1/3Nb2/3)0.68Ti0.32O3 (PSMNT) film were studied systematically.Methods The PSMNT and LNO films were prepared using a sol-gel method. First, niobium ethoxide (Nb(OC2H5)5) was dissolved in 2-methoxyethanol at room temperature. And tetrabutyl titanate (Ti(OC4H9)4) was stabilized in acetylacetone. Second, lead (II) acetate trihydrate (Pb(CH3COO)23H2O) with 10% excess Pb, samarium (III) nitrate hexahydrate (Sm(NO3)36H2O), and magnesium (II) acetate tetrahydrate (Mg(CH3COO)24H2O) were dissolved together in a mixed solvent of glacial acetic acid and 2-methoxyethanol (volume ratio of 2:1) at room temperature. Then, the solutions above were mixed to obtain the PSMNT precursor. To prepare the LNO precursor, the lanthanum (III) nitrate hexahydrate (La(NO3)36H2O) and nickel (II) acetate tetrahydrate (Ni(CH3COO)24H2O) were dissolved in 2-methoxyethanol. The concentration of the PSMNT and LNO precursors were 0.2 mol·L-1 and 0.1 mol·L-1, respectively. The flexible mica substrate was separated from the bulk fluorphlogopite mica crystal by mechanical exfoliation using a razor blade in deionized water. When the thickness of the mica substrate was reduced to ~15 μm, good flexibility could be realized. The LNO precursor solution was firstly spin-coated onto the mica substrate, followed by an annealing process at 750 ℃ for 2 min. Then, the PSMNT precursor was spin-coated on the surface of the freshly prepared LNO layer and then the wet film was annealed at 700 ℃. The spin-coating and annealing process was repeated to achieve a desirable film thickness. Finally, Au top electrodes, ~200 μm in diameter, were sputtered on the film surface through a shadow mask for electrical properties measurements.Results and discussion PSMNT and PMNT thin films were directly deposited on LaNiO3 buffered mica substrate via simple one-step fabrication process. X-ray diffraction (XRD) results indicated that the crystal structure of PSMNT film was pure perovskite phase without detectable secondary phases. Scanning electron microscope (SEM) measurement revealed that the film exhibited compact microstructure with uniform crystal grain distribution, indicating that the PSMNT film can be successfully grown on the LaNiO3 buffered mica substrate. In terms of polarization characteristics, slim hysteresis loop with a large maximum polarization Pmax (~74.5 μC/cm2) and a small remnant polarization Pr (~16.4 μC/cm2) was observed in the PSMNT film under the electric field of 2 468 kV/cm, while fatted P-E loop was observed in the PMNT film. The leakage current density in the PSMNT film is almost an order of magnitude lower than the pure PMNT sample, indicating the success of the introduction of Sm in improving of electric resistance. The recoverable energy storage density for the PSMNT film capacitor at the maximum electric field was 40.7 J/cm3, and the corresponding energy-storage efficiency was 70% due to its high breakdown strength and strong relaxor dispersion. The PSMNT film capacitor also exhibits excellent stability in energy storage performance in a wide operating frequency (1-20 kHz) and broad temperature (25-120 ℃) ranges. With the assistance of a mica substrate, the all-inorganic PSMNT/LNO/mica capacitor possesses an outstanding mechanical-bending resistance without obvious deterioration in its energy storage performance even down to a bending radius of 2 mm or repeated bending for 103 cycles. Conclusions The main conclusions of this paper are summarized as following. Flexible Pb0.99Sm0.01(Mg1/3Nb2/3)0.68Ti0.32O3 (PSMNT) film was successfully deposited on LaNiO3 buffered mica substrate by a simple sol-gel method. A high recoverable energy density of 40.7 J/cm3 and efficiency of 70% were realized in the fabricated film capacitor. The energy storage performance was quite stable in a wide temperature (25-120 ℃) and frequency (1-20 kHz) ranges. Meanwhile, the designed PSMNT film capacitor exhibited superior mechanical-bending resistance since it is attached on the bendable mica substrate, and its energy storage behavior did not show obvious deterioration even under a small bending radius of R=2 mm and 1 000 mechanical bending cycles (R=4 mm). This study showed that flexible PSMNT thin film on mica platform has bright prospects in future ?exible electronics application for energy storage.