Recently, ferroelectric ceramics with high maximum polarization, low remnant polarization and high electric breakdown strength (BDS) have attracted much attention due to their potential applications in energy storage capacitors. In this work, we show a novel kind of (Ba,Sr)TiO3 (BST)-based lead-free ferroelectric ceramics, i.e., (1-x)Ba0.9Sr0.1TiO3-xBi(Zn0.5Zr0.5)O3 (BST-xBZZ) solid solutions, which were fabricated by the traditional solid-state reaction process. By introducing the BZZ into BST with a content from 0.05 to 0.20, purely pseudocubic perovskite phases and highly dense structures are obtained. The increase of the BZZ content not only shifts the TC toward to lower temperature, but also induces strong relaxor behaviors with diffuse phase transition characteristics, thus improving the temperature stability of dielectric properties. Of special interest is the improved energy storage properties, which were systematically evaluated by measuring the polarization-electric field (P-E) hysteresis loops as a function of electric field, frequency and loading cycle. It is found that BT-0.15BZZ ceramic achieves a maximum energy density of 1.11 J/cm3, which is attributed to the improvement of BDS. In addition, relatively good frequency stability and fatigue resistance of this composition suggest its potential application in energy storage devices.