Energy Storage Performance Of KNN-B'(Mn_0.5Ni_0.5)O₃(B'=La,Bi) Ferroelectric Ceramics

With the increasingly serious energy crisis and environmental pollution,there is an urgent need to develop efficient and environmentally friendly energy storage devices to achieve energy storage and effective use.Among many energy storage devices,ceramic dielectric capacitors can be widely used in modern electronic equipment and pulse power systems owing to their ultra-high power density and super fast charge-discharge capabilities.However,an inferior energy storage density and efficiency of ceramic dielectric capacitors hinders their practical application compared with other energy storage devices.Hence,it is of great practical significance to design and develop energy storage ceramic materials with excellent comprehensive performance.Among them,K0.5Na0.5NbO3(KNN)ceramics show great application potential in the field of energy storage due to its high saturation polarization intensity,high Curie temperature and environmental friendliness.But the high residual polarization intensity and relatively low breakdown electric field are the main factors limiting its energy storage characteristics.Along the way in this paper,the K0.5Na0.5NbO3 ceramics were selected as the base system,and through composition design strategy to reduce the grain size and enhance relaxor characteristics,it is expected to obtain KNN-based ceramics with excellent energy storage properties and charge-discharge performances.The research content mainly includes:1.Relaxor ferroelectric ceramics(1-x)K0.5Na0.5NbO3-xLa(Mn0.5Ni0.5)O3(0 ? x?0.07;(1-x)KNN-xLMN)featuring with great charge-discharge performance and energy storage properties were designed and prepared using traditional solid-state sintering technique,and the effects of LMN doping on the phase structure,microstructure and electrical properties of the ceramics were systematically studied.The results have shown that(1-x)KNN-xLMN ceramics phase structure gradually changes from the orthogonal phase to the pseudo-cubic phase,the introduction of LMN effectively inhibit the growth of the ceramic grain,won a fine-grain submicron(180 ± 10 nm),which is advantageous to the ceramic get high breakdown field strength and density.The introduction of unequal cations at the A/B site has made the dielectric peak of the ceramic significantly broadened,showing a strong relaxor behavior.The hysteresis loop changes from square with large residual polarization intensity to thin strip,and the energy storage performance is greatly improved.The recoverable energy storage density Wrec of 0.97KNN-0.03LMN ceramics has achieved 1.65 J/cm3 under an electric field of 190 kV/cm,the corresponding energy storage efficiency ? is as high as 76%.In addition,0.97KNN-0.03LMN ceramics have the superfast discharge velocity(t0.9?55 ns),the current density CD and power density PD can reach 1719.75 A/cm2 and 154.78 mW/cm3 at the applied electric field of 180 kV/cm.2.Bi3+ with high polarizability was introduced to replace La3+ at the A position to increase the Pmax of ceramics,(1-x)K0.5Na0.5NbO3-xBi(Mn0.5Ni0.5)O3(x=0.02?0.07;(1-x)KNN-xBMN)ceramics were synthesized successfully.The phase structure,microstructure,dielectric relaxor behavior,energy storage and charge-discharge properties of(1-x)KNN-xBMN ceramics were systematically studied.The results have shown that the phase structure of(1-x)KNN-xBMN ceramics are pseudo-cubic phase with good symmetry,and the grain size is much smaller than that of the pure potassium sodium niobate.When x=0.05,the grain size has reached the minimum of about 118 nm,which effectively improves the breakdown electric field of(1-x)KNN-xBMN ceramics.According to the dielectric behavior of(1-x)KNN-xBMN ceramics,have shown the relaxation-like properties of the diffusion phase transition,and achieving pinched and linear like P-E loops toward enhancing the energy storage performance.When x=0.02,the Pma of ceramics has increased to 40.35 ?C/cm2.But the Pmax decreases gradually as the increases of BMN fraction.Resultantly,0.96KNN-0.04BMN ceramics attained an exceptionally high energy storage properities(Wrec=1.826 J/cm3,?=77.4%)at 240 kV/cm,superior frequency-stable(1?500 Hz)and fatigue resistance(1?5000)guarantee the practical use.Meanwhile,an extremely high PD?98.90 MW/cm3,CD?1236.31 A/cm2 and ultra-fast discharge speed(t0.9<70 ns)among the wide working temperature range(30?180?)are achieved in 0.96KNN-0.04BMN ceramics.Our investigation illustrates that the 0.96KNN-0.04BMN ceramics can be used as alternative materials for high temperature ceramic capacitors.