In recent years, rechargeable aqueous zinc‐ion batteries (ZIBs) have received much attention. However, the disproportionation effect of Mn2+ seriously affects the capacity retention of ZIBs during cycling. Here, the capacity retention of the Mn3O4 cathode is improved by effective valence engineering. The valence engineering of Mn3O4 is caused by bulk oxygen defects, which are in situ derived from the Mn‐metal organic framework during carbonization. Bulk oxygen defects can change the (MnO6) octahedral structure, which improves structural stability and inhibits the dissolution of Mn2+. The ZIB assembled from bulk oxygen defects Mn3O4@C nanorod arrays (Od‐Mn3O4@C NA/CC) exhibits an ultra‐long cycle life, reaching 84.1 mAh g−1 after 12 000 cycles at 5 A g−1 (up to 95.7% of the initial capacity). Furthermore, the battery has a high specific capacity of 396.2 mAh g−1 at 0.2 A g−1. Ex situ characterization results show that initial Mn3O4 is converted to ramsdellite MnO2 for insertion and extraction of H+ and Zn2+. First‐principles calculations show that the charge density of Mn3+ increases greatly, which improves the conductivity. In addition, the flexible quasi‐solid‐state ZIB is successfully assembled using Od‐Mn3O4 @ C NA/CC. Valence engineering induced by bulk oxygen defects can help develop advanced cathodes for aqueous ZIB.

Zinc metal batteries show tremendous applications in wide-scale storages still impeded by aqueous electrolytes corrosion and interfacial water splitting reaction. Herein, a zincophobic electrolyte containing succinonitrile (SN) additive is proposed, the SN electrolyte shows a lower affinity for zinc but a stronger affinity for solid-state interphase (SEI). In the SN electrolyte, zinc hydroxide sulfate (ZHS) is more inclined to accumulate horizontally, forming a dense SEI protective layer on the surface of the Zn anode, effectively slowing down the corrosion of Zn and dendrite growth. The zincophobic SN electrolyte enables excellent performance: zinc plating/stripping Coulombic efficiency of 99.71% for an average of 400 cycles; stable cycles in a symmetric cell for 4000 h (0.9% zinc utilization) and 325 h (86.1% zinc utilization). The soft pack battery using limited zinc delivers maximum energy density of 57.0 Wh kg −1 (based on mass loading of cathode materials and anode materials). Such a simple additive strategy provides a theoretical reference for zinc chemistry in a mild electrolyte environment in practical applications.

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Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) have drawn much attention in the ferroelectric field because of their excellent piezoelectric properties and high electromechanical coupling coefficients (d33∼2000 pC/N, kt∼60%) near the morphotropic phase boundary (MPB). Ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals also possess outstanding performance comparable with PMN-PT single crystals, but have higher phase transition temperatures (rhombohedral to tetragonal Trt, and tetragonal to cubic Tc) and larger coercive field Ec. Therefore, these relaxor-based single crystals have been extensively employed for ultrasonic transducer applications. In this paper, an overview of our work and perspectives on using PMN-PT and PIN-PMN-PT single crystals for ultrasonic transducer applications is presented. Various types of single-element ultrasonic transducers, including endoscopic transducers, intravascular transducers, high-frequency and high-temperature transducers fabricated using the PMN-PT and PIN-PMN-PT crystals and their 2-2 and 1-3 composites are reported. Besides, the fabrication and characterization of the array transducers, such as phased array, cylindrical shaped linear array, high-temperature linear array, radial endoscopic array, and annular array, are also addressed.

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5–6 MHz PMNT/epoxy 1–3 composites were prepared by a modified dice-and-fill method. They exhibit excellent properties for ultrasonic transducer applications, such as ultrahigh thickness electromechanical coupling coefficient kt (85.7%), large piezoelectric coefficient d33 (1209 pC/N), and relatively low acoustic impedance Z (1.82 × 107 kg/(m2·s)). Besides, two types of Time-of-Flight Diffraction (TOFD) ultrasonic transducers have been designed, fabricated, and characterized, which have different matching layer schemes with the acoustic impedance of 4.8 and 5.7 × 106 kg/(m2·s), respectively. In the detection on a backwall of 12.7 mm polystyrene, the former exhibits higher detectivity, the relative pulse-echo sensitivity and −6 dB relative bandwidth are −21.93 dB and 102.7%, respectively, while the later exhibits broader bandwidth, the relative pulse-echo sensitivity and −6 dB relative bandwidth are −24.08 dB and 117.3%, respectively. These TOFD ultrasonic transducers based on PMNT/epoxy 1–3 composite exhibit considerably improved performance over the commercial PZT/epoxy 1–3 composite TOFD ultrasonic transducer.

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