LAUSR

DOI: 10.1002/aenm.201900801 globe.[4,5] However, lack of economical energy scavenging technologies has been restricting the development of largescale blue energy harvesting. Recently, triboelectric nanogenerator (TENG) is invented as a profound new technology in converting ambient mechanical energy into electricity and attracts great attention worldwide.[6–9] Different from electromagnetic generator, the TENG based on triboelectrification and electrostatic induction has superior advantages in light-weight, low-cost, and is suitable for harvesting mechanical energy in low oscillating frequency, which is promising to be used in energy harvesting in the ocean wave situation.[10–12] In the past few years, TENG has been growing quickly in output performance with the efforts of over 40 research groups around the world.[13–15] However, to build a TENG network that can harvest blue energy with both high efficiency and durability, there are still many technical hurdles to be addressed.[10,16,17] Most previously reported TENGs can achieve optimal energy output in the rough seas, but they perform poorly in the halcyon seas, which is common in the actual sea.[18,19] To expand the application of TENG in halcyon seas, a highly sensitive TENG for small water waves is indispensable. TENG shapes usually designed for blue energy harvesting are limited in sphere,[18–20] cylinder,[21–23] and cuboid.[24–26] The mobile object inside these TENGs would lead to the imbalance of gravity center under the water waves, and lose its posture for optimal output performance, even the centrosymmetric sphere cannot survive due to its lack of centrosymmetric electrode pattern on its surface. Additional fixture for every TENG in a large-scale array would be intricate, and the cost would increase in the fabrication, installment, and maintenance. In short, a novel design of TENGs with self-stabilization and high sensitivity is in urgent need to further boost the TENG for blue energy dream. Herein, for the first time we introduce the oblate spheroidal triboelectric nanogenerator (OS-TENG) elaborately designed with two novel TENG parts for all-weather blue energy harvesting. As shown in Figure 1a, the TENG in the upper part consists of three basic units based on spring steel plates with a pie iron to suppress, which would output substantial electricity under rough seas without coil springs support, thus it occupies less space and reduces cost tremendously. For the TENG in the lower part, due to the gentle slope at the bottom of the oblate Triboelectric nanogenerators (TENGs) provide one of the most promising techniques for large-scale blue energy harvesting. However, lack of reasonable designs has largely hindered TENG from harvesting energy from both rough and tranquil seas. In this paper, an oblate spheroidal TENG assembled by two novel TENG parts is elaborately designed for both situations. The TENG in the upper part is based on spring steel plates without other substrate materials, which makes it possible to output considerable power in rough seas and occupy small space. The TENG in the lower part consists of two copper-coated polymer films and a rolling ball which can capture small wave energy from tranquil seas. The working mechanism and output performance are systematically studied. A maximum open-circuit voltage of 281 V and a short-circuit current of 76 μA can be achieved by one upper part, enough to charge a commercial capacitor for potential applications. More important, the proposed oblate spheroidal shell not only guarantees high sensitivity of the TENG in the lower part, but also qualifies the TENG with unique self-stabilization and low consumables for the next generation of TENGs with new structural design toward all-weather blue energy harvesting.