Boosting output charge density is top priority for achieving high-performance triboelectric nanogenerators (TENGs). The charge-excitation strategy is demonstrated to be a superior approach to acquire high output charge density. Meanwhile, the molecular charge behaviors in the dielectric under a strong electric field from high charge density bring new physics that are worth exploring. Here, a rapid self-polarization effect of a polar dielectric material by the superhigh electric field in a charge-excitation TENG is reported, by which the permittivity of the polar dielectric material realizes self-increase to a saturation, and thus enhances the output charge density. Consequently, an ultrahigh charge density of 3.53 mC m −2 is obtained with 7 µm homemade lead zirconate titanate−poly(vinylidene fluoride) composite film in the atmosphere with 5% relative humidity, which is the highest charge density for TENGs with high durability currently. This work provides new guidance for dielectric material optimization under charge excitation to boost the output performance of TENGs toward practical applications.

According to the output mode, TENGs can be classified into four categories: i) Mechanical rectification DC TENG (coupling CE and electrostatic induction) [8,9] ; ii) constant DC TENG (Coupling CE and air breakdown) [10,11] ; iii) ordinary AC TENG (coupling CE and electrostatic induction) [12,13] ; iv) inverting AC TENG (Coupling CE with air breakdown). [14] Besides, TENGs can convert ambient mechanical energy from rain, [15,16] wind, [17,18] water flow, [19,20] and body motion [21,22] , etc. into electrical energy at relatively low frequency, so it has superiority to electromagnetic generators in the specific low-frequency mechanical energy harvesting field. [23][24][25] With structure flexibility, TENG can be integrated with other research fields in practical applications, for example, electrocatalysis, [26] biosensing, [27] autoclaving, [28] high-voltage application, [29][30][31][32] artificial intelligence, [3,14] environmental monitoring, [33] which greatly exhibits TENG properties in adjustability, compatibility and high efficiency. [34][35][36][37] The application capability of TENGs is determined by the electric energy output density per cycle, which largely depends on the surface charge density originating from the contact electrification effect. For this reason, many strategies are carried out to boost TENG output charge density, such as vacuum environment, [38] temperature [37] difference, [13] surface modification, [39] and hydrophobic treatment, [40] , etc. Recently, charge excitation methods have achieved a 3.53 mC m −2 output charge density by self-polarization of polar high-k material in charge excitation process. [41] Similarly, the optimal output charge of Miura folding-based TENG has been elevated 4.61 times with the charge excitation strategy. [42] Space-accumulation effect is an effective method for the sliding TENG, which can make 2.3 times improvement compared with the normal sliding TENG in ambient conditions. [43] Nevertheless, the output of TENG based on the coupling of CE and electrostatic induction is still limited by air-breakdown. [35] Solving the problem of air breakdown would be one of the effective ways for TENG to achieve the higher output. After increasing electrodes to 50 units, Wang, et al. achieve an output charge density of 8.80 mC m -2 and an average power density of 0.2 W m -2 for the DC-TENG Triboelectric nanogenerators (TENGs) are regarded as a promising technology to convert ambient low-frequency mechanical energy into electricity for distributed power supply. Although TENGs based on triboelectrification (TE) of metal-dielectric and air breakdown have the advantage of direct current (DC) output, the unidirectional and single-channel output mode limits their energy utilization efficiency. Here, a bidirectional and double-channel (BDC-TENG) based on TE of dielectric-dielectric and local corona discharge is proposed. Different from traditional DC-TENGs, the TE process of the BDC-TENG occurs in two dielectrics, and the double-channel output is generated from simultaneous dis...

The modification of triboelectric materials is an important means to improve the output performance of triboelectric nanogenerator (TENG), and the surface charge or ion implantation is an effective way among many modification methods. However, the output enhancement via optimizing triboelectric materials is still limited. Herein, a fast surface charge injection technique based on air breakdown effect is reported, which utilizes an excitation circuit to realize the directional accumulation of charge. Consequently, the output charge density of the Polyimide (PI) film after charge injection reaches 880 µC m -2 , which is the highest of the series of modified triboelectric materials. Moreover, a novel charge transfer mechanism with electrostatic induction competition is proposed, in which significant difference between surface charge density and output charge density is highlighted clearly. Meanwhile, the method of quantifying surface charge density is further given. This work provides a more effective method for the modification of dielectric materials and also offers an important insight towards the charge transfer mechanism in TENG.

potential in the field of energy harvesting due to its advantages, such as being easy to manufacture, [4] light weight, [5] of low cost and with a wide selection of materials. [6] TENG working mode can be divided into horizontal sliding mode and vertical contact-separate mode. [7] Relatively, sliding mode TENGs have higher triboelectrification efficiency and output power, and are more suitable for harvesting natural energy, such as wind and water energy. [8] In recent years, the output energy of TENGs has been improved, and those high output power TENGs are able to power some small electronic devices. [9] However, the surface wear formed in the triboelectrification process has a great impact on the stability of their output, and improving the durability has always been a great challenge.It is shown that the output energy of TENG is proportional to the square of output charge density. [10] In previous works, some researchers have greatly improved the output charge density of TENGs by various strategies, such as charge excitation, [11] increase of contact area, [12] charge space accumulation effect, [9b,13] synthesis of high permittivity tribolayers and so on. [14] For improving charge density, the researchers also realized that only increasing the output was not sufficient for practical applications, since the vertical pressure or friction area increases inevitably in the same time and thus increases mechanical abrasion. As a result, a lot of work has been carried out to improve the durability of TENGs. The strategies include the soft contact to reduce resistance, [15] intermittent contact-separate mode to reduce friction time, [16] rolling friction instead of sliding friction, [17] non-contact mode to avoid friction directly, [8a,18] liquid lubrication to reduce friction coefficient, etc. [18a,19] Those strategies have to sacrifice the output while improving the durability, except for the liquid lubrication strategy, in which the liquid interface lubrication and charge space accumulation effect are combined to achieve higher charge density and higher durability. [19c] However, the TENG with liquid interface lubrication is still based on direct friction in operation, which is sure to have some surface abrasion. In addition, in previous works about liquid lubrication, liquid was To enhance the durability of triboelectric nanogenerator (TENG), liquid lubrication has been used to reduce mechanical abrasion. However, as the charge transportation behavior in dielectric liquid is not clearly understood, the output energy is still low although some improvements have been reported. Herein, the charge transportation behaviors in dielectric liquid by self-excited liquid suspension triboelectric nanogenerator (LS-TENG) are systematically investigated. The important role of solid-liquid triboelectrification effect, charge-liquid transmission and dissipation effect, and the homogeneous dielectric induction effect in promoting its output performance is found. The LS-TENG with a dual dielectric tribolayer has advantage...

Although charge excitation is an effective approach to achieve high charge density for triboelectric nanogenerators (TENGs), high output charge is limited by air-breakdown. Due to capacitor structure, there are two ways to reduce the influence of air-breakdown in TENG: decrease in thickness and increase in permittivity of dielectric film. Obviously, the increase in permittivity is more reliable in applications. Herein, a double-layer TENG shared with one floating metal electrode is proposed, on which charge is injected by a self-excitation circuit. An ultrafast self-polarization effect is found in two barium titanate filled poly(vinylidene fluoride) composite films in the TENG by high electrical field produced from the floating electrode. According to comparison and analysis, the speed of polarization to saturation of dielectric composite films in self-charge excitation approach is ≈3 times faster than that of external-charge excitation. Optimization of various parameters is investigated to enhance the output performance of the TENG. A large output charge density of 1.67 mC m -2 is achieved in the atmosphere with 40% relative humidity due to self-polarization effect of the dielectric composite film. This study provides insights into understanding the polarized behavior of molecules in dielectrics and further optimizing the output performance of TENGs in self-charge excitation systems.