Capsule Triboelectric Nanogenerators: Toward Optional 3D

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Capsule Triboelectric Nanogenerators: Toward Optional 3D Integration for High Output and Efficient Energy Harvesting from Broadband-Amplitude Vibrations Chaoxing Wu, Jae Hyeon Park, Bonmin Koo, Xiangyu Chen, Zhong Lin Wang, and Tae Whan Kim ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b03824 • Publication Date (Web): 01 Oct 2018 Downloaded from http://pubs.acs.org on October 3, 2018

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Capsule

Triboelectric

Nanogenerators:

Toward

Optional 3D Integration for High Output and Efficient Energy Harvesting from BroadbandAmplitude Vibrations Chaoxing Wu1, Jae Hyeon Park1, Bonmin Koo1, Xiangyu Chen2, Zhong Lin Wang3 and Tae Whan Kim1* 1

Department of Electronic and Computer Engineering, Hanyang University, Seoul 04763,

Republic of Korea 2

Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Science, and National

Center for Nanoscience and Technology (NCNST), Beijing 100083, People’s Republic of China 3

School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia

30332, United States of America

ABSTRACT: The technology of triboelectric nanogenerators (TENGs) has made great progress as a promising approach to generate electricity from ambient vibration energy. However, finding a way to generate enough electrical output efficiently from vibrations with a broadband of

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amplitudes is crucial when the relatively low current output of existing TENGs and the existence of natural vibrations with diverse amplitudes are considered. In this work, a freestanding and lightweight triboelectric nanogenerator with a capsule structure, namely a Capsule-TENG, is demonstrated with an aim toward optional 3-dimensional integration and efficient harvesting of energy from vibrations with a broadband of amplitudes. The Capsule-TENGs can be easily integrated to form 1-dimensional, 2-dimensional, and 3-dimensional structures to realize high electrical output. Under the ideal condition, the total output power of an integrated CapsuleTENG pack can be approximately estimated as p × n2, where p is the peak output power per Capsule-TENG and n is the number of Capsule-TENGs. When Capsule-TENGs with hybrid structures, such as different lengths of the capsule tube and different numbers of paired electrodes, are assembled, energy can be more efficiently harvested from vibrations with a broadband of amplitudes. Three parameters, the active area-to-volume ratio, the power-tovolume ratio, and the power-to-weight ratio, which are important parameters for 3D-integrated TENGs, are proposed. The results of this research show that Capsule-TENGs are versatile devices that can potentially be used for efficient harvesting of ambient vibration energy.

KEYWORDS: triboelectric nanogenerator, capsule structure, 3D integration, electric output enhancement, broadband-amplitude vibration

Harvesting energy from the ambient environment and converting it to electricity can address the international problem of the availability of energy and is critical in satisfying the world’s demands for green and renewable energy. Recently, triboelectric nanogenerators (TENGs) based


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on Maxwell’s displacement current have been proven to be promising candidates for potential sustainable power sources due to their cost-effective and robust approaches to harvesting various kinds of mechanical energies, including vibrational energies from the motions of the human body, wind, sound, and water waves.1-10 Predictions are that triboelectric energy-harvesting transducers will be a $400 million market in 2027.11 Even though the development of TENGs as sustainable power sources has made great progress, the needs for high output power and for high energy-to-electricity conversion efficiency are the prime issues when practical applications in power sources are considered. One solution is to integrate multiple units to maximize the output power. Typically, TENGs can be vertically stacked to enhance the electrical output (left panel of Figure 1a-i).12-14 As an improved approach, a TENG with an integrated rhombic gridding structure is developed owing to a further increase in the number of structurally multiplied unit cells (right panel of Figure 1a).15 Another approach to integrating multiple units is to increase the friction area. TENGs with pinned finger structures (Figure 1a-ii) and with layer-by-layer stacked friction layers have been developed (Figure 1a-iii).16-18 Even though the TENGs with multiple integrated units have improved electrical output, the device structure cannot be changed once the device has been fabricated. In other words, the TENGs cannot be optionally integrated to increase the total output. Freestanding TENGs hold promise for the realization of TENG networks, in which the number of freestanding TENGs can be increased infinitely (Figure 1a-iv).19-21 However, additional electricity management systems are necessary to synchronize the outputs of the individual units, which increases the complexity of the entire system. On the other hand, most research on TENGs has focused on the ability to harvest energy effectively from vibrations with a broadband of frequencies.22-26 Worth noting is that vibrations


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in ambient environments are generally distributed over a wide amplitude spectrum and that the vibration energy increases with increasing vibration amplitude. Thus, the approach of efficient energy harvesting from vibrations with different amplitudes should be important. According to the working mechanisms, the in-plane sliding mode holds the potential to harvest energies from vibrations with both small and large amplitudes. However, the electrical output from vibrations with small amplitudes is far lower than that from vibrations with large amplitudes.27-29 As a result, the development of TENGs that can efficiently harvest energy from vibrations with a broadband of amplitudes is another important issue that must be addressed in the search for TENGs with high vibration-energy-to-electricity conversion efficiencies. A good reference for obtaining a high enough output is the electric battery pack. One important feature of a battery is that an optional electrical output can be easily obtained by simply integrating batteries to increase the total output, as schematically shown in the center panel of Figure 1a. This is a promising way to extend the TENG from a two-dimensional (2D) planar structure to a three-dimensional (3D) structure. Thus, the development of simple TENGs with robust and optional integration ability to realize various electrical outputs is very significant from the viewpoint of actual applications. In this work, a freestanding, lightweight triboelectric nanogenerator with a capsule structure, namely, a Capsule-TENG, is demonstrated, as shown in Figure 1b, with an aim toward optional integration to achieve high electrical output and efficient harvesting of energy from vibrations with a broadband of amplitudes. The advantages and the characteristics of our Capsule-TENG are: (1) The key feature of our freestanding CapsuleTENGs is that they can be optionally and easily integrated to form a Capsule-TENG pack with a 1D line structure, 2D planar structure or 3D structure, with these structures functioning like electric battery packs to increase the electrical output, as shown in Figure 1c. (2) Through


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assembly of the Capsule-TENGs with hybrid structures, such as structures with different lengths of the capsule tube and different numbers of paired electrodes, energy can be more efficiently harvested from vibrations with a broadband of amplitudes. We also propose three parameters, the active area-to-volume ratio, the power-to-volume ratio, and the power-to-weight ratio, that are important parameters for 3D-integrated TENGs and can be used to evaluate the performances of future integrated TENG packs. This work establishes a fundamentally versatile solution for realizing optional integration of 3D TENGs to achieve both high electrical output and efficient harvesting of energy from vibrations with a broadband of amplitudes.

Figure 1. Integration for increasing the total electrical output. a) Schematics for the integrated structures of electrical batteries and TENGs for high electrical output. The center panel shows the batteries optionally integrated in parallel and in series, which is a crucial model for use as a reference for the design of the integrable TENGs. a-i) Schematic for TENGs with a zigzagshaped structure and an integrated rhombic gridding structure. a-ii) Schematic for a TENG with a pinned fingers structure. a-iii) Schematic for a TENG with a layer-by-layer stacked structure. aiv) Schematic for a TENG network. b) Photograph of the as-fabricated Capsule-TENG. c) Photograph of the integrated Capsule-TENGs, which serve a function similar to that of an electric battery pack.

RESULTS AND DISCUSSION


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A schematic diagram of the Capsule-TENG is shown in Figure 2a. The Capsule-TENG consists of an inner Al slider enclosed in a polyvinyl chloride (PVC) tube and a pair of aluminum electrodes coated on the outside surface of the PVC tube. The diameter of the Al slider is a little smaller than the inner diameter of the PVC tube so that the Al slider can slide freely inside the tube. An optical image of a fabricated Capsule-TENG is shown in Figure 2b. The CapsuleTENG is lightweight, weighing approximately 0.73 g per unit, which makes it suitable for applications in portable and wearable electronics.

Figure 2. Structure of a Capsule-TENG and its working principle. a) Schematic illustration of the Capsule-TENG. The inset is a cross-sectional view. b) Photograph showing the weight of an as-fabricated Capsule-TENG. c) Schematics for the working principle of the Capsule-TENG in one-way operation. c-i) At the initial state, the induced negative charges accumulate on electrode A. c-ii) As the Al slider moves toward electrode B, the free electrons are driven from electrode A to electrode B. c-iii) As the Al slider reaches the final state, the induced negative charge accumulates on electrode B.

The working principle of the Capsule-TENG is described on the basis of both the sliding of the charged Al slider and the electrostatic induction effect, as demonstrated in Figure 2c. When


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the law of charge conservation is considered, the density of positive charges on the Al slider is much larger than that of negative charges on the inner surface of the PVC tube. The initial and the final states are defined as the states when the Al slider is aligned with electrode A and with electrode B, respectively. At the initial state (Figure 2c-i), the induced negative charges accumulate on electrode A, and an equal number of positive charges accumulate on electrode B. As the Al slider moves toward electrode B, the positive-charged Al slider will cause the free electrons to flow from electrode A to electrode B, as shown in Figure 2c-ii, so a current spike through the external load will be detected. When the Al slider reaches the final state, the charge densities on the two electrodes will be reversed in polarity compared to those on the two electrodes in the initial state, as shown in Figure 2c-iii. When the Al slider moves in the opposite direction, the electron transfer between electrode A and electrode B will be similar, but with opposite polarity. Therefore, an alternating current is generated by the periodic movement of the Al slider. Parameter optimization can have a large influence on the output power of a Capsule-TENG. However, because of the needs for small size and lightweight, the length and the external diameter are fixed as 23 and 7 mm, respectively. Thus, the length of the aluminum electrode is the most important parameter to be considered (the length of the Al slider is the same as that of the aluminum electrode). As shown in Figure 3a, the maximum output can be obtained when the length of aluminum electrode is 10 mm.


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Figure 3. Electrical output performances of a Capsule-TENG. a) The output VOC of CapsuleTENGs with different electrode lengths. LE is the length of the aluminum electrode, and 2LT is the length of the tube (2LT = 23 mm). b) Increase in the generated ISC when the Al slider is preprocessed for different times. The inset presents a schematic diagram of the Al slider with externally introduced positive charges. c) Stability of the Capsule-TENG undergoing a continuous operation of over 104 cycles. The inset shows the time stability of the device. d) Dependence of the peak power on the resistance of the external load. e) Electrical energies generated during a periodic vibration at a resistance of 7.5 MΩ at various frequencies. The inset presents a detailed plot of the output voltage as a function of time. f) Output voltages as a function of time for various values of the relative humidity.

On the other hand, the surface charges, which lead to the process of electrostatic induction in TENGs, are another key parameter affecting the electrical outputs.30 Typically, the triboelectric surface charges can only come from the triboelectrification process between the negative side and the positive side of the TENG. Even though this triboelectrification process is effective and practical, the introduction of external static surface charges holds promising potential for further improvements in the electrical output. However, due to the open structure of most TENGs, a static charge density on the surface of the friction layer decreases gradually as a result of recombination between the static surface charges and opposite polarity ions or particles adsorbed


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from the air.31,32 Because the PVC tube is fully enclosed, externally induced static charges can be preserved for a very long time. Thus, the electric output of our Capsule-TENG can be enhanced by simply introducing additional static charges to the Al slider. In this work, the additional static charges are simply introduced to the Al slider by shaking it in a polyvinylidene fluoride (PVDF) jug before sealing it in a capsule (inset of Figure 3b), namely, Al slider preprocessing. This simple method makes enhancing the electrical output of the Capsule-TENG very easy by controlling the preprocessing time. On the basis of the theory of freestanding triboelectric nanogenerators,33 the short-circuit current is proportional to the triboelectric charge density on the Al slider. At first, the peak short-circuit current of the Capsule-TENG is tested without preprocessing (defined as ‘0’s), as shown in Figure 3b. In that case, all of the static surface charges on the Al slider are generated due to the triboelectrification between the Al slider and the PVC tube. Because PVDF has a stronger ability than PVC to attract electrons, the static positive charge density on the Al slider after preprocessing is improved. Thus, the longer the Al slider rubs against the PVDF, the higher the static positive charge density on the Al slider is, and the higher the electrical output is. Note that the static positive charge density on the Al slider cannot increase infinitely. The peak current is seen to approach a saturation value of about 5.0 µA with increasing preprocessing time to 120 s. In the following sections, all Al sliders should be considered to have been preprocessed by shaking them in a PVDF jug for 120 s. Due to the fully enclosed structure,34-36 the static surface charges introduced to the Al slider are expected to be preserved for a long time, and the Capsule-TENG is expected to be able to generate an elevated output for a long time. In order to investigate the stability of the surface charges existing on the Al slider, we measured the open-circuit voltage (VOC) of a CapsuleTENG undergoing a continuous operation of over 104 cycles. As shown in Figure 3c, the peak


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output VOC is stable. We also measured the time stability, and no obvious degradation of the electrical output is observed after three months (inset of Figure 3c). These results clearly show that introducing external charges to the Al slider is an effective and simple method for our Capsule-TENG to realize a greatly enhanced output for a sufficiently long time. Not that in this work, we just show the results for Al sliders preprocessed by shaking them in a PVDF jug to increase the static charge density. When practical applications are considered, the static charge density of the Al slider can be further increased by using the ion-injection method.37 Furthermore, other polymers or composites with strong electron-gain ability can be utilized to fabricate the enclosed tube, and lightweight materials with strong electron-loss properties can be used to fabricate the sliders. The actual output power from the Capsule-TENG is tested under a vibration frequency of 5.0 Hz. The voltage is increase gradually with increasing resistance. The Capsule-TENG reached a maximum peak power of approximately 2.6 µW at a load resistance of 7.5 MΩ (Figure 3d). The maximum generated electrical energy (Eelectrical) with an optimized load resistance of 7.5 MΩ can be calculated as = ( ) / ∙ ,

(1)

where V(t) is the instantaneous voltage and R is the load resistance. The inset of Figure 3e presents a typical output voltage of the Capsule-TENG at a load resistance of 7.5 MΩ, from which the corresponding energy on the load can be calculated. As shown in Figure 3e and Figure S1, the electrical energy during a periodic vibration increases with increasing vibration frequency, and the highest electrical energy at a vibrational frequency of 5.0 Hz is 165 nJ. One should note that the value of the optimal resistance increases slightly with decreasing vibration frequency (Figure S2).38 However, that change in the optimal resistance is relatively small.


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Furthermore, considering the fact that the load resistance is typically fixed in practical applications, we measured the energy output under different vibration frequencies at a fixed load resistance of 7.5 MΩ. Humidity is one of the critical parameters that significantly affect TENG performance. Typically, the output performances of TENGs might decrease when the humidity increases.39 If the effect of humidity on the performance of a TENG is to be minimized, the TENG should be tightly sealed.40-42 In our work, the fully enclosed structure of the Capsule-TENG insulates the charged Al slider and the charged PVC surface from external shocks, such as the effect of humidity on the generation of static charges. As shown in Figure 3f, the electrical output performance does not change significantly with varying humidity. Thus, the Capsule-TENG is relatively insensitive to the humidity in its surroundings, indicative of its suitability for harvesting energy from vibrations in high-humidity environments. The greatest feature of our Capsule-TENG is that the total electrical output can be easily enhanced by optionally integrating Capsule-TENGs in parallel or in series to form a 1D line structure, a 2D planar structure, or a 3D structure, as schematically demonstrated in Figure 4a. A Capsule-TENG box for integrating Capsule-TENGs is designed, as shown in Figure 4b. There are two aluminum electrodes in the bottom of the box, thus the Capsule-TENGs can easily contact the electrodes due to their outer ring electrodes (Figure 4c). The Capsule-TENGs stacked in the box are automatically electrically connected in parallel (Figure 4d), which can decrease the complexity of the Capsule-TENG pack.19-21 Thus, the number of Capsule-TENGs in a pack can be easily increased or decreased to control the output power, which serves a function similar to that of a commercial electric battery pack. In addition to direct integration in parallel to form a planar structure, the Capsule-TENGs can be integrated in series to form a line structure, as


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shown in Figure 4e. In this case, the unit cells are also electrically connected in parallel. Furthermore, the 3D-integrated Capsule-TENG pack, with goals of increasing the electrical output further and using space more efficiently, can be easily integrated. As demonstrated in Figure 4f, 25 Capsule-TENGs are first integrated in parallel by using a big Capsule-TENG box to form a 5×5 array. Then, this kind of Capsule-TENG packs can be further assembled to form a 3D structure. All the unit cells in the 3D integrated structure are electrically connected in parallel. Worth noting is that the Capsule-TENGs are closely packed in the integration structure. When a Capsule-TENG is driven by vibrations with relatively large amplitudes the Al sliders will move synchronously, and the outputs of all the units in the pack will be synchronized. Thus, only one rectifier has to be used for a Capsule-TENG pack, which can dramatically decrease the complexity of the electricity management system.

Figure 4. Demonstration of the optional integration of Capsule-TENGs. a) Schematic showing that the Capsule-TENGs can be electrically integrated in parallel to form 1D, 2D, and 3D structures. b) Photograph of the as-designed box for integrating Capsule-TENGs. c,d)


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Photographs showing that the Capsule-TENGs can be easily electrically integrated in parallel by using this box. e) Photograph showing that the Capsule-TENGs can be integrated in series to form a 1D line structure by using this box. In this case, all the Capsule-TENGs are electrically connected in parallel. f) Photograph showing that 50 Capsule-TENGs can be electrically integrated in parallel by using the as-designed boxes. In each box, 25 Capsule-TENGs are integrated.

The relationship between the output of the integrated Capsule-TENGs and the number of units is investigated. The output ISC at a vibrational frequency of 5.0 Hz increases linearly with increasing number of units, as shown in Figure 5a. Also, the output ISC increases linearly with increasing volume of the Capsule-TENG pack. Thus, the ISC volume density of the Capsule-TEG pack is found to be a constant of 16.9 µA/cm3. Considering the fact that the load resistance is typically fixed in practical applications, we further measure the output power at a fixed load resistance of 7.5 MΩ. The output voltages of Capsule-TENG pack with diverse numbers of units (n) at a vibrational frequency of 5.0 Hz are presented in Figure 5b and Figure S3, and the output voltages of 1D-integrated Capsule-TENGs are presented in Figure S4. The amplitude of the peak voltage increases approximately in a linear relationship with the number of units. As demonstrated in Figure 5b, the linear fitting equation can be approximated as = 4.6 (V) × .

(2)

When the number of units is increased to 25 and then to 50, the amplitudes of the peak voltages are consistent with the linear relationship between the peak output voltage and the number of units (Figure 5c and Figure S5). The relationship between the peak power and the number of integrated units was obtained by fitting a binomial curve to the data; the resulting quadratic equation is -1.5×n+2.8×n2 (blue line in Figure 5d). However, for easy prediction of the output of the capsule-TENG pack and the related discussion, we use the simplified formula


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2.8×n2 (black dot line in Figure 5d). As can be easily seen, with increasing number of units, the relative error decreases. Thus, we believe the margin of error is acceptable for our simplified discussion. Thus, the peak output power of the integrated Capsule-TENGs increases approximately with increasing number of units and can be calculated by using = 2.8 (μW) × .

(3)

As a result, we can estimate the output of a Capsule-TENG pack by using Equation 2 and 3. Worth noting is that the total weight of the TENG pack will increase with increasing number of units. Thus, if the Capsule-TENG pack is to vibrate normally following an external mechanical stimulation, the external mechanical energy should be high enough for this to happen. In other word, the trend shown in Equation 3 can only be obtained under the ideal condition that the external mechanical energy is high enough to drive the Capsule-TENG pack. In the following discussion, we assume that the Capsule-TENG pack is operating under this ideal condition. The coefficients of 4.6 and 2.8 in Equation 2 and 3 are obtained from the experiment fittings. However, there is no doubt that the coefficients are related to the electrical output of a CapsuleTENG. According to Equation 2 and 3, when n is 1, the Vpeak and the Ppeak are 4.6 V and 2.8 µW, respectively. These two values are close to the real outputs of the single Capsule-TENG (3.8 V, shown in Figure S1; 2.6 µW shown in Figure 3d). Thus, one can predict that by optimizing the geometry of a Capsule-TENG, the electrical output can be enhanced (Figure 3a); furthermore, naturally, the coefficients in the equations for predicting the output of an integrated CapsuleTENG will be larger. The peak voltage of a Capsule-TENG pack with 50 Capsule-TENGs reaches as high as about 230 V, which is high enough to light 360 LEDs connected in series (Figure 5e, Video S1). By combining a Capsule-TENG pack and a capacitor with a rectifier, a self-powered device can be


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obtained, as schematically shown in Figure 5f. By shaking the Capsule-TENG pack (vibration frequency: 5 Hz) for one minute, a 680-µF capacitor is charged to 1.5 V, which is used to power a digital clock for 30 seconds (Figure 5g, Video S2) and a digital calculator for 40 seconds (Figure 5h, Video S3) .

Figure 5. Electrical output performances of integrated Capsule-TENG. a) Plot of the output ISC and ISC density as functions of the number of units and the volume f the Capsule-TENG pack, respectively. b) Plot of the voltage’s amplitude as a function of the number of units. The voltage’s amplitude increases linearly with increasing number of units. c) Amplitudes of the output voltages of TENG packs with 25 and with 50 Capsule-TENGs. The amplitudes of the output voltage appear to follow a linear trend. d) Dependence of peak output power on the number of units. e) Photograph of 370 LEDs electrically connected in series that are directly lit in complete darkness by using 50 Capsule-TENGs. f) Equivalent electrical circuit of the selfpowered system. g) Photographs of a digital clock driven by using the self-powered system. h) Photographs of a digital calculator driven by using the self-powered system. As is well known, the introduction of a linear grating allows efficient energy harvesting.43 Here, we increase both the length of the PVC tube and the number of paired electrodes (PEs) to accomplish a similar goal. The basic structure of the Capsule-TENG with multiple PEs is similar


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to that of the above-demonstrated Capsule-TENG with a single PE (Figure 6a). The Al PEs with uniform period are coated on the outside of a long PVC tube. Loads (7.5 MΩ) are applied to the two electrodes of each PE. The operation is schematically presented in Figure 6b, and the total output voltage is presented in Figure 6c. The working principle is similar to that of the CapsuleTENG with a single PE. As shown in Figure 6b-I, when the positively charged Al slider is far away from the first PE, electrode A and electrode B have almost the same electric potential. No electric output is generated from the first PE (Stage I of Figure 6d). When the Al slider moves toward electrode A, negative charges are accumulated on electrode A, and an equal number of positive charges are accumulated on electrode B (Figure 6b-II). Thus, a current spike can be generated through the external load (Stage II of Figure 6d). When the Al slider moves toward electrode B, the Al slider will drive free electrons back to electrode B (Figure 6b-III). Thus, a current spike with an opposite polarity can be detected (Stage III of Figure 6d). When the Al slider keeps on sliding toward the second, third and fourth PEs, similar charge transfers happen, as shown in Figure 6d. When the Al slider moves in the opposite direction, a similar electrical output with a different pulse sequence is seen, as shown in Figure 6e. Therefore, an alternating current is generated as a result of the periodical sliding of the Al slider (Figure 6c). In a roundtrip sliding process across the whole tube, the induced charges can be pumped a total of 4N times, where N is the number of PEs. The above analysis indicates that the total number of transferred charges linearly increases with increasing number of PEs. For a roundtrip sliding process, the energies generated by a multiple-PE Capsule-TENG containing 1, 2, 3 and 4 PEs are presented in Figure 6f. The generated energy linearly increases with increasing number of PEs. The electrical energy generated during a periodic vibration reaches as high as 300 nJ for the device with 4 PEs.


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Similar to the single-PE Capsule-TENG, the multiple-PE Capsule-TENG can also be integrated optionally to increase the total electricity output (inset of Figure 6g). The amplitude of the peak output voltage of the integrated multiple-PE Capsule-TENG is observed to increase monotonically with increasing number of units whereas the peak output power is observed to increase proportionally to n2, as shown in Figure 6g and 6h.

Figure 6. Electrical output performances of a multiple-PE Capsule-TENG. a) Schematic for the Capsule-TENG with multiple PEs. b) Schematics for the working principle for the CapsuleTENG with multiple PEs. c) Total output voltage as a function of time for the Capsule-TENG with four PEs. d) Enlarged view of a cycle of the output voltage when the Al slider is moving forward. The voltage outputs labeled as Stages I, II, and III correspond to the processes depicted in (b-I), (b-II), and (b-III), respectively. e) Enlarged view of a cycle of the output voltage when the Al slider is moving backward. f) Histogram showing the electrical energy generated during a periodic vibration for a Capsule-TENG with 1, 2, 3, and 4 PEs. g) Dependence of the output voltage on the number of units. The inset presents a schematic showing the Capsule-TENG with multiple PEs integrated to form a 3D structure. h) Dependence of peak output power on the number of units. The peak output power increases proportionally to n2.


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The development of TENGs for harvesting energy from vibrations with a broadband of amplitudes is highly desirable for achieving high vibration-energy-to-electrical-energy conversion efficiency. The TENGs with vertical contact-separation mode have been widely used to harvest vibration energy. However, the amplitude of the input vibration should be higher than the distance between the upper friction layer and the bottom friction layer (Figure S6). On the other hand, the in-plane sliding mode holds potential for harvesting energy from vibrations with amplitudes ranging from small to large.28 However, the electrical output from a vibration with small amplitude is much lower than that of a vibration with large amplitude due to inefficient charge transfer. As a comparison, we firstly show the output voltages of a TENG pack consisting of seven two-PE Capsule-TENGs electrically connected in parallel Figure 7a. The output voltages from the two electrode pairs are measured to investigate the performances of the TENG pack. The length of the Capsule-TENG is 6.5 cm, which is the threshold value (L0) for realizing high output. The output of the TENG is directly determined by the amplitude of the vibration. The output voltage is given as follows: = ∙ ∆#/∆ ,

(4)

where R is the load resistance, ∆Q is the number of transported charges, and ∆t is the time. Given the same vibration frequency and ∆Q, a higher vibration amplitude leads to a higher scan velocity of the inside Al slider, a smaller ∆t, and a larger peak voltage. As a result, under the vibrations with small amplitudes, only a small amount of output electricity can be randomly generated (right panel of Figure 7a). A vibration with larger amplitude leads to a fuller sliding of


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ACS Nano

the Al slider, resulting in a higher output voltage. Thus, the output voltages from the two electrode pairs are almost the same (Light panel of Figure 7a). As the above analysis shows, the small electrical output under a small amplitude-vibration limits the high vibration-energy-to-electrical-energy conversion efficiency. On the bases of the ability of the single-PE Capsule-TENG to harvest small amounts of vibration energy and the strong integrability of our Capsule-TENG, we can integrate single-PE Capsule-TENGs with twoPE Capsule-TENGs to form a hybrid Capsule-TENG pack. The integration of the hybrid Capsule-TENG pack and the related operation principle are shown in Figure S7. As shown in Figure 7b, when 7 two-PE Capsule-TENGs and 8 single-PE Capsule-TENGs are integrated, energy can be efficiently harvested from vibrations with amplitudes from 0.5 to 10 cm. In this case, the single-PE Capsule-TENGs with a short tube collect energy from vibrations with small amplitudes (red line in Figure 7b) while the two-PE Capsule-TENGs with a longer PVC tube, together with the single-PE Capsule-TENGs, can collect energy from vibrations with large amplitudes. As shown in the right panel of Figure 7b, an output voltage as high as 20 V can be generated under a vibration with an amplitude of 0.5 cm, which is much higher than that in Figure 7a.


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Figure 7. Efficient harvesting of energy from vibrations with a broadband of amplitudes. a) Dependence of the output voltage on the vibration’s amplitude for a Capsule-TENG pack with two PEs. The dark cyan line indicates the output voltage of the first PE, and the blue one indicates the output voltage of the second PE. The left and the right insets present the detailed output voltages under relatively large- and small-amplitude vibrations, respectively. b) Dependence of the output voltage on the vibration’s amplitude for the hybrid TENG pack. The black line represents the output voltage of the two-PE Capsule-TENGs, and the red one represents the output voltage of the single-PE Capsule TENGs. The left and the right insets present the detailed output voltages under relative large- and small-amplitude vibrations, respectively. c) Charging curve of a 0.22-µF capacitor charged by using a two-PE CapsuleTENG pack under a 0.5-cm-amplitude vibration. d) Charging curve of a 0.22-µF capacitor charged by using a hybrid Capsule-TENG pack under a 0.5-cm-amplitude vibration. (e) Electrical energies generated during a periodic vibration at various vibration amplitudes for both the two-PE Capsule-TENG pack and the hybrid Capsule-TENG pack. The red dots represent the ratios of the energies from the hybrid Capsule-TENG pack to those from the two-PE CapsuleTENG pack.


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In order to quantify the higher vibration-energy-to-electrical-energy harvesting ability of the hybrid Capsule-TENG-pack, we use the two-PE Capsule-TENG pack and the hybrid CapsuleTENG pack separately to harvest energy from a vibration with an amplitude of 0.5 cm. By using the two-PE Capsule-TENG pack, a 0.22-µF capacitor can be charged to 0.09 V under one vibration period (Figure 7c). However, the 0.22-µF capacitor can be charged to 0.29 V by using the hybrid Capsule-TENG pack (Figure 7d). It means that the hybrid Capsule-TENG pack can generate more than 10 times energy. For the hybrid Capsule-TENG pack and the two-PE Capsule-TENG pack, the generated electrical energies during a periodic vibration and their ratios under different amplitudes are presented in Figure 7e. Even though the generated energies exhibit a tendency to increase with increasing amplitude for both packs, the hybrid CapsuleTENG pack can generate a much higher energy, especially under vibrations with small amplitudes. As shown in Figure 7e, the amounts of energy harvested from vibrations with 0.5-cm and 1-cm amplitudes by using the hybrid Capsule-TENG pack are 10 and 13 times, respectively, higher than those that can be harvested by using the two-PE Capsule-TENG pack. The results indicate the hybrid Capsule-TENG pack has relatively high efficient energy harvesting from broadband-amplitude vibrations. The principle demonstrated for the integrated TENG can be applied to other modified configurations, with an aim toward extending the amplitude broadband of the available vibration energy. In addition to the above-demonstrated TENG consisting of two-PE Capsule-TENGs and single-PE Capsule-TENGs, the single-PE Capsule-TENGs can be scaled down by shortening the PVC tube to harvest energy from vibrations with even smaller amplitudes. When the PVC tube is lengthened and the number of PEs is increased, the energy from vibrations with larger amplitudes can also be harvested. With these diverse designs, the Capsule-TENG should become


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a universal device for harvesting energy efficiently from ambient vibrations with a broadband of amplitudes. A discussion of the active area-to-volume ratio, the power-to-volume ratio, and the power-toweight ratio achieved by our 3D TENG, which can be used to evaluate the performance of integrated TENGs, would be meaningful. The electrical output of the TENG is created by the coupling of triboelectrification and electrostatic induction. The output dominantly depends on triboelectrification, a universally applicable charging effect that is confined to contact surfaces. As a precondition, the larger the active area is, the higher the number of total static charges that can be generated is, and the larger the total output that can be obtained is. Thus, the total active area-to-volume ratio of the TENG is an important parameter for evaluating the design of a TENG. The total active area-to-volume ratio (SV) can be approximately evaluated as follows: &

$% = , %

(5)

where S is the total active area of the TENG, and V is the occupied space. If the vertical contactseparation mode TENG shown in inset of Figure S6 is taken as an example, the SV is as low as 2 cm-1. When the space of the packaging is considered, the SV will be decreased further. For our 3D TENG with a honeycomb-like structure, the SV is as high as 13.9 cm-1. This result indicates that the total friction area of our Capsule-TENGs is larger than that of a conventional TENG occupying the same volume, which makes the generation of more static charges possible. On the other hand, the power-to-volume ratio (power density) is important for evaluating the output performance of an electricity generator. The areal power density is typically used for most TENGs because the total number of generated static charges is strongly associated with the size of the contact area between friction layers. Actually, an evaluation of the relationship between the space occupied by the TENG and the electricity generated by the TENG is more important


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ACS Nano

when considering practical applications of TENGs, especially when their potential application in portable electronics is considered. In other words, the amount of electrical energy generated per unit of volume of the generator is a key parameter of the TENG. However, a discussion of the volume power density is not necessary because most TENGs cannot be integrated into a 3D configuration. In this work, the ability of optionally integrating our Capsule-TENGs into a 3D configuration makes evaluating their volume power density meaningful. The relationship between the peak power (PVf) generated by 3D-integrated Capsule-TENGs and the volume they occupy (V) can be approximately evaluated as follows: %

%' = ∙ (' = ) + ∙ (' , *

(6)

where n is the number of the Capsule-TENGs in a 3D-integrated TENG, pf is the peak power harvested by a single Capsule-TENG from a vibration with frequency f, and v is the equivalent volume of a single Capsule-TENG, which is calculated as 0.300 cm3. Even though lightweight is one of the attractive advantages of TENGs, the power-to-weight ratio is important for evaluating the performance of TENGs that are applied in portable and wearable electronics. Thus, the amount of electrical energy generated per unit weight of the generator, namely, the mass power density, is an important parameter for evaluating the design of a TENG. Thus, the ability of optional integration of our Capsule-TENGs makes evaluating their mass power density meaningful. The relationship between the peak power (PMf) generated by our 3D-integrated Capsule-TENGs and their total mass (M) can be approximated as follows: ,

,' = ∙ (' = ) + ∙ (' , -

(7)

where m is the mass of a single Capsule-TENG, which is 0.73 g. Note that the Al slider and the PVC tube contribute most of the Capsule-TENG’s mass. Thus, when practical applications are


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considered, the mass of the Capsule-TENG can be further decreased by decreasing the wall thickness of the PVC tube and by utilizing a hollow Al slider.

CONCLUSIONS In summary, we have demonstrated an innovative design for lightweight (0.73 g per unit) Capsule-TENGs with an aim toward optional integration for efficient harvesting of energy from vibrations with a broadband of amplitudes in harsh environments. Compared with other TENGs, the Capsule-TENG is distinct in its approach to implementation from the point of view of increasing the total electrical output. The Capsule-TENG is freestanding and has an extremely simple and stable configuration, which allows the option to integrate Capsule-TENGs to form a stable compact honeycomb structure. Just as with an electrical battery pack, we can easily adjust the total output of the Capsule-TENG by changing the number of integrated units. When diverse Capsule-TENGs with different lengths and PE numbers are assembled, the energies of vibrations with a broadband of amplitudes can be efficiently harvested. Three parameters, the active areato-volume ratio, the power-to-volume ratio, and the power-to-weight ratio, which are important parameters for 3D-integrated TENGs are proposed and can be used to evaluate the performances of integrated TENGs. Because of the variety of possible designs, Capsule-TENGs hold potential as versatile devices for efficiently harvesting energy from vibrations.

METHODS Fabrication of a Capsule-TENG. For the optimized Capsule-TENG with a single pairedelectrode, an enclosed PVC tube with a length of 23 mm, an external diameter of 7 mm, and an


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ACS Nano

internal diameter of 4.5 mm is prepared. Two Al foils electrodes with widths of 10 mm are coated on the outside surface of the PVC tube, one on the upper part of the surface and the other on the lower part. The gap between the two electrodes is 3 mm. A cylindrical Al rod with a length of 10 mm and a diameter of 4 mm is placed inside the PVC tube. Fabrication of a Multiple PE Capsule-TENG. For the Capsule-TENG with a multi-pairedelectrode, a long enclosed PVC tube with an external diameter of 7 mm and an internal diameter of 4.5 mm is prepared. In a manner similar to that described above, Al paired-electrodes with widths of 10 mm are coated on the outside surface of the tube. The gap between the two electrodes is 3 mm. An identical cylindrical Al rod with a length of 10 mm and a diameter of 4 mm is placed inside the PVC tube. Characterization. An oscilloscope (Tektronix TDS2024C) and a current meter (Keithley DMM7510) are used for measuring the electrical output.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org The additional movie files include 360 LEDs that are lit by using a Capsule-TENG pack (avi) A digital clock driven by using the self-powered system (avi) A digital calculator driven by using the self-powered system (avi) AUTHOR INFORMATION Corresponding Author


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* E-mail: [email protected]

Author Contributions C. W. and T. W. K. conceived the project, C. W., J. H. P., B. Koo, and T. W. K. designed and performed the experiments and collected the data. C. W., J. H. P., X. C., Z. L. W., and T. W. K. analyzed and discussed the data. All authors discussed the results and contributed to the writing of the manuscript.

ACKNOWLEDGMENTS This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2016R1A2A1A05005502). C.W. was supported by the Korea Research Fellowship Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2015H1D3A1062276).

REFERENCES (1) Wang, Z. L.; Jiang, T.; Xu, L. Toward the Blue Energy Dream by Triboelectric Nanogenerator Networks. Nano Energy 2017, 39, 9−23. (2) Fan, F. R.; Tang, W.; Wang, Z. L. Flexible Nanogenerators for Energy Harvesting and SelfPowered Electronics. Adv. Mater. 2016, 28, 4283−4305. (3) Wu, H.; Huang, Y.; Xu, F.; Duan, Y.; Yin, Z. Energy Harvesters for Wearable and Stretchable Electronics: From Flexibility to Stretchability. Adv. Mater. 2016, 28, 9881−9919.


26

Page 27 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(4) Wang, Z. L. On Maxwell's Displacement Current for Energy and Sensors: The Origin of Nanogenerators. Mater. Today 2017, 20, 74−82. (5) Hinchet, R.; Seung, W.; Kim, S.-W. Recent Progress on Flexible Triboelectric Nanogenerators for SelfPowered Electronics. ChemSusChem. 2015, 8, 2327−2344. (6) Xu, Z.; Wu, C.; Li, F.; Chen, W.; Guo, T.; Kim, T. W. Triboelectric Electronic-Skin Based on Graphene Quantum Dots for Application in Self-Powered, Smart, Artificial Fingers. Nano Energy 2018, 49, 274−282. (7) Wang, J.; Wu, C.; Dai, Y.; Zhao, Z.; Wang, A.; Zhang, T.; Wang, Z. L. Achieving Ultrahigh Triboelectric Charge Density for Efficient Energy Harvesting. Nat. Commun. 2017, 8, 88. (8) Wu, C.; Kim, T. W.; Sung, S.; Park, J. H.; Li, F. Ultrasoft and Cuttable Paper-Based Triboelectric Nanogenerators for Mechanical Energy Harvesting. Nano Energy 2018, 44, 279−287. (9) Wu, C.; Kim, T. W.; Li, F.; Guo, T. Wearable Electricity Generators Fabricated Utilizing Transparent Electronic Textiles Based on Polyester/Ag Nanowires/Graphene Core-Shell Nanocomposites. ACS Nano 2016, 10, 6449−6457. (10) Zhao, L.; Zheng, Q.; Ouyang, H.; Li, H.; Yan, L.; Shi, B.; Li, Z. A Size-Unlimited Surface Microstructure

Modification

Method

for

Achieving

High

Performance

Triboelectric

Nanogenerator. Nano Energy 2016, 28, 172−178. (11) Xi, F.; Pang, Y.; Li, W.; Jiang, T.; Zhang, L.; Guo, T.; Liu, G.; Zhang, C.; Wang, Z. L. Universal Power Management Strategy for Triboelectric Nanogenerator. Nano Energy 2017, 37, 168−176.


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Page 28 of 32

(12) Bai, P.; Zhu, G.; Lin, Z.-H.; Jing, Q.; Chen, J.; Zhang, G.; Ma, J.; Wang, Z. L. Integrated Multilayered Triboelectric Nanogenerator for Harvesting Biomechanical Energy from Human Motions. ACS Nano 2013, 7, 3713−3719. (13) Wang, J.; Wen, Z.; Zi, Y.; Zhou, P.; Lin, J.; Guo, H.; Xu, Y.; Wang, Z. L. All-PlasticMaterials Based Self-Charging Power System Composed of Triboelectric Nanogenerators and Supercapacitors. Adv. Funct. Mater. 2016, 26, 1070−1076. (14) Gao, S.; Wang, M.; Chen, Y.; Tian, M.; Zhu, Y.; Wei, X.; Jiang, T. An Advanced ElectroFenton Degradation System with Triboelectric Nanogenerator as Electric Supply and BiomassDerived Carbon Materials as Cathode Catalyst. Nano Energy 2018, 45, 21−27. (15) Guo, H.; Yeh, M.-H.; Zi, Y.; Wen, Z.; Chen, J.; Liu, G.; Hu, C.; Wang, Z. L. Ultralight CutPaper-Based Self-Charging Power Unit for Self-Powered Portable Electronic and Medical Systems. ACS Nano 2017, 11, 4475−4482. (16) Yang, W.; Chen, J.; Jing, Q.; Yang, J.; Wen, X.; Su, Y.; Zhu, G.; Bai, P.; Wang, Z. L. 3D Stack Integrated Triboelectric Nanogenerator for Harvesting Vibration Energy. Adv. Funct. Mater. 2014, 24, 4090−4096. (17) Du, W.; Han, X.; Lin, L.; Chen, M.; Li, X.; Pan, C.; Wang, Z. L. A Three Dimensional Multi-Layered Sliding Triboelectric Nanogenerator. Adv. Energy Mater. 2014, 4, 1301592. (18) Tang, W.; Zhang, C.; Han, C. B.; Wang, Z. L. Enhancing Output Power of Cylindrical Triboelectric Nanogenerators by Segmentation Design and Multilayer Integration. Adv. Funct. Mater. 2014, 24, 6684−6690. (19) Chen, J.; Yang, J.; Li, Z.; Fan, X.; Zi, Y.; Jing, Q.; Guo, H.; Wen, Z.; Pradel, K. C.; Niu, S.; Wang, Z. L. Networks of Triboelectric Nanogenerators for Harvesting Water Wave Energy: A Potential Approach toward Blue Energy. ACS Nano 2015, 9, 3324−3331.


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(20) Zhang, H.; Yang, Y.; Su, Y.; Chen, J.; Adams, K.; Lee, S.; Hu, C.; Wang, Z. L. Triboelectric Nanogenerator for Harvesting Vibration Energy in Full Space and as Self ‐ Powered Acceleration Sensor. Adv. Funct. Mater. 2014, 24, 1401−1407. (21) Wang, X.; Niu, S.; Yin, Y.; Yi, F.; You, Z.; Wang, Z. L. Triboelectric Nanogenerator Based on Fully Enclosed Rolling Spherical Structure for Harvesting Low-Frequency Water Wave Energy. Adv. Energy Mater. 2015, 5, 1501467. (22) Gupta, R. K.; Shi, Q.; Dhakar, L.; Wang, T.; Heng, C. H.; Lee, C. Broadband Energy Harvester Using Non-Linear Polymer Spring and Electromagnetic/Triboelectric Hybrid Mechanism. Sci. Rep. 2017, 7, 41396. (23) Zi, Y.; Guo, H.; Wen, Z.; Yeh, M.-H.; Hu, C.; Wang, Z. L. Harvesting Low-Frequency (

Capsule Triboelectric Nanogenerators: Toward Optional 3D

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