Perovskite Piezoelectric-Based Flexible Energy Harvesters for Self-Powered Implantable and Wearable IoT Devices

In the ongoing fourth industrial revolution, the internet of things (IoT) will play a crucial role in collecting and analyzing information related to human healthcare, public safety, environmental monitoring and home/industrial automation. Even though conventional batteries are widely used to operate IoT devices as a power source, these batteries have a drawback of limited capacity, which impedes broad commercialization of the IoT. In this regard, piezoelectric energy harvesting technology has attracted a great deal of attention because piezoelectric materials can convert electricity from mechanical and vibrational movements in the ambient environment. In particular, piezoelectric-based flexible energy harvesters can precisely harvest tiny mechanical movements of muscles and internal organs from the human body to produce electricity. These inherent properties of flexible piezoelectric harvesters make it possible to eliminate conventional batteries for lifetime extension of implantable and wearable IoTs. This paper describes the progress of piezoelectric perovskite material-based flexible energy harvesters for self-powered IoT devices for biomedical/wearable electronics over the last decade.

Construction of Bio-Piezoelectric Platforms: From Structures and Synthesis to Applications

Piezoelectric materials, with their unique ability for mechanical-electrical energy conversion, have been widely applied in important fields such as sensing, energy harvesting, wastewater treatment, and catalysis. In recent years, advances in material synthesis and engineering have provided new opportunities for the development of bio-piezoelectric materials with excellent biocompatibility and piezoelectric performance. Bio-piezoelectric materials have attracted interdisciplinary research interest due to recent insights on the impact of piezoelectricity on biological systems and their versatile biomedical applications. This review therefore introduces the development of bio-piezoelectric platforms from a broad perspective and highlights their design and engineering strategies. State-of-the-art biomedical applications in both biosensing and disease treatment will be systematically outlined. The relationships between the properties, structure, and biomedical performance of the bio-piezoelectric materials are examined to provide a deep understanding of the working mechanisms in a physiological environment. Finally, the development trends and challenges are discussed, with the aim to provide new insights for the design and construction of future bio-piezoelectric materials.

Progress in lead-free piezoelectric nanofiller materials and related composite nanogenerator devices

Current piezoelectric device systems need a significant reduction in size and weight so that electronic modules of increasing capacity and functionality can be incorporated into a great range of applications, particularly in energy device platforms. The key question for most applications is whether they can compete in the race of down-scaling and an easy integration with highly adaptable properties into various system technologies such as nano-electro-mechanical systems (NEMS). Piezoelectric NEMS have potential to offer access to a parameter space for sensing, actuating, and powering, which is inflential and intriguing. Fortunately, recent advances in modelling, synthesis, and characterization techniques are spurring unprecedented developments in a new field of piezoelectric nano-materials and devices. While the need for looking more closely at the piezoelectric nano-materials is driven by the relentless drive of miniaturization, there is an additional motivation: the piezoelectric materials, which are showing the largest electromechanical responses, are currently toxic lead (Pb)-based perovskite materials (such as the ubiquitous Pb(Zr,Ti)O3, PZT). This is important, as there is strong legislative and moral push to remove toxic lead compounds from commercial products. By far, the lack of viable alternatives has led to continuing exemptions to allow their temporary use in piezoelectric applications. However, the present exemption will expire soon, and the concurrent improvement of lead-free piezoelectric materials has led to the possibility that no new exemption will be granted. In this paper, the universal approaches and recent progresses in the field of lead-free piezoelectric nano-materials, initially focusing on hybrid composite materials as well as individual nanoparticles, and related energy harvesting devices are systematically elaborated. The paper begins with a short introduction to the properties of interest in various piezoelectric nanomaterials and a brief description of the current state-of-the-art for lead-free piezoelectric nanostructured materials. We then describe several key methodologies for the synthesis of nanostructure materials including nanoparticles, followed by the discussion on the critical current and emerging applications in detail.

Flexible Energy Harvester on a Pacemaker Lead Using Multibeam Piezoelectric Composite Thin Films

Implantable medical devices, such as cardiac pacemakers and defibrillators, rely on batteries for operation. However, conventional batteries only last for a few years, and additional surgeries are needed for replacement. Harvesting energy directly from the human body enables a new paradigm of self-sustainable power sources for implantable medical devices without being constrained by the battery's limited lifetime. Here, we report the design of a multibeam cardiac energy harvester using polydimethylsiloxane (PDMS)-infilled microporous P(VDF-TrFE) composite films. We first added ZnO nanoparticles and multiwall carbon nanotubes into microporous P(VDF-TrFE) films to increase the energy output. The mixing ratios of 30% ZnO and 0.1% MWCNTs yielded 3.22 ± 0.24 V output, which resulted in a voltage output 46 times higher than that of pure P(VDF-TrFE) films. Next, we discovered that the voltage generated by the composite film with PDMS is approximately 105% higher than that of the one without PDMS. For the application in cardiac pacemakers, we developed a facile fabrication method by building a cylindrical multibeam device that resides on the pacemaker lead to harvest energy from the complex motion of the lead driven by the heartbeat. Since the energy harvesting component is integrated into the pacemaker, it significantly reduces the risks and expenses associated with pacemaker-related surgeries. This work paves the way toward the new generation of energy harvesters that will benefit patients with a variety of implantable biomedical devices.

Perovskite Oxides Prepared by Hydrothermal and Solvothermal Synthesis: A Review of Crystallisation, Chemistry, and Compositions

Perovskite oxides with general composition ABO₃ are a large group of inorganic materials that can contain a variety of cations from all parts of the Periodic Table and that have diverse properties of application in fields ranging from electronics, energy storage to photocatalysis. Solvothermal synthesis routes to these materials have become increasingly investigated in the past decade as a means of direct crystallisation of the solids from solution. These methods have significant advantages leading to adjustment of crystal form from the nanoscale to the micron-scale, the isolation of compositions not possible using conventional solid-state synthesis and in addition may lead to scalable processes for producing materials at moderate temperatures. These aspects are reviewed, with examples taken from the past decade's literature on the solvothermal synthesis of perovskites with a systematic survey of B-site cations, from transition metals in Groups 4-8 and main group elements in Groups 13, 14 and 15, to solid solutions and heterostructures. As well as hydrothermal reactions, the use of various solvents and solution additives are discussed and some trends identified, along with prospects for developing control and predictability in the crystallisation of complex oxide materials.

Flexible Piezoelectric Nanogenerators Using Metal-doped ZnO-PVDF Films

Piezoelectric nanomaterial-polymer composites represent a unique paradigm for making flexible energy harvesting and sensing devices with enhanced devices' performance. In this work, we studied various metal doped ZnO nanostructures, fabricated and characterized ZnO nanoparticle-PVDF composite thin film, and demonstrated both enhanced energy generation and motion sensing capabilities. Specifically, a series of flexible piezoelectric nanogenerators (PENGs) were designed based on these piezoelectric composite thin films. The voltage output from cobalt (Co), sodium (Na), silver (Ag), and lithium (Li) doped ZnO-PVDF composite as well as pure ZnO-PVDF samples were individually studied and compared. Under the same experimental conditions, the Li-ZnO based device produces the largest peak-to-peak voltage (3.43 Vpp) which is about 9 times of that of the pure ZnO based device, where Co-ZnO, Na-ZnO and Ag-ZnO are 1.2, 4.9 and 5.4 times, respectively. In addition, the effect of doping ratio of Li-ZnO is studied, and we found that 5% is the best doping ratio in terms of output voltage. Finally, we demonstrated that the energy harvested by the device from finger tapping at ~2 Hz can charge a capacitor with a large output power density of 0.45 W/cm3 and light up an ultraviolet (UV) light-emitting diode (LED). We also showed the device as a flexible wearable motion sensor, where different hand gestures were detected by the device with distinctive output voltage amplitudes and patterns.

Magnetic and Electric Energy Harvesting Technologies in Power Grids: A Review

With the development of intelligent modern power systems, real-time sensing and monitoring of system operating conditions have become one of the enabling technologies. Due to their flexibility, robustness and broad serviceable scope, wireless sensor networks have become a promising candidate for achieving the condition monitoring in a power grid. In order to solve the problematic power supplies of the sensors, energy harvesting (EH) technology has attracted increasing research interest. The motivation of this paper is to investigate the profiles of harnessing the electric and magnetic fields and facilitate the further application of energy scavenging techniques in the context of power systems. In this paper, the fundamentals, current status, challenges, and future prospects of the two most applicable EH methods in the grid-magnetic field energy harvesting (MEH) and electric field energy harvesting (EEH) are reviewed. The characteristics of the magnetic field and electric field under typical scenarios in power systems is analyzed first. Then the MEH and EEH are classified and reviewed respectively according to the structural difference of energy harvesters, which have been further evaluated based on the comparison of advantages and disadvantages for the future development trend.

Ferroelectric Polymers Exhibiting Negative Longitudinal Piezoelectric Coefficient: Progress and Prospects

Piezoelectric polymers are well-recognized to hold great promise for a wide range of flexible, wearable, and biocompatible applications. Among the known piezoelectric polymers, ferroelectric polymers represented by poly(vinylidene fluoride) and its copolymer poly(vinylidene fluoride-co-trifluoroethylene) possess the best piezoelectric coefficients. However, the physical origin of negative longitudinal piezoelectric coefficients occurring in the polymers remains elusive. To address this long-standing challenge, several theoretical models proposed over the past decades, which are controversial in nature, have been revisited and reviewed. It is concluded that negative longitudinal piezoelectric coefficients arise from the negative longitudinal electrostriction in the crystalline domain of the polymers, independent of amorphous and crystalline-amorphous interfacial regions. The crystalline origin of piezoelectricity offers unprecedented opportunities to improve electromechanical properties of polymers via structural engineering, i.e., design of morphotropic phase boundaries in ferroelectric polymers.

The selective laser sintering of a polyamide 11/BaTiO3/graphene ternary piezoelectric nanocomposite

Piezoelectric materials featuring the capability of converting mechanical energy to electricity are very important for harvesting discrete mechanical energy to meet the rapidly increasing demand for cleaner energy. However, the intrinsic poor flexibility and processability make it difficult for current piezoelectric materials to fulfill their potential. This study reports a novel polyamide 11 (PA11)/BaTiO₃ (BT)/graphene (Gr) ternary nanocomposite 3D printed part with significantly enhanced dielectric and piezoelectric properties due to its special discontinuous graphene network and microspores. The piezoelectric BT nanoparticles with excellent piezoelectric properties were uniformly dispersed into PA11 via a solid-state shear milling (S³M) technology. Moreover, via ultrasonic coating and selective laser sintering (SLS) technology, the discontinuous graphene network and microporous structures were both fabricated in the prepared 3D printed parts. The graphene interfaces acted as electrodes, and thus significantly increased the poling efficiency, while the porous structure further magnified the stress concentration. As a result, a piezoelectric coefficient (d₃₃) of 3.8 pC N⁻¹ and open-circuit voltage of 16.2 ± 0.4 V were obtained, exhibiting better comprehensive performances than those of most reported piezoelectric materials.

Polyamide 11/BaTiO₃/graphene nanocomposite SLS part with enhanced dielectric and piezoelectric properties due to its special discontinuous graphene network and microspores.

Modulation of surface physics and chemistry in triboelectric energy harvesting technologies

Mechanical energy harvesting technology converting mechanical energy wasted in our surroundings to electrical energy has been regarded as one of the critical technologies for self-powered sensor network and Internet of Things (IoT). Although triboelectric energy harvesters based on contact electrification have attracted considerable attention due to their various advantages compared to other technologies, a further improvement of the output performance is still required for practical applications in next-generation IoT devices. In recent years, numerous studies have been carried out to enhance the output power of triboelectric energy harvesters. The previous research approaches for enhancing the triboelectric charges can be classified into three categories: i) materials type, ii) device structure, and iii) surface modification. In this review article, we focus on various mechanisms and methods through the surface modification beyond the limitations of structural parameters and materials, such as surficial texturing/patterning, functionalization, dielectric engineering, surface charge doping and 2D material processing. This perspective study is a cornerstone for establishing next-generation energy applications consisting of triboelectric energy harvesters from portable devices to power industries.

Dual-Structured Flexible Piezoelectric Film Energy Harvesters for Effectively Integrated Performance

Improvement of energy harvesting performance from flexible thin film-based energy harvesters is essential to accomplish future self-powered electronics and sensor systems. In particular, the integration of harvesting signals should be established as a single device configuration without complicated device connections or expensive methodologies. In this research, we study the dual-film structures of the flexible PZT film energy harvester experimentally and theoretically to propose an effective principle for integrating energy harvesting signals. Laser lift-off (LLO) processes are used for fabrication because this is known as the most efficient technology for flexible high-performance energy harvesters. We develop two different device structures using the multistep LLO: a stacked structure and a double-faced (bimorph) structure. Although both structures are well demonstrated without serious material degradation, the stacked structure is not efficient for energy harvesting due to the ineffectively applied strain to the piezoelectric film in bending. This phenomenon stems from differences in position of mechanical neutral planes, which is investigated by finite element analysis and calculation. Finally, effectively integrated performance is achieved by a bimorph dual-film-structured flexible energy harvester. Our study will foster the development of various structures in flexible energy harvesters towards self-powered sensor applications with high efficiency.

Biomimetic Porifera Skeletal Structure of Lead-Free Piezocomposite Energy Harvesters

The elastic composite-based piezoelectric energy-harvesting technology is highly desired to enable a wide range of device applications, including self-powered wearable electronics, robotic skins, and biomedical devices. Recently developed piezoelectric composites are based on inorganic piezoelectric fillers and polymeric soft matrix to take advantages of both components. However, there are still limitations such as weak stress transfer to piezoelectric elements and poor dispersion of fillers in matrix. In this report, a highly enhanced piezocomposite energy harvester (PCEH) is developed using a three-dimensional electroceramic skeleton by mimicking and reproducing the sea porifera architecture. This new mechanically reinforced PCEH is demonstrated to resolve the problems of previous reported conventional piezocomposites and in turn induces stronger piezoelectric energy-harvesting responses. The generated voltage, current density, and instantaneous power density of the biomimetic PCEH device reach up to ∼16 times higher power output than that of conventional randomly dispersed particle-based PCEH. This work broadens further developments of the high-output elastic piezocomposite energy harvesting and sensor application with biomimetic architecture.

Lead-Free Perovskite Nanowire-Employed Piezopolymer for Highly Efficient Flexible Nanocomposite Energy Harvester

In the past two decades, mechanical energy harvesting technologies have been developed in various ways to support or power small-scale electronics. Nevertheless, the strategy for enhancing current and charge performance of flexible piezoelectric energy harvesters using a simple and cost-effective process is still a challenging issue. Herein, a 1D-3D (1-3) fully piezoelectric nanocomposite is developed using perovskite BaTiO₃ (BT) nanowire (NW)-employed poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) for a high-performance hybrid nanocomposite generator (hNCG) device. The harvested output of the flexible hNCG reaches up to ≈14 V and ≈4 µA, which is higher than the current levels of even previous piezoceramic film-based flexible energy harvesters. Finite element analysis method simulations study that the outstanding performance of hNCG devices attributes to not only the piezoelectric synergy of well-controlled BT NWs and within P(VDF-TrFE) matrix, but also the effective stress transferability of piezopolymer. As a proof of concept, the flexible hNCG is directly attached to a hand to scavenge energy using a human motion in various biomechanical frequencies for self-powered wearable patch device applications. This research can pave the way for a new approach to high-performance wearable and biocompatible self-sufficient electronics.