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High energy density picoliter-scale zinc-air microbatteries for colloidal robotics
Abstract
The recent interest in microscopic autonomous systems, including microrobots, colloidal state machines, and smart dust, has created a need for microscale energy storage and harvesting. However, macroscopic materials for energy storage have noted incompatibilities with microfabrication techniques, creating substantial challenges to realizing microscale energy systems. Here, we photolithographically patterned a microscale zinc/platinum/SU-8 system to generate the highest energy density microbattery at the picoliter (10 ⁻¹² liter) scale. The device scavenges ambient or solution-dissolved oxygen for a zinc oxidation reaction, achieving an energy density ranging from 760 to 1070 watt-hours per liter at scales below 100 micrometers lateral and 2 micrometers thickness in size. The parallel nature of photolithography processes allows 10,000 devices per wafer to be released into solution as colloids with energy stored on board. Within a volume of only 2 picoliters each, these primary microbatteries can deliver open circuit voltages of 1.05 ± 0.12 volts, with total energies ranging from 5.5 ± 0.3 to 7.7 ± 1.0 microjoules and a maximum power near 2.7 nanowatts. We demonstrated that such systems can reliably power a micrometer-sized memristor circuit, providing access to nonvolatile memory. We also cycled power to drive the reversible bending of microscale bimorph actuators at 0.05 hertz for mechanical functions of colloidal robots. Additional capabilities, such as powering two distinct nanosensor types and a clock circuit, were also demonstrated. The high energy density, low volume, and simple configuration promise the mass fabrication and adoption of such picoliter zinc-air batteries for micrometer-scale, colloidal robotics with autonomous functions.
... We propose a model microrobot with steering capabilities based on practically feasible microelectronic and actuation components. Our proposed design integrates microrobotic elements demonstrated in the literature, including a microbattery as a power source, [41,42] a resistive sensor, [43][44][45] and an electromechanical actuator [7,12,13] to modulate conformational changes in a self-propelled microparticle (Figure 1a). The presence of a stimulus signal alters the resistance of the sensor and the conformation of the actuator, leading to a larger conformational change in the entire device ( Figure 1b). ...
... Recently, Zhang et al. demonstrated a free-standing Zn-air battery with a volume of ≈1 pL that functions in an external electrolyte. [41] This battery produces an open-circuit potential of ≈1.2 V. Miskin et al. demonstrated a Pt-Ti actuator that also operates in an electrolyte and operates over a range of 0.2 V. [7] We propose using a similar actuator as a cathode in conjunction with a Zn anode in series with a resistive sensor to modulate the actuator's conformation. Consider a battery with an open circuit potential V 0 and internal resistance r in series with a reversible resistive sensor (Figure 7a). ...
Microrobotic platforms hold significant potential to advance a variety of fields, from medicine to environmental sensing. Herein, minimally functional robotic entities modeled on readily achievable state‐of‐the‐art features in a modern lab or cleanroom are computationally simulated. Inspired by Dou and Bishop (Phys Rev Res. 2019;1(3):1–5), it is shown that the simple combination of unidirectional steering connected to a single environmental (chemical) sensor along with constant propulsion gives rise to highly complex functions of significant utility. Such systems can trace the contours orthogonal to arbitrary chemical gradients in the environment. Also, pairs of such robots that are additionally capable of emitting the same chemical signal are shown to exhibit coupled relative motion. When the pair has unidirectional steering in opposite directions within the 2D plane (i.e., counter‐rotating), they move in parallel trajectories to each other. Alternatively, when steering is in the same direction (corotation), the two move in the same epicyclical trajectory. In this way, the chirality of the unidirectional steering produces two distinct emergent phenomena. The behavior is understood as a ratchet mechanism that exploits the differential in the radii of curvature corresponding to different spatial locations. Applications to environmental detection, remediation, and monitoring are discussed.
... This work exemplified the application of MBs in which different parts could reach a collaborative capability. Besides, Strano et al. explored the possibilities of MBs in various application scenarios [142]. Utilizing multi-step photolithography and deposition, zinc-air MBs with picoliter-scale size were elaborately constructed. ...
Microbatteries (MBs) are crucial to power miniaturized devices for the Internet of Things. In the evolutionary journey of MBs, fabrication technology emerges as the cornerstone, guiding the intricacies of their configuration designs, ensuring precision, and facilitating scalability for mass production. Photolithography stands out as an ideal technology, leveraging its unparalleled resolution, exceptional design flexibility, and entrenched position within the mature semiconductor industry. However, comprehensive reviews on its application in MB development remain scarce. This review aims to bridge that gap by thoroughly assessing the recent status and promising prospects of photolithographic microfabrication for MBs. Firstly, we delve into the fundamental principles and step-by-step procedures of photolithography, offering a nuanced understanding of its operational mechanisms and the criteria for photoresist selection. Subsequently, we highlighted the specific roles of photolithography in the fabrication of MBs, including its utilization as a template for creating miniaturized micropatterns, a protective layer during the etching process, a mold for soft lithography, a constituent of MB active component, and a sacrificial layer in the construction of micro-Swiss-roll structure. Finally, the review concludes with a summary of the key challenges and future perspectives of MBs fabricated by photolithography, providing comprehensive insights and sparking research inspiration in this field.
... To this end, Tiny Machine Learning (TinyML) [16] can contribute by enabling tiny robots to process data locally, reducing the need for continuous communication with external servers, and therefore saving power and bandwidth. Important technological advancements are also being made on microcontrollers (MCUs) [17] and batteries [18] that power tiny robots. ...
Detecting objects in mobile robotics is crucial for numerous applications, from autonomous navigation to inspection. However, robots are often required to perform tasks in different domains with respect to the training one and need to adapt to these changes. Tiny mobile robots, subject to size, power, and computational constraints, encounter even more difficulties in running and adapting these algorithms. Such adaptability, though, is crucial for real-world deployment, where robots must operate effectively in dynamic and unpredictable settings. In this work, we introduce a novel benchmark to evaluate the continual learning capabilities of object detection systems in tiny robotic platforms. Our contributions include: (i) Tiny Robotics Object Detection (TiROD), a comprehensive dataset collected using a small mobile robot, designed to test the adaptability of object detectors across various domains and classes; (ii) an evaluation of state-of-the-art real-time object detectors combined with different continual learning strategies on this dataset, providing detailed insights into their performance and limitations; and (iii) we publish the data and the code to replicate the results to foster continuous advancements in this field. Our benchmark results indicate key challenges that must be addressed to advance the development of robust and efficient object detection systems for tiny robotics.
The advent of small-scale robots holds immense potential for revolutionizing various industries, particularly in the domains of surgery and operations within confined spaces that are currently inaccessible to conventional tools. However, their tethered nature and dependence on external power sources impede their progress. To surmount these challenges, the integration of batteries into these diminutive robots emerges as a promising solution. This article explores the integration of batteries in small-scale robots, focusing on “hard” and “soft” approaches. The challenges of integrating rigid batteries into microrobots are discussed. Various battery materials suitable for microfabrication are explored, along with creating three-dimensional structures to optimize performance within limited space. The “soft” integration emphasizes the need for flexible and deformable battery technologies that seamlessly integrate with soft robotic systems. Challenges related to flexibility, stretchability, and biocompatibility are addressed. The concept of distributed and mobile energy units, where smaller batteries assemble into a larger power bank, is proposed for scalability and adaptability. Extracting energy from the environment, inspired by fuel cells, reduces reliance on traditional batteries. This article offers valuable insights into battery integration for small-scale robots, propelling advancements in autonomous and versatile systems. By overcoming current limitations, integrated batteries will unlock the full potential of small-scale robots across various industries.
Graphical abstract
Zn batteries show promise for microscale applications due to their compatibility with air fabrication but face challenges like dendrite growth and chemical corrosion, especially at the microscale. Despite previous attempts in electrolyte engineering, achieving successful patterning of electrolyte microscale devices has remained challenging. Here, successful patterning using photolithography is enabled by incorporating caffeine into a UV‐crosslinked polyacrylamide hydrogel electrolyte. Caffeine passivates the Zn anode, preventing chemical corrosion, while its coordination with Zn²⁺ ions forms a Zn²⁺‐conducting complex that transforms into ZnCO3 and 2ZnCO3·3Zn(OH)2 over cycling. The resulting Zn‐rich interphase product significantly enhances Zn reversibility. In on‐chip microbatteries, the resulting solid‐electrolyte interphase allows the Zn||MnO2 full cell to cycle for over 700 cycles with an 80% depth of discharge. Integrating the photolithographable electrolyte into multilayer microfabrication creates a microbattery with a 3D Swiss‐roll structure that occupies a footprint of 0.136 mm². This tiny microbattery retains 75% of its capacity (350 µAh cm⁻²) for 200 cycles at a remarkable 90% depth of discharge. The findings offer a promising solution for enhancing the performance of Zn microbatteries, particularly for on‐chip microscale devices, and have significant implications for the advancement of autonomous microscale devices.
A full integration of miniaturized transparent energy device (lithium-ion battery), electronic device (thin-film transistor) and sensing device (photodetector) to form a monolithic integrated microsystem greatly enhances the functions of transparent electronics. Here, InGaZnO is explored to prepare the above devices and microsystem due to its multifunctional properties. A transparent lithium-ion battery with InGaZnO as anode (capacity~9.8 μAh cm⁻²) is proposed as the on-chip power source. Then, thin-film transistor with InGaZnO as channel (mobility~23.3 cm² V⁻¹ s⁻¹) and photodetector with InGaZnO as photosensitive layer (responsivity~0.35 A W⁻¹) are also prepared on the substrate for constructing an fully integrated transparent microsystem. Each device displays acceptable performance. Moreover, alternating-current signals can be successfully charged into the lithium-ion battery by using the thin-film transistor as the on-chip rectifier and also the photodetector works well by using the charged battery as the on-chip power, demonstrating collaborative capabilities of each device to achieve systematic functions.
Wearable transdermal iontophoresis eliminating the need for external power sources offers advantages for patient-comfort when deploying epidermal diseases treatments. However, current self-powered iontophoresis based on energy harvesters is limited to support efficient therapeutic administration over the long-term operation, owing to the low and inconsistent energy supply. Here we propose a simplified wearable iontophoresis patch with a built-in Mg battery for efficient and controllable transdermal delivery. This system decreases the system complexity and form factors by using viologen-based hydrogels as an integrated drug reservoir and cathode material, eliminating the conventional interface impedance between the electrode and drug reservoir. The redox-active polyelectrolyte hydrogel offers a high energy density of 3.57 mWh cm ⁻² , and an optimal bioelectronic interface with ultra-soft nature and low tissue-interface impedance. The delivery dosage can be readily manipulated by tuning the viologen hydrogel and the iontophoresis stimulation mode. This iontophoresis patch demonstrates an effective treatment of an imiquimod-induced psoriasis mouse. Considering the advantages of being a reliable and efficient energy supply, simplified configuration, and optimal electrical skin-device interface, this battery-powered iontophoresis may provide a new non-invasive treatment for chronic epidermal diseases.
Accessing high voltages (>9 V) and high power density in microbatteries with volumes below ∼0.25 cm³ is challenging. At such scales, energy density and voltage are highly constrained by packaging and serial integration of cells. Here, we demonstrate hermetically sealed, durable, compact (volume ≤ 0.165 cm³) batteries with low package mass fraction (10.2%) in single- (∼4 V), double- (∼8 V), and triple-stacked (∼12 V) configurations with energy densities reaching 990 Wh Kg⁻¹ and 1,929 Wh L⁻¹ (triple-stacked battery discharged at C/10) and high power density for continuous and pulsed discharge (∼124 mW cm⁻² for triple-stacked battery at C/2 continuous discharge, ∼75 mW cm⁻² for double-stacked battery at 2C pulsed discharge). We achieve the high voltage-power-energy density landscape by using current collectors as the package and serial stacking of bifancial dense electrodeposited LiCoO2 cathode, Li-metal anode electrodes. Our microbatteries power wireless communication electronics, motors, and actuators, paving the way toward highly functional microdevices.
As substantial progress has been made to miniaturize intelligent microsystems to the sub‐square‐millimeter scale, there is a desperate need to move beyond existing microbattery technologies to offer adequate energy at the same footprint. A micro‐origami technology able to wind up a flat layer stack into a Swiss roll presents a promising approach in this regard because it mimics the most successful way to make energy‐dense full‐sized batteries. Here, an on‐chip Swiss‐roll current collector made via the micro‐origami process is developed and it is infused with a MnO2 slurry comprising a zincophilic binder. The zincophilic binder layer enhances zinc ion transportability and suppresses MnO2 dissolution. The MnO2 Swiss‐roll microelectrode is used to create an on‐chip microbattery with a small electrode footprint area of 0.75 mm², which shows a footprint capacity up to 3.3 mAh cm–2. The microbattery demonstrates a reversible capacity of more than 1 mAh cm–2 for 150 cycles. The battery stability can be improved to over 600 cycles at a 50% depth of discharge. An on‐chip integration of a microsystem with the microbattery is demonstrated. The microbatteries set foot in the untrodden sub‐square‐millimeter area providing adequate energy for ever more miniaturized intelligent microsystems.
Advances in microelectronics have enabled the use of miniaturized computers for autonomous intelligence at the size of a dust particle less than one square millimeter across and a few hundred micrometers thick, creating an environment for ubiquitous computing. However, the size mismatch between microbatteries and microelectronics has emerged as a fundamental barrier against the take‐off of tiny intelligent systems requiring power anytime anywhere. Mainstream microbattery structures include stacked thin films on the chip or electrode pillars and on‐chip interdigitated microelectrodes. Nevertheless, available technologies cannot shrink the footprint area of batteries while maintaining adequate energy storage. Alternatively, the on‐chip self‐assembly process known as micro‐origami is capable of winding stacked thin films into Swiss‐roll structures to reduce the footprint area, which exactly mimics the manufacture of the most successful full‐sized batteries—cylinder batteries. In addition to discussing in detail the technical difficulties of reducing the size of on‐chip microbatteries with various structures and potential solutions, this Perspective highlights the following two basic requirements for eventual integration in microcomputers: minimum energy density of 100 microwatt‐hour per square centimeter and monolithic integration with other functional electric circuits on the chip.
Micrometer-scale robots capable of navigating enclosed spaces and remote locations are approaching reality. However, true autonomy remains an open challenge despite substantial progress made with externally supervised and manipulated systems. To accelerate the development of autonomous microrobots, alternatives to conventional top-down lithography are sought. Such additive technologies like printing, coating, and colloidal self-assembly allow for rapid prototyping and access to novel materials, such as polymers, bio- and nanomaterials. On the basis of recent experimental findings that memristive networks can be rapidly printed and lifted off as electronic microparticles, an alternative design paradigm is introduced based on arrays of two-terminal memristive elements, which enables real-time use of memory, sensing, and actuation in microrobots. Several memristor-based designs are validated, each representing a key building block toward robotic autonomy: tracking elapsed time, timestamping a rare event, continuously cataloguing time-indexed data, and accessing the collected information for a feedback-controlled response as in a robotic glucose-responsive insulin. The computational results establish an actionable framework for microrobotic design—tasks normally requiring complex circuits can now be achieved with self-assembled and printed memristor arrays within microparticles.
Today’s smallest energy storage devices for in-vivo applications are larger than 3 mm ³ and lack the ability to continuously drive the complex functions of smart dust electronic and microrobotic systems. Here, we create a tubular biosupercapacitor occupying a mere volume of 1/1000 mm ³ (=1 nanoliter), yet delivering up to 1.6 V in blood. The tubular geometry of this nano-biosupercapacitor provides efficient self-protection against external forces from pulsating blood or muscle contraction. Redox enzymes and living cells, naturally present in blood boost the performance of the device by 40% and help to solve the self-discharging problem persistently encountered by miniaturized supercapacitors. At full capacity, the nano-biosupercapacitors drive a complex integrated sensor system to measure the pH-value in blood. This demonstration opens up opportunities for next generation intravascular implants and microrobotic systems operating in hard-to-reach small spaces deep inside the human body.
Electrical stimulation of cells offers a viable alternative route to treat diseases like cancer that account for several deaths despite sophisticated treatments. While micro/nanoscale systems have demonstrated to regulate cell activity by inducing electrical signals, many of these rely on external excitation sources for operation. In this work, we present an array of Al-H2O based microbatteries of dimensions smaller than a single cell to induce localized electrical impulses by involving no excitation sources outside the cellular environment, i.e., self-stimulation, for a limited operation time. The fabricated structure allows microbattery activation, i.e., produces a voltage or current flow, on contact with the ionic species in biological medium. The study explores the response of human osteosarcoma cells (Saos-2) under the influence of these generated electrical impulses. The microbatteries allowed proliferation of Saos-2 cells when configured to operate in an open-circuit fashion, while they induced cell death in a short-circuited operation due to a current flow causing a drastic reduction in cell viability to 13.5%. The self-stimulated current produced a profound cytotoxic effect up to 24 h of incubation before the microbatteries became inactive. An up-scaled model and fabricated test-structure further explores the electrochemical characteristics of Al-H2O based batteries and their effect on relevant parameters like pH. The overall results suggest prospects for a non-invasive treatment in cancer therapy, neuromuscular system, neurological disorders, chronic treatments, tissue regeneration and other electrically active systems by the application of a self-stimulated electrical signal.
Owing to their high safety and reversibility, aqueous microbatteries using zinc anodes and an acid electrolyte have emerged as promising candidates for wearable electronics. However, a critical limitation that prevents implementing zinc chemistry at the microscale lies in its spontaneous corrosion in an acidic electrolyte that causes a capacity loss of 40% after a ten‐hour rest. Widespread anti‐corrosion techniques, such as polymer coating, often retard the kinetics of zinc plating/stripping and lack spatial control at the microscale. Here, a polyimide coating that resolves this dilemma is reported. The coating prevents corrosion and hence reduces the capacity loss of a standby microbattery to 10%. The coordination of carbonyl oxygen in the polyimide with zinc ions builds up over cycling, creating a zinc blanket that minimizes the concentration gradient through the electrode/electrolyte interface and thus allows for fast kinetics and low plating/stripping overpotential. The polyimide's patternable feature energizes microbatteries in both aqueous and hydrogel electrolytes, delivering a supercapacitor‐level rate performance and 400 stable cycles in the hydrogel electrolyte. Moreover, the microbattery is able to be attached to human skin and offers strong resistance to deformations, splashing, and external shock. The skin‐mountable microbattery demonstrates an excellent combination of anti‐corrosion, reversibility, and durability in wearables. A zinc blanket created by the coordination between carbonyl oxygen atoms in a polyimide coating and zinc ions overcomes the thermodynamic instability and facilitates plating/stripping kinetics. Patterning this zinc blanket for a Zn microanode allows for the development of a skin‐mountable microbattery with an outstanding rate capability and stable cycling performance, providing promise for microbatteries integrable for electronic skin.
Fabrication of high‐energy‐density and high‐power‐density packaged long‐cycle‐life rechargeable microbatteries remains a considerable challenge. Here, high‐performance microbatteries with high active volume fraction, thick, 3D‐structured electrodes (V2O5 cathode and Li metal anode) are realized through a combination of imprint lithography, self‐assembly, and electrodeposition. To assist the critical challenge of hermetic packaging, the microbattery is infilled with a gel electrolyte. The packaged cell exhibits high areal energy and power densities of 1.24 J cm⁻² and 75.5 mW cm⁻², respectively, and can be cycled 550 times in argon or 200 times in air with 75% capacity retention of the initial discharge capacity. An unpackaged cell, using a liquid electrolyte, provides a power density of 218 mW cm⁻². As far as it is known, the microbatteries have the highest peak power density among all reported microbatteries.
The rapid development of printed and microscale electronics imminently requires compatible micro-batteries (MBs) with high performance, applicable scalability, and exceptional safety, but faces great challenges from the ever-reported stacked geometry. Herein the first printed planar prototype of aqueous-based, high-safety Zn//MnO2 MBs, with outstanding performance, aesthetic diversity, flexibility and modularization, is demonstrated, based on interdigital patterns of Zn ink as anode and MnO2 ink as cathode, with high-conducting graphene ink as a metal-free current collector, fabricated by an industrially scalable screen-printing technique. The planar separator-free Zn//MnO2 MBs, tested in neutral aqueous electrolyte, deliver a high volumetric capacity of 19.3 mAh/cm3 (corresponding to 393 mAh/g) at 7.5 mA/cm3, and notable volumetric energy density of 17.3 mWh/cm3, outperforming lithium thin-film batteries (≤10 mWh/cm3). Furthermore, our Zn//MnO2 MBs present long-term cyclability having a high capacity retention of 83.9% after 1300 cycles at 5 C, which is superior to stacked Zn//MnO2 batteries previously reported. Also, Zn//MnO2 planar MBs exhibit exceptional flexibility without observable capacity decay under serious deformation, and remarkably serial and parallel integration of constructing bipolar cells with high voltage and capacity output. Therefore, low-cost, environmentally benign Zn//MnO2 MBs with in-plane geometry possess huge potential as high-energy, safe, scalable and flexible microscale power sources for direction integration with printed electronics.
Fifty years of Moore’s law scaling in microelectronics have brought remarkable opportunities for the rapidly evolving field of microscopic robotics1–5. Electronic, magnetic and optical systems now offer an unprecedented combination of complexity, small size and low cost6,7, and could be readily appropriated for robots that are smaller than the resolution limit of human vision (less than a hundred micrometres)8–11. However, a major roadblock exists: there is no micrometre-scale actuator system that seamlessly integrates with semiconductor processing and responds to standard electronic control signals. Here we overcome this barrier by developing a new class of voltage-controllable electrochemical actuators that operate at low voltages (200 microvolts), low power (10 nanowatts) and are completely compatible with silicon processing. To demonstrate their potential, we develop lithographic fabrication-and-release protocols to prototype sub-hundred-micrometre walking robots. Every step in this process is performed in parallel, allowing us to produce over one million robots per four-inch wafer. These results are an important advance towards mass-manufactured, silicon-based, functional robots that are too small to be resolved by the naked eye.
Miniaturization of batteries lags behind the success of modern electronic devices. Neither the device volume nor the energy density of microbatteries meets the requirement of microscale electronic devices. The main limitation for pushing the energy density of microbatteries arises from the low mass loading of active materials. However, merely pushing the mass loading through increased electrode thickness is accompanied by the long charge transfer pathway and inferior mechanical properties for long‐term operation. Here, a new spiral microelectrode upon stress‐actuation accomplishes high mass loading but short charge transfer pathways. At a small footprint area of around 1 mm², a 21‐fold increase of the mass loading is achieved while featuring fast charge transfer at the nanoscale. The spiral microelectrode delivers a maximum area capacity of 1053 µAh cm⁻² with a retention of 67% over 50 cycles. Moreover, the energy density of the cylinder microbattery using the spiral microelectrode as the anode reaches 12.6 mWh cm⁻³ at an ultrasmall volume of 3 mm³. In terms of the device volume and energy density, the cylinder microbattery outperforms most of the current microbattery technologies, and hence provides a new strategy to develop high‐performance microbatteries that can be integrated with miniaturized electronic devices.
Humans live today in a high‐tech and informationalized society. With the development of the emerging electronic information age, various electronic systems are inclined to be multifunctional and miniaturized. It is urgent to develop “small and powerful” micro‐batteries with flexibility and high electrochemical performance to meet the diverse needs of microelectronic components. However, low electrochemical performance exists in traditional microenergy storage devices, which fail to satisfy the energy needs for microdevices. Here, for the first time, a planar integrated flexible rechargeable dual‐ion microbattery (DIMB) is reported, which is fabricated from an interdigital pattern of graphite as an electrode and lithium hexafluorophosphate as an electrolyte. As a microbattery, the DIMB exhibits a high reversible capacity of 56.50 mAh cm−3, and excellent cycle stability with 90% capacity retention after 300 cycles under a high working voltage. The application of DIMB in microdevices, such as light‐emitting diodes (LEDs), digital electronic game consoles, and electrochromic glasses is also investigated, fully demonstrating its “small and powerful” performance. The integrated DIMB is a high‐voltage microdevice that reaches a nonpareil discharge voltage of about 100 V and a charging capacity of 102 mAh g−1. This dual ion‐based flexible microbattery could become a promising candidate for energy storage and conversion components in next‐generation microelectronic devices and integrated electronic devices. A “small and powerful” planar integrated flexible rechargeable dual‐ion microbattery (DIMB) is developed to meet the diverse needs of microelectronic components including light‐emitting diodes, digital electronic game console, and electrochromic glasses. The DIMB exhibits a high reversible capacity and excellent cycle stability under high working voltage, which could be candidates for energy storage and conversion components in next‐generation microelectronic devices.
Recent advances in materials, mechanics and design have led to the development of ultrathin, lightweight electronic devices that can conformally interface with human skin. With few exceptions, these devices rely on electrical power to support sensing, wireless communication and signal conditioning. Unfortunately, most sources of such power consist of batteries constructed using hazardous materials, often with form factors that frustrate incorporation into skin-like, or epidermal, electronic devices. Here we report a biocompatible, sweat-activated battery technology that can be embedded within a soft, microfluidic platform. The battery can be used in a detachable electronic module that contains wireless communication and power management systems, and is capable of continuous on-skin recording of physiological signals. To illustrate the practical utility of our approach, we show using human trials that the sweat-activated batteries can operate hybrid microfluidic/microelectronic systems that simultaneously monitor heart rate, sweat chloride and sweat pH. Sweat-activated, biocompatible batteries can be used to power flexible on-skin electronic systems that monitor and wirelessly transmit physiological signals.
Nanocage-chain fuel cell catalysts
The expense and scarcity of platinum has driven efforts to improve oxygen-reduction catalysts in proton-exchange membrane fuel cells. Tian et al. synthesized chains of platinum-nickel alloy nanospheres connected by necking regions. These structures can be etched to form nanocages with platinum-rich surfaces that are highly active for oxygen reduction. In fuel cells running on air and hydrogen, these catalysts operated for at least 180 hours.
Science , this issue p. 850
Zn-air batteries are under revival. They have large theoretical energy density and potentially very low manufacturing cost compared to the existing Li-ion technology. However, their full potentials have not been fulfilled due to challenges associated with air cathodes and Zn anodes. In this minireview, we present the current status and technical hurdles of Zn-air batteries, and discuss the possible direction of their future improvements. We show that in contrast to tremendous efforts on the design and development of efficient cathode electrocatalysts over recent years, the pursuit of stable and cyclable Zn anodes is equally important but receives far less attention than deserved. We therefore call for a shift of future research focus from cathode electrocatalysts to Zn anodes in order to render this century old technology a truly commercial reality.
The rapid development of smart wearable and integrated electronic products has urgently increased the requirement for high‐performance microbatteries. Although few lithium ion microbatteries based on organic electrolytes have been reported so far, the problems, such as undesirable energy density, poor flexibility, inflammability, volatility toxicity, and high cost restrict their practical applications in the above‐mentioned electronic products. In order to overcome these problems, a low cost quasi‐solid‐state aqueous zinc ion microbattery (ZIMB) assembled by a vanadium dioxide (B)‐multiwalled carbon nanotubes (VO2 (B)‐MWCNTs) cathode, a zinc nanoflakes anode, and a zinc trifluoromethanesulfonate‐polyvinyl alcohol (Zn(CF3SO3)2‐PVA) hydrogel electrolyte is exploited. As expected, the ZIMB exhibits excellent electrochemical performance, e.g., a high capacity of 314.7 µAh cm⁻², an ultrahigh energy density of 188.8 µWh cm⁻², and a high power density of 0.61 mW cm⁻². Furthermore, the ZIMB also shows high flexibility and excellent high temperature stability: the capacity has no obvious decay when the bending angle is up to 150° and the temperature reaches 100 °C. The ZIMB provides a way to develop next‐generation miniature energy storage devices with high performance.
A chemical stability map is advanced by incorporating ion complexation, solubility, and chemical trajectories to predict ZnO, Zn(OH)2, ZnCO3, ZnCl2, Zn5(CO3)2(OH)6, and Zn5(OH)8Cl2·H2O precipitation as a function of the total Zn content and pH of an NaCl solution. These calculations demonstrate equilibrium stability of solid Zn products often not considered while tracking the consumed and produced aqueous Zn ion species concentrations through chemical trajectories. The effect of Cl-based ligand formation is incorporated into these stability predictions, enabling enhanced appreciation for the local corrosion conditions experienced at the Zn surface in chloride-containing environments. Additionally, the complexation of Cl- with Zn2+ is demonstrated to compete with the formation of solid phases, making precipitation more difficult. The present work also extends the chemical stability diagram derivations by incorporating a Gibbs-Thompson curvature relation to predict the effect of nanoscale precipitate phase formation on species solubility. These thermodynamic predictions correlate well with experimental results for Zn corrosion in full and alternate NaCl immersion, and have far-reaching utility in a variety of fields requiring nanoscale, semiconductor, and/or structural materials.
The rapid development and further modularization of miniaturized and self‐powered electronic systems have substantially stimulated the urgent demand for microscale electrochemical energy storage devices, e.g., microbatteries (MBs) and micro‐supercapacitors (MSCs). Recently, planar MBs and MSCs, composed of isolated thin‐film microelectrodes with extremely short ionic diffusion path and free of separator on a single substrate, have become particularly attractive because they can be directly integrated with microelectronic devices on the same side of one single substrate to act as a standalone microsized power source or complement miniaturized energy‐harvesting units. The development of and recent advances in planar MBs and MSCs from the fundamentals and design principle to the fabrication methods of 2D and 3D planar microdevices in both in‐plane and stacked geometries are highlighted. Additonally, a comprehensive analysis of the primary aspects that eventually affect the performance metrics of microscale energy storage devices, such as electrode materials, electrolyte, device architecture, and microfabrication techniques are presented. The technical challenges and prospective solutions for high‐energy‐density planar MBs and MSCs with multifunctionalities are proposed. The development of and recent advances in planar microbatteries and micro‐supercapacitors from the fundamentals and design principle to 2D and 3D planar microdevices in both in‐plane and stacked geometries are highlighted. Additonally, a comprehensive analysis of the aspects that eventually affect the performance metrics of microscale energy storage devices, such as electrode materials, electrolyte, device architecture, and microfabrication techniques are explored.
On‐chip microbatteries have attracted growing attention due to their great feasibility for integration with miniaturized electronic devices. Nevertheless, it is difficult to get both high energy/power densities in microbatteries. An increase in the thickness of microelectrodes may help to boost the areal energy density of device, yet it often leads to terrible sacrifice in its power density due to the longer electron and ion diffusion distances. In this work, a quasi‐solid‐state on‐chip Ni–Zn microbattery is designed based on a hierarchical ordered porous (HOP) Ni@Ni(OH)2 microelectrode, which is developed by an in situ anodizing strategy. The fabricated microelectrode can optimize ion and electron transport simultaneously due to its interconnected ordered macropore–mesopore network and high electron conductivity. As the thickness of microelectrode increases, the areal energy density of HOP Ni@Ni(OH)2 microelectrode shows an ascending trend with negligible sacrifice in power density and rate performance. Impressively, this Ni–Zn microbattery achieves excellent energy/power densities (0.26 mW h cm−2, 33.8 mW cm−2), outperforming most previous reported microenergy storage devices. This study may provide new direction in high‐performance and highly safe microenergy storage units for next‐generation highly integrated microelectronics. A quasi‐solid‐state on‐chip Ni–Zn microbattery with excellent performance is demonstrated based on a hierarchical ordered porous (HOP) Ni@Ni(OH)2 microelectrode. Attributed to the optimized ion and electron transport of the HOP Ni@Ni(OH)2 microelectrode, the Ni–Zn microbattery achieves ultrahigh energy/power densities and excellent rate performance simultaneously, outperforming most of reported microenergy storage devices.
Batteries constructed via 3D printing techniques have inherent advantages including opportunities for miniaturization, autonomous shaping, and controllable structural prototyping. However, 3D‐printed lithium metal batteries (LMBs) have not yet been reported due to the difficulties of printing lithium (Li) metal. Here, for the first time, high‐performance LMBs are fabricated through a 3D printing technique using cellulose nanofiber (CNF), which is one of the most earth‐abundant biopolymers. The unique shear thinning properties of CNF gel enables the printing of a LiFePO4 electrode and stable scaffold for Li. The printability of the CNF gel is also investigated theoretically. Moreover, the porous structure of the CNF scaffold also helps to improve ion accessibility and decreases the local current density of Li anode. Thus, dendrite formation due to uneven Li plating/stripping is suppressed. A multiscale computational approach integrating first‐principle density function theory and a phase‐field model is performed and reveals that the porous structures have more uniform Li deposition. Consequently, a full cell built with a 3D‐printed Li anode and a LiFePO4 cathode exhibits a high capacity of 80 mA h g⁻¹ at a charge/discharge rate of 10 C with capacity retention of 85% even after 3000 cycles.
Graphene and other two-dimensional materials possess desirable mechanical, electrical and chemical properties for incorporation into or onto colloidal particles, potentially granting them unique electronic functions. However, this application has not yet been realized, because conventional top-down lithography scales poorly for producing colloidal solutions. Here, we develop an ‘autoperforation’ technique that provides a means of spontaneous assembly for surfaces composed of two-dimensional molecular scaffolds. Chemical vapour deposited two-dimensional sheets can autoperforate into circular envelopes when sandwiching a microprinted polymer composite disk of nanoparticle ink, allowing liftoff into solution and simultaneous assembly. The resulting colloidal microparticles have two independently addressable, external Janus faces that we show can function as an intraparticle array of vertically aligned, two-terminal electronic devices. Such particles demonstrate remarkable chemical and mechanical stability and form the basis of particulate electronic devices capable of collecting and storing information about their surroundings, extending nanoelectronics into previously inaccessible environments.
A previously unexplored property of two-dimensional electronic materials is their ability to graft electronic functionality onto colloidal particles to access local hydrodynamics in fluids to impart mobility and enter spaces inaccessible to larger electronic systems. Here, we demonstrate the design and fabrication of fully autonomous state machines built onto SU-8 particles powered by a two-dimensional material-based photodiode. The on-board circuit connects a chemiresistor circuit element and a memristor element, enabling the detection and storage of information after aerosolization, hydrodynamic propulsion to targets over 0.6 m away, and large-area surface sensing of triethylamine, ammonia and aerosolized soot in inaccessible locations. An incorporated retroreflector design allows for facile position location using laser-scanning optical detection. Such state machines may find widespread application as probes in confined environments, such as the human digestive tract, oil and gas conduits, chemical and biosynthetic reactors, and autonomous environmental sensors.
Robots have components that work together to accomplish a task. Colloids are particles, usually less than 100 µm, that are small enough that they do not settle out of solution. Colloidal robots are particles capable of functions such as sensing, computation, communication, locomotion and energy management that are all controlled by the particle itself. Their design and synthesis is an emerging area of interdisciplinary research drawing from materials science, colloid science, self-assembly, robophysics and control theory. Many colloidal robot systems approach synthetic versions of biological cells in autonomy and may find ultimate utility in bringing these specialized functions to previously inaccessible locations. This Perspective examines the emerging literature and highlights certain design principles and strategies towards the realization of colloidal robots.
Autonomous robots comprise actuation, energy, sensory and control systems built from materials and structures that are not necessarily designed and integrated for multifunctionality. Yet, animals and other organisms that robots strive to emulate contain highly sophisticated and interconnected systems at all organizational levels, which allow multiple functions to be performed simultaneously. Herein, we examine how system integration and multifunctionality in nature inspires a new paradigm for autonomous robots that we call Embodied Energy. Whereas most untethered robots use batteries to store energy and power their operation, recent advancements in energy-storage techniques enable chemical or electrical energy sources to be embodied directly within the structures and materials used to create robots, rather than requiring separate battery packs. This perspective highlights emerging examples of Embodied Energy in the context of developing autonomous robots. The concept of 'Embodied Energy'—in which the components of a robot or device both store energy and provide a mechanical or structural function—is put forward, along with specific robot-design principles.
Autonomous electronic microsystems smaller than the diameter of a human hair (<100 μm) are promising for sensing in confined spaces such as microfluidic channels or the human body. However, they are difficult to implement due to fabrication challenges and limited power budget. Here we present a 60 × 60 μm electronic microsystem platform, or SynCell, that overcomes these issues by leveraging the integration capabilities of two-dimensional material circuits and the low power consumption of passive germanium timers, memory-like chemical sensors, and magnetic pads. In a proof-of-concept experiment, we magnetically positioned SynCells in a microfluidic channel to detect putrescine. After we extracted them from the channel, we successfully read out the timer and sensor signal, the latter of which can be amplified by an onboard transistor circuit. The concepts developed here will be applicable to microsystems targeting a variety of applications from microfluidic sensing to biomedical research.
Shape-memory actuators allow machines ranging from robots to medical implants to hold their form without continuous power, a feature especially advantageous for situations where these devices are untethered and power is limited. Although previous work has demonstrated shape-memory actuators using polymers, alloys, and ceramics, the need for micrometer-scale electro–shape-memory actuators remains largely unmet, especially ones that can be driven by standard electronics (~1 volt). Here, we report on a new class of fast, high-curvature, low-voltage, reconfigurable, micrometer-scale shape-memory actuators. They function by the electrochemical oxidation/reduction of a platinum surface, creating a strain in the oxidized layer that causes bending. They bend to the smallest radius of curvature of any electrically controlled microactuator (~500 nanometers), are fast (<100-millisecond operation), and operate inside the electrochemical window of water, avoiding bubble generation associated with oxygen evolution. We demonstrate that these shape-memory actuators can be used to create basic electrically reconfigurable microscale robot elements including actuating surfaces, origami-based three-dimensional shapes, morphing metamaterials, and mechanical memory elements. Our shape-memory actuators have the potential to enable the realization of adaptive microscale structures, bio-implantable devices, and microscopic robots.
Improve materials and architectures to shrink microscopic devices. Improve materials and architectures to shrink microscopic devices.
Tiny devices have been developed that can act as the legs of laser-controlled microrobots. The compatibility of these devices with microelectronics systems suggests a path to the mass manufacture of autonomous microrobots. Actuators that propel microrobots through liquids.
Batteries with conformal shape and multiple functionalities could provide new degrees of freedom in the design of robotic devices. For example, the ability to provide both load bearing and energy storage can increase the payload and extend the operational range for robots. However, realizing these kinds of structural power devices requires the development of materials with suitable mechanical and ion transport properties. Here, we report biomimetic aramid nanofibers–based composites with cartilage-like nanoscale morphology that display an unusual combination of mechanical and ion transport properties. Ion-conducting membranes from these aramid nanofiber composites enable pliable zinc-air batteries with cyclic performance exceeding 100 hours that can also serve as protective covers in various robots including soft and flexible miniaturized robots. The unique properties of the aramid ion conductors are attributed to the percolating network architecture of nanofibers with high connectivity and strong nanoscale filaments designed using a graph theory of composite architecture when the continuous aramid filaments are denoted as edges and intersections are denoted as nodes. The total capacity of these body-integrated structural batteries is 72 times greater compared with a stand-alone Li-ion battery with the same volume. These materials and their graph theory description enable a new generation of robotic devices, body prosthetics, and flexible and soft robotics with nature-inspired distributed energy storage.
The creation of autonomous subgram microrobots capable of complex behaviors remains a grand challenge in robotics largely due to the lack of microactuators with high work densities and capable of using power sources with specific energies comparable to that of animal fat (38 megajoules per kilogram). Presently, the vast majority of microrobots are driven by electrically powered actuators; consequently, because of the low specific energies of batteries at small scales (below 1.8 megajoules per kilogram), almost all the subgram mobile robots capable of sustained operation remain tethered to external power sources through cables or electromagnetic fields. Here, we present RoBeetle, an 88-milligram insect-sized autonomous crawling robot powered by the catalytic combustion of methanol, a fuel with high specific energy (20 megajoules per kilogram). The design and physical realization of RoBeetle is the result of combining the notion of controllable NiTi-Pt–based catalytic artificial micromuscle with that of integrated millimeter-scale mechanical control mechanism (MCM). Through tethered experiments on several robotic prototypes and system characterization of the thermomechanical properties of their driving artificial muscles, we obtained the design parameters for the MCM that enabled RoBeetle to achieve autonomous crawling. To evaluate the functionality and performance of the robot, we conducted a series of locomotion tests: crawling under two different atmospheric conditions and on surfaces with different levels of roughness, climbing of inclines with different slopes, transportation of payloads, and outdoor locomotion.
A central ambition of the robotics field has been to increasingly miniaturize such systems, with perhaps the ultimate achievement being the synthetic microbe or cell sized machine. To this end, we have introduced and demonstrated prototypes of what we call Colloidal State Machines (CSMs) as particulate devices capable of integrating sensing, memory, energy harvesting as well as other functions onto a single particle. One technique that we have introduced for creating CSMs based on 2D materials such as graphene or monolayer MoS2 is “autoperforation”, where the nanometer scale film is fractured around a designed strain field to produce structured particles upon liftoff. While CSMs have been demonstrated with functions such as memory, sensing, and energy harvesting, the property of locomotion has not yet been demonstrated. In this work, we introduce an inversion molding technique compatible with autoperforation that allows for the patterning of an external catalytic surface to be introduced to enable locomotion in an accompanying fuel bath. Optimal processing conditions are elucidated for adding a catalytic Pt layer to one side of an autoperforated CSM. The resulting propulsion is studied, including the average velocity, as a function of fluid surface tension and H2O2 concentration in the bath. Lastly, since machines have to encode for a specific task, this work summarizes efforts to create a microfluidic testbed that allows for CSM designs to be evaluated for the ultimate purpose of navigation through complex fluidic networks, such as the human circulatory system. We introduce a CSM design that mimic aspects of human immunity to solve search and recruitment tasks in such environments. These results advance CSM design concepts closer to promising applications in medicine and other areas.
Significance
The smallest objects resolvable by the unaided human eye are approximately 100 μm in size. This limit sets a boundary between the familiar and the microscopic, the visible and invisible worlds. Here we describe the fabrication of tiny wireless sensors, optical wireless integrated circuits (OWICs) for optical wireless integrated circuits. OWICs are truly microscopic in size, visible to the naked eye at best as a tiny, undifferentiated speck, yet they can sense their environment and report the information back to the macroscopic world. They have potential applications in many areas of science and technology, ranging from neuroscience to chemical sensing.
We report a scheme for the integrated fabrication of MEMS-scale, series-connected battery cells. The approach exploits multilayer electrodeposition of active and sacrificial layers to generate structures that can be formed into high voltage power sources. Aqueous, non-vacuum-based fabrication, via electrodeposition, enables high throughput and deterministic control of layer thicknesses and battery performance. Batteries manufactured using this technique offer the potential to match supply voltages to system needs, ranging from conventional electronics to direct drive of high voltage electrostatic or piezoelectric MEMS.
One potential direction to fabricate battery-on-chip is photo-patterning electrochemical energy storage materials directly on electronics through lithography, but applicable materials are primarily limited to transparent photo-curable resins. The transparency of photoresist would be sacrificed after extra addition of insoluble inorganic battery materials and conductors. Given the importance of radical polymers for their appropriate solubility, optical transparent and radical robust, they may have opportunity for on-chip energy storage, transport, and conversion devices. Herein, an anodic photoresist is proposed by modifying MicroChem SU8 resist with radical polymer poly(2,2,6,6-tetramethyl-4-piperidinyl-N-oxyl methacrylate) and ionic conductor lithium perchlorate. It can be photo-patterned on silicon wafer with 10 μm scale resolution, and it exhibits charge/discharge potentials at ca. 0.68 V vs. silver chloride electrode, the coulomb efficiency is regarded as nearly equaling 100%. Although the specific capacity of photo-patterned film electrode is found as modest of 1×10-5 mAh·cm-2, it presents 1/8 of its theoretical electron storage ability. All-solid-state half-cell with circular features 30 μm in diameter is prepared by means of overlay exposure using as-prepared photoresist and lithium perchlorate modified SU8 as anodic electrode and solid electrolyte, respectively. These results suggest a promising direction of using radical polymers for the integration of electrochemical energy in microelectronics.
The progress of electronic textiles relies on the development of sustainable power sources without much sacrifice of convenience and comfort of fabrics. Herein, we present a rechargeable textile alkaline Zn microbattery (micro-AZB) fabricated by a process analogous to traditional resist dyeing techniques. Conductive patterned electrodes are realized first by resist-aided electroless/electro-deposition of Ni/Cu films. The resulting coplanar micro-AZB in a single textile, with electroplated Zn anode and Ni0.7Co0.3OOH cathode, achieves high energy density (256.2 Wh kg⁻¹), high power density (10.3 kW kg⁻¹) and stable cycling performances (82.7% for 1500 cycles). The solid-state micro-AZB also shows excellent mechanical reliability (bending, twisting, tailoring, etc.). The improved reversibility and cyclability of textile Zn electrode over conventional Zn foil are found to be due to the significantly inhibited Zn dendrite growth and suppressed undesirable side reactions. This work provides a new approach for energy-storage textile with high rechargeability, high safety, and aesthetic design versatility.
A pW-power versatile relaxation oscillator operating from sub-threshold (0.3V) to nominal voltage (1.8V) is presented, having Hz-range frequency under sub-pF capacitor. The wide voltage and low sensitivity of frequency/absorbed current to the supply allow the suppression of the voltage regulator, and direct powering from harvesters (e.g., solar cell, thermal from machines) or 1.2-1.5V batteries. A 180nm testchip exhibits a frequency of 4 Hz, 10%/V supply sensitivity at 0.3-1.8V, 8-18pA current, 4%/°C thermal drift from −20°C to 40°C.
Recording neural activity in live animals in vivo with minimal tissue damage is one of the major barriers to understanding the nervous system. This paper presents the technology for a tetherless opto-electronic neural interface based on 180 nm CMOS circuits, heterogeneously integrated with an AlGaAs diode that functions as both a photo voltaic and light emitting diode. These microscale opto-electrically transduced electrodes (MOTEs) are powered by, and communicate through an optical interface, simultaneously enabling high temporal-resolution electrical measurements without a tether or a bulky RF coil. The MOTE presented here is 250 μm × 57 μm, consumes 1 μW of electrical power, and is capable of capturing and encoding neural signals before transmitting the encoded signals. The measured noise floor is as low as 15 μV
at a 15 KHz bandwidth.
Continuously growing and miniaturizing autonomous electronic devices and sensors for large temperature window is mostly depends on stability and performance of power-up systems. The net achievable power and energy densities of such miniatured rechargeable energy storage systems are largely dominated by internal hardware and external packaging materials. Similarly, temperature stability of electrochemically active materials and packaging components is also crucial to realize desired activity at few millimeter scale devices. Herein, we explore energy storage devices at tunable miniatured scale by selecting optimal electroactive materials, thermally stable packaging components, and their fabrication process. Further, an assembled device is subjected to evaluate its energy and power density per foot-print-area along with other key electrochemical parameters such as internal resistance, self-discharge, and thermal stability. Detailed studies reveal that the presently packaged millimeter size rechargeable batteries (2 mm–5 mm) have the ability to work up to 120 °C with minimal load loss and compatible with energy harvesting renewable source of the solar cell.
The ever-increasing demand for smart personal electronics has promoted the rapid development of wearable multiple functionalities integrated configurations. However, it is still a great challenge to realize both high-performance energy storage devices and functional sensors in a single device to obtain a stable, self-powering, multifunctional, miniaturized integrated system. Herein, we report an ultrathin microbattery-pressure sensor integrated system to simultaneously achieve energy storage and pressure detection in a single device. Energy storage is achieved by an in-plane, interdigitated, flexible, all-solid-state, aqueous rechargeable Zn-MnO2 microbattery in a thin polydimethylsiloxane film, using MnO2 nanosheets directly deposited on highly conductive 3D Ni skeletons (Ni@MnO2) as an advanced binder-free cathode. Benefiting from synergy between the high electrochemical performance of MnO2 and the outstanding conductivity of 3D highly conductive Ni skeletons, the assembled Ni@MnO2//Zn microbattery displays a high capacity of 0.718 mAh cm-2 and a correspondingly impressive energy density of 0.98 mWh cm-2. More importantly, the wearable pressure sensor, which is powered by the integrated Ni@MnO2//Zn microbattery, can achieve real-time health monitoring both statically and dynamically. Thus, this work paves the way to develop high-performance, multifunctional, miniaturized integrated configurations for portable and wearable electronics.
Microbatteries have recently attracted considerable attention due to its small-size, high energy and voltage output. However, the commonly used non-aqueous electrolytes are flammable and sensitive to moisture and oxygen contaminations. In this work, an aqueous Zn-MnO2 rechargeable microbattery (micro-ZMB) with good electrochemical performance is developed. By simple laser carving and electrodeposition, the in-plane interdigitated current collectors and active materials are obtained. The micro-ZMB exhibits a high specific capacity of 253.8 mAh g-1 (58.4 Ah cm-2) at a current density of 0.5 A g-1 (0.11 mA cm-2), approaching to the level of the conventional Zn-ion batteries. With a proper package, a reversible specific capacity of 200 mAh g-1 is achieved even after 150 cycles. Compared with the microbatteries reported previously, the as-prepared micro-ZMB owns the longer cycle stability. Considering the safety of the aqueous electrolyte and stability of the metal Zn anode, the micro-ZMB has great promise in miniaturized electronic devices.