Flexible hybrid electrochromic zinc battery

Electrochromic batteries, with simultaneous colour-changing and energy-storage capabilities, have great commercial interest, ranging from renewable energy systems, electric vehicles to consumer electronics. Recently, the development of these devices has skewed towards those that could conform to non-planar and curvature surfaces, as to cater to the rising demand for futuristic wearables such as energy-saving wearable displays and expressive garments. However, the current bottleneck in conformable devices lies in their poor mechanical durability due to limited availability of suitable materials. In this dissertation, efforts are invested in developing a flexible electrochromic zinc battery based on innovative designs and selection of materials. The undertaking was first approached by studying the prospect of chemically anchored electrochromic materials via electropolymerization process. Particularly, electropolymerizable iron-centred coordination polymer has been deployed, showing not only effective in manipulating thicknesses and surface morphologies, but also demonstrated robust electrochromic and cathodic performances. Despite these promising features, the construction of flexible devices is still limited by a lack of suitable electrolyte and substrate. Traditional liquid and gel electrolytes are not competent due to their poor environmental stability, leakage tendency and poor processability. Considering the low oxygen solubilities of poly(ionic liquid)s, solid-state ionogels were developed via facile in-situ photopolymerization approach, establishing electrolytes with high transparency, stretchability and excellent physicochemical stabilities (e.g., thermal, electrochemical and air stability). Benefitting from the versatility of the materials, they were modified to tailor for an electrochromic Zn battery. By coupling with zinc mesh anode, the compatibilized materials were readily assembled on an ultra-thin-ITO glass, realizing a flexible EC battery device that delivers a capacity of 19.3 mAh m-2 at 0.01 mA cm-2 which could be bent repeatedly with minimal damage and powering up a wireless portable device, paving the road towards the advancement of wearable electronics.Doctor of Philosoph

Electropolymerized 1D growth coordination polymer for hybrid electrochromic aqueous zinc battery

Organic materials are always viewed as promising electrochromic (EC) materials due to their synthetic versatility, color tunability, ready processability, and derivability from sustainable feedstocks. Most organic materials, however, are prone to undesirable redox side reactions in the presence of oxygen and water. As such, redox-active organic layers are often used in tandem with organic electrolytes to preserve their electrochemical stability. With the growing interest in electronics that are environmentally sustainable and biologically safe, developing aqueous-compatible organic materials is gaining growing interest. Herein, a rationally designed iron terpyridyl coordination polymer (CP) is prepared by controlled electropolymerization for realization of aqueous compatible EC and energy storage applications. Detailed analysis is established, showing that the CP grows in a 1D fashion and exhibits a predominant capacitive behavior which is reflected from its rapid charge-transfer kinetics. Taking this as an advantage, an integrated hybrid electrochromic zinc battery device is demonstrated with high color contrast, fast response time, and good endurance.National Research Foundation (NRF)Published versionW.C.P. and X.G. contributed equally to this work. W.C.P. is supported by NTU Research Scholarship awarded by the Nanyang Technological University. The authors acknowledge the funding from Campus for Research Excellence and Technological Enterprise (CREATE) that is supported by the National Research Foundation, Prime Minister’s Office, Singapore

A highly stretchable, self-healable, transparent and solid-state poly(ionic liquid) filler for high-performance dielectric elastomer actuators

By incorporating fillers into dielectric elastomers, electromechanical sensitivities can be enhanced to lower the required operating electrical field for actuation. However, existing solid and liquid fillers suffer from increased stiffness and filler leakage problems respectively, hindering the actuation performance of dielectric elastomer actuators (DEAs). To address these challenges, a soft, stretchable (∼300%), transparent (∼99%), and solid-state poly(ionic liquid) (PIL) is introduced to DEAs as a compliant filler. The mechanical properties of the PIL can be tuned by controlling the solvent ratio within precursors. When the PIL filler is introduced to a very high bonding elastomer (VHB), the effective dielectric constant increases from 4.7 to 16.4 at 1 kHz and the Young's modulus decreases to 0.21 MPa. The resulting planar DEA could achieve an area strain of 133% at 17 V μm−1, exceeding that of most DEAs with fillers. Notably, the PIL achieves adhesion and rapid self-healability, which eliminates filler leakage problems and endows DEAs with recoverability. A unimorph DEA demonstrates a bending angle of 44.7° at 12.6 V μm−1, two times greater than that exhibited by a DEA without the PIL filler. Simultaneous dynamic motion and light emission are further realized by integrating a unimorph DEA with an electroluminescent layer. Thus, the solid-state PIL filler provides high-performing and safer DEAs for soft robotics, interactive lighting, or wearables.Ministry of Education (MOE)Nanyang Technological UniversityNational Research Foundation (NRF)The research was supported by the SGSR project grant from the National Research Foundation, Prime Minister's Office, Singapore under its Campus of Research Excellence and Technological Enterprise (CREATE) programme. The work was also supported in part by the Ministry of Education, AcRF Tier 2, award no. MOE-T2EP50122-0002. H. W acknowledges the scholarship awarded by the Nanyang Technological University, Singapore

Rapidly photocurable solid-state poly(ionic liquid) ionogels for thermally robust and flexible electrochromic devices

Formation of ionogels through in situ polymerization can effectively improve electrolyte processability; however, the curing process has been slow and oxygen-sensitive. Considering the low oxygen solubility of poly(ionic liquid)s (PILs), in situ polymerized ionogels are designed to realize excellent electrolytes. Herein, two in situ polymerized ionogels (PIL A & PIL B) are formulated, and they can be rapidly photocured within a minute. The ionogels are highly transparent, stretchable, and exhibit excellent physicochemical stability, including thermal, electrochemical, and air stability, allowing them to perform in various conditions. Benefitting from these properties, two high-performance electrochromic devices (ECDs) are assembled, with iron-centered coordination polymer (FeCP) and tungsten oxide (P-WO3 ) electrochromic materials, achieving high color contrast (45.2% and 56.4%), fast response time (1.5/1.9 and 1.7/6.4 s), and excellent cycling endurance (>90% retention over 3000 cycles). Attributed to the thermal robustness of the ionogels, the ECDs can also be operated over a wide temperature range (-20 to 100 °C). With the use of deformable substrates (e.g., ultrathin ITO glass), curved electrochromic eye protector and flexible electrochromic displays are realized, highlighting their potential use in futuristic wearables.Ministry of Education (MOE)Nanyang Technological UniversityNational Research Foundation (NRF)W.C.P. is supported by NTU Research Scholarship awarded by Nanyang Technological University. The authors acknowledge the funding from Ministry of Education AcRF Tier 1 RG64/21, and Campus for Research Excellence and Technological Enterprise (CREATE) that is supported by the National Research Foundation, Prime Minister’s Office, Singapore

Solid‐State and Flexible Black Electrochromic Devices Enabled by Ni‐Cu Salts Based Organohydrogel Electrolytes

Abstract Solid‐state black electrochromic devices (ECDs) are promising for smart window applications, particularly when privacy protection and low leakage are required. Herein, a Ni–Cu salts/poly(vinyl alcohol) based organohydrogel electrolyte is developed with superior visible‐light transparency (83.8%), ionic conductivity (0.11 mS cm−1), and mechanical properties (tensile strength: 11.1 kPa, breaking strain: 242.6%). Due to the high viscosity of the organohydrogel electrolyte, a homogeneous Ni–Cu alloy film with a surface roughness of around 11.2 nm can be electrodeposited under −3 V for 5 min, and the resulting black color can be retained for over 350 min with a transmittance increase of only 5% at the voltage‐off state. The solid‐state rigid ECD exhibits an outstanding optical contrast between the transparent and colored states (visible light transmittance: 70.8% vs 0.085%), excellent cycling stability with over 90% retention of optical contrast after 2000 cycles. Finally, a flexible ECD is fabricated with the organohydrogel electrolyte and annealed indium tin oxide (ITO)‐coated polyethylene naphthalate (PEN) films as flexible and durable electrodes. It exhibits good mechanical flexibility with transmittance modulation degradation of 10% after 800 bending cycles and switching stability for 400 cycles with up to 43% optical contrast

Printed sustainable elastomeric conductor for soft electronics

The widespread adoption of renewable and sustainable elastomers in stretchable electronics has been impeded by challenges in their fabrication and lacklustre performance. Here, we realize a printed sustainable stretchable conductor with superior electrical performance by synthesizing sustainable and recyclable vegetable oil polyurethane (VegPU) elastomeric binder and developing a solution sintering method for their composites with Ag flakes. The binder impedes the propagation of cracks through its porous network, while the solution sintering reaction reduces the resistance increment upon stretching, resulting in high stretchability (350%), superior conductivity (12833 S cm-1), and low hysteresis (0.333) after 100% cyclic stretching. The sustainable conductor was used to print durable and stretchable impedance sensors for non-obstructive detection of fruit maturity in food sensing technology. The combination of sustainable materials and strategies for realizing high-performance stretchable conductors provides a roadmap for the development of sustainable stretchable electronics.National Research Foundation (NRF)Published versionThis work is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Campus of Research Excellence and Technological Enterprise (CREATE) program, Smart Grippers for Soft Robotics (SGSR)

Ion rectification based on gel polymer electrolyte ionic diode

Biological ion channels rely on ions as charge carriers and unidirectional ion flow to produce and transmit signals. To realize artificial biological inspired circuitry and seamless human-machine communication, ion-transport-based rectification devices should be developed. In this research, poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) gel polymer electrolytes (GPEs) are assembled to construct a novel ionic diode, enabling ion rectification through ion-diffusion/migration that emulates biological systems. This ion rectification results from the different diffusion/migration behaviors of mobile ions transporting in the GPE heterojunction. The electrical tests of the GPE heterojunction reveal outstanding rectifying ratio of 23.11. The GPE ionic diode operates in wide temperature window, from -20 °C (anti-freezing) to 125 °C (thermal tolerance). The absence of redox reactions is verified in the cyclic voltammogram. The GPE ionic diodes are used to construct ionic logic gates for signal communication. Furthermore, rectification of a triboelectric nanogenerator and potential for synaptic devices are demonstrated.Ministry of Education (MOE)Published versionThe project is funded by the Ministry of Education Tier 1 Grant Award No. RT15/20

Heat-insulating black electrochromic device enabled by reversible nickel-copper electrodeposition

An electrochromic device (ECD), which can switch between black and transmissive states under electrical bias, is a promising candidate for smart windows due to its color neutrality and excellent durability. Most of the black ECDs are achieved through a reversible electrodeposition and dissolution mechanism; however, they typically suffer from relatively poor cycling stability and a slow coloration/bleaching time. Herein, we present a heat-insulating black ECD with a gel electrolyte that operates via reversible Ni-Cu electrodeposition and dissolution. With the adoption of a Cu alloying strategy and a compatible gel electrolyte, this two-electrode ECD (5.0 cm × 2.5 cm) can achieve a cycling stability of 1500 cycles with transmittance modulation up to 55.2% in short coloration (6.2 s) and bleaching times (13.2 s) at a wavelength of 550 nm. Additionally, the ECD can be switched from the transparent state (visible light transmittance: 0.566) to the opaque state (visible light transmittance: 0.003) within 1 min, reaching transmittance less than 5% across the visible-near-infrared spectrum (400-2000 nm) to efficiently block solar heat. Besides, in the voltage-off state, the black Ni-Cu alloy film can be sustained for more than 60 min (at room temperature, λ = 550 nm). Under infrared irradiation (170 W/m2) for 30 min, the black ECD blocks up to 35.0% of infrared radiation, which not only effectively prevents the heat transmission for energy management but also finds potential applications for promoting indoor human health and indoor farming.Ministry of Education (MOE)National Research Foundation (NRF)This work was funded by the Ministry of Education AcRF Tier 1 (2021-T1-002-115) and the Campus for Research Excellent and Technological Enterprise (CREATE), National Research Foundation, Singapore

Self-powered and light-adaptable stretchable electrochromic display

A stretchable electrochromic display with a self-powered feature is an attractive concept in addressing the demands of information visualization and interaction without an external power supply for next-generation wearable and portable electronics. Herein, a self-powered stretchable electrochromic display is proposed for the first time, with WO3 on the stretchable conductor as the electrochromic electrode integrated in parallel with the Zn/carbon electrodes and topped with a ZnCl2-based organohydrogel. This geometrically designed electrochromic device can be self-colored by the chemical potential gap between WO3/Zn electrodes. The self-bleaching process caused by the oxidation of the reduced WO3 electrode is facilitated by the leakage current between the WO3/carbon electrodes. In this constructed self-powered system, the electrochromic electrode shows reversible coloring/bleaching performance up to 50% strain and maintains favorable stability with power-free reversible electrochemical switching for 400 cycles. Optical contrast retention at 81% is maintained for 200 stretching/recovery cycles. The prepared device combined with a phosphorescent substrate is demonstrated as a light-adaptable stretchable display, where the “on/off” states of the display are shown in both bright and dark conditions without power consumption. This work provides broad application prospects for futuristic multifunctional stretchable and portable display electronics.Ministry of Education (MOE)This work was supported by funding from the Ministry of Education (MOE) Singapore, AcRF Tier 1, Project No. RG64/21 and National Natural Science Foundation of China (No. 51902250). The author W.W. thanks the support from the China Scholarship Council (Grant No 202006280507) and Basic Scientific Research of Xi’an Jiaotong University (Grant No. xzy022022028)

Ionic covalent organic framework based electrolyte for fast-response ultra-low voltage electrochemical actuators

Electrically activated soft actuators with large deformability are important for soft robotics but enhancing durability and efficiency of electrochemical actuators is challenging. Herein, we demonstrate that the actuation performance of an ionic two-dimensional covalent-organic framework based electrochemical actuator is improved through the ordered pore structure of opening up efficient ion transport routes. Specifically, the actuator shows a large peak to peak displacement (9.3 mm, ±0.5 V, 1 Hz), a fast-response time to reach equilibrium-bending (~1 s), a correspondingly high bending strain difference (0.38%), a broad response frequency (0.1-20 Hz) and excellent durability (>99%) after 23,000 cycles. The present study ascertains the functionality of soft electrolyte as bionic artificial actuators while providing ideas for expanding the limits in applications for robots.Ministry of Education (MOE)National Research Foundation (NRF)Published versionWe acknowledge financial support from Singapore Ministry of Education Tier 1, RG63/ 20 (2020-T1-001-165) and the National Research Foundation, Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) program