Electropolymerized 1D Growth Coordination Polymer for Hybrid Electrochromic Aqueous Zinc Battery

Innovative Energy Storage Smart Windows Relying on Mild Aqueous Zn/MnO2 Battery Chemistry

Rechargeable mild aqueous Zn/MnO2 batteries are currently attracting great interest thanks to their appealing performance/cost ratio. Their operating principle relies on two complementary reversible electrodeposition reactions at the anode and cathode. Transposing this operating principle to transparent conductive windows remains an unexplored facet of this battery chemistry, which is proposed here to address with the development of an innovative bifunctional smart window, combining electrochromic and charge storage properties. The proof-of-concept of such bifunctional Zn/MnO2 smart window is provided using a mild buffered aqueous electrolyte and different architectures. To maximize the device's performance, transparent nanostructured ITO cathodes are used to reversibly electrodeposit a high load of MnO2 (up to 555 mA h m-2 with a CE of 99.5% over 200 cycles, allowing to retrieve an energy density as high as 860 mA h m-2 when coupled with a zinc metal frame), while flat transparent FTO anodes are used to reversibly electrodeposit an homogenous coating of zinc metal (up to ≈280 mA h m-2 with a CE > 95% over 50 cycles). The implementation of these two reversible electrodeposition processes in a single smart window has been successfully achieved, leading for the first time to a dual-tinting energy storage smart window with an optimized face-to-face architecture.

A Reversible MnO2 Deposition-Enabled Multicolor Electrochromic Device with Efficient Tunability of Ultraviolet-Visible Light

Electrochromic technology offers exciting opportunities for smart applications such as energy-saving and interactive systems. However, achieving dual-band regulation together with the multicolor function is still an unmet challenge for electrochromic devices. Herein, an ingenious electrochromic strategy based on reversible manganese oxide (MnO2) electrodeposition, different from traditional ion intercalation/deintercalation-type electrochromic materials is proposed. Such a deposition/dissolution-based MnO2 brings an intriguing electrochromic feature of dual-band regulation for the ultraviolet (UV) and visible lights with high optical modulation (93.2% and 93.6% at 400 and 550 nm, respectively) and remarkable optical memory. Moreover, a demonstrative smart window assembled by MnO2 and Cu electrodes delivers the electrochromic properties of effective dual-band regulation accompanied by multicolor changes (transparent, yellow, and brown). The robust redox deposition/dissolution process endows the MnO2-based electrochromic device with excellent rate capability and an areal capacity of 570 mAh m-2 at 0.1 mA cm-2. It is believed that the metal oxide-based reversible electrodeposition strategy would be an attractive and promising electrochromic technology and provide a train of thought for the development of multifunctional electrochromic devices and applications.

Decoupling Electrochromism and Energy Storage for Flexible Quasi-Solid-State Aqueous Electrochromic Batteries with High Energy Density

Currently, reported aqueous electrochromic batteries (ECBs) show only limited capacity with insufficient energy density and power density. Such a limitation is naturally imposed by the rationale that the cathode of ECBs stores charge by an ion intercalation/deintercalation mechanism, where the inherent inhibition of ion diffusion and structural collapse of cathode materials through repetitive charge/discharge cycles lead to low areal capacity and unsatisfactory electrochemical performance with short lifetime. Herein, we decouple the dual functions of electrochromism and energy storage in conventional cathodes of ECBs by introducing a polyaniline/triiodide composite cathode that is in situ formed by direct electrolysis of an iodide-based quasi-solid-state aqueous electrolyte during charging. When paired with a zinc metal anode, the composite cathode can synergistically utilize the electrochromic property of polyaniline, the high-efficiency energy storage of the Zn-I2 system, as well as the effective anchorage of polyiodide by polyaniline to suppress the shuttle effect of triiodide. By selecting 1-butyl-3-methylimidazolium ion (BMI+) as the cation, a liquid-solid cathode/quasi-solid-state electrolyte interface can be achieved to facilitate the interfacial charge transfer, rendering quasi-solid-state aqueous electrochromic batteries with a high areal capacity of 1363 μAh cm-2, energy density of 1650 μWh cm-2, and power density of 5186 μW cm-2.

Hewettite ZnV6 O16 ⋅ 8H2 O with Remarkably Stable Layers and Ultralarge Interlayer Spacing for High-Performance Aqueous Zn-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) are promising candidates for grid-scale energy storage because of their intrinsic safety, low-cost and high energy-intensity. Vanadium-based materials are widely used as the cathode of ZIBs, especially A₂ V₆ O₁₆  ⋅ nH₂ O (AVO, A=NH₄ ⁺ , Na, K). However, AVO suffers from serious dissolution, phase transformation and narrow gallery spacing (∼3 Å), leading to poor cycling stability and rate capability. Herein, we unveiled the root cause of the performance degradation in the AVO cathode and therefore developed a new high-performance cathode of ZnV₆ O₁₆  ⋅ 8H₂ O (ZVO) for ZIB. Through a method of ion exchange induced phase transformation, AVO was converted to hewettite ZVO with larger gallery spacing (∼6 Å) and more stable V₆ O₁₆ layers. ZVO cathode thus constructed delivers a high capacity of 365 and 170 mAh g^-1 at 0.5 and 15 A g^-1 , while 86 % and 70 % of its capacity are retained at 0.5 A g^-1 after 300 cycles and at 15 A g^-1 after 10000 cycles, substantially better than conventional AVO.

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.

Recent progress in electrochromic energy storage materials and devices: a minireview

Integration of several functionalities into one isolated electrochemical body is necessary to realize compact and tiny smart electronics. Recently, two different technologies, electrochromic (EC) materials and energy storage, were combined to create a single system that supports and drives both functions simultaneously. In EC energy storage devices, the characteristic feature of EC materials, their optical modulation depending on the applied voltage, is used to visually identify the stored energy level in real time. Moreover, combining energy-harvesting and EC storage systems by sharing one electrode facilitates the realization of further compact multifunction systems. In this minireview, we highlight recent groundbreaking achievements in EC multifunction systems where the stored energy levels can be visualized using the color of the device.

Gel polymer electrolyte for reversible metal electrodeposition dynamic windows enables dual-working electrodes for faster switching and reflectivity control

Dynamic windows based on reversible metal electrodeposition are an attractive way to enhance the energy efficiency of buildings and show great commercial potential. Dynamic windows that rely on liquid electrolytes are at risk of short circuiting when two electrodes contact, especially at larger-scale. Here we developed a poly (vinyl alcohol) (PVA) gel polymer electrolyte (GPE) with 85% transmittance, that is, sufficiently stiff to act as a separator. The GPE is implemented into windows that exhibit comparable electrochemical and optical properties to windows using a liquid electrolyte. Furthermore, the GPE enables the fabrication of windows with dual-working electrodes (WE) and a metal mesh counter electrode in the center without short-circuiting. Our dual-WE PVA GPE window reaches the 0.1% transmittance state in 101 s, more than twice the speed of liquid windows with one working electrode (207 s). Additionally, each side of the dual-WE GPE window can be tinted individually to demonstrate varied optical effects (i.e., more reflective, or more absorptive), providing users and intelligent building systems with greater control over the appearance and performance of the windows in a single device architecture.

Organic electrochromic energy storage materials and device design

While not affecting electrochemical performance of energy storage devices, integrating multi-functional properties such as electrochromic functions into energy storage devices can effectively promote the development of multifunctional devices. Compared with inorganic electrochromic materials, organic materials possess the significant advantages of facile preparation, low cost, and large color contrast. Specifically, most polymer materials show excellent electrochemical properties, which can be widely used in the design and development of energy storage devices. In this article, we focus on the application of organic electrochromic materials in energy storage devices. The working mechanisms, electrochemical performance of different types of organics as well as the shortcomings of organic electrochromic materials in related devices are discussed in detail.