Extraordinarily Stable Aqueous Electrochromic Battery Based on Li₄Ti₅O₁₂ and Hybrid Al³⁺/Zn²⁺ Electrolyte

Abstract

Aqueous electrochromic battery (ECB) is a multifunctional technology that shows great potential in various applications including energy-saving buildings and wearable batteries with visible energy levels. However, owing to the mismatch between traditional electrochromic materials and the electrolyte, aqueous ECBs generally exhibit poor cycling stability which bottlenecks their practical commercialization. Herein, we present an ultrastable electrochromic system composed of lithium titanate (Li4Ti5O12, LTO) electrode and Al3+/Zn2+ hybrid electrolyte. The fully compatible system exhibits excellent redox reaction reversibility, thus leading to extremely high cycling stabilities in optical contrast (12 500 cycles with unnoticeable degradation) and energy storage (4000 cycles with 82.6% retention of capacity), superior electrochromic performances including high optical contrast (∼74.73%) and fast responses (4.35 s/7.65 s for bleaching/coloring), as well as excellent discharge areal capacity of 151.94 mAh m–2. The extraordinary cycling stability can be attributed to the robust [TiO6] octahedral frameworks which remain chemically active even upon the gradual substitution of Li+ with Al3+ in LTO over multiple operation cycles. The high-performance electrochromic system demonstrated here not only makes the commercialization of low-cost, high-safety aqueous-based electrochromic devices possible but also provides potential design guidance for LTO-related materials used in aqueous-based energy storage devices.

A highly transparent ion conducting film enabling a visual electrochromic battery

“…Electrochromic energy storage devices (ECESDs) are capable of monitoring energy storage levels in real time and have attracted great research interests in recent years. [1][2][3][4] The currently-studied ECESDs include EC supercapacitors and EC batteries. [4][5][6][7] The latter feature the advantages of high energy density and stable charging/discharging platform.…”

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

“…Alternatively, Lee et al assembled hierarchical MnO 2 –PANI hybrid on transparent PEDOT:PSS/Ag@Ni nanowires thin film and fabricated a flexible aqueous ECB with a high area capacity of 127 μAh cm –2 that can continuously work for 400 cycles, yet the low intercalation/deintercalation rate of multivalent ions in the cathode still leads to unsatisfactory rate performance. Overall, reported ECBs have only exhibited low areal capacity (2.2–127.0 μAh cm –2 ), ,,,,,− limited energy density (1.0–114.3 μWh cm –2 ), ,,,,,,− and power density (12.3–243.4 μW cm –2 ). ,,,,,− …”

“…With the rapid development of smart electronics, there is an increasing interest to study power sources that have multiple functions other than energy storage. − Electrochromic batteries (ECBs) can change their colors during charging/discharging and realize visualization of the state of charge (SOC), , showing great promise in applications ranging from smart windows to intelligent displays …”

“…Recently, aqueous ECBs with multivalent-ion (Zn 2+ , Ca 2+ , Al 3+ , etc.) electrolytes have attracted much attention due to their inherent advantages of high safety, low cost, and environmental friendliness. ,,− In these devices, electrochromic cathode materials such as lithium titanate, tungsten oxide, nickel­(II) oxide, Prussian white, polyaniline, , and polypyrrole have been used, where charge is generally stored via the ion intercalation/deintercalation mechanism. For instance, Wang et al selected the lithium titanate (Li 4 Ti 5 O 12 ) cathode and Al 3+ /Zn 2+ hybrid aqueous electrolyte to prepare ECBs with excellent cycling stability (4000 cycles with 82.6% retention of capacity).…”

“…For instance, Wang et al selected the lithium titanate (Li 4 Ti 5 O 12 ) cathode and Al 3+ /Zn 2+ hybrid aqueous electrolyte to prepare ECBs with excellent cycling stability (4000 cycles with 82.6% retention of capacity). While the robust [TiO 6 ] octahedral framework remained chemically active over long-term working, the device only exhibited a poor area specific capacity of 15.19 μAh cm –2 due to the limited thickness of the Li 4 Ti 5 O 12 film . Alternatively, Lee et al assembled hierarchical MnO 2 –PANI hybrid on transparent PEDOT:PSS/Ag@Ni nanowires thin film and fabricated a flexible aqueous ECB with a high area capacity of 127 μAh cm –2 that can continuously work for 400 cycles, yet the low intercalation/deintercalation rate of multivalent ions in the cathode still leads to unsatisfactory rate performance.…”