Photo-Energized MoS2/CNT Cathode for High-Performance Li–CO2 Batteries in a Wide-Temperature Range

Abstract

Li–CO2 batteries are considered promising energy storage systems in extreme environments such as Mars; however, severe performance degradation will occur at a subzero temperature owning to the sluggish reaction kinetics. Herein, a photo-energized strategy adopting sustainable solar energy in wide working temperature range Li–CO2 battery was achieved with a binder-free MoS2/carbon nanotube (CNT) photo-electrode as cathode. The unique layered structure and excellent photoelectric properties of MoS2 facilitate the abundant generation and rapid transfer of photo-excited carriers, which accelerate the CO2 reduction and Li2CO3 decomposition upon illumination. The illuminated battery at room temperature exhibited high discharge voltage of 2.95 V and mitigated charge voltage of 3.27 V, attaining superior energy efficiency of 90.2% and excellent cycling stability of over 120 cycles. Even at an extremely low temperature of −30 °C, the battery with same electrolyte can still deliver a small polarization of 0.45 V by the photoelectric and photothermal synergistic mechanism of MoS2/CNT cathode. This work demonstrates the promising potential of the photo-energized wide working temperature range Li–CO2 battery in addressing the obstacle of charge overpotential and energy efficiency.

1. Introduction

The rechargeable Li–CO2 battery emerges as a newly conceptual and promising energy conversion and storage device to alleviate the environmental crisis and energy crisis, which can convert carbon dioxide into sustainable electricity with a standout theoretical specific capacity of 1876 Wh kg–1 [1–9]. However, in spite of the above-mentioned favorable factors and promising prospects, the development of Li–CO2 battery has been plagued by high voltage gap and slow kinetics of decomposition during charging due to the insulated discharge product Li2CO3 with high thermodynamic stability [10–12]. In recent years, some advances have been made for Li–CO2 batteries with various catalysts including metal, alloy, single atom, and oxide, but their improved voltage gaps were still beyond 1 V and the challenging problem of high overpotential still exists to be addressed [13–17]. In response to this issue, the introduction of energy supplements from the external environment presents a promising strategy for energy conversion and storage [18, 19]. In this way, solar energy, as a clean, abundant and sustainable energy source, has generated wide interest and been adopted to devices for CO2 reduction or electricity conversion and storage of electrical energy [20–24].

However, the overall impression from the previous works on electrode design of Li–CO2 batteries is confined to operating only at room temperature. For the practical use of Li–CO2 batteries in applications, such as mars landing and deep space exploration, low-temperature operation is an essential requirement [25–27]. The decrease of ambient temperature inevitably leads to increased viscosity of electrolyte, increased charge-transfer resistance at the electrode/electrolyte interface, so that more energy is needed to urge the discharge and charge process [28–31]. The electrolyte for low-temperature Li–CO2 batteries was replaced by the low-temperature adaptive electrolyte as previous work reported, which limited the application of room temperature [32]. In order to adapt to wide temperature environments, the thermal effect of solar energy could assist Li–CO2 batteries without electrolyte replaced in self-heating to meet the requirements [33]. As for photo-energized Li–CO2 batteries, photoelectric effect efficiently accelerates the reaction kinetics of electrochemical reduction of CO (COER) by leap of photons-excited electrons, and strong photothermal effect enhances visible light absorption and the conversion of solar energy to heat [34–37]. Therefore, photoelectric and photothermal synergistic mechanism of photo-energized cathode can effectively speed up the interfacial charge transfer of low-temperature environments, but stable cycling at low temperatures remains an urgent issue to be addressed.

In this study, we design a photo-energized binder-free Li–CO2 battery with semiconducting 2H–MoS2 on carbon nanotube (CNT) conductive substrate (MoS2/CNT) as a photocathode to content the requirement of wide temperature range application. Combining DFT calc...