Weizi Cai

Flexible Zn– and Li–air batteries: recent advances, challenges, and future perspectives

The demand for flexible power sources with high energy density and durability has increased rapidly with the development of flexible and wearable electronic devices. Metal–air batteries are considered as the most promising candidates for these applications due to their excellent theoretical energy densities. In particular, rechargeable zinc–air and lithium–air batteries have attracted much attention because of their potential to offer high energy density while maintaining a long operational life. Although significant progress has been made in enhancing the electrochemical performance of these batteries, many technical challenges still remain to achieve the mechanical flexibility required for wearable electronic devices while maintaining high performance. This article describes the most recent advances and challenges in the development of flexible zinc–air and lithium–air batteries. We start with an overview of the latest innovations in the exploration of various battery configurations to effectively accommodate stresses and strains associated with the use of flexible electronic devices. This is followed by a detailed review of the advancements made in the design of flexible battery components: the metal electrode, the electrolyte membrane, and the air electrode. Furthermore, the effects of operating conditions on battery performance characteristics and durabilities are discussed, including the effect of the operating temperature and the contaminants commonly encountered in ambient air (e.g., carbon dioxide and moisture). Finally, challenges facing the development of a new generation of flexible metal–air batteries are highlighted, together with further research directions and perspectives.

An investigation on the kinetics of direct carbon solid oxide fuel cells

A direct carbon solid oxide fuel cell (DC-SOFC) is an all-solid-state electricity generation device that operates directly with solid carbon as fuel, without any liquid medium and feeding gas. Tubular electrolyte-supported solid oxide fuel cells (SOFCs), with silver-gadolinium doped ceria (Ag-GDC) as both anode and cathode materials, are fabricated and operated directly with activated carbon as fuel. The kinetics of the DC-SOFCs is carried out through analyzing the correlations of the cell reaction rates to the emitting rates of CO and CO2. It turns out that higher operating current corresponds to higher rates of consuming and producing CO, through electrochemical oxidation at the anode and the Boudouard reaction at the carbon fuel, respectively. The rate of consuming CO can be maintained constant by controlling the operating current while the rate of producing CO decreases with time because of carbon consumption. When the CO producing rate becomes smaller than the CO consuming rate, the operation will be terminated. Compared to the rates of the chemical reactions, the diffusion rates of CO and CO2 are so fast that their impeding effect on the cell performance can be neglected.

Co3O4 Nanosheets as Active Material for Hybrid Zn Batteries

The rapid development of electric vehicles and modern personal electronic devices is severely hindered by the limited energy and power density of the existing power sources. Here a novel hybrid Zn battery is reported which is composed of a nanostructured transition metal oxide-based positive electrode (i.e., Co3 O4 nanosheets grown on carbon cloth) and a Zn foil negative electrode in an aqueous alkaline electrolyte. The hybrid battery configuration successfully combines the unique advantages of a Zn-Co3 O4 battery and a Zn-air battery, achieving a high voltage of 1.85 V in the Zn-Co3 O4 battery region and a high capacity of 792 mAh gZn-1 . In addition, the battery shows high stability while maintaining high energy efficiency (higher than 70%) for over 200 cycles and high rate capabilities. Furthermore, the high flexibility of the carbon cloth substrate allows the construction of a flexible battery with a gel electrolyte, demonstrating not only good rechargeability and stability, but also reasonable mechanical deformation without noticeable degradation in performance. This work also provides an inspiring example for further explorations of high-performance hybrid and flexible battery systems.

Electrical Performance of Ag-Based Ceramic Composite Electrodes and Their Application in Solid Oxide Fuel Cells

Silver-based ceramic composite electrodes are expected to be widely applied in mediumor lowtemperature solid oxide fuel cells (SOFCs), SOFCs operated on carbon-containing fuels, and solid oxide electrolysis cells (SOECs). To optimize the composition of a silver-based ceramic composite electrode, the performances of Ag-YSZ (yttrium-stabilized zirconia) and Ag-GDC (gadolinium doped ceria) are investigated. First, they are used as electrode materials to make symmetric electrodes on a YSZ electrolyte, to which impedance spectra are measured in an ambient atmosphere to evaluate their feasibility as cathode materials. It was found that that Ag-YSZ reaches the lowest polarization resistance when the content of Ag is 65% (w, mass fraction), while for Ag-GDC, the value is 70% (w). The Ag-YSZ and Ag-GDC with the lowest polarization resistance are used as electrode materials to make SOFC single cells whose electrochemical performances are tested. The polarization resistance of an anode of the SOFCs can be obtained by subtracting the cathode 503 Acta Phys. -Chim. Sin. 2016 Vol.32 1 引 言 固体氧化物燃料电池(SOFCs)是一种能将燃料 中的化学能直接而连续地转化为电能的电化学发 电装置,具有系统结构简单、电转换效率高、对 环境友好、适用燃料范围广及寿命长等优点,被 公认为具有良好发展前景的新型发电技术 -。为 了大幅度地降低成本、拓宽材料的选择范围和提 高SOFC系统的稳定性,近年来研究者做了大量的 工作,旨在把 SOFC的操作温度从传统的 1000 °C 降到600-800 °C-。目前普遍采用的SOFC电解质 材料为钇稳定化氧化锆[(ZrO2)0.92(Y2O3)0.08,YSZ], 阳极材料采用镍和 YSZ 复合的金属陶瓷 (NiYSZ), 阴 极 材 料 采 用 掺 锶 的 锰 酸 镧 (La0.8Sr0.2MnO3, LSM)和 YSZ 的复合陶瓷 LSMYSZ。YSZ电解质在较低的工作温度下欧姆电阻较 大,严重地影响电池的性能,因此,降低SOFC工 作温度的一种主要手段就是将YSZ电解质薄膜化 以减小电解质的欧姆电阻损失 ;此外,还有一 种方法就是采用在低温下具有较高离子电导率的 电解质材料,例如氧化铈基 和镓酸镧基 材料。 然而,随着电池工作温度的降低,LSM电极的极 化电阻明显增大,由此带来的电极极化损失就凸 显出来。已有研究表明,银与陶瓷的复合材料可 作为高性能的中低温 SOFC的阴极材料 。银具 有很高的电子电导率,与之复合的材料为具有氧 离子导电性的陶瓷,例如 YSZ或掺杂氧化铈。 YSZ具有很好的稳定性,掺杂氧化铈不仅具有较 高的离子导电率,而且对SOFC电极的氧化还原反 应具有很好的催化活性 。由于银在高温氧化气 氛和含碳气体中相对稳定,最近,银和钆掺杂的 氧化铈(GDC)的复合材料(Ag-GDC)被广泛用于直 接碳固体氧化物燃料电池(DC-SOFC)的阴极和阳极 上 -。此外,由于银基陶瓷复合电极不需要事先 经过还原处理,还可被用于固体氧化物电解池 (SOEC)中 。然而,目前还没有对此类银基电极的 成分进行优化。在本文中,采用YSZ电解质,分 别采用Ag-YSZ或Ag-GDC为电极材料,通过对不 同组分电极在空气中的阻抗谱进行测试,分别选 出Ag-YSZ和Ag-GDC电极的最佳成分比;结合相 应电极材料组装成的SOFC电化学性能测试结果, 区分出阴极和阳极的极化电阻,并对实验结果进