Hierarchically-structured electrodes for Li-air batteries

锂-空气电池是所有电池系统中理论能量密度最高的二次电池。为了在实践中实现这一目标，必须首先解决许多技术问题。限制高倍率放电容量的一个关键问题是氧气通过阴极材料的扩散。在较高的放电速率下，阴极空气侧的氧气在被消耗之前没有时间扩散到整个电极，导致空气侧的放电产物积聚。这导致最终的孔隙堵塞和阴极体积利用不足。影响电池能量效率的另一个问题是由于放电和充电时氧还原和进化反应的缓慢动力学引起的高过电位。该项目的主要目标之一是了解高放电速率下锂空气电池的氧扩散率与放电容量之间的关系。在这个项目中，氧通过阴极的扩散率最初将通过激光加工碳纳米管（CNT）垫来控制。在此基础上，可以采用更先进的材料合成方法，例如纳米光刻来定义一种图像化催化剂，然后是碳纳米管森林生长。该阴极材料的材料性能和电化学性能将被表征，并与通过电极的有效氧扩散率相关。以该系统为实验基础，利用operando XRD和气体压力监测，详细研究不同氧扩散率和循环速率对细胞动力学的影响。随后，将合成具有催化纳米粒子功能化的阴极，并对其电化学性能进行表征。该项目早期开发的operando技术将用于研究非均相催化对锂空气电池放电产物形成的影响。这些研究将有助于提高锂空气电池的电池容量和效率，特别是与商业应用相关的高放电率。

Li-air batteries are secondary batteries with the highest theoretical energy density of any battery system. In order to achieve this in practice, many technical problems must first be resolved. One key issue limiting the discharge capacity at higher rates is that of oxygen diffusion through the cathode material. At higher discharge rates, oxygen from the air side of the cathode does not have time to diffuse throughout the whole electrode before being consumed, resulting in a build up of discharge product at the air side. This results in eventual pore blockage and the underutilisation of the cathode volume. Another issue affecting the energy efficiency of these batteries is the high overpotentials caused by the slow kinetics of the oxygen reduction and evolution reactions on discharge and charge. One of the main goals of this project is to develop an understanding of the relationship between oxygen diffusivity and discharge capacity of Li-air batteries at high discharge rates. In this project, the oxygen diffusivity through the cathode will initially be controlled via laser processing of carbon nanotube (CNT) mats. Building from this, more advanced material synthesis methods can be employed, such as nano-lithography to define a patterned catalyst followed by CNT forest growth. The material properties and electrochemical performance of this cathode material will be characterised, and correlated with the effective oxygen diffusivity through the electrode. Using this system as an experimental basis, operando XRD and gas pressure monitoring will be used to study the effects of varying oxygen diffusivity and cycling rate on cell kinetics in detail. Following this, cathodes functionalised with catalytic nanoparticles will be synthesised and have their electrochemical performance characterised. The operando techniques developed earlier in the project will be used to study the effects of heterogeneous catalysis on discharge product formation in Li-air batteries. These studies will help improve the cell capacity and efficiency of Li-air batteries, particularly athigh discharge rates, relevant for commercial applications.