通过高效锂氧反应界面的构筑调控Li2O2形态提高锂空气二次电池性能的研究

Lithium-air (or Li-O2) batteries have attracted much attention because they can deliver much larger energy densities than conventional lithium ion batteries. However, many critical scientific and technical problems with respect to cycle life, energy efficiency and rate performance must be solved taking into account their real application. The Li-O2 battery delivers the energy through formation of Li2O2 during discharge and gain the reversibility by decomposition of Li2O2 on charge. It is clear that the formation of Li2O2 during discharge is the prerequisite to gain the rechargeability of the Li-O2 batteries. The morphology, size and defect chemistry of Li2O2 play important role in its decomposition on charge and the resulting overpotential. Control of Li2O2 growth process is an effective means to promote its decomposition and improve the cycle life, energy efficiency and rate capability of the battery. Therefore, this project is to construct interfaces of lithium-oxygen reaction with good kinetics through tailoring of the morphology, structure and defect chemistry of transition-metal oxides. Such interfaces presumably can change the nucleation and growth of Li2O2 during discharge and regulate the crystallinity and morphology of Li2O2, with the result of decreasing the potential of Li2O2 decomposition on charge and reducing cycle polarization. It is expected that the role of the interface playing in Li2O2 formation and decomposition can be obtained. The achieved effective means to control the crystallinity and morphology of Li2O2 would be helpful for greatly improving of the battery performance.

锂空气电池具有远高于锂离子电池的理论能量密度，受到国内外研究者的广泛关注。但走向实际应用它还需要解决循环寿命、能量效率及倍率性能等诸多方面的关键科学和技术问题。锂空气电池通过放电时Li2O2的生成输出能量，通过Li2O2的充电分解实现可逆循环。其中，Li2O2的生成是锂空气电池可逆工作的前提。它的形貌、尺寸及缺陷等因素制约着其分解的难易，影响着电池的充电过电势。而控制生长过程中Li2O2的形态是促进其分解，改善电池循环寿命、能量效率和倍率性能的关键。为此，本项目将通过调控过渡金属氧化物正极材料的形貌、结构、缺陷，构筑高效锂氧反应界面，从而改变放电过程中Li2O2的成核、生长，实现对Li2O2形态的调控；通过形态调控降低Li2O2的充电分解电位，减小电池的循环极化。预期将获得锂氧反应界面影响Li2O2生长与分解的作用规律，掌握主动调控Li2O2形态的有效方法，实现锂空气电池性能的大幅提升。

随着电动交通工具的大规模应用，对电池的能量密度和安全性提出了更高的要求。锂空气电池具有数倍于锂离子电池的理论能量密度受到了研究者的广泛关注。尽管锂空气电池具有能量密度方面的优势，但它的可逆工作还面临着诸多难题。本基金针对锂空气电池的可逆性问题，开展了以下几方面的研究。首先，锂氧电池是一个开放体系，实用化的锂氧电池需要能够在大气环境中可逆工作。本项目分析了大气环境中非氧组分对锂空气电池性能的影响。发现非氧组分不仅会导致锂氧反应产物由Li2O2转变为Li2CO3或LiOH，而且会对金属锂负极造成严重的侵蚀，使其转变形成LiOH。这些问题的发生严重的制约了锂空气电池在大气环境中的可逆工作。其次，开展高效氧正极的探索研究。碳基正极被发现难以在锂氧反应中保持自身稳定，这一发现激发研究者开始探索非碳材料。本项目中通过对正极在锂氧反应中的作用和锂氧反应特性进行分析，总结了高效锂氧正极所应具备的基本特征。并以非金属化合物氮化碳为基体、RuO2纳米颗粒为催化剂设计了一种分工合作的复合正极。使该正极的锂氧电池可稳定工作超过200次循环。该优异的电化学性能主要得益于所设计的正极具有优异的稳定性和催化活性，大幅减少了副产物的累积。最后，基于材料制备过程中发现，建立了采用茂金属和硫共升华制备碳包覆纳米金属硫化物的新方法，和以碳包覆单分散磷化镍复合结构为示例高性能电极设计的新思路。