Mn掺杂TiO2（101）提高锂空电池阴极催化活性的第一性原理研究

First principle study of Mn-doped TiO2 enhancing cathode catalysis in lithium-oxygen batteries

本文基于密度泛函理论对TiO2(101)和MnxTi1-xO2(101)作为锂空电池阴极催化材料进行了研究,发现其表面能够生成两种不同结构的Li2O2,进一步地研究了其中最稳定的生成结构并通过计算锂空电池首次充放电过程中的过电势来评价催化性能.结果表明,Mn掺杂进入TiO2(101)对充放电的过电势均有降低作用,深入分析发现掺杂Mn对TiO2促进阴极催化反应的本质因素源于掺杂原子Mn的d态轨道的分布以及其平均能量.掺杂原子的d态轨道在费米能级处的峰态诱导了附近O的p态轨道,二者共同作用在MnxTi1-xO2(101)的总态密度的费米能级处形成多个新峰,改变了催化剂的导电方式.此外,由于掺杂原子Mn的d态轨道的平均能量高于Ti原子,使得O的p态轨道受到更多的激发,促使在Mn掺杂原子附近的氧空位形成能降低,为放电过程阴极催化反应的氧还原提供了更多的活性位点并且有利于氧气的吸附与还原.

Based on the density functional theory,pure and doped TiO2(101)(MnxTi1-xO2(101))were investigated as cathode catalytic materials for lithium-oxygen batteries.It was found that Li2O2 was formed on the surface with two different structures.We chose the most stable structure to further explore,and the catalytic performance is evaluated by the overpotential during the first charging and discharging process of the lithium-oxygen batteries.The results show that the doping of Mn has a lowering effect on the overpotential of both charge and discharge.Through further calculation and analysis of electron state density,we found that the essential factor of Mn doping in TiO2 to promote cathodic catalytic reaction is due to the distribution of d-state orbitals and the average energy of d-state orbitals of doped atom Mn.The distribution of the d-state orbital of the doping atom Mn at the Fermi level induces the p-state orbit of the nearby O atom,and these make the formation of new impurity peaks at the Fermi level of the total density of states of MnxTi1-xO2(101),which changes the conductivity of the catalyst.In addition,since the average energy of the d-state orbital of the doped atom Mn is higher than Ti atom,the p-state orbital of the oxygen atom is more excited,which promotes the formation of oxygen vacancies on the surface when Mn atom is doped.It provides more active sites for ORR of cathodic catalytic reaction in discharge process and is beneficial to oxygen adsorption and reduction.