控制晶向MnO2薄膜电极制备及其电荷迁移机理

Basing on the facts that the specific capacitance of transition metal oxide is far more below its theoretical value and its cyclic performance can not meet the requirement of supercapacitor, we propose to improve the adsorb/desorb velocity of cation in electrolyte on the surface of electrde, the transfer speed of cation in the metal oxide crystal and between the interface of active material and current collector. To investigate the impact of the interface resistance on the specific capacitance and cyclic performance of transition metal oxide, electrode in which single crystal metal such as aluminum,nickel or copper with various orientation is used as current collector, single crystal manganese dioxide acting as active material deposited directly on the surface of current collector was constructed.MnO2 crystals with differen oriental was prepared by change the preparation conditions such as additives, reaction temperature. Electrodes consist of a single crystal metal as current collector and two layers of manganese dioxide with differen crystal orientation were assembled to study the relationship between the crystal structure such as the orientation of MnO2 and the tunnel size for cations to transfer, and the transfer rate of cation in it. The processes of cations adsorb/desorb on the surface of variuous crystal face of MnO2,and transfer in various crystal orientation of MnO2 will be monitored by material studio software. According to the experimental and simulated results, optimized MnO2(2)/MnO2(1)/metal electrode will be fabricated and its electrochemical properties will be tested. This results will be used to correct the simulated model.

针对过渡金属氧化物超级电容器存在比电容远低于理论值和循环寿命不理想的事实，本项目拟通过提高电解液中阳离子在电极表面的吸附/解吸速率、电荷在电极表层内部以及活性物质/集流体界面的迁移速率达到提高过渡金属氧化物电极的实际比电容和循环性能的目标。采用不同晶向生长的铝、镍或铜单晶为集流体，通过电化学、水热或脉冲激光溅射等方法，在其表面直接生长一层沿一定晶向生长MnO2纳米薄膜。研究MnO2晶体生长方向对电荷在其晶格内的迁移行为与速率的影响；通过改变暴露于电解液中的MnO2晶面获得电极表面原子/离子排列状态与其电容性能间的关系，探讨电解液中阳离子在不同排列状态电极表面的吸附/脱附动力学；通过电荷在不同生长方向排列的MnO2内部、MnO2/集流体界面的迁移，及其在不同暴露晶面上的吸附/解吸行为模拟与实验结果，优化电极晶向与结构，为高比能量、高功率密度、长寿命超级电容器电极的设计、制备与组装提供依据。

项目针对过渡金属氧化物超级电容器存在比电容远低于理论值和循环寿命不理想的事实，通过提高电解液中阳离子在电极表面的吸附/解吸速率、电荷在电极表层内部以及活性物质/集流体界面的迁移速率达到提高过渡金属氧化物电极的实际比电容和循环性能。本项目通过化学沉积、电化学沉积等方法制备了在不基底上制备了各类二氧化锰薄膜，并探索了沿不同晶向生长的二氧化锰的制备方法。研究结果表明，通过上述方法制备的薄膜电极均为δ型二氧化锰，其作为超级电容器电极材料的最优晶面为（001）面。为了研究其它晶型二氧化锰的电化学性能与暴露晶面的关系，本项目采用水热法处理δ型二氧化锰得到晶面取向高度一致的α型二氧化锰纳米线，并研究了其在暴露了特定晶面的超级电容器性能。同时还发现通过静电自组装石墨烯原位包覆α型二氧化锰可有效的提高其循环寿命，得到的材料在10000次循环后容量保持率高达96.24%。由于超级电容器作为大电流充放电装置，材料的比表面积和导电性比暴露晶面的影响更大。所以我们还提供了一系列的高比表面积碳包覆低价态锰氧化物及其他金属氧化物的方法。针对二氧化锰材料控制晶向生长较难的问题，我们通过电化学沉积其它低价态锰氧化物并将其应用于超级电容器和锂离子电池的研究。