Binary-pore anodic aluminum oxide template based fabrication and advanced microscopic characterization of three-dimensional sodium-ion micro-batteries

由于成本上升和全球锂储量分布不均，对锂离子电池的严重依赖引起了全球的关注。由于钠的丰富来源以及钠和锂的电化学相似性，钠离子电池被认为是一种可持续的、具有价格竞争力的电池技术。尤其是钠离子微电池是锂离子微电池的理想补充，以满足快速发展的微电子技术对微型电源日益增长的需求。然而，传统的二维薄膜MBS面临着能源和电力之间的妥协。提出了一种三维(3D)MBS设计，通过利用第三维高度来有效地解耦能量-功率折衷。获得3DMBS的一个关键挑战是在不降低可获得的能量和功率的情况下，在有限的空间和单个衬底上精细地集成阳极、阴极、电解液、隔膜和集流器。在这个项目中，我们计划使用双孔阳极氧化铝(AAO)模板实现第一个完全可操作的3D SIMB。在双孔AAO模板中，两组独立的纳米孔允许通过原子层沉积独立地沉积阳极(SnO2)和阴极(NaxCoO2，NaxMnO2和NaxVO2)材料，在小体积内获得交错的阳极和阴极纳米柱阵列，克服了在单一衬底上构建完整电池的挑战。用固体电解质渗透交替的阳极和阴极纳米管之间的自由空间后，将得到固态3D SIMB。这种阳极和阴极的3D互穿电极内部结构将在电极和电解液中提供较短的电子/离子传输路径(产生高功率密度)，同时保持高容量的电极材料(产生高能量密度)。同时，所提出的3DSIMB是研究电极在有限的小空间中的(去)电离行为的理想方法，到目前为止，关于这方面的知识还很少。我们将利用扫描电子显微镜、聚焦离子束层析成像和原位电子显微镜来深入了解电极在(脱)钠过程中的结构和表面演变，揭示其对电荷储存的动力学和热力学以及对固体电解质界面层形成的影响。通过理解原子尺度上的电化学机理，将建立3D SIMB的几何-性能关系，为提高电池性能提供指导。最后，我们的目标是实现固态3D SIMB，其能量密度超过10 MWh cm-3，功率密度超过150 mW cm-3，循环寿命高达5000次。该项目的完成将为电池基础研究做出贡献，推动下一代微电子技术的进步。

The heavy reliance on lithium-ion batteries has caused global concern due to the rising cost and uneven global distribution of lithium reserves. Owing to the abundance of sodium sources and electrochemical similarities between sodium and lithium, sodium-ion batteries are regarded as sustainable and price-competitive battery technology. Especially, sodium-ion micro-batteries (SIMBs) are the desirable complementation to lithium-ion MBs to satisfy the increasing demand for micro power sources toward matching the rapid progress of microelectronics. Yet, traditional two-dimensional thin-film MBs face a compromise between energy and power. A three-dimensional (3D) MBs design has been proposed to effectively decouple the energy-power compromise by taking advantage of the third dimension of height. A key challenge for obtaining a 3D MBs is to delicately integrate anode, cathode, electrolyte, separator, and current collector in a limited space and on a single substrate without deteriorating the attainable energy and power. In this project, we propose to realize the first fully operational 3D SIMBs using binary-pore anodic aluminum oxide (AAO) templates. Two separate sets of nanopores in binary-pore AAO templates allow independently deposit anode (SnO2) and cathode (NaxCoO2, NaxMnO2 and NaxVO2) materials by atomic layer deposition to obtain interdigitated nanopillar arrays of anode and cathode within a small volume, overcoming the challenge of constructing full cells on a single substrate. Solid-state 3D SIMBs will be obtained after infiltrating free space between alternated anode and cathode nanopillars with solid-state electrolytes. Such 3D interpenetrating-electrode internal architecture of anode and cathode will provide short electron/ion transport pathways in electrodes and electrolytes (yielding high-power density) while maintaining a high volume of electrode materials (yielding high-energy density). Meanwhile, the proposed 3D SIMBs are ideal for studying the (de)sodiation behaviors of electrodes in a confined small space, on which so far there is little knowledge. We will employ scanning electron microscopy, focused ion beam tomography and in-situ transmission electron microscopy to get insights into the structural and surface evolution of electrodes occurring in (de)sodiation process and reveal its influence on the kinetics and thermodynamics of charge storage as well as on formation of solid electrolyte interphase layer. By understanding the underlying electrochemical mechanism up to the atomic scale, a geometry-performance relationship for 3D SIMBs will be established to provide a guideline to improve the battery performance. Finally, we aim to realize solid-state 3D SIMBs with an energy density of more than 10 mWh cm-3, a power density of above 150 mW cm-3, and a cycle life of up to 5000 cycles. The accomplishment of this project shall contribute to the fundamental battery research and promote the advance of future generation microelectronics.