摘 要

锂离子电池的能量密度和功率密度暂时无法满足电动汽车的需求，限制了锂离子电池产业的进一步发展。高效储能器件的研发设计，是建立在对电化学充放电过程深刻理解的基础上的。原位单根电化学器件的研究有助于增强对电化学过程的理解，优化和控制。通过构筑原位单根电化学器件，分析电化学反应在不同外界物理场影响下的变化，可以帮助建立外界物理因素（如电场，温度场）与电化学性能之间的联系，与此同时，通过测量外界物理场导致的器件基本物性的演化，可以帮助清晰地建立基本物性与微观电化学动力学之间的联系。

本文采用溶剂法合成纳米线电极材料K_0.51V₂O₅，通过超声分散得到纳米线悬浮液，利用光刻，电子束刻蚀，物理气相沉积（PVD），磁控溅射，原子层沉积构筑单根纳米线电化学微纳器件。采用I-V曲线表征其基本物性（电子电导率，场效应管特性曲线），利用循环伏安曲线表征其电化学特性，并探究电子电导率，离子电导率，面积比容量和电化学极化特性在外加电场和温度场作用下的变化，同时，通过CV分容量方法计算了电化学器件容量的贡献来源，并根据以上现象详细分析了电场和温度场对微观电化学动力学过程的影响途径和作用机理。具体结果如下：

1. 在测量的的温度范围内（298.15 K-328.15 K），K_0.51V₂O₅的电化学性能随着温度的升高而不断优化。随着温度的升高，水系锂离子电池的容量逐渐提高，还原峰电位逐渐增大，极化减小；

2. 通过控制栅极电压施加电场，水系锂离子电池的面积比容量和极化特性可以得到调控，在栅极电压为-2.7 V时，水系锂离子电池容量提高一倍；

3. 计算了不同温度和外加电压作用下的电子和离子电导率的变化。温度升高时，离子扩散系数为25℃时的2.5倍；外加电压时，，离子电导率在接近临界电压时提高为无栅极电压时的2倍。

基于以上数据，我们结合电化学反应动力学微观机制，建立了温度场和电场对电化学过程的影响机制：当温度升高时，材料的热力学性能得到提高，电极材料由非活性变为活性的，而外加电压时，促进了离子扩散，增大了反应动力学，从而提高了电化学性能。

关键词：单根电化学微纳器件；储能器件；原位电化学表征；多物理场耦合

Abstract

The energy density and power density of lithium ion battery associate the driving mileage and climbing ability of electric cars directly. The design and development of lithium ion batteries with high energy density, high power density and long life can greatly promote the development of electric car. The understanding of charge/discharge processes and the structure evolution of electrode materials is valuable to analyze the electrochemical processes and can further improve the electrochemical performance of batteries. The single nanowires electrochemical device provides a unique platform for us to improve our understanding of the electrochemical process by in-situ probing the basic physical properties and electrochemical performance, where we can analyze the association between the basic physical properties and electrochemical properties. The single nanowire devices is a useful tool to shed light on how to optimize and control the electrochemical reaction thermodynamics and kinetics. Additionally, it provides a platform to detect the basic physical properties and electrochemical properties in-situ. On account of single nanowires electrochemical devices, it is possible to investigate the effect of external field on the electrochemical performance accurately and quantitatively, which is of great significance to help us to establish a clear physical picture of the specific electrochemical micro kinetics mechanism.

Based on the hydrothermal synthesis of nanowires electrode materials K_0.51V₂O₅, nanowire suspension is obtained by ultrasonic dispersion, which is then used to construct single nanowire electrochemical device by using photolithography, e-beam lithography and physical vapor deposition (PVD) method. I-V curve is introduced to characterize the basic physical properties (electrical conductivity), and Cyclic voltammograms (CV) test is conducted to characterize electrochemical properties (specific areal capacity), and explore the changes of the electronic conductivity and specific areal capacity under different gate voltage and temperature. Furthermore, based on the CV curves under different sweep rate, the surface reaction induced capacitance and intercalation part capacitance are seperated according to the related electrochemical theory model. At last, we proposed the mechanism of the electric field and temperature induced electrochemical performance and basic physical properties evolution according to all the above observed phenomenon and related data and theory from the point of both Thermodynamics and dynamics. Specific results are as follows:

1. In the measured temperature range (from 298.15 K to 298.15 K), the electro-chemical performance of K_0.51V₂O₅ nanowires is optimized continuously as the temperature tested increases. With the increase of temperature, the capacity of aqueous lithium ion battery increases to 2 times at low scan rate, and the reduction peak potential at which the lithium ion intercalates

into the crystal structure of K_0.51V₂O₅ gradually moves to a higher potential ,which indicates a smaller polarization during the electrochemical reaction process ;

2. By applying a controlled gate voltage, the specific areal capacity, polarization characteristics and the capacity contribution ratio of the surface reaction controlled and diffusion controlled part of the aqueous lithium ion battery can be regulated.

3. The electronic and ionic conductivity of K_0.51V₂O₅ under different temperature and applied gate voltage were calculated. At higher temperatures, the electrical conductivity of the active material does not change a lot, but the ion diffusion coefficient at 40 Celsius degree is 2.5 times as lagre as that at 25 Celsius degree; Under the applied gate voltage, the electronic conductivity also basically remains unchanged, and ionic conductivity around the near critical voltage increases 6% approximately.

Based on the above data and combined with micro-electrochemical reaction kinetics principles, we suggested the mechanism about the infulence of the temperature field and the gate voltage induced electric field on the electrochemical reaction: the increased temperature changes the thermodynamic properties of the active materials, which activates the electrode materials from inactive state, and the applied gate voltage increases the reaction kinetics by promoting the ion diffusion rate, and thus improves the electrochemical performance.

Keywords: single nanowires electrochemical device; energy storage device; in-situ electrochemical characterization