长寿命水系钠离子电池电极与电解液界面层的设计

Aqueous sodium ion battery (ASIB) shows good potential for stationary energy storage applications because its benefits in safety, environmental impact, and cost. However, The lack of stable interface layer between electrode and electrolyte in aqueous sodium ion battery is a core problem to limit its long cycle performance. And the narrow electrochemical stability window (about 1.23 V) of the aqueous electrolyte sets a limit on their energy output. In our previous work, by adding sodium dodecyl sulfate (SDS) to the aqueous electrolyte, the electrochemical stability window of the electrolyte was expanded to about 2.5 V. The battery which delivered a capacity retention of 75% over 2000 cycles at a rate of 5 C. The results of the experiments and calculations based on the density functional theory indicate that SDS can not only inhibit the decomposition of water, suppress the dissolution of Mn, but also increase the cycle life and rate capability. .In this project, by the addition of SDS, urea or other additives into the electrolyte, together with the pretreatment of the surface of electrode materials with TiO2 and so on, we propose to design the stable interface layer between electrolyte and electrode. We want to study the influence of the stable interface layer on the electrochemical stability window of the aqueous electrolyte and the long cycle life of the battery. We wish to master the methods of forming stable interface layer, and make 1-2 kinds of aqueous sodium ion whole batteries with the electrochemical stability window of the aqueous electrolyte higher than 2.5 V, with long cycle performance of capacity retention no less than 80 % over 2000 times at 1 C, and energy storage density no less than 40 Wh kg -1. High resolution transmission electron microscopy (HRTEM), synchrotron radiation photoelectron spectroscopy and other techniques will be applied to investigate the stability of the interface layer during the process of electrochemical cycle, and to reveal the mechanism of how the stable interface layer expands the electrochemical stability window of the aqueous electrolyte and inhibits the interface side reaction to improve the cycle life of aqueous sodium ion batteries.

在水系钠离子电池中电极和电解液之间缺少稳定的界面层，是限制水系钠离子电池长循环寿命的一个核心问题；另外，界面层也影响水的电化学稳定窗口。申请人前期在电解液中加入SDS后，形成的电极和电解液界面层，把水的电压窗口扩至2.5V，5C循环2000圈容量保留75%。本项目通过在电解液中加入SDS、尿素等添加剂，为电解液和电极间形成稳定的界面层，同时对电极材料表面用TiO2等预处理；实现水系钠离子电池更宽的稳定电压窗口和长循环寿命；掌握形成稳定界面层的方法，做成1-2种水的稳定电压窗口不低于2.5V，1C下循环寿命超过2000次，储能密度不低于40Wh/kg，容量保持率不低于80%的水系钠离子全电池；采用高分辨率电镜、同步辐射光电子能谱等研究电化学循环过程中界面层的稳定性，揭示界面层扩宽水的稳定电压窗口、提高电池循环寿命的机制。

在水系钠离子电池中电极和电解液之间缺少稳定的界面层，限制水系钠离子电池长循环寿命，且界面层也影响水的电化学稳定窗口。本项目通过在电解液中加入尿素等添加剂，在电极表面原位形成无机有机复合界面层，水的电化学稳定窗口可以扩展到3.0 V；对集流体表面构建氧化物钝化膜，提高水分子在集流体表面的分解活化能，从而有效的抑制析氢、析氧反应，拓宽电解液电化学稳定窗口至3.5V；在电极表面非原位构筑了无机快离子导体、纳米纤维素-石墨烯复合保护膜等，保证电极/电解液离子传导的同时抑制了电极表面析氢析氧等副反应，有效的提升了电池的可逆性和稳定性。做成 了2 种水的稳定电压窗口不低于 2.5 V，循环寿命超过 2000 次，储能密度大于40 Wh·kg-1，容量保持率高于 80%的水系混合钠离子全电池。电解液添加剂、集流体的改性等策略可以获得稳定的电极界面，使得水系电解液的电化学稳定窗口大幅扩大，为更多电极材料选择以及实现水系电池系统的高能量密度提供了新思路；对制造高安全、低成本、长寿命的水系离子电池具有重要的指导意义。在Energy Environ. Sci., Adv. Mater.，Adv. Energy Mater.，Adv. Funct. Mater.等期刊发表论文18篇；已授权专利2项。

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