Developing aqueous electrolyte with wide electrochemical stability window (ESW) is one of the key technologies to boosting the energy density of aqueous electrochemical double-layer capacitors (EDLCs). However, expanding the ESW using super-concentrated electrolytes comes at the expense of cost, ionic conductivity and the mass density of the device. Herein, we selected a cost-effective and environmentally friendly molecular crowding agent, polyethylene glycol dimethyl ether (PEGDME-250), as the electrolyte additive designed to achieve high ESW at low salt concentrations. First, PEGDME can reduces the activity of water and increases the ESW of the electrolyte by forming hydrogen bonds with free water molecule. In addition, PEGDME does not have the interaction between terminal groups compared to conventional polyethylene glycols (PEG), which helps to reduce the viscosity and improve the ionic conductivity of the electrolyte. By adjusting the composition of the electrolyte, the optimal electrolyte with a high ESW of 2.96 V was achieved with the formula of 3 m NaClO-25 % HO-75 % PEGDME. The EDLCs assembled with this diluted aqueous electrolyte and YP-50 F electrodes presents a high operational voltage window of 2.4 V and outstanding cycle stability (>10000 cycles), and maintains excellent rate performance in a temperature range of −10–35 ℃.

中文翻译：

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稀水混合电解质赋予超级电容器高电压窗口


开发具有宽电化学稳定性窗口（ESW）的水系电解质是提高水系电化学双层电容器（EDLC）能量密度的关键技术之一。然而，使用超浓缩电解质扩展 ESW 是以牺牲成本、离子电导率和设备的质量密度为代价的。在此，我们选择了一种经济高效且环保的分子拥挤剂聚乙二醇二甲醚（PEGDME-250）作为电解液添加剂，旨在在低盐浓度下实现高ESW。首先，PEGDME可以通过与自由水分子形成氢键来降低水的活性并增加电解质的ESW。此外，与传统的聚乙二醇（PEG）相比，PEGDME不存在端基之间的相互作用，这有助于降低电解质的粘度并提高离子电导率。通过调整电解液的组成，以3m NaClO-25% HO-75% PEDME的配方得到了ESW高达2.96V的最佳电解液。用这种稀释水电解质和YP-50F电极组装的EDLC具有2.4V的高工作电压窗口和出色的循环稳定性（>10000次循环），并在-10-35℃的温度范围内保持优异的倍率性能。