PDF(Sci-hub)
Abstract：
The electrochemical intercalation/deintercalation of solvated sodium ions into graphite is a highly reversible process, but leads to large, undesired electrode expansion/shrinkage (\"breathing\"). Herein, two strategies to mitigate the electrode expansion are studied. Starting with the standard configuration (-) sodium | diglyme (2G) electrolyte | graphite (poly(vinylidene difluoride) (PVDF) binder) (+), the PVDF binder is first replaced with a binder made of the sodium salt of carboxymethyl cellulose (CMC). Second, ethylenediamine (EN) is added to the electrolyte solution as a co-solvent. The electrode breathing is followed in situ (operando) through electrochemical dilatometry (ECD). It is found that replacing PVDF with CMC is only effective in reducing the electrode expansion during initial sodiation. During cycling, the electrode breathing for both binders is comparable. Much more effective is the addition of EN. The addition of 10 v/v EN to the diglyme electrolyte strongly reduces the electrode expansion during the initial sodiation (+100% with EN versus +175% without EN) as well as the breathing during cycling. A more detailed analysis of the ECD signals reveals that solvent co-intercalation temporarily leads to pillaring of the graphite lattice and that the addition of EN to 2G leads to a change in the sodium storage mechanism.
摘要：
溶剂化钠离子在石墨中的电化学嵌入/脱嵌是一个高度可逆的过程，但导致大，不希望的电极膨胀/收缩（“呼吸”）。在这里，研究了两种减轻电极膨胀的策略。从标准配置（-）钠|二甘醇二甲醚（2G）电解质|石墨（聚偏二氟乙烯（PVDF）粘合剂）（+）开始，首先用由羧甲基纤维素(CMC)的钠盐制成的粘合剂代替PVDF粘合剂。第二,将乙二胺(EN)作为共溶剂添加到电解质溶液中。通过电化学膨胀法（ECD）在原位（操作）跟踪电极呼吸。发现用CMC代替PVDF仅在减少初始酸化期间的电极膨胀方面有效。骑自行车时,两种粘合剂的电极呼吸是相当的。更有效的是添加EN。向二甘醇二甲醚电解质中添加10v/vEN会大大降低初始酸化过程中的电极膨胀（EN为100％，而没有EN为175％）以及循环过程中的呼吸。对ECD信号的更详细的分析表明，溶剂共嵌入会暂时导致石墨晶格的柱撑，并且向2G中添加EN会导致钠储存机制的变化。
