製備羧甲基纖維素相關之高吸水性高分子與其作為矽負極黏著劑之性能研究

Abstract

本研究目的是探討羧甲基纖維素(Carboxymethyl cellulose, CMC)在高吸水性高分子與鋰離子電池負極應用的發展。第一部分吸水性高分子研究中，目前天然聚合物類的效能與合成聚合物類相比，仍然較低，因而限制其實際上的應用。第一部分會以羧甲基纖維素天然聚合物類作為高吸水性高分子的主體，目標是提供一種吸水率高，成本效益高的天然聚合物類的超吸水性聚合物。先從纖維素製備CMC，不同實驗條件組成和醚化溫度等得到不同取代度(Degrees of substitution, DS)，探討不同取代度對材料行為的影響。這些自製得不同取代度CMC並通過檸檬酸交聯以提升其吸水性能，結果表明，DS 0.71與1%檸檬酸呈現最 大平衡吸水率為58 g/g。 第二主題為羧甲基纖維素應用於鋰離子電池的領域，目前商業化CMC作為黏著劑仍然以CMC搭配丁苯橡膠的電極材料表現出良好的電化學性能。此研究導向單純CMC作為黏著劑於矽負極的表現，從製備了不同取代度的CMC作為鋰離子電池負極的黏著劑，使用不同比例與條件的黏著劑與矽組裝電池。藉由電極漿料配比、pH值和CMC取代度等因素，都會不同程度地影響CMC/Si電極的電化學性能。電的測試包括恆電流充放電，循環伏安法，交流阻抗等進行評估矽負極。結果表明，矽負極Si:KS-6:CMC= 6:3:1，在經過51圈循環中使用取代度0.71的CMC都展現優於其他取代度的循環表現。首圈鋰化(lithiation)、去鋰化(delithiation)比容量分別為3431.6 mAh / g Si和3131.4 mAh / g Si，經過51圈平均循環去鋰化比容量可維持於2148.3 mAh / g Si。此研究證實，單純CMC作為黏著劑仍能維持高的電容量穩定性，有利於電池負極材料發展。

This thesis contains two parts which are the development of carboxymethyl cellulose (CMC) in the application of superabsorbent polymers and negative electrodes for lithium-ion batteries. In the first part of the superabsorbent polymers, the performance of natural polymers is still lower than that of synthetic polymers, thus natural polymers limit their practical application. In this study, carboxymethyl cellulose as natural polymers will be applied in the major portion of superabsorbent polymers. The goal is to provide a superabsorbent polymer with high swelling ratio and cost-effective natural polymers. First, CMC was prepared from cellulose. Different experimental conditions, composition, and the temperature of the esterification were used to obtain different degrees of substitution (DS). The effects of DS on the materials analysis were discussed. The synthetic CMCs cross-linked with citric acid to improve the swelling ratio. The results show DS 0.71 of prepared CMC and 1% citric acid achieved the equilibrium swelling ratio up to 58 g/g. The second part is the application of carboxymethyl cellulose in the field of lithium- ion batteries. Up to now, commercial binders of CMC still need CMC with styrene-butadiene rubber electrode materials to achieve great electrochemical performance. This research leads to the performance of the sole CMC as a binder in silicon negative electrodes. CMC with different degrees of substitution were prepared as binders for negative electrodes of lithium-ion batteries, using different ratios and conditions of binders and silicon to assemble batteries. The electrochemical performance of the CMC/Si electrode will be discussed to the effects of the electrode slurry ratio, pH value, and DS of CMC. Electrochemical analysis includes charge and discharge tests, cyclic voltammetry, AC impedance, etc. to evaluate the silicon negative electrode. The results showed that the silicon negative electrode Si:KS-6:CMC= 6:3:1, and the CMC with DS of 0.71 after 51 cycles showed better cycle performance than other DS. The capacity of lithiation and delithiation in the first cycle are 3431.6 mAh / g Si and 3131.4 mAh / g Si, respectively. The average capacity of delithiation after 51 cycles can be maintained at 2148.3 mAh / g Si. This study confirmed the sole CMC as binders can still maintain high stability of capacity, which is beneficial to the development of anode materials.