Preparation Of High Viscosity Sodium Carboxymethyl Cellulose And Its Application On Silicon Cathode

Carboxymethyl cellulose(CMC),the carboxymethylated derivatives of natural celulose,was widely used in many industries,such as food additive,petroleum thickener,binder of batteries' electrode.CMC was synthesized by using nature cellulose as raw materials through alkalization and etherification processes.In present work,CMC of high viscosity and high degree of substitution was prepared by using solvent slurry method with cotton pulp as raw material.And the effect of various process conditions on the properties of CMC were systematically studied.Then,CMC as the silicon anode binder was successfully applied to the lithium-ion battery and the mechanism of the CMC-Si system was studied.Meanwhile,the effect of CMC's inhibitory on silicon volume expansion with different kinds of buffer salt system was discussed.The main results of this work are as follow:Firstly,the synthetic process of high viscosity CMC with battery grade was systematically studied.On the basis,the effect of kinds of solvent,alkalization temperature,alkalization time,etherification temperature,etherification time and the amount of water in reaction system,were studied.Under optimum condition(isopropanol as solvent,alkalization temperature 35 ?within 1.5h,etherification temperature 55 within 2h,the mass ratio of sodium chloroacetate and cotton pulp as ?1.2),the viscosity of obtained CMC were 20000 mPa·s.In the meantime,related tests on the chlorinity,acid resistance and salt resistance of CMC was analyzed,and the test results indicated CMC could reach the standard of electrode binder in batteries.Secondly,the synthesized CMC was successfully applied to the lithium-ion battery with silicon anode currently.And the binding effect of different types of CMC was discussed.and the electrochemical cycle performance of the battery was tested.Then,the interaction mechanism in different kinds of buffer salt system was emphatically discussed.The effect of acid molecular structure on the interface connection mode between CMC and Si was mainly explored,including tartaric acid,malic acid,citric acid and lactic acid.The mechanism was further demonstrated by the infrared spectroscopy,scanning electron microscope,electrochemical test.It was found that the tartaric acid showed best performance during the tests.The average hydroxyl group content and carboxyl group content are 0.5 hydroxyl per C and 0.5 carboxyl per C,respectively.The component content ratio(Si: CB: CMC)of this hydroxy fatty acids buffer salt system is 7:2:1.The battery capacity was stable and could keep more than 800 mAh/g after 45 cycles test.The results showed that hydroxy carboxylic acid could promote the binding of CMC on silicon.And the carboxyl and hydroxyl groups among the hydroxy carboxylic acid molecule can react with the carboxyl group on CMC and the hydroxyl group on the surface of the silicon in the esterification reaction.After that,CMC molecule firmly fixed on the surface of silicon as a binder.This enhanced the interaction force between CMC and silicon and weaken silicon volume expansion.In conclusion,the stable cycle performance of the battery was improved.