Effect Of Sodium Carboxymethyl Cellulose Modification On Electrochemical Properties Of SiO_x Anode Materials

Lithium-ion batteries have grown rapidly over the past three decades and successfully occupied the field of power sources for portable electronic devices due to their significant advantages such as portability,high specific capacity and no memory effect.However,in the last decade,the requirements for energy storage devices in the new technology field,led by electric vehicles,have been increasing remarkably,and the existing commercial lithium-ion batteries can hardly meet the demand.With higher energy density,lower manufacturing cost,and abundant raw material reserves,Si O_x-based anode materials have the potential to replace graphite anode as the anode material for next-generation lithium-ion batteries.However,as an alloy type anode material,silicon oxide undergoes huge volume expansion（about 200%）during lithium ion lithiation,leading to electrode pulverization,flaking,significant capacity degradation,and even safety issues,which seriously limit its commercialization.Current researches show that the cycling stability of silicon oxide materials can be improved simply and effectively by modifying polymer binders.In this paper,two binders with three-dimensional network structure were successfully prepared from a commercial linear binder sodium carboxymethyl cellulose（CMC）,which effectively improved the electrochemical properties of silicon oxide materials,and the main studies are as follows.（1）A new binder with a cross-linked mesh structure,CMC-PA,was prepared by covalently cross-linking the small-molecule diacid phthalic acid（PA）with sodium carboxymethyl cellulose（CMC）in the organic solvent dimethyl sulfoxide（DMSO）as a cross-linking agent.When the cross-linked binder participates in the preparation of Si O_x-based electrode,the specific capacity of Si O_x@CMC+10%PA is 671.1 m Ah g^-1 after 200cycles at a current density of 500 m A g^-1,while its multiplicative performance was significantly enhanced by the more stable SEI film.（2）In order to further optimize the reaction process,a more environmentally friendly aqueous sodium hydroxide（Na OH）solution was selected as the solvent,and a small molecule epichlorohydrin（ECH）containing an epoxy group was chosen as the crosslinking agent to chemically crosslink sodium carboxymethyl cellulose（CMC）to prepare a network binder CMC-ECH with stronger interaction with the Si O_x-based electrode and robust bonding strength.The chemical cross-linking enables the binder to better adapt to the volume change of the Si O_x-based anode,and the Si O_x@CMC+10%ECH can still maintain a capacity of 442.5 m Ah g^-1 after 200 cycles at a current density of 500 mAg^-1.