Effect of Molecular Weight and Degree of Substitution of a Sodium-Carboxymethyl Cellulose Binder on Li4Ti5O12 Anodic Performance

This paper presents a detailed investigation of the influence of molecular weight (MW) and degree of substitution (DS) of sodium-carboxymethyl cellulose (CMC) used as binder of Li4Ti5O12 (LTO) anodes. CMC MW and DS were in the range of 90 000 to 700 000 and 0.7 to 1.2, respectively. As demonstrated by coin cell tests, the LTO electrode that contained relatively low MW and high DS CMC showed excellent cyclic performance above 150 mAh g(-1) even after 100 cycles. Unlike typical electrodes, the adhesion strength of the LTO electrodes was not a critical factor for cell performance. On the contrary, low coverage of CMC on the surface of LTO, which leads to weak adhesion, was more favorable to the cell performance than strong adhesion caused by high coverage. Both an increase in the DS and a decrease in the MW of CMC gave rise to low charge transfer resistance, high ion conductivity, good wettability with the electrolyte, and good lithium ion mobility owing to a relatively large amount of LTO exposed to directly the electrolyte so long as critical adhesion is guaranteed in the LTO electrode.