Enhancing the electrochemical performance of free-standing electrodes using multi-walled carbon nanotubes functionalized with PVP/SDBS mixed dispersant

Abstract

The demand for lithium-ion batteries with high energy density has been gradually increasing. Free-standing electrodes without current collectors and binders are a promising approach for enhancing energy density. Multi-walled carbon nanotubes (MWCNTs) are suitable materials for free-standing electrodes due to their outstanding electrical conductivity and robust mechanical properties. However, pristine MWCNTs exhibit severe agglomeration, making surface functionalization essential for enhancing their dispersibility. Herein, two functionalization methods for improving the dispersibility of MWCNT, namely non-covalent using dispersants and covalent functionalization using acidic solutions, are reported. The mixed dispersant of polyvinylpyrrolidone (PVP) and sodium dodecylbenzene sulfonate (SDBS) exhibits superior dispersibility compared to the use of individual dispersants, which is due to the synergistic between the non-ionic polymer PVP and the anionic surfactant SDBS. Furthermore, in comparison to acid-treated CNTs, this approach not only preserves the intrinsic structure of CNTs but also sustains exceptional dispersibility. In this study, LiMn₂O₄ (LMO) is selected as the active material, and two types of electrodes are fabricated via vacuum filtration using CNTs functionalized with PVP/SDBS (PSLMO) and CNTs functionalized with acidic solutions (HNO₃ and H₂SO₄) (OLMO). PSLMO achieves a superior specific capacity of 103.5 mAhg⁻¹ at 0.5C after 150 cycles, compared to OLMO, which exhibits a specific capacity of 87.6 mAg⁻¹. Furthermore, PSLMO maintains an outstanding capacity retention of 95.5 % at 0.5C after 150 cycles. This study offers an effective method for the functionalization of CNTs used in the vacuum filtration method, providing an efficient approach to enhancing energy density.