Rigid-Flexible Thiophene-Based Block Copolymer/Multiwalled Carbon Nanotube for Enhancing Anode Performance by Extended π-Conjugation.

Abstract

Polythiophene emerges as a promising anode with a high theoretical capacity, rapid redox kinetics, and low storage voltage. However, two challenges persist: rapid capacity degradation because of low conductivity and hindered ion intercalation pathways due to entanglements of polymer. This work presents a novel copolymer design of thiophene/butylthiophene (TH/BT) blocks integrated with multiwalled carbon nanotubes (MWCNTs). The rigid TH blocks enhance molecular crystallinity to expose electrochemically active thiophene rings, while the flexible BT segments promote the growth of copolymers around MWCNTs to establish an efficient 3D electron transport network. Through optimizing TH:BT ratio to 3:1, the balance between crystallinity and solubility is achieved and yields a block copolymer composite, designated as Cob(3:1)-TH+BT@CNT. Consequently, the anode shows superior performances: 1) enhances reversible capacity of 920 mAh g^{- 1} at 100 mA g^{- 1} (only 300 mAh g^-1 for unmodified polythiophene@CNT); 2) maintains 105.0% and 100.6% capacity after 500 cycles at 1 and 2 A g^{- 1}, respectively; and 3) preserves storage characteristics of thiophene rings near 0.2 V with an excellent rate performance. This novel rigid-flexible block structure increases the capacity of thiophene-based anode without the introduction of additional active groups, which provides new insights for the design of conjugated organic anode materials.