In-Situ Growth of LiMn2O4 Nanocrystals Embedded in Three-Dimension Single-Walled Carbon Nanotube Macrofilms as Stretchable Composite Cathode for Lithium-Ion Batteries

Electrode materials with total flexibility including not only the bendability but also the stretchability play the key roles in the emerging stretchable energy storage devices especially for the stretchable lithium-ion batteries (LIB). Herein, a stretchable composite for LIB cathode was fabricated by in-situ growth of LiMn₂O₄ (LMO) nanocrystals in the 3D macrofilms of single-walled carbon nanotube (SWNT) network via a low-temperature hydrothermal synthesis. Tomographic cross sections by focus ion beam (FIB) reveals the homogenous embedment of LMO nanocrystals spreading over the entire SWNT scaffold. X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) have confirmed the strong chemical bonding between LMO and the carboxyl groups on activated CNT surface through the in-situ growth. Such intense interactions ensure the mechanical property and electrical conductivity inherited from SWNT. The as-prepared 3D composites could be laminated with elastomeric substrate such as polydimethylsiloxane (PDMS) to form stretchable cathodes with full flexibility. The electrochemical performance of the freestanding LMO-SWNT macrofilm composite has been evaluated by galvanostatic charge-discharge cycling measurements, cyclic voltammetry and electrochemical impedance spectroscopy in CR2032 coin-cell configuration with lithium metals. The capacity retention exhibits a decreasing specific discharge capacity from initial 120 mAhg^-1 approaching more stable to 100 mAhg^-1 at the rate of 0.1 C (~ 15 mAg^-1) for over 250 cycles. Correspondingly the Coulombic efficiency starts increasing from about 70% to over 95% at the end of cycling. Then the potential intermittent titration technique (PITT) was employed to analyze the Li⁺ chemical diffusivity of the freestanding composite related to the electrochemical performance. This present work provides a necessarily preliminary examination on the feasibility of the stretchable cathode before developing the fully stretchable LIB in the future.