Abstract:

Objective Tungsten trioxide (WO₃) is a promising functional material for both electrochromic devices and lithium-ion battery anodes by virtue of its high theoretical capacity, reversible ion intercalation behavior, and low cost. However, the large volume variation of WO₃ during cycling may deteriorate the structural stability and electrochemical durability. In this work, a sheath-core structured tungsten trioxide-reduced graphene oxide/lithium titanate-MXene (WO₃-rGO/LTO-MXene) yarn electrode was designed and fabricated for integrated lithium storage and electrochromic applications.

Method LTO-MXene core yarns were first prepared by conjugated electrospinning using conductive silver yarn as the core, followed by MXene coating and freeze-drying. Rod-like WO₃-rGO composites were then synthesized by electrospinning and calcination, and subsequently coated onto the core yarn with sodium alginate (SA) as the binder to form the sheath layer. By using conjugated electrospinning technology, LTO nanofiber yarns were obtained with conductive silver yarn as the core yarn. The nanofiber yarns were immersed in the prepared MXene water dispersion for ultrasonic treatment for 15 min. The obtained LTO-MXene nanofiber yarns were subsequently freeze-dried to obtain LTO-MXene nanofiber yarn electrodes. Rod-like WO₃-rGO composites were prepared by electrospinning combined with high-temperature calcination. Subsequently, a WO₃-rGO coating solution was prepared, in which SA/WO₃-rGO/H₂O mass ratio is 1∶5∶100. The mixture was stirred continuously at room temperature for 12 h, and then the core layer LTO-MXene yarn electrode was coated. The morphology and structure of the material and yarn were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and their electrochemical and electrochromic properties were tested.

Results It was revealed that the LTO MXene yarn in the core layer presented a dense and regularly oriented microstructure, with MXene layers tightly coated on the surface of LTO. The outer layer of WO₃ micro/nano-fibers was uniformly anchored on the surface of multiple layers of rGO and uniformly coated with LTO MXene core layer, forming a clear pore structure of sheath-core structure yarn. The uniformity of element distribution verified the effectiveness of the composite structure. Electrochemical testing showed that the charge transfer impedance (R_ct) of the yarn electrode was 200 Ω. At a 3C rate, the initial Coulombic efficiency reached 96.93%, and after 120 cycles in the voltage range of 0-2.5 V, the discharge capacity retention rate was 99.64%. The electrochromic test showed that the yarn electrode demonstrated a reversible color conversion (gray → blue → gray) in the -1-1.5 V range. After 100 cycles, the coloring/fading time remained stable at 16.38 s/5.48 s, exhibiting significant RGB value changes.

Conclusion Based on the sheath-core structure design, the WO₃-rGO/LTO-MXene composite yarn electrode was successfully prepared. The sheath-core structure was successfully constructed with MXene-coated LTO fiber porous conductive yarn as the core layer and rod-like WO₃ anchored rGO sheet layer as the sheath layer. The core layer provides high electrical conductivity and mechanical support, while the outer rGO network optimizes electron transport and prohibits volume changes, jointly improving the structural stability and electrochemical performance of the electrode. The high stability is attributed to the zero strain characteristic of LTO, the high conductivity of MXene/rGO, and the synergistic stabilizing effect of the sheath-core structure. This sheath-core structure design effectively integrates high-stability energy storage (LTO-MXene) and electrochromic (WO₃-rGO) functions through a collaborative mechanism of core layer support-outer layer functionalization. It provides a feasible strategy for the development of new high-performance intelligent textile electrodes.

Key words: tungsten trioxide-reduced graphene oxide, yarn electrode, sheath-core structure, electrochemical property, electrochromic property, electrospinning