Novel Cellulosic Fiber Composites with Integrated Multi-Band Electromagnetic Interference Shielding and Energy Storage Functionalities

Abstract

In an era where technological advancement and sustainability converge, developing renewable materials with multifunctional integration is increasingly in demand. This study filled a crucial gap by integrating energy storage, multi-band electromagnetic interference (EMI) shielding, and structural design into bio-based materials. Specifically, conductive polymer layers were formed within the 2,2,6,6-tetramethylpiperidine-1-oxide (TEMPO)-oxidized cellulose fiber skeleton, where a mild TEMPO-mediated oxidation system was applied to endow it with abundant macropores that could be utilized as active sites (specific surface area of 105.6 m2 g−1). Benefiting from the special hierarchical porous structure of the material, the constructed cellulose fiber-derived composites can realize high areal-specific capacitance of 12.44 F cm−2 at 5 mA cm−2 and areal energy density of 3.99 mWh cm−2 (2005 mW cm−2) with an excellent stability of maintaining 90.23% after 10,000 cycles at 50 mA cm−2. Meanwhile, the composites showed a high electrical conductivity of 877.19 S m−1 and excellent EMI efficiency (>99.99%) in multiple wavelength bands. The composite material’s EMI values exceed 100 dB across the L, S, C, and X bands, effectively shielding electromagnetic waves in daily life. The proposed strategy paves the way for utilizing bio-based materials in applications like energy storage and EMI shielding, contributing to a more sustainable future.

1. Introduction

In recent years, there are increased interests in utilizing cellulosic fiber-based materials for application in energy storage devices [1–4]. Owing to the abundant functional groups and active sites on the surface of cellulose fibers, this type of energy storage devices exhibit fast charging and discharging capabilities, high power density, and robust cycle stability [5, 6]. To improve the energy storage performance of cellulosic fiber-based materials, the inherent three-dimensional framework structure derived from natural wood was utilized. Cellulose fiber skeleton (CFS) is prepared first via the delignification of wood to improve the accessibility of the wood cell wall and expose cellulose on the surface.

2,2,6,6-Tetramethylpiperidine-1-oxide (TEMPO) oxidation treatment is a common technique to further improve the reactivity of cellulose [7–9] that is used to enhance energy storage performance [10]. This modification method can also improve the surface charge density of the fiber [11]. However, in the conventional TEMPO/NaClO/NaBr modification system (pH=10) [12] [13, 14], C-6 aldehyde produced by TEMPO/NaClO oxidation under alkaline conditions leads to the depolymerization of cellulose, resulting in a loss of fiber mechanical performance [15, 16]. Therefore, a mild TEMPO/NaClO/NaClO2 (pH=7) modification system has been developed, where the C6 aldehyde generated by TEMPO/NaClO oxidation is further oxidized by NaClO2 under neutral conditions to prevent extensive cellulose depolymerization [11, 17]. Nevertheless, the production of cellulose-based energy storage devices often requires harsh processing conditions, such as carbonization and etching, to achieve high performance. This undoubtedly increases costs and significantly limits the commercial application of these devices [18, 19].

To simplify the fabrication of cellulose-based energy storage materials, intrinsic conductive polymers, like polypyrrole (PPy), polyanilines (PANI), and polythiophene (PT), have emerged as potential alternatives to carbon-based materials in recent years [20, 21]. These materials offer comparable conductivity and high pseudo-capacitance, and their straightforward synthesis and processing make them attractive for flexible and lightweight energy storage devices.