Cellulose Elementary Fibrils as Deagglomerated Binder for High-Mass-Loading Lithium Battery Electrodes

Abstract

Amidst the ever-growing interest in high-mass-loading Li battery electrodes, a persistent challenge has been the insufficient continuity of their ion/electron conduction pathways. Here, we propose cellulose elementary fibrils (CEFs) as a class of deagglomerated binder for high-mass-loading electrodes. Derived from natural wood, CEF represents the most fundamental unit of cellulose with nanoscale diameter. The preparation of the CEFs involves the modulation of intermolecular hydrogen bonding by the treatment with a proton acceptor and a hydrotropic agent. This elementary deagglomeration of the cellulose fibers increases surface area and anionic charge density, thus promoting uniform dispersion with carbon conductive additives and suppressing interfacial side reactions at electrodes. Consequently, a homogeneous redox reaction is achieved throughout the electrodes. The resulting CEF-based cathode (overlithiated layered oxide (OLO) is chosen as a benchmark electrode active material) exhibits a high areal-mass-loading (50 mg cm–2, equivalent to an areal capacity of 12.5 mAh cm–2) and a high specific energy density (445.4 Wh kg–1) of a cell, which far exceeds those of previously reported OLO cathodes. This study highlights the viability of the deagglomerated binder in enabling sustainable high-mass-loading electrodes that are difficult to achieve with conventional synthetic polymer binders.

1. Introduction

The ongoing surge in demand for smart portable electronics, electric vehicles, and grid-scale energy storage systems has catalyzed the relentless pursuit of high-energy–density lithium (Li) batteries with electrochemical sustainability [1–3]. Many previous studies implemented to reach this goal have concentrated on synthesizing and engineering new electrode active materials [4, 5]. Along with these material-driven approaches, the design of high-mass-loading electrodes has recently emerged as a practical strategy owing to its simplicity and scalability in realizing high-energy–density cells [6–8].

However, a longstanding challenge with the high-mass-loading electrodes has been the difficulty in achieving sufficient interconnectivity of their ion/electron conduction pathways [9–12]. The random and nonuniform intermolecular interactions between electrode components, including carbon conductive additives and polymer binders, often lead to their poor dispersion in electrode slurries [13–17]. This issue becomes more pronounced with the incorporation of carbon nanotubes (CNTs), which tend to aggregate due to their strong van der Waals interactions, thus limiting their effectiveness in forming conductive networks [18]. To address these challenges, both physical methods (e.g., high-shear mixing, three-roll milling) and chemical methods (e.g., surface functionalization, polymer grafting) have been explored [19, 20]. However, these approaches often cause structural damage to the components, require additional dispersants, and complicate fabrication processes, thereby hindering their practical application [21–23]. Consequently, this issue hinders the formation of bi-continuous ion/electron conduction networks across the electrode thickness, resulting in a loss of electrochemical performance and energy densities in the resulting cells [24, 25].

To achieve well-developed ion/electron conduction pathways in the electrodes, it is necessary to inhibit electrode components’ aggregation while enhancing intermolecular interactions between heterogeneous components [26–28]. Previous approaches have primarily centered on the chemical modification of electrode binders [29–32], including the amphiphilic bottlebrush polymers to enhance component dispersion, elastic and composite binders to improve mechanical stability, and polymer-wrapped SWCNTs to establish conductive networks. However, these efforts have often failed to address the complexity that arises from the interactions of multi-components. Furthermore, the intricate multiscaling of binder architecture, coupled with its interact...