One Dimensional Building Blocks-Internetworked Heteronanomats As a Platform Architecture for High-Performance Ultrahigh-Capacity Lithium-Ion Battery Cathodes
Authors: Kim Ju-Myung , Kim Se-Hee , Kim Jung-Hwan , Lee Dong-Gue , Lee Sang-Young 
Published: February 2020

Ever-increasing demand for high-performance portable electronics, electric vehicles (EVs) and grid-scale energy storage systems (ESSs) has been in relentless pursuit of advanced energy storage systems with reliable electrochemical properties. Among a vast variety of rechargeable power sources, undoubtedly, lithium-ion batteries have been most widespread and still garnered considerable attention due to their well-customized battery characteristics. From the electrode architecture point of view, most conventional electrodes are characterized with simple and random pile-up of electrode active materials, carbon powder conductive additives and polymer binders on top of metallic foil current collectors. Unfortunately, such a stereotyped electrode architecture often gives rise to non-uniform and sluggish electron/ion transport particularly in their through-thickness direction and is also vulnerable to structural disruption upon mechanical deformation. In particular, the poorly-developed electron/ion conduction pathways of the electrodes eventually provoke unwanted electrochemical polarization, which becomes more serious at harsh operating conditions such as high-mass loading electrodes and fast charge/discharge current densities that are urgently needed for high-energy EV batteries. Due to these unavoidable limitations, the conventional electrode architecture has posed a formidable challenge to sustainable progress of battery performance, thus pushing us to search for alternative solutions.
Here, as a facile and versatile electrode strategy to resolve the long-standing challenges of conventional electrodes mentioned above, we demonstrate a new class of heteronanomat-architectured electrodes (referred to as HM electrodes), which comprise one-dimensional (1D) nanobuilding blocks of polyacrylonitrile (PAN) nanofibers/multi-walled carbon nanotubes (MWNTs)-mediated heteronanomat and densely-packed electrode active particles. The HM electrodes are fabricated through simultaneous electrospraying (for MWNTs/electrode active powders) and electrospinning process (for PAN nanofibers) without the use of typical polymer binders, carbon powder conductive additives and metallic foil current collectors. Figure 1 shows the Schematic illustration of the manufacturing procedure of HM cathodes through simultaneous electrospraying/electrospinning process. Notably, the electrospryaed MWNTs and electrospun PAN nanofibers are internetworked in close contact with the electrode active particles, eventually leading to electrode active particles-embedded self-standing heteronanomat electrodes. The PAN nanofibers act as a mechanically-reinforcing building element and also 1D-shaped electrode binders. The MWNTs build well-interconnected electronic networks and also play a role as an alternative current collector. Such uniqueness in the materials/architecture of the HM electrodes is anticipated to enable substantial improvements in the electrochemical performance and mechanical flexibility far beyond those accessible with conventional electrode technologies. Furthermore, the Al foil current collector-free, PAN/MWNT heteronanomat allowed the HM cathodes to be multiple-stacked in series, which eventually produced the user-tailored, ultrathick cathodes that lie far beyond those accessible with conventional cathode technologies. We envision that the 1D nanobuilding blocks-mediated heteronanomat cathode strategy presented herein holds a great deal of promise as an effective and versatile platform technology to open a new route toward high-performance ultrahigh-capacity cathodes in urgent need for forthcoming smart power sources.
Figure 1. Schematic illustration depicting the manufacturing procedure of HM cathodes through simultaneous electrospraying/electrospinning process.

Figure 1