RESUMEN
Despite the recent attention for Li metal anode (LMA) with high theoretical specific capacity of ≈3860 mA h g-1 , it suffers from not enough practical energy densities and safety concerns originating from the excessive metal load, which is essential to compensate for the loss of Li sources resulting from their poor coulombic efficiencies (CEs). Therefore, the development of high-performance LMA is needed to realize anode-minimized Li metal batteries (LMBs). In this study, high-performance LMAs are produced by introducing a hierarchically nanoporous assembly (HNA) composed of functionalized onion-like graphitic carbon building blocks, several nanometers in diameter, as a catalytic scaffold for Li-metal storage. The HNA-based electrodes lead to a high Li ion concentration in the nanoporous structure, showing a high CE of ≈99.1%, high rate capability of 12 mA cm-2 , and a stable cycling behavior of more than 750 cycles. In addition, anode-minimized LMBs are achieved using a HNA that has limited Li content (≈0.13 mg cm-2 ), corresponding to 6.5% of the cathode material (commercial NCM622 (≈2 mg cm-2 )). The LMBs demonstrate a feasible electrochemical performance with high energy and power densities of ≈510 Wh kgelectrode -1 and ≈2760 W kgelectrode -1 , respectively, for more than 100 cycles.
RESUMEN
The galvanostatic lithiation/sodiation voltage profiles of hard carbon anodes are simple, with a sloping drop followed by a plateau. However, a precise understanding of the corresponding redox sites and storage mechanisms is still elusive, which hinders further development in commercial applications. Here, a comprehensive comparison of the lithium- and sodium-ion storage behaviors of hard carbon is conducted, yielding the following key findings: 1) the sloping voltage section is presented by the lithium-ion intercalation in the graphitic lattices of hard carbons, whereas it mainly arises from the chemisorption of sodium ions on their inner surfaces constituting closed pores, even if the graphitic lattices are unoccupied; 2) the redox sites for the plateau capacities are the same as those for the closed pores regardless of the alkali ions; 3) the sodiation plateau capacities are mostly determined by the volume of the available closed pore, whereas the lithiation plateau capacities are primarily affected by the intercalation propensity; and 4) the intercalation preference and the plateau capacity have an inverse correlation. These findings from extensive characterizations and theoretical investigations provide a relatively clear elucidation of the electrochemical footprint of hard carbon anodes in relation to the redox mechanisms and storage sites for lithium and sodium ions, thereby providing a more rational design strategy for constructing better hard carbon anodes.
RESUMEN
The non-aqueous asymmetric lithium ion hybrid capacitor (LIHC) is a tactical energy storage device composed of a faradic and non-faradic electrode pair, which aims to achieve both high energy and great power densities. On the other hand, the different types of electrode combinations cause severe imbalances in energy and power capabilities, leading to poor electrochemical performance. Herein, waste pinecone-derived hierarchically porous pyropolymers (WP-HPPs) were fabricated as a surface-driven pseudocapacitive electrode, which has the advantages of both faradic and non-faradic electrodes. The unique materials properties of WP-HPPs possessing high effective surface areas and hierarchically open nanopores led to high specific capacities of ~412 mA h g-1 and considerable rate/cycling performance as a cathode for LIHCs. In particular, nanometer-scale pores, approximately 3 nm in size, plays a key role in the pseudocapacitive charge storage behaviors because open nanopores can transport solvated Li-ions easily into the inside of complex carbon structures and a large specific surface area can be provided by the effective active surface for charge storage. In addition, WP-HPP-based asymmetric LIHCs assembled with a pseudocapacitive counterpart demonstrated feasible electrochemical performance, such as maximum specific energy and specific power of ~340 Wh kg-1 and ~11,000 W kg-1, respectively, with significant cycling stability.
RESUMEN
Nanoporous carbon, including redox-active functional groups, can be a promising active electrode material (AEM) as a positive electrode for lithium-ion batteries owing to its high electrochemical performance originating from the host-free surface-driven charge storage process. This study examined the effects of the nanopore size on the pseudocapacitance of the nanoporous carbon materials using nanopore-engineered carbon-based AEMs (NE-C-AEMs). The pseudocapacitance of NE-C-AEMs was intensified, when the pore diameter was ≥2 nm in a voltage range of 1.0~4.8 V vs Li+/Li under the conventional carbonate-based electrolyte system, showing a high specific capacity of ~485 mA·h·g-1. In addition, the NE-C-AEMs exhibited high rate capabilities at current ranges from 0.2 to 4.0 A·g-1 as well as stable cycling behavior for more than 300 cycles. The high electrochemical performance of NE-C-AEMs was demonstrated by full-cell tests with a graphite nanosheet anode, where a high specific energy and power of ~345 Wh·kg-1 and ~6100 W·Kg-1, respectively, were achieved.