Discrete Graphitic Crystallites Promise High‐rate Ion Intercalation for KC₈ Formation in Potassium Ion Batteries

Abstract

conversion efficiency, and simple maintenance. [1] However, the rapid consumption and uneven distribution of lithium sources prevent it from being the only means of energy storage. [2] Potassium ion batteries (PIBs) have attracted tremendous attention as a complement to LIBs due to the higher abundance of the metal (K with 1.5 wt.% of the Earth's crust compared to 0.0017 wt.% for Li) and the higher ionic conductivity of K + in the electrolyte and their higher cell voltage than LIBs. [3] Most importantly, efficient intercalation of K + in graphite makes PIBs potentially match with the well-established graphite anode for LIBs. Graphite delivers a satisfactory theoretical capacity (279 mAh g −1 ) for K + by forming the stage-one intercalation compound (GIC) KC 8 at low potential, which gives a high energy density at the full-cell level. [4] However, compared with the small Li + (0.76 Å), the larger K + (1.38 Å) always has lower mobility in graphite resulting in a poor rate performance and a low capacity for PIBs, and leads to serious structural damage during K + intercalation/deintercalation and thus poor capacity retention. [3b,4a,5] Identifying a superior carbon anode to commercial graphite for K + storage is the major challenge in developing high-energy and high-power PIBs.Two approaches to solving this problem have been developed: modifying the microstructure of graphite and developing other non-graphitic carbons as anodes. For the former, strategies such as increasing the interlayer spacing, [6] modifying morphology, [7] and disordering graphitic crystallites [8] have been explored to facilitate K + diffusion and precisely tune the void space to buffer the expansion of electrodes. These modified graphitic anodes generally exhibit high slope capacity due to additional defects or surfaces introduced for K + adsorption, excellent rate performance, and cycle stability. However, their material densities and low-potential plateau capacity need to be enhanced. Nongraphitic carbons, both soft and hard, have been extensively explored as high-performance anodes for PIBs. [9] They usually deliver a remarkable rate performance due to their disordered structures with abundant edges for fast K + diffusion. They also have a large capacity and a long cycling life due to their large d 002 (interlayer spacing) and enough porosity for K + storage, and to accommodate the expansion. However, their low densities and high operating potential reduce both the gravimetric and volumetric energy densities at the full-cell level. Therefore, it remains a challenge to improve the power characteristics and Graphite has paved the way for commercial lithium-ion batteries and shows great potential as an anode for high-energy potassium-ion batteries (PIBs) due to its low-potential charge/discharge plateau. However, the restricted diffusion of large K + in graphite causes difficulties in generating the stageone graphite-intercalation compound (GIC) KC 8 at high rates and results in a low plateau capacity and an inferior rate performance. It i...

Constructing Active BN Sites in Carbon Nanosheets for High‐Capacity and Fast Charging Toward Potassium Ion Storage

“…where k 1 ν and k 2 ν 1/2 represent the surface-driven process and diffusion-controlled behavior, respectively. [56,57] For example, at the scan rate of 0.5 mV s −1 , the calculated capacitance percentage of BNC-2 is about 63.4%, higher than that of NC (55.6%) and BNC-1 (59.6%), but lower than that of BNC-3 (72.2%) (Figure 4c and Figure S11, Supporting Information). This implies that the attendance of B can modulate the storage kinetics via the regulation on storage behavior, which is consistent with Figure 4b.…”

Defect Engineering of Disordered Carbon Anodes with Ultra-High Heteroatom Doping Through a Supermolecule-Mediated Strategy for Potassium-Ion Hybrid Capacitors

“…Low-temperature pyrolyzed amorphous carbons with large interlayer spacing (> 3.7 Å) could provide excellent rate performance for the anodes of PIHCs due to their tunable structure (large layer spacing, abundant defects, and rich pores) and abundant adsorption active sites [ 4 ]. The excellent potassium storage performance of amorphous carbon is mainly ascribed to the adsorption/desorption of K + in the defect sites [ 17 , 18 ], which is different from the (de)intercalation mechanism of graphite [ 19 – 21 ]. However, most amorphous carbons show low capacities because of the presence of cross-linked sp 3 linkage in carbon skeletons.…”

Electrospun carbon-based nanomaterials for next-generation potassium batteries

“…[7][8][9] Potassium-ion batteries (PIBs) have recently drawn wide research enthusiasm due to the natural abundance (2.09 wt%), ubiquitous distribution, and low price of potassium (K) resources, as well as the analogous working principles with LIBs. [10][11][12][13][14][15] Notably, inexpensive aluminium foil can be used to replace traditional copper as the current collector for both cathodes and anodes since K does not alloy with aluminium, which can further reduce the overall cost of PIBs. 16,17 In addition, the weak Lewis acidity and the small Stokes radius of the K-ion are conducive to its diffusion in the bulk electrolyte and desolvation of the electrolyte, promising a tantalizing rate performance.…”