Engineering Electronic Transfer Dynamics and Ion Adsorption Capability in Dual-Doped Carbon for High-Energy Potassium Ion Hybrid Capacitors

Abstract

Sodium and potassium ions energy storage systems with low cost and high energy/power densities have recently drawn increasing interest as promising candidates for grid-level applications, while the lack of suitable anode materials with fast ion diffusion kinetics highly hinders their development. Herein, we develop a nanoscale confined in situ oxidation polymerization process followed by a conventional carbonization treatment to generate phosphorus and nitrogen dualdoped hollow carbon spheres (PNHCS), which can realize superior sodium and potassium ion storage performance. Importantly, the density functional theory calculation and combined characterizations, e.g., in situ Raman spectroscopy and ex situ X-ray photoelectron spectroscopy, decipher that the P/N doping can enhance the electronic transfer dynamics and ion adsorption capability, which are responsible for enhanced electrochemical performance. Inspiringly, the practicability of the PNHCS anode is demonstrated by assembling the potassium ion hybrid capacitors (KIHCs), where the prominent energy density is 178.80 Wh kg −1 at a power density of 197.65 W kg −1 , with excellent cycling stability, can be achieved. This work not only promotes the development of efficient anode material for sodium/potassium ion storage devices but also deciphers the embedded ion storage mechanism.

Unraveling the Effect of Intrinsic Carbon Defects on Potassium Storage Performance

“…Previous reports have proven that high capacitive contribution related to external defects produced by heteroatoms doping can largely improve reversible capacity and prolong cycle lifespan. [47,48] So, high capacity and capacity retention ratio of ECM-800 are also tightly associated with its capacitive contribution ratio enabled by abundant intrinsic defects, which well confirms our speculation above. The Galvanostatic intermittent titration (GITT) technique was carried out to assess the impact of intrinsic defects on K + diffusion coefficient (D K ) during discharging/charging process.…”

“…All these values are very close to 1 (capacitive behaviors dominated potassium storage) rather than 0.5 (diffusion-controlled potassium storage), suggesting a fast kinetic governed by capacitive behaviors, especially in ECM-800. To further quantify capacitive contribution ratio to total capacity, a commonly used formula (i = k 1 v+k 2 v 1/2 ) is utilized, in which k 1 v and k 2 v 1/2 represent the capacitive-and diffusion-controlled contribution, [47,48] respectively. The capacitive contribution of ECM-800 at 1.0 mV s −1 is calculated to be 76.1% (Figure 4d), and a maximin value of 86.0% is achieved when scan rate is extended to 5.0 mV s −1 (Figure 4e).…”

Nitrogen‐Doped Hollow Carbon Spheres Based on Schiff Base Reaction as an Anode Material for High‐Performance Lithium and Sodium Ion Batteries

“…The initial coulombic efficiencies were 51.9, 59.4, and 56.5 %. The lower coulombic efficiencies were attributed to the formation of SEI layer and irreversible side reactions [39] . It can be seen that the charge–discharge curves of the three samples have no obvious platform area.…”

“…The lower coulombic efficiencies were attributed to the formation of SEI layer and irreversible side reactions. [39] It can be seen that the chargedischarge curves of the three samples have no obvious platform area. Based on the adsorption-intercalation mechanism, the voltage in the slope region primarily corresponds to the adsorption of Li + on the surface active sites, and the platform region corresponds to interlayer carbon insertion.…”

Nitrogen/Phosphorus Dual‐Doped Hard Carbon Anode with High Initial Coulombic Efficiency for Superior Sodium Storage

“…[31] As shown in Figure 3(e), the N 1s high-resolution spectrum can be made up of pyridinic-N (398.7 eV), pyrrolic-N (400.8 eV), graphitic-N (402.6 eV), and oxidized-N (404.3 eV). [32,33] The high-resolution spectrum of O 1s (Figure 3f) can be divided into C=O, CÀ O, and OÀ C=O. [34] Meanwhile, Figure 3(g) shows the peak of P 2p spectrum at 133.0 eV is PÀ C, which reveals that the P doping achieved by this method is bonded by a chemical bond.…”