Synthesis of Nitrogen-Doped Graphene as Highly Effective Cathode Materials for Li-Ion Hybrid Supercapacitors

Abstract

In this paper, we report the possibility of utilizing nitrogen-doped graphene (N-G) as a novel cathode material for Li-ion hybrid supercapacitors (Li-HSCs) applications. N-G was prepared by a simple one-pot hydrothermal method, followed by freeze-drying in a vacuum treatment. Li-ion hybrid supercapacitors was fabricated using N-G as the cathode along with lithium-ion intercalated compound LiMn 2 O 4 as the anode in an aqueous medium. The energy density of the Li-HSCs can increase up to 22.15Wh kg −1 when the power density reached was 132 W kg −1 , and still retained 13 Wh kg −1 at a power density of 2000 W/kg. The LiMn 2 O 4 / N-G Li-HSCs assembly also shows good cyclic performance with about 80% of the initial value retained after 2000 galvanostatic cycles under high rate cyclic conditions. This result clearly indicates that N-G is a promising candidate for future application in a Li-HSCs configuration.Energy storage has become a global concern in modern society, and high-performance energy storage devices are in great demand. Among various electrical energy storage devices, lithium ion batteries (LIBs) with high energy density and supercapacitors (SCs) with excellent power density are currently considered to be two excellent candidates as novel, environmentally friendly, low-cost, and high-performance energy storage devices to meet the increasing demand. The LIBs commonly can store a large amount of energy, as high as 150-200 Wh kg −1 , but are confined by their low power density (below 1000 W kg −1 ) and poor cycle life (usually less than 1000 cycles). In contrast, SCs can provide much higher power density (10 kW kg −1 ), long cycle life (exceeding 10 5 cycles), and fast charge-discharge processes (within seconds), but suffer from much lower energy density (only 5-10 Wh kg −1 ). 1 Therefore, there has been great and urgent demand for high-performance energy storage devices with both high energy density and high power density.With a combination of the fast charging rate of SCs and the high energy density of LIBs, a novel supercapacitor-battery energy storage system, also called lithium ion hybrid supercapacitors (Li-HSCs) has emerged, which is expected to possess the best features of both SCs and LIBs. 2-8 In principle, Li-HSCs are composed of a capacitor-type electrode and a lithium ion battery-type electrode in a Li + containing electrolyte. Therefore, compared with LIBs and SCs, Li-HSCs undergo different charge storage mechanism due to the unique reaction mechanisms of each electrode. Capacitor-type electrode store energy by a reversible adsorption/desorption of ions, while battery-type electrode store energy though a Li-ion insertion/extraction reaction. 9-11 It is possible to aim at much larger energy density without sacrificing power energy and cycle life. Because of its competitive characteristics it is expected to be useful power sources for hybrid electric vehicles and electric vehicles. [12][13][14] In Li-HSCs, adsorption/desorption of ions occurs on the surface of the capacitor-type electrode while t...

Fabrication of High‐Performance Aqueous Li‐Ion Hybrid Capacitor with LiMn2O4 and Graphene

“…The observed peaks are related to the lithium ion intercalation and de‐intercalation in the spinel host structure of LiMn 2 O 4 . The possible mechanism of charge storage occurred at the positive (LiMn 2 O 4 ) electrode can be explained using the Equation : …”

“…The fabricated device shows good stability and retained its initial capacitance of about 90.24 % even after 1000 cycles. This decrease in the initial capacitance is due to the nature of the LiMn 2 O 4 , which undergoes Jahn‐Teller distortion and also due to the dissolution of electrodes into the electrolyte over prolonged cycles . In order to understand this, the Nyquist plot of the fabricated LiMn 2 O 4 ∥graphene LHC device after cyclic tests was measured and is shown in inset of Figure b.…”

“…The Li‐ion hybrid capacitor uses battery‐type as well as capacitive‐type electrode materials in the system, which results in significant improvements in the overall electrochemical energy storage properties. The advantage of Li‐ion hybrid capacitors over conventional batteries and supercapacitors is that it can provide the fast charging and discharging rate of the supercapacitor together with the high energy density of a battery . Furthermore, charge storage mechanism in the Li‐ion capacitors relies on the formation of electrical double layer at the capacitive type electrode and ion intercalation/de‐intercalation occurs at the battery type electrode .…”

All graphene electrode for high‐performance asymmetric supercapacitor

“…[47][48][49] CV and GCD curves of FG were obtained in the potential window of 0 to 0.6 V (shown in Figure 5A,B). The capacitance is calculated using GCD discharge curves.…”

“…It has a larger discharging curve than charging curve, which is probably because of the surface reaction happening between the surface of cathode and ions of electrolyte and hysteresis in intercalation/ deintercalation of ions at anode in process of charging and discharging. [49][50][51][52][53] The key factor in obtaining ultra-high energy density is the kinetic stability between the electrodes at wide working potentials of this device. The device delivers an E-P density of 91 W h kg −1 and 424.95 W kg −1 , respectively, which is higher than previous reports (40-70 Wh kg −1 at maximum).…”