Second generation ‘nanohybrid supercapacitor’: Evolution of capacitive energy storage devices

Abstract

Nanoscience and nanotechnology can provide tremendous benefits to electrochemical energy storage devices, such as batteries and supercapacitors, by combining new nanoscale properties to realize enhanced energy and power capabilities. A number of published reports on hybrid systems are systematically reviewed in this perspective. Several potential strategies to enhance the energy density above that of generation-I electric double layer capacitors (EDLC: activated carbon/activated carbon) are discussed and some fundamental issues and future directions are identified. We suggest a new hybrid supercapacitor system that is able to meet the energy and power demands for a variety of applications, ranging from microelectronic devices to electrical vehicles, which presents itself as a breakthrough improvement. Two practical hybrid supercapacitor systems, namely, a lithium-ion capacitor (LIC: graphite/activated carbon) and a nanohybrid capacitor (NHC: (nc-Li 4 Ti 5 O 12 /CNF composite)/activated carbon), are featured and compared. The proposed NHC can pave the way toward generation-II supercapacitor systems by taking advantage of a novel, high quality, high efficiency and inexpensive nanomaterial preparation procedure. With such a breakthrough in nanofabrication-nanohybridization technology, the NHC, which utilizes an ultrafast nano-crystalline Li 4 Ti 5 O 12 , is considered to be an alternative for conventional generation-I EDLCs.

Development of a 4.2 V aqueous hybrid electrochemical capacitor based on MnO2 positive and protected Li negative electrodes

“…The cell voltage is even higher than EC devices operating in non-aqueous electrolytes, such as non-aqueous electric double-layer capacitors ((C2H5)4NBF4/acetonitrile; ~2.7 V), [28] ionic liquids (1-methyl-3-buthylimidazolium tetrafluoroborate; 3.5 V), [29] or commercial LICs (3.8 V). [30] Discharge curves at high current density exhibited a linear change with time, typical of capacitive charge release (Fig. 5 (B)).…”

Facile synthesis of T-Nb2O5 nanosheets/nitrogen and sulfur co-doped graphene for high performance lithium-ion hybrid supercapacitors

“…LIBs deliver high energy density using conversion, intercalation or alloying mechanisms, but they have the shortcomings of low power density and rapid capacity fading [7,8]. Driven by the demand of energy storage devices with both high power and energy densities, lithium-ion hybrid supercapacitors (Li-HSCs) with the advantages of both SCs and LIBs have emerged [7,[9][10][11]. Li-HSCs are constructed from SCs-type carbonaceous electrodes as cathodes and LIBs-type electrode materials as anodes under lithium-salt-containing electrolyte.…”

Stabilization of Si Negative Electrode by Li Pre-doping Technique and the Application to a New Energy Storage System

“…Electric double-layer capacitors (EDLCs) possess advantages of high rate capability and semi-permanent long cycle life, which are attributed to the fast charge/discharge (adsorption/ desorption) reaction at activated carbon (AC) electrodes, regardless of the faradaic reaction; however, the charge/discharge mechanism causes low energy density compared with that of other energystorage devices, such as Li-ion (LIBs) and nickel-hydrogen batteries. [1][2][3][4] To overcome this weak point, many hybrid capacitor systems with asymmetric electrodes have been studied. Li-ion capacitors (LICs) using a Li pre-doped graphite or hard carbon negative electrode (NE) have recently been developed and released as commercial products.…”

“…Li-ion capacitors (LICs) using a Li pre-doped graphite or hard carbon negative electrode (NE) have recently been developed and released as commercial products. 4 The cell voltage of LIC systems is much higher than that of EDLCs because the LIC contains a Li pre-doped graphite NE with a low redox potential, around 0.02 V, [5][6][7] resulting in an energy density ca. three times higher than that of the EDLC (ca.…”

“…To apply LICs to large-scale devices, such as electric vehicles and stationary energy-storage facilities, further improvement of the discharge capacity and energy density is needed. Many researchers have intensively studied titanium oxide materials, 4 such as Li 4 Ti 5 O 12 (LTO), [8][9][10] and TiO 2 (B); [11][12][13] however, these NEs have relatively high redox potentials of around 1.6 V vs. Li/Li + and lower theoretical capacities (175 and 335 mAh g ¹1 for LTO and TiO 2 (B), respectively) than that of graphite (372 mAh g ¹1 ), so the discharge capacity and energy density of such LIC cells do not increase as expected.…”