Dual-Cation Electrolytes for High-Power and High-Energy LTO//AC Hybrid Capacitors

Abstract

Dual-cation electrolyte systems, which contain two cations [Li + and spiro-1,1′-bipyrrolidinium (SBP + ), are proposed to enhance the power capability of hybrid capacitors composed of thick Li 4 Ti 5 O 12 (LTO) negative (200 μm) and activated carbon (AC) positive electrodes (400 μm), which thus reduces the resistive overvoltage in the system. Detailed studies of the mass transport properties based on the combination of spectroscopy and electrochemical analysis have shown that the presence of SBP + , despite slower Li + transport in the electrolyte bulk, further reduces overvoltage associated with migration limitation in the thick LTO electrode macropores. This study on the dual-cation electrolyte quantifies the influence of the addition of a supporting electrolyte and shows interest in SBPBF 4 addition for increasing the output power density of hybrid capacitors with a thick electrode configuration.

Impact of Total Ionic- and Individual Li+-Conduction in Dual-Cation Electrolytes on Power Performances for Thick Electrode Li4Ti5O12//AC Hybrid Capacitors

“…The SBP-based dual-cation system (1 M LiBF 4 + 2 M SBPBF 4 /PC) enhanced the power density owing to its higher ionic conductivity (7.7 mS cm –1 ) than the single-cation electrolytes (1 M LiBF 4 /PC, 3.4 mS cm –1 ). We also revealed that such increase in the “total” ionic conductivity associated with all electrolyte ions (Li + , SBP + , and BF 4 – ) brought about the acceleration of the charge-transfer reaction at the LTO/electrolyte interface (lithiation/delithiation of LTO), despite the decreased “individual” ionic conductivity of Li + …”

“…Furthermore, we performed EIS measurements on the SOC-controlled LTO//LTO symmetric laminate-type cells (Figure S1c, a 4-electrodes cell, SOC = 25%) to evaluate the R ct of the LTO electrodes. Detailed information on the preparation process of the 4-electrodes cell, which has the advantage of not unnecessarily disassembling the cells before the EIS measurements (Figure S1c), is described in our previous paper . The EIS measurements were conducted at T = 298 K with a perturbation signal of ± 10 mV in the frequency range of 0.01–65.5 kHz.…”

“…In this connection, lithium tetrafluoroborate (LiBF 4 ) which shows better stability against moisture is widely employed in LTO//AC systems, ,, although the LiBF 4 -based electrolytes exhibit a lower ionic conductivity (∼3.4 mS cm –1 ) than the LiPF 6 -based electrolytes. To overcome the above challenges, we have developed “dual-cation” electrolytes for LTO//AC thick-electrode hybrid capacitor systems. , The reported dual-cation electrolyte comprised LiBF 4 and a supporting electrolytic salt of spiro-(1,1′)-bipyrrolidinium tetrafluoroborate (SBPBF 4 ) that were dissolved in propylene carbonate (PC). The SBP-based dual-cation system (1 M LiBF 4 + 2 M SBPBF 4 /PC) enhanced the power density owing to its higher ionic conductivity (7.7 mS cm –1 ) than the single-cation electrolytes (1 M LiBF 4 /PC, 3.4 mS cm –1 ).…”

“…Hence, we chose an aprotic ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4 ), as a replacement of SBPBF 4 in dual-cation electrolytes. EMIBF 4 has been widely investigated both for EDLC and LIB applications because of its high ionic conductivity, relatively wide electrochemical window, and low vapor pressure . Good compatibility between EMIBF 4 and PC enables a higher maximum molar concentration of EMIBF 4 in PC (∼6.5 M) than that of SBPBF 4 (∼3.3 M). , Consequently, the addition of EMIBF 4 (>3 M) imparts higher ionic conductivity to the 1 M LiBF 4 /PC electrolyte ( ca.…”

Durable Supercapattery Film with Dual-Branched Dense Hexagonal Fe(II)-Based Coordination Nanosheets for Flexible Power Sources

“…However, the energy density is insufficient. − A metal-ion battery, on the other hand, has high energy density, but the power density is low. − Under these circumstances, “supercapattery” is becoming popular as a new type of energy storage device. − Supercapattery is defined as a combination of a supercapacitor and a battery and expected to achieve high energy density, high power density, high-rate charge storage capability, and longer charge/discharge durability. It is different from a metal-ion capacitor, composed of a battery-type anode and a capacitor-type cathode, or a hybrid capacitor, made of the combination of an electrical double-layer capacitor (EDLC) and a pseudocapacitor. In addition, to date, research has been focused on developing flexible energy storage for wearable electronics that can deliver good performance under folded or bent conditions. , However, the low ion mobility, poor reversibility, and inactivation in flexible energy storage are major concerns for the durability.…”