Design Rationale and Device Configuration of Lithium‐Ion Capacitors

Abstract

In contrast, EDLCs can provide high power density (≥10 kW kg −1 ), and is capable for high power system like light rail etc. [5] However, its low energy density (≤10 Wh kg −1 ) blocks its path to long period power supply. [3] Lithium-ion capacitors (LICs), as a hybrid of EDLCs and LIBs, are a promising energy storage solution capable with high power (≈10 kW kg −1 , which is comparable to EDLCs and over 10 times higher than LIBs) and high energy density (≈50 Wh kg −1 , which is at least five times higher than SCs and 25% of the stateof-art LIBs). [6] The comparison of device configurations, their charge/discharge profiles as well as performance characteristics of LIBs, EDLCs and LICs are shown in Figure 1. LIBs contain two insertion-type electrodes as positive and negative electrodes respectively, which store/output energy via Li + insertion/extraction. The plateaus are observed on charge/discharge curve while peaks can be pointed out in cyclic voltammetry curve, reflecting the insertion/extraction of cation and the redox reactions in the bulk material. With the massive cation storage in the bulk materials, LIBs demonstrate high energy density. However, the power performance of LIBs is limited by the slow ion diffusion in the bulk material, though the self-discharge rate (<5% of the stored capacity over 1 month) is suppressed. [7] With the high energy density, flammable electrolyte, and chemical reaction during charge/ discharge, safety issue is critical for LIBs application. [8] Differently, EDLCs contain two adsorption-type electrodes which adsorb/ desorb ions during charge/discharge. The easily accessible surface ion storage site permits the rapid charge/discharge capability of EDLCs. The physical change during charge/discharge and low-energy density enable the high safety of EDLCs. But the selfdischarge (≈50-80% loss in energy per day) is serious due to the poor interaction between the ion and the active material surface. [9] Taking the much lower energy density into consideration, the energy-based cost ($ kW h −1 ) of EDLCs (≈$10000 kW h −1 ) is much higher than LIBs ($100-200 kW h −1 ). [10] To combine the advantages of both LIBs and EDLCs, the first type of LICs was introduced by Amatucci et al. in 2001, which used an activated carbon cathode capturing PF 6 − via adsorption/desorption and a nanostructured Li 4 Ti 5 O 12 anode storing Li + through insertion/extraction. [11] The typical hybrid configuration of LICs, as shown in Figure 1a, contains a LIBs electrode and an EDLCs electrode with an organic lithium-ion containing electrolyte, e.g., activated carbon (AC)//graphite and AC//Li 4 Ti 5 O 12 (LTO). [12] Later, in order to improve the power density, capacitor//capacitor asymmetric LICs, like AC//AC, and AC//MXene were investigated. [13] The

Intertwined CNT Assemblies as an All-Around Current Collector for Volume-Efficient Lithium-Ion Hybrid Capacitors

“…In the final step, a full cell of LIHCs is assembled with AC–CNTs and LIG–CNTs as cathodes and anodes, respectively. According to previous studies on LIHCs, the energy storage mechanism is divided into two stages based on the OCV where OCVs of LIHCs are defined as the OCP differences between the cathodes and anodes. − The cathode stored energy via an EDL mechanism involving the adsorption and desorption of PF 6 – anions (above the OCV) and solvated Li + ions (below the OCV). Additionally, the reversible intercalation and deintercalation processes of Li + ions occur in the anode regardless of the OCV.…”

Enabling rapid pseudocapacitive multi-electron reactions by heterostructure engineering of vanadium oxide for high-energy and high-power lithium storage

“…24,25 Also, the same electrode material can facilitate electrode kinetics balance for enhancing the electrochemical performance of the full cell. 26,27 However, the development of symmetric cells has been limited due to the lack of suitable electrode materials. In general, symmetric cells are based on certain bipolar materials with two distinct potential plateaus.…”

A perspective on the evolution and journey of different types of lithium-ion capacitors: mechanisms, energy-power balance, applicability, and commercialization

“…In contrast, EDLC-type electrodes with a higher ion-storage surface area can lead to higher capacitance and higher energy manifestation, which can therefore be considered as a candidate of choice for LIC electrodes. 1,2,[12][13][14][15][16] The basic conguration of a LIC is depicted schematically in Fig. 1.…”