**Abstract**

Lithium-ion capacitors (LICs) have a wide range of applications in the fields of hybrid electric vehicles (HEVs) and electric vehicles (EVs) for their both high energy density and high power density. Lithium-ion capacitors have become a potential alternative for next-generation chemical energy storage equipment owing to high energy density, high power density, and excellent cycle performance. The prelithiated multiwalled carbon nanotubes (MWCNTs) electrode was prepared by internal short circuit (ISC) and doping to intercalate lithium into MWCNTs. SLMP and lithium metal were used as lithium resources, respectively. The prelithiated carbon nanotubes were used as anode and activated carbon electrode as cathode. The capacitors were assembled in a glove box filled with argon. The prelithiated MWCNTs electrode eliminated irreversible capacity and improved substantially electrochemical performance of lithium-ion capacitors.

**Keywords:** prelithiation, stabilized lithium metal powder, graphite, multiwalled carbon nanotubes, activated carbon, lithium-ion capacitors

## **1. Introduction**

The fossil energy's shortage and the use of fossil fuels cause environmental pollution and climate anomalies. The development and utilization of new energy sources, especially renewable energy, such as solar energy, wind energy, biomass, and hydrogen energy, have attracted increasing attention [1, 2]. And the development of new energy and energy storage equipment has become the focus of the investigation [3, 4]. Lithium-ion batteries (LIBs) and electrochemical capacitors (EC) are two important chemical energy storage devices. LIBs have high energy density but lower power density and cycle performance. EC has high power density and long cycle performance, but much lower energy density than the LIBs [5–8].

Lithium-ion capacitors, which combined the merits of lithium-ion batteries and electrochemical capacitors, are a new type of energy storage devices between the lithium-ion batteries and the electrochemical capacitors [9, 10]. In LICs, the anions adsorption and desorption in the electrolyte occurs on surface of positive electrode and simultaneously cations redox reaction occurred in the negative electrodes [11–15]. The ionic adsorption of electrical double layer and the faradaic electrochemical process (redox reaction) caused by lithium-ion intercalation and deintercalation contribute to high energy and powder density of lithium-ion capacitors than traditional capacitors [16–20].

In the carbon-based lithium-ion capacitors, the lithium ions are mainly derived from the electrolyte. But the solid-electrolyte interface (SEI) film formed during cycles will consume an amount of lithium ions which are irreversibly embedded in negative materials. That will bring down the capacity and cycle performance of LICs. So it is particularly important for the lithium predoping in negative electrode [21]. MWCNTs composed of unique one-dimensional systems with nanostructure have better stability, excellent conductivity, and lithium capacitance. It has become a popular research object for lithium-ion batteries [22]. SLMP applied to negative electrode can effectively prevent the problem of lithium ions deficiency and increase the capacity and rate performance of the LICs [23]. There is a potential difference between carbon electrode and lithium metal, which will promote the continuous flow of lithium ions into the carbon electrode when the carbon electrode and lithium metal are connected by short circuiting [9, 24, 25]. The final potential of the carbon anode will drop close to 0 V (vs. Li/Li+). Here, we introduce two new type LICs with different preintercalated lithium anodes.

It is generally known that graphite has a high theoretical Li intercalation capacity and widely was used as anode materials for lithium-ion capacitors because of natural abundance and relatively low cost [26–30]. However, lithiumion intercalation tended to the same direction, and the dynamics of lithium-ion intercalation is slow. So it is difficult to perform charge/discharge work for lithium-ion capacitor at high current density with a poor rate performance [31, 32]. Compared to graphite, MWCNTs have higher stability. In this chapter, we report internal short circuit (ISC) approach was applied to high-performance LICs with activated carbon as cathode and prelithiated multiwalled carbon nanotubes/graphite composite as anode. Electrochemical performance of lithium-ion capacitors was investigated.
