# Novel Q-Carbon Anodes for Sodium-Ion Batteries
## 1 Introduction  
The generation of CO\({}_{2}\) due to human activities since the industrial revolution has led to an existential crisis for humanity, and transitioning away from fossil fuels is becoming the need of the hour [1, 2, 3, 4]. Using renewable sources of energy can mitigate the issue of CO\({}_{2}\) generation. However, these intermittent sources of energy require efficient storage, which is a hot topic of research today [5]. The use of electric vehicles (EVs) is another attractive means of mitigating the climate crisis, as they represent zero-emission propulsion systems [6]. Lithium-ion batteries (LIBs) have become the prime choice as an energy storage means for EVs and electrical grid storage. LIBs are made of critical materials such as lithium, cobalt, nickel, and graphite, which are expensive and found in sensitive regions of the world [7]. Sodium-ion batteries (SIBs) have recently become prominent in the battery ecosystem due to their low cost and use of earth-abundant materials such as sodium, manganese, aluminum, iron, and Prussian blue (iron cyanide) [8]. SIBs have a few other advantages in terms of their wider range of operating temperature, faster charging rate, longer life span, and safety considerations. They can be also transported at 0 V due to use of copper-free current collectors and have similar form factors as LIBs [9]. Initially, SIBs were considered only for grid storage applications, but recently a few automotive andbattery manufacturing companies have announced that they will be using SIBs in EVs. The performance of SIBs is appropriate for two-wheelers and other lower-range vehicles which are available in the market. For premium vehicles, the strategic use of SIBs along with LIBs has been proposed, where the energy density requirements will be met by LIBs and the high power requirements by SIBs with lower energy densities and longer life spans [10; 11]. There are a multitude of hard carbons derived from the carbonization of organic biomass which have shown some potential for use as anodes for sodium-ion batteries; however, their varying microstructures exhibit diverse electrochemical behaviors, making practical applications very challenging. Soft carbons possess more graphitic crystallinity and higher electronic conductivity, which lead to superior rate performance. However, soft carbon still suffers from a lower specific capacity and poor low initial coulombic efficiency (ICE). Diamond-like carbon (DLC) films with a comparatively higher sp\({}^{3}\) content have been used as anodes for lithium-ion batteries in the literature [12; 13]. Therefore, the search for a low-cost alternative to current carbon anodes for SIBs is an ongoing topic of research. [PERSON] et al. [14] and [PERSON] et al. [15] have conducted detailed reviews on the performance of different hard and soft carbons. Table 1 lists the performance of a few selected hard carbons. In this paper, we focus on quenched carbon (Q-carbon), which is a new allotrope of carbon which provides an alternative anode material for SIBs with higher initial coulombic efficiency (ICE), power, and stability. Q-carbon consists of randomly packed tetrahedra with about 80% sp\({}^{3}\) and 20% sp\({}^{2}\) bonding. Q-carbon was synthesized originally by pulsed laser melting and quenching from an undercooled state. More recently, we have synthesized Q-carbon via plasma-enhanced chemical vapor deposition (PECVD) and arc discharge methods, which are suitable for wafer-scale integration of thin-film heterostructures and bulk scale-up processing, respectively. The Q-phases of carbon possess many extraordinary properties, including a higher hardness than diamond, room-temperature ferromagnetism, enhanced field emission, and record BCS superconductivity upon doping with boron [1]. In this paper, we compared two carbons, namely Q1 and Q2, where Q1, the control for this study, is an amorphous nanocarbon that has a slower cooling and Q2 is Q-carbon with rapid undercooling.