**2.4 Na-β based batteries**

Following chemical composition and reaction mechanisms, Na-*β* based batteries are classified into the following two types: Sodium-sulfur (Na-S) and sodium-metal halide. A tubular-shaped beta-alumina (*βAl*2*O*3) ceramic is employed as an electrolyte, which acts as a superionic conductor and a separator (between the anode and cathode) simultaneously. All these materials are naturally abundant and inexpensive. In Na-S based batteries, both the cathode (S) and anode (Na) are in molten form. Due to oxidation, *Na*<sup>+</sup> ions are generated at the cathode, which are carried by the *β*-alumina based solid electrolyte. Later, these ions recombine at the anode and vice versa for the reduction reaction. The overall redox reaction for this chemistry is shown in Eq. (10).

$$\mathsf{2Na} + \mathsf{xS} \leftrightarrow \mathsf{Na\_2S\_x} \tag{10}$$

Their energy density and self-discharging rate fall in the range of 140–240 Wh/kg and 1% respectively [96, 97]. Additionally, these batteries have a short response time (1 ms), higher energy efficiency (75–90%), and good recyclability (99%) [69]. At 100% DOD, their lifecycle is around 2500, whereas it increases to 4500 by dropping DOD to 80% [97]. Moreover, this battery system has shown efficient results and is capable of voltage stability (short duration), peak shaving (medium duration), and

load leveling (long duration) grid service requests. These batteries operate at 300– 350°C in a thermal enclosure and have a significant tolerance for running in both cold and hot temperatures. However, the operation in a high temperature promotes corrosion and explosion. Hence, this battery system requires a mandatory thermal management system. In September 2011, a 2000 kW – NaS-based battery system from NGK, consisting of 40 battery modules, exploded at Tsukuba in Japan [98]. Another fire incident occurred in a 30-megawatt Kahuku wind farm in Hawaii [99]. Apart from reasons related to other interconnected components, the main reason on the battery side was that one of the faulty cells was ignited by inundating the molten materials over the filler portion of the blocks and was causing a short between the cells.

The other sodium-based chemistry, Sodium metal halide (*Na* � *MeCl*2) is another alternative and promising battery for the next generation stationary energy storage systems. They have compatible features, which include reliability, resiliency, and higher roundtrip efficiency. The anode and electrolyte of this battery is similar to the Na-S based batteries. However, the cathode is made from a porous transition metal (Ni or Fe) halide matrix infused by an additional secondary electrolyte, sodium tetrachloro-aluminate (*NaAlCl*4). This inorganic electrolyte provides higher ionic conductivity and superior battery safety [100]. The transport mechanism of the *Na*<sup>+</sup> ions through *β*-*Al*2*O*<sup>3</sup> and *NaAlCl*<sup>4</sup> are reversible for the charging-discharging processes. The reaction mechanism between pyrophoric metal (Na) and hygroscopic metal halides is as shown in Eq. (11), where 'Me'stands for Ni or Fe metals.

$$\text{MeCl}\_2 + 2\text{Na} \leftrightarrow \text{Me} + 2\text{NaCl} \tag{11}$$

The theoretical specific energies for Ni and Fe are as high as 788 Wh/kg and 729 Wh/kg respectively. However, the energy density of these batteries lies between 120 and 240 Wh/kg [100, 101]. These batteries can operate over 20 kWh which indicates that they are strong candidates for EV and RES applications. There is no selfdischarge (that is, a coulombic efficiency of 100%) occurrence in this battery, and their cycle life is over 1000 at 100% DOD. Additionally, these batteries are corrosionprotective and can operate in the lower resistive cell-failure mode with better charging/discharging tolerance, which ensures higher safety than that of the Na-S battery system. However, their high manufacturing cost, intricate cell architecture, high operating temperature (300–350°*C*), and performance deterioration with cycling are still a constraint [102, 103]. The high operating temperature is the cause of the high corrosion rate. A high-cost hermetic sealing is essential in this system to prevent this corrosion of the materials and degradation of the performances at high temperatures. All of the comparative features of this chemistry are also tabulated in **Table 2**.

### **2.5 Aluminum-ion (Al-ion) batteries**

In the past few years, Al-ion batteries are considered as one of the promising categories of rechargeable batteries for electric vehicles, renewable energy, and mobile devices. Aluminum, being an abundant material, makes these batteries reasonably accessible with low price in comparison with Li-ion batteries (Lithium is only 0.0065 wt% of the earth's crust) [82, 104, 105]. Lin et al. (Dai group) from Stanford University reported the first paper on such kind of batteries, which consist of aluminum as the anode, an aqueous ionic electrolyte from vacuum dried *AlCl*3/1-ethyl-3 methylimidazolium chloride, and graphite as the cathode [83]. The charging and

*Sizing and Lifecycle Assessment of Electrochemical Batteries for Electric Vehicles… DOI: http://dx.doi.org/10.5772/intechopen.110121*

discharging mechanisms of these batteries rely on the electrochemical deposition/ dissolution of Al at the anodic electrode and the intercalation/deintercalation of chloraluminate ions (*AlCl*� <sup>4</sup> ) in the cathodic electrode based on the reactions shown in Eq. (12) and (13).

$$2\text{Al}\_2\text{Cl}\_7^- + 2\text{e}^- \leftrightarrow \text{Al} + 7\text{AlCl}\_4^- \tag{12}$$

$$\rm AlCl\_4^- \leftrightarrow 2Al\_2Cl\_7^- + Cl^- \tag{13}$$

The nominal voltage obtained from this reaction is around 2 V, and the coulombic efficiency was as high as 98% [105]. These batteries can maintain their lifecycle at around 7500 without compromising significant power density (specific power). Their maximum specific energy and power were obtained to be 3000 Wh/kg and 40 Wh/kg respectively [83]. Moreover, they have a superior recharging ability (1.1 – 60s, with a specific capacity in the range of 60–110 mAh/g) due to their active electrode kinetics and reduced polarization effect. This chemistry is new and still in the research phase. All the comparative features of this chemistry are also tabulated in **Table 2**.

#### **2.6 Flow batteries**

In Vanadium Redox batteries (VRB), Vanadium-anolyte and –catholyte half cells are stored in electrolyte tanks which allow flow through the adjacent half cells and are separated by an ion exchange membrane. During the charge process, Vanadium ions catholyte half-cell, *V* 3+ are converted into *V* 2+ resulting in an electron attracted by the positive electrode (cathode) and hydronium (*H*<sup>+</sup> ) which diffuses into the anode half-cell via the membrane. At the anolyte half-cell, the electron from the cathode (via the external load) converts existing *VO*<sup>þ</sup> <sup>2</sup> in anode to *VO*2+ thereby balancing (with *H*<sup>+</sup> ion) and storing the chemical energy. During discharge process, the stored chemicals start feeding the external load. During this process, the *VO*<sup>þ</sup> <sup>2</sup> ion is oxidized to *VO*2+ releasing the hydronium ion and the process continues until the anode contains *V* 3+ ion and is completely discharged. The applicable redox reaction is shown in Eq. (14) [106].

$$\text{V}^{2+} + \text{VO}\_2^{+} + 2\text{H}^{+} \leftrightarrow \text{VO}^{2+} + \text{V}^{3+} + \text{H}\_2\text{O} \tag{14}$$

Although VRB's have long cycle life and high energy efficiency, they constitute only 30% of the energy storage market share [107]. This is mainly because of its limitations which include high form factor, low volumetric energy storage capacity, expensive ion exchange membrane, and low specific energy in comparison to Li-ion, which constitutes 60% of market share [108].

Another redox flow chemistry used in renewable energy storage, Zinc bromine (Zn-Br) batteries, categorized as hybrid redox flow batteries, include carbon-polymer composites as electrodes isolated by microporous polyolefin membrane (separator). One of these electrodes is submerged into the aqueous solution of zinc bromide as the anolyte. The catholyte comprises of two aqueous phases: a solution of Zn-Br at the top layer and dense bromine in the form of a complex organic solution at the bottom [109]. Aqueous zinc bromide is converted into metallic zinc through the electrolyzation process during charging, and the zinc bromide salt is altered back from Zn and bromine during the discharging process. The applicable redox reaction is shown in Eq. (15).

$$Zn + Br^{-3} \leftrightarrow ZnBr\_2 + Br^- \tag{15}$$

The bromine is expelled during this process and is poisonous, highly oxidative, and less soluble in water. Hence, an additional compound, organic amine, is added to dissolve it in the solution as viscous bromine adduct oil. Additionally, Zn also tends to deposit on the electrode during charging in the form of a dendrite crystal structure with a high current density, which may cause short circuits through the polyolefin membrane [110]. The surface morphology of this electroplated Zn is determined by the current density, temperature of the solution, and the flow velocity [111]. Hence, the overall capacity of energy storage in this battery system relies on the electrolyzation process and the surface area of the electrode, that is, the stacks size and the volume of the electrolyte storage reservoirs. Therefore, the energy ratings of these batteries are not entirely distinct. This battery system requires an obligatory temperature (below 50°C) and oxidation control system for safety, which makes it expensive [112]. The energy density (75–85 Wh/kg), efficiency (65–75%), and cycle life (>2000 cycles) of this battery vary within a moderate range [113]. Some significant advantages of these batteries are their flexibility in ambienttemperature operation, compatible power density in RES and EV applications, fast charging capability, and 100% DOD without any damage to the battery system [11, 89]. All of the comparative features of both of these chemistries are also tabulated in **Table 2**.
