**2. Battery electrochemistry performances evaluation**

Specifications comparison is a major preliminary requirement for a battery to be implemented for any defined application [12]. This section discusses the performance, *Sizing and Lifecycle Assessment of Electrochemical Batteries for Electric Vehicles… DOI: http://dx.doi.org/10.5772/intechopen.110121*

#### **Figure 1.**

*Technology readiness levels of EV and RES electrochemical batteries.*

internal electrochemical phenomenon details, and redox reactions of the 14 EV and RES chemistries analyzed in **Figure 1**. The effect of Depth-of-Discharge (DOD%) on separate chemistries is also studied in this section, which is an important factor for the case studies discussed in Section 4.

#### **2.1 Lithium based batteries**

Lithium is a highly researched cell chemistry because of its high specific energy, high cycle life, low self-discharge, and high nominal voltage [13–20]. It supersedes other chemistries such as Lead-acid, Nickel Cadmium (Ni-Cd), and Nickel Metal Hydride (Ni-MH) in almost every category except in over charge and over discharge situations [21]. This sub-section compares and evaluates various commercially available and under development Li-ion chemistries used in EVs and RES systems. Common Lithium chemistries categorized by their properties, composition, along with their possible uses are listed in **Table 1**.

Lithium Manganese Oxide (LMO or *LiMn*2*O*4) has a spinel structure with a nominal voltage of 3*.*8 *V* (Eq. 1) [43, 44]. Its low cost and high thermal stability are attributable to the addition of Manganese. Manganese is cheap and low in toxicity, but does not have a high specific energy. This has led to the development of the Lithium Nickel Manganese Cobalt Oxide (NMC or *LiNiMnCoO*2) chemistry. NMC type lithium cells are created through the addition of Nickel [43, 44]. Nickel, on its own,


*Labels: Poor (), Good (+), Very Good (++), Excellent (+++).*

*RES: Renewable Energy Storage; EV: Electric Vehicles; HEV: Hybrid Electric Vehicles; R&D: Research and Development; Dem.: Demonstration Stage; Com.: Commercialized.*

*\*as per [41, 42], still undergoing R&D.*

*† Manufacturer dependent. Standard organic solution is ethylene carbonate (EC)–dimethyl carbonate (DMC) mixture.*

#### **Table 1.**

*Lithium based batteries comparison based on their electro-chemistries.*

provides high energy density but lower thermal stability, therefore Manganese is added to create a more stable chemistry (in NMC) that increases cycle life and stability (Eq. 2) [45].

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

$$LiC\_6 + Mn\_2O\_4 \leftrightarrow LiMn\_2O\_4 + C\_6\tag{1}$$

$$LiC\_6 + NiMnCoO\_2 \longleftrightarrow LiNiMnO\_2 + C\_6 \tag{2}$$

Lithium Iron Phosphate (LFP or *LiFePO*4) batteries, on the other hand, have improved safety and thermal stability due to the addition of Iron that creates the olivine structure (Eq. 3) [43, 44]. Subsequently, these cells can operate at higher temperatures effectively, however, their specific energy tends to be lower than that of other lithium chemistries, especially Nickel Cobalt Aluminum Oxide (NCA or *LiNiCoAlO*2) [45, 46]. NCA has a high specific energy and lower thermal stability, both owing to the addition of Nickel [45, 47]. Aluminum present in NCA creates a similar layered crystal structure like in NMC (Eq. 4) [43, 44]. Comparison between LFP, NMC, and NCA in [48] showed that an increasing SOC % increases the temperature of LFP by around 0.8°C per SOC value. The corresponding values for NMC and NCA increase by 1.02°C, and 1.74°C per SOC % respectively. The NCA lithium battery has twice the potential to catch fire if overcharged, when compared to LFP. This further emphasizes the importance in selection of correct lithium chemistries and in general, an effective battery management system for EV and RES applications.

$$\rm LiC\_6 + FePO\_4 \leftrightarrow LiFePO\_4 + C\_6 \tag{3}$$

$$\rm LiC\_6 + NiCoAlO\_2 \leftrightarrow LiNiCoAlO\_2 + C\_6 \tag{4}$$

Lithium Titanate (LTO or *Li*4*Ti*2*O*12) has a low specific energy and high cost (Eq. 5) [43]. In addition, its nominal voltage is very low. An EV or RES manufacturer would need to practically double the number of cells in series to reach the same voltage as the NMC/NCA/LMO chemistries. This will greatly increase the cost and weight of the vehicle and decrease the amount of usable space. These batteries also contain a unique anode composed of LTO which drastically increases its thermal stability and cycle life when compared to other Lithium chemistries. The improved safety/lifespan of LTO can be attributed to the limited expansion of the anode (only 0*.*2% of volume changes) during charge/discharge operation [45].

$$Li\_4Ti\_5O\_{12} + Mn\_2O\_4 \leftrightarrow Li\_2Ti\_5O\_{12} + LiMn\_2O\_4 \tag{5}$$

Combination of phenomena of Lithium oxidation at the anode, and oxygen reduction at the cathode, using electrolytes ranging from solid state, to aqueous, nonaqueous, or aprotic solvent variants, results in the formation of the Lithium Air (*LiO*2) battery. This anode and cathode pair creates a practical specific energy of 18.7 MJ/Kg, which is about 10–15 times higher than that of a commercially available Li-ion battery [49]. Oxygen molecules entering cathode through the porous cathode react with *Li*<sup>+</sup> ions moving from the anode via an electrolyte, to form Lithium Peroxide (*Li*2*O*2) while the electrons flow through the external load during a discharge operation, constituting the redox reaction shown in Eq. (6).

$$2Li^{+} + O\_{2} + 2e^{-} \leftrightarrow LiO\_{2} + Li^{+} + e^{-} \tag{6}$$

*LiO*<sup>2</sup> batteries can operate effectively at temperatures up to 140°*C* [50]. They are still under development mainly due to their varying performances with changing electrolytes. *LiO*<sup>2</sup> started off as an accidental discovery by K. M. Abraham in 1995 while using a non-aqueous electrolyte [51] however deposition of *Li*2*O*<sup>2</sup> on the cathode electrode with time called for more exploratory research. Liu et al. [52] in 2015 proposed the addition of lithium iodide and water to make the electrodes spongy along with a hybrid (combination of solid state and aqueous) electrolyte, thereby resulting in Lithium Hydroxide crystals which do not coat the surface and impede the flow of electrons, allowing continuous voltage supply. Although this research improves the operational lifetime of the battery, it reduces the overall specific energy due to the inclusion of water.

NCA, LTO, and NMC have sloping discharge curves while LMO, LFP, and *LiO*<sup>2</sup> have flat discharge curves (**Table 1**). Understanding charge/discharge characteristics of each chemistry is important when selecting a cell to be tested for an application. Generally, the sloping discharge curve reduces the complexity in model selection since the voltage level decreases almost proportionally with SOC%.

The ease with which the electrochemical reaction will occur depends on the ionic/ electrical conductivities. Lower conductivities will result in greater resistance and lower efficiency in the conversion from chemical to electrical energy. These values heavily depend on the central testing conditions [17]. Furthermore, for the electrolyte, the ionic conductivity is an important consideration with high conductivity being ideal. During charge and discharge cycles, Lithium ions are shuttled across the electrolyte to the anode and cathode, respectively. Decreased resistance from Lithium ions traversing from anode to cathode and vice versa will mean less heat generation and increased efficiency of the cell [53–56].

Every Lithium chemistry eventually degrades over time from a variety of factors. Solid electrolyte interphase (SEI) development is one of the main contributing factors to degradation. The formation of this layer is important because it allows Li-ion transportation but prevents electrons from moving through resulting in further decomposition of the electrolyte [57].

In addition to charging or discharging operations, factors like storage and thermal conditions also play a major role in SEI formation. The authors in [58] show that the capacity of batteries being stored drastically declines with the increase in temperature. Lithium batteries have a good shelf life but are still prone to losing capacity if stored for an extended period. Increased depth of discharge (DOD) also decreases the cycle life of the cell. Data from [59] shows that discharging the cell too deeply will greatly impact its capacity after many cycles. After 25*,*000 cycles, a cell discharged at a consistent 30% DOD lost 53% of its capacity, while a cell discharged at 20% DOD lost 40% percent of its capacity with both being at 20°C. Based on these findings, it can be concluded that DOD has a substantial effect on the cycle life of a Lithium-ion battery. Moreover, a decrease in the cell's capacity over many cycles caused by the aforementioned conditions leads to internal issues that are reflected in the cell's available capacity. Some examples are Lithium plating at the anode from high charge current, SEI formation on the anode from electrolyte decomposition due to high temperature/ DoD, and volume changes on the anode and cathode due to all of the above stated conditions [60]. Other additional comparative features of the discussed Lithium based chemistries are tabulated in **Table 1**.

#### **2.2 Pb-acid based batteries**

Physicist Gaston Plante invented the Pb-acid based battery, which is comprised of lead dioxide (*PbO*2) as the anode, lead (Pb) plate as the cathode, and aqueous sulfuric acid (*H*2*SO*4) as the electrolyte. The reaction mechanism of these batteries relies on

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

oxidation (on the anode) and reduction (on cathode) reactions and follows the redox reaction shown in Eq. (7):

$$Pb + PbO\_2 + 2H\_2SO\_4 \leftrightarrow 2PbSO\_4 + 2H\_2O \tag{7}$$

The electrical turnaround efficiency of these batteries is 75–80% with specific energy ranging between 30 and 50 Wh/kg [61], which is much lower than other EV or RES battery chemistries. Also, the cycle life of these batteries is comparatively short (< 2000 cycles) [62]. Sulfation is one of the major causes of this lower cycle life, which impedes recharging and causes cracking into the electrode plate [63]. This incident causes inadequate charging during regular operation due to amorphous lead sulfate deposits on the negative electrode, which turns into a crystalline structure in a progression. Consequently, the active materials of the negative electrode are covered with this additional layer. This issue can be resolved by integrating the high content of carbon into the lead electrode, which promotes the self-recharging rate and cycle life [63]. The formation of the carbon-Pb alloy accelerates water loss and inner pressure due to the hydrogen evolution reaction [64, 65]. This reaction mechanism involves either absorption or desorption of the intermediate hydrogen by the electrode surface in two separate routes termed as the Volmer-Tafel and Volmer-Heyrovsky mechanisms [66, 67]. The activated carbon doped with heteroatoms (e.g., N, P, B, or S) in the graphene ring improve the charge acceptance and charge retention ability of the Pb-acid based battery and inhibits the hydrogen evolution reaction. Also, Pb-acid requires an additional mandatory thermal management system for reliable temperature efficiency. Moreover, they are bulky in weight, require prolonged charging time and cyclic water maintenance, and suffer from premature failure and degradation at high power operation. However, on the upside, these batteries are cost-effective (in manufacturing and maintenance) and easily recyclable (≥ 97% recycling efficiency) [68]. Additionally, their charge retention capability is compatible with both grid and automotive applications. For obtaining the required power/energy ratings, an array of Pb-acid battery cells are connected in such a way that each cell voltage and range of charging rate are 2.15 V and 0.25–4, respectively [69]. Pb-acid batteries are mostly employed as a backup power supply in the range of kWs to tens of MWs for grid utilities and hybrid electric vehicles. All the comparative features of this chemistry are tabulated in **Table 2**.

#### **2.3 Ni-based batteries**

Ni-based batteries are classified into two broad categories: Ni-Cd based batteries, and Ni-MH based batteries. Generally, nickel oxyhydroxide is used as the anode, and Cd or MH, are employed as the cathode. The electrolyte is an aqueous alkaline solution, such as aqueous potassium hydroxide (KOH), used for both Ni-MH and Ni-Cd based batteries. Zn, Fe, or *H*2-based Ni batteries are also used in the applications tabulated in **Table 2**.

Compared with Ni-Cd or Ni-MH based batteries, these Ni-based chemistries have limitations in terms of energy density (low), efficiency (low), maintenance cost (high), lifecycle (low), and self-discharging issues [92]. Contrarily, Ni-Cd performs with 70–90% efficiency, has moderate energy density (50–75 Wh/kg), higher lifecycles (2000–2500), a 10%/month self-discharging rate, and better temperature tolerances [69, 93, 94]. However, both the Cd and Ni chemistries are considered as hazardous substances, and the manufacturing costs of Ni-Cd batteries are also


 *Renewable Energy Storage; EV: Electric Vehicles; HEV: Hybrid Electric Vehicles; R&D: Research and Development; Dem.: Demonstration Stage; Com.: \*StillundergoingR&D.*

#### **Table 2.**

*Pb, Ni, Na, Al-based and redox batteries comparison based on their electro-chemistries.*

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

relatively high (\$1000/kWh and ten times higher than Pb-acid based batteries). The electrodes, electrolyte, and separator (insulator between anode and cathode) are placed in a low cost and flame-retardant polymer (e.g., polypropylene, polystyrene) container for these batteries. The redox reaction for Ni-Cd based batteries is shown by Eq. (8).

$$\text{Cd} + 2\text{NiOOH} + 2\text{H}\_2\text{O} \leftrightarrow \text{Cd}(\text{OH})\_2 + 2\text{Ni}(\text{OH})\_2 \tag{8}$$

Ni–MH batteries are the other category which is commercially established for the uninterrupted power supply in different applications, such as grid systems, hybrid electric vehicles, and communication systems. Different metal hydrides and Nickel hydroxide (NiOOH) are employed as the anode and cathode, respectively [73]. The overall charging and discharging reaction mechanism in Ni-MH based batteries follows Eq. (9):

$$\text{MH} + \text{NiOOH} + 2\text{H}\_2\text{O} \leftrightarrow \text{M} + 2\text{Ni}(\text{OH})\_2\tag{9}$$

Both the anode and cathode are porous in structure. Therefore, they have a large surface area, which enhances the rate of reaction and internal conductivity. Hence, their energy density (40–110 Wh/kg) is higher than Ni-Cd based batteries. Additionally, this battery system is environmentally benign, has high charging and discharging tolerance, longer shelf, cycle life (�3000 cycles) and can operate in a wide temperature range (30–70°C). However, both above-mentioned Ni-based chemistries suffer from the "memory effect", which happens due to incomplete discharges in preceding uses. Consequently, the energy capacity and rated output potential abruptly deteriorate leading to another effect termed as the "voltage depression effect" [95]. However, this effect can be mitigated by proper charging-discharging management of the battery systems. All the comparative features of both of these chemistries are also tabulated in **Table 2**.
