1
Fundamentals of Nanomaterials in Energy Systems

Ricardo Antonio Escalona-Villalpando1, Fabiola Ilian Espinosa-Lagunes1, Luis Gerardo Arriaga Hurtado2, and Janet Ledesma-García1

1Universidad Autónoma de Querétaro, Facultad de Ingeniería, División de Investigación y Posgrado, Cerro de las Campanas s/n, Santiago de Querétaro, 76010, México

2Tecnológico de Monterrey, Institute of Advanced Materials for Sustainable Manufacturing, Epigmenio González 500, Santiago de Querétaro, 76130, México

1.1 Introduction

Nanomaterials, such as nanoparticles, nanotubes, nanowires, and quantum dots, are of interest in various application areas of technology. They are revolutionizing energy systems and improving the efficiency of energy conversion, storage, and utilization processes due to their properties, such as surface with excellent electron transport capacity, physicochemical properties, mechanical strength, and unique dimensions, which offer advantages and advances in new technologies [1-5]. These properties of nanomaterials have become interesting for supercapacitors, fuel cells, solid-state batteries, photocatalysis, light-emitting diodes, hydrogen storage systems, etc. [1, 2, 6-10].

However, the integration of nanomaterials into energy systems is associated with challenges, such as sustainability and renewable energy, improving energy storage, reducing environmental impact, and conditioning materials with specific system properties [1, 11]. For example, suppose that the size of nanomaterials in semiconductors is reduced (Figure 1.1). In this case, the band gap increases due to the quantum confinement effect, and the optical properties such as absorption, emission, and excitation can be adjusted [12-14]. In solar energy applications, nanomaterials can significantly improve the light absorption and conversion efficiency of photovoltaic cells. In battery technology, these materials achieve higher energy densities, fast charging times, and a long service life [10, 15, 16]. For the development of fuel cells, supercapacitors, and hydrogen storage, nanomaterials facilitate efficient electrochemical reactions in the storage of large amounts of energy in a compact form, making them indispensable in the search for next-generation energy solutions [6, 12, 17-21]. Compared to carbon-based nanomaterials, which have minimal surface defects, this composition is critical as an alternative to stainless steel or iron for mechanical strength and stability. Further studies are required to confirm its feasibility as a replacement.

Figure 1.1 Schematic overview of the applications of nanomaterials in various fields.

Understanding the fundamentals of nanomaterials and their applications in energy systems is critical for research groups seeking to innovate and improve energy technologies [4, 13, 22, 23]. This introduction provides an overview of the progress and potential future directions in the field of nanomaterials for energy storage and conversion of energy systems.

This chapter highlights future research opportunities and proposes solutions to bridge the gap between fundamental research and real-world applications in next-generation energy technologies.

1.1.1 Nanomaterials in Battery Systems

Nanomaterials have significantly improved energy conversion and storage in battery systems, especially in lithium-ion, Li-S, metal-air, and solid-state batteries. They improve electrochemical reaction kinetics; reduce ion diffusion pathways; and improve stability, surface area, cycle life, and miniaturization. The main components of battery systems in which energy conversion takes place are the cathode, the anode, the separator, and the electrolyte. Together they ensure the cell voltage (E), the energy and potential density, the stability, and the service life.

Lithium-ion batteries (LIBs), as shown in Figure 1.2, typically use graphite for the anode and LiCoO2 for the cathode, resulting in an energy density of around 150?Wh?kg-1. This energy density is achieved by the movement of lithium ions through the internal passageway and electrons through the external circuit, which eventually return to the positive electrode. The following equation illustrates the ideal electrochemical reactions that take place during the charge/discharge process, with the cathode reaction represented by given Eqs. (1.1) and (1.2) showing what happens in the anode [24].

Figure 1.2 Schematic of a lithium-ion battery (LIB).

Research into nanomaterials in LIBs has significantly improved their efficiency in meeting new energy needs, e.g. in electric vehicles and trains, and even in meeting lower energy needs, e.g. in biomedical devices. For example, Si-based nanomaterials have attracted interest as anode electrode materials due to their theoretical capacity of 4200?mAh?g-1 compared to that of graphite (372?mAh?g-1).

1. Nanomaterials for the Anode

   Conventionally, graphite is the most widely used material in LIBs, although this material tends to degrade, limiting its useful life. Carbon-based nanomaterials, such as carbon nanotubes (CNTs), carbon nanofibers, porous carbon, and graphene, have been investigated to reduce this drawback. In addition, other nanostructured materials that are not carbon-based have been reported. These include Ti/TiO2-based materials, Si-based materials, spinel Li4Ti5O12, germanium, and metal oxides as iron and cobalt, which have the potential to improve the performance of the anode [25].

2. Nanomaterials for the Cathode

   Lithium nickel manganese cobalt oxide (NMC) and lithium manganese oxide (LMO) usually have a long lifetime with about 500 charge/discharge cycles. NMC offers specific capacities of 150-220?Wh?kg-1, while LMO delivers 100-150?Wh?kg-1. Other Li-based nanomaterials have been reported, such as LiCoO2, LiMn2O4, LiNiO2, LiFePO4, LiMnPO4, LiFeSO4F, LiCoNiMnO2, LiNiCoMnO2O, and lithium-nickel-cobalt-manganese (Li-Ni-Co-Mn), in which there are several monoanionic and polyanionic compounds whose chemistry is favored for their high-energy storage capacity [24].

3. Separator

   The separator is usually a porous material that separates the anode and cathode to prevent short circuits, allowing the battery to charge/discharge. Polymers such as polyethylene and polypropylene are usually used, but they have limitations such as low stability in mechanical strength, low melting points, and lower chemical resistance, which reduce the efficiency of the battery's overall performance. Nanomaterials such as SiO2, TiO2, Al2O3, and SiO2 are alternatives to these inconvenient materials, which mainly bring advantages such as high porosity and chemical and mechanical resistance [25].

4. Electrolyte

   Electrolytes enable the movement of positive lithium ions between the electrodes in LIBs. There are two types of electrolyte materials: solid polymer electrolytes (SPEs) and liquid electrolytes (LEs). An SPE consists of a solid polymer matrix infused with lithium salts. Ceramic nanopowders investigated in this context include Al2O3, SiO2, TiO2, and Li1.4Al0.4Ti1.6(PO4)3, which can be incorporated into polyethylene-based electrolytes to improve stability. In addition, SiO2 (MA-SiO2)-nanostructured materials functionalized with methacrylate are used for electrolytes in LIBs. In recent years, solid-state and gel electrolytes have been investigated and nanomaterials or nanostructured additives have been integrated to improve ion transport in batteries [25].

5. Lithium-Sulfur Batteries (LSBs)

   Another type of battery used in energy systems are lithium-sulfur batteries (LSBs), which have a theoretical capacity of 1675?mA?hg-1 and a gravimetric and volumetric energy density of 2500?Wh?kg-1 and 2800?W?h?L-1, respectively, compared to LIBs. The components of this type of battery are the same as those of LIBs: cathode, anode, separator, and electrolyte. Nanomaterials such as LiCoO2, LiFePO4, LiMnO2, tetratitanium heptoxide (Ti4O7), and Ti-O2-TiN heterostructure have been described for use as cathodes for LSBs, with a discharge capacity of 704?mAh?g-1 at the 2000th cycle. In addition, perovskite-based materials such as La0.6Sr0.4CoO3-d and Ba0.5Sr0.5Co0.8Fe0.2O3?-?d can immobilize polysulfides through chemical bonding between lithium and oxygen or sulphidic and sulfur, resulting in improved performance [26].

   CNTs were used for the anode. Graphene, a 2D nanomaterial, forms nanoparticles together with 3D hybrid nanomaterials and a metal oxide or sulfide clusters, which are added to the sulfur-carbon nanostructures to achieve high performance. Examples are CeO2, Al2O3, La2O3, MgO, and CaO.

6. Zinc-Air Batteries

   Zinc-air batteries (ZABs) use Zn as the reaction electrode due to their cost advantage, reversibility, and a promising...