People know that perovskite materials have qualities like being able to carry electricity, being superconducting, not being magnetic, being dielectric, ferroelectric, and piezoelectric. They are shaped like the substance CaTiO3 and can hold about 90% of the metals in the periodic table at spots A and/or B while still having the unique perovskite structure. Because of the full or partial replacements of cations, this makes it possible to make many different mixtures and molecules with a wide range of qualities.
Because of their electrical, visual, and magnetic qualities, perovskite materials have been studied in a lot of different ways. Because they are stable at high temperatures and can break down substances, they have also been used to clean up waste. Sensing and adsorbing different water- and gas-phase species are some of the other uses.
In the area of electrochemistry, perovskite materials have been used as fuel cells and reusable batteries? EuTiO3 and CaMnO3 are perovskite materials that are used in engineering. They are used to make energy-harvesting devices, solid oxide fuel cells, doped LaFeO3 and LaCoO3, oxygen membrane separation, gas sensing, photocatalytic cells, and doped BaSrO3 and BaFeO3.
Perovskite materials have also been looked at for use in batteries, like as negative electrodes in Ni/MH batteries and Li-ion and Li-air batteries. This chapter is mostly about going over perovskite materials that can be used in batteries and explaining the key ideas in this area.
Perovskite Structure
The mineral Perovskite (CaTiO3) was found by Gustav Rose in Russia in 1839 and gave the materials their name. They have a crystal cubic structure with space group Pnma (Pm3−m cubic system). ABO3 is the general formula for ideal perovskite oxides. A is a rare or alkaline earth metal, and B is a first-row transition metal. In this form, cations with a big ionic radius connect to 12 oxygen atoms and live in A-sites. On the other hand, cations with a smaller ionic radius connect to 6 oxygen atoms and live in B-sites.
Goldschmidt’s tolerance factor (t) shows that the perovskite structure is most stable when it is close to the unit, which makes a cube-shaped structure. When t is not the same as the unit, the crystal structure changes from cube-shaped to orthorhombic, hexagonal, tetragonal, and monoclinic. In the range of 0.75 to 1, perovskites form.
There are hundreds of substances with the perovskite structure, including bridgmanite, FeMgSiO3, and Sr3Ti2O7, which is often found in rocks. Layered perovskites are different from ideal cubic perovskites because they have a double-perovskite structure made up of blocks of ABO3 structure that are divided by a secondary structure. There are three main types of layered perovskite structures that can be separated: hexagonal-type structures, Perovskite-like layered structures (PLS), and Dion-Jacobson-type structures. Because they have interesting ferroelectric and electrical qualities, the AnBnO3n+2 PSL family has gotten a lot of attention for use in technology.
Preparation Methods
There are different ways to make perovskite oxides, but the three main ones are the glycine-nitrate method, the solid-state reaction route, and the sol-gel process. Nitrates are used as sources in the glycine-nitrate method, nitric or stearic acid is used as a solvent, and glycine is used as fuel. The mixture is heated until the extra water disappears. The thick liquid that is left is self-ignites and is calcined at 1200 K for 3 to 5 hours. People have used this method to get perovskite powders that can be used in batteries for things like making negative electrodes for Ni/MH batteries.
In the solid-state reaction method, pure reactant oxides and carbonates or salts are mixed mechanically and then heated to 1500 K. This path is usually taken for 8 to 24 hours, which lets the cations move around and helps the perovskite-type structure form. Most of the time, the processes happen at the point where two objects meet, where ions move from the body to the point where the particles meet. Often, the material that has been fused is ground to make micrometric powders that are then used to make battery electrodes.
A popular way to make perovskite-type oxides is with the sol-gel method, especially the “Pechini” method. To use this method, you need to mix compounds (nitrates and/or oxides) with a chelating agent, ethylene glycol as the sol-forming product, dry the mixture, and heat it up. Using this method, researchers have made ABO3 perovskite-type powders in the past.
The sol-gel method is often used when very small particles are needed because it can make powders of nanometric size while keeping the makeup uniform. This makes it appealing for use in batteries, where the processes of diffusion and kinetic depend on the surface area and chemical make-up of the materials.
It is thought that the solid-state reaction method is a high-temperature process that can make micrometric powders. To get pure oxide crystals, the calcination temperature needs to be higher and the time needs to be longer. One example is a stacked perovskite-type oxide (Nd2Ti2O7) that was made using the sol-gel method. As building blocks for Ti and Nd, tetrabutyl titanate (Ti(OBu)4) and Nd2O3 were used. An equal amount of Nd and Ti was used, and the amount of citric acid was found by dividing nCitricAcid by (nNd + nTi).
The neodymium titanate powder that had been heated up was studied using DSC–TGA curves in air that was not heated up and a heat-moving speed of 20 °C/min. X-ray diffraction (XRD) with a specular reflection mode was used to look at the crystal structure of the calcined neodymium titanate powder. The XRD pattern showed that the result has a high level of crystallinity. It is a single phase of stacked perovskite Nd2Ti2O7 that is numbered based on a monoclinic structure.
Scanning electron microscopes (SEM) and laser diffraction tools were used to look at the calcined powder’s shape and particle size distribution. The results showed that the particles were not round and made groups of small nanometric powders with an average particle width of 3.601 lm.
Any of these ways can be used to get perovskite-type oxide powders, which are then usually further processed to make electrodes or bulk parts that are used in batteries. In the next part, we’ll talk about specific ways that perovskites can be used in batteries.
Perovskite Materials in Batteries
A lot of research has been done on perovskite-type materials to find uses in metal-air, Li–ion, and Ni–metal hydride (Ni–MH) batteries. Metals are oxidised at the anode of the metal-air technology, and oxygen is reduced at the air-breathing cathode during discharge. On the air diffusion cathode’s surface, catalyst particles are often used to remove O2 from the air. Aqueous or aprotic electrolytes are often used in these kinds of batteries.
The Li–ion battery technology has also been a good place for perovskite materials to be used. When the cell is charged (positive delithiation) and then discharged (positive lithiation), lithium ions can move back and forth between the positive and negative electrodes. This is how the cell works. For each anode, there are “active materials” or “intercalation materials” that can be put into or taken out of their solid structure by lithium ions.
When it is used, the negative electrode lets go of lithium ions that move through the liquid (ions conductor) and join the active material’s crystal structure at the positive electrode, where a reduction process takes place. Each lithium-ion that goes through the battery’s internal circuit is perfectly balanced by an electron going through the external circuit. This keeps the terminals electrically neutral and creates an electric current.
Another type of battery technology that uses perovskite materials is called Ni–MH or Ni–oxide technology. The positive electrode (cathode) in this technology changes from a +2 to a +3 oxidation state when it is charged. This is caused by an electrochemical process. When protons are released from the cathode, they mix with hydroxide ions in the solution again. A molecule that stores hydrogen in the anode does so in a way that can be undone. When the battery is being charged, the voltage splits water molecules into hydroxide ions and hydrogen protons. This lets the hydrogen protons come into touch with the metal that stores hydrogen. A hydride is made when protons enter the mass of the metal. This is caused by the voltage and the diffusion caused by the concentration difference.
A lot of research has been done on perovskite oxides as catalysts for Li–air batteries. These are needed to lower kinetic losses caused by the splitting and re-forming of the O–O bond at the cathode that breathes air. They are very good at catalysing reactions and are often used as fuel cell catalysts. LaNiO3 is an example of a perovskite oxide that is used as a catalyst in Li–air batteries. It has high catalytic activity when the structure in the B-site has a single electron filled, which makes the bond energy for the O–O bond for the ORR and OER better.
Perovskite materials have also been looked at as cathode materials for Li–ion batteries. For a high energy density, the cathode materials need to be able to conduct both ions and electrons well. Researchers are interested in perovskite oxides because they can change their electronic properties by adding A- or B-sites. In addition, perovskite materials can be used to help Li–ions move in and out of cells during the charging and discharging processes. La1-xLixTiO3 and LiNi1/3Co1/3Mn1/3O2 are two perovskite oxides that have been studied as cathode materials for Li–ion batteries.
ABO3 perovskite systems have mostly been studied for their electrical qualities for the anode of Ni/MH batteries, which is how what are usually called Ni–oxide batteries are made. Previous research has shown interesting things about their electrical ability and cycle life, especially when they are in harsh environments. According to research, perovskite materials can act as catalysts in hydrogen-rich environments. This is what led to the study of these materials as electrolytic hydrogen storage.
Perovskite oxides are used in Ni–oxide batteries because they are good at catalysis and electrical transport. For example, different types of elements and ratios can be added to perovskite oxides’ A- and B-sites to change their electrical properties. Perovskite oxides are also useful for Ni-battery applications because they are resistant to rust and don’t change much when heated.
Esaka et al. did one of the first studies to use perovskite oxides in Ni–oxide batteries. They found that (SrCe0.95Yb0.05O3) was used as the negative electrode material for these batteries. At room temperature, the mixture was able to absorb and release hydrogen ions in water. Perovskite oxides have been studied a lot as negative electrode materials for Ni–oxide batteries that work in water.
Adding hydrogen to perovskite oxides, which are used as negative electrodes in Ni–oxide batteries, affects the system’s ability to store electricity. Hydrogen is absorbed when the amount of water at the contact between the solution and the electrode decreases. This is where hydrogen protons are added to the perovskite structure.
Because they have better electrical qualities, perovskite oxides show promise as a negative electrode material in Ni-oxide batteries. What makes the chemical bond between oxygen and the hydrogen protons in perovskites stronger depends on how strong the link is between the oxygen and the transition metals on the perovskite structure. Researchers have found that doping changes the chemical links and electronic structure, which makes the electrical qualities better.
The electrochemical capacity of perovskite oxides increases with temperature because the atoms move more freely at the electrode/electrolyte contact, and the oxides don’t rust. While the exact ways that higher temperatures may lead to better electrochemical capacities have not been fully studied, it is thought that more hydrogen protons may be added to the perovskite structure. It has been said by some writers that perovskites usually have free hydrogen atoms because the H-O bonds break down with temperature.
However, not much research has been done on using stacked perovskite materials as negative electrodes for Ni-oxide batteries. The basic lattice arrangement is a key factor that affects the electrical qualities of perovskites. It might be interesting to compare how stacked perovskites work with how traditional ABO3 compounds work. This book part talks about one of the first studies that looked at layered perovskites as negative electrode materials for Ni-oxide batteries. It focusses on how to make the electrodes and the electrochemical tests that were done on a layered perovskite oxide.
Layered Perovskites as New Electrode Materials
in Ni–Oxide Batteries
Compared to regular ABO3 oxides, layered perovskite oxides have a more complicated structure that includes channels and different shapes. This difference could affect how well they work electrochemically. Layered perovskites can allow the introduction of hydrogen protons because they can absorb hydrogen in places related to oxygen. This work shows a new way to look at stacked perovskites as an electrode material in Ni-oxide batteries. We made a nanometric powder of the Nd2Ti2O5-layered perovskite substance using the sol-gel method. This powder was then used to make negative electrodes for a Ni-oxide cell.
Nd2Ti2O5 Electrode Preparation and Electrochemical
Setup
The “latex” method was used to make the Nd2Ti2O7 electrodes. This involved mixing the Nd2Ti2O7 nanometric powder with black carbon and polytetrafluoroethylene (PTFE) to make sure the electrodes would carry electricity well and be easy to handle during electrochemical tests. The weight ratio was 90:5:5, and ethylene glycol was added to make a paste that was both thick and stretchy. As a current collector, a 1 cm2 Ni-mesh was used. The paste was then dried for two hours to get rid of the solvent. The active material was then put on the Ni-mesh by pressing it down with 40 MPa of force. A normal three-electrode open-air cell was used to test how well the electrodes worked with electricity.
Nd2Ti2O5 Electrochemical Performance
To look into the electrochemical processes of the Nd2Ti2O7 electrode in a 6 M KOH solution, cyclic voltammetry tests were done. A peak for oxidation was seen at -0.9 V compared to the Hg/HgO reference electrode, and a peak for reduction was seen at -0.625 V compared to the Hg/HgO reference electrode. These redox peaks show that an electrochemical process can be turned around on the Nd2Ti2O7 working electrode. When compared to the electrodes that are usually used in Ni–MH batteries, these peaks show similar potential values.
The hydrogen desorption peak shows up before the hydrogen electrochemical oxidation peak, which suggests that hydrogen may be able to chemisorb. The decrease peak also gets clearer as the number of cycles goes up, which suggests that the Nd2Ti2O7 electrode may be working. The area under the curve of the stacked perovskite is bigger than that of the Ni-mesh, which shows that the material has a higher ability to conduct electricity.
We used the chronopotentiometry method to measure the charge/discharge features of the Nd2Ti2O7 negative electrode in order to figure out how much power the stacked perovskite electrode could hold. It was possible to fully charge and discharge the working electrodes at steady current levels of 10, 30, 60, and 125 mA/g.
In Table 2, the electrochemical capacity of the stacked Nd2Ti2O7 perovskite molecule is about the same as the electrochemical capacity of regular ABO3 perovskite oxides. How much electricity the electrodes can hold depends on how many rounds they go through. No matter what current density is used, the electrodes’ capacity rises to a maximum and then stays the same. Based on this finding, it seems that this stacked perovskite material needs to be energised electrochemically, like intermetallic electrodes used in regular Ni–MH batteries do.
In this study, the potential-step discharge method was used to figure out the hydrogen diffusion coefficient of the Nd2Ti2O7 oxide. Using a potential step and keeping an eye on the anodic current–time reaction is what this method does. This experiment gave us a semi-logarithmic curve that is often split into two time regions. In the first one, the current drops quickly because the hydrogen on the electrode’s surface is used up so quickly. In the first area, charge transfer kinetics or charge transfer and diffusion (mixed kinetics) tell the story. In the second-time region, on the other hand, the hydrogen diffusion controls the current as it slowly drops over time in a straight line.
What we found in this chapter suggests that stacked perovskite materials can be used as electrodes for Ni–oxide batteries because they can work both ways and store hydrogen electrochemically. To compare the ways that conventional perovskites and stacked perovskites work, more research should be done using methods like impedance and molecular dynamic models.
Perspectives and Suggestions Regarding the Selection
of Perovskite Materials for Ni–Oxide and Metal–Air
Batteries
Ni-oxide batteries work better when the perovskite electrode is made of a doped material. The ABO3 product has mostly orthorhombic or rhombohedral structures, which depend on the dopants that are used. ABO3 perovskite materials need a lot of different elements, some of which are rare, in order to have good electrical abilities. Understanding how layered perovskite materials like A2B2O7-type molecules behave is just the start. More tests with different ratios need to be done.
For metal-air batteries, the main goal is to create anode materials that are better at catalysis, ideally small bits with a lot of surface area. Because it holds a lot of energy, reusable metal-air battery technology is likely to become one of the most popular technologies in the future. The slow rate of charging and draining at the air electrode is an important problem that needs to be fixed before the metal-air technology can be used in real life.
Concluding Remarks
A lot of research has been done on perovskite materials and how they can be used in batteries, especially as catalysts and anode materials in Ni–oxide, Li–ion, and metal–air batteries that can be charged and used again and again. These materials have changeable electrical behaviour, are easy to make, don’t cost much, and are safe for the environment. They are often used to move ions around in whole cells. Different chemistry methods can be used to make different kinds of structure perovskites, which opens up possibilities in different kinds of batteries. One example is stacked perovskite, which hasn’t been looked into yet as a material for the negative electrode of Ni–oxide batteries. Stacks of perovskite materials can be used as a replacement for the electrodes in Ni–oxide batteries. ABO3 perovskite oxides have a high charging rate at high temperatures. This makes them a popular choice for negative electrode materials in Ni/oxide batteries that work well at high temps. It is believed that more study will help improve the features and performance of A2B2O7 stacked molecules. This will help find the perovskite-type structure that works best for electrochemistry.
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