Analysis Of Sodium Cations In Batteries
When looking at this topic, it’s relevant to explain how a battery works. A battery is a container consisting of one or more cells, in which chemical energy is converted into electricity and used as a source of power. The battery setup helps electrons more freely in a circuit. One end of the circuit is positive, called a cathode, and it attracts the electrons in the system. The other end, the anode, is negative and sends the electrons to the cathode. The part in the middle is the electrolyte, and it helps prevent electrons from going straight from the cathode to the anode without frying the system. When batteries are recharged, the system is flipped so that the anode and cathode can be restored and continue working.
There are two main types of batteries, primary and secondary. Primary batteries are not rechargeable, and the chemical reaction within those types of batteries cannot be reversed. Secondary batteries are rechargeable, and when the chemical reaction is reversed, the electrons flow back to the anode and are reduced back to their original charge, giving the battery full power again. If secondary batteries can be recharged, there is a common question as to why primary batteries are still used today, and that is because the primary batteries have a longer shelf life due to their lower self-discharge rate, but they remain as effective as secondary batteries.
Common types of batteries include biobatteries, dry-cell batteries, zinc-carbon batteries, alkaline cell batteries, mercury cell batteries, and lithium ion batteries. All of these have different uses. Biobatteries are devices that generate electric energy via digestion of proteins, carbohydrates, and fat by enzymes. Dry-cell batteries are also called Lelanche cells and are batteries with a paste electrolyte in the middle cylinder attached to metal electrodes. These are the batteries that most people are familiar with: AA, AAA, etc. Zinc-carbon batteries have a zinc anode and a carbon cathode, with a redox reaction happening inside of that battery. Alkaline cells are much like zinc-carbon batteries but better because it has a longer shelf life. Alkaline cells produce more volts than other batteries. Mercury cells are small, circular, metal batteries used in watches. They have a 10-year shelf life but were pulled from public sale because of an environmental issue they propose. The lithium ion battery contains a metal oxide cathode coated onto an aluminum current collector, an anode made from carbon/graphite coated on a copper current collector, a separator, and an electrolyte made from lithium salt in an organic solvent.
Work began on the lithium battery in 1912 under G.N Lewis, however, the battery wasn’t first commercialized until 1991 by Sony. Sony patented their design and a graduate student from Japan under John B. Goodenough fought to get the patent removed as he and Goodenough discovered the battery earlier, but the graduate student took it with him back to Japan. The two failed to get the patent removed and neither got credit for their efforts. Lithium batteries have a multitude of uses, including in pacemakers, personal cameras, Personal Digital Assistants (PDAs), cell phones, watches, thermometers, remote car locks, MP3 players, hearing aids, calculators, and backup battery systems.
Lithium batteries have a general make up much like other batteries. There is an outer casing made of metal or ceramics. The casing holds an anode usually made of carbon graphite, a cathode made of lithium metal, a separator made of a microperforated plastic, and an electrolyte usually made of an ether solvent. These batteries can be either cylindrical or prismatic.
The cathode is usually a lithiated metal oxide, which can be either layered, spinal, or a polyanion material. Layered oxides are usually either lithium cobalt oxide (LiCoO2), or something like it that follows the molecular formula LixCoO2. The polyanion materials are either LiFePO4 or Li2FeSiO4, and spinal oxides are usually Li2Mn2O4. There is then an electrolyte made of a lithium-containing material that allows the lithium to diffuse throughout the cell. Liquid electrolytes are most commonly used, using either LiPF6, or a different lithium salt and ethylene carbonate as a solvent. If a solid-state electrolyte is used it is either Li10Zn3(GeO4)4. The anode almost always contains lithiated graphite following the form: LixC6. The general reaction that happens is a redox reaction. Lithium is oxidized in the anode from Li to Li+ (C6Li à 6C(graphite) + Li+ + e-). The lithium ions go through the electrolyte to the cathode where it is made into lithium cobalt oxide where the cobalt is reduced. (Li1-xCoO2Cs + xLi+ + xe- à LiCoO2[s]) To recharge the cell, the reactions are run in reverse with the lithium ions traveling back to the anode and incorporate themselves back into the graphite.
There are many advantages of using the lithium battery. There is a high specific energy and high load capabilities with power cells. There is a long cycle and an extended shelf-life, making it maintenance-free. This is because the battery has a relatively low self-discharge. The lithium battery holds its charge much better than other rechargeable batteries. It can also handle hundreds of recharge cycles. This is possible due to the simple charge algorithm giving it a reasonably short charge time. When using a lithium battery, you don’t have to fully use the charge within before charging like other batteries due to its low internal resistance and its good coulombic efficiency.
Like any battery source, there are downfalls as well. For all lithium batteries made, the degradation begins immediately after the battery is made whether the battery is in use or not. Lithium batteries are also extremely sensitive to high temperatures. The higher the temperature, the faster the degradation speed. If the battery cell is completely used up, the cell becomes ruined and if a pack fails, the battery can become combustible. Each lithium cell must have a small computer of sorts to help manage the battery to make sure that the cell doesn’t become completely used up. The cell also requires a protection circuit to prevent thermal runway if that runway becomes stressed. The cell cannot rapidly charge at freezing temps either (The emerging science is the idea of using sodium cations in replacement of lithium ions. Many scientists are questioning whether this is a plausible switch. Sodium ions are very like lithium ions. The sodium ions come in Na+ as a natural form. It is a monoatomic monocation alkali metal ion. It is also a monovalent inorganic cation. It is used in the human body as a necessary metabolite and it is also necessary for the regulation of blood and body fluids. Sodium has a molecular weight of 22.9898 g/mol. The cation is a natural solid with a specific heat of 3.582 J/K. The melting point of sodium is 97.82 degrees C, with a density of 0.971 g/mL at 20 degrees C. Sodium has an ionic radius of 1.16 angstroms.
The lithium ion is much alike the sodium ion. It is also a monovalent inorganic cation, a monoatomic alkali metal cation, and comes in Li+ as a natural form. Lithium is used as a mood stabilizer in the human body and prescribed as an antidepressant. Even though sodium and lithium both have a known charge of positive one, lithium has a larger charge and a smaller diameter than Na+. Lithium has a much smaller molecular weight at 6.941 g/mol and is also a naturally occurring solid. The melting point is around 180.5 degrees C with a density of 0.534 g/mL at 20 degrees C. Lithium has a specific heat of 1.228 J/K and an ionic radius of 0.9 angstroms.
Both ions are alkali metals. This means that they should both react the same way, as we’ve found is the case with other columns of the periodic table. Both ions make up a part of the earth’s crust and are both highly reactive, so they’re rarely found alone and generally found in nature combined with other elements. Both elements react violently with water, and that makes sense because anytime a battery comes in contact with water it ceases to stop working.
Sodium ions are much more abundant than that of Lithium ions and that is one of the reasons why scientists are looking into it as a replacement. Some of the obstacles to overcome are the different molecular weights, different melting points, and different properties. Lithium acts more like group 2a when it comes to the chemical reactivity as it tends to react more with nitrogen, carbon, and hydrogen than it does with water, oxygen, and halogens like the rest of group 1a metals. Lithium easily forms a stable hydride and other group 1a metals form relatively reactive hydride bonds. The biggest obstacle for scientists when looking into a replacement is that sodium is a larger ion than lithium and therefore it requires more power to run that battery. In the case of most alkali metals, as the atomic number increases, the electronegativity decreases, and the alkali-graphite bond stabilizes. With lithium, the covalent contribution of lithium-graphite bonds further stabilizes the bonding state. With sodium, there is no covalent contribution and its atomic diameter is smaller than other alkali metals, making it more unstable. Graphite also cannot be used in a sodium battery because the local repulsive interaction between Na+ and the graphene layer predominantly destabilizes Na-GIS as an anode.
The chemistry in a sodium ion battery runs along the same premises of that of the lithium battery but has some challenges to overcome. The cathode is made of a ceramic oxide compound, but when ions arrive there, the electrode swells in size and shrinks yet again when they leave, having the ceramic crack and break from that swelling and shrinking, causing it to break away from the electrolyte and it kills the battery. The anode is the site where the sodium loses an electron to become Na+. Graphite anodes don’t work here, so scientists have investigated synthesizing carbon to act like graphite and are having relative success. Some other possibilities that scientists have isolated are Na2V3O7 and NiMoO4.
There are ways to improve this chemical process. Different scientists have found multiple ways one of which being a high-performance anode material developed by binding an antimony-based mineral onto sulfur-doped graphene sheets. It allowed the battery to perform at 83% for over 900 charging cycles. Another option is to sandwich the ceramic electrolyte pellet between two ultrathin poly (ethylene glycol) methyl ether acrylate layers. There is not much research about this option. One more option is redesigning the cathode by finding a flexible compound called pyrene-4,5,9,10-tetraone (PTO) that holds two times as many sodium cations. This allows it to compete with the standard lithium ion cathodes currently in use. This is the most promising option to improving the chemical processes.
