Introduction ions in the electrolyte solution mean that

Introduction The development and growth of humanity have created a world where technology and mobile devices are listed as one of the basic necessities of our lives. Smartphones and other portable devices are used by a vast population because they give us the opportunity to access endless digital information with ease and strengthens our communication with each other, encouraging the expansion our social network. Currently, 95% of Americans have a cell phone and more than 80% own desktop or laptop computers. (Pew Research Center, 2017) As a main component of electronics, it is mandatory for batteries to develop and progress according to the demands proposed by new technologies such as compact smartphones, tablets, lightweight laptops and other portable devices. Through the great development of old batteries, the invention of the lithium-ion battery in 1980 greatly impacted the world as a vital source of power for our mobile phones, laptops and portable technological devices. Problem Prior to the influential invention of lithium-ion batteries, rechargeable Nickel-cadmium battery and non-rechargeable zinc-carbon batteries were widely used for consumer electronics. However, Nickel-cadmium batteries have a comparatively low energy density, resulting to less power compared to other battery types – a sheer voltage of 1.2V in comparison to 3.6V from the lithium-ion battery (Battery University, 2011), which means that approximately three nickel-cadmium batteries would equal efficiency as one lithium-ion battery. With low voltage, more of this battery would be needed for high voltages, leading to its reputation for inefficient and inconvenient. This battery also acquires memory effect, reducing the recharge life of the battery due to previous partial discharge before recharging. The main issue with the Nickel-cadmium battery is its environmentally unfriendly toxic main component, Cadmium, which can result in consequential pollution if disposed of in a landfill or incinerated. Because of its harmful and increased carbon footprint, the use of Nickel-cadmium batteries is regulated by most countries including the USA and the EU. When inhaled, cadmium has severe health issues such as irreversible damage to the kidneys and respiratory tract, making it unsafe for use in personal electronics. (Toxic Substances and Disease Registry, 2013) The numerous and serious disadvantages of Nickel-cadmium batteries made it ineffective for use in mobile devices, increasing the demand for a rechargeable, safer, and more efficient battery for use in advanced technology. Solution The Lithium-ion battery is the solution to and replacement for inefficient, heavy batteries that were previously used in personal and mobile devices. Being relatively lighter than rechargeable batteries of the same size and non-toxic, lithium-ion batteries consists of a lithium-metal-oxide (usually Lithium Cobalt Oxide LiCoO2) as the cathode, a porous carbon material (graphite) as the anode, and a salt solution as the electrolyte connecting with both ends, with the purpose of acting as a passage for the flow of lithium ions between the two terminals of the battery. It tends to be a solution of lithium salts dissolved in solvents, as lithium ions in the electrolyte solution mean that lithium ions from either side of the battery can travel shorter distances. When lithium ions travel from the anode to the cathode, ions in the electrolyte solution can easily intercalate into the cathode instead of the ion traveling the full distance between the anode and cathode and vice versa, improving the efficiency of the battery. The cathode of a lithium-ion battery is usually Lithium Cobalt Oxide, made up of layers of cobalt oxide octahedral structures (six atoms arranged in a symmetrical form around a central atom) which are separated by layers of lithium. This structure allows the change of valence states of the cobalt ions between Co+3 and Co+4 as negatively charged electrons are lost and gained during the process of the battery being charged and discharged. The two lightweight electrodes, carbon and lithium cobalt oxide, are able to intercalate a large number of lithium ions, six carbon atoms in the graphite holding one lithium ion to be exact, allowing them to obtain the highest energy density out of all variations of lithium-ion batteries. As a highly reactive element, Lithium can store plenty of energy in its atomic bonds, supporting the high energy density of the battery. image 2 intercalationThe usage of the lithium-ion battery begins at a state of full discharge, where all lithium ions in the battery are intercalated in the layered structures of the lithium cobalt oxide cathode of the battery. When the battery is being charged, the cathode goes through an oxidation reaction as it loses negatively charged electrons (e-) to the anode while the equal amount of lithium ions (Li+) move to the anode through the electrolyte in order to maintain the charge balance in the cathode. The battery becomes fully charged when all the lithium-ions in the battery are closely intercalated within the lattice layers of carbon atoms in the anode. The intercalate process is reversed when the battery is being discharged (in use), as valence electrons from the lithium atoms in the anode pass through external wires to the cathode following its attraction to the positive charge of the cathode.The flow of electrons through the external wires generate electric power, successfully converting chemical energy into electrical energy. The external wires connecting the anode to the cathode during the battery’s discharge is what drives the reaction because it triggers the movement of electrons and lithium ions within the battery. When the negatively charged electrons are free to move, the positively charged lithium ions are allowed to do the same in efforts to balance the movement of their negative electron charge. (Australian Academy of Science, 2016)  After giving off its electron, the lithium atoms become ions which de-intercalate from the layered structures of carbon in the anode due to the stronger attraction to the negatively charged cathode, causing it to travel from the anode back through the electrolyte solution to the cathode.                                                                            image 1An oxidation reaction occurs in the anode as electrons are lost, increasing the oxidation state, while a reduction reaction occurs in the cathode as it gains electrons from the anode, causing a decrease in oxidation state. The reaction comes to an end when the lithium ions completely fill the cathode, causing the need to recharge the battery in order to reverse the movement of lithium ions with a charger by pushing the lithium ions back to the anode from the cathode, allowing the discharge process to repeat. Below are the half-cell reactions: Charging Cathode : xLiCoO2 ? CoO2 + xLi+ + xe- Anode : xLi+ + xe- + C ? LixCDischarge Cathode : CoO2 + xLi+ + xe- ? xLiCoO2 Anode: LixC ? xLi+ + xe- + C However, the battery’s performance is affected by the deterioration of graphite anode due to repeated intercalation of lithium ions into the layers of graphite in the carbon anode, eventually halting the use of the battery. In fact, their thermal instability can make them perilous due to the possibility of overheating in the anode which triggers the production of oxygen in the cathode as it decomposes from the heat. The combination of oxygen and heat gives the battery a high chance of starting a fire. If placed together with a flammable chemical electrolyte solution, the battery can become extremely dangerous. High temperatures can also increase the speed of degradation of the battery due to its extreme sensitivity. The chemical process between the electrodes in the battery can be explained with the metal reactivity series. Lithium is more reactive in comparison to Carbon, meaning that it has a greater tendency to give off electrons in order to form positive ions. When put into the context of the lithium-ion battery, the higher reactivity of the lithium explains why it is lithium and not carbon that loses electrons to the other electrode.

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