Abstract
The new advance in nanotechnology has exposed the ability of battery nanowires to make them more powerful. When paired with lithium-ion battery technology, silicon and other nanowires contribute to reduced mass, tremendous electrical power storage and prolonged life in several charging periods. Because of their composition, nanowires are often called quantum wires and they are capable of absorbing electric charges. They do not break, but they grow in thickness. Silicon, germanium or other variations, such as amorphous silicon and tin oxides, are made of nanowires. The basic electrodes in a lithium-ion battery are modified by nanotechnology to improve performance. The aim of this article is to address the priorities of nanowire battery technology. The essential characteristics and the developments behind these batteries are discussed along with their advantages. Finally, it poses the problems and applications of Nanowire batteries.
Introduction
At an unprecedented rate, the speed of activity of current-generation machines, other technological devices and even electric vehicles is growing. This presents a need for similar batteries with large size to fuel them at a high rate of charge and discharge. Due to chemical limitations, the batteries that power high-speed computers such as tablets, cell phones, video games, and even hybrid vehicles neglect these functions. Traditional lithium-ion batteries pass lithium ions to a metal oxide cathode from a carbon anode. The charge density in these batteries is poor as the amount of lithium-ion retained by one carbon ion is just one. The Silicon Anode, on the other side, has the potential to accommodate 4.4 lithium ions in one silicon atom. Stanford University researchers (Chan. C.K., Zhang. X. F. & Cui Y., 2008) have studied the usage of silicon and germanium nanowires for better battery capacity. This essay is intended to discuss the scientific insights of this device for the Nano Wire battery.
Objectives
In terms of electrical charge density as well as lifespan, the current rechargeable batteries are restricted. Lithiated graphite as anode, LiPF6 as the electrolyte and LiCoO2 as cathode are the common lithium-ion batteries used in portable electronic devices and automobiles. Their key weaknesses are high manufacturing costs and a shortage of capital for mass production, such as Co. The new system for the Nanowire battery seeks to eliminate the limitations of this lithium-ion battery. The key goals of this technology are to use cathodes and anodes with higher energy capacity materials and to optimise the higher efficiency configuration of the batteries.
Features and Advantages of Nanowire batteries
Silicon and germanium nanowires are the anodes used in the nanowire battery (chan et al., 2008). Since Silicon has a low discharge potential and a load capacity of 4200 mAh/g, it is preferred to Germanium with a possible load capacity of 1600 mAh/g. The accompanying diagram. 1. The Silicon nanowires developed on the electrodes are seen.
Figure. 1. Silicon Nanowires grown on the electrodes.
The possible benefits of the nature of the Nano Wire are a high surface-to-volume ratio that makes further electrode interaction with the electrolyte, offers constant conduction of electrons inside the electrode, and finally, they are good at fast strain relaxation due to the fibrous design. Compared to the current carbon anodes, these anodes of Silicon nanowire have ten times more storage space.
The most important parameter for a battery’s healthy activity is the Solid-Electrode-Interface (SEI). In nanowire batteries, where there is lithium insertion onto Silicon layers, the SEI formation is stronger. An inner layer of inorganic lithium compound and an outer layer of organic lithium compound provide the SEI in Silicon nanowire batteries. The voltage dependency of the anatomy of the SEI often facilitates further charge and discharge cycles. The study of these batteries’ impedance level reveals that the impedance is attributable to both the diffusion mechanism and the resistance of the soil. The surface resistance in turn depends on the SEI. The diffusion coefficient of lithium into silicon is estimated to be 2 x 10-10. When the lithium composition is less than the electrode impedance increases. The Columbia efficiency of such batteries is about 99% and the charge capacity after 80 cycles is about 2000 mAh/g. The silicon nanowires designed with core-shell design provide high power and have longer life. Amorphous silicon is more electrochemically active compared to crystalline silicon. While crystalline silicon is mechanically stable, amorphous silicon stores Li+ ions. The cathode composition proposed by (chan et al., 2008) for nanowire batteries include the abundantly available Spinel Lithium Manganese Oxide (LiMnO4). This material is also an environmentally friendly less expensive material. The nanorods are of crystalline MnO2. According to Galvanostatic testing for batteries, these nanorods are characteristic of high storage capacity. Also, Aluminum doped cathodes are more stable and have more retention capacity.
Another research by Ajayan lab of Rice University demonstrate a battery of nanoscale which is an array of supercapacitor devices (Zyga. L., 2011). This battery has the cathode inside a nanowire and acts not only as a battery but also as an insulator. The main components in this battery are polyethylene oxide electrolyte, nickel tin anode and the cathode is of polyaniline. (Dickinson. B., 2011).
Li. Y. (2008), propose a Lithium-ion battery made of arrays of mesoporous Co3O4 nanowire anode. The capacity of such a nanowire battery is 700 mAh/g for 20 cycles of charging and discharging. These Co3O4 nanowire batteries have the capability of being synthesized on a large scale with good electrochemical properties.
Kim. D.W (2007) fabricated a hetero-structured SnO2 – InO2 nanowire by a method of thermal evaporation. The nucleation growth and electronic conductivity of SnO2 – InO2 nanowires is twice the magnitude of SnO2 nanowires. The SnO2 – InO2 nanowires also exhibit high lithium storage capacity.
Recent research by Etacheri.V. et al (2011) has studied the impact of Fluro Ethylene Carbonate (FEC) in improving the performance of nanowire batteries. When used as the co-solvent, Fluro Ethylene Carbonate is seen to increase the electrochemical performance of Silicon Nanowire anodes. This also resulted in less irreversible capacity and stable reversible capacities. The surface films formed with FEC added electrolytes were thinner compared to ordinary electrolytes.
Challenges
The major challenges in the nanowire battery technology are the pulverization due to the swelling or expanding nature of silicon and germanium when they are charged. Chan. C. K., et al (2008) say that “silicon anodes have limited applications because silicon’s volume changes by 400% upon insertion and extraction of lithium which results in pulverization and capacity fading”. Though their nanostructure prevents them from breakages, the charge capacity may fade as time passes. Another challenge is the behavior of a nanowire when it is immersed in an electrolyte (Chiang. Y.M., 2010). This behavior called as the lithiation behavior affects the basic structure of nanowires after initial charging.
Applications
The nanowire batteries are essentially useful in high power applications. Their capability to store more amount of charge can be utilized in driving electric cars making them more economical in terms of fuel efficiency and safety. This application also reduced the threat due to pollution and other greenhouse effects. The long-lasting capability of nanowire batteries enable them to be used in mobile electronic gadgets. When combined with solar cells, nanowire batteries can be used to replace the traditional power systems providing a cleaner and more efficient energy source. These batteries also act as capacitors and store electrical power and then it can be utilized during peak times when there is energy crunch. These nanowire batteries can be used as backups to reduce the cost of emergency power generators that are costly in terms of fuel, servicing, maintenance and testing.
Thus, nanowire batteries provide a promising future in the field of rechargeable batteries.
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