Combining the powers of Si and C to build a better tomorrow: Production of high yield Si-C for anodes in Li batteries
Novel composite combining the high energy storage capacity of silicon and the elastic property of carbon.
Lithium ion batteries find wide applications in everyday use objects, but the number of ions that can be stored in their graphite anodes is limited. One potential solution is the silicon-based anode, which allows high ion and energy storage, except that it has a major limitation: silicon expands significantly during charging, affecting the life cycle of these batteries. Scientists now reveal a novel technique whereby silicon can be combined with carbon to counter this limitation.
Ever since the discovery of batteries by Volta, investigating the capability of materials to store ions, or simply electrical power, is a sought-after topic. The rising demand for energy, portable energy more so, saw the development of rechargeable batteries. At the forefront of this is the Nobel prize worthy discovery of lithium ion batteries in conjunction with carbon-based anodes. The impact of this invention can be understood by the rapid conversion of this technology from research into application in everyday use ？ in phones, tablets and electric cars. While developments have pushed the theoretical limits on the energy yield, there persists fundamental challenges which limit the performance of these batteries.
In a nutshell, lithium ion batteries store energy when ions are directed to flow from the cathode (positive electrode) to the anode (negative electrode) where they are stored in stacks for use. During discharging, the stored lithium ions are readily released from anode and electrons (electric current carrier) travel through the wire. When all the ions have been transferred from the anode to the cathode, the battery can be charged again by reversing the flow of ions. This is what happens when we charge our phones after a day’s use. Commonly, graphite is used as the anode. But there is a limitation on the number of ions that graphite can store. In this regard, silicon-based anodes emerge as a more efficient and sustainable alternative due to their high ion storage and energy storage capacity. However, during the charging process, when the lithium ions are stacked and stored, the silicon-based anode tends to expand up to four times its regular size. This expansion results in the cracking of silicon which ultimately disrupts the core conductive pathway of the battery resulting in reduced conductivity, waste of lithium ions, and fractures in the transmission networks. This significantly affects the recharge life cycles of such batteries.
It is possible to counter this with silicon-carbon composites that combine the high energy storage capacity of the silicon with the elastic property of carbon. The carbon not only buffers the expansion but also enhances the electrical conductivity. But the fabrication of these hybrids is time-consuming and cost-intensive. This poses as a barrier for wide-scale application.
Now, a group of researchers from Prof. Jun Kang’s lab have reported a simple procedure that could reduce the fabrication time and cost while providing a good yield. They used silicon and carbon precursors prepared in a solution. The principle of their studies, Prof. Kang states, was that “when a solution is subjected to a bipolar DC pulse, a spontaneous directional flow of silicon ions called the plasma discharge is observed. These silicon particles then travel to the carbon unit in the solution and a deep, stable dispersion of the silicon is observed in the carbon collective.” The thus formed silicon-carbon composite when used as an anode exhibited stable performance over many recharge cycles.
“We are optimistic that the simultaneous production of the silicon nanoparticles and their subsequent dispersion into the carbon unit will significantly reduce the time and cost,” reports Prof. Kang. The compact nature of the lithium ion batteries has afforded its indispensable place in our lives today. The easy scalability of the abovementioned technique is expected to expand the global reach of rechargeable batteries. Afterall, it isn’t every day that silicon and carbon join forces to help us achieve the fossil-free wireless society of tomorrow.
Keywords: Lithium ion battery, Silicon anode, green energy, energy storage
Name of invention: High yield Si-C for anodes in Li batteries