The potential of silicon anode based lithium ion batteries

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Lithium ion batteries (LIBs) have been successfully deployed in a myriad numbers of consumer electronics and are increasingly adopted in electric vehicles. The development of high energy density LIBs is critical for meeting the existing and anticipated energy requirements of consumer electronics and electric vehicles. In that regard, silicon (Si) is considered as a potential next-generation anode material for LIBs and is projected to provide large increase in energy density. Despite over 5000 journal articles on Si anode in the past decade, there is a lack of clarity on the extent of practical improvement in energy density that can be accomplished by switching the anode from graphite to Si in LIBs. Issues related to initial loss of capacity and cyclability of Si anode have been reported extensively in these articles. Experimental data have shown that up to 40% increase in gravimetric energy density can be achieved using Si anode. However, such increase in energy density is achieved when you allow the LIBs to swell beyond permissible limits. Unlike graphite which expands only ∼10% when charged, Si expands 300–400% when charged. Such large volume change of Si will lead to swelling of LIBs if the amount of Si in Si-carbon composite (SCC) exceeds a threshold level that is required to avoid external dimensional change of the anode. The porosity of anode should be adjusted according to amount of Si in the SCC anode. Swelling of LIBs is an important practical issue and has major safety and performance implications.

A porous silicon layer results from an electrochemical etching of a crystalline silicon wafer in a hydrofluoric acid based electrolyte. Various morphologies can be obtained depending on the type, the doping level, the crystalline orientation of the Si wafer and also on the electrolyte composition. Pores are open and “grow” mainly in the current direction. Their sizes vary from a few nanometers (mesoporous) to several micrometers (macroporous). The porous layer thickness mainly depends on the applied current density and duration.

Based Graphene

Graphene is an atomic-scale honeycomb lattice made of carbon atoms.

Graphene is an allotrope of carbon in the form of a two-dimensional, atomic-scale, hexagonal lattice in which one atom forms each vertex. It is the basic structural element of other allotropes, including graphite, charcoal, carbon nanotubes and fullerenes. It can also be considered as an indefinitely large aromatic molecule, the limiting case[clarification needed] of the family of flat polycyclic aromatic hydrocarbons.

Graphene has many extraordinary properties. It is about 207 times stronger than steel by weight, conducts heat and electricity efficiently and is nearly transparent.Researchers have identified the bipolar transistor effect, ballistic transport of charges and large quantum oscillations in the material.

The global market for graphene is reported to have reached $9 million by 2014 with most sales in the semiconductor, electronics, battery energy and composites industries

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