Functionalized graphene-based materials for li-ion batteries : from anode to cathode

Abstract

With the overconsumption of fossil fuels and the associated more and more complex Earth's climate system, it is important and critical to develop clean energy for a sustainable world. [1] A series of renewable energy technologies, for instance, solar cells, wind generators and piezoelectric systems, have thus been developed to harvest different types of renewable energy (e.g., solar, wind, and hydro), and electricity is the most direct and predominant form of such energy been used. [2] Considering the intermittent and localized features of such energy, they must be efficiently stored prior to be transported and used for specific applications. Among various energy storage technologies, rechargeable LIB, one kind of electrochemical storage systems, is the most desirable candidate featured by its extraordinary energy storage capability and environmental friendliness. [3] The energy storage in a LIB is on the basis of reversible shuttle of ions between the cathode (typically, lithium transition metal oxides/phosphates) and anode (commonly, graphite) materials inside the battery, with respect to the shift of electrons outside the battery during the charge/discharge process. [4, 5] Since the birth in 1990s, LIBs-because of the superior specific energy (gravimetric energy density) and energy density (volumetric energy density) than their counterparts (i.e., nickel-metal hydride, nickel-cadmium and lead-acid batteries), are currently becoming the dominant power source for portable electronics. [6] Unfortunately, the energy storage performance of LIBs cannot keep pace with the ever-growing demand for energy, in particular the rate of progress in emergent electric vehicles and smart grids. [7] Li ions and the oxygen functional groups at high potential (>2 V; vs. Li/Li +), e.g., carbonyl, carboxyl, hydroxyl or epoxy groups. [24, 25] Therefore, the electrochemical performance GO-based cathode is highly dependent upon the content of oxygen functional groups; meaning, higher oxygen content can deliver larger specific capacity. Notably, when the oxygen content in GO exceeds a certain level, a Regarding the cathodic application, the construction of redox-reversible oxygen functional groups grafted graphene while achieving good conductivity could be an effective route towards high performance GO-based cathodes. [29] To this end, powerful methods that capable of precisely controlling oxygen functional