DFT study of doped and functionalized fullerene based materials for lithium-ion battery applications
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The transition metal oxides (TMO) currently used as cathode materials are expensive, strategically scarce, toxic and have environmental implications. The crystal structure of these materials sets an upper bound on the amount of lithium they can intercalate which limits the energy density of the device. Consequently, there is intense effort to develop novel and better cathode materials. Carbon based materials present a promising alternative because carbon is inexpensive, abundant and environmentally friendly. While the domain of carbon based materials is quite extensive, the high stability and electron affinity of C60 make C60 based materials attractive for positive electrode applications in lithium ion batteries (LIBs). The rich chemistry of carbon allows fullerene based materials to be doped and functionalized and thereby their properties can be tailored in a specific direction. Recently, devices based on functionalized CNTs and showing high energy and power densities have been fabricated. In these devices, the unique combination of properties has been attributed to the presence of oxygen containing functional groups (OCFGs). It has been reported that higher cell voltages can be obtained using benzoquinones functionalized with strongly electron withdrawing functional groups (SEWFGs) which render the parent chemical structure electron deficient. In this work, the effect of doping and functionalization on the redox and electronic properties of fullerene based materials has been studied. We have investigated the effect of functionalization with OCFGs and SEWFGs on the redox and electronic properties of pristine fullerene. Since heterofullerenes obtained by replacing one or more carbon atoms on C60 with another atom have already been synthesized, we have investigated the effect of replacing one carbon atom on fullerene with X i.e. the material C59X (X=B. N, S, Si and P). Our computation results show that some dopants and functional groups are quite effective in increasing the redox potential of C60. Using DFT, we have quantitatively explored whether doping and functionalization have synergistic effect. The correlation between electronic properties and redox potentials of doped and functionalized C60 based materials has been investigated so as to be able to rapidly screen functionalized and doped fullerene based materials for cathode applications.