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www.us- tech.com


September, 2019


Graphite May Be the Key to Longer Battery Life


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Raman Microscopy The researchers used optical and


Raman microscopy to perform direct, real-time monitoring of stage transi- tions in H2SO4-GIC made from high- ly oriented pyrolytic graphite (HOPG). They observed that the stage transitions in HOPG-based GIC occur very differently than those in GIC made from natural flake graphite. During the stage-2 to


stage-1 transition, forma- tion of the stage-2 phase be- gins nearly simultaneously over the entire graphite sur- face that is exposed to the media. This was attributed to the movement of the small intercalant portions toward the points of attraction, thus growing continuous islands. However, during the reverse


process, the stage-1 to stage-2 tran- sition begins strictly from the edges of the graphite sample and propa- gates toward its center. The most striking observation was that the deintercalation front was discontin- uous. Namely, the selected micron- sized domains of the graphite sur- face deintercalate preferentially to release the strain that had been in- duced by the intercalation. The intercalant dynamics in the


2D graphite galleries, occurring at a speed of greater than 240 µm/s, has fast kinetics. The initial intercalation process is different from the rest of the reintercalation cycles. The differ- ence in the mechanisms of the stage transitions in natural flake graphite- based GICs and in the HOPG-based GICs exemplifies the role of the graphite structure for the intercalant dynamics in 2D graphite galleries.


Possible Applications The findings made in this study


advance the field of graphene and have several potential applications. GICs can be considered stacks of doped graphene, which can be easily prepared by fully reversible reac- tions. The doping level can be easily controlled by the reaction conditions.


Optical micrograph showing transition of stage-2 (greenish-white) GIC to stage-1 (blue) HOPG GIC.


Secondly, intercalation weak-


ens the adhesive forces between the adjacent graphene layers, thus, GICs serve as precursors for obtaining sin- gle-layer graphene and graphene nanoplatelets by using liquid phase exfoliation. Third, GICs serve as im- portant and unavoidable intermedi- ates en route to covalent functional- ization of graphene, due to the charged condition of carbon atoms. Finally — and most importantly


— lithium ion battery operation is based on the cyclic intercalation- deintercalation of lithium ions with graphite. Understanding the stage transition mechanism will help to ad- vance each of these applications. Ayrat Dimiev concludes, “The


studied stage transitions in the H2SO4-GICs are accompanied by the transfer of protons to and from the intercalated sulfuric acid that occurs by the Grotthuss mechanism, i.e. it is ultrafast and ‘frictionless.’ We are thinking of checking if that is true. If yes, these systems can be used as proton conductors in hydrogen fuel cells. Another direction is developing an efficient and high-throughput pro- cedure for the liquid phase exfolia- tion of graphite to mono-layer graphene.” Web: www.kpfu.ru/eng r


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