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Nitrogen doped graphene monoyne: a new type of alkali metal secondary battery material with high specific capacity

wallpapers News 2020-12-07
The development of

high-efficiency energy storage devices (such as lithium-ion sodium ion secondary batteries) is considered as one of the effective ways to improve energy environmental problems. Carbon materials have become the mainstream anode materials for secondary batteries due to their excellent chemical stability good conductivity electrochemical lithium storage capacity. Graphite is widely used in various commercial lithium-ion batteries. However its limited lithium storage capacity (372 MAH g-1) can not meet the needs of new generation electric vehicles other electrical equipment.

γ - graphene is a new type of two-dimensional carbon nanomaterials which is composed of SP SP2 hybrid carbon atoms. It can be seen that the adjacent benzene ring is connected by an alkynyl group. There are a lot of π - π conjugated electrons in the molecular structure of γ - graphite monoyne which endows the material with good intermolecular conjugation structure chemical stability. Compared with graphite (0.34 nm) it has wider carbon layer spacing (0.36 ~ 0.38) At the same time the unique large triangular conjugated structure in the molecular structure of γ - graphene provides additional lithium (sodium) storage sites. However due to the steric hindrance effect of the total substitution reaction of alkynyl group on benzene ring it is impossible to prepare γ - graphene by conventional organic synthesis which greatly limits the application of γ - graphene.

Cui Xiaoli research group Department of materials science Fudan University based on mechanochemical synthesis method proposed the first successful preparation of γ - graphite monoyne (carbon 2018 136 248-254) using calcium carbide halogenated benzene as precursors applied it to the field of energy storage conversion (Journal of materials chemistry a 2018 6 20947-20955; small 2019 15 1804710; Journal of materials chemistry a 2018 6 20947-20955; small 2019 15 1804710; Journal of materials chemistry a 2018 6 20947-20955; small 2019 15 1804710) Materials Chemistry A 2019 7 5981-5990)。 In inert atmosphere through ball milling process calcium carbide halogenated benzene react under strong mechanical stress alkynyl substituted halogen group is connected with benzene ring to obtain intermediate of γ - graphite monoyne; further annealing treatment improves the structural order of the material obtains two-dimensional nitrogen doped γ - graphite monoyne with large amount of pores. Previous studies show that γ - graphite monoyne has good lithium storage performance (1104.5 MAH g-1 at 100 mag-1 small 2019 15 180 4710). On this basis nitrogen doped γ - graphite monoynes were prepared by using NH4HCO3 as nitrogen source step heating strategy. Through morphology evolution the formation mechanism of its unique two-dimensional planar structure was revealed its application in alkali metal sodium ion secondary batteries was broadened. Electrochemical tests show that nitrogen doped γ - graphite monoynes have excellent lithium storage capacity (1037 MAH g-1) sodium storage capacity (570 MAH g-1) high rate performance. The mechanochemical segmented heating method proposed in this work provides a new idea for the preparation of new two-dimensional carbon materials heteroatom doping modification.

Wang Songyou Department of Optical Science engineering Fudan University based on the experimental results the possible doping position of nitrogen in γ - graphite monoyne the diffusion path of Li / Na ions were studied by first principles method. The calculation of the formation energy of nitrogen in different positions of γ - graphite monoyne shows that the imine structure formed by nitrogen substituting for the carbon atom in the acetylene bond is the best alternative position. The gradient elastic b method is used to calculate the potential barriers of Li / Na ions in different diffusion paths. It is found that the conjugated ring structure in n-doped γ - graphite monoyne has obvious advantage of adsorbing Li / Na the conjugated ring structure is Li / Na which improves the best migration channel in the direction perpendicular to the molecular plane. The theoretical calculation results are helpful to underst the intrinsic structure of nitrogen doped γ - graphite monoyne the energy storage mechanism of Li / Na secondary battery thus providing a theoretical basis for material design.

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