Graphdiyne-Based Materials For High-Energy-Density Fast-Charging Lithium-Ion Batteries

Graphdiyne,as a novel type of two-dimensional carbon material with independent intellectual property rights in China,has received extensive attention and application in various fields.The unique chemical and electronic structures endow graphdiyne with many fascinating properties,including rich chemical bonds,highly conjugated,super-large π structures and infinite distribution of pores.With the rapid development of graphdiyne,plenty of researches in energy conversion and storage,catalysis,intelligent information and life sciences about graphdiyne increasingly emerge,demonstrating the revolutionary properties of graphdiyne.In the report of "2020 Research Frontier" released by Clarivate and the Literature and Intelligence Center of the Chinese Academy of Sciences,graphdiyne was voted as one of the TOP frontier hotspots of chemistry and material.The unique property of facile and controllable growth on any substrate makes graphdiyne exhibit incomparable advantages over most traditional materials.Graphdiyne is thus regarded as a highly competitive candidate for construction of new-type high-performance electrodes and electrochemical interface.In addition,graphdiyne has the characteristics of providing abundant ion channels,catalytic active sites and selfaccelerating in-plane/out-of-plane migration of lithium(Li)ions through self-reversible conversion of chemical bonds with different bond lengths which also bring new opportunities to effectively address the scientific challenges of fast-charging batteries.Considering the special chemical and electronic structural advantages of graphdiyne,this thesis focused on the design of electrode structure and the construction of selective Li-ion transport interface,systematically studied the performance of graphdiyne-based materials in fast-charging Li-ion batteries.The obtained innovative research results are as follows:(1)Based on the uniquely porous structure and the new concept of alkyne-alkene transition in graphdiyne,self-expanded Li-ion transport channels were constructed for the first time,which accelerated the Li-ion transport,and thus realized high performance fast-charging Li-ion batteries.In graphdiyne,the reversible alkyne-alkene transition induced by the Li+-alkyne interaction enables the self-expanded Li-ion transport channels which highly reduce the energy barrier of Li-ion transport.The Li ions adsorbed on benzene ring and triangular alkyne ring efficiently migrate out of plane through the self-expanded Li-ion transport channels motivated by the mutual repulsion among the adsorbed Li ions,further promoting the rapid solid-state Liion diffusion.Thus,severe voltage polarization and Li metal plating are effectively eliminated.Experimental results demonstrate that graphdiyne with the self-expanded Li-ion transport channels shows excellent electrochemical performance when used as the anode material for fast-charging Li-ion batteries.The assembled graphdiyne‖LiNi0.6Mn0.2Co0.2O2 full cells exhibit high capacity,long cycle life and excellent capacity retention even at low temperatures(e.g.,10℃).(2)The heterostructure of graphdiyne/graphite was designed and constructed.As an ion pumping interphase,graphdiyne significantly improved the ion transport kinetics of graphdiyne/graphite,and realized its application in high-performance fast-charging Li-ion batteries.The strong interaction between graphdiyne and Li ions changes the solvation/desolvation behavior of electrolyte near the electrode surface,accelerates the Li-ion desolvation process,and induces the formation of functional anion-derived SEI layer with high Li-ion conductivity.In addition,the built-in electric field generated at the graphdiyne/graphite heterojunction self-pumps Li ions to diffuse into the graphite layer,thus significantly enhancing the Li-ion transport kinetics within graphite and effectively eliminating the severe Li plating as well as high-voltage polarization.Thanks to these properties,the graphdiyne/graphite anode exhibits high capacity(217.8 mA h g-1 at 6 C,139.2 mA h g-1 at 20 C),long cycle life(2000 cycles at 6 C,1650 cycles at 20 C)and excellent capacity retention(81.5%after 2000 cycles at 6 C and 86.2%after 1650 cycles at 20 C).Especially at-20℃,the graphdiyne/graphite anode still delivers a high capacity of 128.4 mA h g-1 over 500 cycles.(3)Graphdiyne/Li1.2Ni0.2Mn0.6O2(graphdiyne/LNMO)heterojunction was constructed by in-situ growth of few-layer graphdiyne on the cobalt-free Li/Mn-rich layered metal oxide cathode to improve the fast-charging performance of traditional high-voltage cathode.The interaction between graphdiyne and LNMO accelerates the ion-transport kinetics at high voltage,and eliminates the issues of cracking,oxygen evolution,lattice structure collapse,severe voltage polarization and poor cycle life of LNMO under fast-charging conditions.With the protection of graphdiyne interfacial layer,the fast-charging performance and cycling stability of LNMO are greatly improved.The integrity of the lattice structure is also successfully maintained during charging/discharging processes.As a result,high capacity,excellent capacity retention and long cycle life at high rates(170 m A h g-1 of discharge capacity for 500 cycles at 3 C)in a wide voltage range(2.0～4.8 V)are achieved by the constructed graphdiyne/LNMO cathodes.(4)The fast-charging performance of hydrogen substituted graphdiyne anode material at low temperatures was systematically studied to reveal the interaction between hydrogen substituted graphdiyne surface and the solvated shell of Li ions,the changes of Li-ion solvation behavior and the surface assisted desolvation effect in liquid electrolytes.Hydrogen substituted graphdiyne induced Li-ion solvation/desolvation behavior promotes the formation of LiF-rich SEI layer,enhances the conductivity of Li ions,and accelerates the Li-ion transport kinetics between the electrolyte/electrode interface at low temperatures.Meanwhile,the largely porous structure of hydrogen substituted graphdiyne benefits the fast Li-ion transport in the bulk phase of the electrode material at low temperatures.Experimental results show that the hydrogen substituted graphdiyne anode exhibits excellent fast-charging performance at low temperatures.At-10℃,a high capacity of 100 mA h g-1 over 500 cycles is delivered at 3 A g-1.Even at the-30℃,high capacities of 133.9 mA h g-1 at 1 A g-1 and 113.4 mA h g-1 at 2 A g-1 with long cycle lives of 550 and 800 cycles are also obtained,indicating the great potential of hydrogen substituted graphdiyne as promising anode material for low-temperature fast-charging Li-ion batteries.