Theoretical Study On The Three-dimensional Layered Non-metal Materials As Anode For Ion Batteries

Ion battery is a new energy storage device that researchers are keen on.Li-ion batteries that provide energy for portable electronics,stationary energy storage,and electric vehicles continue to evolve.In 2019,three researchers who contributed greatly to their research in ion batteries won the Nobel Prize in Chemistry.Two-dimensional materials have been widely used as anode materials for ion batteries since their discovery.Two-dimensional materials have many advantages such as high stability and large specific surface area,but they have problems such as high cost and easy stacking of nano-layers.Compared with two-dimensional materials,three-dimensional layered materials could maintain some of the advantages of two-dimensional materials,also they have the advantages of short migration paths and good electron transport properties.In addition,in terms of material selection,non-metallic materials are lighter in weight,richer in resources,and more affordable than metal materials.Based on the understanding of the above issues,this dissertation uses first-principles calculation methods to systematically study the stable structural morphology of layered stacked C₃N materials,layered C₃N-based materials,and layered SiC materials and their applications as anode materials for ion batteries.The main contents are as follows:A theoretical study was conducted on the potential of C₃N material that has been synthesized experimentally as a negative electrode material for Li-ion batteries.The theoretical calculation method was used to explain the experimental work of Professor Xu Jiantie's team,and the theoretical models of layered C₃N materials and C₃N materials with defects were established.The process of Li ions embedded in C₃N materials were studied by first-principles simulation.The results show that the theoretical capacity of pure C₃N Li ions is only 133.94 mAh·g^-1,which is significantly lower than the experimental value.The chemical composition of the C_xN structure generated by the experiment is actually C_2.67N,which is an excess of N,and the theoretical capacity is 837.06 mAh·g^-1.Some Li ions are irreversibly trapped in C_2.67N,resulting in capacity loss.Reasonable modification calculations were performed on the known layered C₃N materials,and experiments showed that C₃N(C_3.33N)with low chemical activity and excessive C as Li ion battery electrode material has a low open circuit voltage?0.12 V?,High reversible capacity(840.35 mAh·g^-1),fast charge and discharge and good conductivity.It shows that C₃N with excessive C is a potential anode material for Li-ion batteries.The development of Li-ion batteries has encountered resource and capacity limitations.As a representative of non-Li batteries,Na-ion batteries have become the most ideal alternative to Li-ion batteries.In order to make full use of the excellent performance of layered C₃N-based anode materials in Na-ion batteries,the first-principles calculations are used to study the physical and chemical properties of modified layered C₃N-based materials.The results show that the S atoms can be successfully inserted into the layered C₃N to form a stable structure.However,during the charge and discharge processes,the S atoms have a very low migration barrier?0.23 eV?in C₃N and will migrate out from the C₃N during the operation processes,causing the material itself to be destroyed.Among the doped transition metal elements,both Sc and W show good stability.The theoretical capacity of the W intercalated C₃N layered structure as the anode material for Na-ion batteries is 275 mAh·g^-1.The minimum migration barrier is 0.28 eV,which is a promising anode material for Na-ion batteries.The theoretical method was used to understand the potential application of experimentally avaliable layered SiC as the anode material of Na-ion battery.The results show that the theoretical capacity of layered SiC is as high as 1339.44 mAh·g^-1,which is almost the highest among the already known anodes of Na-ion batteries.Combining a low diffusion barrier,a moderate open circuit voltage,and good electronic conductivity,layered SiC is a promising material that can be used as the anode electrode for Na-ion batteries.More importantly,we found that by increasing the contents of covalent components in the Na-C bonds,the intercalation strength?or corresponding theoretical capacity,working voltage?of Na ions in the C-based layered material can be enhanced.This could be achieved by doping atoms with a lower electronegativity than C atoms?such as Li,Be,B,Al,Si or P?.