Study On Sodium Storage Performance Of In-situ Carbon Composites Based On Transition Metal Nitrides

As the global energy demand continues to grow,the rational storage and efficient use of energy has become the primary challenge for today’s researchers.Lithium-ion batteries are widely used in various electronic devices by virtue of their stable performance and mature process.However,the scarcity of lithium resources has seriously hindered the sustainable development of lithium-ion batteries.Sodium and lithium are adjacent elements of the same main group,and sodium resources are abundant.Sodium-ion batteries work similarly to lithium-ion batteries and are expected to replicate the success of lithium-ion batteries and become the best candidate for large-scale energy storage applications.However,the radius and mass of sodium ions are larger than those of lithium ions,and their embedding/detachment ability is lower than that of lithium ions,resulting in the inactivity or poor reaction kinetics of some materials in sodium-ion batteries,especially cathode materials.Therefore,developing anode materials with excellent performance is of great importance for developing sodium-ion batteries.In this paper,through the structural characteristics and sodium storage performance performance of transition metal nitride,we adopt such methods as carbon material encapsulation,controlled selenization,structural modulation and heterogeneous interface construction to prepare transition metal nitride composites,so as to improve the sodium storage performance of the composites and systematically study the influence law of each component in the composites on the sodium storage performance.The main research of this paper is shown below:（1）、A simple self-polymerization method designed the vanadium-polymer framework with yolk-shell structure.Ultrafine VN（quantum dots）were grown in-situ during the subsequent calcination process and stably encapsulated in N-doped carbon nanospheres with yolk-shell structure（VN QDs/N-C）.VNs at the quantum dot level can provide short-range ion diffusion paths and reduce the internal stress of sodium ion embedding.Carbon nanospheres with open yolk-shell structure have stable spatial structure,good spatial limitation,and sufficient internal voids,which can effectively slow down the volume expansion of VN quantum dots and promote ion/electron transfer kinetics.VN QDs/N-C has a high reversible capacity of 486.8 m Ah g^-1 at 0.05A g^-1 when tested as the negative electrode of sodium ion batteries.The results illustrate that the yolk-shell structure of N-doped carbon nanospheres with in situ encapsulation of quantum dot-level VN composites has better performance in sodium ion battery anode materials and can also provide some reference for the design and development of sodium ion battery anode materials.（2）、The designed rod-like molybdenum-polyaniline framework was used as a precursor to prepare carbon encapsulated nitrogen-rich Mo_xN composites（Mo Se₂@Mo_xN/C-I）with few-layer Mo Se₂ surface modification after calcination,selenization and nitridation treatments.The in situ encapsulation of carbon nanorods contributes to the structural stability of Mo_xN;the nitrogen-rich Mo_xN and the modified layer less Mo Se₂ can form rich heterogeneous interfaces and additional active sites for fast sodium ion storage,thus promoting the reaction kinetics and increasing the actual capacity.Using Mo Se₂@Mo_xN/C-I as the negative electrode material for sodium ion batteries,a reversible capacity of 254.3 m Ah g^-1 can be obtained after 6000 cycles at 5A g^-1,exhibiting excellent sodium ion storage performance.The results show that the carbon-encapsulated nitrogen-rich Mo_xN composites with few-layer Mo Se₂ surface modification exhibit better sodium storage properties,the formation of heterogeneous interfaces promotes the ion transport and reaction kinetics,and the enhancement of the sodium storage properties of the composites by few-layer Mo Se₂ surface modification has great potential for application.