Preparation And Electrochemical Behavior Of Nb₂CTx-LiFePO₄ Composite As High Performance Cathode Material

Under the international strategic trend of environmental protection and energy security,the concept of low-carbon and green has penetrated into people’s production and life,and the demand for green energy has accelerated the development of the application of lithium-ion batteries in the new energy industry.Lithium-ion batteries are also facing new challenges,with cost,performance and safety being the focus of attention.As the"host material"of lithium-ion batteries,cathode material largely affects the parameters of lithium-ion batteries.Due to the advantages of low price,environmental friendliness and high thermal stability,lithium iron phosphate has been considered the most promising cathode material for lithium-ion batteries.However,the low lithium-ion diffusion rate and electronic conductivity have become key factors limiting the development of lithium iron phosphate cathode material applications.Therefore,improving the ion and electron transport of lithium iron phosphate and preparing high-performance lithium iron phosphate cathode materials have been a hot topic of research.Layered MXenes materials with excellent electron conductivity and lithium ion transport mechanism are also a research hotspot in the field of energy storage materials research.In this paper,monolayer Nb₂CTx with excellent carrier dynamics is combined with different shapes of lithium iron phosphate particle groups to design large particle lithium iron phosphate composites with more mesoporous structures and nano-plate lithium iron phosphate composites with Nb₂CTx as the backbone structure.The structural characteristics of the composites were analyzed by scanning electron microscopy,transmission electron microscopy,nitrogen adsorption,etc.The composites were fabricated and assembled into button half-cells,and the electrochemical properties of the composites were analyzed by constant current charging and discharging,AC impedance spectroscopy,cyclic voltammetry and other methods.The main research contents and results are as follows.（1）Nb₂CTx was wrapped on the surface of iron phosphate by electrostatic interaction and used as a precursor to synthesize lithium iron phosphate composites（LFP/C-Nb₂CTx）with in situ wrapped C-Nb₂CTx layer by carbon thermal reduction method.the LFP/C-Nb₂CTx composites are characterized by large particle size and high vibronic density.The C-Nb₂CTx cladding layer on the particle surface effectively improves the ion and electron transport of lithium iron phosphate.Moreover,due to the presence of Nb₂CTx,the composite particles have more mesoporous structure,which increases the contact area between electrolyte and material.Therefore,the composites with the optimal Nb₂CTx content exhibit excellent electrochemical properties with high bulk energy density.（2）The nano-plate lithium iron phosphate prepared by hydrothermal reaction shortens the migration path of lithium ions and electrons inside the particles,and then the nano-plate is loaded on the Nb₂CTx skeleton structure using surfactant to form a composite material with excellent conduction structure.The LFP/Nb₂CTx composite has excellent multiplicative performance,with a discharge capacity of 164.6 m Ah?g^-1 at 0.1 C multiplication when Nb₂CTx is added at 1.5 wt%.The discharge capacity of the composite at a magnification of 0.1 C was164.6 m Ah?g^-1 at a high magnification of 5 C,and 134.3 m Ah?g^-1 at a high magnification of 5C was maintained.（3）The modification of the lithium iron phosphate surface using the ultrafast carrier dynamics of Nb₂CTx can effectively enhance the lithium ion and electron transport between lithium iron phosphate particles.However,when too much Nb₂CTx is added,the electrochemical properties of the composites are reduced.Excessive Nb₂CTx tends to stack itself and hinder the diffusion of lithium ions,and will reduce the proportion of active material（lithium iron phosphate）in the electrode,making the actual discharge specific capacity of the material lower.