Neuronal Bionic Structure Composite Electrode Under Fast Charging Condition Material Construction And Mechanism Research

Lithium-ion batteries have become the most popular energy storage solution in modern society,especially for providing energy sources for transportation,reducing fossil energy consumption,and having a transformative impact on the automotive industry.The continuous and in-depth research on lithium-ion battery energy storage technology has been one of the world’s hot spots at the forefront of science and technology.Olivine lithium iron phosphate（LiFePO₄）has been widely used in power battery cathode materials because of its high safety,low cost and environmental friendly advantages.However,the sluggish electrode reaction kinetics of LiFePO₄ cannot fully meet the demand of power battery use under extreme operating conditions such as fast charging,which limits its further development.Therefore,in order to enhance the ion diffusion rate and electronic conductivity of LiFePO₄,reduce the electrode material polarization during the electrochemical reaction,and fundamentally solve the slow electrode reaction kinetics thus enhancing the fast charging performance the following studies were carried out in this thesis:（1）In this thesis,a structural model of Mn²⁺doped LiFePO₄ was constructed based on the first-principles calculation method of density generalization theory,and the electronic energy band structure and electronic density of states（DOS）of the gradient Mn content-doped LiFePO₄ model were investigated separately to derive the optimized Mn²⁺doping ratio according to the change law of electronic conductivity of the electrode.It is found that the DOS peak near the Fermi energy level of Mn²⁺doped LiFePO₄ is significantly elevated,while the energy band gap decreases and the conduction band bottom shifts downward near the Fermi surface,which may be due to the new LiFe_1-xMn_xPO₄ valence and conduction bands formed by the doped Mn 3d electron orbitals together with Fe3d electron orbitals.This facilitates the jump of electrons from the valence band to the conduction band,which results in the electrode exhibiting better electronic conductivity.（2）Based on the calculated optimal Mn²⁺doping ratio,LiFe_0.78Mn_0.22PO₄/C and LiFePO₄/C,were synthesized by the solid-phase method,and the physical properties analysis showed that LiFe_0.78Mn_0.22PO₄ still maintained the intact olivine structure.In addition,the specific capacity of LiFe_0.78Mn_0.22PO₄/C was 139.2 m Ah/g and 136.1 m Ah/g after 10C high rate charge/discharge followed by 0.5C,respectively.136.1 m Ah/g,with a capacity retention rate of 97%compared to the initial charge/discharge specific capacity.Electrochemical impedance spectroscopy tests revealed that the charge transfer impedance R_ct at the conductive bonding of LiFe_0.78Mn_0.22PO₄/C was significantly lower than that of LiFePO₄/C,which may be related to the doping of Mn²⁺to enhance the electronic conductivity of the electrode material.（3）To further in order to investigate the electron conductivity and ion diffusion rate enhancing effects of new carbon cladding materials on LiFePO₄ electrodes,this paper draws on Murray’s law,a highly hierarchical interconnected structure evolved by living organisms,which is prevalent in nature,and uses electrostatic spinning combined with controlled pyrolysis to prepare LiFePO₄ electrode materials with neuron-like structure and morphological characteristics.LiFePO₄ nanoparticles are uniformly distributed on the three-dimensional interconnected（biological neuron-like structure）conductive channels co-constructed by CNFs and r GO,which not only effectively alleviates the agglomeration caused by the high specific surface energy of LiFePO₄ nanoparticles,but also makes the electrolyte to LiFePO₄ active particles with enhanced wettability,and at the same time may have a positive effect on the electron and ion transport properties.LiFePO₄@r GO/CNFs show a more excellent multiplier charge/discharge performance compared to LiFePO₄/CNFs and the pre-prepared LiFe_0.78Mn_0.22PO₄/C electrode material,especially the reversible charging specific capacity at ultra-high multiplier（15C）can still reach93.7 m Ah/g,which is significantly higher than that of LiFePO₄/CNFs（61.4 m Ah/g at 10C）.The lithium-ion diffusion coefficient of 8.82×10^-12 cm²/s for LiFePO₄@r GO/CNFs was obtained according to the constant current intermittent titration test（GITT）technique compared with 6.04×10^-13 cm²/s for LiFePO₄/CNFs,and the excellent electronic conductivity and ion diffusion rate may be related to the fact that graphene and carbon The excellent electronic conductivity and ion diffusion rate may be strongly correlated with the synergistic mechanism of the neuron-like structure constructed by graphene and carbon nanofibers.