Controlled Preparation And Electrochemical Research Of Porous Electrode For Lithium/Sodium Ion Batteries

As the most important components of lithium/sodium ion batteries,electrode materials are the key for the development of lithium/sodium ion batteries.Therefore,the development and search for low-cost and high-performance electrode materials is particularly important for the development of lithium/sodium ion batteries.In lithium/sodium ion batteries,fabricating porous structured electrode materials can improve the energy storage performance of the batteries through effects of increasing surface area,promoting infiltration of electrolyte,reducing diffusion distance of ions in solid phase,alliviating stress and preventing pulverization,et al.In this paper,three kinds of electrode materials,LiMnPO₄,MnCo₂O_4.5 and carbon materials with commercial application potential are studied.Different problems faced by each three electrode materials in application are solved by constructing different types of porous structures resulting in improvement of energy storage performance.Details are as following:1.In solvothermal synthesis of LiMnPO₄,oleic acid was used as growth aid to induce heterogeneous nucleation of LiMnPO₄ crystals resulting in forming a sandwich-type LiMnPO₄ material with stacked slit-pore structure.In carbon-coating process,the stacked slit-pore structure allowed the pyrolytic carbon to be uniformly coated on the surface of each nanosheet.The stacked slit-pore structure can not only improve the conductivity of the material and reduce the polarization by imparting a more uniform carbon coating to the LiMnPO₄ material,but also enhance the energy storage activity of the material by increasing the contact area between the active material and the electrolyte.LiMnPO₄/C with stacked slit-pore structure as a cathode material of lithium ion batteries achieved a discharge specific capacity of 164.9 m Ah g^-1 at current density of 0.05 C(171 m Ah g^-1 for theoretical specific capacity).2.The MnCo₂O_4.5 material with internally closed mesoporous structure was synthesized in one step without using any templates,and the electrochemical performance of MnCo₂O_4.5 as an anode material for lithium ion batteries was tested for the first time.Compared with MnCo₂O_4.5 material with open-type stacked nanoporous structure,MnCo₂O_4.5 material with internally closed mesoporous structure had higher capacity with more stable cycling performance.After 100 cycles at current density of300 m A g^-1,a reversible specific capacity of 413 m Ah g^-1 was obtained.The internally closed mesoporous structure is effective in alleviating the stress caused by the large volume change of MnCo₂O_4.5 during charge and discharge resulting in high ability to avoid pulverization of the material.3.A nitrogen-doped carbon material with hierarchically porous structure was prepared by using glycine as carbon/nitrogen source and Na Cl as template through spray drying in combination with atmospheric pyrolysis.The nitrogen-doped carbon material with hierarchically porous structure exhibited high specific capacity and rate performance as well as ultra-stable cycling performance as an anode material for sodium-ion batteries.After 3000 cycles at current density of 500 m A g^-1,a reversible specific capacity of 413 m Ah g^-1 was obtained with capacity retention as high as91.4%.Kinetic calculations showed that the high electrochemical performance of the nitrogen-doped carbon material with hierarchically porous structure was resulted in synergistic effect of hierarchically porous structure and nitrogen doping which enhanced capacitive energy storage.