In-situ nitrogen-doped porous core-shell-structured carbon/selenium composite material, and preparation method and application thereof

Abstract

The invention relates to an in-situ nitrogen-doped porous core-shell-structured carbon / selenium composite material. According to the invention, a core-shell-structured porous carbon nano-material withnitrogen-containing ZIF-8 selected from metal-organic frameworks as a core and ZIF-67 selected from metal-organic frameworks as a shell is used as a precursor, and the prepared porous carbon nano-material has a core shell structure; a metal-organic framework material having a three-dimensional interlocking-pore structure and containing nitrogen is used as a precursor; and the prepared porous carbon / selenium composite positive-electrode material is large in the pore size of the core and small in the pore size of the shell. The prepared composite material is uniform in pore size distribution and small in the size of carbon nanoparticles, can be thoroughly infiltrated by an electrolyte and shortens an electron transport path; and micropores and mesopores in the composite material improve theload capacity of selenium and have good restriction effect on the shuttle effect of selenium, so the composite positive-electrode material is effectively improved in cycle stability and capacity retention ratio.

Description

technical field [0001] The invention belongs to the technical field of electrode material synthesis, and specifically relates to an in-situ nitrogen-doped porous core-shell structure carbon / selenium composite positive electrode material and its preparation method and application. Background technique [0002] With the improvement of people's quality of life and the rapid development of electronic products, the existing lithium-ion batteries are limited by the positive electrode materials, and it is difficult to meet the needs of the market, forcing people to further research and develop small electrode material. Lithium-sulfur batteries have the advantages of abundant raw materials, low cost, high theoretical energy density (up to 2600Wh / kg, theoretical capacity up to 1673mA h / g), non-toxic, safe and environmentally friendly during use, which has attracted great attention. However, lithium-sulfur batteries usually have three disadvantages that are difficult to overcome: 1) ...

AI Technical Summary

Problems solved by technology

However, lithium-sulfur batteries usually have three disadvantages that are difficult to overcome: 1) Both elemental sulfur and lithium sulfide generated by discharge are insulating, which is very unfavorable to charge transfer; 2) polysulfide generated during charging and discharging The substances will dissolve in the organic electrolyte and diffuse to the negative electrode to form a "shuttle effect", resulting in the loss of active materials, reducing the utilization rate of active materials, making the irreversible capacity of the battery large and the capacity reduced; 3) the positive and negative electrodes in the process of charging and discharging The volume change of the material is huge. He et al. pointed out through research that the lithium of the negative electrode is consumed during the reaction to reduce the volume, and the positive electrode will expand at the same time. The huge volume change will destroy the electrode structure, and the volume change will lead to rapid capacity decay and poor cycle performance.

However, using selenium as the positive electrode material also faces this formidable challenge. The specific performance is as follows: 1) the dissolution of polyselenium compounds; The negative electrode reacts with it, causing a "shuttle effect"; the insulating insoluble Li 2 Se and Li 2 Se 2 Deposited on the surface of the positive electrode material, the electrolyte contact of the active material is hindered, and the cycle stability is reduced; 2) the volume change of the active material; due to the elemental selenium (4.81g / cm 3) and lithium selenide (2.07g / cm 3 ) has a large difference in density, which causes a large volume change during the charge and discharge process, resulting in the pulverization of the electrode structure

[0005] The defects of lithium-selenium batteries lead to problems such as poor cycle stability, fast capacity decay, and low Coulombic efficiency during use of lithium-selenium batteries. Therefore, further exploration of new electrode materials has important research and application significance

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