Rational Design And Lithium Storage Properties Of The Carbon-Selenium Composite

Lithium selenide battery is a new type of lithium storage secondary battery based on active material selenium as cathode material.Lithium-selenium battery is expected to become a lithium-sulfur battery due to its high theoretical capacity(675 mA h g^-1),volumetric specific capacity(3253 mA h cm^-3)and selenium with good electrical conductivity(1×10^-3 S/m).Alternatives in the future.However,lithium-selenium batteries,like lithium-sulfur batteries,face two major problems:the shuttle effect and volume expansion.These two problems make lithium-selenium batteries have poor cycle stability and fast capacity decay.Therefore,solving the above two major problems is to study the core of lithium selenium batteries.In order to develop high-performance lithium-selenium batteries,the paper designs and synthesizes a carbon-selenium composite cathode material with in-situ nitrogen-doped porous structure to improve the electrochemical performance of lithium-selenium batteries.In this paper,the lithium storage properties of in-situ nitrogen-doped porous carbon-selenium,in-situ nitrogen-doped core-shell structure grade pore porous carbon-selenium,and in-situ nitrogen-doped porous carbon nanofiber-selenium were studied.1.ZIF-8 and ZIF-67 are precursors of porous carbon materials,and selenium carbon is compounded by co-melting method to obtain Se/C-ZIF-8 and Se/C-ZIF-67.Due to the nitrogen content of the ligand synthesized by the precursor,the resulting carbon is nitrogen-doped in situ.Both Se/C-ZIF-8 and Se/C-ZIF-67 showed good rate performance.Because the stability of precursor ZIF-8 was not as good as that of ZIF-67,the structure collapsed seriously during calcination,resulting in Se/C.-ZIF-8 has less cycle stability than Se/C-ZIF-67.2.Based on the experimental results of work 1,in order to obtain a porous carbon material with a small particle size and a stable structure,ZIF-8@ZIF-67 with a core-shell structure is a precursor of a porous carbon material.An in-situ nitrogen-doped core-shell structure grade pore carbon material?Se/N-CSHPC?was obtained by calcination.Three kinds of metal source ratio precursors ZIF-8@ZIF-67 were synthesized by normal temperature stirring method.The results show that the lithium selenide battery achieves the best electrochemical performance when the metal source molar ratio is 1:1.3.Based on work 2,the best performance precursor was fibrillated by electrospinning,calcined to obtain flexible porous carbon nanofibers,and Se/N-HPCFs were obtained by co-melting method.This method improves the cycle stability of the lithium selenium battery and greatly increases the reversible capacity.