Gelatin Carbon Modified Lithium Secondary Battery Electrode Materials And Their Applications

As one of the next-generation electrochemical energy-storage devices,Lithium（Li）secondary batteries have received increasing attention and researches due to their high energy density and other advantages.However,it is still a big challenge to realize the practical applications of the Li secondary batteries,which are limited by the preparation and electrochemical performance of electrode materials.As a commonly used cathode material for the Li secondary batteries,Li Fe PO₄（LFP）has low electronic conductivity and ionic mobility,thus showing poor rate performance and limited cycle life;In addition,Li metal anodes have problems including Li dendrite formation and infinite volume expansion,resulting in short lifetime and potential safety problems of the Li secondary batteries.In view of the existing problems in the preparation and application of the electrode materials for the Li secondary batteries,gelatin was used to modify the electrode materials in this thesis.Gelatin-derived carbon modified Li Fe PO₄cathode（4-BM6h-20）with an average particle size of～175 nm and a continuous conductive network structure was prepared by efficient ball-milling and low-temperature pyrolysis processes.The gelatin-derived carbon network can not only significantly enhance the electron transport of the LFP cathode but also improve the structural stability of the LFP cathode during Li intercalation and delithiation processes.Moreover,no additional conductive agents and binders were needed for the 4-BM6h-20 cathode,which further enhanced its reversible capacity.Therefore,the 4-BM6h-20 cathode exhibited excellent rate performance(with reversible specific capacities of 160 m Ah g^-1 at 0.2 C and107 m Ah g^-1 at 10 C)and good cycle life（without capacity decay after 280cycles）.In addition,N,S-doped porous carbon nanobelts containing Mo S₂ sheets（Mo S₂@NSPCB）were prepared by electrospinning method using gelatin and metal salt as carbon precursor and auxiliary agent,respectively.The as-prepared Mo S₂@NSPCB possessed a flexible self-supporting structure due to the complexation between transition metal and gelatin precursor.Li anode modified by the Mo S₂@NSPCB fiber membrane showed good cycling performance(with stable Li deposition/stripping for over 2000 h at 1 m A cm^-2/1 m Ah cm^-2 and a small voltage hysteresis of～22.7 m V)and excellent practical performance(with stable Li deposition/stripping for over 1500 h at 3 m A cm^-2/3 m Ah cm^-2).In addition,the modification mechanism of the Mo S₂@NSPCB for Li metal anode was revealed by in-situ/ex-situ characterization,demonstrating that lithiophilic sites of N/S atoms and metal compounds can induce uniform Li deposition and suppress Li metal dendrites.The continuous three-dimensional conductive framework structure can effectively accommodate the volume expansion of the Li metal anode.