| Due to the low theoretical specific capacity of 372 m A h g-1,the graphite anode commonly used in commercial lithium-ion batteries is difficult to meet the current market demand for high energy density lithium-ion batteries.Tin based and silicon-based materials are expected to become the next generation of commercial anode materials for lithium-ion batteries due to their high theoretical specific capacity,large reserves and low cost.However,tin based and silicon-based anode materials have alloying reaction with lithium ion in the process of lithium intercalation,resulting in huge volume expansion,which makes it difficult for active materials to maintain stable electrical contact with current collectors and conductive additives,and makes the cycle life of batteries difficult to meet the needs of practical life.In addition,problems such as poor conductivity also limit the practicability of tin based and silicon-based anode materials.In order to solve the above problems,the main research work of this paper is as follows:（1）A highly stable composite electrode with nano Sn O2 as active material,carbon nanotube（CNT）as framework and polyvinylidene fluoride（PVDF）derived carbon as carbon matrix was prepared by slurry coating and heat treatment.In this electrode,PVDF derived carbon and CNT framework replace PVDF to form an"all carbon binder".Compared with the traditional PVDF binder,all carbon binder has stronger bonding ability,which can effectively combine the particles of anode material and current collector,and provide good mechanical stability and conductivity.The reversible specific capacity of the composite electrode is 861.4 m A h g-1 after 500 cycles at a current density of 0.75 A g-1,and the capacity retention rate reaches 87.3%.Compared with the electrode prepared by traditional method,the structural stability and electrochemical performance of the composite electrode are improved significantly.In addition,the cycling performance of the"all carbon binder"based composite electrode with high loading is also excellent.The electrode can maintain a stable cycling of 100cycles with an area specific capacity reaches 2 m A h cm-2,which meets the standard of commercial battery.It proves that this simple and effective preparation method has considerable practical value.（2）By using silane coupling agent KH560 as a single silicon source and carbon source,two dimensional Si/C composites were prepared in molten KCl/Li Cl mixed salts with magnesium powder at high temperature.In this reaction process,the carbon atoms in the organosilicon will be induced to recombine in the molten salt system to form a two-dimensional sheet structure,and the silicon oxygen（Si-O）bond will be reduced by magnesium powder,which will be converted into silicon in situ and embedded in the two-dimensional carbon substrate.This two-dimensional carbon substrate not only provides excellent conductivity and ion transport rate,but also inhibit the large volume expansion of silicon during cycling.In addition,with TEOS as the organic silicon source,the gas mixture containing argon and hydrogen was used in the same system for in-situ the reduction of Si-O bonds.The two-dimensional structure with partially reduced Si Ox embedded in carbon substrate could also be obtained.The first discharge capacity of Si/C material is 1660.4 m A h g-1,and the discharge capacity remains 1340.7 m A h g-1 after 150 cycles at 0.5 C.The Si Ox/C composite material also shows stable cycle performance.The reversible specific capacity is 781.6 m A h g-1 and the capacity retention rate remains 70.5% after 100 cycles at 0.5 A g-1. |
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