Preparation And Electrochemical Performance Of Si/C And Titanium Niobium Oxide Anode Materials For High Performance Lithium-ion Batteries

In recent years,silicon-based material has been considered as the most promising and prospective anode material for the next-generation lithium-ion batteries?LIBs?,which is ascribed to its ultrahigh theoretical specific capacity(3752 m Ah g^-1),wide sources,and environmental friendliness.However,the large volume expansion effect and low intrinsic conductivity of silicon during the process of Li⁺de-intercalation lead to the initial coulomb efficiency?ICE?and poor cycle stability of the LIBs,which seriously restrict the industrial application of silicon as a high-performance LIBs anode material.Similarly,the Ti₂Nb_2xO_4+5xhas been widely studied because of its stable crystal structure and high charge-discharge platform,which has excellent cycle stability during the?de?lithiation processes.However,Ti₂Nb_2xO_4+5xmaterials also have the problem of poor intrinsic conductivity.Aiming at the many problems of silicon and Ti₂Nb_2xO_4+5xas anode materials for LIBs,we have designed and prepared the silicon and Ti₂Nb_2xO_4+5xmaterials with different morphologies and structures,and then combined with good conductivity materials,which can solve the shortcomings of silicon and Ti₂Nb_2xO_4+5xas anode electrode materials and achieve excellent electrochemical performance.The innovative results obtained in this article are as follows:?1?The chestnut-like structure MSN@C@void@NC Si/C composite is prepared by using the stober and in-situ polymerization method,which the effects of dual-carbon layer and cavity on the structural maintenance and electrochemical performance of composite are systematically studied.And the results show that MSN@C@void@N-C composite shows the excellent electrochemical performance.Under the conditions of a voltage window of 0.01-2 V and a current density of 0.1 A g^-1,the first discharge specific capacity of the MSN@C@void@NC electrode is 2499m Ah g^-1.After 150 cycles at 0.3 A g^-1,the discharge capacity is still 1372 m Ah g^-1with the capacity retention rate of 54.9%.Besides,the discharge specific capacity still maintain in 816 m Ah g^-1under the large current density of 4 A g^-1.The cooperation of the double carbon layer and intermediate cavity can not only protect the silicon core from corrosion by the electrolyte,but also increase the electron transmission rate of the silicon-based material and provide space for the volume expansion of the silicon without damaging the electrode structure.?2?A simple hydrothermal method and a high-temperature calcination process are used to prepare the Ti Nb₂O₇?TNO?nano-particle decorated activated carbon cloth?ACC@TNO?composite with flexible self-supporting structure.And the electrochemical performance tests show that the ACC@TNO electrode displays a high discharge specific capacity of 356 m Ah g^-1and the ICE of 87%at a current density of 0.1 C and a voltage window of 1.0-3.0 V,After 500 cycles at 0.5 C,the discharge specific capacity is still 290 m Ah g^-1with the capacity retention rate of 81%.In addition,at a current density of 6 C,the discharge specific capacity is 183 m Ah g^-1.The excellent cycling and rate performance of ACC@TNO benefits from the synergistic effects between ACC and TNO.The introduction of N,S-ACC can provides a good 3D conductive network to enhance the conductivity for ACC@TNO composite.Moreover,ACC has a large specific surface area,which can accelerate charge collection and improve charge transfer capabilities,while TNO as an active material provides specific capacity for the overall ACC@TNO composite.?3?Based on the principle of synergistic effects,the single-core/double-shell m-TNO@Ti C@NC composite is prepared by using the m-TNO as the base material and introducing the ceramic material Ti C with excellent electrical conductivity,and then m-TNO@Ti C nanospheres are encapsulated by a nitrogen-doped carbon layer.via the solvent method and in-situ polymerization method.Electrochemical results show that the first discharge specific capacity is 378 m Ah g^-1and the ICE is 88.6%at the current density of 0.1 C.After 200 cycles at 0.5 C,the specific discharge capacity is as high as 328.6 m Ah g^-1.Similarly,m-TNO@Ti C@NC composite also shows excellent rate performance.At 5 C,the specific discharge capacity is 186.4 m Ah g^-1.The TNO@Ti C@NC material has excellent electrochemical performance,which can be attributed to the hierarchical structure that can not only provide a complete conductive network to improve the conductivity of m-TNO,but also establish a stable structure to maintain the stability of the anode.