Novel Two-dimensional Li-ion Battery Anode Of TiO₂/Carbon Composite

Interfacial energy storage contributes a new mechanism to the emergence of energy storage device with not only a high-energy density of batteries but also a high-power density of capacitors and it shows obvious pseudocapacitive mechanisms in lithium storage applications.2D metal-oxide nanosheets have already been extensively studied as electrode materials for the potential application in energy storage devices due to their short ion paths and highly-exposed active sites on/in surface/interface.Herein,we report on three different two-dimensional nanosheet materials for lithium-ion battery.(1)In this study,a success was achieved in preparing high-ordered two-dimensional(2D)carbon/TiO₂(C/TiO₂)nanosheet composite by using commercially available organic molecules with multifunctional groups and taking advantage of the wedge effects,oxidative polymerization and carbonization.An experiment was conducted to validate the excellent performance of this 2D composite in respect of interfacial energy storage.The coin cell with2D C/TiO₂ nanosheet composite demonstrates a specific capacity of as high as 510 m Ah g^-1and a high specific energy of 390.9 Wh kg^-1 at a specific power of 75.9 W kg^-1 with the current density of 0.1 A g^-1,and it also remains 39.0 Wh kg^-1 at a specific power of 8.2 k W kg^-1 with the high current density of 12.8 A g^-1.The excellent electrochemical performance can be attributed to the superior artificial interface capacitive Li⁺storage capability,which would bridge the energy and power density gap between batteries and capacitors.(2)Herein,Benzidine is used as the starting material to generate carbon nanosheets stacks through polymerization and carbonization,following by a wet-chemical etching to remove the template.The oriented nanosheet structures can provide accessible electrochemical channels for rapid diffusion of electrolyte ions,while the interconnected interlayer can also maintain high electronic conductivity and fast electron transfer,leading to a remarkably rate capability.Typically,the as prepared carbon nanosheets stack is capable to deliver a high specific capacity of 681.2 m Ah g^-1 at a current density of 0.1 A g^-1,a high specific capacity of 120.0 m Ah g^-1 can be maintained at a current density of 12.8 A g^-1,as well as long cycle life over 7000 cycles with a capacity of 100 m Ah g^-1 at a current density of 3 A g^-1.The outstanding rate performance and cyclability of carbon nanosheets can be attributed to the hierarchically porous and oriented nanosheets structure,which provide interconnected charge-transfer pathways,enable large contact area and interface channel between the electrolytes ions and the electrode material,and shorten diffusion length of lithium ions.(3)In this work,Small-sized TiO₂ nanoparticles intercalated into carbon nanosheets(CNS@TiO₂SNP-600)was successfully synthesized via in-situ polymerization-carbonization method,utilizing layered H₂Ti₄O₉(HTO)as template and benzidine as carbon source.The morphology and size of TiO₂ is greatly influenced by carbonization temperatures.The coin cell with the CNS@TiO₂SNP-600 electrode demonstrates a discharge specific capacity of as high as 430.4 m Ah g^-1 at a current density of 0.1 A g^-1,and the capacity retention rate is 88.1%after100 cycles;and it also displays a high discharge specific capacity of 101.8 m Ah g^-1 at a high current density of 12.8 A g^-1.The excellent electrochemical performances can be ascribed to the capacitance effect originating from the intercalated structure of in-situ grown CNS and TiO₂nanoparticles.