Research On Controllable Synthesis And Lithium Storage Properties Of Mixed-Transition Metal Oxide Composites

As an important part of the new energy field,lithium-ion batteries?LIBs?have received widespread attention in the increasingly prominent context of today's energy and environmental issues.However,most of the commercial anode materials are graphite-based materials which have a low theoretical specific capacity of372mAh·g^-1.Such low capacity cannot meet the demand of energy storage applications.Therefore,the development of lithium-ion batteries with higher energy density and excellent rate performance is urgent.Transition metal oxides?TMOs?with high electrochemical performance have been considered as potential anodes candidate to replace graphite for future lithium-ion batteries in high power density fields.Even though the single TMO has a relatively high specific capacity,its development is largely restricted due to the severe volume effect and the particle pulverization during the charge/discharge cycles.The appropriately designed nanostructures and components of mixed-transition metal oxides?MTMOs?would shorten the electrons and ions transportation pathways and increase the contact interface of the electrode with electrolyte which would lead to higher electrochemical properties.In this paper,titanium-based,manganese-based and cobalt-based nanomaterials were prepared by hydrothermal synthesis and applied to lithium ion batteries.The detailed researches are as follows.?1?Co_2+xTi_1-xO₄ nano-octahedron single crystals covered by{111}planes with an average edge length of 200nm were successfully synthesized by a simple hydrothermal reaction using economical TiO₂ as titanium source.As anode materials for lithium ion batteries,Co_2+xTi_1-xO₄ delivered a high specific capacity of over766.5mAh·g^-11 at the current of 100mA·g^-11 after 60 cycles,as well as provided stable rate capability and lithium storage performance at high current density(680mAh·g^-1after 400 cycles at 1000mA·g^-1),which suggested its great potential to be an efficient electrode material candidate.?2?We used the C₄H₆MnO₄·4H₂O as raw material to prepare mesoporous manganese-nickel oxide with core-shell structure,and its structure and composition were analyzed by a series of characterization methods.The existence of NiO was confirmed by XPS and TEM.Then,the electrochemical performance test was carried out.The capacity of NiO-Mn₃O₄ was steady,and the coulomb efficiency remained above 96%.In the subsequent high current rate test,the reversible capacity could quickly recover and even higher than the initial cycle.?3?Co₃O₄@MnO₂ nanomaterials were prepared by the two-step hydrothermal synthesis method.The materials retained the basic morphology structure of the Co?CO₃?_0.5?OH?·_0.11H₂O precursor,and each Co₃O₄@MnO₂ nanorod was assembled into a urchin-like composites by sharing a common center.After the lithium-ion reactivation process,the reversible capacities of the electrode materials were promoted.We tested the pseudo-capacity and found that the contributions of the battery capacity at other potentials were mainly attributed to capacitive behavior except for the redox potentials.It showed that the capacitive capacity behavior could not be ignored,and the material possessed super electrochemical performance.The electrochemical impedance spectroscopy proved that the total impedance of the electrodes became smaller and the lithium ion diffusion coefficient increased in the subsequent charge/discharge cycles.?4?We used pure anatase TiO₂ and rutile TiO₂ to obtain H₂Ti₂O₅-Ana and H₂Ti₂O₅-Rut nanomaterials respectively,which possessed good mechanical properties.The comprehensive electrochemical test showed that the two electrode materials could overcome the volume effect during the charge/discharge cycles,and keep the structure stable.