| Lithium is the metal element with the smallest density in the world.It has a very high theoretical specific capacity(3860 m Ah g-1)and the most negative electrode potential（-3.040 V vs.SHE）when used as the anode material of secondary battery.Li metal batteries are therefore endowed with prominent theoretical energy densities highly desirable as next-generation energy storage devices.However,the lithium metal anode is prone to lithium dendrite and“dead lithium”in the process of battery use,and with the expansion of the electrode volume,the battery efficiency is reduced and the service life is shortened.Therefore,there is a long way to go for commercialization of lithium metal anodes.In this paper,TiO2-B nanowires with high specific surface area of lithium battery anode material were prepared,and then TiO2-B/Li composite anode was prepared by mixing intertwined nanowires with lithium metal.Finally,the composite anode was prepared by pouring molten lithium into the 3D nickel foam skeleton with different surfaces to inhibit the growth and volume expansion of lithium dendrites.The specific work mainly included the following aspects:（1）Preparation of TiO2-B nanowires as anode materials for high-performance lithium-ion batteries.Titanium dioxide P25 nanowires were transformed into titanate nanowires in alkaline solution by hydrothermal method,and TiO2-B nanowires were prepared by acid pickling and then hydrothermal treatment.The prepared anode material for lithium-ion battery had a high specific surface area of 120.67 m2g-1,and the morphology of nanowires changes with the change of hydrothermal temperature.With the increase of hydrothermal temperature,the nanowires were gradually transformed into nanorods.The electrochemical properties of TiO2-B nanowires prepared under different hydrothermal conditions were tested.The results showed that the samples prepared at the first hydrothermal temperature of 220℃and the second hydrothermal temperature of 160℃exhibited the best electrochemical performance.At the current density of 1 C(1 C=300 m A g-1),the initial discharge capacity of the material was 227.9 m Ah g-1.The battery capacity could still be stabilized at 209.8m Ah g-l,and the capacity retention rate was 92.07%after 200 cycles.In addition,the initial discharge capacity was 182.3 m Ah g-1at 10 C,and the battery capacity could still maintain 93.2%(about 169.9 m Ah g-1)after 100 cycles.（2）Preparation and electrochemical performance of TiO2-B/Li composite anode.On the basis of the previous chapter,the composite negative electrodes containing different proportions of lithium metal and TiO2-B were prepared by mechanical mixing method and melt mixing method,respectively.After assembling the half battery,through the test of rate performance and long cycle performance,we found that the lithium metal and TiO2-B composite negative electrode with the ratio of 5:5 by melting mixing method showed the best electrochemical performance.There was no obvious lithium dendrite and"dead lithium"formation on the surface of the composite anode after battery cycle.The symmetrical battery composed of TiO2-B/Li（5:5）composite negative electrode could stably cycle 1000 cycles and the polarization voltage could be controlled at about 68 m V at 3 m A cm-2and 1.5 m Ah cm-2.In addition,the composite anode was assembled with cathode material NCM811 and S@NC,respectively,and the long cycle performance was tested at 1 C and 0.5 C,respectively.Under the condition of 0.5C,the TiO2-B/Li-S@NC full battery could still maintain 640.3 m Ah g-lafter 500 cycles,and the capacity retention rate was 85.37%.In addition,the TiO2-B/Li-NCM811 full battery still had a capacity retention rate of 83.32%after cycling at 1 C for 500 cycles.（3）Preparation and performance study of modified nickel foam and lithium metal composite anode.The Ni3N/NF collector prepared by hydrothermal method had large specific surface area and high contact area with molten lithium,which could greatly shorten the infiltration time of molten lithium and absorb more lithium.The mass specific capacity of the composite anode was as high as 2523.3 m Ah g-1.In the constant current charge-discharge test of the symmetrical battery,under the current density of 1m A cm-2 and the area capacity of 1 m Ah cm-2,the Li-Ni3N/NF symmetrical battery showed the best stability and the lowest polarization voltage（45m V）.The whole battery was assembled with the cathode material NCM 811of lithium ion battery,and the long cycle performance was tested at 1 C.The initial discharge capacity of the Li-Ni3N/NF whole battery could reach 168.5 m Ah g-1.And the capacity could still be stabilized at 149.2 m Ah g-1,and the capacity loss was 11.5%after 500cycles.In this work,the anode material TiO2-B for lithium-ion battery was prepared firstly.And then,by using it as the framework,the TiO2-B/Li composite anode was prepared.Compared with pure lithium anode,the composite cathode showed better cycling stability.Finally,Ni O and Ni3N were grown in situ on the surface of the nickel foam to construct the composite negative electrode with two different structures.It showed better lithiophilic property and better cycling stability compared with the simple nickel foam skeleton.This paper provided a new choice to design stable hosts with high capacity and high stability in lithium metal anode. |
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