Microstructure-controllable Lithium Battery Electrode Materials With Optimized Electrochemical Performances

The theoretical specific capacities of commercial graphite anode and several commercial cathodes are relatively low.In order to develop lithium batteries with higher energy density and to meet the ever-expanding social needs,it is necessary to develop electrode materials with higher specific capacities.The microstructure of the electrode material greatly affects its electrochemical performances.Therefore,reasonable control of the microstructure can significantly optimize the electrochemical performances of electrode material.By virtue of the high theoretical specific capacity and the low working potential,Si is recognized as an ideal next-generation lithium-ion battery anode.However,Si has low Li+and electronic conductivity,and huge volume changes during the lithiation/delithiation process,which restricts the rate performance and cycling performance of Si anode.Here,3D nanoporous SiGe composite anodes were synthesized by chemical dealloying method.Because of the good ionic and electronic conductivity of Ge,the SiGe composite anodes exhibit better rate performances than Si anode.By adjusting the composition of the precursor,the microstructure of SiGe composite anodes can be controlled effectively.In particular,the Si12Ge8 anode presents uniformly coral-like microstructure with hierarchical micropores-mesopores distribution and continuous ligaments with size of?50 nm.The nanopores can shorten Li+diffusion distance,offer more electrode/electrolyte contacts and accommodate the volume change during the lithiation/delithiation process,so that Si12Ge8 anode deliver good rate performance and cycling performance.The reversible specific capacity maintained 1158 mAh g-1 after 150 cycles at a current density of 1000 mA g-1.Li metal anode has theoretical specific capacity higher than Si,extremely small density and the lowest working potential.It is regarded as the "Holy Grail" for the next generation lithium batteries with higher energy density.However,the unevenly deposited Li metal anode might generate "dead" lithium and lithium dendrites,which will reduce the coulombic efficiency of the battery,shorten its life span,and cause major accidents such as fires and explosions.Therefore,the deposition morphology of Li metal anode should be well controlled.To this end,a 3D current collector with anisotropic interfacial activity was prepared.The surface of the current collector was covered by a dense ZnO layer with poor conductivity,which can reduce the interfacial activity in the horizontal direction.Passed through the ZnO layer,the Cu nanosheet arrays vertically grown on the current collector.The Cu nanosheet arrays have low tortuosity and good conductivity,and the surfaces of Cu nanosheets are uniformly modified with lithiophilic ZnO particles,so that the Cu nanosheet arrays can increase the interfacial activity in the vertical direction.The anisotropic interfacial activity inside the 3D current collector can induce the preferential lateral deposition and uniform dendrite-free deposition of lithium and significantly optimize the electrochemical performance of the Li metal anode.With a current density of 0.5 mA cm-2 and a deposition capacity of 0.5 mAh cm-2,the Li metal symmetric cell can work stably for more than 3000 h,and the coulombic efficiency of the Li metal half-cell maintains about 98%after 1300 cycles.With a current density of 2.0 mA cm-2 and a deposition capacity of 1.0 mAh cm-2,the Li metal anode can work stably for more than 2500 h,showing a long cycle life.Nickel sulfide cathodes have also attracted increasing attention due to their high theoretical specific capacity.Nickel sulfides are mostly prepared by solid-state sulfidation,wet chemical method and gas-phase sulfidation.These methods usually require a long period,high energy consumption,and complicated processes.In addition,wet chemical method needs to use toxic solvents,which might cause pollution.Herein,a solvent-free microwave plasma reaction method was proposed,which can quickly prepare Ni3S2 free-standing lithium battery cathodes within 1?6 min without any solvents or toxic reagents.By adjusting the composition of the plasma,the microstructures of Ni3S2 cathodes can be effectively controlled.In particular,the stone-forest-like Ni3S2(SF-NS)has both high material integrity and internal nanopores.The high material integrity can take advantage of the good conductivity of Ni3S2,and the internal nanopores can promote the penetration of electrolyte,increase Li+transferability and buffer the volume change of SF-NS.Therefore,SF-NS shows good rate performance and cycling performance.The universality of the microwave plasma reaction method for morphology control of materials has also been verified,indicating its great application potential.