Syntheses And Electrochemical Performances Of Anode Materials For Lithium Metal Batteries

As the most successful commercial secondary batteries,lithium-ion batteries(LIBs)have been widely used in various fields.However,with the rapid development of society,the demand for high energy density of energy storage equipment is getting higher.Lithium metal batteries(LMBs)use metallic lithium as negative electrode.Compared with graphite,metallic lithium has the lowest redox potential(-3.04 V vs Standard Hydrogen Electrode),ultra-high specific capacity(3860 mAh g-1),and low mass density(0.534 g cm-3),which greatly improves the energy density of batteries.However,the commercialization of lithium metal batteries still faces many problems:metallic lithium,due to its high reducibility,can spontaneously react with electrolyte,which leads to low Coulombic efficiency.Fresh metallic lithium is constantly exposed during the charge/discharge process,which will further aggravate electrolyte consumption;lithium dendrites will be produced when metal lithium is deposited unevenly on the negative electrode.Lithium dendrite will pierce the separator,causing a slight short circuit of the battery and seriously shortening the battery life.This thesis mainly studied the electrochemical behavior of metallic lithium on the negative electrode.A series of protection strategies for lithium metal anode were proposed,the main contents are as follows:(1)Through the method of alkaline solution oxidation,a uniform copper oxide nanosheet array was grown on the surface of the copper foam,which increased the lithophilicity of the material and reduced the energy barrier of lithium deposition;the electric field coupling inside the current collector was changed by pressure-tuned,and the electric field distribution was also homogenized so that metallic lithium was deposited uniformly on the anode.In the electrochemical performance test of the symmetrical battery,it can cycle more than 5000 times under the current density of 5 mAh cm-2.The full battery paired with lithium iron phosphate cathode material can cycle more than 500 times,meanwhile the capacity retention is above 97%(2)The above method is extended to a cheap copper mesh to obtain a copper mesh with in-situ grown copper oxide nano-layers on the surface.Compared with copper foam,the copper mesh has a lower electrode thickness,which is beneficial to the uniform deposition of metallic lithium in along the current direction.At the same time,it also effectively retained the structural advantages of copper foam,such as:the grid structure can ease the volume change during charge and discharge process;the oxide layer reduced the nucleation/growth overpotential of lithium metal deposition.In a half-cell test with a current density of 3 mA cm-2 and a capacity of 1 mAh cm-2,the cycle life can exceed 230 cycles;the electrochemical performance is also excellent in the full-cell tests paired with lithium iron phosphate and LiNi0.6Co0.2Mn0.2O2 cathode materials,the cycle life is more than 300 cycles under the current density of 1C.