| Lithium metal is considered to be the preferred anode material for the next generation of high energy density batteries due to the high theoretical capacity (3860 mAh/g) and the low redox potential (-3.045 V vs SHE). In the cycle process, the security problems of lithium dendrite growth bring the seriously negative influence on the commercialization process of lithium secondary battery. At the same time, lithium metal reacts with the electrolyte continuously because of its high activity, so the cycle efficiency of the battery is affected. In order to solve these problems, we prepared the coating layers with different materials on the surface of lithium by sputtering technology and studied the performance of lithium electrode and mechanism of coating modification through characterization test. The research contents are as follows:(1) Failure mechanism of the lithium secondary battery, the electrochemical process of lithium electrode, the growth of dendrite, and the cycle efficiency were investigated on the assembled Li-Cu battery. Li3N thin films with high ionic conductivity were grown on the surface of the lithium metal electrode by ion beam sputtering technology. Interfacial stability and cycle performance of lithium electrode were studied after nitriding process. The test results proved that the Li3N coating layer could inhibit the side reaction on the interface of electrode, enhance the stability of the electrode interface and improve the long cycle life performance.(2) Al2O3 as the sputtering target, nano-coating layer was deposited on the surface of lithium metal by magnetron sputtering for the first time. The effects of Al2O3 on the surface morphology of lithium electrode and the electrochemical properties were studied. The results indicated that the Al2O3 coating layer evenly distributed on the surface of the electrode and the electrolyte soaking test of 96 h showed a high degree of stability. The cycle life of lithium electrode coated with 20 nm Al2O3 was more than doubled (up to 600 cycles) under the current density of 0.5 mA/cm2. In all-solid state battery test, the coated lithium electrode also exhibits stable polarization potential. In the cyclic test of Li-S battery, the discharge capacity of the battery with 20 nm the Al2O3of at a rate of 0.2 C after 100 cycles is 697.9 mAh/g, the capacity retention rate of 65.8%, which is far higher than the uncoated lithium electrode with a capacity retention of only 38%. AC impedance of different cycles showed that the impedance of the electrode coated with 20 nm Al2O3 did not increase during the 200 cycles, and there was no obvious dendrite on the surface of lithium electrode coated with 20 nm Al2O3 after 200 cycles.(3) Li3PO4 as coating material,which has chemical stability and high ionic conductivity, was deposited on the surface of the lithium electrode by magnetron sputtering technology. Mechanism of coating Li3P04 to enhance the performance of the lithium electrode was studied. Amorphous films with different thickness were prepared on the surface of metal lithium by sputtering technique at room temperature, which was observed by TEM. The amorphous film has ion conductivity of 2.8x10-8 S/cm while the electron conductivity was 1.4×10-10 S/cm. Lithium electrode with 30 nm Li3PO4 coating has better interface stability and showed excellent cycle life under current densities of 0.5 mA/cm2 and 1 mA/cm2. After 100 cycles, 74 ?m thick "dead Li" and SEI layer on the surface of the uncoated electrode were observed by SEM, while there is smooth without dendrite on the surface of the coated electrode Li-S battery test showed that the coated electrode has a higher capacity retention rate and coulombic efficiency. Finally,we think the amorphous Li3P04 nano-coating layer with uniform and dense distribution on the surface of the lithium electrode with the characteristics of isotropic can provide a uniform current distribution, forming a homogeneous metal lithium deposition, reducing lithium dendrite growth. |
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