Study On The Modification And Electrochemical Performance Of Lithium Anode By Lithium Affinity Composite Structure

As one of the most important energy storage devices in the 21st century,lithium-ion battery has been widely concerned.With the rapid development of science and technology,the development and progress of all walks of life are closely related to the continuous innovation and upgrading of energy storage devices.At present,mature and commercialized lithium-ion batteries are used in our lives.The anode materials used are carbon based materials with low theoretical specific capacity(374 m Ah/g).Although carbon materials have stable performance in the battery cycle,they can no longer meet people's demand for higher energy density batteries.Therefore,researchers have turned their attention to lithium metal anode materials again.Lithium metal negative electrode has a high theoretical specific capacity(3780 m Ah/g)and the most negative electrode potential,which is known as the"Holy Grail"of lithium-ion battery.However,it is easy to form dendrites under high current,which affects the capacity and cycle stability of the battery.When the lithium dendrite grows to a certain extent,it will break through the diaphragm and cause the internal short circuit of the battery to explode,so the safety is low.This paper aims to solve the problem of dendrite when lithium metal is used as anode material of lithium-ion battery.Through the construction of the surface modification layer structure of lithium metal anode,the protection of lithium metal anode in the process of battery cycle is realized.The mechanism of tin carbon composite fiber network as a modified layer to protect lithium metal negative electrode was explored,and the performance of symmetrical battery and all battery was tested.Compared with the unmodified lithium metal anode,the stability of the modified lithium metal anode is improved.The symmetrical cell can stably cycle for250 h at a small current density of 1 m A/cm~2 and 50 h at 5 m A/cm~2 and 5 m Ah/cm~2.The modified lithium metal negative electrode and the positive material lithium iron phosphate have excellent energy retention and cycle stability at 0.5 C and 1 C.On this basis,this paper analyzes the failure mechanism of the battery after the cyclic failure of tin carbon fiber modified lithium metal anode.After cycling failure,the surface of lithium anode matrix is seriously etched and has a large roughness.The uneven surface of matrix is the main cause of lithium dendrite growth,and lithium dendrite is the main cause of battery failure.In this paper,the surface of lithium metal negative electrode is alloyed by magnetron sputtering,in order to protect the lithium metal negative electrode from the surface of the root matrix and inhibit the formation of lithium dendrites.The surface alloying lithium metal and tin carbon composite fiber three-dimensional network are combined organically to form a double-layer composite structure modified on the lithium metal negative electrode,and the mechanism of protecting the lithium metal negative electrode is studied.Compared with the single-layer modified lithium metal anode,the double-layer modified lithium metal anode has better electrochemical performance in the test of high current density and high capacity density.The results show that the synergistic effect of the double-layer composite modified structure is more effective than that of the single-layer modified structure for the protection of lithium metal anode.Subsequently,this paper also applies the practical idea of double-layer composite modified structure to the study of other materials to protect the lithium metal negative electrode.It uses the lithium-friendly and low overpotential relative to lithium,and also applies to the surface modification of lithium metal negative electrode.The well-developed lithium silicon alloy is used as the surface gold modified layer,plus the three-dimensional network of pure carbon fiber is used to uniform electric field and reduce current density Compared with the pure lithium metal anode,the modified layer can protect the lithium metal anode by the synergistic action of the two.It shows excellent cycle stability at low current density,and stable cycle for 50 h(25 weeks)under the test condition of 5 m A/cm~2 5m Ah/cm~2.Therefore,the double-layer modified structure can be further extended to other kinds of materials as modified structure of lithium metal anode protection.