Study On Protection Of Li Metal Anode By Artificial Construction Of Solid Electrolyte Interphase

With the improvement of people's living standard,the requirement of ecological environment has been strengthened.Based on this,it is urgent to development of green energy.In recent decades,lithium-ion batteries have been recognized as one of the most successful new energy electrochemical devices.It can be used as a power source for consumer electronics and as a power system for electric vehicles.However,with emergence of new electronic devices,more energy-specific electrochemical devices are urgently needed.Due to its high theoretical specific capacity(3860 mA h g^-1),Li metal anode has attracted great attention of researchers.However,there are still some problems in Li metal anode.On the one hand,uneven deposition of Li⁺on the surface of Li metal anode leads to the formation of Li dendrite during cycling.The increasing dendrite will penetrate membrane,and lead to the contact of cathode and anode,which will make the battery short-circuit.This will cause serious security problems.On the other hand,due to its intrinsic fragile characteristics,the natural SEI is difficult to adapt the expansion of electrode during cycling.The rupture of SEI will increase the contact area between Li mental anode and electrolyte,increasing consumption of electrolyte.In addition,side reactions between the electrode and the electrolyte interface can also reduce the efficiency and capacity of the battery.The focus of the paper is to carry out experiments by using simple physical methods.A series of polymer films are prepared by spin-coating to inhibit the formation of Li dendrite.Specific work includes the design of polymer films with high ionic conductivity.Basis on this,polymer film is prepared with strength and high conductivity.Finally,the polymer film is designed with lithium ion affinity site.The purpose of this paper is to construct artificial SEI film to protect Li anode effectively,inhibit the formation of Li dendrite,improve the compatibility between Li metal and electrolyte,and improve the cycle stability of Li metal anode in battery system.It provides a scientific basis for application of Li metal anode.Specific work is carried out as follows:?1?A flexible polymer film with high ionic conductivity and low resistivity is prepared with18-crown-6 as main component.The polymer film can provide more Li⁺channels during cycling.At the same time,the direct contact between Li metal anode and electrolyte is avoided.In presence of polymer film,the interface protective layer with high ionic conductivity is formed on the surface of Li metal anode,which effectively inhibited the appearance of Li dendrite.Li-Cu battery which is modified by this method has a stable cycle and high efficiency after 200 cycles at a current density of 0.2 mA cm^-2.There is also no large polarization voltage in long-term cycles of Li-Li symmetrical battery.In full battery,it is also shows a higher capacity.?2?High toughness ionic conductivity film is prepared.Sulfonated poly?ether ether ketone?with good stability and high conductivity was added.Lithium ions are deposited uniformly on anode surface with polymer film,and the goal of two-dimensional dendrite growth is achieved.In Li-Cu half-cell,Coulomb efficiency is more than 96%after 200 cycles at the current density is 0.2 mA cm^-2.Compared with unmodified batteries,Coulomb efficiency decreased to less than 80%under the same conditions.In Li-Li symmetrical battery,voltage of battery shows no large polarization after 500 h at the current density is 1mA cm^-2,while unmodified battery exhibits large polarization after 80 h.Both Li-S battery and ternary lithium-ion battery achieve excellent electrical performance with polymer film.?3?Ag particles as nucleophiles'deposition sites of lithium ions are introduced to polymer films?Ag-PF?.The film has a certain resistance at initial stage,after activation,a good conductive path between polymer film and Li metal anode surface has been established.At the same time,Ag particles in polymer film can induce the deposition of lithium at its designated nucleation site.A stable solid-liquid conductive interface is formed in cycle process of battery,and Li metal anode is protected successfully.In Li-Cu half-cell,Coulomb efficiency of modified battery has been stabilized above 95%at a current density of 0.2mA cm^-2.In Li-Li symmetric cells,batteries are stabilized for 434 hours at 1 mA cm^-2.In Li-S battery,the discharge specific capacity of modified batteries is 80.7 mA h g^-1 higher at a cycle of 100th cycle than that of blank with cycle at 0.2 C.