Study On The Design,Preparation And Performance Of Artificial SEI Film For Lithium-Sulfur Battery Anode

The replacement of traditional fossil energy by clean renewable energy is the key to achieve the goal of“peak carbon,carbon neutrality”,but the intermittency and uncertainty of clean renewable energy limit its wide application.The application of electrochemical energy storage in the grid is an important means to increase the proportion of renewable energy sources on the grid.Lithium-ion batteries are currently the most widely used electrochemical energy storage system.However,limited by the lower theoretical energy density of cathode material,the actual energy density of lithium-ion batteries is low and cannot meet the demand.Lithium-sulfur(Li–S)batteries based on conversion-type reactions with very high theoretical energy density(2570 Wh kg^-1)are expected to be the next generation of electrochemical energy storage systems.At present,the uncontrollable lithium dendrite growth and the rapid failure of the lithium cathode caused by severe side reactions are the bottlenecks limiting the development of Li–S batteries,which need to be solved urgently.In this paper,the strategy of constructing artificial SEI films is mainly used to improve the stability of metallic lithium anodes in Li–S batteries.Through the rational design of the components and structure of the artificial SEI films,the electrical and mechanical properties are regulated,and then the regulation of charge transport in the artificial SEI film,lithium-ion deposition kinetics,and lithium growth mode is achieved.The details of the study are as follows.A lithiated Nafion artificial SEI film was prepared on the lithium metal anode surface by applying the strategy of drop casting.The interaction between sulfonate groups and lithium ions in the Nafion artificial SEI film can homogenize the lithium-ion mass transfer flux on the lithium anode surface and prevent the uneven nucleation and growth of lithium,which in turn inhibits the formation of lithium dendrites.Meanwhile,the large number of sulfonate groups in the Nafion artificial SEI film can also shield the contact between Li PSs and lithium metal through the electrostatic shielding effect and reduce the corrosion behavior of Li PSs.The Li–S battery with lithiated Nafion artificial SEI film applied to protect the lithium anode has a discharge specific capacity of 791.5m Ah g^-1 after 250 cycles at a current density of 0.5 C,with a cycle retention rate of77.6%.The Li F and Na F-rich composite ultra-thin inorganic artificial SEI films were prepared on the lithium anode surface by a two-step in situ chemical reaction of lithium metal with Na PF₆ and Li PF₆ solutions.The Li F component has a high electron tunneling barrier,which can effectively improve the insulating property of the artificial SEI film and reduce the ectopic nucleation of lithium.The introduction of the Na F component can further improve the electron tunneling resistance of the SEI film and accelerate the transport of lithium ions in the SEI film.The introduction of Na F component can further improve the electron tunneling resistance of the SEI film and accelerate the transport of lithium ions in the SEI film.The Li-Li symmetric cells protected by Li F/Na F artificial SEI film can operate stably for 1500 h at a current density of 1 m A cm^-2 and a capacity of 1 m Ah cm^-2.In the near-practical Li–S battery,the cycle life of the Li–S battery with Li F/Na F artificial SEI film protecting the lithium anode can reach 150 cycles,while the bare Li anode fails after only 36 cycles.An organic/inorganic hybridized Li_xSi S_y/Nafion artificial SEI film was designed and synthesized.Among them,Li_xSi S_y in the bottom layer of the SEI film acts as a good ion conductor,providing a fast channel for the transport of lithium ions,reducing the impedance of the SEI film,and improving the reactivity of lithium ions;the lithiated Nafion component in the top layer effectively improves the migration number of lithium ions with the suppression of shuttle effect,which helps the uniform nucleation of lithium ions and reduces the side reactions.In addition,the Young's modulus of the Li_xSi S_y/Nafion artificial SEI film is as high as 14.2 GPa,which avoids the rupture of the SEI film and prevents the formation of lithium dendrites and the consumption of electrolyte.There is no dendrite generation and“dead lithium”accumulation on the electrode surface after 1400 h of cycling.At a current density of 0.1 C,by applying Li_xSi S_y/Nafion artificial SEI film to protect the lithium anode,the Li–S battery can reach a capacity retention rate of 79%and an average CE of more than 98%for 150cycles.An artificial SEI film composed of Li PAA and Li NO₃ was constructed on the surface of the lithium metal anode.The Li PAA/Li NO₃ artificial SEI film can continuously release NO₃^-during battery operation and decompose on the surface of the lithium anode to form a Li₃N-and Li N_xO_y-rich SEI film.The Li₃N and Li N_xO_y-rich SEI film can enhance the migration rate of lithium ions within the SEI film and the exchange current density of lithium deposition on the lithium anode surface,reduce the energy required for lithium ions to cross the SEI film,and induce a dendrite-free,uniform,and dense lithium deposition morphology.The average Coulomb efficiency of deposition/stripping of lithium electrodes protected with the Li PAA/Li NO₃ artificial SEI film can reach 99.15%.The cycle stability and lifetime of the Li–S cells were also significantly improved under near-utility test conditions.