Structural Design Of Artificial Protective Layer For Lithium Metal Anode And Its Effect On The Performance Of Lithium-sulfur Battery

Rapid progress in portable electronic devices,electric vehicles,and smart grids has driven the booming development of energy storage devices such as lithium-ion batteries.However,the energy density of lithium-ion batteries based on intercalation chemistry is approaching its limits,which is difficult to meet the demand for high energy density energy storage devices for sophisticated electronic devices.Therefore,it is urgent to develop new types of energy storage devices to address this issue.Lithium–sulfur（Li–S）batteries are considered to be the most promising alternative to lithium-ion batteries due to their extremely high theoretical specific capacity(1675 m Ah g^–1)and energy density(2600 Wh kg^–1),cost-effectiveness,and environmental friendliness.However,the growth of lithium dendrites on the lithium anode and serious side reactions lead to poor cycle performance,low coulomb efficiency,and safety issues,which limit its commercialization process.In recent years,including three-dimensional current collectors,electrolyte modification,separator modification,and artificial protective layer strategies have provided a new idea to address the above issues.However,the high weight of the three-dimensional current collector limits the energy density of the battery,the electrolyte modification and separator modification involve high costs and complex processes,which are not suitable for practicality.In contrast,the artificial protective layers are a more promising method owing to their low cost,simple manufacturing process,and efficient suppression of lithium dendrites and side reactions.Therefore,to address the above issues and needs,this paper develops a series of artificial protective layers to eliminate the growth of lithium dendrites and reduce the occurrence of side reactions,thereby greatly improving the cycling stability of the lithium anode.The specific research contents are as follows:（1）To address the growth of lithium dendrites,a Li F-rich artificial protective layer was first developed by a solid-liquid reaction method to homogenize the Li-ion（Li⁺）flux at the interface.The protective layer effectively promotes the uniform distribution of Li⁺at the anode interface,accelerates the migration of Li⁺and guides the uniform deposition of lithium,thus avoiding the formation of lithium dendrites.As a result,the symmetric cells with a protective layer can be cycled stably for more than 800 hours at1 m A cm^–2 and 1 m Ah cm^–2.The Li–S cells with a protective layer show a high specific capacity of 760 m Ah g^–1 after 100 cycles at the current density of 0.1 C.The excellent cycling stability is demonstrated even at 0.5 C.In addition,the rate performance is improved compared to the Li–S cells using bare lithium anode.（2）To further avoid the growth of lithium dendrite in the long term,a"two-pronged"strategy of homogenizing the Li⁺flux and introducing the lithiophilic sites was proposed.A robust and homogeneous Sb-based hybrid lithiophilic artificial protective layer was constructed by an ion-exchange reaction approach to regulate the lithium nucleation behavior.As evidenced theoretically and experimentally,the as-prepared protective layer has excellent electrolyte wettability and fast charge transfer kinetics,which can promote the uniform distribution of Li⁺at the interface.In addition,the lithiophilic Sb embedded in the protective layer provides rich sites for lithium nucleation,which effectively reduces the overpotential and induces homogeneous lithium deposition.As a result,the symmetric cells with a lithiophilic protective layer exhibit a long lifetime of over 1600 hours at 1 m A cm^-2 and 1 m Ah cm^-2.Furthermore,applying the protective layer technology of the lithium anode,the Li–S cells obtained a capacity retention of 60%after 800 cycles at 1 C,which is much higher than that of Li–S cells without a protective layer（only 24%capacity retention after 800 cycles at 1 C）.The Li–S cells with the protective layer can also cycle stably for 60 cycles even at a high-loading cathode,an ultrathin anode,and a low electrolyte/sulfur ratio.（3）To avoid the growth of lithium dendrites while further suppressing the side reactions,a MOF/PDMS composite bionic artificial protective layer was constructed on the lithium anode by a drop coating method.This protective layer can not only homogenize the Li⁺flux and promote the uniform deposition of lithium,but can rely on flexibility to adapt to volume changes.In addition,the MOF in the protective layer has a high electronegativity,which can form an electrostatic shielding effect with polysulfides.This can effectively prevent the lithium anode from contact with polysulfide/electrolyte,and prevents the corrosion of the lithium metal anode.As a result,the symmetric cells with a protective layer demonstrate cycle stability for up to 1400 hours at 0.5 m A cm^-2and 0.5 m Ah cm^-2.When applied to Li–S cells,the Li–S cells modified with the protective layer exhibit excellent rate performance and cycling stability（69%capacity retention in 100 cycles at 0.1 C,77%capacity retention in 200 cycles at 0.5 C）.