High-Capacity Silicon-Based Composite Anodes Interface With Solid-State Electrolytes In Solid-State Lithium-Ion Batteries

The demand for portable electronic devices and electric vehicles for energy storage equipment has increased sharply,among which the safety of lithium-ion batteries using with flammable and volatile organic electrolytes is worrying.In addition,traditional anode materials such as graphite(～370 m Ah g^-1)exhibit limited specific capacity,and it is urgent to seek anode materials with high energy density to promote the development of lithium-ion batteries.Silicon is a one of the most promising candidates because it has an ultra-high theoretical capacity(～3600 m Ah g^-1)and a relatively low discharge potential（～0.5 V vs.Li/Li⁺）,while also being one of the most abundant materials on Earth.However,the main reasons that limit the commercial development of silicon are:silicon is a semiconductor material,and its electrical conductivity is relatively poor;the huge volume expansion（～400%）during lithiation,the stress generated by the expansion leads to electrode pulverization/shedding,decreasing the cycle life of the battery;the huge volume effect during lithiation leads to the rupture of the stable solid electrolyte interphase（SEI）film on the silicon surface,which will form a new SEI film on the exposed new silicon surface.During the long-term cycle,the SEI film becomes thicker and thicker,eventually leading to a rapid decrease in capacity and low Coulombic efficiency.In view of the above problems,this paper uses the low activity of the solid electrolyte to reduce the reaction between the electrode and the electrolyte,and designs the double-coated structure of ion conductor and electronic conductor on the silicon surface to keep the electrode structure intact,improve the ionic and electronic conductivity of silicon-based anode,improve its electrochemical performance,and explore the dynamic evolution process and regulatory mechanism of its interface with solid electrolyte,as follows:（1）A solid electrolyte was prepared by compounding LATP electrolyte powder and PEO polymer,and modified by adding nanocellulose,which greatly improved the ionic conductivity of the electrolyte.The ionic conductivity of PEO/LATP/NCF at 50°C reached 1.62×10^-4 S cm^-1.The assembled Li//Li symmetric battery not only has a high ion transfer number（0.437）,but also can cycle stably for 1000 h at current of 0.05 m A cm^-2.The formation of a Li F-rich SEI layer facilitates the rapid diffusion of Li⁺,induces uniform deposition of Li⁺,thus prolongs the cycle life of the battery.The solid-state battery assembled with PEO/LATP/NCF electrolyte and LFP cathode exhibits good cycle performance at a charge-discharge rate of 0.2 C（2）Designing SiO₂@Li₃PO₄@C core-shell structure coated on micron-sized Si（MSi）（denoted as Si@SiO₂@LPO@C）can release stress generated by silicon volume expansion and maintain structure integrity while forming a stable SEI.Through theoretical simulation,the SiO₂ sandwich formed in situ can reduce the energy barrier of Li⁺from the Li₃PO₄ shell to Si shell.In addition,by cryo-TEM and XPS tests,it was found that the SEI of silicon-based anodes in solid-state batteries only grew on the outer surface of MSi,and the SEI formed contained abundant and stable Li F and a bit of Li₂CO₃ Therefore,Si@SiO₂@LPO@C anode shows high capacity and stable cycling performance in liquid and solid-state batteries.It exhibits a high reversible specific capacity of 2072 m Ah g^-1 at 0.2 A g^-1 with a 100%capacity retention after 100 cycles,and retaining a high specific capacity of 1435.2 m Ah g^-1 after 200cycles when paired with the NMC811 cathode to assemble a full cell.In addition,the electrode still exhibits stable cycling performance in solid-state batteries,maintaining capacities of1012.4 m Ah g^-1after 200 cycles and 1441.0 m Ah g^–1 after 80 cycles in half and full solid-state cells.（3）By sol-gel method and microwave heat treatment technology,a structurally stable Mg O layer is designed on MSi,and reduces the content of PAN to 30%from previous chapter.This Mg O@C cladding helps to relieve stress caused by the huge volume expansion,and in-situ Li-Mg alloy during charging and discharging process,accelerates the diffusion of Li⁺and electron transport,and enhances the mechanical performance of the silicon-based anode.Combining with PEO/LATP/NCF solid-state electrolyte,a Li F-rich SEI film is formed on the outer surface of MSi,which significantly enhances the stability of the interface.Therefore,Si@Mg O@C anode exhibits high capacity and excellent cycle stability in liquid and solid-state lithium batteries.At 0.2 A g^-1,the Si@Mg O@C electrode shows a high reversible specific capacity of2449.7 m Ah g^-1 and initial coulombic efficiency of 90.6%.After 500 cycles at 1 A g^-1 and 5 A g^-1,maintaining specific capacities of 876.6 m Ah g^-1 and 818 m Ah g^-1.The full cell assembled with the NMC811 has an initial high reversible specific capacity of 2606.7 m Ah g^-1,delivering a capacity of 1538.8 m Ah g^-1 after 400 cycles.In solid-state batteries,at 0.2 A g^-1,it has a reversible specific capacity of 2360.4 m Ah g^-1,and maintain 1670.9 m Ah g^-1 after 100 cycles,and the capacity retention rate is 70.8%.