Rational Design And Intensive Study Of High Performance Silicon And Lithium Metal For Lithium-Batteries Anode

In order to respond to the rapid development of new electronic devices and electric vehicles,it is particularly important to develop high-performance lithium-ion batteries.Therefore,these new types of positive and negative electrode materials including positive electrodes such as silicon,tin and lithium negative electrodes,and sulfur and oxygen attract many researchers' attention.Silicon is considered to be a very promising electrode material due to its huge reserves,environmental friendliness,low operating potential and extremely high specific capacity(equivalent to ten times higher than that of the currently used graphite cathode).However,relative to these significant advantages,the disadvantage of silicon as a negative electrode is also obvious.The main problem is that the huge volume expansion(approximately 4 times)of the silicon negative electrode in the battery cycle leads to electrode pulverization and unstable solid electrolyte interface,thus seriously affect its cycle stability and life.In the last decade,researchers have focused on a variety of different nano-silicon structures such as nanoparticles,nanowires,nanotubes,and nanopores,which have shown good mechanical properties to ease the huge volume expansion in the cycle and thus increase the cycle life.Lithium metal has a very high theoretical capacity(3860 mAh/g),a very low density and the lowest electrochemical reaction potential.These good characteristics make metal lithium battery systems a hot topic of research.However,the lithium metal battery system also has a series of problems,for example,because the lithium metal negative electrode will generate lithium dendrites during the battery cycle,and thus easily lead to short circuit and cause fire and other safety hazards.Some recent studies have found that the growth of lithium dendrites can be limited by optimizing the composition of the electrolyte.Another idea is to protect the growth of dendritic lithium and stabilize the solid electrolyte interface by designing a nanoscale protective layer structure on the lithium negative electrode to protect the lithium metal electrode.Although these methods have improved the performance of silicon/lithium negative electrodes in the past,designing a simpler structure,simplifying the synthesis process,and further improving the cycle stability performance are still the research goals of silicon/lithium negative electrodes,and are of great significance for future industrialization.This paper aims at the silicon anode and the lithium metal cathode.We proposed various new preparation methods and structural designs to simplify the preparation and synthesis process and further improve the performance of the battery.For silicon,we applied an ultra-thin zinc oxide protective layer on the surface of silicon negative electrodes by atomic layer deposition(ALD),and proceeded from industrial crude silicon sources to propose a low-cost,controllable method for synthesizing silicon nanoparticles;there is a process for synthesizing doped porous silicon nanoparticles;for lithium metal we have proposed a layer based on PDMS film designed to protect metal lithium.The following results have been achieved:1.ALD zinc oxide protection of the work of the silicon electrode:We first proposed through the atomic layer deposition method of zinc oxide film coated on the silicon nanoparticle negative electrode,thereby enhancing the stability of the silicon negative electrode in the cycle,showing a high specific capacity.The main advantages are:(1)the zinc oxide thin film obtained by atomic layer deposition is relatively uniform.When lithium is first intercalated,lithium ions first react with zinc oxide to form lithium oxide and zinc crystal grains.This reaction is an irreversible reaction and the resulting oxidation occurs.Lithium becomes the actual protective layer,and the zinc crystal grains dispersed in the lithium oxide matrix improve the conductivity of the entire protective layer;(2)the intact and uniform zinc oxide film protects the silicon particles from electrochemical contact in the recycling reaction,the cycle stability of the specific capacity is improved;(3)the highly stable and stable zinc oxide film provides a stable adhesion layer for the solid electrolyte layer formed in the reaction,stabilizes the SEI film,and improves the circulation of Coulombic efficiency.This method provides a new idea for solving the serious problems brought about by the large volume change in the silicon negative electrode cycle,and this method is compatible with the commercialized slurry process and promotes the commercialization of the silicon negative electrode.2.Industrial crude silicon is the source of low-cost and controllable preparation of silicon nano-particle anodes:We have proposed a new and simple method for the preparation of nano-silicon anode materials that can be synthesized in large scale,starting directly from low-cost industrial silicon.The resulting particle size is controllably adjusted by high-energy ball milling.Both types of silicon coated with carbon showed excellent electrochemical performance,and the capacity retention after 100 cycles of deep circulation was above 97%.We hope that this work will provide a highly efficient choice for the production of nano-silicon particles in a large scale and at a low cost.3.Simultaneous realization of perforation and doping preparation of silicon nanoparticles:We proposed a completely new and simple process for mass production and simultaneous perforation and doping of nano-silicon particles.We successfully prepared nano-silicon particles with a P doping concentration of 3.7 at%and a porosity of 45.8%.The particles have very good electrochemical properties,performing 100 charge-discharge cycles at a current density of 0.5 C and still maintaining a mass specific capacity of 2000 mA h/g.At the same time,it has very good rate performance,maintaining a mass specific capacity of 1600 mA h/g at a current density of 5 C.After the carbon coating treatment,it can meet the requirement of large current and long cycle.After 940 cycles at a current density of 1 C,the capacity of 1500 mA h/g can be maintained.In general,our process has many advantages:(1)this simple process simultaneously achieves perforation and doping of silicon nanoparticles;(2)porosity and doping concentration of nano-silicon particles can be changed by changing P2O5 and Si.The proportion of the regulation;(3)the process only includes ball milling and pickling,and the raw material prices are low,and simple mass production can be foreseen.This preparation method will play an extremely important role in achieving price advantage for energy storage of P-doped porous nano-silicon particles,and has great potential in the application of thermoelectricity and photovoltaics.4.Work of a Lithium metal protective layer based on a PDMS thin film:We have demonstrated that a PDMS protective film used for a lithium metal anode can greatly improve the electrochemical performance.With the protection of thin films and porous PDMS membranes,the cyclic coulomb efficiency can be stabilized at about 95%over more than 200 cycles of conventional carbonate electrolytes.Combining PDMS protective films with other ongoing efforts,such as the development of new electrolytes,is expected to further improve performance.In summary,this modified PDMS-based protective layer offers several advantages as listed below:(1)PDMS thin films are chemically and mechanically stable in the electrochemical cycle to suppress dendrite formation and at the same time flexibly adapt Li deposits change in volume;(2)nanopores can achieve efficient lithium ion transport;(3)the entire process is highly scalable,and because PDMS is chemically inert,this method is associated with other developments such as electrolyte development.The strategy is compatible.This work not only proposes a new solution with cost advantages and improved performance of lithium negative electrodes,but also provides new ideas for the large-scale production of metallic lithium negative electrodes.In addition,its proposed use can be matched with the development of new electrolytes,providing more possibilities for the future development of higher performance lithium battery systems.The above results point out a new path for solving the problems of low cycle efficiency,poor cycle stability,and complicated preparation and synthesis processes for lithium negative electrode and lithium negative electrode,and is of great significance for the development of a new type of high performance,commercially available lithium battery.