ИСТИНА

Lithium is known as the anode material with the highest possible specific capacity for li-ion and li-sulfur cells. However, lithium tends to form ramified needle-like or bush-like structures (“dendrites”) during electrodeposition. Formation of such structures may be driven by the solid electrolyte interphase layer – SEI. This phase is formed on the surface of lithium due to its high reactivity and mainly consists of lithium and electrolyte reaction products. Composition and structure of this layer highly depend on composition of electrolyte and cycling conditions. Both reasons of needle-like lithium deposition and morphology and properties of SEI are not clearly understood. Difficulties with such interfacial analysis are associated with high sensitivity of lithium to environment. Any impact on surface of lithium can dramatically change properties of interface, which makes it different than it was in the cell. The best way to overcome this issue is to utilize in situ methods of analysis. A good method to monitor morphology of interphase is neutron reflectometry, which is based on specular scattering of neutrons from flat interface. The benefit of use of neutrons is that it have high attenuation length and they are non-destructive. It allows us to make this method useful for in situ conditions. For in situ neutron reflectometry a special electrochemical cell was designed. The main feature of such experiments is that it collects overall information from all electrode, what gives us statistical information of morphology. It allows us to quantitatively evaluate various approaches to suppress uneven deposition of lithium and get indirect structural and compositional information. Using this method, we have monitored the formation and development of SEI and electrodeposition of metal lithium on the electrode in two various electrolytes. The first contained lithium salt and the second contained additive which should have suppressed needle-like growth according to our preliminary results. It have revealed that deposition occurs very unevenly and further data processing requires additional chemical composition information. In case of presence of additive it is observed that no deposition occurs due to additive decomposition.