Design And Performances Of Layered Cathode Materials(NCM523)/Electrolyte Interface For Lithium Ion Batteries

Enhancing the stability of cathode/electrolyte interface and reducing the side reaction at the interface is the key to improve the cycling stability of cathode materials under high cut-off voltage.In this work,Ni-rich LiNi_0.5Co_0.2Mn_0.3O₂?NCM523?cathode materials are taken as the pristine materials.NiF₂ artificial interface was proposed for the first time to construct a stable cathode/electrolyte interface layer to improve the cycling stability of LiNi_0.5Co_0.2Mn_0.3O₂ cathode material under high cut-off voltage by a wet chemical method.At the same time,the tris?trimethylsilyl?phosphite?TMSPi?and prop-1-ene-1,3-sultone?PES?were added in electrolyte to improves the stability of LiNi_0.5Co_0.2Mn_0.3O₂/electrolyte interface at high cut-off voltage,and thus enhancing the cycling performance of LiNi_0.5Co_0.2Mn_0.3O₂cathode material under high cut-off voltage.NiF₂-coated LiNi_0.5Co_0.2Mn_0.3O₂ cathode materials were synthesized by a wet chemistry method.XRD,SEM and TEM analyses show that NiF₂ was successfully coated on the surface of LiNi_0.5Co_0.2Mn_0.3O₂ particles.NiF₂ coating can effectively improve the electrochemical performances of LiNi_0.5Co_0.2Mn_0.3O₂.After 100 cycles under 4.5 V,the 1.0wt.%NiF₂-coated LiNi_0.5Co_0.2Mn_0.3O₂ possesses a higher capacity retention?86.9%?than pristine LiNi0.5Co0.2Mn0.3O2?69.0%?.XPS,SEM and TEM analyses after cycles reveal that the NiF₂ layer successfully inhibites the side reaction of electrolyte and cathode material,thus reducing the growth of SEI film on the surface of cathode,leading to a lower growth of impedance and polarization.NiF₂ coating can effectively improve the cycling stability of LiNi_0.5Co_0.2Mn_0.3O₂ at high temperature.The capacity retention of the LiNi_0.5Co_0.2Mn_0.3O₂ materials increases from 24.4%to75.6%after 100 cycles at 55 ? under 4.5 V by 1.0wt.%NiF₂ coating.TMSPi effectively improves the cycling stability of LiNi_0.5Co_0.2Mn_0.3O₂ cathode materials under 4.5 V.After 100 cycles at 30 ?,the capacity retention of cells with2.0wt.%TMSPi has a higher capacity retention?96.4%?than bare sample?69.0%?.In addition,the discharge capacity increases from 84.0 mAh g^-1 to 138.9 mAh g^-1 at 5.0C,indicating TMSPi-added sample has a better rate performance.The SEM and XPS analyses show that TMSPi can be oxidized and decomposed on LiNi_0.5Co_0.2Mn_0.3O₂surface.The TMSPi-addition can effectively inhibit the decomposition of electrolyte and reduce the impedance growth of cells under high cut-off voltage.In addition,TMSPi enhances the cycling performance of LiNi_0.5Co_0.2Mn_0.3O₂ cathode materials at high temperature.By adding 2.0wt.%TMSPi,the capacity retention of LiNi_0.5Co_0.2Mn_0.3O₂ increases from 24.4%to 75.3%after 100 cycles at 55 ? under4.5V.PES can effectively improve the cycling stability of LiNi_0.5Co_0.2Mn_0.3O₂ cathode materials under 4.5 V.After 100 cycles at 30 ?,the capacity retention of cells with3.0wt.%PES has a higher capacity retention?98.7%?than bare sample?69.0%?.SEM,TEM and XPS results show that the SEI film formed by PES addition is very continuous and compact,which can provide continuous protection for the electrolyte,thus inhibiting the growth of impedance.PES effectively enhances the cycling performance of LiNi_0.5Co_0.2Mn_0.3O₂ cathode materials at high temperature.By adding3.0wt.%PES,the capacity retention of LiNi_0.5Co_0.2Mn_0.3O₂ increases from 24.4%to82.4%after 100 cycles at 55 ? under 4.5 V.