Research On Surface Modification For Lithium-rich Manganese-based Layered Cathode

Li-rich manganese-based cathode materials are considered to be one of the most valuable cathode materials for the next generation of high-energy density lithium-ion batteries for their high specific capacity,high capacity density and low cost.However,their practical implementation in LIBs is still hindered by the rapid voltage/capacity decay on cycling,the long-standing contradictions between redox kinetics and volumetric energy density and poor calendaring compatibility.In order to solve the above problems,in this paper,a stable interface coating and a cathode-electrolyte interphase（CEI）film were constructed on the surface of Li-rich manganese-based cathode materials through a surface modification strategy,regulating the effects of the coatings and CEI films on their structural degradation.Finally,a cathode material with excellent electrochemical performance and industrial rolling performance is obtained.The main contents are summarized as follows:（1）A coherent near-zero-strain interphase was constructed on the grain boundaries of cathode secondary particles by infusing LiAlO₂ material through the reactive infiltration method（RIM）.The interphase with near-zero-strain feature upon electrochemical（de）lithiation inhibits volume changes of the lattice and structural degradation of cathode primary particles during cycling.Moreover,the ionically conductive LiAlO₂ nanolayer can not only promote the rapid Li⁺migration,but also act as a physical barrier to reduce the corrosion of the electrolyte.In addition,the penetration into the secondary particles can also reduce the porosity and effectively improve the mechanical strength of the material.The modified material exhibited excellent electrochemical cycling performance（capacity retention rate up to 81.84%after 300 cycles at 1 C）,good rate performance(discharge specific capacity of 140 m Ah·g^-1 at 10C rate),and industrial processing performance(calendering density up to 3.3 g·cm^-3).（2）Based on LiAlO₂ modified Li-rich manganese-based cathode material,using pentafluorophenylboronic acid（PFPBA）as electrolyte additive and to design a high-performance Li-rich lithium-ion battery.The addition of PFPBA will be pre-oxidized at a lower potential to build a uniform CEI film on the surface of the cathode material,to protect the cathode material that was not covered by LiAlO₂ from the electrolyte during high-voltage cycling.It could inhibit the dissolution of transition metal ions and structural degradation on the surface of the material,thereby further improving the voltage stability and cycle stability of the material.When the additive content is 0.2%,the thickness of the CEI film constructed on the surface at the initial stage of the cycle is about 5 nm,which demonstrates the stability of the CEI films.After 400 cycles at 1 C,the electrolyte system can still achieve a specific discharge capacity of 188.1 m Ah·g^-1,a high cycle retention rate of 86.21%,and a voltage decay rate of 1.09 m V per cycle.