Study On The Design And Mechanism Of Anode Interface For High Performance Lithium-ion Battery

Alloy-type materials are regarded as promising candidates for next-generation lithium-ion batteries because of their high specific capacity and suitable voltage plateau.Unfortunately,these anodes undergo dramatic volume changes during charge-discharge processes,resulting in a fast capacity degradation.To solve this problem,most study focus on the design of various electrode material structure,while the understanding and design of the solid electrolyte interface?SEI?is still lacking.Based on understanding the electrode/electrolyte interface,here,we control the interface by adjusting the surface structure of the electrode and discuss its impact on battery performance,mainly including the following two aspects:?1?By building an ultraconformal layer of Sb on the surface of the alloy anode?Ge,Si?with high specific capacity,we can significantly enhance their structural and interfacial stability.Combined with experimental and theoretical studies reveal that the ultraconformal Sb layer is dynamically converted to Li₃Sb during cycling.Then the Li₃Sb layer can selectively adsorb and catalyze the decomposition of electrolyte additives,while suppressing the decomposition of the electrolyte solvent to form a thin,dense,and LiF-dominated SEI.Therefore,the Sb-coated Ge electrode exhibits higher initial coulombic efficiency?85%?and higher reversible capacity(1046 m Ah g^-1)after200 cycles of 500 m A g^-1,which is significantly higher than porous Ge.The initial Coulomb efficiency is only 72%,and the capacity is 170 m Ah g^-1 after 200 cycles.?2?Currently,many works have reported that LiF is a beneficial ingredient of SEI.However,the ionic conductivity of LiF itself is very low(<10^-9 S cm^-1),which damages the rate performance.In addition to the fluorinated SEI,Li₃N-dominated interfacial layer has recently attracted more and more attention due to its much high Li⁺conductivity(?10^-3 S cm^-1 at room temperature)and low electronic conductivity(?10^-12 S cm^-1),but the problems of thermodynamic instability of Li₃N and easy decomposition when the voltage is higher than 0.44 V vs Li/Li⁺still need to be solved.Here,we build a melamine?MA?layer on the porous Ge to in situ form lithiophilic,Li⁺-enriched Li-N interface by reacting with Li⁺during charging and discharging,and we note it as MA@Ge.Electrochemical test results show that at a current density of500 m A g^-1,the capacity of the MA@Ge electrode is 1176 m Ah g^-1 after 300 cycles while the porous Ge electrode is only 65 m Ah g^-1.More importantly,the electrode has high rate performance,and it still has 921 m Ah g^-1 after 2000 cycles at 2000 m A g^-1,which means that the introduction of Li-N interface with superior Li⁺conductivity can significantly improve the long-term cycle stability of the alloy anode.Besides,when it assembled with LiFe PO₄ into a full battery,which can deliver more than 120 m Ah g^-1after 200 cycles at 100 m Ah g^-1,showing a potential application prospect.The innovations of this study:?1?the Li₃Sb interface with selective catalytic decomposition of the electrolyte is constructed in situ on the electrode surface to obtain a thin,dense and LiF-rich SEI,which significantly improved the alloy anodes?Ge,Si?cycling stability;?2?a MA coating layer was build on the surface of the alloy electrode,which in situ obtained a lithiophilic,highly efficient Li⁺conduction and a rich Li-N interface,significantly improving the cycle life and rate performance of the alloy anode.This study provides guidance for the construction of interface layers with special functions on the surface of high specific capacity electrodes,and helps deeply understanding of the electrode/electrolyte interface.