Performance Degradation Analysis And Optimization Of Halide All-Solid-State Batteries With Ni-Rich NCM Cathodes

Lithium-ion batteries have the characteristics of high energy density,long cycle life and good safety.Widely used in 3C products,new energy vehicles,electric power storage and other fields.In view of the vision of the large-scale popularization of lithium-ion batteries in the fields of energy power and power storage,it is necessary to further improve their energy density,safety and reliability,and all-solid-state lithium-ion batteries have become an important development direction.The study addresses the electrochemical performance and improvement strategies of single-crystal LiNi0.83Co0.14Mn0.03O2(NCM83)in Li3InCl6-based solid-state batteries to understand the charge/discharge performance,multiplicity performance and cycling performance of NCM83 in Li3InCl6.The focus is to investigate the interfacial interaction between NCM83 and Li3InCl6 and its influence mechanism in performance decay,and further develop the improvement strategies such as polytetrafluoroethylene(PTFE)dry electrode,LiNbO3 surface coated NCM83 material and Li3InCl6 surface composite NCM83 material.The research of the paper is of great scientific significance and application value for the development of all-solid-state lithium-ion batteries with high nickel ternary materials based on halide solid-state electrolytes.First,this thesis investigates the electrochemical performance of NCM83 in Li3InCl6based solid-state batteries.The results show that the charge/discharge performance,multiplicity characteristics,and cyclability of NCM83 in Li3InCl6 differ from those in liquid electrolyte,with significantly lower multiplicity and cyclability.Using the constant current charge/discharge(0.1C,2.8-4.3 V)test method,the charge capacity of NCM83 in Li3InCl6 solid-state battery was 204.39 mAh/g Coulomb efficiency of 85.03%,respectively,which was lower than that of NCM83 in liquid electrolyte of 222.88 mAh/g and 91.6%.Comparing the results of dV/dQ curve and dQ/dV curve analysis in the first and second cycle,the charging and discharging processes of NCM83 in Li3InCl6 and liquid electrolyte underwent the same phase transition,H1-M,M-H2 and H2-H3.but the first cycle in Li3InCl6 had lower capacity contributed by H1-M and H2-H3 for the charging process and higher polarization for the discharging process;A capacity drop attributed to the loss of active matter was also found in the second cycle.The charge/discharge cycle tests showed that the cyclability of NCM83 in Li3InCl6 was closely related to the charge/discharge multiplier and the charge cut-off voltage,and the charge/discharge cycles at 0.02C,0.1C,0.3C and 1C multipliers showed a pattern of poor cyclability at low multipliers and good cyclability at high multipliers.V,the capacity retention rate was 49.9%and 38.6%respectively,and only at 4.25 V,it showed good cycling stability with a capacity retention rate of 76.8%for 300 cycles.Secondly,the thesis analyzed the interfacial behavior of NCM83/Li3InCl6 at high potentials and before and after cycling,and the results showed that the NCM83/Li3InCl6 interfacial impedance increased and the interfacial structure,composition and interfacial contacts changed at high potentials and during cycling.AC impedance analysis showed that the NCM83/Li3InCl6 interfacial impedance increased with increasing potential at high potentials≥4.3 V,and the interfacial impedance at constant current-constant voltage charging was significantly higher than that at constant current charging,reflecting the interfacial instability of NCM83/Li3InCl6 at high potentials.The surface structure of NCM83 was analyzed by high-resolution transmission electron microscopy(HR-TEM),and the rock salt phase was found on the inner surface with a thickness of 5 nm at 0.1C magnification charging up to 4.3 V.The thickness of the rock salt phase increased to about 12 nm at charging up to 4.5 V,and a lattice distortion layer with a thickness of about 15 nm appeared between the surface layer of the rock salt phase and the lamellar phase.The L3-edge X-ray absorption spectroscopy(XAS)test for Ni elements showed that the Ni3+/4+on the surface of NCM83 charged to 4.3 V was partially reduced to Ni2+,which also reflected the surface rock salt phase generation.X-ray photoelectron spectroscopy(XPS)analysis of Li3InCl6 charged to 4.5 V revealed the presence of Cl-O and In-O compounds.Based on these results,an interfacial reaction between NCM83 and Li3InCl6 occurred at ≥4.3 V.The layered phase on the surface of NCM83 was converted to the rock salt phase,while the compounds of ClO,In-O were generated on the surface of Li3InCl6 In addition,scanning electron microscopy(SEM)analysis also revealed that cracks appeared at the NCM83/Li3InCl6 interface and cracks in the Li3InCl6 electrolyte after cycling,producing interfacial contact loss and changing the electrode dense structure.In situ X-ray diffraction(XRD)tests showed that the rapid change in cell volume caused by the H2-H3 phase transition of NCM83 during the charge/discharge cycle induced the interfacial contact loss.As a result,the interfacial reaction and interfacial contact loss during cycling and electrode dense structure damage in Li3InCl6-based solid-state batteries with NCM83 at high potentials led to the accelerated decay of electrochemical performance at high potentials.Finally,the study of the paper investigates the improvement strategy of the electrochemical performance of NCM83 in Li3InCl6-based solid-state batteries,and develops the PTFE-based dry electrode process,LiNbO3-coated NCM83 material and Li3InCl6 composite NCM83 material for the high potential interfacial reaction and contact loss and structural damage during cycling,which substantially improves the NCM83 in Li3InCl6-based solid-state batteries in charge/discharge cycle performance.1)The 0.1C charging specific capacity was 234.4 mAh/g Coulomb efficiency of 88%with the addition of 0.15%PTFE to the NCM83/Li3InCl6 composite solid-state electrode powder;SEM analysis revealed that the solid-state electrode after cycling with the addition of PTFE did not produce significant interfacial contact loss,electrode structural damage.2)LiNbO3 was coated on the surface of NCM83,and the capacity retention of 2%LiNbO3@NCM83 in Li3InCl6 for 100 cycles was 80%.The analysis showed that 2%LiNbO3 coating slowed down the structural phase change on the surface of the cathode material and also inhibited the generation of oxygen-containing compounds from Li3InCl6.3)Wet mixing-heat treatment prepared 10%Li3InCl6@NCM83 composite was prepared by wet mixing and heat treatment,and Li6PS5Cl was used as the solid electrolyte,and the battery capacity retention rate was 92%after charging to 4.3 V,0.1C charge-discharge cycle for 100 cycles,which was significantly higher than that of 53%for 100 cycles without the composite;the analysis revealed that Li3InCl6 in the composite uniformly coated the surface of NCM83 and inhibited the decomposition reaction of LPSC1 decomposition reaction at high potential.In summary,the paper investigated the electrochemical performance of NCM83 in Li3InCl6-based solid-state batteries,elucidated the mechanism of the role of interfacial stability in the decay of electrochemical performance,and proposed targeted improvement strategies.The results show that NCM83 exhibits good cycling stability at a charge cut-off potential of 4.25 V and a charge-discharge multiplier of 0.3C;while at≥4.3 V,interfacial reactions occur between NCM83 and Li3InCl6,resulting in interfacial contact loss,electrode structure damage,and accelerated decay of cycling performance;an improvement strategy represented by the composite NCM83 on the surface of Li3InCl6 can effectively suppress the interfacial interaction.The paper clarifies the influence of Li3InCl6 on the electrochemical performance of NCM83,and investigates the mechanism of interfacial failure at high potentials and its role in the performance degradation,and proposes improvement measures to suppress interfacial failure.