Study On Dual Modification (Doped And Coated) Of Nickel-Rich Cathode Materials For Lithium Ion Batteries

Layer-structured Ni-rich materials have been considered as promising cathode candidates for the next-generation lithium ion batteries(LIBs)owing to their high energy density and low cost compared with LiCoO2.However,the practical applications of Ni-rich cathodes are still impeded by surfacial/interfacial instability as well as poor structural stability of the cathode particles.To solve these problems,in this work,we report several strategies such as surface modification,i on dopi ng a nd dual-modification of co ating and doping t o enhance t he electerochemical performance of LiNi0.8Co0.1Mn0.1O2-The main contents are as follows:Using Zr(CH3COO)2,Li OH-H20 a nd Ni0.8Co0.1Mn0.1(OH)2 as r aw m aterials,t he structure and electrochemical pe rformance of Zr doping to the lithium sites and transition metals ites separately of the LiNi0.8Co0.1Mn0.1O2 have been studied.The Li0.99Zr0.01Ni0.8Co0.1Mn0.1O2 sample exhibits t he b est el ectrochemical p erformance.Under the vol tage r ange of 2.7-4.3 V,the i nitial d ischarge c apacity at a r ate o f 0.1 C w as 195.1 mAh·g-1 with th e coulombic efficiency o f 8 5%,a h igh r eversible s pecific cap acity of 1 42 mAh·g-1 at 10 C and maintains a reversible capacity of 141.9 mAh.g"1 after 200 cycles at 1 C with 0.089%decay per cycle.X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HRTEM)and fast Fourier transform(FFT)analyses confirmed that the surface of the Li0.99Zr0.01Ni0.8Co0.1Mn0.1O2 sample has a s table solid e lectrolyte Li6Zr2O7 coating 1 ayer and t he appropriate a mount of Z r bul k dopi ng.Li6Zr2O7 coating la yer can r educe the c athode-liquid e lectrolyte in terfacial r eactions by relieving the e rosion o f e lectrolytes o n h igh n ickel ma terials and t he pr oper Zr dopi ng effectively in hibits the detrimental phase transition from H2 to H3,thereby i mproving the surface/interface stability and structural integrity of the cathode material.Using C16H36O4Ti,Li OH-H2O and Ni0.8Co0.1Mn0.1(OH)2 as raw materials,the structure and electrochemical performance of Ti-doped LiNi0.8Co0.1Mn0.1O2(0%,0.5%,1%,2%)have been studied.The dopant of Ti can keep the layered structure materials with one phase and high-quality crystallinity.The Li(Ni0.8Co0.1Mn0.1)0.99Ti0.01O2 sample exhibits t he be st electrochemical p erformance.Under t he vol tage range o f 2.7-4.3 V,the in itial discharge capacity at a rate of 0.1 C was 203.21 mAh·g-1 with the coulombic efficiency of 83.23%,a high reversible specific capacity of 140.2 mAh·g-1 at 10 C and maintains a reversible capacity of 143.5 mAh·g-1 after 200 cycles at 1 C with 0.086%decay percycle.Electrochemical impedance spectroscopy(EIS)and cyclic voltammetry(CV)show that Ti doping can not only reduce t he electrochemical i mpedance and increase t he d iffusion r ate of 1 ithiium i ons i n cathode m aterials,but a lso i nhibit t he pha se t ransition of H 2-H3 dur ing charge-discharge cycle,thus improving the structural integrity of materials.Based on the density functional theory(DFT)of the migration energy difference between La and T i f rom the s urface to t he i nside of N CM,i t is reasonable that La at oms tend t o accumulate on the surface of NCM particles and Ti atoms are more likely doped into the bulk NCM.I nformed b y first-principle c alculations,we h ave designed a nd synthesized a LiNi0.8Co0.1Mn0.1O2(NCM)cathode with Ti-doping and La4NiLiO8-coating b y synchronous in-situ dual m odification t hrough as mart r oute f or th e f irst time.The opt imized double modified s amples(0.25 mol%La4NiLiO8 coating and 1 mol%Ti doping)exhibit excellent rate performance and enhanced cycle stability at room temperature and high temperature.In the range of 2.7-4.3 V,the capacity retention is 90.55%after 200 cycles at room temperature and 83.28%after 150 cycles a t hi ght emperature(60?).The attained dual-modified architecture inherits the advantages of both La4NiLiO8 coating and Ti doping.The La4NiLiO8 coating functions as a protector and can effectively prevent the electrolyte attack,leading to a significant improvement of t he NCM surficial stability and conductivity.Ti4+ ions serve as pillars and electrons accumulators that reduce the degree of cation mixing and detrimental H2-H3 phase transition during cycling,and further suppress the formation of intergranular cracks.By using transmission electron microscopy(TEM),ex-nuclear magnetic resonance(NMR),full-field tr ansmission X-ray m icroscopy(TXM)a nd nano X-ray a bsorption near-edge structure(nano-XANES),we revealed the relationship between the generation of microcracks and the phase change of NCM during cycling.At the same time,the nanoscale structural d egradation o n m aterial s urfaces an d the i ntergranular cr acks associated w ith the inconsistent e volution of s tructural de gradation at the pa rticle-level can b e effectively suppressed by the synergetic effect of the conductive La4NiLiO8 coating layer in combination with the strong Ti-O bond.