Binary Synergistic Doping Modification Of Lithium Nickelate Cathode Materials With Ti⁴⁺ And Fe³⁺/Al³⁺/Mg²⁺ And Their Electrochemical Properties

Li-ion batteries have been widely used in 3C electronic products,electric vehicles and energy storage,but they are still constrained by low energy density,high safety risks and high manufacturing costs.However,there are problems such as structural degradation,irreversible phase change and poor thermal stability during the charging and discharging process.Elemental substitution doping is an effective way to improve the physicochemical properties from the material itself.In this thesis,the effect of Ti⁴⁺co-doping with cations such as Fe³⁺,Al³⁺and Mg²⁺on the structure,morphology and electrochemical properties of Li Ni_0.95Ti_aB_0.05-aO₂-based cathode materials was investigated using a rapid and convenient acetate sol-gel method.The specific studies are as follows:Firstly,the effect of systematic variation of aluminium and titanium doping by a=0,0.015,0.025,0.035,0.05 was investigated.TEM characterization showed that there was a cationic mixed layer on the surface of Li Ni_0.95Al_0.025Ti_0.025O₂ sample,which was conducive to improving the reversibility of H2-H3 phase transition.Through electrochemical performance tests,it can be seen that the discharge specific capacity of A25T25 samples doped with 2.5%Al³⁺and Ti⁴⁺is 222.99 m Ah·g^-1 at 0.1C,the capacity retention rate after 100 cycles is 66.22%,and the reversible specific capacity of 207 m Ah·g^-1 can be provided at 1 C,and the capacity retention rate is72.75%after 300 cycles,which is much higher than the 45.88%of LNO.Secondly,the effect of varying the amount of Fe and Ti doping by a=0,0.015,0.025,0.035 and 0.05 systems was examined.XRD results showed that with the increase of Fe³⁺doping,the R value first increased and then decreased,and the R value of F25T25 sample was the largest（R=1.65）,indicating that the degree of lithium-nickel mixing was the smallest.It can be seen from the electrochemical performance test that the discharge specific capacity of the sample shows a trend of first increasing and then decreasing with the increase of Fe³⁺doping,and the capacity retention rate of the sample doped with 2.5%Fe³⁺after 0.1 C cycle 100 cycles is69.2%,which is higher than that of Li Ni O₂ by 66.59%.The initial discharge specific capacity of F25T25 at a high magnification of 1 C was 173.26 m Ah·g^-1,which was higher than that of LNO of 149.07 m Ah·g^-1.Finally,the effect of systematic variation of Mg and Ti doping by a=0,0.015,0.025,0.035,0.05 was investigated.The XRD results showed that with the increase of Mg²⁺doping amount,the R value first increased and then decreased,and the degree of cation mixing decreased and then increased.From the results of the constant current charge-discharge cycle test,it can be seen that the initial discharge specific capacity of M25T25 samples doped with 2.5%Mg²⁺and Ti⁴⁺is 201.1 m Ah·g^-1 at 0.1 C,and the capacity retention rate after 100 cycles is as high as 88.27%,which is much higher than that of LNO materials,and the discharge specific capacity is 171.68 m Ah·g^-1 at 1C,and the capacity retention rate is 62.56%,which is higher than that of 45.88%of undoped LNO materials.