Preparation And Properties Of Manganese-based Cathode Material For Aqueous Lithium-ion Batteries

This paper mainly adjusts the preparation process of lithium manganate cathode material,and improves the performance of lithium manganate material by means of doping modification,and obtains the excellent performance of manganese-based cathode material.Mixed precursors containing Mn₃O₄ andγ-Mn OOH were synthesized at different hydrothermal temperatures,and single crystal lithium manganate containing nanorods and nanoparticles was synthesized by solid phase method at different calcination temperatures with different molar ratios of Li OH·H₂O.The structure and morphology of lithium manganate were determined by XRD,SEM and other characterization methods.The battery was assembled in 1 M Li₂SO₄ hydrolysate and the electrochemical test was carried out.It was found that Li_1.02Mn_1.98O₄ synthesized at hydrothermal temperature of 180℃,lithium dosage of 1.02 and calcination temperature of 700℃has a homogeneous mixture morphology,the first discharge capacity of 92.3m Ah·g^-1 at 1 C rate,the capacity retention rate of 200 cycles of 67.6%,and the electrochemical performance is the best.After determining the best preparation technology of lithium manganate cathode material,doping Al³⁺and Se by different methods to further modify Li_1.02Mn_1.98O₄.Firstly,2%Al³⁺lithium manganate was synthesized by adding Al source in the hydrothermal synthesis and grinding steps respectively.The results show that the cycle performance of G-LLAMO synthesized by adding Al source in the grinding step is better.By doping 1%,1.5%and 2%Al³⁺with this method,the specific initial discharge capacity of Li_1.02Al_0.015Mn_1.965O₄ at 1 C rate is 110.4 m Ah·g^-1,and the capacity retention rate of 200cycles is 76.8%.Compared with Li_1.02Mn_1.98O₄,the performance has been greatly improved.Secondly,2%Se doped lithium manganate was synthesized under different calcination atmosphere.The results show that the sample synthesized in hydrogen argon mixture has better cycling performance at 7 C ratio.In this atmosphere,Se doped with1%,2%and 3%were synthesized.The results show that the initial discharge capacity of Li_1.02Mn_1.98O_3.98Se_0.02 at 7 C ratio is 101.0 m Ah·g^-1,the capacity retention rate of 200cycles is 87.3%,and the initial discharge capacity of Li_1.02Mn_1.98O₄ is 90.4 m Ah·g^-1.The capacity retention rate of 200 cycles is 76.1%),which is a great improvement in performance.Finally,with Li_1.02Mn_1.98O_3.98Se_0.02 as the working electrode,the reference electrode of calomel electrode and the auxiliary electrode of platinum electrode,the full battery was assembled in the mixed electrolyte of Li₂SO₄ and Na₂SO₄ to explore the influence of electrolyte concentration on the performance of the full battery.The results show that the optimal concentration is the mixed electrolyte composed of 1 M Li₂SO₄ and 1 M Na₂SO₄,and the capacity retention rate of 200 cycles at 7 C rate is 78.3%.Using Li_1.02Al_0.015Mn_1.965O₄ as the working electrode,the capacity retention rate of the full battery is 61.0%after 200 cycles at 1 C rate.