Preparation And Study Shell Structure Spinel Lithium Manganese Cathode Materials For Lithium-ion Batteries

Spinel LiMn2O4is currently one of the most promising cathode materials forLIBs because of its low cost, abundant Mn resources and environmental friendliness.Unfortunately, the wide practical use of the spinel electrode has been hindered by atleast two issues: one is manganese dissolution, especially when operating attemperatures above ambient, e.g., above40°C, caused by the presence of acidsolution and the Jahn–Teller effect, leading to rapid decrease of storage capacity; theother comes from the low power density due to a large polarization at high currentdensities, resulting from sluggish Li+ion diffusion in the bulk materials. In this thesis,a hollow micro-/nano-hybrid structures and coated-modified strategies have beenconsidered to overcome these drawbacks in LiMn2O4.Four different structure spinel-phase LiMn2O4materials were prepared byone-step solid state method. Then the structural and physical chemistry properties ofthese spinel LiMn2O4cathode materials were discussed. Results showed that thehollow structure microspheres,which used2h pre-calcination MnO2as precursor,exhibit a best rate capability and stability, due hollow micro-/nano-hybrid structurescould increase the surface area, lessen the compounded internal stresses, and preventnanoparticles from agglomerating.To solve the problem of manganese dissolution, a novel core-shell LiMn2O4@Li4Ti5O12hollow microspheres have been designed and synthesized using2hpre-calcination MnO2as precursor. The outer shell Li4Ti5O12was a successful shieldfor inner shell LiMn2O4, avoiding the directly contact of LiMn2O4with the electrolyte,then effectively depressing the dissolution of Mn-ion and suppressing the change ofcrystal structure of inner shell LiMn2O4. Hence, the unique core-shell hollowmicrospheres structure could provide superior rate capacity and good cycling stability.When valued as cathode materials for LIBs, the product exhibit a high capacityretention (90%) after55cycles at0.5rate and superior rate capacity,90mAh g-1at2Crate.However, the Li4Ti5O12surface modifications decreased the quality of the activesubstance. To achieve a high-energy-density capability LiMn2O4, a active materialLiNi0.5Mn1.5O4has been considered as the shield layer. And an efficient route toprepare double-shelled LiMn2O4@LiNi0.5Mn1.5O4hollow microsphere cathode materials has been demonstrated. Significantly, these highly crystalline spinels presentan admirable reversible capacity, superior rate capability and excellent cyclingstability, even operation at60°C. At a high current density of2,5,10C, this materialdelivered a reversible capacity of106,97,90mA h g–1, respectively.It also exhibithigh cycling stability, retention of90%after the whole500cycles at10C.