Synthesis And Modification Of LiNi_0.5Mn_1.5O₄ As Lithium-Ion Batteries Cathode Materials And Their Lithium-storage Properties

With the development of mobile phone, notebook, electric vehicles and other energy storage systems, the application of lithium-ion battery in our daily life becomes increasingly important. The main obstacle is the restricted performance of cathode material, which leads to very low energy density of lithium-ion battery. Therefore, it is imminent to develop a kind of cathode material with large capacity. Spinel Li Ni0.5Mn1.5O4 has high potential(4.7 V vs. Li/Li+), large energy density(686Wh kg-1), good rate performance, for which it has been considered to be one of the most promising cathode candidates for the next generation lithium ion battery. However, the specific capacity of the Li Ni0.5Mn1.5O4 under high current density is very low and showing poor cyclability at elevated temperature. In this paper, constructing a hollow micro/nano structure, ion doping and surface modification has been used to improve the electrochemical performance of Li Ni0.5Mn1.5O4.(1) High voltage Li Ni0.5Mn1.5O4 cathode with hollow micro/nano spherical morphology has been successfully synthesized through a facial solid-state method, where Li2CO3/Li OH was chosen as eutectic salt. The final products can maintain the morphology of its precursor by controlling the calcinations process, and the release of carbon dioxide gas results in the formation of hollow micro/nano spherical structure. The hollow micro/nano structure is in favor of the contact between electrolyte and electrode, shortening the Li+ diffusion path. Electrochemical test results demonstrate that the materials exhibit excellent electrochemical performances. The Li Ni0.5Mn1.5O4 delivers high reversible capacities of 135.5, 132.1 m Ah g-1 at 0.1, and 2 C, respectively. Even at a high rate of 5 C,the electrode still retains 93.4% of the initial capacity at 0.1 C. Moreover, the electrode shows excellent cycle stability with the discharge capacity of 110 m Ah g-1 at 1 C after 80 cycles at elevated temperature. The enhanced performance can be attributed to the hollow spherical morphology, which reduces deformation of the structure change during charge-discharge cycle.(2) Na-doped spinel Li1-x Nax Ni0.5Mn1.5O4 materials have been prepared via sol-gel method. The structural characterization reveals that the Na doping leads to a more ordered structure and enhanced the Li slab space. In addition, the electrochemical tests show that the Na-doped Li0.92Na0.08Ni0.5Mn1.5O4 electrode exhibits good electrochemical performances, delivering a reversible discharge capacity of 137.3 m Ah g-1, greatly improved rate capacity(66 m Ah g-1 at 5C) and cycling stability(86.5% capacity retention after 200 cycles at 1C). The superior electrochemical performances of the Na-doped material are due to the enlargement of the Li slab space of the spinel material, whichallow rapid diffusion of Li ions in the bulk lattice.(3) Spinel Li Ni0.5Mn1.5O4 nanostructure material prepared through sol-gel method was coated with Ru O2 and Al-Zn O, respectively. The results demonstrate that the performance of Li Ni0.5Mn1.5O4 cathode material is remarkably improved by nanoarchitectured Ru O2 or Al-Zn O coating layer. On the one hand, the Ru O2 layer effectively reducing the barrier for lithium ion transfer at the electrode/electrolyte interface, thence the cycling performance of as-prepared materials was markedly improved, the initial cycle discharge capacity is 117.3 m Ah g-1 at a current density of 1C, the capacity remains 108.9 m Ah g-1 after 350 cycles, giving 93% capacity retention. On the other hand, the Al-Zn O oxide coating layer suppresses the formation of thick cathode electrolyte interphase layer, the cyclability of spinel is significantly enhanced. The first cycle discharge capacity is 114.5 m Ah g-1 at a current density of 1 C, the capacity retention of Al-Zn O@Li Ni0.5Mn1.5O4 is 75.4%(remain 86.3 m Ah g-1) after 500 cycles.