Enhanced Electrochemical Performance of LiMn₂O₄ Cathode Materials by Al-Co Co-Doping AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY23100017

Chinese Library Classification Number:TM912

Citation Information:

As a clean energy storage and conversion technology，lithium-ion batteries have received widespread attention. Spinel LiMn₂O₄ is an important cathode material for lithium-ion batteries，which has low cost，environmental friendliness，high safety，and three-dimensional channel for Li⁺ conduction. However，its capacity decays quickly during charge/discharge cycles，which limits the application of this cathode material. The problem is mainly caused by the Mn dissolution，Jahn-Teller effect，and oxygen defects generated by the material during the charge/discharge cycles. In order to solve the problems of poor cycle stability and rapid capacity decay of spinel LiMn₂O₄ cathode materials. LiAl_0.08Mn_1.92O₄ and Al-Co co-doped LiAl_0.08Co_xMn_1.92-xO₄ （x=0.01，0.03 and 0.05） cathode materials were synthesized by a solid-phase combustion using Li₂CO₃ and MnCO₃ as lithium and manganese sources，and Al（NO₃）₃·9H₂O and CoCO₃ as Al and Co dopants. Powder X-ray diffraction （XRD），scanning electron microscopy （SEM），transmission electron microscopy （TEM），and X-ray photoelectron spectroscopy （XPS） were combined to characterize the crystal structure and microstructure morphology of materials. The LANHE land battery test system was used to test the electrochemical properties of the materials，and cyclic voltammetry （CV） and electrochemical impedance spectroscopy （EIS） tests were carried out on the materials by electrochemical workstation to analyze the kinetic properties of the materials and calculate the relevant parameters. From the perspective of crystal structure and micromorphology，with the increase of Co doping，the lattice constant gradually decreased，and Al-Co co-doping promoted the crystallinity of the material and the selective growth of {111}，{100} and {110} crystal faces，so that MnO₆ skeleton in e LiMn₂O₄ lattice shrank and LiO₄ skeleton expanded，which helped to improve the crystal structure stability of the material and effectively inhibit Jahn-Teller effect. Further observed the micromorphology of the materials with the aid of SEM and TEM，the amount of Co doping increased，the particle size of the material decreased，the particle size distribution became uniform，as well as the truncated octahedral morphological particles containing {111}，{100}，and {110} crystal planes were obtained，among which the truncated octahedral morphology particles in LiAl_0.08Co_0.03Mn_1.89O₄ material had more and the most complete morphology. The smaller particle size could increase the contact area between the particles and the electrolyte，making it easier for Li⁺ to quickly enter the particle from the electrolyte and diffuse inside the pellet，which could improve the diffusion rate of Li⁺，thereby improving the power performance of the battery. In addition，during the battery charging and discharging process，due to the slow diffusion rate of Li⁺ in the material，it might cause some Li⁺ to accumulate near the surface of the particles，forming polarization phenomenon，and reducing the utilization rate of Li⁺. When the particle size was small，the diffusion path of Li⁺ from the surface of the particle to the inside of the particle was shorter，which could reduce the accumulation phenomenon of Li⁺ and improve the utilization rate of Li⁺. The average valence state +3.56 of Mn in LiAl_0.08Co_0.03Mn_1.89O₄ was higher than that of LiMn₂O₄ （theoretical value was +3.50），which effectively inhibited Jahn-Teller effect. It could be seen from the battery test system results that LiAl_0.08Co_0.03Mn_1.89O₄ material showed excellent high rate capacity and long cycle life，and the initial discharge specific capacity of LiAl_0.08Co_0.03Mn_1.89O₄ material was 112.4 mAh·g⁻¹ at 5C，which was higher than that of LiAl_0.08Mn_1.92O₄. The capacity retention after 1000 charge/discharge cycles was 81.3%，which was also significantly higher than that of LiAl_0.08Mn_1.92O₄ （66.4%）. At a higher current rate of 10C，the first discharge specific capacity of LiAl_0.08Co_0.03Mn_1.89O₄ was 103.0 mAh·g⁻¹，which was higher than that of LiAl_0.08Mn_1.92O₄. CV test results showed that LiAl_0.08Co_0.03Mn_1.89O₄ had good electrochemical cycle reversibility，and Al-Co co-doping significantly reduced the polarization during the material cycling process. EIS was further tested and calculated that LiAl_0.08Co_0.03Mn_1.89O₄ had a large Li⁺ diffusion coefficient （1.935×10⁻¹⁶ cm²·s⁻¹） and a lower apparent activation energy （29.16 kJ·mol⁻¹），and Li⁺ needed to overcome a lower energy barrier and fast diffusion speed in the embedding and detachment process，because {100} and {110} crystal planes provided additional diffusion channels for Li⁺. And smaller particle sizes would shorten the diffusion path of Li⁺ and increase the diffusion rate of Li⁺. The combination of Al-Co co-doping and truncated octahedral particle morphology not only inhibited Jahn-Teller effect of the spinel LiMn₂O₄，but also slowed down Mn dissolution and increase the number of Li⁺ diffusion channels，stabilizing the crystal structure of the material，hence significantly improving the high rate capacity and long cycle life of LiMn₂O₄ cathode material. Al-Co co-doping modify spinel LiMn₂O₄ was of great significance in the field of lithium-ion batteries，and this research provided a new idea and experimental basis for the design and preparation of high-performance cathode materials for lithium-ion batteries，and promoted the development and application of clean energy technologies. Although further research was needed，the method of Al-Co co-doping with single crystal morphology to modulate modified spinel-type LiMn₂O₄ cathode materials provided hope for the sustainable development of lithium-ion batteries.