Na-Mn-O正极材料的合成及电化学性能

Preparation and Electrochemical Performance of Na-Mn-O Cathode Materials

以Mn(CH3COO)2·4H2O为锰源,以Na2CO3为钠源,通过溶液-凝胶法合成干凝胶前驱体,将前驱体在空气气氛中焙烧得到Na-Mn-O正极材料.并用傅立叶红外光谱(FT-IR),热重分析(TG),X射线衍射(XRD),扫描电镜(SEM),恒流充放电测试等对材料结构和性能进行研究.结果表明,600℃焙烧的样品为结构稳定的层状锰酸钠,属于六方层状P2结构,空间群为P63/mmc,通过PowderX软件计算得到其晶胞参数为a=0.284nm,c=1.116nm.Na-Mn-O正极材料在Li+嵌入和脱出过程中,部分Na+从层状主晶格中脱出,使得Li+在MnO6层间的嵌/脱阻力减小(由于Na+(0.095nm)半径比Li+(0.076nm)大),电化学性能明显改善.在充放电电流密度为25mA·g-1,电压在2.0-4.3V范围时,600℃焙烧的样品第二次放电容量高达176mAh·g-1,20次循环后,容量保持率仍有90.9%.

The precursor of sodium manganese oxide xerogel was prepared from Mn（CH3COO）2·4H2O and Na2CO3 solution by sol-gel method, then sodium manganese oxide cathode materials were prepared through calcinating xerogel precursors in air atmosphere. The structure and performance of as-prepared cathode materials were characterized by Flourier-infrared spectra （FT-IR）, thermogravimetric analysis （TG）, X-ray diffractometer （XRD）, scanning electron microscope （SEM）, and galvanostatic charge/discharge. The results showed that layered sodium manganese oxide with a stable phase could be obtained at a temperature of about 600 ℃, and its crystal system was hexagonal P2 structure with space group P63/mrnc. It had been found by PowderX calculation that the lattice parameters a was 0.284 nm and c was 1.116 nm. Since the radius of Na^＋ （0.095 nm） was bigger than Li^＋ （0.076 nm）, limited removal of sodium ions from the layered host lattice could decrease the resistance of lithium insertion/deinsertion in MnO6 layers, and thus the electrochemical performance of the material could be apparently improved. The second discharge capacity of the material reached 176 mAh ·g^-1 at a rate of 25 mA ·g^-1 in the cutoff voltage range of 2.0-4.3 V, and the capacity retention was still 90.9% after 20 cycles.