钠掺杂碳包覆磷酸锰锂纳米材料的制备及电化学性能

Preparation and Electrochemical Properties of Carbon-Coated Sodium-Doped Lithium Manganese Phosphate

采用高温固相法一步合成掺杂钠型碳包覆Li_(1-x)Na_(x)MnPO_(4)纳米材料,利用现代仪器分析手段表征了材料的物相、形貌和晶体结构,并考察了其作为锂离子电池正极材料的电化学性能. XRD分析结果表明,钠的掺杂没有改变LiMnPO4材料的橄榄石型正交结构,样品的结晶度好、纯度较高;SEM分析结果显示,随着钠含量的增加,样品粒径逐渐减小,当钠含量为20%时,颗粒直径减小到50 nm;TG分析结果说明,在样品制备过程中采用550℃的煅烧温度完全可行;BET分析结果得出,不同钠含量的Li_(1-x)Na_(x)MnPO_(4)纳米材料均为介孔结构,钠含量为20%的样品比表面积最大. Li_(1-x)Na_(x)MnPO_(4)纳米材料的电化学性能如下:CV测试结果表明,钠含量15%的样品电化学反应更为迅速,电极具有更好的电子导电性;EIS测试结果显示,钠含量为20%的样品电荷转移阻抗最小,说明钠的掺杂有利于疏通锂离子脱嵌的通道.充放电测试结果显示,钠含量为20%的材料充放电性能更稳定.

Carbon-coated Li_(1-x)Na_(x)MnPO_(4) nanomaterials were synthesized by high-temperature solid-state method, and their phase, morphology and crystal structure were characterized by modern instrument analysis. Moreover their electrochemical properties as for cathode materials of lithium-ion batteries were investigated. XRD analysis shows that the doping of sodium do not change the olivine type orthogonal structure of the LiMnPO4 with good crystallinity and purity of the samples. SEM analysis shows that with the increase of sodium content, the particle size of the samples is decreased gradually, and the particle diameter is 50 nm when the sodium content is 20%. TG analysis indicates that the calcination temperature of 550°C is feasible during the sample preparation. Furthermore, BET analysis demonstrates that the prepared nanomaterials with different sodium content are mesoporous materials, and the specific surface area of the sample with 20% sodium content is the largest. The electrochemical properties of the prepared materials are as follows. The electrochemical reaction of the sample containing 15% sodium is more rapid, and its electrode has better electronic conductivity. The charge transfer impedance of the sample containing 20% sodium is the smallest, which signifies that the doping of sodium is conducive to clearing the channel of lithium ion transmission. The charge and discharge test shows that the material with 20% sodium content is more stable in the charge and discharge performance.