原位XRD表征富锂锰基正极材料的结构
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摘要
首次利用原位X射线衍射光谱法(XRD)分析了富锂锰基材料在H2气氛下,温度从25℃逐步升至400℃的过程中结构发生的变化,结果表明:富锂锰基材料最终被还原为MnO和单质Co、Ni,过程中并未出现正交相的LiMnO_2,这与三方相(空间群R-3m)的LiMn_(1/3)Ni_(1/3)Co_(1/3)O_2还原过程一致,但明显不同于单斜相(空间群C2/m)的Li2MnO_3被还原为LiMnO_2和Mn O的情况,验证了富锂锰基材料的结构为单一的三方相,而非单斜相和三方相的复合相。电化学测试表明:均相结构的三方相富锂锰基材料放电比容量在250 m Ah/g左右,充放电循环100次后容量保持率在80%以上。准确地表征富锂锰基材料的三方相结构将有助于改进制备工艺,获得循环性能更好的材料。
Changes of the crystalline structures of lithium-rich and manganese-based cathode materials were examined by in-situ X-ray diffraction in H_2 from 25 to 400 ℃. The results show that x Li2 Mn O3·(1-x)Li Mn_(1/3_Ni_(1/3_Co_(1/3)O_2 is reduced to Mn O and Co/Ni without orthorhombic LiMnO_2, which is the same as trigonal(space group: R-3 m)Li Mn_(1/3_Ni_(1/3)Co_(1/3)O_2. The monoclinic(space group: C2/m) Li2 Mn O3 is reduced to orthorhombic LiMnO_2 and Mn O at the same condition. It is deduced that lithium-rich and manganese-based layered material possess trigonal structure(R-3 m space group), instead of trigonal and monoclinic compound phase. The electrochemical test results show that the average discharge capacity of the homogeneous trigonal R-3 m lithium-rich and manganese-base cathode material can reach 250 m Ah/g, and the capacity remains 80% after 100 cycles. The accurate determination of lithium-rich and manganese-based cathode materials with trigonal R-3 m structure is essential for improving the preparation process and obtaining materials with better cycle performance.
Changes of the crystalline structures of lithium-rich and manganese-based cathode materials were examined by in-situ X-ray diffraction in H_2 from 25 to 400 ℃. The results show that x Li2 Mn O3·(1-x)Li Mn_(1/3_Ni_(1/3_Co_(1/3)O_2 is reduced to Mn O and Co/Ni without orthorhombic LiMnO_2, which is the same as trigonal(space group: R-3 m)Li Mn_(1/3_Ni_(1/3)Co_(1/3)O_2. The monoclinic(space group: C2/m) Li2 Mn O3 is reduced to orthorhombic LiMnO_2 and Mn O at the same condition. It is deduced that lithium-rich and manganese-based layered material possess trigonal structure(R-3 m space group), instead of trigonal and monoclinic compound phase. The electrochemical test results show that the average discharge capacity of the homogeneous trigonal R-3 m lithium-rich and manganese-base cathode material can reach 250 m Ah/g, and the capacity remains 80% after 100 cycles. The accurate determination of lithium-rich and manganese-based cathode materials with trigonal R-3 m structure is essential for improving the preparation process and obtaining materials with better cycle performance.
引文
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[2]SAROHA R,GUPTA A,PANWAR A K.Electrochemical performances of Li-rich layered-layered Li2MnO3-LiMnO2solid solutions as cathode material for lithium-ion batteries[J].Journal of Alloys and Compounds,2017,696:580-589.
[3]JOHNSON-PECK A C,LEVIN I,HERZING A A,et al.Structural studies of Li1.2Mn0.55Ni0.15Co0.1O2electrode material[J].Materials Characterization,2016,119:120-128.
[4]KIM D J,CHUNG H S,YU K.Cobalt powder from Co(OH)2by hydrogen reduction[J].Materials Research Bulletin,2002,37(13):2067-2075.
[5]任国兴,潘炳,谢美求,等.含锰废旧聚合物锂离子电池还原熔炼回收有价金属试验研究[J].矿冶工程,2015,35(3):75-78.
[6]RICHARDSON J T,SCATES R,TWIGG M V.X-ray diffraction study of nickel oxide reduction by hydrogen[J].Applied Catalysis A(General),2003,246(1):137-150.
[7]BOULINEAU A,CROGUENNEC L,DELMAS C,et al.Structure of Li2MnO3with different degrees of defects[J].Solid State Ionics,2009,180(40):1652-1659.
[8]THACKERAY M M,KANG S H,JOHNSON C S,et al.Comments on the structural complexity of lithium-rich Li1+xM1-xO2electrodes(M=Mn,Ni,Co)for lithium batteries[J].Electrochemistry Communications,2006,8(9):1531-1538.
[9]SON J T,JEON H J,LIM J B.Synthesis and electrochemical characterization of Li2MnO3-LiNixCoyMnzO2cathode for lithium battery using co-precipitation method[J].Advanced Powder Technology,2013,24(1):270-274.
[10]CHEN J,ZHAO N,LI G D,et al.High rate performance of LiNi1/3-Co1/3Mn1/3O2cathode material synthesized by a carbon gel-combustion process for lithium ion batteries[J].Materials Research Bulletin,2016,73:192-196.