Roles of transition metals interchanging with lithium in electrode materials
Roles of transition metals interchanging with lithium in electrode materials
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DOI：
10.1039/c5cp00940e
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发表时间：
2015-01-01
影响因子：
3.3
通讯作者：
Matsubara, Eiichiro
中科院分区：
文献类型：
--
作者：
Kawaguchi, Tomoya;Fukuda, Katsutoshi;Matsubara, Eiichiro
利用一种新的直接标记方法——Ni - k边缘附近的粉末衍射异常精细结构（P-DAFS），阐明了锂过渡金属复合物氧化物电极材料中对位过渡金属与Li原子交换的作用。在锂离子电池（LIB）电化学插入/提取锂离子过程中，Ni原子主要占据NiO2主层位点和部分占据主层之间的层间Li位点，研究了Ni在Li0.89Ni1.11O2中的价态和局部结构。通过P-DAFS方法评估的位置选择性x射线近边缘结构显示，与主层位置相比，层间Ni原子表现出更低的电化学活性。此外，利用P-DAFS方法进行的位点选择性扩展x射线吸收精细结构分析表明，在初始电荷期间，层间空间残余Ni原子周围的局部结构发生了变化；它倾向于聚集在层间镍周围形成岩盐状的镍畴。层间空间中NiO-like畴的存在局部减小了层间距离，并且由于晶格不匹配而产生应变能，从而在热力学和动力学上延缓了随后的Li插入。这种对Li插入的限制不可避免地使类nio结构域在电化学上不活跃，导致初始充电后具有可观的不可逆容量，但实现了相邻NiO2层的强大连接，这些层在没有Li占据的情况下往往会解离。反位过渡金属与Li原子交换的P-DAFS表征补充了对电极材料中详细的电荷补偿和降解机制的理解。
Roles of antisite transition metals interchanging with Li atoms in electrode materials of Li transition-metal complex oxides were clarified using a newly developed direct labeling method, termed powder diffraction anomalous fine structure (P-DAFS) near the Ni K-edge. We site-selectively investigated the valence states and local structures of Ni in Li0.89Ni1.11O2, where Ni atoms occupy mainly the NiO2 host-layer sites and partially the interlayer Li sites in-between the host layers, during electrochemical Li insertion/extraction in a lithium-ion battery (LIB). The site-selective X-ray near edge structure evaluated via the P-DAFS method revealed that the interlayer Ni atoms exhibited much lower electrochemical activity as compared to those at the host-layer site. Furthermore, the present analyses of site-selective extended X-ray absorption fine structure performed using the P-DAFS method indicates local structural changes around the residual Ni atoms at the interlayer space during the initial charge; it tends to gather to form rock-salt NiO-like domains around the interlayer Ni. The presence of the NiO-like domains in the interlayer space locally diminishes the interlayer distance and would yield strain energy because of the lattice mismatch, which retards the subsequent Li insertion both thermodynamically and kinetically. Such restrictions on the Li insertion inevitably make the NiO-like domains electrochemically inactive, resulting in an appreciable irreversible capacity after the initial charge but an achievement of robust linkage of neighboring NiO2 layers that tend to be dissociated without the Li occupation. The P-DAFS characterization of antisite transition metals interchanging with Li atoms complements the understanding of the detailed charge-compensation and degradation mechanisms in the electrode materials.