Structural transformation of a lithium-rich Li1.2Co0.1Mn0.55Ni0.15O2 cathode during high voltage cycling resolved by in situ X-ray diffraction
Structural transformation of a lithium-rich Li1.2Co0.1Mn0.55Ni0.15O2 cathode during high voltage cycling resolved by in situ X-ray diffraction
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DOI：
10.1016/j.jpowsour.2012.11.144
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发表时间：
2013-05-01
影响因子：
9.2
通讯作者：
Daniel, Claus
中科院分区：
文献类型：
--
作者：
Mohanty, Debasish;Kalnaus, Sergiy;Daniel, Claus
具有 Li1+yM1-yO2（M = Co、Mn 和 Ni）组成的富锂层状氧化物已成为电动汽车 (EV) 应用中高能量密度和高压锂离子电池的有吸引力的阴极材料。然而，它们在电动汽车中的效用会受到电压和容量衰减的影响。电压衰减与这些富锂氧化物的结构转变有关，必须彻底了解。在这项工作中，我们利用原位 X 射线衍射来监测富锂和富锰的 Li1.2Co0.1Mn0.55Ni0.15O2 氧化物阴极在高电压（4.8 V）循环过程中的这些结构转变，这在以前没有报道过。对第一个循环的阴极晶格参数进行监测，并与后续循环进行比较。根据我们的结果，c 晶格参数在初始充电过程中增加，并最终在充电超过 4.4 V 时下降，这验证了由于 Li2MnO3 相在高电压下的激活，锂从过渡金属层中脱出。 α晶格参数在第一个循环平台区域保持恒定的事实表明，在第一个循环充电期间，结构中存在氧损失，这归因于从第一个循环获得的不可逆容量。对于第一个和后续循环，c 晶格参数在放电期间增加至 3.5 V 和低于 3.5 V，观察到这些值的下降。在随后的循环之后，在低压放电过程中观察到（440）立方尖晶石反射，这揭示了晶格中的层到类尖晶石的相变，并且被认为是观察到的电压衰减的原因。在随后的循环后观察到单斜晶相的显着减少，并被认为导致重复循环后的结构不稳定和容量衰减。由 Elsevier B.V. 出版
Lithium-rich layered oxides having compositions of Li1+yM1-yO2 (M = Co, Mn, and Ni) have become attractive cathode materials for high energy density and high voltage lithium ion batteries for electric vehicle (EV) applications. However, their utility in EVs suffers from both voltage and capacity fade. The voltage fade is related to structural transformation in these lithium-rich oxides and must be thoroughly understood. In this work, we have utilized in situ X-ray diffraction in order to monitor these structural transformations during high voltage (4.8 V) cycling of a lithium- and manganese-rich Li1.2Co0.1Mn0.55Ni0.15O2 oxide cathode, which has not been reported previously. The lattice parameters of the cathode were monitored for first cycle and compared with the subsequent cycles. Based on our results, the c-lattice parameter increases during the course of initial charging and eventually decreases upon charging beyond 4.4 V, which verifies lithium extraction occurs from transition metal layers due to activation of Li2MnO3 phase at high-voltage. The fact that the a-lattice parameter remains constant at the first cycle plateau region indicates oxygen loss from the structure during first cycle charging which is attributed to irreversible capacity obtained from first cycle. For first and subsequent cycles, the c-lattice parameter increases during discharge up to 3.5 V and below 3.5 V, the decrease in those values was observed. After subsequent cycling, (440) cubic spinel reflections were observed during low voltage discharge process, which reveals a layer to spinel-like phase transformation in the lattice and is thought to be the reason for the observed voltage fade. A significant decrease in monoclinic phase was observed after subsequent cycles and is believed to contribute to the structural instability and capacity fade after repeated cycling. Published by Elsevier B.V.