Layered LixNiyMnyCo1-2yO2 Cathodes for Lithium Ion Batteries:

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• 作者：Natasha A. Chernova ; Miaomiao Ma ; Jie Xiao ; M. Stanley Whittingham ; Julien Breger ; Clare P. Grey
• 刊名：Chemistry of Materials
• 出版年：2007
• 出版时间：September 18, 2007
• 年：2007
• 卷：19
• 期：19
• 页码：4682 - 4693
• 全文大小：657K
• 年卷期：v.19,no.19(September 18, 2007)
• ISSN：1520-5002

文摘

The magnetic properties of layered LiNi_yMn_yCo_1-2yO₂ (y = 0.5, 0.45, 0.4, and ¹/₃) compounds arestudied in order to understand the transition metal ion distributions via their magnetic interactions. InLiNi_0.5Mn_0.5O₂, an increase of magnetization is found below 100 K with ac magnetic susceptibility revealingbroad peaks at 96, 40, 13, and 7 K. The low-temperature neutron diffraction and heat capacity studies donot reveal long-range magnetic ordering; the magnetic component of heat capacity shows a broad peakat 10 K. This behavior is explained by assuming a nonrandom distribution of transition metals. The 96K transition is attributed to the ordering of clusters of Ni²⁺ spins in the transition metal and lithiumlayers, which are coupled by a 180 superexchange mechanism. The wide 40 K peak is explained by anincrease of the cluster size due to intralayer Ni and Mn spin ordering, by analogy with antiferromagneticordering transitions in Li₂MnO₃ at 36.5 K and in NaNi_0.5Mn_0.5O₂ at 55 K. The continuing increase of netmagnetization in this temperature range indicates at least partial ferromagnetic interlayer ordering inLiNi_0.5Mn_0.5O₂ as opposed to Li₂MnO₃ and NaNi_0.5Mn_0.5O₂, which is caused by Ni²⁺ ions in the lithiumlayer. The 7-13 K anomalies are ascribed to the freezing of cluster magnetic moments. With increasingCo content, the amount of Ni²⁺ in the transition metal layer decreases, the cluster ordering transitionsdisappear, and only the spin-glass freezing is observed in LiNi_0.4Mn_0.4Co_0.2O₂ and LiNi_1/3Mn_1/3Co_1/3O₂ at10 and 7 K, respectively. This is consistent with the lack of long-range ordering of the transition metalions in these compounds. The evolution of the magnetic properties upon electrochemical cycling of LiNi_0.5Mn_0.5O₂ is studied. Oxidation of Ni²⁺ (S = 2) to Ni³⁺ (S = ¹/₂) to Ni⁴⁺ (S = 0) is observed upon lithiumremoval as well as breakage of the partial magnetic ordering when 0.3 Li is removed. The latter isexplained by the preferential oxidation of the Ni ions in the transition metal layers involved in the 180magnetic exchange.