Voltage Fade of Layered Oxides: Its Measurement and Impact on Energy Density
Voltage Fade of Layered Oxides: Its Measurement and Impact on Energy Density
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DOI：
10.1149/2.034311jes
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发表时间：
2013-01-01
影响因子：
3.9
通讯作者：
Abraham, Daniel P.
中科院分区：
文献类型：
--
作者：
Bettge, Martin;Li, Yan;Abraham, Daniel P.
层状锂嵌入过渡金属氧化物的电压衰减是由不可逆的结构变化引起的。提出了一种使用电阻校正的平均电压的方法，以可再现和时间有效的方式跟踪和量化电压衰减，这里使用它来比较几种层状氧化物的衰减程度。所研究的材料包括当前技术上重要的一些材料，例如LiNi0.8Co0.15Al0.05O2（NCA）、Li-1.05（Ni1/3Mn1/3Co1/3）（0.95）O-2（NMC）和Li1.2Ni0.15Mn0.55Co0.1O2，一种富含Li和Mn的NMC，也表示为0.5Li（2）MnO（3）中心点0.5LiMn（0.375）Ni（0.375）Co（0.25）O（2），以及其他一些具有纳米复合结构的富锂氧化物。这些材料的电化学测试表明，电压衰减是常见的许多，如果不是全部，层状氧化物。对于大多数材料，电阻校正的平均电压的衰减速率在每个周期几毫伏的量级上，通常在开始时衰减得稍微快一些。这里特别注意富含Li和Mn的NMC，当氧化物在升高的温度（55 ℃）和高电压（4.7 V vs. Li/Li+）下循环时，其电压衰减速率显示出增加。在20次循环后，电压衰减显著降低了材料的能量输出，并且在标准循环条件下（即，2.0 V-4.7 V vs. Li/Li+，30 ° C），电压衰减可以超过由于容量损失和电阻上升而导致的能量损失。尽管其初始电压衰减，但富含Li和Mn的NMC在感兴趣的材料中表现出最高的氧化物比能量密度。电压衰减似乎也与电压滞后有关，电压滞后在这些材料中的一些材料中特别大。可逆和不可逆过程之间的相互作用，如过渡金属迁移之间的金属和锂层的结构转变过程中，可以解释一些观察到的循环特性。(C)2013年电化学学会。All rights reserved.
Voltage fade of layered, Li-intercalating transition metal oxides is caused by irreversible, structural changes. A method that uses a resistance-corrected average voltage is proposed to track and quantify voltage fade in a reproducible and time-efficient manner, it is used here to compare several layered oxides in terms of their degrees of fade. The materials studied include some that are of current technological importance, such as LiNi0.8Co0.15Al0.05O2 (NCA), Li-1.05(Ni1/3Mn1/3Co1/3)(0.95)O-2 (NMC), and Li1.2Ni0.15Mn0.55Co0.1O2, a Li- and Mn-rich NMC, also denoted as 0.5Li(2)MnO(3)center dot 0.5LiMn(0.375)Ni(0.375)Co(0.25)O(2), as well as some other Li-rich oxides with nano-composite structures. Electrochemical testing of these materials shows that voltage fade is common to many, if not all, layered oxides. For most materials, the decay rate of the resistance-corrected average voltage is on the order of a few millivolts per cycle, often with a slightly faster decay in the beginning. Particular attention is paid here to the Li- and Mn-rich NMC for which the rate of voltage fade is shown to increase when the oxide is cycled at elevated temperatures (55 degrees C) and to high voltages (4.7 V vs. Li/Li+). After 20 cycles,-voltage fade significantly reduces the material's energy output and can outweigh energy losses due to capacity loss and resistance rise under standard cycling conditions (i.e. 2.0 V-4.7 V vs. Li/Li+, 30 degrees C). Despite its initial voltage fade, the Li- and Mn-rich NMC exhibits the highest oxide-specific energy density among the materials of interest. Voltage fade also appears to be related to the voltage hysteresis, which is particularly large in some of these materials. The interplay between reversible and irreversible processes, such as transition metal migration between the metal- and the Li-layer during the structural transformation, may explain some of the observed cycling characteristics. (C) 2013 The Electrochemical Society. All rights reserved.