Direct Observation of Active Material Concentration Gradients and Crystallinity Breakdown in LiFePO(4) Electrodes During Charge/Discharge Cycling of Lithium Batteries.
Direct Observation of Active Material Concentration Gradients and Crystallinity Breakdown in LiFePO(4) Electrodes During Charge/Discharge Cycling of Lithium Batteries.
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DOI：
10.1021/jp411152s
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发表时间：
2014-04-03
期刊：
影响因子：
--
通讯作者：
Hector AL
中科院分区：
文献类型：
--
作者：
Roberts MR;Madsen A;Nicklin C;Rawle J;Palmer MG;Owen JR;Hector AL
在由LiFePO4、碳和PTFE粘合剂组成的电极放电期间发生的相变已经在锂半电池中通过使用反射几何中的X射线衍射测量来研究。LiFePO4电极的正面和背面之间的充电状态的差异已经被可视化。通过改变X射线入射角，改变了X射线束穿透电极的深度，允许检查电极内存在的任何浓度梯度。在高放电速率下，面向集电器的电极侧经历有限的锂插入，而电极作为整体经历大于50%的放电。该行为与电极孔中所含电解质的锂含量以高速率消耗一致。衍射峰宽度的增加表明在循环期间甚至在这些实验的相对短的持续时间期间活性材料内的结晶度的破坏，这也可以与高速率下的循环有关。
The phase changes that occur during discharge of an electrode comprised of LiFePO4, carbon, and PTFE binder have been studied in lithium half cells by using X-ray diffraction measurements in reflection geometry. Differences in the state of charge between the front and the back of LiFePO4 electrodes have been visualized. By modifying the X-ray incident angle the depth of penetration of the X-ray beam into the electrode was altered, allowing for the examination of any concentration gradients that were present within the electrode. At high rates of discharge the electrode side facing the current collector underwent limited lithium insertion while the electrode as a whole underwent greater than 50% of discharge. This behavior is consistent with depletion at high rate of the lithium content of the electrolyte contained in the electrode pores. Increases in the diffraction peak widths indicated a breakdown of crystallinity within the active material during cycling even during the relatively short duration of these experiments, which can also be linked to cycling at high rate.
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