Thermal Stability and Reactivity of Cathode Materials for Li-Ion Batteries

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• 作者：Yiqing Huang ; Yuh-Chieh Lin ; David M. Jenkins ; Natasha A. Chernova ; Youngmin Chung ; Balachandran Radhakrishnan ; Iek-Heng Chu ; Jin Fang ; Qi Wang ; Fredrick Omenya ; Shyue Ping Ong ; M. Stanley Whittingham
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：March 23, 2016
• 年：2016
• 卷：8
• 期：11
• 页码：7013-7021
• 全文大小：526K
• ISSN：1944-8252

文摘

The thermal stability of electrochemically delithiated Li_0.1Ni_0.8Co_0.15Al_0.05O₂ (NCA), FePO₄ (FP), Mn_0.8Fe_0.2PO₄ (MFP), hydrothermally synthesized VOPO₄, LiVOPO₄, and electrochemically lithiated Li₂VOPO₄ is investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis, coupled with mass spectrometry (TGA-MS). The thermal stability of the delithiated materials is found to be in the order of NCA < VOPO₄ < MFP < FP. Unlike the layered oxides and MFP, VOPO₄ does not evolve O₂ on heating. Thus, VOPO₄ is less likely to cause a thermal run-away phenomenon in batteries at elevated temperature and so is inherently safer. The lithiated materials LiVOPO₄, Li₂VOPO₄, and LiNi_0.8Co_0.15Al_0.05O₂ are found to be stable in the presence of electrolyte, but sealed-capsule high-pressure experiments show a phase transformation of VOPO₄ → HVOPO₄ → H₂VOPO₄ when VOPO₄ reacts with electrolyte (1 M LiPF₆ in EC/DMC = 1:1) between 200 and 300 °C. Using first-principles calculations, we confirm that the charged VOPO₄ cathode is indeed predicted to be marginally less stable than FP but significantly more stable than NCA in the absence of electrolyte. An analysis of the reaction equilibria between VOPO₄ and EC using a multicomponent phase diagram approach yields products and reaction enthalpies that are highly consistent with the experiment results.