Interplay between Electrochemistry and Phase Evolution of the P2-type Nax(Fe1/2Mn1/2)O2 Cathode for Use in Sodium-Ion Batteries
Interplay between Electrochemistry and Phase Evolution of the P2-type Nax(Fe1/2Mn1/2)O2 Cathode for Use in Sodium-Ion Batteries
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DOI：
10.1021/acs.chemmater.5b00943
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发表时间：
2015-04-28
影响因子：
8.6
通讯作者：
Guo, Zaiping
中科院分区：
文献类型：
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作者：
Pang, Wei Kong;Kalluri, Sujith;Guo, Zaiping
钠离子电池是下一代电池技术；然而，其电极性能阻碍了商业开发。具有六方结构和P6(3)/mmc空间群的P2型Na - 2/3(Fe1/2Mn1/2)O - 2因其高容量（约190 mAh·g⁻¹）和能量密度（约520 mWh·g⁻¹），被认为是一种钠离子电池候选正极材料，其容量和能量密度与商业磷酸铁锂和锰酸锂锂离子电池正极相当，而此前无法解释的较差循环性能是其商业应用的主要障碍。我们使用原位同步辐射X射线粉末衍射来了解Na - 2/3(Fe1/2Mn1/2)O - 2材料在相对较宽的1.5 - 4.2 V（相对于Na）电压窗口循环过程中容量衰减的原因。我们发现了一个复杂的相演变过程，在Na - 2/3(Fe1/2Mn1/2)O - 2正极脱钠和嵌钠过程中，涉及从P6₃/mmc（开路电压下为P2型）到P6₃（完全充电时为OP4型）到P6₃/mmc（3.4 - 2.0 V时为P2型）再到cmon（2.0 - 1.5 V时为P2型）对称结构的转变。与多次两相反应相关的较大的晶胞体积变化可能是导致循环性能差的原因，这明确表明2.0 - 4.0 V的工作窗口是提高循环性能的一种策略。我们在此证明，P2型Na - 2/3(Fe1/2Mn1/2)O - 2正极在该策略性工作窗口下能够实现约25%的更好循环性能。循环性能的这一显著提高意味着，通过表征电池运行过程中的相演变和反应机制，我们能够对电池使用条件提出改进建议以提高性能，突出了结构和电化学之间相互作用的重要性。
Sodium-ion batteries are the next-generation in battery technology; however, their Commercial development is hampered by electrode performance. The P2-type Na-2/3(Fe1/2Mn1/2)O-2 With a hexagonal structure and P6(3)/mmc space group is considered a candidate sodium-ibn battery cathode Material due to its high capacity (similar to 190 mAh.g(-1)) and energy density (similar to 520 mWh-g(-1)); which are comparable to those of the commercial LiFePO4 and LiMn2O4 lithium-ion battery tathodes, with previously unexplained poor cycling performance being the major barrier to its commercial -application. We use operando synchrotron X-ray powder diffraction to understand the origins of the capacity fade of the Na-2/3(Fe1/2Mn1/2)O-2 material during cycling over the relatively wide 1.5-4.2 V (vs Na) window. We found a compleir phase-evolution, involving transitions from P63/mmc (P2-type at the open-circuit voltage) to P63 (OP4-type when fully charged) to P63/mmc (P2-type at 3.4-2.0 V) to cmon (P2-type at 201.5 V) symmetry structures during the desodiation and sodiation of the Na-2/3(Fe1/2Mn1/2)O-2 cathode. The associated large cellvolume changes with the multiple two-phase reactions are likely to be responsible for the poor cycling performance, clearly suggesting a 2.0-4.0 V window of operation as a strategy to improve cycling performance. We demonstrated here that the P2-type Na-2/3(Fe1/2Mn1/2)O-2 cathode is able to deliver similar to 25% better cycling performance with the strategic operation window. This significant improvement in cycling performance implies that by characterizing the phase evolution and reaction mechanisms during battery function we are able to propose these modifications to the conditions of battery use that improve performance, highlighting the importance of the interplay between structure and electrochemistry.