Fluoroalkyl ether-diluted dimethyl carbonate-based electrolyte solutions for high-voltage operation of LiNi0.5Co0.2Mn0.3O2 electrodes in lithium ion batteries
Fluoroalkyl ether-diluted dimethyl carbonate-based electrolyte solutions for high-voltage operation of LiNi0.5Co0.2Mn0.3O2 electrodes in lithium ion batteries
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DOI：
10.1039/c8se00036k
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发表时间：
2018-05
影响因子：
5.6
通讯作者：
T. Doi;Ryo Matsumoto;Ziyang Cao;M. Haruta;M. Hashinokuchi;M. Inaba
中科院分区：
文献类型：
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作者：
T. Doi;Ryo Matsumoto;Ziyang Cao;M. Haruta;M. Hashinokuchi;M. Inaba
锂离子电池的能量密度可以通过提高电池电压和/或比容量来提高。然而，传统的电解质溶液在高压下会氧化分解。通过增加锂盐的浓度可以提高电解质溶液的抗氧化稳定性。接近饱和的8.67 mol kg−1 LiBF4/二甲基碳酸酯（DMC）电解质溶液使LiNi0.5Co0.2Mn0.3O2正极在4.6 V下高压工作，并将放电容量提高到约200 mA h g−1。高浓度稳定了BF4−阴离子和DMC溶剂。为了降低粘度和Li浓度，同时又不失去实际应用中抗氧化的高稳定性，用低供体能力的氟化助溶剂稀释高浓度电解质溶液。拉曼光谱显示，用特定的氟烷基醚稀释后，LiBF4/DMC的溶剂化结构保持不变。只要DMC/LiBF4的摩尔比保持较低，得到的低粘度、低浓度电解质溶液在LiNi0.5Co0.2Mn0.3O2电极上具有很高的抗氧化稳定性。其充放电性能明显优于传统的1 M LiPF6/碳酸乙烯基电解质溶液，能量密度也远远超过5 V级LiNi0.5Mn1.5O4电极。
The energy density of lithium-ion batteries can be increased by improving the battery voltage and/or specific capacity. However, conventional electrolyte solutions decompose oxidatively at high voltages. The stability against oxidation of electrolyte solutions could be enhanced by increasing the concentration of lithium salts. The nearly saturated 8.67 mol kg−1 LiBF4/dimethyl carbonate (DMC) electrolyte solution enabled high-voltage operation of LiNi0.5Co0.2Mn0.3O2 positive-electrodes at 4.6 V, and extended the discharge capacity to ca. 200 mA h g−1. BF4− anions, as well as DMC solvents, were stabilized at the high concentration. To reduce the viscosity and Li concentration without losing the high stability against oxidation toward practical use, the highly concentrated electrolyte solution was diluted with fluorinated co-solvents having a low donor ability. Raman spectroscopy revealed that the solvation structure of LiBF4/DMC was maintained after dilution with a specific fluoroalkyl ether. The resultant low-viscosity and -concentration electrolyte solution was highly stable against oxidation at the LiNi0.5Co0.2Mn0.3O2 electrodes as long as the DMC/LiBF4 molar ratio was kept low. The charge/discharge performance was much better than that for a conventional 1 M LiPF6/ethylene carbonate-based electrolyte solution and the energy density far exceeded that of 5 V class LiNi0.5Mn1.5O4 electrodes.