Mixtures of N-butyl-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid (IL) and conventional organic carbonate electrolyte are used for high-capacity LiNi0.8Co0.15Al0.05O2 (LNCA) ...electrodes in Li-ion batteries. Increasing the IL content ratio in the mixtures can increase the electrolyte's thermal stability and retard its flammability. However, the optimal electrolyte composition depends on the operating temperature. At 25 degree C, the plain organic electrolyte is preferred due to its highest ionic conductivity among the tested electrolytes. This electrolyte is volatile at 50 degree C, and thus the incorporation of 25 wt% IL can improve the cyclic stability of the LNCA electrode. The LNCA dissolution and electrolyte decomposition at 75 degree C are clearly suppressed with a high IL ratio in the mixed electrolyte. At such a high temperature, with 75 wt% of IL incorporation a high electrode capacity of 195 mA h g-1 is obtained at 30 mA g-1; 50% of this capacity can be retained when the charge-discharge rate increases to 700 mA g-1. Moreover, less than 20% capacity decay is found after 100 cycles.
NaFePO4 with an olivine structure is synthesized via chemical delithiation of LiFePO4 followed by electrochemical sodiation of FePO4. Butylmethylpyrrolidinium–bis(trifluoromethanesulfonyl)imide ...(BMP–TFSI) ionic liquid (IL) with various sodium solutes, namely NaBF4, NaClO4, NaPF6, and NaN(CN)2, is used as an electrolyte for rechargeable Na/NaFePO4 cells. The IL electrolytes show high thermal stability (>350 °C) and nonflammability, and are thus ideal for high-safety applications. The highest conductivity and the lowest viscosity of the electrolyte are obtained with NaBF4. At an elevated temperature (above 50 °C), the IL electrolyte is more suitable than a conventional organic electrolyte for the sodium cell. At 75 °C, the measured capacity of NaFePO4 in a NaBF4-incorporated IL electrolyte is as high as 152 mAh g–1 (at 0.05 C), which is near the theoretical value (154 mAh g–1). Moreover, 60% of this capacity can be retained when the charge–discharge rate is increased to 1 C.
Lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are used as Li salts in butylmethylpyrrolidiniumabis(trifluoromethanesulfonyl)imide (BMPaTFSI) ionic liquid ...(IL) electrolyte for Li/LiFePO4 cells. This kind of IL electrolyte shows high thermal stability (>400 degree C) and non-flammability, and is thus ideal for high-safety applications. At 25 degree C, a maximum capacity of 113 mAh ga1 (at 0.1 C) is found for LiFePO4 in the IL with 0.5 M LiTFSI. An excessive LiTFSI concentration leads to a capacity decrease due to reduced electrolyte ionic conductivity. At 50 degree C, the measured capacity and rate capability are significantly improved compared to those at 25 degree C. With 1 M LiTFSI-doped IL electrolyte (the optimum concentration at 50 degree C), a capacity of 140 mAh ga1 is found at 0.1 C and 45% of the capacity can be retained when the rate increases to 5 C, values which are comparable to those found in a traditional organic electrolyte. In the IL electrolyte, the LiFePO4 electrode shows better cyclic stability at 50 degree C than it does at 25 degree C; this trend is opposite to that found in the organic electrolyte. At 50 degree C, there is negligible capacity loss of LiFePO4 after 100 charge-discharge cycles in 1 M LiTFSI-doped BMPaTFSI IL electrolyte.
Lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are used as Li salts in butylmethylpyrrolidinium–bis(trifluoromethanesulfonyl)imide (BMP–TFSI) ionic liquid ...(IL) electrolyte for Li/LiFePO4 cells. This kind of IL electrolyte shows high thermal stability (>400°C) and non-flammability, and is thus ideal for high-safety applications. At 25°C, a maximum capacity of 113mAhg−1 (at 0.1 C) is found for LiFePO4 in the IL with 0.5M LiTFSI. An excessive LiTFSI concentration leads to a capacity decrease due to reduced electrolyte ionic conductivity. At 50°C, the measured capacity and rate capability are significantly improved compared to those at 25°C. With 1M LiTFSI-doped IL electrolyte (the optimum concentration at 50°C), a capacity of 140mAhg−1 is found at 0.1 C and 45% of the capacity can be retained when the rate increases to 5 C, values which are comparable to those found in a traditional organic electrolyte. In the IL electrolyte, the LiFePO4 electrode shows better cyclic stability at 50°C than it does at 25°C; this trend is opposite to that found in the organic electrolyte. At 50°C, there is negligible capacity loss of LiFePO4 after 100 charge–discharge cycles in 1M LiTFSI-doped BMP–TFSI IL electrolyte.
•LiTFSI is better than LiPF6 as solute in BMP–TFSI IL for Li/LiFePO4 cells.•LiTFSI concentration in IL greatly affects the cell performance.•At 50°C, the cell performance with IL is close to that with organic electrolyte.•The cell shows little decay after 100 cycles at 50°C in the IL electrolyte.•IL electrolyte is ideal for high-temperature and high-safety applications.
Orthorhombic Na sub(0.44)MnO sub(2) with wide structural tunnels for sodium ion transport is synthesized. Butylmethylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (BMP-TFSI) ionic liquid (IL) with ...various Na solutes, namely NaBF sub(4), NaClO sub(4), NaTFSI, and NaPF sub(6), is used as an electrolyte for rechargeable Na/Na sub(0.44)MnO sub(2) cells. The cell with NaClO sub(4)-incorporated IL electrolyte exhibits superior charge-discharge performance due to it having the lowest solid-electrolyte-interface resistance and charge transfer resistance at both the Na and Na sub(0.44)MnO sub(2) electrodes. The IL electrolyte shows high thermal stability and is suitable for use at an elevated temperature. At 75 degreesC, the measured capacity of Na sub(0.44)MnO sub(2) in the IL electrolyte with NaClO sub(4) is as high as 115 mAh g super(-1) (at 0.05 C), which is close to the theoretical value (121 mAh g super(-1)). Moreover, 85% of this capacity can be retained when the charge-discharge rate is increased to 1 C. These properties are superior to those of a conventional organic electrolyte.
