LAAN-A-LC-E195 No.L417 High Performance Liquid Chromatography Analysis of the Decomposition Products of Lithium Hexafluorophosphate in the Electrolytic Solution of Lithium-Ion Rechargeable Batteries b : SHIMADZU (Shimadzu Corporation)

LAAN-A-LC-E195 No.L417 High Performance Liquid Chromatography Analysis of the Decomposition Products of Lithium Hexaﬂuorophosphate in the Electrolytic Solution of Lithium-Ion Rechargeable Batteries by Column-Switching Ion Chromatography Lithium hexafluorophosphate, which serves as the electrolytic solution in lithium-ion rechargeable batteries, is hydrolyzed by the small amounts of water contained in the electrolytic solution. Since fluoride ions formed as a result of the hydrolytic decomposition can affect battery performance, analysis of the decomposition products is necessary as part of the quality control process. Here, we introduce an analysis of the decomposition products of lithium hexaﬂuorophosphate used as the electrolytic solution in lithium-ion rechargeable batteries, in which we constructed a column-switching system using the Shimadzu Prominence HIC-SP ion chromatography system. n Analysis of Standard Solution Two decomposition products of lithium hexafluorophosphate, the fluoride ion (F) and monofluorophosphate ion (PO3F) were selected as analytes. Fig. 1 shows a ﬂow diagram of the column switching system constructed for analysis. Since the hexaﬂuorophosphate ion contained in the electrolytic solution is retained in the analytical column more strongly than the decomposition products, a single analysis for all components takes a relatively long time. In the dual-column system, the sample is ﬁrst introduced in the 10 mm-long column (1) for a rough or qualitative separation, where only the peak consisting of the decomposition products is sent to column (2) (analytical column) for a more complete separation. After the decomposition products are sent to column (2), pump 2 elutes the hexaﬂuorophosphate ion to waste and washes the column in preparation for the next sample. Fig. 2 shows the results of analysis of 10.87 g/L (20 to 1 dilution of 1.5 mol/L LiPF6) hexaﬂuorophosphate ion spiked with 10 mg/L fluoride ion and 100 mg/L monoﬂuorophosphate ion. The analytical conditions are shown in Table 1. Table 1 Analytical Conditions Fig. 1 Flow Diagram Fig. 2 Chromatogram of Standard Solution Column : (1) Shim-pack IC-SA2 (G) (10 mm L. × 4.6 mm I.D.) (2) Shim-pack IC-SA2 (250 mm L. × 4.0 mm I.D.) Mobile Phase : 12 mmol/L NaHCO3, 0.6 mmol/L Na2CO3 in Water Flow Rate : 1.0 mL/min (Pump1, Pump 2) Injection Vol. : 10 μL Column Temp. : 30 °C Detection : CDD-10ASP (Suppressor) Pump 1 Pump 2 Autosampler 6-Port Valve Column(2) Detector Column(1) Waste Mobile Phase 0.0 2.5 5.0 7.5 10.0 12.5 min -1 0 1 2 3 4 5 6 7 8 9 10 μS/cm 1 2 To Waste To Column(2) ■Peak 1. PF6 (10.87 g/L) ■Peaks 1.F¯ (10 mg/L) 2.PO3F²¯ (100 mg/L) 0.0 2.5 5.0 min 0 50 100 150 200 250 300 μS/cm 1 Column(1) Column(2)

SHIMADZU CORPORATION. International Marketing Division 3. Kanda-Nishikicho 1-chome, Chiyoda-ku, Tokyo 101-8448, Japan Phone: 81(3)3219-5641 Fax. 81(3)3219-5710 No.L417 n Linearity Fig. 3 shows the calibration curves generated using standard solutions of 0.1 to 10 mg/L F - , and 1 to 100 mg/L PO3F, respectively. Excellent linearity was obtained for both, with R 2 values greater than 0.999. n Repeatability Table 2 shows the relative standard deviation (n = 6) obtained for retention times and peak areas in analysis of the standard solutions (F - 1 mg/L, PO3F 10 mg/L). Excellent repeatability of retention time and peak area were obtained for both. n Analysis of Electrolytic Solution for Lithium-Ion Rechargeable Battery Fig. 4 Chromatogram of Electrolytic Solution for Lithium-Ion Rechargeable Battery (New) Fig. 5 Chromatogram of Electrolytic Solution for Lithium-Ion Rechargeable Battery (After 24 Hours) Fig. 4 and Fig. 5 show the results of analysis of the electrolytic solution of a commercially available lithium-ion rechargeable battery. Fig. 4 is the chromatogram obtained using a new sample, and Fig. 5 is that obtained after leaving the new sample exposed to the air for 24 hours. Each sample was analyzed after diluting 20 to 1 with pure water, and filtering through a membrane ﬁlter. * Regarding the difluorophosphate ion (PO2F2), only peak identiﬁcation was conducted because a stable standard substance could not be obtained. In addition, it could not be ascertained whether the fluoride ion, diﬂuorophosphate ion and monoﬂuorophosphate ion were present from the start in the electrolytic solution, or if they were formed instead at the time of dilution. 0 50000 100000 150000 200000 0 25000 50000 75000 100000 0 2 4 6 8 10 12 0 20 40 60 80 100 120 Concentration (mg/L) Peak Area ◆F ■PO3F Concentration (mg/L) Peak Area Fig. 3 Linearity Table 2 Repeatability of Retention Time and Peak Area F PO3F Retention Time Peak Area Retention Time Peak Area 1st 3.93 7573 12.19 14987 2nd 3.93 7329 12.17 14471 3rd 3.93 7482 12.18 14764 4th 3.92 7434 12.17 14700 5th 3.92 7480 12.14 14630 6th 3.92 7523 12.13 14809 %RSD 0.05 1.12 0.20 1.18 μS/cm ■Peaks 1. F 2. PO2F2 1 2 25.0 22.5 20.0 17.5 15.0 12.5 10.0 7.5 5.0 2.5 0.0 -2.5 0.0 2.5 5.0 7.5 10.0 12.5 min 0.0 2.5 5.0 7.5 10.0 12.5 min -2.5 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 μS/cm ■Peaks 1.F 2.PO2F2 3.PO3F 1 2 3 11.0 12.0 13.0