Performance Evaluation and Analysis of Rolechem's Lithium Fluorosulfonate (LiFS)

Rolechem has launched its new additive product, Lithium Fluorosulfonate (LiFS). Applicable Scenarios: Suitable for lithium-ion batteries requiring high standards in high- and low-temperature performance, fast-charging capability, and high-temperature stability. It holds significant application potential particularly in power batteries and energy storage batteries. Through evaluations of LiFS at concentrations of 0%, 0.1%, 0.5%, and 1%, 1.0% LiFS demonstrated the best performance across high- and low-temperature discharge, rate capability, high-temperature storage, and cycling performance, making it the ideal optimal additive amount to balance various performance metrics.

Cell Type: 1Ah pouch cell Chemistry System: LFP / Artificial Graphite Voltage Window: 2.5 V – 3.65 V Electrolyte Baseline (Common Components): EC : EMC = 3 : 7 ，1M LiPF6, with 2% VC additive Base Group: Common Components + 0% LiFS Scheme A: Common Components + 0.1% LiFS Scheme B: Common Components + 0.5% LiFS Scheme C: Common Components + 1.0% LiFS

01 Impact of Additive Amount: When the LiFS content is 1.0%, the improvement effect on cell capacity and ICE is remarkable. In LFP/artificial graphite pouch cells, the initial discharge capacity of the 1.0% LiFS group reached 0.7079 mAh, and the ICE was 80.65%, both of which are higher than those of the 0.1%, 0.5%, and baseline (Base) groups. 02 SEI Film Optimization: Analysis of the dQ/dV curves reveals that the peak for the 1.0% LiFS group shifts to the left at around 2.15V, indicating that LiFS can enhance additive activity and promote the formation of an SEI film with a superior structure. This reduces side reactions between the electrode and the electrolyte, thereby improving initial performance.

01 Impedance Reduction: Under low-temperature conditions of -20°C, the charge/discharge direct current resistance (DCR) of the cells in the 1.0% LiFS group was significantly lower than that of the baseline group. Specifically, the discharge DCR decreased from 0.398 mΩ in the baseline group to 0.340 mΩ, and the charge DCR dropped from 0.716 mΩ to 0.620 mΩ. Combined with EIS testing, this indicates that LiFS effectively reduces film resistance at low temperatures. 02 Discharge Capacity Retention Rate: In environments of ≤10°C, the discharge capacity retention rate of the 1.0% LiFS group showed obvious advantages. For example, at -20°C, the retention rate was 18.35% (compared to 15.17% for the baseline group), and at 10°C it reached 81.06% (compared to 77.41% for the baseline group), demonstrating favorable low-temperature discharge capability.

01 High-Rate Charging: When the charging rate is ≥2C, the 1.0% LiFS group stands out. At 4C charging, the capacity retention rate is 49.8% (compared to 37.9% for the baseline group), representing an 11.9% increase over the baseline. As the rate increases, the advantages become even more pronounced, reflecting LiFS's adaptability to high-power charging. 02 High-Rate Discharging: At discharge rates of ≥2C, the 1.0% LiFS group shows significant advantages. At 3C discharge, the capacity retention rate is 82.2% (baseline group 74.8%), and at 5C it reaches 48.1% (baseline group 41.7%), both being over 6% higher than the baseline group. This indicates that LiFS effectively enhances the discharge efficiency of cells at high rates.

01 Capacity Retention and Recovery: The capacity retention rates (90.56%, 91.42%) and recovery rates (94.98%, 94.99%) of the 0.5% and 1.0% LiFS groups were superior to those of the baseline group (82.39%, 90.96%) and the 0.1% group (82.54%, 90.44%), exhibiting excellent high-temperature stability. 02 Impedance and Thickness Changes: As the additive amount increased, the internal resistance change rate and thickness swelling rate decreased significantly. For the 1.0% LiFS group, the internal resistance change rate was 69.04% (baseline group 116.88%) and the thickness change rate was 1.70% (baseline group 6.67%), indicating that LiFS suppresses electrolyte decomposition and electrode swelling at high temperatures.

01 Cycling Performance: Due to an insufficient amount, the 0.1% LiFS group actually degraded high-temperature cycling performance; however, the 0.5% and 1.0% groups performed better than the baseline group. Among them, the 1.0% LiFS group showed the longest cycling life trend, indicating that an appropriate additive amount can effectively enhance cycling stability at high temperatures.

In summary, LiFS reduces active sites of additives and promotes the early formation of the SEI film with a more compact structure, thereby reducing continuous electrolyte decomposition and protecting the electrode. As the additive amount increases (0–1.0%), the cell alternating current impedance (EIS) decreases significantly, indicating reduced charge transfer resistance and improved interfacial reaction kinetics. At the same time, it has a remarkable effect on improving the comprehensive performance of cells (especially in terms of high/low temperatures, rate capability, and high-temperature stability). Its effects are closely related to the additive amount, with 1.0% being the recommended optimal addition level.