Performance Evaluation and Analysis of ARC-S40 Electrolyte Additive

As a sulfur-containing cyclic compound, Rolechem’s novel electrolyte additive ARC-S40 has been evaluated for both short-term and long-term performance. The results lead to the following conclusions:

The core value of ARC-S40 lies in its ability to form a film ahead of DTD, suppress solvent decomposition, and thereby significantly improve voltage drop behavior, high-temperature storage performance, and high-temperature cycling performance.

Performance varies significantly with the addition level. An addition level of 1.5% delivers the best results in storage, cycling, and voltage drop performance, but compromises initial Coulombic efficiency, low-temperature performance, and high-rate discharge capability. At 0.5%, insufficient film formation can actually deteriorate high-temperature storage performance.

An addition level of 1.0% offers the best overall balance. It maintains initial Coulombic efficiency, significantly reduces charge-transfer resistance (Rct), and provides clear advantages in high-temperature storage and cycling without compromising low-temperature or rate performance

1. Cell System and Electrolyte Formulations

1.1 Cell System

Cell chemistry: LFP/artificial graphite Cell capacity and format: 1.4 Ah pouch cell Voltage range: 2.5–3.65 V

1.2 Electrolyte Formulations

Base electrolyte formulation: EC = 3:7, 0.4 M LiPF₆ + 0.6 M LiFSI Experimental formulations: Base formulation + 1.0% DTD Base formulation + 0.5% S40 Base formulation + 1.0% S40 Base formulation + 1.5% S40

2. Experimental Results and Analysis

① Initial Coulombic Efficiency and Initial Discharge Capacity

ARC-S40 consumes a small amount of active lithium during film formation. When the addition level exceeds 1.0%, side reactions associated with the excess additive begin to affect initial Coulombic efficiency and initial capacity utilization. The 1.5% addition level shows a slight deterioration in these initial performance metrics. At addition levels of 1.0% or below, initial Coulombic efficiency is essentially maintained, indicating that appropriate film formation does not compromise initial electrochemical performance.

② EIS, dQ/dV, and Voltage Drop Analysis

The dQ/dV results indicate that ARC-S40 forms a film ahead of DTD, effectively suppressing solvent decomposition. The resulting low-impedance interfacial film significantly reduces charge-transfer resistance (Rct). The measured Rct follows this trend: 1.5%-S40 ≈ 1.0%-S40 < 0.5%-S40 < BASE These results suggest that ARC-S40 can improve interfacial properties through preferential film formation, helping to reduce charge-transfer resistance and improve voltage drop behavior.

③ High- and Low-Temperature Discharge Performance

At 55°C, all experimental groups exhibit discharge retention approximately 1.0 percentage point higher than the baseline group. At −20°C, the 1.5% addition level shows slight performance deterioration. These results indicate that an appropriate amount of ARC-S40 can improve interfacial stability at elevated temperatures without significantly affecting low-temperature performance. However, excessive addition at 1.5% may slightly hinder low-temperature reaction kinetics, potentially due to an excessively thick interfacial film or increased impedance.

④ Rate Capability

At low discharge rates, improvements in the interfacial film provide a modest performance benefit. However, this improvement cannot necessarily be attributed solely to the influence of ARC-S40 film formation on lithium-ion insertion and extraction. At high discharge rates, excessive ARC-S40 addition at 1.5% restricts lithium-ion transport and impairs discharge rate capability. In contrast, charge rate capability improves slightly as the ARC-S40 addition level increases, suggesting that the interfacial film may have a positive effect on lithium-ion insertion kinetics at the anode.

⑤ High-Temperature Storage Performance

At addition levels of 1.0%–1.5%, both capacity retention and capacity recovery show clear improvements. In contrast, the 0.5% addition level results in some deterioration. The difference is also evident in the DCR change rate. At addition levels of 1.0%–1.5%, the DCR change rate remains below 30%, substantially lower than the 41.5% recorded for the baseline group and the 85.8% recorded for the 0.5% group. One possible explanation is that 0.5% ARC-S40 is insufficient to form a complete protective film, leaving the electrode interface inadequately protected and resulting in poorer storage performance than the baseline formulation. At 1.0%–1.5%, more complete film formation significantly improves SEI film stability and interfacial protection, thereby enhancing high-temperature storage performance.

⑥ High-Temperature Cycling Performance

ARC-S40 provides improvements in interfacial stability during extended high-temperature cycling. The cycling advantage generally becomes more consistent as the addition level increases. However, the 1.0% group exhibits signs of capacity degradation toward the end of the test. This highlights the need to evaluate differences in film durability at different addition levels. Further improvements may be achievable through the synergistic use of multiple additives.

3. Recommended Addition Levels

1.0% — Recommended for balanced overall performance Suitable for LFP battery systems requiring strong high-temperature storage performance, high-temperature cycling stability, and improved voltage drop behavior, while maintaining initial Coulombic efficiency, low-temperature performance, and high-rate discharge capability. 1.5% — For applications prioritizing high-temperature stability Recommended only for applications with stringent requirements for voltage drop control and high-temperature stability, where high-rate discharge capability is less critical, particularly at discharge rates below 2C. 0.5% — Not recommended Insufficient film formation at this concentration can lead to deterioration in high-temperature storage performance, resulting in the least favorable overall cost-performance balance among the tested formulations.