24th International Colloquium Tribology - January 2024 39 Next-Generation Anti-Wear for EV Lubricants Christelle Chretien 1* 1 SOLVAY, Bristol, PA - USA * christelle.chretien@solvay.com 1. Introduction To protect our health and our environment, cleaner transportation is urgently needed, with an ultimate goal of zero emissions and carbon neutrality. To achieve this goal, solutions must be developed for E-Driveline lubricants providing: - more robust anti-wear/ extreme pressure (AW/ EP) capacities - a low friction for energy efficiency - Metal-free and Sulfur-free features for compatibility with E-driveline materials. The objective of this presentation is to introduce a next-generation anti-wear technology called Polymeric AW and to highlight its potential in E-Driveline Lubricants. The objective of this paper is to: - Introduce the technology of next-generation anti-wear - Describe its main benefits especially in EV Driveline lubricants 2. Purpose of this project The objective of this project is to develop a next generation anti-wear additive presenting the following features: - Ashless, Sulfur-free, and low phosphorus content - Providing benefits in EV driveline lubricants 3. Technology description As the toolbox of chemicals is more and more limited, the idea is to look out-of-the-box and develop a technology of anti-wear brand new to the industry. The technology we propose as a next-generation anti-wear is very unique as: - The phosphorous, which is the anchoring group, is outside of the backbone of the polymer bringing a freer access to the surface vs. technologies containing phosphorus in their backbone - It is based on a co-polymer leading to the use of different monomers to achieve an appropriate balance between surface adhesion and oil solubility. This technology can be depicted as the following: Figure 1: Polymeric Anti-Wear (Polymeric AW) 4. Prior art analysis This analysis of the prior art shows the uniqueness of this Polymeric AW technology as: - It directly coats the surface as a polymer vs. ZDDP which reacts first with the surface to form a polymeric tribofilm on the surface [1]. Figure 2: Tribofilm formation by ZDDP [2] - It has multiple anchoring groups while single molecules contain only one group. - Its anchoring group is easily reachable as it is outside of the backbone. 5. An Innovative solution under development A set of testings was performed on tribology properties as a first step. 5.1 Anti-wear performances In terms of performances, the core of this technology is its anti-wear feature . This was evaluated on one of our lead candidates using the 4 ball wear test (ASTM D4172). EDS (Energy Dispersive X-Ray Spectroscopy) surface analysis was conducted on the wear scar. The wear performance shows that the polymeric anti-wear candidate is equivalent to ZDDP, while being Ashless and Sulfur-free and while providing a concentration of Phosphorus 95% lower than what ZDDP brings in the lubricant: Figure 3: 4 ball wear evaluation 40 24th International Colloquium Tribology - January 2024 Next-Generation Anti-Wear for EV Lubricants By analysing the surface of the wear scar, the P level on the surface is the same either using ZDDP or the polymeric anti-wear candidate: Figure 4: EDS Analysis In conclusion, even if the Polymeric anti-wear brings in the lubricant 95% less Phosphorus than ZDDP, the Phosphorus level adhering on the surface is the same either using ZDDP or the polymeric anti-wear candidate. The hypothesis is that the Polymeric anti-wear might provide a higher phosphorus adhesion power on the surface than ZDDP. 5.2 Additional benefits Among the different candidates developed at lab scale, one candidate (ref. D.097) has shown leading performances with 11 benefits identified: - Metal-free, Sulfur-free and very low Phosphorus content - Good anti-wear performance - Friction level similar to ZDDP - Tremendous thermo-oxidative stability - Very low sludging tendency - Harmless on viscometrics - Not impacting foam - Equivalent on corrosion protection - Excellent solubility in standard base oils - Very low acidity level It is especially important to highlight the high thermal stability of this candidate illustrated by TGA (Thermogravimetric Analysis). The onset temperature of the Polymeric AW is 61°C higher than. ZDDP. In addition, the Polymeric AW leaves no residue thanks to its ashless nature. In addition, The Polymeric AW lead candidate (ref. D097) shows a good oxidation stability with no impact on the aging and deposit generation after 192 hours at 160°C. In addition to the development of the lead candidate, 9 additional candidates were developed and prepared showing different features. 3 new candidates were added to the first lead candidate as they show potential for good performance. 5.3 Application to EV Among these 3 new candidates, 2 show potential to be used in EV drivelines. - 4 performances were evaluated: - The electrical conductivity showed a 75% and 95% lower level than ZDDP at 150°C. - Cu corrosion protection is also a benefit brought by this technology. The 2 candidates showed a significantly better corrosion rating vs. ZDDP and a polysulfide. - In terms of anti-wear protection, the Polymeric AW technology shows an equivalent performance to ZDDP. - Finally, in terms of stability, the Polymeric AW technology is stable after 1 month at 3 temperatures. 6. Conclusion The Polymeric AW technology shows strong potential as a next-generation anti-wear thanks to the different benefits it provides, on top of anti-wear prevention. Further evaluations are ongoing in fully formulated formulation and specifically in the EV segment to assess its potential. References [1] “ZDDP’s uncertain future” in the TLT Tribology & Lubrication Technology - September 2019 [2] “Overview of automotive engine friction and reduction trends-Effects of surface, material, and lubricant-additive technologies”: DOI 10.1007/ s40544-016-0107-9