Mitigating electrical discharge damage in EV bearings: A critical review from inverter design to bio-based greases

Research on electric vehicles (EVs) has gained increasing attention due to the global transition toward cleaner and more sustainable transportation. However, ensuring the efficiency, reliability and long-term durability of EV drivetrains remains a major challenge. In EV bearings, inverter-induced shaft voltage and bearing currents can trigger electrical discharge across the lubricating film when the local electric field exceeds the dielectric strength of the grease. These discharge events can result in surface damage and lubricant degradation, leading to premature bearing failure and affecting the motor reliability. This review critically discusses the mechanisms of electrical discharge damage in EV bearings and reviews recent mitigation strategies including motor and inverter design optimisation, bearing materials and surface engineering, and specialised lubricant formulation. This review further discusses the development of bio-based greases for EV bearing applications, including formulation requirements, bio-based oil selection, thickener system design and additive strategies. The key challenge is to balance conductivity, dielectric stability, tribofilm formation, and grease durability under coupled mechanical, thermal, and electrical stresses. Overall, this review provides a framework for developing high-performance bio-based EV bearing greases that can mitigate electrical discharge damage while supporting sustainable lubrication technologies.