Understanding Inconsistencies in Reported Relationships Between Vibration Frequency and Capacity Degradation of Lithium-Ion Batteries in Electric Vehicles : A Conceptual Framework Based on Structured Literature Review

Sammanfattning

The rapid growth of electric vehicles has increased the demand for reliable, durable lithium-ion battery systems. Mechanical vibration is an unavoidable operating condition for lithium-ion batteries used in electric vehicles. Nevertheless, its effect on capacity degradation remains insufficiently understood. Existing studies indicate that vibration can affect battery performance; however, reported findings remain inconsistent regarding critical vibration frequencies, the extent of degradation, the timing of performance loss, and whether measurable capacity loss occurs at all. This thesis addresses these inconsistencies through a structured literature review aimed at explaining why existing research reports divergent findings on the relationship between mechanical vibration frequency and capacity degradation in lithium-ion batteries used in electric vehicles. The findings suggest that vibration frequency alone does not sufficiently explain the variations in degradation behaviour reported across the literature. Instead, vibration-induced capacity degradation appears to be conditioned by several moderating factors, including the structural configuration of the battery cell, the timing of post-vibration performance assessment, the electrochemical state of charge during vibration exposure, and the severity of mechanical loading. Based on these findings, a conceptual framework is proposed to illustrate how these moderating factors shape the degradation outcomes reported across different experimental contexts in the literature. The study concludes that the inconsistencies reported in the literature should be understood as variations arising from differences in battery characteristics and experimental approaches, rather than as direct contradictions. This thesis contributes to a clearer understanding of vibration-induced capacity degradation in lithium-ion batteries and provides a foundation for future empirical research that systematically examines these moderating conditions.