Modelling the degradation of electric vehicle batteries based on initial state of health and charging conditions in Kenya

Abstract

The lifespan of electric vehicle (EV) batteries is a critical determinant of performance, safety, and consumer confidence, particularly in Kenya, where over 80% of EVs are second-hand imports. This study investigated the degradation patterns of lithium - ion EV batteries based on initial State of Health (SoH), charging voltage, charging current, and operational temperature— factors that influence the usable life of imported EVs. An experimental approach was adopted, involving the cycling of 26650.format lithium – ion battery cells under controlled laboratory conditions to simulate real-world usage patterns. The test matrix included batteries with initial SoH levels of 60%, 80%, 90%, and 100%, subjected to charging currents of 0.5C, 1.0C, and 1.5C, voltages of 3.4V, 3.65V, and 4.02V, and ambient temperatures of 15°C, 27°C, and 35°C. Battery capacity fade was monitored over successive charge. discharge cycles, and regression models were developed to quantify degradation trends. The findings indicate that battery degradation is significantly affected by the initial SoH. Batteries starting at 60% and 80% SoH exhibited a slight capacity gain of 0.0029 Ah per cycle, likely due to initial electrochemical stabilization. In contrast, new batteries with 100% SoH showed a consistent degradation rate of 0.0005 Ah per cycle. Charging current had a notable impact: batteries charged at 1.5C degraded at a rate of 0.0008 Ah per cycle—50% faster than those charged at 0.5C, which degraded at 0.0004 Ah per cycle. Charging voltage also played a critical role. Overvoltage conditions at 4.02V resulted in a degradation rate of 0.0008 Ah per cycle, while undervoltage charging at 3.4V preserved battery health but reduced usable capacity by approximately 10%, yielding 2.98 Ah compared to the nominal 3.3 Ah. Temperature effects were equally significant. Low temperatures (15°C) accelerated degradation, with a fade rate of 0.0019 Ah per cycle and corresponding capacity loss, while moderate temperatures between 27°C and 35°C yielded the most stable performance at a degradation rate of 0.0005 Ah per cycle. The study highlights the urgent need for the regulation of public charging infrastructure to mitigate degradation risks. It recommends that national policies incorporate measures to ensure optimal thermal management, standardized charging protocols, and increased consumer awareness to enhance battery lifespan. These insights are crucial for policymakers, regulators, and EV buyers, as they help align Kenya’s e-mobility transition with sustainability goals while minimizing the environmental and economic consequences of premature battery failure.