A comprehensive review of state of charge estimation in lithium-ion batteries used in electric vehicles

In the recent era, Electric Vehicles (EVs) has been emerged as the top concern in the automobile sector because of their eco-friendly nature. The application of Lithium-ion batteries as an energy storage device in EVs is considered the best solution due to their high energy density, less weight, and high specific power density. The battery management system plays a significant part in ensuring the safety and reliability of lithium-ion batteries. The State of Charge (SOC) acts as the performance indicator of the battery. Incorrect estimation of SOC leads to overcharging or over-discharging. SOC estimation has become a challenging task due to the considerable changes occurring in battery characteristics due to the aging effect, temperature effect, and existence of non-linear characteristics of the battery. In recent years, estimation of SOC has become an active research area. Many researchers strive to develop a novel SOC estimation method that is highly robust, accurate, and has low complexity in implementation and computation. In this paper, a comprehensive review of various SOC estimation methods, including direct methods, model-based methods, observer-based methods, filter-based methods, and data-driven methods, were summarized. A detailed discussion on the benefits and drawbacks of each method was held. Finally, future aspects in SOC estimation for developing novel estimation methods were presented.