OPTIMIZATION OF HEAT PROCESSES IN ENERGY SOURCES OF ELECTRIC VEHICLES

ABSTRACT

To address the global climate crisis and achieve net-zero emissions by 2050, the European Union has mandated a significant reduction in greenhouse gas emissions from road transport. As an intermediary step, average emissions of new cars and vans must decrease by 55% and 50% respectively by 2030. The President of Uzbekistan became familiar with an idea on the development of the electric vehicle industry. Based on the instructions and standards of European Union, the proposals were prepared for organizing the production of electric vehicles and increasing the number of charging stations in Uzbekistan. This article explains the need of optimization of heat process in energy sources of electric vehicles in Uzbekistan.

АННОТАЦИЯ

Для решения глобального климатического кризиса и достижения нулевых выбросов к 2050 году Европейский союз утвердил существенное снижение выбросов парниковых газов от дорожного транспорта. Как промежуточный этап, средние выбросы новых автомобилей и фургонов должны сократиться соответственно на 55% и 50% к 2030 году. Президент Узбекистана ознакомился с идеей развития отрасли электрических транспортных средств. На основе инструкций и стандартов Европейского союза были подготовлены предложения по организации производства электромобилей и увеличению числа зарядных станций в Узбекистане. В данной статье рассматривается необходимость оптимизации тепло процессов в энергетических источниках электрических транспортных средств в Узбекистане.

Keywords: Electric vehicles, heat process, energy sources, battery, Li-Ion.

Ключевые слова: Электрические транспортные средства, тепло процесс, энергетические источники, аккумулятор, Li-Ion.

Introduction

To address the global climate crisis and achieve net-zero emissions by 2050, the European Union has mandated a significant reduction in greenhouse gas emissions from road transport. As an intermediary step, average emissions of new cars and vans must decrease by 55% and 50% respectively by 2030. This necessitates a rapid shift towards electric vehicles (EVs) within the automotive industry.

The President of Uzbekistan became familiar with an idea on the development of the electric vehicle industry. Based on the instructions and standards of European Union, the proposals were prepared for organizing the production of electric vehicles and increasing the number of charging stations in Uzbekistan. The President noted the need for popularizing the use of electric vehicles and stimulating their purchase among the population. Taking this into account, it is envisaged that the state will compensate a certain part of the interest on the loan issued for the purchase of locally produced electric vehicles. In 2023-2025, support will also be provided for the purchase of electric vehicles by government agencies and also president mentioned to develop electric vehicles engineering in educational institutes step by step It is evident that electric vehicles have gained significant traction in recent years as a more sustainable alternative to conventional fossil-fueled automobiles. The global energy resources and environmental crisis promotes and motivate the improvement of electric vehicles. However, the efficient operation and longevity of electric vehicle batteries heavily rely on the proper management of their thermal characteristics. The cooling system of EVs’ batteries play an important role in maintaining optimal operating temperatures in order to directly impact the driving performance, efficiency, and lifespan of the batteries. This PhD research proposal aims to investigate and enhance the thermal management system of EVs’ batteries in challenging weather conditions in Uzbekistan. Thermal management refers to the controlling of heat flows in vehicles. Thermal management is of particular importance when it comes to electric vehicles. This is because, in order to be able to operate an electric vehicle with high efficiency, it is essential to maintain the temperature of the electric motor, power electronics and the battery within an optimum temperature range. Just like with vehicles that are powered by an internal combustion engine, the heating and cooling of the interior also plays an important role. To be able to meet these extensive requirements, you need a powerful thermal management system. It is very important to improve the accuracy of the electric vehicle battery thermal management, because it ensures battery safety, extends battery life, reduces energy consumption, and increases driving range. This research focuses on improving the accuracy of electric vehicle battery estimation and control of the control system for electric vehicles. As the demand for electric vehicles (EVs) continues to improve, the efficient usage of energy sources becomes paramount for enhancing overall performance and extending the range of these vehicles. A critical aspect in this regard is the optimization of heat processes within the energy sources of electric vehicles. The effective management and dissipation of heat generated during charging, discharging, and operational phases are essential to improve energy conversion efficiency, battery life, and overall thermal performance. Addressing the challenges associated with heat processes in EVs is crucial for advancing the technology and ensuring sustainable and reliable transportation solutions. Therefore, this research aims to explore and implement innovative strategies for optimizing heat processes in the energy sources of electric vehicles, with the ultimate goal of enhancing energy efficiency, extending battery life, and contributing to the widespread adoption of electric mobility.

Main Part of the research purpose
In this article, we have already set actual objectives and purposes;

a) Investigate the current situation of EVs battery cooling technologies and systematic methods.

b) Identify the challenges and limitations of existing thermal management systems (cooling and heating).

c) Improve innovative approaches to improve efficiency, reliability, and safety.

d) Propose a prototype implementation for enhanced EVs battery thermal management according to challenging weather conditions in Uzbekistan.

e) Evaluate the proposed prototype against industry-standard benchmarks and scheduling an experiment.

The primary research method for this study is to conduct an extensive review of existing literature patents, research papers (articles, thesis, dissertations), and international and regional industry reports focused on EV battery thermal systems. Analyze the strengths, weaknesses, and recent advancements and issues in thermal management technologies for electric vehicle batteries.

In the second stage of this study is literature review, experimental analysis, simulations, and propose innovative solutions to address the identified challenges in EV battery thermal management. Explore novel materials, advanced control algorithms, solid-state cooling methods. Study of existing heat management systems for electric vehicles and determine their features.

In the third stage of the study is to perform laboratory experiments to evaluate the thermal characteristics of EV battery systems under various operating conditions. Measure temperature profiles, heat dissipation rates, and the overall efficiency of cooling mechanisms especially at the state of charging. Consider factors such as battery chemistry, size, and architecture. Validation of the proposed thermal management system and power condition assessment technique through experimental testing and analysis.

Finally, the process will be evaluated by techno-economic, life cycle methodology, and energetic assessment [2].

Generally, this stay will have a considerable impact on my research and professional career by achieving the following results:

• Development of an optimized thermal management system that ensures accurate control of the battery temperature during charging.

• Improve battery safety and life through more accurate temperature control.

• Reducing energy consumption by optimizing the charging process.

• Increases the operational period of electric vehicles, i.e. increases the distance of movement.

• Improving electric vehicle technology and providing a sustainable vehicle.

• Based on those cases, techno-economic, energy, and efficiency will be evaluated, and conduct a comparative study.

• As a deliverable of the research stay, all works being done in Slovakia will be reflected by research papers in collaboration with my supervisor at the host institution.

Thermal Characteristics of Li-Ion Battery

The thermal characteristics of the Li-ion battery affect its performance and thus the autonomy of EVs. Increasing energy density causes high heat generation in Li-ion batteries under extreme operating conditions. The heat generation of Li-ion batteries is directly related to their thermal behavior. The heat generation in Li-ion batteries and the thermal issues of Li-ion batteries are elaborated. The total heat generation of a Li-ion battery is dominated by two components: namely, reversible heat and irreversible heat. The change in entropy results in reversible heat generation whereas polarization results in irreversible heat. The heat generation could be estimated using Bernardi’s equation as presented [3];

Picture 1: Bernardi’s equation

Thermal Issues in Li-Ion Battery

A higher amount of heat is generated in the battery during fast charging and discharging operations; the heat generation at the positive tab is particularly high. The higher temperature owing to the higher heat generation affects the specific power, efficiency, and life cycle of the battery. In addition, the higher battery temperature can cause a reaction within the cathode and electrolyte, decomposition of the electrolyte and anode, and film formation at the interface of the electrolyte One of the major consequences of high battery temperature is capacity/power loss. The capacity or power loss of the battery causes a self-discharge, short life cycle, and autonomy losses. It is very complex to evaluate the capacity or power loss in batteries because of the various electrode materials and chemistries associated with them. In effective thermal management in the case of battery discharge operation at high temperatures is not able to dissipate the heat from the battery which results in the overheating of the battery. The carbon-based anode dissolution, cathode material with the formation of solid electrolyte formation, and crystal structure volatility pump up the internal resistance and thus it causes the capacity to fade, power reduction, and at last the energy loss of battery. The high temperature of the battery creates the issue of an electrical imbalance which is defined as a cell-capacity difference in the battery pack because the battery capacity depends on the battery’s temperature. Under an electrical imbalance state, the energy produced by the battery pack reduces [5]. The cell charging under an electrical imbalance condition causes the overcharging of a weak cell and thus issues of power loss and temperature rise are observed in the battery pack. The increase in battery temperature under extreme conditions can cause thermal runaway propagation within battery cells. The main source of thermal runaway is a larger amount of heat generation with gases as a result of exothermic reactions which starts the chain of chemical reactions during improper charging/discharging modes. The battery temperature can reach up to 500 C^o when additional heat is released during thermal runaway as a result of the thermal shrink. When the temperature approaches 90 C^o, the metastable part within solid electrolytes decomposes exothermally. The graphite electrode, approaching 200 C^o, can exothermally react with solvent at 100 C^o under the condition that it is partially exposed to a solid electrolyte interface. However, this reaction could be slowed down due to the presence of LiPF6 salt. The interface of solid electrolyte decomposes on the graphite electrode during the exothermal reaction when the battery’s temperature approaches 85 C^o. With a further increase in the battery’s temperature to up to 110 C^o, the decomposition of the secondary layer occurs which causes electrolyte evaporation and the temperature reaches 140 C^o. At this temperature, the separator can melt which creates a short circuit in the battery pack. Furthermore, the state of charge of the battery varies with the temperature of the thermal runaway.

The thermal issues, which occurred as consequences of the failure to maintain the operating temperature of the battery within the desired permissible limit, have been discussed. The temperature of the Li-ion battery should be maintained within the stated permissible limit to achieve the desired performance and avoid a thermal runaway. The thermal management of the battery could be addressed by implementing a suitable cooling strategy with excellent heat dissipation characteristics.

Battery Thermal Management with Conventional Cooling Strategies

A battery thermal management system enables control of the temperature characteristics of a battery in normal and extreme operating conditions and thus assures its safety and performance [6]. An efficient battery thermal management system can prevent electrolyte freezing, lithium plating, and thermal runaways, helping to provide favorable operating conditions for Li-ion batteries [7]. The commercially employed battery thermal management system includes air cooling and indirect liquid cooling as conventional cooling strategies.

The battery thermal management system with air cooling is widely used in EVs owing to its advantages such as low cost, simple structure, easy installation, and maintenance, as well as the lower weight of the overall system and lack of leakage when compared with other cooling techniques [8]. However, the air has poor thermophysical properties, so the air-cooled battery thermal management system is only suitable for applications with low heat dissipation requirements. When operating in extreme conditions, it cannot control the temperature rise and maintain a uniform temperature of the battery pack [9].

As an alternative to air cooling, indirect liquid cooling has gained popularity as a widely adopted commercial battery thermal management technique owing to the superior thermophysical properties of liquid compared to air [10]. Indirect liquid cooling enables better control over temperature rise and assures great improvement in temperature uniformity for the battery when compared to air cooling [11].

Conclusion

In conclusion, after revising above mentioned articles and thesis, dissertations we can sum up that thermal management system in heat process of batteries is important to handle efficiency of its performance and improve life span of usage of battery.

References:

1. Kunal Sandip Garud, Le Duc Tai, Seong-Guk Hwang, Nghia-Huu Nguyen and Moo-Yeon Lee “A Review of Advanced Cooling Strategies for Battery Thermal Management Systems in Electric Vehicles” Department of Mechanical Engineering, Dong-A University, Korea 2022.
2. Eddahech, A. Modélisation du Vieillissement et Détermination de L’état de Santé de “Batteries Lithium-Ion Pour Application Véhicule Électrique et Hybride”. Ph.D. Thesis, University of Bordeaux, Bordeaux, France, 2013.
3. Bernardi, D.; Pawlikowski, E.; Newman, J. “A general energy balance for battery systems”. J. Electrochem. Soc. 1985.
4. Heubner, C.; Schneider, M.; Lämmel, C.; Michaelis, A. “Local heat generation in a single stack lithium ion battery cell”. Electrochim Acta 2015.
5. Zhang, Z.; Fouchard, D.; Rea, J.R. “Differential scanning calorimetry material studies: Implications for the safety of lithium-ion cells”. J. Power Sources 1998.
6. Singirikonda, S.; Obulesu, Y.P. “Adaptive secondary loop liquid cooling with refrigerant cabin active thermal management system for electric vehicle”. J. Energy Storage 2022.
7. Cheng, L.; Garg, A.; Jishnu, A.K.; Gao, L. “Surrogate based multi-objective design optimization of lithium-ion battery air-cooled system in electric vehicles”. J. Energy Storage 2020.
8. Chen, K.; Chen, Y.; She, Y.; Song, M.; Wang, S.; Chen, L. “Construction of effective symmetrical air-cooled system for battery thermal management”. Appl. Therm. Eng. 2020.
9. Hou, J.; Wu, X.; Chen, K.; Dong, Y. “A direct optimization strategy based on field synergy equation for efficient design of battery thermal management system”. Int. J. Heat Mass Transf. 2022
10. Deng, Y.; Feng, C.; Jiaqiang, E.; Zhu, H.; Chen, J.; Wen, M.; Yin, H. “Effects of different coolants and cooling strategies on the cooling performance of the power lithium ion battery system: A review”. Appl. Therm. Eng. 2018.
11. Roe, C.; Feng, X.; White, G.; Li, R.; Wang, H.; Rui, X.; Li, C.; Zhang, F.; Null, V.; Parkes, M.; “Immersion cooling for lithium-ion batteries—A review. J. Power Sources 2022.