Battery Aging Prediction In Electric Vehicle Application Electric Vehicle Battery Aging Prediction Methods Manoz Kumar M Tirupati, Tata Elxsi [email protected] © Tata Elxsi 2019 1 Battery Aging Prediction In Electric Vehicle Application TABLE OF CONTENTS INTRODUCTION ............................................................................................................................................. 3 DEFINITION ................................................................................................................................................... 5 BATTERY AGING PHENOMENA ..................................................................................................................... 6 ANODE ACTIVE MATERIAL ........................................................................................................................ 6 CATHODE ACTIVE MATERIAL .................................................................................................................... 6 ELECTROLYTE ............................................................................................................................................ 8 SEPARATOR ............................................................................................................................................... 8 CURRENT COLLECTOR ............................................................................................................................... 8 NEED FOR PREDICTION ................................................................................................................................. 9 BATTERY PERFORMANCE PREDICTION MODELS ........................................................................................ 11 EMPIRICAL MODEL .................................................................................................................................. 11 ELECTROCHEMICAL MODEL .................................................................................................................... 12 EQUIVALENT CIRCUIT MODEL ................................................................................................................. 13 PHYSICS-BASED MODEL .......................................................................................................................... 14 OUR APPROACH-THE EMPIRICAL METHOD ................................................................................................ 15 ASSUMPTIONS/LIMITATIONS .................................................................................................................. 16 INPUTS .................................................................................................................................................... 17 RESULTS & DISCUSSION .......................................................................................................................... 17 CONCLUSION ............................................................................................................................................... 20 FUTURE SCOPE ............................................................................................................................................ 20 ABOUT TATA ELXSI ...................................................................................................................................... 21 REFERENCES ................................................................................................................................................ 22 [email protected] © Tata Elxsi 2019 2 Battery Aging Prediction In Electric Vehicle Application INTRODUCTION Energy storage systems, usually batteries are essential for electric drive vehicles such as Hybrid Electric Vehicles (HEV), Plug-in Hybrid Electric Vehicles (PHEV) and Electric Vehicles (EV). Different types of batteries are used in electric vehicles such as lead-acid, nickel- metal hydride (NiMH), zebra and lithium-ion batteries. At present, lithium-ion batteries (LIB) are most commonly used for a broad range of electronic products and in the automotive sector for energy storage. Figure 1: Battery Electric Vehicle Architecture Lithium-ion (Li-ion) batteries are an excellent option for primary energy storage devices as it is capable of delivering a high power rate in a relatively small and lightweight package with low self-discharge rate and no memory effect. The primary functional components of a lithium-ion battery are the positive and negative electrodes and electrolyte (See Fig 2). Generally, the negative electrode of a conventional lithium-ion cell is made of carbon. The positive electrode is a metal oxide and the electrolyte is a lithium salt in an organic solvent. Lithium-ion batteries are now considered to be the standard for modern battery electric vehicles. There are many types of Lithium-ion batteries, each having different characteristics. Vehicle manufacturers are [email protected] © Tata Elxsi 2019 3 Battery Aging Prediction In Electric Vehicle Application however focused on variants that have a high energy and power density with excellent durability. Lithium-ion batteries offer many benefits compared to other mature battery technologies. For example, it has excellent specific energy (140 Wh/kg) and energy density, making it ideal for battery electric vehicles. Lithium-ion batteries are also excellent in retaining energy with a low self-discharge rate (about 5% per month) which is an order of magnitude lower than NiMH batteries. Lithium-ion batteries are now considered to be the standard for modern battery electric vehicles. The commonly available types of Lithium-ion batteries in the market are: Lithium-Cobalt Oxide Battery Figure 2: Cylindrical Cell Construction Lithium-Titanate Battery Lithium-Iron Phosphate Battery Lithium-Nickel Manganese Cobalt Oxide Battery and Lithium-Manganese Oxide Battery [email protected] © Tata Elxsi 2019 4 Battery Aging Prediction In Electric Vehicle Application DEFINITION Aging is the reliability and life span of a component or Cyclic Aging (Driving & Charging Mode) a system. Lithium-Ion Batteries also deteriorate over time. This gradual deterioration in its performance is due to irreversible physical and chemical changes that take place during its usage. These changes occur due to variations in the operating temperature, current demand and frequency and depth of charge and discharge cycles. The aging process can occur while the vehicle is running or charging (cyclic aging) or when idle (calendric aging) as explained in Fig 3. Battery aging results in a change in the operational characteristics including a reduction in the capacity, decrease in energy output, reduced performance and Cyclic aging is associated with utilization of the efficiency. This degradation is reflected in the reduced battery during operation of the electric vehicle, with the battery being subject to recurring charging and performance and range of electric vehicles. discharging cycles. The severity of cyclic aging State-of-Health (SoH) is an indicator that characterizes depends on the load on the battery, operating the system parameter related to aging. An additional temperature, depth of discharge and current rates. parameter that defines the life of a battery is End-of- Calendric Aging (Parking Mode) Life (EoL). The EoL of a battery is reached when the energy content or power delivery is not enough to support the application. The battery standards ISO 12405-1, ISO 12405-2 on “test specifications for lithium-ion traction battery packs and systems of electrically-propelled road vehicles” and IEC 62660-1 on “performance testing of secondary lithium-ion cells for the propulsion of electric road vehicles” does not specify any EoL criteria. Batteries tend to degrade when it is stored in the idle A similar standard IEC 61982 on “performance and condition, independent of charge-discharge cycling. endurance tests of secondary batteries (except lithium) This irreversible process contributing to a loss in the capacity of the battery is termed Calendric Aging. for the propulsion of electric road vehicles” defines EoL as 80% of the nominal capacity. Figure 3: Cyclic and Calendric Aging [email protected] © Tata Elxsi 2019 5 Battery Aging Prediction In Electric Vehicle Application BATTERY AGING PHENOMENA The battery aging phenomenon occurs due to various factors that influence its structural and chemical composition. The phenomena can be factored into the aging processes of the Anode, Cathode, Electrolyte, Separator and Current Collectors. It is also understood that the major contribution is from the anode and cathode. Anode Active Material The negative electrode of the Li-Ion Batteries is commonly made of Graphite. The aging effects at the graphite anode are attributed to the following - Solid Electrolyte Interphase (SEI) Layer Decomposition reactions tend to occur along the lithium intercalation when the cells are operated beyond the thermodynamic stability of organic electrolytes. These products form films on the surface of the anode active material (see Fig 4), termed SEI Layer. The SEI layer formed has low conductivity and its formation consumes cyclable lithium leading to an irreversible capacity fade. Over a period of time, the SEI layer penetrates into the pores of the electrode and the separator and reduce the active surface area. Lithium Plating Lithium plating occurs when batteries are being charged. It occurs due to the reduction of lithium ions dissolved in the electrolyte to metallic lithium at the surface of the anode