Battery Pack Design. Mechanical and electrical layout, Thermal modeling, Battery management. Avo Reinap, IEA/LU

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1 mvkf25vt18 Battery Pack Design Mechanical and electrical layout, Thermal modeling, Battery management Avo Reinap, IEA/LU Energy Management Battery management system Information Energy Monitoring measure what is important Control keep it optimal and constrained Diagnosis keep battery cells healthy Avo R MVKF25-vt18 Battery Pack Design 81

2 Battery usage & degradation vs control & management Battery = most costly component respect both usage and durability Durability = calendric + cyclic Loss of active material = power and capacity fade Degradation cannot be eliminated, only inhibited. Operating parameters vs state functions Avo R MVKF25-vt18 Battery Pack Design 82 Battery degradation basics Chemical origin Loss of capacity & Increased self discharge Loss of power & increased internal resistance Mechanical origin Loss of electric contact Avo R MVKF25-vt18 Battery Pack Design 83

3 Battery degradation mechanisms Loss of energy loss in active electrode materials and voltage Loss of power capability loss in active materials (side reactions) increase resistance and decrease carging/discarging current Loss of capacity reduced capability to preserve charge Avo R MVKF25-vt18 Battery Pack Design 84 Control parameters current: charge and discharge rates, especially high currents voltage: upper and lower cut-off voltages SOC: range and variations temperature: maximum and minimum, as well as temperature cycling energy throughput Avo R MVKF25-vt18 Battery Pack Design 85

4 Modeling Capacity Fade of Lithium-Ion Batteries Challenges in Identifying and Quantifying Possible Mechanisms AIChe 2009 Capacity fade Capacity fade regions i-iv loss of cyclable lithium due to the build-up of an Solid Elelctrolyte Interphase layer Loss of negative electrode active material is dominant loss of active material in the positive electrode starts to be accountable the amount of active material is less than the amount of cyclable lithium ions, Avo R MVKF25-vt18 Battery Pack Design 86 A. Kraytsberg, Y- Ein-Eli, A critical review-promises and barriers of conversion electrodes for Li-ion batteries B. Journal of Solid State Electrochemistry July 2017, Volume 21, Issue 7, pp Origins of capacity fade Loss of cyclable lithium Loss of active electrode material Loss of cyclable lithium and loss of active electrode material Avo R MVKF25-vt18 Battery Pack Design 87

5 H. Berg, Accelerated degradation vs ideal operating conditions Temperature Optimal range, can be narrowed down during life Voltage Within SOC range Current rates C-rate (energy vs power) Avo R MVKF25-vt18 Battery Pack Design 88 Building a safer, denser lithium ion battery, IEEE Spectrum Mar 2018 Degradation of cells Identification of degradation mechanisms and their rate of speed Irreversible chemical reaction Mechanical stress and distortion Changes Mechanical and electrical Bulk materials Interfaces between components Side reactions Avo R MVKF25-vt18 Battery Pack Design 89

6 Common degradation mechanisms Avo R MVKF25-vt18 Battery Pack Design 90 H. Berg 7.3 Degradation analysis methods Galvanostatic cycling Electrochemical impedance spectroscopy Incremental capacity Differential voltage Half cell Post-mortem Avo R MVKF25-vt18 Battery Pack Design 91

7 Physics coupled equivalent circuits Battery equivalent circuit models Rint model Eo, Ro First order (adds) R1, C1 Second order (adds) R2, C2 Impedance model Electrochemical impedance spectroscopy (EIS) Coupled to pfysics (?) Avo R MVKF25-vt18 Battery Pack Design 92 Testing batteries Electrochemical dynamic response Respons is related to ioncurrent/diffusion rate in the cell Slower response for weaker batteries Characterization LF dubbed diffusion MF charge transfer HF migration Batteries with faded capacity suffer from low charge transfer and slow active Liion diffusion. Avo R MVKF25-vt18 Battery Pack Design 93

8 State functions State of charge Ratio of available capacity SOC(t)=Q(t)/Qn [%] Current counting, voltage look up table, battery model State of health Remaining full battery capacity State of function or power Chargeability or power capability Avo R MVKF25-vt18 Battery Pack Design 94 Battery management system Charge and discharge control and methods Control of energy flows Thermal control and management Maintain (thermal) boundary conditions Battery monitoring State functions for usage Avo R MVKF25-vt18 Battery Pack Design 95

9 Battery Management System - BMS Best and safe use of energy Voltage U+ U and temperature + management: cell balancing or equalizer, check margins Charge/discharge Integration of current SoC Power and capacity fade SoH Avo R MVKF25-vt18 Battery Pack Design 96 Charge and discharge control maintain the voltage limits while respecting the current and temperature limits LOW Constant current charging followed by voltage and temperature control HIGH current for CV charging Combined CV+CC Avo R MVKF25-vt18 Battery Pack Design 97

10 Cell balancing Voltage equalization, which is to fill up energy and maximize capacity and life by removing unbalanced weak links Active/passive taking/wasting energy Avo R MVKF25-vt18 Battery Pack Design 98 BMS development Overall functional safety is better match to global FPGA than to local micro processor units parallelism for performance with fail-safe logic Avo R MVKF25-vt18 Battery Pack Design 99

11 Ageing model Thermal model Electrical model BMS function structure I/O, monitoring, decisions and safety relevant funtions Avo R MVKF25-vt18 Battery Pack Design BMS control sequence Intelligent batteries due to base functions of a battery management system Avo R MVKF25-vt18 Battery Pack Design 101

12 BMS basic functions Cell protection, charge control, demand management, SoC and SoH determination, cell balancing, authentication and identification, communication are some objectives for BMS Avo R MVKF25-vt18 Battery Pack Design BMS Scope and Failure Consequences Avo R MVKF25-vt18 BTMS Battery Pack Design 103

13 BMS architectures for xevs Communication, reliability and accuracy Practical attachment, number of components and connections Few architectures with different features in connections and communication Avo R MVKF25-vt18 Battery Pack Design 104 Practical implementation Added intelligence, where and how? Sharing information, history and communication Avo R MVKF25-vt18 Battery Pack Design 105

14 Multicell Battery Stack Monitor Component name LTC6802-1, Up to 12 cells, 13 ms measurement interval, up to 1000V, passive cell balancing Avo R MVKF25-vt18 Battery Pack Design BMS sensor module MM9Z Cell Lithium Battery BMS unit battery stack monitor IC can measure a number of cell voltages and provide for the discharge of individual cells to bring them into balance with the rest of the stack Avo R MVKF25-vt18 Battery Pack Design 107

15 Some future trends by Bosch Avo R MVKF25-vt18 Battery Pack Design 108 Back to Battery modelling power_battery, power_pattery_temperature State of the art model for concept development and evaluation Avo R MVKF25-vt18 Battery Pack Design 109

16 Design impact on reliability and safety Manufacturing constrains, identification of actual cells / modules, BMS Small cell variation at BOL can grow large and bring to EOL Thermal chock due to welding termination of cell-to-cell Avo R MVKF25-vt18 Battery Pack Design 110 Useful links and Aknowledgement mpoweruk.com Batteryuniversity.com liionbms.com/php/cells.php Aknowledged authors and their results shown on the previous pages (with some links and references) Avo R MVKF25-vt18 Battery Pack Design 111

17 Thermal control and management..by thermal design and active cooling J. Li, Z. Zhu, Battery Thermal Management Systems of Electric Vehicles, MSc Chalmers /17.7 kwh 1700/270 kg Avo R MVKF25-vt18 Battery Pack Design 112