Assessment Of Potential Lithium-ion Battery Safety Issues .

DOT HS 812 418October 2017Lithium-ion Battery SafetyIssues for Electric andPlug-in Hybrid Vehicles

DisclaimersThis report is a work prepared for the United States Government by Battelle. Inno event shall either the United States Government or Battelle have anyresponsibility or liability for any consequences of any use, misuse, inability touse, or reliance on any product, information, designs, or other data containedherein, nor does either warrant or otherwise represent in any way the utility,safety, accuracy, adequacy, efficacy, or applicability of the contents hereof.This publication is distributed by the U.S. Department of Transportation, NationalHighway Traffic Safety Administration, in the interest of information exchange.The opinions, findings, and conclusions expressed in this publication are those ofthe authors and not necessarily those of the Department of Transportation or theNational Highway Traffic Safety Administration. The United States Governmentassumes no liability for its content or use thereof. If trade or manufacturers’ namesor products are mentioned, it is because they are considered essential to the objectof the publication and should not be construed as an endorsement. The UnitedStates Government does not endorse products or manufacturers.Suggested APA Format Citation:Stephens, D., Shawcross, P., Stout, G., Sullivan, E., Saunders, J., Risser, S., & Sayre, J. (2017,October). Lithium-ion battery safety issues for electric and plug-in hybrid vehicles(Report No. DOT HS 812 418). Washington, DC: National Highway Traffic SafetyAdministration.

TECHNICAL REPORT DOCUMENTATION PAGE1. Report No.2. Government Accession No.3. Recipient’s Catalog No.DOT HS 812 4184. Title and Subtitle5. Report DateLithium-ion Battery Safety Issues for Electric and Plug-in HybridVehiclesOctober 20176. Performing Organization Code000073889-07037. Authors8. Performing Organization ReportStephens, D., Shawcross, P., Stout, G., Sullivan, E., Saunders, J.,Risser, S., Sayre, J.9. Performing Organization Name and Address10. Work Unit No. (TRAIS)Battelle505 King Ave.Columbus, OH 4320111. Contract or Grant No.12. Sponsoring Agency Name and Address13. Type of Report and Period CoveredNational Highway Traffic Safety AdministrationJanuary 1,2011 to May 20131200 New Jersey Avenue SE.Washington, DC 2059014. Sponsoring Agency CodeDTNH22-08-D-00085Task Order 215. Supplementary NotesPhil Gorney and Barbara Hennessey (NHTSA CORs)16. AbstractThis report summarizes an assessment of potential lithium-ion (Li-ion) battery vehicle safety issues toprovide NHTSA information it can use to assess needs and prioritize its future research activities on Liion battery vehicles. This analysis is intended to assist NHTSA in identifying potential critical operationalsafety issues it may want to consider and in assessing if further testing is needed to evaluate safetyconcerns. This document is the comprehensive final report for the project, compiling and summarizing thekey background information and assessment of results developed. The scope of this investigation includesplug-in hybrid electric vehicles, hybrid-electric vehicles, and battery electric vehicles. This report reviewsthe literature for cell chemical and mechanical design and safety, battery architecture and design, vehiclesystems relative to battery power, battery management and control systems, safety standards, and a surveyof experimental, concept, prototype, and production-scale vehicles that employ Li-ion battery systems forpropulsion.17. Key Words18. Distribution StatementHybrid vehicle, battery electric vehicle, Lithiumion, Li-ion, battery safetyNo restrictions. This document is available to thepublic through the National Technical InformationService, www.ntis.gov.19. Security Classif. (of this report)20. Security Classif. (of this page)UnclassifiedUnclassifiedForm DOT F 1700.721. No. of Pages261Reproduction of completed page authorized.i22. PriceN/A

Authors and Contributors:Brown, VincentDodaro, CynthiaDodson, CliffordGlenn, BradleyHeywood, TimothyLinden, CoreyManning, Andrew J. (Consultant)Pape, DouglasReuther, JamesRisser, StevenRose, SusanSaunders, JamesSayre, JayShawcross, PaulSlattery, KathleenSomogye, RyanSowell, GarnellStasik, MarkStephens, DennyStout, GabeSullivan, EdwardZimmer, Robertii

Table of ContentsPageLIST OF ABBREVIATIONS . XIIIEXECUTIVE SUMMARY .XVReport Overview . xvSummary of Observations and Considerations . xviReferences . xx1INTRODUCTION. 1-11.1Project Objectives . 1-11.2Purpose, Overview, and Organization of this Document . 1-22LI-ION CELL ELECTROCHEMISTRY AND SAFETY PERFORMANCE . 2-12.1Li-ion Cell Components . 2-12.1.1 Cathode . 2-32.1.2 Anode . 2-62.1.2.1 Solid electrolyte interface (SEI) Layer . 2-62.1.3 Electrolyte . 2-72.1.3.1 Solvents . 2-82.1.3.2 Salts . 2-82.1.3.3 Electrolyte Additives . 2-92.1.3.4 Li-ion Gel/Polymer Electrolyte . 2-92.1.3.5 Ionic Liquids . 2-92.1.4 Separator . 2-92.2Li-ion Cell Electrochemical General Characteristics and PerformanceComparisons . 2-142.3Li-ion Cell Electrochemical Degradation and Failure Mechanisms . 2-162.3.1 Cell Overcharge and Overdischarge . 2-172.3.1.1 Cell Overcharge . 2-172.3.1.2 Cell Over-Discharge . 2-182.3.2 Excessive Temperatures. 2-182.3.2.1 Recharging Battery in Low Temperatures . 2-182.3.2.2 Storing the Battery at Elevated Temperatures . 2-182.3.3 Internal Short Circuit . 2-182.3.4 External Abuse . 2-202.3.4.1 External Mechanical Abuse . 2-202.3.4.2 External Short Circuit . 2-202.3.5 Aging and Internal Mechanical Stress . 2-202.3.5.1 Other Sources of Internal Mechanical Stress . 2-222.3.6 Damage Mechanics Perspective . 2-222.4Cell Electrochemical Failure Mitigation Methods . 2-232.5Electrochemistry of Cell Thermal Runaway. 2-242.6Electrolytic Solvent Combustion Properties . 2-282.7Summary . 2-312.8References . 2-31iii

3LI-ION CELL DESIGN AND SAFETY PERFORMANCE . 3-13.1Cell Design and Construction . 3-13.1.1 Cylindrical Cells . 3-13.1.2 Prismatic Cells . 3-33.1.3 Pouch Cells . 3-43.1.4 Large Format Cells . 3-53.2Design Considerations . 3-73.2.1 Thermal Design Considerations and Thermal Management . 3-73.2.2 Mechanical Design Considerations. 3-83.2.3 Charge and Discharge Management . 3-93.3Cell Safety and Failure Mitigation Measures . 3-93.4Potential Li-ion Cell Failure Hazards . 3-113.4.1 Primary Combustion and Flammability Hazards . 3-123.4.2 Secondary Toxic and Incompatible Materials Hazards . 3-153.4.3 Secondary Asphyxiation Hazards . 3-173.4.4 Secondary Ignition of Adjacent Flammable Vehicle Componentsand Surfaces . 3-183.4.5 Secondary High-Voltage Electrical Shock Hazard . 3-183.5References . 3-184LI-ION BATTERY SYSTEM ARCHITECTURE . 4-14.1Battery Modules . 4-14.1.1 Cell Arrays . 4-24.1.1.1 Series Arrays . 4-24.1.1.2 Parallel Arrays . 4-34.1.2 Charge and Discharge Management . 4-64.1.2.1 Active Current Limiting . 4-64.1.2.2 Current Limiting by Fuse or Circuit Breaker . 4-84.1.2.3 Charge and Discharge Current Monitoring . 4-94.1.3 Thermal Management . 4-104.1.3.1 Heat Exchange System . 4-104.1.3.2 Conduction Matrix. 4-104.1.3.3 Module Temperature Monitoring . 4-124.1.3.4 Passive Phase Change Materials . 4-144.1.4 Other Safety Considerations . 4-164.1.4.1 Interlock . 4-164.1.4.2 Pressure Detection . 4-174.1.4.3 Communication, Control, and Reporting . 4-174.1.5 Battery Module Conclusion . 4-194.2Battery Packs . 4-204.2.1 Pack-Module Boundary . 4-204.2.2 Module Arrays . 4-204.2.3 Pack Power Contactors and Interlock Control . 4-234.2.4 Thermal Management . 4-244.2.5 Current Limiting – Fusing . 4-264.2.6 Additional Battery Pack System Safety Features . 4-274.2.7 Communication, Control, and Reporting . 4-28iv

4.34.44.2.8 Supercapacitors . 4-30Integration With the Vehicle. 4-34References Cited and Reviewed . 4-355HEV, PHEV, AND BEV BATTERY SYSTEM ANALYSIS . 5-15.1Introduction . 5-15.2HEVs . 5-15.2.1 Micro HEVs . 5-15.2.2 Mild HEVs . 5-45.2.3 Strong HEVs . 5-55.3PHEVs. 5-65.4BEVs . 5-75.5Summary . 5-86BATTERY MANAGEMENT AND CONTROL SYSTEMS . 6-16.1Control Approach. 6-16.2Battery Management and Control System Functions . 6-26.2.1 Measurement Block . 6-36.2.2 Battery Algorithm Block (State of Charge and State of Health) . 6-36.2.3 Capability Estimation Block . 6-46.2.4 Cell Equalization Block . 6-46.2.5 Thermal Management Block. 6-46.3Charging and Discharging Control . 6-46.3.1 Phenomena . 6-56.3.2 Charging. 6-66.3.3 Discharging . 6-86.3.4 Cell Balancing. 6-86.4References . 6-97BATTERY CONDITIONS THAT ENHANCE THE INITIATION ANDGROWTH OF INTERNAL SHORTS . 7-17.1Background on Internal Shorting . 7-17.2Operating Window for Li-ion Batteries . 7-37.3Undesired Side Reactions and Loss Mechanisms . 7-57.3.1 Lithium Plating . 7-57.3.2 Electrolyte Breakdown and Resistive Film Formation . 7-67.3.3 Copper Dissolution . 7-77.3.4 Positive Electrode Dissolution . 7-77.3.5 Effect of Temperature . 7-97.3.6 Summary . 7-97.4Lithium-ion Battery Model . 7-107.5Simulation Results . 7-117.5.1 Open Circuit Potential and Loss Ranges . 7-127.5.2 . Charging Results . 7-137.5.3 Discharging Results . 7-147.6Operating Conditions and Driving Cycle Implications . 7-167.7Areas for Future Research . 7-187.8References . 7-18v

8OVERVIEW OF RELEVANT SAFETY STANDARDS . 8-18.1Electric and Hybrid Vehicle Propulsion Battery System Safety Standard –Lithium-Based Rechargeable Cells, SAE J2929 (2011) . 8-68.2Electric and Hybrid Vehicle Rechargeable Energy Storage System Safetyand Abuse Testing, SAE J2464 (2009) . 8-138.3U.N. Transport of Dangerous Goods Manual of Tests and Criteria, 5thRevision, Section 38.3 (2010). 8-208.4Safety Tests for Li-ion Batteries in UL1642 (2005) . 8-238.5Batteries for Use in Electric Vehicles, UL 2580 (2011) . 8-248.6Criteria That Must Be Met to Obtain IEEE 1725 (2011) Certification . 8-328.7References Cited and Reviewed . 8-359CODES AND STANDARDS COMPARISON AND GAP ASSESSMENT . 9-19.1High-Level Risk Assessment Context . 9-29.2Potential Gaps in Component and System Safety Standards . 9-59.3Potential Gaps in Performance-Based Design Qualification Requirements . 9-89.3.1 Potential Gaps in Consideration of Damage, Damage Growth,and Damage Tolerance . 9-89.3.2 Potential Gaps in Life Cycle Durability Test Requirements forSystem Level . 9-109.3.3 Potential Gaps in Misuse and Abuse Considerations forDurability

This report summarizes an assessment of potential lithium-ion ( Li-ion) battery vehicle safety issues to provide NHTSA information it can use to assess needs and prioritize its future research activities on Li- ion battery vehicles. This analysis is i ntended to assist NHTSA in identifying potential critical operational safety issues it may want to consider and in assessing if further testing .