Failure Modes & Effects Criticality Analysis of Lithium-Ion Battery Electric and Plug-in Hybrid Vehicles Project Overview

Transcription

1 Failure Modes & Effects Criticality Analysis of Lithium-Ion Battery Electric and Plug-in Hybrid Vehicles Project Overview Denny Stephens, Battelle Phillip Gorney, Barbara Hennessey, NHTSA January 26, 2012 SAE 2012 Government/Industry Meeting 1

2 Project Objective and Scope Objective Develop an FMECA for Li-ion battery vehicle high voltage systems - Provide NHTSA information it can use to assess needs and prioritize its future research activities. - Help NHTSA identify potential critical operational safety issues it may want to consider - Help NHTSA identify if further testing is needed to assess safety concerns Use FMECA as a tool to understand and compare potential failure modes, hazards, mitigation strategies and risk Scope Plug-in hybrid-electric vehicles (PHEVs), hybrid-electric vehicles (HEVs), and battery electric vehicles (BEVs) Take into account propulsion system hazards and controls at the cell, module, pack, system and vehicle level 2

3 Program Team Introductions NHTSA Team Phillip Gorney, COTR Barbara Hennessey, COTR Battelle Multidisciplinary Project Team Program Manager and Vehicle Systems Safety Lead: Denny Stephens Battery Chemistry and Cells: Jay Sayre, Corey Linden Battery System and Charging Design: Ed Sullivan, Gabe Stout Control Systems: Jim Saunders, Brad Glenn Combustion Hazards: James Reuther, Paul Shawcross FMECA: Tim Heywood, Cynthia Dodaro, Jon Luedeke Field Experience: Cliff Dodson Basic Research and Support: Garnell Sowell, Katie Slattery Report Integration and Editing: Doug Pape, Vince Brown 3

4 Technical Approach - Flow Chart Task 2. Conduct Technology and Vehicle Inventory Review Task 3. Develop Li-ion Vehicle Concept Model for FMECA Task 4. Develop a Hazards Matrix Task 5. Conduct the FMECA Relevant Standards Task 6. Compare FMECA to Codes and Standards and Identify Gaps Task 7. Compile Final Project Report and Conduct Peer Review 4

5 Presentation Outline Background Electrochemical charging and discharging mechanisms Battery chemistries and performance Failure mechanisms Safety features Hazards FMECA Approach Observations 5

6 Illustration of Li-ion cell discharge Source: U.S. DOE (2007, pg. 11). [Reprint permission pending with copyright owner.] Li-ions shuttle between anode and cathode in an electrochemical intercalation process Solid electrolyte interface (SEI) layer protects Li-ions in anode graphite from reacting aggressively with solvent from electrolyte SEI is semi-permanent layer formed on the anode and cathode during the first cycle Damage to SEI layer can be a precursor to internal short circuit and thermal runaway Potential causes of damage include external short, mechanical damage, excessive heat, aging through longterm charge/discharge cycling 6

7 Comparisons of Li-ion battery chemistry performance parameters Tesla Roadster Sport Tesla S-model Lithium-nickelcobalt-aluminum (NCA) Specific energy Cost Specific power Lithium-nickelmanganese-cobalt (NMC) Specific energy Cost Specific power Cost Lithium-manganesespinel (LMO) Specific energy Specific power Chevy Volt Ford Focus Mitsubishi imiev Nissan Leaf Volvo C30 Life span Safety Life span Safety Life span Safety Performance Lithium titanate (LTO) Specific energy Performance Lithium-iron phosphate (LFP) Specific energy Performance Cost Specific power Cost Specific power Coda Life span Safety Life span Safety Performance Performance Source: Batteries for Electric Cars: Challenges, Opportunities, and the Outlook to , The Boston Consulting Group, Inc. Reproduced with permission. 7

8 Potential Li-Ion Cell Failure Mechanisms Internal short circuit and overheating could result from internal damage such as Dendrite growth Separator failure Lithium plating Nano-particles detaching from electrodes others Externally Causes (mechanical, electrical, thermal abuse) Mechanical Damage External Short Circuit Cell Overcharge Cell Over-discharge Low Temperature Recharging High Temperature Storage Improper Design Manufacturing contamination Sequential combinations of all of the above 8

9 Illustration of Chemical Breakdown of Li-Ion Cell Components in Example Thermal Runaway Event Electrolyte Decomposition o C Reactions produce heat Lithium/Binder Reactions o C Reactions produce heat and H 2 gas Lithium Reactions 300 o C + Reactions produce heat, metallic lithium 300 o C o C Lithium/Electrolyte Solvent Reactions 110 o 290 o C 2 nd SEI layer forms and breaks down ( o C) Lithium reaches melting point (180 o C) Cathode Decomposition 178 o o C Reactions produce heat, O 2 gas 240 o C 210 o C 180 o C SEI Layer Decomposition 60 o 130 o C Reactions produce heat, flammable gases, and O 2 Reactions produce heat, flammable gases, lithium oxides Thermal shutdown separator pore closure o C 150 o C 120 o C 90 o C 60 o C 9

10 18650 Li-ion cell cutaway illustrating safety features Source: Jeevarajan (2010, pg. 7). [Reprint permission pending with copyright owner.] Cell is made of a rolled anode, separator, cathode, and filled with electrolyte The protective components are located at the positive terminal Each component performs a specific protective or packaging function Cylindrical cells depend on heat conduction away from the case to keep the cell at an appropriate temperature 10

11 Potential Hazards and Hazard Matrix (adopted from EUCAR) Potential Hazards Thermal runaway Cell/battery rupture Flammability hazards Secondary effects Asphyxiation hazards Toxicity 11

12 Technical Approach - Flow Chart Task 2. Conduct Technology and Vehicle Inventory Review Task 3. Develop Li-ion Vehicle Concept Model for FMECA Task 4. Develop a Hazards Matrix Task 5. Conduct the FMECA Relevant Standards Task 6. Compare FMECA to Codes and Standards and Identify Gaps Task 7. Compile Final Project Report and Conduct Peer Review 12

13 Generic System Design for FMECA Charger - + Cell Balancing Control Cell 11 Cell12 Cell 13 Cell Voltage Monitoring Cell Balancing Control Cell 21 Cell22 Cell 23 Cell Voltage Monitoring Cell Balancing Control Cell 31 Cell32 Cell 33 Cell Voltage Monitoring Array System Levels Electrochemistry Cell Array Module Pack Powertrain Load Electric or Hydraulic Steering Electric Grid Vacuum Assist Pump 110, 220, or 440 Vac Wall Power Wall Charger/ Other - Steering + Very Large Traction Motor Full Electric Operation Gas Petal Brakes Hydraulic Pump Brake Petal Cool. Motor Heating/ Cooling Transition Wheels Hyd. Motor Traction Motor AC AC to DC/ DC to AC DC Pack Control Electroncis Start Stop Control Battery Module(s) Lithium Ion Battery Module > 200V Starter Rotating Equipment Alternator Lead Acid Starter-Lighting- Ignition Battery Higher Specific Power Radiator Engine Fan Internal Combustion Engine Comp. Motor Battery Pack Fan Heating/ Cooling Air Conditioning Environmental Controls 12V Lighter/ Accessories Lighting Entertainment /Navigation Automotive Control CAN Bus and Interlock Powertrain Ignition Module 13

14 Cooling Inlet Manifold/Conductor Cooling Outlet Manifold/Conductor CAN Bus Failure Modes and Effects Criticality Analysis Approach A safety assessment tool to understand and compare potential failure modes, hazards, mitigation strategies and risk Comparison to standards Are there failure modes that haven t been identified? Are there gaps in coverage by test procedures? Are there gaps in coverage by standards? Temperature Data T Inlet Temperature Sensor Inputs Interlock In Module 1 Temperature Heat Exchange Media Module 2 Temp. Module 3 Temp. P Pressure Sensor A Accelerometer X-Y-Z S Smoke Detector - CAN Bus Signal Cond. Interlock In CAN Bus Interlock In Coolant In Module Return CAN Bus Interlock In Coolant In Module Return CAN Bus Interlock In Coolant In Module Return Pack Control Electroncis Battery Module 1 Control Electronics Battery Array Battery Module 2 Control Electronics Battery Array Battery Module 3 Control Electronics - State Monitoring Heat Exchange Media Conduction Matrix Heat Exchange Media Conduction Matrix Heat Exchange Media Conduction Matrix Battery Array Wall Charger/ Other - + AC to DC/ DC to AC Generator/ Motor + Electric or Hydraulic Steering Safe On Interlock Out Interlock Out Coolant Out 110, 220, Electric Module Power or Out 440 Vac Grid Wall Power Interlock Out Coolant Out Module Power Out Interlock Out Coolant Out Module Power Out Vacuum Assist Pump Safe On/Fail Trip Off Recharging Diodes Wall Charger/ Other - + Steering Very Large Traction Motor Full Electric Operation Gas Petal Brakes Hydraulic Pump Brake Petal Transition Wheels Hyd. Motor Traction Motor AC AC to DC/ DC to AC DC Pack Control Electroncis Start Stop Control Battery Module(s) Cool. Heat Exchange Media Motor Lithium Ion Battery Module > 200V + Parallel Blocking Heating/ Diodes Cooling Current Sensor Starter Rotating Equipment T Higher Outlet Temperature Specific Power Fuse Alternator Lead Acid Starter-Lighting- Ignition Battery Interlock Out Radiator Engine Fan Internal Combustion Engine Comp. Motor Battery Pack Heating/ Cooling Air Conditioning Environmental Controls 12V Lighter/ Accessories Lighting Entertainment /Navigation Automotive Control CAN Bus and Interlock Fan Ignition 14

15 Observations: Electrochemical damage may lead to delayed failure Damage initiation and growth Damaged defined here as electrochemical reactions outside the range of normal charge/discharge duty cycles - Outside the (green) boundary of safe operations - Examples: SEI layer breakdown, dendrite growth May be initiated by different abuse events May incubate to the point of initiation from aging - Aging can be electrochemical breakdown of components from hundreds of charge/discharge cycles in long-term service Once initiated, damage may grow in normal service cycles - May grow during excursions outside boundary - In some cases, may grow due to normal charge/discharge operational cycles Damage growth over time may cause failure, such as short circuits 15

16 Observations: Standards may need Life Cycle Durability and Damage Tolerance Testing SAE J2464 and J2929 tend to focus on the individual units subjected to a single abuse test. They do not appear to address cumulative abuse or the long-term effects of an abusive event. In contrast, SAE J2579 testing for hydrogen vehicle fuel systems, specifies tests covering a series of abuse conditions in sequence with normal charge/discharge cycles which is more representative of actual service. Example life cycle durability tests for Hydrogen fuel systems 16

17 Closing Summary of Observations Li-Ion batteries are valuable because of their ability to charge, discharge and store substantial energy Substantial energy storage also implies substantial energy release in the case of failure Li-ion electrochemistry is not self-limiting in failure process and requires various controls for management and safety - Li-ion failure processes incubate, initiate and grow at the cell electrochemistry level - Failure is a time dependent process, resulting in delayed failure some time after the damage is caused Key parameters relevant to detecting and controlling damage growth are not currently measured, but are inferred through models, simplistic or sophisticated Li-Ion battery technology is in the development stage and is not yet settled Substantial research and development is in progress to achieve greater Li-ion battery performance at lighter weight and lower cost - R&D is exploring more energetic chemistries and is expanding the operating range of batteries through electrochemical modeling - Increasing the bounds of performance implies operating the battery cells closer to limits where damage initiation and growth, leading to failure, can occur Li-ion battery safety can be managed, but requires insight, knowledge and modeling at the electrochemistry level 17

18 Failure Modes & Effects Criticality Analysis of Lithium-Ion Battery Electric and Plug-in Hybrid Vehicles Project Overview Denny Stephens, Battelle Phillip Gorney, Barbara Hennessey, NHTSA January 26, 2012 SAE 2012 Government/Industry Meeting 18