Li-ion Battery Safety Technologies and Their...

© 2015 CAMX Power

CAMX Power35 Hartwell Avenue

Lexington, MA02421-3102

www.CAMXPOWER.com

Fort Lauderdale, FLMarch 24th 2016

Li-ion Battery Safety Technologies and Their Implementation

Presentation at 33rd Annual International Battery Seminar & Exhibit

C. McCoy, S. Sriramulu and Brian Barnett

[email protected]

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OUTLINE OUTLINE

Let’s watch thermal runaway

Taking a closer look at internal shorts

Short detection technology and its implementation

If a cell needs to get to a certain temperature before …

Investigation of the nail penetration test and the “hard” short

Summary

B.Barnett, D.Ofer, S.Sriramulu, R. Stringfellow (Safety Issues in Li-Ion Batteries) in: Robert A. Meyers (Ed.), Encyclopedia of Sustainability Science and Technology, Springer Science, 2012

Lithium-Ion Battery Safety Technologies and Their Implementation

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There are three broad categories of safety failures: each can lead to thermal runaway yet each exhibits very different physics.

Discussed later in this presentation


Heat Exposure

Over Charge• Homogeneous Temperature Distribution• Variable Stresses of T and t

Simple Abuse

(Not discussed further today)

Examples of TriggersSome Important CharacteristicsCategory of

Safety Failure

Each category brings different implications for safety testers, safety modelers, regulators, first responders, battery developers, product developers.


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Lithium-Ion Cell: Stimulated to a Thermal Runaway

What does a thermal runaway look like … if you were there?


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Peak temperatures are very impressive – in this case, nearly 700ºC.

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Cell with internal short


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A combination of non-invasive evaluation and post-mortem examination can help reconstruct the progression of the safety incident.


Photos of post-mortem cells are removed for reasons of confidentiality.

Photos illustrate silver-colored beads characteristic of re-condensed aluminum (which melts at 660ºC).

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The electrical energy in the cell alone is sufficient to raise the cell temperature over 700°C under adiabatic conditions.

Safety Perspective for Lithium-Ion Batteries

Adiabatic temperature rise from heat release in a 2.6 Ah, LCO 18650 cell

800°C

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460°CTypical auto-ignition temperature of battery solvents

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1. But these events aren1. But these events aren’’t still t still happening, right ??happening, right ??

2. We couldn2. We couldn’’t reproduce them !t reproduce them !

Safety Perspectives for Lithium-Ion Batteries

Sometimes we hear ……

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Recall date: MARCH 21, 2016

Recall Summary

Name of product:Lithium-ion Computer Battery Packs

Hazard:Conductive foreign material was mixed into the battery cells during manufacturing, posing a risk of fire.

Remedy:View Details

Safety Perspectives for Lithium-Ion Batteries

…… but this week, during this conference, …

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Taking a closer look at Taking a closer look at internal shorts internal shorts ……


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CAMX Power has augmented a commercial FEA program with subroutines for transient 3-d simulations of safety-related field-failures.

Heat generation associated with a short circuit:

• Distribution of T, Qdot at selected time intervals.

• Temperature histories at selected points in the cell.

• Total cell heat generation rates, surface heat loss, etc.

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Kinetic models for thermal decomposition reactions in anode and cathode

3-D transient FEA model with coupled decomposition rates & heat transfer

Outputs:

Thermal properties for all cell constituents: • density• specific heat• conductivityBoundary

conditions:• Surface heat transfer

coefficient• Ambient temperature

Model properties:

Perspectives on Factors Controlling Thermal Runaway of Li-Ion Batteries

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Li-ion cells contain energetic materials, which are stimulated to release heat in a field-failure.

90 – 126 kJ

~2.5 – 5.4 kJ

~ 16.8 – 30 kJ

~ 9.6 – 13.3 kJ

18 kJ / g solventAuto-ignition

temperature ~ 450

Complete combustion of solvent2

1500 – 1800 J / g-cathode150 - 300Decomposition

at cathode

900 J/g electrolyte250 - 400Self-reaction of salt with solvent

300 – 450 J/ g-anode

1200 – 1400 J/g-anode

80 -120

150 - 300Decomposition at anode

Energy release in an 18650 Energy release in an 18650 cellcellEnergy releaseEnergy release11Temperature Temperature

Range (Range (ººC)C)ProcessProcess

1 Approximate values estimated from DSC and ARC testing of cell components: charged anodes and cathodes, and typical electrolyte compositions;

2 Please note that there is insufficient oxygen available inside an 18650 cell to effect complete combustion of the solvent. However, if vented at high temperatures or vented in the presence of an ignition source the solvent can burn outside the cell.

Perspectives on Factors Controlling Thermal Runaway of Li-Ion Batteries

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FEA simulations show the temperature evolution and heat release profiles when an internal short results in a thermal runaway.

Temperature distribution

Distribution of heat generation from thermal decomposition reactions

Location of the internal short

Understanding Lithium-Ion Thermal Runaway 10 watt short leads to thermal runaway

B.Barnett, D.Ofer, R.Stringfellow, S.Sriramulu (Safety Issues in Li-Ion Batteries) in: Robert A. Meyers (Ed.), Encyclopedia of Sustainability Science and Technology, Springer Science, 2012

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This is what the customer reports

Understanding Lithium-Ion Battery Safety 10W short leads to thermal runaway

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This is new insight• Regardless of the input power, we appear to have several minutes before thermal runaway

is inevitable, i.e., we exceed threshold power and then exceed threshold energy• Intervention may be possible, but can be very difficult.

Understanding Lithium-Ion Battery Safety 10W short leads to thermal runaway

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At what point does an internal short become a threat to cell safety?

Threshold Conditions for Thermal Runaway

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Estimated threshold values of energy & power for Estimated threshold values of energy & power for thermal runaway of an 18650 cell from an internal shortthermal runaway of an 18650 cell from an internal short

Threshold energy

Threshold power

Safe zone: No thermal runaway

* For a 2.6 Ah 18650 cell with an external heat transfer coefficient of 10 W/m2-K. The threshold values depend on the external heat transfer coefficient, cell design & chemistry.

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Implementation of short Implementation of short detection technologydetection technology


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Thermal runaway in a Li-ion cell induced using unique particle implantation methodologies developed by CAMX Power.

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a) This cell ran away after a particle was implanted. Aluminum beads indicate cell temperatures exceeding 660oC.

b) Runaway in this cell resulted in aluminum melting

(beads can be seen on the end of the jellyroll) and partial ejection of the jellyroll core.

Li-Ion Battery Safety: Challenges and Progress

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We successfully demonstrated that we can induce thermal runaway during normal operation of an 18650 cell (≥ 2.6 Ah).

Runaway in this cell resulted in aluminum melting (beads can be seen on the end of the jellyroll) and partial ejection of the jellyroll core.

This cell ran away after a particle was implanted. Aluminum beads indicate cell temperatures exceeding 660oC.

Deliberate Metal Particle Implantation in 18650 Cells Key results

We have succeeded in creating an internal short AND a thermal runaway after many charge-discharge cycles in an 18650 cell.

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• Short resistance is initially >1000 ohms, giving rise to only a few milliamps of current – a level extraordinarily difficult to discern from the currents of normal charge and discharge in cells, which are three orders of magnitude larger.

Characterization of an internal short produced in a lithium-ion cell in CAMX Power labs by implantation of a metal particle

Internal Short Maturation

An internal short may develop over multiple cycles and/or over a long period of time, remaining virtually invisible to battery management for most of its life.

Analytically we determined a threshold power of ~ 4 W (a short resistance of ~4Ω)dissipated in an internal short or for thermal runaway of an 18650 cell

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The CAMX Power internal short circuit detection technology provides sensitive monitoring for internal shorts and can detect and quantify shorts (even minor shorts) in the 1000 ohm range.

Internal Short Circuit Detection Technology 1 Test Results

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The prototype on the right is part of a paid technology demonstration now underway at a major automotive manufacturer.

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Automotive drive cycles pose one of the most challenging detection environments.

Standard BMS monitoring does not reveal the presence of a short

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Signals Warning of Potential Thermal Runaway Key results Automotive Drive Cycles

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Metal particle (aka FOD)

seeds dendrites

• Non-Homogeneous Temp. Distribution• Variable Stresses include short resistance, heat transfer, cell design• “Long” but variable incubation period

Grown-In Internal Short

Heat Exposure

Over Charge• Homogeneous Temperature Distribution• Variable Stresses of T and tSimple Abuse


Safety Failure



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Implementation of short Implementation of short detection technologydetection technology


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The CAMX Power Short Detection Technology is being adapted for a wide range of applications for enhanced safety and reduced costs.

CAMX Power Internal Short Detection Technology

• Pack – field monitoring of cells

PHEV battery trials

Cap-lamps worn by miners

Navy batteries

• Pack Assembly – cell screening

Underwater submersibles

• Failure Audits - screening of cells/packs post-use

Dreamliner battery investigation

• Cell Factory – reduced aging time during formation

Defense Logistics Agency

CAMX Power Internal Short

Detection Technology

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One of the technologies is being adopted for detecting internal short circuits in cap lamps worn by miners (courtesy NIOSH*).

• Li-on based batteries (e.g., in cap lamps) are extensively employed in mining today.

• Internal short circuits in these batteries can pose a significant danger.

• Early warning of growing internal short circuits can enable intervention and prevent catastrophic/cascading failures.

NLT Eclipse

Initial prototype board with CAMX Power electronics to demonstrate internal short detection

Example: Short Detection for Mining Application

*Disclaimer: The findings and conclusions in this presentation have not been formerly disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy. Mention of any commercial product does not imply endorsement.

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Our technology can provide real-time detection of internal short circuits in cells used in the miner’s cap lamps.


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“The findings and conclusions in this presentation have not been formerly disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy. Mention of any commercial product does not imply endorsement.”

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Our technology can provide real-time detection of internal short circuits in cells used in the miner’s cap lamps.


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“The findings and conclusions in this presentation have not been formerly disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy. Mention of any commercial product does not imply endorsement.”

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Energy injection, timing to runawayEnergy injection, timing to runaway

If a cell needs to get to a certain If a cell needs to get to a certain temperature before temperature before ……


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Heating the cell to 100°C or 150°C takes a significantly long time under typical abuse conditions.

Thermal power input needed to raise typical 18650 cell to given temperature

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Instantaneous thermal power input to an 18650 when a cold cell is placed in a hot-box at 150 °C

Facing the Myths of Lithium-Ion Battery Safety

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Heating the cell to 130°C takes a significantly long time under typical abuse conditions.

Thermal power input needed to raise typical 18650 cell to 130°C

Instantaneous thermal power input to a 2.6 Ah 18650 cell when the cold cell is placed in a hot-box at 130 °C

Instantaneous thermal power input to a 10.4 Ah 36650 cell when the cold cell is placed in a hot-box at 130 °C

Facing the Myths of Lithium-Ion Battery Safety

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Investigation of the Nail Investigation of the Nail Penetration Test and the Penetration Test and the

““Hard ShortHard Short””


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t = 126 ms after nail penetrated the can wall



Factors That Influence Thermal Runaway During a Nail Penetration Test

During the nail penetration test, it is not uncommon to observe explosions within 200 ms of nail penetration.

Fast nail, 8 cm/s

Our experimental setup allows us to characterize the nail penetration process in detail.

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Analysis of the nail penetration data shows that the outcome in the nail penetration is governed by phenomena in the vicinity of the nail.




During the nail penetration test, venting and explosions occur typically < 500 ms

However, the cell surface temperature barely increases in this short time period.

18650 cell

Nail

Location of thermocouple of temperature measurement

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Li-ion Battery Safety Insights from Nail Penetration Tests

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We undertook a detailed study of the hard-short situation in a nail penetration test using a combination of experiments and analysis.

Nail Penetration Testing







High-speed photography of nail penetration

200 ms

Simulation of Nail Penetration

Low temperature far from the nail

Temperatures exceeding 1000oC in the vicinity of the nail

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Assuring Safety in Li-Ion Batteries: The hard short

This cell shows violent thermal runaway in nail penetration tests.

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These cells with only modest modification but exactly the same anode and cathode show more benign response.

Assuring Safety in Li-Ion Batteries: The hard short

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SUMMARYSUMMARY


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Impact Crash Crush

• Non-Homogeneous Temp. Distribution• Variable Stresses include speed, angle, penetration, momentum

Impact/Mechanical Intrusion


seeds dendrites

• Non-Homogeneous Temp. Distribution• Variable Stresses include short resistance, heat transfer, cell design• “Long” but variable incubation period


Heat Exposure

Over Charge• Homogeneous Temperature Distribution• Variable Stresses of T and tSimple Abuse


Safety Failure



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There are three broad categories of safety failures and we need somewhat different testing, modeling and design approaches for each category.

ImpactCrashCrush

• It would be desirable that ANY cell of a given cell design exhibit the “same” safety result in response to the same trigger.• In practice, stochastic results are often observed.

Impact/Mechanical Intrusion


seeds dendrites

• Very rare; less than one cell in 1-10 million• Dependent on specific conditions of cell fabrication and subsequent field exposure


Heat Exposure

Over Charge

• ANY Li-ion cell of a given cell design and using the same materials WILL exhibit the same safety “result” in response to the same trigger.

Simple Abuse


Safety Failure


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A “grown-in” internal short-circuit begins from infinite/high resistance and matures to lower resistances, heating the cell, until the cell is “dead” or a thermal event occurs …

Depiction of the expected “steady state” power dissipation through an internal short circuit as a function of the short resistance and cell power capability

Development of an Internal Short

… but the nail penetration short (s) initiates with extremely low short resistance, with little cell heating possible before an explosion occurs.

Resistance of the Short (m)

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