STAFF REPORT - AC Transit · and battery-electrics use lithium batteries, including the Toyota Prius, Chevy Volt, Nissan Leaf, and Tesla. Pike Research's paper on lithium technology

T~NS/T Report No:

Meeting Date:

Alameda-Contra Costa Transit District

STAFF REPORT TO: Operations Committee

AC Transit Board of Directors

FROM: David J. Armijo, General Manager

SUBJECT: lithium Battery Usage and Safety

BRIEFING ITEM

RECOMMENDED ACTION(S):

Consider receiving a report on the use and safety of lithium batteries.

EXECUTIVE SUMMARY:

13-086 AprillO, 2013

On January 7, a lithium battery overheated and started a fire in an empty Boeing 787 at Boston's Logan International Airport. On January 9, United Airlines reported a wiring problem in the same area as the Boeing 787 battery fire. Subsequently, the U.S. National Transportation Safety Board {NTSB) began a safety investigation, and on January 16 the FAA grounded all 787 planes. While NTSB has not issued an official public report, preliminary findings indicate that the lithium-ion batteries in the first incident likely short-circuited resulting in a "thermal runaway" and fire which completely destroyed the battery. It is estimated, however, that more than one million lithium batteries are now used in the automotive sector, and forecasts for lithium batteries in light-duty transportation show growth from $1.6 billion in 2012 to nearly $22 billion in 2020.

AC Transit's fuel cell bus fleet utilizes lithium-ion batteries designed and manufactured by EnerDel Inc., a U.S. battery manufacturer, which has more than 1,500 lithium batteries installed in vehicles worldwide with more than five million miles of service. EnerDel's batteries on AC Transit's fleet have more than 300,000 miles of service since September 2010. In July 2011, a connecting cable on one battery overheated causing heat damage, but not a fire, in two of the seven modules that make up the battery pack. The EnerDel battery management system worked as designed to minimize thermal damage.

BUDGETARY/FISCAL IMPACT:

There is no budgetary impact associated with this report.

BACKGROUND/RATIONALE:

Lithium batteries are used in a variety of applications including consumer electronics and transportation, where they are primarily used for energy storage on hybrid, plug-in hybrid, and battery-electric vehicles. Two Boeing 787' s had reported lithium battery incidents in January 2013 and an AC Transit fuel cell bus experienced an incident in July 2011.

Report No. 13-086 Page 2 of 3

AC Transit Batterv Incident: AC Transit's fuel cell bus number 6 experienced an overheated battery in July 2011 while in passenger service near the Oakland Airport. The problem stemmed from a cable connection between two of the seven modules that make up a single battery pack. The driver was alerted to the problem by the visual and audible alarms. The battery went into a shut-down mode requiring the driver to pull to the side of the road. The safety mechanisms controlled by the battery management system operated properly and safely vented heated gases and activated the battery's fire-suppression system; as a result, limiting thermal damage.

EnerDel conducted a root cause investigation and found a component failure in the seating of an electrical cable connection, which caused high electrical resistance in that connection point, producing high voltage across the battery cells and resulting in abnormally high battery pack temperatures. The individual lithium-ion batteries did not fail or perform abnormally.

To address this problem, EnerDel immediately inspected, cleaned, and aligned all high voltage connections and changed the software operating parameters to limit the state of charge of the battery packs to reduce the likelihood of future over-voltage events. EnerDel has since redesigned the high voltage electrical connection circuit in the battery pack assembly, utilizing a more robust terminal connection, and retrofitted all of the District's batteries in 2012.

Boeing Comparison: The AC Transit battery incident was unlike the battery on the Boeing plane, where a fire erupted and the entire battery was destroyed threatening the integrity of the plane. The AC Transit battery safely limited the damage due to battery design, cell packaging, and the battery management system. There was no damage to the bus, and the battery was restored and returned to service.

• Chemistry: The battery chemistry used in the Boeing plane and many small consumer electronics is composed of a lithium cobalt oxide cathode material and graphite anode. The EnerDel battery used on AC Transit buses features a mixed-oxide cathode, which has a higher temperature threshold of more than 50 degrees Celcius, along with a hard carbon anode that is less susceptible to short circuits.

• Battery Management System: The EnerDel battery management system takes into account both the temperature and state of charge (SOC) of the battery to effectively regulate charge and discharge rates to reduce the chance of short circuits and overheating.

• Architecture: The EnerDel battery cells are prismatic and packaged in a soft laminate pouch to effectively "breathe" to minimize particulate debris and temperature increases, compared to the cylindrical and hard metal-cased packaging used by the Boeing battery manufacturer that has a greater likelihood of generating debris. Prismatic architecture provides for improved packaging that requires less highly flammable electrolytes used in all lithium batteries and has more cells with lower capacity and more compartmentalization of the cells within a battery pack. These features distribute the available energy and reduce the chance of propagating temperature increases and thermal runaways.

Automotive and Heavy-Dutv Applications: Nearly all new automotive hybrids, plug-in hybrids, and battery-electrics use lithium batteries, including the Toyota Prius, Chevy Volt, Nissan Leaf, and Tesla. Pike Research's paper on lithium technology growth in the automotive sector reported that "in 2012, Toyota introduced the fifth-generation Prius, powered for the first time with lithium ion (Li-ion) batteries. The shift from nickel-metal hydride (NiMH) batteries to Li-ion

Report No. 13-086 Page 3 of 3

represents a major endorsement of this chemistry as well as its ability to perform consistently in an automotive environment."

ADVANTAGES/DISADVANTAGES:

While lithium batteries are subject to "thermal runaways," improvements in chemistry, architecture and design, manufacturing, and battery management minimize the threat of damage or fires. The benefits of using lithium batteries in comparison with other storage technologies, such as nickel metal hydride or lead acid, are significant reductions in weight and size, without compromising power and energy density. lithium batteries are lighter, smaller, more powerful, and capable of storing more energy to enable sustained power output.

ALTERNATIVES ANALYSIS:

Nearly all of the automotive sector, including heavy-duty buses and trucks, are gravitating to lithium battery storage options due to their enhanced performance characteristics, and because improvements in the design, manufacturing, and software management systems are able to ensure safe and reliable operation.

PRIOR RELEVANT BOARD ACTIONS/POLICIES:

There are no prior relevant Board actions or policies associated with this report.

ATTACHMENTS:

1. EnerDel White Paper on lithium-ion Energy Storage Safety

2. AC Transit EnerDel Battery Safety Features

Department Head Approval: James Pachan, Director of Environmental Technology

Reviewed by: Ken Scheidig, Interim General Counsel

Prepared by: Jaimie Levin, Director of Environmental Technology

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Wheth_er energy storage systems are mechanical storage, or compressed or

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Care. Monitor. Manage. EnerDel's Holistice Approach to Lithium-Jon Energy Storage Safety. Pagel

phases are managed in a controlled manner to ensure

the system performs reliably and safely.

Nearly everyone is familiar with Aristotle's saying, "The whole is more than the sum of its parts," and nowhere

is this more true than in the design of an energy storage

system. The saying also underpins EnerDel's safety phi­losophy, which in one word, can be stated as "holistic." With any energy storage system, safety must begin at

the lowest component level, but must also include every

subsequent building block that goes into producing the entire system. Each and every level of assembly adds to the amount of stored energy, but it also adds complexity,

which must be managed properly to ensure safety.

Cell chemistry selection - EnerDel's cathode material is

a mixed oxide, namely lithium nickel manganese cobalt (NMC) oxide. The earliest available cathode material for

lithium-ion cells was lithium cobalt oxide (LCO), which is still used in batteries for small consumer products, such

as mobile phones and laptops. EnerDel's NMC cathode

material is inherently safer than LCO; it has a thermal runaway onset temperature that is 50 degrees Celsius higher than that of LCO. When discussing lithium-ion

batteries, thermal runaway refers to a situation where

the cell temperature reaches a threshold that causes an uncontrollable rapid release of energy and corresponding temperature rise resulting in a thermal event, such as a

fire.

EnerDel's anode material is hard carbon. Most com­Safety Begins at the Cell Level While cell chemistry, packag­

ing, design, and manufactur-

ing are each important build-

+--C-ha_r&_e_ e Discharge

mercially available lithium-ion

cells utilize graphite, which has many positive attributes. However, hard carbon ex­

ceeds graphite in providing

higher power density and smaller volume changes when charged and discharged, which encourages longer mechanical stability and life

expectancy. Hard carbon is

also more resistant to deg­radation reactions, such as dendrite formation, and offers

more chemical stability.

ing blocks in EnerDel's holistic

approach to lithium-ion battery

safety, cell chemistry is a criti­cal starting point.

Current Collector

Current Collector

ll+

The essential parts of a

lithium-ion battery cell are the cathode, anode, separator,

electrolyte, packaging, and tabs. The cathode is a mate­rial that contains lithium ions

within its crystal structure.

The anode accepts the lithium ions from the cathode dur- Carbon

Anode Separator layered Insertion

Cathode The electrolyte in commercial­

ly available lithium-ion cells, such as EnerDel's Moxie+

Prismatic Cells, contains

ing charge and then releases

them during discharge. The separator, which electrically

Figure 1: Diagram of a discharging lithium-ion cell

isolates the cathode from the anode to prevent internal short circuits, contains small pores that allow the lithium

ions in the electrolyte to travel between the cathode and anode during charge and discharge (see Figure 1). The cell package contains the cathode, anode, separator, and

electrolyte, while tabs allow electrical connections to be made. Careful selection of these components and cell design improve the safety, life expectancy and perfor­

mance of a lithium-ion cell.

organic solvents and a salt. Familiar battery technolo­

gies such as lead-acid, alkaline, nickel cadmium, and

nickel metal hydride use a water-based electrolyte, which is compatible to their voltage range of about 1.2V to 2.1V. The higher voltage lithium-ion cell requires use of

organic, solvent-based electrolyte because water would be decomposed if used. The organic solvents used in lithium-ion cell electrolyte are flammable, so it is critically

important that they are properly sealed and contained

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Care. Monitor. Manage. EnerDe/'s Holistice Approach to Lithium-/on Energy Storage Safety. Page3

within the packaging. EnerDel cells use just enough electrolyte to fill the pores of the electrodes and separa­

tor. This minimizes the chance of electrolyte leaking from

the packaging should a breach occur.

The EnerDel separator is a polymer that encases the cathode and anode electrodes using Z-fold winding, which immobilizes the electrodes so their alignment is

maintained though the life of the cell. The separator helps shut down the cell by melting and thus closing its

pores if high temperatures are experienced.

EnerDel's cells are packaged in laminate, which allows for efficient packing. Appropriately-sized tabs are eas-

ily sealed into laminate packaging with high mechani-cal strength. Since the multi-layer laminate consists of

aluminum foil sandwiched between layers of electrically­insulating polymers, the risk of shorting to the metal case is eliminated. In contrast, cylindrical cells require the use

of many more parts, which can increase the risk of manu­facturing flaws and short-circuits.

There are two tabs per lithium-ion cell, one for the cath­

ode and one for the anode. Connections to the external load are made using these tabs. Many lithium-ion cells

have top tabs that are extremely close to each other. En­

erDel's cells feature wide-plated tabs situated at opposite sides of the prismatic cell. This side tab configuration

offers several advantages:

Minimizing the chance of inadvertent shorting Wide, opposite tabs support a larger current density

with less temperature rise Wide tabs have a thinner cross section providing bet­

ter sealing characteristics Plated tabs are less prone to corrosion, which main­tain low contact resistance and result in less heat and

longer life expectancy thereby enhancing safety

Cell design - Some lithium-ion cells have a cylindrical configuration with long sheet of electrodes and separa­tors wound-up inside. EnerDel's cells are configured in

a flat stack of electrodes, which results in better unifor­mity of their electrical, mechanical, and thermal proper­

ties. The flat stack also provides a more uniform current density enabling prismatic cells to support higher currents

Figure 2: Infrared image of a 4 Ah cylindrical cell with 100 A continuous current

Figure 3: Infrared image of a 4 Ah capacity prismatic cell with 1 OOA continuous current

60,.0 57 54 51 48 45 42 39 36 33 30 27

23.0 ·c

60.0 57 54 51 48 45 42 39 36 33 30 27 24 22.0 ·c

with lower temperature rise than cylindrical cells. This

is particularly important in large format cells with high

capacity (See Figures 2 & 3).

Cell manufacturing- EnerDel purchases high-quality

raw materials and manufactures cells according to strict manufacturing standards to ensure uniformity and con­

sistency. Cell uniformity is essential for safety, durability, and performance.

Product Design Philosophy Three key directives of the EnerDel product design

philosophy are care, monitor and manage. Any design developed by EnerDel must care for the cell, monitor the

health of the cell and manage the cell environment. We care for the cell by providing a compliant location for it

© 2013 All rights reserved. www EnerDel. com ::CENERDEL

Care. Monitor. Manage. EnerDel's Ho/istice Approach to Lithium-/on Energy Storage Safety. Page4

to occupy. We monitor cell health through voltage and temperature measurements, and we manage the cell

environment by giving it a method to better manage heat

dissipation.

Stacked prismatic cells offer benefits in packaging ef­

ficiency and heat removal. However, they present a set

EnerDel designs products with safety as the paramount consideration stemming from its deep

knowledge of lithium-ion cell behavior.

of unique needs that must be addressed to successfully package them into a module. The first requirement is

that the cell stack, or the layers of anodes and cathodes

that are interleaved in the prismatic cell, must be stabi­lized within the module. Whether the module is used for a mobile or

stationary application, mechanical

retention of the anode and cath­ode layers is critical. The second requirement is that the cell must be

allowed to 'breathe.' This breath­ing function is the natural expan­sion and contraction of the cell as it undergoes charge and discharge

cycles. This is caused by the transport of lithium-ions within the

cell that results in a natural volume change or "breathing" of each electrode.

EnerDel addresses stabilization

and volume change needs through the use of a foam sheet that is

paired with each cell of our mod­

ule design (see Figure 4). The foam sheet, in conjunction with the module end-plates and cell ele-

could cause internal shorts. The foam also allows the

cell to breathe by providing a compliant layer between a

cell and its adjacent neighboring cell. In conjunction with

the foam, the module assembly is designed to compress the cells. This force promotes ionic conductivity and results in low internal cell resistance and heat generation.

The mechanical pieces that form the module are made

from an electrically-insulating material, which is self­extinguishing per UL 94. The material is also chemically­resistant. In addition to providing the backbone for the

compressed cells, the mechanical module also protects the prismatic cells from mechanical intrusion.

At every electrical connection level, special attention

must be given to connection points. This starts from the

moment the two cell tabs are joined and continues to the

Cell Elements

Cells per Element

Side Tabs

ments, stabilizes the cell stack by applying a uniform pressure across

Figure 4: Expanded view of EnerDel module construction

the entire surface area of the cell face. The foam hangs

over the active area of the cell creating a 'picture frame' around the periphery of the cell stack. In effect, the cell stack is restrained from any physical movement which

point where two high voltage power busses are brought

together. Loose connections can be the cause of poten­tial system failures by creating high electrical resistance which generates heat. Consequently, this is why EnerDel

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Care. Monitor. Manage. EnerDel's Holistice Approach to Lithium-Jon Energy Storage Safety. Page5

pays close attention to all the mechanical and electrical

connections it makes. Beginning with the mechanical cell

tab joint, dynamic closed-loop torque control is employed

to provide real-time confirmation of joint integrity every

time during manufacturing, which allows non-conforming

connections to be immediately flagged and rejected so

they can be rectified. Also, a threadlocker on the fastener

is employed to ensure that it remains in place throughout

the life of the module.

EnerDel has field-tested thousands of modules using

this joining method and has never experienced a failure.

Module-to-module connections and system connections

are also treated just as carefully. Permanent connections

utilize plated fasteners, torque control and thread-locker

as part of the design requirement. When paired with our

manufacturing and quality systems, we deliver a robust

assembly process. In stationary applications, the ability

to remove a module from the system quickly and easily

is important. EnerDel has developed a tool-less intercon­

nect that is easily removed by maintenance personnel

wearing Personal Protective Equipment (PPE). The tool­

less interconnect provides positive, tactile feedback when

connecting and is designed to meet the directives of "IEC 60664-1 , Insulation coordination for equipment within low

voltage systems", pertaining to creepage and clearance.

EnerDel utilizes a systems architecture approach that

dictates the system be broken-up into discrete cells of

the appropriate capacity. Starting at the module level,

cells are compartmentalized from their neighbors (see

Figure 4) in one-or-two cell groupings commonly referred

to as an element. Building the system from the module

level up, modules are packed into module groupings.

Sometimes an intermediate package called a sub-pack is

used, which is a method of packaging modules where the

enclosure provides compartmentalization. This detailed

attention to packaging provides the best approach to

mitigate thermal runaway from the lowest building block

to the entire energy storage system.

While cells are an important aspect, other factors must be

taken into account for a successful systems design. For

example, incorrect sizing of high-voltage buss bars and

poor connection methodology can create a high resis-

tance joint which will become a "hot spot." In essence,

it can become a bottleneck to the flow of energy which

can become a potential safety issue. A battery system's

electrical string configuration, including the location of

contactors, fuses and current sensing all the way down

to the sizing of high voltage buss bars, contribute to the

safety of the product.

In a mobile or transportation application , modules are

electrically strung together to form a pack that meets

the demands of this market. EnerDel prides itself with

numerous pack designs that have successfully and safely

provided battery solutions for the transportation industry. EnerDel has experience in designing packs that meet the

demanding test and validation requirements of the United

States Advanced Battery Consortium (USABC) and the

United Nations Department of Transportation (UNDOT). EnerDel has designed packs that are exposed to the

elements on the underside of a vehicle and are subject to

crash testing by the manufacturer where the performance demands placed on the battery pack are significant.

The level of design and testing for EnerDel's stationary

energy storage system is just as thorough as it is with EnerDel's transportation packs. From requirements listed

by the Institute of Electrical and Electronics Engineers

(IEEE), Underwriters Laboratories (UL), to the Interna­

tional Electrotechnical Commission (IEC) and the Uni­

form Building Code (UBC), EnerDel has the experience

to design/build energy storage systems that meet these

requirements.

All of EnerDel's packs, both mobile and stationary, are

designed to meet the stringent IEC 60529 requirements,

which defines the degrees of protection required for

electrical equipment. Even packaging materials used to

ship our products are designed and tested to ensure the

product reaches its destination in good, safe condition.

Additionally, complementing the Battery Management

System (BMS) safety features, at the request of specific

customers, EnerDel has successfully integrated an op­

tional fully autonomous (independent from control by the

BMS) fire suppression system that is activated by high

heat in both a custom heavy-duty transportation pack and

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Care. Monitor. Manage. EnerDe/'s Ho/istice Approach to Lithium-/on Energy Storage Safety. Page6

a large scale energy storage system.

Battery Management System Design While the cells provide the brawn of the battery system,

the Battery Management System (BMS) is the brains of

the operation. The BMS coordinates information from the

EnerDel's Battery Management System is designed to safely monitor and control the

lithium-ion battery system.

cells, contactors, current sensors and end-user inputs to

continually monitor and adjust the operation of the battery

system. The BMS embedded controllers include soft­

ware with highly developed algorithms for diagnostic and

control decisions. While safety may seem to be the only

function of the BMS, it is important to note that the BMS

is the health care provider that ensures a long lifespan for

the battery system.

The BMS is the mechanism where safety, cell life, optimal

capacity, and application controller communications are

all handled.

At the lithium energy controller (LEC) level, EnerDel's

BMS design safety protection features include:

Cell-level monitoring for over-temperature detection

Cell-level monitoring for over-charge detection

Cell-level monitoring for over-discharge detection

System-level monitoring for over-current I current

surge detection System-level monitoring for contactor malfunction

detection

High-voltage measurement and isolation detection

implementation (EN 60950 compliant)

Cell voltage measurement and cell balance circuit

hardware isolation between electronic controllers

(CAN Bus topology) HVIUEPO hardware and software ENABLE imple­

mentation

Software HEARTBEAT ENABLE implementation for

contactor-CLOSE request

At the system level, EnerDel's BMS design safety protec­

tion features include:

Dual primary contactor implementation

Automatic service disconnect implementation (some­

times referred to as a mid-pack disconnect)

High-speed, low arc voltage, low energy let-through

(12t) fuse implementation

All high-voltage nodes require a minimum of two

levels of fault tolerance

No other BMS electronics on the market today contain

comparable capabilities to EnerDel's BMS electronics. EnerDel has significant intellectual property (IP) tied to

being able to monitor and manage functions like state-of­

charge (SOC), state-of-health (SOH), contactor control,

pre-charge, cell balancing and high voltage isolation

detection.

EnerDel mandates redundant design and management

features in its battery systems to prevent the possibility

for thermal runaway to occur. These features include

the ability to monitor temperatures via a comprehensive

array of sensors adjacent to the cells and controllers, and

correspondingly limit or cease electrical current based on temperature and/or SOC.

Product Design to Manufacturing Process From the product concept phase through the manufactur­

ing process EnerDel controls the entire process. EnerDel

employs a careful and deliberate method to ensure we

achieve safe and reliable products. Starting with the

desires of our customers, EnerDel brings each concept

EnerDel employs a careful and deliberate process to assure that the product design is

faithfully carried out by manufacturing.

to life through the use of cutting edge design tools and

simulation software. Using Computer Aided Design

(CAD) software, 3D models are created and then ana­

lyzed for mechanical and thermal performance. Analysis software that allows us to perform Finite Element Analy­

sis (FEA) to confirm structural integrity and Computation­

al Fluid Dynamics (CFD) software that helps us confirm

the performance of a thermal management system are all

part of the process. Once a design has met the criteria,

the physical testing and validation process continue the

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Care. Monitor. Manage. EnerDel's Holistice Approach to Lithium-/on Energy Storage Safety Page 7

maturation of the product. Using proprietary in-house

test methods and those tests spelled out by USABC,

UNDOT, Society of Automotive Engineers (SAE) and IEC,

EnerDel is able to use the validation process to physically

verify the functionality and safety of the design and verify

that the manufacturing process is capable of making the

product as designed. This helps to ensure the product's

safe operation and performance. EnerDel believes that

the test and validation process is the bridge between the

virtual model and manufacturing a safe physical product.

Also, the manufacturing team is involved from the earli­

est concepts through the maturation of a product. Early

involvement helps ensure a smooth and safe manufactur­

ing process for every battery manufactured by EnerDel.

Industry-leading manufacturing systems such as the de­

liverables of the Automotive Industry Action Group (AIAG)

and the adherence to the advanced product quality

planning (APQP) process help EnerDel achieve customer

production part approval process (PPAP) certification.

Quality Management System

EnerDel employs an automotive-grade quality system

based on AIAG product and manufacturing, development

and qualification processes. Quality begins with a thor-

EnerDel's Quality Management System (QMS) helps ensure we build safe products that meet

both our internal and customer demands.

ough understanding of a customer's requirements and

how EnerDel's product will be used in the application.

EnerDel uses disciplined document and change control

processes to convey and manage those requirements

throughout our organization to each functional group,

from sales to engineering to shipping.

As product realization moves from design to manufactur­

ing, process flow diagrams, FMEAs, and control plans

are utilized to define and control a manufacturing system

that is built around product requirements and is respon­

sive to variations that might lead to non-conforming prod­

uct. In-process and final testing are employed throughout

cell and pack manufacturing processes to ensure critical

customer and design requirements are met. Special han­

dling methods are defined where appropriate to protect

fragile or sensitive parts or material. Non-conforming

material is immediately removed from the manufacturing

area, tagged and processed through controlled steps to

ensure it is properly disposed of and does not get mixed

in wtih conforming, final product. Shainin, Six Sigma and

statistical problem solving methods and tools are applied

to continuously improve our products and processes as

well as to efficiently and effectively resolve manufacturing

issues.

Suppliers are assessed for their capability to deliver

quality parts prior to receiving an order from EnerDel

and the component parts and raw materials they provide

are approved through application of PPAP requirements.

Incoming materials are verified against product draw­

ings and specifications to ensure they meet our design

requirements. Additionally, equipment, gages and instru­

ments used to test product as it is manufactured are all

calibrated to maintain their accuracy.

Summary Lithium-ion battery system safety is EnerDel's first and

foremost consideration. From product concept to ship­

ment, EnerDel's dedication to safety takes a holistic approach by addressing the care, management and

monitoring of the energy storage system at every step of

the process. We're pleased to provide you with a more

in-depth look at our safety processes, procedures and

protocols. Contact us via email at

[email protected]. :C

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:CENERDEL SR 13-086 Attach. 2

AC Transit Lithium-lon Battery Pack Safety Features

EnerDel has a strong focus on safety that touches every aspect of our business and is reflected in the products we develop and manufacture for our customers. We value our relationship with AC Transit and have outlined the various safety features represented in our cells, packs and battery management systems to demonstrate the features and approach given to safety in the packs installed on AC Transit's clean energy buses.

Quality System Automotive-grade quality system based on Automotive Industry Action Group (AIAG) product and manufacturing development and qualification processes

Cells Cells are manufactured using strictly controlled processes and material standards to promote consistently high quality and uniformity

• Cell chemistry is temperature tolerant and therefore harder to induce thermal runaway Hard Carbon helps inhibit dendrite growth and promotes higher C-rates resulting in improved reliability Cells utilize a Z-fold process for separator installation stabilizing the cell stack reducing chances of internal shorts Prismatic cells have thin cell cross sections and large surface areas to promote heat removal

• Prismatic cells have fewer components compared to cylindrical cells

• Laminate packaging is electrically case neutral by design • Side terminals promote uniform current density and thermal

profile resulting in higher currents with less heat compared to cylindrical cells Wide terminals on opposite sides of the cell promote safety due to increased creepage and clearance distances. Wide terminals result in a thinner cross section which improves cell sealing

• Side terminals reduce risk of terminal-to-terminal shorts (direct shorts or salt bridging) Terminals are nickel-plated to reduce long-term electrical resistance

Battery Management System • High speed CAN bus vehicle interface

Low-voltage to high-voltage isolation Synchronized pack voltage and pack current measurements

• Cell voltage monitoring and balancing Module temperature sensing Contactor, fuse, and service disconnect status detection Isolation fault detection Contactor control/ high voltage interlock

• Pack pre-charge control • Power PC processor for high processing capability

On-board diagnostics and self·test capability improve safety Integrated precision measurements promote safer control of the battery Redundant voltage measurements Multiple zone temperature measurements on both modules and BMS circuit boards

• Contactor control of high voltage interlock Isolation fault detection High voltage isolation fully compatible with EN 60950 standards All high voltage nodes require a minimum of two levels of fault tolerance - not just failsafe. Improved protection against over charge, over discharge

• Continuous cell balancing in all modes of operation

Packaging Cells are packaged in an electrically insulating frame that also inhibits mechanical intrusion

• Cell frames and endplates in conjunction with the elemental foam keep the cells in compression to promote ionic conductivity which promotes low internal cell resistance and heat generation Elemental foam "picture frames" the electrode stack within the laminate packaging to prevent physical movement and the possibility of internal electrical shorts Elemental foam provides a non-rigid uniform force load distribution on the surface of the cell while allowing the cell to expand and contract under charge/discharge cycling Battery module max voltage is less than 50V for safe assembly, handling, storage and service

• All module components are electrolyte/chemical resistant and have a minimum fire rating of UL94 HB

• All power buss connections utilizing mechanical fasteners are applied using dynamic/close loop torque control with thread-locker to ensure joint integrity for the life of the product All power bussing mechanical fastener hardware is plated to promote low electrical resistance and long term mechanical integrity Sub pack cover provides insulated mounting surfaces for RLEC's and mounting snap features to the case for ease of service (no loose hardware that could cause electrical shorts) Sub pack enclosure provides compliance to EN 60950 standards Sub pack serves as the lowest level field serviceable unit in battery system Sub pack is ergonomically friendly with integrated lift assist features

• All major system components down to the discrete cell level are serialized for traceability Pack enclosures and connectors are IP67 rated

• Module and pack enclosures are steel with protective coatings to protect battery from harsh environmental elements System architecture is broken up in to discrete cells of the appropriate capacity which in turn minimizes impact of thermal runaway and magnitude of event

Thermal Event Countermeasures (Non-BMS dependent)

Integrated module frame out-gassing ventilation ports All battery module components compliant to UL94 HB (minimum requirement) Modules and entire battery packaged in to a steel case to prevent thermal event propagation

• Independent fire suppression system activated by high heat (autonomous from BMS system) Directionally controlled rupture disks for high pressure outgassing

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