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Phosphates in Li-ion batteries and automotive applications

MY. Saidi*, H. Huang, TJ. Faulkner(Batteries 2009)

Valence Technology, Inc.,(NV USA)

Yazid.Saidi@Valence.com

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Li-ion - HEV market

Conventional lithium-ion batteries for HEVs are almost ready for commercialization

Intent is displacement of NiMH batteries, Li-ion promises long term reduced cost, with a higher level of performance combined with alonger life.

Major hurdle is cost reduction and safety; current cost is approximately twice the goal. Additional improvements include

Calendar life projections of 8-12 years are based on limited data

Abuse tolerance and improved safetyLow-temperature performance

Other existing technologies: LMO, NCA, NMC and phosphates as cathodes

Li4Ti5O12 and alloy composite as anodes

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1000-3000~1000Cycle Life: EV (# cycles)

>10> 10 Calendar Life (years)

300,0002300,000Cycle Life: HEV (# cycles)

-30 to +50-10 to +40Temperature Range (°C)

> 9590In/Out Efficiency (%)

2-520Self Discharge (% / month)

30-3535Cost ($/kWh)

>300200Volumetric Energy Density (Wh/L)

>30001600Power Density (W/kg)

~150<70Energy Density (Wh/kg)

Li-IonNi-MHAttributeHigher power density for HEVHigher energy density for PHEV/EVHigher voltage/cell: allows fewer cells/pack (need to meet capacity target as well) NiMH approaching technology limits?Environmentally friendly chemistry? Certainly LMO and phosphates.

Li-ion for the automotive industry

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A power-assist HEV battery

What are power-assist HEV requirements?Must absorb and release high power pulses (25kW / 10sec) efficiently (90% energy recapture) and repeatedly (300,000 charge-discharge pulse cycles over life of vehicle)Must be inexpensive, lightweight and fit a small spaceCapacity is not necessary only needs to store and release short pulses.

Much higher specific power than PHEV Power assist battery has to be smaller in size and capacity to meet cost and weight targets,

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Application power/energy

Different applications : different requirements

1 10 100

EV

PHEV

HEV

Energy kWh

P/E 20 20- 40 liters

P/E = 3-15 40-80 liters

P/E ~ 2 170 liters

1-2 KWh

4-15 KWh

> 40KWh

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FreedomCAR specifications (HEV)

FreedomCAR Battery Test Manual For Power-Assist Hybrid Electric Vehicles

Characteristics Units

Power-Assist (Min) 2003

Power-Assist (Max) 2003 IFR PC

Pulse discharge power (10s) kW 25 40 Spec (25)Peak regenerative pulse power (10s) kW 20 35 Spec (20)Total available energy (over DOD range where power goals are met) KWh

0.3 (1C rate) 0.5 (1C Rate) ?Spec (0.3)

Minimum round-trip energy efficiency % 90 (25-Wh

cycle) 90 (50-Wh

cycle)?

> 90Cold cranking power at -30°C (three 2-s

pulses, 10-s rests between (oC) kW 5 7

8 (m

-25

Cycle life for specified SOC increments cycles

300,000 25-Wh cycles (7.5MWh)

300,000 50-Wh cycles (15MWh)

? 300,000 mixed pulse cycles

Calendar Life years 15 158 ( ?

Maximum weight kg 40 60 <17 (cells only)

Maximum volume liter 32 45 <8 (cells only)

Operating Voltage limits Vdc

max<400 min>(0.55 x

Vmax)

max<400 min>(0.55 x

Vmax)?2.1 - 3.82 (single

cell)

Power Margin %max 30% max 30% ?

<30% (projected)

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Advantages of LithiumAdvantages of Lithium IonIon

1

10

100

1,000

10,000

100,000

0 20 40 60 80 100 120 140 160 180 200

Specific Energy, Wh/kg at Cell Level

Lead acid

Lead acidspirally wound

Ni-Cd Ni-MH

LiM-Polymer

Supercapacitors

Na / NiCl2

Li-ionHigh

Energy

Li-IonHigh Power

Li-IonVery High Power

1

10

100

1,000

10,000

100,000

0 20 40 60 80 100 120 140 160 180 200

Specific Energy, Wh/kg at Cell Level

Lead acid

Lead acidspirally wound

Ni-Cd Ni-MH

LiM-Polymer

Supercapacitors

Na / NiCl2

Li-ionHigh

Energy

Li-IonHigh Power

Li-IonVery High Power

Source: SAFT

HEV applications require a cell to deliver at least 1000W/Kg. At this Level of power, Li-ion delivers twice the energy density than Ni-MH. Phosphates in a power design easily meet the power requirements

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Voltage vs. Rate (IFR26650)

26650: power design shows very little polarization at higher rates (min. self heating lag)

1.5

2.0

2.5

3.0

3.5

0.0 0.5 1.0 1.5 2.0 2.5

Time / h

2.1A

20A

30A

40A

Capacity / Ah

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50C (100A) pulse on IFR 26650

Pulsing at

t/s Pow er/WPow er

density (W /kg)*

Pow er density (W /kg)**

5 235.8 2948 336910 232.1 2901 331620 226.9 2837 324230 223.8 2798 3197

55% SO C 10 208.4 2605 2977

100% SO C

* 80g/cell; ** if 70g/cell

Specific power capability derived from a fixed 100A pulse.

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High-rate pulse on IFR 26650

Pulse I @ 100%SOC

Rate t/s Power/WPower density (W/kg)*

Power density (W/kg)**

100A 50 5 235.8 2948 3369150A 75 5 278.8 3485 3983180A 90 5 278.5 3482 3979200A 100 5 288.2 3602 4117216A 108 5 273.4 3417 3905

* 80g/cell; ** if 70g/cell

Specific power capability derived or a fixed pulse time of 5s.

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Hybrid Pulse Power Capability (HPPC)

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

3.8

4.0

2.725 2.73 2.735 2.74 2.745 2.75Time Hr

Vol

ts

-20

-10

0

10

20

30

40

50

Cur

rent

A

VoltageCurrent

Pulse train consisting of 10-sec discharge and charge pulses with 40-sec rest betweenDetermines the DCIR under realistic operating currents (25%-75% of max)Repeated at 10% SOC intervals over 1 complete discharge half-cycle

FreedomCar test manual 2003 IFR Power Cell (18650)

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10-Second DCIR at 36A (IFR26650)

0.00

0.01

0.02

0.03

0.04

0.05

0% 20% 40% 60% 80% 100%DOD / %

LiFe(Mg)PO4 flat operating voltage combined with a flat DCiR helps to further extend the useable DOD range.

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Available Power & Energy (IFR26650)

0

10000

20000

30000

40000

50000

0 500 1000 1500

Wh @ 1C (xBSF)

0

10000

20000

30000

40000

Reg

en P

PC

(W

, xB

SF

)

BSF = 200

Power capability (HPPC) of a 26650 power design using LiFe(Mg)PO4 at BOL

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Cold cranking test (IFR26650)

-25oC/45%DOD

1.5

2.0

2.5

3.0

3.5

-2 2 6 10 14 18 22 26 30 34 38

Time / s

Cel

l vol

tage

/ V

0

1000

2000

3000

4000

5000

Pul

se p

ower

/ W

(x

BS

F)

Voltage Power

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0%

20%

40%

60%

80%

100%

0 100000 200000 300000

Cycles

% o

f in

itia

l PP

C @

4

0%

DO

D

0%20%40%60%80%

100%

0 100000 200000 300000

Cycles

% o

f in

itia

l ca

pa

city

0

10000

20000

30000

40000

0% 20% 40% 60% 80% 100%

DOD / %

disc

harg

e P

PC

(W

, xB

SF

)

0

6000

12000

18000

24000

30000

Reg

en P

PC

(W

, xB

SF

)

Power goal

d/0 cycles

d/90K cycles

d/120K cycles

d/150k cycles

d/180k cycles

d/210k cycles

d/240k cycles

d/240k cycles

d/270k cycles

d/300k cycles

R/0 cycles

R/90K cycles

R/120K cycles

R/150K cycles

R/180k cycles

R/210k cycles

R/240k cycles

R/240k cycles

R/270k cycles

R/300k cycles

Poly. ( d/0 cycles)

HEV cycling target: 300K CyclesHPPC vs. cycles

Capacity vs. cycles Power vs. cycles

IFR-PC exhibits excellent power and energy retentions under HEV cycling regime

Meets HEV cycle life target: 300K (HEV cycles)

>77% >80%

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Why phosphates for the HEV application?

A flat and relatively low OCVWide usable range for power/regen pulsesOvercharge voltage is a safe margin above the normal end of charge voltageOperating range can be extended close to fully charged

Low power fade over 300,000 mixed pulse cyclesMade from the least expensive transition metals available via most efficient and cost effective method (carbothermal)High thermal stability built in robustnessPhosphate lithium ion can meet most HEV requirements

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Introduction

In this segment, lithium-ion is also viewed as the most commercially viable chemistry for PHEVs due to its potential for much higher energy and power density than traditional technologies.

Within Li-ion, phosphates offer the distinct advantage of paramount importance in large format applications: improved safety

Further improvements are needed before a larger penetration of HEVs and PHEVs can take place into the marketplace.

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Plug-In hybrid application (PHEV)

Motivation:Hybrid electric vehicles: 40-50 MPG using fossil fuelsPHEV: >100 MPG by displacing fossil fuels with grid electricity

New technological challenges for PHEV batteries:Must store significant amount of energy to displace fossil fuels

Larger, heavier battery is requiredAdditional battery weight increases vehicle fuel/electricity usage 10Wh/mile for each 100kg (Rousseau, 2007)

Li-ion = Higher energy density battery = better vehicle performance

Must use as much as possible of this stored energySignificant depth of discharge on cycling (DOD) produces more wear and tear

Lithium-ion technology: one of the few chemistries that can meet energy density and high DOD cycle life requirements

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Application power/energy

Different applications : different requirements

1 10 100

EV

PHEV

HEV

Energy kWh

P/E 20 20- 40 liters

P/E = 3-15 40-80 liters

P/E ~ 2 170 liters

1-2 KWh

4-15 KWh

> 40KWh

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PHEV Battery Specifications

Table 1 is cited from Battery Test Manual For Plug-In Hybrid Electric Vehicles U.S. DOE Vehicle Technologies Program.Specifications for PHEV10 and PHEV40.

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Maximizing Cell Energy Density

Cell energy optimization calls for a balance of higher utilization, less inert material and more active materialPowder morphology is key to maximizing energy

Increase utilization of active material:

Smaller primary particle sizeMore conductive additiveThinner electrodesMore porous electrodes

Increase amount of active material:

Larger primary particle sizeMore dense electrodes

Reduce amount of inert material:

Lighter enclosureThinner separatorLess conductive additiveThicker electrodes

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IFR-EC 26650 wide useable SOC range

Regen power capability is > 75% above the target at EOL (margin), even at very low DOD.

DODMIN can be reduced from 10% to 5%, or even lower, extending available energy.

More available energy for CD mode = BSF can be further decreased by 6% to 12%.

45kW (EOL)

58.5kW(BOL)

5%D

OD

80%

DO

D

10%

DO

D0

100002000030000400005000060000700008000090000

0 1000 2000 3000 4000 5000 6000

Wh @ 10KW (xBSF)

Dis

. PP

C (

W, x

BS

F)

0

7500

1500022500

30000

37500

45000

5250060000

Reg

en P

PC

(W

, xB

SF)

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PHEV: Long Cycle Life at 100% DOD

IFR18650EC exhibits very long life at e.g. C/2 cycling, 100% DODAfter 4000 cycles, 80% of initial capacity is retained.

0%

20%

40%

60%

80%

100%

0 1000 2000 3000 4000

Cycle number

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0%

20%

40%

60%

80%

100%

0 500 1000 1500 2000 2500 3000

Cycles

Higher Rate over Shorter Range

Shorter range, higher rate, PHEV designs (PHEV10 etc.) mitigate the higher cost of larger packs and have a a higher chance for commercialization

Without sacrificing cell capacity, IFR18650 energy design s rate capability has been improved significantly through cell design to meet this challenge Constant current cycle life at 2C charge, 2C discharge rate, 100% DOD, is predicted to reach more than 2300 cycles to 80% of its initial capacity.

20082009

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FreedomCar PHEV10 CD Cycling

One CD cycle is a series of 5 above profiles, followed by a recharge.Energy throughput / cycle = 3.4kWh5000 CD cycles are required over lifetime of the battery.

From Battery Test Manual For Plug-In Hybrid Electric Vehicles U.S. DOE Vehicle Technologies Program.

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0%

20%

40%

60%

80%

100%

120%

0 2000 4000 6000

Cycles

% o

f rem

aini

ng e

nerg

y

IFR18650EC: CD Cycle Life (Projected)

Charge depleting (CD) cycle life criterion: 5000 cyclesThis 360s-pulsing profile is repeated five times as a single discharge before recharging battery at 1.4kW rateThe IFR18650EC is predicted to deliver 5000 cycles under CD operation.

-12

-8

-4

0

4

0.1 0.2 0.3 0.4 0.5 0.6 0.7

Time / h

Cu

rren

t / A

One single CD mode discharge

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Valence and PHEVs

Battery supplier to PHEV integrators as early as 2005.Testing conducted at cell, module, and pack levels.Incorporated feedback from early adopters to improve performance, design, and functionality.

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Early adoption

First pack was assembled in Feb, 2005.

Consisted of 18 U1 off the shelf modules (12.8V/40Ah) in series and controlled by Energy CS Battery Management System

Originally charged with PFC-20 charger.

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Engineering Evolution

Most recent system includes 18 modules (12.8V/40Ah), but not set inside a case.

Laid out for better thermal management. Integrated BMS.

Uses updated battery management system from Energy CS which includes: Built in data loggingGPSAround the clock balancingCommunication with charger

.

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Pack Performance

The Energy CS conversion provides the greatest range of all other conversions on the market (provided boosted electrical assistance for approximately 66 miles while averaging 107 mpg per Argonne National Lab testing).

This performance cost only about $1 worth of electricity with overnight charging.

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Promising New Materials

These new materials promise more energy through higher voltage

1.0

2.0

3.0

4.0

5.0

6.0

0 100 200 300 400 500 600Energy / WhKg-1

LCP LVP LVPF

LMP LFP LCO

LCO is used as a reference

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Enabling technologies

MaterialsSafety of phosphates

Overcharge prevention simpler than layered oxidesBalancing is a functionality issue rather than a safety issueThermal runaway does not propagate through pack

CTRLow-cost high-performance materials

CellsLarger format cells will reduce complexity and cost of modules, packs

PacksEpoch BMS provides intelligent interface, balancing and soft fail modes

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Summary

PhosphatesAn enabling technology especially in the large format arenaThe most thermally stable Li-ion chemistryExhibit excellent performance characteristics for a variety of applicationsOffer a competitive cost advantage due to inexpensive raw materials, design simplicity and longevityShow a high tolerance under abuse conditionsHave the least impact on the environment (LFP)

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