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www.valence.com 1
Phosphates in Li-ion batteries and automotive applications
MY. Saidi*, H. Huang, TJ. Faulkner(Batteries 2009)
Valence Technology, Inc.,(NV USA)
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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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