Phosphates in Li-ion batteries and
automotive applications
MY. Saidi*, H. Huang, TJ. Faulkner
(Batteries 2009)
Valence Technology, Inc.,
(NV USA)
[email protected]
www.valence.com
1
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2
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 a
longer 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 safety
Low-temperature performance
Other existing technologies:
LMO, NCA, NMC and phosphates as cathodes
Li4Ti5O12 and alloy composite as anodes
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Li-ion for the automotive industry
Higher power density for
HEV
Higher energy density
for PHEV/EV
Higher voltage/cell:
allows fewer cells/pack
(need to meet capacity
target as well)
NiMH approaching
technology limits?
Environmentally friendly
chemistry? Certainly
LMO and phosphates.
Attribute
Ni-MH
Li-Ion
Energy Density (Wh/kg)
<70
~150
Power Density (W/kg)
1600
>3000
Volumetric Energy Density
(Wh/L)
200
>300
Cost ($/kWh)
35
30-35
Self Discharge (% / month)
20
2-5
In/Out Efficiency (%)
90
> 95
Temperature Range (°C)
-10 to +40
-30 to +50
Cycle Life: EV (# cycles)
~1000
1000-3000
Cycle Life: HEV (# cycles)
300,000
300,0002
> 10
>10
Calendar Life (years)
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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 space
Capacity 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
1-2 KWh
HEV
P/E 20
20- 40 liters
4-15 KWh
PHEV
P/E = 3-15
40-80 liters
> 40KWh
EV
P/E ~ 2
170 liters
1
10
100
Energy kWh
Different applications : different requirements
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FreedomCAR specifications (HEV)
Characteristics
Pulse discharge power (10s)
Peak regenerative pulse power (10s)
Total available energy (over DOD range
where power goals are met)
Minimum round-trip energy efficiency
Cold cranking power at -30°C (three 2-s
pulses, 10-s rests between (oC)
Units
kW
kW
PowerPowerAssist (Min) Assist (Max)
2003
2003
25
40
20
35
KWh
%
kW
0.3 (1C rate) 0.5 (1C Rate) ?
90 (25-Wh
cycle)
5
Cycle life for specified SOC increments
cycles
300,000 25Wh cycles
(7.5MWh)
Calendar Life
years
15
Maximum weight
kg
40
Maximum volume
liter
32
Operating Voltage limits
Vdc
max<400
min>(0.55 x
Vmax)
Power Margin
%
max 30%
IFR PC
Spec (25)
Spec (20)
Spec (0.3)
90 (50-Wh
?
cycle)
> 90
8
7
(
-25
m
300,000 50Wh cycles ? 300,000 mixed
pulse cycles
(15MWh)
8
15
?
(
60
<17 (cells only)
45
<8 (cells only)
max<400
min>(0.55 x ?2.1 - 3.82 (single
Vmax)
cell)
<30%
max 30% ?
(projected)
FreedomCAR Battery Test Manual For Power-Assist
Hybrid Electric Vehicles
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Advantages of Lithium Ion
100,000
Super
capacitors
10,000
Li-Ion
Lead acid
spirally wound Very High Power
Li-Ion
High
Power
Ni-Cd
Ni-MH
1,000
Na / NiCl2
100
LiM-Polymer
Lead acid
Li-ion
High
Energy
10
1
0
20
40
60
80
100
120
140
160
180
200
Specific Energy, Wh/kg at Cell Level
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
Source: SAFT
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Voltage vs. Rate (IFR26650)
3.5
2.1A
3.0
20A
30A
2.5
40A
2.0
1.5
0.0
0.5
1.0
1.5
2.0
2.5
Capacity
Time / h / Ah
26650: power design shows very little polarization
at higher rates (min. self heating lag)
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50C (100A) pulse on IFR 26650
P u ls in g
at
100% SO C
55% SO C
t/s
P o w e r/W
5
10
20
30
10
2 3 5 .8
2 3 2 .1
2 2 6 .9
2 2 3 .8
2 0 8 .4
Pow er
d e n s ity
(W /k g )*
2948
2901
2837
2798
2605
Pow er
d e n s ity
(W /k g )**
3369
3316
3242
3197
2977
* 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/W
Power
density
(W/kg)*
100A
150A
180A
200A
216A
50
75
90
100
108
5
5
5
5
5
235.8
278.8
278.5
288.2
273.4
2948
3485
3482
3602
3417
Power
density
(W/kg)**
3369
3983
3979
4117
3905
Specific power capability derived or a fixed pulse time of 5s.
* 80g/cell; ** if 70g/cell
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Hybrid Pulse Power Capability (HPPC)
IFR Power Cell (18650)
4.0
3.8
3.6
50
Voltage
Current
40
30
3.2
20
V o lts
3.4
3.0
2.8
10
2.6
0
2.4
-10
2.2
2.0
2.725
C u rre n t A
FreedomCar test manual 2003
-20
2.73
2.735
2.74
Time Hr
2.745
2.75
Pulse train consisting of 10-sec discharge and charge
pulses with 40-sec rest between
Determines the DCIR under realistic operating currents
(25%-75% of max)
Repeated at 10% SOC intervals over 1 complete
discharge half-cycle
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10-Second DCIR at 36A (IFR26650)
0.05
0.04
0.03
0.02
0.01
0.00
0%
20%
40%
60%
DOD / %
80%
100%
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)
40000
40000
30000
30000
20000
20000
10000
10000
BSF = 200
0
0
500
1000
Regen PPC (W, xBSF)
50000
0
1500
Wh @ 1C (xBSF)
Power capability (HPPC) of a 26650 power design
using LiFe(Mg)PO4 at BOL
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Cold cranking test (IFR26650)
Power
Cell voltage / V
3.5
5000
4000
3.0
3000
2.5
2000
2.0
1000
1.5
Pulse power / W (x BSF)
Voltage
0
-2
2
6
10
14
18
22
Time / s
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30
34
38
-25oC/45%DOD
16
HEV cycling target: 300K Cycles
HPPC vs. cycles
40000
Power goal
d/0 cycles
d/90K cycles
d/120K cycles
30000
24000
18000
20000
12000
10000
6000
d/150k cycles
Regen PPC (W, xBSF)
discharge PPC (W, xBSF)
30000
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
0
0%
20%
40%
0
80% 100%
60%
IFR-PC exhibits excellent power and
energy retentions under HEV cycling
regime
Meets HEV cycle life target:
300K (HEV cycles)
R/240k cycles
R/240k cycles
R/270k cycles
R/300k cycles
DOD / %
Capacity vs. cycles
100%
80%
60%
40%
20%
0%
% of initial PPC @
40%DOD
% of initial capacity
Poly. ( d/0 cycles)
>77%
0
100000
200000
300000
Power vs. cycles
100%
80%
60%
40%
>80%
20%
0%
0
100000
200000
300000
Cycles
Cycles
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Why phosphates for the
HEV application?
A flat and relatively low OCV
Wide usable range for power/regen pulses
Overcharge voltage is a safe margin above the normal
end of charge voltage
Operating range can be extended close to fully charged
Low power fade over 300,000 mixed pulse cycles
Made from the least expensive transition metals available
via most efficient and cost effective method (carbothermal)
High thermal stability
built in robustness
Phosphate 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 fuels
PHEV: >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 required
Additional 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 energy
Significant 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
1-2 KWh
HEV
P/E 20
20- 40 liters
4-15 KWh
PHEV
P/E = 3-15
40-80 liters
> 40KWh
EV
P/E ~ 2
170 liters
1
10
100
Energy kWh
Different applications : different requirements
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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
Reduce amount of inert
material:
Lighter enclosure
Thinner separator
Less conductive additive
Thicker electrodes
Increase utilization of active
material:
Smaller primary particle size
More conductive additive
Thinner electrodes
More porous electrodes
Increase amount of active
material:
Larger primary particle size
More dense electrodes
Cell energy optimization calls for a balance of higher utilization, less
inert material and more active material
Powder morphology is key to maximizing energy
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58.5kW(BOL)
80%DOD
45kW (EOL)
0
60000
52500
45000
37500
30000
22500
15000
7500
0
Regen PPC (W, xBSF)
90000
80000
70000
60000
50000
40000
30000
20000
10000
0
5%DOD
10%DOD
Dis. PPC (W, xBSF)
IFR-EC 26650 wide useable SOC range
1000 2000 3000 4000 5000 6000
Wh @ 10KW (xBSF)
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%.
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PHEV: Long Cycle Life at 100% DOD
100%
80%
60%
40%
20%
0%
0
1000
20 0 0
3000
4000
C ycle num b er
IFR18650EC exhibits very long life at e.g. C/2 cycling,
100% DOD
After 4000 cycles, 80% of initial capacity is retained.
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Higher Rate over Shorter Range
100%
2009
80%
2008
60%
40%
20%
0%
0
500
1000 1500 2000 2500 3000
Cycles
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.
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FreedomCar PHEV10 CD Cycling
From Battery
Test Manual
For Plug-In
Hybrid Electric
Vehicles U.S.
DOE Vehicle
Technologies
Program.
One CD cycle is a series of 5 above profiles, followed by a recharge.
Energy throughput / cycle = 3.4kWh
5000 CD cycles are required over lifetime of the battery.
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IFR18650EC: CD Cycle Life (Projected)
4
Current / A
% of remaining energy
120%
100%
80%
0
-4
-8
-12
0.1
60%
0.2
0.3
0.4
0.5
0.6
0.7
Time / h
40%
One single CD
mode discharge
20%
0%
0
2000
4000
Cycles
6000
Charge depleting (CD) cycle life criterion: 5000 cycles
This 360s-pulsing profile is repeated five times as a single discharge before
recharging battery at 1.4kW rate
The IFR18650EC is predicted to deliver 5000 cycles under CD operation.
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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 logging
GPS
Around the clock balancing
Communication 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
6.0
LCP
LVP
LVPF
LMP
LFP
LCO
5.0
4.0
3.0
2.0
LCO is used as a reference
1.0
0
100 200 300 400 500 600
Energy / WhKg-1
These new materials promise more energy through
higher voltage
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Enabling technologies
Materials
Safety of phosphates
Overcharge prevention simpler than layered oxides
Balancing is a functionality issue rather than a safety issue
Thermal runaway does not propagate through pack
CTR
Low-cost high-performance materials
Cells
Larger format cells will reduce complexity and cost of
modules, packs
Packs
Epoch BMS provides intelligent interface, balancing
and soft fail modes
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Summary
Phosphates
An enabling technology especially in the large format
arena
The most thermally stable Li-ion chemistry
Exhibit excellent performance characteristics for a
variety of applications
Offer a competitive cost advantage due to inexpensive
raw materials, design simplicity and longevity
Show a high tolerance under abuse conditions
Have the least impact on the environment (LFP)
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