NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Optimizing Battery Usage 

and Management for Long Life

Kandler Smith, Ying Shi, Eric Wood, Ahmad Pesaran

Transportation and Hydrogen Systems Center 

National Renewable Energy Laboratory

Golden, Colorado

Advanced Automotive Battery Conference

Detroit, Michigan June 16, 2016

NREL/PR-5400-66708
2

1) Models & methods

2) Analysis: PHEV 10-year / 150k-mile life

3) Battery control research projects

Outline

PHEV: plug-in hybrid electric vehicle
3

NREL Battery Modeling Tools

1) Multi-Scale Multi-Domain Model

o 3D electrochemical/thermal physics

o 3D thermal/electrical/mechanical abuse

 DOE Computer-Aided Eng. of Batteries (CAEBAT) program

2) Battery Life Predictive Model

o Energy/power performance degradation as a

function of time, Ncycles, T, SOC, ΔSOC, C-rate

o Integrated in BLAST

3) BLAST (Battery Lifetime Analysis and 

Simulation Tool)

o Load profile, climate & thermal simulation (vehicles, 

stationary)

15°C

20°C

25°

C

30°C

10°C

Minneapolis

Houston

Phoenix

Li-ion graphite/nickelate life:

PHEV20, 1 cycle/day 54% ∆DoD

SOC: state of charge
4

Electrochemical Operating Window Potential vs. Li (V)

SOC

(x in LixC6 or y in Li1-0.6yCoO2)

0% SOC 100% SOC

Potential 

measured at 

cell terminals

charge

discharge

Figure credit:

Ilan Gur (ARPA-E) & Venkat 

Srinivasan (LBNL), 2007
5

Electrochemical Window – Degradation Potential vs. Li (V)

SOC

(x in LixC6 or y in Li1-0.6yCo)O2)

Figure : Ilan Gur (ARPA-E) & Venkat Srinivasan (LBNL) 2007

Time at high 

SOC & T

Time at high 

SOC & T. 

Accelerated 

with DOD

Cycling at

• High T & high DOD

• Low T, & high C-rate

Cycling at low T, 

& fast charging

DOD: depth of discharge
6

Set of trial equations representing physical fade 

mechanisms, e.g.:

• Solid-electrolyte interphase (SEI) growth & damage

• Particle fracture

• Electrode isolation

• Electrolyte decomposition

• Gas generation, delamination

• Li plating

(Non)linear combinations of mechanisms describe 

performance metrics changes with time & cycles

• Capacity (generally min. of several limiting 

mechanisms)

• Resistance (generally additive)

NREL Life Predictive Modeling – Approach 

S. Santhanagopalan, K. Smith, J. Neubauer, G.-H. Kim, A. Pesaran, M. Keyser,

Design and Analysis of Large Lithium-Ion Battery Systems, Artech House, 2015
7

• Experience with 

8-10 NCA, FeP, 

NMC 

technologies

• NCA model, 

shown here, 

implemented in 

BLAST

NREL Life Predictive Modeling – NCA Example

FeP: iron-phosphate

NCA: Ni-Co-Al

NMC: LiNi0.4Mn0.4Co0.2O2
8

Life Comparison of 5 Li-ion Technologies

In addition to aging condition, 

life changes significantly with 

Li-ion technology

Temperature and electrical cycling assumptions:

• Temperature: 28oC

• Cycling: 2-hr charge to 100% SOC; 10-hr rest; 2-hr dischg; 10-hr rest

*Faster fade at 30% DOD relative to 90% DOD in this scenario is due to longer dwell time at high SOC for the 30% DOD case.

o Power/energy ratio

o Chemistry

o Design heritage 

(85% SOCavg ) (55% SOCavg )
9

BLAST-Lite Standalone Model GUI

• Versions for 

vehicle (shown) 

and stationary 

energy storage 

applications

• Downloadable 

from NREL 

website later 

this year
10

BLAST-Lite Sample Model Results
11

Cell-to-Cell Capacity Imbalance

1C Energy Temperature

• Pack thermal imbalance testing 

and simulation

• Expert interviews & teardown 

analysis of NCA automotive pack 

aged to 70% remaining energy

• Simulation of sources of cell-to-cell aging variability

Non-uniform degradation includes ±10% random perturbation on 

life model degradation rates

±5.5% variation at EOL

±5%

Tmax cell

Tavg cell

Tmin cell

Tambient

BOL: beginning of life

EOL: end of life
12

Cooling System Impact on Cell Aging Imbalance

BLAST simulation of xEVs across 5 driving patterns, 4 climates
13

1) Lifetime models & methods

2) Analysis: PHEV 10-year / 150k-mile life

3) Battery control research projects
14

Impacts on PHEV Lifetime

• AT-PZEV 10-yr/150k-mi warranty

• Presently no remaining capacity requirement

• But important for long-term customer satisfaction and resale 

value

• Nominal assumptions (variations noted on each slide)

o Graphite/NCA life model

o 20oC

o 90% SOCmax

o Average cell degradation (margin required for worst cell if passive balancing)

o 1 cycle per day

o 2/3 of rest time spent at SOCmax

o 1/3 of rest time spent at SOCmin
15

Calendar versus Cycle Limitations on Years Life

Electrode site limited

(cycle life)

Cyclable Li limited

(calendar life, coupled with cycling)

• Low temperature 

• Low average SOC • Low SOCmax

• Delayed/slow

 charging

• High temperature 

• High average SOC & high DOD

• Low DOD & C-rate

• Fewer cycles/day

• ~Room temperature

• High DOD & C-rate

• More cycles/day

• Low min temperature

• High max temperature
16

Impact of Number of Cycles per Day

• PHEV40 typical worst case is 1 cyc/day: 10 yrs ~ 68% DOD

• PHEV20 could experience 2 cyc/day: 10 yrs ~ 56% DOD

• PHEV10 could experience 4 cyc/day: 10 yrs ~ 43% DOD

10 cyc/day

4 cyc/day

2 cyc/day

1 cyc/day
17

Impact of Maximum SOC

100%

95%

90%

85%

• Plot below assumes constant SOCmax. Alternately, can be varied with 

o Seasonal or battery temperature (e.g., low in summer, high in winter)

o Service life (e.g., gradually increasing SOCmax to maintain available energy)
18

All rest at SOCmax

 (opportunity charging)

2/3 of rest at SOCmax

1/3 of rest at SOCmax

Zero rest at SOCmax

 (just-in-time charging)

Impact of rest time at maximum SOC

• Impacted by charging behavior

• Huge calendar lifetime benefit w/ delayed charging

o Must be traded with providing customer full charge just in time for next trip
19

Impact of Lifetime Average Temperature

• Hot climates require some combination of

o Chilled thermal management

o Restricting SOCmax< 90% [when battery is hot and/or during hot seasons]

o Increasing SOC window

 over 10 years

o Delayed charging

o Reducing 10-year

 remaining capacity

 requirement < 80%

35oC

30oC

25oC

20oC
20

1) Lifetime models & methods

2) Analysis: PHEV 10-year / 150k-mile life

3) Battery control research projects
21

Battery Prognostic-Based Control for xEVs

• ARPA-E AMPED project led by Eaton Corporation

• Issue: xEV battery packs are oversized & controls are

 conservatively tuned to achieve typical life of 10 years. Oversizing is expensive

• Solution: 35% smaller HEV battery by providing vehicle controller with real-time 

knowledge of battery degradation 

• NREL roles: Developed battery prognostic model with 6 months accelerated cell 

testing. Validated model and controls with 33-month 4-season HIL pack testing 

0 50 100 150 200 250

30oC, hCmDoD

Time (days)

30oC, hChDoD

30oC, hChDoD

45oC, hChDoD

45oC, hCmDoD

45oC, hCmDoD50

45oC, hChDoD50

30oC, hCmDoD 45oC, mCmDoD

30oC, utility

45oC, utility

45oC, mClDoD

30oC, mCmDoD 30oC, mClDoD

0oC, mCmDoD

55oC, Storage100

55oC, Storage50

55oC, Storage20

45oC, Storage100 45oC, Storage50

30oC, Storage100

0oC, mClDoD

0oC, utility

Cell Test Data

25 aging 

conditions, 

Const T

0 50 100 150 200 250

2

5

3

5

4

5

5

5

6

 0

30oC, hCmDoD

Time (days)

30oC, hChDoD 45oC, hChDoD

45oC, hCmDoD

45oC, hCmDoD50

45oC, hChDoD50

30oC, hCmDoD

45oC, mCmDoD

30oC, utility

45oC, utility

45oC, mClDoD 30oC, mCmDoD 30oC, mClDoD

0oC, mCmDoD

55oC, Storage100

55oC, Storage50

55oC, Storage20

45oC, Storage100

45oC, Storage50 30oC, Storage100

0oC, mClDoD

0oC, utility

Model Prediction Pack-level Validation

4-season 

test

Figure: http://www.eaton.com/Eaton/ ... 

ProductsServices/HybridPower/Applications/index.htm 
22

Robust Cell-Level Control of xEV Batteries

• ARPA-E AMPED project led by Utah State, with Ford, CU-Boulder, UCCS, NREL

• Life extension: 30% to 45% xEV battery life extension using new hardware and 

controls to differentially cycle weak cells & extend their life

• Cost neutral: Active cell balancing hardware supplies vehicle auxiliary 12V loads. 

Replaces HV  12V DC-DC converter (~$200 component)

• NREL roles: Benefits modeling, control strategy, validation w/ 1.5-year accel. aging

BLAST model 

prediction

Validation testing on PHEV pack

• 35oC amb., 4-5 US06 cyc./day

• Bottom cells: Passive balancing

• Top cells: Life balancing
23

• Utah State 

University 

AMPED balancing 

system 

compensates for 

non-uniform cell 

aging

• Thermal 

management still 

needed to 

remove heat load 

and suppress 

maximum cell 

temperature

Life Balancing Control Strategy Reduces Need 

for Tight Cell-to-Cell Thermal Control

BLAST simulation. Individual data points are same scenarios as shown on slide 12.
24

Summary

• Main calendar life factors: Average T & SOC

o DODmax secondary (inverse correlation with avg. SOC)

• Main cycle life factors: DOD & C-rate (max, RMS); 

high/low T extremes

• Today’s life models reasonably extrapolate test 

data forward in time

o Extrapolation to untested duty cycles still uncertain

o Integration with physics models needed to optimize next 

generation cell designs

• Advanced controls show promise for 

o 35% smaller HEV battery

o 30%-45% longer PHEV & BEV life
25

Acknowledgements

• DOE Vehicle Technologies Office

o Brian Cunningham

o David Howell

• DOE ARPA-E AMPED Program

o Pat McGrath

o Russell Ross

o Ilan Gur

• ARPA-E AMPED Teams

o Eaton Corporation – Chinmaya Patil

o Utah State Team – Regan Zane, Dyche Anderson, 

Dragan Maksimovic, Gregory Plett, Scott Trimboli,