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Project ID #BAT339 

PI: Matthew Keyser

Presenter: Kandler Smith

National Renewable Energy Laboratory

June 19, 2018

DOE Vehicle Technologies Office

2018 Annual Merit Review and Peer Evaluation Meeting

Team: Andrew Colclasure, Francois Usseglio-Viretta, Shriram Santhanagopalan, 

National Renewable Energy Laboratory

Venkat Subramanian, Andy Jansen, Bryant Polzin, Steven Trask, Dennis Dees,

Ira Bloom, David Robertson, Ahmed Shabbir, Rita Browski, Daniel Abraham, 

Argonne National Laboratory

Eric Dufek, Tanvir Tanim, Lee Walker, Idaho National Laboratory

Micro/Macro-Scale Modeling for Battery 

Fast Charge Applications
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Overview

• Project start date: FY18

• Project end date: FY19

• Percent complete: 30%

• Long charge times for electric vehicles

• Today’s fast charge batteries use thin 

electrodes to avoid electrolyte 

transport limits and lithium plating

– Thin electrodes have higher cost and lower 

energy density however

• Safety and degradation concerns with 

lithium plating

Timeline Barriers

• Lead: Argonne National Laboratory (ANL)

• Interactions/collaborations

– Idaho National Laboratory (INL)

– University College of London (UCL)

– Brigham Young University (BYU)

Partners

• Total project funding $1.1M

– DOE share: 100%

– Contractor share: 0

• Funding for FY 2018: $550k

• Funding for FY 2019: $550k

Budget
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Relevance – Prediction of Transport Limits and 

Consequences for Extreme Fast Charge (XFC)

Electrolyte transport is the 

most common limiter of fast 

charge rate for energy dense 

(thick electrode) battery 

electric vehicle (BEV) cells 

Depletion results in non-uniform 

current in negative electrode, 

promoting lithium (Li) plating 

near separator

1) Li+ depletion in 

electrolyte

2) Li saturation @ 

graphite surface

3) Li depletion @ 

NMC surface

NMC: Nickel-Manganese-Cobalt Oxide
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Relevance – DOE Goals

• Battery goals1

– Cost: $80/kWh

– Energy: 275 Wh/kg, 550 Wh/L

– Vehicle range: 300 miles

– Charge time: 80% ∆SOC in 15 min

• Electrode-level challenges (present focus)

Pros Cons

Thick 

electrodes

Lower battery cost

Higher energy density

Increases electrolyte ionic transport 

distance

(leads to polarization, heat, Li plating)

Thin 

electrodes

Capable of fast charge ~ 2x increase in cell cost 

(from $103/kWh to $196/kWh)

~ 20% less energy density

(from 220 to 180 Wh/kg)

1. “Enabling Fast Charging: A Technology Gap Assessment” U.S. DOE, October 2017.

SOC: state of charge

• System challenges:

– Thermal management

– Safety, controls

– Infrastructure
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Relevance – Objectives

• Through modeling studies, quantify

– Limits of today’s graphite-based electrode technologies for 

varying electrode designs (loadings, porosities, etc.)

– Why some electrodes are better suited to XFC than others

• Electrode tortuosity based on electrode morphology

– Electrode and electrolyte improvements needed to enable 

XFC

• Develop first case studies with 3D microstructure model 

to explore

– Interaction of electrode morphology with heterogeneous 

utilization, increasing probability of degradation

Leverage tools developed under DOE’s Computer-Aided Engineering of Batteries 

(CAEBAT) program for XFC
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Approach

• Electrochemical modeling tools for XFC 

– Macro-homogeneous modeling

 Guide electrode design and electrolyte 

requirements 

– Microstructure modeling

 Effective properties determined via 

homogenization and geometric analysis 

(tortuosity, surface area, porosity, 

morphology)

 3D electrochemical models assess electrode 

heterogeneity

• ANL-CAMP electrodes: Experimental characterization

– Related CAEBAT work: Toda NMC532 / Phillips A12 

graphite of varying porosity and thickness (Ref. 

poster bat299)

– Present XFC project: Extend to additional graphite 

material types (1 of 6 thus far)

0.73 × cs,max

0.95 × cs,max

Graphite 

lithiation

Ref: ES030 Cell Analysis, Modeling, and Prototyping (CAMP) Research Activities

+
NREL | 7

Milestones

Remaining FY18 milestones Due (end 

of 

quarter)

Go/

No-go

Status

M1. Use macro model to determine limits 

of varying electrode designs for 

accomplishing XFC

Q1 Yes Complete

M2. Build first case of microstructure 

models for fast charge

Q2 No Complete

M3. Report summarizing measurement of 

electrochemical parameters for graphitic 

electrodes and impact on cell-level 

performance

Q3 No On track

M4. Comparison of model predictions 

against test data

Q4 No On track
Technical Accomplishments:

Macro-homogeneous 

Modeling
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Fast Charging of Full Cell with Thin (~42-μm) Electrodes

Data: Andy Jansen, Stephen Trask, and Bryant Polzin

(ANL)

Model: Andrew Colclasure (NREL)

• 180 Wh/kg, 450 Wh/L design

• Phillips A12 graphite/Toda NMC532

electrochemical parameters taken from

CAEBAT project (Ref. bat298 & bat299

posters)

• Tortuosity: 6.0 and 2.9 for anode and

cathode, respectively

• Assumes 10% loss of cycle-able lithium due to

solid-electrolyte interphase formation
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Lithium (Li) Plating Likely Near End of 7C 

Constant Current Charge
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Electrolyte Li+ Concentration Gradients at Transition 

from Constant Current to Constant Voltage Charge Step

Electrolyte transport severely limits charging rate at higher loadings

Medium Electrode Loading

2.5 mAh/cm2 cathode (71 μm)

3.07 mAh/cm2 anode (87 μm)

Low Electrode Loading

1.5 mAh/cm2 cathode (42 μm)

1.84 mAh/cm2 anode (43 μm)

When electrolyte is depleted at the back of the electrode, only the front portion of the 

electrode remains active. Excessive local C-rates lead to Li plating near the separator.
NREL | 12

Projections Next-Generation (NG) Electrolyte

Reduced chance of Li plating with hypothetical “NG” electrolyte

• Anode tortuosity same as cathode (τ- = 6.0  2.85)

• Electrolyte with 1.5x conductivity, 3x diffusivity, and t+ improved by 

0.1 (baseline: κ=10 mS/cm, De=1.6E-6 cm2/s, and t+=0.46 @ 1M)
Technical Accomplishment:

Prediction of Microstructure 

Tortuosity
NREL | 14

Calculation of Tortuosity from Microstructure

• What is tortuosity, τ?

• Homogenization calculation

Images: Juliette Billaud et al. (ETHzürich) “Enhanced Rate Performance in Electrode Materials for Lithium-ion Batteries,” 

International Battery Seminar & Exhibit, March 20-23, 2017.

D0 (bulk diffusion coefficient)
NREL | 15

Background CAEBAT Project Work (Poster bat299) –

Comparison of Three Microstructure Tortuosity 

Prediction Methods

CAEBAT-3 Team: NREL, ANL (Abraham), 

UCL (Shearing), Purdue (Mukherjee), and 

BYU (Wheeler)

Francois L.E. Usseglio-Viretta et al. “Resolving the Discrepancy in Tortuosity Estimation for Li-ion Battery Electrodes ...” submitted.
NREL | 16

First XFC Sample, SLC1506T, Imaged with X-ray Tomography, Tortuosity 

Calculated & Compared to CAEBAT Library. Additional XFC graphites underway.

Toda NMC532

Superior 

graphite 

SLC1506T

A12 

graphite

Superior SLC1506T gr. 

(XFC)

Phillips A12 gr. (CAEBAT)

Porosity, ε

Tortuosity, 

τ

• A12 tortuosity ~7.6, SLC1506T tortuosity ~4.5

• Particle morphology and orientation play 

strong role
NREL | 17

Particle Elongation in Electrode In-plane 

Direction Strongly Correlates with Tortuosity

• Ideally, elongated particles 

would be aligned in through- plane direction for fast Li+

electrolyte transport

• Without control of particle 

alignment however, increasing 

sphericity is valuable approach 

to reduce the through-plane 

tortuosity as well as tortuosity 

anisotropy

NMC Baseline 34 μm thick

High aspect-ratio & 2-3 particles 

only along through-plane dimension 

bias the anisotropy analysis

More spherical

More tortuous

Tortuosity vs. particle elongation Anisotropy vs. particle elongation
Technical Accomplishment:

3D Microstructure Modeling 

of Heterogeneity
NREL | 19

3D Microstructure Modeling*

Electrolyte 

domain

Objective: Establish a tool that predicts electrochemical heterogeneity induced by 

microstructure morphology. Heterogeneity increases probability of degradation. Li electrode Current collector

Solid domain 

(active material) Simulation domain 

and physics

• Li & econservation

• Charge transfer

Representative 

volume analysis

Geometry

• X-ray 

tomography & 

segmentation

Grey-level Segmented Meshing

• Tetrahedral 

(iso2mesh)

• Density control

*Initiated under CAEBAT in FY17. Activity transferred to XFC program in FY18.

Numerical implementation

• FEniCS finite element package

• Implemented on high 

performance computer 

through message passing 

interface (MPI)

Independent 

subdomains

Photo: https://www.nrel.gov/hpc/peregrine-system.html
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Example 1: NMC Spherical Particles Packed in Series

0.729 x cs,max

Li 

electrode

Positive 

current 

collector 

interface

Solid-phase concentration 

@ 1050s, 1C

0.609 x cs,max

Electrolyte-phase concentration 

@ 2,250s, 1C

Preferential use of active material close to 

separator and particle surfaces

Electrolyte stabilizes to steady 

state in first ~300 seconds

NMC

(solid phase)

Separator

interface

Positive 

current 

collector 

interface

NMC

(pore phase)

Separator

(homogenous medium)

1.09 × ce,0

0.85 × ce,0

Micro vs. macro model comparison

Overpotential,

ηη = φφss − φφee − UU

@ 500s, 1C @ 1,500s, 1C

Similar change of slope

Position along through-plane direction [μm]

Electrolyte 

concentration, ccee⁄ccee,0

(superposed curves, 500s to 2,000s)

Oscillations due to 

variations of 

microstructure parameters

along through-plane

Similar profile

between macromicro model
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Example 2: Graphite Actual Geometry

• Multi-modal feature where large particle lags behind small platelets Separator

0.95 × cs,max

0.63 × cs,max

Separator

10 μm

Local morphology controls the 

local concentration distribution Cumulative 

function

Distribution 

function

Time = 472s, mean intercalation fraction = 0.82
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Example 2: Graphite Actual Geometry

In-plane heterogeneities (none of which is captured by macro model)

0.95 

×

cs,max

0.73 

×

cs,max

Distance from the separator

19 μm

Separator

14 μm

6 μm

0.5 μm

20 μm

Actual graphite, @1C, 200s 

Intercalation fraction displayed slice per 

slice, normal to the electrode thickness

• Significant in-plane heterogeneity, 

with very low concentration located 

on some geometric features (e.g., 

protrusion)

• Probability of degradation increases 

with heterogeneity
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Collaboration and Coordination with 

Other Institutions

Category Institution Role

National 

Laboratories

Argonne National Lab Electrode/cell prototyping, 

characterization, graphite 

transport modeling, post-test 

analysis

Idaho National Lab Charge protocols, aging 

studies, Li plating diagnostics

Universities Purdue University 

(sub to NREL under CAEBAT project)

Stochastic reconstruction for 

microstructure studies

University College of London 

(informal collaboration)

Nano and micro X-ray 

computed tomography

Brigham Young University 

(informal collaboration)

Tortuosity measurement
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Remaining Challenges and Barriers

XFC

• Achieving electrode and electrolyte systems capable of XFC

• System challenges

– Cell, pack and thermal management design

– Safety, control. Avoiding lithium plating

– Infrastructure

Modeling

• Enhance description of transport and interfacial physics in both micro/macro 

models + carbon-binder domain representation in the micromodel

• Determine importance (or not) of electrode-level heterogeneity by coupling 

with degradation mechanisms 

– Lithium plating

– Mechanical stress

• Efficient scale-up of microstructure simulations (~10x)

Graphite NMC

– Present: 20 x 20 x 20 μm3 30 x 30 x 30 μm3

– Goal: 30 x 30 x thickness μm3 40 x 40 x thickness μm3
NREL | 25

Responses to Previous Year Reviewers’ 

Comments

• This project began in FY18 and, hence was not reviewed last 

year.

• Support for this work from Battery R&D, Office of Vehicle 

Technologies, DOE-EERE, is gratefully acknowledged – Samm

Gillard, Steven Boyd, and David Howell

Acknowledgements
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Proposed Future Research

• XFC electrode-level studies 

– Continue graphite microstructure characterization as samples become available (FY18)

– Adopt multi-phase graphite transport model under investigation by ANL (FY18)

– Evaluate fast charge protocols using models (FY18)

– Validate Li plating onset conditions based on ANL, INL, NREL experiments (FY19)

• Perform macro and micro calorimetry at NREL on ANL half cells and full cells (FY18-19)

– Determine heat removal requirements

– Probe calorimetry for onset of lithium plating

• Future extensions (FY19+)

– Couple microstructure heterogeneity 

with degradation

 Predict onset of lithium plating

 Mechanical stress

– Numerical scaling studies with microstructure model

– Optimize/test various 3D electrode architectures

with microstructure model

– 3D cell, pack and thermal management design

Any proposed future work is subject to change based on funding levels.

De-lithiation of graphite electrodes with various morphology
NREL | 27

Summary

• Multi-lab team working to characterize graphite electrodes and better understand transport and 

lithium plating phenomena on fast charge

• Leveraged and enhanced CAEBAT micro/macro models to aid XFC electrode-level studies

• 3D microstructure model was demonstrated and validated with macro model

– Extensible platform for 3D architecture and physics research

– In-plane heterogeneity, not captured by macro models, important for degradation analysis

• Quantified impact of different graphite and NMC morphologies:

– 35% variation in tortuosity, τ, between two graphites characterized thus far 

• Helps quantify reason for electrochemical performance difference measured by ANL-CAMP

– In absence of through-plane alignment, spherical particles better. At porosity, ε ≈ 0.35

 CPG-A12 aspect ratio of 0.65  τ = 7

 Superior SLC1506T aspect ratio of 0.78  τ = 4.5

 Toda NCM523 aspect ratio of 0.85  τ = 3

• Established preliminary electrode/electrolyte requirements

– With present electrolytes, electrodes must have <45μm thickness to avoid Li plating at 6C

– Requirements for 10-minute fast charge of BEV200+ with >85μm electrode

 Electrolytes with enhanced transport (1.5x conductivity, 3.0x diffusivity, transference num. increased by 0.1)

 Low electrode tortuosity (graphite same as NMC, reduced from 6.0 to 2.85)

– Increasing electrode porosity increases fast charge capability at expense of 1C energy density
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.

www.nrel.gov

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.

This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for 

Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. 

Funding provided by U.S. Department of Energy Office of Energy Efficiency and Vehicle Technologies 

Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. 

Government. The U.S. Government retains and the publisher, by accepting the article for publication, 

acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to 

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NREL/PR-5400-71254

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