3D-Electrochemistry Designing and resolving the

microstructure of an electrode Gaëtan Damblanc

Addition of a 3D electrochemistry model

Applies to idealised or ‘real’ geometries

Battery Cell Battery modules/packs In Situ

Increasing Length Scale

Extension to the Development

MicroStructure

Modeling

Battery Simulation Module

Motivations

What is a Li-ion Battery?

Designing the microstructure: The 3D approach

STAR-CCM+ Li-ion Battery Cell Model

Example of a 3D Numerical model

Future developments and conclusion

Agenda

Cost reduction for the design

– Minimise the number of tests and experiments

– Identify at the early stages of the development potential problems

Process and research speed up

– Parameterisation and optimisation methods

Improvement of the understanding of the phenomena taking place

– Performance

– Ionic and electronic transport

– Ageing

– Short circuit

Motivations

What is a Lithium -ion Battery?

𝑳𝒊𝑪𝒐𝑶𝟐 𝑳𝒊𝟏−𝒙 𝑪𝒐𝑶𝟐 + 𝒙𝑳𝒊+ + 𝒙𝒆−

𝒙𝑳𝒊+ + 𝒙𝒆− + 𝟔𝐂 𝑳𝒊𝒙𝑪𝟔

Positive and negative half reactions for a LiCoO2 cathode:

The electrodes are made of porous active materials placed in a liquid

non-aqueous electrolyte

What is inside a Li-ion Electrode?

+ -

Geometrically resolved electrode – Interfacial surface area

– Volume/porosity fraction

– Tortuosity

Local interactions – Voltage distribution

– Li-ion pathways

– Li-ion concentration

– Short circuiting

– Thermodynamic effects

– SEI growth

Material interactions – Active material

– Liquid or Solid Electrolyte

– Binders, conductive additives

Contraction and Expansion – During the intercalation process

Advantages of the 3D approach

SEI

Tortuosity

The Li-ion Battery Cell model

Section across a typical Li-ion cell

Solid particles structure is to be resolved or

represented by a simpler, regular structure (e.g.

cylinders, grid etc.)

Geometry-resolved model

We suggest to discretize separately solid and fluid regions within an electrode, with the desired level of complexity Within solid structure, one can account for active and passive materials (e.g. active material and conducting aid).

Chemical reactions take place at the solid-electrolyte interphase (SEI): standard form of equations can be used, with special conditions at interfaces.

The model of a Li-ion battery requires solution of the following equations: – Salt concentration in electrolyte;

– Concentration of Li in solid part of electrodes;

– Potential in solid;

– Potential in electrolyte;

– Thermal energy.

Flow will initially be neglected, but may be included in the future (as well as volume change during charging and discharging to account for expansion/contraction).

Crucial: conditions at the interfaces...

The Li-ion Battery Cell model

Lithium (Li+) is transported into and out of particles by diffusion:

We assume here a binary electrolyte and express the

conservation equation for Li-salt in the liquid phase as follows

The potential in the solid phase, Φ1, is computed from the

following equation:

The potential in liquid, Φ2, can be computed from the following equation:

The main equations

Interface Conditions

Local current density at solid active surface is modelled as (Buttler-Volmer relation):

cs – Site concentration of solid phase

(maximum possible value of c1).

k – Rate constant

Rsei

– Solid-electrolyte-interface resistance

Ueq

– Equilibrium potential of the active material

with

The 3D Numerical Model Definition

• Cathode Collector – Aluminum foil 10µm thick (δkp),

• Cathode active material – LiMn2O4 80µm thick (δp), particle diameter 10µm, target porosity 40%

• Separator - 10µm thick (δs), porosity 40%, MacMullin number 5

• Anode active material – Graphite 96µm thick (δn), particle diameter 20µm, target porosity 40%

• Anode Collector – Copper foil 10µm thick (δkn)

• Electrolyte – ethylene carbonate/ethyl methyl carbonate 50:50 mix, salt - LiFP6

• Overall unit cell dimensions - 25 µm by 25 µm by 206 µm

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Model Definition - Cathode

Polyhedral mesh

2.8 million cells

Solid & electrolyte resolved

STAR-CCM+ CAD tool

40% Porosity

17

Model Definition - Anode

Polyhedral mesh

1.2 million cells

Solid & electrolyte resolved

STAR-CCM+ CAD tool

40% Porosity

Anode Active Material - Graphite

Mesh Details

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Conformal Mesh

Prism Layer at the SEI

Active Material

Electrolyte

The full electrode to be resolved – Mesh view

Symmetrical boundaries on all external walls

The properties of the Active Material are

defined in the physics continua

– Electrical conductivity

– Diffusion coefficient

– The parameter can also account for

a dependence on the Temperature and

Li-Ion Concentration

The Butler-Volmer relations parameters

are defined in a panel under the relevant

Liquid/Solid phases interfaces

The Physics set-up and Butler-Volmer relation

Open questions:

• After setup: cell capacity (Ah / coulomb)

• During simulation: State Of Charge (SOC) and

corresponding Open Circuit Voltage (OCV)

• Additional: average electrode concentrations to reinitialize at different SOC / OCV

Provide only:

• Initial Setup (electrode regions & initial conditions)

• (Open Circuit) Voltages where cell is defined as fully

charged / discharged

Report computes amount of Li+ which can be shuttled

between electrodes until upper / lower voltage attained

Report for Battery Cell state

Report for Battery Cell state

Results:

C/10 full discharge rest

Results during Charge

Lithium salt concentration at 3 transient points through a charge

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3D model

1D model

Solid Phase Concentration – Liquid Phase Electric

Potential

1 min 2 min 3 min

Li-ion Concentration diffusion in solid phase

Electric Potential in Electrolyte

Next Steps and Conclusion

Initial results presented

Publication of validation paper

Begin working with external users

Available in STAR-CCM+ 7.06

Future developments

• Improve the model build process

• Extend work to “real” geometries

• Model half-electrode to focus on the Cathode or Anode design

• Measure SEI overpotential

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Many thanks to my colleagues who actively work on this innovative topic

– Dr Robert Spotnitz from Battery Design LLC

– Milovan Peric

– Steve Hartridge

– Boris Kaludercic

– Christian Walchshofer

THANK YOU!

Aknowledgement