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WIR SCHAFFEN WISSEN – HEUTE FÜR MORGEN
Enhanced rate performance in electrode materials for lithium-ion batteries
Juliette Billaud, Florian Bouville, Tommaso Magrini, Fabio Bargardi, Claire Villevieille, André R. Studart
International Battery Seminar & Exhibit
March 20-23, 2017
Page 2
SLS
SINQ
The Paul Scherrer Institut
Page 3
New, better performing materials?
Engineering of existing materials?
Reduced charging times
More autonomy
Low cost
Lifetime
Safety
New, better performing materials?
Engineering of existing materials?
Lithium-ion batteries
Lithium-ion batteries
Page 4
LiCoO2
Graphite
Specific energy
= Specific charge
* Voltage
Slow rates
Low loadings
The example of graphite
Page 5
ca. 95% of commercial rechargeable Li-ion batteries
Low volumetric expansion (10%)
Reasonable specific charge
Low potential
Graphite vs. fast cycling
Page 6 M. Hess, PhD Thesis No. 21240, ETH Zürich Electrodes: SFG6 graphite - ca. 50 µm - 4 mg
Limitation from
stage dense 2 to 1
Limitation from stage 1-2 but
compensated by following transitions
50 mV
overpotential
Graphite vs. different electrode thicknesses?
Page 7 M. Hess, PhD Thesis No. 21240, ETH Zürich
Despite graphite’s:
low cost,
good reversibility,
high energy density
Graphite does not limit discharge performance but
does limit charge performance
Problem: diffusion of Li+ through thick
electrodes
Page 8 Buqa et al., Journal of The Electrochemical Society, 152, A474 (2005)
Graphite vs. particle size & electrode thickness
What improvements have been made so far?
Diffusion of Li in graphite:
very anisotropic
(only within the
crystallographic basal
plane)
SFG 44 (ca. 40 µm) SFG 6 (2-5 µm)
Thin
electrodes
Thick
electrodes High tortuosity
Use of smaller graphite flakes
Improvements for graphite so far
Page 9
Tran et al., Journal of applied electrochemistry (1996)
Aurbach et al., Solid State Ionics (2002)
Use of particles with different morphologies
Other approach, cheaper? Reduction of tortuosity?
Tortuosity?
Page 10
𝜏 =𝐿′
𝐿
Graphics: M. Magrini
Ebner et al., Journal of the Electrochemical Society, 162, A3064 (2015)
Tortuosity = 1
Tortuosity > 1
L’ : Path of a Li+ that intercalates
through an electrode
L : Thickness of the electrode
Average ratio of the length of the actual path taken between
two points and the straight distance between them
Lower tortuosity believed to increase the accessibility of
the intercalation planes of graphite to the Li+
Tortuosity – homogeneisation strategy
Page 11 Doyle et al., Journal of the Electrochemical Society (1996)
Credit: Tommaso Magrini
𝐷𝑒𝑓𝑓 =𝜀
𝜏𝐷0
(diffusion coefficient) (effective diffusion
coefficient)
Use of magnetic alignment with
sacrificial solids
How to reduce the tortuosity?
Page 12
Freeze-casting
Sander et al., Nature Energy (2016) Bahrami et al., Green Chem. (2017)
Co-extrusion with a sacrificial pore former
Bae et al., Advanced Materials (2013)
Can we work directly on the active materials to optimise the architecture?
Reduction of the tortuosity by magnetic alignment
Page 13
Fe3O4 nanoparticles
Only 0.01 – 0.5 vol. % Fe3O4 needed
Studart, Erb, Libanori, Patent WO2011120643, 2011
Erb et al. Science. 2012
Principle of the magnetic alignment
Page 14 Erb et al. Science. 2012
Can we apply this to battery materials…?
Bouville, Le Ferrand et al. Nature Materials. 2015
Approach to reduce the tortuosity
Page 15
Li+
Li+
Aligning perpendicular to the current collector:
- Enhances accessibility of intercalation planes
- Reduces tortuosity of electrolyte in intercalation direction
Shorter and easier pathway
for Li diffusion, even in
thick/highly loaded
electrodes
Simple, scalable and
inexpensive
technique consisting
in applying a low
magnetic field during
fabrication of anode
x 20
Hrot
Electrodes preparation
Page 16
Slurry preparation:
80% graphite flakes
10% PVP
10% super P
Magnet: 100 mT
J. Billaud, F. Bouville et al., Nature Energy, 1, 16097 (2016)
Graphite used: SFG44
XRD
Page 17
Degree of alignment probed by tracking the intensity of the
(002) Bragg peak (corresponding to the basal plane spacing)
C. E. Banks and R. G. Compton, The Analyst, 131, 15 (2006)
(002)
In-plane alignment of the flakes
Cross-section SEM
Page 18
Aligned electrodes Non-aligned electrodes
Orientation not totally random…
FIB-tomography
Page 19
𝐷𝑒𝑓𝑓 =𝜀
𝜏𝐷0
Non-aligned electrodes Aligned electrodes
Rate capability tests
Page 20
Galvanostatic profiles
Page 21
Galvanostatic profiles
Page 22
Overpotential increased by two times more for non-aligned electrodes
Aligned Non-aligned
Long term cycling on thick electrodes
Page 23
Current collector
Current collector
27% Qth
18% Qth
Effect of the calendering on the alignment
Page 24
Intensity of the (002) peak does not increase
until the thickness is reduced of 30 %
Compression with SEM
Page 25
Initial
thickness
Conclusions and outlook
Page 26
Simple and cheap method to align graphite particles and decrease tortuosity of the lithium
paths
High loading electrodes for fast rate cycling obtained
Performance improved solely by changing the inner architecture of the electrode
But:
- large graphite flakes
- high porosity electrodes calendering allows densification by 30%, tests in progress
- optimisation of the process (carbon, binder, ..)
Many more materials to look at!
Page 27
Acknowledgements
BatMat group at the PSI
Complex materials group at the ETHZ
Thank you for your
attention!
Page 28
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