Beyond Li-ion batteries
The Challenge of Li-Sulfur Batteries
The problems with Li-oxygen batteries
The challenge of rechargeable Mg batteries
Dr. Ran Elazari
Ariel Rosenman
Prof. Gregory Salitra
Daniel Sharon
Doron Aurbach
Bar Ilan university, Israel
Prof. Elena Levi
Dr. Yossi Goffer
Dr. Arnd Garsuch (BASF)
Supported by
BASF
Advantages of Li-S over Li-ion systems
• Higher Theoretical capacity, energy and power density.
• Low cost (1$ per 100g) and abundant raw materials (350 ppm).
• Operability at low temperature (-40˚C).
Bruce, P. G., Freunberger, S. A., Hardwick, L. J., Tarascon, J.-M.. Nature materials 11, 19–29 (2012).
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Outline

What leads to capacity fading of Li-S batteries?
 Lithium metal surface analysis.
 Morphological changes of the composite sulfur cathode.

How Li-S cells’ cycle life can be improved ?




Encapsulation of sulfur inside porous templates.
Carbonate solvent based Li–S batteries.
Sulfur impregnated activated carbon cloth/binder.
The effect of lithium nitrate as an additive for DOL:DME based
electrolyte solution on the cathode side.
Is it possible to have Li-ion-Sulfur batteries instead of

Li-S cells, in order to overcome safety issues ?

 Tin sulfur lithium ion batteries.
 Rechargeable Lithiated Silicon-Sulfur (SLS) Battery Prototypes.
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Working Mechanism
Formation and re-oxidizing Li2Sn
Sulfur-cathode
Discharge
+
+
S8
Li2S8
Li2S6
Li2S4
Li2S2
Li2S
Li-anode
Li-Polysulfudes
diffuse to the anode
Insoluble products
Shuttle
effect
Charge
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Bar Ilan University
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Rechargeable Li sulfur cells: The highest energy
density due to the high electrodes capacity
Ethereal solvents such as DOL:DME with an electrolyte such as LiN(SO2CF3)2
A major problem: limited capacity of the sulfur cathode due to shuttle mechanism.
2Li+S ⇄Li2S ΔG=-425 kJ/mol
Theoretical Energy Density Comparison
Li-S ~2.4V
Li-Ion ~3.8V
1,3 DOL
1,2 DME
LiTFSI
LiNO3
A ‘magic’ additive
The effect of LiNO3 on the surface chemistry and impedance of Li anodes.
Adding lithium nitrate remarkably decreases the
impedance.
The ‘magic’ solution
DOL + DME + LiTFSI + LiNO3
PS = poly-sulfide, Li2Sn
• Impedance spectra of Li electrodes after 18h of storage at OCV in various
electrolyte solutions.
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Accessories for preparation Li slices and
studying Li surface chemistry
FTIR accessory
Lithium
slice
KBr
window
Sealing
gasket
Lithium slice
1 mm thick
Lithium slicing in
solution inside a glove
box
Lithium
slicer
Lithium rod
0.5”- 1 ”
XPS transference holder
cell attached
to Glove Box
cell attached
to XPS
Cell with
tested solution
The effect of LiNO3 on the surface chemistry and impedance of Li anodes
NO3- in solutions oxidizes sulfur up to sulfate (6+)
Solution containing only Li2S6
Solution containing both Li2S6 and LiNO3
• Sulfur XPS spectra of Li electrodes prepared and stored in 1,3-dioxolane
solutions
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Effect of LiNO3 on Lithium metal surface chemistry and impedance.
spectra of Li surfaces prepared and stored for two weeks in:
PURE DOL
Various DOL reduction products.
DOL/0.38M LiTFSI
DME much less reactive.
Li ions enhance DOL reduction by electrophilic assistance.
νn-o peaks are visible between 1000-1250 cm-1.
Pronounced IR bands below 700 cm−1 relates to S-S & Li-S bonds.
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The effect of LiNO3 on Lithium metal surface chemistry and impedance.
• The presence of LiNO3 in solution affectss the surface chemistry of Li
electrodes.
• Its reduction forms LixNOy . It oxidizes Li2Sn (PS) to LixSOy surface species.
• This prevents the shuttle mechanism that avoids full charging of sulfur
electrodes in Li–S cells
Mapping the surface chemistry of Li anodes in DOL/LiTFSI/PS/LiNO3
LiTFSI
LiNO3
LiF
PS
LiXCFY
DOL
Li2NSO2CF3
Li2SO2CF3
LixSOy
Li2S , Li2S2
HCO2Li
LiOR
RCOOLi
LixNOy
Li electrode
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Morphological changes of composite sulfur cathodes.
Opened Li-S pouch
Cells for
post mortem analysis.
Sulfur composite electrodes:
Current collector:
Carbon coated Aluminum foil.
Components:
Elemental sulfur as the active material.
Carbon black as electronically conductive agent.
Polymeric binder.
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AFM topography and comparative
electronic conductivity of cathode surfaces.
Instrumentation
 AFM measurements were performed inside an Ar filled glove-box.
 The glove-box is hanged on bungee chords to reduce vibration.
 Topography, friction and conductivity were measured simultaneously.
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As cycling proceeds - the sulfur cathodes surface becomes
smoother and less electronically conductive.
Ratio of
conductive
areas

Non conductive layers comoposed of
granular features, such as Li2S and
Li2S2, are accumulated on of electrode
surface.
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Cracks are formed during cycling exposing “fresh” internal surface.
0µm2
4
6
0µm 1
8 10 12 14 16 18
0
1.27µm
2
2
3
4
5
6
0
0.39µm
1
4
6
2
8
3
10
12
4
14
5
16
18
0µm
0µm 1
0
2
3
4
5
6
7
1.52µm
1
6
0.07µm
0µm 0.5
0
1.0 1.5
2.0
2.5
0.79µm
0.5
2
1.0
3
1.5
4
2.0
5
2.5
6
7
0µm
0.10µm
 Why cracks are formed during cycling?
 What is happening in the bulk of the sulfur electrodes?
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Sulfur may not be dispersed fully uniformly in
conventional composite electrodes.
AFM
Raman Spectra
SEM and EDS
Green – Carbon , Yellow Sulfur
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Pristine sulfur electrodes:
Non conductive areas are observed due to low
electronic conductivity of large sulfur particles.
AFM, topography, conductivity
Epoxy
Current collector
Carbon – Sulfur
matrix
Epoxy
 Electron diffraction indexed in
terms of the unit cell of α-S8
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Electrodes’ morphology after 16 Cycles:
No elemental sulfur was found.
Li2S was clearly indicated as the main discharge product.
Topography
Upper layer Formed
after cycling
Deflection
 Electron diffraction indexed in
terms of the unit cell of Li2S
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How the changes in the cathode may
affect the cell performance?
Pristine composite
Precipitation
of non sulfur cathodes may contain sulfur
chunks that
are not well mixed with the carbon powder.
conductive
insoluble
Li2S slabs reduce the
During
themass.
first cycles, the sulfur react and dissolve, creating
active
voids and cracks in the composite matrix.
Electrolyte Solution
Non conductive layer
Carbon + Sulfur Matrix
Aluminum Current Collector
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How the changes in the cathode may
affect the cell performance?
Precipitation of non
The carbon matrix collapses in parts,
conductive insoluble
Allowing penetration of electrolyte
The
instability
of the
integrity,
and
thebut
loss
of active
Li
reduce
theelectrode
solution
into the
bulk
negatively
2S slabs
mass
may
lead to the significant
capacity
fading
and poor
active
mass.
affect the
electronic
transport.
cell performance.
Electrolyte Solution
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