AIMCAL 2016Memphis, TN

Thin film coatings on lithium metal for Li-S batteries

Stephen Lawes, Research Scientist

OXIS Company Background

$70 million raised to date

Expanding rapidly: 3 fold increase in the number of employees since 2012, 60

today Highly trained staff (14 PhDs, 13 MSc/MA)

Cutting edge R&D facilities (i.e. second largest high specification dry room in Europe)

Strong patent portfolio protecting IP (79 patents granted, 97 pending, encompassing 27 families)

OXIS have been working on Li-S since 2005 at CulhamScience Centre (Oxfordshire, UK)

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Benefits of Li-S technology High gravimetric energy

Theoretical: 2500 Wh/kg vs. 500 Wh/kg for Li-ion Practical: 400 Wh/kg achieved vs. 250 Wh/kg for Li-ion

Low cost No expensive cathode material

Environmentally friendly No heavy metals such as Cobalt and Nickel

Safety Tolerant to mechanical abuse, nail and bullet penetration,

overcharge, short circuit

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REVB

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Introduction to Li-S batteries

Li

Curr

entc

olle

ctor

Curr

entc

olle

ctor

Li+

Li+

Li+

Li+

Li+

Li+

(-) (+)

Sepa

rato

r

+-

Discharge

Load / Charger

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Elemental sulfur

Conductivecarbon

Binder

Li-S Li-ion

Specific capacity 1675 mAh/g 200 mAh/g

Theoretical energy density

2500 Wh/kg2800 Wh/L

500 Wh/kg1800 Wh/L

Achievable energy density

500 Wh/kg700 Wh/L

300 Wh/kg900 Wh/L

Current cycle life ~100 1000+

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Introduction to Li-S batteries

Li anode S/C cathodeElectrolyte

Li+e-

Li+e-

Li+e-

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Introduction to Li-S batteries

Li anode S/C cathodeElectrolyte

Li+ e-

Li+ e-

Li+ e-

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Problems with lithium metal anodes

1. Dendrites/mossy lithium

3. Large volume change

2. Dead lithium

4. Electrolyte decomposition

5. Irreversible Li corrosion

G. Zheng et al. Interconnected hollow carbon nanospheres for stable lithium metal anodes. Nature Nanotechnology, 2014

Other, 5% Separator, 5%

Lithium, 15%

Cathode, 25%

Electrolyte 50%

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Lithium protection Less electrolyte needed

A typical distribution ofmasses in an Li-S cell

Electrolyte can represent up to 50% of the weight of a cell!

Successful lithium protection will mean less electrolyte is required

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Lithium metal protective coatings

Coating requirements: Stable against lithium and electrolyte Mechanically strong Uniform thickness Flexible Ionically conductive Electrically insulating High transference number

"The ideal protective layer for a lithium metal anode needs to be chemically stable to protect

against the chemical reactions with the electrolyte and mechanically strong to

withstand the expansion of the lithium during charge.“ – Prof. Yi Cui, Stanford

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Lithium protection extends cycle life

80% BoL

Protected lithium

Unprotected lithium

Increase in surface area leads to electrolyte

depletion and cell failure

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Lithium protection at OXIS Energy

Unprotected lithium50 cycles

High surface area Electrolyte depletion

Protected lithium50 cycles

Less mossy growth Longer cycle life

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Polymers vs. ceramics

Polymer coatings: Flexible Easy to process Ionically conductive Low interfacial

resistance Swells in electrolyte Delamination Low shear modulus

Ceramic coatings: Hard Ionically conductive No swelling in

electrolyte Single-ion transport Brittle High interfacial

resistance Hard to process

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Hybrid coatings

Combining the benefits of both polymers and ceramics Flexible to withstand large volume changes

Hardness to prevent mossy lithium growth

Ionically conductive to allow fast lithium transport

Stable against electrolyte

Processable for low-cost, scalable coatings

Polymer/ceramic nanocomposite

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Coating techniques

Requirements for coating technique: Low temperature (< 150°C) Dry atmosphere (0.25% RH) Thin coatings (100nm – 5µm) Pinhole-free coatings Double-sided coatings Able to handle flexible, soft substrate Scalable

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Conclusions

Reduced mossy lithium growth and electrolyte depletion with protective coating on lithium

Improved cycle life for high energy density lithium-sulfur cells

Developing new materials for lithium protection

Optimizing coating technique for uniformity, thickness, etc.

All components are strongly interdependent (anode, electrolyte, cathode)

How do we maintain/improve cycle life when going to higher energy density?

www.oxisenergy.com

Thank You For Listening