AIMCAL Web Coating Conference Paper AB5, 1:00 … · AIMCAL Web Coating Conference Paper AB5, 1:00...

The Rechargeable Battery Company™

Vacuum and Atmospheric

Coating and Lamination

Techniques Applied to Li-S

Battery Fabrication

AIMCAL Web Coating Conference

Paper AB5, 1:00 PM

Wednesday, October 26, 2011

John Affinito,

Sion Power Corporation

Chief Technical Officer

520-822-6008

[email protected]

Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 2

Upper Plateau: ~420 mAh/gS

Lower Plateau: ~1260 mAh/gS

1,672 mAh/gs

2,572 Wh/kg

2,835 Wh/l

Outline of Presentation

Li-S Basics

– Why develop Li-S? – Specific Energy.

– The Li-S Discharge Characteristic.

– The Upper Plateau Polysulfide Shuttle.

– Lower Plateau Li2S precipitation,

in relation to cathode porosity,

microstructure and solvent effects.

Sion’s solutions for Li-S Cycle Life,

Safety and Energy improvements.

The Future Li-S Cell.

Sion’s Old Technology Li-S cells

enabled a record setting UAV Flight.

Summary.

Soluble

Polysulfide

species diffuse

from the

cathode to the

anode and self-

discharge the

Upper Plateau,

with loss of

~400 mAh/gS.

Li2S

precipitation

clogs the

cathode,

polarizes the

cell and leads to

~400 mAh/gS

capacity loss at

the end of the

Lower Plateau.

Leaving

~800-900 mAh/gS


Why Choose Lithium and Sulfur?

For high specific energy and volumetric energy density.

Li-S: <OCV> ~2.18 V

Theoretical ~2,572 Wh/kg

Theoretical ~2,835 Wh/l

Compare With Li-ion Energies:

Theoretical ~600 Wh/kg

Theoretical ~1,800 Wh/l

ΔG ~ - 422 kJ/mol

S8 + 16e- + 16Li+ → 8Li2S The Li-S couple has the highest

theoretical specific energy and energy

density of any pair of solid elements.

Li-ion is currently at/near, practical limit of ~40% of theoretical specific energy (<250 Wh/kg).

At 350 Wh/kg, Sion’s baseline Li-S cell is only at 14% of theoretical specific energy.


First Discharge Only

The Li-S Discharge Characteristic

Tells Much, but not all, of the Story

828 22 SLiLieS

4282 222 SLiLieSLi

2242 4442 SLiLieSLi

SLiLieSLi 222 8884

~1,672 mAh/g(S)

Theoretical: ~2,572 Wh/kg(S+Li)

~2,835 Wh/l(S+Li)

1-Li2S Nucleation

Polarization Begins.

2-Highest Conc. Li2Sx Species.

3-Highest Viscosity.

High Solubility

Solid

Moderate

Solubility

Very Low

Solubility

Upper

Plateau

Upper

Plateau

- Fast

Kinetics

Lower

Plateau

- Slow

Kinetics Lower

Plateau

Very Low

Solubility


The high solubility and fast kinetics of

the Upper Plateau species leads to the

Polysulfide Shuttle that results in near

complete loss of the upper plateau

capacity, ~400 mAh/gS.

First Problem: Polysulfide Shuttle

The Li-S discharge curve looks great.

But…..What are the real world problems?


The Polysulfide Shuttle Causes

Massive Self-Discharge of Li-S Cells

Soluble Li2Sx

species on the

Upper Plateau

diffuse to the

anode where

they are

reduced to

Li2S.

This results in

Rapid Self-

Discharge and

loss of the

Upper Plateau

capacity, ~400

mAh/gS.

Polysulfide

Shuttle


About ¼ of Total Li-S Cell Discharge Capacity

is Lost Due to the Polysulfide Shuttle

. Still ~400 mAh/gS missing?


With typical cathodes and solvents used in Li-S

cells, the low solubility and slow kinetics of the

Lower Plateau species, and clogging susceptible

cathode structures, result in polarization that is

responsible for loss of another ~400 mAh/gS: this

time from the end of the Lower Plateau.

– This effect becomes more severe as the discharge rate is

increased and/or as solvent is depleted in parasitic Li-

Solvent reactions.

– Controlling cathode porosity, detailed cathode

microstructure, solvent type and solvent level are

absolutely critical to optimize specific energy.

Second Problem: Li2S Precipitation


Cathode Diffusion Limitations, and Li2S Precipitation at the

End of the Lower Voltage Plateau, Limit Li-S Cell Capacity

Li2S deposits

block cathode

porosity on anode

facing surface,

limiting capacity to

<1,250 mAh/gS, in

current high

energy-high rate

Li-S cell designs.

Without anode

protection, solvent

is also lost on

each cycle, further

increaseing Li2S

precipitation and

capacity loss on

each cycle. Anode facing cathode surface at the end of the

lower voltage plateau after the 20th discharge.


Sion’s Electrochemical Model Predicts that Blocking

of the Cathode Porosity Leads to End of Cycle

Porosity is not blocked

on the Upper Plateau

(blue trace) due to the

high solubility of upper

plateau polysulfides.

Blocking begins as the

lower plateau

discharge begins, due

to the low solubility of

species. Polarization

spikes up, ending the

cycle as blockage of

the anode facing

surface of the cathode

reaches the percolation

limit (~16% open, red

trace) at a sulfur

utilization of ~70%.

Cathode Blocking of Baseline Cathode as a

Function of State of Charge and Distance

from Anode Surface, at C/5 discharge rate


Cell Capacity is Strongly Influenced

by Electrolyte/Solvent Selection Cathode Specific Capacity vs. Solvent Type, at C/5 Discharge Rates

(350 Wh/kg design, No Anode Protection and Cells Not Cycled Under Externally Applied Pressure)

Specific Capacity for 5 hour discharge (mAh/g)

(for 350 Wh/kg cell formats)

Many solvent

systems can re-

solubilize Li2S.

However, to be useful

with an unprotected

metallic Li anode, the

solvent must be

relatively benign

towards metallic Li.

To date, this has

limited S-Utilization

to less than about

1,250 mAh/gS at

reasonable

discharge rates

(>C/5).

Solvent 7

Solvent 6

Solvent 5

Solvent 4

Solvent 3

Solvent 2

Solvent 1


Li DoD ~50%

Increasing

Cycle #’s

Cell Performance as a Function of

Cathode Structure (without anode protection)

With conventional cathode structure:

– The pores plug while cycling.

• Cell reaches polarization induced

voltage cut-off at lower capacity

with each cycle as solvent

depletes.

Cycling with Cathode Structure

Typical of Current Li-S Cathodes Cycling with Cathode with Engineered

Topology, Microstructure and Porosity

With engineered cathode structure:

– Pores don’t plug while cycling.

• Cathode polarization is reduced

and capacity stays higher longer,

even as solvent depletes.


Cycle Life, Safety and Capacity issues with the

1st Generation of Li-S Cells (the last 40 years)

When the shuttle is stopped, solvent depletion, due to the

metallic Li anode reacting with the electrolyte, limits cycle life.

Safety is limited by metallic Li reacting with sulfur species.

Specific Energy is limited by Upper Plateau self-discharge,

through the Polysulfide Shuttle, by Lower Plateau

precipitation of Li2S/cathode clogging and by cell design.

– The shuttle can be suppressed by Sion’s NOx additives, or by

physical membranes protecting the anode.

• NOx additives do not stop solvent depletion, membranes can.

– Li2S precipitation can be mitigated by either, or both, of:

• Solvents more aggressive to Li2Sx in the cathode; or

• A high permeability/high throughput cathode microstructure that

doesn’t clog and improves overall transport through the cathode.


How can the Li-S cycle life,

safety and capacity issues be

overcome?

What are Sion’s approaches?


Increasing Li-S Cycle Life (the Future Cell)

Key to increasing cycle life is stopping the metallic Li anode

from reacting with solvents and controlling Li morphology.

– Sion’s Approach – Protect the Metallic Lithium Anode

and Decouple the Anode and Cathode Chemistries:

• An atmospherically coated, thin film, releasable substrate;

• A vacuum deposited current collector;

• Vacuum Deposited Li (VDLi);

• Vacuum Deposited Anode Stabilization Laminates (ASLs);

comprising multi-layer ceramic/polymer protective coatings;

• A compliant, atmospherically coated, polymer gel separator;

• A dual phase solvent system; and

• Externally applied uniaxial pressure (controls morphology).

Cathode issues are secondary with respect to cycle life.


Functional Description of Sion’s Future

Li-S EV Cell Layered Elements Stabilizes Li Morphology and ASL structure

Increases Li smoothness and specific energy

Increases cycle life/smoothness, carries current

Allows thinner, smoother, Li. Allows reactive

doping of Li to improve electrochemistry

Blocks solvents from contacting, and

reacting with, metallic Li anode Transmits pressure uniformly to Li, stabilizes

ASL, reservoir for dual phase anode solvent

Reservoir for polysulfide aggressive dual

phase cathode solvent, increases S-utilization

Structurally stable cathode does not collapse

under applied pressure, and optimized pore

structure increases S-utilization

Tie layer adheres cathode to current collector

Carries current to/from cathode

Stabilizes Li Morphology and ASL structure


In Sion’s Future Li-S EV Cell Construction,

All Major Elements are Coated

Vacuum

Coated

Atmospherically

Coated

Atmospherically Coated


– Sion’s Approach – Protect the Metallic Lithium Anode

and Decouple the Anode and Cathode Chemistries: (all the same methods used to increase cycle life on the previous slide)

• An atmospherically coated, thin film, releasable substrate;

Improving Li-S Safety (the Future Cell)

Key to improving safety is stopping the metallic Li anode

from reacting with sulfur and controlling Li morphology.

• A vacuum deposited current collector;

• Vacuum Deposited Li (VDLi);

• Vacuum Deposited Anode Stabilization Laminates (ASLs);

comprising multi-layer ceramic/polymer protective coatings;

• A compliant, atmospherically coated, polymer gel separator;

• A dual phase solvent system; and

• Externally applied uniaxial pressure.

Cathode issues are secondary with respect to safety.


Improved Safety with Sion-BASF Compliant Gel

Layer Cycling Under Pressure (the Future Cell)

Thermal Ramp Test: Fully charged Li-S cells ramped at ………

………………………. 5 oC/min after 20 cycles, Li DoD ~50%.


Metallic Li Anode Morphology is Stabilized by Uniaxial

Pressure: Smoother is Safer and Promotes Cycle Life

A highly mud cracked

coated cathode.

Very smooth

plateaus separated

by large mud-cracks

500 µm

100 µm

100 µm

Top: Cycled under pressure:

•Remains dense Li metal;

•Retains original 50 µm

thickness; and

• Is very smooth except for

extrusion into cathode

mud-cracks and negative

impressions of the

cathode the surface.

2 Anodes initially 50 µm

thick, cycled from each

side, after 50 cycles

At a Li DoD of ~50%.

Bottom: Cycled without pressure:

•Becomes highly mossy;

• Is over 200 µm thick; and

• Is very rough on all scales and

surfaces.


Under Pressure, Anode Surfaces Mimic Cathode Surfaces

and Cathode Imprints are Muted by a Gel Layer

A differently

coated cathode.

Relatively smooth,

without mud-cracks

and with relatively

small features.

50 µm 50 µm

Anode cycled under

pressure:

•Remains dense Li

metal;

•Retains original 50 µm

thickness;

• Is very smooth and

approximately mimics

the cathode surface;

and

•Cathode features are

muted on anode

surface due to

intervening gel layer.

A single anode.

Initially 50 µm thick,

cycled from each side,

after 450 cycles - with a

semi-compliant gel layer

between anode and

cathode. Cycled at a Li

DoD of ~50%.


Increasing Li-S Capacity (the Future Cell)

Key to increasing Li-S capacity is reduction of cell mass, increasing

S-utilization by optimizing porosity, solvent type and solvent level.

Sion’s Approaches:

• A variety of anode protection methods reduce solvent loss and maintain

proper cathode function/capacity while minimizing solvent requirements;

• With the anode protected, and employing Sion’s dual phase electrolyte

methodology, use solvents more aggressive towards polysulfides, particularly

towards Li2S, on the cathode side of the cell to increase sulfur utilization;

• Engineer cathode topology, microstructure and porosity to limit pore blocking

to increase transport and permeability to increase S-utilization.

While the previous two techniques/bullets improve cathode function/sulfur

utilization, resulting in a small cycle life increase, the cells will still fail due

to solvent depletion, eventually, without anode protection.

Anode issues are secondary with respect to energy.

• Optimize cell design to minimize the mass of inactive components.


Use Of New Technologies (the Future Cell)

Dramatically Improves Li-S Cycle Life

The new technology

cells are still cycling

End of Life of

Old Technology Cells End of Life of

New Technology Cells


First Commercial Li-S Application is Unmanned

Aerial Vehicles – UAVs (using Sion’s old technology Li-S cells)

Flew to >70,000 ft where temperature is < -60oC.

“QinetiQ's Zephyr 7 UAV Exceeds Official World

Record for Longest Duration Unmanned Flight.”

23 meter Wing Span

July, 2010

Used solar power to fly & recharge batteries by day.

Official world record: >14 days of continuous flight.

Flight was powered by Sion Li-S batteries at night.


Projected Discharge Capacity of Sion

EV Cell by the End of 2013 (the Future Cell)


It is Unlikely that Li-ion Specific Energy Will

Match Even 2010 Li-S Specific Energy by 2020

For Li-ion to continue on this trend line will require either new anode

materials, new cathode materials or both. Li-S requires a new

cathode structure and anode protection.


Comparison of 2010 Li-S Performance

Parameters to Projected 2013 Li-S Cells

Current Sion Li-S Cell

• 63 mm x 43 mm x 11.5 mm

• 2.8 Ah, 350 Wh/kg, 320 Wh/l,

25-80 cycles

• Wound Prismatic Design

Projected Sion Li-S Cell in 2013 (the Future Cell)

• 121 mm x 106 mm x 8.5 mm

• 25 Ah, >500 (Wh/kg, Wh/l, cycles)

• Stacked Plate Design

Project: >600 (Wh/kg, Wh/l) and >1,000 cycles by 2016


Summary

Li-S cycle life is dominated by anode-electrolyte reactions.

– The cathode plays a secondary role in Li-S cycle life.

Li-S safety is dominated by anode-sulfur reactions.

– The cathode plays a secondary role in Li-S safety.

Li-S specific energy is dominated by cathode structure,

solvent and discharge product volume requirements.

– Solvent type and cell design also play important roles.

• When nitrates or barrier layers control Upper Plateau capacity loss due to the

shuttle, the anode plays only a secondary role in Li-S cell specific energy.

With Sion’s new hardware coming online, cells

fabricated with Sion’s new anode and cathode coating

technologies are beginning to show dramatic cycle life

improvement over old technology Li-S cells.


Some of the Sion Team and One of

the Anode Vacuum Web Coaters Thank You.

Any Questions?

Acknowledgements: This work has been supported in part by the United

States Department of Energy, Advanced Research Projects Agency –

Energy (ARPA-E), under Award Number DE-AR0000067.

Now hiring,

process

Scientists,

Engineers and

Technicians for

both Vacuum

and Atmospheric

coating. Call:

(520) 822-6008

AIMCAL Web Coating Conference Paper AB5, 1:00 … · AIMCAL Web Coating Conference Paper AB5, 1:00...

Documents

Transcript of AIMCAL Web Coating Conference Paper AB5, 1:00 … · AIMCAL Web Coating Conference Paper AB5, 1:00...