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Green Materials & Processes of Lithium-Ion Battery

Paul Ho

Nano and Advanced Materials Institute (NAMI)

Content

• NAMI Lithium-ion Battery Researches • Green Materials & Processes for Lithium-

ion Battery – Sustainable and Biodegradable Polymeric

Separator – Non-fluorinated Binding Materials for

Battery Electrode – Green Manufacturing Process for Lithium-

ion Battery

• Summary

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NAMI: An Applied Research Centre

Ideas Research

Traditional Research, Development & Implementation Cycle

Bench-top Prototypes

Technology Development “Scale-up”

Manufacturing Refinement

Industry, Startups

Academia, Universities

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NAMI established in 2006 by Hong Kong Government to be

an integral part of Hong Kong’s Applied Research Eco-system

Applied R&D Centres

Applied Research Eco-system

The Promise of NAMI

Developing core competencies on

advanced materials

Providing technology

upgrade to local enterprises

Training researchers for

HK’s talent pool

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NAMI’s mission is to develop competencies on advanced materials to support industries with technology upgrade while developing talents

Market Sector & Core Competence

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Construction Materials Environmental Technologies

Sustainable Energy

Solid State Lighting & Display

Bio & Healthcare

Areas of Research

Chemistry/Chemical Engineering/Biochemistry

Material Science/Materials Engineering

Physics

Mechanical/Electrical/Electronic Engineering/Civil

Engineering

Biochemistry/Biotechnology/Environmental

Engineering

NAMI Talents

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NAMI Mentoring Program

Develop talent pool

Provide motivation

Offer support

Share the skills,

knowledge, experience and insight

Establish a network of

professionals

PhD 51% Master

32%

Degree 17%

Academic Qualification

~150+ experts conduct materials

R&D for industries

HK Graduate

74%

Overseas Graduate

15%

Mainland Graduate

11%

NAMI Lithium-ion Battery Researches

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Rechargeable Lithium-ion Battery Market

• Lithium-ion battery is growing rapidly because of the excellent energy density and reasonable cost

• The market is ~ $22 billion in 2012 and will grow to ~ $78 billion in 2020.

• Growth is expected in all segments, with significant growth in renewable energy storage and HEVs/EVs.

• We are concurrently running more than 10 Lithium-ion battery applied research projects for our industrial sponsors

Global Lithium-based Battery Market (in USD Billion), 2009-2020

Source: International Information Technology

NAMI’s Lithium-ion Battery Materials

Cathode Anode Electrolyte Separator

Doped nano-LMO with high power density

Li-rich NMC with high energy capacity

Core@shell Si with high energy density

Doped nano-LTO with high power density

Electrospun PVDF with high porosity

Ceramic-coated separator

Additives offers overcharge protection

Additives offers thermal protection

High voltage electrolyte formulation

LTO-coated graphite with good low-temperature performance

Products and Applications from NAMI’s Lithium-ion Battery Materials

Wearable Devices

Fast-Charging High Power

Safe Extreme

Temperature

Green Materials & Processes for Lithium-ion Battery

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Lithium-ion Battery Manufacturing Steps for Lithium-ion Battery Manufacturing

• Electrode Coating: The active electrode materials are coated on metallic foils

• Cell Assembly: Separator is sandwiched between the anode and the cathode and assembled into casing

• Formation: Activate the battery materials and transforming them into a cell ready to be used

Mixing Coating Pressing Assembly

Formation Aging Products

Lithium-ion Battery Manufacturing Challenges for Environment and Sustainability

Conventional

Organic solvent-based slurry for electrode preparation Issues: 100% recycled required, high energy consumption due to high boiling point

Fluorinated polymer as binder for electrode materials Issues: Waste and pollution

Synthetic polymer as separator Issues: Waste and pollution

Lithium-ion Battery Manufacturing

NAMI Green Materials & Processes NAMI Green LIB

Water as Solvent for both cathode and anode electrodes preparation

Non-fluorinated Water Soluble Binder

Natural Polymer derived separator

Separators Characteristics and Structures

• Requirements for separator in Lithium-ion Battery

– Chemically and electrochemically stable even under repeated cycles of charging-discharging

– No release of impurities over time

– Compatible with corrosive electrolyte at elevated temperatures

• Structure of separators

– Microporous membrane separators (Fig. 1)

– Modified microporous membrane separators (Fig. 2)

– Non-woven mat separators (Fig. 3)

Fig. 1 Fig. 2 Fig. 3

Typical Separator Materials • Base Materials for Common Separators in Lithium-ion Battery

– Microporous membrane separators, e.g. poly(propylene (PP), poly(ethylene) (PE), poly(vinylidene fluoride) (PVDF), poly(acrylonitrile) (PAN) and poly(methyl methacrylate) (PMMA)

– Modified microporous membrane separators, e.g. PP, PE and PVDF

– Non-woven mat separators , e.g. PVDF, PAN and poly(imide) (PI)

PP PE PVDF

PAN PMMA PI

• Impacts to Environment

– All are non-biodegradable polymers

– The production of these polymers emits greenhouse gases

– PVDF is a fluorinated polymer and will emit fluorinated gas during incineration

Green Separators

• Sustainable Polymeric Materials

– A sustainable polymer is a plastic material that addresses the needs of consumers without damaging our environment

– The feedstock for sustainable plastics are renewable, such as plants.

– Cellulose in plants is one of sustainable and renewable feedstock as the base materials for the separator in lithium-ion battery

• Cellulose-based Composite Nonwoven Separator

– Nonwoven separator has higher porosity and thus higher conductivity and better rate capability and capacity retention

– Good electrolyte wettability

– High thermal stability due to low shrinkage

– Needs to functionalize to improve stability

Cellulose

A SEM image of cellulose-based composite nonwoven separator

Typical Binder and Solvent • Requirements for Binders used in Lithium-ion Battery

– Chemically and electrochemically stable, under repeated charging-discharging cycles

– Compatible with electrolyte at elevated temperatures

• Common Electrode Binder and solvent

– Poly(vinylidene fluoride) or PVDF is widely adopted as binder for both the anode and cathode slurries

– Organic solvent N-methyl-2-pyrrolidone or NMP is used to dissolve PVDF for the preparation of slurry in the electrode coating step.

• Impacts to Environment

• PVDF is a non-biodegradable fluorinated polymers, which release fluorinated gas during incineration

• NMP is an organic solvent which needs to be 100% recovered

• Impacts to Lithium-ion Battery Cost and Performance

• PVDF and NMP are relative expensive

• Fluorinated compound from PVDF degradation can shorten the battery lifespan

PVDF

NMP

Green Binder Materials

• Candidates include sodium carboxymethyl cellulose (CMC) / styrene-butadiene rubber (SBR), polyvinyl pyrrolidone (PVP) and polyethyleneimine (PEI) and their derivatives

• They allow the use of water as solvent (water soluble binders) and create less environmental problem

• Ease of processing

– NMP has a boiling point of > 200 C and thus reduce energy cost of drying

– Reduce burden on exhaust and humidity control

• Use of natural polymer will further enhance the sustainability

CMC SBR Sodium Alginate

Typical Cell Manufacturing Process

• Mixing of the electrode materials

• Coating of the substrate and drying of the NMP organic solvent

• Minimization of porosity by means of compression

• Film cutting, cell stacking and electrolyte filling

• Activation by specific charging-discharging program

Mixing Coating Pressing Assembly

Formation Aging Products

Green Cell Manufacturing Process • Water is used as solvent comparing to the use of expensive and harmful

organic solvent NMP

• Green binder that is soluble in water will be used, natural and/or fluorine-free polymer will be used

• Ease of process control (humidity), no VOC issue, save energy for the drying process

Water Vapor to be removed instead of NMP

Comparison Table

Conventional lithium-ion battery Green lithium-ion battery

Binder for electrode fabrication Binders soluble in organic solvent

only (e.g. PVDF) Water-soluble binders

Solvent for electrode fabrication N-methyl-2-pyrrolidone (NMP) Water

Solvent toxicity High Nil

Operational / material costs High

NMP, ~US$ 25/L PVDF, ~US$ 20/kg

Low Deionized water, ~US$ 0.015/L

Water-based binder, ~US$ 5.6 /kg

Processing energy for electrode coating High

NMP b.p. > 200 C Low

Water b.p. 100 C

Waste treatment / Exhaust or solvent recovery

Complicated Simple

Green Cell Manufacturing Process in NAMI

Anode Slurry Anode Coating Cathode Slurry Cathode Coating

Anode drying Cathode drying

Coating steps of anode and cathode electrodes

Green Lithium-ion Battery Cell Performance

For comparison, same cathode and anode formulations were used except the binders • The first cycle efficiency is virtually the same between the two batch of cells made by

the two different binders shown • The impedances of the two cells are comparable • There is no difference in cycling performance

Battery cell: Anode: graphite Cathode: LCO Separator: ceramic coated nonwoven PET

0 20 40 60 80 1000

20

40

60

80

100

120

NMP-based Process (PVDF binder)

Water-based Process (water-based binder)

Cycle number

Ca

pa

cit

y R

ete

nti

on

/ %

Summary

• Green materials and processes can be used in Lithium-ion battery manufacturing without impacting the cell performance

• The overall manufacturing is more sustainable and the cost can be reduced

• More research and development is needed to formulate and functionalize new materials to allow the use of these green materials and processes

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ENERGY SAVING

ENERGY STORAGE

ENERGY GENERATION