Study of a buffer layer based on block copolymer electrolytes, between the lithium metal and a ceramic electrolyte for aqueous Lithium-air battery

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electrolytes, between the lithium metal and a ceramic electrolyte for aqueous Lithium-air battery

Louise Frenck

To cite this version:

Louise Frenck. Study of a buffer layer based on block copolymer electrolytes, between the lithium metal and a ceramic electrolyte for aqueous Lithium-air battery. Electric power. Université Grenoble Alpes, 2016. English. �NNT : 2016GREAI041�. �tel-01532066�

THÈSE

Pour obtenir le grade de

DOCTEUR DE LA COMMUNAUTE UNIVERSITE GRENOBLE ALPES

Spécialité : Matériaux, Mécanique, Génie civile, Electrochimie

Arrêté ministériel : 7 août 2006

Présentée par

Louise FRENCK

Thèse dirigée par le Pr Renaud Bouchet

préparée au sein du Laboratoire d'Electrochimie et Physicochimie des Matériaux et Interfaces dans l'École Doctorale IMEP²

Study of a buffer layer based on block copolymer electrolytes, between the lithium metal and a ceramic electrolyte for aqueous Lithium-air battery

Thèse soutenue publiquement le «16 septembre 2016», devant le jury composé de :

Dr, Elisabeth, Siebert

Directeur de recherche, LEPMI, Grenoble, Présidente Dr, Michel, Rosso

Directeur de recherche, LPMS, Palaiseau, Rapporteur Pr, Sylvain, Frang

er

Professeur ICMMO, Orsay, Rapporteur Pr, Nitash, Balsara

Professeur UC Berkeley and LBNL, Berkeley, Examinateur Pr, Renaud, Bouchet

Professeur LEPMI, Grenoble, Directeur de thèse Dr, Philippe, Stevens

Chercheur senior, EDF, Moret sur Loing, Co-encadrant

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A la mémoire de mon grand-père Dr Allan Gustav Ringheim et de ma grand-mère Julie Ringheim

A mes Chers parents et à ma Chère sœur

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"Expérimenter, c'est imaginer."

Nietzsche

Un voyage de milles lieues commence toujours par un premier pas.

Lao Tseu

"We live on an island surrounded by a sea of ignorance. As our island of knowledge grows, so does the shore of our ignorance."

John Archibald Wheeler

"Not everything that can be counted counts, and not everything that counts can be counted."

Albert Einstein

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Remerciements

This PhD was for me a unique experience made of travels in France (between Paris and Grenoble), but also to the US (Berkeley) and I had the chance to make numerous happy encounters during these few years. If I was able to finish this ordeal, it was through the help of many people and I would like here to thank them.

I would like to start by expressing my gratitude to all the members of my PhD committee, who gave me the honor to evaluate my PhD work. First of all, I would like to acknowledge the two referees, Sylvain Franger and Michel Rosso; they have taken the time to read and correct my "small" manuscript and I would like to thank both of them for their constructive critics and comments. Also I would like to thank Elisabeth Siebert to have accepted to be the president of my committee and for the very interesting and pertinent discussion that we had.

Now, I would like to thank all of my three advisors for their help during those "three years".

This research work could not exist without the EDF project, therefore I would like to thank Philippe Stevens for giving me the opportunity to work with him and his team on the Li-Air project, but also to introduce me on the complexity of batteries and the industrial research.

Be a French researcher for one year at the Lawrence Berkeley National Laboratory was a great experience for me and I would like to warmly thank Nitash Balsara for hosting me and making me feel part of his laboratory. Furthermore, it was a great pleasure to work with him and to have such stimulating individual meetings.

Last but not least, I would like to thank my PhD director Renaud Bouchet for his help and his support from the beginning to the final end of this project including the worst part, "la redaction".

Thank you to have guided me on the path of lithium dendrites; starting from nothing it was not easy

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but I have learn so much all along this journey. You have showed me the way to become a scientist with persistence, determination and scientific rigor. Thank you for all your guidance.

As a matter of fact, I had the chance to be in a great lab at the LBNL and I would like to thank the whole Balsara group to welcome me and to show me how the lab works. I would like to thank particularly some members: Chelsea for her help with the STEM. Dula and Katherine for their help at the tomography beamline and for the data reconstruction. Adriana and Jacob for their help with the SAXS experiment and treatment. Mahesh for your kindness in the office. And finally, Didier and Irune for everything that you have done for me as super nice colleagues and great researchers, but also as incredible friends ! In addition, I have met nice persons during this year in California, therefore I would like to thank the "Frenchies" Juliette, Paul, Thomas and Igor for all the good moments at the terrace of the Molecular Foundry and outside work, but also for the great weekends at Yosemite and all the hiking trips, without forgetting Mike the American, Georg and Herman the Germans. And also I can't forget my amazing neighbors: Ani, my favorite hippie, Jeff my amazing firefighter and paramedic neighbor and Melissa his beautiful and kind wife. You were an inspiration source of how to live as a real Californian. I really enjoyed all the moments at our rooftop. Sheila, thank you for showing me your beautiful Arizona State, the discovery of such amazing landscapes was extraordinary.

J'aimerais maintenant remercier les personnes que j'ai rencontrées à EDF sur le site bien connu

des Renardières caché près du village fortifié de Morêt sur Loing. Tout d'abord, je dois remercier tout

le groupe M29 pour m'avoir accueillie et pour tous les bons moments passés avec eux. J'aimerais

remercier en particulier Gwenaëlle pour son aide au labo et au MEB, Marie-Christine pour toute son

aide avec tous les papiers administratifs (et il y en a eu beaucoup...) et pour sa bonne humeur

quotidienne. Merci à Delphine pour la bonne ambiance et nos discussions. Par ailleurs, j'ai eu la chance

de partager mon bureau avec mon Cher voisin Patrick, merci pour tous les fous rires et la bonne humeur

dans notre bureau plein de voyages, et merci de m'avoir fait découvrir le Club peinture. J'ai découvert

une autre partie de moi même à travers la peinture, merci à tous les membres du Club pour tous ces

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déjeuners artistiques. En particulier, merci à Patricia notre Présidente et à Pascale notre professeur avec qui j'ai tant appris, mais aussi à Greg et Minh, qu'est ce qu'on a bien rigolé !

Les longues heures de train accumulées pendant ces années m'ont permis de faire de belles rencontres, merci à mes chers collègues de navette et de Transilien : Thomas, Ken, Samuel, Adrien, Houssam, Luis, Camille, Kevin et Jose pour tous nos papotages et rigolades, qui ont transformé ces trajets en bons souvenirs.

Et oui; il reste encore un laboratoire dont je n'ai pas parlé, le LEPMI ! Malgré ma présence intermittente; j'ai eu la chance d'être très bien accueillie par tous ses membres que j'aimerais chaleureusement remercier. Par ailleurs, pour tous les très bons moments inoubliables que j'ai passé, j'aimerais spécialement remercier Filou, Guillaume, Marc, Shayenne, Seng-Kian, Juan, Clément G pour m'avoir introduit au monde de la fanfare, Clément M pour les nombreuses parties de jeu de go, Marine pour toutes nos interminables discussions sur le Japon, Lulu pour toutes les bonnes soirées, Toc pour ta joyeuse folie contagieuse, Lazou pour toutes les fois où tu es venu me changer les idées dans mon bureau quand je rédigeais, et Juju pour toutes nos discussions scientifiques, non scientifiques, pour les papotages et les cours photos. Grace à vous je me suis sentie entourée et soutenue dans cette ville qui m'était inconnue.

Je souhaite maintenant remercier mes amis avec qui malgré la distance et les années passées rien

n'a changé, toujours la même joie de vous revoir et de passer du temps ensemble. Merci à Giselle pour

tous les bons moments passés à Berkeley. Merci à Jérem, Virgile et Prisca, Andrea et Basilus,

Chaussong, Kevin et Arnaud pour tous les super bons moments, les soirées, les verres et les rigolades à

la colloc ! Merci à Leslie pour toutes les randos, les soirées et pour tes encouragements pendant ma

rédaction. Alex et Fabien, merci pour tous les japonais, tous les fous rires et votre soutien. My Choupy,

cela fait maintenant bien trop d'années qu'on se connait pour les compter, merci d'avoir été là. Benj et

Stannou, c'est en grande partie grâce à vous que je me suis dirigée vers la thèse pour le meilleur et pour

le pire, merci de votre soutien et de votre amitié, à très vite pour un petit verre au St Hil ! Ma Clémence

merci pour tous les inoubliables moments à Stockholm, Orléans, Paris, San Francisco et Grenoble.

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Ma Chère Manue, merci pour ta bonne humeur infaillible qui m'a souvent reboostée, je ne peux plus compter tous les fous rires que j'ai eu avec toi ! Marie, c'est grâce à toi que je me suis sentie bien entourée au LEPMI, merci et à très vite pour de nouvelles aventures au Canada ou ailleurs sur la planète.

Irune, my Dear friend, it was a great surprise to find a beautiful person like you in the US, thanks to you I felt at home and I was always surrounded by your positivity, your warm attitude and your smiling face. Thank you a lot. Ma belle Yuki, mille mercis pour ta générosité, ton soutien, tes encouragements et tes messages plein de pâtisseries ! Ma Len-chan, nous avons partagé tellement de beaux moments ensemble, je n'ai qu'une hâte, c'est de repartir avec toi à la découverte de nouveaux pays. Merci pour ta belle amitié.

Il n'y a pas assez de mots pour exprimer toute ma reconnaissance et ma gratitude à Juan- Manuel. Tu es mon soutien de tous les instants et ta présence même lointaine me réconforte. Avec toi tout semble plus facile...

Enfin, mes profonds remerciements vont à mes parents qui m'ont depuis toujours soutenue et

encouragée à aller plus loin. En dernier lieu, je remercie tendrement ma sœur Laura, pour sa belle

énergie, notre complicité et notre grande amitié.

Tables of contents

Introduction. . . 1

Chapter 1. General context and battery state of the art . . . 5

1. Societal and environmental context. . . 7

2. The main battery technologies. . . 11

3. Metal-air batteries. . . 18

a. General context and metal-air batteries. . . 18

b. Non aqueous lithium-air battery. . . 20

c. Aqueous lithium-air battery. . . 26

4. Solid lithium ionic conductor as separator between the lithium and the aqueous electrolyte. . . . . . . 30 5. Possible ways to protect the ceramic. . . 33

a. Liquid electrolytes. . . 34

b. Lithium phosphorus oxynitride or LiPON. . . 34

c. PEO-polymer based electrolytes. . . 36

d. Block copolymer electrolytes. . . 40

e. Single-ion electrolytes. . . 43

6. Lithium metal. . . 45

a. The solid Electrolyte Interphase (SEI) . . . 45

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b. Model of nucleation and growth of lithium dendrite. . . 47

c. Lithium dendrite prevention. . . 55

7. Conclusion. . . . . . 63

References of Chapter 1. . . 65

Chapter 2. LiPON as a protective layer for the ceramic. . . 73

1. Experimental section. . . 75

a. Materials. . . . . . 75

b. SEM characterization. . . 75

c. Electrode sputtering and cell assembly. . . 76

d. EIS measurement. . . 76

2. Results and discussion. . . 77

a. Micro-structural analysis. . . 77

b. Ohara GC results. . . 78

c. LiPON-Ohara GC-LiPON results. . . 81

3. Conclusion. . . . . . 89

References of Chapter 2. . . 91

Chapter 3. Chemical and physical characterization of block copolymer electrolytes 93 1. Block copolymer : presentation and preparation. . . 95

2. Thermodynamical properties of block copolymer electrolytes. . . 97

3. Morphology studies. . . 99

a. Small angle X ray scattering. . . 99

b. Dark field scanning transmission electron microscopy. . . 108

4. Material electrical properties. . . 109

a. Cell preparation. . . 109

b. Cell optimization. . . 110

c. Conductivity measurements. . . 111

5. Transference number. . . 118

6. Conclusion. . . . . . 123

References of Chapter 3. . . 124

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Chapter 4. Dendritic growth in lithium symmetric cells. . . 127

1. Cycling experiments followed by electrochemical impedance spectroscopy. . . 129

a. Cycling routine. . . 129

b. Neutral block copolymers. . . 131

c. Single -ion block copolymers. . . 136

2. Dendrites morphologies studied by hard X-ray microtomography. . . 145

a. Hard X-ray microtomography. . . 145

b. Protocol. . . . . . . 146

c. Neutral block copolymer. . . 147

d. Single-ion block copolymer. . . 152

3. Conclusion. . . . . . 157

References of the Chapter 4. . . 159

Chapter 5. The polymer-ceramic composite. . . 163

I. Study of the polymer-ceramic composite. . . 165

1. Experimental procedure. . . 165

2. Results and discussion. . . 167

a. Electrical properties. . . 167

b. Cycling. . . . . . . 175

c. Characterization by hard X-ray microtomography. . . 185

II. Quantification of polarization loss at the polymer-ceramic interface. . . 190

1. State of the art. . . 190

2. Experimental procedure. . . 191

3. Results and discussion. . . 192

a. Experimental results. . . 192

b. Discussion. . . 196

Conclusions. . . 201

References of Chapter 5. . . 204

Conclusions and perspectives. . . 207

Résumé en français 211

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Abstract. . . . . . . 214

Introduction

The concept of sustainable development has been established in the XX

century, it was defined as “a development that meets the needs of the present without compromising the ability of future generations to meet their own needs”

. In a society more concerned by its impact on the environment, and willing to have a sustainable development, energy plays an important role if not the main. However, everything starts form the use of sustainable energy generated from clean and renewable sources. One of the main issues for their development since there are intermittent technologies is the energy storage. Therefore, it becomes a crucial challenge to get different energy storage and especially electrochemical energy storage.

Nowadays, a large panel of electrochemical energy storage technologies are developed, among them the lithium-air (Li-air) technology is one of the most promising. In particular, the aqueous Li-air exhibits the highest specific energy and energy density compared to the other technologies already developed or even compared to the technologies under development like the lithium-sulfur technnology

.

However, the aqueous Li-air battery presents some issues which need to be addressed in

order to make this technology viable. One of the main issue is the reactivity of the lithium metal

electrode. The use of an aqueous electrolyte implies the protection of the negative electrode,

Visco et al.

have proposed a protected lithium anode (PLA) composed of a bilayer of solid

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electrolytes composed of Lithium Phosphorus OxiNitride (LiPON), which is stable in contact with lithium metal, and a lithium ion conductor ceramic LATP (Li

Al

Ti

(PO

)

) which is stable in contact of the alkaline electrolyte. On the other hand, these materials are hard and fragile, and during the charge of the Li-air battery, the volume variation of lithium leads to mechanical constrains at the interface which results in a loss of contact at the lithium- LiPON interface and then a loss of the active surface area. This is why, the protective layer should be replaced by a material which exhibits: at first, softness property to keep the contact with the lithium metal and secondly, it needs to mitigate dendritic growth during cycling to protect the ceramic.

Block copolymer electrolytes (BCE) based on poly (ethylene oxide) (PEO) are good candidates as protective buffer layers for the ceramic. Indeed, this materials is stable versus lithium

and they have been recently highlighted for their high performances in lithium metal polymer battery

. The aim of this work is to study the use of the polymer electrolytes in the Li- air technology, i.e. to replace the LiPON with BCE which will have two main goals, firstly to assure the good contact between the lithium and the ceramic and secondly to protect the ceramic from the lithium dendrites.

Such protective layer has to fulfill several criteria: to be stable and to ensure a good interface with both lithium and ceramic, to present a high lithium ionic conductivity, to be feasible in order to keep the contact with lithium even with the volume variation in charge and discharge and finally to be resistive to dendritic growth in order to protect the ceramic from the contact with the lithium metal.

In the Chapter 1, we will first introduced the general context of the energy, in order to

understand why the world needs to develop new electrochemical energy storage systems with

increased energy density, reliability, safety, etc. A state-of-the-art of the different battery

technologies will then be given, followed by a focus on the lithium air battery technology. The

insight of the aqueous Li-air technology will be developed and more particularly, what are the

possible suitable electrolytes which can be considered as a protective layer for the lithium ion

conductor ceramic, as well with the different issues encountered with the use of the lithium

metal electrode. The different models of dendritic growth, which have been developed, will then

be introduced, and finally the different methods used to prevent or mitigate the dendrite

nucleation and growth will be discussed.

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The Chapter 2 is dedicated to the study of the actual solution to protect the ceramic, i.e the thin lithium phosphorus oxinitride (LiPON) films on the ceramic. The study of the electrical properties of the ceramic on one side and the LiPON in the sandwich on the other side will be studied by electrochemical impedance spectroscopy (EIS). Ionic conductivities and activation energy will be calculated.

The physico-chemical characterizations (ionic conductivity morphologic property and transport properties) of the BCEs used in this study will be given and discussed in the chapter 3.

Several techniques, such as differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS) and EIS will be used.

A cycling study of the BCE-lithium symmetric cells along with the morphological characterization obtained in situ by hard X-ray micro-tomography of the cell before and after cycling (post mortem) will then be discussed in Chapter 4.

Finally, in Chapter 5, the composite ceramic-BCE/lithium will be studied (interface by EIS, cycling with EIS and finally DC polarization analysis and hard X-ray micro-tomography).

References of the Introduction

1. WCED, 1987; Bojo et al., 1992

2. Bruce, P. G., Freunberger, S. A., Hardwick, L. J. & Tarascon, J.-M. Li-O2 and Li-S batteries with high energy storage. Nat. Mater. 11, 19–29 (2012).

3. Visco, S. J. & Nimon, Y. S. Protected lithium electrodes having tape cast ceramic and glass-ceramic membranes. (2015).

4. Stone, G. M. et al. Resolution of the Modulus versus Adhesion Dilemma in Solid Polymer Electrolytes for Rechargeable Lithium Metal Batteries. J. Electrochem. Soc. 159, A222–A227 (2012).

5. Bouchet, R. et al. Single-ion BAB triblock copolymers as highly efficient electrolytes for lithium- metal batteries. Nat. Mater. 12, 452–457 (2013).

6. Devaux, D. et al. Optimization of Block Copolymer Electrolytes for Lithium Metal Batteries. Chem.

Mater. 27, 4682–4692 (2015).

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Chapter 1.

General context and battery state of the art

Abstract

In a society where the energy demand continuously increases and where the fossil energy is limited by the planet resources, the development of renewable energies and electrical vehicles is a necessity. However, known energy storage technologies do not exhibit sufficient high capacities for the needs of today and tomorrow society.

Therefore, new electrochemical storage technologies with higher capacities are required

for example to the development and the widespread of electrical vehicles. This first

chapter will introduce the general societal and environmental context in which this

project takes place. The main electrochemical storage will be then reviewed, before to

discuss more specifically around metal-air batteries. The discussion will highlight the

advantages of the aqueous lithium-air battery developed by EDF. Nevertheless, the

negative electrode as it is conceived today presents issues which still need to be

addressed. Therefore, alternative materials will be presented. Finally, a state of the art

of lithium dendrite will be given.

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Table of contents

Chapter 1. General context and battery state of the art ... 5

1. Societal and environmental context ... 7

2. The main battery technologies ... 11

3. Metal-air batteries ... 18

a. General context and metal-air batteries ... 18

b. Non aqueous lithium-air battery ... 20

c. Aqueous lithium-air battery... 26

4. Solid lithium ionic conductor as separator between lithium and aqueous electrolyte ... 30

5. Possible ways to protect the ceramic ... 33

a. Liquid electrolytes ... 34

b. Lithium phosphorus oxynitride or LiPON ... 34

c. PEO polymer based electrolytes ... 36

d. Block copolymer electrolytes ... 40

e. Single-ion electrolytes ... 43

6. Lithium metal ... 45

a. The Solid Electrolyte Interphase (SEI) ... 45

b. Model of nucleation and growth of lithium dendrites ... 47

c. Lithium dendrite prevention ... 55

7. Conclusion ... 63

References of Chapter 1 ... 65

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1. Societal and environmental context

Energy is known as "the lifeblood of modern societies"

. Indeed, it is critical for human activities such as industrial manufacturing, agriculture, transportations, and communications.

Unfortunately, the high dependence of the global economy on fossil fuel makes it vulnerable to two types of crisis that could arise in the near future : a supply disruption and an environmental disaster.

Indeed fossil fuel supplies are by definition finite and under growing demand; on the other hand reserves are concentrated in a small number of regions which increases geopolitical tension.

However the main concern is the rise of atmospheric, sea and land pollutions, which lead to dramatic consequences on human and animal health, as well as on water quality and agricultural production. The main greenhouse gas, cause of global warming, emitted by human activities to the atmosphere is carbon dioxide (CO

), produced by fossil fuel use.

Society is becoming more conscious of the situation, and there is an increasing demand to massively introduce renewable energies in the energy mix in order to mitigate CO

emissions and their effects on climate change

. In order to address climate change, countries from all around the world met in Paris for the 21

Conference of the Parties to the United Nations Framework Convention on Climate change (COP21) in 2015, to negotiate an international agreement and set a direction for combating climate change and keep global warming below 2 ᵒ C

.

To be able to stay on the 2 ᵒ C scenario, a rise in renewable energies in the global power

generation is necessary. The International Energy Agency (IEA) asks for a rise of 45% of

renewable electricity generation between 2012 and 2020

. Figure 1 presents renewable power

generation by region from 2000 to 2020.

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Figure 1. Renewable power generation by region

.

Figure 2 shows the breakdown of global renewable energy use in 2010 and an evolution perspective for 2030 (REmap 2030), by technology and sector. The International Renewable Energy Agency (IRENA) is expected to have 3% of electricity coming from solar sources and 11% coming from wind sources by 2030. Production from energy sources cannot be dispatched, since technologies such as solar or wind are intermittent energies, and they are often generated far from where they are consumed. These aspects of renewable energies represent a real challenge for the management and reliability of the electrical grid

. The unpredictable nature of energy from renewable sources means that it has to be stored to be available when required by consumers. In order to provide the flat energy production curve to the grid, it is necessary to couple the energy source to an energy storage. Energy storage has therefore emerged as one of the greatest issues of the 21

century. The main interest of these technologies is that they can be placed close to the place of consumption and they can be adapted in size.

0%

10%

20%

30%

0 2 000 4 000 6 000 8 000 10 000 12 000 14 000

2000 2005 2012 2020 2025

Share of Renewable Generation

T W h

Other non-OECD Brazil India

China OECD Europe OECD Asia Oceania

OECD Americas Share of renewable generation Share of renewable generation 2025

Forecast Targets

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Figure 2. Breakdown of global renewable energy use in 2010 and in REmap 2030, by technology and sector

. One potential good candidate for energy storage is electrochemical storage thanks to batteries; the technology used for renewable energies must satisfy several criteria such as a long lifetime, low cost, effectiveness and safety

.

Besides, stationary storage of electrical energy from renewable sources that completes the energy mix and limits the use of fossil energies, a sustainable modern society requires to electrify its transport by providing electric vehicles that can compete with cars powered by internal combustion engine. Moreover, according to the International Energy Agency (IEA), in order to keep the increase in global temperature below 2 ᵒ C, it is necessary to have a decrease of at least 50% of greenhouse gas emissions by 2050 compared to 2005 levels

. This requires not only a universal climate agreement, which implies strong climate policies (see the recent international meeting COP 21), but also the widespread use of electric and hybrid vehicles (see Figure 3), which can contribute to a decrease of 30% of the greenhouse gas emissions.

However, the transition to mass development of these technologies is directly related to

battery improvements, which is the struggling point of today. Indeed, today none of the

conventional batteries have met all the required specifications, which are in order of priority

safety, cost, long lifetime and a high energy density

.

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Figure 3. Annual light duty vehicle sales by technology

.

Tomorrow's electrochemical storage has therefore to fulfill a certain number of criteria starting with safety, sustainable components, high energy density, scalability, ease of use and cost of maintenance. However, for each applications the order of priorities are different. Indeed, for stationary applications such as solar, wind or even tidal, weight and space are not critical whereas the energy stored, power, lifetime and cost are crucial. In addition, stationary applications are expected to have a lifetime between one and two decades, which implies around 3000 cycles. The last specification for such application is the capacity which does not necessarily need to be very high due to the possible over sizing. Whereas for loaded applications such as EV or HEV, weight and space are very important on the contrary. Safety in both applications are very important but need to be specific for each applications.

Nowadays, lithium ion (Li-ion) technology is extensively widespread for consumer portable electronics such as cell phones or computers. This technology stays expensive and more importantly the environmental cost is high due to some components for Li-ion electrodes, such as cobalt, which are rare, expensive and toxic, as well as the presence of organic solvents in the electrolyte. A battery for cell phone is a 4 Wh battery, when an EV needs 40 kWh. Thus, to build an EV battery 10 000 cell phone batteries are needed. In other words, the 5 billion cell phones on the planet is equivalent to only 500 000 of potential EVs, which is unfortunately a drop in the car's ocean.

In the following sections, we will first review the main battery technologies since the

discovery of the voltaic pile to lithium-sulfur batteries including lithium-ion batteries and lithium

metal polymer batteries. Metal-air batteries will then be reviewed and the difference between

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non-aqueous and aqueous technologies will be discussed. Their advantages and disadvantages will be addressed and finally the discussion will focus on the evolution of materials composing the aqueous lithium-air battery. Finally, the use of lithium metal and its related issues will be discussed. The formation of passivation layers, the different models of dendritic growth and how to prevent or limit the nucleation and growth of dendrites will be approached.

2. The main battery technologies

In this thesis, we will use the terms cathode for the positive electrode (where the reduction takes place with a consumption of electrons during the discharge) and anode for the negative electrode (where an oxidation reaction takes place with a production of electrons at the discharge), these terms are usually used by the Anglo-Saxon scientific community.

As seen in Figure 4, the historical roots of the development of rechargeable battery can be found in the 19

century. Alessandro Volta, an Italian physicist and chemist was the first to see a continuous and stable current with his invention "the Volta pile", in 1800

. In 1803 J. W. Ritter, a German chemist physicist and philosopher, was the first to build a secondary battery

.

Figure 4. Historical roots of the development of secondary batteries from 1803 to 1994

.

Lead acid battery. A few decades later, reliable rechargeable battery history started with

Gaston Planté in 1859

, a French physicist who invented the lead-acid battery. Figure 5

represents Planté's lead acid battery, where a spiral roll of two sheets of pure lead were separated

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by a linen cloth immersed in a glass jar of sulfuric acid solution. The redox couples involved at the electrodes are PbSO

/Pb at the cathode and PbO

/PbSO

at the anode.

Twenty years later, the first commercial rechargeable lead-acid battery was marketed

. More than a century after its invention, this battery is still widely used, and it represents 70% of the secondary battery market mainly due to its use as starter batteries (in thermal motors), vehicle lighting, engine ignition, but also as emergency power and backup systems.

Figure 5. First lead acid battery by G. Planté

.

Nickel-Cadmium battery. In 1899, four decades after Gaston Planté, a new type of battery, based on nickel-cadmium (Ni-Cd), was born with the discovery by Ernst Waldemar Jungner

. In these batteries, the positive electrode is composed of nickel hydroxide (NiO(OH)) and the redox couple involved is Ni(OH)

/NiO(OH), whereas the negative electrode is composed of metallic cadmium (Cd) and the redox couple is Cd(OH)

/Cd. The commercialization was achieved in the 20

century with G. Neumann and his Ni-Cd sealed cell in 1947

.

The nickel metal hydride battery (Ni-MH) is a technology similar to the Ni-Cd. Indeed, both the positive electrode and the electrolyte are similar; the main difference lies on the use of hydrogen absorbed in a metal alloy at the anode instead of cadmium. It was in the late 1960s, at Dutch Philips Research Laboratories, that the LaNi

compound was found to be able to absorb reversibly large amounts of hydrogen

. A mature and reliable technology was commercialized in the early 1990s

. This new battery type, which is cadmium free, is considered to be more environmentally friendly and in addition it is recyclable. The metal alloy used is a mix of rare earth and nickel (LaNi

).

Lithium-Ion Battery. In the continuous race for an always higher specific and volumetric

energy in battery technology because of the fast nomad electronics development, lithium has

been considered as a good candidate for the negative electrode as active material. In 1979 at

- 13 -

Oxford University, an American professor John B. Goodenough created a cathode material based on lithium cobalt and lithium-manganese spinels

, which set the bases to the lithium ion (Li-ion) battery. More than a decade later in 1991, Sony was the first to commercialize a lithium ion battery also called "rocking chair" battery

.

Lithium batteries firstly employed intercalation compounds as cathode and lithium metal as the anode. However, the anode was then replaced by lithiated carbon due to safety issues leading to the so called "Li-ion" technology. Years of research have produced a wide choice of cathode materials for Li-ion batteries, among them lamellar compounds such as LiCoO

, lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA), spinel compounds like LiM

O

(with M = Ni, Mn) or even olivine compounds such as lithium iron phosphate (LFP). Both cathode and anode materials are insertion materials and have a structure adapted to lithium ion intercalation during oxidation and reduction processes. The electrolyte is an organic liquid composed of a lithium salt (LiBF

, LiPF

, LiClO

, LiBC

O

(LiBOB)) dissolved in a mixture of organic solvents (ethylene carbonate EC, diethylene carbonate DEC, propylene carbonate PC or dimethyl carbonate DMC) and impregnated in a porous polymer separator made of polyolefin (polypropylene PP, polyethylene PE)

.

Figure 6 shows a schematic of a classical Li-ion battery during discharge. The operating

temperatures in charge range from -20 ᵒ C to 60 ᵒ C, whereas in discharge from -40 ᵒ C to 65 ᵒ C

. In

addition, thanks to the Li-ion battery, the specific energy density has increased compared to Ni-

MH technology and range from 100 to 250 Wh.kg

(or 220 to 400 Wh.L

)

. This technology is

ideal for nomad applications and it has quickly conquered this market. However, Li-ion battery

has a high cost and safety issues due to the use of flammable electrolytes.

- 14 -

Figure 6. Scheme of a common Li-Ion battery during the discharge

.

PLiON battery. In 1994, Bellcore (former Telcordia) patented a plastic lithium ion battery called PLiON

. The main difference from a classic Li-ion is that the electrolyte is a copolymer, PVdF-HFP (polyvinylidene fluoride-hexofluoropropylene), which contains two different domains. One amorphous domain (HFP), which is gelled by the liquid electrolyte composed of LiPF

and a mixture of EC-PC, and a crystalline domain (PVdF) which assures mechanical properties of the entire electrolyte in order to obtain a free standing film

. Figure 7 represents a schematic of the PLiON battery. Despite similar specifications (150 Wh.kg

and 300 Wh.l

) to Li-ion battery, PLiON shows an interesting size and design, indeed the assembly process of this battery is lamination and thus can be made as thin as a credit card.

Figure 7. Schematic diagram showing the construction of a polymer Li-ion cell (PLiON)

.

In 1995, the introduction on the market of pouch cell, which uses flexible and heat sealable foils, simplified battery packaging. Few years later, in 1999, US Oak Ridge National Laboratories patented the first marketable lithium ion polymer battery

.

Nevertheless, scaling up Li-ion technology, to store efficiently energy from the intermittent

renewable power resources and to widespread EV's and HEV's onto the consumer market,

- 15 -

remains a challenge due to issues such as safety because of flammable organic solvents, cost (higher than 250-400 $/kWh) or even material availability

. In 2014, Tesla in cooperation with Panasonic launched the Tesla Gigafactory project in order to reduce Li-ion battery cost by more than 30% by 2020

. Figure 8 represents the expected evolution of Li-ion battery cost for the next decade.

Figure 8. Evolution of Li-ion battery pack cost ($/KWh) from 2015 to 2025

.

The battery community realized the need to go further than Li-ion batteries. Thus a novel fundamental research activity has been started which focuses on different kinds of battery technologies, often referred as "beyond Li-ion". Figure 9 represents practical specific energy for electrochemical storage systems from lead acid system to beyond Li-ion technologies such as metal-air, including zinc air and lithium-air batteries.

It is important to note that a real breakthrough is necessary in order to have a widespread adoption of electric vehicles into the public market. We only have two options to increase the energy densities, which is proportional to the product of the specific capacity by the emf, :

- increase the electro motive force (that is the future Li-ion see in Figure 9)

- increase the specific capacity of the active materials, which corresponds to metal-air and

lithium-sulfur technologies

- 16 -

Figure 9. Practical specific energy perspective for some rechargeable batteries, along with estimated pack prices

. In the quest for high energy density for the negative electrode, lithium metal has inevitably emerged from the others candidates as a promising active material, because its electrochemical characteristics are unique. Indeed, metallic lithium can be considered as the ultimate negative electrode due to its high theoretical specific capacity (3862 Ah.kg

) and its very negative potential (-3.05 vs SHE)

. The idea to use lithium metal in an electrochemical device dated back to 1949, when J.J. Halek patented a primary battery using lithium metal as an anode

. Few years later, in 1957 this idea was specified by D. Herbert and J. Ulam in a secondary battery

, and in 1970, Watanabe and Fukuda for Panasonic (former Matsushita Electronic Co. Ltd) started its production

. At this time, lithium metal battery was assembled with a cathode of TiS

, and an electrolyte composed of a lithium salt (lithium perchlorate (LiClO

)) dissolved in a mixture of organic electrolytes, which is made of 70% of tetrahydrofuran (THF) and 30%

dimethylformamide (DMF)

. However, the reactivity of the high surface area of lithium that is formed during cycling leads to a poor cyclability and safety issues

. This was due to irregular lithium deposition during charge

. This heterogeneous electro deposition, also called

"dendrites", shows needle-like and mossy morphologies that can shortcut the battery by passing through the electrolyte and potentially causing fire or explosion

. For example, in 1989 a lithium metal battery in a cellular phone burned during operation, this was due to an internal short of the battery

.

Lithium metal polymer. In order to prevent these kinds of safety issues, two research axes

have been developed. The first one, which was already described above, consists in replacing

- 17 -

lithium metal by an intercalation compound, lithiated carbon, lithium titanate (Li

Ti

O

) or metal alloys, which have led to the Li-ion battery technology. The second one consists on replacing the organic liquid electrolyte by a dry solid polymer electrolyte, the lithium metal polymer (LMP) technology was born. The first to suggest a polymer as a good electrolyte for lithium batteries was M. Armand during the Second International Meeting of Solid Electrolytes in 1978

. He opened new perspectives for the development of solid polymer electrolytes which led 40 years later to a wide variety of polymer electrolytes and new lithium salts. Polymer electrolytes are composed of a lithium salt (typically LiClO

or lithium bis (trifluoromethane)sulfoimide salt (LiTFSI)) incorporated into a polymer matrix (mostly based on poly (ethylene oxide) PEO) which is then cast into thin films. LMP presents some advantages compared to the classic Li-ion, a good flexibility of polymers which enables the design of thin batteries to be made in a wide variety of configurations, and a higher safety thanks to a volatile solvent free technology.

However, the ionic conductivity at room temperature for such electrolytes is low and therefore the operating temperature needs to be increased to 80 ᵒ C. This technology has been developed for electric vehicles such as the Bluecar and the Bluebus by Blue solutions-Bollore and is now widespread in Paris as the Autolib

.

Lithium-Sulfur battery. In order to renew the interest in the lithium metal battery concept, radical changes in the approach of the fundamental electrochemical processes are necessary. In this context, another type of battery is under intense scrutiny, the lithium sulfur battery (Li-S

).

Indeed, this technology shows appealing specifications, such as a practical energy density ranging from 400 to 600 Wh.kg

, a cathode active material abundance (lower cost) and the non-toxicity of elemental sulfur (environmental friendly)

. However, after its discovery in 1957

, this technology sank into oblivion because of its poor performances at that time. Since 2009, after Nazar

reported a Li-S battery with improved cycling performance, this Li-S battery got back on track, becoming one of the most studied technologies for next generation electrochemical storage. Nevertheless, some important barriers still prevent the realization of a practical Li-S battery with a high energy density and a long lifetime.

The Li-S

battery is composed of elemental sulfur (S

) as the positive electrode, lithium metal

as the negative electrode and an electrolyte in between (which can be a liquid electrolyte, an ionic

liquid based electrolyte or a solid polymer electrolyte)

. The overall reaction involved in the cell

is 16 Li + S

↔ 8 Li

S. However, before obtaining the ultimate product, the lithium sulfide

(Li

S), intermediate polysulfides (Li

S

with x = 2-8) are generated by the reduction of S

during

the discharge process. Those molecules are dissolved in the electrolytes, which leads to an

- 18 -

irreversible capacity fade

. They can migrate through the electrolyte to the lithium metal electrode in a so called, shuttle effect, and form an electrochemical insulating layer composed of Li

S

and Li

S leading to a deterioration of the battery performance and a poor rate capability.

Figure 10 shows the polysulfide shuttle mechanism and the deterioration of the lithium anode.

Figure 10. Schematic illustration of the polysulfide shuttle mechanism during the charge

.

In addition, growth of dendrites from the lithium metal anode still causes internal short cut issues. These lithium metal issues, such as dendrite growth, remain unsolved and scientists need to dive into the complex life of interfaces and mechanisms involved at this attractive material surface. In spite of their potential attractive advantages, Li-S

batteries are not yet a mature technology and need further improvements.

After introducing the evolution of battery technologies since its first stammering on the early Nineteenth century, the following section will focus on a new kind of batteries, the metal-air batteries.

3. Metal-air batteries

a. General context and metal-air batteries

The metal-air battery is a good candidate for EV's and large electricity storage systems due to

its high gravimetric and volumetric energy density (see Table 1). Metal-air batteries are composed

of :

- 19 -

· A metallic negative electrode; which can be made of lithium (Li), sodium (Na), magnesium (Mg), aluminum (Al), iron (Fe) or zinc (Zn).

· An air positive electrode which uses oxygen from the ambient air as the active material, and is composed of catalysts for O

reduction reaction (ORR) and oxygen evolution reaction (OER) in a porous network of an electrically conducting supporting materials.

· An electrolyte which can be either an organic electrolyte or an aqueous electrolyte

. One of the main advantage of such a device is, in principle, that the oxygen is supplied by the surrounding atmosphere and does not need to be stored inside the battery

. Thus, this type of battery has a reduced weight and more available space for energy storage. Consequently, metal-air batteries presents high theoretical specific energy ranging from 1086 Wh.kg

for zinc- air system to 3582 Wh.kg

for aqueous lithium-air system.

Table 1. Theoretical cell voltage with specific energy and energy density for various metal-air battery compared to Li-ion

.

based on the volume of ZnO at the end of the discharge.

Based on the sum of the volume of Li at the

beginning and Li

O

at the end of the discharge.

Based on the sum of the volume of Li + H

O consumed and LiOH at the end of the discharge.

Based on the sum of the volume of Li at the beginning and Li

S at the end of discharge.

Based on (Na

and Na

O

).

Based on the sum of the volume of Mg at the beginning and Mg(OH)

at the end of the discharge

Figure 11 is a general scheme of a metal-air battery. This schematic view includes a lithium

ion conducting membrane to protect the lithium metal for example in the case of aqueous Li-air

battery. During the discharge, the metal is oxidized and the metal ions produced migrate through

the electrolyte to the positive electrode where the oxygen is reduced.

- 20 -

Figure 11. Schematic principle of a metal-O

battery during discharge

.

Despite their attractive specifications, metal-air batteries are still under development. Indeed, only few realistic prototypes of metal-air batteries exist. This is due to complex challenges facing i) the design of a rechargeable metal-air battery, ii) the difficulties to reach theoretical specific energy due to parasitic chemistry occurring during metal-air electrochemistry and iii) safety issues.

Lithium-air batteries have the highest potential energy density above all other metal-air technologies, this is due to the use of light materials for the negative electrode, i.e. the lithium metal.

Two types of Li-air batteries exist, the non-aqueous lithium-air battery and the aqueous lithium-air battery. The principle of each type of technology will be discussed in sections hereafter. Moreover, their different advantages and disadvantages will be considered.

b. Non aqueous lithium-air battery

Non aqueous lithium-air battery was first reported by Galbraith in 1976

, but it was only

twenty years later in 1996 that Jiang and Abraham demonstrated the working principle in a

secondary battery

. The first Li-O

cell was composed of a conductive organic polymer

electrolyte sandwiched between a thin Li metal foil and a thin carbon composite electrode (the

air electrode). One decade later, the interest in Li-air battery increased thanks to Bruce and

Ogasawara, who proved in 2006 that Li

O

could potentially form a rechargeable couple

, they

actually showed that Li

O

is removed from the electrode during charge. Consequently, the

- 21 -

overall reaction 2 Li

+ 2e

+ O

↔ Li

O

may be reversible. In 2009, IBM and Energy Laboratories started exploratory research programs on Li-air battery, since then this research field has grown exponentially

.

There have been controversies about the mechanism of O

reduction in the presence of lithium ions leading to the formation of lithium peroxide . Indeed, nowadays the consensus is that the reduction of O

during discharge follows a mechanism in three steps ((1) to (3))

:

O

+ e

→ O

(1) O

+ Li

→ LiO

(2)

2LiO

→ Li

O

+ O

(3)

Reduction mechanism of O

implies firstly the formation of a superoxide O

which then reacts with Li

to form LiO

on the surface of the electrode. Then, because LiO

is unstable, it will disproportionate in Li

O

following equation (4).

However, other studies proposed the direct reduction of O

into Li

O

.

2Li

+ O

+ 2e

→ Li

O

(4) Which may be further reduced to lithium oxide according to:

Li

O

+ 2Li

+2e

→ 2Li

O (5) During the charge process (OER) the pathway is different to the discharge and follows equation (6) hereafter:

Li

O

→ 2Li

+ 2e

+ O

(6) Indeed, it was proved that the oxidation of Li

O

is direct and does not pass through LiO

as an intermediate

. A result of these different pathways is the observed gap in charge and

discharge voltages (see Figure 12) resulting in an extremely low energy efficiencies, which would

limit the use of this battery in practical applications.

- 22 -

Figure 12. Voltage gap for a non-aqueous lithium-air battery

.

A suitable electrolyte is the key component of this system and remains a real challenge.

Indeed, it has to fulfill various requirements coming from both the anode side and the cathode side specific needs. From the anode side, the electrolyte in contact with lithium metal will react and form a SEI like layer (solid electrolyte interphase), which has to be cohesive and flexible to ensure the anode protection. In addition, this layer has to be sufficiently Li

conducting in order to ensure smooth lithium plating without dendritic growth.. Moreover, contaminants such as oxygen, water, nitrogen and carbon dioxide, coming from the air electrode must not cross through the electrolyte and react with the lithium surface

.

From the cathode side, the electrolyte has to present a low volatility to avoid its evaporation

at the open air electrode. It also has to present a high O

solubility and diffusion to ensure

satisfactory rate capability, and to be able to wet the electrode surface. However, the most

challenging requirement for the electrolyte is to be stable to both O

and its reduced species as

LiO

compounds that form during the discharge. Indeed, historically carbonate based organic

electrolytes were used, mostly because they were well known to be compatible with lithium

metal, they present a low volatility and a high oxidation stability (> 4,5V vs Li

/Li). An example

of a typical electrolyte is a lithium salt (LiPF

) in a mixture of propylene carbonate and dimethyl

carbonate (50/50). However, studies have shown that O

in aprotic solvent reacts with organic

substrates via nucleophilic attack

. In 2010, Mizuno et al. reported that carbonates based

electrolytes are degraded by the superoxide radical O

.

- 23 -

Other organic electrolytes were therefore investigated in order to find the ideal one. Ester- based electrolytes were potential candidates but a computational study on esters by Bryantsev et al.

revealed that, similarly to carbonates, the superoxide radical attacks the ethereal carbon atom in both cases of linear and cyclic ester. Another study of Bryantsev et al.

has focused on predicting the stability of a wide range of solvents for non-aqueous Li-air batteries. They computed free energy barriers (∆G

) for reactions with superoxide O

, and showed that solvents with a ∆G

< 20 kcal/mol are chemically unstable against the superoxide, whereas solvents with ∆G

> 24 kcal/mol do not present reactivity with the superoxide, which make them good candidates as electrolyte. Among them, tetraethylene glycol dimethyl ether (TEGDME), presents a low vapor pressure, a high lithium salt solubility as well as a large electrochemical window spanning up to 4.5 V. However, ethers show an auto oxidation under oxygenated radicals. The main product of the discharge appears to be ether decomposition

, similar behavior was found with cyclic ethers. Nitrile-based solvents have also been investigated.

In fact, acetonitrile presents a sufficient stability towards oxygen reduction species. However, it shows a high vapor pressure at room temperature, which will leads to an evaporation of the electrolyte at the positive electrode

. In addition, it is not stable against lithium metal. Therefore, in order to have a low vapor pressure, alternative nitriles have to be studied. It is important to notice that studies about nitrile-based solvents for non-aqueous Li-air battery are still on their primary stages. In addition, the long term stability of nitrile components towards superoxide ion are not yet proven.

Another approach has been investigated, the use of solid polymer electrolyte (SPE). Indeed, numerous polymer systems have been studied for lithium batteries, the most used is based on a poly(ethylene) oxide matrix hosting a lithium salt, generally lithium trifluoromethanesulfoimide LiCF

SO

or LiTFSI. SPE is a promising alternative for the volatile organic solvents

. Polymers are expected to react slowly due to the absence of convection and diffusion selective if compared to organic solvents

. However, the electrochemical stability of the very long molecular chain glymes is debatable because the short chain glymes react with lithium oxides species

. In addition, the recharge ability of such system has not been yet proven

. Moreover, the challenge facing SPE is to improve their ionic conductivity and manage the huge volume change in the air electrode between charge and discharge

.

Since almost two decades, an intense research to find the perfect suitable electrolyte for non-

aqueous lithium-air battery has been started. However, the formation of a superoxide ion O

- 24 -

that is very reactive over organic compounds, have complicated the task and nowadays no electrolytes have been found stable under long term cycling.

The theoretical specific energy and energy density are calculated from the weight of active components of the battery. In non-aqueous Li-air battery, in a fully charged state the active component corresponds to lithium metal alone, indeed the O

is coming directly from the ambient air. In a fully discharged state, the active component is Li

O

and Li

O

. In Table 1, specific energy and energy density are calculated if there is a stoichiometric quantity of lithium and if the cathode is only composed by Li

O

(no porosity, no binders and no carbon)

. However, nowadays no practical prototype exists, therefore it is difficult to predict specific energies or energy densities which will be achievable.

Indeed, some factors influencing the practical energy of a non-aqueous Li-air battery are to be taken into account. On one hand, there is the excess of lithium necessary in order to compensate the lithium loss during cycling. Figure 13 presents the evolution of specific energies and energy densities for different excesses of lithium. On the other hand, the porosity inside the positive electrode is important to take into account. Bruce et al. have calculated a potential specific energy and energy density if the positive electrode is composed in volume of 20% of carbon, 20 % of the electrolyte and 60 % of active material (Li

O

or Li

O)

. Figure 13 b) represents the results for Li

O

in green and Li

O in orange, when a stoichiometric amount of lithium is taken at the negative electrode (compared to Li-ion specifications).

It appears that compared to Li-ion, this technology stays very attractive.

a)