Na-ion battery technology has recently aroused great interest among all the scientific community, as a valid and more environmentally friendly alternative to Li-ion batteries. The PhD research activity has been mostly devoted to the investigation of reliable active materials for sodium ion battery technology. All the investigated materials, either anode or cathode, have been investigated trying to highlight the major limits and difficulties connected to sodium intercalation and conversion reactions. Among these, some are: i)assessment of Na diffusion in an intercalating host structure, ii)products and reversibility of transition metal oxides conversion reactions, iii) effects of materials crystalline properties on electrochemical performances and iv) features influencing the overall stability of a functional material. In order to keep the most broad-based overview of the problem, it has been chosen to systematically start, for each species electrochemically investigated, from its synthesis and thorough chemical-physical characterization. Rather than a pure electrochemical analysis, a continuous parallelism between morphological features, structural characteristics and performances was encouraged, eventually obtaining a detailed overlook of different classes of active materials for sodium batteries. What has been screened all along the three year-long research period has been a comprehensive investigation of new generation electrochemically active materials for energy storage applications. This implied an inter-disciplinary work in which advanced electro-analytical techniques have been widely used to characterize inorganic compounds or ad-hoc synthesized composites keeping in mind precise structure-performance correlations. Among the investigated classes, a role of relevance has been reserved to intercalating cathode species and conversion anode materials. The former, typically layered transition metal oxides, phosphates and pyrophosphates, are capable of sodium cations insertion, with fast kinetics, between layers or inside channels generated from peculiar atoms arrangement. Conversion anode materials on the other hand, carries out the sodium storage via spontaneous chemical reactions with oxide-based material, such as Co3O4 or Fe2O3, a chalcogenide or a halide. Compared to intercalation materials, conversion ones are more challenging to deal with, due to the following difficulties: i)their not negligible volume change during conversion reaction and the correlated induced mechanical stresses leading to electrode fracturing and pulverization, ii)occurrence of irreversible and parasitic reactions and iii)material operating potentials is often too high (around 1.0 V vs. Na/Na+) and thus not suitable for being used as anode materials inside a sodium cell. A positive feature that makes these material worthy to be studied is the high sodium uptake they are able to bare, bestowing them high theoretical specific capacities (>800 mAh∙g-1). All these aspects have been tackled in designing a conversion anode that might constitute a valid solution toward a sodium secondary battery whole-cell assembly. Together with anode materials also a high-performing and low-cost cathode material has been investigated. The exploratory study of pyrophosphate-MWCNT composite intercalation material led to interesting results referred to fast kinetics and material reliability throughout the cycles. To TiO2 nanocrystals synthesis and crystalline appearance-electrochemical properties correlation has beeb dedicated an exhaustive analysis which allowed to achieve significative advancements in defining the sodium uptake mechanism for pseudo-capacitive oxide-based anode material for sodium-ion batteries.

La tecnologia delle batterie Sodio-ione ha negli ultimi tempi suscitato una crescente attenzione da parte della comunità scientifica mondiale grazie al fatto di poter rappresentare una valida alternativa alla tecnologia Litio-ione, più sostenibile dal punto di vista ambientale ed economico. Il lavoro di Dottorato è stato principalmente dedicato alla ricerca di materiali attivi per batterie Sodio ione. I materiali presi in considerazione, sia catodici che anodici, sono stati indagati ponendo particolare attenzione ai limiti e difficolta pratiche che gli stessi possono manifestare nei confronti dell'intercalazione di sodio. Tra questi sono stati considerati: i) la valutazione della diffusione di Na+ in una struttura host intercalante, ii) e prodotti, gli intermedi e la reversibilità di reazione di conversione di ossidi dei metalli di transizione, iii) gli effetti delle proprietà cristalline dei materiali sulle performance elettrochimiche e iv) le caratteristiche chimico-fisiche caratterizzanti la generale stabilità di un materiale funzionale per batterie. Durante il lavoro di tesi è stato perpetrato un continuo parallelismo tra le caratteristiche morfologiche e strutturali e le performance elettrochimiche, ottenendo infine una dettagliata visione di molteplici classi di materiali attivi per sodio-ione. Ciò ha reso necessario un approccio inter-disciplinare in cui ad avanzate tecniche analitiche di tipo elettrochimico, è stato affiancato un approccio più specificatamente ingegneristico dei materiali stessi, al fine di evidenziare le correlazione proprietà-struttura. Tra le classi di materiali attivi investigate un ruolo di primaria importanza è stato riservato a materiali ad intercalazione catodici e materiali a conversione basati su ossidi di metalli di transizione. I primi, tipicamente materiali con struttura cristallina lamellare di natura ossidica, o a base di fosfati e pirofosfati, promuovono l’intercalazione di sodio con cinetiche veloci e con molteplici geometrie e pattern assunti dai cationi intercalati. I materiali a conversione invece permettono di ottenere lo stoccaggio energetico tramite reazione chimiche spontanee che avvengono tra materiale attivo e lo ione sodio. Paragonati a materiali ad intercalazione, i materiali a conversione presentano molteplici problematiche, tra cui: i) la variazione di volume considerevole che accompagna la reazione di conversione che introduce stress meccanici considerevoli e porta alle tipiche frammentazioni d’elettrodo e ii) processi irreversibili che solitamente corredano la reazione di conversione. Un aspetto che rende tali materiali meritevoli di essere studiati è la loro capacità di stoccare elevate quantità di sodio rendendoli capaci di capacità specifiche teoriche straordinarie (> 800 mAh/g). Tutti questi aspetti sono stati affrontati e tenuti in profonda considerazione al fine di mettere a punto un materiali a conversione anodica nano-strutturato a base di Co3O4 che rappresentasse una valida soluzione al problema di perfezionamento delle batterie sodio-ione. Assieme a materiali anodici, è stato altresì condotto lo studio di materiali catodici caratterizzati da elevate performance ma bassi costi di sintesi. Lo studio preliminare del composito ad intercalazione Na2FeP2O7/MWCNT a condotto ad interessanti risultati legati ad estremamente veloci cinetiche di diffusione di sodio all’interno del network di canali del materiale e ad una generale stabilità durante la ciclazione. All’anatasio (TiO2) nano-crystallino sintetizzato ad-hoc è stata dedicata l’ultima parte del lavoro di ricerca. Tale lavoro ha permesso di confermare importanti correlazioni tra le caratteristiche cristalline superficiali dei nano-cristalli e i meccanismi di interazione con sodio attraverso meccanismi pseudocapacitivi; e significativi avanzamenti sono stati ottenuti nella definizione di tale meccanismo e nella messa a punto di un efficiente materiale anodico a basso costo.

(2017). Investigation of Sodium-ion Battery Materials. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2017).

Investigation of Sodium-ion Battery Materials

LONGONI, GIANLUCA
2017

Abstract

Na-ion battery technology has recently aroused great interest among all the scientific community, as a valid and more environmentally friendly alternative to Li-ion batteries. The PhD research activity has been mostly devoted to the investigation of reliable active materials for sodium ion battery technology. All the investigated materials, either anode or cathode, have been investigated trying to highlight the major limits and difficulties connected to sodium intercalation and conversion reactions. Among these, some are: i)assessment of Na diffusion in an intercalating host structure, ii)products and reversibility of transition metal oxides conversion reactions, iii) effects of materials crystalline properties on electrochemical performances and iv) features influencing the overall stability of a functional material. In order to keep the most broad-based overview of the problem, it has been chosen to systematically start, for each species electrochemically investigated, from its synthesis and thorough chemical-physical characterization. Rather than a pure electrochemical analysis, a continuous parallelism between morphological features, structural characteristics and performances was encouraged, eventually obtaining a detailed overlook of different classes of active materials for sodium batteries. What has been screened all along the three year-long research period has been a comprehensive investigation of new generation electrochemically active materials for energy storage applications. This implied an inter-disciplinary work in which advanced electro-analytical techniques have been widely used to characterize inorganic compounds or ad-hoc synthesized composites keeping in mind precise structure-performance correlations. Among the investigated classes, a role of relevance has been reserved to intercalating cathode species and conversion anode materials. The former, typically layered transition metal oxides, phosphates and pyrophosphates, are capable of sodium cations insertion, with fast kinetics, between layers or inside channels generated from peculiar atoms arrangement. Conversion anode materials on the other hand, carries out the sodium storage via spontaneous chemical reactions with oxide-based material, such as Co3O4 or Fe2O3, a chalcogenide or a halide. Compared to intercalation materials, conversion ones are more challenging to deal with, due to the following difficulties: i)their not negligible volume change during conversion reaction and the correlated induced mechanical stresses leading to electrode fracturing and pulverization, ii)occurrence of irreversible and parasitic reactions and iii)material operating potentials is often too high (around 1.0 V vs. Na/Na+) and thus not suitable for being used as anode materials inside a sodium cell. A positive feature that makes these material worthy to be studied is the high sodium uptake they are able to bare, bestowing them high theoretical specific capacities (>800 mAh∙g-1). All these aspects have been tackled in designing a conversion anode that might constitute a valid solution toward a sodium secondary battery whole-cell assembly. Together with anode materials also a high-performing and low-cost cathode material has been investigated. The exploratory study of pyrophosphate-MWCNT composite intercalation material led to interesting results referred to fast kinetics and material reliability throughout the cycles. To TiO2 nanocrystals synthesis and crystalline appearance-electrochemical properties correlation has beeb dedicated an exhaustive analysis which allowed to achieve significative advancements in defining the sodium uptake mechanism for pseudo-capacitive oxide-based anode material for sodium-ion batteries.
RUFFO, RICCARDO
Sodium-ion; battery,; Electrochemistry,; Energy; Storage
Sodium-ion; battery,; Electrochemistry,; Energy; Storage
BIO/07 - ECOLOGIA
English
13-mar-2017
SCIENZE - 80R
29
2015/2016
open
(2017). Investigation of Sodium-ion Battery Materials. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2017).
File in questo prodotto:
File Dimensione Formato  
phd_unimib_787814.pdf

accesso aperto

Descrizione: tesi di dottorato
Tipologia di allegato: Doctoral thesis
Dimensione 10.35 MB
Formato Adobe PDF
10.35 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/153278
Citazioni
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
Social impact