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LiFePO4-coated carbon fiber electrodes for structural batteries
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.ORCID iD: 0009-0007-7850-585X
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lithium-ion batteries (LIBs) have a central role in products, from portable devices to large-scale energy storage for the electric grid and continue to undergo rapid development. The surge in electric vehicles has intensified the focus on technological advancements and new-generation technologies. Structural batteries have received considerable attention for their multifunctionality and lightweight properties. These batteries utilize carbon fibers to combine their mechanical strength with battery functionalities in a single structure, consequently reducing overall weight and increasing energy density. Similar to traditional LIBs, structural batteries comprise negative and positive electrodes, reinforced within a structural battery electrolyte (SBE). While extensive research has been conducted on carbon fibers as negative electrodes, there has been a relative scarcity in the development of positive electrodes that align with the structural battery concept.

            This thesis explores coating methodologies on polyacrylonitrile (PAN)-based carbon fibers (CF) with positive electrode active material, specifically focusing on the utilization of lithium iron phosphate (LFP). Electron microscopy and electrochemical tests were conducted to evaluate the relation between structure with long-term and rate performances of these electrodes in half-cells. 

            Spray coating and siphon impregnation (later referred to as ‘powder impregnation’ in this thesis) techniques were employed to coat the carbon fibers, which serve as current collectors instead of conventional aluminum foil. The spray coating method utilized a standard electrode slurry based on an organic solvent, with efforts made to optimize parameters such as the height of the spray gun and plate temperature. The sprayed coating was quite thin, resulting in excellent rate capability. In the powder impregnation method, a water-based slurry was utilized with polyethylene glycol (PEG) as a binder. Efforts were made to obtain good fiber distribution within a homogeneous matrix of coating in the electrode. The parameters, including slurry viscosity, binder effect, electrode design, cell design, electrode preparation, and drying temperatures, were regulated for the best electrochemical performance and cell life. It was found that a binder is necessary for ensuring robust electrodes. Elevated drying temperatures are essential to eliminate moisture from the water-based process and components. Additionally, conductive carbon additives such as carbon black and graphene were incorporated, and their impact was assessed. A small amount of carbon additive (< 1 wt.%) improved performance at higher cycling rates. 

            The electrodes produced via powder impregnation were finally integrated into double-sided full cells versus uncoated PAN-derived CFs serving as negative electrodes in commercial liquid electrolyte or SBE, respectively. The LFP-coated CF electrodes exhibited good performance in full cells, indicating promising performance for the structural battery. The main limitation was observed in the power losses in the CF negative electrodes and in the ionic conductivity of the SBE. Overall, the thesis shows that the encapsulation of individual PAN-derived carbon fiber filaments using the applied coating methodologies was successful and that the use of carbon fibers as current collectors proved to be effective.

Abstract [sv]

Litiumjonbatterier (LIB) har en central roll i produkter, allt från bärbar elektronik till stora energilager för elnätet, och fortsätter att utvecklas snabbt. Utvecklingen av elfordon har inneburit ett intensifierat fokus på tekniska framsteg och nya generationer av teknologier. Strukturella batterier har fått stor uppmärksamhet för sin multifunktionalitet och sina lättviktegenskaper. Dessa batterier använder kolfibrer för att kombinera mekanisk styvhet och styrka med en batterifunktion i ett enda material, vilket minskar den totala vikten och ökar energitätheten. I likhet med traditionella LIB består strukturella batterier av negativa och positiva kolfiberelektroder i en strukturell batterielektrolyt (SBE). Även om omfattande forskning har bedrivits på kolfibrer som negativa elektroder, har det saknats lämpliga metoder för att utveckla positiva elektroder som är kompatibla med konceptet för strukturella batterier.

            Den här avhandlingen utforskas beläggningsmetoder på polyakrylnitril (PAN)-baserade kolfibrer (CF) med positivt elektrodaktivt material, i detta fall litiumjärnfosfat (LFP). Spraybeläggning och sifonimpregnering (senare kallad "pulverimpregnering" i denna avhandling) utvecklades för att belägga kolfibrerna, som fungerar som lastbärare och strömtilledare i stället för en konventionell aluminiumfolie. Elektronmikroskopi och elektrokemiska tester utfördes för att utvärdera strukturens påverkan på livslängd och prestanda för dessa elektroder i halvcell. 

            Spraybeläggningsmetoden utgick från en typisk elektrodslura med ett organiskt lösningsmedel, där själva spraymetoden justerades så som höjden på sprutpistolen och plattans temperatur. Beläggningen med spraymetoden blev relativt tunn vilket resulterade i mycket små förluster vid högre cyklingsströmmar. I pulverimpregneringsmetoden användes en vattenbaserad slura med polyetylenglykol (PEG) som bindemedel. Metoden förbättrades för god fördelning av fibrerna i en homogen matris som beläggningen utgjorde i elektroden. Parametrarna, inklusive slurans viskositet, bindemedelseffekt, elektroddesign, celldesign, elektrodberedning och torkningstemperaturer, justerades för bästa prestanda och livslängd. Det visade sig att bindemedel är nödvändigt för att säkerställa robusta elektroder. Förhöjda torkningstemperaturer är avgörande för att eliminera fukt från den vattenbaserade processen och komponenterna. Dessutom undersöktes inverkan av tillsatser av ledande kol som kimrök och grafen i elektroden. En liten mängd av koltillsats (< 1 wt.%) förbättrade prestandan vid högre cyklingshastigheter. 

            Elektroderna som producerades via pulverimpregnering integrerades slutligen i dubbelsidiga helceller både i kommersiell flytande elektrolyt och med polymerelektrolyt SBE, med obelagda PAN-baserade kolfibrer som negativa elektroder. De LFP-belagda CF-elektroderna uppvisade god cyklingsbarhet i helcellerna, vilket tyder på lovande prestanda för strukturbatteriet. Begränsningarna låg huvudsakligen i effektförluster kopplade till den negativa elektroden och i ledningsförmågan i SBE:n. Sammantaget visar avhandlingen att inkapslingen av enskilda PAN-baserade kolfiberfilament med det två beläggningsmetoderna var framgångsrik och att användningen av kolfibrer som strömtilledare fungerade väl. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2024. , p. 79
Series
TRITA-CBH-FOU ; 2024:9
Keywords [en]
Lithium-ion battery, structural batteries, positive electrodes, PAN-based carbon fibers, lithium iron phosphate
Keywords [sv]
Litiumjonbatteri, strukturella batterier, positiva elektroder, PAN-baserade kolfibrer, litiumjärnfosfat
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-344628ISBN: 978-91-8040-887-5 (print)OAI: oai:DiVA.org:kth-344628DiVA, id: diva2:1846392
Public defence
2024-04-18, E3, Osquars backe 2, floor 2. Via Zoom: https://kth-se.zoom.us/webinar/register/WN_tlfpCwy2So2--moYgvclVg, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20240325

Available from: 2024-03-25 Created: 2024-03-22 Last updated: 2024-04-09Bibliographically approved
List of papers
1. LiFePO4-coated carbon fibers as positive electrodes in structural batteries: Insights from spray coating technique
Open this publication in new window or tab >>LiFePO4-coated carbon fibers as positive electrodes in structural batteries: Insights from spray coating technique
2024 (English)In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 160, p. 107670-, article id 107670Article in journal (Refereed) Published
Abstract [en]

This study presents the fabrication of LiFePO4 (LFP)-coated carbon fibers (CFs) as a positive electrode component for structural batteries, utilizing a spray coating technique. The successful coating of CFs through this method demonstrated their usefulness as efficient current collectors. The electrodes obtained using this method underwent electrochemical evaluations. Throughout the extended cycling tests at C/7, the maximum specific discharge capacity reached 146 mAh/g, maintaining a 77% capacity retention after 100 cycles. In rate performance assessments at the faster C-rate of 1.5C, the capacity measured 123 mAh/g, with a retention of 96%. The application of spray coating emerges as a promising technique for electrode production in structural batteries, showcasing its potential for optimizing performance in multifunctional energy storage systems.

Place, publisher, year, edition, pages
Elsevier BV, 2024
Keywords
Carbon fibers, LiFePO 4, Lithium-ion battery, Spray coating, Structural battery
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-343468 (URN)10.1016/j.elecom.2024.107670 (DOI)001174772800001 ()2-s2.0-85184141114 (Scopus ID)
Note

QC 20240219

Available from: 2024-02-15 Created: 2024-02-15 Last updated: 2024-04-05Bibliographically approved
2. Powder-impregnated carbon fibers with lithium iron phosphate as positive electrodes in structural batteries
Open this publication in new window or tab >>Powder-impregnated carbon fibers with lithium iron phosphate as positive electrodes in structural batteries
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2023 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 241, p. 110153-, article id 110153Article in journal (Refereed) Published
Abstract [en]

A structural battery is a multifunctional battery that can carry a load while storing energy. Structural batteries have been a cutting-edge research focus in the last decade and are mainly based on polyacrylonitrile (PAN)-carbon fibers (CFs). In this work, positive electrodes based on PAN-carbon fibers were manufactured with powder impregnation (siphon impregnation) technique using a water-based slurry containing lithium iron phosphate (LFP) as the active electrode material and the water-soluble binder polyethylene glycol (PEG). Different coating compositions, electrode-drying temperatures, and coating parameters were investigated to optimize the coating uniformity and the electrochemical performances. Scanning electron microscopy results showed that the electrode materials coat the CFs uniformly, conformably, and individually. Electrochemical characterization of pouch cells shows that the electrodes containing 6 wt% PEG dried at 140 degrees C have the best battery performance, delivering a first discharge capacity of 151 mAh g-1 and capacity retention higher than 80% after 100 cycles. Moreover, excellent capacity reversibility was achieved when the electrodes were cycled at multiple C-rates attesting to their stability. The results demonstrate that CFs perform excellently as current collectors in positive electrodes.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
Carbon fibers, Structural positive electrode, LiFePO4, Lithium-ion battery, Siphon impregnation
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-334696 (URN)10.1016/j.compscitech.2023.110153 (DOI)001044167200001 ()2-s2.0-85166619398 (Scopus ID)
Note

QC 20230824

Available from: 2023-08-24 Created: 2023-08-24 Last updated: 2024-03-22Bibliographically approved
3. Enhancing Structural Battery Performance: Investigating the Role of Conductive Carbon Additives in LiFePO4-Impregnated Carbon Fiber Electrodes
Open this publication in new window or tab >>Enhancing Structural Battery Performance: Investigating the Role of Conductive Carbon Additives in LiFePO4-Impregnated Carbon Fiber Electrodes
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

This study centers on investigating the influence of conductive additives, carbon black (Super P) and graphene, within the context of LiFePO4 (LFP)-impregnated carbon fibers (CFs) produced using the powder impregnation method. The performance of these additives was subject to an electrochemical evaluation. The findings reveal that there are no substantial disparities between the two additives at lower cycling rates, highlighting their adaptability in conventional energy storage scenarios. However, as cycling rates increase, graphene emerges as the better performer. At a rate of 1.5C in a half-cell versus lithium, electrodes containing graphene exhibited a discharge capacity of 83 mAh g-1LFP ; those with Super P and without any additional conductive additive showed a capacity of 65 mAh g-1LFP  and 48 mAh g-1LFP , respectively. This distinction is attributed to the structural and conductivity advantages inherent to graphene, showing its potential to enhance the electrochemical performance of structural batteries. Furthermore, LFP-impregnated CFs were evaluated in full cells versus pristine CFs, yielding relatively similar results, though with a slightly improved outcome observed with the graphene additive. These results provide valuable insights into the role of conductive additives in structural batteries and their responsiveness to varying operational conditions, underlining the potential for versatile energy storage solutions. 

Keywords
Carbon fiber, conductive additive, LiFePO4, Lithium-ion battery
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-344626 (URN)
Note

QCR 20240326

Available from: 2024-03-22 Created: 2024-03-22 Last updated: 2024-03-26Bibliographically approved
4. Structural Batteries with LiFePO4-Impregnated Carbon Fibers
Open this publication in new window or tab >>Structural Batteries with LiFePO4-Impregnated Carbon Fibers
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

This study focuses on the fabrication and evaluation of structural batteries, emphasizing their electrochemical performance. LiFePO4 (LFP)-impregnated carbon fibers (CFs), produced via the powder impregnation method, were employed as positive electrodes. These electrodes underwent infusion with structural battery electrolyte (SBE) and curing to yield positive structural battery electrodes. A structural battery fully based on CFs was constructed and subjected to electrochemical testing, with positive electrodes assembled versus pristine CF of T800S as negative electrodes. The results revealed specific discharge capacities of 123 mAh g-1LFP for the structural positive electrode and 178 mAh g-1T800S for the structural battery, both at similar current densities. Both the half and full structural cells maintained capacities of 94% and 96%, respectively, during rate capability tests when reverting to their initial current densities. The electrochemical impedance spectroscopy (EIS) results revealed that, the structural battery demonstrated a relatively improved surface impedance, with the values ranging between 186 Ω cm² and 2000 Ω cm². Additionally, similar comparative studies were conducted on full cells in a commercial liquid electrolyte consisting of 1M LiPF6 in EC: DEC (1:1 vol.%). The research introduces a prototype of laminated composite batteries, showing their potential, especially when utilizing fully carbon fiber-based electrodes.

Keywords
Carbon fibers, LiFePO4, polymer electrolyte, structural battery, Lithium-ion battery
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-344629 (URN)
Note

QCR 20240326

Available from: 2024-03-22 Created: 2024-03-22 Last updated: 2024-03-26Bibliographically approved

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Yucel, Yasemin Duygu

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