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Lityum iyon sonrası batarya sistemleri için katı elektrolitlerin geliştirilmesi

Development of solid electrolytes for post-lithium-ion battery systems

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  1. Tez No: 997716
  2. Yazar: MUSTAFA ÇELİK
  3. Danışmanlar: PROF. DR. TUĞRUL ÇETİNKAYA
  4. Tez Türü: Doktora
  5. Konular: Enerji, Metalurji Mühendisliği, Seramik Mühendisliği, Energy, Metallurgical Engineering, Ceramic Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2026
  8. Dil: Türkçe
  9. Üniversite: Sakarya Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: Belirtilmemiş.

Özet

Küresel enerji talebindeki hızlı artış ve fosil yakıtlardan yenilenebilir enerji kaynaklarına geçiş süreci, yüksek performanslı enerji depolama teknolojilerine olan ihtiyacı her geçen gün artırmaktadır. Günümüzde mobil elektronik cihazlardan elektrikli araçlara kadar geniş bir kullanım alanına sahip olan lityum iyon bataryalar, teorik enerji yoğunluğu sınırlarına yaklaşmış olmaları ve bünyelerinde barındırdıkları sıvı elektrolitlerin yanıcılık, sızıntı ve termal kararsızlık gibi güvenlik riskleri nedeniyle, geleceğin enerji ihtiyaçlarını karşılamada yetersiz kalmaktadır. Bu bağlamda, Lityum İyon (Li- iyon) sonrası teknolojiler olarak adlandırılan Lityum-Sülfür (Li-S) ve Lityum-Hava (Li-hava) batarya sistemleri, sundukları yüksek teorik enerji yoğunlukları ile öne çıkmaktadır. Ancak bu sistemlerin güvenli, verimli ve uzun ömürlü bir şekilde hayata geçirilebilmesi, sıvı elektrolitlerin yerini alabilecek, yüksek iyonik iletkenliğe, geniş elektrokimyasal kararlılık penceresine ve üstün mekanik özelliklere sahip katı hal elektrolitlerin geliştirilmesine bağlıdır. Bu tez çalışması, söz konusu ihtiyaca yönelik olarak, yüksek oksidasyon kararlılığına sahip oksit esaslı Lityum Alüminyum Titanyum Fosfat (LATP) ve yüksek iyonik iletkenlik potansiyeli taşıyan sülfür esaslı Lityum Fosfor Sülfür (LPS) inorganik katı elektrolitlerinin sentezlenmesi, karakterizasyonu ve polimer matrislerle hibritleştirilerek performanslarının optimize edilmesini konu almaktadır. Çalışmanın ilk aşamasında, sentez yöntemlerinin malzeme özellikleri üzerindeki etkileri sistematik olarak incelenmiştir. Oksit esaslı Li1.33l0.3Ti1.7(PO4)3 (LATP) elektroliti, bileşenlerin atomik düzeyde homojen karışımını sağlayan sol-jel yöntemiyle sentezlenmiş ve 1,62 × 10-4 S·cm-1 iletkenlik değeri elde edilmiştir. Sülfür esaslı Li7P3S11 (LPS) elektrolitinin üretimi için ise“Sıvı Faz Sentezi”ve“Mekanik Aktivasyon”yöntemleri karşılaştırmalı olarak değerlendirilmiştir. Yapısal analizler ve iyonik iletkenlik ölçümleri sonucunda, mekanik aktivasyon yönteminin faz saflığı ve iyonik iletkenlik açısından belirgin bir üstünlük sağladığı tespit edilmiştir. Mekanik aktivasyon ile üretilen amorf öncülerin, çekirdeklenme ve büyüme süreçlerinin ayrıştırıldığı optimize edilmiş iki kademeli bir ısıl işlem protokolü ile kristalleştirilmesi sonucunda, oda sıcaklığında 1,98 × 10-3 S·cm-1 gibi literatürdeki yüksek değerlerle yarışabilir bir iyonik iletkenliğe ulaşılmıştır. Saf inorganik elektrolitlerin batarya hücrelerinde kullanımı sırasında karşılaşılan“mekanik kırılganlık”,“yetersiz katı-katı teması”ve“ara yüzey kimyasal kararsızlığı”problemlerini aşmak amacıyla, çalışma kompozit elektrolit tasarımı ile derinleştirilmiştir. LPS elektroliti, sülfür kimyasıyla uyumlu PMMA polimeri ile; LATP elektroliti ise elektrokimyasal olarak kararlı PVDF-HFP polimeri ile birleştirilerek esnek, işlenebilir ve ara yüzey uyumu yüksek kompozit membranlar üretilmiştir. Elde edilen katı elektrolitlerin elektrokimyasal performansı, Li-iyon, Li-S ve Li-hava hücre konfigürasyonlarında kapsamlı bir şekilde test edilmiştir. Li-iyon batarya testlerinde, saf inorganik elektrolitler ara yüzey dirençleri nedeniyle sınırlı performans gösterirken; PVDF-HFP matrisli C-LATP10 kompozit elektroliti, LFP katodu ile oluşturduğu kararlı ara yüzey sayesinde 100 döngü sonunda 138 mAh g⁻¹ kapasite koruyarak %99 üzerinde Coulombik verim sergilemiştir. Li-S batarya testlerinde, saf LPS elektroliti sülfür katodunun hacimsel genleşmesine uyum sağlayamayarak mekanik çatlaklar oluşturmuş ve hızla kapasite kaybetmiştir. Buna karşın, PMMA katkılı C-LPS85 kompozit elektroliti, esnek yapısı sayesinde elektrot–elektrolit ara yüzey bütünlüğünü korumuş; katı fazlı yapısı sayesinde ise sıvı elektrolit sistemlerinde görülen polisülfit göçünü (shuttle effect) tamamen ortadan kaldırmış ve 100 çevrim boyunca kararlı bir deşarj kapasitesi sergilemiştir. Li-hava batarya testlerinde ise saf LATP elektroliti, lityum metal ile temasında gerçekleşen Ti4+ iyonlarının indirgenmesi ve malzemenin kırılgan yapısı nedeniyle kısa sürede yapısal bozunmaya uğramıştır. Buna karşın C-LATP10 kompozit elektroliti, polimerin sağladığı koruyucu etkisi ve gözenekli katot içerisine nüfuz ederek oluşturduğu yumuşak temas (arayüzey uyumu) sayesinde, hücrenin 37 döngü boyunca kararlı bir şekilde çalışmasını mümkün kılmıştır. Sonuç olarak bu tez çalışması; inorganik katı elektrolitlerin yüksek iyonik iletkenlik potansiyelini, polimerlerin mekanik esnekliği, işlenebilirliğini ve kimyasal kararlılık avantajlarıyla birleştiren“kompozit elektrolit”stratejisinin başarısını deneysel olarak kanıtlamıştır. Bu yaklaşım, yeni nesil bataryaların ticarileşmesi önündeki en kritik engeller olan yüksek ara yüzey direnci ve elektrokimyasal kararsızlık problemlerine karşı ölçeklenebilir ve etkin bir çözüm sunmaktadır. Geliştirilen kompozit malzemeler, sıvı elektrolitlerin güvenlik risklerini ortadan kaldırarak, geleceğin yüksek enerji yoğunluklu ve uzun ömürlü enerji depolama sistemleri için sağlam bir teknolojik zemin oluşturmaktadır.

Özet (Çeviri)

The global demand for efficient energy storage has increased rapidly due to the widespread use of portable electronics, electric vehicles, and large scale renewable energy systems. This trend has highlighted well known limitations in conventional lithium-ion (Li-ion) battery technologies. While Li-ion batteries have dominated the market for decades, they are approaching their theoretical physicochemical limits in terms of achievable energy density. Furthermore, the reliance on organic liquid electrolytes introduces significant safety risks, including flammability and leakage. These liquid electrolytes also restrict the electrochemical stability window required for high-voltage applications. Consequently, there is a strong scientific and industrial drive to develop post lithium ion battery technologies. Examples include Lithium-Sulfur (Li-S) and Lithium-Air (Li-air) batteries, which offer substantially higher theoretical energy densities than conventional intercalation based systems. However, the practical realization of these advanced battery chemistries is limited by significant material and interfacial challenges. These challenges have accelerated research interest in solid state electrolytes as alternatives to liquid systems. Solid state electrolytes have the potential to provide enhanced safety, wider electrochemical stability windows, and sufficient mechanical rigidity to suppress lithium dendrite growth, thereby enabling the use of high capacity lithium metal anodes. This dissertation focuses on the development, characterization, and optimization of inorganic solid electrolytes and their polymer composite derivatives to address key bottlenecks in post lithium ion systems. The research is structured around two primary classes of inorganic solid electrolytes: oxide-based systems, specifically NASICON-type lithium aluminum titanium phosphate (LATP), and sulfide based systems, specifically lithium phosphorus sulfide (LPS). The study systematically investigates synthesis parameters, structural and transport properties, and integration into composite electrolytes to mitigate the mechanical brittleness and interfacial instability associated with pure ceramic electrolytes. The first phase of this research focused on the synthesis and characterization of oxide-based LATP electrolytes. LATP was selected due to its high oxidative stability and relative resistance to ambient moisture, making it a suitable candidate for high voltage and semi open battery systems such as Li–air configurations. A sol-gel synthesis route was employed to achieve improved homogeneity of the precursors. Citric acid and ethylene glycol were used to form a polymeric network that entrapped lithium, aluminum, titanium, and phosphate species. This approach enabled the formation of a phase pure rhombohedral NASICON structure at lower calcination temperatures than those typically required for conventional solid state methods. X-ray diffraction analysiS·confirmed high crystallinity, while scanning electron microscopy revealed a dense microstructure consisting of well sintered polyhedral grains. Electrochemical impedance spectroscopy measurements indicated a room temperature ionic conductivity of 1.62 × 10-4 S·cm-1, which iS·competitive among oxide-based solid electrolytes. Despite these favorable bulk properties, electrochemical testing revealed notable limitations. These limitations became evident when LATP was placed in direct contact with lithium metal anodes. Cyclic voltammetry and galvanostatic cycling experiments indicated partial reduction of Ti4+ to Ti3+ at potentials below approximately 2.5 V vs. Li/Li+. This process led to the formation of a mixed ionic-electronic interphase, increasing electronic leakage at the interface and promoting short circuit like behavior, ultimately resulting in rapid cell degradation. In addition, the intrinsic rigidity of ceramic pellets limited effective physical contact with the electrodes, leading to elevated interfacial resistance. To mitigate the interfacial instability and mechanical rigidity of LATP, a composite electrolyte strategy was adopted. LATP particles were dispersed within a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) matrix to produce a flexible and processable membrane. The PVDF–HFP polymer served dual functions by acting as a mechanical binder and providing a protective coating for the ceramic particles. The C-LATP10 composite, containing 10 wt% LATP, exhibited a favorable balance between ionic conductivity and mechanical integrity. In cell testing, particularly in Li-air configurations, thiS·composite electrolyte demonstrated a significant improvement compared with the pure ceramic electrolyte. The polymer matrix isolated LATP particles from direct contact with the lithium metal anode and suppressed parasitic titanium reduction. In addition, the polymer phase penetrated the porous gas diffusion cathode, thereby expanding the effective triple-phase boundary for oxygen redox reactions. As a result, Li-air cells utilizing the C-LATP10 composite operated stably for up to 37 cycles, overcoming the rapid failure typically observed for pure LATP based cells and supporting the effectiveness of the polymer ceramic composite strategy for oxide-based systems. The second phase of the research transitioned to sulfide-based electrolytes to address the need for higher ionic conductivity, which is particularly important for high power applications and battery systems involving substantial volume changes, such as Li-S batteries. The study focused on LPS, a superionic conductor widely reported for its high lithium-ion mobility. Two synthesis routes were comparatively evaluated: a liquid-phase synthesis using acetonitrile and a mechanochemical route employing high-energy ball milling. The experimental results indicated a clear performance advantage for the mechanical activation method. The liquid-phase route led to residual solvent entrapment and the formation of low-conductivity secondary phases, such as Li4P2S6, during the drying and crystallization process. In contrast, the mechanochemical approach was followed by an optimized two-step heat treatment. This procesS·consisted of a nucleation step at 180 °C and a crystal growth step at 250 °C, resulting in a phase pure material with a highly interconnected microstructure. The optimized LPS electrolyte exhibited a room-temperature ionic conductivity of 1.98 × 10-3 S·cm-1, approximately one order of magnitude higher than that of LATP and comparable to typical liquid electrolyte systems. Although LPS exhibited superior bulk ionic conductivity, significant challenges were observed in Li-S battery configurations. The sulfur cathode undergoes significant volumetric expansion, reported in the literature to reach up to approximately 80% during lithiation. The rigid LPS pellets were unable to accommodate this mechanical stress, leading to particle fracture, loss of interparticle contact, and rapid capacity fading. In addition, direct contact between the sulfide electrolyte and the lithium metal anode promoted the formation of resistive interfacial decomposition products, which further degraded electrochemical performance. To address these limitations, a polymer ceramic composite electrolyte was developed using poly(methyl methacrylate) (PMMA) as the polymer matrix. PMMA was selected due to itS·chemical compatibility with sulfide electrolytes and its processability in non-polar solvents such as toluene, thereby minimizing moisture-induced degradation. The optimized C-LPS85 composite, consisting of 85 wt% LPS and 15 wt% PMMA, exhibited enhanced mechanical flexibility and improved chemical stability. The PMMA phase acted as a mechanical buffer, accommodating the volumetric expansion of the sulfur cathode and preserving electrode integrity during repeated cycling. Furthermore, the polymer coating reduced moisture sensitivity and suppressed the generation of H2S gas. Electrochemical testing of Li-S·cells incorporating the C-LPS85 composite demonstrated stable cycling behavior. These cells retained a reversible discharge capacity of approximately 420 mAh g-1 after 100 cycles, whereaS·cells based on pure LPS electrolytes exhibited rapid performance degradation. In conclusion, this dissertation demonstrates that although inorganic solid electrolytes provide high intrinsic ionic conductivity and enhanced safety characteristics, their practical implementation in next-generation battery systems strongly depends on resolving critical interfacial and mechanical challenges. The integration of ceramic electrolytes with polymer matrices into composite architectures was shown to be an effective strategy to bridge the gap between material-level properties and device level performance. The developed C-LATP10 and C-LPS85 composite electrolytes successfully combined the favorable transport characteristics of ceramic phases with the mechanical compliance and interfacial stability of polymer matrices. This work provides a scalable and scientifically robust framework for the development of safe, high energy density solid state battery systems and contributes to advancing the understanding of composite electrolyte design in electrochemical energy storage technologies. The results indicate that continued optimization of ceramic polymer interfaces and processing strategies will be essential for future technological progress in this field. The findings of this dissertation demonstrate the viability of inorganic organic composite electrolytes in mitigating interfacial and mechanical limitations associated with post lithium ion battery technologies. However, the transition from laboratory scale proof of concept demonstrations to commercially viable energy storage systems still requires the resolution of several technical challenges. The insights obtained from the synthesis, structural characterization, and electrochemical evaluation of LATP and LPS systems provide a foundation for defining strategic directions for future research, aimed at bridging the gap between fundamental materials science and practical engineering applications. One of the primary areas identified for future optimization is the enhancement of the intrinsic ionic conductivity of ceramic fillers to more closely approach that of conventional liquid electrolytes. Although the LATP and LPS electrolytes developed in this study achieved competitive conductivity values, further improvements may be realized through targeted crystal lattice engineering. In the oxide based LATP system, isovalent or aliovalent substitution at the aluminum site with elements of varying ionic radii, such as germanium, zirconium, or gallium, has the potential to expand migration bottlenecks within the NASICON framework and facilitate faster lithium ion transport. Similarly, for the sulfide based LPS system, partial substitution of sulfur anions with halogen species such aS·chlorine, bromine, or iodine may weaken the electrostatic interactions between lithium ions and the host lattice, thereby reducing activation energy for ion hopping and enhancing room-temperature ionic conductivity. Such atomic scale modifications are expected to contribute to improved power densities in composite electrolyte systems. Beyond the bulk properties of solid electrolytes, the stability of the electrode–electrolyte interface remains a critical research priority. The polymer coating strategy employed in this dissertation effectively reduced interfacial resistance and mitigated undesirable side reactions; however, more robust interfacial protection is required for long-term cycling under high-voltage conditions. Future work should explore the use of advanced thin-film deposition techniques, including atomic layer deposition (ALD) and molecular layer deposition (MLD), to create artificial solid electrolyte interphase (SEI) layers. The deposition of ultra-thin, conformal filmS·composed of lithium ion conducting but electronically insulating materials, such as lithium niobate or lithium tantalate, onto ceramic particles or lithium metal surfaceS·could serve as effective barriers against parasitic reactions and interfacial degradation. To gain a more comprehensive understanding of degradation mechanisms occurring during electrochemical cycling, future research should prioritize the use of in situ and operando characterization techniques. While the ex situ analyses performed in this study provided valuable insights, they capture material states only after cell disassembly and may overlook transient phenomena. Advanced techniques such as in situ X-ray diffraction for monitoring phase evolution, in situ Raman spectroscopy for detecting polysulfide shuttling and interfacial decomposition, and in situ scanning electron microscopy for visualizing volume changes and dendrite growth in real time can provide critical feedback for materials optimization. These diagnostic approaches are expected to enable a more precise identification of failure mechanisms specific to solid-state battery architectures. Finally, the scalability of manufacturing processes must be addressed to ensure the industrial relevance of these technologies. Although the solution-casting method employed in this work is suitable for laboratory scale fabrication, dependence on organic solvents introduces environmental, safety, and economic challenges, particularly for moisture sensitive sulfide electrolytes. Future research should therefore expand toward solvent free processing strategies, such as dry electrode coating and hot extrusion. These approaches have the potential to reduce production costs and minimize the risks associated with solvent residues. In addition, to maximize practical energy density, future cell designs should focus on increasing cathode active material loading while reducing the thickness of the solid electrolyte layer to below 50 µm, without compromising mechanical stability. By addressing these multidisciplinary challenges, the composite electrolyte technologies developed in this dissertation can serve as a foundation for the realization of safe, high energy density solid state energy storage systems.

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