Interface effects in solid electrolytes for Li-ion batteries

Diese Arbeit konzentriert sich auf die Untersuchung von heterogenen Oxysulfiden (100-x) Li3PS4-xLi3PO4 (10 ≤ x ≤ 40) und mehrschichtigen Dünnschicht-LiON-Al2O3-Festkörperelektrolyten (SEs) für Lithium-Ionen-Batterien (LIBs). Insbesondere wurden heterostrukturierte Oxysulfide vom Bulk-Typ und mehrschichtige Dünnschicht LiON-Al2O3 SEs durch zweistufiges mechanisches Mahlen bzw. Atomlagenabscheidung (ALD) synthetisiert. Ihre physikochemischen und elektrochemischen Eigenschaften wurden mit verschiedenen Techniken untersucht und die Arbeit an SEs ist in zwei Abschnitte unterteilt, wie nachstehend beschrieben: (I) Heterogene Oxysulfide (100-x)Li3PS4-xLi3PO4 (10 ≤ x ≤ 40) SEs. Eine Reihe von (100-x)Li3PS4-xLi3PO4 mit glaskeramischen Eigenschaften wurde erfolgreich durch Beimischung von Li3PO4 in Li3PS4 hergestellt. Dabei wurden die Oxysulfideinheiten [PS3O]3-, [PS2O2]3- und [PSO3]3- in den Gemischen durch 31P MAS NMR (Magic-Angle-Spinning Kernspinresonanz) nachgewiesen. In der Impedanzspektroskopie zeigen Oxysulfide (100-x)Li3PS4-xLi3PO4 mit x = 20 und 15 eine höhere Wechselstrom-Ionenleitfähigkeit (1,6 x 10-4 S/cm) als reines Li3PS4 (1,6 x 10-4 S/cm) bei Zimmertemperatur (RT). Dieses Phänomen wird auf die gegensätzlichen Einflüsse des Raumladungseffekts gegenüber dem Blockierungseffekt zurückgeführt. Nach der Stabilisierung durch Li-Plating und -Stripping steigen die Gleichstrom-Ionenleitfähigkeiten von Li/80Li3PS4-20Li3PO4/Li und Li/85Li3PS4-15Li3PO4/Li bei RT auf 2,4 × 10-3 S/cm bzw. 9,5 × 10-4 S/cm. Die Einführung von Li3PO4 in Li3PS4 führt zu einer verbesserten Grenzflächenstabilität zwischen Li und den Oxysulfiden, was mittels zeitaufgelöster Impedanzspektroskopie und Li-Plating und -Stripping festgestellt wurde. Für Li3PS4 wurden dagegen durch Cyclovoltammetrie an symmetrischen Zellen Li/Li3PS4/Li starke Nebenreaktionen beobachtet. Darüber hinaus wurde eine LiCoO2-Kathode in einer Machbarkeitsstudie zusammen mit den heterogenen Oxysulfid-SEs für x = 20 und x = 15 untersucht, die im Vergleich zu reinem Li3PS4 eine verbesserte Kapazität und Zyklen-Stabilität aufweisen. Die ausgezeichnete Stabilität der SEs/Li-Grenzfläche dieser beiden Oxysulfide wurde in der Vollzelle ebenfalls durch ihren stabilen Widerstand nach über 60 Lade-Entlade-Zyklen bewiesen. Trotz ihrer Verbesserungen leidet die positive LiCoO2-Elektrode in den ersten Zyklen aufgrund des enormen Widerstands der Grenzfläche zwischen SE und LiCoO2 immer noch unter Kapazitätsverlust. (II) Mehrschichtige Dünnschicht-LiON-Al2O3 SEs. Eine Reihe von flachen und defektfreien mehrschichtigen Dünnschicht-LiON-Al2O3 wurde erfolgreich hergestellt. Die amorphe Struktur von bei 200 °C abgeschiedenem LiON-Al2O3 wurde durch Röntgenbeugung unter streifendem Anfall (GIXRD) und Magic-Angle-Spinning Kernspinresonanzspektroskopie (MAS-NMR) nachgewiesen. Die schichtweise Struktur und Zusammensetzung von dünnschichtigem LiON-Al2O3 wurde unter Verwendung von Querschnitt-HRTEM und XPS Tiefenprofilen bestätigt, wobei die LiON-Lagen hauptsächlich aus LiOH, Li2CO3, Li-N und Li2O bestehen und durch Al2O3-Lagen getrennt sind. LiON-Al2O3-Dünnschichten zeigen aufgrund der Einführung von Stickstoff und Al2O3 eine verbesserte Ionenleitfähigkeit im Vergleich zur reinen 600LiON-Dünnschicht, da Al2O3 Hetero-Grenzflächen eingebracht werden, wobei die Ionenleitung entlang dieser Grenzflächen beschleunigt ist. Bemerkenswerterweise ist die Gesamtkonzentration an Li+-Ionen in diesen Heterostrukturen im Vergleich zum reinen LiON-Dünnschicht geringer, aber die Gesamtionenleitfähigkeit wird trotz zunehmender Aktivierungsenergie erhöht. Raumladungseffekte an der Hetero-Grenzfläche werden als der Mechanismus für diese Verbesserung angesehen, wobei lokale strukturelle Unordnung, induziert durch die isolierenden Al2O3-Zwischenschichten die Ursache der erhöhten Aktivierungsenergien sein können. Die Kombination von einer 3,2 nm dicken LiON-Zwischenschicht und einer 1 nm dicken Al2O3-Zwischenschicht zeigt die höchste Ionenleitfähigkeit (6,2 x 10-4 S/cm at 160 °C) und die niedrigste Aktivierungsenergie (0,57±0.02 eV) unter allen eingesetzen mehrschichtigen Heterostrukturen. Diese Arbeit bietet einen neuen Ansatz für das Design heterostrukturierter mehrschichtiger Dünnschicht-Festkörperelektrolyte mit hochionenleitenden Grenzflächen über ALD für ionische Bauteile

Functionalization of Graphite Electrodes with Aryl Diazonium Salts for Lithium‐Ion Batteries

The functionalization of electrode surfaces is a useful approach to gain a better understanding of solid–electrolyte interphase formation and battery performance in lithium-ion batteries (LIBs). Electrografting and deprotection of alkyl silyl protected ethynyl aryl diazonium salts on graphite electrodes were performed. Furthermore, electrografting of aryl diazonium salts carrying functional groups such as amino, carboxy and nitro, and their influence on the electrochemical performance in LIBs were investigated. The drawbacks of electrografted and especially deprotected samples were evaluated and compared to corresponding in situ grafted samples. While electrografted samples tend to lower the delithiation capacities, in situ grafted samples, except amino groups, reveal higher capacities. Ethynyl (TMS) shows improved capacities at 1 C and better capacity retention compared to the pristine graphite electrode. Additionally, the Coulombic efficiency of the first cycle was enhanced for in situ grafted samples

The Interaction Between Electrolytes and Sb2O3–based Electrodes in Sodium Batteries: Uncovering Detrimental Effects of Diglyme

Conversion materials are promising to improve the energy density of sodium‐ion‐batteries (NIB). Nevertheless, they suffer from the drawback of phase transitions and pronounced volume changes during cycling, which causes cell instability. When using these types of electrodes, all cell‐components have to be adjusted. In this study, a tremendous influence of the electrolyte solution on Sb$_{2}$O$_{3}$ conversion electrodes for NIBs is discussed. Solutions based on three solvents and solvent combinations established for NIBs, ethylene carbonate/dimethyl carbonate (EC/DMC), EC/DMC+5 % fluoroethylene carbonate (FEC), and diglyme, lead to a massively divergent electrochemical behavior of the same Sb$_{2}$O$_{3}$ electrode. Sb$_{2}$O$_{3}$ demonstrates the highest stability in solutions containing FEC, because this component forms a flexible, protecting surface film that prevent disintegration. One key finding of this work is that electrolyte solutions based on ether solvents like diglyme can remove Sb‐ions from Sb$_{2}$O$_{3}$ during cycling. Diglyme has the ability to coordinate and extract Sb$^{3+}$ during the oxidation of Sb$_{2}$O$_{3}$. This leads to contaminations of all cell components and a strong capacity loss together with an irregular electrochemical signature. Due to its poor reactivity at low potentials, diglyme forms a thin or even no surface layer. Thereby, there are no protecting films on the Sb$_{2}$O$_{3}$ electrodes that can avoid Sb$^{3+}$ ion dissolution. A critical examination of the electrolyte solutions components’ impact is essential to match them with conversion reaction anodes

Choosing the right carbon additive is of vital importance for high-performance Sb-based Na-ion batteries

Electrodes based on alloying reactions for sodium-ion batteries (NIB) offer high specific capacity but require bespoken electrode material design to enable high performance stability. This work addresses that issue by systematically exploring the impact of carbon properties on antimony/carbon composite electrodes for NIBs. Since the Sb surface is covered by an insulating oxide layer, carbon additives are crucial for the percolation and electrochemical activity of Sb based anodes. Instead of using complex hybridization strategies, the ability of mechanical mixing to yield stable high-performance Sb/C sodium-ion battery (NIB) electrodes is shown. This is only possible by considering the physical, chemical, and structural features of the carbon phase. A comparison of carbon nanohorns, onion-like carbon, carbon black, and graphite as conductive additives is given in this work. The best performance is not triggered by the highest or lowest surface area, and not by highest or lowest heteroatom content, but by the best ability to homogenously distribute within the Sb matrix. The latter provides an optimum interaction between carbon and Sb and is best enabled by onion-like carbon. A remarkable rate performance is attained, electrode cracking caused by volume expansion is successfully prevented, and the homogeneity of the solid/electrolyte interphase is significantly improved as a result of it. With this composite electrode, a reversible capacity of 490 mA h g-1 at 0.1 A g-1 and even 300 mA g-1 at 8 A g-1 is obtained. Additionally, high stability with a capacity retention of 73% over 100 cycles is achieved at charge/discharge rates of 0.2 A g-1 This journal is © The Royal Society of Chemistry

Electrochemical Investigations of Sulfur‐Decorated Organic Materials as Cathodes for Alkali Batteries

Alkali metal–sulfur batteries (particularly, lithium/sodium- sulfur (Li/Na–S)) have attracted much attention because of their high energy density, the natural abundance of sulfur, and environmental friendliness. However, Li/Na–S batteries still face big challenges, such as limited cycle life, poor conductivity, large volume changes, and the “shuttle effect” caused by the high solubility of Li/Na–polysulfides. Herein, novel organosulfur-containing materials, i.e., bis(4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS-OH) and 2,4-thiophene/arene copolymer (TAC) are proposed as cathode materials for Li and Na batteries. BiTEMPS-OH shows an initial discharge/charge capacity of 353/192 mAh g−1 and a capacity of 62 mAh g−1 after 200 cycles at 100 mA g−1 in ether-based Li-ion electrolyte. Meanwhile, TAC has an initial discharge/charge capacity of 270/248 mAh g−1 and better cycling performance (106 mAh g−1 after 200 cycles) than BiTEMPS-OH in the same electrolyte. However, the rate capability of TAC is limited by the slow diffusion of Li-ions. Both materials show inferior electrochemical performances in Na battery cells compared to the Li analogs. X-ray powder diffraction reveals that BiTEMPS-OH loses its crystalline structure permanently upon cycling in Li battery cells. X-ray photoelectron spectroscopy demonstrates the cleavage and partially reversible formation of S−S bonds in BiTEMPS-OH and the formation/decomposition of thick solid electrolyte interphase on the electrode surface of TAC

Study of the Lithium Storage Mechanism of N-Doped Carbon-Modified Cu₂S Electrodes for Lithium-Ion Batteries

Owing to their high specific capacity and abundant reserve, Cu$_{x}$S compounds are promising electrode materials for lithium-ion batteries (LIBs). Carbon compositing could stabilize the Cu$_{x}$S structure and repress capacity fading during the electrochemical cycling, but the corresponding Li$^{+}$ storage mechanism and stabilization effect should be further clarified. In this study, nanoscale Cu$_{2}$S was synthesized by CuS co-precipitation and thermal reduction with polyelectrolytes. High-temperature synchrotron radiation diffraction was used to monitor the thermal reduction process. During the first cycle, the conversion mechanism upon lithium storage in the Cu$_{2}$S/carbon was elucidated by operando synchrotron radiation diffraction and in situ X-ray absorption spectroscopy. The N-doped carbon-composited Cu$_{2}$S (Cu$_{2}$S/C) exhibits an initial discharge capacity of 425 mAh g$^{-1}$ at 0.1 A g$^{-1}$, with a higher, long-term capacity of 523 mAh g$^{-1}$ at 0.1 A g$^{-1}$ after 200 cycles; in contrast, the bare CuS electrode exhibits 123 mAh g$^{-1}$ after 200 cycles. Multiple-scan cyclic voltammetry proves that extra Li+ storage can mainly be ascribed to the contribution of the capacitive storage

High‐Voltage Aqueous Mg‐Ion Batteries Enabled by Solvation Structure Reorganization

Herein, an eco-friendly and high safety aqueous Mg-ion electrolyte (AME) with a wide electrochemical stability window (ESW) $≈$ 3.7 V, containing polyethylene glycol (PEG) and low-concentration salt (0.8 m Mg(TFSI)$_2$), is proposed by solvation structure reorganization of AME. The PEG agent significantly alters the Mg$^{2+}$ solvation and hydrogen bonds network of AMEs and forms the direct coordination of Mg$^{2+}$ and TFSI-, thus enhancing the physicochemical and electrochemical properties of electrolytes. As an exemplary material, V$_2$O$_5$ nanowires are tested in this new AME and exhibit initial high discharge/charge capacity of 359/326 mAh g$^{-1}$ and high capacity retention of 80% after 100 cycles. The high crystalline $α$-V$_2$O$_5$ shows two 2-phase transition processes with the formation of $ε$-Mg$_{0.6}$V$_2$O$_5$ and Mg-rich Mg$_x$V$_2$O$_5$ (x $≈$1.0) during the first discharge. Mg-rich Mg$_x$V$_2$O$_5$ (x $≈$ 1.0) phase formed through electrochemical Mg-ion intercalation at room temperature is for the first time observed via XRD. Meanwhile, the cathode electrolyte interphase (CEI) in aqueous Mg-ion batteries is revealed for the first time. MgF$_2$ originating from the decomposition of TFSI- is identified as the dominant component. This work offers a new approach for designing high-safety, low-cost, eco-friendly, and large ESW electrolytes for practical and novel aqueous multivalent batteries

Electrochemical performance and reaction mechanism investigation of V₂O₅ positive electrode material for aqueous rechargeable zinc batteries

The electrochemical performance and reaction mechanism of orthorhombic V$_2$O$_5$ in 1 M ZnSO$_4$ aqueous electrolyte are investigated. V$_2$O$_5$ nanowires exhibit an initial discharge and charge capacity of 277 and 432 mA h g$^{−1}$, respectively, at a current density of 50 mA g$^{−1}$. The material undergoes quick capacity fading during cycling under both low (50 mA g$^{−1}$) and high (200 mA g$^{−1}$) currents. V$_2$O$_5$ can deliver a higher discharge capacity at 200 mA g$^{−1}$ than that at 50 mA g$^{−1}$ after 10 cycles, which could be attributed to a different type of activation process under both current densities and distinct degrees of side reactions (parasitic reactions). Cyclic voltammetry shows several successive redox peaks during Zn ion insertion and deinsertion. In operando synchrotron diffraction reveals that V$_2$O$_5$ undergoes a solid solution and two-phase reaction during the 1st cycle, accompanied by the formation/decomposition of byproducts Zn$_3$(OH)$_2$V$_2$O$_7$·2(H$_2$O) and ZnSO$_4$Zn$_3$(OH)$_6$·5H$_2$O. In the 2nd insertion process, V$_2$O$_5$ goes through the same two-phase reaction as that in the 1st cycle, with the formation of the byproduct ZnSO$_4$Zn$_3$(OH)$_6$·5H$_2$O. The reduction/oxidation of vanadium is confirmed by in operando X-ray absorption spectroscopy. Furthermore, Raman, TEM, and X-ray photoelectron spectroscopy (XPS) confirm the byproduct formation and the reversible Zn ion insertion/deinsertion in the V$_2$O$_5$