Elucidating the Role of Prelithiation in Si-based Anodes for Interface Stabilization

Prelithiation as a facile and effective method to compensate the lithium inventory loss in the initial cycle has progressed considerably both on anode and cathode sides. However, much less research has been devoted to the prelithiation effect on the interface stabilization for long-term cycling of Si-based anodes. An in-depth quantitative analysis of the interface that forms during the prelithiation of SiOx is presented here and the results are compared with prelithiaton of Si anodes. Local structure probe combined with detailed electrochemical analysis reveals that a characteristic mosaic interface is formed on both prelithiated SiOx and Si anodes. This mosaic interface containing multiple lithium silicates phases, is fundamentally different from the solid electrolyte interface (SEI) formed without prelithiation. The ideal conductivity and mechanical properties of lithium silicates enable improved cycling stability of both prelithiated anodes. With a higher ratio of lithium silicates due to the oxygen participation, prelithiated SiO1.3 anode improves the initial coulombic efficiency to 94% in full cell and delivers good cycling retention (77%) after 200 cycles. The insights provided in this work can be used to further optimize high Si loading (>70% by weight) based anodes in future high energy density batteries

Insights into lithium inventory quantification of LiNi_0.5Mn_1.5O₄–graphite full cells

High voltage spinel cathode LiNi0.5Mn1.5O4 (LNMO) offers higher energy density and competitive cost compared to traditional cathodes in lithium-ion batteries, making it a promising option for high-performance battery applications. However, the fast capacity decay in full cells hinders further commercialization. The Li inventory evolution upon cycling in the LNMO–graphite pouch cell is systematically studied by developing lithium quantification methods on the cathode, anode, and electrolyte. The findings reveal that active Li loss is a primary factor contributing to capacity decay, stemming from an unstable anode interphase caused by crosstalk. This crosstalk primarily originates from electrolyte degradation on the cathode under high-voltage operation, leading to increased moisture and acidity, subsequently corroding the anode interphase. In response, two approaches including an aluminum oxide (Al2O3) surface coating layer on the cathode and lithium difluoro(oxalato)borate (LiDFOB) electrolyte additives are evaluated systematically, resulting in cycling stability enhancement. This study offers a quantitative approach to understanding the Li inventory loss in the LNMO–Gr system, providing unique insights and guidance into identifying critical bottlenecks for developing high voltage (>4.4 V) lithium battery technology

Quantitative Analysis of Sodium Metal Deposition and Interphase in Na Metal Batteries

Sodium-ion batteries exhibit significant promise as a viable alternative to current lithium-ion technologies owing to their sustainability, low cost per energy density, reliability, and safety. Despite recent advancements in cathode materials for this category of energy storage systems, the primary challenge in realizing practical applications of sodium-ion systems is the absence of an anode system with high energy density and durability. Although Na metal is the ultimate anode that can facilitate high-energy sodium-ion batteries, its use remains limited due to safety concerns and the high-capacity loss associated with the high reactivity of Na metal. In this study, titration gas chromatography is employed to accurately quantify the sodium inventory loss in ether- and carbonate-based electrolytes. Uniaxial pressure is developed as a powerful tool to control the deposition of sodium metal with dense morphology, thereby enabling high initial coulombic efficiencies. In ether-based electrolytes, the Na metal surface exhibits the presence of a uniform solid electrolyte interphase layer, primarily characterized by favorable inorganic chemical components with close-packed structures. The full cell, utilizing a controlled electroplated sodium metal in ether-based electrolyte, provides capacity retention of 91.84% after 500 cycles at 2C current rate and delivers 86 mAh/g discharge capacity at 45C current rate, suggesting the potential to enable Na metal in the next generation of sodium-ion technologies with specifications close to practical requirements

Mitigating Anisotropic Changes in Classical Layered Oxide Materials by Controlled Twin Boundary Defects for Long Cycle Life Li-Ion Batteries

The classical layered NMC oxides LiNixMnyCo1–x–yO2 (0 < (x,y) < 1) are promising high energy density cathodes for Li-ion batteries. However, their inherent structure instability at the highly delithiated state causes capacity degradation as cycling proceeds. Here, we report a mitigating strategy for addressing the capacity decay problem in multiple classical NMC materials through the design of controlled twin boundary defects. The radially aligned twin boundary defects are engineered in nanosized NMC cathodes through polyol synthesis. The crystallographic orientation of each subgrain rotates across the twin boundaries, and the particles have maximum exposure to the electrolyte with the (003) planes (which are more stable than other planes). Increased cation disorder and the formation of rocksalt-like phase are consistently observed along the twin boundaries through scanning transmission electron microscopy (STEM), acting as a rigid framework that mitigates anisotropic changes in NMC during cycling. Operando X-ray diffraction confirms this hypothesis as the degree of anisotropic changes is minimized in NMC with twin boundaries. The synthesized NMC materials with twin boundary defects exhibits enhanced electrochemical performance compared to the corresponding microsized materials with identical composition. The twin boundary defects engineering in NMC structure can effectively suppress the phase transformation and material degradation, serving as a novel and universal approach in designing stable intercalation compounds for high voltage long-cycle life Li-ion batteries

Design principles for enabling an anode-free sodium all-solid-state battery

Anode-free batteries possess the optimal cell architecture due to their reduced weight, volume and cost. However, their implementation has been limited by unstable anode morphological changes and anode–liquid electrolyte interface reactions. Here we show that an electrochemically stable solid electrolyte and the application of stack pressure can solve these issues by enabling the deposition of dense sodium metal. Furthermore, an aluminium current collector is found to achieve intimate solid–solid contact with the solid electrolyte, which allows highly reversible sodium plating and stripping at both high areal capacities and current densities, previously unobtainable with conventional aluminium foil. A sodium anode-free all-solid-state battery full cell is demonstrated with stable cycling for several hundred cycles. This cell architecture serves as a future direction for other battery chemistries to enable low-cost, high-energy-density and fast-charging batteries

Evaluating Electrolyte–Anode Interface Stability in Sodium All-Solid-State Batteries

All-solid-state batteries have recently gained considerable attention due to their potential improvements in safety, energy density, and cycle-life compared to conventional liquid electrolyte batteries. Sodium all-solid-state batteries also offer the potential to eliminate costly materials containing lithium, nickel, and cobalt, making them ideal for emerging grid energy storage applications. However, significant work is required to understand the persisting limitations and long-term cyclability of Na all-solid-state-based batteries. In this work, we demonstrate the importance of careful solid electrolyte selection for use against an alloy anode in Na all-solid-state batteries. Three emerging solid electrolyte material classes were chosen for this study: the chloride Na2.25Y0.25Zr0.75Cl6, sulfide Na3PS4, and borohydride Na2(B10H10)0.5(B12H12)0.5. Focused ion beam scanning electron microscopy (FIB-SEM) imaging, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS) were utilized to characterize the evolution of the anode–electrolyte interface upon electrochemical cycling. The obtained results revealed that the interface stability is determined by both the intrinsic electrochemical stability of the solid electrolyte and the passivating properties of the formed interfacial products. With appropriate material selection for stability at the respective anode and cathode interfaces, stable cycling performance can be achieved for Na all-solid-state batteries

Advanced Characterization Methods for Reaction Mechanism Investigation in Next Generation Energy Storage Systems

Continuous increase in global energy demand along with supply chain risks associated with Li metal has underscored the need for advanced energy storage technologies in the past decade. Generally modern energy storage systems are divided into primary (non-rechargeable) and secondary (rechargeable) types of batteries, both of which currently suffer from the lack of high energy density for emerging technologies and compatibility with the harsh and extreme environments. This thesis is an effort to design, fabricate, and characterize two energy storage systems that hold a great promise as an alternative for the future of primary and secondary energy storage systems.Lithium/fluorinated graphite (Li/CFx) batteries are one of the most well-known primary batteries due to their high energy density (&gt;2100 Wh kg-1) and low self-discharge rate (&lt; 0.5% per year at 25 °C). While the electrochemical performance of the CFx cathode is indeed promising, the discharge reaction mechanism is not thoroughly understood. Here, we use a combination of titration gas chromatography, X-ray diffraction, focused ion beam scanning electron microscopy, and cryogenic scanning transmission electron microscopy with electron energy loss spectroscopy methods to propose a more comprehensive discharge mechanism in CFx cathodes. We further investigate the possible rechargeability of the CFx-based cathode using a hybrid structure with FeF3. Next, we focus on Sodium-ion batteries as one of the most promising alternatives to rechargeable lithium-based battery technologies. Implementation of this technology has been practically hindered due to a lack of high energy density cathode materials and stable anode materials with a desired cycle-life. To address these points, we implement uniaxial pressure as a knob to control sodium metal deposition with dense morphology to enable high initial coulombic efficiencies. Moreover, we use titration gas chromatography to precisely quantify the sodium capacity loss in ether- and carbonate-based electrolytes. With that, we enabled a long cycling battery using a controlled electroplated sodium metal as the anode with high-rate performance. Implementation of advanced characterization for fundamental understanding of reaction mechanisms and interface properties in conjunction with synthesis and performance evaluation as demonstrated in this thesis is critical for designing next generation of energy storage systems

An Air Breathing Lithium-Oxygen Battery

Given that the current Li-ion battery technology is approaching theoretical specific capacity and specific energy values that are still not enough for powering satisfactorily electric vehicles or providing enough grid level storage capacities, interest in other electrochemical energy conversion and storage devices have emerged. Although systems based on multi-valent cations (Mg2+, Zn2+, etc.) are also been studied, metal air batteries have shown the highest theoretical capacity and energy densities of any other battery chemistries. However, some fundamental challenges have hampered the applications of this class of batteries as the alternative for metal-ion batteries. In brief, the major challenges holding the metal air system from large scale applications are: (i) absence of an effective air electrode which easily transfer oxygen to the heterogenous reaction interphase for oxygen reduction and evolution reactions. (ii) electrolyte instability in large voltage windows which usually occurs because of high charge overpotentials. (iii) anode poisoning and corrosion due to oxidation or reaction with air species such as CO2 and moisture. Given such obstacles, development of novel materials is needed to overcome these challenges in metal air batteries. In this thesis, a system comprised of a protected anode based on lithium carbonate, molybdenum disulfide cathode, and ionic liquid/dimethyl sulfoxide electrolyte is studied that work together, in presence of air components, such as Nitrogen, Carbon dioxide, and humidity, as a real Li-air battery with high cyclability performance up to 700 cycles. The combination of experimental and computational studies are used to provide insight into how this system operates in air and revealed that the long-life performance of this system is due to (i) a suppression of side reactions on the cathode side, which prevent the formation of by-products such as Li2CO3 and LiOH, and (ii) an effective protected anode covered with a Li2CO3 coating that effectively blocks the diffusion of the actual air components e.g., N2, CO2, and H2O and allowing only for Li ion transport. The Li-air battery developed in this work, which for the first time successfully operates in a realistic atmosphere with high cycle-life, is a promising step toward engineering the next generation of Li batteries with much higher specific energy density than Li-ion batteries

Morphology Control to Enable High Capacity Li-Rich Disordered Rock Salt Cathodes

Li-rich disordered rock salt (DRS) oxides are a promising class of cathode materials with the wide chemical space to be explored. The high capacity (&gt;300mAh/g) of this class of material can be explained by the reversible redox chemistry of the oxide anions, which sets it apart from the conventional layered cathode materials that rely only on the transition metal redox. However, these materials suffer from poor ionic and electronic transport properties: Most previous studies report electrochemical performance at low current rate and elevated temperature. Even then, the particle size needs to be reduced to sub-micrometer size, often by high-energy ball milling, to get reasonable capacities. To mitigate this issue, we performed a detailed study of the synthesis of three different Nb-based Li-rich DRS materials - Li3NbO4, Li1.3Fe0.4Nb0.3O2, and Li1.3Mn0.4Nb0.3O2. Systematic evaluation shows that both the synthesis conditions and the reagents used have a large effect on the phase and morphology of the material synthetized, and therefore on its electrochemical performance. Without varying the synthesis method, the extent of cation ordering, the particle morphology, and the degree of elemental segregation can be controlled by a careful choice of the metal oxide precursors. This study helps the community to distinguish important synthesis criteria in order to design Li-rich DRS cathode materials with improved electrochemical performance