Cathode Electrolyte Research Articles

Direct Evidence of Reversible Changes in Electrolyte and its Interplay with LiO2 Intermediate in Li-O2 Batteries.

Lithium-oxygen batteries show promising energy storage potential with high theoretical energy density; however, further investigation of chemical reactions is required. In this study, experimental Raman and theoretical analyzes are performed for a Li-O2 battery with LiClO4/dimethyl sulfoxide (DMSO) electrolyte and carbon cathode to understand the role of intermediate species in the reactional mechanism of the cell using a high donor number solvent. Operando Raman results reveal reversible changes in the DMSO bands, in addition to the formation and decomposition of Li2O2. On discharge, a decrease in DMSO polarizability is observed and bands of DMSO-Li+-anion interactions are evidenced and supported by abinitio density functional theory (DFT) calculations. Molecular dynamics (MD) force field simulations and operando Raman show that DMSO interacts with LiO2(sol), highlighting the stability of the electrolyte compared to the interaction with reactive . On charging, the presence of Li+ indicates the formation of a lithium-deficient phase, followed by the release of Li+ and oxygen. Therefore, this study contributes to understanding the discharge/charge chemistry of a Li-O2 cell, employing a common carbon cathode and DMSO electrolyte. The combination of a simple characterization technique in operando mode and theoretical studies provides essential information on the mechanism of Li-O2system.

Development of the ReaxFF Reactive Force Field for Li/Mn/O Battery Technology with Application to Design a Self-Healing Cathode Electrolyte Interphase

Development of the ReaxFF Reactive Force Field for Li/Mn/O Battery Technology with Application to Design a Self-Healing Cathode Electrolyte Interphase

Concerted Effect of Ion- and Electron-Conductive Additives on the Electrochemical and Thermal Performances of the LiNi0.8Co0.1Mn0.1O2 Cathode Material Synthesized by a Taylor-Flow Reactor for Lithium-Ion Batteries.

To address the issue that a single coating agent cannot simultaneously enhance Li+-ion transport and electronic conductivity of Ni-rich cathode materials with surface modification, in the present study, we first successfully synthesized a LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material by a Taylor-flow reactor followed by surface coating with Li-BTJ and dispersion of vapor-grown carbon fibers treated with polydopamine (PDA-VGCF) filler in the composite slurry. The Li-BTJ hybrid oligomer coating can suppress side reactions and enhance ionic conductivity, and the PDA-VGCFs filler can increase electronic conductivity. As a result of the synergistic effect of the dual conducting agents, the cells based on the modified NCM811 electrodes deliver superior cycling stability and rate capability, as compared to the bare NCM811 electrode. The CR2032 coin-type cells with the NCM811@Li-BTJ + PDA-VGCF electrode retain a discharge specific capacity of ∼92.2% at 1C after 200 cycles between 2.8 and 4.3 V (vs Li/Li+), while bare NCM811 retains only 84.0%. Moreover, the NCM811@Li-BTJ + PDA-VGCF electrode-based cells reduced the total heat (Qt) by ca. 7.0% at 35 °C over the bare electrode. Remarkably, the Li-BTJ hybrid oligomer coating on the surface of the NCM811 active particles acts as an artificial cathode electrolyte interphase (ACEI) layer, mitigating irreversible surface phase transformation of the layered NCM811 cathode and facilitating Li+ ion transport. Meanwhile, the fiber-shaped PDA-VGCF filler significantly reduced microcrack propagation during cycling and promoted the electronic conductance of the NCM811-based electrode. Generally, enlightened with the current experimental findings, the concerted ion and electron conductive agents significantly enhanced the Ni-rich cathode-based cell performance, which is a promising strategy to apply to other Ni-rich cathode materials for lithium-ion batteries.

Illuminating Polysulfide Distribution in Lithium Sulfur Batteries; Tracking Polysulfide Shuttle Using Operando Optical Fluorescence Microscopy.

High-energy-density lithium sulfur (Li-S) batteries suffer heavily from the polysulfide shuttle effect, a result of the dissolution and transport of intermediate polysulfides from the cathode, into the electrolyte, and onto the anode, leading to rapid cell degradation. If this primary mechanism of cell failure is to be overcome, the distribution, dynamics, and degree of polysulfide transport must first be understood in depth. In this work, operando optical fluorescence microscope imaging of optically accessible Li-S cells is shown to enable real-time qualitative visualization of the spatial distribution of lithium polysulfides, both within the electrolyte and porous cathode. Quantitative determinations of spatial concentration are also possible at a low enough concentration. The distribution throughout cycling is monitored, including direct observation of polysulfide shuttling to the anode and consequent dendrite formation. This was enabled through the optimization of a selective fluorescent dye, verified to fluoresce proportionally with concentration of polysulfides within Li-S cells. This ability to directly and conveniently track the spatial distribution of soluble polysulfide intermediates in Li-S battery electrolytes, while the cell operates, has the potential to have a widespread impact across the field, for example, by enabling the influence of a variety of polysulfide mitigation strategies to be assessed and optimized, including in this work the LiNO3 additive.

Simultaneous Solid Electrolyte Deposition and Cathode Lithiation for Thin Film Batteries and Lithium Iontronic Devices

Simultaneous Solid Electrolyte Deposition and Cathode Lithiation for Thin Film Batteries and Lithium Iontronic Devices

Dry-processed technology for flexible and high-performance FeS2-based all-solid-state lithium batteries at low stack pressure

All-solid-state lithium batteries (ASSLBs) are considered promising energy storage systems due to their high energy density and inherent safety. However, scalable fabrication of ASSLBs based on transition metal sulfide cathodes through the conventional powder cold-pressing method with ultrahigh stacking pressure remains challenging. This article elucidates a dry process methodology for preparing flexible and high-performance FeS2-based ASSLBs under low stack pressure by utilizing polytetrafluoroethylene (PTFE) binder. In this design, fibrous PTFE interweaves Li6PS5Cl particles and FeS2 cathode components, forming flexible electrolyte and composite cathode membranes. Beneficial to the robust adhesion, the composite cathode and Li6PS5Cl membranes are tightly compacted under a low stacking pressure of 100 MPa which is a fifth of the conventional pressure. Moreover, the electrode/electrolyte interface can sustain adequate contact throughout electrochemical cycling. As expected, the FeS2-based ASSLBs exhibit outstanding rate performance and cyclic stability, contributing a reversible discharged capacity of 370.7 mAh g−1 at 0.3C after 200 cycles. More importantly, the meticulous dQ/dV analysis reveals that the three-dimensional PTFE binder effectively binds the discharge products with sluggish kinetics (Li2S and Fe) to the ion–electron conductive network in the composite cathode, thereby preventing the electrochemical inactivation of products and enhancing electrochemical performance. Furthermore, FeS2-based pouch-type cells are fabricated, demonstrating the potential of PTFE-based dry-process technology to scale up ASSLBs from laboratory-scale mold cells to factory-scale pouch cells. This feasible dry-processed technology provides valuable insights to advance the practical applications of ASSLBs.

Self-repaired cathode electrolyte interphase to stabilize the high-nickel cathode interface by a sustained-release multifunctional electrolyte additive

Increasing the nickel content in high-nickel LiNixCoyMn1-x-yO2 cathode materials (NCM) can boost their energy density. However, the consequence of rising Ni content in NCM consists in the heightened stress buildup, intensified irreversible phase transition and severe electrolyte decomposition, and consequently accelerating the battery’s degradation. In the current study, we have revealed that the 4-fluoro-N, N dimethylbenzenesulfonamide (FBSN) as an electrolyte additive can refrain the typical dehydrogenation of EC. Furthermore, a continuously repaired cathode electrolyte interphase (CEI) is designed elaborately on LiNi0.9Co0.05Mn0.05O2 (NCM90) surface by employing the FBSN as a sustained-release electrolyte additive to enhance cycling stability of NCM90||Li cells. This CEI, composed of high mechanical strength LiF and benzene ring skeleton, along with conductive Li+ moieties (S-rich and N-rich species), can be effectively self-repaired in time when damaged, reduce the interaction between the NCM90 and sensitive electrolyte, and mitigate the devastation to the NCM90 cathode surface. As a result, the NCM90||Li cells with 2 % FBSN-containing electrolyte delivers a capacity retention of 90.2 % after 200 cycles at 1C, and 83.1 % after 200 cycles even at higher voltage of 4.5 V, superior than that of Base electrolyte (70.0 % at 4.3 V and 68.0 % at 4.5 V). This study provides an engaging approach to design electrolytes for high-nickel cathodes by autonomously interfacial repair.

Navigating the Energy Storage Landscape: A Comprehensive Analysis of Lithium-Ion Batteries and Improvements

Lithium-ion batteries (LIBs) are the cornerstone of the transition to renewable energy and can power a wide range of devices such as smartphones as well as electric vehicles, although they face some major challenges such as resource scarcity, safety risks and thermal runaway. This paper provides an insightful discussion on the mechanism of operation of LIBs, their applications, and its limitations, emphasizing that LIBs, while widely used in electric vehicles and portable electronics, have certain limitations, like thermal instability. The paper also explores new alternatives, including solid-state and lithium-metal batteries, which have higher energy densities but also suffer from problems such as dendrite growth, for which it cites improvement strategies, such as innovative cathode and negative electrode materials and electrolyte additives, with which to increase the lifetime, safety and performance of the batteries. At the same time, the paper also considers the issue of resource constraints and proposes a scalable and sustainable approach to energy storage needs with a multi-pronged strategy necessary to overcome existing barriers.

Reconstructing Inorganic‐Rich Interphases by Nonflammable Electrolytes for High‐Voltage and Low‐Temperature LiNi0.5Mn1.5O4 Cathodes

AbstractCobalt‐free and spinel LiNi0.5Mn1.5O4 (LNMO) cathodes commonly suffer from undesirable solvent decomposition, serious transition‐metal dissolution, and unstable cathode electrolyte interphase (CEI) layers, incurring rapid capacity decay at high voltages and low temperatures. Herein, these issues are well addressed by utilizing fluorinated solvents with a low coordination number and ethyl propionate with a low melting point. A Li2CO3/LiF‐rich heterostructured CEI layer, which possesses good electron blocking capability of LiF, fast Li+ transport kinetics of Li2CO3 and good mechanical stability, is generated by the synergistic decomposition of hybrid solvents. The robust, homogeneous, and well‐balanced CEI layers subsequently prevent catalyzed parasitic side reactions, prohibit transition‐metal dissolution, and ensure fast interfacial reaction kinetics crossover to the LNMO cathode, thus improving its cycling stability. Consequently, the LNMO cathode delivers a high‐capacity retention of 95.8% over 500 cycles at 25 °C and 97.5% after 180 cycles at −20 °C. This work provides an encouraging alternative to design the high‐voltage and low‐temperature electrolyte for pushing the ongoing research to stabilize Co‐free LNMO materials toward practical applications.

Improved Performance of High‐Entropy Disordered Rocksalt Oxyfluoride Cathode by Atomic Layer Deposition Coating for Li‐Ion Batteries

Lithium‐excess cation‐disordered rocksalt materials are a promising class of transition metal‐based cathodes that exhibit high specific capacity and energy density. The exceptional performance is achieved through participation of anionic redox in addition to cationic redox reactions in the electrochemistry. However, anionic redox reactions accompanied by oxygen evolution, accelerated electrolyte breakdown, and structural evolution lead to voltage hysteresis and low initial Coulombic efficiency. Herein, an Al2O3 layer with varying thickness has been coated onto a high‐entropy disordered rocksalt oxyfluoride cathode through atomic layer deposition to enhance battery performance. The results indicate that the utilization of a uniform Al2O3 coating improves the capacity retention and rate capability of the cathode, with the performance being strongly dependent on the layer thickness. Further investigation into cathode–electrolyte interfacial reactions reveals that the thin protecting Al2O3 coating can reduce the decomposition of electrolyte on the cathode surface but cannot prevent bulk phase degradation during prolonged cycling. These findings highlight the need for optimized coating design on the disordered rocksalt cathode to improve battery performance.

Biomass-derived porous carbon with single-atomic cobalt toward high-performance aqueous zinc-sulfur batteries at room temperature

Aqueous zinc-sulfur batteries at room temperature hold great potential for next-generation energy storage technology due to their low cost, safety and high energy density. However, slow reaction kinetics and high activation energy at the sulfur cathode pose great challenges for the practical applications. Herein, biomass-derived carbon with single-atomic cobalt sites (MMPC-Co) is synthesized as the cathode in Zn-S batteries. The catalysis of single-atom Co sites greatly promotes the transform of cathode electrolyte interface (CEI) on the cathode surface, while offering accelerated charge transfer rate for high conversion reversibility and large electrochemical surface area (ECSA) for high electrocatalytic current. Furthermore, the rich pore structure not only physically limits sulfur loss, but also accelerates the transport of zinc ions. In addition, the large pore volume of MMPC-Co is able to relieve the stress effect caused by the volume expansion of ZnS during charge/discharge cycles, thereby maintaining the stability of electrode structure. Consequently, the sulfur cathode maintains a high specific capacity of 729.96 mA h g−1 after 500 cycles at 4 A g−1, which is much better than most cathode materials reported in the literature. This work provides new insights into the design and development of room-temperature aqueous Zn-S batteries.

Activation and degradation mechanisms of α-V2O5 cathode materials in Zn-ion battery

Vanadium oxides with high specific capacity have been widely used as cathode materials for aqueous Zn-ion batteries. However, the interactions between the aqueous electrolytes and Vanadium oxides are still unclear. In particular, the intercalation of proton and water which can play a critical role in the degradation process is less well understood. Moreover, the mechanism for the capacity increase during the electrochemical cycling, known as the activation process, is still under debate. In this study, we systematically investigated the α-V2O5||Zn battery system with state-of-the-art characterization tools and electrochemical testing techniques to reveal the activation and degradation processes. It is discovered that the activation can be mainly attributed to the intercalation of protons and water in the first 100 cycles, which destabilizes the overall structural integrity, leading to capacity degradation afterward. It is also revealed that two main cathode electrolyte interface (CEI) components can be formed on the cathode surface, namely Zn3(V2O7)(OH)2·2H2O and Znm(CF3SO3)n(OH)2m-n·nH2O. The formation of Zn3(V2O7)(OH)2·2H2O-based CEI component is irreversible, while Znm(CF3SO3)n(OH)2m-n·nH2O-based CEI component can be reversibly cycled. Different structure-stabilizing charge/discharge protocols are proposed accordingly, which could leverage the structural integrity with thorough phase transition in the activation stage to enhance the cycling performance of the V-based cathodes. We hope to spur further interest in the fundamental understanding of the cathode materials in Zn-ion batteries.

Numerical simulation of the residual stress of solid oxide fuel cells with a three-dimensional nonplanar cathode–electrolyte interface

The longevity of solid oxide fuel cells is influenced by internal residual stresses, which may induce deformation or fracturing of components. This study investigates the residual stress distribution at the nonplanar cathode–electrolyte interface by approximating the actual interface with trigonometric functions and developing a three-dimensional (3D) model. The model reveals that the stress patterns at nonplanar interfaces can elucidate the genesis of interfacial cracks. During fabrication, anode contraction results in compressive stress within the electrolyte and tensile stress within the anode, with thermal discrepancies between layers being the primary cause of residual stresses. The reduction process diminishes these stresses, thus enhancing the mechanical integrity of the cell. Mitigating interface nonplanarity is beneficial for minimizing residual stress. At each interface crest, the electrolyte exhibits a local minimum in compressive stress, and a local maximum in shear stress occurs between each crest and trough. Furthermore, decreasing the initial porosity and NiO volume fraction can slightly lessen interlayer thermal discrepancies, with little effect on residual stresses.

Stabilizing Interfacial Behaviors of Ni‐rich Cathodes by Upcycling of Oyster Shells Waste

AbstractLayered lithium oxides (LNCM), with over 60% Ni, are promising cathode materials for electric vehicles due to their high capacity. however, reliable cycling retention cannot easily achieved owing to the instability of the interface. Here, recycled oyster shell (OS) is employed as an efficient precursor for the surface modification of LNCM cathodes; subsequently, Ca‐based artificial cathode–electrolyte interphases (CEI) are obtained at the LNCM interfaces through a simple calcination process. When the pulverized OS is calcined with LNCM cathode materials at elevated temperatures, CaCO3 is converted to CaO via thermal decomposition at the LNCM interface, which effectively protects the unstable interface. Microscopic analyses indicate the nanodomain island‐type CEI layers embedded after OS calcination. The OS‐coated LNCM cathode materials increase the cycling retention after 100 cycles (93.8% vs. 62.7%) and decrease the internal cell pressure by preventing electrolyte decomposition. Incorporating Ca into the LNCM cathode materials also inhibits microcrack formation because of the improvement in particle hardness and the remarkable decrease in the irreversible dissolution of transition metals from LNCM cathodes, considering that Ca plays a crucial role in scavenging fluoride species. Consequently, recycling OS as a functional LNCM precursor is an innovative approach for enhanced cycling retention.

Development and Innovative Application of Main Equipment for Zinc Electrowinning

The latest development and application of zinc electrowinning equipment in China are introduced. The characteristics and innovative applications of main equipment for zinc electrowinning, such as cathode and anode, electrolytic cell, cathode and anode multifunctional crane, zinc stripping and cathode washing machine, zinc sheet conveyor, anode temper mill and solution cooling tower, are analyzed. It is pointed out that the application of advanced equipment characterized by large-scale and automation will dominate the upgrading and transformation of existing zinc electrowinning capacity.

Hybrid ion/electron interfacial regulation stabilizes the cobalt/oxygen redox of ultrahigh-voltage lithium cobalt oxide for fast-charging cyclability

High-voltage and fast-charging LiCoO2 (LCO) is key to high-energy/power-density Li-ion batteries. However, unstable surface structure and unfavorable electronic/ionic conductivity severely hinder its high-voltage fast-charging cyclability. Here, we construct a Li/Na-B-Mg-Si-O-F-rich mixed ion/electron interface network on the 4.65 V LCO electrode to enhance its rate capability and long-term cycling stability. Specifically, the resulting artificial hybrid conductive network enhances the reversible conversion of Co3+/4+/O2−/n− redox by the interfacial ion–electron cooperation and suppresses interface side reactions, inducing an ultrathin yet compact cathode electrolyte interphase. Simultaneously, the derived near-surface Na+/Mg2+/Si4+-pillared local intercalation structure greatly promotes the Li+ diffusion around the 4.55 V phase transition and stabilizes the cathode interface. Finally, excellent 3 C (1 C = 274 mA g−1) fast charging performance is demonstrated with 73.8% capacity retention over 1000 cycles. Our findings shed new insights to the fundamental mechanism of interfacial ion/electron synergy in stabilizing and enhancing fast-charging cathode materials.

Enhanced performance of lithium metal batteries via cyclic fluorinated ether based electrolytes

To address the challenges associated with applying high-voltage cathodes in lithium metal batteries (LMBs) there is a need for new electrolytes enabling stable interphases at both electrodes. Here we attack this by using a dioxolane-derived cyclic fluorinated ether, 2,2-bis(trifluoromethyl)-1,3-dioxolane (BTFD), as a fluorinated diluent to a 1,2-dimethoxyethane (DME) based electrolyte. The cells using the resulting BTFD-based electrolytes exhibit higher Coulombic efficiencies for lithium stripping and plating as compared to those using the non-fluorinated ether-based electrolyte. This originates from the reduced formation of ‘dead Li’ at the anode, as shown by using electrochemical impedance spectroscopy (EIS). In practice, the BTFD-based electrolytes are shown to improve the performance of Li||NMC cells, which is due to the formation of a predominantly inorganic cathode electrolyte interphase (CEI) that suppresses the cathode degradation during cycling. We used X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) to characterize the CEIs’ overall composition and structure. To obtain more details on the CEI speciation, Raman and nuclear magnetic resonance (NMR) spectroscopies were employed, assisted by molecular level computations. Overall, we demonstrate how the very design of the electrolyte composition influences the performance of LMBs.

Boosting the capacity and stability of Na3V2(PO4)2F3-2xO2x microspheres, using atomic layer deposition of artificial CEI

Phosphate-based materials [e.g. Na3V2(PO4)2F3-2xO2x; (NVPFO2x;0 < x < 1)] are regarded as a promising intercalation cathodes for Sodium-ion batteries (SIBs) due to their high reversible specific capacity and stability. However, so far only 2 Na ion were demonstrated to be active in these polyanionic cathodes, which limit their capacity. Herein we provide a strategic approach towards electrochemical activation of a 3rd Na ion, which leads to higher capacity, and preserves structural integrity. We synthesize and study a series of NVPFO2x (0 < x < 1) with well-controlled surface morphology and vanadium oxidation state, and study the dependence of the electrochemical behavior on the various composition and morphology. The optimized NVPFO cathode exhibited highest initial specific discharge capacity (131 mA h g−1) indicating the activation of 3rd Na ion. Nevertheless, the material suffers rapid capacity fading within ~50 cycles. We demonstrate how this instability is suppressed profoundly through the formation of a thin artificial cathode electrolyte interface (CEI) layer of TiO2 (ca. 2 nm) on the surface of NVPFO by atomic layer deposition (ALD). This TiO2 coating enabled even further extraction of sodium through higher voltage domain, but more importantly, it facilitated excellent long-term stability over 200 cycles. The structural stability of the cathode material was revealed by post cycling HRSEM, XPS, and XRD study. All these studies demonstrate that the thin TiO2 layer effectively contributes to formation of a robust CEI layer, diminishes the parasitic reaction on the electrode surface, reduces carbonate formation, and restricts the electrolyte decomposition.

Round‐robin test of all‐solid‐state battery with sulfide electrolyte assembly in coin‐type cell configuration

AbstractThe replacement of conventional lithium‐ion batteries with solid‐state batteries is currently under investigation by many players both from academia and industry. Sulfide‐based electrolytes are among the materials that are regarded as most promising, especially for application in the transport sector. The performance of anode, cathode, and solid electrolyte materials of this type of solid electrolyte is typically evaluated using manually assembled cells such as Swagelok cells, EL‐CELLs, and in‐house built pressure devices. Coin cells, however, are often disregarded. Though coin cells cannot accurately predict how a material will perform in an end‐use application battery cell format, they are easy to assemble and can provide reproducible data compared to the other cell types, which make them an interesting option for testing the materials under conditions more relevant for their envisioned application. The coin cell preparation method presented in this work has been evaluated interlaboratory for reproducibility and, in addition, can be modified depending on the optimization parameters of the solid electrolyte, cathode material, bilayer comprised on cathode and solid electrolyte, lithium metal anode, and cell in general. Besides, an interlab round‐robin test (RRT) is carried out between four laboratories, measuring defined electrochemical tests of sulfide solid‐state batteries in coin cell configuration. This RRT for the preparation of coin cell solid‐state batteries with sulfide solid electrolyte, lithium nickel manganese cobalt oxides cathode, and lithium metal anode is intended for academic researchers and provides guidelines of research in this field.

In Situ Construction of Inorganics-Rich Cathode-Electrolyte Interface toward Long-Life Prussian White Cathode.

Prussian white (PW) is one of the most promising candidates as a cathode for sodium-ion batteries (SIBs) because of its high theoretical capacity, excellent rate performance, and low production cost. However, PW materials suffer severe capacity decay during long-term cycling. In this work, a robust cathode electrolyte interface (CEI) is designed on the PW cathode by employing cresyl diphenyl phosphate (CDP) and adiponitrile (ADN) as electrolyte additives. CDP and ADN possess higher highest occupied molecular orbital energy levels (HOMO) than other solvents, leading to the preferential decomposition of CDP and ADN to construct an inorganics-rich CEI layer in situ on the PW cathode. Benefiting from this CEI layer, the degradation of PW is effectively inhibited during the long cycling. The Na||PW cell achieves an excellent cycling performance with a capacity retention of 85.62% after 1400 cycles. This work presented here provides a feasible strategy for improving the cycling performance of PW by electrolyte modification.