Intercalation Cathode Research Articles

Design Strategies of Spinel Oxide Frameworks Enabling Reversible Mg-Ion Intercalation.

ConspectusReversible Mg2+ intercalation in metal oxide frameworks is a key enabler for an operational Mg-ion battery with high energy density needed for the next generation of energy storage technologies. While functional Mg-ion batteries have been achieved in structures with soft anions (e.g., S2- and Se2-), they do not meet energy density requirements to compete with the current rechargeable lithium-ion batteries due to their low insertion potentials. It emphasizes the necessity of finding an oxide-based cathode that operates at high potentials. A leading hypothesis to explain the limited availability of oxide Mg-ion cathodes is the belief that Mg2+ has sluggish diffusion kinetics in oxides due to strong electrostatic interactions between the Mg2+ ions and oxide anions in the lattice. From this assessment, it can be hypothesized that such rate limiting kinetic shortcomings can be mitigated by tailoring an oxide framework through creating less stable Mg2+-O2- coordination.Based on theoretical calculations and preliminary experimental data, oxide spinels have been identified as promising cathode candidates with storage capacity, insertion potential, and cation mobility that meet the requirements for a secondary Mg-ion battery. However, spinels with a single redox metal, such as MgCr2O4 or MgMn2O4, were not found to demonstrate sufficiently reversible Mg-ion intercalation at high redox potentials when coupled with nonaqueous Mg-electrolytes. Therefore, a materials development effort was initiated to design, synthesize, and evaluate a new class of solid-solution oxide spinels that can satisfy the required properties needed to create a sustainable Mg-ion cathode. These were designed by bringing together electrochemically active metals with stable redox potentials and charged states against the electrolyte, for instance, Mn3+, in combination with a structural stabilization component, typically Cr3+. Furthermore, common spinel structural defects that degrade performance, i.e., antisite inversion, were controlled to see correlation between structures and electrochemical overpotentials, thus controlling overall hysteresis. The designed materials were characterized by both short- and long-range structure in both ex situ and in situ modes to confirm the nature of solid-solution and to correlate structural changes and redox activity to electrochemical performance. Consistent and reproducible results were observed for facile bulk Mg2+-ion activity without phase transformations, leading to enhanced energy storage capability based on reversible intercalation of Mg2+, enabled by understanding the variables that control the electrochemical performance of the spinel oxide. Based on these observations, with proper materials design, it is possible to develop an oxide cathode material that has many of the desired properties of a Li-ion intercalation cathode, representing a significant mile marker in the quest for high energy density Mg-ion batteries.This Account describes strategies for the design and development of new spinel oxide intercalation materials for high-energy Mg-ion battery cathodes through a combination of theoretical and experimental approaches. We will review the key factors that govern the kinetics of Mg2+ diffusion in spinel oxides and illustrate how material complexity correlates with the electrochemical Mg2+ activity in oxides and is supported by secondary characterization. The understanding gained from the fundamental studies of cation diffusion in oxide cathodes will be beneficial for chemists and materials scientists who are developing rechargeable batteries.

Design and analysis of Lithium-ion pouch cell with LMO-NMC blended cathode using coupled thermo-electro-chemical model

In this study, a Lithium-ion pouch cell is studied considering a blended cathode, made of dual intercalating cathode materials. The proposed battery designs are thoroughly investigated through the pseudo-two-dimensional thermo-electro-chemical coupled model, developed with the help of the COMSOL Multiphysics computational tool. Therefore, the major objective of this study is to analyse the thermo-electro-chemical performance of Lithium-ion pouch cell made of LMO-NMC blended cathodes, for different electrode designs arrived by varying the design parameters. The battery performance attributes include: discharge voltage, energy capacity, power output, and heat generation. Furthermore, a parametric study on the design parameters of blended electrode, such as: thickness of electrode, particle radius, volume fraction of active material, and blend ratio is also carried out to study their influence on the battery performance. The results indicate that the cell with blended cathode incorporates the properties of its constituent materials. A 50:50 LMO-NMC blended cathode is observed to improve the energy capacity of the cell by 26.48% with respect to the cell with LMO cathode. Also, at 10C discharge rate, the improvement in capacity utilization and reduction in heat generation are observed to be 12.87% and 12.77%, respectively, as compared to the cell with NMC cathode. Furthermore, all the electrode design parameters are found to significantly influence the battery performance, particularly at higher discharge rates. Moreover, inter dependency among the design parameters has also been identified. Therefore, the present study can help the designers of Lithium-ion batteries to come up with efficient designs considering blended cathodes.

Electrical Double Layer Formation at Intercalation Cathode–Organic Electrolyte Interfaces During Initial Lithium‐Ion Battery Reactions

AbstractInformation on the cathode/organic–electrolyte interface structure provides clues regarding the rate and reversibility of lithium intercalation reactions in lithium‐ion batteries. Herein, structural changes within the LiCoO2 electrode, throughout the interphase region, and in the LiPF6/propylene carbonate electrolyte are observed concurrently by in situ neutron reflectometry. The formation of an electrical double layer (EDL) during the early stages of charging and discharging is investigated and compared with that at an intercalation‐inactive Nb:SrTiO3 electrode. At the intercalation‐inactive interface between Nb:SrTiO3 and the electrolyte, a voltage‐dependent ionic distribution corresponding to the EDL forms on the electrolyte side without the formation of a cathode/electrolyte interphase (CEI) layer. In contrast, at the intercalation‐active LiCoO2/electrolyte interface, a CEI layer forms immediately after cell construction, and the ionic distribution in the electrolyte formed outside the CEI layer scarcely changes upon voltage application. The CEI/electrolyte interface is shielded from potential changes by the electronically insulating CEI; therefore, structural changes in the EDL are restricted. This supports the prevailing understanding that the CEI layer defines the rates of solvation/de‐solvation and adsorption/desorption reactions of lithium ions.

Developing rapid electrochemical relithiation protocols for scalable relithiation of lithium-ion battery cathode materials

The recent and ongoing boom in electric vehicle sales has caused the circularity of the supply chain for electric vehicle battery materials to come under a great deal of scrutiny. Innovative recycling processes, or direct recycling, that offer the possibility of reducing the cost of recycling are one possible solution to regaining resources from end-of-life (EoL) electric vehicle batteries. Electrochemically shuttling lithium back into the cathode, or electrochemical relithiation, is a possible technique for restoring lithium content to NMC materials (EoL) in a direct recycling process. This study provides essential understanding towards developing an electrochemical relithiation protocol that will restore lithium loss in intercalation cathode materials that reach EoL by loss of lithium inventory (LLI) as opposed to other degradation mechanisms like loss of active material (LAM), cation mixing or phase transition. Electrochemically aged NMC cathode materials have been prepared and characterized to establish the extent of EoL material structural degradation and lithium loss. A model-informed experimental process is used to identify the optimal electrochemical relithiation protocol to minimize the time taken to relithiate EoL materials and maximize the amount of lithium restored. Protocols were evaluated based on their ability to enable rapid lithium intercalation, maintain structural uniformity in the EoL material and fully restore lithium content. An optimal protocol was identified at elevated temperatures utilizing a novel scanning voltage step.

Unveiling the effect of alloy-type coating for lithium metal plating and stripping on anode-free lithium metal batteries

Li dendrite formation is the root cause of capacity fading in anode-free lithium metal batteries (AFLMBs). Previous studies have shown that Au coating on Cu can seed Li nucleation by forming Li3Au for smooth Li plating and improves the cycle life of Li||Cu cells. However, unlike Li||Cu cells with excessive Li supply, in practical AFLMBs (i.e., full-cell), the active lithium is limited from the lithium intercalation cathode. The introduction of alloy-type coatings may adversely affect the cycling stability due to the pulverization effect during alloying with Li (e.g., the volume expansion rate from Au to Li3Au is 337%). Here, we evaluate the full-cell performance of AFLMBs focusing on different thicknesses of Au coating (20, 50, and 100nm) and four coating layers (alloy-type: Au, Ag; non-alloy-type: Ni, Ti). Our results show that although the alloy-type coatings (i.e., Au and Ag) lower the lithiation overpotential, the full-cells equipped with these coatings experience faster capacity fading than those with pristine and non-alloy-type coatings. When the Au-coated Cu is paired with high-mass loading NMC622 cathode, the full-cells AFLMBs exhibit inferior performance with a low initial Coulombic efficiency (89.97% and 79.75% for 20 and 100nm thick Au coating) and accelerated capacity fading, producing plated Li with porous structure and carbonyl-rich solid electrolyte interphase. This study underscores the necessity of employing a full-cell configuration for evaluating Li plating-stripping efficacy in AFLMBs, emphasizing a transition from laboratory research to practical applications.

Exploring Calcium Manganese Oxide as a Promising Cathode Material for Calcium-Ion Batteries.

The dependence on lithium for the energy needs of the world, coupled with its scarcity, has prompted the exploration of postlithium alternatives. Calcium-ion batteries are one such possible alternative owing to their high energy density, similar reduction potential, and naturally higher abundance. A critical gap in calcium-ion batteries is the lack of suitable cathodes for intercalating calcium at high voltages and capacities while also maintaining structural stability. Transition metal oxide postspinels have been identified as having crystal structures that can provide low migration barriers, high voltages, and facile transport pathways for calcium ions and thus can serve as cathodes for calcium-ion batteries. However, experimental validation of transition metal oxide postspinel compounds for calcium ion conduction remains unexplored. In this work, calcium manganese oxide (CaMn2O4) in the postspinel phase is explored as an intercalation cathode for calcium-ion batteries. CaMn2O4 is first synthesized via solid-state synthesis, and the phase is verified with X-ray diffraction (XRD). The redox activity of the cathode is investigated with cyclic voltammetry (CV) and galvanostatic (GS) cycling, identifying oxidation potentials at 0.2 and 0.5 V and a broad insertion potential at -1.5 V. CaMn2O4 can cycle at a capacity of 52 mAh/g at a rate of C/33, and calcium cycling is verified with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) and modeled with density functional theory (DFT) simulations. The results from the investigation concluded that CaMn2O4 is a promising cathode for calcium-ion batteries.

Dual Salt Cation-Swing Process for Electrochemical CO2 Separation.

Electrochemical CO2 separations, which use electricity rather than thermal energy to reverse sorption of CO2 from concentrated point sources or air, are emerging as compelling alternatives to conventional approaches given their isothermal, ambient operating conditions, and ability to integrate with renewable energy inputs. Despite several electrochemical approaches proposed in previous studies, further explorations of new electrochemical CO2 separation methods are crucial to widen choices for different emissions sources. Herein, we report an electrochemical cation-swing process that is able to reversibly modulate the CO2 loading on liquid amine sorbents in dimethyl sulfoxide (DMSO) solvent. The process exploits a reversible carbamic acid-to-carbamate conversion reaction that is induced by changing the identity of Lewis acid cations (e.g. K+, Li+, Ca2+, Mg2+, and Zn2+) coordinated to the amine-CO2 adduct in the electrolyte. Using ethoxyethylamine (EEA) as a model amine, we present NMR-based speciation studies of carbamic acid-to-carbamate conversion as a function of amine/salt concentrations and cation identity. The reaction is further probed using gas-flow reaction microcalorimetry, revealing the energetic driving forces between cations and the amine-CO2 adduct that play a key role in the described re-speciation. A prototype electrochemical cell was further constructed comprising a Prussian white (PW) potassium (K+) intercalation cathode, zinc (Zn) foil anode, and EEA/DMSO electrolyte containing a dual KTFSI/Zn(TFSI)2 salt. A low CO2 separation energy of ∼22-39 kJ/mol CO2 (0.1-0.5 mA cm-2) was achieved with a practical CO2 loading delta of ∼0.15 mol CO2/mol amine. Further optimizations in electrolyte design and cell architectures toward continuous CO2 capture-release are expected to enhance rate performance while retaining favorable separation energies.

(Invited) Rational Composition and Structure Designs for Layered Oxide Cathodes

Since its birth nearly three decades ago, lithium-ion battery (LIB) has changed all aspects of our life, from portable electronics, electric vehicles (EVs) to large-scale energy storage systems and the emerging electric flight applications. Currently, the bottleneck of the energy density of LIB is set by the intercalation cathode materials, which has been a significant push to develop high energy density and low-cost cathodes in response to rapidly expanding market. In this talk, I will focus on the identification of key failure modes and development of mitigation strategies for facilitating the future application of battery technologies. I will present some insights into the failure mechanism of battery materials that differ from the existing paradigms. Further, I will discuss how we can utilize rational composition and structure design to improve energy density, battery life without compromising safety, speed up battery charging, and reduce the cost of batteries.

Performance of Several Excellent Oxide-Based Intercalation Cathodes for Aqueous Zn-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have garnered significant interest in recent years due to their advantages in safety, cost, and energy density, which make them suitable for large-scale stationary energy storage. Cathode materials have been a primary research focus in the early stage of ZIBs development since they are widely deemed a limiting factor to the performance. In general, good ZIB cathode materials are found in oxides with layered and open framework structures, and inorganic/organic hybrids, and follow mechanisms of “intercalation”, “conversion” or a combination of both to store Zn2+ and H+ during discharge. However, dissolution of these cathodes into aqueous electrolytes has been a major cause of the performance degradation of aqueous ZIBs. In this presentation, we first show our fundamental understanding of cathode dissolution mechanisms and development of engineering solutions to address the dissolution and instability issues. We then show through several examples how specially engineered V-oxides based cathodes achieve better dissolution resistance and performance stability using aqueous Zn(OTf)2 and ZnSO4 electrolytes as examples. We expect that the insights in this presentation will advance the understanding of dissolution mechanisms and provide design principles for better cathode materials.

(Invited) Enabling Next-Generation High-Performing Sodium Metal Batteries

The increasing energy demands of society today have led to pursue alternative energy storage systems that can fulfill rigorous requirements like cost-effectiveness and high storage capacities. Based fundamentally on earth-abundant sodium sources, sodium-based batteries are a promising solution in applications where existing lithium-ion technology remains less economically viable, particularly in large-scale stationary systems such as grid-level storage. Although simply replacing lithium with sodium in current lithium-ion batteries is not a viable solution due to deteriorating electron transfer in conventional intercalation cathodes, sodium is highly attractive when leveraging other battery chemistries due to its unique redox reactions. Sodium metal holds great promise as an attractive anode material for sodium-based batteries owing to its high theoretical specific capacity, low electrochemical potential, low cost and high natural abundance. However, its highly reactive nature with organic electrolyte leads to the formation of unstable solid electrolyte interphase (SEI) and dendritic/mossy sodium growth. In this talk, I will present a series of versatile strategies to realize diverse high-energy sodium metal battery systems through multi-faceted tactical regulations of the electrode-electrolyte interface, electrode structural design, and electrolyte engineering.

Novel Structural Motif To Promote Mg-Ion Mobility: Investigating ABO4 Zircons as Magnesium Intercalation Cathodes.

There is an increasing need for sustainable energy storage solutions as fossil fuels are replaced by renewable energy sources. Multivalent batteries, specifically Mg batteries, are one energy storage technology that researchers continue to develop with hopes to surpass the performance of Li-ion batteries. However, the limited energy density and transport properties of Mg cathodes remain critical challenges preventing the realization of high-performance multivalent batteries. In this work, ABO4 zircon materials (A = Y, Eu and B = V, Cr) are computationally and experimentally evaluated as Mg intercalation cathodes. Remarkably good Mg-ion transport properties were predicted and Mg-ion intercalation was experimentally verified in sol-gel synthesized zircon YVO4, EuVO4, and EuCrO4. Among them, EuVO4 exhibited the best electrochemical performance and demonstrated repeated reversible cycling. While we believe that the one-dimensional diffusion channels and redox-active species tetragonal coordination limit the value of many zircons as high-performance cathodes, their unique structural motif of overlapping polyhedra along the diffusion pathway appears instrumental for promoting good Mg-ion mobility. The motif results in a favorable "6-5-4" change in coordination that avoids unfavorable sites with lower coordination along the diffusion pathway and a structural design metric for future Mg cathode development.

Polyaniline-derived nitrogen-doped carbon/MoS2 nanocomposites as cathode for efficient hybrid capacitive deionization

Molybdenum disulfide (MoS2) has become an attractive faradic material for capacitive deionization (CDI) process, but it still suffers from several drawbacks, such as low electrical conductivity, inferior hydrophilicity and easy restacking. Hence, we integrated MoS2 with high nitrogen content carbonized polyaniline (MoS2/CP) as intercalation cathode for CDI. The disordered entanglement between MoS2 and CP nanosheets enlarged interlayer spacing, improved pore structure and surface area which can provide multiple charge transfer routes and endow more embedding sites to storage Na+. The Mo-N-C bonds improve the electrical conductivity and wettability to facilitate ions diffusion process as well as ensure the cyclic stability of composites electrode. Moreover, the charge transfer between Na+ and N-containing functional groups is beneficial to forming pseudo-capacitance. Accordingly, the MoS2/CP electrode possess a large specific capacitance of 99.1 F g-1 at 5 mV s-1, which is 36% higher than MoS2. The hybrid cell AC//MC-2 delivers a remarkable desalination capacity (29.14 mg g-1), a rapid desalination rate (2.9 mg g-1 min-1) and favorable cyclic durability at 1.2 V in 500 mg L-1 NaCl solution. The superior desalination performance of MoS2/CP electrode was evaluated based on a capacitance-controlled contribution of 85.8% and a diffusion-controlled contribution of 14.2%.

An Amorphous Molybdenum Polysulfide Cathode for Rechargeable Magnesium Batteries.

Rechargeable magnesium batteries (RMBs) attract research interest owing to the low cost and high reliability, but the design of cathode materials is the major difficulty of their development. The bivalent magnesium cation suffers from a strong interaction with the anion and is difficult to intercalate into traditional magnesium intercalation cathodes. Herein, an amorphous molybdenum polysulfide (a-MoSx ) is synthesized via a simple one-step solvothermal reaction and used as the cathode material for RMBs. The a-MoSx cathode provides a high capacity (185 mAh g-1 ) and a good rate performance (50 mAh g-1 at 1000 mA g-1 ), which are much superior compared with crystalline MoS2 and demonstrate the privilege of amorphous RMB cathodes. A mechanism study demonstrates both of molybdenum and sulfur undergo redox reactions and contribute to the capacity. Further optimizations indicate low-temperature synthesis would favor the magnesium storage performance of a-MoSx .

The Promotion of Research Progress of Zinc Manganate Cathode Materials for Zinc-Ion Batteries by Characterization and Analysis Technology.

Zinc-ion batteries (ZIBs) have recently attracted great interest and are regarded as a promising energy storage device due to their low cost, environmental friendliness, and superior safety. However, the development of suitable Zn-ion intercalation cathode materials remains a great challenge, resulting in unsatisfactory ZIBs that cannot meet commercial demands. Considering that spinel-type LiMn2O4 has been shown to be a successful Li intercalation host, spinel-like ZnMn2O4 (ZMO) is expected to be a good candidate for ZIBs cathodes. This paper first introduces the zinc storage mechanism of ZMO and then reviews the promotion of research progress in improving the interlayer spacing, structural stability, and diffusivity of ZMO, including the introduction of different intercalated ions, introduction of defects, and design of different morphologies and in combination with other materials. The development status and future research directions of ZMO-based ZIBs characterization and analysis techniques are summarized.

Effects of chelating agent on the nanostructure of nickel hexacyanoferrate and its performance in seawater battery application

With the increasing demand for cost-effective and safe energy storage systems, seawater batteries (SWBs) are establishing themselves in the field of rechargeable batteries. In particular, cathode materials based on the intercalation mechanism have received considerable attention owing to their low overpotential and high energy efficiency. In this study, nickel hexacyanoferrate (NiHCF) is used as an intercalation cathode material for SWB. NiHCF, a type of Prussian blue analog, has the advantages of a large interstitial volume to insert Na-ions and stability into seawater; however, it is often fabricated in a defect-rich structure. Therefore, the chelating effect of NiHCF is studied, and its structural and electrochemical properties are investigated. After introducing a chelating agent, defect-less NiHCF can be fabricated, and the well-constructed structure affects the electrochemical properties of the NiHCF. The structural behavior of NiHCF based on the insertion/extraction of Na-ions in the SWB full-cell is studied, and the chelated NiHCF cathode shows reversible cycling ability up to 2000 cycles with a capacity retention of 92.8%. This study offers a comprehensive understanding of the electrochemical properties of NiHCF and the operating mechanisms of intercalation cathode materials in SWB systems.

A New (De)Intercalation MXene/Bi Cathode for Ultrastable Aqueous Zinc‐Ion Battery

AbstractThe emerging aqueous zinc‐ion batteries (ZIBs) have received extensive attention and research due to their unique advantages of low cost, safety, and environmental friendliness. However, the development of appropriate cathode materials to improve battery performance remains a major challenge. Herein, a new MXene and Bi (MXene/Bi) composite material is first applied as the (de)intercalation cathode of ZIB. The dispersed MXene nanosheets in the composite materials greatly improve the conductivity and hydrophilicity of the electrode, and prevent the stacking and the volume expansion in the charge/discharge process of 2D Bi fragments. The experimental results show that composite MXene/Bi electrode has remarkable capacity and ultralong life. Next, the good kinetics and (de)intercalation energy storage mechanism of ZIB are revealed through abundant electrochemical tests and ex situ characterization. The quasi‐solid‐state (QSS) ZIB is also constructed, showing superior electrochemical performance, flexibility, pressure resistance, and heat resistance. Besides, the QSS ZIB can be used directly as a self‐powered pressure sensor to monitor the external pressure in real time based on the response current. This study not only demonstrates that MXene/Bi is a potential cathode for ZIBs, but also offers a feasible path to explore and design the next generation of high‐performance multifunctional ZIBs.

MoS2-CuS-EG/carbon cloth Flexible cathode with Long‐Cycling Life for Hybrid Mg-Li ion Batteries

Recently proposed hybrid Mg-Li ion battery (MLIBs) with excellent kinetics and safety characteristics combines the advantages of low-cost dendrite-free magnesium metal anode with a fast Li+ intercalation cathode. The MoS2 is usually used as the cathode for MLIBs because of its proficient theoretical lithium embedding ability; however, a conventional MoS2 cathode suffers from low electronic conductivity and poor cycling performance. The problem of low electronic conductivity has been initially solved by compounding MoS2 with CuS and expanded graphite (EG). In this work, MoS2-CuS-EG cathode is loaded on flexible carbon cloth to avoid the use of metal collectors and improves the cycling stability of the MLIBs. The MoS2-CuS-EG cathodes/carbon cloth flexible cathode of the MLIBs can present significantly improved cycle performance. The retention of MoS2-CuS-EG cathodes/carbon cloth flexible cathode after 200 cycles at 50 mA•g−1 is 85.37 %, which is much higher than that of MoS2-CuS-EG cathode (23.69 %). Furthermore, the sample after carbon cloth loading can be directly used as the cathode of MLIBs after cutting, which is highly practical for electronic products that need to work in special occasions.

Modeling of Magnesium Intercalation into Chevrel Phase Mo6S8: Report on Improved Cell Design

AbstractA good understanding of the limiting processes in rechargeable magnesium batteries is key to develop novel high‐capacity/high‐voltage cathode materials. Thereby, the performance of magnesium‐ion batteries can strongly depend on the morphology of the intercalation cathode. Moreover, high mass loadings are essential for commercialization. In this work the influence of different mass loadings are studied in addition to the impact of the particle size distribution of the active material. Therefore, a detailed continuum model is developed, which is able to describe the complex intercalation of magnesium into a Chevrel phase (CP) cathode. The model considers the thermodynamics, kinetics and interplay of the two energetically different intercalation sites of Mo6S8, which results from its unique crystal structure, as well as the impact of the desolvation on the electrochemical reactions and possible ion agglomeration. Ideal combinations of mass loading and electrolyte concentration as well as the desired CP particle size are determined for the state‐of‐the‐art magnesium tetrakis(hexafluoroisopropyloxy)borate Mg[B(hfip)4]2 electrolyte.

Pom-Pom Flower-like Morphology of δ-MnO2 with Superior Electrochemical Performances for Rechargeable Aqueous Zinc Ion Batteries

A rechargeable aqueous zinc-ion battery is an encouraging alternative for grid-scale energy storage applications, owing to its advantages of high safety, low cost, and environmental benignity. Since MnO2 is found to be one of the most efficient intercalation cathode materials for ZIBs, the layered type δ-MnO2 polymorph exhibits reversible intercalation/de-intercalation of Zn2+ ions with a high capacity. Unfortunately, the δ-MnO2 cathode suffers from poor cyclability, low-rate capability, and structural degradation during charge–discharge cycles. Therefore, δ-MnO2 with Pom-Pom Flower-like morphology have been synthesized using a facile hydrothermal method. The unique morphology of δ-MnO2 provides a high surface area with numerous reaction sites, leading to excellent electrochemical performance. The obtained results revealed that the δ-MnO2 electrode retained ~99% of its initial capacity even after 250 cycles, which can be ascribed to the reversible Zn2+ insertion/de-insertion from the current unique morphology of the layered δ-MnO2 nanostructure. In addition, the electrochemical and structural investigation also indicates a two-step co-insertion of H+ and Zn2+ ions into the interlayer of δ-MnO2 during the discharge process. Thus, the superior electrochemical performances of the δ-MnO2 cathode paves a way for the high capacity and a long lifespan of zinc-ion batteries.

Stabilizing cathodes and interphases for next-generation Li-ion batteries

The past-30-year advances enable lithium (Li)-ion batteries to reshape our daily life from living, work and entertainment to transportation. Yet current Li-ion batteries cannot fulfill the boosting market needs. To build higher performance and lower-cost batteries, it is crucial to comprehend the fundamentals of battery chemistries and consider both electrodes, electrolyte, as well as their interphases, namely anode solid-electrolyte interphase (SEI) and cathode solid electrolyte interphase (CEI). While many prior articles have focused on anodes and their SEIs, few reviews and analyses covered the materials and interfacial issues on the cathode side. Here we offer a critical overview of the current status and challenges for Li-ion battery cathodes and their CEIs. We discuss the impact of the CEI on both the intercalation and conversion-type cathode performance characteristics, summarize various strategies used for the CEI and cathode stabilizations, offer design guidelines and outline promising future directions for the development and applications for next-generation Li-ion batteries.