Interfacial Strategies for Suppression of Mn Dissolution in Rechargeable Battery Cathode Materials

Eliminating the "Dead By-Product" Effect Realizes Powerful Vanadium-Based Zinc-Ion Batteries: An Overlooked Case

The accumulation of inactive by-products caused by the parasitic side reaction on cathode side is an overlooked question leading to performance degradation of zinc-ion batteries. In this research, taking the MnV2O4 as a model, an amorphous carbon interphase is proposed as a pre-implanted cathode-electrolyte interphase (CEI) to design ultrafast-kinetics MnV2O4@C cathode. It is noted that such CEI integrates hydrophobic and conductive characteristics, contributing to dissolution shielding, continuous interfacial conductive channel, and thus preventing inactive by-product accumulation on the cathode interface. Unexpectedly, such electrode shows superior storage performance at a wide temperature range of -20-55 °C. It can deliver a specific capacity of 253.3 mAh g-1 at the high current density of 10 A g-1 even after 8000 cycles. Moreover, a high specific capacity of 393.8 mAh g-1 (0.1 A g-1) can be retained after 300 cycles at 55 °C, as well as 205.1 mAh g-1 at the condition of -20 °C and 5 A g-1. Beyond that, flexible solid-state zinc-ion batteries based on MnV2O4@C cathode with excellent wide temperature performance are demonstrated. This work highlights the importance of eliminating the dead by-product effect to design advanced cathode materials for zinc-ion batteries.

Data-Knowledge-Dual-Driven Electrolyte Design for Fast-Charging Lithium Ion Batteries

Electric vehicles (EVs) starve for minutes-level fast-charging lithium-ion batteries (LIBs), while the heat gathering at high-rate charging and torridity conditions has detrimental effects on electrolytes, triggering rapid battery degradation and even safety hazards. However, the current research on high-temperature fast-charging (HTFC) electrolytes is very lacking. We revolutionized the conventional paradigm of developing HTFC electrolytes integrating with high-throughput calculation, machine-learning techniques, and experimental verifications to establish a data-knowledge-dual-driven approach. Ethyl trimethylacetate was efficiently screened out based on the approach and enabled batteries to work under high temperatures with distinctly restricted side reactions. A stable and highly safe fast-charging (15-min charging to 80% capacity) cycling without Li plating was achieved over 4100 cycles at 45 °C based on 181 Wh kg-1 pouch cells, demonstrating the state-of-the-art in this field.

Electrolyte Regulation toward Cathodes with Enhanced-Performance in Aqueous Zinc Ion Batteries

Enhancing cathodic performance is crucial for aqueous zinc-ion batteries, with the primary focus of research efforts being the regulation of the intrinsic material structure. Electrolyte regulation is also widely used to improve full-cell performance, whose main optimization mechanisms have been extensively discussed only in regard to the metallic anode. Considering that ionic transport begins in the electrolyte, the modulation of the electrolyte must influence the cathodic performance or even the reaction mechanism. Despite its importance, the discussion of the optimization effects of electrolyte regulation on the cathode has not garnered the attention it deserves. To fill this gap and raise awareness of the importance of electrolyte regulation on cathodic reaction mechanisms, this review comprehensively combs the underlying mechanisms of the electrolyte regulation strategies and classifies the regulation mechanisms into three main categories according to their commonalities for the first time, which are ion effect, solvating effect, and interfacial modulation effect, revealing the missing puzzle piece of the mechanisms of electrolyte regulation in optimizing the cathode.

Coherent Strain-Inhibiting Phase Construction of Lithium-Rich Manganese-Based Oxide Toward High Mechanochemical Stability

A layered lithium-rich manganese-based oxide cathode, containing R3̅m (LiTMO2, TM = Mn, Ni, Co) and C2/m (Li2MnO3) nanodomains, utilizes both transition metals and oxygen redox to yield substantial energy density. However, the inherent heterogeneous nature and distinct nanodomain redox chemistries of layered lithium-rich oxides will inevitably cause pernicious lattice strain and structural displacement, which can hardly be eliminated by conventional doping or coating strategies and result in accelerated performance decay. Herein, we incorporate a strain-inhibiting perovskite phase coherently grown within the layered structure to effectively restrain the displacement and lattice strain during uneven Li-ion extraction. The enhanced mechanochemical stability of the designed cathode benefits the persistent structure and reversible oxygen redox, thereby achieving high initial Coulombic efficiency and stable cycling and voltage profiles. Our approach of lattice engineering alleviates the strain and displacement caused by inhomogeneous reactivity between heterogeneous nanodomains and promotes the development of advanced cathode materials with long durability.

Ti Doping Decreases Mn and Ni Dissolution from High-Voltage LiNi0.5Mn1.5O4 Cathodes

LiNi0.5Mn1.5O4 (LNMO), with its high operating voltage, is a favorable cathode material for lithium-ion batteries. However, Ni and Mn dissolution and the associated low cycle life limit their widespread adoption. In this work, we investigate titanium doping as a strategy to mitigate Mn and Ni dissolution from LNMO electrodes. We demonstrate bulk doping of Ti in LNMO up to nominal compositions of x = 0.15 in LiNi0.5Mn1.5-x Ti x O4. Electrochemical characterization shows that titanium doping enhances the cycle life in LNMO-based half- and full cells with a negligible decrease in capacity or rate capability. Half-cells with LiNi0.5Mn1.35Ti0.15O4 cathodes and lithium anodes exhibited a capacity retention of 90% after 300 cycles at 1C. Li4Ti5O12/LiNi0.5Mn1.35Ti0.15O4 full cells with Li4Ti5O12 anodes cycled at 1C rate to 100% depth of discharge retained ∼73% of the original capacity at the end of 1000 cycles. Our work shows that cathode modification strategies could still be used for enhancing the electrochemical performance of high-voltage cathodes, while using conventional Li-ion battery electrolytes. Improving the cathode stability in conjunction with electrolyte modification could enable the development of practical high-voltage Li-ion batteries.

A Mechanistic Insight into the Acidic-stable MnSb2O6 for Electrocatalytic Water Oxidation

The abundant, active, and acidic-stable catalysts for the oxygen evolution reaction (OER) are rare to proton exchange membrane-based water electrolysis. Mn-based materials show promise as electrocatalysts for OER in acid electrolytes. However, the relationship between the stability, activity and structure of Mn-based catalysts in acidic environments remains unclear. In this study, phase-pure MnSb2O6 was successfully prepared and investigated as a catalyst for OER in a sulfuric acid solution (pH of 2.0). A comprehensive mechanistic comparison between MnSb2O6 and Mn3O4 revealed that the rate-determining step for OER on MnSb2O6 is the direct formation of MnIV=O from MnII-H2O by the 2H+/2e- process. This process avoids the rearrangement of adjacent MnIII intermediates, leading to outstanding stability and activity.

Interface Issues of Layered Transition Metal Oxide Cathodes for Sodium-Ion Batteries: Current Status, Recent Advances, Strategies, and Prospects

Sodium-ion batteries (SIBs) hold significant promise in energy storage devices due to their low cost and abundant resources. Layered transition metal oxide cathodes (NaxTMO2, TM = Ni, Mn, Fe, etc.), owing to their high theoretical capacities and straightforward synthesis procedures, are emerging as the most promising cathode materials for SIBs. However, the practical application of the NaxTMO2 cathode is hindered by an unstable interface, causing rapid capacity decay. This work reviewed the critical factors affecting the interfacial stability and degradation mechanisms of NaxTMO2, including air sensitivity and the migration and dissolution of TM ions, which are compounded by the loss of lattice oxygen. Furthermore, the mainstream interface modification approaches for improving electrochemical performance are summarized, including element doping, surface engineering, electrolyte optimization, and so on. Finally, the future developmental directions of these layered NaxTMO2 cathodes are concluded. This review is meant to shed light on the design of superior cathodes for high-performance SIBs.

K-Mn3O4-NCs@PANI nanochains for high-rate and stable aqueous zinc-ion batteries: A doping and morphology-tailored synthesis strategy

Aqueous zinc ion batteries (AZIBs) are promising energy storage solutions due to their high energy density and safety. However, developing cathode materials that offer both high energy density and durability for Zn2+ ions storage remains challenging. Manganese (Mn) oxide-based cathodes have been developed for AZIBs due to their high discharge voltage and desirable capacity, but face challenges like poor conductivity, slow reaction kinetics, and dissolution during cycling. Doping, morphology/structure design, and protective layers are effective for enhancing the structure, conductivity, and electronic properties of Mn-based oxides. A synthetic strategy combining these methods for Mn3O4 cathodes is proposed for AZIBs. K+ ions doping in Mn3O4 (K-Mn3O4) can regulate local electronic structure, induce oxygen vacancies, improve conductivity, and provide more active sites for Zn2+ ions diffusion. Additionally, K-Mn3O4 nanochain (K-Mn3O4-NCs), with a unique chain-like nanostructure (NCs) and high aspect ratio, synthesized via Mn2+ ions chelation with nitrilotriacetic acid (NTA) and calcination, show reduced interparticle contact resistance, shorter Zn2+ ions diffusion length, and faster reaction kinetics. Meanwhile, the in-situ polymerized polyaniline (PANI) layer on K-Mn3O4-NCs shields against corrosion (K-Mn3O4-NCs@PANI), connects 1D K-Mn3O4-NCs into a continuous conductive network, suppresses volume expansion, and improves stability. Electrochemical analysis shows that K-Mn3O4-NCs@PANI exhibits higher stability and faster reaction kinetics due to a reduced bandgap, increased oxygen defects, and less coulombic repulsion between Zn2+ ions and Mn oxide hosts. The K-Mn3O4-NCs@PANI cathode achieved a high capacity of 510 mAh/g at 0.1 A/g and excellent rate capacity of 203.2 mAh/g at 5 A/g. After 20,000 cycles, it maintained a capacity of 90.3 mAh/g at 5 A/g, showing exceptional long-term stability with a minimal decay rate of 0.026 ‰ per cycle.

Seed-Assisted Reversible Dissolution/Deposition of MnO2 for Long-Cyclic and Green Aqueous Zinc-Ion Batteries

Manganese oxide (MnO2) based aqueous zinc-ion batteries (AZIBs) are considered to be a promising battery for grid-scale energy storage. However, they usually suffer from the great challenge of capacity attenuation due to Mn dissolution and irreversible structural transformation. Herein, full use of the shortcomings is made to design high-performance cathode-free AZIBs. Manganese-based Prussian blue analog (Mn-PBA) is selected as a seed layer to provide a stable MnO2 electrodeposition surface. Thanks to the large specific surface area and manganophilic nature of Mn-PBA, the deposition/dissolution kinetics between Mn2+ and MnO2 are significantly enhanced. Systematic studies revealed the mechanism of MnO2 deposition-dissolution related to the reversible transformation of manganese oxide hydroxide and zinc hydroxide sulfate hydrate. Based on this, the developed cathode-free AZIBs exhibit outstanding rate performance (with a specific capacity of 273.7 mAh g-1 at 1 A g-1) and extraordinary cycle stability (maintaining a specific capacity of 52.3 mAh g-1 after 50 000 cycles at 20 A g-1). Furthermore, the AZIBs with non-toxic, biocompatible materials can be directly discarded after use, without causing pollution to the environment, which is expected to help achieve the sustainable development goals.

An XPS Study of Electrolytes for Li-Ion Batteries in Full Cell LNMO vs Si/Graphite

Two different types of electrolytes (co-solvent and multi-salt) are tested for use in high voltage LiNi0.5Mn1.5O4||Si/graphite full cells and compared against a carbonate-based standard LiPF6 containing electrolyte (baseline). Ex situ postmortem XPS analysis on both anodes and cathodes over the life span of the cells reveals a continuously growing SEI and CEI for the baseline electrolyte. The cells cycled in the co-solvent electrolyte exhibited a relatively thick and long-term stable CEI (on LNMO), while a slowly growing SEI was determined to form on the Si/graphite. The multi-salt electrolyte offers more inorganic-rich SEI/CEI while also forming the thinnest SEI/CEI observed in this study. Cross-talk is identified in the baseline electrolyte cell, where Si is detected on the cathode, and Mn is detected on the anode. Both the multi-salt and co-solvent electrolytes are observed to substantially reduce this cross-talk, where the co-solvent is found to be the most effective. In addition, Al corrosion is detected for the multi-salt electrolyte mainly at its end-of-life stage, where Al can be found on both the anode and cathode. Although the co-solvent electrolyte offers superior interface properties in terms of the limitation of cross-talk, the multi-salt electrolyte offers the best overall performance, suggesting that interface thickness plays a superior role compared to cross-talk. Together with their electrochemical cycling performance, the results suggest that multi-salt electrolyte provides a better long-term passivation of the electrodes for high-voltage cells.

Sulfur-Assisted Surface Modification of Lithium-Rich Manganese-Based Oxide toward High Anionic Redox Reversibility

Energy storage via anionic redox provides extra capacity for lithium-rich manganese-based oxide cathodes at high voltage but causes gradual structural collapse and irreversible capacity loss with generation of On - (0 ≤ n < 2) species upon deep oxidation. Herein, the stability and reversibility of anionic redox reactions are enhanced by a simple sulfur-assisted surface modification method, which not only modulates the material's energy band allowing feasible electron release from both bonding and antibonding bands, but also traps the escaping On - via an as-constructed SnS2- x - σ Oy coating layer and return them to the host lattice upon discharge. The regulation of anionic redox inhibits the irreversible structural transformation and parasitic reactions, maintaining the specific capacity retention of as-modified cathode up to 94% after 200 cycles at 100 mA g-1 , along with outstanding voltage stability. The reported strategy incorporating energy band modulation and oxygen trapping is promising for the design and advancement of other cathodes storing energy through anion redox.

Progress, Challenge, and Prospect of LiMnO2 : An Adventure toward High-Energy and Low-Cost Li-Ion Batteries

Lithium manganese oxides are considered as promising cathodes for lithium-ion batteries due to their low cost and available resources. Layered LiMnO2 with orthorhombic or monoclinic structure has attracted tremendous interest thanks to its ultrahigh theoretical capacity (285 mAh g-1 ) that almost doubles that of commercialized spinel LiMn2 O4 (148 mAh g-1 ). However, LiMnO2 undergoes phase transition to spinel upon cycling cause by the Jahn-Teller effect of the high-spin Mn3+ . In addition, soluble Mn2+ generates from the disproportionation of Mn3+ and oxygen release during electrochemical processes may cause poor cycle performance. To address the critical issues, tremendous efforts have been made. This paper provides a general review of layered LiMnO2 materials including their crystal structures, synthesis methods, structural/elemental modifications, and electrochemical performance. In brief, first the crystal structures of LiMnO2 and synthetic methods have been summarized. Subsequently, modification strategies for improving electrochemical performance are comprehensively reviewed, including element doping to suppress its phase transition, surface coating to resist manganese dissolution into the electrolyte and impede surface reactions, designing LiMnO2 composites to improve electronic conductivity and Li+ diffusion, and finding compatible electrolytes to enhance safety. At last, future efforts on the research frontier and practical application of LiMnO2 have been discussed.

Accelerated aging of lithium-ion batteries: bridging battery aging analysis and operational lifetime prediction

The exponential growth of stationary energy storage systems (ESSs) and electric vehicles (EVs) necessitates a more profound understanding of the degradation behavior of lithium-ion batteries (LIBs), with specific emphasis on their lifetime. Accurately forecasting the lifetime of batteries under various working stresses aids in optimizing their operating conditions, prolonging their longevity, and ultimately minimizing the overall cost of the battery life cycle. Accelerated aging, as an efficient and economical method, can output sufficient cycling information in short time, which enables a rapid prediction of the lifetime of LIBs under various working stresses. Nevertheless, the prerequisite for accelerated aging-based battery lifetime prediction is the consistency of aging mechanisms. This review, by comprehensively summarizing the aging mechanisms of various components within LIBs and the battery degradation mechanisms under stress-accelerated conditions, provides a reference for evaluating the consistency of battery aging mechanisms. Furthermore, this paper introduces accelerated aging-based lifetime prediction models and offers constructive suggestions for future research on accelerated lifetime prediction of LIBs.

Enhancing Temperature Adaptability of Aqueous Zinc Batteries via Antifreezing Electrolyte and Site-Selective ZnSe-Ag Interface Layer Design

Rechargeable aqueous zinc batteries (RAZBs) represent a sustainable, environmentally benign, cost-efficient energy storage solution for the scaled renewable power system. However, the cycling endurance and temperature adaptability of RAZBs are hindered by practical technological barriers such as the subzero freezing point of aqueous electrolyte, severe cation dissolution of the cathode, and dendrite growth on the Zn anode. Herein, we optimize the hybrid electrolyte formulation of 8 M ZnCl2 in the ethylene glycol-water mixed solvent to reconfigure the hydrogen bonding and [Zn(H2O)1.80(EG)0.23]2+ solvation sheath, which well balances the ionic conductivity and the antifreezing property until -125 °C. As monitored by operando X-ray diffraction, meanwhile, the structural dissolution of the V2O5 cathode upon the dynamic cycling and static idling storage at elevated temperature are effectively restrained. At the anode side, the thermally induced substitution between the Ag2Se overcoating and Zn foil in situ constructs the site-selective, mosaic interface layer, in which the solvophilic ZnSe facilitates the desolvation, while the Ag species provide zincophilic nucleation sites for high-throughput Zn deposition. The synergistic coupling of the antifreezing electrolyte and anode interfacial design enables the wide-temperature-range adaptability of the RAZB prototype (10 μm Zn foil and 1 mAh cm-2 V2O5 cathode), which balances the cycling endurance (92.5% capacity retention rate for 1000 cycles), 84.7% mitigation of the self-discharge rate at 55 °C, as well as the secured cyclability even at -40 °C.

Operando characterization and regulation of metal dissolution and redeposition dynamics near battery electrode surface

Mn dissolution has been a long-standing, ubiquitous issue that negatively impacts the performance of Mn-based battery materials. Mn dissolution involves complex chemical and structural transformations at the electrode-electrolyte interface. The continuously evolving electrode-electrolyte interface has posed great challenges for characterizing the dynamic interfacial process and quantitatively establishing the correlation with battery performance. In this study, we visualize and quantify the temporally and spatially resolved Mn dissolution/redeposition (D/R) dynamics of electrochemically operating Mn-containing cathodes. The particle-level and electrode-level analyses reveal that the D/R dynamics is associated with distinct interfacial degradation mechanisms at different states of charge. Our results statistically differentiate the contributions of surface reconstruction and Jahn-Teller distortion to the Mn dissolution at different operating voltages. Introducing sulfonated polymers (Nafion) into composite electrodes can modulate the D/R dynamics by trapping the dissolved Mn species and rapidly establishing local Mn D/R equilibrium. This work represents an inaugural effort to pinpoint the chemical and structural transformations responsible for Mn dissolution via an operando synchrotron study and develops an effective method to regulate Mn interfacial dynamics for improving battery performance.

An Artificial MnWO4 Cathode Electrolyte Interphase Enabling Enhanced Electrochemical Performance of δ-MnO2 Cathode for Aqueous Zinc Ion Battery

The dissolution of active material in aqueous batteries can lead to a rapid deterioration in capacity, and the presence of free water can also accelerate the dissolution and trigger some side reactions that affect the service life of aqueous batteries. In this study, a MnWO₄ cathode electrolyte interphase (CEI) layer is constructed on a δ-MnO₂ cathode by cyclic voltammetry, which is effective in inhibiting the dissolution of Mn and improving the reaction kinetics. As a result, the CEI layer enables the δ-MnO₂ cathode to produce a better cycling performance, with the capacity maintained at 98.2% (vs. activated capacity at 500 cycles) after 2000 cycles at 10 A g^-1. In comparison, the capacity retention rate is merely 33.4% for pristine samples in the same state, indicating that this MnWO₄ CEI layer constructed by using a simple and general electrochemical method can promote the development of MnO₂ cathodes for aqueous zinc ion batteries.

Solution NMR of Battery Electrolytes: Assessing and Mitigating Spectral Broadening Caused by Transition Metal Dissolution

NMR spectroscopy is a powerful tool that is commonly used to assess the degradation of lithium-ion battery electrolyte solutions. However, dissolution of paramagnetic Ni²⁺ and Mn²⁺ ions from cathode materials may affect the NMR spectra of the electrolyte solution, with the unpaired electron spins in these paramagnetic solutes inducing rapid nuclear relaxation and spectral broadening (and often peak shifts). This work establishes how dissolved Ni²⁺ and Mn²⁺ in LiPF₆ electrolyte solutions affect ¹H, ¹⁹F, and ³¹P NMR spectra of pristine and degraded electrolyte solutions, including whether the peaks from degradation species are at risk of being lost and whether the spectral broadening can be mitigated. Mn²⁺ is shown to cause far greater peak broadening than Ni²⁺, with the effect of Mn²⁺ observable at just 10 μM. Generally, ¹⁹F peaks from PF₆ ^- degradation species are most affected by the presence of the paramagnetic metals, followed by ³¹P and ¹H peaks. Surprisingly, when NMR solvents are added to acquire the spectra, the degree of broadening is heavily solvent-dependent, following the trend of solvent donor number (increased broadening with lower solvent donicity). Severe spectral broadening is shown to occur whether Mn is introduced via the salt Mn(TFSI)₂ or is dissolved from LiMn₂O₄. We show that the weak ¹⁹F and ³¹P peaks in spectra of electrolyte samples containing micromolar levels of dissolved Mn²⁺ are broadened to an extent that they are no longer visible, but this broadening can be minimized by diluting electrolyte samples with a suitably coordinating NMR solvent. Li₃PO₄ addition to the sample is also shown to return ¹⁹F and ³¹P spectral resolution by precipitating Mn²⁺ out of electrolyte samples, although this method consumes any HF in the electrolyte solution.

Mg Substitution Induced TM/Vacancy Disordering and Enhanced Structural Stability in Layered Oxide Cathode Materials

Anionic redox is an effective way to increase the capacity of the cathode materials. Na₂Mn₃O₇ [Na_4/7[Mn_6/7□_1/7]O₂, □ for the transition metal (TM) vacancies] with native and ordered TM vacancies can conduct a reversible oxygen redox and be a promising high-energy cathode material for sodium-ion batteries (SIBs). However, its phase transition at low potentials (∼1.5 V vs Na⁺/Na) induces potential decays. Herein, magnesium (Mg) is doped on the TM vacancies to form a disordered Mn/Mg/□ arrangement in the TM layer. The Mg substitution suppresses the oxygen oxidation at ∼4.2 V by reducing the number of the Na-O-□ configurations. Meanwhile, this flexible disordering structure inhibits the generation of the dissolvable Mn²⁺ ions and mitigates the phase transition at ∼1.6 V. Therefore, the Mg doping improves the structural stability and its cycling performance in 1.5-4.5 V. The disordering arrangement endows Na_0.49Mn_0.86Mg_0.06□_0.08O₂ with a higher Na⁺ diffusivity and improved rate performance. Our study reveals that oxygen oxidation is highly dependent on the ordering/disordering arrangements in the cathode materials. This work provides insights into the balance of anionic and cationic redox for enhancing the structural stability and electrochemical performance in the SIBs.

Interfacial Stabilization of Li2O-Based Cathodes by Malonic-Acid-Functionalized Fullerenes as a Superoxo-Radical Scavenger for Suppressing Parasitic Reactions

The utilization of an anionic redox reaction as an innovative strategy for overcoming the limitations of cathode capacity in lithium-ion batteries has recently been the focus of intensive research. Li₂O-based materials using the anionic (oxygen) redox reaction have the potential to deliver a much higher capacity than commercial cathodes using cationic redox reactions based on transition-metal ions. However, parasitic reactions attributed to the superoxo species (such as LiO₂), derived from the Li₂O active material of the cathode, deteriorate the stability of the interface between the cathode and electrolyte, which has limited the commercialization of Li₂O-based cathodes. To address this issue, malonic-acid-functionalized fullerenes (MC₆₀) were applied in the electrolyte as an additive for scavenging the superoxo radicals (O₂^1- in LiO₂) that trigger parasitic reactions. MC₆₀ can efficiently capture superoxo radicals using the π-conjugated surface and the malonate functionality on the surface. As a result, MC₆₀ considerably enhanced the available capacity and cycling performance of the Li₂O-based cathodes, decreased the interfacial layer formed on the cathode surface, and hindered the generation of byproducts, such as Li₂CO₃, CO₂, and C-F₃, derived from parasitic reactions. In addition, the loss of Li₂O from the cathode surface during cycling was also suppressed, validating the ability of MC₆₀ to capture superoxo radicals. This result confirms that the introduction of MC₆₀ can effectively alleviate the parasitic reactions at the cathode/electrolyte interface and improve the electrochemical performance of Li₂O-based cathodes by scavenging the superoxo species.