Regulating cathode surface hydroxyl chemistry enables superior potassium storage.

Potassium vanadium fluorophosphate (KVPO4F) is regarded as a promising cathode candidate for potassium-ion batteries due to its high working voltage and satisfactory theoretical capacity. However, the usage of electrochemically inactive binders and redundant current collectors typically results in inferior electrochemical performance and low energy density, thus implying the important role of rational electrode structure design. Herein, we have reported a scalable and cost-effective synthesis of a cellulose-derived KVPO4F self-supporting electrode, which features a special surface hydroxyl chemistry, three-dimensional porous and conductive framework, as well as super flexible and stable architecture. The cellulose not only serves as a flexible substrate, a pore-forming agent, and a versatile binder for KVPO4F/conductive carbon but also enhances the K-ion migration ability. Benefiting from the special hydroxyl chemistry-induced storage mechanism and electrode structural stability, the flexible freestanding KVPO4F cathode exhibits high-rate performance (53.0% capacity retention with current densities increased 50-fold, from 0.2 C to 10 C) and impressive cycling stability (capacity retention up to 74.9% can be achieved over 1,000 cycles at a rate of 5 C). Such electrode design and surface engineering strategies, along with a deeper understanding of potassium storage mechanisms, provide invaluable guidance for better electrode design to boost the performance of potassium-ion energy storage systems.

Entropymetry for detecting microcracks in high-nickel layered oxide cathodes.

Electric vehicles (EVs) are imposing ever-challenging standards on the lifetime and safety of lithium-ion batteries (LIBs); consequently, real-time nondestructive monitoring of battery cell degradation is highly desired. Unfortunately, high-nickel (Ni) layered oxides, the preferred LIB cathodes for EVs, undergo performance degradation originating from microcrack formation during cycling. Entropymetry is introduced as a real-time analytic tool for monitoring the evolution of microcracks in these cathodes along the state of charge. The entropy change of the layered cathode is associated with the lattice configuration and reflects the structural heterogeneity relevant to the evolution of these microcracks. The structural heterogeneity was correlated with peak broadening in in-situ X-ray diffractometry while varying the experimental conditions that affect crack formation such as the upper cutoff voltage during charging and the Ni-content of the active material. Entropymetry, proposed here as a nondestructive diagnostic tool, can contribute greatly to the safe and reliable operation of LIBs for EVs.

Recycling spent LiNi1-x-yMnxCoyO2 cathodes to bifunctional NiMnCo catalysts for zinc-air batteries.

SignificanceIn recent years, lithium-ion batteries (LIBs) have been widely applied in electric vehicles as energy storage devices. However, it is a great challenge to deal with the large number of spent LIBs. In this work, we employ a rapid thermal radiation method to convert the spent LIBs into highly efficient bifunctional NiMnCo-activated carbon (NiMnCo-AC) catalysts for zinc-air batteries (ZABs). The obtained NiMnCo-AC catalyst shows excellent electrochemical performance in ZABs due to the unique core-shell structure, with face-centered cubic Ni in the core and spinel NiMnCoO4 in the shell. This work provides an economical and environment-friendly approach to recycling the spent LIBs and converting them into novel energy storage devices.

Cathode Electrolyte Interphase Engineering for Prussian Blue Analogues in Lithium-Ion Batteries.

The increasing use of low-cost lithium iron phosphate cathodes in low-end electric vehicles has sparked interest in Prussian blue analogues (PBAs) for lithium-ion batteries. A major challenge with iron hexacyanoferrate (FeHCFe), particularly in lithium-ion systems, is its slow kinetics in organic electrolytes and valence state inactivation in aqueous ones. We have addressed these issues by developing a polymeric cathode electrolyte interphase (CEI) layer through a ring-opening reaction of ethylene carbonate triggered by OH- radicals from structural water. This facile approach considerably mitigates the sluggish electrochemical kinetics typically observed in organic electrolytes. As a result, FeHCFe has achieved a specific capacity of 125 mAh g-1 with a stable lifetime over 500 cycles, thanks to the effective activation of Fe low-spin states and the structural integrity of the CEI layers. These advancements shed light on the potential of PBAs to be viable, durable, and efficient cathode materials for commercial use.

New Insights into Anionic Redox in P2-Type Oxide Cathodes for Sodium-Ion Batteries.

Manganese/nickel-based layered transition metal oxides have caught the attention of studies as promising cathodes for sodium-ion batteries (SIBs). It is reported that utilizing both cationic and anionic redox reactions is a promising method for higher energy density cathodes. However, the anionic redox reaction comes at the expense of irreversible oxygen release. Hence, a Li-Mg cosubstituted P2-Na0.67Li0.07Mg0.07Ni0.28Mn0.58O2 material with a honeycomb-ordered superstructure was designed. The Ni3+/Ni4+ redox couple and the anionic redox reaction are proven to have a competitive relationship. Density functional theory calculations reveal the effect of O 2p nonbonding states from Li and prove that Mg-O bonds can stabilize the Ni-O eg states. In situ electrochemical impedance spectroscopy measurements and galvanostatic charging/discharging derived dV/dQ, representing resistance changes with time, are obtained to reveal the mechanism of the anionic redox reaction. This study presents the effect and mechanism of the O 2p nonbonding state and Mg-O bonds of manganese/nickel-based layered oxides.

Two-Dimensional Transition Metal Phosphides As Cathode Additive in Robust Lithium-Sulfur Batteries.

The development of advanced cathode materials able to promote the sluggish redox kinetics of polysulfides is crucial to bringing lithium-sulfur batteries to the market. Herein, two electrode materials: namely, Zr2PS2 and Zr2PTe2, are identified through screening several hundred thousand compositions in the Inorganic Crystal Structure Database. First-principles calculations are performed on these two materials. These structures are similar to that of the classical MXenes. Concurrently, calculations show that Zr2PS2 and Zr2PTe2 possess high electrical conductivity, promote Li ion diffusion, and have excellent electrocatalytic activity for the Li-S reaction and particularly for the Li2S decomposition. Besides, the mechanisms behind the excellent predicted performance of Zr2PS2 and Zr2PTe2 are elucidated through electron localization function, charge density difference, and localized orbital locator. This work not only identifies two candidate sulfur cathode additives but may also serve as a reference for the identification of additional electrode materials in new generations of batteries, particularly in sulfur cathodes.

Interfacial Robustness and Improved Kinetics of Single-Crystal Ni-Rich Co-Free Cathodes Enabled by Surface Crystal-Facet Modulation.

The elimination of Co from Ni-rich layered cathodes is critical to reduce the production cost and increase the energy density for sustainable development. Herein, a delicate strategy of crystal-facet modulation is designed and explored, which is achieved by simultaneous Al/W-doping into the precursors, while the surface role of the crystal-facet is intensively revealed. Unlike traditional studies on crystal structure growth along a certain direction, this work modulates the crystal-facet at the nanoscale based on the effect of W-doping dynamic migration with surface energy, successfully constructing the core-shell (003)/(104) facet surface. Compared to the (003) plane, the induced (104) facet at the surface can provide more space for Li+-activity, enabling lower interfacial polarization and higher Li+-transport rate. Additionally, bulk Al-doping is beneficial for enhancing the Li+-diffusion from the exterior surface to the interior lattice. With improved interfacial stability and restrained surface erosion, the product exhibits superior capacity retention and boosted rate performance under the elevated temperature.

Synchronously Consolidating Li, Se, S, and C for Robust Li-SeS Batteries.

S-redox involving solvated polysulfides is accompanied by volumetric change and structural decay of the S-based cathodes. Here, we propose a synchronous construction strategy for consolidating Li, Se, S, and C elements within a composite cathode via a paradigm reaction of 8Li+2Se+CS2 = 2Li4SeS+C. The obtained composite features crystalline Li4SeS encapsulated in a carbon nanocage (Li4SeS@C), exhibiting ultrahigh electrical conductivity, ultralow activation barrier, and excellent structural integrity, accordingly enabling large specific capacity (615 mAh g-1) and high capacity retention (87.3% after 350 cycles) at 10 A g-1. TOF-SIMS demonstrates its superior volumetric efficiency to a similar derivative SeS@C (2Se+CS2 = 2SeS+C), and DFT reveals its lower activation barrier than Li2S@C and Li2Se@C. This consolidation design significantly improves the electrochemical performance of S-based cathodes, and the paradigm reaction guarantees structural diversity and flexibility. Moreover, employing a synchronous construction mechanism to maximize the synergistic effect between element consolidation and carbon encapsulation opens up a new approach for developing robust S or chalcogenide cathodes.

Air-Stable High-Entropy Layered Oxide Cathode with Enhanced Cycling Stability for Sodium-Ion Batteries.

O3-type layered oxides have been extensively studied as cathode materials for sodium-ion batteries due to their high reversible capacity and high initial sodium content, but they suffer from complex phase transitions and an unstable structure during sodium intercalation/deintercalation. Herein, we synthesize a high-entropy O3-type layered transition metal oxide, NaNi0.3Cu0.05Fe0.1Mn0.3Mg0.05Ti0.2O2 (NCFMMT), by simultaneously doping Cu, Mg, and Ti into its transition metal layers, which greatly increase structural entropy, thereby reducing formation energy and enhancing structural stability. The high-entropy NCFMMT cathode exhibits significantly improved cycling stability (capacity retention of 81.4% at 1C after 250 cycles and 86.8% at 5C after 500 cycles) compared to pristine NaNi0.3Fe0.4Mn0.3O2 (71% after 100 cycles at 1C), as well as remarkable air stability. Finally, the NCFMMT//hard carbon full-cell batteries deliver a high initial capacity of 103 mAh g-1 at 1C, with 83.8 mAh g-1 maintained after 300 cycles (capacity retention of 81.4%).

Unlocking a Fast Track for Magnesium Migration in Cu1.8S1-xSex via Anion-Tuning Chemistry.

Rechargeable magnesium batteries (rMBs) are promising candidates for next-generation batteries in which sulfides are widely used as cathode materials. The slow kinetics, low redox reversibility, and poor magnesium storage stability induced by the large Coulombic resistance and ionic polarization of Mg2+ ions have obstructed the development of high-performance rMBs. Herein, a Cu1.8S1-xSex cathode material with a two-dimensional sheet structure has been prepared by an anion-tuning strategy, achieving improved magnesium storage capacity and cycling stability. Element-specific synchrotron radiation analysis is evidence that selenium incorporation has indeed changed the chemical state of Cu species. Density functional theory calculations combined with kinetics analysis reveal that the anionic substitution endows the Cu1.8S1-xSex electrode with favorable charge-transfer kinetics and low ion diffusion barrier. The principal magnesium storage mechanisms and structural evolution process have been revealed in details based on a series of ex situ investigations. Our findings provide an effective heteroatom-tuning tactic of optimizing electrode structure toward advanced energy storage devices.

Exceptional Rate Performances of Li-Rich Mn-Based Cathodes Enabled by Boron-Based Additives-Driven Self-Optimized Interface.

Li-rich Mn-based cathode material (LRM), as a promising cathode for high energy density lithium batteries, suffers from severe side reactions in conventional lithium hexafluorophosphate (LiPF6)-based carbonate electrolytes, leading to unstable interfaces and poor rate performances. Herein, a boron-based additives-driven self-optimized interface strategy is presented to dissolve low ionic conductivity LiF nanoparticles at the outer cathode electrolyte interface, leading to the optimized interfacial components, as well as the enhanced Li ion migration rate in electrolytes. Being attributed to these superiorities, the LRM||Li battery delivers a high-capacity retention of 92.19% at 1C after 200 cycles and a low voltage decay of 1.08 mV/cycle. This work provides a new perspective on the rational selection of functional additives with an interfacial self-optimized characteristic to achieve a long lifespan LRM with exceptional rate performances.

Praseodymium-Cerium Oxide-Infiltrated Perovskite Cathode with Superior Electrochemical Performance for Solid Oxide Fuel Cells.

This study presents a high-performance solid oxide fuel cell employing a perovskite cathode, strontium iron molybdenum oxide [Sr2Fe1.5Mo0.5O6-δ (SFM)], infiltrated with praseodymium-cerium oxide [Pr0.2Ce0.8O2-δ (PCO)], a fluorite. This infiltration notably enhances the oxygen reduction reaction kinetics and long-term stability. Evidence of enhanced stability is seen through minimized impedance degradation over 50 h. Furthermore, PCO infiltration improves the cathode's resistance to chromium poisoning by suppressing strontium degradation. Compared to the bare SFM cathode, the PCO-infiltrated SFM composite cathode doubles the cell's power density at 800 °C.

Double-Layered Perovskite Oxyfluoride Cathodes with High Capacity Involving O-O Bond Formation for Fluoride-Ion Batteries.

Developing electrochemical high-energy storage systems is of crucial importance toward a green and sustainable energy supply. A promising candidate is fluoride-ion batteries (FIBs), which can deliver a much higher volumetric energy density than lithium-ion batteries. However, typical metal fluoride cathodes with conversion-type reactions cause a low-rate capability. Recently, layered perovskite oxides and oxyfluorides, such as LaSrMnO4 and Sr3Fe2O5F2, have been reported to exhibit relatively high rate performance and cycle stability compared to typical metal fluoride cathodes with conversion-type reactions, but their discharge capacities (∼118 mA h/g) are lower than those of typical cathodes used in lithium-ion batteries. Here, we show that double-layered perovskite oxyfluoride La1.2Sr1.8Mn2O7-δF2 exhibits (de) intercalation of two fluoride ions to rock-salt slabs and further (de) intercalation of excess fluoride ions to the perovskite layer, leading to a reversible capacity of 200 mA h/g. The additional fluoride-ion intercalation leads to the formation of O-O bond in the structure for charge compensation (i.e., anion redox). These results highlight the layered perovskite oxyfluorides as a new class of active materials for the construction of high-performance FIBs.

High throughput selection of organic cathode materials.

Efficient and affordable batteries require the design of novel organic electrode materials to overcome the drawbacks of the traditionally used inorganic materials, and the computational screening of potential candidates is a very efficient way to identify prospective solutions and minimize experimental testing. Here we present a DFT high-throughput computational screening where 86 million molecules contained in the PUBCHEM database have been analyzed and classified according to their estimated electrochemical features. The 5445 top-performing candidates were identified, and among them, 2306 are expected to have a one-electron reduction potential higher than 4 V versus (Li/Li+ ). Analogously, one-electron energy densities higher than 800 Whkg-1 have been predicted for 626 molecules. Explicit calculations performed for certain materials show that at least 69 candidates with a two-electron energy density higher than 1300 Whkg-1 . Successful molecules were sorted into several families, some of them already commonly used electrode materials, and others still experimentally untested. Most of them are small systems containing conjugated CO, NN, or NC functional groups. Our selected molecules form a valuable starting point for experimentalists exploring new materials for organic electrodes.

DFT Guided Design and Preparation of Quasi-Nanocrystalline Hf-La2O3 Cathode with Unprecedented Thermal Emission Performance.

With the guidance of density functional theory (DFT), a high-performance hafnium (Hf) cathode for an air/water vapor plasma torch is designed and the concepts and principles for high performance are elucidated. A quasi-nanocrystalline hexagonal close-packed (HCP) Hf-La2O3 cathode based on these design principles is successfully fabricated via a powder metallurgy route. Under identical voltage and temperature conditions, the thermal emission current density of this quasi-nanocrystalline Hf-La2O3 cathode is ≈20 times greater than that of conventional Hf cathodes. Additionally, its cathodic lifespan is significantly extended. Quasi-nanocrystalline Hf-La2O3 products are manufactured into cathode devices with standard dimensions. This fabrication process is straightforward, requires minimal doped oxides, and is cost-effective. Consequently, the approach offers substantial performance enhancements over traditional Hf melting methods without incurring significantly additional costs.

Chemical Cross-linked Electrode-Electrolyte Interface Boosting the Structural Integrity of High Nickel Cathode Materials.

High nickel cathode material LiNixCoyMn1-x-yO2 (NCM) (x ≥ 0.6) has represented the most critical material in virtue of outstanding specific capacity and low self-discharge. However, the high surface alkalinity and detrimental interfacial stability lead to the parasitic reaction and a series of phase deterioration. Herein, in situ cross-linking binder molecular chains with a 3D network structure to construct a stable and robust electrode-electrolyte interface, which can maintain the structural integrity and restrain side reactions is designed. Simultaneously, the cross-linked polymer can form stable hydrogen bonds with the pristine binder, greatly enhancing the bonding property. More importantly, the functional groups contained in the cross-linked co-polymers can chemically anchor transition metals, effectively preventing the dissolution of transition metals. Theoretical calculations confirm the feasibility and advancement of the anchoring mechanism, driving excellent structural stability and inhibition of the NiO impurity phase. This work provides a practical strategy to realize the high stability of cathode materials.

Boosting the Cycle Performance of Iron Trifluoride Based Solid State Batteries at Elevated Temperatures by Engineering the Cathode Solid Electrolyte Interface.

Iron trifluoride (FeF3) is attracting tremendous interest due to its lower cost and the possibility to enable higher energy density in lithium-ion batteries. However, its cycle performance deteriorates rapidly in less than 50 cycles at elevated temperatures due to cracking of the unstable cathode solid electrolyte interface (CEI) followed by active materials dissolution in liquid electrolyte. Herein, by engineering the salt composition, the Fe3O4-type CEI with the doping of boron (B) atoms in a polymer electrolyte at 60 °C is successfully stabilized. The cycle life of the well-designed FeF3-based composite cathode exceeds an unprecedented 1000 cycles and utilizes up to 70% of its theoretical capacities. Advanced electron microscopy combined with density functional theory (DFT) calculations reveal that the B in lithium salt migrates into the cathode and promotes the formation of an elastic and mechanic robust boron-contained CEI (BOR-CEI) during cycling, by which the durability of the CEI to frequent cyclic large volume changes is significantly enhanced. To this end, the notorious active materials dissolution is largely prohibited, resulting in a superior cycle life. The results suggest that engineering the CEI such as tuning its composition is a viable approach to achieving FeF3 cathode-based batteries with enhanced performance.

An Ultrathin Composite Polymer Electrolyte Dual-Reinforced by a Polymer of Intrinsic Microporosity (PIM-1) and Poly(tetrafluoroethylene) (PTFE) Porous Membrane.

The performances of solid-state polymer electrolytes are urgently required to be further improved for high energy density lithium metal batteries. Herein, a highly reinforced ultrathin composite polymer electrolyte (PLPP) is successfully fabricated in a large scale by densely filling the well-dispersed mixture of polyethylene oxide (PEO), Li-salt (LiTFSI) and a polymer of intrinsic microporosity (PIM-1) into porous poly(tetrafluoroethylene) (PTFE) matrix. Based on the macro-plus-micro synergistic enhancement of the PTFE with excellent mechanical properties and the soluble PIM-1 with suitable functional groups, the PLPP electrolyte exhibits excellent properties including mechanical stress, thermal stability, lithium-ion transference number, voltage window and ionic conductivity, which are all superior to the typical PEO/LiTFSI electrolytes. As a result, the Li/PLPP/Li symmetric cell can stably cycle for > 2000 h, and the LiFePO4/PLPP/Li full cell exhibits excellent rate performance (>10 C) and high cycling stability with an initial capacity of 158.8 mAh g-1 and a capacity retention of 78.8% after 300 cycles. In addition, the excellent mechanical properties as well as the wide voltage window reasonably result in the stable operation of full cells with either high-loading cathode up to 28.1 mg cm-2 or high voltage cathode with high energy density.

A Novel 4-Fluorophenyl Isocyanate Additive Constructing Solid Cathodes-Electrolyte Interface for High-Performance Lithium-Ion Batteries.

Building a stable cathode-electrolyte interface (CEI) is crucial for achieving high-performance layered metal oxide cathode materials LiNixCoyMn1-x-yO2 (NCM). In this work, a novel 4-fluorobenzene isocyanate (4-FBC) electrolyte additive that contains isocyanate and benzene ring functional groups is proposed, which can form robust and homogeneous N-rich and benzene ring skeleton CEI film on the cathode surface, leading to significant improvement in the electrochemical performance of lithium-ion batteries. Taking LiNi0.5Co0.2Mn0.3O2 (NCM523) as an example, the NCM523/SiO@Graphite pouch full cells with electrolytes containing a mass fraction of 1% 4-FBC additives demonstrate improved capacity retention after 200 cycles, retaining capacity retention rates of 81.3%, which is much higher than that of 39.1% without additive. The improvement can be ascribed to the mitigation of electrolyte decomposition and inhibition of transition metal ions the dissolution from the cathode material due to the stable CEI film. Moreover, the electrochemical performance enhancement can also be achieved in high voltage and Ni-rich cathode materials, indicating the universality and effectiveness of this strategy for the practical applications of high energy density lithium-ion batteries.

Waste to Wealth: One-Step Exfoliating of Spent Graphite to Build a Low-Cost Cathode for Lithium-Sulfur Batteries.

With the booming development of Li-ion batteries (LIBs), the recycling and reusing of spent graphite (SG) from LIBs is becoming increasingly crucial. Meanwhile, developing low-cost and efficient carbon hosts for lithium-sulfur (Li-S) batteries has gained widespread attention in the past decade. Nevertheless, the processing of carbon materials as sulfur hosts is often energy-consuming and complex. Herein, a simple and environmental-friendly strategy is proposed to reuse the SG to prepare graphene/sulfur composite cathode for Li-S batteries. Due to expanded layer spacing and defects of SG, sulfur molecules can strip it into a graphene-type host via ball milling. By optimizing the S/SG ratio and ball milling time, the as-prepared graphene/sulfur composite cathode with 70 wt.% sulfur content exhibits a high capacity of 1000 mAh g-1. With a high sulfur loading of 4.68 mg cm-2, the graphene/sulfur cathode can maintain 526 mAh g-1 after 400 cycles. This work provides a novel waste-to-wealth perspective for recycling spent graphite from LIBs to reuse in Li-S batteries.