Dilute Electrolytes with Fluorine-free Ether Solvents for 4.5 V Lithium Metal Batteries.

The limited oxidation stability of ether solvents has posed significant challenges for their applications in high-voltage lithium metal batteries (LMBs). To tackle this issue, the prevailing strategy either adopts a high concentration of fluorinated salts or relies on highly fluorinated solvents, which will significantly increase the manufacturing cost and create severe environmental hazards. Herein, an alternative and sustainable salt engineering approach is proposed to enable the utilization of dilute electrolytes consisting of fluorine (F)-free ethers in high-voltage LMBs. The proposed 0.8 M electrolyte supports stable lithium plating-stripping with a high Coulombic efficiency of 99.47% and effectively mitigates the metal dissolution, phase transition, and gas release issues of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode upon charging to high voltages. Consequently, the 4.5 V high-loading Li||NCM 811 cell shows a capacity retention of 75.2% after 300 cycles. Multimodal experimental characterizations coupled with theoretical investigations demonstrate that the boron-containing salt plays a pivotal role in forming the passivation layers on both anode and cathode. The present simple and cost-effective electrolyte design strategy offers a promising and alternative avenue for using commercially mature, environmentally benign, and low-cost F-free ethers in high-voltage LMBs.

In Situ Surface Reaction for the Preparation of High-Performance Li-Rich Mn-Based Cathode Materials with Integrated Surface Functionalization.

Li-rich Mn-based cathode materials (LLOs) are often faced with problems such as low initial Coulombic efficiency (ICE), limited rate performance, voltage decay, and structural instability. Addressing these problems with a single approach is challenging. To overcome these limitations, we developed an LLO with surface functionalization using a simple fabrication method. This two-step process involved a liquid-stage NaBF4 treatment followed by an in situ chemical reaction during sintering. This reaction led to the creation of oxygen vacancies (OV), spinel structures, and doping with Na at the Li site, B at the tetrahedral interstitial spaces of O in both the transition-metal (TM) layer and Li layers as well as the octahedral interstices in the TM layer, and F at the O site. We have carried out a thorough study and employed density functional theory calculations to reveal the hidden mechanisms. The treatment not only increases the electrical conductivity but also changes the oxygen charge environment and inhibits lattice oxygen activity. Surprisingly, the B-O bond is so strong that it prevents the migration of TM within the tetrahedral interstitial spaces of O in both the TM and Li layers, hence stabilizing its structure. This bonding interaction strengthens the transition of the TM 3d and O 2p states to lower energy levels, thus causing an increase in the redox potentials. Hence, a rise in the operating voltage occurs. Of special importance, this therapy dramatically increases the ICE to 90.29% and keeps a specified capacity of 203.3 mAh/g after 100 cycles at 1C, which is an excellent capacity retention of 89.94%. This study introduces ideas and methods to tackle the challenges associated with LLOs in batteries. It also provides compelling evidence for the development of high-energy-density Li-ion batteries.

Closed-Loop Direct Upcycling of Spent Ni-Rich Layered Cathodes into High-Voltage Cathode Materials.

Facing the resource and environmental pressures brought by the retiring wave of lithium-ion batteries (LIBs), direct recycling methods are considered to be the next generation's solution. However, the contradiction between limited battery life and the demand for rapidly iterating technology forces the direct recovery paradigm to shift toward "direct upcycling." Herein, a closed-loop direct upcycling strategy that converts waste current collector debris into dopants is proposed, and a highly inclusive eutectic molten salt system is utilized to repair structural defects in degraded polycrystalline LiNi0.83Co0.12Mn0.05O2 cathodes while achieving single-crystallization transformation and introducing Al/Cu dual-doping. Upcycled materials can effectively overcome the two key challenges at high voltages: strain accumulation and lattice oxygen evolution. It exhibits comprehensive electrochemical performance far superior to commercial materials at 4.6 V, especially its fast charging capability at 15 C, and an impressive 91.1% capacity retention after 200 cycles in a 1.2 Ah pouch cell. Importantly, this approach demonstrates broad applicability to various spent layered cathodes, particularly showcasing its value in the recycling of mixed spent cathodes. This work effectively bridges the gap between waste management and material performance enhancement, offering a sustainable path for the recycling of spent LIBs and the production of next-generation high-voltage cathodes.

Doping Engineering in Manganese Oxides for Aqueous Zinc-Ion Batteries.

Manganese oxides (MnxOy) are considered a promising cathode material for aqueous zinc-ion batteries (AZIBs) due to their high theoretical specific capacity, various oxidation states and crystal phases, and environmental friendliness. Nevertheless, their practical application is limited by their intrinsic poor conductivity, structural deterioration, and manganese dissolution resulting from Jahn-Teller distortion. To address these problems, doping engineering is thought to be a favorable modification strategy to optimize the structure, chemistry, and composition of the material and boost the electrochemical performance. In this review, the latest progress on doped MnxOy-based cathodes for AZIBs has been systematically summarized. The contents of this review are as follows: (1) the classification of MnxOy-based cathodes; (2) the energy storage mechanisms of MnxOy-based cathodes; (3) the synthesis route and role of doping engineering in MnxOy-based cathodes; and (4) the doped MnxOy-based cathodes for AZIBs. Finally, the development trends of MnxOy-based cathodes and AZIBs are described.

Constructing a Cr-Substituted Co-Free Li-Rich Ternary Cathode with a Spinel-Layered Biphase Interface.

Lithium-rich manganese-based layered oxides (LRMOs) have recently attracted enormous attention on account of their remarkably big capacity and high working voltage. However, some inevitable inherent drawbacks impede their wide-scale commercial application. Herein, a kind of Cr-containing Co-free LRMO with a topical spinel phase (Li1.2Mn0.54Ni0.13Cr0.13O2) has been put forward. It has been found that the high valence of Cr6+ can reduce the Li+ ion content and induce the formation of a local spinel phase by combining more Li+ ions, which is beneficial to eliminate the phase boundary between the spinel phase and the bulk phase of the LRMO material, thus dramatically avoiding phase separation during the cycling process. In addition, the introduction of Cr can also expand the layer spacing and construct a stronger Cr-O bond compared with Mn-O, which enables to combine the transition metal (TM) slab to prevent the migration of TM ions and the transformation of the bulk phase to the spinel phase. Simultaneously, the synergistic effect of the successfully constructed spinel-layered biphase interface and the strong Cr-O bond can effectively impede the escape of lattice oxygen during the initial activation process of Li2MnO3 and provide the fast diffusion path for Li+ ion transmission, thus further reinforcing the configurable stability. Besides, Cr-LRMO presents an ultrahigh first discharge specific capacity of 310 mAh g-1, an initial Coulombic efficiency of as high as 92.09%, a good cycling stability (a capacity retention of 94.70% after 100 cycles at 1C), and a small voltage decay (3.655 mV per cycle), as well as a good rate capacity (up to 165.88 mAh g-1 at 5C).

Comparative impact of surface and bulk fluoride anion doping on the electrochemical performance of co-free Li-rich Mn-based layered cathodes.

Li-rich Mn-based (LMR) layered oxides are considered promising cathode materials for high energy-density Li-ion batteries. Nevertheless, challenges such as irreversible oxygen loss at the surface during the initial charge, alteration of the bulk structure, and poor rate performance impede their path to commercialisation. Most modification methods focus on specific layers, making the overall impact of modifications at various depths on the properties of materials unclear. This research presents an approach by using doping to adjust both surface and bulk properties; the materials with surface and bulk fluoride anion doping are synthesised to explore the connection between doping depth, structural and electrochemical stability. The surface-doped material significantly improves the initial Coulombic efficiency (ICE) from 77.85% to 85.12% and limits phase transitions, yet it does not enhance rate performance. Conversely, doping in bulk stands out by improving both rate performance and cyclic stability: it increases the specific discharge capacity by around 60 mAh g-1 and enhances capacity retention from 57.69% to 82.26% after 300 cycles at 5C. These results highlight a notable dependence of material properties on depth, providing essential insights into the mechanisms of surface and bulk modifications.

Anion Substitution to Suppress the Voltage Hysteresis of Na3MnTi(PO4)3 as a Cathode Material for Sodium-Ion Batteries.

The Mn-based polyanion compound Na3MnTi(PO4)3 (NMTP) with a Na superionic conductor (NASICON) structure has attracted incremental attention as a potential cathode material for sodium-ion batteries. However, the occupation of Mn2+ on Na+ vacancies usually leads to severe voltage hysteresis, which in turn results in significant capacity loss, slow Na+ diffusion kinetics, and poor cycling stability. Herein, anion-substituted compounds Na3MnTi(PO4)3-x(SiO4)x (x = 0.1, 0.2, and 0.3) are synthesized. It reveals that the SiO44- substitution could induce partial oxidation of Mn2+ to Mn3+, and the latter has a lower occupancy preference on Na+ vacancies. By the proposed charge compensation strategy, the Mn2+ occupation on Na+ vacancies can be significantly suppressed. As a result, the voltage hysteresis is substantially inhibited, and greatly improved electrochemical performance is achieved. This study offers an alternative strategy to address the voltage hysteresis associated with NMTP and other Mn-based NASICON cathode materials.

Cut-off voltage influencing the voltage decay of single crystal lithium-rich manganese-based cathode materials in lithium-ion batteries.

The voltage decay of Li-rich layered oxide cathode materials results in the deterioration of cycling performance and continuous energy loss, which seriously hinders their application in the high-energy-density lithium-ion battery (LIB) market. However, the origin of the voltage decay mechanism remains controversial due to the complex influences of transition metal (TM) migration, oxygen release, indistinguishable surface/bulk reactions and the easy intra/inter-crystalline cracking during cycling. We investigated the direct cause of voltage decay in micrometer-scale single-crystal Li1.2Mn0.54Ni0.13Co0.13O2 (SC-LNCM) cathode materials by regulating the cut-off voltage. The redox of TM and O2- ions can be precisely controlled by setting different voltage windows, while the cracking can be restrained, and surface/bulk structural evaluation can be monitored because of the large single crystal size. The results show that the voltage decay of SC-LNCM is related to the combined effect of cation rearrangement and oxygen release. Maintaining the discharge cutoff voltage at 3 V or the charging cutoff voltage at 4.5 V effectively mitigates the voltage decay, which provides a solution for suppressing the voltage decay of Li-rich and Mn-based layered oxide cathode materials. Our work provides significant insights into the origin of the voltage decay mechanism and an easily achievable strategy to restrain the voltage decay for Li-rich and Mn-based cathode materials.

Calcium-Pillar Boosting Smooth Phase Transition in Potassium Vanadate Nanobelts toward Superior Cycling Performance in Potassium-Ion Batteries.

The depletion of lithium resources has prompted exploration into alternative rechargeable energy storage systems, and potassium-ion batteries (PIBs) have emerged as promising candidates. As an active cathode material for PIBs, potassium vanadate (KxV2O5) usually suffers from structural damage during electrochemical K-ion insertion/extraction and hence leading to unsatisfactory cycling performance. Here, we introduce Ca2+ ions as pillars into the potassium vanadate to enhance its structural stability and smooth its phase transition behavior. The additional Ca2+ not only stabilizes the layered structure but also promotes the rearrangement of interlayer ions and leads to a smooth solid-solution phase transition. The optimal composition K0.36Ca0.05V2O5 (KCVO) exhibits outstanding cyclic stability, delivering a capacity of ∼90 mA h g-1 at 20 mA g-1 with negligible capacity decay even after 700 cycles at 500 mA g-1. Theoretical calculations indicate lower energy barriers for K+ diffusion, promoting rapid reaction kinetics. The excellent performances and detailed investigations offer insights into the structural regulation of layered vanadium cathodes.

Preparation of Expanded Graphite-VO2 Composite Cathode Material and Performance in Aqueous Zinc-Ion Batteries.

Due to safety problems caused by the use of organic electrolytes in lithium-ion batteries and the high production cost brought by the limited lithium resources, water-based zinc-ion batteries have become a new research focus in the field of energy storage due to their low production cost, safety, efficiency, and environmental friendliness. This paper focused on vanadium dioxide and expanded graphite (EG) composite cathode materials. Given the cycling problem caused by the structural fragility of vanadium dioxide in zinc-ion batteries, the feasibility of preparing a new composite material is explored. The EG/VO2 composites were prepared by a simple hydrothermal method, and compared with the aqueous zinc-ion batteries assembled with a single type of VO2 under the same conditions, the electrode materials composited with high-purity sulfur-free expanded graphite showed more excellent capacity, cycling performance, and multiplicity performance, and the EG/VO2 composites possessed a high discharge ratio of 345 mAh g-1 at 0.1 A g-1, and the Coulombic efficiency was close to 100%. The EG/VO2 composite has a high specific discharge capacity of 345 mAh g-1 at 0.1 A g-1 with a Coulombic efficiency close to 100%, a capacity retention of 77% after 100 cycles, and 277.8 mAh g-1 with a capacity retention of 78% at a 20-fold increase in current density. The long cycle test data demonstrated that the composite with expanded graphite effectively improved the cycling performance of vanadium-based materials, and the composite maintained a stable Coulombic efficiency of 100% at a high current density of 2 A/g and still maintained a specific capacity of 108.9 mAh/g after 2000 cycles.

Synergistic Theoretical and Experimental Insights into NH4+-Enhanced Vanadium Oxide Cathodes for Aqueous Zinc-Ion Batteries.

This study explores the enhancement of aqueous zinc-ion batteries (AZIBs) using ammonium-enhanced vanadium oxide cathodes. Density Functional Theory (DFT) calculations reveal that NH4+ incorporation into V6O16 lattices significantly facilitates Zn2+ ion diffusion by reducing electrostatic interactions, acting as a structural lubricant. Subsequent experimental validation using (NH4)2V6O16 cathodes synthesized via a hydrothermal method corroborates the DFT findings, demonstrating remarkable electrochemical stability with a capacity retention of 90% after 2000 cycles at 5 A g-1. These results underscore the potential of NH4+ in improving the performance and longevity of AZIBs, providing a pathway for sustainable energy storage solutions.

Enhancing Proton Co-Intercalation in Iron Ion Batteries Cathodes for Increased Capacity.

Recently, aqueous iron ion batteries (AIIBs) using iron metal anodes have gained traction in the battery community as low-cost and sustainable solutions for green energy storage. However, the development of AIIBs is significantly hindered by the limited capacity of existing cathode materials and the poor intercalation kinetic of Fe2+. Herein, we propose a H+ and Fe2+ co-intercalation electrochemistry in AIIBs to boost the capacity and rate capability of cathode materials such as iron hexacyanoferrate (FeHCF) and Na4Fe3(PO4)2(P2O7) (NFPP). This is achieved through an electrochemical activation step during which a FeOOH nanowire layer is formed in situ on the cathode. This layer facilitates H+ co-intercalation in AIIBs, resulting in a high specific capacity of 151 mAh g-1 and 93% capacity retention over 500 cycles for activated FeHCF cathodes. We found that this activation process can also be applied to other cathode chemistries, such as NFPP, where we found that the cathode capacity is doubled as a result of this process. Overall, the proposed H+/Fe2+ co-insertion electrochemistry expands the range of applications for AIBBs, in particular as a sustainable solution for storing renewable energy.

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.

Comprehensive review and comparison on pretreatment of spent lithium-ion battery.

Pretreatment, the initial step in recycling spent lithium-ion batteries (LIBs), efficiently separates cathode and anode materials to facilitate key element recovery. Despite brief introductions in existing research, a comprehensive evaluation and comparison of processing methods is lacking. This study reviews 346 references on LIBs recycling, analyzing pretreatment stages, treatment conditions, and method effects. Our analysis highlights insufficient attention to discharge voltage safety and environmental impact. Mechanical disassembly, while suitable for industrial production, overlooks electrolyte recovery and complicates LIBs separation. High temperature pyrolysis flotation offers efficient separation of mixed electrode materials, enhancing mineral recovery. We propose four primary pretreatment processes: discharge, electrolyte recovery, crushing and separation, and electrode material recovery, offering simplified, efficient, green, low-cost, and high-purity raw materials for subsequent recovery processes.

Mo-Doped Na4Fe3(PO4)2P2O7/C Composites for High-Rate and Long-Life Sodium-Ion Batteries.

Na4Fe3(PO4)2P2O7/C (NFPP) is a promising cathode material for sodium-ion batteries, but its electrochemical performance is heavily impeded by its low electronic conductivity. To address this, pure-phase Mo6+-doped Na4Fe3-xMox(PO4)2P2O7/C (Mox-NFPP, x = 0, 0.05, 0.10, 0.15) with the Pn21a space group is successfully synthesized through spray drying and annealing methods. Density functional theory (DFT) calculations reveal that Mo6+ doping facilitates the transition of electrons from the valence to the conduction band, thus enhancing the intrinsic electron conductivity of Mox-NFPP. With an optimal Mo6+ doping level of x = 0.10, Mo0.10-NFPP exhibits lower charge transfer resistance, higher sodium-ion diffusion coefficients, and superior rate performance. As a result, the Mo0.10-NFPP cathode offers an initial discharge capacity of up to 123.9 mAh g-1 at 0.1 C, nearly reaching its theoretical capacity. Even at a high rate of 10 C, it delivers a high discharge capacity of 86.09 mAh g-1, maintaining 96.18% of its capacity after 500 cycles. This research presents a new and straightforward strategy to enhance the electrochemical performance of NFPP cathode materials for sodium-ion batteries.

Chemical-Free Recycling of Cathode Material and Aluminum Foil from Waste Lithium-Ion Batteries by Combining Plasma and Ultrasonic Technology.

With the rapid demand for lithium-ion batteries due to the widespread application of electric vehicles, a significant amount of battery electrode pieces requiring urgent treatment are generated during battery production and disposal. The strong bonding caused by the presence of binders makes it challenging to achieve thorough separation between the cathode active materials and Al foil, posing difficulties in efficient battery material recycling. To address this issue, a plasma-ultrasonically combined physical separation method is proposed in this study. This method utilizes plasma-generated excited-state radicals assisted by ultrasonic waves to separate active materials and current collectors. The results indicate that the binders are effectively decomposed under plasma treatment at 13.56 MHz, 100 W, and 10 min in an oxygen atmosphere, resulting in a separation efficiency of 96.8 wt % for the cathode materials. Characterization results demonstrate that the morphology, crystal structure, and chemical composition of the recycled cathode active materials remain unchanged, facilitating subsequent direct restoration and hydrometallurgical recycling. Simultaneously, the Al foil is also completely recycled for subsequent reuse. Compared with traditional methods of separating cathode active materials and aluminum foil, the method proposed in this study has significant economic and environmental potential. It can promote the recycling of battery materials and the development of sustainable transportation.

Regenerated Ni-Doped LiCoO2 from Spent Lithium-Ion Batteries as a Stable Cathode at 4.5 V.

In the context of the increasing number of spent lithium-ion batteries, it is urgent to explore cathode regeneration and upcycling solutions to reduce environmental pollution, promote resource reuse, and meet the demand for high-energy cathode materials. Here, a closed-loop recycling method is introduced, which not only reclaims cobalt and lithium elements from spent lithium-ion batteries but also converts them into high-voltage LiCoO2 (LCO) materials. This approach involved pretreatment, chlorination roasting, water leaching, and ion doping to regenerate nickel-doped LCO (Ni-RLCO) materials. The doping of nickel effectively enhances the electrochemical stability of the LCO cathode at 4.5 V. The Ni-RLCO cathode exhibited a high discharge specific capacity of 185.28 mAh/g at a rate of 0.5 C with a capacity retention of 86.3% after 50 cycles and excellent rate capacity of 156.21 mAh/g at 2 C. This work offers a approach in significance for upcycling spent LCO into high-energy-density batteries with long-term cycling stability under high voltage.

Recent Advances in Catalyst Design and Performance Optimization of Nanostructured Cathode Materials in Zinc-Air Batteries.

This review focuses on the advanced design and optimization of nanostructured zinc-air batteries (ZABs), with the aim of boosting their energy storage and conversion capabilities. The findings show that ZABs favor porous nanostructures owing to their large surface area, and this enhances the battery capacity, catalytic activity, and life cycle. In addition, the nanomaterials improve the electrical conductivity, ion transport, and overall battery stability, which crucially reduces dendrite growth on the zinc anodes and improves cycle life and energy efficiency. To obtain a superior performance, the importance of controlling the operational conditions and using custom nanostructural designs, optimal electrode materials, and carefully adjusted electrolytes is highlighted. In conclusion, porous nanostructures and nanoscale materials significantly boost the energy density, longevity, and efficiency of Zn-air batteries. It is suggested that future research should focus on the fundamental design principles of these materials to further enhance the battery performance and drive sustainable energy solutions.

Doping Effects on Ternary Cathode Materials for Lithium-Ion Batteries: A Review.

The ongoing advancements in lithium-ion battery technology are pivotal in propelling the performance of modern electronic devices and electric vehicles. Amongst various components, the cathode material significantly influences the battery performance, such as the specific capacity, capacity retention and the rate performance. Ternary cathode materials, composed of nickel, manganese, and cobalt (NCM), offer a balanced combination of these traits. Recent developments focus on elemental doping, which involves substituting a fraction of NCM constituent ions with alternative cations such as aluminum, titanium, or magnesium. This strategic substitution aims to enhance structural stability, increase capacity retention, and improve resistance to thermal runaway. Doped ternary materials have shown promising results, with improvements in cycle life and operational safety. However, the quest for optimal doping elements and concentrations persists to maximize performance while minimizing cost and environmental impact, ensuring the progression towards high-energy-density, durable, and safe battery technologies.

Toward Circular Energy: Exploring Direct Regeneration for Lithium-Ion Battery Sustainability.

Lithium-ion batteries (LIBs) are rapidly developing into attractive energy storage technologies. As LIBs gradually enter retirement, their sustainability is starting to come into focus. The utilization of recycled spent LIBs as raw materials for battery manufacturing is imperative for resource and environmental sustainability. The sustainability of spent LIBs depends on the recycling process, whereby the cycling of battery materials must be maximized while minimizing waste emissions and energy consumption. Although LIB recycling technologies (hydrometallurgy and pyrometallurgy) have been commercialized on a large scale, they have unavoidable limitations. They are incompatible with circular economy principles because they require toxic chemicals, emit hazardous substances, and consume large amounts of energy. The direct regeneration of degraded electrode materials from spent LIBs is a viable alternative to traditional recycling technologies and is a nondestructive repair technology. Furthermore, direct regeneration offers advantages such as maximization of the value of recycled electrode materials, use of sustainable, nontoxic reagents, high potential profitability, and significant application potential. Therefore, this review aims to investigate the state-of-the-art direct LIB regeneration technologies that can be extended to large-scale applications.