Toward Direct Regeneration of Spent Lithium-Ion Batteries: A Next-Generation Recycling Method.

The popularity of portable electronic devices and electric vehicles has led to the drastically increasing consumption of lithium-ion batteries recently, raising concerns about the disposal and recycling of spent lithium-ion batteries. However, the recycling rate of lithium-ion batteries worldwide at present is extremely low. Many factors limit the promotion of the battery recycling rate: outdated recycling technology is the most critical one. Existing metallurgy-based recycling methods rely on continuous decomposition and extraction steps with high-temperature roasting/acid leaching processes and many chemical reagents. These methods are tedious with worse economic feasibility, and the recycling products are mostly alloys or salts, which can only be used as precursors. To simplify the process and improve the economic benefits, novel recycling methods are in urgent demand, and direct recycling/regeneration is therefore proposed as a next-generation method. Herein, a comprehensive review of the origin, current status, and prospect of direct recycling methods is provided. We have systematically analyzed current recycling methods and summarized their limitations, pointing out the necessity of developing direct recycling methods. A detailed analysis for discussions of the advantages, limitations, and obstacles is conducted. Guidance for future direct recycling methods toward large-scale industrialization as well as green and efficient recycling systems is also provided.

Engineering the interfacial orientation of MoS2/Co9S8 bidirectional catalysts with highly exposed active sites for reversible Li-CO2 batteries.

Sluggish CO2 reduction reaction (CO2RR) and evolution reaction (CO2ER) kinetics at cathodes seriously hamper the applications of Li-CO2 batteries, which have attracted vast attention as one kind of promising carbon-neutral technology. Two-dimensional transition metal dichalcogenides (TMDs) have shown great potential as the bidirectional catalysts for CO2 redox, but how to achieve a high exposure of dual active sites of TMDs with CO2RR/CO2ER activities remains a challenge. Herein, a bidirectional catalyst that vertically growing MoS2 on Co9S8 supported by carbon paper (V-MoS2/Co9S8@CP) has been designed with abundant edge as active sites for both CO2RR and CO2ER, improves the interfacial conductivity, and modulates the electron transportation pathway along the basal planes. As evidenced by the outstanding energy efficiency of 81.2% and ultra-small voltage gap of 0.68 V at 20 µA cm-2, Li-CO2 batteries with V-MoS2/Co9S8@CP show superior performance compared with horizontally growing MoS2 on Co9S8 (H-MoS2/Co9S8@CP), MoS2@CP, and Co9S8@CP. Density functional theory calculations help reveal the relationship between performance and structure and demonstrate the synergistic effect between MoS2 edge sites and Co9S8. This work provides an avenue to understand and realize rationally designed electronic contact of TMDs with specified crystal facets, but more importantly, provides a feasible guide for the design of high-performance cathodic catalyst materials in Li-CO2 batteries.

Sulfion oxidation assisting self-powered hydrogen production system based on efficient catalysts from spent lithium-ion batteries.

Converting spent lithium-ion batteries (LIBs) and industrial wastewater into high-value-added substances by advanced electrocatalytic technology is important for sustainable energy development and environmental protection. Here, we propose a self-powered system using a home-made sulfide fuel cell (SFC) to power a two-electrode electrocatalytic sulfion oxidation reaction (SOR)-assisted hydrogen (H2) production electrolyzer (ESHPE), in which the sulfion-containing wastewater is used as the liquid fuel to produce clean water, sulfur, and hydrogen. The catalysts for the self-powered system are mainly prepared from spent LIBs to reduce the cost, such as the bifunctional Co9S8 catalyst was prepared from spent LiCoO2 for SOR and hydrogen evolution reaction (HER). The Fe-N-P codoped coral-like carbon nanotube arrays encapsulated Fe2P (C-ZIF/sLFP) catalyst was prepared from spent LiFePO4 for oxygen reduction reaction. The Co9S8 catalyst shows excellent catalytic activities in both SOR and HER, evidenced by the low cell voltage of 0.426 V at 20 mA cm-2 in ESHPE. The SFC with Co9S8 as anode and C-ZIF/sLFP as cathode exhibits an open-circuit voltage of 0.69 V and long discharge stability for 300 h at 20 mA cm-2. By integrating the SFC and ESHPE, the self-powered system delivers an impressive hydrogen production rate of 0.44 mL cm-2 min-1. This work constructs a self-powered system with high-performance catalysts prepared from spent LIBs to transform sulfion-containing wastewater into purified water and prepare hydrogen, which is promising to achieve high economic efficiency, environmental remediation, and sustainable development.

Uncoordinated chemistry enables highly conductive and stable electrolyte/filler interfaces for solid-state lithium-sulfur batteries.

Composite-polymer-electrolytes (CPEs) embedded with advanced filler materials offer great promise for fast and preferential Li+ conduction. The filler surface chemistry determines the interaction with electrolyte molecules and thus critically regulates the Li+ behaviors at the interfaces. Herein, we probe into the role of electrolyte/filler interfaces (EFI) in CPEs and promote Li+ conduction by introducing an unsaturated coordination Prussian blue analog (UCPBA) filler. Combining scanning transmission X-ray microscope stack imaging studies and first-principle calculations, fast Li+ conduction is revealed only achievable at a chemically stable EFI, which can be established by the unsaturated Co-O coordination in UCPBA to circumvent the side reactions. Moreover, the as-exposed Lewis-acid metal centers in UCPBA efficiently attract the Lewis-base anions of Li salts, which facilitates the Li+ disassociation and enhances its transference number (tLi+). Attributed to these superiorities, the obtained CPEs realize high room-temperature ionic conductivity up to 0.36 mS cm-1 and tLi+ of 0.6, enabling an excellent cyclability of lithium metal electrodes over 4,000 h as well as remarkable capacity retention of 97.6% over 180 cycles at 0.5 C for solid-state lithium-sulfur batteries. This work highlights the crucial role of EFI chemistry in developing highly conductive CPEs and high-performance solid-state batteries.

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.

In Situ Construction of a Multifunctional Interphase Enabling Continuous Capture of Unstable Lattice Oxygen Under Ultrahigh Voltages.

The use of nickel-rich layered materials as cathodes can boost the energy density of lithium batteries. However, developing a safe and long-term stable nickel-rich layered cathode is challenging primarily due to the release of lattice oxygen from the cathode during cycling, especially at high voltages, which will cause a series of adverse effects, leading to battery failure and thermal runaway. Surface coating is often considered effective in capturing active oxygen species; however, its process is rather complicated, and it is difficult to maintain intact on the cathode with large volume changes during cycling. Here, we propose an in situ construction of a multifunctional cathode/electrolyte interphase (CEI), which is easy to prepare, repairable, and, most importantly, capable of continuously capturing active oxygen species during the entire life span. This unique protective mechanism notably improves the cycling stability of Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) cells at rigorous working conditions, including ultrahigh voltage (4.8 V), high temperature (60 °C), and fast charging (10 C). An industrial 1 A h graphite||NCM811 pouch cell achieved stable operation of 600 cycles with a capacity retention of 79.6% at 4.4 V, exhibiting great potential for practical use. This work provides insightful guidance for constructing a multifunctional CEI to bypass limitations associated with high-voltage operations of nickel-rich layered cathodes.

Self-Assembly of Ultrathin, Ultrastrong Layered Membranes by Protic Solvent Penetration.

Flexible membranes with ultrathin thickness and excellent mechanical properties have shown great potential for broad uses in solid polymer electrolytes (SPEs), on-skin electronics, etc. However, an ultrathin membrane (<5 µm) is rarely reported in the above applications due to the inherent trade-off between thickness and antifailure ability. We discover a protic solvent penetration strategy to prepare ultrathin, ultrastrong layered films through a continuous interweaving of aramid nanofibers (ANFs) with the assistance of simultaneous protonation and penetration of a protic solvent. The thickness of a pure ANF film can be controlled below 5 µm, with a tensile strength of 556.6 MPa, allowing us to produce the thinnest SPE (3.4 µm). The resultant SPEs enable Li-S batteries to cycle over a thousand times at a high rate of 1C due to the small ionic impedance conferred by the ultrathin characteristic and regulated ionic transportation. Besides, a high loading of the sulfur cathode (4 mg cm-2) with good sulfur utilization was achieved at a mild temperature (35 °C), which is difficult to realize in previously reported solid-state Li-S batteries. Through a simple laminating process at the wet state, the thicker film (tens of micrometers) obtained exhibits mechanical properties comparable to those of thin films and possesses the capability to withstand high-velocity projectile impacts, indicating that our technique features a high degree of thickness controllability. We believe that it can serve as a valuable tool to assemble nanomaterials into ultrathin, ultrastrong membranes for various applications.

Insights into the solvation chemistry in liquid electrolytes for lithium-based rechargeable batteries.

Lithium-based rechargeable batteries have dominated the energy storage field and attracted considerable research interest due to their excellent electrochemical performance. As indispensable and ubiquitous components, electrolytes play a pivotal role in not only transporting lithium ions, but also expanding the electrochemical stable potential window, suppressing the side reactions, and manipulating the redox mechanism, all of which are closely associated with the behavior of solvation chemistry in electrolytes. Thus, comprehensively understanding the solvation chemistry in electrolytes is of significant importance. Here we critically reviewed the development of electrolytes in various lithium-based rechargeable batteries including lithium-metal batteries (LMBs), nonaqueous lithium-ion batteries (LIBs), lithium-sulfur batteries (LSBs), lithium-oxygen batteries (LOBs), and aqueous lithium-ion batteries (ALIBs), and emphasized the effects of interactions between cations, anions, and solvents on solvation chemistry, and functions of solvation chemistry in different types of electrolytes (strong solvating electrolytes, moderate solvating electrolytes, and weak solvating electrolytes) on the electrochemical performance and redox mechanism in the abovementioned rechargeable batteries. Specifically, the significant effects of solvation chemistry on the stability of electrode-electrolyte interphases, suppression of lithium dendrites in LMBs, inhibition of the co-intercalation of solvents in LIBs, improvement of anodic stability at high cut-off voltages in LMBs, LIBs and ALIBs, regulation of redox pathways in LSBs and LOBs, and inhibition of hydrogen/oxygen evolution reactions in LOBs are thoroughly summarized. Finally, the review concludes with a prospective outlook, where practical issues of electrolytes, advanced in situ/operando techniques to illustrate the mechanism of solvation chemistry, and advanced theoretical calculation and simulation techniques such as "material knowledge informed machine learning" and "artificial intelligence (AI) + big data" driven strategies for high-performance electrolytes have been proposed.

Fundamentals, status and challenges of direct recycling technologies for lithium ion batteries.

Advancement in energy storage technologies is closely related to social development. However, a significant conflict has arisen between the explosive growth in battery demand and resource availability. Facing the upcoming large-scale disposal problem of spent lithium-ion batteries (LIBs), their recycling technology development has become key. Emerging direct recycling has attracted widespread attention in recent years because it aims to 'repair' the battery materials, rather than break them down and extract valuable products from their components. To achieve this goal, a profound understanding of the failure mechanisms of spent LIB electrode materials is essential. This review summarizes the failure mechanisms of LIB cathode and anode materials and the direct recycling strategies developed. We systematically explore the correlation between the failure mechanism and the required repair process to achieve efficient and even upcycling of spent LIB electrode materials. Furthermore, we systematically introduce advanced in situ characterization techniques that can be utilized for investigating direct recycling processes. We then compare different direct recycling strategies, focussing on their respective advantages and disadvantages and their applicability to different materials. It is our belief that this review will offer valuable guidelines for the design and selection of LIB direct recycling methods in future endeavors. Finally, the opportunities and challenges for the future of battery direct recycling technology are discussed, paving the way for its further development.

Room-Temperature Salt Template Synthesis of Nitrogen-Doped 3D Porous Carbon for Fast Metal-Ion Storage.

The water-soluble salt-template technique holds great promise for fabricating 3D porous materials. However, an equipment-free and pore-size controllable synthetic approach employing salt-template precursors at room temperature has remained unexplored. Herein, we introduce a green room-temperature antisolvent precipitation strategy for creating salt-template self-assembly precursors to universally produce 3D porous materials with controllable pore size. Through a combination of theoretical simulations and advanced characterization techniques, we unveil the antisolvent precipitation mechanism and provide guidelines for selecting raw materials and controlling the size of precipitated salt. Following the calcination and washing steps, we achieve large-scale and universal production of 3D porous materials and the recycling of the salt templates and antisolvents. The optimized nitrogen-doped 3D porous carbon (N-3DPC) materials demonstrate distinctive structural benefits, facilitating a high capacity for potassium-ion storage along with exceptional reversibility. This is further supported by in situ electrochemical impedance spectra, in situ Raman spectroscopy, and theoretical calculations. The anode shows a high rate capacity of 181 mAh g-1 at 4 A g-1 in the full cell. This study addresses the knowledge gap concerning the room-temperature synthesis of salt-template self-assembly precursors for the large-scale production of porous materials, thereby expanding their potential applications for electrochemical energy conversion and storage.

Interface Engineering via Manipulating Solvation Chemistry for Liquid Lithium-Ion Batteries Operated ≥ 100 °C.

High-performance and temperature-resistant lithium-ion batteries (LIBs), which are able to operate at elevated temperatures (i.e., >60 °C) are highly demanded in various fields, especially in military or aerospace exploration. However, their applications were  impeded by the poor electrochemical performance and unsatisfying safety issues, which was induced by the severe side reactions between electrolytes and electrodes at high temperatures. Herein, with the synergetic effects of solvation chemistry and functional additive in the elaborately designed weakly solvating electrolyte, a unique robust organic/inorganic hetero-interphase, composed of gradient F, B-rich inorganic components and homogeneously distributed Si-rich organic components, was successfully constructed on both cathodes and anodes, which would effectively inhibit the constant decomposition of electrolytes and dissolution of transition metal ions. As a result, both cathodes and anodes, without compromising their low-temperature performance, operate at temperatures ≥100 ℃, with excellent capacity retentions of 96.1 % after 500 cycles and 93.5% after ≥200 cycles, respectively, at 80 ℃. Ah-level LiCoO2||graphite full cells with a cut-off voltage of 4.3 V also exhibited superior temperature-resistance with a capacity retention of 89.9% at temperature as high as 120 ℃. Moreover, the fully charged pouch cells exhibited highly enhanced safety, demonstrating their potentials in practical applications at ultrahigh temperatures.

Highly Reversible Sodium-ion Storage in A Bifunctional Nanoreactor Based on Single-atom Mn Supported on N-doped Carbon over MoS2 Nanosheets.

Conversion-type electrode materials have gained massive research attention in sodium-ion batteries (SIBs), but their limited reversibility hampers practical use. Herein, we report a bifunctional nanoreactor to boost highly reversible sodium-ion storage, wherein a record-high reversible degree of 85.65% is achieved for MoS2 anodes. Composed of nitrogen-doped carbon-supported single atom Mn (NC-SAMn), this bifunctional nanoreactor concurrently confines active materials spatially and catalyzes reaction kinetics. In-situ/ex-situ characterizations including spectroscopy, microscopy, and electrochemistry, combined with theoretical simulations containing density functional theory and molecular dynamics, confirm that the NC-SAMn nanoreactors facilitate the electron/ion transfer, promote the distribution and interconnection of discharging products (Na2S/Mo), and reduce the Na2S decomposition barrier.As a result, the nanoreactor-promoted MoS2 anodes exhibit ultra-stable cycling with a capacity retention of 99.86% after 200 cycles in the full cell. This work demonstrates the superiority of bifunctional nanoreactors with two-dimensional confined and catalytic effects, providing a feasible approach to improve the reversibility for a wide range of conversion-type electrode materials, thereby enhancing the application potential for long-cycled SIBs.

Amorphous FeSnOx Nanosheets with Hierarchical Vacancies for Room-Temperature Sodium-Sulfur Batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries, noted for their low material costs and high energy density, are emerging as a promising alternative to lithium-ion batteries (LIBs) in various applications including power grids and standalone renewable energy systems. These batteries are commonly assembled with glass fiber membranes, which face significant challenges like the dissolution of polysulfides, sluggish sulfur conversion kinetics, and the growth of Na dendrites. Here, we develop an amorphous two-dimensional (2D) iron tin oxide (A-FeSnOx) nanosheet with hierarchical vacancies, including abundant oxygen vacancies (Ovs) and nano-sized perforations, that can be assembled into a multifunctional layer overlaying commercial separators for RT Na-S batteries. The Ovs offer strong adsorption and abundant catalytic sites for polysulfides, while the defect concentration is finely tuned to elucidate the polysulfides conversion mechanisms. The nano-sized perforations aid in regulating Na ions transport, resulting in uniform Na deposition. Moreover, the strategic addition of trace amounts of Ti3C2 (MXene) forms an amorphous/crystalline (A/C) interface that significantly improves the mechanical properties of the separator and suppresses dendrite growth. As a result, the task-specific layer achieves ultra-light (~0.1 mg cm-2), ultra-thin (~200 nm), and ultra-robust (modulus=4.9 GPa) characteristics. Consequently, the RT Na-S battery maintained a high capacity of 610.3 mAh g-1 and an average Coulombic efficiency of 99.9 % after 400 cycles at 0.5 C.

A Semisolvated Sole-Solvent Electrolyte for High-Voltage Lithium Metal Batteries.

Lithium metal batteries (LMBs) coupled with a high-voltage Ni-rich cathode are promising for meeting the increasing demand for high energy density. However, aggressive electrode chemistry imposes ultimate requirements on the electrolytes used. Among the various optimized electrolytes investigated, localized high-concentration electrolytes (LHCEs) have excellent reversibility against a lithium metal anode. However, because they consist of thermally and electrochemically unstable solvents, they have inferior stability at elevated temperatures and high cutoff voltages. Here we report a semisolvated sole-solvent electrolyte to construct a typical LHCE solvation structure but with significantly improved stability using one bifunctional solvent. The designed electrolyte exhibits exceptional stability against both electrodes with suppressed lithium dendrite growth, phase transition, microcracking, and transition metal dissolution. A Li||Ni0.8Co0.1Mn0.1O2 cell with this electrolyte operates stably over a wide temperature range from -20 to 60 °C and has a high capacity retention of 95.6% after the 100th cycle at 4.7 V, and ∼80% of the initial capacity is retained even after 180 cycles. This new electrolyte indicates a new path toward future electrolyte engineering and safe high-voltage LMBs.

Topotactic Transformation of Surface Structure Enabling Direct Regeneration of Spent Lithium-Ion Battery Cathodes.

Recycling spent lithium-ion batteries (LIBs) has become an urgent task to address the issues of resource shortage and potential environmental pollution. However, direct recycling of the spent LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode is challenging because the strong electrostatic repulsion from a transition metal octahedron in the lithium layer provided by the rock salt/spinel phase that is formed on the surface of the cycled cathode severely disrupts Li+ transport, which restrains lithium replenishment during regeneration, resulting in the regenerated cathode with inferior capacity and cycling performance. Here, we propose the topotactic transformation of the stable rock salt/spinel phase into Ni0.5Co0.2Mn0.3(OH)2 and then back to the NCM523 cathode. As a result, a topotactic relithiation reaction with low migration barriers occurs with facile Li+ transport in a channel (from one octahedral site to another, passing through a tetrahedral intermediate) with weakened electrostatic repulsion, which greatly improves lithium replenishment during regeneration. In addition, the proposed method can be extended to repair spent NCM523 black mass, spent LiNi0.6Co0.2Mn0.2O2, and spent LiCoO2 cathodes, whose electrochemical performance after regeneration is comparable to that of the commercial pristine cathodes. This work demonstrates a fast topotactic relithiation process during regeneration by modifying Li+ transport channels, providing a unique perspective on the regeneration of spent LIB cathodes.

Regulating the Spin State Configuration in Bimetallic Phosphorus Trisulfides for Promoting Sulfur Redox Kinetics.

Lithium-sulfur (Li-S) batteries suffer from sluggish kinetics due to the poor conductivity of sulfur cathodes and polysulfide shutting. Current studies on sulfur redox catalysis mainly focus on the adsorption and catalytic conversion of lithium polysulfides but ignore the modulation of the electronic structure of the catalysts which involves spin-related charge transfer and orbital interactions. In this work, bimetallic phosphorus trisulfides embedded in Prussian blue analogue-derived nitrogen-doped hollow carbon nanocubes (FeCoPS3/NCs) were elaborately synthesized as a host to reveal the relationship between the catalytic activity and the spin state configuration for Li-S batteries. Orbital spin splitting in FeCoPS3 drives the electronic structure transition from low-spin to high-spin states, generating more unpaired electrons on the 3d orbit. Specifically, the nondegenerate orbitals involved in the high-spin configuration of FeCoPS3 result in the upshift of energy levels, generating more active electronic states. Such tailored electronic structure increases the charge transfer, influences the d-band center, and further modifies the adsorption energy with lithium polysulfides and the potential reaction pathways. Consequently, the cell with FeCoPS3/NC host exhibits an ultralow capacity decay of 0.037% per cycle over 1000 cycles. This study proposed a general strategy for sculpting geometric configurations to enable spin and orbital topology regulation in Li-S battery catalysts.

Clay-Originated Two-Dimensional Holey Silica Separator for Dendrite-Free Lithium Metal Anode.

Lithium metal anode is the ultimate choice to obtain next-generation high-energy-density lithium batteries, while the dendritic lithium growth owing to the unstable lithium anode/electrolyte interface largely limits its practical application. Separator is an important component in batteries and separator engineering is believed to be a tractable and effective way to address the above issue. Separators can play the role of ion redistributors to guide the transport of lithium ions and regulate the uniform electrodeposition of Li. The electrolyte wettability, thermal shrinkage resistance, and mechanical strength are of importance for separators. Here, clay-originated two-dimensional (2D) holey amorphous silica nanosheets (ASN) to develop a low-cost and eco-friendly inorganic separator is directly adopted. The ASN-based separator has higher porosity, better electrolyte wettability, much higher thermal resistance, larger lithium transference number, and ionic conductivity compared with commercial separator. The large amounts of holes and rich surface oxygen groups on the ASN guide the uniform distribution of lithium-ion flux. Consequently, the Li//Li cell with this separator shows stable lithium plating/stripping, and the corresponding Li//LiFePO4 , Li//LiCoO2, and Li//NCM523 full cells also show high capacity, excellent rate performance, and outstanding cycling stability, which is much superior to that using the commercial separator.

Vacancy-Rich MoSSe with Sulfiphilicity-Lithiophilicity Dual Function for Kinetics-Enhanced and Dendrite-Free Li-S Batteries.

The sluggish redox kinetics of sulfur and the uncontrollable growth of lithium dendrites are two main challenges that impede the practical applications of lithium-sulfur (Li-S) batteries. In this study, a multifunctional host with vacancy-rich MoSSe vertically grown on reduced graphene oxide aerogels (MoSSe/rGO) is designed as the host material for both sulfur and lithium. The embedding of Se into a MoS2 lattice is introduced to improve the inherent conductivity and generate abundant anion vacancies to endow the 3D conductive graphene based aerogels with specific sulfiphilicity-lithiophilicity. As a result, the assembled Li-S batteries based on MoSSe/rGO exhibit greatly improved capacity and cycling stability and can be operated under a lean electrolyte (4.8 µL mg-1) and a high sulfur loading (6.5 mg cm-2), achieving a high energy density. This study presents a unique method to unlock the catalysis capability and improve the inherent lithiophilicity by heteroatom doping and defect chemistry for kinetics-enhanced and dendrite-free Li-S batteries.

Suppressed Lattice Oxygen Release via Ni/Mn Doping from Spent LiNi0.5Mn0.3Co0.2O2 toward High-Energy Layered-Oxide Cathodes.

LiCoO2 has suffered from poor stability under high voltage as a result of insufficient Co-O bonding that causes lattice oxygen release and lattice distortions. Herein, we fabricated a high-voltage LiCoO2 at 4.6 V by doping with Ni/Mn atoms, which are obtained from spent LiNi0.5Mn0.3Co0.2O2 cathode materials. The as-prepared high-voltage LiCoO2 with Ni/Mn substitutional dopants in the Co layer enhances Co-O bonding that suppresses oxygen release and harmful phase transformation during delithiation, thus stabilizing the layered structure and leading to a superior electrochemical performance at 4.6 V. The pouch cell of modified LiCoO2 exhibits a capacity retention of 85.1% over 100 cycles at 4.5 V (vs graphite). We found that our strategy is applicable for degraded LiCoO2, and the regenerated LiCoO2 using this strategy exhibits excellent capacity retention (84.1%, 100 cycles) at 4.6 V. Our strategy paves the way for the direct conversion of spent batteries into high-energy-density batteries.

Freestanding and Sandwich MXene-Based Cathode with Suppressed Lithium Polysulfides Shuttle for Flexible Lithium-Sulfur Batteries.

Flexible lithium-sulfur (Li-S) batteries with high mechanical compliance and energy density are highly desired. This manuscript reported that large-area freestanding MXene (Ti3C2Tx) film has been obtained through a scalable drop-casting method, significantly improving adhesion to the sulfur layer under the continuously bent. Titanium oxide anchored on holey Ti3C2Tx (TiO2/H-Ti3C2Tx) was also produced by the well-controlled oxidation of few-layer Ti3C2Tx, which greatly facilitates lithium ion transport as well as prevents the shuttling of lithium polysulfides. Therefore, the obtained sandwich electrode has demonstrated a high capacity of 740 mAh g-1 at 2 C and a high capacity retention of 81% at 1 C after 500 cycles. Flexible Li-S batteries based on this sandwich electrode have a capacity retention as high as 95% after bending 500 times. This work provides effective design strategies of MXene for flexible batteries and wearable electronics.