A new sealed lithium-peroxide battery with a co-doped Li2O cathode in a superconcentrated lithium bis(fluorosulfonyl)amide electrolyte

Implanting Transition Metal into Li2 O-Based Cathode Prelithiation Agent for High-Energy-Density and Long-Life Li-Ion Batteries

Compensating the irreversible loss of limited active lithium (Li) is essentially important for improving the energy-density and cycle-life of practical Li-ion battery full-cell, especially after employing high-capacity but low initial coulombic efficiency anode candidates. Introducing prelithiation agent can provide additional Li source for such compensation. Herein, we precisely implant trace Co (extracted from transition metal oxide) into the Li site of Li2 O, obtaining (Li0.66 Co0.11 □0.23 )2 O (CLO) cathode prelithiation agent. The synergistic formation of Li vacancies and Co-derived catalysis efficiently enhance the inherent conductivity and weaken the Li-O interaction of Li2 O, which facilitates its anionic oxidation to peroxo/superoxo species and gaseous O2 , achieving 1642.7 mAh/g~Li2O prelithiation capacity (≈980 mAh/g for prelithiation agent). Coupled 6.5 wt % CLO-based prelithiation agent with LiCoO2 cathode, substantial additional Li source stored within CLO is efficiently released to compensate the Li consumption on the SiO/C anode, achieving 270 Wh/kg pouch-type full-cell with 92 % capacity retention after 1000 cycles.

Reversible Discharge Products in Li-Air Batteries

Lithium-air (Li-air) batteries stand out among the post-Li-ion batteries due to their high energy density, which has rapidly progressed in the past years. Regarding the fundamental mechanism of Li-air batteries that discharge products produced and decomposed during charging and recharging progress, the reversibility of products closely affects the battery performance. Along with the upsurge of the mainstream discharge products lithium peroxide, with devoted efforts to screening electrolytes, constructing high-efficiency cathodes, and optimizing anodes, much progress is made in the fundamental understanding and performance. However, the limited advancement is insufficient. In this case, the investigations of other discharge products, including lithium hydroxide, lithium superoxide, lithium oxide, and lithium carbonate, emerge and bring breakthroughs for the Li-air battery technologies. To deepen the understanding of the electrochemical reactions and conversions of discharge products in the battery, recent advances in the various discharge products, mainly focusing on the growth and decomposition mechanisms and the determining factors are systematically reviewed. The perspectives for Li-air batteries on the fundamental development of discharge products and future applications are also provided.

Metal-air batteries: progress and perspective

The metal-air batteries with the largest theoretical energy densities have been paid much more attention. However, metal-air batteries including Li-air/O₂, Li-CO₂, Na-air/O_2, and Zn-air/O₂ batteries, are complex systems that have their respective scientific problems, such as metal dendrite forming/deforming, the kinetics of redox mediators for oxygen reduction/evolution reactions, high overpotentials, desolution of CO₂, H₂O, etc. from the air and related side reactions on both anode and cathode. It should be the main direction to address these shortages to improve performance. Here, we summarized recently research progress in these metal-air/O₂ batteries. Some perspectives are also provided for these research fields.

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.

Unexpectedly Large Contribution of Oxygen to Charge Compensation Triggered by Structural Disordering: Detailed Experimental and Theoretical Study on a Li3NbO4-NiO Binary System

Dependence on lithium-ion batteries for automobile applications is rapidly increasing. The emerging use of anionic redox can boost the energy density of batteries, but the fundamental origin of anionic redox is still under debate. Moreover, to realize anionic redox, many reported electrode materials rely on manganese ions through π-type interactions with oxygen. Here, through a systematic experimental and theoretical study on a binary system of Li₃NbO₄-NiO, we demonstrate for the first time the unexpectedly large contribution of oxygen to charge compensation for electrochemical oxidation in Ni-based materials. In general, for Ni-based materials, e.g., LiNiO₂, charge compensation is achieved mainly by Ni oxidation, with a lower contribution from oxygen. In contrast, for Li₃NbO₄-NiO, oxygen-based charge compensation is triggered by structural disordering and σ-type interactions with nickel ions, which are associated with a unique environment for oxygen, i.e., a linear Ni-O-Ni configuration in the disordered system. Reversible anionic redox with a small hysteretic behavior was achieved for LiNi_2/3Nb_1/3O₂ with a cation-disordered Li/Ni arrangement. Further Li enrichment in the structure destabilizes anionic redox and leads to irreversible oxygen loss due to the disappearance of the linear Ni-O-Ni configuration and the formation of unstable Ni ions with high oxidation states. On the basis of these results, we discuss the possibility of using σ-type interactions for anionic redox to design advanced electrode materials for high-energy lithium-ion batteries.

Understanding anion-redox reactions in cathode materials of lithium-ion batteries throughin situcharacterization techniques: a review

As the demand for rechargeable lithium-ion batteries (LIBs) with higher energy density increases, the interest in lithium-rich oxide (LRO) with extraordinarily high capacities is surging. The capacity of LRO cathodes exceeds that of conventional layered oxides. This has been attributed to the redox contribution from both cations and anions, either sequentially or simultaneously. However, LROs with notable anion redox suffer from capacity loss and voltage decay during cycling. Therefore, a fundamental understanding of their electrochemical behaviors and related structural evolution is a prerequisite for the successful development of high-capacity LRO cathodes with anion redox activity. However, there is still controversy over their electrochemical behavior and principles of operation. In addition, complicated redox mechanisms and the lack of sufficient analytical tools render the basic study difficult. In this review, we aim to introduce theoretical insights into the anion redox mechanism andin situanalytical instruments that can be used to prove the mechanism and behavior of cathodes with anion redox activity. We summarized the anion redox phenomenon, suggested mechanisms, and discussed the history of development for anion redox in cathode materials of LIBs. Finally, we review the recent progress in identification of reaction mechanisms in LROs and validation of engineering strategies to improve cathode performance based on anion redox through various analytical tools, particularly,in situcharacterization techniques. Because unexpected phenomena may occur during cycling, it is crucial to study the kinetic properties of materialsin situunder operating conditions, especially for this newly investigated anion redox phenomenon. This review provides a comprehensive perspective on the future direction of studies on materials with anion redox activity.

High-voltage liquid electrolytes for Li batteries: progress and perspectives

Since the advent of the Li ion batteries (LIBs), the energy density has been tripled, mainly attributed to the increase of the electrode capacities. Now, the capacity of transition metal oxide cathodes is approaching the limit due to the stability limitation of the electrolytes. To further promote the energy density of LIBs, the most promising strategies are to enhance the cut-off voltage of the prevailing cathodes or explore novel high-capacity and high-voltage cathode materials, and also replacing the graphite anode with Si/Si-C or Li metal. However, the commercial ethylene carbonate (EC)-based electrolytes with relatively low anodic stability of ∼4.3 V vs. Li⁺/Li cannot sustain high-voltage cathodes. The bottleneck restricting the electrochemical performance in Li batteries has veered towards new electrolyte compositions catering for aggressive next-generation cathodes and Si/Si-C or Li metal anodes, since the oxidation-resistance of the electrolytes and the in situ formed cathode electrolyte interphase (CEI) layers at the high-voltage cathodes and solid electrolyte interphase (SEI) layers on anodes critically control the electrochemical performance of these high-voltage Li batteries. In this review, we present a comprehensive and in-depth overview on the recent advances, fundamental mechanisms, scientific challenges, and design strategies for the novel high-voltage electrolyte systems, especially focused on stability issues of the electrolytes, the compatibility and interactions between the electrolytes and the electrodes, and reaction mechanisms. Finally, novel insights, promising directions and potential solutions for high voltage electrolytes associated with effective SEI/CEI layers are proposed to motivate revolutionary next-generation high-voltage Li battery chemistries.

Electrode Protection in High-Efficiency Li-O2 Batteries

The aprotic Li-O2 battery possessing the highest theoretical energy density, approaching that of gasoline, has been regarded as one of the most promising successors to Li-ion batteries. Before this kind of battery can become a viable technology, a series of critical issues need to be conquered, like low round-trip efficiency and short cycling lifetime, which are closely related to the continuous parasitic processes happening at the cathode and anode during cycling. With an aim to promote the practical application of Li-O2 batteries, great effort has been devoted to identify the reasons for oxygen and lithium electrodes degradation and provide guidelines to overcome them. Thus, the stability of cathode and anode has been improved a lot in the past decade, which in turn significantly boosts the electrochemical performances of Li-O2 batteries. Here, an overlook on the electrode protection in high-efficiency Li-O2 batteries is presented by providing first the challenges of electrodes facing and then the effectiveness of the existing approaches that have been proposed to alleviate these. Moreover, new battery systems and perspectives of the viable near-future strategies for rational configuration and balance of the electrodes are also pointed out. This Outlook deepens our understanding of the electrodes in Li-O2 batteries and offers opportunities for the realization of high performance and long-term durability of Li-O2 batteries.

Cation-Disorder-Assisted Reversible Topotactic Phase Transition between Antifluorite and Rocksalt Toward High-Capacity Lithium-Ion Batteries

Multielectron reaction electrode materials using partial oxygen redox can be potentially used as cathodes in lithium-ion batteries, as they offer numerous advantages, including high reversible capacity and energy density and low cost. Here, a reversible three-electron reaction is demonstrated utilizing topotactic phase transition between antifluorite and rocksalt in a cation-disordered antifluorite-type cubic Li₆CoO₄ cathode. This cubic phase is synthesized by a simple mechanochemical treatment of conventionally prepared tetragonal Li₆CoO₄. It displays a reversible capacity of 487 mAh g^-1, a high value because of a reversible three-electron reaction using Co²⁺/Co³⁺, Co³⁺/Co⁴⁺, and O^2-/O₂^2- redox, occurring without O₂ gas evolution. The mechanochemical treatment is assumed to reduce its lattice distortion by cation-disordering and facilitate a reversible topotactic phase transition between antifluorite and rocksalt structures via a dynamic cation pushing mechanism.

Electrochemical Characteristics of Co-Substituted α- and β-Li5AlO4 as High-Specific Capacity Positive Electrode Materials

Electric vehicles and hybrid electric vehicles require batteries with higher energy densities than conventional batteries. Anion redox-type active materials have been proposed as new high-capacity positive electrode materials for Li-ion batteries with high-energy densities. Co-substituted Li₅AlO₄ is a novel and promising high-capacity positive electrode material for Li-ion batteries. In this study, we investigated the influence of different synthesis conditions on the enhancement of the specific capacity. The material prepared via mechanical alloying of β-Li₅AlO₄ with LiCoO₂ at 300 rpm for 24 h exhibited a higher specific capacity than that prepared from α-Li₅AlO₄ and LiCoO₂. Co-substituted β-Li₅AlO₄ demonstrated a specific capacity of approximately 250 mA h g^-1. The specific capacity of Co-substituted α and β-Li₅AlO₄ increased with increasing Co content in the samples. According to X-ray absorption near edge structure measurements, the irreversible oxygen redox reaction and a reversible reaction involving the formation and consumption of peroxide were responsible for the charge compensation of Co-substituted β-Li₅AlO₄ and α-Li₅AlO₄, respectively.

Effect of Vinylethylene Carbonate and Fluoroethylene Carbonate Electrolyte Additives on the Performance of Lithia-Based Cathodes

Nanolithia-based materials are promising lithium-ion battery cathodes owing to their high capacity, low overpotential, and stable cyclic performance. Their properties are highly dependent on the structure and composition of the catalysts, which play a role in activating the lithia to participate in the electrochemical redox reaction. However, the use of electrolyte additives can be an efficient approach to improve properties of the lithia-based cathodes. In this work, vinylethylene carbonate (VEC) and fluoroethylene carbonate (FEC) were introduced as electrolyte additives in cells containing lithia-based cathode (lithia/(Ir, Li₂IrO₃) nanocomposite). The use of additives enhanced the electrochemical performance of the lithia-based cathodes, including the rate capability and cyclic performance. Especially, their available capacity increased without modifying the cathodes. Results of X-ray photoelectron spectroscopy (XPS) analysis confirmed that the additives form interface layers at the cathode surface, which contain Li₂CO₃, more carbon reactants, and more LiF than the interface layer formed with the pristine electrolyte. The Li₂CO₃ and carbon reactants may improve rate capability by facilitating Li⁺ transport, and LiF may stabilize the Li₂O₂ (and/or LiO₂) produced by the oxygen redox reaction with lithia. Therefore, the additive-enhanced electrochemical performance of the cell is attributed to the effects of the interface layer derived from additive decomposition during cycling.

Construction of MnO2 Artificial Leaf with Atomic Thickness as Highly Stable Battery Anodes

The leaf-like structure is a classic and robust structure and its unique vein support can reduce structural instability. However, biomimetic leaf structures on the atomic scale are rarely reported due to the difficulty in achieving a stable vein-like support in a mesophyll-like substrate. A breathable 2D MnO₂ artificial leaf is first reported with atomic thickness by using a simple and mild one-step wet chemical method. This homogeneous ultrathin leaf-like structure comprises of vein-like crystalline skeleton as support and amorphous microporous mesophyll-like nanosheet as substrate. When used as an anode material for lithium ion batteries, it first solves the irreversible capacity loss and poor cycling issue of pure MnO₂ , which delivers high capacity of 1210 mAh g^-1 at 0.1 A g^-1 and extremely stable cycle life over 2500 cycles at 1.0 A g^-1 . It exhibits the most outstanding cycle life of pure MnO₂ and even comparable to the most MnO₂ -based composite electrode materials. This biomimetic design provides important guidelines for precise control of 2D artificial systems and gives a new idea for solving poor electrochemical stability of pure metal oxide electrode materials.

Cationic and anionic redox in lithium-ion based batteries

This review will present the current understanding, experimental evidence and future direction of anionic and cationic redox for Li-ion batteries.

Building Safe Lithium-Ion Batteries for Electric Vehicles: A Review

Abstract

Lithium-ion batteries (LIBs), with relatively high energy density and power density, have been considered as a vital energy source in our daily life, especially in electric vehicles. However, energy density and safety related to thermal runaways are the main concerns for their further applications. In order to deeply understand the development of high energy density and safe LIBs, we comprehensively review the safety features of LIBs and the failure mechanisms of cathodes, anodes, separators and electrolyte. The corresponding solutions for designing safer components are systematically proposed. Additionally, the in situ or operando techniques, such as microscopy and spectrum analysis, the fiber Bragg grating sensor and the gas sensor, are summarized to monitor the internal conditions of LIBs in real time. The main purpose of this review is to provide some general guidelines for the design of safe and high energy density batteries from the views of both material and cell levels.

Graphic Abstract

Safety of lithium-ion batteries (LIBs) with high energy density becomes more and more important in the future for EVs development. The safety issues of the LIBs are complicated, related to both materials and the cell level. To ensure the safety of LIBs, in-depth understanding of the safety features, precise design of the battery materials and real-time monitoring/detection of the cells should be systematically considered. Here, we specifically summarize the safety features of the LIBs from the aspects of their voltage and temperature tolerance, the failure mechanism of the LIB materials and corresponding improved methods. We further review the in situ or operando techniques to real-time monitor the internal conditions of LIBs.

Multistaged discharge constructing heterostructure with enhanced solid-solution behavior for long-life lithium-oxygen batteries

Inferior charge transport in insulating and bulk discharge products is one of the main factors resulting in poor cycling stability of lithium-oxygen batteries with high overpotential and large capacity decay. Here we report a two-step oxygen reduction approach by pre-depositing a potassium carbonate layer on the cathode surface in a potassium-oxygen battery to direct the growth of defective film-like discharge products in the successive cycling of lithium-oxygen batteries. The formation of defective film with improved charge transport and large contact area with a catalyst plays a critical role in the facile decomposition of discharge products and the sustained stability of the battery. Multistaged discharge constructing lithium peroxide-based heterostructure with band discontinuities and a relatively low lithium diffusion barrier may be responsible for the growth of defective film-like discharge products. This strategy offers a promising route for future development of cathode catalysts that can be used to extend the cycling life of lithium-oxygen batteries.

Lithia-Based Nanocomposites Activated by Li2RuO3 for New Cathode Materials Rooted in the Oxygen Redox Reaction

Lithia-based materials are promising cathodes based on an anionic (oxygen) redox reaction for lithium ion batteries due to their high capacity and stable cyclic performance. In this study, the properties of a lithia-based cathode activated by Li₂RuO₃ were characterized. Ru-based oxides are expected to act as good catalysts because they can play a role in stabilizing the anion redox reaction. Their high electronic conductivity is also attractive because it can compensate for the low conductivity of lithia. The lithia/Li₂RuO₃ nanocomposites show stable cyclic performance until a capacity limit of 500 mAh g^-1 is reached, which is below the theoretical capacity (897 mAh g^-1) but superior to other lithia-based cathodes. In the XPS analysis, while the Ru 3d peaks in the spectra barely changed, peroxo-like (O₂)^n- species reversibly formed and dissociated during cycling. This clearly confirms that the capacity of the lithia/Li₂RuO₃ nanocomposites can mostly be attributed to the anionic (oxygen) redox reaction.

Probing the dynamic evolution of lithium dendrites: a review of in situ/operando characterization for lithium metallic batteries

During the operation of lithium metal batteries, the direct observation of the evolving characteristics of the deposited lithium is rather challenging in consideration of the requirements for the fast-tracking and high spatial resolution of the signals within native organic electrolytes. However, the weak scattering of electrons and X-rays with low-atomic-number lithium deteriorates the spectral resolution of the signals. Therefore, this mini-review compares various influencing factors that determine the lithium nucleation process based on electrochemical performance evaluations, including the artificial protective layer, electrolyte formulation, lithiophilic sites and hierarchies of the substrate; additionally, the possibility of the dynamic observations of chemical, electronic, and geometric changes during the operation of metallic batteries is exhibited. For each category of the technique, a brief account of the advancements of the characterizing equipment is followed with novel cell designs. Finally, the prospects that advance the precise description of the lithium nucleation process are summarized. This mini-review highlights the mitigating strategies of lithium dendrites at molecular, electrode, and device levels and summarizes the state-of-the-art in operando techniques, thereby promoting the future design of metallic battery systems.

Lithia/(Ir, Li2IrO3) nanocomposites for new cathode materials based on pure anionic redox reaction

Anionic redox reactions attributed to oxygen have attracted much attention as a new approach to overcoming the energy-density limits of cathode materials. Several oxides have been suggested as new cathode materials with high capacities based on anionic (oxygen) redox reactions. Although most still have a large portion of their capacity based on the cationic redox reaction, lithia-based cathodes present high capacities that are purely dependent upon oxygen redox. Contrary to Li-air batteries, other systems using pure oxygen redox reactions, lithia-based cathodes charge and discharge without a phase transition between gas and condensed forms. This leads to a more stable cyclic performance and lower overpotential compared with those of Li-air systems. However, to activate nanolithia and stabilize reaction products such as Li₂O₂ during cycling, lithia-based cathodes demand efficient catalysts (dopants). In this study, Ir based materials (Ir and Li₂IrO₃) were introduced as catalysts (dopants) for nanolithia composites. Oxide types (Li₂IrO₃) were used as source materials of catalyst because ductile metal (Ir) can hardly be pulverized during the milling process. Two types of Li₂IrO₃ were prepared and used for catalyst-sources. They were named ‘1-step Li₂IrO₃’ and ‘2-step Li₂IrO₃’, respectively, since they were prepared by ‘1-step’ or ‘2-step’ heat treatment. The nanocomposites prepared using lithia & 2-step Li₂IrO₃ presented a higher capacity, more stable cyclic performance, and lower overpotential than those of the nanocomposites prepared using lithia & 1-step Li₂IrO₃. The voltage profiles of the nanocomposites prepared using lithia & 2-step Li₂IrO₃ were stable up to a limited capacity of 600 mAh·g⁻¹, and the capacity was maintained during 100 cycles. XPS analysis confirmed that the capacity of our lithia-based compounds is attributable to the oxygen redox reaction, whereas the cationic redox related to the Ir barely contributes to their discharge capacity.

Understanding the Reaction Chemistry during Charging in Aprotic Lithium-Oxygen Batteries: Existing Problems and Solutions

The aprotic lithium-oxygen (Li-O₂ ) battery has excited huge interest due to it having the highest theoretical energy density among the different types of rechargeable battery. The facile achievement of a practical Li-O₂ battery has been proven unrealistic, however. The most significant barrier to progress is the limited understanding of the reaction processes occurring in the battery, especially during the charging process on the positive electrode. Thus, understanding the charging mechanism is of crucial importance to enhance the Li-O₂ battery performance and lifetime. Here, recent progress in understanding the electrochemistry and chemistry related to charging in Li-O₂ batteries is reviewed along with the strategies to address the issues that exist in the charging process at the present stage. The properties of Li₂ O₂ and the mechanisms of Li₂ O₂ oxidation to O₂ on charge are discussed comprehensively, as are the accompanied parasitic chemistries, which are considered as the underlying issues hindering the reversibility of Li-O₂ batteries. Based on the detailed discussion of the charging mechanism, innovative strategies for addressing the issues for the charging process are discussed in detail. This review has profound implications for both a better understanding of charging chemistry and the development of reliable rechargeable Li-O₂ batteries in the future.

Material Design Concept of Lithium-Excess Electrode Materials with Rocksalt-Related Structures for Rechargeable Non-Aqueous Batteries

Dependence on lithium-ion batteries for automobile applications is rapidly increasing, and further improvement, especially for positive electrode materials, is indispensable to increase energy density of lithium-ion batteries. In the past several years, many new lithium-excess high-capacity electrode materials with rocksalt-related structures have been reported. These materials deliver high reversible capacity with cationic/anionic redox and percolative lithium migration in the oxide/oxyfluoride framework structures, and recent research progresses on these electrode materials are reviewed. Material design strategies for these lithium-excess electrode materials are also described. Future possibility of high-energy non-aqueous batteries with advanced positive electrode materials is discussed for more details.

Exploration and Size Engineering from Natural Chalcopyrite to High-Performance Electrode Materials for Lithium-Ion Batteries

Compared to chemosynthetic CuFeS₂, natural chalcopyrite (CuFeS₂) can be regarded as a promising anode material for exploring ultrafast and stable Li-ion batteries benefiting from it being firsthand, eco-friendly, and resource-rich. Considering the nonuniform size distribution in it and the fact that homogeneous grain distributions can effectively restrain the aggregation of active materials, the engineering of size is deemed an effective strategy to achieve excellent Li-storage performances. Herein, varisized natural CuFeS₂ are obtained by facial mineral processing technology and outstanding Li-storage performances are exhibited. Along with the decreasing of size, the contribution of pseudocapacitive as well as the ion transfer rates are significantly boosted. As expected, even at 1 A g^-1, a remarkable capacity of 1009.7 mA h g^-1 is displayed by the sample with the smallest size and most uniform distributions even after 500 cycles. Furthermore, supported by the detailed analysis of in situ X-ray diffraction and kinetic features, a hybrid of multiple lithium-metal sulfur systems and the major origin of the enhanced capacity upon long cycles are confirmed. Remarkably, this work is expected to increase the far-ranging applications of natural chalcopyrite as a firsthand anode material for lithium-ion batteries (LIBs) and inform the readers about the effects of particle size on Li-storage performances.

Dramatically Enhanced Li-Ion Storage of ZnO@C Anodes through TiO2 Homogeneous Hybridization

Amorphous nanoparticles of ZnO and TiO₂ embedded in carbon nanocages (AZT⊂CNCs) were successfully synthesized through a simple annealing process of TiO₂ -coated zeolitic imidazolate framework-8 (ZIF-8). In the current anode of AZT⊂CNCs, tiny ZnO and TiO₂ nanoparticles were uniformly distributed in the carbon matrix (carbon nanocages), which could effectively buffer the volume expansion of electroactive ZnO and provide excellent electric conductivity. After fully investigating the electrochemical performance of the AZT⊂CNCs samples obtained with different additive amounts of tetrabutyl orthotitanate (TBOT) for TiO₂ coating, it has been found that AZT-30 (0.1 g ZIF-8 with 30 mL TBOT) shows the best cycle stability (510 mA h g^-1 after 350 cycles at 200 mA g^-1 ) and a superior rate capability (610 mA h g^-1 after 3500 cycles at 2 A g^-1 ). The greatly enhanced Li-ion storage performance could be ascribed to the fact that the introduction of amorphous TiO₂ could activate the reversible lithiation/delithiation reaction of ZnO during the charge/discharge process.

Novel Concentrated Li[(FSO2)(n-C4F9SO2)N]-Based Ether Electrolyte for Superior Stability of Metallic Lithium Anode

Lithium (fluorosulfonyl)(n-nonafluorobutanesulfonyl)imide [Li[(FSO₂)(n-C₄F₉SO₂)N] (LiFNFSI)] is investigated as a conducting salt, which can form a relatively stable solid-electrolyte-interphase film in concentrated ether electrolyte to achieve favorable protection for lithium metal anodes. Li|Cu and Li|Li cells with concentrated LiFNFSI-based electrolyte have been demonstrated to display high average Coulombic efficiency (≈97%) and excellent cycling stability (over 1,000 h) of metallic lithium anodes, compared to concentrated lithium bis(trifluoromethanesulfonyl)imide [Li[N(SO₂CF₃)₂] (LiTFSI)]-based electrolyte. The morphologies and compositions of the lithium-metal anode surface are also comparatively analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Moreover, superior electrochemical performance in the concentrated LiFNFSI-based electrolyte for Li|LiFePO₄ cells is also presented herein. These results indicate that concentrated LiFNFSI-based electrolyte is a promising candidate for metallic lithium rechargeable batteries.

Reaction chemistry in rechargeable Li–O2batteries

This progress report reviews the most recent discoveries regarding Li–O₂chemistry during each discharge and charge process.

Origin of stabilization and destabilization in solid-state redox reaction of oxide ions for lithium-ion batteries

Further increase in energy density of lithium batteries is needed for zero emission vehicles. However, energy density is restricted by unavoidable theoretical limits for positive electrodes used in commercial applications. One possibility towards energy densities exceeding these limits is to utilize anion (oxide ion) redox, instead of classical transition metal redox. Nevertheless, origin of activation of the oxide ion and its stabilization mechanism are not fully understood. Here we demonstrate that the suppression of formation of superoxide-like species on lithium extraction results in reversible redox for oxide ions, which is stabilized by the presence of relatively less covalent character of Mn⁴⁺ with oxide ions without the sacrifice of electronic conductivity. On the basis of these findings, we report an electrode material, whose metallic constituents consist only of 3d transition metal elements. The material delivers a reversible capacity of 300 mAh g^-1 based on solid-state redox reaction of oxide ions.

High-capacity electrode materials for rechargeable lithium batteries: Li3NbO4-based system with cation-disordered rocksalt structure

Rechargeable lithium batteries have rapidly risen to prominence as fundamental devices for green and sustainable energy development. Lithium batteries are now used as power sources for electric vehicles. However, materials innovations are still needed to satisfy the growing demand for increasing energy density of lithium batteries. In the past decade, lithium-excess compounds, Li2MeO3 (Me = Mn(4+), Ru(4+), etc.), have been extensively studied as high-capacity positive electrode materials. Although the origin as the high reversible capacity has been a debatable subject for a long time, recently it has been confirmed that charge compensation is partly achieved by solid-state redox of nonmetal anions (i.e., oxide ions), coupled with solid-state redox of transition metals, which is the basic theory used for classic lithium insertion materials, such as LiMeO2 (Me = Co(3+), Ni(3+), etc.). Herein, as a compound with further excess lithium contents, a cation-ordered rocksalt phase with lithium and pentavalent niobium ions, Li3NbO4, is first examined as the host structure of a new series of high-capacity positive electrode materials for rechargeable lithium batteries. Approximately 300 mAh ⋅ g(-1) of high-reversible capacity at 50 °C is experimentally observed, which partly originates from charge compensation by solid-state redox of oxide ions. It is proposed that such a charge compensation process by oxide ions is effectively stabilized by the presence of electrochemically inactive niobium ions. These results will contribute to the development of a new class of high-capacity electrode materials, potentially with further lithium enrichment (and fewer transition metals) in the close-packed framework structure with oxide ions.

High rate and stable cycling of lithium metal anode

Lithium metal is an ideal battery anode. However, dendrite growth and limited Coulombic efficiency during cycling have prevented its practical application in rechargeable batteries. Herein, we report that the use of highly concentrated electrolytes composed of ether solvents and the lithium bis(fluorosulfonyl)imide salt enables the high-rate cycling of a lithium metal anode at high Coulombic efficiency (up to 99.1%) without dendrite growth. With 4 M lithium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane as the electrolyte, a lithium|lithium cell can be cycled at 10 mA cm⁻² for more than 6,000 cycles, and a copper|lithium cell can be cycled at 4 mA cm⁻² for more than 1,000 cycles with an average Coulombic efficiency of 98.4%. These excellent performances can be attributed to the increased solvent coordination and increased availability of lithium ion concentration in the electrolyte. Further development of this electrolyte may enable practical applications for lithium metal anode in rechargeable batteries.

Lithium metal is an ideal anode material for rechargeable batteries, but lithium dendritic growth and limited Columbic efficiency prevent its applications. Here, the authors report the use of highly concentrated electrolytes composed of ether solvents and the salt lithium bis(fluorosulfonyl)imide to enable high-rate cycling of lithium anode.