Lithium Hydride in the Solid Electrolyte Interphase of Lithium-Ion Batteries as a Pulverization Accelerator of Silicon.

As a highly promising next-generation high-specific capacity anode, the industrial-scale utilization of micron silicon has been hindered by the issue of pulverization during cycling. Although numerous studies have demonstrated the effectiveness of regulating the inorganic components of the solid electrolyte interphase (SEI) in improving pulverization, the evolution of most key inorganic components in the SEI and their correlation with silicon failure mechanisms remain ambiguous. This study provides a clear and direct correlation between the lithium hydride (LiH) in the SEI and the degree of micron silicon pulverization in the battery system. The reverse lithiation behavior of LiH on micron silicon during de-lithiation exacerbates the localized stress in silicon particles and contributes to particle pulverization. This work successfully proposes a novel approach to decouple the SEI from electrochemical performance, which can be significant to decipher the evolution of critical SEI components at varied battery anode interfaces and analyze their corresponding failure mechanisms.

Interphase Regulation by Multifunctional Additive Empowering High Energy Lithium-Ion Batteries with Enhanced Cycle Life and Thermal Safety.

High energy density lithium-ion batteries (LIBs) adopting high-nickel layered oxide cathodes and silicon-based composite anodes always suffer from unsatisfied cycle life and poor safety performance, especially at elevated temperatures. Electrode /electrolyte interphase regulation by functional additives is one of the most economic and efficacious strategies to overcome this shortcoming. Herein, cyano-groups (-CN) are introduced into lithium fluorinated phosphate to synthesize a novel multifunctional additive of lithium tetrafluoro (1,2-dihydroxyethane-1,1,2,2-tetracarbonitrile) phosphate (LiTFTCP), which endows high nickel LiNi0.8 Co0.1 Mn0.1 O2 /SiOx -graphite composite full cell with an ultrahigh cycle life and superior safety characteristics, by adding only 0.5 wt % LiTFTCP into a LiPF6 -carbonate baseline electrolyte. It is revealed that LiTFTCP additive effectively suppresses the HF generation and facilitates the formation of a robust and heat-resistant cyano-enriched CEI layer as well as a stable LiF-enriched SEI layer. The favorable SEI/CEI layers greatly lessen the electrode degradation, electrolyte consumption, thermal-induced gassing and total heat-releasing. This work illuminates the importance of additive molecular engineering and interphase regulation in simultaneously promoting the cycling and thermal safety of LIBs with high-nickel NCMxyz cathode and silicon-based composite anode.

Transforming a Primary Li-SOCl2 Battery into a High-Power Rechargeable System via Molecular Catalysis.

Li-SOCl2 batteries possess ultrahigh energy densities and superior safety features at a wide range of operating temperatures. However, the Li-SOCl2 battery system suffers from poor reversibility due to the sluggish kinetics of SOCl2 reduction during discharging and the oxidation of the insulating discharge products during charging. To achieve a high-power rechargeable Li-SOCl2 battery, herein we introduce the molecular catalyst I2 into the electrolyte to tailor the charging and discharging reaction pathways. The as-assembled rechargeable cell exhibits superior power density, sustaining an ultrahigh current density of 100 mA cm-2 during discharging and delivering a reversible capacity of 1 mAh cm-2 for 200 cycles at a current density of 2 mA cm-2 and 6 mAh cm-2 for 50 cycles at a current density of 5 mA cm-2. Our results reveal the molecular catalyst-mediated reaction mechanisms that fundamentally alter the rate-determining steps of discharging and charging in Li-SOCl2 batteries and highlight the viability of transforming a primary high-energy battery into a high-power rechargeable system, which has great potential to meet the ever-increasing demand of energy-storage systems.

Revealing Capacity Degradation of Ge Anodes in Lithium-Ion Batteries Triggered by Interfacial LiH.

The Germanium (Ge), as a fast-charging and high specific capacity (1568 mAh g-1 ) alloy anode, is greatly hampered in practical application by poor cyclability. To date, the understanding of cycling performance degradation remains elusive. This study illustrates that, contrary to conventional beliefs, most of the Ge material in failed anodes still retains good integrity and does not undergo severe pulverization. It is revealed that capacity degradation is clearly correlated to the interfacial evolution of lithium hydride (LiH). Tetralithium germanium hydride (Li4 Ge2 H), as a new species derived from LiH, is identified as the culprit of Ge anode degradation, which is the dominant crystalized component in an ever-growing and ever-insulating interphase. The significantly increased thickness of the solid electrolyte interface (SEI) is accompanied by the accumulation of insulating Li4 Ge2 H upon cycling, which severely retards the charge transport process and ultimately triggers the anode failure. We believe that the comprehensive understanding of the failure mechanism presented in this study is of great significance to promoting the design and development of alloy anode for the next generation of lithium-ion batteries.

Charge-Compensation in a Displacement Mg2+ Storage Cathode through Polyselenide-Mediated Anion Redox.

Chalcogenides have been viewed as important conversion-type Mg2+ -storage cathodes to fulfill the high volumetric energy density promise of magnesium (Mg) batteries. However, the low initial Columbic efficiency and the rapid capacity degradation remain challenges for the chalcogenide cathodes, as the clear Mg2+ -storage mechanism has yet to be clarified. Herein, we illustrate that the charge storage mechanism of the Cu2-x Se cathode is a reversible displacement reaction along with a polyselenide (PSe) mediated solution process of anion-compensation. The unique anion redox improves charge storage, while the dissolution of PSe also leads to performance degradation. To address this issue, we introduce Mo6 S8 into the Cu2-x Se cathode to immobilize PSe, which significantly improves performance, especially the reversible capacity (from 140 mAh g-1 to 220 mAh g-1 ). This work provides inspiration for the modification of the Mg2+ -storage cathode, which is a milestone for high-performance Mg batteries.

Bioinspired Antiaging Binder Additive Addressing the Challenge of Chemical Degradation of Electrolyte at Cathode/Electrolyte Interphase.

For layered transition metal oxides cathode-based lithium batteries, the chemical degradation of electrolytes leads to fast battery capacity decay, severely challenging their practical applications. This kind of chemical degradation of electrolytes is caused by the oxidation of reactive oxygen (e.g., singlet oxygen) and the attack of free radicals during cycling. To address this, we first report a biologically inspired antiaging strategy of developing the photostabilizer with singlet oxygen- and free radicals-scavenging abilities as a cathode binder additive. It is fully evidenced that this binder system consisting of the binder additive and a commercially available polyvinylidene difluoride can scavenge singlet oxygen and free radicals generated during high-voltage cycling, thus significantly restraining electrolyte decomposition. As a result, high-voltage layered transition metal oxides-based lithium batteries with reproducibly superior electrochemical performance, even under elevated temperatures, can be achieved. This bioinspired strategy to scavenge reactive oxygen and free radicals heralds a new paradigm for manipulating the cathode/electrolyte interphase chemistry of various rechargeable batteries involving layered transition metal oxides-based cathodes.

Leakage-Proof Electrolyte Chemistry for a High-Performance Lithium-Sulfur Battery.

Electrolyte leakage is a severe safety concern in lithium batteries. With highly volatile 1,2-dimethoxyethane as solvent, the leakage related hazards are more pronounced in lithium-sulfur (Li-S) batteries. To address this concern, a leakage-proof electrolyte is delicately designed through functionalizing the commercial electrolyte by Li6 PS5 Cl-grafted poly(ethyl cyanoacrylate), which can interact readily with the aluminum-plastic packing through hydrogen bond to immobilize the electrolyte. The moisture from ambient can also catalyze a further polymerization of the macromolecules to seal the leaking points and thereby to solve the leakage issue, endowing Li-S batteries superior safety even in an artificial cut pouch cell. With a bare S loading of 4.9 mg cm-2 , the battery can deliver good endurance owing to the suppressed polysulfide shuttle by its polar groups. This work enlightens the design of leakage-proof electrolyte and makes a milestone for high performance Li-S batteries.

The Formation/Decomposition Equilibrium of LiH and its Contribution on Anode Failure in Practical Lithium Metal Batteries.

Discovering the underlying reason for Li anode failure is a critical step towards applications of lithium metal batteries (LMBs). In this work, we conduct deuterium-oxide (D2 O) titration experiments in a novel on-line gas analysis mass spectrometry (MS) system, to determine the content of metallic Li and lithium hydride (LiH) in cycled Li anodes disassembled from practical LiCoO2 /Li LMBs. The practical cell is comprised of ultrathin Li anode (50 µm), high loading LiCoO2 (17 mg cm-2 , 2.805 mAh cm-2 ) and different formulated electrolytes. Our results suggest that the amount of LiH accumulation is negatively correlated with cyclability of practical LMBs. More importantly, we reveal a temperature sensitive equilibrium (Li + 1/2 H2 ⇌ LiH) governing formation and decomposition process of LiH at Li anode. We believe that the unusual understanding provided by this study will draw forth more insightful efforts to realize efficient Li protection and the ultimate applications of "holy grail" LMBs.

A Novel Regulation Strategy of Solid Electrolyte Interphase Based on Anion-Solvent Coordination for Magnesium Metal Anode.

Magnesium (Mg) metal anode is a highly desirable candidate among various high energy density metal anodes, possessing higher volumetric capacity and better safety characteristic compared to lithium metal. However, most Mg salts in conventional Mg electrolytes easily react with Mg metal to form blocking layers, leading to inferior reversibility of Mg plating/stripping. Here, a stable Mg2+ -conducting solid electrolyte interphase (SEI) is successfully constructed on Mg metal anode by regulating the molecular-orbital-energy-level toward an aluminum(III)-centered anion Mg salt through anion-solvent coordination. Of which, the LUMO energy level of perfluorinated pinacolatoaluminate (Al(O2 C2 (CF3 )4 )2 - , abbreviated as FPA) anion has been adjusted by coordinating with solvent molecule (tetrahydrofuran) for facilitating the formation of advantageous SEI. The existence of SEI formed by FPA anion greatly improves the reversibility and long-term stability of Mg plating/stripping process. More importantly, based on this aluminum(III)-centered Mg electrolyte, the Mo6 S8 /Mg batteries can achieve a fantastic cycle performance of 9000 cycles, proving the beneficial effect of SEI on the cycling stability of Mg battery system. These findings open up a promising avenue to construct stable and compatible SEI on Mg metal anode, and lay significant foundations for the successful development of rechargeable Mg metal batteries.

Formulation of Blended-Lithium-Salt Electrolytes for Lithium Batteries.

Blended-salt electrolytes showing synergistic effects have been formulated by simply mixing several lithium salts in an electrolyte. In the burgeoning field of next-generation lithium batteries, blended-salt electrolytes have enabled great progress to be made. In this Review, the development of such blended-salt electrolytes is examined in detail. The reasons for formulating blended-salt electrolytes for lithium batteries include improvement of thermal stability (safety), inhibition of aluminum-foil corrosion of the cathode current collector, enhancement of performance over a wide temperature range (or at a high or low temperature), formation of favorable interfacial layers on both electrodes, protection of the lithium metal anode, and attainment of high ionic conductivity. Herein, we highlight key scientific issues related to the formulation of blended-salt electrolytes for lithium batteries.

Highly Reversible Cuprous Mediated Cathode Chemistry for Magnesium Batteries.

Sluggish kinetics and poor reversibility of cathode chemistry is the major challenge for magnesium batteries to achieve high volumetric capacity. Introduction of the cuprous ion (Cu+ ) as a charge carrier can decouple the magnesiation related energy storage from the cathode electrochemistry. Cu+ is generated from a fast equilibrium between copper selenide electrode and Mg electrolyte during standing time, rather than in the electrochemical process. A reversible chemical magnesiation/de-magnesiation can be driven by this solid/liquid equilibrium. During a typical discharge process, Cu+ is reduced to Cu and drives the equilibrium to promote the magnesiation process. The reversible Cu to Cu+ redox promotes the recharge process. This novel Cu+ mediated cathode chemistry of Mg battery leads to a high reversible areal capacity of 12.5 mAh cm-2 with high mass loading (49.1 mg cm-2 ) of the electrode. 80 % capacity retention can be achieved for 200 cycles after a conditioning process.

Additive-Assisted Novel Dual-Salt Electrolyte Addresses Wide Temperature Operation of Lithium-Metal Batteries.

In this study, self-synthesized lithium trifluoro(perfluoro-tert-butyloxyl)borate (LiTFPFB) is combined with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to formulate a novel 1 m dual-salt electrolyte, which contains lithium difluorophosphate (LiPO2 F2 ) additive and dominant carbonate solvents with low melting point and high boiling point. The addition of LiPO2 F2 into this novel dual-salt electrolyte dramatically improves cycleability and rate capability of a LiNi0.5 Mn0.3 Co0.2 O2 /Li (NMC/Li) battery, ranging from -40 to 90 °C. The NMC/Li batteries adopt a Li-metal anode with low thickness of 100 µm (even 50 µm) and a moderately high cathode mass loading level of 10 mg cm-2 . For the first time, this paper provides valuable perspectives for developing practical lithium-metal batteries over a wide temperature range.

Fluorescence Probing of Active Lithium Distribution in Lithium Metal Anodes.

The uncontrollable growth of Li dendrites and the accumulation of byproducts are two severe concerns for lithium metal batteries, which leads to safety hazards and a low Coulombic efficiency. To investigate the deterioration of the cell, it is important to figure out the distribution of active Li species on the anode surface and distinguish Li dendrites from byproducts. However, it is still challenging to identify these issues by conventional visual observation methods. In this work, we introduce a novel fluorescent probing strategy using 9,10-dimethylanthracene (DMA). By marking the cycled Li-anode surface, the active Li distribution can be visualized by the fluorescence quenching of DMA reacting with active Li. The method demonstrates validity for electrolyte selection and predictive detection of uneven Li deposition on Li metal anodes. Furthermore, the location of dendrites can be clearly identified after destructive utilization of the anode, which will contribute to the development of failure-analysis technology for Li metal batteries.

Aliphatic Polycarbonate-Based Solid-State Polymer Electrolytes for Advanced Lithium Batteries: Advances and Perspective.

Conventional liquid electrolytes based lithium-ion batteries (LIBs) might suffer from serious safety hazards. Solid-state polymer electrolytes (SPEs) are very promising candidate with high security for advanced LIBs. However, the quintessential frailties of pristine polyethylene oxide/lithium salts SPEs are poor ionic conductivity (≈10-8 S cm-1 ) at 25 °C and narrow electrochemical window (<4 V). Many innovative researches are carried out to enhance their lithium-ion conductivity (10-4 S cm-1 at 25 °C), which is still far from meeting the needs of high-performance power LIBs at ambient temperature. Therefore, it is a pressing urgency of exploring novel polymer host materials for advanced SPEs aimed to develop high-performance solid lithium batteries. Aliphatic polycarbonate, an emerging and promising solid polymer electrolyte, has attracted much attention of academia and industry. The amorphous structure, flexible chain segments, and high dielectric constant endow this class of polymer electrolyte excellent comprehensive performance especially in ionic conductivity, electrochemical stability, and thermally dimensional stability. To date, many types of aliphatic polycarbonate solid polymer electrolyte are discovered. Herein, the latest developments on aliphatic polycarbonate SPEs for solid-state lithium batteries are summarized. Finally, main challenges and perspective of aliphatic polycarbonate solid polymer electrolytes are illustrated at the end of this review.

Dendrite-Free Lithium Deposition via Flexible-Rigid Coupling Composite Network for LiNi0.5 Mn1.5 O4 /Li Metal Batteries.

Notorious lithium dendrite causes severe capacity fade and harsh safety issues of lithium metal batteries, which hinder the practical applications of lithium metal electrodes in higher energy rechargeable batteries. Here, a kind of 3D-cross-linked composite network is successfully employed as a flexible-rigid coupling protective layer on a lithium metal electrode. During the plating/stripping process, the composite protective layer would enable uniform distribution of lithium ions in the adjacent regions of the lithium electrode, resulting in a dendrite-free deposition at a current density of 2 mA cm-2 . The LiNi0.5 Mn1.5 O4 -based lithium metal battery presents an excellent cycling stability at a voltage range of 3.5-5.0 V with the induction of 3D-cross-linked composite protective layer. From an industrial field application of view, thin lithium metal electrodes (40 µm, with 4 times excess lithium) can be used in LiNi0.5 Mn1.5 O4 (with industrially significant loading of 18 mg cm-2 and 2.6 mAh cm-2 )-based lithium metal batteries, which reveals a promising opportunity for practical applicability in high energy lithium metal batteries.

Nanostructured Bimetallic Iron Molybdenum Nitride as a Non-Precious Cathode Catalyst for Li­O2 Batteries.

Herein we report the facile fabrication and electrocatalytic activity of nanostructured bimetallic iron molybdenum nitride (Fe3Mo3N), which was prepared by an ammonolysis process directly towards the solid state mixture of Mo precursor and Fe precursor. The prepared nanostructured Fe3Mo3N presented remarkable electrocatalytic activities towards both oxygen reduction reaction and oxygen evolution reaction in nonaqueous phase, due to the modulation of electronic configuration of catalyst by Fe element and porous structure. Then, lithium-O2 batteries with nanostructured Fe3Mo3N as cathode catalysts were assembled, which show alleviated polarization and enhanced cyclability.

A Perspective on Uniform Plating Behavior of Mg Metal Anode: Diffusion Limited Theory versus Nucleation Theory.

Utilizing metal anode is the most attractive way to meet the urgent demand for rechargeable batteries with high energy density. Unfortunately, the formation of dendrites, which is caused by uneven plating behavior, always threaten the safety of the batteries. To explore the origin of different plating behavior and predict the plating morphology of anode under a variety of operating conditions, multifarious models have been developed. However, abuse of models has led to conflictive views. In this perspective, to clarify the controversial reports on magnesium (Mg) metal plating behavior, the previously proposed models are elaborated that govern the plating process. Through linking various models and clarifying their boundary conditions, a scheme is drawn to illustrate the strategy for achieving the most dense and uniform plating morphology, which also explains the seemingly contradictory of diffusion limited theory and nucleation theory on uniform plating. This perspective will undoubtedly enhance the understanding on the metal anode plating process and provide meaningful guidance for the development of metal anode batteries.

Fusion Bonding Technique for Solvent-Free Fabrication of All-Solid-State Battery with Ultrathin Sulfide Electrolyte.

For preparing next-generation sulfide all-solid-state batteries (ASSBs), the solvent-free manufacturing process has huge potential for the advantages of economic, thick electrode, and avoidance of organic solvents. However, the dominating solvent-free process is based on the fibrillation of polytetrafluoroethylene, suffering from poor mechanical property and electrochemical instability. Herein, a continuously solvent-free paradigm of fusion bonding technique is developed. A percolation network of thermoplastic polyamide (TPA) binder with low viscosity in viscous state is constructed with Li6PS5Cl (LPSC) by thermocompression (≤5 MPa), facilitating the formation of ultrathin LPSC film (≤25 µm). This composite sulfide film (CSF) exhibits excellent mechanical properties, ionic conductivity (2.1 mS cm-1), and unique stress-dissipation to promote interface stabilization. Thick LiNi0.83Co0.11Mn0.06O2 cathode can be prepared by this solvent-free method and tightly adhered to CSF by interfacial fusion of TPA for integrated battery. This integrated ASSB shows high-energy-density feasibility (>2.5 mAh cm-2 after 1400 cycles of 9200 h and run for more than 10 000 h), and energy density of 390 Wh kg-1 and 1020 Wh L-1. More specially, high-voltage bipolar cell (≥8.5 V) and bulk-type pouch cell (326 Wh kg-1) are facilely assembled with good cycling performance. This work inspires commercialization of ASSBs by a solvent-free method and provides beneficial guiding for stable batteries.

Understanding the Cathode-Electrolyte Interfacial Chemistry in Rechargeable Magnesium Batteries.

Rechargeable magnesium batteries (RMBs) have garnered significant attention due to their potential to provide high energy density, utilize earth-abundant raw materials, and employ metal anode safely. Currently, the lack of applicable cathode materials has become one of the bottleneck issues for fully exploiting the technological advantages of RMBs. Recent studies on Mg cathodes reveal divergent storage performance depending on the electrolyte formulation, posing interfacial issues as a previously overlooked challenge. This minireview begins with an introduction of representative cathode-electrolyte interfacial phenomena in RMBs, elaborating on the unique solvation behavior of Mg2+, which lays the foundation for interfacial chemistries. It is followed by presenting recently developed strategies targeting the promotion of Mg2+ desolvation in the electrolyte and alternative cointercalation approaches to circumvent the desolvation step. In addition, efforts to enhance the cathode-electrolyte compatibility via electrolyte development and interfacial engineering are highlighted. Based on the abovementioned discussions, this minireview finally puts forward perspectives and challenges on the establishment of a stable interface and fast interfacial chemistry for RMBs.

Deciphering the Lithium-Ion Conduction Mechanism of LiH in Solid-Electrolyte Interphase.

Lithium hydride (LiH) has been widely recognized as the critical component of the solid-electrolyte interphase (SEI) in Li batteries. Although the formation mechanism and structural model of LiH in SEI have been extensively reported, the role in electro-performance of LiH in SEI is still ambiguous and has proven challenging to explored due to the complicated structure SEI and the lack of advanced in situ experimental technology. In this study, the isotopic exchange experiments combined with isotopic tracer experiments is applied to solidly illustrate the superior conductivity and Li+ conduction behavior of the LiH in natural SEI. Importantly, in situ transmission electron microscopy analysis is utilized to visualize the self-electrochemical decomposition of LiH, which is significantly distinctive from LiF and Li2O. The critical experimental evidence discovered by the work demonstrates ion transport behaviors of key components in the SEI, which is imperative for designing novel SEI and augurs a new area in optimizing the performance of lithium batteries.