Suspension electrolyte with modified Li+ solvation environment for lithium metal batteries

Superior Li+ Kinetics by "Low-Activity-Solvent" Engineering for Stable Lithium Metal Batteries

The structure of solvated Li+ has a significant influence on the electrolyte/electrode interphase (EEI) components and desolvation energy barrier, which are two key factors in determining the Li+ diffusion kinetics in lithium metal batteries. Herein, the "solvent activity" concept is proposed to quantitatively describe the correlation between the electrolyte elements and the structure of solvated Li+. Through fitting the correlation of the electrode potential and solvent concentration, we suggest a "low-activity-solvent" electrolyte (LASE) system for deriving a stable inorganic-rich EEI. Nano LiF particles, as a model, were used to capture free solvent molecules for the formation of a LASE system. This advanced LASE not only exhibits outstanding antidendrite growth behavior but also delivers an impressive performance in Li/LiNi0.8Co0.1Mn0.1O2 cells (a capacity of 169 mAh g-1 after 250 cycles at 0.5 C).

Extended Battery Compatibility Consideration from an Electrolyte Perspective

The performance of electrochemical batteries is intricately tied to the physicochemical environments established by their employed electrolytes. Traditional battery designs utilizing a single electrolyte often impose identical anodic and cathodic redox conditions, limiting the ability to optimize redox environments for both anode and cathode materials. Consequently, advancements in electrolyte technologies are pivotal for addressing these challenges and fostering the development of next-generation high-performance electrochemical batteries. This review categorizes perspectives on electrolyte technology into three key areas: additives engineering, comprehensive component analysis encompassing solvents and solutes, and the effects of concentration. By summarizing significant studies, the efficacy of electrolyte engineering is highlighted, and the review advocates for further exploration of optimized component combinations. This review primarily focuses on liquid electrolyte technologies, briefly touching upon solid-state electrolytes due to the former greater vulnerability to electrode and electrolyte interfacial effects. The ultimate goal is to generate increased awareness within the battery community regarding the holistic improvement of battery components through optimized combinations.

12.6 μm-Thick Asymmetric Composite Electrolyte with Superior Interfacial Stability for Solid-State Lithium-Metal Batteries

Solid-state lithium metal batteries (SSLMBs) show great promise in terms of high-energy-density and high-safety performance. However, there is an urgent need to address the compatibility of electrolytes with high-voltage cathodes/Li anodes, and to minimize the electrolyte thickness to achieve high-energy-density of SSLMBs. Herein, we develop an ultrathin (12.6 µm) asymmetric composite solid-state electrolyte with ultralight areal density (1.69 mg cm-2) for SSLMBs. The electrolyte combining a garnet (LLZO) layer and a metal organic framework (MOF) layer, which are fabricated on both sides of the polyethylene (PE) separator separately by tape casting. The PE separator endows the electrolyte with flexibility and excellent mechanical properties. The LLZO layer on the cathode side ensures high chemical stability at high voltage. The MOF layer on the anode side achieves a stable electric field and uniform Li flux, thus promoting uniform Li+ deposition. Thanks to the well-designed structure, the Li symmetric battery exhibits an ultralong cycle life (5000 h), and high-voltage SSLMBs achieve stable cycle performance. The assembled pouch cells provided a gravimetric/volume energy density of 344.0 Wh kg-1/773.1 Wh L-1. This simple operation allows for large-scale preparation, and the design concept of ultrathin asymmetric structure also reveals the future development direction of SSLMBs.

Solvation-Tailored PVDF-Based Solid-State Electrolyte for High-Voltage Lithium Metal Batteries

Poly(vinylidene fluoride) (PVDF)-based polymer electro-lytes are attracting increasing attention for high-voltage solid-state lithium metal batteries because of their high room temperature ionic conductivity, adequate mechanical strength and good thermal stability. However, the presence of highly reactive residual solvents, such as N, N-dimethylformamide (DMF), severely jeopardizes the long-term cycling stability. Herein, we propose a solvation-tailoring strategy to confine residual solvent molecules by introducing low-cost 3 Å zeolite molecular sieves as fillers. The strong interaction between DMF and the molecular sieve weakens the ability of DMF to participate in the solvation of Li+, leading to more anions being involved in solvation. Benefiting from the tailored anion-rich coordination environment, the interfacial side reactions with the lithium anode and high-voltage NCM811 cathode are effectively suppressed. As a result, the solid-state Li||Li symmetrical cells demonstrates ultra-stable cycling over 5100 h at 0.1 mA cm-2, and the Li||NCM811 full cells achieve excellent cycling stability for more than 1130 and 250 cycles under the charging cut-off voltages of 4.3 V and 4.5 V, respectively. Our work is an innovative exploration to address the negative effects of residual DMF in PVDF-based solid-state electrolytes and highlights the importance of modulating the solvation structures in solid-state polymer electrolytes.

Bipolar Polymeric Protective Layer for Dendrite-Free and Corrosion-Resistant Lithium Metal Anode in Ethylene Carbonate Electrolyte

The unstable interface between Li metal and ethylene carbonate (EC)-based electrolytes triggers continuous side reactions and uncontrolled dendrite growth, significantly impacting the lifespan of Li metal batteries (LMBs). Herein, a bipolar polymeric protective layer (BPPL) is developed using cyanoethyl (-CH2CH2C≡N) and hydroxyl (-OH) polar groups, aiming to prevent EC-induced corrosion and facilitating rapid, uniform Li+ ion transport. Hydrogen-bonding interactions between -OH and EC facilitates the Li+ desolvation process and effectively traps free EC molecules, thereby eliminating parasitic reactions. Meanwhile, the -CH2CH2C≡N group anchors TFSI- anions through ion-dipole interactions, enhancing Li+ transport and eliminating concentration polarization, ultimately suppressing the growth of Li dendrite. This BPPL enabling Li|Li cell stable cycling over 750 cycles at 10 mA cm-2 for 2 mAh cm-2. The Li|LiNi0.8Mn0.1Co0.1O2 and Li|LiFePO4 full cells display superior electrochemical performance. The BPPL provides a practical strategy to enhanced stability and performance in LMBs application.

Recent Advances and Opportunities in Reactivating Inactive Lithium in Batteries

The loss of active materials is one of the main culprits of the battery failures. As a typical example, the presence of inactive lithium, also known as "dead lithium", contributes to the rapid capacity deterioration and reduces energy output in lithium batteries. This phenomenon has long been recognized as irreversible. In this Minireview, the first of this kind, we aim to summarize the formation of inactive lithium and reassess its impact on battery performance metrics. Additionally, we explore various strategies that have been devised to rejuvenate inactive lithium. This comprehensive overview of the latest advancements in reactivating inactive lithium not only offers insights into restoring capacity and enhancing battery performance metrics but also provides a foundation for future research in reviving other inactive materials found in next-generation batteries, such as lithium metal batteries, lithium-sulfur batteries, other alkali metal batteries, and liquid flow batteries.

Deshielding Anions Enable Solvation Chemistry Control of LiPF6-Based Electrolyte toward Low-Temperature Lithium-Ion Batteries

Severe capacity decay under subzero temperatures remains a significant challenge for lithium-ion batteries (LIBs) due to the sluggish interfacial kinetics. Current efforts to mitigate this deteriorating interfacial behavior rely on high-solubility lithium salts (e.g., Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Lithium bis(fluorosulfonyl)imide (LiFSI))-based electrolytes to construct anion participated solvation structures. However, such electrolytes bring issues of corrosion on the current collector and increased costs. Herein, the most commonly used Lithium hexafluorophosphate (LiPF6) instead, to establish a peculiar solvation structure with a high ratio of ion pairs and aggregates by introducing a deshielding NO3 - additive for low-temperature LIBs is utilized. The deshielding anion significantly reduces the energy barrier for interfacial behavior at low temperatures. Benefiting from this, the graphite (Gr) anode retains a high capacity of ≈72.3% at -20 °C, which is far superior to the 32.3% and 19.4% capacity retention of counterpart electrolytes. Moreover, the LiCoO2/Gr full cell exhibits a stable cycling performance of 100 cycles at -20 °C due to the inhibited lithium plating. This work heralds a new paradigm in LiPF6-based electrolyte design for LIBs operating at subzero temperatures.

Enabling Stable and Low-Strain Lithium Plating/Stripping with 2D Layered Transition Metal Carbides by Forming Li-Zipped MXenes and a Li Halide-Rich Solid Electrolyte Interphase

Two-dimensional (2D) layered materials demonstrate prominent advantage in regulating lithium plating/stripping behavior by confining lithium diffusion/plating within interlayer gaps. However, achieving effective interlayer confined lithium diffusion/plating without compromising the stability of bulk-structural and the solid electrolyte interphase (SEI) remains a considerable challenge. This paper presents an electrochemical scissor and lithium zipper-driven protocol for realizing interlayer confined lithium plating with pretty-low strain and volume change. In this protocol, lithium serves as a "zipper" to reunite the adjacent MXene back to MAX-like phase to markedly enhance the structural stability, and a lithium halide-rich SEI is formed by electrochemically removing the terminals of halogenated MXenes to maintain the stability and rapid lithium ions diffusion of SEI. When the Ti3 C2 I2 serves as the host for lithium plating, the average coulomb efficiency exceeds 97.0 % after 320 lithium plating/stripping cycles in conventional ester electrolyte. Furthermore, a full cell comprising of LiNi0.8 Mn0.1 Co0.1 O2 and Ti3 C2 I2 @Li exhibits a capacity retention rate of 73.4 % after 200 cycles even under high cathode mass-loading (20 mg cm-2 ) and a low negative/positive capacity ratio of 1.4. Our findings advance the understanding of interlayer confined lithium plating in 2D layered materials and provide a new direction in regulating lithium and other metal plating/stripping behaviors.

Lithium Metal Anodes: Advancing our Mechanistic Understanding of Cycling Phenomena in Liquid and Solid Electrolytes

Lithium metal anodes have the potential to be a disruptive technology for next-generation batteries with high energy densities, but their electrochemical performance is limited by a lack of fundamental understanding into the mechanistic origins that underpin their poor reversibility, morphological evolution (including dendrite growth), and interfacial instability. The goal of this perspective is to summarize the current state-of-the-art understanding of these phenomena, and highlight knowledge gaps where additional research is needed. The various stages of cycling are described sequentially, including nucleation, growth, open-circuit rest periods, and electrodissolution (stripping). A direct comparison of lessons learned from liquid and solid-state electrolyte systems is made throughout the discussion, providing cross-cutting insights between these research communities. Major themes of the discussion include electro-chemo-mechanical coupling, insights from in situ/operando analysis, and the interplay between experimental observations and computational modeling. Finally, a series of fundamental research questions are proposed to identify critical knowledge gaps and inform future research directions.

Interfacial solvation-structure regulation for stable Li metal anode by a desolvation coating technique

Rechargeable lithium (Li) metal batteries face challenges in achieving stable cycling due to the instability of the solid electrolyte interphase (SEI). The Li-ion solvation structure and its desolvation process are crucial for the formation of a stable SEI on Li metal anodes and improving Li plating/stripping kinetics. This research introduces an interfacial desolvation coating technique to actively modulate the Li-ion solvation structure at the Li metal interface and regulate the participation of the electrolyte solvent in SEI formation. Through experimental investigations conducted using a carbonate electrolyte with limited compatibility to Li metal, the optimized desolvation coating layer, composed of 12-crown-4 ether-modified silica materials, selectively displaces strongly coordinating solvents while simultaneously enriching weakly coordinating fluorinated solvents at the Li metal/electrolyte interface. This selective desolvation and enrichment effect reduce solvent participation to SEI and thus facilitate the formation of a LiF-dominant SEI with greatly reduced organic species on the Li metal surface, as conclusively verified through various characterization techniques including XPS, quantitative NMR, operando NMR, cryo-TEM, EELS, and EDS. The interfacial desolvation coating technique enables excellent rate cycling stability (i.e., 1C) of the Li metal anode and prolonged cycling life of the Li||LiCoO2 pouch cell in the conventional carbonate electrolyte (E/C 2.6 g/Ah), with 80% capacity retention after 333 cycles.

Self-Induced Dual-Layered Solid Electrolyte Interphase with High Toughness and High Ionic Conductivity for Ultra-Stable Lithium Metal Batteries

Lithium (Li) metal is considered as one of the most promising candidates of anode material for high-specific-energy batteries, while irreversible chemical reactions always occur on the Li surface to continuously consume active Li, electrolyte. Solid electrolyte interphase (SEI) layer has been regarded as the key component in protecting Li metal anode. Herein, a controllable dual-layered SEI for Li metal anode in a scalable, low-loss manner is constructed. The SEI is self-induced by the predeposited LiAlO2 (LAO) layer during the initial cycles, in which the outer organic layer is produced due to the electrons tunneling through LAO, resulting in the reduction of electrolyte. The robust inner LAO layer can promote uniform Li deposition owing to its favorable mechanical strength and ionic conductivity, and the outer organic layer can further improve the stability of SEI. Benefiting from the remarkable effects of this dual-layered SEI, enhanced electrochemical performance of the LAO-Li anode is achieved. Additionally, a large-size LAO-Li sample can be easily obtained, and the preparation of the modified Li metal anode shows huge potential for large-scale production. This work highlights the tremendous potential of this self-induced dual-layered SEI for the commercialization of Li metal anode.

Potassium-Based Dual-Ion Batteries Operating at -60 °C Enabled By Co-Intercalation Anode Chemistry

Battery performance at subzero is restricted by sluggish interfacial kinetics. To resolve this issue, potassium-based dual-ion batteries (K-DIBs) based on the polytriphenylamine (PTPAn) cathode with anion storage chemistry and the hydrogen titanate (HTO) anode with K+ /solvent co-intercalation mechanism are constructed. Both the PTPAn cathode and the HTO anode do not undergo the desolvation process, which can effectively accelerate the interfacial kinetics at subzero. As revealed by theoretical calculations and experimental analysis, the strong K+ /solvent binding energy in the dilute electrolyte, the charge shielding effect of the crystal water, and the uniform SEI layer with high content of the flexible organic species synergically promote HTO to undergo K+ /solvent co-intercalation behavior. The special co-intercalation mechanism and anion storage chemistry enable HTO||PTPAn K-DIBs with superior rate performance and cycle durability, maintaining a capacity retention of 94.1% after 6000 cycles at -40 °C and 91% after 1000 cycles at -60 °C. These results provide a step forward for achieving high-performance energy storage devices at low temperatures.

Origin of Li+ Solvation Ability of Electrolyte Solvent: Ring Strain

Developing new organic solvents to support the use of Li metal anodes in secondary batteries is an area of great interest. In particular, research is actively underway to improve battery performance by introducing fluorine to ether solvents, as these are highly compatible with Li metal anodes because fluorine imparts high oxidative stability and relatively low Li-ion solvation ability. However, theoretical analysis of the solvation ability of organic solvents mostly focuses on the electron-withdrawing capability of fluorine. Herein, we analyze the effect of the structural characteristics of solvents on their Li+ ion solvation ability from a computational chemistry perspective. We reveal that the structural constraints imposed on the oxygen binding sites in solvent molecules vary depending on the structural characteristics of the N-membered ring formed by the interaction between the organic solvent and Li+ ions and the internal ring containing the oxygen binding sites. We demonstrate that the structural strain of the organic solvents has a comparable effect on Li+ solvation ability seen for the electrical properties of fluorine elements. This work emphasizes the importance of understanding the structural characteristics and strain when attempting to understand the interactions between solvents and metal cations and effectively control the solvation ability of solvents.

Dry-Processable Polymer Electrolytes for Solid Manufactured Batteries

Designing a solid-state electrolyte that satisfies the operating requirements of solid-state batteries is key to solid-state battery applications. The consensus is that solid-state electrolytes need to allow fast ion transport, while providing better interfacial compatibility and mechanical tolerance. Herein, a simple but effective strategy is proposed, combining hard and soft component polymer systems, to exploit a solid polymer electrolyte (SPE) with a 3D network via an in situ graft polymerization. The 3D structure is constructed by a hard cellulose nanocrystal (CNC) as the skeleton and a soft polyacrylonitrile (PAN) as the filler through a dry-processing method. The reported systems have several advantages, including ease of processing, only requiring using an exceedingly small amount of solvent, light weight (ρ = 1.2 g cm-3), excellent mechanical stability (tensile strength of 9.5 MPa), and high ionic conductivity (3.9 × 10-4 S cm-1, 18 °C) and migration number (tLi+ = 0.8). In particular, the high conductivity is enabled: the efficient Li+ transportation path constructed between CNC-PAN powders and abundant sulfonate radicals and hydroxyl groups on the CNC surface acts as the bridge of Li+ transition. When the CNCs are grafted onto the PAN polymer, the dipole-dipole interaction between the nitrile groups of the PAN and the hydroxyl groups of the CNCs can help to improve the mechanical stability and ionic conductivity of the SPE. Moreover, a tightly formed interface between SPE and LiFePO4 (LFP)/carbon black/SPE cathode can be achieved in an assembled solid-state battery by hot pressing, thus further enhancing the battery's performance.

Modulating Ionic Transport and Interface Chemistry via Surface-Modified Silica Carrier in Nano Colloid Electrolyte for Stable Cycling of Li-Metal Batteries

Tailoring the Li+ microenvironment is crucial for achieving fast ionic transfer and a mechanically reinforced solid-electrolyte interphase (SEI), which administers the stable cycling of Li-metal batteries (LMBs). Apart from traditional salt/solvent compositional tuning, this study presents the simultaneous modulation of Li+ transport and SEI chemistry using a citric acid (CA)-modified silica-based colloidal electrolyte (C-SCE). CA-tethered silica (CA-SiO2 ) can render more active sites for attracting complex anions, leading to further dissociation of Li+ from the anions, resulting in a high Li+ transference number (≈0.75). Intermolecular hydrogen bonds between solvent molecules and CA-SiO2 and their migration also act as nano-carrier for delivering additives and anions toward the Li surface, reinforcing the SEI via the co-implantation of SiO2 and fluorinated components. Notably, C-SCE demonstrated Li dendrite suppression and improved cycling stability of LMBs compared with the CA-free SiO2 colloidal electrolyte, hinting that the surface properties of the nanoparticles have a huge impact on the dendrite-inhibiting role of nano colloidal electrolytes.

Long-Life Quasi-Solid-State Anode-Free Batteries Enabled by Li Compensation Coupled Interface Engineering

Initially, anode-free Li metal batteries present a promising power source that merges the high production feasibility of Li-ion batteries with the superb energy capabilities of Li-metal batteries. However, their application confronts formidable challenges of extremely short lifespan due to the inadequacy of zero-Li-excess cell configuration against irreversible Li loss. A Li compensation coupled interface engineering strategy is reported for realizing long-life quasi-solid-state anode-free batteries. The Li2 S is utilized as a sacrificial Li supplement to effectively counterbalance irreversible Li loss without damage to cell chemistry. Meanwhile, it demonstrates remarkable efficacy in establishing a robust yet slender inorganic-organic hybrid solid-state interphase for inhibiting cell degradation by dead and dendritic Li. This strategy enables quasi-solid-state anode-free batteries with a long lifespan of 500 cycles. The Ah-scale quasi-solid-state pouch cells, featuring a high-loading LiFePO4 cathode and lean gel polymer electrolyte, exhibit a high specific energy of 300 Wh kgcell -1 . This achievement translates into an improvement of 46% in gravimetric energy and 94% in volumetric energy compared to LiFePO4 ||graphite batteries while outperforming LiFePO4 ||Li-metal batteries by 22-47% in volumetric energy. Such quasi-solid-state anode-free cells also demonstrate good safety, showcasing remarkable resistance against nail penetration in ambient air without failure, smoke, or fire accidents.

Low-temperature anode-free potassium metal batteries

In contrast to conventional batteries, anode-free configurations can extend cell-level energy densities closer to the theoretical limit. However, realizing alkali metal plating/stripping on a bare current collector with high reversibility is challenging, especially at low temperature, as an unstable solid-electrolyte interphase and uncontrolled dendrite growth occur more easily. Here, a low-temperature anode-free potassium (K) metal non-aqueous battery is reported. By introducing Si-O-based additives, namely polydimethylsiloxane, in a weak-solvation low-concentration electrolyte of 0.4 M potassium hexafluorophosphate in 1,2-dimethoxyethane, the in situ formed potassiophilic interface enables uniform K deposition, and offers K||Cu cells with an average K plating/stripping Coulombic efficiency of 99.80% at -40 °C. Consequently, anode-free Cu||prepotassiated 3,4,9,10-perylene-tetracarboxylicacid-dianhydride full batteries achieve stable cycling with a high specific energy of 152 Wh kg-1 based on the total mass of the negative and positive electrodes at 0.2 C (26 mA g-1) charge/discharge and -40 °C.

A Radical Pathway and Stabilized Li Anode Enabled by Halide Quaternary Ammonium Electrolyte Additives for Lithium-Sulfur Batteries

Passivation of the sulfur cathode by insulating lithium sulfide restricts the reversibility and sulfur utilization of Li-S batteries. 3D nucleation of Li2 S enabled by radical conversion may significantly boost the redox kinetics. Electrolytes with high donor number (DN) solvents allow for tri-sulfur (S3 ⋅- ) radicals as intermediates, however, the catastrophic reactivity of such solvents with Li anodes pose a great challenge for their practical application. Here, we propose the use of quaternary ammonium salts as electrolyte additives, which can preserve the partial high-DN characteristics that trigger the S3 ⋅- radical pathway, and inhibit the growth of Li dendrites. Li-S batteries with tetrapropylammonium bromide (T3Br) electrolyte additive deliver the outstanding cycling stability (700 cycles at 1 C with a low-capacity decay rate of 0.049 % per cycle), and high capacity under a lean electrolyte of 5 μLelectrolyte  mgsulfur -1 . This work opens a new avenue for the development of electrolyte additives for Li-S batteries.

Fluorinated Carbamate-Based Electrolyte Enables Anion-Dominated Solid Electrolyte Interphase for Highly Reversible Li Metal Anode

Li metal is regarded as the most promising battery anode to boost energy density. However, being faced with the hostile compatibility between the Li anode and traditional carbonate electrolyte, its large-scale industrialization has been in a distressing circumstance due to severe dendrite growth caused by unsatisfying solid electrolyte interphase (SEI). With this regard, accurate control over the composition of the SEI is urgently desired to tackle the electrochemical and mechanical instability at the electrolyte/anode interface. Herein, we report a rationally designed fluorinated carbamate-based electrolyte employing LiNO3 as one of the main salts to induce the preferable anion decomposition to achieve a homogeneous and inorganic (LiF, Li3N, Li2O)-rich SEI. Thus, this electrolyte achieves a high Coulombic efficiency of 99% of the Li metal anode, a stable cycling over 1000 h for Li|Li symmetric cells, more than 100 cycles in 40-μm-thin Li|high-loading-NCM811 full batteries, and >50 cycles in Cu|LiFePO4 pouch cells, which is a promising electrolyte for highly reversible Li metal batteries.

Mechano-Electrochemically Promoting Lithium Atom Diffusion and Relieving Accumulative Stress for Deep-Cycling Lithium Metal Anodes

Lithium metal batteries (LMBs) can double the energy density of lithium-ion batteries. However, the notorious lithium dendrite growth and large volume change are not well addressed, especially under deep cycling. Here, an in-situ mechanical-electrochemical coupling system is built, and it is found that tensile stress can induce smooth lithium deposition. Density functional theory (DFT) calculation and finite element method (FEM) simulation confirm that the lithium atom diffusion energy barrier can be reduced when the lithium foils are under tensile strain. Then tensile stress is incorporated into lithium metal anodes by designing an adhesive copolymer layer attached to lithium in which the copolymer thinning can yield tensile stress to the lithium foil. Elastic lithium metal anode (ELMA) is further prepared via introducing a 3D elastic conductive polyurethane (CPU) host for the copolymer-lithium bilayer to release accumulated internal stresses and resist volume variation. The ELMA can withstand hundreds of compression-release cycles under 10% strain. LMBs paired with ELMA and LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) cathode can operate beyond 250 cycles with 80% capacity retention under practical condition of 4 mAh cm-2 cathode capacity, 2.86 g Ah-1 electrolyte-to-capacity ratio (E/C) and 1.8 negative-to-cathode capacity ratio (N/P), five times of the lifetime using lithium foils.

A host potassiophilicity strategy for unprecedentedly stable and safe K metal batteries

Creating high-performance host materials for potassium (K) metal anodes remains a significant challenge due to the complex preparation process and poor K reversibility. In our work, we developed a potassiophilicity strategy using an oxygen-modified carbon cloth (O-CC) network as a host for K metal anodes. The O-CC network exhibited superior potassiophilic ability, and this improvement was also observed in other carbon hosts using the same process. The oxygen-induced epoxy group in the carbon network regulates interface electrons and enables strong binding of K adatoms through orbital hybridization, resulting in fewer side reactions with the electrolyte and promoting K-ion desolvation and uniform deposition. These factors result in unprecedented stability of the carbon network host, with a long lifespan of over 5500 hours at 0.5 mA cm-2/0.5 mA h cm-2 and 3500 h at 1 mA cm-2/0.5 mA h cm-2 in symmetric cells for K metal anodes, surpassing the cycle life of all previously reported K metal anodes. Furthermore, a high average coulombic efficiency of over 99.3% is demonstrated in O-CC//K cells during 210 cycles. The O-CC also exhibited a stable electrochemical performance, with a capacity retention of 73.3% in full cells coupled with a perylene-3,4,9,10-tetracarboxylic dianhydride cathode. We believe that this new strategy holds great promise for metal anodes in battery applications.

Supramolecular Polymer Ion Conductor with Weakened Li Ion Solvation Enables Room Temperature All-Solid-State Lithium Metal Batteries

Improved durability, enhanced interfacial stability, and room temperature applicability are desirable properties for all-solid-state lithium metal batteries (ASSLMBs), yet these desired properties are rarely achieved simultaneously. Here, in this work, it is noticed that the huge resistance at Li metal/electrolyte interface dominantly impeded the normal cycling of ASSLMBs especially at around room temperature (<30 °C). Accordingly, a supramolecular polymer ion conductor (SPC) with "weak solvation" of Li+ was prepared. Benefiting from the halogen-bonding interaction between the electron-deficient iodine atom (on 1,4-diiodotetrafluorobenzene) and electron-rich oxygen atoms (on ethylene oxide), the O-Li+ coordination was significantly weakened. Therefore, the SPC achieves rapid Li+ transport with high Li+ transference number, and importantly, derives a unique Li2 O-rich SEI with low interfacial resistance on lithium metal surface, therefore enabling stable cycling of ASSLMBs even down to 10 °C. This work is a new exploration of halogen-bonding chemistry in solid polymer electrolyte and highlights the importance of "weak solvation" of Li+ in the solid-state electrolyte for room temperature ASSLMBs.

Proximity Matters: Interfacial Solvation Dictates Solid Electrolyte Interphase Composition

The composition of the solid electrolyte interphase (SEI) plays an important role in controlling Li-electrolyte reactions, but the underlying cause of SEI composition differences between electrolytes remains unclear. Many studies correlate SEI composition with the bulk solvation of Li ions in the electrolyte, but this correlation does not fully capture the interfacial phenomenon of SEI formation. Here, we provide a direct connection between SEI composition and Li-ion solvation by forming SEIs using polar substrates that modify interfacial solvation structures. We circumvent the deposition of Li metal by forming the SEI above Li+/Li redox potential. Using theory, we show that an increase in the probability density of anions near a polar substrate increases anion incorporation within the SEI, providing a direct correlation between interfacial solvation and SEI composition. Finally, we use this concept to form stable anion-rich SEIs, resulting in high performance lithium metal batteries.

Integrated Gradient Cu Current Collector Enables Bottom-Up Li Growth for Li Metal Anodes: Role of Interfacial Structure

3D Cu current collectors have been demonstrated to improve the cycling stability of Li metal anodes, however, the role of their interfacial structure for Li deposition pattern has not been investigated thoroughly. Herein, a series of 3D integrated gradient Cu-based current collectors are fabricated by the electrochemical growth of CuO nanowire arrays on Cu foil (CuO@Cu), where their interfacial structures can be readily controlled by modulating the dispersities of the nanowire arrays. It is found that the interfacial structures constructed by sparse and dense dispersion of CuO nanowire arrays are both disadvantageous for the nucleation and deposition of Li metal, consequently fast dendrite growth. In contrast, a uniform and appropriate dispersity of CuO nanowire arrays enables stable bottom Li nucleation associated with smooth lateral deposition, affording the ideal bottom-up Li growth pattern. The optimized CuO@Cu-Li electrodes exhibit a highly reversible Li cycling including a coulombic efficiency of up to ≈99% after 150 cycles and a long-term lifespan of over 1200 h. When coupling with LiFePO4 cathode, the coin and pouch full-cells deliver outstanding cycling stability and rate capability. This work provides a new insight to design the gradient Cu current collectors toward high-performance Li metal anodes.

Electrolytes with moderate lithium polysulfide solubility for high-performance long-calendar-life lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with high energy density and low cost are promising for next-generation energy storage. However, their cycling stability is plagued by the high solubility of lithium polysulfide (LiPS) intermediates, causing fast capacity decay and severe self-discharge. Exploring electrolytes with low LiPS solubility has shown promising results toward addressing these challenges. However, here, we report that electrolytes with moderate LiPS solubility are more effective for simultaneously limiting the shuttling effect and achieving good Li-S reaction kinetics. We explored a range of solubility from 37 to 1,100 mM (based on S atom, [S]) and found that a moderate solubility from 50 to 200 mM [S] performed the best. Using a series of electrolyte solvents with various degrees of fluorination, we formulated the Single-Solvent, Single-Salt, Standard Salt concentration with Moderate LiPSs solubility Electrolytes (termed S6MILE) for Li-S batteries. Among the designed electrolytes, Li-S cells using fluorinated-1,2-diethoxyethane S6MILE (F4DEE-S6MILE) showed the highest capacity of 1,160 mAh g-1 at 0.05 C at room temperature. At 60 °C, fluorinated-1,4-dimethoxybutane S6MILE (F4DMB-S6MILE) gave the highest capacity of 1,526 mAh g-1 at 0.05 C and an average CE of 99.89% for 150 cycles at 0.2 C under lean electrolyte conditions. This is a fivefold increase in cycle life compared with other conventional ether-based electrolytes. Moreover, we observed a long calendar aging life, with a capacity increase/recovery of 4.3% after resting for 30 d using F4DMB-S6MILE. Furthermore, the correlation between LiPS solubility, degree of fluorination of the electrolyte solvent, and battery performance was systematically investigated.

Radiation effects on lithium metal batteries

The radiation tolerance of energy storage batteries is a crucial index for universe exploration or nuclear rescue work, but there is no thorough investigation of Li metal batteries. Here, we systematically explore the energy storage behavior of Li metal batteries under gamma rays. Degradation of the performance of Li metal batteries under gamma radiation is linked to the active materials of the cathode, electrolyte, binder, and electrode interface. Specifically, gamma radiation triggers cation mixing in the cathode active material, which results in poor polarization and capacity. Ionization of solvent molecules in the electrolyte promotes decomposition of LiPF₆ along with its decomposition, and molecule chain breaking and cross-linking weaken the bonding ability of the binder, causing electrode cracking and reduced active material utilization. Additionally, deterioration of the electrode interface accelerates degradation of the Li metal anode and increases cell polarization, hastening the demise of Li metal batteries even more. This work provides significant theoretical and technical evidence for development of Li batteries in radiation environments.

Production of high-energy 6-Ah-level Li | |LiNi0.83Co0.11Mn0.06O2 multi-layer pouch cells via negative electrode protective layer coating strategy

Stable lithium metal negative electrodes are desirable to produce high-energy batteries. However, when practical testing conditions are applied, lithium metal is unstable during battery cycling. Here, we propose poly(2-hydroxyethyl acrylate-co-sodium benzenesulfonate) (PHS) as negative electrode protective layer. The PHS contains soft poly (2-hydroxyethyl acrylate) and poly(sodium p-styrene sulfonate), which improve electrode flexibility, connection with the Cu current collector and transport of Li ions. Transmission electron cryomicroscopy measurements reveal that PHS induces the formation of a solid electrolyte interphase with a fluorinated rigid and crystalline internal structure. Furthermore, theoretical calculations suggest that the -SO₃^- group of poly(sodium p-styrene sulfonate) promotes Li-ion motion towards interchain migration through cation-dipole interaction, thus, enabling uniform Li-ion diffusion. Electrochemical measurements of Li | |PHS-coated-Cu coin cells demonstrate an average Coulombic efficiency of 99.46% at 1 mA/cm², 6 mAh/cm² and 25 °C. Moreover, when the PHS-coated Li metal negative electrode is paired with a high-areal-capacity LiNi_0.83Co_0.11Mn_0.06O₂-based positive electrode in multi-layer pouch cell configuration, the battery delivers an initial capacity of 6.86 Ah (corresponding to a specific energy of 489.7 Wh/kg) and, a 91.1% discharge capacity retention after 150 cycles at 2.5 mA/cm², 25 °C and 172 kPa.

Origin of dendrite-free lithium deposition in concentrated electrolytes

The electrolyte solvation structure and the solid-electrolyte interphase (SEI) formation are critical to dictate the morphology of lithium deposition in organic electrolytes. However, the link between the electrolyte solvation structure and SEI composition and its implications on lithium morphology evolution are poorly understood. Herein, we use a single-salt and single-solvent model electrolyte system to systematically study the correlation between the electrolyte solvation structure, SEI formation process and lithium deposition morphology. The mechanism of lithium deposition is thoroughly investigated using cryo-electron microscopy characterizations and computational simulations. It is observed that, in the high concentration electrolytes, concentrated Li⁺ and anion-dominated solvation structure initiate the uniform Li nucleation kinetically and favor the decomposition of anions rather than solvents, resulting in inorganic-rich amorphous SEI with high interface energy, which thermodynamically facilitates the formation of granular Li. On the contrary, solvent-dominated solvation structure in the low concentration electrolytes tends to exacerbate the solvolysis process, forming organic-rich mosaic SEI with low interface energy, which leads to aggregated whisker-like nucleation and growth. These results are helpful to tackle the long-standing question on the origin of lithium dendrite formation and guide the rational design of high-performance electrolytes for advanced lithium metal batteries.

Lithiophilic Magnetic Host Facilitates Target-Deposited Lithium for Practical Lithium-Metal Batteries

Lithium-metal shows promising prospects in constructing various high-energy-density lithium-metal batteries (LMBs) while long-lasting tricky issues including the uncontrolled dendritic lithium growth and infinite lithium volume expansion seriously impede the application of LMBs. In this work, it is originally found that a unique lithiophilic magnetic host matrix (Co₃ O₄ -CCNFs) can simultaneously eliminate the uncontrolled dendritic lithium growth and huge lithium volume expansion that commonly occur in typical LMBs. The magnetic Co₃ O₄ nanocrystals which inherently embed on the host matrix act as nucleation sites and can also induce micromagnetic field and facilitate a targeted and ordered lithium deposition behavior thus, eliminating the formation of dendritic Li. Meanwhile, the conductive host can effectively homogenize the current distribution and Li-ion flux, thus, further relieving the volume expansion during cycling. Benefiting from this, the featured electrodes demonstrate ultra-high coulombic efficiency of 99.1% under 1 mA cm^-2 and 1 mAh cm^-2 . Symmetric cell under limited Li (10 mAh cm^-2 ) inspiringly delivers ultralong cycle life of 1600 h (under 2 mA cm^-2 , 1 mAh cm^-2 ). Moreover, LiFePO₄ ||Co₃ O₄ -CCNFs@Li full-cell under practical condition of limited negative/positive capacity ratio (2.3:1) can deliver remarkably improved cycling stability (with 86.6% capacity retention over 440 cycles).

Tuning the Li+ Solvation Structure by a "Bulky Coordinating" Strategy Enables Nonflammable Electrolyte for Ultrahigh Voltage Lithium Metal Batteries

In battery electrolyte design principles, tuning Li⁺ solvation structure is an effective way to connect electrolyte chemistry with interfacial chemistry. Although recent proposed solvation tuning strategies are able to improve battery cyclability, a comprehensive strategy for electrolyte design remains imperative. Here, we report a solvation tuning strategy by utilizing molecular steric effect to create a "bulky coordinating" structure. Based on this strategy, the designed electrolyte generates an inorganic-rich solid electrolyte interphase (SEI) and cathode-electrolyte interphase (CEI), leading to excellent compatibility with both Li metal anodes and high-voltage cathodes. Under an ultrahigh voltage of 4.6 V, Li/NMC811 full-cells (N/P = 2.0) hold an 84.1% capacity retention over 150 cycles and industrial Li/NMC811 pouch cells realize an energy density of 495 Wh kg^-1. This study provides innovative insights into Li⁺ solvation tuning for electrolyte engineering and offers a promising path toward developing high-energy Li metal batteries.

Design Principles for Fluorinated Interphase Evolution via Conversion-Type Alloying Processes for Anticorrosive Lithium Metal Anodes

Over the past decade, lithium metal has been considered the most attractive anode material for high-energy-density batteries. However, its practical application has been hindered by its high reactivity with organic electrolytes and uncontrolled dendritic growth, resulting in poor Coulombic efficiency and cycle life. In this paper, we propose a design strategy for interface engineering using a conversion-type reaction of metal fluorides to evolve a LiF passivation layer and Li-M alloy. Particularly, we propose a LiF-modified Li-Mg-C electrode, which demonstrates stable long-term cycling for over 2000 h in common organic electrolytes with fluoroethylene carbonate (FEC) additives and over 700 h even without additives, suppressing unwanted side reactions and Li dendritic growth. With the help of phase diagrams, we found that solid-solution-based alloying not only facilitates the spontaneous evolution of a LiF layer and bulk alloy but also enables reversible Li plating/stripping inward to the bulk, compared with intermetallic compounds with finite Li solubility.

Lithiophilic Interface Layer Induced Uniform Deposition for Dendrite-free Lithium Metal Anodes in a 3D Polyethersulfone Frame

Lithium metal anodes possess ultrahigh theoretical specific capacity for next-generation lithium metal batteries, but the infinite volume expansion and the growth of lithium dendrites remain a huge obstacle to their commercialization. Therefore, here, we construct a CuO-loaded 3D polyethersulfone (PES) nanofiber frame onto a lithiophilic Cu₂O/Cu substrate to promote the lithium storage performance of the composite anode, and the 3D frame can effectively alleviate the volume expansion of lithium (Li) metal anodes. Meanwhile, lithium reacts with CuO in the composite nanofiber and Cu₂O of the substrate to generate Li₂O, which can strengthen the solid electrolyte interface (SEI) layer and achieve the uniform deposition of lithium. In addition, the combination of the heat treatment method and electrospinning technology solves the problem of poor adhesion between the fiber film and the substrate. As a result, the PES/CuO-Cu₂O (PCC) composite current collector still maintains a smooth and flat lithium-depositing layer at 5 mA cm^-2. The PCC-assembled Li||Cu half-cell can operate stably for 320 cycles at 0.5 mA cm^-2, which is about 4 times that of bare Cu. Furthermore, symmetrical batteries with PCC@Li can maintain excellent cycle stability for 1770 h. Accordingly, this work provides a low-cost and highly effective strategy for stabilizing the lithium metal anode.

Self-Assembly Monolayer Inspired Stable Artificial Solid Electrolyte Interphase Design for Next-Generation Lithium Metal Batteries

Lithium metal is widely regarded as the "ultimate" anode for energy-dense Li batteries, but its high reactivity and delicate interface make it prone to dendrite formation, limiting its practical use. Inspired by self-assembled monolayers on metal surfaces, we propose a facile yet effective strategy to stabilize Li metal anodes by creating an artificial solid electrolyte interphase (SEI). Our method involves dip-coating Li metal in MPDMS to create an SEI layer that is rich in inorganic components, allowing uniform Li plating/stripping under a low overpotential over 500 cycles in carbonate electrolytes. In comparison, pristine Li metal shows a rapid increase in overpotential after merely 300 cycles, leading to failure soon after. Molecular dynamics simulations demonstrate that this uniform artificial SEI suppresses Li dendrite formation. We further demonstrated its enhanced stability pairing with LiFePO₄ and LiNi_1-x-yCo_xMn_yO₂ cathodes, highlighting the proposed strategy as a promising solution for practical Li metal batteries.

Enabling 420 Wh kg-1 Stable Lithium-Metal Pouch Cells by Lanthanum Doping

Lithium (Li) metal, a promising anode for high-energy-density rechargeable batteries, typically grows along the low-surface energy (110) plane in the plating process, resulting in uncontrollable dendrite growth and unstable interface. Herein, an unexpected Li growth behavior by lanthanum (La) doping is reported: the preferred orientation turns to (200) from (110) plane, enabling 2D nuclei rather than the usual 1D nuclei upon Li deposition and thus forming a dense and dendrite-free morphology even at an ultrahigh areal capacity of 10 mAh cm^-2 . Noticeably, La doping further decreases the reactivity of Li metal toward electrolytes, thereby establishing a stable interface. The dendrite-free, stable Li anode enables a high average Coulombic efficiency of 99.30% at 8 mAh cm^-2 for asymmetric Li||LaF₃ -Cu cells. A 3.1 Ah LaF₃ -Li||LiNi_0.8 Co_0.1 Mn_0.1 O₂ pouch cell at a high energy density (425.73 Wh kg^-1 ) with impressive cycling stability (0.0989% decay per cycle) under lean electrolyte (1.76 g Ah^-1 ) and high cathode loading (5.77 mAh cm^-2 ) using this doped Li anode is further demonstrated.

Strongly Solvating Ether Electrolytes for High-Voltage Lithium Metal Batteries

Ethers are promising electrolytes for lithium (Li) metal batteries (LMBs) because of their unique stability with Li metal. Although intensive research on designing anion-enriched electrolyte solvation structures has greatly improved their electrochemical stabilities, ether electrolytes are approaching an anodic bottleneck. Herein, we reveal the strong correlation between electrolyte solvation structure and oxidation stability. In contrast to previous designs of weakly solvating solvents for enhanced anion reactivities, the triglyme (G3)-based electrolyte with the largest Li⁺ solvation energy among different linear ethers demonstrates greatly improved stability on Ni-rich cathodes under an ultrahigh voltage of 4.7 V (93% capacity retention after 100 cycles). Ether electrolytes with a stronger Li⁺ solvating ability could greatly suppress deleterious oxidation side reactions by decreasing the lifetime of free labile ether molecules. This study provides critical insights into the dynamics of the solvation structure and its significant influence on the interfacial stability for future development of high-efficiency electrolytes for high-energy-density LMBs.

Advanced Nonflammable Organic Electrolyte Promises Safer Li-Metal Batteries: From Solvation Structure Perspectives

Batteries with a Li-metal anode have recently attracted extensive attention from the battery communities owing to their high energy density. However, severe dendrite growth hinders their practical applications. More seriously, when Li dendrites pierce the separators and trigger short circuit in a highly flammable organic electrolyte, the results would be catastrophic. Although the issues of growth of Li dendrites have been almost addressed by various methods, the highly flammable nature of conventional organic liquid electrolytes is still a lingering fear facing high-energy-density Li-metal batteries given the possibility of thermal runaway of the high-voltage cathode. Recently, various kinds of nonflammable liquid- or solid-state electrolytes have shown great potential toward safer Li-metal batteries with minimal detrimental effect on the battery performance or even enhanced electrochemical performance. In this review, recent advances in developing nonflammable electrolyte for high-energy-density Li-metal batteries including high-concentration electrolyte, localized high-concentration electrolyte, fluorinated electrolyte, ionic liquid electrolyte, and polymer electrolyte are summarized. Then, the solvation structure of different kinds of nonflammable liquid and polymer electrolytes are analyzed to provide insight into the mechanism for dendrite suppression and fire extinguishing. Finally, guidelines for future design of nonflammable electrolyte for safer Li-metal batteries are provided.

Negatively Charged Holey Titania Nanosheets Added Electrolyte to Realize Dendrite-Free Lithium Metal Battery

Electrolyte modulation and electrode structure design are two common strategies to suppress dendrites growth on Li metal anode. In this work, a self-adaptive electrode construction method to suppress Li dendrites growth is reported, which merges the merits of electrolyte modulation and electrode structure design strategies. In detail, negatively charged titania nanosheets with densely packed nanopores on them are prepared. These holey nanosheets in the electrolyte move spontaneously onto the anode under electrical field, building a mesoporous structure on the electrode surface. The as-formed porous electrode has large surface area with good lithiophilicity, which can efficiently transfer lithium ion (Li⁺ ) inside the electrode, and induce the genuine lithium plating/stripping. Moreover, the negative charges and nanopores on the sheets can also regulate the lithium-ion flux to promote uniform deposition of Li metal. As a result, the symmetric and full cells using the holey titania nanosheets containing electrolyte, show much better performance than the ones using electrolyte without holey nanosheets inside. This work points out a new route for the practical applications of Li-metal batteries.

Revealing the Multifunctions of Li3N in the Suspension Electrolyte for Lithium Metal Batteries

Inorganic-rich solid-electrolyte interphases (SEIs) on Li metal anodes improve the electrochemical performance of Li metal batteries (LMBs). Therefore, a fundamental understanding of the roles played by essential inorganic compounds in SEIs is critical to realizing and developing high-performance LMBs. Among the prevalent SEI inorganic compounds observed for Li metal anodes, Li₃N is often found in the SEIs of high-performance LMBs. Herein, we elucidate new features of Li₃N by utilizing a suspension electrolyte design that contributes to the improved electrochemical performance of the Li metal anode. Through empirical and computational studies, we show that Li₃N guides Li electrodeposition along its surface, creates a weakly solvating environment by decreasing Li⁺-solvent coordination, induces organic-poor SEI on the Li metal anode, and facilitates Li⁺ transport in the electrolyte. Importantly, recognizing specific roles of SEI inorganics for Li metal anodes can serve as one of the rational guidelines to design and optimize SEIs through electrolyte engineering for LMBs.

Taming Solvent-Solute Interaction Accelerates Interfacial Kinetics in Low-Temperature Lithium-Metal Batteries

Lithium (Li)-metal batteries promise energy density beyond 400 Wh kg^-1 , while their practical operation at an extreme temperature below -30 °C suffers severe capacity deterioration. Such battery failure highly relates to the remarkably increased kinetic barrier of interfacial processes, including interfacial desolvation, ion transportation, and charge transfer. In this work, the interfacial kinetics in three prototypical electrolytes are quantitatively probed by three-electrode electrochemical techniques and molecular dynamics simulations. Desolvation as the limiting step of interfacial processes is validated to dominate the cell impedance and capacity at low temperature. 1,3-Dioxolane-based electrolyte with tamed solvent-solute interaction facilitates fast desolvation, enabling the practical Li|LiNi_0.5 Co_0.2 Mn_0.3 O₂ cells at -40 °C to retain 66% of room-temperature capacity and withstand remarkably fast charging rate (0.3 C). The barrier of desolvation dictated by solvent-solute interaction environments is quantitatively uncovered. Regulating the solvent-solute interaction by low-affinity solvents emerges as a promising solution to low-temperature batteries.

Locking Active Li Metal through Localized Redistribution of Fluoride Enabling Stable Li-Metal Batteries

The creation of fluorinated interphase has emerged as an effective strategy for improving Li-metal anodes for rechargeable high-energy batteries. In contrast to the introduction of fluorine-containing species through widely adopted electrolyte engineering, a Li-metal composite design is reported in which LiF can locally redistribute on the Li-metal surface in liquid electrolytes via a dissolution-reprecipitation mechanism, and enable the formation of a high-fluorine-content solid electrolyte interphase (SEI). For validation, a Li/Li₂₂ Sn₅ /LiF ternary composite is investigated, where the as-formed LiF-rich SEI locks the active Li metal from corrosive electrolyte. The Li/Li₂₂ Sn₅ /LiF anode displays an impressive average Coulombic efficiency (ACE, ≈99.2%) at 1 mA cm^-2 and 1 mAh cm^-2 in a carbonate electrolyte and a remarkable cycling life of over 1600 h at 1 mA cm^-2 and 2 mAh cm^-2 . Applied to a LiCoO₂ full cell with a high cathode areal capacity of 4.0 mAh cm^-2 , a high capacity retention of ≈91.1% is realized for 100 cycles at 0.5 C between 2.8 to 4.5 V with a low negative/positive (N/P) ratio of 2:1. This design is conceptually different from the design employing the widely used fluorine-containing electrolyte additive and provides an alternative approach to realize reliable Li-metal batteries.

High interfacial-energy heterostructure facilitates large-sized lithium nucleation and rapid Li+ desolvation process

High interfacial energy Li⁰-electrolyte interface contributes to larger Li⁰ nucleation embryos and a more stable interface, so the interfacial energy is essential for highly reversible Li⁰ deposition/stripping. Herein, a high interfacial-energy artificial solid electrolyte interphase (SEI) with rich LiF embedded in lithiated poly-2-acrylamido-2-methylpropane sulfonic acid (PAMPS-Li) network is designed to realize favorable Li⁰ nucleation and rapid desolvation of Li⁺ simultaneously. The Li-F bonds in LiF (001) exhibit stronger ion-dipole interactions with Li atoms, offering higher interfacial energies. When the growth surface energy and total interfacial energy of Li⁰ are balanced, the high interfacial energy SEI with abundant LiF can promote the formation of larger Li⁰ nucleation embryos. In addition, the PAMPS-Li with immobilized anions presents weaker interaction with Li⁰ and possesses higher polymer-Li interfacial energy, and its amide and sulfonic acid groups exhibit higher binding energies with Li⁺. Therefore, PAMPS-Li can easily promote the Li⁺ to escape from the solvent sheath and weaken the desolvation energy barrier. The highly reversible Li⁰ deposition behavior with restricted side reactions is achieved based on the synergistic modification of high interfacial energy SEI with heterostructure. Most importantly, lifespan of multi-layered Li⁰ pouch cell (330 Wh kg^-1) with a low N/P ratio (1.67) is over 100 cycles, verifying its potential practical application.

Regulating Solvation Structures Enabled by the Mesoporous Material MCM-41 for Rechargeable Lithium Metal Batteries

For developing the reversible lithium metal anode, constructing an ideal solid electrolyte interphase (SEI) by regulating the Li⁺ solvation structure is a powerful way to overcome the major obstacles of lithium dendrite and limited Coulombic efficiency (CE). Herein, spherical mesoporous molecular sieve MCM-41 nanoparticles are coated on a commercial PP separator and used to regulate the Li⁺ solvation structure for lithium metal batteries (LMBs). The regulated solvation structure exhibits an agminated state with more contact ion pairs (CIPs) and ionic aggregates (AGGs), which successfully construct a homogeneous inorganic-rich SEI in the lithium anode. Meanwhile, the regulated solvation structure weakens the interaction between the solvents and Li⁺, resulting in low Li⁺ desolvation energy and uniform Li deposition. Thus, a high CE (∼96.76%), dendrite-free Li anode, and stable Li plating/stripping cycling for approximately 1000 h are achieved in the regulated carbonate-based electrolyte without any additives. Therefore, regulating the Li⁺ solvation structure in the electrolyte by employing a mesoporous material is a forceful way to construct an ideal SEI and harness lithium metal.

Designing better electrolytes

Electrolytes and the associated interphases constitute the critical components to support the emerging battery chemistries that promise tantalizing energy but involve drastic phase and structure complications. Designing better electrolytes and interphases holds the key to the success of these batteries. As the only component that interfaces with every other component in the device, an electrolyte must satisfy multiple criteria simultaneously. These include transporting ions while insulating electrons between the electrodes and maintaining stability against electrodes of extreme chemical natures: the strongly oxidative cathode and the strongly reductive anode. In most advanced batteries, the two electrodes operate at potentials far beyond the thermodynamic stability limits of electrolytes, so the stability therein has to be realized kinetically through an interphase formed from the sacrificial reactions between electrolyte and electrodes.

Revisiting the Role of Physical Confinement and Chemical Regulation of 3D Hosts for Dendrite-Free Li Metal Anode

Lithium metal anode has been demonstrated as the most promising anode for lithium batteries because of its high theoretical capacity, but infinite volume change and dendritic growth during Li electrodeposition have prevented its practical applications. Both physical morphology confinement and chemical adsorption/diffusion regulation are two crucial approaches to designing lithiophilic materials to alleviate dendrite of Li metal anode. However, their roles in suppressing dendrite growth for long-life Li anode are not fully understood yet. Herein, three different Ni-based nanosheet arrays (NiO-NS, Ni₃N-NS, and Ni₅P₄-NS) on carbon cloth as proof-of-concept lithiophilic frameworks are proposed for Li metal anodes. The two-dimensional nanoarray is more promising to facilitate uniform Li⁺ flow and electric field. Compared with the NiO-NS and the Ni₅P₄-NS, the Ni₃N-NS on carbon cloth after reacting with molten Li (Li-Ni/Li₃N-NS@CC) can afford the strongest adsorption to Li⁺ and the most rapid Li⁺ diffusion path. Therefore, the Li-Ni/Li₃N-NS@CC electrode realizes the lowest overpotential and the most excellent electrochemical performance (60 mA cm^-2 and 60 mAh cm^-2 for 1000 h). Furthermore, a remarkable full battery (LiFePO₄||Li-Ni/Li₃N-NS@CC) reaches 300 cycles at 2C. This research provides valuable insight into designing dendrite-free alkali metal batteries.

Nanocomposite of Conducting Polymer and Li Metal for Rechargeable High Energy Density Batteries

The structure and electrochemical performance of lithium (Li) metal degrade quickly owing to its hostless nature and high reactivity, hindering its practical application in rechargeable high energy density batteries. In order to enhance the electrochemical reversibility of metallic Li, we designed a Li/Li₂S-poly(acrylonitrile) (LSPAN) composite foil via a facile mechanical kneading approach using metallic Li and sulfurized poly(acrylonitrile) as the raw materials. The uniformly dispersed Li₂S-poly(acrylonitrile) (Li₂S-PAN) in a metallic Li matrix buffered the volume change on cycling, and its high Li ion conductivity enabled fast Li ion diffusion behavior of the composite electrode. As expected, the LSPAN electrode showed reduced voltage polarization, enhanced rate capability, and prolonged cycle life compared with the pure Li electrode. It exhibited stable cycling for 600 h with a symmetric cell configuration at 1 mA cm^-2 and 1 mA h cm^-2, far outperforming the pure metallic Li counterpart (400 h). Also, the LiCoO₂||LSPAN full cells with a cathode mass loading of ∼16 mg cm^-2 worked stably for 100 cycles at 0.5 C with a high capacity retention of 96.5%, while the LiCoO₂||Li full cells quickly failed within only 50 cycles.

Commercially Viable Hybrid Li-Ion/Metal Batteries with High Energy Density Realized by Symbiotic Anode and Prelithiated Cathode

The energy density of commercial lithium (Li) ion batteries with graphite anode is reaching the limit. It is believed that directly utilizing Li metal as anode without a host could enhance the battery's energy density to the maximum extent. However, the poor reversibility and infinite volume change of Li metal hinder the realistic implementation of Li metal in battery community. Herein, a commercially viable hybrid Li-ion/metal battery is realized by a coordinated strategy of symbiotic anode and prelithiated cathode. To be specific, a scalable template-removal method is developed to fabricate the porous graphite layer (PGL), which acts as a symbiotic host for Li ion intercalation and subsequent Li metal deposition due to the enhanced lithiophilicity and sufficient ion-conducting pathways. A continuous dissolution-deintercalation mechanism during delithiation process further ensures the elimination of dead Li. As a result, when the excess plating Li reaches 30%, the PGL could deliver an ultrahigh average Coulombic efficiency of 99.5% for 180 cycles with a capacity of 2.48 mAh cm^-2 in traditional carbonate electrolyte. Meanwhile, an air-stable recrystallized lithium oxalate with high specific capacity (514.3 mAh g^-1) and moderate operating potential (4.7-5.0 V) is introduced as a sacrificial cathode to compensate the initial loss and provide Li source for subsequent cycles. Based on the prelithiated cathode and initial Li-free symbiotic anode, under a practical-level 3 mAh capacity, the assembled hybrid Li-ion/metal full cell with a P/N ratio (capacity ratio of LiNi_0.8Co_0.1Mn_0.1O₂ to graphite) of 1.3 exhibits significantly improved capacity retention after 300 cycles, indicating its great potential for high-energy-density Li batteries.

Ion sieve membrane: Homogenizing Li+ flux and restricting polysulfides migration enables long life and highly stable Li-S battery

Limited by the notorious Li dendrites growth and serious polysulfide shuttle effect, the development of lithium-sulfur (Li-S) batteries is stagnant. Herein, a multifunctional separator composed of Cu-based metal-organic framework (Cu-MOF) and Li-Nafion was proposed to address the above intractable issues. The Cu-MOF with homogeneous porous structure and abundant Lewis acidic sites not only promotes uniform Li⁺ flux, but also exhibits a strong chemical interaction with polysulfides to inhibit the shuttle effect. Moreover, the narrow pore size distribution in the Cu-MOF and negatively charged gap endowed by the -SO₃^- groups both act as ion sieve to facilitate the passage of Li⁺ and restrict the migration of polysulfide anions, synergistically mitigating the dendritic Li growth and polysulfides shuttling. As a result, the symmetric cell with MOF/Nafion separator achieves ultralong cycling stability (1000 h) and ultralow overpotential of 20 mV at a current density of 1.0 mA cm^-2. Importantly, in the assembled Li-S full battery, the modified PP separator presents the superior cycle stability with capacity retention of 90% after 300 cycles at 0.5 C. Current outcomes open up a new route to design functional separators with ion permselective for realizing the dendrite-free and high-performance Li-S battery.

Stable Solvent-Derived Inorganic-Rich Solid Electrolyte Interphase (SEI) for High-Voltage Lithium-Metal Batteries

The inorganic-rich solid electrolyte interphase (SEI) has attracted wide attention due to its good compatibility with the lithium (Li) metal anode. Herein, a stable solvent-derived inorganic-rich SEI is constructed from a hydrofluoroether-diluted low-concentration electrolyte, which simultaneously possesses the merits of nonflammability and low cost (0.5 M LiPF₆). The addition of hydrofluoroether enhances the coordination strength between Li⁺ and solvents, altering the decomposition path of solvents to yield more Li₂O. The abundant Li₂O crystals endow the SEI with improved passivating ability and ion conductivity. The 30 μm Li|NCM523 (3.8 mAh cm^-2) batteries with solvent-derived Li₂O-rich SEI deliver 96.1% capacity retention after 200 cycles. Notably, a 1.1 Ah Li|NCA pouch cell delivers an energy density of 374 Wh kg^-1 and achieves 45 stable cycles. This study points out that tuning the decomposition of solvents provides a new approach to construct stable inorganic-rich SEI for practical Li-metal batteries.