Unraveling New Role of Binder Functional Group as a Probe to Detect Dynamic Lithium-Ion De-Solvation Process toward High Electrode Performances

Binder plays a pivotal role in the development of lithium-ion batteries as it must be used to adhere electrode materials on current collectors tightly to guarantee stability. Then, many binder molecules have been designed to enhance the adhesion capability, and conductivity, and/or form a robust solid electrolyte interphase layer for better performance. However, the binder effect on the lithium-ion (i.e., Li⁺) de-solvation on the electrode surface has never been reported before. Herein, it is reported that the binder can influence the Li⁺ (de-)solvation process significantly, where its functional group can serve as a probe to detect the dynamic Li⁺ (de-)solvation process. It is discovered that different binder functional groups (e.g., *─COO⁻ versus *─F) can affect the Li⁺-solvent arrangement on the electrode surface, leading to different degrees of side-reactions, rate capabilities, and/or the tolerance against Li⁺-solvent co-insertion for the graphite anode, such as in the propylene carbonate-based electrolyte. A molecular interfacial model related to the electrolyte component's behaviors and binder functional group is proposed to interpret the varied electrode performance. This discovery opens a new avenue for studying the interactions between the binder and electrolyte solvation structure, in turn helping to understand electrode performances underlying the micro-structures.     

Uncovering the Function of a Five-Membered Heterocyclic Solvent-Based Electrolyte for Graphite Anode at Subzero Temperature

Ethylene carbonate (EC) is taken as the essential electrolyte component in lithium-ion batteries (LIBs) due to its high permittivity and film-forming ability. However, its high melting point (36.4 °C) and strong solvation energy severely hinder Li⁺ transportation and Li⁺ desolvation process under low temperatures, resulting in capacity loss and even Li plating on graphite anode. Herein, a five-membered heterocyclic compound isoxazole (IZ), similar to EC molecule, is well-formulated to substitute EC for low-temperature operation of graphite anode. It is revealed that IZ with dispersed charge distribution exhibits a weaker solvation ability than EC with highly polar carbonyl group, which induces relatively more anions into the solvation sheath to form contact ion pairs and aggregates. The tamed electrolyte not only exhibits high ionic conductivities over wide-temperature range but also generates an inorganic-rich interphase with low activation barrier for smooth Li⁺ ions threading. This enables graphite anode with an impressive reversible capacity of 263 mAh g^-1 at the low temperature of −30 °C (a room-temperature retention of as high as 71.5%), nearly twice higher than graphite with EC-based electrolyte. This study provides an alternative electrolyte recipe to relieve the anxiety of LIBs operated under harsh conditions.     

Enhanced Interfacial Stability of Hybrid‐Electrolyte Lithium‐Sulfur Batteries with a Layer of Multifunctional Polymer with Intrinsic Nanoporosity

The use of lithium‐ion conductive solid electrolytes offers a promising approach to address the polysulfide shuttle and the lithium‐dendrite problems in lithium‐sulfur (Li‐S) batteries. One critical issue with the development of solid‐electrolyte Li‐S batteries is the electrode–electrolyte interfaces. Herein, a strategic approach is presented by employing a thin layer of a polymer with intrinsic nanoporosity (PIN) on a Li⁺‐ion conductive solid electrolyte, which significantly enhances the ionic interfaces between the electrodes and the solid electrolyte. Among the various types of Li⁺‐ion solid electrolytes, NASICON‐type Li_1+xAl_xTi_2‐x(PO₄)₃ (LATP) offers advantages in terms of Li⁺‐ion conductivity, stability in ambient environment, and practical viability. However, LATP is susceptible to reaction with both the Li‐metal anode and polysulfides in Li‐S batteries due to the presence of easily reducible Ti⁴⁺ ions in it. The coating with a thin layer of PIN presented in this study overcomes the above issues. At the negative‐electrode side, the PIN layer prevents the direct contact of Li‐metal with the LATP solid electrolyte, circumventing the reduction of LATP by Li metal. At the positive electrode side, the PIN layer prevents the migration of polysulfides to the surface of LATP, preventing the reduction of LATP by polysulfides.     

Hydrofluoric Acid-Removable Additive Optimizing Electrode Electrolyte Interphases with Li+ Conductive Moieties for 4.5 V Lithium Metal Batteries

High-voltage lithium metal batteries (LMBs) are capable to achieve the increasing energy density. However, their cycling life is seriously affected by unstable electrolyte/electrode interfaces and capacity instability at high voltage. Herein, a hydrofluoric acid (HF)-removable additive is proposed to optimize electrode electrolyte interphases for addressing the above issues. N, N-dimethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) aniline (DMPATMB) is used as the electrolyte additive to induce PF₆⁻ decomposition to form a dense and robust LiF-rich solid electrolyte interphase (SEI) for suppressing Li dendrite growth. Moreover, DMPATMB can help to form highly Li⁺ conductive Li₃N and LiBO₂, which can boost the Li⁺ transport across SEI and cathode electrolyte interphase (CEI). In addition, DMPATMB can scavenge traced HF in the electrolyte to protect both SEI and CEI from the corrosion. As expected, 4.5 V Li|| LiNi_0.6Co_0.2Mn_0.2O₂ batteries with such electrolyte deliver 145 mAh g⁻¹ after 140 cycles at 200 mA g⁻¹. This work provides a novel insight into high-voltage electrolyte additives for LMBs.     

Controlling Solvation and Solid-Electrolyte Interphase Formation to Enhance Lithium Interfacial Kinetics at Low Temperatures

Operation of lithium-based batteries at low temperatures (<0 °C) is challenging due to transport limitations as well as sluggish Li⁺ kinetics at the electrode interface. The complicated relationships among desolvation, charge transfer, and transport through the solid electrolyte interphase (SEI) at low temperatures are not well understood, hindering electrolyte development. Here, an ether/hydrofluoroether and fluoroethylene carbonate (FEC)-based ternary solvent electrolyte is developed to improve Li cycling at low temperatures (Coulombic efficiency of 93.3% at -40 °C), and the influence of the local solvation structure on interfacial Li⁺ kinetics and SEI chemistry is further revealed. The hydrofluoroether cosolvent allows for modulation of the solvation structure, thereby enabling facile Li⁺ desolvation while forming an inorganic-rich SEI, which are both beneficial for lowering Li⁺ kinetic barriers at the interface. This cosolvent also increases the oxidative stability of the electrolyte to over 4.0 V versus Li/Li⁺, thereby enabling cycling of NMC-based full cells at −40 °C. This study advances the understanding of the influence of Li⁺ solvation structure, SEI chemistry, and interfacial Li⁺ kinetics on Li electrochemistry at low temperatures, providing new design considerations for creating effective low-temperature electrolyte systems.     

Lithium-Ion Desolvation Induced by Nitrate Additives Reveals New Insights into High Performance Lithium Batteries

Electrolyte additives have been widely used to address critical issues in current metal (ion) battery technologies. While their functions as solid electrolyte interface forming agents are reasonably well-understood, their interactions in the liquid electrolyte environment remain rather elusive. This lack of knowledge represents a significant bottleneck that hinders the development of improved electrolyte systems. Here, the key role of additives in promoting cation (e.g., Li⁺) desolvation is unraveled. In particular, nitrate anions (NO₃⁻) are found to incorporate into the solvation shells, change the local environment of cations (e.g., Li⁺) as well as their coordination in the electrolytes. The combination of these effects leads to effective Li⁺ desolvation and enhanced battery performance. Remarkably, the inexpensive NaNO₃ can successfully substitute the widely used LiNO₃ offering superior long-term stability of Li⁺ (de-)intercalation at the graphite anode and suppressed polysulfide shuttle effect at the sulfur cathode, while enhancing the performance of lithium–sulfur full batteries (initial capacity of 1153 mAh g⁻¹ at 0.25C) with Coulombic efficiency of ≈100% over 300 cycles. This work provides important new insights into the unexplored effects of additives and paves the way to developing improved electrolytes for electrochemical energy storage applications.     

Highly‐Cyclable Room‐Temperature Phosphorene Polymer Electrolyte Composites for Li Metal Batteries

Despite significant interest toward solid‐state electrolytes owing to their superior safety in comparison to liquid‐based electrolytes, sluggish ion diffusion and high interfacial resistance limit their application in durable and high‐power density batteries. Here, a novel quasi‐solid Li⁺ ion conductive nanocomposite polymer electrolyte containing black phosphorous (BP) nanosheets is reported. The developed electrolyte is successfully cycled against Li metal (over 550 h cycling) at 1 mA cm^?2 at room temperature. The cycling overpotential is dropped by 75% in comparison to BP‐free polymer composite electrolyte indicating lower interfacial resistance at the electrode/electrolyte interfaces. Molecular dynamics simulations reveal that the coordination number of Li⁺ ions around (trifluoromethanesulfonyl)imide (TFSI^?) pairs and ethylene‐oxide chains decreases at the Li metal/electrolyte interface, which facilitates the Li⁺ transport through the polymer host. Density functional theory calculations confirm that the adsorption of the LiTFSI molecules at the BP surface leads to the weakening of N and Li atomic bonding and enhances the dissociation of Li⁺ ions. This work offers a new potential mechanism to tune the bulk and interfacial ionic conductivity of solid‐state electrolytes that may lead to a new generation of lithium polymer batteries with high ionic conduction kinetics and stable long‐life cycling.     

An Intrinsically Nonflammable Electrolyte for Prominent-Safety Lithium Metal Batteries with High Energy Density and Cycling Stability

Nex-generation high-energy-density storage battery, assembled with lithium (Li)-metal anode and nickel-rich cathode, puts forward urgent demand for advanced electrolytes that simultaneously possess high security, wide electrochemical window, and good compatibility with electrode materials. Herein an intrinsically nonflammable electrolyte is designed by using 1 M lithium difluoro(oxalato)borate (LiDFOB) in triethyl phosphate (TEP) and N-methyl-N-propyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [Pyr₁₃][TFSI] ionic liquid (IL) solvents. The introduction of IL can bring plentiful organic cations and anions, which provides a cation shielding effect and regulates the Li⁺ solvation structure with plentiful Li⁺-DFOB⁻ and Li⁺-TFSI⁻ complexes. The unique Li⁺ solvation structure can induce stable anion-derived electrolyte/electrode interphases, which effectively inhibit Li dendrite growth and suppress side reactions between TEP and electrodes. Therefore, the LiNi_0.9Co_0.05Mn_0.05O₂ (NCM90)/Li coin cell with this electrolyte can deliver stable cycling even under 4.5 V and 60 °C. Moreover, a Li-metal battery with thick NCM90 cathode (≈ 15 mg cm⁻²) and thin Li-metal anode (≈ 50 µm) (N/P ≈ 3), also reveals stable cycling performance under 4.4 V. And a 2.2 Ah NCM90/Li pouch cell can simultaneously possess prominent safety with stably passing the nail penetration test, and high gravimetric energy density of 470 Wh kg⁻¹ at 4.4 V.     

Solvation Engineering Enables High-Voltage Lithium Ion and Metal Batteries Operating Under −50 and 80 °C

Extreme temperatures (<-20 °C or >50 °C) would seriously impair the performance of lithium batteries through deteriorating bulk ion transport and electrode interfaces. Here, a rational design of weak solvent and anti-solvent combination is presented for wide-temperature electrolytes. The weak solvent provides accelerated desolvation kinetics of Li⁺ around the anode region, while the anti-solvent not only functions as an antifreeze agent for smooth ion migration at low temperatures but also interacts with the weak solvent to boost the formation of ionic aggregates. The weak and anti-solvent electrolyte (WAE) exerts excellent compatibility with both lithium metal and graphite. Under −40 °C, Li anode delivers 98.5% Coulombic efficiency and graphite outputs capacity over 230 mAh g^-1. Lithium-ion/metal batteries by pairing graphite anode with LiCoO₂ cathode with a negative to positive capacity ratio of 0.75 can realize steady operation at −50 °C with an average coulombic efficiency of 99.9%. Lithium metal batteries with 4.2 mAh cm^-2 high LiCoO₂ cathode loading and 50 µm thin lithium anode deliver 73.8% capacity output at −40 °C. Besides, the cells are stable up to 80 °C with an average coulombic efficiency of 99.7%. This research demonstrates a relatively loose Li⁺ solvation environment in WAE systems and provides wide-temperature electrolyte for high-performance lithium ion and metal batteries.     

Hexafluoroisopropyl Trifluoromethanesulfonate-Driven Easily Li+ Desolvated Electrolyte to Afford Li||NCM811 Cells with Efficient Anode/Cathode Electrolyte Interphases

Solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) with optimized components and structures are considered to be crucial for lithium-ion batteries. Here, gradient lithium oxysulfide (Li₂SO_x, x = 0, 3, 4)/uniform lithium fluoride (LiF)-type SEI is designed in situ by using hexafluoroisopropyl trifluoromethanesulfonate (HFPTf) as electrolyte additive. HFPTf is more likely to be reduced on the surface of Li anode in electrolytes due to its high reduction potential. Moreover, HFPTf can make Li⁺ desolvated easily, leading to the increase in the flux of Li⁺ on the surface of Li anode to avoid the growth of Li dendrites. Thus, the cycling stability of Li||Li symmetric cells is improved to be 1000 h at 0.5 mA cm⁻². In addition, HFPTf-contained electrolyte could make Li||NCM811 batteries with a capacity retention of 70% after 150 cycles at 100 mA g⁻¹, which is attributed to the formation of uniform and stable CEI on the cathode surface for hindering the dissolvation of metal ions from the cathode. This study provides effective insights on the strong ability of additives to adjust electrolytes in “one phase and two interphases” (electrolyte and SEI/CEI).     

A Salt-in-Metal Anode: Stabilizing the Solid Electrolyte Interphase to Enable Prolonged Battery Cycling

Metallic lithium (Li) is the ultimate anode candidate for high-energy-density rechargeable batteries. However, its practical application is hindered by serious problems, including uncontrolled dendritic Li growth and undesired side reactions. In this study a concept of “salt-in-metal” is proposed, and a Li/LiNO₃ composite foil is constructed such that a classic electrolyte additive, LiNO₃, is embedded successfully into the bulk structure of metallic Li by a facile mechanical kneading approach. The LiNO₃ reacts with metallic Li to generate Li⁺ conductive species (e.g., Li₃N and LiN_xO_y) over the entire electrode. These derivatives afford a stable solid electrolyte interphase (SEI) and effectively regulate the uniformity of the nucleation/growth of Li on initial plating, featuring a low nucleation energy barrier and large crystalline size without mossy morphology. Importantly, these derivatives combined with LiNO₃ can in-situ repair the damaged SEI from the large volume change during Li plating/stripping, enabling a stable electrode-electrolyte interface and suppressing side reactions between metallic Li and electrolyte. Stable cycling with a high capacity retention of 93.1% after 100 cycles is obtained for full cells consisting of high-loading LiCoO₂ cathode (≈20 mg cm⁻²) and composite metallic Li anode with 25 wt% LiNO₃ under a lean electrolyte condition (≈12 µL) at 0.5 C.     

3D Ordered Porous Hybrid of ZnSe/N-doped Carbon with Anomalously High Na+ Mobility and Ultrathin Solid Electrolyte Interphase for Sodium-Ion Batteries

Transition metal selenides have been widely used in alkali metal ion batteries owing to their high specific capacities and low cost. However, their reaction kinetics and structural stability are usually poor during cycling, along with ambiguous differences in Li/Na/K-storage behaviors. Herein, it is revealed that ZnSe possesses better Na⁺-diffusion kinetics (including lower diffusion barrier, smaller activation energy, and higher diffusion coefficients) in comparison with Li⁺ and K⁺, as evidenced by theoretical calculations and electrochemical studies. The architectural designs of ZnSe-based anode, including nitrogen-doped carbon (N,C) and 3D ordered hierarchical pores (3DOHP) to form a 3DOHP ZnSe@N,C hybrid combined with regulating solid electrolyte interphase (SEI), significantly enhance Na⁺ reaction kinetics and accommodate volume changes. The resulting 3DOHP ZnSe@N,C electrodes exhibit outstanding rate capability and good cycling stability (241.6 mAh g⁻¹ in sodium-ion batteries (SIBs) at 10 A g⁻¹ after 800 cycles), originating from improved electrical conductivity and shortened ion diffusion paths, accompanied by ultrathin and stable SEI with less Na₂CO₃/NaF in organic components and boosted Na₂Se adsorption as sodiation. Moreover, the Na-storage mechanism in 3DOHP ZnSe@N,C hybrid is further revealed by in situ studies. Accordingly, this study provides a new perspective for designing high-performance electrode materials for SIBs.     

Electrolytes Enriched by Crown Ethers for Lithium Metal Batteries

Lithium (Li) metal battery is considered the most promising next-generation battery due to its low potential and high theoretical capacity. However, Li dendrite growth causes serious safety problems. Herein, the 15-Crown-5 (15-C-5) is reported as an electrolyte additive based on solvation shell regulation. The strong complex effect between Li⁺ ion and 15-C-5 can reduce the concentration of Li ions on the electrode surface, thus changing the nucleation, and repressing the growth of Li dendrites in the plating process. Significantly, the strong coordination of Li⁺/15-C-5 would be able to make them aggregate around the Li crystal surface, which could form a protective layer and favor the formation of a smooth and dense solid electrolyte interphase with high toughness and Li⁺ ion conductivity. Therefore, the electrolyte system with 2.0 wt% 15-C-5 achieves excellent electrochemical performance with 170 cycles at 1.0 mA cm⁻² with capacity of 0.5 mA h cm⁻² in symmetric Li|Li cells. The obviously enhanced cycle and rate performance are also achieved in Li|LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) full cells. The 15-C-5 demonstrates to be a promising additive for the electrolytes toward safe and efficient Li metal batteries.     

Electrolyte Interphase Built from Anionic Covalent Organic Frameworks for Lithium Dendrite Suppression

Lithium (Li) metal batteries hold considerable promise for numerous energy-dense applications. However, the dendritic Li anode produced during Li⁺/Li deposition-stripping endangers battery safety and shortens cycle lifespan. Herein, an electrolyte interphase built from 2D anionic covalent organic frameworks (ACOF) is coated on Li for dendrite suppression. The ACOF with Li⁺-affinity facilitates rapid and exclusive passage of Li-ions from the electrolyte, yielding near-unity Li⁺ transference number (0.82) and ionic conductivity beyond 3.7 mS cm^-1 at the interphase. Such high transport efficiency of Li-ions can fundamentally circumvent the Li⁺ deficiency that results in dendrite formation. Pairing the ACOF-coated Li against a high-voltage LiCoO₂ cathode (4.5 V) achieves exceptional cycle stability, mitigated polarization, as well as improved rate capability. Accordingly, this strategy vastly expands the pool of electrolyte interphases that can be used for coating and protecting Li anode.     

Low Resistance and High Stable Solid–Liquid Electrolyte Interphases Enable High-Voltage Solid-State Lithium Metal Batteries

Solid-state batteries (SSBs) with addition of liquid electrolytes are considered to possibly replace the current lithium-ion batteries (LIBs) because they combine the advantages of benign interfacial contact and strong barriers for unwanted redox shuttles. However, solid electrolyte and liquid electrolyte are generally (electro)-chemically incompatible and the resistance of the newly formed solid–liquid electrolyte interphase (SLEI) appears as an additional contribution to the overall battery resistance. Herein, a boron, fluorine-donating liquid electrolyte (B, F-LE) is introduced into the interface between the high-voltage cathode and ultrathin composite solid electrolyte (CSE), which is fabricated by adhering a high content of nanosized Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), to generate a low resistance and high stable SLEI in situ, giving a stable high-voltage output with a reinforced cathode|CSE interface. B, F-LE, consisting of a highly fluorinated electrolyte with a lithium bis(oxalato)borate additive, exhibits good chemical compatibility with CSE and enables rapid and uniform transportation of Li⁺, with its electrochemically and chemically stable interface for high-voltage cathode. Eventually, the B, F-LE assisted LiNi_0.6Co_0.2Mn_0.2O₂|Li battery displays the enhanced rate capability and high voltage cycling stability. The findings provide an interfacial engineering strategy to turn SLEI from a “real culprit” into the “savior” that may pave a brand-new way to manipulate SLEI chemistry in hybrid solid–liquid devices.     

Molecular Adsorption-Induced Interfacial Solvation Regulation to Stabilize Graphite Anode in Ethylene Carbonate-Free Electrolytes

Many organic solvents have excellent solution properties, but fail to serve as lithium-ion batteries (LIBs) electrolyte solvents, due to their electrochemical incompatibility with graphite anodes. Herein, a new strategy is proposed to address this issue by introducing a surface-adsorbed molecular layer to regulate the interfacial solvation structure without the alteration of electrolyte composition and properties. As a proof-of-concept study, it is demonstrated for the first time that the intrinsically incompatible propylene carbonate (PC)-based electrolyte becomes completely compatible with graphite anodes by introducing a layer of adsorbed hexafluorobenzene (HFB) molecules to weaken the Li⁺-PC coordination strength and facilitate the interfacial desolvation process. As a consequence, the graphite/ NCM811 pouch cells using the PC-based electrolyte containing only 1 vol.% HFB demonstrate excellent long-term cycling stabilities over 1150 cycles. This strategy is also proved to be applicable to other ethylene carbonate (EC)–free electrolytes, thus providing a new avenue for developing advanced LIB electrolytes.     

Facile Design of Sulfide-Based all Solid-State Lithium Metal Battery: In Situ Polymerization within Self-Supported Porous Argyrodite Skeleton

All solid-state batteries holds great promise for superiorly safe and high energy electrochemical energy storage. The ionic conductivity of electrolytes and its interfacial compatibility with the electrode are two critical factors in determining the electrochemical performance of all solid-state batteries. It is a great challenge to simultaneously demonstrate fantastic ionic conductivity and compatible electrolyte/electrode interface to acquire a well-performed all solid-state battery. By in situ polymerizing poly(ethylene glycol) methyl ether acrylate within a self-supported 3D porous Li-argyrodite (Li₆PS₅Cl) skeleton, the two bottlenecks are tackled successfully at once. As a result, all solid-state lithium metal batteries with a 4.5 V LiNi_0.8Mn_0.1Co_0.1O₂ cathode designed by this integrated strategy demonstrates a high Coulombic efficiency exceeding 99% at room temperature. Solid-state nuclear magnetic resonance data suggest that Li⁺ mainly migrates along the continuous Li₆PS₅Cl phase to result in a room temperature conductivity of 4.6 × 10⁻⁴ S cm⁻¹, which is 128 times higher than that of the corresponding polymer. Meanwhile, the inferior solid–solid electrolyte/electrode interface is integrated via in situ polymerization to lessen the interfacial resistance significantly. This study thereby provides a very promising strategy of solid electrolyte design to simultaneously meet both high ionic conductivity and good interfacial compatibility towards practical high-energy-density all solid-state lithium batteries.     

Perfluoro Macrocyclic Ether as an Ambifunctional Additive for High-Performance SiO and Nickel 88%-Based High-Energy Li-ion Battery

State-of-the-art lithium (Li)-ion batteries employ silicon anode active material at a limited fraction while strongly relying on fluoroethylene carbonate (FEC) electrolyte additive exceeding 10 wt.% to enable stable cycling. The swelling issue of silicon in the aspect of solid electrolyte interphase (SEI) instability and a risk of safety hazards and high manufacturing cost due to FEC has motivated the authors to design a well-working fluorinated additive substitute. High-capacity cells employing nickel-rich oxide cathode are pursued by operating at > 4.2 V versus Li/Li⁺, for which anodic stability of electrolyte is required. Herein, a highly effective new ambifunctional additive of icosafluoro-15-crown 5-ether is proposed at a little fraction of 0.4 wt.% for the stabilized interfaces and reduced swelling of high capacity (3.5 mAh cm⁻²) 5 wt.% SiO-graphite anode and LiNi_0.88Co_0.08Mn_0.04O₂ cathode. Utilizing together with a lowered fraction of FEC, reversible long 300 cycles at 4.35 V and 1 C (225 mA g⁻¹) are achieved. Material characterization results reveal that such stabilization is derived from the surface passivation of both anode and cathode with perfluoro ether, LiF, and Li_xPF_y species. The present study gives insight into electrolyte formulation design with lower cost and both-side stabilization strategies for silicon and nickel-rich active materials and their interfaces.     

Amorphous Dual-Layer Coating: Enabling High Li-Ion Conductivity of Non-Sintered Garnet-Type Solid Electrolyte

Garnet-type oxide Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) has attracted considerable attention as a highly promising solid state electrolyte. However, its high ionic conductivity is achievable only after high temperature sintering (≈1200 °C) to form dense pellets but with detrimental brittleness and poor contact with electrodes. Herein, a novel strategy to achieve high Li⁺ ion conductivity of LLZTO without sintering is demonstrated. This is realized by ball milling LLZTO together with LiBH₄, which results in a LLZTO composite with unique amorphous dual coating: LiBO₂ as the inner layer and LiBH₄ as the outer layer. After cold pressing the LLZTO composite powders under 300 MPa to form electrolyte pellets, a high Li⁺ ion conductivity of 8.02 × 10^–5 S cm^–1 is obtained at 30 °C, which is four orders of magnitude higher than that of the non-sintered pristine LLZTO pellets (4.17 × 10^–9 S cm^–1). The composite electrolyte displays an ultrahigh Li⁺ transference number of 0.9999 and enables symmetric Li–Li cells to be cycled for 1000 h at 60 °C and 300 h at 30 °C. The significant improvements are attributed to the continuous ionic conductive network among LLZTO particles facilitated by LiBH₄ that is chemically compatible and electrochemically stable with Li metal electrode.     

Tandem Design of Functional Separators for Li Metal Batteries with Long-Term Stability and High-Rate Capability

The lithium (Li) dendrite growth seriously hinders the applications of lithium metal batteries (LMBs). Numerous methods have been proposed to restrict the formation of Li dendrites by improving the Li-ion transference number (t_Li⁺) through separator modification according to Sand's time equation. However, ignoring the positive contribution of anion motion to solid electrolyte interphase (SEI) formation will result in insufficient inorganic components, which impedes practical implementation of LMBs. Herein, a “tandem” separator is constructed (ZSM-5-Poly dimethyl diallyl ammonium chloride (PDDA)/Polyethylene (PE)/SbF₃), which anchored anions and built an inorganic-rich SEI at the same time. The resulting SEI from SbF₃ (SBF) coating on side facing Li is rich in Li-Sb alloy (Li₃Sb) and LiF. Li₃Sb can significantly reduce the migration energy barrier of Li ion (Li⁺) and facilitate Li⁺ transport. Simultaneously, ZSM-5-PDDA (Z5P) coating at the other side can effectively immobilize anions and increase the t_Li⁺. Moreover, the regular pore structure is conducive to homogenizing Li⁺ flux and also capable to uniform temperature distribution, significantly improving safety. Hence, the lifespan of Li|Li and Li|Cu cells assemble with Z5P/PE/SBF separator is significantly extended. In addition, full cells with LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) and LiFePO₄ (LFP) cathodes show excellent cycle stability and superior rate performance.