Enhanced Stability of Li Metal Anodes by Synergetic Control of Nucleation and the Solid Electrolyte Interphase

Use of a protective coating on a lithium metal anode (LMA) is an effective approach to enhance its coulombic efficiency and cycling stability. Here, a facile approach to produce uniform silver nanoparticle‐decorated LMA for high‐performance Li metal batteries (LMBs) is reported. This effective treatment can lead to well‐controlled nucleation and the formation of a stable solid electrolyte interphase (SEI). Ag nanoparticles embedded in the surface of Li anodes induce uniform Li plating/stripping morphologies with reduced overpotential. More importantly, cross‐linked lithium fluoride‐rich interphase formed during Ag⁺ reduction enables a highly stable SEI layer. Based on the Ag‐LiF decorated anodes, LMBs with LiNi_1/3Mn_1/3Co_1/3O₂ cathode (≈1.8 mAh cm^?2) can retain >80% capacity over 500 cycles. The similar approach can also be used to treat sodium metal anodes. Excellent stability (80% capacity retention in 10 000 cycles) is obtained for a Na||Na₃V₂(PO₄)₃ full cell using a Na‐Ag‐NaF/Na anode cycled in carbonate electrolyte. These results clearly indicate that synergetic control of the nucleation and SEI is an efficient approach to stabilize rechargeable metal batteries.     

Polymer‐in‐“Quasi‐Ionic Liquid” Electrolytes for High‐Voltage Lithium Metal Batteries

Due to the limited oxidation stability (<4 V) of ether oxygen in its polymer structure, polyethylene oxide (PEO)‐based polymer electrolytes are not compatible with high‐voltage (>4 V) cathodes, thus hinder further increases in the energy density of lithium (Li) metal batteries (LMBs). Here, a new type of polymer‐in‐“quasi‐ionic liquid” electrolyte is designed, which reduces the electron density on ethereal oxygens in PEO and ether solvent molecules, induces the formation of stable interfacial layers on both surfaces of the LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) cathode and the Li metal anode in Li||NMC batteries, and results in a capacity retention of 88.4%, 86.7%, and 79.2% after 300 cycles with a charge cutoff voltage of 4.2, 4.3, and 4.4 V for the LMBs, respectively. Therefore, the use of “quasi‐ionic liquids” is a promising approach to design new polymer electrolytes for high‐voltage and high‐specific‐energy LMBs.     

Electrokinetic Phenomena Enhanced Lithium‐Ion Transport in Leaky Film for Stable Lithium Metal Anodes

The application of lithium (Li) metal anodes in Li metal batteries has been hindered by growth of Li dendrites, which lead to short cycling life. Here a Li‐ion‐affinity leaky film as a protection layer is reported to promote a dendrite‐free Li metal anode. The leaky film induces electrokinetic phenomena to enhance Li‐ion transport, leading to a reduced Li‐ion concentration polarization and homogeneous Li‐ion distribution. As a result, the dendrite‐free Li metal anode during Li plating/stripping is demonstrated even at an extremely high deposition capacity (6 mAh cm^?2) and current density (40 mA cm^?2) with improved Coulombic efficiencies. A full cell battery with the leaky‐film protected Li metal as the anode and high‐areal‐capacity LiNi_0.8Co_0.1Mn_0.1O₂ (NCM‐811) (≈4.2 mAh cm^?2) or LiFePO₄ (≈3.8 mAh cm^?2) as the cathode shows improved cycling stability and capacity retention, even at lean electrolyte conditions.     

High Voltage Operation of Ni‐Rich NMC Cathodes Enabled by Stable Electrode/Electrolyte Interphases

The lithium (Li) metal battery (LMB) is one of the most promising candidates for next‐generation energy storage systems. However, it is still a significant challenge to operate LMBs with high voltage cathodes under high rate conditions. In this work, an LMB using a nickel‐rich layered cathode of LiNi_0.76Mn_0.14Co_0.10O₂ (NMC76) and an optimized electrolyte [0.6 m lithium bis(trifluoromethanesulfonyl)imide + 0.4 m lithium bis(oxalato)borate + 0.05 m LiPF₆ dissolved in ethylene carbonate and ethyl methyl carbonate (4:6 by weight)] demonstrates excellent stability at a high charge cutoff voltage of 4.5 V. Remarkably, these Li||NMC76 cells can deliver a high discharge capacity of >220 mA h g^?1 (846 W h kg^?1) and retain more than 80% capacity after 1000 cycles at high charge/discharge current rates of 2C/2C (1C = 200 mA g^?1). This excellent electrochemical performance can be attributed to the greatly enhanced structural/interfacial stability of both the Ni‐rich NMC76 cathode material and the Li metal anode using the optimized electrolyte.     

Efficient Li‐Ion‐Conductive Layer for the Realization of Highly Stable High‐Voltage and High‐Capacity Lithium Metal Batteries

Recently, a consensus has been reached that using lithium metal as an anode in rechargeable Li‐ion batteries is the best way to obtain the high energy density necessary to power electronic devices. Challenges remain, however, with respect to controlling dendritic Li growth on these electrodes, enhancing compatibility with carbonate‐based electrolytes, and forming a stable solid–electrolyte interface layer. Herein, a groundbreaking solution to these challenges consisting in the preparation of a Li₂TiO₃ (LT) layer that can be used to cover Li electrodes via a simple and scalable fabrication method, is suggested. Not only does this LT layer impede direct contact between electrode and electrolyte, thus avoiding side reactions, but it assists and expedites Li‐ion flux in batteries, thus suppressing Li dendrite growth. Other effects of the LT layer on electrochemical performance are investigated by scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic intermittent titration technique analyses. Notably, LT layer‐incorporating Li cells comprising high‐capacity/voltage cathodes with reasonably high mass loading (LiNi_0.8Co_0.1Mn_0.1O₂, LiNi_0.5Mn_1.5O₄, and LiMn₂O₄) show highly stable cycling performance in a carbonate‐based electrolyte. Therefore, it is believed that the approach based on the LT layer can boost the realization of high energy density lithium metal batteries and next‐generation batteries.     

High Voltage LiNi0.5Mn0.3Co0.2O2/Graphite Cell Cycled at 4.6 V with a FEC/HFDEC‐Based Electrolyte

A high voltage LiNi_0.5Mn_0.3Co_0.2O₂/graphite cell with a fluorinated electrolyte formulation 1.0 m LiPF₆ fluoroethylene carbonate/bis(2,2,2‐trifluoroethyl) carbonate is reported and its electrochemical performance is evaluated at cell voltage of 4.6 V. Comparing with its nonfluorinated electrolyte counterpart, the reported fluorinated one shows much improved Coulombic efficiency and capacity retention when a higher cut‐off voltage (4.6 V) is applied. Scanning electron microscopy/energy dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy data clearly demonstrate the superior oxidative stability of the new electrolyte. The structural stability of the bulk cathode materials cycled with different electrolytes is extensively studied by X‐ray absorption near edge structure and X‐ray diffraction.     

A Novel Strategy to Suppress Capacity and Voltage Fading of Li‐ and Mn‐Rich Layered Oxide Cathode Material for Lithium‐Ion Batteries

Poor cycling stability is one of the key scientific issues needing to be solved for Li‐ and Mn‐rich layered oxide cathode. In this paper, sodium carboxymethyl cellulose (CMC) is first used as a novel binder in Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ cathode to enhance its cycling stability. Electrochemical performance is conducted by galvanostatic charge and discharge. Structure and morphology are characterized by X‐ray diffraction, scanning electronic microscopy, high‐resolution transmission electron microscopy, and X‐ray photoelectron spectroscopy. Results reveal that the CMC as binder can not only stabilize the electrode structure by preventing the electrode materials to detach from the current collector but also suppress the voltage fading of the Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ cathode due to Na⁺ ions doping. Most importantly, the dissolution of metal elements from the cathode materials into the electrolyte is also inhibited.     

Lithium Difluorophosphate‐Based Dual‐Salt Low Concentration Electrolytes for Lithium Metal Batteries

The safety hazards and low Coulombic efficiency originating from the growth of lithium dendrites and decomposition of the electrolyte restrict the practical application of Li metal batteries (LMBs). Inspired by the low cost of low concentration electrolytes (LCEs) in industrial applications, dual‐salt LCEs employing 0.1 m Li difluorophosphate (LiDFP) and 0.4 m LiBOB/LiFSI/LiTFSI are proposed to construct a robust and conductive interphase on a Li metal anode. Compared with the conventional electrolyte using 1 m LiPF₆, the ionic conductivity of LCEs is reduced but the conductivity decrement of the separator immersed in LCEs is moderate, especially for the LiDFP–LiFSI and LiDFP–LiTFSI electrolytes. The accurate Coulombic efficiency (CE) of the Li||Cu cells increases from 83.3% (electrolyte using 1 m LiPF₆) to 97.6%, 94.5%, and 93.6% for LiDFP–LiBOB, LiDFP–LiFSI, and LiDFP–LiTFSI electrolytes, respectively. The capacity retention of Li||LiFePO₄ cells using the LiDFP–LiBOB electrolyte reaches 95.4% along with a CE over 99.8% after 300 cycles at a current density of 2.0 mA cm^?2 and the capacity reaches 103.7 mAh g^?1 at a current density of up to 16.0 mA cm^?2. This work provides a dual‐salt LCE for practical LMBs and presents a new perspective for the design of electrolytes for LMBs.     

A 3D Lithium/Carbon Fiber Anode with Sustained Electrolyte Contact for Solid‐State Batteries

To reconcile the energy storage ability and operational safety of lithium metal batteries (LMBs), a transformation from a liquid to a solid‐state system is required. However, Li volume variation, poor interfacial contact, and high operation temperatures hinder its practical applications. To address the above issues, here, an integral structure design for solid‐state LMBs is shown, in which a Li‐preinfused 3D carbon fiber (Li/CF) anode is ionically connected to a cathode via an autopolymerized gel electrolyte. The gel electrolyte helps to encapsulate the liquid electrolyte within the Li/CF anode and the cathode to improve the interfacial contact. The gel also serves as a reservoir that balances the liquid electrolyte supply during repeated Li stripping/plating process. As a result, the symmetrical cells and full cells with Li/CF electrodes exhibit improved cycling stability and effective suppression of dendrites at ambient temperature. This work facilitates the realization of solid‐state LMBs with high energy and high safety.     

Exploiting Lithium‐Depleted Cathode Materials for Solid‐State Li Metal Batteries

Solid‐state lithium metal batteries (SSLMBs) may become one of the high‐energy density storage devices for the next generation of electric vehicles. High safety and energy density can be achieved by utilizing solid electrolytes and Li metal anodes. Therefore, developing cathode materials which can match with Li metal anode efficiently is indispensable. In SSLMBs, Li metal anodes can afford the majority of active lithium ions, then lithium‐depleted cathode materials can be a competitive candidate to achieve high gravimetric energy density as well as save lithium resources. Li_0.33MnO₂ lithium‐depleted material is chosen, which also has the advantages of low synthesis temperature and low cost (cobalt‐free). Notably, solid‐state electrolyte can greatly alleviate the problem of manganese dissolution in the electrolyte, which is beneficial to improve the cycling stability of the battery. Thus, SSLMBs enable practical applications of lithium‐depleted cathode materials.     

Toward the Sustainable Lithium Metal Batteries with a New Electrolyte Solvation Chemistry

Herein, a new solvation strategy enabled by Mg(NO₃)₂ is introduced, which can be dissolved directly as Mg²⁺ and NO₃^? ions in the electrolyte to change the Li⁺ ion solvation structure and greatly increase interfacial stability in Li‐metal batteries (LMBs). This is the first report of introducing Mg(NO₃)₂ additives in an ester‐based electrolyte composed of ternary salts and binary ester solvents to stabilize LMBs. In particular, it is found that NO₃^? efficiently forms a stable solid electrolyte interphase through an electrochemical reduction reaction, along with the other multiple anion components in the electrolyte. The interaction between Li⁺ and NO₃^? and coordination between Mg²⁺ and the solvent molecules greatly decreases the number of solvent molecules surrounding the Li⁺, which leads to facile Li⁺ desolvation during plating. In addition, Mg²⁺ ions are reduced to Mg via a spontaneous chemical reaction on the Li metal surface and subsequently form a lithiophilic Li–Mg alloy, suppressing lithium dendritic growth. The unique solvation chemistry of Mg(NO₃)₂ enables long cycling stability and high efficiency of the Li‐metal anode and ensures an unprecedented lifespan for a practical pouch‐type LMB with high‐voltage Ni‐rich NCMA73 cathode even under constrained conditions.     

High‐Voltage‐Driven Surface Structuring and Electrochemical Stabilization of Ni‐Rich Layered Cathode Materials for Li Rechargeable Batteries

Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li⁺/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni‐rich NCM LiNi_0.895Co_0.085Mn_0.02O₂ is presented. The improved electrochemical performance at a high working voltage at 4.9 V is attributed to the removal of the resistive Ni²⁺O rock‐salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni²⁺O rock‐salt phase along with the structural evolution related to the metal dissolution are probed using in situ X‐ray diffraction, neutron diffraction, transmission electron microscopy, and X‐ray absorption spectroscopy. The findings help unravel the structural complexities associated with high working voltages and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni‐rich NCM materials.     

Native Vacancy Enhanced Oxygen Redox Reversibility and Structural Robustness

Cathode materials with high energy density, long cycle life, and low cost are of top priority for energy storage systems. The Li‐rich transition metal (TM) oxides achieve high specific capacities by redox reactions of both the TM and oxygen ions. However, the poor reversible redox reaction of the anions results in severe fading of the cycling performance. Herein, the vacancy‐containing Na_4/7[Mn_6/7(?_Mn)_1/7]O₂ (?_Mn for vacancies in the Mn? O slab) is presented as a novel cathode material for Na‐ion batteries. The presence of native vacancies endows this material with attractive properties including high structural flexibility and stability upon Na‐ion extraction and insertion and high reversibility of oxygen redox reaction. Synchrotron X‐ray absorption near edge structure and X‐ray photoelectron spectroscopy studies demonstrate that the charge compensation is dominated by the oxygen redox reaction and Mn³⁺/Mn⁴⁺ redox reaction separately. In situ synchrotron X‐ray diffraction exhibits its zero‐strain feature during the cycling. Density functional theory calculations further deepen the understanding of the charge compensation by oxygen and manganese redox reactions and the immobility of the Mn ions in the material. These findings provide new ideas on searching for and designing materials with high capacity and high structural stability for novel energy storage systems.     

Stable Lithium Electrodeposition at Ultra‐High Current Densities Enabled by 3D PMF/Li Composite Anode

Lithium metal batteries (LMBs) are promising candidates for next‐generation energy storage due to their high energy densities on both weight and volume bases. However, LMBs usually undergo uncontrollable lithium deposition, unstable solid electrolyte interphase, and volume expansion, which easily lead to low Coulombic efficiency, poor cycling performance, and even safety hazards, hindering their practical applications for more than forty years. These issues can be further exacerbated if operated at high current densities. Here a stable lithium metal battery enabled by 3D porous poly‐melamine‐formaldehyde (PMF)/Li composite anode is reported. PMF with a large number of polar groups (amine and triazine) can effectively homogenize Li‐ion concentration when these ions approach to the anode surface and thus achieve uniform Li deposition. Moreover, the 3D structured anode can serve as a Li host to mitigate the volume change during Li stripping and plating process. Galvanostatic measurements demonstrate that the 3D composite electrode can achieve high‐lithium Coulombic efficiency of 94.7% at an ultrahigh current density of 10 mA cm^?2 after 50 cycles with low hysteresis and smooth voltage plateaus. When coupled with Li₄Ti₅O₁₂, half‐cells show enhanced rate capabilities and Coulombic efficiencies, opening great opportunities for high‐energy batteries.     

Multifunctional Silanization Interface for High‐Energy and Low‐Gassing Lithium Metal Pouch Cells

Lithium (Li) metal has attracted unprecedented attention as the ultimate anode material for future rechargeable batteries, but the electrochemical behavior (such as Li dendrites and gassing problems) in real Li metal pouch cells has received little attention. To achieve realistic high‐energy Li metal batteries, the designed solid electrolyte interface to suppress both Li dendrites and catastrophic gassing problems is urgently needed at cell level. Here, an efficient multifunctional silanization interface (MSI) is proposed for high‐energy Li metal pouch cells. Such an MSI not only guides uniform nucleation and growth of Li metal but also suppresses interfacial parasitic reactions between Li metal and electrolyte. As a result, under harsh conditions (negative to positive electrode capacity ratio of 2.96 and electrolyte weight to cathode capacity ratio of 2.7 g Ah^?1), a long‐running lifespan (over 160 cycles with a capacity retention of 96% at 1 C), and low‐gassing behavior of realistic high‐energy Li metal pouch cell (1 Ah, 300 Wh kg^?1) is achieved. This work opens a promising avenue toward the commercial applications of high‐energy Li metal batteries.     

Suppressing Manganese Dissolution from Lithium Manganese Oxide Spinel Cathodes with Single‐Layer Graphene

Spinel‐structured LiMn₂O₄ (LMO) is a desirable cathode material for Li‐ion batteries due to its low cost, abundance, and high power capability. However, LMO suffers from limited cycle life that is triggered by manganese dissolution into the electrolyte during electrochemical cycling. Here, it is shown that single‐layer graphene coatings suppress manganese dissolution, thus enhancing the performance and lifetime of LMO cathodes. Relative to lithium cells with uncoated LMO cathodes, cells with graphene‐coated LMO cathodes provide improved capacity retention with enhanced cycling stability. X‐ray photoelectron spectroscopy reveals that graphene coatings inhibit manganese depletion from the LMO surface. Additionally, transmission electron microscopy demonstrates that a stable solid electrolyte interphase is formed on graphene, which screens the LMO from direct contact with the electrolyte. Density functional theory calculations provide two mechanisms for the role of graphene in the suppression of manganese dissolution. First, common defects in single‐layer graphene are found to allow the transport of lithium while concurrently acting as barriers for manganese diffusion. Second, graphene can chemically interact with Mn³⁺ at the LMO electrode surface, promoting an oxidation state change to Mn⁴⁺, which suppresses dissolution.     

Optimized Bicompartment Two Solution Cells for Effective and Stable Operation of Li–O2 Batteries

Lithium–oxygen batteries are in fact the only rechargeable batteries that can rival internal combustion engines, in terms of high energy density. However, they are still under development due to low‐efficiency and short lifetime issues. There are problems of side reactions on the cathode side, high reactivity of the Li anode with solution species, and consumption of redox mediators via reactions with metallic lithium. Therefore, efforts are made to protect/block the lithium metal anode in these cells, in order to mitigate side reactions. However, new approach is required in order to solve the problems mentioned above, especially the irreversible reactions of the redox mediators which are mandatory to these systems with the Li anode. Here, optimized bicompartment two solution cells are proposed, in which detrimental crossover between the cathode and anode is completely avoided. The Li metal anode is cycled in electrolyte solution containing fluorinated ethylene carbonate, in which its cycling efficiency is excellent. The cathode compartment contains ethereal solution with redox mediator that enables oxidation of Li₂O₂ at low potentials. The electrodes are separated by a solid electrolyte membrane, allowing free transport of Li ions. This approach increases cycle life of lithium oxygen cells and their energy efficiency.     

Lithium Polyacrylate (LiPAA) as an Advanced Binder and a Passivating Agent for High‐Voltage Li‐Ion Batteries

Intensive studies of an advanced energy material are reported and lithium polyacrylate (LiPAA) is proven to be a surprisingly unique, multifunctional binder for high‐voltage Li‐ion batteries. The absence of effective passivation at the interface of high‐voltage cathodes in Li‐ion batteries may negatively affect their electrochemical performance, due to detrimental phenomena such as electrolyte solution oxidation and dissolution of transition metal cations. A strategy is introduced to build a stable cathode–electrolyte solution interphase for LiNi_0.5Mn_1.5O₄ (LNMO) spinel high‐voltage cathodes during the electrode fabrication process by simply using LiPAA as the cathode binder. LiPAA is a superb binder due to unique adhesion, cohesion, and wetting properties. It forms a uniform thin passivating film on LNMO and conducting carbon particles in composite cathodes and also compensates Li‐ion loss in full Li‐ion batteries by acting as an extra Li source. It is shown that these positive roles of LiPAA lead to a significant improvement in the electrochemical performance (e.g., cycle life, cell impedance, and rate capability) of LNMO/graphite battery prototypes, compared with that obtained using traditional polyvinylidene fluoride (PVdF) binder for LNMO cathodes. In addition, replacing PVdF with LiPAA binder for LNMO cathodes offers better adhesion, lower cost, and clear environmental advantages.     

SiO2 Hollow Nanosphere‐Based Composite Solid Electrolyte for Lithium Metal Batteries to Suppress Lithium Dendrite Growth and Enhance Cycle Life

The low Coulombic efficiency and serious security issues of lithium (Li) metal anode caused by uncontrollable Li dendrite growth have permanently prevented its practical application. A novel SiO₂ hollow nanosphere‐based composite solid electrolyte (SiSE) for Li metal batteries is reported. This hierarchical electrolyte is fabricated via in situ polymerizing the tripropylene gycol diacrylate (TPGDA) monomer in the presence of liquid electrolyte, which is absorbed in a SiO₂ hollow nanosphere layer. The polymerized TPGDA framework keeps the prepared SiSE in a quasi‐solid state without safety risks caused by electrolyte leakage, meanwhile the SiO₂ layer not only acts as a mechanics‐strong separator but also provides the SiSE with high room‐temperature ionic conductivity (1.74 × 10^?3 S cm^?1) due to the high pore volume (1.49 cm³ g^?1) and large liquid electrolyte uptake of SiO₂ hollow nanospheres. When the SiSE is in situ fabricated on the cathode and applied to LiFePO₄/SiSE/Li batteries, the obtained cells show a significant improvement in cycling stability, mainly attributed to the stable electrode/electrolyte interface and remarkable suppression for Li dendrite growth by the SiSE. This work can extend the application of hollow nanooxide and enable a safe, efficient operation of Li anode in next generation energy storage systems.     

Self-Assembled Lithiophilic Interface with Abundant Nickel-Bis(Dithiolene) Sites Enabling Highly Durable and Dendrite-Free Lithium Metal Batteries

Despite its ultrahigh theoretical capacity and ultralow redox electrochemical potential, the practical application of lithium metal anodes is still hampered by severe dendrite growth and unstable solid electrolyte interphase (SEI). Herein, a self-assembled lithiophilic interface (SALI) for regulating Li electroplating behavior is constructed by introducing a meticulously synthesized Ni-bis(dithiolene)-based molecule (NiS₄-COOH) into a hybrid fluorinated ester-ether electrolyte. The NiS₄-COOH molecules with carboxyl functional groups can spontaneously anchor on the Li metal surface to form a SALI, whose abundant Ni-bis(dithiolene) sites can effectively reduce the initial Li deposition overpotential and guide the subsequent uniform Li electrodeposition. Moreover, due to the interaction between the coordination unsaturated Ni atom and the negatively charged PF₆⁻, the NiS₄-COOH additive can significantly change the ionic coordination environment in the electrolyte, which is greatly conducive to suppressing PF₆⁻ decomposition, optimizing SEI composition and accelerating Li-ion transfer. Consequently, the NiS₄-COOH-modified electrolyte leads to impressive electrochemical performance of Li||LiFePO₄ and Li||LiNi_0.8Co_0.1Mn_0.1O₂ batteries, delivering ultrahigh Coulombic efficiencies, considerable capacity retention, and good rate performance even at high areal active material loadings. This study presents the great potential of SALIs derived from multifunctional metal-organic hybrid electrolyte additives toward high-specific-energy Li metal batteries.