Li Metal Batteries Research Articles

Molecular Design of Solid Polymer Electrolytes with Enthalpy-Entropy Manipulation for Li Metal Batteries with Aggressive Cathode Chemistry.

Solid polymer electrolytes (SPEs) with high ion conductivity, high Li+ transference number, and a wide electrochemical window are promising for the next-generation high-energy Li metal batteries (LMBs). Here we describe an enthalpy-entropy manipulation strategy enabling a class of polycarbonate-based copolymeric electrolytes (PCCEs) with regulated cation/anion solvation via a molecular design of the polymer backbone. By integrating a weakly solvating linear carbonate with another strongly solvating cyclic carbonate segment in the polymer backbone, the cation-dipole coordination for Li+ ions (with two types of carbonyl groups) is weakened (low enthalpy penalty) and nondirectional (high entropy penalty), which enables a weak solvation and rapid diffusion of Li+. We further introduce a bis-acrylamide-based cross-linking segment which, other than imparting high mechanical strength, exhibits dihydrogen bonding with the difluoro(oxalate) borate anions, which is strong (high enthalpy penalty) and directional (low entropy penalty), thus restricting the migration of anions. As a result, the PCCE delivers a high ionic conductivity of 0.66 mS cm-1 with a high Li+ transference number (0.76) at 25 °C, as well as high oxidation stability. By an in situ polymerization approach, the PCCE enables LMBs using high-nikel LiNi0.8Co0.1Mn0.1O2 cathodes with a high capacity retention of 82.2% over 800 cycles with a cutoff voltage of 4.5 V and further LMBs using aggressive LiNi0.5Mn1.5O4 cathodes with a 96.4% capacity retention over 300 cycles with a cutoff voltage of 5.0 V. The described enthalpy-entropy manipulation approach offers a unique perspective for the molecular design of high-performance SPEs for high-energy Li metal batteries.

Constructing Donor–Acceptor-Linked COFs Electrolytes to Regulate Electron Density and Accelerate the Li+ Migration in Quasi-Solid-State Battery

HighlightsDonor–acceptor-linked covalent organic framework (COF)-based electrolyte can not only fulfill highly-selective Li+ conduction, but also offer a crucial opportunity to understand the role of electronic density in quasi-solid-state Li metal batteries.Donor–acceptor-linked COF electrolyte results in Li+ transference number 0.83, high ionic conductivity 6.7 × 10–4 S cm−1 and excellent cyclic ability in Li metal batteries.In situ characterizations, density functional theory calculation and time-of-flight secondary ion mass spectrometry are adopted to expound the mechanism of the rapid migration of Li+ in the “donor–acceptor” electrolyte system.

Regulating the Manganese Valence State Improves the Kinetic Properties of Manganese‐Based Cathodes

AbstractManganese (Mn)‐based lithium (Li)‐ion batteries with high energy density and low cost have recently attracted considerable attention. One drawback of Mn‐based batteries is the severe capacity attenuation caused by the Jahn‐Teller effect, which distorts the crystal structure and reduces the kinetics of Li‐ion insertion/extraction in the cathodes. In this study, the Mn valence state is regulated on the surface of Mn‐based oxide particles and oxygen vacancies are introduced to facilitate rapid Li‐ion transport and charge storage by adding succinonitrile (SN) to Mn‐based cathodes. Because of the reaction between SN and Mn‐based cathode particles, the contents of Mn3+ ions and oxygen vacancies increase, leading to an improvement in the Li‐ion kinetic properties of the cathodes as well as a reduction in the dissolution of Mn from the cathodes. By regulating the Mn valence state, Li‐ion and Li metal batteries with LiMn2O4 or Li‐rich Mn‐based layered oxide cathodes show significantly enhanced discharge capacity and improved cyclic performance. This study demonstrates that regulating the valence state of Mn ions is an effective strategy for enhancing the electrochemical performance of Mn‐based Li batteries and that adding SN to the cathodes is a cost‐effective method for mass production.

Unveiling Cu Nanoparticles Formed During Li Deposition in Anode-Free Batteries.

Developing high-energy-density Li metal batteries is essential for sustainable progress, necessitating in-depth studies of complex battery reactions. The presence of metallic Cu impurities detrimentally impacts battery performance, leading to issues such as self-discharging and internal soft short-circuit. Nevertheless, their formation mechanism and structural characteristics have not been revealed clearly. Here the formation of single-crystalline Cu nanoparticles during the Li deposition process in anode-free cells was identified by transmission electron microscopy. Through investigation of the chemical state of Cu before and after Li deposition, the formation of Cu NPs was attributed to the reduction of the oxide layers formed on the surface of Cu current collectors. Additionally, it was observed that Cu nanoparticles can be formed inside of deposited Li metal. This work reveals the formation pathway and microstructural characteristics of Cu nanoparticles appearing during Li deposition, underscoring the importance of nanoscale investigations into the underlying battery reactions.

Dual Ionic Pathways in Semi-Solid Electrolyte based on Binary Metal-Organic Frameworks Enable Stable Operation of Li-Metal Batteries at Extremely High Temperatures.

The rapid development of the electronics market necessitates energy storage devices characterized by high energy density and capacity, alongside the ability to maintain stable and safe operation under harsh conditions, particularly elevated temperatures. In this study, a semi-solid-state electrolyte (SSSE) for Li-metal batteries (LMB) is synthesized by integrating metal-organic frameworks (MOFs) as host materials featuring a hierarchical pore structure. A trace amount of liquid electrolyte (LE) is entrapped within these pores through electrochemical activation. These findings demonstrate that this structure exhibits outstanding properties, including remarkably high thermal stability, an extended electrochemical window (5.25V vs Li/Li+), and robust lithium-ion conductivity (2.04×10-4Scm-1), owing to the synergistic effect of the hierarchical MOF pores facilitating the storage and transport of Li ions. The Li//LiFePO4 cell incorporating prepared SSSE shows excellent capacity retention, retaining 97% (162.8mAhg-1) of their initial capacity after 100 cycles at 1C rate at an extremely high temperature of 95°C. It is believed that this study not only advances the understanding of ion transport in MOF-based SSSE but also significantly contributes to the development of LMB capable of stable and safe operation even under extremely high temperatures.

Interfacial challenges and recent advances of solid‐state lithium metal batteries

AbstractGrowing market demands on portable electronics, electric vehicles, and energy storage system calls for the development of high‐energy density lithium (Li) batteries. Li metal is considered as a promising anode material owing to their high capacity and low electrochemical potential. However, high reactivity of Li metal with conventional flammable liquid electrolytes easily forms Li dendrites, which may cause short‐circuit and even catching fire, obstructing the wide application of Li metal batteries. Although non−/less‐flammable solid electrolytes have replaced the conventional liquid electrolytes, solid‐state Li metal batteries (SSLMBs) suffer from lower Li+ conductivities, chemical/electrochemical incompatibilities toward Li metal, and inhomogeneous Li+ flux at the interfaces. Therefore, many researchers have devoted themselves to solve these problems. For a better understanding on the current issues and recent advances, this article provides (1) a review on various solid electrolytes with high Li+ conductivity and their interfacial issues in SSLMBs, and (2) recent progress in stabilization of the interface between the Li node and solid electrolytes, including an electrolyte modification (e.g., composition, additives) and introduction of an interlayer.

Few-layered graphene from cathodic exfoliation in binary solvents and application as a protective layer for lithium metal anodes

Electrochemical exfoliation is a top-down method recognized for its environmentally friendly and scalable approach for producing solution-processable graphene. Among its variation, cathodic exfoliation stands out for its potential in generating few-layer graphene with minimal defects. In this study, we developed a cathodic exfoliation method for graphite foil using a binary solvent system to produce graphene with a reduced number of layers. By employing a 0.1 M LiClO4 solution in a dimethyl sulfoxide and dimethyl carbonate solvents mixture at a 1:2 vol ratio, we enhanced the intercalation of solvated lithium ions into graphite, successfully exfoliating graphene with 5–6 layers. The exfoliated graphene exhibited a low defect density (ID/IG ∼0.05) and a C/O ratio of 33.2. Furthermore, when used as a coating on a separator, the exfoliated few-layered graphene (FLG) sheets demonstrated notable performance as a protective layer for Li metal anode in Li metal battery technology.

Dynamic interface layer enables epitaxial Li deposition for anode-free Li metal batteries

Anode-free Li-metal batteries are the best high-energy-density Li-ion batteries. However, the lack of active Li on anode side exacerbates dendritic Li growth, dead Li formation and parasitic reactions. In this study, we develop a lithiophilic Mg modification layer on Cu foil surface using magnetron sputtering. The epitaxial and dense Li deposition are manipulated, attributing to excellent Li affinity, favorable charge transfer and self-diffusion kinetics of the functional layer. Consequently, the coulombic efficiency of Li deposition/stripping on the Mg-coated Cu substrate remains at 83.7 % even after 50 cycles under 0.5 mA cm−2. Importantly, this approach enable the pouch cells paired with LiFePO4 cathodes to achieve a lifespan of over 70 cycles under 0.5 mA cm−2 without experiencing a significant capacity drop. This straightforward strategy is promising for developing long-lasting anode-free Li batteries.

Li2ZnCu3 modified Cu current collector to regulate Li deposition

Rationally designing a current collector that can maintain low lithium (Li) porosity and smooth morphology while enduring high‐loading Li deposition is crucial for realizing the high energy density of Li metal batteries, but it is still challengeable. Herein, a Li2ZnCu3 alloy‐modified Cu foil is reported as a stable current collector to fulfill the stable high‐loading Li deposition. Benefiting from the in‐situ alloying, the generated numerous Li2ZnCu3@Cu heterojunctions induce a homogeneous Li nucleation and dense growth even at an ultrahigh capacity of 12 mAh cm‐2. Such a spatial structure endows the overall Li2ZnCu3@Cu electrode with the manipulated steric hindrance and outmost surface electric potential to suppress the side reactions during Li stripping and plating. The resultant Li||Li2ZnCu3@Cu asymmetric cell preserves an ultrahigh average Coulombic efficiency of 99.2% at 3 mA cm‐2/6 mAh cm‐2 over 200 cycles. Moreover, the Li‐Li2ZnCu3@Cu||LiFePO4 cell maintains a cycling stability of 87.5% after 300 cycles. After coupling with the LiCoO2 cathode (4 mAh cm‐2), the cell exhibits a high energy density of 407.4 Wh kg‐1 with remarkable cycling reversibility at an N/P ratio of 3. All these findings present a doable way to realize the high‐capacity, dendrite‐free, and dense Li deposition for high‐performance Li metal batteries.

Li2ZnCu3 Modified Cu Current Collector to Regulate Li Deposition.

Rationally designing a current collector that can maintain low lithium (Li) porosity and smooth morphology while enduring high-loading Li deposition is crucial for realizing the high energy density of Li metal batteries, but it is still challengeable. Herein, a Li2ZnCu3 alloy-modified Cu foil is reported as a stable current collector to fulfill the stable high-loading Li deposition. Benefiting from the in situ alloying, the generated numerous Li2ZnCu3@Cu heterojunctions induce a homogeneous Li nucleation and dense growth even at an ultrahigh capacity of 12 mAh cm-2. Such a spatial structure endows the overall Li2ZnCu3@Cu electrode with the manipulated steric hindrance and outmost surface electric potential to suppress the side reactions during Li stripping and plating. The resultant Li||Li2ZnCu3@Cu asymmetric cell preserves an ultrahigh average Coulombic efficiency of 99.2 % at 3 mA cm-2/6 mAh cm-2 over 200 cycles. Moreover, the Li-Li2ZnCu3@Cu||LiFePO4 cell maintains a cycling stability of 87.5 % after 300 cycles. After coupling with the LiCoO2 cathode (4 mAh cm-2), the cell exhibits a high energy density of 407.4 Wh kg-1 with remarkable cycling reversibility at an N/P ratio of 3. All these findings present a doable way to realize the high-capacity, dendrite-free, and dense Li deposition for high-performance Li metal batteries.

LiNO3 regulated rigid-flexible-synergistic polymer electrolyte boosting high-performance Li metal batteries

Conventional polymer electrolytes suffer from low ionic conductivity, poor interface compatibility, low mechanical strength and certain flammability. Herein, a rigid-flexible synergistic ultrastrong nonflammable polymer electrolyte (LiNO3-PPT@PI) regulated by LiNO3 is developed, which consists of rigid polyimide (PI) fiber skeleton and flexible poly pentaerythritol tetraacrylate (PPT) plasticized with LiNO3/triethyl phosphate (TEP)/fluoroethylene carbonate (FEC). PI fiber skeleton enhances tensile strength of LiNO3-PPT@PI to 21.8 MPa. TEP effectively enhances ionic conductivity to 7.57 × 10−4 S cm−1 at 30 °C and improves flame retardancy. LiNO3 is creatively utilized as the only lithium salt for LiNO3-PPT@PI to construct Li3N-rich solid electrolyte interphases (SEIs) and promote FEC to form LiF-rich SEIs/cathode-electrolyte interphases (CEIs) to improve interface stability, thereby enabling high-efficiency, long-term and dendrite-free cycling of LiFePO4 (LFP)||Li cells and LiNi0.8Mn0.1Co0.1O2 (NCM811)||Li cells, which is superior to the LiPF6-based polymer electrolytes. LFP||Li cells with LiNO3-PPT@PI exhibit excellent cycle performance over 650 cycles with 81.8 % capacity retention. This work presents a promising design strategy of safe and efficient polymer electrolytes for Li metal batteries.

Leveraging Ion Pairing and Transport in Localized High-Concentration Electrolytes for Reversible Lithium Metal Anodes at Low Temperatures.

Coulombic efficiency of over 99 % is rarely achieved for Li metal anode below -40 °C, hindering the practical application of high-energy-density Li metal batteries under extreme conditions. Herein, limiting factors for Li metal reversibility are investigated utilizing ether-based localized high-concentration electrolytes of different solvent-diluent combinations. We find that along with the desolvation barrier, bulk ion transport properties including ionic conductivity, transference number, and diffusivity are also crucial factors for low-temperature Li deposition behavior. Superior Li metal reversibility was observed within the combination of the solvent with moderately weak solvating power and the diluent with minimal viscosity, highlighting the role of ion transport and the necessity for a trade-off with desolvation. The optimized electrolyte composed of lithium bis(fluorosulfonyl)imide, methyl n-propyl ether, and 1,1,2,2-tetrafluoroethyl methyl ether delivers exceptional Coulombic efficiency of 99.34 % at -40 °C and 98.96 % at -60 °C under a current density of 0.5 mA cm-2. Furthermore, Li||LiCoO2 (2.7 mAh cm-2) cells demonstrate impressive reversible capacity and cycling stability at these temperatures. This work sheds light on the less-recognized relevance of bulk ion transport to low-temperature performance and provides guidelines for the electrolyte design of Li metal batteries operating in cold environments.

Boron Surface Treatment of Li7La3Zr2O12 Enabling Solid Composite Electrolytes for Li-Metal Battery Applications.

Despite being promoted as a superior Li-ion conductor, lithium lanthanum zirconium oxide (LLZO) still suffers from a number of shortcomings when employed as an active ceramic filler in composite polymer-ceramic solid electrolytes for rechargeable all-solid-state lithium metal batteries. One of the main limitations is the detrimental presence of Li2CO3 on the surface of LLZO particles, restricting Li-ion transport at the polymer-ceramic interfaces. In this work, a facile way to improve this interface is presented, by purposely engineering the LLZO particle surfaces for a better compatibility with a PEO:LiTFSI solid polymer electrolyte matrix. It is shown that a surface treatment based on immersing LLZO particles in a boric acid solution can improve the LLZO surface chemistry, resulting in an enhancement in the ionic conductivity and cation transference number of the CPE with 20 wt % of boron-treated LLZO particles compared to the analogous CPE with non-treated LLZO. Ultimately, an improved cycling performance and stability in Li//LiFePO4 cells was also demonstrated for the modified material.

Enhanced Long-Term Cycling Life of Ni-Rich NMC Cathodes in High-Voltage Lithium-Metal Batteries.

Li metal batteries (LMBs) have revived people's interest due to their high energy density. This work compares the cycling stability, structure stability, and thermal stability of Li||0.7Nb-NMC 9055 (0.7% Nb-modified LiNi0.9Co0.05Mn0.05O2) system in commercial carbonate electrolyte (1.0 M LiPF6 in EC/DMC) and designed carbonate electrolyte (1.0 M LiPF6-0.125 M LiNO3-0.025 M Mg(TFSI)2 in FEC-EMC). Li||0.7Nb-NMC 9055 battery with designed carbonate electrolyte exhibited superior capacity retention, 80% after ∼500 cycles. This can be explained by the improved mechanical integrity of the secondary particles and large reduced charge transfer resistance. Further, the real-time thermal monitoring of full cell via a high-precision, multimode calorimeter TAM IV Micro XL shows that the designed carbonate electrolyte with multisalt additive and FEC cosolvent has less heat release during the charging and discharge process, allowing these high-nickel (Ni) cathodes to reach closer to their full potential.

Unraveling the Deposition and Dissolution Behavior of the Ag-Modified Li Surface Based on Electrochemical Atomic Force Microscopy.

Lithium is a promising anode material for advanced batteries because of its high capacity and low redox potential. However, its practical use is hindered by nonuniform Li deposition and dendrite formation, leading to safety concerns in Li metal batteries. Our study shows that Ag-based materials enhance the uniformity of Li deposition on Ag-modified Li (AgLi) surfaces, thereby addressing these key challenges. This improvement is due to the strong affinity of Ag for Li, which promotes uniform deposition and dissolution. Additionally, the AgLi surface demonstrated an improved cycling stability, which is crucial for long-term battery reliability. Emphasizing our analytical approach, we utilized comprehensive techniques such as Kelvin probe force microscopy (KPFM) and electrochemical atomic force microscopy (EC-AFM) to locally analyze the electrical properties and unravel the Li deposition/dissolution mechanisms. KPFM analysis provided crucial insights into surface potential variations, while EC-AFM highlighted topographical changes during the Li deposition and dissolution processes, contributing significantly to the development of safer and more efficient Li metal batteries.

Aluminum Corrosion Chemistry in High-Voltage Lithium Metal Batteries with LiFSI-Based Ether Electrolytes.

High-voltage Li metal batteries (LMBs) based on ether electrolytes hold potential for achieving high energy densities exceeding 500 Wh kg-1, but face challenges with electrolyte oxidative stability, particularly concerning aluminum (Al) current collector corrosion. However, the specific chemistry behind Al corrosion and its effect on electrolyte components remains unexplored. Here, our study delves into Al corrosion in the representative LiFSI-DME electrolyte system, revealing that low-concentration electrolytes exacerbate Al current collector corrosion and solvent decomposition. In contrast, high-concentration electrolytes mitigate these issues, enhancing long-term stability. Remarkably, LiFSI-0.7DME electrolyte demonstrates exceptional stability with up to 1000 cycles at high voltage without significant capacity decay. These findings offer crucial insights into Al corrosion mechanisms in ether-based electrolytes, advancing our comprehension of high-voltage LMBs and facilitating their development for practical applications.

Dual Li ion transport channels in a dynamical supramolecular solid electrolyte toward safety and high-performance Li metal batteries

The polymer based quasi-solid electrolyte (QSE), which combines the high ionic conductivity of the liquid electrolytes with the excellent mechanical flexibility of the polymer matrix, is highly desired and most promising for Li metal batteries (LMBs). However, the Li+ transfer pathways in QSE is not clear enough, and the practical applications in LMBs are also hindered by safety hazards arising from risks of mechanical damage, flammability and high voltage instability. Here, a dynamical supramolecular QSE with abundant hydrogen bonds to fabricate stable and safety LMBs, is reported. In this designed electrolyte, both thermal stability and superior interface stability with anode/cathode electrodes were achieved. Notably, the dual Li+ transport channels in QSE were investigated using in-situ FTIR technology and DFT calculations, providing insights into both the “wet” liquid phase and “dry” polymer chain channels. Benefiting from this design, the Li||NCM622 full batteries based on this QSE exhibit excellent long-term cycling stability.

Entropy-Driven 60mol% Li Electrolyte for Li Metal-Free Batteries.

Highly Li-concentrated electrolytes are acknowledged for their compatibility with Li metal negative electrodes and high voltage positive electrodes to achieve high-energy Li metal batteries, showcasing stable and facile interfaces for Li deposition/dissolution and high anodic stability. This study aims to explore a highly concentrated electrolyte by adopting entropy-driven chemistry for Li metal-free (so-called anode-free) batteries. The combination of lithium bis(fluorosulfonyl)amide (LiFSA) and lithium trifluoromethanesulfonate (LiOTf)salts in a pyrrolidinium-based ionic liquid is found to significantly modify the coordination structure, resulting in an unprecedented 60mol% Li concentration and a low solvent-to-salt ratio of 0.67:1 in the electrolyte system. This novel 60mol% Li electrolyte demonstrates unique coordination stricture, featuring a high ratio of monodentate-anion structures and aggregates, which facilitates an enhanced Li+ transference number and improved anodic stability. Moreover, the developed electrolyte provides a facile de-coordination process and leads to the formation of an anion-based solid electrolyte interface, which enables stable Li deposition/dissolution properties and demonstrates excellent cycling stability in the Li metal-free full cell with a Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) positive electrode.

In Situ Inorganic/Organic Protective Layer on Carbon Paper as Advanced Current Collector for Robust Li Metal Anode.

Lithium (Li) metal is regarded as the most promising anode for next-generation batteries with high energy density. However, the uncontrolled dendrite growth and infinite volume expansion during cycling seriously hinder the application of Li metal batteries (LMBs). Herein, an inorganic/organic protective layer (labeled as BPH), composed of in situ formed inorganic constituents and PVDF-HFP, is designed on the 3D carbon paper (CP) surface by hot-dipping method. The BPH layer can effectively improve the mechanical strength and ionic conductivity of the SEI layer, which is beneficial to expedite the Li-ion transfer of the entire framework and achieve stable Li plating/stripping behavior. As a result, the modified 3D CP (BPH-CP) exhibits an ultrahigh average Coulombic efficiency (CE) of ≈99.7% over 400 cycles. Further, the Li||LiFePO4 (LFP) cell exhibits an extremely long-term cycle life of over 3000 cycles at 5 C. Importantly, the full cell with high mass loading LiFePO4 (20mgcm-2) or LiNi0.8Co0.1Mn0.1O2 (NCM, 16mgcm-2) cathode exhibits stable cycling for 100 or 150 cycles at 0.5 C with high-capacity retention of 86.5% or 82.0% even at extremely low N/P ratio of 0.88 or 0.94. believe that this work enlightens a simple and effective strategy for the application of high-energy-density and high-rate-C LMBs.

Engineering Moderately Lithiophilic Paper-Based Current Collectors with Variable Solid Electrolyte Interface Films for Anode-Free Lithium Batteries.

Compared to traditional lithium metal batteries, anode-free lithium metal batteries use bare current collectors as an anode instead of Li metal, making them highly promising for mass production and achieving high-energy density. The current collector, as the sole component of the anode, is crucial in lithium deposition-stripping behavior and greatly impacts the rate of Li depletion from the cathode. In this study, to investigate the lithiophilicity effect of the current collector on the solid electrolyte interface (SEI) film construction and cycling performance of anode-free lithium batteries, various lightweight paper-based current collectors were prepared by electroless plating Cu and lipophilic Ag on low-dust paper (LDP). The areal densities of the as-prepared LDP@Cu, LDP@Cu-Ag, and LDP@Ag were approximately 0.33 mg cm-2. The use of lipophilic Ag-coated collectors with varying loadings allowed for the regulation of lipophilicity. The impacts of these collectors on the distribution of SEI components and Li depletion rate in common electrolytes were investigated. The findings suggest that higher loadings of lipophilic materials, such as Ag, on the current collector increase its lipophilicity but also lead to significant Li depletion during the cycling process in full-cell anode-free Li metal batteries. Thus, moderately lithiophilic current collectors, such as LDP@Cu-Ag, show more potential for Li deposition and striping and stable SEI with a low speed of Li depletion.