Li Metal Anode Research Articles

All-Solid-State Lithium-Sulfur Batteries of High Cycling Stability and Rate Capability Enabled by a Self-Lithiated Sn-C Interlayer.

All-solid-state lithium-sulfur batteries (ASSLSBs) have attracted intense interest due to their high theoretical energy density and intrinsic safety. However, constructing durable lithium (Li) metal anodes with high cycling efficiency in ASSLSBs remains challenging due to poor interface stability. Here, a compositionally stable, self-lithiated tin (Sn)-carbon (C) composite interlayer (LSCI) between Li anode and solid-state electrolyte (SSE), capable of homogenizing Li-ion transport across the interlayer, mitigating decomposition of SSE, and enhancing electrochemical/structural stability of interface, is developed for ASSLSBs. The LSCI-mediated Li metal anode enables stable Li plating/stripping over 7000h without Li dendrite penetration. The ASSLSBs equipped with LSCI thus exhibit excellent cycling stability of over 300 cycles (capacity retention of ≈80%) under low applied pressure (<8MPa) and demonstrate improved rate capability even at 3C. The enhanced electrochemical performance and corresponding insights of the designed LSCI broaden the spectrum of advanced interlayers for interface manipulation, advancing the practical application of ASSLSBs.

Regulating the horizontal confined deposition of lithium metal by Co-Nx modified honeycomb-like carbon nanosheets

The uncontrollable Li dendrite growth as well as the severe volume expansion of Li metal anodes during cycling significantly impedes the practical applications of high-energy-density Li metal batteries. In this work, an innovative modulation strategy has been developed by constructing honeycomb-like nitrogen-doped carbon nanosheets with uniformly anchored cobalt nanoparticles (denoted as Co@HNC) for regulating the Li deposition behavior and meanwhile alleviating volume change during cycling. On one hand, the lithiophilic Co-Nx sites can largely reduce the energy barrier of Li nucleation and subsequently guide horizontal confined Li deposition in the honeycomb-like holes of Co@HNC, which is verified by the density functional theory calculations and in-situ optical microscopy observations. On the other hand, the honeycomb-like carbon framework with good structural integrity can endure the huge volume change during repeated Li plating/stripping processes. Consequently, the optimized Co@HNC electrode delivered a promoted cycling life for over 600 times with high Coulombic efficiency of 98.5 % at 1 mA cm−2. When matched with the high-mass-loading LiFePO4 (20 mg cm−2) or high-voltage LiNi0.8Mn0.1Co0.1O2 cathode, the Li@Co@HNC anode exhibited outstanding cycling stability and rate capability under low negative/positive capacity ratio, demonstrating its great potential in practical applications of high-energy-density lithium metal batteries.

Dead Lithium in Lithium Metal Batteries: Formation, Characterization and Strategies.

Lithium (Li) metal anode (LMA) replacing graphite anode for developing Li metal batteries (LMB) with the higher energy density has attracted much attention. However, LMA faces many issues, e. g., Li dendrites, dead Li and the side reactions, which causes the safety hazards and low coulomb efficiency (CE) of battery, therefore, LMB still cannot replace the current Li ion battery for practical use. Among those issues, dead Li is one of the decisive factors affecting the CE of LMB. To better understand dead Li, we summarize the recent work about the generation of dead Li, its impact on batteries performance, and the strategies to reuse and eliminate dead Li. Finally, the prospect of the future LMA and resultant LMB is also put forward.

Lightweight Electrolyte Design for Li/Sulfurized Polyacrylonitrile (SPAN) Batteries.

Sulfurized polyacrylonitrile (SPAN) recently emergesas a promising cathode for high-energy lithium (Li) metal batteries owing to its high capacity, extended cycle life, and liberty from costly transition metals. As the high capacities of both Li metal and SPAN lead to relatively small electrode weights, the weight and specific energy density of Li/SPAN batteries are particularly sensitive to electrolyte weight, highlighting the importance of minimizing electrolyte density. Besides, the large volume changes of Li metal anode and SPAN cathode require inorganic-rich interphases that can guarantee intactness and protectivity throughout long cycles. This work addresses these crucial aspects with an electrolyte design where lightweight dibutyl ether (DBE) is used as adiluent for concentrated lithium bis(fluorosulfonyl)imide(LiFSI)-triethyl phosphate (TEP) solution. The designed electrolyte (d = 1.04g mL-1) is 40%-50% lighter than conventional localized high-concentration electrolytes (LHCEs), leading to 12%-20% extra energy density at the cell level. Besides, the use of DBE introduces substantial solvent-diluent affinity, resulting in a unique solvation structure with strengthened capability to form favorable anion-derived inorganic-rich interphases, minimize electrolyte consumption, and improve cell cyclability. The electrolyte also exhibits low volatility and offers good protection to both Li metal anode and SPAN cathode under thermal abuse.

Reactive Solid Polymer Layer: From a Single Fluoropolymer to Divergent Fluorinated Interface

AbstractControlling the structure and chemistry of solid electrolyte interphase (SEI) underpins the stability of electrolyte‐electrode interface, and is crucial for advancing rechargeable lithium metal batteries (LMBs). Here, we utilized photo‐controlled copolymerization to achieve the on‐demand synthesis of fluorosulfonyl fluoropolymers as unprecedented artificial SEI layers on Li metal anodes. This work not only enables instant formation of a hybrid polymer‐inorganic interphase that consists of a polymer‐enriched top layer and a LiF‐fortified bottom layer, originating from a single polymeric component, but also imparts various desirable physical properties (e.g., good mechanical strength and flexibility, high ion conductivity, low overpotential) to SEI via a single‐to‐divergent strategy. Model reactions and structural characterizations supported the formation of a divergent fluorinated interphase, which furnished prolonged stabilization of Li deposition, high coulombic efficiency and improved cycling behavior in electrochemical experiments. This work highlights the great potential of exploring reactive polymers as versatile coatings to stabilize Li metal anodes, providing a promising avenue to solve electrode‐electrolyte interfacial problems for LMBs.

Revealing the Role of Lithium Carbonate at Lithium Metal Anodes Through Study of Gas-Reacted Interphases

A stable, ionically-conductive solid electrolyte interphase (SEI) is vital to lithium (Li) metal anodes, yet key properties of common SEI phases remain unknown. Among these, Li2CO3, central to foundational SEI models, has been difficult to probe given its metastability on Li. To address this, we adopted two approaches: (i) synthesis and study of model Li2CO3-based SEI and (ii) cycling and titration-based analysis of SEI from Li–Cu cells with or without additive CO2, with the aim of modulating Li2CO3 content natively. In (i), reductive instability of Li2CO3 led to co-formation of Li2O and Li2C2 in a multiphasic film with a Li+ conductivity (∼8 × 10−9 S cm−1) more than 4x higher than previously-measured Li2O or LiF films. Li2CO3 content in native interphases from (ii) was found to correlate with decreased inactive Li0 accumulation and improved Coulombic efficiency (CE) across diverse electrolytes having moderate CE. In high CE electrolytes, however, capacity losses become dominated by SEI formation rather than inactive Li0, and Li2CO3 enrichment had negligible impact. This work updates understanding of SEI Li2CO3 formed in modern electrolytes, reveals a leading mechanism by which Li2CO3 can boost CE despite its metastability, and indicates the potential and limitations of enriching this phase through electrolyte design.

Synergistic effect of infinite and finite solid solution enabling ultrathin Li–Cu–Ag alloy toward advanced Li metal anode

Synergistic effect of infinite and finite solid solution enabling ultrathin Li–Cu–Ag alloy toward advanced Li metal anode

Gradient Lithium Ion Regulation Current Collectors for High-Performance and Dendrite-Free Li Metal Batteries.

Lithium metal anode has attracted wide attention due to its ultrahigh theoretical specific capacity, lowest reduction potential, and low density. However, uncontrollable dendritic growth and volume change caused by uneven Li+ deposition still seriously hinder the large-scale commercial application of lithium metal batteries, even causing serious battery explosions and other safety problems. Hence, gold nanoparticles with a gradient distribution anchored on 3D carbon fiber paper (CP) current collectors followed by the encapsulation of polydopamine (PDA) (CP/Au/PDA) are constructed for stable and dendrite-free Li metal anodes for the first time. Significantly, lithiophilic Au nanoparticles showing a gradient distribution in the carbon fiber paper could guide the transfer of Li+ from the outside to the inside of the CP/Au/PDA electrode as well as lower the nucleation overpotential of Li, thereby obtaining the uniform Li deposition. Meanwhile, the PDA layer could in situ be converted to Li-PDA which could serve as an efficient Li+ conductor to further facilitate uniform Li+ transport among the whole CP/Au/PDA electrode. Besides, 3D carbon fiber paper could effectively accommodate the volume change during the plating/stripping process of Li metal. As a result, CP/Au/PDA electrodes deliver a low nucleation overpotential (∼9 mV) and a high Coulombic efficiency (mean value of ∼98.8%) at a current density of 1 mA cm-2 with the capacity of 1 mA h cm-2. Furthermore, Li@CP/Au/PDA electrodes also can demonstrate an ultralow voltage hysteresis (∼20 mV) and a long cycle life (1000 h) in symmetric cells. Finally, with LiFePO4 (LFP) as the cathode, the Li@CP/Au/PDA-LFP full cell delivers a high discharge capacity of 136 mA h g-1 even after 350 cycles at 1C, exhibiting a per cycle loss as low as 0.01%. This gradient lithium ion regulation current collector is of great significance for the development of lithium metal anodes.

Application of artificial SEI layers for lithium metal battery anodes

Unpredictable lithium dendrite growth on the metal anode and repeated destruction and creation of the solid electrolyte interphase (SEI) layer result in hidden risks and low Coulombic efficiencies (CEs). Researchers have found that designing a high-quality SEI layer can prevent the growth of dendrite. However, designing and forming a high-quality SEI layer is still a problem. Making trade-off between capacity reduction caused by the SEI layer and better cycle stability significantly limits the general performance of lithium metal batteries. In this research, characteristics of SEI layers and some significant advancements made in SEI formation are outlined. Some designs for the SEI layers on the lithium metal anodes include designing hybrid polymer SEI layers, producing synthetic SEI layers. By controlling the behaviours of Li ions throughout the stripping and depositing processes, the capacity and stability of Li metal anodes may be improved. Finally, some case studies of the applying of SEI in lithium metal battery systems are introduced.

Heterogeneous Solid Electrolyte Interphase Interactions Dictate Interface Instability in Sodium Metal Electrodes.

Sodium (Na) metal batteries have attracted recent attention due to their low cost and high abundance of Na. However, the advancement of Na metal batteries is impeded due to key challenges such as dendrite growth, solid electrolyte interphase (SEI) fracture, and low Coulombic efficiency. This study examines the coupled electro-chemo-mechanical interactions governing the electrodeposition stability and morphological evolution at the Na/electrolyte interface. The SEI heterogeneities influence transport and reaction kinetics leading to the formation of current and stress hotspots during Na plating. Further, it is demonstrated that the heterogeneity-induced Na metal evolution and its influence on the stress distribution critically affect the mechanical overpotential, contributing to a faster SEI failure. The analysis reveals three distinct failure mechanisms-mechanical, transport, and kinetic-that govern the onset of instabilities at the interface. Finally, a comprehensive comparative study of SEI failure in Na and lithium (Li) metal anodes illustrates that the electrochemical and mechanical characteristics of the SEI are crucial in tailoring the anode morphology and interface stability. This work delineates mechanistic stability regimes cognizant of the SEI attributes and underlying failure modes and offers important guidelines for the design of artificial SEI layers for stable Na metal electrodes.

Synergistic Evolution of Alloy Nanoparticles and Carbon in Solid-State Lithium Metal Anode Composites at Low Stack Pressure.

Solid-state batteries with Li metal anodes can offer increased energy density compared to Li-ion batteries. However, the performance of pure Li anodes has been limited by morphological instabilities at the interface between Li and the solid-state electrolyte (SSE). Composites of Li metal with other materials such as carbon and Li alloys have exhibited improved cycling stability, but the mechanisms associated with this enhanced performance are not clear, especially at the low stack pressures needed for practical viability. Here, we investigate the structural evolution and correlated electrochemical behavior of Li metal composites containing reduced graphene oxide (rGO) and Li-Ag alloy particles. The nanoscale carbon scaffold maintains homogeneous contact with the SSE during stripping and facilitates Li transport to the interface; these effects largely prevent interfacial disconnection even at low stack pressure. The Li-Ag is needed to ensure cyclic refilling of the rGO scaffold with Li during plating, and the solid-solution character of Li-Ag improves cycling stability compared to other materials that form intermetallic compounds. Full cells with sulfur cathodes were tested at relatively low stack pressure, achieving 100 stable cycles with 79% capacity retention.

Review on Artificial Interphases for Lithium Metal Anodes: From a Mechanical Perspective

AbstractLithium (Li) metal is a promising candidate for next‐generation high‐energy‐density rechargeable batteries. However, the solid electrolyte interphase (SEI) inevitably suffers from mechanical fracture owing to the large morphological change during Li cycling, leading to the uncontrollable growth of Li dendrites, low Coulombic efficiency, and short cycle life. The fabrication of an artificial interphase is an effective strategy for improving the performances of Li metal anodes. The ideal artificial interphase should provide sufficient mechanical robustness to suppress dendritic Li growth and accommodate large volume changes during Li deposition‐dissolution cycles. In this review, we focus on the fabrication of mechanically robust artificial interphases for stabilizing Li‐metal anodes, including the underlying mechanism of SEI fracture, quantitative requirements for mechanical properties, measurements of mechanical properties, and recent progress in the fabrication of mechanically stable artificial interphases.

Functional Separators for Modulating Li‐Ion Flux Toward Uniform Li Deposition: A Review

AbstractHomogeneous Li‐ion flux is a significant precondition of uniform Li‐ion deposition in Li metal batteries (LMBs). Numerous methodologies have been presented for homogenizing Li‐ion flux before Li deposition based on the features of Li‐ion deposition. Separators that provide Li‐ion transfer channels and are directly exposed to Li metal anodes have attracted rising attention for their role in guiding regular Li‐ion distribution. More novel functional separators have been proposed aiming to achieve dendrite‐free deposition. Herein, the factors and strategies that regulate Li‐ion distribution through functional separators toward LMBs are concentrated on. The current mechanisms of Li‐ion flux regulation by functional separators are first highlighted, including physical properties, interactions with the electrolyte, and modification of the solid‐state electrolyte interphase. According to these mechanisms, functional separator strategies for regulating Li‐ion flux are divided into three methodologies, and typical examples are introduced. Finally, current limitations and suggestions for future functional separator studies are presented, aiming to inspire engaged researchers and newcomers to trigger more exciting works in this area.

An Ion‐Management Membrane with Vertically Aligned Uniform Electronegative Nanochannels Toward Dendrite‐Free Lithium Metal Anodes

AbstractLithium (Li) metal anodes have received sustained attention due to their remarkable theoretical specific capacities and low electrochemical potentials. However, the nucleation and growth of Li dendrites during cycling have hindered their application in Li metal batteries (LMBs). As an indispensable battery component, separators offer an ideal platform for mitigating Li dendrites. Herein, an ion‐management membrane (IMM) concept utilizing polydopamine (PDA)‐modified polyetherimide track‐etched membranes (PEITEMs) is proposed. The PDA@PEITEM‐based IMM features vertically aligned uniform electronegative nanochannels, serving as ion distributors and “Li‐ion guides” to simultaneously smooth ion concentration fluctuations and accelerate Li+ selective conduction. The IMM's unique structural and chemical properties yield exceptional ionic conductivity (0.73 mS cm−1) and high Li+ transfer number (0.80) while minimizing Li+ concentration fluctuations. When employed in Li/Cu cells, the IMM facilitates a Coulombic efficiency exceeding 96% over 100 cycles at 0.5 mA cm−2. Moreover, it extends the cycle lifespan of Li/Li cells to 1 200 h at 1.0 mA cm−2. For Li/LiFePO4 cells, this approach enables a specific capacity of 146 mAh g−1, maintaining capacity retention of 79.84% after 1 000 cycles. This novel strategy for constructing free‐standing functional separators is convenient, efficient, and scalable, providing valuable insights into multifunctional separators for dendrite‐free LMBs.

Suppressing sulfur crosstalk lowers the bar of lithium metal anode for practical Li-S pouch cells

The obscure cause of early failure in lithium-sulfur batteries has long hindered their practicality. In this work, the shortboard factor has been ascertained as the lithium metal anode. Capacity-type sulfur cathode amplifies the intrinsic dendrite growth of Li metal through higher capacity requirements (> 8 mAh/cm2). More significantly, sulfur crosstalk seriously destroys the chemical-electrochemical stability of Li metal and directly leads to the unexpected capacity diving, which has been identified as more dominant and crucial. Herein, to lower the bar of the Li metal anode for the practicality of Li-S batteries, we proposed a hybrid sulfur-rich cathode to suppress the sulfur crosstalk. Our innovations reduced the lithium porosity by 26.7 % and the lithium corrosion rate by 27.4 % after cycling. As a result, our demonstrated pouch cells achieved superior energy densities of 460 Wh/kg and 985 Wh/L, and a stable cycle life above 75 cycles with an excellent capacity retention of 80 %. Our work is anticipated to provide a meticulous and thorough view to let the community rethink how to realize the practicality of Li-S batteries.

Holistic view on cation interdiffusion during processing and operation of garnet all-solid-state batteries

All-solid-state batteries based on the active cathode material LiCoO2 (LCO), a garnet-type Li7La3Zr2O12 (LLZO) electrolyte and a Li-metal anode are attracting a lot of attention as a robust and safe alternative to conventional lithium-ion batteries. The challenges in the practical realization of such cells are related to high-temperature sintering, which compacts the ceramic powder but also leads to undesirable material interactions such as cation interdiffusion and secondary phase formation. Even if high initial capacities can be achieved, the all-inorganic cells suffer from a strong capacity drop due to various degradation phenomena during processing and operation, which are not yet fully understood. In this study, the thermodynamic and kinetic aspects of co-sintering as well as the structural evolution of materials and interfaces during processing and operation of co-sintered LCO-LLZO cathodes are investigated in detail. A thermodynamic model for the interdiffusion of cations is derived and the effects of the diffusion of Al- and Co-ions, which occurs during the processing and cycling of the cells, are investigated. In LLZO, the diffusion of 0.13 Co per formula unit (pfu) has a negligible effect on ionic and electronic conductivity and electrochemical stability. In contrast, the substitution of 0.01 pfu Al and the induced disorder in the layer structure of LCO increases the polarization during cycling. All-inorganic cells fabricated with optimized sintering parameters to minimize interdiffusion between LCO and LLZO show good initial performance but similar degradation during cycling, as the used processing parameters result in a more porous microstructure leading to the development of cracks along the LLZO/LCO interface. The results obtained highlight the inherent instabilities of all-ceramic cathodes with unprotected LCO/LLZO interfaces, which require precise tuning of materials and processing parameters to achieve both high mechanical stability and low interdiffusion.

Three-dimensional carbon microclusters organized by hollow carbon nanospheres for stable Li metal anodes: enabling high packing density and low tortuosity via self-assembly

Three-dimensional carbon microclusters organized by hollow carbon nanospheres for stable Li metal anodes: enabling high packing density and low tortuosity via self-assembly

Reactive strontium nitride Additive: Constructing ion/electronic conductive paths for garnet-based solid-state lithium metal batteries

Solid-state lithium metal batteries (SSLMBs) using the garnet electrolyte Li6.4La3Zr1.4Ta0.6O12 (LLZTO) offer high safety and energy density compared to liquid organic electrolyte lithium-ion batteries. However, the interfacial electrochemical stabilization of Li metal anode with LLZTO leads to problems such as high interfacial resistance and Li dendrite growth, which hinders the wide application of SSLMBs. In this work, a multifunctional Li-Sr-N composite anode by mixing molten Li with Sr3N2 is constructed, in which the reactive wetting of in situ-formed Li3N achieves intimate interfacial contact, and the ionic/electronic conductive paths created by Li-Sr alloys and Li3N effectively homogenise Li deposition and suppress Li dendrites. The interfacial resistance is reduced to 40.42 Ω cm2, and the symmetric cell is stably cycled for 5500 h and 600 h at current densities of 0.1mA cm−2 and 0.4 mA cm−2, respectively, and the full cell of Li-Sr-N|LLZTO|LiFePO4 could be stably cycled for 200 cycles at 0.5C. The preparation of composite anodes using Sr3N2 as an additive may be a new strategy for producing of garnet-based SSLMBs with outstanding energy density and safety performance.

Constructing efficient lithium salt dissociation solid-state electrolytes with high conductivity and transference number of Li ions for stable all-solid-state lithium batteries

The broad application of solid-state polymer electrolytes (SPEs) has been hindered by the extremely low transference number of lithium ions and ionic conductivities. This study innovatively introduces Co-doped Li4Ti5O12 (CLTO) into poly(ethylene oxide) (PEO) matrix, CLTO not only brings a stronger interaction with TFSI−, but also weakens the Li-O bond in Li4Ti5O12 and reduces the diffusion activation energy of Li+. Thus, CLTO introducing PEO-based polymer solid electrolytes could simultaneously promote the dissociation of Li+ from LiTFSI and Li4Ti5O12, constructing efficient dual lithium salt dissociation regions and rapid Li+ conduction channels. The experimental tests and density functional theory calculations have confirmed the operational mechanisms of CLTO within the polymer matrix. As a result, the obtained SPEs exhibit a high ionic conductivity (1.09 × 10−4 S cm−1) and a quite large tLi+ of 0.83 at 60 °C. Moreover, the low (Highest Occupied Molecular Orbital) HOMO energy (−7.25 eV) of the CLTO-LiTFSI-PEO-10 (CLP-10) endow it can accommodate both the Li-metal anode and high-voltage cathodes. The all-solid-state LiFePO4||Li and NCM811|| Li batteries offer exceptional specific capacities of 164.61 and 194.95 mAh/g at 60 °C, respectively. In addition, the pouch cell assembled with CLP-10 works stably under extreme conditions such as bending and shearing.

Regulating the Solvation Structure in Polymer Electrolytes for High‐Voltage Lithium Metal Batteries

AbstractSolid polymer electrolytes are promising electrolytes for safe and high‐energy‐density lithium metal batteries. However, traditional ether‐based polymer electrolytes are limited by their low lithium‐ion conductivity and narrow electrochemical window because of the well‐defined and intimated Li+‐oxygen binding topologies in the solvation structure. Herein, we proposed a new strategy to reduce the Li+‐polymer interaction and strengthen the anion‐polymer interaction by combining strong Li+‐O (ether) interactions, weak Li+‐O (ester) interactions with steric hindrance in polymer electrolytes. In this way, a polymer electrolyte with a high lithium ion transference number (0.80) and anion‐rich solvation structure is obtained. This polymer electrolyte possesses a wide electrochemical window (5.5 V versus Li/Li+) and compatibility with both Li metal anode and high‐voltage NCM cathode. Li||LiNi0.5Co0.2Mn0.3O2 full cells with middle‐high active material areal loading (~7.5 mg cm−2) can stably cycle at 4.5 V. This work provides new insight into the design of polymer electrolytes for high‐energy‐density lithium metal batteries through the regulation of ion‐dipole interactions.