Practical Lithium Metal Batteries Research Articles

“Dead Lithium” Formation and Mitigation Strategies in Anode‐Free Li‐Metal Batteries

AbstractThin lithium‐metal foil is a promising anode material for next‐generation batteries due to its high theoretical specific capacity and low negative potential. However, safety issues linked to dendrite growth, low‐capacity retention, and short cycle life pose significant challenges. Also, it has excess energy that must be minimized in order to reduce the battery costs. To limit excess lithium, practical lithium metal batteries need a negative‐to‐positive electrode ratio as close to 1 : 1 as possible, which can be achieved through limiting excess lithium or using an “anode‐free” metal battery design. However, both designs experience fast capacity fade due to the irreversible loss of active lithium in the cell, caused by the formation of the solid electrolyte interphase (SEI), dendrite formation and “dead lithium,” – refers to lithium that has lost its electronic connection to the anode electrode or current collector. The presence of dead lithium in batteries negatively affects their capacity and lifespan, while also raising internal resistance and generating heat. Additionally, dead lithium encourages the growth of lithium dendrites, which poses significant safety hazards. Within this fundamental review, we thoroughly address the phenomenon of dead lithium formation, assessing its origins, implications on battery performance, and possible strategies for mitigation. The transition towards environmentally friendly and high‐performance metal batteries could be accelerated by effectively tackling the challenge posed by dead lithium.

Designing Cooperative Ion Transport Pathway in Ultra‐Thin Solid‐State Electrolytes toward Practical Lithium Metal Batteries

AbstractSolid polymer electrolytes (SPEs) are promising for high‐energy‐density solid‐state Li metal batteries due to their decent flexibility, safety, and interfacial stability. However, their development was seriously hindered by the interfacial instability and limited conductivity, leading to inferior electrochemical performance. Herein, we proposed to design ultra‐thin solid‐state electrolyte with long‐range cooperative ion transport pathway to effectively increase the ionic conductivity and stability. The impregnation of PVDF−HFP inside pores of fluorinated covalent organic framework (CF3−COF) can disrupt its symmetry, rendering rapid ion transportation and inhibited anion immigration. The functional groups of CF3−COF can interact with PVDF−HFP to form fast Li+ transport channels, which enables the uniform and confined Li+ conduction within the electrolyte. The introduction of CF3−COF also enhances the mechanical strength and flexibility of SPEs, as well as ensures homogeneous Li deposition and inhibited dendrite growth. Hence, a remarkably high conductivity of 1.21×10−3 S cm−1 can be achieved. Finally, the ultra‐thin SPEs with an extremely long cycle life exceed 9000 h can be obtained while the NCM523/Li pouch cell demonstrates a high capacity of 760 mAh and 96 % capacity retention after cycling, holding great promises to be utilized for practical solid‐state Li metal batteries.

Designing Cooperative Ion Transport Pathway in Ultra-Thin Solid-State Electrolytes toward Practical Lithium Metal Batteries.

Solid polymer electrolytes (SPEs) are promising for high-energy-density solid-state Li metal batteries due to their decent flexibility, safety, and interfacial stability. However, their development was seriously hindered by the interfacial instability and limited conductivity, leading to inferior electrochemical performance. Herein, we proposed to design ultra-thin solid-state electrolyte with long-range cooperative ion transport pathway to effectively increase the ionic conductivity and stability. The impregnation of PVDF-HFP inside pores of fluorinated covalent organic framework (CF3-COF) can disrupt its symmetry, rendering rapid ion transportation and inhibited anion immigration. The functional groups of CF3-COF can interact with PVDF-HFP to form fast Li+ transport channels, which enables the uniform and confined Li+ conduction within the electrolyte. The introduction of CF3-COF also enhances the mechanical strength and flexibility of SPEs, as well as ensures homogeneous Li deposition and inhibited dendrite growth. Hence, a remarkably high conductivity of 1.21×10-3 S cm-1 can be achieved. Finally, the ultra-thin SPEs with an extremely long cycle life exceed 9000 h can be obtained while the NCM523/Li pouch cell demonstrates a high capacity of 760 mAh and 96 % capacity retention after cycling, holding great promises to be utilized for practical solid-state Li metal batteries.

Remodeling Highly Fluorinated Electrolyte via Shielding Agent Regulation toward Practical Lithium Metal Batteries.

Highly fluorinated electrolytes have proved effective in improving electrochemical stability of lithium metal batteries. However, excessive fluorination not only detrimentally impacts the electrolyte ionic conductivity, but also inevitably forms the over-fluorinated interphases with sluggish ion diffusivity. Herein, a strategy on remodeling Li+ solvation structure in highly fluorinated electrolyte aided is proposed by fluorinated amide (FDMA), which denoted as "shielding agent". Benefitting from FDMA's high donor number (DN)value (22.1), the Li+-dipole (fluoroethylene carbonate (FEC) or trans-4,5-Difluoroethylenecarbonate (DFEC)) interaction is interrupted and the participation of FDMA in primary solvation sheath fructify the solid-electrolyte interphase without scarifying the privilege of fluorinated electrolyte on interphase chemistry. Eventually, the optimal high-fluorinated electrolyte (FDMA/DFEC + 1.0mol L-1 LiTFSI) with this unique shielding effect displays high ionic conductivity and rapid Li+ desolvation behavior, enabling Li||LiNi0.6Co0.2Mn0.2O2 (Li||NCM622) to achieve an ultralong cycle-life of 2000 cycles at 1C with 84.7% capacity retention. Even under extreme conditions (NCM622: 10mg cm-2; electrolyte: 20µL; Li: 50µm), the Li||NCM622 displays excellent electrochemical performance. Additionally, 447Wh kg-1 Li||LiNi0.8Co0.1Mn0.1O2 (Li||NCM811) pouch cells have been successfully fabricated and demonstrate an exceptional cycle-life over 150 cycles. The proposed "shielding" strategy to modulate the solvation structure paves the way for developing practical LMBs with fluorinated electrolytes.

Boosting High-Voltage Practical Lithium Metal Batteries with Tailored Additives

HighlightsFGN-182 electrolytes exhibit highly reversible Li plating/stripping with an average Coulombic efficiency reaching up to 99.56% determined from Auerbach’s test.The gas-evolution process of LiNO3 in high-voltage lithium cobalt oxide (LCO) cathodes is revealed by in situ differential electrochemical mass spectrometry.Pouch cells equipped with high-loading LCO (3 mAh cm−2) cathodes, ultrathin Li chips (25 μm), and lean electrolytes (5 g Ah−1) using optimized electrolyte (FGN-182 + 1%HTCN) demonstrate outstanding cycling performance.

Rational Molecular Engineering via Electron Reconfiguration toward Robust Dual-Electrode/Electrolyte Interphases for High-Performance Lithium Metal Batteries.

High-energy-density lithium-metal batteries (LMBs) coupling lithium-metal anodes and high-voltage cathodes are hindered by unstable electrode/electrolyte interphases (EEIs), which calls for the rational design of efficient additives. Herein, we analyze the effect of electron structure on the coordination ability and energy levels of the additive, from the aspects of intramolecular electron cloud density and electron delocalization, to reveal its mechanism on solvation structure, redox stability, as-formed EEI chemistry, and electrochemical performances. Furthermore, we propose an electron reconfiguration strategy for molecular engineering of additives, by taking sorbide nitrate (SN) additive as an example. The lone pair electron-rich group enables strong interaction with the Li ion to regulate solvation structure, and intramolecular electron delocalization yields further positive synergistic effects. The strong electron-withdrawing nitrate moiety decreases the electron cloud density of the ether-based backbone, improving the overall oxidation stability and cathode compatibility, anchoring it as a reliable cathode/electrolyte interface (CEI) framework for cathode integrity. In turn, the electron-donating bicyclic-ring-ether backbone breaks the inherent resonance structure of nitrate, facilitating its reducibility to form a N-contained and inorganic Li2O-rich solid electrolyte interface (SEI) for uniform Li deposition. Optimized physicochemical properties and interfacial biaffinity enable significantly improved electrochemical performance. High rate (10 C), low temperature (-25 °C), and long-term stability (2700 h) are achieved, and a 4.5 Ah level Li||NCM811 multilayer pouch cell under harsh conditions is realized with high energy density (462 W h/kg). The proof of concept of this work highlights that the rational ingenious molecular design based on electron structure regulation represents an energetic strategy to modulate the electrolyte and interphase stability, providing a realistic reference for electrolyte innovations and practical LMBs.

Hybridizing carbonate and ether at molecular scales for high-energy and high-safety lithium metal batteries

Commonly-used ether and carbonate electrolytes show distinct advantages in active lithium-metal anode and high-voltage cathode, respectively. While these complementary characteristics hold promise for energy-dense lithium metal batteries, such synergy cannot be realized solely through physical blending. Herein, a linear functionalized solvent, bis(2-methoxyethyl) carbonate (BMC), is conceived by intramolecularly hybridizing ethers and carbonates. The integration of the electron-donating ether group with the electron-withdrawing carbonate group can rationalizes the charge distribution, imparting BMC with notable oxidative/reductive stability and relatively weak solvation ability. Furthermore, BMC also offers advantages including the ability to slightly dissolve LiNO3, excellent thermostability and nonflammability. Consequently, the optimized BMC-based electrolyte, even with typical concentrations in the single solvent, demonstrates high-voltage tolerance (4.4 V) and impressive Li plating/stripping Coulombic efficiency (99.4%). Moreover, it fulfills practical lithium metal batteries with satisfactory cycling performance and exceptional tolerance towards thermal/mechanical abuse, showcasing its suitability for safe high-energy lithium metal batteries.

Lithium Dredging and Capturing Dual‐Gradient Framework Enabling Step‐Packed Deposition for Dendrite‐Free Lithium Metal Anodes

AbstractDue to the sterile lithium affinity and poor Li+ regulation ability, lithium metal tends to deposit on the top of substrate materials, which lowers the space utilization and deteriorates the dendrites growth, further increasing the risk of short circuits. It is necessary to guide lithium deposition and adjust Li+ flux at the base of substrate toward alleviating those issues of lithium metal anodes (LMAs). Herein, a dredging and capturing dual‐gradient framework is conveniently fabricated toward inducing the Li+ migration and deposition. The dual‐gradient framework combined with upper Ni3S2 nanowires with lower Li+ migration barrier and bottom Ni2P nanowires with stronger Li affinity, such reasonable distribution of components conquers the ionic concentration gradient to acquire a “step‐packed” lithium deposition mode. Moreover, the in situ formation of Li2S/Li3P‐enriched SEI further promotes Li+ transport to the interior framework. Consequently, a high average Coulombic efficiency of 98% over 230 cycles and a lifespan of 180 h (10 mA cm−2, 5 mAh cm−2) are achieved. The LiFePO4 full cells also exhibit a considerable capacity retention. This work provides a feasible strategy of step‐packing lithium deposition for significant framework design insight to boost practical lithium metal batteries (LMBs) development.

Towards practical lithium metal batteries with composite scaffolded lithium metal: an overview

Towards practical lithium metal batteries with composite scaffolded lithium metal: an overview

Toward thin and stable anodes for practical lithium metal batteries: A review, strategies, and perspectives

AbstractThe lithium metal battery (LMB) is a promising energy storage platform with a distinctively high energy density in theory, outperforming even those of conventional Li‐ion batteries. In practice, however, the actual achievable energy density of LMBs is significantly limited due to the Li metal anode (LMA) being too thick (50–250 μm), and there are difficulties with expanding the highly reactive Li metal into large‐format cells due to safety concerns. Therefore, the recent focus of LMB research is headed toward the development of a thin and stable LMA. However, as the thickness of Li anode decreases (≤20 μm) and the absolute size of the battery cell increases, interfacial reactions on the Li surface become more active, potentially leading to fatal thermal runaway. In this regard, there is still much demand for the development of novel manufacturing technologies to overcome this issue and produce thin and stable Li metal. Considering these things, in this review, we initially examine the fundamentals regarding the deployment of LMAs using a number of essential metrics. Then, we introduce recent strategies employed for designing thin and stable Li anodes including host matrix architecturing, interface stabilization, and other advanced modifications. Finally, we propose future directions for the realization of practical LMBs and their potential applications in various battery systems, encompassing Na, K, and Zn‐based batteries. We anticipate that ultra‐thin and ultra‐stable metal anodes would find widespread utilization in secondary battery applications with high‐power requirements.image

Probing the Stability of Lithium Carbonate in the Lithium-Metal Solid Electrolyte Interphase

The chemical composition and structure of the solid electrolyte interphase (SEI) are two of the key factors that determine the reversibility of lithium-metal (Li) anodes for next-generation batteries. As a result, much of the research aimed at enabling practical Li-metal batteries emphasizes tuning SEI composition, either via electrolyte formulation1–5 or synthesis of artificial SEIs.6–8 Ideally, the lithium SEI should minimize parasitic side reactions by effectively passivating Li while also promoting facile conduction of lithium ions (Li+). To do this, SEI materials must have high (electro)chemical stability, be ionically conductive, and be sufficiently mechanically robust to accommodate substantial volume changes. However, studying these properties in bulk-scale materials often yields values that diverge by orders of magnitude from those observed in SEIs. For example, typical SEI ionic conductivities lie in the range of 10-7-10-9 S cm-1, yet bulk ionic conductivity measurements of relevant materials such as lithium carbonate, lithium fluoride, and lithium oxide ranges from 10-18 and 10-10 S cm-1.9 Our group has developed a technique to directly study these materials at realistic length scales by synthesizing model interphases through the reaction of gases with Li.10,11 Our previous work on Li2O and LiF revealed that Li2O is a better Li+ conductor than LiF (~1 x 10-9 S cm-1 vs ~5.2 x 10-10 S cm-1),11 and that these species’ chemical stability varies substantially in different electrolytes.12 One of the remaining key SEI materials is lithium carbonate, which has been proposed to act as a metastable phase in the outer portion of the SEI.13 In this work, we have developed a technique to synthesize Li2CO3 films via sequential reaction of oxygen and carbon dioxide with clean lithium surfaces. Using scanning electron microscopy and air-exposure tests, we can confirm that these films are conformal and generally pinhole-free. Titration gas chromatography (TGC)14 was used to quantify relative proportions of lithium carbonate, metallic lithium, and lithium carbide, and X-ray photoelectron spectroscopy (XPS) offers insights into how composition changes across the depth of the film. These films were then used as a platform to further investigate the reactivity of Li2CO3 with different electrolytes, comparing carbonates versus ethers and varying the lithium salt used. Electrochemical impedance spectroscopy (EIS) offers insights into the evolution of transport properties at these interphases, while electrolyte soak tests coupled with gas chromatography of gas-phase products and TGC of solid-phase products can track their chemical evolution. Taken together, this work illuminates how lithium carbonate may evolve during battery cycling, offering perspective that can help guide future design of Li-metal SEIs.References Liu, Y. et al. Solubility-mediated sustained release enabling nitrate additive in carbonate electrolytes for stable lithium metal anode. Nat. Commun. 1–10 (2018).Suo, L. et al. Fluorine-donating electrolytes enable highly reversible 5-V-class Li metal batteries. Proc. Natl. Acad. Sci. 115, 1156–1161 (2018).Chae, O. B., Adiraju, V. A. K. & Lucht, B. L. Lithium Cyano Tris(2,2,2-trifluoroethyl) Borate as a Multifunctional Electrolyte Additive for High-Performance Lithium Metal Batteries. ACS Energy Lett. 6, 3851–3857 (2021).Li, Y. et al. Correlating Structure and Function of Battery Interphases at Atomic Resolution Using Cryoelectron Microscopy. Joule 2, 2167–2177 (2018).Zhao, Q. et al. Upgrading Carbonate Electrolytes for Ultra‐stable Practical Lithium Metal Batteries. Angew. Chemie Int. Ed. 61, e2021162 (2021).Zhao, J. et al. Surface Fluorination of Reactive Battery Anode Materials for Enhanced Stability. J. Am. Chem. Soc. 139, 11550–11558 (2017).Li, Y. et al. Robust Pinhole-free Li3N solid electrolyte grown from molten lithium. ACS Cent. Sci. 4, 97–104 (2018).Kozen, A. C. et al. Next-Generation Lithium Metal Anode Engineering via Atomic Layer Deposition. ACS Nano 9, 5884–5892 (2015).Lorger, S., Narita, K., Usiskin, R. & Maier Films of Li, J. Enhanced ion transport in Li2O and Li2S films. Chem. Commun 57, 6503–6506 (2021).He, M., Guo, R., Hobold, G. M., Gao, H. & Gallant, B. M. The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium. PNAS 117, 73–79 (2020).Guo, R. & Gallant, B. M. Li 2 O Solid Electrolyte Interphase: Probing Transport Properties at the Chemical Potential of Lithium. Chem. Mater 32, 5525–5533 (2020).Guo, R., Wang, D., Zuin, L. & Gallant, B. M. Reactivity and Evolution of Ionic Phases in the Lithium Solid−Electrolyte Interphase. ACS Energy Lett. 877–885 (2021) doi:10.1021/acsenergylett.1c00117.Han, B. et al. Poor Stability of Li2CO3 in the Solid Electrolyte Interphase of a Lithium-Metal Anode Revealed by Cryo-Electron Microscopy. Adv. Mater. 33, 2100404 (2021).Hobold, G. M. & Gallant, B. M. Quantifying Capacity Loss Mechanisms of Li Metal Anodes beyond Inactive Li0. ACS Energy Lett. 4, 3458–3466 (2022).

Quantifying Capacity Loss Mechanisms of Li Metal Anodes Beyond Inactive Li0

Lithium metal anodes are promising alternatives to graphite for use in next-generation lithium-ion batteries due to their higher capacity (3,860 mAh/g vs. 372 mAh/g). However, Li anodes still display excessive capacity loss over cycling, leading to underwhelming Coulombic efficiency (CE, <99.9%) compared to graphite (>99.95%).1 These losses can derive from: (1) the formation of electronically isolated Li0 (often referred to as ‘dead’ or inactive’); and (2) the parasitic reactions between Li and the electrolyte that form the solid electrolyte interphase (SEI). Characterization of the Li anode has historically relied on surface characterization techniques such as XPS and FTIR, which cannot quantitatively reveal the total amounts of specific SEI phases. More precise quantification has recently become possible due to advances in chemical titration, which notably revealed that inactive Li0 is the dominant loss mechanism at low-to-moderate CE (<90%).2 At high CE (>90%), SEI losses are increasingly dominant and become the loss mode to minimize. Despite its importance, titration of SEI losses have thus far largely focused on LiH,3-5 with precise quantification of other accompanying phases still lacking.To bridge this gap, here we apply quantitative titration based on GC, ICP-AES and NMR to track an extended array of key SEI phases: semicarbonates (ROCO2Li), lithium carbide (Li2C2), olefins (RLi), LiF, P-containing phases, and total Li loss with, which teach new insights beyond inactive Li0. In 1 M LiPF6 EC/DEC, we demonstrate chemical resolution up to 71% of Li loss and 33% of SEI loss inventory. The analysis was also expanded to additional carbonate electrolytes of varying CEs (from <10% to >96%). Soluble SEI phases were particularly important at ultra-low CE (<10%), and their formation was suppressed higher CEs. Among the quantifiable SEI phases, ROCO2Li was consistently the major phase, but its proportions were invariant with CE. Instead, Li2C2, a minor phase, exhibited clear inverse correlation with CE. These results add further nuance beyond inactive Li0 to the current understanding of capacity loss, and demonstrate that, while minor phases often receive less focus and are harder to characterize, they can play governing roles in SEI function, particularly at high CE when formation of inactive Li0 is minimized. Hobold, G. M.; Lopez, J.; Guo, R.; Minafra, N.; Banerjee, A.; Shirley Meng, Y.; Shao-Horn, Y.; Gallant, B. M., Moving Beyond 99.9% Coulombic Efficiency for Lithium Anodes in Liquid Electrolytes. Nat. Energy 2021, 6 (10), 951-960. Fang, C.; Li, J.; Zhang, M.; Zhang, Y.; Yang, F.; Lee, J. Z.; Lee, M. H.; Alvarado, J.; Schroeder, M. A.; Yang, Y.; Lu, B.; Williams, N.; Ceja, M.; Yang, L.; Cai, M.; Gu, J.; Xu, K.; Wang, X.; Meng, Y. S., Quantifying Inactive Lithium in Lithium Metal Batteries. Nature 2019, 572 (7770), 511-515. Tao, M.; Xiang, Y.; Zhao, D.; Shan, P.; Sun, Y.; Yang, Y., Quantifying the Evolution of Inactive Li/Lithium Hydride and Their Correlations in Rechargeable Anode-Free Li Batteries. Nano Lett. 2022. Xu, G.; Li, J.; Wang, C.; Du, X.; Lu, D.; Xie, B.; Wang, X.; Lu, C.; Liu, H.; Dong, S.; Cui, G.; Chen, L., The Formation/Decomposition Equilibrium of LiH and Its Contribution on Anode Failure in Practical Lithium Metal Batteries. Angew. Chem. Int. Ed. Engl. 2021, 60 (14), 7770-7776. Xiang, Y.; Tao, M.; Zhong, G.; Liang, Z.; Zheng, G.; Huang, X.; Liu, X.; Jin, Y.; Xu, N.; Armand, M.; Zhang, J. G.; Xu, K.; Fu, R.; Yang, Y., Quantitatively Analyzing the Failure Processes of Rechargeable Li Metal Batteries. Sci. Adv. 2021, 7 (46), eabj3423.

Microenvironment engineering for guiding spatially and epitaxially uniform lithium plating in lithium metal batteries

The manipulation of plated lithium morphology is the crucial for extending the cycle life of lithium metal batteries. Dendritic growth, a major concern, is influenced by the microenvironment of lithium plating, including the curvature of lithium-ion transfer path, as well as the inner space and surface chemistry of the separator and scaffold. In this study, we report a novel separator-interface-scaffold microenvironment for practical lithium metal batteries (LMBs), in which surface chemistry of scaffold and separator are tuned to create a transmission path with low curvature and induce spatially and epitaxial lithium plating. With such an elaborate design, the resulting LMB demonstrates exceptional stability, exhibiting dendrite-free cycling for 5542 h with a low voltage hysteresis of 13 mV at 5 mA cm−2/5 mAh cm−2. It also demonstrates stable cycling for 500 h under ultrahigh currents of 50 mA cm−2 and deep plating/stripping up to 20 mAh cm−2. Notably, a remarkable cumulative plating capacity of 13,855 mAh cm−2 is achieved. The full cells paired with commercial cathodes with high loading mass delivered remarkably improved rate and cycling stability performance. This study highlights the critical role of the plating microenvironment in enhancing LMBs for high-energy storage devices.

Li-Alloy texture creates in-built Li(110) epitaxy in a thin Li-metal anode allowing high depth-of-discharge cycling in carbonate electrolyte

A thin Li metal anode is imperative for practical lithium metal batteries (LMBs). Fabricating and stabilizing <50 μm Li-metal anode is daunting due to the poor processability of Li and its inherent instability in liquid electrolytes. Here, we found that doping Li with 8.9 at% Sn yields a Li-Li22Sn5 dual-phase alloy with impressive processability that allows rolling of <40 μm thin foils. Intriguingly, in the thin Li-Sn foil, the rolling process built a strong Li22Sn5(822) texture that can regulate Li electro-crystallization along the densely packed Li(110) facets. Such in-built Li(110) epitaxy is a result of >99% lattice match of Li(110)-Li22Sn5(822) and gives rise to a greatly stabilized Li growth front due to the low binding energy of solvated-Li+ with Li(110) surface. Partial de-alloy treatment can fully activate the in-built Li(110) epitaxy, achieving stable plate-strip cycling in symmetric cells over 300 h at 80% depth-of-discharge (DOD). Stable 2.5 mAh/cm2 full pouch cells in carbonate electrolyte (EC:EMC: DEC = 1:1:1, 5 % FEC) were achieved at a low N:P ratio of 2.1. Conversely, conventional Li-Sn and neat Li, even possessing more abundant active Li, quickly failed. The uncovered critical crystallography-electrochemistry correlation in textured Li-alloys sheds light on thin Li-metal anode development.

Ultra-thin and ultra-light self-lubricating layer with accelerated dynamics for anode-free lithium metal batteries

Fabricating superior artificial interlayer with ingeniously controlled charge and mass transport channels without compromise in cell mass and volume is urgent but challenging for practical Lithium metal batteries (LMBs). Herein, inspired by Brasenia schreberi, a natural aquatic plant with unique polysaccharides biological channels for lubricating H2O transport, an ultrathin (137 nm) and ultralight (0.1 mg cm−2) self-lubricating ion-confined artificial layer (SLIC) is proposed to improve charge/mass transport of LMBs. A large-scale feasibility roll-to-roll technology coupled with self-assembly of phase-transitioned lysozyme (PTL) was employed to construct the flexible and cost-effective SLIC. The luxurious polar functional groups of PTL favor Li+ transport by facilitating Li+ de-solvation and charge transfer processes, while the unique microporous channels within PTL can regulate the Li+ concentration field and accelerate homogenized mass transport. Therefore, with such unique SLIC, dendrite-free Li plating/stripping was achieved and superior cycle performance for 850 cycles in Li||Cu cells was realized. Furthermore, the SLIC endows pouch cells and coin cells with remarkably improved performance in harsh conditions (high cathode loading, low N/P up to anode-free). More importantly, all processes for preparing such controllable and scalable SLIC film are done in ambient conditions without specific engineering difficulties, showing excellent prospects for practical application.

Delineating the relationship between separator parameters and practical lithium metal batteries characteristics

Lithium metal batteries (LMBs), composed of lithium anodes and high-nickel-content LiNixMnyCozO2 (x + y + z = 1), are considered the pinnacle of next-generation batteries. Despite the importance of evaluating LMB in practical conditions, there is a lack of clear standards for LMB separators, which critically affects battery performance and energy density. Here, we investigated the effects of separator thickness on the cell performance and energy density of a practical LMB by using various-thickness polyethylene (PE) separators. As the separator thickness decreases the volumetric energy density increases and LMB performance improves. We also showed that pore closure in separators is a major roadblock hindering the long-term operation of LMBs. Therefore, we establish the ideal LMB separator design, which is a thin and robust separator having pore closure suppression functionality for ensuring long-term stable high-energy-density LMBs.

Elastomeric Electrolyte for High Capacity and Long-Cycle-Life Solid-State Lithium Metal Battery.

High room-temperature ionic conductivity and good compatibility with lithium metal and cathode materials are prerequisites for solid-state electrolytes used in lithium metal batteries. Here, the solid-state polymer electrolytes (SSPE) are prepared by combining the traditional two-roll milling technology with interface wetting. The as-prepared electrolytes consisting of elastomer matrix and high-mole-loading of LiTFSI salt show a high room temperature ionic conductivity of 4.6×10-4 S cm-1 , a good electrochemical oxidationstability up to 5.08V, and improved interface stability. These phenomena are rationalized with the formation of continuous ion conductive paths based on sophisticated structure characterization including synchrotron radiation Fourier-transform infrared microscopy, wide- and small-angle X-ray scattering. Moreover, at room temperature, the Li||SSPE||LFP coin cell shows a high capacity (161.5 mAh g-1 at 0.1 C), long-cycle-life (retaining 50% capacity and 99.8% Coulombic efficiency after 2000 cycles), and good C-rate compatibility up to 5 C. This study, therefore, provides a promising solid-state electrolyte that meets both the electrochemical and mechanical requirements of practical lithium metal batteries.

Recent advances in lithiophilic materials: material design and prospects for lithium metal anode application

The rapid development of electronic technology and energy industry promotes the increasing desire for energy storage systems with high energy density, thus calling for the exploration of lithium metal anode. However, the enormous challenges, such as uncontrollable lithium deposition, side reaction, infinite volume change and dendrite generation, hinders its application. To address these problems, the deposition behavior of lithium must be exactly controlled and the anode/electrolyte interface must be stabilized. The deposition of lithium is a multi-step process influenced by multi-physical fields, where nucleation is the key to final morphology. Hence, increasing investigations have focused on the employment of lithiophilic materials that can regulate lithium nucleation in recent years. The lithiophilic materials introduced into the deposition hosts or solid electrolyte interphases can regulate the nucleation overpotential and facilitate uniform deposition. However, the concept of lithiophilicity is still undefined and the mechanism is still unrevealed. In this review, the recent advances in the regulation mechanisms of lithiophilicity are discussed, and the applications of lithiophilic materials in hosts and protective interphases are summarized. The in-depth exploration of lithiophilic materials can enhance our understanding of the deposition behavior of lithium and pave the way for practical lithium metal batteries.

Towards durable practical lithium–metal batteries: advancing the feasibility of poly-DOL-based quasi-solid-state electrolytes via a novel nitrate-based additive

TEGDN-QSSE could form a N-rich SEI on the surface of a Li metal anode, protecting it from parasitic reactions and preventing Li dendrites. A pouch-type Li–S cell with TEGDN-QSSE could stably cycle 50 times.

Exploiting the Steric Effect and Low Dielectric Constant of 1,2-Dimethoxypropane for 4.3 V Lithium Metal Batteries

1,2-Dimethoxyethane (DME) has been widely used as an electrolyte solvent for lithium metal batteries on account of its intrinsic reductive stability; however, its low oxidative stability presents a major challenge for use in high-voltage Li metal batteries (LMBs). In this direction, herein, we introduce a new low-dielectric solvent, 1,2-dimethoxypropane (DMP), as an electrolyte solvent. Compared to DME, DMP has decreased solvation power owing to its increased steric effects, thus promoting anion–Li+ interactions. This controlled solvation structure of the 2 M LiFSI-in-DMP electrolyte facilitated the formation of an anion-driven, stable interface at the lithium metal anode and oxidative stability for compatibility with widely adopted cathodes to afford Li|LiFePO4 and Li|LiNi0.8Co0.1Mn0.1O2 cells with decent cycling stability. These results imply the usefulness of steric control as an alternative strategy to commonly used fluorination to fine-tune the solvation power and, in general, the design of new solvents for practical lithium metal batteries.