High-energy Density Lithium Metal Batteries Research Articles

UV cross-linked highly stable polymer garnet composite electrolyte with improved interphase for lithium metal batteries

The next-generation electric vehicles heavily rely on high-energy–density lithium metal batteries with enhanced safety. Replacing liquid electrolytes with solid-state polymer electrolytes offers superior protection, high flexibility, and stability. However, inadequate ionic conductivity and poor compatibility at the interfaces with the electrodes hinder the practical application of solid-state electrolytes. In this work, we developed a polyethylene glycol-based, highly cross-linked polymer electrolyte with a garnet-type, fast Li+ conductive Li6.2Al0.24La3Zr2O12 (Al-LLZO) filler. The Al-LLZO filler was incorporated into a cross-linking functional polymeric matrix of polyethylene glycol diacrylate, pentaerythritol tetrakis (3-mercaptopropionate), and lithium perchlorate salt. The cross-linked polymer garnet composite electrolyte (CPGCE) was prepared via UV-induced photo-polymerization. The resulting CPGCE exhibits superior free-standing flexibility, a desired ionic conductivity of 4.4 × 10−4 S cm−1, and a wide potential window up to 4.2 V. The Li|CPGCE|Li symmetric cell underwent stripping and plating at varying current densities of 0.05 to 0.3 mA cm−2, displaying a low overpotential range from ±0.02 V to ±0.08 V over 500 cycles. Similarly, the as-cycled Li|CPGCE|Li showed excellent stripping and plating performance at 0.1 mA cm−2 for 500 cycles at 60 °C. The incorporation of the Al-LLZO nanofiller provided active sites with continuous Li+ conducting pathways, suppressing the growth of dead lithium dendrites. The Li|CPGCE|LiFePO₄ full cell exhibited a discharge capacity of 155 mAh g−1 at a rate of 0.1C, with a coulombic efficiency of 96 % over 50 cycles at 25 °C. This work offers a straightforward and convenient approach to creating highly durable polymer composite electrolytes with enhanced interfacial stability, advancing the implementation of all-solid-state lithium metal batteries.

Compliant Solid Polymer Electrolytes (SPEs) for Enhanced Anode-Electrolyte Interfacial Stability in All-Solid-State Lithium-Metal Batteries (LMBs).

Practical application of high energy density lithium-metal batteries (LMBs) has remained elusive over the last several decades due to their unstable and dendritic electrodeposition behavior. Solid polymer electrolytes (SPEs) with sufficient elastic modulus have been shown to attenuate dendrite growth and extend cycle life. Among different polymer architectures, network SPEs have demonstrated promising overall performance in cells using lithium metal anodes. However, fine-tuning network structures to attain adequate lithium electrode interfacial contact and stable electrodeposition behavior at extended cycling remains a challenge. In this work, we designed a series of comb-chain cross-linker-based network SPEs with tunable compliance by introducing free dangling chains into the SPE network. These dangling chains were used to tune the SPE ionic conductivity, ductility, and compliance. Our results demonstrate that increasing network compliance and ductility improves anode-electrolyte interfacial adhesion and reduces voltage hysteresis. SPEs with 56.3 wt % free dangling chain content showed a high Coulombic efficiency of 93.4% and a symmetric cell cycle life 1.9× that of SPEs without free chains. Additionally, the improved anode compliance of these SPEs led to reduced anode-electrolyte interfacial resistance growth and greater capacity retention at 92.8% when cycled at 1C in Li|SPE|LiFePO4 half cells for 275 cycles.

Interfacial fusion-enhanced 11 µm-thick gel polymer electrolyte for high-performance lithium metal batteries

In the pursuit of ultrathin polymer electrolyte (<20 μm) for lithium metal batteries, achieving a balance between mechanical strength and interfacial stability is crucial for the longevity of the electrolytes. Herein, 11 μm-thick gel polymer electrolyte is designed via an integrated electrode/electrolyte structure supported by lithium metal anode. Benefiting from an exemplary superiority of excellent mechanical property, high ionic conductivity, and robust interfacial adhesion, the in-situ formed polymer electrolyte reinforced by titanosiloxane networks (ISPTS) embodies multifunctional roles of physical barrier, ionic carrier, and artificial protective layer at the interface. The potent interfacial interactions foster a seamless fusion of the electrode/electrolyte interfaces and enable continuous ion transport. Moreover, the built-in ISPTS electrolyte participates in the formation of gradient solid-electrolyte interphase (SEI) layer, which enhances the SEI’s structural integrity against the strain induced by volume fluctuations of lithium anode. Consequently, the resultant 11 μm-thick ISPTS electrolyte enables lithium symmetric cells with cycling stability over 600 h and LiFePO4 cells with remarkable capacity retention of 96.6% after 800 cycles. This study provides a new avenue for designing ultrathin polymer electrolytes towards stable, safe, and high-energy–density lithium metal batteries.

Interphase Engineering via Solvent Molecule Chemistry for Stable Lithium Metal Batteries.

Lithium metal battery has been regarded as promising next-generation battery system aiming for higher energy density. However, the lithium metal anode suffers severe side-reaction and dendrite issues. Its electrochemical performance is significantly dependant on the electrolyte components and solvation structure. Herein, a series of fluorinated ethers are synthesized with weak-solvation ability owing to the duple steric effect derived from the designed longer carbon chain and methine group. The electrolyte solvation structure rich in AGGs (97.96 %) enables remarkable CE of 99.71 % (25 °C) as well as high CE of 98.56 % even at -20 °C. Moreover, the lithium-sulfur battery exhibits excellent performance in a wide temperature range (-20 to 50 °C) ascribed to the modified interphase rich in LiF/LiO2. Furthermore, the pouch cell delivers superior energy density of 344.4 Wh kg-1 and maintains 80 % capacity retention after 50 cycles. The novel solvent design via molecule chemistry provides alternative strategy to adjust solvation structure and thus favors high-energy density lithium metal batteries.

In-situ Construction of Poly(tetraisopentyl acrylate) based Gel Polymer Electrolytes with Lix La2-x TiO3 for High Energy Density Lithium-Metal Batteries.

As promising alternatives to liquid electrolytes, polymer electrolytes attract much research interest recently, but their widespread use is limited by the low ionic conductivity. In this study, we use electrostatic spinning to introduce particles of an ionic conductor into polyacrylonitrile (PAN) fibers to prepare a porous membrane as the host of gel polymer electrolytes (GPEs). The relevant in-situ produced GPE performs a high ionic conductivity of 6.0×10-3 S cm-1 , and a high lithium transfer number (tLi + ) of 0.85 at 30 °C, respectively. A symmetrical Li cell with this GPE can cycle stably for 550 h at a current density of 0.5 mA cm-2 . While the capacity retention of the NCM|GPE|Li cell is 79.84 % after 500 cycles at 2 C. Even with an increased cut-off voltage of 4.5 V, the 1st coulomb efficiency reaches 91.58 % with a specific discharge capacity of 213.4 mAh g-1 . This study provides a viable route for the practical application of high energy density lithium metal batteries.

In situ construction of robust artificial solid-electrolyte interphase layer on lithium-metal anode by a facile one-step solution route

Development of high energy density lithium-metal batteries (LMBs) is markedly hindered by the interfacial instability on lithium-metal anode side. Solid-electrolyte interphase (SEI) is a fundamental factor to regulate dendrite growth and enhance the stability of lithium-metal anodes. Here, trithiocyanuric acid, a triazine derivative with sulfhydryl groups, is used as an efficient promoter to favor the construction of a robust artificial SEI layer on the lithium metal surface, which greatly benefits the stability and efficiency of LMBs. With the assistance of trithiocyanuric acid facilely introduced on the Li surface via a one-step solution route, a highly uniform artificial SEI layer rich in Li2S and Li3N is formed, which efficiently facilitates uniform lithium deposition and suppresses lithium dendrite growth. Remarkably, the Li|Li cell displays stable lithium plating/stripping cycling over 800 h at 0.5 mA cm−2, 1 mAh cm−2, and the Li|LFP cells exhibit prolonged lifespan over 700 cycles at 3 C and superior rate performance from 2 to 20 C. This work provides a facile design strategy for constructing a superb artificial SEI layer for high-performance LMBs.

Upgrading the Separators Integrated with Desolvation and Selective Deposition toward the Stable Lithium Metal Batteries.

A practical and effective approach to improve the cycle stability of high-energy density lithium metal batteries (LMBs) is to selectively regulate the growth of the lithium anode. The design of desolvation and lithiophilic structure have proved to be significant means to regulate the lithium deposition process. Here, a fluorinated polymer lithiophilic separator (LS) loaded with a metal-organic framework (MOF801) is designed, which facilitates the rapid transfer of Li+ within the separator owing to the MOF801-anchored PF6 - from the electrolyte, Li deposition is confined in the plane resulting from the polymer fiber layer rich in lithiophilic groups (C─F). The numerical simulation results confirm that LS induces a uniform electric field and Li+ concentration distribution. Visualization technology records the behavior of regular Li deposition in Li||Li and Li||Cu cells equipping LS. Therefore, LS exhibits an ultrahigh Li+ transference number (tLi + = 0.80) and a large exchange current density (j0 = 1.963mA cm-2). LS guarantees the stable operation of Li||Li cells for over 1000h. In addition, the LiNi0.8Co0.1Mn0.1O2||Li cell equipped with LS exhibits superior rate and cycle performances owing to the formation of LiF-rich robust SEI layers. This study provides a way forward for dendrite-free Li anodes from the perspective of separator engineering.

Novel Current Collector for High Energy Density Lithium-Metal Batteries

The energy density of lithium-metal batteries (LMBs) relies to a substantial fraction on the thickness of the lithium-metal anode.1,2 Additionally, the commonly used copper current collector adds a significant mass to the electrode weight (e.g., 77% when considering a 50 μm thick lithium and 10 μm thick copper), but the thinner the lithium foil, the more important becomes the current collector to provide suitable mechanical properties and ensure a good electronic contact across the whole negative electrode.Herein, we report the design of a novel current collector (patent application pending) that enables a substantial reduction in mass, while providing high electronic conductivity and suitable mechanical properties. Moreover, LMBs with a thin lithium foil and a Ni-rich NMC cathode comprising such new current collector reveal a superior performance compared to those containing a standard copper foil. References 1 Liu, J. et al. Pathways for practical high-energy long-cycling lithium metal batteries. Nat. Energy 4, 180-186, (2019).2 Niu, C. et al. Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries. Nat. Energy, 6, 723–732, (2021).

Localized High-Concentration Electrolytes with Low-Cost Diluents Compatible with Both Cobalt-Free LiNiO2 Cathode and Lithium-Metal Anode.

High-nickel layered oxide cathodes and lithium-metal anode are promising candidates for next-generation battery systems due to their high energy density. Nevertheless, the instability of the electrode-electrolyte interphase is hindering their practical application. Localized high-concentration electrolytes (LHCEs) present a promising solution for achieving uniform lithium deposition and a stable cathode-electrolyte interphase. However, the limited choice of diluents and their high cost are restricting their implementation. Four novel cost-effective diluents and their performance with highly reactive LiNiO2 cathode and Li-metal anode are reported here. The results show that all the LHCE cells exhibit a Coulombic efficiency of >99.38% in Li | Cu cells and a capacity retention of >85% in Li | LiNiO2 cells after 250 cycles. Advanced characterizations unveil that the stable cell operation is due to well-tuned electrode-electrolyte interphases and Li deposition morphology. In addition, online electrochemical mass spectroscopy and differential scanning calorimetry reveal that the gas generation and heat-release are greatly reduced with the LHCEs presented. Overall, the study provides new insights into the role of diluents in LHCEs and offers valuable guidance for further optimization of LHCEs for high energy density lithium-metal batteries.

Enhancing the performance of Ni-rich lithium metal batteries through the utilization of amine-functionalized 1D/3D nano shields and additives in high-voltage operation

The development of high-energy–density lithium metal batteries (LMB) is of paramount importance for various emerging energy storage applications, and high-voltage operating system based on high-capacity nickel-rich layer LiNixCoyMn1−x−yO2 (Ni-rich NCM, x ≥ 0.6) cathode combined with a Li metal anode is a representative promising solution. However, it is challenging to stabilize the lithium metal anodes with severe operating conditions, mainly because dissolved transition metal (TM) ions from the cathode trigger harmful side reactions, such as electrolytic decomposition and the growth of dendritic Li structures, resulting in serious safety hazards. In this study, we fabricated an ion-entrapping functional separator using amine-functionalized 1D or 3D inorganic particles confirmed by DFT calculation. Then, we applied in the Ni-rich LMB, demonstrating suppression of TM ion cross-over of 47% compared to conventional PE separators leading to improved cycle numbers and capacity retention at high-voltage operation. Further, combining functional additive introduction with the transition metal cross-over shielding separator resulted in synergistic ion capturing up to 84%. The results of this study provide new insights into the design of advanced LMB for high-energy–density.

Study on Stable Lithiophilic Ag Modification Layer on Copper Current Collector for High Coulombic-Efficiency Lithium Metal Anode

High energy-density lithium metal batteries will be crucial in improving the driving range and promoting electric vehicles. The lithophilic modification layer is usually introduced to improve CE and cycle stability. However, the stability of the lithophilic modified layer in long-term cycling and lithophilic modification strategies for anode current collectors in all-solid-state anode-free lithium batteries are rarely investigated. Here, we prove the failure process of the silver lithophilic modified layer towards lithium metal anode through electrochemical cycling in liquid electrolytes. Combined with EIS, SEM, and XPS analysis, the failure is due to the formation of SEI on the Ag surface and the silver particles’ peeling off from the current collector during cycling, which forms “dead silver.” And we construct carbon-incorporated lithium phosphorous oxynitride (LiCPON) -based all-solid-state Li/Cu half-cells to evaluate the stability of the lithophilic Ag layer. The introduction of Ag between solid electrolyte (LiCPON) and current collector enables the long-term cycle (367th) of all-solid-state Li/Cu half cells with high CE. Our work clarifies the issue of Ag deactivation and provides a method for evaluating modified layers’ use and building stable electrolyte/anode interfaces in all-solid-state anode-free lithium batteries.

Understanding Li creep in Li-metal pouch cells and the role of separator integrity

To realize the advantages of high energy density lithium-metal batteries, their cycle life and safety need to be improved to meet practical and commercial demands. External compression has been shown to improve the performance of lithium-metal batteries through suppressing dendrite growth, densifying the lithium deposit, and improving the lithium deposition morphology. Here, we report the behavior of high-capacity Li||LFP pouch cells in pyrrolidinium-based ionic liquid electrolytes at elevated temperature (50 °C) under various levels of compression and discuss the compression-related mechanisms that affect the performance and failure of the cells. Using scanning electron microscopy, we observed more uniform and less dendritic Li deposition at high levels of compression. However, cell pressure evolution data shows significant lithium metal creep above 800 kPa, effectively limiting the maximum applicable compression. Reducing the testing temperature to 25 °C and maintaining high compression led to suppressed Li creep and extended the cell cycle life by 40%. The adverse effect of lithium creep on the separator is identified as an important mechanism on the pouch cell cycling behavior and is further discussed herein.

Improved ionic conductivity and enhancedinterfacial stability of solid polymer electrolytes with porous ferroelectric ceramic nanofibers

Solid polymer electrolyte has aroused widespread research interest due to the potential to achieve high-safety and high-energy density lithium metal batteries. However, its practical application has been hampered by low ion conductivity. In this work, we innovatively prepare porous ferroelectric ceramic Bi4Ti3O12 nanofibers (BIT NFs) to construct fast conductive networks of Li+ ions in the poly(ethylene oxide) (PEO)/lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) system to achieve the great improvement of lithium ion conductivity (6.25 × 10−4 S cm−1 at 50 °C). Various electrochemical characterizations and density functional theory (DFT) calculations reveal that the abundant oxygen vacancies possessed by the ferroelectric ceramic nanofibers help the accelerated dissociation of LiTFSI and promote the rapid transfer of free Li+ ions. Notably, thanks to the piezoelectric properties of BIT NFs, the dynamic regulation of the electrolyte/lithium interface is realized. The assembled lithium symmetric cells with the composite electrolyte exhibit excellent cycle stability (without short circuiting after 3000 h at 50 °C), and the all-solid-state LiFePO4||Li cells present a superior cycling performance (remained 118.2 mA h g − 1 after 1000 cycles at 0.2 mA cm−2).

In situ formation of a lithiophilic surface on 3D current collectors to regulate lithium nucleation and growth for dendrite-free lithium metal anodes

As the most promising anode material for lithium batteries, lithium metal faces rigorous challenges such as uncontrollable Li dendrite growth and safety risks, which hinder its practical applications. Herein, a uniform indium layer-decorated Ni foam is constructed as a three-dimensional current collector by electroplating to understand the effects of different substrates on the Li deposition morphology and electrochemical performance and to explore the mechanism for Li dendrite growth. The results indicate that an In3Li13 alloy layer is formed by an alloying reaction, which provides abundant nucleation sites for uniform Li deposition. Both simulations and experiments demonstrate that Li ions tend to deposit on the In3Li13 substrate rather than the Li nucleus, while they prefer to plate onto Li particles rather than onto the Ni substrate. Benefiting from the strong interaction, the In3Li13 substrate shows dispersed Li deposition behavior with a grain-like shape, which is different from the severe dendrite formation of bare Ni substrate. As a result, the In3Li13@NF electrode delivers an enhanced Coulombic efficiency of 97.4% for 300 cycles even under a severe cycling condition of 2 mA cm−2, and the Li-In3Li13@NF anode presents increased cycling stability in symmetric cells. Impressively, the Li-In3Li13@NF//LiFePO4 full cell delivers a remarkable capacity retention of 82.8% for 1000 cycles at 2 C. This work not only sheds light on the growth mechanism for Li dendrites but also provides a new strategy to develop high-energy density lithium metal batteries.

Suppressing lithium dendrite growth on lithium-ion/metal batteries by a tortuously porous γ-alumina separator

The challenges of dendrite propagation limit the operational safety and long-term cycling stability of lithium-ion batteries and development of high energy density lithium-metal batteries. Solid state electrolytes may eliminate the propagation of dendrites, but they fail to achieve high Li-ion conductivity and charge transfer rate at room temperature resulting in undesired cell performance. Here we report the usage of electrode-coated plate-structured γ-alumina separators with liquid electrolyte for high performance, safe lithium-ion batteries. The γ-alumina separators, made of γ-alumina plates of high aspect ratio, are mechanically strong and tortuously porous, and therefore effective in preventing passage of dendrites. Nickel-manganese-cobalt-oxide/lithium cells with a plate-structured γ-alumina separator show stable cycle performance without passage of dendrites up to 3 C-rate of charging and discharging. Same cells with commercial polypropylene (PP-2500) separator or spherical-structured α-alumina separator of similar pore size to γ-alumina separator, could not achieve the above-mentioned dendrite free cycling even at much lower C-rates (0.2 C and 1.0 C respectively). A comparison of the three cells with different separators clearly shows that the hardness and high tortuosity of the separator are effective in preventing dendrite propagation. This work results in the development of a lithium-ion-battery with improved safety and shows a new direction in the design and fabrication of high performance and safe lithium-metal batteries.

Combining Organic Plastic Salts with a Bicontinuous Electrospun PVDF-HFP/Li7La3Zr2O12 Membrane: LiF-Rich Solid-Electrolyte Interphase Enabling Stable Solid-State Lithium Metal Batteries.

Solid-state electrolytes can guarantee the safe operation of high-energy density lithium metal batteries (LMBs). However, major challenges still persist with LMBs due to the use of solid electrolytes, that is, poor ionic conductivity and poor compatibility at the electrolyte/electrode interface, which reduces the operational stability of solid-state LMBs. Herein, a novel fiber-network-reinforced composite polymer electrolyte (CPE) was designed by combining an organic plastic salt (OPS) with a bicontinuous electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)/Li7La3Zr2O12 (LLZO) membrane. The presence of LLZO in the composite helps to promote the dissociation of FSI- from OPSs. Subsequently, the dissociated FSI- is then involved in the formation of a LiF-rich solid electrolyte interphase (SEI) layer on the lithium anode via a reductive decomposition reaction, which was affirmed by theoretical calculations and experimental results. Due to the LiF-rich SEI layer, the Li/Li symmetric cell was able to demonstrate a long cyclic life of over 2600 h at a current density of 0.1 mA cm-2. More importantly, the as-prepared CPE achieved a high ionic conductivity of 2.8 × 10-4 S cm-1 at 25 °C, and the Li/LiFePO4 cell based on the CPE exhibited a high discharge capacity and 83.3% capacity retention after 500 cycles at 1.0 C. Thus, the strategy proposed in this work can inspire the future development of highly conductive solid electrolytes and compatible interface designs toward high-energy density solid-state LMBs.

An organosulfide-based energetic liquid as the catholyte in high-energy density lithium metal batteries for large-scale grid energy storage

An organosulfide-based energetic liquid as the catholyte in high-energy density lithium metal batteries for large-scale grid energy storage

A dual lithiated alloy interphase layer for high-energy–density lithium metal batteries

Lithium metal batteries represent potential candidates for high-energy–density batteries. However, non-uniform Li deposition and dendrite growth limit the practical applications of Li anodes in solid-state and liquid-phase battery systems. This report investigates the conversion mechanism of an aluminum coordination compound (Al(MMP)3) at the interface of a lithium metal anode. Based on the proposed mechanism, a novel dual alloy comprising a LixAl-LixP hybrid interphase is designed to promote interfacial charge balance. Under the synergic effect of a fluoropolymer, the organic/inorganic protective layer containing the dual lithiated alloy exhibits short-term Li storage and rapid Li+ transport, thereby limiting the accumulation of inactive lithium and decreasing the Li+ migration barrier. Upon implementing the hybrid anode, the electrochemical life span of the Li metal battery exceeds 2000 h. Moreover, pairing with a Ni-rich cathode leads to excellent capacity retention and stable coulomb efficiency. The developed strategy can guide future advancements in lithium metal batteries with long cycle lives.

Quantitatively analyzing the failure processes of rechargeable Li metal batteries.

Practical use of lithium (Li) metal for high–energy density lithium metal batteries has been prevented by the continuous formation of Li dendrites, electrochemically isolated Li metal, and the irreversible formation of solid electrolyte interphases (SEIs). Differentiating and quantifying these inactive Li species are key to understand the failure mode. Here, using operando nuclear magnetic resonance (NMR) spectroscopy together with ex situ titration gas chromatography (TGC) and mass spectrometry titration (MST) techniques, we established a solid foundation for quantifying the evolution of dead Li metal and SEI separately. The existence of LiH is identified, which causes deviation in the quantification results of dead Li metal obtained by these three techniques. The formation of inactive Li under various operating conditions has been studied quantitatively, which revealed a general “two-stage” failure process for the Li metal. The combined techniques presented here establish a benchmark to unravel the complex failure mechanism of Li metal.

Bottom-up lithium growth guided by Ag concentration gradient in 3D PVDF framework towards stable lithium metal anode

Three-dimensional (3D) frameworks have received much attention as an effective modification strategy for next-generation high-energy–density lithium metal batteries. However, the top-growth mode of lithium (Li) on the 3D framework remains a tough challenge. To achieve a uniform bottom-up Li growth, a scheme involving Ag concentration gradient in 3D PVDF framework (C-Ag/PVDF) is proposed. Ag nanoparticles with a concentration gradient induce an interface activity gradient in the 3D framework, and this gradient feature is still maintained during the cycle. As a result, the C-Ag/PVDF framework delivers a long lifespan over 1800 h at a current density of 1 mA cm−2 with a capacity of 1 mAh cm−2, and shows an ultra-long life (>1300 h) even at a high current density of 4 mA cm−2 with a capacity of 4 mAh cm−2. The advantage of concentration gradient provides further insights into the optimal design of the 3D framework for stable Li metal anode.