High-voltage Li Metal Batteries Research Articles

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.

Construction of flexible asymmetric composite polymer electrolytes for high-voltage lithium metal batteries with superior performance

The primary obstacle hindering the application of composite solid electrolytes lies in the varying demands posed by the Li metal anode and the cathode, which needs to be capable of suppressing dendrite growth and resisting high voltage simultaneously. In this work, a new asymmetric composite solid-state electrolyte prepared via electrospinning and in-situ polymerization is proposed to address these shortcomings. In this bilayer architecture, polyacrylonitrile (PAN) layer of high-voltage tolerance, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) layer of robust mechanical strength and good compatibility towards Li-anode are constructed, and metal-organic-frameworks (MOFs) are pre-embedded within both layers. The unique design provides a wide electrochemical stability window meanwhile ensures uniform lithium deposition. Remarkably, it exhibits a superior lithium utilization of 41 mAh cm−2 using a lean polymer electrolyte precursor and a high critical current density of 2.2 mA cm−2 with a thickness of 40 μm. Beneficial from the formation of a self-adjustable gradient solid electrolyte interphase in the Li/PVDF-HFP interface, the asymmetric electrolyte endows Li||Li and Li||NCM811 cells with excellent cycling stability. Moreover, the solid-state pouch cell exhibits reliable operation under extreme conditions. This work provides inspiration for the design and fabrication of composite solid electrolytes for next-generation high-voltage Li metal batteries.

High-Concentrated Binary-Salt Ether Electrolytes for High-Voltage Lithium Metal Batteries with Ni-Rich Cathode.

The incompatibility of ether electrolytes with a cathode dramatically limits its application in high-voltage Li metal batteries. Herein, we report a new highly concentrated binary salt ether-based electrolyte (HCBE, 1.25 M LiTFSI + 2.5 M LiFSI in DME) that enables stable cycling of high-voltage lithium metal batteries with the Ni-rich (NCM83, LiNi0.83Co0.12Mn0.05O2) cathode. Experimental characterizations and density functional theory (DFT) calculations reveal the special solvation structure in HCBE. A solvation structure rich in aggregates (AGGs) can effectively broaden the electrochemical window of the ether electrolyte. The anions in HCBE preferentially decompose under high voltage, forming a CEI film rich in inorganic components to protect the electrolyte from degradation. Thus, the high-energy-density Li||NCM83 cell has a capacity retention of ≈95% after 150 cycles. Significantly, the cells in HCBE have a high and stable average Coulombic efficiency of over 99.9%, much larger than that of 1 M LiPF6 + EC + EMC + DMC (99%). The result emphasizes that the anionic-driven formation of a cathode electrolyte interface (CEI) can reduce the number of interface side reactions and effectively protect the cathode. Furthermore, the Coulombic efficiency of Li||Cu using the HCBE is 98.5%, underscoring the advantages of using ether-based electrolytes. This work offers novel insights and approaches for the design of high-performance electrolytes for lithium metal batteries.

A fluorine rich borate ionic additive enabling high-voltage Li metal batteries

Lithium-metal batteries (LMBs) are promising alternatives to state-of-the-art Lithium-ion batteries (LIBs) to achieve higher energy densities. However, the poor cyclability of LMBs resulting from Li metal anode (Li0) irreversibility and concomitant electrolyte decompositions limits their practical applications. In this study, we reported a per-fluorinated salt, lithium tetrakis(perfluoro-tertbutyloxy)borate (abbreviated as Li-TFOB) as an electrolyte additive for Li-metal batteries, which contains 36 F atoms per molecule. This newly designed ionic additive tuned the chemical composition of the solid-electrolyte interphase (SEI) on Li0 by increasing the amount of LiF and Li-B-O inorganic species. DFT calculations and Molecular dynamics (MD) simulations indicated the preferential reduction of the TFOB anions at Li0, which occurs with a lower free energy change than PF6− anions. The designed ionic additive enables the 4.6 V Li||LiNi0.6Mn0.2Co0.2O2 (NMC622) cell to achieve an average CE of 99.1 % and a high-capacity retention of > 50 % after 500 cycles. This experiment-simulation joint study illustrated an attractive approach to accelerating the design of electrolytes and interphases for LMBs.

Sustained Release-Driven Interface Engineering Enables Fast Charging Lithium Metal Batteries.

LiNO3 has attracted intensive attention as a promising electrolyte additive to regulate Li deposition behavior as it can form favorable Li3N, LiNxOy species to improve the interfacial stability. However, the inferior solubility in carbonate-based electrolyte restricts its application in high-voltage Li metal batteries. Herein, an artificial composite layer (referred to as PML) composed of LiNO3 and PMMA is rationally designed on Li surface. The PML layer serves as a reservoir for LiNO3 release gradually to the electrolyte during cycling, guaranteeing the stability of SEI layer for uniform Li deposition. The PMMA matrix not only links the nitrogen-containing species for uniform ionic conductivity but also can be coordinated with Li for rapid Li ions migration, resulting in homogenous Li-ion flux and dendrite-free morphology. As a result, stable and dendrite-free plating/stripping behaviors of Li metal anodes are achieved even at an ultrahigh current density of 20mA cm-2 (>570h) and large areal capacity of 10 mAh cm-2 (>1200h). Moreover, the Li||LiFePO4 full cell using PML-Li anode undergoes stable cycling for 2000 cycles with high-capacity retention of 94.8%. This facile strategy will widen the potential application of LiNO3 in carbonate-based electrolyte for practical LMBs.

Fluorine-rich deep eutectic electrolytes enabling robust interphases and nonflammability of high-voltage lithium metal batteries

High-voltage Li metal batteries (LMBs) are characterized by the superior energy density over state-of-the-art Li-ion batteries, but it is an essential challenge to develop electrolytes which can be stably and...

Stable Cycling of High-Voltage Lithium Metal Batteries Enabled By Highly Concentrated Sulfolane-Based Gel Electrolytes

High-voltage lithium (Li) metal batteries are promising candidates for next-generation batteries. To enable high-voltage Li metal batteries, an electrolyte having high anodic stability and excellent compatibility with Li metal anodes is essential. Here, we report a gel electrolyte comprising poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) and a highly concentrated electrolyte of lithium bis(fluorosulfonyl)imide (LiFSI) and sulfolane (SL), which provides both high anodic stability and high Coulombic efficiency of Li metal anodes. This gel electrolyte achieves the deposition of dense Li metal with larger particles. We have found that the FSI−–Li+ association is intensified in the presence of PVDF–HFP, leading to the formation of a low-resistance solid electrolyte interphase (SEI) enriched with LiF and sulfurous compounds derived from FSI−. These results suggest that the SEI with a superior Li+ transport property as well as the liquid-retaining ability of the gel electrolyte facilitate the deposition of dense Li and thus effectively prevents Li loss owing to electrolyte decomposition and dead Li formation, resulting in high Coulombic efficiency of Li metal anodes. We have also demonstrated the stable charge/discharge cycling of a high-voltage Li metal battery with a 5 V-class LiNi0.5Mn1.5O4 cathode using the gel electrolyte.

Organic Nitrate Additive for High-Rate and Large-Capacity Lithium Metal Anode in Carbonate Electrolyte.

Lithium nitrate has been widely used to improve the interfacial stability of Li metal anode in ether electrolyte. However, the low solubility limits its application in carbonate electrolytes for high-voltage Li metal batteries. Herein, nitrated polycaprolactone (PCL-ONO2 ), which is prepared via the acylation of polycaprolactone diol (PCL-diol) followed by the grafting of nitrate group, has been proposed as an electrolyte additive to introduce high-concentration NO3 - into carbonate electrolytes for the first time. The theoretical calculations and X-ray photoelectron spectroscopy depth profiling demonstrate that the PCL-ONO2 additive preferentially reacts with Li metal and in situ constructs a stable dual-layered solid electrolyte interphase film, presenting an inner nitride-rich layer and an outer flexible PCL-based layer on the surface of Li metal anode. As a result, the Li metal anode delivers an impressive long-term cycling performance over 1400h at an elevated area capacity of 10.0mAhcm-2 and an ultrahigh current density of 10.0mAcm-2 in the Li symmetrical cells. Moreover, the PCL-ONO2 additive enables the full cells constructed by coupling high-loading LiFePO4 (20.0mgcm-2 ) or LiNi0.5 Co0.2 Mn0.3 (16.5mgcm-2 ) cathode and thin Li metal anode (≈50µm) to demonstrate greatly improved cycling stability and rate capability.

Unique double-layer solid electrolyte interphase formed with fluorinated ether-based electrolytes for high-voltage lithium metal batteries

Li metal batteries using high-voltage layered oxides cathodes are of particular interest due to their high energy density. However, they suffer from short lifespan and extreme safety concerns, which are attributed to the degradation of layered oxides and the decomposition of electrolyte at high voltage, as well as the high reactivity of metallic Li. The key is the development of stable electrolytes against both high-voltage cathodes and Li with the formation of robust interphase films on the surfaces. Herein, we report a highly fluorinated ether, 1,1,1-trifluoro-2-[(2,2,2-trifluoroethoxy) methoxy] ethane (TTME), as a co-solvent, which not only functions as a diluent forming a localized high concentration electrolyte (LHCE), but also participates in the construction of the inner solvation structure. The TTME-based electrolyte is stable itself at high voltage and induces the formation of a unique double-layer solid electrolyte interphase (SEI) film, which is embodied as one layer rich in crystalline structural components for enhanced mechanical strength and another amorphous layer with a higher concentration of organic components for enhanced flexibility. The Li||Cu cells display a noticeably high Coulombic efficiency of 99.28% after 300 cycles and Li symmetric cells maintain stable cycling more than 3200 h at 0.5 mA/cm2 and 1.0 mAh/cm2. In addition, lithium metal cells using LiNi0.8Co0.1Mn0.1O2 and LiCoO2 cathodes (both loadings ∼3.0 mAh/cm2) realize capacity retentions of >85% over 240 cycles with a charge cut-off voltage of 4.4 V and 90% for 170 cycles with a charge cut-off voltage of 4.5 V, respectively. This study offers a bifunctional ether-based electrolyte solvent beneficial for high-voltage Li metal batteries.

High-Voltage Li Metal Batteries Enabled by Adsorption-Defluorination Mechanism

High-Voltage Li Metal Batteries Enabled by Adsorption-Defluorination Mechanism

Efficient anion solvation modulation in carbonate electrolytes enables high-voltage lithium metal batteries

Developing electrolytes qualified for high-voltage (>4 V vs Li/Li+) conditions is of great significance for high-energy density Li-metal batteries (LMBs). Carbonate-based electrolytes possess high oxidation stability, whereas the uneven Li deposition, low Coulombic efficiency (CE) and poor anodic stability of such electrolytes severely impede the practical application in high-voltage LMBs. Herein, a 1.8 M lithium bis(trifluoromethanesulphonyl)imide (LiTFSI)-carbonate electrolyte with high compatibility with both Li anode and high-voltage cathode is designed. LiNO3 is introduced into the electrolyte as an additive with the assistance of CuF2 cosolvent, which efficiently enables robust and conductive interfaces at both anode and cathode sides. As a consequence, an average CE of 98.0% is achieved for Li||Cu half-cell at 1 mA cm−2. Li||LiNi0.8Co0.1Mn0.1O2 full cell fabricated with cathode areal capacity of 2.4 mAh cm−2 and 5× excess Li achieves a high capacity retention of 80.7% after 200 cycles with cut-off voltage of 4.3 V. This work provides a facile and effective approach to improve the application of carbonate-based electrolytes in high-voltage LMBs.

Crystallographic oriented plating by using lithiophilic ionic additives in carbonate electrolyte for enabling high voltage lithium metal batteries

The practical utilizations of high voltage (>4.0 V) lithium (Li) metal batteries are severely hindered by the unstable solid electrolyte interphase (SEI) and uncontrolled growth of dendritic Li in carbonate electrolyte. In this work, lithiophilic active ionic additives (In(NO3)3, lithium difluoro(oxalate)borate (LiDFOB), and LiNO3) are adopted to generate a multi-layer SEI in commercial carbonate electrolyte and promote the preferential Li plating along the (200) direction. As evidenced theoretically and experimentally, it is found that In(NO3)3 ionic additive generates a lithiophilic In-containing inner SEI layer, which induces the oriented Li plating along the (200) plane and a low surface energy of deposited Li. In addition, the LiDFOB additive is used to obtain LiF-rich middle SEI to improve the interfacial energy of SEI, and the LiNO3/tetramethylene sulfone (TMS) additive generates a Li3N-rich outer SEI to accelerate Li+ transport. As a result, the modified carbonate electrolyte can ensure the Li (50 μm) ‖LiNi0.8Co0.1Mn0.1O2 full cell to realize an ultra-high average CE of 99.3 % and a high-capacity retention of 94.2 % after 100 cycles. This work reveals the mechanism of multi-layer SEI induced crystallographic oriented Li plating and the internal mechanism of Li+ transport, and provides a simple approach to bring Li metal into practical high voltage Li metal batteries.

High-Voltage Solid-State Lithium Metal Batteries with Stable Anodic and Cathodic Interfaces by a Laminated Solid Polymer Electrolyte.

Solid polymer electrolyte (SPE) is quite an attractive candidate for constructing high-voltage Li metal batteries (LMBs) with high energy density and excellent safety. However, sim ultaneous achievement of high-voltage stability against the cathode and good compatibility with the Li anode remains challenging for the current SPE technology. Herein, a dual-layered solid electrolyte (DLSE) consisting of an oxidation-resistant poly(acrylonitrile) (PAN) layer facing a high-potential cathode and a reduction-compatible poly(vinylidene fluoride) (PVDF) layer incorporated by Li6.4La3Zr1.4Ta0.6O12 (LLZTO) nanoparticles and an ionic liquid plasticizer in contact with a Li anode was fabricated. The uniquely designed DLSE holds favorable overall properties in ionic conductivity, Li+ transference number, and mechanical strength. Moreover, the combined advantages of two polymer electrolyte layers greatly address the interface issues on both the cathode and anode. Consequently, the high-voltage LMBs employing the DLSE exhibit excellent room-temperature performances including high rate capacity and long cycle life.

Non-polar ether-based electrolyte solutions for stable high-voltage non-aqueous lithium metal batteries

The electrochemical instability of ether-based electrolyte solutions hinders their practical applications in high-voltage Li metal batteries. To circumvent this issue, here, we propose a dilution strategy to lose the Li+/solvent interaction and use the dilute non-aqueous electrolyte solution in high-voltage lithium metal batteries. We demonstrate that in a non-polar dipropyl ether (DPE)-based electrolyte solution with lithium bis(fluorosulfonyl) imide salt, the decomposition order of solvated species can be adjusted to promote the Li+/salt-derived anion clusters decomposition over free ether solvent molecules. This selective mechanism favors the formation of a robust cathode electrolyte interphase (CEI) and a solvent-deficient electric double-layer structure at the positive electrode interface. When the DPE-based electrolyte is tested in combination with a Li metal negative electrode (50 μm thick) and a LiNi0.8Co0.1Mn0.1O2-based positive electrode (3.3 mAh/cm2) in pouch cell configuration at 25 °C, a specific discharge capacity retention of about 74% after 150 cycles (0.33 and 1 mA/cm2 charge and discharge, respectively) is obtained.

Enabling uniform Li deposition behavior by introducing a NO3−-based ionic liquid additive into carbonate electrolyte for high-voltage Li metal batteries

The nonuniform lithium deposition behavior and low deposition/dissolution reversibility are the most significant obstacles for practical high-energy-density lithium metal batteries (LMBs). Herein, a novel 1-ethyl-3-methylimidazolium nitrate ionic liquid ([EMIm][NO3] IL) is proposed to incorporate into the conventional carbonate electrolyte with a small amount of 1,2-dimethoxyethane (DME) as the cosolvent. A high solubility of 0.5 M [EMIm][NO3] in the carbonate electrolyte is achieved for high-voltage LMBs by replacing traditional lithium nitrate with [EMIm][NO3] IL, where the DME cosolvent with high donicity enables the solvation of NO3− in the electrolyte system. Benefitting from the electrochemical reduction of NO3− anions, the designed electrolyte promotes the formation of highly conductive and stable solid electrolyte interface abundant with N-containing species and achieves stable Li stripping/plating behavior. As a result, the IL-modified electrolyte enables excellent electrochemical performances with improved Coulombic efficiency (>98.5%) in Li|Cu cell and stable cyclability (900 h) in Li|Li symmetric cell, respectively. More importantly, a Li|LiNi0.8Co0.1Mn0.1O2 pouch-type battery composed of high mass loading cathode (20 mg cm−2) and thin Li foil (50 μm) maintains an impressive cycling lifespan of 100 cycles. The exploration of NO3− containing IL as a novel electrolyte additive offers a promising opportunity for achieving high-performance Li metal batteries.

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.

Salt-in-Salt Reinforced Carbonate Electrolyte for Li Metal Batteries.

The instability of carbonate electrolyte with metallic Li greatly limits its application in high-voltage Li metal batteries. Here, a "salt-in-salt" strategy is applied to boost the LiNO3 solubility in the carbonate electrolyte with Mg(TFSI)2 carrier, which enables the inorganic-rich solid electrolyte interphase (SEI) for excellent Li metal anode performance and also maintains the cathode stability. In the designed electrolyte, both NO3 - and PF6 - anions participate in the Li+ -solvent complexes, thus promoting the formation of inorganic-rich SEI. Our designed electrolyte has achieved a superior Li CE of 99.7 %, enabling the high-loading NCM811||Li (4.5 mAh cm-2 ) full cell with N/P ratio of 1.92 to achieve 84.6 % capacity retention after 200 cycles. The enhancement of LiNO3 solubility by divalent salts is universal, which will also inspire the electrolyte design for other metal batteries.

Targeted stabilization of solid electrolyte interphase and cathode electrolyte interphase in high-voltage lithium-metal batteries by an asymmetric sustained-release strategy

High-voltage lithium (Li)-metal batteries with cell-level energy density over 350 Wh kg−1 are promising energy storage systems. However, the aggressive interphase chemistries associated with highly reactive Li-metal anode and high-voltage cathodes impede their practical applications. Herein, we demonstrate the targeted stabilization of solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) in high-voltage Li-metal batteries by asymmetrically sustained-releasing different additives. An asymmetric sustained-release film loaded with lithium bis-(oxalate)borate (LiBOB) and LiNO3 on each side is investigated as a proof-of-concept. The sustained-releasing of LiBOB and LiNO3 can maintain a localized concentration at the high-voltage cathode and Li-metal anode fronts respectively, thus forming a stable B-containing CEI and N-containing SEI. As such, issues like dendrites growth, parasitic side reactions and transition metals dissolution under high-voltage are addressed simultaneously. Based on this strategy, the 30 μm Li|LiNi0.5Co0.2Mn0.3O2 (4.1 mAh cm−2) batteries deliver a capacity retention of 80% after 173 cycles under a cut-off voltage of 4.5 V.

Practical 4.4 V Li||NCM811 batteries enabled by a thermal stable and HF free carbonate-based electrolyte

Fluoroethylene carbonate (FEC) is widely recognized as an effective cosolvent coupling with commercial carbonate-based electrolyte to enable stable high-voltage Li metal batteries (LMBs). However, FEC reacts with the decomposition product (PF5) of the LiPF6 salt in the presence of trace amount of water, producing corrosive species such as HF, deteriorating the stability of the Li metal batteries (LMBs). In this work, we employed a non-nucleophilic organic base, ethoxy(pentafluoro) cyclotriphosphazene (PFN), as a multifunctional additive to simultaneously enhance the chemical stability and safety of the FEC-LiPF6 carbonate-based electrolytes. The electron-donating -PN- group of PFN makes it able to catch the Lewis acid PF5 and HF in the electrolyte, while the steric hindrance from the resembles benzene structure of PFN prevents it from attacking the FEC. Furthermore, the PFN additive also improve the safety and processability of the battery since it has a superior flame retardancy and good wettability with the separator. As a result, adding 3 wt% of PFN is able to make a FEC containing carbonate electrolyte self-extinguishing, and significantly improve the stability of high-voltage Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) batteries, especially when it couples with lithium difluoro(oxalato)borate (LiDFOB) as a film-forming additive. Specifically, using a FEC-LiPF6 carbonate-based electrolyte that containing 3 wt% PFN and 2 wt% LiDFOB, the Li||NCM811 coin cell, which consists of an ultrathin Li anode (35 µm) and a NCM811 cathode with a high areal capacity of 6 mAh·cm−2, presents a capacity retention of 97.2% after 50 cycles, which is much better than that cycled in a blank electrolyte (86.6%) without the studied additives. 3Ah Li||NCM811 pouch cells were also assembled, gassing during cycling was significantly suppressed and a capacity retention of 84.2% after 100 cycles at 0.3CC/0.5CD was be obtained. This work provides a convenient strategy for developing highly stable carbonate electrolyte for practical lithium-metal batteries.

Integrated Ring-Chain Design of a New Fluorinated Ether Solvent for High-Voltage Lithium-Metal Batteries.

Ether‐based electrolytes offer promising features such as high lithium‐ion solvation power and stable interface, yet their limited oxidation stability impedes application in high‐voltage Li‐metal batteries (LMBs). Whereas the fluorination of the ether backbone improves the oxidative stability, the resulting solvents lose their Li+‐solvation ability. Therefore, the rational molecular design of solvents is essential to combine high redox stability with good ionic conductivity. Here, we report the synthesis of a new high‐voltage fluorinated ether solvent through integrated ring‐chain molecular design, which can be used as a single solvent while retaining high‐voltage stability. The controlled Li+‐solvation environment even at low‐salt‐concentration (1 M or 2 M) enables a uniform and compact Li anode and an outstanding cycling stability in the Li|NCM811 full cell (20 μm Li foil, N/P ratio of 4). These results show the impact of molecular design of electrolytes towards the utilization of LMBs.