Li Loss Research Articles

Roll-to-roll Prelithiation of Li-ion Batteries Anodes Using Ultrathin Lithium Strips

The irreversible formation of solid electrolyte interphase (SEI) reduces lithium-ion batteries’ capacity and energy density (LIBs), prompting the prelithiation strategies to compensate for the Li loss. However, the accuracy of the prelithiation degree and the SEI formation under prelithiation conditions remain key issues, especially for practical industrial production. Herein, we demonstrate that roll-to-roll prelithiation of graphite anodes can be done using ultrathin lithium strips (6-μm-thick), and the prelithiation degree can be precisely tuned by the topological distribution. More importantly, the formation of SEI during the prelithiation process and its influence on the long-term cycling performance of the prelithiated LiFePO4 || graphite pouch cells was revealed. Afterward, the prelithiated pouch LiFePO4 || graphite cell at the optimized conditions exhibits the upgraded energy density after even 1200 cycles. This study shall provide an industrial-scale prelithiation technique for high-energy–density LIBs and a pioneering systematic investigation of SEI chemistry during prelithiation.

Precise regulation of layered-to-rock structure of spent Li-ion cathodes achieving ultrahigh lithium recovery rate

With the rapid development of electric vehicles and digital devices, the accumulated spent lithium-ion batteries (LIBs) cause severe anxiety about lithium resources and environmental safety. However, the low capture rate of Li+ and the high chemical consumption of the existing recovery methods lead to high Li loss, treatment costs and disposal fees. Herein, we propose a universal strategy of spent LIBs recovery via precise directional regulating structures (from layered to rock) to achieve ultrahigh lithium recovery rate with super-low chemical and energy consumption. Experimental characterization and theoretical calculations reveal the dissociation of structure, reorganization of Li–O bonds and phase transformation of the cathode materials in the limited-domain reduction process, realizing the complete recovery of Li+ without consuming acid leaching agent. This process realizes an extra-high Li separation index (19154) and extra-long cycle half-life (173 cycles) which are far superior to those of traditional methods (9–191 and 7 cycles). Besides, ecological and economic analysis shows that the consumptions of chemicals and energy are only 9 % and 9.7 % those of the existing literature, respectively, providing a bright pathway for industrializable lithium batteries recycling.

A Room‐Temperature Lithium‐Restocking Strategy for the Direct Reuse of Degraded LiFePO4 Electrodes

The sustainable development of lithium iron phosphate (LFP) batteries calls for efficient recycling technologies for spent LFP (SLFP). Even for the advanced direct material regeneration (DMR) method, multiple steps including separation, regeneration, and electrode refabrication processes are still needed. To circumvent these intricacies, new regeneration methods that allow direct electrode reuse (DER) by rejuvenating SLFP electrodes without damaging its structure are desired. Here, a 0.1 M lithium triethyl borohydride/tetrahydrofuran solution, which has the proper reductive capability to reduce Fe3+ in SLFP to Fe2+ without alloying with the aluminum current collector, is selected as the lithiation/regeneration reagent to restock the Li loss and regenerate SLFP electrodes. By soaking the SLFP electrodes in the lithiation solution, we successfully rejuvenated the crystal structure and electrochemical activity of SLFP electrodes with structural integrity within only 6 minutes at room temperature. When being directly reused, the regenerated LFP electrodes deliver a high specific capacity of 162.6 mAh g‐1 even after being exposed to air for 3 months. The DER strategy presents significant economic and environmental benefits compared with the DMR method. This research provides a timely and innovative solution for recycling spent blade batteries using large‐sized LFP electrodes, boosting the closed‐loop development of LFP batteries.

A Room-Temperature Lithium-Restocking Strategy for the Direct Reuse of Degraded LiFePO4 Electrodes.

The sustainable development of lithium iron phosphate (LFP) batteries calls for efficient recycling technologies for spent LFP (SLFP). Even for the advanced direct material regeneration (DMR) method, multiple steps including separation, regeneration, and electrode refabrication processes are still needed. To circumvent these intricacies, new regeneration methods that allow direct electrode reuse (DER) by rejuvenating SLFP electrodes without damaging its structure are desired. Here, a 0.1 M lithium triethyl borohydride/tetrahydrofuran solution, which has the proper reductive capability to reduce Fe3+ in SLFP to Fe2+ without alloying with the aluminum current collector, is selected as the lithiation/regeneration reagent to restock the Li loss and regenerate SLFP electrodes. By soaking the SLFP electrodes in the lithiation solution, we successfully rejuvenated the crystal structure and electrochemical activity of SLFP electrodes with structural integrity within only 6 minutes at room temperature. When being directly reused, the regenerated LFP electrodes deliver a high specific capacity of 162.6 mAh g-1 even after being exposed to air for 3 months. The DER strategy presents significant economic and environmental benefits compared with the DMR method. This research provides a timely and innovative solution for recycling spent blade batteries using large-sized LFP electrodes, boosting the closed-loop development of LFP batteries.

Low Temperature Sintering Al-B Doped-LLZO for All-Solid-State Lithium Battery

This research synthesizes a double Al-B doped LLZO following a composition of Li7+0.5xLa1.14Al1.43xB0.5xZr2-3xO12-δ through a solid-state reaction. The materials were sintered at a low temperature of 900 °C, giving an advantage in reducing Li loss. The material was analyzed to understand the phase content, the crystal structure and cell parameters, the surface morphology, the impedance, the electrical conductivity, and the activation energy for ionic migration. As a result, the Al-B doped-LLZO with x composition of 0.3 (Li7.15La1.14Al0.429B0.15Zr1.1O12-) and ball milling time of 120 h, LLZBAO(0.3)120 h, provides the highest ionic conductivity of 6.898×10–4 Scm–1 at room temperature, and it increases as the temperature increases confirming activation energy of 0.135 eV. A prototype of LCO-LLZBAO(0.3)120h-Li metal battery was produced and tested to investigate the solid electrolyte performance. A cyclic voltammetry analysis confirms a quasi-reversible reaction involving extraction-insertion of Li ions into LiCoO2. However, the excess capacity and a long plateau at low voltage also indicate the reduced Li+ into zero valent-metal, which is poorly reversible, causing the battery capacity to decrease and become stable after 20 cycles.

Nondisassembly Repair of Degraded LiFePO4 Cells via Lithium Restoration from the Solid Electrolyte Interphase.

The disposal of degraded batteries will be a severe challenge with the expanding market demand for lithium iron phosphate (LiFePO4 or LFP) batteries. However, due to a lack of economic and technical viability, conventional metal extraction and material regeneration are hindered from practical application. Herein, we propose a nondisassembly repair strategy for degraded cells through a lithium restoration method based on deep discharge, which can elevate the anodic potential to result in the selective oxidative decomposition and thinning of the solid electrolyte interphase (SEI) on the graphite anode. The decomposed SEI acts as a lithium source to compensate for the Li loss and eliminate Li-Fe antisite defects for degraded LFP. Through this design, the repaired pouch cells show improved kinetic characteristics, significant capacity restoration, and an extended lifespan. This proposed repair scheme relying on SEI rejuvenation is of great significance for extending the service life and promoting the secondary use of degraded cells.

Development of High-Performance LLZO Separators for Solid-State Batteries: Balancing Li Loss, Stability, and Morphology in a Tape Casting Process

Ceramic solid-state batteries (SSBs) are considered a viable alternative to lithium-ion batteries with liquid electrolytes, as they offer greater safety at the cell level. The Li7La3Zr2O12 garnet (LLZO) is a promising solid electrolyte for SSBs due to its stability with lithium metal anode and its good ionic conductivity of up to 2 mS cm-1. However, scalable and economically feasible techniques for producing LLZO-based batteries are required to make them competitive in the market.Tape casting is an industrially scalable process for producing customizable ceramic components. Successful implementation of this method requires a deep understanding of the transformation of the LLZO powder during the whole process chain, especially the effects of Li loss due to air and protic solvents interaction as well as Li evaporation during sintering.In this talk, a novel approach for fabricating thin LLZO ceramic separators by tape casting will be presented, in which lithium saltis used as a lithium mediator source in different process steps to optimize the separator properties. Using XRD, Raman spectroscopy, NMR spectroscopy, and SEM, we systematically investigate the effects of material composition and process conditions on the compositional and electrochemical performance of tape-cast LLZO separators in symmetric cells. This research provides important insights for optimizing the manufacturing process and enables the development of high-performance LLZO ceramic separators for all-solid-state batteries.

Characterization of Degradation Mechanisms of Alternative Electrolytes Solutions in Fast Charging Li-Ion Batteries

While the idea that fast charging batteries could be utilized in electric vehicles is enticing, current fast charging batteries face significant challenges that must be mitigated before this application is realized. Fast charging batteries currently suffer from capacity loss and degradation over time which not only affects battery life but poses a safety hazard. The current electrolyte, 1.2 M LiPF6 in 3:7 wt.% EC/EMC (Gen2), contains the salt LiPF6 that when exposed to moisture can form dangerous hydrofluoric acid and contains a carbonate-based solvent that when exposed to oxygen can ignite. In addition, batteries experience degradation over many cycles of fast charging which results in capacity fade and poor battery performance. However, previous studies have shown the potential for other electrolyte systems to mitigate these problems, specifically by using highly concentrated electrolytes1. These studies claim that using these electrolytes results in the formation of a solid electrolyte interphase (SEI) that passivates Li ions better than the Gen2 electrolyte. The SEI is a layer that forms on the anode within the battery and serves as a protective layer that allows for Li intercalation into graphite and can therefore protect against degradation. By using different electrolytes, a different SEI is formed, and different degradation mechanisms are observed. In this way, the SEI can be tuned to improve Li passivation and ionic conductivity by changing the electrolyte’s composition and concentration2. This research focuses on such alternative electrolyte systems and aims to characterize the different degradation mechanisms corresponding to each electrolyte. Favorable performance has been observed using 1.2 M LiFSI in 3:7 wt.% EC/EMC as an electrolyte. We are studying LiFSI in acetonitrile (AN) at higher concentrations than traditional Gen2 to quantify the SEI. We expect AN to form an anion derived SEI, a composition of which results in improved passivation of Li ions1. In this study, we characterize degradation of alternative electrolyte systems through x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Through these methods we can observe and quantify both crystalline, amorphous degradation products due to loss of Li inventory and loss of active material. XPS allows quantification of compositional changes in the SEI layer at the surface of the electrode. The SEM provides qualitative information on degradation such as visualizing lithium plating and dendrite formation. We implement quantitative XRD to measure the crystalline phases of the graphite anode, showing the degree of lithium intercalation and further quantifying degradation such as Li plating. Putting the results of these three characterization techniques together in tandem with electrochemical cycling data paints a picture of the degradation that happens on the anode of a fast-charging lithium-ion battery with respect to electrolyte composition.[1] Yamada, Y., Wang, J., Ko, S., Watanabe, E., & Yamada, A. (2019). Advances and issues in developing salt-concentrated battery electrolytes. Nature Energy. [2] Logan, E. R., & Dahn, J. R. (2020). Electrolyte Design for Fast-Charging Li-ion Batteries. Trends in Chemistry.

A process for preferential recovery of lithium and manganese from spent NCM by vacuum carbothermal reduction method

In this study, a process was developed for the preferential recovery of lithium and manganese from spent ternary lithium batteries using the vacuum carbothermal reduction method. Firstly, the electrolyte and PVDF in the cathode and anode wafers of the spent ternary lithium batteries were removed. Subsequently, lithium in the cathode powder was preferentially recovered under vacuum conditions using the anodic powder as a reducing agent. The findings show that at 1623 K and 25 %for 2 h, the reduction process generates Li2O, (NiO)m-(MnO)n, Ni, and Co as the ultimate products. Reduction roasting enables the preferential extraction of 99.99 % Li and 99.82 % Mn, which condense on the condensation tray as Li2O and MnOx, while Ni and Co are present in the residue as oxides and monomers. In summary, the whole process of the vacuum carbothermal reduction method achieves efficient extraction of Li and Mn while avoiding the subsequent recovery of Ni, Co, and Mn. It also minimizes Li loss and Mn contamination during the recovery of Ni and Co. Additionally, by utilizing the cathode material from waste LIBs. This process realises the use of waste for waste management, resulting in significant cost savings in recycling and reducing environmental harm.

Impact of the Li-loss mechanisms inherent to the physical vapor deposition of LiCoO2 cathode on its electrochemical performance

GPa-resistant conformal LiCoO2 cathodes grown by physical vapor deposition (PVD), with negative chemical expansion coefficients, are promising systems for mechanically stabilizing cathode/solid electrolyte interfaces in solid-state lithium-ion batteries. However, exploiting its potential preliminarily requires that we are able to control the reversibility of Li stoichiometry under PVD conditions, which represents a major challenge since metal Li is lightweight, volatile and has high diffusivity. By combining different chemical and structural analysis techniques, we identify the mechanisms of Li loss by PVD and demonstrate that unlike the electrochemical delithiation of LiCoO2, the crystallization of LiCoO2 admits only a small amount of Li vacancies, so that in a Li-deficient regime, segregated phases of fully stoichiometric LiCoO2 and Li-free Co oxides are formed. From the laterally- and depth-resolved concentrations of the coexisting phases, we can conclude that PVD-grown LiCoO2 is partially stabilized into morphological features with reduced specific surface areas (i.e., large isotropic faceted grains and thick films), resulting in an improvement of its specific electrochemical properties and performance.

Potential-Regulated Design for Direct Recycling of Degraded LiFePO4 Cathode.

The rapid proliferation of power sources equipped with lithium-ion batteries poses significant challenges in terms of post-scrap recycling and environmental impacts, necessitating urgent attention to the development of sustainable solutions. The cathode direct regeneration technologies present an optimal solution for the disposal of degraded cathodes, aiming to non-destructively re-lithiate and straightforwardly reuse degraded cathode materials with reasonable profits and excellent efficiency. Herein, a potential-regulated strategy is proposed for the direct recycling of degraded LiFePO4 cathodes, utilizing low-cost Na2SO3 as a reductant with lower redox potential in the alkaline systems. The aqueous re-lithiation approach, as a viable alternative, not only enables the re-lithiation of degraded cathode while ignoring variation in Li loss among different feedstocks but also utilizes the rapid sintering process to restore the cathode microstructure with desirable stoichiometry and crystallinity. The regenerated LiFePO4 exhibits enhanced electrochemical performance with a capacity of 144mA h g-1 at 1 C and a high retention of 98% after 500 cycles at 5 C. Furthermore, this present work offers considerable prospects for the industrial implementation of directly recycled materials from lithium-ion batteries, resulting in improved economic benefits compared to conventional leaching methods.

Evaluating Polyacrylic Acid as a Universal Aqueous Binder for Ni-Rich Cathodes NMC811 and Si Anodes in Full Cell Lithium-ion Batteries.

Silicon (Si) and silicon/graphite (Si/Gr) composite anodes are promising candidates due to their high theoretical capacity, low operating potential and natural abundance for high energy density Li-ion batteries. Green electrode production, eliminating organic volatile solvents require advancement of aqueous electrodes. Engineering the binder plays a critical role for improving waterborne electrodes. Lithium substituted polyacrylic acid LiPAA has been demonstrated as a promising binder for Si/Gr anodes and for Ni-rich cathodes in different cell configurations. LiPAA is utilized to minimize the volume expansion during cycling for Si/Gr anodes. LiPAA is formed in situ during cathode slurry preparation to regulate the pH and dimmish the Li loss. Using advanced characterization techniques, we investigated the slurries, electrodes, and active material reaction with LiPAA and its effect to the cycling performance. Our results indicate that the performance of high Si containing anode is limited by the amount of Si in the electrode. The failure mechanism with respect to high Si content was studied thoroughly. Aqueous processed cathodes with LiPAA binder in combination with Si anodes outperformed NMP based cathodes. Hence, LiPAA was successfully utilized as an active binder for both a high Si containing anode and for a Ni rich cathode.

Electroanalytical Exploration of Li Loss at the Solid Electrolyte-Anode Interface in Anode-Free Batteries with Polymer Electrolytes

Li loss during cycling at the solid electrolyte∣anode interface strongly determines the cycle life of anode-free solid-state batteries (SSBs). Here, this loss is probed electroanalytically for polymer electrolyte (PE)-based SSBs in anode-free coin cells with practical pressures. A wide range of parameters expected to impact the measured average coulombic efficiency (CE) were explored to estimate the expected range of performance. These factors include PE type, cycling profiles, current collector type, and the presence of a thin Li seed layer. Low CE values in the ∼50%–85% range are observed for all electrolytes and test conditions. Other than the electrolyte type, a strong dependence of the CE on the electrochemical cycling profile and the type of metallic current collector is observed. Compared to the anode-free setup, the presence of a thin (5 μm) Li seed layer did not improve the average CE for two out of three PEs, suggesting its presence to be a weak contributor in minimizing the Li loss. This work provides baseline data on the Li losses in low-pressure anode-free configuration cells with PEs.

SEI/dead Li-turning capacity loss for high-performance anode-free solid-state lithium batteries

Anode-free solid-state lithium metal batteries (AF-SSLBs) have the potential to deliver higher energy density and improved safety beyond lithium-metal batteries. However, the unclear mechanism for the fast capacity decay in AF-SSLBs, either determined by dead Li or solid electrolyte interface (SEI), limits the proposal of effective strategies to prolong cycling life. To clarify the underlying mechanism, herein, the evolution of SEI and dead Li is quantitatively analyzed by a solid-state nuclear magnetic resonance (ss-NMR) technology in a typical LiPF6-based polymer electrolyte. The results show that the initial capacity loss is attributed to the formation of SEI, while the dead Li dominates the following capacity loss and the growth rate is 0.141 mA h cm−2 cycle−1. To reduce the active Li loss, the combination of inorganic-rich SEI and self-healing electrostatic shield effect is proposed to improve the reversibility of Li deposition/dissolution behavior, which reduces the capacity loss rate for the initial SEI and following dead Li generation by 2.3 and 20.1 folds, respectively. As a result, the initial Coulombic efficiency (ICE) and stable CE increase by 15.1% and 15.3% in Li-Cu cells, which guides the rational design of high-performance AF-SSLBs.

LFO modified separator for the initial anode irreversibility compensation in lithium-ion rechargeable full cells

Lithium-ion batteries (LIBs) dominate portable electronics and electric vehicles for their high energy density and long cycle life. However, a part of active Li loss in the initial charge process for the solid electrolyte interphase (SEI) formation at the anode surface, which reduces the energy density and cycle life of LIBs. Prelithiation attempts have been widely regarded as providing additional active lithium to address this issue. Li5FeO4 (LFO) as a cathode prelithiation additive with high donable lithium ions is very promising. But the residues of the gas release limited its further application due to its low conductivity in the first charge process. Here, we prepared CNT/ Polyacrylonitrile (PAN) /LFO/polypropylene (PP) separator by an electrospinning method, the CNT/PAN/LFO/PP separator can effectively improve cycle performance of LFP batteries, benefiting from Li2O participation in the construction of SEI and higher infiltration rate of the electrolyte resulting in faster interfacial Li+ transfer kinetics. The LFP pouch cell with CNT/PAN/LFO/PP separator can maintain a stable output over 1000 cycles (capacity fade rate per cycle of 0.005 %) with a highercapacity increased by 6.2 %.

Analysis and design of fast flow liquid Li divertor for fusion nuclear science facility (FNSF) using coupled plasma boundary and LM MHD/heat transfer codes *

The SOLPS-ITER code is utilized to analyze the boundary plasma associated with a fast-flow lithium (Li) divertor configuration in the fusion nuclear science facility (FNSF) tokamak and identify operational regimes with acceptable divertor and core conditions. Plasma transport from the SOLPS-ITER code has been coupled with a liquid metal (LM) MHD/heat transfer code to model a Li open-surface divertor design and assess its impact on the scrape-off-layer (SOL) and core plasma performance. Simulations with only Neon (Ne) impurity seeding have been conducted to evaluate its impact on meeting FNSF design demands for the divertor and upstream plasma parameters. Simulation results indicate that Ne seeding significantly mitigates divertor heat flux but potentially reduces both upstream electron and main ion density due to fuel dilution. The combined application of Ne seeding and deuterium (D2) puffing is required to satisfy the FNSF design requirements on upstream density ( ne,sepOMP ∼1× 1020 m−3) and divertor energy flux ( q⊥,maxOdiv < 10 MW m−2). D2 puffing plays a role in counteracting upstream density drops and augmenting energy and momentum losses through atomic and molecular processes.The inlet Li flow velocity is systematically varied across a wide range to identify acceptable flows and corresponding LM surface temperatures. This comprehensive analysis identifies the acceptable Li flow parameters, LM surface temperature, and emitted Li fluxes necessary to meet the major design constraints. The emitted Li fluxes exhibit minimal impact on the main plasma at surface temperatures up to approximately ∼525 ∘C, corresponding emitted Li fluxes of up to φ Li ∼2 ×1023 atoms s−1. Uncertainties in the Li emission processes from the surface are also investigated, primarily influencing Li loss in the lower surface temperature range ( <525∘ C), with simulation results indicating a minor impact on the divertor and upstream plasma. Conversely, evaporation predominantly drives the Li loss processes at higher surface temperature ranges ( >525∘ C), contaminating both the divertor and upstream plasma.

Stable ultrathin lithium metal anode enabled by self-adapting electrochemical regulating strategy

Ultrathin lithium (Li) metal foils with controllable capacity could realize high-specific-energy batteries; however, the pulverization of Li metal foils due to its extreme volume change results in rapid active Li loss and capacity fading. Here, we report a strategy to stabilize ultrathin Li metal anode via in-situ transferring Li from ultrathin Li foil into a well-designed three-dimensional gradient host during a cycling process. A three-dimensional carbon fiber with gradient distribution of Ag nanoparticles is placed on the ultrathin Li foil in advance and acts as a Li reservoir, guiding Li deposition into its interior and thus alleviating the volume change of ultrathin Li foil anodes. Hence, a high reversibility of Li metal is achieved and Li pulverization is suppressed, which can be witnessed by a long cyclic life in the symmetric cells. The proposed method offers a versatile and facile approach for protecting ultrathin Li metal anodes, which will boost their commercial application process.

Improved carrier collection efficiency in CZTS solar cells by Li‐enhanced liquid‐phase‐assisted grain growth

AbstractThe liquid‐phase‐assisted grain growth (LGG) process is a promising strategy to fabricate large‐grain pure sulfide Cu2ZnSnS4 (CZTS) layers that span the absorber thickness and improve the carrier collection efficiency in photovoltaic devices. Li doping is an effective route to promote such LGG process of Cu2ZnSn(S,Se)4 (CZTSSe) as it can provide liquid Li‐Se phase facilitating the growth of large‐grain CZTSSe. However, the detailed function of the added Li in grain growth has rarely been investigated in both CZTS and CZTSSe, as the reported in situ, and pre‐deposition doping strategies usually suffer from substantial Li losses during the spin‐coating process and/or the high‐temperature sulfurization process. Herein, by monitoring the temperature‐dependent Li loss during the sulfurization process, we demonstrate that a small proportion of the added Li can remain at the CZTS film from the early sulfurization stage and provide Li‐S flux to promote the LGG process. An encouraging efficiency of 10.53%, with a remarkably high short‐circuit current density of 22.6 mA/cm2 and open‐circuit voltage of 0.744 V, is achieved by a significantly enlarged grain size of 3 μm with Li addition. This work could enhance the knowledge of employing Li‐S as flux for growing large‐grain chalcogenide absorbers for high performance devices with better carrier transport.

Temperature‐Mediated Dynamic Lithium Loss and its Implications for High‐Efficiency Lithium Metal Anodes

AbstractLithium (Li) metal has been strongly regarded as the ultimate anode option for next‐generation high‐energy‐density batteries. Nevertheless, the insufficient Coulombic efficiency induced by the extensive active Li loss largely hinders the practical operation of Li metal batteries under wide temperature range. Herein, the temperature‐mediated dynamic growth of inactive Li from −20 to 60°C via titration gas chromatograph measurements is quantitatively decoupled. Combined X‐ray photoelectronic spectroscopy, cryo‐transmission electronic microscopy, and scanning electronic microscopy methods depicted that both solid electrolyte interphase (SEI) characteristics and Li deposition compactness can be profoundly manipulated by working temperature. The elevation of temperature is found to fundamentally aggravate the parasitic reactions and deteriorate the spatial uniformity of SEI, yet promote the lateral growth of Li by kinetic reason. The opposite effects of temperature on SEI properties and Li deposition compactness can properly explain the intricate temperature‐dependent growth rates of SEI‐Li+ and dead Li0 capacity loss observed under titration gas chromatograph measurements. Design implications towards more stable Li metal anodes with higher reversibility can thus be yielded.

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.