Commercial Carbonate-based Electrolyte Research Articles

Advancing Towards Commercialization with Enhanced Stability and Efficiency in Lithium Metal Batteries Using TTE as a Co-Solvent in Carbonate Electrolytes

Lithium metal batteries are considered ideal anode materials for next-generation battery systems due to their high theoretical specific capacity (3,860 mAh g-1) and low negative electrochemical potential (−3.040 V vs. the standard hydrogen electrode), which are essential for high energy density. However, the fatal dendritic growth on the lithium metal surface, which occurs during repetitive cycling, acts as a significant barrier to commercially successful lithium metal battery application. Therefore, regulating the morphology of lithium plating in commercial carbonate-based electrolytes is a critical challenge for the stable operation of lithium metal batteries. Additionally, this leads to the formation of inhomogeneous lithium dendrites in carbonate-based electrolytes, manifesting as uneven current density and lithium-ion concentration gradients. The uneven current leads to inconsistent charging/discharging rates in the corresponding Ni-rich cathode, which in turn causes overpotentials and deteriorates cell safety, culminating in a reduction of capacity. this has been clarified through Kelvin probe force microscopy analysis to demonstrate an uneven state of charge distribution in the Ni-rich cathode.In this work, we propose a new strategy for high-performance lithium metal batteries, utilizing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) as a co-solvent with carbonate electrolytes. By using TTE as a co-solvent, we observed a reduction in the viscosity of the electrolyte, leading to improved ionic conductivity and a decrease in the overpotential during the lithium plating/stripping process via in-situ electrochemical atomic force microscopy. This resulted in more uniform Li deposition compared to conventional carbonate-based electrolytes, forming a dense and stable Li metal layer. Furthermore, by leveraging our control over stable lithium plating morphologies via TTE co-solvent system, we observed long-term cycling stability (capacity retention of 78% at 300 cycles) with the use of an ultra-thin Li layer (40 µm). Through these results, we have effectively enhanced the stability and efficiency of high-energy-density (380 Wh kg-1) electrodes based on carbonate electrolytes, and we believe that this study can contribute to the commercialization of lithium metal batteries. Figure 1

Stable sodium metal batteries by in-situ construction of multifunctional Mg-based interfacial layer in commercial carbonate-based electrolyte

Sodium metal batteries (SMBs) are attractive energy storage devices due to the low electrochemical potential of metallic sodium and large abundance of sodium element in the earth crust. However, sodium metal anode faces challenges of inevitable dendrite and unstable interface, which blocks the commercial application of SMBs. Herein, a multifunctional sodiophilic Mg-based interfacial layer is constructed on the surface of sodium metal anode by a simple and scalable in-situ reduction strategy. The Mg-based interfacial layer can effectively suppress the growth of sodium dendrite and improve the interfacial stability. First-principles calculations prove that a strong interaction is constructed between the Mg and Na atoms, which indicates that the Mg-based interfacial layer can anchor the Na atom and guide Na deposition. The calculation results also show the Mg-based interfacial layer can obviously decrease the diffusion barriers during the electrochemical process. Under the regulation of the multifunctional Mg-based interfacial layer, the electrochemical performance of symmetric and full cells is obviously improved in commercial carbonate-based electrolytes. This work provides an avenue to build protective layer on metal-based anodes for developing high-security and high-energy-density rechargeable batteries.

Rationalizing Na-ion solvation structure by weakening carbonate solvent coordination ability for high-voltage sodium metal batteries

Commercial carbonate-based electrolytes feature highly reactive activities with alkali metals, yielding low Coulombic efficiencies and poor cycle life in lithium metal batteries, which possess much higher chemical activity in the rising star sodium metal batteries. To be motivated, we have proposed that decreasing the solvent solvation ability in carbonate-based electrolytes stepwise could enable long-term stable cycling of high-voltage sodium metal batteries. As the solvation capacity reduces, more anions are enticed into the solvation sheath of Na+, resulting in the formation of the more desirable interphase layers on the surface of the anode and the cathode. The inorganic-dominated interphases allow highly efficient Na+ deposition/stripping processes with a lower rate of dead sodium generation, as well as maintain a stable structure of the high-voltage cathode material. Specifically, the assembled Na||Na3V2(PO4)2F3 battery exhibits an accelerated ion diffusion kinetics and achieves a higher capacity retention of 85.9% with during the consecutive 200 cycles under the high voltage of 4.5 V. It is anticipated that the tactics we have proposed could be applicable in other secondary metal battery systems as well.

Activating ultra-low temperature Li-metal batteries by tetrahydrofuran-based localized saturated electrolyte

For realizing the commercialization of Li-metal batteries (LMBs), the discharge-blocking obstacles under ultra-low temperatures must be conquered besides the long-term reversibility. Nevertheless, commercial carbonate-based electrolytes are not only incompatible with the aggressive Li anode, but also have poor fluidity at low temperatures. The prevailing chain-ether-based electrolyte designing tactics, such as the common-used DME, improve the affinity with Li metal to some extent, but the multiple Lewis-acid binding sites of chain ethers are not conducive to the de-solvation of Li+. Herein, for the first time, the cheap cyclic-type tetrahydrofuran (THF) with ultra-low melting point and weak solvating power is adopted for designing an original THF-based localized saturated electrolyte (Tb-LSCE), demonstrating excellent adaptability for low-temperature LMBs. Computational and experimental evidence verify the original solvated structure is modified via the addition of fluorinated antisolvent, further contributing to the Li+-THF de-solvation. Therefore, equipped with Tb-LSCE, the assembled Li-NCM523 cells achieve powerful anti-polarization capability at low temperatures (73.3% discharge capacity retention at -30 °C). Furthermore, the unique solvated sheath structure of Tb-LSCE also regulates the interfacial chemistry and uniformity of Li depositing behavior, highlighted by the outstanding reversibility of Li-Li cells (a long lifespan of exceeding 1600 h at 30 °C and 1100 h at -30 °C, respectively) and Li-NCM523 cells (80.7%, 160 cycles) even remarkably stable operation within 50 cycles (ultra-high cathode loading of 19.7 mg cm−2). This work outlines a cheap and effective electrolyte design solution to activate the potential LMBs under practical conditions, especially those operated under cryogenic environments.

An in-situ formed bifunctional layer for suppressing Li dendrite growth and stabilizing the solid electrolyte interphase layer of anode free lithium metal batteries

Anode-free lithium metal batteries (AFLMBs) can achieve a high energy density. However, achieving high-capacity retention and Coulombic efficiency (CE) are challenging without a continuous Li supply from the Cu anode side. The lower CE and rapid capacity decay in AFLMBs are primarily due to non-uniform Li deposition and electrolyte decomposition during cycling. Herein, strontium fluoride (SrF2) nanoparticles are applied on Cu foils to attain the in-situ forming of a bifunctional interfacial layer, a Li-Sr alloy, and a LiF-rich SEI composite layer during Li plating. The derived Cu@SrF2 electrode has excellent plating/stripping stability and outstanding performance. AFLMB full cell (Cu@SrF2//NCM111) attains an average Coulombic efficiency (ACE) of 98.6 % and capacity retention of 51.0 % at the 60th cycle using a commercial carbonate-based electrolyte. In contrast, the bare AFLMB full cell (BCu//NCM111) only has an ACE of 94.9 % with a capacity retention of 10.2 % under the same conditions. The concept is proven in lithium metal batteries (LMBs). This strategy provides a simultaneous Li nucleation and formation of LiF-rich SEI layers, rendering it promising to realize AFLMBs and LMBs with long lifespans and high CE.

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.

Self-assembled, highly-lithiophilic and well-aligned biomass engineered MXene paper enables dendrite-free lithium metal anode in carbonate-based electrolyte

Lithium metal anode is the ideal candidate for high-energy–density rechargeable batteries. However, uncontrolled dendrite growth hampers its commercialization. Herein, a dendrite-free composite Li metal anode is realized by a flexible, freestanding, well-aligned and highly-lithiophilic MXene paper designed by a facile electrostatic self-assembly of the exfoliated MXene nanosheets and natural polysaccharide-chitosan (MX@CS). The MX@CS paper gets a well-aligned layered-3D structure with a micro-crumpled surface that can effectively decrease the local current density, guide even Li plating and suppress dendritic Li growth. More importantly, surface-adsorbed chitosan endows enhanced lithiophilicity for MXene substrate and thus reduces the Li nucleation overpotential, which is confirmed by the density functional theory calculations. Abundant lithiophilic groups on MX@CS surface provide high-concentration Li+ anchoring site promoting Li nucleation and laterally inducing uniform Li deposition, which effectively avoids the formation of dendritic Li. As a result, the MX@CS-Li anode with a dendrite-free Li morphology shows a significantly improved cycling life in commercial carbonate-based electrolyte. When coupled with LiNi0.8Co0.1Mn0.1O2 cathode, the full cell exhibits a low capacity decay and steady ultrahigh Coulombic efficiency of 99.6% at a current density of 5C. These findings develop a new approach for designing high-performance metal-based rechargeable batteries.

Lithiophilic perovskite-CaTiO3 engineered separator for dendrite-suppressing 5 V-class lithium metal batteries with commercial carbonate-based electrolyte

High theoretical specific capacity and the lowest electrochemical potential of Li metal have made it one of the most promising materials for metal anode. Nonetheless, shortened lifespan and even safety issues induced by uncontrollable growth of Li dendrite severely impede the development of lithium metal batteries (LMBs). In this work, a facile and economic strategy is introduced by casting lithiophilic CaTiO3 micro-particles onto the commercial polyethylene separators. The CaTiO3 coating could not only enhance the thermal stability of the separator, but also decrease the nucleation overpotential and facilitate homogeneous Li deposition, finally achieving suppression of the Li dendrite. Consequently, with the CaTiO3-coated separators, the cycling lifespan of Li||Li symmetric cells was remarkably improved to 1500 h in carbonate electrolyte. Moreover, 5 V-class full cells coupled with CaTiO3-coated separators exhibit prolonged lifespan and superior rate performance, indicating the good potential of the modified separators for application. Considering the fabrication of CaTiO3-coated separators is completely industry-available, this work could accelerate the proceeding of practical application of high-energy-density lithium metal battery systems.

Lithium dendritic growth inhibitor enabling high capacity, dendrite-free, and high current operation for rechargeable lithium batteries

There is no doubt that lithium-metal batteries (LMBs) are considered as attractive power sources owing to their extraordinarily high energy density. However, the formation of lithium dendrites during repeated plating/stripping processes hinders their practical application. Herein, we introduce phosphorous pentoxide (P2O5) as an additive to commercial carbonate-based electrolytes to effectively suppress the dendritic growth on the surface of a lithium-metal anode. Significant improvement of the lifespan and coulombic efficiency of the cell were observed with the addition of P2O5 to the electrolyte in Li || Li, Li || Type 316L SS, Li || Cu, and Li || graphite cells. According to surface analyses and microscopic studies, we found reduction mechanism of the P2O5-induced solid-electrolyte interphase (SEI) formation on Li metal. Namely, electrolytic decomposition product, LiF, reacts with P2O5 additive in electrolyte, so that LiPO2F2 is produced by following reaction: 6LiF + 2P2O5 → 3LiPO2F2 + Li3PO4, of which those products suppress dendritic growth of lithium as visualized by operando Synchrotron tomography. The compatibility and outstanding rate performance of the additive-based electrolyte were also demonstrated in Li || NCM full cells. As a result, this finding confirms an effective way to stabilize SEI layers in LMBs via a facile and inexpensive route.

Scalable Synthesis of Nano-Sized Bi for Separator Modifying in 5V-Class Lithium Metal Batteries and Potassium Ion Batteries Anodes.

With the advantages of high theoretical-specific capacity and lowest working potential, lithium metal anode is considered as the most promising anode for next-generation batteries. Here, a scalable dealloying method is developed to prepare nano-sized bismuth (Bi). It is found that the Bi-modification can not only enhance the wettability of the commercial polyethylene separator but also suppresses the lithium dendrite growth. With the nano-sized Bi modified separator, 5V-class lithium metal batteries with commercial carbonate-based electrolyte show a 91% capacity retention ratio after 800 cycles. First-principle calculations prove that lithium atoms tend to deposit smoothly on the Bi surface. Moreover, for potassium ion batteries, nano-sized Bi shows a stable cycling performance and high capacity. The results may be useful for the development of high-energy and high-safety batteries.

In-situ thermal polymerization boosts succinonitrile-based composite solid-state electrolyte for high performance Li-metal battery

Solid-state electrolytes with high room temperature ionic conductivity, broad electrochemical window, and favorable thermal stability are crucial for the practical application of all-solid-state lithium-metal batteries. Here, a novel succinonitrile (SN)-based composite solid-state electrolyte (SN-CSSE) is fabricated directly inside the glass-fiber (GF) membrane via in-situ thermal-crosslinking ethoxylate trimethylolpropane triacrylate (ETPTA) monomer, coupled with the liquid SN-based electrolyte. The ionic conductivity, oxidation potential and lithium-ion transference number (TLi+) of SN-CSSE are 0.78 mS/cm, 5.20 V (vs. Li/Li+) and 0.68 at ambient temperature, respectively. The coin full cells equipped with high-voltage LiCoO2 (LCO) and modified Li metal anode deliver excellent interfacial stability, cycling reversibility, and rate capability. Moreover, the LCO/SN-CSSE/Li pouch cell exhibits more superior thermal stability than that of cell with commercial carbonate-based electrolyte during thermal shock test.

Ultrathin and Non‐Flammable Dual‐Salt Polymer Electrolyte for High‐Energy‐Density Lithium‐Metal Battery

AbstractRechargeable batteries with Li‐metal anodes and Ni‐rich LiNixMnyCozO2 (x + y + z = 1, NMC) cathodes promise high‐energy‐density storage solutions. However, commercial carbonate‐based electrolytes (CBEs) induce deteriorative interfacial reactions to both Li‐metal and NMC, leading to Li dendrite formation and NMC degradation. Moreover, CBEs are thermally unstable and flammable, demonstrating severe safety risks. In this study, an ultrathin and non‐flammable dual‐salt polymer electrolyte (DSPE) is proposed via lightweight polytetrafluoroethylene scaffold, poly(vinylidene fluoride‐co‐hexafluoropropylene) polymeric matrix, dual‐salt, and adiponitrile/fluoroethylene carbonate functional plasticizers. The as‐obtained DSPE exhibits an ultralow thickness of 20 µm, high room temperature ionic conductivity of 0.45 mS cm−1, and a large electrochemical window (4.91 V versus Li/Li+). The dual‐salt synergized with functional plasticizers is used to fabricate a stable interface layer on both anode and cathode. In‐depth experimental and theoretical analyses have revealed the formation of stable interfaces between the DSPE and the anode/cathodes. As a result, the DSPE effectively prevents Li/DSPE/Li symmetric cell from short‐circuiting after 1200 h, indicating effective suppression of Li dendrites. Moreover, the Li/DSPE/NMC cell delivers outstanding cyclic stability at 2 C, maintaining a high capacity of 112 mAh g−1 over 1000 cycles.

Cathode-Electrolyte Interphase in Lithium Batteries Revealed by Cryogenic Electron Microscopy

Summary Cathode electrolyte interphase (CEI), the intimate coating layer formed on the positive electrode, has been thought to be critical. However, many aspects of CEI remain unclear. This originates from the lack of effective tools to characterize structural and chemical properties of these sensitive interphases at nanoscale. Here, we develop a protocol to preserve the native state and directly visualize the interface on the positive electrode using cryogenic electron microscopy. We find that under normal operation conditions, there does not exist an intimate coating layer at the single-particle level in carbonate-based electrolyte. However, upon brief external electrical shorting, a solid-electrolyte interphase, which usually forms on anodes, could form on cathodes and be electrochemically converted into a stable, conformal CEI in situ. The conformal CEI helps improve Coulombic efficiency and overall capacity retention of the battery. This generates a different perspective of CEI in commercial carbonate-based electrolytes than previously understood.

Interfacial passivation by room-temperature liquid metal enabling stable 5 V-class lithium-metal batteries in commercial carbonate-based electrolyte

Lithium (Li) metal is a promising anode for next-generation high-energy-density lithium-ion batteries (LIBs). Nevertheless, the stability of Li-metal anode is poor due to the severe corrosion by liquid electrolyte, uncontrollable growth of Li dendrites, huge volume expansion, and unstable solid electrolyte interphase (SEI). The high chemical reactivity of Li metal is the main inducement for the unstability of Li-metal anode. Herein, the stability of Li-metal anode is improved by passivating its surface with 3°C GaInSnZn liquid metal (LM). A Li-based alloy framework with submicron-scale grains is formed on the surface of Li metal through the spontaneous reaction between metallic Li and LM at room temperature. The Li-based alloy framework is tightly attached on Li metal without exfoliation and mechanical rupture even under bending and folding. The framework has higher Li+ diffusion coefficient, lower chemical reactivity, and better lithiophilicity than pure Li. Under the regulation of the multifunctional framework, the corrosion, uneven Li deposition, and unstable interface are effectively relieved even in a more corrosive carbonate-based electrolyte. When paired with 5 V-class cathodes, the full cells with passivated Li-metal anodes exhibit superior electrochemical performances. This passivation strategy also shows great potentials for high-reactive Na-metal and K-metal anodes.

Ag-modified hydrogen titanate nanowire arrays for stable lithium metal anode in a carbonate-based electrolyte

Abstract In the investigation of the next-generation battery anode, Li metal has attracted increasing attention owing to its ultrahigh specific capacity and low reduction potential. However, its low columbic efficiency, limited cycling life, and serious safety hazards have hindered the practical application of rechargeable Li metal batteries. Although several strategies have been proposed to enhance the electrochemical performance of Li metal anodes, most are centered around ether-based electrolytes, which are volatile and do not provide a sufficiently large voltage window. Therefore, we aimed to attain stable Li deposition/stripping in a commercial carbonate-based electrolyte. Herein, we have successfully synthesized hydrogen titanate (HTO) nanowire arrays decorated with homogenous Ag nanoparticles (NPs) (Ag@HTO) via simple hydrothermal and silver mirror reactions. The 3D cross-linked array structure with Ag NPs provides preferable nucleation sites for uniform Li deposition, and most importantly, when assembled with the commercial LiNi0.5Co0.2Mn0.3O2 cathode material, the Ag@HTO could maintain a capacity retention ratio of 81.2% at 1 C after 200 cycles, however the pristine Ti foil failed to do so after only 60 cycles. Our research therefore reveals a new way of designing current collectors paired with commercial high voltage cathodes that can create high energy density Li metal batteries.

Enabling Rapid Charging Lithium Metal Batteries via Surface Acoustic Wave-Driven Electrolyte Flow.

Both powerful and unstable, practical lithium metal batteries have remained a difficult challenge for over 50 years. With severe ion depletion gradients in the electrolyte during charging, they rapidly develop porosity, dendrites, and dead Li that cause poor performance and, all too often, spectacular failure. Remarkably, incorporating a small, 100 MHz surface acoustic wave device (SAW) solves this problem. Providing acoustic streaming electrolyte flow during charging, the device enables dense Li plating and avoids porosity and dendrites. SAW-integrated Li cells can operate up to 6 mA cm-2 in a commercial carbonate-based electrolyte; omitting the SAW leads to short circuiting at 2 mA cm-2 . The Li deposition is morphologically dendrite-free and close to theoretical density when cycling with the SAW. With a 245 µm thick Li anode in a full Li||LFP (LiFePO4 ) cell, introducing the SAW increases the uncycled Li from 145 to 225 µm, decreasing Li consumption from 41% to only 8%. A closed-form model is provided to explain the phenomena and serve as a design tool for integrating this chemistry-agnostic approach into batteries whatever the chemistry within.

Pre-Lithiation Method with Span-CNT Cathode in Li-S Batteries

Lithium-sulfur (Li-S) batteries with a theoretical specific energy density up to 2,600 Wh·kg-1 is regarded as one of the most promising energy chemical power systems. However, the development of Li-S batteries still faces numerous technical challenges. Both sulfur and Li2S is electrically insulating, leading to a low power capability; the polysulfide generated during charging and discharging processes is highly soluble in electrolytes, resulting in loss of active material and severe redox shuttle effect. To address above issues, sulfurized polyacrylonitrile (SPAN) has been developed as a novel composite cathode material. The strong bonding between sulfur and polyacrylonitrile enables SPAN cathode to operate in commercial carbonate-based electrolyte with an exceptional cycle ability, inhibiting the shuttle effect and self-discharge phenomenon observed in conventional Li-S batteries. In this study, a freestanding SPAN/CNT composite is developed as the cathode material for Li-S batteries, which is capable to deliver a high specific capacity of 1303 mAh g-1 at 0.2 C and a desirable high-rate performance of 1085 mAh g-1 at 2.0 C. Furthermore, Li-ion sulfur full batteries based on SPAN/CNT cathode and graphite anode was assembled using pre-lithiation method. Both the cathode and anode pre-lithiation method was investigated for optimization of system performance. With a high specific capacity and good cycle life, the proposed Li-ion sulfur full battery system provides an alternative approach to fabricate safe and low cost metal-free Li-ion batteries.

Three-Dimensional Graphene/Ag Aerogel for Durable and Stable Li Metal Anodes in Carbonate-Based Electrolytes.

The use of Li metal as the anode for Li-based batteries has attracted considerable attention due to its ultrahigh energy density. However, the formation of Li dendrites, uneven deposition, and huge volume changes hinder its reliable implementation. These issues become much more severe in commercial carbonate-based electrolytes than in ether-based electrolytes. Herein, a rationally designed three-dimensional graphene/Ag aerogel (3D G-Ag aerogel) is proposed for Li metal anodes with long cycle life in carbonate-based electrolytes. The modified lithiophilic nature of G-Ag aerogel, realized through decoration with Ag NPs, effectively decreases the energy barrier for Li nucleation, regulating uniform Li deposition behavior. Moreover, the highly flexible, conductive 3D porous architecture with hierarchical mesopores and macropores can readily accommodate deposited Li and ensures the integrity of the conductive network during cycling. Consequently, high coulombic efficiency (over 93.5 %) and a significantly long cycle life (1589 h) over 200 cycles, with a relatively high cycling capacity of 2.0 mAh cm-2 , can easily be achieved, even in a carbonate-based electrolyte. Considering the intrinsic high voltage windows of carbonate-based electrolytes, matching the G-Ag aerogel Li metal anode with a high-voltage cathode can be envisaged for the fabrication of high-energy-density Li secondary batteries.

Locally Concentrated LiPF6 in a Carbonate-Based Electrolyte with Fluoroethylene Carbonate as a Diluent for Anode-Free Lithium Metal Batteries.

Currently, concentrated electrolyte solutions are attracting special attention because of their unique characteristics such as unusually improved oxidative stability on both the cathode and anode sides, the absence of free solvent, the presence of more anion content, and the improved availability of Li+ ions. Most of the concentrated electrolytes reported are lithium bis(fluorosulfonyl)imide (LiFSI) salt with ether-based solvents because of the high solubility of salts in ether-based solvents. However, their poor anti-oxidation capability hindered their application especially with high potential cathode materials (>4.0 V). In addition, the salt is very costly, so it is not feasible from the cost analysis point of view. Therefore, here we report a locally concentrated electrolyte, 2 M LiPF6, in ethylene carbonate/diethyl carbonate (1:1 v/v ratio) diluted with fluoroethylene carbonate (FEC), which is stable within a wide potential range (2.5-4.5 V). It shows significant improvement in cycling stability of lithium with an average Coulombic efficiency (ACE) of ∼98% and small voltage hysteresis (∼30 mV) with a current density of 0.2 mA/cm2 for over 1066 h in Li||Cu cells. Furthermore, we ascertained the compatibility of the electrolyte for anode-free Li-metal batteries (AFLMBs) using Cu||LiNi1/3Mn1/3Co1/3O2 (NMC, ∼2 mA h/cm2) with a current density of 0.2 mA/cm2. It shows stable cyclic performance with ACE of 97.8 and 40% retention capacity at the 50th cycle, which is the best result reported for carbonate-based solvents with AFLMBs. However, the commercial carbonate-based electrolyte has <90% ACE and even cannot proceed more than 15 cycles with retention capacity >40%. The enhanced cycle life and well retained in capacity of the locally concentrated electrolyte is mainly because of the synergetic effect of FEC as the diluent to increase the ionic conductivity and form stable anion-derived solid electrolyte interphase. The locally concentrated electrolyte also shows high robustness to the effect of upper limit cutoff voltage.

New Artificial Interphase with Li-Ion Pathway between Li Metal and Electrolytes for Secure Lithium Metal Anodes

While Li-ion batteries were firstly studied with Li metal as anodes due to its high theoretical specific capacity (3860 mA h g-1) and lowest negative electrochemical potential (-3.040 V vs SHE), commercial Li-ion batteries since 1992 consisted of graphite as an anode because of critical safety issues. However, for several decades, many strategies have been developed to surmount difficulties like problems of dendrite growth using modifications of electrolytes with additives, a change of lithium metal morphology, and an introduction of chemical/physical coating layers on Li metal. Herein, we report a simple approach to improve the electrochemical performance of Li metal anodes in Li-ion batteries with commercial carbonate-based electrolytes by utilizing a high Li-ion conductor, Li2TiO3, on Li metal anodes. Monoclinic Li2TiO3 is electrochemically inert in a wide voltage range with excellent structural stability in a liquid electrolyte. In addition, it structurally has a 3D path for Li-ion diffusions, leading to more uniform Li-ion flux. Li2TiO3 nanoparticles with a size of sub-100 nm were synthesized via a sol-gel method, and then the resulting particles were mixed with carbon as a conducting material and PVDF-HFP as a binder. A bright Li metal surface was covered with gray Li2TiO3 films in Figure 1a. From various Li plating and striping tests with pristine and modified Li metal as working electrodes, the modified Li metal exhibited outstanding electrochemical performances such as stable coulombic efficiency over 100th cycles at 1 mA/cm2 as shown in Figure 1c. Moreover, the modified Li metal was applied for practical lithium-ion batteries as a counter electrode to confirm the protective effects with LMO as a working electrode at a room temperature (25 oC) and high temperature (60 oC). Figure 1