High-voltage Lithium Metal Batteries Research Articles

Stable cycling of high nickel Li-metal batteries with limited Li anode in fluorine rich flame retardant electrolytes

Traditional carbonate-based electrolytes are not suitable for high voltage lithium metal batteries (LMBs), which seriously hinders the development of high-energy density LMBs. Here, a novel flame retardant fluorine-rich electrolyte (termed FFT) composed of 1.2 M lithium hexafluorophosphate (LiPF6) in a mixed solvents of fluoroethylene carbonate (FEC), 3,3,3-fluoroethylmethyl carbonate (FEMC) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) was rationally designed and studied. It exhibits noninflammability, low viscosity, good wettability and fluidity, and high oxidation stability. The designed electrolyte enables Li||NMC622 with limited Li anode (50 µm thickness) and high cathode active material loading of 13.8 mg cm−2 (2.5 mAh cm−2) to remain 80% capacity after 160 cycles and 135 cycles with a high cut-off of 4.4 V and 4.5 V under charge at C/5 and discharge at C/2 at 25 °C, respectively. Moreover, the Li||NMC622 using FFT also exhibits excellent low temperature discharge capacity, which could deliver 122 mAh g−1 (about 62% of the discharge capacity at 25 °C) even at −40 °C. Further analyses reveal the stable and conductive CEI and SEI with LiF-rich are formed on both cathode and anode, which contributes to the stable cycle of the battery.

Stable cycling and fast charging of high-voltage lithium metal batteries enabled by functional solvation chemistry

Dimethyl ether (DME)-based localized high-concentration electrolytes (LHCEs) with Li+: DME ratio ∼ 1: 1.5 could ensure stable cycling of LMBs with high Coulombic efficiency but suffer from oxidation decomposition at high voltages and poor charging ability due to its low conductivity. Herein, we design an electrolyte consisting of lithium bis(fluorosulfonyl) imide (LiFSI, 1.0 M) along with lithium hexafluorophosphate (LiPF6, 0.1 M) in DME-hydrofluoroether (TTE) (with Li+: DME = 1: 4), which could both enhance the Li+ ion transportation kinetics of electrolyte and the interfacial stability of both Li metal and LiNi0.9Mn0.05Co0.05O2 (NMC90) cathode. Additive amounts of PF6− anions are found to reduce the probability of FSI− anions entering into the first solvation sheath and simultaneously strengthen the interaction between Li+ and DME, hence stabilizing the DME solvent against reduction/oxidation. Meanwhile, the polymerization of free DME is initiated by PF5, forming a flexible SEI layer on the Li metal anode. On the other hand, PF6− anions facilitate stabilizing NMC90 cathode by forming a LiF-rich interfacial layer. These enable the Li||NMC90 (40 µm Li, 20 mg cm−2 NMC90, 12 μL electrolytes) battery to achieve outstanding capacity retention of 93.7% after 250 cycles at a high charging current density of 4.0 mA cm−2 with a charge cut-off voltage of 4.3 V. These fundamental understandings emphasize the importance in the rational design of electrolyte solvation structures and chemistry to promote the interfacial stability and kinetics, and thus promoting the practical application of high-energy LMBs.

Bifunctional additive phenyl vinyl sulfone for boosting cyclability of lithium metal batteries

One of the bottlenecks limiting the cycling stability of high voltage lithium metal batteries (LMBs) is the lack of suitable electrolytes. Herein, phenyl vinyl sulfone (PVS) is proposed as a multifunctional additive to stabilize both cathode and anode interfaces as it can be preferentially oxidized/reduced on the electrode surfaces. The PVS derived solid electrolyte interphase films can not only reduce the transition metal dissolution on the cathode side, but also suppress the Li dendrite spread on the lithium anode side. The Li||Li symmetric battery with PVS addition delivers longer cycle life and a higher critical current density of over 3.0 mAh cm−2. The LiNi0.8Co0.1Mn0.1O2 (NCM811)||Li full cell exhibits excellent capacity retention of 80.8% or 80.0% after 400 cycles at 0.5 C or 1 C rate with the voltage range of 3.0–4.3 V. In particular, the NCM811||Li cell under constrained conditions remains operation over 150 cycles. This work offers new insights into the electrolyte formulations for the next generation of LMBs.

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

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

Conductivity gradient modulator induced highly reversible Li anodes in carbonate electrolytes for high-voltage lithium-metal batteries

Lithium metal has been considered as the ultimate anode for rechargeable batteries due to its lowest redox potential and ultra-high theoretical capacity. Nevertheless, uneven Li deposition, uncontrolled dendrite growth, and fragile solid electrolyte interphase (SEI) seriously impede the widespread application of lithium-metal batteries (LMBs), especially those cycled in carbonate electrolytes. Herein, a flexible LiNO3-modified conductivity gradient host (LNOCGH), which comprises a dielectric top layer with excess decorated LiNO3 particles and carbon nanofiber layers with upward attenuation of electrical conductivity, is demonstrated to manipulate Li deposition behavior in carbonate electrolytes. The top layer can steadily release LiNO3 to form a robust nitride-rich SEI while the conductivity gradient structure endows Li deposited in a dendrite-free manner by shifting the preferential deposition spots from the anode/separator interface to the anode bottom, which is confirmed through experiments and simulations. Benefiting from the elaborate and comhensive design, the stability of LNOCGH electrodes was significantly improved. The full cell with limited LNOCGH@Li anodes and high mass-loading LiNi0.8Co0.1Mn0.1O2 cathodes (N/P ratio of 2.3) can work stably for over 60 cycles with 72.9% capacity retention. As a proof-of-concept, flexible quasi-solid electrolyte can also be assembled with the as-obtained anode enables flexible LMB with excellent electrochemcial performance.

Electrolyte Engineering for High-Voltage Lithium Metal Batteries.

High-voltage lithium metal batteries (HVLMBs) have been arguably regarded as the most prospective solution to ultrahigh-density energy storage devices beyond the reach of current technologies. Electrolyte, the only component inside the HVLMBs in contact with both aggressive cathode and Li anode, is expected to maintain stable electrode/electrolyte interfaces (EEIs) and facilitate reversible Li+ transference. Unfortunately, traditional electrolytes with narrow electrochemical windows fail to compromise the catalysis of high-voltage cathodes and infamous reactivity of the Li metal anode, which serves as a major contributor to detrimental electrochemical performance fading and thus impedes their practical applications. Developing stable electrolytes is vital for the further development of HVLMBs. However, optimization principles, design strategies, and future perspectives for the electrolytes of the HVLMBs have not been summarized in detail. This review first gives a systematical overview of recent progress in the improvement of traditional electrolytes and the design of novel electrolytes for the HVLMBs. Different strategies of conventional electrolyte modification, including high concentration electrolytes and CEI and SEI formation with additives, are covered. Novel electrolytes including fluorinated, ionic-liquid, sulfone, nitrile, and solid-state electrolytes are also outlined. In addition, theoretical studies and advanced characterization methods based on the electrolytes of the HVLMBs are probed to study the internal mechanism for ultrahigh stability at an extreme potential. It also foresees future research directions and perspectives for further development of electrolytes in the HVLMBs.

A highly conductive and stable hybrid solid electrolyte for high voltage lithium metal batteries

A hybrid solid electrolyte (HSE) is prepared by using ionomer P(VDF-HFP)-Lix, as matrix and LATP as ceramic filler. The obtained HSE exhibits high ionic conductivity (7.88 × 10−4 S cm−1 at 25 °C) and electrochemical stability (5.16 V vs. Li/Li+).

Superior Cycling Stabilized of High Voltage Lithium Metal Batteries Enabled by Surface Engineered Garnet Electrolyte Coated with a Grafted Aromatics Layer

Superior Cycling Stabilized of High Voltage Lithium Metal Batteries Enabled by Surface Engineered Garnet Electrolyte Coated with a Grafted Aromatics Layer

A nonflammable phosphate-based localized high-concentration electrolyte for safe and high-voltage lithium metal batteries

The well-designed electrolyte enables high-voltage Li‖Ni6Mn2Co2O2 batteries with both enhanced safety and superior reversibility.

Targeted Stabilization of Solid Electrolyte Interphase and Cathode Electrolyte Interphase in High-Voltage Lithium-Metal Batteries by an Asymmetric Sustained-Release Strategy

Targeted Stabilization of Solid Electrolyte Interphase and Cathode Electrolyte Interphase in High-Voltage Lithium-Metal Batteries by an Asymmetric Sustained-Release Strategy

A functional electrolyte additive enabling robust interphases in high-voltage Li‖LiNi0.8Co0.1Mn0.1O2 batteries at elevated temperatures

Stability issues affect the commercialization of high-voltage lithium metal batteries. Modulating the electrodes' interphases through simple additive engineering improves the electrochemical performance of high-voltage Li metal‖Ni-rich batteries at elevated temperatures.

Salt–solvent synchro-constructed robust electrolyte–electrode interphase for high-voltage lithium metal batteries

A simple electrolyte formula of “single salt single solvent” —1 M LiDFOB in ES—enables the stable operation of an NCM622|Li full cell (2.5 mA h cm−2, N/P = 4) under harsh conditions of high voltage (4.6 V) and wide temperature range (−30 to 60 °C).

Tert-Butyl(diphenyl)silyl] trifluoromethanesulfonate acts as an effective additive for high-voltage lithium metal batteries

Lithium metal is an ideal anode to replace graphite because of its high theoretical specific capacity.

Mild and Controllable Solid Electrolyte Interphase Formation for High-Voltage Lithium Metal Batteries in a Wide-Temperature Range from -40 °C to 80 °C

Mild and Controllable Solid Electrolyte Interphase Formation for High-Voltage Lithium Metal Batteries in a Wide-Temperature Range from -40 °C to 80 °C

Low concentration electrolyte with non-solvating cosolvent enabling high-voltage lithium metal batteries

SummaryDeveloping low cost, yet high-voltage electrolyte is significant to improve the energy density and practicability of lithium metal batteries (LMBs). Low concentration electrolyte has significant merits in terms of cost and viscosity; however, their poor compatibility with high-voltage LMBs hinders its applications. Here, we develop a diluted low concentration electrolyte by replacing solvating cosolvent with a non-solvating cosolvent to facilitate the interaction between BF4− and Li+, resulting in optimized interfacial chemistry and suppressed side reaction. Thus, the high-loading Li-LiCoO2 full cells (20.4 mg cm−2) deliver outstanding cycling stability and rate performance at a cutoff voltage of 4.6 V. More impressively, a Li-LiCoO2 pouch cell achieves an energy density of more than 400 Wh kg−1 under practical conditions with thin Li (50 μm) and lean electrolyte (2.7 g Ah−1). This work provides a rational approach to design a low concentration electrolyte, which can be extended to other high voltage battery systems.

Boosting practical high voltage lithium metal batteries by butyronitrile in ether electrolytes via coordination, hydrolysis of C[tbnd]N and relatively mild concentration strategy

Currently ether solvents have been regarded as the most compatible organic solvents with lithium metal in electrolytes of lithium batteries. However, ether solvents are unstable under high voltage (>4.0 V), and prone to side reactions with nickel-rich high-voltage cathode materials. In this work, a novel dual-solvent electrolyte in ethylene glycol dimethyl ether (DME) and butyronitrile (BN) mixed solvent was designed and fabricated for Li/LiNi0.5Mn0.3Co0.2O2-based lithium metal batteries. When charged to high voltage 4.3 V, the battery cycled in this optimal electrolyte can maintain the capacity at 133.7 mAh g−1 with a retention of 88.84% after 150 cycles at 0.2 C and −10 °C. During long-term cycling, the battery also exhibits excellent cycling performance with capacity maintained at about 112.0 mAh g−1 after 500 cycles at 1 C and −10 °C. BN has strong oxidation resistance and high conductivity, which can inhibit the decomposition of ether solvents under high voltage and improve the low temperature performance of battery effectively. Additionally, the cyano (–CN) group in BN molecular has a strong coordination ability with the high-valent metal ions and can mask the active ions on the cathode, correspondingly reducing the corrosion of cathode material by the electrolyte. Moreover, cyano group can participate in the hydrolysis to remove trace amounts of water and acidic by-products such as HF in the electrolyte. Therefore, the boosting effect of butyronitrile for ether solvents can provide a promising strategy for enhancing the performance of high voltage lithium metal batteries for practical industrialization.

Stabilization of high-voltage lithium metal batteries using a sulfone-based electrolyte with bi-electrode affinity and LiSO2F-rich interphases

High-voltage cathodes paired with lithium metal anode have aroused extensive interests owing to their application potentials for high-density energy storage. Nevertheless, conventional electrolytes fail to maintain the stability of high-voltage cathodes and Li anode, due to their rigid interfacial chemistry with low adsorption of transition metal and strong bonding with Li+ ions. These inadequate interactions exacerbate issues such as transition metal dissolution and non-uniform Li+ transference, ultimately resulting in low cyclability of high-voltage lithium metal batteries (HVLMBs). By incorporating fluoroethylene carbonate (FEC) into lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)/tetramethylene sulfone (TMS) solution, we design a sulfone-based electrolyte to improve the cyclability of HVLMBs with bi-electrode affinity characteristic—the TMS solvent with outstanding anti-oxidation stability preferentially tends to the aggressive cathodes while the FEC solvent with excellent film-forming ability approaches to the Li anode, attributed to the different adsorption energy between various solvents and electrodes. In addition, the sulfone electrolyte forms ultra-thin fluorine and sulfur-rich interphases, containing LiSO2F with S=O bonds of low electron density, associated with Li+ and e− species attacking the S-C and S-N bonds of LiTFSI and the S-C bonds of TMS. As confirmed by in-situ Raman, Ab initio molecular dynamics, and phase field simulations, the LiSO2F uniformizes in-plane Li+ transfer and mitigates transition metal dissolution, owing to the smallest Li+-LiSO2F bonding value (-1.95 eV) and the largest transition metal absorption value with LiSO2F (-3.86 eV) ever reported in the interfacial components. With Coulombic efficiency of 99.3%, the electrolyte enables an 86.1% retention after 500 cycles for Li/NMC811 (4.40 V) batteries.

Hybrid Electrolyte with Dual-Anion-Aggregated Solvation Sheath for Stabilizing High-Voltage Lithium-Metal Batteries.

Lithium (Li)-metal batteries (LMBs) with high-voltage cathodes and limited Li-metal anodes are crucial to realizing high-energy storage. However, functional electrolytes that are compatible with both high-voltage cathodes and Li anodes are required for their developments. In this study, the use of a moderate-concentration LiPF6 and LiNO3 dual-salt electrolyte composed of ester and ether co-solvents (fluoroethylene carbonate/dimethoxyethane, FEC/DME), which forms a unique Li+ solvation with aggregated dual anions, that is, PF6 - and NO3 - , is proposed to stabilize high-voltage LMBs. Mechanistic studies reveal that such a solvation sheath improves the Li plating/stripping kinetics and induces the generation of a solid electrolyte interphase (SEI) layer with gradient heterostructure and high Young's modulus on the anode, and a thin and robust cathode electrolyte interface (CEI) film. Therefore, this novel electrolyte enables colossal Li deposits with a high Coulombic efficiency (≈98.9%) for 450 cycles at 0.5 mA cm-2 . The as-assembled LiǁLiNi0.85 Co0.10 Al0.05 O2 full batteries deliver an excellent lifespan and capacity retention at 4.3 V with a rigid negative-to-positive capacity ratio. This electrolyte system with a dual-anion-aggregated solvation structure provides insights into the interfacial chemistries through solvation regulation for high-voltage LMBs.

Improving interfacial stability of ultrahigh-voltage lithium metal batteries with single-crystal Ni-rich cathode via a multifunctional additive strategy

Electrode (including cathode and anode) /electrolyte interfaces play a vital role in determining battery performance. Especially, high-voltage lithium metal batteries (HVLMBs) with the Ni-rich layered oxide ternary cathode (NCM) can be considered a promising energy storage technology due to their outstanding energy density. However, it is still extremely challenging to address the unstable electrode/electrolyte interface and structural collapse of polycrystalline NCM at high voltage, greatly restraining its practical applications. In this work, a novel electrolyte additive, tris(2-cyanoethyl) borate (TCEB), has been used to construct the robust nitrogen (N) and boron (B)-rich protective films on single-crystal LiNi0.6Co0.1Mn0.3O2 (SNCM) cathode and lithium metal anode surfaces, which could effectively mitigate parasitic reactions against electrolyte corrosion and retain the structural integrity of electrode. Remarkably, the SNCM||Li metal cell using TCEB-containing electrolyte maintains unprecedentedly superb capacity retention of 80% after 100 cycles at an ultrahigh charging voltage of 4.7 V (versus Li/Li+). This finding provides a valuable reference to construct a stable electrode/electrolyte interface for the HVLMBs with achieving high-energy density.

Dual‐Salt Electrolyte Additives Enabled Stable Lithium Metal Anode/Lithium–Manganese‐Rich Cathode Batteries

Although lithium (Li) metal anode/lithium–manganese‐rich (LMR) cathode batteries have an ultrahigh energy density, the highly active Li metal and structural deterioration of LMR can make the usage of these batteries difficult. Herein, a multifunctional electrolyte containing LiBF4 and LiFSI dual‐salt additives is designed, which enables the superior cyclability of Li/LMR cells with capacity retentions of ≈83.4%, 80.4%, and 76.6% after 400 cycles at 0.5, 1, and 2 C, respectively. The dual‐salt electrolyte can form a thin, uniform, and inorganic species‐rich solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). In addition, it alleviates the bulk Li corrosion and enhances the structural sustainability of LMR cathode. Moreover, the electrolyte design strategy provides insights to develop other high‐voltage lithium metal batteries (HVLMBs) to enhance the cycle stability.