Multifunctional Electrolyte Additive Stabilizes Electrode-Electrolyte Interface Layers for High-Voltage Lithium Metal Batteries

LiF/Li3N-Rich Electrode-Electrolyte Interfaces Enabled by Multi-Functional Electrolyte Additive to Achieve High-Performance Li/LiNi0.8Co0.1Mn0.1O2 Batteries

LiPF6-based carbonate electrolytes have been extensively employed in commercial Li-ion batteries, but they face numerous interfacial stability challenges while applicating in high-energy-density lithium-metal batteries (LMBs). Herein, this work proposes N-succinimidyl trifluoroacetate (NST) as a multifunctional electrolyte additive to address these challenges. NST additive could optimize Li+ solvation structure and eliminate HF/H2O in the electrolyte, and preferentially be decomposed on the Ni-rich cathode (LiNi0.8Co0.1Mn0.1O2, NCM811) to generate LiF/Li3N-rich cathode-electrolyte interphase (CEI) with high conductivity. The synergistic effect reduces the electrolyte decomposition and inhibits the transition metal (TM) dissolution. Meanwhile, NST promotes the creation of solid electrolyte interphase (SEI) rich in inorganics on the Li metal anode (LMA), which restrains the growth of Li dendrites, minimizes parasitic reactions, and fosters rapid Li+ transport. As a result, compared with the reference, the Li/LiNi0.8Co0.1Mn0.1O2 cell with 1.0 wt.% NST exhibits higher capacity retention after 200 cycles at 1C (86.4% vs. 64.8%) and better rate performance, even at 9C. In the presence of NST, the Li/Li symmetrical cell shows a super-stable cyclic performance beyond 500 h at 0.5 mA cm-2/0.5 mAh cm-2. These unique features of NST are a promising solution for addressing the interfacial deterioration issue of high-capacity Ni-rich cathodes paired with LMA.

Rapidly Prepared Lithophilic Frameworks Stabilizes Lithium Anodes via Altered Lithium Deposition Patterns

Lithium metal batteries are regarded as promising candidates for next-generation energy storage systems. However, their anodes are susceptible to interfacial instability due to significant volume changes, which significantly impacts the cycle life of lithium metal batteries. Here, a rapid method for the fabrication of 3D-hosts with interface modified layers is reported. A simple infiltration and heating process enables the transformation of copper foam into Zn-BDC-modified copper foam within 1 min, rendering it suitable for use as a current collector for lithium metal anodes. The Zn-BDC nanosheets with high lithiophilicity are uniformly distributed on the surface of the current collector, facilitating the uniform deposition of lithium and reducing the volume change. Consequently, the half cell exhibits a remarkably low overpotential (26 mV) at a current-density of 4 mA cm-2 and is cycled stably for 1000 h. Furthermore, it demonstrates a significant enhancement in performance in the LiFePO4 full cell. This study provides a crucial reference on the connection between the interfacial modification of the current collector and the lithium deposition behavior, which promotes the practicalization of lithium metal anodes.

Artificial Layer Construction via Cosolvent Enables Stable Ni-Rich Cathodes for Enhanced Lithium Storage

Ni-rich cathodes have recently gained significant attention as next-generation cathodes for lithium-ion batteries. However, their relatively high oxidative surface should be reduced to control the high surface reactivity because the capacity retention decreases rapidly in the batteries. Herein, a simple and effective method to pretreat LiNi0.8Mn0.1Co0.1O2 (NMC811) particles using a cosolvent for improving the battery performance is reported. Imitating the interfacial reaction in practical cells, an artificial layer is created via a spontaneous redox reaction between the cathode and the organic solvent. The artificial layer comprises metal-organic compounds with reduced transition-metal cations. Benefiting from the artificial layer, the cells deliver high capacity retention at a high current density and better rate capability, which might result from the low and stable interfacial resistance of the modified NMC811 cathode. Our approach can effectively reduce the high oxidative surface of most oxide cathode materials and induce a long cyclic lifespan and high capacity retention in most battery systems.

Hybrid Dynamic Covalent Network-Based Protecting Layer for Stable Li-Metal Batteries

Metallic lithium (Li) is considered as the "Holy Grail" anode material for next-generation energy storage systems due to its extremely high theoretical capacity and low electrochemical potential. Before the commercialization of the Li electrode, dendritic Li growth and the unstable solid electrolyte interphase layer should be conquered. Herein, a hybrid covalent adaptable polymer network (HCAPN) is prepared via the random copolymerization of poly(ethylene glycol) methyl ether methacrylate and -acetoacetoxyethyl methacrylate, followed by chemical cross-linking with polyethylenimine (PEI) and amine-modified silicon dioxide (SiO2). Such a hybrid network, where PEI and amine-modified SiO2 formed a vinylogous urethane-based dynamic covalent bond with the copolymer, respectively, shows improved mechanical properties, solvent resistance, and excellent healability/recyclability. As the protecting layer on the Li electrode, the assembled HCAPN@Li||HCAPN@Li symmetric cell shows a long cycle life of 800 h with low overpotential at a current density of 1 mA cm-2, and superior electrochemical performance can be achieved in the HCAPN@Li||LiFePO4 full cell (capacity retention of 77% over 400 cycles at 1.5 C) and HCAPN@Li||NCM811 cell (capacity retention of 79% after 300 cycles). Surface morphology analysis is also performed for physical insight into their role as protecting layer. This work provides a new perspective for constructing a hybrid dynamic covalent network-based polymer protecting layer for inhibiting Li dendrite growth.

Design of a new Li-rich Mn-based ternary cathode material based on the Ni, Co, and Mn action mechanism

Rechargeable lithium-ion batteries, as the most advanced energy storage devices currently available, urgently require the development of cathode materials with high capacity, large specific energy, and fast charge/discharge performance to satisfy the continuous technological innovation. Here, a Li-rich Mn-based ternary cathode material Li7/6Nil/6Co1/6Mn1/2O2 is designed, and the geometrical structure, electronic properties, and thermodynamic properties of this material are investigated employing the first-principles method. Six layered structure models are established by adjusting the ratio of Ni, Co, and Mn elements, and the effects of various elements on the material properties are evaluated. Based on the performance of Ni, Co, and Mn in the structure, Li1.2Ni0.15Co0.1Mn0.55O2 features favorable electrical conductivity, thermal conductivity, and excellent stability. This material obtained through co-precipitation using a high temperature solid phase synthesis presents a high actual capacity (245 mA h g-1) and superior cycling performance (the capacity retention rate of the material is 84% after 60 cycles at 0.2C). This effort discusses the Li-rich Mn-based cathode materials in terms of the structural basis, reaction mechanism, and application exploration, which are valuable for guiding their theoretical design, optimization modification, and industrial application.

Charge-clustering induced fast ion conduction in 2LiX-GaF3: A strategy for electrolyte design

2LiX-GaF3 (X = Cl, Br, I) electrolytes offer favorable features for solid-state batteries: mechanical pliability and high conductivities. However, understanding the origin of fast ion transport in 2LiX-GaF3 has been challenging. The ionic conductivity order of 2LiCl-GaF3 (3.20 mS/cm) > 2LiBr-GaF3 (0.84 mS/cm) > 2LiI-GaF3 (0.03 mS/cm) contradicts binary LiCl (10-12 S/cm) < LiBr (10-10 S/cm) < LiI (10-7 S/cm). Using multinuclear 7Li, 71Ga, 19F solid-state nuclear magnetic resonance and density functional theory simulations, we found that Ga(F,X)n polyanions boost Li+-ion transport by weakening Li+-X- interactions via charge clustering. In 2LiBr-GaF3 and 2LiI-GaF3, Ga-X coordination is reduced with decreased F participation, compared to 2LiCl-GaF3. These insights will inform electrolyte design based on charge clustering, applicable to various ion conductors. This strategy could prove effective for producing highly conductive multivalent cation conductors such as Ca2+ and Mg2+, as charge clustering of carboxylates in proteins is found to decrease their binding to Ca2+ and Mg2+.

Multifunctional Acetamide Additive Combined with LiNO3 Co-Assists Low-Concentration Electrolyte Interfacial Stability for Lithium Metal Batteries

Lithium metal batteries (LMBs) are expected to upgrade their energy density to meet the growing battery market demand; however, intractable lithium dendrites and prominent electrode-electrolyte interface problems have been the stumbling block to their practical applications. Electrolytes play a crucial role in LMBs and are directly involved in the establishment of the electrode-electrolyte interface. In particular, low-concentration electrolytes (LCEs) can significantly save electrolyte costs, but the interface issue is more noteworthy. Here, multifunctional acetamide (N-methyl-N-(trimethylsilyl)-trifluoroacetamide, MTA) and lithium nitrate (LiNO3) additives were introduced together to enhance the performance of LMBs in LCEs. The MTA additive effectively removes the trace water and corrosive HF from the electrolyte, thus suppressing lithium salt decomposition and enhancing the stability of LCEs. Moreover, the MTA additive can construct an inorganic-rich interphase layer on the cathode/anode surface to protect the electrode. Especially, MTA can cooperate with LiNO3 additive to suppress lithium dendrites and reduce interfacial impedance, thus effectively enhancing lithium metal anode stability. Benefiting from the introduction of MTA and LiNO3 additives in the LCEs, the Li||NMC811 metal battery still has a capacity of 110 mA h g-1 after 500 cycles at room temperature, while the reference batteries have failed. The rate capacity and high temperature (50 °C) performance of the Li||NCM811 batteries have also been significantly improved. Significantly, this research explores a cost-effective method of using multifunctional additives to enhance LMBs' stability in LCEs.

Stable Operation Induced by Plastic Crystal Electrolyte Used in Ni-Rich NMC811 Cathodes for Li-Ion Batteries

The LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material has been of significant consideration owing to its high energy density for Li-ion batteries. However, the poor cycling stability in a carbonate electrolyte limits its further development. In this work, we report the excellent electrochemical performance of the NMC811 cathode using a rational electrolyte based on organic ionic plastic crystal N-ethyl-N-methyl pyrrolidinium bis(fluorosulfonyl)imide C2mpyr[FSI], with the addition of (1:1 mol) LiFSI salt. This plastic crystal electrolyte (PC) is a thick viscous liquid with an ionic conductivity of 2.3 × 10-3 S cm-1 and a high Li+ transference number of 0.4 at ambient temperature. The NMC811@PC cathode delivers a discharge capacity of 188 mA h g-1 at a rate of 0.2 C with a capacity retention of 94.5% after 200 cycles, much higher than that of using a carbonate electrolyte (54.3%). Moreover, the NMC811@PC cathode also exhibits a superior high-rate capability with a discharge capacity of 111.0 mA h g-1 at the 10 C rate. The significantly improved cycle performance of the NMC811@PC cathode can be attributed to the high Li+ conductivity of the PC electrolyte, the stable Li+ conductive CEI film, and the maintaining of particle integrity during long-term cycling. The admirable electrochemical performance of the NMC811|C2mpyr[FSI]:[LiFSI] system exhibits a promising application of the plastic crystal electrolyte for high voltage layered oxide cathode materials in advanced lithium-ion batteries.

1,3,5-Trifluorobenzene, an electrolyte additive with high thermal stability and superior film-forming properties for lithium-ion batteries

The introduction of 1,3,5-trifluorobenzene (F3B) as an additive for lithium-ion battery electrolytes can produce a LiF-rich solid electrolyte interface (SEI). Meanwhile, F3B has superior thermal stability compared with traditional fluorinated additives and is less likely to produce hydrogen fluoride to damage the cathode.

Liquid electrolyte chemistries for solid electrolyte interphase construction on silicon and lithium-metal anodes

Next-generation battery development necessitates the coevolution of liquid electrolyte and electrode chemistries, as their erroneous combinations lead to battery failure. In this regard, priority should be given to the alleviation of the volumetric stress experienced by silicon and lithium-metal anodes during cycling and the mitigation of other problems hindering their commercialization. This review summarizes the advances in sacrificial compound-based volumetric stress-adaptable interfacial engineering, which has primarily driven the development of liquid electrolytes for high-performance lithium batteries. Besides, we discuss how the regulation of lithium-ion solvation structures helps expand the range of electrolyte formulations and thus enhance the quality of solid electrolyte interphases (SEIs), improve lithium-ion desolvation kinetics, and realize longer-lasting SEIs on high-capacity anodes. The presented insights are expected to inspire the design and synthesis of next-generation electrolyte materials and accelerate the development of advanced electrode materials for industrial battery applications.

High-performance Li/LiNi0.8Co0.1Mn0.1O2 batteries enabled by optimizing carbonate-based electrolyte and electrode interphases via triallylamine additive

Lithium (Li) metal batteries (LMBs), paired with high-energy-density cathode materials, are promising to meet the ever-increasing demand for electric energy storage. Unfortunately, the inferior electrode-electrolyte interfaces and hydrogen fluoride (HF) corrosion in the state-of-art carbonate-based electrolytes lead to dendritic Li growth and unsatisfactory cyclability of LMBs. Herein, a multifunctional electrolyte additive triallylamine (TAA) is proposed to circumvent those issues. The TAA molecule exhibits strong nucleophilicity and contains three unsaturated carbon-carbon double bonds, the former for HF elimination, the later for in-situ passivation of aggressive electrodes. As evidenced theoretically and experimentally, the preferential oxidation and reduction of carbon-carbon double bonds enable the successful regulation of components and morphologies of electrode interfaces, as well as the binding affinity to HF effectively blocks HF corrosion. In particular, the TAA-derived electrode interfaces are packed with abundant lithium-containing inorganics and oligomers, which diminishes undesired parasitic reactions of electrolyte and detrimental degradation of electrode materials. When using the TAA-containing electrolyte, the cell configuration with Li anode and nickel-rich layered oxide cathode and symmetrical Li cell deliver remarkably enhanced electrochemical performance with regard to the additive-free cell. The TAA additive shows great potential in advancing the development of carbonate-based electrolytes in LMBs.

Lithiophilic Interface Layer Induced Uniform Deposition for Dendrite-free Lithium Metal Anodes in a 3D Polyethersulfone Frame

Lithium metal anodes possess ultrahigh theoretical specific capacity for next-generation lithium metal batteries, but the infinite volume expansion and the growth of lithium dendrites remain a huge obstacle to their commercialization. Therefore, here, we construct a CuO-loaded 3D polyethersulfone (PES) nanofiber frame onto a lithiophilic Cu₂O/Cu substrate to promote the lithium storage performance of the composite anode, and the 3D frame can effectively alleviate the volume expansion of lithium (Li) metal anodes. Meanwhile, lithium reacts with CuO in the composite nanofiber and Cu₂O of the substrate to generate Li₂O, which can strengthen the solid electrolyte interface (SEI) layer and achieve the uniform deposition of lithium. In addition, the combination of the heat treatment method and electrospinning technology solves the problem of poor adhesion between the fiber film and the substrate. As a result, the PES/CuO-Cu₂O (PCC) composite current collector still maintains a smooth and flat lithium-depositing layer at 5 mA cm^-2. The PCC-assembled Li||Cu half-cell can operate stably for 320 cycles at 0.5 mA cm^-2, which is about 4 times that of bare Cu. Furthermore, symmetrical batteries with PCC@Li can maintain excellent cycle stability for 1770 h. Accordingly, this work provides a low-cost and highly effective strategy for stabilizing the lithium metal anode.

LiF-Rich Interfaces and HF Elimination Achieved by a Multifunctional Additive Enable High-Performance Li/LiNi0.8Co0.1Mn0.1O2 Batteries

Li-metal batteries (LMBs), especially in combination with high-energy-density Ni-rich materials, exhibit great potential for next-generation rechargeable Li batteries. Nevertheless, poor cathode-/anode-electrolyte interfaces (CEI/SEI) and hydrofluoric acid (HF) attack pose a threat to the electrochemical and safety performances of LMBs due to aggressive chemical and electrochemical reactivities of high-Ni materials, metallic Li, and carbonate-based electrolytes with the LiPF₆ salt. Herein, the carbonate electrolyte based on LiPF₆ is formulated by a multifunctional electrolyte additive pentafluorophenyl trifluoroacetate (PFTF) to adapt the Li/LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) battery. It is theoretically illustrated and experimentally revealed that HF elimination and the LiF-rich CEI/SEI films are successfully achieved via the chemical and electrochemical reactions of the PFTF additive. Significantly, the LiF-rich SEI film with high electrochemical kinetics facilitates Li homogeneous deposition and prevents dendritic Li from forming and growing. Benefiting from the collaborative protection of PFTF on the interfacial modification and HF capture, the capacity ratio of the Li/NCM811 battery is boosted by 22.4%, and the cycling stability of the symmetrical Li cell is expanded over 500 h. This provided strategy is conducive to the achievement of high-performance LMBs with Ni-rich materials by optimizing the electrolyte formula.

Multifunctional Electrolyte Additive for Bi-electrode Interphase Regulation and Electrolyte Stabilization in Li/LiNi0.8Co0.1Mn0.1O2 Batteries

Rechargeable lithium metal batteries (LMBs) with high energy densities can be achieved by coupling a lithium metal anode (LMA) and a LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode. Nevertheless, Li dendrite growth on the LMA surface and structural collapse of the NCM811 material, closely tied with the fragile cathode-/solid-electrolyte interphases (CEI/SEI) and corrosive hydrogen fluoride (HF), seriously deteriorate their performances. Herein, trimethylsilyl trifluoroacetate (TMSTFA) as a multifunctional electrolyte additive is proposed for regulation of the CEI/SEI films and elimination of HF. For one thing, the TMSTFA-derived CEI film rich in C-O species is conductive to Li⁺ transport and structural stability of NCM811 materials, and the TMSTFA-derived SEI film mainly consisting of inorganics (Li₂CO₃ and LiF) and organics (C-O and O-C═O species) can significantly promote Li⁺ homogeneous deposition and impede the Li dendrite growth. For another thing, the undesired reactions of the solvents and LiPF₆ salt are effectively retarded by the TMSTFA additive. Consequently, in the presence of TMSTFA, the capacity retention of Li/NCM811 cell is increased by 17% after 200 cycles at 1C, and the lifespan of symmetrical Li/Li cells is prolonged beyond 600 h at 0.5 mA cm^-2.