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

Fully Methylated Siloxane-Based Electrolyte for Practical Lithium Metal Batteries

Developing solvents with balanced physicochemical properties for high-voltage cathodes and lithium metal anodes is crucial for a sustainable and intelligent future. Herein, we report fully methylated tetramethyl-1,3-dimethoxydisiloxane (TMMS) as a single solvent for lithium metal batteries. We demonstrate that the fully methylated structure and Si-O bonds within TMMS can effectively elevate the dehydrogenation energy barrier, migrating the oxidation decomposition of the electrolyte. Additionally, the weak solvating power of TMMS favors the formation of an anion-rich solvation structure that induces the generation of an inorganic-rich electrode/electrolyte interphase layer at both the cathode and anode. Accordingly, the formulated electrolyte exhibits remarkable stability against high-voltage cathodes and lithium metal anodes. Notably, LiNi0.8Co0.1Mn0.1O2||Li (NCM811||Li) full cells with TMMS-based electrolytes realize a significant improvement in capacity retention compared with a dimethoxyethane-based electrolyte at both room temperature and 50 °C. This work provides insight into full methylation and the Si-O bond strategy and paves the way for the development of high-voltage lithium metal batteries.

Improving Oxygen-Redox-Active Layered Oxide Cathodes for Sodium-Ion Batteries Through Crystal Facet Modulation and Fluorinated Interfacial Engineering

Layered oxides with active oxygen redox are attractive cathode materials for sodium-ion batteries (SIBs) due to high capacity but suffer from rapid capacity/voltage deterioration and sluggish reaction kinetics stemming from lattice oxygen release, interfacial side reactions, and structural reconstruction. Herein, a synergistic strategy of crystal-facet modulation and fluorinated interfacial engineering is proposed to achieve high capacity, superior rate capability, and long cycle stability in Na0.67Li0.24Mn0.76O2. The synthesized single-crystal Na0.67Li0.24Mn0.76O2 (NLMO{010}) featuring increased {010} active facet exposure exhibits faster anionic redox kinetics and delivers a high capacity (272.4 mAh g-1 at 10 mA g-1) with superior energy density (713.9 Wh kg-1) and rate performance (116.4 mAh g-1 at 1 A g-1). Moreover, by incorporating N-Fluorobenzenesulfonimide (NFBS) as electrolyte additive, the NLMO{010} cathode retains 84.6% capacity after 400 cycles at 500 mA g-1 with alleviated voltage fade (0.27 mV per cycle). Combined in situ analysis and theoretical calculations unveil dual functionality of NFBS, which results in thin yet durable fluorinated interfaces on the NLMO{010} cathode and hard carbon anode and scavenges highly reactive oxygen species. The results indicate the importance of fast-ion-transfer facet engineering and fluorinated electrolyte formulation to enhance oxygen redox-active cathode materials for high-energy-density SIBs.

Dual Function of Hydrogen Bond and CEI to Enhanced Lithium-Ion Battery Performance

The stability of the commercial electrolyte is linked to the internal solvent molecule, particularly in enhancing the stability of these molecules. Hereby, we introduce a dual function strategy involving hydrogen bond induced solvent molecules and the in situ fabrication cathode-electrolyte interphase (CEI) to address this issue. The additive N-(4-(2,5-dioxo-4-oxazolidinyl)butyl)-2,2,2-trifluoroacetamide (DOTFA), with its oxazolidinyl and trifluoroacetamide functional units, establishes hydrogen bonds with the solvent, forming CEI films on the cathode surface that enhance the antioxidation ability of the electrolyte. These hydrogen bonds contribute to enhancing the high-pressure structural stability of the solvent molecule. Additionally, the uniform and robust in situ constructed CEI films act as a shield, protecting the cathode from various side reactions and enhancing interface compatibility. By incorporation of the DOTFA additive in the electrolyte, lithium-ion batteries with NCM811 cathodes exhibit excellent cycling performance. The work highlights the significance of dual function in solvent molecules and provides an effective method for enhancing the antioxidation ability of the electrolyte.

In Situ Forming Asymmetric Gel Polymer Electrolyte Enhances the Performance of High-Voltage Lithium Metal Batteries

With the rapid evolution of electric vehicle technology, concerns regarding range anxiety and safety have become increasingly pronounced. Battery systems with high specific energy and enhanced security, featuring ternary cathodes paired with lithium (Li) metal anodes, are poised to emerge as next-generation electrochemical devices. However, the asymmetric configuration of the battery structure, characterized by the robust oxidative behavior of the ternary cathodes juxtaposed with the vigorous reductive activity of the Li metal anodes, imposes elevated requisites for the electrolytes. Herein, a well-designed gel polymer electrolyte with asymmetric structure was successfully prepared based on the Ritter reaction of cyanoethyl poly(vinyl alcohol) (PVA-CN) and cationic ring-opening polymerization of s-Trioxane. With the aid of the sieving effect of separator, the in situ asymmetric gel polymer electrolyte has good compatibility with both the high-voltage cathodes and Li anodes. The amide groups generated by PVA-CN after the Ritter reaction and additional cyano groups can tolerate high voltages up to 5.1 V, matching with ternary cathodes without any challenges. The functional amide and cyano groups participate in the formation of the cathode electrolyte interface and stabilize the cathode structure. Meanwhile, the in situ formed ether-based polyformaldehyde electrolyte is beneficial for promoting uniform Li deposition on anode surfaces. Li-Li symmetric cells demonstrate sustained stability over 2000 h of cycling at a current density of 1 mA cm-2 for 1 mAh cm-2. Furthermore, the capacity retention rate of Li(Ni0.6Mn0.2Co0.2)O2-Li cells with 0.5 C cycling after 300 cycles is 92.2%, demonstrating excellent cycle stability. The electrolyte preparation strategy provides a strategy for the progress of high-performance electrolytes and promotes the rapid development of high-energy-density Li metal batteries.

Stable and Fast Ion Transport Electrolyte Interfaces Modified with Novel Fluorine- and Nitrogen-Containing Solvents for Ni-Rich Cathode Materials

Ternary nickel-rich layered oxide LiNi0.8Co0.1Mn0.1O2 (NCM811) is recognized as a cathode material with a promising future, attributed to its high energy density. However, the pulverization of cathode particles, structural collapse, and electrolyte decomposition are closely associated with the fragile cathode-electrolyte interphases (CEI), which seriously affect the electrochemical performances of ternary high-nickel materials. In this paper, fluorine- and nitrogen-containing methyl-2-nitro-4-(trifluoromethyl)benzoate (MNTB) was selected, which was synergistically regulated with fluoroethylene carbonate (FEC) to generate a robust CEI film. The preferential decomposition of MNTB/FEC results in the formation of an inorganic-rich (Li3N, LiF, and Li2O) CEI film with uniformly dense and stable characteristics, which is conducive to the migration of Li+ and the stability of the NCM811 structure and enhances the cycling stability of the battery system. Simultaneously, MNTB effectively suppresses the adverse reaction associated with increased polarization caused by higher interface impedance due to conventional single FEC additives, further improving the rate capability of the battery. Moreover, MNTB/FEC can effectively eliminate HF, preventing its corrosion on the NCM811 cathode. Under the synergistic effect of MNTB/FEC, after 300 discharge cycles at a high cutoff voltage of 4.3 V and a current density of 1 C (2 mA cm-2), the discharge capacity of the NCM811||Li battery was 150.12 mA h g-1 with a capacity retention of 81.10%, while it was only 32.8% for the standard electrolyte (STD). The discharged capacity of the MNTB/FEC-containing battery was about 115.43 mA h g-1 at the high rate of 7 C, which was considerably higher than that of the STD (93.34 mA h g-1). In this study, the designed MNTB as a novel solvent synergistically regulated with FEC will contribute to the enhanced stability of NCM811 materials at high cutoff voltages and at the same time provide an effective modified strategy to enhance the stability of commercial electrodes.

Constructing the Polymer Molecules to Regulate the Electrode/Electrolyte Interface to Enhance Lithium-Metal Battery Performance

Lithium-ion batteries, with high energy density and long cycle life, have become the battery of choice for most vehicles and portable electronic devices; however, energy density, safety and cycle life require further improvements. Single-functional group electrolyte additives are very limited in practical applications, a ternary polymer bifunctional electrolyte additive copolymer (acrylonitrile-butyl hexafluoro methacrylate- poly (ethylene glycol) methacrylate- methyl ether) (PMANHF) was synthesized by free radical polymerization of acrylonitrile, 2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate and poly (ethylene glycol) methyl ether methacrylate. A series of characterizations show that in Li metal anodes, the preferential reduction of PMANHF is conducive to the formation of a uniform and stable solid electrolyte interphase layer, and Li deposition is uniform and dense. At the NCM811 cathode, a film composed of LiF- and Li3N-rich is formed at the cathode-electrolyte interface, mitigating the side reaction at the interface. At 1.0 mA cm-2, the Li/Li cell can be stabilized for 1000 cycles. In addition, the Li/NCM811 cell can stabilize 200 cycles with a cathode capacity of 153.7 mAh g-1, with the capacity retention of 89.93 %, at a negative/positive capacity ratio of 2.5. This study brings to light essential ideas for the fabrication of additives for lithium-metal batteries.

Revealing the Nanoscopic Corrosive Degradation Mechanism of Nickel-Rich Layered Oxide Cathodes at Low State-of-Charge Levels: Corrosion Cracking and Pitting

Ni-rich layered oxides have received significant attention as promising cathode materials for Li-ion batteries due to their high reversible capacity. However, intergranular and intragranular cracks form at high state-of-charge (SOC) levels exceeding 4.2 V (vs. Li/Li+), representing a prominent failure mechanism of Ni-rich layered oxides. The nanoscale crack formation at high SOC levels is attributed to a significant volume change resulting from a phase transition between the H2 and H3 phases. Herein, in contrast to the electrochemical crack formation at high SOC levels, another mechanism of chemical crack and pit formation on a nanoscale is directly evidenced in fully lithiated Ni-rich layered oxides (low SOC levels). This mechanism is associated with intergranular stress corrosion cracking, driven by chemical corrosion at elevated temperatures. The nanoscopic chemical corrosion behavior of Ni-rich layered oxides during aging at elevated temperatures is investigated using high-resolution transmission electron microscopy, revealing that microcracks can develop through two distinct mechanisms: electrochemical cycling and chemical corrosion. Notably, chemical corrosion cracks can occur even in a fully discharged state (low SOC levels), whereas electrochemical cracks are observed only at high SOC levels. This finding provides a comprehensive understanding of the complex failure mechanisms of Ni-rich layered oxides and provides an opportunity to improve their electrochemical performance.

Regulating the Electrode-Electrolyte Interfaces of Lithium-High Nickel Batteries via a Multifunctional Additive

Lithium metal batteries with high nickel ternary (LiNixCoyMn1-x-yO2, x ≥ 0.8) as the cathode hold the promise to meet the demand of next-generation high energy density batteries. However, the unsatisfactory stability of electrode-electrolyte interfaces limits their practical applications. In this work, N-methyl-N-trimethylsilyltrifluoroacetamide (NMTFA) is suggested as a new functional electrolyte additive to stabilize the Li∥LiNi0.9Co0.05Mn0.05O2 chemistry by forming robust and effective electrode-electrolyte interphases, namely the anode-electrolyte interphase (AEI, or conventionally called SEI) and cathode-electrolyte interphase (CEI). The NMTFA-derived SEI/CEI greatly enhances the battery performance that a capacity retention of 82.1% after 200 cycles at 1C charge/discharge is achieved, significantly higher than that without NMTFA addition (52.5%). Moreover, the NMTFA also improves the thermal stability of the electrolyte and inhibits the hydrolysis of LiPF6. This work provides new clues for the optimization of electrolyte formulation for lithium-high nickel batteries through modulating interfaces.

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.