Dual-Salt Localized High-Concentration Electrolyte for Long Cycle Life Silicon-Based Lithium-Ion Batteries

A nitrile solvent structure induced stable solid electrolyte interphase for wide-temperature lithium-ion batteries

Lithium-ion batteries (LIBs) are extensively employed in various fields. Nonetheless, LIBs utilizing ethylene carbonate (EC)-based electrolytes incur capacity degradation in a wide-temperature range, which is attributable to the slow Li+ transfer kinetics at low temperatures and solvent decomposition during high-rate cycling at high temperatures. Here, we designed a novel electrolyte by substituting nitrile solvents for EC, characterized by low de-solvation energy and high ionic conductivity. The correlation between the carbon chain length of nitrile solvents with reduction stability and the Li+-solvated coordination was investigated. The results revealed that the valeronitrile (VN) solvent displayed an enhanced lowest unoccupied molecular orbital energy level and low de-solvation energy, which helped construct robust SEI interfacial layers and improved kinetics of interfacial ion transfer in wide-temperature LIBs. The VN-based electrolyte employed in graphite‖NCM523 pouch cells achieved a discharge capacity of 89.84% at a 20C rate at room temperature. Meanwhile, the cell exhibited 3C rate cycling stability even at a high temperature of 55 °C. Notably, the VN-based electrolyte exhibited a high ionic conductivity of 1.585 mS cm-1 at -50 °C. The discharge capacity of pouch cells retained 75.52% and 65.12% of their room temperature capacity at -40 °C and -50 °C, respectively. Wide-temperature-range batteries with VN-based electrolytes have the potential to be applied in various extreme environments.

Double-Salts Super Concentrated Carbonate Electrolyte Boosting Electrochemical Performance of Ni-Rich LiNi0.90Co0.05Mn0.05O2 Lithium Metal Batteries

Current lithium-ion batteries cannot meet the requirement of higher energy density with further large-scale application of electrical vehicles. Lithium metal batteries combined with Ni-rich layered oxides cathode are expected as the one of promising solutions, while the poor electrode and electrolyte interface impedes the commercial development of lithium metal batteries. A new double-salts super concentrated (DSSC) carbonate electrolyte is proposed to improve the electrochemical performance of LiNi0.90Co0.05Mn0.05O2 (NCM9055)||Li metal battery which exhibits stable cycling performance with the capacity retention of 93.04% and reversible capacity of 173.8 mAh g-1 after 100 cycles at 1 C, while cells with conventional 1 m diluted electrolyte remains only 60.55% and capacity of 114.2 mAh g-1. The double salts synergistic effect in super concentrated electrolyte promotes the formation for more balanced stable cathode electrolyte interface (CEI) inorganic compounds of CFx, LiNOx, SOF2, Li2SO4, and less LiF by X-ray photoelectron spectroscopy (XPS) test, and the uniform 2-3 nm rock-salt phase protection layer on the cathode surface by transmission electron microscope (TEM) characterization, improving the cycling performance of the Ni-rich NCM9055 layered oxide cathode. The DSSC electrolyte also can relief the Li dendrite growth on Li metal anode, as well as exhibit better flame retardance, promoting the application of more safety Ni-rich NCM9055||Li metal batteries.

Multiple Functional Bonds Integrated Interphases for Long Cycle Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have garnered significant interest as one of the most promising energy suppliers for power grid energy storage. However, the poor electrode/electrolyte interfacial stability leads to continual electrolyte decomposition and transition metal dissolution, resulting in rapid performance degradation of SIBs. In this work, we propose a strategy integrating multiple functional bonds to regulate electrode/electrolyte interphase by triple-coupling of succinonitrile (SN), sodium hexafluorophosphate (NaPF6) and fluorinated ethylene carbonate (FEC). Theoretical calculation and experiment results show that the solvation structure of Na+ and ClO4 - is effectively reconfigured by the solvated FEC, SN and PF6 - in PC-based carbonate electrolyte. The newly developed electrolyte demonstrates increased Na+-FEC coordination, weakened interaction of Na+-PC and participation of SN and PF6 - anions in solvation, resulting in the formation of a conformal interfacial layer comprising of sodium oxynitrides (NaNxOy), sodium fluoride (NaF) and phosphorus oxide compounds (NaPxOy). Consequently, a 3 Ah pouch full cell of hard carbon//NaNi1/3Fe1/3Mn1/3O2 exhibits an excellent capacity retention of 90.4 % after 1000 cycles. Detailed postmortem analysis of interface chemistry is further illustrated by multiple characterization methods. This study provides a new avenue for developing electrolyte formulations with multiple functional bonds integrated interphases to significantly improve the long-term cycling stability of SIBs.

A highly conductive and robust micrometre-sized SiO anode enabled by an in situ grown CNT network with a safe petroleum ether carbon source

SiO-based materials as lithium-ion anodes have attracted huge attention owing to their ultrahigh capacity. However, they usually undergo severe volume expansion over the repeated lithiation/delithiation processes and have low electronic conductivity, leading to an inferior cycling stability and poor rate capability. In this study, carbon nanotubes in situ grown on the surface of commercially available micro-sized SiO (D50 = 5 μm) were prepared. The conductive network composed of one-dimensional carbon nanotubes could enhance its conductivity and enhance the structural stability during the cycling. The synthesized 3D-SiO@C material demonstrates good long-term cycling stability, with a reversible capacity of up to 687.7 mA h g-1 after 1000 cycles, and it maintains a high reversible capacity of 736.8 mA h g-1, even at a high current density of 1 A g-1.

Dual immobilization of porous Si by graphene supported anatase TiO2/carbon for high-performance and safe lithium storage

Smart surface coatings have been proven to be an effective strategy to significantly enhance the electronic conductivity and cycling stability of silicon-based anode materials. However, the single/conventional coatings face critical challenges, including low initial Coulomb efficiency (ICE), poor cyclability, and kinetics failure, etc. Hence, we proposed a dual immobilization strategy to synthesize graphene supported anatase TiO2/carbon-coated porous silicon composite (denoted as PSi@TiO2@C/Graphene) using industrial-grade ferrosilicon as lithium storage raw materials through the simple etching, combined with sol-gel and hydrothermal coating processes. In this work, the dual immobilization from the "confinement effect" of the inner TiO2 shell and the "synergistic effect" of the outer carbon shell, improves the kinetics of the electrochemical reaction and ensures the integrity of the electrode material structure during lithiation. Furthermore, the introduction of the graphene substrate offers ample space for dispersing and anchoring the Si-based granules, which in turn provides a stable 3D conductive network between the particles. As a result, the PSi@TiO2@C/Graphene electrode delivers high reversible capacity of 1605.4 mAh g-1 with 93.65% retention at 0.5 A g-1 after 100 cycles (vs. 4th discharge), high initial Coulomb efficiency (82.30%), and superior cyclability of 1159.9 mAh g-1 after 250 cycles. The above results suggest that the particle structure has great potential for applications in Si-based anode and may provide some inspiration for the design of other energy storage materials.

Active Diluent-Anion Synergy Strategy Regulating Nonflammable Electrolytes for High-Efficiency Li Metal Batteries

High-energy Li metal batteries (LMBs) consisting of Li metal anodes and high-voltage cathodes are promising candidates of the next generation energy-storage systems owing to their ultrahigh energy density. However, it is still challenging to develop high-voltage nonflammable electrolytes with superior anode and cathode compatibility for LMBs. Here, we propose an active diluent-anion synergy strategy to achieve outstanding compatibility with Li metal anodes and high-voltage cathodes by using 1,2-difluorobenzene (DFB) with high activity for yielding LiF as an active diluent to regulate nonflammable dimethylacetamide (DMAC)-based localized high concentration electrolyte (LHCE-DFB). DFB and bis(fluorosulfonyl)imide (FSI- ) anion cooperate to construct robust LiF-rich solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), which effectively stabilize DMAC from intrinsic reactions with Li metal anode and enhance the interfacial stability of the Li metal anodes and LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) cathodes. LHCE-DFB enables ultrahigh Coulombic efficiency (98.7 %), dendrite-free, extremely stable and long-term cycling of Li metal anodes in Li || Cu cells and Li || Li cells. The fabricated NCM811 || Li cells with LHCE-DFB display remarkably enhanced long-term cycling stability and excellent rate capability. This work provides a promising active diluent-anion synergy strategy for designing high-voltage electrolytes for high-energy batteries.

Stable electrode/electrolyte interfaces regulated by dual-salt and localized high-concentration strategies for high-voltage lithium metal batteries

High-voltage lithium metal batteries (LMBs) have faced application obstacles derived from the unstable interfacial layers on both the cathode and anode sides. Herein, a dual-salt localized high-concentration electrolyte (LHCE) is optimized to modify the anion-derived inorganic-rich interfacial layers with conductive inorganic and robust organic components.

Recent Progress in Silicon-Based Materials for Performance-Enhanced Lithium-Ion Batteries

Silicon (Si) has been considered to be one of the most promising anode materials for high energy density lithium-ion batteries (LIBs) due to its high theoretical capacity, low discharge platform, abundant raw materials and environmental friendliness. However, the large volume changes, unstable solid electrolyte interphase (SEI) formation during cycling and intrinsic low conductivity of Si hinder its practical applications. Various modification strategies have been widely developed to enhance the lithium storage properties of Si-based anodes, including cycling stability and rate capabilities. In this review, recent modification methods to suppress structural collapse and electric conductivity are summarized in terms of structural design, oxide complexing and Si alloys, etc. Moreover, other performance enhancement factors, such as pre-lithiation, surface engineering and binders are briefly discussed. The mechanisms behind the performance enhancement of various Si-based composites characterized by in/ex situ techniques are also reviewed. Finally, we briefly highlight the existing challenges and future development prospects of Si-based anode materials.