Full-Dimensional Analysis of Electrolyte Decomposition on Cathode-Electrolyte Interface: Establishing Characterization Paradigm on LiNi0.6Co0.2Mn0.2O2 Cathode with Potential Dependence

Elucidating Gas Reduction Effects of Organosilicon Additives in Lithium-Ion Batteries

Lithium-ion batteries (LIBs) with nonaqueous liquid electrolytes are prone to gas generation at elevated voltages and temperatures, degrading battery performance and posing serious safety risks. Organosilicon (OS) additives are an emerging candidate solution for gassing problems in LIBs, but a detailed understanding of their functional mechanisms remains elusive. In this work, we present a combined computational and experimental study to elucidate the gas-reducing effects of OS additives. Cell volume measurements and gas chromatography-mass spectrometry reveal that OS additives can substantially reduce gas evolution in LIBs, particularly CO2 regardless of source. Through density functional theory calculations, we identify multiple plausible pathways for CO2 evolution, including (1) nucleophile-induced ring-opening of ethylene carbonate (EC) and the subsequent electro-oxidation and (2) direct electro-oxidation of lithium carbonate (Li2CO3). Correspondingly, we find that OS additives function via two primary mechanisms: (1) scavenging of nucleophiles such as superoxide (O2•-), peroxide (O22-), and carbonate ion (CO32-); (2) oligomerization with ethylene carbonate oxide ion and ethylene dicarbonate ion. Moreover, we discover that OS additives possess strong lithium coordination affinity, which helps further reduce the nucleophilic reaction energies and hence increases their nucleophile-scavenging efficiency. Finally, we provide a mechanistic interpretation for the enhanced gas-reduction effects observed with fluorinated OS compounds, corroborated by surface analysis results from X-ray photoelectron spectroscopy. Our study offers the first molecular-level insights into how OS additives contribute to reduced gas formation in LIBs, paving the way for improved safety and performance of LIBs.

Spray-Drying Synthesis of Na4Fe3(PO4)2P2O7@CNT Cathode for Ultra-Stable and High-Rate Sodium-Ion Batteries

Iron-based phosphate is a promising cathode for sodium-ion batteries due to its low cost and abundant resources; however, the practical application is hindered by poor electronic conductivity, sluggish Na+ diffusion, and a lack of low-cost and scalable synthesis methods. To address such issues, herein, we present a low-cost and scalable spray-drying strategy to synthesize Na4Fe3(PO4)2P2O7@CNT (NFPP@CNT) hollow microspheres. The NFPP@CNT composite has the following advantages: highly conductive CNT can significantly improve the electronic conductivity of the cathode, and the flexible CNT-based microsphere architecture facilitates Na+ diffusion and guarantees excellent mechanical properties to mitigate structural degradation during cycling. These merits make the NFPP@CNT cathode display outstanding electrochemical performances: the NFPP@CNT-1% electrode demonstrates a high reversible capacity of 103.9 mAh g-1 at 0.1 C and maintains a very high capacity retention of 99.9% after 1000 cycles even at a high rate of 5 C.

Utilizing the Elimination Reaction of Linear Fluorinated Carbonate to Stabilize LiCoO2 Cathode up to 4.6 V

Stabilizing LiCoO2 (LCO) cathode at high voltages is still challenging in lithium-ion batteries (LIBs). Although fluorinated solvents are utilized in high-voltage systems for their superior oxidation resistance, linear fluorinated carbonates still undergo elimination reactions at high voltages, producing corrosive substances that compromise electrode materials. This study addresses the elimination reaction of methyl trifluoroethyl carbonate (FEMC) by incorporating tris(trimethylsilyl)-based additives, thereby constructing a homogeneous and robust polymer-rich cathode-electrolyte interphase (CEI). With the incorporation of tris(trimethylsilyl)phosphite in the optimized electrolyte, the capacity of the coin cell with LCO as the cathode can maintain 95% after 500 cycles with a high cut-off voltage of 4.6 V. This study establishes a foundational framework for employing linear fluorocarbonates in high-voltage systems and provides innovative insights into CEI design and construction.

Revealing the Dynamic Evolution of Electrolyte Configuration on the Cathode-Electrolyte Interface by Visualizing (De) Solvation Processes

Electrolyte engineering is crucial for improving cathode electrolyte interphase (CEI) to enhance the performance of lithium-ion batteries, especially at high charging cut-off voltages. However, typical electrolyte modification strategies always focus on the solvation structure in the bulk region, but consistently neglect the dynamic evolution of electrolyte solvation configuration at the cathode-electrolyte interface, which directly influences the CEI construction. Herein, we reveal an anti-synergy effect between Li+-solvation and interfacial electric field by visualizing the dynamic evolution of electrolyte solvation configuration at the cathode-electrolyte interface, which determines the concentration of interfacial solvated-Li+. The Li+ solvation in the charging process facilitates the construction of a concentrated (Li+-solvent/anion-rich) interface and anion-derived CEI, while the repulsive force derived from interfacial electric field induces the formation of a diluted (solvent-rich) interface and solvent-derived CEI. Modifying the electrochemical protocols and electrolyte formulation, we regulate the "inflection voltage" arising from the anti-synergy effect and prolong the lifetime of the concentrated interface, which further improves the functionality of CEI architecture.

Protecting Li-metal anode with LiF-enriched solid electrolyte interphase derived from a fluorinated graphene additive

As the holy-grail material, the Li-metal anode has been considered the potential anode of the next generation of Li-metal batteries (LMBs). However, issues of undesirable dendrite growth and unsatisfactory reversibility of the Li-plating/stripping process during the electrochemical cycling impede further application of LMBs. Herein, we innovatively introduce fluorinated graphene (F-Gr) species as a sacrificial effective electrolyte additive into EC/EMC-based electrolyte, which effectively triggers LiF-enriched (composition) and organic/inorganic species uniform-distributed (structure) SEI film architecture that features robustness and denseness, as well as good stability. With the F-Gr additive, efficient Li-metal anode protection (dendrite-free morphology on Li-metal surface and improved Li plating/stripping reversibility during electrochemical cycling) and significantly enhanced long-term lifespan of LMBs is achieved. Remarkably, classical electrochemical techniques, combined with the surface-sensitive characterizations (XPS and TOF-SIMS), comprehensively and systematically highlight critical structure-activity relationships between the SEI architecture (both composition and structure) and electrochemical performance. These techniques provide deep insights into the optimal electrolyte designation of Li-metal anode in LMBs.

Stable interphase inducer based on montmorillonite clay mineral to enhance stability and fire safety for lithium metal batteries

Heat buildup from factors like mechanical, electrical, or thermal stress is the main safety issue in lithium metal batteries (LMBs). Even without such stressors, however, LMBs may remain fire-prone because of the development of unstable electrode-electrolyte interphase on charge-discharge, potentially leading to internal short circuits. In this study, a stable cathode-electrolyte interphase inducer (SCEI-I) is proposed to tackle both the cycling stability issue and safety concerns. SCEI-I is synthesized by incorporating montmorillonite, a clay mineral, and methylphosphonic acid dimethyl ester, a flame-retardant material, onto a porous polyethylene film. On cycling, SCEI-I can induce a thin (<8 nm), uniform and robust cathode-electrolyte interphase layer, contributing to a steady and high Coulombic efficiency of 99.6%-99.8% with decreased impedance. SCE-I improves electrochemical performance by reducing the capacity degradation from ∼21.9% to ∼8.9% after 100 cycles. SCE-I also demonstrates strong thermal stability as the endothermic energy of SCEI-I is only -32.4 J/g (24 °C-280 °C), which is less than one-third of that of polypropylene separator (-118.9 J/g). Furthermore, when exposed to fire, the SCEI-I membrane instantly extinguished flames by disrupting combustion chain reaction. The present study proposes an interfacial engineering approach to improve the stability and safety of LMBs.

Achieving Uniform Li Deposition and Suppressed Electrolyte Flammability in Li-Metal Batteries via Designing Localized High-Concentration Electrolytes

The increasing need for energy storage devices with high energy density has led to significant interest in Li-metal batteries (LMBs). However, the use of commercial electrolytes in LMBs is problematic due to their flammability, inadequate performance at low temperatures, and tendency to promote the growth of lithium dendrites and other flaws. This study introduces a localized high-concentration electrolyte (LHCE) that addresses these issues by employing non-flammable electrolyte components and incorporating carefully designed additives to enhance flame retardancy and low-temperature performance. By incorporating additives to optimize the electrolyte, it is possible to attain inorganic-dominated solid electrolyte interphases on both the cathode and anode. This achievement results in a uniform deposition of lithium, as well as the suppression of electrolyte decomposition and cathode deterioration. Consequently, this LHCE achieve over 300 stable cycles for both LiNi0.9Mn0.05Co0.05O2||Li cells and LiCoO2||Li cells, as well as 50 cycles for LiNi0.8Mn0.1Co0.1O2 (NCM811||Li) pouch cells. Furthermore, NCM811||Li cells maintain 84% discharge capacity at -20 °C, in comparison to the capacity at room temperature. The utilization of this electrolyte presents novel perspectives for the safe implementation of LMBs.

Anion-modulated Ion Conductor with Chain Conformational Transformation for stabilizing Interfacial Phase of High-Voltage Lithium Metal Batteries

In solid-state lithium metal batteries (SSLMBs), the inhomogeneous electrolyte-electrode interphase layer aggravates the interfacial stability, leading to discontinuous interfacial ion/charge transport and continuous degradation of the electrolyte. Herein, we constructed an anion-modulated ionic conductor (AMIC) that enables in situ construction of electrolyte/electrode interphases for high-voltage SSLMBs by exploiting conformational transitions under multiple interactions between polymer and lithium salt anions. Anions modulate the decomposition behavior of supramolecular poly (vinylene carbonate) (PVC) at the electrode interface by changing the spatial conformation of the polymer chains, which further enhances ion transport and stabilizes the interfacial morphology. In addition, the AMIC weakens the "Li+-solvation" and increases Li+ vehicle sites, thereby enhancing the lithium-ion transport number (tLi +=~0.67). Consequently, Li || LiNi0.8Co0.1Mn0.1O2 cell maintains about 85 % capacity retention and Coulombic efficiency >99.8 % in 200 cycles at a charge cut-off voltage of 4.5 V. This study provides a new understanding of lithium salt anions regulating polymer chain segment behavior in the solid-state polymer electrolyte (SPE) and highlights the importance of the ion environment in the construction of interfacial phases and ionic conduction.

Ether-Based High-Voltage Lithium Metal Batteries: The Road to Commercialization

Ether-based high-voltage lithium metal batteries (HV-LMBs) are drawing growing interest due to their high compatibility with the Li metal anode. However, the commercialization of ether-based HV-LMBs still faces many challenges, including short cycle life, limited safety, and complex failure mechanisms. In this Review, we discuss recent progress achieved in ether-based electrolytes for HV-LMBs and propose a systematic design principle for the electrolyte based on three important parameters: electrochemical performance, safety, and industrial scalability. Finally, we summarize the challenges for the commercial application of ether-based HV-LMBs and suggest a roadmap for future development.

Implanting Transition Metal into Li2 O-Based Cathode Prelithiation Agent for High-Energy-Density and Long-Life Li-Ion Batteries

Compensating the irreversible loss of limited active lithium (Li) is essentially important for improving the energy-density and cycle-life of practical Li-ion battery full-cell, especially after employing high-capacity but low initial coulombic efficiency anode candidates. Introducing prelithiation agent can provide additional Li source for such compensation. Herein, we precisely implant trace Co (extracted from transition metal oxide) into the Li site of Li2 O, obtaining (Li0.66 Co0.11 □0.23 )2 O (CLO) cathode prelithiation agent. The synergistic formation of Li vacancies and Co-derived catalysis efficiently enhance the inherent conductivity and weaken the Li-O interaction of Li2 O, which facilitates its anionic oxidation to peroxo/superoxo species and gaseous O2 , achieving 1642.7 mAh/g~Li2O prelithiation capacity (≈980 mAh/g for prelithiation agent). Coupled 6.5 wt % CLO-based prelithiation agent with LiCoO2 cathode, substantial additional Li source stored within CLO is efficiently released to compensate the Li consumption on the SiO/C anode, achieving 270 Wh/kg pouch-type full-cell with 92 % capacity retention after 1000 cycles.