Effect of propylene carbonate-Li+ solvation structures on graphite exfoliation and its application in Li-ion batteries

Formulation and Recycling of a Novel Electrolyte Based on Bio-Derived γ-Valerolactone and Lithium Bis(trifluoromethanesulfonyl)imide for Lithium-Ion Batteries

This work introduces a novel electrolyte comprising lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt dissolved in bio-based γ-valerolactone (GVL) for lithium-ion batteries (LIBs). Moreover, a simple and sustainable aqueous-based recycling approach for recovering the imide-based lithium salt is proposed. Beyond the sustainable origin of the GVL solvent, this electrolyte exhibits reduced flammability risk, characterized by a flash point of 136 °C, along with favorable transport properties (conductivity of 6.2 mS cm-1 at 20 °C) and good electrochemical stability (5.0 V vs Li+/Li). Its good compatibility with graphite and lithium iron phosphate electrodes ensures remarkable cycling stability in LIB full-cells after 200 galvanostatic cycles at 1  C. Furthermore, the proposed liquid-liquid phase electrolyte recycling method allows for a nearly complete recovery of the LiTFSI salt (97-99%) and the GVL solvent (78%). The feasibility of the recycling process is validated by the reutilization of the recovered LiTFSI salt in electric double-layer capacitors, achieving performances similar to that of the pristine salt with exceptional long-term stability.

Side Reactions/Changes in Lithium-Ion Batteries: Mechanisms and Strategies for Creating Safer and Better Batteries

Lithium-ion batteries (LIBs), in which lithium ions function as charge carriers, are considered the most competitive energy storage devices due to their high energy and power density. However, battery materials, especially with high capacity undergo side reactions and changes that result in capacity decay and safety issues. A deep understanding of the reactions that cause changes in the battery's internal components and the mechanisms of those reactions is needed to build safer and better batteries. This review focuses on the processes of battery failures, with voltage and temperature as the underlying factors. Voltage-induced failures result from anode interfacial reactions, current collector corrosion, cathode interfacial reactions, overcharge, and over-discharge, while temperature-induced failure mechanisms include SEI decomposition, separator damage, and interfacial reactions between electrodes and electrolytes. The review also presents protective strategies for controlling these reactions. As a result, the reader is offered a comprehensive overview of the safety features and failure mechanisms of various LIB components.

Unraveling the origin of reductive stability of super-concentrated electrolytes from first principles and unsupervised machine learning

Developing electrolytes with excellent electrochemical stability is critical for next-generation rechargeable batteries. Super-concentrated electrolytes (SCEs) have attracted great interest due to their high electrochemical performances and stability. Previous studies have revealed changes in solvation structures and shifts in lowest unoccupied molecular orbitals from solvents to anions, promoting the formation of an anion-derived solid-electrolyte-interphase (SEI) in SCE. However, a direct connection at the atomic level to electrochemical properties is still missing, hindering the rational optimization of electrolytes. Herein, we combine ab initio molecular dynamics with the free energy calculation method to compute redox potentials of propylene carbonate electrolytes at a range of LiTFSI concentrations, and moreover employ an unsupervised machine learning model with a local structure descriptor to establish the structure-property relations. Our calculation indicates that the network of TFSI- in SCE not only helps stabilize the added electron and renders the anion more prone to reductive decomposition, but also impedes the solvation of F- and favors LiF precipitation, together leading to effective formation of protective SEI layers. Our work provides new insights into the solvation structures and electrochemistry of concentrated electrolytes which are essential to electrolyte design in batteries.

Deciphering the Influence of Electrolytes on the Energy Storage Mechanism of Vertically-Oriented Graphene Nanosheet Electrodes by Using Advanced Electrogravimetric Methods

Electrolyte composition is a crucial factor determining the capacitive properties of a supercapacitor device. However, its complex influence on the energy storage mechanisms has not yet been fully elucidated. For this purpose, in this study, the role of three different types of electrolytes based on a propylene carbonate (PC) solution containing tetrabutylammonium perchlorate (TBAClO₄), lithium perchlorate (LiClO₄) and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N₁₁₁₄TFSI) ionic liquid on vertically-oriented graphene nanosheet electrodes has been investigated. Herein, in situ electrochemical quartz crystal microbalance (EQCM) and its coupling with electrochemical impedance spectroscopy (EIS), known as ac-electrogravimetry, have allowed the dynamic aspects of the (co)electroadsorption processes at the electrode-electrolyte interface to be examined. A major contribution of ClO₄⁻ anions (TBAClO₄) was evidenced, whereas in the PC/N₁₁₁₄TFSI mixture (50:50 wt%) both anions (TFSI⁻) and cations (N₁₁₁₄⁺) were symmetrically exchanged during cycling. In the particular case of LiClO₄, solvation of Li⁺ cations in PC was involved, affecting the kinetics of electroadsorption. These results demonstrate the suitability of dynamic electrogravimetric methods to unveil the interfacial exchange properties of mobile species for the conception of new high performance energy storage devices.

Degradation Mechanisms and Mitigation Strategies of Nickel-Rich NMC-Based Lithium-Ion Batteries

Abstract

The demand for lithium-ion batteries (LIBs) with high mass-specific capacities, high rate capabilities and long-term cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNixMnyCo1−x−yO2, $$x \geqslant 0.5$$x⩾0.5) cathodes and graphite (LixC6) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid electrolyte interfaces are also reviewed, and trade-offs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions.

Graphic Abstract

The demand for lithium-ion batteries (LIBs) with high mass specific capacities, high rate capabilities and longterm cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNixMnyCo1−x−yO2, x ≥ 0.5) cathodes and graphite (LixC6) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid-electrolyte interfaces (SEIs) are also reviewed and tradeoffs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions.

High-Safety Nonaqueous Electrolytes and Interphases for Sodium-Ion Batteries

Rapidly developed Na-ion batteries are highly attractive for grid energy storage. Nevertheless, the safety issues of Na-ion batteries are still a bottleneck for large-scale applications. Similar to Li-ion batteries (LIBs), the safety of Na-ion batteries is considered to be tightly associated with the electrolyte and electrode/electrolyte interphase. Although the knowledge obtained from LIBs is helpful, designing safe electrolytes and obtaining stable interphases in Na-ion batteries is still a huge challenge. Therefore, it is of significance to investigate the key factors and develop new strategies for the development of high-safety Na-ion batteries. This comprehensive review introduces the recent efforts from nonaqueous electrolytes and interphase aspects of Na-ion batteries, proposes their design strategies and requirements for improving safety characteristics, and discusses the potential issues for practical applications. The insight to formulate safe electrolytes and design the stable interphase for Na-ion batteries with high safety is intended to be provided herein.

Concentrated electrolyte boosting high-temperature cycling stability of LiCoO2/graphite cell

A strategy employing a concentrated electrolyte was proposed to boost the cycling life-span of LiCoO₂/graphite full cells at a high temperature up to 90 °C.

Cobalt Disulfide Nanoparticles Embedded in Porous Carbonaceous Micro-Polyhedrons Interlinked by Carbon Nanotubes for Superior Lithium and Sodium Storage

Transition metal sulfides are appealing electrode materials for lithium and sodium batteries owing to their high theoretical capacity. However, they are commonly characterized by rather poor cycling stability and low rate capability. Herein, we investigate CoS₂, serving as a model compound. We synthesized a porous CoS₂/C micro-polyhedron composite entangled in a carbon-nanotube-based network (CoS₂-C/CNT), starting from zeolitic imidazolate frameworks-67 as a single precursor. Following an efficient two-step synthesis strategy, the obtained CoS₂ nanoparticles are uniformly embedded in porous carbonaceous micro-polyhedrons, interwoven with CNTs to ensure high electronic conductivity. The CoS₂-C/CNT nanocomposite provides excellent bifunctional energy storage performance, delivering 1030 mAh g^-1 after 120 cycles and 403 mAh g^-1 after 200 cycles (at 100 mA g^-1) as electrode for lithium-ion (LIBs) and sodium-ion batteries (SIBs), respectively. In addition to these high capacities, the electrodes show outstanding rate capability and excellent long-term cycling stability with a capacity retention of 80% after 500 cycles for LIBs and 90% after 200 cycles for SIBs. In situ X-ray diffraction reveals a significant contribution of the partially graphitized carbon to the lithium and at least in part also for the sodium storage and the report of a two-step conversion reaction mechanism of CoS₂, eventually forming metallic Co and Li₂S/Na₂S. Particularly the lithium storage capability at elevated (dis-)charge rates, however, appears to be substantially pseudocapacitive, thus benefiting from the highly porous nature of the nanocomposite.

Lithium Difluorophosphate as a Dendrite-Suppressing Additive for Lithium Metal Batteries

The notorious lithium (Li) dendrites and the low Coulombic efficiency (CE) of Li anode are two major obstacles to the practical utilization of Li metal batteries (LMBs). Introducing a dendrite-suppressing additive into nonaqueous electrolytes is one of the facile and effective solutions to promote the commercialization of LMBs. Herein, Li difluorophosphate (LiPO₂F_2, LiDFP) is used as an electrolyte additive to inhibit Li dendrite growth by forming a vigorous and stable solid electrolyte interphase film on metallic Li anode. Moreover, the Li CE can be largely improved from 84.6% of the conventional LiPF₆-based electrolyte to 95.2% by the addition of an optimal concentration of LiDFP at 0.15 M. The optimal LiDFP-containing electrolyte can allow the Li||Li symmetric cells to cycle stably for more than 500 and 200 h at 0.5 and 1.0 mA cm^-2, respectively, much longer than the control electrolyte without LiDFP additive. Meanwhile, this LiDFP-containing electrolyte also plays an important role in enhancing the cycling stability of the Li||LiNi_1/3Co_1/3Mn_1/3O₂ cells with a moderately high mass loading of 9.7 mg cm^-2. These results demonstrate that LiDFP has extensive application prospects as a dendrite-suppressing additive in advanced LMBs.

A highly concentrated phosphate-based electrolyte for high-safety rechargeable lithium batteries

We prepare a totally nonflammable phosphate-based electrolyte composed of 5 mol L-1 (M) Li bis(fluorosulfonyl) imide (LiFSI) in a trimethyl phosphate (TMP) solvent. The concentrated 5 M LiFSI/TMP electrolyte shows good compatibility with graphite and no Al corrosion. More attractively, such a concentrated electrolyte can effectively suppress the growth of Li dendrites in Li metal batteries because of a stable LiF-rich SEI layer. Therefore, this highly concentrated electrolyte is promising for safe Li batteries.