Stable Solid Electrolyte Interphase Layer Research Articles

Design of a LiF-rich solid electrolyte interphase layer through a fluorinated carbon (CFX) complex separator for stable lithium metal batteries

The formation of a stable solid electrolyte interphase (SEI) layer is very important for improving the cycling stability and safety of lithium metal batteries (LMBs). However, since the reactivity of lithium metal anodes (LMAs) is very high, controlling the movement of Li+ at the anode/electrolyte interface remains challenging. In this study, an approach involving coating a fluorine functional-controlled fluorinated carbon (CFX) layer onto a commercial PE separator to form a stable SEI layer was proposed. The strong reaction between the fluorine functional groups constituting CFX and Li+ facilitated the rapid formation of a LiF-rich SEI layer in the resting and initial cycling stages. This initial stable SEI layer promoted a subsequent homogeneous Li+ flux, thus improving the LMA stability. In addition, the mechanism by which the total amount of fluorine and the fluorine functional groups control the Li+ dynamics through the CFX-coated PE separator with controlled fluorine functional groups was used to identify the mechanism by which the total amount of fluorine and the fluorine functional groups provide the advantage of the creation of a stable SEI layer. Therefore, this study contributes to the energy storage field by solving the cycling stability problem related to LMAs and emphasizes that a stable SEI layer can be formed based on the important interface control according to the type of fluorine functional group.

In Situ Generated Li2S-Li3N Dual Component Protective Layers Enable High Stability for High-Temperature Li Metal Batteries.

Li metal has been considered as a promising anode for next-generation high-energy-density Li metal batteries. However, the uncontrollable Li dendrite growth, infinite volume change, and unstable solid electrolyte interphase (SEI) layer cause serious safety issues and poor cycling performances, inhibiting its practical application. Herein, N-doped CoS2 needle-like nanoarrays are decorated on carbon cloth. The N-doped CoS2 nanoarrays with a lithiophilic nature can decrease Li nucleation barriers and induce uniform Li deposition. Furthermore, during the prelithiation process, the in situ reaction between Li and N-doped CoS2 has formed stable Li2S and Li3N dual-component protective layers, which efficiently suppresses the dendrite growth and stabilizes the electrolyte-electrode interface. As a result, the N-CoS2@CC electrode shows an excellent rate performance and a long lifespan of 800 h under a 5 mA cm-2/1 mA h cm-2 electrode with a low overpotential (12 mV). When paired with a LiFePO4 (LFP) cathode, the obtained N-CoS2@CC@Li||LFP cell exhibits outstanding electrochemical performances at the high temperature of 60 °C as well as mass loading of 10 mg cm-2. This work provides a rational approach to constructing a 3D lithiophilic host with stable SEI layers toward practical Li metal batteries.

Achieving stable lithium metal anode via constructing lithiophilicity gradient and regulating Li3N-rich SEI

Three-dimensional (3D) current collectors are studied for the application of Li metal anodes in high-energy battery systems. However, they still suffer from the preferential accumulation of Li on the outermost surface, resulting from an inadequate regulation of the Li+ transport. Herein, we propose a deposition regulation strategy involving the creation of a 3D lithiophilicity gradient structure of MoN on Cu3N nanowire-grown Cu foam (MCNCF) to induce a “bottom-up” Li deposition. During the initial Li deposition, the reaction between Li and Cu3N leads to the formation of Li3N while the lithiophilic MoN located at the bottom promotes the downward Li+ migration, resulting in the generation of a Li3N gradient. Such a “bottom-up” Li3N distribution results in the formation of a stable and Li3N-rich solid electrolyte interphase layer, facilitating the Li⁺ transport and promoting a uniform Li nucleation. Computational simulations and experimental results corroborate the preferential deposition of Li on the bottom of the substrate, leading to a uniform Li nucleation and growth throughout the electrode. The MCNCF electrode offers a significantly improved reversibility of the Li deposition, achieving a lifespan of more than 1200 h at a current density of 1 mA cm−2 in symmetric Li||Li cells. Furthermore, full-cells incorporating MCNCF@Li as the negative electrode and LiFePO4 cathodes exhibit outstanding electrochemical performance with a capacity retention of over 99.5 % after 250 cycles at 1 C, which significantly surpasses the performance achieved with CF@Li or CCF@Li electrodes. This innovative design strategy for 3D metallic current collectors, featuring a lithiophilicity gradient, provides new perspectives for the development of stable Li metal anodes and, as a result, for the advancement of Li-metal batteries.

Multidimensional core-shell nanocomposite of iron oxide-carbon tube and graphene nanosheet: A lithium-ion battery anode with enhanced performance through structural optimization

A novel multidimensional composite of 1D iron oxide (Fe3O4)-carbon tube and 2D graphene nanosheet (GNS) was demonstrated to be used as the anode material for lithium-ion batteries (LIBs). Fe3O4-carbon tube-GNS manifested a unique core–shell composite structure, where the Fe3O4 nanoparticles were embedded in the carbon tube with the GNS. The material characterization confirmed that the Fe3O4 nanoparticles were embedded in the highly graphitized carbon tube with the dispersed GNS. Fe3O4-carbon tube-GNS exhibited a high porosity (surface area: 62.3 m2/g, pore volume: 0.112 m3/g). It also exhibited an excellent electrochemical performance with a high reversible capacity (900 mAh/g at 1 A/g), a high coulombic efficiency (∼100 % for 100 cycles), and good rate capability (491 mAh/g at 5 A/g). The excellent electrochemical performance of our composite is attributed to the suppressed/accommodated volume expansion of Fe3O4 and formation of a stable solid electrolyte interphase (SEI) layer during lithiation/delithiation caused by unique multidimensional composite structure of Fe3O4-carbon tube-GNS with a continuous transport path for electrons and Li+. In addition, such the enhanced lithium storage of our composite is confirmed with the kinetic characterization at various scan rates by analyzing their storage and capacitive contributions.

Unveiling the Role of Filler Characteristics in Enhancing the High-Voltage Performance of Succinonitrile-Based Solid-State Lithium-Metal Batteries.

For exploiting high-energy lithium-metal batteries, it is of utmost importance to develop electrolytes that possess exceptional ionic conductivity and an extensive electrochemical stability range. In this study, 3D PAN nanofibers and polymer electrolytes incorporating various inorganic fillers with different Lewis acid-base properties were fabricated. PAN@Al-SSE exhibits exceptional ionic conductivity (0.48 mS·cm-2 at room temperature), a high Li+ transference number (0.41), and a wide electrochemical window (5.26 V). The device is able to operate stably in Li symmetric cells for more than 1000 h under a potential of 0.03 V under a current density of 0.2 mA·cm-2. Besides, the groundbreaking technology equips high-voltage Li-LiCoO2 solid-state batteries with exceptional cycling performance (91.3% and 82.1% retention after 100 cycles at 0.2 and 1 C, respectively) at room temperature. Mechanistic studies indicate that the Lewis acid-base properties of surface fillers are instrumental and crucial to form a stable solid-electrolyte interphase layer. γ-Al2O3, in particular, with more Lewis acid sites, ensures the dissociation of LiTFSI and induces the excessive decomposition and polymerization of succinonitrile. There exists an equilibrium effect between dissociation and polymerization in a succinonitrile-based solid electrolyte, which plays a critical role in improving the manifestation of succinonitrile-based solid-state lithium cells, especially under high-voltage conditions.

Multi-Component Lithiophilic Alloy Film Modified Cu Current Collector for Long-Life Lithium Metal Batteries by a Novel FCVA Co-Deposition System.

Surface modification of Cu current collectors (CCs) is proven to be an effective method for protecting lithium metal anodes. However, few studies have focused on the quality and efficiency of modification layers. Herein, a novel home-made filtered cathode vacuum arc (FCVA) co-deposition system with high modification efficiency, good repeatability and environmental friendliness is proposed to realize the wide range regulation of film composition, structure and performance. Through this system, ZnMgTiAl quaternary alloy films, which have good affinity with Li are successfully constructed on Cu CCs, and the fully enhanced electrochemical performances are achieved. Symmetrical cells constructed with modified CCs maintained a fairly low voltage hysteresis of only 13mV after 2100h at a current density of 1mA cm-2. In addition, the capacity retention rate is as high as 75.0% after 100 cycles in the full cells. The influence of alloy films on the dynamic evolution process of constructing stable artificial solid electrolyte interphase (SEI) layer is revealed by in situ infrared (IR) spectroscopy. This work provides a promising route for designing various feasible modification films for LMBs, and it displays better industrial application prospects than the traditional chemical methods owing to the remarkable controllability and scale-up capacity.

S@FeS2 Core-Shell Cathode Nanomaterial for Preventing Polysulfides Shuttling and Forming Solid Electrolyte Interphase in High-Rate Li-S Batteries.

Lithium-sulfur (Li-S) battery is a potential next-generation energy storage technology over lithium-ion batteries for high capacity, cost-effective, and environmentally friendly solutions. However, several issues including polysulfides shuttle, low conductivity and limited rate-capability have hampered its practical application. Herein, a new class of cathode active material with perfect core-shell structure is reported, in which sulfur is fully encapsulated by conductivity-enhancing FeS2 (named as S@FeS2), for high-rate application. Surface-stabilized S@FeS2 cathode exhibits a stable cycling performance under 2 - 20 times higher rates (1-2 C, charged in 30-60min) than standard rates (e.g., 0.1-0.5C, charged in 2-10h), without polysulfides shuttle event. Surface analysis results reveal the unprecedented formation of a stable solid electrolyte interphase (SEI) layer on S@FeS2 cathode, which is distinguished from other sulfur-based cathodes that are not able to form the SEI layer. The data suggest that the prevention of polysulfides shuttling is owing to the surface protection effect of FeS2 shell and the SEI layer formation overlying core-shell S@FeS2. This unique and potential material concept proposed in the present study will give insight into designing a prospective fast charging Li-S battery.

Modulating the Inner Helmholtz Plane towards Stable Solid Electrolyte Interphase by Anion-π Interactions for High-Performance Anode-Free Lithium Metal Batteries.

Anode-free lithium (Li) metal batteries (AFLBs) featured high energy density are viewed as the viable future energy storage technology. However, the irregular Li deposition and unstable solid electrolyte interphase (SEI) on anode current collectors reduce their cycling performance. Here, we propose a concept of anion-recognition electrodes enabled by anion-π interactions to regulate the inner Helmholtz plane (IHP) and electrolyte solvation chemistry for high-performance AFLBs. By engineering the electrodes with electron-deficient aromatic-π systems that possess high permanent quadrupole moment (Qzz), the anion-π interactions can be generated to concentrate the anions on the electrode surface and tune the IHP structure to construct a stable anion-derived SEI layer, thus achieving highly reversible Li plating/stripping process. Through designing various current collectors with different Qzz values, the intimate correlations among the surface charge of the electrode, competitive adsorption of the IHP, and SEI structures are demonstrated. Particularly, the modified carbon cloth current collector with a high Qzz value (+35.1) delivers a high average Li stripping/plating Coulombic efficiency of 99.1 % over 230 cycles in the carbonated electrolyte, enabling a long lifespan and high capacity retention of LiNi0.8Co0.1Mn0.1O2-based AFLBs with a commercial-level areal capacity (4.1 mAh cm-2).

Enhanced electrochemical cyclability of composite sodium metal anode with inorganic-rich solid electrolyte interphase

The practical application of sodium (Na) metal anode in rechargeable batteries is impeded by inferior electrochemical properties and safety hazards arising from uneven Na plating/stripping behaviors. The Na-ion diffusion within the solid electrolyte interphase (SEI) plays a pivotal role in influencing these behaviors and the electrochemical performance of the Na metal anode. In this study, we leveraged the spontaneous reaction between red phosphorus (P) and metallic Na to fabricate a Na/Na3P (NNP) composite foil using a straightforward folding and mechanical rolling method at room temperature. The in-situ formed Na3P phase fosters the formation of an inorganic-rich SEI layer with high ionic conductivity, effectively enhancing the Na-ion diffusion kinetics and curbing the formation of Na dendrites. Moreover, the Na3P present in the NNP composite can continually replenish the functional component and promptly repair the fracture of the SEI layer, thereby ensuring the stability of its structure and properties. Consequently, the NNP composite electrode significantly extends the Na plating/stripping cyclic lifespan compared to a bare Na anode. As a demonstration, the Na3V2(PO4)3||NNP full cell exhibits stable performance over 400 cycles with 96.7 % capacity retention at 5C. This work paves the way for designing stable SEI layers with fast ion diffusion capability for alkali metal anodes, and the findings are anticipated to propel the development of alkali metal batteries.

Promoting uniform lithium deposition with Janus gel polymer electrolytes enabling stable lithium metal batteries

AbstractLithium metal batteries (LMBs) are desirable candidates owing to their high‐energy advantage for next‐generation batteries. However, the practical application of LMBs continues to be constrained by thorny safety issues with the formation and growth of Li dendrites. Herein, the ZIF‐67 MOFs are in situ coupled onto a single face of 3D porous nanofiber to fabricate an asymmetric Janus membrane, harnessing their anion adsorption capabilities to promote the uniform deposition of Li ions. In addition, the poly(ethylene glycol) diacrylate and trifluoromethyl methacrylate are introduced into nanofiber skeleton to form Janus@GPE, which preferentially reacts with Li metal to form a LiF‐rich stable SEI layer to inhibit Li dendrite growth. Importantly, the synergistic effect of the MOFs and stable solid electrolyte interphase (SEI) layer results in superior cycling performance, achieving a remarkable 2500 h cycling at 1 mA cm−2 in the Li/Janus@GPE/Li configuration. In addition, the Janus@GPE electrolyte has a certain flame retardant, which can self‐extinguish within 3 s, improving the safety performance of the batteries. Consequently, the Li/Janus@GPE/LFP flexible pouch cell exhibits favorable cycling stability (the capacity retention rate of 45 cycles is 91.8% at 0.1 C). This work provides new insights and strategies to improve the safety and practical utility of LMBs.image

In Situ Formation of an Artificial Lithium Oxalate-Rich Solid Electrolyte Interphase on 3D Ni Host for Highly Stable Lithium Metal Batteries.

Li metal, with a high theoretical capacity, is considered the most promising anode for next-generation high-energy-density batteries. However, the commercialization of the Li metal anode is limited owing to its high reactivity, significant volume expansion, continuous solid electrolyte interphase (SEI) layer degradation caused by undesirable Li deposition, and uncontrollable dendrite growth. This study demonstrates the in situ construction of a Li2C2O4-enriched SEI layer from NiC2O4 nanowires on three-dimensional Ni foam. The lithiophilic Li2C2O4-enriched SEI layer provides a uniform distribution of the electrical field and sufficient nucleation and deposition sites for Li without dendrite formation. Consequently, the stable Li2C2O4-enriched SEI layer successfully inhibits the formation of lithium dendrites, resulting in reversible Li stripping/plating behavior, maintained over an extended period of 5000 h with a deposition capacity of 1 mAh cm-2 at 1 mA cm-2. Additionally, a high cycling stability is observed in the full cell test with ∼70% capacity retention after 1300 cycles at 3 C. This approach offers a large-scale and facile synthesis process via the in situ precipitation growth of NiC2O4 followed by lithiation to form Li2C2O4. Furthermore, the significant stability of the Li2C2O4-enriched SEI layer aids the design of in situ-constructed SEI layers for highly stable Li metal batteries.

Cycling performance of SiOx-Si-C composite anode with different blend ratios of PAA-CMC as binder for lithium sulfur batteries

Silicon (Si) -based materials have been identified as a potential alternative anode owing to their superior theoretical capacity compared to conventional graphitic carbon. Nevertheless, the huge volume change (approximately 300%) that occurs while cycling still hampers this system from 100% practical applications. Silicon-monoxide (SiOx)-based anode materials, on the other hand, are being explored extensively due to their unique properties such as high theoretical capacity, formation of Li2O and LiSiO4 during initial lithiation process that act as a natural volume buffer matrix to accommodate volume changes and formation of a stable solid electrolyte interphase layer, which improves the cyclability and capacity retention. Although poly (vinylidene fluoride) (PVdF) is widely used as a binder, the weak van der Waals forces between PVdF and silicon-based particles fail to bind particles effectively, when substantial volume change occurs. Herein, we prepare a series of SiOx-Si-C electrodes with different binders poly (acrylic acid) (PAA), carboxyl methyl cellulose (CMC) and their blends as binder. The prepared polymeric blends are subjected to thermal, morphological, mechanical and physico-chemical analyses. The Li/ SiOx-Si-C cell assembled with 100% PAA as binder delivered a discharge capacity of 1908 mAh g−1 on its first cycle and 724 mAh g−1 on its 100th cycle with a fade in capacity of 11.8 mAh g−1 per cycle. Upon the incorporation of CMC in the PAA blend the cycling performance was found to be poor. Among the various investigated compositions, the electrode with sole poly (acrylic acid) as a binder offers the highest discharge capacity and this is attributed to the high concentration of the functional (carboxylic) group which forms strong hydrogen bonds with - OH groups on the SiOx or carbon surface. The interfacial properties of the polymeric binders are thoroughly investigated by spectroscopies and electrochemical tests.Graphical abstract

Unlocking fast‐charging capabilities of lithium‐ion batteries through liquid electrolyte engineering

AbstractGlobal trends toward green energy have empowered the extensive application of high‐performance energy storage systems. With the worldwide spread of electric vehicles (EVs), lithium‐ion batteries (LIBs) capable of fast‐charging have become increasingly important. Nonetheless, state‐of‐the‐art LIBs have failed to satisfy the demands of prospective customers, including rapid charging, extended cycle life, and high energy density. Addressing these challenges through innovations in material science and other advanced battery technologies is essential for meeting the growing demands of prospective customers. Besides the choice of active materials, electrolyte formulation has a significant impact on the fast‐charging performance and cycle life of LIBs over a wide range of temperatures. The liquid electrolyte is typically composed of lithium salts to provide an ion source, solvents to carry Li+ ions, and functional additives to build a stable solid electrolyte interphase (SEI). To enable the fast movement of Li+ ions, the liquid electrolytes should have low viscosity and high ionic conductivity. Meanwhile, SEI layers must be thin, uniform and ionically conductive. Furthermore, the low binding energy of the solvent facilitates desolvation of the solvation sheath, enabling fast Li+ ion transport to the anode during fast charging. This review provides the latest insights into rapid Li+ ion transport during fast charging, focusing on ensuring a deeper understanding of liquid electrolyte chemistry. The involvement of existing electrolyte mechanisms in materials discovery will develop electrolyte engineering techniques to improve the fast‐charging performance of batteries over a wide temperature range and will also facilitate the development of EV‐adoptable advanced electrodes.image

Construction of sub micro-nano-structured silicon based anode for lithium-ion batteries

The significant volume change experienced by silicon (Si) anodes during lithiation/delithiation cycles often triggers mechanical-electrochemical failures, undermining their utility in high-energy-density lithium-ion batteries (LIBs). Herein, we propose a sub micro-nano-structured Si based material to address the persistent challenge of mechanic-electrochemical coupling issue during cycling. The mesoporous Si-based composite submicrospheres (M-Si/SiO2/CS) with a high Si/SiO2 content of 84.6 wt.% is prepared by magnesiothermic reduction of mesoporous SiO2 submicrospheres followed by carbon coating process. M-Si/SiO2/CS anode can maintain a high specific capacity of 740 mAh g−1 at 0.5 A g−1 after 100 cycles with a lower electrode thickness swelling rate of 63%, and exhibits a good long-term cycling stability of 570 mAh g−1 at 1 A g−1 after 250 cycles. This remarkable Li-storage performance can be attributed to the synergistic effects of the hierarchical structure and SiO2 frameworks. The spherical structure mitigates stress/strain caused by the lithiation/delithiation, while the internal mesopores provide buffer space for Si expansion and obviously shorten the diffusion path for electrolyte/ions. Additionally, the amorphous SiO2 matrix not only servers as support for structure stability, but also facilitates the rapid formation of a stable solid electrolyte interphase layer. This unique architecture offers a potential model for designing high-performance Si-based anode for LIBs.

1,3,6-Hexanetricarbonitrile as electrolyte additive to inhibit sodium dendrites in sodium-metal batteries

Sodium-metal batteries (SMBs) offer substantial competitiveness owing to their wide elemental distribution and high specific capacity. However, SMBs face safety issues such as unstable properties of the Solid Electrolyte Interphase (SEI) layer due to irregular sodium dendrites. In this paper, we constructed a stable and uniform SEI layer by introducing the 1,3,6-Hexanetricarbonitrile (HTCN) electrolyte additive, replacing the conventional, insoluble nitrate. HTCN facilitates the generation of substances like Na3N with high electrical conductivity on the Na anode surface. This accelerates Na+ shuttling and provides high-flux nucleation sites. Molecular dynamics simulations were employed to elucidate the solvated structure of electrolyte and radial distribution of Na+ after HTCN addition. Moreover, in-situ optical microscopy revealed a stable and robust SEI layer, effectively inhibiting the disorderly growth of sodium dendrites. The superior cycling performance of the Na3V2(PO4)3 (NVP)/Na full cell further demonstrates the addition of HTCN.

LiF-Rich Solid Electrolyte Interphase Formation by Establishing Sacrificial Layer on the Separator.

The formation of a stable solid electrolyte interphase (SEI) layer is crucial for enhancing the safety and lifespan of Li metal batteries. Fundamentally, a homogeneous Li+ behavior by controlling the chemical reaction at the anode/electrolyte interface is the key to establishing a stable SEI layer. However, due to the highly reactive nature of Li metal anodes (LMAs), controlling the movement of Li+ at the anode/electrolyte interface remains challenging. Here, an advanced approach is proposed for coating a sacrificial layer called fluorinated self-assembled monolayer (FSL) on a boehmite-coated polyethylene (BPE) separator to form a stable SEI layer. By leveraging the strong affinity between the fluorine functional group and Li+, the rapid formation of a LiF-rich SEI layer in the cell production and early cycling stage is facilitated. This initial stable SEI formation promotes the subsequent homogeneous Li+ flux, thereby improving the LMA stability and yielding an enhanced battery lifespan. Further, the mechanism behind the stable SEI layer generation by controlling the Li+ dynamics through the FSL-treated BPE separator is comprehensively verified. Overall, this research offers significant contributions to the energy storage field by addressing challenges associated with LMAs, thus highlighting the importance of interfacial control in achieving a stable SEI layer.

On the Specific Capacity and Cycle Stability of Si@void@C Anode: Effects of Electrolytes

Electrolytes play a critical role in the formation of stable solid electrolyte interphase (SEI) for Si anodes. This study investigates the impacts of five different electrolytes on the specific capacity and cycle stability of Si-based anodes and confirms the advantages of the second-generation (Gen2) electrolyte over the first-generation (Gen1) electrolyte in the first 200 cycles, beyond which the advantages of Gen2 electrolyte disappear. Addition of more FEC and VC additives to Gen2 electrolyte does not offer significant advantages in the cycle stability and specific capacities. However, very high FEC electrolytes with 20 wt% FEC and 80% dimethyl carbonate exhibits strong dependance on the lithiation cutoff voltage. This electrolyte results in durable SEI layers when the lithiation cutoff voltage is at 0.01 V vs Li/Li+. Furthermore, lowering the lithiation cutoff voltage from 0.1 V to 0.01 V vs Li/Li+ has raised the specific capacity of Si-based anodes, leading to higher specific capacities than those of graphite anodes at the electrode level for 380 cycles investigated in this study. The understandings developed here provide unambiguous guidelines for selection of electrolytes to achieve long cycle stability and high specific capacity of Si-based cells simultaneously in the future.

Thermodynamic Understanding of Formation and Evolution of Solid Electrolyte Interface in Li‐Ion Batteries

AbstractFormation is an essential process in the manufacturing of lithium‐ion batteries and determines the performance of batteries, including life time, rate capability and so forth. The core of formation is to form a stable solid electrolyte interphase (SEI), which profoundly influences interfacial reactions and ion transport within Li‐ion batteries, on the surface of electrode. It is crucial to fully and deeply understand the intricate structure and evolution of SEI, which remains largely uncharted. This paper aims to systematically analyze SEI thermodynamics, encompassing energy distribution, entropy dynamics during SEI formation, and enthalpy changes. SEI evolves towards an equilibrium state, maximizing entropy. The intricate relationship between SEI thermodynamics and battery performance is established by dissecting the impacts of temperature and current density on SEI thermodynamic parameters and battery characteristics. Elevated temperatures and higher current densities foster the development of a more porous and high‐entropy outer SEI layer, rendering organic SEI constituents prone to decompose into high‐energy gases and low‐energy inorganic compounds. Notably, a fast formation strategy within a high state‐of‐charge range offers a potential solution to high quality SEI. This review strives to bridge the divide between fundamental thermodynamics and practical battery performance, ultimately contributing to the advancement of battery manufacturing.

Functionalized interfacial cover design toward pure silicon anode for high power density lithium–ion capacitor

A lithium–ion capacitor, comprising a capacitor–type cathode and battery–type anode, exhibits high power and energy density; however, the integration of different charge storage mechanisms in one cell naturally leads to a kinetic mismatch between the two electrodes, reducing the power density and cycle stability. To solve this problem, high–capacity anode materials with thinner electrodes are required. Silicon, with its high specific capacity, is considered a promising anode material with high energy and power density; however, pure Si anodes undergo rapid capacity fading and exhibit increased internal resistance owing to volume changes during cycling. In this study, both sides of the electrode are covered with functional layers consisting of functionalized herringbone–type carbon nanofibers to protect the Si electrode from degradation. The polar functional groups on the nanofibers weakly interact with the native oxide layer of the Si surface and the carboxyl groups of the binder, ensuring stable contact between electrode materials over repeated cycles. Moreover, the conductive functional cover promotes uniform lithium ion fluxes, aiding the formation of a stable solid electrolyte interphase layer. This study investigates the effects of this strategy on pure Si electrodes by surface morphology analysis, assessment of chemical interactions, and electrochemical testing. This approach has the potential to overcome the degradation of Si electrodes and significantly improve the power and energy density of lithium–ion capacitors.

In Situ Polymerized Quasi-Solid Electrolytes Compounded with Ionic Liquid Empowering Long-Life Cycling of 4.45 V Lithium-Metal Battery.

High-voltage resistant quasi-solid-state polymer electrolytes (QSPEs) are promising for enhancing the energy density of lithium-metal batteries in practice. However, side reactions occurring at the interfaces between the anodes or cathodes and QSPEs considerably reduce the lifespan of high-voltage LMBs. In this study, a copolymer of vinyl ethylene carbonate (VEC) and poly(ethylene glycol) diacrylate (PEGDA) was used as the framework, with a cellulose membrane (CE) as the supporting layer. Based on density functional theory calculations, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI), an ionic liquid, was screened because of its lowest unoccupied molecular orbital energy level as a modifying agent for the in situ P(VECx-EGy)/Pyrz/LiTFSI@CE QSPEs synthesis. Pyr14+, with a lithiophobic alkyl chain, forms a dense positive ion shielding layer on the protruding tips of deposited lithium, facilitating uniform and smooth lithium deposition. Pyr14TFSI assists in constructing a stable solid electrolyte interphase (SEI) layer on the Li surface enriched with LiF, Li3N, and RCOOLi. The modulation of lithium deposition behavior on the anode by Pyr14TFSI ensures stable Li plating/stripping for >1500 h. A Li-Cu cell exhibits stable cycling for >200 cycles at a current density of 0.05 mA cm-2, with an average Coulombic efficiency of 92.7%. In situ polymerization ensures that P(VECx-EGy)/Pyrz/LiTFSI@CE QSPEs exhibit excellent interface compatibility with the anode and the cathode. The CR2032 button cell Li|P(VEC1-EG0.06)/Pyr0.4/LiTFSI@CE|LiCoO2 demonstrates stable cycling with a negligible capacity decay of 0.083% per cycle for >390 cycles at 25 °C and 0.2 C when using a high-voltage LiCoO2 (4.45 V) cathode. Furthermore, a 7.1 mAh pouch cell achieves stable charge-discharge cycles, confirming the pronounced stability of the as-fabricated QSPE at the interfaces of the high-voltage LiCoO2 cathode and Li anode.