Solid Electrolyte Interphase Layer Research Articles

Acetamide-based deep eutectic solvents as efficient electrolytes for K–MnHCFe//Zn dual-ion batteries

In this study, a cost-effective, eco-friendly deep eutectic solvent (DES), comprising acetamide, sodium perchlorate, and zinc chloride serves as an innovative electrolyte for dual ion batteries. Notably, the DES exhibits a broad electrochemical stability window, self-extinguishing behavior, and great resilience in low temperatures. The interplay between the electrolyte components is being thoroughly scrutinized, with a particular focus on the benefits of adding a co-solvent to the DES. This addition prevents unwanted reactions and zinc dendrite growth through the formation of a solid electrolyte interphase (SEI) layer, ultimately leading to enhanced coulombic efficiency and cyclic stability. The electrochemical performance of zinc ion batteries (ZIBs) using a Prussian blue analog (K–MnHCFe) as cathode is being examined in the dual-ion DES electrolyte. The device displays a discharge capacity of 76.4 mAh g−1 at 0.3 A g−1 and a maximum energy density of 111.7 Wh kg−1 at a power density of 437.5 W kg−1. Furthermore, it retains 65 % of its initial specific capacity even after 3000 cycles at 0.5 A g−1. It is noteworthy that the ZIB device with dual-ion DES operates normally in temperatures as low as −20 °C, outperforming traditional cells with aqueous electrolytes.

Ultra‐Long and Rapid Operating Sodium Metal Batteries Enabled by Multifunctional Polarizable Interface Stabilizer

AbstractAbundant and economical sodium (Na) metal batteries promise superior energy densities compared to lithium‐ion batteries; however, they face commercialization challenges owing to problematic interfacial reactions leading to dendrite formation during cycling. This paper reports the ultra‐long and rapid operation of Na metal batteries enabled by the introduction of a vinylpyrrolidone (VP)‐based multifunctional interface stabilizer in the electrolyte. The VP electrolyte additive provides benefits such as surface flattening, durable solid electrolyte interphase layer formation, preservation of fresh Na, and acceleration of horizontal crystal growth along the (110) plane. Symmetric Na–Na cells with the stabilizer exhibit notably stable operation for over 5 000 cycles at a high current density of 5 mA cm−2, surpassing previous research. Performance improvement is also demonstrated in a full‐cell configuration with an Na3V2(PO4)2O2F cathode. This approach offers a promising solution for achieving performance levels comparable to lithium‐ion batteries in Na metal battery technology.

Electrochemical and Cycle Analysis of Water-in-Salt K-Acetate Electrolyte Zn-Ion Batteries Under Commercially-Relevant Conditions

Water-in-salt electrolyte (WiSE) promises high-voltage battery technology with low fire risk. Here we assess potassium acetate (KAc) WiSE for Zn ion batteries under commercially relevant conditions. Rotating disc electrode analysis of WiSE degradation and Zn plating/deplating suggest a solid electrolyte interphase (SEI) layer dominates. Butler-Volmer kinetics and Koutecky-Levich mass-transfer are of secondary importance. Measurements of chemical potential reveal that bulk solvation of H2O (in KAc WiSE or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) WiSE) is an insignificant process compared to SEI blocking. Zinc cycling in KAc WiSE with practical rates (∼0.3 to 8.0 mA cm−2) and areal capacities (>20 mAh cm−2) shows dendrites are less prominent than in KOH, but the SEI layer suppresses the electrochemical reaction too much for commercial feasibility. Dilution or convection of the WiSE alleviates the SEI blocking effects. Cu substrate shows good Zn adhesion, but Ti, Sn, and Ni show poor adhesion. Cathodes made with Chevrel (Mo6S8) reversibly intercalate Zn2+ to form a novel battery technology when paired with Zn foil, but yield <1.0 V cell voltage. Cathodes made with zinc-containing Prussian blue analogues (ZnHCF or ZnMnHCF) yield a voltage near 2.0 V but don't cycle in the present KAc WiSE formulation. Future research directions for KAc WiSE are proposed, focussing on SEI dynamics and Prussian blue compatibility.

Regulating the inner Helmholtz plane with an electrophilic cation additive enabled stacked stratiform growth for highly reversible Zn anodes

Achieving consecutive flattening and dendrite-free deposition for the zinc anodes is essential to avoid internal short circuits or premature failure in the Zn-ion hybrid supercapacitor (ZHSC), which largely depends on the crystal growth during the electrocrystallization process. Herein, the tetrapropyl ammonium bromide additive was employed to reconstruct the inner Helmholtz plane (IHP) structure for manipulating the Zn deposition behavior and stabilizing the interfacial electrochemistry. Joint experimental and theoretical results show that electrophilic quaternary ammonium cations (TPA+) provoke the linkage effect after the specifical adsorption at IHP of the Zn electrode, which includes the molecular/ion distribution regulation, electrostatic shielding effect, crystallographic optimization, and solid electrolyte interphase (SEI) layer formation. The adsorbed TPA+ cations at IHP expel SO42− anions, bringing a reconfiguration of the ion/molecule distribution, which leads to a relatively uniform Zn2+ions distribution at electrode/electrolyte interface and a sluggish electroreduction reaction kinetics. Meanwhile, the electrostatic shielding effect regulates the crystallographic energetic preference of Zn deposits and induces the stratiform Zn growth and dominant Zn (002) texture. Concomitantly, the partial interfacial adsorbed TPA+ cations were electrochemically reduced to form the inorganic-organic hybrid SEI layer to further enhance the corrosion resistance and stability of the Zn electrode. Consequently, TPA+ cations mediated electrolyte enables Zn||Zn cells to exhibit a reversible plating/stripping performance for more than 2800 h. Additionally, a long-term cycling life can be obtained in the Zn||activated carbon ZHSC with this electrolyte. The electrolyte mediation strategy to realize the complementary interface effect and crystalline optimization provides promising feasibility on highly reversible Zn anodes.

Novel composite electrolyte additive for enhancing the thermal and cycling stability of SiO/C anode Li-ion battery

SiO/C anode materials have gained significant attention due to their high specific capacity and environmental friendliness in high-energy-density lithium-ion batteries (LIBs). However, due to the volume effect generated during the long-term cycle, the battery capacity will decay rapidly and cause thermal safety problems. PFPN/TTFEB is employed as a compound electrolyte additive in this study to enhance the electrochemical performance and safety of Li/SiO@C batteries. The blank control electrolyte (BE) is the commercial electrolyte, which is 1.0 M LiPF6 dissolved in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a 3:7 vol/vol ratio. The battery with the PFPN/TTFEB addition demonstrated a substantially higher capacity retention rate than the battery with BE, increasing from 45.23 % to 74.34 %, as indicated by the electrochemical and characterization test results. This suggests that the cycling stability of the battery was improved by the synergistic influence of ethoxy(pentafluoro)cyclotriphosphazene (PFPN) and tris(2,2,2-trifluoroethyl) borate (TTFEB). In addition, a LiF-rich solid electrolyte interphase layer was observed on the surface of the anode, increasing interface stability by reducing the direct contact between the electrolyte and electrode. Differential scanning calorimetry, thermogravimetric analysis, and thermokinetic analysis revealed that the addition of PFPN/TTFEB increased apparent activation energy from 439.56 to 1090.01 kJ/mol and increased initial exothermic reaction temperature from 233.67 to 292.83 °C. The thermal stability of the battery also considerably increased, and the exothermic reaction was substantially delayed. Overall, the multifunctional electrolyte additive developed in this study offers a feasible pathway for developing LIBs with excellent cycling performance and safety.

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

Design of Ultrathin Asymmetric Composite Electrolytes for Interfacial Stable Solid-State Lithium-Metal Batteries.

Ultrathin composite electrolytes hold great promise for high energy density solid-state lithium metal batteries (SSLMBs). However, finding an electrolyte that can simultaneously balance the interfacial stability of the lithium anode and high-voltage cathode is challenging. The present study utilized the both-side tape casting technique to fabricate ultrathin asymmetric composite electrolytes reinforced with polyimide (PI) fiber membrane, with a thickness of 26.8 μm. The implementation of this asymmetric structural design enables SSLMBs to attain favorable interfacial characteristics, such as exceptional resistance to lithium dendrite puncture and compatibility with high voltages. The suppression of lithium dendrite growth and the extension of the cycle life of lithium symmetric batteries by 4000 h are both experimental and theoretically demonstrated under the dual confinement of PI fiber membrane and Li7La3Zr2O12 ceramic fibers. Furthermore, the integration of multicomponent solid electrolyte interphase and cathode electrolyte interface interfacial layers into the lithium anode and high-voltage cathode enhance theirs cycling stability. With a gravimetric/volumetric energy density of 333.1 Wh kg-1/713.2 Wh L-1, the assembled LiNi0.8Co0.1Mn0.1O2 pouch cell demonstrates exceptional safety. The extensive application of this design concept to SSLMBs enables the resolution of electrode/electrolyte interface issues.

Interfacial fusion-enhanced 11 µm-thick gel polymer electrolyte for high-performance lithium metal batteries

In the pursuit of ultrathin polymer electrolyte (<20 μm) for lithium metal batteries, achieving a balance between mechanical strength and interfacial stability is crucial for the longevity of the electrolytes. Herein, 11 μm-thick gel polymer electrolyte is designed via an integrated electrode/electrolyte structure supported by lithium metal anode. Benefiting from an exemplary superiority of excellent mechanical property, high ionic conductivity, and robust interfacial adhesion, the in-situ formed polymer electrolyte reinforced by titanosiloxane networks (ISPTS) embodies multifunctional roles of physical barrier, ionic carrier, and artificial protective layer at the interface. The potent interfacial interactions foster a seamless fusion of the electrode/electrolyte interfaces and enable continuous ion transport. Moreover, the built-in ISPTS electrolyte participates in the formation of gradient solid-electrolyte interphase (SEI) layer, which enhances the SEI’s structural integrity against the strain induced by volume fluctuations of lithium anode. Consequently, the resultant 11 μm-thick ISPTS electrolyte enables lithium symmetric cells with cycling stability over 600 h and LiFePO4 cells with remarkable capacity retention of 96.6% after 800 cycles. This study provides a new avenue for designing ultrathin polymer electrolytes towards stable, safe, and high-energy–density lithium metal batteries.

High-modulus solid electrolyte interphase layer with gradient composition enables long-cycle all-solid-state lithium-sulfur batteries

All-solid-state lithium-sulfur batteries (ASSLSBs) have become one of the most potential candidates for the next-generation high-energy systems due to their intrinsic safety and high theoretical energy density. However, PEO-based ASSLSBs face the dilemma of insufficient Coulombic efficiency and long-term stability caused by the coupling problems of dendrite growth of anode and polysulfide shuttle of cathode. In this work, 1,3,5-trioxane (TOX) is used as a functional additive to design a PEO-based composite solid-state electrolyte (denoted as TOX-CSE), which realizes the stable long-term cycle of an ASSLSB. The results show that TOX can in-situ decompose on the anode to form a composite solid electrolyte interphase (SEI) layer with rich-organic component. It yields a high average modulus of 5.0 GPa, greatly improving the mechanical stability of the SEI layer and thus inhibiting the growth of dendrites. Also, the robust SEI layer can act as a barrier to block the side reaction between polysulfides and lithium metal. As a result, a Li-Li symmetric cell assembled with a TOX-CSE exhibits prolonged cycling stability over 2000 h at 0.2 mA cm−2. The ASSLSB also shows a stable cycling performance of 500 cycles at 0.5 C. This work reveals the structure–activity relationship between the mechanical property of interface layer and the battery’s cycling stability.

Non-flammable polymer electrolyte with fast ion conductivity for high-safety Li batteries

The safety and ionic conductivity of solid polymer electrolytes have hindered their large-scale application. Tetrabromobisphenol A (TBBA) is regarded as an efficient flame retardant for polymers. However, the -OH group of TBBA is active during electrochemical process and results in the sacrifice of capacity in battery cycling. Herein, a new organic filler, TBBA-dichlorobutane (TD) is generated by replacing the H of -OH in TBBA using the 1,4-dichlorobutane through copolymerization modification. The electrochemical stability of TD has been improved, which facilitates the generation of the solid electrolyte interphase (SEI) layer of LiBr, improving interface ionic conductivity. Meanwhile, the addition of TD significantly reduces the crystallinity of polyacrylonitrile (PAN), improving the ionic conductivity of the electrolyte. Furthermore, the electrochemical mechanism has been characterized by in-situ Raman and Fourier transform infrared (FT-IR) spectra, revealing the high stability and fast ion transfer ability of electrolytes. From the theoretical calculation (density functional theory (DFT), COMSOL, and molecular dynamics (MD)), the priority combination between lithium-ion and the bromine in PAN-TD (P-TD), as well as uniform lithium-ion flux, can be certified. Therefore, the LiFePO4//Li battery exhibits a specific capacity of 157 mA h g−1 at 0.5 C and maintains 154 mA h g−1 after 100 cycles. At the same time, the safety properties have been improved by the formation of the carbon layer and the capture of free radicals through bromine, exhibiting an oxygen index as high as 29 %.

Origin of Performance Improvements in Lithium‐Ion Cells after Fast Formation

AbstractThe formation process of lithium‐ion batteries commonly uses low current densities, which is time‐consuming and costly. Experimental studies have already shown that slow formation may neither be necessary nor beneficial for cell lifetime and performance. This work combines an experimental formation variation with physicochemical cell and solid electrolyte interphase (SEI) modeling to reveal formation‐induced changes within the cells. Formation at C/2 without full discharge compared to a standard C/10 formation at 20 °C notably improves the discharge and charge capacities at 2C by up to 41 % and 63 %, respectively, while reducing the formation time by over 80 %. Model‐based cell diagnostics reveal that these performance gains are driven by improved transport in the anode electrolyte phase, which is affected by SEI formation, and by enhanced transport on the cathode side. Hence, the focus on the dense SEI layer is insufficient for a comprehensive understanding and, ultimately, optimization of cell formation. All formation procedures were also tested at temperatures of 35 °C and 50 °C. Despite often surpassing the 2C discharge capacity of the standard formation at 20 °C, these cells showed comparable or lower 2C charge capacities. This suggests a pivotal role of local temperature in the formation of large‐format cells.

Plasma Coupled Electrolyte Additive Strategy for Construction of High-Performance Solid Electrolyte Interphase on Li Metal Anodes.

High-performance lithium metal anodes are crucial for the development of advanced Li metal batteries. Herein, this work reports a novel plasma coupled electrolyte additive strategy to prepare high-quality composite solid electrolyte interphase (SEI) on Li metal to achieve enhanced performance and stability. With the guidance of calculations, this work selects diethyl dibromomalonate (DB) as an additive to optimize the solvation structure of electrolytes to modify the SEI. Meanwhile, this work groundbreakingly develops DB plasma technology coupled with DB electrolyte additive to construct a combinatorial SEI: inner plasma-induced SEI layer composed of LiBr and Li2CO3 plus additive-reduced SEI containing LiBr/Li2CO3/organic lithium compounds as an outer compatible layer. The optimized hybrid SEI has strong affinity toward Li+ and good mechanical properties, thereby inducing horizontal dispersion and uniform deposition of Li+ and keep structure stable. Accordingly, the symmetrical cells exhibit enhanced cycling stability for 1200h at an overpotential of 23.8mV with average coulombic efficiency (99.51%). Additionally, the full cells with LiNi0.8Co0.1Mn0.1O2 cathode deliver a capacity retention of 81.7% after 300 cycles at 0.5 C, and the pouch cell achieves a volumetric specific energy of ≈664Wh L‒1. This work provides new enlightenment on plasma technology for fabrication of advanced metal anodes for energy storage.

Anti-corrosive and carbonyl-rich interlayer enables highly reversible zinc anode

Aqueous zinc ion batteries (AZIBs) are considered as highly promising candidates for large-scale energy storage due to their exceptional safety profile, environmental sustainability, and cost-effectiveness. However, the progress of AZIBs is impeded by several challenges including the formation of zinc dendrites, self-corrosion issues, and hydrogen evolution. Herein, we demonstrate the in-situ fabrication of a hydrophobic and carbonyl-rich zinc phthalate (ZCHO) solid electrolyte interphase (SEI) layer on the zinc foil through a facile liquid deposition method. The incorporation of carbonyls into the ZCHO layer enhances ion migration dynamics by attracting Zn2+, while also promoting preferential deposition onto the (002) surface, effectively mitigating water-induced corrosion and hydrogen evolution, likewise reducing charge transfer resistance. These inherent advantages contribute to a homogeneous distribution of Zn2+ concentration on the zinc anode surface, thereby suppressing dendrite growth. The results demonstrate that the symmetric battery exhibits an impressive cycle life of over 2300 h under a current density of 1 mA cm−2, with an areal capacity of 0.5 mAh cm−2. Additionally, it demonstrates stable cycling for more than 700 h at 5 mA cm−2, 0.25 mAh cm−2. Furthermore, when assembled with NH4V4O10, the full battery delivers a specific capacity of 222.9 mAh g−1 after undergoing 1000 cycles under a current density of 5 A g−1 while maintaining a capacity retention rate of 86.26 %. This study presents a novel and facile approach to advance research on high-performance AZIBs.

Enhancing performance and longevity of solid-state zinc-iodine batteries with fluorine-rich solid electrolyte interphase

Rechargeable zinc-iodine (ZnI2) batteries have gained popularity within the realm of aqueous batteries due to their inherent advantages, including natural abundance, intrinsic safety, and high theoretical capacity. However, challenges persist in their practical applications, notably battery swelling and vulnerability in aqueous electrolytes, primarily linked to the hydrogen evolution reaction and zinc dendrite growth. To address these challenges, this study presents an innovative approach by designing a solid-state ZnI2 battery featuring a solid perfluoropolyether based polymer electrolyte. The results demonstrate the formation of a solid electrolyte interphase layer on zinc, promoting horizontal zinc growth, mitigating dendrite penetration, and enhancing battery cycle life. Moreover, the solid electrolyte hinders the iodine ion shuttle effect, reducing zinc foil corrosion. Symmetric batteries employing this electrolyte demonstrate excellent cycle performance, maintaining stability for approximately 5000 h at room temperature, while solid-state ZnI2 batteries exhibit over 7000 cycles with a capacity retention exceeding 72.2%. This work offers a promising pathway to achieving reliable energy storage in solid-state ZnI2 batteries and introduces innovative concepts for flexible and wearable zinc batteries.

Optimizing Electrode Efficiency in Lithium Titanate: Investigating the Impact of Electrolyte Additives on Cylindrical Li‐Ion Capacitor Cells

Recent advancements in lithium‐based energy storage focus on new electrode materials for lithium‐ion batteries (LIBs) and capacitors. Lithium titanate (LTO) emerges as a key player, offering minimal volume change, rapid charging, and enhanced safety. A critical discovery is the formation of a solid electrolyte interphase (SEI) layer on LTO electrodes, especially with electrolyte additives, improving electrochemical performance. This study investigates additive effects on LTO. Large‐scale Li‐ion capacitors (LIC) of LTO//activated carbon (AC) are crafted and evaluated. Notably, adding just 1% of methylene methanedisulfonate (MMDS) or fluoroethylene carbonate (FEC) to a 1 m LiPF6 electrolyte markedly increases capacities and maintains performance over 500 cycles, outperforming other additives. These additives also boost large‐scale capacitor capacities, showing exceptional stability for over 1600 cycles. This underlines the potential of customized electrolyte additives in elevating LTO‐based energy storage, leading to more durable and efficient lithium‐based solutions.

Effects of Electrolyte Solvent Composition on Solid Electrolyte Interphase Properties in Lithium Metal Batteries: Focusing on Ethylene Carbonate to Ethyl Methyl Carbonate Ratios

This study investigated the influence of variations in the mixing ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) on the composition and effectiveness of the solid electrolyte interphase (SEI) in lithium-metal batteries. The SEI is crucial for battery performance, as it prevents continuous electrolyte decomposition and inhibits the growth of lithium dendrites, which can cause internal short circuits leading to battery failure. Although the properties of the SEI largely depend on the electrolyte solvent, the influence of the EC:EMC ratio on SEI properties has not yet been elucidated. Through electrochemical testing, ionic conductivity measurements, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, the formation of Li2CO3, LiF, and organolithium compounds on lithium surfaces was systematically analyzed. This study demonstrated that the EC:EMC ratio significantly affected the SEI structure, primarily owing to the promotion of the formation of a denser SEI layer. Specifically, the ratios of 1:1 and 1:3 facilitated a uniform distribution and prevalence of Li2CO3 and LiF throughout the SEI, thereby affecting cell performance. Thus, precise control of the EC:EMC ratio is essential for enhancing the mechanical robustness and electrochemical stability of the SEI, thereby providing valuable insights into the factors that either enhance or impede effective SEI formation.

Tuning MgCl2 content in BMIMPF6 to optimize mg-ion battery performance

This study aims to explore magnesium chloride salt-ionic liquid as an efficient electrolyte for Magnesium-ion Batteries (MIBs) using graphite as a cathode material. A complete physicochemical and electrochemical characterizations were performed on a number of electrolyte compositions and important properties including ion solvation, specific conductivity, ion transport behaviour, dominant ionic species, and electrochemical stability were tested. Also, the effect of magnesium salt concentration on specific capacity, reversibility, stability, charge retention, and rate capability were examined. Moreover, the effect of graphite electrodes on Solid Electrolyte Interphase (SEI) layer, its practicality, and cyclability of the different electrolyte compositions afforded interesting conclusions by this comprehensive comparison of electrode-electrolyte pairings. This evaluation is further supported by life cycle analysis, which gave an important information on how to keep electrodes structurally intact even after several uses. Though there were differences in the three electrolyte systems with respect to reversibility, stability, cyclicbility, capacity fading, and unexpected failures, the 0.2 M electrolyte showcased a notable feature of a high ionic conductivity (4.6 × 10−3 mS cm−1) at room temperature and strong anodic stability (4.0 V vs. Mg/Mg2+). Thus, endorsing the developed system as promising lead for further exploration. Additionally, magnesium dissolution and deposition on a Pt working electrode in this electrolyte was also thoroughly examined in this study. The process of PF6¯ ion intercalation and de-intercalation into graphite layer structure was examined using Cyclic Voltammetry (CV). Based on the analysis by Field Emission- Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS), a change in the active-material morphology was observed and we hypothesize that this might be the reason for the improved performance.

Sustainable release of borate- and nitrate- electrolyte additives via metal-organic frameworks nanocapsules for stable lithium metal batteries

Constructing robust electrolyte interphase through inorganic electrolyte additives is an effective strategy to improve the electrochemical performance of lithium metal batteries (LMBs). However, the limited solubility of such additives in electrolyte hinders their further application. Herein, we apply metal–organic frameworks (MOFs) as nanocapsules to sustainably release lithium nitrate (LiNO3) and a novel salt of potassium tetraborate (K2B4O5(OH)4). LiNO3 is inclined to undergo reduction on lithium anode to form a nitride-rich solid electrolyte interphase (SEI) layer; while K2B4O5(OH)4 preferentially decomposes on high-voltage cathodes to create a boron-rich cathode electrolyte interphase (CEI) layer. Although both salts exhibit poor solubility in commercial carbonate electrolyte, they can be continuously consumed on the electrode surface and concurrently replenished from the nanocapsules during long-term cycling process. As a result, a compact lithium deposition is achieved and the dissolution of transition metals is restrained. Upon the sacrifice of LiNO3 and K2B4O5(OH)4, the lifespan of LMBs is remarkbly improved. The Li||LiNi0.5Co0.2Mn0.3 (NCM523) cells at 4.3 V and Li||LiNi0.6Co0.2Mn0.2 (NCM622) cells at 4.4 V can respectively deliver high capacity retentions of 87 % and 80.1 % for 200 cycles.

Conductive layer coupled mesoporous hard carbon enabling high rate and initial Coulombic efficiency for potassium ion battery

Hard carbon with rich mesopores is considered as one of the most promising anodes for potassium-ion batteries, resulting from its shortened ions diffusion distance, good electrolyte penetration ability, and highly released stress. However, the well-developed pore channels tend to separate graphite-domains and enlarge direct contact area between electrode/electrolyte, which easily cause discontinuous electrons transfer paths and extra electrolyte depletion, thus leading to poor rate performance and initial Coulombic efficiency (ICE). Hence, we propose polyaniline conductive layer coated hollow mesoporous carbon spheres (HMCS@PAN) tailored based on local protonation reaction strategy, which can enhance conductivity and simultaneously maintain considerable pore structure, accounting for an ultrahigh-rate performance (233.9 mAh/g at 5 A/g) and long cycling life (216.8 mAh/g at 5 A/g over 2000 cycles). Besides, PAN coating can inhibit the direct contact between inner pore channels and electrolyte and reduce the excessive depletion of active ions in the filling of pores with larger pore size, which is conducive to building an even, stable, and inorganic-rich solid electrolyte interphase (SEI) layer, resulting in an excellent ICE (70.7%). This work provides a guidance for the structure design of mesopore hard carbon to improve its rate and ICE.

Air-Stable Na3.5C6O6 as a Sodium Compensation Additive in Cathode of Na-Ion Batteries.

Sodium-ion battery (SIB) is a candidate for the stationary energy storage systems because of the low cost and high abundance of sodium. However, the energy density and lifespan of SIBs suffer severely from the irreversible consumption of the Na-ions for the formation of the solid electrolyte interphase (SEI) layer and other side reactions on the electrodes. Here, Na3.5C6O6 is proposed as an air-stable high-efficiency sacrificial additive in the cathode to compensate for the lost sodium. It is characteristic of low desodiation (oxidation) potential (3.4-3.6V vs. Na+/Na) and high irreversible desodiation capacity (theoretically 378 mAh g-1). The feasibility of using Na3.5C6O6 as a sodium compensation additive is verified with the improved electrochemical performances of a Na2/3Ni1/3Mn1/3Ti1/3O2ǀǀhard carbon cells and cells using other cathode materials. In addition, the structure of Na3.5C6O6 and its desodiation path are also clarified on the basis of comprehensive physical characterizations and the density functional theory (DFT) calculations. This additive decomposes completely to supply abundant Na ions during the initial charge without leaving any electrochemically inert species in the cathode. Its decomposition product C6O6 enters the carbonate electrolyte without bringing any detectable negative effects. These findings open a new avenue for elevating the energy density and/or prolonging the lifetime of the high-energy-density secondary batteries.