Stable Cathode Electrolyte Interface Research Articles

Stabilizing SPAN in Non-Flammable Acetonitrile Electrolytes for Long-Life Graphite||SPAN Batteries.

Sulfurized polyacrylonitrile (SPAN) presents an opportunity to replace elemental sulfur as a "shuttle-free" cathode for secondary Li-S batteries, which can be an ideal choice for stationary energy storage due to its abundance, low cost, and sustainability. The electrolyte options for the state-of-the-art SPAN batteries have been limited to the flammable carbonate and ether ones, which raises safety concerns. Here, we explored the use of a non-flammable acetonitrile (AN) electrolyte for SPAN battery for the first time and identified the irreversible cleavage of C-S bonds of SPAN as the main reason for the failure of SPAN in AN electrolyte. Fortunately, by introducing 10 wt % fluoroethylene carbonate into the AN electrolyte, the bond cleavage in SPAN is suppressed and a stable cathode electrolyte interface is formed, both contributing to stabilizing the structure of SPAN during electrochemical process. Consequently, we achieved a stable cycling for 900 cycles in Li||SPAN cells. Moreover, by pairing with a pre-lithiated graphite (pGr) anode, the newly formulated electrolyte enables extended cycle life for 1500 cycles with a capacity retention of 91 % and superb safety in pGr||SPAN full cell. The present exploitation broadens the electrolyte choices of SPAN-based batteries and paves the way for future applications for these batteries.

Robust interface for O3-type layered cathode towards stable ether-based sodium-ion full batteries

Developing a robust cathode-electrolyte interface (CEI) is crucial for stable layered cathode in sodium-ion batteries (SIBs). A CEI based on ester electrolytes often exhibit poor stability and robustness, which cannot address the issues of structural collapse and material dissolution in layered cathodes. However, there are few reports on constructing a stable CEI for layered cathode based on ether electrolytes. Here we develop a robust CEI for O3-type cathode via DME solvent, which enables a long-term stability of full SIBs. The results indicate that unique decomposition process of DME yields favorable organic component (e.g. RCH2ONa) and high content of inorganic components (e.g. NaF and Na2CO3) in the CEI, which is quite different from ester electrolyte, improving Na+ diffusion kinetic and interfacial stability. Notably, the O3-NaNi0.5Mn0.5O2||Na cell with the designed electrolyte demonstrates outstanding stability up to 500 cycles. Furthermore, the full cell exhibits remarkable cycling performance with a capacity retention of 85 % over 200 cycles. This work provides an opportunity for stable operation of layered cathode materials via inexpensive ether electrolytes.

Multifunctional carbonyl-rich compounds for constructing “corrosion-resistant electrodes and electrolyte interface” in high-voltage sodium-metal batteries

In recent years, there has been notable advancement in the development of high-performance materials for sodium-ion batteries, particularly in layered oxide cathodes. However, research on enhancing the interface between electrolytes and cathodes remains nascent. One promising approach involves the addition of electrolyte additives, recognized for their cost-effectiveness and efficiency in bolstering the electrode/electrolyte interface to enhance material stability during high-voltage cycling. In this work, we investigate the use of glutaric anhydride (GA) as an electrolyte additive to improve the cycling stability of NaNi1/3F1/3M1/3O2/Na (NFM/Na) high-voltage sodium-metal batteries. Batteries using GA-containing electrolytes demonstrate impressive capacity retention: 80.51 % after 200 cycles at 4.0 V and 76.01 % after 150 cycles at 4.1 V. The research delves into the mechanistic insights behind GA’s effectiveness in enhancing cyclic stability. Theoretical calculations reveal that GA plays a crucial role in modifying the structure of the first solvation shells, promoting the formation of an elastic cathode-electrolyte interface (CEI) film enriched with OCO groups. This uniform and stable CEI film effectively preserves the material’s crystal structure and mitigates the dissolution of transition metals, thereby prolonging battery lifespan under demanding extremely cycling conditions.

Design Lithium Exchanged Zeolite Based Multifunctional Electrode Additive for Ultra‐High Loading Electrode Toward High Energy Density Lithium Metal Battery

AbstractThe practicalization of a high energy density battery requires the electrode to achieve decent performance under ultra‐high active material loading. However, as the electrode thickness increases, there is a notable restriction in ionic transport in the electrodes, limiting the diffusion kinetics of Li+ and the utilization rate of active substances. In this study, lithium‐ion‐exchanged zeolite X (Li‐X zeolite) is synthesized via Li+ exchange strategy to enhance Li+ diffusion kinetics. When incorporated Li–X zeolite into the ultra‐high loading cathodes, it possesses i) high electron conductivity with a uniform network by reducing tortuosity, ii) decent ion conductivity attributes to modulated Li+ diffusivity of Li‐X and iii) high elasticity to prevent particle‐level cracking and electrode‐level disintegration. Moreover, Li–X zeolite at the solid/liquid interface facilitates the formation of a stable cathode electrolyte interface, which effectively suppresses side reactions and mitigates the dissolution of transition cations. Therefore, an ultra‐high loading (66 mg cm−2) cathode is fabricated via dry electrode technology, demonstrating a remarkable areal capacity of 12.7 mAh cm−2 and a high energy density of 464 Wh kg−1 in a lithium metal battery. The well‐designed electrode structure with multifunctional Li–X zeolite as an additive in thick cathodes holds promise to enhance the battery's rate capability, cycling stability, and overall energy density.

A Novel 4-Fluorophenyl Isocyanate Additive Constructing Solid Cathodes-Electrolyte Interface for High-Performance Lithium-Ion Batteries.

Building a stable cathode-electrolyte interface (CEI) is crucial for achieving high-performance layered metal oxide cathode materials LiNixCoyMn1-x-yO2 (NCM). In this work, a novel 4-fluorobenzene isocyanate (4-FBC) electrolyte additive that contains isocyanate and benzene ring functional groups is proposed, which can form robust and homogeneous N-rich and benzene ring skeleton CEI film on the cathode surface, leading to significant improvement in the electrochemical performance of lithium-ion batteries. Taking LiNi0.5Co0.2Mn0.3O2 (NCM523) as an example, the NCM523/SiO@Graphite pouch full cells with electrolytes containing a mass fraction of 1% 4-FBC additives demonstrate improved capacity retention after 200 cycles, retaining capacity retention rates of 81.3%, which is much higher than that of 39.1% without additive. The improvement can be ascribed to the mitigation of electrolyte decomposition and inhibition of transition metal ions the dissolution from the cathode material due to the stable CEI film. Moreover, the electrochemical performance enhancement can also be achieved in high voltage and Ni-rich cathode materials, indicating the universality and effectiveness of this strategy for the practical applications of high energy density lithium-ion batteries.

Surface Coating of NCM523 Cathode Electrodes by the Difunctional Block Copolymer/Lithium Salt Composites.

Nickel-rich layered oxide cathodes, such as LiNi0.5Co0.2Mn0.3O2 (NCM523), are prevalent in high-power batteries owing to their high energy density. However, these cathodes suffer from undesirable side reactions occurring at the cathode/liquid electrolyte interface, leading to inferior interface stability and poor cycle life. To address these issues, herein, an amphiphilic diblock copolymer poly(dimethylsiloxane)-block-poly(acrylic acid) (PDMS-b-PAA) along with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is utilized for modifying the electrode surface. This modification causes a thin and stable cathode-electrolyte interface (CEI) on the surface of NCM523 particles, as evidenced by XPS, TEM, and EIS analysis. The introduction of this modified interface successfully suppresses the capacity fading of NCM523. After 200 cycles at a rate of 1.0 C, the capacity of the modified NCM523 cathode is 108.7 mAh g-1, with a capacity retention of 82.8%, while the control samples without the polymer modification display a capacity retention of 72.7%. These results outline the distinct advantage of electrode surface modification with diblock copolymers/LiTFSI for the stabilization of Ni-rich layered oxide cathodes.

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

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

Dynamically constructing robust cathode-electrolyte-interphase on nickel-rich cathode by organic boron additive for high-performance lithium-ion batteries

Nickel-rich ternary cathode materials LiNi0.8Co0.1Mn0.1O2 (NCM811) have attracted broad attention due to their high voltage and high energy density for lithium-ion batteries. However, rapid capacity decay due to unstable particle surface inhibit the application. Artificial cathode electrolyte interface (CEI) is undoubtedly a more effective and simpler way to solve this issue. Here, stable and highly conductive in situ CEI is designed using a low-cost organic boron additive isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (ITD). Higher occupied molecular orbital energy endows ITD ability to participate in forming CEI. ITD-contained CEI can reduce nickel dissolving, resulting in a lower self-discharge rate, which is benefit from the uniform and stable CEI on the NCM811 surface. As expected, ITD-based CEI can restrain NCM811crystal cracking in Li||NCM811 half batteries, improving capacity retention from 29.4 % to 93.0 % after 200 cycles at 1C (1C = 200 mA g−1). It is worth mentioning that ITD–derived CEI is conducive to ion migration, which improve the rate capacity retention from 91.5 % to 95.5 %.

Pentafluorophenyl diethoxy phosphate: An electrolyte additive for high-voltage cathodes of lithium-ion batteries

Increasing the upper limit of the charging voltage in commercial lithium-ion batteries (LIBs) can enable them to have a higher energy density, but during high-voltage charging and discharging, the electrolyte will accelerate the decomposition, and the interfacial adverse reaction among the cathode and electrolyte is serious, which corrodes the cathode active material and consumes excessive electrolyte, and ultimately lead to a shorter service life of lithium-ion batteries. To address this issue, an electrolyte additive with properties suitable for high voltage cathodes, named pentafluorophenyl diethoxy phosphate (FPOP), was synthesized in this work and successfully applied to LiNi0.8Co0.1Mn0.1O2 cathode (NCM-811). Density Functional Theory (DFT) computations reveal that the FPOP additive undergoes preferential oxidation and self-polymerizes on the NCM-811 cathode surface to establishing a safeguarding film at the cathode-electrolyte interface (CEI). This film effectively inhibits detrimental side reactions. The electrochemical performance test data indicated that the retention rate of discharge-specific capacity in batteries was markedly enhanced with 0.1 wt% of FPOP when added to the standard electrolyte. Specifically, after subjecting the batteries to 200 cycles at a current of 0.2C and under voltages ranging from 4.2 V to 4.5 V, the retention of discharge ratio capacity increased by 37.6 %, 39.2 %, 26.9 %, and 37.1 % correspondingly. Morphology characterization and spectroscopic characterization showed that FPOP could not only construct a stable CEI film by oxidation during the first stages of lithium precipitation but also remove HF by strongly binding to the HF in the electrolyte or dissociating H+ and F− from HF, which ultimately enhanced the batteries' capacity to operate effectively at elevated voltage levels. Therefore, incorporating FPOP as an additive in electrolyte presents a cost-efficient approach to achieving elevated energy density.

BF4- Tailoring Solvation Chemistry of Ether-Based Electrolytes to Construct Stable Electrode/Electrolyte Interfaces for Sodium-Ion Full Batteries.

The ether-based electrolytes show excellent performance on anodes in sodium-ion batteries (SIBs), but they still show poor compatibility with the cathodes. Here, ether electrolytes with NaBF4 as the main salt or additive were applied in NFM//HC full cells and showed enhanced performance than the electrolyte with NaPF6. Then, BF4- was found to have a stronger interaction with Na+, which could reduce the solvation of Na+ with the solvent, thus inducing the formation of the cathode electrolyte interface (CEI) and solid electrolyte interface (SEI) layers rich in inorganic species. Moreover, the morphology, structure, composition, and solubility of CEI and SEI were explored, concluding that NaBF4 could induce more stable CEI and SEI layers rich in B-containing species and inorganics. This work proposes using NaBF4 as the main salt or additive to improve the performance of ether electrolytes in NFM//HC full cells, which provides a strategy to improve the compatibility of ether-based electrolytes and cathodes.

In Situ Formation of a LiBO2 Coating Layer and Spinel Phase for Ni-Rich Cathode Materials from a Boric Acid-Etched Precursor.

Ni-rich cathode materials exhibit superior energy densities and have attracted interest among both research and industrial fields; whereas, their practical application is hindered by the intrinsic drawbacks brought by the high nickel content such as structural instability and rapid capacity fading. Herein, in situ formation of a LiBO2 coating layer and spinel phase layer is achieved on the surface of a Ni-rich cathode material via a boric acid etching method at the precursor state. The spinel phase is considered to have a 3D lithium diffusion tunnel and hence faster diffusion kinetics. Moreover, the LiBO2 layer possesses excellent (electro)chemical inertness and can suppress electrolyte decomposition, resulting in a more inorganic and stable cathode-electrolyte interface. The surface reconstructed sample exhibits better cyclic stability (93.3% capacity retention vs 85.3% for the pristine sample at 1 C for 100 cycles) and rate performance. The superiority of this surface reconstruction is demonstrated by a series of electrochemical techniques and characterization methods including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), post-mortem X-ray photoelectron spectroscopy (XPS) analysis, and density functional theory (DFT) calculations.

Elastic Interfacial Layer Enabled the High-Temperature Performance of Lithium-Ion Batteries Via Utilization of Synthetic Fluorosulfate Additive

The key to producing high-energy Li-ion cells is ensuring the interfacial stability of Si-containing anodes and Ni-rich cathodes. Herein, 4-(allyloxy) phenyl fluorosulfate (APFS), a multi-functional electrolyte additive that forms a mechanical strain-adaptive solid electrolyte interphase (SEI) comprising LiF and polymeric species, and a thermally stable cathode–electrolyte interface containing S–O and S–F species. The radical copolymerization of vinylene carbonate (VC) with APFS via electrochemical initiation creates a spatially deformable polymeric SEI on the SiG-C (30 wt.% graphite + 70 wt.% SiC composite) anode, with large volume changes during cycling. Moreover, the APFS-promoted interfacial layers reduce Ni dissolution and deposition. Furthermore, APFS deactivates the Lewis acid PF5, thereby inhibiting hydrolyses that produce unwanted HF. These results indicate that the combined use of VC with APFS allows capacity retentions of 72.5% with a high capacity of 143.5 mAh g−1 in SiG-C/LiNi0.8Co0.1Mn0.1O2 full cells after 300 cycles at 45 °C.

Transitioning Towards Asymmetric Gel Polymer Electrolytes for Lithium Batteries: Progress and Prospects

AbstractThe utilization of liquid electrolytes (LEs) concerns inevitable dendrite growth and safety issues. In contrast, solid polymer electrolytes suffer from unsettled low ionic conductivity and interfacial impedance issues. The intermediary gel polymer electrolytes (GPEs) improve safety by incorporating a sturdy polymer matrix and ionic conductivity as an advantage of percolating LEs responsible for gelation. The overall stability and compatibility of GPEs with different electrode materials depend on the polymers, plasticizers, and precursors utilized. No single polymer has a wide energy gap to exhibit stability against Li metal anodes and oxidative stability against high‐voltage cathodes. Thereafter, symmetric GPEs (SGPEs) possess limitations while simultaneously satisfying the two electrode requirements, which hinders their practical applications. Asymmetric GPEs (ASGPEs) generally comprise a bilayer or gradient structure, wherein the side contacting the cathode is modified to promote oxidative stability for a stable cathode electrolyte interface (CEI). The corresponding side in contact with the anode is modified to be mechanically and chemically compatible with dendritic lithium. Overall, asymmetric structural engineering enables electrode compatibility while maintaining the physical competency of GPEs. Herein, the focus is to summarize the current transition from SGPEs to asymmetric ones, which promotes multifunctionality while overcoming specific constraints associated with the electrodes.

Fluorine grafted gel polymer electrolyte by in situ construction for high-voltage lithium metal batteries

Gel polymer electrolytes (GPEs) are promising candidates for next generation lithium metal batteries (LMBs) due to their reassuring safety and high ionic conductivity at room temperature. However, they are still plagued by incompatible interfaces and poor compatibility with Ni-rich cathodes, imposing great restrictions on the scalability of high-voltage cathodes. To overcome these problems, a GPE with a polyacrylonitrile porous membrane, together with 2,2,3,4,4,4-hexafluorobutyl acrylate grafted pentaerythritol tetraacrylate, is fabricated via in-situ thermal polymerization. By virtue of the effective transport channels provided by PAN and PETEA molecules, our GPE exhibits both a high lithium-ion transference number and a high ionic conductivity of 0.87 and 4.06 × 10−3 S cm−1, respectively at 30 °C. Moreover, the GPE ensures a high electrochemical window, stable at potentials up to 5.35 V, enabling the application of LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes. Due to the uniform cathode electrolyte interface (CEI) formed by our GPE on the surface of NCM811, the assembled NCM811|GPE|Li batteries present an excellent cycling life of 300 cycles in the voltage range of 3 ∼ 4.5 V with a capacity retention of 84% at 2C. Our study provides a novel strategy for constructing fast Li+ transport channels and stable CEI membranes in LMBs operating at high voltages.

Olivine-based nano-filling layer empowering Ni-rich layered cathodes with enhanced surface stability and thermal shock resistance

Irreversible phase transition and nerve-racking thermal runaway of NCM811 especially cycled at high charge cut-off potential hinder its full-scale commercialization. In this study, we use a facile and powerful surface modification strategy to construct modified NCM811 whose ravines are completely filled/embedded by sand-milled LiMn0.6Fe0.4PO4 (LMFP), forming the nano-filled NCM811 (LMFP@NCM811). By virtue of this compact & uniform LMFP layer, a thin and stable cathode-electrolyte interface (CEI) layer can be established on the surface of LMFP@NCM811, which leads to prominent electrochemical properties with a high capacity retention of ∼ 80% after 450 cycles at 100 mAh/g. Moreover, due to the intrinsic stability of olivine structure (LMFP), the LMFP-embedded NCM811 showcases admirable thermal stability and thermal shock resistance at high de-lithiation state. We believe that such success at the performance improvement of Ni-rich ternary cathodes can provide a good guidance for future work to achieve more efficient energy storage and utilization.

Cathode Electrolyte Interface Engineering by Gradient Fluorination for High‐Performance Lithium Rich Cathode

AbstractDespite their ultrahigh specific capacity, lithium‐rich layered oxide cathodes are still plagued by challenges such as poor cycle stability and notorious voltage decay, which are primarily attributed to surface issues such as the release of lattice oxygen and interfacial side reactions. In this study, a facial strategy of gradient fluorination is adopted to construct a thin but robust LiF‐rich cathode electrolyte interface (CEI), highly enhancing the stability of the interface of lithium‐rich oxides. Experimental results and theoretical calculations both demonstrate that the stable CEI not only promotes oxygen participation in redox reactions and simultaneously inhibits oxygen release and structural transition, but also facilitates the transport kinetics of lithium ions. As a result, the gradient fluorinated lithium‐rich cathode delivers highly enhanced rate performance (133 mAh g−1 at 5 C), superior cycling stability with a capacity retention of 81.9% after 100 cycles at 1 C (250 mAh g−1), and alleviated voltage fade (only 1.75 mV per cycle). Moreover, a unique formation mechanism for LiF‐rich surfaces is proposed according to theoretical calculations. This work not only provides a fresh understanding of the CEI formation mechanism, but also show a promising avenue for designing LiF‐rich CEIs applicable to other layered oxide cathodes.

Elastic Interfacial Layer Enabled the High‐Temperature Performance of Lithium‐Ion Batteries via Utilization of Synthetic Fluorosulfate Additive

AbstractThe key to producing high‐energy Li‐ion cells is ensuring the interfacial stability of Si‐containing anodes and Ni‐rich cathodes. Herein, 4‐(allyloxy)phenyl fluorosulfate (APFS), a multi‐functional electrolyte additive that forms a mechanical strain‐adaptive solid electrolyte interphase (SEI) comprising LiF and polymeric species, and a thermally stable cathode–electrolyte interface containing SO and SF species. The radical copolymerization of vinylene carbonate (VC) with APFS via electrochemical initiation creates a spatially deformable polymeric SEI on the SiG‐C (30 wt.% graphite + 70 wt.% SiC composite) anode, with large volume changes during cycling. Moreover, the APFS‐promoted interfacial layers reduce Ni dissolution and deposition. Furthermore, APFS deactivates the Lewis acid PF5, thereby inhibiting hydrolyses that produce unwanted HF. These results indicate that the combined use of VC with APFS allows capacity retentions of 72.5% with a high capacity of 143.5 mAh g−1 in SiG‐C/LiNi0.8Co0.1Mn0.1O2 full cells after 300 cycles at 45 °C.

Phosphate-Rich Interface for a Highly Stable and Safe 4.6V LiCoO2 Cathode.

Increasing the upper cut-off voltage of LiCoO2 (LCO) is one of the most efficient strategies to gain high-energy density for current lithium-ion batteries. However, surface instability is expected to be exaggerated with increasing voltage arising from the high reactivity between the delithiated LCO and electrolytes, leading to serious safety concerns. This work is aimed to construct a physically and chemically stable phosphate-rich cathode-electrolyte interface (CEI) on the LCO particles to mitigate this issue. This phosphate-rich CEI is generated during the electrochemical activation by using fluoroethylene carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyletherare as the solvents. Both solvents also demonstrate high thermal stability, reducing the intrinsic flammability of the commercial organic electrolyte, thereby eliminating the safety concern in the LCO-based systems upon high-voltage operation. This stable CEI layer on the particle surface can also enhance the surface structure by blocking direct contact between LCO and electrolyte, improving the cycling stability. Therefore, by using the proposed electrolyte, the LCO cathode exhibits a high-capacity retention of 76.1% after 200 cycles at a high cut-off voltage of 4.6V. This work provides a novel insight into the rational design of high-voltage and safe battery systems by adopting the flame-retardant electrolyte.

Carboxylate-derived conductive, sodium-ion storable surface of Prussian Blue with a stable cathode-electrolyte interface

Considering the high binding affinity between carboxylate ligands (−O–CO) and alkaline Na ions, Prussian blue (PB) with a carboxylate-derived conductive, Na-ion storable surface is developed as a cathode material for Na-ion rechargeable batteries. Here, citric acid (CA) (C6H8O7) is introduced as a carboxylate source because, in a neutral aqueous solution, it loses two H ions of each molecule to reach an acid-base equilibrium and is stabilized in a chemical form with two −O–CO ligands that are accompanied by two delocalized electrons. Consequently, these functional groups newly formed from CA remain on the surfaces of PB particles even when PB is co-precipitated using CA and sodium citrate as dual chelating agents. Specifically, they strongly bind to high-spin Fe (FeHS) ions on the PB surface, providing additional active sites for Na-ion storage via a quasi-reversible, surface redox process (i.e., FeHS–R–C–O– ↔ FeHS–R–C–O–Na) in the low-voltage region close to 3.0 V (vs. Na+/Na). During charge/discharge cycling, inserted Na ions prefer to be stored in the activated surface sites instead of being used to produce unstable by-products by electrolyte decomposition, which resultantly inhibits the thick growth of cathode-electrolyte interface (CEI) layers on the PB particles. As a result, 2 wt% CA-assisted PB exhibits high first discharge capacity (∼110 mA h g−1) and low average capacity decay rate (−0.39 mA h g−1/cycle) at a current density of 0.2 C.

Cathode-Electrolyte Interface Modification by Binder Engineering for High-Performance Aqueous Zinc-Ion Batteries.

A stable cathode-electrolyte interface (CEI) is crucial for aqueous zinc-ion batteries (AZIBs), but it is less investigated. Commercial binder poly(vinylidene fluoride) (PVDF) is widely used without scrutinizing its suitability and cathode-electrolyte interface (CEI) in AZIBs. A water-soluble binder is developed that facilitated the in situ formation of a CEI protecting layer tuning the interfacial morphology. By combining a polysaccharide sodium alginate (SA) with a hydrophobic polytetrafluoroethylene (PTFE), the surface morphology, and charge storage kinetics can be confined from diffusion-dominated to capacitance-controlled processes. The underpinning mechanism investigates experimentally in both kinetic and thermodynamic perspectives demonstrate that the COO- from SA acts as an anionic polyelectrolyte facilitating the adsorption of Zn2+ ; meanwhile fluoride atoms on PTFE backbone provide hydrophobicity to break desolvation penalty. The hybrid binder is beneficial in providing a higher areal flux of Zn2+ at the CEI, where the Zn-Birnessite MnO2 battery with the hybrid binder exhibits an average specific capacity 45.6% higher than that with conventional PVDF binders; moreover, a reduced interface activation energy attained fosters a superior rate capability and a capacity retention of 99.1% in 1000 cycles. The hybrid binder also reduces the cost compared to the PVDF/NMP, which is a universal strategy to modify interface morphology.