Cathode Electrolyte Interphase Research Articles

Highly-solvating Electrolyte Enables Mechanically Stable and Inorganic-rich Cathode Electrolyte Interphase for High-performing Potassium-ion Batteries.

Cathode-electrolyte interphase (CEI) is crucial for the reversibility of rechargeable batteries, yet receives less attention compared to solid-electrolyte interphase (SEI). The prevalent weakly-solvating electrolyte is usually proposed from the standing point of obtaining robust SEI, however, the resultant weak ion-solvent interaction gives rise to excessive free solvents and forms thick CEI with high kinetic barriers, which is disadvantageous for interfacial stability at the high working voltage. Herein, we report a highly-solvating electrolyte to immobilize free solvents by generating stable ternary complexes and facilitate the growth of homogeneous and ultrathin CEI to boost the electrochemical performances of potassium-ion batteries (PIBs). Through time-of-flight secondary ion mass spectrometry and cryogenic transmission electron microscopy, we reveal that the deliberately coordinated complexes are the key to forming mechanically stable and inorganic-rich CEI with superior diffusion kinetics for high-performing PIBs. Coupling with a K0.5MnO2 cathode and a soft carbon (SC) anode, we achieve a high energy density (202.3Wh kg-1) with an exceptional cycle lifespan (92.5% capacity retention after 500 cycles) in a SC||K0.5MnO2 full cell, setting new performance benchmarks for PIBs. This article is protected by copyright. All rights reserved.

Cu-N Synergism Regulation to Enhance Anionic Redox Reversibility and Activity of Li- and Mn-Rich Layered Oxides Cathode.

Anionic redox chemistry enables extraordinary capacity for Li- and Mn-rich layered oxides (LMROs) cathodes. Unfortunately, irreversible surface oxygen evolution evokes the pernicious phase transition, structural deterioration, and severe electrode-electrolyte interface side reaction with element dissolution, resulting in fast capacity and voltage fading of LMROs during cycling and hindering its commercialization. Herein, a redox couple strategy is proposed by utilizing copper phthalocyanine (CuPc) to address the irreversibility of anionic redox. The Cu-N synergistic effect of CuPc could not only inhibit surface oxygen evolution by reducing the peroxide ion O2 2- back to lattice oxygen O2-, but also enhance the reaction activity and reversibility of anionic redox in bulk to achieve a higher capacity and cycling stability. Moreover, the CuPc strategy suppresses the interface side reaction and induces the forming of a uniform and robust LiF-rich cathode electrolyte, interphase (CEI) to significantly eliminate transition metal dissolution. As a result, the CuPc-enhanced LMRO cathode shows superb cycling performance with a capacity retention of 95.0% after 500 long-term cycles. This study sheds light on the great effect of N-based redox couple to regulate anionic redox behavior and promote the development of high energy density and high stability LMROs cathode.

Carbonated Beverage Chemistry for High-Voltage Battery Cathodes.

Advanced lithium-ion batteries utilize high upper cut-off voltages up to 4.8V versus lithium metal to reach extraordinary energy densities. Such a harsh environment challenges the cathode stability and requires the construction of robust cathode electrolyte interphases at their electrochemical interface. Inspired by carbonated beverages with supersaturated CO2, here we propose a surface modification strategy that produces effective passivation layer of low modulus from the weakest link. CO2 bubbles preferentially nucleate and grow at rough surfaces, which in oxide cathodes are also the local regions offering fast degradation pathway. Metal ion exchange on carbonated layer assist the construction of highly elastic interface under the guidance of packing factor. Our method enables surface reconstruction at both primary and secondary particle levels, for various cathodes exemplified by high-voltage LiNi0.8Co0.1Mn0.1O2 and LiCoO2. Remarkably, with ultra-high upper cut-off voltage of 4.8V versus Li+/Li, over 235 mAh g-1 discharge capacity and over 900W h kg-1 discharge energy at cathode level, ∼90% capacity retention can be obtained for LiNi0.8Co0.1Mn0.1O2 over 100 cycles at 0.5 C with commercial carbonate electrolytes. This carbonated beverage chemistry is promising for constructing high-quality surface passivation in many extreme-condition applications beyond battery cathodes. This article is protected by copyright. All rights reserved.

Optimization of NMC cathode inks for cost-effective and eco-friendly screen-printed lithium-ion batteries

Li-ion batteries are life-saving energy storage technology. However, the battery manufacturing process still needs complicated and expensive production lines because of the sensitive nature of active materials towards the open atmosphere. Additionally, employing hazardous N-Metil-2-Pirrolidon (NMP) solvents, which are also restricted by the World Health Organization for electrode preparation, contributes to unsafe working conditions. In this study, water-based LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode inks were produced and printed by the screen-printing method, which is widely used in sensors and electronics fabrication due to its potential practical applications and low-cost production possibilities. Despite their suitability for operation at high voltage ranges, NMC811 cathodes typically exhibit rapid capacity drops over time because of side reactions and Cathode-Electrolyte Interphase (CEI) thickening. In this study, to overcome the capacity drop issue and make it possible to produce water-based cathode inks, NMC811 particles were encapsulated with reduced graphene oxide (rGO) via a hydrothermal method. Water-based Carboxymethyl cellulose (CMC) - Polyethylene oxide (PEO) binders are compared with conventional Polyvinylidene fluoride (PVDF)-NMP binders and exhibited promising electrochemical stability of 75 % after 50 cycles within a high voltage range of 2.8–4.6 V. Therefore, the water-based novel cathode ink presented in this study is not only well-suited for advancing the development of printed batteries but also stride towards more eco-friendly processes thanks to replacing the toxic NMP with water. Moreover, battery printing technologies have also a strategic importance by reducing the investment cost of battery-producing.

Stabilized Nickel‐Rich‐Layered Oxide Electrodes for High‐Performance Lithium‐Ion Batteries

Next‐generation Li‐ion batteries are expected to exhibit superior energy and power density, along with extended cycle life. Ni‐rich high‐capacity layered nickel manganese cobalt oxide electrode materials (NMC) hold promise in achieving these objectives, despite facing challenges such as capacity fade due to various degradation modes. Crack formation within NMC‐based cathode secondary particles, leading to parasitic reactions and the formation of inactive crystal structures, is a critical degradation mechanism. Mechanical and chemical degradation further deteriorate capacity and lifetime. To mitigate these issues, an artificial cathode electrolyte interphase can be applied to the active material before battery cycling. While atomic layer deposition (ALD) has been extensively explored for active material coatings, molecular layer deposition (MLD) offers a complementary approach. When combined with ALD, MLD enables the deposition of flexible hybrid coatings that can accommodate electrode material volume changes during battery operation. This study focuses on depositing ‐titanium terephthalate thin films on a electrode via ALD‐MLD. The electrochemical evaluation demonstrates favorable lithium‐ion kinetics and reduced electrolyte decomposition. Overall, the films deposited through ALD‐MLD exhibit promising features as flexible and protective coatings for high‐energy lithium‐ion battery electrodes, offering potential contributions to the enhancement of advanced battery technologies and supporting the growth of the EV and stationary battery industries.

Amphoteric Supramolecular Nanofiber Separator for High‐Performance Sodium‐Ion Batteries

The separator is an essential component of sodium‐ion batteries (SIBs) to determine their electrochemical performances. However, the separator with high mechanical strength, good electrolyte wettability and excellent electrochemical performance remains an open challenge. Herein, a new separator consisting of amphoteric nanofibers with abundant functional groups was fabricated through supramolecular assembly of natural polymers for SIB. The uniform nanoporous structure, remarkable mechanical properties and abundant functional groups (e.g. −COOH, −NH2 and −OH) endow the separator with lower dissolution activation energy and higher ion migration numbers. These metrics enable the separator to lower the barrier for desolvation of Na+, accelerate the migration of Na+, and generate more stable solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). The battery assembled with the amphoteric nanofiber separator shows higher specific capacity and better stability than that assembled with glass fiber (GF) separator.

In Situ Construction of a Multifunctional Interphase Enabling Continuous Capture of Unstable Lattice Oxygen Under Ultrahigh Voltages.

The use of nickel-rich layered materials as cathodes can boost the energy density of lithium batteries. However, developing a safe and long-term stable nickel-rich layered cathode is challenging primarily due to the release of lattice oxygen from the cathode during cycling, especially at high voltages, which will cause a series of adverse effects, leading to battery failure and thermal runaway. Surface coating is often considered effective in capturing active oxygen species; however, its process is rather complicated, and it is difficult to maintain intact on the cathode with large volume changes during cycling. Here, we propose an in situ construction of a multifunctional cathode/electrolyte interphase (CEI), which is easy to prepare, repairable, and, most importantly, capable of continuously capturing active oxygen species during the entire life span. This unique protective mechanism notably improves the cycling stability of Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) cells at rigorous working conditions, including ultrahigh voltage (4.8 V), high temperature (60 °C), and fast charging (10 C). An industrial 1 A h graphite||NCM811 pouch cell achieved stable operation of 600 cycles with a capacity retention of 79.6% at 4.4 V, exhibiting great potential for practical use. This work provides insightful guidance for constructing a multifunctional CEI to bypass limitations associated with high-voltage operations of nickel-rich layered cathodes.

Constructing sulfur-rich interphase to promote the cycle stability of graphite/LiNi0.8Co0.1Mn0.1O2 pouch battery at elevated temperature

Lithium-ion batteries (LIBs) with LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes have a high energy density, but their long-cycle performance, especially at high temperature, should still be improved due to the instability of the NCM811 cathode-electrolyte interphase. In this work, 2, 2, 2-Trifluoroethyl p-Toluenesulfonate (TPTS) is introduced as a functional film-forming electrolyte additive design to improve the long-term stability of graphite/NCM811 batteries. The preferential redox reactions of TPTS molecules play a pivotal role in fostering the creation of a sulfur-riched interphase, characterized by low impedance. This interphase works to fortify the interfacial structure, effectively inhibiting the dissolution of transition metal ions. Therefore, in comparison to the graphite/NCM811 pouch batteries lacking additive, TPTS enhance the long-cycle capacity retention from 47 % to 80 % after 450 cycles at 45 °C. What's more, TPTS suppresses outgassing and demonstrates enhanced capacity maintenance for the battery even after storage at 60 °C. This work not only demonstrates the stabilizing impacts of TPTS on the electrode-electrolyte interphase and its enhancement of cycling performance at elevated temperatures but also introduces a novel approach for the practical utilization of functional electrolytes matching high-nickel LIBs.

Revealing the origin of enhanced structural stability for nickel-rich LiNi0.83Co0.11Mn0.06O2 cathodes in situ modified with multifunctional polysiloxane

Multifunctional polysiloxane (MPS) layer is elaborately constructed on the surface of LiNi0.83Co0.11Mn0.06O2 (NCM83) particles via in situ hydrolysis-polycondensation of tetraethyl orthosilicate. Impressively, optimal NCM83 (NCM83-2) electrode covered with average 7 nm-thickness of fresh MPS layer delivers improved capacity retention ratio of 81.8 % after 150 cycles at 25 °C and retains the value of 78.7 % after 200 cycles at 60 °C and 1.0 C. Moreover, NCM83-2 electrode presents lower polarization degree with sluggish growth of the capacity platform. The significant advantages of NCM83-2 can be interpreted by the fact that the MPS layer effectively mitigates microcracks generation by inhibiting phase transition and lattice oxygen loss. Moreover, the MPS protective layer suppresses the thickening of cathode electrolyte interphase film and boosts the structural stability of NCM83 electrode to optimize electrochemical properties. Therefore, this strategy may provide promising enlightenments for preserving structural integrity and improving interfacial stability of nickel-rich cathodes for lithium-ion batteries.

Nonflammable Phosphate-Based Electrolyte for Safe and Stable Potassium Batteries Enabled by Optimized Solvation Effect.

Current potassium-ion batteries (PIBs) are limited in safety and lifetime owing to the lack of suitable electrolyte solutions. To address these issues, herein, we report an innovative non-flammable electrolyte design strategy that leverages an optimal moderate solvation phosphate-based solvent which strikes a balance between solvation capability and salt dissociation ability, leading to superior electrochemical performance. The formulated electrolyte simultaneously exhibits the advantages of low salt concentration (only 0.6 M), low viscosity, high ionic conductivity, high oxidative stability, and safety. Our electrolyte also promotes the formation of self-limiting inorganic-rich interphases at the anode surface, alongside robust cathode-electrolyte interphase on iron-based Prussian blue analogues, mitigating electrode/electrolyte side reactions and preventing Fe dissolution. Notably, the PIBs employing our electrolyte exhibit exceptional durability, with 80% capacity retention after 2,000 cycles at high-voltage of 4.2 V in a coin cell. Impressively, in a larger scale pouch cell, it maintains over 81% of its initial capacity after 1,400 cycles at 1C-rate with high average Coulombic efficiency of 99.6%. This work represents a significant advancement toward the realization of safe, sustainable, and high-performance PIBs.

Tailoring Electric Double Layer by Cation Specific Adsorption for High-voltage Quasi-solid-state Lithium Metal Batteries.

The interfacial instability of high-nickel layered oxides severely plagues practical application of high-energy quasi-solid-state lithium metal batteries (LMBs). Herein, a uniform and highly oxidation-resistant polymer layer within inner Helmholtz plane is engineered by in-situ polymerizing 1-vinyl-3-ethylimidazolium (VEIM) cations preferentially adsorbed on LiNi0.83Co0.11Mn0.06O2 (NCM83) surface, inducing formation of anion-derived cathode-electrolyte interphase with fast interfacial kinetics. Meanwhile, the copolymerization of [VEIM][BF4] and vinyl ethylene carbonate (VEC) endows P(VEC-IL) copolymer with the positively-charged imidazolium moieties, providing positive electric fields to facilitate Li+ transport and desolvation process. Consequently, the Li||NCM83 cells with a cut-off voltage up to 4.5 V exhibit excellent reversible capacity of 130 mAh g-1 after 1000 cycles at 25 °C and considerable discharge capacity of 134 mAh g-1 without capacity decay within 100 cycles at -20 °C. This work provides deep understanding on tailoring electric double layer by cation specific adsorption for high-voltage quasi-solid-state LMBs.

A dual-functional electrolyte additive for stabilizing the solid electrolyte interphase and solvation structure to enable pouch sodium ion batteries with high performance at a wide temperature range from −30 °C to 60 °C

An electrolyte containing a sodium difluorophosphate (NaDFP) dual-functional additive is developed to enhance the temperature performance of NaNi0.33Fe0.33Mn0.33O2 (NFM)/hard carbon (HC) sodium-ion batteries (SIBs). The addition of NaDFP in the electrolyte not only induces solid electrolyte interphases (SEIs) and cathode electrolyte interphases with excellent properties on the anode and cathode surfaces but also optimizes of the solvation structure of sodium ions, resulting in a better cycle stability of NFM/HC SIBs over a wide temperature range from −30 °C to 60 °C. In addition, high capacity retentions of 85 % after 700 cycles at 25 °C, 90 % after 150 cycles at −10 °C and 90 % after 150 cycles at 45 °C are achieved, respectively. And those common problems such as gas generation and sodium evolution of pouch NFM/HC SIBs are also effectively relieved, indicating the promising application prospect of NaDFP additive in the functional electrolyte of NFM/HC SIBs.

Borate modified Co-free LiNi0.5Mn1.5O4 cathode material: A pathway to superior interface and cycling stability in LNMO/graphite full-cells

Cobalt-free LiNi0.5Mn1.5O4 (LNMO) holds great promise as a next-generation cathode material for high-energy and high-power density lithium-ion batteries (LIBs), making it a key contender for large-scale energy storage systems (ESS) and transportation applications. Despite its potential, the commercial utilization of LNMO has been impeded by its rapid capacity deterioration attributed to an unstable LNMO/electrolyte interface caused by the intrinsically high operating voltage of LNMO. Here, we present a pragmatic and scalable strategy to improve the LNMO/electrolyte interface through borate-based surface coating of the LNMO. Optimizing the coating process yielded high-rate capability and stable LNMO/electrolyte interface analyzed by extended float tests. Borate-LNMO materials show superior cycling stability at 25 °C and 45 °C, attributed to a robust cathode electrolyte interphase (CEI) formation. The bare LNMO and 0.25-B2O3-LNMO demostrated a cycling stability of around 41.20 % and 62.50 % respectively after 1000 cycles in LNMO/graphite full-cells. Post-mortem X-ray photoelectron spectroscopy (XPS) analysis revealed fewer side reaction products on borate-LNMO cathodes compared to bare LNMO. Additionally, scanning electron microscopy (SEM) revealed a thicker and denser solid-electrolyte interphase (SEI) layer on cycled graphite anodes from bare LNMO cells, while a thin and robust SEI was observed on graphite from borate-LNMO cells. Finally, we have conclusively demonstrated that the primary aging mechanism in LNMO/graphite full cells stems from the instability at the LNMO/electrolyte or/and graphite/electrolyte interface, rather than material-related degradation phenomenon. These compelling outcomes underscore the potential of cathode material surface coating in general and especially of borate coating on LNMO as a promising and cost-effective enabler for the use of LNMO in next-generation LIBs.

Quenching-Induced Ultrathin LiF-Rich Interphases on LiNi0.8Co0.1Mn0.1O2 Cathode

Nickel-rich layered oxides (NCM) are a promising contender material for the cathode electrode of high-energy lithium-ion batteries (LIBs) due to their large reversible capacity and high operating voltage. However, the poor surface/interfacial stability and the dissolution of transition metal ions hinder the commercial application of NCM. To create an artificial cathode electrolyte interphase (CEI) with LiF-rich inorganic phase on the NCM surface, a practical and efficient way of quenching the NCM powder from high temperature in 1,1,2,2-Tetrafluoroethyl 2,2,2-trifluoroethyl ether (HFE) was devised. With this artificial CEI film, the side reactions between NCM and electrolytes are inhibited, and the dissolution of TM ions is retarded. The quenched-NCM achieved fantastic cycling performance and suppressed voltage decay. Our research offers an efficient and worthy approach for improving the surface/interfacial stabilization of nickel-rich cathode materials for high-energy-density LIBs.

Boron- and calcium-interspersed cathode-electrolyte interphases on Ni-rich layered oxide cathodes for advanced performance lithium-ion batteries

Although Ni-rich layered oxides (Ni-rich NCM) have become the preferred cathode materials in the electric vehicle market, their unsustainable cycling behavior arising from the extremely high reactivity at the interface has become a formidable challenge. To alleviate this problem, we propose modifying the cathode-electrolyte interphase (CEI) of Ni-rich L-NCM cathodes by incorporating B/Ca functional groups. Dual-functionalized CEI layers are prepared by heating boric acid (H3BO3) and calcium oxide (CaO) in a one-step process. Islands of B- and Ca-functionalized CEI layer are observed at the Ni-rich L-NCM cathode, and the thickness is controlled to approximately 2.4 nm. The B-functional group not only lowers the concentration of residual lithium but also compensates for the longer Li+ migration distance by providing a desirable pathway based on ion-hopping sites. The Ca functional groups increase the mechanical rigidity of the Ni-rich L-NCM cathode, which inhibits the appearance of microcracks. In terms of its cycling behavior, the capacity retention of the cell with the B/Ca-incorporated Ni-rich L-NCM cathode improves markedly (72.4%), whereas the bare Ni-rich L-NCM material only retains 44.3% of its capacity after 100 cycles.

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

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

Gradient fluorination engineering through interdiffusion reaction for high-voltage LiCoO2

The advancement of high charging cut-off voltage stands as a crucial avenue to enhance the energy density of LiCoO2 (LCO). However, LCO faces severe interface and bulk phase issues at high voltage (≥ 4.6 V), resulting in poor cycling stability. In this study, we reconstruct the surface structure of LCO based on the interdiffusion reaction between LCO and MgF2 in a high-temperature sintering process. Specifically, this interdiffusion reaction yields an ultra-thin LiF coating layer, artificially reinforcing the chemical structure of the cathode-electrolyte interphase (CEI) during cycling. This LiF-rich CEI not only effectively protects the surface structure of LCO, but also facilitates the lithium-ion diffusion. Furthermore, the diffusion of F and Mg into the LCO lattice significantly strengthens the structure, which inhibits unfavorable phase transitions from the O3 phase to the H1-3 phase at high voltage. Consequently, such modified LCO with concurrently enhanced interface and bulk structure exhibits outstanding long-term cycling performance within 3.0–4.6 V at 1 C, achieving a capacity retention of 84.9% after 1000 cycles. Meanwhile, it also demonstrates excellent high-temperature performance, with a capacity retention of 85.0% after 200 cycles under 45 °C.

Long‐Life High‐Voltage Sodium‐Ion Batteries Enabled by Electrolytes with Cooperative Na+‐Solvation

AbstractStabilizing the electrode interphases is urgently required to enhance the lifetime of high‐voltage sodium‐ion batteries (SIBs). However, the continuous anode solid–electrolyte interphase (SEI) growth associated with electron leakage and the fragile cathode–electrolyte interphase (CEI) lead to capacity fade at high voltage; and yet the solvation‐interphase‐performance relationship is inadequately addressed. Herein, a cooperative Na+‐solvation strategy is reported to stabilize the interphases by a holistic design of electrolytes combining soft and moderate co‐solvents. The rationally regulated Na+‐solvation leads to CEI/SEI with the desired thickness and component stability. As such, remarkable cycling stability is achieved for 4.3‐V Na3V2O2(PO4)2F (NVOPF) cathodes with 83.3% capacity retention over 3000 cycles at 1 C, significantly outperforming the carbonate counterpart (41.6% capacity retention). Meanwhile, the restrained SEI growth via reducing the formation of electron‐leaking Na2CO3 stabilizes the long‐term cycling of the hard carbon (HC) anode. The assembled NVOPF||HC full cells achieve superior rate capability (up to 15 C) and stable cycling stability over 500 cycles. The demonstrated engineering of electrolyte chemistry, Na+‐solvation, and interphase structure/component contributes toward the rational establishment of design rules for high‐voltage SIBs and possibly other similar chemistries.

Low‐Strain and High‐Energy KVPO4F Cathode with Multifunctional Stabilizer for Advanced Potassium‐Ion Batteries

KVPO4F with excellent structural stability and high operating voltage has been identified as a promising cathode for potassium‐ion batteries (PIBs), but limits in sluggish ion transport and severe volume change cause insufficient potassium storage capability. Here, a high‐energy and low‐strain KVPO4F composite cathode assisted by multifunctional K2C4O4 electrode stabilizer is exquisitely designed. Systematical electrochemical investigations demonstrate that this composite cathode can deliver a remarkable energy density up to 530 Wh kg−1 with 142.7 mAh g−1 of reversible capacity at 25 mA g−1, outstanding rate capability of 70.6 mAh g−1 at 1000 mA g−1, and decent cycling stability. Furthermore, slight volume change (~5%) and increased interfacial stability with thin and even cathode–electrolyte interphase can be observed through in situ and ex situ characterizations, which are attributed to the synergistic effect from in situ potassium compensation and carbon deposition through self‐sacrificing K2C4O4 additive. Moreover, potassium‐ion full cells manifest significant improvement in energy density and cycling stability. This work demonstrates a positive impact of K2C4O4 additive on the comprehensive electrochemical enhancement, especially the activation of high‐voltage plateau capacity and provides an efficient strategy to enlighten the design of other high‐voltage cathodes for advanced high‐energy batteries.

Double additive electrolyte solvation engineering to achieve long cycle and high capacity sodium-ion battery

Sodium-ion batteries are a promising energy storage system due to their rich sodium resources and many other advantages. However, its development is severely hampered by the electrolyte's low compatibility with the electrode contact. Herein, we propose a solvation control strategy with ethoxy (pentafluoro) cyclotriphosphazene (PFPN) and NaClO4 double additives to reconstruct the solvation structure of sodium ions in electrolytes. This enables the electrolyte to form a dense and stable solid electrolyte interlayer (SEI) and double-layer cathode electrolyte interphase (CEI) on the surface of the electrode material to achieve long-cycle and high-capacity sodium-ion batteries. PFPN can form a stable SEI rich in inorganic components at the anode interface. ClO4- can first reach the cathode surface to create a NaCl and polymer-like chain CEI with sodium ions and solvents, and then the PFPN derivatives are migrated to the cathode surface to open the ring and decompose, thus forming a double-layer stable CEI. Therefore, the PEDN electrolyte can simultaneously improve the interface stability of the battery's cathode and anode solid electrolyte. Hence, the capacity retention rate of the 4.5 Ah Na3Fe2(PO4)P2O7 (NFP)||hard carbon (HC) pouch cell after 2500 cycles at 1C is 88.26%.