Cathode Electrolyte Interphase Layer Research Articles

A sacrificial separator facilitating in situ creation of a durable CEI layer and tailoring lithium dendrites for practical lithium metal batteries

The TBB–PE separator can form a robust and uniform boron-rich CEI (cathode electrolyte interphase) layer on the cathode surface via electrochemical oxidation as well as inhibit the growth of lithium dendrites by anion anchoring.

A facile approach to form an artificial CEI layer induced by residual Li compounds on LiNi0.9Co0.05Mn0.05O2 and Li6PS5Cl for all-solid-state batteries

All-solid-state batteries (ASSBs) are attracting significant attention as alternatives to conventional lithium-ion batteries due to their safety and higher energy density. However, electrochemical reactions between the solid electrolytes and active materials result in the degradation of electrochemical cell performances. A conventional approach is to employ protective layers onto the active materials, but this approach could have the drawback of being costly and time-consuming. The artificial cathode electrolyte interphase (CEI) layer generated by reactions between components within the electrode could provide a solution to these challenges. However, this approach can cause component degradation due to its intrinsically degradative nature of the forming process. In this study, we demonstrate the ASSBs with enhanced electrochemical performances by introducing lithium oxy-thiophosphate species (P-Ox-Sy-···Li+, LPOS) and LiCl artificial CEI layer, which could be spontaneously formed during heat treatment by chemical reactions between the solid electrolytes and residual Li compounds on the LiNi0.9Co0.05Mn0.05O2 (NCM) without the degradation. The LPOS-LiCl layer effectively suppresses the side reactions between solid electrolytes and NCM during the repeated electrochemical cyclings. As a result, the NCM full-cell (3.7 mAh cm−2) with the LPOS-LiCl artificial CEI layer exhibits 80.0 % cycle retention after 300 cycles at 0.2 C rate and room temperature. Moreover, it demonstrates 58 % higher Li-ion mobility and 36 % lower internal resistance after cycling compared to the NCM full-cell without the LPOS-LiCl artificial CEI layer.

Electrical Double Layer Formation at Intercalation Cathode–Organic Electrolyte Interfaces During Initial Lithium‐Ion Battery Reactions

AbstractInformation on the cathode/organic–electrolyte interface structure provides clues regarding the rate and reversibility of lithium intercalation reactions in lithium‐ion batteries. Herein, structural changes within the LiCoO2 electrode, throughout the interphase region, and in the LiPF6/propylene carbonate electrolyte are observed concurrently by in situ neutron reflectometry. The formation of an electrical double layer (EDL) during the early stages of charging and discharging is investigated and compared with that at an intercalation‐inactive Nb:SrTiO3 electrode. At the intercalation‐inactive interface between Nb:SrTiO3 and the electrolyte, a voltage‐dependent ionic distribution corresponding to the EDL forms on the electrolyte side without the formation of a cathode/electrolyte interphase (CEI) layer. In contrast, at the intercalation‐active LiCoO2/electrolyte interface, a CEI layer forms immediately after cell construction, and the ionic distribution in the electrolyte formed outside the CEI layer scarcely changes upon voltage application. The CEI/electrolyte interface is shielded from potential changes by the electronically insulating CEI; therefore, structural changes in the EDL are restricted. This supports the prevailing understanding that the CEI layer defines the rates of solvation/de‐solvation and adsorption/desorption reactions of lithium ions.

Promoting reversibility of layered potassium cathode through interstitial doping

With the increasing needs for large-scale and low-cost energy storage devices, Mn-based layered oxide cathodes have achieved considerable researching interests for potassium-ion batteries owing to their high energy density, abundant resource and low toxicity. However, their developments are challenged by the absence of suitable cathode materials to tolerate large-sized K-ion insertion/extraction and the presence of Jahn-Teller distortion of Mn3+. To address this issue, we present a strategy of embedding boron into interstitial tetrahedral sites to obtain a P3-K0.5Mn0.8Co0.2B0.1O2 cathode. Strong B-O covalent bonds facilitate the construction of robust orthorhombic framework and alleviate the undesired elongation of Mn-O bonds, contributing to excellent electrochemical performance. In addition, boron ions are verified to promote the formation of a homogeneous cathode electrolyte interphase layer, improving interfacial stability and realizing highly reversible cycling in a wide voltage range (1.4–4.3 V). This strategy provides a new pathway towards the development of high-performance cathode materials for potassium-ion batteries.

Trimethylsilyl Compounds for the Interfacial Stabilization of Thiophosphate-Based Solid Electrolytes in All-Solid-State Batteries.

Argyrodite-type Li6 PS5 Cl (LPSCl) has attracted much attention as a solid electrolyte for all-solid-state batteries (ASSBs) because of its high ionic conductivity and good mechanical flexibility. LPSCl, however, has challenges of translating research into practical applications, such as irreversible electrochemical degradation at the interface between LPSCl and cathode materials. Even for Li-ion batteries (LIBs), liquid electrolytes have the same issue as electrolyte decomposition due to interfacial instability. Nonetheless, current LIBs are successfully commercialized because functional electrolyte additives give rise to the formation of stable cathode-electrolyte interphase (CEI) and solid-electrolyte interphase (SEI) layers, leading to supplementing the interfacial stability between electrolyte and electrode. Herein, inspired by the role of electrolyte additives for LIBs, trimethylsilyl compounds are introduced as solid electrolyte additives for improving the interfacial stability between sulfide-based solid electrolytes and cathode materials. 2-(Trimethylsilyl)ethanethiol (TMS-SH), a solid electrolyte additive, is oxidatively decomposed during charge, forming a stable CEI layer. As a result, the CEI layer derived from TMS-SH suppresses the interfacial degradation between LPSCl and LiCoO2 , thereby leading to the excellent electrochemical performance of Li | LPSCl | LiCoO2 , such as superior cycle life over 2000 cycles (85.0% of capacity retention after 2000 cycles).

Solution-processed ZnO coated on LiNi0.8Mn0.1Co0.1O2(NMC811) for enhanced performance of Li-ion battery cathode

The LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material, widely used in Li-ion batteries (LIBs) for electric vehicles (EVs), has gained a fair amount of attention in the industry due to its advantages of high energy capacity and low production cost. However, during charge-discharge cycles, NMC811 cathode faces issues such as hydrofluoric acid (HF) attack, leaching of transition metals and unstable formation of the cathode electrolyte interphase (CEI), which leads to undermining cathode performance. To address these issues, extensive research has been conducted on coating materials based on metal oxides. In this study, our research team chose Li-doped ZnO (LZO) material, known for its high Li+ ion conductivity and structural stability. Employing sol-gel synthetic method, we successfully coated LZO material on commercial NMC811 particles, therefore ensuring its coating uniformity through X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy energy dispersive spectroscopy analyses. Evaluation of the coated samples (1 wt%, 2 wt%, and 3 wt% LZO on NMC811) revealed their superior electrochemical performance compared to bare NMC811; furthermore, the 2 wt% LZO-coated sample exhibited the highest cycling performance among the coated samples. These findings could be attributed to the lower charge transfer resistance verified by electrochemical impedance spectroscopy (EIS) analysis. Thus, we confirmed the LZO coating layers could provide stability for the NMC811 surface structure, mitigate the leaching of transition metal ions in the NMC811, and promote the formation of an enhanced CEI layer, therefore facilitating Li+ ion diffusion.

Carrageenan as A Sacrificial Binder for 5V LiNi0.5 Mn1.5 O4 Cathodes in Lithium-Ion Batteries.

5V-class LiNi0.5 Mn1.5 O4 (LNMO) with its spinel symmetry is a promising cathode material for lithium-ion batteries. However, the high-voltage operation of LNMO renders it vulnerable to interfacial degradation involving electrolyte decomposition, which hinders long-term and high-rate cycling. Herein, we overcome this longstanding challenge presented by LNMO by incorporating a sacrificial binder, namely, λ-carrageenan (CRN), a sulfated polysaccharide. This binder not only uniformly covers the LNMO surface via hydrogen bonding and ion-dipole interaction but also offers an ionically conductive cathode-electrolyte interphase layer containing LiSOx F, a product of the electrochemical decomposition of the sulfate group. Taking advantage of these two auspicious properties, the CRN-based electrode exhibited cycling and rate performance far superior to that of its counterparts based on the conventional poly(vinylidene difluoride) and sodium alginate binders. This study introduces a new concept, namely "sacrificial" binder, for battery electrodes known to deliver superior electrochemical performance but be adversely affected by interfacial instability. This article is protected by copyright. All rights reserved.

Boosting the “Solid–Liquid–Solid” Conversion Reaction via Bifunctional Carbonate‐Based Electrolyte for Ultra‐long‐life Potassium–Sulfur Batteries

AbstractPotassium–sulfur (K−S) batteries have attracted wide attention owing to their high theoretical energy density and low cost. However, the intractable shuttle effect of K polysulfides results in poor cyclability of K−S batteries, which severely limits their practical application. Herein, a bifunctional concentrated electrolyte (3 mol L−1 potassium bis(trifluoromethanesulfonyl)imide in ethylene carbonate (EC)) with high ionic conductivity and low viscosity is developed to regulate the dissolution behavior of polysulfides and induce uniform K deposition. The organic groups in the cathode electrolyte interphase layer derived from EC can effectively block the polysulfide shuttle and realize a “solid–liquid–solid” reaction mechanism. The KF‐riched solid‐electrolyte interphase inhibits K dendrite growth during cycling. As a result, the achieved K−S batteries display a high reversible capacity of 654 mAh g−1 at 0.5 A g−1 after 800 cycles and a long lifespan over 2000 cycles at 1 A g−1.

Boosting the "Solid-Liquid-Solid" Conversion Reaction via Bifunctional Carbonate-Based Electrolyte for Ultra-long-life Potassium-Sulfur Batteries.

Potassium-sulfur (K-S) batteries have attracted wide attention owing to their high theoretical energy density and low cost. However, the intractable shuttle effect of K polysulfides results in poor cyclability of K-S batteries, which severely limits their practical application. Herein, a bifunctional concentrated electrolyte (3 mol L-1 potassium bis(trifluoromethanesulfonyl)imide in ethylene carbonate (EC)) with high ionic conductivity and low viscosity is developed to regulate the dissolution behavior of polysulfides and induce uniform K deposition. The organic groups in the cathode electrolyte interphase layer derived from EC can effectively block the polysulfide shuttle and realize a "solid-liquid-solid" reaction mechanism. The KF-riched solid-electrolyte interphase inhibits K dendrite growth during cycling. As a result, the achieved K-S batteries display a high reversible capacity of 654 mAh g-1 at 0.5 A g-1 after 800 cycles and a long lifespan over 2000 cycles at 1 A g-1 .

Probing the Formation of Cathode-Electrolyte Interphase on Lithium Iron Phosphate Cathodes via Operando Mechanical Measurements.

Interfacial instabilities in electrodes control the performance and lifetime of Li-ion batteries. While the formation of the solid-electrolyte interphase (SEI) on anodes has received much attention, there is still a lack of understanding the formation of the cathode-electrolyte interphase (CEI) on the cathodes. To fill this gap, we report on dynamic deformations on LiFePO4 cathodes during charge/discharge by utilizing operando digital image correlation, impedance spectroscopy, and cryo X-ray photoelectron spectroscopy. LiFePO4 cathodes were cycled in either LiPF6, LiClO4, or LiTFSI-containing organic liquid electrolytes. Beyond the first cycle, Li-ion intercalation results in a nearly linear correlation between electrochemical strains and the state of (dis)-charge, regardless of the electrolyte chemistry. However, during the first charge in the LiPF6-containing electrolyte, there is a distinct irreversible positive strain evolution at the onset of anodic current rise as well as current decay at around 4.0 V. Impedance studies show an increase in surface resistance in the same potential window, suggesting the formation of CEI layers on the cathode. The chemistry of the CEI layer was characterized by X-ray photoelectron spectroscopy. LiF is detected in the CEI layer starting as early as 3.4 V and LixPOyFz appeared at voltages higher than 4.0 V during the first charge. Our approach offers insights into the formation mechanism of CEI layers on the cathode electrodes, which is crucial for the development of robust cathodes and electrolyte chemistries for higher-performance batteries.

In-situ constructed protective bilayer enabling stable cycling of LiCoO2 cathode at high-voltage

The practical application of high-voltage lithium cobalt oxide (LCO) has been hampered by the severe degradation of its structural integrity. In this work, a protective bilayer was fabricated on LCO surfaces by means of large-scale and facile electrolyte engineering. The protective bilayer consisting of a LiF-rich cathode-electrolyte interphase (CEI) as the outermost layer and a layer of disordered spinel structure as the inner layer was uniformly fabricated in-situ. The high-resistance CEI layer inhibited the fast transfer of Li ions from LCO to bulk electrolyte during the first few cycles, resulting in the significantly increased local overpotential on the LCO surface. As a consequence, the LCO surface underwent a phase transformation from the layered phase to the spinel phase first, forming the spinel phase inner layer due to the voltage rising beyond 4.55 V (vs. Li/Li+). The CEI and spinel layers effectively blocked the dissolution of transition-metal (TM) ions into the electrolyte during cycling and inhibited the formation of the structurally defective rock-salt phase that would hasten cycling-induced structural degradation. The formation of the protective bilayer effectively prevented the phase transition from the bulk layered LCO structure into spinel and then rock salt, thereby reducing decay of its cycling capacity. Remarkably, the graphite||LCO pouch cell with optimized electrolyte retained 78.9% of its capacity even after 1000 cycles under the operation voltage window of 3.0–4.55 V (vs. Li/Li+). This study provides guidance for the development of effective surface treatment strategies for stable layered cathodes with high capacity and cyclability.

Solid Electrolytes As Li-Ion Conducting Additive and Interfacial Stabilizer for High-Voltage Cathodes

Li-ion batteries (LIBs) have been a great facilitator to enable portable devices and electric vehicles (EVs) because of their high energy and power densities compared with other energy-storage devices. The high energy of LIBs is attributed to the high operating voltages of oxide-based cathodes (e.g., ~ 4 Vvs.Li) and wide electrochemical stability windows of organic liquid electrolytes (e.g., 1 – 4 Vvs.Li). In pursuit of extending energy density and lowering cost of LIBs further, R&D efforts have been devoted to finding the chemistries that can increase the cell operating voltages.However, increasing the voltages beyond the highest occupied molecular orbital (HOMO) of the electrolytes (c.a., ~ 4 Vvs.Li) leads to unwanted parasitic reactions at cathode-electrolyte interphase (CEI). In addition to the electrolyte oxidations at CEI, the reaction byproducts such as transition metal ions, HF, and CO2 can migrate to anodes and degrade their solid-electrolyte interphase (SEI) layers. As a result, high-voltage LIBs suffer from rapid capacity fading, growth of cell impedance, and gas generation.To mitigate the issue, various approaches have been proposed such as artificial CEI layer on cathode, tuning chemical compositions of cathodes, coating graphite anodes, using electrolyte additives, and adopting functional binders for cathodes. However, there is no simple solution to resolve all the complex issues occurring in the high-voltage cells. Considering that such parasitic reactions originate from the CEI and propagate to the SEI of anodes, there is a dire need of multimodal strategies that can create synergistic effect on stabilizing the electrode-electrolyte interphases in cell-level.Our research team has been developing multi-strategy that can coherently improve the high-voltage stability of LIB cells. Among them, we will present our recent approach of using solid-electrolyte (SE) powders as Li-ion conducting additive and interfacial stabilizer for high-voltage cathodes. As the proof-of-concept, Li6.7La3Zr1.7Ta0.3O12 (LLZT) SE was blended with Ni-rich Li(Ni1-xMnx/2Cox/2)O2 (NMC) or LiNi0.5Mn1.5O4 (LNMO) cathodes by relying on conventional electrode fabrication processes in LIB cells. This simple process offers advantages over the conventional coating methods in terms of manufacturing friendliness, energy saving, and cost effectiveness.Among various SE materials, garnet-type LLZT shows great promises based on its wide electrochemical stability window, good mechanical properties, and reasonable Li-ion conductivity (10-3 – 10-4 S/cm). First, the LLZT blended cathode significantly improved specific capacity and its retention during cycling at high voltages: e.g., 4.5 Vvs.Li for Ni-rich NMC and 5.0 Vvs.Li for LNMO spinel. Compared with the SE-free cathodes (baseline samples), the SE blended cathodes consistently delivered improved specific capacities, capacity retentions, and Coulombic efficiencies in full-cells made with graphite anodes.The improvement mechanism of the LLZT blended cathodes can be explained by two folds. First, LLZT contacts with cathodes (e.g., NMC or LNMO) and improves Li-ion transport properties of CEI layer, as evidenced by electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analyses. Second, LLZT can scavenge moisture/proton in the liquid electrolytes and subsequently suppress the degradation of CEI and SEI layers during extended cycles, as evidenced by X-ray photoelectron spectroscopy (XPS). As a result, 5 wt% LLZO blended cathodes delivered a stable electrochemical performance even at the presence of 5000 ppm moisture (and thus HF) in an electrolyte. In contrast to the traditional surface coating methods, solid-electrolyte blending approach is cost-effective and manufacturing/environmentally friendly, and thereby can serve as a practical pathway for improving performances and stability of current battery cells for EV and small electronics.

Insights into the Chemistry of the Cathodic Electrolyte Interphase for PTFE-Based Dry-Processed Cathodes.

Dry processing is a promising method for high-performance and low-cost lithium-ion battery manufacturing which uses polytetrafluoroethylene (PTFE) as a binder. However, the electrochemical stability of the PTFE binder in the cathodes and the generated chemistry of the cathode electrolyte interphase (CEI) layers are rarely reported. Herein, the CEI properties and PTFE electrochemical stability are studied via cycling the high-loading dry-processed electrodes in electrolytes with LiPF6 or LiClO4 salt. Using LiClO4 salt can eliminate other possible F sources, allowing the decomposition of PTFE to be studied. The detection of LiF in cells with the LiClO4 salt confirms that PTFE undergoes side reaction(s) in the cathodes. When compared with LiClO4, the CEI layer is much thicker when LiPF6 is used as the electrolyte salt. These results provide insights into the CEI layer and may potentially enlighten the development of binders and electrolytes for the high efficiency and long durability of DP-based LIBs.

Li0.5La0.5TiO3 as an Ionic Conducting Additive Enhancing the High-Voltage Performance of LiNi0.8Mn0.1Co0.1O2 Cathodes in Lithium-Ion Batteries.

Although high-voltage (e.g., >4.3 VvsLi) operation can increase specific capacity and energy of Ni-rich NMC cathodes, it accelerates the oxidative decomposition of electrolytes and surface degradation of NMC cathodes, leading to rapid capacity fading. This work presents a novel approach that employs Li0.5La0.5TiO3 (LLTO) solid-electrolyte as a Li-ion conductor and surface passivation agent to stabilize the cathode/electrolyte interphase (CEI) layer of the LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode and enhance its high-voltage performances. The LLTO particles improve Li-ion transportation across the CEI layer, as evidenced by its reduced impedance in Nyquist plots. Furthermore, passivation of CEI by LLTO mitigates parasitic reactions (e.g., transition metal dissolution) that occur on the graphite solid electrolyte interphase layer during extended cycles of pouch-cells. As a result, pouch-cells with the 1 or 5 wt % LLTO-blended NMC811 cathodes can deliver 19-23% increase in specific capacity and improved cycle life (1000 cycles) at high voltages (up to 4.4 V), comparing to bare NMC811 cathodes. Post-mortem characterization of pouch-cells quantitatively identified the degradation sources of NMC811 cathode at high-voltages, which highlighted the improvement mechanisms of LLTO blended-cathodes.

Synergistic interphase modification with dual electrolyte additives to boost cycle stability of high nickel cathode for all-climate battery

B-containing electrolyte additives are widely used to enhance the cycle performance at low temperature and the rate capability of lithium-ion batteries by constructing an efficient cathode electrolyte interphase (CEI) to facilitate the rapid Li+ migration. Nevertheless, its wide-temperature application has been limited by the instability of B-derived CEI layer at high temperature. Herein, dual electrolyte additives, consisting of lithium tetraborate (Li2TB) and 2, 4-difluorobiphenyl (FBP), are proposed to boost the wide-temperature performances of LiNi0.6Co0.2Mn0.2O2 (NCM) cathode. Theoretical calculation and electrochemical performances analyses indicate that Li2TB and FBP undergo successive decomposition to form a unique dual-layer CEI. FBP acts as a synergistic filming additive to Li2TB, enhancing the high-temperature performance of NCM cathode while preserving the excellent low-temperature cycle stability and the superior rate capability conferred by Li2TB additive. Therefore, the capacity retention of NCM||Li cells using optimal FBP-Li2TB dual electrolyte additives increases to 100% after 200 cycles at −10 °C, 99% after 200 cycles at 25 °C, and 83% after 100 cycles at 55 °C, respectively, much superior to that of base electrolyte (63%/69%/45%). More surprisingly, galvanostatic charge/discharge experiments at different temperatures reveal that NCM||Li cells using FBP-Li2TB additives can operate at temperatures ranging from −40 °C to 60 °C. This synergistic interphase modification utilizing dual electrolyte additives to construct a unique dual-layer CEI adaptive to a wide temperature range, provides valuable insights to the practical applications of NCM cathodes for all-climate batteries.

Triallyl Borate as an Effective Separator/Cathode Interphase Modifier for Lithium-ion Batteries

Ni-rich layered oxides cathode has recently gained attention as an advanced cathode material due to their applicable energy density. However, as the Ni component in the layered site is increased, the high reactivity of Ni<sup>4+</sup> results in parasitic reaction associated with decomposing electrolyte, which leads to a rapid decreasing the lifespan of the cell. The electrolyte additive triallyl borate (TAB) improves interfacial stability, leading to a stable cathode–electrolyte interphase (CEI) layer on the LNCM83 cathode. A multi-functionalized TAB additive can produce a uniformly distributed CEI layer via electrochemical oxidation, which implies an increase in long-term cycling performance. After 100 cycles at elevated temperature, the cell tested by 0.75 TAB retained 88.3% of its retention ratio, whereas the cell performed by TAB-free electrolyte retained 64.1% of its retention. Once the TAB additive formed CEI layers on the LNCM83 cathode, it inhibited the decomposition of carbonate-based solvents species in addition to the dissolution of transition metal components from the cathode. The addition of TAB to LNCM83 cathode material is believed to be a promising way to increase the electrochemical performance.

Osmotically Delaminated Silicate Nanosheet-Coated NCM for Ultra-Stable Li+ Storage and Chemical Stability Toward Long-Term Air Exposure.

To ensure the safety and performance of lithium-ion batteries (LIBs), a rational design and optimization of suitable cathode materials are crucial. Lithium nickel cobalt manganese oxides (NCM) represent one of the most popular cathode materials for commercial LIBs. However, they are limited by several critical issues, such as transition metal dissolution, formation of an unstable cathode-electrolyte interphase (CEI) layer, chemical instability upon air exposure, and mechanical instability. In this work, coating fabricated by self-assembly of osmotically delaminated sodium fluorohectorite (Hec) nanosheets onto NCM (Hec-NCM) in a simple and technically benign aqueous wet-coating process is reported first. Complete wrapping of NCM by high aspect ratio (>10000) nanosheets is enabled through an electrostatic attraction between Hec nanosheets and NCM as well as by the superior mechanical flexibility of Hec nanosheets. The coating significantly suppresses mechanical degradation while forming a multi-functional CEI layer. Consequently, Hec-NCM delivers outstanding capacity retention for 300 cycles. Furthermore, due to the exceptional gas barrier properties of the few-layer Hec-coating, the electrochemical performance of Hec-NCM is maintained even after 6 months of exposure to the ambient atmosphere. These findings suggest a new direction of significantly improving the long-term stability and activity of cathode materials by creating an artificial CEI layer.

Construction of Inorganic-Rich Cathode Electrolyte Interphase on Co-Free Cathodes.

Lithium-rich layered oxides (LRLOs), with the chemical formula of xLi2MnO3·(1 - x)LiMO2, delivering higher specific discharge capacity, are potential cathode materials for lithium-ion batteries. However, the dissolution of transition metal ions and the instability of the cathode-electrolyte interphase (CEI) hinder the commercial application of LRLOs. Herein, a simple and affordable method is developed for the construction of a robust CEI layer by quenching a kind of cobalt-free LRLO, Li1.2Ni0.15Fe0.1Mn0.55O2 (denoted as NFM), in 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether solvent. This robust CEI, with well-distributed LiF, TMFx, and partial organic component CFx, performs as a physical barrier to prevent NFM from direct contact with the electrolyte, suppresses the oxygen release, and ensures the CEI layer stability. The customized CEI with LiF and TMFx-rich phase considerably enhances the NFM cycle stability and the initial coulomb efficiency and inhibits voltage fading. This work provides a valuable strategy for designing stable interface chemistry on the cathode of lithium-ion batteries.

Full-Dimensional Analysis of Electrolyte Decomposition on Cathode-Electrolyte Interface: Establishing Characterization Paradigm on LiNi0.6Co0.2Mn0.2O2 Cathode with Potential Dependence.

Cathode electrolyte interphase (CEI) layers derived from electrolyte oxidative decomposition can passivate the cathode surface and prevent its direct contact with electrolyte. The inorganics-dominated inner solid electrolyte layer (SEL) and organics-rich outer quasi-solid-electrolyte layer (qSEL) constitute the CEI layer, and both merge at the junction without a clear boundary, which assures the CEI layer with both ionic-conducting and electron-blocking properties. However, the typical "wash-then-test" pattern of characterizations aiming at the microstructure of CEI layers would dissolve the qSEL and even destroy the SEL, leading to an overanalysis of electrolyte decomposition pathway and misassignment of CEI architecture (e.g., component and morphology). In this study, we established a full-dimensional characterization paradigm (combining Fourier transform infrared, solution NMR, X-ray photoelectron spectroscopy, and mass spectrometry technologies) and reconstructed the original CEI layer model. Besides, the feasibility of this characterization paradigm has been verified in a wide operating voltage range on a typical LiNixMnyCozO2 cathode.

An Artificial MnWO4 Cathode Electrolyte Interphase Enabling Enhanced Electrochemical Performance of δ-MnO2 Cathode for Aqueous Zinc Ion Battery.

The dissolution of active material in aqueous batteries can lead to a rapid deterioration in capacity, and the presence of free water can also accelerate the dissolution and trigger some side reactions that affect the service life of aqueous batteries. In this study, a MnWO4 cathode electrolyte interphase (CEI) layer is constructed on a δ-MnO2 cathode by cyclic voltammetry, which is effective in inhibiting the dissolution of Mn and improving the reaction kinetics. As a result, the CEI layer enables the δ-MnO2 cathode to produce a better cycling performance, with the capacity maintained at 98.2% (vs. activated capacity at 500 cycles) after 2000 cycles at 10 A g-1. In comparison, the capacity retention rate is merely 33.4% for pristine samples in the same state, indicating that this MnWO4 CEI layer constructed by using a simple and general electrochemical method can promote the development of MnO2 cathodes for aqueous zinc ion batteries.