Dissolved Metal Ions Research Articles

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.

Restraining migration and dissolution of transition-metal-ions via functionalized separator for Li-rich Mn-based cathode with high-energy-density

Lithium-rich manganese-based materials (LRMs) are promising cathode for high-energy-density lithium-ion batteries due to their high capacity, low toxicity, and low cost. However, LRMs suffer from serious voltage decay and capacity fade due to continual migration and dissolution of transition metal ions (TMs) during cycling process. Herein, a novel strategy is proposed to inhibit the TMs migration of LRMs through a modified separator by means of functionalized carbon coating layer, which depends on the chemical constraint of the abundant functional groups in the modified super P. In addition, it has been found that the dissolution of TMs can be restrained based on the Le Chatelier’s principle. Moreover, the modified separator owns good wettability toward the electrolyte. As a result, the LRMs cathode with the modified separator delivers a high discharge capacity of 329.93 mA h g−1 at 0.1 C, and achieves good cyclic performance, the enhanced reaction kinetics and low voltage decay. Therefore, this work provides a new idea to promote the comprehensive electrochemical performances of Li-ion batteries with LRMs cathode through a strategy of separator modification.

Efficient mineralization of coal pyrolysis wastewater in a heterogeneous electro-Fenton system using a novel Fe3O4-LaFeO3/C/GF heterojunction cathode

A bifunctional electro-Fenton (EF) cathode with Fe3O4-LaFeO3/C embedded graphite felt (GF) was synthesized through a hydrothermal process, which was used for in situ electrochemical formation of active oxygen species (ROS) for coal pyrolysis wastewater (CPW) removal. Experimental results illustrated that the mineralization efficiency of dimethylphenol (DMP) was achieved at 90.7 % within 150 min reaction. On the basis of quenching test and free radical detection, the ∙OH and ∙O2− were the detectable ROS in the hetero-EF system for DMP removal. Meanwhile, the formed oxygen vacancies (OVs) and the redox of Fe2+/Fe3+ promoted the oxygen adsorption and H2O2 activation. Density functional theory (DFT) calculations further discussed that the Fe3O4-LaFeO3 interface possessed more downward spin density of states in the conduction band, resulting in a higher total density of states (DOS) value near the Fermi level. Moreover, the Fe3O4-LaFeO3/C/GF cathode displayed good recyclability with low metal ion dissolution for 5 times (99.5 % DMP removal and 78.6 % TOC removal) and underlying actual CPW application potential (80.2 % of COD removal and 100 % of total phenol (Tph) removal). Overall, this work invented a novel and stable bifunctional cathode for the efficient removal of refractory CPW in the hetero-EF system.

High-Voltage and High-Temperature LiCoO2 Operation via the Electrolyte Additive of Electron-Defect Boron Compounds

Commercial LIBs have the problem of instability interface of electrolyte/cathode at high voltage and high temperature. This work reports a novel series of electron-defect boron compounds to construct stable interfaces of LCO/electrolyte. The results of theoretical calculation indicate that compounds of DPD scaffold can win in the competitive oxidation decomposition for interface regulation. F-rich and B-rich interface is designed by modifying the functional group of DPD scaffold. This strategy of in situ interface design successfully suppresses the dissolution of harmful transition metal ions and the nucleophilic reaction between electrolyte and cathode. Li/LCO cell can remain stable at high voltage (4.5 V) and high temperature (70 °C) in commercial carbonate electrolyte after DPD-F interphase formation. Meanwhile, faster Li+ extraction and insertion kinetics of DPD-F-interface make the Li/LCO cell stable at 4.6 V. Spectral characterizations and theoretical calculations uncover the secret of the forming process of this DPD-F-interface.

Rational Design of a Stable Fe‐rich Ni‐Fe Layered Double Hydroxide for the Industrially Relevant Dynamic Operation of Alkaline Water Electrolyzers

AbstractNickel‐iron layered double hydroxides (Ni‐Fe LDHs) consist of stacked Fe3+‐doped positively charged Ni‐hydroxide layers containing charge‐balancing anions and water molecules between the layers. Although Ni‐Fe LDHs are highly active in the oxygen evolution reaction (OER) under alkaline conditions, their poor operational stability remains an issue. Herein, based on density functional theory calculations, it is proposed that the inclusion of a higher Fe content (>40%) than the theoretical Fe3+ limit (≈25%) permitted by Ni‐Fe LDHs can lead to improved structural stability. An Fe‐rich Ni‐Fe LDH electrode is therefore prepared via a growth strategy based on the controlled oxygen corrosion of an Fe substrate, by enabling the incorporation of additional Fe2+ into the Ni2+‐Fe3+ LDH structure. Indeed, microstructural and elemental analysis confirm the presence of additional Fe2+. This Fe‐rich Ni‐Fe LDH electrode not only offers a low OER overpotential (≈270 mV at 200 mA cm−2) but also exhibits an excellent operational stability under dynamic operating environments without any significant performance degradation or metal ion dissolution. Finally, the practical feasibility of the Fe‐rich Ni‐Fe LDH electrode is demonstrated in a single‐cell (34.56 cm2) operation. These findings are expected to aid in the development of reliable OER electrodes for use in commercial water electrolyzers.

Dual Modification of Stainless Steel by Small Molecule Oxalic Acid for Oxygen Evolution Reaction

A electrocatalyst with low cost and high performance is the key to achieve the industrial application of hydrogen energy. In this work, inexpensive commercial stainless steel is modified by a simple hydrothermal method. For the first time, surface corrosion modification and active substance loading are realized simultaneously with small-molecule oxalic acid. Compared with 304-type stainless steel mesh (SSM-304), the overpotential of the sample after two-step treatment (noted as OESSM) is largely decreased (125 mV), and exceptional stability (48 h) is achieved. In acidic hydrothermal corrosion, the metal on the surface of stainless steel is eroded into the solution. Then, the C2O42– recomplexes with the dissolved metal ions, and the oxalate is grown on the surface. The excellent catalytic activity and stability come from the unique framework structure of the metal oxalate crystals. Oxalic acid is widely available and with double carboxyl group in C2O42–. The electrons enriched in C═O can enhance the adsorption energy on the catalyst surface and induce the production of active catalytic sites *OOH. In addition, the oxalate crystal framework provides critical support for maintaining positive catalytic activity and stability. This work creates the possibility of realizing the large-scale application of stainless steel-based electrocatalysts in actual production.

Metal ion/metal hydroxide loaded resin for ammonia removal from solutions containing high salinity by ligand exchange: Stability of metal ions during decomplexation of ammonia ligand

Ligand exchange of ammonia with ammine-complexing transition metals loaded on the substrate has received more attention for removing ammonia from solutions containing high salinity. However, the stability between transition metal and substrate was destroyed by the desorbent in the process of the ligand exchanger recycling and ammonia ligand decomplexation, leading to metal elution and reducing the adsorption competency of the ligand exchanger. Herein, metal(ion)-loaded resins (Me(ion)-LR) were prepared and the stability of metal ions during the three-round ammonia adsorption–desorption process was studied. The results showed the ammonia adsorption capacity of Cu2+-D751, Cu2+/Ni2+-D751 and Cu2+/Zn2+-D751 resin were 5.39, 5.80 and 5.65 mg/g, respectively and the shedding percent of Cu2+ is lower than that of Ni2+ and Zn2+. Aimed for the high ammonia selectivity and low metal ion dissolution, metal(ion)-loaded resins were modified with NaOH to obtain metal(hydroxides)-loaded resins (Me(hydroxides)-LR). The stability of metal ions during the three-round ammonia adsorption–desorption process was also investigated. Meanwhile, the mechanism of the Me(hydroxides)-LR for ammonia removal was explored. The results suggested that the Cu(OH)x-D751, Cu(OH)x/Ni(OH)x-D751 and Cu(OH)x/Zn(OH)x-D751 resin have higher ammonia adsorption capacity and reached 5.79, 8.25 and 7.94 mg/g, respectively. The shedding percent of Cu2+ and Zn2+ decreased obviously. Experimental and characterization results show that the ammonia removal by Me(hydroxides)-LR was primarily due to coordination complexation and electrostatic interaction.

Investigating the leaching performance of ferric chloride solution for metallic alloys resulting from reduction smelting of spent lithium-ion batteries

Smelting reduction of spent lithium-ion batteries (LIBs) produces metallic alloys containing Co, Ni, Cu, Mn, and Fe. Finding suitable reagents in terms of efficiency, economics, and friendly environment for the dissolution of these metals from the alloys is very important for the recovery process of the metals. In this work, the employment of ferric chloride solution for the dissolution of the metals from the alloys was studied. The effect of parameters like FeCl3 concentration, temperature, time, and pulp density on the leaching efficiency of metals was investigated. Our results indicate that ferric ions in the leaching solutions act as oxidizing agents for the dissolution of the metals, while chloride anions as ligands for the formation of the complexes of the dissolved metal ions. The best conditions for the dissolution of full metals were 0.7 mol/L FeCl3, 12.5 g/L pulp density, 22oC, and 30 min. In comparison with HCl or H2SO4 leaching agents, ferric chloride shows some advantages like a decrease in the dosage of acids and oxidizing agents, fast reaction kinetics, and low energy consumption. With its advantages, ferric chloride solution is considered a potential leaching agent in the recovery process of valuable metals from spent LIBs.

One-step electrochemical in-situ Li doping and LiF coating enable ultra-stable cathode for sodium ion batteries

Despite of the higher energy density and inexpensive characteristics, commercialization of layered oxide cathodes for sodium ion batteries (SIBs) is limited due to the lack of structural stability at the high voltage. Herein, the one-step electrochemical in-situ Li doping and LiF coating are successfully achieved to obtain an advanced Na0.79Lix[Li0.13Ni0.20Mn0.67]O2@LiF (NaLi-LNM@LiF) cathode with superlattice structure. The results demonstrate that the Li+ doped into the alkali metal layer by electrochemical cycling act as “pillars” in the form of Li-Li dimers to stabilize the layered structure. The supplementation of Li to the superlattice structure inhibits the dissolution of transition metal ions and lattice mismatch. Furthermore, the in-situ LiF coating restrains side reactions, reduces surface cracks, and greatly improves the cycling stability. The electrochemical in-situ modification strategy significantly enhances the electrochemical performance of the half-cell. The NaLi-LNM@LiF exhibits high reversible specific capacity (170.6 mA h g−1 at 0.05 C), outstanding capacity retention (92.65% after 200 cycles at 0.5 C) and excellent rate performance (80 mA h g−1 at 7 C) in a wide voltage range of 1.5–4.5 V. This novel method of in-situ modification by electrochemical process will provide a guidance for the rational design of cathode materials for SIBs.

Mo–F Co-Doping LiNi0.83Co0.11Mn0.06O2 Stabilizes the Structure and Induces Compact Primary Particle To Improve the Electrochemical Performance

The Li+/Ni2+ cation disorder, material pulverization, surface phase transition, and transition metal (TM) ion dissolution are important issues that plague nickel-rich layered oxide cathode materials. In this paper, doping LiNi0.83Co0.11Mn0.06O2 with Mo6+ cation and F– anion effectively alleviates the above problems. The Mo6+ reduces the cations mixing, and the strong electronegativity of F strengthens the bonding with transition metal ions to resist HF corrosion. Furthermore, compact primary particles with interfused and radially aligned morphology induced by Mo–F co-doping reduce stress damage during cycling. The enhancement of electrochemical performance by Mo–F co-doping is systematically researched in terms of structure, morphology, secondary spherical pulverization, structural phase transition, and dissolution of transition metal ions.

Factors affecting the toxicity and oxidative stress of layered double hydroxide-based nanomaterials in freshwater algae

Layered double hydroxide (LDH) nanomaterials are utilized extensively in numerous fields because of their distinctive structural properties. It is critical to understand the environmental behavior and toxicological effects of LDHs to address potential concerns caused by their release into the environment. In this work, the toxicological effects of two typical LDHs (Mg-Al-LDH and Zn-Al-LDH) on freshwater green algae (Scenedesmus obliquus) and the main affecting factors were examined. The Zn-Al-LDH exhibited a stronger growth inhibition toxicity than the Mg-Al-LDH in terms of median effect concentration. This toxicity difference was connected to the stability of particle dispersion in water and the metallic composition of LDHs. The contribution of the dissolved metal ions to the overall toxicity of the LDHs was lower than that of their particulate forms. Moreover, the joint toxic action of different dissolved metal ions in each LDH belonged to additive effects. The Mg-Al-LDH induced a stronger oxidative stress effect in algal cells than the Zn-Al-LDH, and mitochondrion was the main site of LDH-induced production of reactive oxygen species. Scanning electron microscope observation indicated that both LDHs caused severe damage to the algal cell surface. At environmentally relevant concentrations, the LDHs exhibited joint toxic actions with two co-occurring contaminants (oxytetracycline and nano-titanium dioxide) on S. obliquus in an additive manner mainly. These findings emphasize the impacts of the intrinsic nature of LDHs, the aqueous stability of LDHs, and other environmental contaminants on their ecotoxicological effects.

Rescue the cycle life of LiNi0.5Mn1.5O4 cathode on high voltage via glyceryl triacetate as the multifunction additive

The poor cyclic stability is the key point to restricting the commercial application of LNi0.5Mn1.5O4-based lithium-ion batteries (LNMO-based LIBs) on high voltage (5 V-class). Once the working voltage is over 4.3 V, the parasitic reactions on the LNMO interphase will be the trigger for a series of problems such as the continuous decomposition of electrolytes and dissolution of transition metal ions. The glyceryl triacetate (GT) has been used as a functional additive to reconstruct a cathode electrolyte interphase (CEI) film to suppress the parasitic reactions and safeguard the LNMO structure. Compared to the influence of GT and propionic anhydride (PA) on the electrochemical performance of LNMO on high voltage, the LNMO/Li cell with GT exhibits exciting discharge capacity retention of 84.9 % compared with PA (17.6 %) and base electrolyte (BE, 8.6 %) after 500 cycles at 1C. The LNMO/Li cell with GT also has a remarkable rate performance in which capacity retention of 5C/2C is 85.7%, higher than 0.5 wt% PA (75.5%) and BE (62.1%). By characterizations, it is reasoningly demonstrated that the GT not only can be preferentially oxidized to form a robust CEI film on the LNMO surface to prevent the parasitic reaction but also rapidly capture the free transition metal ions and bind trace H2O in the electrolyte to improve the stability of LIBs. Simultaneously, the electrons from the carboxyl group of GT occupy the d-orbital of transition metal from LNMO, further effectively reducing the activity of LNMO. Particularly, the glycerol generated by the reaction of GT with H2O can effectively capture HF, H2O, and other small molecules under hydrogen-bond interaction, thereby improving the stability of LNMO LIBs.

Weakly Solvating Cyclic Ether Electrolyte for High-Voltage Lithium Metal Batteries

The commercialization of high-voltage lithium (Li) metal batteries (LMBs) has been severely hindered due to the lack of advanced electrolytes that can simultaneously support a stable lithium metal anode (LMA) and high-voltage cathode (>4 V vs Li+/Li). Here, we propose a tetrahydropyran (THP)-based weakly solvating electrolyte (WSE) to regulate Li+ solvation structures and interfacial behaviors. The anion-rich Li+ solvation in THP-based WSE effectively promotes the formation of inorganic-rich solid electrolyte interphase (SEI) layers, firm cathode electrolyte interphase (CEI) films, and protective passivation films on an Al current collector. The optimized interfacial behaviors contribute to the highly compact Li deposition, high-voltage stability, and inhibition of transition metal ion dissolution and Al corrosion. Finally, the Li||LiNi0.5Co0.2Mn0.3O2 full cell delivered stable cycling performance at high cutoff voltages of 4.3 and even 4.5 V. This study demonstrates an exciting approach to enable ether-based electrolytes for high-voltage LMBs and could be developed for other battery systems.

Interface Engineering via Regulating Electrolyte for High-Voltage Layered Oxide Cathodes-Based Li-Ion Batteries.

Li-rich and Ni-rich layered oxides as next-generation high-energy cathodes for lithium-ion batteries (LIBs) possess the catalytic surface, which leads to intensive interfacial reactions, transition metal ion dissolution, gas generation, and ultimately hinders their applications at 4.7V. Here, robust inorganic/organic/inorganic-rich architecture cathode-electrolyte interphase (CEI) and inorganic/organic-rich architecture anode-electrolyte interphase (AEI) with F-, B-, and P-rich inorganic components through modulating the frontier molecular orbital energy levels of lithium salts are constructed. A ternary fluorinated lithium salts electrolyte (TLE) is formulated by mixing 0.5m lithium difluoro(oxalato)borate, 0.2m lithium difluorophosphate with 0.3m lithium hexafluorophosphate. The obtained robust interphase effectively suppresses the adverse electrolyte oxidation and transition metal dissolution, significantly reduces the chemical attacks to AEI. Li-rich Li1.2 Mn0.58 Ni0.08 Co0.14 O2 and Ni-rich LiNi0.8 Co0.1 Mn0.1 O2 in TLE exhibit high-capacity retention of 83.3% after 200 cycles and 83.3% after 1000 cycles under 4.7V, respectively. Moreover, TLE also shows excellent performances at 45 °C, demonstrating this inorganic rich interface successfully inhibits the more aggressive interface chemistry at high voltage and high temperature. This work suggests that the composition and structure of the electrode interface can be regulated by modulating the frontier molecular orbital energy levels of electrolyte components, so as to ensure the required performance of LIBs.

New insight into the mechanism of ferric hydroxide-based heterogeneous Fenton-like reaction.

The heterogeneous Fenton-like reaction (HeFR) has always been a research focus for environmental applications. However, it has long been difficult to reach a consensus on the reaction mechanism because the process of metal ions dissolution and its role were not well understood. In this paper, we propose the courses of organics-mediated coordination or/and reduction dissolution of ferric hydroxide to initiate the autocatalytic kinetics of phenol degradation and illustrate it through density functional theory (DFT) and experiments. With the increase of hydrogen peroxide concentration, the degradation of phenol changes from autocatalytic kinetics to first-order kinetics. Furthermore, a novel "limit segmentation method" initiated by us indicates that homogeneous reaction plays a decisive role in the phenol degradation process. The dominant roles of the reactive organics in both iron dissolution and the iron cycle and of the homogeneous reaction in the whole degradation process in the ferric hydroxide-based HeFR system are brand-new insights that pave the pathway for future research.

Improving Membrane Filtration for Copper Speciation: Optimal Salt Pretreatments of Polyethersulfone Membranes to Prevent Analyte Retention.

Membrane filtration has been increasingly used to separate dissolved metal ions from dispersed particles, commonly using ultrafiltration membranes, for example, polyethersulfone (PES) membranes with a molecular weight cut-off of 3 kDa. The disadvantage of this technique is an undesired retention of ions, resulting from Coulomb interactions with sulfonic acid groups of the membrane. Therefore, such a membrane acts similar to a cation exchanger column. We solved this drawback by a pretreatment of the PES membrane by other cations. Using CuSO4 as a model compound, we compared the effectiveness of five cations using their salt solutions (Ca2+, Mg2+, Fe2+, Ag+, Ba2+) as pretreatment agents and identified the most effective pretreatment component for a high recovery of copper ions. After membrane filtration without pretreatment, only 52 ± 10%, 64 ± 5%, 75 ± 8%, and 89 ± 7% of nominal Cu concentrations were obtained using initial concentrations of 0.2, 0.5, 1.0, and 4.0 mg L-1, respectively. The efficiency of the investigated cations increased in the order Fe < Ag < Mg < Ca < Ba. Furthermore, we analyzed the most efficient concentration of the pretreatment agent. The best performance was achieved using 0.1 mol L-1 CaCl2 which increased copper recovery to slightly below 100%, even at the lowest tested Cu concentration (recovery 93 ± 10% at 0.2 mg L-1). In the environmentally relevant Cu concentration range of 0.2 mg L-1, 0.1 mol L-1 BaCl2 was identified as the most efficient pretreatment (103 ± 11%).

Flavone as a novel multifunctional electrolyte additive to improve the cycle performance of high-voltage LiNi0.5Mn1.5O4 batteries

The high operating voltage of LiNi0.5Mn1.5O4 (LNMO) material poses a challenge to conventional carbonate-based electrolyte, whose continuous decomposition leads to the fast capacity fading of battery. Herein, flavone (FLA) as a novel multifunctional electrolyte additive is introduced into basic electrolyte (1.0 M LiPF6 - ethylene carbonate + dimethyl carbonate) to significantly improve the cycle performance of LNMO/Li battery. Experiments and density functional theory (DFT) calculations manifest that FLA can be preferentially oxidized and reduced to generate stable surface films to ameliorate the decomposition of other electrolyte solvent. Besides, the FLA-derived Li2CO3-rich surface films can improve interfacial stability and ensure high ionic conductivity. In addition, FLA is more inclined to react with HF compared with EC and DMC, thereby alleviating LNMO corrosion and transition metal ions dissolution by HF, and consequently enhance the stability of bulk structure. The preferential reduction of FLA contributes to the formation of a stable passivation layer with high ionic conductivity on Li anode, which is conducive to uniform lithium deposition during the cycling and prolonging battery cycle life. The cycle performances of LNMO/Li and LNMO/Graphite batteries using the electrolyte containing 1 wt% FLA are significantly improved compared with those using basic electrolyte.

Combined effect of Cu- and ZnO- NPs on antibiotic resistance genes in an estuarine water

Most studies of whether and how nanoparticles (NPs) affect antibiotic resistance genes (ARGs) focus on testing single NPs type. In this study, we determined the combined effect of Cu- and ZnO- NPs in the water samples collected from the Yangtze River Estuary and found the effect differs greatly from that produced by individual NPs. The results showed that the Cu- and ZnO- NPs co-exposure resulted in an enrichment of ARGs, whereas individual Cu- and ZnO- NPs exposure decreased the abundance of ARGs. Furthermore, the co-exposure of Cu- and ZnO- NPs induced obvious changes in the microbial communities compared to the control communities. Redundancy analysis suggested that the microbial community contributed the most (43.5%) to the ARG profiles, followed by dissolved metal ions (25.7%), MRGs, (19.4%), and MGEs (4.4%). Network analysis found several potential hosts (such as Mycobacterium and Escherichia coli) and implied the extent of the risk of ARG transmission into various environmental niches by these common microbes.

Role of MoOx Surficial Modification in Enhancing the OER Performance of Ru-Pyrochlore.

Pyrochlore ruthenate (Y2 Ru2 O7-δ ) is highlighted as a promising oxygen evolution reaction (OER) catalyst for water splitting in polymer electrolyte membrane electrolyzers. However, an efficient electronic modulation strategy for Y2 Ru2 O7-δ is required to overcome its electrochemical inertness. Herein, a surface manipulation strategy involving implanting MoOx moieties on nano Y2 Ru2 O7-δ (Mo-YRO) using wet chemical peroxone method is demonstrated. In contrast to electronic structure regulation by intramolecular charge transfer (i.e., substitutional strategies), the heterogeneous Mo-O-Ru micro-interfaces facilitate efficient intermolecular electron transfer from [RuO6 ] to MoOx . This eliminates the bandgap by inducing Ru 4d delocalization and band alignment rearrangement. The MoOx modifiers also alleviate distortion of [RuO6 ] by shortening Ru-O bond and enlarging Ru-O-Ru bond angle. This electronic and geometric structure tailoring enhances the OER performance, showinga small overpotential of 240mV at 10mAcm-2 . Moreover, the electron-accepting MoOx moieties provide more electronegative surfaces, which serve as a protective "fence" to inhibit the dissolution of metal ions, thereby stabilizing the electrochemical activity. This study offers fresh insights into the design of new-based pyrochlore electrocatalysts, and also highlights the versatility of surface engineering as a way of optimizing electronic structureand catalytic performance of other related materials.

Fundamental Understanding of the Effect of a Polyaniline Coating Layer on Cation Mixing and Chemical States of LiNi0.9Co0.085Mn0.015O2 for Li-Ion Batteries

A high nickel content of the cathode usually results in a large discharge capacity but causes structural collapse. Ni2+ ions move to the Li layer when Li+ ions are deintercalated during discharge, resulting in irreversible phase transition, cation mixing, dissolution of transition metal ions, and side reactions. A protective barrier is essential for maintaining the layered structures of cathode materials, even after several charge/discharge cycles of Li-ion batteries. Polyaniline (PANi) is an organic coating material with high conductivity and flexibility. PANi-coated cathodes have been widely reported for improving electrochemical performances. However, it is insufficient to prove the correlation between the PANi coating layer and structural stability through further analysis after an electrochemical test. Therefore, we focused on the structural stability and chemical states of the PANi-coated cathode after a cycle test by observing the morphology, lattice patterns, and chemical states of the surface. PANi-coated LiNi0.9Co0.085Mn0.015O2 (NCM; PANi@NCM) exhibited an initial discharge capacity of 221 mAh g–1 and a capacity retention of 81% after 50 cycles at 45 °C, which corresponded to an improved performance compared to pristine NCM. The cycled PANi@NCM showed an identical morphology to that of the cathode before the test. The R3̅m layered structure of PANi@NCM was maintained even after 50 cycles, as confirmed by transmission electron microscopy analysis with fast Fourier transform patterns and high-angle annular dark-field images. In addition, PANi@NCM maintains a thinner passivation layer (8 nm) compared with that of pristine NCM (27 nm). According to the X-ray photoelectron spectroscopy results, the surface chemical state of PANi@NCM showed that side reactions between the cathode and the electrolyte were suppressed during the cycle test. Therefore, it is demonstrated that the PANi coating layer prevents cation mixing and side reactions.