Surface Side Reactions Research Articles

Achieving Dendrite-Free Zinc Deposition by Large-Size Anion-Reinforced Solvated Structures for Highly Reversible Zinc Anode

The electrochemical instability of zinc anode caused by surface side reactions and irregular zinc deposition severely hinders the practical application of aqueous zinc ion batteries (AZIBs). In this work, diethylenetriaminepentaacetic acid, pentasodium salt (DTPA) was used as a novel electrolyte additive to modulate the electrochemical stability of Zn anode. The DTPA anion can strongly coordinate with Zn2+, thus enabling the formation of a unique large-size anion-enhanced solvation structure of electrolyte. In this, not only the generation of by-products on Zn anode can be effectively inhibited, but more importantly, the deposition kinetics of Zn2+ can be well regulated to induce even and stable zinc deposition. In addition, DTPA is more prone to chemically adsorbed on the surface of Zn anode than H2O, contributing to the resistance of electrochemical corrosion. Synergistically, the Zn anode demonstrates excellent cycling stability (3850 h at 1 mA cm−2, 1 mAh cm−2, and 500 h at 10 mA cm−2, 10 mAh cm−2), enhanced coulombic efficiency (99.83% upon 3500 cycles at 5 mA cm−2, 1 mAh cm−2), and high reversibility of 1050 h even at a stringent discharge depth of 80%. Particularly, the full cell assembled with NaV3O8·1.5H2O (NaVO) cathode can also operate stably for 1800 cycles at 2 A g−1 with a high capacity retain of 90.8%. This work may pave a new route to achieve high-performance AZIBs by regulating the deposition process of Zn2+ based on large-size anion-enhanced solvation structure of electrolyte.

An Utrastable Mg/Zr Modified P2‐Type Na2/3Ni1/3Mn2/3O2 Cathode Material for High‐Power Sodium‐Ion Batteries

AbstractP2‐Na2/3Ni1/3Mn2/3O2 demonstrates high energy density owing to its high specific capacity and high discharge voltage, but suffering from rapid performance decay due to severe structural degradation and aggravated surface side reaction during high‐voltage cycling. Herein, a Mg/Zr modified Na0.67Ni0.25Mg0.08Mn0.64Zr0.03O2 cathode is proposed with good structural stability and excellent cycling performance, showing reversible capacity of 123.2 mAh g−1 (0.1 C) and capacity retention of 99.1% after 100 cycles. The cycling stability is outstanding among P2‐type cathodes reported so far. In situ XRD analyses reveal a suppressed P2‐O2 phase transition after Mg modification, further incorporation of Zr greatly stabilizes the layered structure as some Zr ions reside in the Na layer providing a pinning effect to reduce the slide of TMO2 layer. First‐principles calculations suggest that oxygen loss in Na0.67Ni0.25Mg0.08Mn0.64Zr0.03O2 cathode is suppressed as Zr incorporation prevents the formation of oxygen vacancies. XPS analyses verify a Zr─O protective layer self‐segregated on particle surface during material synthesis. The expanded Na+ transport channel confirmed by the XRD analysis well explains the favored Na‐ion mobility verified by a high reversible capacity of 105.5 mAh/g at 20 C. This work sheds new light on providing a practical P2‐structured cathode material for high‐power sodium ion batteries.

Fabrication of Ti/Zr-SnO2/PbO2-Nd Electrode for Efficient Electrocatalytic Degradation of Alizarine Yellow R

Introduction: A novel attempt to degrade alizarine yellow R (AYR) by lead dioxide (PbO2)/ neodymium (Nd) coated Ti anode was investigated. Method: Ti/Zr-SnO2/PbO2-Nd electrode showed high oxygen evolution potential, high current density, and neutral conditions, which favored the degradation of AYR. The PbO2-Nd layer on Ti/Zr-SnO2 was further characterized by scanning electron microscopy, and X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The electrochemical properties of Ti/Zr- SnO2/PbO2-Nd electrode were evaluated by cyclic voltammetry, AC impedance spectroscopy, and accelerated life test. Result: The relatively higher oxygen evolution overpotential (~1.80 V) of the developed electrode can effectively suppress the occurrence of surface side reactions and oxygen evolution. A relatively lower charge transfer resistance (Rct, 18.0 Ω) of Ti/Zr-SnO2/PbO2-Nd electrode could be found. The Ti/Zr-SnO2/PbO2-Nd electrode exhibited an accelerated lifetime of 110 min under a very high current density of 10,000 A/m2. The doping of Nd could produce loosely-stacked sheet-like structures, thus, the number of active sites on the electrode surface increases. Conclusion: Moreover, an outstanding conductivity of Ti/Zr-SnO2/PbO2-Nd electrode was obtained, which favored the electron transfer and catalytic activity of the modified electrode. The Ti/Zr-SnO2/PbO2-Nd electrode exhibited improved electrochemical performances and higher oxygen evolution potential, and the highest oxygen evolution potential is 1.80 V. Under the current density of 30 mA/cm2, the electrocatalytic degradation of 92.3% could be achieved in 180 min. The electrochemical oxidation of AYR at the Ti/Zr-SnO2/PbO2-Nd electrode proved to be feasible and effective, indicating that it might be used for the elimination of AYR from wastewater. conclusion: The electrochemical oxidation of AYR at the Ti/Zr-SnO2/PbO2-Nd electrode proved to be feasible and effective, indicating that it might be used for the elimination of AYR from wastewater.

Mo-doped LiNi0.8Co0.1Mn0.1O2 cathode materials with improved performance for lithium ion batteries

The high nickel ternary LiNi[Formula: see text]Co[Formula: see text]Mn[Formula: see text]O2 (NCM811) cathode material has attracted much attention owing to its advantages of high capacity and low price. However, NCM811 suffers from surface side reactions and cation mixing, which results in an unstable crystal structure and lower Coulomb efficiency and capacity in lithium ion batteries. In this work, Mo-doped cathode material NCM811 is effectively synthesized by high-temperature solidification approach. The characterization results show that the doped NCM811 can form a coating layer on the surface, preventing electrolyte side reactions with the electrode. As the cathode for lithium ion batteries, the Mo-doped NCM811 electrode shows an initial discharge capacity of 185.21[Formula: see text]mAh/g and obtains 156.33[Formula: see text]mAh/g with a capacity retention of 84.5% after 100 cycles at 1C. This study provides a simple and reliable method of fabricating high-performance NCM811 cathode materials.

Zwitterionic hydrogels with high interfacial affinity for zinc metal batteries

Zinc metal batteries are expected to be the next generation of energy storage devices due to their high safety, but their application is hampered by irreversible hydrogen evolution reaction and surface side reactions of zinc anodes. Here, a zwitterionic hydrogel electrolyte is reported based on polymerization of acrylamide and 1-(3-Sulfopropyl)-2-Vinylpyridinium betaine, and it exhibits the following advantages: the sulfonic acid group of 1-(3-Sulfopropyl)-2-Vinylpyridinium betaine can be preferentially adsorbed on metal Zinc to avoid side reactions and refine the affinity at the zinc-electrolyte interface; and the coordination of the negatively charged sulfonic acid group with Zn2+ alters the solvation structure of Zn2+, which further improves the restriction ability of side reactions. Consequently, Zn||Zn symmetric batteries can be stabilized for 1, 200 h of plating stripping at 1 mA cm−2. Zn||Cu batteries exhibit an impressive average coulombic efficiency of 99.8 % over a remarkable span of 1, 800 cycles at a current density of 15 mA cm−2. Furthermore, the Zn||MnO2/Carbon nanotube batteries have been cycled more than 2, 000 cycles at a current density of 0.5 A g−1, and the zinc hybrid capacitors for more than 18, 000 cycles at 1 A g−1. And an ionic skin (i-skin) based on acrylamide and 1-(3-Sulfopropyl)-2-Vinylpyridinium betaine of polymer hydrogel electrolyte is assembled and it can stably detect physiological signals.

High voltage electrochemical performance of ultrahigh-Ni cathode via in situ constructed nano-LiF and CNT composite cathode electrolyte interphase layer

Ultrahigh-nickel LiNixCoyMn1-x-yO2 cathode material (Ni content ≥ 0.9) is of great significance for the development of high energy density of lithium-ion batteries. However, its high surface activity leads to more surface residual lithium formation and deterioration of electrochemical performance, especially at high voltage. Here we add NH4F and nitrogen-doped carbon nanotubes (CNT) during the dimethyl carbonate (DMC) washing process, and constructed in situ the nano-LiF and CNT composite cathode electrolyte interphase (CEI) layer while removing part of residual lithium, effectively optimizing the surface environment of LiNi0.9Co0.05Mn0.05O2. The modified LiNi0.9Co0.05Mn0.05O2 has a capacity retention rate of 61.3 % after 200 cycles between 2.8 and 4.5 V at 1C, significantly higher than the 46.7 % of the unwashed sample, and a specific discharge capacity of 146.9 mAh g−1 at 5C, compared to 127.5 mAh g−1 for the unwashed sample. Benefit from the alleviation of polarization and the increase of Li+ diffusion coefficient, the stable CEI layer provides effective protection for LiNi0.9Co0.05Mn0.05O2 under 4.5 V, alleviating surface side reactions. In this paper, a simple and effective strategy is developed to optimize the surface of Ni-rich cathode material, which provides a new insight for the treatment of surface residual lithium.

Enhanced structural stability and durability in lithium-rich manganese-based oxide via surface double-coupling engineering

Lithium-rich manganese-based oxides (LRMOs) exhibit high theoretical energy densities, making them a prominent class of cathode materials for lithium-ion batteries. However, the performance of these layered cathodes often declines because of capacity fading during cycling. This decline is primarily attributed to anisotropic lattice strain and oxygen release from cathode surfaces. Given notable structural transformations, complex redox reactions, and detrimental interface side reactions in LRMOs, the development of a single modification approach that addresses bulk and surface issues is challenging. Therefore, this study introduces a surface double-coupling engineering strategy that mitigates bulk strain and reduces surface side reactions. The internal spinel-like phase coating layer, featuring three-dimensional (3D) lithium-ion diffusion channels, effectively blocks oxygen release from the cathode surface and mitigates lattice strain. In addition, the external Li3PO4 coating layer, noted for its superior corrosion resistance, enhances the interfacial lithium transport and inhibits the dissolution of surface transition metals. Notably, the spinel phase, as excellent interlayer, securely anchors Li3PO4 to the bulk lattice and suppresses oxygen release from lattices. Consequently, these modifications considerably boost structural stability and durability, achieving an impressive capacity retention of 83.4% and a minimal voltage decay of 1.49 mV per cycle after 150 cycles at 1 C. These findings provide crucial mechanistic insights into the role of surface modifications and guide the development of high-capacity cathodes with enhanced cyclability.

Insights into the effects of coating and single crystallization on the rate performance and cycle life of LiNi0.9Mn0.1O2 cathode

Coating and single crystal are two common strategies for cobalt-free nickel-rich layered oxides to solve its poor rate performance and cycle stability. However, the action mechanism of different modification protocols to suppress the attenuation are unclear yet. Herein, the Li2MoO4 layer-coated polycrystalline LiNi0.9Mn0.1O2 (1.0 %-Mo + NM91) and single crystal LiNi0.9Mn0.1O2 (SC-NM91) are prepared to investigate this difference, respectively. By focusing on the interior of particles, the relationship between structure evolution and electrochemical behavior is systematically studied, and the intrinsic mechanism of coating/single-crystallization modifications on suppressing the attenuation is clarified. The results show that microcracks in LiNi0.9Mn0.1O2 (NM91) are the main culprit leading to the rate capability decay, and the coating can effectively prevent the radial diffusion of microcracks from the center to surface, inhibiting the generation of surface side reactions. Therefore, the coating has a more advantage in improving the rate performance at 5.0C, the discharge capacity of 1.0 %-Mo + NM91 (130.6 mAh/g) is 7.9 % higher than that of SC-NM91 (121.0 mAh/g). In contrast, the single-crystallization can effectively prevent the formation of intergranular cracks arising from the anisotropic stress in NM91, which causes the severe cycle degradation. Correspondingly, the grain boundary-free SC-NM91 shows superior cyclability. The capacity retention rate of SC-NM91 (80.8 %) at 0.2C after 100cycles is 6.3 % higher than that of 1.0 %-Mo + NM91 (74.5 %). This work concludes the effect difference of different modification methods on enhancing the electrochemical performance, which provides theoretical and technical guidance for the optimized and targeted modification design in the cobalt-free high nickel cathode materials.

The critical role of titanium cation for the enhanced Na-ion layer spacing of O3 layered oxide cathode materials

O3-NaNi1/3Fe1/3Mn1/3O2 layered cathode material has been widely concerned by the industry for its advantages of simple preparation, low cost and high theoretical specific capacity. However, due to a series of surface side reactions, some transition metal ions are reduced, resulting in structural Jahn-Teller distortion, leading to poor structural stability. Herein, Ti element is introduced into O3-NaNi1/3Fe1/3Mn1/3O2 cathode material, and the effect of Ti doping on the phase structure and electrochemical properties of the material is analyzed in detail. The results show that Ti doping can enlarge the Na layer spacing and decrease the transition metal layer spacing. Thus, the modified material has a smaller Na ion diffusion barrier and a more stable structure. These advantages give a sample with a doping rate of 2.5 wt% a rate capacity of 74.8 mAh g−1 at 10 C, a capacity retention rate of 86.2 % after 100 cycles at 1 C, and an energy density of 320.5 Wh kg−1 for a full cell structure using a hard carbon anode. This strategy provides a valuable reference for cationic doping to improve the properties of O3 layered transition metal oxides.

Surface Modification of High Voltage Spinel LiNi0.5Mn1.5O4 Cathode Material Manufactured via Co-precipitation

Spinel-structured LiNi0.5Mn1.5O4 (LNMO) can provide high energy density due to its high operating voltage of 4.7 V. LNMO materials synthesized through co-precipitation are suitable for commercialization because of their easily controllable particles and structure. However, their practical application is difficult due to electrolyte and surface-side reactions. In this study, TiO2 was coated with LNMO using the sol–gel method to evaluate its electrochemical properties and thermal stability. Consequently, the TiO2 coating improved the rate performance and long-term battery cycling. Additionally, the cycling characteristics at high temperatures were improved by enhancing the thermal stability of the charged LNMO particles.

Ultra-High Temperature Operated Ni-Rich Cathode Stabilized by Thermal Barrier for High-Energy Lithium-Ion Batteries.

The pursuit of high energy density batteries has expedited the fast development of Ni-rich cathodes. However, the chemo-mechanical degradation induced by local thermal accumulation and anisotropic lattice strain is posing great obstacles for its wide applications. Herein, a highly-antioxidative BaZrO3 thermal barrier engineered LiNi0.8Co0.1Mn0.1O2 cathode through an in situ construction strategy is first reported to circumvent the above issues. It is found that the Zr ions are incorporated to Ni-rich material lattice and influence on the topotactic lithiation as well as enhance the oxygen electronegativity through the rigid Zr─O bonds, which effectively alleviates the lattice strain propagation and decreases the excessive oxidization of lattice oxygen for charge compensation. More importantly, the BaZrO3 thermal barrier with an ultra-low thermal conductivity validly impedes the fast heat exchange between electrode and electrolyte to mitigate the severe surface side reactions. This helps an ultra-high mass loading Li-ion pouch cell deliver a specific energy density of 690Wh kg-1 at active material level and an excellent capacity retention of 92.5% after 1400 cycles under 1 C at 25°C. Tested at a high temperature of 55°C, the pouch type full-cell also exhibits 88.7% in capacity retention after 1200 cycles.

Reinforcing the stability of cobalt-free lithium-rich layered oxides via Li-poor Ni-rich surface transformation

We report a lithium-rich layered oxide Li1.2Mn0.6Ni0.2O2 (LMNO) with an electrochemically stable Li-poor nickel-rich surface by simple excessive calcination treatment, greatly suppressing the surface side reactions and Mn-ion dissolution.

Surface Degradation of NMC Electrodes Exposed to Air and Impact on Subsequent Cycling

To meet the ambitious international emissions commitments laid out in the Paris climate agreement making the transition of society from being dependent on fossil fuels towards increased use of renewable energy sources possible, lithium-ion batteries (LIBs) are a key enabling technology. Even though LIBs are already extensively used in portable electronics and the rapidly expanding market of hybrid- and full-electric vehicles, more extensive deployment requires longer cycle-lifetimes, enhancements in energy density, and reductions in cost. In electric vehicles one of the most common materials for the positive electrodes is based on the lithium nickel manganese cobalt oxide (LixNi1-y-zMnyCozO2, NMC) compound with different ratios of transition metals. The NMC materials are well known for consisting of reasonably abundant materials, their high energy density and good cyclebility. In order to decrease the price while also further improving the energy density, it has become more popular during the last few years to increase the nickel content, being responsible for the redox process thereby contributing to a larger capacity. By increasing the nickel content, the quantity of cobalt required will decrease further, reducing the price. However it is also well known that in materials where the nickel content is high the surface side reactions will be augmented leading to more degradation and shorter cycle life. A high nickel content will not only affect the electrochemical side reactions during cycling, it has also been found that as NMC materials are exposed to air they will react differently, with more reactions for the nickel rich materials.It has been found that the NMC can react with H2O to form a LiOH layer and that once the layer is thick enough further side reactions would be prevented.1 It was assumed that the passivation was caused by the deintercalation of lithium, where the thin disordered rock salt layer would mitigate the Li+-water reactions through decreasing the amount of lithium deintercalation.1 Furthermore, the surface impurities formed during the air exposure have been observed to directly impact electrochemical performance during the first couple of cycles. Hatsukade et al. used isotopic labelling in order to measure the CO2 formation during the first cycles originating from the oxidative decomposition of these impurities.2 Air exposure has been shown to affect not only the first few cycles but also long term cycling as well.3 The degradation of the NMC has been found to be caused by phase transformation into rock salt and spinel structure, leading to nickel reduction and as a result formation of inter granular cracks, eventually leading to isolation of the active particles and increased charge transfer resistance.4 In this study the surface interactions at NMC electrodes during air exposure will be presented, showing both how the interactions take place as well as how the air exposure will affect the electrode-electrolyte interfaces during cycling. The NMC surface is analysed by x-ray photoelectron spectroscopy (XPS), photoemission electron microscopy (PEEM) and x-ray absorption spectroscopy (XAS). Zou, L. et al. Unlocking the passivation nature of the cathode–air interfacial reactions in lithium ion batteries. Nat. Commun. 11, (2020).Hatsukade, T., Schiele, A., Hartmann, P., Brezesinski, T. & Janek, J. Origin of Carbon Dioxide Evolved during Cycling of Nickel-Rich Layered NCM Cathodes. ACS Appl. Mater. Interfaces 10, 38892–38899 (2018).Meatza, I. De, Landa-medrano, I., Sananes-israel, S. & Eguia-barrio, A. Powder and Electrodes on the Electrochemical Performance in Li-ion Technology. Batteries 8, 1–18 (2022).Busà, C., Belekoukia, M. & Loveridge, M. J. The effects of ambient storage conditions on the structural and electrochemical properties of NMC-811 cathodes for Li-ion batteries. Electrochim. Acta 366, (2021).

Trace Ti/Mg co-doped O3-type layered oxide cathodes with enhanced kinetics and stability for sodium-ion batteries

O3-type layered oxide cathodes are identified as a promising cathode material for sodium-ion batteries (SIBs) due to their high specific capacity and moderate operating voltage, yet it usually suffers from sluggish Na-ion diffusion and structure instability. Herein, we demonstrate the synthesis of a trace Ti/Mg co-doped NaNi1/3Fe1/3Mn1/3O2 (TiMg-NFM) cathode, in which Ti-ion is distributed in transition metal layers and Mg-ion is doped into sodium layers. The co-doping can enlarge the Na-layer spacing inside the layered structure to reduce Na-ion diffusion barrier. Meanwhile, the structural stability is effectively reinforced via the stronger Ti-O bond and the pillar effect of Mg-ions, further reducing surface side reaction with electrolyte. These merits endow a high reversible capacity of the TiMg-NFM cathode with 144.5 mAh g−1 at 0.1C, and much higher capacity retention of 111.4 mAh g−1 at 5C versus the pristine NFM (62.1 mAh g−1). More impressively, 80.1% of initial capacity can be maintained after 300 cycles at 2C. This work presents a feasible strategy to enhance the reaction kinetics and structure stability for developing advanced O3-type layered oxide cathodes.

Simultaneously promoting the surface/bulk structural stability of Fe/Mn-based layered cathode for sodium ion batteries

Layered sodium iron manganese oxide cathodes have attracted great interest owing to their high specific capacity and cost-effective metal resources, while the detrimental phase transitions and surface structural degradation severely limit their commercial applications. In this work, the bulk and surface structure stability of a P2-Na0.67Fe0.5Mn0.5O2 cathode can be synergically enhanced by a one-step Li/Nb co-doping strategy. Structural characterizations reveal that Li doping promotes the formation of P2/O3 biphasic structure and makes the unfavorable P2-OP4 phase transition convert into a smooth solid-solution reaction. Nb doping enhances the mobility of sodium ions and forms strong Nb-O bonds, thereby enhancing the stability of the TMO2 layer structure. In particular, the Nb element induces the surface reorganization of an atomic-scale NaNbO3 coating layer, which could effectively prevent the dissolution of metals and surface side reactions. The synergistic mechanism of enhanced electrochemical performance is proved by multiple characterizations during cycling. As a result, the as-prepared Na0.67Li0.1Fe0.5Mn0.38Nb0.02O2 exhibits improved capacity retention of 85.4 % than raw material (45.7 %) after 100 cycles at 0.5C (1C = 174 mA g−1) within 2.0–4.0 V. This co-regulating strategy provides a promising approach to designing highly stable sodium-ion battery cathodes. Furthermore, a full cell of Na0.67Li0.1Fe0.5Mn0.38Nb0.02O2 with hard carbon displays excellent cycling stability (85.1 % capacity retention after 100 cycles), making its commercial operation possible. This synergistic strategy of biphasic structure and surface reorganization is a critical route to accelerate the application of layer oxide cathodes.

Constructing electronic and ionic conductive double coating to achieve superior structure stability and electrochemical properties of LiNi0.90Co0.04Mn0.03Al0.03O2

In the work, an improvement strategy for surface covering the quaternary layered oxide LiNi0.90Co0.04Mn0.03Al0.03O2 with the ionic conductor (Li3BO3) and electronic conductor (polypyrrole) is put forward to relieve the interface troubles and ameliorate the electrochemical properties of Ni-rich cathode. Benefiting from the multiple advantages of the double conductors, surface residual alkali and cation mixing of LiNi0.90Co0.04Mn0.03Al0.03O2 are remarkably decreased, as well as the surface side reactions, which are helpful to enhance the interfacial and crystal structure stability during long-term working. As a result, the PPy-LBO coated cathode delivers the large discharge capacity of 149.5 mA h g−1 with 10.0C high rate, outstanding capacity of 167.5 mA h g−1 with −30 °C discharging, and prominent cyclic stability with 90.5 % capacity conservation rate after 200 cycles at 1.0C with 45 °C. Meanwhile, the full batteries prepared with PPy-LBO coated sample also demonstrate the brilliant performance including the safety capability (Nail penetration, Overcharging and Impact test) and long-term cycling when compared to the pristine cathode.

Synergistic effect of B[sbnd]Nb co-modified to achieve crystal structure and interface tuning for Ni-rich cathode

Nickel-rich cathode materials play a pivotal role in the functioning of lithium-ion batteries, but their crystal structure defects and surface side reactions significantly affect battery performance. This has slowed down the commercialization process of nickel-rich cathodes. To remedy these problems, a new strategy utilizing B and Nb for crystal structure and interface control of LiNi0.8Co0.1Mn0.1O2 (NCM811) is proposed in this study. The BNb modified cathode exhibits strong radial orientation and exposes a large number of active (003) lattice plane on the particle surface. This structural control reduces micro-cracks and accelerates lithium-ion diffusion kinetics. Additionally, the LiNbO3 coating effectively avoids immediate contact between secondary particles and the electrolyte, greatly alleviating side reactions. Consequently, the optimal cathode B-NCM@LNO5 modified cathode maintains a capacity retention of 86.71% after 200 cycles at 1 C, outperforming the original material (76.11% retention). Meanwhile, it demonstrates attractive rate capability of 158.4 mAhg−1 under 5 C. This research provides valuable insights for addressing anisotropic strain and interface compatibility issues in nickel-rich cathodes.

Reusing the steel slag to design a gradient-doped high-entropy oxide for high-performance sodium ion batteries

Herein, a high-entropy layered oxide (HEO) is proposed as an outstanding cathode material for long-life sodium-ion batteries. Based on the self-segregation of elements from surface to bulk phase, a multi-element gradient doped high-entropy cathode material is prepared by doping steel slag with available elements (Mg, Al, Si, Fe, Ca). The surface high-entropy region vastly improves the air stability of materials and reduces surface impurities and side reactions. The Na-O-Mg configuration of near-surface high-entropy region continuously stimulates the anionic redox activity, and the DEMS shows the high-strength Al-O bonding achieves zero oxygen release. Therefore, the LNSM-0.01 reveals a stable capacity of ∼24 mA h g−1 in the range of 4.0–4.5 V. The Ca2+ in bulk phase high-entropy region disrupts the Na+/vacancy ordering transition and enhances the kinetic performance (90 mA h g−1 at 1000 mA g−1), while Fe2+/3+ provides a large amount number of charge compensation. Further, DFT calculations prove that the entropy stability based on synergistic effect immeasurably reinforce the layered oxide configuration, building a more robust structural framework during cycling. This work deepens the understanding on multi-element gradient doping to prepare HEOs, and provides a novel pathway for resource utilization of solid waste.

Facile Solid-State Synthesis to In Situ Generate a Composite Coating Layer Composed of Spinel-Structural Compounds and Li3PO4 for Stable Cycling of LiCoO2 at 4.6 V.

Due to its high energy density, high-voltage LiCoO2 is the preferred cathode material for consumer electronic products. However, its commercial viability is hindered by rapid capacity decay resulting from structural degradation and surface passivation during cycling at 4.6 V. The key to achieving stable cycling of LiCoO2 at high voltages lies in constructing a highly stable interface to mitigate surface side reactions. In this study, we present a facile in situ coating strategy that is amenable to mass production through a simple wet-mixing process, followed by high-temperature calcination. By capitalizing on the facile dispersion characteristics of nano-TiO2 in ethanol and the ethanol dissolubility of LiPO2F2, we construct a uniform precoating layer on LiCoO2 with nano-TiO2 and LiPO2F2. The subsequent thermal treatment triggers an in situ reaction between the coating reagents and LiCoO2, yielding a uniform composite coating layer. This composite layer comprises spinel-structured compounds (e.g., LiCoTiO4) and Li3PO4, which exhibit excellent chemical and structural stability under high-voltage conditions. The uniform and stable coating layer effectively prevents direct contact between LiCoO2 and the electrolyte, thereby reducing side reactions and suppressing the surface passivation of LiCoO2 particles. As a result, coated LiCoO2 maintains favorable electronic and ionic conductivity even after prolonged cycling. The synergistic effects of spinel-structured compounds and Li3PO4 contribute to the superior performance of LiCoO2, demonstrating a high capacity of 202.1 mA h g-1 (3.0-4.6 V, 0.5 C, 1 C = 274 mA g-1), with a capacity retention rate of 96.7% after 100 cycles.

Surface Passivation of LiCoO2 by Solid Electrolyte Nanoshell for High Interfacial Stability and Conductivity.

The practical application of lithium cobalt oxide (LiCoO2 ) cathodes at high voltages is hindered by the instability of the surface structure and side reactions with the electrolyte. Herein, we prepared a multifunctional hierarchical core@double-shell structured LiCoO2 (MS-LCO) cathode material using a scalable sol-gel method. The MS-LCO cathode material comprised an outer shell with fast lithium-ion conductivity, a La/Zr co-doped inner shell, and a bulk LiCoO2 core. The outermost shell prevented direct contact between the electrolyte and LiCoO2 core, which alleviated the electrolyte decomposition and loss of active cobalt, while the La/Zr co-doped shell improved the structural stability at higher voltages in a half-cell with a liquid electrolyte. The MS-LCO cathode exhibited a stable capacity of 163.1 mAh g-1 after 500 cycles at 0.5 C, and a high specific capacity of 166.8 mAh g-1 at 2 C. In addition, a solid lithium battery with the surface-passivated MS-LCO cathode and a polyethylene oxide (PEO)-based inorganic/organic composite electrolyte retained 85.8 % of its initial discharge capacity after 150 cycles at a charging cutoff voltage of 4.3 V. Thus, the introduction of a surface-passivating shell can effectively suppress the decomposition of PEO caused by highly reactive oxygen species in LiCoO2 at high voltages.