Alleviating Surface Degradation of Nickel-Rich Layered Oxide Cathode Material by Encapsulating with Nanoscale Li-Ions/Electrons Superionic Conductors Hybrid Membrane for Advanced Li-Ion Batteries

Surface and Grain Boundary Coating for Stabilizing LiNi0.8Mn0.1Co0.1O2 Based Electrodes

The widespread use of high-capacity Ni-rich layered oxides such as LiNi0.8Mn0.1Co0.1O2 (NMC811), in lithium-ion batteries is hindered due to practical capacity loss and reduced working voltage during operation. Aging leads to defective NMC811 particles, affecting electrochemical performance. Surface modification offers a promising approach to improve cycle life. Here, we introduce an amorphous lithium titanate (LTO) coating via atomic layer deposition (ALD), not only covering NMC811 surfaces but also penetrating cavities and grain boundaries. As NMC811 electrodes suffer from low structural stability during charge and discharge, We combined electrochemistry, operando X-ray diffraction (XRD), and dilatometry to understand structural changes and the coating protective effects. XRD reveals significant structural evolution during delithiation for uncoated NMC811. The highly reversible phase change in coated NMC811 highlights enhanced bulk structure stability. The LTO coating retards NMC811 degradation, boosting capacity retention from 86 % to 93 % after 140 cycles. This study underscores the importance of grain boundary engineering for Ni-rich layered oxide electrode stability and the interplay of chemical and mechanical factors in battery aging.

An effective co-modification strategy to enhance the cycle stability of LiNi0.8Co0.1Mn0.1O2 for lithium-ion batteries

Ni-rich cathode materials suffer from rapid capacity fading caused by interface side reactions and bulk structure degradation. Previous studies show that Co is conducive to bulk structure stability and sulfate can react with the residual lithium (LiOH and Li2CO3) on the surface of Ni-rich cathode materials and form a uniform coating to suppress the side reactions between the cathode and electrolyte. Here, CoSO4 is utilized as a modifier for LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode materials. It reacts with the residual lithium on the surface of the NCM811 cathode to form Li-ion conductive Li2SO4 protective layers and Co doping simultaneously during the high-temperature sintering process, which can suppress the side reactions between the Ni-rich cathode and electrolyte and effectively prevent the structural transformation. As a result, the co-modified NCM811 cathode with 3 wt% CoSO4 exhibits an improved cycling performance of 81.1% capacity retention after 200 cycles at 1C and delivers an excellent rate performance at 5C of 187.4 mA h g-1, which is 10.2% higher than that of the pristine NCM811 cathode.

Sol/Antisolvent Coating for High Initial Coulombic Efficiency and Ultra-stable Mechanical Integrity of Ni-Rich Cathode Materials

The Ni-rich cathode holds great promise for high energy density lithium-ion batteries because of its high capacity and operating voltage. However, crucial problems such as cation disorder, structural degradation, side reactions, and microcracks become serious with increasing nickel content. Herein, a novel and facile sol/antisolvent coating modification of Ni-rich layered oxide LiNi_0.85Co_0.1Mn_0.05O₂ (NCM) is developed where we use ethanol to disperse the nanosized LiBO₂ to form the sol and adopt tetrahydrofuran (THF) as antisolvent to prepare the cluster of nanoparticles to be coated on the surface of NCM. The coating thickness can be tuned through the THF addition amount. The LiBO₂ nanorod deposition is formed as well over the crack of the NCM cathode, likely acting as a patch to repair the original defect of the intrinsic crack. The uniform LiBO₂ nanospherical particle coating together with LiBO₂ nanorod wrapping provides a double protection against electrolytes. Compared with the raw material, LiBO₂-coated LiNi_0.85Co_0.1Mn_0.05O₂ (LiBO₂-coated NCM) exhibits a high initial Coulombic efficiency of 90.3% at 0.2 C between 2.8 and 4.3 V vs Li⁺/Li, a superior rate capability, enhanced fast charge property at 3 C, and restricted microcrack formation. This simple in-site modification and repairing technology guarantees a good mechanical integrity of the polycrystalline Ni-rich cathode.

A Low-Cost Liquid-Phase Method of Synthesizing High-Performance Li6PS5Cl Solid-Electrolyte

Li₆PS₅Cl is an extensively studied sulfide-solid-electrolyte for developing all-solid-state lithium batteries. However, its practical application is hindered by the high cost of its raw material lithium sulfide (Li₂S), the difficulty in its massive production, and its substandard performance. Herein we report an economically viable and scalable method, denoted as "de novo liquid phase method", which enables in synthesizing high-performance Li₆PS₅Cl without using commercial Li₂S but instead in situ making Li₂S from cheap materials of lithium chloride (LiCl) and sodium sulfide. LiCl, a raw material needed for making both Li₂S and Li₆PS₅Cl, can be added at a full-scale in the beginning and unrequired to separate when making the intermediate Li₃PS₄. Such a consecutive feature makes this method time-efficient; and the excess amount of LiCl in the step of making Li₂S also facilitates removing the byproduct of sodium chloride via the common ion effect. The materials cost of this method for Li₆PS₅Cl is ∼ $55/kg, comparable with the practical need of $50/kg. Moreover, the obtained Li₆PS₅Cl shows high ionic conductivity and outstanding cyclability in full battery tests, that is, ∼2 mS/cm and >99.8% retention for 400+ cycles at 1 C, respectively. Thus, this innovative method is expected to pave the way to develop practical sulfide-solid-electrolytes for all-solid-state lithium batteries.

Induction and Maintenance of Local Structural Durability for High-Energy Nickel-Rich Layered Oxides

Nickel-rich layered oxides are one of the most promising cathode candidates for next-generation high-energy-density lithium-ion batteries. However, due to similar ion radius between Li⁺ and Ni²⁺ (0.76 and 0.69 Å), the Li⁺ /Ni²⁺ mixing phenomenon seriously hinders the migration of Li⁺ and increases kinetic barrier of Li⁺ diffusion, resulting in limited rate capability. In this work, the introduction of Ce⁴⁺ to effectively improve electrochemical properties of Ni-rich cathode materials is proposed. The LiNi_0.8 Co_0.15 Al_0.05 O₂ (LNCA) is modified with an additional precursor oxidization process using an appropriate amount of (NH₄ )₂ Ce(NO₃ )₆ . The Ce(NO₃ )₆ ^2- easily obtains electrons and generates reduction reactions, while Ni(OH)₂ is prone to electron loss and oxidation reaction. The participation of (NH₄ )₂ Ce(NO₃ )₆ can promote the oxidation of Ni²⁺ to Ni³⁺ , thereby reducing the Li⁺ /Ni²⁺ mixing and increasing the structural stability of LNCA samples. Ce⁴⁺ cation doping can impede Li⁺ /Ni²⁺ mixing of LNCA cathode materials upon the long-term cycles. Both rate performance and long-term cyclability of Li[Ni_0.8 Co_0.15 Al_0.05 ]_0.97 Ce_0.03 O₂ (LNCA-Ce0.03) sample are significantly improved. Besides, a practical pouch cell based on the cathode presents sufficient gravimetric energy density (≈300 Wh kg^-1 ) and cycling stability (capacity retention of 81.3% after 500 cycles at 1 C).

Preparation of ultrathin carbon-coated CdS nanobelts for advanced Li and Na storage

In this paper, we report a simple hydrothermal method for preparation of ultrathin carbon-coated CdS (CdS@C) nanobelts. The CdS@C nanobelts show superior electrochemical properties as an anode material for Li-ion batteries. The optimized CdS@C composites deliver a reversible capacity around 910 mAhg^-1 and 48 mAhg^-1 at 0.1 Ag^-1 and 30.0 Ag^-1, respectively. Moreover, the optimized nanobelts are also potential materials for Na storage. A stable capacity around 240 mAhg^-1 is obtained at 0.1 Ag^-1, even after 100 cycles.

Organic Electroactive Molecule-Based Electrolytes for Redox Flow Batteries: Status and Challenges of Molecular Design

This is a critical review of the advances in the molecular design of organic electroactive molecules, which are the key components for redox flow batteries (RFBs). As a large-scale energy storage system with great potential, the redox flow battery has been attracting increasing attention in the last few decades. The redox molecules, which bridge the interconversion between chemical energy and electric energy for RFBs, have generated wide interest in many fields such as energy storage, functional materials, and synthetic chemistry. The most widely used electroactive molecules are inorganic metal ions, most of which are scarce and expensive, hindering the broad deployment of RFBs. Thus, there is an urgent motivation to exploit novel cost-effective electroactive molecules for the commercialization of RFBs. RFBs based on organic electroactive molecules such as quinones and nitroxide radical derivatives have been studied and have been a hot topic of research due to their inherent merits in the last decade. However, few comprehensive summaries regarding the molecular design of organic electroactive molecules have been published. Herein, the latest progress and challenges of organic electroactive molecules in both non-aqueous and aqueous RFBs are reviewed, and future perspectives are put forward for further developments of RFBs as well as other electrochemical energy storage systems.

Nanoscale Phenomena in Lithium-Ion Batteries

The electrochemical properties and performances of lithium-ion batteries are primarily governed by their constituent electrode materials, whose intrinsic thermodynamic and kinetic properties are understood as the determining factor. As a part of complementing the intrinsic material properties, the strategy of nanosizing has been widely applied to electrodes to improve battery performance. It has been revealed that this not only improves the kinetics of the electrode materials but is also capable of regulating their thermodynamic properties, taking advantage of nanoscale phenomena regarding the changes in redox potential, solid-state solubility of the intercalation compounds, and reaction paths. In addition, the nanosizing of materials has recently enabled the discovery of new energy storage mechanisms, through which unexplored classes of electrodes could be introduced. Herein, we review the nanoscale phenomena discovered or exploited in lithium-ion battery chemistry thus far and discuss their potential implications, providing opportunities to further unveil uncharted electrode materials and chemistries. Finally, we discuss the limitations of the nanoscale phenomena presently employed in battery applications and suggest strategies to overcome these limitations.

A novel all-fiber-based LiFePO4/Li4Ti5O12 battery with self-standing nanofiber membrane electrodes

Electrodes with high conductivity and flexibility are crucial to the development of flexible lithium-ion batteries. In this study, three-dimensional (3D) LiFePO₄ and Li₄Ti₅O₁₂ fiber membrane materials were prepared through electrospinning and directly used as self-standing electrodes for lithium-ion batteries. The structure and morphology of the fibers, and the electrochemical performance of the electrodes and the full battery were characterized. The results show that the LiFePO₄ and Li₄Ti₅O₁₂ fiber membrane electrodes exhibit good rate and cycle performance. In particular, the all-fiber-based gel-state battery composed of LiFePO₄ and Li₄Ti₅O₁₂ fiber membrane electrodes can be charged/discharged for 800 cycles at 1C with a retention capacity of more than 100 mAh·g^-1 and a coulombic efficiency close to 100%. The good electrochemical performance is attributed to the high electronic and ionic conductivity provided by the 3D network structure of the self-standing electrodes. This design and preparation method for all-fiber-based lithium-ion batteries provides a novel strategy for the development of high-performance flexible batteries.

Degradation Mechanisms and Mitigation Strategies of Nickel-Rich NMC-Based Lithium-Ion Batteries

Abstract

The demand for lithium-ion batteries (LIBs) with high mass-specific capacities, high rate capabilities and long-term cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNixMnyCo1−x−yO2, $$x \geqslant 0.5$$x⩾0.5) cathodes and graphite (LixC6) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid electrolyte interfaces are also reviewed, and trade-offs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions.

Graphic Abstract

The demand for lithium-ion batteries (LIBs) with high mass specific capacities, high rate capabilities and longterm cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNixMnyCo1−x−yO2, x ≥ 0.5) cathodes and graphite (LixC6) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid-electrolyte interfaces (SEIs) are also reviewed and tradeoffs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions.

Enhanced Cyclability and High-Rate Capability of LiNi0.88Co0.095Mn0.025O2 Cathodes by Homogeneous Al3+ Doping

To suppress capacity fading of nickel-rich materials for lithium-ion batteries, a homogeneous Al³⁺ doping strategy is realized through tailoring the Al³⁺ diffusion path from the bulk surface to interior. Specifically, the layered LiNi_0.88Co_0.095Mn_0.025O₂ cathode with the radial arrangement of primary grains is successfully synthesized through optimization design of precursors. The Al³⁺ follows the radially oriented primary grains into the bulk by introduction of nano-Al₂O₃ during the sintering process, realizing the homogeneous Al³⁺ distribution in the whole material. Particularly, a series of nano-Al₂O₃-modified LiNi_0.88Co_0.095Mn_0.025O₂ are investigated. With the 2% molar weight of Al³⁺ doping, the capacity retention ratio of the cathode is tremendously improved from 52.26 to 91.57% at 1 C rate after 150 cycles. Even at a heavy current density of 5 (&10) C for the LiNi_0.88Co_0.095Mn_0.025O₂-Al_2% cathode, a high reversible capacity of 172.3 (&165.7) mA h g^-1 can be acquired, which amount to the 84.46 (&81.25) % capacity retention at 0.2 C. Moreover, voltage deterioration is significantly suppressed by homogeneous Al³⁺ doping from the results of median voltage and dQ/dV curves. Therefore, homogeneous Al³⁺ doping benefited from the radial arrangement of primary grains provides an effective and practical way to prolong lifespan, as well as improves rate performance and voltage stability of nickel-rich ternary materials.

The Effects of Reversibility of H2-H3 Phase Transition on Ni-Rich Layered Oxide Cathode for High-Energy Lithium-Ion Batteries

Although LiNi_0.8Co_0.1Mn_0.1O₂ is attracting increasing attention on account of its high specific capacity, the moderate cycle lifetime still hinders its large-scale commercialization applications. Herein, the Ti-doped LiNi_0.8Co_0.1Mn_0.1O₂ compounds are successfully synthesized. The Li(Ni_0.8Co_0.1Mn_0.1)_0.99Ti_0.01O₂ sample exhibits the best electrochemical performance. Under the voltage range of 2.7–4.3 V, it maintains a reversible capacity of 151.01 mAh·g⁻¹ with the capacity retention of 83.98% after 200 cycles at 1 C. Electrochemical impedance spectroscopy (EIS) and differential capacity profiles during prolonged cycling demonstrate that the Ti doping could enhance both the abilities of electronic transition and Li ion diffusion. More importantly, Ti doping can also improve the reversibility of the H2-H3 phase transitions during charge-discharge cycles, thus improving the electrochemical performance of Ni-rich cathodes.

Triclinic Off-Stoichiometric Na3.12Mn2.44(P2O7)2/C Cathode Materials for High-Energy/Power Sodium-Ion Batteries

The application of sodium-ion batteries (SIBs) requires a suitable cathode material with low cost, nontoxic, high safety, and high energy density, which is still a big challenge; thus, a basic research on exploring new types of materials is imperative. In this work, a manganic pyrophosphate and carbon compound Na_3.12Mn_2.44(P₂O₇)₂/C has been synthesized through a feasible sol-gel method. Rietveld refinement reveals that Na_3.12Mn_2.44(P₂O₇)₂ adopts a triclinic structure ( P1̅ space group), which possesses spacious ion diffusion channels for facile sodium migration. The off-stoichiometric phase is able to offer more reversible Na⁺, delivering an enhanced reversible capacity of 114 mA h g^-1 at 0.1 C, and because of the strong "inductive effect" that (P₂O₇)^4- groups imposing on the Mn³⁺/Mn²⁺ redox couple, Na_3.12Mn_2.44(P₂O₇)₂/C presents high platforms above 3.6 V, contributing a remarkable energy density of 376 W h kg^-1, which is among the highest Fe-/Mn-based polyanion-type cathode materials. Furthermore, the off-stoichiometric compound also presents satisfactory rate capability and long-cycle stability, with a capacity retention of 75% after 500 cycles at 5 C. Ex situ X-ray diffraction demonstrates a single-phase reaction mechanism, and the density functional theory calculations display two one-dimensional sodium migration paths with low energy barriers in Na_3.12Mn_2.44(P₂O₇)₂, which is vital for the facile sodium storage. We believe that this compound will be a competitive cathode material for large-scale SIBs.

Conductive Polymers Encapsulation To Enhance Electrochemical Performance of Ni-Rich Cathode Materials for Li-Ion Batteries

Ni-rich cathode materials have drawn lots of attention owing to its high discharge specific capacity and low cost. Nevertheless, there are still some inherent problems that desiderate to be settled, such as cycling stability and rate properties as well as thermal stability. In this article, the conductive polymers that integrate the excellent electronic conductivity of polyaniline (PANI) and the high ionic conductivity of poly(ethylene glycol) (PEG) are designed for the surface modification of LiNi_0.8Co_0.1Mn_0.1O₂ cathode materials. Besides, the PANI-PEG polymers with elasticity and flexibility play a significant role in alleviating the volume contraction or expansion of the host materials during cycling. A diversity of characterization methods including scanning electron microscopy, energy-dispersive X-ray spectrometer, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared have demonstrated that LiNi_0.8Co_0.1Mn_0.1O₂ cathode materials is covered with a homogeneous and thorough PANI-PEG polymers. As a result, the surface-modified LiNi_0.8Co_0.1Mn_0.1O₂ delivers high discharge specific capacity, excellent rate properties, and outstanding cycling performance.

Effect of Nb and F Co-doping on Li1.2Mn0.54Ni0.13Co0.13O2 Cathode Material for High-Performance Lithium-Ion Batteries

The Li_1.2Mn_0.54-xNb_xCo_0.13Ni_0.13O_2-6xF_6x (x = 0, 0.01, 0.03, 0.05) is prepared by traditional solid-phase method, and the Nb and F ions are successfully doped into Mn and O sites of layered materials Li_1.2Mn_0.54Co_0.13Ni_0.13O₂, respectively. The incorporating Nb ion in Mn site can effectively restrain the migration of transition metal ions during long-term cycling, and keep the stability of the crystal structure. The Li_1.2Mn_0.54-xNb_xCo_0.13Ni_0.13O_2-6xF_6x shows suppressed voltage fade and higher capacity retention of 98.1% after 200 cycles at rate of 1 C. The replacement of O^2- by the strongly electronegative F^- is beneficial for suppressed the structure change of Li₂MnO₃ from the eliminating of oxygen in initial charge process. Therefore, the initial coulombic efficiency of doped Li_1.2Mn_0.54-xNb_xCo_0.13Ni_0.13O_2-6xF_6x gets improved, which is higher than that of pure Li_1.2Mn_0.54Co_0.13Ni_0.13O₂. In addition, the Nb and F co-doping can effectively enhance the transfer of lithium-ion and electrons, and thus improving rate performance.

Lightweight Reduced Graphene Oxide@MoS2 Interlayer as Polysulfide Barrier for High-Performance Lithium-Sulfur Batteries

The further development of lithium-sulfur (Li-S) batteries is limited by the fact that the soluble polysulfide leads to the shuttle effect, thereby reducing the cycle stability and cycle life of the batteries. To address this issue, here a thin and lightweight (8 μm and 0.24 mg cm^-2) reduced graphene oxide@MoS₂ (rGO@MoS₂) interlayer between the cathode and the commercial separator is developed as a polysulfide barrier. The rGO plays the roles of both a polysulfide physical barrier and an additional current collector, while MoS₂ has a high chemical adsorption for polysulfides. The experiments demonstrate that the Li-S cell constructed with an rGO@MoS₂-coated separator shows a high reversible capacity of 1122 mAh g^-1 at 0.2 C, a low capacity fading rate of 0.116% for 500 cycles at 1 C, and an outstanding rate performance (615 mAh g^-1 at 2 C). Such an interlayer is expected to be ideal for lithium-sulfur battery applications because of its excellent electrochemical performance and simple synthesis process.