Highly Stabilized Ni-Rich Cathode Material with Mo Induced Epitaxially Grown Nanostructured Hybrid Surface for High-Performance Lithium-Ion Batteries

Molybdenum-Doped Cobalt-Free Cathode Realizing the Electrochemical Stability by Enhanced Covalent Bonding

The doping strategy effectively enhances the capacity and cycling stability of cobalt-free nickel-rich cathodes. Understanding the intrinsic contributions of dopants is of great importance to optimize the performances of cathodes. This study investigates the correlation between the structure modification and their performances of Mo-doped LiNi0.8Mn0.2O2 (NM82) cathode. The role of doped Mo's valence state has been proved functional in both lattice structural modification and electronic state adjustment. Although the high-valence of Mo at the cathode surface inevitably reduces Ni valence for electronic neutrality and thus causes ion mixing, the original Mo valence will influence its diffusion depth. Structural analyses reveal Mo doping leads to a mixed layer on the surface, where high-valence Mo forms a slender cation mixing layer, enhancing structural stability and Li-ion transport. In addition, it is found that the high-valence dopant of Mo6+ ions partially occupies the unfilled 4d orbitals, which may strengthen the Mo─O bond through increased covalency and therefore reduce the oxygen mobility. This results in an impressive capacity retention (90.0% after 200 cycles) for Mo-NM82 cathodes with a high Mo valence state. These findings underscore the valence effect of doping on layered oxide cathode performance, offering guidance for next-generation cathode development.

Microstructures of layered Ni-rich cathodes for lithium-ion batteries

Millions of electric vehicles (EVs) on the road are powered by lithium-ion batteries (LIBs) based on nickel-rich layered oxide (NRLO) cathodes, and they suffer from a limited driving range and safety concerns. Increasing the Ni content is a key way to boost the energy densities of LIBs and alleviate the EV range anxiety, which are, however, compromised by the rapid performance fading. One unique challenge lies in the worsening of the microstructural stability with a rising Ni-content in the cathode. In this review, we focus on the latest advances in the understanding of NLRO microstructures, particularly the microstructural degradation mechanisms, state-of-the-art stabilization strategies, and advanced characterization methods. We first elaborate on the fundamental mechanisms underlying the microstructural failures of NRLOs, including anisotropic lattice evolution, microcracking, and surface degradation, as a result of which other degradation processes, such as electrolyte decomposition and transition metal dissolution, can be severely aggravated. Afterwards, we discuss representative stabilization strategies, including the surface treatment and construction of radial concentration gradients in polycrystalline secondary particles, the fabrication of rod-shaped primary particles, and the development of single-crystal NRLO cathodes. We then introduce emerging microstructural characterization techniques, especially for identification of the particle orientation, dynamic changes, and elemental distributions in NRLO microstructures. Finally, we provide perspectives on the remaining challenges and opportunities for the development of stable NRLO cathodes for the zero-carbon future.

An effective tellurium surface modification strategy to enhance the capacity and rate capability of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode material

LiNi0.8Co0.1Mn0.1O2 (NCM) layered oxide is contemplated as an auspicious cathode candidate for commercialized lithium-ion batteries. Regardless, the successful commercial utilization of these materials is impeded by technical issues like structural degradation and poor cyclability. Elemental doping is among the most viable strategies for enhancing electrochemical performance. Herein, the preparation of surface tellurium-doped NCM is done by utilizing the methodology solid-state route at high temperatures. Surface doping of the Te ions leads to structural stability owing to the inactivation of oxygen at the surface via the binding of slabs of transition metal-oxygen. Remarkably, 1 wt% of Te doping in NCM exhibits enhanced electrochemical characteristics with an excellent discharge capacity, i.e., 225.8 mAh/g (0.1C), improved rate-capability of 156 mAh/g (5C) with 82.2% retention in capacity (0.5C) over 100 cycles within 2.7-4.3V as compared to all other prepared electrodes. Hence, the optimal doping of Te is favorable for enhancing capacity, cyclability along with rate capability of NCM.

Evolution Path of Precursor-Induced High-Temperature Lithiation Reaction during the Synthesis of Lithium-Rich Cathode Materials

High-temperature lithiation is one of the crucial steps for the synthesis of Li- and Mn-rich layered metal oxide (LMLO) cathodes. A profound insight of the micromorphology and crystal structure evolution during calcination helps to realize the finely controlled preparation of final cathodes, finally achieving a desired electrochemical performance. In this work, two typical precursors (hydroxide and oxalate) were selected to prepare LMLO. It is found that the influence of the lithium source on reaction pathways is determined by the properties of precursors. In the case of hydroxide as a precursor, whatever lithium sources it is, the flake morphology of LMLO is inherited from hydroxide precursors. This is because the crystal structure of cathode products has a high similarity with its precursor in terms of the oxygen array arrangement, and the topological transformation occurs from hydroxide (P-3ml) to LMLOs (C/2m and R3m). Thus, the morphology and microstructure of LMLO cathodes could be well controlled only by tuning the properties of hydroxide precursors. Conversely, the decomposition of a lithium source has a great influence on the intermediate transformation when oxalate is used as the precursor. This is because a large amount of CO2 is released from the oxalate precursor after the decomposition reaction, resulting in drastic structural changes. At this time, the diffusion ability of the lithium source leads to the competition between the spinel phase and layered phase. Based on this point, the formation of a spinel intermediate phase can be reduced by accelerating the decomposition of the lithium source, contributing to the generation of a highly pure layered phase, thus exhibiting higher electrochemical performance. These insights provide an exciting cue to the rational selection and design of raw materials and lithium sources for the controlled synthesis of LMLO cathodes.

Modification of the Ni-Rich Layered Cathode Material by Hf Addition: Synergistic Microstructural Engineering and Surface Stabilization

The rapid decline of the reversible capacity originating from microcracks and surface structural degradation during cycling is still a serious obstacle to the practical utilization of Ni-rich LiNixCoyAl1-x-yO2 (x ≥ 0.8) cathode materials. In this research, a feasible Hf-doping method is proposed to improve the electrochemical performance of LiNi0.9Co0.08Al0.02O2 (NCA90) through microstructural optimization and structural enhancement. The addition of Hf refines the primary particles of NCA90 and develops them into a short rod shape, making them densely arranged along the radial direction, which increases the secondary particle toughness and reduces their internal porosity. Moreover, Hf-doping stabilizes the layered structure and suppresses the side reactions through the introduction of robust Hf-O bonding. Multiple advantages of Hf-doping allowed significant improvement of the cycling stability of LiNi0.895Co0.08Al0.02Hf0.005O2 (NCA90-Hf0.5), with a reversible capacity retention rate of 95.3% after 100 cycles at 1 C, as compared with only 82.0% for the pristine NCA90. The proposed synergetic strategy combining microstructural engineering and crystal structure enhancement can effectively resolve the inherent capacity fading of Ni-rich layered cathodes, promoting their practical application for next-generation lithium-ion batteries.

Improved Electrochemical Performance of Li-Rich Cathode Materials via Spinel Li2MoO4 Coating

Li-rich manganese-based cathode materials (LRMs) are considered one of the most promising cathode materials for the next generation of lithium-ion batteries (LIBs) because of their high energy density. However, there are problems such as a capacity decay, poor rate performance, and continuous voltage drop, which seriously limit their large-scale commercial applications. In this work, Li1.2Mn0.54Co0.13Ni0.13O2 coated with Li2MoO4 with a unique spinel structure was prepared with the wet chemistry method and the subsequent calcination process. The Li2MoO4 coating layer with a spinel structure could provide a 3D Li+ transport channel, which is beneficial for improving rate performance, while protecting LRMs from electrolyte corrosion, suppressing interface side reactions, and improving cycling stability. The capacity retention rate of LRMs coated with 3 wt% Li2MoO4 increased from 69.25% to 81.85% after 100 cycles at 1 C, and the voltage attenuation decreased from 7.06 to 4.98 mV per cycle. The lower Rct also exhibited an improved rate performance. The results indicate that the Li2MoO4 coating effectively improves the cyclic stability and electrochemical performance of LRMs.

Fabricating Heterostructures for Boosting the Structure Stability of Li-Rich Cathodes

Li-rich Mn-based oxides are regarded as the most promising new-generation cathode materials, but their practical application is greatly hindered by structure collapse and capacity degradation. Herein, a rock salt phase is epitaxially constructed on the surface of Li-rich Mn-based cathodes through Mo doping to improve their structural stability. The heterogeneous structure composed of a rock salt phase and layered phase is induced by Mo⁶⁺ enriched on the particle surface, and the strong Mo-O bonding can enhance the TM-O covalence. Therefore, it can stabilize lattice oxygen and inhibit the side reaction of the interface and structural phase transition. The discharge capacity of 2% Mo-doped samples (Mo 2%) displays 279.67 mA h g^-1 at 0.1 C (vs 254.39 mA h g^-1 (pristine)), and the discharge capacity retention rate of Mo 2% is 79.4% after 300 cycles at 5 C (vs 47.6% (pristine)).

Effective and Low-Cost In Situ Surface Engineering Strategy to Enhance the Interface Stability of an Ultrahigh Ni-Rich NCMA Cathode

Ultrahigh Ni-rich quaternary layered oxides LiNi_1-x-y-zCo_xMn_yAl_zO₂ (1 - x - y - z ≥ 0.9) are regarded as some of the most promising cathode candidates for lithium-ion batteries (LIBs) because of their high energy density and low cost. However, poor rate capacity and cycling performance severely limit their further commercial applications. Herein, an in situ coating strategy is developed to construct a uniform LiAlO₂ layer. The NH₄HCO₃ solution is added to a NaAlO₂ solution to form a weak alkaline condition, which can reduce the hydrolysis rate of NaAlO₂, thus enabling uniform deposition of Al(OH)₃ on the surface of a Ni_0.9Co_0.07Mn_0.01Al_0.02(OH)₂ (NCMA) precursor. The LiAlO₂-coated samples show enhanced cycling stability and rate capacity. The capacity retention of NCMA increases from 70.7% to 88.3% after 100 cycles at 1 C with an optimized LiAlO₂ coating amount of 3 wt %. Moreover, the 3 wt % LiAlO₂-coated sample also delivers a better rate capacity of 162 mAh g^-1 at 5 C, while that of an uncoated sample is only 144 mAh g^-1. Such a large improvement of the electrochemical performance should be attributed to the fact that a uniform LiAlO₂ coating relieves harmful interfacial parasitic reactions and stabilizes the interface structure. Therefore, this in situ coating approach is a viable idea for the design of higher-energy-density cathode materials.

A New Insight into the Capacity Decay Mechanism of Ni-Rich Layered Oxide Cathode for Lithium-Ion Batteries

Understanding the mapping relationship between electrochemical characteristics and physicochemical properties of layered LiNi_0.80 Co_0.15 Al_0.05 O₂ (NCA) cathodes is important to develop high energy density lithium-ion batteries (LIBs). Combining in situ and ex situ characterization, the effect of the H2-H3 phase transition on the capacity decay and aging mechanism of NCA materials are systematically investigated. With the increase of cut-off voltage, the cathode electrolyte interphase (CEI) on the NCA interface shows an evolutionary path of formation-thickening-rupture. This phenomenon is closely related to the H2-H3 phase transition. The volumetric stresses and strains caused by the H2-H3 phase transition accelerate the formation and expansion of secondary particle microcracks in the electrode material, leading to the growth of interfacial CEI variations. The capacity of the electrode material can decrease even if the material does not experience the H2-H3 phase transition due to the persistence of interfacial side reactions with calendar aging from long cycles. This work opens up a valuable perspective for the study of the mapping relationship between phase transition and electrochemical properties in Ni-rich layered oxide cathodes and provides guidance for developing high capacity and long cycle life LIBs.

Effects of Oxygen Pressurization on Li+/Ni2+ Cation Mixing and the Oxygen Vacancies of LiNi0.8Co0.15Al0.05O2 Cathode Materials

Ni-rich cathode materials are a low-cost and high-energy density solution for high-power lithium-ion batteries. However, Li⁺/Ni²⁺ cation mixing and oxygen vacancies are inevitably formed during the high-temperature calcination process, resulting in a poor crystal structure that adversely affects the electrochemical performance. In this work, the LiNi_0.8Co_0.15Al_0.05O₂ cathode material with a regular crystal structure was prepared through oxygen pressurization during lithiation-calcination, which effectively solved the problems caused by the high calcination temperature, such as oxygen loss and a reduction of Ni³⁺. The co-effect of oxygen pressure and calcination temperature on the properties of Ni-rich materials was systematically explored. Oxygen pressurization increased the redox conversion temperature, thus promoting the oxidation of Ni²⁺ and reducing Li⁺/Ni²⁺ cation mixing. Moreover, due to the strong oxidizing environment provided by the elevated calcination temperature and oxygen pressurization, the LiNi_0.8Co_0.15Al_0.05O₂ material synthesized under 0.4 MPa oxygen pressure and a calcination temperature of 775 °C exhibited few oxygen vacancies, which in turn suppressed the formation of microcracks during the electrochemical cycling. An additional feature of the LiNi_0.8Co_0.15Al_0.05O₂ material was the small specific surface area of the particles, which reduced both the contact area with the electrolyte and side reactions. As a result, the LiNi_0.8Co_0.15Al_0.05O₂ material exhibited remarkable electrochemical performance, with an initial discharge capacity of 191.6 mA h·g^-1 at 0.1 C and a capacity retention of 94.5% at 0.2 C after 100 cycles.

Developments in Surface/Interface Engineering of Ni-Rich Layered Cathode Materials

Ni-rich layered cathodes with high energy densities reveal an enormous potential for lithium-ion batteries (LIBs), however, their poor stability and reliability have inhibited their application. To ensure their stability over extensive cycles at high voltage, surface/interface modifications are necessary to minimize the adverse reactions at the cathode-electrolyte interface (CEI), which is a critical factor impeding electrode performance. Therefore, this review provides a comprehensive discussion on the surface engineering of Ni-rich cathode materials for enhancing their lithium storage property. Based on the structural characteristics of the Ni-rich cathode, the major failure mechanisms of these structures during synthesis and operation are summarized. Then the existing surface modification techniques are discussed and compared. Recent breakthroughs in various surface coatings and modification strategies are categorized and their unique functionalities in structural protection and performance-enhancing are elaborated. Finally, the challenges and outlook on the Ni-rich cathode materials are also proposed.

Recent progress on the low and high temperature performance of nanoscale engineered Li-ion battery cathode materials

Lithium ion batteries (LIB) are the domain power house that gratifies the growing energy needs of the modern society. Statistical records highlight the future demand of LIB for transportation and other high energy applications. Cathodes play a significant role in enhancement of electrochemical performance of a battery, especially in terms of energy density. Therefore, numerous innovative studies have been reported for the development of new cathode materials as well as improving the performance of existing ones. Literature designate stable cathode-electrolyte interface (CEI) is vital for safe and prolonged high performance of LIBs at different cycling conditions. Considering the context, many groups shed light on stabilizing the CEI with different strategies like surface coating, surface doping and electrolyte modulation. Local temperature variation across the globe is another major factor that influences the application and deployment of LIB chemistries. In this review, we discuss the importance of nano-scale engineering strategies on different class of cathode materials for their improved CEI and hence their low and high temperature performances. Based on the literature reviewed, the best nano-scale engineering strategies investigated for each cathode material have been identified and described. Finally, we discuss the advantages, limitations and future directions for enabling high performance cathode materials for a wide range of applications.

Effects of Co/Mn Content Variation on Structural and Electrochemical Properties of Single-Crystal Ni-Rich Layered Oxide Materials for Lithium Ion Batteries

The development of single-crystal nickel-rich layered LiNi_xCo_yMn_1-x-yO₂ materials (S-NCMs) represents the most significant progress for the electrification applications of nickel-rich ternary materials. There has been prior research on the important role of transition metal elements in agglomerated materials, supplemented by surface and internal lattice optimization to drive the performance improvements. However, studies on S-NCMs, especially on the role of transition metals (TM, i.e., Co and Mn), have not been reported. In this study, we synthesized four kinds of S-NCMs with different Co/Mn contents and studied their structural, electrochemical, kinetic, and thermodynamic properties with different Co/Mn contents. The results were as follows: (1) Electrochemically, Co was more effective than Mn at 25 °C at enhancing the intercalation/deintercalation kinetics, which resulted in an increased discharge capacity, an improved rate capability, and a reduced energy loss. (2) Thermodynamically, Mn was more effective at maintaining a higher thermal stability than Co, especially at a low cutoff voltage, but at a high cutoff voltage, the difference between the action of Co and Mn decreased. The main finding of this work was the enhanced structural stability provided by Co, which could be attributed to the following: (i) the absence of the H2/H3 phase transformation when Co exceeded 15%, which inhibited the irreversible phase transformation and reduced the volume strain, and (ii) the lower degrees of decrease in the cell parameters a and c with higher contents of Co, which contributed to a low cracking degree along the (003) crystal plane. The current work provides an important reference for the single-crystallization strategy of nickel-rich materials.

A study on Ti-doped Fe3O4 anode for Li ion battery using machine learning, electrochemical and distribution function of relaxation times (DFRTs) analyses

Among many transition-metal oxides, Fe₃O₄ anode based lithium ion batteries (LIBs) have been well-investigated because of their high energy and high capacity. Iron is known for elemental abundance and is relatively environmentally friendly as well contains with low toxicity. However, LIBs based on Fe₃O₄ suffer from particle aggregation during charge–discharge processes that affects the cycling performance. This study conjectures that iron agglomeration and material performance could be affected by dopant choice, and improvements are sought with Fe₃O₄ nanoparticles doped with 0.2% Ti. The electrochemical measurements show a stable specific capacity of 450 mAh g⁻¹ at 0.1 C rate for at least 100 cycles in Ti doped Fe₃O₄. The stability in discharge capacity for Ti doped Fe₃O₄ is achieved, arising from good electronic conductivity and stability in microstructure and crystal structure, which has been further confirmed by density functional theory (DFT) calculation. Detailed distribution function of relaxation times (DFRTs) analyses based on the impedance spectra reveal two different types of Li ion transport phenomena, which are closely related with the electron density difference near the two Fe-sites. Detailed analyses on EIS measurements using DFRTs for Ti doped Fe₃O₄ indicate that improvement in interfacial charge transfer processes between electrode and Li metal along with an intermediate lithiated phase helps to enhance the electrochemical performance.

Stabilization of crystal and interfacial structure of Ni-rich cathode material by vanadium-doping

Stable structure and interface of nickel-rich metal oxides is crucial for practical application of next generation lithium-ion batteries with high energy density. Bulk doping is the promising strategy to improve the structural and interfacial stability of the materials. Herein, we report the impact of vanadium-doping on the structure and electrochemical performance of LiNi_0.88Co_0.09Al_0.03O₂ (NCA88). Vanadium doped in high oxidation state (+5) would lead to alteration of the crystal lattice and Li⁺/Ni²⁺ cation mixing. Those are the main factors determining the cycling and rate capability of the materials. With optimization of vanadium-doping, the preservation of the integrity of the secondary particles of the materials, the enhancement of the diffusion of Li⁺ ions, and alleviation of the side reactions of the electrolyte can be efficiently achieved. As a result, NCA88 doped with vanadium of 1.5 mol % can provide superior cycling stability with capacity retention of 84.3% after 250 cycles at 2C, and rate capability with capacity retention of 65.5% at 10C, as compared to the corresponding values of 58.6% and 55% for the pristine counterpart, respectively. The results might be helpful to the selection of dopants in the design of the nickel-rich materials.

Identifying surface degradation, mechanical failure, and thermal instability phenomena of high energy density Ni-rich NCM cathode materials for lithium-ion batteries: a review

Among the existing commercial cathodes, Ni-rich NCM are the most promising candidates for next-generation LIBs because of their high energy density, relatively good rate capability, and reasonable cycling performance. However, the surface degradation, mechanical failure and thermal instability of these materials are the major causes of cell performance decay and rapid capacity fading. This is a huge challenge to commercializing these materials widely for use in LIBs. In particular, the thermal instability of Ni-rich NCM cathode active materials is the main issue of LIBs safety hazards. Hence, this review will recapitulate the current progress in this research direction by including widely recognized research outputs and recent findings. Moreover, with an extensive collection of detailed mechanisms on atomic, molecular and micrometer scales, this review work can complement the previous failure, degradation and thermal instability studies of Ni-rich NMC. Finally, this review will summarize recent research focus and recommend future research directions for nickel-rich NCM cathodes.

Recent Development of Nickel-Rich and Cobalt-Free Cathode Materials for Lithium-Ion Batteries

The exponential growth in the production of electric vehicles requires an increasing supply of low-cost, high-performance lithium-ion batteries. The increased production of lithium-ion batteries raises concerns over the availability of raw materials, especially cobalt for batteries with nickel-rich cathodes, in which these constraints can impact the high price of cobalt. The reliance on cobalt in these cathodes is worrisome because it is a high-cost, rare material, with an unstable supply chain. This review describes the need and feasibility of developing cobalt-free high-nickel cathode materials for lithium-ion batteries. The new type of cathode material, LiNi1−x−yMnxAlyO2 promises a completely cobalt-free composition with almost the same electrochemical performance as that of the conventional high-nickel cathode. Therefore, this new type of cathode needs further research for its commercial applications.

Transition metal-doped Ni-rich layered cathode materials for durable Li-ion batteries

Doping is a well-known strategy to enhance the electrochemical energy storage performance of layered cathode materials. Many studies on various dopants have been reported; however, a general relationship between the dopants and their effect on the stability of the positive electrode upon prolonged cell cycling has yet to be established. Here, we explore the impact of the oxidation states of various dopants (i.e., Mg²⁺, Al³⁺, Ti⁴⁺, Ta⁵⁺, and Mo⁶⁺) on the electrochemical, morphological, and structural properties of a Ni-rich cathode material (i.e., Li[Ni_0.91Co_0.09]O₂). Galvanostatic cycling measurements in pouch-type Li-ion full cells show that cathodes featuring dopants with high oxidation states significantly outperform their undoped counterparts and the dopants with low oxidation states. In particular, Li-ion pouch cells with Ta⁵⁺- and Mo⁶⁺-doped Li[Ni_0.91Co_0.09]O₂ cathodes retain about 81.5% of their initial specific capacity after 3000 cycles at 200 mA g⁻¹. Furthermore, physicochemical measurements and analyses suggest substantial differences in the grain geometries and crystal lattice structures of the various cathode materials, which contribute to their widely different battery performances and correlate with the oxidation states of their dopants.

Long-term efficient cycling stability is of paramount importance for the development of high-energy Li-ion batteries. Here, the authors investigate the effect of transition metal dopants on the electrochemical, morphological, and structural properties of Ni-rich cathode active materials.

Synergistic Effect of Microstructure Engineering and Local Crystal Structure Tuning to Improve the Cycling Stability of Ni-Rich Cathodes

Ultrahigh Ni-rich layered oxides have been regarded as one of the most promising cathode candidates. However, cycling instability induced by interfacial reactions and irreversible H2-H3 lattice distortion is yet to be demonstrated by an effective strategy that could construct a stable grain interface and microstructure. Here, Ni-rich cathode LiNi_0.92Co_0.05Mn_0.03O₂ is modified by B and Ti to realize the synchronous regulation of a microstructure and the oxygen framework robustness. Compared with the large equiaxed crystalline grains for the pristine cathode, highly elongated grains with a strong radially oriented crystallographic texture in which the (003) facet is maximized are produced for Ti and B-modified LiNi_0.92Co_0.05Mn_0.03O₂. With the suppressed H2-H3 phase transition and cation mixing provided by radially oriented grains and turned local crystal oxygen framework robustness during cycling, the co-modified cathode exhibits enhanced Li⁺ diffusion kinetics and a capacity retention of 78.3% after 100 cycles, which outperformed the 38.5% for the pristine cathode. The improved cycling performance suggests the significance of the turned microstructure and local crystal structure in suppressing internal strain and crystal structure degradation. The synchronous realization of microstructure engineering and local crystal structure turning by optimal element combination would provide a heuristic solution for the construction of high perform Ni-rich cathodes.

Rational design of a cobalt sulfide nanoparticle-embedded flexible carbon nanofiber membrane electrocatalyst for advanced lithium-sulfur batteries

Both the sluggish redox kinetics and severe polysulfide shuttling behavior hinders the commercialization of lithium-sulfur (Li-S) battery. To solve these obstacles, we design a cobalt sulfide nanoparticle-embedded flexible carbon nanofiber membrane (denoted as CoS₂@NCF) as sulfiphilic functional interlayer materials. The hierarchically porous structure of carbon nanofiber is conducive to immobilizing sulfur species and facilitating lithium-ion penetration. Moreover, electrocatalytic CoS₂nanoparticles can significantly enhance the catalytic effect, achieving favorable adsorption-diffusion-conversion interface of polysulfide. Combined with these synergistic features, the assembled Li-S cell with CoS₂@NCF interlayer exhibited a great discharge capacity of 950.9 mAh g^-1with prolonged cycle lifespan at 1 C (maintained 648.1 mAh g^-1over 500 cycles). This multifunctional interlayer material used in this contribution provides an advanced route for developing high-energy-density Li-S battery.

Studies of Nickel-Rich LiNi0.85Co0.10Mn0.05O2 Cathode Materials Doped with Molybdenum Ions for Lithium-Ion Batteries

In this work, we continued our systematic investigations on synthesis, structural studies, and electrochemical behavior of Ni-rich materials Li[NixCoyMnz]O2 (x + y + z = 1; x ≥ 0.8) for advanced lithium-ion batteries (LIBs). We focused, herein, on LiNi0.85Co0.10Mn0.05O2 (NCM85) and demonstrated that doping this material with high-charge cation Mo6+ (1 at. %, by a minor nickel substitution) results in substantially stable cycling performance, increased rate capability, lowering of the voltage hysteresis, and impedance in Li-cells with EC-EMC/LiPF6 solutions. Incorporation of Mo-dopant into the NCM85 structure was carried out by in-situ approach, upon the synthesis using ammonium molybdate as the precursor. From X-ray diffraction studies and based on our previous investigation of Mo-doped NCM523 and Ni-rich NCM811 materials, it was revealed that Mo6+ preferably substitutes Ni residing either in 3a or 3b sites. We correlated the improved behavior of the doped NCM85 electrode materials in Li-cells with a partial Mo segregation at the surface and at the grain boundaries, a tendency established previously in our lab for the other members of the Li[NixCoyMnz]O2 family.

New Insights into the Mechanism of Enhanced Performance of Li[Ni0.8Co0.1Mn0.1]O2 with a Polyacrylic Acid-Modified Binder

A binder is an important component in lithium-ion batteries and plays a significant role in maintaining the properties of active substances. Most studies in the field of binders have only focussed on physical properties such as bonding performance. Here, a polyacrylic acid-modified binder was designed and adapted to Li[Ni_0.8Co_0.1Mn_0.1]O₂, which enhanced the electrochemical stability of Li[Ni_0.8Co_0.1Mn_0.1]O₂ from 30.2 to 66.6% (300 cycles at 1 C). We for the first time discovered that this was caused by a chemical reaction between polyacrylic acid and the residual lithium on the surface during the cycling, which formed a lithium propionic acid coating layer and maintained the stability of the layered structure.

Nanowelding to Improve the Chemomechanical Stability of the Ni-Rich Layered Cathode Materials

To satisfy the increasing energy density requirements for electric vehicles and grid-scale energy storage systems, Ni-rich layered oxide cathode materials are often fabricated as micron-sized secondary spherical particles consisting of nanosized single crystals. Unfortunately, the hierarchical structure inevitably induces intergranular cracks and parasitic reactions at the cathode-electrolyte interphase, aggravating chemomechanical instability and seriously hindering their practical application. Here, we propose a nanowelding strategy to build consolidation points at the grain boundary of the primary particles, which dramatically enhances the capacity retention and chemomechanical stability. Meanwhile, the oxygen vacancies in the ceria-based solid electrolyte possessing oxygen adsorbing and storage capability can restrain the active oxygenates in the surficial lattice to avoid oxygen evolution. Experimental characterization further confirms that this unique architecture can effectively prevent the liquid electrolyte from penetrating into the active material along the grain boundary and consequently eliminate the adverse effects, including intergranular cracks, cathode electrolyte interface formation and growth, and the layered structure-rock salt phase irreversible transition. This finding provides a promising approach to realize the rapid commercialization of highly stabilized nickel-rich cathode materials for high-performance lithium-ion batteries.

Regulating the Grain Orientation and Surface Structure of Primary Particles through Tungsten Modification to Comprehensively Enhance the Performance of Nickel-Rich Cathode Materials

Nickel-rich layered oxides, as the most promising commercial cathode material for high-energy density lithium-ion batteries, experience significant surface structural instabilities that lead to severe capacity deterioration and poor thermal stability. To address these issues, radially aligned grains and surface Li_xNi_yW_zO-like heterostructures are designed and obtained with a simple tungsten modification strategy in the LiNi_0.91Co_0.045Mn_0.045O₂ cathode. The formation of radially aligned grains, manipulated by the WO₃ modifier during synthesis, provides a fast Li⁺ diffusion channel during the charge/discharge process. Moreover, the tungsten tends to enter into the lattice of the primary particle surface, and the armor-type tungsten-rich heterostructure protects the bulk material from microcracks, structural transformations, and surface side reactions. First-principles calculations indicate that oxygen is more stable in the surface tungsten-rich heterostructure than elsewhere, thus triggering an improved surface structural stability. Consequently, the 2 wt % WO₃-modified LiNi_0.91Co_0.045Mn_0.045O₂ (NCM@2W) material shows outstanding prolonged cycling performance (capacity retention of 80.85% after 500 cycles) and excellent rate performance (5 C, 188.4 mA h g^-1). In addition, its layered-to-rock salt phase transition temperature is increased by 80 °C compared with that of the pristine cathode. This work provides a novel surface modification approach and an in-depth understanding of the overall performance enhancement of nickel-rich layered cathodes.

CoSe2/N-doped carbon porous nanoframe as an anode material for potassium-ion storage

Transition metal selenides (TMS), on account of their relatively high theoretical capacity, unique electrical properties, easy compositing and low cost, are considered to be a candidate anode material for potassium-ion batteries. However, the cycling stability of TMS is unsatisfactory owing to the large intercalation/deintercalation of K ions. Herein, a CoSe₂/N-doped carbon porous frame (CoSe₂@NC) is successfully synthesized through a simple mixing and sintering approach and displays excellent potassium storage performance. Plentiful C-N bonds in the precursor can induce the formation of homogeneous N-doped carbon matrix and C-N-Co bonds, thus endowing robust structure and high electronic conductivity for superior cycling stability. Therefore, the unique porous nanoframe suppresses volume expansion and provides more diffusion paths for K ions. After 1000 cycles at 50 mA g^-1, a high capacity of 311.3 mA h g^-1 is acquired. When the current density increases to 500 mA g^-1, the CoSe₂@NC can still maintain a capacity of 184.5 mA h g^-1 after 1000 cycles. The high performance, easy compositing and low cost of the CoSe₂@NC make it a favorable material for application in KIBs.

Surface Modification of the LiNi0.8Co0.1Mn0.1O2 Cathode Material by Coating with FePO4 with a Yolk-Shell Structure for Improved Electrochemical Performance

Coating with FePO₄ with the size of 20-30 nm on the surface of a LiNi_0.8Co_0.10Mn_0.1O₂ (NCM811) cathode produces an LFP3@NCM811 cathode via a sol-gel method, which markedly reduces secondary crystal cracking. A stable particle structure greatly improves the cycling stability of the LFP3@NCM811cathode, which retains 97% of its initial discharge capacity compared to NCM811 (78%) after 100 cycles at 2.7-4.5 V. Furthermore, it retains 86 and 63% of its initial discharge capacity after 400 cycles for LFP3@NCM811 and NCM811, respectively. The initial discharge capacity of the LFP3@NCM811 cathode is 218.8 mAh g^-1 at 0.1 C, and the discharge capacity of the LFP3@NCM811 cathode is achieved to be 151.4 mAh g^-1 at 5 C, which is 15 mAh g^-1 higher than that of the NCM811 cathode. These are due to the reduction of cation mixing for a certain amount of Fe²⁺/Fe³⁺ or PO₄^3- doped into the NCM811 surface, and the yolk-shell structure formed by coating with FePO₄ helps improve the electronic conductivity and accelerate the Li⁺ transport. The cycling stability is mainly due to the secondary cleavage inhibition, which maintains the structural integrity of the cathode particles during the long cycle process and protects the inside of the particle from harmful electrolytes.

Enhanced Surface Chemical and Structural Stability of Ni-Rich Cathode Materials by Synchronous Lithium-Ion Conductor Coating for Lithium-Ion Batteries

Ni-rich cathode materials LiNi_xCo_yMn_1-x-yO₂ (x ≥ 0.6) have attracted much attention due to their high capacity and low cost. However, they usually suffer from rapid capacity decay and short cycle life due to their surface/interface instability, accompanied by the high Ni content. In this work, with the Ni_0.9Co_0.05Mn_0.05(OH)₂ precursor serving as a coating target, a Li-ion conductor Li₂SiO₃ layer was uniformly coated on Ni-rich cathode material LiNi_0.9Co_0.05Mn_0.05O₂ by a precoating and syn-lithiation method. The uniform Li₂SiO₃ coating layer not only improves the Li-ion diffusion kinetics of the electrode but also reduces mechanical microstrain and stabilizes the surface chemistry and structure with a strong Si-O covalent bond. These results will provide further in-depth understanding on the surface chemistry and structure stabilization mechanisms of Ni-rich cathode materials and help to develop high-capacity cathode materials for next-generation high-energy-density Li-ion batteries.

Interfacial Regulation of Ni-Rich Cathode Materials with an Ion-Conductive and Pillaring Layer by Infusing Gradient Boron for Improved Cycle Stability

Ni-rich cathodes LiNi_xCo_yAl_1-x-yO₂ (0.8 < x < 1) with high energy density, environmental benignity, and low cost are regarded as the most promising candidate materials for next-generation lithium batteries. Unfortunately, capacity fading derived from unstable surface properties and intrinsic structural instability under extreme conditions limits large-scale commercial utilization. Herein, an interface-regulated Ni-rich cathode material LiNi_0.87Co_0.10Al_0.03O₂ with a layer (R3̅m) core, a NiO salt-like (Fm3̅m) phase, and an ultrathin amorphous ion-conductive LiBO₂ (LBO) layer is constructed by gradient boron incorporation and lithium-reactive coating during calcination. The ultrathin LBO layer not only exhausts residual lithium species but also acts as a layer for Li⁺ transport and insulation of detrimental reaction. The NiO salt-like phase in the subsurface could enhance the structural stability of the layer core for the pillar effects. With the positive role provided by the functional hybrid surface layer and boron doping, the modified cathode exhibits enhanced Li⁺ conductivity, structural stability, reversibility of the H2-H3 phase transition, suppressed side reactions, ameliorated transition-metal dissolution, and excellent electrochemical performance. Especially, a 1% wt boron-modified cathode delivers a discharge capacity of 211.99 mA h g^-1 in the potential range of 3.0-4.3 V at 0.2 C and excellent cycle life with a capacity retention of 89.43% after 200 cycles at 1 C.

Multifunctional Integration of Double-Shell Hybrid Nanostructure for Alleviating Surface Degradation of LiNi0.8Co0.1Mn0.1O2 Cathode for Advanced Lithium-Ion Batteries at High Cutoff Voltage

Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode is considered to be among the most promising candidates for high-energy-density lithium-ion batteries (LIBs). However, both capacity fading and structural degradation occur during long-term cycling, which extremely limit the commercial applications of NCM811, especially at a high cutoff voltage (>4.3 V). Here, we design a double-shell hybrid nanostructure consisting of a Li₂SiO₃ coating layer and a cation-mixed layer (Fm3̅m phase) to improve its electrochemical performance. Consequently, the Si-modified NCM811 electrode shows outstanding cycling stability with a 95.2% capacity retention at 4.3 V after 100 cycles and 87.3% at a 4.5 V high cutoff voltage after 100 cycles. This designed double-shell hybrid nanostructure alleviates side reactions, structural degradation, and internal cracking, effectively enhancing the surface structural stability. This efficient strategy provides a valuable step toward further commercial applications of the LiNi_0.8Co_0.1Mn_0.1O₂ cathode and enriches the fundamental understanding of layered cathode materials.

Dopant Segregation Boosting High-Voltage Cyclability of Layered Cathode for Sodium Ion Batteries

As a widely used approach to modify a material's bulk properties, doping can effectively improve electrochemical properties and structural stability of various cathodes for rechargeable batteries, which usually empirically favors a uniform distribution of dopants. It is reported that dopant aggregation effectively boosts the cyclability of a Mg-doped P2-type layered cathode (Na_0.67 Ni_0.33 Mn_0.67 O₂ ). Experimental characterization and calculation consistently reveal that randomly distributed Mg dopants tend to segregate into the Na-layer during high-voltage cycling, leading to the formation of high-density precipitates. Intriguingly, such Mg-enriched precipitates, acting as 3D network pillars, can further enhance a material's mechanical strength, suppress cracking, and consequently benefit cyclability. This work not only deepens the understanding on dopant evolution but also offers a conceptually new approach by utilizing precipitation strengthening design to counter cracking related degradation and improve high-voltage cyclability of layered cathodes.

Three-Dimensional Hierarchical Flowerlike FeP Wrapped with N-Doped Carbon Possessing Improved Li+ Diffusion Kinetics and Cyclability for Lithium-Ion Batteries

Transition-metal phosphides have a potential application in lithium-ion batteries (LIBs) because of their high theoretical capacities and low cost; nevertheless, they possess dramatic volumetric variation during cycling associated with poor conductivity, limiting their practical applications. Here, a three-dimensional (3D) hierarchical flowerlike FeP coated with nitrogen-doped carbon layer (FeP@N,C hybrid) was constructed through a solvothermal method, followed by a phosphating approach under low temperature. N-doped carbon not only suppresses the volume fluctuation of FeP, but also promotes electron transfer, accompanied by catalyzing the decomposition of Li₃P to improve the reversibility of the FeP@N,C hybrid during cycling processes. In addition, a 3D flowerlike architecture assembled from porous nanosheets is also beneficial for shortening the migration path of ions as well as improving the contact area of electrode with electrolyte, which enhances the reaction kinetics and is proved by both experimental measurement of Li⁺ diffusion coefficient and resistivity, along with the calculation of density functional theory. Consequently, the 3D hierarchical flowerlike FeP@N,C hybrid performs excellent cyclic stability (569 mA h g^-1 at a current density of 500 mA g^-1 for the 300th cycle) and rate performance (331.94 mA h g^-1 at a high current density of 5 A g^-1) for LIBs. Based on above results, the fabrication strategy in this work could offer a thought to design other high-performance metal phosphide hybrids.

Voltage fade mitigation in the cationic dominant lithium-rich NCM cathode

In the archetypal lithium-rich cathode compound Li1.2Ni0.13Co0.13Mn0.54O2, a major part of the capacity is contributed from the anionic (O2−/−) reversible redox couple and is accompanied by the transition metal ions migration with a detrimental voltage fade. A better understanding of these mutual interactions demands for a new model that helps to unfold the occurrences of voltage fade in lithium-rich system. Here we present an alternative approach, a cationic reaction dominated lithium-rich material Li1.083Ni0.333Co0.083Mn0.5O2, with reduced lithium content to modify the initial band structure, hence ~80% and ~20% of capacity are contributed by cationic and anionic redox couples, individually. A 400 cycle test with 85% capacity retention depicts the capacity loss mainly arises from the metal ions dissolution. The voltage fade usually from Mn4+/Mn3+ and/or On−/O2− reduction at around 2.5/3.0 V seen in the typical lithium-rich materials is completely eliminated in the cationic dominated cathode material.