Decreasing Li/Ni Disorder and Improving the Electrochemical Performances of Ni-Rich LiNi0.8Co0.1Mn0.1O2 by Ca Doping

Rational design of dual-ion doped cobalt-free Li-rich cathode materials for enhanced cycle stability of lithium-ion pouch cell batteries

The synergistic effect of single-crystal structure and dual doping in Li-rich cobalt-free cathode materials was thoroughly investigated. Lithium-ion pouch cells employing Sb/Sn doped Li1.2Mn0.6Ni0.2O2 and graphite exhibited a specific capacity of 191.01 mA h g-1 at 1C rate and exceptionally stable performance upon cycling, with capacity retention of 87.24% of their initial capacity after 250 cycles at 1C rate. The strategic combination of morphology manipulation and dual ion doping has markedly diminished cation mixing and expanded the Li interstitial sites within the cathode lattice. This work offers significant insights into the mechanisms responsible for the structural decline of Li-rich cobalt-free cathodes, emphasizing the importance of stabilizing the cathode lattice structure at high potential. These findings suggest promising potential for this material to meet the demanding energy density criteria for electric vehicles. Finally, this research provides practical strategies for effectively implementing high-voltage cobalt-free cathodes, offering valuable guidance for future applications.

A multifunctional dual cation doping strategy to stabilize high-voltage medium-nickel low-cobalt lithium layered oxide cathode

High-voltage medium-nickel low-cobalt lithium layered oxide cathode materials are intriguing for lithium-ion batteries (LIBs) applications because of their relatively low cost and high capacity. Unfortunately, high charging voltage induces bulk layered structure decline and interface environment deterioration, low cobalt content reduces lithium diffusion kinetics, severely limiting the performance liberation of this kind of cathode. Here, a multifunctional Al/Zr dual cation doping strategy is employed to enhance the electrochemical performance of LiNi0.6Co0.05Mn0.35O2 (NCM) cathode at a high charging cut-off voltage of 4.5 V. On the one hand, Al/Zr co-doping weakens the Li+/Ni2+ mixing through magnetic interactions due to the inexistence of unpaired electrons for Al3+ and Zr4+, thereby increasing the lithium diffusion rate and suppressing the harmful coexistence of H1 and H2 phases. On the other hand, they enhance the lattice oxygen framework stability due to strong Al-O and Zr-O bonds, inhibiting the undesired H2 to H3 phase transition and interface lattice oxygen loss, thereby enhancing the stability of the bulk structure and cathode-electrolyte interface. As a result, Al/Zr co-doped NCM (NCMAZ) shows a 94.2 % capacity retention rate after 100 cycles, while that of NCM is only 79.4 %. NCMAZ also exhibits better rate performance than NCM, with output capacities of 92 mAh/g and 59 mAh/g at a high current density of 5C, respectively. The modification strategy will make the high-voltage medium-nickel low-cobalt cathode closer to practical applications.

Systematic study of Co-free LiNi0.9Mn0.07Al0.03O2 Ni-rich cathode materials to realize high-energy density Li-ion batteries

The growing use of EVs and society's energy needs require safe, affordable, durable, and eco-friendly high-energy lithium-ion batteries (LIBs). To this end, we synthesized and investigated the removal of Co from Al-doped Ni-rich cathode materials, specifically LiNi0.9Co0.1Al0.0O2 (NCA-0), LiNi0.9Mn0.1Al0.0O2 (NMA-0), LiNi0.9Mn0.07Al0.03O2 (NMA-3), intending to enhance LIB performance and reduce the reliance on cobalt, a costly and scarce resource. Our study primarily focuses on how the removal of Co affects the material characteristics of Ni-rich cathode material and further introduces aluminum into the cathode composition to study its impacts on electrochemical properties and overall performance. Among the synthesized samples, we discovered that the NMA-3 sample, modified with 3 mol% of Al, exhibited superior battery performance, demonstrating the effectiveness of aluminum in promoting cathode stability. Furthermore, the Al-modified cathode showed promising cycle life under normal and high-temperature conditions. Our NMA-3 demonstrated remarkable capacity retention of ∼ 88 % at 25 °C and ∼ 81 % at 45 °C after 200 cycles at 1C, within a voltage range of 2.8-4.3 V, closely matching the performances of conventional NCM and NCA cathodes. Without cobalt, the cathodes exhibited increased cation disorder leading to inferior rate capabilities at high C-rates. In-situ transmission XRD analysis revealed that the introduction of Al has reduced the phase change and provided much-needed stability to the overall structure of the Co-free NMA-3. Altogether, the findings suggest that our aluminum-modified NMA-3 sample offers a promising approach to developing Co-free, Ni-rich cathodes, effectively paving the way toward sustainable, high-energy-density LIBs.

Advancements and Challenges in High-Capacity Ni-Rich Cathode Materials for Lithium-Ion Batteries

Nowadays, lithium-ion batteries are undoubtedly known as the most promising rechargeable batteries. However, these batteries face some big challenges, like not having enough energy and not lasting long enough, that should be addressed. Ternary Ni-rich Li[NixCoyMnz]O2 and Li[NixCoyAlz]O2 cathode materials stand as the ideal candidate for a cathode active material to achieve high capacity and energy density, low manufacturing cost, and high operating voltage. However, capacity gain from Ni enrichment is nullified by the concurrent fast capacity fading because of issues such as gas evolution, microcracks propagation and pulverization, phase transition, electrolyte decomposition, cation mixing, and dissolution of transition metals at high operating voltage, which hinders their commercialization. In order to tackle these problems, researchers conducted many strategies, including elemental doping, surface coating, and particle engineering. This review paper mainly talks about origins of problems and their mechanisms leading to electrochemical performance deterioration for Ni-rich cathode materials and modification approaches to address the problems.

Enhanced Electrochemical Performance of Ca-Doped Na3V2(PO4)2F3/C Cathode Materials for Sodium-Ion Batteries

Na3V2(PO4)2F3 (NVPF) with a NASICON structure has garnered attention as a cathode material owing to its stable 3D structure, rapid ion diffusion channels, high operating voltage, and impressive cycling stability. Nevertheless, the low intrinsic electronic conductivity of the material leading to a poor rate capability presents a significant challenge for practical application. Herein, we develop a series of Ca-doped NVPF/C cathode materials with various Ca2+ doping levels using a simple sol-gel and carbon thermal reduction approach. X-ray diffraction analysis confirmed that the inclusion of Ca2+ does not alter the crystal structure of the parent material but instead expands the lattice spacing. Density functional theory calculations depict that substituting Ca2+ ions at the V3+ site reduces the band gap, leading to increased electronic conductivity. This substitution also enhanced the structural stability, preventing lattice distortion during the charge/discharge cycles. Furthermore, the presence of the Ca2+ ion introduces two localized states within the band gap, resulting in enhanced electrochemical performance compared to that of Mg-doped NVPF/C. The optimal NVPF-Ca-0.05/C cathode exhibits superior specific capacities of 124 and 86 mAh g-1 at 0.1 and 10 C, respectively. Additionally, the NVPF-Ca-0.05/C demonstrates satisfactory capacity retention of 70% after 1000 charge/discharge cycles at 10 C. These remarkable results can be attributed to the optimized particle size, excellent structural stability, and enhanced ionic and electronic conductivity induced by the Ca doping. Our findings provide valuable insight into the development of cathode material with desirable electrochemical properties.

A review on nickel-rich nickel-cobalt-manganese ternary cathode materials LiNi0.6Co0.2Mn0.2O2 for lithium-ion batteries: performance enhancement by modification

The new energy era has put forward higher requirements for lithium-ion batteries, and the cathode material plays a major role in the determination of electrochemical performance. Due to the advantages of low cost, environmental friendliness, and reversible capacity, high-nickel ternary materials are considered to be one of ideal candidates for power batteries now and in the future. At present, the main design idea of ternary materials is to fully consider the structural stability and safety performance of batteries while maintaining high energy density. Ternary materials currently face problems such as low lithium-ion diffusion rate and irreversible collapse of the structure, although the battery performance can be improved utilizing coating, ion doping, etc., the actual demand requires a more effective modification method based on the intrinsic properties of the material. Based on the summary of the current research status of the ternary material LiNi0.6Co0.2Mn0.2O2 (NCM622), a comparative study of the modification paths of the material was conducted from the level of molecular action mechanism. Finally, the major problems of ternary cathode materials and the future development direction are pointed out to stimulate more innovative insights and facilitate their practical applications.

Design of Nb5+-doped high-nickel layered ternary cathode material and its structure stability

LiNi0.8Co0.1Mn0.1O2(NCM811) is one of the most promising cathode materials for high-energy lithium-ion batteries, but there are still problems such as rapid capacity decay during charge and discharge and poor cycle performance. Elemental doping can significantly improve the electrochemical performance of high nickel ternary cathode materials. In this work, Nb5+-doped NCM811 cathode material was successfully synthesized. The results show that Nb5+doping helps to increase the interlayer spacing of the lithium layer, electron transport, and structural stability, thereby significantly improving the conductivity of Li+. At a high voltage of 4.6 V, the initial discharge specific capacity of 1% Nb5+-doped NCM811 cathode material at 0.1 C is 222.3 mAh·g-1, and the capacity retention rate after 100 cycles at 1 C is 92.03%, which is far more than the capacity retention rate of NCM811 under the same conditions (74.30%). First-principles calculations prove that 1% Nb5+-doped NCM811 cathode material shows the highest electronic conductivity and Nb5+doping will not change the lattice structure, demonstrating the effectiveness of the proposed strategy.

Manganese and Cobalt-Free Ultrahigh-Ni-Rich Single-Crystal Cathode for High-Performance Lithium Batteries

Current commercial nickel (Ni)-rich Mn, Co, and Al-containing cathodes are employed in high-energy-density lithium (Li) batteries all around the globe. The presence of Mn/Co in them brings out several problems, such as high toxicity, high cost, severe transition-metal dissolution, and quick surface degradation. Herein, a Mn/Co-free ultrahigh-Ni-rich single-crystal LiNi_0.94Fe_0.05Cu_0.01O₂ (SCNFCu) cathode with acceptable electrochemical performance is benchmarked against a Mn/Co-containing cathode. Despite having a slightly lower discharge capacity, the SCNFCu cathode retaining 77% of its capacity across 600 deep cycles in full-cell outperforms comparable to a high-Ni single-crystal LiNi_0.9Mn_0.05Co_0.05O₂ (SCNMC; 66%) cathode. It is shown that the stabilizing ions Fe/Cu in the SCNFCu cathode reduce structural disintegration, undesirable side reactions with the electrolyte, transition-metal dissolution, and active Li loss. This discovery provides a new extent for cathode material development for next-generation high-energy, Mn/Co-free Li batteries due to the compositional tuning flexibility and quick scalability of SCNFCu, which is comparable to the SCNMC cathode.

Controlled Synthesis of Single-Crystalline Ni-Rich Cathodes for High-Performance Lithium-Ion Batteries

Single-crystalline LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) has been considered as one of the most promising cathode materials. It addresses the pulverization issue present in its polycrystalline counterpart by eliminating intergranular cracks. However, synthesis of high-performance single-crystalline NCM is still a challenge owing to the lower structure stability of NCM811 at high calcination temperatures (≥900 °C), which is often required to grow single crystals. Herein, we report a synthesis process for microsized single-crystalline NCM811 particles with exposed (010) facets on their lateral sides [named as SC-NCM(010)], which includes the preparation of a well-dispersed microblock-like Ni_0.8Co_0.1Mn_0.1(OH)₂ precursor through coprecipitation assisted with addition of PVP and Na₂SiO₃ and subsequent lithiation of the precursor at 800 °C. The SC-NCM(010) cathode exhibits an excellent capacity retention rate (91.6% after 200 cycles at 1 C, 4.3 V) and a high rate capability (152.2 mAh/g at 20 C, 4.4 V), much superior to those of polycrystalline NCM811 cathodes. However, despite the removal of interparticle boundaries, when cycled between 2.8 and 4.5 V, the SC-NCM(010) cathode still suffers from structural changes including lattice gliding and intragranular cracking. These structural changes are correlated with the interior structural inhomogeneity, which is evidenced by the coexistence of H2 and H3 phases in the fully deintercalated state.

Single-Crystal Nickel-Based Cathodes: Fundamentals and Recent Advances

Lithium-ion batteries (LIBs) represent the most promising choice for meeting the ever-growing demand of society for various electric applications, such as electric transportation, portable electronics, and grid storage. Nickel-rich layered oxides have largely replaced LiCoO2 in commercial batteries because of their low cost, high energy density, and good reliability. Traditional nickel-based oxide particles, usually called polycrystal materials, are composed of microsized primary particles. However, polycrystal particles tend to suffer from pulverization and severe side reactions along grain boundaries during cycling. These phenomena accelerate cell degradation. Single-crystal materials, which exhibit robust mechanical strength and a high surface area, have great potential to address the challenges that hinder their polycrystal counterparts. A comprehensive understanding of the growing body of research related to single-crystal materials is imperative to improve the performance of cathodes in LIBs. This review highlights origins, recent developments, challenges, and opportunities for single-crystal layered oxide cathodes. The synthesis science behind single-crystal materials and comparative studies between single-crystal and polycrystal materials are discussed in detail. Industrial techniques and facilities are also reviewed in combination with our group’s experiences in single-crystal research. Future development should focus on facile production with strong control of the particle size and distribution, structural defects, and impurities to fully reap the benefits of single-crystal materials.

Graphical abstract

Challenges and Modification Strategies of Ni-Rich Cathode Materials Operating at High-Voltage

Ni-rich cathode materials have become promising candidates for lithium-based automotive batteries due to the obvious advantage of electrochemical performance. Increasing the operating voltage is an effective means to obtain a higher specific capacity, which also helps to achieve the goal of high energy density (capacity × voltage) of power lithium-ion batteries (LIBs). However, under high operating voltage, surface degradation will occur between Ni-rich cathode materials and the electrolytes, forming a solid interface film with high resistance, releasing O₂, CO₂ and other gases. Ni-rich cathode materials have serious cation mixing, resulting in an adverse phase transition. In addition, the high working voltage will cause microcracks, leading to contact failure and repeated surface reactions. In order to solve the above problems, researchers have proposed many modification methods to deal with the decline of electrochemical performance for Ni-rich cathode materials under high voltage such as element doping, surface coating, single-crystal fabrication, structural design and multifunctional electrolyte additives. This review mainly introduces the challenges and modification strategies for Ni-rich cathode materials under high voltage operation. The future application and development trend of Ni-rich cathode materials for high specific energy LIBs are projected.

Multi-Role Surface Modification of Single-Crystalline Nickel-Rich Lithium Nickel Cobalt Manganese Oxides Cathodes with WO3 to Improve Performance for Lithium-Ion Batteries

Compared with the polycrystalline system, the single-crystalline ternary cathode material has better cycle stability because the only primary particles without grain boundaries effectively alleviate the formation of micro/nanocracks and retain better structural integrity. Therefore, it has received extensive research attention. There is no consistent result whether tungsten oxide acts as doping and/or coating from the surface modification of the polycrystalline system. Meanwhile, there is no report on the surface modification of the single-crystalline system by tungsten oxide. In this paper, multirole surface modification of single-crystalline nickel-rich ternary cathode material LiNi0.6Co0.2Mn0.2O2 by WO3 is studied by a simple method of adding WO3 followed by calcination. The results show that with the change in the amount of WO3 added, single-crystalline nickel-rich ternary cathode material can be separately doped, separately coated, and both doped and coated. Either doping or coating effectively enhances the structural stability, reduces the polarization of the material, and improves the lithium-ion diffusion kinetics, thus improving the cycle stability and rate performance of the battery. Interestingly, both doping and coating (for SC-NCM622-0.5%WO3) do not show a more excellent synergistic effect, while the single coating (for SC-NCM622-1.0%WO3) after eliminating the rock-salt phase layer performs the most excellent modification effect.

Biomineralized Prussian Blue Nanotherapeutic for Enhanced Cancer Photothermal Therapy

Photothermal therapy is a promising tumor ablation technique that converts light into heat energy to kill cancer cells. Prussian blue (PB), a biocompatible photothermal reagent, has been widely explored for...

Gospel for Improving the Lithium Storage Performance of High-Voltage High-Nickel Low-Cobalt Layered Oxide Cathode Materials

High-voltage high-nickel low-cobalt lithium layered oxide cathodes show great application prospects for lithium-ion batteries due to their low cost and high capacity. However, deterioration of the bulk structure and the electrode-electrolyte interface will significantly endanger the cycle life and thermal stability of the battery as the nickel content and voltage increase. We present here a lattice doping strategy to greatly improve the cell performance by doping a small dose of Ti (2 mol %) in LiNi_0.6Co_0.05Mn_0.35O₂. Through density functional theory calculations, we know that the diffusion energy barrier of Li⁺ decreases and the activation energy of surface lattice oxygen atom loss increases after Ti doping, thereby improving the rate performance and inhibiting the undesired phase transition. The battery in situ X-ray diffraction (XRD) pattern demonstrates that Ti doping tunes the H1-H2 phase-transition process from a two-phase reaction to a single-phase reaction and inhibits the undesired H2-H3 phase transition, minimizing the mechanical degradation. The variable temperature in situ XRD reveals delayed phase-transition temperature to improve thermal stability. These improvements can be attributed to Ti doping to passivate the reactivity of the layered oxide cathode, which is fundamentally related to the strong Ti-O bond and no unpaired electrons for Ti⁴⁺. This work provides valuable strategic guidelines for the use of high-voltage high-nickel low-cobalt cathodes in lithium-ion batteries.

Elucidating the Effect of the Dopant Ionic Radius on the Structure and Electrochemical Performance of Ni-Rich Layered Oxides for Lithium-Ion Batteries

The merits of Ni-rich layered oxide cathodes in specific capacity and material cost accelerate their practical applications in electric vehicles and grid energy storage. However, detrimental structural deterioration occurs inevitably during long-term cycling, leading to potential instability and capacity decay of the cathodes. In this work, we investigate the effect of the doped cation radius on the electrochemical performance and structural stability of Ni-rich cathode materials by doping with Mg and Ca ions in LiNi_0.8Co_0.1Mn_0.1O₂. The results reveal that an increase in the doping ion radius can enlarge the interlayer spacing but lead to the collapse of the layered structure if the ion radius is too large, which undermines the cycling stability of the cathode material. Compared with the Ca-doped sample and the pristine material, Mg-doped LiNi_0.8Co_0.1Mn_0.1O₂ presents improved structural stability and superior thermal stability due to the pillar and glue roles of medium-sized Mg ions in the lithium layer. The results of this study suggest that a suitable ionic radius of the dopant is critical for stabilizing the structure and improving the electrochemical properties of Ni-rich layered oxide cathode materials.

Chemomechanically Stable Ultrahigh-Ni Single-Crystalline Cathodes with Improved Oxygen Retention and Delayed Phase Degradations

The pressing demand in electrical vehicle (EV) markets for high-energy-density lithium-ion batteries (LIBs) requires further increasing the Ni content in high-Ni and low-Co cathodes. However, the commercialization of high-Ni cathodes is hindered by their intrinsic chemomechanical instabilities and fast capacity fade. The emerging single-crystalline strategy offers a promising solution, yet the operation and degradation mechanism of single-crystalline cathodes remain elusive, especially in the extremely challenging ultrahigh-Ni (Ni > 90%) regime whereby the phase transformation, oxygen loss, and mechanical instability are exacerbated with increased Ni content. Herein, we decipher the atomic-scale stabilization mechanism controlling the enhanced cycling performance of an ultrahigh-Ni single-crystalline cathode. We find that the charge/discharge inhomogeneity, the intergranular cracking, and oxygen-loss-related phase degradations that are prominent in ultrahigh-Ni polycrystalline cathodes are considerably suppressed in their single-crystalline counterparts, leading to improved chemomechanical and cycling stabilities of the single-crystalline cathodes. Our work offers important guidance for designing next-generation single-crystalline cathodes for high-capacity, long-life LIBs.

Utilizing the Intrinsic Thermal Instability of Swedenborgite Structured YBaCo4O7+δ as an Opportunity for Material Engineering in Lithium-Ion Batteries by Er and Ga Co-Doping Processes

We firstly introduce Er and Ga co-doped swedenborgite-structured YBaCo4O7+δ (YBC) as a cathode-active material in lithium-ion batteries (LIBs), aiming at converting the phase instability of YBC at high temperatures into a strategic way of enhancing the structural stability of layered cathode-active materials. Our recent publication reported that Y0.8Er0.2BaCo3.2Ga0.8O7+δ (YEBCG) showed excellent phase stability compared to YBC in a fuel cell operating condition. By contrast, the feasibility of the LiCoO2 (LCO) phase, which is derived from swedenborgite-structured YBC-based materials, as a LIB cathode-active material is investigated and the effects of co-doping with the Er and Ga ions on the structural and electrochemical properties of Li-intercalated YBC are systemically studied. The intrinsic swedenborgite structure of YBC-based materials with tetrahedrally coordinated Co2+/Co3+ are partially transformed into octahedrally coordinated Co3+, resulting in the formation of an LCO layered structure with a space group of R-3m that can work as a Li-ion migration path. Li-intercalated YEBCG (Li[YEBCG]) shows effective suppression of structural phase transition during cycling, leading to the enhancement of LIB performance in Coulombic efficiency, capacity retention, and rate capability. The galvanostatic intermittent titration technique, cyclic voltammetry and electrochemical impedance spectroscopy are performed to elucidate the enhanced phase stability of Li[YEBCG].

Preparation and Electrochemical Characterization of La and Al Co-doped NCM811 Cathode Materials

LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) became a research hot point because of its low cost, environmental friendliness, and excellent electrochemical performance. However, Li⁺/Ni²⁺ intermixing is an essential factor affecting its applicability. Doping could be an important method to improve the electrochemical performance of NCM811-based cathode materials. In this work, La and Al co-doped NCM811 was prepared by a solid-state method. Results from X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) and electrochemical performance were discussed in depth. These showed that when La and Al doping concentrations were 1 and 0.5%, the samples showed the best performance. The as-improved performances were mainly attributed to the reduced Li⁺/Ni²⁺ intermixing, suppressed phase transition, and decreased potential polarization and impedance.

Nickel-Rich Layered Cathode Materials for Lithium-Ion Batteries

Nickel-rich layered transition metal oxides are considered as promising cathode candidates to construct next-generation lithium-ion batteries to satisfy the demands of electrical vehicles, because of the high energy density, low cost, and environment friendliness. However, some problems related to rate capability, structure stability, and safety still hamper their commercial application. In this Review, beginning with the relationships between the physicochemical properties and electrochemical performance, the underlying mechanisms of the capacity/voltage fade and the unstable structure of Ni-rich cathodes are deeply analyzed. Furthermore, the recent research progress of Ni-rich oxide cathode materials through element doping, surface modification, and structure tuning are summarized. Finally, this review concludes by discussing new insights to expand the field of Ni-rich oxides and promote practical applications.

NCA, NCM811, and the Route to Ni-Richer Lithium-Ion Batteries

The aim of this article is to examine the progress achieved in the recent years on two advanced cathode materials for EV Li-ion batteries, namely Ni-rich layered oxides LiNi0.8Co0.15Al0.05O2 (NCA) and LiNi0.8Co0.1Mn0.1O2 (NCM811). Both materials have the common layered (two-dimensional) crystal network isostructural with LiCoO2. The performance of these electrode materials are examined, the mitigation of their drawbacks (i.e., antisite defects, microcracks, surface side reactions) are discussed, together with the prospect on a next generation of Li-ion batteries with Co-free Ni-rich Li-ion batteries.

Research Progress on the Surface of High-Nickel Nickel-Cobalt-Manganese Ternary Cathode Materials: A Mini Review

To address increasingly prominent energy problems, lithium-ion batteries have been widely developed. The high-nickel type nickel–cobalt–manganese (NCM) ternary cathode material has attracted attention because of its high energy density, but it has problems such as cation mixing. To address these issues, it is necessary to start from the surface and interface of the cathode material, explore the mechanism underlying the material's structural change and the occurrence of side reactions, and propose corresponding optimization schemes. This article reviews the defects caused by cation mixing and energy bands in high-nickel NCM ternary cathode materials. This review discusses the reasons why the core-shell structure has become an optimized high-nickel ternary cathode material in recent years and the research progress of core-shell materials. The synthesis method of high-nickel NCM ternary cathode material is summarized. A good theoretical basis for future experimental exploration is provided.

Assembly of MXene/PP Separator and Its Enhancement for Ni-Rich LiNi0.8Co0.1Mn0.1O2 Electrochemical Performance

In this work, a few-layer MXene is prepared and sprinkled on a commercial polypropylene (PP) separator by a facile spraying method to enhance the electrochemistry of the Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode. Scanning electron microscope (SEM) and X-ray diffraction (XRD) are used to characterize the morphology and structure of MXene. Fourier transform infrared spectroscopy (FT-IR) and a contact angle tester are used to measure the bond structure and surface wettability PP and MXene/PP separator. The effect of the MXene/PP separator on the electrochemical performance of ternary NCM811 material is tested by an electrochemical workstation. The results show that the two-dimensional MXene material could improve the wettability of the separator to the electrolyte and greatly enhance the electrochemical properties of the NCM811 cathode. During 0.5 C current density cycling, the Li/NCM811 cell with MXene/PP separator remains at 166.2 mAh/g after the 100 cycles with ~90.7% retention. The R_ct of MXene/PP cell is measured to be ~28.0 Ω. Combining all analyses results related to MXene/PP separator, the strategy by spraying the MXene on commercial PP is considered as a simple, convenient, and effective way to improve the electrochemical performance of the Ni-rich NCM811 cathode and it is expected to achieve large-scale in high-performance lithium-ion batteries in the near future.

A comprehensive study of the multiple effects of Y/Al substitution on O3-type NaNi0.33Mn0.33Fe0.33O2 with improved cycling stability and rate capability for Na-ion battery applications

O3-NaNi0.33Mn0.33Fe0.33O2 layered oxide has attracted increasing attention as one of the most promising materials for Na-ion battery applications due to air stability and environmental friendliness, but the complex phase transitions and inferior cycling stability are extremely challenging to overcome. Cation substitution has been widely used to stabilize crystal structures and improve electrochemical performance for SIBs. Based on past experimental results, it was discovered that the transition metal-oxygen bond energy of the introduced dopant is an important factor for optimizing electrochemical performance. In this study, we validated our hypothesis that yttrium (Y)-which possesses high bond energy for oxygen-is most likely to be an ideal doping element by conducting a comparative study of substituting Mn in O3-NaNi0.33Mn0.33Fe0.33O2 layered oxide with aluminum (Al) and Y through elemental doping. As hypothesized, the electrochemical properties of NaNi0.33Mn0.33Fe0.33O2 have increased markedly by introducing a small amount of Y and Al, and the Y-doped materials showed superior rate performance and cycling stability due to enhanced Na+ diffusion reaction kinetics and layered structure stability. Furthermore, the substitution of Y for Mn can improve thermal stability and alleviate phase transformations. The improvement mechanism of Y substitution can be attributed to a larger d-spacing and stronger metal-oxygen bond. These results suggest that structural modulation is an effective strategy to reinforce electrochemical properties of layered oxides and provides some guidance about designing promising electrode materials.

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.

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.

Li-Nb-O Coating/Substitution Enhances the Electrochemical Performance of the LiNi0.8Mn0.1Co0.1O2 (NMC 811) Cathode

High-nickel layered oxides, such as NMC 811, are very attractive high energy density cathode materials. However, the high nickel content creates a number of challenges, including high surface reactivity and structural instability. Through a wet chemistry method, a Li-Nb-O coated and substituted NMC 811 was obtained in a single step treatment. This Li-Nb-O treatment not only supplied a protective surface coating but also optimized the electrochemical behavior by Nb⁵⁺ incorporation into the bulk structure. As a result, the 1st capacity loss was significantly reduced (13.7 vs 25.1 mA h/g), contributing at least a 5% increase to the energy density of the full cell. In addition, both the rate (158 vs 135 mA h/g at 2C) and capacity retention (89.6 vs 81.6% after 60 cycles) performance were enhanced.

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.

Probing the Structural Transition Kinetics and Charge Compensation of the P2-Na0.78Al0.05Ni0.33Mn0.60O2 Cathode for Sodium Ion Batteries

Although the layered P2-type Na_0.67Ni_0.33Mn_0.67O₂ materials show high discharge voltage and specific capacity, they suffer from severe structural instabilities and surface reaction upon Na exchange for sodium-ion batteries (SIBs). Therefore, it is quite necessary to reveal the underlying structural evolution mechanism and diffusion kinetics to improve the structural/electrochemical stability for application in SIBs. Here, we synthesize a P2-type Na_0.78Al_0.05Ni_0.33Mn_0.60O₂ material by a small dose of Al replacing the Mn, aiming at enhancing the structural stability without sacrificing the average discharge voltage and theoretical capacity. The etching X-ray photoelectron spectroscopy and energy-dispersive X-ray mapping/line scan results indicate that the Al doping induces dual effects of the Al₂O₃ surface coating and the bulk lattice doping, which efficiently suppress the accumulation of structural irreversible changes from P2 to O2, the volume changes, and surface reactions at high voltage. Obvious improvements are further found on the diffusion kinetics of Na ions as well as the decrease of overall voltage polarization. Interestingly, the dual effects of Al doping lead to the significant increase of capacity retention after 50 cycles and improvement of rate capability compared with the undoped counterpart between 2.0 and 4.5 V. Hence, this work sheds new light on stabilizing the P2-Na-Ni-Mn-O materials, which provides a rewarding avenue to develop better SIBs.

Nonflammable quasi-solid-state electrolyte for stable lithium-metal batteries

Rechargeable lithium batteries with high-voltage/capacity cathodes are regarded as promising high-energy-density energy-storage systems. Nevertheless, these systems are restricted by some critical challenges, such as flammable electrolyte, lithium dendrite formation and rapid capacity fade at high voltage and elevated temperature. In this work, we report a quasi-solid-state composite electrolyte (QCE) prepared by in situ polymerization reactions. The electrolyte consists of polymer matrix, inorganic filler, nonflammable plasticizers and Li salt, and shows a good thermal stability, a moderate ionic conductivity of 2.8 × 10⁻⁴ S cm⁻¹ at 25 °C, and a wide electrochemical window up to 6.7 V. The batteries with the QCE show good electrochemical performance when coupled with lithium metal anode and LiCoO₂ or LiNi_0.8Mn_0.1Co_0.1O₂ cathodes. Pouch-type batteries with the QCE also exhibit stable cycling, and can tolerate abuse testes such as folding, cutting and nail penetration. The in situ formed fluorides and phosphides from the plasticizers stabilize the interfaces between the QCE and electrodes, which enables stable cycling of Li metal batteries.

A nonflammable quasi-solid-state composite electrolyte was prepared by in situ polymerization for safe, stable Li metal batteries.

Energy Storage and Thermostability of Li3VO4-Coated LiNi0.8Co0.1Mn0.1O2 as Cathode Materials for Lithium Ion Batteries

The electrochemical performances and thermostability of LiNi_0.8Co_0.1Mn_0.1O₂ is affected by temperature. High ambient temperature or irregular heat distribution accelerates the decline of LiNi_0.8Co_0.1Mn_0.1O₂ performance, shortens cathode material life. In this work, the energy storage and thermostability of the Li₃VO₄-coated LiNi_0.8Co_0.1Mn_0.1O₂ cathode material were studied for the first time by electrochemical calorimetry methode at different temperatures and rates. Results show that Li₃VO₄-coated LiNi_0.8Co_0.1Mn_0.1O₂ cathode material has excellent rate and cycle performance. The thermal electrochemical experiments further show that the thermal stability of Li₃VO₄-coated LiNi_0.8Co_0.1Mn_0.1O₂ cathode material in charge-discharge energy storage and conversion system is better than LiNi_0.8Co_0.1Mn_0.1O₂ at 30, 40, and 50°C. The enhanced performance can be attributed to the fact that Li₃VO₄ coating promotes the transmission of lithium ions and protects the active material from electrolyte corrosion at different temperature, as well as reduces side reaction, electrode polarization and heat generation of cathode materials. The Li₃VO₄-coated LiNi_0.8Co_0.1Mn_0.1O₂ cathode material has excellent energy storage properties and thermostability, which are beneficial to the development of electronic equipment.

Towards deriving Ni-rich cathode and oxide-based anode materials from hydroxides by sharing a facile co-precipitation method

Although intensive studies have been conducted on layered transition metal oxide(TMO)-based cathode materials and metal oxide-based anode materials for Li-ion batteries, their precursors generally follow different or even complex synthesis routes. To share one route for preparing precursors of the cathode and anode materials, herein, we demonstrate a facile co-precipitation method to fabricate Ni-rich hydroxide precursors of Ni0.8Co0.1Mn0.1(OH)2. Ni-rich layered oxide of LiNi0.8Co0.1Mn0.1O2 is obtained by lithiation of the precursor in air. An NiO-based anode material is prepared by calcining the precursor or multi-walled carbon nanotubes (MWCNTs) incorporated precursors. The pre-addition of ammonia solution can simplify the co-precipitation procedures and the use of an air atmosphere can also make the heat treatment facile. LiNi0.8Co0.1Mn0.1O2 as the cathode material delivers a reversible capacity of 194 mA h g-1 at 40 mA g-1 and a notable cycling retention of 88.8% after 100 cycles at 200 mA g-1. This noticeable performance of the cathode arises from a decent particle morphology and high crystallinity of the layered oxides. As the anode material, the MWCNTs-incorporated oxides deliver a much higher reversible capacity of 811.1 mA h g-1 after 200 cycles compared to the pristine oxides without MWCNTs. The improvement on electrochemical performance can be attributed to synergistic effects from MWCNTs incorporation, including reinforced electronic conductivity, rich meso-pores and an alleviated volume effect. This facile and sharing method may offer an integrated and economical approach for commercial production of Ni-rich electrode materials for Li-ion batteries.

Synthesis Method for Long Cycle Life Lithium-Ion Cathode Material: Nickel-Rich Core-Shell LiNi0.8Co0.1Mn0.1O2

High-nickel materials with core-shell structures, whose bulk is rich in nickel content and the outer shell is rich in manganese content, have been demonstrated to improve cycle stability. The high-nickel cathode material LiNi_0.8Co_0.1Mn_0.1O₂ is a very promising material for lithium-ion batteries; however, its low rate performance and especially cycle performance currently hamper further commercialization. This study presents a new synthesis method to prepare this core-shell material (LiNi_0.8Co_0.1Mn_0.1O₂@ x[Li-Mn-O], x = 0.01, 0.03, 0.06). Electrochemical data show that LiNi_0.8Co_0.1Mn_0.1O₂@ x[Li-Mn-O] ( x = 0.03, CS-0.03) exhibits the best high-rate performance, cycle stability, and thermal stability. The initial discharge capacity of the core-shell sample CS-0.03 is 118 mAh g^-1, which is almost the same as the discharge capacity of pristine LiNi_0.8Mn_0.1Co_0.1O₂ (117 mAh g^-1) at the rate of 10 C in the voltage range of 3.0-4.3 V. Notably the capacity decay of CS-0.03 is 18.4% after 200 cycles compared to 27% decay in capacity of the pristine sample. Furthermore, CS-0.03 exhibits better thermal cycling stability. The capacity retention of the CS-0.03 sample reached 65.1% which is over 1.3 times than that of the pristine one, whose capacity retention is 49.2% after 105 cycles (55 °C). Evidently, the core-shell structured CS-0.03 sample has excellent cycle stability and this synthesis method can be applied to other cathode materials.

Exposing the {010} Planes by Oriented Self-Assembly with Nanosheets To Improve the Electrochemical Performances of Ni-Rich Li[Ni0.8Co0.1Mn0.1]O2 Microspheres

A modified Ni-rich Li[Ni_0.8Co_0.1Mn_0.1]O₂ cathode material with exposed {010} planes is successfully synthesized for lithium-ion batteries. The scanning electron microscopy images have demonstrated that by tuning the ammonia concentration during the synthesis of precursors, the primary nanosheets could be successfully stacked along the [001] crystal axis predominantly, self-assembling like multilayers. According to the high-resolution transmission electron microscopy results, such a morphology benefits the growth of the {010} active planes of final layered cathodes during calcination treatment, resulting in the increased area of the exposed {010} active planes, a well-ordered layer structure, and a lower cation mixing disorder. The Li-ion diffusion coefficient has also been improved after the modification based on the results of potentiostatic intermittent titration technique. As a consequence, the modified Li[Ni_0.8Co_0.1Mn_0.1]O₂ material exhibits superior initial discharges of 201.6 mA h g^-1 at 0.2 C and 185.7 mA h g^-1 at 1 C within 2.8-4.3 V (vs Li⁺/Li), and their capacity retentions after 100 cycles reach 90 and 90.6%, respectively. The capacity at 10 C also increases from 98.3 to 146.5 mA h g^-1 after the modification. Our work proposes a novel approach for exposing high-energy {010} active planes of the layered cathode material and again confirms its validity in improving electrochemical properties.