Ni-rich Layered Oxide Cathode Research Articles

Tungsten-based Li-rich rock salt stabilized Co-free Ni-rich layered oxide cathodes

Tungsten-based Li-rich rock salt stabilized Co-free Ni-rich layered oxide cathodes

Surface to bulk design empowering Ni-rich layered oxide cathode in sulfide-based All-Solid-State batteries

All-solid-state batteries (ASSBs) employing sulfide solid electrolytes (SSE) and high-nickel layered oxide cathodes have attracted considerable attention, attributed to their superior safety and great potential for high energy densities. However, the interface compatibility between SSE and nickel-rich oxide cathode remains a challenge. Here, a dual-functional strategy of Li6.25La3Zr2Al0.25O12 surface coating and bulk Zr doping in LiNi0.8Co0.1Mn0.1O2 was proposed (NCM811@CD-LLZAO), aiming to enhance the interfacial compatibility toward sulfide-based ASSBs. The fabricated ASSBs exhibit an impressive capacity retention rate of 91.1% after 100cycles at 0.1C and can sustain an ultra-long cycling performance over 1000cycles at 1.0C. Remarkably, even at a high rate of 11.0C, the battery still maintains a high capacity, highlighting its excellent rate performance. The distribution of relaxation time (DRT) analysis reveals that the LLZAO buffering layer can enhance the kinetics at the cathode/electrolyte interface. Theoretical calculation further confirms that the strong Zr-O bond formed by Zr doping can stabilize the lattice oxygen and effectively prevent the sulfide solid electrolyte from further electrochemical oxidation, thereby enhancing the interfacial dynamic and stability. These encouraging results provide a new strategy for the practical application of high-energy–density ASSBs, enabling fast charge transfer, extended cycle longevity and enhanced safety.

A short review on fast charging of Ni-rich layered oxide cathodes

A short review on fast charging of Ni-rich layered oxide cathodes

Influence of Cathode Calendering Density on the Cycling Stability of Li-Ion Batteries Using NMC811 Single or Poly Crystalline Particles

Calendering of battery electrodes is a commonly used manufacturing process that enhances electrode packing density and therefore improves the volumetric energy density. While calendering is standard industrial practice, it is known to crack cathode particles, thereby increasing the electrode surface area. The latter is particularly problematic for new Ni-rich layered transition metal oxide cathodes, such as NMC811, which are known to have substantial surface-driven degradation processes. To establish appropriate calendering practices for these new cathode materials, we conducted a comparative analysis of uncalendered electrodes with electrodes that have a 35% porosity (industrial standard), and 25% porosity (highly calendered) for both single crystal (SC) and polycrystalline (PC) NMC811. PC cathodes show clear signs of cracking and decrease in rate capability when calendered to 25% porosity, whereas SC NMC811 cathodes, achieve better cycling stability and no penalty in rate performance at these high packing densities. These findings suggest that SC NMC811 cathodes should be calendered more densely, and we provide a comprehensive overview of both electrochemical and material characterisation methods that corroborate why PC and SC electrodes show such different degradation behaviour. Overall, this work is important because it shows how new single-crystal cathode materials can offer additional advantages both in terms of rate performance and cycling stability by calendaring them more densely.

Surface Coating of NCM523 Cathode Electrodes by the Difunctional Block Copolymer/Lithium Salt Composites.

Nickel-rich layered oxide cathodes, such as LiNi0.5Co0.2Mn0.3O2 (NCM523), are prevalent in high-power batteries owing to their high energy density. However, these cathodes suffer from undesirable side reactions occurring at the cathode/liquid electrolyte interface, leading to inferior interface stability and poor cycle life. To address these issues, herein, an amphiphilic diblock copolymer poly(dimethylsiloxane)-block-poly(acrylic acid) (PDMS-b-PAA) along with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is utilized for modifying the electrode surface. This modification causes a thin and stable cathode-electrolyte interface (CEI) on the surface of NCM523 particles, as evidenced by XPS, TEM, and EIS analysis. The introduction of this modified interface successfully suppresses the capacity fading of NCM523. After 200 cycles at a rate of 1.0 C, the capacity of the modified NCM523 cathode is 108.7 mAh g-1, with a capacity retention of 82.8%, while the control samples without the polymer modification display a capacity retention of 72.7%. These results outline the distinct advantage of electrode surface modification with diblock copolymers/LiTFSI for the stabilization of Ni-rich layered oxide cathodes.

Study on the role of d electronic donor in Ni-rich layered oxide cathode materials for Li-ion battery

The further development of electrochemical devices and electric vehicles requires advanced Li-ion battery with higher energy density and longer lifetimes. Ni-rich LiNi0.8Co0.1Mn0.1O2 layered oxide cathodes are receiving increased attention due to its high specific capacity. Nevertheless, the role of d electrons in Ni-rich cathodes has not been uniformly reported, which hinders the design of high-performance Ni-rich cathodes. To address this issue, the role of d electronic donor in Ni-rich layered oxide cathode materials was investigated by first principles calculations and explored the mechanism for enhancing the electrochemical performance in this work. The results show that the d electronic donor V and Mo can elevate the intercalation potential, improve the stability, and enhance the diffusion rate of Li-ions in Ni-rich cathode. This theoretical study complements the mechanism for improving the electrochemical performance of Ni-rich cathode, and provides a theoretical basis for the design of high-performance Li-ion battery.

Ni-Rich Layered Oxide Cathodes/Sulfide Electrolyte Interface in Solid-State Lithium Battery.

Because of the high specific capacity and low cost, Ni-rich layered oxide (NRLO) cathodes are one of the most promising cathode candidates for the next high-energy-density lithium-ion batteries. However, they face structure and interface instability challenges, especially the battery safety risk caused by using an intrinsic flammable organic liquid electrolyte. In this regard, a solid electrolyte with high safety is of great significance to promote the development of energy storage. Among them, sulfide electrolytes are considered to be the most potential substitutes for liquid electrolytes because of their high ionic conductivity and good processing properties. Nevertheless, the interfacial incompatibility between the sulfide electrolyte and NRLO cathode is the critical challenge for high-performance sulfide all-solid-state lithium batteries (ASSLBs). In this review, we summarize the problems of the Ni-rich cathode/sulfide solid electrolyte interface and the strategies to improve the interface stability. On the basis of these insights, we highlight the scientific problems and technological challenges that need to be resolved urgently and propose several potential directions to further improve the interface stability. The objective of this study is to provide a comprehensive understanding and insightful recommendations for the enhancement of the sulfide ASSLBs with NRLO cathode.

A Plastic-Crystal Electrolyte Layer Promotes Interfacial Stability of Ni-Rich Oxide Cathode in Li6PS5Cl-Based All-Solid-State Rechargeable Li Batteries.

Unfavorable parasitic reactions between the Ni-rich layered oxide cathode and the sulfide solid electrolyte have plagued the realization of all-solid-state rechargeable Li batteries. The accumulation of inactive by-products (P2Sx, S, POx n- and SOx n-) at the cathode-sulfide interface impedes fast Li-ion transfer, which accounts for sluggish reaction kinetics and significant loss of cathode capacity. Herein, we proposed an easily scalable approach to stabilize the cathode electrochemistry via coating the cathode particles by a uniform, Li+-conductive plastic-crystal electrolyte nanolayer on their surface. The electrolyte, which simply consists of succinonitrile and Li bis(trifluoromethanesulphonyl)imide, serves as an interfacial buffer to effectively suppress the adverse phase transition in highly delithiated cathode materials, and the loss of lattice oxygen and generation of inactive oxygenated by-products at the cathode-sulfide interface. Consequently, an all-solid-state rechargeable Li battery with the modified cathode delivers high specific capacities of 168 mAh g-1 at 0.1 C and a high capacity retention >80 % after 100 cycles. Our work sheds new light on rational design of electrode-electrolyte interface for the next-generation high-energy batteries.

Surface-to-bulk synergistic modification enables stable interface of Ni-rich oxide cathode for all-solid-state lithium batteries

All-solid-state lithium batteries (ASSLBs) are supposed to a highly forward-looking battery technology by reason of their conspicuous energy density and excellent safety. Ni-rich layered oxide cathodes have been extensively studied in ASSLB systems with sulfide electrolytes owing to their high voltage and preeminent specific capacity. However, the electrochemical performance of ASSLBs is severely degraded due to the interfacial physical contact failure, space charge layer effect, and chemical/electrochemical side reactions between sulfide electrolytes and Ni-rich oxide cathodes. In this work, the surface of LiNi0.92Co0.04Mn0.04O2 (NCM92) is coated with a nano-level CeO2 buffer layer and is simultaneously doped with Ce element (NCM92–1%Ce) by one-step wet chemical method. Ce doping is beneficial for maintaining structural stability and suppressing irreversible phase transition. The CeO2 buffer layer can efficaciously avoid the oxidation and decomposition phenomenon at the interface between NCM92 and sulfide electrolyte. As expected, NCM92–1%Ce cathode shows the discharge specific capacity of 141.46 mAh g−1 after 80 cycles at 0.2C with 79.32% capacity retention rate, which is much higher than that of the unmodified NCM92 cathode. The results indicate that the surface-to-bulk synergistic modification strategy can successfully improve the structure toughness and interface stability of Ni-rich oxide cathode for ASSLBs with sulfide electrolytes.

High Safety Electrolyte Design for Enabling High Energy-Density System of LiNi0.8Co0.1Mn0.1O2//Phosphorus by Simultaneously Adjusting Dual Electrode/Electrolyte Interfaces.

The demand for state-of-the-art high-energy-density lithium-ion batteries is increasing. However, the low specific capacity of electrode materials in conventional full-cell systems cannot meet the requirements. Ni-rich layered oxide cathodes such as Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) have a high theoretical specific capacity of 200 mAh g-1, but it is always accompanied by side reactions on the electrode/electrolyte interface. Phosphorus anode possesses a high theoretical specific capacity of 2596 mAh g-1, but it has a huge volume expansion (≈300%). Herein, a highly compatible and secure electrolyte is reported via introducing an additive with a narrow electrochemical window, Lithium difluoro(oxalato)borate (LiDFOB), into 1m LiPF6 EC/DMC with tris (2,2,2-trifluoroethyl) phosphate (TFEP) as a cosolvent. LiDFOB participates in the formation of organic/inorganic hybrid electrode/electrolyte interface layers at both the cathode and anode sides. The side reactions on the surface of the NCM811 cathode and the volume expansion of the phosphorus anode are effectively alleviated. The NCM811//RP full cell in this electrolyte shows high capacity retention of 82% after 150 cycles at a 0.5C rate. Meanwhile, the electrolyte shows non-flammability. This work highlights the importance of manipulating the electrode/electrolyte interface layers for the design of lithium-ion batteries with high energy density.

Boron- and calcium-interspersed cathode-electrolyte interphases on Ni-rich layered oxide cathodes for advanced performance lithium-ion batteries

Although Ni-rich layered oxides (Ni-rich NCM) have become the preferred cathode materials in the electric vehicle market, their unsustainable cycling behavior arising from the extremely high reactivity at the interface has become a formidable challenge. To alleviate this problem, we propose modifying the cathode-electrolyte interphase (CEI) of Ni-rich L-NCM cathodes by incorporating B/Ca functional groups. Dual-functionalized CEI layers are prepared by heating boric acid (H3BO3) and calcium oxide (CaO) in a one-step process. Islands of B- and Ca-functionalized CEI layer are observed at the Ni-rich L-NCM cathode, and the thickness is controlled to approximately 2.4 nm. The B-functional group not only lowers the concentration of residual lithium but also compensates for the longer Li+ migration distance by providing a desirable pathway based on ion-hopping sites. The Ca functional groups increase the mechanical rigidity of the Ni-rich L-NCM cathode, which inhibits the appearance of microcracks. In terms of its cycling behavior, the capacity retention of the cell with the B/Ca-incorporated Ni-rich L-NCM cathode improves markedly (72.4%), whereas the bare Ni-rich L-NCM material only retains 44.3% of its capacity after 100 cycles.

Origins and Importance of Intragranular Cracking in Layered Lithium Transition Metal Oxide Cathodes.

Li-ion batteries have a pivotal role in the transition toward electric transportation. Ni-rich layered transition metal oxide (LTMO) cathode materials promise high specific capacity and lower cost but exhibit faster degradation compared with lower Ni alternatives. Here, we employ high-resolution electron microscopy and spectroscopy techniques to investigate the nanoscale origins and impact on performance of intragranular cracking (within primary crystals) in Ni-rich LTMOs. We find that intragranular cracking is widespread in charged specimens early in cycle life but uncommon in discharged samples even after cycling. The distribution of intragranular cracking is highly inhomogeneous. We conclude that intragranular cracking is caused by local stresses that can have several independent sources: neighboring particle anisotropic expansion/contraction, Li- and TM-inhomogeneities at the primary and secondary particle levels, and interfacing of electrochemically active and inactive phases. Our results suggest that intragranular cracks can manifest at different points of life of the cathode and can potentially lead to capacity fade and impedance rise of LTMO cathodes through plane gliding and particle detachment that lead to exposure of additional surfaces to the electrolyte and loss of electrical contact.

Surface reactivity versus microcracks in Ni-rich layered oxide cathodes: Which is critical for long cycle life？

Capacity fading of Ni-rich cathode is thought to originate from the formation of inactive rock-salt phase induced by surface reactivity and the isolation of active material caused by microcracks due to anisotropic volume contraction of grains. It is generally assumed that inhibiting the formation of microcracks within secondary particle by radially aligned microstructure is a vital aspect for suppressing capacity fading. However, the new researches about reduction of microcracks simply by certain electrolytes call a question on the origin of microcracks and the critical factor for the cycle life of cathodes. Herein, LiNi0.92Co0.04Mn0.04O2 cathodes with different surface characteristic and radially aligned microstructure were synthesized by doping with high valence elements using some hydroxide precursor. The effects of W6+ and/or Mo6+ induced surface phase and microstructure on electrochemical performance were investigated. Despite the inferior radially aligned, size-refined primary grains and higher degree of microcracks, W6+ doped cathode still possesses alleviated parasitic reactions, higher crystal structural stability and capacity retention than Mo6+ doped materials, because of the enhanced cathode-electrolyte interfacial stability. The results contend that the consequence of surface reactivity on determining cycle life of Ni-rich cathodes is more critical than that of microcracks, and efforts relating to constructing intact and uniform stable surface phase will exhibit greater potential to promote the performance of Ni-rich cathodes than microstructural refinement.

Advancements in Addressing Microcrack Formation in Ni–Rich Layered Oxide Cathodes for Lithium–Ion Batteries

AbstractNickel–rich layered oxides of LiNi1–x–yCoxMn(Al)yO2 (where 1–x–y>0.6) are considered promising cathode active materials for lithium‐ion batteries (LIBs) due to their high reversible capacity and energy density. However, the widespread application of NCM(A) is limited by microstructural degradation caused by the anisotropic shrinkage and expansion of primary particles during the H2→H3 phase transition. In this mini–review, we comprehensively discuss the formation of microcracks, subsequent material degradation, and related alleviation strategies in nickel–rich layered NCM(A). Firstly, theories on microcracks′ formation and evolution mechanisms are presented and critically analyzed. Secondly, recent advancements in mitigation strategies to prevent degradation in Ni–rich NCM/NCA are highlighted. These strategies include doping, surface coating, structural optimization, and morphology engineering. Finally, we provide an outlook and perspective to identify promising strategies that may enable the practical application of Ni–rich NCM/NCA in commercial settings.

Effective incorporation of cobalt near surface region for cobalt-free cathodes in lithium-ion batteries

Cobalt-free cathode materials, particularly Ni-rich layered oxide cathode materials, are ideal for electric vehicle Li-ion batteries, offering high energy density and cost-effectiveness. However, high Ni content in high-temperature synthesis leads to issues like increased Li/Ni cation mixing and reduced rate capability, mainly due to the absence of Co. Therefore, this study investigated the utilization of a small amount of Co instead of completely removing it to enhance electrochemical performance. A simple pre-calcination process was used to induce Co substitution beneath the Ni-rich layered oxide cathode materials surface. A coating process was also performed for comparison. The Li/Ni cation mixing in the Co-substituted sample during high-temperature calcination was 2.43%, demonstrating a superior value compared to the Co-coating process. Rate capability tests showed superior performance for Co-substituted sample (164.2 mAh g−1) at 2 C compared to coated sample (151.0 mAh g−1). Moreover, Co substitution improved not only the cycle stability but also the high-temperature stability at an elevated state of charge.This study focuses on the surface modification of cobalt-free cathode, providing direct insight into the effects of Co substitution and typical Co coating and suggests an optimal process that uses small amounts of Co.

Regulating interfacial chemistry and kinetic behaviors of F/Mo co-doping Ni-rich layered oxide cathode for long-cycling lithium-ion batteries over −20 °C–60 °C

Ni-rich layered oxide cathodes have shown promise for high-energy lithium-ion batteries (LIBs) but are usually limited to mild environments because of their rapid performance degradation under extreme temperature conditions (below 0 °C and above 50 °C). Here, we report the design of F/Mo co-doped LiNi0.8Co0.1Mn0.1O2 (FMNCM) cathode for high-performance LIBs from −20 to 60 °C. F– doping with high electronegativity into the cathode surface is found to enhance the stability of surface lattice structure and protect the interface from side reactions with the electrolyte by generating a LiF-rich surface layer. Concurrently, the Mo6+ doping suppresses phase transition, which blocks Li+/Ni2+ mixing, and stabilizes lithium-ion diffusion pathway. Remarkably, the FMNCM cathode demonstrates excellent cycling stability at a high cutoff voltage of 4.4 V, even at 60 °C, maintaining 90.6% capacity retention at 3 C after 150 cycles. Additionally, at temperatures as low as −20 °C, it retains 77.1% of its room temperature capacity, achieving an impressive 97.5% capacity retention after 500 cycles. Such stable operation under wide temperatures has been further validated in practical Ah-level pouch-cells. This study sheds light on both fundamental mechanisms and practical implications for the design of advanced cathode materials for wide-temperature LIBs, presenting a promising path towards high-energy and long-cycling LIBs with temperature adaptability.

In situ and Real-time Monitoring the Chemical and Thermal Evolution of Lithium-ion Batteries with Single-crystalline Ni-rich Layered Oxide Cathode.

High-capacity Ni-rich layered oxides are promising cathode materials for fabrication of lithium-ion batteries (LIBs) with high energy density. However, thermal runaway of LIBs with these cathodes leads to great safety concerns. In this study, single crystalline LiNi0.9Co0.05Mn0.05O2 (NCM-SC) has been prepared and a flexible optical fiber was buried inside the pouch-type LIBs with NCM-SC cathode to in situ study its real-time temperature evolution during charge/discharge process. NCM-SC exhibits an enhanced Li+ ions transportation efficiency and electrode reaction kinetics, which can effectively reduce the generation of polarization heat and mitigate the internal temperature rise of the pouch-type battery. Meanwhile, solid-electrolyte interface (SEI) film decomposition and gas accumulation are effectively alleviated, due to the enhanced thermal stability of SEI film formed on NCM-SC. Moreover, the single crystal architecture can effectively retard layered to spinal and rock-salt phase transition, mitigate the crack formation and structural collapse. Consequently, NCM-SC exhibits an excellent electrochemical performance and enhanced thermal stability.

Jahn-Teller Distortions and Phase Transitions in LiNiO2: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction.

The atomistic structure of lithium nickelate (LiNiO2), the parent compound of Ni-rich layered oxide cathodes for Li-ion batteries, continues to elude a comprehensive understanding. The common consensus is that the material exhibits local Jahn-Teller distortions that dynamically reorient, resulting in a time-averaged undistorted R3̅m structure. Through a combination of ab initio molecular dynamics (AIMD) simulations and variable-temperature X-ray diffraction (VT-XRD), we explore Jahn-Teller distortions in LiNiO2 as a function of temperature. Static Jahn-Teller distortions are observed at low temperatures (T < 250 K) via AIMD simulations, followed by a broad phase transition that occurs between 250 and 350 K, leading to a highly dynamic, displacive phase at high temperatures (T > 350 K), which does not show the four short and two long bonds characteristic of local Jahn-Teller distortions. These transitions are followed in the AIMD simulations via abrupt changes in the calculated pair distribution function and the bond-length distortion index and in X-ray diffraction via the monoclinic lattice parameter ratio, amon/bmon, and δ angle, the fit quality of an R3̅m-based structural refinement, and a peak sharpening of the diffraction peaks on heating, consistent with the loss of distorted domains. Between 250 and 350 K, a mixed-phase regime is found via the AIMD simulations where distorted and undistorted domains coexist. The repeated change between the distorted and undistorted states in this mixed-phase regime allows the Jahn-Teller long axes to change direction. These pseudorotations of the Ni-O long axes are a side effect of the onset of the displacive phase transition. Antisite defects, involving Li ions in the Ni layer and Ni ions in the Li layer, are found to pin the undistorted domains at low temperatures, impeding cooperative ordering at a longer length scale.

Constructing Matching Cathode-Anode Interphases with Improved Chemo-mechanical Stability for High-Energy Batteries.

Coupling Ni-rich layered oxide cathodes with Si-based anodes is one of the most promising strategies to realize high-energy-density Li-ion batteries. However, unstable interfaces on both cathode and anode sides cause continuous parasitic reactions, resulting in structural degradation and capacity fading of full cells. Herein, lithium tetrafluoro(oxalato) phosphate is synthesized and applied as a multifunctional electrolyte additive to mitigate irreversible volume swing of the SiOx anode and suppress undesirable interfacial evolution of the LiNi0.83Co0.12Mn0.05O2 (NCM) cathode simultaneously, resulting in improved cycle life. Benefiting from its desirable redox thermodynamics and kinetics, the molecularly tailored additive facilitates matching interphases consisting of LiF, Li3PO4, and P-containing macromolecular polymer on both the NCM cathode and SiOx anode, respectively, modulating interfacial chemo-mechanical stability as well as charge transfer kinetics. More encouragingly, the proposed strategy enables 4.4 V 21700 cylindrical batteries (5 Ah) with excellent cycling stability (92.9% capacity retention after 300 cycles) under practical conditions. The key finding points out a fresh perspective on interfacial optimization for high-energy-density battery systems.

Unravelling the peculiar role of Co and Al in highly Ni-rich layered oxide cathode materials

Currently, the limited availability of cobalt resources has had a negative impact on the progress of commercial batteries, prompting the development of cobalt-free Ni-rich cathodes. However, the complete replacement of cobalt has faced challenges due to the lack of understanding the influence of dopants on cathode material performance. In this study, we aimed to address this knowledge gap by designing and preparing LiNi0.95Co0.05-xAlxO2 (x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) cathode materials. The impact of cobalt and aluminum doping on the morphology, crystallographic structure and electrothermal performance of Ni-rich cathode materials has been systematically investigated. Our findings confirmed the significant role of cobalt in increasing energy density and mitigating cationic disordering. However, it is found that cobalt doping contributes to the release of lattice oxygen during cycling, leading to rapid capacity fading. Conversely, aluminum doping could stabilize the crystal structure of the cathode material, resulting in slower capacity degradation. Furthermore, the substitution of aluminum effectively mitigates the crystal growth during the synthesis of highly Ni-rich cathode materials, leading to a reduced Li+ diffusion length and thereby excellent rate performance. Specifically, LiNi0.95Al0.05O2 could deliver a high discharge capacity of around 163 mAh g−1 at 10C. This study provides valuable insights for the design of cobalt-free Ni-rich cathodes and sheds light on the possibility of cobalt elimination.