Layered Lithium Transition Metal Research Articles

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.

Chiral Molecular Coating of a LiNiCoMnO2 Cathode for High-Rate Capability Lithium-Ion Batteries.

The growing demand for energy has increased the need for battery storage, with lithium-ion batteries being widely used. Among those, nickel-rich layered lithium transition metal oxides [LiNi1-x-yCoxMnyO2 NCM (1 - x - y > 0.5)] are some of the promising cathode materials due to their high specific capacities and working voltages. In this study, we demonstrate that a thin, simple coating of polyalanine chiral molecules improves the performance of Ni-rich cathodes. The chiral organic coating of the active material enhances the discharge capacity and rate capability. Specifically, NCM811 and NCM622 electrodes coated with chiral molecules exhibit lower voltage hysteresis and better rate performance, with a capacity improvement of >10% at a 4 C discharge rate and an average improvement of 6%. We relate these results to the chirally induced spin selectivity effect that enables us to reduce the resistance of the electrode interface and to reduce dramatically the overpotential needed for the chemical process by aligning the electron spins.

Toward a high-voltage practical lithium ion batteries with ultraconformal interphases and enhanced battery safety

Nickel-rich layered lithium transition metal oxides, LiNixCoyMn1-x-yO2, are key cathode materials for high-energy lithium–ion batteries owing to their high specific capacity. However, the commercial deployment of nickel-rich oxides is hampered by their parasitic reactions and the associated safety issues at high voltages. Developing a stable cathode–electrolyte interphase (CEI) is a promising strategy to overcome this problem. Herein, we report a novel approach, based on the in situ polymerization reaction, to build a protective polymer skin on LiNi0.6Co0.2Mn0.6O2 (NCM622) cathode materials. The artificial CEI skin was found to drastically improve the intrinsic thermal stability, mitigate the evolution of phase transition, and effectively inhibit the associated parasitic reactions between cathodes and the electrolyte in the high-charge states. This coating approach leads to enhanced capacity retention and battery safety under high-voltage operations. The CEI design concept offers a promising strategy for develop advanced nickel-rich cathodes for batteries.

Material Selection for Fundamental Investigation of High Temperature Processes in Lithium-Ion Cathode Production

Rapid upscaling of current and near-future lithium-ion battery (LIB) technologies is one of the main remaining challenges for road transport electrification. Among cathode materials high-Ni layered lithium transition metal oxides, Li(NixCoyMn1-x-y)O2 (LNMC, x ≥ 0.7), show large potential for application in next-generation LIB’s because of their high energy density, low cost, and superior electrochemical properties 1–3.To optimize current cathode production technologies, and to select the most optimal future technologies, a thorough understanding of the synthesis fundamentals of lithium-ion cathode calcination processes is a prerequisite. In this context, in-situ X-ray diffraction (XRD) and thermogravimetric analysis (TGA) have emerged as powerful tools for investigating the high-temperature reaction mechanism of the synthesis of these materials 4,5. However, most research does not address some challenges that come with studying complex high temperature synthesis reactions at the inherit small scale of these in-situ techniques. One issue, is that detailed information on the materials used for supporting the samples is seldomly mentioned, making it difficult to distinguish possible side reactions from the main reactions occurring during high temperature characterization. In only a limited number of studies on the high temperature interaction between ternary lithium-ion battery cathode materials and common substrate materials, evidence of direct contact-corrosion of refractory materials due to lithium compounds has been observed 6. To obtain meaningful insights from these in-situ techniques on the synthesis mechanism of LIB cathode materials that are transferable to mass production processes, these unwanted side reactions must be avoided as much as possible.The purpose of the current study is to select the optimal support material for high temperature in-situ characterization of LIB calcination processes. Several LNMC blends, containing a Li compound and a NMC precursor, were calcined in different crucible materials under a 100% O2 flow at 900 °C for 10-12 hours. The selected crucibles for this investigation include common oxide refractories: Al2O3, SiO2 (fiber and quartz) and MgO, as well as Au, as a frequently used inert material for lab scale experiments. Chemical composition of the precursor blend and calcined products are compared by inductively coupled plasma optical emission spectroscopy ICP-OES. Additionally, weight increase of each crucible material is tracked over multiple calcination cycles, and the formed corrosion products are characterized with SEM-EDS and XRD. The ICP-OES measurements show that the final Li:TM ratio of the calcined LNMC material is heavily influenced by the used crucible material, indicating that selecting an appropriate support material is crucial to avoid side reactions and thus ensure that small scale in situ characterization methods such as in-situ XRD and TGA provide relevant data. Nitta, N., Wu, F., Lee, J.T. & Yushin, G. Mater. Today 18, 252–264 (2015).Schipper, F. et al. J. Electrochem. Soc. 164, A6220–A6228 (2017).Julien, C.M. & Mauger, A. Energies 13, 6363 (2020).Wang, D. et al. Adv. Mater. 29, 1606715 (2017).Gao, M. et al. Ionics 27, 3729–3737 (2021).Zhai, P. et al. J. Eur. Ceram. Soc. 38, 2145–2151 (2018).

Antioxidant layer enables chemically stable cathode-electrolyte interface towards durable and safe Li-ion batteries

Although nickel-rich layered lithium transition metal oxides are one of the most promising candidates for high energy-density Li-ion batteries in electric vehicle applications, they yet suffer from irreversible capacity fading and poor safety properties due to the unstable cathode-electrolyte interphase (CEI), especially at high voltage and high temperature. This instability is mainly caused by the attack of free radicals generated from electrolyte decomposition and active oxygen species (especially singlet oxygen) released from the surface lattice. Here, we propose a novel modification method to construct a protective antioxidant layer on the surface of LiNi0.8Co0.1Mn0.1O2 (NCM). By scavenging free radicals and singlet oxygen, the antioxidant layer greatly reduces the interfacial side reactions and significantly suppresses irreversible rock-salt phase transitions and the associated oxygen species release, leading to the stabilization of the interface. As a result, superior electrochemical performance and enhanced thermal stabilities are achieved. Specifically, the modified NCM exhibits a capacity retention of 92.0% over 1000 cycles in full cells and a dramatic increase of onset temperature (T1) from 75.2 °C to 114.2 °C. This antioxidant layer modification by scavenging free radicals and singlet oxygen provides a new strategy for addressing challenges of CEI design, which is theoretically applicable to all layered transition metal oxide cathode materials.

Application of high energy X-ray diffraction and Rietveld refinement in layered lithium transition metal oxide cathode materials

Application of high energy X-ray diffraction and Rietveld refinement in layered lithium transition metal oxide cathode materials

Boosting the interfacial superionic conduction of halide solid electrolytes for all-solid-state batteries

Designing highly conductive and (electro)chemical stable inorganic solid electrolytes using cost-effective materials is crucial for developing all-solid-state batteries. Here, we report halide nanocomposite solid electrolytes (HNSEs) ZrO2(-ACl)-A2ZrCl6 (A = Li or Na) that demonstrate improved ionic conductivities at 30 °C, from 0.40 to 1.3 mS cm−1 and from 0.011 to 0.11 mS cm−1 for Li+ and Na+, respectively, compared to A2ZrCl6, and improved compatibility with sulfide solid electrolytes. The mechanochemical method employing Li2O for the HNSEs synthesis enables the formation of nanostructured networks that promote interfacial superionic conduction. Via density functional theory calculations combined with synchrotron X-ray and 6Li nuclear magnetic resonance measurements and analyses, we demonstrate that interfacial oxygen-substituted compounds are responsible for the boosted interfacial conduction mechanism. Compared to state-of-the-art Li2ZrCl6, the fluorinated ZrO2−2Li2ZrCl5F HNSE shows improved high-voltage stability and interfacial compatibility with Li6PS5Cl and layered lithium transition metal oxide-based positive electrodes without detrimentally affecting Li+ conductivity. We also report the assembly and testing of a Li-In||LiNi0.88Co0.11Mn0.01O2 all-solid-state lab-scale cell operating at 30 °C and 70 MPa and capable of delivering a specific discharge of 115 mAh g−1 after almost 2000 cycles at 400 mA g−1.

Electrolytes, Additives and Binders for NMC Cathodes in Li-Ion Batteries—A Review

Among the current battery technologies, lithium-ion batteries (LIBs) are essential in shaping future energy landscapes in stationary storage and e-mobility. Among all components, choosing active cathode material (CAM) limits a cell’s available energy density (Wh kg−1), and the CAM selection becomes critical. Layered Lithium transition metal oxides, primarily, LiNixMnyCozO2 (NMC) (x + y + z = 1), represent a prominent class of cathode materials for LIBs due to their high energy density and capacity. The battery performance metrics of NMC cathodes vary according to the different ratios of transition metals in the CAM. The non-electrode factors and their effect on the cathode performance of a lithium-ion battery are as significant in a commercial sense. These factors can affect the capacity, cycle lifetime, thermal safety, and rate performance of the NMC battery. Additionally, polycrystalline NMC comprises secondary clusters of primary crystalline particles prone to pulverization along the grain boundaries, which leads to microcrack formation and unwanted side reactions with the electrolyte. Single-crystal NMC (SC-NMC) morphology tackles the cycling stability issue for improved performance but falls short in enhancing capacity and rate capability. The compatibility of different combinations of electrolytes and additives for SC-NMC is discussed, considering the commercial aspects of NMC in electric vehicles. The review has targeted the recent development of non-aqueous electrolyte systems with various additives and aqueous and non-aqueous binders for NMC-based LIBs to stress their importance in the battery chemistry of NMC.

Safety Issues of Layered Nickel-Based Cathode Materials for Lithium-Ion Batteries: Origin, Strategies and Prospects

Layered lithium transition metal (TM) oxides LiTMO2 (TM = Ni, Co, Mn, Al, etc.) are the most promising cathode materials for lithium-ion batteries because of their high energy density, good rate capability and moderate cost. However, the safety issue arising from the intrinsic thermal instability of nickel-based cathode materials is still a critical challenge for further applications in electric vehicles and energy storage power stations. The main reasons include side reactions between the highly reactive Ni3+/4+ and liquid electrolyte, oxygen release accompanied by structural phase transition, and internal microcrack propagation owing to the low strength of spherical secondary particles. Great efforts have been invested to modify nickel-based cathode materials such as stabilization of bulk structure by element doping, surface engineering, nanostructure design, and particle mono-crystallization. In this review, we summarize these advances and try to give an in-depth insight into the origin of the thermal instability of nickel-based cathode materials. More importantly, some effective strategies to improve thermal stability are outlined, expecting to accelerate the future development of layered TM oxides with high safety.

The Structural Stability Limit of Layered Lithium Transition Metal Oxides Due to Oxygen Release at High State of Charge and Its Dependence on the Nickel Content

The composition of layered transition metal oxides (LiMO2, M = Ni, Co, Mn) as cathode active materials (CAMs) is currently trending towards higher nickel contents, which can provide more capacity and energy. The origin of this performance improvement is often ascribed to the lower potential of nickel-rich CAMs, suppressing detrimental electrochemical electrolyte oxidation. In this study, it is shown that the stability limit of LiMO2-based CAMs is not determined by the stability window of typical electrolytes in terms of potential but by the CAM composition, governing the structural stability at high degrees of delithiation. The latter is investigated for five CAMs with distinct composition (LCO, NCM111, NCM622, NCM851005, and LNO) as a function of upper cutoff potential and thus state of charge (SOC). Short-term cycling experiments with an increasing upper cutoff potential as well as extended cycling to selected SOCs reveal stability limits between 66 and 86 %SOC depending on the CAM composition. On-line electrochemical mass spectrometry (OEMS) does not only allow to exclude any impact of electrochemical electrolyte oxidation on the determined stability window of the CAMs but also illuminates the concurrence of capacity fade and lattice oxygen release, with the latter being the origin of the CAM degradation.

Origin and characterization of the oxygen loss phenomenon in the layered oxide cathodes of Li-ion batteries.

Li-ion batteries have been widely applied in the field of energy storage due to their high energy density and environment friendliness. Owing to their high capacity of ∼200 mA h g-1 and high cutoff voltage of ∼4.6 V vs. Li+/Li, layered lithium transition metal oxides (LLMOs) stand out among the numerous cathode materials. However, the oxygen loss of LLMO cathodes during cycling hampers the further development LLMO cathode-based Li-ion batteries by inducing a dramatic decay of electrochemical performance and safety issues. In this regard, the oxygen loss phenomenon of LLMO cathodes has attracted attention, and extensive efforts have been devoted to investigating the origins of oxygen loss in LLMO cathodes by various characterization methods. In this review, a comprehensive overview of the main causes of oxygen loss is presented, including the state of charge, side reactions with electrolytes, and the thermal instability of LLMO cathodes. The characterization methods used in the scope are introduced and summarized based on their functional principles. It is hoped that the review can inspire a deeper consideration of the utilization of characterization techniques in detecting the oxygen loss of LLMO cathodes, paving a new pathway for developing advanced LLMO cathodes with better cycling stability and practical capabilities.

Microstructure and surface engineering through indium modification on Ni-rich layered cathode materials for enhanced electrochemical performance of lithium-ion batteries

Ni-rich layered lithium transition metal oxides have been considered as one of the most promising cathodes for next-generation lithium-ion batteries (LIBs) because of their high capacities and affordable costs. However, they still suffer bulk and surface structural instability, leading to rapid performance decay and subsequent cathode failure. In this context, Ni-rich layered cathodes with indium modified crystal and surface structures are developed by a simple one-pot calcination approach. Battery tests manifest that the indium modified LiNi0.8Co0.1Mn0.1O2 electrodes exhibit remarkably enhanced rate capability and cycling stability compared to the pristine one, including under high operating voltage condition. Further studies evidence a simultaneous mitigation of intra/inter-granular mechanical cracks and resistive surface films growth, which directly embodied in a dramatically suppressed ohmic loss after long-term cycling. The improved microstructural and surface stability are attributed by the synergistic functions of indium modification. On the one hand, trace amount of In3+ occupy crystalline Li+-site, which not only dissipate the intrinsic lattice strain during cycling, but also reduce Li+/Ni2+ antisite to avoid the undesired layer to rock-salt phase transformation. On the other hand, the rest of indium deplete lithium residues, and form conductive LiInO2 adherent coatings to protect the cathode from side reactions with electrolyte. The present work demonstrates that microstructure and surface engineering through indium modification offers a promising design strategy for further improvements of Ni-rich layered cathodes.

Study on the Structural Degradation of the Polyaniline(PANi) Coated LiNi0.90Co0.85Mn0.15o Particles

The nickel content of the layered lithium transition metal oxide cathodes is proportional to the discharge capacity of energy storage systems. Ni2+ ion, the oxidation state of Ni, moves to the Li sites when Li+ ion is deintercalated during discharge process due to the similar size of ion (Ni2+: 0.069 nm, Li+: 0.076 nm). The spatial transition of Ni2+ ion causes gradual cation mixing and structure degradation of cathode, resulting in the failure of the battery. Also, thick cathode-electrolyte interphase (CEI) is formed on the cathode surface because of the transition metal dissolution, the degradation of electrolyte, and the residual gas such as H2O and CO2.Coating technology is one of the strategies for the physical protection of the cathode surface and the control of CEI layer thickness. Polyaniline(PANi) is a conductive polymer with stable oxidation state. PANi can enhance the electrochemical property and structural stability as a protective layer. In this study, we synthesized PANi material by the oxidative polymereization and coated NCM with the synthesized PANi by sonication method.The PANi-coated NCM(PANi@NCM) has uniform coating layer with 5 nm thickness. PANi@NCM exhibits an initial discharge capacity of 208 mAhg-1 and a capacity retention of 81% after 50 cycles at 45 oC in Figure 1(a) and (b). After the cycling test, pristine and coated cathodes were disassembled for the comparison of the microstructure. Pristine NCM only shows the structural transition from layered structure to structure in the XRD pattern of Figure 1(c). Cross-sectional SEM image of the pristine NCM after cycling test shows micro and macro cracks are distributed from the bulk to the surface of the cathode as shown in Figure 1(d). On the other side, cracks are barely observed on the PANi@NCM particles in Figure 1(e). The layered structure of PANi@NCM is maintained even after cycling test, which are confirmed by TEM analysis with FFT patterns and HAADF images. Figure (f) and (g) show the FFT pattern of the two cathode surfaces after cycling test. Mixed phase is observed on the pristine cathode surface, while the layered structure is maintained on the PANi@NCM surface. Also, the PANi@NCM maintains a thinner passivation layer compared with that of the pristine NCM (6 nm vs 35 nm). In conclusion, the PANi coating layer prevents the degradation of structure and the formation of thick CEI layer. The structural stability enhances the electrochemical performance. Figure 1

(Invited) ALD Coatings for Li-Ion Battery and All-Solid-State Battery Applications

Lithium-ion batteries (LIBs) are essential for modern life, and their improvement is crucial for the more widespread adoption of electric vehicles.[1] Layered lithium transition metal oxides, such as LiNixCoyMnzO2 (often referred to as NCM or NMC), are among the most widely used cathode active materials (CAMs) for automotive applications, owing to their technological maturity and high energy density. However, they typically require a surface coating for stabilizing interfaces, both in liquid-electrolyte based LIBs and in solid-state battery (SSB) environments. For the preparation of protective CAM coatings, atomic layer deposition (ALD) stands out with its ability to produce conformal films on complex substrates.This presentation encompasses several examples of successful improvements in cycling performance of Ni-rich NCM CAMs in LIBs and SSBs by ALD of binary oxides. The low-temperature deposition of AlxOy onto ready-to-use cathode sheets will be discussed.[2] ALD or ALD-related surface protection enables increased stability by suppressing detrimental surface corrosion and metal leaching (side reactions) in LIBs.[2,3] Moreover, we report about the application of ALD coatings to Ni-rich NCM CAMs in SSBs with lithium thiophosphate solid electrolytes. Specifically, the effect that both HfO2 and ZrO2 have on the cell cyclability will be shown, with emphasis placed on the role of post annealing.[4] [1] Goodenough et al. J. Am. Chem. Soc. 2013, 135, 1167.[2] Neudeck et al. Sci. Rep. 2019, 9, 5328.[3] Neudeck et al. Chem. Commun. 2019, 55, 2174.[4] Kitsche et al. ACS Appl. Energy Mater. 2021, 4, 7338.

Electrochemical and Structural Study on PVDF-Based Polymer Electrolytes for Solid-State Batteries

Lithium-ion batteries are widely used today in powering devices from portable electronics to electric vehicles. Despite their great success, this battery chemistry relies on organic solvent-based liquid electrolytes which are highly flammable, leading to major safety concerns. In contrast, solid-state batteries, which are based on solid-state electrolytes, are regarded to have much better safety characteristics and potentially higher energy density than the conventional lithium-ion batteries. Solid-state electrolytes usually include ceramics, polymers, gels, and composites. Among them, polymer materials have attracted considerable attention due to their great interfacial contact, flexibility, and easy fabrication. In particular, polyvinylidene fluoride (PVDF) polymer electrolyte is a promising candidate as it can potentially provide a high voltage window and enable high energy density solid-state batteries. However, the current PVDF-based polymer electrolyte is still not compatible with high voltage cathodes, such as layered lithium transition metal oxides and the interaction between the salt and PVDF polymer has not been fully elucidated.We have systematically studied the PVDF-based electrolytes with different salts and salt combinations, including lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(pentafluoroethanesulfonyl)imide (LiBETI). The optimized electrolyte delivers excellent performance for solid-state Li||LiFePO4 cells, achieving a specific capacity of over 150 mAh/g and lasting more than 50 cycles with over 99% capacity retention. Similar tests have also been applied to lithium nickel manganese cobalt oxides (NMC), and the preliminary results show promising cycling stability and capacity retention. In addition to electrochemical study, we employed a range of synchrotron-based X-ray techniques, including diffraction, pair distribution function analysis, and absorption spectroscopy, to investigate the interactions between the polymer and lithium salt in the polymer electrolytes. This knowledge will provide valuable information for designing new polymer electrolyte systems.Acknowledgments: The work at Brookhaven National Laboratory was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program under contract DE-SC0012704. This research used beamline 23-ID-2 and 28-ID-2 of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.

The Air Stability of Sodium Layered Oxide Cathodes

Sodium-ion batteries (NIBs) are listed as one of the ideal alternatives for lithium-ion batteries (LIBs), due to the abundant sodium resources, cost-effective electrode materials of NIBs, and same architecture of NIBs to LIBs. To enable the practical implementation of NIBs, advanced cathodes with higher energy/power densities, better safety and cycle life, as well as lower cost are required. Layered lithium transition metal oxides (LiTMO2) are one of the most successful cathode materials for commercial LIBs. Similarly, layered sodium transition metal oxides (NaxTMO2, also termed as sodium layered oxides) are of particular interest for commercial NIBs owing to their high specific capacity, a wide variety of redox-active elements, and the possibility for the manufacturers to employ established synthesis processes as their lithium counterparts.Sodium layered oxides are built up by ordered stacking of alternate alkali-metal (Na+) layers and transition metal layers (TmO2). The two-dimensional structure makes them the natural hosts for alkali-metal ions and other ions or small molecules, such as H2O. Therefore, when exposed to moist atmospheres, layered oxide materials tend to react with H2O which adsorbed on their surface and thus deteriorate their structure and electrochemical performances. Accordingly, the air-sensitive sodium layered oxides should be well protected from the moist atmospheres, rendering a higher manufacturing and preservation cost.Here, based on the reaction mechanisms, critical influencing factors, and modification methods of layered oxides in moisture, we try to reach a comprehensive understanding of the air-stability of sodium layered oxides. Moreover, future efforts to resolve the air-stability of sodium layered oxides from Argonne National Laboratory will be also presented.

State-of-Charge Distribution of Single-Crystalline NMC532 Cathodes in Lithium-Ion Batteries: A Critical Look at the Mesoscale.

The electrochemical response of layered lithium transition metal oxides LiMO2 [M=Ni, Mn, Co; e. g., Li(Ni0.5 Mn0.3 Co0.2 )O2 (NMC532)] with single-crystalline architecture to slow and fast charging protocols and the implication of incomplete and heterogeneous redox reactions on the active material utilization during cycling were the subject of this work. The role of the active material size and the influence of the local microstructural and chemical ramifications in the composite electrode on the evolution of heterogeneous state of charge (SOC) distribution were deciphered. For this, classification-single-particle inductively coupled plasma optical emission spectroscopy (CL-SP-ICP-OES) was comprehensively supplemented by various post mortem analytical techniques. The presented results question the impact of surface-dependent failure mechanisms of single crystals for the evolution of SOC heterogeneity and identify the deficient structural flexibility of the composite electrode framework as the main driver for the observed non-uniform active material utilization.

Building a Self-Adaptive Protective Layer on Ni-Rich Layered Cathodes to Enhance the Cycle Stability of Lithium-Ion Batteries.

Layered Ni-rich lithium transition metal oxides are promising battery cathodes due to their high specific capacity, but their poor cycling stability due to intergranular cracks in secondary particles restricts their practical applications. Surface engineering is an effective strategy for improving a cathode's cycling stability, but most reported surface coatings cannot adapt to the dynamic volume changes of cathodes. Herein, a self-adaptive polymer (polyrotaxane-co-poly(acrylic acid)) interfacial layer is built on LiNi0.6 Co0.2 Mn0.2 O2 . The polymer layer with a slide-ring structure exhibits high toughness and can withstand the stress caused by particle volume changes, which can prevent the cracking of particles. In addition, the slide-ring polymer acts as a physicochemical barrier that suppresses surface side reactions and alleviates the dissolution of transition metallic ions, which ensures stable cycling performance. Thus, the as-prepared cathode shows significantly improved long-term cycling stability in situations in which cracks may easily occur, especially under high-rate, high-voltage, and high-temperature conditions.

High-Voltage Induced Surface and Intragranular Structural Evolution of Ni-Rich Layered Cathode.

Layered Ni-rich lithium transition metal oxides are promising cathode materials for high-energy-density lithium-ion batteries. These cathodes, however, suffer from rapid performance decay under high-voltage operation. In this work, the electrochemical properties and structural evolution of the LiNi0.8 Mn0.1 Co0.1 O2 (NMC811) cathode upon high-voltage cycling are investigated. The results show that the NMC811 cathode not only experiences surface evolution with the formation of Li-deficient rock-salt layers, but also suffers from drastic intragranular structural changes inside bulk grains after high-voltage cycling. Direct evidence for the formation of transition-metal/Li disordering domains with uneven Li content and lattice plane distortion at the internal grains of 4.6V-cycled NMC811 are provided with their atomic ordering and spatial distribution clearly resolved. The complex intragranular structural changes impede Li+ diffusion inside bulk material, resulting in kinetic limitation and capacity loss. The results demonstrate that the high-voltage cycling would induce severe structural degradation at the grain interior of the cathode material beyond surface evolution, which contributes significantly to the rapid performance decay of the NMC811 cathode. The findings provide new insights for developing effective countermeasures to mitigate this degradation pathway.

Temperature-dependence of calcination processes of Ni-rich layered oxides

High-Ni layered lithium transition metal oxides, LiNi1−x−yMnxCoyO2 (1-x-y≥0.7), show great promise for application in next-generation lithium ion batteries because of their high energy density, low cost, and superior electrochemical properties. However, preparation of stoichiometric LiNi1−x−yMnxCoyO2 oxides with highly ordered layered structure is challenging, largely due to the Li/O loss during high-temperature calcinations. Thus, understanding the reaction mechanism is crucial for calcination design. Herein, X−ray diffraction in combination with nuclear magnetic resonance, are conducted to track the structural evolution in preparing LiNi1−x−yMnxCoyO2 below 500 °C. Our results reveal that a lithiated intermediate, Ni0.7Mn0.15Co0.15(OHy)2Lix, between the precursory transition metal hydroxide and the destination layered LiNi1−x−yMnxCoyO2 phase is generated, bypassing the formation of transition metal oxide phases. The unique reaction enables the calcination optimization at low temperature. Accordingly, high-ordered LiNi0.7Mn0.15Co0.15O2 is achieved via a developed two-step calcination at 500 °C, and it exhibits an excellent electrochemical performance, especially the high initial columbic efficiency.