Ni-rich Layered Oxide Cathode Research Articles

(Digital Presentation) Mapping of Degradation Processes in Ni-Rich Layered Oxide Cathode Materials in State-of-the-Art Commercial Li-Ion Cells Based on Battery Usage Conditions

Ni-rich oxide cathode active materials are today key components in Li-ion batteries used for electric vehicles (EV). The high capacity of LiNixCoyMnzO2 and LiNixCoyAlzO2 (NCA) with x≥0.6 has enabled a continued increase in energy density and decrease in cost at the pack level, enabling the rapid growth of the EV market in recent years. Despite a wide use, rather fast material ageing results in the batteries being a source of considerable environmental impact [1]. Various degradation sources are highlighted in the literature, these include transition metal dissolution, surface layer reconstruction, particle cracking, etc [2]. However, when extrapolating the knowledge from a model cell to a commercial battery the relevance and the degree of degradation impact can drastically change [3]. The importance of approaching real conditions is a key to a full understanding of the ageing processes occurring in commercial cells. In the given work, we analyse commercial state-of-art 2170 cylindrical cells. The cells were aged at various temperatures and state of charge windows, targeting divergent usage scenarios. The degradation processes were accessed with a wide range of analytical techniques applied to extracted electrodes (x-ray diffraction, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, cycling voltammetry, incremental capacity analysis, electrochemical impedance spectroscopy and intermittent current interruption). In the current work we show that depending on the operating conditions, influence of ageing sources varies. Additionally, ageing mapping within cell geometry is presented highlighting “hot spots” of the cell [4].

The Effect of Annealing on the Structure, Composition and Electrochemistry of NMC811 Coated with Al2O3 Using an Alkoxide Precursor

Increasing capacities and lowering costs of the cathode material is a key challenge in lithium ion-battery research. Towards this end, nickel-rich layered oxides of the formula Li[NixMnyCoy]O2 (NMC) with x ≥ 0.8 were developed. Compared to previously used cathodes such as LiCoO2 , nickel-rich NMCs reach lower costs by replacing most of the cobalt with nickel and they enable higher discharge capacities.1 Despite the presence of small amounts of cobalt and manganese as dopants to improve stability and rate-capability, these materials still show fast capacity fade during electrochemical cycling which cannot be overcome by modifying the ratio of their elements.2 New strategies to mitigate this degradation are therefore urgently needed for the use of these materials in practical applications such as electric vehicles.3 Most of the degradation that occurs in nickel-rich NMCs upon cycling starts at the cathode-electrolyte interface via surface reactions,oxygen evolution followed by rock-salt formationand transition metal dissolution.4–6 One way to slow down or stop these processes is by changing the nature of this interface through coatings. Although there is a large number of studies showing the benefits of using them, knowledge on the design of coatings with specific properties is still lacking.7,8 In this work, we develop a new solution-based deposition method for the synthesis of aluminium oxide coatings onto LiNi0.8Mn0.1Co0.1O2 (NMC811) secondary particles (Figure 1) and study the effect of annealing on their structure and electrochemical lifetime as new-generation cathode for lithium-ion batteries. Using energy dispersive X-ray spectroscopy (EDS) and X-ray fluorescence spectroscopy (XRF) we quantify the amount and distribution of aluminium oxide on the cathode particles. By using solid-state nuclear magnetic resonance (SS-NMR) and X-ray photoelectron spectroscopy (XPS), we track changes in the coating phase and composition as a function of annealing temperature. 27Al NMR spectroscopy provides direct evidence of the diffusion of the coating into the bulk of the particles leading to surface-layer doping. Finally, we evaluate the electrochemical performance of the coated materials in half cells using long-term galvanostatic cycling. This work provides insight on the effects of surface coating and doping on battery degradation and shows how, by carefully selecting synthetic conditions, coatings of cathode particles with tailored properties can be prepared.(1) Myung, S.-T.; Maglia, F.; Park, K.-J.; Yoon, C. S.; Lamp, P.; Kim, S.-J.; Sun, Y.-K. Nickel-Rich Layered Cathode Materials for Automotive Lithium-Ion Batteries: Achievements and Perspectives. ACS Energy Letters 2017, 2 (1), 196–223. https://doi.org/10.1021/acsenergylett.6b00594.(2) Noh, H.-J.; Youn, S.; Yoon, C. S.; Sun, Y.-K. Comparison of the Structural and Electrochemical Properties of Layered Li[NixCoyMnz]O2 (x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) Cathode Material for Lithium-Ion Batteries. Journal of Power Sources 2013, 233, 121–130. https://doi.org/10.1016/j.jpowsour.2013.01.063.(3) Kim, J.; Lee, H.; Cha, H.; Yoon, M.; Park, M.; Cho, J. Prospect and Reality of Ni-Rich Cathode for Commercialization. Advanced Energy Materials 2018, 8 (6), 1702028. https://doi.org/10.1002/aenm.201702028.(4) Rinkel, B. L. D.; Hall, D. S.; Temprano, I.; Grey, C. P. Electrolyte Oxidation Pathways in Lithium-Ion Batteries. J. Am. Chem. Soc. 2020, 142 (35), 15058–15074. https://doi.org/10.1021/jacs.0c06363.(5) Wandt, J.; Freiberg, A.; Thomas, R.; Gorlin, Y.; Siebel, A.; Jung, R.; Gasteiger, H. A.; Tromp, M. Transition Metal Dissolution and Deposition in Li-Ion Batteries Investigated by Operando X-Ray Absorption Spectroscopy. J. Mater. Chem. A 2016, 4 (47), 18300–18305. https://doi.org/10.1039/C6TA08865A.(6) Xu, C.; Märker, K.; Lee, J.; Mahadevegowda, A.; Reeves, P. J.; Day, S. J.; Groh, M. F.; Emge, S. P.; Ducati, C.; Layla Mehdi, B.; Tang, C. C.; Grey, C. P. Bulk Fatigue Induced by Surface Reconstruction in Layered Ni-Rich Cathodes for Li-Ion Batteries. Nat. Mater. 2020. https://doi.org/10.1038/s41563-020-0767-8.(7) Shi, Y.; Zhang, M.; Qian, D.; Meng, Y. S. Ultrathin Al2O3 Coatings for Improved Cycling Performance and Thermal Stability of LiNi0.5Co0.2Mn0.3O2 Cathode Material. Electrochimica Acta 2016, 203, 154–161. https://doi.org/10.1016/j.electacta.2016.03.185.(8) Neudeck, S.; Strauss, F.; Garcia, G.; Wolf, H.; Janek, J.; Hartmann, P.; Brezesinski, T. Room Temperature, Liquid-Phase Al2O3 Surface Coating Approach for Ni-Rich Layered Oxide Cathode Material. Chemical Communications 2019, 55 (15), 2174–2177. https://doi.org/10.1039/C8CC09618J. Figure 1

Challenges and prospects of nickel-rich layered oxide cathode material

The increasing electromobility demands rechargeable batteries with high energy density and enhanced electrochemical properties. However, the commercialized lithium-ion batteries experience several critical challenges related to cost-effectiveness, long-term safety and calendar life. Ni-rich layered oxides, LiNixCoyMnzO2 (NCM) and LiNixCoyAlzO2 (NCA) (x + y + z = 1, x ≥ 0.8) have been considered as next-generation cathode materials with the capability to achieve high energy density (800 Wh kg−1) and high operating voltage with low cost. However, their intrinsic unstable behavior, including surficial/interfacial issues, fatigue, inter/intragranular cracking, parasitic side reactions and thermal runway, causes severe capacity and voltage fading, deprived rate capability, and safety concerns during the charge/discharge process. This review article focuses on degradation mechanisms, challenges, and the most recent approaches, including doping, surface coating, structural engineering, dual modification, concentration gradient, and single-crystal cathodes were precisely summarized. Besides, the new series of Ni-based cathodes were discussed to alter the primary microstructural particle by replacing Co/Mn/Al in NCM and NCA. Notably, the compatibility and interfacial challenges of Ni-rich cathodes with solid-state electrolytes were elaborated to stabilize the electrochemical performance of this high-voltage cathode in all-solid-state batteries (ASSBs). The outlook presents a perception towards the practical application of Ni-rich layered oxide cathode materials in electromobility.

Interfacial and cycle stability of sulfide all-solid-state batteries with Ni-rich layered oxide cathodes

The interfacial compatibility between sulfide solid electrolyte (SSE) and Ni-rich layered oxide (NRLO) cathode is critical for high-performance sulfide all-solid-state Li-ion batteries (SASSLIBs). However, the reasons for interfacial/capacity degradation of SASSLIBs are not yet clearly resolved. Herein, the impacts of surface structures and chemical environments of LiNi0.83Co0.11Mn0.06O2 (NCM83) on SASSLIB performances are systematically investigated. Surface lithium vacancies of NCM83 facilitate Li ion migration from SSE to NCM83 side, suppressing the H1 phase transformation of NCM83 and expanding the space charge layer. Surface LixNi1−xO type rock salt phases inhibit oxygen-participating interfacial reactions at high voltages due to their low susceptibility to oxygen evolutions, enhancing the H2/H3 phase transformation of NCM83. Surface Li2O and Li2CO3 mitigate the space charge layer effect and interfacial reactions at high voltages, activating H1 and H2/H3 phase transformations of NCM83. On the other hand, the combination of LiOH and Li2CO3 causes severe side reactions with SSE, resulting in escalated interfacial resistance and drastic capacity fading over cycling. Importantly, while the suppression of H1 and H2/H3 transformations reduces the reversible capacity, it mitigates the internal stress and micro-cracks in NCM83 particles, contributing to superior cycling stability of NCM83-sulfide ASSLIBs (94.1 % capacity retention over 500 cycles).

Thermochemical Cyclization Constructs Bridged Dual-Coating of Ni-Rich Layered Oxide Cathodes for High-Energy Li-Ion Batteries.

Enhancing microstructural and electrochemical stabilities of Ni-rich layered oxides is critical for improving the safety and cycle-life of high-energy Li-ion batteries. Here we propose a thermochemical cyclization strategy where heating polyacrylonitrile with LiNi0.8Co0.1Mn0.1O2 can simultaneously construct a cyclized polyacrylonitrile outer layer and a rock-salt bridge-like inner layer, forming a compact dual-coating of LiNi0.8Co0.1Mn0.1O2. Systematic studies demonstrate that the mild cyclization reaction between polyacrylonitrile and LiNi0.8Co0.1Mn0.1O2 induces a desirable "layered to rock-salt" structural transformation to create a nano-intermedium that acts as the bridge for binding cyclized polyacrylonitrile to layered LiNi0.8Co0.1Mn0.1O2. Because of the improvement of the structural and electrochemical stability and electrical properties, this cathode design remarkably enhances the cycling performance and rate capability of LiNi0.8Co0.1Mn0.1O2, showing a high reversible capacity of 183 mAh g-1 and a high capacity retention of 83% after 300 cycles at 1 C rate. Notably, this facile and scalable surface engineering makes Ni-rich cathodes potentially viable for commercialization in high-energy Li-ion batteries.

Reinforcement of binder adhesion for nickel-rich layered oxide in lithium-ion batteries using perfluorinated molecular surface modification

Ni-rich layered oxides are considered the most promising candidates for cathode materials for use in electric vehicles because of their high energy density and low cost. However, the cyclability of Ni-rich layered oxide needs to be improved because it suffers from contact loss by microcracks owing to the large anisotropic volume changes during cycling. Furthermore, its unstable surface, which releases lithium impurities by water contamination, must also be mitigated. To improve the adhesive force with a polyvinyl fluoride (PVdF) binder as well as the air-stability, a self-assembled monolayer of 1H,1H–2H,2H-perfluorodecyltriethoxysilane (PFDTES) is introduced onto the surface of Ni-rich layered oxide cathode powder. A molecular functional monolayer with fluorocarbons on Ni-rich layered oxide powder is delivered to achieve an ∼ 13 Å thin homogeneous molecular-level functional coating at a negligible weight ratio. The functionalized surface improves the adhesion between PVdF and cathode powder by F⋯F interaction, relieving the electrode detachment. As a result, cycling failure mode is remarkably mitigated. The fluorinated hydrophobic surface alleviates water contamination, thereby reducing lithium impurities.

Stable Ni-rich layered oxide cathode for sulfide-based all-solid-state lithium battery

Sulfide-based all-solid-state lithium-ion batteries (ASSLIBs) are one of the most promising energy storage technologies due to their high safety and ionic conductivity. To achieve greater energy density, a Ni-rich layered oxide LiNixCoyM1-x-yO2 (NCM, M ​= ​Mn/Al, x ​≥ ​0.6) is desirable due to its relatively high voltage and large capacity. However, interfacial side reactions between the NCM and sulfide solid electrolytes lead to undesirable interfacial passivation layers and low ionic conductivity, thereby degrading the electrochemical performance of NCM sulfide all-solid-state batteries. Herein, a time-/cost-effective sulfidation strategy is exploited to sulfidize a Ni-rich NCM88 cathode in a mixed gas atmosphere of N2 and CS2. A new type of cathode (NCM88-S) with an ultrathin (∼2 ​nm) surface layer is obtained, which significantly reduces the interfacial side reactions/resistance and improves the interfacial stability. The resulting NCM88-S/Li6PS5Cl/Li4Ti5O12 ASSLIB exhibits superior performance, including a high discharge specific capacity (200.7 mAh g−1) close to that of liquid batteries, excellent cycling performance (a capacity retention of 87% after 500 cycles), and satisfactory rate performance (158.3 mAh g−1 at 1C).

Pre-pulverizing Ni-rich layered oxide cathodes via “liquid explosive” infiltration toward highly endurable 4.5 V lithium batteries

The mechanical strain derived from anisotropic lattice distortion would lead to the spread of microcracks in LiNixMnyCo1-x-yO2 (NMC) secondary particles and therefore the rapid capacity deterioration. Herein, we propose a ‘liquid explosion’ strategy to pre-pulverize the agglomerated secondary particle system of LiNi0.8Mn0.1Co0.1O2 (NMC811) massively into an unusual primary particle system via the infiltration of P3N3Cl6 (PNCL) melt and its following gasification. This primary particle system avoids the prevalence of microcracks and degradation of electric contact in electrode network. The high dispersity of particles enables the more homogenous and compact electrode network, which is well preserved even after long-term cycling. The residual PNCL releases N, Cl and P elements, which are implanted into an ultrathin cathode electrolyte interphase (CEI) and lithiated into conductive Li3N, LiCl and LixPOyFz components. The modified Li-NMC cells exhibit the ultralong cycling life (at least 1100 cycles at 1 C) with very small capacity fading rate (0.043% per cycle) even under the protocol of high cut-off voltage (4.5 V). This endurable discrete-particle-type electrode network also endows the high-loading cathode with excellent capacity retention even under the configuration of pouch cell. The concept of ‘liquid explosive’ provides a scalable solution to high-performance NMC based materials for practical battery application.

Trimethoxyboroxine as an electrolyte additive to enhance the 4.5 ​V cycling performance of a Ni-rich layered oxide cathode

Ni-rich layered oxides are attractive cathode materials for advanced lithium-ion batteries (LIBs) due to their high energy density. However, their large-scale application is seriously hindered by their interfacial instability, especially at a high cut-off potential. Here, we demonstrate that trimethoxyboroxine (TMOBX) is an effective film-forming additive to address the interfacial instability of LiNi0.8Co0.1Mn0.1O2 (NCM811) material at a high cut-off voltage of 4.5 ​V. We find that TMOBX decomposes before carbonate solvent and forms a thin cathode electrolyte interphase (CEI) layer on the surface of the NCM811 material. This TMOBX-formed CEI significantly suppresses electrolyte decomposition at a high potential and inhibits the dissolution of transition metals from NCM811 during cycling. In addition, electron-deficient borate compounds coordinate with anions (PF6−, F−, etc.) and H2O in the battery, further improving the battery's stability. As a result, adding 1.0 ​wt% of TMOBX boosts the capacity retention of a Li||NCM811 ​cell from 68.72% to 86.60% after 200 cycles at 0.5C in the range of 2.8–4.5 ​V.

Regulating the cationic rearrangement of Ni-rich layered oxide cathode for high-performance Li-ion batteries

Enormous effort has been paid to improve Ni-rich cathode's performance by suppressing surface residues and enhancing microscopic surface ordering (high Ni3+/Ni2+). Herein, strong alkali-mediated chemical oxidation of commercial precursor is employed to directly synthesize Ni-rich NCA cathode sintering under an oxygen atmosphere. Because of the limited lithium source, the lithium residue over the polycrystalline material is controlled; of course, a certain fraction of lithium has been lost and substituted by Ni2+, even pre-oxidized the precursor. XPS studies suggest that the percentage of oxidized nickel (Ni3+) is comparably higher at the surface than core (∼100 nm in depth) and retained during the lithiation. The synthesized material initially shows a high reversible lithiation efficiency of 90.6% at 0.05 C. The capacity degradation in the life-cycle study at 0.2 C could be endorsed to the combination of lithium inventory and active metal loss along with typical kinetic limitations, as diagnosed from the derivative dQ/dV plot. The high initial coulombic efficiency and discharge capacity with low polarization further confirm superior surface ordering and low surface residue. This study demonstrates that the pretreatment of the precursor is one of the effective strategies to regulate the cationic arrangement to achieve improved electrochemical performance.

Anionic redox reaction and structural evolution of Ni-rich layered oxide cathode material

The Ni-rich layer-structured oxide is one of the most promising candidate cathode materials for the high energy-density Li-ion batteries. However, the commercial applications of these materials are hindered with drawbacks such as structural instability and poor cycling performance at high potentials. Herein, we comprehensively studied the oxygen redox reaction and the structural reversibility of LiNi0.83Co0.12Mn0.05O2 at deep delithiation using the synchrotron X-ray absorption spectroscopy, scanning transmission electron microscopy and density functional theory calculations. The oxygen redox occurs due to the cation mixing upon delithiation in this material though there are no Li-O-Li configurations in its pristine form. The formation of the I41 structure was attributed to the migration of the transition metals in the deeply delithiated material, extending the route of the phase transformation from the layered to the rock-salt structure. These findings are helpful to enrich the understanding of the origin of the oxygen redox and reveal its impact on the structural transformations in the Ni-rich layered oxides. These will spur new strategies to enhance the performance of the cathode materials for the next-generation Li-ion batteries.

Structure modification of Ni-rich layered oxide cathode toward advanced lithium-ion batteries

Structure modification of Ni-rich layered oxide cathode toward advanced lithium-ion batteries

Stress-Tolerant Printed Architectures Toward Stable Cycling of Ultrahigh-Loading Ni-Rich Layered Oxide Cathodes for Wearable Energy Storage Devices

Fast-charging and high-energy density wearable energy storage devices working under high mass loading are in urgent demand for the state-of-the-art devices. However, the slow reaction kinetics and sluggish ion diffusion still impede their authentic commercialization. Herein, a thick and robust Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) layered oxide cathode grid-structured electrode is developed using a three-dimensional (3D) direct ink writing (DIW) technique. On the strength of the 3D interconnected channels and conductive scaffolds, both the wettability and the Li+ ion/electron transfer in the electrode are enhanced, which improves the utilization of active materials during the charging and discharging process. As expected, the 3D-printed (3DP) LiNi0.8Co0.1Mn0.1O2 (NCM811) grid-structured electrode delivers a high areal capacity of 7.48 mAh cm–2 (∼200 mAh g–1) even at an ultrahigh mass loading of 36.6 mg cm–2 and a low capacity fading of 0.22% per cycle after 100 cycles at 200 mA g–1. A customized cell module composed of the 3DP NCM811 grid-structured thick cathode and the 3DP artificial graphite grid-structured thick anode, coupled with the ultralow-power offline artificial intelligence electronic module, can power smart glasses and realize augmented-reality time display. The 3D extrusion technique provides a new venue for future smart, flexible, and wearable electrons.

In situ multiscale probing of the synthesis of a Ni-rich layered oxide cathode reveals reaction heterogeneity driven by competing kinetic pathways.

Nickel-rich layered oxides are envisaged as key near-future cathode materials for high-energy lithium-ion batteries. However, their practical application has been hindered by their inferior cycle stability, which originates from chemo-mechanical failures. Here we probe the solid-state synthesis of LiNi0.6Co0.2Mn0.2O2 in real time to better understand the structural and/or morphological changes during phase evolution. Multi-length-scale observations-using aberration-corrected transmission electron microscopy, in situ heating transmission electron microscopy and in situ X-ray diffraction-reveal that the overall synthesis is governed by the kinetic competition between the intrinsic thermal decomposition of the precursor at the core and the topotactic lithiation near the interface, which results in spatially heterogeneous intermediates. The thermal decomposition leads to the formation of intergranular voids and intragranular nanopores that are detrimental to cycling stability. Furthermore, we demonstrate that promoting topotactic lithiation during synthesis can mitigate the generation of defective structures and effectively suppress the chemo-mechanical failures.

Gradient doping Mg and Al to stabilize Ni-rich cathode materials for rechargeable lithium-ion batteries

Nickel-rich layered oxides are attracting extensive interest as cathode materials to build high-energy lithium-ion batteries, but their intrinsic structural instability and interfacial parasitic reactions deteriorate the cycling performance. Herein, we report concentration-gradient Mg and Al doped LiNi0.95Co0.03Al0.01Mg0.01O2 (NCAMg) as a stable and high-capacity cathode material. The obtained NCAMg microparticles exhibit outstanding cyclability (capacity retention of 95.6% after 100 cycles) and remarkable rate capability (172.9 mAh g−1 at 10 C). The gradient Mg and Al doping boosts the electrochemical performance by restraining the undesirable H2–H3 phase conversion and the anisotropic volume change. Moreover, the enrichment of Mg and Al at particle shell enhances the Li-ion diffusivity, inhibits the growth of microcracks, and significantly improves the thermal stability over LiNiO2. The results indicate that Mg and Al gradient co-doping is an efficient and practical route to upgrade Ni-rich layered oxide cathode materials for LIBs.

Spinel LiNi0.5Mn1.5O4 shell enables Ni-rich layered oxide cathode with improved cycling stability and rate capability for high-energy lithium-ion batteries

Increasing the charging cut-off voltage is an effective strategy to achieve high energy density Ni-rich layered oxide cathode materials, however the dramatic deterioration of cycling lifespan and thermal stability still remain great challenges in large-scale practical applications. Herein, a rationally designed core-shell structure LiNi0.9Co0.1O2@LiNi0.5Mn1.5O4 composite composed of spinel structure Mn-rich LiNi0.5Mn1.5O4 shell and layered structure Ni-rich LiNi0.9Co0.1O2 core is proposed to enhance the structure stability and thermal stability under high-voltage application scenario. Compared to the pristine LiNi0.9Co0.1O2 cathode, the core-shell structure LiNi0.9Co0.1O2@LiNi0.5Mn1.5O4 composite with optimized LiNi0.5Mn1.5O4 shell exhibits high reversible specific capacity (195.5 mA h g − 1 at 0.5 C), remarkable cycling stability (86% capacity retention after 100 cycles) and superior rate capability (162.5 mA h g − 1 at 5.0 C) within 2.8 V-4.5 V. The comprehensively improved electrochemical performance is mainly attributed to the Mn-rich LiNi0.5Mn1.5O4 shell, which not only effectively prevents the phase transition and microstructural collapse, but also ameliorates the Li+ transport ability, high-voltage charging capability and thermal stability. Such novel core-shell structure LiNi0.9Co0.1O2@LiNi0.5Mn1.5O4 composite as promising cathode is highly expected to greatly promote the practical application of high energy density lithium-ion batteries.

Suppressing Ni/Li disordering in LiNi0.6Mn0.2Co0.2O2 cathode material for Li-ion batteries by rare earth element doping

The growing demand for efficient lithium-ion batteries to power vehicles and energy storage entails improving cathode material properties. Maintaining the stability of Ni-rich layered structure oxide cathodes is critical for long-term Li-ion battery operation. In this work, a series of LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode materials doped with selected rare earth metal ions (La, Nd, Eu) of various concentrations (0.5-1.5 mol%) was synthesized and systematically studied (XRD, XPS, TEM, STEM-EDX, galvanostatic charge/discharge tests, cyclic voltammetry). The main goal of the research was to suppress the mixing of Ni/Li cations, which influences the electrochemical performance of LiNi0.6Mn0.2Co0.2O2 cathode materials by introducing rare earth elements using co-precipitation. The results showed that the La, Nd, Eu-doped materials exhibit significantly improved electrochemical properties, such as capacity, rate performance, capacity retention and Li+ diffusivity compared to the pristine material. A clear dependence of the doped Ni-rich cathode material capacity on the degree of Ni/Li cation mixing was determined. The presence of a dopant (La, Nd or Eu) with a large radius, the tendency to form strong bonds with oxygen, and electrochemically inactive reduces Ni/Li disordering. It stabilizes the cathode structure, ensuring its better performance. The optimal content of La, Nd and Eu is 1.0, 0.5, and 0.5 mol%, respectively.

Probing the Air Storage Failure Mechanism of Ni-Rich Layered Cathode Materials

Ni-rich layered oxide cathode materials, such as LiNi0.83Co0.12Mn0.05O2 (NCM811), exhibit high specific capacity and low cost, and become cathode material preference of high-energy-density Li-ion batteries. However, these cathode materials are not stable and will form Li-poor reconstructed layers and alkaline compounds (Li2CO3, LiOH) on the surface during the storage and processing in humid air, resulting in serious deterioration of electrochemical properties. During the past two decades, the consensus on the surface instability mechanism during humid air storage has not been reached. The main controversy focuses on the unstable octahedron mechanism and the Li/H exchange mechanism. Herein, we investigate the instability mechanism in the humid air by conducting scanning electronic microscopy, scanning transmission electron microscopy, and x-ray photoelectron spectroscopy analysis on NCM811 samples stored in designed atmospheres, etc., and realize that the surface instability of the NCM811 during storage should be mainly originated from Li/H exchange when it contacts with moisture.

Hydrophobic surface coating against chemical environmental instability for Ni-rich layered oxide cathode materials

Ni-rich layered oxide LiNi0.8Co0.1Mn0.1O2 (NCM) as a most promising cathode material for Li-ion batteries suffers easily from the deterioration of electrochemical performance during storage because of the chemical environmental instability. Herein, a simple and scalable strategy is reported to overcome these issues by a hydrophobic coating with dihexadecyl phosphate (DHP) on NCM particle surface, which is composed of an outer-layer hydrophobic alkyl surface and an inner-layer phosphate-based coating with O=POLi covalent bonds. The former layer can alleviate the absorption of H2O/CO2 on the particle surface in the humid environment, and the later can improve Li+ transportation coefficient during charge–discharge process. As a result, profiting from these two synergistic effects, the DHP-coated NCM shows excellent rate performance and cycling stability, particularly, after 14 days of exposure to air, the DHP-coated NCM delivers the initial capacity of 168.7 mAh g−1 at 2 C rate, but only 134.7 mAh g−1 for the pristine NCM. This work provides an effective approach to improve the environmental stability in Ni-rich layered oxide cathodes.

Magnesium Substitution in Ni‐Rich NMC Layered Cathodes for High‐Energy Lithium Ion Batteries (Adv. Energy Mater. 8/2022)

Li-Ion Batteries In article number 2103045, Aurora Gomez-Martin, Richard Schmuch, and co-workers report the effect of Mg substitution on mitigating the structural challenges of Ni-rich layered oxide cathode materials upon cycling in lithium-ion batteries. While partial substitution of Mg in Li sites linearly reduces the initial capacities at a given upper cut-off cell voltage, the attainable cycle life is significantly extended.