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Undoubtedly, the enormous progress observed in recent years in the Ni-rich layered cathode materials has been crucial in terms of pushing boundaries of the Li-ion battery (LIB) technology. The achieved improvements in the energy density, cyclability, charging speed, reduced costs, as well as safety and stability, already contribute to the wider adoption of LIBs, which extends nowadays beyond mobile electronics, power tools, and electric vehicles, to the new range of applications, including grid storage solutions. With numerous published papers and broad reviews already available on the subject of Ni-rich oxides, this review focuses more on the most recent progress and new ideas presented in the literature references. The covered topics include doping and composition optimization, advanced coating, concentration gradient and single crystal materials, as well as innovations concerning new electrolytes and their modification, with the application of Ni-rich cathodes in solid-state batteries also discussed. Related cathode materials are briefly mentioned, with the high-entropy approach and zero-strain concept presented as well. A critical overview of the still unresolved issues is given, with perspectives on the further directions of studies and the expected gains provided. [ABSTRACT FROM AUTHOR]

Nickel-rich layered oxides LiNi x Co y Mn1- x - y O2 (x ≥ 0.8) have been recognized as the preferred cathode materials to develop lithium-ion batteries with high energy density (>300 Wh kg-1). However, the poor cycling stability and rate capability stemming from intergranular cracks and sluggish kinetics hinder their commercialization. To address such issues, a multi-scale boron penetration strategy is designed and applied on the polycrystalline LiNi0.83Co0.11Mn0.06O2 particles that are pre-treated with pore construction. The lithium-ion conductive lithium borate in grain gaps functions as the grain binder that can bear the strain/stress from anisotropic contraction/expansion, and provides more pathways for lithium-ion diffusion. As a result, the intergranular cracks are ameliorated and the lithium-ion diffusion kinetics is improved. Moreover, the coating layer separates the sensitive cathode surface and electrolyte, helping to suppress the parasitic reactions and related gas evolution. In addition, the enhanced structural stability is acquired by strong B-O bonds with trace boron doping. As a result, the boron-modified sample with an optimized boron content of 0.5% (B5-NCM) exhibits a higher initial discharge capacity of 205.5 mAh g-1 at 0.1C (1C = 200 mA g-1) and improved capacity retention of 81.7% after 100 cycles at 1C. Furthermore, the rate performance is distinctly enhanced by high lithium-ion conductive LBO (175.6 mAh g-1 for B5-NCM and 154.6 mAh g-1 for B0-NCM at 5C).

Highlights A series of layered oxide cathode materials were synthesized by high-temperature shock strategy for the first time. The approaching ultimate solid reaction rate of the layered nickel-rich layered oxide LiNixCoyMnzO2 was investigated for the first time. Ultrafast average reaction rate of phase transition from Ni0.6Co0.2Mn0.2(OH)2 to Li-containing oxides is 66.7 (% s-1), that is, taking only 1.5 s.

Highlights: A series of layered oxide cathode materials were synthesized by high-temperature shock strategy for the first time. The approaching ultimate solid reaction rate of the layered nickel-rich layered oxide LiNixCoyMnzO2 was investigated for the first time. Ultrafast average reaction rate of phase transition from Ni0.6Co0.2Mn0.2(OH)2 to Li-containing oxides is 66.7 (% s-1), that is, taking only 1.5 s. Nickel-rich layered oxide LiNixCoyMnzO2 (NCM, x + y + z = 1) is the most promising cathode material for high-energy lithium-ion batteries. However, conventional synthesis methods are limited by the slow heating rate, sluggish reaction dynamics, high energy consumption, and long reaction time. To overcome these challenges, we first employed a high-temperature shock (HTS) strategy for fast synthesis of the NCM, and the approaching ultimate reaction rate of solid phase transition is deeply investigated for the first time. In the HTS process, ultrafast average reaction rate of phase transition from Ni0.6Co0.2Mn0.2(OH)2 to Li- containing oxides is 66.7 (% s−1), that is, taking only 1.5 s. An ultrahigh heating rate leads to fast reaction kinetics, which induces the rapid phase transition of NCM cathodes. The HTS-synthesized nickel-rich layered oxides perform good cycling performances (94% for NCM523, 94% for NCM622, and 80% for NCM811 after 200 cycles at 4.3 V). These findings might also assist to pave the way for preparing effectively Ni-rich layered oxides for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • PO 4 3−-doping and Li 3 PO 4 -coating of dual modification of LiNiO 2 are achieved. • PO 4 3− doping improves the reversibility of crystal structure. • PO 4 3− doping induces surface structural transformation of the material. • Li 3 PO 4 coating could ameliorate the interface stability. Lithium nickel oxide (LiNiO 2) cathode materials are featured with high capacity and low cost for rechargeable lithium-ion batteries but suffer from severe structure and interface instability. Bulk doping together with surface coating has been proven to be an efficient approach to improve the inner structure and interfacial stability of the LiNiO 2 cathode material. Nevertheless, the role of anion doping seems to be quite different from that of cation doping, and a deep insight will be desirable for the structure design of the LiNiO 2 cathode material. In this paper, PO 4 3−-doped and Li 3 PO 4 -coating of dual modification of LiNiO 2 are achieved via a facile approach. It is demonstrated that the PO 4 3− anions are doped into the tetrahedron vacant sites of the crystal structure, alleviating the phase transition and improving the reversibility of crystal structure. Besides, the Li 3 PO 4 coating layer ameliorates the interface stability to restrain the side reactions. Therefore, the dual modification enhances overall structural stability of the material to provide excellent performance. Moreover, the consumption of the Li residues by the formation of Li 3 PO 4 coating layer, and the enlarged interlayer spacing of the crystal structure by PO 4 3− doping can facilitate the Li+ ions diffusion, resulting in a superior rate capability. [ABSTRACT FROM AUTHOR]

Nickel-rich layered oxides LiNixCoyMn1-x-yO2 (x ≥ 0.8) have been recognized as the preferred cathode materials to develop lithium-ion batteries with high energy density (>300 Wh kg−1). However, the poor cycling stability and rate capability stemming from intergranular cracks and sluggish kinetics hinder their commercialization. To address such issues, a multi-scale boron penetration strategy is designed and applied on the polycrystalline LiNi0.83Co0.11Mn0.06O2 particles that are pre-treated with pore construction. The lithium-ion conductive lithium borate in grain gaps functions as the grain binder that can bear the strain/stress from anisotropic contraction/expansion, and provides more pathways for lithium-ion diffusion. As a result, the intergranular cracks are ameliorated and the lithium-ion diffusion kinetics is improved. Moreover, the coating layer separates the sensitive cathode surface and electrolyte, helping to suppress the parasitic reactions and related gas evolution. In addition, the enhanced structural stability is acquired by strong B-O bonds with trace boron doping. As a result, the boron-modified sample with an optimized boron content of 0.5% (B5-NCM) exhibits a higher initial discharge capacity of 205.5 mAh g−1 at 0.1C (1C = 200 mA g−1) and improved capacity retention of 81.7% after 100 cycles at 1C. Furthermore, the rate performance is distinctly enhanced by high lithium-ion conductive LBO (175.6 mAh g−1 for B5-NCM and 154.6 mAh g−1 for B0-NCM at 5C).

Nickel-rich layered oxides have stood out among cathode materials for lithium-ion batteries because of their inexpensive costs and large specific capacity. However, large-scale commercial uses of nickel-rich cathodes are constrained by structural degradation and air-storage instability. Herein, we synthetize a Mg and Nb co-modified LiNi0.8Co0.1Mn0.1O2 cathode (MgNb-NCM) through acid co-precipitation combined with solid-state reaction. Combining the characterizations of X-ray diffraction (XRD), in situ XRD, and high-resolution transmission electron microscopy (HRTEM), the results demonstrate that Mg2+ and Nb5+ doped into the crystal structures of NCM can reduce the Li+/Ni2+ mixing and alleviate irreversible H2-H3 phase. Meanwhile, through the interactions of Nb ion and residual lithium compounds, a nanoscale Li-Nb-O interfacial protective coating is created on the pristine NCM surface, which helps to suppress side reactions and strengthen the air storage stability of the NCM. After 100 cycles, the MgNb-NCM displays increased cycling stability with 92.9% capacity retention at 1C, much higher than NCM (79.9%). More importantly, the air-storage stability of NCM is highly improved by such co-modification. After 21 days of exposure to air, NCM presents structural degradation, and the capacity drops to 50.0 mAh g−1, while MgNb-NCM appears excellent structural stability, and the capacity retains 151.9 mAh g−1 with a higher capacity retention of 78.8% over 300 cycles at 1C. [ABSTRACT FROM AUTHOR]

Nickel‐rich layered oxides have attracted many attentions for their superior specific capacity and low cost, but they are subjected to fast structural degradation during cycling. Herein, the Al and Sm co‐doped LiNi0.83Co0.07Mn0.10O2 (SC‐NCM‐AS) single‐crystal is demonstrated to overcome their cycling instability issue, and its mechanistic origin for improved structural stability is investigated. It is found that soluble Al ions are homogenously incorporated in the LiNi0.83Co0.07Mn0.10O2 (SC‐NCM) lattice, while Sm ions tends to aggregate in the SC‐NCM outer surface layer. The Li/Ni cation disordering is greatly suppressed through the pillaring effect of stronger AlO bond in SC‐NCM single crystals. Sm‐concentrated outer surface layer can effectively prevent the dissolution of transition metals from SC‐NCM‐AS and inhibit undesirable side reactions induced by the organic electrolyte. This synergistic effect facilitates to suppress the formation of LiOH/Li2CO3 and oxygen vacancies, resulting in released the internal strain, decreased in‐plane transition metals migration and gliding, and eventually preventing formation of nanocracks in SC‐NCM‐AS single crystals upon cycling at high cut‐off voltage. Consequently, Al and Sm co‐doped SC‐NCM exhibits a high specific capacity of 222.4 mAh g−1 and remarkable cycling performance with a capacity retention of 91.1% for 100 cycles. [ABSTRACT FROM AUTHOR]

The Ni‐rich layered oxide cathode is pushing the frontier of battery powered electric vehicles toward longer driving range and lower cost, whilst facing a major challenge with the compromised cycle life and thermal robustness. It is well recognized that irreversible oxygen evolution at the cathode‐electrolyte interphase is critical to the electrochemical and thermal stability of the Ni‐rich cathode. Herein, combining experiments with density functional theory (DFT) calculations, the authors focus on manipulating the irreversible oxygen evolution to solve the performance degradation and safety hazard. An oxygen ion conductor introduced to the surface of the cathode restrains the activated surficial lattice oxygen ions by its stable oxygen vacancies. Meanwhile, a Li‐rich fast ion conductor incorporated in the coating layer synergistically reinforces the Li diffusion path through the cathode‐electrolyte interphase. This sophisticated multifunctional surficial modification implemented by a neat one‐step treatment represents a successful design and development of a thermally stable Ni‐rich cathode and approximately 400‐cycle state‐of‐health up to 80% with the operating voltage range extended up to 4.5 V. Therefore, this study provides an encouraging strategy to overcome the capacity versus robustness dilemma of high‐energy cathodes. [ABSTRACT FROM AUTHOR]

To achieve a broader public acceptance for electric vehicles based on lithium-ion battery (LIB) technology, long driving ranges, low cost, and high safety are needed. A promising pathway to address these key parameters lies in the further improvement of Ni-rich cathode materials for LIB cells. Despite the higher achieved capacities and thus energy densities, there are major drawbacks in terms of capacity retention and thermal stability (of the charged cathode) which are crucial for customer acceptance and can be mitigated by protecting cathode particles. We studied the impact of surface modifications on cycle life and thermal stability of LiNi0.90Co0.05Mn0.05O2 layered oxide cathodes with WO3 by a simple sol–gel coating process. Several advanced analytical techniques such as low-energy ion scattering, differential scanning calorimetry, and high-temperature synchrotron X-ray powder diffraction of delithiated cathode materials, as well as charge/discharge cycling give significant insights into the impact of surface coverage of the coatings on mitigating degradation mechanisms. The results show that successful surface modifications of WO3 with a surface coverage of only 20% can prolong the cycle life of an LIB cell and play a crucial role in improving the thermal stability and, hence, the safety of LIBs. [ABSTRACT FROM AUTHOR]

To drive electrical vehicles for long‐range, the energy density of Li‐ion batteries must be further enhanced, which requires high‐energy cathode materials. Among them, Ni‐rich LiNixMnyCo1−x–yO2 (x > 0.5, NMC) is one of the most promising candidates. However, traditional poly‐crystal (PC) NMC materials, whose particles are secondary clusters consisting of many primary crystalline particles, are susceptible to pulverization along the inter grain/particle boundaries, resulting in poor cycle stability. Recently, single crystal (SC)‐NMC cathodes are proposed as they are believed to have several merits such as high structural integrity, lower interface with electrolyte, and potentially better energy storage performance. Nevertheless, several queries, such as the merits of SC structure and the mechanism for their structure degradation, are still controversial and required to be addressed. Herein, the synthesis parameters, properties, energy storage as well as safety of SC‐ and PC‐NMC cathodes with various Ni contents are critically reviewed, for clarifying the merits and drawbacks of SC. Furthermore, the study focuses on the recent advances of insight mechanisms and strategies for stabilizing the structure/interface by doping, morphology engineering, surface coating, and composition tailoring. The remaining challenges, safety concerns, and perspectives to enhance the electrochemical performance of SC‐NMC cathodes for electric vehicle application are followed. [ABSTRACT FROM AUTHOR]

This study investigated the impact of various process conditions on the aqueous, direct recycling of LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathodes. Three model systems were used. The first system assumes that the current collector delamination is performed in a dry environment without the use of water as a process medium. Consequently, the NMC811 is only exposed to water during classification, where no aluminum foil is present. The second model system assumes that the current collector delamination occurs in water. Therefore, the NMC811 is exposed to water in the presence of aluminum foil. Due to the pH increase caused by the Li + /H + exchange reaction, the pH value surpasses the stability window of the aluminum-oxide passivation layer (pH 4.5-8.5), resulting in the deposition of aluminum-containing species on the NMC811 surface. The third model system is identical to the second, with the exception that H 3 PO 4 is added. This causes the pH to decrease and prevents corrosion of the aluminum foil. The findings reveal that process conditions significantly affect the surface chemistry on NMC811, influencing electrochemical performance. Notably, aluminum-containing species increase polarization. Heat treatment simulating regeneration led to cation mixing as surface species diffused into the NMC811 bulk structure, highlighting the need to control recycling process conditions., (© 2024 The Author(s). ChemSusChem published by Wiley-VCH GmbH.)

With the rapid growth of global electro‐mobility, the demand for cobalt is rapidly increasing because it is currently an indispensable component of the cathode materials in lithium‐ion batteries (LIBs). However, the use of Co raises moral issues caused by its exploitation and the geographic limitations of Co resources may result in risking the supply of LIBs. Thus, the development of cobalt‐free (Co‐free) cathodes has become a focus in the LIBs industry. Currently, Co‐free cathodes of lithium‐rich oxides, nickel‐rich layered oxides and spinel lithium nickel manganese oxide (LNMO) are promising candidates but face severe problems. This review article is the first to synthesize and present the progress of Co‐free cathodes made with Li‐rich oxides, Ni‐rich layered oxides and spinel LNMO, identifying their performance, problems and potential development trends. In particular, the roles of cobalt are further clarified, and the full‐cell performance and related commercialization prospects of the three above‐mentioned Co‐free cathodes are also objectively assessed. The focus of this work is to distill detailed and timely insights from the corresponding research progress on these materials and to demonstrate the associated urgency, challenges and opportunities in this field, thus facilitating a faster industrialization of Co‐free cathodes. [ABSTRACT FROM AUTHOR]

Ni‐rich LiNi1−x−yMnxCoyO2 (NMC) layered oxides are promising cathode materials for high‐energy density lithium ion batteries but suffer from severe capacity fading upon cycling. Elemental substitution (= doping) with Mg has repeatedly attracted attention in NMC materials to overcome instability problems at reasonable cost, yet rational compositional tuning is needed to guarantee sufficient cycle life without compromising energy density on the material level. Herein, a series of Mg‐substituted NMC materials with 90 mol% Ni are investigated regarding key performance metrics in NMC || graphite full‐cells benchmarked against LiNi0.80Mn0.10Co0.10O2 and LiNi0.90Mn0.05Co0.05O2 synthetized using the same co‐precipitation route. A linear correlation between cycle life and attainable gravimetric capacities is demonstrated, which are directly influenced by the degree of Mg substitution and the amount of Li+ cycled upon (de‐)lithiation processes. A Mg content <2 mol% should be considered to take notable benefit from the increase in Ni content from 80 to 90 mol% to achieve a higher energy density. The present study highlights the importance of evaluating the true implications of elemental substitution on cell performance and is expected to be an insightful guideline for the future development of NMC‐type cathode materials in particular with high Ni and low Co content. [ABSTRACT FROM AUTHOR]

To achieve a broader public acceptance for electric vehicles based on lithium-ion battery (LIB) technology, long driving ranges, low cost, and high safety are needed. A promising pathway to address these key parameters lies in the further improvement of Ni-rich cathode materials for LIB cells. Despite the higher achieved capacities and thus energy densities, there are major drawbacks in terms of capacity retention and thermal stability (of the charged cathode) which are crucial for customer acceptance and can be mitigated by protecting cathode particles. We studied the impact of surface modifications on cycle life and thermal stability of LiNi0.90Co0.05Mn0.05O2 layered oxide cathodes with WO3 by a simple sol–gel coating process. Several advanced analytical techniques such as low-energy ion scattering, differential scanning calorimetry, and high-temperature synchrotron X-ray powder diffraction of delithiated cathode materials, as well as charge/discharge cycling give significant insights into the impact of surface coverage of the coatings on mitigating degradation mechanisms. The results show that successful surface modifications of WO3 with a surface coverage of only 20% can prolong the cycle life of an LIB cell and play a crucial role in improving the thermal stability and, hence, the safety of LIBs.

Detrimental rock‐salt and/or spinel surface phases parasitic to Ni‐rich layered oxides with high theoretical capacity are quite formidable which are reported to be eliminated only through alien element dopings and/or surface modifications. Herein, these surface phases are directly eliminated successfully during the synthesis of pristine LiNi0.8Co0.2O2 and LiNi0.9Co0.1O2 using an expanded graphites (EGs) template approach, accompanied by the formation of unique 3D porous structures. The elimination of surface phases may be ascribed to the 3D porous structures formed during the calcination processes at both low and high temperatures, which enables the access of sufficient oxygen to individual nanoparticles and thus promotes the oxidization of Ni2+ to Ni3+ to reduce Li/Ni disordering. Both LiNi0.8Co0.2O2 and LiNi0.9Co0.1O2 show excellent rate capability, long‐term cycling stability, and high initial Coulombic efficiencies (ICEs), such as 210.4 (149) and 222.6 (133) mAh g−1, ICEs of 94.9% and 93.8% at 0.1 C (20 C), and capacity retentions of 74% after 500 cycles at 1 C and 76% after 300 cycles at 1 C, respectively, far better than those synthesized using a conventional sol–gel recipe. This study provides a simple and novel platform for directly synthesizing detrimental surface phases free and chemically stoichiometric Ni‐rich layered oxides with high performance. [ABSTRACT FROM AUTHOR]

Abstract: Nickel‐rich layered oxide cathodes with the composition LiNi1−x−yCoxMnyO2 (NCM, (1−x−y) ≥ 0.6) are under intense scrutiny recently to contend with commercial LiNi0.8Co0.15Al0.05O2 (NCA) for high‐energy‐density batteries for electric vehicles. However, a comprehensive assessment of their electrochemical durability is currently lacking. Herein, two in‐house cathodes, LiNi0.8Co0.15Al0.05O2 and LiNi0.7Co0.15Mn0.15O2, are investigated in a high‐voltage graphite full cell over 1500 charge‐discharge cycles (≈5–10 year service life in vehicles). Despite a lower nickel content, NCM shows more performance deterioration than NCA. Critical underlying degradation processes, including chemical, structural, and mechanical aspects, are analyzed via an arsenal of characterization techniques. Overall, Mn substitution appears far less effective than Al in suppressing active mass dissolution and irreversible phase transitions of the layered oxide cathodes. The active mass dissolution (and crossover) accelerates capacity decline with sustained parasitic reactions on the graphite anode, while the phase transitions are primarily responsible for cell resistance increase and voltage fade. With Al doping, on the other hand, secondary particle pulverization is the more limiting factor for long‐term cyclability compared to Mn. These results establish a fundamental guideline for designing high‐performing Ni‐rich NCM cathodes as a compelling alternative to NCA and other compositions for electric vehicle applications. [ABSTRACT FROM AUTHOR]

Nickel-rich layered oxides LiNi x Co y Mn 1- x - y O 2 ( x  ≥ 0.8) have been recognized as the preferred cathode materials to develop lithium-ion batteries with high energy density (>300 Wh kg -1 ). However, the poor cycling stability and rate capability stemming from intergranular cracks and sluggish kinetics hinder their commercialization. To address such issues, a multi-scale boron penetration strategy is designed and applied on the polycrystalline LiNi 0.83 Co 0.11 Mn 0.06 O 2 particles that are pre-treated with pore construction. The lithium-ion conductive lithium borate in grain gaps functions as the grain binder that can bear the strain/stress from anisotropic contraction/expansion, and provides more pathways for lithium-ion diffusion. As a result, the intergranular cracks are ameliorated and the lithium-ion diffusion kinetics is improved. Moreover, the coating layer separates the sensitive cathode surface and electrolyte, helping to suppress the parasitic reactions and related gas evolution. In addition, the enhanced structural stability is acquired by strong B-O bonds with trace boron doping. As a result, the boron-modified sample with an optimized boron content of 0.5% (B5-NCM) exhibits a higher initial discharge capacity of 205.5 mAh g -1 at 0.1C (1C = 200 mA g -1 ) and improved capacity retention of 81.7% after 100 cycles at 1C. Furthermore, the rate performance is distinctly enhanced by high lithium-ion conductive LBO (175.6 mAh g -1 for B5-NCM and 154.6 mAh g -1 for B0-NCM at 5C)., Competing Interests: The authors declare that they have no conflicts of interest in this work., (© 2022 The Authors. Publishing Services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.)

A series of Zr4+ and/or Al3+ doped LiNi 0.83 Co 0.11 Mn 0.06 O 2 are synthesized via a solid phase method. TEM shows that the co-doped specimen consists of a layered core and a coherent interface cation-mixed shell. XRD and XPS results clarify that Zr4+ doping increases the Li+/Ni2+ cation site exchange degree and the concentration of Ni2+. The morphology and structural integrity of the co-doped electrode maintains well, and it provides a higher cycle retention (89.7%) than blank (60.1%) after 150 cycles and a superior capacity of 152.8 mAh g−1 at 7C (only 57.7 mAh g−1 for blank) and an enhanced elevated temperature cycle retention (83.0%) than blank (33.7%) after 100 cycles at 55 °C. Generally, Zr4+ raises the concentration of Ni2+ to keep electric neutrality and then reconstruct a stable interfacial structure to inhibit side reactions, the structural stability could be also enhanced by the strong Zr–O and Al–O bonds. Meanwhile, Al3+ served as centers of positive charge can suppress the phase transformation. Benefiting from the synergistic effect of Zr4+/Al3+, as well as the induced coherent interface cation-mixed shell, co-doped specimen shows enhanced structural stability and the superior electrochemical performance. This study provides a route to prepare advanced layered cathodes for lithium-ion batteries. [Display omitted] • Nickel-rich layered oxides were modified by Zr4+/Al3+ co-doping method. • The structural integrity of electrode maintains well through Zr4+/Al3+ co-doping. • NCM-Zr/Al exhibits superior rate and cycling performance. • The CICM shell inhibits the structure instability and side reactions. [ABSTRACT FROM AUTHOR]

All-solid-state batteries (ASSBs) present a promising route toward safe and high-power battery systems in order to meet the future demands in the consumer and automotive market. Composite cathodes are one way to boost the energy density of ASSBs compared to thin-film configurations. In this manuscript, we investigate composites consisting of β-Li 3 PS 4 (β-LPS) solid electrolyte and high-energy Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 (NMC622). The fabricated cells show a good cycle life with a satisfactory capacity retention. Still, the cathode utilization is below the values reported in the literature for systems with liquid electrolytes. The common understanding is that interface processes between the active material and solid electrolyte are responsible for the reduced performance. In order to throw some light on this topic, we perform 3D microstructure-resolved simulations on virtual samples obtained via X-ray tomography. Through this approach, we are able to correlate the composite microstructure with electrode performance and impedance. We identify the low electronic conductivity in the fully lithiated NMC622 as material inherent restriction preventing high cathode utilization. Moreover, we find that geometrical properties and morphological changes of the microstructure interact with the internal and external interfaces, significantly affecting the capacity retention at higher currents.

The formation of metallic lithium microstructures in the form of dendrites or mosses at the surface of anode electrodes (e.g., lithium metal, graphite, and silicon) leads to rapid capacity fade and poses grave safety risks in rechargeable lithium batteries. We present here a direct, relative quantitative analysis of lithium deposition on graphite anodes in pouch cells under normal operating conditions, paired with a model cathode material, the layered nickel-rich oxide LiNi 0.61 Co 0.12 Mn 0.27 O 2 , over the course of 3000 charge-discharge cycles. Secondary-ion mass spectrometry chemically dissects the solid-electrolyte interphase (SEI) on extensively cycled graphite with virtually atomic depth resolution and reveals substantial growth of Li-metal deposits. With the absence of apparent kinetic (e.g., fast charging) or stoichiometric restraints (e.g., overcharge) during cycling, we show lithium deposition on graphite is triggered by certain transition-metal ions (manganese in particular) dissolved from the cathode in a disrupted SEI. This insidious effect is found to initiate at a very early stage of cell operation (<200 cycles) and can be effectively inhibited by substituting a small amount of aluminum (∼1 mol %) in the cathode, resulting in much reduced transition-metal dissolution and drastically improved cyclability. Our results may also be applicable to studying the unstable electrodeposition of lithium on other substrates, including Li metal.