Physics-Based Modeling of Aging in NMC/Graphite Cell Under High Voltage Operation at Different Temperatures

High voltage high energy cathode materials for Li-ion battery are highly needed. High nickel content NMC (e.g. NMC811) is believed to be a promising candidate. When raised the upper cutoff voltage of NMC811 cathode to 4.5 V vs. Li+/Li, the cathode materials could deliver a capacity above 215 mAh g-1, which is very attractive to the electric vehicle application. However, raising the upper cutoff voltage will also greatly accelerate the capacity fade of the full cell. Of the various causes proposed by the battery community, a large volume of gases generated at high voltage is believed to be one of the major issues. In this study, we constructed full pouch cells composed of graphite anode, NMC811 cathode and standard GEN2 electrolyte which is 1.2M LiPF6 in EC/EMC (3/7 by weight). We also constructed anode and cathode symmetric pouch cells to investigate the gas evolution and crosstalk at specific sides. Using Archimedes’ Principle, we measured the generated gas volume along cycles within the pouch cells with different cutoff voltages. We found out that the full cells using 4.2 V cutoff voltage barely generated gases along the course of 100 cycles while the ones using 4.4 V cutoff voltage generated a large amount of gases in the first 20 cycles, but the gases would be gradually consumed in the subsequent cycles. By using GC-MS, we determined the main gas species generated in the full cell to be carbon dioxide and alkanes. Moreover, the relative amount of carbon dioxide decreased along cycles while the amount of alkanes would increase. In cathode symmetric cells, CO2 remained the major component after 100 cycles and its signal was much stronger than in full cells. Interestingly, some fluorinated alkanes not seen in the full cells were also identified in cathode symmetric cells, suggesting potential involvement and loss of LiPF6 from electrolyte due to the parasitic side reactions on the cathode. In anode symmetric cells, hydrocarbons attributed to electrolyte decomposition were the main products. Unlike CO2 and fluorinated alkanes formed on the cathode, these species were relatively stable and remained in the full cell after extensive cycling. It was also shown that gas crossover to the anode leads to the depletion of gaseous products during cycling, which could stabilize the cell cycle performance. Although some inactive surface reconstruction layer was formed on the cathode at high voltage operation, impedance buildup and active lithium inventory loss contributed to the significant capacity loss in the full cell. Our study revealed the important role of crossover effect in stabilizing Ni-rich layered oxide cathode, and provided a better understanding on capacity fading to take more effective measures for improving the full cell cycle life.

Modelling of electrochemical impedance spectroscopy (EIS) to predict aging in lithium ion batteries is a useful tool when performing a diagnosis of the state of health (SOH) of the battery. Aging of lithium ion batteries happens in applications from electric vehicles to stationary systems and is associated to capacity fade and impedance increase [1]. By predicting the aging parameters through modeling of EIS from separated electrodes, it is possible to estimate the SOH of the full cell and therefore improve its performance. In this work NCA and graphite electrodes were harvested from cylindrical cells aged under an off-grid PV/Battery system conditions and analyzed by means of EIS to determine the causes of electrode deterioration. The NCA/graphite cylindrical cells were calendar aged and cycle-aged between SOC 20-50 %, 35-65 %, 60-90 % and 20-95 % until end of test (EOT) is reached (e.g. 1000 cycles). The impedance behavior of the calendar and cycle aged cells were measured. Each electrode is carefully harvested once reached the EOT and electrochemically characterized using symmetric cells by means of EIS. A physics-based impedance model is employed to fit the experimental EIS of symmetrical cells using a least square fitting tool in COMSOL® Multiphysics 5.4. It is based on the pseudo two-dimensional (P2D) model [2] incorporating intercalation kinetics, mass and charge transport based on concentrated solution porous electrode theory. The model additionally accounts for double layer effect and aging mechanisms. Using the model, useful aging parameters were parameterized, and the variation of the aging parameters with different aging history was validated with the support of scattered electron microscopy (SEM) technique. Among the aging mechanisms described, an increase in the local contact resistance between the active material and the conductive carbon, and decrease in particle size due to particle cracking and further film formation due to SEI are considered. The impedance model parameters from both electrodes are then linked to the aging process observed on experimental full cell. Figure 1 shows the fitting and experimental curves for graphite Nyquist plot, in which we observe a good fitting specifically at low frequencies. Although the model predicts a second semicircle in the middle requency range, the experimental curve also shows a time constant element which can be considered as a truncated semicircle in the same region. [1] T. G. Zavalis, M. Klett, M. H. Kjell, M. Behm, R. W. Lindström, G. Lindbergh, Electrochemica Acta, 110 (2013) 335-348. [2] J. Newman and W. Tiedemann, AIChE J., 21, 25–41 (1975). Figure 1

Due to growing demand for electric vehicles (EVs) and energy storage systems (ESS), it is essential to meet the requirement for high energy density of Li secondary batteries. In this sense, an electrode chemistry matching high-Ni cathode materials and thin Li metal anode has been investigated most actively under high voltage operation. As a result, there are a variety of degradation issues on both electrodes like high-resistance cathode electrolyte interphase (CEI) as well as solid electrolyte interphase (SEI) on the anode, electrolyte depletion, or Li dendritic growth. Thus, advanced electrolytes containing functional additives are extensively being developed to mitigate those stresses occurred in the high-energy-density Li-metal secondary batteries (LMSBs). Especially, to minimize the amount of expensive additives, many research groups have made much effort in discovering new or multi-functional additives for LMSBs.In this work, we report a bis(2-fluoroethyl) carbonate (B-FEC) as a new fluorine-based linear carbonate electrolyte additive to stabilize the SEI even in the high voltage conditions (4.5 V cut-off). To confirm the role of B-FEC on electrochemical properties, we evaluated its electrochemical properties with Li/Li symmetric cells as well as LiNi0.6Co0.2Mn0.2O2 (NCM 622)/Li cells with or without B-FEC. Also, various analysis data were also gathered to check the morphological and compositional changes caused by B-FEC through SEM, XPS, etc.

Preventing the decomposition reactions of electrolyte solutions is essential for extending the lifetime of lithium-ion batteries. However, the exact mechanism(s) for electrolyte decomposition at the positive electrode, and particularly the soluble decomposition products that form and initiate further reactions at the negative electrode, are still unknown. In this work, a combination of operando gas measurements and solution NMR was used to study decomposition reactions of the electrolyte solution at NMC (LiNixMnyCo1-x-yO2) and LCO (LiCoO2) electrodes. A partially delithiated LFP (LixFePO4) counter electrode was used to selectively identify the products formed through processes at the positive electrode. Based on the detected soluble and gaseous products, two distinct routes with different onset potentials are proposed for the decomposition of the electrolyte solution at NMC electrodes. At low potentials (<80% state-of-charge, SOC), ethylene carbonate (EC) is dehydrogenated to form vinylene carbonate (VC) at the NMC surface, whereas at high potentials (>80% SOC), 1O2 released from the transition metal oxide chemically oxidises the electrolyte solvent (EC) to CO2, CO and H2O. The formation of water via this mechanism was confirmed by reacting 17O-labelled 1O2 with EC and characterising the reaction products via 1H and 17O NMR spectroscopy. The water that is produced initiates secondary reactions, leading to the formation of the various products identified by NMR spectroscopy. Noticeably fewer decomposition products were detected in NMC/graphite cells compared to NMC/LixFePO4 cells, which is ascribed to the consumption of water (from the reaction of 1O2 and EC) at the graphite electrode, preventing secondary decomposition reactions. The insights on electrolyte decomposition mechanisms at the positive electrode, and the consumption of decomposition products at the negative electrode contribute to understanding the origin of capacity loss in NMC/graphite cells, and are hoped to support the development of strategies to mitigate the degradation of NMC-based cells.

The high voltage spinel LiNi0.5Mn1.5O4 (LNMO) is an attractive positive electrode due to its operating voltage around 4.7 V (vs Li/Li+) and high power capability. However, problems including electrolyte decomposition at high voltage and transition metal dissolution, especially at elevated temperatures, have limited its potential use in practical full cells. In this paper, a fundamental study for LiNi0.5Mn1.5O4 || Li4Ti5O12 (LTO) full cells has been performed to understand the effect of different capacity fading mechanisms contributing to overall cell failure. Electrochemical characterization of cells in different configurations (regular full cells, back-to-back pseudo-full cells and 3-electrode full cells) combined with an intermittent current interruption technique have been performed. Capacity fade in the full cell configuration was mainly due to progressively limited lithiation of electrodes caused by a more severe degree of parasitic reactions at the LTO electrode, while the contributions from active mass loss from LNMO or increases in internal cell resistance were minor. Comparison of cell formats constructed with and without the possibility of cross-talk indicate that the parasitic reactions on LTO occur because of the transfer of reaction products from the LNMO side. The efficiency of LTO is more sensitive to temperature causing a dramatic increase in the fading rate at 55 °C. These observations show how important the electrode interactions (cross-talk) can be for the overall cell behaviour. Additionally, internal resistance measurements showed that the positive electrode was mainly responsible for the increase of resistance over cycling, especially at 55 °C. Surface characterization showed that LNMO surface layers were relatively thin when compared to the SEI on LTO. The SEI on LTO does not contribute significantly to overall cell resistance even though these films are relatively thick. XANES measurements showed that the Mn and Ni observed on the anode were not in metallic state; the presence of elemental metals in the SEI is therefore not implicated in the observed fading mechanism through a simple reduction process of migrated metal cations.

Layered transition metal oxides, such as lithium nickel manganese cobalt oxide (NMC) and lithium nickel cobalt aluminum oxide (NCA), have been an area of active research to further improve their capacity, cycle life and lower their cost of production. Over the years, researchers and scientists have come to realize that improving the capacity of these oxides by increasing their nickel content will inevitably compromise their cycle life, which hinder their application in commercial lithium-ion cells. Limited cycle life of layered nickel-rich transition metal oxides, on one hand, is due to the large anisotropic unit cell volume change that causes active material loss and impedance growth due to microcracking of polycrystalline particles during charge-discharge cycling, which universally occurs in all nickel-rich layered oxides1,2. On the other hand, at the top of charge, the presence of highly oxidizing Ni4+ has been shown by many reports to be responsible for parasitic reactions like electrolyte oxidation that create harmful products and damage the surface of active particles3.The use of surface coatings, which act as a barrier to avoid the direct contact of the active materials with the electrolyte, is a common method to stabilize the interface between nickel-rich electrodes and electrolyte especially at high voltage. However, commonly adopted coating materials such as Al2O3, TiO2, etc4,5. have low Li+ and electron conductivity and do not contribute to any specific capacity in a lithium-ion cell. Moreover, coating these “non-active” materials onto lithiated layered transition metal oxides is an extra step in a large-scale industrial synthesis process that will inevitably increase the cost of production. Therefore, a more cost-effective approach is required to solve the problems of nickel-rich materials.In a core-shell structure, a nickel-rich core with high capacity and a low nickel content shell with high structural stability are utilized. A low nickel content shell prevents direct contact of the nickel-rich core with the electrolyte, therefore enabling improved cycle life over the nickel-rich core alone. In contrast to the commonly adopted coatings, which contribute no capacity to the coated material and require an extra coating process, the low nickel shell not only minimizes the loss of material specific capacity due to “non-active” coatings, but also can be easily synthesized by co-precipitation method without an extra step. Based on these merits, the core-shell structure with a nickel-rich core and a low nickel shell possesses great potential as a high capacity and long cycle life positive electrode materials.It has been demonstrated in the Dahn group that interdiffusion of transition metal occurs between core and shell6. Mn was shown to have a lower interdiffusion coefficient than Mg and Al. Therefore, Mn would be a better element to use in the shell than Mg and Al without compromising the overall core-shell structure during heat treatment. Co is expensive and less abundant than Ni and Mn. Minimizing or complete elimination of Co has been an area of active research. Li et al7 have demonstrated that the presence of Co in layered transition metal oxides brings no value to NCA-type materials with high nickel content.In this presentation, a core-shell structure precursor with a Ni(OH)2 core and a Ni0.8Mn0.2(OH)2 shell was heated with LiOH·H2O at 750oC and 800oC. The cross-sectional EDS mapping shows a well-defined core-shell structure when lithiated at 750oC (CS-750) and a diminished core-shell structure at 800oC (CS-800). Compared to single crystal and polycrystalline NMC811 (SC811 and PC811, respectively), CS-750 shows higher specific capacity and comparable capacity retention without any Co, which makes it a promising positive electrode material as an alternative to NMC811. References Y. Liu, J. Harlow, and J. Dahn, J. Electrochem. Soc., 167, 020512 (2020).H. Li et al., Chem. Mater., 31, 7574–7583 (2019).S. R. Li, C. H. Chen, X. Xia, and J. R. Dahn, J. Electrochem. Soc., 160, A1524–A1528 (2013).S. T. Myung et al., Chem. Mater, 17, 3695–3704 (2005)P. Karayaylali et al., J. Electrochem. Soc., 166, A1022–A1030 (2019).N. Zhang et al., Chem. Mater., 31, 10150–10160 (2019).7. H. Li et al., J. Electrochem. Soc., 166, A429–A439 (2019). Figure 1

The degradation of Ni‐rich cathodes during long‐term operation at high voltage has garnered significant attention from both academia and industry. Despite many post‐mortem qualitative structural analyses, precise quantification of their individual and coupling contributions to the overall capacity degradation remains challenging. Here, by leveraging multiscale synchrotron X‐ray probes, electron microscopy, and post‐galvanostatic intermittent titration technique, the thermodynamically irreversible and kinetically reversible capacity loss is successfully deconvoluted in a polycrystalline LiNi0.83Mn0.1Co0.07O2 cathode during long‐term charge/discharge cycling in full cell configuration. Contradicting the dramatic capacity loss, the layered structure remains highly alive even after 1000 cycles at 4.6 V while undergoing a three‐order of magnitude reduction in the mass transfer kinetics, leading to almost fully recoverable capacity under kinetic‐free conditions. Such kinetic dormant behavior after cycling is not simply ascribed to poor chemical diffusion by reconstructed cathode surface but highly synchronizes with the lattice strain evolution stemming from the structural heterogeneity between deeply delithiated layered and degraded rock‐salt phases at high voltage. These findings deepen the degradation mechanism of high‐voltage cathodes to achieve long‐cycling and fast‐charging performance.

Introduction Recent research has resulted in significant improvements in the energy density and cycle life of Na batteries. For instance, FEC electrolyte additive has shown to be beneficial for cycling hard carbon and NaNi1/2Mn1/2O2electrodes [1]. However, Na-ion studies have almost exclusively employed Na half-cells, in which severe dendrite and impedance growth can occur at the Na electrode during cycling [1,2]. Another disadvantage half-cells is that the counter electrode provides a huge excess of Na or Li metal, potentially masking the effects of alkali metal consuming reactions unless the coulombic efficiency (CE) is precisely measured [3]. This effect can make the working electrode appear to have long cycle life when in a full cell it would perform poorly. Recently symmetric cells have been suggested for testing the performance of Li-ion electrode materials and electrolytes [3], enabling the precise measurement of CE, cycle life and electrolyte reactions without the need for a Li metal electrode. In this study the detrimental effects of Na metal electrodes on the cycling of half-cells were confirmed. Half cells with electrolytes containing NaPF6 or NaTFSI salts with EC/DEC 1/2 v/v were found to cycle well, while NaPF6 or NaTFSI in PC-based electrolytes suffered from reactions with the Na electrode leading to severe capacity fade after only about 10 cycles. NaCrO2symmetric cells were then used to investigate the cycling performance of the same electrolytes. Electrolytes that performed poorly in half-cells were found to perform well in symmetric cells. Experimental Electrodes were an 80/10/10 weight ratio of NaCrO2, carbon black and PVDF on Al foil. 2325 coin-type half and symmetric cells used electrolytes comprising either EC/DEC (1:2) or PC solvent with 1M NaPF6, 1M NaTFSI or a combination of 0.7M NaTFSI and 0.3M NaPF6. Symmetric cells were constructed from two nominally identical NaCrO2 electrodes, one charged to 3.5 V and the other charged to 3.5 V and then discharged to 2.0 V (vs Na/Na+). Cells were cycled at a rate of C/10 (assuming 125 mAh/g capacity). Results and Discussion Figure 1 shows the voltage curve of a NaCrO2 half-cell (Fig. 1a) and a NaCrO2 symmetric cell (Fig. 1b) using 1M NaPF6 in PC. The half-cell suffers from impedance growth and rapid capacity fade after about 20 cycles. The symmetric cell exhibits no growth in impedance and little capacity fade after 50 cycles. In this case, the half-cell results might lead one to believe that NaCrO2 with 1M NaPF6in PC is a poor choice and therefore does not merit further study. However, the symmetric cell result shows this to be an excellent combination of electrode and electrolyte, achieving a CE of 99.94%. CEs of 99.97% were achieved with other conventional electrolytes with no additives. We believe these are the highest CEs for Na-ion battery materials reported so far.Electrolytes in which good cycling is achieved in half-cells may not be optimum for the working electrode. In a symmetric cell, there is no Na metal, so any capacity fade that occurs is a reflection of the working electrode performance alone. Since Na metal has proven to be much more reactive towards electrolyte than Li metal, symmetric cells are especially important for evaluating Na battery material and electrolyte performance. References. 1. S. Komaba, T. Ishikawa, N. Yabuuchi, W. Murata, A. Ito, Y. Ohsawa, ACS Applied Materials & Interfaces, 3(11) , 4165 (2011).2. D.A. Stevens, J.R. Dahn, Journal of The Electrochemical Society, 148(8) , A803 (2001).3. J.C. Burns, L.J. Krause, D.-B. Le, L.D. Jensen, a. J. Smith, D. Xiong, J.R. Dahn, Journal of The Electrochemical Society, 158 (12) , A1417 (2011).

This paper deals with the occurrence of a graphite irreversible degradation mechanism in commercial Graphite (C) / lithium Nickel Manganese Cobalt oxide (NMC) lithium-ion batteries, challenging metallic lithium deposition as the major aging mechanism at low temperature cycling. In this study, commercial 16 Ah C/NMC Li-ion cells were aged during cycling at 5°C at a rate of 1C between 2.7 V and 4.2 V (namely between 0 and 100% of state of charge (SOC), respectively), with significant performance fading after 50 cycles only, while up to 4000 cycles can be performed at 45°C with the same commercial cells. The monitoring of the potential of each electrode during cycling has been performed through the successful introduction of lithium metal as reference electrode into the commercial cell. This technique demonstrated that it was more and more difficult to extract lithium ions from graphite particles to intercalate into the positive electrode as the number of cycles increased. Graphite electrodes remained unexpectedly lithiated after cells were dismantled in discharged state. A part of exchangeable lithium detected being trapped into the negative electrode as graphite intercalation compounds was observed with X-Ray Diffraction (XRD). Lithium-7 Nuclear Magnetic Resonance (7Li NMR) performed on graphite electrode led to the distinction between lithium intercalated into graphite, oxidized lithium in the Solid Electrolyte Interphase (SEI) and metallic lithium present in low amounts. Coupling Focused Ion Beam (FIB) / Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Photoelectron Spectrometry (XPS) techniques demonstrated the presence of an untypical layer composed of electrolyte degradation products, hindering graphite electrode pores, particularly concentrated in the regions corresponding to interparticle cavities where lithium was found enriched and trapped.

1- (P-toluenesulfonyl)imidazole (PTSI) as the novel bifunctional electrolyte for LiCoO2-based cells with improved performance at high voltage

Spinel LiNi0.5 Mn1.5 O4 (LNMO) is the most promising cathode material for achieving high energy density lithium-ion batteries attributed to its high operating voltage (≈4.75 V). However, at such high voltage, the commonly used battery electrolyte is suffered from severe oxidation, forming unstable solid-electrolyte interphase (SEI) layers. This would induce capacity fading, self-discharge, as well as inferior rate capabilities for the electrode during cycling. This work first time discovers that the electrolyte oxidation is effectively negated by introducing an electrochemically stable silk sericin protein, which is capable to stabilize the SEI layer and suppress the self-discharge behavior for LNMO. In addition, robust mechanical support of sericin coating maintains the structural integrity during the fast charging/discharging process. Benefited from these merits, the sericin-based LNMO electrode possesses a much lower Li-ion diffusion energy barrier (26.1 kJ mol-1 ) for than that of polyvinylidene fluoride-based LNMO electrode (37.5 kJ mol-1 ), delivering a remarkable high-rate performance. This work heralds a new paradigm for manipulating interfacial chemistry of electrode to solve the key obstacle for LNMO commercialization, opening a powerful avenue for unlocking the current challenges for a wide family of high operating voltage cathode materials (>4.5 V) toward practical applications.

To improve the energy density in Li-ion batteries, development of cathode materials with higher capacities are required, where much of the current focus is on Ni-rich lithium nickel manganese oxides (NMC). However, higher Nickel content is typically accompanied by accelerated degradation and thus poor cycle life, with undesired reactions at the electrode-electrolyte interfaces strongly implicated. There have been numerous attempts to mitigate this, using various methods including surface coatings, structural doping and advanced synthesis techniques such as core-shell or concentration gradient particles with much lower nickel concentrations at their surface. Designing improved solutions, requires a deeper mechanistic understanding of the underlying interfacial processes involved in degradation and their relative contributions. In this study these reactions are investigated in LiNi0.8Mn0.1Co0.1O2–graphite cells cycled using LP57 electrolyte (1 M LiPF6 in EC:EMC, 3:7) for different number of cycles, providing information about how interfacial degradation proceeds. Electrochemical measurements are combined with post mortem techniques including surface sensitive soft X-ray absorption spectroscopy, and photoelectron spectroscopy measured with different excitation energies. Based on fitted differential voltage analysis (DVA) data from the cells it is shown how the initial capacity fading during the first 300 cycles is almost fully attributable to excessive electrolyte reduction exhibited as SEI thickening, whereas further cycling leads to a larger contribution to capacity fading from loss of active NMC material. The initial capacity fading due to electrolyte reduction can be correlated with more plating of manganese, as compared to nickel, onto the graphite electrode, see figure. However, after 600 cycles both nickel and manganese are found in similar concentrations within the SEI. The changing ratio between the amount of plated nickel and manganese with cycle number indicates that manganese on the NMC surface initially dissolves more easily than the nickel, but as the unstable manganese ions are dissolved more and more nickel will contribute to the transition metal dissolution. The nickel ions in the SEI are also found to change their chemical surrounding as the cycling proceeded, showing that they do not form stable species and are thus likely to contribute to continued breakdown of the SEI. We compare the observed evolution of the SEI that results from cross talk between the NMC and graphite electrodes, to the case where EC-free electrolytes are used and graphite is replaced with Li4Ti5O12 (LTO) such that contributions from electrolyte reduction at the anode are expected to be minimised [1,2].In addition to the side reactions at the graphite other important side reactions take place on the NMC, some of which are potentially initiated by the graphite electrode [3]. For instance it was found that the Li2CO3 impurities present on the NMC surface decompose throughout the cells’ cycle life rather than just during the initial cycles. Previous studies have shown how Li2CO3 coatings severely decrease the cycle life, and therefore the observations here show that decomposition related to Li2CO3 is a problem that does not disappear during the formation cycling. Instead minimizing the initial Li2CO3 formation is critical. The insights obtained here on the evolution of surface layers coupled with the individual electrochemical degradation of the electrodes will advance the understanding of the Ni-rich NMC’s capacity retention behaviour and inform future efforts to achieve longer cycle lifetimes.[1] Björklund, E., Göttlinger, M., Edström, K., Younesi, R. & Brandell, D. Sulfolane‐Based Ethylene Carbonate‐Free Electrolytes for LiNi0.6Mn0.2Co0.2O2−Li4Ti5O12 Batteries. Batter. Supercaps 3, 201– 207 (2020).[2] Björklund, E., Göttlinger, M., Edström, K., Brandell, D. & Younesi, R. Investigation of Dimethyl Carbonate and Propylene Carbonate Mixtures for LiNi0.6 Mn0.2Co0.2O2-Li4 Ti5 O12 Cells. ChemElectroChem 6, 3429–3436 (2019).[3] Björklund, E., Brandell, D., Hahlin, M., Edström, K. & Younesi, R. How the Negative Electrode Influences Interfacial and Electrochemical Properties of LiNi1/3Co1/3Mn1/3O2 Cathodes in Li-Ion Batteries. J. Electrochem. Soc. 164, A3054–A3059 (2017). Figure 1

Lithium-ion battery (LIB) has gained significant recognition for the power cell market owing to its impressive energy density and appealing cost benefit. Among various cathodes, a high-voltage cobalt-poor lithium nickel manganese cobalt oxide cathode (Co-poor NCM cathode) has been considered as a promising strategy to enhance its energy density. Despite these advantages, high-voltage Co-poor NCM cathode-graphite full battery usually suffers from poor rate performance. However, fast charging has been a key indicator for widespread application of power batteries. Although many efforts have been made to improve the charging performance of fresh batteries, few works investigate the charging ability during calendar aging and cycling aging of high-voltage Co-poor NCM cathode-graphite full battery. In this work, we found that the charging ability becomes worse during calendar aging and cycling aging. Results showed that the increasing charge transfer resistance from the cathode is the major obstacle to achieving fast charging during the aging process. To address the problem, high-voltage Al2O3-coated Co-poor NCM cathode successfully prepared via a simple atomic layer deposition (ALD) method has been developed to reduce the decay of charging performance during calendar aging and cycling aging. Al2O3-coated NCM cathode can effectively reduce the growth rate of the resistance of cathode, which is benefiting from the conversion of Al2O3 into LiAlO2 with high ionic conductivity and the restriction formation of rock salt phase. Benefiting from the decreased charge transfer resistance of the NCM cathode, the mismatch of the lithium-ion reaction kinetics is well alleviated, thus effectively reducing the polarization under fast charging. As a result, Al2O3-coated NCM cathode-graphite full battery shows the slow deterioration of charging performance during the aging process. This work provides a promising strategy for constructing fast-charging batteries during calendar aging and cycling aging.

• Optimized single-stage Li 2 CO 3 precipitation in closed-loop recycling process • Heterogeneous precipitation achieved 97.1% of recoverable Li 2 CO 3 with high purity • Obtained Li 2 CO 3 produces recycled NMC cathodes with comparable electrochemical performance • Both precipitation methods ensure profitability while mitigating CO 2 eq emissions The growing demand for lithium-ion batteries (LIBs) highlights the need for efficient lithium recovery. Developing cost-effective, environmentally friendly extraction methods from secondary sources, such as end-of-life (EoL) Li-ion batteries, is essential for a sustainable lithium supply chain. This study optimizes Li 2 CO 3 recovery, ensuring battery-grade quality, seamless integration into cathode active material (CAM) synthesis, and economic feasibility within hydrometallurgical recycling. Two approaches for single-stage Li recovery in a hydrometallurgical process with integrated CAM production from black mass of lithium nickel manganese cobalt oxide (NMC) LIBs are compared: homogeneous precipitation with Na 2 CO 3 and heterogeneous precipitation using CO 2 gas. The analysis focuses on process efficiency, Li purity, and suitability for battery applications. Results show that selective CO 2 -based precipitation demonstrated higher selectivity, achieving 97.10% Li recovery (recoverable as Li 2 CO 3 ) , compared to 77.97% for Na 2 CO 3 precipitation, with both methods yielding battery-grade purity and morphology. Recycled NMC622 cathodes synthesized from recovered Li 2 CO 3 achieved over 95% of the discharge capacity of those from commercial Li 2 CO 3 . Recycled materials demonstrated excellent capacity retention and high coulombic efficiency (∼100%) after 30 cycles. Full-scale modeling assessed economic and environmental impacts in European LIBs recycling scenarios. Heterogeneous precipitation showed higher profitability (+0.73 M€/year) and greater net GHG reduction (986 t CO 2 /year) but was more energy price-sensitive. Homogeneous precipitation demonstrated stable profitability (+0.62 M€/year); however, reduction in GHG emissions was more limited, reaching 518 t CO 2 /year. This study integrates lithium recovery and water reclamation into a closed-loop process, enabling direct NMC cathode production, offering a sustainable and economically viable solution for LIBs manufacturing.

Progress in direct recycling of spent lithium nickel manganese cobalt oxide (NMC) cathodes