Ni-Rich NMC Cathodes Research Articles

Effects of Main Aging Mechanism and State of Charge on the Safety of 21700 Li-Ion Battery Cells with Ni-Rich NMC Cathode

It is known that both the material used in Li-ion battery cells, as well as their aging history and state of charge (SOC), strongly impact the safety of such cells. This study investigates the safety characteristics of new or aged 21700 cells containing silicon-graphite blend anodes together with Ni-rich NMC cathodes by accelerating rate calorimetry (ARC) at different SOC. Cells underwent cyclic aging at 0 °C, room temperature, or 50 °C to induce different aging mechanisms including Li plating and solid electrolyte interphase growth. The quasi-adiabatic heat-wait-seek ARC tests show lower temperatures for self-heating (SH), CID triggering, venting, and thermal runaway (TR) with increasing SOC, indicating reduced safety levels. Furthermore, the mass loss and TR intensity increase as the SOC of the cell increases. Aged cells show a similar SOC dependence as new cells in view of venting and TR, although both temperatures are reduced. The onset of SH at around 35 °C, independent of SOC, reveals a significant safety issue in cells with Li plating. Additional cell voltage monitoring and on-line mass spectrometry provide further insights into the decomposition processes. Our findings provide essential knowledge to improve the safety and design of Li-ion battery cells by identifying unsafe states.

Enhanced Long-Term Cycling Life of Ni-Rich NMC Cathodes in High-Voltage Lithium-Metal Batteries.

Li metal batteries (LMBs) have revived people's interest due to their high energy density. This work compares the cycling stability, structure stability, and thermal stability of Li||0.7Nb-NMC 9055 (0.7% Nb-modified LiNi0.9Co0.05Mn0.05O2) system in commercial carbonate electrolyte (1.0 M LiPF6 in EC/DMC) and designed carbonate electrolyte (1.0 M LiPF6-0.125 M LiNO3-0.025 M Mg(TFSI)2 in FEC-EMC). Li||0.7Nb-NMC 9055 battery with designed carbonate electrolyte exhibited superior capacity retention, 80% after ∼500 cycles. This can be explained by the improved mechanical integrity of the secondary particles and large reduced charge transfer resistance. Further, the real-time thermal monitoring of full cell via a high-precision, multimode calorimeter TAM IV Micro XL shows that the designed carbonate electrolyte with multisalt additive and FEC cosolvent has less heat release during the charging and discharge process, allowing these high-nickel (Ni) cathodes to reach closer to their full potential.

(Invited) Advanced Electrode Processing for Next Generation Batteries

The development of environmentally friendly processing techniques is a key requisite for future sustainable battery development. The so-called DRYtraec® process is a solvent-free process developed as a viable approach to replace slurry-based binders by fibrous polymers and produce laminated electrodes with a low carbon footprint. It has been demonstrated to work for both, liquid and solid electrolyte batteries. NMC cathodes can be produced in a wide range of loading. For lithium sulfur batteries carbon/sulfur composites can be processed without sulfur loss. In particular in the field of solid state batteries it shows significant advantages. All-solid-state lithium-ion batteries are promising candidates to overcome safety and energy limitations of established lithium-ion batteries (LIBs). Excellent results have been reported for sulfide based electrolytes on a small scale. More and more companies announce their first pilot production lines. Therefore, scalable concepts for material and component development are of crucial need. We evaluate this process for the fabrication of thin argyrodite separator films and compare it with slurry-based separators in ASSBs. To test new cell concepts and components under relevant conditions, it is important to manufacture prototype cells with thin separator layers and flexible housing. Therefore, we prepared slurry-free pouch cells based on Ni-rich NMC cathodes and PVD-synthesized Si anodes.The presentation highlights recent developments of the DRYtraec® process and its application to ASSBs, LiS and LIBs.

Scalable Synthesis of Single Crystal Ni-Rich Cathodes for Advanced Lithium-Ion Batteries

Long-range electrical vehicles require high energy density lithium-ion batteries that utilize stable, high-energy cathode materials. Among various cathodes, Ni-rich NMC cathodes with a layered structure, knows for their high capacity, high voltage, and cost-effectiveness, stand out as one of the most promising cathodes. Traditional polycrystalline Ni-rich NMC encounter issues such as pulverization, gas generation and moisture sensitivity, limiting their widespread use in EV batteries on large scale. The single crystal format of Ni-rich cathode can effectively eliminate and mitigate these issues. However, synthesizing of high-performance single crystal Ni rich NMC, especially when Ni ≥0.8, presents a significant challenge.We’ve explored an innovative phase separation approach for direct synthesis of high-performance single crystal NMC811. The comprehensive investigation into the reaction mechanism of single crystal growth was conducted to understand the relationship between synthesis, morphology, and performance in growing single crystal NMC811. The enhanced performance of these materials was realized through the precise morphological and structural control of precursors and has been confirmed in practical 2Ah pouch cells. The developed approach is readily adaptable to current industry manufacturing processes and provides valuable new insights that can be broadly applied to cost-efficient large-scale synthesis of single crystals and various advanced battery materials technologies.

Efficacy of atomic layer deposition of Al2O3 on composite LiNi0.8Mn0.1Co0.1O2 electrode for Li-ion batteries

LiNi0.8Mn0.1Co0.1O2 (NMC811) is a popular cathode material for Li-ion batteries, yet degradation and side reactions at the cathode-electrolyte interface pose significant challenges to their long-term cycling stability. Coating LiNixMnyCo1−x−yO2 (NMC) with refractory materials has been widely used to improve the stability of the cathode-electrolyte interface, but mixed results have been reported for Al2O3 coatings of the Ni-rich NMC811 materials. To elucidate the role and effect of the Al2O3 coating, we have coated commercial-grade NMC811 electrodes with Al2O3 by the atomic layer deposition (ALD) technique. Through a systematic investigation of the long-term cycling stability at different upper cutoff voltages, the stability against ambient storage, the rate capability, and the charger transfer kinetics, our results show no significant differences between the Al2O3-coated and the bare (uncoated) electrodes. This highlights the contentious role of Al2O3 coating on Ni-rich NMC cathodes and calls into question the benefits of coating on commercial-grade electrodes.

Stability and Redox Mechanisms of Ni-Rich NMC Cathodes: Insights from First-Principles Many-Body Calculations

Stability and Redox Mechanisms of Ni-Rich NMC Cathodes: Insights from First-Principles Many-Body Calculations

Exploring the Role of an Electrolyte Additive in Suppressing Surface Reconstruction of a Ni-Rich NMC Cathode at Ultrahigh Voltage via Enhanced In Situ and Operando Characterization Methods.

Vinylene carbonate (VC) is a widely used electrolyte additive in lithium-ion batteries for enhanced solid electrolyte interphase formation on the anode side. However, the cathode electrolyte interphase (CEI) formation with VC has received a lot less attention. This study presents a comprehensive investigation employing advanced in situ/operando-based Raman and X-ray absorption spectroscopy (XAS) to explore the effect of electrolyte composition on the CEI formation and suppression of surface reconstruction of LixNiyMnzCo1-y-zO2 (NMC) cathodes. A novel chemical pathway via VC polymerization is proposed based on experimental results. In situ Raman spectra revealed a new peak at 995 cm-1, indicating the presence of C-O semi-carbonates resulting from the radical polymerization of VC. Operando Raman analysis unveiled the formation of NiO at 490 cm-1 in the baseline system under ultrahigh voltage (up to 5.2 V). However, this peak was conspicuously absent in the VC electrolyte, signifying the effectiveness of VC in suppressing surface reconstruction. Further investigation was carried out utilizing in situ XAS compared X-ray absorption near edge structure spectra from cells of 3 and 20 cycles in both electrolytes at different operating voltages. The observed shift at the Ni K-edge confirmed a more substantial reduction of Ni in the baseline electrolyte compared to that in the VC electrolyte, thus indicating less CEI protection in the former. A sophisticated extended X-ray absorption fine structure analysis quantitatively confirmed the effective suppression of rock-salt formation with the VC electrolyte during the charging process, consistent with the operando Raman results. The in situ XAS results thus provided additional support for the key findings of this study, establishing the crucial role of VC polymerization in enhancing CEI stability and mitigating surface reconstruction on NMC cathodes. This work clarifies the relationship between the enhanced CEI layer and NMC degradation and inspires rational electrolyte design for long-cycling NMC cathodes.

Inorganic Ultra-Rich Solid Composite Electrolytes for High-Voltage Solid-State Batteries

Solid-state batteries (SSB), in which flammable organic liquid electrolytes are replaced by inherently safer solid electrolytes (SEs), are considered to be the evolution of current Li-ion battery technology toward greater safety and higher energy density. Among the various SEs, the PEO-LiTFSI system has been the most studied due to its low cost and ease of processing. However, the relatively low oxidation stability of PEO-LiTFSI at about 4.0 V vs. Li/Li+ does not allow the use of high-voltage cathode active materials, which limits the available energy density [1]. We propose that a high content of Li-ion conductive ceramic in the PEO-LiTFSI matrix increases oxidation stability, allowing stable cell cycling with Ni-rich NMC cathode at higher voltages. This class of inorganic ultra-rich composite SEs has attracted much interest recently [2, 3].In this work, we present a self-standing, dense, flexible (Fig.1a), and thermally stable (Fig.1b) composite solid electrolyte (INURSE 30) that has an ultra-high content of Li-ion conductive LLZO (90 wt%, as confirmed by TGA in Fig. 1b)in the PEO-LiTFSI matrix. The ionic conductivity of INURSE 30 is 1.4x10-5 S/cm at 60ºC. The INURSE 30 electrolyte shows long-term cycling stability of more than 2000 h at a current density of 0.01 mA/cm2 in symmetric cells with Li electrodes. In addition, the high-voltage stability of INURSE 30 was demonstrated in solid-state cells with a composite solid-state cathode containing 75 wt% NMC622 and a Li metal anode. The Li/INURSE 30/NMC622 coin cell shows good coulombic efficiency and capacity retention, as shown in Fig.1c. K.V. acknowledges the financial support from Fundacíon CIDETEC and DESTINY PhD programme which received funding from the European Union's Horizon2020 research and innovation programme under the Marie Skłodowska-Curie Actions COFUND - Grant Agreement No: 945357.

(Best Poster Award - 3rd Place) Development of Bipolar All-Solid-State Lithium-Ion Cell

For large-scale electricity storage applications such as automotive and stationary energy storage, the battery system requires a high voltage and energy density, which can be achieved by bipolar architectures. In conventional batteries, the cells are assembled in series. The amount of current collector and packaging substances (case, wires) increases the battery weight, reducing its energy density, and complicates the manufacturing. The switch to bipolar technology simplifies the cell architecture. The cathode and anode material layers are separately coated on both sides on a same current collector. This gives to the creation of electrolyte-separated units. External connectors are no longer necessary as the electron transfer between the two electrodes is through the current collector. As a result, the ohmic resistance is reduced and less heat is generated. The bipolar architecture leads to a simple and compact design for a high specific energy and a high-voltage and current output for a high specific power.Over the 15 past years, CEA developed an expertise on bipolar lithium-ion batteries1. However, the development of bipolar cells with liquid electrolyte has been rather limited in industrial applications due to electrolyte leakage: it is imperative to avoid liquid junction and to prevent the ion flow between each adjacent unit. The use of solid- electrolyte appears as the optimal solution and simplifies the manufacturing process and reduces cost2.Astrabat project focused on all-solid-state lithium-ion batteries and the development of two tailored polymer electrolytes. These results are transferred and adapted to a bipolar architecture, composed of two units. The silicon anode and Ni-rich NMC cathodes are coated on an Al/Cu clad, serving as a current collector. This work will report the fabrication process and the electrochemical performances of the two-units bipolar architecture. 1M. Chami, S. Mailley, Y. Reynier, F. Masse, S. Martinet and F. Fusalba, World Electric Vehicle Journal Vol. 3 - ISSN 2032-6653 2 H.-S. Shin, W.-G. Ryu, M.-S. Park, K.-N. Jung, H. Kim and J.-W. Lee, ChemSusChem 2018, 11, 3184 – 3190 Figure 1

Extending Cycle Life of Li-Ion Batteries Via Gas-Phase Nanocoating of Cathode Active Materials

The further penetration of the electric vehicles is dependent on the development of high-performance Li-ion batteries in terms of cost, cycle life, energy density, safety as well as sustainability. It is expected, in the short term, EVs will rely more on Li-ion technologies using active materials such as Ni-rich NMC cathode and Si anode for developing high specific energy and lower cost batteries1.However, these active materials are facing multiple serious challenges which could hinder their targeted performance. Regarding this, Ni-rich NMC cathode active materials (CAM), in spite of their high energy density as a result of higher Ni content, tend to undergo dramatic capacity fade. Since most degradation mechanisms are related to the surface of active materials, immense research and development efforts have been dedicated to surface modification techniques, and especially coating strategies2,3.Examples of surface modification strategies include sol-gel, hydro/solvothermal deposition, and dry coating. A main drawback of these techniques is that they are not capable of precise control of the film thickness and uniformity. On the other hand, gas-phase coating techniques, such as atomic or molecular layer deposition, can address these shortcomings by offering a precise thickness control even in the range of angstroms and pinhole-free conformal coatings. As such, these coatings are better suited at mitigating interfacial degradation. Various nanocoating chemistries, such as oxides, fluorides, nitrides, phosphates and aluminates protect and stabilize the surface of Ni-rich cathode materials through the different pathways. In this talk, we explore the benefits of gas-phase nanocoatings, and will show how we can produce surface modified Ni-rich CAM (e.g. NMC-811) in a continuous process that is ready for mass production. References M. S. E. Houache, C. H. Yim, Z. Karkar, and Y. Abu-Lebdeh, Batteries, 8 (2022).D. Weber, Đ. Tripković, K. Kretschmer, M. Bianchini, and T. Brezesinski, Eur. J. Inorg. Chem., 2020, 3117–3130 (2020).M. Lee et al., Chem. Mater., 34, 3539–3587 (2022).Y. Zhao, K. Zheng, and X. Sun, Joule, 2, 2583–2604 (2018).

Aqueous Processing of Ni-Rich NMC Electrodes with High Areal Capacity and Excellent Long-Term Cycling Stability

Research efforts in the last three decades have resulted in a steady increase in the energy density of Li-ion batteries (LIBs), leading to their integration into electric vehicles (EVs). Therefore, car manufacturers have increased the number of EVs in their fleets and successfully introduced them to the mass market, with 200M of EVs expected to be sold by 2025 [1] . In such a fast-growing market, the cost and environmental impact of LIB production play major roles. A crucial step in battery manufacturing is the processing of active materials to produce electrode coatings. Commercial cathode electrodes (i.e. LiNixMnxCoxO2 (NMC), LiNi0.5Mn1.5O4 (LNMO) etc.) are still largely processed using organic solvents, specifically N-methyl-2-pyrrolidone (NMP), with poly(vinylidene difluoride) (PVDF) as a binder. However, the NMP-PVDF combination has many disadvantages [2]. Firstly, the binder is considerably more expensive than water-soluble binders and not easy to dispose of at the end of the battery life. Secondly, NMP is costly and toxic, and being a volatile organic compound (VOC), needs solvent recovery at commercial scale. On the other hand, water-soluble binders such as Na-carboxymethylcellulose (Na-CMC) and styrene butadiene rubber (SBR) are not only cheaper but also easier-to-recycle [3]. Additionally, the use of water as a solvent would remove the need for solvent recovery. It is then clear that switching to water-based processing for cathode materials would decrease cost and improve the environmental sustainability of LIB production. Nevertheless, aqueous cathode processing has many challenges [2], the major one being the instability of the active material in water. The leaching of Li+ ions gives rise to very high pH (~ 12) values which, in turn, leads to the corrosion of the current collector (aluminium) and gas evolution during coating. Consequently, electrodes usually show cracks and pinhole defects and exhibit poor flexibility. These issues are even more enhanced for thick coatings, which are needed to achieve high energy density cells. Therefore, the electrochemical performance of water-based cathode electrodes is generally poorer than that for NMP-based electrodes.In this work, the effect of additions of phosphoric acid (H3PO4) on slurry rheology, adhesion strength, electrode morphology and the electrochemical performance of Ni-rich NMC cathodes prepared via water-based processing was investigated. To effectively bridge the gap between lab-scale investigations and industrially applicable procedures, pH control of the slurries and roll-to-roll electrode coating were performed at the pilot scale, and only electrodes exhibiting commercially relevant areal capacities (~ 4-4.5 mAh cm-2), high active material contents (> 90%) and low binder amounts (3 wt.%) were investigated. Phosphoric acid was added in amounts between 1.5 and 3 wt.%, and a fast-mixing procedure was developed to minimize the contact time between the NMC particles and water. The pH evolution over time showed that at least 2 wt.% of H3PO4 is required to keep the pH below the corrosion threshold of aluminium (pH < 9) for 6-8 hours, which is a usual time scale for industrial electrode processing. All slurries showed shear thinning behaviour with the viscosity of the water-based slurries being slightly lower than that for NMP-based slurries at the shear rate used for coating. Optical micrographs of coated electrodes showed no evidence of defects or agglomerates and good homogeneity. The adhesion to the current collector decreased with increasing amount of acid, e.g., electrodes prepared using 3 wt.% H3PO4 showed cracks at the edges of the coating and delamination.The long-term performance and rate capability of the electrodes were investigated in full-cell configuration vs graphite (coin-cell setup). NMC cathodes prepared with 1.5 wt.% acid showed a specific capacity of around 180 mAh g-1 at C/10 and 165 mAh g-1 at C/3. The specific capacity of the cells decreased with increasing amount of acid. The water-based and NMP electrodes retained around 50% and 60% of the initial capacity at 1C, respectively. Furthermore, electrodes prepared with 1.5 wt.% and 2.25 wt.% acid achieved a capacity retention above 90% after 500 cycles, which is comparable to NMP-based electrodes. In a further step, the production of the electrodes was upscaled in order to manufacture NMC/graphite pouch cells of 10 Ah capacity. These cells showed excellent cycling stability, reaching 80% SoH after 1500 cycles.

Scaling a Gas Phase Residual Lithium Conversion Process on Ni-Rich NMC Cathode Materials in Commercial Fluidized Bed Reactors

‘Residual lithium’, the LiOH and Li2CO3 surface contamination that is ubiquitous to Ni-rich NMC manufacturing, is a significant obstacle in the large-scale production and handling of high-nickel layered oxides. These hydroxide and carbonate surface phases influence reproducibility and shelf stability of the NMC powder and cause gelation and particle aggregation during electrode casting. There is ample evidence in the literature that atomic layer deposition (ALD) possesses a two-fold solution to this problem.1-3 First, reactive organometallic species such as trimethylaluminum (TMA) can convert insulating residual lithium to a Li-rich LixAlyO conducting layer. Customizable ALD layers can then be added to inhibit the re-formation of the carbonate layer and to deter negative side reactions of the CAM surface with the liquid electrolyte. While highly impactful, these studies have mostly been relegated to small, lab-scale demonstrations of <50 g. As such, there remains a need to enable this ALD-assisted-technology for high-throughput commercial applications.In this talk, we will explore the progression of a residual lithium conversion process from lab (10 – 1000 mL) to industrial-scale (10 L – 100 L) fluidized bed equipment and how scale and material-dependent parameters can impact performance. Using a commercial NMC 811 cathode as a case study, we first applied aluminum phosphate ALD coatings on a lab-scale fluidized bed reactor to examine the interfacial and electrochemical changes of the CAM material under various process conditions. ICP-OES measurements confirmed linear and reproducible deposition versus ALD cycle number between 200- 300°C. XPS analysis showed the ALD coated NMC 811 powder had an 80% reduction in Li2CO3 versus the pristine material and that a reduction persisted even after 10 days of storage in atmospheric conditions. At standard (0.5C/1C) cycling to 4.4V, AlPO4 coatings increased cycle life by 44% versus the uncoated powder. Under optimized conditions, the process was scaled first to 1 kg and finally to 10 kg in a pilot-scale reactor. In-situ mass spectrometry indicated that residual lithium conversion byproducts such as CO2 could be used to monitor reaction progress and optimize chemical usage efficiency. Fluidization aids including vibration and mechanical stirring were used to inhibit and break up powder agglomerates. ICP-OES and electrochemical cycling data confirmed reproducible deposition and cycle life benefits versus the small scale runs and pristine materials, demonstrating a pathway for these ALD-enhanced materials to transition from lab-scale demonstration to viable product. We will discuss strategies for continuing the scaling process to 100 kg batches for commercial applications.[1] M. Young et al., The Journal of Physical Chemistry C 2019 123 (39), 23783-23790[2] P. Darapaneni et al., ACS Applied Energy Materials 2022, 5, 8, 9870–9876[3] J. Li et al., Coatings 2022, 12(1), 84

Novel Current Collector for High Energy Density Lithium-Metal Batteries

The energy density of lithium-metal batteries (LMBs) relies to a substantial fraction on the thickness of the lithium-metal anode.1,2 Additionally, the commonly used copper current collector adds a significant mass to the electrode weight (e.g., 77% when considering a 50 μm thick lithium and 10 μm thick copper), but the thinner the lithium foil, the more important becomes the current collector to provide suitable mechanical properties and ensure a good electronic contact across the whole negative electrode.Herein, we report the design of a novel current collector (patent application pending) that enables a substantial reduction in mass, while providing high electronic conductivity and suitable mechanical properties. Moreover, LMBs with a thin lithium foil and a Ni-rich NMC cathode comprising such new current collector reveal a superior performance compared to those containing a standard copper foil. References 1 Liu, J. et al. Pathways for practical high-energy long-cycling lithium metal batteries. Nat. Energy 4, 180-186, (2019).2 Niu, C. et al. Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries. Nat. Energy, 6, 723–732, (2021).

Dual application of non-fluorinated polymer: Influence on mitigating dendrite growth and structural integrity of high energy density lithium metal battery

Fluorine-based polyvinylidene difluoride is one of the most widely used binders for Lithium-ion batteries due to good thermal and electrochemical stability. However, PVDF has several significant disadvantages, which could greatly restrict its practical application. PVDF is not suitable for Lithium metal batteries with cutting-edge cathode materials and lithium metal anode because of the swelling and degradation of electrode particles as well as unstable solid electrolyte interface on the Lithium anode in liquid electrolytes at elevated temperatures. Herein, the non-fluorinated polymer of Poly-1-Vinyl-2-pyrrolidinone-crosslinked-prop-2-enoic acid is developed as both binders for Ni-rich LiNi0.8Mn0.1Co0.1O2 cathode and artificial SEI layer for stable lithium-metal anodes, enabling all Li metal batteries, with excellent mechanical integrity. As a binder, Ni-rich NMC cathode (LiNi0.8Mn0.1Co0.1O2) displays an initial discharging capacity of 232.6 mAh g−1 with Coulombic efficiency of nearly 89.9 % compared to PVDF (77.6 %). It also demonstrated good cycling stability even after 200 cycles by exhibiting a 146.2 mAh g−1 discharging capacity at a 1C rate with 92 % capacity retention. In addition, Li/Poly-VPCPEA@PP/Li symmetric cell revealed a low voltage hysteresis of 10 mV over 1000 h for 1 mA cm2 and 200 h for 5 mA cm−2.

High Areal Capacity Ni-Rich NMC Water-Based Electrodes with Excellent Long-Term Cycling Stability

Research efforts in the last three decades have resulted in a steady increase in the energy density of Li-ion batteries (LIBs), leading to their integration into electric vehicles (EVs). Therefore, car manufacturers have increased the number of EVs in their fleets and successfully introduced them to the mass market, with 200M of EVs expected to be sold by 2025 [1] . In such a fast-growing market, the cost and the environmental impact of LIB production play major roles. A crucial step in battery manufacturing is the processing of anode and cathode active materials to produce electrode coatings. While commercial anode electrodes (i.e. graphite, silicon-graphite) are already water-based, cathode electrodes (i.e. LiNixMnxCoxO2 (NMC), LiNi0.5Mn1.5O4 (LNMO) etc.) are still largely processed using organic solvents, specifically N-methyl-2-pyrrolidone (NMP), with poly(vinylidene difluoride) (PVDF) as a binder. However, the NMP-PVDF combination has many disadvantages [2]. Firstly, the binder is considerably more expensive than water-soluble binders and not easy to dispose of at the end of the battery life. Secondly, NMP is also costly and toxic, and being a volatile organic compound (VOC), needs solvent recovery at commercial scale. On the other hand, water-soluble binders such as Na-carboxymethylcellulose (Na-CMC) and styrene butadiene rubber (SBR) are not only cheaper but also easier-to-recycle [3]. Additionally, the use of water as a solvent would remove the need for solvent recovery. It is then clear that switching to water-based processing for cathode materials would decrease cost and improve the environmental sustainability of LIB production. Nevertheless, aqueous cathode processing has many challenges [2], the major one being the instability of the active material in water. The leaching of Li+ ions gives rise to very high pH (~ 12) values which, in turn, leads to the corrosion of the current collector (aluminium) and gas evolution during coating. Consequently, electrodes usually show cracks and pinhole defects and exhibit poor flexibility. These issues are even more enhanced for thick coatings, which are needed to achieve high energy density cells. Therefore, the electrochemical performance of water-based cathode electrodes is generally poorer than that for NMP-based electrodes.In this work, the effect of additions of phosphoric acid (H3PO4) on slurry rheology, adhesion strength, electrode morphology and the electrochemical performance of Ni-rich NMC cathodes prepared via water-based processing was investigated. To effectively bridge the gap between lab-scale investigations and industrially applicable procedures, pH control of the slurries and roll-to-roll electrode coating were performed at the pilot scale, and only electrodes exhibiting commercially relevant areal capacities (~ 4 mAh cm-2), high active material contents (> 90%) and low binder amounts (3 wt.%) were investigated. Phosphoric acid was added in amounts between 1.5 and 3 wt.%, and a fast-mixing procedure was developed to minimize the contact time between the NMC particles and water. The pH evolution over time showed that at least 2 wt.% of H3PO4 is required to keep the pH below the corrosion threshold of aluminium (pH < 9) for 6-8 hours, which is a usual time scale for industrial electrode processing. All slurries showed shear thinning behaviour with the viscosity of the water-based slurries being slightly lower than that for NMP-based slurries at the shear rate used for coating. Optical micrographs of coated electrodes showed no evidence of defects or agglomerates and good homogeneity. The adhesion to the current collector decreased with increasing amount of acid, e.g., electrodes prepared using 3 wt.% H3PO4 showed cracks at the edges of the coating and delamination.The electrochemical performance of the electrodes was studied in full-cell configuration vs graphite. NMC cathodes prepared with 1.5 wt.% acid showed a specific capacity of around 180 mAh g-1 at C/10 and 165 mAh g-1 at C/3. The specific capacity of the cells decreased with increasing the acid amount. However, electrodes prepared with 1.5 wt.% and 2.25 wt.% acid showed excellent cycling stability, achieving a capacity retention above 90% after 500 cycles, which is comparable to NMP-based electrodes.

Thermal Degradation of Polycrystalline Ni-Rich Cathodes, New Insights from Total Scattering and Machine-Learning Assisted Tomography

Alkali metal-based batteries (e.g., lithium batteries) are considered the most effective energy storage candidate for portable electronics, power grids, and electric vehicles due to their considerable energy density, power density, cycle life, safety, and competitive prices. The Ni-rich Co-less ternary LiNi x Mn y Co1-x-y O2 (NMC) (Ni>80%) is one of the candidate materials due to its high discharge capacity (>200 mAh g-1) and high energy density (>750 Wh kg-1). However, the thermal stability of charged Ni-rich NMCs is inferior, following a general negative correlation between Ni content and stability. Such severer degradation in Ni-rich NMCs might lead to dysfunctionality, thermal runaway, and eventually catastrophic failure and explosion of batteries, raising enormous safety concerns. Therefore, it is critical to understand the thermal behavior of charged Ni-rich NMC cathode from different perspectives in order to conduct material design for better thermal stability.After literature survey of typical and widely used probes by this community (e.g., diffraction, spectroscopy, imaging), we found these approaches subject to compromise to some degree in the experimental design, resulting in an inadequate description of the thermal degradation mechanism. Here we offer two novel approaches, neutron total scattering and energy-resolved 3D nano-tomography, to probe the reaction and evolution of the charged NMCs under non-ambient conditions in real-time. Such in situ measurements were only accomplished by deliberate experimental design at beamlines and deep integrations of neutron or synchrotron facilities with battery science. In situ heating neutron scattering captures the transition of crystal structure in reciprocal space (by Rietveld refinements), as well as of the local atomic framework in real space (by pair distribution function analysis). Moreover, machine learning algorithms were applied to the 3D nano-tomography datasets to reveal the detailed microstructural and oxidation state progression inside the charged particles. Thereafter, we discussed the key factors which have previously been overlooked by the community and offer constructive suggestions on particle design for thermally stable cathodes from our unique perspective.The work was supported by the National Science Foundation under Grant no. DMR-1832613 (F.L.). The machine-learning assisted tomography analysis was partially supported from NASA under 80NSSC21M0333 and NSF under NSF-2119688 (X.-D.Z)

Li0.5La0.5TiO3 as an Ionic Conducting Additive Enhancing the High-Voltage Performance of LiNi0.8Mn0.1Co0.1O2 Cathodes in Lithium-Ion Batteries.

Although high-voltage (e.g., >4.3 VvsLi) operation can increase specific capacity and energy of Ni-rich NMC cathodes, it accelerates the oxidative decomposition of electrolytes and surface degradation of NMC cathodes, leading to rapid capacity fading. This work presents a novel approach that employs Li0.5La0.5TiO3 (LLTO) solid-electrolyte as a Li-ion conductor and surface passivation agent to stabilize the cathode/electrolyte interphase (CEI) layer of the LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode and enhance its high-voltage performances. The LLTO particles improve Li-ion transportation across the CEI layer, as evidenced by its reduced impedance in Nyquist plots. Furthermore, passivation of CEI by LLTO mitigates parasitic reactions (e.g., transition metal dissolution) that occur on the graphite solid electrolyte interphase layer during extended cycles of pouch-cells. As a result, pouch-cells with the 1 or 5 wt % LLTO-blended NMC811 cathodes can deliver 19-23% increase in specific capacity and improved cycle life (1000 cycles) at high voltages (up to 4.4 V), comparing to bare NMC811 cathodes. Post-mortem characterization of pouch-cells quantitatively identified the degradation sources of NMC811 cathode at high-voltages, which highlighted the improvement mechanisms of LLTO blended-cathodes.

Synthesis and Size Control of Single Crystal Ni-Rich Layered Oxide Cathodes Using Statistical Analysis-Guided Molten Salt Method

Rechargeable Li ion batteries have been widely applied in daily lives. The demand for Li ion batteries with higher energy density has been increasing especially with the thriving development of electric vehicles in the past decade. Li(Ni1−x−yMnxCoy)O2 (NMC) is one of the most successful commercial cathodes with various transition metal (Ni, Mn, and Co) ratios. Higher Ni content in the composition of NMC gives rise to higher energy density but at the price of structural and thermal stability. Recently, synthesizing single-crystal cathode particles has been extensively investigated as a strategy to enhance the stability of NMC cathodes. Most commercial NMC cathode particles possess polycrystalline structure, which is prone to induce intergranular cracking and parasitic reactions with the electrolyte upon cycling due to grain boundaries and large surface area. In contrast, single crystal NMC cathodes show higher cycling stability than their polycrystalline counterparts. However, the synthesis of single crystal normally requires higher temperatures and longer calcination duration than that of the polycrystalline counterparts for solid state synthesis. Alternatively, molten salt synthesis of single crystals is less energy-intensive and capable of tuning particle morphology and size. However, there is not yet a systematic guideline for the molten salt synthesis of single crystal Ni-rich NMC cathodes. Herein, we studied the effect of different synthetic parameters on the performance of single crystal Ni-rich NMC cathodes. We applied statistical analysis tools to correlate the synthetic conditions with cathode properties and optimized the synthetic parameters. Furthermore, we investigated the effect of single crystal size on the cathode performance. Our findings provided new insights into the synthesis and understanding of single crystal Ni-rich cathodes.

Electrolytes with flame retardant pentafluoro(phenoxy)cyclotriphosphazene for nickel-rich layered oxide/graphite cells

Ni-rich NMC cathode materials with a Ni content of over 80% are currently regarded as a promising pathway to further boost the energy density of rechargeable lithium-ion batteries. Meanwhile, cell safety is an important aspect when commercializing high-capacity batteries. Here, the compatibility of the flame retardant pentafluoro(phenoxy)cyclotriphosphazene (FPPN) when added to an ethylene carbonate/ethyl methyl carbonate/lithium hexafluorophosphate (LiPF6 in EC:EMC) electrolyte is studied for Ni-rich NMC/graphite full cells. Addition of 15 wt.% FPPN to the baseline electrolyte renders it non-flammable as defined by a self-extinguishing time of zero. When compared to the baseline electrolyte, both coin and pouch cells containing the electrolyte with FPPN show promising electrochemical performance. In addition, fluorinated carbonates are combined with FPPN to reduce the amount of FPPN additive. Excellent flame retardancy is found when combining 35 vol.% methyl 2,2,2-trifluoroethyl carbonate with just 5 wt.% FPPN. The results of this study confirm that FPPN is a potent flame retardant for carbonate electrolytes and indicate good compatibility with Ni-rich NMC cathode materials.

One-Pot Synthesis of LiAlO2-Coated LiNi0.6Mn0.2Co0.2O2 Cathode Material

The chemistry of lithium-ion batteries (LIBs) is an active area of research, notably through the increasing demand for high energy and power density in LIBs, especially for application in electric vehicles (EVs) and hybrid electric vehicles (HEVs).Among the various cathode materials, LiNixCoyMn1-x-yO2 (NMC) intercalation compounds are the best candidates for applications in high performance LIBs. However, Ni-rich NMC suffers mainly from parasitic side reactions at the interface with the electrolyte, which leads to a lower thermal and electrochemical stability. Surface modification via coating is an effective concept to counter the capacity degradation of NMC and to improve the particles’ structural stability for enhancing their cycle-life [1], [2]. Different processing techniques that usually requires several steps are presented in the literature. However, to facilitate the integration of a new product in the current battery market, it is preferable to reduce the number of steps during the synthesis process. In this work, we propose a one-pot synthesis of LiAlO2-coated LiNi0.6Mn0.2Co0.2O2 particles, by using a continuous stirred-tank reactor (CSTR).Firstly, the composition and morphology of the coated and uncoated cathode materials are characterized by SEM, TEM, EDX and XPS. Then, the structural characterization of our materials is validated by XRD analysis. Consequently, we will compare the electrochemical performance and thermal stability of coated and uncoated NMC particles.We will demonstrate that our approach provides an easy way to apply surface treatment onto Ni-rich NMC particles and simplifies the synthesis process at large scale production.KEYWORDS: Lithium-ion battery, Ni-rich NMC cathode, LiAlO2 coating, surface protection. Negi, R.S., et al., Enhancing the Electrochemical Performance of LiNi0.70Co0.15Mn0.15O2 Cathodes Using a Practical Solution-Based Al2O3 Coating. ACS Applied Materials & Interfaces, 2020. 12(28): p. 31392-31400.Kim, H.-S., et al., Enhanced electrochemical properties of LiNi1/3Co1/3Mn1/3O2 cathode material by coating with LiAlO2 nanoparticles. Journal of Power Sources, 2006. 161(1): p. 623-627.