Li-ion Battery Cathode Research Articles

A novel in-situ fabrication of N-doped carbon fibers wrapped nano-LiFePO4 composites as cathode of advanced Li-ion batteries

In this work, we first report a novel in-situ fabrication of N-doped carbon fibers-wrapped nano-LiFePO4 composites by reducing low- cost FePO4 with nitrilotriacetic acid (NTA). The crystallization temperature, particle morphology, composition, phase have been investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS) and scanning electron microscopy (SEM). The proper content of NTA is 10 wt%. As cathode of lithium-half batteries, the LiFePO4 composites with 10 wt% NTA deliver superior lithium storage performance to the previously reported LiFePO4. Specifically, the composites approach a capacity of 155.5 mA h g−1 after 500 cycles at 0.1C, 98 mAh g−1 after 2000 cycles at 10C, and good rate capability, which is suitable for the development of power batteries.

Design of Dispersant in Cathode of Li-Ion Batteries for Cathode Slurry with High Solid Content and High Battery Performance

Generally, cathode of Li-ion batteries was fabricated through the process that cathode slurry composed of active material, conductive agent, binder and N-Methyl-2-pyrrolidone (NMP) as organic solvent was coated on the aluminum foil, dried and pressed. In recent years, decreasing an amount of NMP has been required in terms of low environmental impact and due to cost reduction regarding material, shipping and machining price. However, the decreasing is possible to raise the viscosity of the cathode slurry and cause the defect of manufacturing process such as mixing, carrying and coating. One of the means of the resolving is addition of dispersant to cathode slurry. The dispersant can make an effect to reduce the slurry viscosity with low amount of solvent because it spreads the distance between each particle and also keep the condition of particle distribution. However, the dispersant may have the potential to be the resistance of the battery reaction because the material is polymer. In this study, we have designed dispersants that have the low viscosity of the cathode slurry with low amount of NMP, and hardly block the battery reaction by means of clarifying the function of dispersants and optimizing the component. The cathode slurry was prepared by the following steps: firstly, acetylene black (AB) as conductive agent, polyvinylidene difluoride (PVdF) as binder and dispersants were mixed with NMP. This paste is commonly called ‘AB paste’. Secondly as active material was added to the AB paste and mixed. The weight ratio of each material is as follows, active material:AB:PVdF:dispersant=89.8:8:1.5:0, 0.16, 0.20. Three solid content concentrations were considered as 48, 56 and 62.5 wt.% by adjusting the amount of NMP. Two dispersant materials were considered as a polyvinyl alcohol (PVA) with the role adsorbing to AB, and an acrylate copolymer including amid groups (ACA) with the role adsorbing to not only AB and but also active materials. They were composed of polymers not to be resistant according to previous study. And three samples were evaluated such as PVA only, PVA/ACA mix (weight ratio; PVA:ACA=85:15) and dispersant free. Cathode was prepared through the process coated the slurry on aluminum foil, dried and pressed. The test cells were assembled with the prepared cathode, anode composed of graphite, separator, and electrolyte including LiPF6. The viscosity of cathode slurry was evaluated under 1S-1 shear rate condition by using Dynamic viscoelasticity measuring device (DMA). And the discharge resistance was evaluated under -30℃, 1C as battery performance. Fig.1 shows the results of cathode slurry viscosity with various solid content concentrations. The tendency that the viscosity increases with increasing solid content concentration is observed. Especially at the 62.5 wt.%, the viscosity with added dispersant had much lower than dispersant-free. Furthermore, the effect to decrease the viscosity with PVA/ACA mix was higher than that with PVA only and the viscosity with PVA/ACA mix is less than 10000 mPas-1 as the target with no defect in the mass production process. These results imply the repulsive force with not only AB but also active material is required at 62.5 wt.% due to the distance between each particle is shorter under higher solid content concentration. Fig.2 shows the discharge resistances with various weight ratios of dispersant / AB used by cathode slurry at 62.5 wt.%. The tendency that the discharge resistance with PVA/ACA mix is slightly higher than PVA only is observed. These results imply that ACA with the role adsorbing to active material may affect to the reaction at the surface of active material. However, the resistance with added dispersant at dispersant / AB = 2 php is close to that with dispersant free is appeared. These results may be mainly depended on the effect of dispersant components not to be resistant and less dispersion performance with dispersant free. More detailed and integrated analysis about the dispersant components will be presented and discussed in this work. Figure 1

Real-Time Detection and Speciation of Mn Dissolution in a Li-Ion Battery Cathode

Rechargeable lithium-ion batteries (LIB) are widely used in portable electronic devices, electric vehicles, medical devices, etc. thanks to their improved performance in recent decades. The properties of the cathode still largely limit the overall performance, as the cathode usually has lower theoretical capacity and suffers from more serious degradation effects.1 Among these, dissolution of transition metals is an important but poorly understood side reaction. On the one hand, it dominates the cathode capacity fading by causing irreversible loss of active redox sites, phase transformation, cation mixing, grain fracture, etc. On the other hand, the dissolved transition metal ions can exacerbate the formation of the solid electrolyte interphase (SEI) on the anode through a dissolution-migration-deposition (DMD) process.2 Here, we focus on the dissolution of manganese from LiMn2O4 (LMO), a benchmark cathode material, through real-time analysis of the electrolyte by combining online inductively coupled plasma–optical emission spectroscopy (online ICP-OES) and rotating ring-disc electrode (RRDE) collection, Figure 1. Both methods offer real-time dissolution information as functions of time and potential/state of charge, while the former shows superior detection limits and the latter provides oxidation state information of the dissolving species.According to online ICP-OES, we find that Mn dissolves readily from fully lithiated LMO when brought in contact with aqueous 0.2 M Li2SO4, but that a dissolution-passivation process stops further detectable dissolution until well past fully delithiated λ-MnO2. The dissolution becomes detectable again on the returning scan to the potential of pristine LMO, and grows exponentially in the overlithiated region.3 Our RRDE results indicate that Mn2+ is the dominating dissolved Mn species only in overlithiation region, whereas it only accounts for a minor proportion in the dissolved species from delithiation region. The data from both techniques suggest that the dissolution of Mn is related to the surface state of the electrode, rather than its degree of lithiation, as widely believed in the past.4 Our results provide a better understanding of the mechanism of transition metal dissolution in cathode materials, as well as an entry point for screening next-generation cathodes and metal ion batteries with superior degradation characteristics.5

Li-Ion and Na-Ion Intercalation in Layered MnO2 Cathodes Enabled by Using Bismuth as a Cation Pillar

Rechargeability of low-cost MnO2 cathodes in aqueous cells has the potential to be an enabling technology for low-cost (<$50/kWh) grid-scale batteries. This rechargeability is imparted by modifying the MnO2 with Bi. In this talk we detail using Bi doping for structural stabilization of MnO2 cathodes for Li-ion and Na-ion batteries in dry, non-aqueous electrolyte. We do this by preparing a series of Bi-doped layered MnO2 compounds, which also contain K ions and crystal water. These phyllomanganates or birnessite-type compounds have the general formula KxBiy-MnO2 • nH2O. The materials are structurally characterized by synchrotron X-ray powder diffraction (XPD) and confocal Raman microscopy. It is found that incorporation of Bi in the structure increases the crystallinity of the material by ordering the interlayer cations. This ordering results in the emergence of a structural superlattice in the material, which has been reported previously for birnessite inserted with other heavy, multivalent cations such as as Sr2+, Ba2+, and Ca2+.We selected three Bi doping levels to study in Li-ion and Na-ion batteries: undoped (y = 0), low-doping (y = 0.013 or 1.3%), and high doping (y = 0.043 or 4.3%). Both doped materials had capacity over 200 mAh/g and allowed for far more stable cell cycling than the undoped Kx-MnO2. The cells made with 4.3% doping of Bi were by far more stable. These cycled at 175-190 mAh/g specific capacity through 100 cycles with a nominal voltage of 2.9 V. Operando XRD experiments to characterize the cathodes within sealed coin cells showed that high-level doping (4.3%) promoted dehydration of the KxBiy-MnO2 interlayer, which had a distance of 6.4 Å. This showed that loss of the crystal water from the interlayer was key to achieving maximum stability during cycling. Lower Bi doping (1.3%) did not cause loss of the crystal water once the cathode was wetted with electrolyte. Previous reports have suggested that Bi doping of 20% results in stabilized Li-ion cycling in layered MnO2. However, these reports involved largely amorphous active material. Our results showed that Bi doping of only 1.3% still provided a large stability benefit, and the high crystallinity of our material allowed it to be structurally characterized, both in the as-prepared state and operando during battery cycling. Results from Na-ion cells will also be presented.Stabilized MnO2-based cathodes that cycle with good capacity and somewhat lower cell voltage than traditional Li-ion cells are a promising strategy for low-cost batteries for the grid. The possibility of using Na as the working ion is also useful for large-scale deployment of batteries to balance renewable power. Acknowledgments This work was supported by the U.S. Department of Energy (DOE) Office of Electricity Delivery and Energy Reliability, Dr. Imre Gyuk, Energy Storage Program Manager. This research used resources of the Advanced Photon Source beamline 6-BM, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This research also used resources at beamlines 7-BM (QAS) and 28-ID-2 (XPD) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.

LT-LiMn0.5Ni0.5O2: A Unique Co-Free Cathode for High Energy Li-Ion Cells

Over the past decade, designing advanced, high energy density lithium-ion batteries has become necessary because of the increasing demand for electric vehicles and energy storage devices. Research efforts have focused largely on developing layered, Ni-rich cathode materials due to their high specific capacity. However, their structural and thermal instability and the relatively high cost of nickel raises a concern about their long-term viability.1 Developing next generation cathode materials, based on earth abundant elements such as manganese and iron, has therefore attracted much research interest.2 In the late 1990s, the Mn-based spinel cathode, LiMn2O4 (LMO), dominated the early development of Li-ion batteries for the electric vehicle market. The 3-D network of channels provided by the Mn2O4 spinel framework for Li+-ion diffusion channels enables a good rate performance. However, the operational capacity of Li1-xMn2O4 spinel cathodes in a lithium cell at ~4 V over the range 0<x£1 is limited by its low electrochemical capacity relative to layered cathodes. Although deep-discharging the cell at ~3 V allows the insertion of extra Li ions into the spinel framework (i.e., Li1+xMn2O4, 0£x£1), a rapid fade of capacity occurs as a result of a severe crystallographic (Jahn Teller) distortion, which prevents the use of the lower voltage reaction in commercial cells.In this presentation, a novel LT-LiMn0.5Ni0.5O2 (LT-LMNO) cathode material with unique electrochemical properties will be reported, where LT refers to its low synthesis temperature (400 °C). In striking contrast to a layered electrode with the same composition, HT-LiMn0.5Ni0.5O2 (where HT = high temperature synthesis, ~850 °C), LT-LMNO has a composite configuration with structurally-integrated lithiated spinel- and layered-like components.3, 4 It provides an electrochemical capacity almost twice that of LMO. This discovery provides a new strategy for developing next-generation. Mn-rich spinel-based cathodes.References Bianchini, M.; Roca-Ayats, M.; Hartmann, P.; Brezesinski, T.; Janek, J., There and Back Again - The Journey of LiNiO2 as a Cathode Active Material. Chem. Int. Ed. Engl. 2019, 58 (31), 10434-10458.Croy, J. R.; Gutierrez, A.; He, M.; Yonemoto, B. T.; Lee, E.; Thackeray, M. M., Development of Manganese-rich Cathodes as Alternatives to Nickel-rich Chemistries. Power Sources 2019, 434, 226706.Thackeray, M. M.; Lee, E.; Shi, B.; Croy, J. R., Review: From LiMn2O4 to Partially-Disordered Li2MnNiO4: The Evolution of Lithiated-Spinel Cathodes for Li-Ion Batteries. Electrochem. Soc. 2022, 169 (2), 020535.Shi, B.; Gim, J.; Li, L.; Wang, C.; Vu, A.; Croy, J. R.; Thackeray, M. M.; Lee, E., LT-LiMn5Ni0.5O2: A Unique Co-free Cathode for High Energy Li-ion Cells. Chem. Comm. 2021, 57 (84), 11009-11012.

Uncovering the Mysterious Transformations during Cycling in Li-Ni-Mn-O Cathode Materials

Layered transition metal oxides, specifically LiNixMnyCozO2, lead the market for Li-ion battery cathode materials. Cobalt is a problematic metal to include in such a high-volume product like Li-ion batteries, as it is expensive, and it is mined using unethical practices. Contemporary electrodes use metal compositions with < 0.33 Co. However, even as the least abundant element in the material, eliminating Co entirely remains an important objective, but is so far necessary as it increases material stability leading to improved cycle life. Thus, research has been active in the Li-Ni-Mn-O system, looking for potential replacements for Co-containing layered oxides. The Li-Ni-Mn-O pseudo ternary system has been investigated in the past decade, revealing some interesting materials. Several compositions (including Li0.568Ni0.073Mn0.359O2 studied here) have been uncovered that show anomalous increasing capacity while cycling over 100 cycles, with some materials reaching 300 % capacity compared to their first cycle.1 It has been hypothesized that this is due to a phase transition occurring in the material, but to date the precise mechanism remains elusive. Other materials (including Li0.586Ni0.071Mn0.343O2 studied here), though very near to these compositions, show relatively stable capacities but dramatic voltage fade.2 In both materials, structural transformations are clearly at play during extended cycling. This work leverages X-ray absorption spectroscopy (XANES/EXAFS) and X-ray photoemission spectroscopy (XPS) to uncover the subtleties in the local environments of Ni and Mn before, during, and after cycling. XANES/XPS reveal to what extent there is a contrast between the oxidation states of the Ni/Mn cations at the surface vs. the bulk of the particles, which has been shown to be important in Ni containing cathodes.3 Interestingly, in both materials, no important changes are seen in the X-ray diffraction patterns, while the pair distribution functions from EXAFS evolve dramatically as shown in the figure here for the Ni environment. Interestingly, the material that shows capacity growth shows a less reversible , while there is no significant difference in the Mn site between the materials before and after charging. Analysis of the final structures shows conversion towards spinel-like structures in both cases, despite the dramatic differences in progression of the capacities, hinting that the spinel-like phases can behave very differently depending on composition. Figure 1

The Effect of Particle Size and the Material Loading to the Performance and Stability of the LFP Batteries

LiFePO4 (LFP) is one of the most studied materials for Li-ion battery cathodes. It provides excellent safety and long cycle life; however, it displays limited capacity when compared to other cathode materials. The physical properties of LFP strongly affect the performance and stability of the final battery. Among them, particle size is known to be crucial and, in addition, the maximum acceptable electrode loading certainly depends on it. Herein, the effect of particle size as well as the loading of the coating on the performance and stability of the LFP electrode is studied by using both galvanostatic charge-discharge and electrochemical impedance spectroscopy. Two powders displaying average particle sizes of 0.88 µm (LFP-1) and 0.26 µm (LFP-2) have been selected to prepare two different sets of electrodes via water-based spray with Xanthan Gum binder. Different coating loadings were prepared on circular current collectors (Æ = 1.55 mm): 3 mg (1.59 mg/cm2), 6 mg (3.17 mg/cm2) and 12 mg (6.35 mg/cm2). Half-cells were analysed according to their capacity, electrochemical properties and capacity retention after cycling.First, the effect the loading on the capacity of the cells was determined within both LFP-1 and LFP-2 sample groups (Figure 1). Results show that both groups are indeed affected by increasing the active mass loading, but the LFP-2 series to a lower extent, whatever the cycling rate. In the meantime, the rate capabilities of the electrodes were studied by comparing the electrode capacity as a function of the C-rates. Overall, electrodes with the lowest loading (3 mg) can sustain their capacity on higher C-rates regardless of the sample group. It confirms that lower loadings of the coating are preferable for high C-rate applications. The difference between LFP-1 and LFP-2 sets are much more apparent for 6 mg and 12 mg-loaded electrodes as the relative difference can reach 25%; this result shows that active materials with smaller particle size are more suitable for high C-rate applications.Capacities and capacity retention results were investigated by using EIS in order to understand the electrochemical property difference between the two powders as well as between the different electrode loadings. Firstly, effect of loading amount has been observed and for LFP-1 cells, when the loading increases (from 3 mg to 12 mg), a resistance (Rs) increase (from 15 to 56 Ω) can be observed. Secondly, effect of particle size change has been observed and it has been seen that the charge transfer resistance (Rct) decreases strongly (from 93 to 53 Ω) between LFP-1 and LFP-2 for 3mg loading cells respectively. This is a direct consequence of higher surface area of LFP-2.Second, the stability of the electrodes was examined. To that aim, half-cells were submitted to a sequence of varied C-rate cycling similar to the performance measurement. Then, they were cycled for 100 cycles at C and, finally, the varied C-rate sequence was applied again. The first and second sequences were compared with each other to obtain capacity retention between the the first and second sequences, which enables observing the effect of ageing.Results (Table 1) show electrodes with lower loading get less effected by the degradation, regardless of the LFP used. For both powders, the capacity remains high even at high C-rates. The reverse can be told for the electrodes with the highest loading. Regardless of the LFP chosen, the degradation is quite harsh as it can go as low as 28% capacity retention. This suggests that thin coatings are affected less by the degradation while it is quite dramatic when the loading increases. Comparison between LFP-1 and LFP-2 shows the impact of the powder particle size: electrodes made of smaller particles are less effected by the degradation. The difference can go up to 36% and 69% between LFP-1 and LFP-2 respectively.Electrochemical properties were investigated for 3 mg-loaded electrodes with the EIS before and after cycling. Increase in all observed values (Rs and Rct) has been observed after cycling (Table 2). The increase in values are much more dramatic for LFP-1, which explains the worse stability performance upon long-term cycling.Overall, LFP-2 cells display lower Rs and Rct as a direct result of high surface area resulting from their lower particle size. Those properties give them the advantage of being more tolerant to increasing loadings and increasing C-rate. In addition, cells prepared with smaller LFP particles are affected less by the degradation, possibly because the morphology is less affected by the cycling. Further study of morphology or crystallography modifications will be conducted to determine the origin of degradation. Figure 1

Lessons Using an Electrochemical Method to Produce Lithium Manganese Oxide Cathodes for Lithium-Ion Batteries

Lithium manganese oxide (LMO) has been a well-studied Li-ion battery cathode material for for many years. It offers high thermal stability for high-temperature battery applications and a prolonged cycle life compared to other materials. LMO also has an acceptably high energy density from a naturally abundant, inexpensive, and environmentally benign material, i.e. manganese (Mn). The cathodes for LIBs are conventionally synthesized via solid-state reaction techniques, which require harsh and complex conditions including high temperature (> 700oC) and high pressure. The resulting powders are incorporated into a slurry that is cast onto a current collector using a binder, additives, and solvent. Though this results in high-performing electrodes, it also usually increases the production cost. Another approach that is gaining traction to make LMOs is electrodeposition. Electrodeposition can allow for the direct synthesis of the active material on the current collector without using any binder or additives. Using electrodeposition not only could eliminate the mass and volume of inactive material but also reduce the cost of electrode fabrication. It also can facilitate recycling by depositing the active material from lower purity, material-digested streams.A few reports in the literature have discussed the electrochemical preparation of LMO cathode from the following steps: electrodeposition of manganese oxide (s) (MnxOy) onto a substrate followed by chemical lithiation and heat treatment of MnxOy [1,2]. Although a few reports showed the active materials with reasonable capacity, it is presently unknown what LiMnxOy phase or phases are active and which MnxOy is responsible. However, without sufficient physicochemical investigation, multiple works have postulated that the LMO is created from crystalline MnO2 or Mn3O4. It is also not known what the typical active phase yield is or what physical structures or conditions are responsible for increased capacity. If electrodeposition-to-LMO is to become a viable commercial pathway, a rational understanding of the solid-state chemistry for the LMO formation is needed.This talk will discuss the deposition and lithiation of multiple manganese oxide phases – linking the chemistry and morphology of the surface features to their charge/discharge properties. It will be shown that traditional crystalline phases are not responsible for the formation of LMOs. It will also be shown that the LMOs do not fully delithiate during charging. Lastly, the precise morphology of the active phase – separated out through new processing approaches – will be identified. The composition, structure, and crystallinity of the Mn oxides and LMOs were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The resulting LMO electrodes were incorporated into coin cells, cycled – achieving a capacity of 261 mAh g-1, and post-characterized.References J. Rana, M. Stan, R. Kloepsch, J. Li, G. Schumacher, E. Welter, I. Zizak, J. Banhart, and M. Winter, Adv. Energy Mater., 4, 1300998 (2014).Z. Quan, S. Ohguchi, M. Kawase, H. Tanimura, and N. Sonoyama, J. Power Sources, 244, 375 (2013).

(Invited) Understanding the Role of Dopants (Al, Zn, Zr) in Altering Charge-Storage Capacity and Cycling Profiles of VFe2Ox

Vanadium ferrite (VFe2Ox) is a defective spinel system that can incorporate substantial Li+ and exhibits a high charge–discharge rate, particularly when structured as a nanoscale aerogel.1 Cations such as Zr, Zn and Al,2 can readily enter the structure substitutionally and have strong, but differing effects on the charge-storage capacity of the material. These earth abundant, cost- effective constituent elements give this class of materials strong potential as future Li-ion battery cathodes but optimizing the stoichiometry for maximum capacity and stability will require understanding the redox sequence of the host cations (Fe, V) and role of intentional dopants.We use density functional theory calculations in concert with in situ and operando X-ray absorption near-edge spectroscopy (XANES) spectra obtained using an in-lab X-ray absorption spectrometer to uncover the quantum mechanical-level effects that underpin relevant energy- storage behaviors of doped and undoped VFe2Ox. Our experimental V K-edge and Fe K-edge spectra indicate reduction of both species during discharge but cannot distinguish between tetrahedral and octahedral Fe redox sites or fully resolve the valency of each element as a function of state of charge. Using a hybrid form of density functional theory that accounts for the strong correlation present in 3d elements, we show that both V and Fe are indeed reduced, but that only tetrahedral Fe is redox active until fully converted to Fe2+. Furthermore, both octahedral and tetrahedral Fe3+ are high spin configuration, but the 5μB moments in the fully filled majority spin channel at each symmetry site are anti-aligned. This arrangement allows for easy exchange of electrons and facilitates conduction. We also calculate XANES spectra based on first principles calculations to be compared directly to those measured in the lab. This cross- check allows us to understand the effect of Al, Zr, and Zn dopants on the redox sequence and relate these results to site preference and capacity. Our combined experimental and calculational investigation sheds light on how these complex materials store Li ions and points toward future alterations that may further improve their properties.

A Low-Temperature Boron-Based Composite Coating for Ni-Rich Li-Ion Battery Cathode with Enhanced Cycle Life and Safety

Due to the continuously aggravating global warming crisis, the aim of reducing CO2 emissions by replacing fossil fuels with clean energy sources has raised the demand for electric vehicles (EVs) and driven research in pursuing high-energy rechargeable lithium-ion batteries (LIBs). For the cathode component, Ni-rich cathode materials such as LiNixCoyMn1-x-yO2 (NCM) have been widely adopted in commercial EVs due to their high specific capacity (~200 mAh/g) and high operating voltage (~ 4V vs. Li/Li+). However, Ni-rich cathode materials are still confronting challenges such as poor cycle stability and safety issues. To tackle these problems, a boron-based surface modification of Ni-rich cathode material (NCM) is achieved via a low-temperature process in this work. The coated NCM shows comparable rate capability but with substantially improved cycle stability. In terms of safety issues (thermal runaway process), the onset temperature of the thermal runaway process in presence of electrolyte is delayed by 40°C while the total heat release and the maximum heat flow are both decreased by over 40%. Post mortem and in situ X-ray characterizations using synchrotron radiation further illustrate the reasons of the enhanced cycle stability and safety. Results show that the boron-based composite coating is able to decrease the extent of reaction between NCM and the electrolyte during both cycling and the thermal runaway process. Our results demonstrate the use of a low-temperature boron-based composite coating as an effective surface modification method of Ni-rich cathode materials to achieve long-life and high-safety lithium-ion batteries.

Operando X-Ray Analyses of NMC811/Li Batteries: Progress Towards Understanding Capacity Fading Mechanisms at High Voltage and Fast Charge

LiNi0.8Mn0.1Co0.1O2 (NMC811) is a commercially successful Li-ion battery cathode due to its high energy density and cyclability. Utilizing this system under fast charge and high potential charge conditions is of great interest as this will help facilitate widespread electric vehicle adoption; however, these aggressive charging conditions lead to enhanced capacity fade. To design next-generation NMC811 batteries with longer life and higher capacity the origins of the capacity fade must be understood. Operando X-ray characterization techniques are critical for this endeavor as they allow the acquisition of information about the evolution of structure, oxidation state, and coordination environment as the material (de)lithiates in a functional battery. Charging to high potential (4.7 V) leads to greater delivered initial capacity but much more significant fading; while fast charging (4C) leads to slightly reduced capacity but with similar fading. Operando XRD and SEM results indicated that secondary particle fracture from increased structural distortions at >4.3 V was a contributor to capacity fade. On the other hand, fast charging led to a slight reduction in structural distortions consistent with the reduced capacity fade. Operando hard XAS revealed significant Ni and Co redox during cycling as well as a Jahn-Teller distortion at the discharged state (Ni3+). Greater bulk redox was observed when charged to 4.7 V while less bulk redox was observed at 4C, consistent with the different delivered capacities. Soft XAS analyses revealed significant surface reconstruction after cycling to 4.7 V. Overall, charging to 4.7 V leads to more structural distortions and particle fracture, as well as surface reconstruction that lead to increased capacity fading. Fast charge does not induce additional structural distortion or surface reconstruction as compared to the slower, moderate charging potential cycling suggesting that the phenomena at the anode may be more critical under fast charge.

Tailored Deep Eutectic Solvents for Effective Leaching and Electrochemical Recovery of Spent Li-Ion Battery Cathode Materials

The increase in demand for Lithium-ion battery (LIB) raw materials such as cobalt, nickel and lithium are expected to exacerbate exploitative resource extraction and have negative geopolitical implications. A solution to ameliorate this issue is to recycle LIBs. Unfortunately, the existing LIB recycling market is dominated by energy inefficient and environmentally harmful processes such as pyrometallurgy and hydrometallurgy which produce products that require further processing before downstream use. Deep Eutectic Solvents (DESes) are a class of compounds that are formed by mixing hydrogen bond donors and acceptors and exhibit high capability for dissolving metal oxides. In this work, we tailored the electrochemical stability window of selected, high leaching efficiency DESes by incorporating additives (such as ammonium salts and glymes), thereby expanding their electrochemical window and gaining the ability to electrochemical plate out dissolved metals from the DES in addition to facilitating leaching at high recovery rates. The electrochemical window of our baseline DES, the extensively studied system consisting of choline chloride and ethylene glycol (ChCl: EG), is ca 1-3 V (vs AgCl). This system can be tailored with additives to yield DESes with extended electrochemical stability window of ca 4-5 V (vs AgCl) while retaining its excellent leaching. The ability of this class of DESes to efficiently leach metals from LiCoO2 (LCO) and LiMnxNiyCo(1-x+y)O2 (LMNCO) cathodes and corresponding leaching efficiencies for Li, Co, Mn and Ni was examined over a range of temperatures and by subjecting the mixture to microwave or sonication in addition to (or in lieu of) heating. Selective tailored DES were shortlisted depending on the high leaching efficiency and leached elements were electrochemically recovered. The microstructure of the electrodeposited material was examined using x-ray diffraction and scanning electron microscopy for phase identification, purity, and stability of the individual elements. Keywords: LIB, Cathode, Electrodeposition, Leaching, Sonication, DES Figure 1. Effect of additives on the electrochemical window of a ChCl:EG DES (left); Photograph of leach liquors of different cathode materials (LCO, LNO, LMO and LNMCO from left to right) dissolved in selected DES (right) Figure 1

In situ formation of partially carbonized polyvinylpyrrolidone as a green binder for high-voltage Li-ion battery cathode with improved electrochemical performance

We propose the in situ formation of partially carbonized polyvinylpyrrolidone (PC-PVP) as a green binder for high-voltage LiNi0.5Mn1.5O4 (LNMO) cathodes. A mixture of water and ethanol with an equal volume ratio is shown to enable a more uniform dispersion of LNMO particles in the active material matrix with fewer crevices rather than pure water or pure ethanol. Conformal coverage of LNMO with PC-PVP can be achieved through a stepwise thermal process, which not only enhances the electrical conductance of the cathode material but also protects the electrode surface from overreaction with the electrolyte at high voltages. This can be attributed to the coral reef-like structure of the PC-PVP coating layer, which offers abundant electrical contact without sacrificing ion transport pathways. In addition, the specific nitrogen-containing groups of PC-PVP promote ion transport within the electrode. Furthermore, a carbon paper (CP) substrate is introduced as a current collector to support the PC-PVP/LNMO material layer and to establish a good interconnection. Owing to these features, the PC-PVP/LNMO/CP electrode outperforms the PVDF/LNMO/Al counterpart in terms of high-voltage cycling stability and rate capability. The improved electrode performance is supported by the reduced cathode–electrolyte interphase (CEI) resistance, which corresponds to mitigated electrolyte decomposition and stable CEI formation.

4d Lithium-Rich Cathode System Reinvestigated with Electron Paramagnetic Resonance: Correlation between Ionicity, Oxygen Dimers, and Molecular O2.

Layered lithium-rich (Li-rich) oxide cathodes with additional capacity contribution via oxygen redox are promising high energy density cathodes for next generation Li-ion batteries. However, the chemical states of the oxidized oxygen in charged materials are under fierce debate, including the O2- with stable electron holes, O-O dimer (O2)n- (n > 0), molecular O2, and oxygen π redox. Here, we show using electron paramagnetic resonance (EPR) spectroscopy that in the 4d Li-rich ruthenate compounds, Li2Ru0.75Sn0.25O3 and Li2Ru0.5Sn0.5O3, strong covalency between 4d transition metal and oxygen can inhibit the formation of trapped molecular O2 but not suppress the formation of O-O dimer. As the covalent bond of Ru-O weakens and the ionic bond Sn-O becomes dominant in Li2Ru0.25Sn0.75O3, (O2)- will detach from Sn4+, eventually leading to the formation of trapped molecular O2 during the deep oxygen redox. We propose two possible evolution paths of oxidized oxygen as (1) oxygen electron holes → Ru-(O2)m- (m > 1) → Ru-(O2)- or (2) oxygen electron holes → Sn-(O2)m- (m > 1) → Sn-(O2)- → O2, and the species to which they will evolve are related to which metal (O2)- bonds to and whether the ionicity dominates.

Doping of group IVB elements for nickel-rich cobalt-free cathodes

Hetero-element doping is a promising strategy to improve the cycling stability of nickel-rich cobalt-free cathodes for the next-generation high energy-density Li ion batteries. To make doping effective, it is important to understand the mechanism of how the dopants regulate the electronic band, lattice parameter adjusting, or hetero-phase formation to achieve high stability. In this study, we investigate LiNi0.9Mn0.1O2 cathodes doped with IVB grouping elements via multiple characterization techniques. By utilizing in situ XRD and TEM methods, we found that the stronger Ti–O bond effectively improves the cathode stability via a dual protection mechanism. Specifically, the bulk lattice of cathode is well-preserved during cycling as a result of the suppressed H2-H3 phase transition, while a in situ formed Ti-rich surface layer can prevent continuous surface degradation. As a result, the 5% Ti doped LiNi0.9Mn0.1O2 cathode exhibits a high capacity retention of 96% after 100 cycles. Whereas, despite IVB group elements Zr and Hf have stronger bonding energy with oxygen, their larger ionic radii actually impede their diffusion into the cathode, thereby they can not improve the cycling stability. Our findings uncover the functional origin of doped elements with their dynamic modification on cathode structure, providing mechanistic insights into the design of nickel-rich cobalt-free cathodes.

Direct Regeneration of NCM Cathode Material with Aluminum Scraps.

Hydrothermal-based direct regeneration of spent Li-ion battery (LIB) cathodes has garnered tremendous attention for its simplicity and scalability. However, it is heavily reliant on manual disassembly to ensure the high purity of degraded cathode powders, and the quality of regenerated materials. In reality, degraded cathodes often contain residual components of the battery, such as binders, current collectors, and graphite particles. Thorough investigation is thus required to understand the effects of these impurities on hydrothermal-based direct regeneration. In this study, we focus on isolating the effects of aluminum (Al) scraps on the direct regeneration process. We found that Al metal can be dissolved during the hydrothermal relithiation process. Even when the cathode material contains up to 15 wt.% Al scraps, no detrimental effects were observed on the recovered structure, chemical composition, and electrochemical performance of the regenerated cathode material. The regenerated NCM cathode can achieve a capacity of 163.68 mAh/g at 0.1 C and exhibited a high-capacity retention of 85.58 % after cycling for 200 cycles at 0.5 C. Therefore, the hydrothermal-based regeneration method is effective in revitalizing degraded cathode materials, even in the presence of notable Al impurity content, showing great potential for industrial applications.

Heteroatoms-doped carbon effect on LiFePO4 cathode for Li-ion batteries

Surface modification with heteroatoms-doped carbon is applied to improve the electrochemical properties of LiFePO4 (LFP) as a cathode for lithium-ion batteries (LIBs). The preparation of nitrogen and sulfur dual-doped (N, S-doped) carbon-coated LFP (NSC@LFP) with a uniform carbon coating layer involves a solid-state method together with thermal treatment. Methionine is utilized as a source of N, S-doped carbon. Applying physical and electrochemical characterizations, the effects of surface modification with heteroatom-doped carbon have been examined. The results demonstrate that the surface-coated samples exhibit improved electrochemical activity as a cathode for LIBs, with a specific capacity of 155 mAh g−1 at 0.1 C, 126 mAh g−1 at 1 C, and a capacity retention of 99% after 200 cycles. Additionally, the rate capability shows an increasing difference as the current density increases, indicating that the N, S-doped carbon coating layer enhances the ionic/electronic conductivity and shortens the ion diffusion channels, which leads to the better electrochemical kinetics of NSC@LFP.

High redox potential transition metals incorporated olivine structure: LiFe0.7(Mn1/3Co1/3Ni1/3)3x−yVyPO4 (x = 0.1, 0.0 ≤ y ≤ 0.10) cathode for Li-ion battery

High redox potential transition metals incorporated olivine structure: LiFe0.7(Mn1/3Co1/3Ni1/3)3x−yVyPO4 (x = 0.1, 0.0 ≤ y ≤ 0.10) cathode for Li-ion battery

Determining the fundamental failure modes in Ni-rich lithium ion battery cathodes

Challenges associated with in-service mechanical degradation of Li-ion battery cathodes has prompted a transition from polycrystalline to single crystal cathode materials. Whilst for single crystal materials, dislocation-assisted crack formation is assumed to be the dominating failure mechanism throughout battery life, there is little direct information about their mechanical behaviour, and mechanistic understanding remains elusive. Here, we demonstrated, using in situ micromechanical testing, direct measurement of local mechanical properties within LiNi0.8Mn0.1Co0.1O2 single crystalline domains. We elucidated the dislocation slip systems, their critical stresses, and how slip facilitate cracking. We then compared single crystal and polycrystal deformation behaviour. Our findings answer two fundamental questions critical to understanding cathode degradation: What dislocation slip systems operate in Ni-rich cathode materials? And how does slip cause fracture? This knowledge unlocks our ability to develop tools for lifetime prediction and failure risk assessment, as well as in designing novel cathode materials with increased toughness in-service.

Organic-catalysis-free and low-temperature synthesis of vertically aligned graphene nano-stripes for enhancing performance of LiFePO4-based Li-ion batteries

Practical and efficient integrations of graphene into real applications are identically important as their various superior properties. Among various graphene-related materials, vertical graphene stripes (VGSs, in nanoscale) are one kind of interconnected graphene sheet oriented perpendicularly to the growth substrate with 3-dimensional porous structures. Due to the high surface-to-volume ratio, VGSs could be an even better candidate than pure graphene when considering the physical mixing of graphene-related materials with other substances. In this study, we demonstrate an organic-catalysis-free and low-temperature approach (<300 °C) to efficiently grow VGSs without utilizing any environmentally harmful chemicals. The as-synthesized VGSs were comprehensively characterized by means of different microscopes, Raman spectra, X-ray diffractometers, and electrochemical tests. Compare with existing literature, a discrepancy in terms of growth mechanism was first discovered via time-independent Raman spectra, showing that the horizontal buffer layers are not necessary prior to the formation of VGSs. More importantly, the as-synthesized VGSs were introduced into the cathode of Li-ion batteries, and outstanding functionalities such as specific capacity and charge/discharge stabilities were found to even outperform carbon black (C65), the classic commercial conductive additive.