Li-ion Battery Cathode Research Articles

Microstructural Refinement and Surface Modification of Ni-Rich Cathodes for High-Performance Li-Ion Battery

Li[Ni1–x–y–zCoxMnyAlz]O2 (NCMA) cathodes have attracted public attention owing to their improved durability by leveraging the advantages of NCM and NCA cathodes. The combination of Mn and Al in a NCMA cathode effectively stabilizes the host layered structure to increase its resistance to microcracking; consequently, NCMA cathodes outperform both NCM and NCA cathodes with the same Ni contents, in terms of cycle life, without sacrificing energy density. However, as the Ni contents of the cathodes exceed 90%, a simple, compositionally engineered NCMA cathode lacks the chemical and mechanical stability to suppress surface degradation and the development of permanent microcracks due to the high incidence of highly reactive Ni4+ species on its surface.1,2 Considering the limitations of NCMA cathodes, a combination strategy involving microstructural engineering to inhibit microcracking, by enabling the efficient dissipation of local strain,3 and the modification of the exposed cathode surface, to protect it against deleterious electrolyte attack, is expected to afford superior Ni-rich layered cathodes.In this study, we improved the cycling stability of a conventional NCMA cathode with a Ni content of 93% (a NCMA93 cathode) using a combination strategy involving microstructural engineering and surface modification. To this end, we prepared a Sb-doped NCMA93 (denoted as Sb-NCMA93) cathode; Sb was incorporated to refine its microstructure and radially align and elongate its primary particles. Furthermore, we generated a protective F layer on the cathode surface through a chemical reaction between residual lithium compounds and a NH4F coating agent. To comprehensively investigate the synergetic effect of this combination strategy, conventional and Sb-doped NCMA93 cathodes with and without F coatings were synthesized and characterized and their fundamental properties and electrochemical performances compared. Post-mortem analyses were performed to elucidate the origins of the remarkable long-term cycling stability of the optimized cathodes. Reference s : [1] H.-J. Noh, S. Youn, C. S. Yoon, Y.-K. Sun, J. Power Sources, 2013, 233, 121.[2] H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater. 2018, 30, 1155.[3] U.-H. Kim, H.-H. Ryu, J.-H. Kim, R. Mücke, P. Kaghazchi, C. S. Yoon, Y.-K. Sun, Adv. Energy Mater. 2019, 9, 1803902.

Alluaudites: From Sulfates to Tungstates

Alluaudites are essentially naturally occurring mixed metal (Mn and Fe) phosphate-based minerals [1] consisting of an open framework structure to support fast alkali migration. The general formula for alluaudite can be expressed by A(1)A(2)M(1)M(2)2(XO4)3 where A and M sites are alkali ion and transition metals respectively and X can be S, P, As, Mo, W, V and so on [2]. The presence of polyanionic moieties (XO4) assures structural stability and high-voltage operation arising from the inductive effect [3]. Till date, a variety of phosphate and sulfate-based alluaudites have been reported as cathodes for Li-ion and Na-ion batteries [4,5]. In 2014, Yamada group reported a Fe-based sulfate alluaudite, Na2Fe2(SO4)3, acting as a 3.8 V SIB cathode material with excellent rate capability and energy density. It ushered the discovery of various high-voltage sulfate alluaudites materials by optimizing different synthesis routes. While they offer high-voltage performance, the presence of SO4 species makes them susceptible to thermal decomposition and moisture-sensitive. We have observed a clear phase transition from alluaudite to hydrated bloedite with exposure to the humid atmosphere [6]. As compared to sulfates, phosphate alluaudites are moisture stable but suffer from lower voltage operation due to the lower inductive effect of P. On the other hand, they had shown excellent electrocatalytic activity for both ORR and OER mechanism [7]. Recently, Gao et al. reported the first molybdate-based alluaudite Na2.67Mn1.67(MoO4)3 working as a 3.45 V Mn-based insertion cathode for SIBs [8]. Inspired by this work, we have extended the molybdate alluaudite chemistry towards its Co, Ni and Cu- analogue, Na3.36Co1.32(MoO4)3, Na2.4Ni0.8(MoO4)2 and Na4Cu(MoO4)3. The Co- molybdate was found to act as 4.0 V cathode material against Na/Na+. All three molybdates have been found to show excellent activity while cycling within the lower voltage region by exploiting its Mo- redox which has been probed by different ex-situ post-mortem analysis. Moreover, both Co- and Ni- analogues had shown excellent activity in ORR and OER reaction as an add-on to its battery application. We have detected the mechanism by using in-situ Raman spectroscopy, TEM and XPS analysis. Finally, for the first time, we have synthesized Na4Mn(WO4)3, a tungstate alluaudite whose structure and electrochemistry are not reported anywhere to the best of our knowledge. Using inductive effect principle, various alluaudite systems will be discussed.

Does Anisotropic ‘Lattice’ Collapse Always Lead to Cracking in Ni-Rich Layered Oxide Cathode Particles?

Single-crystalline Ni-rich layered oxides (LiNi x Mn y Co1−x−y O2; x ≥ 0.8) are promising high-energy-density cathodes for future Li-ion batteries as they can withstand cathode particle cracking, which is a significant contributor to electrochemical capacity loss. The absence of grain/particle boundaries substantially mitigates the build-up of bulk structural strain in these materials generated from the anisotropic structural evolution (i.e., lattice collapse) during electrochemical cycling. However, compared to their polycrystalline counterparts, rigorous evaluations of their long-term electrochemical performance and their dependence on electrode structure changes, impedance, and particle cracking, are still necessary to take it towards commercialisation. Operando X-ray diffraction (XRD) and absorption spectroscopy (XAS) are ideal probes of these bulk electrode structure properties and provide a direct temporal correlation between the battery electrochemistry and the non-equilibrium structural changes in the electrodes. However, such studies often use electrochemically compromised cells modified for X-ray transmission that are neither representative of a real-world full-cell architecture nor operable long-term under industrially relevant cycling conditions, thereby compromising the results' practicality. This is especially problematic for technologically mature cathodes like single-crystalline Ni-rich layered oxides, which require greater scrutiny of their long-term degradation modes after hundreds of cycles. In this work, using in-house operando X-ray studies and large-area post-mortem electron tomography of a (TRL-5) pilot-line-built A7 pouch full cells with industry-relevant specifications, we demonstrate how single-crystalline LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes can withstand the severe anisotropic structural evolution and show no particle cracking even when cycled under harsh conditions of 2.5–4.4 V at 40 °C for 100 cycles. The bulk structural changes in both electrodes as well as the associated electrochemical performance loss are also evaluated. Furthermore, the validity of the in-house pilot line cell results is benchmarked against a commercially sourced Li-ion cell. In addition to furthering our understanding of single-crystalline Ni-rich cathodes, this work emphasises the need for real-world-relevant reproducible fundamental investigations of academic Li-ion cells and presents a methodology for doing so. Figure 1

Manganese-Based Tunnel and Layered Oxide Cathodes for Secondary Alkali-Ion Batteries

Designing new cathode materials remains crucial in developing (post) Li-ion batteries. Mn-based oxide cathodes have received wide attention due to their sustainable nature, low cost, elemental abundance, structural diversity/polymorphism, and rich oxidation states (2+ to 7+), offering tunable redox potential [1]. Here, we have investigated different oxide-based cathode insertion compounds for secondary metal-ion batteries.i) We have demonstrated tunnel-type sodium insertion material Na44MnO2(NMO) as an intercalation host for Li-ion and K-ion batteries. The solution combustion synthesized Na0.44MnO2 assuming an orthorhombic structure (space group Pbam), exhibited rod-like morphology. After electrochemical ion exchange from NMO, we obtained Na0.11K0.27MnO2 (NKMO) and Na0.18Li0.51MnO2 (NLMO) cathodes for K-ion batteries and Li-ion batteries, respectively [2]. These new compositions, NKMO and NLMO, showed excellent cycling stability with capacities of ∼74 and 141 mAh g–1 (first cycle, C/20 current rate). The underlying mechanistic features concerning charge storage and structural modifications in these cathode compositions were probed by combining ex-situ structural, spectroscopy, and electrochemical tools [3].ii) Using composite formation, we have tried to improve the P2-type layered material. Here, the stable Na7(Li1/18Mn1/18Ni3/18Fe2/18χ1/18)O2–xNa2MoO4 biphasic composite was synthesized using Mo doping. Overall, the redox chemistry was investigated using various spectroscopy techniques to prove the net capacity resulted from both cationic and anionic redox reactions [4]. Keywords: energy storage; batteries; cathode; manganese oxides; intercalation; doping

Probing the Mo-Redox in Alluaudite Battery Materials

Alluaudites are essentially naturally occurring mixed metal (Mn and Fe) phosphate-based minerals [1] consisting of an open framework structure to support fast alkali migration. The general formula for alluaudite can be expressed by A(1)A(2)M(1)M(2)2(XO4)3 where A and M sites are alkali ion and transition metals respectively and X can be S, P, As, Mo, W, V and so on [2]. The presence of polyanionic moieties (XO4) assures structural stability and high-voltage operation arising from the inductive effect [3]. Till date, a variety of phosphate and sulfate-based alluaudites have been reported as cathodes for Li-ion and Na-ion batteries [4,5].In 2017, the first molybdate-based alluaudite material, Na2.67Mn1.67(MoO4)3, was reported as a 3.45 V Mn-based cathode [6]. Inspired by this work, we have explored other 3d (Co, Ni) based molybdate alluaudite homologues as potential compounds with desirable electrochemical and electrocatalytic activities. Solution combustion synthesis was employed to prepare phase pure Na36Co1.32(MoO4)3 by restricting the annealing duration to one minute as compared to the reported solid-state route warranting prolonged (100 h) annealing. It was found to act as a high-voltage cathode (4 V vs Na/Na+ and 4.1 V vs Li/Li+) involving Co3+/Co2+ redox center [7] while cycling between 3.0 V to 4.3 V. The above-mentioned alluaudite consists of Mo species, which can be redox-active at lower voltages. When cycled in a low-voltage window (0.01 V to 3.0 V), this material was found to act as an anode for both Li-ion and Na-ion batteries. High capacity (ca 400-500 mAh/g) was obtained with a central potential ~0.6 V involving conversion and (de)insertion reaction mechanism. The Ni-analogue, Na4Ni0.8(MoO4)2 alluaudite, was studied as an anode material in both Li-ion and Na-ion batteries involving conversion and (de)intercalation redox mechanisms like the Co- analogue. The underlying redox mechanism will be described for both cases involving post-mortem diffraction, electron microscopy, and spectroscopic tools as well as with the help of the density functional theory (DFT) approach. Finally, alluaudite Na4Cu(MoO4)3 was prepared by soft chemistry route, which was found to work as an anode material in the voltage window of 0.01 V to 3.0 V. The phase transformation and underlying redox mechanism will be elucidated.

Phosphonium-Based Ionic Liquid Electrolyte in Combination with Silicon Anodes and LiNi0.5-XMn1.5+XO4 Cathodes for Lithium Ion Batteries

Ionic liquids, like bis(fluorosulfonyl)imide (FSI) ionic liquids, are promising solvents for lithium ion batteries due to their high thermal stability and wide electrochemical window. The performance of ionic liquid electrolytes is however hampered by the low conductivity at room temperature, but the high thermal stability allows for operation at elevated temperatures, at which the conductivity is significantly improved.Electrolytes based on LiFSI and ionic liquids of the cations; pyrrolidinium (PYR13 +), and phosphonium (P111i4 +), with FSI anions, have been shown to exhibit stable cycling at room temperature, and good rate performance for cells composed of silicon anodes and LiFePO4 cathodes at 60 °C [1,2]. The lithium ion mobilities, relative to standard carbonate electrolytes, were determined from the limiting current densities at room temperature and 60 °C. Significant differences in the temperature dependence of the transport properties were revealed, with a considerable increase in the lithium ion mobility from 20 to 60 °C for electrolytes based on P111i4FSI. The best rate performance at 60 °C was demonstrated for the P111i4FSI based electrolyte, with discharge capacities around 1000 mAh/gSi at a 2C rate [2]. The improved performance was attributed to a combination of the improved lithium ion mobility and formation of a more conductive solid electrolyte interphase (SEI) for this electrolyte.In view of the excellent high temperature performance of P111i4FSI, including high thermal stability and a large electrochemical window [1,2], this electrolyte has been selected for further studies as electrolyte for high voltage LiNi0.5-xMn1.5+xO4 (LNMO) cathodes. LiNi0.5-xMn1.5+xO4 (LNMO) is an attractive candidate as a next generation Li-ion battery (LIB) cathode material because it has a high energy density, due to the high operating voltage, and a relatively low cost (Co-free) compared to alternative cathode chemistries. However, the stability of LNMO is not yet satisfactory for commercial applications, especially in full-cell configuration with graphite as the anode material, and at elevated temperatures. One challenge is the transition metal (TM) dissolution, which poisons the graphite anode by degrading the solid electrolyte interface (SEI) [4]. The TM dissolution is affected by the formation of hydrofluoric (HF) acid in carbonate-based electrolytes utilizing the LiPF6 salt [3]. Additionally, the decomposition processes occur with an increased rate at elevated temperatures [4,5]. Another challenge is the side reactions occurring at the high operating voltage, which limits the coulombic efficiency. Previous works have indicated that the carbon conductive additive is more prone to side reactions than the LNMO active material [6].Here, we present a study on the phosphonium-based ionic liquid P111i4FSI, with two different salt concentrations: 0.79 m LiFSI and 3.0 m LiFSI, as an alternative electrolyte for LIBs with an LNMO cathode.The focus of the research is to study the side reactions separately on the carbon conductive additive, and on the LNMO active material. Carbon conductive additives differing in structure and particle size are studied. The electrolyte is tested both in half-cell and full-cell configuration with a graphite anode, as well as at room temperature and elevated temperatures. Using 0.79 m LiFSI P111i4FSI results in similar capacity retention, but higher coulombic efficiencies after 200 cycles in half-cells at room temperature compared to 1 M LiPF6 in 1:1 EC:DEC (v/v). Post-mortem characterization is carried out with SEM, TEM, Raman spectroscopy, and FT-IR.

Effect of Calcination Temperature on the Structural and Electrochemical Properties of NMC Cathodes for Lithium-Ion Batteries

The electrochemical and thermal properties of Li[NixMnyCoz]O2 are strongly dependent on its composition and structural characteristics [1]. Among many options available there is no observed middle ground since each of the component cations has a different, specific function in the cathode material [2]. Developing an ideal cathode material with both high capacity and safety is a challenging task that requires precise control of microstructure and physicochemical properties of the electrode [3]. Firstly, the most promising amendment is the increase of nickel content as it enhances the specific discharge capacity, although the gradual safety characteristics decrease over cycling [4]. The optimum composition of NMC has not yet been found, thus, research aiming at improving its properties is still ongoing. The aim of this study is to analyze the impact of calcination temperature on the structural, morphological, and electrochemical properties of lithium nickel-manganese-cobalt oxides. The research focuses on optimization of the last step of the synthesis process. The results will be further used for the gradient structure material design based on nickel-rich core, since in that case the calcination step seems to be crucial for final material properties.Materials were prepared by coprecipitation method of the complex metal hydroxide precursor NixMnyCoz(OH)2, subsequently mixed with lithium hydroxide and annealed at different temperatures in air to obtain the lithiated powders. Constant monitoring of the conditions, such as synthesis temperature, solution pH, stirring frequency and calcination temperature, enable to control the particle morphology, which has a significant impact on lithium cations migration capability, and performance characteristics of the assembled Li-ion cells. To control the optimization process and furtherly investigate the material structure we used various methods. All NMC samples were analyzed using in-situ temperature dependent XRD, followed by the SEM and chronopotentiometry investigation. As the thermal and electrochemical stabilities are related to the structural stability, the various synthesized NMC materials were subjected to variable temperature measurements of X-ray diffraction (VT-XRD). The nickel-rich NMC are supposed to be calcinated in lower temperatures than its nickel-poor NMC analogs. The VT-XRD makes it possible to presume one optimal calcination temperature for both: nickel-poor and nickel-rich phases within the gradient NMC structure. X-ray powder diffraction was used to characterize the crystal structure of the prepared materials, giving general information about the phases present and their crystallographic parameters. Furthermore, scanning electron microscopy (SEM) was used to explore the morphologies of the prepared powders, both before, and after calcination at different temperatures. Understanding the influence of grain and particle as well as grain boundaries characteristics on overall material properties is also crucial, as small primary particle sizes with high surface areas contribute essentially to discharge capacities. To validate the formed hypothesis electrochemical tests have been conducted. Chronopotentiometry allowed for determination of battery cycling parameters, such as specific discharge capacity and cyclability. The combination of these three methods helps to identify the material characteristics and shows a direction for further material development.A detailed analysis will be presented during the conference. This work was funded by the National Science Center in Poland through the Sonata 17 programme (No. UMO-2021/43/D/ST5/03094).Reference: Amalia Christina Wagner et al. Hierarchical Structuring of NMC111-Cathode Materials in Lithium-Ion Batteries. ACS Applied Energy Materials 2020 3 (12), 12565-12574.Thomas Entwistle et al. Co-precipitation synthesis of nickel-rich cathodes for Li-ion batteries, Energy Reports, Volume 8, Supplement 11, 2022, Pages 67-73, 2352-4847.Dong Ren, et al. Systematic Optimization of Battery Materials. ACS Applied Materials & Interfaces 2017 9 (41), 35811-35819. Hyung-Joo Noh et al. , Comparison of the structural and electrochemical properties of layered Li[NixCoyMnz]O2 cathode material for lithium-ion batteries, Journal of Power Sources, Volume 233, 2013, Pages 121-130, 0378-7753.

Pushing the Energy-Lifetime Frontier of Li-Ion Batteries with Optimized Ni-Rich, Co-Free NMA-W Cathodes

Especially in the electric vehicle industry where both high energy density and long lifetime batteries are sought, Ni-based cathode materials such as LiNi1−x−yMnxCoyO2 (NMC) and LiNi1−x−yCoxAlyO2 (NCA) provide a fitting compromise in capacity and cyclability. In recent years, the high cost of cobalt in addition to the problematic geopolitics surrounding cobalt mining have motivated research efforts toward cobalt-free cathode materials.1 However, Ni-rich materials are subject to inevitable failure mechanisms such as microcracking and parasitic reactions with the electrolyte which are further aggravated with an increase in Ni-content and in the absence of Co.2 Many strategies have been proposed to overcome these challenges such as doping and/or coating the cathode particles,3 but there remains a need to further increase energy density with minimal compromise to lifetime.In this work we present a cathode active material system designed to push Ni-rich and Co-free materials to the limit of their performance. This is done by choosing optimal polycrystalline particle size, a balance of Mn and Al content, and a sufficient amount of high-valence doping. Additionally, appropriate synthesis conditions are needed to obtain the desired morphology and infuse the intergranular boundaries with the W dopant. It is then important to choose an appropriate upper cutoff voltage during cycling to maximize energy while avoiding drastic crystal changes.4 This optimized NMA-W material system delivers specific capacity above 200 mAh/g while retaining 95% of its capacity without relying on any amount of Co.The series of NMA-W materials presented in this work were characterized and tested. Scanning electron microscopy (SEM) images were used to observe morphology and crystallite growth after synthesis. X-ray diffraction (XRD) analysis was conducted to monitor the crystal parameters and accelerated rate calorimetry (ARC) was used to assess the thermal stability and safety of the material. Compression tests were also conducted to study the strength of the particles and their propensity to crack under stress. Choi, J. U., Voronina, N., Sun, Y. K. & Myung, S. T. Recent Progress and Perspective of Advanced High-Energy Co-Less Ni-Rich Cathodes for Li-Ion Batteries: Yesterday, Today, and Tomorrow. Adv. Energy Mater. 10, 1–31 (2020).Li, H. et al. An Unavoidable Challenge for Ni-Rich Positive Electrode Materials for Lithium-Ion Batteries. (2019) doi:10.1021/acs.chemmater.9b02372.Yan, W., Yang, S., Huang, Y., Yang, Y. & Guohui Yuan. A review on doping/coating of nickel-rich cathode materials for lithium-ion batteries. J. Alloys Compd. 819, 153048 (2020).Nam, G. W. et al. Capacity Fading of Ni-Rich NCA Cathodes: Effect of Microcracking Extent. ACS Energy Lett. 4, 2995–3001 (2019).

Surface Degradation of NMC Electrodes Exposed to Air and Impact on Subsequent Cycling

To meet the ambitious international emissions commitments laid out in the Paris climate agreement making the transition of society from being dependent on fossil fuels towards increased use of renewable energy sources possible, lithium-ion batteries (LIBs) are a key enabling technology. Even though LIBs are already extensively used in portable electronics and the rapidly expanding market of hybrid- and full-electric vehicles, more extensive deployment requires longer cycle-lifetimes, enhancements in energy density, and reductions in cost. In electric vehicles one of the most common materials for the positive electrodes is based on the lithium nickel manganese cobalt oxide (LixNi1-y-zMnyCozO2, NMC) compound with different ratios of transition metals. The NMC materials are well known for consisting of reasonably abundant materials, their high energy density and good cyclebility. In order to decrease the price while also further improving the energy density, it has become more popular during the last few years to increase the nickel content, being responsible for the redox process thereby contributing to a larger capacity. By increasing the nickel content, the quantity of cobalt required will decrease further, reducing the price. However it is also well known that in materials where the nickel content is high the surface side reactions will be augmented leading to more degradation and shorter cycle life. A high nickel content will not only affect the electrochemical side reactions during cycling, it has also been found that as NMC materials are exposed to air they will react differently, with more reactions for the nickel rich materials.It has been found that the NMC can react with H2O to form a LiOH layer and that once the layer is thick enough further side reactions would be prevented.1 It was assumed that the passivation was caused by the deintercalation of lithium, where the thin disordered rock salt layer would mitigate the Li+-water reactions through decreasing the amount of lithium deintercalation.1 Furthermore, the surface impurities formed during the air exposure have been observed to directly impact electrochemical performance during the first couple of cycles. Hatsukade et al. used isotopic labelling in order to measure the CO2 formation during the first cycles originating from the oxidative decomposition of these impurities.2 Air exposure has been shown to affect not only the first few cycles but also long term cycling as well.3 The degradation of the NMC has been found to be caused by phase transformation into rock salt and spinel structure, leading to nickel reduction and as a result formation of inter granular cracks, eventually leading to isolation of the active particles and increased charge transfer resistance.4 In this study the surface interactions at NMC electrodes during air exposure will be presented, showing both how the interactions take place as well as how the air exposure will affect the electrode-electrolyte interfaces during cycling. The NMC surface is analysed by x-ray photoelectron spectroscopy (XPS), photoemission electron microscopy (PEEM) and x-ray absorption spectroscopy (XAS). Zou, L. et al. Unlocking the passivation nature of the cathode–air interfacial reactions in lithium ion batteries. Nat. Commun. 11, (2020).Hatsukade, T., Schiele, A., Hartmann, P., Brezesinski, T. & Janek, J. Origin of Carbon Dioxide Evolved during Cycling of Nickel-Rich Layered NCM Cathodes. ACS Appl. Mater. Interfaces 10, 38892–38899 (2018).Meatza, I. De, Landa-medrano, I., Sananes-israel, S. & Eguia-barrio, A. Powder and Electrodes on the Electrochemical Performance in Li-ion Technology. Batteries 8, 1–18 (2022).Busà, C., Belekoukia, M. & Loveridge, M. J. The effects of ambient storage conditions on the structural and electrochemical properties of NMC-811 cathodes for Li-ion batteries. Electrochim. Acta 366, (2021).

Ex-Situ Studies of Hydraulic Pressure Effect on the Electrochemical, Structural and Morphological Properties of Nickel-Rich NMC

The development of industry and technology, as well as the Earth's growing population, is forcing an ever-increasing demand for energy and raw materials. In tandem with this demand, efficient energy storage is also necessary and equally important. One of the most attractive forms of energy storage, has proven to be electrochemical cells, which allow the conversion of chemical reaction energy into electricity. The most promising cell type turned out to be lithium-ion batteries, and this was due to the attractive properties of lithium, which have the high negative standard potential (about -3 V) and high specific capacity (3860 Ah kg-1) 1. The majority of commercial lithium-ion batteries (LIB) are manufactured using roll-to-roll (R2R) wet processing technology (i.e., the slurry method), where active battery powder, conductive carbon powder and inactive binding agent are mixed in a organic solvent , cast onto metallic current collectors and then dried 2. Up next, the electrode layers undergo a calendaring process in which they are compressed. It is important to clarify the effect of hydraulic pressure on the properties of electrode materials and correlate this relationship to its type and characteristics. An inadequate selection of hydraulic pressure conditions can adversely affect the properties of the active battery material, leading to grain cracking and thus the capacity drop. The phenomenon of cracking of nickel-rich NMC secondary particles is considered to be the one of the critical causes that deteriorate the long-term cyclic stability of the NMC cathode in lithium-ion batteries 2,3.In this study various methods are applied to observe and understand the electrode properties that accompany grain fracture and electrode preparation conditions. Morphological changes that occur before and after the electrode calendaring and further the cell’s operation can be examined by scanning electron microscopy (SEM). This technique can be used as a tool to gather information about the composition of cathode materials while tracking a realistically operating battery 3. Another analysis technique is the ex-situ Raman spectroscopy, which allows us to gather detailed information on the local properties of the electrode material. It provides details on phase transitions and the causes of capacity loss over successive battery cycles 4. The information about grain size, crystallographic parameters and the phases present in the sample, can be gathered by X-ray diffraction (XRD). In this research all these methods will be employed to identify possible defects present in electrode materials before and after cycling with regard to applied hydraulic pressure during electrode preparation. We will determine the most suitable hydraulic pressure conditions and correlate our results with initial material morphology and crystallographic structure as well as the electrochemical response. A detailed data analysis will be reported at the conference. Funding for this work was provided by the National Science Center in Poland under the Sonata BIS 11 program (No. UMO-2021/42/E/ST5/00390). A. Czerwiński. Akumulatory, baterie, ogniwa. (2005). Kirsch, D. J. et al. Scalable Dry Processing of Binder-Free Lithium-Ion Battery Electrodes Enabled by Holey Graphene. ACS Appl Energy Mater 2, 2990–2997 (2019). Cheng, X. et al. Real-Time Observation of Chemomechanical Breakdown in a Layered Nickel-Rich Oxide Cathode Realized by in Situ Scanning Electron Microscopy. ACS Energy Lett 6, 1703–1710 (2021). Flores, E., Novák, P. & Berg, E. J. In situ and Operando Raman spectroscopy of layered transition metal oxides for Li-ion battery cathodes. Front Energy Res 6, (2018).

Thermodynamic Stability of LixNiO2 and Polyvinylidene Difluoride Materials for Lithium+ Ion Batteries

LixNiO2 (LNO), a layered Li-ion battery cathode has been investigated for decades. LNO has been shown to proceed through multiple phase transitions at different states of lithiation as well as at different temperatures. However, in these experiments it has always been paired with additional materials typically found in the creation of cathodes, such as carbon black, aluminum foil and polyvinylidene difluoride binder. This paper investigates the thermal stability of LNO as a stand-alone material as well as a component of a traditional cathode through performing thermal gravimetric analysis (TGA), variable temperature powdered X-ray diffraction (VT-PXRD) and solid-state nuclear magnetic resonance (ss-NMR) at different states of lithiation and high temperatures. The reduction to nickel metal was found at temperatures exceeding 500 °C for the traditional cathodes at all states of charge due to the creation of lithium fluoride from hydrogen fluoride gas being released as polyvinylidene difluoride degrades. Nickel metal was also identified for the stand-alone LNO at lithium concentrations greater than x = 0.32 at temperatures of 600 °C as the system becomes depleted of oxygen and lithium due to the creation of lithium oxide. These finding indicate that the thermal stability of LNO at temperatures over 200 °C is sensitive to the presence of fluorine as well as the state of charge of the battery. Typical batteries do not reach these temperatures during cycling, but in the case of thermal runaway and recycling it is important to know the chemical reactions occurring at these temperatures and concentrations as toxic and corrosive hydrogen fluoride gas is released. An investigation into less fluorinated binder options is desirable to reduce the addressed issues.

Analyzing the Li-Al-O Interphase of Atomic Layer-Deposited Al2O3 Films on Layered Oxide Cathodes Using Atomistic Simulations.

Alumina surface coatings are commonly applied to layered oxide cathode particles for lithium-ion battery applications. Atomic layer deposition (ALD) is one such surface coating technique, and ultrathin alumina ALD films (<2 nm) are shown to improve the electrochemical performance of LiNixMnyCo1-x-yO2 materials, with groups hypothesizing that a beneficial Li-Al-O product is being formed during the alumina ALD process. However, the atomic structure of these films is still not well understood, and quantifying the interface of ultrathin (∼1 nm) ALD films is an arduous experimental task. Here, we perform molecular dynamics simulations of amorphous alumina films of varying thickness in contact with the (0001) LiCoO2 (LCO) surface to quantify the film nanostructure. We calculate elemental mass density profiles through the films and observe that the Li-Al-O interphase extends ∼2 nm from the LCO surface. Additionally, we observe layering of Al and O atoms at the LCO-film interface that extends for ∼1.5 nm. To access the short-range order of the amorphous film, we calculated the Al coordination numbers through the film. We find that while [4]Al is the prevailing coordination environment, significant amounts of [6]Al exist at the interface between the LiCoO2 surface and the film. Taken together, these principal findings point to a pseudomorphic Li-Al-O overlayer that approximates the underlying layered LiCoO2 lattice but does not exactly replicate it. Additionally, with sufficient thickness, the Li-Al-O film transitions to an amorphous alumina structure. We anticipate that our findings on the ALD-like, Li-Al-O film nanostructure can be applied to other layered LiNixMnyCo1-x-yO2 materials because of their shared crystal structure with LiCoO2. This work provides insight into the nanostructure of amorphous ALD alumina films to help inform their use as protective coatings for Li-ion battery cathode active materials.

Characterization and process optimization of remote laser cutting of current collectors for battery electrode production

Aluminum (Al) and copper (Cu) metal foils of thickness 6–20 µm are employed as current collectors for the production of Li-ion battery cathodes and anodes. Greater demand for this product is driving up production rate requirements, especially in the field of car manufacturing. Laser-based cutting processes for trimming and cutting electrodes are considered suitable for meeting this demand as they can achieve very high throughput while maintaining process quality. In order to meet market requirements, laser manufacturers are developing new laser sources, optics, and scanning heads that will improve process productivity and quality. Establishing the relationship between the laser system and cut quality will lead to competitiveness, increased productivity, and sustainability production. This paper presents a thorough analysis of the cutting performance of pulsed and continuous-wave lasers with scanning speeds of up to 28 m/s for processing thin Al and Cu current collectors. Comparisons between process outcomes are made in terms of maximum and minimum cutting speed and power, kerf geometry, cut quality, and presence of defects. Identification of configurations leading to high and low cut quality enables detailed process parameter windows to be defined for both laser system systems employing continuous-wave and pulsed sources. By analyzing correlations between the materials, laser source, and process variables, the main outcome is that continuous-wave single-mode fiber lasers enable highest cut quality in the high-productivity regime, surpassing the current state-of-the-art in laser cutting of metal foils.

Scalable Precursor-Assisted Synthesis of a High Voltage LiNiyCo1-yPO4 Cathode for Li-Ion Batteries.

A solid-solution cathode of LiCoPO4-LiNiPO4 was investigated as a potential candidate for use with the Li4Ti5O12 (LTO) anode in Li-ion batteries. A pre-synthesized nickel-cobalt hydroxide precursor is mixed with lithium and phosphate sources by wet ball milling, which results in the final product, LiNiyCo1-yPO4 (LNCP) by subsequent heat treatment. Crystal structure and morphology of the product were analyzed by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Its XRD patterns show that LNCP is primarily a single-phase compound and has olivine-type XRD patterns similar to its parent compounds, LiCoPO4 and LiNiPO4. Synchrotron X-ray absorption spectroscopy (XAS) analysis, however, indicates that Ni doping in LiCoPO4 is unfavorable because Ni2+ is not actively involved in the electrochemical reaction. Consequently, it reduces the charge storage capability of the LNCP cathode. Additionally, ex situ XRD analysis of cycled electrodes confirms the formation of the electrochemically inactive rock salt-type NiO phase. The discharge capacity of the LNCP cathode is entirely associated with the Co3+/Co2+ redox couple. The electrochemical evaluation demonstrated that the LNCP cathode paired with the LTO anode produced a 3.12 V battery with an energy density of 184 Wh kg-1 based on the cathode mass.

A layered/spinel heterostructured cathode for Li-ion batteries prepared by ultrafast Joule heating

Spinel LiMn2O4 is one of the most promising cathode materials due to its low cost, high discharge voltage (∼4.0 V), and non-toxicity. However, it suffers from insufficient cycling performance caused by irreversible phase transition and Mn dissolution. In addition, the low synthesis efficiency caused by the long heating time also plagues its application and depletes the cost merits of raw materials. Herein, we report a heterostructured cathode material of electrochemically-inert layered Li2MnO3 and active spinel LiMn2O4 phases, which is synthesized in seconds by ultrafast Joule heating. The heterostructure is rapidly formed as a result of the non-equilibrium process produced by the ultrafast Joule heating rate. The inert layered phase serves as a structure stabilization agent to suppress the structure damage and Mn dissolution, thus promising an excellent electrochemical performance with a high capacity retention of 83 % after 800 cycles at 5C. Our findings provide an efficient design and synthesis strategy for developing high-performance and low-cost cathode materials.

Imaging Voids and Defects Inside Li-Ion Cathode LiNi0.6Mn0.2Co0.2O2 Single Crystals.

Li-ion battery cathode active materials obtained from different sources or preparation methods often exhibit broadly divergent performance and stability despite no obvious differences in morphology, purity, and crystallinity. We show how state-of-the-art, commercial, nominally single crystalline LiNi0.6Mn0.2Co0.2O2 (NMC-622) particles possess extensive internal nanostructure even in the pristine state. Scanning X-ray diffraction microscopy reveals the presence of interlayer strain gradients, and crystal bending is attributed to oxygen vacancies. Phase contrast X-ray nano-tomography reveals two different kinds of particles, welded/aggregated, and single crystal like, and emphasizes the intra- and interparticle heterogeneities from the nano- to the microscale. It also detects within the imaging resolution (100 nm) substantial quantities of nanovoids hidden inside the bulk of two-thirds of the overall studied particles (around 3000), with an average value of 12.5%v per particle and a mean size of 148 nm. The powerful combination of both techniques helps prescreening and quantifying the defective nature of cathode material and thus anticipating their performance in electrode assembly/battery testing.

Using Laterite-Nickel Ore as Raw Material, Study on the Efficient Separation of Silicon with NaOH Alkaline Auxiliary Agent to Prepare Li2MnSiO4 Cathode for Li-ion Battery

Using Laterite-Nickel Ore as Raw Material, Study on the Efficient Separation of Silicon with NaOH Alkaline Auxiliary Agent to Prepare Li2MnSiO4 Cathode for Li-ion Battery

Migration of binder and conductive agent during drying process of Li-ion battery cathodes

Drying of an electrode film during a wet coating process for Li-ion batteries often leads to a heterogeneous distribution of the binder and conductive agent in the film thickness direction. Because this heterogeneous distribution affects battery performance and durability, understanding and controlling the migration behavior are important. Herein, the distribution of the components (active material/conductive agent/binder) of a cathode is investigated by a novel method and their relationship with the electrode properties is determined. The binder distribution is investigated via two methods: pyrolysis gas chromatography mass spectrometry (Py-GC/MS) analysis of cut electrodes, and low-voltage scanning electron microscopy with energy-dispersive X-ray spectroscopy. In the sample dried at 30 °C, more binder and conductive agent exists in the bottom layer. With increasing drying temperature, the binder and conductive agent migrate from the bottom to the surface because they are transported by capillary-driven convective flow through the pores between the active material particles. Drying at high temperatures causes migration, resulting in reduced adhesion between the electrode film and the current collector, and increases the electrode resistance. The Py-GC/MS method of characterizing the cut electrodes is shown to be a complementary method that can analyze a wider area than cross-sectional observation.

First-principle study on the geometric and electronic structure of Mg-doped LiNiO2 for Li-ion batteries.

Ni-rich layered oxides have been widely studied as cathodes because of their high energy density. However, the gradual structural transformation during the cycle will lead to the capacity degradation and potential decay of the cathode materials. In this paper, first-principle calculations were used to investigate the formation energy, and geometric and electronic structure of Mg-doped LiNiO2 cathode for Li-ion batteries. The results show that Mg doping has little effect on the geometric structure of LiNiO2 but has great effect on its electronic structure. Our data give an insight into the microscopic mechanism of Mg-doped LiNiO2 and provide a theoretical reference for experimental research, which is helpful to the design of safer and higher energy density Ni-rich cathodes. In this work, all calculations were performed by the VASP package; the PBE functional in the generalized gradient approximation (GGA) was employed to describe the exchange-correlation interactions. An energy cutoff of 520eV and a 5 × 5 × 3 Monkhorst-Pack mesh of k-point sampling in the Brillouin zone were chosen for all calculations. All atoms were relaxed until the convergences of 10-5eV/f.u in energy and 0.01eV/Å in force were reached.

Removal of lithium, sodium, and phosphate from the Li-ion battery cathode recycling process using column adsorption

Lithium Ion Battery (LIB) is one type of battery whose demand is increasing every year. After the Li-ion battery usage cycle ends, more and more waste is generated. Wastewater from the LFP battery cathode recycling process still contains metals such as lithium, sodium, and phosphate. This experiment was carried out using the adsorption method. The adsorption method is used to remove metal ions in LFP battery waste. The adsorption process took place in a semi-continuous fixed-bed column made of glass cylinders with a height of 50 cm and a diameter of 2.5 cm. The artificial waste solution flowed into a column containing 135 g of activated carbon with variations in flow rates of 10, 15, and 20 mL/min for 2 hours. The concentration of the initial solution and the filtrate was analyzed using an Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). The experimental results showed that the maximum percentage removal of lithium, sodium, and phosphate at a flow rate of 10 mL/min was 95.22%, 96.42%, and 68.02%, respectively. In addition, the results of the adsorption kinetic studies reviewed using the Thomas and Yoon-Nelson models showed that the column adsorption performance for lithium, sodium, and phosphate was most effective at a flow rate of 10 mL/min with an adsorption capacity of 8.75.105 mg/g, 8.85.105 mg/g, and 3.91.105 mg/g, respectively. Meanwhile, the breakthrough times for lithium, sodium, and phosphate were 335 minutes, 441 minutes, and 126 minutes, respectively.