Surface analytical approaches to reliably characterize lithium ion battery electrodes

Fabrication of Single-Ion Conductors Based on Liquid Crystal Polymer Network for Quasi-Solid-State Lithium Ion Batteries

Single-ion conductive polymer electrolytes can improve the safety of lithium ion batteries (LIBs) by increasing the lithium transference number (tLi+) and avoiding the growth of lithium dendrites. Meanwhile, the self-assembled ordered structure of liquid crystal polymer networks (LCNs) can provide specific channels for the ordered transport of Li ions. Herein, single-ion conductive nematic and cholesteric LCN electrolyte membranes (denoted as NLCN-Li and CLCN-Li) were successfully prepared. NLCN-Li was then coated on commercial Celgard 2325 while CLCN-Li was coated on poly(vinylidene fluoride-hexafluoropropylene) film, coupled with plasticizer, to make NLCN-Li/Cel and CLCN-Li/Pv quasi-solid-state electrolyte membranes, respectively. Their electrochemical properties were evaluated, and it was found that they possessed benign thermal stability and electrolyte/electrode compatibility, high tLi+ up to 0.98 and high electrochemical stability window up to 5.2 V. A small amount (0.5M) of extra Li salt added to the plasticizer could improve the ion conductivity from 1.79 × 10-5 to 5.04 × 10-4 S cm-1, while the tLi+ remained 0.85. The assembled LFP|Li batteries also exhibited excellent cycling and rate performances. The orderliness of the LCN layer played an important role in the distribution and movement of Li ions, thereby affecting the Li deposition and growth of Li dendrites. As the first report of nematic and cholesteric LCN single-ion conductors, this work sheds light on the design and fabrication of ordered quasi-solid-state electrolytes for high-performance and safe LIBs.

An XPS Study of Electrolytes for Li-Ion Batteries in Full Cell LNMO vs Si/Graphite

Two different types of electrolytes (co-solvent and multi-salt) are tested for use in high voltage LiNi0.5Mn1.5O4||Si/graphite full cells and compared against a carbonate-based standard LiPF6 containing electrolyte (baseline). Ex situ postmortem XPS analysis on both anodes and cathodes over the life span of the cells reveals a continuously growing SEI and CEI for the baseline electrolyte. The cells cycled in the co-solvent electrolyte exhibited a relatively thick and long-term stable CEI (on LNMO), while a slowly growing SEI was determined to form on the Si/graphite. The multi-salt electrolyte offers more inorganic-rich SEI/CEI while also forming the thinnest SEI/CEI observed in this study. Cross-talk is identified in the baseline electrolyte cell, where Si is detected on the cathode, and Mn is detected on the anode. Both the multi-salt and co-solvent electrolytes are observed to substantially reduce this cross-talk, where the co-solvent is found to be the most effective. In addition, Al corrosion is detected for the multi-salt electrolyte mainly at its end-of-life stage, where Al can be found on both the anode and cathode. Although the co-solvent electrolyte offers superior interface properties in terms of the limitation of cross-talk, the multi-salt electrolyte offers the best overall performance, suggesting that interface thickness plays a superior role compared to cross-talk. Together with their electrochemical cycling performance, the results suggest that multi-salt electrolyte provides a better long-term passivation of the electrodes for high-voltage cells.

Effect of Potassium Promoter on the Performance of Nickel-Based Catalysts Supported on MnOx in Steam Reforming of Ethanol

The effect of a potassium promoter on the stability of and resistance to a carbon deposit formation on the Ni/MnOx catalyst under SRE conditions was studied at 420 °C for different H2O/EtOH molar ratios in the range from 4/1 to 12/1. The catalysts were prepared by the impregnation method and characterized using several techniques to study their textural, structural, and redox properties before being tested in a SRE reaction. The catalytic tests indicated that the addition of a low amount of potassium (1.6 wt.%) allows a catalyst with high stability to be obtained, which was ascribed to high resistance to carbon formation. The restriction of the amount of carbon deposits originates from the potassium presence on the Ni surface, which leads to (i) a decrease in the number of active sites available for methane decomposition and (ii) an increase in the rate of the steam gasification of carbon formed during SRE reactions.

Efficient and stable perovskite solar cells using manganese-doped nickel oxide as the hole transport layer

The device based on a Mn-doped NiOx HTL retained 70% of its initial efficiency after 35 days’ storage under a continuous halogen lamp matrix exposure.

High Entropy and Low Symmetry: Triclinic High-Entropy Molybdates

Metal molybdates constitute a promising class of materials with a wide application range. Here, we report, to our knowledge for the first time, on the preparation and characterization of medium-entropy and high-entropy metal molybdates, synthesized by an oxalate-based coprecipitation approach. The high-entropy molybdate crystallizes in a triclinic structure, thus rendering it as high-entropy material with the lowest symmetry reported so far. This is noteworthy because high-entropy materials usually tend to crystallize into highly symmetrical structures. It is expected that application of the high-entropy concept to metal molybdates alters the material's characteristics and adds the features of high-entropy systems, that is, tailorable composition and properties. The phase purity and solid solution nature of the molybdates were confirmed by XRD, Raman spectroscopy, TEM, XPS, and ICP-OES.

Lithium containing layered high entropy oxide structures

Layered Delafossite-type Lix(M1M2M3M4M5…Mn)O2 materials, a new class of high-entropy oxides, were synthesized by nebulized spray pyrolysis and subsequent high-temperature annealing. Various metal species (M = Ni, Co, Mn, Al, Fe, Zn, Cr, Ti, Zr, Cu) could be incorporated into this structure type, and in most cases, single-phase oxides were obtained. Delafossite structures are well known and the related materials are used in different fields of application, especially in electrochemical energy storage (e.g., LiNixCoyMnzO2 [NCM]). The transfer of the high-entropy concept to this type of materials and the successful structural replication enabled the preparation of novel compounds with unprecedented properties. Here, we report on the characterization of a series of Delafossite-type high-entropy oxides by means of TEM, SEM, XPS, ICP-OES, Mössbauer spectroscopy, XRD including Rietveld refinement analysis, SAED and STEM mapping and discuss about the role of entropy stabilization. Our experimental data indicate the formation of uniform solid-solution structures with some Li/M mixing.

Synthesis and Characterization of a Multication Doped Mn Spinel, LiNi0.3Cu0.1Fe0.2Mn1.4O4, as 5 V Positive Electrode Material

The suitability of multication doping to stabilize the disordered Fd3̅m structure in a spinel is reported here. In this work, LiNi0.3Cu0.1Fe0.2Mn1.4O4 was synthesized via a sol-gel route at a calcination temperature of 850 °C. LiNi0.3Cu0.1Fe0.2Mn1.4O4 is evaluated as positive electrode material in a voltage range between 3.5 and 5.3 V (vs Li+/Li) with an initial specific discharge capacity of 126 mAh g-1 at a rate of C/2. This material shows good cycling stability with a capacity retention of 89% after 200 cycles and an excellent rate capability with the discharge capacity reaching 78 mAh g-1 at a rate of 20C. In operando X-ray diffraction (XRD) measurements with a laboratory X-ray source between 3.5 and 5.3 V at a rate of C/10 reveal that the (de)lithiation occurs via a solid-solution mechanism where a local variation of lithium content is observed. A simplified estimation based on the in operando XRD analysis suggests that around 17-31 mAh g-1 of discharge capacity in the first cycle is used for a reductive parasitic reaction, hindering a full lithiation of the positive electrode at the end of the first discharge.

In Situ X-ray Diffraction and X-ray Absorption Spectroscopic Studies of a Lithium-Rich Layered Positive Electrode Material: Comparison of Composite and Core-Shell Structures

Lithium- and manganese-rich transition-metal oxide (LMR-NMC) electrodes have been designed either as heterostructures of the primary components ("composite") or as core-shell structures with improved electrochemistry reported for both configurations when compared with their primary components. A detailed electrochemical and structural investigation of the 0.5Li₂MnO₃-0.5LiNi_0.5Mn_0.3Co_0.2O₂ composite and core-shell structured positive electrode materials is reported. The core-shell material shows better overall electrochemical performance compared to its corresponding composite material. While both configurations gave the same initial charge capacity of ∼300 mAh/g when cycled at a rate of 10 mA/g at 25 °C, the core-shell sample gives a discharge capacity of 232 mAh/g compared to 208 mAh/g delivered by the composite sample. Also, the core-shell sample gave better rate capability and a smaller first-cycle irreversible capacity loss than the composite sample. The improved performance of the core-shell material is attributed to its lower surface reactivity and limited structural change since the more stable Li₂MnO₃ shell screens the more reactive Ni-rich core material from interacting with either air or electrolyte at high potentials, thereby preventing electrode surface modification. In situ X-ray diffraction correlated with electrochemical data revealed that the composite sample shows stronger volumetric changes in the lattice parameters during charging to 4.8 V. In addition, X-ray absorption spectroscopy showed an incomplete Ni reduction process after the first discharge for the composite sample. From these results, it was shown that this leads to a more severe degradation in the composite material that affects Li⁺ intercalation in the subsequent discharge, thereby resulting in its poorer performance. Furthermore, to confirm these results, another LMR-NMC material with a different composition (having a Ni-poor core)-0.5Li₂MnO₃-0.5LiNi_0.33Mn_0.33Co_0.33O₂-was investigated. The core-shell structured positive electrode material also gave an improved electrochemical performance compared to the corresponding composite positive electrode material. These results show that the core-shell configuration could effectively be used to improve the performance of the LMR-NMC materials to enable future high-energy applications.

Spinel to Rock-Salt Transformation in High Entropy Oxides with Li Incorporation

High entropy oxides (HEOs) constitute a promising class of materials with possibly new and largely unexplored properties. The virtually infinite variety of compositions (multi-element approach) for a single-phase structure allows the tailoring of their physical properties and enables unprecedented materials design. Nevertheless, this level of versatility renders their characterization as well as the study of specific processes or reaction mechanisms challenging. In the present work, we report the structural and electrochemical behavior of different multi-cationic HEOs. Phase transformation from spinel to rock-salt was observed upon incorporation of monovalent Li+ ions, accompanied by partial oxidation of certain elements in the lattice. This transition was studied by X-ray diffraction, inductively coupled plasma-optical emission spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and attenuated total reflection infrared spectroscopy. In addition, the redox behavior was probed using cyclic voltammetry. Especially, the lithiated rock-salt structure HEOs were found to exhibit potential for usage as negative and positive electrode materials in rechargeable lithium-ion batteries.

Study of Immersion of LiNi0.5Mn0.3Co0.2O2 Material in Water for Aqueous Processing of Positive Electrode for Li-Ion Batteries

The understanding of the phenomena occurring during immersion of LiNi_0.5Mn_0.3Co_0.2O₂ (NMC) in water is helpful to devise new strategies toward the implementation of aqueous processing of this high-capacity cathode material. Immersion of NMC powder in water leads to both structural modification of the particles surface as observed by high-resolution scanning transmission electron microscopy and the formation of lithium-based compounds over the surface (LiOH, Li₂CO₃) in greater amount than after long-time exposure to ambient air, as confirmed by pH titration and ⁷Li MAS NMR analysis. The surface compounds adversely affect the electrochemical performance and are notably responsible for the alkaline pH of the aqueous slurry, which causes corrosion of the aluminum collector during coating of the electrode. The corrosion is avoided by adding phosphoric acid to the slurry as it lowers the pH, and it also enhances the cycling stability of the water-based electrodes due to the phosphate compounds formed at the particles surface, as evidenced by X-ray photoelectron spectroscopy analysis.

In Operando analysis of the charge storage mechanism in a conversion ZnCo2O4 anode and the application in flexible Li-ion batteries

Intermediate phases of LiCo₂O₃, CoO and ZnO are evidenced during the 1^st lithiation of a ZnCo₂O₄ anode.

High electrochemical performance of 3D highly porous Zn0.2Ni0.8Co2O4 microspheres as an electrode material for electrochemical energy storage

3D highly porous Zn_0.2Ni_0.8Co₂O₄ microspheres unveil superior electrochemical energy storage properties.