In Situ and Operando Analyses of Reaction Mechanisms in Vanadium Oxides for Li‐, Na‐, Zn‐, and Mg‐Ions Batteries

Abstract: Due to their diversity in the composition, lattice structures and physical/chemical properties, and various oxidation states (2+, 3+, 4+, and 5+), (V x O y ) nanomaterials have attached much attention for developing new rechargeable batteries, including lithium‐ion batteries (LIBs), sodium‐ion batteries (NIBs), zinc‐ion batteries (ZIBs), and magnesium‐ion batteries (MIBs) as well as new energy storage concepts such as light‐rechargeable batteries. However, to further improve the electrochemical performance of V x O y ‐based batteries, it is crucial to understand the various electrochemical mechanisms taking place in these materials for LIBs, NIBs, ZIBs, and MIBs. This review covers a systematical discussion of in situ and operando analysis methods carried out on V2O5, VO2, Li x V y O z , Na x V y O z , Zn x V y O z , and Mg x V y O z for LIBs, NIBs, ZIBs, and MIBs and the fundamental insights they have provided in the energy storage mechanisms in these batteries

Understanding the limits of Li-NMC811 half-cells

As we push the boundaries of state-of-the-art lithium-ion intercalation materials, such as nickel-rich chemistries, the ability to isolate and understand specific degradation and performance limitations is becoming increasingly important. Half-cells, wherein lithium metal is employed as a dual counter and reference electrode, are commonly used in industry and academia for this purpose. However, the high reactivity of lithium metal drives premature electrolyte degradation and limits cell lifetime, bringing into question the reliability and validity of this cell configuration. Here we explore the limitations of half-cell studies of LiNi0.8Mn0.1Co0.1O2 (NMC811) electrodes with commercially relevant loading. We identify the failure mechanism of this cell configuration through a combination of electrochemical, chemical, and spectroscopic techniques and show that the Li has a direct detrimental impact on the NMC811 chemistry. Our measurements show that vinylene carbonate is critical for these half-cell studies and underpins the cycle limits. Furthermore, we demonstrate the use of Li4Ti5O12 (LTO) as an alternative counter electrode for understanding the performance of NMC positive electrode materials, due to its high coulombic efficiency and low reactivity with the organic carbonates routinely employed in lithium-ion battery cell chemistries. These data confirm that NMC811 electrodes can tolerate high voltages (stressed) conditions and that cell failure is mainly a result of crossover effects

Onset Potential for Electrolyte Oxidation and Ni-Rich Cathode Degradation in Lithium-Ion Batteries

High-capacity Ni-rich layered metal oxide cathodes are highly desirable to increase the energy density of lithium-ion batteries. However, these materials suffer from poor cycling performance, which is exacerbated by increased cell voltage. We demonstrate here the detrimental effect of ethylene carbonate (EC), a core component in conventional electrolytes, when NMC811 (LiNi0.8Mn0.1Co0.1O2) is charged above 4.4 V vs Li/Li+-the onset potential for lattice oxygen release. Oxygen loss is enhanced by EC-containing electrolytes-compared to EC-free-and correlates with more electrolyte oxidation/breakdown and cathode surface degradation, which increase concurrently above 4.4 V. In contrast, NMC111 (LiNi0.33Mn0.33Co0.33O2), which does not release oxygen up to 4.6 V, shows a similar extent of degradation irrespective of the electrolyte. This work highlights the incompatibility between conventional EC-based electrolytes and Ni-rich cathodes (more generally, cathodes that release lattice oxygen such as Li-/Mn-rich and disordered rocksalt cathodes) and motivates further work on wider classes of electrolytes and additives

High voltage structural evolution and enhanced Na-ion diffusion in P2-Na2/3Ni1/3-xMgxMn2/3O2 (0 < x < 0.2) cathodes from diffraction, electrochemical and ab initio studies

We have presented a detailed investigation of the effects of Mg substitution on the structure, electrochemical performance and Na-ion diffusion in high voltage P2-type Na2/3Ni1/3-xMgxMn2/3O2 (0 <x< 0.20) cathode materials for Na-ion batteries. Structural analysis using neutron diffraction showed that Mg2+ substitutes random Ni2+ on the 2b sites from ordered [(Ni2+/Mn4+)O6] honeycomb units along the ab-plane, leading to an AB-type structure that can be indexed using the P63 space group. Within the sodium layers, high Mg-substituting levels (i.e. x = 0.2) caused a disruption in the typical Na zig-zag ordering observed in the undoped material, leading to a more disordered Na distribution in the layers. Load curves of the x = 0.1, 0.2 materials show smooth electrochemistry, indicative of a solid-solution process. Furthermore, DFT calculations showed an increase on Na-ion diffusivity on the Mg-substituted samples. Enhanced cycling stability was also observed in these materials; structural analysis using high-resolution in-operando synchrotron X-ray diffraction show that such an improved electrochemical performance is caused by the suppression of the O2 phase and switch to the formation of an OP4 phase. Ab-initio studies support our experimental evidence showing that the OP4 phase (cf. O2) is the most thermodynamically stable phase at high voltages for Mg-substituted compounds. Finally, we have provided evidence using diffraction for the x = 1/2 and x = 1/3 intermediate Na+-vacancy ordered phases in P2-Na 2/3Ni1/3Mn2/3O2

Synergistic Degradation Mechanism in Single Crystal Ni-Rich NMC//Graphite Cells

Acknowledgments We acknowledge Diamond Light Source for time on beamline I09 under Proposals SI30201-1 and SI30201-2. This work is supported by the Faraday Institution under Grants FIRG044, FIRG024, and FIRG060.Peer reviewedPublisher PD

Heat treated electrolytic manganese dioxide for Li/MnO2 batteries: effect of precursor properties

The present study demonstrates that the properties of heat-treated electrolytic manganese dioxide (EMD) materials can be linked to the key properties of the precursor EMD used. The investigation holds particular significance for the informed selection of precursor EMD materials that result in superior performing heat treated materials in Li/MnO₂ batteries. Kinetic analysis is used to determine the precise heating regime necessary to, theoretically, completely remove structural water from six different EMD samples. It was found that the oxidation of Mn(III) to Mn(IV) occurred to a greater extent for samples with initially high pyrolusite content and a low fraction of cation vacancies after heat treatment at low temperatures. This same Mn(III) to Mn(IV) conversion was also enhanced after high temperature treatment for those samples with a higher manganese content and low cation vacancy fraction. Additionally, at low heat treatment temperatures the parent γ-MnO₂ structure and cation vacancies were better retained in samples with low starting BET surface area. Finally, this work determined that samples with high BET surface area tend to lose proportionally less of this value as a consequence of heat treatment, compared to those with low initial values

Cathode pre-lithiation/sodiation for next-generation batteries

Electrochemical energy storage (EES) is playing a pivotal role in the global pursuit of a clean and sustainable energy future. Lithium-ion batteries (LIBs) are the state-of-the-art technology but future energy requirements demand higher energy densities and a more diverse battery landscape to meet a wide variety of applications. Unfortunately, many next-generation LIB chemistries and beyond-LIB technologies suffer from large first cycle irreversible capacity caused by active ion loss (AIL). The field of pre-lithiation/sodiation have recently emerged as researchers attempt to mitigate AIL and boost the energy density of next-generation LIBs and sodium-ion batteries (SIBs). In this short review, we highlight recent advances in cathode prelithiation/sodiation using sacrificial additives and pre-lithiation/sodiation of cathode active materials (CAMs).W.D. acknowledges support from the Faraday Institution degradation project (FIRG001) and EPSRC (EP/S003053/1). C.J. acknowledges support from the Vehicle Technologies Program, Hybrid and Electric Systems, of the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy. Argonne National Laboratory is operated under Contract No. DE-AC02-06CH1135

Thermal expansion of manganese dioxide using high-temperature in situ X-ray diffraction

High-temperature in situ X-ray diffraction is used to determine the thermal expansion behaviour of manganese dioxide in air at temperatures between 298 and 673 K, the range accessible prior to material decomposition. Two manganese dioxide samples of different origins are investigated to observe the effect of synthesis conditions and resultant material properties on the thermal response. β-MnO2 prepared by a chemical pathway is found to expand linearly over the temperature window with thermal expansion coefficients (in units of K-1) of aa = 9.3 (4) × 10-6, ac = 7.0 (2) × 10-6 and ß = 25.6 (8) × 10-6. Conversely, the thermal expansion of heat-treated electrolytic manganese dioxide is disjointed about 473 K in the a direction and for the overall unit-cell volume, and about 523 K in the c direction. Coefficients are therefore given (in units of K-1) as aa = 23 (4) × 10-6 (298-473 K), 10 (3) × 10-6 (473-673 K); ac = 0.2 (9) × 10-6 (298-523 K), 10 (1) × 10-6 (523-673 K); and ß = 49 (9) × 10-6 (298-473 K), 26 (5) × 10-6 (473-673 K)

Thermal treatment effects on manganese dioxide structure, morphology and electrochemical performance

Kinetic analysis is used to determine the required isothermal heating time at various temperatures to theoretically completely remove water from an electrolytic manganese dioxide (EMD) sample. The effect of the heat treatment regime on material structure, morphology and composition is investigated using various physical techniques, including X-ray diffraction and gas adsorption. Further, the electrochemical performance of heat treated EMD (HEMD) samples at a range of discharge rates finds that material properties such as retention of the γ-MnO₂ structure and high surface area for the sample heat treated at 250°C, and extensive structural conversion and micro-pore closure in the case of the 350°C material, lead to higher capacity and power output. Conversely, significant amounts of structural water in the 200°C sample, and the compromise in structural rearrangement and surface area loss for the material prepared at 300°C, result in poor electrochemical behaviour, especially at high discharge rates. Particularly evident from this study is the complex interplay between the heat treatment regime, resulting HEMD properties and electrochemical performance