Layered Nickel Research Articles

Monitoring the Electrochemical Capacitance By in Situ Impedance Spectroscopy As Indicator for Particle Cracking of (Nickel-Rich) Cathode Active Materials: Development of a Simplified Measurement Setup

Due to their high specific capacity, the market share of nickel-rich layered lithium nickel cobalt manganese oxides (NCMs, LiNixCoyMnzO2, x+y+z = 1) as cathode active materials (CAMs) for lithium-ion batteries is constantly growing. With higher nickel content, however, the increased capacity is often accompanied by shorter cycle life due to undesired side reactions on the CAM/electrolyte interface. As the optimization of the electrochemical performance of lithium-ion batteries by the adjustment of the composition of the cathode active materials has come to a limit, the focus has shifted to the modification of the morphological aspects. One way to minimize side reactions is to reduce the specific surface area of the CAM through a greater NCM crystallite size or through a customized particle morphology, both exhibiting less particle cracking upon charge/discharge cycling [1]. However, new methodologies for the quantification of aspects such as particle size, particle cracking, and surface area change are needed.Recently, we have developed a novel in situ analytical method which is able to quantify the increase of the CAM surface area upon extended charge/discharge cycling using electrochemical impedance spectroscopy (EIS) [2]. There, we make use of the direct correlation between the capacitance and the surface area of the electrode, whereby an increase of the capacitance indicates cracking of CAM particles, caused by the repeated volume change of the NCM material upon (de)lithiation and/or oxygen release at high state of charge [3]. In these works, the direct relationship between capacitance and NCM particle surface area was validated by ex situ krypton physisorption measurements.Unfortunately, this impedance-based method relies on a sophisticated experimental setup, using a micro-reference electrode (i.e., a gold-wire µ-RE) and a partially pre-lithiated lithium titanate (LTO) counter electrode. Therefore, in this study, we deduce a stepwise simplification of the capacitance measurements from the setup with a µ-RE and a pre-lithiated LTO counter electrode to a conventional coin half-cell setup, which is commonly used in industry for quick and routine material benchmarking. Additionally, it will be shown that the capacitance does not have to be extracted from a full impedance spectrum provided by an impedance analyzer, but that it can be obtained solely from a low-frequency single-point impedance measurement performed at a battery cycler. The working principle of this approach is validated using four different cell and potentiostat / battery cycler configurations over several charge/discharge cycles [4].The here demonstrated setup provides a simple method suitable for conventional coin half-cells to identify surface area changes of cathode active materials, being easily implemented in standard cycling procedures. Reference s [1] W. Li, E. M. Erickson, and A. Manthiram, Nature Energy 5 26 (2020).[2] S. Oswald, D. Pritzl, M. Wetjen, and H. A. Gasteiger, J. Electrochem. Soc. 167 100511 (2020).[3] S. Oswald, D. Pritzl, M. Wetjen, and H. A. Gasteiger, J . Electrochem . Soc . 168 120501 (2021).[4] S. Oswald, F. Riewald, H. A. Gasteiger, manuscript in preparation. Acknowledgements This work is financially supported by the BASF SE Network on Electrochemistry and Battery Research.

Enhanced cyclic performance of O2-type Mn-based layered oxide via Al doping for lithium-ion battery

The layered lithium nickel manganese oxide Li y Ni x Mn 1−x O 2 cathode materials with O2 structure exhibit good cyclic stability owing to their special arrangement of oxygen layers. However, the O2-type oxides generally present limited discharge capacity because of Li + ions defects in the lithium layer (as in Li y Ni x Mn 1−x O 2 , y < 1). Herein, an O2-type layered lithium nickel manganese oxide LiNi 0.33 Mn 0.65 Al 0.02 O 2 with high capacity and good capacity retention is obtained by introducing lithium and aluminum into the transition metal layer. The results of structural characterization and performance tests show that the optimal amount of Li + and Al 3+ in the transition metal layer effectively inhibits the disordered migration of transition metal ions and increases the electrochemical stability. The LiNi 0.33 Mn 0.65 Al 0.02 O 2 cathode delivers an initial discharge capacity of 153 mAh g −1 and the capacity only attenuates 13% after 100 cycles at the current density of 200 mA g −1 , which are higher than that of undoped oxide LiNi 0.33 Mn 0.67 O 2 . • O2-type Mn-based oxides with Li and Al in transition metal layer were synthesized. • Al doping amount has important effect on the performance of LiNi 0.33 Mn 0.67−x Al x O 2 . • LiNi 0.33 Mn 0.65 Al 0.02 O 2 has high stability and high initial capacity at 200 mA g −1 .

A layered lithium nickel manganese oxide as environmentally friendly cathode material for secondary batteries

&lt;p&gt;Cobalt-free cathode material development is considered necessity to assure the sustainability of Li-ion batteries. Cobalt is always considered expensive and unsafe for both human and environment. LiNi&lt;sub&gt;0.5&lt;/sub&gt;Mn&lt;sub&gt;0.5&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; (LNMO) is a layer structured cathode material that has similar feature to LiCoO&lt;sub&gt;2&lt;/sub&gt; (LCO). A simple and fast processing of LNMO is proposed. A precipitation of nickel manganese oxalate was obtained in a batch reactor under atmospheric condition. The as-obtained homogenous oxalate precursor was converted to LNMO via high temperature lithiation. Based on the XRD result, a crystalline product with layer structure is successfully obtained. The presence of impurities such as residual Li can be detected from the FTIR spectra. SEM Images confirmed quasi-spherical particles with grain size of less than 10 micrometer. The charge-discharge analysis of LNMO containing cell deliver a capacity of 42 mAh/g. In spite of its promising report, continuous improvement is necessary to obtain cell with better electrochemical performance.&lt;/p&gt;

Anisotropic Crystal Growth of Layered Nickel Hydroxide along the Stacking Direction Using Amine Ligands.

Edge surfaces of two-dimensional crystals play crucial roles in their properties, such as intercalation behavior and catalytic activities; however, reports on the preparation of crystals with a high aspect ratio of thickness to lateral size, typically a prism-like crystal morphology composed of stacked layers, are scarce. We report the anisotropic crystal growth of β-Ni(OH)2 along the stacking direction using bidentate amine ligands, which act as both the base and the reservoir of Ni2+ through the formation of Ni-diamine complexes. Various characterization results of the crystal structure, composition, and crystal orientation indicate the formation of hexagonal prisms of β-Ni(OH)2 with an unusually high aspect ratio of the thickness to the lateral size higher than 1. A systematic investigation focusing on the molar ratio of amine ligands to Ni2+, the concentration of Ni-diamine complexes, and stability constants of the complexes revealed that anisotropic growth was promoted when the supersaturation was relatively high and was maintained constant for a long time. We clarified the role of amine ligands in controlling supersaturation through the controlled release of metal ions from stable complexes. β-Co(OH)2 with a hexagonal prism shape was prepared using this protocol. This study provides valuable indications for developing synthetic chemistry for various layered compounds to achieve a controlled aspect ratio.

Synthesis of NiO Nanoparticles via Calcination of Surfactant Intercalated Layered Nickel Hydroxides and their Application as Adsorbent

Synthesis of NiO Nanoparticles via Calcination of Surfactant Intercalated Layered Nickel Hydroxides and their Application as Adsorbent

A Multifunctional Layered Nickel Silicate Nanogenerator of Synchronous Oxygen Self-supply and Superoxide Radical Generation for Hypoxic Tumor Therapy.

Oxygen consumption but hypoxic tumor environment has been considered as the major obstacle in photodynamic therapy. Although oxygen-supplied strategies have been reported extensively, they still suffer from the complicated system and unsatisfied PDT efficiency. Herein, one-component layered nickel silicate nanoplatforms (LNS NPs) are successfully synthesized using natural vermiculite as the silica source, which can simultaneously supply oxygen (O2) and generate superoxide radicals (O2-•) under near-infrared irradiation. The appropriate electron band structure endows LNS NPs with attractive optical properties, where the bandgap edges determine the performance of redox activity and spectral response characteristic. Evidenced by both in vitro and in vivo investigations, LNS NPs can generate sufficient superoxide radicals under 660 nm laser irradiation to induce tumor cell apoptosis even in a severe hypoxic environment, which benefits from self-supplied oxygen. Besides, the photoacoustic oxy-hem imaging and histologic assay further demonstrated that the generated oxygen can relieve the inherent intratumoral hypoxia. Therefore, LNS NPs not only serve as superoxide radical generator but also produce oxygen to modulate hypoxia, suggesting that it can be used for superoxide radical-mediated photodynamic therapy with enhanced antitumor effect.

Elucidating the Effect of the Morphology of Ni-Rich Cathode Active Materials on Their Long-Term Cycling Performance: Poly- Vs. Single Crystalline NCM851005

The market share of nickel-rich layered lithium nickel cobalt manganese oxides (NCMs, Li1+δNixCoyMnzO2, x+y+z+δ = 1, and 0 < δ < 0.05) as attractive cathode active materials (CAMs) for lithium-ion batteries is constantly growing owed to their high specific capacity. With higher nickel content, however, the increased capacity is often accompanied by a somewhat shorter cycle life due to undesired side reactions. These processes result from the decomposition of residual lithium salts and surface contaminants that are present in greater amounts on Ni-rich materials after synthesis and storage,[1] as well as from the reaction of evolved lattice oxygen with the electrolyte,[2] which occurs at lower potentials for higher nickel content.[3] These processes degrade the NCM active material upon charge-discharge cycling and dramatically increase the impedance of the entire cell, eventually leading to cell failure. One way to minimize side reactions is to reduce the specific surface area of the CAM by increasing the NCM crystallite size, being known in the literature as so-called single crystals,[4] which maintain their pristine surface area upon cycling.[5] In this work, we investigate two NCM851005 materials and their long-term cycling behavior in full-cells: a polycrystalline material (PC, 0.27 m²/g) with secondary agglomerates of ~5-10 µm in diameter that are comprised of primary crystallites with particle diameters on the order of ~0.1 µm, and a single crystalline material (SC, 0.51 m²/g) with primary crystallites of ~1 µm without distinct secondary structure, both shown in the SEM images in Figure 1. Due to the different particle morphology of the two materials, one would expect significant differences in the rate capability, in the long-term cycling behavior, in the extent of gassing at high state of charge (SOC), and in the change of CAM surface area over the course of extended charge/discharge cycling.To examine these aspects, calendered PC or SC NCM851005 electrodes with mass loadings of ~10 mgAM/cm² were assembled in a first set of experiments in half-cells with an additional lithium reference electrode and then subjected to discharge rate tests with potential cutoffs controlled by the lithium reference electrode. In a second set of experiments, the materials were cycled in coin full-cells using graphite as counter electrode for >200 cycles, applying different upper cutoff potentials chosen to be either below or above the limit of oxygen release of NCM851005. In addition, these full-cells were cycled at 25 °C or at 45 °C to illuminate the effect of elevated temperatures on the capacity loss. After cycling, both anode and cathode were harvested from the cycled cells and investigated by post mortem experiments: The NCM cathodes were analyzed in half-cells to differentiate between the contributions of lithium inventory losses and cathode active material losses; the graphite anodes were investigated regarding their elemental composition after cycling to understand the effect of particle morphology (or specific surface area, respectively) on the dissolution of transition metals from the cathode and their deposition at the anode. Finally, the picture of the mechanism behind the capacity losses was completed by in situ capacitance measurements tracking the surface area of the CAMs upon cycling[6] as well as by on-line electrochemical mass spectrometry (OEMS) quantifying the released gas amounts during the first four cycles to >80 %SOC. It is shown that the ratio of the surface area of both materials at high SOC correlates well with the ratio of the amounts of gas released during electrochemical cycling as well as with the detected amounts of deposited transition metals on the graphite anode.In summary, this study gives comprehensive insights into the effects of the morphology on the long-term cycling performance of poly- and single crystalline CAMs and highlights the advantages of SC NCMs for the use in commercial lithium-ion batteries. Reference s : [1] J. Paulsen and J. H. Kim, Patent US2014/0054495A1 (2014).[2] A. T. S. Freiberg, M. K. Roos, J. Wandt, R. de Vivie-Riedle, and H. A. Gasteiger, J. Phys. Chem. A 122 8828 (2018).[3] R. Jung, M. Metzger, F. Maglia, C. Stinner, and H. A. Gasteiger, J. Electrochem. Soc., 164 (7) A1361 (2017).[4] Y. Kim, ACS Appl. Mater. Interfaces 4 2329−2333 (2012).[5] S. Oswald, M. Bock, and H. A. Gasteiger, Meet. Abstr. MA2020-02 144 (2020).[6] S. Oswald, D. Pritzl, M. Wetjen, and H. A. Gasteiger, J. Electrochem. Soc., 167 100511 (2020). Figure 1

(Invited) Ambient Storage and Washing of NCMs: Formation/Removal of Surface Contaminants and NCM Structural Changes upon Heating of Washed/Stored NCMs

Cathode active materials (CAMs) based on Ni-rich layered transition metal oxides, like NCMs or NCAs, are commonly subjected to a final washing step in water to remove residual lithium hydroxide and carbonate, which otherwise lead to gelling of the electrode slurry and gassing during cell operation [1,2]. Washing, however, is accompanied by an increase in the pH of the washing solution (the steady-state pH increasing with Ni content), suggesting a Li+/H+ exchange in the near-surface region of the CAM particles, concomitant with the formation LiOH [3,4]. Due to the latter, small amounts of OH-based surface contaminants remain on the surface after washing, while carbonate-based surface contaminants can be removed completely, as shown by XPS [5]. TGA-MS analysis reveals that the incorporation of protons in washed NCMs results in a mass loss at much lower temperatures than in the case of pristine lithiated NCMs; it is accompanied by the release of H2O at ~160 °C and of O2 at ~270 °C, which are ascribed to the formation of spinel- and rocksalt-like surface phases, respectively [3]. These surface processes may be compared to the bulk conversion of layered nickel oxyhydroxide (NiOOH) to the NiO rocksalt phase that initiates at also »160 °C upon the simultaneous release of H2O and O2 [6]. The formation of these oxygen-depleted surface phases can also be confirmed by XPS and soft-XAS [5, 7] and they result in a significant increase of the CAM impedance [3].The Li+/H+ exchange in the near-surface region of layered transition metal oxide CAMs upon washing was also shown to occur upon their storage at humid ambient air [5]. In this case, however, surface contaminants are accumulated on the CAM surface, consisting of LiOH, Li2CO3, and basic nickel carbonates (NiCO3·2Ni(OH)2·xH2O) [8,9,10]. The total amount of these surface contaminants increases with storage time and particularly with Ni content [5], leading to a deterioration of their cycling performance [8,9,10], which we have ascribed to their high reactivity with the electrolyte [10]. Upon heating of NCMs stored at humid air, surface contaminants other than Li2CO3 can be removed up to 450 °C, while the Li+/H+ exchange leads to the formation of oxygen-depleted surface layers within the same temperature range, identical to what was observed for washed NCMs.This presentation will review and summarize the above described phenomena, outlining the differences and the similarities between the NCM surface changes affected by either washing or storage at ambient humid air.

Two dimensional layered nickel cobaltite nanosheets as an efficient electrode material for high‐performance hybrid supercapacitor

Nickel cobalt oxide (NCO) is considered an auspicious electrode candidate for the reinforcement of energy-storage devices. Currently, an immense interest is devoted to modifying the morphological aspects of the NCO to boost their surface texture and electrochemical performances, which is feasible for the development of high energy density and durable devices. Herein, we report the synthesis of layered NCO nanosheets via solvothermal reaction by tuning the solvent volume ratio (water/N,N-Dimethylformamide [DMF]) for supercapacitor electrode material. The nickel cobalt oxide is prepared utilizing a 1:2 (DMF:water) ratio of solvent (NCO1) displays a controlled growth of 2D nanosheets with excellent surface texture. Moreover, NCO1 demonstrates the battery type charge storage properties with a maximum specific capacitance (Csp) of 731 F g−1, which is far better than NCO2 (623 F g−1) and NCO3 (556 F g−1) prepared in other solvent proportions. Besides, the constructed hybrid supercapacitor utilizing activated carbon (AC) and NCO1 as the negative and positive electrodes, respectively, exhibits the Csp of 120 F g−1, and maximum specific energy 37.33 W h kg−1 for the specific power 691.31 W kg−1 and demonstrates excellent stability ~80.56% for 20 000 cycles.

Hydrolysis of Methoxylated Nickel Hydroxide Leading to Single-Layer Ni(OH)2 Nanosheets

Various methods for the preparation of inorganic nanosheets have been established and they have contributed to the substantial development of the research on diverse two-dimensional materials. Covalent surface modification of layered metal hydroxides with alkoxy groups is known to effectively weaken the interactions between layers, although the modified ligands are irreversibly immobilized. This study proposes the use of methanol as a removable surface modifier forming monodentate alkoxy bonds to prepare nickel hydroxide nanosheets through hydrolysis. Methoxylated layered nickel hydroxide, consisting of randomly stacked nano-sized nickel hydroxide sheets (10-20 nm in size) having Ni-OCH3 groups on its surface, was synthesized in a powder form through the precipitation reaction of a nickel salt in methanol at room temperature. After dispersing the aggregated methoxylated nickel hydroxide in water, single-layer nickel hydroxide nanosheets with a thickness of 1.2 nm and a lateral size of 460 nm at maximum, which is larger than the size of original methoxylated nickel hydroxide were found in the suspension. The time-course experiments during hydrolysis suggested that two-dimensional crystal growth of exfoliated nickel hydroxide sheets proceeded, resulting in the formation of the nanosheets. Moreover, single-layer and nano-sized cobalt hydroxide was prepared through a similar manner. This work demonstrates that two-dimensional alkoxides consisting of polymeric M-O-M bonds are useful precursors for the design of metal-hydroxide-based nanomaterials.

Size Effect of Hydroxide Nanobuilding Blocks and Nonionic Block Copolymer Templates on the Formation of Ordered Mesoporous Structures.

The use of precrystallized nanoparticles as nanobuilding blocks (NBBs) is a promising way to obtain mesoporous materials with crystalline walls. In this study, the size effects of both hydroxide NBBs and nonionic block copolymer (BCP) templates on the formation of ordered mesostructures are investigated. The diameter of layered nickel hydroxide NBBs was controlled at the sub-2 nm scale by an epoxide-mediated alkalinization process. Commercially available nonionic BCPs (gyration radii in the range of 11.9-43.9 Å) were used. Mesoperiodic structures were formed by the evaporation-induced self-assembly process. A proper size combination of hydroxide NBBs, smaller than 12.5 Å, and BCPs, larger than 19.9 Å, is shown to be necessary to form ordered mesostructures.

Organic-Inorganic Hybrid Nanocrystal-based Cryogels with Size-Controlled Mesopores and Macropores.

Nanocrystal-based processing has attracted significant interest for the fabrication of highly functional materials with controlled crystallinity and fine porous structures. In this study, we focused on the template-free synthesis of nanocrystal-based materials with size-tailored pores using layered nickel hydroxide intercalated with acrylate anions. Polymerization of the acrylates encouraged interconnection of the nanocrystals and the formation of homogeneous gel networks. Cryogels after freeze-drying had pores with an average diameter from 4.8 nm (mesoscale) to 68.9 nm (macroscale). It was found that the surface characteristics of starting nanocrystals determined the phase separation tendency of interconnected species from the reaction media and resultant porous structures. We believe that the present study can enable the design of template-free nanocrystal-based porous materials.

High-pseudocapacitance of porous and square NiO@NC nanosheets for high-performance lithium-ion batteries

Layered nickel oxides have been focused with intense research interests as high-performance lithium-ion batterie (LIB) anode. However, it is hard to obtain few layered nickel oxides material directly as it easily forms bulk material with the strong interaction between the interlayer. In this work, two-dimensional (2D) nickel-based coordination polymers were successfully prepared according to aqueous phase copolymerization approach. And then uniform carbon-doped NiO nanosheets were successfully obtained from facile solution assembly and post-thermal treatment. The detailed electrochemical testing shows that the uniform NiO nanocrystals encapsulated into porous N-doped carbon (NiO@NC) nanosheets present much higher rate capability with the discharge specific capacity of 782.7 mAh·g−1 at high current density of 2.0 A·g−1 than pure NiO (690 mAh·g−1). It also shows long-term cycling performance with 91% retention after 50 cycles at 1.0 A·g−1. The high rate capability, cycling stability and the easy synthesis make NiO@NC nanosheets as a promising candidate for LIB anode and build up new way for the fabrication of metal oxides anode materials.

Probing Depth-Dependent Transition-Metal Redox of Lithium Nickel, Manganese, and Cobalt Oxides in Li-Ion Batteries.

Layered lithium nickel, manganese, and cobalt oxides (NMC) are among the most promising commercial positive electrodes in the past decades. Understanding the detailed surface and bulk redox processes of Ni-rich NMC can provide useful insights into material design options to boost reversible capacity and cycle life. Both hard X-ray absorption (XAS) of metal K-edges and soft XAS of metal L-edges collected from charged LiNi0.6Mn0.2Co0.2O2 (NMC622) and LiNi0.8Mn0.1Co0.1O2 (NMC811) showed that the charge capacity up to removing ∼0.7 Li/f.u. was accompanied with Ni oxidation in bulk and near the surface (up to 100 nm). Of significance to note is that nickel oxidation is primarily responsible for the charge capacity of NMC622 and 811 up to similar lithium removal (∼0.7 Li/f.u.) albeit charged to different potentials, beyond which was followed by Ni reduction near the surface (up to 100 nm) due to oxygen release and electrolyte parasitic reactions. This observation points toward several new strategies to enhance reversible redox capacities of Ni-rich and/or Co-free electrodes for high-energy Li-ion batteries.

How Synthetic Quench Rate and Composition Affect the Performance of Lithium Nickel Manganese Oxide Cathode Materials

A survey of layered lithium-rich nickel manganese oxides cathodes, (formula Li[NixLi(1/3–2x/3)Mn(2/3−x/3)]O2), was conducted. We varied the nickel content from 0.1 to x = 0.25, and the post-calcination quench rate was controlled by employing three different methods: direct metal contact, water immersion, and liquid nitrogen immersion. Both composition and quench methodology impacted materials properties and electrochemical function. We observed that there is a synthetic limit for LLRNMO cathodes that occurs in the range of 0.17 > x > 0.10 below which quenching proved to be critically important in determining phase content and electrochemical behavior. Galvanostatic testing revealed the specific discharge capacities of the LLRNMO cathodes increased over the course of cycling, while the XRD characterization after cycling revealed reduced transition metal ordering. We found that the layered lithium-rich nickel manganese oxide materials made with water quenching performed the best with initial C/20 capacities increasing from around 200 mAh g−1 to over 250 mAh g−1 after 28 cycles while retaining C/2 capacities in excess of 200 mAh g−1.

Study on the Effect of Crystal Size on the Performance of Ni-Rich Cathode Active Materials: Poly- Vs. Single Crystalline NCM622

Nickel-rich layered lithium nickel cobalt manganese oxides (NCMs, Li1+δNixCoyMnzO2, x+y+z+δ = 1 and δ > 0) are increasingly used as cathode active materials (CAMs) for lithium-ion batteries due to their high specific capacity; they are also expected to play a major role in future battery technologies, such as all-solid-state batteries. With increasing nickel content, however, the gained capacity is often accompanied by shorter cycle life due to undesired side reactions, resulting e.g. from the decomposition of residual lithium salts and surface contaminants that are present in greater amounts on Ni-rich materials,[1] as well as from the reaction of evolved lattice oxygen with the electrolyte,[2] which occurs at lower potentials for higher nickel content.[3] These processes degrade the NCM active material upon charge-discharge cycling and dramatically increase the impedance of the entire cell, eventually leading to cell failure. One way to minimize side reactions is to reduce the specific surface area through a greater NCM crystallite size, being known in the literature under the name of single crystals, which are expected to maintain their pristine surface area upon cycling.[4,5] By this approach, however, the NCM surface area normalized current of the CAM is significantly increased, possibly leading to critical overpotentials and compromising its rate capability.In this study, we investigate the electrochemical characteristics of two µm-sized NCM622 materials with a similar pristine BET surface area of ~0.3 m²/g: a polycrystalline material (PC) with secondary agglomerate diameters of ~5-10 µm comprised of primary crystallites with particle diameters on the order of ~10-1 µm, and a single crystalline material (SC) with individual primary crystallites of ~5 µm, both shown in the SEM images in Figure 1. Due to the highly unequal particle structure of the two material classes, one would expect significant differences in rate capability, long-term cycling behavior, extent of gassing at high state of charge (SOC), and the change of CAM surface area over the course of extended charge/discharge cycling.Calendered electrodes with PC or SC NCM622 with electrode loadings of ~12 mgAM/cm² were assembled in half-cells with a lithium metal reference electrode and then subjected to charge and discharge rate tests with potential cutoffs controlled by the reference electrode. Since clear differences in the rate-dependent discharge capacity of the two materials are observed, the impact of the particle morphology and the cause on the overpotential during (dis)charge are then further illuminated. In order to show that the difference in rate capability is owed to differences in the CAM surface increase upon cycling due to particle cracking that is induced by the NCM volume change upon (de-)lithiation, the Kr-BET surface area of pristine and charged electrodes of both PC and SC NCM622 is quantified. By this method, it is proven that, depending on the active material type, the CAM surface area may strongly increase, already during the very first charge. Due to this fundamental property, the amount of gas released from both CAMs is expected to differ significantly. We quantify the evolved O2 and CO2 during the first four cycles to >80 %SOC using On-Line Electrochemical Mass Spectrometry (OEMS). It is shown that the ratio of the surface area of both materials in charged state correlates well with the ratio of the amounts of gas released during electrochemical cycling. The obtained results on the fundamental properties of the two material classes on rate capability and gassing are complemented with long-term cycling experiments in full-cells at different upper cutoff potentials, chosen to be either below and or above the limit of oxygen release of NCM622 in order to analyze the evolution of the NCM622 particle morphology over extended charge/discharge cycling.In summary, this study gives comprehensive insights into the fundamental properties of poly- and single crystalline NCMs and into the impact of typical CAM failure mechanisms on the long-term cycling performance of these two material classes. Reference s : [1] J. Paulsen and J. H. Kim, USA Pat. US2014/0054495A1 (2014).[2] A. T. S. Freiberg, M. K. Roos, J. Wandt, R. de Vivie-Riedle, and H. A. Gasteiger, J. Phys. Chem. A, 122, 8828 (2018).[3] R. Jung, M. Metzger, F. Maglia, C. Stinner, and H. A. Gasteiger, J. Electrochem. Soc., 164, A1361 (2017).[4] Yongseon Kim, ACS Appl. Mater. Interfaces, 4, 2329 (2012).[5] G. Liu, M. Li, N. Wu, L. Cui, X. Huang, X. Liu, Y. Zhao, H. Chen, W. Yuan, and Y. Bai, J. Electrochem. Soc., 165, A3040 (2018). Figure 1

Quenching Method and Performance of High Voltage Layered Lithium Rich Nickel Manganese Oxides

Due to their promise of high specific capacity layered lithium rich nickel manganese oxide materials have a large body of literature dedicated to their structure, and electrochemical behaviors[1–5]. Yet these materials have often been marred by significant capacity losses, rate capability limitations, and structural instability over the course of cycling. Several techniques involving surface and structural modifications have been used to mitigate these capacity losses[6–8]. In this work we used a hybrid acetate/nitrate precursors and sol-gel/combustion synthesis to conduct an unprecedented combined survey of the composition of Li(NixLi(1/3-2x/3)Mn(2/3-x/3))O2, and synthetic quench rates to elucidate the effects of these variables on electrochemical cycling behavior, bulk morphology, and surface morphology of the layered lithium rich manganese oxides. We find that the electrochemical behavior of these materials is dependent on both the nickel content as well as the quenching method, with a lower limit on the nickel content beyond which the effects of quenching are minimal. Despite XRD revealing loss of super lattice peaks indicating a loss of transition metal ordering, often associated with capacity loss, galvanostatic cycling of samples saw improved capacities over the course of cycling. SEM found bulk morphology of cathodes differs across nickel contents, yet it did not experience large changes over the course of cycling. The use of TEM found that the surfaces of Li(NixLi(1/3-2x/3)Mn(2/3-x/3))O2 powders is highly sensitive to quenching method, and comparison of surfaces over the course of cycling provided incites into the effects of quenching and nickel content on electrochemical cycling behaviors of the cathode materials. This investigation reveals that careful considerations in synthesis are required for the realization of high-performance layered lithium rich nickel manganese oxides.[1] Y. J. Park, Y.-S. Hong, X. Wu, K. S. Ryu, S. H. Chang, J. Power Sources 2004, 129, 288.[2] Z. Lu, L. Y. Beaulieu, R. A. Donaberger, C. L. Thomas, J. R. Dahn, J. Electrochem. Soc. 2002, 149, A778.[3] Z. Lu, J. R. Dahn, J. Electrochem. Soc. 2002, 149, A1454.[4] M. Jiang, B. Key, Y. S. Meng, C. P. Grey, Chem. Mater. 2009, 21, 2733.[5] J. Bréger, N. Dupré, P. J. Chupas, P. L. Lee, T. Proffen, J. B. Parise, C. P. Grey, J. Am. Chem. Soc. 2005, 127, 7529.[6] D. Eum, B. Kim, S. J. Kim, H. Park, J. Wu, S. P. Cho, G. Yoon, M. H. Lee, S. K. Jung, W. Yang, W. M. Seong, K. Ku, O. Tamwattana, S. K. Park, I. Hwang, K. Kang, Nat. Mater. 2020, 19, 419.[7] H. Z. Zhang, Q. Q. Qiao, G. R. Li, S. H. Ye, X. P. Gao, J. Mater. Chem. 2012, 22, 13104.[8] Y. Wu, A. Manthiram, Solid State Ionics 2009, 180, 50.

Synthesis and stored performance of LiNi0.8Co0.17Al0.03O2 cathode material prepared by using a flocculation precipitation process

Layered lithium nickel cobalt aluminum oxides cathode materials (α-NaFeO2 structure, Space group: R-3 m) are prepared using an unusual flocculation precipitation process. The synthesis strategy utilized the new aluminum precursor containing nickel, cobalt and aluminum hydroxides has a different mechanism from that for conventional coprecipitation process. As-prepared LiNi0.85Co0.17Al0.03O2 delivers a first cycle capacity of 164 mAh g−1 at 1C rate. The stored sample delivers a first cycle capacity of 146 mAh g−1 and the capacity retention rate of 93% in 40 cycles at 1C rate. Its stored cell exhibits a capacity of 99 mAh g−1 at 1C rate. The particle surface of the sample has a coating layer of Li3.62aLi4.31bNi0.172+Ni0.833+Co0.062+Al0.373+O0.98aO12.6b (with the structure of Li2CO3, LiAl5O8 and α-NaFeO2). The coating layer can prevent the reaction between the particles and moisture in the air or the particles and electrolytes in the cell at 55 °C. Therefore, LiNi0.85Co0.17Al0.03O2 exhibits excellent rate performance and stored one for its low polarization, high stability α-NaFeO2 structure and high stable coating layer. The exceptional overall performance of the as-synthesized LiNi0.85Co0.17Al0.03O2 presents itself a promising cathode material for next generation lithium-ion batteries.

A phase separation in a protonated layered nickel titanate to form Ni-doped anatase/rutile TiO2 nanocomposite with efficient visible-light responsive photocatalytic activity

ABSTRACT We report a simple methodology for the preparation of an efficient visible-light responsive TiO2 photocatalyst through acid treatment of a lepidocrocite-type layered nickel cesium titanate (Cs0.7Ti1.65Ni0.35O4) for interlayer protonation and subsequent calcination at different temperatures (400–600°C) to induce structural transformation. The Ni-doped anatase/rutile nanocomposite possessing a morphology similar to that of protonated layered nickel titanate is obtained at all calcination temperatures. The sample obtained at 600°C exhibits the highest visible-light responsive photocatalytic activity for decomposition of the aqueous methylene blue dye under visible-light (λ > 420 nm) irradiation. The activity is 14 times higher than that of P25 (standard TiO2 photocatalyst) modified with Ni2+ and 3 times higher than that of NiTiO3 (visible-light responsive photocatalyst). The efficient visible-light responsive photocatalytic activity is ascribable to the visible-light absorption ability of the TiO2 phase owing to Ni-doping. Also, an efficient electron transfer across anatase–rutile interfaces for inhibition of charge recombination could be responsible for the activity. This methodology is a new route for efficient visible-light responsive photocatalysts based on TiO2 doped with various elemental species. This is because lepidocrocite-type layered titanates are available in a variety of chemical compositions.

Broadband optical response of layered nickel ditelluride towards the mid-infrared regime

The broadband nonlinear optical material towards the mid-infrared spectral range is highly needed for civil and military applications. Here, we have investigated the nonlinear optical response of the nickel ditelluride (NiTe2) single crystal prepared by the chemical vapor deposition (CVD) method, and found that the layered NiTe2 exhibits attractive broadband nonlinear optical absorption performance towards the mid-infrared regime. We further explored the nonlinear optical response of the layered NiTe2 in the erbium-doped fluoride fiber laser, and have realized the stable Q-switched fiber laser with a pulse width of 708 ns and a repetition rate of 81 kHz around 2.8 µm wavelength. The experimental results may not only make inroads towards the understanding the nonlinear optical response of the topological materials, but also explore their broadband applications in mid-infrared photonics.