Rechargeable battery technologies have ignited major breakthroughs in contemporary society, including but not limited to revolutions in transportation, electronics, and grid energy storage. The remarkable development of rechargeable batteries is largely attributed to in-depth efforts to improve battery electrode and electrolyte materials. There are, however, still intimidating challenges of lower cost, longer cycle and calendar life, higher energy density, and better safety for large scale energy storage and vehicular applications. Further progress with rechargeable batteries may require new chemistries (lithium ion batteries and beyond) and better understanding of materials electrochemistry in the various battery technologies. In the past decade, advancement of battery materials has been complemented by new analytical techniques that are capable of probing battery chemistries at various length and time scales. Synchrotron X-ray techniques stand out as one of the most effective methods that allow for nearly nondestructive probing of materials characteristics such as electronic and geometric structures with various depth sensitivities through spectroscopy, scattering, and imaging capabilities. This article begins with the discussion of various rechargeable batteries and associated important scientific questions in the field, followed by a review of synchrotron X-ray based analytical tools (scattering, spectroscopy, and imaging) and their successful applications (ex situ, in situ, and in operando) in gaining fundamental insights into these scientific questions. Furthermore, electron microscopy and spectroscopy complement the detection length scales of synchrotron X-ray tools and are also discussed toward the end. We highlight the importance of studying battery materials by combining analytical techniques with complementary length sensitivities, such as the combination of X-ray absorption spectroscopy and electron spectroscopy with spatial resolution, because a sole technique may lead to biased and inaccurate conclusions. We then discuss the current progress of experimental design for synchrotron experiments and methods to mitigate beam effects. Finally, a perspective is provided to elaborate how synchrotron techniques can impact the development of next-generation battery chemistries.

Abstract:Nanoscale full-field (FF) transmission X-ray microscopy (TXM) and ensembleaveraged soft X-ray absorption spectroscopy (soft XAS) were used to investigate stateof-charge (SOC) heterogeneities in electrochemically charged or discharged and chemically oxidized samples of LiNi0.6Mn0.2Co0.2O2 cathode materials. We observed considerable and similar non-uniformities in terms of Ni oxidation states (and, by proxy, lithium distributions) for all the samples in the bulk. Therefore, the chemically delithiated samples are similar to the electrochemically charged samples in terms of mesoscale charge heterogeneity in large polycrystalline particle ensembles. However, the gradient oxidation states of transition metals on the surface, which is partly responsible for the electrode degradation mechanism known as surface reconstruction, is much less apparent in chemically delithiated samples. T Response to ReviewersThe previous version of this paper was not sent out for peer review. Response to Reviewers Graphical AbstractClick here to download Graphical Abstract graphicalabstract.tif Charge Heterogeneity and Surface Chemistry in Polycrystalline Cathode Materials SummaryNanoscale full-field (FF) transmission X-ray microscopy (TXM) and ensemble-averaged soft Xray absorption spectroscopy (soft XAS) were used to investigate state-of-charge (SOC) heterogeneities in electrochemically charged or discharged and chemically oxidized samples of LiNi0.6Mn0.2Co0.2O2 cathode materials. We observed considerable and similar non-uniformities in terms of Ni oxidation states (and, by proxy, lithium distributions) for all the samples in the bulk. Therefore, the chemically delithiated samples are similar to the electrochemically charged samples in terms of mesoscale charge heterogeneity in large polycrystalline particle ensembles.However, the gradient oxidation states of transition metals on the surface, which is partly responsible for the electrode degradation mechanism known as surface reconstruction, is much less apparent in chemically delithiated samples.

Layered lithium transition metal oxides, in particular, NMCs (LiNiCoMnO) represent a family of prominent lithium ion battery cathode materials with the potential to increase energy densities and lifetime, reduce costs, and improve safety for electric vehicles and grid storage. Our work has focused on various strategies to improve performance and to understand the limitations to these strategies, which include altering compositions, utilizing cation substitutions, and charging to higher than usual potentials in cells. Understanding the effects of these strategies on surface and bulk behavior and correlating structure-performance relationships advance our understanding of NMC materials. This also provides information relevant to the efficacy of various approaches toward ensuring reliable operation of these materials in batteries intended for demanding traction and grid storage applications. In this Account, we start by comparing NMCs to the isostructural LiCoO cathode, which is widely used in consumer batteries. Effects of changing the metal content (Ni, Mn, Co) upon structure and performance of NMCs are briefly discussed. Our early work on the effects of partial substitution of Al, Fe, and Ti for Co on the electrochemical and bulk structural properties is then covered. The original aim of this work was to reduce the Co content (and thus the raw materials cost) and to determine the effect of the substitutions on the electrochemical and bulk structural properties. More recently, we have turned to the application of synchrotron and advanced microscopy techniques to understand both bulk and surface characteristics of the NMCs. Via nanoscale-to-macroscale spectroscopy and atomically resolved imaging techniques, we were able to determine that the surfaces of NMC undergo heterogeneous reconstruction from a layered structure to rock salt under a variety of conditions. Interestingly, formation of rock salt also occurs under abuse conditions. The surface structural and chemical changes affect the charge distribution, the charge compensation mechanisms, and ultimately, the battery performance. Surface reconstruction, cathode/electrolyte interface layer formation, and oxygen loss are intimately related, making it difficult to disentangle the effects of each of these phenomena. They are driven by the different redox activities of Ni and O on the surface and in the bulk; there is a greater tendency for charge compensation to occur on oxygen anions at particle surfaces rather than on Ni, whereas the Ni in the bulk is more redox active than on the surface. Finally, our latest research efforts are directed toward understanding the thermal properties of NMCs, which is highly relevant to their safety in operating cells.

The ever‐increasing demand for stationary energy storage has driven the prosperous investigation of low‐cost sodium ion batteries. The inferior long‐term cycling stability of cathode materials is a significant roadblock toward the wide commercialization of sodium ion batteries. This study enlightens a path toward empowering stable sodium ion batteries through incisive diagnostics of the multiscale surface chemical processes in layered oxide materials (e.g., O3‐NaNi1/3Fe1/3Mn1/3O2). The major challenges are unraveled in a promising sodium layered cathode material using a range of complementary advanced spectroscopic and imaging diagnostic techniques. It is discovered that the cathode–electrolyte interfacial reaction triggers transition metal reduction, heterogeneous surface reconstruction, metal dissolution, and formation of intragranular nanocracks. These surface chemistry driven processes are partly responsible for significant performance decay. This diagnostic study also rationalizes the elemental substitution and surface passivation methods that are widely applied in the field. The prepassivated and Ti‐substituted cathode materials allow for significantly improved cycling stability by inhibiting the metal dissolution. Therefore, incisively diagnosing the interfacial chemistry not only creates scientific insights into understanding sodium cathode chemistry, but also represents an advance toward establishing universal interfacial design principles for all alkali metal ion cathode materials.

Nickel-rich layered materials are emerging as cathodes of choice for next-generation high energy density lithium ion batteries intended for electric vehicles. This is because of their higher practical capacities compared to compositions with lower Ni content, as well as the potential for lower raw materials cost. The higher practical capacity of these materials comes at the expense of shorter cycle life, however, due to undesirable structure and chemical transformations, especially at particle surfaces. To understand these changes more fully, the charge compensation mechanism and bulk and surface structural changes of LiNi 0.6 Mn 0.2 Co 0.2 O 2 were probed using synchrotron techniques and electron energy loss spectroscopy in this study. In the bulk, both the crystal and electronic structure changes are reversible upon cycling to high voltages, whereas particle surfaces undergo significant reduction and structural reconstruction. While Ni is the major contributor to charge compensation, Co and O (through transition metal-oxygen hybridization) are also redox active. An important finding from depth-dependent transition metal L-edge and O K-edge X-ray spectroscopy is that oxygen redox activity exhibits depth-dependent characteristics. This likely drives the structural and chemical transformations observed at particle surfaces in Ni-rich materials. The need for lithium-ion batteries with higher energy density and lower cost than currently available, particularly for transport applications, has led to intensified interest in Ni-rich NMC (LiNi x Mn y Co z O 2 ; x+y+z≈1, where x>y) cathode materials.1-5 These materials deliver higher practical capacities in a typically used voltage range than NMCs with lower Ni content (e.g., LiNi 1/3 Mn 1/3 Co 1/3 O 2 or NMC-333), and most formulations contain less of the expensive Co component, reducing raw material costs. The increase in practical capacity roughly scales with the Ni content, but comes at the expense of cycle life and thermal stability at high states-of-charge (SOC). 6 To circumvent these problems, several different strategies have been utilized to improve cycling, particularly to higher potentials. These include partial substitution with Ti 7-9 or Zr, 10 engineering the micro-or nano-structure to reduce surface Ni content using metal segregation, 11 surface pillared structures, 12 and concentration gradients, 13 coating particle surfaces, 14 and development of electrolyte additives. 15,16 While all of these approaches have resulted in improvements, further understanding of the factors that lead to capacity fading is clearly needed in order to meet the stringent performance requirements of traction applications.The formation of a resistive cathode/electrolyte interphase (CEI), such as an electrolyte decomposition layer, has been observed during cycling of LiNi 0. 20 In the study of NMC-532, it was found that surface reconstruction to a rock salt phase dominates when high voltage (4.8 V) cutoffs are used due to oxygen loss under the highly oxidizing conditions, while ...

A spongy nickel-organic photocatalyst with nearly 100% selective CO2 to CO conversion.

Publications concerning the mechanism of biological activity, especially the immunological mechanism of C(60)(OH)(20) nanoparticles, are relatively limited. However, the structure and characteristics of this carbon allotrope have been widely investigated. In this paper, we have demonstrated that water-soluble C(60)(OH)(20) nanoparticles have an efficient anti-tumor activity in vivo, and show specific immunomodulatory effects to the immune cells, such as T cells and macrophages, both in vivo and in vitro. For example, C(60)(OH)(20) nanoparticles can increase the production of T-helper cell type 1 (Th1) cytokines (IL-2, IFN- gamma and TNF-alpha), and decrease the production of Th2 cytokines (IL-4, IL-5 and IL-6) in serum samples. On the other hand, C(60)(OH)(20) nanoparticles show almost no adverse effect to the viability of immune cells in vitro but stimulate the immune cells to release more cytokines, in particular TNF- alpha, which plays a key role in the cellular immune process to help eliminate abnormal cells. TNF- alpha production increased almost three-fold in treated T lymphocytes and macrophages. Accordingly, we conclude that C(60)(OH)(20) nanoparticles have an efficient anti-tumor activity and this effect is associated with an increased CD(4)(+)/CD(8)(+) lymphocyte ratio and the enhancement of TNF- alpha production. The data suggest that C(60)(OH)(20) nanoparticles can improve the immune response to help to scavenge and kill tumor cells.

Understanding charge heterogeneity can inform designing high performance Li ion battery cathodes.