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Lithium-ion battery (LIB) is a broadly adopted technology for energy storage. With increasing demands to improve the rate capability, cyclability, energy density, safety, and cost efficiency, it is crucial to establish an in-depth understanding of the detailed structural evolution and cell-degradation mechanisms during battery operation. Here, we present a laboratory-based high-resolution and high-throughput X-ray micro–computed laminography approach, which is capable of in situ visualizing of an industry-relevant lithium-ion (Li-ion) pouch cell with superior detection fidelity, resolution, and reliability. This technique enables imaging of the pouch cell at a spatial resolution of 0.5 μm in a laboratory system and permits the identification of submicron features within cathode and anode electrodes. We also demonstrate direct visualization of the lithium plating in the imaged pouch cell, which is an important phenomenon relevant to battery fast charging and low-temperature cycling. Our development presents an avenue toward a thorough understanding of the correlation among multiscale structures, chemomechanical degradation, and electrochemical behavior of industry-scale battery pouch cells.

The lithium-ion battery has demonstrated tremendous economic and social impacts. Upon battery operation under different conditions, lithium changes its chemical state and physical formation, leadin...

The high interfacial resistance and lithium (Li) dendrite growth are two major challenges for solid-state Li batteries (SSLBs). The lack of understanding on the correlations between electronic conductivity and Li dendrite formation limits the success of SSLBs. Here, by diluting the electronic conductor from the interphase to bulk Li during annealing of the aluminium nitride (AlN) interlayer, we changed the interphase from mixed ionic/electronic conductive to solely ionic conductive, and from lithiophilic to lithiophobic to fundamentally understand the correlation among electronic conductivity, Li dendrite, and interfacial resistance. During the conversion-alloy reaction between AlN and Li, the lithiophilic and electronic conductive Li x Al diffused into Li, forming a compact lithiophobic and ionic conductive Li 3 N, which achieved an ultrahigh critical current density of 2.6/14.0 mA/cm 2 in the time/capacity-constant mode, respectively. The fundamental understanding on the effect of interphase nature on interfacial resistance and Li dendrite suppression will provide guidelines for designing high-performance SSLBs.

Transition metal dissolution in layered cathodes is one of the most intractable issues that deteriorate the battery performance and lifetime. It not only aggravates the structure degradation in cathode but also damages the solid electrolyte interphase in anode and even induces the formation of lithium dendrites. In this work, we investigate the dissolution behaviors of polycrystalline and single-crystalline layered cathode via operando X-ray imaging techniques. The cathode particle morphology appears to have a significant impact on the evolution of the dissolution dynamics. As a mitigation strategy, we reveal that doping with a trace amount of Zr in the layered cathode could improve its robustness against the transition metal dissolution. Our finding provides valuable insights for designing the next-generation highly stable layered battery cathodes.

The degradation of nickel-rich cathode materials for lithium-ion batteries upon prolonged electrochemical cycling features a complicated interplay among electronic structure, lattice configuration,...

Crystalline materials are routinely produced via high-temperature synthesis and show size-dependent properties; however, a rational approach to regulating their crystal growth has not been established. Here we show that dopants traditionally used for modifying crystal lattices can also function as growth mediators in molten-salt synthesis by altering the surface energy and thus the nucleation barrier and the critical nuclei size. This was demonstrated by size-tunable synthesis of lithium cobalt oxide (LiCoO2) with a trace amount of titanium oxide or tungsten oxide as the dopant. The understanding of the dopant-mediated growth mechanism allows the rational design and control of the particle size and the doping for LiCoO2, enabling a high energy-density battery cathode with exceptional rate capability and cycle stability at high voltages intolerable for conventional LiCoO2.

Lithium-ion batteries (LIBs) feature structural and chemical complexities across a broad range of length scales. It is the hierarchy of the battery structure that determines its functionality. An in-depth understanding of the battery function, degradation, and failure mechanisms requires a thorough and systematic investigation from structural, chemical, mechanical, and dynamic perspectives. Here we present a macro-to-nano zoom through the hierarchy of a commercial 18650 type LIB using a suite of state-of-the-art X-ray microscopy techniques. Damage, deformation, and heterogeneity at different length scales are visualized and are associated with different degradation phenomena and mechanisms. Our results highlight the importance of the mechanical properties of the cathode material, which could impact both the immediate and the long-term cell behaviors significantly. While this study focuses on a commercial lithium cell with a standard configuration, our findings can be extrapolated and are applicable to the development of next-generation energy storage technology, e.g. solid-state batteries.

Spinel-structured lithium nickel manganese oxide (LiNi0.5Mn1.5O4, LNMO) is a low-cost battery cathode material with a high operating voltage (∼4.7 V vs Li+/Li), relatively high capacity (∼147 mA h ...

Balancing interfacial stability and Li+ transfer kinetics through surface engineering is a key challenge in developing high-performance battery materials. Although conformal coating enabled by atomic layer deposition (ALD) has shown great promise in controlling impedance increase upon cycling by minimizing side reactions at the electrode-electrolyte interface, the coating layer itself usually exhibits poor Li+ conductivity and impedes surface charge transfer. In this work, we have shown that by carefully controlling postannealing temperature of an ultrathin ZrO2 film prepared by ALD, Zr4+ surface doping could be achieved for Ni-rich layered oxides to accelerate the charge transfer yet provide sufficient protection. Using single-crystal LiNi0.6Mn0.2Co0.2O2 as a model material, we have shown that surface Zr4+ doping combined with ZrO2 coating can enhance both the cycle performance and rate capability during high-voltage operation. Surface doping via controllable postannealing of ALD surface coating layer reveals an attractive path toward developing stable and Li+-conductive interfaces for single-crystal battery materials.

Electro-mechanical degradation is commonly observed in various battery electrode materials, which are often prepared as polycrystalline particles consisting of nanoscale primary grains. The anisotropic volume change during lithium extraction/insertion makes these materials intrinsically vulnerable to grain-boundary (inter-granular) fracture that leads to rapid impedance growth and capacity decay. Here, guided by fracture mechanics analysis, we synthesize microsized single-crystal Ni-rich layered-oxide (NMC) cathode materials via an industrially-applicable molten-salt approach. Using single-crystal LiNi0.6Mn0.2Co0.2O2 as a model material, we show that the cycle performance of the Ni-rich NMC can be significantly improved by eliminating the internal grain boundaries and inter-granular fracture. The single-crystal LiNi0.6Mn0.2Co0.2O2 cathodes show high specific capacity (183 ​mAh g−1 ​at 0.1 ​C rate, 4.3–2.8 ​V) and excellent capacity retention (94% after 300 cycles at 1C/1C cycling). Further, it is confirmed for the first time that the single-crystal LiNi0.6Mn0.2Co0.2O2 particles are stable against intra-granular fracture as well under normal operating conditions but do crack if severely overcharged. Electrochemical-shock resistant single-crystal NMC reveals an alternative path towards developing better battery cathode materials, beyond the traditional one built upon polycrystalline NMC.

Metal dendrite is one of the most common issues in a variety of rechargeable batteries. It deteriorates cell capacity, increases interphase adverse reactions, and causes safety concerns. X-ray computed tomography facilitates an operando/in situ visualization of the three-dimensional (3D) morphology of the dendrites and their dynamic evolutions during battery operation. In this Perspective, we discuss the important technical developments and challenges when utilizing X-ray computed tomography for investigating the dendrite formation and growth in several different battery systems. In addition, we provide our perspective for the future directions and challenges in the field.

Summary The manufacturing of commercial lithium-ion batteries (LIBs) involves a number of sophisticated production processes. Various cell defects can be induced, and, depending on their structural and chemical characteristics, they could lead to acute failure and/or chronic degradation. Although tremendous efforts have been devoted to develop a robust quality control (QC) procedure, the functional role of the cell defects is not well understood. Here, we address this question through a systematic experimental study of commercial 18650-type LIBs that have failed the QC inspection due to a self-discharging effect. We identify and recover the defective regions from the cell and conduct a comprehensive investigation from the chemical, structural, and morphological perspectives. Our results reveal how the structural defects affect the cell performance, which is highly important to industry-scale battery production.

Rechargeable battery technologies have revolutionized electronics, transportation and grid energy storage. Many materials are being researched for battery applications, with layered transition metal oxides (LTMO) the dominating cathode candidate with remarkable electrochemical performance. Yet, daunting challenges persist in the quest for further battery developments targeting lower cost, longer lifespan, improved energy density and enhanced safety. This is, in part, because of the intrinsic complexity of real-world batteries, featuring sophisticated interplay among microstructural, compositional and chemical heterogeneities, which has motivated tremendous research efforts using state-of-the-art analytical techniques. In this research field, synchrotron techniques have been identified as a suite of effective methods for advanced battery characterization in a non-destructive manner with sensitivities to the lattice, electronic and morphological structures. This article provides a holistic overview of cutting-edge developments in synchrotron-based research on LTMO battery cathode materials. We discuss the complexity and evolution of LTMO’s material properties upon battery operation and review recent synchrotron-based research works that address the frontier challenges and provide novel insights in this field. Finally, we formulate a perspective on future directions of synchrotron-based battery research, involving next-generation X-ray facilities and advanced computational developments.

Balancing interfacial stability and Li

Incorporation of foreign elements into the cathode material is broadly adopted by both academia and industry to improve the battery performance. The lack of an in-depth understanding for the underlying mechanism, however, makes it a largely try-and-error process with unsatisfactory efficiency and effectiveness. This is particularly true for the electrochemical reaction kinetics that is heterogeneous over a broad range of length scales and is determined collectively by the cathode’s electronic structure, lattice configuration, and micro-morphology. Here we unveiled a facet-dependent dopant segregation effect in Zr-modified single-crystal LiNi0.6Co0.2Mn0.2O2 cathode. By forming kinetically favored corners on the cathode particles, the presence of a trace amount of Zr critically modulates the mesoscale reaction kinetics. Our findings suggest that a delicately controlled dopant distribution is a viable strategy for designing the next-generation battery cathode with superior structural and chemical robustness.

Single-crystal lithium-nickel-manganese-cobalt-oxide (SC-NMC) has recently emerged as a promising battery cathode material due to its outstanding cycle performance and mechanical stability over the tradional polycrystalline NMC. It is favorable to further increase the grain size of SC-NMC particles to achieve a higher volumetric energy density and minimize surface-related degradations. However, the preparation of large-size yet high performance SC-NMC particles faces a challenge in choosing a suitable temperature for sintering. High temperature promotes grain growth but induces cation mixing that negatively impacts the electrochemical performance. Here we report a temperature-swing sintering (TSS) strategy with two isothermal stages that fulfils the needs for grain growth and structural ordering sequentially. A high-temperature sintering is first used for a short period of time to increase grain size and then the reaction temperature is lowered and kept constant for a longer period of time to improve structural ordering and complete the lithiation process. SC-LiNi0.6Mn0.2Co0.2O2 materials prepared via TSS exhibit large grain size (∼4 μm), a low degree of cation mixing (∼0.9%), and outperform the control samples prepared by the conventional sintering method. This work highlights the importance of understanding the process-structure-property relationships and may guide the synthesis of other SC Ni-rich cathode materials.

Nickel-rich layered oxide materials LiNixCoyM1-x-yO2 (x>0.5, M=Mn or Al, NMC or NCA) have been considered as a mainstream choice for electric vehicle (EV) batteries in recent years, which have higher energy density than polyanion-type materials and can remarkably extend the mile range of EVs. In NMC/NCA, the energy density can be improved by increasing the nickel content or the cut-off voltage. Increasing the nickel content can effectively improve the energy density but lead to low thermal stability. Increasing the cut-off voltage to improve the energy density may result in poor structure stability, such as cation mixing on surface and intergranular cracks in bulk. Here we synthesized the Zirconium coating single-crystalline LiNi0.6Co0.2Mn0.2O2 (ZNMC622) by molten salts method to achieving both high energy density and high thermal stability. ZNMC622 can deliver over 190 mAh g-1 at 4.5 V, which is close to the specific discharging capacity (~195 mAh g-1) of LiNi0.8Co0.1Mn0.1O2 at 4.3 V. The cycling tests show that ZNMC (4.5 V) has much higher capacity retention and retained 80% of initial capacity after 600 cycles than the capacity retention of NMC811 (4.3 V). It can be concluded that Zirconium coating can improve the particle surface stability at 4.5 V and single-crystalline structure can eliminate the intergranular cracks in bulk. Meanwhile, lower nickel content of ZNMC has better thermal stability, even at 4.5 V, the exothermic peak temperature and generated heat of ZNMC is obviously smaller than the counterpart of NMC811 (4.3 V). In conclusion, ZNMC is a promising cathode material with both high energy density and safety, especially suitable for EV batteries.

Ni-rich layered oxides LiNi x M1 -x O2 (x ≥ 0.6, M = combinations of Co, Mn and/or Al) are technologically important cathode materials for lithium-ion batteries due to their high energy density, good power capability, and lower material cost than LiCoO2. These materials are usually prepared by a co-precipitation and calcination method that produces micron-sized polycrystalline (PC) particles consisting of densely packed nanoscale grains. The unique microstructure and anisotropic Vegard coefficient of these materials make them vulnerable to grain boundary fracture (“electrochemical shock”), a major cause for battery impedance growth and performance degradation. We have recently developed a scalable method to prepare a variety of single-crystal (SC) Ni-rich cathode materials, such as LiNi0.6Mn0.2Co0.2O2 (NMC622), LiNi0.6Mn0.2Co0.2O2, and LiNi0.8Co0.15Al0.05O2. SC-NMC622 outperforms the commercially available PC-NMC622 in terms of cycling stability, rate performance, and thermal stability. Post-cycling structural characterizations reveal that the SC-NMC622 do not crack even when charged to 4.9 V vs Li+/Li and its surface undergoes less phase transformation than PC-NMC622 during cycling in a normal voltage range (4.3-2.8 V). Single-crystal Ni-rich cathode materials offer hope for fabricating mechanically reliable solid-state batteries and provide a unique platform for studying doping and surface modification methods to further improve the durability of Ni-rich cathode materials.

Even after several years of research, controlled synthesis of photoluminescent carbon nanodots (C-dots) still constitutes a major challenge, and investigation of their photoluminescence (PL) mechanism remains elusive. Various top-down and bottom-up approaches have been reported lately. However, these methods usually suffer from limited control over the major factors that dictate the PL behaviour of these fascinating carbon materials. To this end, we discover a new approach to prepare C-dots from size-tunable single chain polymeric nanoparticles. Taking advantage of the state of the art living radical polymerization technique and unique features of Bergman cyclization, narrowly dispersed C-dots are prepared in a straightforward manner. PL study shows that the optimal emission wavelength of C-dots red-shifts when the size of C-dots decreases, which is different from the trends typically found in semiconductor quantum dots and C-dots prepared from graphitized materials. To clarify the PL mechanism of C-dots prepared from different sources, a theoretical study based on density functional theory is performed. Two series of model compounds, fused aromatic rings and cyclo-1,4-naphthylenes, are chosen for C-dots with different microstructures. The calculation data indicate that PL energy of C-dots is dictated by the size and microstructure of the sp2 carbon core. For a C-dot with a graphitized core, the smaller the size of the core, the higher the PL energy, while for a C-dot with an amorphous core, an inverse trend is revealed. Surface reduction experiments further show that the quantum yield of C-dots is controlled by the surface chemistry.

Hydrophilic polymeric nanoparticles are synthesized through a Bergman cyclization- mediated intramolecular chain collapse of structurally well-defined linear polymers, and then used as size-tunable nanoreactors to fabricate and encapsulate quantum dots in a one-pot reaction. Crystalline quantum dots are formed in all of these nanoreactors and visualized by transmission electron microscopy. Smaller nanoreactors produce one quantum dot each while larger nanoreactors form a number, resulting in fluorescence quenching. By controlling the molecular weight of the linear polymer precursor, a variable number of nanocrystals are fabricated and assembled in a single nanoreactor.

Polymeric nanoparticles were synthesized through Bergman cyclization mediated intramolecular chain collapse. Enediyne moieties were incorporated into linear polymers through copolymerization or post-polymerization modification. The resulted enediyne containing copolymers were then subjected to intramolecular chain collapse under ultra-dilute condition or applying a continuous addition technique. The occurrence of Bergman cyclization was confirmed with IR, NMR and DSC analysis. The intramolecular chain collapse was characterized with GPC, DSC, and AFM. Dramatic decreases of apparent molecular weights of linear copolymers were observed after Bergman cyclization. The structural diversity of enediyne precursors and mild chain collapse condition allow wide monomer selection, which facilitates preparation of a broad range of polymeric nanoparticles. Low-k dielectric thin films were prepared using polymeric nanoparticles through “porogen” approach. The packing tightness of polymeric nanoparticles showed strong influence on film formation behavior with MSSQ matrix. With tightly packed polymeric nanoparticles as sacrificial pore generators, thin films with dielectric constants of as low as 2.1 were obtained.