Quantification of Heterogeneous Degradation in Li‐Ion Batteries

The multiscale chemomechanical interplay in lithium‐ion batteries builds up mechanical stress, provokes morphological breakdown, and leads to state of charge heterogeneity. Quantifying the interplay in complex composite electrodes with multiscale resolution constitutes a frontier challenge in precisely diagnosing the fading mechanism of batteries. In this study, hard X‐ray phase contrast tomography, capable of nanoprobing thousands of active particles at once, enables an unprecedented statistical analysis of the chemomechanical transformation of composite electrodes under fast charging conditions. The damage heterogeneity is demonstrated to prevail at all length scales, which stems from the unbalanced electron conduction and ionic diffusion, and collectively leads to the nonuniform utilization of active particles spatially and temporally. This study highlights that the statistical mapping of the chemomechanical transformation offers a diagnostic method for the particles utilization and fading, hence could improve electrode formulation for fast‐charging batteries.     

Spinel‐Layered Core‐Shell Cathode Materials for Li‐Ion Batteries

In an attempt to overcome the problems associated with LiNiO₂, the solid solution series of lithium nickel‐metal oxides, Li[Ni_1–xM_x]O₂ (with M = Co, Mn, Al, Ti, Mg, etc.), have been investigated as favorable cathode materials for high‐energy and high‐power lithium‐ion batteries. However, along with the improvement in the electrochemical properties in Ni‐based cathode materials, the thermal stability has been a great concern, and thus violent reaction of the cathode with the electrolyte needs to be avoided. Here, we report a heterostructured Li[Ni_0.54Co_0.12Mn_0.34]O₂ cathode material which possesses both high energy and safety. The core of the particle is Li[Ni_0.54Co_0.12Mn_0.34]O₂ with a layered phase (R3‐m) and the shell, with a thickness of < 0.5 μm, is a highly stable Li_1+x[CoNi_xMn_2–x]₂O₄ spinel phase (Fd‐3m). The material demonstrates reversible capacity of 200 mAhg‐1 and retains 95% capacity retention under the most severe test condition of 60 °C. In addition, the amount of oxygen evolution from the lattice in the cathode with two heterostructures is reduced by 70%, compared to the reference sample. All these results suggest that the bulk Li[Ni_0.54Co_0.12Mn_0.34]O₂ consisting of two heterostructures satisfy the requirements for hybrid electric vehicles, power tools, and mobile electronics.     

A New Spinel‐Layered Li‐Rich Microsphere as a High‐Rate Cathode Material for Li‐Ion Batteries

Li‐rich layered materials are considered to be the promising low‐cost cathodes for lithium‐ion batteries but they suffer from poor rate capability despite of efforts toward surface coating or foreign dopings. Here, spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres are reported as a new high‐rate cathode material for Li‐ion batteries. The synthetic procedure is relatively simple, involving the formation of uniform carbonate precursor under solvothermal conditions and its subsequent transformation to an assembled microsphere that integrates a spinel‐like component with a layered component by a heat treatment. When calcined at 700 °C, the amount of transition metal Mn and Co in the Li‐Mn‐Co‐O microspheres maintained is similar to at 800 °C, while the structures of constituent particles partially transform from 2D to 3D channels. As a consequence, when tested as a cathode for lithium‐ion batteries, the spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres obtained at 700 °C show a maximum discharge capacity of 185.1 mA h g^?1 at a very high current density of 1200 mA g^?1 between 2.0 and 4.6 V. Such a capacity is among the highest reported to date at high charge‐discharge rates. Therefore, the present spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres represent an attractive alternative to high‐rate electrode materials for lithium‐ion batteries.     

Single‐Particle Performances and Properties of LiFePO4 Nanocrystals for Li‐Ion Batteries

It has been recently reported that the solution diffusion, efficiency porosity, and electrode thickness can dominate the high rate performance in the 3D‐printed and traditional LiMn_0.21Fe_0.79PO₄ electrodes for Li‐ions batteries. Here, the intrinsic properties and performances of the single‐particle (SP) of LiFePO₄ are investigated by developing the SP electrode and creating the SP‐model, which will share deep insight on how to further improve the performance of the electrode and related materials. The SP electrode is generated by fully scattering and distributing LiFePO₄ nanoparticles to contact with the conductive network of carbon nanotube or conductive carbon to demonstrate the sharpest cyclic voltammetry peak and related SP‐model is developed, by which it is found that the interfacial rate constant in aqueous electrolyte is one order of magnitude higher, accounting for the excellent rate performance in aqueous electrolyte for LiFePO₄. For the first time it has been proposed that the insight of pre‐exponential factor of interface kinetic Arrhenius equation is related to desolvation/solvation process. Thus, this much higher interfacial rate constant in aqueous electrolyte shall be attributed to the much larger pre‐exponential factor of interface kinetic Arrhenius equation, because the desolvation process is much easier for Li‐ions jumping from aqueous electrolyte to the Janus solid–liquid interface of LiFePO₄.     

Design and Performance of Rechargeable Sodium Ion Batteries,and Symmetrical Li‐Ion Batteries with Supercapacitor‐Like Power Density Based upon Polyoxovanadates

The polyanion Li₇V₁₅O₃₆(CO₃) is a nanosized molecular cluster (≈1 nm in size), that has the potential to form an open host framework with a higher surface‐to‐bulk ratio than conventional transition metal oxide electrode materials. Herein, practical rechargeable Na‐ion batteries and symmetric Li‐ion batteries are demonstrated based on the polyoxovanadate Li₇V₁₅O₃₆(CO₃). The vanadium centers in {V₁₅O₃₆(CO₃)} do not all have the same V^IV/V redox potentials, which permits symmetric devices to be created from this material that exhibit battery‐like energy density and supercapacitor‐like power density. An ultrahigh specific power of 51.5 kW kg^?1 at 100 A g^?1 and a specific energy of 125 W h kg^?1 can be achieved, along with a long cycling life (>500 cycles). Moreover, electrochemical and theoretical studies reveal that {V₁₅O₃₆(CO₃)} also allows the transport of large cations, like Na⁺, and that it can serve as the cathode material for rechargeable Na‐ion batteries with a high specific capacity of 240 mA h g^?1 and a specific energy of 390 W h kg^?1 for the full Na‐ion battery. Finally, the polyoxometalate material from these electrochemical energy storage devices can be easily extracted from spent electrodes by simple treatment with water, providing a potential route to recycling of the redox active material.     

Application of Synchrotron Radiation Technologies to Electrode Materials for Li‐ and Na‐Ion Batteries

The search for superior‐energy‐density electrode materials for rechargeable batteries is prompted by the continuously growing demand for new electric vehicles and large energy‐storage grids. The structural properties of electrode materials affect their electrochemical performance because their functionality is correlated to their structure at the atomic scale. Although challenging, a deeper and comprehensive understanding of the basic structural operating units of electrode materials may contribute to the advancement of new energy‐storage technologies and many other technologies. Therefore, we must strategically control both the structure and kinetics of electrode materials to achieve optimal electrochemical performance. In this contribution, advancements in synchrotron radiation techniques, specifically in situ/operando experiments on electrode materials for rechargeable batteries, are presented and discussed. Indeed, the latest synchrotron radiation methods offer deeper insights into pristine and chemically modified electrode materials, opening new opportunities to optimize these materials and exploit new technologies. In particular, the most recent results from in situ/operando synchrotron radiation measurements, which play a critical role in the fundamental understanding of the kinetics processes that occur in rechargeable batteries, are discussed.     

High‐Quality Graphene Microflower Design for High‐Performance Li–S and Al‐Ion Batteries

Poor quality and insufficient productivity are two main obstacles for the practical application of graphene in electrochemical energy storage. Here, high‐quality crumpled graphene microflower (GmF) for high‐performance electrodes is designed. The GmF possesses four advantages simultaneously: highly crystallized defect‐free graphene layers, low stacking degree, sub‐millimeter continuous surface, and large productivity with low cost. When utilized as carbon host for sulfur cathode, the GmF‐sulfur hybrid delivers decent areal capacities of 5.2 mAh cm^?2 at 0.1 C and 3.8 mAh cm^?2 at 0.5 C. When utilized as cathode of Al‐ion battery, the GmF affords a high capacity of 100 mAh g^?1 with 100% capacity retention after 5000 cycles and excellent rate capability from 0.1 to 20 A g^?1. This facile and large‐scale producible GmF represents a meaningful high‐quality graphene powder for practical energy storage technology. Meanwhile, this unique high‐quality graphene design provides an effective route to improve electrochemical properties of graphene‐based electrodes.     

Cyclic Aminosilane‐Based Additive Ensuring Stable Electrode–Electrolyte Interfaces in Li‐Ion Batteries

Ni‐rich cathodes are considered feasible candidates for high‐energy‐density Li‐ion batteries (LIBs). However, the structural degradation of Ni‐rich cathodes on the micro‐ and nanoscale leads to severe capacity fading, thereby impeding their practical use in LIBs. Here, it is reported that 3‐(trimethylsilyl)‐2‐oxazolidinone (TMS‐ON) as a multifunctional additive promotes the dissociation of LiPF₆, prevents the hydrolysis of ion‐paired LiPF₆ (which produces undesired acidic compounds including HF), and scavenges HF in the electrolyte. Further, the presence of 0.5 wt% TMS‐ON helps maintain a stable solid–electrolyte interphase (SEI) at Ni‐rich LiNi_0.7Co_0.15Mn_0.15O₂ (NCM) cathodes, thus mitigating the irreversible phase transformation from layered to rock‐salt structures and enabling the long‐term stability of the SEI at the graphite anode with low interfacial resistance. Notably, NCM/graphite full cells with TMS‐ON, which exhibit an excellent discharge capacity retention of 80.4%, deliver a discharge capacity of 154.7 mAh g^?1 after 400 cycles at 45 °C.     

Ionically Conductive Self‐Healing Binder for Low Cost Si Microparticles Anodes in Li‐Ion Batteries

A self‐healing polymer (SHP) with abundant hydrogen bonds, appropriate viscoelasticity, and stretchability is a promising binder to improve cycle performance of Si microparticle anodes in lithium (Li) ion batteries. Besides high capacity and long cycle life, efficient rate performance is strongly desirable for practical Si anode implementation. Here, polyethylene glycol (PEG) groups are incorporated into the SHP, facilitating Li ionic conduction within the binder. The concept of the SHP‐PEG binder involves improving the interface between Si microparticles and electrolytes after cycling based on the combination of self‐healing ability and fast Li ionic conduction. Through the systematic study of mixing PEG Mw and ratio, the polymeric binder combining SHP and PEG with M_w 750 in an optimal ratio of 60:40 (mol%) achieves a high discharging capacity of ≈2600 mA h g^?1, reasonable rate performance especially when >1C and maintains 80% of their initial capacity even after ≈150 cycles at 0.5C. The described concept for the polymeric binder, embedding both self‐healing ability and high Li ionic conductivity, should be equally useful for next generation batteries utilizing high capacity materials which suffer from huge volume change during cycling.     

Vanadate‐Based Materials for Li‐Ion Batteries: The Search for Anodes for Practical Applications

While the practical application of electrode materials depends intensively on the Li⁺ ion storage mechanisms correlating ultimately with the coulombic efficiency, reversible capacity, and morphology variation of electrode material upon cycling, only intercalation‐type electrode materials have proven viable for commercialization up to now. This paper reviews the promising anode materials of metal vanadates (M_xV_yO_z, M = Co, Cu, Mn, Fe, Zn, Ni, Li) that have high capacity, low cost, and abundant resource, and also discusses the related Li⁺ ion storage mechanism. It is concluded that most of these (M_xV_yO_z, M = Co, Cu, Mn, Fe, Zn, Ni) exhibit irreversible redox reactions upon lithiation/delithiation accompanied by large volume expansion, which is not favorable for industrial applications. In particular, Li₃VO₄ with specific intercalation Li⁺ ion storage mechanism and compatible merits of safety and energy density exhibits great potential for practical application. This review systematically summarizes the latest progress in Li₃VO₄ research, including the representative fabrication approaches for advanced morphology and state‐of‐the‐art technologies to boost performance and the morphology variation associated with Li⁺ ion storage mechanisms. Furthermore, an outlook on where breakthroughs for Li₃VO₄ may be most likely achieved will be provided.     

Structural Changes in Li2MnO3 Cathode Material for Li‐Ion Batteries

Structural changes in Li₂MnO₃ cathode material for rechargeable Li‐ion batteries are investigated during the first and 33^rd cycles. It is found that both the participation of oxygen anions in redox processes and Li⁺‐H⁺ exchange play an important role in the electrochemistry of Li₂MnO₃. During activation, oxygen removal from the material along with Li gives rise to the formation of a layered MnO₂‐type structure, while the presence of protons in the interslab region, as a result of electrolyte oxidation and Li⁺‐H⁺ exchange, alters the stacking sequence of oxygen layers. Li re‐insertion by exchanging already present protons reverts the stacking sequence of oxygen layers. The re‐lithiated structure closely resembles the parent Li₂MnO₃, except that it contains less Li and O. Mn⁴⁺ ions remain electrochemically inactive at all times. Irreversible oxygen release occurs only during activation of the material in the first cycle. During subsequent cycles, electrochemical processes seem to involve unusual redox processes of oxygen anions of active material along with the repetitive, irreversible oxidation of electrolyte species. The deteriorating electrochemical performance of Li₂MnO₃ upon cycling is attributed to the structural degradation caused by repetitive shearing of oxygen layers.     

Na‐Mn‐O Nanocrystals as a High Capacity and Long Life Anode Material for Li‐Ion Batteries

Searching for a new material to build the next‐generation rechargeable lithium‐ion batteries (LIBs) with high electrochemical performance is urgently required. Owing to the low‐cost, non‐toxicity, and high‐safety, the family of manganese oxide including the Na‐Mn‐O system is regarded as one of the most promising electrode materials for LIBs. Herein, a new strategy is carried out to prepare a highly porous and electrochemically active Na_0.55Mn₂O₄·1.5H₂O (SMOH) compound. As an anode material, the Na‐Mn‐O nanocrystal material dispersed within a carbon matrix manifests a high reversible capacity of 1015.5 mA h g^?1 at a current density of 0.1 A g^?1. Remarkably, a considerable capability of 546.8 mA h g^?1 remains even after 2000 discharge/charge cycles at the higher current density of 4 A g^?1, indicating a splendid cyclability. The exceptional electrochemical properties allow SMOH to be a promising anode material toward LIBs.     

Laser‐Assisted Ultrafast Exfoliation of Black Phosphorus in Liquid with Tunable Thickness for Li‐Ion Batteries

Few‐layer black phosphorus (BP) is an emerging 2D material suitable for energy applications. However, its controllable preparation remains challenging. Herein, a highly efficient route is presented for the scalable production of few‐layered BP nanosheets using a pulsed laser in low‐boiling point solvents. Changing the laser irradiation time, energy, and solvent type leads to precise control over the layer number and lateral size of the nanosheets with a narrow distribution. The process is understood by a plasma quenching mechanism and interlayer interaction weakened by the in situ generated vapor bubbles. The excellent control of the BP nanosheets enables morphological effects on Li‐ion battery performance to be studied. Low layer numbers benefit both charge transfer and Li⁺ ion diffusion, while a high aspect ratio can not only improve the charge transfer but also increase the Li⁺ ion diffusion path. This study delivers insights on the tailored fabrication of thin 2D materials using lasers for morphology‐dependent electrochemical energy conversion and storage.     

Ni‐Rich/Co‐Poor Layered Cathode for Automotive Li‐Ion Batteries: Promises and Challenges

To pursue a higher energy density (>300 Wh kg^?1 at the cell level) and a lower cost (<$125 kWh^?1 expected at 2022) of Li‐ion batteries for making electric vehicles (EVs) long range and cost‐competitive with internal combustion engine vehicles, developing Ni‐rich/Co‐poor layered cathode (LiNi_1?x?yCo_xMn_yO₂, x+y ≤ 0.2) is currently one of the most promising strategies because high Ni content is beneficial to high capacity (>200 mAh g^?1) while low Co content is favorable to minimize battery cost. Unfortunately, Ni‐rich cathodes suffer from limited structure stability and electrode/electrolyte interface stability in the charged state, leading to electrode degradation and poor cycling performance. To address these problems, various strategies have been employed such as doping, structural optimization design (e.g., core–shell structure, concentration‐gradient structure, etc.), and surface coating. In this review, five key aspects of Ni‐rich/Co‐poor layered cathode materials are explored: energy density, fast charge capability, service life including cycling life and calendar life, cost and element resources, and safety. This enables a comprehensive analysis of current research advances and challenges from the perspective of both academy and industry to help facilitate practical applications for EVs in the future.     

Spectroscopic Insight into Li‐Ion Batteries during Operation: An Alternative Infrared Approach

Multiple‐internal‐reflection infrared spectroscopy allows for the study of thin‐film amorphous silicon electrodes in situ and in operando, in conditions typical of those used in Li‐ion batteries. It brings an enhanced sensitivity, and the attenuated‐total‐reflection geometry allows for the extraction of quantitative information. When electrodes are cycled in representative electrolytes, the simultaneously recorded infrared spectra give an insight into the solid/electrolyte interphase (SEI) composition. They also unravel the dynamic behavior of this SEI layer by quantitatively assessing its thickness, which increases during silicon lithiation and partially decreases during delithiation. Li‐ion solvation effects in the vicinity of the electrode indicate that lithium incorporation in the solid phase is the rate‐determining step of the electrochemical processes during lithiation. The lithiation of the active material also results in the irreversible consumption of a large quantity of hydrogen in the pristine material. Finally, the evolution of the electronic absorption of the electrode material suggests that lithium diffusion is much easier after the first lithiation than in the pristine material. Therefore, in situ Fourier‐transform infrared spectroscopy performed in a well‐suited configuration efficiently extracts original and quantitative pieces of information on the surface and bulk phenomena affecting Li‐ion electrodes during their operation in realistic conditions.     

Review on Challenges and Recent Advances in the Electrochemical Performance of High Capacity Li‐ and Mn‐Rich Cathode Materials for Li‐Ion Batteries

Li and Mn‐rich layered oxides, xLi₂MnO₃·(1–x)LiMO₂ (M=Ni, Mn, Co), are promising cathode materials for Li‐ion batteries because of their high specific capacity that can exceed 250 mA h g^?1. However, these materials suffer from high 1^st cycle irreversible capacity, gradual capacity fading, low rate capability, a substantial charge‐discharge voltage hysteresis, and a large average discharge voltage decay during cycling. The latter detrimental phenomenon is ascribed to irreversible structural transformations upon cycling of these cathodes related to potentials ≥4.5 V required for their charging. Transition metal inactivation along with impedance increase and partial layered‐to‐spinel transformation during cycling are possible reasons for the detrimental voltage fade. Doping of Li, Mn‐rich materials by Na, Mg, Al, Fe, Co, Ru, etc. is useful for stabilizing capacity and mitigating the discharge‐voltage decay of xLi₂MnO₃·(1–x)LiMO₂ electrodes. Surface modifications by thin coatings of Al₂O₃, V₂O₅, AlF₃, AlPO₄, etc. or by gas treatment (for instance, by NH₃) can also enhance voltage and capacity stability during cycling. This paper describes the recent literature results and ongoing efforts from our groups to improve the performance of Li, Mn‐rich materials. Focus is also on preparation of cobalt‐free cathodes, which are integrated layered‐spinel materials with high reversible capacity and stable performance.