Work Function Evolution in Li Anode Processing

Toward improved understanding and control of the interactions of Li metal anodes with their processing environments, a combined X‐ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) characterization of the effects that O₂, CO₂, and N₂, the main gases in dry‐atmosphere battery production lines, induced on a reproducibly clean Li surface at room temperature is presented here. XPS measurements demonstrate that O₂ is ten times more effective than CO₂ at oxidizing metal Li. Notably, pure N₂ is shown to not dissociate on clean metal Li. UPS results indicate that decomposition of O₂ (CO₂) reduces the work function of the Li surface by almost 1 eV, therefore increasing the reduction energy drive for the treated substrate by comparison to bare metallic Li. DFT simulations semiquantitatively account for these results on the basis of the effects of dissociative gas adsorption on the surface dipole density of the Li surface.     

Introducing Highly Redox‐Active Atomic Centers into Insertion‐Type Electrodes for Lithium‐Ion Batteries

The development of alternative anode materials with higher volumetric and gravimetric capacity allowing for fast delithiation and, even more important, lithiation is crucial for next‐generation lithium‐ion batteries. Herein, the development of a completely new active material is reported, which follows an insertion‐type lithiation mechanism, metal‐doped CeO₂. Remarkably, the introduction of carefully selected dopants, herein exemplified for iron, results in an increase of the achievable capacity by more than 200%, originating from the reduction of the dopant to the metallic state and additional space for the lithium ion insertion due to a significant off‐centering of the dopant atoms in the crystal structure, away from the original Ce site. In addition to the outstanding performance of such materials in high‐power lithium‐ion full‐cells, the selective reduction of the iron dopant under preservation of the crystal structure of the host material is expected to open up a new field of research.     

Cascade‐Type Prelithiation Approach for Li‐Ion Capacitors

An industry‐relevant method for pre‐lithiation of lithium‐ion capacitors to balance the first charge irreversibility is demonstrated, which addresses the prime bottleneck for their market integration. Based on a composite positive electrode that integrates pyrene monomers and an insoluble lithiated base, Li₃PO₄, a “cascade‐type” process involving two consecutive irreversible reactions is proposed: i) oxidative electropolymerization of the pyrene moieties releases electrons and protons; ii) protons are captured by Li₃PO₄ and exchanged for a stoichiometric amount of Li⁺ into the electrolyte. (¹H, ¹⁹F, and ³¹P) NMR spectroscopy, operando X‐ray diffraction, and Raman spectroscopy support this mechanism. By decoupling the irreversible source of lithium ions from electrons, the cascade‐type pre‐lithiation allows the simultaneous enhancement of the capacity of the positive electrode, thanks to p‐doping of the resulting polymer. Remarkably, the proton scavenging properties of Li₃PO₄ also boost the polymerization process, which enables a 16% increase in capacity without detrimental effect on power properties and cyclability. Full cells integrating a cheap carbon black based negative electrode, show much‐improved capacity of 17 mAh g^‐1_electrodes (44 F g^‐1_electrodes, 3–4.4 V) and excellent stability over 2200 cycles at 1 A g^‐1. Thanks to its versatile chemistry and flexibility this approach in principle can be applied to any kind of ion‐battery.     

Hollow Carbon Spheres and Their Hybrid Nanomaterials in Electrochemical Energy Storage

Electrochemical energy storage is of extraordinary importance for fulfilling the utilization of renewable and sustainable energy sources. There is an increasing demand for energy storage devices with high energy and power densities, prolonged stability, safety, and low cost. In the past decade, numerous research efforts have been devoted to achieving these requirements, especially in the design of advanced electrode materials. Hollow carbon spheres (HCS) derived nanomaterials combining the advantages of 3D HCS and porous structures have been considered as alternative electrode materials for advanced energy storage applications, due to their unique features such as high surface‐to‐volume ratios, encapsulation capability, together with outstanding chemical and thermal stability. In this review, the authors first present a comprehensive overview of the synthetic strategies of HCS, and elucidate the design and synthesis of HCS‐derived nanomaterials including various types of HCS and their nanohybrids. Additionally, their significant roles as electrode materials for supercapacitors, lithium‐ion or sodium‐ion batteries, and sulfur hosts for lithium sulfur batteries are highlighted. Finally, current challenges in the synthesis of HCS and future directions in HCS‐derived nanomaterials for energy storage applications are proposed.     

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.     

Conductive Copper Niobate: Superior Li+‐Storage Capability and Novel Li+‐Transport Mechanism

Niobates with shear ReO₃ crystal structures are remarkably promising anode materials for Li⁺ batteries due to their large capacities, inherent safety, and high cycling stability. However, they generally suffer from limited rate capabilities rooted in their insufficient electronic and Li⁺ conductivities. Here, micrometer‐sized copper niobate (Cu₂Nb₃₄O₈₇) bulk as a new anode material having a high electronic conductivity of 2.1 × 10^?5 S cm^?1 and an impressive average Li⁺ diffusion coefficient of ≈3.5 × 10^?13 cm² s^?1 is exploited, which synergistically leads to an excellent rate capability (184 mAh g^?1 at 10 C) while remaining a large reversible capacity and superior cycling stability. Moreover, the fast Li⁺ transport pathways of grain boundary (micrometer scale) → lattice deformation area (nanometer scale) → (010) crystallographic plane (angstrom scale) are demonstrated in Cu₂Nb₃₄O₈₇. Therefore, these results could pave the way for practical application of Cu₂Nb₃₄O₈₇ in high‐performance Li⁺ batteries.     

Highly Tough,Li‐Metal Compatible Organic–Inorganic Double‐Network Solvate Ionogel

Ionogels are considered promising electrolytes for safe lithium‐ion batteries (LIBs) because of their low flammability, good thermal stability, and wide electrochemical stability window. Conventional ionic liquid‐based ionogels, however, face two main challenges; poor mechanical property and low Li‐ion transfer number. In this work, a novel solvate ionogel electrolyte (SIGE) based on an organic–inorganic double network (DN) is designed and fabricated through nonhydrolytic sol–gel reaction and in situ polymerization processes. The unprecedented SIGE possesses high toughness (bearing the deformation under the pressure of 80 MPa without damage), high Li‐ion transfer number of 0.43, and excellent Li‐metal compatibility. As expected, the LiFePO₄/Li cell using the newly developed SIGE delivers a high capacity retention of 95.2% over 500 cycles, and the average Coulombic efficiency is as high as 99.8%. Moreover, the Ni‐rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811)/Li cell based on the modified SIGE achieves a high Coulombic efficiency of 99.4%, which outperforms previous solid/quasi‐solid‐state NCM811‐based LIBs. Interestingly, the SIGE‐based pouch cells are workable under extreme conditions (e.g., severely deforming or clipping into segments). In terms of those unusual features, the as‐obtained SIGE holds great promise for next‐generation flexible and safe energy‐storage devices.     

Microscale Lithium Metal Stored inside Cellular Graphene Scaffold toward Advanced Metallic Lithium Anodes

The volume expansion and dendrite growth of metallic Li anode during charge/discharge processes hinder its practical application in energy storage. Seeking an appropriate host for distributing bulk Li in a 3D manner is an effective way to solve these problems. Here, a novel porous graphene scaffold with cellular chambers for incorporating Li metal is presented. Using such a unique host, ultrathin Li layers of 3 µm in thickness are anchored on graphene to form porous microstructures, which provides much more reaction sites for Li ions compared with that of bulk Li, significantly promoting the reversibility of Li stripping and plating. Also the high current density can be effectively dissipated by the graphene scaffold to remarkably improve the rate capability of Li anode. The symmetrical Li cell using such a Li anode can run stably for 200 cycles at 5 mA cm^?2 and even 70 cycles at 10 mA cm^?2 in an unmodified carbonate‐based electrolyte, which has rarely been achieved in such aggressive working conditions. Lithium‐ion capacitor cells using this anode also show outstanding rate capability and cycling stability, which can work at an ultrahigh current density of 30 A g^?1 and keep steady for over 4000 cycles at 3.75 A g^?1.     

Organohalide Perovskites are Fast Ionic Conductors

Fast ionic conductors constitute a family of materials exhibiting high values of the ionic conductivity while their crystal structure remains rather rigid. Perovskite‐like compounds are known to be good ionic conductors with applications as solid electrolytes. In hybrid halide perovskites both intrinsic (native) and extrinsic defect migration are regarded to occur. Ion diffusivity analysis is inherently ambiguous in all‐solid‐state configurations because of the multicomponent environment. Here, a liquid electrolyte in contact to the perovskite material forms a reservoir of Li⁺ that is forced to intercalate and migrate within the perovskite electrode. This approach decouples different contributions to transport in such a way that ion diffusion kinetics is easily accessible by means of impedance methods. The room‐temperature chemical diffusion coefficient of lithium ion within the perovskite lattice exhibits values as high as D _μ ≈ 10^?7 cm² s^?1, which implies conductivities within the range of 10^?3 Ω^?1 cm^?1 for highly lithiated electrodes. This confirms the superionic intrinsic property of organohalide perovskites from a direct and unambiguous measurement that does not rely upon simulation tools.     

MXene‐Based Mesoporous Nanosheets Toward Superior Lithium Ion Conductors

Although solid polymer electrolytes have some intrinsic advantages in synthesis and film processing compared with inorganic solid electrolytes, low ionic conductivities and mechanical moduli hamper their practical applications in lithium‐based batteries. Here, an efficient strategy is developed to produce a unique solid polymer electrolyte containing MXene‐based mesoporous silica nanosheets with a sandwich structure, which are fabricated via controllable hydrolysis of tetraethyl orthosilicate around the surface of MXene‐Ti₃C₂ under the direction of cationic surfactants. Such unique nanosheets not only exhibit individual, thin, and insulated features, but also possess abundant functional groups in mesopores and on the surface, which are favorable for the formation of Lewis acid–base interactions with anions in polymer electrolytes such as poly(propylene oxide) elastomer, enabling the fast Li⁺ transportation at the mesoporous nanosheets/polymer interfaces. As a consequence, a solid polymer electrolyte with high ionic conductivity of 4.6 × 10^?4 S cm^?1, high Young's modulus of 10.5 MPa, and long‐term electrochemical stability is achieved.     

Hierarchical Carbon Decorated Li3V2(PO4)3 as a Bicontinuous Cathode with High‐Rate Capability and Broad Temperature Adaptability

Developing rechargeable lithium ion batteries with fast charge/discharge rate, high capacity and power, long lifespan, and broad temperature adaptability is still a significant challenge. In order to realize the fast and efficient transport of ions and electrons during the charging/discharging process, a 3D hierarchical carbon‐decorated Li₃V₂(PO₄)₃ is designed and synthesized with a nanoscale amorphous carbon coating and a microscale carbon network. The Brunauer–Emmett–Teller (BET) surface area is 65.4 m² g^?1 and the porosity allows for easy access of the electrolyte to the active material. A specific capacity of 121 mAh g^?1 (91% of the theoretical capacity) can be obtained at a rate up to 30 C. When cycled at a rate of 20 C, the capacity retention is 77% after 4000 cycles, corresponding to a capacity fading of 0.0065% per cycle. More importantly, the composite cathode shows excellent temperature adaptability. The specific discharge capacities can reach 130 mAh g^?1 at 20 C and 60 °C, and 106 mAh g^?1 at 5 C and –20 °C. The rate performance and broad temperature adaptability demonstrate that this hierarchical carbon‐decorated Li₃V₂(PO₄)₃ is one of the most attractive cathodes for practical applications.     

Nanoporous Hybrid Electrolytes for High‐Energy Batteries Based on Reactive Metal Anodes

Successful strategies for stabilizing electrodeposition of reactive metals, including lithium, sodium, and aluminum are a requirement for safe, high‐energy electrochemical storage technologies that utilize these metals as anodes. Unstable deposition produces high‐surface area dendritic structures at the anode/electrolyte interface, which causes premature cell failure by complex physical and chemical processes that have presented formidable barriers to progress. Here, it is reported that hybrid electrolytes created by infusing conventional liquid electrolytes into nanoporous membranes provide exceptional ability to stabilize Li. Electrochemical cells based on γ‐Al₂O₃ ceramics with pore diameters below a cut‐off value above 200 nm exhibit long‐term stability even at a current density of 3 mA cm^?2. The effect is not limited to ceramics; similar large enhancements in stability are observed for polypropylene membranes with less monodisperse pores below 450 nm. These findings are critically assessed using theories for ion rectification and electrodeposition reactions in porous solids and show that the source of stable electrodeposition in nanoporous electrolytes is fundamental.     

High‐Performance Aqueous Rechargeable Li‐Ni Battery Based on Ni(OH)2/NiOOH Redox Couple with High Voltage

New energy storage and conversion systems require large‐scale, cost‐effective, good safety, high reliability, and high energy density. This study demonstrates a low‐cost and safe aqueous rechargeable lithium‐nickel (Li‐Ni) battery with solid state Ni(OH)₂/NiOOH redox couple as cathode and hybrid electrolytes separated by a Li‐ion‐conductive solid electrolyte layer. The proposed aqueous rechargeable Li‐Ni battery exhibits an approximately open‐circuit potential of 3.5 V, outperforming the theoretic stable window of water 1.23 V, and its energy density can be 912.6 W h kg^‐1, which is much higher than that of state‐of‐the‐art lithium ion batteries. The use of a solid‐state redox couple as cathode with a metallic lithium anode provides another postlithium chemistry for practical energy storage and conversion.