Galvanic Corrosion of Lithium‐Powder‐Based Electrodes

Lithium metal is considered to be the most promising anode for the next generation of batteries if the issues related to safety and low coulombic efficiency can be overcome. It is known that the initial morphology of the lithium metal anode has a great influence on the cycling characteristics of a lithium metal battery (LMB). Lithium‐powder‐based electrodes (Li_p‐electrodes) are reported to diminish the occurrence of high surface area lithium deposits. Usually, ultra‐thin lithium foils (<50 µm) and Li_p‐electrodes are prepared on a copper substrate, thus a metal–metal contact area is generated. The combination of these two metals in the presence of an electrolyte, however, can lead to galvanic corrosion. Herein, the corrosion behavior of Li_p‐electrodes is studied. The porosity of such electrodes leads to a high amount of accessible Cu surface in contact with electrolyte. As a consequence, Li_p‐electrodes aged for 1 week in the electrolyte show spontaneous lithium dissolution near the junction to copper and void formation on the lithium‐powder particles. This corrosion process affects the delivered capacity of Li_p‐electrodes and increases the overvoltage of the lithium electrodissolution process. The occurrence of corrosion at the Cu|Li_p interface raises concerns about the practicality of multi‐metallic component systems for LMBs.     

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.     

Coated Lithium Powder (CLiP) Electrodes for Lithium‐Metal Batteries

Safety issues caused by the metallic lithium inside a battery represent one of the main reasons for the lack of commercial availability of rechargeable lithium‐metal batteries. The advantage of anodes based on coated lithium powder (CLiP), compared to plain lithium foil, include the suppression of dendrite formation, as the local current density during stripping/plating is reduced due to the higher surface area. Another performance and safety advantage of lithium powder is the precisely controlled mass loading of the lithium anode during electrode preparation, giving the opportunity to avoid Li excess in the cell. As an additional benefit, the coating makes electrode manufacturing safer and eases handling. Here, electrodes based on coated lithium powder electrodes (CLiP) are introduced for application in lithium‐metal batteries. These electrodes are compared to lithium foil electrodes with respect to cycling stability, coulombic efficiency of lithium stripping/plating, overpotential, and morphology changes during cycling.     

The Configurational Space of Rocksalt‐Type Oxides for High‐Capacity Lithium Battery Electrodes

A unifying theory is presented to explain the lithium exchange capacity of rocksalt‐like structures with any degree of cation ordering, and how lithium percolation properties can be used as a guideline for the development of novel high‐capacity electrode materials is demonstrated. The lithium percolation properties of the three most common lithium metal oxide phases, the layered α‐NaFeO₂ structure, the spinel‐like LT‐LiCoO₂ structure, and the γ‐LiFeO₂ structure, are demonstrated and a strong dependence of the percolation thresholds on the cation ordering and the lithium content is observed. The poor performance of γ‐LiFeO₂‐type structures is explained by their lack of percolation of good Li migration channels. The spinel‐like structure exhibits excellent percolation properties that are robust with respect to off‐stoichiometry and some amount of cation disorder. The layered structure is unique, as it possesses two different types of lithium diffusion channels, one of which is, however, strongly dependent on the lattice parameters, and therefore very sensitive to disorder. In general it is found that a critical Li‐excess concentration exists at which Li percolation occurs, although the amount of Li excess needed depends on the partial cation ordering. In fully cation‐disordered materials, macroscopic lithium diffusion is enabled by ≈10% excess lithium.     

Nanoarchitectured Array Electrodes for Rechargeable Lithium‐ and Sodium‐Ion Batteries

Rechargeable ion batteries have contributed immensely to shaping the modern world and been seriously considered for the efficient storage and utilization of intermittent renewable energies. To fulfill their potential in the future market, superior battery performance of high capacity, great rate capability, and long lifespan is undoubtedly required. In the past decade, along with discovering new electrode materials, the focus has been shifting more and more toward rational electrode designs because the performance is intimately connected to the electrode architectures, particularly their designs at the nanoscale that can alleviate the reliance on the materials' intrinsic nature. The utilization of nanoarchitectured arrays in the design of electrodes has been proven to significantly improve the battery performance. A comprehensive summary of the structural features and fabrications of the nanoarchitectured array electrodes is provided, and some of the latest achievements in the area of both lithium‐ and sodium‐ion batteries are highlighted. Finally, future challenges and opportunities that would allow further development of such advanced electrode configuration are discussed.     

A New Hydrophilic Binder Enabling Strongly Anchoring Polysulfides for High‐Performance Sulfur Electrodes in Lithium‐Sulfur Battery

As one of the important ingredients in lithium‐sulfur battery, the binders greatly impact the battery performance. However, conventional binders have intrinsic drawbacks such as poor capability of absorbing hydrophilic lithium polysulfides, resulting in severe capacity decay. This study reports a new type of binder by polymerization of hydrophilic poly(ethylene glycol) diglycidyl ether with polyethylenimine, which enables strongly anchoring polysulfides for high‐performance lithium sulfur batteries, demonstrating remarkable improvement in both mechanical performance for standing up to 100 g weight and an excellent capacity retention of 72% over 400 cycles at 1.5 C. Importantly, in situ micro‐Raman investigation verifies the effectively reduced polysulfides shuttling from sulfur cathode to lithium anode, which shows the greatly suppressed shuttle effect by the polar‐functional binder. X‐ray photoelectron spectroscopy analysis into the discharge intermediates upon battery cycling reveals that the hydrophilic binder endows the sulfur electrodes with multidimensional Li‐O, Li‐N, and S‐O interactions with sulfur species to effectively mitigate lithium polysulfide dissolution, which is theoretically confirmed by density‐functional theory calculations.     

Si‐Encapsulating Hollow Carbon Electrodes via Electroless Etching for Lithium‐Ion Batteries

Remarkable improvements in the electrochemical performance of Si materials for Li‐ion batteries have been recently achieved, but the inherent volume change of Si still induces electrode expansion and external cell deformation. Here, the void structure in Si‐encapsulating hollow carbons is optimized in order to minimize the volume expansion of Si‐based anodes and improve electrochemical performance. When compared to chemical etching, the hollow structure is achieved via electroless etching is more advanced due to the improved electrical contact between carbon and Si. Despite the very thick electrodes (30 ～ 40 μm), this results in better cycle and rate performances including little capacity fading over 50 cycles and 1100 mA h g^?1 at 2C rate. Also, an in situ dilatometer technique is used to perform a comprehensive study of electrode thickness change, and Si‐encapsulating hollow carbon mitigates the volume change of electrodes by adoption of void space, resulting in a small volume increase of 18% after full lithiation corresponding with a reversible capacity of about 2000 mA h g^?1.     

Extremely High Yield Conversion from Low‐Cost Sand to High‐Capacity Si Electrodes for Li‐Ion Batteries

Although magnesiothermic reduction has attracted immense attention as a facile route for the fabrication of mass‐scale Si nanostructures for high‐capacity lithium‐ion battery applications, its low conversion yield (<50%) and the discovery of a sustainable and low‐cost precursor remain challenging. Here, an unprecedentedly high final conversion yield (>98%) of magnesiothermic reduction based on control of reaction pressure is reported. The successful use of sand as a nearly infinite and extremely low‐cost source for the high‐yield fabrication of nanostructured Si electrodes for Li‐ion batteries is demonstrated. On the basis of a step‐by‐step analysis of the material's structural, morphological, and compositional changes, a two‐step conversion reaction mechanism is proposed that can clearly explain the phase behavior and the high conversion yield. The excellent charge–discharge performance (specific capacities over 1500 mAh g^‐1 for 100 cycles) of the hierarchical Si nanostructure suggests that this facile, fast, and high‐efficiency synthesis strategy from ultralow‐cost sand particles provides outstanding cost‐effectiveness and possible scalability for the commercialization of Si electrodes for energy‐storage applications.     

On the Capacity Losses Seen for Optimized Nano‐Si Composite Electrodes in Li‐Metal Half‐Cells

While the use of silicon‐based electrodes can increase the capacity of Li‐ion batteries considerably, their application is associated with significant capacity losses. In this work, the influences of solid electrolyte interphase (SEI) formation, volume expansion, and lithium trapping are evaluated for two different electrochemical cycling schemes using lithium‐metal half‐cells containing silicon nanoparticle–based composite electrodes. Lithium trapping, caused by incomplete delithiation, is demonstrated to be the main reason for the capacity loss while SEI formation and dissolution affect the accumulated capacity loss due to a decreased coulombic efficiency. The capacity losses can be explained by the increasing lithium concentration in the electrode causing a decreasing lithiation potential and the lithiation cut‐off limit being reached faster. A lithium‐to‐silicon atomic ratio of 3.28 is found for a silicon electrode after 650 cycles using 1200 mAhg^?1 capacity limited cycling. The results further show that the lithiation step is the capacity‐limiting step and that the capacity losses can be minimized by increasing the efficiency of the delithiation step via the inclusion of constant voltage delithiation steps. Lithium trapping due to incomplete delithiation consequently constitutes a very important capacity loss phenomenon for silicon composite electrodes.     

Micro‐ and Nano‐Structured Vanadium Pentoxide (V2O5) for Electrodes of Lithium‐Ion Batteries

Vanadium pentoxide (V₂O₅) has played important roles in lithium‐ion batteries due to its unique crystalline structure. To assist researchers understanding the roles this material plays, a comprehensive and critical review is conducted based on about 250 publications. Here, we report basics and applications of micro‐ and nano‐materials of V₂O₅ and V₂O₅‐based composites. The comparative and statistical analysis leads to the discovery of several interesting phenomena. The V₂O₅ electrodes with two lithium ions have a favorable capacity performance with reversible phase formation. The excellent capacity retention is displayed in the V₂O₅ electrodes with one lithium ion inserted. In the case of three lithium ions insertion, it was found that the irreversible formation of the phase ω in Li_xV₂O₅ leads to its control. In addition, effects of additives on electrode performance, circuitry models of performance, as well as reaction routes are studied. Two unprecedented concepts of the “high capacity band” and “empirical total capacity retention” are proposed though the comprehensive statistical analysis of the reviewed data. This review provides a comprehensive collection of information of state‐of‐the‐art and recent advancement in V₂O₅ and V₂O₅‐based composite materials for electrodes. Researchers could use the information to design and develop advanced electrodes for future batteries.