Lihan Zhang

Advancements in structural engineering are expected to enhance the wide-range commercial application of lithium-ion batteries by enabling the implementation of thicker cathode materials. Increasing the thickness of these cathodes can yield significant increasements in gravimetric energy density while concurrently lowering manufacturing costs. These improvements are pivotal to the successful commercial deployment of sustainable transport systems. However, several substantial barriers persist in the adoption of such microstructures, including performance degradation, manufacturing complexities, and scalability concerns, all of which remain open areas of investigation. This review delves into the obstacles associated with current modifying techniques in thick cathodes and explores the potential opportunities to develop more robust and thicker cathodes, while ensuring long-term performance and scalability. Finally, we provide suggestions on the future directions of thick cathodes to promote their large-scale application.

To meet the growing demand for high-energy-density lithium ion batteries (LIBs), silicon (Si) anodes have emerged as a rising star in next-generation anodes due to their ultrahigh gravimetric capacity. Nevertheless, Si anode suffers from severe volume expansion problems that lead to rapid capacity degradation, greatly hindering its commercialization. Although numerous studies have been conducted on mitigating the volume changes and constructing stable solid electrolyte interphases on Si-based anodes, one crucial factor for their practical application, namely the volumetric capacity, is often overlooked. In fact, the volumetric capacity of Si-based anodes must be considered when it comes to replacing conventional graphite anodes. Therefore, several key factors that determine the volumetric capacity are considered to evaluate Si-based anodes, including gravimetric capacity, active material mass ratio, initial coulombic efficiency, electrode swelling ratio and negative/positive capacity ratio. Firstly, each factor is analyzed, discussed in detail and summarized systematically. Then problems with existing strategies were identified and future research directions concerning the commercialization of Si-based anodes are outlined. Therefore, this paper provides systematic and novel insights into the effective modification and rational design of Si-based anodes, aiming to promote the volumetric capacity towards the large-scale industrialization of next-generation LIBs.

Low-cost sodium-ion batteries have demonstrated great prospects in energy storage, among which layered transition metal oxides hold great potential as a cathode material. However, the notorious phase transition in layered cathode materials has greatly hampered their cycle life due to large volume changes upon desodiation/sodiation. In this study, by adopting an O3-type NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) with controlled synthesis temperatures, we have revealed that the grain size is closely related to its phase transition behaviors. The layered material with a smaller grain size and more distorted lattice tends to experience a shorter plateau of the O3-P3-O3 phase transitions during the charge/discharge process. Despite having a lower nominal discharge capacity without the phase transition plateau, its cycling stability increases from 77.4% to 96.2% after 100 cycles with greatly reduced intragranular cracks. The smaller grain size and lattice distortion act as a barrier that prevents the smooth layer from gliding upon sodium intercalation and deintercalation. This study focuses on the influence of grain size on battery cycle stability and provides a basis for future analysis of the structural instability of layered materials.

Microstructural engineering on nickel‐rich layered oxide (NRLO) cathode materials is considered a promising approach to increase both the capacity and lifespan of lithium‐ion batteries by introducing high valence‐state elements. However, rational regulation on NRLO microstructures based on a deep understanding of its capacity enhancement mechanism remains challenging. Herein for the first time, it is demonstrated that an increase of 14 mAh g⁻¹ in reversible capacity at the first cycle can be achieved via tailoring the micro and nano structure of NRLO through introducing tungsten. Aberration‐corrected scanning transmission electron microscopy (STEM) characterization reveals that the formation of a modified microstructure featured as coherent spinel twin boundaries. Theoretical modeling and electrochemical investigations further demonstrate that the capacity increase mechanism is related to such coherent spinel twin boundaries, which can lower the Li⁺ diffusion barrier and thus allow more Li⁺ to participate in deeper phase transitions. Meanwhile, the surface and grain boundaries of NRLOs are found to be modified by generating a dense and uniform LiW_xO_y phase, which further extends its cycle life by reducing side reactions with electrolytes. This work enables a comprehensive understanding of the capacity‐increased mechanism and endows the remarkable potential of microstructural engineering for capacity‐ and lifespan‐increased NRLOs.

Three-dimensional (3D) porous current collectors play pivotal roles in realizing dendrite-free lithium metal anodes (LMAs) owing to their high specific area. However, uneven local electric field and lack of lithiophilic sites on the reactive interface cause nonuniform lithium ion (Li+) deposition, leading to Li dendrite growth and parasitic reactions. These issues will inevitably incur short cycling life and severe safety hazards of lithium metal batteries. Herein, a 3D self-supporting current collector composed of hollow carbon nanofibers incorporated with silicon (Si) nanoparticles inside (Si-HCF) is constructed as Li metal host by a scalable coaxial electrospinning technique. During the first cycle, the Si nanoparticles is alloyed with Li+ to form lithiophilic Li-Si alloy, contributing to deliver a low nucleation overpotential and homogeneous surface potential confirmed by Kelvin probe force microscopy, finally guiding Li+ flux homogeneously throughout the fibrous mat. As expected, the Li metal can percolate through Si-HCF host reversibly without uncontrollable Li dendrites and the Si-HCF exhibits a stable cycle life of Li plating/stripping over 1400 h. Additionally, the full cell combined with LiFePO4 cathodes presents steady cycling over 400 cycles with a high average coulombic efficiency of 99.4%. This work provides new insights for the synthesis of 3D hosts with controllable nucleation sites to homogenize Li+ deposition in LMAs.

The high energy density and low-cost O3-layered NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) is a representative layered cathode for sodium-ion batteries (SIBs). However, its long-term cycling stability needs further improvement and its high voltage usage is highly desired, which is quite challenging. The lack of full understanding of the cycling-induced failures hinders material optimization. Herein, we utilize advanced microanalysis techniques to comprehensively investigate the failure mechanisms of the O3-NFM layered cathode upon low-voltage (2.0–4.0 V) and high-voltage (2.0–4.3 V) cycling. We found that surface degradations play a dominant role during low-voltage cycling, and bulk failures become prominent upon high-voltage cycling. Surface cracking, corrosion, and structure transition together lead to slow charge transfer kinetics, resulting in chronic capacity decay. Bulk degradations such as intragranular cracking, void formation, and interlayer cation mixing severely deteriorate Na storage performance and Na diffusion kinetics, causing rapid capacity decay and voltage fading issues, which are the main challenges of the NFM layered cathode for high voltage usage. High charging cutoff voltage activates the cation migration and condensation, causing a highly disordered layered structure but no phase transition occurs in the bulk. Synergistically stabilizing the surface and bulk structure of the high-voltage O3-layered cathode is essential for achieving superior electrochemical performance.

Specific inorganic components (e.g., pure LiF-, Li₃N- and LiF/Li₃N composites) were obtained in solid electrolyte interphases (SEIs) for lithium metal batteries and synergistic functional mechanism of the LiF and Li₃N in SEIs were fully investigated.

The ionic conductivity of composite solid-state electrolytes does not meet the application requirements of solid-state lithium (Li) metal batteries owing to the harsh space charge layer of different phases and low concentration of movable Li⁺. Herein, we propose a robust strategy for creating high-throughput Li⁺ transport pathways by coupling the ceramic dielectric and electrolyte to overcome the low ionic conductivity challenge of composite solid-state electrolytes. A highly conductive and dielectric composite solid-state electrolyte is constructed by compositing the poly(vinylidene difluoride) matrix and the BaTiO₃–Li_0.33La_0.56TiO_3–x nanowires with a side-by-side heterojunction structure (PVBL). The polarized dielectric BaTiO₃ greatly promotes the dissociation of Li salt to produce more movable Li⁺, which locally and spontaneously transfers across the interface to coupled Li_0.33La_0.56TiO_3–x for highly efficient transport. The BaTiO₃–Li_0.33La_0.56TiO_3–x effectively restrains the formation of the space charge layer with poly(vinylidene difluoride). These coupling effects contribute to a quite high ionic conductivity (8.2 × 10⁻⁴ S cm⁻¹) and lithium transference number (0.57) of the PVBL at 25 °C. The PVBL also homogenizes the interfacial electric field with electrodes. The LiNi_0.8Co_0.1Mn_0.1O₂/PVBL/Li solid-state batteries stably cycle 1,500 times at a current density of 180 mA g⁻¹, and pouch batteries also exhibit an excellent electrochemical and safety performance.