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The adoption of Li2CuO2has drawn interest as a Li-excess cathode additive for compensating irreversible Li+loss in anodes during cycling, which would move forward high-energy-density lithium-ion batteries (LIBs). Li2CuO2provides a high irreversible capacity (>200 mAh g–1) in the first cycle and an operating voltage comparable with commercial cathode materials, but its practical use is still restricted by the structural instability and spontaneous oxygen (O2) evolution, resulting in poor overall cycling performance. It is thus crucial to reinforce the structure of Li2CuO2to make it more reliable as a cathode additive for charge compensation. Pursuing the structural stability of Li2CuO2, herein, we demonstrate cosubstitution by heteroatoms, such as nickel (Ni) and manganese (Mn), for improving the structural stability and electrochemical performance of Li2CuO2. Such an approach effectively enhances the reversibility of Li2CuO2by suppressing continuous structural degradation and O2gas evolution during cycling. Our findings provide new conceptual pathways for developing advanced cathode additives for high-energy LIBs.

The lithium (Li) metal anode is highly desirable for high-energy density batteries. During prolonged Li plating–stripping, however, dendritic Li formation and growth are probabilistically high, allowing physical contact between the two electrodes, which results in a cell short-circuit. Engineering the separator is a promising and facile way to suppress dendritic growth. When a conventional coating approach is applied, it usually sacrifices the bare separator structure and severely increases the thickness, ultimately decreasing the volumetric density. Herein, we introduce dielectric silicon oxide with the feature of bi-morphological form, i.e., backbone-covered and backbone-anchored, onto the conventional polyethylene separator without any volumetric change. These functionally vary the Li+transference number and the ionic conductivity so as to modulate Li-ion solvation and self-scavenging of Li dendrites. The proposed separator paves the way to maximizing the full cell performance of Li/NCM622 toward practical application.

Recently, Ni-rich layered cathode materials have become the most common material used for lithium-ion batteries. From a structural viewpoint, it is crucial to stabilize the surface structures of such materials, as they are prone to undesirable side reactions and particle cracking in which intergranular microcracks form at the particle surfaces and then propagate inside. As a simplified engineering technique for obtaining Ni-rich cathode materials with high reversibility and long-term cycling stability, we propose a facile surface coating of piezoelectric LiTaO3onto a Ni-rich cathode material to enhance the charge transfer reaction and surface structural integrity. Based on theoretical and experimental investigation, we demonstrate that this surface protection approach is effective at enhancing the reversibility and mechanical strength of Ni-rich cathode materials, leading to a stable cycle performance at up to 150 cycles, even at 60 °C. Furthermore, the piezoelectric characteristics of the surface LiTaO3can enhance the rate capability of Ni-rich cathode materials at current densities of up to 2.0C. The results of this study provide a practical insight on the development of Ni-rich cathode materials for practical use in electric vehicle applications.

High-Ni cathode materials with a layered structure generally suffer from structural instability induced by a highly reactive Ni component, especially at the surface. Crystalline LiNbO3, with excellent thermal stability and ionic conductivity, has the potential to considerably enhance the interfacial stability of these cathode materials. By optimizing the crystalline coating of bifunctional LiNbO3on a high-Ni cathode material, we are able to improve cycle performance and rate capability by minimizing the direct exposure of Ni with electrolytes. Since a LiNbO3coating layer directly affects electrochemical performance, we also focus on the correlation of LiNbO3crystallinity with electrochemical behaviors of Li+in the cathode materials. We show that the Li+conducting behaviors are closely related to the crystallinity of LiNbO3. Highly crystalline LiNbO3effectively suppresses the structural changes of the cathode materials by facilitating strain relaxation induced by repeated Li+intercalation and deintercalation into and from the host structure. Moreover, it offers strong enhancement in mechanical and thermal stabilities at elevated temperatures above 60 °C. In this regard, this research provides a practical solution for successfully utilizing high-Ni layered cathode materials in commercial LIBs.

The use of high-capacity electrode materials (i.e., Si) in Li-ion batteries is hindered by their mechanical degradation. Thus, oxides (i.e., SiO2) are commonly used to obtain high expected capacities and long-term cycle performances. Despite extensive studies of the electrochemical–mechanical behaviors of high-capacity energy storage materials, the mechanical behaviors of amorphous SiO2during electrochemical reaction remain largely unknown. Here, we systematically investigate the stress evolution, electronic structure, and mechanical deformation of lithiated SiO2through first-principles computation and the finite element method. The structural and thermodynamic role of O in the amorphous Li–O–Si system is reported and compared with that in Si. Strong Si–O bonds in SiO2show high mechanical strength and brittle behavior, but as Li is inserted, the Li-rich SiO2phases become mechanically softened. The relaxation kinetics of SiO2, inducing deviatoric inelastic strains under mechanical constraints, is also compared with that of Si. The finite element model including the kinetic model for anisotropic expansion demonstrates that the long-term cycling stability of core–shell Si–SiO2nanoparticles mainly arises from the reaction kinetics and high mechanical strength of SiO2. These results provide fundamental insights into the chemomechanical behavior of SiO2for practical use.

Thanks to the advantages of low cost and good safety, magnesium metal batteries get the limelight as substituent for lithium ion batteries. However, the energy density of state-of-the-art magnesium batteries is not high enough because of their low operating potential; thus, it is necessary to improve the energy density by developing new high-voltage cathode materials. In this study, nanosized Berlin green Fe2(CN)6and Prussian blue Na0.69Fe2(CN)6are compared as high-voltage cathode materials for magnesium batteries. Interestingly, while Mg2+ions cannot be intercalated in Fe2(CN)6, Na0.69Fe2(CN)6shows reversible intercalation and deintercalation of Mg2+ions, although they have the same crystal structure except for the presence of Na+ions. This phenomenon is attributed to the fact that Mg2+ions are more stable in Na+-containing Na0.69Fe2(CN)6than in Na+-free Fe2(CN)6, indicating Na+ions in Na0.69Fe2(CN)6plays a crucial role in stabilizing Mg2+ions. Na0.69Fe2(CN)6delivers reversible capacity of approximately 70 mA h g–1at 3.0 V vs Mg/Mg2+and shows stable cycle performance over 35 cycles. Therefore, Prussian blue analogues are promising structures for high-voltage cathode materials in Mg batteries. Furthermore, this co-intercalation effect suggests new avenues for the development of cathode materials in hybrid magnesium batteries that use both Mg2+and Na+ions as charge carriers.

Silicon oxides (SiOx) have attracted recent attention for their great potential as promising anode materials for lithium ion batteries as a result of their high energy density and excellent cycle performance. Despite these advantages, the commercial use of these materials is still impeded by low initial Coulombic efficiency and high production cost associated with a complicated synthesis process. Here, we demonstrate that Si/SiOxnanosphere anode materials show much improved performance enabled by electroconductive black TiO2–xcoating in terms of reversible capacity, Coulombic efficiency, and thermal reliability. The resulting anode material exhibits a high reversible capacity of 1200 mAh g–1with an excellent cycle performance of up to 100 cycles. The introduction of a TiO2–xlayer induces further reduction of the Si species in the SiOxmatrix phase, thereby increasing the reversible capacity and initial Coulombic efficiency. Besides the improved electrochemical performance, the TiO2–xcoating layer plays a key role in improving the thermal reliability of the Si/SiOxnanosphere anode material at the same time. We believe that this multipurpose interfacial engineering approach provides another route toward high-performance Si-based anode materials on a commercial scale.

The reversible capacity of Chevrel Mo6S8cathode can be increased by the simple addition of the Cu metal to Mo6S8electrodes. However, the exact reaction mechanism of the additional reversible capacity for the Mo6S8and Cu mixture cathode has not been clearly understood yet. To clarify this unusual behavior, we synthesize a novel Cu nanoparticle/graphene composite for the preparation of the mixture electrode. We thoroughly investigate the electrochemical behaviors of the Mo6S8and Cu mixture cathode with the relevant structural verifications during Mg2+insertion and extraction. The in situformation of CuxMo6S8is observed, indicating the spontaneous electrochemical insertion of Cu to the Mo6S8host from the Cu nanoparticle/graphene composite. The reversible electrochemical replacement reaction of Cu in the Mo6S8structure is clarified with the direct evidence for the solid state Cu deposition/dissolution at the surface of Mo6S8particles. Moreover, the Mo6S8and Cu mixture cathode improves the rate capability compared to the pristine. We believe that our finding will contribute to understanding the origin of the additional capacity of the Mo6S8cathode arising from Cu addition and improve the electrochemical performance of the Mo6S8cathode for rechargeable Mg batteries.

Si/SiOxcomposite materials have been explored for their commercial possibility as high-performance anode materials for lithium ion batteries, but suffer from the complexity of and limited synthetic routes for their preparation. In this study, Si/SiOxnanospheres were developed using a nontoxic and precious-metal-free preparation method based on hydrogen silsesquioxane obtained from sol–gel reaction of triethoxysilane. The resulting Si/SiOxnanospheres with a uniform carbon coating layer show excellent cycle performance and rate capability with high-dimensional stability. This approach based on a scalable sol–gel reaction enables not only the development of Si/SiOxwith various nanostructured forms, but also reduced production cost for mass production of nanostructured Si/SiOx.

Si-based anode materials are considered as potential materials for high-energy lithium-ion batteries (LIBs) with the advantages of high specific capacities and low operating voltages. However, significant initial capacity loss and large volume variations during cycles are the primary restrictions for the practical application of Si-based anodes. Herein, we propose an affordable and scalable synthesis of double-layered SiOx/Mg2SiO4/SiOxcomposites through the magnesiothermic reduction of micro-sized SiO with Mg metal powder at 750 °C for 2 h. The distinctive morphology and microstructure of the double-layered SiOx/Mg2SiO4/SiOxcomposite are beneficial as they remarkably improve the reversibility in the first cycle and completely suppress the volume variations during cycling. In our material design, the outermost layer with a highly porous SiOxstructure provides abundant active sites by securing a pathway for efficient access to electrons and electrolytes. The inner layer of Mg2SiO4can constrain the large volume expansion to increase the initial Coulombic efficiency (ICE). Owing to these promising structural features, the composite prepared with a 2:1 molar ratio of SiO to Mg exhibited initial charge and discharge capacities of 1826 and 1381 mA h g–1, respectively, with an ICE of 75.6%. Moreover, it showed a stable cycle performance, maintaining high capacity retention of up to >86.0% even after 300 cycles. The proposed approach provides practical insight into the mass production of advanced anode materials for high-energy LIBs.