Fabricating Hexagonal Al-Doped LiCoO2 Nanomeshes Based on Crystal-Mismatch Strategy for Ultrafast Lithium Storage

Sb-Doped high-voltage LiCoO2 enabled improved structural stability and rate capability for high-performance Li-ion batteries

Sb-Doped high-voltage LiCoO₂ was developed with unique properties. In situ X-ray diffraction and density functional theory reveal that the introduction of Sb helps to shorten the Li⁺ diffusion distance, increase the lattice spacing and keep the structural stability during deep lithiation, thus resulting in improved rate capability and cycling performance.

Electronic Interaction between In Situ Formed RuO2 Clusters and a Nanoporous Zn3V3O8 Support and Its Use in the Oxygen Evolution Reaction

The catalytic activity and durability of RuO₂ clusters toward the oxygen evolution reaction (OER) are strongly associated with their support; however, how the electronic interaction would enhance the catalytic performance is still not quite clear. Herein, hierarchical nanoporous and single-crystal Zn₃V₃O₈ nanosheets are adopted to anchor in situ formed RuO₂ clusters. X-ray photoelectron analysis reveals significant binding energy changes of both Ru and V due to the creation of strong Ru-O-V bonding interaction, which would lead to the reconstruction of the electronic structure of the Zn₃V₃O₈ matrix and RuO₂ clusters. The ultrastrong electronic interaction also results in superior OER activity, indicated by a small overpotential at 10 mA cm^-2 (228 mV) and a shallow Tafel slope of 46 mV dec^-1. First-principles simulation further reveals the synergistic effect derived from the unique RuO₂@Zn₃V₃O₈ couple, which effectively regulates the electronic structure for the OER process. In addition, the created interfacial chemical bond and the confined microporous structure of the Zn₃V₃O₈ substrate could prevent the RuO₂ clusters from detachment and aggregation, making the nanocomposite a promising long-term stable OER electrocatalyst.

Constructing compatible interface between Li7La3Zr2O12 solid electrolyte and LiCoO2 cathode for stable cycling performances at 4.5 V

With high theoretical capacity and tap density, LiCoO2 (LCO) cathode has been extensively utilized in lithium-ion batteries (LIBs) for energy storage devices. However, the bottleneck of structural and interfacial instabilities upon cycling severely restricts its practical application at high cut-off voltage. From another perspective, the compatibility between the electrode and electrolyte is highly valued in the development of all-solid-state batteries. Herein, we construct a compatible interface between Li7La3Zr2O12 (LLZO) and LCO through a facile surface modification strategy, which significantly improves the cycling stability of LCO at a high cut-off voltage of 4.5 V. Characterization results demonstrate that the LCO@1.0 LLZO sample delivers a desirable capacity retention of 76.8% even after 1000 cycles at 3.0-4.5 V with the current density of 1 C (1 C = 274 mA g-1). Further investigation indicates that the LLZO modification layer could protect the LCO electrode through effectively alleviating the side reactions, which not only facilitates the Li+ transportation at the interface but also mitigates the bulk structure degradation. Moreover, it is also established that a small amount of La and Zr ions could gradiently migrate into the surface lattice of LCO to generate a thin layer of the surface solid solution Li-Co-La-Zr-O. Thus formed pinning region between surface modified LLZO and LCO cathode could contribute both to their mechanical compatibility and Li+ kinetics behavior upon repeated cycling. This work not only provides a strategy in broadening the operation potential and extracting higher capacity of LCO but also sheds light on constructing compatible interfaces in LIBs, especially for all-solid-state energy storage and conversion devices.

Probing Al Distribution in LiCo0.96Al0.04O2 Materials Using 7Li, 27Al, and 59Co MAS NMR Combined with Synchrotron X-ray Diffraction

We prepared Al-doped LCO (LCA) powders with low Al content (4%) with a controlled Li/(Co + Al) stoichiometry by a solid-state reaction using Li₂CO₃ and two types of Co/Al precursors: simply mixed (Co₃O₄ and Al₂O₃) or heat-treated (Co₃O₄ and Al₂O₃). These samples were thereby used to propose a reliable protocol with the aim to discuss the homogeneity of the Al doping for LiCo_1-yAl_yO₂ (LCA) prepared with low Al content by evidencing the distribution of Al within the powders, which clearly affects the electrochemical profiles of associated LCA//Li cells. For all samples we initially also characterized the Li/(Co + Al) stoichiometry by ⁷Li MAS NMR, to discard the possible effect of excess Li in the samples. Synchrotron XRD combined with ²⁷Al and ⁵⁹Co MAS NMR then provided a deep understanding of the doping homogeneity at the powder or particle scale. We showed that doping the Co₃O₄ spinel precursor by reacting it with Al₂O₃ may be avoided, as it most likely leads to an inhomogeneous mixture of Co₃O₄ and Co_3-zAl_zO₄ as precursor, eventually reflecting in the final LiCo_0.96Al_0.04O₂ powder, which shows a nonhomogeneous Al distribution. We believe that such a detailed characterization should be the first step toward a deeper understanding of the real beneficial effect(s) of Al doping on the high voltage performance of LCO.

Structural Distortion-Induced Charge Gradient Distribution of Co Ions in Delithiated LiCoO2 Cathode

Layered LiCoO₂ has drawn tremendous attention as a modeling cathode for Li-ion batteries, while its structural instability, especially in the high delithiation region, remains unsolved. With the aim of revealing the structural fundamentals, LiCoO₂ electrodes are investigated at a long delithiation range using both in situ and ex situ techniques. In the highly delithiated LiCoO₂ electrode, the unique charge compensation process leads to a spatial charge gradient of Co²⁺/Co³⁺/Co⁴⁺ ions from surface to bulk, which can be further manipulated by structural distortion, Li extraction, and surface side reactions. The coordinated surface oxygen is shown to be electrochemically active and fully reversible in participating in the charge compensation during cycling. Moreover, the active lattice O can be significantly stabilized by introducing the undesired surface Li-Co antisites, which also play an effective role in accommodating the internal stress induced by volume changes. These findings effectively bridge the structural changes with the Li⁺/e^- migration kinetics to elucidate the degradation of LiCoO₂ cathode upon delithiation, demonstrating a rewarding avenue for improving the electrochemical performance of LiCoO₂ itself and developing high energy density cathodes for the battery community as well.

Hierarchical Nanoporous V2O3 Nanosheets Anchored with Alloy Nanoparticles for Efficient Electrocatalysis

Exploring low-cost bifunctional electrocatalysts for efficient water splitting still faces arduous challenges. Herein, a general and straightforward method is developed to prepare 3D hierarchical nanoporous V₂O₃ nanosheets anchored with different alloy nanoparticles by adopting metal-ion-doped zinc-vanadium (oxy)hydroxides as precursors. To demonstrate this concept, we produced nanoporous V₂O₃ nanosheets dotted with NiFe alloy nanoparticles through high-temperature reduction and free corrosion. Due to the increased number of active sites, accelerated mass transfer originating from the designed nanoporous architecture, and the metallic property of the V₂O₃ matrix, the NiFe@V₂O₃ hybrid exhibits excellent electrocatalytic performances for both oxygen and hydrogen evolution reactions. When adopting the NiFe@V₂O₃ as a bifunctional electrode for overall water splitting, it only requires a cell voltage of 1.56 V to reach 10 mA cm^-2. This work provides a general and practical way to prepare high-efficient and low-cost electrocatalysts.

Crystal structural design of exposed planes: express channels, high-rate capability cathodes for lithium-ion batteries

Developing high-performance lithium ion batteries (LIBs) requires optimization of every battery component. Currently, the main problems lie in the mismatch of electrode capacities, especially the excessively low capacity of cathodes compared with that of anodes. Due to the anisotropy of the crystal structure, different crystal planes play different roles in the transmission of lithium ions. Among these, the {010} facets of layered-structure materials, the (110) planes of spinel cathodes and the (010) planes of olivine cathodes can provide open surface structures, which furnish express channels for the rapid and efficient transmission of lithium ions, leading to enhanced rate performance. However, due to the high-energy surfaces of these crystal planes, they tend to disappear in the synthetic process, forming thermodynamic equilibrium products dominated by low-energy and electrochemically-inactive planes. From the structure design of the material itself, preparing functional materials with specific morphologies and crystal structures is considered to be the most effective way to improve the cyclability and rate performance of LIB cathodes. In this review, we highlight the latest developments in selectively exposing the crystal planes of LIB cathode materials. The synthetic method, the corresponding electrochemical performance, especially the rate capability, and the growth mechanism have been systematically summarized for layered-structure cathodes of LiCoO2, LiNixCoyMn1-x-yO2 and Li2MnO3·LiMO2, spinel cathodes of LiMn2O4 and LiNi0.5Mn1.5O4, and olivine cathodes of LiFePO4. This in-depth discussion and understanding is beneficial for the rational design of well-performing LIB cathodes and can provide direction and perspectives for future work.

Tunneled Mesoporous Carbon Nanofibers with Embedded ZnO Nanoparticles for Ultrafast Lithium Storage

Carbon and metal oxide composites have received considerable attention as anode materials for Li-ion batteries (LIBs) owing to their excellent cycling stability and high specific capacity based on the chemical and physical stability of carbon and the high theoretical specific capacity of metal oxides. However, efforts to obtain ultrafast cycling stability in carbon and metal oxide composites at high current density for practical applications still face important challenges because of the longer Li-ion diffusion pathway, which leads to poor ultrafast performance during cycling. Here, tunneled mesoporous carbon nanofibers with embedded ZnO nanoparticles (TMCNF/ZnO) are synthesized by electrospinning, carbonization, and postcalcination. The optimized TMCNF/ZnO shows improved electrochemical performance, delivering outstanding ultrafast cycling stability, indicating a higher specific capacity than previously reported ZnO-based anode materials in LIBs. Therefore, the unique architecture of TMCNF/ZnO has potential for use as an anode material in ultrafast LIBs.

Triple-Confined Well-Dispersed Biactive NiCo2S4/Ni0.96S on Graphene Aerogel for High-Efficiency Lithium Storage

Layered double hydroxides (LDHs), also known as hydrotalcite-like anionic clay compounds, have attracted increasing interest in electrochemical energy storage, in the main form of LDH precursor-derived transition metal oxides (TMOs). One typical approach to improve cycling stability of the LDH-derived TMOs is to introduce one- and two-dimensional conductive carbonaceous supports, such as carbon nanotubes and graphene. We herein demonstrate an effective approach to improve the electrochemical performances of well-dispersed biactive NiCo₂S₄/Ni_0.96S as anode nanomaterials for lithium-ion batteries (LIBs), by introducing a three-dimensional graphene aerogel (3DGA) support. The resultant 3DGA supported NiCo₂S₄/Ni_0.96S (3DGA/NCS) composite, obtained by sulfuration of NiCo-layered double hydroxide (NiCo-LDH) precursor in situ grown on the 3DGA support (3DGA/NiCo-LDH). Electrochemical tests show that the 3DGA/NCS composite indeed delivers the greatly enhanced electrochemical performances compared with the NiCo₂S₄/Ni_0.96S counterpart on two-dimensional graphene aerogel, i.e., a high reversible capacity of 965 mA h g^-1 after 200 cycles at 100 mA g^-1 and especially a superlong cycling stability of 620 mA h g^-1 after 800 cycles at 1 A g^-1. The enhancements could be ascribed to the compositional and structural advantages of boosting electrochemical performances: (i) well-dispersed NiCo₂S₄/Ni_0.96S nanoparticles with interfacial nanodomains resulting from both the dual surface confinements of the 3DGA support and the crystallographic confinement of NiCo-well-arranged LDH crystalline layer, (ii) an appropriate specific surface area and a wide pore size distribution of mesopores and macropores, and (iii) highly conductive 3DGA support that is measured experimentally by using electrochemical impedance spectra to underlie the enhancement. Our results demonstrate that the tunable LDH precursor-derived synthesis route may be extended to prepare various transition metal sulfides and even transition metal phosphides for energy storage with the aid of tunable cationic type and molar ratio.

Electrode materials with tailored facets for electrochemical energy storage

In recent years, the design and morphological control of crystals with tailored facets have become hot spots in the field of electrochemical energy storage devices. For electrode materials, morphologies play important roles in their activities because their shapes determine how many facets of specific orientation are exposed and therefore available for surface reactions. This review focuses on the strategies for crystal facet control and the unusual electrochemical properties of electrode materials bound by tailored facets. Here, electrode materials with tailored facets include transition metal oxides such as SnO₂, Co₃O₄, NiO, Cu₂O, and MnO₂, elementary substances such as Si and Au, and intercalation compounds such as Li₄Ti₅O₁₂, LiCoO₂, LiMn₂O₄, LiFePO₄, and Na_0.7MnO₂ for various applications of Li-ion batteries, aqueous rechargeable lithium batteries, Na-ion batteries, Li-O₂ batteries and supercapacitors. How these electrode materials with tailored facets affect their electrochemical properties is discussed. Finally, research opportunities as well as the challenges in this emerging research frontier are highlighted.

Adsorption and intercalation of organic pollutants and heavy metal ions into MgAl-LDHs nanosheets with high capacity

The adsorption of MgAl-LDH nanosheets involves precipitation, surface complexation, isomorphic substitution and ion exchange in the interlayer space.​ Based on the efficient removal of heavy metal ions by the nanosheets a filter-type water purification device was designed.