Improved Stability of Layered and Porous Nickel-Rich Cathode Materials by Relieving the Accumulation of Inner Stress

Cellulose-Derived Carbon Dot-Guided Growth of ZnIn2 S4 Nanosheets for Photocatalytic Oxidation of 5-Hydroxymethylfurfural into 2,5-Diformylfuran

Cellulose-derived carbon (CC) dot-directed growth of ZnIn₂ S₄ was achieved through hydrothermal treatment of carboxylated cellulose followed by in situ growth of ZnIn₂ S₄ nanosheets. The carbon dots inherited from carboxylated cellulose equip plenty of surface carboxyl groups, which induce the ionic interaction with Zn²⁺ and In³⁺ and the guided growth of ZnIn₂ S₄ . As a result, the nanosheets of ZnIn₂ S₄ are evenly and intimately grown on the small carbon dots, providing high-speed channels for charges transfer. In conjunction with the reinforced visible-light capture and good conductivity of carbon dots, the resultant CC/ZnIn₂ S₄ shows an outstanding photocatalytic activity. As a proof-of-concept, visible-light-driven 5-hydroxymethylfurfural oxidation into 2,5-diformylfuran was conducted. The evolution of 2,5-diformylfuran over the optimal CC/ZnIn₂ S₄ sample can reach ∼2980 μmol g^-1 , about 3.4 times that of pristine ZnIn₂ S₄ . Additionally, the apparent quantum yield could attain 3.4 % at a wavelength of 400 nm.

Electrolyte Additives for Improving the High-Temperature Storage Performance of Li-Ion Battery NCM523∥Graphite with Overcharge Protection

The overcharge safety performance of lithium-ion batteries has been the major bottleneck in the widespread deployment of this promising technology. Pushing the limitations further may jeopardize cell safety when it is performed at high-temperature storage. On the basis of the lacking systematic research on overcharge protection electrolyte additives with high-temperature storage capacity, we explore the promotion effect of overcharge additives on electrolyte decomposition at 60 °C. Specifically, the addition of tris(trimethylsily) phosphite (TMSP) and lithium difluoro(oxalato)borate (LiDFOB) in the electrolyte can not only form the robust cathode electrolyte interface/solid electrolyte interphase (CEI/SEI) but also improve the thermal stability of the electrolyte. Therefore, we promote the electrolyte system to realize the 18,650 LIB storage at 60 °C for 50 days by optimizing the formula in the electrolyte containing biphenyl (BP) and cyclohexylbenzene (CHB) overcharge protection additives, and the capacity retention rate can reach more than 90% with overcharge safety. Further, the optimized electrolyte system has also been implemented to commercial 18,650 LIBs and demonstrates the widening of the route to the widespread application of the electrolyte under extreme conditions.

Selective aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over nanojunctions of cobalt–ceria binary oxide in water

Non-precious cobalt–ceria binary oxide nanojunctions with rich interfaces were designed to efficiently catalyze 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA).

Roles of Fast-Ion Conductor LiTaO3 Modifying Ni-rich Cathode Material for Li-Ion Batteries

Limited cycling stability hampers the commercial application of Ni-rich materials, which are regarded as one of the most promising cathode materials for Li-ion batteries. Ni-rich LiNi_0.9 Co_0.06 Mn_0.04 O₂ layered cathode was modified with different amounts of LiTaO₃ , and the influences of fast-ion conductor material on cathode materials were explored. Detailed analysis of the materials revealed the formation of a uniformly epitaxial LiTaO₃ coating layer and a little Ta⁵⁺ doping into the lattice structure of Ni-rich materials. The coating-layer thickness increased with the amount of LiTaO₃ added, protecting the electrode from erosion by electrolyte and suppressing undesired parasitic reactions on the cathode-electrolyte interface. Meanwhile, the doped Ta⁵⁺ increased the interplanar spacing of materials, accelerating Li⁺ transfer. Using the positive synergistic effects of LiTaO₃ -coating and Ta⁵⁺ -doping, improved capacity retentions of the modified materials, especially for 0.25 and 0.5 wt%-coated Ni-rich materials, were obtained after long-term cycling, showing the potential applications of LiTaO₃ modification. Further, the relations between one excessively thick coating layer and transfer of Li⁺ /electron between the cathode and electrolyte was established, proving that very thick coating layers, even layers containing Li ions, have adverse effects on electrochemical performances. This finding may help to understand the roles of the coating layer better.

Kinetic Control of the Li0.9Mn1.6Ni0.4O4 Spinel Structure with Enhanced Electrochemical Performance

The development of more sustainable societies has become an urgent goal worldwide. Electrical batteries are currently seen as one of the most important energy storage technologies for the development of decarbonized societies. However, many lithium-ion battery manufacturers currently utilize cobalt, a toxic and hazardous mineral, in their batteries. Lithium-deficient manganese nickel oxide spinels are considered promising candidates owing to their high potential and environmental friendliness. Their electrochemical performance highly depends on their average and local structures, such as phase purities, lattice parameters, and cation sites. Thus, a synthesis protocol should be designed to control these structural parameters to improve their electrochemical performance. In this study, we controlled the average and local structures of Li_0.9Mn_1.6Ni_0.4O₄ spinels obtained by co-precipitation by optimizing their cooling rates. High-resolution techniques, including transmission electron microscopy, synchrotron X-ray diffraction, and Auger-composition analysis combined with density functional theory calculations, X-ray absorption spectroscopy, and electrochemical analysis, were used to understand the average and local structural variations and their effects on the electrochemical properties. As a result, the control of oxygen diffusion at different cooling rates can promote the rearrangement of the structure, resulting in a cation-disordered spinel with minimal variations in lattice parameters and composition. Excellent electrochemical properties were noted in the cation-disordered spinel with high crystallinity and a slightly oxygen-rich surface produced via optimized cooling rates.

Irreversible Transition from GaO6 Octahedra to GaO4 Tetrahedra for Improved Electrochemical Stability in Ga-Doped Li(Ni0.9Co0.1)O2

Trace doping is an efficient way to improve the stability of nickel-rich layered cathodes for lithium-ion batteries, but the structural origin of such improvement, rather than a simple replacement, has been rarely explored. Herein, Ga dopants have been introduced into a nickel-rich host, LiNi_0.9Co_0.1O₂, by a combination of coprecipitation and the solid-state sintering method. Structural analyses based on high-resolution synchrotron powder diffraction data and X-ray absorption spectra suggest that Ga preferentially sits in the NiO₆ slabs, resulting in reduced Ni/Li cationic mixing and depressed lattice vibration. Due to the smaller dissociation energy of Ga-O bonds, some Ga³⁺ cations migrate first toward Li layers upon delithiation and form the GaO₄ tetrahedral symmetry irreversibly during the electrochemical process, which acts as a pillar in the subsequent electrochemical processes. As a result, the doped material exhibits both improved cycling performance and rate capability under a high operating voltage (4.5 V) due to the stabilized structure in the lithiation/delithiation process. This study illustrates how a dopant enhances the electrochemical stability in views of both pristine and charged structure and suggests that a positive effect is expected from the dopant favoring the tetrahedral symmetry (e.g., Al).

High-Temperature Storage Deterioration Mechanism of Cylindrical 21700-Type Batteries Using Ni-Rich Cathodes under Different SOCs

The safety and energy density of lithium-ion batteries (LIBs) are important concerns. The use of high-capacity cathode materials, such as Ni-rich cathodes, can greatly improve the energy density of LIBs, but it also brings some safety hazards. Cylindrical 21700-type batteries using Ni-rich cathodes were employed here to investigate their high-temperature storage deterioration mechanism under different states of charge (SOCs). Electrolyte decomposition was identified as the main problem. It can be worsened by elevated storage temperatures and battery SOCs, with the latter having a more significant influence. Specifically, the decomposition of the LiPF₆ solute and the carbonate solvent will induce hydrofluoric acid (HF) formation and solid-electrolyte interphase (SEI) film regeneration, respectively. HF erosion will aggravate the dissolution of transition metal ions and structural degradation of cathode materials, while the destruction/regeneration of SEI films will consume active lithium and hinder Li⁺ diffusion at the anode side. Besides, the self-discharge behavior will also enlarge the graphite layer spacing, thus decreasing the graphitization degree of graphite anodes and causing anode failure. These findings will aid in the development of strategies for improving the safety of LIBs with high energy density.

Clean the Ni-Rich Cathode Material Surface With Boric Acid to Improve Its Storage Performance

The existence of residual lithium compounds (RLCs) on the surface of layered Ni-rich materials will deteriorate the electrochemical properties and cause safety problem. This work presents an effective surface washing method to remove the RLCs from LiNi_0.90Co_0.06Mn_0.04O₂ material surface, via ethyl alcohol solution that contains low concentration of boric acid. It is a low-cost process because the filter liquor can be recycled. The optimal parameters including washing time, boric acid concentration, and solid-liquid ratio were systematically studied. It has been determined by powder pH and Fourier transform infrared spectra results that the amount of RLCs was reduced effectively, and the storage performance was significantly enhanced for the washed samples. The 150th capacity retentions after storing had increased from 68.39% of pristine material to 85.46-94.84% of the washed materials. The performance enhancements should be ascribed to the surface washing process, which removed not only the RLCs, but also the loose primary particles effectively.