Self-Activation of Inorganic-Organic Hybrids Derived through Continuous Synthesis of Polyoxomolybdate and para-Phenylenediamine Enables Very High Lithium-Ion Storage Capacity

Inorganic-organic hybrid materials with redox-active components were prepared by an aqueous precipitation reaction of ammonium heptamolybdate (AHM) with para-phenylenediamine (PPD). A scalable and low-energy continuous wet chemical synthesis process, known as the microjet process, was used to prepare particles with large surface area in the submicrometer range with high purity and reproducibility on a large scale. Two different crystalline hybrid products were formed depending on the ratio of molybdate to organic ligand and pH. A ratio of para-phenylenediamine to ammonium heptamolybdate from 1 : 1 to 5 : 1 resulted in the compound [C₆ H₁₀ N₂ ]₂ [Mo₈ O₂₆ ] ⋅ 6 H₂ O, while higher PPD ratios from 9 : 1 to 30 : 1 yielded a composition of [C₆ H₉ N₂ ]₄ [NH₄ ]₂ [Mo₇ O₂₄ ] ⋅ 3 H₂ O. The electrochemical behavior of the two products was tested in a battery cell environment. Only the second of the two hybrid materials showed an exceptionally high capacity of 1084 mAh g^-1 at 100 mA g^-1 after 150 cycles. The maximum capacity was reached after an induction phase, which can be explained by a combination of a conversion reaction with lithium to Li₂ MoO₄ and an additional in situ polymerization of PPD. The final hybrid material is a promising material for lithium-ion battery (LIB) applications.

Superlubricity and Antiwear Properties of In Situ-Formed Ionic Liquids at Ceramic Interfaces Induced by Tribochemical Reactions

Several ionic liquids (ILs) are formed in situ with monovalent metal salts and ethylene glycol (EG). The macroscale superlubricity and antiwear properties of the ILs were studied between ceramic materials. Superlow coefficients of friction of less than 0.01 could be obtained for all ILs at silicon nitride (Si₃N₄) interfaces induced by tribochemical reactions. Notably, the IL ([Li(EG)]PF₆) formed with LiPF₆ and EG exhibited the greatest superlubricity and antiwear properties. The results of film thickness calculations and surface analysis showed that the lubrication regime during the superlubricity period was the mixed lubrication, and a composite tribochemical layer (composed of phosphates, fluorides, silica (SiO₂), and ammonia-containing compounds), hydration layer, and fluid film contributed to superlubricity and wear protection. It was found that the small size of metal cations was beneficial for alleviating wear, and PF₆^- anions exhibited the smallest friction and best antiwear performance at Si₃N₄ interfaces. This work studied the lubricity and antiwear properties of ILs with different cations and anions, enriching the range of alternative ILs for macroscale superlubricity and low wear, and is of importance to engineering applications.

Promoting the cyclic and rate performance of lithium-rich ternary materials via surface modification and lattice expansion

Nickel-rich layered lithium transition-metal oxides have been studied intensively as high-energy positive-electrode materials for lithium batteries because of their high specific capacity and relatively low-cost.

A study of the structure–activity relationship of the electrochemical performance and Li/Ni mixing of lithium-rich materials by neutron diffraction

4 mol% Mg-doped and 1 mol% Al-doped lithium-rich 0.3Li₂MnO₃·0.7LiNi_0.5Mn_0.5O₂ materials exhibit enhanced electrochemical performance due to reduced Li/Ni mixing.