The spinel LiMn 2 O 4 is considered a promising cathode option material because it provides three-dimensional pathways for Li-ion diffusion. However, LiMn 2 O 4 exhibits insufficient rate capabilities and rapid structural deterioration during prolonged cycling, particularly under conditions of high current or elevated temperatures. Herein, we introduce a Mg 2+ /Al 3+ co-doping strategy to evade these problems. As a result, the co-doping of Mg 2+ and Al 3+ facilitates the development of a polyhedral morphology, enhancing both structural stability and rapid Li-ion diffusion. Furthermore, the incorporation of Mg 2+ and Al 3+ , which have a stable electronic configuration, enhances structural stability through their relatively stronger Mg O and Al O bonds compared to the Mn O bond. Therefore, the LiMg 0.02 Al 0.08 Mn 1.90 O 4 delivers the first discharge capacity of 107.6 mAh‧g −1 at 1 C. Importantly, the LiMg 0.02 Al 0.08 Mn 1.90 O 4 cathode achieves long cycling lifespans exceeding 1000 cycles at high current rates of 20 C. A capacity retention of 70.0 % is retained at 20 C after 1000 cycles, as well as a high-temperature capacity retention of 47.4 % after 500 cycles at 5 C and 55 °C. Moreover, the Mg 2+ /Al 3+ co-doping facilitates the kinetic process of Li + migration, leading to a relatively high Li + diffusion coefficient and a low apparent activation energy.
High-nickel layered oxide LiNi 0.9 Co 0.1 O 2 is a promising cathode material for lithium-ion batteries due to its high specific capacity and low cost. However, the internal stress generated during deep delithiation can cause microcracks, giving rise to rapid capacity decay and deteriorated thermal stability. In this work, Mg and Al ions are incorporated into the bulk phase of LiNi 0.9 Co 0.1 O 2 via high-temperature solid-state reaction. We demonstrate that Al 3+ doping enhances charge transfer between transition metal (TM) and oxygen layers, strengthening TM-O bonds and stabilizing the structure, thereby alleviating structural distortions under deep delithiation. More impressively, Mg 2+ doping significantly improves structural stability through a pillaring effect, effectively suppressing irreversible phase transitions during charge-discharge cycling. Consequently, Mg-Al co-doping optimizes the overall structural integrity of the high-nickel cathode, enhances its stability, and inhibits lattice oxygen release during long-term cycling. The Mg-Al co-doped LiNi 0.9 Co 0.1 O 2 delivers a remarkable capacity of 177.3 mAh g −1 after 100 cycles with capacity retention of 93.5 %, demonstrating outstanding cyclability. This Mg-Al co-doping strategy provides a simple and practical approach to enhance the electrochemical performance of high-nickel layered cathode materials.
The synthesis of carbonates by using nontoxic feedstocks and ecofriendly heterogeneous catalysts has received great attention but remains a significant challenge. Herein, a series of Mg/Al-codoped porous carbons (MgAl@CM) were developed and applied for transesterification to synthesize methyl phenyl carbonate (MPC). The results showed that MgAl@CM possessed abundant mesopores, large amounts of N/O-containing groups, and dispersed Mg/Al species. And 1Mg5Al@CM-700 exhibited the highest catalytic activity with a diphenyl carbonate conversion of 80.2% and MPC selectivity of 99.6% due to its unique structure and acidic–basic properties, indicating a highly efficient acid–base synergistic catalysis process. Moreover, the catalyst presented good stability and reusability for six recycles without a substantial activity loss. The mechanism based on the synergistic catalysis was investigated. This work provides a novel perspective for the design of heteroatom-doped carbon catalysts to accomplish an efficient MPC synthesis.
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