Jun Chen

Structurally stable, highly conductive, and readily tunable phthalocyanine (Pc) compounds have emerged as promising electrode materials for lithium-ion batteries (LIBs) owing to their distinctive two-dimensional (2D) π-π stacking architecture. In this study, a sacrificial template method was employed to conduct in situ azo polymerization of nickel(II) phthalocyanine precursors, NiPc(NH₂)₄ and NiPc(NO₂)₄, on the surface of a regular dodecahedral zeolitic imidazolate framework-8 (ZIF-8) template, yielding NA-NiPc@ZIF-8(2:1) and NA-NiPc@ZIF-8(1:2). Subsequent selective removal of ZIF-8 by acetic acid etching produced HNA-NiPc(2:1) and HNA-NiPc(1:2) with hollow dodecahedral structures. The covalent coordination between the Pc framework and ZIF-8 suppresses excessive aggregation, while template removal generates abundant defects and interconnected hollow cavities, facilitating electrolyte penetration and exposing more electrochemically active sites. Benefiting from these structural advantages, HNA-NiPc(1:2) delivered an initial discharge capacity of 826.2 mAh g⁻¹at 200 mA g⁻¹, increasing to 1474.6 mAh g⁻¹ after 352 cycles. At 1000 mA g⁻¹, HNA-NiPc(1:2)achieved a capacity increase from 446.2 to 1108.3 mAh g⁻¹ after 1000 cycles, while HNA-NiPc(2:1)increased from 273.7 to 765.5 mAh g⁻¹, both outperforming pristine NA-NiPc. Moreover, HNA-NiPc(1:2) maintained a reversible capacity of 557.8 mAh g⁻¹ at 2 A g⁻¹. These results demonstrate the effectiveness of the hollow Pc-based architecture in enhancing lithium storage and provide valuable insights into the design of high-performance organic anodes for LIBs.

A planar layered MOF material, PTCDA‐Ni, is prepared through a coordination reaction of PTCDA (3,4,9,10‐perylenetetracarboxylic acid) with Ni ions, and the PTCDA‐Ni is activated by solvent exchange activation with trichloromethane (TCM), acetone (AC), and co‐activation with AC and microwaves (AC&Mw) to obtain three MOFs materials ( PTCDA‐Ni@TCM, PTCDA‐Ni@AC, PTCDA‐Ni@AC&Mw ). The results show that the activated PTCDA‐Ni has a different degree of enhancement in the specific surface area, the size of the pore size, and its stacking aggregation compared with the unactivated PTCDA‐Ni . Meanwhile, the activation strategy can reduce the content of guest molecules in the pore structure, exposing more active sites and then improving the electrochemical properties. As a result, the capacity retention of PTCDA‐Ni electrode before activation is 60.8% after 200 cycles at a current density of 0.1 A·g ⁻¹ , while under the same conditions, the capacity retention of PTCDA‐Ni@TCM , PTCDA‐Ni@AC , and PTCDA‐Ni@AC&Mw electrodes are significantly improved to 92.1%, 96.9%, and 96.9%, respectively. The results of the GITT test and the CV curves at different scanning speeds similarly show that the activation strategy can increase the migration rate of lithium ions and further improve its electrochemical performance, which will open up a new idea for the design of anode materials for high‐performance LIBs.

In situ Schiff base reaction is utilized to grow phthalocyanine covalent organic frameworks (TFPB-NiPc) on carbon cloth (CC) to obtain the composite material TFPB-NiPc@CC, which is used as the anode for the binder and conductive agent free Li/Na-ion batteries with enhanced active materials loading. What is more, CC acts as an excellent conductive backbone while reducing the stacking effect of phthalocyanine frameworks (Pc-COFs), which enables TFPB-NiPc to realize the self-exfoliation effect during the in situ synthesis process. This strategy shortens the migration path of Li⁺, efficiently resulting in improving the migration rate of Li⁺ in the electrode. Consequently, the TFPB-NiPc@CC electrode not only shows improved electrochemical behaviors of high capacity and long cycle stability but also displays superior flexibility and folding stability. The specific capacity achieved by the TFPB-NiPc@CC electrode is 1090.2 mA h/g at 200 mA/g, and after 500 cycles, the specific capacity of the TFPB-NiPc@CC electrode can also be maintained at 994.5 mA h/g with a retention ratio of 91.2%, which are all much higher than those of the TFPB-NiPc electrode. Moreover, TFPB-NiPc@CC also shows a high specific capacity and stable cycling behaviors in Na-ion batteries. The strategies designed in this work provide new ideas and methods for preparing practical, high-performance flexible organic anode materials.

Molecular engineering strategy was applied for the first time to improve the lithium storage behavior of phthalocyanine-based COFs anodes

Although many researchers continue to pursue improved battery capacity, battery safety remains a major concern. The main cause of battery fires is the flammability of the currently available commercial organic liquid electrolytes, which are mainly composed of 1 M lithium hexafluorophosphate (LiPF₆) and EC-containing carbonate solvents. Herein, a flame-retardant co-solvent tris(2,2,2-trifluoroethyl) phosphite (TTFP) was applied to improve the flame retardancy of a battery. It could improve the battery's discharging capacities at both 4.2 V and high cut-off voltage (4.5 V). Specifically, at a common voltage of 4.2 V, the cells’ 100th discharge capacity without TTFP was 130 mA h g⁻¹ by 0.2C with a capacity retention (CR) of 69%. In comparison, under the same conditions, the capacity of the 10% TTFP-containing cell was 162.3 mA h g⁻¹ with a CR of 73.9%. This increase in the electrochemical properties of the cell is clearly due to the addition of TTFP. When charging and discharging at 2.75–4.5 V, the capacity of the battery with STD after 100 cycles at 0.2C was 118.7 mA h g⁻¹, and the corresponding CR was 60.93%. Meanwhile, the discharged capacity of the battery containing 10% TTFP was 150.0 mA h g⁻¹ with a corresponding CR of 65.39%. Through combustion test with and without the TTFP electrolyte, it can be concluded that the TTFP-containing electrolyte is difficult to ignite. This result indicates that TTFP can efficiently enhance the safety performance of the battery. Thus, the incorporation of TTFP can be beneficial to improve the flame retardancy of the electrolyte. Moreover, TTFP does not affect the electrochemical stability of batteries. Thus, the present work may provide a good direction for the next generation of high-performance and high-safety lithium-ion batteries.