Effects of Central Metal Ion on Binuclear Metal Phthalocyanine-Based Redox Mediator for Lithium Carbonate Decomposition

Li2CO3 is the most tenacious parasitic solid-state product in lithium-air batteries (LABs). Developing suitable redox mediators (RMs) is an efficient way to address the Li2CO3 issue, but only a few RMs have been investigated to date, and their mechanism of action also remains elusive. Herein, we investigate the effects of the central metal ion in binuclear metal phthalocyanines on the catalysis of Li2CO3 decomposition, namely binuclear cobalt phthalocyanine (bi-CoPc) and binuclear cobalt manganese phthalocyanine (bi-CoMnPc). Density functional theory (DFT) calculations indicate that the key intermediate peroxydicarbonate (*C2O62-) is stabilized by bi-CoPc2+ and bi-CoMnPc3+, which is accountable for their excellent catalytic effects. With one central metal ion substituted by manganese for cobalt, the bi-CoMnPc's second active redox couple shifts from the second Co(II)/Co(III) couple in the central metal ion to the Pc(-2)/Pc(-1) couple in the phthalocyanine ring. In artificial dry air (N2-O2, 78:22, v/v), the LAB cell with bi-CoMnPc in electrolyte exhibited 261 cycles under a fixed capacity of 500 mAh g-1carbon and current density of 100 mA g-1carbon, significantly better than the RM-free cell (62 cycles) and the cell with bi-CoPc (193 cycles).

Lattice Engineering on Li2 CO3 -Based Sacrificial Cathode Prelithiation Agent for Improving the Energy Density of Li-Ion Battery Full-Cell

Developing sacrificial cathode prelithiation technology to compensate for active lithium loss is vital for improving the energy density of lithium-ion battery full-cells. Li2 CO3 owns high theoretical specific capacity, superior air stability, but poor conductivity as an insulator, acting as a promising but challenging prelithiation agent candidate. Herein, extracting a trace amount of Co from LiCoO2 (LCO), a lattice engineering is developed through substituting Li sites with Co and inducing Li defects to obtain a composite structure consisting of (Li0.906 Co0.043 ▫0.051 )2 CO2.934 and ball milled LiCoO2 (Co-Li2 CO3 @LCO). Notably, both the bandgap and Li─O bond strength have essentially declined in this structure. Benefiting from the synergistic effect of Li defects and bulk phase catalytic regulation of Co, the potential of Li2 CO3 deep decomposition significantly decreases from typical >4.7 to ≈4.25 V versus Li/Li+ , presenting >600 mAh g-1 compensation capacity. Impressively, coupling 5 wt% Co-Li2 CO3 @LCO within NCM-811 cathode, 235 Wh kg-1 pouch-type full-cell is achieved, performing 88% capacity retention after 1000 cycles.

A Highly Reversible Long-Life Li-CO2 Battery with a RuP2 -Based Catalytic Cathode

Rechargeable Li-CO₂ batteries have attracted worldwide attention due to the capability of CO₂ capture and superhigh energy density. However, they still suffer from poor cycling performance and huge overpotential. Thus, it is essential to explore highly efficient catalysts to improve the electrochemical performance of Li-CO₂ batteries. Here, phytic acid (PA)-cross-linked ruthenium complexes and melamine are used as precursors to design and synthesize RuP₂ nanoparticles highly dispersed on N, P dual-doped carbon films (RuP₂ -NPCFs), and the obtained RuP₂ -NPCF is further applied as the catalytic cathode for Li-CO₂ batteries. RuP₂ nanoparticles that are uniformly deposited on the surface of NPCF show enhanced catalytic activity to decompose Li₂ CO₃ at low charge overpotential. In addition, the NPCF its with porous structure in RuP₂ -NPCF provides superior electrical conductivity, high electrochemical stability, and enough ion/electron and space for the reversible reaction in Li-CO₂ batteries. Hence, the RuP₂ -NPCF cathode delivers a superior reversible discharge capacity of 11951 mAh g^-1 , and achieves excellent cyclability for more than 200 cycles with low overpotentials (<1.3 V) at the fixed capacity of 1000 mAh g^-1 . This work paves a new way to design more effective catalysts for Li-CO₂ batteries.

Complete Decomposition of Li2CO3 in Li-O2 Batteries Using Ir/B4C as Noncarbon-Based Oxygen Electrode

Instability of carbon-based oxygen electrodes and incomplete decomposition of Li₂CO₃ during charge process are critical barriers for rechargeable Li-O₂ batteries. Here we report the complete decomposition of Li₂CO₃ in Li-O₂ batteries using the ultrafine iridium-decorated boron carbide (Ir/B₄C) nanocomposite as a noncarbon based oxygen electrode. The systematic investigation on charging the Li₂CO₃ preloaded Ir/B₄C electrode in an ether-based electrolyte demonstrates that the Ir/B₄C electrode can decompose Li₂CO₃ with an efficiency close to 100% at a voltage below 4.37 V. In contrast, the bare B₄C without Ir electrocatalyst can only decompose 4.7% of the preloaded Li₂CO₃. Theoretical analysis indicates that the high efficiency decomposition of Li₂CO₃ can be attributed to the synergistic effects of Ir and B₄C. Ir has a high affinity for oxygen species, which could lower the energy barrier for electrochemical oxidation of Li₂CO₃. B₄C exhibits much higher chemical and electrochemical stability than carbon-based electrodes and high catalytic activity for Li-O₂ reactions. A Li-O₂ battery using Ir/B₄C as the oxygen electrode material shows highly enhanced cycling stability than those using the bare B₄C oxygen electrode. Further development of these stable oxygen-electrodes could accelerate practical applications of Li-O₂ batteries.