Non-negligible Influence of Oxygen in Hard Carbon as an Anode Material for Potassium-Ion Batteries

Homogeneous Adsorption of Multiple Potassiation Products of Red Phosphorus Anode toward Stable Potassium Storage

Potassium ion batteries (PIBs) are a viable alternative to lithium-ion batteries for energy storage. Red phosphorus (RP) has attracted a great deal of interest as an anode for PIBs owing to its cheapness, ideal electrode potential, and high theoretical specific capacity. However, the direct preparation of phosphorus-carbon composites usually results in exposure of the RP to the exterior of the carbon layer, which can lead to the deactivation of the active material and the production of "dead phosphorus". Here, the advantage of the π-π bond conjugated structure and high catalytic activity of metal phthalocyanine (MPc) is used to prepare MPc@RP/C composites as a highly stable anode for PIBs. It is shown that the introduction of MPc greatly improves the uneven distribution of the carbon layer on RP, and thus improves the initial Coulombic efficiency (ICE) of PIBs (the ICE of FePc@RP/C is 75.5% relative to 62.9% of RP/C). The addition of MPc promotes the growth of solid electrolyte interphase with high mechanical strength, improving the cycle stability of PIBs (the discharge-specific capacity of FePc@RP/C is 411.9 mAh g-1 after 100 cycles at 0.05 A g-1). Besides, density functional theory theoretical calculations show that MPc exhibits homogeneous adsorption energies for multiple potassiation products, thereby improving the electrochemical reactivity of RP. The use of organic molecules with high electrocatalytic activity provides a universal approach for designing superior high-capacity, large-volume expansion anodes for PIBs.

Preparation of nitrogen doped hyper-crosslinked polymer-based hard carbon for high performance Li+/Na+ battery anode

Hyper cross-linked polymers (HCPs), as a key precursor of hard carbon (HC) anode materials, stand out because of their capacity for molecular-scale structural design and comparatively straightforward preparation techniques, which are not seen in other porous materials synthesized procedure. A novel synthesis method of HCPs is developed in this paper, which is through the incorporation of functional macromolecules, the structural control and heteroatom doping of the product has been achieved, thus augmenting its electrochemical performance in batteries. In this work, carbonized tetraphenylporphyrin zinc (TPP-Zn) doped HCP-based hard carbon (CTHCP) with stable structure was prepared by Friedel-Crafts reaction and carbonization by using naphthalene and trace TPP-Zn as monomers, dimethoxybenzene (DMB) as crosslinking agent and FeCl3 as catalyst. The introduction of TPP-Zn, a functional macromolecule with unique two-dimensional structure, realized the pore structure regulation and N doping of the raw carbonized HCP-based hard carbon (CHCP). The results showed that CTHCP had higher mesoporous volume, N content and wider layer spacing than CHCP. In addition, CTHCP anode exhibited excellent Li+/Na+ storage performance, initial reversible capacity, rate performance and long cycle life. More amount of N-containing (N-5) active sites and mesoporous content in CTHCP anode was the main reason for the improvement of Na+ storage effect. While the increased interlayer spacing had a greater effect on the lithium storage capacity. This study uncovered the design rules of HC anode materials suitable for Li+/Na+ batteries and provided a new idea for the preparation of high-performance HC anode materials.

An oriented tube array porous carbon anode prepared using a self-blowing mold of salt templates for high-rate potassium storage

Porous carbon materials with oriented porosity are very useful in ion batteries, but their high cost and complex fabrication hinder their wide application. In this paper, we used cheap and water-soluble NaHCO3 grains to prepare unique porous carbon with an orderly arranged tube array via one-step carbonization. During the preparation process, a novel self-blowing mold of salt templates was discovered for the first time, and the resulting numerous high-speed gas jets can act as gas state templates to induce the formation of the oriented porous carbon into a mesoscale tube array with rich micropores. Besides, the amount of CO functional groups has been enhanced greatly by the chemical activation of H2O and CO2 derived from the decomposition of NaHCO3, which can improve the reversible specific capacity of the electrode by forming a C-O-K compound with potassium. Thanks to the coupling effect of the hierarchical porous structure with an orderly tube array and rich CO functional groups, the obtained porous carbon materials exhibited excellent kinetics and impressive rate capability as the anode of potassium-ion batteries (PIBs) with high capacities of 209 mA h g-1 at 10 A g-1 and 156 mA h g-1 at 30 A g-1. This work not only provides a facile, green, sustainable approach to fabricating novel carbon materials, but also demonstrates the promising prospect of oriented porous carbon in exploring advanced electrode materials for PIBs.