Fabricating high-energy quantum dots in ultra-thin LiFePO4 nanosheets using a multifunctional high-energy biomolecule-ATP

By using a multifunctional high-energy biomolecule—adenosine triphosphate (ATP)—we fabricated highenergy quantum dots (HEQDs) with a feature size of less than 10 nm and used them in high-power lithium-ion batteries. We introduced high-energy phosphate bonds into the crystal structure of LiFePO₄ nanoparticles and synthesized the mesoporous biocarbon nanowire coated LiFePO₄ with HEQDs (MBCNW-LFP-HEQDs) by using ATP as a phosphorus source, a nucleating agent, a structural template and a biocarbon source. HEGDs were homogeneously formed inside the ultra-thin LiFePO₄ nanosheet and the mesoporous biocarbon nanowire network structure was coated on the surface of the nanosheet. In LiFePO₄ nanoparticles, HEQDs result in more storage sites of Li⁺ ions and easier transfer kinetics of electrons and lithium ions, where the kinetic transformation path between LiFePO₄ and FePO₄ is rather different from the path deduced from its equilibrium phase diagram. Compared to the usual LiFePO4 nanoparticle (10–100 nm) cathode, the MBCNW-LFP-HEQD cathode shows the best first discharge capacity of 197 mA h g^-1 at the 0.1 C rate, which is higher than the theoretical capacity of LiFePO₄ (170 mA h g^-1). After 100 cycles at varied current rates: 0.1, 0.5, 1, 5 and 10 C, this cathode still delivered a high discharge capacity of 180 mA h g^-1 and an ultra-high coulombic efficiency close to 100%. This is attributed to the quantum tunneling of HEQDs in LiFePO₄ nanoparticles and better percolation of mesoporous biocarbon nanowire coating network structures. This work is instructive for fabrication and design of new types of electrochemical energy conversion and storage devices with extraordinary properties and functions.