Abstract
Development of high-energy-density anode is crucial for practical application of Na-ion battery as a post Li-ion battery. Hard carbon (HC), though a promising anode candidate, still has bottlenecks of insufficient capacity and unclear microscopic picture. Usage of the micropore has been recently discussed, however, the underlying sodiation mechanism is still controversial. Herein we examined the origin for the high-capacity sodiation of HC, based on density functional theory calculations. We demonstrated that nanometer-size Na cluster with 3–6 layers is energetically stable between two sheets of graphene, a model micropore, in addition to the adsorption and intercalation mechanisms. The finding well explains the extended capacity over typical 300 mAhg−1, up to 478 mAhg−1 recently found in the MgO-templated HC. We also clarified that the MgO-template can produce suitable nanometer-size micropores with slightly defective graphitic domains in HC. The present study considerably promotes the atomistic theory of sodiation mechanism and complicated HC science.
Highlights
Li-ion batteries (LIBs) have been widely used due to the lightweight, high-energy density, and rechargeability, and even Nobel prize in chemistry 2019 was awarded to the researchers for LIB1–3
We investigate the microscopic origin of Na capacity in the Hard carbon (HC) and reveal the sodiation mechanism using density functional theory (DFT) calculations
Na may be intercalated into the graphitic domains of HC with less organized graphene sheets lowering the reconstruction energy
Summary
Li-ion batteries (LIBs) have been widely used due to the lightweight, high-energy density, and rechargeability, and even Nobel prize in chemistry 2019 was awarded to the researchers for LIB1–3. Na-ion batteries (NIBs) have been attracted as an alternative of LIBs5,6. Sodium is much cheaper and richer than Lithium. They have similar chemical properties since they belong to the same group, alkali metal. The exploration of cathode, anode, and electrolyte materials, referring to the knowledge for the LIBs, has been carried out. Several new transition metal oxides for the cathode (e.g., Na2/3Ni1/3Mn1/2Ti1/6O2) and alloys for the anode have been proposed[7,8], in which the novel principles are involved due to the different ionic radius and ionization potential of Sodium
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