Abstract
Uncontrollable dendrite growth resulting from the non-uniform lithium ion (Li+) flux and volume expansion in lithium metal (Li) negative electrode leads to rapid performance degradation and serious safety problems of lithium metal batteries. Although N-containing functional groups in carbon materials are reported to be effective to homogenize the Li+ flux, the effective interaction distance between lithium ions and N-containing groups should be relatively small (down to nanometer scale) according to the Debye length law. Thus, it is necessary to carefully design the microstructure of N-containing carbon materials to make the most of their roles in regulating the Li+ flux. In this work, porous carbon nitride microspheres (PCNMs) with abundant nanopores have been synthesized and utilized to fabricate a uniform lithiophilic coating layer having hybrid pores of both the nano- and micrometer scales on the Cu/Li foil. Physically, the three-dimensional (3D) porous framework is favorable for absorbing volume changes and guiding Li growth. Chemically, this coating layer can render a suitable interaction distance to effectively homogenize the Li+ flux and contribute to establishing a robust and stable solid electrolyte interphase (SEI) layer with Li-F, Li-N, and Li-O-rich contents based on the Debye length law. Such a physical-chemical synergic regulation strategy using PCNMs can lead to dendrite-free Li plating, resulting in a low nucleation overpotential and stable Li plating/stripping cycling performance in both the Li‖Cu and the Li‖Li symmetric cells. Meanwhile, a full cell using the PCNM coated Li foil negative electrode and a LiFePO4 positive electrode has delivered a high capacity retention of ∼ 80% after more than 200 cycles at 1 C and achieved a remarkable rate capability. The pouch cell fabricated by pairing the PCNM coated Li foil negative electrode with a NCM 811 positive electrode has retained ∼ 73% of the initial capacity after 150 cycles at 0.2 C.
Highlights
With increasing popularity in portable electronic devices and electric vehicles, traditional lithium ion (Li+) batteries are facing challenges of growing demands for higher energy density [1]
3.1 Materials characteristics Porous g-C3N4 microspheres were synthesized by thermal polycondensation of supramolecular aggregates of melamine and cyanuric acid according to the previous work by Liu et al [37]
We have firstly investigated the influence of morphology over g-C3N4 materials on lithium metal (Li) deposition/dissolution behavior
Summary
With increasing popularity in portable electronic devices and electric vehicles, traditional lithium ion (Li+) batteries are facing challenges of growing demands for higher energy density [1]. The Debye length that reflects the range of electrostatic forces to interact with lithium ions in electrolyte is possibly distributed at the nanometer scale Beyond this distance, N-containing groups will basically be shielded from the electrical field of the surrounding opposite particles. When coating PCNMs on Cu or Li foils, the nano-pores inside PCNMs can effectively homogenize the Li+ distribution to promote homogeneous Li+ deposition and construct a robust SEI through the chemical interaction between Li+ and g-C3N4, while the interparticle micro-pores can provide enough space to accommodate and guide Li growth and relieve volume expansion in a physical way This physical and chemical synergic regulation strategy contributes to improved Li deposition/ dissolution, resulting in stable cycling performance of the lithium metal cells
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