The undesirable capacity loss after first cycle is universal among layered cathode materials, which results in the capacity and energy decay. The key to resolving this obstacle lies in understanding the effect and origin of specific active Li sites during discharge process. In this study, focusing on Ah-level pouch cells for reliability, an ultrahigh initial Coulombic efficiency (96.1%) is achieved in an archetypical Li-rich layered oxide material. Combining the structure and electrochemistry analysis, we demonstrate that the achievement of high-capacity reversibility is a kinetic effect, primarily related to the sluggish Li mobility during oxygen reduction. Activating oxygen reduction through small density would induce the oxygen framework contraction, which, according to Pauli repulsion, imposes a great repulsive force to hinder the transport of tetrahedral Li. The tetrahedral Li storage upon deep oxygen reduction is experimentally visualized and, more importantly, contributes to 6% Coulombic efficiency enhancement as well as 10% energy density improvement for pouch cells, which shows great potentials breaking through the capacity and energy limitation imposed by intercalation chemistry.

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.