Long-Lifespan Anode-Free Lithium Metal Batteries by Ag/Conjugated Polymer Wetting Agent Inducing Interfacial Fluorination

Li metal batteries (LMBs) have emerged as a promising energy storage technology for high-energy-density rechargeable batteries. Since the Li metal anode (LMA) has an ultrahigh theoretical specific capacity (3862 mAh g^-1) and the lowest negative electrochemical potential (-3.040 V vs. SHE), its employment ensures higher energy density beyond commercial Li-ion batteries (LIBs) with the limited energy density of less than 250 Wh kg^-1 at the cell level. In this respect, anode-free LMBs (AFLMBs) with no Li excess is considered the ultimate system to achieve a dramatic increase in energy density (&gt;500 Wh kg^-1), in which all the active Li sources are stored in a fully lithiated cathode. In addition, the anode-free design significantly reduces cost and simplifies the manufacturing process compared with traditional LMBs. However, LMA suffers from low coulombic efficiency (CE), rapid capacity fading, and safety hazards, which come from the Li dendrite growth and continuous formation and breakage of solid electrolyte interphase (SEI) during Li plating/stripping processes. Therefore, such uncontrollable interfacial reactions should be seriously addressed, especially in AFLMBs without excess Li inventory to compensate for the loss of active Li sources. Recently, many strategies have been reported to control the interfacial chemistry between Li and electrolyte as well as between Li and current collector (i.e. modification of current collector, electrolyte design, optimization of cycling protocols). Among them, studies about employing lithiopilic wetting agents on the current collector confirm an effective way to stabilize Li plating behavior, which can achieve a favorable life span. In particular, wetting agents show outstanding effects on guiding homogeneous Li deposition and thus suppressing dendritic Li growth by lowering the Li nucleation barrier. However, the critical problem of sequentially irreversible capacity loss before a stable SEI formation still remains, which is a fatal obstacle in no excess Li cells.<br/>Herein, we introduced Ag nanoparticles incorporated p-doped conjugated polymer (Ag-PCP) wetting agent simultaneously to regulate the Li nucleation and promote a rapid stabilization of SEI at the early stage, and further prolong the life span of AFLMBs. Furthermore, we investigate interfacial fluorinated mechanism of the Ag-PCP chains to efficiently control SEI chemistry related to the LiF formation. The Ag-PCP wetting agent is fabricated by a simple one-step synthesis because of the electrostatic interaction between oppositely charged Ag cation and dopant. Critically, the PCP chain with the delocalized π-electron system induces an interfacial fluorinated reaction with F anions derived from TFSI^- decomposition, and thus the F-doped PCP promotes the formation of LiF-rich SEI. Also, the presence of lithiophilic Ag nanoparticles on the PCP wetting agent act as both Li nucleation seeds and polymer chain modifiers about the structural rearrangement and closer packing of the Ag-PCP chains, thus providing both uniform Li nucleation and continuous conductive channel, resulting in an increase of LiF ratio in the SEI. The LiF-rich SEI facilitates Li ion diffusion, which effectively suppresses the Li dendrite growth and the depletion of the Li reservoir. Benefiting from the synergistic effect Ag-Li alloying process and interfacial fluorination, the Ag-PCP wetting agent optimizes Li deposition behavior and a favorable SEI chemistry, leading to superior cycling performances. Consequently, the Ag-PCP/Cu half-cell shows quite stable voltage profiles with low polarization (≈17 mV) over 300 cycles, even at a high current density/areal capacity of 3mA cm^-2/3mAh cm^-2. Moreover, the anode-free LiFePO₄ (LFP) full cell achieves superior cycling stability with a high capacity retention of 72% (Li inventory retention rate 99.8%) at 1C-rate after 200 cycles. This strategy contributes to the applicability of interfacial stabilization for long-life AFLMBs.