# Recent Advances in Lithiophilic Porous Framework toward Dendrite-Free Lithium Metal Anode
## 2 Metal-Based Li Host
### Copper  
The 3D nanostructured copper with a high electroactive surface area is considered as an appealing Li host matrix. Such a framework can lower the current density and provide the room to accommodate the Li and manipulate the electric filed for guiding the Li deposition. To synthesize 3D Cu porous nanostructure, [PERSON] et al. reported the simple solution-based approach with a submicron framework (median pore size 2.1 \(\upmu\)m) by immersing the planar Cu foil in ammonia solution [9]. Figure 2a shows the schematic representation of preparing 3D porous Cu from the planar Cu. Figure 2b shows the lithium-ion flux in planar and 3D porous Cu. In planar Cu, the irregular, rough, and cracks act as a local hotspot for Li-ion accumulation. The Li metal deposition is amplified at those Li-ion accumulation centers with higher plating cycles, which leads to the growth of Li dendrites. The high surface area of Li dendrite consumes an excess amount of electrolyte and Li leading to poor CE and quick capacity fading. Besides, the dendritic Li can pierce the separator, which can cause a short circuit or fire caught, threatening the safety concern of batteries. In contrast, 3D porous Cu has uniformly distributed the Li-ion flux due to the numerous and uniform protuberant tips on the submicron fibers. As a result, the deposited Li fills the pores evenly without any Li dendrites. The high pore volume of the structure can provide sufficient room to accommodate Li that leads to the stable and reversible Li plating/stripping. As a result, the 3D porous Cu showed plating/stripping cycles for 600 h with low voltage hysteresis (\(<\)50 mV) at 0.2 mA cm\({}^{-2}\) and exhibited a CE of 98.5% at 0.5 mA cm\({}^{-2}\). Further Li deposition behavior study on 3D Cu foam with an average pore size 170 \(\upmu\)m showed that Cu foam does not have any effect of the Li space constraint. This led to the Li metal detachment from the backbones of the Cu foam causing electric disconnection, which induces Li dendrite growth. [PERSON] et al. reported a free-standing 3D Cu nanowire (CuNW) network membrane via reducing copper nitrate in the NaOH aqueous solution [26]. The voltage hysteresis was further lowered to 40 mV and the CE, which reached 99.2% after 50 cycles remain stable to 98.6% after 200 cycles at 1 mA cm\({}^{-2}\). The full cell coupled with the LiCoO\({}_{2}\) cathode shows an outstanding 30% increase in the specific capacity at 5 C indicating the advantage of the Li-CuNWs nanocomposite in LMBs at a higher rate. The dealloying mechanism such as the dissolution of zinc (Zn) out of brass (Cu-Zn alloy) using various chemical-solution and vacuum distillation processes results in the formation of voids and microstructures [27; 28; 29]. The porosity can be easily tuned by adjusting the etching condition (such as the concentration of the solution, distillation temperature, and time) depending upon the method used. The interconnected, uniform, and smooth porous Cu provides sufficient electrical conductivity, uniform Li-ion flux, and space for Li accommodation. Besides, 3D porous Cu exhibited the lower voltage hysteresis as shown in Figure 2c,d, and improved cycling performance with a capacity retention of 87.2% after 300 cycles of charge/discharge at 50 mA g\({}^{-1}\) as shown in Figure 2e [28; 29]. The vertically distributed electric field promotes the vertical growth of Li dendrites, which continues to grow towards the separator and cathode and eventually pierce the separator causing short-circuits. To address these issues, it is necessary to constrain the lithium dendrite growth within the porous scaffold and distribute the electric field in the lateral direction. For this, the compartmented and the vertically aligned (VA) 3D porous Cu have been designed by the laser microprocessing system, and a series of processes, including hot lamination, laser ablation, and alkaline etching treatments. [PERSON] et al.