Quantitatively Designing Porous Copper Current Collectors for Lithium Metal Anodes

Abstract

Lithium metal has been an attractive candidate as a next-generation anode material. Despite its popularity, stability issues of lithium in the liquid electrolyte and the formation of lithium whiskers have kept it from practical use. Three-dimensional (3D) current collectors have been proposed as an effective method to mitigate whisker growth. Although extensive research has been done, the effects of three key parameters of the 3D current collectors, namely, the surface area, the tortuosity factor, and the surface chemistry, on the performance of lithium metal batteries remain elusive. Herein, we quantitatively studied the role of these three parameters by synthesizing four types of porous copper networks with different sizes of well-structured microchannels. X-ray microscale computed tomography (micro-CT) allowed us to assess the surface area, the pore size, and the tortuosity factor of the porous copper materials. A metallic Zn coating was also applied to study the influence of surface chemistry on the performance of the 3D current collectors. The effects of these parameters on the performance were studied in detail through scanning electron microscopy (SEM) and titration gas chromatography (TGC). Stochastic simulations further allowed us to interpret the role of the tortuosity factor in lithiation. The optimal range of the key parameters is thereby found for the porous coppers and their performance is predicted. Using these parameters to inform the design of porous copper anodes for Li deposition, Coulombic efficiencies (CEs) of up to 99.63% are achieved, thus paving the way for the design of effective 3D current collector systems.

Assessing Coulombic Efficiency in Lithium Metal Anodes

“…A detailed discussion of the SEM and XPS measurement can be found in the Supporting Information in Figure S5. As previously done in the literature, ,,,− both the reservoir and the conventional methods were applied to evaluate their performance and determine the optimal thickness of the coating layer. As shown in Figure a, the prepared samples show different colors due to interference effects in the thin ZnO layers of varying thicknesses.…”

Mechanistic study of Al2O3 coating effects on lithium deposition and dissolution reaction

“…12,13 Consequently, there has been extensive research into methods to suppress dendrite formation effectively and, thus, improve the safety and cyclic stability of lithium metal batteries. Examples of these methods include (i) the introduction of a 3D current collector [14][15][16] and a 3D host matrix (scaffold) [17][18][19] having a large specic surface area for lithium deposition, which suppresses volume expansion and reduces the local current density; (ii) the in situ formation of ideal SEIs by optimising the electrolyte 20,21 and the inclusion of additives; [22][23][24] (iii) the formation of uniform Li + -ion ow by modifying the inorganic/ organic particles on the separator; 25,26 and (iv) the physical suppression of dendrite growth by enhancing the mechanical strength of the thin lm by coating with an inorganic/organic solid electrolyte 27,28 or a ceramic thin lm. 8,[29][30][31][32][33] In particular, the introduction of an ex situ protective lm on metallic lithium, that is, the introduction of an articial SEI, is a particularly useful method 34 because undesirable side reactions between metallic lithium and the electrolyte, as well as dendrite growth, can be suppressed.…”

On the direct correlation between the copper current collector surface area and ‘dead Li’ formation in zero-excess Li metal batteries

“…In the case of planar Cu foils which have been used as the anode CC in LIBs for decades, a homogeneous Li + ion ux is hardly achievable. 15,20 It has been found that the inhomogeneous Li + ion ux distribution could cause non-uniform Li deposition and dendrite growth. 21 The prevailing understanding regarding CC has reached consensus in the literature that the larger the CC surface area the better the ability to effectively reduce local current density, and therefore minimize 'dead Li' formation.…”

“…As the CC surface area is not inherently inuenced by one factor, it is important to control other factors such as surface features and surface chemistry. 20 On one hand, the use of 3D host materials brings into additional complexity, as various parameters, such as the material components, dispersion homogeneity, particle size distribution, electrode thickness, and electrode porosity, all contribute to 'dead Li' formation. 14 On the other hand, the use of a 3D Cu CC using widely reported methods (e.g., chemical modication, 27,28 dealloying modication, 29,30 and protective layer modication, 31,32 ) oen neglects the surface chemistry difference and is also lacking the ability to precisely control the surface features and tortuosity.…”