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Research Webzine of the KAIST College of Engineering since 2014

Fall 2023 Vol. 21
Engineering

A new structural surface design for anodes in the next generation lithium batteries

August 23, 2023   hit 766

 A copper current collector with increased structural dimensions and hierarchy is developed for high-performance lithium-metal battery anodes. The new surface enables inward nucleation of lithium, thus enhancing the cycle life of lithium-metal battery by 364%


 

In the structurally hierarchical structure, the nanorods inside a microcavity induces a local electric field concentration that maximizes the lithium-ion flux into the microcavities. This phenomenon promotes the selective nucleation of lithium-metal at nanorod tips, resulting in agglomeration of lithium-metal and enhancement of the columbic efficiency and cycle life.

 A research team led by Prof. Sanha Kim in ME department has succeeded in developing an anode current collector for high-performance lithium-metal batteries using micro/nano hierarchical surface structures. As the energy demand continues to increase, the development of batteries with higher energy density and better performance is becoming more important.

 

  Lithium-ion batteries, which are mainly used as commercial batteries, use graphite as an active anode material, which theoretically has a clear limit in energy density. Accordingly, lithium-metal batteries with high energy density that replace the anode material of existing lithium-ion batteries with lithium-metal have been attracting attention. However, in order to  commercialize lithium-metal batteries, the problem of maintaining stability and performance must first be resolved. The main cause of this problem is the formation of dendrite in the form of tree branches. These are formed on the lithium-metal anode surface by heterogeneous electrodeposition of Li due to its inherent instability in organic electrolytes. The team  began research on a copper current collector (Cu CC) based on a micro/nano hierarchical structure to suppress the formation of dendrites and improve the stability and performance of lithium-metal batteries.
Figure 1. Illustration for dendrite failure in Li-metal batteries and research objectives: Structural optimization in microscale, selective nucleation of Li via micro- and nanostructured hierarchical surface, and development of facile/largescale fabrication process of three-dimensional and hierarchically structured current collector with selective nucleation and inward growth characteristics. [Copyright: Advanced Energy Materials 2023, 13, 2202321.]
 The team first manufactured 2.5-dimensional micro-structured Cu CCs via electroforming with a photolithographically patterned surface mold. The introduction of microcavity arrays on the CC surface can condense the Li grains inside the microcavities, and therefore suppress Li dendrite formation. Then, the structural hierarchy was implemented by electrodepositing nanorods inside microcavities. The nanorods inside the microcavities rapidly reduced the electrode current density by maximizing the surface area and enhancing the flux of Li ions into the microcavities, leading Li electrodeposition to predominantly occur inside the microcavities. The inward Li nucleation induces Li agglomeration within these cavities, which can suppress the dendrite formation. Accordingly, the team revealed that the cycle life of lithium-metal batteries improves dramatically by utilizing such structured surface design.
Figure 2. Concentration of electrical field inside microcavities via nanorods resulting in Li nucleation at nanorod tips. [Copyright: Advanced Energy Materials 2023, 13, 2202321.]
  To better utilize the benefits of increased structural dimensions and better hierarchy in the anode CCs, a facile fabrication approach was further introduced. The method is used to manufacture a micro- and nanostructured three-dimensional copper surface easily. The woven Cu mesh structure provided micrometer pores with excellent structural stability, while the electrodeposited nanostructures formed inside the pores induced inward growth of Li. The Li@Cu||LiFePO4 cell test of the three-dimensional hierarchical structure showed that the number of cycles during which 80% of initial capacity was maintained was two-times higher in 3DMN Cu than in 2D Cu.
Figure 3. Facile, large-scale fabrication of hierarchically structured current collectors with selective inward growth characteristics and its performance as a lithium metal battery anode. [Copyright: Advanced Energy Materials 2023, 13, 2202321.]
 Overall, this study introduces a new structural surface design in two different length scales that can overcome the current challenge in lithium-metal batteries, which is considered to be the next generation energy storage device. Inyeong Yang, a Ph.D. student in ME department contributed this work as the leading author and the work has been published in the article titled “Structurally Tailored Hierarchical CU Current Collector with Selective Inward Growth of Lithium for High-Performance Lithium Metal batteries” in Advanced Energy Materials in January 2023.
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