Lithium-Oxygen-Battery Using Lightweight Gas-Diffusion Current Collector
Authors: Miyakawa Shuntaro , Matsuda Shoichi , Yamaguchi Shoji , Ono Manai , Saito Takaya , Masatoshi Goto 
Published: December 2024

Introduction

There is a growing demand for high-energy-density storage devices owing to the increasing number of mobile device applications. On the other hand, an energy-density of currently mainstream lithium-ion batteries (LIBs) has almost reached its theoretical limit, and there is a strong desire for a next-generation batteries that use high-capacity materials based on designs different from conventional ones.
Lithium oxygen batteries (LOBs), comprising gas phase oxygen and lithium metal foil as the positive and negative electrode materials, have received great attention as next generation energy storage devices owing to their superior theoretical energy densities. These days, there has been considerable technological progress in the field of LOBs, however, the progress on gas diffusion layer (GDL) has not been sufficient despite their importance in providing an oxygen supply needed to achieve practical power densities. The current mainstream design of LOBs uses a carbon fiber-based GDL which are used in polymer electrolyte fuel cells, but its heavy-weight makes it hardly to apply to high energy-dense LOBs. A new material design is required to achieve practical power density with minimal weight load.
In this study we demonstrated a gas-diffusible current collector that combines the function of oxygen mass transport and electron transfer by a Ni-coated polymer fiber mesh and investigated its applicability in LOBs.

Experimental Method

A Ni-coated polymer fiber mesh, which is a gas-diffusible current collector, was obtained by electroless plating of 0.5 μm of Ni onto a 0.8 mg/cm2 mesh comprised a 27 μm diameter PET fiber.
The LOB cell was fabricated with the following configuration. Cathode active material: a self-standing KB-based membrane (270 mm thick, 5.4 mg/cm2 carbon-loaded), Anode active material: Li foil (20 μm thick), Separator: polyolefin-based separator (20 μm thick), Electrolyte: 0.5 M LiTFSI + 0.5 M LiNO3 + 0.2 M LiBr in TEGDME, GDL: a carbon fiber membrane (200 μm thick) or the Ni-coated PET mesh, positive electrode current collector: SUS-304 foil (20 μm thick). And a ceramic-based, solid-state separator (LICGC, 90 μm thick), which was sandwiched between polyolefin separator, was used to protect the lithium negative electrode.

Result and Discussion

First, we investigated the effect of the mass loading of the GDL and positive electrode current collector on the energy density of a LOB. A 200 μm carbon fiber membrane (8.4 mg/ cm2) and a 30 μm SUS mesh (3.5 mg/cm2) were used as a GDL and a cathode current collector and total weight of GDL and cathode current collector reached 11.9 mg/cm2.
On the other hand, the weight of the Ni-coated polymer fiber mesh is only 1.4 mg/cm2 (PET fibers: 0.8 mg/cm2, Ni coating layer: 0.6 mg/cm2). Therefore, when this material is used as a gas diffusible current collector, a weight reduction of about 10 mg/cm2 can be achieved. (Based on our calculations [1], it’s equivalent to an increase of approximately 150 Wh/kg in a LOB). These results illustrate the importance of a gas-diffusible current collector in high-energy-density LOBs.
Then we fabricated the following two LOB cells and evaluated their battery performance. (i) Cell A: carbon fiber membrane GDL and SUS mesh current collector (total weight 11.9 mg/cm2), (ii) Cell B: Ni-coated PET fiber mesh gas-diffusible current collector (total weight 1.4 mg/cm2). The schematic illustration of LOB cells is shown in Figure a, b.

Figure c, d shows the discharge profiles of the LOB cells at 0.4 mA/cm2 current density and 4.0 mAh/cm2 areal capacity and this result indicated that the gas-diffusible current collector possesses an oxygen transport ability equivalent to that of a conventional carbon fiber membrane, albeit with a smaller thickness and less weight.
We also conducted a cycling test at current density of at 0.4 mA/cm2 current density and 4.0 mAh/cm2 areal capacity. These two cells displayed stable discharging/charging and showed an equivalent cycle-life performance. These results indicated that equivalent LOB performance can be achieved even when using a lightweight gas-diffusible current collector instead of a conventional thick, heavy carbon fiber membrane.
We believe that the concept of an ultralightweight gas diffusible current collector demonstrated in this study opens future directions in the search for metal air batteries with high energy-density and power densities.
[1] M. Shuntaro et al., ACS Appl. Energy Mater.
2023, 6, 1906−1912

Figure 1