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Long-lasting, rechargeable lithium-ion (Li-ion) batteries have a high energy density and low self-discharge, and are finding their way into aerospace and military applications, among others. As the demand for energy consumption rises at the same time the pressure for reducing our usage of fossil fuels is, our society is working hard to find innovative ways of manufacturing energy storage devices.
3D printing has been used in the past to fabricate porous electrodes for lithium-ion batteries, and even the batteries themselves. A collaborative group of researchers from Manchester Metropolitan University, China’s Central South University, and the University of Chester recently published a paper, titled “Next-Generation Additive Manufacturing: Tailorable Graphene/Polylactic(acid) Filaments Allow the Fabrication of 3D Printable Porous Anodes for Utilisation within Lithium-ion Batteries,” about their work applying Li-ion anodes within 3D printed Li-ion batteries, made with a bespoke graphene/PLA filament that allows the graphene content to be easily tailored.
The abstract reads, “We demonstrate that a graphene content of 20 wt. % exhibits sufficient conductivity and critically, effective 3D printability for the rapid manufacturing of 3D printed freestanding anodes (3DAs); simplifying the components of the Li‐ion battery negating the need for a copper current collector. The 3DAs are physicochemically and electrochemically characterised and possess sufficient conductivity for electrochemical studies. Critically, it is found that if the 3DAs are used in Li‐ion batteries the specific capacity is very poor but can be significantly improved through the use of a chemical pre‐treatment. Such treatment induces an increased porosity, which results in a 200‐fold increase (after anode stabilisation) of the specific capacity (ca. 500 mAh g−1 at a current density of 40 mA g−1). This work significantly enhances the field of additive manufacturing/3D printed graphene based energy storage devices demonstrating that useful 3D printable batteries can be realised.”
Many researchers are working with novel nanomaterials like carbon nanotubes and graphene for the purposes of 3D printing novel energy storage devices, such as Li-based batteries, as the technology can be used to create structures with a large surface area – helpful when it comes to energy capabilities. This particular team used FDM (extrusion-based) technology to create Li-ion anodes out of bespoke 3D printable graphene/PLA filaments. They also performed electrochemical and physicochemical characterization, to make sure that the graphene content was optimized for controlling the conductivity, electrochemical activity, and 3D printability of their 3D printed freestanding anodes, or 3DAs.
The researchers stated that “…this approach simplifies the components of the Li‐ion battery negating the need for a copper current collector.”
The team used Autodesk Fusion 360 to create the 3D printed designs for this work – a circular disc electrode, 1.0 mm thick, with a range of diameters – and printed them at 190 °C, with a direct drive extruder, on a ZMorph 3D printer. The 3D printable graphene/PLA filaments were made with a range of 1, 5, 15, 20 and 40 wt.% graphene nanoplatelets, which were validated using thermogravimetric analysis (TGA).
Physicochemical characterisation and optical images of the graphene/PLA powders, respective filaments and 3DAs. A: Thermogravimetric analysis, B: Resistivity vs. graphene content, C: TEM analysis of 20 wt. % graphene/PLA, D: 3D printing process of the 3DAs (for electrochemical characterisation), E: Raman (inset) and Raman Mapping of the 3DA.
“In brief, the fabrication of graphene/PLA filaments containing percentages over 20 wt. % are extremely brittle and highly unreproducible in terms of both homogeneity, printability and structural integrity; additionally filaments with a wt. % of graphene below 10 % did not offer sufficient percolation (i. e. high resistivity),” the researchers wrote.
“Therefore, we have found that 15–20 % is the optimal wt. % when one is considering graphene nanoplatelets…where the resistivity decreases and conductivity increases.”
After they optimized the graphene content, the team used the filament with 20 wt. % graphene to 3D print test anodes for more physicochemical characterization. They also completed a Raman analysis on the anodes, as well as an XPS analysis; the latter involved taking high-resolution scans “over the C 1s and O 1s photoelectron peaks,” which were broad and strangely shaped. The analysis showed that PLA was present in two forms, at roughly the same levels, as in the graphene/PLA samples.
“In summary, XPS analysis reveals that the high volume of graphene within the graphene/PLA filament is fully dispersed within the PLA creating a conductive pathway throughout the sample, thus corroborating with aforementioned electrochemical and physicochemical characterisation,” the researchers wrote.
SEM images of a typical graphene 3DA pre‐ and post‐NaOH chemical treatment displaying their respective charge‐discharge profiles. The setup used to test the anodes is simpler over traditional coin cells as no copper current collector is required.
Finally, the team evaluated the energy capabilities of the 3DAs in a Li-ion battery setup, and found that that the graphene 3DAs have a relatively low electrochemical response. To further understand, they analyzed the graphene 3DA’s topography, which showed that its surface doesn’t have good porosity for wetting electrolytes. By introducing a simple chemical pre‐treatment of NaOH to the 3DAs for 24 hours, the researchers were able to induce porosity and get past this limitation.
To further understand, they used X-ray diffraction to analyze the crystalline structure of the graphene/PLA both before and after this pre-treatment, explaining that the SEM images and XRD patterns show that the material didn’t lose its 3D structure, “but now offers an excellent electrochemical behaviour/performance.”
“…we suggest that the graphene incorporated within the 3DA, is predominantly graphene‐like in its electrochemical behaviour, and that the increased surface area of the graphene nanoplatelets within the composite provide the improved energy outputs,” the researchers stated. “The results presented herein enhances the field of additive manufacturing/3D printed graphene‐based energy storage devices with the utilisation of a tailorable graphene/PLA filament, and with a simple chemical treatment of the 3D printed anode can exhibit a 200‐fold increase within the specific capacity (after anode stabilisation).”
The team determined that the 3D printed freestanding anodes with a 20 wt. % graphene content had the most effective 3D printability and conductivity.
“The results presented herein significantly enhance the field of additive manufacturing/3D printed graphene based energy storage devices demonstrating that useful 3D printable batteries can be realised,” the paper concluded.
Co-authors are Dr. Christopher W. Foster, Dr. Guo‐Qiang Zou, Yunling Jiang, Dr. Michael P. Down, Dr. Christopher M. Liauw, Alejandro Garcia‐Miranda Ferrari, Prof. Xiaobo Ji, Prof. Graham C. Smith, Prof. Peter J. Kelly, and Prof. Craig E. Banks.
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