In order to achieve efficient energy storage devices, 3D printing is being widely used in the electrochemical field. Recently, the new results of the cooperation between the Northwestern Polytechnical University team and the Additive Manufacturing Laboratory of the National University of Singapore have inspired the industry.

The joint team used digital light processing (DLP) and chemical vapor deposition (CVD) two modern industrial technologies to develop a unique 3D hollow graphite foam (HGF), which has a periodic porous structure and good mechanical properties, and succeeded The high mechanical strength and ultra-high active material loading capacity of the electrode are realized. The result paper was published on "Research".

"This achievement not only provides a new method for preparing electrode materials with excellent mechanical strength and electrochemical properties, but also provides a new path for the large-scale application of advanced energy storage equipment." Corresponding author of the paper, Chinese Academy of Sciences Huang Wei, an academician and chief scientist of the Flexible Electronics Frontier Science Center of Northwestern Polytechnical University, told the China Science Daily.

Sudden emergence

With the rapid development of society, people's demand for energy continues to increase, hoping to find a renewable green energy. 3D printing can achieve rapid prototyping and relatively low cost, so it has attracted wide attention. In the past few years, there has been a lot of research using 3D printing to create electrodes/devices for electrochemical energy conversion and storage. Experts have made considerable progress in this field, but there are still many challenges and shortcomings that need to be resolved. Since 2018, the Northwestern Polytechnical University team has been committed to developing new 3D printed electrodes with higher precision and unique structural design.

"Since its establishment, the team has been struggling to achieve the customization and industrialization of high-performance electrodes through 3D printing technology. By choosing different printing technologies, structural designs and printing materials to achieve diversified customization of electrode materials." According to Guan Cao, the corresponding author of the paper and a professor at the Institute of Flexible Electronics of Northwestern Polytechnical University.

At present, because 3D printing electrodes can provide a higher active material loading capacity to achieve higher energy density and power density, 3D printing technology in the field of energy storage including metal ion batteries, metal air batteries and supercapacitors is gradually becoming hot .

3D printing technology includes fused deposition modeling (FDM), ink jet printing (Ink jetting), selective laser melting (SLM) and stereolithography (SLA), etc.

Electrode is a component that inputs or draws current in a conductive medium. For many years, scientists have continuously adjusted its composition and the chemical reaction it produces in order to pursue better battery performance. The commonly used electrode materials include metals, metal oxides, metal carbides, metal sulfides, carbon-based materials, conductive polymers, metal organic framework materials (MOFs) and their composite materials.

Among them, carbon-based materials, such as graphene and carbon nanotubes (CNTs), are one of the most commonly used electrode materials for flexible transparent conductive electrodes (FTCEs), with excellent electrical, optical and mechanical properties. High-quality graphene is widely used in the preparation of FTCEs due to its good electrical conductivity, strong mechanical flexibility, high optical transparency, and good chemical stability.

However, Professor Ding Jun, one of the authors of this article and the team leader of the National University of Singapore, said that the current exploration of the practical application of 3D printing technology still has certain limitations.

Mechanical stability overwhelms everything

At present, there are two main methods for preparing thin-film electrodes by 3D printing technology: extrusion and inkjet. Although the working principles of the two methods are relatively similar, the properties of the ink used are quite different. Due to the increasing demand for the construction of three-dimensional electrodes, the preparation of 3D printing graphene/graphite electrode materials mostly adopts the direct writing ink printing method (extrusion type).

Because the resolution of this technology is low and usually greater than 200μm, it can only realize some simple 3D structures such as grids and interdigital structures, which limits its application. In addition, for packaging and transportation, the mechanical properties of this 3D carbon material are also indispensable, but previous studies have paid little attention.

What kind of electrode is more promising and can bring excellent mechanical and electrochemical properties?

"The development of a new type of 3D printed electrode with higher precision and unique structural design will be very promising." Guan Cao said. With the help of DLP and CVD, the team designed a lightweight HGF with a simple structure and good porosity. "Finite element calculations and compression tests have proved that the porous HGF with porous structure of the rotating body can effectively prevent structural failure caused by stress concentration, thereby maintaining the stability of the machine." Guan Cao said, the stability of the machine is overwhelming.

The graphite foam is further coated with MnO2 nanosheets, which can be directly used as electrode materials for supercapacitors without the need for additional binders and current collectors. Benefiting from its unique hollow porous structure, it not only can achieve high-quality loads of active materials, but also has a significant high area and volume capacitance.

The results of finite element analysis confirmed that the pre-designed spiral porous structure can provide a uniform stress area and reduce the potential structural failure trend caused by stress concentration. The experimental results show that the prepared graphite foam can achieve high mechanical strength at a lower material density. When the graphite foam surface is covered with ultra-high loading of MnO2, MnO2/HGF can simultaneously achieve high area, volume and mass specific capacity.

In addition, the assembled quasi-solid asymmetric supercapacitors also show excellent mechanical and electrochemical properties. This strategy of three-dimensional porous and strong materials with good mechanical and electrochemical properties will pave the way for the practical application of advanced energy storage devices.

Future and expectations

Talking about future scientific research plans, Huang Wei said, “In the future, we will continue to explore the subject of research and development of multifunctional electrode 3D printing technology, development of suitable 3D printing material systems, and realization of one-step printing of energy storage devices.”

"Discussing the most suitable printing process parameters and structural parameters, promoting the development of energy storage device technology and industry, and realizing the industrialization and industrialization of new energy storage devices is our ultimate goal." Huang Wei further introduced that in electrode material manufacturing At the same time, the development of energy storage devices with high specific capacity and high specific power is increasingly demanding. At the same time, low-cost, simple manufacturing procedures can also help 3D printed battery manufacturers to gain a place in the market. "

There is no doubt that industry-related, rugged metal electrodes are still the material of choice for most prototype devices. Compared with traditional methods, some 3D printed prototype devices show comparable or better performance, from unique electrode structures (for example, surface porosity and roughness) to electrochemical cell designs related to printing capabilities.

However, the differences between different types of 3D printed electrodes and devices with different printing technologies have not been systematically studied, and there is still a large gap in knowledge in this area. Similarly, the current comparative data on traditional systems and industrial systems is also very limited.

Officials believe that with my country’s "Made in China 2025" development strategy, manufacturing technology will face a huge historical opportunity for upgrading and upgrading. 3D printing technology is an effective supplement to traditional processing technology, and is an epoch-making strategic technology. At present, the achievements of 3D printing technology in the field of energy storage have begun to take shape, and a variety of printing technologies and materials are continuously used in 3D printing technology, which will bring opportunities for the development of 3D printing technology in the field of energy storage. "It is believed that with the continuous development of printing technology and materials, 3D printed batteries with good durability, excellent safety, and higher energy density and power density will eventually be widely used in more fields in the future." Fuck said.

Link to this article： 3D printing preparation of graphite foam

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