Journal Club for December 2020: 3D Printing of Batteries: Fabrication, Materials and Challenges

3D Printing of Batteries: Fabrication, Materials and Challenges 

Yaokun Pang, Changyong Cao*

Laboratory for Soft Machines & Electronics, Michigan State University

 

1. Introduction

Given the rapid development and extensive use of mobile electronics, there is an increasing demand for reliable and cost-effective energy storage devices to build power-independent electronics system [1, 2]. Batteries, the most widely used electrical energy devices, have attracted significant attention and have been extensively studied due to their ability to stably store and supply electrical energy as well as their availability in a wide range of forms, capacities, and power densities [3-5]. Over the years, much effort has been put into exploring new electrode materials, electrolytes, cell structures, and novel fabrication approaches to improve the electrochemical performance of batteries, to reduce the cost, and to expand their application. 

3D printing provides a unique opportunity in the rapid prototyping of complex structures and devices with high control accuracy [6]. Compared with conventional fabrication methods, 3D printing has several significant advantages: 1) enabling the fabrication of desired complex architectures; 2) precise controlling of the shape and thickness of the electrodes; 3) printing solid-state electrolyte with high structure stability and safer operation; 4) potential for low cost, environmental friendliness, and ease of operation; and 5) possibility to eliminate the steps of device assembly and packaging via direct integration of batteries and other electronics [7]. Thus, a large amount of research has been dedicated to this field [7, 9], including manufacturing energy devices such as batteries and supercapacitors for specific applications in laboratories [6-8]. 

We recently reviewed the significant advances in 3D printing of batteries (Fig. 1) [10], summarizing the latest progress in 3D printing methods, the printed materials for battery electrodes and electrolytes, as well as the challenges and potential opportunities for future study. With the continuous development of printing techniques and materials, 3D printed batteries with long-term durability, favorable safety, high energy, and power density will be fabricated in a large scale at low costs, enabling their wide applications.  

Fig. 1: Major printing technologies, printed electrode materials, and electrolyte materials for 3D printed batteries. 

2.  Major Printing Methods for 3D Printed Batteries

As an innovative manufacturing approach, 3D printing technologies are able to facilitate the fabrication of batteries, enable versatile and miniature batteries ranging from microscale to macroscale, and improve the electrochemical performance of batteries [11]. However, considering the compatibility among the preparation conditions, materials, and processes, not all of the 3D printing technologies and current materials used in conventional batteries are appropriate for manufacturing printed batteries. The major 3D printing technologies (Fig. 1) used for fabricating batteries include lithography-based 3D printing, template assisted electrodeposition-based 3D printing (TAE), inkjet printing (IJP), direct ink writing (DIW), fused deposition modeling (FDM), and aerosol jet printing (AJP). 

2.1 Lithography-based Printing

Holographic lithography (HL) is based on the multi-beam interference phenomenon without using complex photomasks or optical systems [12, 13]. It is a simple and low-cost technique to fabricate 1D, 2D, and 3D periodic geometries via a single laser exposure. Ning and co-workers used the combination of HL and conventional photolithography to fabricate high-performance Li-ion batteries (Fig. 2a-d) [14]. Projection microstereolithography (PµSL) has been developed to fabricate high resolution 3D polymer structures and devices [15, 16]. For example, Chen et al. utilized the PµSL technology to directly print a 3D microbattery (Fig. 2e-f) [17]. Despite the many advantages of PµSL, the 3D microbattery manufactured via this method exhibited poor cycle performance and low capacity, which should be improved in the future. Stereolithography (SLA) is another promising 3D printing technique that is suitable for manufacturing porous 3D battery electrodes due to its high spatial resolution [18]. In the SLA system, the photosensitized monomer resin or photosensitized monomer solution (mainly acrylic or epoxy-based) is selectively converted into a solidified polymer via the application of visible light and ultraviolet light (UV). Recently, Cohen et al. employed SLA to prepare perforated spherical, cylindrical and cubic polymer substrates with high surface area (Fig. 2g) [19]. 

Fig. 2: Lithography-based printing of 3d printed batteries. (a) Schematic illustration of the printing fabrication process for a 3D microbattery. (b) SEM image of the cross-section of a fabricated AZ9260 structure. (c) SEM image of the cross-section of a nickel scaffold. Inset: Optical image (Right) and microscopic image (Left) of the interdigitated nickel current collector. (d) SEM image of the 3D microbattery [14]. (e) Schematic of the 3D structure for GPE. (f) SEM image of PEG membrane with self-assembled sub-micron scale channels [17].  (g) Optical images of 3D printed perforated spherical, cylindrical and cubic substrates [19].  

2.2 Template Assisted Electrodeposition

The template-assisted electrodeposition (TAE) technique exists as the most typical approach in the synthesis of macroporous materials with tunable pore sizes and structures [20]. It is low-cost, versatile and convenient to control the shape and size of the structure by changing the electrodeposition parameters and choosing templates with different characteristics. The Braun group fabricated high performance batteries using a TAE technique [21]. They designed a self-assembled 3D bicontinuous bulk cathode, which consisted of conductive pathways for ion and electron transport by sandwiching an electrolytically active material (Fig. 3a-e). Following this pioneering work, they further reported a high-power Li-ion microbattery made of interdigitated 3D bicontinuous nanoporous electrodes (Fig. 3f-h) [22]. TAE is one of the few 3D printing techniques that can fabricate nanostructured electrodes. It has been proven to be an attractive method to fabricate microbatteries with supercapacitor-like charge/discharge rate while retaining comparable battery-like storage capacity. However, large scale production is yet to be verified and the mechanical properties of the printed battery electrodes are poor due to their high porosity. 

Fig. 3: Template assisted electrodeposition of printed batteries. (a) Schematic of a battery structure with a bicontinuous cathode. (b) Schematic illustration of four primary resistances in a battery electrode. (c) Schematic illustration of the fabrication process for bicontinuous electrode. (d) SEM and schematic images (inset) of the lithiated MnO2/nickel composite cathode. (e) The charging/discharge curves of a prototype lithium-ion battery [21]. (f) Schematic of a microbattery design. (g) SEM image of the interdigitated electrodes. Inset: NiSn anode (left) and LiMnO2 cathode (right). (h) A top-view SEM image of the interdigitated electrodes [22].

2.3 Inkjet Printing

Inkjet printing (IJP) is a representative droplet-based deposition technique that can directly deposit materials through nozzles onto plastic, paper or other substrates to create complex patterns with high resolution and tunable thickness in accordance to the number of droplets discharged [23, 24]. The ink for IJP usually has specific requirements in surface tension, density, and dynamic viscosity. IJP has been used to fabricate electrochemical storage devices [25, 26]. For example, Lawes and co-workers fabricated thin film silicon anodes for Li-ion batteries via a desktop inkjet printer (Fig. 4a) [27]. Significant progress has also been made to improve the specific surface area of printed electrodes (Fig. 4b-d) [28]. Recently, Hu et.al studied 3D inkjet printing of Li-ion batteries based on LiMn 0.21 Fe0.79 PO4 @C (LMFP) nanocrystal cathodes  (Fig. 4e-f) [29]. IJP has good multi-material capability, high material utilization, and exceptional resolution in printing various designed patterns, beneficial to improving the performance of batteries. The major limitations of IJP are its relatively low printing speed and high requirements for the formulation of inks. Moreover, the printing head is less durable and prone to clogging and damage.

Fig. 4: Inkjet printing of microbatteries. (a) Fabrication process for SiNP anodes on a copper foil [27]. (b) Schematic of the 3D “drop-on-demand” ink jet printer. (c) Schematic illustration of ice template formation. (d) SEM image of MoS2-rGO printed on Ni foam [28]. (e) Schematic illustration of a battery with 3D printed electrodes. (f) Cycling performance of 3D-printed and traditional electrodes at 10 C and 20 C rates for 1000 cycles [29]. 

2.4 Direct Ink Writing

Direct ink writing (DIW) has been the most widely used 3D printing method to fabricate batteries due to its advantages of affordable prices, easy operation, material diversity, and maskless process [30-32]. This method is based on the extrusion of ink materials at room temperature and its resolution is determined by the nozzle diameter [33]. In the recent work by Lewis group, printed Li-ion batteries with thick electrodes were fabricated using the DIW technique [30]. All components in the battery, including the packaging, anode, separator, and cathode, were printed by the DIW method (Fig. 5a-c). Zhang et al. employed DIW to print 3D electrodes with SnO2 quantum dot inks (Fig. 5d-f) [34]. Lyu et al. employed DIW to fabricate a novel MOF-derived hierarchically porous framework for Li-O2 batteries [35]. The printed hierarchically porous network was composed of the micrometer-scale pores generated among Co-MOF-derived carbon flakes and the meso- and micropores within the flakes [35]. The novel structure allowed the deposition of Li2O2 particles inside the framework and promoted the decomposition of these insulating Li2O2 particles to improve the electrochemical performance of a Li-O2 battery (Fig. 5g-h). DIW has high requirements for the gel-based viscoelastic inks, requiring sufficiently high yield stress and storage modulus. Moreover, the poor mechanical strength between the layers is a burning problem to be solved. Thus, great effort needs to be taken to improve the application of the DIW technique in battery manufacturing. 

Fig. 5: Direct ink writing of microbatteries. (a) Optical (left) and schematic (right) images for printing the four kinds of functional inks. (b) Apparent viscosity behavior of these four functional inks. (c) Areal energy density as a function of areal power density for the batteries with different electrode thicknesses [30]. (d) Optical image of the different patterns printed with the SnO2 QDs/GO ink. (e) SEM image of the 3DP-SnO2 QDs/G porous structure. (f) Cycling stability of 3DP-SnO2 QDs/G, SnO2 QDs/G and SnO2 QDs architectures [34]. (g) Schematic illustration of a novel designed cathode. (h) Specific power as a function of specific energy of conventional supercapacitors, Li-ion, Li–S batteries and the fabricated 3D printed Li-O2 battery [35]. 

2.5 Fused Deposition Modeling

Fused deposition modeling (FDM) is one of the most widely used 3D printing technologies to manufacture complex objects with almost no material waste. The main advantages of FDM are its user friendliness, affordable prices, high speed, large size capabilities, and avoidance of chemical post-processing. Wei et al. used this method to print graphene composite structures for the first time  (Fig. 6a-b) [36]. Maurel et al. reported a 3D-printable graphite/polylactic acid (PLA) filament, which can be used to print negative electrodes for Li-ion batteries through a FDM 3D printer (Fig. 6c-e) [37]. The integration of different 3D printed electronics with various shapes and volumes together with conventional batteries is a challenging task and has limited the development of new power-independent electronic systems. This approach is able to facilitate the creation of such kinds of systems. For example, Reyes and co-workers developed a fully printed and customized Li-ion battery with a FDM 3D printer to accommodate a given product design (Fig. 6f-h) [38]. 

Fig. 6: Fused deposition modeling (FDM) manufacturing of Li-ion batteries. (a) Schematic illustration for the printing process of FDM. (b) 3D objects printed via FDM [36]. (c) Optical image and (d) SEM image of a homogeneous filament with 40% PEGDME500. (e) Optical image of a high-resolution complex “3DBenchy” boat [37]. (f) Decomposed assembly of a 3D printed coin cell. (g) 3D printed glasses with an electronic darkening LCD lens and 3D printed batteries integrated into the side temples. (h) 3D printed bangle battery lighting up a LED [38]. 

2.6 Aerosol Jet Printing

Aerosol jet printing (AJP) is an emerging contactless direct write approach. In this process, the functional ink is aerosolized into small droplets of 1–5 µm in diameter and then delivered to the substrate by a carrier gas and focused by an annular sheath gas flow [39]. A wide range of functional materials such as dielectrics, conductors, semi-conductors and encapsulation materials can be printed with AJP technology [40-43]. Due to its features of non-contact, no mask required and high resolution, AJP has been extensively used for printing 2D electronics circuits and electronics [44, 45], and for 3D electronics on the surface of three dimensional objects with an advanced Aerosol Jet 5X model. However, there is no study in manufacturing batteries with this technology until recent work reported by Saleh and co-workers [46]. 

3. Electrode Materials for 3D Printed Batteries

3.1 Carbon materials-based electrodes

Graphene oxide (GO) has demonstrated superior ink-formation ability, unique viscoelastic properties and functional properties that are suitable for 3D printing. With a thermal annealing process, GO can be easily reduced to conductive graphene (i.e., reduced graphene oxide, rGO), which possesses good electrical conductivity and can serve as a promising material for battery electrodes. A majority of 3D printed structures have been developed based on graphene oxide [47], including aerogel microlattices [48], nanowires [49], periodic scaffolds [50], and complex networks [51] (Fig. 7a-c). Kim et al. reported a printed highly conductive CNT microarchitecture (Fig. 7d-f) [52]. Milroy and Manthiram developed a MWCNT-based microelectrode for a Li–S battery via a dispenser printing technique (Fig. 7g) [53]. The MWCNT electrodes had the advantages of high conductivity and ultrahigh porosity, which benefits the electronic and ionic transport and electrolyte permeation inside a battery. 

Fig. 7: Carbon materials-based electrodes for 3D printed batteries. (a) Digital image for the printing process of a multilayered electrode. (b) SEM image of a cross-section of printed electrodes. (c) Digital image of a 3D-printed small electrode array [47]. (d) Schematic illustration and SEM image of the 3D-printing process for carbon nanotube ink. (e) SEM image of a concatenated MWNT bridge-line structure printed on curved glass substrate. (f) SEM and higher magnification (bottom) images of the 3D elliptical hollow architectures [52]. (g) SEM image of the pristine aligned MWNTs and the optical images of the printed electrode as well as glass reservoir filtration assembly [53]. 

3.2 Cellulose nanofiber-based electrodes 

Cellulose nanofibers (CNF) possesses high solubility in water owing to the rich presence of hydroxyl groups on the cellulose molecules [54]. The negative zeta potential of the CNF is as high as 60 mV, enabling CNF to be utilized as a surfactant to enhance the dispersibility of other materials in aqueous solution [55]. Following a oxidation treatment procedure, the carbonized CNFs mixed with LFP and Li metal can be used to print 3D interdigitated cathode and anode, respectively (Fig. 8a-c) [56]. All the ink containing CNF exhibited high viscosity and adhered on the bottom of the inverted vial. Kohlmeyer et al. applied CNF as a conductive additive, charge collector, and porous scaffold in 3D printed lithium-ion batteries (Fig. 8d-f) [57]. 

Fig. 8: Cellulose nanofiber-based electrodes for 3D printed batteries. (a) Schematic illustrations of the fabrication of CNF ink and a printed 3D lithium microbattery. (b) Digital images of different ink with various viscosity. (c) Layer-by-layer printing of a CNF/LFP electrode [56]. (d) Schematic illustration of a flexible composite ink. (e) Schematic illustration of the fabrication process of a printed electrode. (f) Digital image of a printed flexible pattern on a transparency paper [57]. 

3.3 Li4Ti5O12/LiFePO4 based electrodes

Li4Ti5O12 (LTO) and LiFePO4 (LFP) are the most commonly used anode and cathode materials in 3D printed batteries, exhibiting a minimal volumetric expansion, high rate capability, high stability, and high security. A large number of studies on the 3D printing of LTO/LFP-based electrodes have been reported [32, 58]. For example, Lewis and coworkers printed 3D interdigitated microbattery architectures (3D-IMA) with LTO/LFP materials [31]. The composition and rheology of inks were the most important factors in fabricating 3D-IMA, i.e., ensuring a reliable flow through printing nozzles and providing structural integrity. However, the packaged battery had lower long-term cyclability owing to the poor hermeticity of the device, which suggested that more effective packaging are required for broad applications of such 3D printed batteries. 

4. Electrolyte Materials for 3D Printed Batteries

The electrolyte is one of the most important components for Li-ion batteries, which plays an extraordinary, even determining role in electrochemical performance, cycle life, and safety of the battery. Recently, increasing attention has focused upon the fabrication of high-performance electrolytes with the merits of high ionic conductivity, low electronic conductivity, and low activation energy [59]. With the advances of 3D printing technologies, the electrolyte of the batteries can also be directly printed to simplify the fabrication procedures, reducing fabrication time, and manufacturing costs [60]. 

To date, inorganic electrolytes have been extensively studied. However, their poor chemical/electrochemical stability and low mechanical flexibility hinder their practical applications in printed batteries. To resolve this issue, Kim and co-workers designed a novel all-solid-state Li-ion battery with gel composite electrolytes (GCE) via printing (Fig. 9a-c) [61]. Compared with traditional carbonate-based electrolytes, the GCE exhibited a great flame retardance, indicating its potential as an electrolyte to improve battery safety. 

A well-controlled porosity is essential for battery membranes to obtain high rate capability, long-term cyclability, and dendrite suppression [62]. However, it is challenging to fabricate a high-performance membrane with controlled pore size using the traditional methods. Recently, Blake et al. developed a new method to 3D print high-performance and flexible ceramic-polymer electrolytes (CPEs) (Fig. 9d-f) [63]. Differently, Cheng et al. developed a novel method to manufacture hybrid solid-state electrolytes without any post-treatment procedure [64], in which solid poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) matrices were employed to improve Li-ion diffusion and to provide mechanical support while Li-ionic liquid was selected as ionic electrolyte (Fig. 9g-i) [64]. Other materials like garnet-type Li7La3Zr2O12 (LLZO) are also used as electrolyte for solid-state lithium batteries due to its nonflammability and high electrochemical stability with lithium metal [65]. The 3D-printing of solid electrolytes makes the fabrication of uniquely structured electrodes and electrolytes possible, whereas traditional die-pressing and tape-casting methods are limited to random porosities and planar geometries. 

Fig. 9: Electrolyte materials for 3D printed batteries. (a) Optical image of a fabricated GCE sample. (b) Optical image showing the mechanical flexibility of the printed GCE upon the bending cycles. (c) The nonflammability behavior of the GCE (top) and the carbonate-based control electrolyte (bottom) [61]. (d) SEM image and schematic illustration of the polymer electrolyte. (e) Wettability testing for the electrolyte CPE–PI and Celgard 2325. (f) Shrinkage of CPE–PI and Celgard 2325 as a function of temperature [63]. (g) Schematic image of a hybrid solid-state electrolyte ink. (h) SEM image of the dense layer between the MnO2 electrode and the porous layer. (i) Digital image of a full battery cell printed on a 3D Hilbert curved structure [64]. 

5. Challenges and Prospect 

Although much progress has been made in manufacturing 3D printed batteries, there are still numerous challenges that must be addressed before they can be widely used:

1) There are only a few printable materials, especially active materials, that can be used as inks for 3D printing batteries. To obtain highest electrochemical performance, it is needed to develop new electrochemically active materials. The 3D printing inks should have appropriate surface tension, density, and dynamic viscosity. In addition, the inks generally contain other additives to tune the rheological properties of the active electrode materials, there is a need to reduce the influence of additive components on the physical properties of active materials and the performance of printed batteries. 

2) 3D printed electrodes are expected to have a larger specific surface area than those electrodes fabricated with traditional methods due to the  porous structures introduced in the fabrication process. These porous structures increase the power and energy density of the battery at a cost of mechanical strength. Furthermore, the 3D printed structures are produced layer by layer, leading to weakly bonded interfaces between layers. Thus, further research to improve the mechanical properties of 3D printed batteries should be done, especially for robustness requirements in certain applications such as flexible and wearable electronics.

3) Although highly ordered pores can be printed by most 3D printing techniques, their sizes are usually at the micrometer scale. Orderly distributed hierarchical pore systems at both micro and nano scales are particularly important for improving energy storage capacity and rate ability. Additionally, the high temperature post-processing is required for 3D printed batteries, which is time-consuming and inconvenient and may also weaken electrochemical performance of the battery. Current 3D printing also suffers from low efficiency and is challenging to be utilized for low-cost and large-scale manufacturing needed in commercial applications. To solve these issues, more advanced 3D printing techniques or a combined technique with higher resolution, higher efficiency and non-post-processing should be developed.

4) Water vapor and oxygen in the air have significant effects on the performance of active electrode and electrolyte materials. The chemical reactions triggered upon contact will dramatically reduce the performance and service life and may cause possible safety issues of batteries. Effective encapsulation for 3D printed Li-ion batteries is essential to protect them from damage by oxygen/water molecules and other chemicals. Thus, new techniques and materials for printed packaging or encapsulation are also worthy of being developed in the future.

5) Most of the current research regarding 3D printed batteries focuses on the materials of the electrodes and electrolytes. However, for fully 3D printed batteries, the compatibility of the inks for each component to be printed sequentially and successfully remains a big challenge. Additionally, 3D printing may be expected to offer great chances for efficiently integrating printed batteries and electronic devices thanks to its ability of printing arbitrary shapes and sizes. 

It is expected that with the continuous development of printing techniques and materials, 3D printed batteries with long-term durability, favorable safety, high energy, and power density will be facricated in a large scale at low costs, enabling their wide applications. 

 

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