Against the backdrop of rapid iteration in new energy technologies, thin-film lithium-ion batteries have been widely applied in flexible electronics, wearable devices, micro-sensors, and other fields due to their advantages of small size, light weight, high energy density, and long cycle life. Innovation in fabrication processes is the key to achieving performance breakthroughs and cost reduction for thin-film lithium-ion batteries. As a non-contact, digital precision manufacturing technology, inkjet printing—by virtue of its unique advantages—is gradually becoming a research hotspot in the field of thin-film lithium-ion battery fabrication.
I. Compatibility Between Inkjet Printing Technology and Thin-Film Lithium-Ion Batteries
The core structure of thin-film lithium-ion batteries includes the cathode, anode, electrolyte, and current collector. The thickness of each layer typically ranges from nanometers to micrometers, and extremely high requirements are placed on structural uniformity and interfacial compatibility. Inkjet printing technology precisely deposits functional inks onto substrate surfaces in the form of micro-droplets, forming the required functional layers through post-processing steps such as drying and sintering. Its compatibility is mainly reflected in the following three aspects:
1. High Precision and Controllability
The droplet volume in inkjet printing can be precisely controlled at the picoliter to nanoliter level, enabling fine fabrication of electrode patterns with minimum line widths below 10 micrometers. This meets the design requirements for miniaturization and integration of thin-film lithium-ion batteries, especially for the fabrication of micro-battery arrays connected in series/parallel.
2. High Material Utilization
Traditional fabrication processes (such as blade coating and vapor deposition) suffer from severe material waste. In contrast, inkjet printing deposits ink only in designated areas, achieving material utilization rates above 95%. This significantly reduces the consumption of costly materials such as lithium sources and active electrode materials, effectively controlling production costs.
3. Strong Flexibility and Compatibility
Inkjet printing is non-contact and can fabricate structures on various substrates, including flexible polymers (such as PET and PI) and metal foils. It is compatible with different types of functional inks, including water-based, solvent-based, and sol–gel systems, making it possible to develop flexible thin-film lithium-ion batteries and composite-structure electrodes.
II. Specific Applications of Inkjet Printing in Thin-Film Lithium-Ion Battery Fabrication
(I) Electrode Fabrication: Achieving Uniform Distribution and Structural Optimization of Active Materials
Electrodes are the core components determining the energy density and rate performance of thin-film lithium-ion batteries. By adjusting ink formulations and printing parameters, inkjet printing enables precise control of electrode microstructures:
• Cathode Fabrication
Common cathode active materials (such as LiCoO₂ and LiFePO₄) are dispersed in solvents along with conductive agents (e.g., carbon black) and binders (e.g., PVDF) to form inks. Inkjet printing can produce uniform cathode films on current collectors (e.g., aluminum foil), with thickness controlled by the number of printing passes (typically 1–10 micrometers). Compared with traditional blade coating, printed cathode films exhibit more uniform porosity, facilitating lithium-ion transport and improving rate capability and cycling stability.
• Anode Fabrication
Key challenges in inkjet printing anode materials (such as graphite and silicon-based materials) include dispersion stability and film conductivity. By optimizing dispersants (e.g., polyvinylpyrrolidone) and designing conductive networks, highly dispersed and conductive anode films can be fabricated. For example, silicon-based anodes suffer from significant volume expansion, leading to film cracking. Inkjet printing can construct porous silicon/carbon composite structures to mitigate volume expansion and enhance cycle life.
(II) Electrolyte Fabrication: Overcoming Interface Limitations of Traditional Electrolytes
As the medium for lithium-ion transport, electrolyte ionic conductivity and interfacial stability directly affect battery performance. Inkjet printing can fabricate liquid, gel, and solid electrolytes, with unique advantages particularly in solid electrolyte preparation:
• Liquid/Gel Electrolytes
Lithium salts (e.g., LiPF₆) dissolved in organic solvents (e.g., ethylene carbonate/dimethyl carbonate mixtures) or gel matrices form electrolyte inks. Inkjet printing enables uniform deposition of electrolyte films on electrode surfaces, avoiding uneven distribution common in traditional drop-casting methods and reducing interfacial resistance.
• Solid Electrolytes
Solid electrolytes (e.g., oxide Li₇La₃Zr₂O₁₂ and sulfide Li₇P₃S₁₁), which eliminate leakage risks and offer high safety, are a key development direction for next-generation thin-film lithium-ion batteries. However, poor interfacial contact between solid electrolytes and electrodes has been a bottleneck. Inkjet printing can precisely deposit inks composed of solid electrolyte nanoparticles and binders onto electrode surfaces, forming thin and uniform electrolyte films. By optimizing parameters such as droplet impact velocity and drying temperature, interfacial contact can be improved, achieving ionic conductivities of 10⁻⁴–10⁻³ S/cm.
(III) Full Battery Integration: Precise Matching of Multilayer Structures
The digital nature of inkjet printing allows integrated fabrication of all functional layers in thin-film lithium-ion batteries. By sequentially printing the anode, electrolyte, cathode, and current collector within the same equipment, precise alignment and thickness matching can be achieved, reducing interfacial defects. For example, on flexible PI substrates, a full battery structure of “current collector–anode–electrolyte–cathode–current collector” can be fabricated via inkjet printing. The battery thickness can be controlled below 50 micrometers, with a bending radius as small as 5 millimeters, meeting the application requirements of flexible electronic devices.
III. Advantages and Existing Challenges of Inkjet Printing Technology
(I) Core Advantages Compared with Traditional Processes
1. High Process Flexibility
Traditional methods rely on molds or masks for patterning; switching product types requires new molds, resulting in high costs and long cycles. Inkjet printing uses digital control, allowing rapid product specification changes simply by modifying the print file, making it suitable for small-batch, multi-variety production.
2. Low-Temperature Processing
Some flexible substrates (e.g., PET) have limited heat resistance (typically below 150°C). Traditional high-temperature sintering may cause deformation. Inkjet-printed inks can form films via low-temperature drying (60–120°C) or UV curing, avoiding thermal damage and expanding substrate options.
3. High Integration Potential
Inkjet printing can be combined with microfabrication technologies (e.g., photolithography and laser cutting) to integrate thin-film lithium-ion batteries with microelectronic devices (e.g., sensors and chips). For example, micro thin-film batteries can be directly printed on smartwatch circuit boards, reducing the size and weight of external batteries.
(II) Major Current Challenges
1. Complexity of Ink Formulation Design
Inkjet printing imposes strict requirements on ink properties (viscosity typically 5–20 mPa·s; surface tension 25–40 mN/m). Nanoparticles of active materials (e.g., LiFePO₄) tend to agglomerate, clogging nozzles. Meanwhile, binders may affect electrode conductivity and electrolyte ion transport. Balancing ink stability and battery performance remains a core challenge.
2. Balancing Printing Precision and Efficiency
To improve battery performance, thin and uniform functional layers are required, demanding highly uniform droplets and precise deposition. However, smaller droplets reduce printing efficiency (e.g., tens of thousands of droplets may be needed to fabricate a 1 cm² cathode film). Achieving both high precision and industrial-scale productivity is a key bottleneck.
3. Optimization of Post-Processing
Printed films require post-processing such as drying, sintering, and annealing to remove solvents and improve crystallinity and film density. Processing parameters (temperature and time) directly affect battery performance. Excessively high sintering temperatures may decompose active materials, while insufficient temperatures may result in poor conductivity. Therefore, post-processing conditions must be optimized for different material systems.