Abstract As demand for customized wearable electronics grows, free‐form Li‐ion batteries (LIBs) are attracting significant attention. Although substantial advancements have been made in printed LIBs for shape‐versatile electronics, the development of printable solid‐state electrolytes remains challenging due to the difficulty of simultaneously achieving desirable rheological properties and ionic conductivity. In this study, a solvent‐free, non‐flammable solid polymer electrolyte (SPE) is designed as a novel three‐dimensional (3D) printable electrolyte via direct ink writing (DIW) for all‐solid‐state batteries (ASSBs). The solvent‐free nature of this SPE eliminates post‐annealing steps, enhancing safety by mitigating risks of leakage, short‐circuiting, and fire. Additionally, precise control over polymer molecular weight and electrolyte composition enables high printing resolution (~100 μm), high ionic conductivity (0.705 mS cm −1 at 25°C), and intrinsic non‐flammability. A 3D‐printed ASSB, featuring a LiFePO 4 cathode and Li 4 Ti 5 O 12 anode with a mass loading of 7 mg cm −2 , achieves a high areal capacity of 1.14 mAh cm −2 , surpassing all previously reported directly printed ASSBs. This SPE facilitates scalable production of fully DIW‐printed ASSBs with superior design flexibility and space efficiency, enabling printing onto customized targets such as flexible substrates and advancing the development of next‐generation wearable electronics. image

Soft electronic components are essential building blocks for realizing form-factor-free applications; however, most designs are confined to 2D or 2.5D structures due to challenges in maintaining 3D structural integrity. This limitation is particularly critical for electromagnetic devices, such as resonators, where dielectric losses from elastomeric substrates severely hinder high-performance functionality. Here, directly printed 3D electromagnetic soft plasmonic enhanced-quality(Q) factor resonators are proposed, using highly conductive composites. By incorporating an immiscible solvent into an elastomer matrix, emulsion phases are formed that significantly enhance the storage modulus, enabling the fabrication of 3D-printed structures while improving their electrical conductivity. 3D microwave plasmonic resonators with a high degree of design freedom, such as pillars and hooks are demonstrated. These structures exhibit improved resistance to dielectric interference by leveraging the resonance in lossless air. Moreover, integrating a coplanar ground plane further decouples the resonators from lossy substrates, resulting in a 3.4-fold enhancement in the Q-factor (octupole mode) compared to 2D resonators. This improvement enables stable operation on high-permittivity surfaces, such as human skin. Additionally, a single 3D resonator demonstrates wireless deformation-sensing capabilities, facilitating the simultaneous detection of strain amplitude and orientation. This result can pave the way for advanced sensing applications in soft electronics.

Abstract Compliant thermoelectric generators (TEGs) can fully exploit their energy conversion efficiency by establishing conformal interfaces on arbitrarily shaped 3D heat sources. Although additive manufacturing processes allow scalable fabrication with flexibility and customizability, most printable TEGs are fabricated as planar‐type devices that harvest heat only in the in‐plane direction. Herein, 3D‐compliant TEGs fabricated solely using direct ink writing, which enables thermal‐transfer optimization for efficient through‐plane heat‐to‐electricity conversion owing to the out‐of‐plane printing of viscoelastic thermoelectric (TE) inks and unique device design is proposed. The rheological properties of carbon nanotube (CNT) TE inks are engineered to ensure conformal printing along directly written vertical thermal insulators. The ink TE properties are enhanced by the fine‐tuned incorporation of p ‐ and n ‐type dopants, where the electrical conductivity is further facilitated by nozzle‐induced CNT packing to achieve high‐power factors. To minimize the parasitic thermal loss from heat sources, an ultra‐thin bottom substrate is directly printed with polydimethylsiloxane, thereby realizing compliant 3D TEGs for heat harvesting in the out‐of‐plane direction. The TEG exhibits the highest normalized open‐circuit voltage (0.28 mV K −1 cm −2 ) among the additively manufactured TEGs and retains remarkable mechanical reliability against repetitive deformation, promising its potential as body heat harvesters or temperature sensors.

Abstract As demand for customized wearable electronics grows, free‐form Li‐ion batteries (LIBs) are attracting significant attention. Although substantial advancements have been made in printed LIBs for shape‐versatile electronics, the development of printable solid‐state electrolytes remains challenging due to the difficulty of simultaneously achieving desirable rheological properties and ionic conductivity. In this study, a solvent‐free, non‐flammable solid polymer electrolyte (SPE) is designed as a novel three‐dimensional (3D) printable electrolyte via direct ink writing (DIW) for all‐solid‐state batteries (ASSBs). The solvent‐free nature of this SPE eliminates post‐annealing steps, enhancing safety by mitigating risks of leakage, short‐circuiting, and fire. Additionally, precise control over polymer molecular weight and electrolyte composition enables high printing resolution (~100 μm), high ionic conductivity (0.705 mS cm −1 at 25°C), and intrinsic non‐flammability. A 3D‐printed ASSB, featuring a LiFePO 4 cathode and Li 4 Ti 5 O 12 anode with a mass loading of 7 mg cm −2 , achieves a high areal capacity of 1.14 mAh cm −2 , surpassing all previously reported directly printed ASSBs. This SPE facilitates scalable production of fully DIW‐printed ASSBs with superior design flexibility and space efficiency, enabling printing onto customized targets such as flexible substrates and advancing the development of next‐generation wearable electronics. image

Soft electronic components are essential building blocks for realizing form-factor-free applications; however, most designs are confined to 2D or 2.5D structures due to challenges in maintaining 3D structural integrity. This limitation is particularly critical for electromagnetic devices, such as resonators, where dielectric losses from elastomeric substrates severely hinder high-performance functionality. Here, directly printed 3D electromagnetic soft plasmonic enhanced-quality(Q) factor resonators are proposed, using highly conductive composites. By incorporating an immiscible solvent into an elastomer matrix, emulsion phases are formed that significantly enhance the storage modulus, enabling the fabrication of 3D-printed structures while improving their electrical conductivity. 3D microwave plasmonic resonators with a high degree of design freedom, such as pillars and hooks are demonstrated. These structures exhibit improved resistance to dielectric interference by leveraging the resonance in lossless air. Moreover, integrating a coplanar ground plane further decouples the resonators from lossy substrates, resulting in a 3.4-fold enhancement in the Q-factor (octupole mode) compared to 2D resonators. This improvement enables stable operation on high-permittivity surfaces, such as human skin. Additionally, a single 3D resonator demonstrates wireless deformation-sensing capabilities, facilitating the simultaneous detection of strain amplitude and orientation. This result can pave the way for advanced sensing applications in soft electronics.

Abstract Compliant thermoelectric generators (TEGs) can fully exploit their energy conversion efficiency by establishing conformal interfaces on arbitrarily shaped 3D heat sources. Although additive manufacturing processes allow scalable fabrication with flexibility and customizability, most printable TEGs are fabricated as planar‐type devices that harvest heat only in the in‐plane direction. Herein, 3D‐compliant TEGs fabricated solely using direct ink writing, which enables thermal‐transfer optimization for efficient through‐plane heat‐to‐electricity conversion owing to the out‐of‐plane printing of viscoelastic thermoelectric (TE) inks and unique device design is proposed. The rheological properties of carbon nanotube (CNT) TE inks are engineered to ensure conformal printing along directly written vertical thermal insulators. The ink TE properties are enhanced by the fine‐tuned incorporation of p ‐ and n ‐type dopants, where the electrical conductivity is further facilitated by nozzle‐induced CNT packing to achieve high‐power factors. To minimize the parasitic thermal loss from heat sources, an ultra‐thin bottom substrate is directly printed with polydimethylsiloxane, thereby realizing compliant 3D TEGs for heat harvesting in the out‐of‐plane direction. The TEG exhibits the highest normalized open‐circuit voltage (0.28 mV K −1 cm −2 ) among the additively manufactured TEGs and retains remarkable mechanical reliability against repetitive deformation, promising its potential as body heat harvesters or temperature sensors.

Abstract Flexible thermoelectrics that enable conformal contact with heat sources of arbitrary shape are indispensable for self‐powered wearable electronics. Scalable integration of flexible thermoelectric (TE) materials into functional devices has improved over the past few years, however, the practical applications of flexible TE materials are still hindered by low performance. Herein, highly aligned carbon‐nanotube yarns (CNTYs) are proposed, combined with selective doping via picoliter scale inkjet printing. Coagulation assisted by van der Waals forces ensures a highly aligned structure of the CNTY, thus achieving the ultrahigh power factors of 4091 and 4739 µW m −1 K −2 for the p ‐ and n ‐type, respectively. The proposed TE materials can be effortlessly up‐scaled into highly integrated modules via inkjet printing. A highly integrated, flexible CNTY‐based TE generator (TEG) with 600 PN pairs generates unparalleled milliwatt‐scale power at Δ T = 25 K, which is a few orders of magnitude higher than those of previously reported flexible material‐based TEGs. This TEG successfully powers a red light‐emitting diode using body heat alone, requiring no external power sources. For the seamless operation of practical applications requiring high power, this work explores the key design parameters for flexible TEGs with high performance and manufacturability and presents new platforms for self‐powered wearable electronics.

Ultrathin two-dimensional (2D) transition metal dichalcogenides (TMDs) exhibit unique band structures, allowing promising thermoelectric properties. Achieving a high power factor (PF) for thermoelectric generators (TEGs) requires optimizing both the Seebeck coefficient (S) and electrical conductivity (σ). Conventional surface charge-transfer doping can be a solution to enhance σ by introducing additional electrons. However, residual organic dopants act as charged impurities, degrading charge transport and lowering PF due to the intensified trade-off between carrier concentration and S. We propose a charged-impurity-free diffusion doping method for CVD-grown molybdenum disulfide (MoS2) to enhance PF. By depositing organic dopants on the contact region and enabling electron diffusion into the channel via carrier concentration gradients, σ is improved while maintaining high S. This approach achieves a record-high PF of 1698 μW/mK2 for CVD-grown TMDs. Our strategy offers a promising pathway to enhance thermoelectric performance, not limited by the exacerbated trade-off relationship observed in conventional doping methods.