All-Printed, Stretchable Zn-Ag2O Rechargeable Battery via, Hyperelastic Binder for Self-Powering Wearable Electronics

DOI: 10.1002/aenm.201602096 of highly conductive fillers (>107 S m−1, silver nanowires and carbon nanomaterials) into an elastomeric matrix.[23] Unlike deterministic composite, these devices are intrinsically stretchable as fillers maintain electrical contact by sliding along each other during stretching.[22] Intrinsically stretchable batteries have been reported, but none are completely elastic systems.[16–19] The cycle ability, current density, or areal capacity of these batteries are compromised when a rigid component undergoes large physical strain (Table S1, Supporting Information).[17–19,24] Unfortunately, both deterministic and random composite-designed batteries are not economical because they rely on lithographic,[7,20,25] spray/dip coating,[16,26] or “cut-and-paste”[2,19,27] fabrication routes that are extremely expensive and low-throughput. Today, printed, non-rechargeable batteries is an emerging market supporting many wearable and disposable electronics, and expected to reach a value of $1.2 billion by 2017, CAGR 46% from 2012.[28] Individual components are fabricated using a single, inexpensive printing step through either dispensing, screen, roll-to-roll, or inkjet printing of composite inks.[24,29] Unlike comparable coating technologies, such as spray or dip coating that may have high throughputs, screen printing can actively control the design that can potentially combine both deterministic and random composites. The higher viscosity requirements of screen printing enable high loadings of conductive fillers toward superior elastic performance and higher battery operation. The rheology of the ink is controlled by the composite formulation of electroactive fillers, a binder, and a specific solvent.[24,29] The binder plays the role of holding the ink components together and in dictating the flexible and stretchable nature of the inks. The synthesis of stretchable inks is highly challenging since the battery experiences significantly higher strain levels during stretching as compared to just bending. The printing technologies and random compositebased inks can be used to fabricate cost-effective and intrinsically stretchable batteries.[1,30] The fundamental challenge of using random composite is that the electrochemical properties of the fillers and elastic matrix are mutually detrimental to the other. This approach becomes overwhelmingly challenging for printed, stretchable batteries with poorly conductive, electroactive fillers (≈105 S m−1), thus the need for new innovations in highly elastic matrix is imperative.[22] Specially formulated inks must be formulated to allow the printed batteries to be stretched 100% multiple times. While several stretchable batteries utilizing either deterministic or random composite architectures have been described, none have been fabricated using inexpensive printing technologies. In this study, the authors printed a highly stretchable, zinc-silver oxide (Zn-Ag2O) battery by incorporating polystyrene-block-polyisoprene-block-polystyrene (SIS) as a hyperelastic binder for custom-made printable inks. The remarkable mechanical properties of the SIS binder lead to an all-printed, stretchable Zn-Ag2O rechargeable battery with a ≈2.5 mA h cm−2 reversible capacity density even after multiple iterations of 100% stretching. This battery offers the highest reversible capacity and discharge current density for intrinsically stretchable batteries reported to date. The electrochemical and mechanical properties are characterized under different strain conditions. The new stress-enduring printable inks pave ways for further developing stretchable electronics for the wide range of wearable applications.