Deformable energy storage devices are needed to power next‐generation wearable electronics that interface intimately with human skin. Currently, deformable energy storage devices demonstrate poor ...performance compared to their rigid lithium‐ion counterparts, forcing wearable manufacturers to design their devices around bulky battery compartments. However, technological advances to create deformable batteries at the component and device level have yielded continuous improvement in stretchable batteries over the last five years. In this Essay, the major strategies at the component and device level that have been successfully employed to create stretchable batteries are reviewed. The outstanding challenges facing deformable energy storage are also discussed, namely, energy density, packaging, delamination, device integration, and manufacturing. This Essay will give researchers who are interested in contributing to the development of deformable batteries a cursory understanding of the most successful strategies to date, and provide insights into the most important directions to pursue in the future.
Deformable batteries are needed to enable the next generation of skin‐conformable electronics. This Essay describes past strategies to enable stretchable batteries at the device and component level. These strategies demonstrate significant advances in stretchable battery technology; however, there are still limitations that must be overcome. This Essay also describes the five main challenges that the development of deformable batteries encounters.
The increasingly intimate contact between electronics and the human body necessitates the development of stretchable energy storage devices that can conform and adapt to the skin. As such, the ...development of stretchable batteries and supercapacitors has received significant attention in recent years. This review provides an overview of the general operating principles of batteries and supercapacitors and the requirements to make these devices stretchable. The following sections provide an in-depth analysis of different strategies to convert the conventionally rigid electrochemical energy storage materials into stretchable form factors. Namely, the strategies of strain engineering, rigid island geometry, fiber-like geometry, and intrinsic stretchability are discussed. A wide range of materials are covered for each strategy, including polymers, metals, and ceramics. By comparing the achieved electrochemical performance and strain capability of these different materials strategies, we allow for a side-by-side comparison of the most promising strategies for enabling stretchable electrochemical energy storage. The final section consists of an outlook for future developments and challenges for stretchable supercapacitors and batteries.
Deformable energy storage devices are needed to power the next generation of wearable electronics. This review highlights the most recent advances in stretchable energy storage devices with a focus on batteries and supercapacitors.
Human skin has different types of tactile receptors that can distinguish various mechanical stimuli from temperature. We present a deformable artificial multimodal ionic receptor that can ...differentiate thermal and mechanical information without signal interference. Two variables are derived from the analysis of the ion relaxation dynamics: the charge relaxation time as a strain-insensitive intrinsic variable to measure absolute temperature and the normalized capacitance as a temperature-insensitive extrinsic variable to measure strain. The artificial receptor with a simple electrode-electrolyte-electrode structure simultaneously detects temperature and strain by measuring the variables at only two measurement frequencies. The human skin-like multimodal receptor array, called multimodal ion-electronic skin (IE
-skin), provides real-time force directions and strain profiles in various tactile motions (shear, pinch, spread, torsion, and so on).
Due to their high water content and macroscopic connectivity, hydrogels made from the conducting polymer PEDOT:PSS are a promising platform from which to fabricate a wide range of porous conductive ...materials that are increasingly of interest in applications as varied as bioelectronics, regenerative medicine, and energy storage. Despite the promising properties of PEDOT:PSS‐based porous materials, the ability to pattern PEDOT:PSS hydrogels is still required to enable their integration with multifunctional and multichannel electronic devices. In this work, a novel electrochemical gelation (“electrogelation”) method is presented for rapidly patterning PEDOT:PSS hydrogels on any conductive template, including curved and 3D surfaces. High spatial resolution is achieved through use of a sacrificial metal layer to generate the hydrogel pattern, thereby enabling high‐performance conducting hydrogels and aerogels with desirable material properties to be introduced into increasingly complex device architectures.
PEDOT:PSS hydrogels are an important framework for creating conductive porous materials that are of broad interest to researchers in the fields of bioelectronics, tissue engineering, stretchable electronics, and energy. To incorporate these materials into devices, a novel patterning method is presented that uses electrochemically produced ions to rapidly generate PEDOT:PSS hydrogel patterns with high spatial resolution.
The emergence of wearable electronics puts batteries closer to the human skin, exacerbating the need for battery materials that are robust, highly ionically conductive, and stretchable. Herein, we ...introduce a supramolecular design as an effective strategy to overcome the canonical tradeoff between mechanical robustness and ionic conductivity in polymer electrolytes. The supramolecular lithium ion conductor utilizes orthogonally functional H-bonding domains and ion-conducting domains to create a polymer electrolyte with unprecedented toughness (29.3 MJ m
) and high ionic conductivity (1.2 × 10
S cm
at 25 °C). Implementation of the supramolecular ion conductor as a binder material allows for the creation of stretchable lithium-ion battery electrodes with strain capability of over 900% via a conventional slurry process. The supramolecular nature of these battery components enables intimate bonding at the electrode-electrolyte interface. Combination of these stretchable components leads to a stretchable battery with a capacity of 1.1 mAh cm
that functions even when stretched to 70% strain. The method reported here of decoupling ionic conductivity from mechanical properties opens a promising route to create high-toughness ion transport materials for energy storage applications.
Electrolyte solutions are a key component of energy storage devices that significantly impact capacity, safety, and cost. Recent developments in "water-in-salt" (WIS) aqueous electrolyte research ...have enabled the demonstration of aqueous Li-ion batteries that operate with capacities and cyclabilities comparable with those of commercial non-aqueous Li-ion batteries. Critically, the use of aqueous electrolyte mitigates safety risks associated with non-aqueous electrolytes. However, the high cost and potential toxicity of imide-based WIS electrolytes limit their practical deployment. In this report, we disclose the efficacy of inexpensive, non-toxic mixed cation electrolyte systems for Li-ion batteries that otherwise provide the same benefits as current WIS electrolytes: extended electrochemical stability window and compatibility with traditional intercalation Li-ion battery electrode materials. We take advantage of the high solubility of potassium acetate to achieve the WIS condition in a eutectic mixture of lithium and potassium acetate with water-to-cation ratio as low as 1.3. Our work suggests an important direction for the practical realization of safe, low-cost, and high-performance aqueous Li-ion batteries.
Challenge of developing new formulations of water-in-salt electrolytes are addressed
via
mixed cation strategy: cheaper (by at least an order of magnitude) and more soluble salts featuring alkali cations beyond lithium, such as potassium, are used to create the water-in-salt condition.
Electrochemical energy storage devices are becoming increasingly important to our global society, and polymer materials are key components of these devices. As the demand for high-energy density ...devices increases, innovative new materials that build on the fundamental understanding of physical phenomena and structure–property relationships will be required to enable high-capacity next-generation battery chemistries. In this Review, we discuss core polymer science principles that are used to facilitate progress in battery materials development. Specifically, we discuss the design of polymeric materials for desired mechanical properties, increased ionic and electronic conductivity and specific chemical interactions. We also discuss how polymer materials have been designed to create stable artificial interfaces and improve battery safety. The focus is on these design principles applied to advanced silicon, lithium-metal and sulfur battery chemistries.Polymers are ubiquitous in batteries as binders, separators, electrolytes and electrode coatings. In this Review, we discuss the principles underlying the design of polymers with advanced functionalities to enable progress in battery engineering, with a specific focus on silicon, lithium-metal and sulfur battery chemistries.
Novel electrolyte designs to further enhance the lithium (Li) metal battery cyclability are highly desirable. Here, fluorinated 1,6‐dimethoxyhexane (FDMH) is designed and synthesized as the solvent ...molecule to promote electrolyte stability with its prolonged –CF2– backbone. Meanwhile, 1,2‐dimethoxyethane is used as a co‐solvent to enable higher ionic conductivity and much reduced interfacial resistance. Combining the dual‐solvent system with 1 m lithium bis(fluorosulfonyl)imide (LiFSI), high Li‐metal Coulombic efficiency (99.5%) and oxidative stability (6 V) are achieved. Using this electrolyte, 20 µm Li||NMC batteries are able to retain ≈80% capacity after 250 cycles and Cu||NMC anode‐free pouch cells last 120 cycles with 75% capacity retention under ≈2.1 µL mAh−1 lean electrolyte conditions. Such high performances are attributed to the anion‐derived solid‐electrolyte interphase, originating from the coordination of Li‐ions to the highly stable FDMH and multiple anions in their solvation environments. This work demonstrates a new electrolyte design strategy that enables high‐performance Li‐metal batteries with multisolvent Li‐ion solvation with rationally optimized molecular structure and ratio.
A strategy is proposed to optimize the electrolyte formulations for Li‐metal batteries. Li‐ion solvating fluorinated molecules with increasing chain lengths are used as main‐solvents to promote electrolyte stability. 1,2‐Dimethoxyethane (DME) is used as the co‐solvent to enhance the ionic conductivity. The resulting 1 m LiFSI/6FDMH‐DME electrolyte enables dual‐solvent Li‐ion solvation environments, inorganic‐rich solid‐electrolyte interphases, and long cycling of Li‐metal batteries.
Solid polymer electrolytes (SPEs) promise to improve the safety and performance of lithium ion batteries (LIBs). However, the low ionic conductivity and transference number of conventional ...poly(ethylene oxide) (PEO)‐based SPEs preclude their widespread implementation. Herein, crosslinked poly(tetrahydrofuran) (xPTHF) is introduced as a promising polymer matrix for “beyond PEO” SPEs. The crosslinking procedure creates thermally stable, mechanically robust membranes for use in LIBs. Molecular dynamics and density functional theory (DFT) simulations accompanied by 7Li NMR measurements show that the lower spatial concentration of oxygen atoms in the xPTHF backbone leads to loosened O–Li+ coordination. This weakened interaction enhances ion transport; xPTHF has a high lithium transference number of 0.53 and higher lithium conductivity than a xPEO SPE of the same length at room temperature. It is demonstrated that organic additives further weaken the O–Li+ interaction, enabling room temperature ionic conductivity of 1.2 × 10−4 S cm−1 with 18 wt% N,N‐dimethylformamide in xPTHF. In a solid‐state LIB application, neat xPTHF SPEs cycle with near theoretical capacity for 100 cycles at 70 °C, with rate capability up to 1 C. The plasticized xPTHF SPEs operate at room temperature while maintaining respectable rate capability and capacity. The novel PTHF system demonstrated here represents an exciting platform for future studies involving SPEs.
This study provides the first demonstration of crosslinked poly(tetrahydrofuran) as a promising polymer matrix for “beyond poly(ethylene oxide) (PEO)” solid polymer electrolytes. It is shown that the lower spatial concentration of oxygen atoms in the xPTHF backbone leads to loosened O–Li+ coordination. This weakened interaction enhances ion transport; crosslinked poly(tetrahydrofuran) has a lithium transference number of 0.53 and higher lithium ion conductivity than a commonly reported crosslinked PEO system.
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