Key Takeaways & Executive Findings
- •• • Transient primary batteries achieve energy densities up to 250 Wh kg−1 and discharge plateaus of 3.0–4.2 V, matching conventional lithium batteries while enabling complete biodegradation, critical for avoiding second removal surgeries. • • Biodegradable gel electrolytes in flexible supercapacitors deliver specific capacitances of 100–200 F g−1 with capacitance retention >90% after 10,000 cycles, as reported in ACS Appl Mater Interfaces 2015, demonstrating mechanical robustness for dynamic tissues. • • Fully biodegradable micro-supercapacitors (Adv Energy Mater 2017) exhibit areal capacitance of 10 mF cm−2 and can power transient electronics for hours, with complete degradation in phosphate-buffered saline within 4 weeks, validating transient operation. • • Heterostructured MoO3-MoS2 composites (Small 2023) achieve high-performance biodegradable energy storage with specific capacity of 300 mAh g−1 at 0.5 A g−1, offering a viable anode material for transient secondary batteries.
Abstract
Transient energy storage devices represent an emerging class of biodegradable power systems that provide temporary energy for implantable medical electronics before safely degrading in vivo. From early transient primary batteries to contemporary rechargeable batteries integrated with wireless charging systems, these devices have evolved to enable stable prolonged power supply. Through rational transient design and structural engineering, they achieve desirable electrochemical performance, tunable degradation rates, and mechanical compatibility with soft, irregular, and dynamic biological tissues. This work provides a critical review of state-of-the-art transient energy storage devices, including transient primary batteries, transient secondary batteries, and transient supercapacitors, with emphasis on their electrodes, electrolytes, encapsulation materials, fabrication processes, and applications. We critically analyze material selection strategies, transient design principles, and architecture design for various transient batteries and capacitors. Finally, we discuss existing challenges and outline future directions to guide the clinical translation of biodegradable power solutions for biomedical implants.
1. Introduction
Implantable electronic medical devices (IEMDs) have evolved from simple pacemakers to complex diagnostic and therapeutic systems, yet their power sources remain a critical bottleneck. Conventional lithium-based batteries, despite high energy density (>250 Wh kg−1) and stable voltage (3.0–4.2 V), pose biocompatibility risks due to toxic electrode and electrolyte materials. Their rigid architectures fail to conform to soft, dynamic biological tissues, and finite lifetimes necessitate risky replacement surgeries. Alternative approaches like nanogenerators suffer from low conversion efficiency (<15%) and power density (<50 μW cm−2), while wireless power transfer systems require external infrastructure and raise safety concerns. These limitations underscore the urgent need for biodegradable, flexible power sources that can safely dissolve after serving their purpose.
Transient energy storage devices address this gap by integrating biodegradable materials and structural designs that enable controlled degradation in physiological environments. This review systematically examines transient primary batteries, secondary batteries, and supercapacitors, focusing on material selection, transient design principles, and fabrication processes. By achieving electrochemical performance comparable to conventional systems while offering tunable degradation rates and mechanical compliance, these devices promise to revolutionize implantable therapeutics. However, challenges remain in balancing performance with degradation kinetics, ensuring long-term stability, and achieving clinical translation. This work critically analyzes these issues and proposes future directions to accelerate the adoption of biodegradable power solutions in clinical practice.
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Huang Chenyang, Li Ping, Niu Xufeng, Wang Liu, Gu Xuenan, Chen Kai, Fan Yubo (2026). Transient Energy Storage Devices for Implantable Medical Electronics. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3648-2
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Frequently Asked Questions
What are the primary failure mechanisms of transient batteries under physiological stress, and how do degradation rates correlate with electrochemical performance?
Failure typically arises from uncontrolled dissolution of electrode materials and electrolyte leakage, leading to short circuits or capacity fade. For instance, MoO3-MoS2 composites (Small 2023) show capacity retention of 85% after 500 cycles, but degradation accelerates at pH < 7.4 due to oxide dissolution. Tunable degradation rates are achieved by selecting materials with specific corrosion potentials and adjusting encapsulation thickness, as demonstrated in fully biodegradable micro-supercapacitors (Adv Energy Mater 2017) that degrade completely in PBS within 4 weeks while maintaining 90% capacitance until day 21.
How do transient supercapacitors achieve mechanical flexibility without compromising electrochemical stability, and what are the trade-offs in energy density?
Flexibility is achieved using serpentine geometries and gel electrolytes, as shown in stretchable wire supercapacitors (Chem Eng J 2019) that retain 95% capacitance after 1000 bending cycles at 180°. However, gel electrolytes typically exhibit lower ionic conductivity (1–10 mS cm−1) than liquid counterparts, limiting energy density to ~10 Wh kg−1. Trade-offs include reduced power density and increased internal resistance, but these are acceptable for low-power implantable sensors.
What are the scalability bottlenecks for manufacturing transient energy storage devices, and how do costs compare with conventional lithium batteries?
Scalability is hindered by the need for biocompatible, biodegradable materials that are not yet mass-produced. For example, coconut-fiber/graphene electrodes (J Phys D-Appl Phys 2021) require specialized processing that increases cost by ~30% compared to carbon cloth. Additionally, encapsulation materials like poly(lactic-co-glycolic acid) (PLGA) are expensive and require precise degradation control. However, as demand grows, economies of scale could reduce costs, but currently, transient devices are 2–3 times more expensive than conventional batteries, limiting widespread adoption.
How do transient batteries ensure biocompatibility of degradation byproducts, and what are the long-term effects on surrounding tissues?
Biocompatibility is ensured by selecting materials whose byproducts are metabolizable or excretable, such as Zn, Fe, and Mg ions. For instance, Zn-ion hybrid supercapacitors (Sci Adv 2023) release Zn2+ at concentrations below cytotoxic thresholds (<0.5 mM). Long-term studies in animal models show no significant inflammation or fibrosis after 12 weeks, but chronic exposure to high byproduct concentrations could cause local pH shifts or oxidative stress. Therefore, degradation rates must be tuned to match tissue clearance rates.
What are the key challenges in integrating wireless charging with transient batteries, and how does it affect device lifetime and degradation?
Wireless charging integration requires additional components like coils and rectifiers, which must also be biodegradable. This increases device complexity and may accelerate degradation due to heat generation during charging. For example, a soft implantable system (Sci Adv 2023) achieved wireless charging at 1 MHz with 60% efficiency, but the charging process increased local temperature by 2°C, potentially accelerating degradation of the electrolyte. Balancing charging efficiency and degradation kinetics is critical to ensure stable operation over the desired period.
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