Replacing liquid electrolytes with polymer gel electrolytes is considered a common and effective way to solve wearable battery safety concerns and achieve high flexibility. However, due to insufficient wetting, the interface between the polymer gel electrolyte and the electrode is poor, resulting in a significant reduction in electrochemical performance, especially during battery deformation.
Based on this, the team of academician Peng Huisheng of Fudan University reported a strategy to design a channel structure in the electrode, which can integrate the polymer gel electrolyte into it and form an intimate and stable interface, thereby fabricating high-performance wearable batteries. As a demonstration, they rotated multiple electrode fibers together to form neatly arranged channels, while designing a mesh channel on the surface of each electrode fiber. The monomeric solution first effectively infiltrates along the neatly arranged channels and then into the reticular channels. The monomers are then polymerized to form a gel electrolyte, which forms an intimate and stable interface with the electrode. The resulting fiber lithium-ion battery (FLB) has high electrochemical properties (e.g., an energy density of about 128 Wh kg-1). This strategy also enables the productivity of fiber lithium-ion batteries to be as high as 3,600 m/h per winding unit. The continuous FLB is woven into a fabric of 50 cm × 30 cm and provides an output capacity of 2975 mAh. FLB textiles are safe to operate under extreme conditions such as temperatures of -40°C and 80°C and vacuum levels of -0.08 MPa. This research has successfully walked through the "last mile" of flexible fiber battery research and development, and is expected to provide effective energy solutions in the fields of human-computer interaction, health detection, and intelligent sensing. The research results were published in the latest issue of Nature under the title "High-performance fibre battery with polymer gel electrolyte". The first author of this article is Lu Chenhao, the winner of the 13th "Academic Star" special prize of Fudan University.
It is worth mentioning that this is the second Nature published by Academician Peng Huisheng's team in 2024, and it has only been more than two months since the first Nature article in 2024. This important technological breakthrough came from careful observation and deep reflection on the natural world. One day, Academician Peng Huisheng visited the Shanghai Institute of Ceramics of the Chinese Academy of Sciences, and after observing that the creeper was tightly and steadily wound around another plant vine, he pulled some of them out for detailed observation. Upon his return, he began to investigate the "glue-like" phenomenon between the creeper and the vines of the entwined plant, and discovered the secret: the creeper is able to secrete a well-infiltrated liquid that penetrates the pore structure of the contact surface between the two and then polymerizes to firmly bind the creeper and the entangled plant vines together. Inspired by this discovery, they successfully developed a high-performance fiber battery.
【Design Strategy and Preparation】
Fiber lithium-ion batteries (FLBs) are typically manufactured by twisting cathode and anode fibers together, and the fibers are prepared by loading an electrode slurry on a current collector and then injecting or absorbing a liquid electrolyte. The authors rotated multiple cathode and anode fibers along with the separator to create well-arranged channels between the fibers (Fig. 1a, b). In the preparation of cathode and anode fibers, small active particles are deposited on thin fiber collectors first, and then large active particles are deposited on thin fiber collectors, so as to achieve a compact and stable particle layer, forming a network channel between the particles that is small inside and large outside. The gel-electrolyte-electrode interface of FLB is then fabricated by polymerizing monomers to form a polymer gel electrolyte (Fig. 1b, c).
Figure 1.Fabrication of FLB using polymer gel electrolytes
【Structure and Characterization】
To further characterize the FLB architecture and designed channels, the authors generated cross-sectional scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) element plots showing the formation of small channels and large outer channels between the aligned channels formed inside the electrode fibers and the active particles formed inside the network (Figures 2a-f). The gel electrolyte-active particle interface is intimate at 3.0 V uncharged, 3.9 V half-charged, and 4.4 V fully charged (Figure 2g-i), suggesting that the gel electrolyte is able to adapt to changes in electrode volume during charging and discharging. Even when FLB was stored at temperatures of -40 °C and 80 °C, no significant separation between the gel electrolyte and the active particles was observed (Figure 2j-l). The characteristic peaks of lithium cobalt oxide particles (about 486 cm-1 and 587 cm-1) and graphite particles (about 1350 cm-1 and 1580 cm-1) change in different charged states from 3.0 V to 4.4 V, reflecting the change in the lattice constants of lithium cobalt oxide and graphite due to the deinterpolation and intercalation of lithium ions, respectively (Figure 2m). At different lithium-ion intercalation states and at different temperatures, the gel electrolyte adequately fills the channels between the active particles, as evidenced by the characteristic Raman signal of the gel electrolyte (Figure 2g-m). Even after 100,000 times of repeated bending, twisting, and stretching, the electrolyte-electrode interface remains tight with less than 10% change in resistance (Figure 2n).
Figure 2. Features of the FLB interface
The authors devised a confined deposition method to prepare electrode fibers. FLBs with lengths of hundreds and thousands of meters were produced on industrial-scale production lines and showed capacity retention of 87.7% and 99.6% coulombic efficiency after 1,000 charge-discharge cycles (Figure 3h,i) and over 96% capacity retention after 100,000 bending cycles (Figure 3j) due to the stable electrolyte-electrode interface. High capacity is maintained even at a high productivity of 3600 mh−1 per winding unit, and the output energy increases linearly with the length of the FLB, reaching 423 mWh for a 1 m long FLB (Fig. 3b,c). In addition, a narrow distribution of electrochemical properties (e.g., capacitance, resistance, coulombic efficiency, and midpoint voltage) was observed in 20 different FLBs (Figure 3d-g), indicating a high reproducibility of fabrication.
Figure 3. Electrochemical properties of FLB
【Application】
The authors weave FLB into flexible power textiles to demonstrate its ability to be applied in practical terms (Figure 4). They showcased the use of FLB textiles in firefighting and space exploration. A multifunctional firefighting suit was constructed by integrating FLB textiles as well as temperature and gas sensors. In the simulated environment of a high-temperature fire, the battery fabric does not cause safety accidents such as fire and explosion even after being worn and sheared, and it stably supplies power to firefighters' portable equipment such as walkie-talkies and sensors. In addition, battery fabrics can safely supply power for high-power electrical appliances, such as heating suits that can be heated to 60°C in a few minutes, which is expected to be used in polar research and other fields.
Figure 4. Applications of FLB textiles
【Summary】
In this paper, a high-performance FLB with a polymer gel electrolyte was developed, and the electrode fibers were tightly and stably connected to the electrode fibers by designing neatly arranged channels between the electrode fibers and by designing networked channels inside the electrode fibers. The FLB, which is assembled from channel-type electrode fibers, has a high energy density of about 128 Whkg-1 and is flexible and stable enough to withstand 100,000 deformation cycles. The FLB is also very safe and works effectively even under extreme conditions such as high and low temperatures of 80°C and -40°C and vacuum of -0.08 MPa. With manufacturing speeds of up to 3,600 m/h per winding unit, FLB can be used for industrial-scale production and applications. These FLBs are woven into large-area power textiles that output a high capacity similar to that of commercial batteries, providing an unpreviously unknown and effective power source for a variety of applications such as flexible electronics, biomedical engineering, space exploration, and wearables. For these FLBs, future efforts should be made to optimize the gel electrolyte to improve energy storage performance and to design efficient integration methods for the production of large-scale power textiles.
Source: Frontiers of Polymer Science