Wearing a piece of everyday clothes to go out, it can wirelessly charge our mobile phones, and can also power smart medical smart fabrics in the future… Wearable devices that are hot in the frontier of technology have the possibility of further landing – research from China The team provides a new and efficient path for the “heart” of the wearable device, the energy supply.

Wearing a piece of everyday clothes to go out, it can wirelessly charge our mobile phones, and can also power smart medical smart fabrics in the future… Wearable devices that are hot in the frontier of technology have the possibility of further landing – research from China The team provides a new and efficient path for the “heart” of the wearable device, the energy supply.

Wearable New Breakthrough: Fudan Fiber Lithium-ion Battery, Wireless Charging

At 23:00 on September 1st, Beijing time, the top academic journal “Nature” (Nature) published online a new study by Professor Peng Huisheng’s team from the Department of Polymer Science, Fudan University, entitled “Large-scale Construction of High-Performance Fiber Lithium-ion Batteries” (“Scalable production of high-performing woven lithium-ion fibre batteries”), this study discovered the correlation between the internal resistance and length of fiber lithium-ion batteries (FLIBs), effectively solving the problem of interface stability between active materials and fiber electrodes , to continuously build a new type of fiber-polymer lithium-ion battery with both high safety and high performance.
  
Their research results show that at a length of 1 meter, the fiber lithium-ion battery has a capacity of 25mAh, which can provide more than 2 days of power for commercial wearable devices such as heart rate monitors and oximeters. The energy density based on bulk mass exceeds 85 Wh/kg. At the same time, the fiber lithium-ion battery has good cycle stability. After 500 cycles, the capacity retention rate of the battery still reaches 90.5%, and the Coulomb efficiency is 99.8%. Even with a radius of curvature of 1 cm, the capacity retention rate of the fiber lithium-ion battery is still greater than 80% after 100,000 bending times.
  
The research team can further obtain high-performance and high-safety large-area battery fabrics through the textile method. If the battery fabric and the wireless charging transmitter are integrated, the smartphone can be wirelessly charged safely and stably; by integrating the fiber lithium-ion battery and the fiber sensor with the Display fabric, the concentration of sodium ions and calcium ions in human sweat can also be measured. real-time monitoring and signal transmission and display.
  
The reviewers rated this work as “a milestone in the field of energy storage and wearable technology” (“landmark research not only in energy storage but also in wearable technology”) and “a milestone in the field of flexible electronics” (“a milestone in the field of flexible electronics”). towards the prevalence of flexible electronics”).
  
He Jiqing and Lu Chenhao, PhD students of the Department of Polymer Science at Fudan University, are the co-first authors of the paper. The research was supported by the Ministry of Science and Technology, the National Natural Science Foundation of China, and the Shanghai Municipal Science and Technology Commission.
  
The “heart” of wearable devices began to be explored more than a decade ago
  
“In the past ten years, people hope that the fabric is no longer simple and has some single function, but it is still intelligent.” In March this year, Peng Huisheng said when he introduced the smart fabrics he has been researching for many years to the surging news reporter.
  
At that time, the team he led published another blockbuster study in Nature. They used a 1.5-square-meter “cloth” to show the outside world that they could effectively integrate the preparation of Display devices with the weaving process of the fabric. Multifunctional micro light-emitting devices are integrated at the interwoven points of polymer composite fibers, realizing large-area flexible display fabrics and intelligent integrated systems.
  
Such smart fabrics have the advantages of intelligence, softness, adaptability to complex deformation, breathability and moisture conduction, and are an important development direction in the field of wearables in the future. However, one of the prerequisites for widespread application is to obtain a high-performance and safe flexible battery.
  
Fiber lithium-ion batteries with a diameter of tens of microns to hundreds of microns are one of the current mainstream directions. In an interview with reporters this time, Peng Huisheng said, “As early as 2006, I began to hear that some people made lithium-ion batteries into thin films to obtain flexible energy systems. This direction is very important for the future development of human society, and I am very interested.”
  
However, Peng Huisheng is a person who is willing to bite “hard bones”, and he doesn’t really want to do what others have already done. “At that time, I was always thinking about this field, whether I could be something that no one has ever done or even thought about.” After returning to Fudan in 2008, the previously vague pursuit suddenly became concrete. Peng Huisheng thought: If the lithium-ion battery is made of fiber, it must be very interesting. Peng Huisheng ten years ago did not even consider practicality at all.
  
The exploration process is long. Peng Huisheng mentioned that from 2008 to 2013, the world’s first fiber lithium-ion battery was realized, and later it was further expanded to fiber lithium-sulfur battery, fiber zinc-ion battery, fiber metal-air battery and so on. However, after several generations of doctoral students and postdocs conducting engineering research, little progress has been made.
  
He Jiqing said in an interview with reporters that the preparation of fiber lithium-ion batteries mainly faces two difficulties. “First, the internal resistance of the fiber lithium battery has an important influence on its electrochemical performance, but the relationship between the internal resistance and the fiber length is still not very clear; second, because of the completely different device structure, the bulk-oriented The electrode preparation and device construction methods of lithium-ion batteries are difficult to apply to fiber lithium batteries, and the international research on continuous preparation of fiber lithium batteries is almost blank.”
  
To date, publicly reported fiber-based lithium-ion batteries are typically in the centimeter range in length and have relatively low energy densities based on overall battery mass. In addition, the research team also mentioned in the paper that this short-fiber lithium-ion battery is difficult to use on a large scale in reality, because a large number of wire connection points are prone to water and oxygen intrusion, electrolyte leakage and external force damage, resulting in battery performance. Performance degradation or even failure.
  
Mass production of long-fiber lithium-ion batteries while maintaining high performance remains an unmet need.
  
How does the internal resistance of fiber batteries affect performance? The “outsider” wants to give it a try
  
Peng Huisheng’s team’s breakthrough contribution to the field this time was first due to an unexpected discovery.
  
He Jiqing was the first person to complete this research, but when he first joined Peng Huisheng’s team, he was more like a “layman” and had not been exposed to battery-related research before.
  
After graduating with a master’s degree in chemistry in 2012, He Jiqing did not directly continue his Ph.D. In the next five years, he successively worked for two well-known multinational chemical giants. This was regarded by his mentor Peng Huisheng after returning to campus as one of his advantages. “He was very able to focus on problem-solving, extensively collect information, and think carefully and independently to make this discovery. He used to be in the industry and was familiar with R&D work. Of course, we have also accumulated for a long time before, so the design and development of the production line are very efficient.”
  
At the end of 2018, after gradually integrating into the research group, based on the research work of the previous graduates, Jiqing He changed his research ideas in time to face practical applications, and worked closely with the team members to carry out a lot of material screening, design and device construction methods. experimental exploration.
  
In a preliminary attempt, He Jiqing et al. wound together the previously designed positive electrode and the negative electrode wrapped by the separator by hand, and prepared fiber lithium-ion batteries with lengths of 0.1 m, 0.2 m, 0.5 m and 1 m, respectively, and measured them. The electrochemical performance after adding electrolyte.
  
Surprisingly, the research team observed that the internal resistance of the longer fibers did not increase but decrease. This discovery exceeded their expectations. “Mr. Peng saw the result at the time, but he was also very rigorous. He asked us to repeat it first. If there is no problem with the repeatability, we will continue to see what to do next.” He Jiqing mentioned arrive.
  
In the end they extended the length to 10 meters. The paper showed that the internal resistance also decreased when the fiber length range was wider, from 0.01 meters to 10 meters. These results imply that it is possible to obtain high-performance long-fiber lithium-ion batteries.
  
Peng Huisheng has high requirements for scientific research. He hopes that his research results of many years will be industrialized in the future, so he is extremely rigorous about the repeatability of his work. At the same time, he still hopes that there is sufficient theoretical support behind what is feasible, and he knows why it is.
  
In the following nearly one year, the research team conducted a large number of comparative experiments, and finally summed up the variation law of the internal resistance of the fiber battery with the length, which provided theoretical support for the continuous construction of long-fiber lithium-ion batteries.

Wearable New Breakthrough: Fudan Fiber Lithium-ion Battery, Wireless Charging

The internal resistance decreases with increasing fiber length.
  
High-efficiency loading of active materials and continuous construction of batteries
  
After high-performance long-fiber lithium-ion batteries are theoretically feasible, the next step for the research team is to achieve large-scale fabrication at the method level.
  
One of the first challenges is the efficient loading of uniform active material coatings on long-fiber current collectors with micrometer-scale diameters. “The first core point of battery production is how to coat the positive and negative electrode slurry on the battery current collector.” He Jiqing further explained, “Generally speaking, most of the current commercial batteries are on flat substrates. Paint, the process is relatively simple, it can be applied evenly, and its thickness is easy to control.”
  
Doing similar work on fibers is not easy. The paper mentions that the active material coating on the curved fiber surface tends to be non-uniform. The reason for this phenomenon is that during the loading process of the active layer, the curved surface structure makes the active material bear a large surface tension. He Jiqing vividly said, “This makes it easy to produce an uneven beaded structure,” and this uneven active layer is very detrimental to battery performance and stability.
  
According to He Jiqing, the team achieved uniform, stable and high-content loading of active materials in the fiber electrode mainly through the targeted design of the loading device and the systematic regulation of the chemical composition of the active layer.
  
The research results show that on the electrode with a length of 100 meters, the load weight of the active material hardly changes, and there is no obvious shedding phenomenon after tens of thousands of bending times. Subsequently, the research team successively carried out methodological studies such as continuous battery assembly and packaging, and finally realized the continuous and stable preparation of high-performance fiber lithium-ion batteries.

Wearable New Breakthrough: Fudan Fiber Lithium-ion Battery, Wireless Charging

Continuous fabrication and structural characterization of long-fiber lithium-ion batteries.
  
What is still missing to realize the production of fiber lithium-ion batteries?
  
The final results of this study show that the capacity of the fiber lithium-ion battery increases linearly with length. Based on the total mass, the 1-meter-long fiber lithium-ion battery has an energy density of more than 80 Wh/kg, which can provide more than 2 days of usage power for commercial wearable devices such as heart rate monitors and oximeters.
  
At the same time, the fiber lithium-ion battery has good cycle stability. After 500 cycles, the capacity retention rate of the battery still reaches 90.5%, and the Coulomb efficiency is 99.8%. Its comprehensive electrochemical performance is comparable to some small commercial batteries.

Wearable New Breakthrough: Fudan Fiber Lithium-ion Battery, Wireless Charging

Electrochemical performance of fiber lithium-ion batteries.
  
The fibrous lithium-ion battery also has good mechanical properties and can be easily woven into a flexible and breathable fabric.
  
However, before further practical use as a fabric in wearable devices, we still need to confirm its safety, which is especially important for lithium-ion batteries. The research of the paper shows that the fiber battery fabric can work normally under severe conditions such as bending, dynamic deformation, high and low temperature (-20 °C to 60 °C), puncture and water washing, showing good application potential.
  
Safety verification tests have shown, for example, that textiles for fibrous lithium-ion batteries have not burned or exploded, even when folded in various ways or run over by cars. Plus, the tablet can continue to be charged even after a machine wash or puncture. The research team also monitored the temperature around the puncture area using an infrared imager and found no sign of an increase in temperature.

Wearable New Breakthrough: Fudan Fiber Lithium-ion Battery, Wireless Charging

ae) High-performance and high-safety fibrous lithium-ion battery fabrics obtained by textile methods; fh) fibrous lithium-ion battery fabrics for wireless charging of smartphones.
  
The research team further obtained a large-area battery fabric with high performance and high safety through the textile method, and performed some functional demonstrations in real application scenarios. They integrated a battery fabric and a wireless charging transmitter into a piece of clothing that securely and stably wirelessly charge a smartphone placed in the wearer’s pocket. The whole process lasted for 40 minutes, and there was no obvious heating phenomenon, which showed good safety.
  
In addition, the research team integrated the fiber lithium-ion battery and fiber sensor with the display fabric. When the user moves, the fiber sensor detects the concentration of sodium and calcium ions in the sweat and sends the data to a signal processing chip, which can transmit the information to the textile display. This provides the possibility for the application of smart medical care in the future.
  
In the view of the research team, the follow-up work still needs to be improved. “As a battery, what everyone is most concerned about is energy density. Although we can now manufacture fiber batteries in a large-scale and continuous manner, and the energy density is also very high, compared with the existing mobile phone batteries and electric vehicle batteries, its There is still a certain gap in energy density.” Their next major work is to further improve the energy density of fiber lithium-ion batteries.

Furthermore, the fiber lithium-ion battery is an energy storage system whose ultimate mission is to supply power in practical applications. “Another key work that we need to do next is to reduce the distance between it and the real product, or even eliminate it completely.”
  
Peng Huisheng also told the surging news reporter that the scientific community is currently committed to obtaining higher energy density and high safety, and is also developing continuous preparation methods. The industry is working on how to use various fiber batteries, including developing low-cost and high-efficiency production lines, establishing industry standards, and developing integrated application methods.
  
“Judging from the current performance and engineering level of fiber lithium-ion batteries, it is expected to achieve large-scale production and application in 3-5 years. If resources are more concentrated and utilized efficiently, it may be realized in 2-3 years.” Peng Huisheng emphasized, In order to realize the production of fiber lithium-ion batteries, several problems still need to be solved urgently.
  
First of all, in terms of resources, sufficient funds, technical experts with rich battery research and development experience and certain space support are needed. Secondly, it is necessary to determine 3-5 main application directions, and then the mainstream enterprises in these directions put forward application requirements, and carry out subsequent R&D and production around the real application requirements. Finally, in terms of specific technologies, it is necessary to further develop standard continuous production lines and production processes to further provide performance, develop flexible packaging technologies, and obtain high-efficiency integration methods to meet practical application requirements.

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