Chapter 248 I am really hurt by your complete indifference On Friday, Xu Qingzhou came to the optoelectronics laboratory of Peking University after an absence of two months. There is only Gong Yunfei in the office. "Junior brother." Senior Brother Gong was more enthusiastic than before. He held Xu Qingzhou's hand and kept touching it, which gave him goose bumps all over his body. The fear that he had felt a few days ago due to the desire for in-depth communication in private messages came up again. "Senior Brother Gong, you..." Xu Qingzhou took two steps back without leaving a trace, but his hand was still held by Gong Yunfei. Gong Yunfei laughed and said, "I just want to get some of the god's aura." I used to feel pressure in front of this Junior Brother Xu, but now there is no pressure at all. As long as there is no comparison, there will be no harm. "Okay, Xiao Gong, let your junior brother go." Professor Zhao walked out of the experiment. "Professor." Xu Qingzhou finally got rid of Senior Brother Gong. "Xiao Xu, take a seat first. I'll tell you about the experiment."
Professor Zhao first handed Xu Qingzhou a stack of information and said, "You should know that this time we chose a new type of silicon-based negative electrode material. In fact, there is a common problem in the experiments over the past two months - too much lithium deposition." Xu Qingzhou nodded slightly. The lithium insertion potential of silicon is relatively high, which helps to avoid the formation of lithium dendrites to a certain extent, but silicon will undergo a huge volume expansion during the charging and discharging process. This volume change leads to stress accumulation inside the silicon particles, causing the silicon material to pulverize, which may in turn aggravate the formation of lithium dendrites. "Of course, we have been prepared for this situation. Therefore, in subsequent experiments, we will nanosize silicon particles to effectively alleviate the volume effect of silicon negative electrode materials when lithium is inserted and removed." "Nanotation can be divided into zero-dimensional nanotechnology, three-dimensional nanotechnology and two-dimensional nanotechnology." Xu Qingzhou recalled the information he had seen in the past two days. Professor Zhao showed an expression of appreciation, and it could be seen that this young man had carefully read the information on this subject. Next, Professor Zhao told Xu Qingzhou about the progress of the project in detail. Xu Qingzhou is also very clear about his job. Function analysis is required to use linear functions, polynomial functions, etc. to analyze battery performance parameters, such as capacity, voltage, and resistance, which change with cycle number or time. It is also necessary to establish an electrochemical model, a thermal model, and a mechanical model to describe the stress-strain relationship and mechanical failure mechanism of the material during the charging and discharging process. At the end, Professor Zhao sighed: "Data analysis and processing are the bridge between experimental data and experimental conclusions. Through effective processing of experimental data, we can reveal the changing laws of battery performance and provide data support for further optimization of battery design." "Our research group can actually do this, but because we went in the wrong direction a few days ago, our progress is much slower than planned. If we further disperse our manpower, the progress will be delayed." "Besides, I'm definitely not as good as you guys in mathematics." Xu Qingzhou flipped through the information on hand and smiled: "I'll do my best." "Don't feel pressured. Our goal is to improve the thermal stability and energy density of batteries. As long as we can improve by 2% to 4% compared to the market, we will be able to complete the project." Professor Zhao chuckled. "We don't have the funds and manpower to solve the lithium dendrite and diaphragm problems, so we don't even consider them." Xu Qingzhou nodded. Professor Zhao's project was funded by two companies, but the funding seemed to be only about 500 million. This amount of money may seem like a lot, but once you put aside the costs of raw material procurement, equipment purchase, business trips, and labor, it is still not enough to solve big problems like lithium dendrites. Professor Zhao handed the hard drive to Xu Qingzhou, and then after giving the three students instructions on the experimental tasks, he left the laboratory to do other things.
Xu Qingzhou sat down in front of the computer and opened the hard drive. It was filled with experimental data from this period. In addition to the experimental data, there were also more comprehensive experimental materials. Ten minutes later, a girl came in with a stack of magazines in her hands. She took out two and placed them on the table at the door. "Brother Gong, this is the new issue of Physics Reports." "Okay, thank you." Gong Yunfei was processing data. He looked up and saw Xu Qingzhou, who was deep in thought in front of the computer, and hesitated to speak. He waved his hand and smiled, "Hey, are you fascinated?" "Here, there are two papers written by Mr. Xu." The girl's eyes were full of admiration, and she lowered her voice for fear of disturbing Xu Qingzhou. Gong Yunfei was stunned for a moment, then opened the latest "Physics Reports" and read through the table of contents. Sure enough, Xu Qingzhou's name was written behind both papers. "Junior brother, you have published two more SCI papers?" Xu Qingzhou looked up, pulled his thoughts away from the various data, and glanced at the journal in Gong Yunfei's hand. Then he remembered that the editorial department had replied to his email a few days ago, saying that it had been published. "Yeah, that's the result of my last experiment." "." Looking at Xu Qingzhou's calm expression, Gong Yunfei moved his throat and seemed to be hesitant to speak. No, two top journals. I'm a little hurt by the way you don't care at all. If it were him, with two articles published in top magazines, he would have already booked a restaurant, called his friends, and prepared to have a great time. Well, this might be God. Neither of the two top magazines could cause the slightest emotional fluctuation. "Senior brother, is there anything else?" "fine." "Okay, I'll look at the information first." "." All the words in Gong Yunfei's heart were summed up in one sentence: Junior brother is awesome. In the morning, Xu Qingzhou basically spent his time reading materials. At noon, he went to the cafeteria to eat with Gong Yunfei and others. In the afternoon, he did not rush to organize the data, but went into the laboratory with Wang Wei. I want to see the experimental process. In the laboratory, the familiar "buzzing" sound of equipment running could be heard. Hong Yayu was collecting data for sample No. 138 in front of the X-ray diffractometer (XRD). Gong Yunfei stayed next door to clean and filter the data. Wang Wei and Xu Qingzhou, both wearing goggles, are making sample No. 139. Of course, it was mainly Wang Wei who was operating, and Xu Qingzhou was watching from the side. "This time, we selected high-purity nano-silicon as the negative electrode active material." Wang Wei explained to Xu Qingzhou while operating. Conductive agent acetylene black and binder CMC are then mixed in a certain proportion. Then use a coating machine to evenly coat the negative electrode slurry on the copper foil current collector to form a coating of a certain thickness.
Drying and compacting. and positive electrode material assembly. A Celgard diaphragm is installed and an ethylene carbonate electrolyte containing lithium hexafluorophosphate is injected. An ordinary battery appeared in front of Xu Qingzhou. After reading the materials, he actually had a general understanding of the experiment. Although Professor Zhao and his colleagues had made considerable progress in their experiment, there were still many problems to be faced. For example, silicon nanoparticles can alleviate the volume expansion effect that occurs when the silicon material itself inserts and extracts lithium to a certain extent, but the specific surface area and surface energy are increased. That is to say, electrochemical agglomeration is easily generated during the charge and discharge process, and then the contact with the electrolyte increases, consuming a large amount of lithium ions, thereby reducing the cycle performance and capacity retention rate. Xu Qingzhou narrowed his eyes and thought about how to solve the problem. On this end, Wang Wei carefully connected the BTS-5V3A-S1 charge and discharge tester. Seeing that Xu Qingzhou had not spoken, he joked, "Don't worry, it won't explode." Xu Qingzhou smiled. Not to mention the explosion of a small battery, he had even seen big scenes where the entire laboratory exploded. Wang Wei was paying attention to the data on the screen while chatting with Xu Qingzhou: "At a charge and discharge rate of C, the capacity decays slowly. After 20 cycles, the capacity remains stable at 3 mA·h/g, and the capacity retention rate remains at around 500%." "At present, we have produced sample No. 109, in which boron-doped porous silicon nano-silicon is prepared by chemical etching technology. At a charge and discharge current of 2A/g, it can still maintain a capacity of 250 mA·h/g after 2 cycles." "If we continue to experiment, we will definitely get the results we want." Wang Wei was very confident. Xu Qingzhou nodded and felt that there was nothing wrong with it. The results were accumulated from little experiments. (End of this chapter)