Cui Hao and his company hope to push the popular lithium-ion battery to a new height. At present, Panasonic, Samsung, LG Chemical, Apple and Tesla are all working hard to miniaturize, lighten, and increase their capacity. Despite the strong clouds, Cui Wei still maintains a strong momentum. In the battery industry, many people are paying attention to the chemical composition of electrodes or electrolytes, and Cui Wei is looking for ways to combine battery chemistry and nanotechnology.
He is currently creating battery electrodes with complex structures that can absorb and release charged ions more and faster than standard electrodes without causing adverse side reactions.
Luo Jun, a materials and battery expert at the University of Maryland, commented: “He (Cui Hao) is using nanotechnology innovations to manipulate chemistry.â€
Battery market
In a series of demonstration experiments, Cui Hao demonstrated that its unique structure of the electrode can "master" the chemical reaction of the battery. The standard graphite in the lithium ion battery electrode is replaced by silicon; bare metal lithium is used as the electrode material; on the lithium-sulfur chemistry basis, it will provide more powerful energy than the lithium ion battery. The nanostructure he is exploring includes silicon nanowires, which can absorb and release lithium ions correspondingly during expansion and contraction. Its tiny egg-shaped structure has a carbon shell that protects the "yellow yolk" of silicon particles rich in lithium ions. .
Amprius has already started to supply cell phone batteries equipped with silicon electrodes, which is 10% more than the best traditional lithium-ion battery on the market. Another prototype that is under development is even better, and can even store 40% more energy. So far, Cui Wei's company has not yet provided batteries for electric cars. If the technology Cui Wei is developing will one day be successful, then the car battery they make will be 10 times more powerful than the current top product. This will bring a revolution to the automotive industry, because low-cost electric vehicles will be able to travel the same distance as traditional fuel-efficient cars, thereby significantly reducing global carbon emissions.
Cui Wei said that when he first started working on research, he wanted to “change the world and become wealthy at the same time, but mainly change the worldâ€. Their main goal is still the battery industry, but they are also exploring new nanotechnology and incubating startups to provide cheaper, more efficient air and water purification systems. Luo Yu thinks that he is taking an "unusual" road, and Liu Jun, a materials scientist at the Northwest Pacific National Laboratory, is even more straightforward: Cui Ying's nanotechnology contribution to the battery is "huge."
For decades, the performance of Silicon Valley's computer chips has increased exponentially. In contrast, it is much more difficult for battery technology to make big strides. The current best lithium-ion battery energy density is about 700Wh/L, which is about five times that of nickel-cadmium batteries in the 1980s. Although this score is not bad, it is still not a breakthrough. In the past decade, the energy density of commercial batteries has almost doubled.
However, there is no end to the needs of users. It is expected that by 2020, the market share of lithium-ion batteries will reach 30 billion US dollars. The proportion of electric vehicle batteries will increase, and related companies include Tesla, General Motors, and Nissan.
Today's electric cars have a lot of room for development. Taking Tesla Model s as an example, its 70-90 kWh battery weighs 600 kg. For a car with ten thousand dollars, the price of such a battery would be 30,000 U.S. dollars. On one charge, it can only last for 400 kilometers, which is far less than traditional cars. The Nissan Leaf is a lot cheaper as an entry-level small electric vehicle, and the whole vehicle is about 29,000 U.S. dollars. However, its battery pack is small, and the battery life is only 1/3 of Tesla.
The innovation in battery technology will have an important impact. If the energy density of the battery is doubled, car manufacturers can halve the size and cost of the battery while maintaining continuous airlines, or choose to keep the battery constant and double the mileage. Cui Wei said: "The era of electric cars is coming." To complete this transition, "We must do better!"
From scratch
Cui Wei realized this trend long ago. After graduating from the University of Science and Technology of China in 1998, he came to the United States to obtain a doctorate from Harvard University and later went on to postdoctoral research at the University of California at Berkeley. During his time, he was engaged in the synthesis of cutting-edge nanomaterials in the laboratory. At the time of the early development of nanotechnology, researchers were still trying to find reliable methods to make the materials they wanted. The application of nanotechnology was only just beginning.
"In the beginning, I didn't study energy. I have never done battery research," Cui Wei said. Inspired by Steven Chu, Director of the Lawrence Berkeley National Laboratory, Cui Wei embarked on a new path. According to Steven Chu, nanotechnology has brought a "new grip" to the battery field. Researchers will not only be able to control the chemical composition of materials at the smallest scale, but also control the arrangement of atoms in the material and master it. Chemical reactions carried out therein.
After coming to Stanford, Cui Hao quickly integrated the electrochemical technology of nanotechnology and batteries and began to study their practical applications.
The research team has tried a variety of nano-related technologies to prevent the collapse of the silicon anode and prevent fatal side reactions from occurring.
Graphite can be described as the most ideal anode material today, and its high conductivity can easily transfer electrons to the circuit metal wires. However, in the discharge process, the ability of graphite to collect lithium ions is not excellent. "Gaining" a lithium ion requires six carbon atoms. This weak grasping force limits the amount of lithium that can be contained in the electrode, and thus limits how much energy the battery can store.
In this regard, the potential of silicon is better. Each silicon atom can "tie" four lithium ions. In other words, the silicon-based negative electrode stores 10 times more energy than graphite. For decades, electrochemical scientists have been making unremitting efforts to achieve this goal.
Using a silicon material to make a negative electrode is very simple. The problem is that this negative electrode cannot be stably present. In the charging process, lithium ions influx and combine with silicon atoms, and the negative electrode material will expand three times; while in the discharge process, lithium ions flow out and the negative electrode material rapidly shrinks. After several such tortures, the silicon electrode breaks and eventually collapses into tiny particles. The negative electrode, or the entire battery, is so finished.
Cui Wei believes that he can solve this problem. The experience of Harvard University and Berkeley, California, made him understand that the properties of bulk materials often change at the nanometer scale. First, the atomic proportion of the surface of the nanomaterial is higher than that of its interior. At the same time, the surface atoms are less constrained by the adjacent atoms, and they can move freely under pressure and stress. It's like a thin aluminum foil that can be easily bent and not broken compared to a thick aluminum material.
In 2008, Cui Wei proposed to use nano-silicon wire as the negative electrode of silicon, which can relieve the pressure and stress that lead to the collapse of bulk negative electrode. This idea really worked, and he and his colleagues published the results of the study in Nature Nanotechnology, which showed that after the lithium ions flowed in and out through the silicon nanowires, the nanowires were hardly damaged. Even after 10 cycles of charge and discharge, the negative electrode still has 75% of theoretical energy storage.
Unfortunately, silicon nanowires are harder to prepare than bulk silicon and are also more expensive. So Cui Wei and his colleagues began to study the lower cost of silicon anode materials. First, they used spherical silicon nanoparticles to make negative electrodes for lithium-ion batteries. Although this may be cheaper, it also raises the second problem: As lithium atoms come in and out, the shrinkage and swelling of the nanoparticles will cause the glue to crack. The liquid electrolyte will penetrate between the particles and produce a chemical reaction. A non-conductive layer (solid-electrolyte interphase, SEI) is formed on the surface of the silicon nano-particles. The thicker and thicker this film eventually destroys the charge collection ability of the negative electrode. Cui Wei's students describe this way: "It's like a scar tissue."
A few years later, the Cui Wei team tried another nanotechnology. They created egg-shaped nanoparticles that wrap them around tiny silicon nanoparticles (the "yolks"). This highly conductive carbon shell allows lithium ions to pass freely. Carbon shells provide enough space for silicon atoms to expand and contract while protecting them from the formation of SEI layers by electrolytes. An article published in Nano Letters in 2012 showed that after 1,000 cycles of charge and discharge, the Cui Wei team's yolk-shell electrode still has 74% of its electricity storage capacity.
Two years later, they made further breakthroughs. These yolk-shell nanoparticles were assembled into micron-sized structures that resemble a miniature pomegranate. This new silicon nanosphere increases the lithium content of the negative electrode and also reduces side reactions in the electrolyte. In February 2014, Cui Wei announced new progress in Nature Nanotechnology, and their new materials remained at 97% after 1,000 charge-discharge cycles.
Earlier this year, Cui Wei team announced a more excellent program. They knocked the bulk silicon material to the micron level and wrapped it with graphene carbon layers. The resulting silicon particles are larger than the previous “pomegranateâ€. Although this volume is more easily disintegrated after charge and discharge, the coating of graphene can prevent the electrolyte from contacting the silicon material. At the same time, it is easy to keep the broken particles in contact, making it easy to transfer the charge to the metal wires. The related results have been published in Nature Energy. This silicon particle has a larger amount of charge and a higher power per unit volume. The important thing is that its cost is also lower.
Liu Jun said: "His work this time really looked in the right direction."
Driven by this technology, Amprius has raised $100 million for commercial development of lithium negative-electrode silicon anodes. This battery is cheaper and has 10% higher capacity than traditional lithium-ion batteries. At present, they have built factories to produce mobile phone batteries in China, and the sales volume has exceeded 1 million pieces.
The future of batteries
In addition to producing new batteries, Cui Wei also mentioned a prototype with a 40% increase in energy storage. In his words, this is just the beginning of the future excellent silicon negative battery.
Now, his attention has gone beyond silicon. One of the ideas is the negative electrode of pure lithium metal, which has always been considered as the ultimate negative electrode material because it can store more energy and lighter than silicon material.
However, the lithium metal negative electrode also faces difficulties. First, the SEI layer is usually formed around the lithium electrode. This is good news because lithium ions can pass through this layer, so the SEI layer also acts as a protective layer for the lithium electrode. However, the problem is that as the battery is charged and discharged, metallic lithium expands and contracts like silicon particles, and this behavior breaks the SEI protective layer. Lithium ions accumulate at the fracture and form metal "dendrites" that gradually grow in the electrode. Eventually, battery separators will be punctured, short-circuiting the battery and causing fire.
The traditional approach cannot solve this problem. But nanotechnology may bring solutions. When trying to prevent the formation of metal dendrites, Cui Wei team stabilized the SEI layer by attaching negative carbon nanoballs to the negative electrode; another method is to absorb lithium ions in the larger yolk shell through the gold nanoparticles. The egg shells provide space for the expansion and contraction of lithium, thus protecting the SEI layer and the formation of metal dendrites.
The improvement of the negative electrode is only half of this battery battle. The Cui Wei team also uses similar nanotechnology to improve cathode materials, especially sulfur materials. Just like silicon is on the negative electrode, sulfur has long been considered as the cathode material of choice. Each sulfur atom can combine two lithium ions, which theoretically doubles the storage energy of the positive electrode. Just as important, sulfur materials are really cheap. The problem is that sulfur has a general electrical conductivity and reacts with the electrolyte to produce a by-product that harms the battery. The battery may become obsolete after several charges and discharges. In addition, during the discharge, the sulfur cathodes tend to accumulate charge instead of releasing them.
In the search for nano-solutions, Cui Wei's team wrapped sulphur particles with a highly conductive titania shell, which increased the battery capacity by five times compared to conventional batteries, while preventing the formation of byproducts harmful to the battery. The researchers also produced a sulfur-based version of "pomegranate," and immobilized sulfur in long, thin nanofibers. These innovations not only increased battery capacity, but also increased Coulomb efficiency (battery discharge performance) from 86% to 99%.
Cui Wei said: "Now we have high-performance materials at both ends of the battery." He hopes to integrate the two innovations in one place and combine silicon anodes with sulfur cathodes. If successful, it must be able to create high-capacity, low-cost products that can change the world.
Heat sink is a vital component that helps to dissipate heat from electronic devices. These devices generate heat as they operate, which can damage the internal components and cause malfunctions. In this article, we will explore what heat sinks are, how they work, and why they are important.
What is a heat sink?
A heat sink is a hardware device that is used to regulate the temperature of electronic components by dissipating heat. It is usually made out of an aluminum or copper plate with fins, which help to increase the surface area and improve the efficiency of heat transfer. Heat sinks are commonly used in electronic devices such as computers, power supplies, and mobile phones.
How do heat sinks work?
The purpose of a heat sink is to transfer heat from an electronic component to the surrounding environment. When electronic components such as CPUs or GPUs become hot, the heat is transferred to the metal plate of the heat sink. The heat sink then uses its fins to increase the surface area for the transfer of heat to the air. As the air flows over the fins, it absorbs the heat and carries it away, thus cooling the electronic component.
Why are heat sinks important?
Heat sinks play a significant role in ensuring that electronic devices function correctly and have an extended lifespan. Here are a few key reasons why heat sinks are important:
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Improved performance: When electronic components become too hot, they can malfunction or slow down. Heat sinks help to regulate the temperature of these components, allowing them to operate at their full potential.
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Extended lifespan: Overheating can cause damage to electronic components, leading to a shortened lifespan. Heat sinks help to prevent this by ensuring that the components are kept within their safe temperature range.
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Reliability: By preventing excessive overheating, heat sinks contribute to the overall reliability of electronic devices, reducing the risk of malfunctions and failures.
In summary, heat sinks are an essential component of electronic devices that help to regulate the temperature of electronic components. They improve performance, extend the lifespan of devices, and contribute to their overall reliability. Regular maintenance, cleaning, and replacement of damaged heat sinks are crucial for ensuring the optimal functioning of electronic devices.
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