Will lithium-ion batteries bring a new look to the electronics industry?
Source: InternetPublisher:抄写员 Keywords: Lithium Ion Battery Updated: 2021/09/15
Usually for lithium-ion batteries, due to limited battery capacity, to enhance battery life, you must sacrifice a thin and light grip. Some manufacturers have taken a different approach and developed fast charging technology, using charging speed to cover up the embarrassment of insufficient capacity. Some manufacturers have already achieved mass production of 120-watt fast charging. Although this method is feasible, the battery life of the mobile phone does not increase.
Currently, most batteries used on the market are lithium-ion batteries, whose positive/negative electrode materials are lithium metal or lithium alloys and use non-aqueous electrolyte solutions.
It should be noted first that lithium-ion batteries are different from lithium batteries in that the cathode material is manganese dioxide or thionyl chloride. Lithium batteries do not need to be charged and can be used directly. However, the cycle efficiency is poor, and charging can easily cause internal short circuits, which poses a greater safety risk. The button batteries used in early electronic products were lithium batteries.
American chemist Gilbert Newton Lewis first proposed related concepts and studied them.
In the 1970s, Stanley Whittingham (MS Whittingham), known as the "father of lithium rechargeable batteries," used titanium sulfide as the positive electrode material and metallic lithium as the negative electrode material to create the first lithium battery. In 1982, RRAgarwal and JRSelman of the Illinois Institute of Technology discovered that lithium ions have the property of being embedded in graphite. This discovery was of great significance, and graphite once became an important component of batteries.
It was Sony that really launched lithium-ion batteries into the commercial market. The company released the first commercial lithium-ion battery in 1991. Later, lithium-ion batteries revolutionized consumer electronics.
Lithium-ion batteries can be divided into cylindrical, square, button-shaped and thin-film lithium-ion batteries according to their appearance. The batteries used in mobile devices are prismatic lithium-ion batteries.
The structure of lithium-ion batteries generally includes positive electrodes, negative electrodes, separators and organic electrolytes. Some types of lithium-ion batteries also have metal casings.
Positive electrode: The active material is generally lithium manganate or lithium cobalt oxide, lithium nickel cobalt manganate material. The materials used in the positive electrode are divided into different types. The conductive current collector uses electrolytic aluminum foil with a thickness of 10-20 microns.
Negative electrode: The active material is graphite, or carbon with a graphite structure, such as artificial graphite, natural graphite, mesophase carbon microspheres, petroleum coke, carbon fiber, pyrolytic resin carbon, etc. The conductive current collector uses electrolytic copper foil with a thickness of 7-15 microns.
Separator: A specially formed polymer film with a microporous structure that allows lithium ions to pass through freely, but electrons cannot pass through.
Organic electrolyte: It is the carrier for ion transmission in the battery, generally composed of lithium salt and organic solvent. The electrolyte plays a role in conducting ions between the positive and negative electrodes of lithium batteries, which is the guarantee for lithium-ion batteries to obtain the advantages of high voltage and high specific energy.
The working principle of lithium-ion batteries is also relatively simple. During charging, the generated lithium ions enter the electrolyte from the positive electrode, pass through the small holes in the separator, flow to the negative electrode, and combine with the electrons in the negative electrode. During discharge, electrons enter from the negative electrode through the external circuit and reach the positive electrode. At the same time, lithium ions pass through the electrolyte and again pass through the separator and enter the positive electrode.
Compared with batteries made of other materials such as nickel-cadmium and nickel-hydrogen, the capacity per unit density of lithium-ion batteries is already large. However, as the use of devices consumes more and more power, people gradually find that the battery is not enough.
The quest for better batteries means the search for alternative materials, and scientists see silicon as promising. Replacing the graphite component in the cathode with this material can increase the battery's storage capacity by 10 times.
However, due to the characteristics of silicon itself, its durability is not as good as graphite. When the battery is charged and discharged, silicon will expand, contract, and split into small pieces, eventually leading to the degradation of the positive electrode and battery failure.
In order to solve this problem, scientists have proposed some measures, such as making silicon into sponge-like nanofibers or nanospheres. This hole design can relieve the pressure of silicon during expansion and contraction.
Recently, a research team from Clemson University in the United States proposed a new solution. The findings have been published in the journal Applied Materials and Interfaces.
The research team hopes to use carbon nanotube flakes to improve silicon's reliability. Carbon nanotube sheets, also known as Buck paper, have the characteristics of light weight and high hardness. Compared with a steel body of the same volume, its mass is only one-tenth of the former; when Bucky paper is composited and pressed, its hardness is 500 times harder than the same steel.
Bucky paper also conducts electricity and dissipates heat well. Wade Adams, a scientist at Rice University, commented that "these properties of this material are as important as the Holy Grail of Jesus." This material has been used in A new generation of heat shields for aircraft.
The structure of this new solution is similar to a sandwich, with the top and bottom layers being carbon nanotube flakes and silicon nanoions in the middle.
"The individual carbon nanotube flakes allow the silicon nanoparticles to remain electrically connected to each other," said Shailendra Chiluwal, first author of the paper. "These nanotubes form a quasi-three-dimensional structure, even though It also held the silicon nanoparticles together after 500 cycles and reduced the resistance created when the nanoparticles break."
In layman's terms, the conductivity of the carbon nanotube sheets connects the silicon nanoparticles together so that these silicon nanoions do not become disconnected due to expansion and contraction, even after multiple charge and discharge cycles.
At the same time, the beauty of using carbon nanotube sheets is that because the silicon nanoparticles are clamped by the upper and lower layers of picks, even if the silicon nano-ions are disconnected due to frequent charge and discharge cycles, these broken ions are still tightly locked in them. , and can continue to function.
The research team said that this solution will allow the battery to have a higher unit capacity. In addition, the nanotubes can also act as a buffer, allowing the battery to charge at four times the speed of current iterations, effectively increasing the charging rate. If this new plan is implemented, it will play a role in many fields.
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