18650 lithium 3.7 battery

　　An in-depth interpretation of 18650 lithium 3.7 battery technology

　　Clean energy vehicles have developed rapidly in recent years, and electric vehicle companies led by Tesla have launched a variety of electric vehicles full of technology. Through continuous technological innovation, the performance of electric vehicles has been greatly improved, and electric vehicles have gradually entered people's lives from concept products.

　　Electric vehicles conform to the trend of scientific and technological progress and the development of the times, and are loved and accepted by more and more people. However, compared with fuel vehicles, electric vehicles currently have problems such as short cruising range, slow charging speed, and high cost. The key to solving the problem lies in the "fuel tank" of electric vehicles - the power battery. It can be said that the power battery determines the vitality and competitiveness of electric vehicles. At present, lithium-ion batteries, one of the energy storage systems, dominate the development of power batteries because of their advantages of high voltage, high energy density, long life and good safety.

　　What is a 18650 lithium 3.7 battery?

　　Lithium-ion batteries are secondary batteries that can be charged and discharged repeatedly. Its main components are: positive electrode, negative electrode, separator and electrolyte. As shown in the figure below, during charging, lithium ions are released from the positive electrode and enter the negative electrode through the electrolyte. At the same time, the released electrons are transferred from the external circuit to the negative electrode to maintain charge balance; during discharge, lithium ions are released from the negative electrode and enter the positive electrode through the electrolyte, while the electrons are transferred from the negative electrode to the negative electrode through the electrolyte. The negative pole reaches the positive pole through an external circuit. During each charge and discharge cycle, lithium ions (Li+) act as a carrier of electrical energy, moving back and forth from the positive electrode → the negative electrode → the positive electrode, reacting with the positive and negative electrode materials, converting chemical energy and electrical energy into each other, achieving This is the basic principle of lithium-ion batteries.

　　Positive and negative electrodes that are easily "excited"

　　Lithium-ion batteries can convert electrical energy and chemical energy into each other to achieve energy storage and release. One of the conditions is that the materials of the positive and negative electrodes must be active, easy to oxidize and reduce, and "easily" participate in chemical reactions to achieve energy conversion. The second is that there is a need for positive and negative electrode materials with potential differences to achieve charge movement. After long-term research and exploration, people have found several lithium metal oxides, such as lithium cobalt oxide, lithium titanate, lithium iron phosphate, lithium manganate, nickel cobalt manganese ternary and other materials, as battery positive electrode active materials.

　　The negative electrode usually chooses graphite or other carbon materials as the active material, which also follows the above principles. It must be a good energy carrier, relatively stable, and have relatively abundant reserves to facilitate large-scale manufacturing. Carbon element is a relatively optimized s Choice.

　　"Discharge" also needs to be divided into occasions

　　As mentioned above, lithium ions flow through the electrolyte, and the electrons produced by the reaction do work through an external circuit. Therefore, the battery system must ensure the flow of lithium ions and electrons, that is, it must be a good ion conductor and an electronic conductor. Many electrochemically active materials are not good conductors of electrons, so some conductive material such as carbon black needs to be added. In order to hold the electrode material and conductive agent together, some adhesive needs to be added. In this case, electrochemical reactions can only occur where the active material, conductive agent and electrolyte meet.

　　While lithium ions flow through the electrolyte, the positive and negative electrodes must be physically separated. In order to prevent the violent release of energy caused by short circuit, a material needs to be used to "isolate" the positive and negative electrodes. This requires the material to have good ion permeability, open channels for lithium ions to pass freely, and at the same time be an insulator for electrons to achieve insulation between the positive and negative electrodes. Current lithium-ion batteries use porous separators made of polyethylene (pE) and polypropylene (pp).

　　What is the bottleneck in improving the range of electric vehicles?

　　For electronic devices such as mobile phones and laptops, energy storage is key. The more power it can store, the better, and the longer it can operate, the better. For some larger applications, such as batteries in electric vehicles, in addition to the requirements for battery energy density, power is equally important. Materials must be able to quickly provide power to drive the car and recharge quickly when the battery is depleted.

　　The current problem with electric vehicles is limited battery life! The cruising range of a fuel-powered car with a full tank of oil is about 500 kilometers. The cruising range of an electric vehicle depends on its "fuel tank" - the battery. When you see this, someone may ask, why not install a super large battery in the car?

　　Does this idea make sense? The answer is somewhat true, but not entirely correct. It’s not that the bigger the battery, the higher the cruising range!

　　There are two ways to increase the cruising range of electric vehicles: one is to increase the overall capacity by increasing the number of battery packs, which is the "big battery" mentioned earlier. The disadvantage of this method is that the overall weight of the car will also increase. The added battery reduces the internal space of the car, increases the cost of the car, and also increases power consumption. Therefore, it is necessary to consider the relationship between the weight of the battery and the cruising range to find the optimal solution. Take the fuel cars around us as an example. A full tank of fuel can drive about 500-600km. If the fuel tank is enlarged, the amount of fuel stored will increase, but the fuel consumption will also increase accordingly. Taking into account the distribution distance of gas stations, the design It is more appropriate to travel 500-600km for one tank of fuel. Another way to increase the range of electric vehicles is to increase the energy density of batteries and develop lighter, higher-capacity batteries. On the other hand, we can increase the cruising range of electric vehicles by increasing the charging speed of the battery and allowing the car to be fully charged faster and more conveniently.

　　How to make it possible to make an electric car that can charge for five minutes and have a range of 500 miles?

　　"Made in China 2025" issued by the State Council proposes that the energy density of power batteries should reach 300Wh/Kg in 2020, 400Wh/Kg in 2025, and 500Wh/kg in 2030. At present, the energy density of mass-produced power battery cells is 230±20Wh/Kg. According to the requirements of "Made in China 2025" and combined with the current technical route, our country's scientific and technological workers have proposed the use of high-nickel positive electrode + quasi-solid electrolyte + silicon carbon negative electrode Achieve the goal of 300Wh/Kg; use lithium-rich cathode + all-solid electrolyte + silicon carbon / lithium metal anode battery to achieve the goal of 400Wh/Kg in 2025, and use lithium-air batteries and lithium-sulfur batteries to achieve the goal of 500Wh/Kg in 2030.

　　With these data, we also need to consider the battery assembly quality and the weight of the entire vehicle to make a rough inference about the cruising range of the electric vehicle. Taking the Tesla Model S as an example, the battery pack weighs about 1 ton, the battery capacity is about 100KWh, the vehicle mass is about 2.5 tons, and it can reach a cruising range of 600km. According to recent reports, the third-generation supercharging system developed by Tesla has a charging rate of more than 1,000 miles per hour (approximately 1,609 kilometers per hour) and can replenish up to 75 miles of power (approximately 120 kilometers) in 5 minutes. Nearly 270 kilometers can be covered in 15 minutes.

　　"Charging for five minutes, battery life of 500 miles" is currently not achievable. If this idea is realized, it will undoubtedly shake the dominance of fuel vehicles. So, is "charging in five minutes and having a battery life of 500 miles" really elusive?

　　To achieve this goal, there is a high requirement for the charging and discharging speed of the battery. The main reasons are the delithiation and lithium insertion speed of the positive and negative electrode lithium storage materials and the structural stability during rapid charge and discharge. High-speed charging tends to heat the battery, damage its structure, and reduce its lifespan. This in turn puts forward requirements for the stability and safety of the battery. Although there have been many reports on hydrogen fuel cell concept cars in recent years, hydrogen fuel cell cars need to solve a series of complex problems such as hydrogen production, hydrogen storage, fuel cell engines, vehicle body structures, safety, etc., making them difficult to commercialize. Generally speaking, electric vehicle batteries will still be dominated by lithium-ion batteries for a long time to come. If you want to turn "charge in five minutes and last for 500 miles" into a reality, you need to meet the following conditions: (1) The energy density of the material is high, that is, it can store a lot of electrical energy. (3) When lithium ions are inserted and removed, the reaction between the material and lithium must be very rapid. (3) The material is a good conductor of electrons. This will reduce the internal losses of the battery and further improve battery performance. (4) The material is stable. During the charging and discharging process, the material does not change its structure or decompose in other ways, and the material volume does not expand or deform. (5) Low material cost. This determines the price of batteries and electric vehicles. (6) The materials are environmentally friendly. There is no pollution to the environment or the pollution is minimal and controllable.

　　If you want to achieve the goal of "charging in five minutes and driving for 500 miles", you need to conduct more in-depth research and exploration into the battery's process technology and energy storage mechanism. I believe that in the near future, electric vehicles that can charge for five minutes and have a range of five hundred miles will become possible! Editor in charge: wv

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