lithium battery 18650 3.7v

Classification and prospects of lithium battery 18650 3.7v energy storage technology

So far, people have proposed and developed a variety of energy storage technologies to meet different applications in different fields and different needs. Global energy storage technologies mainly include physical energy storage, chemical energy storage (such as sodium sulfur batteries, all-vanadium liquid flow batteries, lead-acid batteries, lithium-ion batteries, supercapacitors, etc.), electromagnetic energy storage and phase change energy storage.

1. Physical energy storage

Physical energy storage technologies mainly include pumped storage, compressed air energy storage, flywheel energy storage, etc. Compared with chemical energy storage, physical energy storage is more environmentally friendly and green, and is achieved by using natural resources. Pumped Storage Hydroelectricity (PSH) is equipped with two upstream and downstream reservoirs. When the load is low, the equipment works in the motor state, pumping the water from the downstream reservoir to the upstream reservoir for storage, and when the load is peak, the equipment works in the generator state, using the water stored in the upstream reservoir to generate electricity, as shown in Figure 1. Due to mature technology, pumped storage power stations have become the most widely used energy storage technology in power systems. At present, the installed capacity of pumped storage power stations under construction in my country is about 11,400 MW, and it is expected that the total installed capacity of pumped storage power stations will reach about 17,500 MW by the end of 2010.

Compressed air energy storage power station (CAES, Compressed Air Energy Storage) is a peak-shaving gas turbine power plant, which mainly uses the surplus power of the grid load at low trough to compress air and store it in a high-pressure sealed facility with a typical gas storage pressure of 7.5 MPa, and releases it during peak power consumption to drive gas turbines to generate electricity. The world's first commercial CAES power station was the Huntdorf power station built in Germany in 1978, with an installed capacity of 290 MW and an energy conversion efficiency of 77%. It has been in operation for more than 7,000 times, mainly used for hot standby and load smoothing. Compared with pumped storage power stations, CAES power stations are flexible in site selection. It does not require the construction of ground reservoirs and the terrain conditions are easy to meet. At present, compressed air storage power stations have been widely used in some developed countries.

Flywheel energy storage (FW, FlyWheels) is achieved by the mutual conversion of mechanical energy and electrical energy to achieve charging and discharging. It uses a high-speed rotating flywheel core as a medium for mechanical energy storage, and uses an electric motor/generator and an energy conversion control system to control the input and output of energy. Flywheel energy storage has high requirements for raw materials and technology for making flywheels. It was not until the 1990s that it was rapidly developed and used in uninterruptible power supply (UPS)/emergency power supply (EPS), grid peak regulation and frequency control. Research in this area has just started in my country.

Physical energy storage such as pumped storage and compressed air energy storage has the advantages of large scale, long cycle life and low operating costs, but requires special geographical conditions and sites, has large construction limitations, and has high one-time investment costs. It is not suitable for off-grid power generation systems with smaller power. From the perspective of development level and practicality, chemical energy storage has a broader application prospect than physical energy storage.

2. Chemical energy storage - lithium-ion battery energy storage is currently the most feasible technical route

Lead-acid batteries are the oldest and most mature chemical energy storage method, with a history of more than 100 years. They are widely used in automobile starting power supplies, electric bicycle or motorcycle power supplies, backup power supplies and lighting power supplies. Lead-acid battery electrodes are mainly made of lead and its oxides, and the electrolyte is sulfuric acid solution. When charging, the main component of the positive electrode is lead dioxide, and the main component of the negative electrode is lead; when discharging, the main components of the positive and negative electrodes are lead sulfate. Lead-acid batteries have good reliability, easy to obtain raw materials, and low prices, but their optimal charging current is about 0.1C, the charging current cannot be greater than 0.3C, and the discharge current is generally required to be between 0.05 and 3C. It is difficult to meet the large-scale power storage requirements that take both power and capacity into consideration. At the same time, lead-acid batteries cannot be deeply charged and discharged. Under 100% discharge conditions, the battery life is greatly affected (the battery cycle life is less than 300 times under full charge and discharge conditions), and water will decompose into hydrogen and oxygen gas at the end of charging, requiring frequent acid and water addition, and heavy maintenance work, so it is not suitable for application in the field of smart grids.

Currently, the chemical power sources that can be applied to the field of smart grids mainly include sodium-sulfur batteries, flow batteries and lithium-ion batteries.

Sodium-sulfur batteries (NaS) were first invented and announced by Ford in the United States in 1967. It uses metallic sodium as the negative electrode, sulfur as the positive electrode, and a ceramic tube as the electrolyte diaphragm. At a certain operating temperature, sodium ions pass through the electrolyte diaphragm and undergo a reversible reaction with sulfur, forming energy release and storage, as shown in Figure 2. Sodium-sulfur batteries have high specific energy (theoretical specific energy up to 760Wh/kg), can be charged and discharged with large currents, and have a long service life (10 to 15 years). They are one of the more economical and practical energy storage methods at present. The main application targets are power station load leveling, UPS emergency power supply and instantaneous compensation power supply. At present, Japan is the leading country in sodium-sulfur battery technology. As of 2007, Japan's annual sodium-sulfur battery production has exceeded 100MW. In 2008, Japan's Nimata Wind Power Station introduced 17 sodium-sulfur battery systems from NGK, with a storage capacity of 34MW, successfully suppressing the power fluctuations of wind power generation equipment with a maximum power of 51MW, realizing planned power output, and providing a basis for the grid-connected power generation of wind power. In 2009, my country's Shanghai Institute of Silicates successfully developed 100kW-level key technologies, becoming the second country in the world after Japan to master the core technology of large-capacity sodium-sulfur monomer batteries. The developed sodium-sulfur battery is shown in Figure 3. However, sodium-sulfur batteries require a high temperature of 350℃ to melt sulfur and sodium, and require additional heating equipment to maintain the temperature. At the same time, it is dangerous when overcharging, so there are deficiencies in safety and maintenance-free.

The research on all-vanadium liquid flow batteries began in 1984 by the Skyllas-kazacos research group at the University of New South Wales, Australia. It is a redox renewable fuel cell energy storage system based on the metal vanadium element. The schematic diagram of its working principle is shown in Figure 4. Liquid flow batteries use proton exchange membranes as the separators of battery packs. The electrolyte solution flows in parallel over the electrode surface and undergoes electrochemical reactions. The chemical energy stored in the solution is converted into electrical energy by collecting and conducting current through the double electrode plates. The rated power and rated capacity of the liquid flow energy storage battery system are independent of each other. The power depends on the battery stack, and the capacity depends on the electrolyte. The battery capacity can be increased by increasing the amount of electrolyte or increasing the concentration of the electrolyte, and "instant recharging" can be achieved by replacing the electrolyte. Liquid flow batteries have an unlimited theoretical shelf life, a long storage life, no self-discharge, and can be 100% deeply discharged without damaging the battery. These characteristics make liquid flow batteries one of the preferred technologies for energy storage technology. At present, liquid flow energy storage technology has been demonstrated in developed countries such as the United States, Germany, Japan and the United Kingdom, and my country is still in the research and development stage. The difficulty of all-vanadium flow batteries is that the total vanadium ion concentration usually used is less than 2 mol/L, resulting in a specific energy of only 25-35 Wh/kg. The electrolyte storage tank is large and difficult to manage, and the pentavalent vanadium in the cathode solution is easy to precipitate vanadium pentoxide when it is left still or the temperature is higher than 45°C, which affects the service life of the battery.

In comparison, lithium-ion battery energy storage is the most feasible technical route for the development of energy storage products. Lithium-ion batteries have the advantages of high energy density, low self-discharge, no memory effect, wide operating temperature range, fast charging and discharging, long service life, and no environmental pollution. They are called green batteries. Table 1 is a comparison of lead-acid batteries, sodium-sulfur batteries, flow batteries, and lithium-ion batteries with lithium titanate as the negative electrode. It can be seen that the service life of lead-acid batteries is short, the disadvantage of sodium-sulfur batteries is that the operating temperature is high, the energy density of flow batteries is low, and lithium-ion batteries with lithium titanate as the negative electrode show comprehensive performance advantages. Figure 5 is a schematic diagram of the working principle of lithium-ion batteries with lithium titanate as the negative electrode.

Since lithium titanate is a zero-strain material, it can avoid structural damage caused by the expansion and contraction of electrode materials, thereby greatly improving the service life of lithium-ion power batteries; and since lithium titanate has a high working potential, it is difficult to form lithium dendrites on the negative electrode even if it is overcharged, thereby greatly improving the safety of lithium-ion power batteries. These improvements make it possible to use lithium-ion power batteries in the field of energy storage. At present, lithium-ion power battery energy storage technology with lithium titanate as the negative electrode is becoming a hot spot for development at home and abroad. In 2008, Altairnano, an American company, developed a 1MW lithium titanate energy storage battery system. After trial operation, it was shown that it can output 250kWh of energy with an energy conversion efficiency of more than 90%. In 2010, Toshiba of Japan announced at its annual business policy meeting that it would use lithium titanate negative electrode materials to develop super lithium batteries (SCiB) for energy storage. With the successful commercialization of high-power SCiB lithium titanate batteries, it is expected that Toshiba's SCiB energy storage batteries will soon be available on the market. After five years of technical development, CITIC Guoan Mengguli Power Technology Co., Ltd. in China developed a 35Ah battery for energy storage in 2010.

The battery has a cycle life of nearly 8,000 times, can be charged and discharged at a rate of 5C, and has excellent safety performance. The company is currently working with partners to develop a megawatt-level energy storage system, and it is expected that the product will be available for sale in the market in 2011.

In addition to lithium-ion power batteries with lithium titanate as the negative electrode, which can be used in the energy storage field, with the application of lithium iron phosphate positive electrode materials, the life and safety of traditional carbon negative electrode lithium-ion power batteries have also been greatly improved, and can also be used in the energy storage field. In 2010, Sony launched a 1.2kWh lithium iron phosphate energy storage battery module with a maximum output power of 2.5kW. However, lithium iron phosphate batteries still have serious consistency problems. Even if the life of a single battery can reach more than 2,000 times, the life of the battery group will be greatly reduced. In addition, the core patents of lithium iron phosphate materials are in the hands of some large international companies, and the production of lithium iron phosphate batteries will face patent disputes. Therefore, the use of lithium titanate lithium-ion batteries for energy storage in lithium-ion energy storage battery products should be the most feasible technical route.

3. Other energy storage technologies

Superconducting electromagnetic energy storage is to convert electrical energy into magnetic energy and store it in the magnetic field of the superconducting coil, and realize the charging and discharging of the energy storage device through electromagnetic mutual conversion. Since the coil has no resistance in the superconducting state, the energy loss of superconducting energy storage is very small. However, since the superconducting state requires the coil to be at an extremely low temperature to be realized, and low temperature consumes a lot of energy and is not easy to miniaturize, this technology is in the research and development stage.

Phase change energy storage is to absorb or release energy through phase change of certain substances at a specific temperature, such as ice storage and water storage. It can be applied to central air conditioning and other fields. It is an emerging energy storage technology.

lithium battery 18650 3.7v energy storage-technology is approaching maturity and overall cost reduction

Lithium-ion batteries are the most common energy storage technology on the market, and are widely used in various personal electronic products, mobile devices and even electric vehicle batteries. The lithium batteries we usually refer to are lithium-ion batteries, which are generally divided into energy storage lithium batteries and power lithium batteries according to their uses. Energy storage lithium batteries are used in photovoltaic or UPS. They have a relatively large internal resistance and a slow charging and discharging speed, generally 0.5-1C. Power batteries are generally used in electric vehicles. They have a small internal resistance and a fast charging and discharging speed, generally reaching 3-5C. They are about 1.5 times more expensive than energy storage batteries.

Energy density, power density, safety performance, charging time, and environmental resistance to high and low temperatures are the five major indicators for evaluating the performance of lithium batteries. At present, my country has initially met the standards for the last four points in lithium battery 18650 3.7v technology, but the energy density needs to be further refined and improved. On March 1, 2017, the Ministry of Industry and Information Technology, the National Development and Reform Commission, the Ministry of Science and Technology, and the Ministry of Finance jointly issued the "Action Plan for Promoting the Development of the Automotive Power Battery Industry". The "Plan" requires major breakthroughs in key materials and components of power batteries. By 2020, key materials and components such as positive and negative electrodes, diaphragms, and electrolytes will reach the world's first-class level, and the upstream industrial chain will achieve balanced and coordinated development, forming innovative backbone enterprises with core competitiveness. The plan's requirements for battery specific energy are bound to trigger a new round of high energy density material boom.

The currently popular lithium titanate material is also worthy of attention. It can replace graphite as a negative electrode material. Although the energy density is not high, lithium titanate can enable the battery to achieve high-rate charge and discharge, and has excellent safety performance and long cycle life. It is reported that the fourth-generation high-energy-density lithium titanate battery currently developed by Yinlong has a 40% lower cost and a 60% higher energy density than the third generation. The industry optimistically predicts that lithium titanate batteries may form a three-legged situation with ternary lithium batteries and lithium iron phosphate batteries in the future.

Although the high cost of lithium-ion batteries is a severe challenge facing the development of the industry, many companies have been committed to improving the cost-effectiveness of lithium-ion batteries. According to the analysis of lithium battery 18650 3.7v prices by EnergyTrend analyst Duff (Lv Lishun), the price of lithium batteries has risen slightly in the first, second and third quarters of 2017, but overall, in recent years, with the continuous expansion of market demand for lithium batteries and the large-scale mass production of lithium batteries, the cost is declining year by year, and the current price is sufficient for commercial development and widespread use.

In addition, after the power lithium battery 18650 3.7v decays to less than 80% of the initial capacity, it can be used in the energy storage field in stages, further reducing the cost of energy storage lithium batteries.

Technology life, policy determines the market

After a long period of development and progress, photovoltaic technology has been widely recognized for its main technical framework and its economic efficiency. With the dual support of national policies and the market, it has developed well. Unlike photovoltaic technology, energy storage technology is still in the stage of continuous breakthroughs, and there is still room for narrowing the technological gap between China and foreign countries. From lithium iron phosphate batteries to ternary lithium batteries, and then to the currently popular lithium titanate materials, technological changes always affect the cost of lithium batteries and the balance of the industrial chain. Therefore, investors have to face the risk of technological upgrading when investing in large-scale production, and they are left behind by a dimension if they are not careful.

In addition, many companies are still waiting for the country to introduce subsidy policies, such as large-scale subsidies for the energy storage industry like subsidies for the photovoltaic industry, so they are still in a wait-and-see attitude. In fact, whether there will be subsidies or not, companies that rush into the market first will inevitably seize the market high ground.

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