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Research progress of electrochemical energy storage technology

 

Abstract: energy storage technology is a technology which may bring revolutionary changes to the future energy system development and operation. Among the many energy storage technologies, the most rapid progress is the electrochemical energy storage technology. Lithium ion batteries, sodium sulfur batteries, and battery operated electrochemical energy storage technologies have made great breakthrough in safety, energy conversion efficiency and economy. In this paper, the principle of electrochemical reaction, the characteristics of the system and the development of various materials are introduced.

 

With the popularization and application of renewable energy in the world, the rapid development of electric vehicle industry and the construction of smart grid, energy storage technology has become the key link to restrict or promote energy development. The essence of energy storage is the storage of electrical energy, which is released when needed. At present, renewable energy technologies include wind, solar, hydro power. They are quite unpredictable and changeable characteristics, which has a great impact on the reliability of the power grid, the development of energy storage technology can effectively solve this problem, the renewable energy technology in a stable form of storage and application. In addition, as the future direction of the development of power grid, smart grid through the energy storage device for peak load regulation, in order to increase the capacity of transmission and distribution systems and optimization efficiency. Energy storage technology can be widely used in the power generation, transmission, distribution and use of the power industry.

 

The current energy storage technologies include mechanical energy storage, chemical energy storage, electromagnetic energy storage and phase change energy storage. Mechanical energy storage can be divided into pumping energy storage, compressed air energy storage and flywheel energy storage. The problem is the high requirements for the site and equipment, which has the characteristics of regional and early investment. Chemical energy storage is a device which can directly convert electric energy by chemical reaction, including electrochemical energy storage. Electromagnetic energy storage mainly refers to the superconducting energy storage, the main problem is the high manufacturing cost and low energy density. In the same way, the energy storage efficiency of the stored energy is lower than that of the stored energy. Compared with other methods, electrochemical energy storage has the advantages of convenient use, less environmental pollution, without geographical restrictions, not by the Kano cycle limit, high conversion efficiency, high specific energy and power in the energy conversion.

 

Since 1859 since the invention of Leclanche battery, all kinds of chemical batteries on behalf of electrochemical energy storage always toward high capacity, high power, low pollution and long life, high safety of the direction of development, involving various forms of energy storage system, has become the most important in the field of energy storage component.

 

Electrochemical energy storage including lead-acid battery, lithium ion battery, sodium sulfur battery and vanadium redox flow battery, zinc air batteries, nickel hydrogen batteries, fuel cells and supercapacitors, including lead-acid battery, lithium ion battery, sodium sulfur batteries and flow battery is a hot research topic and focus. Table 1 gives a detailed comparison of the parameters of these electrochemical energy storage cells.

 

 

  1, lead-acid battery

 

Lead acid battery is the earliest commercial energy storage battery system, which is mainly made up of sulfuric acid solution. Under the condition of the lead-acid battery, the main component is the lead, and the main components of the positive and negative electrodes are in the discharge state. Expressed as a chemical reaction equation:

 

The early use of lead-acid battery electrolyte flow system, when the battery is charging state will consume the water in the electrolyte, anode and cathode respectively in the generation of oxygen and hydrogen, so the need to maintain water electrolyte balance time during use. At the same time, there are many problems in the early lead acid battery, such as overcharge, acid leakage, positive plate deformation and so on.

 

By the end of twentieth Century, the application of valve control technology has brought a major technological breakthrough for lead-acid batteries. The principle of valve regulated lead acid (VRLA) battery is to absorb a certain amount of electrolyte in the pole piece and the partition board, so as to increase the oxygen absorption capacity of the negative electrode and prevent the loss of the electrolyte. In a sealed system, when the battery overcharge to achieve an internal oxygen cycle, oxygen and negative reaction of cathode spongy lead, the cathode part is not full, preparing cathode hydrogen production, so as to effectively solve the problem of the loss of electrolyte and acid leakage etc.. VRLA battery specific energy can reach 35Wh/kg or 70Wh/L at the same time, power and energy efficiency reached 90% and 75%, and the monthly self discharge is lower than 5%, the life cycle can reach 8 years, 1000 charge discharge cycles. Because of its low cost, low cost, good reliability and mature technology, lead-acid batteries have been widely used in automotive batteries and various kinds of standby power supply.

 

The lead-acid battery in the battery market share as high as 30%, but the positive active material of lead acid battery, softening and shedding of grid corrosion, anode active material of irreversible sulfation, resulting in short cycle life, under the condition of high temperature is more serious.

 

In recent years, the use of carbon as the active material carrier of lead-acid battery can greatly increase the specific energy and specific power. The prototype of &mdash battery; — super lead carbon battery, which is equivalent to an electric double layer capacitor lead-acid battery in parallel with the traditional use of lead carbon batteries with high power and high energy capacitor of the traditional lead-acid battery. Because the carbon can buffer sharing charge / discharge current and lead electrode, especially at high rate current charge / discharge, the composite anode plate of carbon in the first rapid response, can reduce the impact of large current lead negative plate, improve the service life of the battery (> 5000). However, the biggest problem is the existence of super batteries in the production process will inevitably lead to heavy metal pollution, although can be inhibited by technological innovation, but

It is difficult to avoid the environmental problems caused by the material itself.

 

2, lithium ion battery

 

Lithium ion batteries have been widely used in portable electronic products such as mobile phones, laptops, cameras and so on. The working principle of lithium ion battery mainly depends on the lithium ion in the cathode material (metal oxide) and the negative electrode (graphite) between the embedded and out of energy storage and release. Expressed as a chemical reaction equation:

It can be seen from the above reaction, lithium ion battery has a high operating voltage (3.7V), the specific energy can reach 150Wh/kg. The performance of lithium ion batteries mainly depends on the development of electrode materials and electrolytes. In 1970, the layered TiS2 embedded materials were first used as cathode materials, and the cathode materials of lithium ion batteries are mainly concentrated in LiCoO2, LiNiO2, LixMn2O4 and LiFePO4.

 

LiCoO2 because of its high electrochemical capacity, high voltage, good cycle performance and other advantages, is the first choice of cathode materials for lithium ion batteries, but due to lack of resources, cobalt toxic and high price reasons, limit the application of more extensive, especially the application of electric vehicles and large-scale energy storage applications. Compared with LiCoO2, LiNiO2 has a higher specific energy than the LiCoO2, at the same time, it has low price, no pollution and low self discharge. However, due to the difficulties of preparation, low safety and poor stability, the development of LiNiO2 cathode materials is slow.

 

LixMn2O4 has a three-dimensional tunnel structure, is beneficial for lithium ion insertion and extraction, and resource reserves, low price, high safety, is a promising cathode material of lithium ion battery, but its capacity is lower than that of LiCoO2 in 30% (110Ah/kg), and the presence of manganese ions dissolved problems caused by the high temperature cycle of the poor, which limits its application in high energy density batteries, but is expected to play a role in the field of mass storage in the future.

 

LiFePO4 is a kind of olivine phosphate compounds, it has the discharge platform stability, structure stability during charge and discharge, high safety, low cost, no environmental pollution, capacity up to 160Ah/kg, is a kind of lithium ion Chi Zhengji material system developed quickly in recent years, widely used in electric vehicles and the field of energy storage. The main problem of LiFePO4 is the low density of solid and the poor conductivity of electrons and ions, which can be used to improve the electrochemical performance of LiFePO4 by the methods of nano materials, two granulation, carbon coating and doping.

 

At present, the commercial anode materials of lithium ion batteries are mainly graphite carbon materials, the theoretical capacity is 372Ah/kg. Some other non carbon materials, such as silicon, tin alloy anode materials, while having high lithium storage capacity, but due to the lithium intercalation structure instability, poor cycle stability, the first week of the irreversible capacity and other factors, there is still a long distance from the commercial road.

 

Overall, the lithium ion battery has high output voltage, high specific energy, high specific power, high charge discharge efficiency, long cycle life, self discharge, the advantages of environmental friendly, but applied to large capacity storage is still facing the safety and cost of the battery problem. The safety problems of lithium-ion batteries will be greatly improved with the safety of the electrode materials, the safety protection measures inside and outside the battery, and the reasonable and safe battery structure design. At the same time, with the improvement of technology development and cell preparation material preparation technology, the cost of lithium ion battery is expected to further reduce, which will lead gradually to the high power lithium ion battery system such as electric vehicles and large-scale energy storage batteries and other areas of expansion, may become a leader in the field of energy storage.

 

3, sodium sulfur battery

 

Sodium sulfur battery was invented by the Ford Motor Co in 1967, originally designed for electric vehicles, and then to the field of energy storage. Sodium sulfur battery using the tubular design center with sodium cathode tube (β -Al2O3 ceramic tube) as electrolyte, and plays the role of sodium containing metal, the outer tube is a composite material or metal material for stainless steel, non metal sulfur containing cathode materials. At a certain operating temperature (above 290 DEG C), sodium ions react reversibly with the electrolyte membrane to form energy release and storage. Expressed as a chemical reaction equation:

 

 

 

Sodium sulfur battery rated voltage is 2V, without any adverse reaction in the work process, with high specific energy (150~240Wh/kg) and power (150~230W/kg), high energy storage and conversion efficiency (90%), no self discharge, long cycle life (3000), friendly to the environment. At present, the capacity of sodium sulfur battery designed in our country is 650Ah, the power is 120W, through the combination of the monomer and the series connection, it can reach megawatt level, which can be used directly in the large energy storage system. China has not yet built a sodium sulfur storage power plant, the Chinese Academy of Sciences, Shanghai Institute of silicate and Shanghai Power Co cooperation in the development of large capacity energy storage sodium sulfur batteries in the demonstration phase. In Japan, there are as many as 30 sodium sulfur battery energy storage power station for peak load regulation, the total power of 20MW. The problem of sodium sulfur battery is the largest in the temperature above 290 DEG C, put forward higher requirements on the stability of electrode materials, especially the corrosion resistance of ceramic membrane and sulfur electrode needs to be further improved, and the high cost of sodium sulfur battery is also restricting the development of the important factors. However, with the development of material technology and the optimization of material cost and production cost, sodium sulfur battery will occupy an important place in the field of energy storage.