As the material basis for the progress of human civilization, energy has always played an important role and is an indispensable guarantee for the development of human society. Together with water, air, food, etc., it constitutes the necessary conditions for human survival and directly affects human life. .

The development of the energy industry has gone through two major changes, from the "era" of firewood to the "era" of coal, and then from the "era" of coal to the "era" of petroleum. It has now begun to move from the "era" of petroleum to the "era" of renewable energy. transformation.

From coal in the early 19th century to petroleum in the mid-20th century, humans have been using fossil energy on a large scale for more than 200 years. However, the global energy structure dominated by fossil energy means that the day when fossil energy is exhausted is no longer far away.

The three traditional economic carriers of fossil energy, represented by coal, oil and natural gas, will be rapidly depleted in the new century. During their use and combustion, they will also cause the greenhouse effect, produce a large amount of pollutants, and pollute the environment.

Therefore, it is imperative to reduce dependence on fossil energy, change the existing irrational energy use structure, and seek clean, pollution-free new renewable energy.

At present, renewable energy mainly includes wind energy, hydrogen energy, solar energy, bioenergy, tidal energy, geothermal energy, etc., and wind energy and solar energy are currently hot research topics around the world.

However, it is currently difficult to achieve efficient conversion and storage of various renewable energy sources, making it difficult to effectively utilize them.

Under this situation, in order to realize the effective utilization of new renewable energy by mankind, it is necessary to develop convenient and efficient new energy storage technology, which is also a hot topic in current social research.

  one

At present, lithium-ion batteries, as one of the most efficient secondary batteries, have been widely used in various electronic devices, transportation, aerospace and other fields. However, with the increase in energy utilization, lithium elements have been sold out due to low reserves and high prices. The development prospects are difficult.

Sodium and lithium have similar physical and chemical properties and have energy storage effects. Because of their rich content, uniform distribution of sodium sources, and low prices, they can be used in large-scale energy storage technologies with low cost and high benefits.

The positive and negative electrode materials of sodium-ion batteries include layered transition metal compounds, polyanion types, transition metal phosphates, core-shell nanometers, metal compounds, hard carbon, etc.

Carbon, as an element that is extremely abundant in nature, is cheap and easy to obtain, and has gained a lot of recognition as an anode material for sodium-ion batteries.

According to the degree of graphitization, carbon materials can be divided into two categories: graphitic carbon and amorphous carbon.

Hard carbon, which belongs to amorphous carbon, shows a specific sodium storage capacity of 300mAh/g. However, carbon materials with a higher degree of graphitization are difficult to meet commercial applications due to reasons such as large surface area and strong order.

Therefore, non-graphite hard carbon materials are mainly used in actual research.

In order to further improve the performance of sodium-ion battery anode materials, the hydrophilicity and conductivity of carbon materials can be improved through ion doping or composite methods to enhance the energy storage performance of carbon materials.

As anode materials for sodium-ion batteries, metal compounds are mainly two-dimensional metal carbides and nitrides. In addition to having excellent properties of two-dimensional materials, they can not only store sodium ions through adsorption and intercalation, but also interact with sodium. Ions combine to generate capacitance through chemical reactions for energy storage, thereby greatly improving the energy storage effect.

Due to the high cost and difficulty in obtaining metal compounds, the current negative electrode materials for sodium-ion batteries are still mainly carbon materials.

The rise of layered transition metal compounds was after the discovery of graphene. The two-dimensional materials currently used in sodium-ion batteries mainly include sodium-based layered NaxMO4, NaxCoO4, NaxMnO4, NaxVO4, NaxFeO4, etc.

Polyanionic cathode materials were first used in lithium-ion battery cathodes, and were later used in sodium-ion batteries. The main representative materials include olivine crystals such as NaMnPO4 and NaFePO4.

Transition metal phosphate was originally used as a cathode material in lithium-ion batteries. The synthesis process is relatively mature and there are many crystal structures.

As a three-dimensional structure, phosphate builds a framework structure that is conducive to the deintercalation and insertion of sodium ions, thereby obtaining a sodium-ion battery with excellent energy storage performance.

The core-shell structural material is a new type of sodium-ion battery cathode material that has emerged in recent years. This material has achieved a hollow structure based on the original material through exquisite structural design.

The more common core-shell structure materials include hollow cobalt selenide nanocubes, Fe-N co-doped core-shell sodium vanadate nanospheres, porous carbon hollow tin oxide nanospheres and other hollow structures.

Due to its excellent characteristics and unique hollow and porous structure, more electrochemical activity is exposed in the electrolyte, and it also greatly promotes the ion mobility of the electrolyte to achieve efficient energy storage.

  two

The continued growth of global renewable energy has promoted the development of energy storage technology.

At present, according to different energy storage methods, it can be divided into physical energy storage and electrochemical energy storage.

Electrochemical energy storage meets the development standards of today's new energy storage technology due to its advantages of high safety, low cost, flexible application, and high efficiency.

According to different electrochemical reaction processes, electrochemical energy storage power sources mainly include supercapacitors, lead-acid batteries, fuel cells, nickel-metal hydride batteries, sodium-sulfur batteries, and lithium-ion batteries.

In energy storage technology, flexible electrode materials have attracted the research interest of many scientists due to their design diversity, flexibility, low cost, and environmental protection.

Carbon materials have special thermochemical stability, good electrical conductivity, high strength, and unusual mechanical properties, making them promising electrodes for lithium-ion and sodium-ion batteries.

Supercapacitors can charge and discharge quickly under high current conditions, and have a cycle life of more than 100,000 times. They are a new type of special electrochemical energy storage power source between capacitors and batteries.

Supercapacitors have the characteristics of high power density and high energy conversion rate, but their energy density is low and they are prone to self-discharge and electrolyte leakage when used improperly.

Although fuel cells have the characteristics of no need for charging, large capacity, high specific capacity and wide specific power range, their high operating temperature, high cost and low energy conversion efficiency make them only be used in certain applications during commercialization. used in some specific fields.

Lead-acid batteries have the advantages of low cost, mature technology, and high safety, and have been widely used in signal base stations, electric bicycles, automobiles, and grid energy storage. However, they are low in energy density, large in size, short in life, and Shortcomings such as environmental pollution make it unable to meet the increasingly higher requirements and standards for energy storage batteries.

Nickel metal hydride batteries have the characteristics of strong versatility, low heat generation, large cell capacity, and stable discharge characteristics. However, they are relatively heavy and have many problems in battery series management, which can easily cause the single cell separators to melt.

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