Electrochemical energy storage mainly includes various secondary batteries, such as lead-acid batteries, lithium-ion batteries, sodium sulfur batteries, and liquid flow batteries. Most of these batteries are technically mature and have become a focus of attention in recent years, and have also obtained many practical applications.

1. Lead-acid battery

Lead acid batteries are one of the most widely used batteries in the world. The anode (PbO2) and cathode (Pb) in lead-acid batteries are immersed in an electrolyte (dilute sulfuric acid), and a 2V potential is generated between the two electrodes, which is the principle of lead-acid batteries.

Lead acid batteries are often used as emergency or backup power sources in power systems, and in the past, most independent photovoltaic power generation systems were equipped with such batteries. There is currently a trend towards being gradually replaced by other batteries, such as lithium-ion batteries.

2. Lithium ion batteries

A lithium-ion battery is actually a lithium-ion concentration cell, with the positive and negative electrodes composed of two different lithium-ion intercalation compounds.

During charging, Li+is removed from the positive electrode and embedded into the negative electrode through the electrolyte. At this time, the negative electrode is in a lithium rich state and the positive electrode is in a lithium poor state; During discharge, on the contrary, Li+is removed from the negative electrode and embedded into the positive electrode through an electrolyte. The positive electrode is in a lithium rich state and the negative electrode is in a lithium poor state.

Due to its application in portable and mobile devices such as electric vehicles, computers, and mobile phones, lithium-ion batteries have become almost the most widely used battery in the world.

The high energy density and power density of lithium-ion batteries are the main reasons for their widespread application and attention.

Its technology has developed rapidly, and in recent years, large-scale production and multiple applications have led to a rapid decline in its price, resulting in an increasing number of applications in power systems.

Lithium ion battery technology is still under continuous development, and current research focuses on further improving its service life and safety, reducing costs, and developing new positive and negative electrode materials.

3. Sodium sulfur battery

The anode of a sodium sulfur battery is composed of liquid sulfur, the cathode is composed of liquid sodium, and there is a beta aluminum tube separated by ceramic material in the middle. The operating temperature of the battery needs to be maintained above 300 ℃ to keep the electrodes in a molten state.

NGK Corporation in Japan is the only manufacturer in the world capable of producing high-performance sodium sulfur batteries. Currently, a 50kW module is used, which can be composed of multiple 50kW modules to form a MW level high-capacity battery module.

More than 200 such energy storage plants have been built in Japan, Germany, France, the United States, and other places, mainly for load leveling, peak shifting, improving power quality, and renewable energy generation. Battery prices are still relatively high.