Energy storage battery-definition, types and technical analysis

Energy storage technologies include four main types:

● Physical energy storage: 

Pumped storage, compressed air energy storage, flywheel energy storage, seawater energy storage, superconducting energy storage;

● Chemical energy storage: 

Hydrogen and carbon storage;

● Electrochemical energy storage: 

Battery energy storage, super capacitor energy storage;

● Heat and cold storage

Among all kinds of energy storage technologies, battery energy storage is the fastest growing and most concerned energy storage technology direction. This article will mainly introduce the types of energy storage batteries and related technical analysis.

What is energy storage battery

Batteries are used to store electricity. In terms of application, they are energy storage batteries. Therefore, all lithium batteries are energy storage batteries. However, in order to distinguish applications, we can divide batteries into:

● Consumer batteries
● Power battery
● Energy storage battery

Consumer applications are in mobile phones, laptops, digital cameras and other consumer products, while power batteries including power wheels battery are actually a kind of energy storage batteries, mainly used in electric vehicles.

Types of energy storage batteries

There are many characteristic parameters to characterize the performance of energy storage battery, among which the most important are the power characteristics and capacity characteristics of the battery. Therefore, energy storage batteries can be roughly divided into three types according to different requirements for battery power capacity ratio in different energy storage application scenarios:

● Capacity type (≤ 0.5C)
● Energy type (≈ 1C)
● Power type (≥ 2C)

The higher the ratio, the higher the power density of the battery, but the lower the capacity density, and the higher the price per unit capacity. At present, among all kinds of energy storage batteries, liquid flow battery and lithium paste battery are typical capacity batteries, and lithium titanate battery in lithium ion battery is a typical power battery.

Other types of batteries can be adjusted to some extent by changing battery materials and processes to adapt to different energy storage application scenarios.

Comparison of power battery and energy storage battery

Due to the limitation of vehicle volume and weight and the requirements of starting and accelerating, power batteries have higher performance requirements than ordinary energy storage batteries, such as:

● High energy density
● Fast charging speed of battery
● Large discharge current

However, the requirements for ordinary energy storage batteries are not so high. According to the standard, power batteries with a capacity lower than 80% can no longer be used in new energy vehicles, but with a little modification, they can also be used in energy storage systems.

From the perspective of application scenarios, power lithium batteries are mainly used in electric vehicles, electric bicycles and other electric tools, while energy storage lithium batteries are mainly used in peak shaving and frequency modulation power auxiliary services, renewable energy grid connection, micro grid and other fields.

Technical analysis of energy storage battery

In the future, the large capacity battery for power peak shaving and energy storage and the large power battery for power frequency modulation and energy storage still need technological innovation and breakthrough. The technical content of energy storage battery mainly includes six aspects:

● Material technology
● Structural technology
● Manufacturing technology
● Application technology
● Repair technology
● Recycling technology

Material technology

The core materials of the battery like 18650 battery include cathode materials, anode materials and electrolyte materials. The auxiliary materials also include separator, collector and battery shell materials.

In the past three decades, the research and development of lithium-ion battery materials mainly focused on improving the energy density, cycle life and safety performance of materials, and developing low-cost material preparation technologies; The research and development of liquid flow battery materials mainly focuses on the modification of electrolyte and separator materials.

Although the progress of materials can bring about significant improvement in battery performance, the process of material innovation that can have practical effects is actually very slow. Therefore, although battery materials are critical, they are not the whole research of battery technology.

Structural technology

Not all batteries can be called energy storage batteries. Those with system power above 1KW can be called energy storage batteries; The system power ≥ 1MW, and the battery used for energy storage power station is called electric energy storage battery.

The structure technology of energy storage battery includes the internal structure technology of battery cell and the external system structure technology. Different from batteries for small consumer electronic products, energy storage batteries are more complex in structure, with the requirements of series and parallel systems and the characteristics of high power and large capacity.

The existing energy storage and power lithium batteries are developed from small and micro lithium-ion batteries such as mobile phone batteries. From the perspective of internal structure, all types of lithium batteries use adhesive film electrode structure, which brings fundamental structural problems to the design of consistent performance of lithium batteries for energy storage.

In addition, when the battery is scrapped and recycled, only the bonding electrodes can be crushed. The internally broken aluminum foil, copper foil materials and Co, Li elements need to be recycled by metallurgy, resulting in high recovery costs and the risk of pollution treatment of acid and alkali waste liquid.

Manufacturing technology

Energy storage battery manufacturing technology is closely related to battery structure design. The series parallel characteristic of the energy storage battery system requires that the batteries must have good consistency, so the intelligent control of the production process is particularly important.

How to use low-cost equipment and technology to manufacture high-performance energy storage batteries is a contradiction, and also a key issue in the development of energy storage battery manufacturing technology. The existing production process of lithium-ion battery is a transition from the past tape manufacturing process to meet the precision requirements of battery film coating electrode.

In addition, the lack of standardization of battery product models has led to low material utilization rate, low product qualification rate, low equipment operation rate and high manufacturing cost in the battery production process.

Application technology

The application technology of energy storage battery mainly refers to:

● BMS

BMS (Battery Management System) is the link between the battery body and the application end. The main object is the secondary battery. The purpose is to improve the utilization rate of the battery and prevent the battery from overcharging and over discharging.

● PCS

PCS (battery energy storage system energy control device) is a system that is matched with the energy storage battery pack, connected between the battery pack and the grid, and stores the grid energy in the battery pack or feeds the battery pack energy back to the grid.

● EMS

EMS (Energy Management System) is the general term of modern power grid dispatching automation system, including computer, operating system and EMS support system, data acquisition and monitoring, automatic generation control and planning, and network application analysis.

At present, many energy storage demonstration projects are implemented directly by energy storage battery companies and grid companies, and lack of responsibility identification standards and application technology standards, which brings difficulties to the later system operation and maintenance and possible accident identification.

Repair technology

The repair technology of energy storage battery includes electrical maintenance technology and online regeneration technology of battery system. Online regeneration technology is a new technology direction for new energy storage lithium battery. The electrical maintenance technology of battery system includes:

● Environmental corrosion repair
● Electrical insulation aging detection
● Electrical connection detection
● Temperature and pressure sensing maintenance
● Battery inspection technology

Theoretically, in addition to the lattice disorder in the active particles of the battery and the corrosion and shedding of the collector fluid, other interface problems of the energy storage lithium battery may be maintained through online regeneration.

After the battery has been used for a period of time, the battery performance can be repaired by in-situ repair of SEI film on the surface of positive and negative electrode materials, supplement and replacement of electrolyte, etc., so as to extend the actual calendar service life of lithium battery for energy storage.

Recycling technology

Any battery has a life span. At present, the total number of consumer small batteries used in China is several hundred million, and most of them are small in size, with low utilization value of waste batteries. In addition, they are scattered in use, and most of them are treated as domestic waste, with potential pollution.

The discarded energy storage battery cannot be discarded in the environment like the small consumer battery, and must be recycled. Recycling technologies of energy storage batteries include:

● Waste battery replacement technology
● Safe transportation technology
● Recycling technology
● Resource reuse technology

At present, the recovery and regeneration technology of lead-acid batteries is relatively mature, but there is a risk of pollution in the non-standard recovery process.

The recycling process and technology of lithium battery are not yet mature, so it is necessary to combine with material technology and structure technology to develop new energy storage battery technology that is convenient for recycling and regeneration, and make innovation and improvement in product design.

Summary

Among the six technologies of energy storage battery, battery materials are the foundation, and it is very important to focus on the research of new battery materials, while technical engineering projects should focus on breakthroughs in other non material technologies.

Based on the experience of existing commercial and demonstration energy storage power stations, and around the overall goal of low cost, long life, high safety, and easy recycling, various capacity peak valley energy storage batteries should be developed.

The power type FM energy storage battery and energy type composite energy storage battery cooperate with other types of energy storage technologies to support the rapid development of energy storage industry.

“Renewable energy+energy storage” is an inevitable choice for the development of new energy, and the complexity of energy storage application scenarios determines the diversified development direction of energy storage battery technology.

In the future, the large capacity battery for power peak shaving and energy storage and the large power battery for power frequency modulation and energy storage still need technological innovation and breakthrough.