Recently, the “Brand power · 2021 China Carbon Neutral Summit Global Top 20 Companies Press Conference on PV/Energy Storage Industry 2021” sponsored by 365 photovoltaic, 365 energy storage and smart energy was successfully held in Hangzhou. Dozens of industry leaders gathered at the scene, and nearly 300 industry colleagues attended the meeting. They conducted in-depth discussions on topics such as dual carbon goals, market development and product technology, and pointed out the direction for energy enterprises to plan their development direction and market strategy.
Sicon Chat Union Electric Co., Ltd. was invited to participate in the forum. Li Shiwei, director of the company’s R & D center, took “lithium battery safety cannot be compromised” as the theme, expounded on the application of lithium battery, energy storage safety, cause analysis and measures, and provided safety solutions for lithium battery management in energy storage application.
What are the hidden dangers of lithium batteries in energy storage applications?
In the commercial energy storage system, lithium batteries are widely used. From the perspective of user side energy storage, peak shaving and valley filling can save a lot of electricity charges for industries and enterprises, and generate higher revenue. In the power generation side and power grid side, it can play the functions of peak load regulation, frequency regulation and power quality adjustment, creating higher value for the whole power system.
While widely used, there are also some security risks. The safety accidents of energy storage power station are mainly fire or explosion accidents. The safety application of battery has become the front-line “focus” of energy storage system technology research and development. What are the main causes of such accidents?
In the final analysis, fire and explosion are a form of energy. From the aspect of battery, firstly, the overheating of the cell is out of control, which will cause serious thermal impact on the surrounding cells; Secondly, if the cell overheats out of control, the electrical insulation of the surrounding cells will be damaged, which will lead to a chain reaction of the battery pack; In addition, after the thermal runaway of the cell, it can not be separated from the system in time, leading to the further expansion of the accident. Even if the fire protection system is involved, the fault is difficult to be effectively suppressed.
How to improve the safety and reliability of energy storage system?
At present, the price war in the energy storage industry is intensifying. “There is no minimum, only lower.” Irrational competition may bury hidden product quality risks and cause safety issues. Faced with the phenomenon of “bad money driving out good money”, SCU insists on “safety first, never compromise”, working hard on technology to improve the core competitiveness of its products.
Selection of battery cell
The selection of battery cells is the first step in safety. At present, the mainstream materials on the market are ternary lithium and lithium iron phosphate. After comparing the performance of the two materials, we chose lithium iron phosphate with higher safety performance.
The key indicators of the safety of high power lithium batteries are reflected in two points: the heat generation rate of the battery and the rate of chemical decomposition of the material.
From the point of view of heat generation rate, in the state of thermal runaway, ternary lithium is 200°C/S, and lithium iron phosphate is 1°C/MIN. The temperature rise of ternary lithium is fast, and there is no emergency treatment time after thermal runaway occurs. The temperature rise characteristics of lithium iron phosphate can buy time for triggering external emergency actions when thermal runaway occurs.
From the perspective of chemical decomposition speed, lithium iron phosphate is about 700°C, and ternary lithium is about 200°C. Undoubtedly, lithium iron phosphate has more stable characteristics and is suitable for energy storage systems.
Design of battery pack
At present, most of the common PACK forms are that all the cells are closely arranged, and there is no gap between the cells. Once a single cell fails, the internal heat is out of control, which will cause the temperature of the cell to rise sharply and the shell thermally expands. The cells are closely arranged, not only the high temperature will be transmitted to other cells, but also the insulation will be destroyed, causing unpreventable short circuits, further expanding the impact of the fault, leading to the paralysis of the entire system.
When designing the battery module, SCU fully considered the gap between the cells and developed and produced a thermally isolated insulating bracket. Adopting 7mm spacing to fix adjacent cells, so that each cell has a good air-cooled channel, which can meet the application of high-rate charging and discharging. In the cell thermal runaway state, it can still ensure that the heat transfer efficiency is less than 0.5% and ensure effective electrical insulation, which significantly improves the safety of the lithium battery system.
Battery Management System
The battery management system is one of the core components of the energy storage system, which can ensure that the battery cells have excellent performance in terms of safety, lifespan, and discharge capacity after they are grouped. SCU adopts two-way active balanced control technology for battery cell management, BMS adopts three-level architecture management, and the system adopts three-level safety prevention and control measures, multiple monitoring and hierarchical linkage, which can ensure the safe and efficient operation of the entire system while also being effective. Make up for the impact of the inconsistent capacity changes of single cells on the cycle life of the entire system.
Practical application of SCU technology in energy storage
GRES System (Microgrid system)
Multi-functional Bidirectional PCS(MPCS)
Intelligent lithium battery system