With the increasingly stringent requirements for global carbon emissions and the energy shortage in European countries caused by the Russian-Uzbekistan war, the application of new energy, mainly represented by solar energy, has reached a climax. Solar power generation has serious instability. With the significant change of power generation in daytime and sunny days, the demand for energy storage becomes more and more important. As a basic small unit of life, household energy storage batteries have also become people's favorite. However, as a new product, what core components are included in the household energy storage battery, and how the current market situation of these core components is, this article will introduce in detail.
Although it is a household energy storage battery, it is basically the same as the battery for other purposes. It is composed of battery cell (battery monomer), battery management system BMS, housing case, input and output terminals, structural parts, etc. The voltage and capacity required by the household energy storage battery are solved through the series-parallel design of the battery cells. The battery cells are fixed in the chassis by combining the structural parts, and connected to the BMS and then connected to the input and output terminals. Finally, the required energy storage battery can be formed by packaging the chassis. Among these components, the real core is the battery cell and battery management system (BMS), which will be described as below.
1. Lithium ion battery
1.1 According to the chemical material system, lithium-ion batteries are divided into ternary lithium batteries and lithium iron phosphate batteries. Due to high chemical activity and poor safety performance, ternary lithium batteries are gradually replaced by lithium iron phosphate batteries with higher safety performance and longer service life in the fields of electric vehicles and household energy storage batteries. From a global perspective, except for Tesla TESLA and LG Chem, which use ternary lithium batteries for household energy storage battery products, other manufacturers have basically chosen the lithium iron phosphate battery route. Let the market lose patience and confidence in ternary lithium batteries.
1.2 Lithium iron phosphate batteries include three structural forms, namely: cylindrical batteries, square aluminum shell batteries and soft-pack batteries. As a finished household energy storage battery, it doesn’t care too much about the structure of its battery core, but many buyers will prefer a certain form of product due to misleading information, and even a few people think that lithium iron phosphate battery The core is the vague concept of the square battery. In fact, these three types of batteries can theoretically be used in household energy storage batteries, the key lies in the design of the structure, optimization of heat dissipation, cost control and other aspects. Most factories use square shell LiFePO4 batteries now. Because it has higher energy density than cylindrical battery and more easy to pack than soft-pack battery.
1.3 Quality for LiFePO4 battery cell
No matter what kind of battery cell, its quality level is uneven. Roughly speaking, the same model of the same manufacturer can be basically divided into three categories: qualified product (A product), downgraded product (B product) and disassembled product, and the quality level of the battery cell used by the household energy storage battery manufacturer is very important to the seller. The language is basically "secret", but the product application experience will vary widely.
1.3.1 Qualified products (A products): Products that meet certain quality standards, but the so-called "standards" will also be different. For small household energy storage battery(5-20KWH), it is not necessary to adopt the automotive grade standard, because it will significantly increase the cost. Generally, batteries that meet the designed capacity, voltage, self-discharge, and more than 2,000 cycles at room temperature under 100% DOD can be applied to household energy storage, but effective pairing of batteries is required.
1.3.2 Degraded products (B products), also known as A-products: it is impossible to really know the reason why they become B products. At the same time, there are many types of degraded products, which may be caused by insufficient capacity, excessive internal resistance, excessive self-discharge, poor internal moisture control, etc. Different degradation causes have different results.
1.3.3 Disassembled products: it is known as second life or old battery. They cycle life would be much less than 2000times.
For consumer, it is hard to recognize which quality level it is from appearance. After a period time of usage, Grade B or disassembled product has shorter working time, service life or other quality problems. So make sure to order the battery from reliable supplier who can assure you Grade A quality.
2. BMS(Battery Management System)
In the energy storage battery, the battery management system BMS is one of the very important components, which determines the safety, life and matching functions and performance of the battery. It can even be said that the BMS is the "brain" of the energy storage battery. As one of the core components of household energy storage batteries, how to identify or identify the quality of BMS has become a difficult problem for many businesses. In my opinion, there are nothing more than the following points:
2.1 All lithium-ion batteries need to be protected by external circuits, which is different from lead-acid batteries and nickel-metal hydride nickel-cadmium batteries. However, there are also differences in protection circuits, which are divided into hardware solution protection circuits (commonly known as: protection boards) and software intelligent control circuits (that is, what we call BMS). The function of the protection board is relatively simple. It mainly protects the lithium battery from overcharge and over discharge, overcurrent, overtemperature and short circuit. The degree of intelligence is not high, and it basically belongs to the form of passive protection. The BMS is relatively intelligent, and can calculate the battery's state of charge SOC and health state SOH, etc., and can even take the initiative to intervene after learning, and carry out effective management through monitoring data in turn. At present, in order to pursue cost, some manufacturers in the world use protection boards to passively protect energy storage batteries for more than 5Kwh, that is not acceptable for customers.
2.2 The core technology of BMS---SOX algorithm. For the state of charge SOC and health status SOH of the battery, only accurate calculation can be effectively managed, so the SOX algorithm has become one of the core technologies of BMS, especially for the lithium iron phosphate battery system that is more common for household energy storage batteries It is more difficult. The traditional algorithm is based on the method of "ampere-hour integration + voltage calibration", which is also commonly used in the world. However, for lithium iron phosphate, the accuracy of this algorithm is poor and the calibration voltage varies greatly, which leads to problems in actual use. Large errors, especially after a period of cycle use will become more and more obvious. At present, there are many kinds of algorithm technologies on the market, but few of them are actually applied. This is also one of the technical bottlenecks in the development of new fields such as new energy vehicles and energy storage.
2.3 BMS communication: In the actual use of household energy storage batteries, the energy storage battery is connected to the inverter (or charging and inverter integrated machine), in the intelligent control and management system, how to let the inverter know the energy storage The real-time status of the battery in order to better use the energy storage battery? This requires a communication protocol to solve. The so-called communication protocol is simply understood as a dialogue language agreed in advance, and there is no novel technology. However, as a BMS of an energy storage battery, how many inverters can communicate with it is very critical, because the existence of inverters in the world is much longer than that of energy storage batteries, so energy storage batteries are required to be compatible with different versions of inverters Device communication, no technical threshold but requires a lot of accumulation.
To sum up, as the two core components of household energy storage batteries, battery cells and BMS are very important in products, especially in the current world, which has brought many uncertain choices to the market, and even vicious competition. It will be a fatal blow to the entire industry, so it is necessary to standardize products including customers and manufacturers to let the market enter a healthy and orderly development path.
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