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For industrial vehicles, the choice of lithium batteries used must be high standards, strict requirements, to protect the quality. Because most industrial vehicles in operation are to complete very difficult operations, or in some field environment to perform special tasks of construction work, so the need for better safety performance of the lithium battery, the current industrial vehicles are basically adopted by the passenger car standards. In the end, the lithium battery is mainly reflected in the excellent performance, derived from the material and process. The following is a specific look at industrial vehicles lithium battery should be selected from which aspects?
First, the choice of materials for the battery cell
Power lithium battery ternary lithium and lithium iron phosphate, compared to the following:
Ternary lithium outer packaging is a soft package, lithium iron phosphate outer packaging is mostly aluminum shell or plastic shell. Ternary lithium energy density is slightly higher than lithium iron phosphate;
Lithium iron phosphate material pyrolysis temperature of about 800 ℃, ternary lithium about 200 ℃. The chemical reaction of ternary lithium is more violent, releasing oxygen molecules and causing rapid combustion of the electrolyte under high temperature. Therefore, ternary lithium is mainly used in 'automotive lightweight' small passenger cars, while lithium iron phosphate is mainly used in buses and industrial vehicles;
the cycle life of ternary lithium batteries is generally only 1/3 to 1/2 that of lithium iron phosphate;
Tributary lithium is higher in price than lithium iron phosphate.
Two, the core manufacturing
The core accounts for 80% of the cost of the finished product after Pack, and there are about 600 lithium battery factories in China. Product type, production scale, quality process, quality, price and customer market vary, the gap is large.
The country is currently the world's largest producer of lithium iron phosphate batteries. Because of its standardized management, strict selection of raw materials (positive and negative electrode materials, electrolyte, diaphragm, etc.), high degree of equipment automation and large production scale, the quality of its lithium battery cells is generally considered the best.
Third, the choice of electric cores
As an industrial product, even if the cells are produced 30 seconds before and after, their capacity, internal resistance, voltage and other parameters are all different to a greater or lesser extent. The consistency of the cells in the finished battery directly affects the life and discharge capacity of the battery. It is recommended to choose batteries with voltage deviation within 20mv between cells; for vehicles with frequent use, choose cells with voltage deviation within 10mv.
The higher the consistency of the battery, the more evenly the cells share the capacity, the more stable the capacity and output of each cell, and the longer the life of the battery, which will not easily produce the phenomenon of rapid decay of new batteries after 1-2 years of use.
Whether a battery is an A-grade or B-grade cell, without professional equipment, it is impossible to tell even if the cells are in front of you. In fact, as long as the cells and Pack finished system through the testing agency certification, is a performance guarantee of lithium batteries!
Four, Pack integration process
Li-ion battery pack safety protection is divided into four stages, from the battery pack inside out protection are: cell protection safety valve, short circuit protection circuit between cells, fuse blowing protection, BMS main circuit on/off protection.
The cell protection safety valve is the most important protection barrier inside the cell, just like an airbag in a car;
Inter-cell short circuit protection is vital for inter-cell short circuits due to external device failure and is equivalent to placing a number of fire hydrants directly on the cell;
Fuse fuse protection is a common device and will not be repeated;
BMS main circuit protection is one of the most basic functions of a BMS. Protection is provided by disconnecting a relay or MOSFET static power electronic switch connected in series on the main circuit to disconnect the main circuit of the battery.
The high safety process standards of the finished Pack system are currently only available to the automotive industry with stringent testing requirements. Only Pack products that have passed strict safety tests can be used in automotive applications. These standards include short circuit, disconnection, misfire, waterproof, heavy pressure, puncture, etc.
V. Battery cell protection
Lithium battery is an active material battery with a very small internal resistance, about one tenth of that of lead-acid batteries. Therefore, the battery overcharge and discharge, high and low temperature, inrush current, short circuit and other hazardous conditions should be monitored in real time to cut off the source of danger in time.
The BMS can respond within microseconds to cut off the main circuit of the battery to ensure the safety of the battery and personal property; at the same time, the BMS with full-time active equalisation circuit can ensure that the battery can be recharged or discharged by the equalisation circuit in time when inconsistencies arise after long-term use, which can effectively extend the life of the battery by at least 30%.
Sixth, the case design
Professional industrial design of the case must take into account the mechanics and thermal model, the energy density of lithium batteries is more than three times that of lead-acid batteries. Therefore, the lithium battery case is smaller than the lead-acid battery case. The lithium battery case must have the functions of impact-proof, puncture-proof, waterproof, heat dissipation and cold-proof. For example, in the north of China, due to long periods of low temperature weather, forklift lithium batteries should be equipped with heating protection devices, access to the cold storage environment to eliminate the risk of short circuit caused by condensation in the design and so on.
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