- Battery module design
The battery module is the basic unit of the battery system, including n NCRI8650PF batteries, current collectors, battery holders, conductive copper poles, temperature sensors and other devices. In the process of designing the battery module, it is necessary to fully consider its insulation and fixation.
(1) Choice of battery cell layout
The size of the battery module is closely related to the arrangement of the battery cells. For cylindrical lithium-ion batteries, the battery arrangement includes parallel arrangement and staggered arrangement. Figure 9-5 shows the battery module area in two arrangements. The dislocation arrangement of battery modules occupies a small volume, but its fixation is more difficult, and after studying the influence of different arrangements on the battery temperature uniformity, it is found that the temperature uniformity of the dislocation arrangement of the battery modules is poor. Based on the consideration of fixation and heat dissipation, the battery cells are arranged in parallel.
- Design of current collector and conductive copper pole
(1) The design of the set flow sheet.
The current collector is mainly used for the current carrying capacity of the battery module, and should be designed to meet the continuous diversion of 49.5A. At present, the more common guide metals are nickel-plated steel and nickel-plated copper. Metal copper has good conductivity and low resistivity, so this section chooses copper sheet as the current collector. Figure 9-6 is the size drawing of the current collector.
When the welding pole of the electric welding machine is welded with the copper sheet of the same material, it is prone to viscous phenomenon, which causes the loss of the welding pole. Therefore, 0.2mm thick nickel is set at the spot welding position of the current collector and the battery, which not only ensures the current collector The current-carrying capacity is required and it has a good welding process. The upper end of the copper sheet has a 9mm mounting hole, which is mainly installed with the conductive electrode column. The copper sheet should also be designed with voltage detection points. Set the process slot at the spot welding position to ensure that the welding stress caused by thermal expansion and contraction is eliminated during the welding process. The thickness of the copper sheet of the current collector is 0.3mm and the width is 50mm. The cross-sectional area of the current collector is the maximum current that can pass if the maximum safe current of the copper sheet is 7A/mm2. When the battery module is discharged at a rate of 1C, the current is known to verify whether the copper sheet meets the requirements for use.
(2) Design of conductive copper pole.
The conductive copper column of the battery module is used as the output terminal of the battery module, and the current carrying capacity of the copper column is mainly considered in the design process.
(3) Selection and fixation of sensors
The temperature sensor is fixed on the side of the battery module. Copper has good thermal conductivity, so the two battery cells in the middle of the battery module are wrapped with copper foil, and then the temperature sensor is fixed on the copper foil with screws and placed on the leeward side to prevent the accumulated heat from being carried away by the airflow.
(4) Design of peripheral unit of battery module
When designing the battery module, it is required that its parts have a certain degree of strength and have an insulating effect. The battery module designed in this section should meet the requirements of air cooling and adopt a semi-closed design. The battery protection unit is composed of an upper base, a side end cover and a lower base.
The upper base and the lower base of the battery are respectively connected to the battery holder through trapezoidal pins, and one side of the side end cover is designed as a trapezoidal groove, which is fixed on the side of the battery by trapezoidal pins with the holder. In order to ensure that the battery module is waterproof, dustproof and insulated, apply a layer of ABS glue before assembling the components. A boss is designed on the upper base for placing conductive steel pillars, and a nut is inlaid under the boss.
A large amount of heat will be generated during the charging and discharging process, which requires the end caps on the upper and lower sides of the battery module to have good flame retardancy. Because ABS has good mechanical properties, good thermodynamic properties, and a certain degree of flame retardancy, ABS is selected as the material of the protection unit.
(5) Calculation of specific energy of battery module
The specific energy is an important parameter of the battery system. According to the design requirements, the specific energy of the battery system should be greater than 120W.h/kg. When designing the battery unit, the battery unit not only meets a certain strength requirement, but also needs to meet a certain specific energy requirement. The total mass of the battery module:
Among them, M unit is the total mass of the battery module; Mi is the mass of each part of the battery module.
The battery module is composed of m battery cells in parallel, so the total energy of the battery module is
Among them, Q unit is the energy in the battery module; m is the number of battery cells connected in parallel; V and C are the voltage and capacity of the battery cells, respectively. The specific energy of the battery module is
Among them, EM is the specific energy of the battery module.