How to make a module design for a lithium-ion battery?

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

The battery module can be understood as a combination of lithium ion batter and a series of cells to monitor and form a cell-formed cell and a PACK. Its structure must be supported, fixed and protected for the battery, which can be summarized into 3 large items: mechanical strength, electrical performance, thermal performance and fault handling ability. Can I complete the position of the battery core and protect the deformation of the loss of lossy performance, how to meet the current-carrying performance requirements, how to meet the control of the electrical core temperature, can be powered off when the serious abnormality can be turned off, can prevent heat loss Spread, etc.

, will be the standard of evaluating the advantages and disadvantages of battery modules. High performance demand battery module, its thermal management solution has been turned to liquid cooling or phase change materials. The soft bag battery cell energy density is most likely to be high in common three lithium-ion battery packages, but to the module design, the task of considering the overall safety of the product, it can be said to be part of electricity The movement of the core gives the module structure.

Important composition of the module is a soft bag battery, and the design selection gap is relatively large. The above-in-picture is a more typical form. The basic components include: module control, BMS slave boards, battery cells, conductive Connectors, plastic frames, cold plates, cooling pipes, on both ends, and fasteners combined with these components together.

Among them, the pressure plates of both ends are in addition to the use of a constant pressure, and the module is often designed in the fixed structure in the PACK. Structural design structure design requirements. Structural reliability: anti-fatigue anti-fatigue; process controllable: no free soldering, noble welding, ensuring 100% of the battery; low cost: Pack production line automation cost, including production equipment, production loss; easy division: battery pack Easy maintenance, repair, low cost, battery core can be used to use; to prevent heat transfer, prevent heat loss from being spread too fast, or put this step to Pack design and then consider.

It is understood that, at present, the integrated assembly of the cylindrical cells in the industry is about 87%. The system is composed of approximately 65%; the functional rate of the soft package core mode is about 85%, and the system is constrained to be about 60%. The module component of the square cell is about 89%, and the system is inclusive.

The efficiency is about 70%. The monomer energy density of the soft bag is higher than the cylinder and square, but the module design is high, the safety is not easy to control, which is the problem that the design is solved. General module optimization.

Improve space utilization is also an important way to optimize the module. Power Lithium Battery Pack can reduce the use of battery boxes by improving the module and thermal management system design. There is also a solution that uses new materials.

For example, the bus bar within the power lithium battery system (bus in the parallel circuit, is generally made of copper plate) from copper to aluminum, and the module fixture is replaced by the sheet metal material to high steel and aluminum, which can also reduce the power lithium Battery weight. The physical structure of the thermal design soft bag battery determines its difficult to explode. Generally only the pressure can be affected by the shell is high enough, it is possible to blow, and the internal pressure inside the soft bag will start the edge of the aluminum film film.

, Leak. At the same time, the soft bag battery is also the best in several batteries. The famous representative of the soft bag battery, LEAF of Nissan, has a full sealed, and does not consider heat dissipation, that is, no heat dissipation.

And the capacity of Leaf's frequent feedback in the market is too fast, and it is not related to this thermal management. Obviously, as people's pursuit of high-performance electric vehicles, forcing soft bag batteries must have active thermal management structures. The current mainstream cooling mode has been converted to liquid cooling and phase change material cooling.

The phase change material cooling can be used with liquid cooling, or use it alone under the conditions of the environment. There is also a process, pneumon, still currently in China. Here is a thermally conductive coefficient of thermal conductivity than air.

The heat of the telecommunications is transmitted to the module housing by thermal conductive gel, further emits into the environment. In this way, the cell is replaced separately, but also prevents thermal out of control from a certain extent. The liquid is cold, in the previously described picture of the module, the cold plate and the liquid cold water pipe are the components of the liquid cooling system.

The module is stacked by the electrical core, and there is a liquid-cooled plate arranged in the battery cell, which guarantees that each of the cells have a large surface contact to liquid cooling board. Of course, the soft bag should be mature, it is not easy to make liquid cooling technology, which must consider the fixation, sealing, insulation, etc. of liquid cold plates.

Electrical design electrical design, contains two parts: low pressure and high pressure. Low voltage design, generally considering several functions. By signaling wire harness, the battery voltage, temperature information is collected to the module from the control board or the so-called module controller installed on the module; the module controller is generally designed to design a balance function (active equalization or passive equalization or both Coefficient); a small amount of relay-off control functions can be designed on the slave controller, or on the module controller; connect the module information to the module information through the CAN communication connection module controller and the main controller.

High pressure design, important is the string parallel joint between the battery and the cell, and the external connection of the module and the module, the general module is only considered in series. These high-pressure connections should be required to reach two aspects: First, the electrical power and contact resistance distribution between the cells should be uniform, otherwise the monomer voltage detection will be interfered; secondary, the resistance is small enough to prevent electrical energy from passing on the path waste. Safety design safety design can be divided into three retroured requirements: good design, do not have an accident; if it doesn't matter, an accident occurs, it is best to war war in advance, give people to reflect the time; the fault has occurred, the target is designed It turns into prevents excessive spread.

To achieve the first purpose, it is a reasonable layout, a good cooling system, a reliable structural design; secondary goals, the sensor is more widely distributed to each possible fault point, fully detect voltage and temperature, preferably monitor each The internal resistance of a battery; the minimum goal can be set by the battery and modules, and the firewall is set between the modules and modules. The design intensity redundancy should collapse after the disaster occurred. This is the direction of high performance soft bag modules.

Lightweight Design Lightweight Design, the most important purpose is to pursue the life of the life, eliminate all the burden, lightly loaded. If it is lighter, it is even more happy to follow the cost. Lightweight roads, such as increasing the battery energy density; in the detail design, ensure the thinness of structural parts in the case of strength (such as the choice of thinning materials, digging more holes on the sheet); replace the aluminum Shell for sheet metal parts; new materials with lower density to create housings, etc.

Standardization design standardization is the long-term pursuit since the large industry, and standardization is the cornerstone of reducing cost increase interchangeability. Specifically to the power lithium battery module, there have been a great purpose of a ladder utilization. That is, but the reality is that the monomer has not been standardized, then the standardization distance of the module is farther away.

The well-known model of the soft bag battery Renault Zoe, September 2016 Renault upgraded ZoE battery pack, the total amount of battery pack is 45.6kWh, the available power is 41kWh, the system rated voltage 360V, the system is 2P96S, A total of 192 batches, consisting of 12 2P8S modules. ZOE battery pack uses a wind cooling management method, from the middle hole, on both sides.

Each 2 cells are wrapped in 1 upper aluminum housing and 1 lower aluminum housing, and the two aluminum housings are joined together by a snap, the thickness of the aluminum housing is 0.4 mm. The aluminum housing is stamped to form a three protrusions, a projection height of 0.

8 mm, a projection of adjacent 2P unit aluminum housing, a gap of the width of 1.6 mm, and the heat of the battery is conducted to the aluminum housing, in the gap Air flow cools the cell, while the gap can also absorb part of the cell expanded. Zoe's battery is supplied from LG chemical, the 2012 version ZOE battery is 36ah, the size is 325x135x11.

2mm, with a weight of about 0.86kg, and the total weight of the battery is 165.12, accounting for 57% of the total PACK.

The 2016 version of ZoE battery is speculated, 65ah, size size is similar to 36ah. Nissan Leaf (no forced cooling) Leaf battery small module, 4 cells in each housing; the small module and the small module are connected to the injection connection connection. The terminal of each module column, according to the number of each module, specializes in injection molding the corresponding junction box, and the form and module of each junction box are one or one.

If the number of modules (2P2S) changes, the junction box cannot be used, unless the number is an integer of an existing module, and the number of parallel modules. For example, if a module is 4×2 (a cell), then the modified module must be 8×2,12×2……Otherwise, its original electrode junction box cannot be used. Soft package battery strong connection mode comparison: Module form is shown below.

Select a factory soft package titanate ion battery for grouping, and its characteristic parameters are shown in the following table. The lithium ion battery module consists of a lithium-ion battery, a module mounting plate, an insulating block, a housing, a long connection row, a short connecting row, a pole column, and a lithium ion battery module structure as shown below. A battery is placed in the middle of the two module mounting plates, forming a structure of 5 and 3 strings, and the string parallel connection uses long connection rows and short connection rows to connect the battery, between the battery and long / short connections, screw nuts Connection mode is fastened.

The polar column is connected to the external output of the lithium ion battery module, which is connected to the short connection, and the connection method is also a screw connection. Between the long connection row and the short connection row in an insulating isolation block for electrical isolation. Connection method 1: The lithium-ion battery module connected to the full screw, that is, the lithium ion battery and long / short connection row, the connection between the short connecting row and the pole column all uses a screw connection.

Connection mode 2: Semi-laser welding semi-screw connection lithium ion battery module, that is, the connection between the lithium ion battery and the long / short connection row is laser welding, while the connection between the short connection row and the pole column uses a screw connection. Connection method three: Laser welding and one-piece cell module of the integrated pole column, that is, the connection between the lithium ion battery and the long / short connection row is laser welding, and the short connection row and the pole column make a whole component. Test method, separate test screw connection and laser welding connection impedance, each take a short connection and a lithium ion battery separate screw connection and laser welding experiment, measurement record respective connection impedance.

At the same time, the internal resistance value of the entire module is obtained by measuring the internal resistance value of the lithium ion battery module, thereby comparing the internal resistance difference of the lithium ion battery module in different connection mode. Connection impedance and internal resistance are obtained by HiOki battery tester measurement. A plurality of thermal resistance or thermocouples are arranged in a lithium ion battery module as a temperature measurement point, and the temperature of different temperature points of the lithium ion battery module is tested by charge and discharge experiment.

The lithium-ion battery module is rated to 100A. Considering the limit current of the overload operation is approximately 120A, it is charged and discharged in the limit of current 120a in the experimental test. Record the highest temperature, temperature rise and temperature difference of each temperature measurement point during charge and discharge.

The temperature measurement point of the lithium-ion battery module of the connection method is 4 (limited by the at the time, only 4 key points are measured), and the thermal resistance temperature is used. The lithium-ion battery module temperature measuring point in connection mode 2 and three is 12, which uses thermocouple temperature measurement. Experimental results analysis, from the data, the connection impedance of the screw connection is much larger than the connection impedance of laser welding.

The important factors that form the connection impedance of the screw connection are: the surface of the joint surface is uneven (large surface roughness); it is affected by environmental factors, oxidation or corrosion in the long / short connection and battery contact surface; screw tightening is not enough, The tightening torque of each screw is inconsistent; the external factor interference causes the screws, including the screws caused by vibration during transportation and handling. Since laser welding is to convert light energy into thermal energy, the material is melted, thereby achieving the purpose of welding, and is equivalent to melting both the two, so the impedance of this connection must be smaller. From the internal resistance of the lithium ion battery module, the lithium-ion battery module of the connection method is superior to the connection mode one and the connection mode.

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