Analysis of the key points in the design of the flexible lithium battery module

The battery module can be understood as the intermediate product of the battery cell and pack formed after the lithium ion battery cells are combined in series and parallel, and the single battery monitoring and management device is installed. Among the three common lithium battery packaging forms, the single energy density of the soft package lithium battery is the most easy to achieve, but when it comes to module design, the task of considering the overall safety of the product is the most important, which can be said to transfer part of the cell activity to the module structure.

Module composition

The typical basic components of the flexible battery include: module control board (often referred to as BMS slave board), battery cell, conductive connector, plastic frame, cold plate, cooling pipe, pressing plates at both ends and a set of fasteners that combine these components. In addition to the function of gathering the single electric core and providing a certain pressure, the pressing plates at both ends often design the fixed structure of the module in the pack.

Structural design


Structural design requirements. Reliable structure: seismic, dynamic and fatigue resistance; Controllable process: no over soldering or faulty soldering, ensuring 100% damage free lithium battery cell; Low cost: the automation cost of PACK production line is low, including production equipment and production loss; Easy to separate: the battery pack is easy to maintain and repair, low cost, and the battery cell has good cascade utilization; Necessary heat transfer isolation shall be achieved to avoid the rapid spread of thermal runaway. This step can also be considered in pack design.


Thermal design

The physical structure of the flexible core determines that it is not easy to explode. Generally, only when the pressure that the shell can withstand is high enough, can it explode. When the internal pressure of the flexible core is high, pressure relief and liquid leakage will start from the edge of the aluminum plastic film. At the same time, the soft core is also the best one among several core structures.


electrical design


Electrical design, including low voltage and high voltage. For low-voltage design, several functions shall be considered generally. Collect the battery voltage and temperature information to the module slave control board or the so-called module controller installed on the module through the signal acquisition harness; The module controller is generally designed with equalization function (active equalization or passive equalization or both); A small number of relay on-off control functions can be designed on the slave control board or the module controller; Connect the module controller and the main control board through CAN communication to transmit the module information.

High voltage design mainly refers to the series and parallel connection between the electric core and the electric core, as well as the external part of the module. The connection and conductive mode between modules are designed. Generally, only the series connection mode is considered between modules. These high-voltage connections need to meet two requirements: first, the conductive parts and contact resistance between the electric cores should be evenly distributed, otherwise the single voltage detection will be interfered; Secondly, the resistance should be small enough to avoid the waste of electric energy on the transmission path.

safety design


The safety design can be divided into three backward requirements: good design to ensure no accident; If not, in case of an accident, it is better to give an early warning in advance to reflect the time; If the fault has occurred, the design goal is to prevent the accident from spreading too fast.

Lightweight design

The main purpose of lightweight design is to pursue the endurance mileage, eliminate all unnecessary burdens and go into battle light. And if lightweight can be combined with cost reduction, it will be even more gratifying. There are many ways to lighten, such as improving the energy density of the cell; In detail design, we should pursue the lightness of structural members while ensuring the strength (such as selecting thinner materials and digging larger holes in plates); Replace sheet metal parts with aluminum; Use new materials with lower density to make shells, etc.





Standardized design





Standardization has been the long-term pursuit of large industry. Standardization is the cornerstone of reducing costs and improving interchangeability. As for the power battery module, there is also a great purpose of cascade utilization. That said, the reality is that the monomer has not yet been standardized, so the standardization distance of modules will be further.