Pack structure optimization is helpful to reduce the cost of power battery

2023-08-09 13:51

Pack structure optimization is helpful to reduce the cost of power battery and improve the utilization rate of car body space

1. From Cell to Module to battery Pack, through the disassembly analysis of the batteries of mainstream electric vehicle manufacturers, we can know that the power battery pack of new energy vehicles is the combination of single cell through series and parallel, plus some management and cooling (air cooling and water cooling) systems. The energy storage unit that drives the car. In the current mainstream battery pack structure, a new energy vehicle power battery pack is mainly composed of battery pack, battery module, battery cell three levels.

2. The battery is installed in the battery pack in the form of module, and its physical structure design can support, fix and protect the cell, which is convenient to manage the mechanical strength, electrical performance, thermal performance and fault handling of the cell. It still has great significance for battery voltage balance, local consistency and overall consistency.

3. In the design process of power battery pack, it is necessary to consider the safety and convenient maintenance of structural electrical system, durability and reliability of battery thermal management system, dustproof/waterproof design of battery pack structure, battery safety failure pressure relief and thermal runaway management. When mainstream automobile enterprises and lithium battery pack departments first entered this field to accumulate design and use experience, In the case of realizing the set function, a certain amount of redundant space is reserved. This process naturally increases the BOM cost of power battery packs and reduces the energy density and performance of battery packs.

Battery Pack processing cost accounts for a large proportion, with room for reduction

In the process of battery pack design in the early stage of the development of electric vehicle industry, electric vehicle manufacturers mainly made changes on existing models, and the main starting point was to use modules to fit the vehicle body structure. There are also various modules corresponding to car models. In the early stage, the modular efficiency of cylindrical cell is about 83%, and the system modular efficiency is about 62%. The modular efficiency of soft packet core is about 86%, and the modular efficiency of system is about 58%. The modular efficiency of square cell is about 88%, and the system efficiency is about 68%. After the subsequent release of special purpose electric vehicles by various manufacturers, the cell group efficiency of modules and systems is gradually improved. However, because it still occupies a large proportion in the absolute value of power battery cost, continuous structural design optimization is still of great significance to reduce the cost of power battery.

Development trend and system of commercial vehicle and passenger vehicle

New energy commercial vehicles are different from passenger vehicles. The optimization of battery Pack structure, improvement of energy density and reduction of cost are the current domestic new energy buses. Due to the requirements of technical indicators, considering the safety and cost factors of power batteries, mainstream automobile enterprises take lithium iron phosphate technology route as the main technical route. Especially after BYD launched thinner, longer blade batteries with better heat dissipation and higher energy density this year, lithium iron phosphate battery packs have become the preferred choice of mainstream car companies. The higher thermal runaway critical value (800℃ vs. 200℃) is also the heavier weight in the selection.

As we know, the lithium iron phosphate itself because of the low energy density of bottlenecks, mainstream car companies in a certain period of time also tend to use ternary system | | fast punching system battery for battery pack; However, in the past technology upgrades, commercial vehicle power battery energy density still improved, while the cost continued to fall. Behind it, on the one hand, is the continuous progressive progress of battery material system (lithium iron phosphate modification, reduction of copper aluminum foil/diaphragm thickness, etc.), on the other hand, is also achieved through continuous optimization and upgrading of power battery pack structure. Blade battery is one of the excellent representatives;

According to industry statistics feedback, the group efficiency of bus power battery packs has been improved from 66% in the early stage to around 90%. At the same time, the domestic first-class electric bus manufacturers, represented by XX Bus, have accumulated rich experience in battery pack through a large number of operating data and progressive battery pack technology optimization, which in turn provides a large number of first-hand data for battery manufacturers to further improve the efficiency of the group. Bus manufacturers are gradually taking a leading position in the field of battery pack design for new energy commercial vehicles.

Development of mode-less and mode-less (CTP) technology

From the decline of subsidies to market competition and the entry of Tesla wholly owned, the design structure of power battery pack has been continuously upgraded. Since 2017, the decline and technological upgrading of national new-energy vehicle subsidies have been the key driving force for rapid technological upgrading of the industry, cost reduction, efficiency improvement and expenditure reduction. With the gradual withdrawal of subsidies, the new energy automobile industry will meet the market-oriented competition with fuel vehicles, and the price range of Model3 will drop to less than 300K (the price may drop further after the further improvement of localization). Whether the battery pack performance can be continuously improved to reduce the cost of battery pack may become the key for different automobile enterprises to maintain rapid development and successfully complete the intelligent upgrade of automobile electrification.

In the aspect of blade battery -- Based on the comparative analysis of public data, the battery structure of BYD's "blade battery" is longer (about 800mm) and 20mm less thick than the previous square battery cell. It is placed side-by-side in the battery pack (heat conduction and insulation between cells). The structural design increases the unit heat dissipation area of the cell, which is conducive to the thermal management of the battery pack. It saves space and improves the energy density of the battery while improving the safety performance. In addition, the change of cell structure makes the pack design scheme iterative and reduces the amount of parts used, thus reducing the cost of battery pack. As the "blade battery" is different from the previous cell structure design, BYD indicated that it will build new production capacity in the future to meet the production demand of the corresponding model of the battery design (car body ADAPTS to the battery); Of course, with the increase of battery size, lithium equipment manufacturers also bring great challenges and opportunities, such as the coater needs wider coating width, how to ensure the horizontal consistency of the pole sheet and the consistency of the service life of repeated maintenance after the die head becomes wider, how to do the laminator of wide cell, and how to do the wide cell adhesive after the laminator. How to ensure the consistency and timeliness of infiltration after the cell size increases has become a practical problem for lithium equipment manufacturers.

In terms of CTP battery technology, Ningde Times released CTP (Cell To Pack) technology (also known as mode-free solution) at the Frankfurt Motor Show in Germany in 2019. According to public information, this solution has obvious effect on improving the mass density and volume energy density of batteries, and greatly reduces the manufacturing cost of power batteries.

In terms of cylindrical batteries, Tesla came out of nowhere in its early years, relying on its excellent battery pack system design, managed the cylinder batteries that people had never imagined (> 7000 18650 series) could be used in automotive power batteries, and greatly promoted the growth and development of its electric vehicles before the advent of square batteries. Through comparison, it is found that the battery pack design of the current mass-produced Tesla Model S and Model 3 has undergone a new iteration (the 21700 series has replaced the original 18650 series). According to Tesla's public introduction, the energy density of the new battery system has increased by more than 20% and the unit capacity has increased by 35% compared with the previous battery system. The system cost is reduced by about 10%. Meanwhile, pack design of Model 3 has been greatly optimized compared with Model S in terms of module design. In the future, with the further optimization of Tesla battery pack structure and the further improvement of localization, it is likely to be a large probability event to use square batteries instead of cylindrical batteries to reduce costs and improve efficiency. This is a major opportunity for power battery manufacturers with advantages in square cell manufacturing and leading position in the world.

The deepening of pack product system integration will increase the difficulty of operation and maintenance in the later use of the system. Therefore, for the power battery system of new energy vehicles, when the automobile enterprises consider the cost reduction and improve the battery pack integration through the solution of fewer modules or no modules, higher requirements are put forward for the effective life quality of battery packs, especially the battery cell components of battery packs: on the premise of realizing the production of products, they also need to have certain economic value of commercial promotion. Therefore, under this trend, the threshold for automobile enterprises to choose power battery manufacturers has been raised. In this context, many third-party pack enterprises are going to merge or go bankrupt. But it also creates a product moat for the highly integrated pack system built by the auto companies themselves. In the field of power battery is still cylindrical, square, soft package three types of cell under the background of three. In contrast to Tesla's unusual use of cylindrical battery solutions, square cells and soft-pack batteries are more widely used by other major global automakers and new car makers (stock market). Considering that the important direction of battery pack structure optimization is to reduce the amount of redundant parts used in battery packs, for the metal shell of cylindrical batteries and square batteries, the mechanical strength of the metal shell itself can reduce the use of the supporting structural parts of modules (which is also the direction of the current enterprise has been improving). A soft-pack cell design that requires modules for mechanical strength presents a disadvantage (the advantage of soft-pack becomes a disadvantage in this respect).