With the rapid popularization of electric vehicles and the increasing consumer base, problems such as short driving range and high cost have become increasingly prominent. As a key component of the electric vehicle power system, the power battery has attracted much attention. Domestic new energy vehicle OEMs and power battery suppliers are all seeking solutions for highly integrated power battery systems to meet user needs. In recent years, the industry has continuously achieved breakthroughs through technological innovation, gradually realizing significant improvements in power battery energy density and integration efficiency, helping vehicles achieve longer driving ranges, alleviating users' range anxiety, and reducing overall vehicle costs.
Against this backdrop, power batteries are gradually developing towards higher energy density and higher integration efficiency. How to improve battery energy density within existing limits has become a common challenge facing the industry. This article mainly reviews the technical characteristics and implementation methods, advantages and disadvantages, and application trends of different types of power battery integration solutions, and provides a comprehensive comparison.
1. Overview of Key Technologies for Power Battery Integration
Figure 1 shows the classification of key technologies for power battery integration. Early power batteries typically adopted a "cell-module-battery system" integration method, characterized by a large number of structural components, low integration efficiency, and low energy density. To meet the needs of vehicles and users and improve the integration efficiency and energy density of power battery systems, the industry has successively introduced module-less integration technologies, such as Cell To Pack (CTP); and integrated integration technologies, such as Cell To Body (CTB) and Cell To Chassis (CTC), achieving innovation in power battery system integration technology. Currently, typical integrated batteries and module-less integrated batteries are widely used, while integrated batteries are less common (Figure 1).
2. Typical Integration
The integration form of power batteries is closely related to the internal cell assembly method. A typical design involves first assembling several cells according to standard dimensions to form battery modules, and then installing and connecting these battery modules to the battery housing to form a battery system. Each module within the battery pack has an end plate, side plate, and top cover structure, and is independently packaged. Typical integrated battery packs generally use bolt connections to fix the battery modules to the battery housing internally, and electrical and assembly clearances need to be reserved between different modules according to design requirements. The power battery assembly designed by Wang Ming et al. uses 24 battery modules, as shown in Figure 2. Each battery module has an end plate and side plate structure, and the modules need to be connected via high-voltage connectors. The battery system designed by Zhou Qi et al. uses 12 battery modules and has similar characteristics, as shown in Figure 3.
The main advantages of the aforementioned typical integrated battery are its simple structure, easy assembly, and low assembly process requirements. If an internal cell fails, the battery module can be replaced individually for repair, resulting in low maintenance costs and good maintainability. However, the internal space of a typical integrated battery is occupied by numerous module end plates and side plates, and a large gap needs to be reserved between each module, leading to limited space for individual cells within the battery pack. Therefore, typical integrated battery packs have the disadvantage of low energy density, generally making it difficult to meet the increasing range requirements of pure electric vehicles. Currently, most vehicles on the market use typical integrated power batteries, including pure electric vehicles and plug-in hybrid electric vehicles.
3. Module-free integration
Currently, through continuous technological innovation and practice, the power battery industry has seen the emergence of a large number of innovative solutions and achievements in battery system integration. Among them, the internal integration design of batteries is mainly based on the concept of "fewer components", which reduces or eliminates internal modules and other structural components of power batteries, thereby increasing the overall usable space of the battery cells and improving the energy density of the battery system.
3.1 CTP Battery
Cell-to-Pack (CTP) is an innovative solution that eliminates the module stage in typical integrated battery pack assembly, directly integrating the cells within the battery pack. Its significant characteristic is a substantial reduction in the number of structural components within the battery pack (such as module end plates, side plates, high-voltage connection busbars between modules, low-voltage sampling harnesses, and structures for fixing modules in typical integrated batteries), thereby increasing the space available for cell placement and reducing the battery pack's weight. Generally, a hybrid thermally conductive adhesive with superior adhesion and high thermal conductivity is used to bond all cell ends to the battery pack housing. This also saves on a large number of standard fixing bolts, as adjacent end plates of cells at both ends of the battery pack no longer bear the burden of bolt tightening. Lightweight non-metallic materials can also be used to further reduce the battery pack's weight.
Furthermore, the battery pack is not limited by standard modules, allowing for wide application in various vehicle models. As shown in Figure 4, the CTP battery designed by You Kaijie et al. has cells arranged inside the battery housing, with each cell bonded to the housing using structural adhesive. This adhesive provides fixation while eliminating the need for the module frame structure found in typical integrated batteries. This results in fewer components within the battery housing, more usable space for cell placement, streamlined processes, improved assembly efficiency, and reduced manufacturing costs.
The main advantages of CTP batteries are high internal integration efficiency, high energy density, and reduced overall cost due to fewer components. This allows CTP batteries to achieve higher capacity within the same vehicle specifications, thus extending the vehicle's driving range. Compared to typical integrated batteries, CTP batteries reduce the number of components by 40%, increase energy density by 10-15%, and improve volume utilization by 15-20%. The cells within the battery pack are primarily fixed by adhesive bonding, and once the structural thermally conductive adhesive has cured, non-destructive disassembly is generally difficult. If a cell fails, it cannot be replaced, resulting in poor overall maintainability of the battery pack. The assembly method within the battery pack necessitates more complex and larger-sized equipment for welding the high-voltage connecting bars between cells, leading to relatively high manufacturing costs. Overall, CTP batteries are better suited to meet the high driving range requirements of electric vehicles and are gradually becoming the mainstream choice for high-range models in the new energy vehicle industry.
3.2 Blade Battery
Blade batteries are another representative solution for module-free integrated batteries, named for the long, thin, blade-shaped cells within the battery pack. Their key design element is also the elimination of the battery module structure through a "few-components" approach, employing elongated cells and side-mounted terminals to achieve battery system innovation. Simultaneously, it reduces or eliminates the use of horizontal and vertical beams within the battery pack, thereby reducing the space occupied by these beams, improving space utilization, and maximizing the placement of more cells within the pack. This results in increased overall capacity, voltage, and driving range, while reducing pack weight and achieving lightweight design. The blade battery designed by Wang Chuanfu et al., as shown in Figure 5, primarily involves arranging several cells within the battery pack to form a battery array. The cell length ranges from 600 to 2500 mm, with terminals extending from both sides. There are no horizontal or vertical beams between the cells, and the bottom of the cells is fixed to the battery casing using adhesive bonding.
4. Integrated design
As the integration technology and market application of power batteries mature, the new energy vehicle industry and the power battery industry are also innovating and exploring integrated technologies between the power battery and the vehicle. Compared with integrated design schemes that reduce the number of structural components inside the battery, the key feature of integrated battery technology is the integration of the battery pack with the vehicle body and chassis components at the vehicle level. Through innovative integration of the external connection interface of the battery pack, the overall weight of the vehicle and the number of structural components are reduced, thereby achieving lightweight design and improving the vehicle's power and economy.
4.1 CTB Battery
Battery-to-Body (CTB) integration optimizes the battery pack cover structure based on CTP or blade batteries, allowing the battery pack cover to replace the vehicle's passenger compartment floor, thus achieving integrated battery pack and vehicle body. Vehicles using CTB batteries reduce the passenger compartment floor compared to traditional vehicles, eliminating the gap between the battery pack and the passenger compartment floor, thereby reducing overall vehicle weight. Simultaneously, at least 10 mm of usable space is gained in the vehicle's height direction. This space can be used to increase battery capacity and improve driving range, and also to reduce the overall vehicle height, optimizing aerodynamics and reducing energy consumption. Since the battery pack cover replaces the passenger compartment floor, the structural design must be strengthened to ensure seals between the cover and the lower battery housing, and between the cover and the vehicle's side beams and frame; therefore, high reliability is required. CTB batteries typically exist as independent structural units, allowing for separate assembly, testing, and rigorous certification. They are generally suitable for vehicles with a monocoque body structure, and their assembly process is similar to that of traditional vehicles.
Figure 6 shows the CTB battery solution designed by PIRES et al. The battery pack cover serves as both the floor of the vehicle's passenger compartment and the seat support structure, eliminating and simplifying body structural components, thereby reducing vehicle weight and increasing driving range. Figure 7 shows the CTB battery solution designed by Ling Heping et al. The battery pack cover simultaneously functions as a liquid cooling plate for the battery and the floor of the passenger compartment. During cooling or heating, the battery exchanges heat with the interior of the passenger compartment, improving passenger comfort, reducing vehicle energy consumption, and increasing driving range. This solution incorporates two sealing gaskets between the battery and the vehicle's side beams, achieving dustproof, noise reduction, heat insulation, and sealing functions.
The main advantages of the aforementioned CTB battery are: reducing the number of structural components at the vehicle level, increasing the available space for the battery or vehicle, or optimizing aerodynamics, thereby reducing the vehicle's total weight, increasing battery capacity, reducing vehicle energy consumption, and ensuring a longer driving range; in terms of manufacturing, the battery pack's assembly method is consistent with traditional vehicles, and the assembly process is mature; in terms of maintainability, the battery pack can be replaced individually if it fails, resulting in good maintainability; in terms of collision safety, because the battery pack retains the main load-bearing structures such as the lower casing, it forms a double layer of protection with the body sill beams and side beams, providing better protection for the internal cells. CTB batteries, due to the high requirements for the sealing and load-bearing capacity of the battery pack cover, still face technical challenges in reliability development and verification that need to be overcome; due to the reduction of one layer of vehicle floor protection, the design needs to be strengthened to ensure the safety of the passenger compartment in terms of battery thermal runaway, especially the safety design of the cell terminal protrusion scheme, which is a difficult point in the new energy vehicle industry.
Overall, CTB batteries, as one of the integrated solutions, have already been piloted by some automakers in the new energy vehicle industry and will gradually become an important development trend in the industry.
4.2 CTC Battery
Battery Chassis Integration (CTC) is an integrated electric intelligent chassis technology that highly integrates the power battery with the vehicle. The battery pack eliminates the primary component in the lower casing that carries the battery cells; instead, the cells are directly integrated and arranged between the vehicle's side beams and crossbeams. Vehicles using CTC batteries typically integrate the frame and chassis components simultaneously, further reducing the number of structural parts compared to traditional vehicles or vehicles using CTB batteries, thereby reducing overall vehicle weight and energy consumption. Since the battery, as a component of this integrated technology, no longer exists as a separate battery pack, its assembly, testing, and rigorous certification cannot be conducted independently. The assembly process between the battery and the vehicle also requires significant changes, and it is generally suitable for vehicles with non-load-bearing bodies.
The integrated chassis with CTC batteries is characterized by its flatness and compactness, which some companies figuratively call a "skateboard chassis." This "skateboard chassis" facilitates the development and application of modular vehicle models. Besides the structural integration between the battery, vehicle, and chassis, the integrated technology also enables the integration and unification of controllers such as the battery control unit with the vehicle's domain controller, thus achieving integration and innovation in the electronic and electrical architecture. Currently, the industry lacks relevant regulations and standards, and CTC battery technology development is still in the pre-research stage; mass production has not yet been achieved in China. Based on the technical characteristics of a non-load-bearing body, the vehicle's passenger compartment can be designed and developed separately; therefore, the integrated chassis platform with CTC batteries will also bring about changes in the overall vehicle business model. The CTC battery designed by Lu Jun et al. is shown in Figure 8, with the cells integrated in the middle of the integrated chassis, adopting a typical non-load-bearing body structure.
The main advantage of the aforementioned CTC battery is that it can further reduce the number of structural components at the vehicle level, thereby reducing the overall vehicle weight and increasing the vehicle's driving range. The non-independent nature of CTC batteries is a significant distinguishing feature from other types of batteries, and compared to other batteries, they have the following three disadvantages:
(1) Manufacturing and assembly processes: The manufacturing and assembly processes of CTC will change the vehicle manufacturing equipment, manufacturing processes, and manufacturing environment, leading to an increase in manufacturing input costs;
(2) Maintenance: Due to the inability to replace the battery pack separately, the maintainability is poor and the maintenance cost is increased;
(3) Collision Safety: Collision safety is reduced due to the reduction of structural components in the battery casing. Overall, CTC batteries are currently a hot and forward-looking technology research direction in the industry, and domestic and foreign manufacturers are actively exploring and researching solutions.
Based on the above analysis, Table 1 lists the comprehensive comparison of different types of power batteries in various dimensions. It can be seen that as the energy density of power batteries increases, it will bring adverse effects such as increased manufacturing process complexity, increased maintenance costs, and reduced technological maturity.
5. Summary and Outlook
This article briefly describes the classification of key integration technologies for power batteries, provides a detailed analysis of different technology types, and elaborates on their technical characteristics, structural schemes, manufacturing processes, maintainability, cost advantages and disadvantages, and application trends.
Power battery systems are gradually developing towards fewer components and integrated systems, moving from typical integrated solutions to module-free and integrated solutions, which has significantly improved the energy density of power batteries, thereby helping vehicles reduce energy consumption and increase driving range.
The integration of power batteries is gradually shifting from internal structural innovation to external integration and deep fusion with vehicle-level components. Power batteries are also gradually transforming from independent systems into integrated vehicle components, such as the CTB battery cover replacing the traditional vehicle floor.
While advancements in power battery integration technology have improved the driving range of vehicles, they have also brought many challenges to vehicle development and verification, such as battery upper support, sealing between the battery and the vehicle body, battery and vehicle assembly processes, and battery maintenance convenience. Further research is needed to improve the maturity and reliability of the technology.
As a key component of new energy vehicles, breakthroughs in power battery system integration technology will bring better power and economy, longer driving range, and a superior user driving experience to the entire vehicle. Key power battery integration technologies will continue to develop and progress along with changes in market demand. Mastering key battery integration technologies will help companies enhance their core product competitiveness, create outstanding products, and better embrace the new era of intelligent new energy electric vehicles.
