The integrated design of battery packs can enhance energy density and power density, improve safety and stability, extend service life, and boost manufacturing efficiency, thereby promoting the sustainable development of the new energy vehicle industry. So far, the main integrated technologies for battery packs include:

Typical Integrated Cell-to-Module (CTM)

Modular-free integration (Cell To Pack, CTP)

Integrated Cell To Body (CTB)

Integrated Cell to Chassis (CTC)

1. Typical integrated (CTM)

The earliest developed battery pack integration technology involves first connecting multiple battery cells in series or parallel, then assembling them with components such as end plates and side plates to form independent battery modules. These modules are subsequently installed into a battery box to create the battery pack, which is finally secured to the vehicle chassis via bolt connections, as illustrated in the figure. Currently, most new energy vehicles on the market employ this typical integration technology.

This type of battery pack features a simple structure and easy assembly. Since the battery modules operate relatively independently, a faulty cell can be replaced by swapping the entire module. However, each module includes components such as end plates, side plates, and top covers, with gaps between modules, resulting in fewer cells that can be installed and a heavier overall weight. The space utilization rate is only 40%, leading to lower energy density and shorter driving range for vehicles.

2. Non modular integration (CTP)

The technology of eliminating the battery module in CTM and directly integrating the battery cells into the battery pack, as shown in the figure.

Compared with CTM technology, the battery pack eliminates the module link, thereby reducing the number of components. As a result, not only has the volume utilization rate been improved, but the reduction in battery pack weight has also led to an increase in the overall energy density of the pack, and material and manufacturing costs have also been reduced accordingly. The cancellation of battery modules has transformed the fixation of battery cells from mechanical to adhesive, that is, by bonding the battery cells to the battery box with a highly adhesive and thermally conductive adhesive. This fixation method eliminates the need for bolts, gaskets and other fixing parts in CTM, reducing the space allocated to the fixed structure of the battery box and improving the space allocated to the battery cells.

The use of CTP technology increases the driving range of cars. Under the same vehicle boundary, the components of CTP technology are reduced by 40% compared to CTM technology, the energy density is increased by 10% to 15%, and the volume utilization rate is increased by 15% to 20%. With the increasing demand for high range of new energy vehicle users, CTP technology has become the main choice for battery packs and is gradually being widely applied in the new energy vehicle industry. In 2019, CATL was the first in the industry to launch CTP battery packs. After years of iteration and technological updates, it launched its third-generation CTP battery pack, the Kirin battery pack, in June 2022. As shown in the figure, its 72% volume utilization rate has received high attention in the industry.

3. Integrated Battery Body (CTB)

The technology of integrating the battery cell directly with the car chassis by combining the battery cover and the vehicle body bottom panel into one while retaining the crossbeam of the battery box, as shown in the figure.

The battery pack cover and passenger compartment floor share the same panel at the vehicle level, reducing the number of components and thus lowering the overall quality and energy consumption of the vehicle. As the battery pack retains the box body while being combined with the sill and edge beams of the vehicle, it forms a dual safety system in the event of a collision, increasing the safety of the vehicle body. The main technical difficulties of CTB lie in the sealing and load-bearing capacity between the upper cover and the floor. In addition, thermal runaway of the battery is a problem that must be considered for new energy vehicles. Therefore, reducing the design of a protective plate brings certain hidden dangers to the safety of passengers in the vehicle. The reliability of CTB technology still needs to be tested, and currently it is only applied as a technical attempt in the new energy vehicle industry.

4. Integrated Battery Chassis (CTC)

The main purpose is to reduce the fixed structure of the battery cells in the lower box of the battery pack, in order to lighten the overall weight of the battery pack. The cells are integrated through the side beams and crossbeams of the vehicle body.

Like CTB technology, integrating battery components directly into the vehicle chassis structure can more effectively utilize vehicle space, reduce waste of chassis space, and improve the overall compactness and internal space utilization of the vehicle. Compared to CTB technology, CTC technology further reduces the number of components in the vehicle body, which also determines that the battery cells no longer exist in the form of separate battery packs, but are integrated with the vehicle body. This integration method has changed the manufacturing, assembly, testing, and maintenance methods of new energy vehicles. When the battery fails, it can no longer be replaced separately, and its maintainability has deteriorated. Therefore, although CTC technology theoretically has attractive advantages, it faces significant challenges in terms of mechanical connections, electrical connections, thermal management, and the impact on the overall structure and performance of vehicles. Therefore, more research and experimental verification of the reliability of this technology are still needed at this stage to meet the safety driving requirements of automobiles.