As the electric vehicle market continues to grow rapidly, battery pack technology is evolving. This article provides a brief introduction and comparison of the current mainstream battery pack structures: CTP (Cell To Pack), CTC (Cell To Chassis), CTB (Cell To Body), and CTM (Cell To Module).

CTP (Cell To Pack)

CTP stands for Cell To Pack, meaning that the cells are directly assembled into the battery pack. In this structure, the cells are connected to form the entire battery pack, eliminating the traditional module assembly process. This approach improves space utilization, reduces the size and weight of the battery pack, making it more compact and reducing energy loss between cells.

CTC (Cell To Chassis)

CTC stands for Cell To Chassis, which integrates the cells directly into the chassis structure. This structure installs the battery cells directly within the vehicle’s chassis, maximizing space efficiency. Although theoretically the most efficient, this structure is challenging to implement with current technology due to the unique requirements and safety considerations of electric vehicles.

CTB (Cell To Body)

CTB stands for Cell To Body, meaning that the cells are integrated directly into the vehicle body structure. This approach combines the battery cells with the vehicle’s body, optimizing space utilization to enhance driving range. While it offers potential advantages in range, the technology is still in its early stages and is less commonly used in practical applications.

CTM (Cell To Module)

CTM stands for Cell To Module, where multiple cells are grouped into a single module, which is then connected in series or parallel to form the entire battery pack. This structure allows for the individual replacement of faulty cells but is relatively simple in manufacturing, with overall performance less competitive compared to other structures.

CTP: A Benchmark Set by CATL

In 2019, CATL introduced a new battery technology known as CTP. The core of CTP technology lies in eliminating the traditional module design by directly combining cells with the battery casing, reducing the use of end plates and partitions, and improving the integration and internal space utilization of the battery pack.

However, this raises challenges in module fixation and cooling. Since CATL's first implementation, the mainstream method has been to secure simple block-shaped cells with steel bands or adhesive tapes and bond large battery blocks to a liquid-cooled plate using thermal conductive glue. The bottom casing is crafted from cast aluminum or aluminum extrusion, which is more suitable for mass production and forward design compared to the previous method of folding and welding large steel plates. Positioning pins or slots are added to the design to limit the cells.

In terms of cooling, large-area cold plates are welded to the tray, which also serves as insulation, temperature control, cushioning, and support. Compared to the previous method of placing individual cooling plates under each module, this manufacturing process effectively eliminates the risk of coolant leakage within the battery pack and offers higher cooling efficiency.

Although CATL's CTP 1.0 design is not a purely module-free design, it is structurally superior to earlier technologies. The more advanced CTP 3.0 “Kirin” battery technology adopts a genuinely module-free design, with cells now side-mounted instead of upright, using a new cooling solution. The cold plate not only dissipates heat but also provides insulation, temperature control, cushioning, and support. The bottom casing employs a corresponding positioning design to secure the battery, bonding the cells into an integrated structure. Externally, CTP 3.0 appears more organized and uniform compared to CTP 1.0.

Today, nearly all new energy vehicles use a similar CTP manufacturing method. However, the bonding method of the cells makes it impossible to replace individual cells post-production. If a fault occurs in any cell within the battery pack, the entire pack must be replaced, leading to its disposal. This was confirmed by an engineer from a leading battery manufacturer. Nonetheless, this structural design demonstrates that the performance stability of current cells has significantly improved, making individual cell replacement unnecessary. The enhanced stability of cells also sets the stage for the successful implementation of CTP technology.

CTB (Cell To Body) and CTC (Cell To Chassis)

There is a fundamental difference between CTB and CTC, primarily centered around the concept of the "chassis." To summarize: CTC is not yet mature as a commercialized structure in passenger vehicles.

Some manufacturers use the term CTC for differentiation in marketing, but true CTC must meet the essential requirement of integrating the battery cells directly with the chassis, forming a single unit. However, most passenger vehicles today use a unibody construction, meaning they lack a traditional “chassis.” Only body-on-frame vehicles, which can continue to drive even with the cabin removed, truly possess a chassis.

In everyday automotive discussions, we often use the term “chassis” to describe the handling and stability of unibody vehicles for simplicity. However, it’s important to recognize that unibody vehicles, which constitute the majority of passenger cars on the market, do not have a true "chassis."

Therefore, the most accurate term for unibody vehicles should be CTB (Cell To Body), implying that what is often referred to as CTC is essentially the same as CTB. Only when true body-on-frame “skateboard chassis” designs emerge can we correctly use the term CTC.

The primary difference between CTB and CTP lies in the sealing integrity of the battery and the vehicle body. CTP retains a complete battery module with an upper and lower casing, independently sealed from the vehicle body; CTB, on the other hand, integrates the battery module’s upper cover with the vehicle’s floor, resulting in one incomplete sealing component between the two.

There’s no need to elaborate on the advantages of having a fully independent vehicle cabin and a separately sealed battery. To explain the differences in partial sealing forms: either the vehicle’s floor seals the battery (e.g., BYD Seal) or the occupant rides on the battery module (e.g., Tesla Model Y).

CTB’s advantage lies in incorporating the battery system into the overall vehicle development process. The layout, body, suspension, and battery departments must work closely together from the early stages of platform and vehicle design, rather than retrofitting the battery system as done in CTP and CTM.

This integration formally includes the battery pack system in the overall vehicle strategy, bringing significant improvements in vehicle coherence, structural design, and ergonomics. Additionally, by eliminating the upper cover or vehicle floor design, the vehicle gains greater freedom in Z-axis space, potentially increasing height by over 10mm. This concept can be compared to adding the thickness of a sunshade.

This also explains why driving a BYD Seal feels ergonomically closer to a traditional internal combustion engine (ICE) car. The comparison to ICE vehicles is positive, as in previous years, electric sedans were noticeably less comfortable than ICE vehicles due to battery structure constraints. However, with BYD’s blade battery technology and CTB design, the battery pack’s thickness is further reduced, resulting in an outstanding ergonomic experience for both front and rear passengers.

It’s important to emphasize that without CTB technology, the difference may not be noticeable in SUVs, but in sedans, the contrast is immediate (e.g., the difference in rear-seat ergonomics between the NIO ET5/ET7 and similar ICE models).

Furthermore, compared to CTM, both CTP and CTB significantly enhance the structural strength of the vehicle, particularly in torsional stiffness. CTM uses mechanical screws to fix the module to the base, and the module components do not participate in load transmission, providing little assistance during vehicle torsion. In contrast, CTP and CTB employ a bonding method between cells and the base.

Tesla’s CTB technology is particularly noteworthy, with the entire battery pack filled with a pink insulating and fixing material that is extremely strong. It can be likened to placing a large iron plate under the vehicle, giving it torsional stiffness exceeding 40,000 Nm/deg, a performance typically found in high-performance and ultra-luxury vehicles.

For instance, BYD Seal claimed that its torsional stiffness rivals that of a Rolls-Royce, and this is not an exaggeration.

Additionally, there’s a design referred to as “MTB” (Module To Body), which uses fixed cell modules and removes the battery’s upper cover for direct installation in the vehicle. Leapmotor currently uses this design.

Overall, each design has its own characteristics, but they all fundamentally aim to maximize space usage and fit in more batteries. Integrating the battery pack with the vehicle body in design and manufacturing also reduces the number of components, increases production efficiency, lowers costs, and enhances vehicle performance.

When purchasing a vehicle, ordinary consumers can easily be misled by marketing language, especially with unverifiable percentage data (e.g., claims like "the chassis rigidity increased by xx%" or "the capacity improved by xx%" without specifying a baseline). Ultimately, we shouldn’t get too caught up in these numbers and should base our decisions on our personal experiences.

After all, no matter how flashy the marketing, if the car doesn’t drive well, isn’t comfortable, or is difficult to maintain, it will eventually be left behind by time.