Thematic analysis of lithium battery new technology CTP and CTC
- Traditional battery pack MTP
- No-module battery pack CTP
- Battery chassis integration technology CTC
- Analysis about new battery technology of key manufacturers
- Changes in battery pack space layout
Battery system technology is upgrading now. CTP structure is gradually becoming mainstream, and CTC is gaining momentum. The battery pack is the power source of the electric vehicle, and the smallest unit is the battery cell.
At this stage, there are two main structural methods in the market, MTP (Module to Pack) and CTP (Cell to Pack), and CTC (Cell to Chassis), as the latest generation of battery system technology, is widely used in Tesla, BYD, Leapmotor, and CATL. With the help of companies such as CATL, it is gradually moving from development and design to mass production in 2022.
1. Traditional battery pack MTP
The traditional battery pack MTP is in the form of batteries and modules to form a battery pack. Multiple cells form a module, and multiple modules plus BMS, counterweight modules and other components are combined to form a battery pack. Under the MTP structure, the cells are fully protected by the external structural parts, so the structural strength is good, and the difficulty of grouping is small.
The space utilization rate of the battery cell for the battery pack is only 40%, of which the space utilization rate of the battery cell to the module is 80%, and the space utilization rate of the module to the battery pack is 50%. The hardware cost of the module accounts for about the total battery cost. 15% of the cost.
The early battery packs used traditional MTP technology, which required the integration of cells→modules→battery packs→body in order. In order to load as much power as possible in the limited chassis space and improve the volume utilization rate of the whole vehicle, it is necessary to consider the feasibility of standardization of each integration step.
Volkswagen took the lead in promoting the standardization of modules. Volkswagen’s first standard is the 355 module, where 355 represents the millimeter length of the battery module. With the increasing demand for cruising range, 390 and 590 modules that can improve space utilization have been proposed. The increasing volume of a single battery module has led to the emergence of CTP solutions.
2. No-module battery pack CTP
Compared with MTP, CTP eliminates the need for intermediate modules. CTP technology directly groups cells into packs, eliminating the need to assemble them into traditional modules. The cells are first integrated into the battery pack and then installed in the car. On the body, the essence is to improve energy density and reduce costs. At present, there are two main ideas.
One is to regard the pack as a complete large module to replace the structure of multiple internal small modules, and to gradually reduce the structural parts such as the end and side plates, which is represented by the CATL, which is one of the top 10 power battery installations in the world. The second is to design. That is to say, a module-free solution is considered, and the battery itself is used as a part of strength to design, represented by BYD blade battery.
3. Battery chassis integration technology CTC
There are two main CTC battery integration solutions. The first is battery pack chassis integration, which is to directly integrate the battery pack into the chassis frame to replace the floor, or directly use the passenger compartment floor as the upper cover of the battery to realize the body floor and chassis.
The second is the integration of battery cell chassis, which is to weld or glue the shell of the battery cell to the chassis structure, which changes the manufacturing form of the battery. The former has high reliability, and the latter has obvious integration advantages but is technically difficult and cannot be replaced.
4. Analysis about new battery technology of key manufacturers
The traditional MTP battery module stacking technology needs to first combine several prismatic cells to form a module, and then install multiple modules to form a battery pack. Due to the requirements of safety and stability, each module is protected by a metal casing, and is equipped with cooling fans, cooling channels, insulation and heat insulation devices, etc. in the battery pack.
It is also necessary to install multiple additional modules, and a large number of screws are used for connections. It greatly reduces the overall energy density of the power battery and increases the cost per unit of electricity.
The CTP scheme directly forms one or several arrays (modules) of single cells and installs them into the battery pack, which greatly reduces the number of modules and eliminates the need to form modules first and then install them. The process and cost of the battery pack can be installed on new energy vehicles after forming the battery pack.
After using CTP technology, the space utilization rate of the battery pack is improved, the volumetric energy density is improved, and unnecessary module components are reduced. However, the requirements for technical capabilities are improved, and the safety performance is not as good as the combination of module stacking.
The CTP solution of CATL adopts multiple long grooves, and the adjacent long grooves are thermally isolated by separators, and the batteries are installed in the grooves to form large modules and fixed. At the same time, the battery cell array is fixedly connected through the fixed connection portion, which improves the strength of the battery pack, thereby enabling the battery pack to be better fixed on the bottom of the vehicle and improving the overall stability.
CATL said at the performance conference that it plans to officially release Kirin batteries in the second quarter of this year. The Kirin battery is the third-generation CTP (high-efficiency grouping) technology of the CATL era. Under the same electrochemical system, the energy density of the Kirin battery is 13% higher than that of the large cylindrical battery.
BYD’s other CTP solution composes power battery packs by simplifying battery modules. First, the single cells are arranged in series in a simplified battery module. The structure of the battery module includes a cooling liquid channel and the length corresponds to that of the battery pack.
Then place the simple module in the power battery pack. BYD invented blade cells for its CTP solution, which are significantly longer and thinner than traditional square cells. These blade cells are arranged in an array and inserted into the battery pack like “blade”.
The blade battery has a relatively large heat dissipation area. As the thickness decreases, the temperature increase of the battery and pack during operation will decrease, and the heat dissipation performance of the battery will be significantly improved.
The CTP scheme adopted by Honeycomb installs the cells into the battery pack by stacking, and replaces the scheme of forming modules by adding thermal isolation partitions to form different cell slots. At the same time, considering the thermal runaway and fire problems in the battery.
The heat dissipation of the battery pack has been improved, so that the installation groove of each cell has a ventilation valve, and the heat dissipation channel is increased. The space utilization rate of the laminated battery is higher than that of the wound battery, so the energy density of the battery cell is higher with less heat generation and longer lithium ion battery life cycle.
Compared with the traditional MTP technology, the comprehensive cost of the CTP solution is reduced and the energy density is improved, but there are still bottlenecks in safety performance and technology research and development. In order to break through the bottleneck and further reduce costs and increase efficiency, the layout of China and other countries’ battery manufacturers and OEMs in CTC is also showing a trend of blooming.
5. Changes in battery pack space layout
Early electric vehicles used split battery packs, and the two battery packs were stored in the original fuel tank and the rear trunk for the spare tire. In order to fully excavate the interior space of the car to load more batteries, the battery pack box of the oil-to-electricity battery began to be designed into I-shaped, T-shaped and soil-shaped.
When the battery adopts the CTC integration technology, the integration of the power battery and the chassis has become a new development direction, and the combination of the integrated battery pack. By modularizing the battery pack and laying it on the ground of the vehicle, the CTC battery pack becomes regular, so as to maximize the use of the interior space.
The battery pack technology has developed from MTP to CTC, and the shape, material and combination of parts have changed with the progress of battery integration technology. The overall direction is integration and integration. The number of independent parts is reduced, and several parts are integrated into one part to form a large part with larger size and multiple functions. Changes in parts will lead to changes in suppliers, and the market landscape will be reshaped.
With the popularization of CTP or CTC in the future, the integration of the system will become higher and higher, and the amount of glue will increase, and the amount of CTP is expected to double. There are three types of glues commonly used in packs: thermally conductive glue, structural glue, and sealant. The largest amount of structural adhesive is used, which can provide a certain strength after solidification and serve as structural support.
Thermally conductive adhesive is used to conduct heat between cells or modules and contact with the water cooling system. Sealant is sealed at the interface and has the lowest value content. The difficulty of gluing is the battery manufacturing environment, and the core is the design of gluing paths and process parameters. Generally, the thermal conductive adhesive is preferentially applied to the bottom, and the application of structural adhesive is determined according to the design.
With the change of the battery pack structure, the water cooling system also changes. First, the water cooling plate has changed from the previous single structure to an integrated structure. For example, in the Volvo CTC technical route, the cooling technology adopts the bottom integrated water cooling plate technology.
The second is to add mica boards or heat insulation pads between the batteries to play their role of strong insulation and high temperature resistance in the entire thermal management system. For example, in Tesla’s 4680+CTC technology, the mica board solution is used at the bottom of the box.
There are still many difficulties in CTC development. For example, it has higher requirements on the consistency of the cells, the deformation and heat dissipation performance of the cells due to the expansion of charge and discharge are deteriorated, and the system design of strength and stiffness needs to be systematically developed.
Midstream battery factories have an advantage in profit distribution. Batteries account for a relatively high proportion of the cost of vehicle parts, as the most valuable parts. If the product integration degree and production rate are improved successfully, it will make its products more competitive on the cost side.
From the perspective of the next technological upgrade direction, the design integration of CTC and chassis system is a promising direction for the future integration of components, and CTC will accelerate the industry’s process of industrialization of skateboard chassis to a certain extent.