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MetaMobility: EV Power Battery Structure Development

Updated: Apr 7

Plugged In: Thoughts on EV Power Battery Structure Development w/John Chen

This article briefly introduces the three major structure level technologies(CMP, CTP, CTC) in the development path of electric vehicle (EV) power batteries, and focuses on the three potential challenges of CTC development (joint development of body/chassis and battery, electrochemical stability of cells and force transfer over cells), And summed up with three major ways of thinking (cross-industry, DFA and TRIZ) from the CTC innovation process.

Three Structure-Level Technologies

At present, one of the most important technical indicators of EV, which is also highly concerned by consumers, is the range. In addition to the vehicle weight reduction, the direct impact on the range is the battery capacity, so increasing the battery capacity has become an effective solution to increase the range of EVs.

In order to achieve higher capacity, innovations are generally focused on the electrochemical materials of the cell (i.e. anode, cathode, separator, electrolyte) and the structure of the battery. Due to the long development cycle of the former, the innovation of battery structure is a feasible strategy in the short term, and integration is one of its important directions.

The integration trend of batteries has developed from small modules (Nissan) to large modules (SVOLT, Benz, BMW, VW, Ford, GM), ultra-large modules (CATL, Tesla), and even a completely module-free solution of blade battery (BYD). This strategy has improved space utilization to a certain extent and increased capacity. See the table above for the EV power battery development path.

In order to pursue more demanding requirements, the technology roadmap has changed from the traditional CMP (cell-module-pack) to CTP (cell-to-pack) that has been mass-produced, and then to the new concept CTC (cell-to-chassis).

The core of CTC technology is the integration of battery and chassis, or the battery is part of the chassis structure. This technology integrates the battery cell with the chassis, and then integrates the motor, electronic control, and vehicle high voltage such as DC/DC, OBC, etc. through innovative architecture, and optimizes power distribution and reduces energy consumption through an intelligent power domain controller.

CTC will enable the cost of new energy vehicles to directly compete with fuel vehicles, with larger riding space and better chassis passability. Some car OEMs and battery suppliers have or claim to explore CTC technology, such as CATL, BYD, Tesla, Rivian, VW, Volvo, SAIC, etc. CTC technology is the current development trend of EV battery and vehicle integration.

Three Challenges in CTC

CTC is a scheme with huge advantages, but also obvious disadvantages. In addition to high maintenance costs, there are at least the following three challenges in early-stage technology development.

Joint development of body/chassis and battery

First of all, it is necessary to have professional experience and capabilities in the two fields of full-vehicle (or chassis) R&D and battery R&D, in order to successfully develop an EV using CTC. The achievements of the two R&D paths of the full-vehicle (especially chassis) and the battery, advance together and finally converge at the same time so that there is a greater possibility of realizing and applying CTC. For example, owning a hardware foundation on the battery R&D path, and at the same time realizing another hardware foundation from the path of the body frame, the combination of the results of these two paths is conducive to promoting CTC.

Electrochemical stability of cells

Secondly, CTC should have high intrinsic safety cells. From an electrochemical point of view, if you want to use a cell without high intrinsic safety as a contribution value of CTC, the risk and difficulty are higher than those with intrinsic safety. Specifically, cells that do not have intrinsic safety generally need to rely on thick firewalls at the battery pack level, thick partitions, multiple layers of fireproof glue, and uninterrupted liquid cooling circuits. Some ternary lithium batteries (i.e. NCM) have low thermal stability and require multiple protections to reduce the high risk of thermal runaway and thermal diffusion.

Force transfer over cells

Thirdly, from the point of view of mechanical force, CTC requires that all cells can be combined or individually formed into multiple force transfer structures. For example, blade batteries transmit force continuously for each cell, and 4680 batteries transmit force in a row of cells. In addition, structural adhesives become more important as structural connections.

All in all, if you ask me which OEMs or suppliers have higher chances to firstly implement the CTC technology in mass-produced EVs, I personally may go for BYD and Tesla. It looks more challenging for other OEMs or battery suppliers to land, due to the viewpoints above, especially considering the two OEMs already have their own battery - blade battery and 4680 battery.

Three Thinkings on CTC Innovation Cross-industry thinking

First, the CTC concept was inspired by aircraft fuel tanks. In the early design of the fuel tank in the wing of the aircraft, the space utilization rate was low, and the lightweight concept was not used. Later, the wing was directly integrated with the fuel tank design, and the wing was the fuel tank. Inspired by innovations in the aircraft industry, the automotive industry embarked on a quest for the body chassis or battery.

The enlightenment learned from this case is that the technology of product structure design has unbalanced development in different industries, some industries are more advanced, and some are more backward. When we want to innovate, we need to think across industries, learn from the advanced experience and existing structures of other industries, stand on the shoulders of giants, and innovate quickly and efficiently.

DFA thinking

One of the applications of DFA (Design for Assembly) thinking is to reduce the number of parts and simplify product design. CTC technology is to reduce the number of parts from two aspects:

(1) the battery is the chassis, removing additional chassis parts, wiring harnesses, and fasteners. (2) the battery provides structural strength and removes the original body structural reinforcements.

TRIZ thinking

According to TRIZ theory, a product or object is a system. The system is composed of multiple subsystems, and certain functions are realized by the interaction between the subsystems. In addition, the system is in the super system, the super system is the environment in which the system is located, and other systems in the environment are the constituent parts of the super system.

One of the evolution directions of TRIZ theory is the evolution to super system. That is to say, when the system's own evolutionary resources disappear, the system turns to a super system, or in other words, it cooperates with other systems to further develop the resources. There are mainly two ways:

(1) the resources of the system and the super system are combined.

(2) a certain subsystem of the system is accommodated in the super system.

According to the law of TRIZ evolution to super system, the evolution of traditional power battery pack to chassis and even body integration is the trend, which is the embodiment of the current development of CTC technology.

Based on this reasoning, it is possible to speculate on the possibility of the future power battery of the post-CTC on EVs. For example, the battery may be integrated with the entire interior and exterior of the body, or it may be driven by solar energy or bioenergy, or the EV itself does not have a battery and is powered by an external transportation system

John Chen

Program Manager - Vehicle/Battery


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