Thoughts on EV Power Battery Structure Development
Posted: September 1, 2022
Guest Post by John Chen
NPI Manager, Vehicle Programs and Business Operations, BYD
At present, one of the most technical indicators of electric vehicle (EV) performance – which is also of high concern to consumers – is the range. In addition to the vehicle weight reduction, the component that has the most direct impact on improving the range is the battery capacity, so increasing the battery capacity has become and effective solution to increase the range of EVs.
To achieve higher capacity, innovations are generally focused on the electrochemical materials of the cell 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.
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 now to the new concept CTC (cell-to-chassis).
The core of CTC integrates the battery cell with the chassis, and then integrates the motor, electronic control, and vehicle high voltage through innovative architecture, optimizing power distribution and reducing energy consumption through an intelligent power domain controller.
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
It is necessary to have professional experience and capabilities in the two fields of full-vehicle (or chassis) R&D and battery R&D 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 eventually converge so 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 allows for the combination of the results of these two paths that is conducive to promoting CTC.
- Electrochemical Stability of Cells
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
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.
Three Modes of Thoughts on CTC Innovation
So what does this mean for professionals working on instituting a CTC strategy? There are a few ways to approach implementation that can work together as we move this technology forward.
- Cross-industry Thinking
First, the CTC concept was inspired by aircraft fuel tanks. In the early design of the fuel tank located 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 as some industries are more advanced. 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.
- Design For Assembly (DFA) Thinking
One of the applications of DFA 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, ultimately evolving into a super system. When the system's own evolutionary resources disappear, the system cooperates with other systems to further develop the resources.
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 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.
The path industry takes is still being decided, but as industry continues toward an electric future, these are the conversations we need to have.