Integration with Vehicles--The Strengths of Toyota's Battery Development Strategy


"Peace of mind" is key to Toyota's battery development concept. What strengths has Toyota cultivated to achieve the aim of this concept? Chief officers leading the effort explain the key points.

Striking a balance among five factors

From here, I would like to explain something that Toyota values in its development of batteries. What Toyota values the most is to develop batteries that its customers can use with peace of mind. Especially, we are focusing on safety, long service life, and high-level quality to produce good, low-cost, and high-performance batteries.

For example, longer service life also affects a vehicle's residual value. In terms of cruising range, high energy density and high-level performance are also necessary. We want to make the charging speed faster, but too fast will affect safety.

Therefore, we think it is important to strike a balance between each of these factors to ensure safe use. This concept has remained unchanged since batteries were installed in the first-generation Prius, and it is the same for the batteries in all of our electrified vehicles.

By applying the technology that we have cultivated through our experience in batteries for HEVs also to the batteries for future BEVs, we believe that we will be able to deliver batteries that can be used with peace of mind.

Although Toyota is committed to balancing the five factors for peace of mind, too much emphasis on one could be detrimental to the others. For example, charging a battery too fast in pursuit of high performance could cause it to catch fire or overheat, affecting safety.

Important here is the integrated development of batteries and vehicles, which is mentioned further down.

How batteries are used depends on how the vehicles in which they are installed are used. For example, taxis are used in a certain way, and it is possible to obtain information such as charging frequency and battery temperatures, which can be fed back into battery evaluation and design in line with usage conditions.

Maeda says that only developing cars or only developing batteries makes things difficult.

To determine the balancing point of the five factors mentioned, it is necessary to obtain driving data that includes driving conditions and usage environments, find out what the conditions would be like if batteries were used instead, and repeatedly verify what is happening inside the batteries.

According to Maeda, Toyota has the advantage of being able to conduct such steady and earnest efforts for both batteries and vehicles.

Toyota’s efforts for batteries that enable peace of mind

Now, I would like to introduce three examples of the many efforts required to produce batteries that can be used safely, using lithium-ion batteries as the focus of my explanation.

This is an example of ensuring safety. It is known that each battery cell shows signs of localized abnormal heat generation during spirited driving or other driving that places a large load on the battery.

By analyzing the phenomena occurring inside the battery and conducting a vast amount of model experiments, we have been able to clarify the effect of driving style on the battery, as well as the mechanism of this effect.

Based on the results, we have been able to detect signs of abnormal local heating of cells through multiple monitoring of voltage, current, and temperature of individual cells, blocks of cells, and the entire battery pack.

The battery is then controlled to prevent abnormal heat generation.

We will maintain our concept of ensuring safety, security, and reliability down to the local areas of each battery even when it comes to BEV systems, and we will continue to refine that concept.

The second example I would like to share with you is our commitment to long service life.

We have applied the technologies that we have cultivated through the development of batteries for HEVs to PHEVs, and the batteries in the C-HR BEV have a greatly higher capacity retention rate after 10 years than the batteries hitherto used in our PHEVs.

Furthermore, for the Toyota bZ4X, which is scheduled to be launched soon, we have set a target of 90 percent endurance performance, which is one of the highest in the world, and we are currently finalizing our development efforts to achieve it.

I would like to introduce some examples of the developments that we are working on to achieve long service life. From a detailed analysis of the inside of lithium-ion batteries, we know that degraded materials on the surface of the anode have a significant impact on the life of a battery.

To suppress the generation of these degraded materials, we are clarifying the generation mechanism and taking measures in various aspects such as material selection, pack structure, and control system.

Careful implementation of detailed analysis and an accumulation of countermeasures has led to improved endurance performance.

The third example I would like to share with you has to do with our efforts for achieving high-level quality. If metallic foreign matter enters the battery during the manufacturing process and directly connects the anode and cathode electrically, there is the possibility of failure.

We confirmed the shape, material, and size of foreign matter that enters the manufacturing process and its effect on endurance, and we clarified how such affects batteries.

Based on this, we are being extremely attentive to the size and shape of foreign matter, and we are managing processes in a way that is aimed at preventing the generation or entry of relevant foreign matter.

What I have explained just now are only a few of the things that we are doing, but with this kind of steady and meticulous analysis and with the experience gained from the feedback of 18.1 million units in the market, we aim to continue to deliver batteries that can be used with peace of mind.

When it comes to batteries, the most fatal problem is catching fire. To ensure that batteries do not catch fire even as they deteriorate, it is necessary to be able to analyze and investigate batteries in advance and monitor them closely.

Up until now, Toyota has been steadily identifying patterns that emerge by analyzing in combination the conditions of temperature, amount of charge, current, and state of degradation. Evaluations have been stored as digital data, and Toyota has recently been able to supplement the related data using AI analysis technology.

This is one of the ways that Toyota’s strengths from having developed batteries in-house for many years can be applied.

Next-generation batteries made with technology cultivated through HEVs

Next, I would like to explain the bipolar nickel-metal hydride battery used in the new Aqua announced in July this year.

We co-developed this battery with Toyota Industries Corporation, taking on the challenge of developing a bipolar structure, and we commercialized it as an onboard battery for driving.

Compared to the batteries used in the previous generation of the Aqua, the output density has been doubled, giving the car a powerful acceleration sensation.

As for batteries for next-generation BEVs, the BEV technologies that we have cultivated since our RAV4 EV launched in 1996 and the latest battery and electrified vehicle technologies that we have cultivated through HEVs have been incorporated into the Toyota bZ4X and will soon be introduced to the market.