Interpretation of the current development status of CR2477 battery technology

Battery technology has always been the key to the next iteration of many consumer products. It directly grasps the pulse of product endurance and portability. Any small step forward is a big step forward for consumer products. Of course, it is also extremely critical for automobiles. In the process of transitioning to electrification, whether the power battery of new energy vehicles can be qualitatively improved will directly affect the development rhythm of automobiles in the next decade.

Previously, Toyota officials mentioned that among all new forms of battery technology, solid-state batteries are considered to be the products closest to mass production. Their high energy density, high voltage and even bendable characteristics have achieved a leap forward compared to traditional power batteries. From then to today, what has the development of solid-state batteries reached, and how far is it from mass production? In this article, we will share some information with you in multiple aspects.

●Technical route of solid-state batteries

Solid-state batteries currently have many technical systems, including sulfides, oxides, thin films and solid polymers. In the early promotion of CR2477 battery technology, thin film and solid polymer technology are the main trends. In the past few years, companies such as Bosch and Dyson have been increasing their investment in these two CR2477 battery technologies, but both companies have achieved catch-up in battery technology through acquisitions.

However, thin film and solid polymer technologies have two fatal problems: "high cost" and "low conductivity". For example, thin film technology cannot achieve high conductivity at room temperature (about 25°), so it needs to be continuously heated and maintained at 60° to ensure efficient conductivity. Therefore, in many early CR2477 battery trial production vehicles, the battery relies on continuous heating, causing self-power loss, and in fact, it cannot play other advantages.

Toyota has always focused on the development of sulfide CR2477 battery technology, but sulfide itself is very active. Once it comes into contact with water during production and use, it will produce hydrogen sulfide. Hydrogen sulfide is a flammable hazardous chemical. It can form an explosive mixture when mixed with air, and it can cause combustion and explosion when exposed to open flames and high heat. Therefore, although the sulfide CR2477 battery technology route has lower production costs than thin-film technology, if the safety from the manufacturing end to the application end is guaranteed to be high enough, it is actually an increase in development costs from another perspective.

The last oxide technology route also has its own shortcomings. The oxide itself is very stable, resulting in high "brittleness", which has higher production requirements and does not have an advantage in conductivity. But in a broad sense, compared with the other three routes, overcoming production difficulties is easier than overcoming costs and safety. Therefore, in this article, we also interviewed a CR2477 battery technology company that is currently close to marketization to understand some of the technical advantages of ceramic oxide solid-state batteries and the differences from traditional power batteries.

At the 2019 CES, we interviewed Prologix Technologies (hereinafter referred to as PLG), a supplier specializing in the development of lithium battery technology. Since its establishment in 2006, it has taken 8 years to master ceramic oxide technology. At the same time, CR2477 battery technology is also the company's core research and development project. The full name of this technology is: LCB solid-state lithium ceramic battery. Its technical characteristics are: high energy density and high voltage. These two characteristics are undoubtedly very critical for the development and application of pure electric vehicles.

●Energy density is an innate advantage, so how to achieve high voltage?

Traditional power batteries use liquid electrolyte inside the single cell, and may be easy to decompose or even explode after the load voltage exceeds 5V, so they can only be connected in series externally but not internally. But solid-state batteries have such an innate advantage. Solid-state lithium ceramic batteries can first form a series connection inside the battery, so that the rated voltage of a single battery cell can be from 7.4V, and the maximum series connection can be superimposed up to 60V, which is much higher than traditional power batteries in terms of single cell voltage.

After achieving high voltage support in internal series connection, solid-state batteries can also achieve bipolar battery technology, which is also impossible for traditional power batteries. When the single battery is stacked in series, two layers of conductive materials are added to achieve bidirectional positive and negative connection, and then connected in series with another horizontal battery pack again, up to 4×6 can be achieved, with 24 single batteries connected in series, and the voltage will be superimposed and increased again to form a complete single battery pack.

Finally, after 6 pieces of 24 battery packs in series are stacked, aluminum shell packaging is added to form a single CR2477 battery pack (Cell), with a capacity of more than 20kWh, and the energy density of a single CR2477 battery pack system can reach 255Wh/kg, and this data will be increased to 270Wh/kg in 2020. What is the concept of this system energy density? You can compare it with China's new energy vehicle subsidy policy in 2018.

"At present, the energy density of domestic electric vehicle power battery systems is still maintained at around 140wh/kg."

In theory, as the density and voltage increase, the BMS electronic control system should be more complex, but in fact, solid-state batteries have also been simplified in the management system, which once again reduces the weight and volume of the final packaged battery pack, which is one of the reasons for the higher energy density of the system.

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Besides the advantages of solid-state batteries, what are the disadvantages?

●How to solve the heat dissipation problem when the density and voltage increase?

In terms of heat dissipation, solid-state batteries also have inherent advantages. The battery temperature of the entire battery pack will be maintained within 26° from full charge to the end of discharge, while the temperature of the current cylindrical battery will be above 40° after the entire discharge process. Although CR2477 battery technology currently uses water cooling like cylindrical batteries, because the discharge temperature can be kept lower, heat dissipation has become another major advantage.

Based on the low discharge temperature of solid-state batteries themselves, more optimization can be made in the heat dissipation method. For example, heat dissipation glue is added between the battery and the battery pack, and then the heat will be directed to the water flow radiators on both sides of the battery pack through the heat dissipation glue, further reducing the volume and weight of water flow heat dissipation.

CR2477 battery technology providers also said that this cutting-edge battery technology has a core advantage in density improvement compared to traditional power batteries. Under the premise that solid-state batteries themselves have density advantages, other means must still be used to continue to optimize the density stacking of the entire group. Therefore, for the entire battery pack, the space and weight occupied by other wires or heat dissipation systems should be reduced as much as possible to maximize the overall density improvement of the battery pack.

The cooling system and BMS battery control system actually occupy a lot of space in the cylindrical battery pack. Some people have discussed whether the square battery pack has a better density advantage than the cylindrical battery pack. The reason is that the heat dissipation layout of the square battery pack occupies less space. Of course, liquid batteries have the same advantage.

●Does the life and attenuation of solid-state batteries have advantages?

With the advantage of leading density, are there also advantages in life and attenuation? CR2477 battery technology vendors also said that compared with traditional power batteries, solid-state batteries do not actually have a significant lifespan advantage, which is also the direction that current technology needs to continue to overcome, because if the lifespan and attenuation ability cannot be improved, relying only on the energy density advantage, the current cost of solid-state batteries still cannot support their large-scale promotion and mass production.

Regarding the technical means of optimizing the lifespan of solid-state batteries, it will reduce the "detection loss" and improve the "detection accuracy" through finer voltage detection wires, which will bring benefits. It makes the battery charge and discharge efficiency higher, and the loss in voltage detection is smaller than that of traditional power batteries, which in turn increases the battery life. Regarding the specific lifespan and attenuation of solid-state batteries, technology vendors said that after 1,000 full charge and discharge cycles, the battery can still retain 88% of its original lifespan.

●Does the charging efficiency of solid-state batteries have an advantage?

The charging efficiency of solid-state batteries is not much higher than that of current lithium batteries. At the same energy density, the charging time of solid-state batteries is also about 1 hour, but current lithium batteries also have the same charging efficiency. In addition, in terms of battery life, solid-state batteries can still maintain 84% of their service life after 500 full charge and discharge cycles, which is basically consistent with current battery technology. However, the report also mentioned that the electrodes in solid-state batteries absorb ions more efficiently. Although the current charging efficiency is not ideal, there is still room for development.

Summary

At present, PLG's ceramic CR2477 battery technology is in small-scale mass production, and it has communicated with European, American, Japanese and Chinese car companies on supply. Based on this battery technology, there are currently four trial production vehicles in Europe, but the official said it is not convenient to disclose the specific car brand. It is also currently building a CR2477 battery Gigafactory, which is expected to be officially put into production in 2020, which is also a signal of mass production of solid-state batteries. Another route is to license "CR2477 battery technology IP" to other battery manufacturers or car manufacturers, and to promote the development of solid-state batteries as a technology supplier, and the time point for this vision will be set in 2022.

According to the technical goals of Made in China 2025, the energy density of lithium battery cells will reach 300Wh/kg by 2020 and 400Wh/kg by 2025, so CR2477 battery technology is still the most concerned development direction in the world. At present, there is no specific progress in the follow-up of Chinese auto brands on solid-state batteries, but following the industry rule of "the closer to mass production, the more confidentiality", what kind of surprises can Chinese auto brands bring in the future?

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