The development trend of lithium batteries

The development trend of lithium batteries

Power batteries and energy storage batteries are currently the two major applications of battery technology. Energy storage batteries correspond to solar energy and other equipment, and power batteries correspond to new energy vehicles. The battery technology companies once led by Japanese and Korean companies have long ago classified the types of power battery packaging into three major forms: cylindrical, square, and soft. Intuitively, they only differ in shape, but at the same time they There are also differences in technology development and application perspectives, so what kind of difference will happen to small batteries due to different shapes? This is the main content of our issue.

Japan's SONY company invented the 18650 lithium battery in 1992, which has become the most common cylindrical battery design at present. For example, the No. 5 and No. 7 alkaline batteries are designed in this shape. In the following time, due to the increase in battery application scenarios, prismatic batteries led by Samsung SDI and soft pack battery designs led by LG Huawei have also entered the market. At present, the three types of technologies are also applied in new energy vehicle products.

For new energy vehicles, the current market structure of the three types of batteries is relatively stable. There is no best but better. Different countries and different car companies have different recognition of the three types of battery technology. I participated in a technical training on soft pack batteries not long ago, so I also want to talk to you in today's content, and feedback to our practical application level, what is the difference between these three types of batteries with different shapes.

Change the standard without changing the cost, and the basic principle must be followed in any change of shape

Because of the different manufacturing and packaging methods, the three types of batteries have obvious differences in shape. But there is no impact on the working principle of the battery itself. The manufacturing method is mainly aimed at different working conditions, equipment applications and more diversified examples, which is not very rigorous, like a cake made into different shapes. , But the principle of baking and fermentation of raw materials is the same. Simply put, lithium ions in the electrolyte complete a discharge from the negative electrode to the positive electrode, and then return from the positive electrode to the negative electrode to complete a charge. Therefore, the design of the three different shapes of the battery will comply with the technical principles of the battery itself, but due to the different shapes, the manufacturing and molding are divided into two different processes: winding and stacking.

Cylindrical battery

All three shapes of batteries will eventually become cylindrical, square and soft-packed batteries through cylindrical winding, square winding and square stacking. But at present, only cylindrical batteries have consistency in manufacturing standards. For example, the well-known cylindrical batteries are divided into 14650, 18650, 21700 and other models. Many people think that this is a battery type, but it only represents a cylindrical battery. The size standard of the battery. Take the 18650 type as an example. It is currently the most mature cylindrical battery standard. Through continuous technological advancement, the 21700 type is likely to replace the 18650 type as the first-choice cylindrical battery product for new energy vehicles.

Square battery

The plasticity of the prismatic battery will be stronger, and the design can be customized according to the specific needs of the product. As a result, there are differences in size. At present, regardless of the manufacturing process or application standards, there is no clear standard division as for cylindrical batteries. But because of its high flexibility, it has been used for a long time in the early new energy vehicles. Car companies can customize the size of the square battery according to the needs of the model, without being restricted by the cylindrical battery standard. The prismatic battery was once considered to be the most suitable battery design for new energy vehicle applications. At present, square batteries are used in many models, such as BMW's i-series models, Roewe ERX5, Weilai's ES8, and the range-extended SUV for cars and homes that will be launched in the future.

Soft pack battery

The soft pack battery adopts a superimposed manufacturing method, so it pursues a slimmer volume and the lightest weight under the same capacity density. Similarly, soft pack batteries can also be customized according to application requirements, as small as the size of our mobile phone batteries, as large as used in new energy vehicles. Soft pack batteries have always been the industry’s first choice for mobile devices, but in automotive applications, they are also valued by car brands because of their volume controllability, especially for plug-in hybrid vehicles, taking into account the layout and layout of the entire vehicle. In terms of weight, the volume advantage of the soft pack battery is more obvious. At present, GM’s Buick’s VELITE5/VELITE5, Cadillac’s CT6 plug-in, XT5 hybrid models, and Nissan’s Sylphy battery all use soft pack batteries.

Comment: The three types of battery designs each have their place in the market by "changing the soup without changing the medicine". From the design point of view, the three are not absolutely good or bad. However, because the most mature cylindrical battery has a fixed global standard, from manufacturing to application, the whole process will be more rigorous. Battery companies build batteries according to standards, and car companies also design and apply according to standards. Consistency. China has tried to use the European VDA standard as a template for prismatic battery technology, but not many companies have cited it. The car companies that first chose to use prismatic batteries are gradually replacing them with cylindrical batteries, just to ensure product safety standards. consistency.

The outstanding advantage of square and soft-pack batteries is that they can be customized. As a result, there are different standards and different processes. Car manufacturers and battery suppliers must reach a strict agreement on design and process requirements, which is obviously higher for both parties. The cost of research and development is paid. At present, car companies have their own preferences and opinions on these three types of batteries, and they will choose their more recognized types for product development. After all, users are concerned about vehicle endurance performance and better counterweight and layout. There is no need for battery shape Likes. Let’s talk about the advantages of the three battery designs in terms of energy density and safety under different shapes?

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How to distinguish between winners and losers in the pursuit of energy density and volumetric weight

The three types of battery designs also have their own characteristics on the basis of different shapes. The three can affect the energy density, safety and weight of the single battery through the shell material and internal design. Let's take the cake as an example. The filling represents the energy density of the single battery, and the flour represents the choice of shell packaging materials.

Stainless steel casings have always been the main packaging materials for cylindrical and square batteries. Due to the different requirements of process standards, lighter aluminum casings have been quickly promoted on square batteries and have also formed an advantage in weight. The soft-pack battery is also packaged with aluminum-plastic film, which is lighter than the aluminum shell, because of the pursuit of a thinner process. You can even feel the flow of the internal liquid battery with your hands.

The different shell materials not only directly affect the weight of the single battery, but also affect the safety and heat generation of the battery. After all, the individual batteries must be packaged into groups and placed in the car. The steel shell is the hardest and the heaviest. It needs to take into account the safety process and the difficulty is relatively low, while the aluminum film shell is the softest and lightest. When it is manufactured in a single body and packaged into a group, the requirements for both heat dissipation and collision safety are also higher. . The prismatic battery will have the same advantages and disadvantages depending on the choice of housing material.

Don't underestimate the weight of the single battery, which will have multiple effects on the final package and put it in the car. Lighter battery packs can make the overall vehicle weight lower, which also provides car companies with more layout methods. With the advancement of technology, lighter single cells have more room for taking into account energy density. For example, the vehicle is designed to be limited to only a set of 300 kg battery packs. Obviously, the lighter the single unit, the higher the energy of the entire battery pack.

The use of cylindrical and square batteries with steel shells has a relatively simple solution for controlling the counterweight when installed on the vehicle body. For example, the current mainstream new energy vehicles using cylindrical battery packs, the layout of the battery packs are directly below the body, so as to ensure that even if it is heavier, it will not affect the front and rear counterweights of the vehicle, but it will affect the ground clearance and compartment of the vehicle. The height of the internal platform will have an impact. In some plug-in hybrid vehicles, the cylindrical battery pack is placed under the trunk, and the weight of the front engine is matched to balance the weight of the vehicle, but the result is that the space in the trunk will change. Very small.

The battery shapes are different, and the three types of batteries have different advantages and disadvantages in terms of safety and heat dissipation of the package. Although the cylindrical battery is heavy and has low energy density, it forms a good heat dissipation space between the cylinder and the cylinder when it is packaged. The square is different. If the battery is tightly arranged without leaving a gap, in addition to the problem of heat dissipation, It is also difficult to guarantee the safety between the monomer and the monomer. The packaging of the soft pack battery will be more complicated. It is necessary to be safe and to ensure heat dissipation without losing the advantage of the soft pack's slim volume. It is conceivable how complicated the packaging process is. Many car companies will carefully consider the cost input of the three types of battery design in the packaging process. At present, relying on the cylindrical battery with lower process difficulty and lower cost is a good choice at this stage.

Comment: Simply put, if the square battery also has the same industry standard as the cylindrical battery, then the advantages and disadvantages of the two in application are basically at the same level. However, soft-pack batteries are more flexible in design and have more obvious advantages such as low weight and high energy density. In the future, they will become the preferred battery type for more car companies. But on the contrary, the requirements for the manufacturing process are also significantly higher than the former two. The additional costs and technical requirements in production and packaging have increased the terminal price of new energy vehicles in disguise. Therefore, the extreme advantages and disadvantages of soft-pack batteries have also discouraged some car companies. Currently, the proportion of new energy vehicles using soft-pack batteries is also the least. To put it bluntly, in the face of cost, more companies have chosen to compromise with the other two.

In addition, the type of single battery is only one of the angles for car companies to choose the direction of research and development, and packaging technology is also a particularly critical link. At present, the first-line new energy vehicle companies have their own battery laboratories. They do secondary research and development on the basis of the battery prototype provided by the supplier, and finally push the research plan back to the supplier, and the two will work together to finalize the required battery plan . Then the packaging work is completed by itself or the supplier, and the final step is to complete the installation of the car through a careful counterweight layout. There are trade-offs between the pros and cons in all aspects of the process, and it is also the key to reverse the type of battery type that car companies will choose.

Closer or even overtake, the win-win cooperation between Chinese battery companies and car companies

From single batteries to vehicle applications, there is a close cooperative relationship between car companies and battery companies. For example, in the application of cylindrical batteries, Panasonic and Tesla have maintained a technical alliance for many years, and General Motors and LG Chem have reached a technical consensus on soft-pack battery technology. Prior to this, Samsung SDI and BMW also had a lot of technical cooperation on square batteries.

The battery supplier determines the reliable battery basic technology, and the secondary research and development of the car company determines the performance of the battery in the vehicle's final battery life, counterweight and safety. The core technology of the three types of batteries has been mastered by Japanese and South Korean companies for a long time, and has become the preferred battery supplier of new energy car companies before. In the past two years, compared with foreign countries, Chinese battery and new energy vehicle companies have not only greatly shortened the battery technology and application level, but also have more say in terms of production capacity, quality control, and practical application performance. It has become the norm for foreign car companies to choose Chinese battery companies as their preferred suppliers.

By 2018, Chinese battery companies already have comprehensive technical capabilities for the manufacture of cylindrical, square, and soft-pack batteries, and they have made great progress in the single energy density of the three types of batteries. In recent years, Chinese battery companies have also transitioned from cylindrical and square batteries to soft-pack battery technology. Several companies headed by Ningde Times, Lishen, and Guoxuan Hi-Tech are choosing to adopt the soft-pack battery technology route.

At the same time, as the domestic new energy vehicle subsidy standard puts forward higher requirements on battery energy density, soft pack technology has become an important means of achieving lightweight and high-density batteries. At the beginning of this year, CATL, Lishen, and Guoxuan Hi-Tech will undertake Enterprises of the new lithium-ion power battery project have all chosen the soft-pack battery technology route, and the energy density of the single cells has reached 300Wh/kg. However, its requirements for high manufacturing processes also require improvements in related aftermarket technologies, such as the process and production capacity of outer packaging aluminum-plastic film, high-precision lamination, electrolyte injection and packaging equipment technology.

However, there are still many practical problems on the road to the soft-pack battery technology. The first is the high cost of aluminum-plastic film technology and the limited level of domestic technology, especially in the control of lamination technology. The requirements are higher than those of winding. Quality control issues will directly affect battery life and safety issues. To maintain the simultaneous growth of production capacity and quality control, the concerted efforts between battery companies and car companies are even more critical.

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