How to determine the winner in the pursuit of energy density and volumetric weight?
While differing in appearance, these three types of battery designs also possess their own unique characteristics. The materials used in the casing and the internal design can influence the energy density, safety, and weight of a single battery cell. To illustrate, the filling represents the energy density of a single battery cell, while the flour represents the choice of packaging material.
Stainless steel casings were once the primary packaging material for cylindrical and prismatic batteries. However, due to different manufacturing standards, lighter aluminum casings were rapidly adopted for prismatic batteries, giving them a weight advantage. Meanwhile, pouch batteries, in pursuit of an even thinner design, utilize aluminum-plastic film packaging, which is even lighter than aluminum casings. The thinness is so extreme that you can even feel the liquid electrolyte flowing inside.
The materials used for the outer casing not only directly affect the weight of a single battery cell, but also impact battery safety and heat dissipation, since the individual cells are ultimately packaged into a battery pack for placement in the vehicle. Steel casings are the hardest and heaviest, requiring a balance between safety and relatively lower manufacturing complexity. Aluminum casings, on the other hand, are the softest and lightest, but require higher standards for heat dissipation and impact safety during both cell manufacturing and battery pack assembly. Square batteries exhibit similar advantages and disadvantages depending on the choice of casing material.
Don't underestimate the importance of individual battery cell weight; it has multiple impacts on the final packaging and placement within the vehicle. Lighter battery packs result in a lower overall vehicle weight, giving automakers more layout options. With technological advancements, lighter individual batteries offer greater flexibility in balancing energy density. For example, if a vehicle's design limits it to a 300kg battery pack, obviously lighter cells result in a higher overall energy density for the entire pack.
For cylindrical and prismatic batteries with steel casings, the weight distribution control methods when installing them onto the vehicle body are relatively limited. For example, in most current new energy vehicles that use cylindrical battery packs, the battery packs are positioned directly under the vehicle body. This ensures that even if the battery is slightly heavier, it won't affect the overall front-rear weight distribution, but it will impact the vehicle's ground clearance and the height of the floor inside the passenger compartment. Some plug-in hybrid vehicles place the cylindrical battery pack under the trunk, using its weight to balance the overall weight distribution in conjunction with the engine at the front. However, this results in a significantly reduced trunk space.
The different battery shapes present varying advantages and disadvantages in terms of safety and heat dissipation during battery pack assembly. While cylindrical batteries are heavier and have lower energy density, the space between the cylinders during packing provides excellent heat dissipation. This is different for prismatic batteries; if they are tightly packed together without gaps, heat dissipation becomes an issue, and the safety of individual cells is compromised. Pouch batteries are even more complex to pack, requiring safety, adequate heat dissipation, and the advantage of a slim profile – the complexity of the pack assembly process is considerable. Many automakers carefully consider the cost investment in the packaging of these three battery types. Currently, cylindrical batteries, with their lower manufacturing complexity and cost, are the best choice.
Commentary: Simply put, if prismatic batteries had the same industry standards as cylindrical batteries, their advantages and disadvantages in application would be roughly the same. However, pouch batteries offer greater design flexibility and have more significant advantages such as lower weight and higher energy density, making them the preferred battery type for more automakers in the future. Conversely, the manufacturing requirements are significantly higher than the other two types, and the additional costs and technical requirements in production and packaging indirectly increase the final price of new energy vehicles. Therefore, the extreme advantages and disadvantages of pouch batteries have deterred some automakers, and currently, the proportion of new energy vehicles using pouch batteries is the smallest. In short, when faced with cost, more companies have chosen to compromise with the other two.
Furthermore, the type of individual battery cell is only one aspect that automakers consider when choosing their R&D direction; packaging technology is also a crucial element. Currently, leading new energy vehicle manufacturers all have their own battery labs. They conduct secondary R&D based on battery prototypes provided by suppliers, and then push the research solutions back to the suppliers, with both parties finalizing the required battery solution. The packaging work is then completed by themselves or their suppliers, and finally, meticulous weight distribution is used for vehicle installation. Every step in this process involves weighing the pros and cons, which is key to understanding which type of battery automakers ultimately choose.
Narrowing the gap or even surpassing the lead, Chinese battery companies and automakers are achieving win-win cooperation.
From individual battery cells to vehicle applications, automakers and battery companies maintain close partnerships. For example, Panasonic and Tesla have maintained a long-standing technological alliance in the application of cylindrical batteries, while General Motors and LG Chem have reached a technical consensus on pouch battery technology. Prior to this, Samsung SDI also had extensive technical cooperation with BMW on prismatic batteries.
Battery suppliers determine the reliable basic battery manufacturing processes, while automakers' secondary R&D determines the battery's performance in vehicles, ultimately impacting three major aspects: range, weight distribution, and safety. For a long time, the core technologies of these three battery types were controlled by Japanese and South Korean companies, making them the preferred battery suppliers for new energy vehicle manufacturers. However, in the past two years, Chinese battery and new energy vehicle companies have not only significantly narrowed the gap with their foreign counterparts in battery technology and applications, but also gained more influence in areas such as production capacity, quality control, and practical application performance. It has become commonplace for foreign automakers to choose Chinese battery companies as their primary suppliers.
By 2018, Chinese battery companies had acquired comprehensive technological capabilities in manufacturing cylindrical, prismatic, and pouch batteries, and had made significant progress in the energy density of individual cells for all three types of batteries. In recent years, Chinese battery companies have also transitioned from cylindrical and prismatic batteries to pouch battery technology, with several companies, led by CATL, Lishen, and Guoxuan High-Tech, choosing to adopt the pouch battery technology route.
Meanwhile, as domestic new energy vehicle subsidy standards place higher demands on battery energy density, pouch cell technology has become a crucial means to achieve lightweight and high-density batteries. At the beginning of this year, CATL, Lishen, and Guoxuan High-Tech, three companies undertaking new lithium-ion power battery projects, all chose the pouch cell technology route, achieving a single cell energy density of 300Wh/kg. However, its high manufacturing process requirements also necessitate improvements in related aftermarket technologies, such as the process and production capacity of the outer packaging aluminum-plastic film, and high-precision lamination, electrolyte injection, and packaging equipment technologies.
However, many practical problems remain on the road to developing pouch batteries. Firstly, aluminum-plastic film technology is costly, and domestic technology is limited, especially in the lamination process, which requires even higher standards than winding. Quality control issues directly impact battery life and safety. To maintain simultaneous growth in production capacity and quality control, close cooperation between battery manufacturers and automakers is crucial.
Before the new energy boom, it may become a trend.
A few years ago, the power batteries for new energy vehicles in China mainly consisted of lithium iron phosphate prismatic batteries, because at that time, Chinese companies' own cylindrical battery technology and cost control capabilities were not as outstanding as those of overseas companies. From the perspective of automakers, customizable prismatic batteries were more conducive to the rapid research and development and design of new energy vehicle models. In retrospect, in order to achieve results more quickly, battery and automakers regarded prismatic batteries as a transitional technology, while currently, cylindrical ternary lithium batteries have become the new mainstream.
However, this doesn't mean any one will ultimately become the dominant technology. Cylindrical, prismatic, and pouch batteries each possess unique value in the market, and their emergence as a new trend will also be influenced by the speed of vehicle development. For us, the real question is whether automakers can maximize the advantages of each technology in their final products. Like the saying goes, "A cat is a good cat as long as it catches mice," and for pouch and cylindrical batteries, the ones that travel the longest are the best.
