I. Basic Concepts of Soft-Pack Lithium Batteries, Lithium Battery Packs, and Aluminum-Cased Lithium Batteries
Soft-pack lithium batteries are liquid lithium-ion batteries encased in a polymer shell and packaged with an aluminum-plastic composite film. Soft-pack lithium batteries have low mechanical strength, and in the event of a safety accident such as an internal short circuit, the battery is prone to bulging and releasing gas, thus reducing the risk of explosion.
Lithium-ion battery packs: "Lithium-ion batteries" are a type of battery that uses lithium metal or lithium alloy as the negative electrode material and a non-aqueous electrolyte solution. Lithium-ion battery packs can be broadly classified into two categories: lithium metal batteries and lithium-ion batteries. The main components of a lithium-ion battery pack are positive and negative electrodes, electrolyte, separator, and casing.
Aluminum-cased lithium batteries:
Aluminum-cased lithium batteries are battery casings made of aluminum alloy. Aluminum-cased batteries come in two types: hard-cased and soft-cased. They are mainly used in prismatic lithium batteries. The reason for using aluminum casings in lithium battery packs is their light weight and perceived safety compared to steel casings. Aluminum-cased lithium batteries are currently the mainstream liquid lithium batteries and are used in almost all areas related to lithium batteries.
II. What are the differences between pouch lithium batteries, lithium battery packs, and aluminum-cased lithium batteries?
① Application areas
Soft-pack lithium batteries are mainly used in mobile internet, power banks, and digital products such as smartphones, laptops, and cameras.
Lithium battery packs have a wide range of applications, including indoor distributed systems such as small computer rooms and low-voltage rooms, outdoor sites for new energy, communication base stations, indoor and outdoor sites without air conditioning, and unmanned sites in broadcasting, military, petroleum, and meteorology industries.
②Structural features
The biggest difference in the key materials used in pouch lithium batteries lies in the soft packaging material (aluminum-plastic composite film), which is the most critical and technically challenging material in pouch lithium batteries. Soft packaging materials typically consist of three layers: an outer barrier layer (usually an outer protective layer made of nylon BOPA or PET), a permeation barrier layer (the middle layer of aluminum foil), and an inner layer (a multifunctional high-barrier layer).
Lithium-ion battery packs: Lithium-ion batteries are assembled into a battery pack, resulting in higher energy density, longer service life, and extended battery life. The main components of a lithium-ion battery pack are positive and negative electrodes, electrolyte, and separator.
③ Energy ratio and weight
Soft-pack lithium batteries are 40% lighter than steel-cased lithium batteries of the same capacity and 20% lighter than aluminum-cased batteries; steel-cased batteries of the same size have 10-15% higher capacity and 5-10% higher capacity than aluminum-cased batteries.
The energy density of lithium battery packs is 3 to 4 times that of lead-acid batteries, 2.5 times that of nickel-cadmium batteries, and 1.8 times that of nickel-metal hydride batteries. Therefore, with the same battery capacity, lithium batteries are smaller and lighter than lead-acid, nickel-cadmium, and nickel-metal hydride batteries.
Lithium-ion battery aluminum casings come in two designs: square and rounded. The material is generally an aluminum-manganese alloy, containing five main alloying elements: Mn, Cu, Mg, Si, and Fe. These five alloys play different roles in the lithium-ion battery casing. For example, Cu and Mg improve strength and hardness, Mn enhances corrosion resistance, Si enhances the heat treatment effect of magnesium-aluminum alloys, and Fe improves high-temperature strength. The lightweight design, safety features, and resulting performance advantages have made aluminum casings the mainstream for lithium-ion batteries. Currently, lithium-ion battery aluminum casings are still evolving towards higher hardness and lighter weight, which will provide the market with more technologically superior lithium-ion battery products.
In regions with higher consumption levels, such as Europe and the United States, pouch lithium battery packs have a dominant market share. However, in most developing countries, such as India and the Middle East, aluminum-cased batteries have a clear advantage.
In terms of technological maturity, aluminum-cased technology is very mature and has low requirements for material technology (such as gas expansion rate and expansion rate), so there are no technological barriers in the industry. However, pouch lithium batteries still face many technical challenges, especially regarding battery cycle expansion indicators, which most cell manufacturers have not yet solved. Aluminum-cased battery manufacturing has a higher degree of automation than pouch lithium battery packs, thus reducing the impact of human factors on product consistency to some extent and saving labor costs.
In terms of manufacturing costs, aluminum-cased lithium battery materials are now completely domestically produced, while the aluminum-plastic film materials used in pouch lithium battery packs still need to be imported. Furthermore, aluminum-cased batteries have lower technical requirements for battery materials than pouch lithium batteries. Therefore, for the same capacity, the overall material cost is about 10% lower than that of pouch lithium batteries. In addition, the finished product is simple to process, reliable, and has a significant cost advantage.
Soft-pack lithium batteries primarily target the mid-to-high-end market, offering higher profit margins per unit. Under the same production capacity, their relative profit is higher than that of aluminum-cased lithium batteries, and their payback period is also shorter. Because aluminum-cased batteries are easier to scale up, and product qualification rates and costs are easier to control, both currently enjoy considerable profits in their respective market segments.
Aluminum-cased lithium batteries use laser sealing technology, while pouch lithium-ion batteries use hot-melt technology. In terms of sealing, aluminum-cased batteries are superior to pouch lithium-ion batteries, avoiding aging and leakage at the seal. The burst pressure of pouch lithium-ion batteries is much lower than that of aluminum-cased batteries. Due to the use of aluminum-plastic composite film packaging, pouch lithium-ion batteries have low mechanical strength. In the event of a safety accident such as an internal short circuit, the battery is prone to bulging and venting, reducing the risk of explosion. Aluminum-cased batteries, on the other hand, use a fully sealed process, and under the same conditions, the gas pressure is not easily released, increasing the safety hazard.
The energy density of pouch lithium batteries is higher than that of aluminum-cased batteries. For batteries of the same volume (2Ah~5Ah), pouch lithium-ion batteries are about 10%-20% lighter than aluminum-cased lithium batteries. As the technology of pouch lithium batteries matures, they have the potential to replace aluminum-cased lithium batteries, and their advantages will become more prominent.
