In the selection process of lithium batteries, many engineers will first encounter a problem: They are also lithium batteries. Why are some labeled "polymer" and others "liquid lithium ion"? What's the difference between the two? How to make choices among projects? This article will start from the material and structure and give a practical comparison and selection reference.

1. The essential difference lies in the electrolyte form

Traditional liquid lithium-ion batteries use liquid organic solvent electrolytes. A separator is required inside the cell to separate the positive and negative electrodes, and the charge and discharge are completed by relying on the migration of lithium ions in the electrolyte. Lithium polymer batteries (lithium polymer) use gel or solid polymer electrolytes. The electrolytes are "fixed" in the polymer matrix and therefore no longer rely on large amounts of free liquid.

This difference has brought about a chain reaction: polymer batteries can be made into aluminum-plastic film flexible packaging, without the need to use steel shells or aluminum shells, and the shape plasticity is greatly improved; at the same time, because there is no large amount of free electrolyte, the risk of bulging and leakage is significantly reduced, and the safety performance is gentler.

2. Key performance comparison

  • Energy density:Polymer batteries are usually 10% to 20% higher in the same volume, which is crucial for portable devices with limited space.
  • Shape freedom:Polymers can be made into ultra-thin (below 0.5mm), special-shaped, and curved shapes, while liquid cylinders/squares are subject to standardized dimensions.
  • Security:When the polymer is overcharged or short-circuited, it will usually cause bulges and smoke, but rarely violent splashing; when the internal pressure of the liquid battery core rises, the pressure relief valve will operate, and it is equally safe if it is properly controlled.
  • Cycle life:Mature liquid systems have a slight advantage in retention rate between 500 and 800 cycles, and polymers have significantly caught up in recent years.
  • cost:The standard model of liquid battery cells has obvious scale effect and lower unit price; the cost of mold opening and certification of customized polymer models is higher.

3. How to choose

If your product pursues thinness, compact appearance, and irregular shape, such as smart wearables, Bluetooth headsets, portable medical detectors, and card-type devices, you should give priority to polymer lithium batteries; if you value cost control, rapid replacement of standard models, and stable mass supply, such as power tools, energy storage modules, and general consumer electronics, liquid cylindrical or square batteries are more suitable.

It needs to be reminded that the selection cannot only look at the battery body. Protection board (PCM/BMS), charge and discharge rate, operating temperature zone, certification requirements (UN38.3, IEC62133, UL, CE, etc.) will all affect the final solution. It is recommended to communicate with battery manufacturers about structural dimensions, capacity targets and certification lists at the project establishment stage to avoid repeated revisions later.

4. Conclusion

The relationship between polymers and liquids is not a simple relationship between advantages and disadvantages, but a branch of technology facing different needs. Only by understanding the structural roots of the two and making a comprehensive judgment based on the space, cost, lifespan and safety objectives of the product can a truly suitable power supply solution be selected.