Cell Types for Portable Power Stations: Lithium-Polymer vs. 18650 Lithium-Ion Batteries – Which Is Safer and More Durable?
The core performance and safety of a portable power station are determined by its cells. The mainstream lithium-polymer cells and 18650 lithium-ion batteries have significant differences in structure, safety, and durability, which directly affect the user experience. Below is a breakdown of their core characteristics from three aspects—principles, comparison, and purchasing guidance—to provide a scientific basis for selection.
1. Structural Principles and Energy Density of the Two Cell Types
Cell structure determines energy density (energy storage per unit volume/weight) and shape flexibility. The key differences are as follows:
• Lithium-Polymer Cells:
◦ Structural Principle: Soft-packaged (aluminum-plastic composite film, thickness 0.1–0.2mm) with gel/solid electrolytes (no liquid electrolyte). They can be customized to be thin or irregularly shaped and do not require a fixed outer casing.
◦ Energy Density: 400–700Wh/L by volume and 150–200Wh/kg by weight; a 10,000mAh portable power station has a volume of ≤108cm³ and weight of ≤200g, which is 20%–30% thinner and lighter than the 18650 version of the same capacity.
◦ Characteristics: No risk of liquid leakage, strong shape adaptability, suitable for ultra-thin and portable portable power stations.
• 18650 Lithium-Ion Batteries:
◦ Structural Principle: Cylindrical hard-shell packaged (steel/aluminum casing, 18mm diameter, 65mm length) with internal liquid electrolyte and wound electrodes. The shape is fixed and cannot be customized.
◦ Energy Density: 300–600Wh/L by volume and 120–180Wh/kg by weight; a 10,000mAh capacity requires 4–5 cells of 2000–2500mAh each, with a volume of ≥182cm³ and weight of ≥250g.
◦ Characteristics: High production standardization, suitable for multi-cell combinations to increase capacity, and commonly used in large-capacity portable power stations.
2. Safety Comparison: Packaging Type Determines Risk Level
Safety hazards of cells stem from “thermal runaway” (sudden temperature rise caused by overcharging, puncturing, or short-circuiting), and the packaging type affects the consequences of thermal runaway:
• Lithium-Polymer Cells: Soft packaging reduces explosion risk:
◦ Protection Mechanism: The aluminum-plastic film has low strength. When gas is generated during thermal runaway, it vents and swells from weak points without exploding; the gel electrolyte does not flow or support combustion, eliminating the risk of liquid leakage.
◦ Test Data: According to the IEC 62133 puncture test (3mm steel needle), only localized heating (max 65℃) and slight swelling occur, with no open flame; when overcharged to 150% of the rated voltage, the cell swells and then stops reacting, posing no safety risk.
• 18650 Lithium-Ion Batteries: Hard packaging carries explosion risks:
◦ Risk Points: Steel/aluminum casings are difficult to vent. During thermal runaway, internal pressure reaches 10–15MPa, easily causing rupture, electrolyte splashing, and ignition; the liquid electrolyte has a flash point of approximately 130℃, which intensifies the fire.
◦ Test Data: Under the same puncture test standard, there is a 50% probability of casing rupture and electrolyte combustion (flame ≤10cm, duration ≤30 seconds); in overcharging tests, 30% of samples explode, resulting in higher safety risks than lithium-polymer cells.
3. Durability Analysis: Replaceability and Cycle Life
Durability is evaluated based on “cycle life” (number of charge-discharge cycles) and “maintainability” (repairability after damage):
• 18650 Lithium-Ion Batteries: Replaceability enhances long-term durability:
◦ Cycle Life: Cells meeting UL 1642 standards retain ≥80% capacity after 500 cycles and ≥60% after 1000 cycles, suitable for high-frequency long-term use.
◦ Replaceability: For multi-cell combinations (e.g., 4 cells in series), a single damaged cell can be detected and replaced with a multimeter, eliminating the need to scrap the entire device; replacement costs are much lower than purchasing a new unit.
◦ High-End Applications: Widely used in outdoor portable power stations with ≥20,000mAh capacity, as their maintainability meets the needs of outdoor fault repair.
• Lithium-Polymer Cells: Integrated packaging limits maintainability:
◦ Cycle Life: Ordinary models retain ≥70% capacity after 500 cycles and ≥50% after 1000 cycles, slightly lower than 18650 cells; high-end solid electrolyte models maintain 80% capacity after 800 cycles but cost 30%–50% more.
◦ Maintainability: Mostly integrated packaging—local damage (swelling, degradation) cannot be repaired, and the entire device must be scrapped, leading to higher long-term costs.
4. Purchasing Guidance: Match Cell Type to Usage Scenario
Choose based on “portability needs,” “usage frequency,” and “scenario risks”:
• Daily Commute Scenarios: Prioritize lithium-polymer cells:
◦ Need Matching: Require thinness and portability (fits in pockets/side bags). Lithium-polymer cells’ thin design (thickness ≤15mm) and light weight (10,000mAh ≤200g) are more suitable; low explosion risk ensures safety when carried on the person.
◦ Purchasing Tips: Select products labeled “lithium-polymer cells” and “CE/UL certified,” focusing on thickness ≤18mm and weight ≤220g. Avoid “three-no” products (only 200-cycle life).
• Outdoor Travel Scenarios: Prioritize 18650 lithium-ion batteries:
◦ Need Matching: Require large capacity (20,000–30,000mAh, charges phones 3–4 times) and maintainability. Spare cells can be carried for emergencies; at -10℃, discharge efficiency (≥70%) is higher than that of lithium-polymer cells (≥50%), making them suitable for cold environments.
◦ Purchasing Tips: Select multi-cell combinations (e.g., 6 cells) and products with heat dissipation holes. Confirm cells meet the “INR18650” standard and avoid single-cell 5000mAh models (poor stability).
Lithium-polymer cells, with their “thinness, light weight, and low explosion risk,” are suitable for daily commutes, while 18650 lithium-ion batteries, with their “replaceability, long cycle life, and low-temperature durability,” are more suitable for outdoor use. When choosing, prioritize cell type labeling and safety certifications (CE, UL, IEC) rather than just comparing capacity: daily users should choose lithium-polymer cells, while frequent outdoor users should opt for 18650 cells to balance needs and long-term costs.
