Knowledge Related to the Quality of Lithium Battery Cells

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Update time : 2026-01-27

I. Core Concept: What Are Lithium Battery Cells? 

Lithium battery cells are the smallest energy storage units encapsulated with positive electrode materials (ternary lithium/lithium iron phosphate), negative electrode materials (graphite), electrolyte, and separators. Common forms include cylindrical (e.g., 18650, 21700 models), prismatic aluminum case, and pouch cells. An e-bike’s battery pack is composed of dozens to hundreds of cells connected in series and parallel — the consistency and stability of cell quality are more important than the capacity of a single cell, which is the core reason many "high-capacity inferior batteries" suffer from severe range degradation and short service life.

II. 4 Key Indicators of Cell Quality

1. Energy Density (Unit: Wh/kg)

Definition: The amount of electrical energy stored per unit weight/volume, directly affecting battery pack weight and maximum range.

Practical Significance: The energy density of mainstream e-bike cells ranges from 150-200Wh/kg. Higher density means longer range for batteries of the same weight (e.g., high-quality 18650 ternary lithium cells reach 180Wh/kg, while inferior ones only hit 120Wh/kg).

Pitfall to Avoid: Beware of false claims like "high capacity with low weight" — energy density has physical limits; excessive labels are mostly false.

2. Cycle Life (Unit: Cycles)

Definition: The number of charge-discharge cycles until the cell capacity degrades to 80% of its initial capacity, a core indicator of battery lifespan.

Grading Standards:

High-Quality Cells: ≥1200 cycles (3-5 years of normal use)

Regular Cells: 800-1000 cycles (2-3 years of normal use)

Inferior Cells: ≤500 cycles (capacity halved in about 1 year)

Related Technology: Echoing the "lithium battery replacement of lead-acid batteries" in development history — lead-acid batteries only have a cycle life of around 300 cycles, so the high cycle life of lithium cells is their core advantage.

3. Consistency (Voltage/Capacity Deviation)

Definition: The degree of variation in voltage, capacity, and internal resistance among all cells in the same battery pack (measured by CV% coefficient of variation in the industry).

Importance: Poor cell consistency leads to the "barrel effect" — even one underperforming cell will drag down the entire battery pack’s range and lifespan, and may even cause overcharging, over-discharging, or fire risks.

Qualification Standard: For high-quality battery packs, cell capacity deviation ≤2%, voltage deviation ≤0.02V, and internal resistance deviation ≤5mΩ.

4. Safety (Thermal Stability/Short-Circuit Resistance)

Core Tests: Puncture test, crush test, overcharge/over-discharge test (complying with safety standards such as UL 2849 and GB 31484).

Material Differences:

Ternary Lithium Cells: High energy density but weak thermal stability; inferior products are prone to fire under high temperature/short circuit (requiring a high-quality BMS protection board).

Lithium Iron Phosphate Cells: Strong thermal stability (no fire when punctured) and longer cycle life, but slightly lower energy density (suitable for commuting scenarios prioritizing safety).

III. Classification of Lithium Battery Cell Quality Grades (200 words)

Grade
Source
Core Features
Application Scenarios
Risk Points
Grade A (Genuine Original)
Produced by top-tier manufacturers such as CATL, BYD, Panasonic, and LG with full-process inspection
High energy density, cycle life ≥1200 cycles, excellent consistency, safety-compliant
Mid-to-high-end e-bikes (Yadea, NIU, Rad Power Bikes, etc.)
No obvious risks; only need to ensure regular channels
Grade B (Slightly Defective)
Cells failing to meet Grade A standards during original production (e.g., slightly excessive capacity deviation, minor appearance flaws)
Cycle life 600-800 cycles, moderate consistency, safety-compliant
Entry-level e-bikes, second-hand batteries
Possible uneven range degradation during long-term use
Grade C (Inferior Defective)
Produced by small factories without inspection processes
Cycle life ≤500 cycles, poor consistency, unsafe
Low-cost no-brand e-bikes, modified batteries
High fire risk, severe capacity false labeling
Recycled Cells (Used/Refurbished)
Re-encapsulated cells disassembled from waste batteries
Severe capacity degradation, extremely poor consistency, high safety hazards
Illegal modified batteries, counterfeit products by unscrupulous merchants
Prone to short circuit and fire, service life only a few months

IV. 5 Practical Methods for Ordinary Users to Identify Cell Quality (200 words)

1. Check Brand and Certification

Request cell supplier information from the merchant (e.g., "CATL ternary lithium cells" or "LG 21700 cells") and reject "no-brand cells".

Verify the battery pack’s safety certifications (UL 2849, CE, CPSC, etc.). Complete certifications indicate the cells have passed compliant inspections.

2. Test Range and Degradation

Actual Riding Test: Ride at daily speed with a full charge and record the real range (a deviation ≤10% from the claimed range indicates high quality).

Long-Term Observation: If the range degrades by more than 30% after 6 months of use, the cells are likely Grade B/C.

3. Inspect Battery Pack Craftsmanship

High-Quality Battery Pack: Tightly sealed shell without leakage traces, neat wiring, and equipped with a temperature sensor (ensuring charging safety).

Inferior Battery Pack: Loose shell, rough interfaces, no brand logo or production batch number.

4. Measure Consistency with Tools (Optional)

Use a multimeter to measure the battery pack’s no-load voltage (after standing for 1 hour). If the voltage fluctuates by more than 0.1V in multiple measurements, the cell consistency is poor.

5. Avoid Low-Price Traps

Market Price: The cost of Grade A ternary lithium cells is about \(1.5-2/Wh. If a battery pack is far cheaper than this (e.g., a 10Ah 48V battery pack priced below \)700), it is likely Grade B/C or recycled cells.

V. Clarification of Common Misconceptions

"The larger the capacity, the better": Capacity false labeling without considering consistency and cycle life is meaningless — 10 Grade A 2000mAh cells are far more durable than 10 Grade C 3000mAh cells.

"Ternary lithium is definitely better than lithium iron phosphate": Ternary lithium is suitable for scenarios pursuing long range, while lithium iron phosphate is ideal for safety-focused and high-frequency charging scenarios (e.g., food delivery bikes). There is no absolute superiority; the key lies in cell quality.

"Fast charging does not damage cells": High-quality cells support 1C-2C fast charging, but inferior cells will accelerate degradation and even cause overheating under fast charging.

Conclusion

Cell quality is the core guarantee for an e-bike’s "range, lifespan, and safety" and a common pitfall for users. Remember: When choosing an electric bicycle, don’t just focus on labeled capacity and price — pay more attention to cell brand, certification qualifications, and battery pack craftsmanship. Prioritize models equipped with Grade A cells from top-tier brands to avoid the trouble of "replacing the battery in one year" and truly enjoy the convenience of green travel.

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Grade	Source	Core Features	Application Scenarios	Risk Points
Grade A (Genuine Original)	Produced by top-tier manufacturers such as CATL, BYD, Panasonic, and LG with full-process inspection	High energy density, cycle life ≥1200 cycles, excellent consistency, safety-compliant	Mid-to-high-end e-bikes (Yadea, NIU, Rad Power Bikes, etc.)	No obvious risks; only need to ensure regular channels
Grade B (Slightly Defective)	Cells failing to meet Grade A standards during original production (e.g., slightly excessive capacity deviation, minor appearance flaws)	Cycle life 600-800 cycles, moderate consistency, safety-compliant	Entry-level e-bikes, second-hand batteries	Possible uneven range degradation during long-term use
Grade C (Inferior Defective)	Produced by small factories without inspection processes	Cycle life ≤500 cycles, poor consistency, unsafe	Low-cost no-brand e-bikes, modified batteries	High fire risk, severe capacity false labeling
Recycled Cells (Used/Refurbished)	Re-encapsulated cells disassembled from waste batteries	Severe capacity degradation, extremely poor consistency, high safety hazards	Illegal modified batteries, counterfeit products by unscrupulous merchants	Prone to short circuit and fire, service life only a few months

Knowledge Related to the Quality of Lithium Battery Cells

I. Core Concept: What Are Lithium Battery Cells?

II. 4 Key Indicators of Cell Quality

1. Energy Density (Unit: Wh/kg)

2. Cycle Life (Unit: Cycles)

3. Consistency (Voltage/Capacity Deviation)

4. Safety (Thermal Stability/Short-Circuit Resistance)

III. Classification of Lithium Battery Cell Quality Grades (200 words)

IV. 5 Practical Methods for Ordinary Users to Identify Cell Quality (200 words)

1. Check Brand and Certification

2. Test Range and Degradation

3. Inspect Battery Pack Craftsmanship

4. Measure Consistency with Tools (Optional)

5. Avoid Low-Price Traps

V. Clarification of Common Misconceptions

Conclusion

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