5 common lithium-ion battery myths explained – 18650 ...

Preface

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Understanding lithium-ion batteries can involve navigating through common myths. In this article, we will debunk five prevalent misconceptions surrounding this technology.

1. Myth #1 - You have individual batteries

Answer: Technically, you have individual cells, not batteries

Consumers often mistakenly refer to a single battery cell as a battery. The terminology describes entities in different ways for engineers and consumers.

1 - Cell

An individual battery is actually a cell. A cell represents the smallest package that a battery can take (usually 4.2V for lithium-ion batteries).

2 - Module

A module includes several connected cells, either in parallel or series, and varies in size based on energy needs.

A lithium-ion battery pack, like that in a BMW i3, comprises these individual battery modules.

3 - Battery (or Battery Pack)

Commonly, a battery pack encompasses multiple cells or modules arranged in series or parallel. Collectively, this assembly functions as a battery pack. While the term 'battery' is often used casually, engineers prefer strict definitions that emphasize safety and efficiency.

• For clarity, a 'pack' is typically smaller than a 'battery.'

While calling a single cell a battery is acceptable in informal contexts, it is important to use precise language in engineering discussions. The self-regulating features of a battery pack, like battery management systems (BMS), highlight critical safety aspects not present in standalone cells.

Myth #2 - What is better, Li-Po or Li-ion?

Answer: You cannot actually compare the two.

The term Li-Po (lithium polymer) has dual interpretations:

1. The original meaning pertains to polymer electrolytes.
2. The more common use refers to pouch-format cells, which share electrochemical similarities with Li-ion batteries.

Usage #1 - (Uncommon) Polymer Electrolyte

While the concept of Li-Po cells employing polymer technology has origins in research, it has not gained widespread commercial acceptance.

Usage #2 - (Common) Polymer Casing

Today, Li-Po refers to batteries that utilize flexible polymer packaging. In terms of energy generation, both Li-Po and cylindrical Li-ion batteries operate on the same fundamental principles.

Myth #3 - When you charge a cell, its capacity increases

Answer: When you charge a cell, its charge increases, not its capacity.

This misconception stems from a misunderstanding of the terms charge and capacity.

The Fuel Gauge Analogy

The state of charge (SOC) can be likened to a fuel gauge in a car, whereby charging affects how much “fuel” (energy) is available, but not the size of the tank (capacity).

Understanding Capacity

Capacity can be visualized as a bucket that holds energy (water). While recharge increases the energy (water level), over time, degradation occurs (sand accumulates) which reduces capacity.

The coulometric capacity, measured in amp hours (Ah), reflects what the battery can deliver, influenced by factors like temperature and current rate during charging and discharging.

Myth #4 - All batteries can be either Primary or Secondary cells

Answer: All lithium-ion batteries are secondary cells.

Primary cells are non-rechargeable, similar to single-use batteries, whereas secondary cells like lithium-ion can be recharged, making them the preferred choice for modern electronics.

Myth #5 - Impedance and Resistance are interchangeable terms

Answer: They are fundamentally different concepts.

Resistance generally refers to direct current (DC), while impedance includes reactive components for alternating current (AC).

Measurement methods differ, impacting the readings of what an internal resistance or impedance yields. Understanding this distinction is vital for accurate usage within electrical engineering contexts.

Finish

In summation, here is a recap of the myths and their answers:

Myth #1 - You have individual batteries
Answer: Technically, you have individual cells, not batteries
Myth #2 - What is better, Li-Po or Li-ion?
Answer: You cannot compare the two.
Myth #3 - When you charge a cell, its capacity increases
Answer: When you charge a cell, its charge increases and not its capacity.
Myth #4 - Batteries can be either Primary or Secondary cells
Answer: All batteries are secondary cells.
Myth #5 - Impedance and Resistance are interchangeable terms
Answer: There is little relationship between the two, the output (in Ohms) differs significantly.