How do polymer batteries work?

You can find "polymer batteries" in locators, smart watches, and medical products. They are lightweight, flexible, and safe, and seem to 

have become the "standard" for modern portable devices. But do you really understand how they work? How are they different from the 

lithium-ion batteries we are familiar with? This article will take you from structure to application and help you understand the working 

principle of polymer batteries in one go.

I. What is a Polymer Battery?

A polymer battery, also known as a Lithium Polymer Battery (Li-Po), is an improved version of lithium-ion batteries. Its basic components 

are similar to those of traditional lithium batteries: an anode, a cathode, and an electrolyte. However, the biggest difference lies in the fact 

that the electrolyte uses solid or gel polymer materials instead of liquid organic electrolytes.

This design eliminates the need for a hard metal casing for the polymer battery, replacing it with a flexible aluminum-plastic film packaging. 

As a result, it is lighter, thinner and safer.

II. Structural Analysis of Polymer Batteries

A typical polymer battery is mainly composed of the following components:

Positive electrode material: Usually lithium cobalt oxide (LiCoO₂), lithium manganese oxide (LiMn₂O₄), and other lithium metal oxides.

Negative electrode material: Graphite is the most common choice.

Electrolyte: Utilizes high-molecular gel electrolytes or solid polymer materials, which possess certain conductivity.

Diaphragm: Prevents the positive and negative electrodes from coming into direct contact, which could cause a short circuit.

Aluminum-plastic film packaging: Replacing the traditional metal casings of batteries, it enhances lightweighting and safety.

III. How does it work?

The charging and discharging process of polymer batteries is essentially still a "migration" process of lithium ions:

1.Discharge process:

When you use a mobile phone or a drone, the polymer battery starts to discharge. At this time:

The lithium ions in the negative electrode (graphite) are released, pass through the electrolyte and the separator, and move into the 

positive electrode material.

Meanwhile, the electrons flow from the negative electrode through the external circuit to the positive electrode, driving the equipment 

to operate.

Lithium ions and electrons eventually "merge" at the positive electrode, enabling the release of electrical energy.

2. Charging process:

When you charge the device, the movement direction of the lithium ions reverses:

The lithium ions "migrate" back from the positive electrode to the negative electrode.

Electricity flows from the charger into the negative electrode and combines with lithium ions to store energy.

This process is reversible, and it is precisely this property that enables polymer batteries to be recharged and used repeatedly.

IV. Polymer Batteries vs Lithium-Ion Batteries: What Are the Key Differences?

Polymer batteries (Li-Po) and lithium-ion batteries (Li-ion) are the most common types of rechargeable batteries currently in use, widely 

employed in devices such as mobile phones, laptops, electric vehicles, and drones. Although they both belong to the lithium battery family 

and have similar working principles, there are numerous differences in material structure, performance, and application scenarios. Now, 

let's compare the differences between the two from several key aspects:

1. Electrolyte type

This is the most fundamental difference between the two:

Lithium-ion batteries use liquid electrolytes, where lithium salts are dissolved in organic solvents, allowing lithium ions to freely migrate 

between the positive and negative electrodes. Polymer batteries use gel-like or solid polymer electrolytes, without or with only a very small 

amount of liquid components. Their overall structure is more stable. The use of polymer electrolytes has enhanced the safety of batteries 

and enabled them to be made thinner and more flexible.

2. Shell Encapsulation Structure

Lithium-ion batteries typically use hard-shell encapsulation (such as cylindrical or square metal shells), which offers high strength but is 

limited in terms of volume and shape. Polymer batteries are packaged using soft pouches made of aluminum and plastic film. They are soft, 

lightweight, and allow for customization of various shapes and sizes. Therefore, polymer batteries are more favored in devices with specific 

requirements for thickness and shape, such as ultra-thin mobile phones, smart watches, drones, etc.

3. Weight and volume advantages

The aluminum-plastic film packaging of polymer batteries is lighter and its overall structure is more compact. Therefore:

Under the same capacity, polymer batteries are lighter and thinner. For devices that require weight reduction or space saving, this is an ideal 

power solution. This is also the reason why many model aircraft and FPV drones prefer to use Li-Po batteries.

4. Energy Density

Lithium-ion batteries typically have a higher energy density, which means they can store more electrical energy in the same volume or weight. 

The energy density of polymer batteries is slightly lower, but the gap is gradually narrowing. If one is looking for a longer battery life (such as 

for laptops or electric vehicles), lithium-ion batteries still have certain advantages.

5. Safety

Due to the relatively small amount of liquid or the absence of liquid inside the polymer battery, even if there are external incidents such as 

squeezing, puncturing, or short circuiting, it is less likely to catch fire or explode. In contrast, the liquid electrolyte in lithium-ion batteries is 

prone to volatilization and combustion, presenting certain safety risks. Furthermore, even if the casing of the polymer battery is damaged, 

it is less likely to "explode" or experience "thermal runaway" like a lithium-ion battery.

6. Cost and Lifespan

In terms of cost: The manufacturing process of polymer batteries is complex and the material cost is slightly higher, thus the overall price 

is higher than that of lithium-ion batteries. In terms of lifespan: The number of cycles for both is similar, but polymer batteries are more 

sensitive to charging methods and temperature. If used improperly, their lifespan may be shorter.

Overall, the main advantages of polymer batteries are flexibility and safety. They can be designed into various shapes according to the 

requirements of the equipment, making them highly suitable for thin electronic products. However, they have higher costs and slightly lower 

energy density, and in some high-performance applications, they still fall short of traditional lithium batteries.