Lithium polymer battery technical parameters

1.Introduction

Lithium polymer battery, English Li Polymer, LiPo for short, is a new type of battery with high energy density and large discharge current. 

At the same time, lithium batteries are relatively fragile to use and are extremely sensitive to overcharge and overdischarge. You should be 

proficient in understanding their performance during use.

The charging and discharging process of lithium polymer batteries is the intercalation and deintercalation process of lithium ions. During 

charging, lithium ions are detached from the negative electrode and embedded in the positive electrode, and during discharge, lithium ions 

are detached from the positive electrode and embedded in the negative electrode.

Once the lithium polymer battery is discharged and the voltage is too low or the charging voltage is too high, the structure of the positive 

and negative electrodes will collapse, causing irreversible damage to the lithium polymer battery.

2.Details

(1) Discharge cut-off voltage 2.75V

The minimum voltage at which a battery cell can safely discharge. Continuing to discharge below this voltage will damage battery 

performance.

(2) Charging cut-off voltage 4.20V

The maximum voltage at which the battery cell can be safely charged. Continuing to charge above this voltage will damage the battery 

performance.

(3) Standard voltage 3.7V

The standard nominal voltage of the battery cell is also the parameter we use when calculating the voltage.

(4) Storage voltage 3.85V

The voltage is suitable for long-term storage. Lithium batteries have the characteristics of low self-discharge. However, during long-term 

storage, there will still be some self-discharge that causes the voltage to decrease, so it should be stored at a voltage higher than 3.7V.

(5) S

When we call the voltage of a battery, we usually call it S. S is the number of batteries connected in series. For example, a 12S lithium 

battery actually refers to 12 cells connected in series. The standard voltage of a single lithium battery is 3.7V. Its voltage is 3.7*12=44.4V. 

S refers to the number of batteries connected in series.

(6)P

P refers to the number of batteries connected in parallel. For example, 3S1P means that the batteries are not connected in parallel; and 

3S2P, the battery is actually composed of 6 batteries connected in parallel.

(7) Internal resistance

Ohmic internal resistance mainly refers to the electrode material, electrolyte, diaphragm resistance and contact resistance of various parts. 

It is related to the size, structure and assembly of the battery. The internal resistance of the battery is very small, and we generally define 

it in units of milliohms. The smaller the internal resistance of the battery, the stronger the discharge capacity, and the larger the internal 

resistance of the battery, the weaker the discharge capacity.

(8)C

Battery discharge rate.

(9) Capacity

The capacity of the battery is expressed in Mah or Ah, which means that the battery is continuously discharged at a certain current for 1 hour.

2. Lithium polymer battery structure

A solid-state maintenance-free lithium polymer battery was jointly developed by 3M Company of the United States and Hgdro-Quebec 

Company of Canada. The electrodes of the lithium battery are made of vanadium oxide (VOx) and graphite, and the electrolyte is Li(CFSO2)2N.

The structure of lithium polymer battery is relatively special and is composed of five layers of films. The first layer uses metal foil as the collector, 

the second layer is the negative electrode, the third layer is the solid electrolyte, the fourth layer uses file foil as the positive electrode, and the 

fifth layer is the insulating layer. The total thickness of the five layers is 0.lmm.

The operating temperature of this lithium polymer battery is 60-100 degrees. In order to prevent the battery from overheating due to 

instantaneous output of large current, the lithium polymer battery has a strict thermal management system to control its normal operating 

temperature.

The main advantage of this lithium polymer battery is the elimination of liquid electrolyte, which can avoid pollution caused by electrolyte 

overflow when the battery fails.

3. Advantages of using lithium polymer batteries

(1) There is no battery leakage problem. The battery does not contain liquid electrolyte and uses colloidal solids.

(2) It can be made into a thin battery: with a capacity of 3.6V400mAh, its thickness can be as thin as 0.5mm.

(3) Batteries can be designed into a variety of shapes

(4) The battery can be bent and deformed: the polymer battery can be bent up to about 90 degrees.

(5) Can be made into a single high-voltage battery: Liquid electrolyte batteries can only achieve high voltage by connecting several batteries 

in series. Since polymer batteries have no liquid, they can be made into multi-layer combinations in a single battery to achieve high voltage.

(6) The capacity will be twice that of a lithium-ion battery of the same size