Why is the battery volume larger, the larger the capacity, the smaller the internal resistance?

In general, the capacity of a battery is proportional to the square root of the plate area and thickness.

The paste-type plate was tested in a density of 1.300 g/cm3 electrolyte to obtain an empirical formula for calculating the capacity of the plate:

Monolithic plate capacity = 0.145 × plate width × plate height × plate square thickness

Single cell capacity = number of single positive plate × single plate capacity

The larger is the capacity, the larger battery volume, and the smaller the resistance of the current.

The internal resistance of the lithium battery must be as small as possible. The smaller the internal resistance, the less energy is wasted for the battery and the heat generation and rate of the battery are helpful.

The internal resistance of the battery is related to the capacity and type of the battery.

Generally speaking, the larger is the capacity, the smaller the internal resistance of the battery.

The internal resistance of the battery rate type under the same capacity is smaller than that of the capacity type.

For example, the most common 18650 battery internal resistance ranges from a dozen to several tens of milliohms.

In addition, the same capacity and type of battery can also reduce the internal resistance by technical process, mainly depending on whether the input cost is feasible.

Lithium polymer battery (Li-polymer, also known as polymer lithium battery): It is also a kind of lithium ion battery, but it has higher energy density, smaller size and thinner than liquid lithium battery (Li-ion). A variety of obvious advantages, such as lightweight, high security, is a new type of battery. In terms of shape, the lithium polymer battery has an ultra-thinning feature and can be fabricated into a battery of any shape and capacity in accordance with the needs of various products. The battery can reach a minimum thickness of 0.5mm. Its nominal voltage, like Li-ion, is also a nominal voltage of 3.7V with no memory effect.

Polymer lithium ion battery

Lithium-ion batteries can be classified into liquid lithium-ion batteries (LILI) and polymer lithium-ion batteries (LIP) according to the electrolyte materials used in lithium-ion batteries. The positive and negative materials used in the polymer lithium ion battery are the same as the liquid lithium ions, and the working principle of the battery is basically the same. The main difference is that the electrolyte is different, the lithium ion battery uses a liquid electrolyte, and the polymer lithium ion battery is replaced by a colloidal polymer electrolyte. When a normal lithium-ion battery occurs during overcharging or short-circuiting, the inside of the battery may be heated, the cathode material is decomposed, and the anode and the electrolyte material are oxidized. This causes the gas to expand and the internal pressure of the battery to increase. When the pressure reaches a certain level, an explosion may occur after the degree. The polymer lithium ion battery uses a colloidal electrolyte, and does not generate a large amount of gas due to the boiling of the liquid, thereby eliminating the possibility of a violent explosion.

At present, most domestic polymer batteries are only soft-packed batteries, which use aluminum plastic film as the outer casing, but the electrolyte has not changed. The battery can also be thinned, its low-temperature discharge characteristics are better than that of polymer batteries, and the material energy density is basically the same as that of liquid lithium batteries and ordinary polymer batteries, but because of the use of aluminum plastic film, it is more than ordinary liquid lithium battery. In terms of safety, when the liquid is just boiling, the aluminum plastic film of the soft pack battery will naturally bulge or rupture, and will not explode.

It should be noted that the new battery may still burn or expand and crack, and the safety aspect is not foolproof.

Compared with liquid lithium ion battery, polymer lithium ion battery not only has high safety, but also has the advantages of thinness, arbitrary area and arbitrary shape, etc. The shell also USES lighter aluminum plastic composite film. However, its low temperature discharge performance may have room for improvement.

Liquid lithium battery

Due to the different production processes of various manufacturers, the polymer lithium battery in the market is divided into two types: winding type (represented by Sony and Toshiba) and laminated type (represented by TCL and ATL). However, most specifications suitable for mobile phones are less than 4mm thick. Compared with the liquid state, the thinner the polymer packaging is, the thinner the aluminum film is, than the steel shell, aluminum shell is thinner, and the production method is different from the liquid lithium battery, the thinner the better the polymer production, theoretically can produce batteries with a thickness of less than 0.5mm.

Liquid lithium battery is just the opposite. The thicker the better the production, the battery with a thickness of less than 4mm is difficult to produce. Even if it is produced, the capacity is obviously not as good as that of polymer lithium battery, and the cost is not superior. Thus, the thinner the battery, the lower the polymer production cost and the higher the liquid production cost.

However, in the thicker specifications, the liquid lithium battery supply chain is mature, the process is mature, the production efficiency is high, the yield is high, and there is a strong manufacturing cost advantage. From the market point of view, the liquid lithium battery of the 5mm, 6mm thickness series is much higher than the 3mm, 4mm thickness series battery, but the price is much lower. In theory, the material cost of the 5mm and 6mm thickness specifications is close to that of the liquid. However, the current process cost of the 5mm and 6mm series batteries is much higher than that of the liquid. Therefore, it is necessary to compete with the liquid in this specification. There are still many distances.

The main structure of a general battery includes three elements: a positive electrode, a negative electrode, and an electrolyte. The so-called polymer lithium ion battery means that at least one or more of the three main structures use a polymer material as a main battery system. In the polymer lithium ion battery system developed, the polymer material is mainly applied to the positive electrode and the electrolyte. The positive electrode material includes a conductive polymer or an inorganic compound used in a general lithium ion battery, and the electrolyte may be a solid or colloidal polymer electrolyte or an organic electrolyte, and the negative electrode is usually a lithium metal or lithium carbon interlayer compound. In general, lithium ion technology uses a liquid or colloidal electrolyte, so a strong secondary package is required to contain the flammable active ingredient, which adds weight and cost, and also limits dimensional flexibility.

The new generation of polymer lithium-ion batteries can be thinned in shape (the thinnest 0.8 mm), arbitrarily area and arbitrarily shaped, greatly improving the flexibility of the battery design, so that it can be made to meet the needs of the product. A battery of any shape and capacity provides application equipment developers with a high degree of design flexibility and adaptability in power solutions to maximize their product performance. At the same time, the unit energy of the polymer lithium ion battery is 50% higher than that of the general lithium ion battery, and its capacity, cycle life (more than 500 times) and environmental performance are greatly improved compared with lithium ion batteries.

Lithium battery coated with carbon foil

First, the material description

Carbon-coated aluminum foil is made of conductive carbon based composite paste and high-purity electronic aluminum foil by transfer coating process.

Second, the scope of application

Power type lithium battery with fine particle active material

Lithium iron phosphate

The positive electrode is a fine particle ternary/lithium manganate.

Used in super capacitors, lithium primary batteries (lithium, lithium manganese, lithium iron, button, etc.) instead of etched aluminum foil.

Third, the performance of the battery / capacitor

Suppress battery polarization, reduce thermal effects, and improve rate performance;

Reduce the internal resistance of the battery and significantly reduce the dynamic internal resistance increase of the cycle;

Improve consistency and increase battery cycle life;

Improve the adhesion of the active material to the current collector, and reduce the manufacturing cost of the pole piece;

Protecting the current collector from corrosion by the electrolyte;

Improve the high and low temperature performance of lithium iron phosphate battery and improve the processing performance of lithium iron phosphate and lithium titanate materials.

Fourth, the recommended parameters

The corresponding coated active material D50 is preferably not more than 4 to 5μm, the compaction density is not more than 2.25 g/cm, and the specific surface area is in the range of 13 to 18 m²/g.

Five, the precautions in use

1. Storage requirements: In the environment where the temperature is 25±5°C and the humidity is not more than 50%, the erosion of aluminum foil by air and water vapor should be avoided during transportation;

2. This product is divided into two types, A and B. The key characteristics of each product are: A is black in appearance, the thickness of conventional coating is 4~8μm on both sides, the conductivity is more prominent; the appearance of B is light gray, regular The coating thickness is 2~3μm on both sides, the coating area can be welded in less layers, and the coating machine can recognize the jump gap;

3.B (grey) coated carbon foil can be directly ultrasonically welded in the coating area, only suitable for coiled battery welding tabs (up to 2-3 layers of pole pieces), but the ultrasonic power and time need to be fine-tuned;

4. The heat dissipation of the carbon layer is worse than that of the aluminum foil, so it is necessary to finely adjust the belt speed and the baking temperature when coating;

5. This product has a considerable improvement on the comprehensive performance of lithium batteries and capacitors, but it cannot be used as a major factor to change the performance of some aspects of the battery, such as battery energy density, high and low temperature performance, high voltage and so on.

Polymer

The difference between a polymer lithium ion battery and a normal battery is on the electrolyte. In the original design of the 1970s, solid polymer electrolytes were used. This type of electrolyte is similar to a plastic film and does not conduct electrons but allows ion exchange (atoms or radicals that can be charged). The polymer electrolyte replaces the conventional porous membrane impregnated with the electrolyte. The design of the dry polymer electrolyte allows for simplified assembly, improved battery mechanical strength, safety, and the ability to be fabricated into an ultra-thin geometry. The thickness of a single battery can be as thin as 1 mm. Equipment designers are able to design the shape and size of the battery based on their imagination. Unfortunately, solid polymer lithium ion batteries are subject to their poor electrical conductivity. The internal resistance is too high to provide the high pulse current required by the current communication device and cannot drive the hard disk of the notebook. Heating the battery to 60 degrees Celsius, the conductivity is rapidly increasing, but such requirements are not suitable for use in portable devices.

As a compromise, some gel electrolytes have been introduced. Most mobile phone polymer lithium-ion batteries sold on the market are hybrid batteries containing gel electrolytes. Lithium-ion polymers are used to modify this system to make it the only polymer power source for portable devices.

Aggregate advantage

What is the difference between a lithium ion polymer battery and a general lithium ion battery after the addition of the gel electrolyte? Although the two batteries are very similar in performance, the lithium ion polymer replaces the porous membrane as the only solid electrolyte. Gel electrolytes only increase ionic conductance. Polymer lithium-ion batteries are not as popular as some analysts have predicted. Its superiority and low manufacturing cost have not been recognized. Because its capacity has not improved, in fact, the capacity is slightly reduced compared to standard lithium-ion batteries. The market for polymer lithium-ion batteries is used in applications such as ultra-thin geometric power supplies, such as credit card power supplies.

The page contains the contents of the machine translation.