Lithium-ion battery: principle of operation and varieties, advantages and rules for operating the battery

In modern mobile phones, cameras and other devices, lithium-ion batteries are most often used, replacing alkaline and nickel-cadmium batteries, which they surpass in many respects. For the first time, batteries with a lithium anode appeared in the 70s of the previous century and immediately became very popular due to their high voltage and energy intensity.

History of appearance

The developments were short-lived, but at the practical level difficulties arose that were resolved only in the 90s of the last century. Due to the high activity of lithium, chemical processes took place inside the element, which led to combustion.

In the early 90s, a number of accidents occurred - telephone users, while talking, received severe burns as a result of spontaneous ignition of the elements, and then the communication devices themselves. In this regard, the batteries were completely discontinued and the previously released batteries were returned from sale.

In modern lithium-ion batteries, pure metal is not used, only its ionized compounds, since they are more stable. Unfortunately, scientists had to go for a significant reduction in the battery's capabilities, but they managed to achieve the main thing - people no longer suffered from burns.

The crystal lattice of various carbon compounds was found to be suitable for intercalation of lithium ions at the negative electrode. During charging, they pass from the anode to the cathode, and during discharge, vice versa.

Principle of operation and varieties

In every lithium-ion battery, the negative electrode is based on carbon-containing substances, the structure of which can be ordered or partially ordered. The process of Li intercalation in C changes depending on the material. The positive electrode is mainly made of lated nickel or cobalt oxide.

Summing up all the reactions, they can be represented in the following equations:

1. LiCoO2 → Li1-xCoO2 + xLi + + xe - for the cathode.
2. С + xLi + + xe → CLix - for the anode.

The equations are presented for the case of a discharge; when charged, they flow in the opposite direction. Scientists are researching new materials consisting of mixed phosphates and oxides. These materials are planned to be used for the cathode.

There are two types of Li-Ion batteries:

1. cylindrical;
2. prismatic.

The main difference is the arrangement of the plates (in prismatic - on top of each other). The size of the lithium battery depends on this. As a rule, prismatic ones are denser and more compact.

In addition, there is a security system inside - a mechanism that increases the resistance when the temperature rises, and when the pressure rises, it breaks the anode-cathode circuit. Thanks to the electronic board, it becomes impossible to short circuit, since it controls the processes inside the battery.

Electrodes of opposite polarity are separated by a separator. The case must be sealed, leakage of electrolyte or ingress of water and oxygen will destroy both the battery and the electronic device itself.

Different manufacturers have a lithium-ion battery can look completely different, there is no uniform shape of the product. The ratio of the active masses of the anode to the cathode should be approximately 1: 1, otherwise the formation of lithium metal is possible, which will lead to fire.

Advantages and disadvantages

Batteries have excellent performance that varies from manufacturer to manufacturer. The nominal voltage is 3.7-3.8 V with a maximum of 4.4 V. Energy density (one of the main indicators) is 110-230 W * h / kg.

Internal resistance is 5 to 15 mΩ / 1Ah. The service life in terms of the number of cycles (discharge / charge) is 1000-5000 units. Time for fast charging is 15-60 minutes. One of the most significant advantages is the slow self-discharge process (only 10-20% per year, of which 3-6% for the first month). The operating temperature range is 0 C - +65 C, at temperatures below zero, charging is impossible.

Charging takes place in several stages:

1. up to a certain point, the maximum charge current flows;
2. upon reaching the operating parameters, the current gradually decreases to 3% of the maximum value.

During storage approximately every 500 hours, periodic recharging is required to compensate for self-discharge. When overcharged, metallic lithium can be deposited, which, interacting with the electrolyte, forms oxygen. This increases the risk of leakage due to increased internal pressure.

Frequent recharging will severely reduce battery life. In addition, the environment, temperature, current, etc. are affected.

The element has disadvantages, among which the following are distinguished:

1. High sensitivity to discharge-charge mode, therefore, built-in safety elements are required.
2. Do not allow the device to completely discharge. This results in a very large reduction in service life.
3. The service life is greatly reduced with an uncontrolled discharge.
4. At different temperature conditions, the discharge occurs at different rates. The higher the temperature, the greater the loss of capacity.
5. If you do not fully charge, subsequently discharging the battery, memory "microeffects" are created. This is due to the dynamics of ions, which, under the considered conditions, noticeably worsens.
6. With incomplete charging, not all ions on the cathode will have time to overcome the release barrier, "stuck" in the boundary state. Then, during the discharge, they, trying to return to their place, encounter the same particles there. All this leads to changes in the structure of the electrode.

Operating conditions

It is best to store the battery under the following conditions: The charge should be at least 40%, and the temperature should not be very low or high. The best option is the range from 0C to + 10C. Usually, about 4% of capacity is lost in 2 years, which is why it is not recommended to buy batteries with earlier dates of manufacture.

Scientists have invented a way to extend the shelf life. An appropriate preservative is added to the electrolyte. However, such batteries should be “trained” in the form of 2-3 full discharge / charge cycles so that they can subsequently operate normally. Otherwise, a "memory effect" and subsequent swelling of the entire structure may occur. With proper use and observance of all storage standards, the battery can serve for a long time, while its capacity remains at a high level.