Autonomous power supply for miniature electronic equipment.

Autonomous power supply of miniature radio-electronic equipment.

Nizhnikovsky Evgeny Aleksandrovich,
candidate of chemical sciences,
Serdyukov Petr Nikolaevich,
doctor of technical sciences

AUTONOMOUS POWER SUPPLY OF MINIATURE RADIO-ELECTRONIC EQUIPMENT

The operation of most types of special-purpose radio-electronic equipment (REA) is impossible without modern, highly efficient and reliable power sources.

Autonomous power supply of REA is provided in the vast majority of cases using chemical power sources.

Chemical current sources (CCS) use the principle of direct conversion of chemical energy into electrical energy. The history of their creation is about two hundred years old, but research and development work in this area continues to this day.

There are many variants of CCS, differing in size, design features and the nature of the electrochemical (or so-called current-generating) reactions occurring in them. Depending on the variant, the indicators and operating parameters change. Such diversity is entirely justified, since CCS are used in a wide variety of conditions and each area of ​​application has its own specific features.

The current source consists of one or more individual cells — galvanic elements. The voltage of an individual element is low (1 — 4 V, depending on the electrochemical system). When a higher voltage is required, the required number of elements are connected in series into a battery.

According to the operating principle, the CCS are divided into groups:

a)primaryHIT – single-use elements, or simply elements. They contain a certain reserve of reagents that provide their energy; after this reserve is used up (after a complete discharge), the primary elements lose their functionality;

b) accumulatorsrechargeable, secondary or reversible elements. After being discharged, batteries allow recharging by passing current from an external circuit in the opposite direction. Thus, during the charging process, electrical energy from an external current source is accumulated in the battery in the form of chemical energy; during discharge, it is returned to the consumer. Batteries allow a large number of charge-discharge cycles (hundreds and thousands), which provides additional opportunities for their use in technology.

There is no clearly defined boundary between the specified groups of chemical power sources: some types of primary cells can be recharged, while batteries are sometimes discharged only once. When choosing between batteries and primary cells, equipment designers usually take into account that the former have greater power, while the latter have a higher specific energy.

The most well-known and widespread primary chemical power sources are zinc-manganese cells. Cells with salt electrolyte and batteries based on them have been known for over 100 years, which are the main type of chemical power sources. Their low performance characteristics (specific energy — up to 100 Wh/dm3*, service life — up to two years) are compensated by low cost and ease of manufacture.

*To compare the energy parameters of the CIT of various electrochemical systems, the value of specific energy is used, either weight — Wh/kg, or volumetric — Wh/dm3.

These parameters take into account the differences in voltage and capacity of various current sources, since they are calculated by multiplying the value of the discharge voltage by the capacity, divided by the weight (volume) of a specific element

Modification of zinc-manganese elements with alkaline electrolyte has 1.5 — 2 times higher capacity and power.

Modern technologies used by a number of leading foreign companies have made it possible to further improve the operating parameters of zinc-manganese HIS (Energizer, Duracell, Sony).

However, advertising claims about a colossal increase in capacity (the power of seven batteries) are a clear exaggeration and relate to specific operating modes.

An alternative to zinc-manganese elements for the last 30 years are mercury-zinc current sources.

In terms of specific energy (300 Wh/dm3) and service life (up to 5 years), they exceed zinc-manganese analogues, and in other parameters, they are not inferior to them. Their performance at negative temperatures is low.

When they discharge, metallic mercury is released, which is extremely dangerous from an ecological point of view. In addition, getting on the elements of the electronic equipment installation, it leads to their failure.

In recent years, manufacturers of these elements have announced a reduction in production, up to and including its complete cessation due to environmental hazards and pressure from public organizations (“greens”).

The presence of the listed shortcomings has led to a search for fundamentally new chemical power supplies, and this search has resulted in the creation of elements with a lithium anode, which significantly surpass all other types of chemical power supplies in terms of a set of operational parameters.

The development of lithium power sources began quite a long time ago, but their industrial production began only in the 70s. They immediately took a leading place in the power supply of a number of areas of technology, including special ones.

The reason for this is the unique operational capabilities of this class of CPS.

They, in turn, are due to the use of high-energy electrode materials, new structural materials and technologies in the specified power sources.

Due to the increased chemical activity of lithium, such elements require improved sealing and special assembly conditions (sealed boxes, inert gas atmosphere).

Depending on the type of electrode materials and electrolytes used, a distinction is made between:

• lithium elements with an inorganic electrolyte (lithium-thionyl chloride, lithium-sulfur dioxide, etc.);
• lithium cells with organic electrolyte (lithium polyfluorocarbon, lithium manganese dioxide, etc.);
• lithium cells with solid electrolyte (lithium iodine).

The highest technical parameters are possessed by cells of the lithium-thionyl chloride system.

They have a discharge voltage of 3.4 V, a service life of up to 10 years and more, high performance at negative temperatures, low self-discharge of -3% per year and high power.

Elements of the lithium-thionyl chloride system have the highest known specific energy — up to 1000 Wh/dm3.

Their use in miniature electronic equipment instead of traditional systems of chemical power supplies leads to an increase in the technical capabilities of the products and an improvement in their weight and size characteristics.

The US Army regulations assume the use of lithium-thionyl chloride power sources in military equipment as the main type of chemical power supplies.

Our country has established the production of a number of miniature lithium-thionyl chloride chemical power supplies, with a capacity from 0.17 Ah (TL-53) to 11 Ah (TL-11).

There is experience in producing elements with a capacity of several hundred ampere hours. The peculiarity of the elements of this system is that thionyl chloride simultaneously serves as a solvent and an active material of the cathode, which leads to a noticeable increase in the efficiency of using active masses.

Along with the unconditional positive qualities of lithium-thionyl chloride CCS, their disadvantages are also known. The main one is explosion hazard.

If the rules for operation and storage of elements are violated (short circuits, overheating, deep discharge, charge, mechanical damage, etc.), explosions are possible, which are dangerous due to the destruction of equipment and injury to personnel.

To improve the explosion safety of elements, in recent years, developers have completed a large program of fundamental and applied research.

As a result, a number of design and technological techniques have been developed.

Internal and external fuses, pressure valves for releasing the gases formed, fusible separation materials, etc. are used.

In addition, it is necessary to comply with a number of rules given in the operating instructions for specific elements. Another disadvantage is the presence of an initial voltage dip.

At the initial moment of time after the element is switched on for discharge, the voltage decreases to values ​​below the final discharge, subsequently increasing to the average discharge.

The most noticeable “voltage dips” are in elements after long-term storage or exposure to elevated temperatures. It has been shown that preliminary discharge of elements helps to eliminate voltage “dips.”

Along with lithium-thionyl chloride, a number of foreign companies produce elements of the lithium-sulfur dioxide system. They are somewhat inferior to the previous ones in terms of specific energy (525 W h/dm3) and discharge voltage (2.7 V), but are considered more explosion-proof.

Voltage dips are also observed for elements of this system.

According to design solutions, there are cylindrical, disk and prismatic designs, rolled and packed.

Rolled sources have large-area electrodes, which ensures their increased power. Packed CHITs have small-area electrodes, have low power, but increased specific energy capacity due to the low content of structural materials.

A number of variants of lithium CCS with organic electrolyte are known, which in terms of the main operational parameters (voltage, specific energy and power) are somewhat inferior to samples based on thionyl chloride — elements with cathodes based on polyfluorocarbon (CFx)n, manganese dioxide MnO2, molybdenum trioxide MoO3, copper oxide CuO, etc.

Elements of both disk and cylindrical design, as well as flat flexible design, have been developed and mastered in production by domestic enterprises.

Since electrode materials for elements with organic electrolyte are solid substances, the technology for manufacturing sources based on them is simpler and cheaper.

The HIT of the listed systems are considered less explosive in operation and cheaper, therefore they have a number of stable areas of application, including in household appliances.

Lithium elements with solid electrolyte have a long service life (10-20 years), but have very low power.

Currently, they are used to power pacemakers, and they can also be used in memory storage systems in computers.

The production of lithium elements has been mastered in several research and production centers of the country: GNPP Kvant, Moscow; NKTBHIT, Novocherkassk; JSC NIAI, St. Petersburg; MP Raduga, Podolsk; MP Kraslit, Krasnoyarsk, JSC Alten, Elektrougli, etc.

Table 1: Primary chemical current sources developed for special equipment

Chemical current sources of all the listed systems can be used to power miniature products of special equipment.

The table shows the performance characteristics of a number of promising domestic primary chemical current sources, the production of which has been mastered by the domestic industry.

The TL marking denotes elements of the lithium-thionyl chloride system, FL — lithium-polyfluorocarbon, ILT — lithium-iodine.

In justified cases, more expensive lithium CCS are used to power electronic equipment, while in less critical cases, sources from other systems are used.

But in any case, the trends in the development of current sources are such that the future belongs to lithium CCS.

Miniature electronic equipment often uses foreign-made CCS.

Table 2 shows the characteristics of the most frequently used imported current sources.

Table 2. Primary foreign-made CCS

CONCLUSIONS

• The main type of autonomous power supply for miniature electronic equipment is primary chemical current sources.
• The highest performance characteristics among primary chemical power sources are possessed by lithium elements, which have been mastered in production and are the most promising for power supply of miniature electronic equipment.
• In justified cases, the use of zinc-manganese and zinc-silver elements is permitted. Use of mercury-zinc chemical power sources should be limited due to their toxicity.