RU2166219C2 - Capacitor with double electric layer - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: invention can be used in design of devices accumulating electric energy and can be employed in systems of emergency power supply operating under conditions of floating or compensation charge, for provision of uninterrupted power supply, for usage in periodically operating power sources, for instance, in wind power and solar power engineering, in devices accumulating energy of recuperative brake on transport, in the capacity of traction batteries on electric transport. Task solved by proposed capacitor with double electric layer lies in design of normally operating device with prolonged service life in combination with high specific energy and power. Technical result of proposed solution is achieved by development of capacitor with double electric layer incorporating molten electrolyte which is provided with thickening agent in accordance with invention. EFFECT: improved design of capacitor with prolonged service life and with high specific energy and power characteristics. 4 cl, 1 dwg, 1 tbl

Description

The invention relates to electrical engineering and can be used to create devices that accumulate electrical energy and is used:
- in emergency power supply systems when operating in the constant or compensating charge mode;
- to ensure a constant energy supply when using periodically operating energy sources, for example, in wind and solar energy;
- in devices that accumulate regenerative braking energy in vehicles;
- as traction batteries for electric vehicles.

 The principle of operation of the known capacitor with a double electric layer or an electrochemical capacitor is based on the use of energy accumulated in the double electric layer arising at the boundary of conductors of the first and second kind (electrode - electrolyte).

 Typically, the electrodes in such capacitors are made of carbon materials with a high specific surface area. The energy capacity of the capacitor is limited by the decomposition voltage and the capacity of the double electric layer, which are inherent in the used electrolyte. In the case of a water electrolyte, the decomposition voltage is 1.23 V.

 Known capacitor with a double electric layer, comprising two electrodes and an aqueous electrolyte (patent RU N 2054723, CL H 01 G 9/00, 1996).

 The use of organic solvents as an electrolyte allows you to raise the operating voltage of the capacitor to 3-4 V.

 However, the implementation of large capacities in a capacitor with a double electric layer with an organic electrolyte is difficult due to the low conductivity of the latter.

 The closest in technical essence to the proposed solution is a capacitor with a double electric layer, including polarizable electrodes, a separator and molten electrolyte (patent US N 5621607, CL H 01 G 9/04, 1993).

 In the known capacitor, molten chlorides and bromides are used as the electrolyte.

For example, the capacity of an electrode of activated carbon material with a surface of 900-1200 m ² / g in an electrolyte from a eutectic mixture of potassium and lithium chlorides is approximately 500 F / g at 400-500 ^o C, with a surface of 1500-2000 m ² / g is 600 F / g The electrical conductivity of this electrolyte at 400 ^° C. is 1.7 S / cm. The decomposition voltage of molten aluminum and magnesium chlorides exceeds 2.5 V, alkali metal chlorides - 3.5 V, and fluorides - 5 V.

 The use of molten salts is associated with solving a number of problems associated with their high corrosiveness at elevated temperatures in relation to structural materials of the housing, down conductors, etc.

 These problems are so significant that they may not allow the creation of a capacitor with molten electrolyte, which has an acceptable resource and service life for practice.

 The problem solved by the proposed capacitor with a double electric layer is to create a workable device with a long resource and service life in combination with high specific energy and power.

 The technical result in the proposed solution is achieved by creating a capacitor with a double electric layer, including electrodes, at least one of which is polarizable, a separator and molten electrolyte, which according to the invention is equipped with a thickener, which is part of the molten electrolyte.

 The invention is characterized in that an inert highly dispersed material is used as a thickener.

 Materials can be powders with particles of any shape (including fibers).

 The invention is characterized in that as a thickener, a finely dispersed material based on aluminum or magnesium oxides, or calcium, or strontium, or boron, or silicon, or zirconium, or yttrium, or beryllium, or mixtures thereof, or mixed oxides of the above elements, or nitrides of the above elements or mixtures thereof, or mixtures of oxides, mixed oxides and nitrides of the above elements.

 The invention is also characterized by the fact that the second electrode is non-polarizable and contains substances as active material that can be reversibly electrochemically oxidized and reduced in the environment of this molten electrolyte.

 This allows you to increase the specific energy of the capacitor.

 As the active material of the substance can be used metals of the first or second, or third groups of the Periodic system, or a mixture thereof, or their alloy with carbon, or silicon, or boron, or other metals.

 Metals and alloys can form during the process of charging a capacitor. They are used as a negative electrode.

 The introduction of a thickener into the electrolyte allows you to create a capacitor with a double electric layer (element), in which the molten electrolyte is fixed by capillary forces in the active material of the electrode and the thickener and does not come into contact with the body parts. In such an element, the thickened electrolyte can simultaneously serve as a separator.

 This allows, firstly, to avoid corrosion of structural materials, and secondly, to create a frameless element - a capacitor with a double electric layer.

 The molten electrolyte may contain a different amount of thickener, i.e. have a different degree of thickening. At a lower thickener content, the electrolyte conductivity and capacitance of the capacitor increase, while at a higher concentration, the mechanical stability of the system increases.

 The essence of the proposed capacitor with a double electric layer is illustrated by the following description and examples, as well as the drawing, which schematically shows the design of the capacitor.

 The capacitor with a double electric layer includes electrodes 1 and 2, at least one of which is polarizable, the separator 3, the active material of the electrode 4, the molten electrolyte 5, the thickener 6 introduced into the electrolyte, the collectors 7.

 Tests of the proposed design were carried out using various materials used as a thickener, active electrode material, etc.

 It is advisable to use electrically conductive materials with a high surface that are stable in the environment of molten electrolyte (activated carbon, carbides, nitrides, oxides, metals) as the material of a polarizable electrode.

 The results are shown in the examples described below.

 Example 1

The capacitor electrodes are made of activated carbon powder with a surface of 900-1200 m ² / g (20-30 wt.%) With the addition of electrolyte and are made in the form of disks with a diameter of 22 mm and a thickness of 1.2 mm. The electrolyte contains a eutectic mixture of lithium and potassium chlorides (59 mol.% LiCl) with a melting point of 352 ^o C. Magnesium aluminate powder (40 wt.%) Is introduced into the electrolyte as a thickener. The separator (aka thickened electrolyte of the same composition) is made in the form of a pressed plate 1 mm thick. The down conductors are graphite disks with a diameter of 24 mm and a thickness of 0.3 mm.

 Example 2

In contrast to example 1, the electrodes are made of activated carbon powder with a specific surface area of 1500-2000 m ² / g.

 Example 3

In contrast to example 1, one electrode is made in the form of a plate of iron disulfide powder (FeS ₂ ) with the addition of an electrolyte 0.5 mm thick.

 Example 4

 In contrast to example 1, one electrode is made in the form of a plate of powder of lithium-aluminum alloy (2-4 wt.% Lithium) with a thickness of 0.5 mm

The characteristics of the capacitors at a temperature of 400 ^o C in accordance with the above examples are described in the table.

 Based on the proposed capacitor with a double electric layer, it is possible to create a battery of a bipolar design, including as many elements as necessary to obtain the necessary voltage, combined into a single housing. The absence of cases for each of the elements will greatly simplify the design of the battery and reduce its weight.

Claims (5)

 1. A capacitor with a double electric layer, comprising electrodes, at least one of which is polarizable, a separator and molten electrolyte, characterized in that a thickener is introduced into the composition of the molten electrolyte.  2. The capacitor with a double electric layer according to claim 1, characterized in that as an thickener introduced into the electrolyte, an inert, finely dispersed material with particles of any shape is used.  3. The capacitor with a double electric layer according to claim 1 or 2, characterized in that as a thickener use a highly dispersed material based on oxides of aluminum, or magnesium, or calcium, or strontium, or boron, or silicon, or zirconium, or yttrium, or beryllium, or mixtures thereof, or mixed oxides of the above elements, or nitrides of the above elements, or mixtures thereof, or mixtures of oxides, mixed oxides and nitrides of the above elements.  4. A capacitor with a double electric layer according to any one of claims 1 to 3, characterized in that the second electrode is non-polarizable and contains substances that are capable of being reversibly electrochemically oxidized and reduced in the environment of this molten electrolyte as an active material.  5. A capacitor with a double electric layer according to any one of claims 1 to 4, characterized in that the non-polarizable electrode contains as the active material a metal of the first, or second, or third groups of the periodic system, or a mixture thereof, or an alloy thereof with carbon, or silicon, or boron, or other metals.

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