Electronic separator SWEL-ES: Main points in brief

Nowadays electrochemical cells such as accumulators and supercapacitors of different types more often than not are used as electric energy storages. Application field of accumulators is really vast – cell phones and automobiles, video cameras and cameras, industrial and consumer UPSs and backup power supplies, etc. Reliable performance and weight-dimension characteristics of this equipment directly depend upon the effective use of accumulators, thus its increase is an important and urgent task.

"SWEL energy" company has been long studied the problem of efficiency increase in electrochemical cells. We have developed an algorithm which allows to decrease the internal resistance of an electrochemical cell during its charge or discharge, and we have got vast experimental materials that confirm the potential use of this algorithm in energy supply systems.

Internal resistance of an electrochemical cell is a sum of active (ohmic) resistance and so called polarization resistance associated with complex electrode reaction process. The value of ohmic resistance of any accumulator is defined by its construction and it cannot be decreased; on the contrary, the polarization component can be lowered almost to zero directly during charge/discharge. We have experimentally proved that by the way of selecting appropriate parameters of the discharge current and voltage it is possible to "separate" chemical and electrical processes in an electrochemical cell (in time in relation one to another). Due to that process it is possible to obtain the following:

• to reduce the heat loss during charge/discharge of the accumulator;
• to get an opportunity to quickly charge an accumulator with a high charging current;
• to increase considerably the quantity of energy supplied during discharge;
• to decrease the initial drop of output voltage of the accumulator at high discharge current and to convert output energy more effectively; thus, the time during which the specified output power is maintained, can be augmented in 1,5 and more times;
• in case of cycle operation the accumulator service life increases;
• moreover, taking into account the accumulator increased efficiency and the decrease of the initial drop of output voltage and heat loss, it is possible to charge an accumulator up to a lower initial voltage (keeping in line with the specified output energy characteristics). It allows to avoid gassing (the process that limits the effective use of Ni-Cd and other serviced accumulators) on the final stage of accumulator charge and thus to considerably simplify its maintenance.

We have conducted the tests on the following chemical cells:

• Ni-Cd (nickel-cadmium) accumulators (used in rail transport and aviation);
• Ni-Zn (nickel-zinc) accumulators (used in radio equipment, electric vehicles, aerospace equipment, underwater vehicles for divers towage, mineral exploration and mining in the offshore area, etc.);
• Ni-Fe (nickel-iron) accumulators (used in electric cars and windpower generators);
• lead-acid accumulators (used in cars, rail transport, communication facilities, UPS systems (uninterruptable power supply systems);
• Li-ion accumulators (used in cell phones, radio phones, portable radio stations, photographic equipment, portable computers, medical equipment, control equipment, standby lighting systems, electricity and heat energy meters);
• Two-layer and hybrid supercapacitors (used in rail transport and cars).

The tests have been executed with the help of charge-discharge test benches (14 V/0.5 kW and 400 V/6 kW), designed on the basis of a special electronic device – an electronic separator – that realizes in practice our proper algorithm of decreasing of the polarization resistance in an electrochemical cell.

In all tests we have observed the effect that declared itself in accumulator performance increase. The tests which consisted in the discharge of lead-acid accumulators with currents in range of 0.25 – 12 С on constant resistance and constant load power have showed that with the electronic separator the accumulator discharge time increases 1.5 – 2 times. For Li-ion accumulators at discharge current 1 – 2 С the increase makes up about 30%.

Thus, the use of "SWEL-ES" electronic separator allows to:

• decrease the weight and dimensions of an accumulator battery 1.5 and more times (keeping in line with the specified energy characteristics);
• increase 1.3 – 2 times the time when the specified voltage and power are preserved during the accumulator discharge process, subject to the accumulator type and discharge current;
• provide reliable accumulator performance in high and low temperatures;
• · considerably increase the accumulator life (the number of charge/discharge cycles);
• facilitate the accumulator service (for serviced accumulators) or entirely eliminate this process.