The Important Information/Disclaimer is incorporated in the catalog where these specifications came from or

available online at www.avx.com/disclaimer/ by reference and should be reviewed in full before placing any order.

22

4.1: ELECTROCHEMICAL EDLC VS. ELEC-

TRONIC TECHNOLOGY - BESTCAP® CON-

STRUCTION

To understand the benefits offered by the BestCap®, it is necessary to

examine how an electrochemical capacitor works. The most significant

difference between an electronic capacitor and an electrochemical

capacitor is that the charge transfer is carried out by the electrons in the

former and by electrons and ions in the latter. The anions and cations

involved in double layer supercapacitors are contained in the electrolyte

which may be liquid (normally an aqueous or organic solution) or solid. The

solid electrolyte is almost universally a conductive polymer.

Cell Case (Anode)

Cell Case (Anode)

Electrode (Cathode)

Carbon

Carbon

Insulation Material

Current Collector

Current Collector

Separator

Vo

Vt

t

V(IR)

V(Q)=I*

t/C( t)

total=I*R + I* t/C( t)

3.6

3.4

3.2

3

0

1000

2000

3000

4000

3.8

4

3

2

1

0

4

5

Time (µSeconds)

Battery Voltage

Battery and Capacitor Voltage

Current Pulse

Electrons are relatively fast moving and therefore transfer charge “instantly.”

However, ions have to move relatively slowly from anode to cathode, and

hence a finite time is needed to establish the full nominal capacitance of

the device. This nominal capacitance is normally measured at 1 second.

The differences between EDLC (Electrochemical Double Layer Capacitors)

and electronic capacitors are summarized in the

table below:

• A capacitor basically consists of two conductive plates (electrodes),

separated by a layer of dielectric material.

• These dielectric materials may be ceramic, plastic film, paper, aluminum

oxide, etc.

• EDLCs do not use a discrete dielectric interphase separating the

electrodes.

• EDLCs utilize the charge separation, which is formed across the

electrode – electrolyte interface.

• The EDLC constitutes of two types of charge carriers: IONIC species on

the ELECTROLYTE side and ELECTRONIC species on the ELECTRODE

side.

4.2: VOLTAGE DROP

Two factors are critical in determining the voltage drop when a capacitor

delivers a short current pulse; these are ESR and “available” capacitance as

shown in Figure 4.

Figure 4. Voltage-time relation of capacitor unit

Figure 5. GSM Pulse

The instant voltage drop ∆VESR is caused by and is directly proportional

to the capacitor’s ESR. The continuing voltage drop with time ∆VC, is a

function of the available charge, i.e. capacitance. From Figures 3 and 4

it is apparent that, for very short current pulses, e.g. in the millisecond

region, the combination of voltage drops in a conventional supercapacitor

caused by a) the high ESR and b) the lack of available capacitance causes

a total voltage drop, unacceptable for most applications. Now compare the

BestCap® performance under such pulse conditions. The ultra-low ESR (in

milliOhms) minimizes the instantaneous voltage drop, while the very high

retained capacitance drastically reduces the severity of the charge related

drop. This is explained further in a later section.

EFFICIENCY/TALKTIME BENEFITS OF BESTCAP®

Since BestCap®, when used in parallel with a battery, provides a current

pulse with a substantially higher voltage than that available just from the

battery as shown in Figure 5, the efficiency of the RF power amplifier is

improved.

Additionally, the higher-than battery voltage supplied by the BestCap® keeps

the voltage pulse above the “cut off voltage” limit for a significantly longer

time than is the case for the battery alone. This increase in “talk time” is

demonstrated in Figures 6(a) (Li-Ion at +25°C), and 6(b) (Li-Ion at 0°C).

BestCap® Ultra-low ESR

High Power Pulse Supercapacitors

Application Notes/BestCap® Construction/Voltage Drop

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