TECHNICAL INFORMATION BESTCAP A NEW DIMENSION IN “FAST” SUPERCAPACITORS Scot Tripp AVX Ltd, Fleet, UK Tel: +44(0) 1252 770043 Email: [email protected] Dr. Arieh Meitav ECR/AVX, Rehovot, Israel Tel: +972 8 940 7920 Email: [email protected] BESTCAP A NEW DIMENSION IN “FAST” SUPERCAPACITORS Scot Tripp AVX Ltd, Fleet, UK Tel: +44(0) 1252 770043 Email: [email protected] Dr. Arieh Meitav ECR/AVX, Rehovot, Israel Tel: +972 8 940 7920 Email: [email protected] Supercapacitors or electrochemical caps are rapidly recognized as an excellent compromise between electronic capacitors such as ceramic, tantalum and aluminum electrolytic devices and batteries (Figure 1). CAPACITOR TYPE CAP (mF) VOLTAGE (V) DIMENSIONS (mm) Tantalum 0.47 1.0 1.5 2.2 2.2 6.3 4.0 4.0 4.0 6.3 6.0 x 7.0 x 3.5 6.0 x 7.0 x 3.6 ø10 x L20 ø12.5 x L22 ø16 x L25 ESR CV/c.c. (mΩ) (mFV /c.c.) 100 20 30 26 15 3.2 10 3.3 15 2.8 4.7 15 22 15 330 250 250 500 600 700 60 120 6.3 6.3 6.3 10 10 8.0 5.5 5.5 4.5 3.5 5.5 5.5 ø16 x L26 ø16 x L35.5 ø18 x L41 ø18 x L35.5 ø76 x L114 52 x 50 x 4.0 48 x 30 x 3.0 48 x 30 x 5.0 48 x 30 x 4.8 48 x 30 x 4.2 28 x 17 x 3.0 28 x 17 x 5.0 100 30 20 30 10 50 60 30 25 20 200 100 Electrolytic Aluminum solid capacitor organic semi-conductive electrolyte Electrolytic Capacitor BestCapTM 6 13 13 17 6 200 300 400 400 400 250 300 Table 1. Performance of BestCapTM vs. Conventional Capacitor Technologies 10,000 SPECIFIC ENERGY 1,000 ECR AVX- ap™ BestC 100 UM AL NT TA ELECTROLYTIC CAPACITOR 10 ER YM TIC POL ROLY M T U C E IN EL LUM A 1 Figure 1. BestCap Electrochemical Cap vs. Conventional TM Generally, supercapacitors have energy densities several orders of magnitude higher than electronic capacitors (Table 1) and power densities significantly superior to batteries. There are, however, two negative characteristics associated with existing electrochemical capacitors, Viz: high ESR and capacitance loss when called upon to supply very short duration pulses at high current. This paper will demonstrate how the BestCap successfully addresses both of these issues. EDLCs 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 maybe liquid, (normally an aqueous or organic solution) or solid. The solid electrolyte is almost universally a conductive polymer. 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. BestCap – A New Dimension in Fast Supercapacitors We may summarize the differences between EDLC (Electrochemical Double Layer Capacitors) and electronic capacitors as shown in Table 2 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 two types of charge carriers: IONIC species on the ELECTROLYTE side and ELECTRONIC species on the ELECTRODE side. Table 2. Because highly activated carbon is used as the electrode material, each carbon particle functions as a double layer capacitor having a capacitance value of Cn (Figure 2). CM Since the EDL capacitor is comprised of capacitors having various resistances, the charge/discharge voltage and charge/discharge time will define the apparent available capacity. Charging or discharging at a high rate may result in an apparently smaller capacitance than when done at a lower rate. This is due to the small capacitors that have large internal resistance not being fully charged or discharged which results in a large voltage drop at the start of measurement. BestCap Pulse Performance BestCap technology is based on a patented, highly conductive polymeric, proton conductive electrolyte. The innovation of BestCap is that this polymer electrolyte possesses very high ionic conductivity, thereby providing low ESR in the range of 20-200 milliohms and maintaining high apparent capacitance for very short pulses. BestCap – A New Dimension in Fast Supercapacitors These two factors are critical in determining the total voltage drop in short pulse operations, such as in GSM and other pulsed-mode digital mobile phones. Figure 3 shows the voltage time relationship for a capacitor. First there is the instantaneous voltage drop V(TR) caused by the ESR, followed by V(Q), which is a function of the available capacitance. V0 ∆V(1R) ∆V(total) = I*R+I*∆t/C(f) ∆V(Q) = I*∆t/C(f) CM V1 Re Rc RI RI Figure 2. Simplified Equivalent Circuit of Electrochemical Capacitor Upon charging the capacitor, the charge has to be transferred through two resistances electronic (Re) at the carbon electrode and at the carbon - current collector interface (Rc), and ionic (Ri) passing through the electrolyte. Therefore, the equivalent circuit of the EDLC is given by the above R-C combination, where R1, R2 and Rn are the internal resistances of the activated carbons. ∆t Figure 3. Voltage-Time Relation of Cap Unit C = It(Vo-Vt-IR) → I = C*(Vo-Vt)/(R*C+t) Spec. Power = I*(Vo-I*R+Vt)/2 per unit Volume Spec. Energy = I* t*(Vo-I*R+Vt)2 per unit Volume R=ESR Now consider the available capacitance for very short pulse widths and for various EDLCs from a number of manufacturers, as shown in Figure 4. It can be clearly seen that virtually all EDLCs with the exception of BestCap lose >>90% of their nominal capacitance when used in the millisecond range. When used in a mobile phone, for example, and placed between the battery and the power amplifier, BestCap reduces the pulsed current drain on the battery thereby significantly increasing “Talk Time” from the battery. Actual Cap. (% of nominal) 100% AJ Electrolytic 80% 60% P - 2X10F M BestCap™ 40% N 20% Other BestCap Characteristics 0% 1000 10 100 1 Pulse width (msec) Figure 4. Actual Capacitance vs. Pulse Width This combined with their higher ESF, means that they will exhibit very high significant voltage drop under short pulse conditions, whereas the voltage drop for BestCap is very small. Tek T Battery Trig'd M Pos: 2.480ms CURSOR Type Voltage Summar y Delta 480mV The high conductivity proton polymer electrolyte utilized in BestCap allows high current, short duration pulses to be delivered with minimal voltage drop. The product uses only “green” material and is physically very robust. Cursor 2 3.40V CH1 500mV CH2 200mV M 1.00ms CH1 -174mV Hybrid: Battery coupled to six parallel Ta capacitors – 330µF each. Tek T Trig'd M Pos: 2.480ms CURSOR Type Voltage Source CH1 Delta 300mV b) While coupling the battery with six Ta - 330 mF parallel connected capacitors. Cursor 1 3.36V Cursor 2 3.56V CH1 500mV CH2 200mV M 1.00ms CH1 -174mV Hybrid: Battery coupled to ECR P-SC Tek T Trig'd M Pos: 2.480ms CURSOR Type Voltage Source CH1 Delta 120mV c) While coupling the battery with an AVX-ECR P-SC (4.5V/200mF/50mW – 48x30x2.2). Cursor 1 3.32V Cursor 2 3.70V CH1 500mV CH2 200mV M 1.00ms CH1 • Totally solid state, no liquids or gels used. • Completely non-toxic. • Capable of very thin formats with thickness down to < 0. 7mm. • Shock resistance to > 30000G’s. • Easy to produce in various voltage ratings. • Non-Polar. • Low leakage current - < 0.05µA/mF. • Capacitance values 40-500mF. Source CH1 Cursor 1 3.36V a) Battery only The material systems used in the BestCap structure features the following characteristics: -174mV Figure 5. Discharge of a 500 mAh Li-ion Battery (48 x 30 x 6.3) at a GSM “talk” Simulation Mode USA EUROPE ASIA-PACIFIC AVX Myrtle Beach, SC Corporate Offices AVX Limited, England European Headquarters AVX/Kyocera, Singapore Asia-Pacific Headquarters Tel: 843-448-9411 FAX: 843-626-5292 Tel: ++44 (0) 1252 770000 FAX: ++44 (0) 1252 770001 Tel: (65) 258-2833 FAX: (65) 350-4880 AVX Northwest, WA AVX S.A., France AVX/Kyocera, Hong Kong Tel: 360-699-8746 FAX: 360-699-8751 Tel: ++33 (1) 69.18.46.00 FAX: ++33 (1) 69.28.73.87 Tel: (852) 2-363-3303 FAX: (852) 2-765-8185 AVX North Central, IN AVX GmbH, Germany - AVX AVX/Kyocera, Korea Tel: 317-848-7153 FAX: 317-844-9314 Tel: ++49 (0) 8131 9004-0 FAX: ++49 (0) 8131 9004-44 Tel: (82) 2-785-6504 FAX: (82) 2-784-5411 AVX Mid/Pacific, MN AVX GmbH, Germany - Elco AVX/Kyocera, Taiwan Tel: 952-974-9155 FAX: 952-974-9179 Tel: ++49 (0) 2741 2990 FAX: ++49 (0) 2741 299133 Tel: (886) 2-2696-4636 FAX: (886) 2-2696-4237 AVX Southwest, AZ AVX srl, Italy AVX/Kyocera, China Tel: 480-539-1496 FAX: 480-539-1501 Tel: ++390 (0)2 614571 FAX: ++390 (0)2 614 2576 Tel: (86) 21-6249-0314-16 FAX: (86) 21-6249-0313 AVX South Central, TX AVX Czech Republic, s.r.o. 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