CA1099090A - Capacitor electrolyte and capacitor containing same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A p-nitrobenzyltrimethylammonium boro-di-salicylate or boro-di-diolate is used as a solute in an electrolytic capacitor electrolyte. The boro-di-diolate anion may be boro-di-2,3-naphthalenediolate or boro-di-catecholate. The electrolyte is non-aqueous, and preferably the solvent is N,N-dimethylformamide.

Description

This invention relates to an electrolytic capacitor and to an electrolyte for such a capacitor. More particularly, this invention relates to an aluminum electrolytic capacitor and to a non-aqueous electrolyte which contain a solute which lowers the equivalent series resistance of the capacitorO
The resistance of a capacitOr affects the amount of ener-gy lost during the charging and discharging of the capacitor.
Resistance also affects the amount of time required for charging and disrharging. If a ripple current is applied, the resistance 10 affects the energy loss caused by heating, which in turn can affect the capacitor adversely by causing the electrolyte to leak or boil-off, thus drying out the capacitor, generating gas, increasing internal pressure, etcO
Prior art capacitors have utilized electrolytes contain-ing selected borodisalicylates and borodidiolates to suppress cathodic gas generation, as described by Ross in US 3,325,697 issued June 13, 1967.
A feature of this invention is the provision of an elec-trolyte with improved resistance propertiesO
In accordance with this invention a p-nitrobenzyltri-methylammonium boro-di-salicylate or boro-di-diolate is used as a solute in an electrolytic capacitor electrolyte.
In a drawing which illustrates embodiments of the inven-tion, The single figure shows a capacitance section in partly unrolled condition and employing the electrolyte of this inventionO
In general, the electrolyte of this invention includes p-nitrobenzyltrimentylammonium borodisalicylate or boro-di-diolate as a solute dissolved in N,N-dimethylformamide. Unlike the gas~
suppressing borodisalicylate and borodidiolate compounds of the prior art, the specific compounds of this invention are used in ~L~ r? ~

electrolytes to reduce si~nificantly the equivalent series resis-tance of capaoitors containin$ th~ml~
The preparation of three of such compounds of this inven-tion is as follows~ Borodi-2,3-naphthalenediolate may be prepared by dissolving naphthalene-2,3~diol and pmnitrobenzyltrimethylammo-niu~ bromide in methanola ~n aqueous boric acid solution is added to the mixture which :is then cooled and filtered yielding7 a crude product, m.p. 31~-319C, after crystallization from a methanol-dimethylformamide mixtureO
The borodisalicylate m~ay be prepared by first adding sil-ver oxide with stirring to an aqueous p-nitrobenzyltrimethylammonium bromide solutionO The resulting mixture is filtered, and the fil-trate is added to a solution of salicylic acid and boric acid in aqueous methanolO The mixture is heated, after adding more metha-nol, until an homogenous solution is obtained. Solvents are removed with a water pump, and the product, mO~pO 158-160C, is crystallized from a 2-propanol-methanol mixtureO
p-nitrobenzyltrimethylammonium borodicatecholate, m.p.
276-278C, may be prepared similarly to the salicylate with pyro-catechol substituted for the salicylic acidO
The drawing shows a capacitance section 10 in partlyunrolled conditionO Anode 11 is aluminum having on its surface a dielectric oxide layerO Cathode 22 may be aluminum or another metalO Electrolyte absorbent films 13 and 14, e.g. of kraft paper, are positioned between the anode 11 and the cathode 120 Tabs 15 and 16 of aluminum are connected to electrodes 11 and 12, respec-tively, as terminals for sertion 10.
The p-nitrobenzyltrimethylammonium borodisalicylate and borodi-2,3-naphthalenediolate are ~he preferred solutes and may be used alone or with other solut4s or additives~ The function of these nitro-substituted oompounds -Is to reduce the r~sistance of the capacitorv Ascordingly7 they may be used with other solutes ~ 3 ~

,a~j~,q~

or addi~ives serving oth~r E~nctions providing they are compati~le and there is no negat-ive synergis~ic effect~ Preferably, 1% of the material is usedO
The following exarnples are presented to show the useful-ness of the electrolytes contalning th~ p-nitroben~yltrimethyl-ammonium borodisalicyla~e or boro~di~diolaces of the present inven-tion in reducLng resistance in alu~in~lm electrolytic capacitorsO

Three formulations were made in N,N-dimethylformamide (DlV~) and compared with an electrolyte not containing the nitro-substituted compound~
Electrolyte #l is the control and consists of OoLM diisopropyl-amm~nium borodi-2,3-naphthalenediolate in DMF;
electrolyte #2 is Oo~M p-nitrobenzyltrimethylammonium borodi-2,3-naphthalenediolate in DMF;electrolyte ~3 is 1% p-nitrobenzyltrimethylammonium borodisalicylate added to electrolyte #l; and electrolyte #4 is 1% p-nitrobenzyltrimethylammonium borodi-2,3-naphthalenediolate added to electrolyte #lo Resistivity (in ohm-cm) at 25C, and capaci~ance ~n ,uF) and RC at both 25C and -55C (average of five units) are presented in the table below. The aluminum capac~ ors were rated 160~ , 50V, and 25 Elec~
trolyte Q- -cm(25C) ~ ~xC ~ RxC
#1 325 16506 65 150.4 361 #2 372 165O7 ~8 153.3 255 #3 300 16600 45 153.1 235 ~4 299 163.3 44 152.9 ~51 Flve units containing formulation ~4 were life-tested at 125~C, 50VDC ancl co~ared with similar uni~s containing formulation ~1 ~control~

_ 0 hrs. 1000 hrsO
~lec-trolyte /uF ~xC ~ ~Fi7~C ~
#1 160~9 55 1.5 15804 57 0066 #~ 16~.5 ~S 1~4 162~5 50 0,5g Exa~ 2 This ~xample shows the effect of the additives on the equivalent series resis~ance (in ohms) at various temperatures for a differen~ set of aluminum capacitors containing formulations as 10 given in Example 1. Results based on the average of five units are presented:
C Elec~rolyte Electrolyte Electrolyte Electrolyte #1 #2 ~3 #4 0.445 0.360 00271 00271 o 00558 0~429 0.417 00424 -10 0.69 0.507 0.463 0.469 ~30 0.99 0.705 00690 0~715 -55 2~40 1.67 1.54 1.6 Example 3 Results of life tests at 125C for 50VDC alumlnum capa-citors containing electrolyte #l (control) and electrolytes #3 and #4 as given in Example 1 are presented below for 0, 500, and 1000 hrs. The data are averages of four units for the control and five units each for the test samplesO
O hrs~ 500 hrsO _ 1000 hrs~
Elec-trolyteCap R~- ~ Cap RC ~ Cap RC ~A
~1160.8 55 105 15808 66 200 15609 57 0066 #316408 46 105 162.5 54 lo9 16106 52 ~o80 ~ 16405 47 1034 11~i~!o6 5~ 1.. 7 1~205 49 0~58 3 ~

The change of resistLvit:y (~ crrl) with temperature i5 given or electrolytes #3 and ~4 and compared to electrolyte #1:
~55C -~0C -30~ 0C 25C 85C 125C
#1 1650 lûO0 770 53~ 50 325 180 140 t~3 1585 1030 765 51':~ 426 300 164 130 #4 1540 980 750 519 ~18 299 162 127 The above exarnples show that aluminum capacitors formula-ted with electrolyte of the present invention have lower resistance, 10 remain stable with time, and have good temperature characteristics.

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrolyte for an electrolytic capacitor comprising a solvent and p-nitrobenzyltrimethlammonium boro-di-salicylate or boro-di-diolate as solute.

2. An electrolyte according to claim 1 wherein said solute is p-nitrobenzyltrimethylammonium borodi-2,3-naphthalenediolate.

3. An electrolyte according to claim 2 wherein said naphtha-lenediolate is present in 0.1M concentration.

4. An electrolyte according to claim 2 wherein 1% of said naphthalenediolate is present.

5. An electrolyte according to claim 4 wherein diisopropyl-ammonium borodi-2,3-naphthalenediolate is present also.

6. An electrolyte according to claim 1 wherein said solute is p-nitrobenzyltrimethylammonium borodisalicylate.

7. An electrolyte according to claim 6 wherein 1% of said borodisalicylate is present.

8. An electrolyte according to claim 7 wherein diisopropyl-ammonium borodi-2,3-naphthalenediolate is present also.

9. An electrolyte according to claim 1 wherein said solute is p-nitrobenzyltrimethylammonium borodicatecholate.

10. An electrolytic capacitor comprising a cathode electrode, an anode electrode bearing a dielectric oxide thereon, and a p-nitrobenzyltrimethylammonium borodisalicylate or boro-di-diolate dissolved in a solvent as an electrolyte in contact with said cathode and said anode.