Title of Invention

"A PROCESS FOR THE PREPARATION OF SOLID STATE SILVER BATTERY"

Abstract

A process for preparation of a solid state silver battery which comprises; i) preparing solid electrolyte from the composition such as herein described by drying Li2S04, Ag2S04 and Agl at a temperature in the range of 100-150°C for a period of 36 to 48 hrs, mixing the said composition in mole ratio [l-y{(l-Xi)Li2S04: (xi) Ag2S04}: y{ (1-X2) Ag2S04: (X2) Agl}] where x1 is in the range of 0.6 to 0.9 mole%, X2 is in the range of 0.3 to 0.60 moie%, and y is in the range of o.i to 0.15 wt% in an organic solvent which is nonreactive with above said salts and heating at a temperature in the range of 100-200°C for 6-8 hrs for complete drying of resultant mixture, heating the dried mixture in a crucible at a temperature 10-20°C above the melting point of the mixture for a period of one to two hours to obtain the homogeneous melt, quenching the molten mass by rapid quenching technique, followed by crushing the resultant mass, the complete process is effected in dark, ii) mixing cathode composite material prepared by the process such as herein described with graphite powder in a ratio in the range of 1:1 to 1:2 followed by palletizing the said mixture at a pressure in the range of 5 to 10 tons/sq cm. to obtain a cathode, iii) embedding the cathode pellet in graphite, sprinkling powdered electrolyte on one side of embedded cathode followed by pressing at a pressure in the range 3-5 tons/sq cm., applying silver paint such as herein described on the surface of electrolyte, iv) mixing silver powder with solid electrolyte, obtained in step (i), in a ratio in the range of 1:1 to 1:2 followed by pressing at a pressure in the range of 5 to 8 tons/sq cm. to obtain an anode, v) placing the anode obtained over the silver painted side of the embedded cathode obtained in step (iv) over the silver painted side of the embedded cathode electrolyte stack obtained in step (iii) followed by pressing at a pressure in the range of 5-8 tones/sq cm to obtain the said solid state silver battery.

Full Text

This invention relates to a process for the fabrication of a solid state silver battery and solid state silver battery made thereby. The solid state batteries offer attractive advantages over their aqueous/non-aqueous counterparts. Many of the problems associated with primary batteries have been ascribed to the presence of liquid electrolytes. These include cell leakage, corrosion, self discharge, drying out of the cell, loss of electrolyte at elevated temperature and several restrictions on the capability for useful discharge at very low temperatures. Solid state batteries are becoming increasingly popular due to their known advantages over mentioned liquid-electrolyte based batteries. The recent research activity in this field is concentrated on providing the new electrical power source for certain applications like micro-batteries in microchip integrated devices, credit cards, pace-makers etc. Lithium batteries have high voltages and high energy density. The secondary solid state batteries using Cu ion conductors have high rate capabilities. But it is known that these are easily damaged in humid atmosphere and thus it is difficult to confirm their high reliability. Most of -the reported work on silver solid state batteries use the solid electrolyte derived from silver iodide . Among the existing silver ion conducting electrolytes, RbAgI5 and Ag3SI possesses very high ionic conductivity, but their utility in specific applications is questionable as earlier one is thermally unsta- ble above 270C and latter one has appreciable electronic conductivity. In addition to this, RbAgI5 and related compounds appear to be more affected by moisture and iodine vapors. The fabrication technique used so far is to obtain the cell by stacking cathode-electrolyte-anode after pressing them separately. Thus obtained stacks were spring packed in a cell holder. Such method do not ensure perfect interfacial contact leading to polarization of cells which is a major drawback. The main object of the present invention is to provide a process for the fabrication of a solid state silver battery and solid state silver battery made thereby which obviates the drawback of hitherto known process. Another object is to provide a solid state silver battery using silver conducting solid electrolyte operating at room temperature. Accordingly, the solid electrolyte was prepared using a composition as described and claimed in co-pending patent application number 643/DEL/96. A solid cathode was prepared using an iodine complex. A process for the preparation of iodine complex useful as a solid cathode is described and claimed in our co-pending patent application No. 685/DEL/96. Tetra methyl ammonium iodide (TMAI) and iodine has been taken in the range 1 to 3:3 to 6 weight ratio. An evacuated glass (to provide oxygen free atmosphere ) tube containing above mix- ture was slowly heated to 60-800 for 30-60 minuets. The tube was slowly cooled to room temperature to obtain complex, followed by crushing and mixing with the powdered electrolyte obtained in step (i) and graphite in a ratio in the range 3:1:1 to 3:4:6 by weight to obtain the composite cathode material, Accordingly, the present invention provides " a process for the fabrication of a solid state silver battery which comprises (i) preparing solid electrolyte from the composition as described in our pat. app. no. 643/del/96 by drying Li2 SO4 , Ag2SO4 and Agl at a temperature in the range of 100-1500C for a period of 36 to 48 hrs, mixing composition in [l-y{(l-x1 )Li2 SO4 :(x1 )Ag2 SO4 }:y{(l-x )Ag2 SO4 :(x2 )AgI}]4 where X1 is in the range of 0.6 to 0.9 mole% , X is in the range 2 of 0.3 to 0.60 mole%, and y is in the range of 0.1 to 0.15 wt % in an organic solvent which is nonreactive with salts and heating at a temperature in the range of 100 -200 C for 6-8 hrs for complete drying of resultant mixture, heating the dried mixture in a crucible at a temperature 10-200C above the melting point of the mixture for a period of one to two hours to obtain the homogeneous melt, quenching the molten mass by rapid quenching technique, followed by crushing the resultant mass, (ii) mixing cathode composite material prepared by the process described in our pat. app. no. 685/del/96 with graphite powder in a ratio in the range of 1:1 to 1:2 followed by pelletizing the said mixture at a pressure in the range of 5 to 10 tons/sq cm. to obtain a cathode, (iii) embedding the cathode pellet in graphite, sprinkling powdered electrolyte on one side of embedded cathode followed by pressing at a pressure in the range 3-5 tons/sq cm., applying silver paint on the surface of electrolyte (iv) mixing silver powder with solid electrolyte, obtained in step (i), in a ratio in the range of 1:1 to 1:2 followed by pressing at a pressure in the range of 5 to 8 tons/sq cm. to obtain an anode, (v) placing the anode obtained over the silver painted side of the embedded cathode obtained in step (iv) over the silver painted side of the embedded cathode electrolyte stack obtained in step (iii) followed by pressing at a pressure in the range of 5-8 tones/sq cm to obtain the said solid state silver battery, encapsulating the battery so obtained, if required . The entire process of preparation of solid electrolyte was carried out in dark ambient. The complete drying of the Li2SO4 , Ag2SO4 and Agl is affected by repetitive cycles of heating and weighing till the constant weight is achieved. The composition was heated to obtain a homogeneous melt o which is effected preferably at 20 C above melting point. The graphite powder used may be of commercial grade The silver paint used may be colloidal silver such as silver powder in butyl acetate The silver powder used may be greater than 350 mesh size and of 99.9% purity. Accordingly the present invention provides a solid state silver battery prepared by the process herein before described. The detailed process of the present invention for fabrication of solid state battery is given below: The weighed amount of iodine complex composite cathode has been pressed at 5 ton/sq cm to get a pellet of 10-12mm diameter and 1-3 mm thickness. It has been latter embedded in the graphite in such a way that only one surface of electrolyte was exposed. The embedding of cathode in graphite helps in protecting iodine losses and at the same time provide electronic conductivity. The weighed amount of electrolyte (Ag-ion conductor) has been pressed over the exposed surface of the cathode at 10 ton/sq cm. Silver paint has been applied on the exposed surface of electrolyte and finally the anode pellet, obtained by mixing silver powder and electrotrolyte, has been kept to get an electrochemical cell of the following configuration: Ag+El/Electrolyte/(TMAI+I +C+E1) The electrochemical cell of the above configuration has been mounted in the plexi- glass holder. The stainless steel plates and wires have been used as current collectors and leads respectively. The battery of the required voltage/current capacity has been obtained making appropriate series and parallel combinations. We claim: 1. A process for the fabrication of a solid state silver battery which comprises (i) preparing solid electrolyte from the composition as described in our pat. app. no. 643/del/96 by drying Li2SO4 , Ag2 SO4 and Agl at temperature in the range of 100-1500C for a period of 36 to 48 hrs, mixing composition in [l-y{(l-x1 )Li2 SO4 :(x1 )Ag4 SO4 }:y{(l-x2 2)Ag2 SO4 :(x2 )AgI}] where X1 is in the range of 0.6 to 0.9 mole% , X2 is in the range 11 of 0.3 to 0.60 mole%, and y is in the range of 0.1 to 0.15 wt % in an organic solvent which is nonreactive with salts and heating at a temperature in the range of 100-2000C for 6-8 hrs for complete drying of resultant mixture, heating the dried mixture in a crucible at a temperature 10-200C above the melting point of the mixture for a period of one to two hours to obtain the homogeneous melt, quenching the molten mass by rapid quenching technique, followed by crushing the resultant mass, (ii) mixing cathode composite material prepared by the process described in our pat. app. no. 685/del/96 with graphite powder in a ratio in the range of 1:1 to 1:2 followed by pelletizing the said mixture at a pressure in the range of 5 to 10 tons/sq cm. to obtain a cathode, (iii) embedding the cathode pellet in graphite, sprinkling powdered electrolyte on one side of embedded cathode followed by pressing at a pressure in the range 3-5 tons/sq cm. , applying silver paint on the surface of electrolyte (iv) mixing silver powder with solid electrolyte, obtained in step (i), in a ratio in the range of 1:1 to 1:2 followed by pressing at a pressure in the range of 5 to 8 tons/sq cm. to obtain an anode, (v) placing the anode obtained over the silver painted side of the embedded cathode obtained in step (iv) over the silver painted side of the embedded cathode electrolyte stack obtained in step (iii) followed by pressing at a pressure in the range of 5-8 tones/sq cm to obtain the said solid state silver battery, encapsulating the battery so obtained, if required . 2. A process as claimed in claim 1 wherein the process of preparation of solid electrolyte in step (i) is effected in dark ambient. 3. A process as claimed in claims 1 & 2 wherein the graphite powder used is of commercial grade. 4. A process as claimed in claims 1 to 3 wherein the silver paint used is colloidal silver such as silver powder in butyl acetate. 5. A process has claimed in claim 4 wherein the silver powder used is of AR grade i.e. 99.9% purity and of greater than 350 mesh size. 6. A solid state silver battery prepared by the process as claimed in claims 1-5. 7. A process for the fabrication of solid state silver battery and solid state silver battery made thereby substantially as herein described.

Documents:

641-del-1996-abstract.pdf

641-del-1996-claims.pdf

641-del-1996-correspondence-others.pdf

641-del-1996-correspondence-po.pdf

641-del-1996-description (complete).pdf

641-del-1996-form-1.pdf

641-del-1996-form-13.pdf

641-del-1996-form-2.pdf

641-del-1996-form-4.pdf

641-del-1996-form-6.pdf