WO2008029419A2

WO2008029419A2 - Lead-acid battery plates

Info

Publication number: WO2008029419A2
Application number: PCT/IN2007/000395
Authority: WO
Inventors: Ajoy Datta
Original assignee: Luminous Power Technologies Pvt Ltd
Priority date: 2006-09-07
Filing date: 2007-09-06
Publication date: 2008-03-13
Also published as: WO2008029419A3

Abstract

Plates for a lead acid battery, the method of preparing the plates and lead acid batteries using the plates are described.

Description

LEAD ACID BATTERY PLATES

FIELD OF THE INVENTION

This invention in general relates to lead acid batteries and in particular relates to a method of preparing battery plates for use in lead acid batteries, the battery plates, and to batteries containing plates so prepared.

BACKGROUND

A lead-acid battery is a secondary electrochemical device that stores energy and makes it available in an electrical form. Lead acid batteries are the most widely used secondary batteries, extensively employed in applications like automobiles. The lead acid battery may comprise of several cells connected in parallel or series.

The basic construction of the cell comprises a positive electrode, a negative electrode, and an electrolyte which is dilute sulphuric acid. The positive electrode and the negative electrode are also referred to as the positive and negative plates respectively. A paste generally comprising lead oxide, lead sulphate, water and certain other additives, taken in a fixed proportion, is applied to a grid to form a plate. Electrical connections are provided between grids acting as positive and negative plates.

The typical or conventional method of preparing battery plates involves a series of steps. Firstly, a grid typically made of metallic lead or a lead-based alloy is produced. The grid is made by conventional techniques such as direct casting, stamping, forging or by mechanical working. Thereafter, a paste typically made of lead oxide, lead sulphate, water and certain other additives is applied to the grid. Subsequent to the application of the paste, the plates are cured. The curing process is carried out under predetermined temperature and humidity conditions and results in change in the morphology of the paste. Following the curing process the plates are allowed to dry. The drying may occur under natural or controlled conditions. Typically, the curing and drying processes may take about 24-72 hours.

After the plates have been cured and dried, the formation of the plates is carried out. The formation is usually carried out by passing a predetermined current through the plates in the presence of dilute sulphuric acid. Plates may be formed independently and are thereafter assembled. Alternatively, plates are first assembled into cells or into a complete battery and are then formed.

Enhanced life and performance of a battery are the major concerns driving most of the modifications in the battery design and manufacturing process. One major factor hindering the life and performance of the battery using plates manufactured by the described conventional method is a sharp rise in temperature immediately following acid filling during manufacture of the battery.

As soon as the electrolyte, i.e. dilute sulphuric acid, is filled into the battery, a sharp rise in the temperature is observed. This rise in the temperature is due to the exothermic reaction between the sulphuric acid and the lead oxide in the paste. The high temperature following the acid fill process accelerates the formation of sulphate on the plate, thereby decreasing the strength of the acid in the battery.

This high temperature rise immediately following acid filling in the battery affects the performance of the battery. The high temperature promotes the formation of a thick sulphate layer on the plate surface, which inhibits acid migration to the plate interior. This leads to low acid concentration in the plate interior and accelerates lead dissolution from the battery grids. Large temperature disparity between cells in the battery following acid fill affects paste morphology and introduces significant non uniformity between cells. The surface sulphate on the plates also contributes to electrolyte temperature build up and hinders the formation of the plate.

In case of a sealed battery, the temperature rise may particularly cause very severe problems. Low acid concentration in sealed batteries can lead to the development of dendrite shorts through the separators and consequent battery failure.

Thus, the high temperature rise in the battery following acid filling is undesirable in all lead-acid batteries and needs to be prevented. Certain approaches that are conventionally used to control the temperature rise in the battery are herein discussed.

One possible approach for controlling the high temperature rise during acid fill in lead acid batteries is to reduce the level of lead oxide in the paste by adding additional sulphuric acid to the paste during paste mixing. However, the additional lead sulphate in the paste adversely affects paste density and paste weight.

Another approach involves a two step formation of batteries wherein batteries are initially filled with low gravity sulphuric acid and formed. At the end of formation, the electrolyte is dumped out and replaced with acid of the correct specific gravity. However, the two step process is generally tedious, time consuming and inefficient.

Yet another approach, commonly practiced in the industry is pre-chilling of the acid prior to filling the battery with the acid. Pre-chilling, however, is time consuming and not cost effective. Thus, there exists a need for a method of preparing the plates of a lead acid battery that controls the high rise in temperature following acid fill in a battery.

SUMMARY

This Summary is provided to introduce a selection of embodiments in a simplified form that are further described below in the Detailed Description. This

Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

In an embodiment of the subject matter described herein, a method of preparing plates for a lead-acid battery is explained. Firstly a plate is formed by application of paste to a grid surface. At this stage typically the lead sulphate in the paste is less than

15%. The plate is immersed in an acid bath containing dilute sulphuric acid having a predetermined specific gravity preferably in the range of about 1.100 to about 1.300

(temperature compensated to 27°C); at a substantially constant predetermined temperature preferably in the range of about 25⁰C to about 45⁰C; and for a specified period of time. The specified time is the time taken to preferably achieve about 20% to

40% lead sulphate in the paste. Subsequently, a curing process is carried out.

Following the curing process, the plates are allowed to dry. These dried plates substantially have no free sulphuric acid present in the paste. The plates are then assembled and used in a lead acid battery.

In another embodiment, firstly a plate is formed by application of paste to a grid surface. At this stage typically the lead sulphate in the paste is less than 15%. Subsequently, a curing process is carried out. Following the curing process; the plates are allowed to dry. After the drying process the plate is immersed in an acid bath containing dilute sulphuric acid having a predetermined specific gravity preferably in the range of about 1.100 to about 1.300 (temperature compensated to 27°C); at a substantially constant predetermined temperature preferably in the range of about 25⁰C to about 45⁰C; and for a specified period of time. The specified time is the time taken to preferably achieve about 20% to 40% lead sulphate in the paste. Following the immersion process, the plates are allowed to dry. These dried plates preferably have about 20% to 40% lead sulphate in the paste and substantially no free sulphuric acid present in the paste. The plates are then assembled and used in a lead acid battery.

In yet another embodiment of the subject matter herein, the lead acid battery using plates prepared by the aforementioned method of preparing plates is described.

Plates prepared by the method of the previous embodiment can be assembled into a battery by means known to the prior art. The assembly typically comprises stacking positive and negative plates with interleaved separators; connecting positive and negative plate groups; and inserting the plate groups into a battery container and thereafter providing inter-cell and terminal connections.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 provides an illustration of a method 100 of preparation of an electrode for the lead acid battery, in accordance with one embodiment of the present subject matter, by means of a flow chart.

Fig. 2 provides an illustration of a method 200 for preparing the electrode for the lead acid battery, in accordance with another embodiment of the present subject matter, by means of a flow chart. DETAILED DESCRIPTION

The subject matter discussed herein relates to plates for a lead acid battery substantially free of sulphuric acid in the paste and a method of preparation of the plates. The method of preparation of plates does not result in high temperature rise in the battery following acid filling. High temperature is controlled by increasing the proportion of lead sulphate in the plate prior to acid filling of the battery. The increase in the proportion of lead sulphate in the plate is achieved during immersion of the plate in the sulphuric acid bath. Since a large proportion of the lead sulphate required for the battery operation is available in the plates prior to battery acid filling, the battery can be filled with lower specific gravity acid and the temperature does not rise as sharply thus obviating the difficulties of the conventional methods. ^:

Aspects of the plates and method of their preparation being described herein can be implemented in any number of different environments, and/or configurations that will be obvious to a person skilled in the art. Different embodiments of the plates and method are herein described in the context of the following exemplary^' method(s) only as examples and are not limiting to the scope of the described subject matter.

Example 1

With reference to Fig. 1, described herein is a method 100 of preparation of a plate for the lead acid battery, in accordance with one embodiment of the present subject matter, by means of a flow chart.

The method 100 is initiated by pasting a grid with paste as in step 102. The grid is generally made of lead or lead based alloys known to the prior art. Any of the various grid fabrication processes such as casting, stamping, forging, punching or rolling, readily known to a person skilled in the art, may be employed to produce the grid structure herein described.

The paste, generally, is a mixture of lead oxide, lead sulphate, water, and sulphuric acid in a predetermined proportion. The lead sulphate in the paste at this stage is typically less than 15%. The grid after being pasted forms a plate.

In the next steplO4, the plate is cured. A typical curing process involves allowing the pasted plate to stand under controlled humidity and temperature conditions for a predetermined period of time. The curing results in a change in the morphological structure of the paste.

Subsequent to the curing, as per the step 106, the plate is dried. The moisture present in the paste is removed by the drying process. The drying process is generally carried out under controlled temperature as in the prior art.

In accordance with step 108 of method 100, the dried plate of step 106 is immersed in an acid bath containing dilute sulphuric acid having a predetermined specific gravity preferably in the range of about 1.100 to about 1.300 (temperature compensated to 27°C); at a substantially constant predetermined temperature preferably in the range of about 25⁰C to about 45⁰C; and for a specified period of time. The specified time is the time taken to preferably achieve about 20% to about 40% lead sulphate. After the desired level of sulphation is achieved, in step 110 of the method 100, the plate is allowed to dry. These dried plates preferably have about 20% to about 40% lead sulphate in the paste and substantially have no free sulphuric acid present in the paste. These plates are then formed and used in a lead acid battery. The process of this embodiment could be used to prepare plates for use either in a conventional or bipolar lead acid battery.

The order in which the method 100 is described is not intended to be construed as a limitation, and the steps described can be combined in other ways obvious to a person skilled in the art. Additionally, individual blocks may be added or deleted from the method without departing from the spirit and scope of the subject matter described.

Example 2

The dried plates of the previous embodiment can be assembled into a flooded or sealed battery by means known to the prior art. The assembly typically comprises stacking positive and negative plates with interleaved separators; connecting positive and negative plate groups; and inserting the plate groups into a battery container.

Thereafter inter-cell and terminal connections are made.

Example 3

In another embodiment the bipolar plates, prepared using the process of Example 1, are assembled into a bipolar battery. The assembling of the bipolar battery comprises stacking bipolar plates with interleaved separators, inserting plate stack into a battery container and providing terminal connections.

Example 4

With reference to Fig. 2, described herein is a method 200 of preparation of a plate for the lead acid battery, in accordance with one embodiment of the present subject matter, by means of a flow chart. The method 200 is initiated by pasting a grid with paste as in step 202. The grid is generally made of lead or lead based alloys known to the prior art. Any of the various grid fabrication processes such as casting, stamping, forging, punching or rolling, readily known to a person skilled in the art, may be employed to produce the grid structure herein described.

In accordance with step 204 of method 200, the pasted plate of step 202 is immersed in an acid bath containing dilute sulphuric acid having a predetermined specific gravity preferably in the range of about 1.100 to about 1.300 (temperature compensated to 27⁰C); at a substantially constant predetermined temperature preferably in the range of about 25⁰C to about 45⁰C; and for a specified period of time.

The specified time is the time taken to preferably achieve about 20% to about 40% lead sulphate in the paste. After a desired level of sulphation is achieved in the paste the plate is removed from the bath. Subsequently, a curing process is carried out in step 206 of method 200. A typical curing process involves allowing the pasted plate to stand under controlled humidity and temperature conditions for a predetermined period of time. The curing results in a change in the morphological structure of the paste. Following the curing process, the plates are allowed to dry. These dried plates preferably have about 20% to about 40% lead sulphate in the paste and substantially have no free sulphuric acid present in the paste. These plates are then formed and used in a lead acid battery. Subsequent to the curing, as per the step 208, the plate is dried. The moisture present in the paste is removed by the drying process. The drying process is generally carried out under controlled temperature as in the prior art.

The process of this embodiment could be used to prepare plates for use either in a conventional or bipolar lead acid battery.

The order in which the method 200 is described is not intended to be construed as a limitation, and the steps described can be combined in other ways obvious to a person skilled in the art. Additionally, individual blocks may be added or deleted from the method without departing from the spirit and scope of the subject matter described.

Example 5

The dried plates of the previous embodiment can be assembled into a flooded or sealed battery by means known to the prior art. The assembly typically comprises stacking positive and negative plates with interleaved separators; connecting positive and negative plate groups; and inserting the plate groups into a battery container. Thereafter inter-cell and terminal connections are made.

Example 6

In another embodiment the bipolar plates prepared using the process of Example 1 is assembled into a bipolar battery. The assembling of the bipolar battery comprises stacking bipolar plates with interleaved separators, inserting plate stack into a battery container and providing terminal connections.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art L that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

I / We claim:

1. A plate for use in a lead acid battery, the plate comprising: a grid; and _; a paste applied to said grid, wherein the proportion of sulphate in said paste is 20-40% by weight and wherein the paste substantially has no free sulphuric acid.

2. A flooded or sealed lead acid battery comprising the plates as claimed in claim 1.

3. A bipolar lead acid battery comprising the plates as claimed in claim 1.

4. A method of preparing a plate for use in lead-acid battery, the method comprising:

(a) pasting a grid with a paste to form a plate;

(b) curing said plate; (c) drying said plate;

(d) immersing said plate in dilute sulphuric acid bath; and

(e) drying said plate.

5. A method of preparing a plate for use in lead-acid battery, the method comprising: (a) pasting a grid with a paste to form a plate;

(b) immersing said plate in a dilute sulphuric acid bath;

(c) curing said plate; and

(d) drying said plate.

6. The method of claim 4 or 5, wherein the sulphuric acid bath contains sulphuric acid of specific gravity between about 1.100 to about 1.300.

7. The method of claim 4 or 5, wherein the sulphuric acid bath is maintained at a substantially constant predetermined temperature range of about 25⁰C to about 45⁰C.

8. The method of claim 4 or 5, wherein the immersing is for such time as needed to achieve about 20% to about 40% lead sulphate in the paste.

9. A method of making a flooded or sealed battery, the method comprising:

(a) preparing a plurality of positive and negative plates in accordance with the method of claim 4 or 5 ;

(b) stacking said plurality of positive and negative plates with interleaved separators to form a plurality of cells;

(c) connecting said plurality of positive plates to form positive plate groups and said plurality of negative plates to form negative plate groups; (d) inserting said plate groups into a battery container;

(e) providing inter-cell and terminal connections for said cells.

10. A method of making bipolar battery, the method comprising: preparing a plurality of bipolar plates in accordance with the method of claim 4 or 5; stacking said plurality of bipolar plates with interleaved separators; inserting said stack into a battery container; and making terminal connections for said stack.