PLASTIC-REINFORCED CONDUCTORS

TECHNICAL FIELD

[0001] The present disclosure generally relates to the field of rechargeable lead-acid batteries. In particular, the present disclosure pertains to Plastic Reinforced Lead Conductor (PRLC) for its utilization in fabrication of high energy density lead-acid batteries. The present disclosure also pertains to method of manufacturing Plastic Reinforced Lead Conductor (PRLC) and high energy density lead-acid batteries made therewith.

BACKGROUND

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Lead-acid batteries find major application in the field of automobiles. Their rechargeable nature enhances their utility despite of low energy-to-weight ratio. Generally known as SLI(starting, lighting and ignition system of the vehicle), their major role is to provide electric current required by starter motors. Additionally, they provide power to lights, ignition system of a vehicle and engine of a vehicle. Despite of the emergence of newer technologies, lead-acid batteries still find a wide array of practical utilities due to their inexpensive operation and other foretold features. Lead-acid/SLI batteries, also known as automotive batteries, include plates of pasted type, both positive and negative plates. Typically, plates include conducting lead grids with lattices into which the appropriate active material is pasted. These batteries, though compact in size and delivering high currents, have a shorter cyclic life due to corrosion of the grids of the positive plates.

[0004] Although, lead-acid batteries for automotive applications amount to near about half the sale of batteries worldwide, there are other types of batteries as well that find wide utility. Among those, Industrial batteries are worth noting. In case of industrial batteries, while the negative plates are of the pasted type, as described above, the positive plates are of tubular type, wherein the lead conductors are having a set of longitudinal spines. Each of these spines is accommodated centrally in an inert woven tubular bag. The annular space between the lead spine and the bag is filled with positive active material. The lead spines are thus inhibited against the anodic corrosion. These batteries give a longer service life of about 5 years or more. However, they are very bulky and heavy, with an energy density of about 80-90 Wh/dm ³ and specific energy of about 30 Wh/kg.

[0005] Batteries, currently in use, are generally made by connecting in series, individual cells of nominal voltage 2 Volts. Each cell includes a positive electrode, made by group welding lugs of a set of positive plates, and a negative electrode made by group welding lugs of a set of matching negative plates. The positive and negative electrodes interleave with each other and are electrically insulated by porous separators. The assemblies of such cells are accommodated in the individual cell compartments and are suitably covered with cell covers. These individual cells are connected in series by welding suitable inter-cell connectors. The cells thus made are filled with dilute sulphuric acid that acts as an electrolyte, which is necessary for the electro-chemical functioning of the battery. During charging or discharging of the batteries, by the electro-chemical reactions of the active materials and electrolyte, a flow of electrical current takes place to/from individual plates of electrodes along the members of lead grid. The electrical current flows through various thin members of the plates internally and through the inter-connectors externally. During the charging process, these thin members of the grids result in non-uniform distribution of currents in the grids and impose a serious limitation on the maximum rate of charging currents at which the battery can be charged without damaging the same. Such construction/design also results in non-uniform current density across the area of plates, which drastically limits the electrical performance of the batteries. It is also observed in the batteries currently in use that, as current density is not uniform throughout the surface area of plates, it results in a non-uniform anodic corrosion of grids of the positive plates, thereby reducing life-expectancy of batteries. As, charge transfer between active material and lead conducting grid depends on the surface area of contact, the best charging time required to recharge up to about 90% of the capacity of a fully discharged battery under carefully regulated conditions is around 2-3 hours when charged according to the Ampere-hour law, given by I _t = Coe ^"1 , where I _t is instantaneous charging current (in Amperes)at any given time t (in hours), and Co is the capacity (in Ampere-hours)to which the battery was discharged from which the recharging was commenced.

[0006] All the foretold limitations of lead-acid batteries seriously limit their practical application in battery operated electric vehicles, solar photo-voltaic applications and other areas with critical performance requirements. There is, therefore, a requirement for improved plates/conductors for lead-acid batteries that enhances the battery performance with an increased battery life while maintaining a healthy energy density. OBJECTIVES OF THE INVENTION

[0007] An objective of the present disclosure is to provide improved plates/conductors that overcome one or more disadvantages associated with previously known pi ates/ conductors .

[0008] Another objective of the present disclosure is to provide reinforced pi ates/ conductors .

[0009] Another objective of the preset disclosure is to provide high density lead-acid batteries utilizing improved plates/conductors.

[0010] Another objective of the present disclosure is to provide a lead-acid battery that has better life expectancy and working range.

[0011] Another objective of the present disclosure is to provide a lead-acid battery that does not exhibit substantial corrosion of electrodes.

[0012] Another objective of the present disclosure is to provide a lead-acid battery that can be recharged in substantially less amount of time.

[0013] Yet another objective of the present disclosure is to provide a lead-acid battery that is lightweight.

[0014] Still another objective of the present disclosure is to provide a lead-acid battery that exhibits significantly higher energy density.

SUMMARY

[0015] The present disclosure generally relates to the field of rechargeable lead-acid batteries. In particular, the present disclosure pertains to Plastic Reinforced Lead Conductor (PRLC) for its utilization in fabrication of fast rechargeable high energy density lead-acid batteries. The present disclosure also pertains to method of manufacturing Plastic Reinforced Lead Conductor (PRLC) and fast rechargeable and high energy density lead-acid batteries made therewith.

[0016] An aspect of the present disclosure provides a Plastic Reinforced Lead Conductor (PRLC) for its utility in fabrication of lead-acid batteries, said Plastic Reinforced Lead Conductor (PRLC) including: a thin lead conductor in substantially sheet form, and a mesh affixed to at least a part of said thin lead conductor on each of its opposing surfaces to provide reinforcement to said thin lead conductor in substantially sheet form, wherein said mesh is made of a material that is substantially resistant to acid and oxidation, and wherein said mesh includes thin, perforated and ribbed mesh made of a plastic material. In an embodiment, said mesh is affixed to at least a part of said thin lead conductor on each of its opposing surfaces by provision of a plurality of holes on said thin lead conductor.

[0017] Another aspect of the present disclosure provides an electrode for its utility in fabrication of lead-acid batteries, said electrode includes: (a) at least one Plastic Reinforced Lead Conductor (PRLC) consisting of: a thin lead conductor in substantially sheet form, and a reinforcing mesh affixed to at least a part on each of opposing surfaces of said thin lead conductor, wherein said mesh is made of a material, substantially resistant to both acid and oxidation, and wherein said mesh includes thin, perforated and ribbed mesh made of a plastic material and (b)a layer of an active material uniformly applied onto at least one of opposing surfaces of said at least one Plastic Reinforced Lead Conductor (PRLC).

[0018] In an embodiment, said electrode can be configured to be a positive electrode consisting of at least one of individual PRLC plate, hereinafter called as positive plate, with the at least one PRLC plate being provided with a layer of active material that is positive active material on at least one of the opposing sides, and includes lead sub-oxide and sulphuric acid. In an embodiment, said positive electrode can further include at least one mat pressed onto said layers of active material, and wherein said mat is made of a material substantially resistant to acid and oxidation. In an embodiment, said mat can be made of a material including any or a combination of non-woven glass and polyester.

[0019] In another embodiment, said electrode can be configured to be a negative electrode including at least one individual PRLC plate, hereinafter called as negative plate, with the at least one PRLC plate being provided with a layer of active material that is negative active material on at least one of the opposing sides, and includes lead sub-oxide, sulphuric acid and expanders such as barium sulphate, lignin and carbon black. In an embodiment, each of the at least one Plastic Reinforced Lead Conductor (PRLC)plate of said negative electrode is substantially enclosed in a micro-porous pouch made of a polymeric material that is substantially resistant to acid and oxidation. In an embodiment, said micro- porous pouch is substantially made of polyethylene.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the Figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

[0021] FIG. 1A illustrates an exemplary exploded view of a positive plate (electrode) in front elevation, in accordance with an embodiment of the present disclosure.

[0022] FIG. IB illustrates an exemplary cross sectional view of a positive plate in accordance with an embodiment of the present disclosure.

[0023] FIG. 2A illustrates an exemplary exploded view of a negative plate (electrode) in front elevation in accordance with an embodiment of the present disclosure.

[0024] FIG. 2B illustrates an exemplary cross sectional view of a negative plate (electrode) in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0025] The present disclosure generally relates to the field of rechargeable lead-acid batteries. In particular, the present disclosure pertains to Plastic Reinforced Lead Conductor (PRLC) for its utilization in fabrication of high energy density lead-acid batteries. The present disclosure also pertains to method of manufacturing Plastic Reinforced Lead Conductor (PRLC) and high energy density lead-acid batteries made therewith.

[0026] An aspect of the present disclosure provides a Plastic Reinforced Lead Conductor (PRLC) for its utility in fabrication of lead-acid batteries, said Plastic Reinforced Lead Conductor (PRLC) including: a thin lead conductor in substantially sheet form, and a mesh affixed to at least a part of said thin lead conductor on each of its opposing surfaces to provide reinforcement to said thin lead conductor in substantially sheet form, wherein said mesh is made of a material, substantially resistant to any or a combination of acid and oxidation, and wherein said mesh includes thin perforated and ribbed mesh made of a plastic material. In an embodiment, the said mesh can be affixed to at least a part of said thin lead conductor on each of its opposing surfaces by provision of a plurality of holes on said thin lead conductor.

[0027] Another aspect of the present disclosure provides a novel configuration for electrodes that can be configured to be a positive electrode or a negative electrode for their use in fabrication of lead-acid batteries. Each of the disclosed electrode, whether negative or positive, comprises: (a) at least one Plastic Reinforced Lead Conductor (PRLC) including: a thin lead conductor in substantially sheet form, and a reinforcing mesh affixed to at least a part on each of opposing surfaces of said thin lead conductor, wherein said mesh is made of a material, substantially resistant to any or a combination of acid and oxidation, and wherein said mesh includes thin, perforated and ribbed mesh made of a plastic material and (b) a layer of an active material applied to at least one side of said at least one Plastic Reinforced Lead Conductor (PRLC).

[0028] In an embodiment, the disclosed electrode can be configured as a positive electrode by providing layer of active material that includes a positive active material including lead sub-oxide and sulphuric acid. In an embodiment, said positive electrode further includes at least one mat pressed onto said layer of active material and wherein, said mat is made of a material substantially resistant to acid and oxidation. In an embodiment, said mat is made of a material including one or a combination of non-woven glass and polyester.

[0029] In an embodiment, the disclosed electrode can be configured as a negative electrode by providing layer of active material that includes a negative active material including lead sub-oxide, sulphuric acid, barium sulphate, lignin and carbon black. In an embodiment, each of the at least one Plastic Reinforced Lead Conductor (PRLC) along with layer of active material of said negative electrode can substantially be enclosed in a micro- porous pouch made of a polymeric material substantially resistant to acid and oxidation. In an embodiment, said micro-porous pouch is substantially made of polyethylene.

[0030] In an embodiment, the lead conductor is predominantly in the form of a thin lead sheet. Meshes made of a suitable plastic material are anchored to the lead sheet on its either sides suitably and thus structurally reinforce the weak thin lead sheets. The active materials required for the delivery of the Ampere-hour capacity of the plate is accommodated in these meshes and are in intimate contact with the thin lead sheet. The construction details of PRLC plates that go into making the positive electrode (referred to hereinafter as positive plate) and those that go into making negative electrode (referred to hereinafter as negative plate) are generally similar. Difference that makes them negative or positive is composition of layer of the active materials on the respective plates, which are different for the positive and negative plates. In addition, in case of positive plates non-woven glass mat retainers pressed into the mass of the active material further support the active material and prevent effectively premature shedding of the same. The negative plates are enveloped with suitable separator envelopes such as PE (polyethylene) separators. Further, construction of lead-acid battery with these plates, as per the invention described herein, is made as per the present state of art.

[0031] In another aspect, the charge transfer between the electrical conductor and the active materials is facilitated through a larger conducting area, the battery made with these plates can be recharged in about an hour or less when charged according to the modified Ampere-hour law given by I _t = k Co e ^"kt , wherein k is a constant called charging index that depends on the constructional details of the plates. In case of batteries made according to the present state of art, the charging index, k is around 1 or less, whereas in case of the batteries made with the plates as per the invention, the charging index has been found to be around 2- 4, meaning that the time for recharging up to 90% of a fully discharged battery can be substantially reduced to less than an hour without damaging the battery, when charged according to the modified Ampere-hour law, I _t = k C ₀ e ^"kt .

[0032] In an embodiment, positive active material being anchored and structurally supported by non-corroding plastic meshes is completely covering the corrodible lead conductors beneath them, the lead conductor of the positive plates is thus inhibited against anodic corrosion. This results in long cyclic life of the battery as the reinforcing plastic meshes are totally inert to anodic corrosion.

[0033] In an embodiment, plastic being substantially lighter than lead, the batteries made using the same, as per the present disclosure, are less bulky as compared to the tubular positive plates made as per the present state of art. As a result, a higher energy density of the order of 32-35Wh/kg and long service life of more than about 5 years are achievable.

[0034] Referring now to FIG. 1A and FIG. 2A, conductor 102 is made of lead predominantly in the form of a sheet. Lug 102a being an appendage of the body of the conductor 102. An array of holes 102b is provided in the conductor 102. Plastic meshes 104made of an acid resistant plastic material being placed one on either side of the conductor 102 are anchored to the same through the array of holes 102b. Typically, the plastic meshes 104 have regularly spaced holes 104a. Ribs 104b, which are equi-spaced, are provided on either side of the plastic meshes 104. This results in a Plastic-Reinforced-Lead-Conductor (PRLC) base plate. In an embodiment, the conductor 102 is made in the form of a sheet and has thickness in the range 0.3 - 0.6mm. The plastic meshes 104 have a thickness of about 0.5 - 1.2mm and are made of an acid resistant plastic material such as poly-propylene (PP) or, poly-ethylene (PE).

[0035] FIGS. 1A and IB show front elevation 100 and cross-sectional plan 150 views with construction details of a positive plate in accordance with an embodiment of the present disclosure. Positive active material 106 is made of lead-sub-oxide and sulphuric acid in the form of a paste applied on to the meshes on either side of a PRLC base plate, the positive active material 106 being firmly supported by the plastic meshes 104, and being in intimate contact with the conductor 102 of the PRLC base plate. Non-woven glass mats 108 pressed into the mass of the positive active material 106, on either side, provide further anchorage to the positive active material 106. [0036] Referring to FIGS. 2 A and 2B, which show exemplary front elevation 200 and cross-sectional plan 250 views with constructional details of a negative plate as per an embodiment of the present disclosure. Negative active material 202 is made of lead-sub- oxide, expanders and sulphuric acid in the form of a paste is applied on to the plastic meshes 104 on either side of yet another PRLC base plate assembly, the negative active material 202 being firmly supported by the plastic meshes 104, and being in intimate contact with the conductor 102 of the negative PRLC base plate. Pouch 204 acts as the separator and envelops the negative plate thus made. In an embodiment, the choice of expanders can be, but not limited to, a mixture of barium sulphate, lignin and carbon black. Likewise, the material of choice for the pouch 204 can be Polyethylene (PE). However, pouch can be made of any other material as known to a person having ordinary skill in the art.

[0037] In a preferred aspect, to make the PRLC base plates, the conductor 102 sheets, preferably of pure lead are rolled to the required thicknesses, preferably of thickness of about 0.3 mm to about 0.5mm and cut or blanked to the required dimensions. Alternatively, they can be cast in preheated cast iron moulds. Although pure lead is specified herein above, use of other alloys made by alloying lead with alloying elements such as antimony, cadmium, tin, arsenic, selenium, calcium and silver are completely within the scope of the present invention. Also, lead alloy used to make the PRLC base plates for positive and negative electrodes may be same or different without any limitation whatsoever.

[0038] In an aspect, the arrays of holes 102b in the conductor 102 are obtained during casting process itself or obtained subsequently in a blanking process. The plastic meshes 104, perforated and ribbed, of desired thickness and width, are made of any plastic material that is acid and oxidation resistant and are preferably used to reinforce the conductor 102.

[0039] In an embodiment, it would be preferable that poly-ethylene (PE) or polypropylene (PP) may be the material of choice for the meshes. However, this does not restrict use of other suitable plastic materials such as high-impact polystyrene, ABS, which are resistant to acid and anodic actions for the meshes. Meshes are placed on either side of the conductor 102 and anchored to the same either by thermally fusing or ultrasonically welding them together through the array of holes 102b, as well as along all the four edges 102c, except near the lug 102a of the conductor 102.

[0040] In an aspect, positive plates with PRLC base are generated by applying the positive active material 106 on to the plastic meshes 104 on either side. The positive active material 106 is prepared by mixing lead oxide, popularly called lead sub-oxide and sulphuric acid in a kneader under carefully controlled conditions and made into dough and subsequently applied on to the two faces (opposing surfaces) of the positive PRLC base. The positive active material 106 is anchored effectively by the spaced holes 104a and ribs 104b, and brought into close contact with the conductor 102. Non-woven glass mats 108 of about 0.25 to about 0.30 mm thickness are cut to required sizes and are pressed into the mass of the positive active material while it is still wet. In an embodiment, use of the non-woven glass mats 108, however, does not preclude use of mats made of similar such materials such as polyester, which are acid and oxidation resistant. The positive plates thus prepared are cured in hydro-setting chambers under carefully controlled conditions and are kept ready for battery assembly.

[0041] In another aspect, negative plates with PRLC bases are generated by applying the negative active material 202 on to the plastic meshes 104 on either side of yet another PRLC base. The negative active material 104 is prepared by mixing lead sub-oxide and sulphuric acid along with the negative expanders comprising essentially of barium sulphate, lignin and carbon black in a kneader under carefully controlled conditions and made into dough and pasted on to the two faces of the negative PRLC base. The negative active material 104 is likewise anchored effectively by the spaced holes 104a and ribs 104b, and brought into close contact with the conductor 102. Thus prepared negative plates with PRLC are cured in hydro- setting chambers under carefully controlled conditions and inserted into the pouch 204. These pouches, beside containing the negative plates, and acting as electrical insulators between the positive and negative plates in the battery, provide free passage to the electrolyte of the battery as they are provided with very fine micro-pores. The negative plates thus prepared are now ready for assembly into the battery.

[0042] In an aspect, the battery with positive and negative plates with PRLC bases is generally made with the standard practices as follows. The capacity of the battery is generally taken to be limited by that of the positive active material while that of the negative would be in excess of the positive. Accordingly the number of positive plates chosen, a stack of alternating positive and negative plates with PRLC bases is made with the lugs 102a of the positive plates coming on one side and that of the negative plates coming on the other side. Generally, the number of negative plates is one more than that of the positive plates, with the result that the end plates on either side would be negative. The lugs 102a of all the like plates are welded together to form bus bars in special lead burning jigs with interconnecting lugs or poles as per the requirements to form a cell assembly of the battery. This cell assembly is now inserted into one of the compartments of the battery container made of plastic. Complete filling of all the cell compartments is likewise affected. To get the desired voltage, the cells are interconnected through-partition welding of the interconnecting bus bars serially, leaving the terminal poles. The plastic battery cover is thermally fused with the plastic container to complete the battery assembly. The battery is activated after filling each cell with the required volume of dilute sulphuric acid as the electrolyte and given the initial charging, generally called the formation charge, by connecting the end terminals of the battery to the charging rectifier. After the positive and negative active materials are completely converted to their respective charged state, charging is stopped. The specific gravity of the electrolyte is adjusted to the required value and the vent plugs are screwed on to each of the cell compartment to complete the battery.

[0043] In an embodiment, a battery thus made as per the proposed invention gives an energy density of about 100-120 Wh/dm3, depending on the size of the battery, that is about 20% more than that of the conventional batteries of the similar size; a life expectancy of 4-5 years. Further, the batteries are found capable of accepting very high rates of charge. A totally discharged battery can be recharged to about 90% of the previously charged capacity in about 35-60 minutes time without causing any damage to the battery, when charged according to the modified Ampere-hour law.

EXAMPLES

[0044] A battery made according to the invention with PRLC plates was assembled in a container, and cover commercially available for making a 40 Ah battery with tubular positive plates. The battery with PRLC plates gave a capacity in excess of 65 Ampere-hours (Ah) at a nominal terminal voltage of 12 V. The energy density for this battery was calculated and that worked out to about 105 Watt-hour/liter (Wh/dm3). As against this, an equivalent commercially available battery with the similar external dimensions, made with tubular positive plates and pasted negative plates, gave about 46 Ah under similar test conditions. To put it another way, the battery made according to the proposed invention had an energy density of about 150% of that of the commercially available tubular battery with similar external dimensions.

[0045] The battery, the one used in previous test, was discharged by 45 Ah. It was then recharged for 45 minutes through a bank of recharging batteries called mother batteries and equipped with a variable rheostat, and an ammeter in series. The charge input was 45 Ah. The charging profile adopted was I _t = 3 x 45 e ^"3t , i.e. Co =45 Ah, k= 3 in the modified Ampere- hour law, I _t = k Co e ^"kt . The battery, when discharged again, delivered about 43.2Ah. That means that the charging efficiency was about 96%. This proves that the charging time required to recharge the battery made according to the proposed invention from a discharged state to 90% charge state was about 45 minutes when charged according to the modified Ampere-hour law, as against about 2.3 hours for the commercially available battery with the best possible charging profile.

[0046] Now, the battery was subjected to an endurance test of 1200 hours at 0.1C ₁₀ , i.e. 6A, in a water bath maintained at a temperature of 40° C as per the Bureau of Indian Standards testing specifications. At the end of the stipulated 1200 h endurance test, the capacity of the battery was found to be more than 90% of the initial C ₁₀ capacity. Any battery that meets the above requirements is deemed to have a life expectancy of more than 5 years. Logically speaking, this means that the battery made according to the present disclosure had a life expectancy in excess of 5 years.

[0047] In an aspect, the proposed PRLC and lead-acid batteries realized there from also find applications where charging is erratic for example, solar Photo- Voltaic (PV) charging.

[0048] It should be understood that various other modifications and combinations of the above embodiments are contemplated and will readily appear to those skilled in the art. Thus, the present invention contemplates that any and all such subject matter is included within the scope of the present invention. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of applicant's general inventive concept.

ADVANTAGES OF THE INVENTION

[0049] The present disclosure provides improved plates/conductors that overcome one or more disadvantages associated with previously known plates/conductors.

[0050] The present disclosure provides reinforced plates/conductors.

[0051] The present disclosure provides high energy density lead-acid batteries utilizing improved plates/conductors.

[0052] The present disclosure provides a lead-acid battery that has better life expectancy and working range.

[0053] The present disclosure provides a lead-acid battery that does not exhibit substantial corrosion of electrodes.

[0054] The present disclosure provides a lead-acid battery that can be recharged in substantially less amount of time.

[0055] The present disclosure provides a lead-acid battery that is lightweight. [0056] The present disclosure provides a lead-acid battery that exhibits significantly higher energy density.

[0057] The present disclosure provides a lead-acid battery suitable for application where charging is erratic, such as solar PV charging.