Rechargeable energy storage devices

Abstract

The electrical storage device (10, 38) comprises a pasted negative electrode (12) and a pasted positive electrode (15) with a porous separator (18) therebetween, and current collectors (20, 22) are disposed between the separator (18) and the negative and positive pastes (13, 16), respectively.

Description

[Technical Field]

[0001] The present invention relates to rechargeable electric cells and batteries, including but not limited to lithium ion batteries, nickel metal hydride batteries, and lead acid batteries. [Background technology]

[0002] Secondary cells are electrochemical cells that can operate as both galvanic and electrolytic cells, meaning they can be discharged by delivering DC power generated from a chemical reaction and charged by supplying a DC current that reverses the chemical reaction. Batteries are a collection of cells connected together in series or parallel and are classified by their chemistry, with lithium-, lead-acid-, and nickel-based systems being the most common, with lithium-ion being the battery of choice for portable devices and electric vehicles. Unless the context makes clear to the contrary, the term "battery" is used herein to refer to both batteries and cells.

[0003] Lead-acid batteries contain a combination of lead plates pasted with electrochemically active materials such as lead dioxide and sponge lead, and immersed in a sulfuric acid electrolyte. When these batteries are overcharged, hydrogen and oxygen are produced, which can form an explosive mixture. The oxygen can also rapidly destroy the pasted positive electrodes.

[0004] Other battery types include nickel-cadmium (NiCad) batteries and the more recently developed lithium-ion battery, which is currently the most popular battery in small electronic devices such as laptop computers, mobile phones, and cordless tools, and is becoming increasingly common in these applications. Despite being superior to NiCad batteries in many ways, lithium-ion batteries have drawbacks, including malfunction when accepting a charge, dendrite growth, and temperature rise with rapid overcharging (which can lead to thermal runaway).

[0005] Lithium batteries are notorious for catching fire. The commonly used lithium-ion battery formulation was lithium cobalt oxide (LiCoO2), which was prone to thermal runaway when overcharged, leading to the battery catching fire and the lithium burning rapidly at high temperatures. However, in 1996, a new method of making lithium-ion batteries was developed using a formulation containing lithium iron phosphate, known as LiFePO4 or LFP. LFP batteries have a slightly lower energy density than lithium cobalt oxide batteries, but are inherently non-flammable and therefore significantly safer.

[0006] One of the challenges hindering the implementation of cells and batteries is that they need to be charged for long periods of time, during which time the cell or battery is unavailable as a power source.

[0007] Attempts have been made to reduce the time required to charge a cell or battery. One approach that has been attempted is to increase the charging current, but this leads to thermal runaway and gassing, which leads to the destruction of the cell or battery. To ensure safe operation and extend the useful life of the cell or battery, it is essential to prevent excessive heat during charging and ensure that the temperature remains below the gassing threshold.

[0008] Another approach that has been followed in attempts to reduce the charge time of a cell or battery is to use a thicker layer of electrochemically active paste on the electrodes or to use thicker electrodes which result in a thicker layer of electrochemically active paste, but this leads to sulfation and dendritic growth within the paste, and the dendrites can damage the separator between the electrodes, potentially damaging or destroying the cell or battery. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a storage cell or battery and components thereof that efficiently regulates the charging current through the electrodes and current collectors, yet allows for rapid recharging of the cell or battery. [Means for solving the problem]

[0010] According to a first aspect of the present invention, there is provided an electrical storage device comprising: a first electrode comprising a metal electrode rubbed with a paste of electrochemically active material that is electrochemically negative; a second electrode comprising a metal electrode rubbed with a paste of electrochemically active material that is electrochemically positive; and a porous separator disposed between the first and second electrodes, the electrical storage device further comprising: a first current collector in the form of a porous conductive layer disposed between the first electrode and the porous separator, the first current collector in contact with the electrochemically negative paste of the first electrode; and a second current collector in the form of a porous conductive layer disposed between the second electrode and the porous separator, the second current collector in contact with the electrochemically positive paste on the second electrode.

[0011] The term "porous" includes structures having openings of any size.

[0012] Each of the first current collector and the second current collector can be constructed from a perforated metal sheet, the term "perforated metal sheet" including any sheet-like structure having holes therethrough, including a metal grid.

[0013] The first and second current collectors may be attached to opposite sides of the porous separator.

[0014] The first current collector and the second current collector can be composed of dissimilar materials.

[0015] The first electrode, the second electrode, the first current collector, and the second current collector may each have a tab to which electrical connection can be made.

[0016] In another configuration, the first current collector can be attached to the side of the first electrode facing the porous separator, and the second current collector can be attached to the side of the second electrode facing the porous separator.

[0017] The power storage device can form a stack rolled into a cylindrical shape, with the separator extending outside the stack.

[0018] According to another aspect of the present invention, there is provided an installation including the above-described electricity storage device of the present specification, wherein the first electrode and the second electrode are connected to a first DC power source, and the first current collector and the second current collector are connected to a second DC power source.

[0019] According to a further aspect of the present invention, there is provided an installation including the above-described power storage device, wherein the first electrode and the second electrode are connected to a DC power source, and the first current collector and the second current collector are connected to an electric circuit that consumes power. Alternatively, the first electrode and the second electrode may be connected to an electric circuit that consumes power, and the first current collector and the second current collector may be connected to a DC power source.

[0020] The first and second electrodes and the first and second current collectors may be connected to an electrical circuit that consumes power.

[0021] The present invention extends to a cell comprising a plurality of the above-described power storage devices of the present specification connected in parallel, wherein the first electrodes of each of the power storage devices are connected together, the second electrodes of each of the power storage devices are connected together, the first current collectors of each of the power storage devices are connected together, and the second current collectors of each of the power storage devices are connected together.

[0022] The present invention also extends to a battery comprising a plurality of the above-described power storage devices of this specification connected in series, wherein the second electrode of a first power storage device of the power storage devices is connected to the first electrode of a second power storage device of the power storage devices, and the first current collector of the first power storage device of the power storage devices is connected to the second current collector of the second power storage device of the power storage devices.

[0023] For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of non-limiting example, to the accompanying drawings in which: [Brief explanation of the drawings]

[0024] [Figure 1] 1 shows an exploded three-dimensional view of a first embodiment of a storage cell according to the invention; [Figure 2] 2 shows a three-dimensional assembly of the cell of FIG. 1. [Figure 3] 2 shows a three-dimensional view of the separator of the cell of FIG. 1 with current collectors on both sides thereof. [Figure 4] 2 shows a second embodiment of a cell according to the present invention, comprising multiple electrodes and separators. [Figure 5] 5 shows a battery according to the invention comprising three cells of FIG. 4. [Figure 6] 1 shows a three-dimensional view of a third embodiment of a cell according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] 1-3, a first embodiment of a cell according to the present invention is generally identified by the numeral 10.1. Cell 10.1 includes a first electrode 12, a second electrode 15, and a porous separator 18 of electrically insulating material extending between the first and second electrodes.

[0026] In the embodiment of the invention shown in FIGS. 1 and 2, the first and second electrodes 12, 15 are conventional lead-acid battery plates, each including a metal substrate (typically a lead alloy), each supporting an electrochemically active material applied in a paste form, commonly referred to as a "paste," even if the paste-like consistency is lost after application. For simplicity, the term "paste" is used in the detailed description of the drawings to refer to such electrochemically active materials, with the term "positive paste" being used for electrochemically positive, suitable for use in a positive electrode, and the term "negative paste" being used for electrochemically negative, suitable for use in a negative electrode. As a non-limiting example, for a lead-acid cell 10.1, a suitable positive paste could include lead dioxide, and a suitable negative paste could include sponge lead.

[0027] The first electrode 12 functions as the negative electrode and has negative paste 13 applied to its opposite sides. The first electrode, or negative electrode 12, has a protruding first tab 14 extending from its lead alloy substrate, thereby making conductive contact with the negative paste 13 and functioning as a negative electrode tab that can be connected to an external electrical circuit. Similarly, the second electrode 15 functions as the positive electrode and has positive paste 16 applied to its opposite sides. The second electrode, or positive electrode 15, has a protruding second tab 17 extending from its lead alloy substrate, thereby making conductive contact with the positive paste 16 and functioning as a positive electrode tab that can be connected to an external electrical circuit.

[0028] The positive electrode 12, negative electrode 15, and separator 18 are immersed in a suitable electrolyte (such as sulfuric acid) contained within a casing (not shown). The construction of cell 10.1 described thus far is similar to that of prior art lead-acid batteries. In other embodiments of the invention, cell 10.1 can be constructed from materials suitable for different types of chemistries; for example, first negative electrode 12 and positive electrode 15 can be conventional lithium-ion cell electrodes having respective electrochemically negative paste 13 and electrochemically positive paste 16. Similarly, cell 10.1 can be constructed from another electrochemistry type, such as nickel metal hydride.

[0029] Separator 18 has a first current collector 20 on the side of the separator facing first or negative electrode 12. First current collector 20 is preferably made of metal, in the illustrated example, aluminum foil, and has a protruding tab 21 that can be connected to an external electrical circuit. On the opposite side of separator 18, a second current collector 22 is provided, which faces second or positive electrode 15. Second current collector 22 is also preferably made of metal, in the illustrated example, copper foil, and has a protruding tab 23 that can be connected to an external electrical circuit. In other embodiments of the present invention, the first and second current collectors may be composed of the same or different conductive materials.

[0030] For purposes of illustration, in FIG. 1 , the upper left corner of negative paste 13 is not shown to reveal the upper left corner of negative electrode 12. Similarly, the lower right corner of first current collector 20 is not shown to reveal the lower right corner of separator 18, and the upper right corner of positive paste 16 is not shown to reveal the upper right corner of positive electrode 15. However, for simplicity, separator 18 is shown as a solid plate (although with multiple openings extending therethrough), and similarly, first current collector 20 is shown in FIGS. 1 and 2 as a continuous plate, although its structure is more complex, as will be explained below with reference to FIG. 3.

[0031] In another embodiment of the present invention, the conductive surfaces of the first and second current collectors 20, 22 may be coated with an electrochemically active material.

[0032] Referring to FIG. 3, separator 18 is shown having a first current collector 20 and its tab 21. A second current collector 22 is identical to first current collector 21 but is on the opposite side of separator 18; only the second current collector's tab 23 is visible in FIG. 3. Separator 18 has a plurality of openings 24, which in the illustrated embodiment are arranged in a horizontal row. First current collector 20 extends from its tab 21 and continues to form a lateral boundary 26 along one edge of separator 18, from which horizontal ribs 28 extend across the surface of separator 18. Horizontal ribs 28 are spaced apart to define openings that coincide with openings 24 in separator 18. The structure of separator 18 and first current collector 20 may be varied in other embodiments of the invention, but the current collector should have a generally outward-facing surface (formed in the illustrated example by boundary 26 and the surfaces of ribs 28) and should not block openings 24 in the separator.

[0033] Once the electrodes 12, 15 and separator 18 are assembled, the separator is compressed so that the faces of the current collectors 20, 22 in intimate contact with the paste 13, 16 of the adjacent electrodes to provide the assembled storage cell shown in FIG.

[0034] In the embodiment of the invention shown in Figures 1-3, current collectors 20, 22 are supported by separator 18; however, in other embodiments, the current collectors may be unsupported or may be supported on their adjacent electrodes 12, 15, with first current collector 20 on the outer surface of negative paste 13 and second current collector 22 on the outer surface of positive paste 16. However, the illustrated embodiment in which current collectors 20, 22 are supported on separator 18 allows for convenient assembly of cell 10.1. Regardless of the preferred embodiment, there should be good electrical contact between the opposing surfaces of first current collector 20 and the adjacent negative paste 13, and between the opposing surface of second current collector 22 and the adjacent positive paste 16.

[0035] Referring to FIG. 4, a second embodiment of a cell according to the present invention is generally identified by the reference numeral 10.2, with components common to the cells shown in FIGS. 1-3 and 4, respectively, being identified by the same reference numerals. Cell 10.2 includes three negative electrodes, each identical to negative electrode 12 shown in FIGS. 1-3, with its negative paste and its tab 14. Cell 10.1 includes two positive electrodes, identical to positive electrode 15 shown in FIGS. 1-3, between the negative electrodes, each with its positive paste and its tab 17. Between each of the positive and negative electrodes in cell 10.2 is a separator 18, each with two current collectors and their tabs 21, 23, identical to the separators shown in FIGS. 1-3, pressed into intimate contact with the adjacent paste of the adjacent electrode.

[0036] Because the electrodes, separators, and current collectors each have a thin, plate-like structure, it is not easy to distinguish these elements in FIG. 4; however, they are all identical to the corresponding elements in FIGS. 1 to 3 and are best identified in FIG. 4 by the locations of their tabs 14, 17, 21, and 23.

[0037] The three negative electrode tabs 14 in cell 10.2 are connected by a negative strap 30 of conductive material, and the two positive electrode tabs 17 are connected by a positive strap 32 of conductive material. Similarly, the four tabs 21 of the first current collector are connected by a first current collector strap, and the tabs 23 of the second current collector are connected by a second current collector strap 36. Electrical connections can be made to straps 30, 32, 34, and 36 to charge or discharge cell 10.2.

[0038] Referring to Figure 5, one embodiment of a battery 38 according to the present invention is shown, which is comprised of three cells 10.2 as shown in Figure 4, which are distinguished from one another in Figure 5 by suffixes. The two outer cells 10.2A and 10.2C of the battery 38 have the same orientation as shown in Figure 4, while the middle cell 10.2B is rotated 180 degrees. The negative strap 30, positive strap 32, first current collector strap 34, and second current collector strap 36 of the three cells 10.2A-10.2C are also identified by their respective cell suffixes.

[0039] Three cells 10.2A, 10.2B, and 10.2C are connected in series with a bridge to form a battery 38. The bridge includes a bridge 40 spanning positive strap 32A and negative strap 30B, a bridge 42 spanning first current collector strap 34A and second current collector strap 36B, a bridge 42 spanning first current collector strap 34B and second current collector strap 36C, and a bridge 44 spanning positive strap 32B and negative strap 30C. Negative strap 30A is unbridged and forms a primary negative terminal 46 of battery 38. Similarly, positive strap 32C is unbridged and forms a primary positive terminal 48 of battery 38. First current collector strap 34C forms a secondary positive terminal 50, and second current collector strap 36A forms a secondary negative terminal 52 of battery 38.

[0040] Cells 10.2A-10.2C are each contained in a separate compartment within the battery casing and are immersed in the electrolyte within that compartment.

[0041] The battery 38 can be used in different operating modes. In a first mode, power can be drawn from the primary positive terminal 46 and the primary negative terminal 48, and the battery 38 is charged by supplying power to the secondary positive terminal 50 and the secondary negative terminal 52. Conversely, in a second mode, power can be drawn from the secondary terminals 50, 52, and the battery 38 is charged by supplying power to the primary terminals 46, 48. In either or both of these operating modes, charging and discharging of the battery 38 can occur simultaneously and / or intermittently, allowing the battery to be used when charging power supply and power demand occur at unrelated times.

[0042] In another mode of operation, the battery 38 can be charged by simultaneously supplying current to the primary terminals 46, 48 and to the secondary terminals 50, 52. This mode of operation has the effect of charging the battery 38 much more rapidly than conventional batteries of the same capacity, without overheating, gassing, or other effects associated with overcharging.

[0043] Another operating mode of the battery 38 involves drawing power from both the primary terminals 46, 48 and the secondary terminals 50, 52 simultaneously, and other operating modes include drawing power from either the primary or secondary terminals, or charging the battery by applying power to either the primary or secondary terminals while leaving the other terminal passive.

[0044] Referring to Figure 6, a third embodiment of a cell according to the present invention is generally identified by the reference numeral 10.3, and features common to the cells shown in Figures 1-3 and 6, respectively, are identified by the same reference numerals.

[0045] Cell 10.3 is a cylindrical cell, constructed from the same layers as the cell shown in Figures 1-3, except that instead of being in the form of rectangular plates, the layers are combined into a stack 54 and rolled to provide an overall cylindrical shape that can be inserted into a cylindrical battery casing.

[0046] The layers of the stack 54 shown in FIG. 6 include (starting from the outside of the stack) the pasted negative electrode 12 and its tab 14, the first current collector 20 and its tab 21, a porous separator 18, a second current collector 22 and its tab 23, the pasted positive electrode 15 and its tab 17, and, internally, another separator 56 for separating the stack from adjacent turns of the stack (i.e., for separating the outer surface of the pasted negative electrode 12 from the outer surface of the pasted positive electrode 15). The porous separator 18 is shown solid in FIG. 6 but is perforated with a plurality of openings. The first and second current collectors 20, 22 are shown as perforated layers, with their perforations aligned with perforations (not shown) in the separator 18.

[0047] Referring to all the drawings, the present invention maintains the advantage of significantly reducing the time required to recharge the cell 10 or battery 38 without significant heat generation, thereby extending battery life, compared to conventional batteries. The present invention increases current flow to the positive and negative pastes 16, 13, reduces dead spots within the paste, and reduces the likelihood of dendrite growth and sulfation on the exterior surfaces of the pasted electrodes. The current collectors 20, 22 on the separator 18 increase electrolyte density, which in turn improves the ampere-hour capacity per mass of the pastes 13, 16. The present invention also provides improved control of recharge or discharge current, reducing the likelihood of thermal runaway during increased electron flow through the cell 10 or battery 38.

[0048] The present invention can be implemented relatively easily into conventional cells and batteries because it can function with pasted positive and negative electrodes of conventional batteries by replacing the conventional separator between adjacent electrodes with the separator 18 of the present invention and its first and second current collectors 20, 22.

[0049] Experimental evaluation Two examples of the energy storage device according to the invention were subjected to experiments to establish recharge times using different connection combinations of their terminals. The experiments were carried out in March 2020 by the South African Bureau of Standards in its laboratory in East London, South Africa, at a temperature of 25±5°C, and the equipment used was Computer Controlled Bitrode Test Units and Control Software LCN 25-48 Universal Battery Testers.

[0050] (Rating 1) A single lead acid battery according to the present invention was tested, and although the cell had primary positive and negative electrodes and secondary positive and negative electrodes, those skilled in the art will appreciate that when using only the primary terminals without connecting the secondary electrodes, the cell performed exactly as would be expected from a conventional lead acid battery. 1.1 The cells were first subjected to a capacity test using the following parameters: Discharge: A constant load of 5 A was applied to the primary terminals. The discharge voltage limit was set at 1.75 V. The cell was then fully recharged by applying a constant current of 5 A to the primary terminals (cutoff at 2.6 V). 1.2 The cells were subjected to discharge-charge cycling testing using the following parameters: Discharge: A constant load of 5 A was applied to the primary terminals. The discharge voltage termination limit was set at 1.75 V. Charging: A constant current of 5 A was applied to the primary terminals until the end of the charging voltage of 2.6 V. 1.3 The cells were subjected to discharge-charge cycles using the following parameters: Discharge: A constant load of 5A was applied to the primary terminals to an end-point voltage of 1.75V. Charging: A constant current of 5A was applied to the primary and secondary terminals separately and simultaneously until the charging voltage reached 2.6V.

[0051] (result) [Table 1]

[0052] The cell's discharge performance was comparable in all three tests, and the cell temperature did not deviate significantly from ambient temperature. From this, it can be concluded that the cell operated within safe parameters and was not damaged. However, the time required to charge the cell with power applied to both the primary and secondary terminals was less than half the time required using only the primary terminals.

[0053] (Rating 2) Lithium-ion battery packs according to the present invention were tested, and although the batteries had primary positive and negative electrodes, and secondary positive and negative electrodes, those skilled in the art will appreciate that when using only the primary terminals without connecting the secondary electrodes, the batteries performed exactly as would be expected from a conventional lithium-ion battery. 2.1 The battery was first subjected to a first discharge-charge cycle and a second discharge-charge cycle with the primary positive terminal and secondary positive terminal connected together and the primary negative terminal and secondary negative terminal connected together. 2.2 The connection between the primary and secondary terminals was removed and only the primary terminals were used (thus mimicking a conventional battery), discharging the battery and then charging it. 2.3 With the connections between the primary and secondary terminals removed: a. Discharge using primary terminals only. b. Two separate test circuits were used to apply separate and simultaneous charges to the primary and secondary terminals. For all tests in Rating 2, the cells were charged at 1 A to an endpoint voltage of 4.1 V and discharged at 1.5 A to an endpoint voltage of 3 V.

[0054] (result) [Table 2]

[0055] Again, the battery discharge performance was comparable across all tests, and the battery temperature did not deviate significantly from the ambient temperature. From this, it can be concluded that the battery operated within safe parameters and was not damaged. However, the time required to charge the battery with power applied to both the primary and secondary terminals was less than half the time required using only the primary terminals.

Claims

1. An electricity storage device, a first electrode comprising a metal electrode pasted with an electrochemically active material that is electrochemically negative; a second electrode comprising a metal electrode pasted with an electrochemically active material that is electrochemically positive; a porous separator disposed between the first electrode and the second electrode; Equipped with The electricity storage device is a first current collector in the form of a porous conductive layer disposed between the first electrode and the porous separator, the first current collector in contact with the electrochemically negative paste of the first electrode; a second current collector in the form of a porous conductive layer disposed between the second electrode and the porous separator, the second current collector in contact with the electrochemically positive paste on the second electrode; Furthermore, The first electrode, the second electrode, the first current collector, and the second current collector each have a tab to which electrical connection can be made.

2. The power storage device of claim 1 , wherein each of the first current collector and the second current collector is constructed from a perforated metal sheet.

3. The electricity storage device according to claim 2 , wherein the first current collector and the second current collector are attached to opposite sides of the porous separator.

4. The electricity storage device according to claim 2 , wherein the first current collector and the second current collector are made of different materials.

5. 3. The electricity storage device according to claim 2, wherein the first current collector is attached to a side of the first electrode facing the porous separator, and the second current collector is attached to a side of the second electrode facing the porous separator.

6. The electricity storage device according to claim 1 , wherein the stack is rolled into a cylindrical shape, and the separator extends outside the stack.

7. 10. An installation comprising the power storage device according to claim 1, wherein the first electrode and the second electrode are connected to a first DC power source, and the first current collector and the second current collector are connected to a second DC power source.

8. 10. An installation comprising the electricity storage device according to claim 1, wherein the first electrode and the second electrode are connected to a DC power source, and the first current collector and the second current collector are connected to an electric circuit that consumes electricity.

9. 10. An installation comprising the power storage device according to claim 1, wherein the first electrode and the second electrode are connected to an electric circuit that consumes power, and the first current collector and the second current collector are connected to a DC power source.

10. 10. An installation comprising the electricity storage device according to claim 1, wherein the first electrode, the second electrode, the first current collector, and the second current collector are connected to an electric circuit that consumes electricity.

11. 10. A cell comprising a plurality of the power storage devices according to claim 1 connected in parallel, wherein the first electrodes of the power storage devices are connected together, the second electrodes of the power storage devices are connected together, the first current collectors of the power storage devices are connected together, and the second current collectors of the power storage devices are connected together.

12. 10. A battery comprising a plurality of the power storage devices according to claim 1 connected in series, wherein the second electrode of a first power storage device among the power storage devices is connected to the first electrode of a second power storage device among the power storage devices, and the first current collector of the first power storage device among the power storage devices is connected to the second current collector of the second power storage device among the power storage devices.

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