Battery electrode plate preparation method

Abstract

A new type of battery electrode plate preparation method is described. The method can include the following steps: a) a mixing process; b) a milling and polishing process; c) an extrusion shearing and extending process; d) cutting to obtain an electrode membrane; and e) pressing at a high temperature and a high pressure to obtain a battery electrode plate. The method can adopt the active material of different electrochemical batteries as the main body to prepare a thick type battery electrode plate with a high conductivity, a high capacity and a high active material loading, which has a viscoelastic body. The electrode plate can have a flexible organic network structure and an excellent mechanical strength, and can still exist in a variety of electrolytes after hundreds of times or even thousands of times of deep charge and discharge cycles. The thick electrode plate prepared by using the method can be applied to a variety of batteries such as lead-acid battery positive and negative electrode plates, a lead carbon battery electrode plate, a lithium ion battery electrode plate, a supercapacitor electrode plate, a Ni-MH battery electrode plate, and others.

Claims

1. A method of preparing a battery electrode plate, comprising the following steps: a) a mixing step comprising of mixing an electrode active materials and a conductive agent with a prescribed polymer, and stirring evenly the electrode active materials, the conductive agent, and the polymer into a paste; b) milling and polishing the paste formed in the step a) to fibrillate the polymer in the paste; c) extruding, shearing and extending the paste obtained in the step b) to turn it into an uniformly compact active membrane that has controllable thickness; d) cutting the active membrane obtained in the step c) into the desired size according to an electroplate design to obtain different size pieces of electrode membranes; and e) inserting a current collector between two pieces of electrode membrane, and then pressing the two pieces of electrode membranes and the current collector into a plate under high temperature and high pressure.

2. The method according to claim 1, wherein said polymer is selected from one or more of polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), fluorinated ethylene propylene (FEP), fluororubber, trifluoro(heptafluoro-1-propoxy) ethylene and Polyfluoroalkoxy (PFA).

3. The method according to claim 2, wherein said polymer is in the form of an emulsion, and has a solid content of from 50% to 60%, a melt index of from 3 to 10, a melting point of from 120° C. to 320° C., and a polymer particle size of from 5 μm to 100 μm.

4. The method according to claim 2, wherein the particle size of said polymer is from 5 μm to 50 μm.

5. The method according to claim 1, wherein the content of said polymer in the battery electrode plate is from 1 wt % to 20 wt %.

6. The method according to claim 5, wherein the content of said polymer in the battery electrode plate is from 3 wt % to 10 wt %.

7. The method according to claim 1, wherein said electrode active materials is selected from any of the positive or negative materials suitable for lead acid battery, lead acid super battery, lead tungsten proton capacitor, graphene battery, lithium ion battery, supercapacitor, and/or NiMH battery.

8. The method according to claim 1, wherein said electrode active materials comprises lead oxide, lead, lithium cobaltate, lithium manganate, ternary or multi-element oxide, lithium iron phosphate, lithium titanate, graphite, graphene, activated carbon, carbon black, nickel oxide, nickel hydroxide, metal hydrogen storage alloy, tungsten oxide, molybdenum oxide, vanadium oxide and/or manganese oxide.

9. The method according to claim 1, wherein said mixing process includes the steps of: adding the prescribed amount of electrode active materials into a mixer; dry mixing the electrode active materials at a dispersion speed of from 300 rpm to 1000 rpm and a revolution speed of from 20 rpm to 200 rpm; spraying said polymer to the mixed content in the mixer, wherein said polymer is from 3 wt % to 20 wt % of the paste; stirring the polymer and the electrode active materials for from 10 minutes to 30 minutes; and extruding the paste, wherein the solid content of the paste is from 60 wt % to 85 wt %.

10. The method according to claim 9, wherein said dispersion speed is from 300 rpm to 600 rpm, said revolution speed is from 20 rpm to 60 rpm, and said polymer is from 3 wt % to 10 wt % of the paste.

11. The method according to claim 1, wherein the number of times of the milling and polishing in step b) is less than 10, and the speed is from 1 m/s to 18 m/s.

12. The method according to claim 11, wherein said number of times of the milling and polishing in step b) is less than 8, and the speed is from 1 m/s to 10 m/s.

13. The method according to claim 1, wherein the thickness of said active material membrane in step c) is from 1 mm to 5 mm, and the solid content of the membrane is from 70% to 90%.

14. The method according to claim 13, wherein the thickness of said active material membrane is from 1 mm to 3 mm.

15. The method according to claim 1, wherein said battery electrode plate preparation method further comprises drying the cut electrode membrane obtained in step d), wherein the solid content of the dried electrode membrane is from about 80% to about 95% and the drying temperature is from 50° C. to 200° C.

16. The method according to claim 15, wherein said drying temperature is from 50° C. to 100° C.

17. The method according to claim 1, wherein said current collector in step e) is a conductive materials.

18. The method according to claim 17, wherein said current collector is selected from one or more lead grid, titanium mesh, copper mesh, aluminum mesh, stainless steel mesh, carbon felt and/or carbon cloth.

19. The method according to claim 1, wherein the step e) specifically comprises: pre-pressing the two pieces of electrode membrane and the current collector with a press machine, wherein the pre-pressing pressure is from 30 MPa to 60 MPa per unit area of membrane, and the pre-pressing dwell time is from 5 s to 180 s; heating the pre-pressed plate in a tunnel kiln for heating; and heating the pre-pressed plate to a temperature of from 140° C. to 320° C., and pressing the heated pre-pressed plate using a pressing pressure of from 70 MPa to 120 MPa per unit area of the membrane and a dwell time of from 10 s to 600 s to form the plate.

20. The method according to claim 19, wherein said pre-pressing pressure is from 30 MPa to 60 MPa per unit area of membrane, the heating temperature of the pre-pressed plate is from 140° C. to 320° C., and the final pressing pressure is 90 MPa to 100 MPa per unit area of the membrane.

21. An energy storage battery comprising an electrolyte and an electrode comprising of the battery electrode plate prepared by the method according to claim 1.

22. The energy storage battery according to claim 21, wherein the energy storage battery is a battery selected from a list comprising of a lead-acid battery, a super battery based on a lead-acid system, a lithium-ion battery, a supercapacitor, and a Ni-MH battery.

23. The energy storage battery according to claim 22, wherein the electrolyte is selected from one or more of sulfuric acid, potassium hydroxide, sodium sulfate solution, and lithium ion battery organic electrolyte and/or ionic liquid.

Description

DRAWINGS

(1) FIG. 1. Photograph of the membrane of a lead-tungsten proton capacitor negative electrode paste formed after the milling process;

(2) FIG. 2a. SEM image of the negative electrode membrane of a lead-tungsten proton capacitor after 8 times of milling.

(3) FIG. 2b. SEM image of the negative electrode membrane of a lead-tungsten proton capacitor after 10 times of milling.

(4) FIG. 2c. SEM image of the negative electrode membrane of a lead-tungsten proton capacitor after 12 times of milling.

(5) FIG. 2d. SEM image of the negative electrode membrane of a lead-tungsten proton capacitor after 14 times of milling.

(6) FIG. 3. Tensile strength relationship of lead-tungsten proton capacitors under different milling times and then membrane photo after 14 times milling.

(7) FIG. 4. Photographs of different specifications of negative electrode plates of lead-tungsten proton capacitors.

(8) FIG. 5a. SEM image of the surface and cross section of a lead-tungsten proton capacitor negative electrode plate.

(9) FIG. 5b. SEM image of a cross section of a lead-tungsten proton capacitor negative electrode plate.

(10) FIG. 6a-c. Photographs of interfaces between the grid and the membrane using three Formulas of the plates which are pressed at high temperature, high pressure and room temperature respectively.

(11) FIG. 6d. Photograph of the interface between the grid and the membrane of the plate pressed at room temperature.

(12) FIG. 7a. The effect of the membrane of Formula 1 under different pre-pressure conditions on the density of the plates.

(13) FIG. 7b. The effect of the membrane of Formula 1 under different pre-pressure conditions on the thickness of the plate.

(14) FIG. 7c. The effect of the membrane of Formula 1 under different pre-pressure conditions on the gram capacity of the plates.

(15) FIG. 8. Photographs of the surfaces of the plates with different solid content of the membranes under the same press conditions.

(16) FIG. 9. The alternating current impedance of the membranes with different Formulas under the same press conditions.

(17) FIG. 10. The performance of a battery assembled with a plate of Formula 2 at different discharge rates.

(18) FIG. 11. The cycle life of lead-tungsten proton capacitors of Formula 1 under 1 hour discharge rate, 0.5 h discharge rate, 0.2 h discharge rate and 0.1 h discharge rate.

DETAILED DESCRIPTION OF THE INVENTION

(19) The advantages of the present invention are further illustrated by the following embodiment, but the scope of the present invention is not limited by the following embodiment. The reagents and raw materials used in the present invention are commercially available.

Embodiment 1: Preparation of the Lead-Tungsten Proton Capacitor Negative Electrode Plate

(20) 1) Formula and Raw Materials:

(21) The raw material of the lead tungsten proton capacitor negative electrode was tungsten trioxide. The preparation method of tungsten trioxide was to use sodium tungstate as the tungsten precursor material. The sodium tungstate was dissolved in deionized water to form a uniform solution with a concentration of 5%. Then appropriate amount of hydrochloric acid was added to make the pH value of the solution 1.5. Subsequently, 5% ammonium sulfate was added to the solution to form an intermediate. The mixed solution was transferred to a reaction vessel and reacted at 160° C. for 72 hours to finally obtain a tungsten trioxide material.

(22) Other raw materials and their weight percentages are shown in Table 1: among them, acetylene black, PTFE and EFP emulsions are commercially available. PVDF solution was prepared by dissolving 200 g of PVDF powder in 1.8 kg of N-Methyl pyrrolidone (NMP) solution and stirring the solution to make a solid content of 10 wt % solution.

(23) TABLE-US-00001 TABLE 1 Formula of lead-tungsten proton capacitor negative plate and mass percentage of each component Weight percentage composition Formula 1 Formula 2 Formula 3 Tungsten trioxide 88% 86% 86% Acetylene black 7% 7% 7% PTFE (solid 5% 5% 5% content of emulsion: 60%) EFP (solid content / 2% / of emulsion: 50%) PVDF (solid / / 2% content of solution: 10%)
2) Method and Steps

(24) The materials mentioned above were added in proportion and dry mixed in a dual planetary mixer. The mixing speed was divided into dispersion speed and revolution speed (dispersion speed and revolution speed here was 300 rpm and 20 rpm respectively). After mixing, a mixture of colloidal emulsion or solution was sprayed in. After stirring the whole mixture for 15 minutes, the solid content of the paste was from 80% to 85%. Then the paste was milled and polished for 6 times. The speed of the milling was 6 m/s. After milling, the membrane was pressed into a dense and uniform membrane by a two-bar calendar. The thickness of the resulting membrane was 1-2 mm and the solid content of the membrane was from 81% to 86%. A photograph of the formed membrane is shown in FIG. 1. It can be seen that the whole membrane is uniform and dense, and the thickness deviation of the membrane does not exceed 0.03 mm. FIG. 2 shows the SEM image of the internal structure of the membrane. It can be clearly seen that, as the times of milling increases, the entire colloid is sheared into a fiber network to encapsulate the active material, but the diffusion of the electrolyte between the electrode active materials is not affected. As the number of milling increases to 14 times, the high-strength shear force will break the fibers and the uniformity of the surface of the membrane is destroyed. See FIG. 3a for the presence of large holes. This result indicates that the times of milling will directly affect the uniformity of the membrane.

(25) In order to further verify the relationship between the mechanical strength of the membrane and the number of times of the milling, the membrane was cut into a size of 100 mm*1.5 mm, and then tested by a tensile strength tester (model QJ210A). Two ends of membrane was fixed to the upper and lower chunk of the tester, the running speed was set to 50 mm/min, and the test was started by pressing the start button. The data results are shown in FIG. 3b. As the number of times of the milling increases, the tensile strength of the membrane also increases. After 12 times of milling, the membrane strength increases slowly. Accordingly, the optimum number of times of milling is from 8 to 12.

(26) The preferred choice of the milled membrane was cut into a membrane the same size as the current collector grid. The membrane was then baked in an electric oven so that the solid content of the membrane is from 85 to 100%. The heating temperature range was from 100 to 180° C. The baked membrane and the grid were then stacked in the grinding tool, heated to from 140 to 320° C. by a muffle furnace, then pressed for 5 minutes under 30 t by a flat vulcanizing machine. The table temperature of the flat vulcanizing machine was from 250 to 300° C. FIG. 4 shows photographs of the different sizes of the electrode plates.

(27) In order to observe the interfacial adhesion between the active material and the polymer binder, we used a scanning electron microscope to observe the surface and cross section of the plate. See FIG. 5. It can be clearly seen that the surface of the entire active material and the cross-section are distributed with fiber network. This flexible network structure has high viscoelasticity and is favorable for the active material and the conductive agent to contact and form a good interface. The structure of material does not change when used, thereby providing a stable conductive network and improvement on the cycle life.

(28) Besides the interface between the active material and the polymer binder, the interface between the entire negative electrode membrane and the grid is equally important. FIGS. 6a, 6b and 6c are the photographs of the adhesion between the grid and the membrane under the three Formulas. It can be seen that the membrane is tightly adhered to the surface of the grid, which greatly enhances the conductivity of the active material, improves the rate capability of the entire plate, and increases the charge and discharge acceptance and cycle life of the lead-tungsten proton capacitor. Therefore, to achieve bonding is an important parameter in the whole process. The polymer involved in the present invention must be involved in a high temperature heating process, in which the heating process is characterized in that the temperature must exceed the glass transition temperature of the polymer to achieve a viscoelastic state. In this heating process, the polymer was pressed inside to form a flexible three-dimensional viscous organic fiber network and the active material becomes a viscous viscoelastic body that tightly adheres to the current collector. As a result, the electrical conductivity and mechanical strength of the plate is greatly improved. If the membrane is pressed at room temperature, there would be no adhesion between the grid and the interface. As a result, the membrane would be completely detached from the grid and would not have enough strength (see FIG. 6d). In order to increase the rate of thermal conductivity of the membrane, a pre-pressing pressure step must be introduced before the final pressing process. This step was introduced because it was easier to embed the grid at the early stage when the membrane was relatively soft, and it is easier to squeeze out most of the air that negatively affects heat transmission. The process mentioned above could greatly increase the density and conductivity of the plates, and further increase the battery capacity, as shown in FIG. 7. Therefore, in the battery plate preparation process, the pre-pressing pressure was from 40 to 50 MPa per unit area of the membrane, the temperature of the plate was from 140 to 320° C., and the final pressing pressure was from 90 to 100 MPa per unit area of the membrane. All of these values are preferred values.

(29) In addition, the solid content of the negative electrode membrane before the pressing process is also one of the important parameters. It determines the severity of the crack on the surface of an electrode plate prepared under high temperature and high pressure. FIG. 8 shows the membrane surface with different solid content under the same pressure condition. It can be seen that, if the solid content is low, the water accumulated in the membrane will evaporate quickly at high temperature. The additional pressure caused by the capillary condensation increases the stress of the membrane, which intensifies the cracks on the surface of the electrode plate. These cracks will cause corrosion of the grid, the loss of active substances and other negative effects. Considering that the milling process would cause a loss of the water in the paste, the optimized range of solid content of the membrane is from 85% to 95%.

(30) 3) Testing and Verifying of Electrochemical Performance

(31) FIG. 9 shows the comparison of AC impedance of Formula 1 and Formula 2 under the same plate forming conditions. The effect of using a single glue and a mixture of glue components on the charge transfer resistance and diffusion internal resistance of the battery electrode plate can be seen from FIG. 9. Firstly, both charge transfer resistance and diffusion internal resistance of Formula 1 (5% PTFE only) were less than that of Formula 2 (5% of PTFE+2% EFP mixture). But the mechanical strength of plate formed according to Formula 2 is better than plate formed according to Formula 1. The reasons of this better mechanical strength are that: 1) an increase in the amount of adhesive content, and 2) the effect of different polymers in the plates is different. The fiber network structure of the whole plate is mainly contributed by PTFE, but the highly symmetrical structure of the PTFE leads to a higher melting point. Once the EFP with lower molecular chain or PVDF with asymmetric structure is introduced, the high temperature in the whole plate preparation process can be reduced to expand the entire process window and indeed form a complete, viscous, three-dimensional fiber network structure. FIG. 10 shows the performance curves of batteries assembled with the plates of Formula 2 at different discharge rates, combined with the data in Table 2, shows that although the internal resistance of the said polymer alone is relatively small, using of polymer mixed with other types of polymer further enhances the structural strength of the electrode plate and still exhibits excellent rate performance. Compared with traditional lead-acid battery, the capacity retention of batteries assembled by plates of Formulas 1-3 is almost 2 to 3 times of that of lead-acid battery.

(32) TABLE-US-00002 TABLE 2 Capacity retention of batteries assembled with plates of different Formulas at different discharge rates Lead tungsten 4 hr 2 hr 1 hr 0.5 hr 0.2 hr proton capacitor Different hour rate of discharge rate rate rate rate rate Capacity Formula 1 100% 98.8% 92.4% 80.6% 62.4% retention Formula 2 100% 96.9% 90.2% 79.5% 56.7% Formula 3 100% 97.9% 90.7% 80.1% 60.8% Lead-acid 10 hr 8 hr 6 hr 5 hr 3 hr 2 hr 1 hr 0.5 hr 0.25 hr battery rate rate rate rate rate rate rate rate rate Capacity 100% 94% 89% 85% 75% 60% 55% 40% 35% retention

(33) In order to further show the influence of this plate preparation process on the cycle life of the battery, we assembled the plates of Formula 2 into four groups of 2V 5Ah batteries, poured 135 ml of 1.18 g/cm3 sulfuric acid electrolyte. The cycle stability through different charge and discharge currents was tested and shown in FIG. 11.

(34) It can be seen from the FIG. 11 that the four groups of batteries are subjected to a fully charged and discharged cycle at a charge and discharge rate of 1 h, 0.5 h, 0.2 h and 0.1 h, respectively. It can be seen that, the capacity retention rate of the four groups of batteries above is still 100% after 400 cycles, while the capacity retention of the traditional lead-acid battery is reduced from 100% to 80% at charge and discharge rates of 5 h or lower with 300 fully charge and discharge cycles. These results further show that changes in the plate preparation process play a very important role in improving overall battery performance.

(35) It should be pointed out that, while the present invention has exemplary embodiments disclosed herein, the exemplary embodiments or their implementations are not intended to limit this present invention in any way. Any person of ordinary skill in the art can use the disclosure herein to make equivalent changes and modifications towards other valid embodiments. As long as the scope of the present invention is not exceeded, any embodiments made by changing or modifying the above embodiments shall be within the scope of this invention.