CORE-SHELL PARTICLES BASED ON RED LEAD FOR LEAD-ACID BATTERIES

Abstract

Core-shell particles may be based on red lead coated with pyrogenically produced titanium dioxide and/or a pyrogenically produced aluminum oxide, and a process may prepare such core-shell particles which may be used in lead-acid batteries. The red lead may include PbO.sub.2 in a range of from 25 to 32 wt. %.

Claims

1. A core-shell particle, comprising: a core comprising red lead; and a shell comprising a pyrogenically produced titanium dioxide and/or a pyrogenically produced aluminum oxide.

2. The particle of claim 1, wherein the red lead comprises PbO.sub.2 in a range of from 25 to 32 wt %.

3. The particle of claim 1, having an average particle size d.sub.50 of not more than 5 μm.

4. The particle of claim 1, wherein a plurality of the particle has a tamped density in a range of from 2.3 to 3.0 g/cm.sup.3.

5. The particle of claim 1, wherein the titanium dioxide and/or the aluminum oxide has an average aggregate particle size d.sub.50 in a range of from 10 to 150 nm, as determined by TEM analysis.

6. The particle of claim 1, wherein the titanium dioxide and/or the aluminum oxide is present in a range of from 0.1 to 10 wt. %, based on total core-shell particle weight.

7. The particle of claim 1, wherein the titanium dioxide and/or the aluminum oxide has a BET surface area in a range of from 5 to 200 m.sup.2/g.

8. The particle of claim 1, comprising tetrabasic lead sulfate (4PbO×PbSO.sub.4).

9. The particle of claim 8, comprising: the tetrabasic lead sulfate in a range of from 0.1 to 10 wt. %, based on by total core-shell particle weight.

10. A process for producing the core-shell particle of claim 1, the process comprising: dry mixing the red lead and the pyrogenically produced titanium dioxide and/or aluminum oxide.

11. The process of claim 10, wherein the dry mixing is conducted with an electric mixing unit at an electrical power in a range of from 0.05 to 1.5 kW per kg of the red lead.

12. A paste composition suitable for a lead-acid battery, the composition comprising: the core-shell particle of claim 1.

13. An electrode suitable for a lead-acid battery, the electrode comprising: the core-shell particle of claim 1.

14. A lead-acid battery, comprising: the core-shell particle of claim 1.

15. A process of making a lead-acid battery, the method comprising: combining the core-shell particle of claim 1 with a component of the lead-acid battery.

16. The particle of claim 1, comprising the titanium dioxide.

17. The particle of claim 1, comprising the aluminum oxide.

18. The particle of claim 1, comprising the titanium dioxide and aluminum oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0095] FIG. 1 shows an SEM image of the inventive core-shell particles prepared according to example 2.

[0096] FIG. 2 shows an image of SEM-EDX mapping of Al atoms (white) in fumed Al.sub.2O.sub.3 coated on red lead (example 2).

EXAMPLES

[0097] Preparation of Red Lead Powder Modified with 5 wt. % of Four-Basic Sulfate

[0098] The preparation of red lead modified with tetrabasic lead sulfate seeds is described in DE102019135155A1.

[0099] Preparation of Core-Shell Particles

Example 1

[0100] 3 kg of red lead powder modified with 5 wt. % of tetrabasic sulfate, having a d.sub.50 of about 3 μm and a tamped density of 3.3 g/cm.sup.3 were mixed with the corresponding quantity (4 wt. % relative to the mass of red lead) of the fumed aluminum oxide Aeroxide® Alu 130 powder (manufacturer Evonik Industries AG) in a laboratory mixer Eirich R01 with a three-stage star-type agitator at a rotation speed of 500 rpm (mixing power 0.125 kW). The obtained orange-red mixture is optically much more flowable than the starting materials. The tamped density of the resulting product was about 2.8 g/cm.sup.3.

Example 2

[0101] The procedure was identical as in example 1, except non-modified red lead (manufactured by PENOX) was used, the rotation speed was 4000 rpm, and the rotation time was 10 minutes.

Example 3

[0102] The procedure was identical as in example 1, except for rotation speed and time, which were 4000 rpm (mixing power 1 kW), and 10 minutes, respectively.

Comparative Example 1

[0103] Lead oxide (PbO) without the addition of red lead was used to prepare the positive active mass (see below).

Comparative Example 2

[0104] Unmodified red lead was used to prepare the positive active mass (see below).

[0105] Preparation of the Positive Active Mass (PAM): A General Procedure.

[0106] 2036.8 g of lead oxide (PbO, 100%) (comparative example 1) or the mixture of lead oxide (PbO, 75 wt %) and modified or unmodified red lead (Pb.sub.3O.sub.4, 25 wt %) (all other examples) was used. The shortcut fibers (5.1 g) were fed in, and the components are then premixed dry at a rotation speed of 500 rpm using the countercurrent principle. In this case, the dry mix of all dry components is typically more homogenous if the mixing vessel/pan is rotating in a counter direction to the rotor tool's stirring blades (countercurrent principle). The deionized water (229.1 g) was then added while constantly stirring the materials at a constant speed of 500 rpm. The addition was finished after 1.5 minutes. Diluted sulfuric acid (229.1 g, d=1.40 g/mL) was added over ca. 2 minutes while the temperature of the paste mixture rose from about 25 C up to 50° C. The paste was stirred for 2 minutes and then actively cooled until the temperature has dropped to below 45° C.

[0107] Production and Curing of Positive Plates

[0108] The positive plates were prepared by manual pasting of the positive mass onto gravity-casted grids. According to a defined curing program, the prepared positive plates were cured in a climatic cabinet. In this work, all plates have been cured to a tetrabasic structure.

[0109] During the curing, the active mass undergoes several steps. Initially, at high temperatures (85° C.) and two hours duration, the crystal growth is facilitated. Afterwards, the humidity in the chamber is reduced to about 70% to allow the free lead within the active mass to be oxidized to lead oxide. Depending on the thickness of the positive plates the oxidation process can take up to 6 hours. Hereafter, the plates were dried until the target residual moisture content of less than one percent by weight was achieved.

[0110] The cured plates' porosity was determined by the water intrusion method and in addition by the high-pressure mercury intrusion method. The latter is using an AutoPore IV 9500 2.03.00.

[0111] The cured plates need to undergo a formation process before the electrical testing. The formation step has a significant impact on transforming the cured active mass structure into the formed active mass structure. Therefore, the formation parameters had been kept constant.

[0112] Electrical Tests with the Positive Plates

[0113] Positive plates with a nominal capacity of 2.5 Ah (C5) were tested in the series of measurements performed. The cells consisted of a positive plate, the test sample, and two negative plates. The capacity was determined with an electrolyte density of 1.28 g/cm.sup.3 (+/−0.05 g/cm.sup.3) at 25° C. The plates' final discharge voltage was set at 1.70V for the five-hour capacity tests, and 0.5 A was used as the discharge current. The test temperature was kept constant at 25° C. by a water bath.

[0114] The aim was to increase the capacity of the positive active mass in the first cycles through the used additive materials. Furthermore, the target was to reach the constant working capacity as quickly as possible. For this purpose, the achieved capacity (in Ah) related to the used active mass (in g) was measured (in Ah/g) in the first charge/discharge cycles.

[0115] Table 1 shows the results of charging/discharging tests with LAB pastes containing PbO without the addition of Pb.sub.3O.sub.4 (comparative example 1).

TABLE-US-00001 TABLE 1 Charging/discharging tests with LAB pastes containing PbO without Pb.sub.3O.sub.4 (comparative example 1). C5 C5 C5 C5 average Mass cured #1**, #2**, #3**, (#1 to utilization*** Test PAM*, g Ah Ah Ah #3**), Ah (#3), g/Ah 1 25.943 2.57 2.89 3.02 2.83 8.59 2 25.914 0.69 2.60 3.00 2.10 8.64 3 25.917 2.54 2.90 3.03 2.82 8.55 average 8.59 here and in other tables: *PAM = positive active mass **C 5#1-#3: number of charging cycles ***Mass utilization (#3) = PAM mass/C5#3.

[0116] Table 2 shows the results of charging/discharging tests with LAB pastes containing 25 wt % Pb.sub.3O.sub.4 (comparative example 2).

TABLE-US-00002 TABLE 2 Charging/discharging tests with a paste containing 25 wt % Pb.sub.3O.sub.4 (comparative example 2). C5 C5 C5 C5 average Mass cured #1**, #2**, #3**, (#1 to utilization*** Test PAM*, g Ah Ah Ah #3**), Ah (#3), g/Ah 1 25.522 2.18 2.98 3.17 2.78 8.06 2 25.548 2.14 2.65 2.98 2.59 8.57 average 8.31

[0117] Table 3 shows the results of charging/discharging tests with LAB pastes containing 25 wt % Pb.sub.3O.sub.4 coated with 4 wt. % fumed Al.sub.2O.sub.3 at 4000 rpm (example 1).

TABLE-US-00003 TABLE 3 Charging/discharging tests with LAB pastes containing 25 wt % Pb.sub.3O.sub.4 coated with 4 wt. % fumed Al.sub.2O.sub.3 at 4000 rpm (example 1). C5 C5 C5 C5 average Mass cured #1**, #2**, #3**, (#1 to utilization*** Test PAM*, g Ah Ah Ah #3**), Ah (#3), g/Ah 1 25.116 2.70 3.18 3.36 3.08 7.47 2 25.363 2.65 3.35 3.50 3.17 7.25 3 25.547 2.62 3.10 3.41 3.05 7.49 4 25.289 2.01 3.04 3.29 2.78 7.69 average 7.48

[0118] Table 4 shows the results of charging/discharging tests with LAB pastes containing 25 wt % (Pb.sub.3O.sub.4+5 wt % 4PbO×PbSO.sub.4) mix coated with 4 wt % fumed Al.sub.2O.sub.3 at 4000 rpm (example 2).

TABLE-US-00004 TABLE 4 Charging/discharging tests with LAB pastes containing 25 wt % (Pb.sub.3O.sub.4 + 5 wt % 4PbO × PbSO.sub.4) mix coated with 4 wt % fumed Al.sub.2O.sub.3 at 4000 rpm (example 2). C5 C5 C5 C5 average Mass cured #1**, #2**, #3**, (#1 to utilization*** Test PAM*, g Ah Ah Ah #3**), Ah (#3), g/Ah 1 25.454 2.59 3.73 3.59 3.30 7.09 2 25.510 2.85 3.62 3.45 3.31 7.39 3 25.327 1.27 3.32 3.46 2.68 7.32 4 25.218 3.15 3.27 3.18 3.20 7.93 average 7.43

[0119] Table 5 shows the results of charging/discharging tests with LAB pastes containing 25 wt % (Pb.sub.3O.sub.4+5 wt % 4PbO×PbSO.sub.4) mix coated with 4 wt. % fumed Al.sub.2O.sub.3 at 500 rpm (example 3).

TABLE-US-00005 TABLE 5 Charging/discharging tests with pastes containing 25 wt % (Pb.sub.3O.sub.4 + 5 wt % 4PbO × PbSO.sub.4) mix coated with 4 wt. % fumed Al.sub.2O.sub.3 at 500 rpm (example 3). C5 C5 C5 C5 average Mass cured #1**, #2**, #3**, (#1 to utilization*** Test PAM*, g Ah Ah Ah #3**), Ah (#3), g/Ah 1 25.531 3.26 3.28 3.19 3.24 8.0 2 25.475 3.29 3.34 3.25 3.29 7.8 average 7.9

[0120] Table 6 summarizes the results of comparative examples 1-2 and examples 1-3 shown in Tables 1-5.

[0121] Table 6 provides an overview of the positive active masses (PAM), which had been studied and characterized in terms of the structural parameters and the related specific capacity, expressed as a mass utilization. The latter is the mass of PAM needed per Ampere hour (Ah) of capacity measured as C5 capacity (at 25° C. and a discharge to 1.70V per cell). The addition of pyrogenic oxides impacts the structure of the cured electrodes and results in better mass utilization, i.e., decreasing the PAM weight needed per Ah.

[0122] One driver for better mass utilization is increased porosity measured as water intrusion. Nevertheless, a simple porosity model does not give a complete explanation since the pores' diameter, and the pore size distribution is also changed by the use of additives. Therefore, table 6 also provides the mercury intrusion, which indicates the buoyance of the pores. Average mass utilization of PAMs in examples 1-3 is lower than in comparative examples 1-2, suggesting that using core-shell particles allows more efficient utilization of the active electrode mass. This effect is more pronounced when the formation of the core-shell particles occurs under higher mixing rates of 4000 rpm (examples 2-3).

[0123] Another important observation was that the paste prepared with the core-shell particles, according to examples 1-3, were more accessible to paste and handle due to a reduced plasticity/viscosity. Furthermore, the aging of the positive active mass, which typically results in a change of color and a hardening of the paste, is significantly reduced. The mixing and handling energy required for the pasting process and applying the paste onto the electrode grids could be significantly reduced. This effect can be attributed to using fumed metal oxides for coating the red lead particles. It was observed that using non-fumed metal oxides in the same dry coating process leads to inferior results in terms of paste viscosity.

TABLE-US-00006 TABLE 6 Comparison of applying different lead oxide types in charging/discharging tests. H.sub.2O- Hg- Hg Pb.sub.3O.sub.4 in 4BS*, wt % fumed Al.sub.2O.sub.3 rotation speed average mass porosity, porosity, Intrusion the paste, related to coating, wt % during mixing results utilization Example [%] [%] ml/g wt % Pb.sub.3O.sub.4 related to Pb.sub.3O.sub.4 with Al.sub.2O.sub.3, rpm (Table) (#3), g/Ah Comparative 40.0 49.0 0.125 0 0 0 — 1 8.6 Example 1 Comparative 43.0 25 0 0 — 2 8.3 Example 2 Example 1 43.4 50.7 0.140 25 5 4  500 3 7.9 Example 2 43.3 45.3 0.130 25 0 4 4000 4 7.5 Example 3 43.3 52.9 0.156 25 5 4 4000 5 7.4 *4BS = tetra-basic lead sulfate (4PbO × PbSO.sub.4);