KR101009995B1 - Lead acid battery having gelled electrolyte - Google Patents

Abstract

A lead acid battery having a gelled electrolyte is provided. The lead acid battery includes a plurality of alternating positive electrode plates and negative electrode plates, a plurality of separators sandwiched between the positive electrode plates and the negative electrode plates, and a gelated electrolyte. This gelled electrolyte comprises dilute sulfuric acid and silica particles in a substantially 0.1% to 3% by weight content based on the weight of the electrolyte. The silica particles are fumed silica particles.

Description

Lead acid battery having gelled electrolyte

1 is a cross-sectional view of a conventional lead acid battery.

FIG. 2 is a diagram comparing the discharge time curves over 300 life cycles of a lead acid battery with a standard battery of the comparative example and a gelled electrolyte.

The present invention relates to a lead acid battery, and more particularly, to an improved valve-regulated lead acid battery having a gelled electrolyte.

The lead acid battery developed in the 1800s was the first commercially available battery. Since the 1950s, rechargeable lead acid batteries have become available and become the most widely used type of battery in the world. The following equation shows the discharge chemical reaction in a lead acid cell:

PbO ₂ + Pb + 2 H ₂ SO ₄ → 2 PbSO ₄ + 2 H ₂ O

Lead acid batteries are still popular because they can produce large or small currents over a wide temperature range and have good shelf life and life cycles. In addition, lead acid batteries are relatively inexpensive to produce and purchase. Another advantage of lead acid batteries is that they vary in shape and size, from home batteries to large submarine batteries.

Sealed lead acid battery (VRLA) is a type of lead acid battery. The VRLA lead acid battery includes a container having a positive electrode plate, a negative electrode plate, a separator, an electrolyte, and a one-way valve. One-way valves are installed to prevent the entry of external gases into the battery where oxygen reacts with the pole plates to cause internal discharges and to release gas from the interior of the battery when a certain internal pressure is exceeded. See FIG. 1. 1 is a cross-sectional view of a conventional lead acid battery. As shown in FIG. 1, the lead acid battery 10 includes a plurality of alternating positive electrode plates 12 and negative electrode plates 14, a separator 16 sandwiched between adjacent electrode plates, and an electrolyte (not shown). The positive electrode plate 12 and the negative electrode plate 14 convert the lead grid pasted with the positive electrode active material such as lead oxide and the lead grid pasted with the negative electrode active material such as lead powder to the positive electrode plate 12 and the negative electrode plate 14, respectively. It is manufactured by a molding process.

In VRLA lead acid batteries, the electrolyte is generally fixed. Since the electrolyte is immobilized in the VRLA lead acid battery, gas generated at one electrode can access the other electrode during charging. As a result, oxygen gas can enter the battery and is reduced at the surface of the negative electrode plate to return to the battery's electrolyte. In addition, since the electrolyte is fixed, the risk of leaking a very acidic and corrosive liquid electrolyte is prevented.

There are two well known categories of methods for fixing electrolytes in lead acid batteries: absorption or gelation. U. S. Patent No. 4,871, 428 is a glass mat separator made of glass microfibers and used to fix a liquid electrolyte by absorption, which firmly and intimately contacts the pole plate, thereby providing good initial electrolyte-pole plate contact and thus Disclosed is a glass mat separator that ensures high energy efficiency. However, the intimate contact of the glass mat separator with the electrode plate surface facilitates the formation of needle-like dendrite in the cathode electrode plate, which grows in a tunnel-like passage way, causing neighboring separator pores. Contact with the positive electrode plate ultimately results in battery shorting.

U. S. Patent No. 4,317, 872 discloses an alternative method of immobilizing an electrolyte by reacting sulfuric acid with silica particles to form a gel electrolyte. However, this gel electrolyte exhibits various bad electrical properties such as high internal electrical resistance, low energy capacity, and reduced cycle characteristics. In addition, this gel electrolyte tends to shrink so that the contact between the gel electrolyte and the active material on the electrode plate may be interrupted. In addition, the initial high viscosity of this gel makes it difficult to fill the battery container and also makes it impossible to efficiently saturate the plate pores.

U.S. Pat.No. 4,889,778 discloses a 1: 3 to 1: 6 volume ratio blend of sulfuric acid with an aqueous colloidal dispersion of about 30% by weight of an alkali metal polysilica having the formula [Y ₂ O] .x [SiO ₂ ] .nH ₂ O. Disclosed is a thixotropic gel electrolyte. The x value is in the range of 20 to 350, Y is an alkali metal, and n is the number of moles of water.

Finally, U.S. Patent Publication No. 2005/0042512 discloses a lead acid battery electrolyte comprising sulfuric acid having a specific gravity of 1,250 to 1.280 and silica particles at a concentration of 2 to 15% by weight. At least 10% by weight of the silica particles are derived from dry precipitated silica slurry.

Although the above prior art discloses an improved gel electrolyte manufacturing method which facilitates filling into a container, this gel electrolyte lead acid battery still increases the internal electrical resistance, decreases during discharge, compared to a lead acid battery made of ordinary liquid electrolyte. General electrical properties such as low energy capacity attributable to a positive amount of active electrolyte material, and potential dropping problems due to high silica content.

It is therefore a main object of the present invention to provide a VRLA lead acid battery based on an gelled immobilized electrolyte to overcome the above problems.

According to the claims of the present invention, the gelled electrolyte of a lead acid battery comprises dilute sulfuric acid and silica particles in the range of substantially 0.1% to 3% by weight, based on the weight of the electrolyte. These silica particles are fumed silica particles.

According to the claims of the present invention, there is also provided a lead acid battery having a gelled electrolyte. The lead acid battery includes a plurality of alternating positive electrode plates and negative electrode plates, a plurality of separators sandwiched between the positive electrode plate and the negative electrode plate, and diluted sulfuric acid and silica in a range of substantially 0.1 wt% to 3 wt% based on the weight of the electrolyte. A gelled electrolyte comprising particles. These silica particles are fumed silica particles.

The lead acid battery having the gelled electrolyte provided in the present invention has much improved electrical properties such as low internal resistance, high rate charging capability, high energy density, and no electrolyte shrinkage problem. This battery is particularly suitable as a cost effective battery in applications requiring high charging rate and high energy capacity.

These and other objects of the present invention will no doubt become apparent to those skilled in the art after reading the following detailed description of the preferred embodiments, which is illustrated in various figures.

The invention will be explained in more detail by the following embodiments and examples. However, the present invention is not limited to the above embodiments and examples.

The present invention is based on the discovery of a new method for fixing electrolytes in lead acid batteries, in particular VRLA lead acid batteries. In this embodiment of the invention, the gelled electrolyte is prepared by mixing sulfuric acid with a specific gravity of 1.28 to 1.34 and a small amount of silica particles. Here, the content of the silica particles is substantially in the range of 0.1% to 3% by weight, more preferably 0.5% to 1% by weight based on the weight of the electrolyte.

First, the gelled electrolyte has a low viscosity and freely flows for a long time. However, after about two to three charge / discharge cycles in lead-acid batteries, a two-phase electrolyte mixed with a hard localized paste-like mass of gel throughout the entire electrolyte, especially in the surface area of the glass mat adjacent to the electrode plate. It begins to form as a mixed two-phase electrolyte. In addition, this mixed two-phase electrolyte of the present invention can return to the liquid phase mostly under high rate charging conditions. Ultimately, the whole electrolyte changes into a hard pasty gel phase during discharge after repeated discharge / charge cycles.

Depending on the form and content of the silica particles used, this gelled electrolyte is substantially transparent or slightly hazy. When fumed silica is used, the electrolyte obtained is slightly hazy and this haze increases gradually over time. Examples of suitable fumed silicas are Degussa AEROSIL ^® 200, 200 V, pre-dispersed AERODISP ^® W 7520 (stabilized with ammonia), or W 7520 N (stabilized with sodium hydroxide).

There is no special need for the mixing device. Acid resistant containers such as various conventional mixers such as propeller stirrers, cowless dissolvers and teflon coated tanks can be used. However, the mixing speed should be appropriate to obtain a homogeneous solution and to avoid or minimize undesirable flocculation or precipitation. For example, a propeller stirrer with a mixing speed of about 1250 to 2000 rpm is used to mix dilute sulfuric acid with the slowly added silica for a time of about 20 minutes, followed by another 10 minutes to complete this mixing. During the mixing, the temperature of this mixture is kept below 40 ° C.

Fixation of the electrolyte is achieved by combining the absorption ability of the glass mat and the light gelling of the electrolyte. In general, the electrolyte is absorbed into the glass mat separator efficiently and without assistance. However, it has been found that the vacuum assisted filling step is advantageous for promoting the absorption of the gelled electrolyte into the separator and the electrode plate.

Because of the low viscosity of the electrolyte in the fully charged state and the presence of hydrophilic silica particles that prevent dry out in the separator pores, the lead acid battery with the gelled electrolyte of the present invention has a low internal resistance for efficient charging. It is noteworthy that it is also possible to achieve high energy densities and also to provide long discharge times and high currents or discharge rates if necessary. Upon discharge, the reversible pasty gel lumps are formed in the pores of the glass mat and are also adjacent to the surface of the electrode plate, so these gel lumps allegedly stop dendrite growth and also fall off of the active paste material from the electrode plate surface. Protects the plates by preventing or slowing down aggravating problems such as shedding. Thus, lead acid batteries with the gelled electrolyte of the present invention generally provide longer cycle life than expected.

It is also possible to form the electrode plate in the assembled battery, but it is preferable that the electrode plate is molded in advance. In addition, although glass mat separators are preferred, alternative electrolyte absorbing separators, such as acid resistant polymeric nonwoven sheets, may also be used. For example, suitable hydrophilic surface treated polyolefin or polyester based nonwovens are suitable absorbent separators.

The following examples are described to illustrate in more detail the preferred embodiment of the present invention. However, these examples are not limiting. It is still possible to generate other embodiments without departing from the inventive concept disclosed herein. Such embodiments are within the capabilities of those skilled in the art.

Example 1

100 g of fumed silica (Degussa AEROSIL ^® 200) was first mixed with 900 g of deionized water to obtain a homogeneous mixture. Separately, 9 kg of diluted sulfuric acid having a specific gravity of 1.32 was placed in an acid resistant tank equipped with a propeller mixer. The mixer was slowly added running at 1457 rpm into sulfuric acid diluted with the fumed silica mixture over 20 minutes. After the fumed silica addition was complete, the mixer was kept on for 10 minutes until a homogeneous mixture was obtained. The viscosity of the obtained gelled electrolyte was slightly higher than that of sulfuric acid before mixing, and the mixture was observed to be slightly cloudy. The blurring level increased over time, but remained free to flow for 3 weeks. A 12-volt battery of 12 amp-hour (AH) discharge capacity was assembled and charged with the gelled electrolyte for testing. The electrical resistance of the electrolyte between two 50 mm spaced copper wires was measured and shown in Table 1 below. The discharge test was conducted on the lead acid battery having the gelled electrolyte of the present invention, and the discharge time under various initial discharge rates was summarized in Table 2 below.

Example 2

Dilute sulfuric acid with a specific gravity of 1.33 was used for the preparation of the electrolyte and was also tested according to the same procedure as in Example 1 except that the mixer was operated at 1360 rpm. General properties of the gelled electrolyte were the same as observed in Example 1. Table 1 shows the electrical resistance of this electrolyte. The results of the initial discharge test are summarized in Table 2.

Comparative Example 1

For comparison, a 12 volt battery with a 12 amp-hour (AH) discharge capacity was assembled and charged with normal sulfuric acid with a specific gravity of 1.32 for testing. Table 1 shows the electrical resistance of this electrolyte. The results of the initial discharge test are summarized in Table 2.

TABLE 1

Example 1 Example 2 Comparative Example 1 Electricity
resistance  3.10Ω 3.00Ω 2.80Ω

1) Measured between two copper wires 50 mm apart.

TABLE 2

Example 1 Example 2 Comparative Example 1 2 Hr. Discharge rate
＠ 0.42 C 02:17:31 02:28:37 02:27:54 5 Hr. Discharge rate
＠ 0.17 C 06:42:16 07:13:57 - 10 Hr. Discharge rate
＠ 0.1 C 11:30:55 12:17:20 - 20 Hr. Discharge rate
＠ 0.05 C 23:09:16 26:43:46 22:10:33 33 Min. Discharge rate
＠ 1 C 50:27 57:09 53:27 7.2 Min. Discharge rate
＠ 3 C 12:35 13:39 13:36

1) All batteries were 12 volt batteries with a 12 amp-hour (AH) discharge capacity.

2) The discharge time was recorded as hours: minutes: seconds.

As shown in Table 1, the electrical resistance of the gelled electrolyte was usually slightly higher than that of dilute sulfuric acid, but the increase was small, and their effect on battery discharge characteristics was negligibly small at the 2 hour discharge rate. In fact, in general, the 20 hour discharge rate of Example 1-2 showed an unpredictable improvement over the performance of the standard sulfuric acid battery of Comparative Example 1. These data indicate that the present invention is particularly suitable for applications requiring long discharge times, such as electric bicycles and outdoor solar lighting.

In addition, Table 2 also shows that high rate discharge test results, such as the 1C and 3C of the present invention, may be in an unpredictably equivalent range or better than standard sulfuric acid batteries.

To further illustrate the improved performance of the present invention, FIG. 2 shows a discharge time curve over 300 life cycles of Example 2. FIG. Importantly and unpredictably, it has been found that the battery of the present invention provides greater ability to sustain longer discharge times than the conventional battery of Comparative Example 1.

As described above, the lead acid battery based on the gelled immobilized electrolyte of the present invention can solve various problems of the conventional lead acid battery.

Those skilled in the art will appreciate that numerous improvements and modifications to the above apparatus and methods can be made while retaining the teachings of the present invention. Accordingly, the above disclosure should be construed as limited only by the following claims.

Claims (12)

As a gelled electrolyte of a lead acid battery, Dilute sulfuric acid with a specific gravity of 1.28 to 1.34; And It comprises silica particles in the content range of substantially 0.1% by weight to 3% by weight based on the weight of the electrolyte, The silica particles are gelled electrolyte, characterized in that the fumed silica (fumed silica) particles. delete The gelated electrolyte of claim 1, wherein the content of the silica particles is in a range of 0.5 wt% to 1 wt% based on the weight of the electrolyte. A lead acid battery having a gelled electrolyte, (a) a container; (b) a positive electrode plate and a negative electrode plate disposed in the container; (c) a separator sandwiched between said positive electrode plate and said negative electrode plate in said container; And (d) a gelled electrolyte providing an electrolyte connection between the positive electrode plate and the negative electrode plate in the vessel, The gelled electrolyte Dilute sulfuric acid with a specific gravity of 1.28 to 1.34; And It comprises silica particles in the content range of substantially 0.1% by weight to 3% by weight based on the weight of the electrolyte, The silica particle is a lead acid battery, characterized in that the fumed silica (fumed silica) particles. delete The lead acid battery of claim 4, wherein the content of the silica particles is in a range of about 0.5 wt% to about 1 wt% based on the weight of the electrolyte. The lead acid battery of claim 4, wherein the lead acid battery is valve-regulated. The lead acid battery according to claim 4, wherein the separator is electrolyte absorbent. The lead acid battery according to claim 8, wherein the separator is a glass mat. The lead acid battery according to claim 8, wherein the separator is a polymer nonwoven sheet. The lead acid battery according to claim 8, wherein the separator is a polyolefin. The lead acid battery according to claim 8, wherein the separator is a polyester nonwoven sheet.

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