The role of fumed silica in batteries

Present situation and development trend of gas phase silica gel in lead-acid batteries

Chen Ping

Shanghai new energy Mstar Technology Ltd, Shanghai, 200237, China

Abstract: fumed silica and its colloid are the important components of lead-acid batteries. In this paper, the application of colloidal silica colloidal dispersions and powders in this field is analyzed.

1 Introduction

Colloidal lead-acid battery is widely used in electric power, telecommunications, communications, energy and electric field, with convenient transportation, no leakage, low fog, strong water retention, long service life, corrosion inhibition and plate deformation, prevent active material shedding, maintenance free advantages of 1-2. China started research and development of colloidal lead-acid battery from the last century in 50s, but because the level of understanding the problem, especially the problem of technology and formula of colloidal electrolyte is not solved, there is a problem of colloid electrolyte hydration, high resistance, short battery life, technology and products have not been a breakthrough in quite a long time in 3. In recent years, domestic manufacturers mainly composed by plate formation formula improvement, process optimization, price adjustment and partition, colloid technology and other comprehensive measures, whether in the base station and the storage battery of gum, or semi gel battery in electric bicycles and motorcycles have made great breakthroughs and success. Colloid battery has gradually become a recognized market products, more and more domestic manufacturers to master the technology. Although the overall level of foreign advanced and some distance, but the prospect is very worth looking forward to.

2 gas phase silica gel in the battery industry overview

In the colloidal electrolyte lead-acid battery industry, the silicon sol gel development to the present in the gas phase silica, after a long and tortuous way, has made great progress, is currently in the best period of development. According to our data, in the domestic battery silica amount has reached more than 1000 tons per year, mostly concentrated in the application of electric bicycle. With the further development of energy storage batteries, there will be further development potential.

The present situation is the backbone of large enterprises have their own procurement of fumed silica powder, used in their own factories around and then dispersed into colloidal dispersion liquid, or sent to the use of foundry related. Technology research and development ability of domestic large enterprises are relatively strong, comprehensive evaluation method, achieved some degree of success in the application of colloid, the related research has been reported in 4-6. But we think there should be room for further improvement in this technology, especially in terms of increasing solids content and reducing the cost of powder.

The number of small and medium-sized battery assembly manufacturers more usually buy their own powder or purchased colloidal colloidal dispersions. However, most of the manufacturers do not have a thorough understanding of colloids, and lack of standards and methods for the determination of colloidal dispersions and their colloidal electrolytes. The actual situation is in the follow suit, I heard that the trend is to add colloid, as long as there is no adverse effect that followed by adding. Due to the lack of awareness of their own lack of colloid, R & D capability, ask in what grade of raw materials manufacturers, manufacturers keep up with grades on the line, not fully realized the importance of the colloidal dispersion process; if outsourcing more consideration to business partnership, as long as the price is right, and for the quality of little or no capacity for in-depth demonstration.

There are a number of colloid suppliers, do not produce their own batteries, fumed silica into a colloidal dispersion to provide for those who do not want to own decentralized or decentralized technical capacity of the battery assembly plant. The level of this group is very uneven. Most suppliers with pure silica system, but due to different companies between master and equipment for the dispersion process of the difference, in the final of the colloidal solid content, viscosity, particle size distribution and stability of difference. A high solid content, low viscosity, particle size distribution of uniform distribution of stable products, such as the company's JG-20; also with high solid content, high viscosity but also the so-called "glue" products; also has low solid content, low viscosity, particle stability or instability of the so-called "liquid rubber products. There are also a variety of polymer additives for the purpose of protecting the stability of the colloid or improving the battery function. At the same time, there are also individual by the addition of silica sol with fake or false content of solid products. The current number of colloid products appear on the urban field, with many small and medium sized battery assembly plant is lack of corresponding knowledge and judgment means, unable to determine which products are suitable for their own, can be said that the current market colloid is chaos.

General in the battery industry to accept fumed silica as an effective additive at the same time, how to judge the merits of the colloid, or how to better use aerobic silica, domestic research in this area and the battery performance of the discussion is not enough. This paper attempts to analyze the dispersion process of fumed silica and the selection of the raw material of silica dioxide, so as to help the industry to understand the evaluation and optimization of colloidal dispersion.

3 fumed silica dispersion process

Before we analyze the colloidal technique can be improved, we first theoretically the process of gas phase silica dispersion.
The process of separation and dispersion of powder particles in the liquid phase and in the liquid phase, including three stages: wetting, agglomeration and dispersion of particles.

3.1 Wetting: the formation of a vapor phase of silica powder into a mixing system (such as high purity water), so that the adsorption on the surface of the powder air or other impurities are replaced by water. Due to its high specific surface area, the surface of the fumed silica has a large number of OH groups, which can form a strong interaction with water and powder. At the same time, the structure of fumed silica is fluffy, containing a large number of micropores and gases, so fumed silica is difficult to wet with respect to other inorganic powders. In order to improve the wetting effect and improve the production efficiency, a small amount of additives can be added appropriately in water.

3.2 Agglomeration: when the fumed silica is fully wetted, the larger particle size aggregates can be dispersed into smaller particles. Form: the original fumed silica particles, agglomerates and aggregates (Figure 2).

The original particle size below 10 nm, but the gas exists in the original size of the state cannot be silica, the dispersion is the powder aggregates by hundreds of nanometers above (Figure 3) distributed to ten to one hundred nm (Figure 2). Due to the particularity of fumed silica, to achieve a better dispersion, the equipment and the dispersion process (speed, time, formula and concentration) have certain requirements. Especially in fully wetting and allow the powder equipment conditions, should be as much as possible in the case of high content of solid dispersion, then the viscosity of the system is high, the shear stress is in the process of dispersion of the powder is large enough, is conducive to the solution of the powder agglomeration.

3.3 stabilization: to ensure the powder particles in the liquid phase system to maintain a long-term uniform dispersion. This is an extremely important step, through the front is not easy wetting and dispersing the dispersion, dispersion if not good stability due to gas phase silica strong surface effect, in the process of storage and transportation, re aggregates condensed into agglomerates, which appear to return the rough phenomenon. In the high solid content system, the viscosity of the system will be increased, so that the so-called solid glue can be formed. These are examples of well dispersed particles that have not been well stable. Some of these changes can be directly observed by the naked eye, and some must be detected by the instrument.
In the theory of stabilization, it can be realized by the way of three-dimensional protection, electrostatic repulsion and solvent chain modification.
Through the above analysis, it is found that only the colloid should be better in wetting, dispersion and stability in order to get a better colloid three.

4 development trend of colloidal silica dispersions in the future

After understanding the three basic processes of dispersion, and with some analysis of the existing market colloids, we can on quality to a certain degree of judgment, and points out the future development direction of the colloidal dispersion.

4.1 the development direction of colloidal dispersion is high concentration and low viscosity
Many technical personnel dispersed gas phase silica do know, high solid content and low viscosity is generally a contradiction, but this contradiction has been solved, the colloid technology also improved, suitable for battery is stronger. Under the condition of high solid content, low viscosity in the intrinsic quality of the product means that the particle size of silica is fine and stable. The dispersion and the particle size stability make the colloid network formed in the battery after filling glue uniform, which is helpful to improve the product quality and stability. If the dispersion is to be transported high solids can also save transportation and packaging costs.

High solid content is the first productivity and cost requirements but also colloid liquor, producing high-quality colloidal requirements. Only with high solid content, powder in wetting after being dispersed at a high concentration of high speed mechanical state, close to the comparison between the particles and the viscosity of the system is higher, more susceptible to mechanical dispersion shear stress, so that the combination between particles to break. If the dispersion is low solid content, the viscosity of the system is low, the mechanical force can not be fully applied to the particles, the system seems to be lower viscosity, the actual dispersion efficiency is not high.

Low viscosity is the requirement of the perfusion process and production efficiency, but also the performance of high quality colloidal products. After a good mechanical dispersion of colloids must be stabilized by a number of means to achieve stability, so as to avoid the re agglomeration of particles. After the stabilization treatment of particles, bridging between particles agglomeration is removed, the viscosity of the system will naturally reduce the particle size is stably controlled, such as the company JG-20 products in 0.1 microns (Figure 4), much lower than the size of the battery diaphragm aperture. Under the condition of high solid content, there will be no agglomeration and precipitation under the condition of thickening and low solid content.

Currently on the market there is the so-called solid glue, that is, high solids content, but the viscosity is very high. Usually customers need to use special equipment before the further mixing, so that the shear thinning. This kind of product is mainly due to problems between the system in such phase silica particles exist interaction is serious, through the hydrogen bond between the aggregates cross-linked with larger viscosity. Although this kind of colloid can be reduced to a lower viscosity by high speed stirring, but once the external mechanical force is lost, the particles will be reunited again. There are no such colloidal particles stably dispersed to the fine size, and customers at a time of shear thinning and end point in the preparation of electrolyte powder reunion recovery size is difficult to control, will affect the stability of battery quality to a great extent.

The viscosity of the colloid is high, which is bad for the gel. Some users may say, anyway, I only add a little bit of colloid, especially AGM electric bicycle electrolyte, fumed silica content accounts for only about 1% of colloidal electrolyte. The viscosity of the mixed electrolyte is not high, but the viscosity of the mixed solution is not too high. But in fact, the thick gel represents the interaction between silica particles, which is not dispersed and stabilized. (Figure 5) the particle size of the solid gum is only fine after ultrasonic dispersion, and it will thicken again. This is not only the need for additional equipment to colloid colloid and shear thinning, diluted even in micro perfusion, but because the nano particles or in agglomeration and non steady state, the larger particle size, many powder surface -OH groups to form cross-linked and sulfuric acid, the properties of nano powder did not give full play, the effect is there is a discount. If you want to achieve the desired state of the need to add more fumed silica to achieve the same effect, so that costs rise. In addition, due to the time and energy of each user can not be properly dispersed, each time the size and distribution of colloidal particles is difficult to accurately control the stability of the battery will have a negative impact.

In contrast with the solid glue, we also see in the market a number of low solid content of the so-called liquid colloidal products, containing solids in most of 10% or less, but very unstable, not long after the deposition will be produced. The low solids content of this kind of colloid is not only the problem of high transportation cost, but also reflects the problem of dispersion and stabilization. The dispersion is in low concentration, shearing particles can not fully withstand mechanical force dispersed, part of particle dispersion limited effect; coupled with the lack of stabilization technology, the particles are easy to produce precipitation and agglomeration.

To sum up, the gas phase silica dispersion is difficult, if you want to achieve a relatively high solid content, low viscosity and colloid to, good stability, fine grain size and uniform distribution, dispersion equipment and technology is bound to put forward higher requirements. However, it is an important guarantee for the quality of the battery to provide a stable dispersion of raw materials with high viscosity and low viscosity. In view of the current market confusion, and the user does not have a professional instrument to identify, we prepared a simple table (Table 1), for the identification of colloidal users, how to try not to use the colloid. At the same time, we hope that if the relevant departments or enterprises in the right time, the formulation of colloidal standards and standards, to improve the level of colloid and battery will be very useful thing.

The content of colloidal electrolyte we now know that the highest was 20%, about 15% of the domestic manufacturers. These colloids are basically stable in colloid.
Shanghai to give the industry a new energy Mstar Technology Ltd production of JG-20 products containing solids 20%. Simple ingredients, does not contain any potential impact on battery performance and additives; viscosity is very low (< 100mPa.s), fine particle size, uniform distribution, good stability, security products six months without any precipitation and coarsening phenomenon, businesses to ensure 6 months warranty period, can be more than one year stability. Due to the low viscosity, and sulfuric acid mixed to form colloidal electrolyte viscosity is very low, as long as the glue within the specified time, even if the production of gum battery (6-8% silica) do not have any glue difficult. Our products have been used for several years by domestic manufacturers, and the customer satisfaction is very high.

Table 1 some examples of poor quality colloids

4.2 raw material costs can be further reduced

At present, the domestic battery industry for the understanding of fumed silica gel is in a phase of gradual deepening. At this stage, many industry followed by gas phase silica colloidal system in recognition and at the same time, focus on brand, light technology, brand choice for fumed silica is more important than to explore the dispersion process. Some manufacturers spend a lot of energy and cost of different grades of fumed silica conducted a comprehensive inspection, and more manufacturers lack of technical means, to see other plants with what powder followed up. In fact, the quality of fumed silica material is important, but it is more important to master the technology of dispersion in the application of colloid battery than the choice of powder. There is no good dispersion technology, even if the use of big powder can not be made to meet the requirements of colloid battery gel.

Although the performance is good and stable, relatively long history of application, but the price is more expensive. In the fierce competition in the market today, although the use of other brands of fumed silica from a single cell count does not affect costs a lot, but if many littles make a mickle. to further reduce costs, if the enterprise can be saved each year, tens of thousands to millions of cost. Many domestic colloid producers in the past until now still suffer in this regard, to buy a very expensive powder, the lack of good dispersion technology, can not see the obvious improvement of battery performance.

We believe that the use of the correct dispersion process, even if the use of other brands and comply with the specifications of the factory, can produce a gel to meet the requirements of the gel battery. Although different manufacturers of equipment, raw material powder because of its origin, and even the packaging in different ways, in the process of dispersion phenomenon may feel slightly different, but as long as with the appropriate dispersion process, the final dispersion results almost no difference. At present, through a large number of our experiments, verified by the five major international brands of fumed silica (indicators such as table 2) can meet the production requirements of the colloid colloid battery, and effectively prevent the falling of the active material, effectively inhibit the growth and osmotic lead dendrite, reduce the battery self discharge, water retention and battery the purpose of life. The gas phase silica production technology matures, many international brands of hydrophilic gas phase silica powder product has become homogeneous, regardless of the material index, or with a good dispersion of the actual application process after, other brands of fumed silica can be used in colloid battery, which provides the possibility for further to reduce the cost of colloid. That there is no have a serious negative impact performance and stability can be an indicator of international brand products or characteristics of the battery, the colloid is added in low (about 1% silica) electric car battery more not so sensitive. So the manufacturers should fully understand the properties of the powder under the condition of brand choice should be analyzed comprehensively and scientifically rational, to avoid misleading the individual businesses propaganda and commercial means to optimize the product price.
While the domestic fumed silica as equipment and production control problem, the specific surface area of frequent fluctuations and chloride ion concentration is high, the self discharge may affect the binding performance is not stable and cause the battery, we think that the application is not yet suitable for battery.

Table 2 common grade of fumed silica and its performance index

5 summary:

5.1 the development direction of colloid should be the direction of high solid content and low viscosity. Only in this way, can the gas phase silica particles reach a

sufficient and stable dispersion, the characteristics of nanoparticles. At the same time, the transportation cost of colloid can be reduced.

5.2 with the appropriate dispersion process, several major international brands of gas-phase silica are suitable for the preparation of colloidal. This is to further reduce

the cost of the enterprise, the production of better price performance of the battery electrolyte provides the possibility. The appropriate dispersion process is more

important than the choice of raw materials.

5.3 Shanghai new energy Mstar Technology Ltd has many years of experience in the application of fumed silica, and is willing to provide technical and commercial

solutions for the majority of colloid battery manufacturers. Contact phone 13601939311, email: michael.chen307@gmail.com.

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