Nickel felt makes optimum electrolysis electrode than nickel foam and nickel mesh

INTRODUCTION

In recent years, with the rapid development of the microelectronics industry, mobile phones, cameras, portable computers, and other electronic and electrical equipment, especially the development of large-capacity electric vehicles, urgently need high-capacity, small-volume rechargeable batteries to adapt to it. The MH-Ni battery is a new alkaline storage battery developed over the past ten years. Compared with nickel-cadmium battery, it has the advantages of high capacity and no pollution. It is known as a green storage battery.

Since the performance of the anode active material framework material in the MH-Ni battery plays a vital role in the battery capacity, charge and discharge performance and cycle life, since the 1980s, foam nickel electrodes, bonded nickel electrodes and fibre nickel electrodes have been born. Among them, foamed nickel as the electrode plate substrate has been widely used in the large-scale production of small civilian batteries. Still, MI-Ni batteries made of foamed nickel have a small specific surface area, low capacitance, low strength, and few charge and discharge times (less than 500 times), short cycle life and other issues affect the development of MH-Ni batteries, and at the same time face the challenge of lithium-ion secondary batteries. To increase the service life of nickel-hydrogen batteries, research and development people the nickel fibre felt anode substituted foamed nickel as anode electrode active material matrix materials can MH-Ni battery charge and discharge times up to thousands of times. At the same time, it can withstand high current impacts. It has good voltage stability, large capacitance, extensive active material filling, increased utilization, low internal resistance, and high plate strength. It is currently one of the main targets for the development of electric vehicle batteries globally. Hence the nickel fibre felts in place of the nickel foam have become a direction MH-Ni batteries.

At present, some developed countries have achieved the scale of production of nickel fibre felt; China has also reported preparation methods, mainly chemical, metallurgy， and mechanical methods, to make the nickel fibre dimensional substrate.

This article reports a new type of nickel fibre anode material for MH-Ni batteries. The process is characterized by using the bundle method to draw the fibres, air-laid and sintered into a fibre mat. It has uniform pore size, high porosity, large specific surface area, high tensile strength, and good flexibility. Physical properties such as pore size, porosity, and specific surface area of the nickel felt are also introduced. The nickel fibre felt has obtained good mechanical properties through the sintering test.

PREPARATION PROCESS

THE PREPARATION PROCESS OF NICKEL FIBER FELT

In the whole process, fibre drawing is a crucial step. The preparation technology adopted by the bundle method to draw the fibres, compared with melt spinning, mechanical cutting, monofilament drawing and other techniques, has uniform wire diameter, easy continuous production, and cost-effective characteristics. Several technical problems in the process of bundle drawing have been solved. It can produce 6μm ~ 40μm different wire diameter nickel fibres and nickel fibre properties to meet additional felt requirements.

The fibre cutting is carried out on a particular cutting machine, which can be cut into different specifications, such as a length of less than 33mm. It has the characteristics of uniform cutting length and high production efficiency.

The nickel fibre is made by Air Flow Method Paving method. The equipment used is an imported felt laying machine. By adjusting various complicated process parameters, the nickel fibre felt is uniform and free of defects such as bundle fibres and fibre agglomeration. , The unit weight can be controlled as required.

Determination of pore size of nickel-dimensional felt by bubble test

Calculate the specific surface area S 

The performance of nickel fiber felt has a great influence on the performance of the MH-Ni battery, which determines the amount of active material and effective utilization rate, which is the key to the successful application of the technology. These properties include fiber diameter, nickel felt thickness, pore size, porosity, unit weight, tensile strength, elongation, and so on.

APERTURE SIZE

The pore size of the nickel fiber felt has a great influence on the filling performance of the active material. If the pore size is too small, the active material is not easy to fill, resulting in the phenomenon that the active material is only concentrated on the electrode surface and cannot be filled inside. The pore size is too large, the active material accumulation phenomenon is serious, the internal resistance of the electrode is increased, the utilization rate of the active material is reduced, and the electrode performance is adversely affected. Due to the different active material filling process methods of various production plants, the requirements for the pore size are also different. The electrode made of nickel fiber felt can effectively control the pore size through the preparation of fibers with different diameters. Generally speaking, in the case of the same unit weight (mass per unit area), the thicker the fiber diameter, the larger the pore size. According to this, the diameter of the fiber can be selected according to the pore size to make the felt that meets the requirements. When φ10 μm nickel fiber is used, the pore size is φ120μm, when φ40 μm nickel fiber is used, the pore size reaches nearly φ700 μm (as shown in Figure 2).

The single weight also has a certain effect on the pore size of the nickel felt. Under the same wire diameter and thickness, as the single weight increases, the fiber pore size becomes smaller (as shown in Figure 3).

The porosity of nickel felt is an important indicator that affects battery performance, and electrodes with high porosity can carry more.

The active material increases the volume-specific energy of the battery. The porosity of nickel fiber felt can reach 95%~98%. The fiber diameter has little effect on the porosity of the nickel felt. Using φ10 μm~φ40 μm fiber diameter, the porosity can reach the level of 94.9%~96.8%.

The effect of unit weight on the porosity of nickel felt is as follows: with the increase of unit weight, only the natural thickness of nickel felt increases, but the change of porosity is not significant. The experimental data are that when the unit weight increases from 300gm-2 to 600gm-2, the porosity meter decreases from 95.8% to 94.8%.

Nickel fiber felt thickness have some influence on the porosity, singlet under the same conditions, the smaller the thickness becomes smaller porosity, singlet for400 gm^-2~480 gm^-2 of the nickel fiber felt, at a thickness of 1.5mm control, it can maintain a high porosity

SPECIFIC SURFACE AREA

Nickel fiber felt having a significant performance feature that has a large surface area, actual test data can be achieved 5×10⁴cm² cm^-3~2.0×10⁵ cm²cm^-3, which mainly consists of nickel fibers dimensional by the characteristics of the preparation process of the felt, the drawn fiber itself has a large surface area, and the fiber is spread into a net to form a mesh structure that is evenly connected to each other. The fiber diameter and the single weight contrast surface area have a certain effect. As the fiber diameter becomes thicker and the single weight increases, the specific surface area shows a downward trend (as shown in Figure 4 and Figure 5).

At present, the big problem facing the development of nickel batteries is that it is difficult to meet the needs of large-capacity, high-current batteries. The problem of foamed nickel electrodes breaking during the winding process severely restricts the development in the direction of industrialization. The high-temperature sintered nickel fiber felt has high tensile strength (see Table 1) and flexibility. Under the premise that the pore size, porosity and other properties meet the requirements, it will not be broken or deformed during the winding process.

The fibers in the sintered fiber felt are bonded to each other, and each fiber is welded to several fibers. The bonding points are in a micro-melt state, and the entire fiber mat forms a complete conductive network (the microstructure is shown in Figure 6), Has excellent electrical properties, the specific resistance value is less than 25mΩ. It is firmly combined with the active substance, and it is not easy to fall off and drop the slag. The sintering test was carried out under the conditions of hydrogen, argon, etc., and the temperature was selected in the range of 1000℃~1300℃, and the tensile strength of the test reached 5MPa~8MPa.

PERFORMANCE COMPARISON WITH NICKEL FOAM

Nickel fiber felt is similar to foam nickel in performance indicators such as pore size, porosity, unit weight, and thickness.

But it has obvious advantages in terms of specific surface area, tensile strength, elongation, etc. (as shown in Table 1)

Table 1 the nickel fiber felt with a foamed nickel-Performance Comparison

CONCLUSION

1) The thickness, pore size, unit weight, porosity and other performance indicators of nickel fiber felt can be comparable to foam nickel

2) Nickel fiber felt has the characteristics of larger specific surface area, higher tensile strength, and good flexibility than a foamed nickel.

3) Suitable for making large-capacity, large current of Ni-MH batteries.