Ni-MH battery pack

Research on the performance of soft-packaged Ni-MH battery pack?

Ni-MH battery pack are a new type of rechargeable battery developed in the past decade. They have high specific energy, no memory effect, are green and environmentally friendly, and their discharge voltage is three times that of nickel-cadmium and nickel-metal hydride batteries. Therefore, they have attracted widespread attention and developed very rapidly since their introduction. At present, only a few countries have achieved industrialization, among which Japan has done the best industrialization work. my country is the earliest developing country to develop Ni-MH battery pack industrially. After the development in recent years, especially under the active promotion of relevant national policy orientation, domestic Ni-MH battery pack have made rapid progress, and various performances of products have made considerable progress. The lithium-ion battery production chain has been increasingly improved, and the degree of industrialization has been increasing, forming a situation of competing with developed countries in the world. With rich natural resources and low labor costs, China's lithium-ion battery industry has obvious advantages in international competition.

Ni-MH battery pack are undoubtedly a new generation of batteries with high scientific and technological content and wide applications. It has high volume energy and mass energy, is rechargeable and pollution-free, and has the three major advantages of the current development of the battery industry. It is called "the most promising chemical power source". There are two common types of lithium-ion battery technology: liquid Ni-MH battery pack with metal shells and polymer Ni-MH battery pack. The shell of liquid Ni-MH battery pack is generally a steel shell or an aluminum shell, and its plasticity is not as good as that of polymer Ni-MH battery pack. The manufacturing process of polymer Ni-MH battery pack is complicated, especially the low yield rate, which greatly limits the industrialization of this battery. The author recommends soft-package Ni-MH battery pack, which are characterized by the combination of the basic electrochemical properties of liquid Ni-MH battery pack and the unique advantages of polymer Ni-MH battery pack in appearance packaging. Liquid electrolytes similar to liquid Ni-MH battery pack are used as the medium for lithium ions to transfer between the positive and negative electrodes, while multi-layer plastic composite films are used in the appearance packaging. The outstanding advantages of soft-package Ni-MH battery pack are simple manufacturing processes, low costs, and high yield rates. Its goal is to replace the market of polymer Ni-MH battery pack and form a competitive state with stainless steel shell Ni-MH battery pack. The comparison of three different technologies of stainless steel shell Ni-MH battery pack, polymer Ni-MH battery pack and soft-package Ni-MH battery pack is listed in Table 1. This paper studies the various electrochemical properties of soft-package Ni-MH battery pack and the differences between them and stainless steel-shell Ni-MH battery pack to verify the feasibility of the industrialization of soft-package Ni-MH battery pack.

Figure 1a shows the relationship curves between battery capacity and voltage of soft-package Ni-MH battery pack at three discharge rates of 0.5C (250mA), 1C (500mA) and 2C (1000mA). Under 2C current discharge, the soft-package lithium-ion battery can release 91.7% of the capacity at 0.5C, indicating that the battery has good large current discharge capability. Figure 1b shows the relationship curves between battery capacity and voltage of stainless steel-shell Ni-MH battery pack at three discharge rates of 0.5C, 1C and 2c. Similarly, under 2c current discharge, the stainless steel-shell lithium-ion battery can release 92.2% of the capacity at 0.5c. For the same battery size, the discharge capacity of the soft-package lithium-ion battery is about 10% higher than that of the stainless steel-shell lithium-ion battery, which is caused by the different internal structures of the two batteries. The reasons are as follows: the outermost layer of the cell after the soft-package lithium-ion battery is wound inside is the positive electrode sheet, and the outermost layer of the cell after the stainless steel shell battery is wound inside is the negative electrode sheet. In terms of structure, the soft-package lithium-ion battery has more positive electrode material dressing, and the discharge capacity of the lithium-ion battery is determined by the positive electrode, so the capacity of the soft-package battery is relatively higher than that of the stainless steel battery. The internal cells of the battery adopt different structures, which is related to the material used in the shell. The shell of the soft-package lithium-ion battery is an aluminum-plastic packaging film with an Al foil isolation layer in the middle layer. If it contacts the internal wound cell with the negative electrode sheet as the outermost layer, it may cause the Al foil isolation layer of the soft package to dissolve at an extremely low potential (about 0.05mVVS.Li when fully charged), causing the battery to fail. If the stainless steel shell battery uses an internal wound cell with the positive electrode sheet as the outermost layer, there is a problem of welding the tabs (usually Al strips) on the positive electrode sheet with the stainless steel shell, so the internal wound cell with the negative electrode sheet as the outermost layer is usually used. Structurally, soft-package Ni-MH battery pack have a competitive advantage over stainless steel-cased Ni-MH battery pack in terms of capacity.

2.2 High and low temperature performance

Figure 2 shows the high and low temperature discharge curves of the two Ni-MH battery pack. The test process was carried out in a high and low temperature test chamber. The battery was charged to 4.2V with a 1C current before the test began, and continued to charge at a constant voltage for 2 hours at this voltage, and then stood for 2 hours.

Studies on the electrochemical properties of soft-package Ni-MH battery pack, such as rate discharge capacity, high and low temperature discharge capacity, and battery cycle stability, have shown that soft-package Ni-MH battery pack have very high application value. It is different from general metal-cased Ni-MH battery pack and polymer Ni-MH battery pack. It is a new type of lithium-ion battery with the advantages of high weight-to-energy ratio, good shape plasticity, and simple production process, and is expected to be mass-produced.

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