Nickel Metal Hydride No. 5 battery

High-voltage technology and industrial development status of Nickel Metal Hydride No. 5 battery

As the requirements of electrical equipment for lithium battery capacity continue to increase, people's expectations for the improvement of lithium battery energy density are getting higher and higher. In particular, various portable devices such as smart phones, tablets, and laptops have put forward higher requirements for Nickel Metal Hydride No. 5 battery with small size and long standby time. Similarly, other electrical equipment, such as energy storage equipment, power tools, and electric vehicles, are also constantly developing Nickel Metal Hydride No. 5 battery with lighter weight, smaller size, higher output voltage and power density. Therefore, the development of high-energy-density Nickel Metal Hydride No. 5 battery is an important research and development direction of the lithium battery industry.

1. Background of high-voltage lithium battery development

In order to design high-energy-density Nickel Metal Hydride No. 5 battery, in addition to continuously optimizing their space utilization, improving the compaction density and gram capacity of the positive and negative electrode materials of the battery, and using highly conductive carbon nano and polymer adhesives to increase the content of positive and negative active materials, increasing the working voltage of Nickel Metal Hydride No. 5 battery is also one of the important ways to increase the energy density of batteries.

The cut-off voltage of Nickel Metal Hydride No. 5 battery is gradually transitioning from the original 4.2V to 4.35V, 4.4V, 4.45V, 4.5V and 5V. Among them, 5V nickel-manganese Nickel Metal Hydride No. 5 battery have excellent characteristics such as high energy density and high power, and will be one of the important directions for the development of new energy vehicles and energy storage in the future. With the continuous development of power research and development technology, Nickel Metal Hydride No. 5 battery with higher voltage and higher energy density will gradually come out of the laboratory and serve consumers in the future.

2. Current status of high-voltage lithium battery applications

1. Current status of research on high-voltage lithium cobalt oxide materials

The most widely studied and applied high-voltage positive electrode material is lithium cobalt oxide, which has a two-dimensional layered structure, α-NaFeO2 type, which is more suitable for the embedding and extraction of lithium ions. The theoretical energy density of lithium cobalt oxide is 274mAh/g. It has the advantages of simple production process and stable electrochemical properties, so it has a high market share. In practical applications, only part of the lithium ions of lithium cobalt oxide materials can be reversibly embedded and extracted, and its actual energy density is about 167mAh/g (working voltage is 4.35V). Increasing its operating voltage can significantly increase its energy density. For example, increasing the operating voltage from 4.2V to 4.35V can increase its energy density by about 16%. However, the repeated embedding and extraction of lithium ions from the material under high voltage will cause the structure of lithium cobalt oxide to change from trigonal system to monoclinic system. At this time, the lithium cobalt oxide material no longer has the ability to embed and extract lithium ions. At the same time, the particles of the positive electrode material loosen and fall off from the current collector, resulting in an increase in the internal resistance of the battery and a deterioration in the electrochemical performance.

At present, the modification of lithium cobalt oxide positive electrode materials is mainly to improve the crystal structure stability and interface stability of the material from two aspects: doping and coating.

At present, lithium cobalt oxide high-voltage materials have been used in large quantities in high-energy density batteries. For example, high-end mobile phone battery manufacturers have higher and higher requirements for battery performance, which is mainly reflected in the higher requirements for energy density. For example, the energy density of 4.35V mobile phone batteries with carbon as the negative electrode is required to be around 660Wh/L, and 4.4V mobile phone batteries have reached around 740Wh/L. This requires the positive electrode material to have a higher compaction density, higher air volume utilization, and better stability of the material structure under high compaction and high voltage. However, lithium cobalt oxide electrode materials have the disadvantages of scarce cobalt resources and high prices. In addition, cobalt ions have certain toxicity. These defects limit their wide application in power Nickel Metal Hydride No. 5 battery.

2. Research status of ternary materials

In order to reduce the amount of cobalt and improve the safety performance of batteries, researchers have begun to focus on the research of layered ternary high-voltage materials (LiNixCoyMn1-x-yO2 or LiNixCoyAl1-x-yO2). In this type of ternary material, the nickel (Ni) element serves to provide capacity, cobalt (Co) can reduce the mixing of lithium (Li) and Ni, and manganese (Mn) or aluminum (Al) can improve the structural stability of the layered material, thereby improving the safety performance of the battery. This type of battery is mainly used in general conventional digital batteries, such as power banks, business backup batteries, etc., and is regarded as a substitute for lithium cobalt oxide to improve the price competitiveness of the battery. The most common ratio of nickel, cobalt and manganese is 5:2:3. In the field of power vehicles, many manufacturers are trying it out. The way to increase the energy density is mainly to increase the working voltage of single Nickel Metal Hydride No. 5 battery and the nickel content in the new ternary materials, but the industry is still in the development stage and there are no mass products. This is mainly because the current power lithium battery must first meet the high safety, consistency, low cost and long life of the battery, and the increase in capacity is not the primary issue.

The important problem of ternary materials is that with the increase of nickel content, the alkalinity of the materials becomes stronger, and the requirements for battery manufacturing process and environment are getting higher and higher; at the same time, the thermal stability of the materials is reduced, and oxygen will be released during the cycle, resulting in poor structural stability of the materials; in the charging state, nickel has strong oxidizing properties, and higher requirements are also put forward for the matching of electrolytes. Therefore, ternary electrode materials have high limitations in promotion and use.

3. Current status of research on manganese-based positive electrode materials

Lithium manganate is a typical spinel-type positive electrode material. The theoretical energy density reported in the literature is 148mAh/g, which is lower than that of lithium cobalt oxide and ternary materials. It has the characteristics of low price, high thermal stability, environmental friendliness and easy preparation, and is expected to be widely used in energy storage batteries and power Nickel Metal Hydride No. 5 battery.

In power Nickel Metal Hydride No. 5 battery, the application of lithium manganate in China is not as extensive as that of ternary materials and lithium iron phosphate. The main reason is that it is limited by its low energy density and poor cycle life, resulting in short battery life and too low service life. The cycling performance of lithium manganese oxide, especially the high temperature (55°C) cycling performance, has been criticized for a long time. Its important influencing factors are divided into three aspects: ① Dissolution of surface Mn3+. Since the lithium salt used in the current conventional electrolyte is lithium hexafluorophosphate (LiPF6), the electrolyte itself contains a certain amount of hydrofluoric acid (HF) impurities. Trace amounts of water in the battery system will cause the decomposition of LiPF6 to produce HF. The presence of HF will corrode lithium manganese oxide (LiMn2O4) and cause Mn3+ to disproportionately dissolve, 2Mn3+ (solid phase) → Mn4+ (solid phase) + Mn2+ (solution phase). At the end of discharge and under high-rate discharge conditions, the Mn3+ content on the surface of the material is higher than that in the bulk phase, which aggravates the dissolution of Mn3+ on the surface of the material. ② Jiang-Taylor effect. During the battery discharge process, especially in the case of over-discharge, the Li1+δ[Mn2]O4 generated on the surface of the material is thermodynamically unstable. At the same time, the material structure changes from cubic phase to tetragonal phase, and the original structure is destroyed, so the cycling performance of the material deteriorates. ③ High oxidation of Mn4+. At the end of charging or under overcharging conditions, Mn4+ in the highly delithiated Li1+δ[Mn2]O4 material has strong oxidation, which can oxidize and decompose organic electrolytes and deteriorate the battery's cycle performance. At present, the energy density of most lithium manganese oxide batteries is less than 100mAh/g, and the normal temperature cycle can only reach 400 to 500 times, and the high temperature cycle can only reach 100 to 200 times, which cannot meet the needs of mass production. But in fact, the battery system of Nissan Leaf, which accounts for nearly 20% of the global electric vehicle sales, uses lithium manganese oxide batteries, and its cruising range can reach about 200km.

Although the performance of lithium manganese oxide batteries is restricted by the structure of the material itself, as long as the shortcomings of low energy density and poor cycle performance are solved, it will still have a very broad application space in the field of power Nickel Metal Hydride No. 5 battery in the future.

In order to improve the energy density and cycle performance of lithium manganese oxide electrode materials, some researchers have increased the voltage of positive electrode materials by doping modification, such as LiMxMn2-xO4〔(M=chromium (Cr), iron (Fe), Co, Ni, copper (Cu)〕5V high-voltage positive electrode materials, among which the nickel-manganese high-voltage material LiNi0.5Mn1.5O4 has been the most widely studied. The discharge capacity of nickel-manganese high-voltage materials is as high as 130mAh/g, and the platform can reach about 4.7V. The energy density is higher than that of lithium cobalt oxide under conventional working voltage, and there is basically no Jiang Taylor effect of Mn3+. When the working voltage is increased to about 5V, nickel-manganese high-voltage materials have the advantages of high gram capacity, high discharge platform, high safety performance and high rate performance compared with traditional lithium cobalt oxide, lithium manganese oxide, ternary and iron lithium. It has great advantages in the matching of battery packs, but its poor high temperature performance and cyclability need to be improved. From the current application point of view, it is still in the small-scale production stage of steel shell batteries. The doping modification and surface coating process of nickel-manganese high-voltage materials are still in the stage of small-scale production of steel shell batteries. There is still a long way to go.

4. Research status of high-voltage electrolytes

Although high-voltage Nickel Metal Hydride No. 5 battery have made great contributions to improving the energy density of batteries, they also have many problems. With the increase in energy density, the compaction density of the positive and negative electrodes is generally large, the electrolyte wettability becomes worse, and the liquid retention volume decreases. Low liquid retention volume will lead to poor battery cycle and storage performance. In recent years, with the continuous emergence and application of high-voltage positive electrode materials, conventional carbonate and lithium hexafluorophosphate systems will decompose in batteries with voltages above 4.5V, and the battery performance will decrease, such as poor cycle performance and poor high-temperature performance, and can no longer fully meet the requirements of high-voltage Nickel Metal Hydride No. 5 battery. Therefore, it is of great significance to study the electrolyte system that matches these high-voltage positive electrode materials.

In view of the problem of poor electrolyte wettability caused by high compaction density, the electrolyte design is constantly screening solvents with high oxidation potential and low viscosity to meet the performance requirements of high-density batteries. In addition, additives or fluorinated solvents that can improve the wettability of the electrolyte are also used to improve it, and the effect is also obvious.

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