402030 lipo battery.What are the key technologies for high-temperature nickel-metal hydride batteries?

Nickel-cadmium (Ni-Cd) batteries have always been one of the targets of environmental protection workers because they contain the highly toxic element cadmium. Organizations such as the European Union continue to issue policies and directives ("Waste Electrical and Electronic Equipment Directive" WEEE and "Restrictions on Restrictions on Electronic and Electrical Equipment"

Nickel-cadmium (Ni-Cd) batteries have always been one of the targets of environmental protection workers because they contain the highly toxic element cadmium. Organizations such as the European Union continue to introduce policies and directives (the "Waste Electrical and Electronic Equipment Directive" WEEE and the "Directive on the Restriction of the Use of Certain Hazardous Substances in Electronic and Electrical Equipment" RoHS), which has accelerated the replacement of nickel-cadmium batteries by other batteries. Nickel-metal hydride (Ni-HM) batteries are the most promising alternative. How to deal with the performance problems of Ni-HM batteries in high-temperature environments is the key to whether they can be used on a wider scale. The charging and discharging process and use environment of nickel-metal hydride batteries inevitably involve the impact of temperature on battery performance and service life. High-capacity mobile power supplies, aerospace, navigation, petroleum, coal, geological exploration and operations, and ice are urgently needed by the military. It has strong strategic significance, scientific value and economic value. In addition, nickel-metal hydride powered lithium-ion batteries also have important prospects for use in hybrid vehicles such as fuel-powered lithium batteries + nickel-metal hydride batteries (electric-electric hybrid) and gasoline + nickel-metal hydride batteries (gas-electric hybrid).


During the charging and discharging process of rechargeable batteries, changes in ambient temperature, etc., have an impact on battery performance. Although all battery materials have a certain impact on battery performance, as far as high-temperature batteries are concerned, improving and optimizing positive and negative electrode materials is a A better way is to improve hydrogen storage alloys except for a few patent disclosures. The important technology still lies in the cathode material, including the use of mechanical mixing methods to add rare earths, rare metals, alkaline earth elements, etc., such as Mg, Ca, etc. to the battery cathode material formula. Sr, Sc, Y, La, lanthanides, Ti, Zr, Cr, Mo, W, Mn, Fe, Co, Cu, Zn, Cd, b, Al, Ga, In, Si, p, As, Sb, biOne or more oxides and hydroxides. Since it is difficult to achieve complete uniformity of several materials with different properties when batching the positive electrode, it is considered to use co-precipitation doping with the above elements when making spherical nickel hydroxide, and it is also considered to coat the spherical nickel with a layer of hydroxide of the above elements.


Although the above methods have played a certain role in improving the performance of high-temperature batteries, there are still many shortcomings and shortcomings. The important methods to deal with the degradation of battery performance are to improve the internal structure of spherical nickel to guard against the occurrence of "gamma;-NiOOH" and hope that "beta" -NiOOH can easily convert with β-Ni(OH)2 during charge and discharge (γ-NiOOH layer spacing is 0.69nm, β-Ni(OH)2 crystal layer spacing is about 0.46nm, β-NiOOH crystal layer spacing The spacing is about 0.48nm, and the presence of γ-NiOOH causes the electrode to expand, causing the loss of active materials and reducing conductivity, seriously reducing the cycle life and efficiency of the electrode); another way is to add conductive materials to improve conductivity, adding CoO or Co( OH)2. However, during the charging and discharging process, the cobalt hydroxide as raw material powder dissolves in the alkaline aqueous solution and precipitates again, and undergoes rapid structural changes. Some cobalt compounds are free, causing changes in the amount of cobalt and reducing battery performance. Although the above-mentioned phenomena related to coated ball nickel have been improved to some extent, there are still phenomena that the coating is not strong enough and the surface layer dissolves and falls off after charging and discharging.


Functional Gradient Materials (FGM) is a high-performance material with step-change changes in microscopic composition, structure, and performance. It has the characteristics of high mechanical strength, thermal shock resistance, and high temperature resistance. It is widely used in electronic components, artificial teeth, automobile engines, brakes, chemical components, etc. The author believes that combining the principles of gradient materials with spherical nickel manufacturing will become the development trend of high-temperature battery cathode materials.
Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

Charging temperature: -20~45℃ -Discharge temperature: -40~+55℃ -40℃ Support maximum discharge rate: 3C -40℃ 3C discharge capacity retention rate ≥70%
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2. Key technologies of high-temperature nickel-metal hydride batteries


2.1. Improvement of cathode materials


2.1.1. Mechanical mixing method of cathode materials


When battery ingredients are added, the main group elements of IIA, IIIb, IVb, VIIb, VIIIb, IIb and the elements, oxides or hydroxides of periods 3, 4 and 5 in the periodic table can be better improved or Improve the high temperature performance of nickel metal hydride. Many of the patents applied for authorization by world-famous battery manufacturing companies in China include analysis, such as Japan's Panasonic and Sanyo; my country's BYD; Germany's H.C. Stark and other companies. See the table below for details:


2.1.2. Chemical co-precipitation method of cathode materials
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During the processing of the spherical nickel hydroxide, the cathode material, the above elements are doped into the layered structure nickel hydroxide, replacing part of the nickel ions to form a solid solution, making the elements more uniform; the spherical nickel hydroxide is wrapped on the outside Coating with a layer of cobalt hydroxide can improve the overall performance of the battery. Representative patents are shown in the table below:


2.2. Improvement of negative electrode materials


The negative electrode material of nickel-metal hydride batteries uses hydrogen storage alloy, and the main component element is M (NiCoMnAl) 5, which is Ab5. M is rare earth La, Ce, pr, Nd.


Liu Huafu adopts a chemical formula composed of Mm0.95～1.05Ni4.08～4.40Co0.38～0.95Mn0.25～0.399Al0.32～0.49M0.04～0.999, Mm is a rare earth alloy of lanthanum, cerium, praseodymium and neodymium, M It is two elements, three elements or four elements among vanadium, bismuth, iron, gallium, zinc, silicon, boron, tungsten, molybdenum, chromium, titanium, lithium, tin and copper. Used for MH-Ni secondary batteries. A hydrogen storage alloy material that can be charged quickly under high temperature conditions and has high electrochemical capacity.


The composition (atomic %) of the negative electrode material by Li Rong and others is: Ab5. In the negative electrode material for high-temperature nickel-hydrogen batteries, A is La, Ce, pr, Nd, and Y elements; b is Ni, Co, Mn, and Al. element;


Sichuan University has developed a low-temperature hydrogen storage alloy with excellent performance, and combined it with unique nickel-metal hydride battery manufacturing technology to prepare a D-type nickel-metal hydride battery with a rated capacity of 8Ah. The battery has been tested by the Tianjin 18th Institute of the Ministry of Information Industry, Changhong Power Supply Company, Chengdu Jianzhong Lithium-ion Battery Factory and Sichuan University itself and found that the normal temperature performance is 0.2C capacity 9.2Ah, 1C capacity 9.0Ah, and its high rate performance is about 98% , the low current (0.2C~0.4C) charge and discharge cycle life is more than 500 times, the 1C high current charge and discharge cycle life is more than 300 times, the self-discharge after being left at room temperature for 28 days is less than 10%; the low temperature performance is -40℃, 0.2C And the discharge capacity reaches 80% of the rated capacity under the conditions of -40℃ and 0.4C, and the discharge capacity reaches 70% of the rated capacity under the conditions of -45℃ and 0.2C; the high temperature performance is 55℃/0.2C after charging for 6.5 hours, 0.2 C discharge capacity is greater than 90% of the rated capacity. After being discharged at 0.2C for 8 hours at 55°C, the discharge capacity is greater than 90% of the actual capacity. No capacity loss was seen after 30 days of storage at 50°C. Under the leadership of Academician Tu Mingjing, Professor Chen Yungui, a former doctoral supervisor at the School of Materials of Sichuan University, presided over the development of neodymium-free nickel-hydrogen power lithium-ion batteries. Its comprehensive performance is in the lead in the competitive experiments of major domestic and foreign brands of batteries. Obtained four national invention patent authorizations and was honored as one of the top ten rare earth science and technology news in my country in 2003. Academician Tu Mingjing and Professor Chen Yungui are actively promoting this wide-temperature nickel-hydrogen battery with excellent performance, developing nickel-hydrogen starting power supplies with excellent low-temperature and high-current discharge performance for aircraft and wide-temperature, long-life and low-cost nickel nickel batteries for electric vehicles. Development of hydrogen batteries [1].


3. Doped infiltration plating gradient composite spherical nickel hydroxide


The industrialization of spherical nickel hydroxide has more than ten years of experience. The commercialization of Cd+Co-doped and Zn+Co-doped spherical nickel is relatively mature, and cobalt-coated (or cobalt-coated) is gradually becoming commercialized. So much so that some people say [2] that the current development of beta-Ni(OH)2 is close to the limit; the research and development prospects of nano-Ni(OH)2 and alpha-Ni(OH)2 materials will be very broad.


Functionally Gradient Materials (FGM) is a new type of functional material developed in response to the needs of high-tech fields such as modern industry and to meet the requirements of repeated normal operation in extreme environments (ultra-high temperature, large temperature drop) [3] . It is an important frontier technology field for the development of international composite functional materials.


Doped infiltration plating gradient composite spherical nickel hydroxide should be divided into two concepts:


1. Doped spherical nickel hydroxide, which is based on the traditional doped Cd+Co and doped Zn+Co spherical nickel, optimizes the selection of Group II elements, rare earth elements, etc., to prepare average composition, microstructure and grain size Spherical nickel hydroxide with small, large layer spacing, large half-width doping, specific surface area and particle size distribution that meets the requirements, and stable quality. In this regard, the author believes that the system microcrystal online three-dimensional control method he developed is domestically leading in terms of product stability and uniformity; ease of process re-online control, precision and reliability of parameters; low equipment investment and overall product cost. status. There was not a single quality complaint among the nearly 1,000 tons of products supplied to Panasonic Battery Company in batches for one year, which was the first of its kind in China [4][5].


2. Gradient composite spherical nickel hydroxide is similar to the current cobalt-coated spherical nickel, but it is also very different. Cobalt-coated spherical nickel is simply deposited and coated with a single layer of cobalt hydroxide in spherical nickel hydroxide; gradient composite spherical nickel hydroxide is made by adding the material to be infiltrated (cobalt, yttrium, titanium, calcium, magnesium or other rare earth elements) The material to be repaired (doped spherical nickel) is placed under strictly controlled conditions. The plating ions and hydroxides are concentrated on the surface of the base material (doped spherical nickel) under the use of additives. The ions continue to move along the surface of the base material. Crystal defects diffuse rapidly into the matrix. Finally, the metal elements to be infiltrated are enriched and crystallized on the surface of the substrate, and penetrate into the matrix to a certain depth. From the surface to the inside, the concentration of the elements to be infiltrated decreases in a gradient, and its organizational structure also changes in a gradient, forming a layer of infiltration on the outer surface of the substrate. The performance of metal, the core of the base material still maintains the original performance, and the performance of the middle layer gradually exceeds the gradient functional material. The densification of the gradient material whose composition continues to change makes the plating material and the matrix firmly bonded. The plating material and the matrix are not easy to fall off during the reaction process of making the battery material, ensuring the consistency of the battery cycle performance and life. By adding selected Group II elements , rare earth elements, etc., to prepare doped and infiltrated gradient composite spherical nickel hydroxide to obtain the effect of high-temperature nickel-hydrogen batteries.


4 Conclusion


Adding rare earth, rare, alkaline earth elements or oxides to the positive electrode ingredients of nickel-hydrogen batteries can improve the performance of nickel-hydrogen batteries at high temperatures. The representative elements are: such as Mg, Ca, Sr, Sc, Y, La, and lanthanum. One or more oxides of series elements, Ti, Zr, Cr, Mo, W, Mn, Fe, Co, Cu, Zn, Cd, b, Al, Ga, In, Si, p, As, Sb, bi ,hydroxide. Among them, there are many analyzes on the research and use of zirconium in new energy materials [6][7][8]. In addition to the actual industrial use of zirconium in (nuclear energy, zirconium plates, pipes), other nickel-hydrogen positive and negative electrode materials And lithium-ion battery cathode material additives do not yet have practical industrial use. The surface mixing of the mechanical mixing method has uniformity problems, which affects the performance; chemical precipitation doping and coating have certain advantages over the mechanical mixing method, and there are still processing technology control technologies; doping, infiltration and plating gradient composite spherical nickel hydroxide may be the best way to deal with the above effective method of defects.