AG4 battery.Introduction to the improvement of scientific research and application technology for lithium iron phosphate battery performance

　　Introduction to the improvement of scientific research and application technology for lithium iron phosphate battery performance

　　The performance of lithium-ion power batteries mainly depends on the positive and negative electrode materials. Lithium iron phosphate as a lithium battery material has only appeared in recent years. The domestic development of large-capacity lithium iron phosphate batteries was only in July 2005. Its safety performance and cycle life are unmatched by other materials, and these are also the most important technical indicators of power batteries. 1C charge-discharge cycle life reaches 2,000 times. A single battery will not burn when overcharged to 30V, and will not explode when punctured. Lithium iron phosphate cathode material makes large-capacity lithium-ion batteries easier to use in series. To meet the needs of frequent charging and discharging of electric vehicles. It has the advantages of non-toxic, pollution-free, good safety performance, wide source of raw materials, cheap price, long life, etc. It is an ideal cathode material for the new generation of lithium-ion batteries. This project belongs to the development of functional energy materials in high-tech projects. It is an area supported by the national "863" plan, "973" plan and the "Eleventh Five-Year Plan" high-tech industry development plan. The cathode of lithium-ion batteries is lithium iron phosphate material, which has great advantages in safety performance and cycle life. These are also one of the most important technical indicators of power batteries. The 1C charge-discharge cycle life can reach 2,000 times, it will not explode when punctured, and it will not burn or explode easily when overcharged. Lithium iron phosphate cathode material makes large-capacity lithium-ion batteries easier to use in parallel and series. The scientific research and application of lithium iron phosphate batteries has been recent. There have been continuous reports about the progress of new batteries and their potential to replace traditional lithium batteries. This has given us the hope of longer battery life for mobile phones and tablets. Unfortunately, most of them remain in laboratory research. It’s hard to say when or even whether it can be put into commercial use on a large scale. Now, the new energy company DebochTEC.GmbH has brought a new energy technology that is closer to reality: iron-containing lithium batteries. The lithium iron phosphate battery technology white paper published by DebochTEC.GmbH shows that after using composite nanomaterials, the energy density of a single cell of 32650 specifications (diameter 32mm/length 65mm) can be increased to 6000mAh, which is equivalent to the current industry's 32650 specifications single cell of 5000mAh. Compared with the specifications, the same volume has been increased by a full 1000mAh, which is 20%. One battery can charge the iPhone 4S almost 4 times. What’s even more gratifying is that when used in a single low-rate charging and discharging environment, this kind of battery still maintains about 80% of its power after being cycled up to 3,000 times, while ordinary lithium batteries perform this well after being cycled about 500 times. . Calculated by charging and discharging once every 3 days, it can be used continuously for 24 years, making it a truly long-life battery. This new battery technology can be widely used in portable mobile power supplies, small UPS, laptop batteries, car batteries and other equipment. For different usage environments, DebochTEC.GmbH also uses different battery core colors according to the number of cycle charging times: The one for special grade is gold, with a cycle number of 3,000 times; the one used in the civilian automotive field is blue, with a cycle count of 2,500 times; the green one, with a cycle count of 2,000 times, is suitable for small portable mobile devices. The positive and negative active materials of lithium-ion batteries are intercalated compounds. During charging, Li+ is detached from the positive electrode and inserted into the negative electrode through the electrolyte; during discharge, the opposite is true. The charging and discharging process of the battery is actually Li+ intercalating back and forth between the two electrodes. The process of escaping, so this kind of battery is also called "Rocking Chair Batteries" (abbreviated as RCB). The reaction schematic diagram and basic reaction formula are as follows:

　　2. Polymer lithium-ion battery technology 2.1 Performance characteristics of polymer lithium-ion batteries Polymer lithium-ion batteries refer to lithium-ion batteries that use solid polymer electrolyte (SPE) as the electrolyte. The battery is composed of a positive electrode current collector, a positive electrode membrane, a polymer electrolyte membrane, a negative electrode membrane, and a negative electrode current collector. The battery is pressed and compositely formed, and is wrapped with an aluminum-plastic composite film and its edges are heat-melted and sealed to obtain a polymer lithium-ion battery. Since the electrolyte membrane is solid, there is no leakage problem, and the battery design has greater freedom. It can be connected in series and parallel or adopt a bipolar structure as needed. Polymer lithium-ion batteries have the following characteristics: ① Shaping flexibility; ② Higher mass specific energy (3 times that of MH-Ni batteries); ③ Wide electrochemical stability window, up to 5V; ④ Perfect safety and reliability; ⑤Longer cycle life and less capacity loss; ⑥High volume utilization; ⑦Wide application fields. Its working performance indicators are as follows: working voltage: 3.8V; specific energy: 130Wh/kg, 246Wh/L; cycle life: >300; self-discharge: <0.1%/month; working temperature: 253-328K; charging speed: 1h 80% capacity; 3h to reach 100% capacity; Environmental factors: non-toxic. 2.2 Cathode material The characteristics and price of lithium-ion batteries are closely related to its cathode material. Generally speaking, the cathode material should meet: ⑴ Have electrochemical compatibility with the electrolyte solution within the required charge and discharge potential range; ⑵ Mild electrode process kinetics; ⑶ High reversibility; ⑷ Good stability in air in full lithium state. With the development of lithium-ion batteries, research on high-performance, low-cost cathode materials is continuously carried out. At present, research mainly focuses on lithium transition metal oxides such as lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide [1] (see Table 1). Table 1 Comparison of three main cathode materials for lithium-ion batteries

　　Lithium cobalt oxide (LiCoO2) belongs to the α-NaFeO2 type structure and has a two-dimensional layered structure, which is suitable for the deintercalation of lithium ions. Due to its relatively simple preparation process, stable performance, high specific capacity, and good cycle performance, most currently commercialized lithium-ion batteries use LiCoO2 as the cathode material. The synthesis methods mainly include high-temperature solid-phase synthesis and low-temperature solid-phase synthesis, as well as soft chemical methods such as oxalic acid precipitation, sol-gel method, hot and cold method, and organic mixing method. Lithium nickel oxide (LiNiO2) is a rock salt type structural compound with good high temperature stability. Due to its low self-discharge rate, low requirements for electrolyte, no environmental pollution, relatively abundant resources and affordable price, it is a promising cathode material to replace lithium cobalt oxide. At present, LiNiO2 is mainly synthesized through solid-phase reaction of Ni(NO3)2, Ni(OH)2, NiCO3, NiOOH and LiOH, LiNO3 and LiCO3. The synthesis of LiNiO2 is more difficult than LiCoO2. The main reason is that the stoichiometric LiNiO2 is easily decomposed into Li1-xNi1+xO2 under high temperature conditions. Excess nickel ions are in the lithium layer between the NiO2 planes, hindering the diffusion of lithium ions. It will affect the electrochemical activity of the material. At the same time, because Ni3+ is harder to obtain than Co3+, the synthesis must be carried out in an oxygen atmosphere [2]. Lithium manganese oxide is a modification of traditional cathode materials. Currently, spinel-type LixMn2O4 is widely used. It has a three-dimensional tunnel structure and is more suitable for the deintercalation of lithium ions. Lithium manganese oxide has abundant raw materials, low cost, no pollution, better overcharge resistance and thermal safety, and has relatively low requirements for battery safety protection devices. It is considered to be the most promising lithium-ion battery cathode material. Mn dissolution, Jahn-Teller effect and electrolyte decomposition are considered to be the main reasons for the capacity loss of lithium-ion batteries using lithium manganese oxide as the cathode material.

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