AA Ni-MH batteries

　　Analysis of AA Ni-MH batteries technology

　　Lithium batteries usually refer to batteries with lithium metal or lithium alloy as the negative electrode and non-aqueous electrolyte. Lithium-ion batteries refer to rechargeable secondary batteries that do not use metal lithium as the negative electrode and rely on the movement of lithium ions between the positive and negative electrodes to work. However, in daily life, people are accustomed to simply referring to lithium-ion batteries as lithium batteries or lithium batteries. Compared with traditional batteries such as lead-acid, nickel-chromium, and nickel-metal hydride, lithium batteries do not produce toxic and harmful heavy metal elements such as lead, mercury, and cadmium, and are relatively light in pollution. In addition, their electrolytes are organic solvents and lithium salts, most of which are non-toxic or low-toxic. Characteristics of lithium-ion batteries (1) Voltage platform Due to the different positive and negative electrode materials used in lithium-ion batteries, the operating voltage range of their single cells is 3.7~4V. Among them, the operating voltage of lithium iron phosphate single cells, which are widely used, is 3.2V, which is 3 times that of nickel-metal hydride batteries and 2 times that of lead-acid batteries. (2) Specific energy The energy density of lithium-ion power batteries for passenger cars is currently close to 200Wh/kg, and is expected to reach 300Wh/kg in 2020. (3) Long battery life Due to the constraints of electrochemical material properties, the number of cycles of lithium-ion batteries is relatively long. Taking lithium iron phosphate as an example, the number of cycles of a single battery can reach more than 2,000 times, but only more than 1,000 times after being grouped. (4) Small impact on the environment Lithium-ion batteries use light metal lithium. Although they do not contain harmful heavy metals such as mercury and lead, they are considered green batteries and have less pollution to the environment. (5) Relatively high cost The initial purchase cost of lithium-ion batteries is high. Taking lithium iron phosphate batteries, the mainstream product of power batteries for buses, as an example, the price is about 2,500 yuan/kWh. With the popularization of electric vehicles, it is expected to drop to less than 1,000 yuan/kWh in 2020. Due to the limitation of the number of cycles of single batteries after being grouped, buses usually need to replace batteries in about 3 years, which puts great pressure on the cost of operating units. (6) Little impact on the power grid. First, the large-scale application of pure electric vehicles will have a large demand for charging, and the harmonic interference of charging equipment on the power grid will be prominent, affecting the power supply quality of the power grid. Secondly, during fast charging, due to the high-rate charging, the charging power is relatively high (passenger cars are 50kW, buses are around 150~250kW), which has a greater impact on the load of the power grid.

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