Analysis on the Causes of Self-discharge of Ni-MH Battery

The reason for the self-discharge of nickel-hydrogen batteries According to the IEC standard, the self-discharge test method of nickel-cadmium and nickel-metal hydride batteries is: discharge a fully charged battery at 205°C and 65±20% humidity for 28 days, and electrify to 1.0v /, Current 0.2c. The ratio of discharge capacity to battery capacity is the charge retention rate. Self-discharge, also known as charge capacity, refers to the energy storage capacity of the Ni-MH battery in the open state under certain environmental conditions. Generally speaking, self-discharge is mainly affected by manufacturing processes, materials, and storage conditions. Self-discharge is one of the important parameters to measure the performance of nickel-hydrogen batteries. Generally speaking, the lower the storage temperature of NiMH batteries, the lower the self-discharge rate. However, it should be noted that the temperature is too low or too high may cause damage to the battery and unusable. Generally, the storage temperature range of conventional batteries is -20~45℃. After the battery is fully charged and turned on for a period of time, a certain degree of self-discharge is normal. The basic types of Ni-MH battery self-discharge: (1) physical self-discharge; (2) chemical self-discharge. (1) Physical self-discharge: refers to the self-discharge caused by physical reasons. When the battery self-discharges, electrons flow from the negative electrode of the battery to the positive electrode of the battery, forming a current, and the ionic current in the electrolyte forms a current loop. Physical self-discharge characteristics: (1) Less affected by temperature; the final open circuit voltage of the battery can be zero. (2) Chemical self-discharge: Self-discharge in the chemical process where no current appears between the positive electrode and the negative electrode of the battery. Chemical self-discharge characteristics: (1) Affected by temperature; (2) Affected by the battery charging state; chemical self-discharge will not cause the battery voltage to be zero. Reasons and characteristics of self-discharge of Ni-MH batteries 1. Diaphragm (1) Poor diaphragm isolation performance, poor tensile strength uniformity (2) Poor electronic insulation (3) Self-discharge characteristics of the diaphragm, physical or chemical automatic discharge occurs in a whole batch The degree of discharge is similar 2. The rod (1) The self-discharge characteristics of the powder that is cut from the powder and the powder falls from the pole A: Physical self-discharge B. The whole batch appears C. The degree of self-discharge is similar D. The dust is removed when the battery is removed (2) Winding Dislocation 3. The liquid collector has burrs in the liquid collection (2) There is a batch of pre-welding at the tab welding (3) The self-discharge characteristics of the collected fluid physical self-discharge personal self-discharge severe short-circuit battery removal is not obvious 4. Impurities in the electrolyte (2) There are impurities in the active material. Positive active material is self-decomposing. Negative active material is self-decomposing. Self-discharge characteristics of active material. A: Chemical self-discharge B. The whole batch appears C. The degree of self-discharge is related to the state of charge (3) Membrane Dissolved matter (4) Impurity self-discharge characteristics, chemical self-discharge, the degree of self-discharge is similar throughout the batch, and the battery is not obvious. 5. Other reasons (1) Statement of conductive material deposited on external micro-short-circuit diaphragm: Some pictures and contents of articles published on this site are from Internet, if there is any infringement, please contact to delete the previous article: Analysis of demand for lithium batteries in recent years